Abstract
Abstract This study evaluated the biooxidation of pyrite contained in a Colombian coal (2.38 mm < particle size < 0.50 mm). The variables were cysteine concentration (0-600 mg/L) and culture type (pure Acidithiobacillus ferrooxidans (ATCC 23270) and a consortium of Acidithiobacillus thiooxidans (ATCC 15494) and Acidithiobacillus ferrooxidans). Pyrite oxidation for the assays without cysteine was 31.14% after 12 days. In the presence of pure A. ferrooxidans, oxidation increased by 8.18% in the assays containing 60 mg Cys/L. In contrast, the counterpart using the consortium exhibited a significant increase in redox potential, which improved oxidation by 28.44%. Since all the assays had a similar kaolinite removal (around 31.45%), and the experiments without cysteine did not show differences in behaviour, the A. thiooxidans-cysteine interactions might have been responsible for increasing Fe3+ regeneration, alleviating the toxic effect of Al3+ ion dissolution, thus improving pyrite oxidation. The consortium-cysteine-coal interactions contrasted with those proposed by other authors for A. ferrooxidans-cysteine-pure pyrite and A. thiooxidans-cysteine, indicating different metabolic pathways in the presence of inorganic and organic coal matrices. On the other hand, the biooxidation rate decreased for both cultures in the presence of 600 mg Cys/L, showing similar inhibition to that reported in the literature.
Highlights
Several researches have evaluated biological oxidation of pyrite for industrial applications because it has many economic and environmental advantages over chemical and physical options
Coal plays an important role in the pyrite oxidation process mediated by A. ferrooxidans, because the interactions of this material with the liquid phase can affect the different pathways involved in the reaction mechanism
Since aluminium is toxic to the microorganism, this affected the regeneration of Fe3+ ions in solution
Summary
Several researches have evaluated biological oxidation of pyrite for industrial applications (e.g., gold extraction, coal biodesulphurisation, bioflotation and metal recovery) because it has many economic and environmental advantages over chemical and physical options. These processes have lower operational costs, are designed and built, and do not require high temperatures or pressures for their operation. Previous studies have shown that cysteine can behave as a corrosive agent and a chemical energy carrier, improving bacterial attack and enhancing oxidation This has only been proved in pure pyrite
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