Gold extraction using novel ionic thiourea derivatives

Abstract

Cyanidation has been used worldwide for over a century as the primary method for gold extraction from ore. Unfortunately, accidents have occurred that released toxic cyanide and resulted in devastation of the environment and surrounding communities. For this reason, alternatives to cyanidation have been of great interest but have yet to be implemented owing to the high costs of materials and necessary changes to infrastructure, which make these alternatives economically unfeasible. Reported herein is the use of novel ionic thiourea derivatives for the extraction of gold without the use of cyanide. A series of six pyrrolidinium and imidazolium salts have been functionalized with a thiourea group and either the anion hexafluorophosphate ([PF6]−) or dodecyl sulfate ([DS]−). Gold(iii) extraction up to 90% was achieved from an aqueous solution with a methyl imidazolium-tagged [DS] salt. Extraction experiments using gold(i) showed a decrease in extraction efficiency, suggesting the oxidation state of the gold is important for complex formation. The extraction selectivity for gold(iii) and silver(i) over copper(ii), iron(ii) and zinc(ii) was demonstrated for all ionic thiourea derivatives.