Abstract: Factories using fatty acid anionic collector to reverse floating iron ore have problems of large amounts dosage of collectors，higher flotation temperature and bad flotation index.To solve those problems，a new type amide-carboxylic acid collector DWD-3 was developed，which applied to reverse flotation on magnetic mixed concentrate of Sijiaying.Laboratory test results show that，when the flotation temperature is 25 ℃，with rough flotation pH is 11.5，DWD-3 dosage is 400 g/t，CaCl2 dosage is 400 g/t，and corn starch dosage is 1 000g/t by one roughing，one cleaning and three scavenging closed-circuit flotation，concentrate with iron grade of 66.48%，iron recovery of 80.32% and tailings grade 16.35% is obtained.When using collector DWD-3 instead of collector GK-68 by on-site process in Sijiaying，flotation temperature may lowered from 40 ℃ to 25 ℃，iron grade and recovery of flotation concentrate increased by 0.39 and 2.23 percentage points，tailings grade decreased by 1.57 percentage points.Analysis of flotation products shows that，flotation concentrate have large mounts of tightly connected minerals below 20 μm，a large number big size tightly connected minerals exist in flotation tailings，its iron minerals and gangues even mutual interdependent，which maybe the reason for higher iron grade in tailings.

Key words: Collector DWD-3, Magnetic mixed concentrate, Reverse flotation