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Mike TekePresident, Chamber of Mines of South Africa

Mosebenzi ZwaneMinister of Mineral Resources, South Africa

Rob DaviesMinister of Trade and Industry, South Africa

Naledi PandorMinister of Science and Technology, South Africa

R.T. Jones

C. Musingwini

S. NdlovuA.S. Macfarlane

J.L. Porter

C. Musingwini

Z. Botha G. NjowaV.G. Duke A.G. SmithI.J. Geldenhuys M.H. SolomonM.F. Handley J.D. SteenkampW.C. Joughin M.R. TlalaM. Motuku D. TudorD.D. Munro D.J. van Niekerk

N.A. Barcza G.V.R. Landman R.D. Beck J.C. Ngoma J.R. Dixon S.J. Ramokgopa M. Dworzanowski M.H. Rogers F.M.G. Egerton G.L. Smith H.E. James W.H. van Niekerk

Botswana L.E. DimbunguDRC S. MalebaJohannesburg I. AshmoleNamibia N.M. NamateNorthern Cape C.A. van WykPretoria P. BredellWestern Cape A. MainzaZambia D. MumaZimbabwe S. NdiyambaZululand C.W. Mienie

Australia: I.J. Corrans, R.J. Dippenaar, A. Croll, C. Workman-Davies

Austria: H. WagnerBotswana: S.D. WilliamsUnited Kingdom: J.J.L. Cilliers, N.A. BarczaUSA: J-M.M. Rendu, P.C. Pistorius

The Southern African Institute of Mining and Metallurgy

*Deceased

* W. Bettel (1894–1895)* A.F. Crosse (1895–1896)* W.R. Feldtmann (1896–1897)* C. Butters (1897–1898)* J. Loevy (1898–1899)* J.R. Williams (1899–1903)* S.H. Pearce (1903–1904)* W.A. Caldecott (1904–1905)* W. Cullen (1905–1906)* E.H. Johnson (1906–1907)* J. Yates (1907–1908)* R.G. Bevington (1908–1909)* A. McA. Johnston (1909–1910)* J. Moir (1910–1911)* C.B. Saner (1911–1912)* W.R. Dowling (1912–1913)* A. Richardson (1913–1914)* G.H. Stanley (1914–1915)* J.E. Thomas (1915–1916)* J.A. Wilkinson (1916–1917)* G. Hildick-Smith (1917–1918)* H.S. Meyer (1918–1919)* J. Gray (1919–1920)* J. Chilton (1920–1921)* F. Wartenweiler (1921–1922)* G.A. Watermeyer (1922–1923)* F.W. Watson (1923–1924)* C.J. Gray (1924–1925)* H.A. White (1925–1926)* H.R. Adam (1926–1927)* Sir Robert Kotze (1927–1928)* J.A. Woodburn (1928–1929)* H. Pirow (1929–1930)* J. Henderson (1930–1931)* A. King (1931–1932)* V. Nimmo-Dewar (1932–1933)* P.N. Lategan (1933–1934)* E.C. Ranson (1934–1935)* R.A. Flugge-De-Smidt

(1935–1936)* T.K. Prentice (1936–1937)* R.S.G. Stokes (1937–1938)* P.E. Hall (1938–1939)* E.H.A. Joseph (1939–1940)* J.H. Dobson (1940–1941)* Theo Meyer (1941–1942)* John V. Muller (1942–1943)* C. Biccard Jeppe (1943–1944)* P.J. Louis Bok (1944–1945)* J.T. McIntyre (1945–1946)* M. Falcon (1946–1947)* A. Clemens (1947–1948)* F.G. Hill (1948–1949)* O.A.E. Jackson (1949–1950)* W.E. Gooday (1950–1951)* C.J. Irving (1951–1952)* D.D. Stitt (1952–1953)* M.C.G. Meyer (1953–1954)* L.A. Bushell (1954–1955)* H. Britten (1955–1956)* Wm. Bleloch (1956–1957)

* H. Simon (1957–1958)* M. Barcza (1958–1959)* R.J. Adamson (1959–1960)* W.S. Findlay (1960–1961)

D.G. Maxwell (1961–1962)* J. de V. Lambrechts (1962–1963)* J.F. Reid (1963–1964)* D.M. Jamieson (1964–1965)* H.E. Cross (1965–1966)* D. Gordon Jones (1966–1967)* P. Lambooy (1967–1968)* R.C.J. Goode (1968–1969)* J.K.E. Douglas (1969–1970)* V.C. Robinson (1970–1971)* D.D. Howat (1971–1972)

J.P. Hugo (1972–1973)* P.W.J. van Rensburg

(1973–1974)* R.P. Plewman (1974–1975)* R.E. Robinson (1975–1976)* M.D.G. Salamon (1976–1977)* P.A. Von Wielligh (1977–1978)* M.G. Atmore (1978–1979)* D.A. Viljoen (1979–1980)* P.R. Jochens (1980–1981)

G.Y. Nisbet (1981–1982)A.N. Brown (1982–1983)

* R.P. King (1983–1984)J.D. Austin (1984–1985)H.E. James (1985–1986)H. Wagner (1986–1987)

* B.C. Alberts (1987–1988)C.E. Fivaz (1988–1989)O.K.H. Steffen (1989–1990)

* H.G. Mosenthal (1990–1991)R.D. Beck (1991–1992)J.P. Hoffman (1992–1993)

* H. Scott-Russell (1993–1994)J.A. Cruise (1994–1995)D.A.J. Ross-Watt (1995–1996)N.A. Barcza (1996–1997)

* R.P. Mohring (1997–1998)J.R. Dixon (1998–1999)M.H. Rogers (1999–2000)L.A. Cramer (2000–2001)

* A.A.B. Douglas (2001–2002)S.J. Ramokgopa (2002-2003)T.R. Stacey (2003–2004)F.M.G. Egerton (2004–2005)W.H. van Niekerk (2005–2006)R.P.H. Willis (2006–2007)R.G.B. Pickering (2007–2008)A.M. Garbers-Craig (2008–2009)J.C. Ngoma (2009–2010)G.V.R. Landman (2010–2011)J.N. van der Merwe (2011–2012)G.L. Smith (2012–2013)M. Dworzanowski (2013–2014)J.L. Porter (2014–2015)

Van Hulsteyns Attorneys

Messrs R.H. Kitching

The Southern African Institute of Mining and Metallurgy

Fifth Floor, Chamber of Mines Building

5 Hollard Street, Johannesburg 2001 • P.O. Box 61127, Marshalltown 2107

Telephone (011) 834-1273/7 • Fax (011) 838-5923 or (011) 833-8156

E-mail: [email protected]

�iii

ContentsJournal Comment—A Council for our Youthby V. Duke. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv–v

Obituary—Richard Peter Mohringby J.A. Cruise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi

President’s Cornerby R.T. Jones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii

Improving the ventilation system at Rosh Pinah zinc mineby E. Develo, M. Pillalamarry, and E. Garab . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301

Sub-standard practices: effects on safety performance in South African gold minesby G. Kleyn and J.J.L. du Plessis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307

A critical investigation into tyre life on an iron ore haulage systemby G.C. Lindeque . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317

Review of support systems used in poor ground conditions in platinum room and pillar mining: a Zimbabwean case studyby T. Chikande and T. Zvarivadza . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323

Slurry abrasion of WC-4wt%Ni cold-sprayed coatings in synthetic minewaterby N.B.S. Magagula, N. Sacks, and I. Botef . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333

Matte – tap-hole clay – refractory brick interaction in a PGM smelterby J. Du Toit, R.D. Cromarty, and A.M. Garbers-Craig . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339

Separation of kimberlite from waste rocks using sensor-based sorting at Cullinan Diamond Mineby T. Mahlangu, N. Moemise, M.M. Ramakokovhu, P.A. Olubambi, and M.B. Shongwe. . . . . . . . . 343

An evaluation of the thermal fatigue performance of three alloys for casting mould applicationsby V. van der Merwe and C.W. Siyasiya. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 349

The effect of particle size on the rate and depth of moisture evaporationfrom coal stockpilesby Q.P. Campbell, M. le Roux, C.B. Espag de Klerk . . . . . . . . . . . . . . . . 353

R. Dimitrakopoulos, McGill University, CanadaD. Dreisinger, University of British Columbia, CanadaE. Esterhuizen, NIOSH Research Organization, USAH. Mitri, McGill University, CanadaM.J. Nicol, Murdoch University, AustraliaE. Topal, Curtin University, Australia

VVOLU ME 11 6 NO. 4 APRIL 2016

R.D. BeckJ. Beukes

P. den HoedM. Dworzanowski

B. GencM.F. Handley

R.T. JonesW.C. Joughin

J.A. LuckmannC. MusingwiniJ.H. PotgieterT.R. StaceyD.R. Vogt

D. Tudor

The Southern African Institute ofMining and MetallurgyP.O. Box 61127Marshalltown 2107Telephone (011) 834-1273/7Fax (011) 838-5923E-mail: [email protected]

Camera Press, Johannesburg

Barbara SpenceAvenue AdvertisingTelephone (011) 463-7940E-mail: [email protected]

The SecretariatThe Southern African Instituteof Mining and Metallurgy

ISSN 2225-6253 (print)ISSN 2411-9717 (online)

THE INSTITUTE, AS A BODY, ISNOT RESPONSIBLE FOR THESTATEMENTS AND OPINIONSADVANCED IN ANY OF ITSPUBLICATIONS.Copyright© 1978 by The Southern AfricanInstitute of Mining and Metallurgy. All rightsreserved. Multiple copying of the contents ofthis publication or parts thereof withoutpermission is in breach of copyright, butpermission is hereby given for the copying oftitles and abstracts of papers and names ofauthors. Permission to copy illustrations andshort extracts from the text of individualcontributions is usually given upon writtenapplication to the Institute, provided that thesource (and where appropriate, the copyright)is acknowledged. Apart from any fair dealingfor the purposes of review or criticism underThe Copyright Act no. 98, 1978, Section 12,of the Republic of South Africa, a single copy ofan article may be supplied by a library for thepurposes of research or private study. No partof this publication may be reproduced, stored ina retrieval system, or transmitted in any form orby any means without the prior permission ofthe publishers. Multiple copying of thecontents of the publication withoutpermission is always illegal.

U.S. Copyright Law applicable to users In theU.S.A.The appearance of the statement of copyrightat the bottom of the first page of an articleappearing in this journal indicates that thecopyright holder consents to the making ofcopies of the article for personal or internaluse. This consent is given on condition that thecopier pays the stated fee for each copy of apaper beyond that permitted by Section 107 or108 of the U.S. Copyright Law. The fee is to bepaid through the Copyright Clearance Center,Inc., Operations Center, P.O. Box 765,Schenectady, New York 12301, U.S.A. Thisconsent does not extend to other kinds ofcopying, such as copying for generaldistribution, for advertising or promotionalpurposes, for creating new collective works, orfor resale.

VOLUME 116 NO. 4 APRIL 2016

STUDENT EDITION — MINING

STUDENT EDITION — METALLURGY

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Membership of the Southern African Instituteof Mining and Metallurgy (SAIMM) includesmining and metallurgical students and new

graduates from various universities and colleges in thesouthern African region.

Among these young people are those who haveeither authored or co-authored papers similar to theones in this edition of the Journal, and the quality ofthese submissions leads me to believe that we are onthe right track in terms of the academic part of thetraining that we provide in developing our futuremining and metallurgical engineers.

However, these undergraduates also requirevocational training, and after graduation, need anopportunity to develop their knowledge and experiencesufficiently to be allowed to register as a professionalengineer with ECSA. In this regard, we are failing toteach our youngsters properly.

Responsibilities around safety, health, and a dutyof care for the environment while also regularlyengaging with communities, demand much of the timeand attention of our managers, who need to meettransformation and sustainable development targets aswell as production targets. Yes, some miningcompanies are still sponsoring individual students oremploying certain graduates as they enter theworkplace, but the dearth of opportunities for ouryoung people to develop themselves under thementorship of experienced professionals andpractitioners is huge.

After recently checking, I found that 42 years isnow the average age of a SAIMM member who is alsoregistered as a professional engineer. Should thisnumber not be far lower if we are to effectivelycompete in a fast-changing mineral resource industrywhere much of the endowment of Southern Africasits?

For me, this situation was somewhat expected.While working on the mines during the early 1990s Iheard the comment, ‘why train when it is probablymore cost-effective to simply buy in the skills as andwhen needed?’ This mindset coincided with a periodwhen South Africa’s large mining houses startedunbundling, with the consequence that opportunitiesfor young people to find pre- and postgraduateemployment started to dwindle.

In August 2013, our students used a ‘CareerDevelopment in the Minerals Industry’ event to remindus of their plight. Ironically, the main objective of theevent was on ‘mapping a career path’, advisingstudents on what to expect in their first five years ofemployment, and reassuring them that they wouldreceive the necessary training in their chosen careers.

The students complained about uncertaintyregarding career prospects in the mining industry, theneed for on-the-job training for undergraduates witheffective mentoring by suitable mentors, and the lackof experiential training opportunities on a mine fornew graduates.

This forced Council to go back and questionwhether the Institute, as a technical society, actuallymeets the needs of all members, even those recentlygraduated or still at university. It was acknowledgedthat our younger members represent a differentdemographic – one on which the long-term success orfailure of the Institute will eventually depend. Thisresulted in agreement on a need for a renewed focuson the ‘youth’ amongst our current and potentialfuture mining and metallurgical engineers, and that bydeveloping them from within the SAIMM, all of ouryouth within the industry would benefit.

A Career Guidance and Education Committee wasformed some time ago by the SAIMM. It successfullyencouraged new students to enter the mining industryby focusing on the building of a mining andmetallurgy exhibition at the Sci-Bono ExhibitionCentre and by attendance at various school sciencefestivals in South Africa. It seemed logical to widen thefocus of this committee to include the needs of ourundergraduates. This plan did not succeed. There wasvery little support from industry, and it also becameclear that our youth have a very different viewpoint tothat of the majority of the members of the committee,and even Council, when it comes to debating theopportunities or threats to their future careers. Wewere trying to make decisions for younger peoplewithout knowing what their ‘real’ requirements were.At a meeting in July 2014 the question was raisedwhether we should rather be looking at how to enableour youth to help themselves.

Subsequent engagements with undergraduates andyoung postgraduates at various academic institutions

Journal CommentA Council for our Youth

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resulted in overwhelming agreement on the merits ofsuch an approach. So at the same time, volunteerswere nominated from each of the institutions and on12 September 2014 the SAIMM held a ‘Workshop onYouth Development’ at Sci-Bono to map out a wayforward. The outcome exceeded all expectations, withthe formation of a Young Professionals Council (YPC),under the umbrella of the SAIMM Council, toeffectively replace the long-serving but outdatedCareer Guidance and Education Committee.

The YPC’s main focus is to engage with the miningindustry across the SADEC region to assist in findingsupport for younger members of the Institute. Somemembers of the previous committee have stayed on asobservers to advise, guide, and assist whereverpossible in this regard. The YPC is also well positionedto provide students with a better understanding of:

� The various career paths that a mining andmetallurgy qualification affords them

� The training and registrations that they willrequire early on in their careers

� The personal development plans or initiatives thatgraduates can undertake to differentiatethemselves in the marketplace.

The newly elected members of the YPC know thatthey can contribute significantly towards appropriatetransformation, meaningful succession planning, anda solid portfolio of skills from the next generation.

Tshepo Mmola, Chairman of the YPC, talks of sixfocus areas covered with the help of three WorkingGroups (WGs):

� One WG for education to represent the interests ofprimarily pre-graduates in basic and highereducation on matters of career guidance, academicdevelopment, and life skills

� The second WG for career guidance to representthe interests of primarily postgraduates in miningand metallurgy on matters of training,professional development, and life skills

� The third, or Enterprise, WG to concentrate onvarious industry initiatives to serve the interestsof our young professionals

It is my hope that senior executives, minemanagers, retired professionals, and entrepreneurs inthe mining industry will support this initiative. I knowthat these young people can and, if they are helped,will positively impact the future of our industry.

For more information contact the YPC Secretary,Vulani Maseko at [email protected]

V. Duke

Journal Comment (continued)

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Richard Peter MohringIt is with great sadness that we announce the passing of Richard Peter Mohring,fondly known by us all as ‘Rick’.

Rick was born in Johannesburg in 1947 and died in Johannesburg in March2016 after a two-year struggle with cancer. He received his formative educationat King Edward VII School, also in Johannesburg. Therefore, Rick wassurrounded by mine dumps from an early age and it must have been duringthese years that mining crept into his blood, because on leaving school heenrolled at the University of the Witwatersrand to read for a Bachelor’s degree inMining Engineering.

On graduation as a mining engineer in 1972, Rick started his career withRand Mines on Durban Roodepoort Deep gold mine, where he progressedthrough the ranks to that of Underground Manager. In 1975, Rick wastransferred to the Rand Mines coal division, where he began his illustrious

career in coal mining. He underwenr a meteoric rise in the coal division – in 1981 at the age of 34, Rick wasappointed General Manager of Welgedacht Exploration Company and in 1984 he was appointed ManagingDirector of Rand Coal.

Rick was involved with many achievements in the South African coal mining industry, inter alia thedesign and running of Middelburg Mine, a 10 million ton per annum coal mine the development of theKhutala and Majuba collieries utilizing high-capacity continuous miners conducting coal-bed methanedrainage tests (the precursor of ‘fracking’), and combining a large export colliery (Middelburg) with anEskom supply colliery (Duhva). During this time he rose to be the Senior Operations Man ger of Ingwe CoalCorporation and then the Chief Executive Officer of NewCoal, an initiative set up by Anglo Coal and Ingwe tocreate a Black Economic Empowerment entity in the coal mining industry. After an 18-month process thelargest BEE coal company, Eysizwe Coal, was formed with Rick as the Deputy Chief Executive Officer tooversee a smooth transformation. Thus, Rick has played a major role in the transformation of the SouthAfrican coal mining industry to the inclusion of Black entrepreneurs having a major stake in the industry.

Apart from his direct work as a professional mining engineer, Rick was associated with the EngineeringCouncil of South Africa for many years. He served as a Council Member from 1992 to 2008 and as Chairmanof various ECSA committees. He represented ECSA internationally in the negotiation for ECSA’s acceptance inthe Washington Accord and the Engineers Mobility Forum, which gave rise to the recognition of registeredengineers throughout the world.

Rick was also involved with tertiary education. He was not only a member of many of ECSA universityaccreditation teams over the years, but also a member of the Industry Advisory Councils for miningengineering at both the University of Pretoria and the University of the Witwatersrand.

Rick served with many industry associations, including the Chamber of Mines of South Africa, the FossilFuel Foundation, the International Committee for Coal Research, and the International Energy Agency, wherehe represented South Africa on the IEA Coal Industry Advisory Board from 2000 to 2003.

With the Southern African Institute of Mining and Metallurgy, Rick’s involvement has been prolific. Hewas a Member from 1971 and a Council Member since 1988. He served on many committees – TPC Mining,Publications, Membership, Banquet, and Scrutineers among others, and was a trustee of the SAIMMScholarship Fund.

Rick was the President of the SAIMM for the 1997/1998 term and was an Honorary Life Fellow of theInstitute. The Institute’s highest honour, the Brigadier Stokes Memorial Award, was presented to Rick at the115th AGM in August 2012.

Rick, we in the Institute will miss you and remember you fondly.

J.A. Cruise

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One of the characteristic features of a professional society is that its members are governed by a code ofprofessional ethics. The term ‘ethics’ is derived from the Greek word ethos, meaning ‘character’. Ethics andmorals both relate to ‘right’ and ‘wrong’ conduct. ‘Morals’ often refers to an individual’s own principles or

habits that provide a personal compass regarding right and wrong conduct. ‘Ethics’ refers to the rules of conductthat are provided by an external source within a particular context, and can be considered a social system or aframework for acceptable behaviour.

An often-quoted example in the field of law illustrates how professional ethics might apparently conflict withpersonal morals. A lawyer’s morals may tell him/her that murder is reprehensible and that murderers should bepunished, but professional ethics require a lawyer to defend a client to the best of his/her abilities, even if the clientis guilty. There are good reasons for this ethical requirement, as it helps to build a fair society. Ethics is intended tobe practical, and is conceived as shared principles promoting fairness in social and business interactions. However,ethical decisions should recognize the context within which they are set, and must recognize that duties can beranked in a hierarchy (for example, to stop at an accident to render assistance takes precedence over the promise ofmeeting for lunch).

‘The word “good” has many meanings. For example, if a man were to shoot his grandmother at a range of fivehundred yards, I should call him a good shot, but not necessarily a good man.’ – G.K. Chesterton

‘Right is right, and wrong is wrong, and a body ain’t got no business doing wrong when he ain’t ignorant andknows better.’ – Mark Twain, The Adventures of Huckleberry Finn

In South African society in 2016, we are acutely aware of the prevalence of dishonesty and corrupt businessdealings around us. The need for integrity in business and politics has never been greater. I would like to live in aworld where we all work towards the welfare, safety, and health of all people, and care for our environment.

‘Educating the mind without educating the heart is no education at all.’ – Aristotle‘Ethics are more important than laws.’ – Wynton MarsalisWhen people sign up for membership of a professional society such as the SAIMM, it is expected that they will

always conduct themselves in a professional manner, and act with integrity and sincerity in all of their work. TheSAIMM’s Code of Professional Conduct appears as By-law H in the ‘Constitution and By-Laws’ document in the‘About SAIMM’ section of our website, and is worth reading as a reminder about our professional obligations.

In essence, the code of professional conduct requires Members to eschew fraudulent or dishonest practices, notto conceal unethical acts, and to avoid working with others who behave unprofessionally. A professional shouldwork to the highest possible standards, stay up-to-date with their field, and should undertake only work that he orshe is trained for. Conflicts of interest should be avoided, and financial dealings should be open and fair, with nobribery. Honesty and confidentiality are expected. Professional behaviour involves no misrepresentation inadvertising or unfair criticism of the work of others.

Any transgressions of this code are dealt with in terms of our ‘Complaints and Disciplinary Procedure’ (also onthe website) by the Complaints Committee, which gathers facts, and screens complaints to ensure that they areneither frivolous nor malicious, before assessment by the Ethics Committee. The assessment is handled in a firm,fair, and confidential way, and can result in a warning, a reprimand, a requirement for further training, or evensuspension, expulsion, or referral to statutory bodies.

‘Live so that when your children think of fairness and integrity, they think of you.’ – H. Jackson Brown, Jr.

R.T. JonesPresident, SAIMM

EthicsPresident’

s

Corner

‘Never let your sense of morals get in the way of doing what's right’ – Isaac Asimov

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PAPERS IN THIS EDITION

These papers will be available on the SAIMM websitehttp://www.saimm.co.za

Papers — Student Edition–MiningImproving the ventilation system at Rosh Pinah zinc mineby E. Develo, M. Pillalamarry, and E. Garab . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301A number of options were considered In order to improve the ventilation conditions and these were simulated using an appropriate software package. A workable solution was proposed that could improve the overall ventilation in the mine and lead to significant savings in the cost of providing the ventilation.

Sub-standard practices: effects on safety performance in South African gold minesby G. Kleyn and J.J.L. du Plessis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307The purpose of this investigation was to establish the root causes of sub-standard practises and the consequent effect on safety performance at an underground production operation of a gold mine in the Free State. The established methods of addressing sub-standard practices and improving safety performance were found to discourage employees from performing work safely and according to procedure.

A critical investigation into tyre life on an iron ore haulage systemby G.C. Lindeque. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317This investigation compared ‘Best Practi e’ to the current tyre management strategy at the mine to determine the elements that could be improved. A new Tyre Management Strategy was formulated as a Step-by-Step guide on how to implement the proposed changes.

Review of support systems used in poor ground conditions in platinum room and pillar mining: a Zimbabwean case studyby T. Chikande and T. Zvarivadza . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323The results from this study showed that the current support system and mining practices in bad ground areas need to be adjusted to improve safety and productivity. A number of recommendations were made to change the explosive, pillar design, and roof bolting practice.

Papers — Student Edition–MetallurgySlurry abrasion of WC-4wt%Ni cold-sprayed coatings in synthetic minewaterby N.B.S. Magagula, N. Sacks, and I. Botef . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333A number of tests were conducted to assess the wear behaviour of mild steel that had been subjected to a low pressure cold gas dynamic spraying to produce a coating deposit of tungsten carbide containinga known amount of nickel.

Matte – tap-hole clay – refractory brick interaction in a PGM smelterby J. Du Toit, R.D. Cromarty, and A.M. Garbers-Craig. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339This laboratory scale investigation examined the ability of the tap-hole clay to form a protective layer on the brick which could limit the matte penetration into the tap-hole brick.

