Bioleaching of Copper Concentrate by Indigenous Isolates of Iron and Sulfur-Oxidizing Bacteria from Acid Mine Drainage

Chalcopyrite is the most abundant copper mineral in the world, and its bioleaching suffers from low dissolution rates, which is often attributed to passivating layers. Hence, these passivating layers must be overcome to use bioleaching technology to its full potential to process chalcopyrite. Leaching must occur at a low Oxidation/Reduction Potential (ORP) to prevent these passivating layers from forming, but chemical redox control in bioleaching heaps is difficult and costly. As an alternative, selected weak iron-oxidizers could be employed that are incapable of scavenging exceedingly low concentrations of iron and, therefore, raise the ORP just above the onset of bioleaching but not high enough to allow for the occurrence of passivation. This study isolated four bacterial strains from acid mine drainage in one of Mongolia’s most significant copper mining sites. Three of these strains were identified based on their partial sequence of the 16S rRNA gene. Also, we studied the electrochemical properties of the bioleaching process of sulfide ore by one of the isolates obtained from the acid mine drainage. Our results show that strains ER-1a and ER-1c are closely related to Candidate division OP10 bacterium P488 (AM749768), and ER-1d is closely related to Fimbriimonas ginsengisoli Gsoil 348 (GQ339893). Bioleaching of copper concentrate was monitored by the electrochemical method. During 18 days of oxidation, only three types of oxidations were observed. The solubility of copper reached 615 mg/L and 53.37%, while 83.7% of ferrous ions were converted to iron (III). The CV-cyclic voltammetry oxidation current peak intensity gradually increased until day 15 and then decreased on day 18 during the bioleaching experiment.