Relaves y operación (el desafío de la...

RELAVES Y OPERACIÓN

(el desafío de la integración)

Christian Ihle

Advanced Mining Technology CenterDepartamento de Ingeniería de Minas

FCFM UNIVERSIDAD DE CHILE

Seminario Alta LeyFuturo de la Minería: Relaves

18 de agosto de 2016

AMTC 1 / 17

Introducción

Run-of-mine ore (0.5% Cu)

(+5 cm)

Flotation , reagents

Correct size V y j J K 2 S e r

Gyratory crusher

A A water recovery (0.05% Cu)

7 Hydrocyclones

-1 cm Ball

I

mills

Semi-autogenous grinding mill 1

Oversize (+I50 pm)

-

Concentrate (-30% Cu)

Re-cleaner column cells

I 1 scavengers reagents I n

W N

I,

Fig. 3.1. Generalized flowsheet for producing Cu concentrates (-30% Cu) from Cu-Fe-S and Cu-S ores.

(Davenport et al., Extractive Metallurgy of Copper., 4th ed. 2002)

AMTC 2 / 17

Introducción

Una industriaDistintos incentivos

Chancado“mayor tonelaje⇒mayor tamaño”

Planta de flotación“mayor recuperación⇒menor tamaño”

+Espesadores de relaves

“mantener el sistemaoperativo”“no embancar elespesador”

AMTC 3 / 17

Introducción

Waste minimization at the source

Wang et al., 1999) would generally agree that CP issimply the latest of a series of successive environmentalmanagement paradigms (see Fig. 1).

An overabundance of interpretations (see Table 3),however, has made it extremely difficult to apply CP to aspecific sector of industry. The challenge in crafting acredible sector-specific definition of CP for mining,therefore, lies in determining a common set of elementsthat the majority of interpretations are fundamentallybased upon.

One noteworthy trend is the fact that most definitionsof CP are based upon the notion of continuous envi-ronmental improvement. Unlike many of the older pre-ventative approaches (e.g. pollution prevention, toxicwaste reduction, waste minimization, etc.), which tendonly to focus on one key environmental impact, CPexplicitly targets ‘‘the reduction of environmental im-pacts along a product!s lifecycle’’ (Van Berkel, 2000, p.134), containing process and outcome elements for eachof the following areas: (industrial) processes, productsand services. It is against this background that UNEP,and, more recently, a number of other organizations(e.g. UNIDO, various government agencies) and inde-pendent researchers, have been successful in promotingCP as an ‘‘overarching concept’’ (Van Berkel, 2001, p.29).

A second common trend is that most assessmentsstress that CP emphasizes improvements to both pro-duction and products, and can be applied to industrial

processes and products themselves. In the case of pro-duction processes, CP can result from raw materialconservation, reductions in water and energy con-sumption, the elimination of toxic and dangerous rawmaterials, and a reduction in the quantity and toxicity ofall emissions and wastes at the source. In the case ofproducts, CP seeks to reduce the environmental, healthand safety impacts (of products) over their entire lifecycles, from raw materials extraction, through manu-facturing and end use, to disposal (Van Berkel, 2000;UNEP, 2001; Van Berkel and Van Kampen, 2001).

Finally, most researchers, despite having interpretedit differently, are in general agreement that CP can havesignificant influence as a tool, program and philosophy(Geiser, 2001, p. 33). Primary examples include:

1. Technology promoter: At the simplest level, CP pro-grams have advanced more resource intensive andless hazardous production technologies.

2. Managerial catalyst: CP has liberated environmentalvalues ‘‘from the dungeon of residual managementand regulatory compliance’’, and has placed themcloser to the centre of product and process design.

3. Paradigm reformer: By promoting full cost account-ing and green marketing, CP has restructured envi-ronmental economics, converting environmentalprotection investments into productivity benefits.

4. Conceptual bridge connecting industrialization andsustainability.

Fig. 1. History and evolution of CP. Source: Modified from EEA (2002).

