Gold extraction from thiosulfate solution using trioctylmethylammonium chloride

Alkyl phosphorus esters, alkyl amines, amine oxides and their mixtures with amines (Hydrometallurgy 46 (1997) 363; Solv. Extr. Ion Exch. 16 (6), (1998) 1407) were used to extract gold from thiosulfate solution but the re-adjustment of pH was required and extraction efficiency was poor in the alkaline pH range. In this study, trioctylmethylammonium chloride (TOMAC) was used as an extractant to extract gold from thiosulfate leaching solution without pH and other adjustments. The effects of gold concentration, pH, ammonia, thiosulfate and cupric ion concentrations, extractant concentration, diluent and retention time on gold extraction were investigated. It was found that 0.18 mol/L extractant diluted with n-octane+1-hexanol at O/A ratio of 1:1 could extract more than 99% of gold from the thiosulfate solution at the standard leaching condition (1.0 mol/L S2O32−, 0.03 mol/L Cu2+ and 3.0 mol/L NH3/NH4+ at pH 10.2) in 0.6 ks (1 ks=1000 s). The loading capacity and selectivity of the gold extractant, trioctylmethylammonium chloride, were also studied.