Abstract: A new kind of carboxymethyl starch with high degree substitution,DRJ synthesized by the solvent method was used as depressor of iron ore. Technical conditioning tests of reverse flotation for mixed magnetic concentrate in beneficiation plant of Anshan Qidashan Iron Ore with Fe grade of 43.57% were made. The results showed that anionic carboxymethyl starch DRJ has a strong inhibiting effect on iron minerals. Under the condition of the dosage of DRJ 400 g/t，CaCl2 200 g/t，and collector LKY 600 g/t，pH=11.5，the iron concentrate with Fe grade of up to 65.95% and Fe recovery of 89.22% was obtained by one-stage reserve flotation. XRD and SEM analysis indicated that DRJ not only has a strong inhibiting but also with a good depressing effect in iron ore flotation.

Key words: Mixed magnetic iron concentrate, Carboxymethyl starch, Substitute degree