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

/

t

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 and performance of portland cement have been reported. Emphasis has been given to elements that occur in natural and by product materials used for cement manufacturing. The elements for which detailed information has been obtained are dealt with in an order based on the periodic classification of elements. The volatilities of the elements have 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, cadmium mercury, and the lanthanides.

REFERENCE: Bhatty, J. I., Role of Minor Elements in Cement Manufacture and Use, Research and Development Bulletin 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’dtat naturel clans les mat6riaux aussi bien que sur ceux des rclsidus utilisds lors de la fabrication du ciment. Les 416ments pour lesquels de l’information ddtaillde a W obtenue sent abord4s aans un ordre basal sur la classification p(%iodique des Wments. La volatility des Wrnents est aussi traitde lorsque n6cessaire. Parmi les d~ments couverts, 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, le fluore, 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 cuivre, 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 Development Bulletin RD109T, Portland Cement Association [R61e et utilitd des Wirnents mineurs clans la fabrication du ciment, Bulletin de Recherche et D6veloppement RD109T, Association du Ciment Portland], Skokie, Illinois, U. S. A., 1995.

I

PCA R&D Serial No. 1990

PCA Research and Development Bulletin RD109T

Role of Minor Elements in Cement Manufacture and Use by Javed 1. Bhatty

ISBN 0-89312-131-2 @ Portland Cement Association 1995

Role of Minor Elements in Cement Manufacture and Use


Contents

Page

INTRODUCTION ................................................................................................................................. 1 ALTERNATIVE MATERIALS AS PARTIAL RAW FEED OR FUEL IN CEMENT MAKING ................1 DEFINITloNs ...............................................................l...i ....................................................m.............2 Major Elements ...................................................................................................................... 2 Lesser Elements ................................................................................................................... , 3 Minor Elements ...................................................................................................................... 4 Trace Elements ...................................................................................................................... 4 SOURCES OF MINOR ELEMENTS

................................................................................................... 4

MINOR ELEMENTS IN CEMENT MAKING ........................................................................................ 6 ELEMENTS IN GROUP I (Hydrogen, Lithium, Sodium, Potassium, Rubidium, Cesium)., .................. 7 Hydrogen ................................................................................................................................ 7 Lithium .................................................................................................................................... 8 Sodium and Potassium .......................................................................................................... 8 Rubidium and Cesium .......................................................................................................... 11 ELEMENTS IN GROUP II (Beryllium, Magnesium, Calcium, Strontium, Barium) ............................. 11 Beryllium .............................................................................................................................. 11 Magnesium ........................................................................................................................... 11 Calcium ................................................................................................................................ 11 Strontium .......................................................c........i ............................................................. 11 Barium .................................................................................................................................. 11 ELEMENTS IN GROUP Ill (Boron, Aluminum, Gallium, Iridium, Thallium) ....................................... Boron. ................................................................................................................................... Aluminum ............................................................................................................................. Gallium, Iridium, and Thallium ..............................................................................................

12 12 12 12

ELEMENTS IN GROUP IV (Carbon, Silicon, Germanium, Tin, Lead) .............................................. 13 Carbon ................................................................................................................................. 13 Silicon ................................................................................................................................... 13 Germanium .......................................................................................................................... 13 Tin ........................................................................................................................................ 13 Lead ..................................................................................................................................... 13 ELEMENTS IN GROUP V (Nitrogen, Phosphorous, Arsenic, Antimony, Bismuth) ........................... 13 Nitrogen ................................................................................................................................ 13 Phosphorus .......................................................................................................................... 14 Arsenic ................................................................................................................................. 14 Antimony .............................................................................................................................. 15 Bismuth ................................................................................................................................ 15

,,.

Ill


Page

Contents

ELEMENTS IN GROUP VI (Oxygen, Sulfur, Selenium, Tellurium) ................................................... 15 Oxygen ................................................................................................................................. 15 Sulfur .................................................................................................................................... Selenium .............................................................................................................................. 1; Tellurium ............................................................................................................................<. 17 ELEMENTS IN GROUP Vll (Fluorine, Chlorine, Bromine, lodine) .c.................................................. 17 Fluorine ................................................................................................................................ 17 Chlodne ................................................................................................................................ 19 A/ir7iteCements ....................................................j..........................................................c. 19 Bromine ................................................................................................................................ 19 lodine ...................................................................................................................................2O ELEMENTS IN GROUP Vlll (Helium, Neon, Argon, Krypton, Xenon) .............................................. 20 TRANSITION ELEMENTS ................................................................................................................2O Yttrium.. ................................................................................................................................ 20 Titanium ...............................................................................................................................2O Zirconium ..............................d.............................................................................................. 21 Vanadium ............................................................................................................................ 21 Niobium ................................................................................................................................ 22 Tantalum .............................................................................................................................. 22 Chromium,... ......................................................................................................................... 22 Molybdenum .........................................................!.. ............................................................. 23 Tungsten .............................................................................................................................. 23 Manganese .......................................................................................................................... 23 Cobalt ................................................................................................................................... 24 Nickel ................................................................................................................................... 24 Copper ................................................................................................................................. 24 Silver .................................................................................................................................... 24 Zinc ...................................................................................................................................... 24 Cadmium .............................................................................................................................. 25 Mercury ................................................................................................................................ 25 THE RARE EARTHS ......................................................................................................................... 25 CONCLUSIONS

............................................................................................................................... 26

ACKNOWLEDGEMENTS REFERENCES APPENDlx

.................................................................................................................. 26

.................................................................................................................................. 27

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

INDEX ...............................................................................................................................................

iv

38

PCA Research and Development Bulletin RDI09T

Role of Minor Elements in Cement Manufacture and Use by Javed

INTRODUCTION The purpose of this review is to colIect pertinent information on the behavior of minor and trace elements on the manufacture and use of cement. Attempts have been made to identify gaps, if any, in the information thus far available and suggest work for further investigations. As cement manufacturers continually strive to conserve resources, use of alternative raw feeds and seconda~fuels derived from continuously generated industrial byproducts isgaininginterest. The likely concerns from alternative or new natural sources are the incorporation of trace elements into clinker and their effects on the performance of cement. These effects are, to a large extent, dependent upon the type of trace elements contained in the raw feed, their concentration levels, and the operating conditions of the kiln. The effects of minor elements on the production of clinker and performance of cement are summarized in the appendix.

ALTERNATIVE MATERIALS AS PARTIAL RAW FEED OR FUEL IN CEMENT MAKING There has been an increasing move toward using a variety of alternative

materials in cement manufacturing, with the multiple aims of reducing by-product accumulation to address environmental problems and to achieve technical advantages during clinker processing without sacrificing the quality of cement. Chlorideby-products, and wastes from the soda ash industry, when mixed with fly ash and limestone, are reported to have produced low temperature clinkers (1200°C) with comparable compressive strength (Patel, 1989). Phosphogypsumhasbeen used as a source of limeinkilnfeed. Though the clinker attained a different microstructure, the cement compared favorably with the conventional type (Toit, 1988). In separate studies, spent clays from lubricating oil refining, have also been tested as raw feed components for clinker production (Midlam, 1985). Sewage sludge as a partial kiln fuel was reported by Obrist (1987). Heavy metals in the sludge were permanently withdrawn from the biosphere with little toxic emissions. Organic pollutants were reliably destroyed without leaving any toxic byproducts. The only exception maybe mercury which must be controlled adequately. Ostrovlyanchik et al. (1986) reported that the use of fly ash from coal power plants as raw material, in place of argillaceous material, was effective

1.

Bhatty*

for improving the wet process kiln output with savings in the fuel consumption. Bhatty et al. (1985) produced an ASTM C150 Type I cement from the copper-nickel and taconite tailings used as a partial substitute for cement raw feed. The resulting cement had a microstructure and strength properties comparable to that produced with conventional feed. Weatherhead and Blumenthal (1992), of the Scrap Tire Management Council, concluded from a recent field stud y that tires can be used successfully as an alternative fuel in cement kilns. The fuel cost is significantly lowered, and the production rate is enhanced without adversely affecting the quality of cement. No significant change in the environment quality, due to emissions, was noted.** *

Senior Scientist, ConstructionTechnol-

ogy Laboratories, inc., Skokie, lllinois 60077, U.S.A.Tel: (708)965-7500

u’!+ A distinction between the terms “tirederived fuel” and “whole tires” may be made here. The tire derived fuel (TDF) uses shredded tires in combination with other conventional fuels (coal, coke, oil, gas, etc.) usually in the burner end, tire chips are also fed to calciners, whereas the whole tires are fed into the feed end of a precalciner or a preheater kiln or into the calcining zone of a long kiln.

ISBN 0-89312-131-2 0 Portland Cement Association

1995

1


Use of scrap tires and lubricating oil, as alternative fuel in cement manufacturing, has also been reported in a number of test burns in Australia and Canada (McGrath, 1993; and Heron, 1993). The tests suggested substantial reduction in manufacturing costs, improvement in waste minimization, advances in resource recovery, extended life of existing landfills, and better environmental control. De Zorzi (1988) reported Italian experience on the use of municipal solid waste as a partial fuel in cement manufacturing. The chemical and physical characteristics of clinker and cement were comparable to those produced conventionally. No significant change inorganic or inorganic pollutants, such as dioxins, furans, SOX and NOX, were detected in the stack emissions. There were no material handlingproblems,but storage of the solid waste, especially the refuse derived fuel (RDF), was expensive, because it needed to be contained in totally enclosed compartments for technical and environmental reasons. Regarding Norwegian experience, Ingebrigtsen and Haugom (1988) demonstrated that using hazardous liquid wastes containing PCBS” as a partial kiln fuel offered an efficient way to solve a difficult environmental problem. For waste containing chlorine levels in excess of ().()ls~o, the use of a by-pass was recommended. Krogbeumker (1988) also reported that waste oils containing PCBS were tested as effective kiln fuel with adequate atomization of the oils into the gas stream. The levels of polychlorinated dibenzodioxin and dibenzofuran in emissions were very low and close to the limits of detection. Although these tests were very successful, PCBS are not burned in U.S. cement kilns. Huhta (1990) surveyed some twenty North American cementplants operating with wastes as supplement fuel, and noted that the predominant waste being used was waste oil followed by solvent derived fuel and scrap auto tires; wood chips and fluid

2

coke were also mentioned. However, it is projected that the tire derived fuel (TDF) will become the most advantageous fuel in the near future, because of its availability and easy handling. Kelly (1992), and Mantus et al. (1992) reported that the use of wastes as supplemental fuel in well designed and properly operated kilns results in metal emissions too negligible to cause any adverse health effects. It was also demonstrated that the cements and kiln dusts thus produced were not substantially different from those conventionallyproduced. The effects of wastes on the emissions of organic compounds and metals from kilns were also studied by von Seebach et al. earlier in 1990. It was reported that a virtually complete destruction and removal of hazardous organic compounds occurs in the kiln. A destruction and removal efficiency (DRE) of hazardous compounds was recorded at 99.9996Y0. DREs in access of 99.97 are routinely achieved. Siemering, Parsons, and Lochbrunner (1991) have also reported on their experiences of burning wastes as kiln fuel and have reported both technical and economical advantages with minimal adverse environmental impact. In a recent article, Hansen (1993) has strongly advocated the use of solid wastes in cement manufacturing, emphasizing potential environmental and political advantages. It was suggested that using wastes as fuel has two-fold environmental benefits; it would not only avoid fossil fuel extraction and transportation, but would also minimize emissions that would have occurred by disposal of these wastes through treatment or by landfilling. Politically, the liability of landfills and demands for waste minimization in an environmentally sensitive society, such as the United States, can be substantially reduced by waste utilization in cement making. Gossman (1988) pointed out some of the risks and liabilities associated with the use of hazardous waste-de-

rived fuels, and proposed certain analytical means to minimize liabilities in order to achieve full economical and quality control advantages. Although there are opportunities to beneficially use wastes in cement production, their total substitution in the industry is still in the experimental stages. One recommendation has been to limit the use of waste to 5°/Obyweight of the raw feed (Vogelet al.,1987). Huhta (1990), and von Seebach et al. (1990) have reported a potential of 20-307. or even more for waste as a fuel replacement in cement kilns; some plants have already used 50-10O% replacement. Nonetheless, the level of application and degree of success largely depends upon the waste composition in terms of the type and concentration of minor or trace elements. In summary, under favorable practical conditions, wastes can have the following combined benefits: a. Respond to commercial and environmental pressure to use alternate raw materials and waste by-products. b. Recover potential energy value from the wastes. c. Conserve nonrenewable raw materials and fossil fuels. d. Enhance process efficiency. more reactive raw e. Produce mixes. f. Produce cement of improved quality. g. Reduce COZ emissions.

DEFINITIONS Major Elements According to Rompps ChemieLexikon (1987), the elements that are more abundantly present (>.5’XO)in cement clinker are the major elements. These are calcium (Ca), silicon (Si), aluminum (Al), iron (Fe), and oxygen (0). Carbon (C) and nitrogen

●

PCBs=polychlorinated biphenyls


Table 1. Typical Compositions

and Physical Properties

of Portland Cements

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

Compound Composition (O/.)

Gypsum Loss on Ignition

5

5

5

4

4

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

330

250

500

210

250

7-day Heat of Hydration (J/g)

(N), because of their abundance in the raw material and the earth atmosphere respectively, can also be regarded as major elements. In clinker and cement analyses, Ca, Si, Al, and Fe are expressed as the oxide form (CaO, SiOz, A120~, and FezOJ. However, they eventually exist as more complex compounds. The approximate formulae of these compounds, alsoknownasclinker phases, are tricalcium silicate 3CaO*SiOz or C#*; dicalcium silicate 2CaO*SiOz or CZS; tricalcium aluminate 3CaO*A110~ or C~A, and tetracalcium aluminoferrite 4CaO*AlzO~*FezO~ or CgAF. Since the role of major elements in cement manufacturing has been fairly well understood, only a brief summary on the presence of major compounds in cement is given here. Calcium is an essential component of cement, which comes from the decomposition of the primary raw material such as limestone, chalk, marl or cement rock depending upon the geological location of the cement manufacturing plant. Silicon in cement is derived from silica sand, or from clay, shale, or slate, which are also sources of aluminum andiron in the raw material. Iron is sometimes derived from iron ores, or mill scale, and added separately if the raw mix is deficient in iron. Aluminum may be added with bauxite or other sources. Auxiliary materials such as fly ash and blast furnace slag are also often added as raw feed substitutes.

