Thiourea leaching of a copper-gold ore using statistical design

Thiourea was used to leach gold from ore containing 0.4% Cu and 5.6 g/t Au. The parameters studied were acid pretreatment, leaching time, pH, thiourea concentration and the oxidizing agents used. Gold extraction was 89% and thiourea consumption was 3.9 kg/t. No acid consumption was observed during leaching at pH 3. Pretreatment by acid washing is recommended for improved gold leaching and lower thiourea consumption. The best gold recovery results were obtained with ferric sulphate as the oxidizing agent, although it is more expensive. Thiourea dissolves three times less copper than cyanide does. The best leaching conditions achieved were as follows: acid wash pretreatment, an average amount of added thiourea of 12 g/, a leaching duration of 72 h and a pH of 3. The oxidation-reduction potential fluctuated between 410 and 450 mV/SHE.