Role of Minor Elements in Cement Manuf and Use

48
Portland Cement Association Research and Development Bulletin RDIOST Role of Minor lements in Cement anufacture and Use by Javed I. Bhatty

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Transcript of Role of Minor Elements in Cement Manuf and Use

Page 1: Role of Minor Elements in Cement Manuf and Use

Portland Cement Association

Research and Development Bulletin RDIOST

Role of Minor lements in Cement anufacture and Use

by Javed I. Bhatty

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KEYWORDS: manufacturing, minor elements, portland cement, raw materials, trace elements

ABSTRACT: In this review, the effects of almost all the stable minor and trace elements on the production andperformance of portland cement have been reported. Emphasis has been given to elements that occur in naturaland by product materials used for cement manufacturing. The elements for which detailed information has beenobtained are dealt with in an order based on the periodic classification of elements. The volatilities of the elementshave also been discussed where ever necessary. Elements reviewed include: hydrogen, sodium, potassium,lithium, rubidium, cesium, barium, beryllium, strontium, magnesium, boron, gallium, iridium, thallium, carbon,germanium, tin, lead, nitrogen, phosphorus, arsenic, antimony, bismuth, oxygen, sulfur, selenium, tellurium,fluorine, chlorine, bromine, iodine, helium, neon, argon, krypton, xenon, yttrium, titanium, zirconium, vanadium,niobium, tantalum, chromium, molybdenum, tungsten, manganese, cobalt, nickel, copper, silver, zinc, cadmiummercury, and the lanthanides.

REFERENCE: Bhatty, J. I., Role of Minor Elements in Cement Manufacture and Use, Research and DevelopmentBulletin RD109T, Portland Cement Association, Skokie, Illinois, U.S.A., 1995.

MOTS CL ES: ciment portland, 616ments mineurs, 616ments trace, fabrication, mati$res premi?u-es

RESUME: Ce document rapporte les effets de presque tous les Mrnents mineurs stables et Uments trace sur la/

production et la performance du ciment portland. L’accent a W mis sur les dldments qui se trouvent ~ I’dtatnaturel clans les mat6riaux aussi bien que sur ceux des rclsidus utilisds lors de la fabrication du ciment. Les416ments pour lesquels de l’information ddtaillde a W obtenue sent abord4s aans un ordre basal sur la classifica-tion p(%iodique des Wments. La volatility des Wrnents est aussi traitde lorsque n6cessaire. Parmi les d~mentscouverts, on retrouve: l’hydrog~ne, le sodium, le potassium, le lithium, le rubidium, le c&sium, le barium,b&yllium, le strontium, le magn6sium, le bore, le gallium, I’indium, le thallium, le carbone, le germanium, l’6tain,le plomb, l’azote, le phosphore, I’arsenic, l’antimoine, le bismuth, l’oxygtme, le soufre, le sdh%ium, le tenure, lefluore, le chlore, le brome, I’iode, l’h61ium, le neon, l’argon, le krypton, le xdnon, l’yttrium, le titane, le zirconium,le vanadium, le niobium, le tantalum, le chrome, le molybdbne, le tungst$ne, le manganbse, le cobalt, le nickel, le

tcuivre, l’argent, le zinc, le cadmium, le mercure et Ies lanthanides.

REFERENCE: Bhatty, J. I., Role of Minor Elements in Cement Manufacture and Use, Research and DevelopmentBulletin RD109T, Portland Cement Association [R61e et utilitd des Wirnents mineurs clans la fabrication duciment, Bulletin de Recherche et D6veloppement RD109T, Association du Ciment Portland], Skokie, Illinois,U.S. A., 1995.

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PCA R&D Serial No. 1990

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PCA Research and Development Bulletin RD109T

Role of Minor Elements in CementManufacture and Use

by Javed 1.Bhatty

ISBN 0-89312-131-2

@ Portland Cement Association 1995

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Role of Minor Elements in Cement Manufacture and Use

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PCA Research and Development Bulletin RD109T

Contents Page

INTRODUCTION ................................................................................................................................. 1ALTERNATIVE MATERIALS AS PARTIAL RAW FEED OR FUEL IN CEMENT MAKING ................1

DEFINITloNs ...............................................................l...i ....................................................m.............2Major Elements ...................................................................................................................... 2Lesser Elements ................................................................................................................... , 3

Minor Elements ...................................................................................................................... 4Trace Elements ...................................................................................................................... 4

SOURCES OF MINOR ELEMENTS ................................................................................................... 4

MINOR ELEMENTS IN CEMENT MAKING ........................................................................................ 6

ELEMENTS IN GROUP I (Hydrogen, Lithium, Sodium, Potassium, Rubidium, Cesium)., .................. 7Hydrogen ................................................................................................................................ 7Lithium .................................................................................................................................... 8Sodium and Potassium .......................................................................................................... 8Rubidium and Cesium .......................................................................................................... 11

ELEMENTS IN GROUP II (Beryllium, Magnesium, Calcium, Strontium, Barium) ............................. 11Beryllium .............................................................................................................................. 11Magnesium ........................................................................................................................... 11Calcium ................................................................................................................................ 11Strontium .......................................................c........i ............................................................. 11Barium .................................................................................................................................. 11

ELEMENTS IN GROUP Ill (Boron, Aluminum, Gallium, Iridium, Thallium) ....................................... 12Boron. ................................................................................................................................... 12

Aluminum ............................................................................................................................. 12Gallium, Iridium, and Thallium .............................................................................................. 12

ELEMENTS IN GROUP IV (Carbon, Silicon, Germanium, Tin, Lead) .............................................. 13Carbon ................................................................................................................................. 13Silicon ................................................................................................................................... 13Germanium .......................................................................................................................... 13Tin ........................................................................................................................................ 13Lead ..................................................................................................................................... 13

ELEMENTS IN GROUP V (Nitrogen, Phosphorous, Arsenic, Antimony, Bismuth) ........................... 13Nitrogen ................................................................................................................................ 13

Phosphorus .......................................................................................................................... 14Arsenic ................................................................................................................................. 14Antimony .............................................................................................................................. 15

Bismuth ................................................................................................................................ 15

,,.Ill

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Contents Page

ELEMENTS IN GROUP VI (Oxygen, Sulfur, Selenium, Tellurium) ................................................... 15

Oxygen ................................................................................................................................. 15Sulfur ....................................................................................................................................Selenium .............................................................................................................................. 1;Tellurium ............................................................................................................................<. 17

ELEMENTS IN GROUP Vll (Fluorine, Chlorine, Bromine, lodine) .c.................................................. 17

Fluorine ................................................................................................................................ 17Chlodne ................................................................................................................................ 19

A/ir7iteCements ....................................................j..........................................................c. 19Bromine ................................................................................................................................ 19lodine ...................................................................................................................................2O

ELEMENTS IN GROUP Vlll (Helium, Neon, Argon, Krypton, Xenon) .............................................. 20

TRANSITION ELEMENTS ................................................................................................................2OYttrium.. ................................................................................................................................ 20Titanium ...............................................................................................................................2OZirconium ..............................d.............................................................................................. 21Vanadium ............................................................................................................................ 21Niobium ................................................................................................................................ 22Tantalum .............................................................................................................................. 22Chromium,... ......................................................................................................................... 22Molybdenum .........................................................!.. ............................................................. 23Tungsten .............................................................................................................................. 23Manganese .......................................................................................................................... 23Cobalt ................................................................................................................................... 24Nickel ................................................................................................................................... 24Copper ................................................................................................................................. 24Silver .................................................................................................................................... 24Zinc ...................................................................................................................................... 24Cadmium .............................................................................................................................. 25Mercury ................................................................................................................................ 25

THE RARE EARTHS ......................................................................................................................... 25

CONCLUSIONS ............................................................................................................................... 26

ACKNOWLEDGEMENTS .................................................................................................................. 26

REFERENCES .................................................................................................................................. 27

APPENDlx .........................................................................................!c....................................c........35

INDEX ............................................................................................................................................... 38

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PCA Research and Development Bulletin RDI09T

Role of Minor Elements in CementManufacture and Use

by Javed 1. Bhatty*

INTRODUCTION

The purpose of this review is to col-Iect pertinent information on the be-havior of minor and trace elements onthe manufacture and use of cement.Attempts have been made to identifygaps, if any, in the information thusfar available and suggest work forfurther investigations.

As cement manufacturerscontinually strive to conserve re-sources, use of alternative raw feedsand seconda~fuels derived from con-tinuously generated industrial by-products isgaininginterest. The likelyconcerns from alternative or new natu-ral sources are the incorporation oftrace elements into clinker and theireffects on the performance of cement.These effects are, to a large extent,dependent upon the type of trace ele-ments contained in the raw feed, theirconcentration levels, and the operat-ing conditions of the kiln.

The effects of minor elements onthe production of clinker and perfor-mance of cement are summarized inthe appendix.

ALTERNATIVE MATERIALSAS PARTIAL RAW FEED ORFUEL IN CEMENT MAKING

There has been an increasing movetoward using a variety of alternative

materials in cement manufacturing,with the multiple aims of reducingby-product accumulation to addressenvironmental problems and toachieve technical advantages duringclinker processing without sacrific-ing the quality of cement.

Chlorideby-products, and wastesfrom the soda ash industry, whenmixed with fly ash and limestone, arereported to have produced low tem-perature clinkers (1200°C) with com-parable compressive strength (Patel,1989). Phosphogypsumhasbeen usedas a source of limeinkilnfeed. Thoughthe clinker attained a different micro-structure, the cement compared fa-vorably with the conventional type(Toit, 1988). In separate studies, spentclays from lubricating oil refining,have also been tested as raw feedcomponents for clinker production(Midlam, 1985).

Sewage sludge as a partial kilnfuel was reported by Obrist (1987).Heavy metals in the sludge were per-manently withdrawn from the bio-sphere with little toxic emissions. Or-ganic pollutants were reliably de-stroyed without leaving any toxic by-products. The only exception maybemercury which must be controlledadequately.

Ostrovlyanchik et al. (1986) re-ported that the use of fly ash from coalpower plants as raw material, in placeof argillaceous material, was effective

for improving the wet process kilnoutput with savings in the fuel con-sumption.

Bhatty et al. (1985) produced anASTM C150 Type I cement from thecopper-nickel and taconite tailingsused as a partial substitute for ce-ment raw feed. The resulting ce-ment had a microstructure andstrength properties comparable tothat produced with conventionalfeed.

Weatherhead and Blumenthal(1992), of the Scrap Tire Manage-ment Council, concluded from a re-cent field stud y that tires can be usedsuccessfully as an alternative fuel incement kilns. The fuel cost is signifi-cantly lowered, and the productionrate is enhanced without adverselyaffecting the quality of cement. Nosignificant change in the environ-ment quality, due to emissions, wasnoted.**

*

u’!+

Senior Scientist, ConstructionTechnol-ogy Laboratories, inc., Skokie, lllinois60077, U.S.A.Tel: (708)965-7500

A distinction between the terms “tire-derived fuel” and “whole tires” may bemade here. The tire derived fuel (TDF)uses shredded tires in combination withother conventional fuels (coal, coke, oil,gas, etc.) usually in the burner end, tirechips are also fed to calciners, whereasthewhole tires are fed into the feed end ofa precalciner or a preheater kiln or intothe calcining zone of a long kiln.

ISBN 0-89312-131-2

0 Portland Cement Association 1995 1

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Use of scrap tires and lubricatingoil, as alternative fuel in cement manu-facturing, has also been reported in anumber of test burns in Australia andCanada (McGrath, 1993; and Heron,1993). The tests suggested substantialreduction in manufacturing costs, im-provement in waste minimization, ad-vances in resource recovery, extendedlife of existing landfills, and better en-vironmental control.

De Zorzi (1988) reported Italianexperience on the use of municipalsolid waste as a partial fuel in cementmanufacturing. The chemical andphysical characteristics of clinker andcement were comparable to those pro-duced conventionally. No significantchange inorganic or inorganic pollut-ants, such as dioxins, furans, SOX andNOX, were detected in the stack emis-sions. There were no material han-dlingproblems,but storage of the solidwaste, especially the refuse derivedfuel (RDF), was expensive, because itneeded to be contained in totally en-closed compartments for technical andenvironmental reasons.

Regarding Norwegian experi-ence, Ingebrigtsen and Haugom (1988)demonstrated that using hazardousliquid wastes containing PCBS” as apartial kiln fuel offered an efficientway to solve a difficult environmentalproblem. For waste containing chlo-rine levels in excess of ().()ls~o, the useof a by-pass was recommended.Krogbeumker (1988) also reported thatwaste oils containing PCBS were testedas effective kiln fuel with adequateatomization of the oils into the gasstream. The levels of polychlorinateddibenzodioxin and dibenzofuran inemissions were very low and close tothe limits of detection. Although thesetests were very successful, PCBS arenot burned in U.S. cement kilns.

Huhta (1990) surveyed sometwenty North American cementplantsoperating with wastes as supplementfuel, and noted that the predominantwaste being used was waste oil fol-lowed by solvent derived fuel andscrap auto tires; wood chips and fluid

coke were also mentioned. However,it is projected that the tire derived fuel(TDF) will become the most advanta-geous fuel in the near future, becauseof its availability and easy handling.

Kelly (1992), and Mantus et al.(1992) reported that the use of wastesas supplemental fuel in well designedand properly operated kilns results inmetal emissions too negligible to causeany adverse health effects. It was alsodemonstrated that the cements andkiln dusts thus produced were not sub-stantially different from those conven-tionallyproduced. The effects of wasteson the emissions of organic compoundsand metals from kilns were also stud-ied by von Seebach et al. earlier in1990. It was reported that a virtuallycomplete destruction and removal ofhazardous organic compounds occursin the kiln. A destruction and removalefficiency (DRE) of hazardous com-pounds was recorded at 99.9996Y0.DREs in access of 99.97 are routinelyachieved.

Siemering, Parsons, and Loch-brunner (1991) have also reported ontheir experiences of burning wastes askiln fuel and have reported both tech-nical and economical advantages withminimal adverse environmental im-pact.

In a recent article, Hansen (1993)has strongly advocated the use of solidwastes in cement manufacturing, em-phasizing potential environmental andpolitical advantages. It was suggestedthat using wastes as fuel has two-foldenvironmental benefits; it would notonly avoid fossil fuel extraction andtransportation, but would also mini-mize emissions that would have oc-curred by disposal of these wastesthrough treatment or by landfilling.Politically, the liability of landfills anddemands for waste minimization in anenvironmentally sensitive society, suchas the United States, can be substan-tially reduced by waste utilization incement making.

Gossman (1988) pointed out someof the risks and liabilities associatedwith the use of hazardous waste-de-

rived fuels, and proposed certain ana-lytical means to minimize liabilitiesin order to achieve full economicaland quality control advantages.

Although there are opportuni-ties to beneficially use wastes in ce-ment production, their total substitu-tion in the industry is still in the ex-perimental stages. One recommen-dation has been to limit the use ofwaste to 5°/Obyweight of the raw feed(Vogelet al.,1987). Huhta (1990), andvon Seebach et al. (1990) have re-ported a potential of 20-307. or evenmore for waste as a fuel replacementin cement kilns; some plants havealready used 50-10O% replacement.Nonetheless, the level of applicationand degree of success largely dependsupon the waste composition in termsof the type and concentration of mi-nor or trace elements.

In summary, under favorablepractical conditions, wastes can havethe following combined benefits:a.

b.

c.

d.e.

f.

g.

Respond to commercial and en-vironmental pressure to use al-ternate raw materials and wasteby-products.Recover potential energy valuefrom the wastes.Conserve nonrenewable rawmaterials and fossil fuels.Enhance process efficiency.Produce more reactive rawmixes.Produce cement of improvedquality.Reduce COZ emissions.

DEFINITIONS

Major Elements

According to Rompps Chemie-Lexikon (1987), the elements that aremore abundantly present (>.5’XO)incement clinker are the major elements.These are calcium (Ca), silicon (Si),aluminum (Al), iron (Fe), and oxy-gen (0). Carbon (C) and nitrogen

● PCBs=polychlorinated biphenyls

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PCA Research and Development Bulletin RD109T

Table 1. Typical Compositions and Physical Properties of Portland Cements

Compound Composition (O/.) Type I Type II Type Ill Type IV Type V

C,s 58 49 60 25 40

C2S 15 26 15 50 40

C3A 8 6 10 5 4

C,AF 10 10 8 12 10

Gypsum 5 5 5 4 4

Loss on Ignition 1.7 1.5 0.9 0.9 0.9

Blaine (m’/kg) 350 350 450 300 350

1-day Strength (psi) 1000 900 2000 450 900

7-day Heat of Hydration (J/g) 330 250 500 210 250

(N), because of their abundance inthe raw material and the earth atmo-sphere respectively, can also be re-garded as major elements.

In clinker and cement analyses,Ca, Si, Al, and Fe are expressed as theoxide form (CaO, SiOz, A120~, andFezOJ. However, they eventually ex-ist as more complex compounds. Theapproximate formulae of these com-pounds, alsoknownasclinker phases,are tricalcium silicate 3CaO*SiOzor C#*; dicalcium silicate 2CaO*SiOzor CZS; tricalcium aluminate3CaO*A110~ or C~A, and tetracalciumaluminoferrite 4CaO*AlzO~*FezO~ orCgAF. Since the role of major ele-ments in cement manufacturing hasbeen fairly well understood, only abrief summary on the presence ofmajor compounds in cement is givenhere.

