Influence of sulphur on the clinker phases IThe influence of SO CEMENT CHEMISTRY PDF

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CEMENT CHEMISTRY I The influence of SO3 by Sayed Horkoss, Roger Lteif During the past years, the usage of high-sulphur fuel in the cement kilns and Toufic Rizk, University of has gained ground. This change has increased the sulphate levels in Saint Joseph, Lebanon Portland cement clinker, which affe...

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Influence of sulphur on the clinker phases IThe influence of SO CEMENT CHEMISTRY Roger Lteif

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CEMENT CHEMISTRY

I The influence of SO3 by Sayed Horkoss, Roger Lteif and Toufic Rizk, University of Saint Joseph, Lebanon

During the past years, the usage of high-sulphur fuel in the cement kilns has gained ground. This change has increased the sulphate levels in Portland cement clinker, which affects the microstructure of the clinker. In the literature the influence of sulphate on the silicate phases has been documented since 1968, but its effect on the C3A is still not that clear.

T

15, 16

he form and distribution of sulphate in the clinker is not only affected by the total percentage of SO3 in the clinker but also by the ratio of SO3/alkali.9 As long as this ratio is low, the sulphate is present mainly as acranite (K2SO4) and aphtihitalite (K3Na(SO4)2).13 Increasing the ratio will lead to decreased percentages of both previous phases and an increased percentage of calcium langbeinite (Ca2K2(SO4)3)13. In an extremely high ratio of SO3/alkali and SO3 content, the anhydrite (CaSO4) has been detected in a very particular clinker.7, 5, 9, 20 In addition to the above sulphate phases, the sulphate is found in the major clinker phases, principally in alite and belite.19 The concentration in belite is four to five times that in alite.19

Influence of sulphur on the clinker phases Minor or trace components derived from raw meal, fuel, and refractory can affect the reactions of the clinker formation. Eg, moderate sulphate amounts in the raw meal accelerate the clinkering process by reducing the formed melt viscosity.15 The SO3 is present at the clinkering temperature in a separate liquid phase, immiscible with the main clinker liquid. During cooling, some redistribution of alkali cations and sulphate ions between liquids may be expected to occur, the sulphate finally solidify below 900°C.18

Influence of sulphur on silicate phases alite (C3S) and belite (C2S) Sulphate affects the C3S phase from both sides: quantity and size. Moreover, it will influence C2S reactivity and quantity. Sulphates stabilise C2S crystals, and lead to a decreased amount of C3S in the clinker.6 This conclusion was assured by many investigations carried out later. 12,

82 ICR AUGUST 2009

The stabilisation of C2S is due to the reduction in the viscosity and surface tension of the liquid.4 The infiltration of SO3 will improve the reactivity of C2S.2 Alite crystal structure is expanded by replacing SiO2 with up to 1.5 per cent Al2O3 and 0.5 per cent SO3.2 Strunge et al have reported that the alite crystal size grows by a factor of three when the percentage of SO3 increases from 0 to 2.6 per cent.17 In another study, the alite size is related to bulk clinker SO3 in the following linear equation: The median long diameter Y of alite = 45 X +20 where X = SO3 (0.09 to 1.1 per cent) in a clinker.3

Influence of sulphur on aluminates C3A The quantity of aluminates is affected by many parameters including the kiln atmosphere.11 In the literature we found a contradiction in the influence of SO3 on the amount of aluminates. • First opinion In the absence of sulphate, one of the forms of sodium oxide Na2O in the clinker is the Na2O.8CaO.3AL2O3. In the presence of sulphate, this compound is unstable at clinkering temperature, it will react with SO3 to produce Na2SO4 and C3A.14 Increasing the amount of SO3 will lead to raised amount of C3A in the clinker – this was also observed in 1990 by Hamou and Sarker in their study.8 • Second opinion The percentage of C3A is not affected by the level of SO3 in the clinker.10, 16 • Third opinion Increasing the amount of SO3 in the clinker (mineralisation) decreases the percentages of C3A, as the aluminum atoms are to a higher degree incorporated in the silicate phases.1

