Abstract: The concentration of SCN- in the leaching medium is as high as 10 225.9 mg/L，and Cu⁺ concentration is 4 131 mg/L in Qinghai Kunlun Gold Co.，Ltd. Cu⁺ is almost precipitated in the form of CuSCN with the acidification process. The concentration of iron，zinc，lead ions in barren liquor are 4 451 mg/L，2 895 mg/L，2.82 mg/L，respectively，which is not enough to precipitate the iron cyanide complex. Therefore，higher iron ion concentration in the leaching medium will bring adverse effects to the leaching and replacement process. In order to solve the problem，the experiment of adding zinc sulfate to barren liquor was carried out. The results showed that adding zinc sulfate to the barren liquor in acidification stage can obviously reduce the concentration of iron ion. Copper and zinc can be collected separately through asynchronous precipitation. While iron is removed from barren liquor，the dosage of zinc powder in replacement process decreases from 102.5 g/m³ to 86.01 g/m³，the iron grade in gold mud decreases from 5.2% to 4.3%，the gold leaching rate increases by 0.2 percentage points，and the silver leaching rate increased by 1.02 percentage points，achieving the purpose of improving the quality of the leaching medium.

Key words: barren liquor, iron cyanide complex, zinc sulfate, precipitation