308 G. Hilson / Minerals Engineering 16 (2003) 305–321

(Hilson, Miner. Eng., 2003)

AMTC 4 / 17

Introducción

Ejemplo

mately 5 km to feed the paste thickener at the PDF. The pastethickener is required to recover at least 70% of the water inthe underflow of the primary thickener, which is thenpumped back to the main plant. The water returned from theprimary thickener as thickener overflow has a solids concen-tration less than 50 ppm (Figures 7 and 8).

Thickener sizing, selection, and design

The primary thickeners

The primary thickeners operate as clarifiers returning thebulk of the clarified water to the main plant (12 000 to 15 000 m3/hr with a maximum of 18 000 m3/h). Thesethickeners were sized on the basis of the hydraulic loading.

Each primary thickener is equipped with a turbidity meterand an Alcotech flocculant-saving device. Flocculant is addedin proportion to the response of the output signals from theseinstruments.

The feedwell diameter (14.6 m) has been designed on afeedwell duty of 1.5 m/min and a residence time of 1.5 minat a flow rate of 15 000 m3/h. The feedwell has a sloping(45°) bottom shelf. The objective is to divert the coarse

Khumani Iron Ore Mine paste disposal and water recovery systemJournal

Paper

The Journal of The Southern African Institute of Mining and Metallurgy VOLUME 112 MARCH 2012 215 ▲

Figure 6—Overview of the iron ore process at Khumani Iron Ore Mine

Figure 7—Simplified flow sheet of water recovery circuit

FLOWSHEET - WATER RECOVERY BKM, KEP

Screening/JiggingPlant

ThickenerFeed

PotableWater

Flocculant Plant

18 m PasteThickener

90 m PrimaryThickener

Return WaterTank

Flocculant Plant

Paste Disposal Facility

Figure 5—Washing, screening, jigging, and cyclone plant at Parsons

text:Template Journal 27/3/12 14:12 Page 215

(du Toit & Crozier, J. South African Inst. Min. Met., 2012)

AMTC 5 / 17

Balance de masa

Balance de masa en tranqueDescarga de relaves en tranque de relaves

Concentración de sólidos baja

Mayor volumen ocupado

Mayor evaporación

Mayor necesidad derecuperación de agua desdeel tranque

Mayor consumo de energíapor recuperación

Mayor riesgo decontaminación porinfiltración

Concentración de sólidos alta

Mayor estabilidad física

Menor requerimiento deagua

Más energía requerida parael transporte

Mayor desafío para unaoperación estable

AMTC 6 / 17

Balance de masa

Décadas de operaciónRecuperaciones de agua típicas entre un 25 % y un 50 %

200

400

600

800

1000

1200

20 30 40 50 60 70

TSF

volu

me

(20

year

op.

, mill

ion

m3 )

Recycled water from thickener underflow (%)

50 kton/d, Cp = 0.50 50 kton/d, Cp = 0.5550 kton/d, Cp = 0.65

150 kton/d, Cp = 0.50 150 kton/d, Cp = 0.55150 kton/d, Cp = 0.65

∗TSF ≡ Tailing storage facility

La pendiente de cada recta es

proporcional a GR

(1

Cp−1

)Volumen del Estadio Nacional (Ñuñoa,Santiago): 650000m3 ≡ VEN

20

30

40

50

60

70

40 42 44 46 48 50

TSF/

VEN

(1 y

ear o

p.)

Recycled water from thickener underflow (%)AMTC 7 / 17

Balance de masa

Décadas de operaciónRelave convencional: Cp ≈ 50%

200300400500600700800900

10001100

50 52 54 56 58 60 62 64

TSF

volu

me

(20

year

op.

, mill

ion

m3 )

Thickener underflow concentration (%)

50 kton/d, λ = 0.350 kton/d, λ = 0.550 kton/d, λ = 0.7

150 kton/d, λ = 0.3150 kton/d, λ = 0.5150 kton/d, λ = 0.7

152025303540455055

50 50.5 51 51.5 52 52.5 53TS

F vo

lum

e (1

yea

r op.