Separation of kimberlite from waste rocks using sensor-based sorting at Cullinan Diamond Mineby T. Mahlangu, N. Moemise, M.M. Ramakokovhu, P.A. Olubambi, and M.B. Shongwe . . . . . . . . . . . . . . . . . . . 343This paper describes the initial test work that led to the decision to conduct a pilot scale study. The mineralogical characterization of the feed and product streams, to validate the sorting criteria and the operational data obtained during the pilot plant campaign is shown.

An evaluation of the thermal fatigue performance of three alloys for casting mould applicationsby V. van der Merwe and C.W. Siyasiya . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 349The aim of the project was to find an alternative alloy that would outperform the current low alloy cast steel that was experiencing premature thermal fatigue failure of the casting moulds that are used in catalyst production.

The effect of particle size on the rate and depth of moisture evaporationfrom coal stockpilesby Q.P. Campbell, M. le Roux, C.B. Espag de Klerk . . . . . . . . . . . . . . . . . . . . . . . . . . . 353The objective of this project was to determine the effect of coal bed particle size on the rate of evaporation as well as the depth to which evaporation extends in a coal stockpile.

A good mine ventilation system should becapable of providing adequate quantity andquality of air to all working faces, and iscritical to the occupational health, safety, andcomfort of underground employees (Luxbacherand Ramani, 1977; Exikis and Kapageridis,2006). No ventilation system can remainadequate indefinitely; as the mine workingsare extended, the ventilation characteristicssuch as system pressures, air volumes,leakages, and airway resistances changeconsiderably. Continuous improvement of theventilation system is needed to ensurecompliance with health and safety regulations(Lovejoy, 2010). It also ensures that the rightquality and quantity of air is delivered to allthe necessary areas at the lowest possible cost.This can be achieved by identifying inefficientairways and poorly ventilated areas in themine and planning how best to upgrade them.

The latest geological exploration showsthat the focus of production at Rosh Pinahmine is shifting towards the western orefield(WOF). As mining progressed, the workingareas have advanced away from the main fans,which increased the resistance to air flow

drastically and resulted in increasing demandsbeing imposed on the main fan in order tosupply an adequate air flow. This process alsocreated more leakage paths between the fanand the working areas, which has caused theair to short-circuit before it can reach thefaces. Consequently, a much larger quantity ofair has to be circulated by the fan so that thestipulated quantity reaches the face, whichincreases operating costs (Singh et al., 2004).

An investigation was carried out tooptimize the existing ventilation system alongthe WOF at Rosh Pinah, in order toaccommodate the growing ventilation demand.This entailed an evaluation of all the feasiblealternatives available to improve air flow to theworking faces (Mukherjee et al., 1982). Thecurrent distributions of air flow, pressure,leakages, and air quality throughout the mainflow paths of the WOF were quantified byconducting a pressure-quantity survey. Surveydata was used to identify ventilation ineffi-ciencies along the WOF drives and also tosimulate the current ventilation network.Finally, the ventilation network and regulatorswere modified in order to distribute sufficientfresh air at the working faces in the WOF withminimum cost. Ventsim™ software was usedto simulate the ventilation network.

Rosh Pinah is an underground mine thatproduces primarily zinc and lead. The mine isowned by Glencore and is located approxi-mately 360 km southwest of Keetmanshoop inNamibia. This underground operation is 420 mdeep and uses sill-and-bench open stopingmethods. The mine workings are divided into

Improving the ventilation system atRosh Pinah zinc mineby E. Develo*, M. Pillalamarry*, and E. Garab†

Paper written on project work carried out in partial fulfilment of B. Eng. (Mining Engineering)

Recent geological exploration at Rosh Pinah mine revealed that the mine’smajor production is shifting towards the western orefield, which willincrease the demand for air flow to be supplied to this area. A snapshot ofthe ventilation survey carried out in December 2014 at the western orefielddrill drive B (WOF-DDRB) showed that the air flow was well below therequired standards. In order to improve the existing conditions, possibleoptions were considered and simulated using Ventsim™ software.

The best option found was to replace the existing western orefield fanswith the larger fans from the inactive southern orefield workings, toincrease the air flow in the DDRB district. Simulation showed that as muchas 20 m3/s of air can be received at the working faces of WOF 30,compared to the previously received amount of 1.37 m3/s. The economicanalysis indicated that the above option can reduce the ventilation cost byN$1.9 million annually. It was also noticed that after implementing thisoption together with other projects, the ventilation conditions in the minewere greatly improved and currently give no cause for concern.

mine ventilation, simulation.

* Department of Mining and Process Engineering,University of Science and Technology, Namibia,Windhoek.

† Rosh Pinah Zinc C poration, Rosh Pinah,Namibia.

© The Southern African Institute of Mining andMetallurgy, 2016. ISSN 2225-6253. Paper receivedMar. 2016.

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http://dx.doi.org/10.17159/2411-9717/2016/v116n4a1

Improving the ventilation system at Rosh Pinah zinc mine

different sections according to the location of the orebodies,which are termed the western, eastern, southern, andnorthern orefields. Figure 1 shows the layout of the minesections at Rosh Pinah.

Rosh Pinah practices very high safety and healthstandards and the ventilation officers are required to conductdaily ventilation surveys before the underground employeesenter a working area. If these areas do not meet theventilation standards, no personnel are allowed to enter thatparticular area until the conditions are improved by the RoshPinah technical team.

The WOF has three major ventilation intakes, namely the C-mine adit, Quick Access, and the 390 BME adit. Theeastern orefield has one major intake, the eastern orefieldadit. The intake to the southern orefield is the C5 accesstunnel. Figure 2 illustrates the layout of the five main intakesat Rosh Pinah, including the eastern orefield adit. The intakeair is passed through the decline while the exhaust air isreturned to the atmosphere by an exhaust fan connected to araise. Rosh Pinah has a complex ventilation networkrequiring efficient use and management of air control withinthe mine. The deeper sections of the mine are hot and humid,which necessitates the use of auxiliary ventilation.

Rosh Pinah currently has five main exhaust fans installedat the top of the worked-out stopes, which are responsible forextracting the return air out of the stopes and to theatmosphere. Maintenance on the main fans is carried outonce every three months by the mine mechanics, and onceyearly on contract maintenance. The specifications andlocations of these fans are detailed in Table I.

The air flow requirement at the working faces was calculatedaccording to the mine ventilation standards of Namibia(Ministry of Mines and Energy, 1992). The figure includesthe requirements for machinery as well as personnel workingat the face. Prior to the simulation, the current ventilationmodel of Rosh Pinah was updated with the new workingareas by importing extended level plans (survey plans) asDXF files. The extended branches were drawn and edited inVentsim. The ventilation network was then simulated withthe new ventilation data, using various possible options anddifferent control methods. The changes that could be made tothe network were identified from the ventilation survey data.The following two options were considered for simulation.

The WOF decline intake has three portals, namely, Quick

Access, C-mine entrance, and C5 tunnel. This simulation wassimply used to redirect the airflow through the WOF declineby placing a curtain at the entrance to the northern orefieldintake tunnel, since no mining is taking place at this location.

A permanent stopping was also placed close to the QuickAccess portals where the air moves towards the workshopand is returned to the Quick Access through a stope. Theworkshops are dormant and therefore ventilation is notneeded. After the simulation, the airflow distribution wasanalysed. The location of the stopping along the WOF declineis indicated in Figure 3.

Since production is shifting towards the WOF, more air flowwill be required in this area. Two J67 Airtec Davidson fansare installed at the southern orefield stope, which will bemined-out soon (Figure 4). The fan upgrade at WOF includes removing the existing Howden D7 fans, whichsupply 125 m3/s when operating in parallel, and replacingthem with the two J67 Airtec Davidson fans from the SOF(Figure 4).

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Table I

Specifications of main fans used at Rosh Pinah

Fan type Connection Capacity Location

2 × centrifugal Donkin fans Parallel 2 × 160 kW at180 m3/s EOF 310 level2 × axial flow Howden D7 fans Parallel 2 × 110 kW at 125 m3/s WOF 190 level1 × axial flow J67 Airtec Davidson fan Series 185 kW at 100 m3/s Surface, SOF

Prior to the fan installation, a bulkhead with a width of 8m and a height of 4 m was drawn at WOF level 30 to locatethe fan. The purpose of this bulkhead is to reduce the shocklosses that may occur if the fan was to be located perpen-dicular to the direction of the air flow. Three raises wereplanned from WOF 30 to WOF 90 to link the new fan locationwith the return raise at WOF 90. This is shown in Figure 5.The length of the raises from 30 level to 190 level is 163 m.The diameter of the raise that was inserted is 4.0 m. The newairflow distribution along WOF was then simulated. The newlocation of the fans at WOF is shown in Figure 5

The objective of the survey was to assign resistances to allthe branches in the ventilation network by quantifying the airflows and pressure drops (Nixon, 1983). Moreover, accuratequantity and pressure measurements are an absolutenecessity since the validation of the computer-generatedoutput is heavily dependent on the accuracy of the input data(Gelhn et al., 2008; Rostami, 2011). The characteristics ofthe existing mine ventilation system were determined byconducting an underground survey. The direction of theairflow and the location of intakes, returns, stoppings, etc.were determined by inspection of the mine plan.

The ventilation results below are a snapshot fromDecember 2014. No personnel were allowed to enter the areadue to the mine’s safety and health policy. Since these are

newly developed workings, the adequacy of the ventilationunder the existing system was surveyed to improve theconditions in this area. However, no production was takingplace at this area during the survey, and production will bestarted only after the ventilation conditions are improved.

The oxygen concentration at all five working faces (no. 1, 5,6, 8, and 9) in the WOF met the required minimum of 20%.The methane concentration at the working faces was found tobe negligible. The nitrogen oxide levels were minimal, anddid not cause any major concern.

High temperatures and humidity in an undergroundworkplace may result in reduced performance and impair theattention of workers (Rostami, 2011). Therefore, it isimportant to study the humidity levels at the working face toensure comfortable conditions. The humidity measured at allthe working faces of WOF 30L was slightly above themaximum allowable level of 85% (Figure 6). A maximumhumidity of 90% was measured at working face 8. Thehumidity at all the other working faces at WOF level 30 wasfound to be satisfactory.

The air flow required at the working faces of the mine wasdetermined using the mining ventilation standards ofNamibia (Ministry of Mines and Energy, 1992). Rosh Pinahmine makes use of Cat AD 30 trucks in combination withscoops. Usually, there are a maximum of six personnel at aworking face. The cross-sectional areas of the working facesare 22.7 m2, therefore, the calculated minimum requiredairflow at the working face is 18.2 m3/s. The measured airflow at the working faces of the WOF is shown in Figure 7.


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The air flow entering the working faces was 41.0 m3/scompared to the total air flow of 11.41 m3/s. reaching theworking faces. The volumetric efficiency was therefore 27.83 %. In addition, the efficiency of the existing Howdenfans during the ventilation survey was found to be only67.1%.

Sealing the entrance to the workshop near the Quick Accessat level 370 and placing a curtain at the northern orefield fantunnel entrance resulted in the air flow at the WOF increasingfrom 60 m3/s to 83 m3/s. However, air flow at the workingfaces was still inadequate; this increase in air flow was rathersupplied to other areas in the mine. The maximum air flowthat was achieved was 11.2 m3/s, and this was at workingface 8. The air flow entering the working faces increasedslightly to 44 m3/s. The air flow at the working faces afterredirecting is shown in Figure 8.

By replacing the existing WOF fans with the southern orefieldfans, the air flow increased significantly, meeting theregulatory requirements at all the working faces. The air flowentering the WOF was 122 m3/s, and the air flow at workingface 8 increased to 25.2 m3/s. The total air flow reaching theworking faces was 103.2 m3/s; the volumetric efficiencytherefore is 68.8%, and the rest of the air was leakingthrough the stopping to the return raise. The air flow at allfive working faces is given in Figure 9. Working faces 1, 5, 6, 8 at WOF 30 are parallel with working face 9 at WOF 90.

The costs of making changes to the ventilation network atRosh Pinah were evaluated for option 2. The costs to replacethe two main fans at WOF level 90 with the two fans atsouthern orefield level 262 (J67 Airtec Davidson fans) weredetermined.

Since the main fans are not new, the capital costs ofalteration include the fan installation costs and the costs fordrilling the three 160 m raises from 30 level to 90 level ofWOF. According to the project planner at Rosh Pinah, thecosts of drilling and blasting a raise is N$710 per metre,including labour costs. Hence:

Total costs of drilling and blasting the 160 m raise =

Costs of drilling a raise per metre × number of holes × lengthof raise

= N$710 × 21× 160 m = N$2 385 600Total capital costs to install the fans = costs of drilling

and blasting (160 m) raise + installation costs fromcontractor

= N$2 385 600 + N$288 216 = N$2 673 816Equivalent annual costs are therefore,

320 549×0.1(EAC) = = N$501 190.81

(1(1.1)8

-1 )

The annual operating costs for the two fans are(McPherson, 1993):

Operating costs (N$) = Pft × Q × e ×24 ×365̀

where Pft = Fan total pressure (kPa), Q = Air flow (m3/s), e = Cost of electricity in kWh (N$)

2×185Operating costs (N$) = ×0.85×24×365

0.671=N$4 105842.027 per year

The total yearly cost is obtained by adding the cost ofdeveloping the airways/raises and the annual operating costof ventilation.

Total cost to implement option 2 = N$501 190.81 + N$4 105 842.027 = N$4 607 032.84

Ventilation survey results revealed that gas concentration andhumidity levels at the western orefield decline met theNamibian ventilation standards and did not cause any majorconcern (Ministry of Mines and Energy, 1992). Since the

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workings are still at the developing stage, the air flowmeasured at the western orefield decline was below theminimum required. The volumetric efficiency of the westernorefield decline was found to be 27.3%. The most feasiblesolution to increase the air flow at the working faces wouldbe to replace the western orefield main fans with thesouthern orefield main fans. Along the western orefielddecline, 25.23 m3/s of the air is flowing out of the westernorefield into the northern orefield fan tunnels. No miningactivity is currently taking place in this area; therefore it isrecommended that the flow of air can be controlled by placinga brattice cloth at the entrance of the fan tunnel. Real-time airquantity and air quality control would reduce the effort ofventilation surveys. The real-time monitoring ventilationsystem, together with Ventsim™, could improve the accuracyof the simulation and provide the most accurate results.

The authors thank Rosh Pinah Zinc Corporation for theprovision of data and the use of its facilities and ventilationmeasuring instruments during the investigation.

DUCKWORTH, I.J. and LOWNDES, I.S. 2003. Modelling of auxiliary ventilationsystems. Transactions of the Institution of Mining and Metallurgy, vol. 12, no. 2. pp. 2–9

EXIKIS, A. and KAPAGERIDIS, I.K. 2006. Simulation of air and contaminant flow inunderground mine ventilation networks. Proceedings of the 2ndInternational Conference on Advances in Mineral Resources Management

and Environmental Geotechnology (AMREG 2006), Technical UniversityCrete, Chania. pp. 89–93.

GLEHN, F.H., MARX, W.M., and BLUHM, S.J. 2008. Verification and calibration ofventilation network models. Proceedings of the 12th U.S./North AmericanMine Ventilation Symposium 2008, University of Nevada, Reno, NV.Wallace, K.G. (ed.). Society of Mining Engineers of AIME. pp. 275–279.

HARTMAN, H.L., MUTMANSKY, J.M., RAMANI, R.V., and WANG. Y.J. 1997. MineVentilation and Air Conditioning. Wiley, Hoboken, NJ.

LOVEJOY, C. 2010. A breath of fresh air. Mining Magazine, July/August 2010.pp.16-21.

LUXBACHER, G.W. 2008. Developing input data for computer simulation of mineventilation. Kentucky: Pennsylvania State University.

LUXBACHER, G.W. and RAMANI, R.V. 1979. Optimization of coal mine ventilationsystems. AIME Transactions, vol. 286. pp. 1801–1809.

MCPHERSON, M. 1993. Subsurface Ventilation Systems. Chapmann & Hall, NewYork. pp.25-120.

MINISTRY OF MINES AND ENERGY. 1992. Mine Health and Safety Regulations, 10thdraft. Windhoek.

NIXON, T.R., DEAKIN, J.J., and RALPH, A.M. 1983. Ventilation analysis for mineplanning and operation. Computers in Mining Symposium, SouthernQueensland Branch, Australasian Institute of Mining and Metallurgy. pp 231–240.

ROSTAMI, P., DANKO, G., and BAHRAMI, D. 2011. Ventilation and climatesimulation of development ends in metal mines. Proceedings of the SMEAnnual Meeting, Denver, CO. Preprint no. 11–135. pp. 732–735.

SINGH, A.K., AHMAD, I., SAHAY, N., VERMA, N.K., and SINGH, V.K. 2004. Airleakage through underground ventilation stoppings and in situassessment of air leakage characteristics of remote filled cement concreteplug by tracer gas technique. Journal of the South African Institute ofMining and Metallurgy, vol. 104, no. 2. pp 101–106.

TIEN, J. 2008. Determining the optimal mine regulator location using computersimulation. Peabody Coal Company, Kentucky. pp.2-6

WALLACE, K. and MCPHERSON, M.J. 1983. The efficiency and economics of mineventilation systems. TMS/AIME Meeting, Atlanta, GA, 6 March 1983. pp. 2-7. �


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Since the implementation of the Mine Healthand Safety Act, 1996 (Act 29 of 1996) and theMine Health and Safety Regulations, the SouthAfrican mining industry has been striving toimprove health and safety performance andhas placed great emphasis on adherence tomine standards.

The Act requires employers in the miningindustry to report accidents, incidents, anddangerous situations to the Regional PrincipalInspector of Mines in their area. The dataprovided by employers is captured andanalysed by the South African MinesReportable Accident Statistical System(SAMRASS) and made available for publicviewing (Department of Mineral Resources,2011).

A review of the national mine-relatedaccident statistics shows clearly that the SouthAfrican gold mining industry has improved itssafety performance markedly over the pastdecade, but is still facing major challenges

(Figure 1). These include meeting the MineHealth and Safety Milestones (Department ofMineral Resources, 2011).

Most South African mining companieshave adopted a ‘zero harm’ policy in an effortto improve the health and safety of employeesat their operations. After the 2003 Mine Healthand Safety Summit, the following milestonewas set with regard to the gold miningindustry (Department of Mineral Resources,2011):

‘Achieve safety performance levelsequivalent to current internationalbenchmarks for underground metalliferousmines, at the least, by 2013.’

These milestones were revised in 2014 andnew targets for 2024 were set for the SouthAfrican mining industry (Association of MineManagers of South Africa, 2014). The newmilestones that were set in terms of occupa-tional safety are listed below (Association ofMine Managers of South Africa, 2014):

� ‘Every mining company must have atarget of ZERO FATALITIES

� Every Fatality is one too many, we willeliminate fatalities by December 2020

� Up to December 2016, 20% reduction inSerious Injuries per year

� From January 2017, 20% reduction inLost Time Injuries (LTI) per year.’

The 2024 targets include new milestonesfor the implementation of the approved culturetransformation framework (CTF). Thesemilestones included the following (Associationof Mine Managers of South Africa, 2014):� ‘By December 2020 there will be 100%

implementation of:

Sub-standard practices: effects onsafety performance in South Africangold minesby G. Kleyn* and J.J.L. du Plessis*Paper written on project work carried out in partial fulfilment of B. Eng. (Mining Engineering)

Sub-standard practices and their adverse impact on safety performanceremain a challenge in the South African gold mining industry. The purposeof this study was to investigate the root causes of sub-standard practicesand the effect on safety performance in South African gold mines. Thefocus of the study was on the underground production operations at a goldmine in the Free State. The study consisted of three parts: a personalinvestigation into the causes of sub-standard practices at the mine, acomparison with the results of a cultural study performed at the West Witsmines, and a behavioural survey.

The studies described in this article yielded similar results in terms ofthe key drivers behind sub-standard practices. It was found that sub-standard practices had a number of causes, and the origin lies within thehabits, attitude, and behaviour of employees. Current methods ofaddressing sub-standard practices and improving safety performance werefound to discourage employees from performing work safely and accordingto procedure.

It was concluded that the lack of critical behavioural habits for thegiven work environment and job title could possibly be the primary reasonfor the occurrence of sub-standard practices.

sub-standard practices, safety, behaviour, habits.

* Department of Mining Engineering, University ofPretoria, South Africa.

© The Southern African Institute of Mining andMetallurgy, 2016. ISSN 2225-6253. Paper receivedDec. 2015.

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Sub-standard practices: effects on safety performance in South Africa

– The Leadership Pillar of the CTF– The Risk Management Pillar of the CTF– The Bonus and Performance Incentive Pillar of the

CTF– The Data Management Pillar of the CTF– The Diversity Management of the CTF– The Leading Practice pillar of the CTF

� After December 2020 the remaining pillars will beimplemented:

– The Integrated Mining Activity Pillar of the CTF– The Technology Pillar of the CTF– The Inspectorate Pillar of the CTF– Tripartism Pillar of the CTF– Regulatory Framework Pillar of the CTF’

Sub-standard practices compromise the effectiveness ofany safety measures, devices, or procedures that have beenput in place. They create a weak spot in the system that isbound to fail with the slightest amount of interference.Standards and safety are very closely related and standardsare necessary not only to maintain the safety of undergroundemployees, but also to improve current safety practices.

The information below represents some of the safetyperformance statistics at the study mine and was compiledfrom data obtained from the mine’s safety department.

From 17 February 2009 to 22 December 2014 a total of2042 accidents occurred on the study mine. A total of 26 ofthese accidents led to fatalities. Upon analysis, it was foundthat the mine experienced approximately 0.94 accidents perday. The accident distribution by shift is shown in Figure 2.

Figure 2 shows that the majority of accidents at the mineoccurred during the morning shift. The average time ofoccurrence of morning shift accidents was 11:58:17 am.

Figure 3 shows that the largest number of accidents atthe study mine occurred in the stopes. The second highestnumber occurred in development, and the third highest intramming.

Not surprisingly, these are also the departmentsunderground that have shown the greatest amount of sub-standard practices. It is estimated that approximately 40–50%of all accidents underground occur as the inevitable result ofsub-standard acts.

From Figure 1 it is clear that safety performance in goldmining has lagged that in other sectors of the miningindustry for the past 10 consecutive years, and despite therecorded improvements, further efforts are required.

Figure 4 shows the relative distribution of accidents at thestudy mine between the surface and undergroundenvironments. These statistics show that the undergroundwork environment is more hazardous.

The question remains: why do employees at the mine stillengage in sub-standard acts and how does this affect safety?It is this question that gave rise to this investigation into theroot causes of sub-standard practices at the mine.

The hypothesis is that sub-standard practices usuallyhave multiple causes on different organizational levels andhave an adverse effect on the safety performance of SouthAfrican gold mines in general.

To understand the current culture and the need tochange, an investigation into what causes employees toengage in sub-standard acts and how to change thebehaviour at all levels of the organization was required.

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In order to ensure compliance with regulations, the minehas implemented a full compliance policy. However, the sharpincrease in sub-standard practices indicated that the policiesimplemented by the company have not led to the desiredresult.

Furthermore, a major concern is that the new generationof mine employees is adopting a culture where sub-standardpractices are the norm. The language barriers that existamong the majority of the workforce raise a number ofquestions with regards to mine standards in terms of compre-hension.

Figure 5 shows the number of accidents and fatalitiesrecorded at the mining operation over the past 5 years.Although there was a steady decline in the number ofaccidents from 2009 to 2014, this is not reflected in thenumber of fatalities. Thus although the number of accidentshas decreased, their severity has not.

Ideally, the accident statistics should show a steadydecline, indicating that the ‘zero harm’ policy of the companyis becoming a reality. Unfortunately, the fluctuations in theinjury and fatality rates indicate a high probability ofrecurrence of accidents and fatalities. It is believed thatproactive standards have a far greater impact than reactivestandards.

Firstly, it was necessary to carry out research onaccidents related to sub-standard work at the mine. This wasdone in order to identify the root causes of sub-standardpractices in the underground working environment and theeffects on safety performance.

The findings of the study at the mine were compared tothose of a cultural study that was completed at mines in adifferent mining region. The last part of the study involvedconducting Shadowmatch surveys on first line supervisors(shift bosses) and making recommendations for furtherstudies.

A literature study was completed to determine whatinvestigations have been completed in South African goldmines, and the safety performance and factors that influenceit. This included a previous cultural study that was performedat mines in the West Wits region.

Personal interviews were conducted to try to determinethe factors that influence sub-standard practices. Productionsupervisors were also interviewed in order to compare howtheir opinions on sub-standard practices differed from thoseof the underground employees. Questions were posed in sucha way as to determine how the work culture (attitudes andbehaviour) influences the implementation of mine standards.Towards the end of the study, a Shadowmatch survey was

conducted on shift bosses in order to determine benchmarkattitudes and behaviour for this group of employees. The restof the participants’ habits were then compared to thebenchmark and analysed.

