Bioleaching of Pyrrhotite by Moderately and Extremely Thermophilic Bacteria

Abstract

Pyrrhotite ores are always mingled with very finely disseminated gold and other precious metal particles, which raise the disposal of such refractory ores to bacterial leaching level. In this paper, the bioleaching tests of pyrrhotite were carried out in Erlenmeyer flasks with moderately thermophilic Leptospirillum ferriphilum (at 40°C) and extremely thermophilic Acidianus manzaensis(at 65°C). The effects of bacterial strains, temperature, and acid tolerance on the extraction of iron were investigated, and the bioleaching residues were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results indicate that high temperature and low pH have important positive effects on the dissolution of iron under abiotic control, and extreme thermophilies are unsuitable for leaching pyrrhotite. As the pH value rapidly increased to above 4.4 and amounts of sulfur and goethite were generated at the initial stage during the process of bioleaching by A. manzaensis, the cell concentration dramatically declined. In comparison, more than 44% extraction of iron was achieved in the presence of L. ferriphilumafter four days of leaching. At the end of bioleaching, jarosite, sulfur and goethite, which could effectively block bioleaching process, were detected on the surface of residues by using XRD and SEM.