Combined Bacterial and Pressure Oxidation for Processing High-Sulfur Refractory Gold Concentrate

Abstract

Microbially assisted bio-oxidation of sulfide concentrates in stirred-tank reactors (stirred-tank reactor bio-oxidation (STRB)) and acid pressure oxidation (POX) are widely used to pretreat refractory sulfide concentrates and increase gold extraction via cyanidation. Continuous STRB requires a comparatively long residence time; however, in some cases, it cannot effectively oxidize some sulfide minerals. POX enables oxidation in a short residence time. At the same time, if a processed concentrate contains a large amount of sulfur, it decreases the ratio of the solid mineral phase to liquid (pulp density) during POX and limits its economic attractiveness. In the present work, experiments were performed to investigate the problems associated with both processing methods for refractory sulfide concentrates. The experiments combined both treatments (STRB and POX) based on the example of a pyrite–arsenopyrite gold-bearing concentrate. The gold recovery from the untreated concentrate via cyanidation reached 58%. Continuous STRB for 2, 4, and 6 days oxidized 43, 74, and 79% of the sulfide sulfur (Ss), respectively. The gold recovery rates from the bio-oxidation residues were 68, 82, and 88%, respectively. The pressure oxidation of both the concentrate and STRB residues increased Ss oxidation by 97–99% and gold recovery by 96–97%. For 2 days, STRB decreased the Ss content and increased the possible liquid-to-solid ratio for POX. The combined processes result in a new promising direction because the POX stage allows high gold recovery, whereas combining STRB and POX provides products for further POX in terms of Ss content and increases POX productivity.