The results of a cultural survey performed by Dupontwere analysed in order to determine previously known causesof sub-standard practices and their relation to employeebehaviour.

The Society for Mining, Metallurgy and Exploration(SME) Mining Engineering Handbook, (1973) states that allmining operations are required to adhere to local, provincial,and governmental regulations that among other thingsspecify mine safety regulations and standards, environmentalprotection, and labour relations. The nature, scope, andstringency of these regulations ultimately govern the miningoperation.

Over the past three decades, the number and extent ofmining regulations and governing authorities have dramat-ically increased on an annual basis. The major reason behindthis is a continuous effort of governments to promote healthand safety standards in the global mining industry (Hansen,1973). According to Hansen, (1973), a statistical study thatwas performed over a period of 50 years showed thatawareness of the effects of sub-standard practices resulted ina decreased frequency of accidents. The majority of minehealth and safety authorities around the world agree that themajor causes of mine accidents and fatalities are unsafeconditions, poor management, and especially unsafepractices, which according to the SME, is often cited as theprimary cause (Society for Mining, Metallurgy andExploration, 2011).

Due to a combination of sub-standard practices andhazardous conditions, one must consider not only thephysical causes of sub-standard practices, but also elementssuch as training of employees, the mental state of employees,and employee behaviour (American Institute of Mining,Metallurgical and Petroleum Engineers, 1973)

The major shortcoming of most of the approaches used toidentify the causes of sub-standard practices is that thestudies were usually based on hasty investigations, obviousphysical factors, and common causes of sub-standard actswhile neglecting the psychological, cultural, and behaviouraldrivers.

Poor human behaviour, however, is a known detrimentalfactor in mine safety. This is evident from the cyclicalrecurrence of repeat accidents. The key shortcoming ofconsidering only incident and accident frequency rates as thefocus of safety performance is that it neglects the root causesof the incidents (American Institute of Mining, Metallurgicaland Petroleum Engineers Inc., 1973).

The Mine Health and Safety Act (MHSA) aims to enforcehealth and safety measures and legislation in the SouthAfrican mining industry (Department of Mineral Resources,2011). The open question remains whether the implemen-tation of the MHSA was sufficient to create a safety-wiseculture in the mining industry.

Published fatality and injury rates often reveal a falsepicture of what is actually occurring in the mining industry.Deep-level mining unfortunately has associated hazards andrisks and requires commitment and adherence to health andsafety standards (This is Gold, 2015).


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The published data on mine-related incidents andfatalities (Department of Mineral Resources, 2011) showsthat conditions in the underground gold mining environmentcan be extremely challenging. Since most gold mines in SouthAfrica still use conventional methods (drilling and blasting innarrow-reef stopes) it remains a highly labour-intensiveindustry.

The CSIR (2013) conducted a study to develop anaccident investigation tool that can be used to determine theroot causes of incidents and which provides better insightinto the systematic factors that eventually led to theoccurrence of the incident.

The CSIR was of the opinion that the injured person is notthe sole cause of the accident, but that a series of eventsleads to such occurrences, and that supervisory andmanagerial aspects also contribute either directly or indirectlyto such events (CSIR, 2013).

It is important to determine the human error aspect of anaccident as well as the path that led to its occurrence (Societyfor Mining, Metallurgy and Exploration, 2011).

It must be realized that the majority of incidents generallyresult from at least one act and one condition. However, themajority of mine-related accidents are caused by more thanone condition or act. If this is not taken into account, theopportunity to determine the real root cause(s) of the incidentis lost.

An integrated diagnostic review of cultural transfor-mation was performed at the West Wits gold mines in 2012.The purpose of the study was to determine employeeattitudes and behaviour within the company and the factorsthat resulted in a certain attitude or behaviour (Gold Fields,2012).

The study employed a number of different analysis toolsin order to identify all the cultural issues and to ensure thatall the levels of employment within the organization werecovered.

An accident or fatality is usually the outcome of a numberof sub-standard practices that ultimately led to the event. Theprobability of occurrence of the unwanted event (accident orinjury) and its severity are increased by sub-standardpractices. As the number of sub-standard practices increases,the probability of accidents, as well as their severity, alsoincreases.

It is therefore important to look at accident causationtheories in order to link the current situation in the SouthAfrican gold mining industry to sub-standard practices andtheir causes.

A review of the available literature shows clearly that allaccident causation theories have a number of common goals,namely:

� Identifying risks� Identifying influencing factors � Attempting to explain why the accident occurred� Identifying the root causes of the accident� Using the above knowledge to predict and prevent

accidents.

The majority of authors, (e.g. Guttierez, 2010; Mol, 2002;Raouf, 2011; Saari, n.d.) agree that there are several theoriesof accident causation, and that a single theory is often notenough to establish the true cause of the incident.

The different accident causation models often showconflicting perspectives when it comes to establishing thecause of the incident. It is important to understand that thereis no single accident causation theory that is applicable to themining industry, universally speaking. Some models,however, enjoy preference due to their simplicity andperspective on what ultimately led to the accident. (Raouf,2011)

The theories that were investigated included:

� The Domino Theory� Multiple Causation Theory � The Swiss Cheese Model� The Risk Homeostasis Theory� Bird and Germain’s Loss Causation Theory.

Research has found (De Villiers, 2009) that manyindividuals occupy job positions in which they are extremelyunhappy. This was also the case with regard to the workingenvironment. The associated problem lies in this: it results innegative implications not only for the individual, but also forthe working environment and fellow workers.

The Shadowmatch system was developed to prevent theabove-mentioned scenario by allocating individuals toenvironments that best suit them in order to preserveharmony between the individual and the environment. TheShadowmatch system can also be used to identify employeesthat best suit a specific working environment and specific job.The system possesses the capability to provide personaldevelopment programmes for individuals that require specifichabits in order to be successful in their occupation (DeVilliers, 2009).

This process is completed by comparing the habits of theindividual concerned to the habits of employees who aredeemed successful, based on the performance managementsystem of the company, in performing a specific task withinthe organization

The Shadowmatch research team identified a number ofaspects that ultimately define the work environment (adetailed description of each can be found in the Shadowmatche-book available at www.shadowmatch.com):

� Physical environment� Social environment� Emotional environment� Operational environment.

Behaviour, being a complex field of study, can bemotivated by more than one motivator, and a number ofmotivators may be present within a single one. Most peopleare uncertain of why they behave the way they do (DeVilliers, 2009).

It was found that when employees were interviewed in theirspecific working environment, their opinions differed greatlyfrom when interviewed on surface. It was therefore decided toconduct all interviews in the appropriate undergroundworking environment.

Based on the personal interviews with employees at themine and the results of the 2012 cultural survey executed by

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Mandala Consulting, (2012), it came to light that accidentsand fatalities are in the majority of cases not caused by asingle event.

A total of 135 employees were interviewed during theinvestigation. The focus of the study was mainly onunderground production personnel. The majority of theduration of the study was spent in the stopes, thus thegreatest pool of information was obtained from rock-drilloperators, winch drivers, team leaders, miners, and shiftbosses. The previous general manager at the mine stressedthat the area of concern with regard to sub-standard practicesand unsafe acts was the production personnel at the mine.Figure 6 shows the distribution of employees interviewed byoccupation.

The mode of the age categories was 46–55 years. Thegreater amount of employees interviewed were from thehigher age categories, and the majority were from themorning shift. Only six employees interviewed were workingthe night shift.

The final parameter was the number of years’ experienceof employees. This is one of the most important parameters,since it is generally believed that the more experience anemployee has, the less likely they are to perform an unsafeact or be involved in an accident. Table I shows that thelargest category of employees that were interviewed hadbetween 6 and 15 years’ experience in the mining industry.

The behaviour of employees during interviews raisedconcerns in terms of the findings: if employees were tooscared to disclose their occupation, how accurate and honestis the information that they have provided in the question-naires and during personal interviews?

Honesty and fear of losing employment seemed to be amajor problem at the mine. Employees were found to beextremely anxious to voice their opinions while in thepresence of their colleagues. On other occasions, some of the’new ones’ (as new employees are referred to underground)were often silenced by the elder employees when aninterview was conducted.

The interviewees’ behaviour during interviews also opensa window for speculation that employees are hiding certainthings from management as well as their supervisors. Itraises the question of complete honesty – some intervieweesmight have lied and others were maybe too scared to answerthe questions honestly. One can thus not conclude that theresults of this study are absolutely complete and accurate,due to the external influencing factors in the workingenvironment and observed differential behaviour.

Despite the occasional behavioural patterns and trustissues, it was possible to determine trends. From the data-setof interviewees it is clear that a greater number of olderemployees were interviewed (Table I). The data showed nocorrelation between age, years of experience, and theexecution of sub-standard acts, which could indicate one oftwo possible situations:

� The mine currently has a large number of youngemployees who do not have many years’ experience inthe mining industry

� Older people have been appointed in certainoccupations without a great amount of previous miningexperience.

Both of these situations could have influenced thefindings. After discussion with a psychologist specializing inpublic health, it was established that in the mining industry,the following behaviour patterns are expected with regard toage and years’ experience in the mining environment (vanZyl, 2015):

� Younger employees are more likely to exhibit risk-taking behaviour such as engaging in sub-standardpractices, due to the nature of younger persons’thought patterns

� Older employees are the least likely to exhibit risk-taking behaviour due to thought patterns commonlyassociated with age, such as being more careful in thework environment

� The less experience an employee has, the more likelythey would be to engage in sub-standard practices,since they have no recollection of previouslyencountered dangerous situations or loss of life

� Conversely, older employees are seen as the moreresponsible in terms of implementing standards asopposed to risk-taking behaviour. They are more likelyto be focused on issues such as health, job security,and avoiding danger.


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Table I

Number of employees by years' experience in themining industry

Years of experience Number of employees

Less than 3 133-5 176-10 3811-15 3116-20 1821-25 1326-30 431-35 1More than 35 0Overall total 135


There are, however, a great number of factors that couldinfluence any employee, irrespective of age category and levelof experience. These factors include mental health, jobsatisfaction, remuneration, stress, and education, to mentionjust a few.

In order to establish and analyse certain trends inemployee behaviour with regard to sub-standard practices,some of the questions in the questionnaire were groupedtogether in order to analyse them for similarities andconflicting answers.

One group of questions dealt with whether employees hadencountered sub-standard practices, and the other groupdealt with whether employees understood what standardswere and the necessity for them.

More than 80% of the interviewees indicated that theywere aware of sub-standard practices in the workplace. Thismight show that employees were very aware of what sub-standard practices meant in terms of their occupations.

More than 91% of employees that were interviewed feltthat they were trained to understand why standards wererequired and needed to be upheld. The result is somewhatcontradictory, since personal experience and discussions withmanagement indicated that employees often do notunderstand the implementation of standards.

It was found that 89% of the interviewees had a goodunderstanding of standards and their importance. Thecorrelation between understanding standards and implemen-tation is that if employees understand what standards areand why they are important in the working environment,they should also be able to identify sub-standard practiceswithout difficulty.

The 22% of employees that said they were not aware ofany sub-standard practices could have felt this way due to:

� Fear of losing their job� Not understanding the questions� Not understanding what the standards at the mine are

A fairly high percentage (11%) of the interviewees wereof the opinion that they were not adequately trained inunderstanding the standards. This shows a strong feelingamong employees that a lack of training and education onstandards is a root cause of sub-standard practices. It is clearthat an employee who does not understand a standard wouldbe highly likely to implement the standard incorrectly, not beable to identify sub-standard practices due to a lack ofunderstanding of the standard itself.

14% of the interviewees claimed that they did notunderstand the consequences of sub-standard practices.During the interviews, a number of employees oftenapportioned blame on the ’new ones’ for performing sub-standard acts. The problem here might lie in lack ofunderground experience. The majority of interviewees wereconcerned about the consequences of sub-standard acts sincethey had experienced consequences themselves, witnessedthem, or heard accounts of serious injuries from colleagues.

Although 86% of employees claimed to understand theconsequences of sub-standard practices, a shocking 46% ofthem were still prepared to perform sub-standard acts if theopportunity was presented.

These results prompt the question as to why wouldemployees be willing to take the risk of incurring a loss, ifthey understood the probability and severity of the loss? Theanswer lies in the behaviour and mind-set of undergroundproduction personnel.

Supervisory skills seemed to be lacking in the majority ofworkplaces that were visited. Due to a lack of respect and nofixed structure of authority, there was no control overemployees’ behaviour. It was also found that teamwork skillswere not favoured underground. Every employee had themind-set of ’I’m here only to do my job’. Sub-standardpractices were therefore closely related with communicationgaps, lack of teamwork, and apportioning blame to youngeremployees, instead of accepting fault.

It was found that approximately 56% of employees, atsome point in their careers, had performed sub-standardwork and approximately 33% of employees also instructedother employees to do so.

Most of the employees who were interviewed encounteredsome form of sub-standard practice on a weekly basis.Surprisingly, some employees felt that they encountered sub-standard practices only on a yearly basis, which is hard tobelieve based on the author’s personal experience at themine.

Figure 7 shows that 39% of employees said that theirwork was always up to standard, while only 5% said thattheir work was completely sub-standard. This is, however, amisleading result according to personal investigation. If themajority of employees feel that their work is always up tostandard, then why is there a problem with sub-standardpractices?

According to the results, the sub-standard acts that wereencountered varied widely, with some types of sub-standardpractices mentioned more frequently than others. The generaltypes of sub-standard work that were encountered included,but were not limited to, the following:

� Incorrect procedures when entering and exiting mancarriages

� Incorrect tramming procedures (speeding, leaving locosrunning without an operator inside, attaching too manyhoppers etc.)

� T-sprags almost never in place and ventilation doorsalways open, since it interferes with trammingaccording to loco guards

� Unequipped travelling ways (no steps, footwall notcleaned, no handrails or rope guides, sometimes notsufficient support)

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� Incorrect explosive storage, transport, and handlingprocedures

� Incorrect rigging practices� No supervision

The abovementioned examples of sub-standard acts,procedures, and installation are but a few compared to thegreat number of sub-standard practices that wereencountered during the investigation.

Employees’ reasons for performing sub-standard work orinstructing someone else to do so indicated clearly thatengagement in sub-standard practices is a behaviour-basedissue. The majority of employees showed an inclinationtowards taking matters into their own hands when events didnot go according to their personal plan. It was observed thateveryone wanted to be leaders, and seldom followers, evenwhen it was necessary.

Many experienced employees were extremely set onrespect. If they felt that they were not respected, they wouldnot assist in the task or deliberately work slowly in order toannoy the person who had assumed seniority in thesituation. A lack of ‘soft’ skills is definitely a major cause ofsub-standard practices. Teamwork is essential in the miningindustry and interpersonal skills are vital; this is an area thatemployees at the mine need to be trained in.

Ignorance was found to be a major driving force behindsub-standard acts. Employees believed that because theyhave never been involved in an accident, it will never happento them. They have been involved in sub-standard acts for solong that they are now accepting them as the norm. It wasclear that revenge also played a major role in sub-standardprocedures and acts. The belief amongst interviewees wasthat if a colleague has done them wrong, he must pay for it.Sub-standard acts are often the result of payback to try andregain status by being rebellious.

The results confirmed that production supervisors wereoften seen as lead agents by not adhering to safe practices asthey have instructed to their gangs to do. This behaviourresults in a shared anger by production personnel, whichengenders a less motivated work culture. Employees feel thatthey can do as they please, since production supervisors donot care.

Although one might not have expected the physicallocation and working conditions of stopes to be a leadingfactor driving sub-standard practices, the results clearlyshowed the opposite.

Many employees complained about the travel distanceson foot in order to reach the workplace early enough so thatthere was still adequate time available for completing miningactivities. Associated fatigue resulted in employeesperforming work that was of poor quality, as they claimed alack of energy to perform the tasks correctly.

Other employees were of the opinion that they did nothave the correct tools to perform the given tasks to standard.A combination of fatigue, incorrect tools, and limited timeresulted in sub-standard acts.

The responses to a question on what employees felt hadto be done to remedy the problem showed a number ofgeneral ideas to remedy sub-standard practices. Thesuggested actions to take control of the situation can besummarized as follows:

� Improve training� Reward implementation of standards� Address mental wellbeing of employees� Address attitude-related issues� Provide education on standards and their importance

A factor that stood out was that employees at the mineseemed to lack motivation in performing their jobs. Theywant to feel part of something larger than themselves and berewarded for performing a good job.

The level of education of employees influences thetraining methods to a great extent. Interviewees felt that on-the-job training in the underground environment would bemore suited to their level of education than theoreticaltraining in a training centre. The general feeling was thatthere is a major difference between executing tasks in thetraining centre and executing the same task a few hundredmetres underground.

Great variation in the origin of sub-standard practiceswas observed. Some employees believe that this is more of apsychological and behavioural problem, while others tend toblame management and direct supervisors for the issue.

The investigation at the mine indicated a number ofpotential issues that can be further investigated to determinethe root causes of sub-standard acts and their effects onsafety. Perhaps the most interesting question yet to beanswered is if sub-standard acts are largely a result ofhuman behaviour and individual mentality. This questionwill be addressed in the analysis of the results from theShadowmatch survey.

A number of responses to questions in the gold mine studyrevealed that employees were often just there to get the jobdone, not willing to go the extra mile with regard to their jobdescriptions, lacked a feeling of corporate ownership, andoften did not take control of conflict situations.

The cultural transformation study at the West Wits goldmines yielded the same results. About a quarter of theemployees that took part in the study were not interested indoing more than what was expected of them. About 70% ofemployees did not want to take control of situations thatresulted in conflict. This showed that conflict resolution skillswere lacking with most employees.

It was found that employees that took part in the culturalstudy at West Wits also did not feel competent to perform allwork tasks all of the time. The results also showed thatadaptability, tenacity, and resilience were often a problem foremployees. These findings strongly agree with the resultsobtained at the study mine.

The results indicated a strong similarity in the safetyculture at the study mine and in the West Wits mines.Employees did not understand the safety vision clearly anddid not always follow standard procedures. It can therefore bepostulated that employees in the gold sector show a generaldisregard for safety and standards in the undergroundworking environment.

Acceptance of teamwork as an inevitable factor in miningand safety showed exactly the same trend at the West Witsgold mines and the study mine. Almost half of the employees


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believed that interdependence during teamwork played norole in the quality of work and relationships. Employeespreferred working individually, although this is almostimpossible in the production environment.

When performing teamwork, employees had greatdifficulty in trusting each other. This was the case at both thestudy mine and in the West Wits study. However, trust wasnot the only underlying issue. Many employees also felt thatthey were not fully equipped for performing teamwork andthat they were often not informed on their specific role withinthe team.

From the results obtained in the West Wits study, it wasevident that the study mine was not the only operation thatindicated quality of supervision as a major problem. It wasshown that employees did not possess proper supervisoryskills, nor did the supervisors themselves. A lack of on-the-job coaching, lack of motivation and acknowledgement, andrelationships with supervisors again came up as causes ofsub-standard practices.

The studies performed at the study mine and the WestWits study showed that there were almost no differences inthe cultures with regard to safety and sub-standard practices.In fact, most of the influencing factors that were investigatedwere similar, and it can be concluded that the findings maybe applicable to the entire gold mining industry of SouthAfrica.

A total of 88 shift bosses were selected by seniormanagement of the company to participate in theShadowmatch survey. Included in this number was abenchmark study group of 10 shift bosses, who were selectedbased on their performance in terms of safety and production.The purpose of the benchmark group was to determine thehabits exhibited by successful shift bosses and enable theprofiles of the other shift bosses to be compared with those ofthe benchmark group. This was done to determine poorhabits that may result in sub-standard practices and a poorsafety record.

The majority of participants were day-shift stoping shiftbosses. The day-shift vamping shift bosses were the smallestgroup within the data-set.

The Shadowmatch results that were obtained from thebenchmark group showing the most embedded or criticalhabits exhibited by successful shift bosses. were identifiedand are listed below:

1. Team inclination2. Conflict handling3. Discipline4. Resilience5. Altruism

These critical habits correlate well with the problematicareas identified at the mine, indicating that the studydelivered accurate results with regard to the identification ofthe root causes of sub-standard practices.

The benchmark group showed relatively low scores in thefollowing habits:

1. Individual inclination2. Innovation3. Propensity to delegate4. Propensity to change

Successful shift bosses definitely preferred to work inteams, as indicated by the low score for individualinclination.

Based on the results obtained from the behavioural studyperformed at the mine, it was anticipated that employeeswould obtain a low score for innovation in a Shadowmatchsurvey. The reason behind this is that employees showed astrong inclination towards performing tasks the way theywere used to, and not to embrace new technology orinnovative solutions to problems. The group showed athinking style opposite to an out-of-the-box thinking style.As mentioned previously, this type of behaviour couldhamper safety performance due to the fact that new ways ofperforming tasks were often deemed as additional work orunnecessary change.

The score for propensity to delegate is lower than that forpropensity to own. The benchmark group of shift bossesshowed that they preferred to take ownership of problemsand handle challenges themselves as opposed to gettinganother individual to deal with the problem. This habit, in theopinion of the author, should actually be much moreprevalent, since it reflects the shift bosses’ ability to takecontrol of a situation.

The Shadowmatch results with regard to propensity tochange confirmed the findings from the study mine as well asthe West Wits study. In both of the studies, shift bossesfound it difficult to adapt to change in their workingenvironment. They were not comfortable with new methodsof performing work, new environments, and newtechnologies.

The Shadowmatch attitude analysis delivered results thatstrongly correspond to the critical habits that were identifiedwithin the benchmark group. The majority of participants inthe benchmark group formed part of categories 1 and 2, whileequal numbers of participants formed part of category 3 and4. The significance of the attitude distribution is as follows:

� Categories 1 and 2 exhibit a shared habit ofinvolvement.

� Categories 2 and 3 share habits of assertiveness and,sometimes, unaggressive behaviour.

� Categories 3 and 4 exhibit a habit of less involvementor complete uninvolved attitude.

� Categories 1 and 4 represent a shared attitude ofunaggressive behaviour

Figure 8 shows the attitude distribution of the benchmarkgroup.

As shown in Figure 8, the benchmark group displays astrong attitude of involved, unaggressive behaviour. Thisgroup showed positive involvement in their workenvironment. They found it easy to get involved and thisformed part of their natural behaviour. The group thusshowed positivity when working with people and exhibitedoptimism.

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The attitude is associated with altruism since the groupproved to be unconditional in their actions and willing tomake the necessary sacrifices to achieve a greater goal.Importantly, the benchmark group may be seen as materi-alistic, but emphasizing the value of all life. The way theyperform work is not to serve others, but to drive a certainprinciple.

With regards to conflict handling, the benchmark groupresolved conflict in a mature way without feeling compelledto become aggressive. This type of attitude does not seekrevenge or personal gain.

The purpose of the comparison was to establish anydifferences and correlations between the habits andbehaviours exhibited by the two groups.

It was decided to compare the ‘worst’ and ‘best’performers in terms of the Shadowmatch study to the dataobtained from the benchmark group in order to determineany similarities or differences.

First, the results of the best and worst performers werecompared to the results of the benchmark group. The bestperformer’s scores with regards to the critical habits showeda high correlation with the scores of the benchmark group.The comparison of the scores is shown in Table II.

The worst performer scored significantly lower in all thecritical habits of the benchmark group. This individual had ahigh likelihood of being extremely problematic in the workingenvironment due to his/her habits.

The best performer showed significantly stronger habitsthan the benchmark group in conflict handling, discipline,and altruism. For this specific individual, it could be said thatthese three habits are ultimately the drivers behind success.The worst performer scored higher than the benchmark groupin only two habits, namely propensity to delegate andindividual inclination. However, it is necessary to discuss thepossible reasons for these two higher scores. Propensity todelegate is almost self-explanatory. This individual’s criticalhabits showed very low scores. It may be speculated thathe/she would be the type of person who is not involved at all,has no confidence in what he does, showed no altruism, andprefers to give the task at hand to someone else to complete.

The attitude scores in the results of the best performer areof particular interest. Although there is a strong correlationwith the benchmark group in category 1 and 2 attitudes, theindividual showed a significantly stronger category 4 attitudethan the benchmark group. As opposed to the best performer,the worst performer showed strong category 2 and 3 attitudesand a low category 1 attitude.

The recommended personal development programme(PDP) for the worst performer was problem-solving. Asdescribed earlier, the fact that this individual has none of thecritical habits of the benchmark group indicates that he/shewould be likely to see all aspects of the job as a majorchallenge.

A number of different PDPs were recommended for thestudy group, based on the habits that were determined ascritical habits of the benchmark group. The recommendedPDP addresses the habit that needs development.

