EFFECT OF Acidithiobacillus thiooxidans-CYSTEINE INTERACTIONS ON PYRITE BIOOXIDATION BY Acidithiobacillus ferrooxidans IN THE PRESENCE OF COAL COMPOUNDS

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.