IMPACT OF UTILIZATION OF COPPER SLAG ON DEVELOPMENT OF CLINKER MINERAL PHASES

P. S. Sharma, S. Vanguri, M.N.K.P. Bolisetty, S. K. Agarwal and S. Harsh

National Council for Cement Building Materials Ballabgarh, Haryana, India

Abstract

The copper oxide and several other copper bearing compounds are known to effect the burning of cement raw mix resulting in reduction in temperature of clinkerization and improving the reactivity of clinker mineral phases. The copper slag, a by-product of non-ferrous industry, contains copper oxide along with other constituent oxides such as Fe2O3 and Al2O3 and therefore has the compatibility for facilitating clinker formation by improving the liquid properties in the development of clinker mineral phases.

Investigations have been carried out on effect of a typical sample of copper slag on clinkerization reaction of cement raw mix. Different raw mixes were designed with copper slag content varying from 2.0 to 3.25%. Burnability studies of the raw mixes were carried out at 1300, 1350, 1400 and 1450 oC with retention time of 20 minutes. It was found that addition of copper slag resulted in reduction of temperature of clinkerization by about 50oC. The quality of clinker from raw mix containing 3% copper slag and burnt at 1400 oC was found to be comparable to the quality of clinker from control raw mix burnt at 1450 oC. The evaluation of clinker for mineralogy and microstructure using X-ray diffraction (XRD) technique and scanning electron microscopy (SEM) indicated polymorphic modification in alite phase which was stabilized from rhombohedral to monoclinic on addition of copper slag in cement raw mix. This could be attributed to incorporation of Cu2+ ions in the structure of alite phase resulting in better reactivity.

Introduction

Cement rotary kiln provides an effective way of harmless treatment and resource utilization for several industrial wastes. Industrial wastes from several processes have substituted for fuels and alternative raw materials in Portland cement production, have been found to contain certain metal oxides which even at low concentration exert a remarkable effect on sintering process of cement raw mixes. Such compounds may modify the temperature of first liquid phase formation, amount of the melt, change the rate of reactions occurring in the solid state within the liquid phase or at the liquid-solid interface, alter the viscosity and surface tension of the melt and affect both crystal growth and morphology. The properties of melt formed during clinkerization in rotary kiln are indeed very important for the formation and growth of alite phase in the clinker (1-11).

Copper slag is a massive metallurgical residue obtained from the transformation of copper ore concentrates into metallic copper in the copper smelters. Slag is disposed in landfills that occupy large areas of land. Their chemical composition is rich in iron, silicon and aluminium oxide, and in the mineralogical composition, the presence of Fayalite and magnetite has beneficial impact by substituting their natural minerals resources in the manufacture of cement clinker. The benefits of such substitution include lower production costs and energy savings. Their use leads to the question of where these trace elements like copper present in such waste materials absorbed in the cement. The present paper investigated the binding tendency of copper element in different phases of cement.

Materials and Experimentation

The sample of copper slag and other raw materials such as limestone, bauxite, red ochre, laterite, gypsum and fine coal ash used in the present investigation were analyzed as per procedures given in Indian Standards (Table 1). The chemical analysis of copper slag sample indicated the presence of 64.00 percent Fe2O3, 25.35 percent SiO2, 1.63 percent CaO, 4.09 percent Al2O3, 7.48 percent gain on ignition and 0.81 percent MgO when tested as per procedure prescribed in Indian Standard IS:4032-1985. The copper slag sample was also analyzed for heavy elements using inductive coupled plasma spectrometer, (ICP model Vista-MPX, made by Varian) (Table 2). X-ray diffraction (XRD) analysis of copper slag sample is shown in Fig.1 which revealed the presence of fayalite, magnetite, boehmite, corundum and gehlenite. Fayalite was identified as major phase while others were found in minor amounts.

