Abstract: Using citric acid as complex agent，sodium hexametaphosphate as inhibitor，the flotation tests on quality increase and magnesium decrease for No.2 Mine Area of Jinchuan Nickel Mine are made and compared with the laboratory closed-circuit tests under on-site reagent system. The tests indicate that for the raw ores containing nickel of 1.36%，copper of 0.86%，MgO of 28.19%，the final nickel-copper mixed concentrate with Ni grade of 9.68%，Cu grade of 5.04%，MgO content of 6.33%，nickel recovery of 84.32% and copper recovery of 69.13% are obtained by the closed-circuit process of one roughing-two cleanings-three scavengings-middles back to the flow-sheet in turn. Each index in the tests above is better than that in the laboratory closed-circuit tests under the system of on-site pharmacy.

Key words: Citric acid, Copper-nickel sulfide ores, Combination of complex agent-inhibitor, MgO gangues