Aground mixture of the raw material containing major components in a required proportion is burned in a rotary kiln at about 14500C, where the constituents become fully oxidized and form stable solid solutions or the phases as described above. Impure CJS is also frequently known as alite, and C$ as belite”’. After cooling, the clinker is interground with approximate y 5% of gypsum to about 350 m2/kg Blaine fineness, to obtain portland cement. A typical composition of ASTM Type I cement, the most commonly used cement in general construction, is normally 58’70 CaS, 15°/0C2S, 80/0 C~A, 107. CdAF, and 5?0 gypsum. Other ASTM cement types are Type II, III, IV, and V, which vary in composition and are used where special properties are required. Typical cornposition and physical properties of various cement types are given in Table 1 (adapted from CTL, 1993; Mindess and Young, 1981). Type III cement is a high heat of hydration cement with high C.$ content and a finer particle distribution and is used where rapid hardening is required for early strength development. Type IV is a low heat of hydration, slow setting cement because of low C~S and high C2S contents. It is intended for mass concrete in order to avoid thermal cracking, but is now rarely produced. Since the strength development of Type IV cement is low, Type II cement, which can be specified as a moderate heat of hydra-

tion cement, is generally recommended due to its higher strength and market availability. For even lower heat of hydration, Type II cement with fly ash is used. Type V cement is also a low heat of hydration cement because of low C~S and low C~Acontents; it isnormallyused when high sulfate resistance is required. Type II is primarily used as a moderate sulfate resistant cement. A knowledge of the compound composition can reasonably be used to predict the properties of cement. One of the known methods for calculating compound compositions from the oxide analysis are the Bogue formulae (1955). Although a number of sophisticated techniques are now available for Bogue calculations, the simplest Bogue formulation that has been found suitable for most applications is given in the ASTM C 150 specifications.

Lesser Elements Fourlesserelements, i.e., sodium (Na), potassium (K), magnesium (Mg), and sulfur (S), which appear in virtually all 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 forms of C3S and C2Srespectively. Due to the geological source of the raw materials, alite and belites will always have small quantitiesof impuritiesor traceelements.

3


centration, are represented in chemical analyses as oxide forms: NazO, KZO, MgO, and SOS. Rompps ChemieLexikon (1987) has termed these elements as the secondary elements. In cement 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 major and the lesser constituents (i.e. Ca, Si, Al, Fe, O, Na, K, Mg, S) may be considered as minor elements with regard to cement manufacturing. The concentration levels of minor elements in the clinker are almost always less than 17. and are generally categorized on the basis of the frequency with which they occur in the raw material mix.

Trace Elements Blaine et al. (1965) regarded the elements occurring at less than 0.02% each as the “trace” elements. According to Sprung (1988), elements present at levels less than 100 ppm are classified as trace elements. Because of their extremely small concentration levels, it seems unlikely that the presence of trace elements will have any significant effects on cement manufacturing. However, their effects on clinker can significantly change if concentrations are increased beyond certain levels. For the sake of convenience, the terminology “minor elements” has been used throughout the text to cover both minor and trace elements, as defined by Blaine et al. (1965) and Rompps chemie - Lexikon (1987) respectively, unless mentioned otherwise. Rompps Chemie-Lexikon (1987) has exemplified the classification of several major, secondary, and trace elements in cement clinker in Figure 1. Emphasis in this report is given to the minor and trace elements because of their likely presence not only in the wastes but also in the conventional raw materials, and their potential in-

4

1 ppq

1 ppt

1 ppb

1 ppm

0.0019’0 1?40

Figure 1. Concentration ranges (by mass) of main, secondary, trace elements in cement clinker (Sprung, 1988). fluence on cement manufacturing and use. It maybe pointed out that trace elements in a raw feed at one cement plant could significantly differ from another. As an extreme, lead content in one plant maybe 100500 ppm compared to only 1 ppm in another plant (Chadbourne, 1990).

SOURCES OF MINOR ELEMENTS Minor elements in cement primarily come from the raw materials and fuel used in cement making. Examples of these are limestone, clay/ shale, and coal. They also come from the widely used auxiliary materials such as blast furnace slag, fly ash, silica sand, iron oxide, bauxite, and spent catalysts. A secondary but important source of minor elements comes from the wide range of industrial by-products which are partially or totally being substituted for the primary fuel. These include petro!eum coke, used tires, impregnated sawdust, waste oils, lubricants, sewage sludge, metal cutting fluids, and waste solvents, as listed in Table 2. Minor compounds found in several raw feeds for cement manufacturing as quoted by Bucchi (1980) are shown in Table 3. Similar data on

and

major components of raw materials are shown in Table 4 and 5. They are limestone and shale/clay; widely used auxiliary raw minerals, i.e. blast furnace slag (used up to 307. by weight of raw material), and coal fly ash (used up to 15”/.by weight). Minor elements found in conventional kiln fuel (coal), along with two secondary fuels (used oil and petroleum coke) are shown in Table 6. Average values of minor components found in typical clinkers (Moir and Glasser, 1992) are given in Table 7. Although blast furnace slag can be used up to 307. by weight, the level of use maybe reduced due to its magnesium oxide (MgO) content, particularly if the MgO level is already high in the other raw materials. Bauxite is reported to contain 2-87. titanium oxide (TiOz) and 0.04-0.4% chromium oxide (CrzO,). Iron ores frequently contain chromium, arsenic, cadmium, and thallium, and may have adverse environmental consequences because of their toxicity characteristics. A list of metals having regulatory and environmental concerns has been specified by waste characterization regulations under the Resources Conservation and Recovery Act (RCRA) and the Boiler and Industrial Furnace (BIF)


Table 2. Sources of Minor Elements in Cement Manufacturing :Iements

(as per group)

Sources

Sroup I .ithium

Waste lubricating oil

Group II 3eryllium Strontium 3arium

Fly ash Limestone, aragonite, slag, waste lubricating oil Waste lubricating oil, refuse derived fuel (RDF)

Group HI 3oron Gallium, Iridium, Thallium

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

Group IV Germanium Tin Lead

Raw material, coal Fly ash, RDF, fuel Raw material, tires, RDF, WDF, copper shale, fly ash

Group V Nitrogen Phosphorus Arsenic Antimony Bismuth

Coal, air Raw material, slag, sewage sludge, sandstone, Fly ash, secondary fuel, coal, used oils Petroleum, coke Fuel

Group VI Sulfur Selenium, Tellurium

Coal, slag, lubricating oil, petroleum coke, pyrite, tires Fly ash, coal, RDF, coke

Group WI Fluorine Bromine Chlorine lodine

Limestone, fuel Fly ash Coal, slag, fly ash, waste lubricating oil, chlorinated hydrocarbons, Coal

Transition Elements Titanium Zirconium Vanadium Chromium Molybdenum Manganese Cobalt Nickel Copper Zinc Cadmium Mercury

Raw material, clay, shale, iron ore, bauxite, slag, RDF Raw material, silicon ores Petroleum coke, crude oil, black shale, substitute fuel, coke, fly ash Bauxite, slag, recycled refractories, copper shale, tires, WDF, coal Waste lubricating oil Raw material, limestone, clay, shale, bauxite, slag, fly ash Waste oil, fly ash Fly 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, WDF Fly ash, black shale, copper shale, WDF, paint WDF, paint fungicides

RDF

RDF, chlorine-rich fuel

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

5

Role of Minor Elements in Cement Manufacture and Use ,

I

regulations that control treatment of hazardous waste in cement kilns. These are shown in Table 8 (Klemm, 1993). Both RCRA and BIF regulations apply to wastes and require the use of the TCLP (toxicity characteristic leaching procedure) tests. The levels of sulfur and chlorine in bituminous coal, the main fuel for Cement kilns, varies frOIn 0..5 to 4y0 and 0.007 to 0.39Y0, respectively. In some Illinois coals, sulfur is present up to 60/0by weight. Petroleum coke, u~ed as an-auxilia~ fuel, contains up to 5~0 sulfur and 0.6% vanadium OXide, and can contribute certain levels of S and V to clinker when supplementing for coal. Tires have a zinc content of 1.2-2.6 Yo. However, if tires replace 10% of the primary fuel, the resulting zinc oxide (ZnO) contents in clinker are increased by only ().W70 (Sprung, 1985), Additional sources of minor components could be the refractories, chains, and the grinding media such as liners and grinding balls. A damaged chrome refractory lining can enter into the incoming raw mix and incorporate a detectable amount of chromium into the clinker. Partly for this reason, and mostly because of problems with their safe disposal, the use of chrome bricks is being phased out in most parts of the world (Moir and Glasser, 1992).

MINOR ELEMENTS IN CEMENT MAKING The role of minor and trace elements in the formation of clinker and their effect on cement properties are discussed in this report as per their occurrences in raw mixes. The elements chosen for discussion are categorized according to the periodic table, as highlighted in Figure 2. They are discussed in their increasing order of atomic number. The presence of any information gaps are identified and referred for further investigation.

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

1,05

MgO K20 so, Na20 TiO, Mn,O, P20, SrO Cr,O, AS,O, BeO NiO

0.57 0.31 0.17 0,16 0.12 0.09 0.07 0.01 0.002 0.0005 0.003 0.024 0.02 0.06

V*05 cl F

Table 4. Concentrations (ppm) of Some Minor Elements in Limestone and Clay/Shale (Sprung, 1985) Minor Elements As Be Cd Cr Pb Hg Ni Se Ag TI v Zn cl F Br I

Limestone 0.2-12 0.5 0.035-0.1 1.2-16 0.4-13 0.03 1.5-7.5 0.19 n.a. ” 0.05-0.5 10-80 22-24 50-240 100-940 5.9 0.25-0,75

Clay/Shale 13-23 3 0.016-0.3 90-109 13-22 0.45 67-71 0.5 0.07 0.7-1.6 98-170 59-115 15-450 300-990 1-58 0.2-2.2

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

B.F. Slag

Fly Ash

MgO

7.2

K,O so, Na,O TiO Cr,&, MnzO, P20, SrO V206

0.57 3.00 0.44 0.66 n,a.* 0.64 0.03 0.06 n.a. n.a,

5.28 4.05 2.25 1.99 1.21 0.03 0.14 <3.66 0.17 0.09 0.02

AS20, “n.a,= informationnot available

6

Raw Meals

Minor Compounds


ELEMENTS IN GROUP I (Hydrogen, Potassium,

Lithium, Sodium, Rubidium, Cesium)

Groups 1 2

Hydrogen The role of hydrogen (H) in cement manufacturing has not been documented in detail, because hydrogen per se does not exist for long in the kiln as hydrogen is highly combustible. It is present in the kiln as water vapor, which results from the evaporation of physically bound moisture from the raw material, and from the evaporation of water sprayed on the raw feed to control dust during processing. Water vapor can also be present in the kiln gases from combustion of fuel such as CHA + 20Z ~ COZ + 2HZ0 (Hawkins, 1994; Miller, 1994). A portion of water may also come from the dehydration of raw materials such as clays, where it can be present in significant quantities depending upon their mineralogical nature. In a wet plant, water comes from slurry. The water vapor present in the kiln might have an indirect effect on the volatility of alkalies which can increase with vapor pressure at higher temperatures, for example: 2H,0 + 21$S04 -’ 4KOH + 2S02 + 0, less volatile

more volatile

very volatile

Apart from that, hydrogen may not have any significant effect on the anhydrous nature of clinker. As a point of information, it may be mentioned that early cement kilns sometimes used “producer gas” as fuel. The gas was generated (as a mixture of CO and Hz) by the action of steam on hot coal or charcoal as follows: H20+C~CO+H, Currently, no kilns in the USA or Canada use this technology.

6

7

1=” !3s ‘AC Unq Unp Unh Uns Lanthan~de Series Act inide Series

.

L?

Pr’Nd@ml”am” EU ‘ . “ Th

d Kid

lb’

, Pa’

Ua

NP93 Pu” Am’ Cm

DY”

Ho”

Er6 Tm6 ~

v 98 Bk Cf

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

Table 6. Average Concentrations (ppm) of Some Minor Elements Coal aid Used Oil (Sprung; 1985; and Weisweiler and Kr6mar, 1989)

in

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 n.a.

Be

2.27

n.a.

Cd

0.1-10

4

n.a.

Cr

5-80

<5-50

11.0 8.7

Pb

11-270

Hg

0.24

10-21,700 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.

0.8-11.2

n,a.

n.a.

I

“n.a.= information not available

7


Lithium

,

Lithium (Li) is found in some waste materials such as used lubricants, but occurs only in traces in the kiln raw feeds and common fuels. Lithium might behave somewhat differently from sodium or potassium in that it would tend to form a relatively nonvolatile oxide (LizO) at elevated kiln temperatures, Gouda (1980) reported that LizO is most reactive in lowering the temperature of the initial liquid phase; the effectiveness has been shown as LizO>NazO>KzO, The presence of L
Table 7, Average Concentrations of Some Minor Compounds Foundin Conventional Clinkers (Moir and Glasser, 1992) Minor Compounds

Mean Value (%)

MgO

1,48

K,O

0,73

so,

0.80

Na20

0.16

TiO,

0.27

Mn20,

0.06

P*05

0.10

SrO

0.09

Minor Compounds

Mean Value (ppm)

ZnO

120

Cr,O,

103

V*05

100

cl

90

As,O,

56

Cuo

55

PbO

16

CdO T120

0.5 0.3

Table 8. Elements of Regulatory (Klemm, 1993) Elements

‘RCRA Metals

Antimony

and Environmental

RCRA Limit ‘* Using TCLP

“ BIF Metals

1.0 mg/L

Yes

BIF Carcinogen

Arsenic

Yes

5.0 mg/L

Yes

Barium

Yes

100 mg/L

Yes

0.007 mg/L

Yes

Yes Yes

Beryllium Cadmium

Yes

1.0 mg/L

Yes

Chromium

(Total)

Yes

5.0 mg/L

Yes

Chromium

(Vi)

Yes

not defined

Yes

Lead

Yes

5.0 mg/L

Yes

Sodium and Potassium

Mercury

Yes

0.2 mg/L

Yes

70 mg/L

Yes

Since both sodium (Na) and potassium (K) occur together in raw feed, and by virtue of similarities in their behavior in cement manufacture, it is appropriate to discuss them together, Sodium and potassium are mainly derived from the raw materials; their

Selenium

Yes

1.0 mg/L

Yes

Silver

Yes

5.0 mg/L

Yes

7.0 mg/L

Yes

Nickel

8

Concern

Thallium ●

RCRA

“’ TCLP “’* BIF

. Resource Conservation and Recovery Act = Toxicity Characteristic Leaching Procedure = Boiler and Industrial Furnace

Yes

Yes


main carrier is clayey rock. Sedimentary rocks, including the carbonate ores, sometimes contain soluble alkali salts. Lea (1971) has quoted the occurrence of Na and K (by weight O/.)in different components of raw materials used for cement manufacturing as shown in Table 9. Table 9. Presence of Sodium and Potasium in Different Raw Materials (Lea, 1971 ) 7. by wt.

