Study on the oxygen pressure alkaline leaching of gold with generated thiosulfate from sulfur oxidation

Thiosulfate leaching is a promising alternative to cyanidation, but high thiosulfate consumption has restricted its wide commercial application. In this study, the simultaneous gold extraction by generated thiosulfate deriving from the oxidation of added sulfur during oxygen pressure alkaline leaching (OPAL) without cupric-ammonia catalysis was investigated, and the results were encouraging. It has been proven that the sulfur can be produced from the oxidation pretreatment of sulfide gold ores or concentrates. Thus, this study provides an enlightenment to solve the problem of high thiosulfate consumption by a two-step process consisting of an appropriate oxidation pretreatment for sulfide gold ores or concentrates and OPAL. The gold extraction from an ore and terminal thiosulfate concentration after the OPAL in this study reached 78.0% and 0.28 M, respectively, and they were further improved to 83.6% and 0.31 M by the addition of humic acid (HA). The function of HA was proposed that it not only prevented passivation species from coating gold surface but also weakened the decomposition of generated thiosulfate. It can also be concluded that the improvement of temperature and oxygen partial pressure can substitute the cupric-ammonia catalysis for thiosulfate leaching.