Project and methodology Based on the above contradiction we

started our investigation to detect the influence of SO3 on the percentages of C3A using the available technology. The clinker samples were selected from different kilns, different burning conditions and different SO3 and MgO percentages. Two factors were fixed: the theoretical percentages of C3A (2.65*Al2O3 – 1.692* Fe2O3) was fixed between 5-6 per cent and the percentages of alkalis (Na2O and K2O) in the lower levels. For the chemical analysis, the ARL 9800, calibrated with NIST standards, and the Claiss machine for sample preparation at the Cimenterie Nationale Laboratory (CNL) were used. For the percentages of C3A two XRD methods for the determination of the clinker phases were used. The first was the ARL9800 with XRD at CNL, calibrated with special NIST standard for phases in addition to many samples analysed in references laboratories. The second is the XRD using Rietveld method in Titan’s R&D Center, Greece. In addition to the XRD methods, the optic microscope (ZEISS Axioskop 40) technique based on ASTM C1356 was utilised. The sample preparation was done by Struers TegraPol-15 and TegraForce-1, and the etching of the samples was done by Nital (99ml isopropyl-alcohol + 1ml concentrated HNO3) at CNL.

Results and discussion The clinker samples were selected from different clinker burning conditions (large fluctuations in the free lime). The parasite oxides such as P2O5 and TiO2 were fixed to avoid any interaction. The percentages of C3A were measured with the XRD of ARL 9800 (see Table 1). The results in Table 1 show a big influence of the SO3 percentages on the amount of C3A in the clinker. In all

CEMENT CHEMISTRY

Table 1: chemical and mineralogical composition of the clinker samples

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

LOI

SiO2

CaO

Al2O3 Fe2O3 SO3

MgO

Na2O

K 2O

TiO2

P2O5

Free lime

C3A calcul.

C3A measured by ARL

0.11 0.21 0.12 0.28 0.37 0.49 0.22 0.18 0.36 0.14 0.42 0.46 0.42 0.44 0.26 0.36 0.44 0.43 0.29 0.07 0.14 0.06 0.17 0.23 0.07 0.41 0.39 0.07 0.32 0.28

21.17 20.92 20.33 21.05 21.29 20.16 21.37 20.39 20.27 20.05 20.13 20.38 20.41 20.29 20.48 20.66 20.32 20.33 20.27 20.28 20.48 20.22 20.79 20.24 20.81 20.17 20.46 20.71 20.30 20.45

65.30 65.76 65.63 64.93 65.39 65.66 65.40 65.78 65.74 66.12 66.03 65.93 65.99 66.49 65.90 65.85 66.63 65.97 65.09 65.85 66.18 66.89 67.22 67.54 67.88 66.55 66.57 66.09 65.76 65.52

4.35 4.37 4.49 4.51 4.44 4.55 4.57 4.59 4.49 4.53 4.53 4.50 4.52 4.53 4.55 4.42 4.52 4.50 4.53 4.46 4.46 4.29 4.74 4.34 4.46 4.41 4.63 4.59 4.31 4.44

1.41 1.41 1.41 1.39 1.39 1.44 1.39 1.42 1.40 1.44 1.40 1.41 1.38 1.40 1.41 1.37 1.41 1.38 1.39 1.39 1.40 1.41 1.03 1.26 1.29 1.27 1.42 1.48 1.43 1.47

0.05 0.05 0.05 0.05 0.05 0.04 0.03 0.04 0.04 0.06 0.13 0.06 0.05 0.04 0.07 0.05 0.13 0.05 0.12 0.03 0.04 0.05 0.03 0.04 0.05 0.07 0.05 0.07 0.05 0.04

0.36 0.35 0.36 0.38 0.39 0.36 0.33 0.35 0.36 0.36 0.41 0.36 0.37 0.36 0.35 0.34 0.38 0.36 0.41 0.35 0.36 0.30 0.20 0.26 0.24 0.36 0.33 0.35 0.37 0.37

0.39 0.39 0.40 0.41 0.40 0.40 0.43 0.42 0.41 0.42 0.43 0.40 0.43 0.43 0.41 0.40 0.43 0.43 0.43 0.42 0.41 0.39 0.46 0.40 0.40 0.41 0.43 0.43 0.39 0.40