, mill

ion

m3 )

Thickener underflow concentration (%)

Las potencias de impulsión del makeupasociado superan los 10 MW.

AMTC 8 / 17

Variaciones en la producción del relave

El relave es la herencia del yacimiento y del proceso

El relave es la herencia delyacimiento y del proceso

Mineralogía

Aditivos

Calidad de agua

AMTC 9 / 17


Arcillas en proceso

Efectos en recuperación de agua

Finos pueden presentardificultades en proceso defloculación

Disminución en capacidadde espesadores

D.V. Boger / Chemical Engineering Science 64 (2009) 4525 -- 4536 4535

Fig. 23. Uncontrolled versus controlled dispersion.

in a company balance sheet. Often this is an unfunded liability soat the end of the day some companies have managed to escape theliability and the responsibility has been left with the taxpayer. Onesuch example is in the phosphate industry in Florida where the Stateof Florida has had to deal with such issues. Florida is not unique intheworld where there have beenmany cases, particularly in the past,where liabilities have escaped. Often in the past the costs associatedwith cleaning up a disposal area have been deferred until the endof the mine; this liability, although discounted and listed annuallyon a balance sheet, often has been unfunded and hence unless thecompany is a large one with huge resources they have been able toescape the liability. An attitude in the industry has perhaps been bestsummed up in the book Collapse by Gerard Diamond in his chapteron Montana.

. . . In Montana as elsewhere, companies that have acquired oldermines respond to demands to pay for clean-up in either of twoways. Especially if the company is small, its owners may declarethe company bankrupt, in some cases conceal its assets and trans-fer their business effort to other companies or to new companiesthat do not bear responsibility for clean-up at the old mine. If thecompany is so large that it cannot claim that it would be bankruptby clean-up costs the company instead denies its responsibilityor else seeks to minimize the costs. In either case, either the minesite or the areas downstream remain toxic, thereby endangeringpeople, or else US Federal Government and Montana State Gov-ernment (hence, ultimately the taxpayers) pay for the clean-upthrough Federal super fund or correspondingMontana State fund.Montana is not unique in liability for abandoned mine sites beingleft to the taxpayer. Do our industries really want to be subsi-dized by the taxpayer in this way, or are we now in a positionto move to more sustainable and responsible management of thewaste that we produce.

Mining has a very poor record. According to the United States Envi-ronmental Protection Agency, mining has contaminated portions ofthe headwaters of 40% of watershed in the western continental USAand reclamation of 500,000(!!) abandoned mines in 32 states wouldcost tens of billions of dollars.2

2 Environmental Protection Agency. “Liquid Assets 2000: Americans Pay forDirty Water”.

All, however, is not doom and gloom as governments and com-panies are becoming far more responsible. Performance bonds orenvironmental sureties have become a requirement in many com-panies as a means of protecting governments and the taxpayer frommine rehabilitation costs. The USA, Canada, Australia, Japan, SouthAfrica, Indonesia and Malaysia require lodgement of environmentalsureties. Europe will follow suit and perhaps other countries are do-ing the same thing. In addition, some countries are now setting uptrust funds to deal with the ultimate cleanup issue.

Environmental rheology provides a tool to evaluate various wastedisposal strategies for the minerals and energy industries. Technol-ogy exists to significantly reduce the volume of waste produced bythis industry simply by recovering and recycling water. Regulationhas not been successful in forcing industries down this track. Themajor driving force will be the lack of water and the need to recoverwater in the near future. This is already happening. For a compre-hensive discussion on the issues associated with improved environ-mental practices in the resource industries refer to Jewell and Fourie(2006).

Acknowledgements

The author thanks the Australian Research Council for career-longsupport. He is particularly grateful to the Alcoa Corporation (WesternAustralia) for their initial approach in 1974 and for the help of thecorporate champions Peter Colombera (deceased), Don Glenister andDavid Cooling. The students who completed their Ph.D. theses inthe area need special recognition: G. Sarmiento, Q.D. Nguyen, N.Pashias, F. Sofra, D. Cooling and B.C. Hart. Finally, Professor MortDenn should bementioned as a friend and colleaguewho encouragedthe continuance of this work as early as 1980.