Calcium is an essential compo-nent of cement, which comes fromthe decomposition of the primary rawmaterial such as limestone, chalk,marl or cement rock depending uponthe geological location of the cementmanufacturing plant. Silicon in ce-ment is derived from silica sand, orfrom clay, shale, or slate, which arealso sources of aluminum andiron inthe raw material. Iron is sometimesderived from iron ores, or mill scale,and added separately if the raw mixis deficient in iron. Aluminum maybe added with bauxite or othersources. Auxiliary materials such asfly ash and blast furnace slag are alsooften added as raw feed substitutes.

Aground mixture of the raw ma-terial containing major componentsin a required proportion is burned ina rotary kiln at about 14500C, wherethe constituents become fully oxi-dized and form stable solid solutionsor the phases as described above.Impure CJS is also frequently knownas alite, and C$ as belite”’. Aftercooling, the clinker is intergroundwith approximate y 5% of gypsum toabout 350 m2/kg Blaine fineness, toobtain portland cement.

A typical composition of ASTMType I cement, the most commonlyused cement in general construction,is normally 58’70 CaS, 15°/0C2S, 80/0C~A, 107. CdAF, and 5?0 gypsum.Other ASTM cement types are TypeII, III, IV, and V, which vary in com-position and are used where specialproperties are required. Typical corn-position and physical properties ofvarious cement types are given inTable 1 (adapted from CTL, 1993;Mindess and Young, 1981).

Type III cement is a high heat ofhydration cement with high C.$ con-tent and a finer particle distributionand is used where rapid hardening isrequired for early strength develop-ment. Type IV is a low heat of hydra-tion, slow setting cement because oflow C~S and high C2S contents. It isintended for mass concrete in order toavoid thermal cracking, but is nowrarely produced. Since the strengthdevelopment of Type IV cement islow, Type II cement, which can bespecified as a moderate heat of hydra-

tion cement, is generally recom-mended due to its higher strengthand market availability. For evenlower heat of hydration, Type II ce-ment with fly ash is used. Type Vcement is also a low heat of hydrationcement because of low C~S and lowC~Acontents; it isnormallyused whenhigh sulfate resistance is required.Type II is primarily used as a moder-ate sulfate resistant cement.

A knowledge of the compoundcomposition can reasonably be usedto predict the properties of cement.One of the known methods for calcu-lating compound compositions fromthe oxide analysis are the Bogue for-mulae (1955). Although a number ofsophisticated techniques are nowavailable for Bogue calculations, thesimplest Bogue formulation that hasbeen found suitable for most applica-tions is given in the ASTM C 150specifications.

Lesser Elements

Fourlesserelements, i.e., sodium (Na),potassium (K), magnesium (Mg), andsulfur (S), which appear in virtuallyall commercial clinkers at l-5y0 con-

* In cement chemist’s notation S=Si02,C=CaO, A=A1203,F=Fe203and S.S03

** Alites and Mites are never pure formsof C3Sand C2Srespectively. Due to thegeological source of the raw materials,alite and belites will always have smallquantitiesof impuritiesor traceelements.

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Role of Minor Elements in Cement Manufacture and Use

centration, are represented in chemi-cal analyses as oxide forms: NazO, KZO,MgO, and SOS. Rompps Chemie-Lexikon (1987) has termed these ele-ments as the secondary elements. Incement chemist’s notation Na20=N,K20=K, MgO=M, and S0,=3.

Minor Elements

According to Miller (1976) and Gartner(1980), elements other than the majorand the lesser constituents (i.e. Ca, Si,Al, Fe, O, Na, K, Mg, S) may be consid-ered as minor elements with regard tocement manufacturing. The concen-tration levels of minor elements in theclinker are almost always less than 17.and are generally categorized on thebasis of the frequency with which theyoccur in the raw material mix.

Trace Elements

Blaine et al. (1965) regarded the ele-ments occurring at less than 0.02%each as the “trace” elements. Accord-ing to Sprung (1988), elements presentat levels less than 100 ppm are classi-fied as trace elements. Because of theirextremely small concentration levels,it seems unlikely that the presence oftrace elements will have any signifi-cant effects on cement manufacturing.However, their effects on clinker cansignificantly change if concentrationsare increased beyond certain levels.

For the sake of convenience, theterminology “minor elements” hasbeen used throughout the text to coverboth minor and trace elements, as de-fined by Blaine et al. (1965) andRompps chemie - Lexikon (1987) re-spectively, unless mentioned other-wise.

Rompps Chemie-Lexikon (1987)has exemplified the classificationof several major, secondary, and traceelements in cement clinker in Figure 1.

Emphasis in this report is given tothe minor and trace elements becauseof their likely presence not only in thewastes but also in the conventionalraw materials, and their potential in-

1 ppq 1 ppt 1 ppb 1 ppm 0.0019’0 1?40

Figure 1. Concentration ranges (by mass) of main, secondary, andtrace elements in cement clinker (Sprung, 1988).

fluence on cement manufacturingand use. It maybe pointed out thattrace elements in a raw feed at onecement plant could significantly dif-fer from another. As an extreme,lead content in one plant maybe 100-500 ppm compared to only 1 ppm inanother plant (Chadbourne, 1990).

SOURCES OF MINORELEMENTS

Minor elements in cement primarilycome from the raw materials andfuel used in cement making. Ex-amples of these are limestone, clay/shale, and coal. They also come fromthe widely used auxiliary materialssuch as blast furnace slag, fly ash,silica sand, iron oxide, bauxite, andspent catalysts. A secondary but im-portant source of minor elementscomes from the wide range of indus-trial by-products which are partiallyor totally being substituted for theprimary fuel. These include petro-!eum coke, used tires, impregnatedsawdust, waste oils, lubricants, sew-age sludge, metal cutting fluids, andwaste solvents, as listed in Table 2.

Minor compounds found in sev-eral raw feeds for cement manufac-turing as quoted by Bucchi (1980) areshown in Table 3. Similar data on

major components of raw materialsare shown in Table 4 and 5. They arelimestone and shale/clay; widelyused auxiliary raw minerals, i.e. blastfurnace slag (used up to 307. byweight of raw material), and coal flyash (used up to 15”/.by weight).

Minor elements found in con-ventional kiln fuel (coal), along withtwo secondary fuels (used oil andpetroleum coke) are shown in Table6. Average values of minor compo-nents found in typical clinkers(Moir and Glasser, 1992) are given inTable 7.

Although blast furnace slag canbe used up to 307. by weight, thelevel of use maybe reduced due to itsmagnesium oxide (MgO) content,particularly if the MgO level is al-ready high in the other raw materi-als. Bauxite is reported to contain2-87. titanium oxide (TiOz) and0.04-0.4% chromium oxide (CrzO,).Iron ores frequently contain chro-mium, arsenic, cadmium, and thal-lium, and may have adverse envi-ronmental consequences because oftheir toxicity characteristics. A list ofmetals having regulatory and envi-ronmental concerns has been speci-fied by waste characterization regu-lations under the Resources Conser-vation and Recovery Act (RCRA) andthe Boiler and Industrial Furnace (BIF)

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PCA Research and Development Bulletin RD109T

Table 2. Sources of Minor Elements in Cement Manufacturing

:Iements (as per group)

Sroup I.ithium

Group II3erylliumStrontium3arium

Group HI3oron

Gallium, Iridium, Thallium

Group IVGermaniumTinLead

Group VNitrogenPhosphorusArsenicAntimonyBismuth

Group VISulfurSelenium, Tellurium

Group WIFluorineBromine

Chlorinelodine

Transition ElementsTitaniumZirconiumVanadiumChromiumMolybdenumManganeseCobaltNickel

Copper

Zinc

CadmiumMercury

Sources

Waste lubricating oil

Fly ashLimestone, aragonite, slag, waste lubricating oilWaste lubricating oil, refuse derived fuel (RDF)

Raw material, iron ore

Raw material, fly ash, coal, secondary fuel, waste derived fuel (WDF)

Raw material, coalFly ash, RDF, fuelRaw material, tires, RDF, WDF, copper shale, fly ash

Coal, airRaw material, slag, sewage sludge, sandstone, RDFFly ash, secondary fuel, coal, used oilsPetroleum, cokeFuel

Coal, slag, lubricating oil, petroleum coke, pyrite, tiresFly ash, coal, RDF, coke

Limestone, fuelFly ash

Coal, slag, fly ash, waste lubricating oil, chlorinated hydrocarbons, RDF, chlorine-rich fuelCoal

Raw material, clay, shale, iron ore, bauxite, slag, RDFRaw material, silicon ores

Petroleum coke, crude oil, black shale, substitute fuel, coke, fly ashBauxite, slag, recycled refractories, copper shale, tires, WDF, coalWaste lubricating oilRaw material, limestone, clay, shale, bauxite, slag, fly ashWaste oil, fly ashFly ash, black shale, copper shale, waste oil, tires, RDF, WDF, coal, petroleum coke

Fly ash, black shale, copper shale, lubricating oil, tires

Used oil, tires, metallurgical slags, filter cake, furnace dust, RDF, WDFFly ash, black shale, copper shale, WDF, paintWDF, paint fungicides

“ Raw material includes natural materials such as limestone, clay, shale, sand, etc.

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Role of Minor Elements in Cement Manufacture and Use

,

regulations that control treatment ofhazardous waste in cement kilns.These are shown in Table 8 (Klemm,1993). Both RCRA and BIF regula-tions apply to wastes and require theuse of the TCLP (toxicity characteris-tic leaching procedure) tests.

The levels of sulfur and chlorineI in bituminous coal, the main fuel for

Cement kilns, varies frOIn 0..5 to 4y0and 0.007 to 0.39Y0, respectively. Insome Illinois coals, sulfur is presentup to 60/0by weight. Petroleum coke,u~ed as an-auxilia~ fuel, contains upto 5~0 sulfur and 0.6% vanadium OX-ide, and can contribute certain levelsof S and V to clinker when supple-menting for coal. Tires have a zinccontent of 1.2-2.6 Yo.However, if tiresreplace 10% of the primary fuel, theresulting zinc oxide (ZnO) contentsin clinker are increased by only ().W70(Sprung, 1985),

Additional sources of minor com-ponents could be the refractories,chains, and the grinding media suchas liners and grinding balls. A dam-aged chrome refractory lining can en-ter into the incoming raw mix andincorporate a detectable amount ofchromium into the clinker. Partly forthis reason, and mostly because ofproblems with their safe disposal, theuse of chrome bricks is being phasedout in most parts of the world (Moirand Glasser, 1992).

MINOR ELEMENTS INCEMENT MAKING

The role of minor and trace elementsin the formation of clinker and theireffect on cement properties are dis-cussed in this report as per their oc-currences in raw mixes. The elementschosen for discussion are categorizedaccording to the periodic table, ashighlighted in Figure 2. They arediscussed in their increasing order ofatomic number. The presence of anyinformation gaps are identified andreferred for further investigation.

Table 3. Average Concentrations (%) of Some Minor Com~ounds inRaw M-eals Used in European Cement Plants (Adopted fromSprung et al., 1984; and Bucchi, 1980) - “

Minor Compounds

MgO

K20

so,

Na20

TiO,

Mn,O,

P20,

SrO

Cr,O,

AS,O,BeO

NiOV*05clF

Raw Meals

1,05

0.570.31

0.17

0,16

0.12

0.09

0.07

0.01

0.0020.00050.0030.024

0.02

0.06

Table 4. Concentrations (ppm) of Some Minor Elements inLimestone and Clay/Shale (Sprung, 1985)

Minor Elements

AsBeCdCrPb

HgNi

Se

AgTI

vZn

clF

BrI

Limestone

0.2-120.5

0.035-0.11.2-160.4-13

0.031.5-7.5

0.19n.a. ”

0.05-0.5

10-8022-24

50-240100-940

5.90.25-0,75

Clay/Shale

13-233

0.016-0.390-10913-22

0.4567-71

0.5

0.07

0.7-1.6

98-17059-11515-450

300-9901-58

0.2-2.2

Table 5. Average Concentrations (%) of Some Minor Compounds inMajor Auxiliary Raw Materials, i.e. Blast Furnace (B. F.) Slagand Fly Ash (Moir and Glasser, 1992: and Smith et al.. 1979}

Minor Compounds

MgOK,O

so,

Na,OTiOCr,&,MnzO,

P20,SrO

V206

B.F. Slag

7.2

0.57

3.000.44

0.66n,a.*

0.64

0.03

0.06

n.a.AS20, n.a,

“n.a,= informationnot available

Fly Ash

5.28

4.05

2.251.99

1.210.03

0.14

<3.66

0.17

0.090.02

6

Page 13: Role of Minor Elements in Cement Manuf and Use

ELEMENTS IN GROUP I(Hydrogen, Lithium, Sodium,Potassium, Rubidium, Cesium)

Hydrogen

The role of hydrogen (H) in cementmanufacturing has not been docu-mented in detail, because hydrogenper se does not exist for long in the kilnas hydrogen is highly combustible. Itis present in the kiln as water vapor,which results from the evaporation ofphysically bound moisture from theraw material, and from the evapora-tion of water sprayed on the raw feedto control dust during processing.Water vapor can also be present in thekiln gases from combustion of fuel suchas CHA + 20Z ~ COZ + 2HZ0(Hawkins, 1994; Miller, 1994). A por-tion of water may also come from thedehydration of raw materials such asclays, where it can be present in signifi-cant quantities depending upon theirmineralogical nature. In a wet plant,water comes from slurry.

The water vapor present in thekiln might have an indirect effect onthe volatility of alkalies which can in-crease with vapor pressure at highertemperatures, for example:

2H,0 + 21$S04 -’ 4KOH + 2S02 + 0,less more very

volatile volatile volatile

Apart from that, hydrogen may nothave any significant effect on the an-hydrous nature of clinker.

As a point of information, it maybe mentioned that early cement kilnssometimes used “producer gas” as fuel.The gas was generated (as a mixture ofCO and Hz) by the action of steam onhot coal or charcoal as follows:

H20+C~CO+H,

Currently, no kilns in the USACanada use this technology.

or

PCA Research and Development Bulletin RD109T

Groups

1

2

6

7 1=” !3s ‘AC Unq Unp Unh Uns

Lanthan~deSeries

Act inideSeries

. L? dPr’Nd@ml”am”EU ‘ Kid lb’ DY” Ho” Er6 Tm6 ~

.

“ Th Pa’,

Ua NP93 Pu” Am’ Cm Bkv

Cf98

Figure 2. Elements from the periodic table selected for studies.

Table 6. Average Concentrations (ppm) of Some Minor Elements inCoal aid Used Oil (Sprung; 1985; and Weisweiler andKr6mar, 1989)

Minor Elements Coal Used Oil Petroleum Coke

Sb 1.19 n.a.* 0.0429

.4s 9-50 <0.01-100 0.6

Ba 24.5 0-3,906 8.4

Be 2.27 n.a. n.a.

Cd 0.1-10 4 n.a.

Cr 5-80 <5-50 11.0

Pb 11-270 10-21,700 8.7

Hg 0.24 n.a. n.a.

Ni 20-80 3-30 208.0

Se 3.56 n.a. 0,1

Ag 0.06 n.a. n.a.

TI 0.2-4 <0.02 0.1

v 30-50 n.a. 778.0

Zn 16-220 240-3,000 n.a,

Sr n.a. n.a. 4.3

cl 100-2,800 10-2,200 n.a.

F 50-370 n.a. n.a.

Br 7-11 n.a. n.a.

I 0.8-11.2 n,a. n.a.

“n.a.= information not available

7

Page 14: Role of Minor Elements in Cement Manuf and Use

Role of Minor Elements in Cement Manufacture and Use

Lithium

Lithium (Li) is found in some wastematerials such as used lubricants, butoccurs only in traces in the kiln raw

, feeds and common fuels.Lithium might behave somewhat

differently from sodium or potassiumin that it would tend to form a rela-tively nonvolatile oxide (LizO) at el-evated kiln temperatures, Gouda(1980) reported that LizO is most reac-tive in lowering the temperatureof the initial liquid phase; theeffectiveness has been shown asLizO>NazO>KzO, The presence of L<Oalso disturbs the course of the burningprocess during which lime dissolvesin the liquid phase and results in higherreactivity. As a negative effect, Li10also inhibits the conversion of CZS toC,S. The effects are more pronouncedwith Li.O comuared to Na.O and K.O.

Ra~garao’(1977) poin~ed out t~atup to l% of Li10 in the raw mix im-parts a mineralizing effect, but limefixation is impaired afterwards. At alower LizO addition (0.1-0.3% byweight), limestone dissociation acti-vation energy is reduced, and mineralformation becomes more intensive.

If present in adequate amounts asan admixture, Li can have beneficialeffects on cement properties, since it isknown to greatly reduce the alkali-silica reaction (ASR) in concrete. Re-cent studies by Stark et al. (1993) havedemonstrated that Li salts like LiOHand Li carbonates (if added in appro-priate amounts) reduce the ASR sig-nificantly. It is conceivable that Li inclinkers could also have the same af-fect on ASR.

