In this study, a selective depressant sodium alginate (SA) was used to improve the flotation performance of separating apatite from dolomite. The flotation results show that SA can completely depress dolomite with a slight effect on apatite flotation in pH 8-11. The contact angle tests and adsorption tests indicate that depressant SA absorbed onto both apatite and dolomite surfaces and the adsorption intensity of the latter was greater than that of the former. The FTIR and XPS analysis indicate that SA absorbed onto apatite surface mainly through hydrogen bonding between hydroxyl groups on apatite surface and hydroxyl and carboxyl groups on polymer SA, while onto dolomite surface mainly through chemical chelating between Ca on dolomite surface and hydroxyl and carboxyl groups on polymer SA. Therefore, the adsorption of SA on dolomite was stronger than on apatite, which resulted in a selective depression for dolomite (C) 2020 Elsevier B.V. All rights reserved.