Based on the results of the benchmark group, theShadowmatch system recommended the following PDPs forshift bosses that were not part of the benchmark group(ranked in terms of number of recommendations from high tolow):

1. Handling frustration2. Routine3. Problem solving4. Propensity to delegate5. Individual inclination6. Team inclination


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Table II

Comparison between critical habit scores ofbenchmark group and the best and worstperforming individuals

Habit Benchmark Best performer Worst performer

Team inclination 63 61 46Conflict handling 59 67 38Discipline 58 65 39Resilience 57 57 32Altruism 57 64 43


Again, the set of PDPs that were recommended by thesystem fits the results obtained from the study mine and thecultural study extremely well. It further emphasizes thehabits and behavioural patterns that were identified thatcould lead to sub-standard practices in the workingenvironment with adverse effects on safety.

Figure 9 shows the different PDPs that wererecommended for the study group as well as the number ofeach recommended PDP. It is clear from the figure that thehabit of being able to simplify problems is a major concern.This habit is closely related to the habit of problem-solvingwhich was recommended for eight individuals. Frustrationhandling is the third habit that requires intervention. Theunderground working environment is full of challenges anddefinitely requires a radical habit of frustration handling.

Sub-standard practices and their adverse effects on safetyremains a challenge in the South African gold miningindustry. Although a number of previous efforts have beenmade to determine the root causes of sub-standard practices,the results were inconclusive or addressed the same technicalissues that have long been present in the mining industry.

The origin of sub-standard practices in the undergroundworking environment was found to be in the habits,attitudes, and behaviour of employees. However, it isimportant to realize that habits and attitude are not fixedcharacteristics like personality. Habits and attitude can bechanged and developed with the correct instruments.

The research described in this paper (the study performedat a gold mine in the Free State, the cultural survey conductedat West Wits, and the Shadowmatch survey) all highlightedcorrelating causes of sub-standard practices which had theirroots in the habits and behaviour of employees. The absenceof certain radical habits (such as team inclination, conflicthandling, leadership, altruism, discipline, and resilience) for aspecific working environment and a specific job title (in thiscase underground production employees with the focus onshift bosses) could be the primary reason behind sub-standard practices.

Aspects such as a lack of education, inappropriate on-the-job training, and shortcomings in managerial style werefound to increase the occurrence of sub-standard practices,which in turn had adverse effects on the safety culture at thegold mine.

The problem extends beyond a specific section at onemine or a specific shaft, and is most likely an industry-wideissue that needs to be addressed. The best solution would beto determine whether the habits and attitude of an individualare suited for a specific job position and workingenvironment before employing that person. This would avoidthe need for subsequent remedial action on sub-standardpractices.

However, there is no single solution that would alleviatethe current problem. In order to address the different aspectsof the problem, a number of solutions such as aShadowmatch survey, improved training, basic education,revision of risk control programs, are suggested.

Finally, the gold mining environment in South Africaposes some of the most extreme challenges with regards toworking conditions. Looking forward, it would be impossible

to improve on the current situation if the necessary habitssuch as propensity to change, simplification of problems, self-motivation, and team inclination are not addressed.

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The study focused on the tyre life on the mainhaul fleet at an open pit iron ore mine. Thehaul fleet consisted of 17 Komatsu 730 (180 t)haul trucks and 12 CAT 777 (90 t) haultrucks.

The haulage operation consists entirely oftyre-based haul trucks. Five per cent of thetotal mining budget is related to tyre costs.Since 2012 there has been a steady decrease intyre life as measured in operating hours(Figure 1) due to the high percentage of tyresthat fail prematurely. In 2014 a total of 41% ofall tyres failed prematurely and 61% wereclassified as ‘worn out’.

The purpose of this study was to evaluate thecurrent tyre management strategy at the mineand to identify possible aspects that can bealtered in order to increase tyre life. A detailedbreakdown of the objectives and method-ologies followed during the project is shown inTable I.

Two main methods of increasing tyre life wereidentified:

� Method A: reducing the site wear rate oftyres, as measured in millimetres per1000 hours

� Method B: reducing the percentage oftyres that fail prematurely.

The most common reason to scrap a tyre issimply because it is worn out. In 2014 it wasdetermined that 59% of all tyres scrapped wereclassified as worn out. A tyre that is worn outhas reached its maximum life achievable dueto a specific wear rate. The wear rate at themine in terms of each tyre classification isshown in Table II. The data shows that theachievable tyre life for each truck is signifi-cantly higher than the recorded tyre life. Thisis due to abnormal wear of tyres or tyres thatfail prematurely.

In 2014 it was determined that 41% of alltyres failed prematurely. This is an increase of 8% from the previous year. The increasingnumber of tyres that fail prematurely is the biggest contributor to the decreasing trend intyre life over the last two years. If fewer tyresfail prematurely, more tyres will be worn outand therefore the overall tyre life will beincreased. Figure 2 shows the monthly costsassociated with each premature failure modefor a period from 2012 to 2014. In November2014 the year-to-date premature failure costtotalled R2.5 million (Jordaan, 2014), anincrease of 92% from November 2013 (R1.3million).

The cost associated with tyre failure isbased on the value of remaining tread on a

A critical investigation into tyre life onan iron ore haulage systemby G.C. Lindeque*Paper written on project work carried out in partial fulfilment of B. Eng. (Mining Engineering)

A downward trend in tyre life on haul trucks at an open pit iron ore mineprompted an investigation into the current tyre management strategy inorder to improve tyre life. ‘Best practice’ was compared to the current tyremanagement strategy at the mine to determine aspects that could beimproved. Aspects that showed significant room for improvement includedemployee tyre awareness, tyre pressure maintenance, and road conditions.For each of these aspects a plausible alternative was suggested.

A new tyre management strategy was formulated as a step-by-stepguide on how to implement the proposed changes. Each step introducesnew initiatives but at the same time builds on the previous step’s success.A sensitivity analyses was performed to determine the impact of theproposed changes, with the variables being the reduction in the percentageof premature tyre failure, and the reduction of the site wear rate.

The ‘most likely’ scenario showed an increase in tyre life of 41% forthe Komatsu 730 trucks and 105% for the CAT 777 trucks if the entire tyremanagement model is implemented. This would result in a possible annualsaving related to tyre usage of R9.2 million.

tyre life, tyre management, wear rate, premature tyre failure, tyreawareness.

* University of Pretoria, South Africa.© The Southern African Institute of Mining and

Metallurgy, 2016. ISSN 2225-6253. Paper receivedJan. 201 .

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A critical investigation into tyre life on an iron ore haulage system

scrapped tyre, which is referred to as lost tread. The lost treadvalue of scrapped tyres for 2014 was in the range of R5.5–6.0million. This is the total value of tread left on all the tyresthat were scrapped in the year. Lost tread is caused not onlyby the various premature failure modes, but also abnormalwear of tyres.

From the literature survey it was determined that a singletyre failure mode cannot be associated with a certain aspectof tyre management. This led to the conclusion that the entire

tyre management strategy has to be aligned with ‘bestpractice’ in order to significantly improve tyre life. The resultsfrom the literature survey suggested that a ‘best practice’ tyremanagement strategy should consist of the key elements thatare summarized in Table III.

The operational practices at the mine were then evaluated todetermine whether the following elements were adequatelyaddressed.

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Table II

Tyre wear rate

Truck Tyre size Target tyre life Tread available Wear rate (mm per 1000 hours Tyre life at actual wear rate (hours)

(hours) (mm) To achieve target tyre life Actual

Komatsu 730 40.00×R57 7200 87.0 12.1 9.0 9667CAT 777 27.00×49 5600 79.0 14.1 8.0 9875

Table I

Objectives and methodologies

Objective Methodology

Quantify the problem The tyre performance history was thoroughly investigated to:• Determine the tyre life trend and outlook• Determine the current tyre-associated targets• Determine the cost of premature tyre failure• Determine the main causes of premature tyre failure through analysing component failure reports

and general monthly tyre management reports

Identify all the parameters that can influence tyre life A literature survey was conducted to:• Determine the different factors that influence tyre life• Identify the main element of a proper tyre management strategy (best practice)

Determine the impact of each parameter on tyre life Each factor that was identified through the literature survey was investigated to determine the extent of the impact if not managed properly

Investigate the operational practises. The current tyre management strategy was investigated and analysed through:• On-site observations• Historical tyre failure data• Historical road and pit conditions data

Determine which aspects of the current tyre After the evaluation of each aspect of the current tyre management strategy a plausible alteration was management strategy can be altered to comply with suggested, if found unsatisfactorybest practice in order to increase the tyre life of both the waste and ore haul trucks

Determine the impact of the proposed changes. The qualitative impact of the proposed alterations was estimated and the financial impact thereof wascalculated.

The tyre pairs on the rear axle of a truck need to match inorder to ensure even wear of both tyres. The mine does thiswell, as matching spare tyre pairs are kept in a tyre bank.The tyre bank is kept well stocked by replacing tyres on thefront axle after 30% tread wear with new tyres (Jordaan,2014). Pairs of equally worn tyres are made up from thereplaced tyres and stored in the tyre bank. The mine keeps awell-stocked tyre bank, with 99 Komatsu 730 tyres and 69CAT 777 tyres recorded during November 2014.

TKPH is a measure of the heat buildup in a tyre due to theload it has to carry and the speed at which it is travelling. TheTKPH is currently not being monitored. A TKPH study wasdone to determine the suitability of the current tyres for theworking conditions. The results are summarized in Table IV. The table shows the average TKPH of the tyres onthe axle with the heaviest load, thus showing the averagemaximum TKPH of each cycle. From Table IV it is clear thatthe actual TKPH for tyre types is well below the TKPH ratingof the manufacturer. This suggests that the correct tyres foreach truck type in terms of TKPH are being used, and that thetyres are not failing prematurely due to the work load.

The average vehicle speed is well within the limits prescribedby the mine. There is, however, no means of live monitoringof acceleration and braking. This is where the real danger totyres lies.

Some elements of the mine’s current tyre managementstrategy showed room for improvement.

Only 90% of tyres are correctly inflated at any given time –thus 20 tyres in the haul fleet are at an incorrect tyrepressure. To what extent these tyres are incorrectly inflated isunknown. A sensitivity analyses was done and the resultswere based on the assumption that the 10% of tyres that areat an incorrect tyre pressure are 90% inflated. Results would

differ if the actual amount of incorrect inflation was known.According to the tyre management contractor (Woodman,2002), 10% underinflation in very demanding conditionssuch as an iron ore mine can lead to a reduction in tyre life of27%. Another concern is that an individual tyre is onlychecked seven times per month, and not the minimumrequired frequency of once a day.

It was found that the mine adheres strictly to the payloadpolicy of Komatsu (2014) in the case of the Komatsu 730trucks, due to the built-in system on those trucks. This is,however, not the case for the CAT 777 truck. The payloadstudy revealed that only 44% of all loads were less than theoptimum load of 90.5 t. Of the 56% of the loads thatexceeded the optimum, 13% were overloaded more than 20%.This data is summarized in Figure 3.


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Table III

Key elements of ‘best practice’ tyre management

Maintenance • Tyre pressure maintenance• Haul road maintenance• Tyre maintenance• Vehicle maintenance

Haul road design • Horizontal and vertical alignment• Cross fall• Drainage• Super elevation• Curve radius• Road construction• Road width

Loading practice The payload policy of the haul truck manufacturer should be strictly adhered to and monitored

Vehicle speed Specific attention to maximum speed, acceleration, and braking

Tons-kilometres per hour (TKPH) The TKPH rating of the tyre should never be exceeded due to the site work load (speed and payload)

Matching of tyres In order to ensure even wear, tyre assemblies operating as dual pairs must:• Have the same outside diameter• Be from the same manufacturer• Be of the same type (industry code).

Table IV

TKPH study results

Truck Tyre type TKPH rating Actual site TKPH

Komatsu 730E - 7 40.00×R57 960 523.9Komatsu 730E - 8 40.00×R57 960 785.7CAT 777 27.00×49 480 386.4


Road conditions can be assessed according to two categoriesof road – permanent and in-pit. Currently, the permanentroads are monitored and assessed using an assessment andreporting system. This system has a number of drawbacks,the main one being the lack of communication betweenassessor and operator who can correct the error. A newsystem is proposed (Dust-a-Side, 2013) that will fill thecommunication gap. This new system will make continuousroad evaluation possible, because road defects can beidentified and logged by using a handheld device. Thisinformation is immediately shared with the operators of roadmaintenance equipment by using wireless technology.

The main challenge at the mine is not the tyre managementstrategy, but the level of tyre awareness amongst employees.Figure 4 show the results of a questionnaire completed byemployees of various levels. The employees would haveknown the correct answers to the questions if their level oftyre awareness was adequate. The most concerning fact isthat the operators, who have the largest impact on tyre life,showed the lowest level of tyre awareness.

If tyre awareness increases amongst employees, commonoperator errors would decrease. These include:

� Reversing onto the muck pile while loading� Speeding around corners while loaded� Spillage in the loading area� Driving through spillage and water� Incorrect loading practices.

The results were reworked into a physical and realisticimplementable tyre management model. The model consistsof a step-by-step strategy, with different aspect of tyremanagement to be implemented or changed at specific stages.The model focuses on the three main elements of the currenttyre management strategy that showed room forimprovement. These are:

� Tyre awareness� Tyre pressure maintenance� Road conditions.

The tyre management model consists of three phases.Each phase uses different tools to improve tyre management,but at the same time builds on the previous phase. Table Vdescribes the initiatives in each phase. It also indicates whichtyre life improvement method (A or B) each initiative willhave the most significant positive effect on.

The employee mind-set and tyre awareness have to changebefore large sums of capital are spent on technology in aneffort to increase tyre life. Phase 1 consisted of most of thechanges to the current tyre management strategy, and thus itwas estimated to have the most significant positive impact ontyre life.

Phase 2 is associated with automated information regarding

certain aspects of tyre- and road-related elements. This stepinvolves some capital cost and the associated increasedoperating costs. Phase 2 builds on Phase 1. The initiativesimplemented in Phase 1 continue to be practised, with theadditional changes described in Table V.

Phase 3 is the culmination of the tyre management model.This phase involved the majority of the capital spend and hasthe highest additional operating cost. This step can beimplemented only if Phase 1 and 2 were successful.

By thoroughly analysing all the results, informed estimationsof the cumulative effect of the various initiatives under eachphase could be made. A sensitivity analysis was done todetermine the impact of different scenarios for each step.These scenarios were classified as ‘worst case’, ‘most likely’,and ‘best case’. Each of these scenarios is characterized by adifferent impact of each step on:

� Reducing premature tyre failure (improvement methodB)

� Reducing the site wear rate (improvement method A)

This is demonstrated by Table VI. The results of the sensitivity analysis are shown in

Figure 5 by displaying the calculated savings associated witheach phase. Phase 1 has the largest positive impact on tyrelife and results in the largest possible annual saving. Phases2 and 3 have a smaller positive impact on tyre life, resultingin less annual saving. This is due to the fact that phases 2and 3 involve fewer changes to the tyre management system.The better the tyre life on a mine becomes, the harder it is toimprove it.

A tyre forum needs to be established at the mine. This forumshould include representatives from various divisions of themine. It is recommended that the tyre forum implement Phase1 of the tyre management model. The most significantpositive impact on tyre life is associated with Phase 1, withan increase in tyre life of 20% for the Komatsu 730 tyres and75% for the CAT 777 tyres according to the ‘most likely’scenario. Such an increase in tyre life will reduce the annualtyre usage and result in an annual saving of approximatelyR6 million.

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Table V

Tyre management model description

Phase Initiatives Method DescriptionB A

1 Tyre awareness campaign Based on similar tyre awareness campaign results at another mine. Cost based on one full-timeemployee salary to drive the programme

Tyre life monitoring Work with people, give information but also hold them accountable. Information is distributed using theand feedback current systems and discussed in the daily 09:00 production meeting and during the daily Operator

Caucus sessions

Operator education √ In house (no extra cost)

Incentives Exact incentive strategy will be designed by a tyre forum but will be based on individual truck tyreperformance. This will single out and reward hard-working employees and will serve as extra motivationto take good care of tyres

Payload control √ √ Only CAT 777 trucks. Payloads will be manually monitored by operators with much more care

Vehicle speed √ Vehicle speed will be manually monitored by all truck operators with much more care

Pressure monitoringIncrease the number of pressure checks to two per truck per shift. This will require two new employees.Manual pressure checks √ √

(4 per day)

Road conditions

Site severity survey √ Reinstate the site severity survey as discussed previously. No extra cost

Specialist grader √ This requires the training of current grader operators by outside specialist to become specialist graders. operator training R100 000 annual fee converted to a rand per month value. New training and refresher courses would be

needed

Supervisor application √ This entails the supervisors of grader operators to be trained by outside specialist in order to become engineering training experts in the field of grading (know what to look at in terms of grader performance, advice to give to

operators, and how to apply the equipment to achieve the best result). R100 000 annual fee converted toa rands per month value. New training and refresher courses would be needed

Total impact 15% 0.1

2 Road conditions

Permanent roads √ Implementation of the new monitoring system for main haul roads. Capital cost for units and operatingcost for information processing

Grader operator made √ Four specialist grader operators are appointed and a new career path is created with the total salary higher level status increased to match that of a haul truck operator. This will ensure that graders are operated only by

grader specialists

Pressure monitoring

iTrack for CAT 777 fleet √ √

iTrack TPMS installed for CAT 777 fleet. Operating cost includes two dedicated employees to monitorthe system.

Vehicle speed √

TKPH monitoring √

Total impact 2.5% 0.3

3 Pressure Monitoring

iTrack for entire fleet √ √ iTrack System for entire fleet. Free trial period is available. Operating cost includes three dedicatedemployees to monitored and drive the system. Capital cost includes the installation of system on theremaining 17 Komatsu 730 trucks

Vehicle speed √ √

TKPH monitoring √

Road conditions

Grader operator made √ √ Six specialist graders operators are appointed and a new career path is created with the total salary increased higher level status to match that of a haul truck operator. This will ensure that graders are operated

only by grader specialists

Total impact 2.5% 0.1


The main component of Phase 1 is the tyre awarenesscampaign. The exact details and specifications of thisprogramme need to be designed and driven by the tyre forumto specifically suit the mine. Tyre life improvement needs tobe a dynamic and ever-improving process.

Due to the capital sensitivity of the current miningenvironment, implementation of phases 2 and 3 is optional.The sensitivity analysis showed that the largest opportunityfor savings lies with phase 1, which has virtually no extracost associated with it.

It is the role of the tyre forum to conduct monthlymeetings where the newly formulated tyre managementmodel is discussed and evaluated, focusing on four majorareas:

� Conditions� Operations� Maintenance� Tyre performance.

This paper is based on project work carried out in partialfulfilment of the degree B Eng (Mining Engineering)

DUST-A-SIDE. 2013. Dasmetrics introduction and overview.http://www.dustaside.com/services/quality-management-systems/das-metrics

JORDAAN, A. 2014. General Monthly Report-November, Mine X: OTRACOInternational, Redcliffe, Western Australia.

JORDAAN, T. 2015. Mining Manager. Personal communication.

KOMATSU. 2014. About Komatsu. http://www.komatsu.com.au/AboutKomatsu[Accessed 10 December 2014].

MICHELIN. 2015. Technical Data- Earthmover Tyres.

WOODMAN, C.A. 2002. Tyre selection, use and operational issues to maximisetyre life. OTRACO International, Redcliffe, Western Australia. �

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Table VI

Sensitivity analysis estimations

Phase Tyre life improvement method Scenario

Worst case Most likely Best case

1 B 15% 20% 25%

A 0.1 0.2 0.35

2 B 2.5% 5.0% 6.5%

A 0.3 0.6 0.8

3 B 2.5% 5.0% 6.5%

A 0.1 0.2 0.35

The presence of geological discontinuities suchas faults and joints weakens the rock mass.Adequate support is critical in achieving zeroharm in underground mines. This paperreviews the current support systems used inpoor ground conditions at a Zimbabweanplatinum mine. The area of research is locatedon the Great Dyke of Zimbabwe. The mineexploits platinum group elements (PGEs) andbase metals. It is shallow, having a maximumdepth of less than 300 m. The Great Dyke isthe second largest reserve of PGEs, followingthe South African Bushveld Complex(Oberthür et al., 2012). It is a linear layeredintrusion that extends for about 550 km with amaximum width of 11 km (Prendergast,1989). The generalized section of the Great

Dyke is almost like a trumpet, comprisinglayers that dip towards the centre. The reefexploited at the mine, the Mineralised SulphideZone (MSZ), is located in the pyroxenitelayer, which is hosted in the ultramaficsequence. The MSZ is a uniform layer about 2–3.5 m thick, dipping at around 10–14° fromsurface outcrop towards the axis of the basin,and located between bronzite and websteritehorizons. The visible disseminated sulphidemineralization shows a typical and consistentvertical distribution of platinum group metal(PGM) and base metal values. The researchwas undertaken to review the current supportsystems used in geotechnically poor groundconditions in a bid to improve both safety andproductivity.

The mine is fully mechanized and uses thebord and pillar mining method. Access is viatwo declines, one for access of men andmaterials and the other for hoisting ore. Themining layout used in poor ground conditionsis shown in Figure 1.

The area investigated is characterized byupthrows usually related to sympathetic faultsand increased joint frequency. This imposeschallenging mining conditions and increasesthe risk of rockfalls. The reef-subparallelplanes in the hangingwall can give rise tounstable hangingwall environments, resultingin block and wedge failures when the planes ofweakness are intersected by the J1 and J2 joint(discontinuity) sets. As the number of jointsets increases, the strength of the rock massdeteriorates. There are three prominent jointsets at the mine:

Review of support systems used in poorground conditions in platinum room andpillar mining: a Zimbabwean case studyby T. Chikande* and T. Zvarivadza*Paper written on project work carried out in partial fulfilment of BSc. (Mining Engineering)

Falls of ground pose costly hazards to personnel and equipment and thusmeasures should be taken to prevent them. This study endeavours to improvethe support systems used in geotechnically poor ground at a Zimbabweanplatinum mine by analysing the status quo and recommending an effectivesupport system. Various techniques were used to determine the quality ofground conditions, predict the rock mass behaviour, and to identify theappropriate rockbolt type. An analysis of the current ground control methodsand their limitations was also undertaken.

The results showed that the current support system and mining practicesin poor ground need to be modified to improve safety and productivity.Stoping overbreak is influenced by poor ground conditions and the explosivescurrently used. The use of emulsion is recommended to replace ANFO.Redesigning of pillars is also recommended in poor ground conditions. Anevaluation of the current roofbolt system indicated an opportunity forimprovement. With new insight on the performance of the shorter lengthroofbolts currently in use, a new support system was recommended takinginto consideration cost-benefit analysis. Barring down using pinch bars inpoor ground was seen as a risky and time-consuming exercise, hence the useof mechanical scalers is recommended to achieve zero harm and to meetproduction targets. Smoothwall blasting is recommended in poor ground tominimize excavation damage. Other recommendations include the use ofhydrological surveys to determine groundwater levels and implementcorrective measures. Both empirical and numerical modelling approachesneed to be utilized in determining the optimum support.

bord and pillar mining, support systems, pillar design, explosives, roofbolts.

* School of Mining Engineering, University of theWitwatersrand, Johannesburg, South Africa.

© The Southern African Institute of Mining andMetallurgy, 2016. ISSN 2225-6253. Paper receivedDec. 2015.

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Review of support systems used in poor ground conditions

� J1, which trends east-west with an average dip of 70°and a strike of close to 90°

� J2, which trends north-south and has an average strikeof 008°

� J3, which comprises a shallow-dipping plane parallel tosub-parallel to the orebody.

Talc and serpentine are the common types of joint infillmaterial.

The company uses a mechanized room and pillar miningmethod. As mining progresses, the intensity of faulting andjointing increases. This has led to general support failure anda challenge in maintaining a stoping width of 2 m. Associatedproblems and consequences of this include stopingoverbreak, grade dilution, unpredictable unravelling of rocks,a decreased factor of safety, increased support costs, andfailure to meet production targets.

The problems and consequences of poor groundconditions led to the need to review the current supportsystem at the mine. Figure 2 shows the mine layout and thearea where the research was conducted.

The need to conduct the research is justified by thefollowing:

� The obligation to improve safety by ensuring that thereis adequate regional and local support

� The need to improve productivity by meetingproduction targets in the required time

� The need to minimize PGE grade dilution� The need to minimize cost of re-supporting� The opportunity to add value to the company.

The main objectives were to analyse and improve the currentsupport systems used in poor ground. This was done by:

� Reviewing the current support system and identifyingits limitations

� Designing an effective support system to be used inpoor ground

� Making recommendations that can be used to improvethe support systems.

