Leaching of gold from a free milling gold ore in copper-citrate-thiosulfate solutions at elevated temperatures

For the last two decades, a considerable amount of research has focused on developing a completely safe and non-toxic leaching process for gold to replace cyanidation. In this research, a free milling gold ore is leached using copper-citrate-thiosulfate solutions at elevated temperatures, where citrate serves as a stabilizer of cupric ion. Experimental factors such as agitation speed, temperature, initial pH, concentration of copper, citrate and thiosulfate have been investigated. Meanwhile, effects of these parameters on the thiosulfate consumption and Cu2Cit2H−24− complex stability are also examined in the leaching process. The experimental results show that the copper-citrate-thiosulfate system has a similar extraction capacity for gold compared to the traditional cyanidation. The results of kinetic analysis of dissolution rate of gold indicate the leaching process gold from free milling ores may be controlled by the product layer diffusion under the experimental conditions, with an activation energy of 34.48 kJ/mol. The copper-citrate-thiosulfate system has some advantages over cyanidation, such as green, nontoxic and shorter leaching time, although a high leaching temperature above 70 °C is usually required to an acceptable gold extraction. Obviously, the system still needs to be further developed to ensure its commercial viability.