Implementation of sodium hydroxide pretreatment for refractory antimonial gold and silver ores

Alkaline pretreatment of a refractory gold–silver ore containing antimony minerals such as stibnite, andorite (Sb3PbAgS6) and zinkenite (Pb9Sb22S42) was tested using sodium hydroxide in order to determine its effectiveness in improving the recovery of gold and silver. Mineralogical investigations show that silver was present as andorite and Au/Ag alloy. Gold particles have been observed as associated with quartz and inclusions within the antimony minerals. Increasing the sodium hydroxide concentrations from 0.5 to 5 mol/L, increasing the temperature from 20 to 80 °C, and reducing the particle size from 50 to 5 μm enhanced the removal of antimony from the ore. Up to about 75.5% Sb removal was achieved by alkaline pretreatment, which in turn remarkably improved the extraction of silver from levels of less than 18.7% to 90% and gold from less than 49.3% to 85.4% during subsequent cyanidation. These findings, consistent with mineralogical results, suggest that alkaline leaching can effectively be used as chemical pretreatment method as an alternate to the alkaline sulfide leaching in the processing of refractory antimonial gold–silver ores.