%’

800 –

30

60020 ‘“\

400 –

10 200 –

NaCl

1000 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 auxiliarv raw materi~ls su~h as blast furna~e slag and fly ash as shown in Table 5. NazO and KZO in European fuels range between 0.05 -O.6?40and ().5-2%, respectively (Bucchi, 1980); for typical raw feed, their average concentration Ievek are 0.177. and ().57Y0, respectively, as shown in Table 3. Jawed and Skalny(1977, 1978) and Skalny and Klemm (1981) have reviewed in detail the effects of alkalies in cement manufacture and use. NazO and KZOare volatile in nature, giving rise to a cycle inside the kiln. The extent of alkali volatilization varies with raw material composition; for instance, volatilization of alkalies in clays is higher than those found in feldspar. About half of the total alkalies by weight in the feed are volatilized between 8OO-1OOO’Cas the mix nears the burning zone, but condenses at cooler parts of the system, such as in suspension preheater riser ducts or in chain systems in dry kilns. The formation of rings and coatings on kiln lining resulting from this heating-cooling cycle are generally attributed to alkali condensation and reaction with refractories or incoming material. To

E’

1“100

1200 1300 Temperature, ‘C

1400

Figure 3. Vapor pressure of Na and K chlorides (Bucchi, 1980). avoid excessive buildups in the kiln or preheater vessels, a percentage of gases may be bled through a by-pass, so that the alkali sulfates and chlorides maybe continuously removed and end up in the cement kiln dust (CKD). Thus,CKDs collected from by-pass dust collector are typically high in alkali contents. Usually potassium compounds are more volatile than the sodium compounds. According to Bucchi (1981), the intensity of the alkali cycle depends upon the nature of their presence in raw material, on operating practices, and on type of kiln. The retention of alkalies in clinker is generally higher for high efficiency kiln systems (Lea, 1971). With gas and oil as fuels, the alkalies tend to volatilize more as compared to coal used as a fuel. This may be due to the high intensity of the flame with oil and gas compared to coal. In the presence of chlorides and sulfate, the volatilization behavior of both Na and K is modified greatly, as shown by the vapor pressure-kiln temperature relationship in Figure 3. The vapor pressures of alkali carbonates resemble those of sulfates and they exhibit similar effects. In the presence of sulfur, alkalies preferentially form sulfates. If their amount is more than the required stoichiometric balance, the excess will be dissolved in the silicates, aluminates, and ferrites. The common alkali sulfate phases formed are K2S01,

1500

and sulfates

also known as arcanite, sodium potassium sulfate, also known as aphthitalite of a general solid solution composition (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 raw materials in the North America and Europe varies. There is usually a substantial excess of KZO over NazO. Therefore, in the presence of sufficient amount of SO~ a range of double alkali sulfates, as described later in this report, is formed depending upon the KIO to Na20 ratio. If KZO is in excess of that required to produce aphthitalite, it forms arcanite. Burning conditions also significantly influence the formation of sulfate so that oxidatizingconditions produce calcium-potassium sulfate and a reducing condition produces sodiumpotassium sulfate. Potassium is twice as likely to produce soluble sulfates as sodium. According to Pollitt and Brown (1968), the calcium potassium salt, calcium langbeinite 2CaSOA”KzSOq**, is also sometimes found. Introducing SO, jointly with K20 and NazO into clinker melt leads to phase separation. Since alkalies re.

Commonly written as K3N54in cement chemist’s notation

**

Also written as 2CS.KS-

9


duce the melt temperature, and the rate of C$ formation is proportional to the amount of liquid phase, a positive effect on C$ formation could be expected. However, Johansen (1977) reported that C~S,with or without the presence of alkali, has the same amount of free lime after firing at 1400-15000C. Alkali sulfate melt and clinker liquid are immiscible phases. Alkalies inhibit the formation of C,S from CzSand lime bystabilizinglower energy CZSin the absence of sulfates. After allocating for the sulfates, the remaining alkalies are distributed between silicates, aluminates, and aluminoferrite. Lea (1971) has reported ranges of alkalies in the major clinker phases shown in Table 10. The values are in general agreement with those quoted by Taylor (1990) tin the distribution of alkalies in different clinker phases. Gartner (1980) and Gies et al. (1986) reported that in the absence of SO~, Na20 is preferentially incorporated in CqA by replacing CaO and forms “alkali-aluminate” of an approximate composition NaO*8CaO*3AlzO~*, thereby reducing its reactivity. This results in clinkers rich in free lime and aluminate, and can reduce the burnability. K is substituted in C$ as a compound with an approximate composition of KzO*23CaO*12SiOz,** and the overall reactivity of clinker is decreased due to the slower reaction with CaO to form C~S in the burning process. In the presence of sulfate, KZOincreases the C,Areactivity(Strungeet al., 1986). Richartz (1986) reported that SOS reduces the extent of alkali solid solution in C~A and hence the reactivity, but improves the cement properties. The mineralizing effectiveness of alkalies (in terms of decreasing melt viscosity, and free lime contents in clinker) also appears to be a function of their cation size, electronegativity, or the ionic potential. Such relationships for K, Na, Li and other relevant cations are given in Table 11 (Grachian et al.), and in Figure 4 (Teoreanu and

10

Table 10. Range of Alkali Distribution

I

Clinker Phase

L

in Clinker Phases (Lea, 1971)

Na,O (wt.%)

K,O (wt.%)

C3S C*S

0.1-0.3

0.1-0.3

0.2-1.0

0.3-1.0

C,A

0.3-1.7

0.4-1.1

C,AF

0.0-0.5

0,0-0.1

Table 11. Effect of Ionic Potential of Minor Elements on the Melt Viscosity (Grachian et al., 1971) Effect of Different Ions on Melt Viscosity (in decreasing order)

Ionic Potential of Elements (ratio of number of iogic charge/cationic, Rvl in Al)

Be+2

5.71

Mg+2

2.50

.942

1.65

Li+l

1.22

Ba+2

1.39

Na+l K+l

0.91 0.68

7 I [Cao]o= [@O],

❑

Free CEO in the Absence of Mineralizer (%) Free Cso in the Presence of Mineralizer (%)

Mg+2 ●

6

~+2

5

●

4-

0

0.1

0.2

0.3

0.4

0.5

Field Strength, m-2

Figure 4. Mineralizing effectiveness of cations for clinker with LSF=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 although alkalies, NazO in particular, may act as fluxes, they are technically less desirable compounds than many of the other available minor compounds @ucchi, 1980).

If present in excess, alkalies often lead to higher pH and better early strength, but lower later strengths. They are not desirable because of *

Commonly written as NC8A3

**

Also written as KC,3S,j


their deleterious alkali-silica reaction (ASR) with reactive aggregates that leads to expansive reactions and can cause serious cracking in concrete. ASR can be prevented with proper use of pozzolans. Butt et al. (1971) reported that the deleterious effects of alkalies on the mechanical properties of cement may be reduced by gypsum addition to the raw feed. They considered this because of the possible elimination of solid solutions of alkalies with clinker minerals. One possible speculation derived from the microscopic studies by Prout (1985), is that gypsum would either increase the volatilization, or eliminate NaO”8Ca0-3Al,0~ or K,0*23CaO”12SiOz formation. According to Lokot et al. (1969), the addition of gypsum to raw feed produces cement of high 28-day strength, enhancing kiln output and fuel savings.

Rubidium and Cesium The remaining Group I elements, rubidium (Rb) andcesium (Cs),arefound only as traces in cement raw mix or in the fuel. Rubidium generally occurs in cement at 0.017. or less (Blaine, 1965). Both Rb and Cs are expected to behave similarly to Na and K, in that they would both form stable sulfates and volatile chlorides in the kiln (Gartner, 1980). On the other hand, their concentrations may be too low to effectively influence the clinker formation or cement properties.

ELEMENTS

IN GROUP Ii

(Beryllium, Magnesium, Strontium, Barium)

Calcium,

Beryllium Beryllium (Be) would be present only in trace amounts in the raw feed and fuel (see Tables 4 and 6). It is found only occasionally in the fine fractions of fly ash, an auxiliary material frequently used as substitute raw mate-

rial. Beryllium is found at a 55 ppm levelin=4 pm fraction compared to 12 ppm in >45 p,m fraction of fly ash (Davison et al., 1974). It maybe suggested that because of its low volatile oxides, beryllium would stay in the clinker, Nonetheless, beryllium has not been measured in significant amounts in clinkers to have any measurable effects on clinker formation or cement use. Beryllium in todays cements has occured up to 3 ppm (PCA, 1992).

Magnesium Magnesium (Mg) in portland cement is mainly derived from magnesium carbonates present in the limestone in the form of dolomite CaCO,*MgCO,, while smaller amounts coming from clay and shale (Lea, 1971), ordiopside(Fundal, 1980). If present in small quantities, magnesium improves the burnability of clinker (Christensen, 1978). According to Long (1983), the behavior of MgO in clinker formation primarily depends upon the cooling rate. When clinker is burnt at high temperature (>15Cr0°C) and rapidly cooled, it retains the bulk of the MgO mostly in aluminate and ferrite phases, with a lesser amount in alite. Under conditions of slow cooling, ody 1..57. of MgO is retained in solid solution and the rest is crystallized as large periclase crystals. MgO in cement is usually limited to under 5’Yo,because MgO content in excess of 2?40can occur as periclase (Taylor, 1990), The presence of larger crystals of periclase in cement slowly reacts with water to form expansive Mg(OH)z and can lead to destructive expansion of concrete. ASTM C150 specifications allow MgO contents up to 6% in portland cements. Magnesium salt solutions (sulfate and chloride) are aggressive towards concrete and react with the calcium hydroxide phase to form basic salts. The reactions are expansive and may lead to deterioration of concrete.

Calcium The role of calcium (Ca) in cement manufacturing has alread ybeen dealt with in the section of major elements.

Strontium A major portion of strontium (Sr) found in clinker as SrO comes from limestone and aragonite. Strontium as SrO, frequently occurs in clinkers. The mean value quoted by Moir and Glasser (1992) in Table 7 is O.09%. Brisi et al, (1965) and Gilioli et al. (1972, 1973), demonstrated that small amounts of S@ favor alite formation, but at 4-5y0 addition, Sr preferentially distributes in belite rather than alite, Sr in belite inhibits Phase equilibrium alite formation. studies indicate that Sr in raw feed also favors free lime formation, with SrO preferably going into solid solution and displacing CaO from other compounds, The tendency of free CaO release during clinkering makes SrCOq more labile than SrSO~, and the clinkers having a high lime saturation factor (LSF) maybe more vulnerable to free lime expansion during hydration. Butt et al, (1968) reported that the hydraulicity and strengths developed by Sr-doped alites are significantly lower than the normal alites. This may be attributed to the smaller sizes of the lattice voids in strontium-incorporated alite. Kantro (1975) reported a slight set acceleration effect withS~lz~ 6HZ0 used as an admixture in CaS paste.

Barium Barium (Ba) occurs in varying amounts in limestones, mostly as barite (BaSOd). It can also occur in clayey sediments in appreciable amounts. The average amount of barium in cement is 280 mg/kg. The average for CKD is 172 mg/kg (PCA, 1992).

11


Timashev et al. (1974) reported a decrease in clinkerization temperature from 1450 to 1400”C and increase in the clinker production rate from 8.2 to 9 tonnes/hr, when using raw mixes containinghigheramounts of barium. They also noted an improvement in the mineralogical composition of the resulting clinker. However, Kurdowski (1974) reported only a marginal usefulness of BaO when added in small amounts, stating that it did not significantly affect either the properties of the liquid phase or the rate of lime assimilation; Ba replaced Ca in all the clinker phases, except for the ferrite phase. The optimum BaO concentration was between 0.3 to 0.57., preferably for clinker containing less flux (silica modulus >30) and high CIS levels. According to a number of studies, Ba also appears to be an effective activator of hydraulicity and strength. The strength obtained from Ba incorporated clinkers is 1O-2O’7O higher than that of regular clinker of all ages tested under identical 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 increase the free lime content of clinker due to CaO displacement and can cause expansion in concrete under certain circumstances. It can also lead to paste shrinkage.

ELEMENTS IN GROUP Ill (Boron, Aluminum, Thallium)

Gallium, Iridium,

Boron Boron (B) is generally found in traces (3 ppm) in most cement raw materials, particularly those containing iron ore. Fromearlystudiesby Mircea (1965), it appears that BzO~ reacts with CJS to form CZS, C~BS*, and free lime. Upon further addition of BzO~,C~Scompletely disappears. Timashev (1980) established a relationship between the electronegativity of boron and the melt viscosity,

12

957

0 CaZn VBe NiKCr

AsPb S

Cd Cl TI

Figure 5. Relative volatilities of elements in clinker burning in a cyclone preheater kiln (Sprung, 1988). ‘Restive volatility as a percentage of ratio between the total external and internal balance for a given element. and noted a similarity between berates, phosphates, and sulfates. Boron inhibited the formation of C$ and affected the stability of the other major clinker phases. In the presence of boron C$ is decomposed to a stabilized C2S as follows: C,S

~ C2S + Cao

It was also pointed out that although B20q may not be a useful addition for regular alite clinker required for early strength development, it might be useful as a mineralizer for clinkers rich in belite. Gartner (1980) has reported on the effectiveness of BzO~ to stabilize /1-C2Sand to improve its hydraulicity. According to Miller (1976), boron can also stabilize ~-CzSin alumina andironpoor systems. However, Miller (1976) has cautioned that the indiscriminate addition of boron can produce unpredictable hydration results. Gartner (1980) explained that this behavior of boron is probably sensitive to the presence of other trace elements. Bozhenov et al. (1962) reported that even small additions of BzO~ (-0.040/.), as an admixture, to cements can have adverse ef-

fects on setting properties. These observations indicate that B20~is a strong retarder of cement hydration.

Aluminum Role of aluminum (Al) in cement manufacturing has been dealt with in the section of major elements.

