Solubilization of heavy metals from gold ore by adjuvants used during gold phytomining

Adjuvants such as cyanide, thiocyanate, and thiosulfate are applied to gold-bearing ores to increase gold solubility and plant uptake of gold during phytomining. The influence of these three adjuvants, added at rates comparable to field application (1 g kg DW−1 ore), on the leaching of heavy metals from gold ore from the Davis stockpile at the Stawell Gold Mines was examined in batch and column studies. The overall goal was to provide data that specifically addressed the possible collateral impacts that could occur during adjuvant-assisted phytomining in terms of heavy metal solubilization and leaching. Leachate from the cyanide-amended ore had the highest concentrations of Au, Co, Cu, and Ni, with the Au concentration representing ∼22% of the total gold present. Thiosulfate-amended ore leached the highest Fe concentration while thiocyanate-amended ore leached the highest Al and Zn concentrations. The results suggest that for this ore, while these adjuvants are present, there is the potential for the mobilization of undesirable elements and Au out of the ore and potentially into groundwater unless adequate hydraulic controls are implemented following adjuvant addition.