Unraveling interfacial interaction mechanism: Towards selective depression of ankerite by carboxymethyl cellulose in columbite flotation

Columbite is a strategic mineral resource, and its surface physical and chemical properties are similar to those of associated Fe-bearing gangue mineral dolomite, making flotation separation and enrichment difficult. This study achieved the effective separation of columbite from ankerite by employing carboxymethyl cellulose (CMC) as a biodegradable depressant in a benzohydroxamic acid (BHA) collector system. Flotation tests showed that CMC strongly depressed ankerite while having a minimal effect on columbite. Increasing the CMC concentration from 0 to 7.5 mg/L caused a sharp drop in ankerite recovery from 90.34 % to 10.33 %, in contrast to a moderate decrease in columbite recovery from 85.31 % to 70.41 %. Under these optimal conditions, artificial mixed-ore flotation produced a concentrate with a Nb 2 O 5 grade of 69.45 % and a columbite recovery of 81.15 %. Particle-bubble contact tests, zeta potential, FTIR, XPS and AFM analyses demonstrated that the carboxyl groups of CMC exhibited a strong affinity for the Ca, Mg, and Fe active sites on the ankerite surface. This interaction induced chemical adsorption and the formation of stable Ca/Mg/Fe-COOR complexes, which effectively masked the ankerite surface and prevented subsequent adsorption of BHA, thereby resulting in significant depression. In contrast, the weak interaction between CMC and columbite allowed the chemisorption of BHA on the Fe and Nb active sites of columbite to be preserved, maintaining its excellent floatability. This selective mechanism enabled the highly efficient separation of columbite from ankerite. Consequently, CMC is identified as a potential high-efficiency and biodegradable depressant for the flotation separation of columbite and ankerite.