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

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.