Abstract: The flotation separation of chalcopyrite from pyrite using locust bean gum as depressant has been studied and the mechanism has been discussed.The results show that both chalcopyrite and pyrite are floatable in the tested pH range from 3 to 9, and the flotation separation of chalcopyrite from pyrite can't be realized without the addition of depressant.Locust bean gum can adsorb on the surfaces of both chalcopyrite and pyrite and depress the flotation of these two minerals.But the depressing intensity and adsorption way of locust bean gum on chalcopyrite and pyrite are different.The adsorption way of locust bean gum on chalcopyrite surface is chemisorption, while pyrite is absorbed by physical way.After the addition of locust bean gum, pyrite flotation recovery was low under all the test pH.Different from pyrite, the recovery of chalcopyrite is high under the condition of pH less than 9 and is low under strong base conditions.The flotation test on mixed mineral sindicates that the use of locust bean gum as depressant can achieve the flotation separation of chalcopyrite from pyrite.A concentrate with Cu grade of 21.67% and recovery of 82.13% was achieved with the addition of 100 mg/L locust bean gum at pH 7.This study provides an excellent organic depressant for high efficiency separation of copper and sulfur.