Simultaneous sulfide oxidation and gold dissolution by cyanide-free leaching from refractory and double refractory gold concentrates
Riina Ahtiainen, Jussi Liipo, Mari Lundström
Abstract
Pyrite and arsenopyrite are known to be the most common gold-bearing sulfide minerals in refractory gold ores. Traditionally, these minerals have been first oxidized by roasting, acidic pressure oxidation or bio-oxidation to release gold, after which the gold is dissolved in the subsequent cyanide leaching step. The chloride (chloride-bromide) solution presents an alternative cyanide-free media, which is able not only to leach gold-bearing sulfide minerals, but also gold, in a single unit process. Therefore, the current study presents an investigation of simultaneous sulfide oxidation and gold leaching from refractory (sulfidic) and double refractory (sulfidic and preg-robbing) gold concentrates. The results show that gold extraction from the investigated refractory concentrate was linearly dependent on the sulfide oxidation: 97% sulfide oxidation resulting in 99% gold extraction, 67% sulfide oxidation resulting in 81% gold extraction, and 46% sulfide oxidation resulting in 67% gold extraction. However, with double refractory concentrate, gold extraction was as low as 18% despite 97% sulfide oxidation ([Cl-]aq,0 = 6.3 mol/L, [Br-]aq,0 = 1.0 mol/L, and [Cu2+]aq,0 = 1.6 mol/L). In order to mitigate the challenges related to gold losses due to preg-robbing, active carbon in chloride leach (CICl) as well as the addition of lead nitrate were investigated. With CICl, the gold recovery could be increased significantly (67%). Further, addition of lead nitrate to CICl was shown to improve gold recovery substantially (88%). The investigation shows that the presented cyanide-free leaching approach can address the refractory nature of gold concentrates in atmospheric pressure - the simultaneous oxidation of sulfide minerals and gold in a single unit process providing new horizons for the future of the utilization of refractory gold ores.