Gallium, Iridium, and Thallium Gallium (Ga), iridium (In), and thallium (Tl) are found only in traces in raw material; their typical concentrations in coal are 5-10 ppm, 0.07 ppm, and 1.1 ppm respectively. Thallium and gallium are also found sometimes in the coal fly ashes. Thallium may also be found in some pyritic minerals used as an iron source for raw feed. The average concentration of thallium in cement is 1.08 mg/kg, ranging from nondetectable to 2.68 mg/kg. The average concentration of thallium in CKD is 43.24 mg/kg (PCA, 1992). *

B is B103 in C5BS


Although thallium occurs in traces in the raw feed, it is the most volatile element* after mercury in the kiln (melting point=30~C), and is most likely to concentrate in the kiln dust. The volatility of T1relative to other elements in the kiln is shown in Figure 5 (Sprung et al., 1984). Sprung et al. determined the volatility on the basis of the difference between the external and internal balances of individual elements during the clinker burning in a cyclone preheater kiln. Iridium is also volatile and largely ends up in the kiln dust. Since thallium may concentrate in the fly ash from the coal firing power plants, in the cement kiln operation it tends to build up in extremely large internal cycles if no dust is 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 the limestone. A significant amount of carbon can also present in flyashas unburnt coal. Carbon as C02 is extensively present in cement kiln systems, but is not present in any significant levels in clinker. Because of the limestone and fuel that are used in the kiln, the gases emitted from the kiln system are constituted mainly of COz,~O, and N2. Limestone (CaCO~) decomposes to CaO and C02 at about 9000C. Roughly for every ton of clinker, one ton of COZ is generated in the kiln, which essentially is released through stack emissions.

Silicon Role of silicon (Si) in cement manufacturing has already been discussed in the section on major elements.

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

Germanium oxide (GeOz), is not volatile (Gartner, 1980), and is likely to concentrate in clinker. When present in larger amounts, GeOz can form C~G**, tricalcium germanate with CaCO~ at 1500”C and isstablebetween 1335”C-1880”C. At temperatures below 1335°C, C,G decomposes to CZG and free lime (Hahn et al., 1970; Boikova et al., 1974). These forms of calcium germinates are similar to C~S and CZSrespectively. COGis hydraulic and produces calcium germanate hydrate (C-G-H) and calcium hydroxide (CH) with water, whereas ~G is assumed to be non-hydraulic. According to Gartner (1980), it is unlikely that the trace amounts of Ge would seriously affect the formation of clinker and the properties of the resulting cement.

Tin Tin (Sri) is a trace element in both the raw feed and fuel. Tin is reasonably nonvolatile (boiling point=2265°C). Tin oxide (SnO) or natural cassiterite melts at 1630”C and sublimes between 1800 and 1900°C. It is very likely that tin will stay in the clinker. The presence of trace amounts of tin in clinker should not affect cement properties, although not much is known about the effect of tin in clinker manufacture.

been studied in some detail, Lead compounds are fairly volatile. They tend to vaporize in the kiln, and exit the kiln as fines and are collected in the kiln dust. There is also evidence that despite the partitioning of lead into the CKD, some lead can still be retained in the clinker (Davison et al. (1974), and Berry et al. (1975)). However, Pb has been shown to have no adverse effect on cement properties if present below 70 ppm. The effect of lead levels higher than that in clinker is uncertain (Sprung et al., 1978). According to a recent PCA study (PCA 1992) the average lead levels in the CKDS and cements produced in North America are 434 ppm and 12 ppm respectively. Some research on the effect of lead compound additions on hydrating cement properties has recently been studied, where Bhattyand West (1992) have noted that additions either as a soluble compound (PbNO~: 7,300 ppm level ) or insoluble oxide (PbO:38,000ppm level) substantially retards the hydration of pastes, but enhances the workability, The retardation effects are more pronounced with oxides. The initial setting time is increased with a consequent loss in early strength, but the 28- and 90-day strengths are comparable to or higher than those of the control.

ELEMENTS Lead Lead (Pb) can be present in trace amounts in raw material mainly in clay and shale. It would be present at appreciable levels in coals, used oils, lubricating oils, and scrap tires. In fly ash, lead tends to concentrate in the fine fractions (Coles, 1979), Lead levels in coal, used oil, and petroleum coke are shown in Table 6. Another source of lead could also be the lead shot from shot gun shells used to shoot out rings. The effect of lead in cement manufacturing and properties has

IN GROUP V

(Nitrogen, Phosphorus, Antimony, Bismuth)

Arsenic,

Nitrogen Nitrogen (N) can be present up to 0.01’% by weight in the raw materials, but in coal and other fuels nitrogen can be as high as 1-2Y0, often as hetrocyclic nitrogen compounds. Clinker made under reducing conditions tend to have up to 0.057. N *

Nonvolatile elements are often called refractory elements.

““

G= GeO,

13


as nitrides. Under normal oxidizing conditions, nitrogen in clinker is present only at a few ppm. High concentration of nitrogen, higher residence temperatures, partial pressure in the flame zone, and the subsequent oxidation of nitrogen leads to the formation of several oxides of nitrogen (NO and NOZ and NZO1) in the kiln emissions collectively known as NOX. Total NOX results from fuel nitrogen NO, thermal NO, and prompt NO. In the cement manufacturing, fuel nitrogen NO and thermal NO play a significant role. The prompt NO which is formed by the participation of CH in the oxidation of nitrogen in air, plays a less significant role (Bretrup, 1991). The quantity of thermal NO formed is closely related to the burning zone temperature (BZT). According to Lowes et. al (1989), a reduction in BZT from 15000C to 1300”C can reduce the NO, levelsby200-400 ppm. Nitrogen in coal orotherfuels,present at about the 1-2% level, is considered significant in producing NO emissions from cement plants. However, it is not known to the degree in which the nitrogen in the kiln raw feed also contributes to NO, emissions (Gartner, 1980). In precalciners, fuel nitrogen may play a role, but in the burning zone the temperature is so high that thermal NO is virtually in equilibrium.

Phosphorus Phosphorus (P) as phosphates is present in limestone and shale (Moir et al. 1992); they are also present in sandstones, sands, and in detritalclays (Bucchi, 1980). Phosphorus also occurs in the blast furnace slags, electric furnace slags, convectorslags, and fly ash which are often used as substitute raw feed for cement manufacturing. Phosphate is found in sewage sludge which is a potential partial kiln fuel. Cement clinkers contain typically around 0.2% PzO~(Lea, 1971). A high PzO~concentration decomposes C~S

14

to CZS and excess lime. If PZ05 is present in excess of 2..57. by weight, the formation of free lime occurs (Nurse, 1952). However, by correct proportioning and proper burning, sound clinker can be produced, but cement hardening becomes slower. Matkovich et al. (1986) reported higher hydraulic actively for (x’CzS stabilized by PZ05 than for the &CzS. Odler et al. (1980-1) reported the addition of hydroxyapatite Ca~(PO1)~OOHleads to an increased formation of free lime at 1300”C, being directly proportional to the PzO~content. This was attributed to the preferential stabilization of CZS solid solution and formation of free lime at increasing P205 additions. However, Halicz et al. (1983) demonstrated that a satisfactory C~S phase in clinker was formed by adding PzO~in the raw feed and maintaining lime salmation factor (LSF) and silica ratio (SR) at 1.0 and 2.75 respectively. In a CaO-CzS-C~P* system at 1500°C, raw mix with more than a few percent P,O, does not yield C,S. However, in the presence of fluorine, the tolerance to PzO~is somewhat improved. It is very likely that the thermodynamics of the system favor the fluoride-aluminum-CIS solid solution rather than P-C$ solid solution (Gurevich et al., 1977) and apparently form a fluoroapatite phase (10Ca0.3Pz05*CaFz) which is dissolved in C,’S. Gartner (1980) suggested that chlorides may also help stabilize PzO~ in C~S by forming a stable chloroapatite (10CaO*3P,0,*CaC12) which also forms a stable solid solution with fluoroapatite. Coleman (1992) reported that an appropriate level of PzO~in clinker reduces the negative effects of alkali on the strength properties of cements. He reported that in cement clinkers with “normal” NazO contents of 0.8Y0, the maximum 28day strength was achieved at 1.07. PZ05 level.

Arsenic Arsenic (As) bearing mineral arsenolite or claudite AszO~ (or AslOG), occurs only in small amounts in coal and used oils, and are unlikely to influence cement manufacturing in any way. Smith et al. (1979) have indicated that in coal-fired power plants, As tends to concentrate in the fly ash, but its concentration level, as detected by the XRF method, is extremely low. It tends to concentrate in the fine fractions of fly ash where the levels can go up to 70 ppm. Weisweiler et al. (1989) has reported up to 5 ppm of As in raw material and only 0.6 ppm in petroleum coke. Arsenic levels found in various materials are shown in Tables 4-6. The average concentration of As in cement and CKD is 19 mg/kg and 18 mg/kg respectively (PCA, 1992). Although AszO~ is volatile (sublimes at 1930C) and should be expected to condense on kiln dust particles, Weisweiler et al. (1989) observed that a substantial amount of As is incorporated in the clinkers, and only a negligible portion of As ends up in the dust. The cause of As entering into clinker was attributed to the excess CaO, oxidizing conditions in the kiln, and high kiln temperature. Under oxidation conditions, As is primarily oxidized to AszO~and forms a series of low volatile calcium arsenates, among which Ca,(AsO,), is more stable at 13000C. Czamarska (1966) found that 0.157. AS+5significantly decreased the rate of C~S formation at 1450”C. As a metalloid occurring in different oxidation states, arsenic can have complex effects on the hydration properties of cement (Conners, 1990). Tashiroet al. (1977) reported that AszO~ only slightly retards the paste hydration when added up to 5’Yo. It was found that the As leaching rate from hardend cement mortars using either ordinaray water or sea water, although measurable, was very low. *

P=P20,


Antimony Antimony (Sb) occurs as traces in cement raw materials. It has been reported to occur at 0.08 ppm in the raw feed and 0.0429 ppm in petroleum coke (Weisweiler et al., 1989), Sprunge (1985) has quoted 1.19ppm Sb in coal. According to measurements in BIF certification of compliance (C.O. C.) and other authors, the Sb levels in raw materials are higher. Like arsenic, a considerable portion of antimony is incorporated in clinker in the form of low volatile calcium antimonates under oxidizing kiln conditions at high temperatures (Weisweiler et al., 1989), The mechanics of stable calcium antimonate is more likely the same as for arsenate formation. The oxides, SbzOj, natural seranmontite, and valentinite, are not very volatile at kiln temperatures; they sublime at 1550”C. Although usually not detected in cement and CKD, Sb levels as high as 4.0 and 3.4 mg/kg have been reported for cement and CKD, respectively (PCA, 1992).

Bismuth Bismuth (Bi) occurs as a trace element in the raw feed and fuel. The stable oxide BizOqis not volatile at clinkering temperature (boiling point =186WC). Little is available on the influence of Bi in cement manufacturing and cement hydration, but, owing to trace concentration, it is conceivable that the effects will be practically insignificant.

ELEMENTS IN GROUP VI (Oxygen, Sulfur,

Selenium,

Tellurium)

Oxygen The role of oxygen (0) per se on the manufacture and use of cement has not been studied. Nonetheless a considerable portion of raw material and clinker phases incorporate oxygen

Possible carry-through of complex calcium sulfides in clinker

S02 prominent in vapor pressure

Molten sulfates

S-2 present as organic and inorganic forms in fuel, etc

Sulfites, SO; in solids which become increasingly unstable with rising temperature

Sulfate solids S03vapors

ReducedS Species

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 material is primarily composed of CaCO~ (-75%),Si0, (-20%), and A1,O, (-2%). CaCO~ in the raw mix is derived from limestone; SiOz and AlzOqfrom clays, shales, sandstones, and bauxite, and FezO~from iron oxides andiron ores. The clinker is formed by heating a powdered raw material of an appropriate proportion to 1400-1550”C in a kiln having a z-s~. oxygen level. As stated previously, the final four phases in clinker are in the fully oxidized forms. They are: tricalcium silicate 3CaO”SiOz, known as alite; dicalcium silicate 2Ca”SiOz, known as belite; tricalcium aluminate 3CaO”A110q, known as aluminate, and tetracalcium aluminoferrite, 4CaO”A120~”FezO~,known as ferrite. The importance of oxygen levels is also related to the effect on the environment of the kiln and the kind of reactions that are favored. Thus, the presence of oxydizing or reducing atmosphere greatly influence the reaction into which the various elements will enter. Clinker made under oxidizing conditions tends to incorporate trace metals of higher oxidation states than clinker prepared Exunder reducing conditions. amples of chromium and sulfur can be cited here. Cr+s would tend to form under oxidizing conditions, instead of Cr+3, which results under

reducing conditions. Cr has also been reported to occur as CrA, Cr~s, and Cr+5(Johansen, 1972), but eventually they disproportionate to more stable Cr+3or Cr+swhen mixed with water. Alkali sulfates formed in the kiln are preferably decomposed under reducing conditions. Kilns having strongly oxidizing conditions and low burning zone temperature tend to retain more sulfur in clinker than those produced under reducing conditions and for high burning zone temperature. Thus, the oxidation or reducing conditions in the kiln can lead to significant phase modifications in clinker. Clinker produced under reducing conditions are brownish as compared to darker gray clinkers made under oxidation conditions, most probably because of the oxidation state of iron. Burning conditions ma y also have an effect on the crystallinity of major phases. The effects can be pronounced if trace metals are also present.

