Facile and novel method for the recovery of gold from a calcined concentrate via copper–ammonia -thiourea system and activated carbon

Cyanidation, as the primary method for gold extraction, poses significant risks to the environment and animals. Therefore, an eco-friendly, sustainable, and effective leaching approach has been devised for extracting gold from a gold concentrate after calcination, utilizing copper(II)-ammonia and thiourea. This research focuses primarily on optimizing leaching conditions, gold recovery from leach solution, and cyclic utilization of the leaching solution. Furthermore, we investigated the potential mechanisms behind the leaching and recovery processes using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and thermodynamic analysis. The leaching process exhibits a spontaneous reaction, and the mechanism for alkaline thiourea leaching of gold is as follows: (a) reduction of Cu(NH₃)₄²⁺ to Cu(TU)₄⁺, (b) oxidation of Au(0) to Au(TU)₂⁺ and (c) oxidation of Cu(TU)₄⁺ back to Cu(NH₃)₄²⁺, in the presence of oxygen, regenerating the catalyst. Under optimal leaching conditions, the proposed method achieves a gold extraction efficiency of approximately 86.6%, approaching that of cyanidation. The barren leach solution can be reused for subsequent leaching experiments, with consistent gold extraction efficiency and thiourea consumption. Therefore, this method presents a promising alternative to gold leaching via cyanidation.