To effectively pin down the research problem and come upwith effective solutions, a critical review of relevant literaturewas undertaken. Rock masses experience primitive stressbefore mining and induced stresses after openings are

excavated. Virgin stresses exist in rocks prior to anyexcavations (Brady, 1985). The magnitude of the verticalcomponent of virgin stress is given (Brady, 1985) by:

virgin = g h [1]

where is the density of the rock mass, g is acceleration dueto gravity, and h is the depth below the surface in metres.

Wood (1987) pointed out that instability can be caused bythe following:

� A decrease in strength to stress ratios, which results infailure of material around the excavation

� Geological structures that result in collapse� A combination of the above two points� Seismic events.

The authors investigated the strength to stress ratios in abid to determine the factor of safety. There is no history ofseismic events in the area of the investigation, hence seismicforces were ignored: however, the authors recommended thatthe mine install seismic monitoring devices.

Brady (1985) noted that when there is no core available butthere are traces of geological discontinuities, Equation [2]can be used to determine Rock Quality Designation (RQD).

RQD = 115 - 3.3 Jv [2]

where Jv is the sum of the number of joints per unit length forall discontinuity sets, and is known as the volumetric jointcount.

RQD is a directionally dependent factor when determinedusing drill core. The use of volumetric joint count is ofparamount importance in reducing this directionaldependence (Brady, 1985). RQD is envisioned to indicate thequality of the in situ rock mass. The calculated RQD will thenbe used to determine the Q rating and Rock Mass Rating(RMR).

The RMR system incorporates the sum of six parameters(Bieniawski, 1989):

1. Uniaxial compressive strength of rock material2. Rock Quality Designation (RQD)3. Spacing of discontinuities4. Condition of discontinuities5. Groundwater condition.6. Orientation of discontinuities.

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The relationship between RMR and Q is given by (Brownand Hoek, 1980):

RMR = 9ln Q + 44

Barton et al. (1974) noted that the Q system classification isbased on the following three aspects:

� Block size (RQD/Jn)� Inter-block shear strength (Jr /Ja)� Active stress (Jw/SRF)

Q = Jn

RQDx Ja

Jr x SRFJw [3]

The authors used the Q system to estimate the requiredsupport based on charts, which are discussed under results.

A sound strategy for overall mine stability is critical to avoidaccidents or conditions that may give rise to incidents. Themajor hazards addressed by a sound mining method designand layout include uncontrolled collapses, surfacesubsidence, and major fall of ground incidents.

The pillar support system is the chief basis of support inunderground mines using the room and pillar miningmethod. In order to design pillars for supporting mine

openings, pillar strengths and pillar stresses need to bedetermined (Wilson, 1972). After determining pillar strengthsand stresses, separate pillars and pillar layouts will bedesigned depending on the degree of stability needed.

The strength of pillars depends on:

� The strength of the intact rock that makes up the pillarmaterial, suitably downrated to take into account thescale effect

� The geometry of the pillar, taking into account theshape and width to height (W:H) ratio.

For W:H ratios less than 4.5, the strength of hard rockpillars is given by:

Ps = K.Weff0.5/H0.75 [4]

wherePs is the pillar strengthK is the design rock mass strength (DRMS) in MPaWeff is the effective pillar width. Weff = 4 × pillar area / pillarperimeter.

In situ stress conditions, together with local and regionalextents of mining, will determine the stresses acting on apillar (Wilson, 1972). For a horizontal mining layout, pillarstress (Pstress) is given by


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Table I

66nbg 18 10 1.8 0.3 18.00 7.00 2.6 0.4 9.0 2.3 3.9 100 8.3 8865nbg 23 11 2.1 0.4 14.00 6.50 2.2 0.2 8.0 2.2 3.6 52 7.9 8964ntb 18 14 1.3 0.4 15.00 6.00 2.5 0.3 8.0 2.3 3.5 48 7.3 9164nbg 17 10 1.7 0.30 18.00 6.00 3.0 0.20 9.0 2.0 4.5 98 9.2 8563ntg 19 8 2.4 0.3 13.00 6.00 2.2 0.5 14.0 2.0 7.0 79 11.5 7763nbg 25 11 2.3 0.4 18.00 5.00 3.6 0.4 14.0 2.1 6.7 100 12.5 7462nbg 22 10 2.2 0.4 17.00 6.00 2.8 0.3 15.0 2.3 6.5 100 11.6 7762ntg 21 8 2.6 0.35 18.00 6.00 3.0 0.30 12.0 2.1 5.7 89 11.3 7861nbg 23 9 2.6 0.2 14.00 6.00 2.3 0.3 11.0 2.1 5.2 200 10.1 8267nbg 22 11 2.0 0.2 17.00 6.00 2.8 0.2 13.0 2.2 5.9 87 10.7 8068nbg 21 9 2.3 0.3 20.00 6.00 3.3 0.5 11.0 2.1 5.2 203 10.9 7968ntg 22 12 1.8 0.4 18.00 5.00 3.6 0.4 14.0 2.2 6.4 200 11.8 7682ntg 23 11 2.1 0.2 17.00 6.20 2.7 0.4 13.0 2.0 6.5 96 11.3 7883nbg 25 11 2.3 0.3 16.00 6.00 2.7 0.3 14.0 2.0 7.0 200 11.9 7683ntg 22 13 1.7 0.4 15.00 5.40 2.8 0.4 13.0 2.2 5.9 202 10.4 8184nbg 26 14 1.9 0.3 17.00 6.00 2.8 0.4 12.0 2.2 5.5 97 10.1 8284ntg 21 9 2.3 0.4 16.00 5.00 3.2 0.3 11.0 2.2 5.0 93 10.5 8085ntg 22 10 2.2 0.2 19.00 6.50 2.9 0.5 13.0 2.2 5.9 89 11.0 7981nbg 23 11 2.1 0.3 18.00 6.20 2.9 0.3 11.0 2.1 5.2 55 10.2 8181ntg 18 6 3.0 0.3 18.00 6.00 3.0 0.3 13.0 2.1 6.2 100 12.2 7586nbg 17 8 2.1 0.4 17.00 5.40 3.1 0.4 14.0 2.2 6.4 200 11.6 7786nbg 22 10 2.2 0.3 15.00 6.00 2.5 0.4 13.0 2.2 5.9 102 10.6 8087nbg 22 14 1.6 0.3 17.00 5.00 3.4 0.3 12.0 2.2 5.5 100 10.4 8187ntg 21 8 2.6 0.3 18.00 6.50 2.8 0.3 15.0 2.2 6.8 100 12.2 7588nbg 17 6 2.8 0.3 21.00 6.20 3.4 0.3 14.0 2.1 6.7 58 12.9 7288ntg 19 6 3.2 0.2 16.00 6.00 2.7 0.4 15.0 2.1 7.1 55 13.0 72

nbg: north bottom gully, ntb: north top gully)


Pstress = 1-e, v [5]

where: v is the vertical field stress and e is the extractionratio

After determining the pillar strength and pillar stress, thefactor of safety (FoS) of the pillar can be calculated asfollows:

Pillar FoS = Pstrength/Pstress [6]

For primary extraction, the minimum design FoS of pillarsis 1.6. Due to the effect of the explosives used and poorground conditions, the authors reviewed the current practicesby measuring the actual pillar dimensions in a bid tocalculate the actual factor of safety. Redesigning of pillarswas considered where current pillar system is not adequate.The conclusion will be drawn after analysis of the results.

Ammonium nitrate-fuel oil (ANFO) is a supreme explosiveused in the mining industry. Its advantages include simpleproduction, low cost, and lack of sensitivity to mechanicalimpact during mechanical loading into drill-holes (Mather,1997). ANFO has also some disadvantages, which includelack of water resistance and low detonation parameters,which reduce its use to dry blast-holes in truncated compactrock masses (Maranda, 2011). Since the type of explosiveused has an effect on support systems, the authors reviewedthe literature on ANFO as well as the other bulk explosives,which include emulsion and watergel. The merits of bulkemulsion explosives over ANFO and packaged productsinclude easy transportation and handling, increased safety,string charging, low gas emissions, water resistance, fullcoupling, increased velocity of detonation, detonatorsensitivity, and improved work environment (Maranda,2011). ANFO generates a lot of gases upon detonation,thereby widening pre-existing cracks. ANFO usage willtherefore result in the formation of keyblocks, which will leadto an unstable hangingwall. In addition, the cut slice willincrease due to overbreak and more poor hangings will beformed that require intense barring-down. Barring downbecomes a risky operation due to frequent keyblocks and isalso time-consuming, leading to failure to meet productiontargets.

A comprehensive revision of the background literature wasconducted as per the requirements of the project objectives.The background literature was then combined with contri-butions from the relevant experts in the field of study, suchas rock mechanics engineers on a practical level. A field studyof the areas of concern was supplemented by the contributionof experts in order to assemble a system of results that wouldbe used for analysis.

The research started with the literature review on geologicaland geotechnical factors, underground support systems,mining methods, and types of explosive used. In order toobtain a clear understanding of the existing mining and

support system, a study was carried out in all sections of themine with poor ground conditions, which included Levels 14to 24. Underground observations, recordings, and datacollection were done in these sections. Observations andanalysis were carried out on the geological structure of theorebody to identify the nature and magnitude of the jointingand faulting system. The effects of current mining practicesand explosives used were assessed. Interviews were alsoconducted as part of the study approach. Observations weremade in each level and the following parameters weremeasured and noted:

� Structural data – number of joints, separation of jointsetc.

� Pillar dimensions� Stope widths of each gully� Time taken to support one gully� Fallout heights� Type of support used.

The results of these observations were analysed usingrock engineering principles.

This exercise comprised the methodical collection of allfracture statistics of the underground rock face. The datacollected included joint roughness, joint sets, joint alteration,joint water, stress reduction factor, and RQD. Theseparameters were used in the calculation of the Q rating of thepillars.

The determination of the rock mass state was critical to theinvestigation. Various techniques were applied to determinethe ground classes in the research area. A comparativeanalysis of these techniques was then conducted to select themost effective method. Substantiated recommendations of thesuitable support to be installed were based on the chosenmethod. The methods that were used include:

� The Q system� RMR� MRMR.

Installed support elements used at the mine include rockbolts,shotcrete, and straps. These were analysed for theirperformance and effectiveness with regard to the falloutheights and the ground characteristics by means of log dataand previous reports to ascertain whether failures could beattributed to the support, the conditions, or both. Theanalyses included examining situations of failure and oflikely failure.

The pillar strength calculations were carried out throughmeasurement of pillar heights and widths. The stress actingon a selected pillar was determined by calculation. Pillars areusually less than the designed size due to poor blasting andcan undergo spalling attributed to poor ground. Thefrequency of such occurrences was investigated with the viewto highlight the short-term and long-term problemsassociated with these practices.

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326 VOLUME 116

The current blast design and explosives used were analysedto:� Attain the planned face advance through efficient

blasting� Mitigate overbreak for grade control and mine design

purposes� Reduce damage to rock� Identify the explosives suitable for use in poor ground

conditions.

Constrains encountered during the research included thefollowing:� Measuring of pillars was rather dangerous as rockfalls

are mostly from the shoulders of pillars� Difficulties in logging of some ends due to

waterlogging or delays in pumping out water.

The results are based mainly on geotechnical data collectedfrom the area of research. This includes results from rockmass classification methods, numerical modelling, reef-subparallel planes, FoS approach, stoping dimensions, andpillar strength. The current support system data was alsoincluded.

The rock mass was classified according to each of the threesystems, which are the RMR, MRMR, and the Q system. The

three methods were compared to identify the most suitablemethod of ground classification.

Table II shows the data used to calculate Q in each bord.Jx = number of joints per unit distance [7]

where Jx represents Js, Jd, and Jh.

Jv = Js + Jd + Jh [8]

Using Equation [2], RQD = 115-3.3Jv

Table III shows the RMR calculated from Bieniawski’s sixparameters for each gully.

The calculated RMR was adjusted to calculate the MRMR. Ablasting effect adjustment of 97% was used, together with aweathering adjustment of 96%, and 80% for joint orientation.Table IV shows the adjusted RMR to give the MRMR.

RMR = 9lnQ + 44

The average RMR is below 50, which shows that the rockmass is poor. RMR values from Bieniawski are comparablewith calculated values from Q ratings.

Rock-related risks due to the three joint sets are reducedby cutting larger pillars and through the use of cable bolts. InGround Control District-D (GCD-D), the bord is reduced to 6 m and the in situ pillars are designed to be 3 × 3 m forshallower areas (up to 160 m depth) and 3.5 × 3.5 m fordepths greater than 160 m. The main pillars measure 3 ×


VOLUME 116 327 �

Table II

Jn Jr Ja Jw

66nbg 88 3 1.5 6.0 1.00 7.5 0.97 4465nbg 89 6 1.5 6.0 1.00 4.0 0.93 4364ntb 91 6 1.5 6.0 1.00 6.0 0.63 4064nbg 85 6 1.5 6.0 1.00 8.0 0.44 3763ntg 77 6 1.5 3.0 1.00 6.0 1.07 4563nbg 74 12 3.0 5.0 1.00 6.0 0.61 4062nbg 77 3 1.5 6.0 1.00 10.0 0.64 4062ntg 78 6 1.5 3.0 1.00 4.0 1.62 4861nbg 82 4 3.0 6.0 1.00 4.0 2.55 5267nbg 80 9 1.5 3.0 1.00 10.0 0.44 3768nbg 79 3 1.5 3.0 1.00 6.0 2.19 5168ntg 76 6 2.0 2.0 1.00 6.0 2.11 5182ntg 78 3 3.0 6.0 1.00 8.0 1.62 4883nbg 76 3 1.5 3.0 1.00 6.0 2.10 5183ntg 81 4 3.0 6.0 1.00 4.0 2.52 5284nbg 82 9 1.5 3.0 1.00 10.0 0.45 3784ntg 80 9 1.5 3.0 1.00 6.0 0.74 4185ntg 79 9 2.0 2.0 1.00 6.0 1.46 4781nbg 81 9 1.5 3.0 1.00 8.0 0.56 3981ntg 75 9 1.5 3.0 1.00 6.0 0.69 4186nbg 77 4 3.0 6.0 1.00 4.0 2.39 5286nbg 80 9 1.5 3.0 1.00 10.0 0.44 3787nbg 81 9 1.5 3.0 1.00 6.0 0.75 4187ntg 75 9 2.0 2.0 1.00 6.0 1.38 4788nbg 72 9 1.5 3.0 1.00 8.0 0.50 3888ntg 72 9 1.5 3.0 1.00 6.0 0.67 40

nbg: north bottom gully, ntg: north top gully


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Table III

66nbg 53 88 100 mm 1–5 mm Completely dry Unfavourable 47 44

7 17 8 10 15 -10


7 17 5 10 15 -10


7 17 5 10 15 -10

64ntg 53 85 98 1 5 mm Completely dry Unfavourable 47 37

7 17 8 10 15 -10


7 17 8 -10 15 -10

63ntg 53 74 100 mm 1–5 mm Completely dry Unfavourable 43 40

7 13 8 10 15 -10


7 11 8 10 15 -10

62ntg 53 78 89 mm 1–5 mm Completely dry Unfavourable 47 48

7 17 8 10 15 -10


7 17 10 10 15 -10

Table IV

66nbg 44 0.96 0.97 0.8 3365nbg 43 0.96 0.97 0.8 3264ntb 40 0.96 0.97 0.8 3064nbg 37 0.96 0.97 0.8 2763ntg 45 0.96 0.97 0.8 3363nbg 40 0.96 0.97 0.8 3062nbg 40 0.96 0.97 0.8 3062ntg 48 0.96 0.97 0.8 3661nbg 52 0.96 0.97 0.8 3967nbg 37 0.96 0.97 0.8 2768nbg 51 0.96 0.97 0.8 3868ntg 51 0.96 0.97 0.8 3882ntg 48 0.96 0.97 0.8 3683nbg 51 0.96 0.97 0.8 3883ntg 52 0.96 0.97 0.8 3984nbg 37 0.96 0.97 0.8 2784ntg 41 0.96 0.97 0.8 3185ntg 47 0.96 0.97 0.8 3581nbg 39 0.96 0.97 0.8 2981ntg 41 0.96 0.97 0.8 3086nbg 52 0.96 0.97 0.8 3986nbg 37 0.96 0.97 0.8 2787nbg 41 0.96 0.97 0.8 3187ntg 47 0.96 0.97 0.8 3588nbg 38 0.96 0.97 0.8 2888ntg 40 0.96 0.97 0.8 30Average 33



10 m and 10 × 3.5 m in most sections. The authors alsomeasured the main pillar dimensions and calculated theinfringements. The actual pillar dimensions of in situ pillarswere measured and the FoS in the gullies calculated.

J3 structures are found in the hangingwall and groundpenetrating radar (GPR) is used to identify these structures.The authors, with the assistance of geotechnicians, took GPRdata and assessed the orientations and the average depthinto the hangingwall. Analysis was conducted to ascertainwhether the 1.8 m resin bolts and cable bolts currently usedare sufficient. Figure 3 shows a typical slice obtained. Aclino-rule was used to determine the dip of J1 and J2structures. The authors deduced that J1 joint set is thedominant joint set, with an average strike direction of 088°and an average dip of 70°. The J2 joint set has an averagestrike of 005° and dips at an average of 65°. The J1, J2, andJ3 joint set data from GPR was used in numerical modelling.

The Q values obtained indicated that the rock is extremelyweak. The values of the measured RMR were comparablewith the calculated values from the Q values. From this, itcan be deduced that the ground conditions in the area ofresearch pose a risk due to high probability of potentialunstable blocks. The authors recommend that the mine usesmore systems for rock mass classification, since a singlesystem cannot give a clear indication of the quality of therock due to its inherent limitations. For GCD D, 1.8 m boltsare currently used and are spaced at 1 m by 1 m. Barton’s Qchart was used to determine the appropriate support systemfor GCD D as shown in Figure 4.

Based on this chart, the current support system usedseems to be adequate, although other systems need to beconsidered also in the design of the required parameters. Thefallout height was found to be 1.8 m in the research area.Roofbolts with a length of 1.8 m are therefore consideredinadequate to clamp the overlying layers, since there will beno bond length. The use of shorter roofbolts has resulted insupport failure, hence new systems of tendons need to bedesigned. The issue of reef-subparallel planes and numericalmodelling will be discussed later in this paper.

All joints in the area of research are currently assumed tobe dry; however, the authors recommend the use ofhydrological surveys to obtain a clear picture of the

groundwater. Groundwater reduces the stabilizing normalstress acting on discontinuity planes, hence weakening therock. From the results of rock mass classification, it can beconcluded that adequate support is required for safe miningpractices. A new roofbolt system envisaged to improve safetyand productivity is discussed later in this paper.

A slice showing reef-subparallel planes is shown in Figure 3.It can be noted that shallow-dipping planes occur at a depthgreater than 1.8 m into the hangingwall. The current supportsystem of 1.8 m length is not adequate to clamp these layers,hence a new system that uses longer roofbolts needs to beimplemented to reduce the risk of support failure andpossible injuries, fatalities, and equipment damage. All thesefactors lead to heavy cost to the mine, hence it is ofparamount importance to improve safety and productivitythrough the implementation of the new support system. Theauthors therefore recommend the use of longer roofbolts inaddition to the cable bolts used.

JBlock was used to deduce the probability of failure ofkeyblocks in the gully. The structural data for the three jointsets, together with tendon data, was used to simulateunstable keyblocks. The authors started by simulatingunstable keyblocks using the current support system of 1.8 mroofbolts spaced at 1 m by 1 m. The area simulated is a 6 mgully in order to check the effectiveness of the currentsupport.

Figure 5 shows the probability at which various blocksfail using the current support system consisting of groutedtendons 1.8 m in length spaced at 1 m by 1 m in poor groundconditions. From the histograms, it can be seen that theprobability of block failure for 1 m3 blocks is 30% and theprobability of maximum support failure is 16%. Theprobability of both block falls and support failure is thus toohigh. The current support system is inadequate. Integratingthe results from all the techniques used, longer roofbolts arerequired to give improved safety.

The new support system designed and simulated by theauthors consists of grouted tendons with a capacity of 160 kN, 2.1 m length, and spaced at 1.2 × 1.2 m. The newsystem yields the results shown in Figure 6. The probabilityof block failure for 1 m3 blocks decreases to 11%, and themaximum support failure to 4%.


VOLUME 116 329 �


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330 VOLUME 116

Taking into account a cost-benefit analysis, a comparisonwas made between the current support system and the newsupport system Although the 2.1 m tendons are moreexpensive than the current 1.8 m tendons, taking intoconsideration the cost-benefit analysis it can be concludedthat the recommended system gives more benefits than thecurrent support system. As well as improved safety, the newsystem leads to a decrease in support density since thetendons will be spaced at 1.2 × 1.2 m as opposed to thecurrent roofbolts spaced at 1 × 1 m.

The authors evaluated the pillar design and cuttingpractices in poor ground conditions. Actual pillar dimensionsin various bords were measured and the resulting factors ofsafety were calculated (Figure 7).

The results show that most teams have failed to maintainthe required safety factor of 1.6 due to stoping overbreak.Figure 8 shows how overbreak reduces the FoS.

Stoping overbreak is caused by poor ground whichunravels unpredictably, and also by ANFO explosive beingused. It is thus critical to redesign pillars so that they are lessinfluenced by a small change in overbreak. Pillar robbing alsoaffects the FoS. Zvarivadza (2012) illustrated the relationshipof probability of failure and FoS as shown in Figure 9.

From Figure 9 it can be seen that for a FoS of 1.6, theprobability of pillar failure is 0.5%, and at the lowest FoS of1.33 obtained for Bord 66 (Figure 7), the probability offailure increases to 5%. A decrease in FoS thereforeincreases the probability of failure, hence it is critical toimplement a pillar design that is less influenced by overbreaksince the ground conditions are poor. Moreover, analternative to ANFO needs to be considered to reduce stopingoverbreak and unravelling of the rocks. Ore dilution occurs asa result of overbreak, as seen in Figure 10, since the grade ofPGMs decreases above and below the required slice.

Safe mining practices and installation of adequate supportlead to stable excavations. This review of the current supportsystems used in poor ground at a Zimbabwean platinummine shows that the current support systems are notadequate in poor ground conditions. The presence of reef-

subparallel planes at depths greater than 1.8 m into thehangingwall implies that the current tendons used will fail tosupport keyblocks. The current type of explosives used alsoresults in stoping overbreak, which decreases the factor ofsafety and increases PGE dilution. The ground conditionsthus require redesigning of the pillars and tendon system toimprove productivity and safety. The current design assumesthat all joints at the mine are dry, but the effect ofgroundwater weakens the cohesion of some joints, whichincreases the frequency of unstable keyblocks. Barring downusing pinch bars is time-consuming and is regarded as arisky exercise, since the barring team is exposed to unstableblocks with a higher probability of failure. Because offrequent unstable blocks, barring down using pinch barswastes more cycle time, which has led to most sections failingto meet their production targets since fewer faces areprepared.

� A study of the new support system designed by theauthors is recommended. Longer roofbolts of 2.1 mlength spaced at 1.2 × 1.2 m are proposed, as opposedto the current bolts of 1.8 m length spaced at 1 × 1 m.The 2.1 m roofbolts are more expensive than thecurrent roofbolts; however, there is improved safetyand less support density with the 2.1 m roofbolts. Theextra cost of the roofbolts will be offset by theincreased spacing, since fewer roofbolts will be used


VOLUME 116 331 �

in situ


� A study of alternative explosives is recommended tominimize rockfalls. ANFO explosives generate a lot ofgases, which widen the joints. The authors recommendthat the mine uses bulk emulsion, which is a low-energy explosive, in poor ground conditions

� Additional support is required where there is pillarrobbing. The use of timbers and pillar bolting isrecommended to improve strength

� The mine should use both empirical and numericalmodelling to design the optimum support, since relyingon one system has limitations

� The use of hydrological surveys is recommended todetermine joint water. Hydrological surveys will give anindication of the exact groundwater conditions withinjoints, thereby increasing safety by designing for theactual groundwater conditions

� The use of mechanical scalers is recommended in poorground conditions to improve both worker safety andproductivity. Fewer faces being prepared result infailure to meet production targets, hence the use ofmechanical scalers will improve productivity

� The authors recommend redesigning of pillars toimprove safety and production

� Smoothwall blasting is recommended in poor groundconditions to minimize excavation damage

� Adequate training of workers and close monitoring isrequired when drilling.

BROWN, E.T. and HOEK, E. 1980. Rock mass classification. Underground

Excavations in Rock. Institution of Mining and Metallurgy, London.

pp. 40–60.

BARTON, N., LIEN, R., and LUNDE, J. 1974. Engineering classification of rock

masses for the design of tunnel support. International Journal of Rock

Mechanics, vol. 6, no. 4. pp. 190–235.

BIENIAWSKI, Z.T. 1989. Engineering Rock Mass Classification. 1st edn. Wiley,

New York.

