Abstract:Silver, renowned for its exceptional exceptional electrical conductivity and chemical stability, is extensively utilized in electronics, chemical engineering, medical devices, jewelry, currency and other fields. Currently, cyanide leaching dominates silver extraction due to its efficiency and low cost, yet its high toxicity poses significant environmental and operational risks. Addressing the issue, considering the characteristics of fine particle size and complex chemical composition of silver-bearing residues, this study systematically investigated a direct cyanide-free leaching process alternative for recovering silver from silver-bearing residues. The formation mechanism of Ag(S2O3)?3? complexes ions in thiosulfate systems was systematically investigated through multi-scale characterization approaches, including X-ray diffraction (XRD) for crystal structure analysis, inductively coupled plasma (ICP) spectroscopy for elemental quantification, and laser granulometry for particle size distribution monitoring. Complementary thermodynamic simulations using HSC Chemistry software revealed the complexation energetics, ultimately validating sodium thiosulfate as an effective lixiviant for selective silver extraction. The research on the leaching process of cyanide-free systems was carried out. The selective silver extraction from silver-bearing residues were studied using the sodium thiosulfate system. The sodium thiosulfate leaching system was optimized through parametric studies, revealing three key determinants: 1) thiosulfate concentration, 2) ammonia dosage, and 3) copper sulfate catalyst. Under optimal conditions (20% reagent dosage, 4:1 liquid-solid ratio, 2 g·L?1 ammonia concentration, 5 g·L?1 copper sulfate addition, 20°C leaching temperature, 1 h leaching time), a remarkable 94.07% average silver leaching rate was achieved. This process enables selective silver recovery with minimized environmental impact, demonstrating significant advantages over conventional cyanide-based methods.

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