Keywords: alkaline thiourea, gold leaching, stable reagents, oxidising agents, Na2SO3, sodium sulphite, (NaPO3)6, sodium hexametaphosphate, Na2S2O8, sodium persulphate, hydrometallurgy, optimisation, finely disseminated gold ore, cyanide
Optimisation of efficient auxiliary agents of gold leaching in an alkaline thiourea solution for a finely disseminated gold ore
Thiourea as a kind of green and eco–friendly gold lixiviant, was employed to substitute cyanide in the present study of gold leaching. The investigation was carried out on a finely disseminated gold ore from Hongmiao (Hunan province, China) in alkaline thiourea solution with indispensable stable reagents of Na2SO3 and (NaPO3)6. The main aim was to seek suitable stable reagents and oxidising agents required in leaching gold. Na2SO3 and (NaPO3)6 were determined as the best stable reagents and Na2S2O8 was a more appropriate oxidant compared with K3[Fe(CN)6] in this study. Meantime, the effects of leaching parameters, i.e., the molar ratio of SO32−, PO3−, TU and S2O82−, pH, mixing time and grinding fineness were examined in detail and the optimum condition was obtained. The experimental results show that the molar ratio of SO32−, PO3−, TU and S2O82− greatly affected gold leaching extent and thiourea decomposition. No more than 72.6% leaching rate could be reached due to deactivation of elemental sulphur created by thiourea and other negative factors, while lower leaching rate (69.4%) of gold leaching rate was obtained in acidic thiourea media compared with alkaline media.