Copper and zinc sulfides bioleaching by an extremely thermophilic archaeon in high NaCl concentration

Chloride bioleaching has received attention of several mineral processing industries, particularly in countries where there is scarcity of freshwater and only chloride-containing waters can be used. Therefore, the present work investigated the effect of NaCl (1.0 mol L⁻¹) on the bioleaching of three sulfide minerals: chalcopyrite, bornite, and sphalerite by the thermophilic archaea Sulfolobus acidocaldarius. Chalcopyrite dissolution was only 25 % in the biotic experiment in the absence of chloride, but reached 90 % in the presence of both microorganisms and chloride, while less than 60 % extraction was observed in the abiotic experiment with chloride. In the experiments of bornite bioleaching, 86 % and 77 % of copper were extracted in the biotic and abiotic tests with chloride, respectively. In the absence of NaCl, the biotic and abiotic experiments presented similar copper dissolution (∼35 %). Finally, bioleaching experiments carried out with sphalerite showed zinc extractions below 35 % in all conditions tested. The main contribution from the archaea was its ability to produce low concentrations of ferric ion, which was partially precipitated as jarosite, resulting in low redox potential values (< 450 mV vs. Ag/AgCl), and efficiently bioleached bornite and chalcopyrite. Furthermore, XRD and SEM-EDS analyses demonstrated that sphalerite was practically not leached while bornite was transformed into new copper sulfide phases (CuS and Cu₃FeS₄). Jarosite and elemental sulfur were products of chalcopyrite and bornite bioleaching in the presence of chloride.