Sulfur SUIfur (S) is frequently present in coals and some fuel oils; sulfates and sulfides are also often present in the limestones. Clayey sediments, marls, also contain both sulfides and sulfates. Lecher et al. (1972) have re-

15


ported occasional use of gypsum and anhydrite as mineralizers and modifiers of the alkali cycle in the kiln. Sulfides and sulfur from raw materials and fuel are oxidized and are incorporated into the solid phases as sulfates in the clinker, though some sulfur as SOZ will almost always escape with the exiting gases. Sulfur forms volatile compounds and its behavior in a kiln is a complex one. Depending upon the burning conditions in the kiln, both oxidized and reduced species may occur in solid, molten and vapor phases, as explained by Choi et al. (1988) in Figure 6. Under oxidizing conditions at high temperature, the formation of SOzis most likely. In the presence of lime, S02 is partly removed to form CaSO1 by the following mechanism:

S02 + CaO ~ CaSOz + l/20z ~

CaSO, CaSO1

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

condensates, from liquids and solids, contribute to build up problems in various kiln systems. Intermediate compounds such as “sulfospurrite”, 2C2SOC~,and the ternary compound “sulfoaluminate” C1@ also condense at lower temperatures. Another well known problem of sulfur being volatile is its cycle of vaporization and condensation with alkalies. They are volatilized at high temperatures and subsequently condense on the relatively cooler incoming raw feed resulting in high sulfur and alkali levels in the middle zone of kiln, especially with preheater. The use of an alkali by-pass is often effective to break this cycle and lead to the reduction of sulfur and alkalies in the incoming kiln feed. However, alkali sulfate levels are significantly increased in the by-pass dust, which is captured by the dust-collector and generally discarded. Sulfates preferably combine with alkalies to give alkali sulfates in clinker as (K, Na)#O1, known as aphthitalite, or K2S01 known as

arcanite. If sulfate is ptesent in excess, the balance between alkali is achieved by forming calcium langbeinite, Caz~(SO,)Y which is stable up to 10110C in a CaW1-KzWi system. However, this phase is known to evaporate inconWuently at high temperatures, and vaporizes K and S (Arceo et al., 1990). Major alkali salts formed with sulfates and their approximate melting temperatures according to Gartner et al. (1987) and Skalny and Klemm(1981) are shown in Table 12. Strungeet al. (1985) reported that increasing sulfate contents distinctly decreases alite, increases belite; the aluminates and ferrite contents are unchanged in clinkers irrespective of their silica modulus (SM) values. On the other hand with increasing SM, irrespective of the sulfate, the alite contents are higher, belite are unchanged, and aluminates and ferrite are somewhat lower. Relationships between clinker phases and sulfate content in the clinker are shown in Figure 7. With increasing sulfate

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

Chemical

Sulfate (arcanite)

Formulae

Melting Temperatures

Melting Temperature

K,SO,

1074

Sodium Sulfate (thenardite)

NapSO,

884

Calcium Sulfate (anhydrite)

CaSO,

‘C

1450 to CaO + S03 and 02at about 1200”C)

(Decomposes

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 at lower temperature)

16


contents, the alite crystals in clinker grow larger, and the tendency ofbelite inclusion in alite is progressively reduced. The crystal size of aluminate and ferrite phases are also significant y reduced. Gies et al. (1986, 1987) reported the development of a belite-rich cement by using increased sulfate contents in alkali free raw materials; this clinker showed reasonable hydraulic activity which was attributed to the presence of 0.6-0 .8% sulfate in belite. The rate of clinker cooling did not have any significant effect on the strength properties of resulting cement pastes. To the contrary, Gartner (1980) suggested that sulfate in clinker is rather unreactive and does not necessarily contribute to set control or to the hardening of paste. So, even a high sulfate clinker may require additional sulfate, which generally comes from gypsum interground with clinker to achieve adequate set control. This, however, depends upon the C~A content, and sulfate should not exceed the maximum limit specified by ASTM C150 without the sulfate expansion test. It might be noted that excessive sulfate in cement can lead to expansion problems in concrete. Clinkers might also contain certain amounts of unreactive sulfate, which unfortunately can lead to other problems due to insufficient available sulfate for reaction with the aluminate phase. Another related concern is the level of SOz in the kiln exhaust area. Very frequently, 15-40% of pyritic (sulfide) sulfur in raw material is converted to SOZ in the emissions (Neilson, 1991). It should be pointed out that in the preheater system much of the SOZ in the kiln is taken up by the incoming raw material. This reaction is also observed in plants which use kiln exhaust to provide heat to the raw milling system. Significant amounts of SOZ may still escape if its original concentration is high, or if reducing conditions are generated locally.

SM=l .6

I

SM=3.2

SM=2.4

Alite

Belite

Belite

Belite

Aluminate /

d

/ Ferrite

0123

I

Ferrite

Aluminate Ferrite

0123

0123 SOS Content, % mass

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

Selenium Selenium (Se) could be associated with sulfur in coal, but only in traces. It is also present in fly ash where it tends to concentrate in the fine fractions (Coles, 1979). Selenium is usually not detectable in cement but is detected in CKD in small amounts (PCA, 1992). Selenium is volatile (boiling point=684°C) and expected to end up in kiln dust or in the emissions. Selenium could form less stable selenates (SeO,), which are unlikely to stay in clinker (Gartner, 1980). Since their concentration is extremely low in the kiln feed, it is very unlikely that they will have any significant effect onthemanufacture or properties of cement.

Tellurium Like selenium, traces of tellurium (Te) are generally associated with sulfur in coal. At optimum kiln temperature tellurium could be somewhat volatile depending upon the form in which it is present (amorphous form boiling

point= 990°C; rhombohedral form boiling point =1390°C). Gartner (1980) suggests that tellurium might form unstable tellurates in clinkers and end up in the kiln dust or the emissions.

ELEMENTS

IN GROUP WI

(Fluorine, Chlorine, Bromine, lodine) The halogens fluorine, chlorine, bromine, and iodine, are frequently found in kiln raw feed and primary as well as alternative fuels, and therefore play an important role in cement manufacturing. Some halides such as fluorides are also frequently used as mineralizers in clinker production andinlow-temperature manufacturing of belite-rich cements. Mishulovich (1994) addresses halides as catalysts for calcination. Concentration of halogens found in raw materials and fuels is given in Tables 3, 4 and 6.

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

17


et al., 1968, 1985) as a minor element and plays an important role in cement making. In raw feed, fluorine could be up to 0.06%by weight (see Table 3), whereas in limestone and clay/shale it can go upto 940 and 990 ppm respectively (Table 4). Calcium fluoride (CaF2) isalsofrequently added to raw meal as a mineralizer and flux to lower the burning temperature and accelerate the formation of C,S (Klemm et al., 1976, 1979). Miller (1976) has, however, cautioned not to use fluoride beyond 0.2570 to avoid adverse effects on clinker behavior by selectively incorporating it into the aluminates or silicate phases at certain burning temperatures. At lower temperatures, fluoroaluminates (C1lA+CaF,) are formed, which are decomposed at high temperatures to CqA and fluorides. These fluorides are then incorporated into silicates at higher temperatures to form often stable fluorosilicates but their excessive amounts can cause decomposition of alite. Gartner (1980) also reported the formation of alkali fluorides as NaF and KF at higher alkali presence; these fluorides being somewhat volatile (boiling points 1700° and 1500”C respectively) are expected to end up in the fine kiln dust. However, Sprung et al. (1968) reported that between 88’7. to 987. of fluorides are incorporated in the clinker and only a small fraction end up in the kiln dust, probably as CaFz Fluoride emissions were reported low (0.009-1 .42 mg F/Nm3) depending not necessarily on the magnitude of fluoride balance but on the efficiency of the precipitators. Akstinat et al. (1988), reported that fluorides have no adverse effects on the cement production process, and the fluoride cycle does not cause any operational problems like coating, because of their presence in small amounts. However, recent experiences have shown that use of fluoride based compounds can occasionally cause plugging. Gartner (1980) reported that the presence of fluorides

18

600

3oo-

0

40

3-day {r

1

~

20–

0 0

I 1.0

I 0.5

Fluoride

I

1.5 (Yo

2.0

mass)

Figure 8. Effect of fluoride on strength and setting time of high alite cements (Moir, 1983). beyond ()..5~o can cause both operational and quality control problems, which, under certain situations, can be controlled by PzO~addition. Goswami et al. (1991), Bolio-Arceo et al. (1990), and Gilioli et al. (1979), have reported the formation of spurrite (2Cz9CaCO~), and fluor-ellestadite that cause kiln deposits, but the resulting low burning temperatures control the alkali cycle and reduce the alkali-sulfate deposits. Palomo et al. (1985) suggested that 0.2?4. fluoride promotes low temperature formation of aluminates such as fluorinated CIZA,, C,A, and CZAS (gehlenite); however, the final aluminate mineralogy was not significantly affected, as both ferrite and CqA were present at 1250°C and above. Perez Mendez et al. (1986) reported that with the addition of 0.5-1.50/. fluorides, as

CaFz, clinkering reactions were completed in 0.5 hr at 13540C; the clinkers had much of C$ developed, with P-C,S, C,AF, and C,A also present therein. Imlach (1974) observed that fluoraluminate CllAToCaFz, forms at fluorine levels of about 0.5% in clinkers fired below 1320°C or slowly cooled from 1340”C to 12650C. Fluoroaluminate imparts rapid setting to cement pastes compared to the normal cements. According to Aldous (1983), and Shame et al. (1987), the presence of F and Al beyond the threshold level renders C,S a rhombohedral symmetry, which is associated with improved hydraulic properties. Moir (1983) demonstrated that by optimizing the levels of F, alumina, alkalies, and sulfates, the C3S in clinker could be maximized to enhance the setting properties of


cement. Figure 8 shows the relationship between the fluoride addition and compressive strength of cement pastes at various curing ages. An optimum fluoride addition for maximum strength at early ages (24 hours) was 0.27., for later strengths (7 days and 28 days) addition of ().75Y0 were acceptable.

Chlorine As mentioned above, chlorine (Cl) as chlorides is frequently found in limestone, clays and in some cases in both the primary and secondary fuels. In limestone and clay the predominant chloride is sodium chloride (Akstinat et al., 1988). Some coals can contain up to 0.28°/oCl, mainly as rock salt (NaCl). The formation of stable yet volatile alkali chlorides NaCl (boiling temperature= 1413°C) and KC1 (subliming temperature= 1500°C) at clinkering temperature is well known. Both the chlorides volatilize in the burning zone and condense in the cooler parts to form kiln rings or preheater build-ups which impair plant performance. Bhatty (1985) also concluded that agglomeration due to the presence of molten alkali chlorides was one of the major reasons for the build-ups. Cl also enhances the formation of spurrite and sulfospurrite (2C,S.CaSO,). In cases of plants without preheater, the volatile chlorides end up in the kiln dust. In preheater kilns, up to 9%J’ochlorides are recaptured by the incoming feed in the calcining zone (Ritzmann, 1971); the concentration of chloride at that point could be extremely high (>lYo) compared to that of raw feed (-0.017.). Relative volatility of Cl, and other elements in the kiln system is already shown in Figure 5 (Sprung et al., 1984). The wet processing plant and grate preheater may tolerate raw feed with higher chlorides, but the limits primarily depend upon the efficiency of dust collecting and the level of kiln dust recycling. With the advent of the alkali by-pass, the chlorine cycle can be

broken at the most intense point of kiln and the alkali chloride can be conveniently directed to the dust collectors. Otherwise, as reported by Norbom (1973), a total chloride intake of 0.015% (in both raw material and fuel) can result in build-ups in a preheater without a by-pass. Since most of the chlorides are volatile, the amount retained in clinker is extremely small (d.03~0). VOlatile chlorides react readily with alkalies, so that the alkali level in the clinker is often reduced when chloride is present. The combined influence of alkali chloride on cement properties is therefore regarded as insignificant. In some cases, calcium chloride is added to the kiln for the express purpose of increasing alkali volatilization and removal, and result in the production of a low alkali clinker. According to Mishulovich (1994), the addition of calcium chloride and chlorine-containingorganiccompounds at the clinkering stage, accelerated both lime reaction and alkali volatilization. In a preheater klin, the addition of calcium chloride in the burning zone, resulted in 2070 increased production with corresponding fuel saving. In waste-derived fuels such as waste-oils contaminated with chlorides, chlorinated hydrocarbons and scrap tires, the chlorides would occur indifferent compounds at much higher concentrations (Akstinat et al., 1988), and cause serious operational problems even in kilns equipped with bypass. In order to make their use feasible, a larger portion of by-pass dust would have to be discarded to prevent building up a large chloride cycle High chlorides in the raw feed have also been reported to form condensation plumes in the emission stacks in long wet or dry kilns which are difficult to remove at times. Such detached plumes are generally the result of NHAC1 formation. Excessive chlorides can also have a deleterious effect on kiln basic brick lining. Chlorides, particularly CaClz, accelerate the hydration and hardening

of cement paste and increase the very early strength but, at the same time, chloride ions are also known to promote corrosion of steel reinforcing bars in concrete. AliniteCements: The development of less energy intensive “alinite cements” from the CaClz incorporated raw material has generated great interest (Nudelman, 1980). The formula ascribed to the alinite phase is close to 21 CaO”6SiOz”A110q* CaClz with some MgO inclusion (Lecher, 1986). The burning temperature for alinite clinker is between 1000-11 OO”C. The raw mix is composed of 6-2370 CaClz by weight. MgO is added to stabilize the alinite phase at 60-80?40, belite at l&30~o, calcium aluminoat 5-1OYO, and calcium chloride aluminoferrite 2-107. (Bikbaou, 1980). Ftikos et al. (1991) reported that the strength development of alinite cement was comparable to that of regular portland cement.

Bromine With some exceptions, bromine (Br) plays a minor role in cement manufacturing. Bromine occurs only as a minor 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). Bromine has also been detected at measurable levels in some of the fly ashes generated at coal operated power plants. Bromine is volatile and expected to end up instackemissions (Akstinat, 1988). Under oxidation conditions, bromine gas (Br2) would form and end up in emissions. Retention of bromine in clinker is negligible. Alkali bromides can also be found in cement kiln dust. Between 5–10 ppm of bromine was reported in one CKD sample using fly ash as a partial raw feed (Klemm 1995). At higher levels of bromides, the formulation of bromine-alinites analogous to chlorinealinites, as mentioned above, has also been reported by Kurdowski et al.

19

Role of Minor Elements in Cement Mmzufactureand Use

(1987, 1989). Bromine-alinites are much more reactive than the alites (I@rdowski et al, (1989). Kantro (1975) reported that at equivalent concentrations CaBrz is a stronger accelerator for C~Spastes than the chlorides or iodides.

Iodine

11.2 ppm

Ti

Aluminate

r

v Cr Mn co Ni Cu

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

Belite

Aluminoferrite

et al.), and between is found

in coal

I

I

I

I

of the low levels

of io-

t

I

5

01234

Weight

0.8 to (Sprung

1985). Because

Zn

Figure 9. Distribution (Hornain, 1971).

;oo15i

0 0.5 Y.

of transition elements in clinker phases

dine in the feed, the effect on the burn-

ing process is negligible. Iodine salts are volatile in nature and mostly end up in emissions. Conversion of io-

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

dine gas (IJ from iodides is easier than bromides. Their concentration

in clinker is detected at very low levels. There is no literature report on iodine presence in the CKD. The concentration of iodine in CKD is expected to be extreamly low, maybe in the ppb, because of its’ presence in small amounts in the raw materials. CaIz is reported to accelerate C~S pastes though not as effective as bromides or chlorides (Kantro, 1975).

ELEMENTS IN GROUP Vlll (Helium, Neon, Argon, Krypton, Xenon) Helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon (Xc), being inert gases, are not known to impart any noticeable effect on clinker manufacturing or cement hydration properties.

TRANSITION

ELEMENTS

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

20

Clinker Phases Alite Belite Aluminate Ferrite TiOp in Clinker (wt.”A)

Hornain (1971)

Regourd et. al. (1974)

Knofel (1977)

1 2

1 1.7

1 2

0.8

3.3

3

6

10.8

7

0.78

(not reprinted)

1.0

The elements 21-30,39-48, and 57-80 in the periodic table are known as the transition elements. Not all of these elements have been studied in cement manufacturing, but the ones that have been studied in some detail are dealt with in this section. Some of these transition elements are introduced into the clinkering process through the use of spent catalysts as an alumina source.

