A review of gold leaching in acid thiourea solutions

Since the initial report of thiourea as a complexing reagent for gold leaching, considerable research has been directed toward the use of thiourea as an alternative to cyanide for gold extraction from different auriferous mineral resources. At the same time, some fundamental investigations of the system have been reported. In this article, a review of both applications and fundamental research is made, including a review of the recent results from laboratory studies at the University of Utah. Recent research results demonstrate that thiourea decomposition is quite slow in the presence of ferric sulfate for simple solutions. Ferric sulfate and formamidine disulfide (FDS) are effective oxidants with fast kinetics. No passivation of the gold surface is observed in simple acidic solutions. However, in actual leaching systems, some sulfide minerals significantly catalyze the redox reaction between thiourea and ferric ion, causing high thiourea consumption if ferric ion is present in excess. The presence of copper has a deleterious influence on this leaching system.