Bio-Oxidation Process of a Polymetallic Sulfide Mineral Concentrate for Silver Recovery

In this research, the bio-oxidative capacity of three acidophilic bacterial strains (Acidithiobacillus thiooxidans, Leptospirillum ferriphilum, and an unidentified native consortium) are analyzed through the dissolution of cyanicidal species in a polymetallic sulfide mineral mainly composed of pyrite, quartz, sphalerite, and chalcocite. The main objective is the reduction in the amount of sodium cyanide used for the recovery of Au and Ag for the improvement of economic and environmental benefits in the processing of these minerals. Additionally, through a 23 factorial experimental design, the effect of pH and pulp density (%) on bio-oxidation is evaluated. The results reveal that the bio-oxidation process of the mineral sulfide concentrate has been favored at low pH values and pulp density, favoring Cu species above all dissolution, which form stable complexes with cyanide, leading to excessive cyanide consumption. Therefore, at pH = 1.0 and pulp density of 10%, the catalytic activity of Acidithiobacillus thiooxidans achieves 73.30% Cu, 19.92% Pb, 57.37% Zn, and 25.17% Fe dissolution at the flask level and 83.18% Cu, 12.18% Pb, 55.36% Zn, and 40.98% Fe dissolution at the bioreactor level, allowing the dissolution of 89.5% and 80.4% of Au and Ag, respectively.