Intensified Ash Rejection in Coal Flotation by the Aggregation of Gangue Minerals Induced by Polyaluminum Chloride

It is difficult to obtain a low-ash clean coal from a coal sample containing a high proportion of gangue minerals by traditional flotation methods due to the severe gangue contamination of the concentrate. In this article, a novel flotation method, using polyaluminum chloride (PAC) is described that showed better ash rejection. The aggregation due to PAC addition was verified with a concentration around 20 mg/L, and PAC selectively aggregated the high-ash gangue minerals (> 2.0 g/cm(3)) but did not aggregate the low-ash coal (< 1.4 g/cm(3)). With higher concentrations of PAC, both coal and gangue minerals were dispersed. The scanning electron microscope pictures of the flotation concentrate indicated that the contamination of gangue minerals was reduced using a low concentration of PAC. The zeta-potential measurements showed that charge neutralization with a low PAC concentration was the main aggregation mechanism of the gangue minerals. The zeta potential of the low-ash coal was highly positive when PAC was added, which means that the coal particles were dispersed due to the electrostatic double-layer repulsion.