Sodium and Potassium

Since both sodium (Na) and potas-sium (K) occur together in raw feed,and by virtue of similarities in theirbehavior in cement manufacture, it isappropriate to discuss them together,

Sodium and potassium are mainlyderived from the raw materials; their

Table 7, Average Concentrations of Some Minor CompoundsFoundin Conventional Clinkers (Moir and Glasser, 1992)

Minor Compounds

MgO

K,O

so,

Na20

TiO,

Mn20,

P*05

SrO

Minor Compounds

ZnO

Cr,O,

V*05

clAs,O,

Cuo

PbO

CdO

T120

Mean Value (%)

1,48

0,73

0.80

0.16

0.27

0.06

0.10

0.09

Mean Value (ppm)

120

103

100

90

56

55

16

0.5

0.3

Table 8. Elements of Regulatory and Environmental Concern(Klemm, 1993)

Elements

Antimony

Arsenic

Barium

Beryllium

Cadmium

Chromium (Total)

Chromium (Vi)

Lead

Mercury

Nickel

Selenium

Silver

Thallium

‘RCRAMetals

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

RCRA Limit‘* Using TCLP

1.0 mg/L

5.0 mg/L

100 mg/L

0.007 mg/L

1.0 mg/L

5.0 mg/L

not defined

5.0 mg/L

0.2 mg/L

70 mg/L

1.0 mg/L

5.0 mg/L

7.0 mg/L

“ BIFMetals

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

● RCRA . Resource Conservation and Recovery Act

“’ TCLP = Toxicity Characteristic Leaching Procedure

“’* BIF = Boiler and Industrial Furnace

BIFCarcinogen

Yes

Yes

Yes

Yes

8

Page 15: Role of Minor Elements in Cement Manuf and Use

PCA Research and Development Bulletin RD109T

main carrier is clayey rock. Sedimen-tary rocks, including the carbonateores, sometimes contain soluble alkalisalts. Lea (1971) has quoted the occur-rence of Na and K (by weight O/.)indifferent components of raw materi-als used for cement manufacturing asshown in Table 9.

Table 9. Presence of Sodium andPotasium in DifferentRaw Materials (Lea, 1971 )

7. by wt. Na20 K20

Typical raw mix 0.13 0.52

Limestone 0.26 0.11

Chalk 0.09 0.04

Marl 0.12 0.66

Clay 0.74 2.61

Shale 0.82 4.56

Alkalies frequently occur in auxil-iarv raw materi~ls su~h as blast fur-na~e slag and fly ash as shown in Table5. NazO and KZO in European fuelsrange between 0.05 -O.6?40and ().5-2%,respectively (Bucchi, 1980); for typicalraw feed, their average concentrationIevek are 0.177. and ().57Y0, respec-tively, as shown in Table 3.

Jawed and Skalny(1977, 1978) andSkalny and Klemm (1981) have re-viewed in detail the effects of alkaliesin cement manufacture and use. NazOand KZOare volatile in nature, givingrise to a cycle inside the kiln. Theextent of alkali volatilization varieswith raw material composition; forinstance, volatilization of alkalies inclays is higher than those found infeldspar. About half of the total alka-lies by weight in the feed are volatil-ized between 8OO-1OOO’Cas the mixnears the burning zone, but condensesat cooler parts of the system, such as insuspension preheater riser ducts or inchain systems in dry kilns. The forma-tion of rings and coatings on kiln lin-ing resulting from this heating-cool-ing cycle are generally attributed toalkali condensation and reaction withrefractories or incoming material. To

%’800 –

600-

400 – ‘“\

200 – NaCl

30

20

10

1000 1“100 1200 1300 1400 1500Temperature, ‘C

Figure 3. Vapor pressure of Na and K chlorides and sulfates(Bucchi, 1980).

avoid excessive buildups in the kiln orpreheater vessels, a percentage of gasesmay be bled through a by-pass, so thatthe alkali sulfates and chlorides maybecontinuously removed and end up inthe cement kiln dust (CKD). Thus,CKDscollected from by-pass dust collectorare typically high in alkali contents.Usually potassium compounds aremore volatile than the sodium com-pounds.

According to Bucchi (1981), the in-tensity of the alkali cycle depends uponthe nature of their presence in raw ma-terial, on operating practices, and ontype of kiln. The retention of alkalies inclinker is generally higher for high effi-ciency kiln systems (Lea, 1971). Withgas and oil as fuels, the alkalies tend tovolatilize more as compared to coalused as a fuel. This may be due to thehigh intensity of the flame with oil andgas compared to coal.

In the presence of chlorides andsulfate, the volatilization behavior ofboth Na and K is modified greatly, asshown by the vapor pressure-kiln tem-perature relationship in Figure 3. Thevapor pressures of alkali carbonatesresemble those of sulfates and they ex-hibit similar effects. In the presence ofsulfur, alkalies preferentially form sul-fates. If their amount is more than therequired stoichiometric balance, theexcess will be dissolved in the silicates,aluminates, and ferrites. The commonalkali sulfate phases formed are K2S01,

E’

also known as arcanite, sodiumpotassium sulfate, also known asaphthitalite of a general solid solutioncomposition (K,Na)2S01*, and NazSO1,also known as thenardite (Taylor,1990).

According to Skalny et al. (1981),the ratio of Na to K in cement rawmaterials in the North America andEurope varies. There is usually a sub-stantial excess of KZO over NazO.Therefore, in the presence of suffi-cient amount of SO~ a range of doublealkali sulfates, as described later inthis report, is formed depending uponthe KIO to Na20 ratio. If KZO is inexcess of that required to produceaphthitalite, it forms arcanite.

Burning conditions also signifi-cantly influence the formation of sul-fate so that oxidatizingconditions pro-duce calcium-potassium sulfate and areducing condition produces sodium-potassium sulfate. Potassium is twiceas likely to produce soluble sul-fates as sodium. According to Pollittand Brown (1968), the calcium potas-sium salt, calcium langbeinite2CaSOA”KzSOq**, is also sometimesfound.

Introducing SO, jointly with K20and NazO into clinker melt leads tophase separation. Since alkalies re-

. Commonly written as K3N54in cementchemist’s notation

** Also written as 2CS.KS-

9

Page 16: Role of Minor Elements in Cement Manuf and Use

Role of Minor Elements in Cement Manufacture and Use

duce the melt temperature, and therate of C$ formation is proportionalto the amount of liquid phase, a posi-tive effect on C$ formation could beexpected. However, Johansen (1977)reported that C~S,with or without thepresence of alkali, has the sameamount of free lime after firing at1400-15000C. Alkali sulfate melt andclinker liquid are immiscible phases.Alkalies inhibit the formation of C,Sfrom CzSand lime bystabilizinglowerenergy CZSin the absence of sulfates.

After allocating for the sulfates,the remaining alkalies are distributedbetween silicates, aluminates, andaluminoferrite. Lea (1971) has re-ported ranges of alkalies in the majorclinker phases shown in Table 10.

The values are in general agree-ment with those quoted by Taylor(1990) tin the distribution of alkaliesin different clinker phases.

Gartner (1980) and Gies et al.(1986) reported that in the absence ofSO~, Na20 is preferentially incorpo-rated in CqA by replacing CaOand forms “alkali-aluminate”of an approximate compositionNaO*8CaO*3AlzO~*, thereby reducingits reactivity. This results in clinkersrich in free lime and aluminate, andcan reduce the burnability. K is sub-stituted in C$ as a compound withan approximate composition ofKzO*23CaO*12SiOz,** and the overallreactivity of clinker is decreased dueto the slower reaction with CaO toform C~S in the burning process. Inthe presence of sulfate, KZOincreasesthe C,Areactivity(Strungeet al., 1986).Richartz (1986) reported that SOS re-duces the extent of alkali solid solu-tion in C~A and hence the reactivity,but improves the cement properties.

The mineralizing effectiveness ofalkalies (in terms of decreasing meltviscosity, and free lime contents inclinker) also appears to be a functionof their cation size, electronegativity,or the ionic potential. Such relation-ships for K, Na, Li and other relevantcations are given in Table 11 (Grachianet al.), and in Figure 4 (Teoreanu and

Table 10. Range of Alkali Distribution in Clinker Phases (Lea, 1971)

I Clinker Phase

LC3SC*SC,A

C,AF

Na,O (wt.%)

0.1-0.3

0.2-1.0

0.3-1.7

0.0-0.5

K,O (wt.%)

0.1-0.3

0.3-1.0

0.4-1.1

0,0-0.1

Table 11. Effect of Ionic Potential of Minor Elements on theMelt Viscosity (Grachian et al., 1971)

Effect of Different Ions Ionic Potential of Elementson Melt Viscosity (ratio of number of iogic(in decreasing order) charge/cationic, Rvl in Al)

Be+2Mg+2

.942

Li+l

Ba+2

Na+lK+l

5.71

2.50

1.65

1.22

1.39

0.91

0.68

7 I[Cao]o= Free CEO in the Absence of Mineralizer (%) Mg+2

[@O], ❑ Free Cso in the Presence of Mineralizer (%) ●

6

5 ~+2●

4-

0 0.1 0.2 0.3 0.4 0.5

Field Strength, m-2

Figure 4. Mineralizing effectiveness of cations for clinker withLSF=O.96, SM=2.2, AF=2.O at 1350°C (Teoteanu and Tran von Huynh,1970).

Tran van Huynh, 1970) respectively.It might be mentioned that althoughalkalies, NazO in particular, may actas fluxes, they are technically lessdesirable compounds than many ofthe other available minor compounds@ucchi, 1980).

If present in excess, alkalies oftenlead to higher pH and better earlystrength, but lower later strengths.They are not desirable because of

* Commonly written as NC8A3** Also written as KC,3S,j

10

Page 17: Role of Minor Elements in Cement Manuf and Use

PCA Research and Development Bulletin RD109T

their deleterious alkali-silica reaction(ASR) with reactive aggregates thatleads to expansive reactions and cancause serious cracking in concrete. ASRcan be prevented with proper use ofpozzolans.

Butt et al. (1971) reported that thedeleterious effects of alkalies on themechanical properties of cement maybe reduced by gypsum addition to theraw feed. They considered this be-cause of the possible elimination ofsolid solutions of alkalies with clinkerminerals. One possible speculationderived from the microscopicstudies by Prout (1985), is thatgypsum would either increasethe volatilization, or eliminateNaO”8Ca0-3Al,0~ or K,0*23CaO”12SiOzformation. According to Lokot et al.(1969), the addition of gypsum to rawfeed produces cement of high 28-daystrength, enhancing kiln output andfuel savings.

Rubidium and Cesium

The remaining Group I elements, ru-bidium (Rb) andcesium (Cs),arefoundonly as traces in cement raw mix or inthe fuel. Rubidium generally occurs incement at 0.017. or less (Blaine, 1965).

Both Rb and Cs are expected tobehave similarly to Na and K, in thatthey would both form stable sulfatesand volatile chlorides in the kiln(Gartner, 1980). On the other hand,their concentrations may be too low toeffectively influence the clinker forma-tion or cement properties.

ELEMENTS IN GROUP Ii(Beryllium, Magnesium, Calcium,Strontium, Barium)

Beryllium

Beryllium (Be) would be present onlyin trace amounts in the raw feed andfuel (see Tables 4 and 6). It is foundonly occasionally in the fine fractionsof fly ash, an auxiliary material fre-quently used as substitute raw mate-

rial. Beryllium is found at a 55 ppmlevelin=4 pm fraction compared to 12ppm in >45 p,m fraction of fly ash(Davison et al., 1974).

It maybe suggested that becauseof its low volatile oxides, berylliumwould stay in the clinker, Nonethe-less, beryllium has not been measuredin significant amounts in clinkers tohave any measurable effects on clin-ker formation or cement use. Beryl-lium in todays cements has occuredup to 3 ppm (PCA, 1992).

Magnesium

Magnesium (Mg) in portland cementis mainly derived from magnesiumcarbonates present in the lime-stone in the form of dolomiteCaCO,*MgCO,, while smalleramounts coming from clay and shale(Lea, 1971), ordiopside(Fundal, 1980).

If present in small quantities, mag-nesium improves the burnability ofclinker (Christensen, 1978). Accord-ing to Long (1983), the behavior ofMgO in clinker formation primarilydepends upon the cooling rate. Whenclinker is burnt at high temperature(>15Cr0°C) and rapidly cooled, it re-tains the bulk of the MgO mostly inaluminate and ferrite phases, with alesser amount in alite. Under condi-tions of slow cooling, ody 1..57. ofMgO is retained in solid solution andthe rest is crystallized as large periclasecrystals. MgO in cement is usuallylimited to under 5’Yo,because MgOcontent in excess of 2?40can occur aspericlase (Taylor, 1990), The presenceof larger crystals of periclase in ce-ment slowly reacts with water to formexpansive Mg(OH)z and can lead todestructive expansion of concrete.ASTM C150 specifications allow MgOcontents up to 6% in portland cements.

Magnesium salt solutions (sulfateand chloride) are aggressive towardsconcrete and react with the calciumhydroxide phase to form basic salts.The reactions are expansive and maylead to deterioration of concrete.

Calcium

The role of calcium (Ca) in cementmanufacturing has alread ybeen dealtwith in the section of major elements.

Strontium

A major portion of strontium (Sr)found in clinker as SrO comes fromlimestone and aragonite.

Strontium as SrO, frequently oc-curs in clinkers. The mean valuequoted by Moir and Glasser (1992) inTable 7 is O.09%. Brisi et al, (1965) andGilioli et al. (1972, 1973), demonstratedthat small amounts of S@ favor aliteformation, but at 4-5y0 addition, Srpreferentially distributes in beliterather than alite, Sr in belite inhibitsalite formation. Phase equilibriumstudies indicate that Sr in raw feedalso favors free lime formation, withSrO preferably going into solid solu-tion and displacing CaO from othercompounds, The tendency of freeCaO release during clinkering makesSrCOq more labile than SrSO~, and theclinkers having a high lime saturationfactor (LSF) maybe more vulnerableto free lime expansion during hydra-tion.

Butt et al, (1968) reported that thehydraulicity and strengths developedby Sr-doped alites are significantlylower than the normal alites. Thismay be attributed to the smaller sizesof the lattice voids in strontium-in-corporated alite.

Kantro (1975) reported a slightset acceleration effect withS~lz~ 6HZ0used as an admixture in CaS paste.

Barium

Barium (Ba) occurs in varyingamounts in limestones, mostly as bar-ite (BaSOd). It can also occur in clayeysediments in appreciable amounts.The average amount of barium in ce-ment is 280 mg/kg. The average forCKD is 172 mg/kg (PCA, 1992).

11

Page 18: Role of Minor Elements in Cement Manuf and Use

Role of Minor Elements in Cement Manufacture and Use

Timashev et al. (1974) reported adecrease in clinkerization temperaturefrom 1450 to 1400”C and increase in theclinker production rate from 8.2 to 9tonnes/hr, when using raw mixes con-taininghigheramounts of barium. Theyalso noted an improvement in the min-eralogical composition of the resultingclinker. However, Kurdowski (1974)reported only a marginal usefulness ofBaO when added in small amounts,stating that it did not significantly af-fect either the properties of the liquidphase or the rate of lime assimilation;Ba replaced Ca in all the clinker phases,except for the ferrite phase. The opti-mum BaO concentration was between0.3 to 0.57., preferably for clinker con-taining less flux (silica modulus >30)and high CIS levels.

According to a number of studies,Ba also appears to be an effective activa-tor of hydraulicity and strength. Thestrength obtained from Ba incorporatedclinkers is 1O-2O’7Ohigher than that ofregular clinker of all ages tested underidentical conditions (Kurdowski, 1974;Butt et al., 1968; Kurdowski et al,, 1968;Kruvchenko, 1970; Peukert, 1974).

Barium can be present in used oils.Excessive amounts in raw mix can in-crease the free lime content of clinkerdue to CaO displacement and can causeexpansion in concrete under certain cir-cumstances. It can also lead to pasteshrinkage.

ELEMENTS IN GROUP Ill(Boron, Aluminum, Gallium, Iridium,Thallium)

Boron

Boron (B) is generally found in traces (3ppm) in most cement raw materials,particularly those containing iron ore.

Fromearlystudiesby Mircea (1965),it appears that BzO~reacts with CJS toform CZS, C~BS*, and free lime. Uponfurther addition of BzO~,C~Scompletelydisappears. Timashev (1980) establisheda relationship between the electronega-tivity of boron and the melt viscosity,

0CaZn VBe NiKCr AsPb S

957

Cd Cl TI

Figure 5. Relative volatilities of elements in clinker burning in acyclone preheater kiln (Sprung, 1988).‘Restive volatility as a percentage of ratio between the totalexternal and internal balance for a given element.

and noted a similarity between be-rates, phosphates, and sulfates. Boroninhibited the formation of C$ and af-fected the stability of the other majorclinker phases. In the presence of bo-ron C$ is decomposed to a stabilizedC2S as follows:

C,S ~ C2S + Cao

It was also pointed out that althoughB20q may not be a useful addition forregular alite clinker required for earlystrength development, it might be use-ful as a mineralizer for clinkers rich inbelite. Gartner (1980) has reported onthe effectiveness of BzO~ to stabilize/1-C2Sand to improve its hydraulicity.According to Miller (1976), boron canalso stabilize ~-CzSin alumina andiron-poor systems.

