Effect of polyaluminum chloride on the flotation separation of coal from kaolinite

•PAC reduced the concentrate ash content in coal flotation.•PAC aggregated kaolinite with low concentration.•PAC dispersed kaolinite with high concentration.•PAC did not aggregate coal particles.

The effect of the polyaluminum chloride (PAC) on reducing the kaolinite entrainment in coal flotation is studied in this paper. The settling experiments show that the settling velocity of kaolinite was the highest when pH was around 5.5. With the addition of PAC, the settling velocity of kaolinite increased at low PAC concentration whereas it reduced at high PAC concentration. The flotation results show that PAC significantly reduced the concentrate ash content. The particle size measurements and the aggregate images show that kaolinite was aggregated by low concentration PAC and was dispersed by high concentration PAC while coal was not aggregated by PAC. The zeta potential measurements indicate that PAC neutralized the negative charge of kaolinite at low concentration and then increased the positive charge of kaolinite at high concentration. The electrostatic double layer repulsion induced the dispersion of kaolinite when the PAC concentration was high.

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