Influence of additives on electrodissolution of Au in a thiosulfate Electrolyte

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The environmental concerns related to the use of cyanide in the leaching of gold have stimulated considerable efforts to develop more environmentally friendly technologies. Of these thiosulfate appears to be the most promising alternative to cyanidation. However, passivation of gold during leaching from the thiosulfate electrolyte slows down this reaction significantly. It has been observed that certain organic additives such as thiourea, thioacetamide and sulphanilamide significantly improve the dissolution of gold in thiosulfate solutions. The nature of the passivation of gold and the effect of organic additives on leaching of gold in thiosulfate solutions are poorly understood. The objective of research described in this proposal is to employ in situ infrared reflection absorption spectroscopy (IRRAS), surface enhanced Raman spectroscopy and surface imaging techniques such as atomic force microscopy and scanning tunneling microscopy to determine the nature of the passive layer and the role of the organic additives. Specifically we will identify the nature of species adsorbed at a gold electrode surface and will determine surface concentrations of these species as a function of the electrode potential and electrolyte composition. We will determine if a complex between Au+ and the organic additive (ligand) is formed at the electrode surface. We will provide information concerning orientation of the adsorbed additive. We will determine the effect of the additive on the rate of gold dissolution and the mechanism of the gold-dissolution reaction. The information provided by this project will be used by Barricks Gold Corporation for the development of new technologies of gold leaching from ores.