BRADY, B.H. 1985. Rock Mechanics for Underground Mining. 2nd edn. Allen

and Unwin, London.

MARANDA, A. 2011. ANFO detonation parameters. Central European Journal of

Energetic Materials, vol 8, no. 4. pp. 280–291.

MATHER, W. 1997. Bulk Explosives. https://miningandblasting.files.

wordpress.com [Accessed 13 December 2014].

OBERTHÜR, T., MELCHER, F., BUCHHOLZ, P., and LOCMELIS, M. 2012. The oxidized

ores of the main sulphide zone, Great Dyke, Zimbabwe: turning resources

into minable reserves – mineralogy is the key. Platinum 2012.

Proceedings of the Fifth International Platinum Conference. 'A Catalyst for

Change', Sun City, South Africa, 17–21 September 2012. Southern Afican

Institute of Mining and Metallurgy, Johannesburg. pp. 647–671.

PRENDERGAST, M.D. 1989. The platinum deposits of the, Great Dyke, Zimbabwe.

Magmatic Sulphides – The Zimbabwe Volume. Proceedings of the 5th

Magmatic Sulphide Field Conference, 3–13 August 1987. Prendergast M.D.

and Jones, M.J. (eds). 1st edn. Institution of Mining and Metallurgy,

London. pp. 43–69.

WILSON, A.H. 1972. A hypothesis concerning pillar stability. The Mining

Engineer, vol. 131, no. 1. pp. 409–417.

WOOD, D. 1987. Support in underground hard rock mines.

https://rocscience.com [Accessed 10 December 2014].

ZVARIVADZA, T. 2012. Evaluation of pillar design systems for low reef platinum

mining. MSc thesis, University of Witwatersrand, Johannesburg, South

Africa. �

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332 VOLUME 116

Slurry abrasion is a common phenomenon inmining operations, particularly in pipelinestransporting, for example, sand-water slurries.This type of wear can cause pipeline fracture,shortened operational lifetimes, and impedepipeline efficiency. To reduce or limit abrasion,thermally sprayed tungsten-carbide-basedcoatings are often used as pipe linings(Kanchan et al., 2010). This is due to theirattractive mechanical properties, which includehigh wear resistance, stiffness, hardness,compressive strength, and tensile strength.These properties are provided by the coatingmicrostructure and composition, which is ablend of hard, wear-resistant tungsten carbide(WC) particles embedded in a fracture-toughmetallic binder phase (Brookes, 1997). Cobalt(Co) is the most commonly used binder due toits excellent wetting of the WC phase andmoderate mechanical properties; however, itsapplication is limited to non-corrosiveenvironments as it has a low corrosion andoxidation resistance (Andren, 2001). Nickel(Ni) may also be used as a binder, and hasbeen shown to have superior oxidation andcorrosion resistance, but in some applications

may not have the required mechanicalproperties (Kim et al., 2006).

The WC-based coatings are generallydeposited by flame, arc, plasma, or high-velocity oxy-fuel (HVOF) spraying, all ofwhich require melting or partial melting of thefeedstock powder constituents (Jacobs et al.,1998; Kear et al., 2000; Zikin et al., 2012).These high-temperature deposition processesmay adversely affect the properties of thecoating, as oxidation, decarburization,unwanted phase transformations, and tensileresidual stresses may occur. An alternativedeposition method that claims to reduce and/oreliminate these undesirable effects is the cold-gas dynamic spray process (CGDS)(Champagne, 2007). In this technique, thefeedstock powders are heated only to lowtemperatures which are below the meltingpoints of the constituent materials. Thisprocess has been shown to produce coatingswith low porosity and good wear and corrosionresistance, comparable to HVOF coatings, andmay have compressive residual stresses whichcould improve the coating’s mechanicalproperties (Lima et al., 2002). Due to the lowtemperatures employed, this cold spraytechnique also has significantly lower energyrequirements compared to the high-temperature deposition processes, which makeit attractive in an energy-conscious society(Papyrin et al., 2006).

In the current study, the use of a low-pressure cold gas dynamic spray system toproduce WC-4wt%Ni coatings wasinvestigated. The aim of the research was to

Slurry abrasion of WC-4wt%Ni cold-sprayed coatings in synthetic minewaterby N.B.S. Magagula*†, N. Sacks*†, and I. Botef‡Paper written on project work carried out in partial fulfilment of BSc. Eng. (Metallurgical andMaterials Engineering)

Low-pressure cold gas dynamic spraying was used to deposit WC-4wt%Niand WC-4wt%Ni-1wt%Mo coatings onto mild steel. Dense coatings withvery low porosities were produced. No decarburization occurred duringdeposition and no deleterious phases were formed. The coatings weresubjected to standardized material characterization tests, as well as slurryabrasion testing to assess their wear behaviour. The wear tests wereconducted in synthetic minewater-silica slurries, while distilled water-silica slurries were used as a control. The hardness of the coatings,512HV0.3 and 458HV0.3 for WC-4wt%Ni and WC-4wt%Ni-1wt%Mo respec-tively, are comparable to those achieved using high-temperature coatingprocesses. The abrasion wear rates for both coatings were less than 5 mg/min and 10 mg/min in the distilled water-silica and synthetic minewater-silica slurries respectively. The approximately 50% increase in wearrate in the synthetic minewater slurry is attributed to a synergisticcorrosive wear mechanism. The predominant wear mechanisms wereidentified as binder smearing and delamination, with carbide grainfracture and pull-out.

tungsten carbide, nickel, cold spray, coatings, abrasion, minewater.

* School of Chemical and MetallurgicalEngineering, University of the Witwatersrand,Johannesburg, South Africa.

† DST-NRF Centre of Excellence in StrongMaterials, South Africa.

‡ School of Mechanical, Aeronautical andIndustrial Engineering, University of theWitwatersrand, Johannesburg, South Africa.

© The Southern African Institute of Mining andMetallurgy, 2016. ISSN 2225-6253. Paper receivedFeb. 2016.

333VOLUME 116 �


Slurry abrasion of WC-4wt%NI cold-sprayed coatings in synthetic minewater

produce coatings that have a good resistance to slurryabrasion, and which may find application in a miningenvironment. Nickel was selected as the binder due to itssuperior corrosion properties compared to Co, which wouldmake it more suitable for mining applications. In addition, asmall amount of molybdenum (Mo) was added to investigateits effect on the coating properties. A brief review of the coldspray process will be given first, followed by the methodologyand results of the research.

Cold gas dynamic spraying (CGDS) is a process wherebymetal powder particles are utilized to form a coating bymeans of ballistic impingement upon a suitable substrate(Champagne, 2007). The fine powder particles, usually 5–45 m, may be accelerated at supersonic speeds of 300–1200 m.s-1 towards the substrate, using air or a suitablecarrier gas (Figure 1). The process was first developed in themid-1980s at the Institute for Theoretical and AppliedMechanics of the Siberian Division of the Russian Academyof Science in Novosibirsk (Stoltenhoff et al., 2002). Thediscovery began as a study of the erosive behaviour ofparticle-laden flow on an object in a wind tunnel. Above acertain minimum particle velocity, the particles adhered to thetarget rather than abrading it, leading to the formation ofcoatings; a trend found to be characteristic for each of themetal powders tested. Further depositions were then made ofa wide range of pure metals, metallic alloys, polymers, andcomposites onto a variety of substrate materials.

Since its initial discovery, CGDS has developed into twofundamental deposition methods, namely high-pressure coldgas spraying and low-pressure cold gas spraying, in whichthe operational parameters such as pressure, temperature,and the carrier gases differ (Villafuerte, 2010). High-pressuresystems typically use nitrogen or helium gas with pressuresreaching approximately 7 MPa to accelerate the gas flow tothe supersonic regime. Low-pressure systems typically useair (sometimes nitrogen) with pressures between 0.550–0.695 MPa. Due to the low temperatures used, limited or nomelting occurs during deposition, so that the chemicalcomposition of the coatings typically remains identical to thefeedstock powders (Papyrin et al., 2006).

In order to achieve sufficient adhesion and coating build-up, the powder particles must undergo severe plasticdeformation on impact; hence the successful deposition ofductile metals such as nickel, copper, and aluminium.According to Hussain et al. (2009), during impact thepressure that is generated causes material interlocking and

mechanical bonding. The deposition of ceramic materialssuch as WC is difficult. Due to their hard and brittle nature,such materials tend to shatter on impact, often leading toerosion of the substrate and previously deposited layers(Karthikeyan, 2007; Ang et al., 2011). For successfuldeposition, hard materials must be co-deposited with ductilebinders (Wang and Villafuerte, 2009; Lioma et al., 2015).

An additional advantage of the CGDS process over manyhigh-temperature processes is that it may be applied bymeans of a portable system, which enables on-site repairs tobe done. This is more cost-effective than having componentsdisassembled and shipped off-site for repairs.

In this study two different coatings were investigated, namelya WC-4wt%Ni coating and a WC-4wt%Ni-1wt%Mo coating.The coatings were deposited onto mild steel substrates, 20 ×20 mm in size, which were grit-blasted with -300+100 μmalumina grit prior to the deposition process in order tofacilitate adhesion of the coatings. A low-pressure cold spraymachine (Centreline Series P SST) was used to deposit thepowder blends onto the mild steel using air as the carrier gas.Following deposition, the coatings were polished to a 1 msurface finish for material characterization tests. Themicrostructure was studied using a Carl Zeiss Sigma fieldemission scanning electron microscope (FESEM) coupled withan energy dispersive X-ray spectrometer (EDS), which wasused for elemental composition analysis and mapping. Thecoating thickness, porosity, WC grain size, and Ni bindermean free path were measured using lineal analysis on theFESEM images. Phase identification was done using aBRUKER D2 X-ray diffraction (XRD) instrument with Co-Kradiation and PANalytical X'Pert High Score software. Vickersmicro-hardness tests were done according to ASTM E384(2011).

Slurry abrasion testing of the coatings were conductedusing a modified ASTM G105 (2002) machine. A schematicdiagram of the machine is shown in Figure 2. Three sampleswere tested simultaneously using an applied load of 22 N persample, with the abrasion wheel rotating at 0.66 m.s-1. Silicasand with an angular morphology and an average hardnessof 1084 ± 156HV was used as the abrasive medium. Thesilica was mixed with two different liquid media, namelydistilled water and synthetic minewater. The composition of the synthetic minewater was 37 ppm Ca2+, 1500 ppm Cl-, 40 ppm Mg2+, 980 ppm SO2-, and 943 ppm Na+ (Machio etal., 2005). The distilled water slurry was used as a control toassess the aggressiveness of the synthetic minewater slurry.The test duration was 60 minutes, with the mass loss of each

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334 VOLUME 116

coating being measured at 5-minute test intervals for the first20 minutes, and thereafter in 10-minute intervals. Theabrasion wear rate was calculated as mass loss as a functionof time. The abraded surfaces were examined using electronmicroscopy (FEI SEM Quanta 200) in order to identify thewear mechanisms.

Figure 3 shows the FESEM images of the two coatingmicrostructures adjacent to their respective XRD patterns. Aninhomogeneous distribution of the WC carbide phase withinthe Ni matrix was observed for both coatings. The smallerWC particles are due to fracturing of the carbide phase duringdeposition as the particles impact the substrate. Similarobservations have been made by other authors (Bhaumik etal., 1991). The XRD patterns show the main phases of WC,Ni, and Mo, and it is noted that no decarburization occurred.A summary of the coating properties is listed in Table I. TheWC-4wt%Ni coating has a higher average hardness than theWC-4wt%Ni-1wt%Mo coating. This is due to the smalleraverage WC grain size measured for the WC-4wt.%Ni coating.It is well known that cemented tungsten carbide materialswith finer WC grain sizes have higher hardness values(Brookes, 1997). It was noted that the addition of 1wt %Moto the WC-4wt%Ni coating reduced the hardness by 10.5%,which is quite significant given the small amount of Moadded. The reason for this effect is as yet unclear. Despite thedifferences in the carbide grain sizes, the Ni binder mean freepath and wt% retained WC of both coatings were similar. The

average amount of WC retained in the coatings was 41wt%,which is low given the original feedstock powder compositionof 95–96wt%. This is a common phenomenon in cold-spraycoatings when hard ceramic particles are deposited asmentioned earlier. Due to their hard and brittle nature, acertain percentage of the particles will bounce off thesubstrate during deposition, while some particles fracture onimpact. The porosity of both coatings is very low andacceptable, suggesting that fairly dense coatings wereproduced.

The slurry abrasion wear rates of the two coatings are shownin Figure 4. The average wear rate of the WC-4wt%Ni coatingis slightly lower than that of the WC-4wt%Ni-1wt%Mocoating in both slurries tested. This concurs with the higheraverage hardness of the WC-4wt%Ni coating, which aligns


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Table I

Summary of the coating properties

Coating composition Hardness (HV30) WC retained (wt%) DWC ( m) Ni (μm) Porosity (%)

WC-4wt.%Ni 512 ± 42 41 ± 1.0 0.71 ± 0.08 0.10 ± 0.01 0.01WC-4wt.%Ni-1wt.%Mo 458 ± 36 41 ± 4.2 0.78 ± 0.09 0.11 ± 0.02 0.02


with well-established theory that a higher hardness shouldprovide better resistance against wear (Hutchings, 1992).The wear rates of the coatings in the synthetic minewaterslurries are approximately 50% higher than those in thedistilled water slurries. This large increase was unexpectedgiven that the pH of the distilled water was 7, while that ofthe synthetic minewater was only 6.2. However, these wearrates indicate the extent to which synergistic action betweenwear and corrosion can lead to high material removal rates.While abrasion may be the dominant degradation mechanismbased on the direct contact between the silica abrasiveparticles and the coating, the breakdown of the coatingsurface provides access for the liquid medium to attack thesubsurface material. Thus while abrasion proceeds on thecoating surface in contact with the silica, corrosion of thecoating occurs simultaneously at subsurface level. Thiscorrosive process facilitates material removal by preferentiallyattacking the binder phase, thereby weakening the bondingbetween binder and carbide, and subsequently making iteasier for larger volumes of material to be removed asabrasion continues. Figure 5 is an elemental mapping of oneof the WC-4wt%Ni-1wt%Mo coating surfaces exposed tosynthetic minewater. Apart from the expected coatingelements, traces of sulphur were found on the surface, whichare remnants of the chemical salts used to produce thesynthetic minewater solution.

According to Hutchings (1992), when the ratio of thehardness of the abrasive to the hardness of a surface isgreater than 1.2 (Ha/Hs >1.2) then hard abrasion associatedwith plastic indentation is expected to occur on the surface. Inthis research, the Ha/Hs ratios for both coatings were 2.1 and2.4 for WC-4wt%Ni and WC-4wt%Ni-1wt%Mo respectively.Thus both coatings experienced hard abrasion, with the silicaparticles indenting the coating surface. The precisemechanisms of material removal were identified using SEM,and examples of the worn surfaces are shown in Figures 6and 7. The predominant mechanisms observed were carbidegrain cracking, chipping, and removal, with extensive bindersmearing and delamination. Grooving of the surfaces wasalso observed, which indicates the path followed by the silicaparticles and wear debris. These wear mechanisms are similarto those typically observed for cemented WC materialssubjected to abrasion (Larsen-Basse, 1985). The angularityof the hard silica particles facilitated the preferential removalof the softer nickel binder phase from between the carbide

grains. This leaves the carbide grains unsupported, makingtheir removal easier as abrasion proceeds. The removedmaterial tends to form hard micro-abrasives which then

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subject the coating to additional wear, causing fracture of theembedded carbide grains. The wear mechanisms were similarfor both slurry types, although larger volumes of materialwere removed from the coatings subjected to the syntheticminewater.

This research showed that a low-pressure cold gas dynamicspray system could be used to deposit WC-4wt%Ni and WC-4wt%Ni-1wt%Mo coatings onto mild steel. Dense coatingsexhibiting very low porosities, an average of 41wt% retainedWC, and hardnesses comparable to high-temperaturedeposited coatings, were produced. No decarburization ordeleterious phases were formed in the coatings. The additionof 1wt% Mo to the WC-4wt%Ni coating did not improve thehardness or abrasion resistance. Both coatings showed anapproximate 50% increase in abrasion wear rate whensubjected to a synthetic minewater-silica slurry. This wasattributed to a synergistic corrosive-wear mechanism. Thepredominant wear mechanisms for both coatings are thosetypically experienced by cemented tungsten carbide coatingswhen subjected to abrasion.

Although the coatings have shown good abrasion resistanceunder laboratory conditions, further detailed research needsto be undertaken to determine their suitability for industrialapplication. This should include field testing on carefullymonitored slurry transportation pipelines to observe theperformance of the coatings. As slurries may also have acorrosive nature, corrosion testing should be done on thecoatings, with exposure to varying media found in miningoperations. Pipelines have elbows which experienceeccelerated erosion, often leading to pipe failure, andtherefore the coatings should be subjected to erosion testingat various impact angles and using different slurry media.Finally, an in-depth financial analysis should be done toassess the viability of substituting the cold spray process forsome of the high-temperature processes currently being usedto produce wear-resistant pipe linings.

The authors wish to acknowledge the financial supportreceived from the Department of Science and Technology andthe National Research Foundation in South Africa. Theassistance of Ms D. Lioma, Mr N. Nelwalani, Mr S.Maqobelane, Professor A. Ziegler, and the workshop staff ofthe School of Chemical and Metallurgical Engineering,University of the Witwatersrand, is greatly appreciated.

ANDREN, H-O. 2001. Microstructures of cemented carbides. Materials andDesign, vol. 22, no. 6. pp. 491–498.

ANG, A.S.M., BERNDT, C.C., and CHEANG, P. 2011. Deposition effects of WCparticle size on cold sprayed WC-Co coatings. Surface and CoatingsTechnology, vol. 205, no. 10. pp. 3260–3267.

ASTM E384. 2011. Standard Test Method for Knoop and Vickers Hardness ofMaterials. ASTM International, West Conshohocken, NJ.

ASTM G105-02. 2002. Standard Test for Conducting Wet Sand/Rubber Wheel

Abrasion Tests. ASTM International, West Conshohocken, NJ.

BHAUMIK, S.K., UPADHYAYA, G.S., and VAIDYA, M.L. 1991. Properties andmicrostructure of WC-TiC-Co and WC-TiC-Mo2-Co(Ni) cemented carbides.Materials Science and Technology, vol. 7. pp. 723–727.

BROOKES, K.J.A. 1997. Hardmetals and other Hard Materials. 6th edn.International Carbide Data, UK.

CHAMPAGNE, V.K. 2007. The Cold Spray Materials Deposition Process:Fundamentals and Applications. Woodhead Publishing, Cambridge.

HUSSAIN, T., MCCARTNEY, D.G., SHIPWAY, P., and ZHANG, D. 2009. Bondingmechanisms in cold spraying: the contributions of metallurgical andmechanical components. Journal of Thermal Spray Technology, vol. 18,no. 3. pp. 364–379.

HUTCHINGS, I.M. 1992. Tribology: Friction and Wear of Engineering Materials.Edward Arnold, London.

JACOBS, L., HYLAND, M.M., and DE BONTE, M. 1998. Comparative study of WC-cermet coatings sprayed via the HVOF and the HVAF process. Journal ofThermal Spray Technology, vol. 7, no. 2. pp. 213–218.

KANCHAN, K., ANAND, K., BELLACCI, M., and GIANNOZZI, M. 2010. Effect ofmicrostructure on abrasive wear behaviour of thermally sprayed WC-10Co-4Cr coatings. Wear, vol. 268, no. 11-12. pp. 1309–1319.

KARTHIKEYAN, J. 2007. The advantages and disadvantages of the cold spraycoating process. The Cold Spray Materials Deposition Process. ChampagneV.K. (ed.). Woodhead Publishing Series in Metals and SurfaceEngineering, Woodhead Publishing, Cambridge. pp. 62–71.

KEAR, B.H., SADANGI, R.K., JAIN, M., YAO, R., KALMAN, Z., SKANDAN, G., and MAYO,W.E. 2000. Thermal sprayed nanostructured WC/Co hardcoatings. Journalof Thermal Spray Technology, vol. 9, no. 3. pp. 399–406.

KIM, H-J., LEE, C-H., and HWANG, S-Y. 2005. Superhard nano WC-12%Cocoating by cold spray deposition. Materials Science and Engineering A,vol. 391, no. 1–2. pp. 243–248.

KIM, H-C., SHON, I-J., YOON, J-K., and DOH, J-M. 2006. Comparison of sinteringbehaviour and mechanical properties between WC-8Co and WC-8Ni hardmaterials produced by high-frequency induction heating sintering. Metalsand Materials International, vol. 12, no. 2. pp. 141–146.

LARSEN-BASSE, J. 1985. Binder extrusion in sliding wear of WC-Co alloys. Wear,vol. 105. pp. 247–256.

LIMA, R.S., KARTHIKEYAN, J., KAY, C.M., LINDEMANN, J., and BERNDT, C.C. 2002.Microstructural characteristics of cold-sprayed nanostructured WC-Cocoatings. Thin Solid Films, vol. 416, no. 1–2. pp. 129–135.

LIOMA, D., SACKS, N., and BOTEF, I. 2015. Cold gas dynamic spraying of WC-Nicemented carbide coatings. International Journal of Refractory Metals andHard Materials, vol. 49. pp. 365–373.

MACHIO, C.N., AKDOGAN, G., WITCOMB, M.J., and LUCKYX, S. 2005. Performance ofWC-VC-Co thermal spray coatings in abrasion and slurry erosion tests.Wear, vol. 258. pp. 434–442.

PAPYRIN, A., KOSAREV, V., KLINKOV, S., ALKHIMOV, A., and FOMIN, V. 2006. ColdSpray Technology. 1st edn. Elsevier Science.

STOLTENHOFF, T., KREYE, H., and RICHTER, H.J. 2002. An analysis of the coldspray process and its coatings. Journal of Thermal Spray Technology, vol. 11, no. 4. pp. 542–550.

VILLAFUERTE, J. 2010. Recent trends in cold spray technology: looking at thefuture. Surface Engineering, vol. 26, no. 6. pp.393–394.

WANG, J., and VILLAFUERTE, J. 2009. Low pressure cold spraying of tungstencarbide composite coatings. Advanced Materials and Processes, vol. 167,no. 2. pp. 54.

ZIKIN, A., ILO, S., KULU, P., HUSSAINOVA, I., KATSICH, C., and BADISCH, E. 2012.Plasma transferred arc (PTA) hardfacing of recycled hardmetal reinforcednickel-matrix surface composites. Materials Science (Medziagotyra), vol. 18, no. 1. pp. 12–17. �


VOLUME 116 337 �

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Floatation concentrate from ore from theeastern Bushveld Complex of South Africa,specifically the Platreef, Merensky, and UG2reefs, forms the feed to the Polokwaneplatinum smelter (Hundermark, De Villiers,and Ndlovu, 2006). The ore from the UG2 Reefhas high chromite content, which requireshigh operating temperatures (1500–1700°C) toavoid chromium spinel build-up in the furnacehearth. These high operating temperatureslead to matte superheats in the vicinity of 500–600°C, which put increased demands on therefractory materials (Nelson et al., 2005).

Upon tapping, the matte moves throughthe tap-hole, which consists of an alumina-chrome refractory brick-lined tapping channel(Hundermark, De Villiers, and Ndlovu, 2006).The flow of molten matte is stopped by theinjection of tap-hole clay to form a plug in thetap-hole. The tap-hole clay hardens andstrengthens during curing to obtain therequired hardness and refractoriness againstpenetration, corrosion and erosion (Nelson andHundermark, 2014).

The amount and positioning of tap-holeclay in the tap-hole and tapping channel affectthe shape and length of the tapping channel,which in turn affect the consistency that canbe achieved in the tapping process (Nelson andHundermark, 2014). Wear of the tap-hole andtapping channel results in less control beingpossible on the tapping process and less safeoperating conditions due to the possibility ofburn-through and unintentional reopening ofthe tap-hole. Worn refractories have to bereplaced, requiring significant expenses anddowntime (Nelson and Hundermark, 2014).

It is generally accepted that refractory wearby matte occurs in three steps. Penetration ofthe matte into the bricks occurs first.Penetration is followed by corrosion anderosion, during which the worn refractorybricks are corroded and pieces of brick areremoved from the tapping channel along withmolten material (Nelson and Hundermark,2014). The extent of refractory wear dependson the amount of matte that penetrates intothe brick and the temperature and viscosity ofthe matte. An increase in matte temperatureleads to a decrease in matte viscosity and anassociated increase in matte fluidity and abilityto penetrate into the refractory brick (Nelson etal., 2005).

Brick wear may be minimized throughprotection provided by the tap-hole clay.Ideally, upon injection of the tap-hole clay intothe tapping channel and tap hole, interactionbetween the tap-hole clay and brick wouldmake matte penetration into the brick moredifficult since matte would be required to movethrough the clay before penetration into thebrick is possible. This interaction between tap-hole clay and brick and the associated extentof matte penetration formed the focus of thisstudy.

