Pyrite Oxidation by Moderately Thermophilic Microorganisms

摘要

The goal of the present work was to compare the rates of pyrite oxidation by different microorganisms, representatives of the groups predominating in biohydrometallurgical processes. The experiments were conducted in flasks with 100 mL of the medium containing mineral salts, 0.02% of yeast extract, and 2 g of pyrite at 45°C on rotation shaker (200 rpm) for 30 days. Strains Acidithiobacillus caldus MBC-1, Sulfobacillus thermosulfidooxidans VKMV 1269~T, and Acidiplasma sp. MBA-1 were used in the study. Different combinations of the strains were used in the experiments (pure cultures of S. thermosulfidooxidans VKMV 1269~T, Acidiplasma sp. MBA-1, A. caldus MBC-1, as well as the mixed cultures S. thermosulfidooxidans VKMV 1269~T + A. caldus MBC-1, Acidiplasma sp. MBA-1 + A. caldus MBC-1, S. thermosulfidooxidans VKMV 1269~T + Acidiplasma sp. MBA-1). Iron concentrations in the medium were the highest in the variants "S. thermosulfidooxidans VKMV 1269~T + A. caldus MBC-1", "Acidiplasma sp. MBA-1 + A. caldus MBC-1", and "Sb. thermosulfidooxidans VKMV 1269~T + Acidiplasma sp. MBA-1" and achieved 3.8, 3.5, and 3.3 g/L, respectively. Iron concentrations in sterile control as well as in the experiments with pure cultures of Acidiplasma sp. MBA-1 and A. caldus MBC-1 were very low. It demonstrated that in these variants pyrite was almost not oxidized. In the experiment with the pure culture of S. thermosulfidooxidans VKMV 1269~T, the rate of oxidation was high during 10 d of the experiment but then the oxidation activity drastically decreased. The ferric iron concentration achieved a maximum of 1.8 g/L and then decreased, whereas the ferrous iron concentration began to increase. Revealed differences in pyrite oxidation rates can be explained by differences in the physiological properties between the microorganisms. Results of the present work suggest that different groups of microorganisms have different impact in pyrite biooxidation.