Gold Extraction from kaymaz gold ore by thiourea leaching

Abstract For over one hundred years, gold has traditionally been extracted from ores by cyanide leaching. In recent years, due to pressure by environmentalists and to certain disadvantages of the cyanidation process, investigations were directed towards alternative gold lixiviants. The most promising results in gold leaching were obtained by use of thiourea, a complexing/extracting agent, together with ferric sulfate as an oxidizing agent. The study was carried out on finely disseminated Kaymaz gold ore from Turkey (4.0 g/t Au). The effect of various leaching parameters on gold extraction was examined, such as the concentration of thiourea, concentration of ferric sulfate, molar ratio of ferric sulfate/thiourea, leaching duration and particle size. The investigations indicated that at room temperature, with a 15.96 kg/t consumption of thiourea at pH 1.35, it was possible to obtain gold extraction at 80.5%, for a 100%, 106 μm feed in 6 h. Higher extractions such as 92.5% were also possible, with a finer feed and lower pH values. Thiourea consumption for different leaching conditions was also examined.