Bioleaching of a complex sulphide ore with moderate thermophilic and extreme thermophilic microorganisms

Abstract

Biooxidation of a fine-grained, complex zinc and gold-containing sulphide ore has been performed in a series of experiments at bench scale with 201 leaching volume in a series of three continuously stirred reactors. A mixed culture of moderate thermophilic bacteria was used for bioleaching at 45°C and a mixed culture of extreme thermophilic archea were used for bioleaching at 65°C. The leaching yields for zinc were in the range 80–87% with the moderate thermophilic bacteria and 96–98% with the extremely thermophilic microorganisms. It was found that, to obtain a high zinc recovery with a low degree of pyrite oxidation, a fine particle size was essential. Changes in retention time did not influence zinc solubilisation to any greater extent. Due to a high limestone content in the ore, the bioleaching was acid consuming. The acid consumption was strongly dependent on the throughput of ore in the leaching system. Recoveries of gold and silver, of ∼90% and 60–80%, respectively, after cyanidation of the bioleaching residue were obtained, irrespective of experimental conditions.