Abstract: The leaching process of silver from zinc-smelting slag of sulfur-bearing pyrite with thiourea as chelating agent and H₂O₂ as oxidant in HNO₃ was studied.The effects of stirring speed，reaction time，reaction temperature，HNO₃ initial concentration，H₂O₂ concentration，and thiourea concentration etc. on the leaching efficiency of silver were investigated.Results showed that the leaching ratio of silver first increased and then kept constant with the increase of the stirring speed and the reaction time，while it first increased and then decreased with the increase of reaction temperature，HNO₃ initial concentration， H₂O₂ concentration，and thiourea concentration.The optimal conditions for leaching of silver with thiourea were found as follows：the stirring speed was 200 r/min，HNO₃ initial concentration was 4.11 mol/L，H₂O₂ concentration was 0.82 mol/L， thiourea concentration was 3.25 mol/L，reaction temperature was 50 ℃，and reaction time was 1.0 h.Under these conditions， the leaching ratio of silver was up to 82.0%.

Key words: thiourea, zinc-smelting slag, silver