References

Barnes, H.A., Carnelli, J.O., 1990. The vane in cup as a novel rheometer geometryfor shear thinning and thixotropic materials. J. Rheol. 34 (6), 841.

Cooling, D.J., 2006. Improving the sustainability of bauxite residue management:evaluation of bauxite residue carbonation. Ph.D. Thesis.

de Guingand, N., 1986. The behaviour of flocculated suspensions in compression. M.Eng. Sci. Thesis.

Fisher, D.T., Scales, P.J., Boger, D.V., 2007. The bucket rheometer for the viscositycharacterization of yield stress suspensions. J. Rheol. 51 (5), 82.

2006. In: Jewell, R.J., Fourie, A.B. (Eds.), Paste and Thickened Tailings—A Guide,seconded. Australian Centre for Geomechanics, Nedlands, Western Australia.

Efectos en transporte y disposición

Reología (relación entre flujo ydeformación)

Segregación (separación de fasesdurante el transporte)

D.V. Boger / Chemical Engineering Science 64 (2009) 4525 -- 4536 4527

Fig. 1. Typical red mud shear stress–shear rate behaviour illustrating thixotropicbehaviour. The data were obtained after shearing the mud at high shear rate fordifferent times.

In ideal thixotropic behaviour the two timescales are the same andthere is no difference between breakdown and structural recovery.The enquiry was made by Alcoa because of the realisation that thecurrent practice, which was pumping the red mud to the disposalarea (a dam) at a concentration of between 15% and 20% by weightsolids as a Newtonian fluid, at a pH of 13, into lakes of about asquare mile in area, was presenting a problem; in fact, there wasevidence that the lakes were leaking caustic into the ground water.They were motivated therefore to look at techniques whereby themud could be dewatered and handled at as high a concentration aspossible. They needed to understand the rheological characteristicsof this material! Preliminary investigation determined that at lowconcentrations, i.e. at the level at which they were pumping, the ma-terial exhibited Newtonian fluid behaviour, while at higher concen-trations, non-Newtonian shear thinning characteristics and a yieldstress were observed. At even higher concentrations thixotropy wasobserved. Fig. 1 shows shear stress–shear rate data for a concentratedred mud suspension after being subjected to significant periods ofshear with a helical ribbon mixer. The thixotropic characteristics ofthe material are obvious as the shear stress at a particular shear ratedecreases significantly with mixing time. Fig. 2 illustrates the be-haviour more graphically, where a filter cake is shown which can beformed into a spherical shape which, after mixing, flows like a paste.

What was also apparent simply by examining the mixing processwas that the structural breakdown process occurred far more rapidlythan the restructuring process. Thus one could exploit the thixotropiccharacteristics in the transportation of a high concentration mud tothe disposal area, i.e., dewater the material, shear the mud to breakthe structure, and then transport it out to the tailings facility wherethe material would restructure slowly. To quantify this behaviour asingle point flow property measurement was required. It was fromthis observation that the vane device was adopted from soil mechan-ics by Professor Dzuy Nguyen in his Ph.D. thesis and developed forthe single point measurement of the rheological yield stress (Nguyenand Boger, 1983, 1985). Some very early data obtained with the vaneshowing the breakdown and recovery of the red mud are shown inFig. 3. While the timescale of the breakdown process is measured in

Fig. 2. Illustration of the effect of shear on a red mud filter cake.

Fig. 3. Use of the vane yield stress measurement to illustrate the breakdown andrecovery of the red mud structure.

hours, the recovery process is measured in days, and the parameterused to establish this behaviour was the yield stress measured orig-inally with the vane device. The vane was a perfect instrument toexamine the thixotropic characteristics of the red mud.

