Optimization of Thiourea-Promoted Gold and Silver Leaching from Pyrite Cinders Using Response Surface Methodology (RSM)

The cyanidation of precious metals from ores and secondary resources has been classified as a hazardous process due to the release of toxic gases. The use of environmentally friendly and cost-effective processes is a suitable alternative to cyanidation. Thiourea leaching has been shown to be one of the best alternative reagents to cyanide. The present work aims to evaluate the efficiency of the thiourea leaching of gold and silver from pretreated pyrite cinders. The use of pre-chemical activation prior to leaching helped to increase the amount of free gold and silver particles. A preliminary leaching test led to the selection of Fe2(SO4)3 as a suitable oxidizing agent for Au and Ag leaching. To select suitable leaching parameters, the response surface methodology (RSM) was used to optimize some parameters that can considerably affect sulfuric acid–thiourea leaching and identify the greatest interaction between them. The optimized parameters of 30 g/L thiourea, 10% pulp density, pH = 1, and 50 °C over 4 h of leaching time allowed for Au and Ag recoveries of 98.31 and 88.57%, respectively.