Pyrrhotite Biooxidation by Moderately Thermophilic Acidophilic Microorganisms
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Pyrrhotite Biooxidation by Moderately Thermophilic Acidophilic Microorganisms A. G. Bulaev* Winogradsky Institute of Microbiology, Research Center of Biotechnology, Russian Academy of Sciences, Moscow, 119071 Russia *e-mail: [email protected] Received April 6, 2020; revised May 2, 2020; accepted May 29, 2020
Abstract—The goal of the present work was to study the oxidation of sulfide mineral pyrrhotite by members of microbial groups predominant in biohydrometallurgical processes (mixotrophic iron- and sulfur-oxidizing bacterium Sulfobacillus thermosulfidooxidans strain VKMV 1269T, autotrophic sulfur-oxidizing bacterium Acidithiobacillus caldus strain MBC-1, and heterotrophic iron- and sulfur-oxidizing archaeon Acidiplasma sp. strain MBA-1) to evaluate the role of microorganisms with different physiological properties in the leaching of this mineral. It was shown that pyrrhotite was most actively leached by the sulfur-oxidizing strain Acidithiobacillus caldus MBC-1, as well as by mixed cultures in which this strain was present: S. thermosulfidooxidans VKMV 1269T + A. caldus MBC-1 and Acidiplasma sp. MBA-1 + A. caldus MBC-1. These cultures leached 70, 43, and 60% of pyrrhotite, respectively, after 30 days of the experiment. In experiments with pure cultures S. thermosulfidooxidans VKMV 1269T, Acidiplasma sp. MBA-1 and a mixed culture S. thermosulfidooxidans VKMV 1269T + Acidiplasma sp. MBA-1, the rates of pyrrhotite leaching were significantly lower: 29, 37 and 30%, respectively. An experiment on sulfur biooxidation by pure cultures of the studied microorganisms demonstrated that A. caldus strain MBC-1 was the most active sulfur oxidizer. Thus, it was shown that the bioleaching of pyrrhotite was carried out mainly by sulfur-oxidizing microorganisms, with sulfur biooxidation as the most important process. Active biooxidation of the Fe2+ ion by iron-oxidizing microorganisms did not increase activity of pyrrhotite oxidation, but, on the contrary, led to inhibition of pyrrhotite leaching. Thus, active biooxidation of sulfur, which is formed during the leaching of pyrrhotite, was a factor determining the leaching rate for this sulfide mineral. Keywords: biohydrometallurgy, pyrrhotite, acidophilic microorganisms, sulfur and iron biooxidation, Sulfobacillus, Acidiplasma, Acidithiobacillus DOI: 10.1134/S0026261720050057
The mechanisms of biooxidation of various sulfide minerals by acidophilic iron- and sulfur-oxidizing microorganisms have been actively studied for several decades, since the processes of sulfide minerals biooxidation are the basis for biohydrometallurgical technologies (Johnson, 2014; Mahmoud et al., 2017). It was shown that differences in the structure of sulfide minerals lead to differences in biooxidation mechanisms. Pyrite (the most widespread sulfide mineral), molybdenite, and tungstenite are leached via the thiosulfate mechanism, in which thiosulfate is the main intermediate oxidized to sulfate, while sulfur is a byproduct (Schippers et al., 1996; Sand et al., 2001). Most other sul
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