Cationic flotation of scheelite from calcite using quaternary ammonium salts as collector: Adsorption behavior and mechanism

•Flotation of scheelite from calcite can be obtained with QACs as collector.•Van der Waals force also plays an important role in the adsorption of QACs.•Selectivity of QACs is also due to their large van der Waals force.

Cationic flotation is a promising method for separating scheelite from calcite at room temperature, because of the significant difference between their surface charges. Three quaternary ammonium salts, i.e., didecyldimethylammonium chloride (DDAC), trioctylmethylammonium chloride (TOAC), and dodecyltrimethylammonium chloride (DTAC), were investigated as cationic collectors in the flotation of scheelite from calcite. The flotation behaviors of scheelite and calcite with the three quaternary ammonium salts were studied using single-mineral and mixed-mineral flotations; flotation with oleate was used for comparison. The results show that flotation of scheelite from calcite was possible around pH 8 with DDAC and TOAC as collectors. The collecting powers and selectivities of these compounds for scheelite were higher than those of oleate. The molecular structures, Fourier-transform infrared spectra, and zeta potentials indicated that when quaternary ammonium salts are used as collectors, electrostatic interactions play a primary role in the flotation of scheelite from calcite. The adsorptions of the three quaternary ammonium salts fitted a general adsorption isotherm well, but the Langmuir isotherm only fitted the adsorption of DDAC well. It can be concluded from the adsorption isotherm parameters that the role of van der Waals forces is as significant as that of electrostatic forces in the interactions of quaternary ammonium salts with the two minerals, and that the selectivities of the quaternary ammonium salts for scheelite result from their large van der Waals forces, as well as the opposite charges on scheelite and calcite. The van der Waals forces of quaternary ammonium salts significantly affect the adsorption processes and consequently the isotherm plots.