Yttrium Isomorphismbetweenyttrium (Y) and calcium frequently occurs in natural materials; for instance fluoroapatite, Ca2Ca~(P01)F,can contain up to 10.6% YzO~(Povarennykh, 1966). But presumably in cement raw materials, yttrium occurs only in traces. Yttrium substitutes for Ca in both C~Sand CZS(Boikova, 1986). It yields

both triclinic and monoclinic forms of C~S. In a CZS-Yg(SiOi)~system, the region of homogeneity can exist up to 35% YA(SiOA)~ by weight (Toropov et al., 1962-2). Yttrium chloride is reported to have an accelerating effect on CqS paste when added as an admixture (Kantro, 1975). Since yttrium is unlikely to volatilize at kiln temperature(melting point= 1522°C), it can hardly be expected to concentrate in the kiln dust. It should preferentially become incorporated in clinker.

Titanium Titanium (Ti) as oxide could be present in typical cement raw material at the ().()2-O.4~0level by weight (Bucchi, 1980). Gartner (1980) reported a higher concentration of O.1-


1.0’?4.Ti02 in many raw mixes. Concentrations of TiOz in some of the auxiliary raw materials is even higher. Blast-furnace slag for instance, can contain 1.!7~0TiOz, and the bauxites may have between 28% TiOz by weight. TiOzisarefractory material (boiling point= 2500-3000°C) and is essentially incorporated in clinker. At low levels the effects of Ti on the manufacturing of cement is insignificant (Miller, 1976), higher levels of up to 2% may improve the compressive strength of clinker (Knofel, 1979). Hornain (1971), and Marinho et al. (1984), reported that TiOz is preferentially distributed in ferrite phase. Distribution of other selected transition elements indifferent clinker phases, as determined by Hornain (1971), is also shown in Figure 9. Relative ratios of TiOz distribution in clinker phases as reported by different workers is also given in Table 13 for comparison. Titanium from ilmenite (FeTiOJ additions to kiln feed has been used to produce a patented buff-colored cement. Knofel (1977) observed a sharp reduction in alite with equal gain in the belite phase when Ti02 was increased in the raw mix; the variation in ferrite and aluminate was not significant. Calcium titanate (CaTiOJ is apparently the major phase present in clinker. It was also reported that about 1’ZOTiOz addition in the raw mix reduces the melt temperature by 5O-1OO”C,probably because of a favorable relationship between ionic potentials and the melt viscosities as shown in Figure 10, This relationship was developed by Timashev (1980). It shows that increasing the ionic potential of transition elements in groups of elements with equivalent atomic radii decreases the clinker melt viscosity. Although TiOz enhances the early hydraulicity of alite (Kondo, 1968), the clinkers have shown slow initial setting. However, 1% TiOz clinker 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 to radius ratio, and cation-oxygen bond of transition elements at 1450”C (Timachev, 1980). 3-and 90-day strengths (Knofel, 1977, 1979).

increased the early strength of cement.

Zirconium

Vanadium

Zirconium (Zr)isconcentrated mostly in siliceous ores which can be used as a raw feed component (Miller, 1976). Blaine (1965) reported about 0.5% zirconium, probably in the fully oxidized form of ZrOz, in US. clinkers. Kakali et al. (1990) found no significant change in the burning and cooling conditions for clinker prepared with 0.73-1 .45% ZrzOJ; the principal phases, alite, belite, aluminate, and ferrite, were satisfactorily crystallized. However, ZrzO~ changed the size and shape of alite, while the type of belite crystal was modified. Zr20~ also imparted a noticeable color change in clinker (Kakali, 1988). A significant retarding effect and a subsequent delay in strength for cements prepared with ZrO containing raw mixes was also reported (Kakali et al. , 1989). However, earlier studies by Blaine et al. (1966) indicated that smaller ZrO additions

Vanadium (V) occurs at a measurable level in cement raw material (10-80 ppm inlimestone,98-170 ppm in clay/ shale, and 30-50ppm in coal) (Sprung, 1985). It is also present in fly ash where it tends to concentrate in the finer fractions (Coles, 1979). Fairly high levels of vanadium are also reported in crude oils (Gartner, 1980). In one study, Weisweiler et al, (1990) has reported nearly 800 ppm vanadium in petroleum coke used in cement manufacturing. Ash from petroleum coke also contains very high levels of VzO~ (up to 607.). Because the petroleum coke has a low overall ash content, Moir et al. (1992) found no more than 0.08% VzO~ in clinker produced in modern cement plants that use 50% petroleum coke as a substitute fuel. Use of vanadium is known to decrease the melt viscosity primarily because of its higher ionic potential as

compressive

21


shown in Figure 10. Vanadium is present as VzO~in cement clinker. It concentrates in alite and forms larger crystals. However, according to Hornain (1971), vanadium preferably concentrates in belite rather than alite, as shown in Figure 9. VzO~is unlikely to vaporize at normal kiln temperatures. On the other hand, vanadium present in fuel may not have adequate contact with the reacting mass in the kiln and largely ends up in the kiln dust as suggested by data from Weisweiler et al. (1990). Odler et al. (1980-1) reported that l% V20~ can significantly reduce the free lime in clinker when fired at 1200°C. Xinji et al. (1986) used V20~ for stabilizing B-CZSin clinker apparently by substituting V01-3 for Si014. A concentration of 1.57. V20~ is reported to increase hydraulicity of alite; however, higher concentrations adversely affect the grindability of resulting clinkers. High VzO~levels as found in some crude oils could also deteriorate kiln lining in some cases (Gartner, 1980). V,O, in clinker can also increase sulfate expansion under certain circumstances (Blaine et al., 1966).

Niobium Niobium (Nb) is another element to be found in traces in cement raw materials. Weisweiler et al. (1990) has reported more than 30 ppm niobium in the raw feed of a German plant. Because of the low level presence in the raw mix, niobium would have very little effect either on the clinker formatitm or on the cement hydration properties. Kakali et al. (1990) reported a very feeble effect of Nb+5addition (up to 1.5% by weight) on the mineralogical texture and the viscosity of clinker melts because of its low ionic charge to atomic radius ratio. Cementpastesprepared from these clinkers did not show any noticeable change in their setting or strength properties when compared to regular cement pastes (Kakali et al., 1989).

22

Table 14. Chromium Distribution in Typical Clinker* Phases Containing 0.55YI0 Cr,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 temperature metal (melting point =24680C), it would unlikely concentrate in the kiln dust or in the stack emissions.

Tantalum Tantalum (Ta) is only a trace element in cement raw material. It reported to be present at less than 9 ppm in raw material and 0.3 ppm in the oil coke used as fuel in cement manufacturing (Weisweiler et al., 1990). Since tantalum is present as trace in both the raw feed and fuel, it is unlikely to impart any noticeable effect on the clinker formation and cement use. Weisweiler et al. (1990) have reported 14.3 ppm and 3.3 ppm tantalum respectively in clinker and kiln dust prepared from a raw material containing 8.9 ppm tantalum.

Chromium Chromium (Cr) can be present in raw feed immeasurable quantities. Sprung (1985) has reported up to 16 ppm in limestone, nearly 100 ppm in clay and shales. Coals and used oils may contain up to 80 ppm and 50 ppm Cr respectively. Some of the auxiliary raw materials, such as bauxites, which are used up to 4°/0 in cement manufacturing, may contain between 0.04-0.40/. CrzO~. In addition to that, a proportion of Crcanalsoentercement from the grinding media during raw meal preparation and finished cement grinding, and refractory linings. The presence of Cr in raw materials is known to reduce the viscosity of

clinker melt due to its high ionic charge as is shown in Figure 10. Miller (1976) has reported improved clinker burnability at 1°/0CrzO~addition. Chromium can exist in a number of oxidation states in clinker, the most stable being Cr+3and Cr+b. Their formation is sensitive to the oxygen level in kiln. High oxygen tends to form Cr%compounds as chromates which are readily soluble in water and markedly affect the hydration characteristics of the paste. Reducing conditions favor the formation of Cr+3compounds which are less soluble in mix water. Under oxidation conditions, Cr can also exist as Cr~ and Cr+5in C2S, which can then disproportionate to the more stable Cr+3 and Cr% upon mixing with water (Feng Xiuji, 1988). Johansen (1972) has reported Cr”, Cr-b, and Cr+5 in alite substituting for Si+4.Hornain (1971) reported that Cr preferentially resides in belite followed by ferrite, alite, and aluminates, as shown in Table 14 (see also Figure 9), Although Cr+b can be present in both alite and belite, it is reported to be stabilizing the ~-CzS form (Hornain, 1971, and Kondo, 1963). Subarao et al. (1987) developed an active belite-rich cement from raw feed containing 4-5% CrzOJ by weight. Imlach (1975) used O.11I.qzy. Cr203 in the raw feed as a flux. The resulting cement exhibited improved 8- and 24-hour strengths, but 28-day strengths always decreased. A significant portion of Cr can also enter the finished cement from chrome-rich grinding media (Klemm, 1994). It is reported that the level of


Cr4in ground cement is almost doubled by the use of high-chromium alloy balls during grinding. A number of patents report the use of inorganic reductants to control the Cr+Aleaching from cement. Most of these patents are of European origin and use ferrous sulfate heptahydrate, ammonium-ferrous sulfate, and manganese sulfate during intergrinding to convert Crk to Cr+3. Chromium is known to accelerate the hydration of paste and improve the early strength, and has thus been used to develop high strength cements. Recent studies (Bhatty et al., 1993) have shown that 0.7570 addition of chromium as chromium chloride and nitrate, accelerate paste hydration and result in high initial hydration peaks. The workability and the initial setting times are reduced, but the early strengths (3 da ys) are significant yimproved over the control. The 28- and 90-day strengths are, however, close to those of the control. The addition of insoluble chromium oxide (Cr20~), even up to 1.37., did not significantly affect the hydration or the strength behavior of the pastes. The degree of Cr stabilization in cement matrices as determined by leachability in both these cases was almost 100Yo. Chromium may also contribute to high sulfate expansion, increased 24-hour shrinkage, and reduced autoclave expansions. Although a major portion of chromium is incorporated in clinker, usually tied up in belite, ferrite, or sulfate phases, chromium can be found in the CKD. Between 100-1000 ppm of Cr have been reported in CKD (Lee et al., 1973; Howes et al., 1975), although recent studies (PCA, 1992) have shown only between <0.01-264 ppm in CKDS produced by burning conventional fuels, and between <0.01-299 ppm in CKDS produced by waste derived fuels. Detectable levels of 20.6 mg/sec and 12.5 mg/sec have also been found in kiln emissions using conventional as well as waste fuels respectively (Mantus et al., 1992). In U.S. cement, total chromium is reported to be between 20 and 450 ppm.

Molybdenum Molybdenum (Mo} is potentially an important trace element in lubricating oil (Gartner, 1980). In coal fly ash, MoOS can be as high as 1.5% by weight. Up to 0.05?’o of Mo has been reported incliners (Blaine et al., 1965). Molybdenum, having small radius and a high charge number, is an effective reducer of the clinker melt viscosity as shown in Figure 10. Kakali et al. (1990) reported the formation of large round alite crystals in clinker prepared with up to 1.57. M003 addition, with some modifications in belite. However, cement pastes prepared from these clinkers exhibited no adverse effects on the engineering properties (Kakali et al., 1989).

Tungsten Tungsten (W) is trace metal in raw mix and is expected to appear in traces in the clinker. Very little work has been reported on the effect of tungsten on clinker formation and use. Kakali et al. (1990) noted that the addition of up to 1.5?4.WO~in the raw mix changed the shape of alite crystals, making them bigger and more roundish; the belite formed was of type III and, to some extent, contained secondary dendritic crystallization probably because of excessive Si~ replacement by W%. Dissolution of W% in the melt decreased the viscosity because of its large charge to radius ratio, as is also exhibited in Figure 10. Ivashchenko (1991) reported that addition of W% also improved the granulometric composition of clinker and decreased dusting. Improved hydraulicity was expected because of enhanced activity of ferrite and alite modification in the clinker. However, cement pastes prepared from these clinkers did not show any significant change in the setting or strength properties when compared to theregularones (Kakaliet al., 1989).

Tungsten is a very high temperature melting metal (melting point=3410°C). Since itwill not volatilize at kiln temperatures, its presence in the CKD, or stack emissions, is exceedingly remote<

Manganese Manganese (Mn) inclinkercomesfrom both the primary and auxiliary raw feeds. Limestone can contain up to 1.91’% Mnz03 as the carbonate mineral rhodochrosite, whereas shales and bauxite canhaveup to O.59% and O.37% by weight respectively (Bucchi, 1981). In blast furnace slags, M~O~ can be present up to 1.2% and in coal fly ash up to 1.447. by weight. Cement produced from slags can contain more than l% Mnz03 and usually imparts a brown color to cement (Lea, 1971). The polymorphism of silicate in clinker is affected by the presence of manganese oxides in the raw material. Knofel et al. (1984) reported that the limit of MnzO~ substitution in CJS is approximately 2.2% at 1550°C. At lower concentrations, say -0.1’XO M~O~, single substitution of Si- by Mn+4 takes place, whereas at 2.27. MnzO~concentration, a double substitution of Si4 by Mn4 and Ca+2by Mn+2 is possible. The stabilized CaS polymorph was identified as monoclinic; Gutt and Osborne (1969) reported it to be triclinic. Miller (1976) demonstrated that at low concentrations (<0.7%), Mn stabilizes monoclinic alite, but at high concentration and in the presence of fluoride, triagonal alite with markedly high hydraulicity is formed. Manganese can occur in a number of oxidation states depending upon the burning conditions in the kiln and can impart different colors in clinkers, ranging from reddish-brown to blue. Puertas et al. (1988) have studied the influence of kiln atmosphere on Mn solid solutions in C~S and C2S. It was reported that under reducing conditions isomorphous replacement of Ca+2 by Mn+2 occurs, while in air having higher oxygen level, MnA replaces Si~.

23


According to Knofel et al. (1983) alite content of clinker increases with Mn addition, with maximum alite attained at 0.57. MnOz and 1?4. Mn20~. High Mn content promotes the formation of belite in the silicate phases, but is more preferentially incorporated into the ferrite phase through the formation of “alumino-manganite”, such as “CAAMn” (see Figure 9). This reduces C~A and marginally increases free lime, thus reducing the early cornpressive strength of the pastes. Manganese will not volatilize at kiln temperature (boiling point= 1960°C), and is unlikely to concentrate in the CKD or be found in stack emissions.

