Bacterial leaching of a sulfide ore by Thiobacillus ferrooxidans and Thiobacillus thiooxidans: I. Shake flask studies

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Abstract
Bacterial leaching of a sulfide ore containing pyrite, chalcopyrite, and sphalerite was studied in shake flask experiments using Thiobacillus ferrooxidans and Thiobacillus thiooxidans strains isolated from mine sites. The Fe2+grown T. ferrooxidans isolates solubilized sphalerite preferentially over chalcopyrite leaching 7–10% Cu, 68–76% Zn, and 10–22% Fe from the ore in 18 days. The sulfur grown T. thiooxidans isolates leached Zn much more slowly and very little Fe, with a Cu–Zn extraction ratio twice the value obtained with T. ferrooxidans. The ore adapted T. ferrooxidans started solubilizing Cu and Zn without a lag period. The ore-adapted T. thiooxidans extracted Cu as well as T. ferrooxidans, but the extraction of Zn or Fe was still much slower in the low-phosphate medium, while in the high-phosphate medium it approached the value obtained with T. ferrooxidans. A high Cu–Zn extraction ratio of 0.34 was obtained with T. thiooxidans in the low phosphate medium. In the mixed-culture experiments with T. ferrooxidans and T. thiooxidans, the culture behaved as T. thiooxidans in the low-phosphate medium with a higher Cu–Zn extraction ratio and as T. ferrooxidans in the high-phosphate medium with a lower Cu–Zn extraction ratio. It is concluded that T. ferrooxidans and T. thiooxidans solubilize sulfide minerals by different mechanisms.

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