Abstract: The lead grade and zinc grade of a lead-zinc ore is 7.31% and 13.70%， respectively， with high sulfur contents and carbonaceous. The zinc minerals mainly exist in the form of sphalerite. The distribution particle of sphalerite is uneven and fine， which embedded with galena and pyrite closely， causing the difficulties in zinc separation. In order to improve the particle size distribution of zinc concentrate and optimize the zinc separation indexes， the process of "rapid branching floatation and middling regrinding cleaning" was adopted to treat the zinc flotation feeding. The condition test involving flotation time， reagent system and middling regrinding fineness were conducted. The results showed that the comprehensive zinc concentrate with zinc grade of 53.88% and zinc recovery of 91.57% could be obtained after the new process， which is 1.56 and 1.13 percentage points higher than the original process， respectively. Also， the particle size distribution of zinc concentrate was significantly improved. The contents above 38 μm increased from 5.93% to 22.50%， and the contents below 7 μm decreased from 47.54% to 29.41%. The new process solves the problems of low selectivity of zinc regrinding， overgrinding of some sphalerite and insufficient dissociation of some sphalerite intergrowth in the original process， and reduced the regrinding loading.

Key words: sphalerite, over regrinding, fractional velocity branch flotation, middling regrinding