However, Miller (1976) has cau-tioned that the indiscriminate addi-tion of boron can produce unpredict-able hydration results. Gartner (1980)explained that this behavior of boronis probably sensitive to the presence ofother trace elements. Bozhenov et al.(1962) reported that even small addi-tions of BzO~ (-0.040/.), as an admix-ture, to cements can have adverse ef-

fects on setting properties. These ob-servations indicate that B20~is a strongretarder of cement hydration.

Aluminum

Role of aluminum (Al) in cementmanufacturing has been dealt with inthe section of major elements.

Gallium, Iridium, andThallium

Gallium (Ga), iridium (In), and thal-lium (Tl) are found only in traces inraw material; their typical concentra-tions in coal are 5-10 ppm, 0.07 ppm,and 1.1 ppm respectively. Thalliumand gallium are also found sometimesin the coal fly ashes. Thallium mayalso be found in some pyritic mineralsused as an iron source for raw feed.The average concentration of thalliumin cement is 1.08 mg/kg, ranging fromnondetectable to 2.68 mg/kg. The av-erage concentration of thallium inCKD is 43.24 mg/kg (PCA, 1992).

* B is B103in C5BS

12

Page 19: Role of Minor Elements in Cement Manuf and Use

PCA Research and Development Bulletin RD209T

Although thallium occurs in tracesin the raw feed, it is the most volatileelement* after mercury in the kiln (melt-ing point=30~C), and is most likely toconcentrate in the kiln dust. The volatil-ity of T1relative to other elements in thekiln is shown in Figure 5 (Sprung et al.,1984). Sprung et al. determined thevolatility on the basis of the differencebetween the external and internal bal-ances of individual elements during theclinker burning in a cyclone preheaterkiln. Iridium is also volatile and largelyends up in the kiln dust. Since thalliummay concentrate in the fly ash from thecoal firing power plants, in the cementkiln operation it tends to build up inextremely large internal cycles if no dustis discarded.

ELEMENTS IN GROUP IV(Carbon, Silicon, Germanium,Tin, Lead)

Carbon

Carbon (C) is a major component of fuel,It is also present as carbonate in thelimestone. A significant amount of car-bon can also present in flyashas unburntcoal.

Carbon as C02 is extensively presentin cement kiln systems, but is not presentin any significant levels in clinker. Be-

cause of the limestone and fuel that areused in the kiln, the gases emitted fromthe kiln system are constituted mainlyof COz,~O, and N2. Limestone (CaCO~)decomposes to CaO and C02 at about9000C. Roughly for every ton of clinker,one ton of COZ is generated in the kiln,which essentially is released throughstack emissions.

Silicon

Role of silicon (Si) in cement manufac-turing has already been discussed in thesection on major elements.

Germanium

Germanium (Ge) is a trace elementfound in raw material and coal.

Germanium oxide (GeOz), is notvolatile (Gartner, 1980), and is likelyto concentrate in clinker. When presentin larger amounts, GeOz can formC~G**, tricalcium germanate withCaCO~ at 1500”C and isstablebetween1335”C-1880”C. At temperatures be-low 1335°C, C,G decomposes to CZGand free lime (Hahn et al., 1970;Boikova et al., 1974). These forms ofcalcium germinates are similar to C~Sand CZSrespectively. COGis hydrau-lic and produces calcium germanatehydrate (C-G-H) and calcium hydrox-ide (CH) with water, whereas ~G isassumed to be non-hydraulic. Ac-cording to Gartner (1980), it is un-likely that the trace amounts of Gewould seriously affect the formationof clinker and the properties of theresulting cement.

Tin

Tin (Sri) is a trace element in both theraw feed and fuel.

Tin is reasonably nonvolatile(boiling point=2265°C). Tin oxide(SnO) or natural cassiterite melts at1630”C and sublimes between 1800and 1900°C. It is very likely that tinwill stay in the clinker. The presenceof trace amounts of tin in clinkershould not affect cement properties,although not much is known aboutthe effect of tin in clinker manufac-ture.

Lead

Lead (Pb) can be present in traceamounts in raw material mainly inclay and shale. It would be present atappreciable levels in coals, used oils,lubricating oils, and scrap tires. In flyash, lead tends to concentrate in thefine fractions (Coles, 1979), Lead lev-els in coal, used oil, and petroleumcoke are shown in Table 6. Anothersource of lead could also be the leadshot from shot gun shells used toshoot out rings.

The effect of lead in cementmanufacturing and properties has

been studied in some detail, Leadcompounds are fairly volatile. Theytend to vaporize in the kiln, and exitthe kiln as fines and are collected inthe kiln dust.

There is also evidence that de-spite the partitioning of lead into theCKD, some lead can still be retainedin the clinker (Davison et al. (1974),and Berry et al. (1975)). However, Pbhas been shown to have no adverseeffect on cement properties if presentbelow 70 ppm. The effect of leadlevels higher than that in clinker isuncertain (Sprung et al., 1978). Ac-cording to a recent PCA study (PCA1992) the average lead levels in theCKDS and cements produced inNorth America are 434 ppm and 12ppm respectively.

Some research on the effect oflead compound additions on hydrat-ing cement properties has recentlybeen studied, where Bhattyand West(1992) have noted that additions ei-ther as a soluble compound (PbNO~:7,300 ppm level ) or insoluble oxide(PbO:38,000ppm level) substantiallyretards the hydration of pastes, butenhances the workability, The retar-dation effects are more pronouncedwith oxides. The initial setting time isincreased with a consequent loss inearly strength, but the 28- and 90-daystrengths are comparable to or higherthan those of the control.

ELEMENTS IN GROUP V(Nitrogen, Phosphorus, Arsenic,Antimony, Bismuth)

Nitrogen

Nitrogen (N) can be present up to0.01’% by weight in the raw materials,but in coal and other fuels nitrogencan be as high as 1-2Y0, often ashetrocyclic nitrogen compounds.

Clinker made under reducingconditions tend to have up to 0.057. N

* Nonvolatile elements are often calledrefractory elements.

““ G= GeO,

13

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Role of Minor Elements in Cement Manufacture and Use

as nitrides. Under normal oxidizingconditions, nitrogen in clinker ispresent only at a few ppm.

High concentration of nitrogen,higher residence temperatures, par-tial pressure in the flame zone, andthe subsequent oxidation of nitrogenleads to the formation of several ox-ides of nitrogen (NO and NOZ andNZO1) in the kiln emissions collec-tively known as NOX. Total NOX re-sults from fuel nitrogen NO, thermalNO, and prompt NO. In the cementmanufacturing, fuel nitrogen NO andthermal NO play a significant role.The prompt NO which is formed bythe participation of CH in the oxida-tion of nitrogen in air, plays a lesssignificant role (Bretrup, 1991).

The quantity of thermal NOformed is closely related to the burn-ing zone temperature (BZT). Accord-ing to Lowes et. al (1989), a reductionin BZT from 15000C to 1300”C canreduce the NO, levelsby200-400 ppm.Nitrogen in coal orotherfuels,presentat about the 1-2% level, is consideredsignificant in producing NO emis-sions from cement plants. However,it is not known to the degree in whichthe nitrogen in the kiln raw feed alsocontributes to NO, emissions (Gartner,1980). In precalciners, fuel nitrogenmay play a role, but in the burningzone the temperature is so high thatthermal NO is virtually in equilib-rium.

Phosphorus

Phosphorus (P) as phosphates ispresent in limestone and shale (Moiret al. 1992); they are also present insandstones, sands, and in detritalclays(Bucchi, 1980). Phosphorus also oc-curs in the blast furnace slags, electricfurnace slags, convectorslags, and flyash which are often used as substituteraw feed for cement manufacturing.Phosphate is found in sewage sludgewhich is a potential partial kiln fuel.

Cement clinkers contain typicallyaround 0.2% PzO~(Lea, 1971). A highPzO~concentration decomposes C~S

to CZS and excess lime. If PZ05 ispresent in excess of 2..57. by weight,the formation of free lime occurs(Nurse, 1952). However, by correctproportioning and proper burning,sound clinker can be produced, butcement hardening becomes slower.Matkovich et al. (1986) reportedhigher hydraulic actively for (x’CzSstabilized by PZ05 than for the &CzS.

Odler et al. (1980-1) reportedthe addition of hydroxyapatiteCa~(PO1)~OOHleads to an increasedformation of free lime at 1300”C,being directly proportional to thePzO~content. This was attributed tothe preferential stabilization of CZSsolid solution and formation of freelime at increasing P205 additions.However, Halicz et al. (1983) dem-onstrated that a satisfactory C~Sphase in clinker was formed by add-ing PzO~in the raw feed and main-taining lime salmation factor (LSF)and silica ratio (SR) at 1.0 and 2.75respectively.

In a CaO-CzS-C~P* system at1500°C, raw mix with more than afew percent P,O, does not yield C,S.However, in the presence of fluo-rine, the tolerance to PzO~is some-what improved. It is very likely thatthe thermodynamics of the systemfavor the fluoride-aluminum-CISsolid solution rather than P-C$ solidsolution (Gurevich et al., 1977) andapparently form a fluoroapatitephase (10Ca0.3Pz05*CaFz) which isdissolved in C,’S. Gartner (1980)suggested that chlorides mayalso help stabilize PzO~ in C~S byforming a stable chloroapatite(10CaO*3P,0,*CaC12) which alsoforms a stable solid solution withfluoroapatite.

Coleman (1992) reported thatan appropriate level of PzO~in clin-ker reduces the negative effects ofalkali on the strength properties ofcements. He reported that in ce-ment clinkers with “normal” NazOcontents of 0.8Y0, the maximum 28-day strength was achieved at 1.07.PZ05 level.

Arsenic

Arsenic (As) bearing mineral arseno-lite or claudite AszO~ (or AslOG), oc-curs only in small amounts in coaland used oils, and are unlikely toinfluence cement manufacturing inany way. Smith et al. (1979) haveindicated that in coal-fired powerplants, As tends to concentrate in thefly ash, but its concentration level, asdetected by the XRF method, is ex-tremely low. It tends to concentratein the fine fractions of fly ash wherethe levels can go up to 70 ppm.Weisweiler et al. (1989) has reportedup to 5 ppm of As in raw material andonly 0.6 ppm in petroleum coke. Ar-senic levels found in various materi-als are shown in Tables 4-6. The aver-age concentration of As in cementand CKD is 19 mg/kg and 18 mg/kgrespectively (PCA, 1992).

Although AszO~is volatile (sub-limes at 1930C) and should be ex-pected to condense on kiln dust par-ticles, Weisweiler et al. (1989) ob-served that a substantial amount ofAs is incorporated in the clinkers,and only a negligible portion of Asends up in the dust. The cause of Asentering into clinker was attributedto the excess CaO, oxidizing condi-tions in the kiln, and high kiln tem-perature. Under oxidation condi-tions, As is primarily oxidized toAszO~and forms a series of low vola-tile calcium arsenates, among whichCa,(AsO,), is more stable at 13000C.Czamarska (1966) found that 0.157.AS+5significantly decreased the rateof C~S formation at 1450”C.

As a metalloid occurring in dif-ferent oxidation states, arsenic canhave complex effects on the hydrationproperties of cement (Conners, 1990).Tashiroet al. (1977) reported that AszO~only slightly retards the paste hydra-tion when added up to 5’Yo. It wasfound that the As leaching rate fromhardend cement mortars using eitherordinaray water or sea water, althoughmeasurable, was very low.

* P=P20,

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PCA Research and Development Bulletin RD109T

Antimony

Antimony (Sb) occurs as traces incement raw materials. It has beenreported to occur at 0.08 ppm in theraw feed and 0.0429 ppm in petro-leum coke (Weisweiler et al., 1989),Sprunge (1985) has quoted 1.19ppmSb in coal. According to measure-ments in BIF certification of compli-ance (C.O. C.) and other authors, theSb levels in raw materials are higher.

Like arsenic, a considerable por-tion of antimony is incorporated inclinker in the form of low volatilecalcium antimonates under oxidiz-ing kiln conditions at high tempera-tures (Weisweiler et al., 1989),The mechanics of stable calciumantimonate is more likely the same asfor arsenate formation. The oxides,SbzOj, natural seranmontite, andvalentinite, are not very volatile atkiln temperatures; they sublime at1550”C. Although usually not de-tected in cement and CKD, Sb levelsas high as 4.0 and 3.4 mg/kg havebeen reported for cement and CKD,respectively (PCA, 1992).

Bismuth

Bismuth (Bi) occurs as a trace elementin the raw feed and fuel. The stableoxide BizOqis not volatile at clinker-ing temperature (boiling point=186WC). Little is available on theinfluence of Bi in cement manufac-turing and cement hydration, but,owing to trace concentration, it isconceivable that the effects will bepractically insignificant.

ELEMENTS IN GROUP VI(Oxygen, Sulfur, Selenium,

Tellurium)

Oxygen

The role of oxygen (0) per se on themanufacture and use of cement hasnot been studied. Nonetheless a con-siderable portion of raw material andclinker phases incorporate oxygen

Possible carry-throughof complex calciumsulfides in clinker

S-2 present as organicand inorganic forms infuel, etc

ReducedS Species

S02 prominent Molten sulfatesin vapor pressure

Sulfites, SO; in solids Sulfate solidswhich become S03vaporsincreasingly unstablewith rising temperature

IntermediateS Species Oxidized S Species

Increasing Oxygen Pressure ~

Figure 6. Formation of different sulfur species in cement clinkering(C~oi and Glasser, 1988).

in one form or the other. Raw mate-rial is primarily composed of CaCO~(-75%),Si0, (-20%), and A1,O, (-2%).CaCO~ in the raw mix is derived fromlimestone; SiOz and AlzOqfrom clays,shales, sandstones, and bauxite, andFezO~from iron oxides andiron ores.

The clinker is formed by heatinga powdered raw material of an ap-propriate proportion to 1400-1550”Cin a kiln having a z-s~. oxygen level.As stated previously, the final fourphases in clinker are in the fully oxi-dized forms. They are: tricalciumsilicate 3CaO”SiOz, known as alite;dicalcium silicate 2Ca”SiOz, knownas belite; tricalcium aluminate3CaO”A110q, known as aluminate,and tetracalcium aluminoferrite,4CaO”A120~”FezO~,known as ferrite.

The importance of oxygen levelsis also related to the effect on theenvironment of the kiln and the kindof reactions that are favored. Thus,the presence of oxydizing or reduc-ing atmosphere greatly influence thereaction into which the various ele-ments will enter. Clinker made un-der oxidizing conditions tends to in-corporate trace metals of higher oxi-dation states than clinker preparedunder reducing conditions. Ex-amples of chromium and sulfur canbe cited here. Cr+s would tend toform under oxidizing conditions, in-stead of Cr+3, which results under

reducing conditions. Cr has also beenreported to occur as CrA, Cr~s, andCr+5(Johansen, 1972), but eventuallythey disproportionate to more stableCr+3or Cr+swhen mixed with water.

Alkali sulfates formed in the kilnare preferably decomposed under re-ducing conditions. Kilns havingstrongly oxidizing conditions and lowburning zone temperature tend toretain more sulfur in clinker thanthose produced under reducing con-ditions and for high burning zonetemperature. Thus, the oxidation orreducing conditions in the kiln canlead to significant phase modifica-tions in clinker.

Clinker produced under reduc-ing conditions are brownish as com-pared to darker gray clinkers madeunder oxidation conditions, mostprobably because of the oxidationstate of iron. Burning conditions ma yalso have an effect on the crystallinityof major phases. The effects can bepronounced if trace metals are alsopresent.

Sulfur

SUIfur (S) is frequently present in coalsand some fuel oils; sulfates and sul-fides are also often present in thelimestones. Clayey sediments, marls,also contain both sulfides and sul-fates. Lecher et al. (1972) have re-

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Role of Minor Elements in Cement Manufacture and Use

ported occasional use of gypsum andanhydrite as mineralizers and modifi-ers of the alkali cycle in the kiln.

Sulfides and sulfur from raw mate-rials and fuel are oxidized and are in-corporated into the solid phases as sul-fates in the clinker, though some sulfuras SOZ will almost always escape withthe exiting gases.

Sulfur forms volatile compoundsand its behavior in a kiln is a complexone. Depending upon the burning con-ditions in the kiln, both oxidized andreduced species may occur in solid,molten and vapor phases, as explainedby Choi et al. (1988) in Figure 6. Underoxidizing conditions at high tempera-ture, the formation of SOzis most likely.In the presence of lime, S02 is partlyremoved to form CaSO1 by the follow-ing mechanism:

S02 + CaO ~ CaSO,CaSOz + l/20z ~ CaSO1

In the presence of alkali, alkali sulfatesare formed which are later condensed atthe lower temperature regions. These

condensates, from liquids and solids,contribute to build up problems invarious kiln systems. Intermediatecompounds such as “sulfospurrite”,2C2SOC~,and the ternary compound“sulfoaluminate” C1@ also condenseat lower temperatures.

Another well known problem ofsulfur being volatile is its cycle ofvaporization and condensation withalkalies. They are volatilized at hightemperatures and subsequently con-dense on the relatively cooler incom-ing raw feed resulting in high sulfurand alkali levels in the middle zoneof kiln, especially with preheater.The use of an alkali by-pass is ofteneffective to break this cycle and leadto the reduction of sulfur and alkaliesin the incoming kiln feed. However,alkali sulfate levels are significantlyincreased in the by-pass dust, whichis captured by the dust-collector andgenerally discarded.

