Reverse cationic flotation of low-grade phosphate ore using quaternary ammonium salt as a collector and its adsorption mechanism

Abstract

A novel quaternary ammonium salt collector, LH-01, was employed for the reverse cationic flotation of a magnesium-depleted concentrate (P2O5 grade of 19.72wt%, SiO2 content of 44.26wt%). We achieved an outstanding phosphate concentrate with a P2O5 grade of 35.16wt%, a SiO2 content of 6.06wt%, and a P2O5 recovery of 75.88%. This process was accomplished through two sequential reverse cationic flotation processes designed for quartz removal. Importantly, the quartz removal by LH-01 reached 94.17%, far superior to that by dodecyltrimethylammonium chloride, achieving highly selective separation of quartz and apatite. To understand the adsorption mechanism and kinetics of the collector LH-01 on quartz and apatite surfaces, various techniques, such as quartz crystal microbalance with dissipation, atomic force microscopy, and X-ray photoelectron spectroscopy, were employed. Results revealed that the adsorption layer of LH-01 on the apatite surface was thin and rigid, with a significantly lower hydrophobic effect than that of the viscoelastic multiple adsorption layer formed by LH-01 on the quartz surface. This disparity was identified as the primary factor contributing to the selective flotation separation of apatite and quartz. Moreover, the adsorption of LH-01 on the quartz surface was the result of multiple forces, including electrostatic adsorption, multiple-hydrogen-bond adsorption, and intermolecular hydrophobic association.