It was apparent that once the material reached an equilibriumstate in shear it took a long time for the recovery to take place andone could define the equilibrium shear stress–shear rate data, orthe equilibrium viscosity-shear rate data. Such results as a functionof concentration are shown in Fig. 4. The shear thinning character-istics of the material are apparent as the concentration increases,from Newtonian behaviour at the lowest concentration (36.2%) byweight. Data like that shown in Figs. 1, 3 and 4 formed a basis forunderstanding how to handle, pump, and produce the higher con-centration material. Alcoa went through piloting processes to lookat various dewatering devices and eventually ended up with the su-per thickeners which they now use today in the dry stacking tech-nology. Figs. 5 and 6 compare the wet lakes of the 1970s to the drydisposal of the 1990s, while Fig. 7 illustrates the paste-like materialproduced with a compression thickener.

The impact of the alumina industry on research in rheology wasimmense because it became apparent that techniques were requiredfor measuring the flow characteristics of these concentrated suspen-sions and one needed to understand yielding and thixotropic be-haviour. Also, once the techniques were developed one could startmaking comparisons across this industry and others. For example,

(Boger, Chem. Eng. Sci., 2009)

AMTC 10 / 17


Caolinita

No es expansiva

Partículas relativamente grandes(0.2µm–2µm)

Superficie efectiva entre 10 m2/g y 30 m2/g

Arcilla común en tierras altamentemeteorizadas

Barra de 1µm, Murray, Appl. Clay Sci., 2000

AMTC 11 / 17


EsmectitaEj. Montmorillonita, http://www.mindat.org/

Las capas tiene uniones O–O débiles oenlaces catión-oxígeno

Los cationes son adsorbidos entre las capas ymantienen las capas unidas

Expansivas (las más expansivas entre todaslas arcillas)

Superficie efectiva entre 650 m2/g y800 m2/g

Murray, Appl. Clay Sci., 2000

AMTC 12 / 17

http://www.mindat.org/


Ejemplo en capacidad de espesamiento y transporteCapacidad de recuperación ∝ tasa de sedimentación

Dependencia de flujo y pre-tratamiento enresultado

Efecto de aditivo y dosis en resultado

A igual concentración de sólidos laviscosidad depende del mineral

equivalent solids concentrations of each mineral, the degree ofcomplexity in the structures that form in suspension, may decreasein the order of talc = kaolinite > illite > quartz, under normal pro-cessing conditions. Based on the differences in their charge anisot-ropy, such behaviour is expected for talc and illite. The high degreeof charge anisotropy in talc as derived by differences in the i.e.pand p.z.c (relative to illite and kaolinite) has already been dis-cussed, and this corresponds to the proposed edge–edge andedge–face interactions likely to occur in suspension. Illite has alower degree of charge anisotropy, and while this may play a rolein the observed lower yield stresses, it is likely that the typical highaspect ratio and effective volume fraction of particles are impor-tant factors in the formation of illite structures in suspension,based on knowledge of its typical smooth surface morphology. Inthis case, it is likely that the yield stresses are further depressedby the re-alignment into face–face agglomerates which are lessrheologically complex. Based solely on differences in chargeanisotropy, one would expect kaolinite suspensions to exhibit rhe-ological behaviour more closely representing illite, as this wouldlikely result in dispersed suspensions. Lower yield stresses wouldalso be observed, if the assumptions of high particle asymmetryand crystallinity were true, as this would result in a transition tobetter face–face agglomeration as proposed for illite. However,the elevated yield stresses observed indicate that kaolinite existsin more complex structures than illite; a likely consequence ofirregularities and poor crystallisation, promoting the formation ofstructures which exist in several randomised alignments, includingcombinations of EE and EF agglomeration.

A comparison of the Bingham viscosities of talc, kaolinite, illiteand quartz suspensions is given in Fig. 7. The efficient operation ofmany unit operations rests on the knowledge of medium viscosity.For example, grinding efficiency, throughput, product fineness andenergy efficiency can all be optimised through the monitoring ofviscous effects in stirred mills (Boger, 1999; Shi and Napier-Munn,2002). In flotation, the prediction of cell hydrodynamics is depen-dent on several factors including slurry viscosity (Schubert andBischofberger, 1978; Furstenau and Huang, 2003; Schubert, 2008;Bakker et al., 2009). Medium viscosity values are also importantin predicting the pumping conditions for the preferred semi-drydisposal and materials transportation during tailings treatment(Nguyen and Boger, 1998).

