Two-stage bacterial–chemical oxidation of refractory gold-bearing sulfidic concentrates

The chemical oxidation of the arsenopyrite and pyrite gold-bearing concentrates with the microbially-produced Fe3+ solution was investigated. During the chemical stage, the most easily oxidized sulfidic elements were shown to be removed from the concentrates. After chemical leaching of the arsenopyrite concentrate, the oxidation levels for sulfidic iron and arsenic were 64.3% and 31.1%, respectively; for the pyrite concentrate, the oxidation levels of sulfidic iron and sulfur were 21.2 and 25.8%, respectively. Biooxidation of the arsenopyrite and pyrite gold-bearing concentrates has been carried out in the onestage (control) and two-stage (experimental) variants in reactors in feed batch mode. An activity of biooxidation of sulphidic concentrates without preliminary oxidation by Fe3+ solution (one-stage process) during the control experiments and after preliminary oxidation of Fe3+ solution (two-stage process) in experimental variants was studied. At 4 days residence time, the oxidation level for sulfidic arsenic from the arsenopyrite concentrate was 38.4% in the control process and 92.8% in the experimental one; gold recovery by cyanidation was 67.76% and 92.95%, respectively. At 8 days residence time, the results of the control process were lower, than of experimental process after 4 days of oxidation: the oxidation level of sulfidic arsenic was 59.7%; gold recovery was 82.38%. In the control variant, the time of biooxidation of the pyrite concentrate was 36 days; in the experimental variant, it was 5 days. The oxidation levels for sulfidic iron and sulfur were 40.3 and 55.7%, respectively; gold recovery by cyanidation was 76.9%. The results obtained demonstrate that two-stage bacterial–chemical processes are promising for intensification of the biohydrometallurgical processing of refractory sulfidic concentrates containing not only nonferrous metals, but noble metals as well.