Selective gold recovery from pregnant thiocyanate leach solution using ion exchange resins

Gold leaching using thiocyanate in acidic media is an alternative to cyanidation which is less toxic and can be done sequentially in one system without further preparation such as neutralization after acidic (bio)oxidation. Previous research activity in gold-thiocyanate leaching and gold recovery from thiocyanate pregnant leach solution (PLS) is limited. The current study deals with the selective recovery of gold over copper from synthetic and real thiocyanate PLS using ion exchange resins. Consequently, selective adsorption of Au(I) by ion exchange resins and selective Au(I) elution by proper eluent is proposed to obtain a high-purity Au(I) solution. First, the functionality of MTA 5011 and Amberjet 4200 resins at ambient temperature, and pH 2 for 24 h shaking at different resin mass (g) to PLS (L) ratios with synthetic PLS was compared. Then, 100 g/L MTA 5011 was chosen as the optimum resin/PLS (g/L) ratio for the highest separation with 99% gold and 12% copper extraction. Moreover, it was observed that over 24 h adsorption by 100 g/L MTA 5011, the copper extraction decreased, causing an increase in gold adsorption. Among the different reagents that were employed for gold elution, a solution of 0.01 M thiourea (TU) and 0.1 M H2SO4 was the most efficient with 70% gold and 4% copper elution. Adsorption experiments with MTA 5011 were repeated on the original thiocyanate PLS obtained after pyrite biooxidation and thiocyanate leaching using 0.2 M NaSCN and 0.01 M Fe3+. It was determined that the adsorption using 100 g/L MTA 5011 extracted ca. 99% gold and 5% copper, and for elution, a mixed solution of 0.01 M TU and 0.1 M H2SO4 recovered 99.2% gold and < 1% copper which validated the results from the synthetic PLS.