The results show that all the phyllosilicates are characterised byrelatively low viscosities, as they fall within the range of quartzsuspensions. This indicates that at high shear conditions, talc, kao-linite and illite are not likely to present viscous effects when pres-ent in suspension. Nonetheless, clear differences in the viscosityvalues of the different minerals are observed. The differences canbe correlated to the ease of particle alignment in the direction ofshear. The introduced shear force induces restructuring of theagglomerates into delaminated platelets. This property is used inthe raking process in assisting dewatering, by rearrangement ofEF and EE structures with high retention properties, to higher den-sity FF structures with improved settling rates (Du et al., 2010). Theresults show that the Bingham viscosities of talc and kaolinite aresimilar, with few discernible differences. Both minerals have high-er viscosities than illite suspensions. It is suggested that the reasonfor these differences is that the resistance to collapse of pre-exist-ing EF and EE structures in kaolinite and talc suspensions is greaterthan in illite, where it is likely that the alignment of proposedexisting FF aggregates is merely improved. This resistance maybe enhanced by poor mineral crystallinity.

4.4. Rheological classification of phyllosilicate group minerals

The rheological properties of talc, kaolinite and illite can now becompared to other phyllosilicates which have been previously ana-lysed in a similar manner. Using minerals that are representative ofeach group, a preliminary rheological classification has been con-ducted. Fig. 8 gives a comparison of the Bingham yield stresses ofthe phyllosilicate group of minerals. The details on the analysesof the other minerals can be found in previous publications (Las-kowski et al., 2010; Ndlovu et al., 2011a, b). Perhaps the most rel-evant outcome of such a comparison, to the minerals processingindustry, is the critical concentration of each phyllosilicate min-eral. This is the concentration beyond which each mineral is likelyto present intractable processing problems, and can be estimatedfrom the concentration beyond which exponential increments inthe suspension yield stress and viscosity are observed (shown forchrysotile in Fig. 8).

Fig. 6. A comparison of the Bingham yield stresses of talc, kaolinite, illite and quartzsuspensions. The error bars represent the 95% confidence interval of the averagevalues.

Fig. 7. A comparison of the Bingham viscosities of talc, kaolinite, illite and quartzsuspensions. The error bars represent the 95% confidence interval of the averagevalues.

B. Ndlovu et al. / Minerals Engineering 53 (2014) 190–200 197

(Ndlovu et al., Miner. Eng., 2014)

infra-red moisture balance. All tests were carried out at pH 7.5and 22.0±0.1 °C.

3. Results

3.1. Settling rate

The initial settling rates for smectite and kaolinite disper-sions are shown in Fig. 3 as a function of shear rate. Optimumrates with respect to shear-mediated flocculation performanceexist at which higher or lower rates produced slower settlingflocs. Under the optimum orthokinetic conditions, flocaggregation and disaggregation processes may occur simulta-neous. It appears that initially, the overall process is dominatedby aggregation, leading to larger flocs and maximum settlingrates. Inadequate mixing due to lower shear rates does not allowflocs to grow sufficiently into larger and/or denser units in thetime available, whilst excessive agitation reduces the maximumpossible sizes through erosion and/or floc rupture.

PAM S produced the fastest settling flocs for both kaoliniteand smectite dispersions, followed by PEO, PAMA and PAMNin that order. Polymer solution viscosity data analysis suggeststhat PAM N has a relatively smaller conformation incomparison with the other polymers, which would lead tolower clay–polymer collision frequency and/or limited bridging

capacity. In contrast, PAM A and PAM S flocculated pulpsettling rates are notably higher as a result of their largerconformation induced by intra-polymer electrostatic repulsion.Zeta potential measurement of kaolinite and smectite particlesbefore and after PEO flocculation indicates that the adsorbedpolymer retains a large interfacial conformation whereby PAMflocculants quickly reconform. Thus, PAM A, PAM S and PEOappear to build larger flocs more effectively than PAM N as aresult of their bridging capacity, which is in turn related to theirability to attain large conformation. What is not currently clearis the greater capacity of PAM S with respect to PAM A toproduce fast settling flocs, in spite of apparently similar solutionand interfacial behaviour.

