Evaluation of submerged bio-oxidation concept for refractory gold ores

As the quality of gold (Au) deposits decreases, processes which can economically extract Au from low grade ores will grow in importance to the minerals industry. In situ, in-place and vat leaching methods can be attractive alternatives for low grade ores that are uneconomical to process using conventional open-pit or underground mining and processing methods. The objective of this study was to evaluate at laboratory scale a submerged bio-oxidation process concept to potentially improve the recovery of Au from refractory ore bodies that may be amenable to in-place or vat processing. The process included biological generation of ferric iron in a bioreactor followed by ferric iron oxidation of pyrite in submerged upflow columns. The results showed that oxidation of pyrite is possible using ferric iron that is biologically generated either externally or using underground aeration in the ore body. The simulated underground aeration and the presence of bioleaching microorganisms clearly enhanced the oxidation of pyrite. Moreover, microorganisms decreased the accumulation of elemental-S, the presence of which may have a negative effect on subsequent gold leaching and recovery.