Improvement mechanism of graphite flotation from kaolinite induced by laboratory synthesized polyaluminum chloride

Abstract

The effect of laboratory synthesized polyaluminum chloride (PAC), which was prepared by alkali titration method, on the flotation performance of graphite was systematically studied in this work. Flotation tests using natural graphite ore demonstrated that PAC could enhance flotation yield while maintaining concentrate quality. Further flotation tests using artificial mixed graphite-kaolinite minerals demonstrated that the addition of PAC at around 30 mg/L can improve graphite recovery and separation efficiency, and has no significant negative effect on the loss on ignition in concentrate. The possible improvement mechanism of PAC on graphite flotation including water entrainment, slime coating, bubble-graphite attachment was revealed by characterization methods such as zeta potential measurements, focused beam reflectance measurement (FBRM), particle vision and measurement (PVM), single bubble loading tests and contact angle measurements. Zeta potential measurements show that PAC at 30 mg/L neutralized the negative charge on the surface of kaolinite, while graphite was positive charged. The real-time FBRM results show that the average chord length of kaolinite particles increased significantly when PAC concentration was 30 mg/L and decreased at PAC concentration of 90 mg/L, while graphite particles remained in a dispersion state. However, the PVM results indicated that the slime coating between kaolinite and graphite surface was aggravated when PAC was 30 mg/L and then got diminished at 90 mg/L. The single bubble loading tests and contact angle measurements proved that PAC at 30 mg/L significantly increased the attachment probability between bubble and graphite particles. Meanwhile, the contact angle of graphite remained stable without significant reduction, effectively maintaining the surface hydrophobicity of graphite and ultimately promoting graphite flotation recovery. This work is expected to provide theoretical understanding and technical support for graphite flotation by the adjustment of PAC concentration.