Abstract: The effects of pulp pH values, dispersants and auxiliary collectors on direct reverse flotation of carbonate-containing iron ores were explored. Floatation experiment results show a sharp increase in iron grade as the pH value raises from 11.0 to 11.8, and the maximum grade can be obtained at pH 11.8, after which the iron grade has almost no change. When the pH value is 12.0, sodium tripolyphosphate is a kind of effective dispersant and sodium dodecyl sulfate is an effective auxiliary collector of KS-Ⅲ, both the iron recovery and grade increase with the action of sodium dodecyl sulfate or sodium tripolyphosphate. Theoretical calculations indicate that the floatation results are related to the solution chemistry of siderite and interactions between particles. Structure-activity calculations of collectors show that sodium dodecyl sulfate has perfect selectivity, emulsion and solubility.