A Review of Thiocyanate Hydrometallurgy for the Recovery of Gold

Abstract

Over the past century, numbers of hydrometallurgical processing technologies have been conducted for gold leaching in mining and second resource, such as cyanidation, being with high toxicity and low reaction rate, and non-cyanide---thiosulphate leaching and thiourea leaching, etc, having relatively high reagent consumption. Recently, ammonium thiocyanate was selected as leaching reagent in the laboratory study. Just as some papers shown, thiocyanate can be complexed tightly with Au+ or Au3+ to form water-soluble complexes according to the dynamic and thermodynamic system of thiocyanate gold and regenerated or obtained as a by-product in technological processes. And the extraction process is affected by many factors, such as thiocyanate concentration, oxidant concentration, liquid-solid ratio, temperature, and reaction time, especially pH and the category of oxidants, which can be chosen properly to make the method extensively applied in industrialization. Recent studies have shown that the gold leaching with thiocyanate under alkaline conditions is also viable using oxygen as oxidant. Then this article compares and analyzes the use of different oxidants in acid or alkali environment reaching a 96% leaching efficiency and the techniques of gold recycle from thiocyanate gold solutions. However, as the restriction for post-processing cost of thiocyanate and the strict requirement for the equipment in the acidic conditions or high pressure conditions, additional research should be directed towards making incorporation with other extraction methods perfectly. Two development tendencies are presented in this paper: (1) as additive; (2) as the lixiviant under alkaline or neutral conditions.