Abstract: The leaching process of silver from zinc-smelting slag of sulfur-bearing pyrite with modified thiourea method was studied.Effect of process parameters，such as H2O2 concentration［X1/（mol·L-1）］， HNO3 concentration［X2/（mol·L-1）］， thiourea concentration[X3/（mol·L-1）]， and leaching temperature（X4/℃），on the leaching ratio（Y/%） was researched by response surface method，and leaching technology was also optimized.A second order model representing the leaching ratio of silver was expressed as a function of process parameters：Y=-476.0-40.17X1+58.20X2+82.15X3+12.30X4-22.65X1X3+5.03X1X4-0.51X2X4-1.08X3X4-81.47X12-3.65X22-1.30X32-0.11X42.The results showed that the linear effects and the quadratic effects of HNO3 initial concentration were highly significant，and the linear effects of leaching temperature，and the quadratic effects of H2O2 concentration and thiourea concentration were significant while the linear effects of H2O2 concentration and thiourea concentration were insignificant.There were highly significant interactions between H2O2 concentration and thiourea concentration，leaching temperature and H2O2 concentration，leaching temperature and HNO3 concentration，and leaching temperature and thiourea concentration，respectively.The obtained model，revealed the optimized reaction parameters as follows：H2O2 concentration was 0.96 mol/L，HNO3 concentration was 4.12 mol/L，thiocarbamide concentration was 2.17 mol/L，and leaching temperature was 55 ℃.The confirmatory test for these optimum parameters showed a leaching ratio of 91.3%，which was close to the predicted leaching ratio（92.7%）.Compared with the results of the single factor experiment，the leaching ratio of silver was increased by about 10%.

Key words: thiourea, zinc-smelting slag, silver, response surface method