Sulfates preferably combinewith alkalies to give alkali sulfatesin clinker as (K, Na)#O1, known asaphthitalite, or K2S01 known as

arcanite. If sulfate is ptesent in ex-cess, the balance between alkali isachieved by forming calcium lang-beinite, Caz~(SO,)Y which is stableup to 10110C in a CaW1-KzWi sys-tem. However, this phase is knownto evaporate inconWuently at hightemperatures, and vaporizes K and S(Arceo et al., 1990).

Major alkali salts formed withsulfates and their approximate melt-ing temperatures according toGartner et al. (1987) and Skalny andKlemm(1981) are shown in Table 12.

Strungeet al. (1985) reported thatincreasing sulfate contents distinctlydecreases alite, increases belite; thealuminates and ferrite contents areunchanged in clinkers irrespective oftheir silica modulus (SM) values. Onthe other hand with increasing SM,irrespective of the sulfate, the alitecontents are higher, belite are un-changed, and aluminates and ferriteare somewhat lower. Relationshipsbetween clinker phases and sulfatecontent in the clinker are shown inFigure 7. With increasing sulfate

Table 12. Major Alkali Sulfates Formed During Clinkering and their Approximate Melting Temperatures(Adopted from Skalny and Klemm, ~981; and Gartner et aL~1987)

Alkali Compounds Chemical Formulae Melting Temperature ‘C

Potassium Sulfate (arcanite) K,SO, 1074

Sodium Sulfate (thenardite) NapSO, 884

Calcium Sulfate (anhydrite) CaSO, 1450

(Decomposes to CaO + S03and 02at about 1200”C)

Sodium Potassium Sulfate (aphthitalite) K, S0,”Na2S0,

or 968

(K, Na)2S0,

Calcium Potassium Sulfate (calcium Iangbeinite) 2CaS0,+K2S0,

or 1o11

Ca,K2(SO&

Calcium Potassium Sulfate (syngenite) K2SO~CaSO;H20

or 1004

Ca, K2(S0,)ZOHZ0

(Partial decomposition atlower temperature)

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PCA Research and Development Bulletin RD109T

contents, the alite crystals in clinkergrow larger, and the tendency ofbeliteinclusion in alite is progressively re-duced. The crystal size of aluminateand ferrite phases are also signifi-cant y reduced.

Gies et al. (1986, 1987) reportedthe development of a belite-rich ce-ment by using increased sulfate con-tents in alkali free raw materials; thisclinker showed reasonable hydraulicactivity which was attributed to thepresence of 0.6-0 .8% sulfate in belite.The rate of clinker cooling did nothave any significant effect on thestrength properties of resulting ce-ment pastes. To the contrary, Gartner(1980) suggested that sulfate in clin-ker is rather unreactive and does notnecessarily contribute to set controlor to the hardening of paste. So, evena high sulfate clinker may requireadditional sulfate, which generallycomes from gypsum interground withclinker to achieve adequate set con-trol. This, however, depends uponthe C~A content, and sulfate shouldnot exceed the maximum limit speci-fied by ASTM C150 without the sul-fate expansion test. It might be notedthat excessive sulfate in cement canlead to expansion problems in con-crete. Clinkers might also containcertain amounts of unreactive sulfate,which unfortunately can lead to otherproblems due to insufficient avail-able sulfate for reaction with the alu-minate phase.

Another related concern is thelevel of SOz in the kiln exhaust area.Very frequently, 15-40% of pyritic (sul-fide) sulfur in raw material is con-verted to SOZ in the emissions(Neilson, 1991).

It should be pointed out that inthe preheater system much of the SOZin the kiln is taken up by the incomingraw material. This reaction is alsoobserved in plants which use kilnexhaust to provide heat to the rawmilling system. Significant amountsof SOZmay still escape if its originalconcentration is high, or if reducingconditions are generated locally.

SM=l .6

Belite

d

Aluminate

Ferrite

I SM=2.4

Belite

/

I Ferrite

SM=3.2

Alite

/

Belite

Aluminate

Ferrite

0123 0123 0123

SOS Content, % mass

Figure 7. Different phases of clinker as a function of S03 content anddifferent values of silica modulus (Strunge et al., 1985). -

Selenium

Selenium (Se) could be associated withsulfur in coal, but only in traces. It isalso present in fly ash where it tends toconcentrate in the fine fractions (Coles,1979). Selenium is usually not detect-able in cement but is detected in CKD insmall amounts (PCA, 1992).

Selenium is volatile (boilingpoint=684°C) and expected to end upin kiln dust or in the emissions. Sele-nium could form less stable selenates(SeO,), which are unlikely to stay inclinker (Gartner, 1980). Since their con-centration is extremely low in the kilnfeed, it is very unlikely that they willhave any significant effect onthemanu-facture or properties of cement.

Tellurium

Like selenium, traces of tellurium (Te)are generally associated with sulfur incoal.

At optimum kiln temperature tel-lurium could be somewhat volatile de-pending upon the form in which it ispresent (amorphous form boiling

point= 990°C; rhombohedral formboiling point =1390°C). Gartner (1980)suggests that tellurium might form un-stable tellurates in clinkers and end upin the kiln dust or the emissions.

ELEMENTS IN GROUP WI(Fluorine, Chlorine, Bromine, lodine)

The halogens fluorine, chlorine, bro-mine, and iodine, are frequently foundin kiln raw feed and primary as well asalternative fuels, and therefore play animportant role in cement manufactur-ing. Some halides such as fluorides arealso frequently used as mineralizers inclinker production andinlow-tempera-ture manufacturing of belite-rich ce-ments. Mishulovich (1994) addresseshalides as catalysts for calcination. Con-centration of halogens found in rawmaterials and fuels is given in Tables 3,4 and 6.

Fluorine

Fluorine (F) is commonly present inlimestone, clay/ shale, and coal (Sprung

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Role of Minor Elements in Cement Manufacture and Use

et al., 1968, 1985) as a minor elementand plays an important role in cementmaking. In raw feed, fluorine couldbe up to 0.06%by weight (see Table 3),whereas in limestone and clay/shaleit can go upto 940 and 990 ppm respec-tively (Table 4).

Calcium fluoride (CaF2) isalsofre-quently added to raw meal as a miner-alizer and flux to lower the burningtemperature and accelerate the forma-tion of C,S (Klemm et al., 1976, 1979).Miller (1976) has, however, cautionednot to use fluoride beyond 0.2570 toavoid adverse effects on clinker be-havior by selectively incorporating itinto the aluminates or silicate phasesat certain burning temperatures. Atlower temperatures, fluoroaluminates(C1lA+CaF,) are formed, which are de-composed at high temperatures to CqAand fluorides. These fluorides are thenincorporated into silicates at highertemperatures to form often stablefluorosilicates but their excessiveamounts can cause decomposition ofalite.

Gartner (1980) also reported theformation of alkali fluorides as NaFand KF at higher alkali presence; thesefluorides being somewhat volatile(boiling points 1700° and 1500”C re-spectively) are expected to end up inthe fine kiln dust. However, Sprunget al. (1968) reported that between88’7. to 987. of fluorides are incorpo-rated in the clinker and only a smallfraction end up in the kiln dust, prob-ably as CaFz Fluoride emissions werereported low (0.009-1 .42 mg F/Nm3)depending not necessarily on the mag-nitude of fluoride balance but on theefficiency of the precipitators.

Akstinat et al. (1988), reportedthat fluorides have no adverse effectson the cement production process,and the fluoride cycle does not causeany operational problems like coat-ing, because of their presence in smallamounts. However, recent experi-ences have shown that use of fluoridebased compounds can occasionallycause plugging. Gartner (1980) re-ported that the presence of fluorides

600

3oo-

0

40

{r ~3-day

1

20–

0 I I I

0 0.5 1.0 1.5 2.0

Fluoride (Yo mass)

Figure 8. Effect of fluoride on strength and setting time of high alitecements (Moir, 1983).

beyond ()..5~o can cause both opera-tional and quality control problems,which, under certain situations, can becontrolled by PzO~addition. Goswamiet al. (1991), Bolio-Arceo et al. (1990),and Gilioli et al. (1979), have reportedthe formation of spurrite (2Cz9CaCO~),and fluor-ellestadite that cause kilndeposits, but the resulting low burn-ing temperatures control the alkalicycle and reduce the alkali-sulfate de-posits.

Palomo et al. (1985) suggested that0.2?4. fluoride promotes low tempera-ture formation of aluminates such asfluorinated CIZA,, C,A, and CZAS(gehlenite); however, the final alumi-nate mineralogy was not significantlyaffected, as both ferrite and CqA werepresent at 1250°C and above. PerezMendez et al. (1986) reported that withthe addition of 0.5-1.50/. fluorides, as

CaFz, clinkering reactions were com-pleted in 0.5 hr at 13540C; the clinkershad much of C$ developed, withP-C,S, C,AF, and C,A also presenttherein. Imlach (1974) observed thatfluoraluminate CllAToCaFz, forms atfluorine levels of about 0.5% in clin-kers fired below 1320°C or slowlycooled from 1340”C to 12650C.Fluoroaluminate imparts rapid settingto cement pastes compared to the nor-mal cements.

According to Aldous (1983), andShame et al. (1987), the presence of Fand Al beyond the threshold level ren-ders C,S a rhombohedral symmetry,which is associated with improved hy-draulic properties. Moir (1983) dem-onstrated that by optimizing the levelsof F, alumina, alkalies, and sulfates,the C3S in clinker could be maximizedto enhance the setting properties of

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cement. Figure 8 shows the relation-ship between the fluoride addition andcompressive strength of cement pastesat various curing ages. An optimumfluoride addition for maximumstrength at early ages (24 hours) was0.27., for later strengths (7 days and 28days) addition of ().75Y0 were accept-able.

Chlorine

As mentioned above, chlorine (Cl) aschlorides is frequently found in lime-stone, clays and in some cases in boththe primary and secondary fuels. Inlimestone and clay the predominantchloride is sodium chloride (Akstinatet al., 1988). Some coals can contain upto 0.28°/oCl,mainly as rock salt (NaCl).

The formation of stable yet vola-tile alkali chlorides NaCl (boilingtemperature= 1413°C) and KC1 (sub-liming temperature= 1500°C) at clin-kering temperature is well known.Both the chlorides volatilize in theburning zone and condense in thecooler parts to form kiln rings orpreheater build-ups which impairplant performance. Bhatty (1985) alsoconcluded that agglomeration due tothe presence of molten alkali chlorideswas one of the major reasons for thebuild-ups. Cl also enhances the for-mation of spurrite and sulfospurrite(2C,S.CaSO,). In cases of plants with-out preheater, the volatile chloridesend up in the kiln dust. In preheaterkilns, up to 9%J’ochlorides are recap-tured by the incoming feed in the cal-cining zone (Ritzmann, 1971); the con-centration of chloride at that pointcould be extremely high (>lYo) com-pared to that of raw feed (-0.017.).Relative volatility of Cl, and other ele-ments in the kiln system is alreadyshown in Figure 5 (Sprung et al., 1984).

The wet processing plant and gratepreheater may tolerate raw feed withhigher chlorides, but the limits prima-rily depend upon the efficiency of dustcollecting and the level of kiln dustrecycling. With the advent of the al-kali by-pass, the chlorine cycle can be

broken at the most intense point ofkiln and the alkali chloride can beconveniently directed to the dust col-lectors. Otherwise, as reported byNorbom (1973), a total chloride intakeof 0.015% (in both raw material andfuel) can result in build-ups in apreheater without a by-pass.

Since most of the chlorides arevolatile, the amount retained in clin-ker is extremely small (d.03~0). VOla-

tile chlorides react readily with alka-lies, so that the alkali level in the clin-ker is often reduced when chloride ispresent. The combined influence ofalkali chloride on cement properties istherefore regarded as insignificant. Insome cases, calcium chloride is addedto the kiln for the express purpose ofincreasing alkali volatilization and re-moval, and result in the production ofa low alkali clinker. According toMishulovich (1994), the addition ofcalcium chloride and chlorine-con-tainingorganiccompounds at the clin-kering stage, accelerated both lime re-action and alkali volatilization. In apreheater klin, the addition of calciumchloride in the burning zone, resultedin 2070 increased production with cor-responding fuel saving.

In waste-derived fuels such aswaste-oils contaminated with chlo-rides, chlorinated hydrocarbons andscrap tires, the chlorides would occurindifferent compounds at much higherconcentrations (Akstinat et al., 1988),and cause serious operational prob-lems even in kilns equipped with by-pass. In order to make their use fea-sible, a larger portion of by-pass dustwould have to be discarded to preventbuilding up a large chloride cycle

High chlorides in the raw feedhave also been reported to form con-densation plumes in the emissionstacks in long wet or dry kilns whichare difficult to remove at times. Suchdetached plumes are generally the re-sult of NHAC1 formation. Excessivechlorides can also have a deleteriouseffect on kiln basic brick lining.

Chlorides, particularly CaClz, ac-celerate the hydration and hardening

of cement paste and increase the veryearly strength but, at the same time,chloride ions are also known to pro-mote corrosion of steel reinforcingbars in concrete.

AliniteCements: The developmentof less energy intensive “alinite ce-ments” from the CaClz incorporatedraw material has generated great in-terest (Nudelman, 1980). The for-mula ascribed to the alinite phase isclose to 21 CaO”6SiOz”A110q* CaClzwith some MgO inclusion (Lecher,1986). The burning temperature foralinite clinker is between 1000-11 OO”C.The raw mix is composed of 6-2370CaClz by weight. MgO is added tostabilize the alinite phase at 60-80?40,belite at l&30~o, calcium alumino-

chloride at 5-1OYO, and calciumaluminoferrite 2-107. (Bikbaou, 1980).Ftikos et al. (1991) reported that thestrength development of alinite ce-ment was comparable to that of regu-lar portland cement.

Bromine

With some exceptions, bromine (Br)plays a minor role in cement manu-facturing. Bromine occurs only as aminor element in raw materials, i.e.limestone (6 ppm), clay (10-58 ppm),and coal (7-1 lppm). (Akstinat et al.,1988) and Sprung et al. (1985). Bro-mine has also been detected at mea-surable levels in some of the fly ashesgenerated at coal operated powerplants.

Bromine is volatile and expectedto end up instackemissions (Akstinat,1988). Under oxidation conditions,bromine gas (Br2) would form andend up in emissions. Retention ofbromine in clinker is negligible. Al-kali bromides can also be found incement kiln dust. Between 5–10 ppmof bromine was reported in one CKDsample using fly ash as a partial rawfeed (Klemm 1995). At higher levelsof bromides, the formulation of bro-mine-alinites analogous to chlorine-alinites, as mentioned above, has alsobeen reported by Kurdowski et al.

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Role of Minor Elements in Cement Mmzufactureand Use

(1987, 1989). Bromine-alinites aremuch more reactive than the alites

(I@rdowski et al, (1989).Kantro (1975) reported that at

equivalent concentrations CaBrz is astronger accelerator for C~Spastes thanthe chlorides or iodides.

Iodine

The presence of iodine(I) in limestoneand clay is negligible. Up to 0,75 ppmin limestone, 2.2ppm in clay and shales

(Mantus et al.), and between 0.8 to

11.2 ppm is found in coal (Sprung

1985).

Because of the low levels of io-

dine in the feed, the effect on the burn-

ing process is negligible. Iodine saltsare volatile in nature and mostly endup in emissions. Conversion of io-

dine gas (IJ from iodides is easierthan bromides. Their concentrationin clinker is detected at very lowlevels. There is no literature report oniodine presence in the CKD. The con-centration of iodine in CKD is ex-pected to be extreamly low, maybe inthe ppb, because of its’ presence insmall amounts in the raw materials.

CaIz is reported to accelerate C~Spastes though not as effective as bro-mides or chlorides (Kantro, 1975).

ELEMENTS IN GROUP Vlll(Helium, Neon, Argon, Krypton,Xenon)

Helium (He), neon (Ne), argon (Ar),krypton (Kr), and xenon (Xc), beinginert gases, are not known to impartany noticeable effect on clinkermanufacturing or cement hydrationproperties.

TRANSITION ELEMENTS(Yttrium, Titanium, Zirconium,Vanadium, Niobium, Tantalum,Chromium, Molybdenum, Tungsten,Manganese, Cobalt, Nickel, Copper,Silver, Zinc, Cadmium, Mercury)

Ti

vCr

Mn

co

Ni

Cu

Zn

Aluminoferrite

I I I I I t

01234 5 0 0.5

Weight Y.

Belite

r

Aluminate

;oo15i

Figure 9. Distribution of transition elements in clinker phases(Hornain, 1971).

Table 13. Relative Ratios of Ti02 in Different Clinkers Phases,(After Different Workers)

Clinker Hornain Regourd KnofelPhases (1971) et. al. (1974) (1977)

Alite 1 1 1

Belite 2 1.7 2

Aluminate 0.8 3.3 3

Ferrite 6 10.8 7

TiOp in Clinker (wt.”A) 0.78 (not reprinted) 1.0

The elements 21-30,39-48, and 57-80in the periodic table are known as thetransition elements. Not all of theseelements have been studied in cementmanufacturing, but the ones that havebeen studied in some detail are dealtwith in this section. Some of thesetransition elements are introducedinto the clinkering process throughthe use of spent catalysts as an alu-mina source.

