Abstract
Mesophilic bacteria (Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans, and Leptospirillum ferrooxidans) and moderate thermophiles (Acidithiobacillus caldus and Sulfobacillus thermosulfidooxidans) were used in bioleaching experiments with five select sphalerite samples, which varied in the Zn- and Fe-content. Each sample was leached with and without additional Fe2+ and S0 under mesophilic and moderately thermophilic conditions. A sphalerite sample with a high Fe-content (8.95% Fe) reached a higher yield of zinc bioleaching than those with less iron (0.20–2.04% Fe). The maximum Zn recovery in the mesophilic tests was 82%, obtained with the sample of the highest Fe-content. In the moderately thermophilic experiments, the highest Zn recovery was 32%. The mesophiles increased the oxidation reduction potential due to the oxidation of Fe2+. The formation of jarosite-type precipitates and sulfur on sphalerite surfaces in the mesophilic tests and the formation of sulfur in the moderate thermophilic tests were indicated by analysis with powder X-ray diffraction and scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy.
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