Effect of metals on recovery of gold from ammoniacal thiosulphate leach solutions by precipitation using trimercapto-s-triazine (TMT)

Abstract

There are significant technical challenges/shortcomings in recovering gold from thiosulphate leach solutions. This study presents a new approach for the recovery of gold from ammoniacal thiosulphate leach solutions using an environmentally friendly organo-sulphide reagent, trimercapto-s-triazine (TMT; C₃N₃S₃³⁻). Precipitation of gold by TMT was investigated using synthetic gold and multi-metal solutions (Au-Ag, Au-Cu, Au-Ag-Cu) to investigate the effect of the co-presence of metals commonly present in thiosulphate leach solution. The effect of TMT concentration (by up to 115 mM), temperature (25–60 °C) and ammonia (0.25–1 M NH₃) on the precipitation of gold was also investigated. The results showed that gold precipitation with TMT was relatively low (i.e., limited to only 37.7% over 15 min) from the solution containing only gold. However, the presence of silver and/or copper significantly improved the precipitation of gold. Silver concentrations at ≥20 mg/L led to a complete recovery of gold in 15 min, producing stable gold precipitates. The results have also indicated that silver readily precipitates when compared to gold. The effectiveness of the TMT precipitation process was also tested on a real leach solution from which complete recovery of gold and silver was readily achieved. The findings demonstrated that gold could be readily but unselectively recovered by precipitation with TMT from ammoniacal thiosulphate leach solutions containing silver, in particular, at the expense of co-precipitation of other metals such as copper and zinc.