Precipitation of zinc from cyanide leach solutions using Trimercapto-s-triazine (TMT)

Abstract

Cyanide leach solutions produced from gold/silver ores can be contaminated with zinc due to the gold/silver cementation in Merrill-Crowe process and/or the dissolution of zinc minerals present in the ore. Zinc levels in cyanide solutions should be controlled to avoid potential problems in leaching and downstream processes associated with the accumulation of zinc. In this study, the application of a novel method was demonstrated for the precipitation of zinc from synthetic/real cyanide solutions using Trimercapto-s-triazine (TMT), a non-toxic organic reagent. Experimental studies have shown that precipitation of zinc with TMT is a fast process occurring in a short period of time i.e., ≤15 min. Increasing the concentration of TMT (33–90 mM) and pH (10–12.5) was found to improve the precipitation of zinc, which was unaffected by increasing the temperature (20–60 °C). Response surface methodology was adopted for detailed investigation of the effect of [TMT]/[Zn] ratio (2.70–16.25), [CN−]/[Zn] ratio (3.00–8.00) and initial concentration of Zn (50–950 mg/L) on the precipitation of zinc. High recoveries (≤95.4%) were obtained under suitable conditions. Precipitation tests were also performed using synthetic multi-metal and real leach solutions. The complete recovery/dissolution of zinc from the precipitates was also demonstrated using different acids (HCl and H2SO4). The findings have shown that TMT can be effectively used as an environmentally friendly reagent for removal of zinc from cyanide leach solutions.