0.59 0.59 0.58 0.58 0.58 0.58 0.56 0.57 0.57 0.59 0.58 0.58 0.58 0.57 0.61 0.58 0.57 0.58 0.57 0.57 0.57 0.55 0.55 0.52 0.52 0.47 0.49 0.57 0.57 0.57

1.46 1.40 2.58 1.55 1.42 2.65 1.56 1.80 2.55 2.76 2.44 3.06 1.90 2.80 3.15 1.77 2.37 1.36 1.20 1.64 1.70 0.82 0.79 1.76 0.46 2.23 1.06 1.56 2.41 2.97

5.50 5.44 5.40 5.91 5.83 5.64 5.44 5.68 5.50 5.57 5.56 5.58 5.57 5.54 5.70 5.57 5.46 5.43 5.41 5.24 5.34 5.07 5.79 5.11 5.32 5.14 5.37 5.53 5.03 5.27

2.15 1.91 2.24 2.07 2.07 2.06 2.33 2.12 2.16 2.04 2.29 2.04 2.30 2.14 2.25 1.99 2.52 2.13 2.12 1.97 2.11 3.12 4.19 2.77 3.27 2.58 3.00 2.24 1.95 1.94

samples the measured percentages of C3A were lower than the calculated. The sample with the lower percentage of SO3 (0.65) contains the higher percentage of C3A (4.19). When the percentage of SO3 exceeds 1.5 per cent, the amount of C3A became around two per cent. The correlation between the amount of C3A and the total percentages of SO3 in the clinker was not linear – it is possibly related to the fact that the incorporation of SO3 and Al2O3 in the silicate phases (C2S & C3S) is limited. To assure the above results, parts of the samples were sent to the R&D Center at Titan, Greece, to be tested by XRD Rietveld methods. The tendency of the results found in Greece by Rietveld method (see Table 2

3.56 3.63 3.84 3.57 3.51 3.79 3.94 3.83 3.78 3.80 3.81 3.75 3.79 3.82 3.76 3.63 3.85 3.84 3.90 3.89 3.83 3.72 4.00 3.78 3.84 3.87 4.08 3.92 3.78 3.84

2.00 2.05 2.19 2.10 2.14 1.92 2.03 2.05 2.09 2.06 2.30 2.00 1.87 1.78 1.79 1.88 1.43 1.91 2.61 2.02 1.82 1.51 0.65 1.01 0.70 1.77 0.87 1.91 2.56 1.99

and Figure 1) were comparable with that found by the ARL 9800, the deviation between both methods was acceptable. In order to get better information we did an investigation using the microscope technique. The C3A was detected only on the sample with low SO3 especially sample number 23, as Figure 2 on the next page demonstrates. In the other samples, especially those with over two per cent SO3, the C3A phases were not detected and the colour of the liquid phases became more reflected (Figure 3). The difficulty of C3A crystal detection, when the C3A percentages dropped down less than three per cent, is perhaps the result of the fine size of the C3A crystals in the interstitial material, this could be the results of their microscopic identification limitation.

Conclusion The SO3 in the clinker with low alkali decreased the percentages of C3A. The correlation is not linear which could be due to the influence of several parameters. With calculated C3A between 5-6 per cent the real amount of C3A dropped to around two per cent, when the total clinker SO3 exceeds 1.5 per cent. This finding was also supported by an optical microscope. In the low alkali clinker, increasing the percentages of SO3 will reduce the amount of C3A.This could be due to the high incorporation of aluminum and sulphur in the solid phases. This incorporation is limited at certain level.