Matte — tap-hole clay — refractory brickinteraction in a PGM smelterby J. Du Toit*, R.D. Cromarty*, and A.M. Garbers-Craig*Paper written on project work carried out in partial fulfilment of BEng (MetallurgicalEngineering)

Penetration of matte into tap-hole bricks causes detrimental refractorywear, which can lead to furnace breakouts. The ability of the tap-hole clayto form a protective layer on the brick, thereby limiting matte penetrationwas investigated by examining the interaction between platinum groupmetal (PGM) matte, tap-hole clay, and alumina-chrome refractory brickson a laboratory scale.

Samples containing clay and brick as well as samples containing clay,brick, and matte were heated to different temperatures to establish theclay-brick interaction and the extent of matte penetration. The greatestdegree of physical contact between the brick and clay was achieved atcuring temperatures of 600°C. Poor clay-brick contact was observed in thesample that was heated to 900°C.

Matte displaced the clay in the clay-brick-matte sample that washeated to 1350°C, with significant matte penetration into the brick. Lessmatte penetration was observed when the clay-brick-matte sample washeated to 1500°C. Less matte penetration was also observed in the clay-brick-matte sample in which the clay and brick were pre-baked at 800°C,and the sample then reacted with matte at 1350°C.

tap-hole clay, alumina-chrome refractory bricks, PGM matte, reactioninterface, penetration.

* Department of Materials Science and MetallurgicalEngineering, University of Pretoria.


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Matte — tap-hole clay — refractory brick interaction in a PGM smelter

Primary PGM matte was obtained from the Anglo PlatinumPolokwane smelter, while alumina-chrome bricks and tap-hole clay were obtained from the refractory suppliers to thePolokwane smelter1.

These materials were characterized using X-raydiffraction analysis (XRD), X-ray fluorescence (XRF), andscanning electron microscopy using energy-dispersive X-rayspectroscopy (SEM-EDS).

Quantitative XRD analysis indicated that the nickel-copper-rich PGM matte consisted of 61.9% (Fe, Ni)9S8, 13.3% FeS,6.6% Cu5FeS4, 6.8% SiO2, 6% CaAl2Si2O8, and 3.9% FeCr2O4.

XRF analysis confirmed that the brick contained 75% Al2O3,20.7% Cr2O3, 2.2% P2O5, and 1% SiO2. XRD analysis revealedthat Al2O3 and the (Al,Cr)2O3 solid solution phase were themajor phases present in the brick (56.0% and 40.3% respec-tively), while trace amounts aluminium phosphate (AlPO4)and cristobalite (SiO2) could also be detected.

Microstructurally, the brick consisted of large aluminagrains embedded in an alumina-chrome-based matrix,bonded through the formation of the (Al,Cr)2O3 solid solutionphase (Figure 1).

The tap-hole clay is an organically bound material. XRDanalyses were conducted on the raw clay, and on claysamples that were heated to 950°C and subsequently cooledto room temperature in an oxidizing as well as an inertatmosphere.

The raw clay was found to consist largely of thecrystalline phases corundum and andalusite (55 wt% and 11 wt% respectively) with some silicon carbide, silicon,quartz, mullite, and a small amount of graphite. The carbonbinder present in the clay is an amorphous phase which wasnot quantified by XRD analysis.

Upon heating, graphite is retained in the sample in aninert atmosphere but is oxidized from the system whenheated in air.

In order to allow comparison between types and amountsof phases under oxidizing and inert atmospheric conditions,the analysis of the sample heated under inert atmospherewas normalized to exclude graphite. It was found thatandalusite decomposes into mullite (3Al2O3.2SiO2) and SiO2

or a glassy phase when heated in both the inert and oxidizingatmospheres. According to Schneider and Komarneni (2006),andalusite is stable up to temperatures in the vicinity of780°C, at which decomposition of andalusite into mullite andsilica initiates (Schneider and Komarneni, 2006). Thedecrease in the amount of andalusite in the oxidizing andinert atmospheres is therefore expected with an associatedincrease in mullite and silica. This agrees with the findings ofthe XRD analysis, where mullite increased from 5.3% toalmost 10% and silica from 6.9% to close to 10% in bothsamples.

Thermogravimetric analysis (TGA) was conducted on thetap-hole clay to establish the temperatures at whichdecomposition of the binder takes place (Figure 2). A 4%decrease in mass was observed between 100 and 200°C whenthe sample was heated in both air and nitrogen. Anadditional 10% mass loss was observed at temperaturesbetween 450 and 600°C in air. The mass loss between 100and 200°C can be ascribed to volatiles being driven from thesample. Pérez et al. (2004), obtained similar results throughthermogravimetric analysis of pitch binders. The 450–600°Ctemperature range correlates to the temperature range atwhich oxidation of graphite occurs (Xiaowei, Jean-Charles,and Suyuan, 2004). The sample heated in air underwent alarge mass loss in the 450–600°C range due to graphiteoxidation. The mass of the sample heated in nitrogen overthis temperature range remained unchanged, indicating thecompletion of the pyrolysis of the binder.

Laboratory-scale experiments were performed to simulate theclay-brick (CB) and the clay-brick-matte (CBM) interactions.In both sets of experiments argon gas was used for purgingto avoid the oxidation of sulphur in the matte.

For the clay-brick interaction a Phasecon tube furnacewas used. The furnace was heated to temperatures of 600°Cand 900°C and kept at temperature for one hour. A heatingramp rate of 15°C/min was used upon heating and 50°C/minupon cooling. Technical-grade argon (99.9% argon) was usedto purge the furnace for the heating, dwell, and coolingperiods.

In the clay-brick experiment an alumina crucibleassembly, containing a brick core surrounded by clay, wasused (Figure 3).

The clay-brick-matte experiments were done using aninduction furnace with a graphite susceptor in an insulatedgas-tight chamber. An Ambrell Ekoheat power supply wasused and temperature was controlled using a Eurothermtemperature controller and a type B thermocouple.

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1Names of suppliers omitted for confidentiality reasons

The induction furnace was purged with technical-gradeargon for 30 minutes prior to heating to temperatures of1350°C and 1500°C. Purging continued for the duration ofthe experiment. A heating rate of 20°C/min was used,followed by dwelling at temperature for 60 minutes and thencooling at a rate of 50°C/min.

The crucible assembly consisted of an alumina cruciblewith a section of the brick placed at the bottom and clayadded to the top and around the sides of the brick. Matte wasthen added on top of the clay (Figure 3).

An additional experiment was performed in which theCBM set-up was modified by first baking the clay and brickin an alumina crucible in the Phasecon retort furnace at800°C for one hour. After cooling, the matte was added andthe CBM experiment was performed in the induction furnaceas described previously. The purpose of this experiment wasto establish whether pre-baking would increase the physicalcontact and extent of interaction between the clay and brick,thereby improving the resistance against matte penetration.

The samples were sectioned, and polished samplesprepared for analysis on completion of the CB and CBMexperiments. Reflected light microscopy and SEM-EDSanalysis were used to determine the amount of clay-brickinteraction as well as the extent of matte penetration.

The clay-brick interaction was limited, as areas at the clay-brick interface could be distinguished where no direct contactoccurred. Areas of poorer and better physical contact wereobserved, with overall better contact being achieved in thesample heated to 600°C (Figure 4), compared to the samplethat was heated to 900°C (Figure 5). The gap between theclay and brick implies that chemical interaction did not occur.

The reflected light microscopy images of the samplescontaining clay, brick, and matte indicate that matte (brightlycoloured) penetrated into both the clay (Figure 6A) and thebrick (Figure 6B).

In the CBM sample heated to 1350°C, the matte seemed tohave displaced the clay. The top layer, which initiallyconsisted of matte, contained clay (dark grey, Figure 7A),while the section above the brick, which was initially clay,contained matte only (light grey, Figure 7B). Copper sulphide(light sulphide phase) and an iron sulphide (dark sulphide

phase) could be distinguished in the solidified matte (Figure7B), while an Fe-Ni-Cu-based alloy could also be observed.

The brick (Figure 7C) was also penetrated by the matte.This was expected, since the matte displaced the clay and noprotective layer was present to resist matte penetration intothe brick.

The sample heated to 1500°C also showed significantmatte penetration; although complete displacement of theclay section with matte was not evident. There is a cleardistinction between the initial matte section (light grey) andthe initial clay section (dark grey), although droplets of matteseem to have penetrated into the clay region (Figure 8A). Thebright phases in the clay are alloy droplets and not matte.Alloy droplets, however, were not observed in the brick, butonly matte droplets.

Greater interaction between the clay and the brick wasobserved in the 1350°C CBM sample that contained pre-baked clay. There was, however, still matte penetration intothe clay and the brick sections (Figure 9).

Decomposition of the binder occurs at temperatures up to 600°C with volatiles being driven off in the 100–200°Ctemperature range. Oxidation of graphite occurs at 450–600°C.


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Interaction between tap-hole clay and brick does notoccur extensively at either 600°C or 900°C. Regions of poorphysical contact between the clay and brick were observed.

Without physical contact, chemical interaction could also notoccur. Without clay-brick interaction, the clay provides littleprotection against matte penetration into the brick. Thephysical contact between the clay and the brick proved to bebetter when the clay and brick were reacted at a lowertemperature (600°C), rather than a higher temperature(900°C).

Matte penetrated through the clay and into the brick insamples heated to 1350°C as well as to 1500°C. Less mattepenetration occurred in the 1500°C sample and the 1350°Csample that contained pre-baked tap-hole clay.

In the CBM sample that was reacted at 1500°C, mattereacted with the tap-hole clay to form a Cu-Fe-Ni alloy.

The authors would like to thank Anglo American (Dr LloydNelson, Rodney Hundermark, and Keith Hines) for supplyingthe raw materials as well as for technical assistance. A wordof thanks also goes to colleagues and analytical staff in theDepartment of Material Science and Metallurgical Engineeringat the University of Pretoria.

HUNDERMARK, R., DE VILLIERS, B., and NDLOVU, J. 2006. Process description and

short history of Polokwane Smelter. Southern African Pyrometallurgy2006. Jones, R.T. (ed.). Southern African Institute of Mining and

Metallurgy, Johannesburg. pp. 35–41.

NELSON, L.R. and HUNDERMARK, R.J. 2014. ‘The tap-hole'— key to furnace

performance. Furnace Tapping Conference 2014. Southern African

Institute of Mining and Metallurgy, Johannesburg. pp. 1–32.

NELSON, L.R., STOBER, F., NDLOVU, J., DE VILLIERS, L.P., and WANBLAD, D. 2005.

Role of technical innovation delivery at the Polokwane Smelter. Nickel andCobalt 2005. Challenges in Extraction and Production, Calgary. Donald, J.

and Schonewille, R. (eds.). CIM, Montreal. pp. 91–116.

PEREZ, M., GRANDA, M.S., MORGAN, T., and MENENDEZ, R. 2004. A thermoana-

lytical study of the co-pyrolysis of coal-tar pitch and petroleum pitch. Fuel,vol. 83, no. 9. pp. 1257–1265.

SCHNEIDER, H. and KOMARNENI, S. 2006. Mullite. Wiley, Weinham.

XIAOWEI, L., JEAN-CHARLES, R., and SUYUAN, Y. 2004. Effect of temperature on

graphite oxidation behaviour. Nuclear Engineering and Design,

pp. 273–280. �

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Using near-infrared spectroscopy (NIRS)technology for ore sorting is a new concept forthe mineral processing and mining industry.NIRS has been used for decades in thelaboratory for the identification of pureminerals, and has its roots in the recycling,food, and pharmaceutical industries (Salterand Wyatt, 1991; Robben et al., 2009). Oresorting in itself is not a new concept; it wasintroduced during the Stone Age with hand-sorting being the first method to separatevaluable materials from gangue (Wills andNapier-Munn, 2006; Sassos, 1985). However,over the years the scale of mining hasincreased and hand-sorting has becomechallenging to implement (Joensson, 2014).

Sensor-based sorting is an advancedtechnology that can help overcome problemssuch as ore dilution experienced in mineralprocessing operations. The benefits are lowerenergy and water costs, reduced ore dilution,lower environmental impact, and improvedprofit margin (Mathew, 1974; Jonsson, 2014;

Salter and Wyatt, 2009; Death et al., 2009). Insensor-based sorting, materials are mechan-ically sorted based on certain physicalproperties that are detected by a sensor (Dalm,2013). Research has found that with NIRscanners it is possible to obtain a ‘fingerprint’of a sample that is directly related to itsmineralogical composition. According toWoutruba et al. (2009), molecules absorb NIRradiation by means of electronic andvibrational transitions. Nowadays, there aremany sensors available in the market thatutilize different material properties; the choiceof a sensor is dependent on the mineralogy ofthe ore.

Traditional metallurgical techniques fordiamond winning from kimberlitic ore involvesize reduction, dense medium separation(DMS), and final recovery by X-ray technology(Ketelhodt et al., 2013). These techniqueshave no ability to remove waste rocks that areoften associated with the kimberlite. Thekimberlite orebody at Cullinan Diamond Mine(CDM) is intruded by sills and dykes of wasterock, and the current mining method cannotseparate the waste material (Bartlett, 1994).Waste hoisted from underground is mostlyfrom development areas. This paper evaluatesthe viability of the new COLOR/NIR sortingtechnology to remove the waste rocks from thekimberlite ore stream, thus reducing theamount of waste going into the DMS process.

Separation of kimberlite from wasterocks using sensor-based sorting atCullinan Diamond Mineby T. Mahlangu*†, N. Moemise†, M.M. Ramakokovhu*, P.A. Olubambi‡, and M.B. Shongwe*Paper written on project work carried out in partial fulfilment of BTech. Eng. (Metallurgical Engineering)

Near-infrared (NIR) spectroscopy sorting technology is incorporated in anautomated optical mineral sorter that can discriminate between materialsusing the differences in characteristics when exposed to near-infraredradiation. During September 2014 to April 2015, a pilot plant that utilizedNIR technology to discriminate between kimberlite and waste materialswas commissioned to determine the viability of including this technologyin the diamond winning process flow sheet at Cullinan Diamond Mine. Theplant was used to minimize the waste content in the size fraction -70+35mm that reports to the crushing section and then to the dense mediaseparation process. This paper describes the initial test work, conducted atMintek, that led to the decision to conduct a pilot-scale study. Themineralogical characterization of the feed and product streams to establishthe sorting criteria and the operational data obtained during the pilot plantcampaign are described. The results indicated a good possibility of discrim-inating between the kimberlite and waste material using NIR technology.However, the consistency of discrimination was not good enough to avoidthe risk of potential diamond loss. Furthermore, a lower than expectedavailability of the machine reduced the throughput capabilities.

sensor-based sorting, NIR spetroscopy, kimberlite, preconcentration.

* Institute for NanoEngineering Research,Department of Chemical, Metallurgical andMaterials Engineering, Tshwane University ofTechnology, Pretoria, South Africa.

† Cullinan Diamond Mine, Petra DiamondsSouthern Africa (Pty) Ltd.

‡ Department of Chemical Engineering Technology,University of Johannesburg, Johannesburg,South Africa.


343VOLUME 116 �


Separation of kimberlite from waste rocks using sensor-based sorting

In order to provide background information for sensor-basedsorting, mineralogical characterization of a run of mine(ROM) sample from CDM was performed by X-ray diffraction(XRD). The primary use of XRD is for the identification andcharacterization of compounds based on their diffractionpatterns.The sample, which had a top size of -70 mm, wasreduced using a single toggle jaw crusher followed by ballmilling. The XRD results are shown in Figure 1 and Figure 2.

Both the kimberlite (Figure 1) and the waste (Figure 2)were found to contain NIR-active minerals, and there is thusthe possibility of using NIR technology to discriminatebetween the two streams. Images (Figure 3) extracted fromthe classifier also showed a very good possibility ofseparating kimberlite from the associated waste materials.Classifiers are part of the NIR technology programme and areused to classify materials (Korsten, 2014).

Tests work was conducted with the Pro SecondaryCOLOR/NIR sorter illustrated in Figure 4. The sorter uses acombination of a high-resolution line camera and NIRscanner to provide accurate detection of the mineralfingerprint of each rock (Ketelhodt et al., 2013). The workingwidth of the COLOR/NIR sorter is 1200 mm.

The technical set-up of the sorter is shown in Figure 5.The sorter used was a chute-type sorter, with the material fedby a vibratory feeder and accelerated down a chute undergravity. Scanning is done by means of an NIR and a coloursensor on the free-falling stream of particles. Prior to thesorter, a washing/sizing screen with a 10 mm aperture sizewas installed for the purpose of particle preparation. Sizingwas done to obtained a size ratio of 1:3, because research on

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(a)

(b)

(c)

et al.

sensor based technology has shown that the sorting resultscan deteriorate at a particle size ratio greater than three(Woutruba and Riedel, 2005).

The material that was supplied for the test work was a 12 t sample of Cullinan ROM material. The waste rocks atCDM comprise of gabbro, norite, felsite, and quartzite. Thesample, which was collected by means of a belt cut, waswithin the size range of -70+35 mm. The sorter needs to beprogrammed with information obtained from a pre-classifiedsample. Thus, a 10 kg sample of the kimberlites and wastematerial was collected from underground at Cullinan. Groupswere formed by statistical means and applied into the sortingalgorithm, called the classifier, for bulk sorting. The processflow diagram configuration shown in Figure 6 was testedwith the aim of maximizing overall kimberlite recovery with atarget of 5% kimberlite loss to the waste stream.

The overall results of the tests that were carried out only inthe rougher stage are shown in Table I and Figure 7. Theaverage kimberlite recovery was calculated to be 97.8%,while the average waste removal was calculated to be 90.2%

The scavenger stage was used to recover the kimberlitemisclassified into the waste stream from the rougher stage.Approximately 4.1% of the kimberlite is calculated to be lostat the rougher stage. Table II and Figure 8 show the resultsfor the scavenger stage. The average kimberlite recovery wascalculated to be 99.8% and the average waste removal wascalculated to be 93.1%.

The results clearly indicate that the introduction of ascavenger stage improves the separation efficiency andminimizes the potential for diamond loss. It is also seen thatthe kimberlite recovery decreases at a low classifiersensitivity. This is due to the fact that low classifier

sensitivity reduces the aggressiveness of the machine withrespect to its ejecting potential. In both the rougher andscavenger stage the kimberlite recovery was calculated to beabove 95%, which clearly indicates that the COLOR/NIRsorter is able to discriminate between the CDM kimberliticand waste rocks.


345VOLUME 116 �

et al.

Table II

2 45 1268.0 589.0 679.0 5.87 0.24 587.5 99.75 622.0 91.617 45 1047.0 535.2 511.8 4.83 0.34 533.6 99.69 473.4 92.508 50 992.0 505.8 486.2 6.34 0.22 504.8 99.80 463.0 95.23

Table I

1 50 958.0 457.1 509.9 1.03 - 452.0 98.89 480.0 94.133 55 1220.0 616.5 603.5 5.64 -583.0 94.57 560.5 92.874 65 1149.0 600.0 549.0 1.76 - 591.5 98.58 474.5 86.435 60 1376.0 685.0 691.0 2.93 - 666.0 97.23 629.0 91.026 50 1189.0 581.1 607.9 4.28 - 579.1 99.66 525.5 86.44


Figure 9 compares the kimberlite loss in the rougher andscavenger stages against the target kimberlite loss of 5%. Thekimberlite lost to the waste stream was monitored to preventthe risk of diamond loss.

There is a relatively high loss of the kimberlite ore whenusing only a rougher stage. However, introducing thescavenger stage minimized the risk of kimberlite loss to anaverage of 0.3%. The kimberlite lost was above target fortests 2, 3, and 8 because the agressiveness of the machinewas kept low.

The feed to the pilot plant was the discharge from thescrubber, screened to -70+35 mm size. The main goal of thesorting in this case was to preconcentrate the -70+35 mmmaterial prior to the DMS process. A lower waste content inthe DMS feed would reduce the impact of near-density wastematerial on the cyclone dynamics; with the benefit of thereduction of waste material reporting to the DMS concentrate,which could have a detrimental impact on the subsequent X-ray sorting processes. The pilot plant was run fromSeptember 2014 to April 2015. The commissioning processwas complete within a month. Figure 10 illustrates the pilotplant flow sheet, where only the single pass configurationwas implemented.

Figure 11 shows the average tons treated through the pilotplant for a period of 6 months (November 2014 to -April2015) when the plant was running at full production.

The total tonnage fed to the pilot plant was lower than thedesign tonnage of 50 000 t/ month, due to the fact that theavailability and utilization of the pilot plant was lower thanexpected. The availability of the pilot plant was critical forsuccessful assessment of the sensor-based sorter andeconomic evaluation.

Throughout the duration of the project the tailings streamwas sampled to monitor the average kimberlite loss.Kimberlite loss is an indication of potential diamond loss, andshould be kept at a minimum. The acceptable kimberlite losswas set at a target of below 5%.

Figure 12 shows the kimberlite loss during the pilot plantcampaign. It was possible to keep the kimberlite loss below5% for several months, but in January 2015 a high loss of oreoccurred. It was decided to stop the sorter until the problemwas found and rectified. The sorter was found to have lostprogramming and had to be re-programmed with pre-classified samples. It was also realized that the kimberliteloss was above target when the screen sprays were blockedand the feed coated with mud. After the problem was rectified

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346 VOLUME 116

the kimberlite loss was acceptable, as can be seen in Figure 12.

Based on the test work, the COLOR/NIR sorter is generally agood tool to separate Cullinan kimberlite from waste rocks.The introduction of a scavenger stage will improve thekimberlite recovery and also minimize diamond loss. Thepilot plant test work results were not consistent since thesensing technology is based on the surface properties of thematerial, hence the feed needs to be clean and free of dust ormud prior to sorting. However, this is not always the case ina production environment, particularly for kimberlite ores,which have a high content of clay material. Due to the risk ofdiamond loss as a function of kimberlite lost, it isrecommended that a scavenger stage be implemented infurther kimberlite preconcentration processes using the samesorting system.

The author wishes to express her gratitude to CullinanDiamond Mine (Pty) Ltd for the opportunity and funding forthe project. The deepest thanks are extended to my mentorand supervisor for their guidance and technical input, and tothe CDM laboratory personnel for their assistance during thetest work and analysis. The inputs from Mintek and TomraSorting (Pty) Ltd, South Africa, are also acknowledged.

ASD Inc. 2010. Fieldspec3 User Manual,

http://support.asdi.com/document/documents.aspx [Accessed 28 May

2015].

BARLETT, P.J. 1998. Premier Mine. Proceedings of the 7th International

Kimberlite Conference, Cape Town. pp. 39–49.

BERRY, L.G. and MASON, B. 1959. Mineralogy: Concepts, Description and

Determinants. Springer, San Franciso. pp. 296–298.

CHADWICK, J. 2008. Process progress. International Mining, May 2008.

pp. 24–40.

CHRISTON, J. 2014. Sensor based sorting technology implementation in the

mining and mineral processing. Lund University, Sweden.

COMMODASTULTRASORT. 2009. Sorters reduce mining costs and increase profits.

pp. 34–36.

DALM, M. 2012. TA3690 – Project on sensor based sorting of copper-

molybdenum ore. pp. 1–4.

DEATH, D.L., CUNNINGHAM, A.P., and POLLARD, L.J. 2009. Multi-element and

mineralogical analysis of mineral ores using laser breakdown

spectroscopy. Spectrochimica Acta Part B. Atomic Spectroscopy, vol. 64,

no. 10. pp. 1048–1058.

HARMON, R.S., DELUCIA, F.C., MCMANUS, C.E., MCMILLAN, N.J., JENKINS, T.F.,

WALSH, M.E., and MIZIOLEK, A. 2006. Laser-induced breakdown

spectroscopy – an emerging chemical sensor technology for real-time field-

portable, geochemical, mineralogical, and environmental applications.

Applied Geochemistry, vol. 21, no. 5. pp. 730–747.

HOLLAS, J.M. 2004. Modern Spectroscopy. 5th edn. Wiley. Chapters 1–3.

ROBBEN, M., WOTRUBA, H., BALTHASA, D., and REHIMANN, V. 2009, NIR spectral

imaging in the mineral processing industry. RWTH Aachen University,

Germany. pp. 2–5.

ROBBINSON, D.N. 1973. Magnetite-serpentine-calcite dykes at Premier Mine and

aspects of their relationship to kimberlite and to carbonatite of alkali

carbonatite complexes. Physics and Chemistry of the Earth, vol. 9.

pp. 61–70.

SALTER, J.D. and WYATT, N.P.G. 1991. Sorting in the mineral industry: past,

present and future. Minerals Engineering, vol. 4, no. 7. p. 779–796.

