An electrochemical study of the effect of additives and electrolyte on the dissolution of gold in thiosulfate solutions

Thiosulfate leaching appears to be the most promising alternative to cyanidation for the recovery of gold from ores. The current paper presents a fundamental study on the gold oxidation half reaction in the solutions containing thiosulfate. It will be shown that this electrochemical reaction is unusual, as the presence of the heavier inert cations such as potassium, calcium, and caesium enhance the oxidation of gold in thiosulfate solutions. The use of sulfur-containing species such as thiourea (TU) and potassium ethyl xanthate (PEX) as additives was also studied. It will be shown that in the presence of thiourea, the gold oxidation half reaction is dramatically improved, with a typical Tafel-like polarisation curve being obtained in the presence of thiourea. However, the presence of low concentrations of xanthate were shown to completely block the gold surface and prevent its oxidation in thiosulfate solutions.