Abstract
Fundamental investigations were made on the oxidation of pyrite and consequent dissolution of iron by pure and mixed cultures of Thiobacillus ferrooxidans and Thiobacillus thiooxidans. The release of iron from pyrite was remarkably enhanced with large inocula above ca. 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. Furthermore, 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 iron oxidation ratios (Fe3+/total Fe) above 90% were maintained, coincident with the enhanced release of iron from pyrite. Contrarily, in the absence of T. ferrooxidans, a major portion of iron was in the ferrous form and iron release was not promoted. Thus, it was thought that T. ferrooxidans contributes to the oxidation of pyrite through the regeneration reaction of ferric iron.