The initial settling rates achieved for kaolinite particles weregreater than those of smectite for the same flocculant type anddosage. This may possibly be the result of the lower interfacialarea of the kaolinite particles available for interactions with thesame number of polymeric flocculant chains in dispersion.Furthermore, PAM A based flocs also showed a greater shear-related variation in settling behaviour than did the other

Fig. 3. Initial settling rate of smectite (top) and kaolinite (bottom) dispersions asa function of shear rate flocculated with PAM A (●), PAM S (▴), PAM N (○)and PEO (▵) at 250 g polymer·t−1 solid.

Fig. 4. Settling rate as a function of agitation rate for smectite (top) and kaolinite(bottom) dispersions at pH 7.5, flocculated with 250 g polymer·t−1 solid PAMN(○), PAM A (●), PAM S (▴) and PEO (▵). Estimated shear rates are includedon the top axis for comparison.

81J. Addai-Mensah et al. / Powder Technology 179 (2007) 79–83

(Addai-Mensah et al., Powder Technol., 2007)

AMTC 13 / 17


Diagrama ternario de viscosidad de mezclas de arcillas

93

caolín también se encontró anhidrita, reforzando la idea de que quizás es este mineral el que ejerce el control, sin embargo una mayor investigación debe ser llevada a cabo para determinar con precisión el mecanismo mediante el cual se controla la reología de la bentonita.

FIGURA 79: TERNARIO DE VISCOSIDAD PARA BA, BC Y CC A CV 15% Y PH 7.

(Merrill, tesis de MSc., 2016)

AMTC 14 / 17


Rol del agua (Zhou et al., Chem. Eng. Sci., 2001)

Fig. 3. The shear yield stress of titania suspensions as a function of pHand solids concentration (adapted from Liddell, 1996).

Fig. 4. The shear yield stress as a function of pH for the aluminasuspensions of di!erent particle sizes at volume fraction !"0.30 and ina background electrolyte concentration of 0.01 M KNO

!(adapted

from Zhou, 2000). The average surface area diameters (d!) of the

particles are 0.58, 0.40, 0.25 and 0.19 !m for AKP-15, AKP-20, AKP-30and AKP-50, respectively.

Fig. 5. The normalised shear yield stress of alumina suspensions asa function of !" at various volume fractions (AKP-20) (adapted fromZhou, 2000).

Fig. 6. The normalised shear yield stress as a function of !" for aluminasuspensions of di!erent particle sizes (!"0.30) (adapted from Zhou,2000).

characterised with the parameter of gel point of thesuspensions, !

"which can be determined experimentally.

In addition to the shear hydrodynamic e!ect, the shear#ow properties of the #occulated suspensions are alsostrongly governed by inter-particle interactions. Duemainly to the heterogeneous nature of the suspensionstructure, possible structural fracture and slip, character-isation of the shear #ow behaviour at low shear rates isdi$cult. A steady shear #ow can usually be reached atrelatively high shear rates, such as "# '5 s#$ (Zhou,

2000). An example of shear stress}shear rate data isshown in Fig. 7 for alumina suspensions as a function ofpH (Zhou, 2000). The results show that the suspensionexhibits plastic #ow behaviour within the pH regionexamined. The plastic #ow behaviour is characterised bya non-linear #ow curve which asymptotes to a constantstress value at low shear rate. This constant stress corres-ponds to the yield stress of the suspension. The positionof the plastic #ow curves in Fig. 7 varies with suspensionpH. The #ow curve at pH 8.8 is located at the highest

2906 Z. Zhou et al. / Chemical Engineering Science 56 (2001) 2901}2920

Fig. 7. Flow curves of AKP-20 suspensions (!"0.3) at various pH(adapted from Zhou, 2000).

