Gold and critical element recovery with environmentally benign Deep Eutectic Solvents

Gold concentrates often contain significant enrichments of scarce or critical elements such as Te, Bi and Sb, but there are few financial incentives for recovery of these elements as by-products. Deep eutectic solvents (DES) may provide novel processing opportunities – these are a form of ionic liquid that are mixtures of salts such as choline chloride with hydrogen-bond donors such as urea. DESs are environmentally benign and the components are already produced in large quantities at low cost. We have demonstrated that gold is rapidly dissolved in DES by iodine oxidation, whereas many base metal sulfides are unreactive or react only slowly. However, we show that trace minerals that host the majority of Te, Bi and Sb in a concentrate, such as native Te and Bi, tellurides, and Bi- or Sb-sulfosalts, are rapidly dissolved at similar rates to gold, suggesting routes to recovering gold and critical elements. The etching rate shows systematic patterns in homologous mineral series, e.g. Ag2Te leaches faster than Ag2S which leaches faster than Ag2Se. In all cases the selenide leaches the slowest. These observations, together with liberation analysis, enable us to predict and quantitatively model the bulk leaching behavior of ore concentrates and design bulk leach tests.