Fig. 1: X-Ray Diffractogram of Copper Slag Sample

Laboratory clinker samples CL-1 to CL-5 were prepared by taking the weighed quantities of the above raw materials as per the designed compositions thoroughly blended and ground to achieve the desired fineness in terms of percentage retention on 212 and 90 microns in the range of 4.50 to 5.25 and 22 to 23 percent respectively and firing the raw mix nodules at temperatures of 1300, 1350, 1400 and 1450 OC in laboratory furnace keeping retention time of 20 minutes. The burnt clinker nodules were ground and evaluated for free lime content. The lime saturation factor, silica modulus and alumina modulus was maintained at 0.93 to 0.94, 2.22 to 2.53 and 1.14 to 1.16 respectively incorporating 0, 2.0, 2.5, 3.0 and 3.25 dosage of copper slag. The potential phases C3S, C2S, C3A and C4AF of all the clinker samples CL-1 to CL-5 estimated by Bogue’s equation were found to be in the range of 55.72 to 55.93, 18.85 to 20.97, 5.57 to 5.97 and 12.28 to 13.56 percent (Table 3). The values of liquid content were calculated and found to be in the range of 25.69 to 27.88 percent for the above clinker samples.

Clinker mineral phase transformations were examined by X-ray Diffractometer (XRD) (Rigaku International, Japan, D-Max 2200V/PC, using CuKα radiation, λ= 1.5405Å), scans were run from 2θ = 5 to 65o, with increments of 0.02o and counting time of 1.2 second per step, X-ray tube was operated at an accelerated voltage of 40 kV and current of 30 mA. Scanning electron microscopy studies of the samples were carried out using

JEOL 6510 LV. Secondary electron images were taken to study the sample morphology and microstructure. Energy Dispersive X-ray Analysis (EDXA) was carried out to study the distribution of minor oxides in the clinker mineral phases.

Table 1: Chemical composition of limestone, additives and fuel ash samples

Sample code LOI (%)

CaO (%)

SiO2

(%) Al2O3

(%) Fe2O3

(%) MgO (%)

SO3

(%) Na2O (%)

K2O (%)

Copper slag 7.48** 1.63 25.35 4.09 64.00 0.81 0.00 0.29 0.54 Limestone-1 42.53 52.52 1.88 0.39 0.12 2.18 0.05 0.22 0.04 Limestone-2 35.29 44.58 15.52 1.94 0.74 1.11 0.07 0.22 0.24 Laterite 13.25 4.41 23.85 15.67 39.2 1.36 0 0.21 0.14 Red Ochre 22.21 1.67 11.48 47.77 4.31 0.45 0 0.14 0.02 Bauxite 26.24 1.9 3.96 52.11 3.97 0.36 0 0.17 0.02 Gypsum 17.16* 28.28 12.44# 0.51 0.40 0.74 40.19 0.05 0.04 Coal ash 2.27 9.384 50.68 18.49 4.67 0.64 10.46 0.55 1.06

*Combined water, **gain on ignition, #Silica + Insoluble Residue

Table 2: Heavy Element in Composite Copper slag sample by ICP Percentage

Ba Cd Co Cr Cu Zn Mn Mo Ni Sr 0.020 0.001 0.026 0.052 0.96 0.139 0.021 0.298 0.026 0.009

Table 3: Potential Phase Composition of Clinker Phases Sample

No. Copper slag content, %

Percentage Liquid Content

(%) C3S C2S C3A C4AF

CL-1 0.0 55.93 20.97 5.57 12.28 25.69 CL-2 2.0 55.82 20.67 5.65 12.32 25.82 CL-3 2.5 55.86 20.46 5.65 12.37 25.85 CL-4 3.0 55.82 20.29 5.63 12.49 26.00 CL-5 3.25 55.72 18.85 5.97 13.56 27.88

Results and Discussion

The free lime results indicated comparatively improved burnability characteristics of clinker samples CL-2 to CL-5 containing different doses of copper slag (Table 4). This could be attributed to mineralizing effect of copper oxide present in copper slag sample used (2-6,8). However, compared to control clinker sample, CL-1, the lime assimilation was increased with increase in copper slag content. The clinker samples prepared using 2.0 to 3.0 percent copper slag were found to be with adequate mineral phase developments and was considered to be optimum. The low free lime content (1.06 to 1.18 percent at 1350 oC, 0.31 to 0.54 percent at 1400 oC and 0.24 to 0.30 percent at 1450 oC) in the resultant clinker samples compared to control clinker, CL-1 (1.28, 0.72 and 0.55 at respective temperatures) indicated improved burnability characteristics of raw mix containing copper slag. CuO acts both as mineralizer as well as fluxing agent during clinkerization process. It decreases the melt temperature by at least 50 oC, even for 0.5%

