Abstract: Main valuable mineral of carbonate-containing mixed magnetic separation concentrate from Donganshan is hematite，few siderite and magnetite，gangue minerals are mainly quartz，iron ore is fine desiminated，iron distribution rate in 37 μm accounted for 82.55%.For the effective separation of carbonate-containing mixed magnetic separation concentrate from Donganshan，synergetic flotation of step-by-step flotation and dispersing flotation technology was conducted.Results show that using citric acid as dispersant，starch as inhibitor，KS-Ⅲ as collector，via one step siderite direct flotation，tailings of direct flotation with NaOH as pH regulator，starch as inhibitor，CaO as activator，KS-Ⅲ as collector via one roughing-one cleaning-two scavenging hematite reverse flotation closed-circuit process，iron concentrate with iron grade of 67.89%，iron recovery of 69.35% was obtained.Synergetic flotation of step-by-step flotation and dispersing flotation technology has good separation effect on carbonate-containing mixed magnetic separation concentrate for combination of the step-by-step flotation and dispersing flotation.

Key words: Carbonate, Siderite, Step-by-step flotation, Dispersing flotation, Synergetic flotation