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

The microwave roasting self-leaching process represents an innovative method for recovering gold from high sulfur refractory gold concentrates, without deadly toxic cyanide reagent. However, the mechanism of gold self-leaching, which relies on lixiviant prepared using volatilized sulfur from roasting, has not been fully elucidated. This study employs response surface methodology to optimize the processing parameters, achieving an increased gold extraction rate of 96.17%. Analytical factorization and Tafel curve indicate that CuSO4 and NH3∙H2O significantly influence the self-leaching process. XPS analysis reveals that S²⁻, S₂²⁻, polysulfides (Sn²⁻), sulfur ions, and thiosulfate (S₂O₃²⁻) are involved in the gold leaching reaction, with S₂²⁻ and Sn²⁻ serving as the primary ligands for gold complexation. However, the role of S₂O₃²⁻ in the early stages of the gold-leaching reaction is also noteworthy. The copper-ammonia complex catalyzes the self-leaching gold reaction, but an improper addition ratio can lead to the copper-sulfur compound precipitates reducing the extraction rate.