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Gold dissolution in non-ammoniacal thiosulphate solutions: Comparison of fundamentals and leaching studies

Sitando, O., Dai, X., Senanayake, G. and Nikoloski, A.N. (2015) Gold dissolution in non-ammoniacal thiosulphate solutions: Comparison of fundamentals and leaching studies. In: World Gold Conference 2015, 29 September - 1 October 2015, Misty Hills Conference Centre, Johannesburg



Thiosulphate has received much attention as an alternative non-cyanide lixiviant for gold recovery over the last three decades. In particular, a number of studies have shown that an ammoniacal copper(II)/thiosulphate system offers fast leaching kinetics, but there are difficulties in controlling the complex solution chemistry and there are concerns over the use of ammonia. Recently, thiosulphate leaching of gold in the absence of ammonia has shown to be one of the most promising alternatives to cyanide, as evident from the thiosulphate gold processing plant recently commissioned at Barrick Goldstrike for treating pressure-oxidized double refractory ore. However, the published information on non-ammoniacal thiosulphate systems is limited. In this work, the dissolution of gold in non-ammoniacal thiosulphate solutions has been studied using a rotating electrochemical quartz crystal microbalance (REQCM), rotating gold disk, gold powder, and selected sulphidic gold ores. The electrochemical studies found that gold oxidation is enhanced by increases in temperature, thiosulphate concentration, and the addition of low levels of copper. Oxygen reduction was found to occur much more readily on sulphide mineral surfaces than on the gold surface, offering an opportunity for galvanic interaction. The subsequent leaching tests using REQCM showed that the gold leach rate in the oxygen-thiosulphate system without any additives is in the order of 10-7 mol m-2 s-1 , two orders of magnitude lower than a typical cyanidation rate. However, the use of elevated temperature, high oxygen concentration, and copper addition, in conjunction with the galvanic effect of sulphide minerals, dramatically improved the gold leach rate to the same order of magnitude as a typical cyanidation rate. This was supported by the results obtained from prolonged leaching tests using gold powder and sulphidic gold ores. This study hence shows that the oxygen-thiosulphate system could be a promising alternative to cyanidation for treating some sulphidic gold ores.

Publication Type: Conference Paper
Murdoch Affiliation: School of Engineering and Information Technology
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