Yttrium

Isomorphismbetweenyttrium (Y) andcalcium frequently occurs in naturalmaterials; for instance fluoroapatite,Ca2Ca~(P01)F,can contain up to 10.6%YzO~(Povarennykh, 1966). But pre-sumably in cement raw materials,yttrium occurs only in traces.

Yttrium substitutes for Ca in bothC~Sand CZS(Boikova, 1986). It yields

both triclinic and monoclinic formsof C~S. In a CZS-Yg(SiOi)~system, theregion of homogeneity can exist upto 35% YA(SiOA)~by weight (Toropovet al., 1962-2).

Yttrium chloride is reported tohave an accelerating effect on CqSpaste when added as an admixture(Kantro, 1975).

Since yttrium is unlikely to vola-tilize at kiln temperature(meltingpoint= 1522°C), it can hardly be ex-pected to concentrate in the kiln dust.It should preferentially become in-corporated in clinker.

Titanium

Titanium (Ti) as oxide could bepresent in typical cement raw mate-rial at the ().()2-O.4~0level by weight(Bucchi, 1980). Gartner (1980) re-ported a higher concentration of O.1-

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1.0’?4.Ti02 in many raw mixes. Con-centrations of TiOz in some of theauxiliary raw materials is evenhigher. Blast-furnace slag for in-stance, can contain 1.!7~0TiOz, andthe bauxites may have between 2-8% TiOz by weight.

TiOzisarefractory material (boil-ing point= 2500-3000°C) and is es-sentially incorporated in clinker. Atlow levels the effects of Ti on themanufacturing of cement is insig-nificant (Miller, 1976), higher levelsof up to 2% may improve the com-pressive strength of clinker (Knofel,1979). Hornain (1971), and Marinhoet al. (1984), reported that TiOz ispreferentially distributed in ferritephase. Distribution of other selectedtransition elements indifferent clin-ker phases, as determined byHornain (1971), is also shown in Fig-ure 9. Relative ratios of TiOz distri-bution in clinker phases as reportedby different workers is also given inTable 13 for comparison. Titaniumfrom ilmenite (FeTiOJ additions tokiln feed has been used to produce apatented buff-colored cement.

Knofel (1977) observed a sharpreduction in alite with equal gain inthe belite phase when Ti02 was in-creased in the raw mix; the variationin ferrite and aluminate was not sig-nificant. Calcium titanate (CaTiOJis apparently the major phase presentin clinker. It was also reported thatabout 1’ZOTiOz addition in the rawmix reduces the melt temperatureby 5O-1OO”C,probably because of afavorable relationship between ionicpotentials and the melt viscosities asshown in Figure 10, This relation-ship was developed by Timashev(1980). It shows that increasing theionic potential of transition elementsin groups of elements with equiva-lent atomic radii decreases the clin-ker melt viscosity.

Although TiOz enhances theearly hydraulicity of alite (Kondo,1968), the clinkers have shown slowinitial setting. However, 1% TiOzclinker have roughly 207. higher

-600

- 400

- 200

-o

0.115 0.130 0.145 0.160

Viscosity, Ps sec

Figure 10. Relationship between viscosity and ionic potential toradius ratio, and cation-oxygen bond of transition elements at1450”C (Timachev, 1980).

3-and 90-day strengths (Knofel, 1977,1979).

Zirconium

Zirconium (Zr)isconcentrated mostlyin siliceous ores which can be used asa raw feed component (Miller, 1976).

Blaine (1965) reported about 0.5%zirconium, probably in the fully oxi-dized form of ZrOz, in US. clinkers.Kakali et al. (1990) found no signifi-cant change in the burning and cool-ing conditions for clinker preparedwith 0.73-1 .45% ZrzOJ; the principalphases, alite, belite, aluminate, andferrite, were satisfactorily crystal-lized. However, ZrzO~ changed thesize and shape of alite, while the typeof belite crystal was modified. Zr20~also imparted a noticeable colorchange in clinker (Kakali, 1988).

A significant retarding effectand a subsequent delay in strengthfor cements prepared with ZrO con-taining raw mixes was also reported(Kakali et al. , 1989). However, ear-lier studies by Blaine et al. (1966)indicated that smaller ZrO additions

increased the early compressivestrength of cement.

Vanadium

Vanadium (V) occurs at a measurablelevel in cement raw material (10-80ppm inlimestone,98-170 ppm in clay/shale, and 30-50ppm in coal) (Sprung,1985). It is also present in fly ashwhere it tends to concentrate in thefiner fractions (Coles, 1979). Fairlyhigh levels of vanadium are also re-ported in crude oils (Gartner, 1980).In one study, Weisweiler et al, (1990)has reported nearly 800 ppm vana-dium in petroleum coke used in ce-ment manufacturing. Ash from pe-troleum coke also contains very highlevels of VzO~ (up to 607.). Becausethe petroleum coke has a low overallash content, Moir et al. (1992) foundno more than 0.08% VzO~ in clinkerproduced in modern cement plantsthat use 50% petroleum coke as a sub-stitute fuel.

Use of vanadium is known to de-crease the melt viscosity primarily be-cause of its higher ionic potential as

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Role of Minor Elements in Cement Manufacture and Use

shown in Figure 10. Vanadium ispresent as VzO~in cement clinker. Itconcentrates in alite and forms largercrystals. However, according toHornain (1971), vanadium preferablyconcentrates in belite rather than alite,as shown in Figure 9. VzO~is unlikelyto vaporize at normal kiln tempera-tures. On the other hand, vanadiumpresent in fuel may not have adequatecontact with the reacting mass in thekiln and largely ends up in the kilndust as suggested by data fromWeisweiler et al. (1990).

Odler et al. (1980-1) reported thatl% V20~ can significantly reduce thefree lime in clinker when fired at1200°C. Xinji et al. (1986) used V20~ forstabilizing B-CZSin clinker apparentlyby substituting V01-3 for Si014.

A concentration of 1.57. V20~ isreported to increase hydraulicity ofalite; however, higher concentrationsadversely affect the grindability of re-sulting clinkers. High VzO~levels asfound in some crude oils could alsodeteriorate kiln lining in some cases(Gartner, 1980). V,O, in clinker canalso increase sulfate expansion undercertain circumstances (Blaine et al.,1966).

Niobium

Niobium (Nb) is another element to befound in traces in cement raw materi-als. Weisweiler et al. (1990) has re-ported more than 30 ppm niobium inthe raw feed of a German plant.

Because of the low level presencein the raw mix, niobium would havevery little effect either on the clinkerformatitm or on the cement hydrationproperties. Kakali et al. (1990) reporteda very feeble effect of Nb+5addition (upto 1.5% by weight) on the mineralogi-cal texture and the viscosity of clinkermelts because of its low ionic charge toatomic radius ratio.

Cementpastesprepared from theseclinkers did not show any noticeablechange in their setting or strength prop-erties when compared to regular ce-ment pastes (Kakali et al., 1989).

Table 14. Chromium Distribution in Typical Clinker* PhasesContaining 0.55YI0Cr,O, (Hornain, 1971 )

Phases Cr(%)

Belite 0,87

Ferrite 0.55

Alite 0.39

Aluminate 0.04

*The clinker contained C,S=76.3Y0,C,S=9. 1“A, C~A=5.3°/’,and C,AF=8°/.

Because niobium is a high tem-perature metal (melting point=24680C), it would unlikely concen-trate in the kiln dust or in the stackemissions.

Tantalum

Tantalum (Ta) is only a trace elementin cement raw material. It reported tobe present at less than 9 ppm in rawmaterial and 0.3 ppm in the oil cokeused as fuel in cement manufacturing(Weisweiler et al., 1990).

Since tantalum is present as tracein both the raw feed and fuel, it isunlikely to impart any noticeable ef-fect on the clinker formation and ce-ment use. Weisweiler et al. (1990)have reported 14.3 ppm and 3.3 ppmtantalum respectively in clinker andkiln dust prepared from a raw mate-rial containing 8.9 ppm tantalum.

Chromium

Chromium (Cr) can be present in rawfeed immeasurable quantities. Sprung(1985) has reported up to 16 ppm inlimestone, nearly 100 ppm in clay andshales. Coals and used oils may con-tain up to 80 ppm and 50 ppm Crrespectively. Some of the auxiliaryraw materials, such as bauxites, whichare used up to 4°/0 in cement manufac-turing, may contain between0.04-0.40/. CrzO~. In addition to that, aproportion of Crcanalsoentercementfrom the grinding media during rawmeal preparation and finished cementgrinding, and refractory linings.

The presence of Cr in raw materi-als is known to reduce the viscosity of

clinker melt due to its high ioniccharge as is shown in Figure 10. Miller(1976) has reported improved clin-ker burnability at 1°/0CrzO~addition.Chromium can exist in a number ofoxidation states in clinker, the moststable being Cr+3and Cr+b. Their for-mation is sensitive to the oxygen levelin kiln. High oxygen tends to formCr%compounds as chromates whichare readily soluble in water and mark-edly affect the hydration characteris-tics of the paste. Reducing condi-tions favor the formation of Cr+3com-pounds which are less soluble in mixwater.

Under oxidation conditions, Crcan also exist as Cr~ and Cr+5in C2S,which can then disproportionate tothe more stable Cr+3 and Cr% uponmixing with water (Feng Xiuji, 1988).Johansen (1972) has reported Cr”,Cr-b, and Cr+5 in alite substitutingfor Si+4.Hornain (1971) reported thatCr preferentially resides in belite fol-lowed by ferrite, alite, and alumi-nates, as shown in Table 14 (see alsoFigure 9), Although Cr+b can bepresent in both alite and belite, it isreported to be stabilizing the ~-CzSform (Hornain, 1971, and Kondo,1963). Subarao et al. (1987) devel-oped an active belite-rich cementfrom raw feed containing 4-5% CrzOJby weight. Imlach (1975) used O.11-I.qzy. Cr203 in the raw feed as a flux.The resulting cement exhibited im-proved 8- and 24-hour strengths, but28-day strengths always decreased.

A significant portion of Cr canalso enter the finished cement fromchrome-rich grinding media (Klemm,1994). It is reported that the level of

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PCA Research and Development Bulletin RD109T

Cr4in ground cement is almost doubledby the use of high-chromium alloy ballsduring grinding. A number of patentsreport the use of inorganic reductantsto control the Cr+Aleaching from ce-ment. Most of these patents are ofEuropean origin and use ferrous sul-fate heptahydrate, ammonium-ferroussulfate, and manganese sulfate duringintergrinding to convert Crk to Cr+3.

Chromium is known to acceleratethe hydration of paste and improve theearly strength, and has thus been usedto develop high strength cements. Re-cent studies (Bhatty et al., 1993) haveshown that 0.7570 addition of chromiumas chromium chloride and nitrate, ac-celerate paste hydration and result inhigh initial hydration peaks. The work-ability and the initial setting times arereduced, but the early strengths (3 days)are significant yimproved over the con-trol. The 28- and 90-day strengths are,however, close to those of the control.The addition of insoluble chromiumoxide (Cr20~), even up to 1.37., did notsignificantly affect the hydration or thestrength behavior of the pastes. Thedegree of Cr stabilization in cementmatrices as determined by leachabilityin both these cases was almost 100Yo.Chromium may also contribute to highsulfate expansion, increased 24-hourshrinkage, and reduced autoclave ex-pansions.

Although a major portion of chro-mium is incorporated in clinker, usu-ally tied up in belite, ferrite, or sulfatephases, chromium can be found in theCKD. Between 100-1000 ppm of Crhave been reported in CKD (Lee et al.,1973; Howes et al., 1975), although re-cent studies (PCA, 1992) have shownonly between <0.01-264 ppm in CKDSproduced by burning conventional fu-els, and between <0.01-299 ppm inCKDS produced by waste derived fu-els. Detectable levels of 20.6 mg/secand 12.5 mg/sec have also been foundin kiln emissions using conventional aswell as waste fuels respectively (Mantuset al., 1992). In U.S. cement, total chro-mium is reported to be between 20 and450 ppm.

Molybdenum

Molybdenum (Mo} is potentially animportant trace element in lubricat-ing oil (Gartner, 1980). In coal fly ash,MoOS can be as high as 1.5% byweight.

Up to 0.05?’o of Mo has been re-ported incliners (Blaine et al., 1965).Molybdenum, having small radiusand a high charge number, is an ef-fective reducer of the clinker meltviscosity as shown in Figure 10.Kakali et al. (1990) reported the for-mation of large round alite crystals inclinker prepared with up to 1.57.M003 addition, with some modifica-tions in belite. However, cementpastes prepared from these clinkersexhibited no adverse effects on theengineering properties (Kakali et al.,1989).

Tungsten

Tungsten (W) is trace metal in rawmix and is expected to appear in tracesin the clinker. Very little work hasbeen reported on the effect of tung-sten on clinker formation and use.

Kakali et al. (1990) noted that theaddition of up to 1.5?4.WO~in the rawmix changed the shape of alite crys-tals, making them bigger and moreroundish; the belite formed was oftype III and, to some extent, con-tained secondary dendritic crystalli-zation probably because of excessiveSi~ replacement by W%. Dissolutionof W% in the melt decreased the vis-cosity because of its large charge toradius ratio, as is also exhibited inFigure 10.

Ivashchenko (1991) reported thataddition of W% also improved thegranulometric composition of clin-ker and decreased dusting. Improvedhydraulicity was expected becauseof enhanced activity of ferrite andalite modification in the clinker. How-ever, cement pastes prepared fromthese clinkers did not show any sig-nificant change in the setting orstrength properties when comparedto theregularones (Kakaliet al., 1989).

Tungsten is a very high temp-erature melting metal (meltingpoint=3410°C). Since itwill not volatil-ize at kiln temperatures, its presence inthe CKD, or stack emissions, is exceed-ingly remote<

Manganese

Manganese (Mn) inclinkercomesfromboth the primary and auxiliary rawfeeds. Limestone can contain up to1.91’% Mnz03 as the carbonate mineralrhodochrosite, whereas shales andbauxite canhaveup to O.59% and O.37%by weight respectively (Bucchi, 1981).In blast furnace slags, M~O~ can bepresent up to 1.2% and in coal fly ashup to 1.447. by weight.

Cement produced from slags cancontain more than l% Mnz03 and usu-ally imparts a brown color to cement(Lea, 1971). The polymorphism of sili-cate in clinker is affected by the pres-ence of manganese oxides in the rawmaterial. Knofel et al. (1984) reportedthat the limit of MnzO~ substitution inCJS is approximately 2.2% at 1550°C.At lower concentrations, say -0.1’XOM~O~, single substitution of Si- byMn+4 takes place, whereas at 2.27.MnzO~concentration, a double substi-tution of Si4 by Mn4 and Ca+2by Mn+2is possible. The stabilized CaS poly-morph was identified as monoclinic;Gutt and Osborne (1969) reported it tobe triclinic. Miller (1976) demonstratedthat at low concentrations (<0.7%), Mnstabilizes monoclinic alite, but at highconcentration and in the presence offluoride, triagonal alite with markedlyhigh hydraulicity is formed.

Manganese can occur in a numberof oxidation states depending uponthe burning conditions in the kiln andcan impart different colors in clinkers,ranging from reddish-brown to blue.Puertas et al. (1988) have studied theinfluence of kiln atmosphere on Mnsolid solutions in C~S and C2S. It wasreported that under reducing condi-tions isomorphous replacement of Ca+2by Mn+2 occurs, while in air havinghigher oxygen level, MnA replaces Si~.

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Role of Minor Elements in Cement Manufacture and Use

According to Knofel et al. (1983)alite content of clinker increases withMn addition, with maximum alite at-tained at 0.57. MnOz and 1?4. Mn20~.High Mn content promotes the forma-tion of belite in the silicate phases, butis more preferentially incorporatedinto the ferrite phase through the for-mation of “alumino-manganite”, suchas “CAAMn” (see Figure 9). This re-duces C~A and marginally increasesfree lime, thus reducing the early corn-pressive strength of the pastes.

Manganese will not volatilizeat kiln temperature (boiling point=1960°C), and is unlikely to concentratein the CKD or be found in stack emis-sions.

Cobalt

Cobalt (Co) is present in traces in theraw mix; the maximum reported con-centration is 23 ppm COO. It has alsobeen found at much higher levels (upto 1.27~0) in some of the coal fly ashesthat could be used as partial cementraw feed (Bucchi, 1981).

The bulk of cobalt that is presentin the raw mix is incorporated in clin-ker. The CoO level reported in cementis <130 ppm, but the amounts detectedin the alite and belite phases are onlyin traces as the bulk of cobalt is concen-trated in the ferrite phase by replacingFe3+and forming the “C~ACo” phase(see Figure 9). Cobalt can also givecolor to cement.

Sychev et al. (1964) demonstratedthat Co somewhat reduces the hydrau-lic activity of alite and increases clinkerhardness. According to Miller (1976),cobalt increases the water demand andmarginally reduces the late strength ofcement paste.

Cobalt is unlikely to vaporize inthe kiln (boiling point= 287@C), thus,concentrations in CKD or in stack gasesare expected to be exceedingly small.

Nickel

Sprung (1985) has reported traces ofnickel (Ni) in limestone (1.5-7.5 ppm),clay or shale (61-71 ppm), coal (20-80

ppm), used oil (3-30 ppm), and petro-leum coke (208 ppm). In coal fly ashes,NiOispresentup to 1.9% (Bucchi, 1981).