addition in the raw mix and favours the combination of free lime (2,4,6). The development of clinker phases in clinker samples CL-2 to CL-5 fired at 1400 oC (Fig.2) was found comparable to clinker phases in CL-1 fired at 1450 oC (Fig.3). The effect of CuO on stabilization of monoclinic (M3) form of alite was also seen by monitoring peak at the angular positions 2θ=51-53o. The peak of the rhombohedral alite (R) at about 51.65o is almost singlet observed in the control clinker CL-1 which was observed to be converted gradually into monoclinic (M3) alite with well defined doublet (2θ=51.6 & 51.75o) on increasing copper slag content from 0 to 3.25 percent in raw mix (Fig.4). Keeping in view the increased liquid formation with slag content (26.00 percent in CL-4 and 27.88 percent in CL-5), the clinker sample CL-4 containing 3.0 percent copper slag was considered optimum raw mix which was to be burnt at 1400 oC instead of 1450 oC. It was evident from X-ray diffraction analysis of clinker samples CL-2 to CL-5 fired at 1400 oC (Fig.2), that the clinker phases were well-developed with high degree of crystallinity.

Table 4: Free Lime Content in Clinker samples fired at different Temperatures

Clinker samples Free Lime (CaOf), % 1300 oC 1350 oC 1400 oC 1450 oC

CL-1 (control) 3.19 1.28 0.72 0.55 CL-2 2.85 1.18 0.54 0.30 CL-3 2.74 1.14 0.41 0.26 CL-4 2.45 1.06 0.36 0.24 CL-5 2.49 1.06 0.31 0.24

Fig. 2: X-ray Diffractogram of Clinker Samples CL-1 to CL-5 fired at 1400 oC

Fig. 3: X-ray Diffractogram of Control Clinker Sample CL-1 Fired at 1450 oC

Fig.4: Effect of Copper Slag on Development of Alite Phase Polymorph during Clinkerization at 1400 oC

XRD studies of the resultant clinker samples indicated the formation of well developed crystalline clinker phases. Alite, belite, aluminate, ferrite and quartz phases were identified in clinker samples. Polymorphic transformation in alite phase was observed with increasing copper slag content in the raw mix. Quantitative phase analysis of clinker samples indicated the presence of 58 percent alite, 19 percent belite, 4 percent aluminate and 14 percent ferrite in clinker fired at 1400 oC (CL-4-1400). These results indicated

that CuO accelerates the formation of alite phase and decreases the clinkerization temperature. The copper ion incorporated in the clinker phases were found to be in decreasing order of alite > ferrite > aluminate > belite (12-14). Also, CuO accelerates the C3S formation whose crystals appear larger in size, compact, prismatic and angular in shape (2,15). The clinker samples prepared using increasing dose of CuO were examined under a scanning electron microscope and their micrographs are presented in Fig. 5. The portion of the samples presented in these micrographs selected to be representative as far as size and shape of the alite and belite crystals are concerned. The alite grains in the sample CL-4-1400 prepared using 3.0 percent copper slag fired at 1400 oC were found to be developed in larger size as compared to reference sample CL-1-1450 fired at 1450 oC (Fig.5a & 5b). Alite grain size was found to in the range of 4-20 µm in the clinker sample CL-1-1450 and was found to be in the range of 5-30 µm in the sample CL-4-1400. Belite inclusions were observed in alite grains. As the packing of the alite grains was so compact in CL-4-1400, there is little interstitial matter found between the alite grains (Fig.5b). Fig.5e shows the well developed alite grains in CL-4-1400. At 1450 oC, in CL-4-1450 most of the alite grains were fused into one another as shown in Fig. 5c. EDXA studies indicated the presence of CuO predominantly in alite phase.

(a) (b)

(c) (d)

(e)

Fig 5: SEM images of (a) alite and belite grains along with interstitial matter in CL-1-1450 (b) alite and belite grains along with interstitial matter in CL-3-1400 (c) close packed alite and belite grains in CL-4-1400 (d) fused alite grains in CL-4-1450 & (e) well developed alite grains in CL-4-1400.

