Low-toxicity non-cyanide recovering high-sulfur refractory gold ore via microwave roasting self-leaching process: Response surface optimization and mechanism study

Microwave roasting self-leaching is an innovative method for recovering gold from high-sulfur refractory gold concentrates, without using deadly toxic cyanide reagents. However, the mechanism of gold self-leaching, which relies on lixiviants prepared using volatilized sulfur obtained from roasting, has not been fully elucidated. This study employs the response surface methodology to optimize processing parameters, resulting in an increased gold extraction rate of 96.18%. Analytical factorization and the Tafel curve indicate that CuSO₄ and NH₃∙H₂O significantly influence the self-leaching process. Furthermore, X-ray photoelectron spectroscopy (XPS) analysis reveals that S²⁻, \mathrmS_2^2- , polysulfides ( \mathrmS_n^2- ), sulfur ions, and thiosulfate ( \mathrmS_2\mathrmO_3^2- ) are involved in the gold leaching reaction, with S²⁻, \mathrmS_2^2- and \mathrmS_n^2- serving as primary ligands for gold complexation. The role of \mathrmS_2\mathrmO_3^2- in the early stages of the gold-leaching reaction is also noteworthy. The copper–ammonia complex catalyzes the self-leaching gold reaction; however, an improper addition ratio can lead to copper–sulfur compound precipitates, reducing the extraction rate.