Cobalt Cobalt (Co) is present in traces in the raw mix; the maximum reported concentration is 23 ppm COO. It has also been found at much higher levels (up to 1.27~0) in some of the coal fly ashes that could be used as partial cement raw feed (Bucchi, 1981). The bulk of cobalt that is present in the raw mix is incorporated in clinker. The CoO level reported in cement is <130 ppm, but the amounts detected in the alite and belite phases are only in traces as the bulk of cobalt is concentrated in the ferrite phase by replacing Fe3+and forming the “C~ACo” phase (see Figure 9). Cobalt can also give color to cement. Sychev et al. (1964) demonstrated that Co somewhat reduces the hydraulic activity of alite and increases clinker hardness. According to Miller (1976), cobalt increases the water demand and marginally reduces the late strength of cement paste. Cobalt is unlikely to vaporize in the kiln (boiling point= 287@C), thus, concentrations in CKD or in stack gases are expected to be exceedingly small.

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

24

ppm), used oil (3-30 ppm), and petroleum coke (208 ppm). In coal fly ashes, NiOispresentup to 1.9% (Bucchi, 1981). Nickel preferentially concentrates in the ferrite phase, followed by alite, aluminate, and belite as shown in Figure 9 (Hornain, 1971). Between 0.5 to 1.07. nickel stabilizes alite (Rangaro, 1977). NiO substitutes for CaO up to 4 mole 70in alite and stabilizes the monoclinic form (Enculeseu, 1974). This alite modification apparently enhances the l-day and 5-year compressive strength. Miller (1976) reported that water soluble nickel compounds act as accelerators and tend to give high early strengths. Kantro (1975) and Zamorani et al. (1989)) also found NiCl, to be an accelerator for C~S pastes when used as mix solution. Mostly, Ni compounds are nonvolatile, yet, owing to the volatile nature of some compounds, such as NiCO~, nickel could end up in the kiln dust, although recent PCA studies has shown a maximum of only 60 mg/kg Ni in the CKD. The average amount of Ni in cement is 31 mg/kg (PCA, 1992).

Copper Bucchi (1981) has quoted an average of 16 ppm copper oxide (CUO) in the raw mixes, and a <0.13Y0 in coal fly ash, On average, 90 ppm CUO occurs in commercial clinkers Bucchi (1981). Copper preferentially concentrates in the ferrite phase followed by alite, aluminate, and belite (see Figure 9, Hornain, 1971). Miller (1976) reported that under oxidizing conditions, the small amount of copper present asCuO stabilizes alite, whereas under reducing conditions, copper as C~O adversely affects both the alite and belite phase formations. CUO can also function as a flux, as it decreases the melt temperature considerably (Rumyanstev et al., 1968). Odler et al. (1980-1,2) found that 1% CUO addition was effective in reducing free lime at much lower melt temperatures. It may be mentioned that CUO accelerates C3S formation whereas CUZOinhibits it.

Soluble copper salts are retarders and give low heat of hydration (Takahashi et al., 1973, Miller, 1976; Tashiro et al., 1977). The effect is more pronounced ontheC~Aphase (Tashiro et al., 1979). The addition of copper also gives low sulfate expansion in certain cases (Miller, 1976). Copper oxides are volatile at kiln temperature (melting points CUO=1326”C, CUZO=1235”C). As a result, copper has been found up to 500 ppm in some U.S. cement kiln dusts (Howes et al., 1975).

Silver Silver (Ag) is present only in traces (<0.250 ppm) in both the kiln raw material and coal; in coal it may occur as silver sulfides ,or as a complex, Since silver occurs in traces, it is not expected to significantly contribute in the clinkering process. Silver is present at 9.2 ppm in cement; it is reported in CKD at 6 ppm for kiln operated with conventional fuels and at 2.5 ppm for kilns using waste fuels (PCA, 1992).

Zinc Zinc (Zn) is a trace element in the raw mix, reporting 22-24 ppm in limestone, 59-115 ppm in clay or shale, and 16-220 ppm in coal. However, it can be present up to 3,000 ppm in used oil as a potential secondary fuel (see Table 6), or 10,000 ppm in used tires. Its concentration is also reported to be significant in alternative raw materials 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 raw mix typically becomes incorporated in clinker (Sprung et al., 1978; Knofel, 1978). Approximately half of the zinc is distributed in silicates with preference for alite while reducing belite; the other half is distributed into the matrix with preference for the ferrite phase (Knofel, 1978; Tsuboi et al., 1972). According to Hornain (1971)


zinc in clinker is preferentially retained in ferrite followed by alite, aluminate, and belite (Figure 9). ZnO additions accelerate the clinker formation. Alite and CZ(AF) formations increase at the expense of belite and C~A due to ZnO doping (Odler et al., 1980-3). Stevula and Petrovic (1981) prepared a triclinic modification of C,S of the type T1-TI1 from mixtures of 0.75-1.5% ZnO and pure C~S, fired at about 1600”C and slowly cooled. Additions of 3.0 and 4.5y0 ZnO formed rhombohedral C~Swith no free ZnO. Boikova (1986) reported the change in C~S symmetry from triclinic to monoclinic and to rhombohedral with increasing ZnO additions. Up to 1.0’% ZnO in the raw mix decreases free lime considerably (Odler et al., 1980-1,2), retards the hydration, and reduces strengthwhen added in excess of 1.0’%.(Odler et al., 1980-3). Similar observations were reported by Knofel (1978). Miller (1976) suggested the likelihood of reducingZninclinker by preferentially vaporizing it where the liquid phase is low, thus reducing the potentially deleterious effects on cement setting. ZnO as an admixture also imparts a severe retarding effect on cement hydration; early strength is reduced,andthelate strengths (28-days and beyond) are increased. In fact, zinc also increases the late strengths (5-10 years) but decreases the paste shrinkage during the early ages of 1 and 28 days (Miller, 1976). Arliguie et al. (1982,1985, 1990) demonstrated that C~S, C~A, and cement hydration are delayed by the formation of primary zinc hydroxide and its conversion to a crystalline form around the anhydrous grains. Miller (1976) reported the formation of a complex calcium hydroxo-zincate intermediate compound that inhibits C$ hydration. According to Sprunget al. (1978), the volatility of zinc for preheater kiln could be 1O-2OYO.For a multistage preheater kiln, the capture of

ZnO would be more effective and could result in the total incorporation into the clinker. An average of 149 ppm zinc has been reported in the CKD from the U.S. plants using conventional fuel and 150 ppm for those using hazardous waste fuel (CRI, in Mantus, 1992); thecorrespondingzinc levels in the plant emissions are only 2.97 and 1.53 mg/see, respectively.

Cadmium Cadmium (Cd) occurs in traces in the raw materials and fuels. The average amount of Cd in cement has been reported tobe0.34mg/kg(PCA, 1992). Cadmium in the raw feed reacts with the constituent of kiln gas and can form halides or sulfates, both are readily vaporized at peak kiln temperature (Kirchner, 1985). The form of cadmium incorporated in clinker is not known; however, with increasing chloride input in the kiln, the concentration of Cd in clinker is known to decrease. The addition of CdClz in the raw mix has the same effect. In a cyclone preheater kiln, 74-88?4. of the total Cd entering the kiln is incorporated in the clinker as opposed to 2564% for that produced in the grate preheater kilns; the remaining Cd is captured in the kiln dust (Weiswerler et al., 1987). Cadmium is also volatile in nature, although not as volatile as thallium or chlorine. Volatility of cadmium relative to other elements in the kiln feed is shown in Figure 5 (Sprung et al., 1984). CdO is reported to increase the burnability of the clinker by lowering the melt temperatures (Rumyanstev et al., 1968), whereby Cd+2 most likely enters the silicate phases (Ramankulov et al., 1964). Some improvement in burnability of clinker with CdO addition was also observed by Odler et al. (1980-1). Recent studies (Bhattyet al., 1993) have shown that high CdOconcentrations retard the cement hydration, but the strength properties are not affected. Addition of soluble cadmium

salts (CdC12) has no apparent effect on cement hydration. Cd is not leached from the cement pastes when used as CdO and CdC12 admixtures.

Mercury Mercury (Hg) is a trace element. It is highly volatile and vaporizes at much lower temperatures (boiling point=557°C). Mercury is somewhat inert, and very little is known on its interaction in the clinker making process. It is very likely that mercury and its compounds would volatilize in the pre-calcination region at temperatures closer to 400”C and escape with the stack gasses. Total mercury is well below detection limits for most North American cements. Recent studies (Bhatty et al., 1993) have shown that mercury compounds (bothinsolubleHgOand soluble HgC12) impart little effect on the paste hydration and strength properties.

THE RARE EARTHS Elements 51-71 are commonly known as “the rare earths” or “lanthanides”. They are present only as traces in raw materials and cement clinkers. Owing to their presence at extremely low levels, they have not been a subject of extensive studies in cement manufacturing. Since the rare earths have verysimilar properties to one another, it is assumed that they all will have somewhat similar effects on the clinker formation. Boikova et al. (1964, 1966, 1986) and Toropov et al. (1963) observed the substitution of rare earths for Ca in both C$ and CZS. The solid solution of C~S with oxyorthosilicates of lanthanum (La) and scandium (SC) results from the similarities in ionic size, and chemical properties between Ca, La, and SC. Formation of C$ solid solution with gadolinium (Gal), neodymium (Nd), and Erbium (Er) have also been reported. Jantzen et al. (1979) reported

25

!


that nearly 15’7. of Nd/SiaOlz can be dissolved into ~-C2S,which have identical hydraulicity to that of regular ~CZS. La stabilizes all modifications of C~Ssolidsolutions (Stevula et al,, 1981; and Sinclair et al. 1984). Gd gives the triclinic and monoclinic formulations, whereas SCproduces only the triclinic C# solid solutions. Leaching of Nd stabilized in cement pastes is also fairly low. Lanthanum also stabilizes the solid solution of CZS by substituting for Ca+2 (Toropov et aL, 1962-1,-2). Based on the observations on the rare earths, La, Nd, Gd, and Sc, Boikova (1986) assumed thattheremaining rare earths, for having similar chemical and ionic characteristics, would isomorphously substitute for Ca+2 in C~S and CZS. As a result, a larger distribution of rare earths in wastes could be expected in the clinker silicate phases. Rumyantsev et al. (1970) reported that the addition of LazO~in the raw mix accelerates the formation of clinker under laboratory conditions. The engineering properties of the resulting cements were also enhanced when compared to control. LaCl~ accelerates the C$3 hydration when added as admixture (Kantro, 1975). The idea of studying rare earths in cement manufacturing also stemmed from the possibility of using various medium to low level radioactive wastes that frequently contained significant amounts of rare earth elements. Studies by Jantzen et al. (1982), and Boikova (1986) indicated that 203070 loading of radioactive waste cornposed of La20~, UOq, CeOz, and other oxides, give optimum elemental retention in clinker at processing temperaturesof - 11OO”C-12OO”C.Volatilization and activation of radionuclides occured above 1200”C, whereas clinkeringat 1000”C produced incomplete reaction. Jantzenet al. (1979) developed clinkers by incorporating 15-20% by weight of simulated radioactive wastes and firing at about 1200”C. A number

26

of wastes were designed to incorporate varying combinations of Cs*, Cc*, Nd, Sr*; Lu*, Yb’, other Lanthanons; and Sr, Nd, La, Y*, and Ba silicates. The resulting clinkers were tested for their hydraulic reactivities. The clinkers were slow to react, but the ultimate hydration products were primarily stable insoluble calcium silicates hydrates which had reasonable distribution of the radionuclides. Sichov (1968) reported that La,Nd, and Ce all enhanced the hydraulicity of alite. Rare earths are expected to have low volatilities (Klein et al., 1975) and are very unlikely to be found in the kiln dust or in stack emissions.

available only to a limited extent, Although some progress has been made in understanding the role of these elements on clinker properties, interaction between their nature and the major clinker components still needs to be properly understood Use of trace elements as fluxes or mineralizers to enhance the clinkering process is also being realized, yet, understanding of the underlying physico-chemical mechanism and the potential energy saving aspect requires additional input. Now that the technological advances in cement manufacturing are in place, efforts can be directed towards exploring the following aspects of clinker-element interaction:

CONCLUSIONS The effects of almost all the stable minor and trace elements on the production and performance of portland cement have been reported. Emphasis has been given to elements which occur in natural and by product materials used for cement manufacturing. The elements for which detailed information has been obtained are dealt with in an order based on the periodic classification of elements. The volatilities of the elements have 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, cadmium, mercury, and the lanthanides. The review indicates that although certain elements have been studied in detail for their role in the clinkering process and cement properties, data on a number of elements is

1:

Make use of the minor elements present in raw materials and fuels to enhance the clinkering process and the performance of cement.

2:

Make use of the minor elements in conserving energy during clinker production; elements with proven fluxing/mineralizing characteristics could be prime examples.

ACKNOWLEDGMENTS This report (PCA R&D Serial No. 1990) was prepared by Construction Technology Laboratories, Inc. (CTL) with the sponsorship of the Portland Cement Association (PCA Project Index No. 93-01). The author wishes to acknowledge the contributions of W.A. Klemm and F.M, Miller of CTL for carefully reviewing the manuscript. The contents of the report reflect the views of the author who is responsible for the facts and accuracy of the data presented. The contents do not necessarily reflect the views of the Portland Cement Association. *

Cs = Cesium,Ce = Cerium,Sr = Strontium Lu= Lutetium,Yb= Ytterbium,Y=Yttrium

PCA Research and Development Bulletin R13109T

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33


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34

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APPENDIX.

A Summary of Possible Effects of Minor Elements on the Formation of the Resulting Cements

Trace Elements Group

of Clinker and Properties

Affects on Cement Properties

Affects on Clinker Formation

I

Hydrogen

not known

not known

Lithium

forms oxiide, lowers phase temperature

reduces alkali-silica

reactivity

Sodium

lowers melt temperature,

enhances early strength, increases

(ASR) in concrete promotes internal cycle,

causes phase separation, chloride/sulfate Potassium

forms complex


promotes

causes phase separation, chloride/sulfate

ASR susceptibility

compounds internal cycle,

forms complex

enhances early strength, increases ASR susceptibility

compounds

Rubidium

in traces, forms chlorides/sulfates

n.a.’

Cesium

in traces, forms chlorides/sulfates

n.a.

Beryllium

in traces

no measurable

Magnesium

improves

Group

II burnability,

goes into aluminate and

ferrite phases, forms periclase Strontium

small amount favors alite formation, cause belite formation,

effects

cause magnesium

expansion,

soluble salts are corrosive large amounts

also promotes free-

lime expansion,

low hydraulicity,

Iow strength

lime formation Barium

reduces melt temperature,

replaces Ca in all clinker

phases except ferrite, also improves clinker

activates hydraulicity,

improves

strength

mineralogy Group Ill Boron

decomposes C~S, stabilizes pCpS, promotes freelime formation

unpredictable

hydration and

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

Lead

volatile, goes to CKD but some stays in clinker,

retards of hydration, but final

effects at higher levels uncertain

effects

strength reasonable

‘n.a.= information not available

35


APPENDIX.

