Bioleaching of complex zinc sulphides us

This study investigates the bioleaching of complex Pb/Zn ore/concentrate using mesophilic (at 30°C), moderate (at 50°C), and extreme thermophilic (at 70°C) strains of acidophilic bacteria. The effects of bacterial strain, pH, iron precipitation, and external addition of Fe2+ on the extraction of zinc were evaluated. The results have shown that the ore is readily amenable to the selective extraction of zinc and lead using the acidophilic strains of bacteria, with the majority of lead (>98%) reporting to the residue. Moderate thermophiles displayed superior kinetics of dissolution of zinc compared with the other two groups of bacteria. The pH significantly affected the leaching process, controlling bacterial activity and precipitation of ferric iron, mainly as K-jarosite. The K+ released, presumably from the alteration of silicate phases such as K-feldspar present in the ore, appeared to promote the formation of K-jarosite in moderately thermophilic leaching systems. Furthermore, the external addition of iron was shown to be necessary for the bacteria to efficiently drive the extraction of zinc from the bulk concentrate. These findings emphasize the prime importance of ferric iron for the dissolution of zinc and the mineralogical properties of an ore/concentrate to be treated via bioleaching processes.