Response of thermophiles to the simultaneous addition of sulfur and ferric ion to enhance the bioleaching of chalcopyrite

Abstract

Previous studies identifying Fe 3+ as the main oxidizing agent in CuFeS 2 bioleaching suggests that if the precipitation of additional Fe 3+ could be prevented, the Cu extraction yields should be enhanced. In this respect, the acid-generating nature of the biologically mediated oxidation of additional S 0 to H 2SO 4 should theoretically serve as a pH regulator as well as biomass generator. This should prevent the precipitation of Fe 3+ and attenuate the biomass reduction caused by the inhibitory effect of high Fe 3+ concentrations. To prove the former hypothesis, three thermophile strains were employed for bioleaching of chalcopyrite under various additional S 0 and Fe 3+ concentrations. The hypotheses about additional S 0 application were fully confirmed; the addition of S 0 alone enhanced the leaching rates with A. brierleyi and M. sedula in media at initial pH 2. Although higher initial leaching rates were obtained with additional Fe 3+, its role as the main leaching factor is questioned; leaching with thermophiles appears to depend on the availability of protons and ORP rather than on the prevention of Fe 3+ precipitation. Additional S 0 in media with high Fe 3+ concentrations has shown the best improvements in the case of bioleaching with A. brierleyi, whereas improvements in bioleaching with M. sedula and S. metallicus were less notable.