Toxic inorganic depressants are commonly used in the flotation separation of polymetallic sulfide ores and it is desirable that they can be replaced by environmentally benign substances. Serpentine, a common gangue mineral encountered in complex sulfide ores, has been found to be an efficient depressant for ferric sulfide (e.g., pyrite). Serpentine was tested as a potential selective depressant in the differential flotation separation of galena and pyrite using potassium butyl xanthate (PBX) as a collector. In single mineral flotation, serpentine depressed the -150 + 74 mu m and -74 + 37 mu m galena while the -10 mu m galena was floatable. Different from galena, serpentine has strong depression effect on all the three sizes of pyrite. So the flotation separation of fine grained galena and pyrite can be achieved. A concentrate with Pb grade of 65.09% and recovery of 67.72% can be achieved in the mixed minerals flotation when serpentine was added as depressant. Mechanism studies indicated that serpentine particles attach to the surface of pyrite more easily. (C) 2018 Elsevier B.V. All rights reserved.