A Summary of Possible Effects of Minor Elements on the Formation of the Resulting Cements (Continued)

Trace Elements




Group V n.a.’

Nitrogen

NOX emission

Phosphorus

decomposes C~S to C$

Arsenic

volatile, goes to CKD, also incorporates

and free lime, reduces

slows hardening

negative effects of alkalies as low-volatile

calcium arsenates,

in clinker

retards hydration

reduces C~S

formation Antimony

incorporates

n.a.

in clinker as calcium antimonates

under oxidizing conditions

and at high

temperatures Bismuth

n.a.

n.a.

enhances incorporation of metals with high

n.a.

Group VI Oxygen

oxidation states, modifies phases, formation, results in darker clinkers (reducing condition gives lighter clinkers) Sulfur

volatile, promotes formation of complex alkali

Selenium

gives SOZ emissions in traces, volatile, goes to CKD or emissions, also form unstable tellurates

may

n.a.

Tellurium

in traces, volatile, goes to CKD or emissions,

may

n.a.

aids set control, causes sulfate expansion

sulfates, sulfur cycle, causes plug formation,

also form unstable tellurates Group W Fluorine


enhances

C,S formation

and alkali fluorides, excess levels cause operational Chlorine

and strength

problems

volatile, promotes chlorine cycle, causes ring formation,

no adverse effect on hydration,

preheater build-up, can form

accelerator, corrosive to steel 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

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

Group Vlll

‘n.a.= information not available

36


APPENDIX.

A Summary of Possible Effects of Minor Elements on the Formation of the Resulting Cements (Continued)

Trace Elements




Transition Elements Yttrium

substitutes

Titanium

goes in ferrite, decomposes

Ca in C~S and C2S

melt temperature,

accelerator

alite to belite, reduces

gives buff-color cement

slows initial setting, improves strength

Zirconium

modifies alite and belite crystals, imparts color

retarder, low early strength

Vanadium

goes into alite, forms larger crystals, reduces melt

increases hydraulicity,

Niobium

feeble effect

Chromium

reduces melt viscosity, goes largely to belite,

viscosity, free lime, effects grindability,

lining

causes

sulfate expansion little effect

improves grindability,

imparts color

increases early strength, causes

Molybdenum

reduces melt viscosity, forms large roundish alite

sulfate expansion no adverse effect

Tungsten

crystals, modifies belite crystals reduces melt viscosity, forms large roundish alite

no significant effect

crystals, forms type III belite crystals Manganese

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

reduces early strength

imparts reddish brown to blue color Cobalt

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

Nickel

goes to ferrite, replaces Ca in alite and stabilizes

Copper

goes to ferrite, can adversely effect alite and belite

soluble salts as retardes, reduces

Silver

formation, lowers melt temperature, in traces, no known effect

sulfate expansion no known effect

Zinc

enters belite and alite, modifies alite crystals,

increases hardness

hydraulicity and strength

monoclinic form, volatile, reports in CKD

reduces free-lime,

free-lime

improves clinkering

Cadmium

forms volatile halides/sulfates,

Mercury

somewhat

melt temperature,

increases water demand, reduces

enters CKD, reduce:

enhances strength, soluble salts function as accelerators

oxide as admixture is retarder, low early but high late strengths oxide as admixture is retarder

improves burnability

inert, volatile, goes in stack gases

little effect

Lanthanides Scandium

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

Lanthanum

replaces Ca in CaS and C2S, forms solid solution

no known effect

with C~S of triclinic nature accelerates

alite hydration

accelerates

alite hydration

with C&, enhances clinkering Cesium

gets uniformly distributed little volatilization

Neodymium

forms solid solutions with C~S and CZS, replaces

Uranium

gets uniformly distributed

in clinker, have very

Cain C~S and C2S

improves alite hydration, low leaching

in clinker, shows little

n,a. ”

volatilization Gadolinium

forms both triclinic and monoclinic phases with

n.a.

C,S, replaces Ca in C,S and C,S ].a.= information not a

able

37


Index A Alinite cements, 19 bromine alinite, 19,20 chlorine alinite, 19 Alkalies (sodium and potassium), 8 alkali-cycle, 9 alkali sulfates, 9, 16 in clinker, 10 in raw materials, 9 volatilization behavior, 9 Aluminum, 2, 3, 12 Antimony, 5, 7, 8, 15, 26, 35 Aphthitalite, 9, 16 Arcanite, 9, 16 Argon, 20, 26, 36 Arsenic, 5, 6, 7, 8, 13, 14, 26, 36 calcium arsenates, 14 effect of burning conditions, 14 effect on hydration, 14 volatility, 12 ASR (alkali silica reaction), 8,11

B Barium, 5, 7, 8, 11, 12, 26, 35 effect on free lime, 12 Beryllium, 5, 6, 7, 8, 11, 26, 35 BIF (boiler and industrial furnace), 6, 8, 15 Bismuth, 5, 13, 15, 26, 36 Blast furnace slag (B,F. slag), 3, 4, 9, 14,21,23 Boron, 5, 12, 26, 35 effect on free lime, 12 Berates, 12 as mineralizers, 12 effect on hydration, 12 Bromine, 5, 6, 7, 17, 19, 26, 36 bromine alinite, 19

c Cadmium, 4, 5,6,7, 8,20,25, 26, 37 effect on cement setting/strength, 25 effect on melt viscosity, 21 in CKD, 25 volatility, 12, 25 Calcium, 2, 3, 11 Carbon, 2, 13,26, 35 Cement kiln dust (CKD), 9, 13, 19, 22, 23, 24, 25 Cerium (Cc), 4, 26 effect on alite hydration, 26 Chlorine, 2, 5, 6, 7, 17, 19,25, 26, 35 chlorine alinite, 19 chlorine build-ups, 18 chlorine-cycle, 19 sources, 19

38

Chromium, 4, 5, 6, 7,8, 15,20,21,22, 23, 26, 37 burning conditions vs oxidation states of chromium, 22 chromate, 22 effect on hydration, 22, 23 effect on melt viscosity, 21 in clinker 20, 22, 23, 26 stabilizer for l?-C2S, 22 trivalent chromium (Cr+3) and hexavalent chromium (cr+13),22 Cobalt, 5, 19, 20,23, 26, 36 effect on hydration, 23 effect on melt viscosity, 21 in clinker, 20 Copper, 1, 5, 20, 21,24,26, 37 as C$3 accelerator, 24 CUO vs CU20 on alite stabilization, 24 effect on free lime, 24 effect on hydration, 24 effect on melt viscosity, 21 in clinker, 20

D DRE (destructions and removal efficiency), 2

E Erbium (Er), 25

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

H Helium, 20,26, 36 Hydrogen, 7, 35 I Iridium, 5, 12,26, 35 lodine, 5, 6, 7, 17,20,26,

36

K Krypton, 20, 26, 36

L Langbeinite (calcium Iangbeinite), 9, 16 Lanthanides (rare earlhs), 25 Lanthanum, 25, 36 clinker accelerator, 26 effect on belite hydration, 26 Lead, 4, 5,6, 7, 8, 12, 13,26, 35 effect on hydration, 13, as retarder, 13 in CKD, 13 volatility, 12 Lesser elements, 3 Lithium, 5, 7, 8,26, 35 ASR reducer, 8 mineralizer, 8 Lubricating oils (waste oils), 1, 5, 13, 23 Lutetium (Lu), 26

F Fluorine, 5, 6, 7, 14, 17, 18, 26, 36 Fluorides, 17, 18 as mineralizers/fluxes, 17, 18 C& accelerator, 18 effect on hydration, 18 emissions, 18 Fly ash, source of minor elements, 3,4,5,9,11,12,13,14,17, 19, 22,22,24 G Gadolinium (Gal), 25,26 Gallium, 5, 12, 26, 35 Germanium, 5, 13,26, 35 calcium germanate, 13 calcium germanate hydrate, 13 effect on free lime, 13 effect on hydration, 13 Group 1,5, 7, 35 Group 11,5, 11, 35 Group Ill, 5, 12, 35 Group IV, 5, 13, 35 Group V, 5, 13, 36 Group Vl, 5, 15, 36

M Magnesium, 3,4, 5, 11,26, 35 Major Elements, 2 Manganese 5,20,21,23,26, 37 alite formation, 23 calcium alumino manganite, 24 effect on free lime, 23, 24 effect on melt viscosity, 21 substitution in C&, 20, 23 Mercury, 5, 6, 7, 8, 13,20,25, 26,37 volatility, 25 Minor elements (see also trace elements), 1, 2, 4, 5, 6, 7, 26 as mineralizers, 10 effect on melt viscosity, 10 in clinker, 8 relative volatility, 12 sources 4, 5, 6, 7 auxiliary materials (fly ash, blast furnace slag), 6 fuel (coal, used oil), 7 raw meal (limestone, clay/ shale), 6 summary of effects, 35-37


Index Molybdenum, 23,26, 37 effect on melt viscosity, 21

N Neodymium (Nd), 25,26 effect on alite hydration, 26 effect on silicate formation, 25, 26 Neon, 20,26,36 Nickel, 5,6,7, 8, 10, 12,20,21,24,26, 37 as alite stabilizer, 24, effect on melt viscosity, 21 effect on settingtstrength, 23 in CKD, 24 in clinker, 20 mineralizing effect, 10 relative volatility, 12 Niobium, 20,22, 26, 37 Nitrogen, 1,2, 5, 13, 14,26,35 fuel nitrogen, 14 thermal nitrogen, 14 NO,, 2, 14

0 Oxygen, 15,26, 36 oxidation conditions, 22, 23

P PCBS (Polychlorinated biphenyls), 2 Periodic table, 7 Phosphates, 13, 14 chloroapatite, 14 fluoroapatite, 14,20 hydroxyapatite, 14 Phosphorus, 5, 13, 14,26, 37 effect on free lime,14 Potassium (see also alkalies), 7, 8,9, 26, 35 compounds, 9 vapor pressure, 9 Producer gas, 7

R Rare earths (Ianthanides), 25 RCRA (resources conservation and recovery act), 4, 6, 8 Rubidium, 7, 11, 26, 35

s Scandium {SC), 25 Selenium, 5,6,7,8, 17,26,36 in CKD, 17 selenates, 17 volatility, 17 Sewage sludge, 1,14 partial kiln feed, 1 Silicon, 2,3, 13 Silver, 6,7,8,24,26,37 Sodium (see also alkalies), 7,8,9, 10, 26,35 chlorides,9 sulfate,9 Sex,2 Stack emissions gases, 1,2, 13, 14, 17, 19,22,23,24,25,26 Strontium (Sr), 7, 11,26, 35 effect on alite/belite formation, 11 effect on free lime, 11 effect on hydration, 11 Sulfates, 9, 15, 16, 17 alkali sulfates, 9, 15, 16 effect of burning conditions, 9 effect on clinkering, 15, 16 effect on silica modules (SM), 16,17 Sulfur4, 5,6, 12, 15, 16, 17,26, 35, 36 compound formations, 15, 16 in clinker, 17 pyritic sulfur, 17 sulfur-cycle, 15 Syngenite, 16

T Tantalum, 20,22 TCLP (toxicity characteristics leaching procedure), 6,8 Tellurium, 5, 15, 17,26,36 Thallium, 4,5,6,7,8, 12, 13,26, 35 Thenardite, 9 Tin, 5, 13,26,35 Tires, 1,2,4, 5, 13, 19,24 tire derived fuel (TDF), 1, 2 whole tires, tire chips, 1 Titanium, 5,20, 21,26,37 effect on alite/belite formation, 21 effect on melt viscosity, 21 in clinker, 20, 21

Trace elements (see also minor elements), 1, 2,4, 5, 6, 7, 12, 26 summary of effects, 35-37 Transition elements, 20 effect on melt viscosity, 21 in clinker, 20 Tungsten, 20,23,26, 37 effect on alite morphology, 23 effect on melt viscosity, 21

u Uranium (U), 26 v Vanadium, 5,6,7,20,21,26, 37 effect on alite/belite morphology, 22 effect on clinker grindability, 22 effect on free lime, 22 effect on hydration, 22 effect on melt viscosity, 21, 22 ‘relative volatility, 12

x Xenon, 20,26, 36 Y Ytterbium (Yb), 26 Yttrium, 20,26, 37

z Zinc, 5,6, 7,20, 21,24,25,26, 37 as mineralizer, 25 effect on free lime, 25 effect on hydration, 25 retarder, 25 calcium hydroxo zincate, 25 effect on melt viscosity, 21 in CKD, 25 in clinker, 20, 24, 25 in tires, 24 in used oil, 24 relative volatity, 12 Zirconium, 20, 21,26, 37 effect on alite/belite formation, 21 effect on hydration, 21

39


Metric conversion

table

Following are metric conversions of the measurements used in this text. They are based in most cases on the International

1 in

.

1 sq in

= 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

in 1 Sq ft 1 sq ft per gallon 1 gal 1 kip = 1000 Ibf 1 lb 1 lb per cubic yard 1 psf 1 psi No. 4 sieve No. 200 sieve 1 bag of cement (U. S.) 1 bag of cement (Canadian) 1 bag per cubic yard (U. S.)

deg. C

40

System of Units (S1).

25.40 mm

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 la manufacture y comportamiento de cemento portland. Se ha puesto 6nfasis tanto a 10S elementos que forman parte de materials naturales tambi6n como a aquellos elementos que resultan del desperdicio en la manufacture de cemento. Los elementos para 10S cuales se ha obtenido informaci6n detallada, se han tratado de acuerdo con la tabla 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 Development Bulletin RD109T, Portland Cement Association [Papel de Ios Elementos Menores en la Manufacture y Uso del Cemento, 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 Spurenelementen auf die Herstellung und Eigenschaften von Portlandzement berichtet. Besondere Berucksichtigung gilt den Elementen, die in natiirlichen Mineralien sowie in Abfallen vorkommen, die bei der Herstellung von Portlandzement Verwendung finden. Die Elemente, wofur detallierte Informationen gesammelt wurden, werden nach ihrer Rangordnung im chemischen Periodensystem besprochen. Wo notig, wird such die Volatilit&en der Elemente 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 Development Bulletin 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

This publication is intended SOLELY for use by PROFESSIONAL PERSONNEL who are competent to evaluate the significance and limitations of the information provided herein, and who will accept total responsibility for the application of this information. The Portland Cement Association DISCLAIMS any and all RESPONSIBILITY and LIABILITY for the accuracy of and the application of the information contained in this publication to the full extent permitted by law.

Portland Cement Association

II

m

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

An organization of cement manufacturers to improve and extend the uses of portland cement and concrete through market development, engineering, research, education and public affairs work.

Printed in U.S.A.

RD109.O3T

Role of Minor Elements in Cement Manuf and Use

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