References 1

BORGHOLM, H E and JONS, E AUGUST 2009 ICR 83

CEMENT CHEMISTRY

Table 2: Comparison between the C3A results

1 2 6 10 13 15 17 23 24 29

C3A measured by ARL

C3A measured by Rietveld

C3A calculated

2.15 1.91 2.06 2.04 2.30 2.25 2.52 4.19 2.77 1.95

1.60 1.20 1.30 2.30 1.70 2.00 1.90 4.25 3.00 1.30

5.50 5.44 5.64 5.57 5.57 5.70 5.46 5.79 5.11 5.03

S (2001) Production of mineralised clinker. Lecture 6:10. International Cement Seminar, FLSmidth. 2 BORGHOLM, HANS ERIK (1996) Better but How. In: International Cement Review, June, p66-68. 3 CAMPBELL, DONALD (1999) Microscopical Examination and Interpretation of Portland cement and Clinker. Second edition. Portland Cement Association. 4 CLARK, MICHAEL (2003) Petcoke and Nodulisation. In: International Cement Review, April, p39. 5 FLAMENT, G (1992) Burning 100%

Figure 2: clinker with 0.65 per cent SO3

Figure 3: clinker with 2.05 per cent SO3 84 ICR AUGUST 2009

Figure 1: comparison of C3A percentages calculated and measured

Petroleum Coke with high sulphur– low Alkali raw meal in a 5200t/day Precalciner Kiln, Compagnie des Ciments Belges, p327-351. 6 GUTT, W and SMITH, M A (1968) Studies of the Role of Calcium Sulfate in the manufacture of Portland cement clinker. In: Transactions of the British Ceramic Society, Vol 67, No 10, p487510. 7 GARTNER, E M and TANG, F J (1987) Formation and properties of high sulphate Portland cement clinkers. In: Cemento, Vol 84 , p141-165. 8 HAMOU, A T and SARKAR, S (1990) The influence of varying sulfur content on the microstructure of commercial clinkers and the properties of cement. In: World Cement, September, p389393. 9 HERFORT D, SOERENSEN, J and COUTHARD, E (1997) Mineralogy of Sulfate Rich Clinker and the Potential for Internal Sulfate Attack. In: World Cement Research and Development. May, p77-85. 10 KNÖFEL, D and SPOHN, E (1969) Der quantitative Phasengehalt in Portlandzementklinkern. In: Zement, Kalk, Gips, No 10, p471-476. 11 LOCHER, F W, RICHARTZ, W, SPRUNG, S and SYLLA, H M (1982) Erstarren von Zement, Teil II1: Einfluß der Klinkerherstellung. In: Zement, Kalk, Gips, No 12, p669-676. 12 MORANVILLE-REGOURD, M and BOLKOVA, A I (1992) Chemistry structure, Properties and quality of clinker. 9th International congress of the Chemistry of Cement, New Delhi, Vol 1, p3-45.

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MICHAUD, V and SUDERMAN, R W (1999) Anhydride in high sulfur trioxide (SO3)/alkali clinker: dissolution kinetics and influence on concrete durability. In: Cement, Concrete and Aggregate, ASTM Journal, Vol 21, p196-201. 14 NEWKIRK, TERRY (1951) Effect of SO3 on the Alkali Compounds of Portland Cement Clinker. In: Journal of Research of the National Bureau of Standards, Vol 47, No 5, p349-356. 15 OLDER, I and ZHANG, H (1996) Investigation on high SO3 Portland cement clinkers. In: World Cement Research and Development, p73-77. 16 STRUNGE, J, KNÖFEL, D and DREIZLER, I (1985) Einflusse der alkaline und des Sulfates unter Berucksichtigung des Silicatmoduls auf die Zementeigenschaften. In: Zement, Kalk, Gips, Teil II, No 8, p441-450. 17 STRUNGE, J, KNÖFEL, D and DREIZLER, I (1990) Zusammenfassende Betrachtungen. In: Zement, Kalk, Gips, Teil IV, No 4, p199-208. 18 TAYLOR H F W (1998) Cement Chemistry. Second edition. Thomas Telford Services. 19 TAYLOR H F W (1999) Distribution of sulfate between phases in Portland cement clinkers. In: Cement and Concrete Research, No 29, p11731179. 20 TWOMEY, C, BIRKINSHAW, C and BREEN, S (2004) The identification of sulfur containing phases present in cement clinker manufactured using a high sulfur petroleum coke fuel. In: Journal of Chemical Technology and Biotechnology, Society of chemical industry, No 79, p486-490. _________ I...