Investigation into the impacts and mechanisms of Ca2+ and Mg2+ on flotation of columbite-tantalite in NaOL system

Tantalum (Ta) and Niobium (Nb) are strategic key metals used in aerospace, steel, chemicals, and other industries. Columbite-tantalite is the primary Ta- and Nb- containing mineral. Flotation is widely recognized as an effective and practical approach for the pre-concentration of columbite-tantalite. However, calcium (Ca), magnesium (Mg), and other inevitably introduced ions from process water and mineral dissolution during beneficiation can significantly affect the flotation performance of columbite-tantalite. This study systematically investigates the effects of Ca2+ and Mg2+ on columbite-tantalite flotation in sodium oleate (NaOL) system. The flotation experiments showed that the addition of Ca2+ and Mg2+ reduced the flotation recovery of columbite-tantalite by 94.87% and 92.56%, respectively. Characterization analysis has revealed that NaOL can form a hexagonal ring structure with the Mn site on columbite-tantalite (100) crystal surface. Nevertheless, Ca²⁺ and Mg²⁺ ions interfere with the chemical adsorption of NaOL by reacting with it to form oleate precipitates, which subsequently cover the mineral surface. Hence, excessive NaOL does not facilitate effective flotation of columbite-tantalite. Furthermore, compared with columbite-tantalite surface, NaOL tends to interact with Ca2+ and Mg2+ to deactivate the collector. This paper elucidates the inhibitory effects of Ca²⁺ and Mg²⁺ on the flotation of columbite-tantalite. This implies that when processing ores with high water hardness or those containing easily leachable metal ions, targeted removal of metal ions such as Ca²⁺ and Mg²⁺ from the slurry is necessary to enhance the flotation efficiency and recovery of columbite-tantalite.