Utilisation of by-product jarosite in the manufacture of ordinary Portland cement

Abstract

Jarosite, a residual by-product generated by the zinc industry during the hydrometallurgical process, contains predominantly Fe2O3, SO3 and alkalis with a small amount of ZnO. These constituents are known to contribute significantly in the formation of clinker mineral phases and, therefore, the jarosite could be an effective mineraliser and activator in the manufacture of ordinary Portland cement (OPC) clinker. This paper highlights the effect of the addition of 0·5–2·0% of typical jarosite in cement raw mixes prepared with different grade limestone samples along with other conventional raw materials. The clinker parameters such as LSF, SM and AM were maintained in the range of 0·92, 2·07–2·18 and 1·01–1·14 respectively. Burnability studies conducted at temperatures of 1300, 1350, 1400 and 1450°C with a retention time of 20 min showed an increase in the rate of lime assimilation and rapid formation of clinker mineral phases. The mineral phase developments and microstructures of laboratory clinkers fired at 1400 ± 5°C were found to be adequate in the presence of the optimum dose of 1·5% jarosite and were comparable to the control clinker (without jarosite addition) prepared at 1450 ± 5°C. The physical performance of the OPC sample thus prepared from the above mineralised clinker showed performance comparable to the control cement. As the jarosite contained heavy elements, a leaching study was carried out by immersing 28 d hardened neat cement cubes in 500 ml distilled water over a period of 24 months in air-tight containers. Leachates such as barium, cadmium, cobalt, chromium, copper, manganese, zinc, lead and strontium were found to be in negligible amounts.