A new concept of the biohydrometallurgical technology for gold recovery from refractory sulfide concentrates

A new concept of a biohydrometallurgical technology for gold recovery from refractory sulfide concentrates was proposed and substantiated. The technology implies a two-step process for oxidation of gold-bearing sulfide concentrates. The first step is leaching with biogenic ferric iron at elevated temperature using the ferric iron-containing solution produced during the second step. The second step is biooxidation of the products of the first step by acidophilic chemolithotrophic microorganisms. A flotation concentrate, which contained pyrrhotite, arsenopyrite, pyrite, and antimonite, was used in the study. Effect of temperature on leaching of the concentrate with biogenic ferric was studied. Maximal rates of ferric and ferrous iron concentration change were observed at 80 °C and were 44.3 and 32.2 g L− 1 h− 1 within the first 40 min of the first cycle of the leaching. The level of oxidation after two cycles of pre-leaching with biogenic ferric iron (100 min) at 80 °C was 64.3, 31.1, and 45.4% for iron, arsenic, and sulfur of all sulfide minerals, respectively. Comparison of the two-step and traditional (one-step) technologies was carried out and the flow sheet for the new process was proposed. Gold recovery from the sulfide concentrate by carbon-in-pulp cyanidation was 67.8% in the one-step process and 93.0% in the two-step process at 4 days of biooxidation, while it reached 82.4% and 94.1% in the one-step and two-step processes at 8 days of biooxidation, respectively. Introduction of the pre-leaching of the concentrate with biogenic ferric step was shown to result in decreased duration required for subsequent biooxidation, thus enhancing the economical efficiency of gold recovery.