Pyrite oxidation by using Thiobacillus ferrooxidans and Thiobacillus thiooxidans in pure and mixed cultures

Abstract

Pyrite oxidation reaction was carried out using acidophilic microorganisms, Thiobacillus ferrooxidans and Thiobacillus thiooxidans in pure and mixed cultures of these bacteria. Bioleaching experiments in this study were carried out at 30°C and different parameters such as pH, Fe (II) and Fe (III) concentration were studied. The results showed that mixed cultures of T. ferrooxidans and T. thiooxidans enhanced the dissolution of Fe from pyrite, whereas T. thiooxidans alone did not oxidize pyrite. Amount of sulphuric acid produced in mixed cultures of bacteria was higher than pure cultures of each bacterium. Enhancement of Fe (III) ions was also observed with mixed cultures of T. thiooxidans and T. ferrooxidans, while this did not occur in pure cultures of T. ferrooxidans. The presence of iron (III) showed a negative effect on the bacterial iron oxidation rate. In the case of pure cultures of T. ferrooxidans, pyrite was nearly completely oxidized to sulphate because of the capacity of this culture to oxidize both iron (II) ions and sulphuric compounds. Ferric ions competitively inhibited ferrous ion oxidation by the bacteria. Also it was observed that volatilization of Fe (II) from pyrite is highly pH-dependent.