Potentials of copper slag utilisation in the manufacture of ordinary Portland cement

Abstract

The addition of copper oxide in cement raw mix is known to improve its burnability, with increase in formation of the alite phase. Copper slag, a by-product of the metallurgical industry, containing copper oxide can therefore be a useful additive in the manufacture of cement, particularly for hard burning raw mixes. This paper presents a study on the effect of addition of 1·5–2·5% of a typical by-product copper slag sample to cement raw mixes prepared from two different limestone samples, with free silica content of 5·52 and 10·97% and average grain sizes of 124 and 175 μm. The clinker parameters such as limestone saturation factor, silica modulus and alumina modulus were in the ranges 0·91–0·92, 2·11–2·29 and 1·0–1·20, respectively. The fineness values of the raw mixes were 3·50–4·20 and 20·80–21·34% retained on 212 and 90 μm sieves, respectively. Burnability studies of these raw mixes were conducted at temperatures of 1300, 1350, 1400 and 1450°C, with retention time of 20 min, and showed increase in the rate of lime assimilation, acceleration in the formation and growth of C3S and lowering in clinkerisation temperature by 50°C. The free silica was found to be completely assimilated at 1400°C in mixes containing copper slag. The mineral phase developments and microstructures of laboratory clinker samples fired at 1400 ± 5°C were comparable to control clinker prepared at 1450 ± 5°C. Physical properties of ordinary Portland cement prepared using this clinker showed performance comparable with control cement. The copper slag contains heavy elements, therefore a leaching study was also conducted by immersing hardened cement pastes in distilled water for 6 months. The leachates, such as barium, copper and chromium, were found to be 0·032, 0·005 and 0·031 ppm, indicating fixation of these elements in the clinker mineral phases.