Process Enhancement of Gold Extraction from a Copper-Rich Gold Ore by EDTA-Assisted Cyanide Leaching

In this study, a new approach based on EDTA-assisted cyanide leaching of gold from a copper-rich gold ore (69 g/t Au, 9.4 g/t Ag, 1.63% Cu) was investigated. The pretreatment of the ore with EDTA was also tested to remove soluble copper ahead of the cyanide leaching of gold. The ore yielded poor extraction (i.e. only 12.5% Au and 2.87% Ag) within a typical 24-h cyanide leaching process at 30.6 mM (1.5 g/L) NaCN, due to the severe interference of copper with gold/silver leaching. A high cyanide concentration of 102 mM (5 g/L) NaCN was required to achieve high gold/silver extractions. EDTA pretreatment (0.08-0.4 M) allowed the leaching of soluble copper (up to 43.0%), leading to a significant improvement in gold extraction from 12.5% to 82.2% coupled with a substantial reduction in cyanide consumption in the subsequent cyanide leaching when compared with direct leaching. The addition of EDTA (0.08-0.4 M) was observed to mitigate the copper interference with cyanide leaching with substantially improved gold extraction up to 85.8%. The results demonstrated that utilization of EDTA for the mitigation of copper interference is a promising approach when used in the pretreatment step ahead of cyanide leaching or as an additive in the cyanide leaching stage.