Abstract: copper and molybdenum mixed concentrate in Inner Mongolia contains 26.14% copper and 0.93% molybdenum.Activation of copper ions produced during the process of grinding and bulk flotation makes it difficult to separate copper from molybdenum.Sodium sulfide is added by 15 kg/t to realize molybdenum floatation and copper depression in on-site process.But it does not achieve the desired effect，even worse.It results in contamination of tailings dam and surroundings.To solve the problem，the dosages of sodium sulfide and self-made DDY3 are investigated respectively by the subject team of Northeastern University，the adaptation of DDY3 and sodium sulfide to the pulp density and pH are contrasted，and the failure time of DDY3 and sodium sulfide solution are found out.The results show that: ①The dosage of DDY3 is much lower than that of sodium sulfide，and DDY3 has a much better adaptability than that of sodium sulfide in the pulp density and pH variation.And the failure time of DDY3 is much slower than sodium sulfide.②Under the conditions of pulp concentration of 25% and pH of 10.5，molybdenum concentrate with molybdenum grade of 9.65% and recovery of 16.23%，and copper concentrate with copper recovery of 98.96% are received by adopting 15 kg/t fresh sodium sulfide.Molybdenum concentrate with molybdenum grade of 10.80% and recovery of 61.33%，and copper concentrate with copper recovery of 94.39% are received with 1 kg/t fresh DDY3.That DDY3 instead of sodium sulfide is used in separation of copper molybdenum mixed concentrate are high efficient and environmental-friendly.

Key words: Copper and molybdenum mixed concentrate, Separation of copper and molybdenum, Depressor, Sodium sulfide, DDY3