Fig. 8. The normalised viscosity (100 s!") vs. pH for AKP-20 suspen-sions of various volume fraction (adapted from Zhou, 2000).

Fig. 9. The compressive yield stress of concentrated zirconia suspen-sions as a function of pH and volume fraction (adapted from Green& Boger, 1997).

part of the stress axis, which represents the maximumdegree of #occulation. The #atter curve shape in Fig.7 indicates highly shear thinning behaviour of the sus-pensions. This behaviour can be attributed to the disrup-tion of #occulated structures in a shear #ow "eld, whichfrees some medium liquid entrapped in the #ocs. There-fore the e!ective concentration of particles and #ocsdecreases as the shear rate increases. Interestingly theshear viscosity displays similar behaviour to that of !

!as

a function of "#. It has been con"rmed that Eq. (7) can beextended by replacing the normalised yield stress witha normalised viscosity (Zhou, 2000), such as

#($% )#!"#

($% )"1!24!&'"#H#

A(1#e!")(8)

where #!"#

($% ) is the maximum viscosity at the pH at theIEP and at the same shear rate as #($% ). When the nor-malised viscosity at a given shear rate is plotted asa function of pH the curves at various solids concentra-tions should collapse to a single curve as the " potential isonly a function of pH. Fig. 8 shows the normalisedviscosity at 100 s!" vs. pH for the alumina suspensions ofdi!erent volume fractions. Similar results were also ob-served for titania suspensions (Liddell, 1996).

In addition to the in#uence on shear-related proper-ties, the net inter-particle interactions also impact signi"-cantly on the compressive behaviour of concentratedmetal oxide suspensions. Fig. 9 displays the compressiveyield stress, P

!, for concentrated zirconia suspensions as

a function of pH and volume fraction (Green & Boger,1997). Similar to the behaviour of !

!, the P

!reaches

a maximum at the isoelectric point and decreases ina parabolic manner as ("( increases. However, comparedto !

!the decreases in P

!with increasing of ("( is much less

and does not reach zero when the suspension is close tobeing dispersed.

The compressive yield stress is closely related to theshear yield stress since both depend on the ability of thenetwork to accommodate elastic strain (Buscall et al.,1987; Buscall, Mills, Goodwin, & Lawson, 1988; Meeten,1994; Green & Boger, 1997; Channell & Zukoski, 1997).They are both controlled by the strength of inter-particleforces and suspension microstructure. Both shear and

Z. Zhou et al. / Chemical Engineering Science 56 (2001) 2901}2920 2907

AMTC 15 / 17


Alta variabilidad entre yacimientos

Yacimiento Origen Tipo de roca % Arcilla

Escondida (Benc 1906) Chile Pórfido/ an-desita

12 % kaolinita + 18 % ilita

Disputada (alta arcilla) Chile Pórfido/cuarzo

10 % montmorrillonita +4 % ilita

Mansa Mina (Veta 3) Chile Andesita/cuarzo

8 % caolinita + 4 % ilita

Escondida (andesita) Chile Andesita 4 % montmorrillonita +2 % bramolita

Minas Conga Perú Pórfido/andesita/cuarzo

22 % caolinita + 18 % ilita

Batu Hijau Indonesia Andesita 11.5 % chamosita + 7 %caolinita + 5 % ilita

(Bulatovic et al., Proc. Copper, 1999)

AMTC 16 / 17

Notas finales

Conclusiones

Es necesario mejorar conexión entre los distintos niveles de producción

La disposición de relaves depende del proceso y condiciona la operación

Es necesario instrumentar y medir variables relevantes para el relave

La producción de relaves debe ser ajustada dinámicamente

Menos agua es mejor

Aspectos futuros relevantes

Problemas locales, con potencial de solución mediante modelos fisicoquímicos ymatemáticos

Búsqueda de protocolos de medición y cálculo abiertos

Separar ciencia de tecnología

AMTC 17 / 17

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