China Nonferrous Metallurgy

Lead-silver slag is produced during smelting of sphalerite with high Fe and In contents in a smelter in Yunnan. This slag contains a high content of metals that are worthy of recovery. At present, the treatment process of such a type of lead-silver slag is dominated by pyrometallurgical volatilization which has shortcomings such as low recovery rate of valuable metals, high energy consumption and environmental pollution. This smelter conducts hydrometallurgical tests about silver and valuable metal recovery, and explores the influence on recovery rates of silver and valuable metals by acidity of nitric acid system and sulfuric acid system and consumption of leaching agents, including ammonia water and sodium sulfite. The final process flow for lead-silver slag treatment is determined as pretreatment—oxidizing roasting—two-stage acid leaching—complexation by ammonia water—silver reduction and extraction by hydrazine hydrate—sponge silver casting. With preferable process parameters, production indicators can be: silver leaching rate＞96%; comprehensive silver recovery rate＞98%; copper leaching rate＞99%; indium leaching rate＞80%. After silver extraction, the Pb content in final residue is up to 45% and can serve as desirable raw material for lead smelting in the next step. This process flow is characterized by low equipment costs, simple process control, high silver recovery rate and a great number of recoverable valuable metals, providing reference for pyrometallurgical zinc smelting companies that conduct comprehensive silver recovery from lead-silver slag.