Optimization of bioleaching and oxidation of gold-bearing pyrite-arsnopyrite ore concentrate in batch mode

Biooxidation of refractory gold-bearing pyrite-arsenopyrite flotation concentrate was optimized and the abundance of predominant groups in the community of thermophilic acidophilic chemolithotrophic microorganisms at various stages of bioleaching was determined. The optimal parameters for growth and leaching/oxidation of the mineral components of the concentrate were pH 1.4–1.8; 47.5°C; and the following salt concentrations in the liquid phase (g/L): K₂HPO₄ · 3H₂O ? 0.53, (NH₄)₂SO₄, 1.6 and MgSO₄ · 7H₂O, 2.5 (or (NH₄)₂SO₄, 1.23; ammophos, 0.41; KOH, 0.1) with 0.03% yeast extract. The optimal conditions resulted in high growth rate, high levels of iron and arsenic leaching, of Fe²⁺ and S^2?/S⁰ oxidation, and predominance of Acidithiobacillus caldus, Sulfobacillus spp., and Ferroplasma spp. in the community.