Nickel preferentially concentratesin the ferrite phase, followed by alite,aluminate, and belite as shown in Fig-ure 9 (Hornain, 1971). Between 0.5 to1.07. nickel stabilizes alite (Rangaro,1977). NiO substitutes for CaO up to 4mole 70in alite and stabilizes the mono-clinic form (Enculeseu, 1974). This alitemodification apparently enhances thel-day and 5-year compressive strength.Miller (1976) reported that water solublenickel compounds act as acceleratorsand tend to give high early strengths.Kantro (1975) and Zamorani et al.(1989)) also found NiCl, to be an accel-erator for C~Spastes when used as mixsolution.

Mostly, Ni compounds are non-volatile, yet, owing to the volatile na-ture of some compounds, such asNiCO~, nickel could end up in the kilndust, although recent PCA studies hasshown a maximum of only 60 mg/kgNi in the CKD. The average amount ofNi in cement is 31 mg/kg (PCA, 1992).

Copper

Bucchi (1981) has quoted an average of16 ppm copper oxide (CUO) in the rawmixes, and a <0.13Y0 in coal fly ash,

On average, 90 ppm CUO occurs incommercial clinkers Bucchi (1981).Copper preferentially concentrates inthe ferrite phase followed by alite, alu-minate, and belite (see Figure 9,Hornain, 1971). Miller (1976) reportedthat under oxidizing conditions, thesmall amount of copper present asCuOstabilizes alite, whereas under reduc-ing conditions, copper as C~O ad-versely affects both the alite and belitephase formations. CUO can alsofunction as a flux, as it decreasesthe melt temperature considerably(Rumyanstev et al., 1968). Odler et al.(1980-1,2) found that 1% CUO additionwas effective in reducing free lime atmuch lower melt temperatures. It maybe mentioned that CUO accelerates C3Sformation whereas CUZOinhibits it.

Soluble copper salts are retardersand give low heat of hydration(Takahashi et al., 1973, Miller, 1976;Tashiro et al., 1977). The effect is morepronounced ontheC~Aphase (Tashiroet al., 1979). The addition of copperalso gives low sulfate expansion incertain cases (Miller, 1976).

Copper oxides are volatile atkiln temperature (melting pointsCUO=1326”C, CUZO=1235”C). As aresult, copper has been found up to500 ppm in some U.S. cement kilndusts (Howes et al., 1975).

Silver

Silver (Ag) is present only in traces(<0.250 ppm) in both the kiln rawmaterial and coal; in coal it may occuras silver sulfides ,or as a complex,

Since silver occurs in traces, it isnot expected to significantly contrib-ute in the clinkering process. Silver ispresent at 9.2 ppm in cement; it isreported in CKD at 6 ppm for kilnoperated with conventional fuels andat 2.5 ppm for kilns using waste fuels(PCA, 1992).

Zinc

Zinc (Zn) is a trace element in the rawmix, reporting 22-24 ppm in limestone,59-115 ppm in clay or shale, and16-220 ppm in coal. However, it canbe present up to 3,000 ppm in usedoil as a potential secondary fuel (seeTable 6), or 10,000 ppm in used tires.Its concentration is also reported to besignificant in alternative raw materi-als such ascertain metallurgical slags,basic oxygen furnace (B.O.F.) dust,and B.O.F. filter cake (Miller, 1976,1994).

Between 80-90% Zno in the rawmix typically becomes incorporatedin clinker (Sprung et al., 1978; Knofel,1978). Approximately half of the zincis distributed in silicates with prefer-ence for alite while reducing belite;the other half is distributed into thematrix with preference for the ferritephase (Knofel, 1978; Tsuboi1972). According to Hornain

et al.,(1971)

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PCA Research and Development Bulletin RDI09T

zinc in clinker is preferentially re-tained in ferrite followed by alite,aluminate, and belite (Figure 9). ZnOadditions accelerate the clinker for-mation. Alite and CZ(AF) formationsincrease at the expense of belite andC~A due to ZnO doping (Odler et al.,1980-3).

Stevula and Petrovic (1981) pre-pared a triclinic modification of C,Sof the type T1-TI1from mixtures of0.75-1.5% ZnO and pure C~S, fired atabout 1600”C and slowly cooled. Ad-ditions of 3.0 and 4.5y0 ZnO formedrhombohedral C~Swith no free ZnO.Boikova (1986) reported the changein C~S symmetry from triclinic tomonoclinic and to rhombohedral withincreasing ZnO additions.

Up to 1.0’% ZnO in the raw mixdecreases free lime considerably(Odler et al., 1980-1,2), retards thehydration, and reduces strengthwhenadded in excess of 1.0’%.(Odler et al.,1980-3). Similar observations werereported by Knofel (1978). Miller(1976) suggested the likelihood of re-ducingZninclinker by preferentiallyvaporizing it where the liquid phaseis low, thus reducing the potentiallydeleterious effects on cement setting.

ZnO as an admixture also im-parts a severe retarding effect on ce-ment hydration; early strength is re-duced,andthelate strengths (28-daysand beyond) are increased. In fact,zinc also increases the late strengths(5-10 years) but decreases the pasteshrinkage during the early ages of 1and 28 days (Miller, 1976). Arliguieet al. (1982,1985, 1990) demonstratedthat C~S, C~A, and cement hydrationare delayed by the formation of pri-mary zinc hydroxide and its conver-sion to a crystalline form around theanhydrous grains. Miller (1976) re-ported the formation of a complexcalcium hydroxo-zincate intermedi-ate compound that inhibits C$ hy-dration.

According to Sprunget al. (1978),the volatility of zinc for preheaterkiln could be 1O-2OYO.For a multi-stage preheater kiln, the capture of

ZnO would be more effective andcould result in the total incorporationinto the clinker. An average of 149ppm zinc has been reported in theCKD from the U.S. plants using con-ventional fuel and 150 ppm for thoseusing hazardous waste fuel (CRI, inMantus, 1992); thecorrespondingzinclevels in the plant emissions are only2.97 and 1.53 mg/see, respectively.

Cadmium

Cadmium (Cd) occurs in traces in theraw materials and fuels. The averageamount of Cd in cement has beenreported tobe0.34mg/kg(PCA, 1992).

Cadmium in the raw feed reactswith the constituent of kiln gas andcan form halides or sulfates, both arereadily vaporized at peak kiln tem-perature (Kirchner, 1985). The formof cadmium incorporated in clinker isnot known; however, with increasingchloride input in the kiln, the concen-tration of Cd in clinker is known todecrease. The addition of CdClz in theraw mix has the same effect. In acyclone preheater kiln, 74-88?4. of thetotal Cd entering the kiln is incorpo-rated in the clinker as opposed to 25-64% for that produced in the gratepreheater kilns; the remaining Cd iscaptured in the kiln dust (Weiswerleret al., 1987).

Cadmium is also volatile in na-ture, although not as volatile as thal-lium or chlorine. Volatility of cad-mium relative to other elements in thekiln feed is shown in Figure 5 (Sprunget al., 1984). CdO is reported to in-crease the burnability of the clinker bylowering the melt temperatures(Rumyanstev et al., 1968), wherebyCd+2 most likely enters the silicatephases (Ramankulov et al., 1964).Some improvement in burnability ofclinker with CdO addition was alsoobserved by Odler et al. (1980-1).

Recent studies (Bhattyet al., 1993)have shown that high CdOconcentra-tions retard the cement hydration, butthe strength properties are not af-fected. Addition of soluble cadmium

salts (CdC12) has no apparent effect oncement hydration. Cd is not leachedfrom the cement pastes when used asCdO and CdC12 admixtures.

Mercury

Mercury (Hg) is a trace element.It is highly volatile and vaporizes atmuch lower temperatures (boilingpoint=557°C).

Mercury is somewhat inert, andvery little is known on its interaction inthe clinker making process. It is verylikely that mercury and its compoundswould volatilize in the pre-calcinationregion at temperatures closer to 400”Cand escape with the stack gasses. Totalmercury is well below detection limitsfor most North American cements.

Recent studies (Bhatty et al., 1993)have shown that mercury compounds(bothinsolubleHgOand soluble HgC12)impart little effect on the paste hydra-tion and strength properties.

THE RARE EARTHS

Elements 51-71 are commonly knownas “the rare earths” or “lanthanides”.They are present only as traces in rawmaterials and cement clinkers. Owingto their presence at extremely low lev-els, they have not been a subject ofextensive studies in cement manufac-turing.

Since the rare earths have verysimi-lar properties to one another, it is as-sumed that they all will have some-what similar effects on the clinker for-mation.

Boikova et al. (1964, 1966, 1986)and Toropov et al. (1963) observed thesubstitution of rare earths for Ca inboth C$ and CZS. The solid solution ofC~S with oxyorthosilicates of lantha-num (La) and scandium (SC) resultsfrom the similarities in ionic size, andchemical properties between Ca, La,and SC. Formation of C$ solid solutionwith gadolinium (Gal), neodymium(Nd), and Erbium (Er) have also beenreported. Jantzen et al. (1979) reported

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!

Role of Minor Elements in Cement Manufacture and Use

that nearly 15’7. of Nd/SiaOlz can bedissolved into ~-C2S,which have iden-tical hydraulicity to that of regular ~-CZS. La stabilizes all modifications ofC~Ssolidsolutions (Stevula et al,, 1981;and Sinclair et al. 1984). Gd gives thetriclinic and monoclinic formulations,whereas SCproduces only the triclinicC# solid solutions. Leaching of Ndstabilized in cement pastes is also fairlylow.

Lanthanum also stabilizes thesolid solution of CZS by substitutingfor Ca+2 (Toropov et aL, 1962-1,-2).Based on the observations on the rareearths, La, Nd, Gd, and Sc, Boikova(1986) assumed thattheremaining rareearths, for having similar chemical andionic characteristics, would isomorph-ously substitute for Ca+2 in C~S andCZS. As a result, a larger distributionof rare earths in wastes could be ex-pected in the clinker silicate phases.

Rumyantsev et al. (1970) reportedthat the addition of LazO~in the rawmix accelerates the formation of clin-ker under laboratory conditions. Theengineering properties of the result-ing cements were also enhanced whencompared to control. LaCl~ acceler-ates the C$3 hydration when added asadmixture (Kantro, 1975).

The idea of studying rare earths incement manufacturing also stemmedfrom the possibility of using variousmedium to low level radioactivewastes that frequently contained sig-nificant amounts of rare earth ele-ments.

Studies by Jantzen et al. (1982),and Boikova (1986) indicated that 20-3070 loading of radioactive waste corn-posed of La20~, UOq, CeOz, and otheroxides, give optimum elemental re-tention in clinker at processing tem-peraturesof - 11OO”C-12OO”C.Volatil-ization and activation of radionuclidesoccured above 1200”C, whereas clin-keringat 1000”C produced incompletereaction.

Jantzenet al. (1979) developed clin-kers by incorporating 15-20% byweight of simulated radioactive wastesand firing at about 1200”C. A number

of wastes were designed to incorpo-rate varying combinations of Cs*, Cc*,Nd, Sr*; Lu*, Yb’, other Lanthanons;and Sr, Nd, La, Y*, and Ba silicates.The resulting clinkers were tested fortheir hydraulic reactivities. The clin-kers were slow to react, but the ulti-mate hydration products were prima-rily stable insoluble calcium silicateshydrates which had reasonable distri-bution of the radionuclides. Sichov(1968) reported that La,Nd, and Ce allenhanced the hydraulicity of alite.

Rare earths are expected to havelow volatilities (Klein et al., 1975) andare very unlikely to be found in thekiln dust or in stack emissions.

CONCLUSIONS

The effects of almost all the stable mi-nor and trace elements on the produc-tion and performance of portland ce-ment have been reported. Emphasishas been given to elements which oc-cur in natural and by product materi-als used for cement manufacturing.The elements for which detailed infor-mation has been obtained are dealtwith in an order based on the periodicclassification of elements. The vola-tilities of the elements have also beendiscussed where ever necessary. Ele-ments reviewed include hydrogen, so-dium, potassium, lithium, rubidium,cesium, barium, beryllium, strontium,magnesium, boron, gallium, iridium,thallium, carbon, germanium, tin,lead,nitrogen, phosphorus, arsenic, anti-mony, bismuth, oxygen, sulfur, sele-nium, tellurium, fluorine, chlorine,bromine, iodine, helium, neon, argon,krypton, xenon, yttrium, titanium, zir-conium, vanadium, niobium, tanta-lum, chromium, molybdenum, tung-sten, manganese, cobalt, nickel, cop-per, silver, zinc, cadmium, mercury,and the lanthanides.

The review indicates that al-though certain elements have beenstudied in detail for their role in theclinkering process and cement prop-erties, data on a number of elements is

available only to a limited extent, Al-though some progress has been madein understanding the role of these el-ements on clinker properties, interac-tion between their nature and themajor clinker components still needsto be properly understood

Use of trace elements as fluxes ormineralizers to enhance the clinker-ing process is also being realized, yet,understanding of the underlyingphysico-chemical mechanism and thepotential energy saving aspect re-quires additional input.

Now that the technological ad-vances in cement manufacturing arein place, efforts can be directed to-wards exploring the following aspectsof clinker-element interaction:

1: Make use of the minor elementspresent in raw materials andfuels to enhance the clinkeringprocess and the performance ofcement.

2: Make use of the minor elementsin conserving energy during clin-ker production; elements withproven fluxing/mineralizingcharacteristics could be primeexamples.

ACKNOWLEDGMENTS

This report (PCA R&D Serial No. 1990)was prepared by Construction Tech-nology Laboratories, Inc. (CTL) withthe sponsorship of the Portland Ce-ment Association (PCA Project IndexNo. 93-01). The author wishes to ac-knowledge the contributions of W.A.Klemm and F.M, Miller of CTL forcarefully reviewing the manuscript.The contents of the report reflect theviews of the author who is respon-sible for the facts and accuracy of thedata presented. The contents do notnecessarily reflect the views of thePortland Cement Association.

* Cs = Cesium,Ce =Cerium,Sr =StrontiumLu=Lutetium,Yb=Ytterbium,Y=Yttrium

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APPENDIX. A Summary of Possible Effects of Minor Elements on the Formation of Clinker and Propertiesof the Resulting Cements

Trace Elements Affects on Clinker Formation Affects on Cement Properties

Group I

Hydrogen not known not known

Lithium forms oxiide, lowers phase temperature reduces alkali-silica reactivity

(ASR) in concrete

Sodium lowers melt temperature, promotes internal cycle, enhances early strength, increases

causes phase separation, forms complex ASR susceptibility

chloride/sulfate compounds

Potassium lowers melt temperature, promotes internal cycle, enhances early strength, increases

causes phase separation, forms complex ASR susceptibility

chloride/sulfate compounds

Rubidium in traces, forms chlorides/sulfates n.a.’

Cesium in traces, forms chlorides/sulfates n.a.

Group II

Beryllium in traces no measurable effects

Magnesium improves burnability, goes into aluminate and cause magnesium expansion,

ferrite phases, forms periclase soluble salts are corrosive

Strontium small amount favors alite formation, large amounts lime expansion, low hydraulicity,

cause belite formation, also promotes free- Iow strength

lime formation

Barium reduces melt temperature, replaces Ca in all clinker activates hydraulicity, improves

phases except ferrite, also improves clinker strength

mineralogy

Group Ill

Boron decomposes C~S, stabilizes pCpS, promotes free- unpredictable hydration and

lime formation setting properties

Gallium in traces, volatile n.a,

Iridium in traces, volatile n.a.

Thallium in traces, highly volatile, goes into CKD, also forms n.a.

internal cycle;

Group IV

Carbon COZ in emissions n.a.

Germanium replaces Si in C~S to form tricalcium germanate C,G is hydraulic but C2G is not,

(C,G) that reduces to dicalcium germanate small amounts ineffective

(C2G) and free-lime

Tin stays in clinker, no effect if in traces no measurable effects

Lead volatile, goes to CKD but some stays in clinker, retards of hydration, but final

effects at higher levels uncertain strength reasonable

‘n.a.= information not available

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APPENDIX. A Summary of Possible Effects of Minor Elements on the Formation of Clinker and Propertiesof the Resulting Cements (Continued)

Trace Elements Affects on Clinker Formation Affects on Cement Properties

Group V

Nitrogen NOX emission n.a.’

Phosphorus decomposes C~S to C$ and free lime, reduces slows hardening

negative effects of alkalies

Arsenic volatile, goes to CKD, also incorporates in clinker retards hydration

as low-volatile calcium arsenates, reduces C~S

formation

Antimony incorporates in clinker as calcium antimonates n.a.

under oxidizing conditions and at high

temperatures

Bismuth n.a. n.a.

