Study on oxygen pressure thiosulfate leaching of gold without the catalysis of copper and ammonia

Abstract

There are several limitations of thiosulfate leaching methods in its industrial application. The main limitation is the addition of copper and ammonia which act as catalysts in the thiosulfate leaching process. The introduction of cupric ions can accelerate the rate of gold leaching but cause massive oxidation of thiosulfate, and cupric ions in the leachates are also adverse to gold recovery. Moreover, the presence of ammonia must be taken into account due to the increasing environment concerns. In this paper, a systematic investigation was carried out during oxygen pressure thiosulfate leaching (OPTL) without adding copper and ammonia at elevated temperature and oxygen pressure. Thermodynamic calculations showed that the improvement of temperature and pressure was favorable to gold leaching by thiosulfate. However, high temperature and pressure also caused high thiosulfate consumption (55.3 kg/t-ore of sodium thiosulfate) and relatively low gold extraction (87.6%) without additives. Addition of ammonium alcohol polyvinyl phosphate (AAPP) in the tests could reduce thiosulfate consumption to 45.7 kg/t-ore, whilst 90.2% of gold extraction can be achieved. XPS and SEM studies indicated that AAPP could also hinder the deposition of some passivation species including FeOOH, Fe2O3, Al2O3, S0, etc. on the ore surface. The gold recovery from oxygen pressure thiosulfate leach solution was conducted by the method of resin adsorption. Over 98% of gold can be loaded at 1 g/L strong base anion exchange resin of Tulsion A-21S and almost 100% of gold on the loaded resin can be stripped with a two component eluent solution comprising chloride and sulfite.