Effect of Organic Carbon Source on Pyrite Biooxidation by Moderately Thermophilic Acidophilic Microorganisms

Abstract

Iron- and sulfur-oxidizing auto-, mixo- and heterotrophic bacteria and archaea dominate in the bioleaching of pyrite from sulfide ores and concentrates both in natural conditions and in biohydrometallurgical processes. The goal of the present work was to study the oxidation of pyrite, the most widespread sulfide mineral, by representatives of microbial groups predominant in biohydrometallurgical processes (mixotrophic iron- and sulfur-oxidizing bacterial strain Sulfobacillus thermosulfidooxidans VKMB1269T, autotrophic sulfur-oxidizing bacterial strain Acidithiobacillus caldus MBC-1, and heterotrophic iron- and sulfur-oxidizing strain of archaea Acidiplasma sp. MBA-1) to evaluate the potential importance of different groups of microorganisms, and to determine the role of interspecies interactions in the population during pyrite oxidation. It was shown that pyrite was most actively leached by the strain of the mixotrophic bacterium S. thermosulfidooxidans VKMB 1269T, in the case when the medium was supplemented with organic substrates. In the experiment with a pure culture of strain VKMV 1269T in a medium with 0.02% yeast extract, 17% of pyrite was leached in 30 days, while in experiments with pure cultures of A. caldus MBC-1 and Acidiplasma sp. MBA-1, less than 1.5% of pyrite were leached. Significantly better results were obtained using mixed cultures of iron-oxidizing strains and A. caldus MBC-1: the rate of pyrite leaching was 26–28%. Moreover, in experiments with a mixed culture of S. thermosulfidooxidans VKMB 1269T and A. caldus MBC-1, addition of an organic carbon source (yeast extract) did not affect the rate of pyrite leaching (25–26%). The highest (38%) leaching rate was in the experiments with a pure culture of S. thermosulfidooxidans VKMV 1269T with periodic addition of yeast extract to the medium: 0.02% at the beginning of the experiment, as well as on days 10 and 20. Thus, in laboratory conditions it was shown that the greatest role in the process of pyrite oxidation was played by the bacterial strain of the genus Sulfobacillus, but its activity was largely dependent on availability of an organic carbon source in the medium, which may be represented by yeast extract or exometabolites of autotrophic bacteria present in the community of microorganisms performing pyrite leaching from sulfide ores and concentrates.