Sassos, M.P. 1985. Mineral sorters. Engineering and Mining Journal, vol. 186,

no. 6. pp 68–72.

SMITH, C.B. 1983. Pb, Sr, and Nd isotopic evidence for sources of southern

African Cretaceous kimberlites. Nature, vol. 304, no. 5921. pp. 51–54

TONG, Y, 2009. Technical amenability study of laboratory scale sensor-based

ore sorting on a Mississippi Valley type lead-zinc ore, MASc thesis,

Department of Mining Engineering, University of British Columbia.

pp. 19–20.

WAGNER, P.A. 1914. The Diamond Fields of South Africa. Transvaal Leader,

Johannesburg. 347 pp.

WESTHYZEN, P., BOUWER, W., and JAKINS, A. 2013. Current trends in the

development of new or optimization of existing diamond processing

plants, with the focus on beneficiation. Journal of the Southern African

Institute of Mining and Metallurgy, vol. 114. pp. 539–545.

WILLS, B.A. and NAPIER-MUNN, T. 2006. Mineral Processing Technology.

7th edn. Elsevier Science & Technology, Brisbane. Chapter 14,

pp. 372–377. �


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The Catalyst Manufacturing Plant (CMP) is adusty environment with temperatures higherthan ambient. Molten mill scale (magnetite,Fe3O4) is tapped from the electric arc furnaceinto the casting moulds at temperatures closeto 1600°C. After 10 seconds the magnetite isquenched with a water spray for 50 seconds toa minimum temperature of 400°C. Sometimesthere is residual water in the pans from thecooling fog process (water sprays) in theempty mould. In a typical plant, the factoryproduces 40–44 batches a day containingbetween 150–300 moulds, depending on thetime required for the specific batch (Buchholz,2014). The typical batch in the CMP usuallyweighs about 6 t. The thickness of the tap,speed of the casting belt, and tilting angle allaffect the number of moulds per batch.

One of the main problems faced during themolten mill scale casting is the prematurefailure of the casting moulds. Cracks initiateon the surface of the mould, which is incontact with the hot catalyst, and propagateinto the interior of the mould. Cracks aregenerally concentrated in the middle area ofthe mould where the catalyst makes firstcontact with the mould, and which experiences

the highest temperature fluctuations. Thissuggests that the cracks are caused by thermalfatigue during the casting process.

In order to prolong the life of the mouldand improve the operational efficiency, arecommendation for a new alloy or animprovement of the existing casting mould hadto be made.

In many instances, there are no service liferecords for specific moulds to track their lifespan, as well as no records regarding thesurface temperatures of the mould during theheating and cooling cycle. The operatingconditions and safety concerns make itimpossible to measure the surface temper-atures. Therefore, the temperature fluctuationscan only be estimated.

On average, the casting moulds last about6 months in this operating environment. Oneof the primary indications that the mould hasreached the end of its life is the sticking of thecatalyst to the mould due to the enlargedsurface area caused by the surface cracks, asseen in Figure 1. This type of surface is calledthe ‘elephant skin’ and is caused by thermalfatigue.

All materials of construction are affected bythermal fatigue. This is a result of cyclicstresses caused by variations in temperature.The damage occurs under repeated thermalcycling in the form of cracking in the metal,specifically where relative movement (differ-ential expansion) is constrained (AmericanPetroleum Institute, 2011).

The failure of the moulds in the currentinvestigation can be classified as a low-cyclehigh-strain fatigue problem, typically with N <104 cycles. The number of cycles to failure is

An evaluation of the thermal fatigueperformance of three alloys for castingmould applicationsby V. van der Merwe* and C.W. Siyasiya*Paper written on project work carried out in partial fulfilment of B. Eng. (Metallurgical Engineering)

A petrochemical company experiences premature thermal fatigue failure ofthe casting moulds used in catalyst production. The aim of the project wasto find an alternative alloy that would outperform the current low-alloycast steel used for the moulds. Based on their thermo-fatigue properties,3CR12 ferritic stainless steel and H11 tool steel were chosen for testingand comparison with the currently used BS3100 B7 cast steel. Samples ofeach material were subjected to temperature cycling in a Gleeble 1500TM

thermo-mechanical processing simulator, followed by surface analyses.The main parameters derived from the test work were the total true strain,the hot strength of the materials, and the number of cycles to failure.Additionally, the coefficient of thermal expansion for each material wasmeasured using a Bähr dilatometer. H11 tool steel yielded the bestperformance by way of having the fewest surface cracks, the lowest totaltrue strain per cycle, the most cycles to failure, the highest hot strength,and the lowest coefficient of thermal expansion.

thermal fatigue, fatigue failure, casting moulds, thermal expansion.

* University of Pretoria, Department of MaterialsScience and Metallurgical Engineering, Pretoria,South Africa.

© The Southern African Institute of Mining andMetallurgy, 2016. ISSN 2225-6253. Paper receivedApr. 2016.

349VOLUME 116 �


An evaluation of the thermal fatigue performance of three alloys

fewer that in typical high-frequency low-cycle fatigue. Inthese casting moulds, the thermal fatigue failure is controlledby a cyclic plastic strain rather than a cyclic stress. The cyclicplastic strain results from the thermal stresses, which are aconsequence of the temperature fluctuations during thecasting process. The number of cycles to failure, Nf , for thistype of fatigue failure can be predicted by the Coffin-Mansonequation.

This approach is similar to what is known as the Parisequation for the stable crack growth regime. The Parisequation for high-frequency low-cycle fatigue is

[1]

whereC2 = Constant

= Cyclic strain amplitude.

Low-cycle fatigue test data are often represented as a plotof the plastic strain range versus cycles to failure. Whenplotted on log-log coordinates, a straight line is obtained,which is represented by the Coffin-Manson relation:

[2]

where p is the plastic strain range, Nf is the number ofcycles to failure (fatigue life), C2 is a constant and is thefatigue ductility exponent (generally -0.5 > < -0.7) (CoffinJr., L.F., 1954; Manson, S.S., 1954)

The physical properties of the three steels that wereinvestigated are given in Table I. The selection of 3CR12 andH11 steels was based on their melting points, coefficients ofthermal expansion, and thermal conductivities. The chemicalcompositions of the steels are given in Tables II.

The thermal fatigue simulation was carried out in aGleeble 1500TM thermo-mechanical processing simulator.This apparatus enables the specimen to be subjected to eitherisothermal compression or tensile tests at elevatedtemperature. However, in this investigation, the specimenswere subjected to temperature cycling without constraint.

Three samples, 10 mm in diameter and 116.5 mm inlength, were prepared of each material (Figure 2). The testzone at the centre of each sample was milled to a thickness of7 mm for entire gauge length of 50 mm so as to create sharpcorners simulating the edges of the mould. Two K-type

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Table I

BS 3100 B7 - 11.9 42H11 tool steel 1427 13.3 28.63CR12 ferritic stainless steel 1430–1510 12.8 40

Table II

BS 3100 B74 0.17 2.25 0.75 1.00 0.4 - - 0.35 - - - 0.025 - 2 3 0.02 - -

3CR12b 0.019 11.01 0.81 0.03 - 0.1 0.02 0.72 0.13 0.017 0.08 0.022 0.012 0.001 - - - 0.001

H11c 0.37 4.95 0.36 1.26 0.22 0.13 0.01 1.08 - 0.019 0.95 0.023 - - 0.0014 0.003 0.04 -

*Balance FeaBuchholz, 2014bASTM A240 and EN 10088-2 (Columbus Stainless, 2015)cDu Toit, 2015

thermocouples were spot-welded onto each specimen: onein the middle and one further away from the centre of thespecimen, to measure the temperature. Each test was run for100 cycles over approximately 3 hours. In a case where thecracks appeared before 100 cycles were completed, theexperiment was stopped prematurely. The temperature wasfluctuated between 400 and 1200°C. In the first 50 seconds,the specimen was heated to 1200°C at a heating rate of20°C/s, followed by another 10 seconds of soaking at theelevated temperature. The specimen was then cooled to 400°Cat a cooling rate of 20°C/s. This cycle was repeated 100 times.

After completion of the test, the surface of each specimenwas examined for cracks or other irregularities. Photographsof the surface were taken, before and after cleaning withHibatex solution to remove oxides, using a stereo microscopeat magnifications of 12× and 15×. The data generated wasused to calculate the total plastic strain in 100 cycles. Threetests were conducted for each steel, and an average value forthe total plastic strain after 100 cycles was obtained.Equation 3 was used to calculate the total plastic strain, ,after 100 cycles.

[3]

where L is the change in length (m) and Lo is the gaugelength of the specimen (m).

The hot strength of the steels was determined at 1100°Cthrough an isothermal hot compression test, see Figure 7.The strain was limited to 0.8 to avoid barrelling effects.

The coefficient of thermal expansion was determinedusing the Bahr dilatometer. This test was done in accordancewith ASTM E831-14 specifications. The thermal expansioncoefficient is a material constant. It is the amount ofexpansion or contraction a material undergoes per kelvinduring heating or cooling and is given by the followingequation:

[4]

where dL = Change in length ( m) dT = Change in temperature respectively (°K)L = Total length of the specimen (m)

= Thermal expansion coefficient ( m/m.°K)

The thermal expansion coefficient should be as low aspossible when the material is used to make moulds used inthe casting process.

The specimens were 5 mm in diameter and 10 mm long.Three of these specimens were machined for each alloy. Thesample was heated to 1220°C (above AC3) at a heating rate of0.25°C/s. The specimen was then soaked for 60 seconds andafterwards cooled to room temperature at a cooling rateequivalent to that of the heating rate. Lastly, Ac3 is thetemperature at which ferrite completes its transformation toaustenite during the heating up cycle.

Figures 3, 4, and 5 show stereo micrographs for BS3100 B7,3CR12, and H11 after 100 thermal cycles between 400 and1200°C.

As expected, the surface of BS3100 B7 was heavilyoxidized. After removing the oxides, cracks were exposedand were visible in the centre area in both longitudinal andtransverse directions (Figure 3). 3CR12, in contrast,exhibited less oxidation than BS3100 B7. However, crackswere visible in the transverse direction in Figure 4. Strainmarks (material flow lines) in the lengthwise direction werealso present. No visible cracks or irregularities like strainmarkings or necking were observed in H11 (Figure 5). Thespecimen was still in sound condition after 100 cycles.

Figure 6 shows a summary of the total plastic strain foreach steel after 100 thermal fatigue cycles. The total trueplastic strain per 100 cycles for BS3100 B7, 3CR12, and H11was 0.148, 0.182, and 0.058 respectively. The total plasticstrain represents the measure of resistance to thermal fatigue.


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The average number of cycles to failure for BS3100 B7, basedon the industrial data, is 11 340 i.e. Nf (BS3100 B7) =11 340cycles. The cycles to failure for 3CR12 and H11 are unknown.However, the ratios of the cycles to failure for BS3100B7:3CR12 and BS3100 B7:H11 can be determined based onthe total true strain per 100 cycles. The number of cycles tofailure for 3CR12 and H11 can then be calculated bymultiplying the respective ratios by Nf (BS3100 B7). The resultsare shown in Table III.

Although H11 tool steel looks promising, it is moreexpensive than BS3100 B7. Therefore, before H11 can berecommended as an alternative material, a comprehensivecost benefit analysis would be required. Based on a roughcalculation regarding the raw material cost, the cost of H11 is3.5 times higher than that of BS3100 B7 (Table IV).

Figure 7 shows the Von Mises true stress versus true strainfor the three steels. H11 exhibited the highest hot strength of31 MPa. The hot strengths of 3CR12 and BS3100 B7 werelower than H11, and similar i.e. 16 and 18 MPa respectively.

Figure 8 shows a typical dilatometer-generated plot of changein length versus temperature. The values for BS3100 B7,3CR12, and H11 were found to be 15.8, 13.1, and 12.8 m/m°.C respectively.

The thermal fatigue behaviours of BS3100 B7, 3CR12, andH11 were compared under similar conditions.

H11 had the lowest total true strain of 0.058 per 100cycles, indicating that it had the highest resistance to thermalfatigue compared with 3CR12 and BS3100 B7. The mould lifewould be longer than for the other two steels, and wasestimated to be about 35 478 cycles.

However, before H11 tool steel can be recommended asan alternative material, a comprehensive cost analysis isrequired. Based on a rough calculation regarding the rawmaterial cost, the cost of H11 is 3.5 times higher than that ofBS3100 B7.

ALIBABA GROUP. 2015. Minerals & Metallurgy.http://www.alibaba.com/showroom/alloy-raw-material-price-h11-tool-steel.html [Accesed 18 October 2015].

AMERICAN PETROLEUM INSTITUTE. 2011. API recommended practice 571: Damagemechanisms affecting fixed equipment in the refining industry. 2nd edn.API Publishing Services, Washington.

ASTM INTERNATIONAL. 1978. Metals Handbook: Properties and selection on ironssteels. Benjamin, D. (ed.). Materials Park, OH. pp. 114–116.

ASTM International. 1980. Metals Handbook: Properties and selection on toolsteels. Benjamin, D. (ed.). Materials Park, OH.

ASTM INTERNATIONAL. 2015. ASTM E831. Standard test method for linearthermal expansion of solid materials by thermomechanical analysis.Materials Park, OH.

AZO MATERIALS. 2014. Investigation of fatigue crack propagation in polymers.http://www.azom.com/article.aspx?ArticleID=11114 [Accessed 17 March2016].

BUCHHOLZ, H. 2014. Catalyst Manufacturing Unit, Secunda. Personal communi-cation and unpublished results.

COFFIN JR., L.F. (1954), A study of the effects of cyclic thermal stresses on aductile metal, Trans. ASME, vol. 76, pp. 931–950.

COLUMBUS STAINLESS. 2015. Unpublished results. Middelburg, South Africa. DU TOIT, W. 2015. Orion Engineering, Pretoria. Unpublished results.HERTZBERG, J.L. 2013. Deformation and Fracture Mechanics of Engineering

Materials. 5th edn. Courier Westford, North Chelmsford, MA.MANSON, S.S. (1954), Behaviour of materials under conditions of thermal

stress, NACA TN-2933, National Advisory Committee for AeronauticsSTUMPF, W. 2014. Department of Materials Science and Metallurgical

Engineering, University of Pretoria. Unpublished results.

VAN AARDE, B. 2015. Steloy, Johannesburg. Personal communication. �

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352 VOLUME 116

Table III

3CR12 1:1.3 13 931H11 1:3.1 35 478

Table IV

BS3100 B7 9 500H11 32 550

Coal stockpiles serve as surge capacity fordownstream utilization processes and can alsobe used for moisture reduction by means ofgravity drainage and evaporation. Excessiveamounts of moisture in coal can causehandling problems and, most importantly, willdecrease the calorific value, leading toinefficient combustion.

Research has shown that evaporation bymeans of wind and solar action is considerablymore effective than gravity drainage(Williams,D.J. 2006), but the effect is limited to arestricted depth from the exterior of thestockpile (Boyapati, E. and Oates, A. 1994;CSEM-UAE, 2010). The effectiveness of windand solar action can be improved by orientingthe stockpile perpendicular to the predominantwind direction, maximizing the surface area ofthe pile, and reclaiming the coal from the pilegradually in shallow cuts over a large area(Williams, D.J. 2006).

The extent of evaporation is mainlyinfluenced by the weather – in particular solarradiation, temperature, wind strength, andrelative humidity (Deodhar, M.J. 2008; Fryer,

J.F. and Szladow, A.J. 1973) – as well as bythe porosity, heat conductivity, and chemicalnature of the coal particles (Karthikeyan, M.,Zhonghua, W., and Mujumdar, A.S. 2009).Moisture from a coal stockpile surface willevaporate until equilibrium is reached betweenthe ambient atmosphere and the coal particles.When the relative humidity increases as thetemperature decreases, the coal particles canreabsorb moisture to re-establish equilibrium(de Korte, G.J. and Mangena, S.J. 2004;Karthikeyan, M., Zhonghua, W., andMujumdar, A.S. 2009). This process ofdesorption and reabsorption can be repeatedon a daily cycle(de Korte, G.J. and Mangena,S.J. 2004).

Washed South African bituminous coal fromthe Witbank No. 2 seam was used for theexperiments. The proximate analysis of thecoal can be seen in Table I.

The coal was used as received and wassieved into three size ranges: fine (-6.7 mm),total range (-13.2 mm), and coarse (-13.2 mm+ 6.7 mm).

The objective of this investigation was toestablish the effect of coal bed particle size on

The effect of particle size on the rateand depth of moisture evaporation fromcoal stockpilesby J. de Goede*, B. Muller*, Q.P. Campbell*, M. le Roux*,and C.B. Espag de Klerk*, Paper written on project work carried out in partial fulfilment of B.Eng. (Chemical Engineeringwith specialisation in mineral processing)

Excessive amounts of moisture in product coal can influence the efficiencyof downstream utilization processes due to a decreased calorific value andhandling problems. Stockpiles can be used to decrease the moisturecontent of coal by means of gravity drainage and evaporation. This paperis focused on the evaporation of moisture from a coal stockpile surfacewith the aim of investigating the effect of particle size on the rate ofevaporation as well as the depth to which evaporation extends.

It was observed that moisture initially evaporates at a higher rate froma stockpile consisting of fine particles (-6.7 mm) than from coarserparticles (-13.2 mm +6.7 mm). This high rate of evaporation is restricted tothe outer shell of the fine coal stockpile. However, for coarse coal, theporous nature increases the depth at which evaporation occurs.Evaporation of moisture was observed up to the fourth day of each experi-mental run, after which steady state was obtained. It was shown thewater can evaporate from the surface into the body of the stockpile,depending on the coal particle size and void spacing. An experimentalreclaim depth of 0.4 m was achieved after 4 days.

coal, stockpile, dewatering, depth of evaporation, rate of evaporation.

* School of Chemical and Minerals Engineering,North-West University, Potchefstroom, SouthAfrica.

© The Southern African Institute of Mining andMetallurgy, 2016. ISSN 2225-6253. Paper receivedFeb 2016.

353VOLUME 116 �


Table I

Inherent moisture content 2.6Ash content 15.9Volatile matter 25.2Fixed carbon 56.4

The effect of particle size on the rate and depth of moisture evaporation from coal

the rate and depth of moisture evaporation. The investigationwas divided into two parts. In both cases saturated samplesof the three different size ranges were prepared. The firstexperiment was designed to determine the depth to whichevaporation extends. The samples were loaded into sectionedPVC pipes, using 12 pipes for each size range, and placedoutside for 10 to 12 days and exposed to ambient conditionsto facilitate the process of evaporation. In the secondexperiment, coal samples were placed in three shallowcontainers to investigate the rate at which moistureevaporates from a coal stockpile surface. These samples wereexposed to ambient conditions while the masses of thecontainers were continuously measured. The experimentalset-up included a weather station that continuously measuredtemperature, relative humidity, and wind speed and direction.

The PVC pipes for the first experiment were cut into seven 0.1 m sections and connected with duct tape as seen inFigure 1.

The shallow containers for the second experiment, withdimensions of 34 cm × 25 cm × 20 cm, were placed on loadcells that continuously recorded the weight of the containers.This set-up can be seen in Figure 2. Both structures werecovered with Perspex roofs.

To determine the depth to which evaporation occurs, one PVCpipe containing each particle size of coal was removed on adaily basis for moisture analysis. The coal samples from eachsection of the three pipes were removed and weighed, thendried for 72 hours in a climate-controlled room at a constanttemperature of 22°C and a constant relative humidity of 40%,and re-weighed. The samples were then placed in a vacuum

oven at a constant pressure of 101.3 kPa and temperature of105–110°C. for 6 hours. The inherent moisture content of thecoal was determined by difference.

The evaporation rate (experiment 2) was determined byanalysing the data from the data logger of the load cells andthe weather station.

From Figure 3, a sharp decrease in total moisture content isnoted from start-up to day two. This is due to drainage ofmoisture under gravity . From day two to day four,evaporation occurred from the top 0.2 m below the surface.From Figure 3 it can be seen that the coal samples reachedsteady state at day four, after which the total moisturecontent remained relatively constant until day twelve. This isan indication that no surface moisture is available toevaporate into the atmosphere. The void spacing of the coalbed had a major influence on the depth to which evaporationoccurs. The coarse (-10 mm +6.7 mm) coal bed was moreporous than the fine (-6.7 mm) coal bed. It was found thatevaporation took place up to 0.4 m below the surface of thecoarse coal bed, and that only the surface of the fine coal bedshowed signs of evaporation.

Figure 4 illustrates the cyclic behaviour in the mass lossprofile of each size range. Evaporation generally occurredfrom 09:00 to 17:00 when the temperatures were high andthe relative humidity low. As evening fell, the temperaturedecreased and the relative humidity increased, resulting inthe reabsorption of moisture into the porous coal particles asthe particles tried to stay in equilibrium with the atmosphere.

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354 VOLUME 116

It can be seen that all coal samples reached the samemoisture content by the end of the experimental run. Thecoarse coal sample reached the final moisture content first.

To compare the effect of particle size on the rate ofevaporation, the daily rates of evaporation were calculated foreach size range as shown in Figure 5. It can be seen thatmoisture initially evaporates faster from the fine coal sample(-6.7 mm) than from the other coal samples. After two days,the surface of the fine coal sample was dry and the rate ofevaporation decreased. The same phenomenon was seen inthe experiments that investigated the depth to whichevaporation occurs. This is attributed to the porous structureof the coarse sample.

During the investigation, it was found that the initialmoisture content had an influence on the rate of evaporation.A lower initial moisture content resulted in a lower maximumrate of evaporation.

This study showed that bed particle size affects the extent ofmoisture evaporation, and that the porous structure of acoarse coal stockpile aids the process. Experimental resultsindicate that moisture drainage takes place within the firsttwo days of exposure to environmental conditions.Evaporation of moisture can be seen up to the fourth day, butthis is a function of the initial moisture content of the coal.Coal with a higher initial moisture content will take a longertime to lose all surface moisture.

It was shown that water can evaporate from underneaththe surface of coal stockpiles. Increased void spacing has apositive influence on the effectiveness of evaporation for coalstockpile drying. The results obtained in this study can beused to manage stockpiles efficiently. Up to 0.4 m of coal canbe reclaimed from the stockpile surface and the remainingcoal can be left to dry for another four days – if no rainoccurs.

The authors would like to thank the following institutions fortheir contributions towards this project:

� Coaltech� NRF (National Research Foundation).

This paper is based on project work carried out in partialfulfilment of a degree in Chemical Engineering at North-West

University (NWU). The research was supported by the SouthAfrican Research Chair’s Initiative of the Department ofScience and Technology and the National ResearchFoundation of South Africa (NRF). Any opinion, finding, orconclusion or recommendation expressed in is that of theauthors and the NRF does not accept any liability in thisregard.

BOYAPATI, E. and OATES, A. 1994. A mathematical model for stockpile

management. 6th International Working Conference on Stored-product

Protection, Canberra, Australia, 17–23 April 1994. pp. 684–688.

CSEM-UAE INNOVATION CENTER. 2010. Water evaporation rate at Ras-Al-

Khaimah, UAE. http://www.csem-uae.com/pdfs/Water%20Evaporation%

20rate%20%20in%20Ras-Al-Khaimah,%20UAE [Accessed 18 June

2014].

DE KORTE, G.J. and MANGENA, S.J. 2004. Thermal Drying of Fine and Ultra-fine

Coal. CSIR.Fryer, J.F. and Szladow, A.J. 1973. Storage of coal samples.

Alberta Geological Survey, Edmonton.

DEODHAR, M.J. 2008. Elementary Engineering Hydrology. Pearson Education,

India. Dorling Kindersley.

KARTHIKEYAN, M., ZHONGHUA, W., and MUJUMDAR, A.S. 2009. Low-rank coal

drying technologies-current status and new developments. Drying

Technology, vol. 27. pp. 403–145.

PRIYAL, D. and TOERIEN, A. 2010. The effect of salinity on evaporation rates of

brines resulting from the treatment of mine

water.http://www.google.co.za/url?sa=t&rct=j&q=&esrc=s&source=

web&cd=1&cad=rja&uact=8&ved=0CCcQFjAA&url=http%3A%2F%2Fww

w.ewisa.co.za%2Fliterature%2Ffiles%2F200_150%2520Dama-87

Fakir.pdf&ei=7I6LU5TcFqzA7AaH6oF4&usg=AFQjCNForf8NhQQ3zVqS90

GVcrPPBldPQw&bvm=bv.67720277,d.ZGU Date of access: 18 June 2014.

WILLIAMS, D.J. 2006. Application of Unsaturated Soil Mechanics to Product Coal

Dewatering. Australian Mining Technology Conference, Hunter Valley,

NSW, 26–27 September 2006. �

The effect of particle size on the rate and depth of moisture evaporation from coal

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