Bacterial pyrite oxidation I. The effect of pure and mixed cultures of Thiobacillus ferrooxidans and Thiobacillus thiooxidans on release of iron.

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Abstract
The oxidation of pyrite and consequent dissolution of Fe by pure and mixed cultures of T. ferrooxidans and T. thiooxidans was studied. The release of Fe from pyrite was remarkably enhanced with large inocula above .apprx. 109 cells per flask (or 1% pulp density) of 2-day (active) cultures of T. ferrooxidans, but not with inoculum of 108 cells or less. A phenomenon was observed that the enhanced oxidation of pyrite always proceeded with the coexistence of a 108 cells or less inoculum of T. ferrooxidans and T. thiooxidans incapable of oxidizing pyrite. During the bacterial oxidation of pyrite, high Fe oxidation ratios (Fe3+/total Fe) above 90% were maintained, coincident with the enhanced release of Fe from pyrite. In the absence of T. ferrooxidans, a major portion of Fe was in the Fe2+ form and Fe- release was not promoted. T. ferrooxidans apparently contributes to the oxidation of pyrite through the regeneration reaction of Fe3+.