The effect of microwave irradiations on the leaching of zinc from bulk sulphide concentrates produced from Rampura–Agucha tailings

This work reports the effect of microwave irradiation on extraction of zinc from a bulk sphalerite (ZnS)/pyrrhotite (FeS) concentrate produced by flotation of tailings from the Rampura Agucha Lead–Zinc mines in India. This material could not be treated economically by conventional hydrometallurgy or pyrometallurgical methods due to low zinc concentration. Consequently, microwave assisted leaching was tested. Zinc leaching in sulphuric acid was rapid with > 90% dissolution after 6 min, further irradiation increased the zinc to 96% after 16 min. Iron dissolution increased up to 12 min irradiation and then decreased due to precipitation. Power consumption for > 90% Zn recovery was 0.36 kWh/kg concentrate. The leach solution contained 50–55 g/L zinc and 18–20 g/L iron which could be reduced to 0.54 g/L by jarosite precipitation. The ratio of Zn/Fe leached was 3.4 compared with the ratio of 0.6 for the concentrate showing significant selectivity for zinc over iron using this method.