Group VI

Oxygen enhances incorporation of metals with high n.a.

oxidation states, modifies phases, formation,

results in darker clinkers (reducing condition

gives lighter clinkers)

Sulfur volatile, promotes formation of complex alkali aids set control, causes sulfate

sulfates, sulfur cycle, causes plug formation, expansion

gives SOZ emissions

Selenium in traces, volatile, goes to CKD or emissions, may n.a.

also form unstable tellurates

Tellurium in traces, volatile, goes to CKD or emissions, may n.a.

also form unstable tellurates

Group W

Fluorine lowers melt temperature, enhances C,S formation no adverse effect on hydration,

and alkali fluorides, excess levels cause and strength

operational problems

Chlorine volatile, promotes chlorine cycle, causes ring accelerator, corrosive to steel

formation, preheater build-up, can form enforcements in concrete

chlorine alinites

Bromine volatile, may form bromine alinites accelerator for C~S pastes

lodine in traces, volatile accelerator for C.$5 pastes

Group Vlll

Helium no known effect no known effect

Neon no known effect no known effect

Argon no known effect no known effect

Krypton no known effect no known effect

Xenon no known effect no known effect

‘n.a.= information not available

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APPENDIX. A Summary of Possible Effects of Minorof the Resulting Cements (Continued)

Trace Elements

TransitionElements

Yttrium

Titanium

Zirconium

Vanadium

Niobium

Chromium

Molybdenum

Tungsten

Manganese

Cobalt

Nickel

Copper

Silver

Zinc

Cadmium

Mercury

Lanthanides

Scandium

Lanthanum

Cesium

Neodymium

Uranium

Gadolinium

].a.= information not a

PCA Research and Development Bulletin RD109T

Elements on the Formation of Clinker and Properties

Affects on Clinker Formation

substitutes Ca in C~S and C2S

goes in ferrite, decomposes alite to belite, reduces

melt temperature, gives buff-color cement

modifies alite and belite crystals, imparts color

goes into alite, forms larger crystals, reduces melt

viscosity, free lime, effects grindability, lining

feeble effect

reduces melt viscosity, goes largely to belite,

improves grindability, imparts color

reduces melt viscosity, forms large roundish alite

crystals, modifies belite crystals

reduces melt viscosity, forms large roundish alite

crystals, forms type III belite crystals

goes to ferrite, can substitute both Si and Ca in C~:

imparts reddish brown to blue color

goes to ferrite, replaces Fe in ferrite, imparts color,

increases hardness

goes to ferrite, replaces Ca in alite and stabilizes

monoclinic form, volatile, reports in CKD

goes to ferrite, can adversely effect alite and belite

formation, lowers melt temperature, free-lime

in traces, no known effect

enters belite and alite, modifies alite crystals,

reduces free-lime, improves clinkering

forms volatile halides/sulfates, enters CKD, reduce:

melt temperature, improves burnability

somewhat inert, volatile, goes in stack gases

replaces Ca in C.$3 and C2S, forms solid solution

with C~S of triclinic nature

replaces Ca in CaS and C2S, forms solid solution

with C&, enhances clinkering

gets uniformly distributed in clinker, have verylittle volatilization

forms solid solutions with C~S and CZS, replaces

Cain C~S and C2S

gets uniformly distributed in clinker, shows little

volatilization

forms both triclinic and monoclinic phases with

C,S, replaces Ca in C,S and C,S

able

Affects on Cement Properties

accelerator

slows initial setting, improves

strength

retarder, low early strength

increases hydraulicity, causes

sulfate expansion

little effect

increases early strength, causes

sulfate expansion

no adverse effect

no significant effect

reduces early strength

increases water demand, reduces

hydraulicity and strength

enhances strength, soluble salts

function as accelerators

soluble salts as retardes, reduces

sulfate expansion

no known effect

oxide as admixture is retarder, low

early but high late strengths

oxide as admixture is retarder

little effect

no known effect

accelerates alite hydration

accelerates alite hydration

improves alite hydration, low

leaching

n,a. ”

n.a.

37

Page 44: Role of Minor Elements in Cement Manuf and Use

Role of Minor Elements in Cement Manufacture and Use

Index

AAlinite cements, 19

bromine alinite, 19,20chlorine alinite, 19

Alkalies (sodium and potassium), 8

alkali-cycle, 9alkali sulfates, 9, 16in clinker, 10in raw materials, 9

volatilization behavior, 9Aluminum, 2, 3, 12Antimony, 5, 7, 8, 15, 26, 35Aphthitalite, 9, 16Arcanite, 9, 16Argon, 20, 26, 36Arsenic, 5, 6, 7, 8, 13, 14, 26, 36

calcium arsenates, 14effect of burning conditions, 14effect on hydration, 14volatility, 12

ASR (alkali silica reaction), 8,11

BBarium, 5, 7, 8, 11, 12, 26, 35

effect on free lime, 12Beryllium, 5, 6, 7, 8, 11, 26, 35BIF (boiler and industrial furnace), 6, 8,

15Bismuth, 5, 13, 15, 26, 36Blast furnace slag (B,F. slag), 3, 4, 9,

14,21,23Boron, 5, 12, 26, 35

effect on free lime, 12Berates, 12

as mineralizers, 12effect on hydration, 12

Bromine, 5, 6, 7, 17, 19, 26, 36

bromine alinite, 19

cCadmium, 4, 5,6,7, 8,20,25, 26, 37

effect on cement setting/strength,25

effect on melt viscosity, 21in CKD, 25volatility, 12, 25

Calcium, 2, 3, 11Carbon, 2, 13,26, 35Cement kiln dust (CKD), 9, 13, 19, 22,

23, 24, 25Cerium (Cc), 4, 26

effect on alite hydration, 26Chlorine, 2, 5, 6, 7, 17, 19,25, 26, 35

chlorine alinite, 19chlorine build-ups, 18chlorine-cycle, 19sources, 19

Chromium, 4, 5, 6, 7,8, 15,20,21,22,23, 26, 37

burning conditions vs oxidationstates of chromium, 22

chromate, 22effect on hydration, 22, 23effect on melt viscosity, 21in clinker 20, 22, 23, 26stabilizer for l?-C2S, 22trivalent chromium (Cr+3) and

hexavalent chromium (cr+13),22Cobalt, 5, 19, 20,23, 26, 36

effect on hydration, 23effect on melt viscosity, 21in clinker, 20

Copper, 1, 5, 20, 21,24,26, 37as C$3 accelerator, 24CUO vs CU20 on alite stabilization,

24effect on free lime, 24effect on hydration, 24effect on melt viscosity, 21in clinker, 20

DDRE (destructions and removal

efficiency), 2

EErbium (Er), 25

FFluorine, 5, 6, 7, 14, 17, 18, 26, 36Fluorides, 17, 18

as mineralizers/fluxes, 17, 18C& accelerator, 18effect on hydration, 18emissions, 18

Fly ash, source of minor elements,3,4,5,9,11,12,13,14,17,19, 22,22,24

GGadolinium (Gal), 25,26Gallium, 5, 12, 26, 35Germanium, 5, 13,26, 35

calcium germanate, 13calcium germanate hydrate, 13effect on free lime, 13effect on hydration, 13

Group 1,5, 7, 35Group 11,5, 11, 35Group Ill, 5, 12, 35Group IV, 5, 13, 35Group V, 5, 13, 36Group Vl, 5, 15, 36

Group Vll, 5, 17, 36Group Vlll, 20,36

HHelium, 20,26, 36Hydrogen, 7, 35

IIridium, 5, 12,26, 35

lodine, 5, 6, 7, 17,20,26, 36

KKrypton, 20, 26, 36

LLangbeinite (calcium Iangbeinite), 9, 16Lanthanides (rare earlhs), 25Lanthanum, 25, 36

clinker accelerator, 26effect on belite hydration, 26

Lead, 4, 5,6, 7, 8, 12, 13,26, 35effect on hydration, 13,

as retarder, 13in CKD, 13volatility, 12

Lesser elements, 3Lithium, 5, 7, 8,26, 35

ASR reducer, 8mineralizer, 8

Lubricating oils (waste oils), 1, 5, 13, 23Lutetium (Lu), 26

MMagnesium, 3,4, 5, 11,26, 35Major Elements, 2Manganese 5,20,21,23,26, 37

alite formation, 23calcium alumino manganite, 24effect on free lime, 23, 24effect on melt viscosity, 21substitution in C&, 20, 23

Mercury, 5, 6, 7, 8, 13,20,25, 26,37volatility, 25

Minor elements (see also traceelements), 1, 2, 4, 5, 6, 7, 26

as mineralizers, 10effect on melt viscosity, 10in clinker, 8relative volatility, 12sources 4, 5, 6, 7

auxiliary materials (fly ash,blast furnace slag), 6

fuel (coal, used oil), 7raw meal (limestone, clay/

shale), 6summary of effects, 35-37

38

Page 45: Role of Minor Elements in Cement Manuf and Use

PCA Research and Development Bulletin RD109T

IndexMolybdenum, 23,26, 37

effect on melt viscosity, 21

NNeodymium (Nd), 25,26

effect on alite hydration, 26effect on silicate formation, 25, 26

Neon, 20,26,36Nickel, 5,6,7, 8, 10, 12,20,21,24,26,

37as alite stabilizer, 24,effect on melt viscosity, 21effect on settingtstrength, 23in CKD, 24in clinker, 20mineralizing effect, 10relative volatility, 12

Niobium, 20,22, 26, 37Nitrogen, 1,2, 5, 13, 14,26,35

fuel nitrogen, 14thermal nitrogen, 14

NO,, 2, 14

0Oxygen, 15,26, 36

oxidation conditions, 22, 23

PPCBS (Polychlorinated biphenyls), 2Periodic table, 7Phosphates, 13, 14

chloroapatite, 14fluoroapatite, 14,20hydroxyapatite, 14

Phosphorus, 5, 13, 14,26, 37effect on free lime,14

Potassium (see also alkalies), 7, 8,9,26, 35

compounds, 9vapor pressure, 9

Producer gas, 7

RRare earths (Ianthanides), 25RCRA (resources conservation and

recovery act), 4, 6, 8Rubidium, 7, 11, 26, 35

sScandium {SC), 25Selenium, 5,6,7,8, 17,26,36

in CKD, 17selenates, 17volatility, 17

Sewage sludge, 1,14

partial kiln feed, 1Silicon, 2,3, 13Silver, 6,7,8,24,26,37Sodium (see also alkalies), 7,8,9, 10,

26,35chlorides,9sulfate,9

Sex,2Stack emissions gases, 1,2, 13, 14, 17,

19,22,23,24,25,26Strontium (Sr), 7, 11,26, 35

effect on alite/belite formation, 11effect on free lime, 11effect on hydration, 11

Sulfates, 9, 15, 16, 17alkali sulfates, 9, 15, 16effect of burning conditions, 9effect on clinkering, 15, 16effect on silica modules (SM), 16,17

Sulfur4, 5,6, 12, 15, 16, 17,26, 35, 36compound formations, 15, 16in clinker, 17pyritic sulfur, 17sulfur-cycle, 15Syngenite, 16

TTantalum, 20,22TCLP (toxicity characteristics leaching

procedure), 6,8Tellurium, 5, 15, 17,26,36Thallium, 4,5,6,7,8, 12, 13,26, 35Thenardite, 9Tin, 5, 13,26,35Tires, 1,2,4, 5, 13, 19,24

tire derived fuel (TDF), 1, 2whole tires, tire chips, 1

Titanium, 5,20, 21,26,37effect on alite/belite formation, 21effect on melt viscosity, 21in clinker, 20, 21

Trace elements (see also minor ele-ments), 1, 2,4, 5, 6, 7, 12, 26summary of effects, 35-37

Transition elements, 20effect on melt viscosity, 21in clinker, 20

Tungsten, 20,23,26, 37effect on alite morphology, 23effect on melt viscosity, 21

uUranium (U), 26

vVanadium, 5,6,7,20,21,26, 37

effect on alite/belite morphology, 22effect on clinker grindability, 22effect on free lime, 22effect on hydration, 22effect on melt viscosity, 21, 22

‘relative volatility, 12

xXenon, 20,26, 36

YYtterbium (Yb), 26Yttrium, 20,26, 37

zZinc, 5,6, 7,20, 21,24,25,26, 37

as mineralizer, 25effect on free lime, 25effect on hydration, 25

retarder, 25calcium hydroxo zincate, 25

effect on melt viscosity, 21in CKD, 25in clinker, 20, 24, 25in tires, 24in used oil, 24relative volatity, 12

Zirconium, 20, 21,26, 37effect on alite/belite formation, 21effect on hydration, 21

39

Page 46: Role of Minor Elements in Cement Manuf and Use

Role of Minor Elements in Cement Manufacture and Use

Metric conversion table

Following are metric conversions of the measurements used in this text.

They are based in most cases on the International System of Units (S1).

1 in

1 sq inin1 Sq ft1 sq ft per gallon1 gal1 kip = 1000 Ibf

1 lb1 lb per cubic yard

1 psf

1 psi

No. 4 sieveNo. 200 sieve

1 bag of cement (U. S.)1 bag of cement (Canadian)1 bag per cubic yard (U. S.)

deg. C

. 25.40 mm

= 645.16 mm2

= 0.3048 m= 0.0929 m2

= 0.0245 m2/L= 3.785 L= 4.446 kN

= 0.4536 kg

= 0.5933 kg/m3. 4.882 kg/m2

= 0.006895 MPa. 4.75 mm

= 75 mm

= 94 lb = 42.6 kg=881b =40kg= 55.8 kg/m3

= (deg. F - 32)/1.8

40

Page 47: Role of Minor Elements in Cement Manuf and Use

PALABRAS CLAVE: manufacture, elementos menores, cemento portland, materia prima, elementos de traza

SINOPSIS: En esta revisi6n se reportan 10S efectos de la mayor parte de 10S elementos menores y de traza en lamanufacture y comportamiento de cemento portland. Se ha puesto 6nfasis tanto a 10S elementos que forman partede materials naturales tambi6n como a aquellos elementos que resultan del desperdicio en la manufacture decemento. Los elementos para 10S cuales se ha obtenido informaci6n detallada, se han tratado de acuerdo con latabla peri6dica de elementos. Cuando necesario, las partes vokitiles de 10S elementos tarnbidn se han considerado.Los elementos que se han revisado incluyen hidr6geno, sodio, potasio, Iitio, rubidio, cesio, bario, berilio, strodio,magnesio, boro, galio, indio, talio, carbono, germanio, estafio, plomo, nitr6geno, f6sforo, arsdnico, antimonio,bismuto, oxigeno, azufre, selenio, telurio, fluoro, cloro, bromo, iodo, helio, neon, argon, kripton, xenon, itrio,titanio, zirconio, vanadio, niobio, tantalum, cromo, molibdeno, tugsteno, magnaneso, cobalto, niquel, cobre, plata,zinc, cadmio, mercurio, y 10S lanttiidos.

REFERENCIA: Bhatty, J. I., Role of Minor Elements in Cement Manufacture and Use, Research and DevelopmentBulletin RD109T, Portland Cement Association [Papel de Ios Elementos Menores en la Manufacture y Uso delCemento, Boletin de Investigaci6n y Desarrollo RD109T, Asociaci6n de Cemento Portland], Skokie, Illinois,U.S.A., 1995.

STICH WORTER: Herstellung, Nebenelemente, Portlandzement, Rohrnaterialien, Spurenelemente

AUSZUG: In dieser ~ersicht wird uber die Wirkung von fast allen stabilen Nebenelementen und Spuren-elementen auf die Herstellung und Eigenschaften von Portlandzement berichtet. Besondere Berucksichtigunggilt den Elementen, die in natiirlichen Mineralien sowie in Abfallen vorkommen, die bei der Herstellung vonPortlandzement Verwendung finden. Die Elemente, wofur detallierte Informationen gesammelt wurden, werdennach ihrer Rangordnung im chemischen Periodensystem besprochen. Wo notig, wird such die Volatilit&en derElemente diskutiert. Zu den untersuchten Elementen gehoren Wasserstoff, Natrium, Kalium, Lithium, Rubidium,Casium, Barium, Beryllium, Strontium, Magnesium, Bor, Gallium, Iridium, Thallium, Kohlenstoff, Germanium,Zim, Blei, Stickstoff, Phosphor, Arsen, Antimon, Wismut, Sauerstoff, Schwefel, Selen, Tellur, Fluor, Chlor, Brom,Jod, Helium, Neon, Argon, Krypton, Xenon, Yttrium, Titan, Zirkonium, Vanadium, Niob, Tantalum, Chrom,Molybdiin, Wolfram, Mangan, Kobalt, Nickel, Kupfer, Silber, Zink, Cadmium, Quecksilber und die Lanthanide.

REFERENZ: Bhatty, J. I., Role of Minor Elements in Cement Manufacture and Use, Research and DevelopmentBulletin RD109T, Portland Cement Association [Einfluf3 der Nebenelemente bei der Zementherstellung und -anwendung, Forschungs-und Entwicklungsbulletin RD109T, Portlandzementverband], Skokie, Illinois, U.S.A,1995.

PCA R&D Serial No. 1990

Page 48: Role of Minor Elements in Cement Manuf and Use

This publication is intended SOLELY for use by PROFESSIONALPERSONNEL who are competent to evaluate the significance andlimitations of the information provided herein, and who will accepttotal responsibility for the application of this information. ThePortland Cement Association DISCLAIMS any and allRESPONSIBILITY and LIABILITY for the accuracy of and theapplication of the information contained in this publication to the

full extent permitted by law.

Portland Cement Association 5420 Old Orchard Road, Skokie, Illinois 60077-1083, (847) 966-6200, Fax (847) 966-9782

m

An organization of cement manufacturers to improve and extend the uses

IIof portland cement and concrete through market development, engineer-ing, research, education and public affairs work.

Printed in U.S.A. RD109.O3T