Conclusions

1. Burnability studies of cement raw mixes containing 2.0-3.25% copper slag showed lowering in clinkerization temperature by about 50 oC and promoted the formation of C3S phase.

2. Addition of copper slag resulted in the increase of alite grain size. Alite grains in the clinker sample prepared using 3.0 percent copper slag fired at 1400 oC were found to be developed in larger size as compared to control sample fired at 1450 oC.

3. Polymorphic transformation of alite from rhombohedral (R) to monoclinic (M3) has been observed with increasing copper slag content in the raw mix

Acknowledgement

This paper is based on the R&D work carried out at National Council for Cement and Building Materials (NCB), Ballabgarh, Haryana, India. This paper is published with kind permission of the Director-General, NCB. The authors express their thanks to Dr. V. P. Chatterjee, Sh S C Sharma and Sh. Sandeep Kumar Gupta (NCB) for their contribution in conducting the experiments.

References

1. Moir GK, Glasser FP.: Mineralizers, modifiers and activators in the clinkering process. Proceedings of the 9th International Congress on the Chemistry of Cement, Delhi, India, Vol. I, 125-52, 1992.

2. Konstantinos G. Kolovos, Stavroula Barafaka, Glykeria Kakali, Sotiris Tsivilis : CuO and ZnO Addition in the Cement Raw Mix - Effect on clinkerizing Process and Cement Hydration and Properties. Ceramics - Silikaty, 49(3), 205-212, 2005.

3. Mohammad M. Ali, Satish K. Agarwal, Ashwani Pahuja: Potential of Copper Slag Utilisation in the Manufacture of Portland cement. Advances in Cement Research, 25(4), 208-216, 2013.

4. Agarwal SK, Chatterjee VP, Sharma PS, Ali MM and Sumathi A: Investigations on mineralizing effect of copper slag on manufacture of OPC. 11th NCB International Seminar on cement and Building Materials, New Delhi, Technical Session VI, 267-269, 2009.

5. Xian-Wei Ma, Hu-Xing Chen, Pei-Ming Wang: Effect of CuO on the formation of Clinker Minerals and the Hydration Properties. Cement and Concrete Research 40, 1681-1687, 2010.

6. G. Kakali, G. Parissakis, D. Bouras ; A Study on the Burnability and the Phase formation of PC Clinker containing Cu oxide. Cement and Concrete Research, 26, 1473-1478, 1996.

7. L. E. Garcia Medina, E. Orrantia Borunda, A. Aquilar Elguezabal : Use of Copper slag in the Manufacture of Cement. Materiales de Construccion, 56(281), 31-40, 2006.

8. K. Kolovos, S. Tsivilis, G. Kakali : The effect of foreign ions on the reactivity of the CaO-SiO2-Al 2O3-Fe2O3 system. Part-II: Cations. Cement and Concrete Research, 32, 463-469, 2002.

9. Taeb A., Faghihi S.: Utilization of Copper slag in cement industry. ZKG International, 55(4), 98-100, 2002.

10. Suhua Ma, Xiaodong Shen, Xueping Gong and Baiqian Zhong : Influence of CuO on the formation and coexistence of CaO.SiO2 and 3CaO.3Al2O3.CaSO4 minerals. Cement and Concrete Research, 36(9), 1784-1787, 2006.

11. V. V. Timashev : The kinetics of clinker formation- the structure and composition of clinker and its phases, Zement-Kalk-Gips 1, I-3/1, 1980.

12. H. Hornain : Sur la repartition des elements de transition et influence sur queques propretes du clinket et du ciment, Revue des Materiaux de Construction, No.671-672, 203-218, 1971.

13. Amira Cipurkovic, Ilvana Trumic, Zorica Hodzic, Vahida Selimbasic and Abdel Djozic. Advances in Applied Science Research, 5(6), 252-259, 2014.

14. Jenwit Krobthong, Manaskorn Rachakornkij and Viboon Sricharoenchaikul : Distributions of Cr, Ni, Cu and Zn in Hazardous Waste Co-Processing in a Pilot-Scale Rotary Cement Kiln. Journal of Applied Sciences, 12: 22-31, 2012.

15. Kolovis K, Tsivilis S., Kakali G.: SEM examination of clinkers containing foreign elements. Cement Concrete Composites, 27, 163, 2005.