Response of low-grade gold ore to cyanidation and thiourea leaching

In this study, leaching tests were conducted on representative samples provided from Hamze-Qarnein gold deposit with grade of 0.8 ppm using cyanidation and thiourea leaching. Effective parameters including particle size, reagent concentration, oxidant concentration, pH, and dissolution time were examined in both cyanidation and acidic extraction with thiourea. Gold recovery and reagent consumptions (lime, cyanide, thiourea, ferric sulfate, and sulfuric acid) were measured under different leaching conditions. The results showed that cyanidation method was efficient with 95.21% gold recovery with following conditions: d(80) = 63 mu m, pH 10.5, cyanide consumption of 1.23 kg/t, and 12 h cyanidation time. The acidic leaching using thiourea, required more chemical reagents and maximum gold recovery of 90.48% was achieved with thiourea consumption, leaching time, and pH equal to 13.32 kg/t, 5 h, and 1.7, respectively. According to the results, there was an interaction between ferric sulfate and thiourea concentrations and modeling of this process utilizing historical data design confirmed that the most effective parameter was the molar ratio of ferric sulfate to thiourea. Maximum recovery of gold obtained at molar ratio of 1/1. In addition, based on the experimental results, kinetics parameters of first-order reaction for gold dissolution were determined for cyanidation and thiourea leaching separately; therefore, for cyanidation, R-infinity and K were 95.59% and 0.59 h(-1) respectively, while R-infinity and K were in order of 78% and 0.87 h(-1) for acidic leaching using thiourea.