Electrochemical study of gold thiosulfate extraction process
Soleymani Naeini, Masih
Gold , Thiosulfate , Electrochemical Study , Eco-Friendly
Thiosulfate has received a specific attention in gold extraction industry as a non-toxic alternative lixiviant for cyanidation process. Barrick Gold Corporation has commercialized thiosulfate gold leaching process in Goldstike mine in Nevada, USA. However, there is still potential for technical improvements to achieve higher process efficiency. The purpose of this study is to examine gold thiosulfate leaching chemistry and to suggest strategies to improve gold extraction efficiency. In the current work, addition of Pb2+ to thiosulfate solution was proposed to increase the gold dissolution rate. It has been demonstrated that 100 mg/L of Pb2+ in 0.2 M thiosulfate solution significantly increased dissolved gold concentration from near 0 to 2 mg/L at an anodic potential of +0.1 V (Vs. Ag/AgCl). In another study, the effect of various mixing ratios of the alkaline and acidic pressure oxidation (POX) discharges was investigated by employing electrochemical methods and leaching experiments. Based on the electrochemical results, the higher ratio of alkaline POX discharge in the calcium thiosulfate (CaTS) slurry resulted in higher gold oxidation rates. However, leaching tests results showed higher gold recovery (75.5%) for the electrolyte containing acidic POX discharge due to the presence of more liberated gold particles, while increasing the alkaline POX discharge ratio decreased the gold recovery to 65.3%. In another part of the study, the effect of trithionate and tetrathionate was investigated on gold leaching process. The leaching and electrochemical results indicated that controlling the initial concentration of tetrathionate in the range of 50 to 100 ppm, and trithionate up to 50 ppm could enhance gold leaching kinetics by controlling surface passivation of reactive minerals. The optimum values of polythionates boosted gold leaching recovery from 583% to 632% and 642% in the presence of tetrathionate and trithionate, respectively. In the last part of this study, electrochemical and analytical techniques were employed to explore the effect of thiosulfate, sulfite, and a mixture of thiosulfate-sulfite species in the electrolyte on gold electrowinning process. It was found that the addition of sulfite to the electrolyte resulted in the formation of Au(S2O3) SO3)25- as the most stable gold complex which decreased the gold reduction rate. However, it restricted thiosulfate decomposition.