Pressure oxidation of refractory gold ores containing carbonate minerals is conducted under neutral/alkaline conditions in order to promote fast kinetics, reduced reagent consumption and suppressing the formation of elemental sulphur and CO2 (which reduces the effectiveness of the process). In this work, both the addition of sodium carbonate and the presence of silica were investigated during the pressure oxidation of pyrite in the presence of calcium carbonate. It was found that the shift to an alkaline leaching environment favours the formation of soluble sulphate products over anhydrite (an industrial scale), but that the increase in kinetics is likely due to an increase in pH and carbonate/bicarbonate concentrations. The presence of silica in the autoclave induces the formation of an in situ iron oxyhydroxide silicate coating and a significant reduction in pyrite oxidation, which was minimized by addition of sodium carbonate.

Pressure oxidation of refractory gold ores containing carbonate minerals is conducted under neutral/alkaline conditions in order to promote fast kinetics, reduced reagent consumption and suppressing the formation of elemental sulphur and CO2 (which reduces the effectiveness of the process). In this work, both the addition of sodium carbonate and the presence of silica were investigated during the pressure oxidation of pyrite in the presence of calcium carbonate. It was found that the shift to an alkaline leaching environment favours the formation of soluble sulphate products over anhydrite (an industrial scale), but that the increase in kinetics is likely due to an increase in pH and carbonate/bicarbonate concentrations. The presence of silica in the autoclave induces the formation of an in situ iron oxyhydroxide silicate coating and a significant reduction in pyrite oxidation, which was minimized by addition of sodium carbonate.