Reducing quartz entrainment in fine coal flotation by polyaluminum chloride

Flotation tests using artificial mixtures of clean coal and quartz were conducted with and without the presence of sodium hexametaphosphate (SHMP) to study the effect of polyaluminum chloride (PAC) on quartz entrainment in fine coal flotation. Comparisons of flotation results show that the degree of quartz entrainment was greatly reduced using a suitable amount (e.g., 20 mg/L) of PAC in the absence of SHMP, however, significant changes of PAC on quartz entrainment did not appear in the presence of SHMP. The possible mechanisms responsible for the reduced quartz entrainment using PAC in fine coal flotation were investigated by particle size distribution measurements, zeta potential measurements, and interaction force calculations. Analysis of particle size distribution results reveals that when SHMP was not added, quartz particles were selectively aggregated with the addition of 20 mg/L PAC and the aggregation of quartz or coal particles was negligible at a high PAC dosage (e.g., 50 mg/L). Meanwhile, the aggregation of quartz particles induced by PAC was eliminated with the presence of SHMP. The electrostatic double layer repulsive force between quartz particles was calculated using the Deyaguin-Landau-Verwey-Overbeek (DLVO) theory with incorporating the results of zeta potential measurements. At 20 mg/L of PAC, the negative surface charge of quartz particle was neutralized and the electrostatic double layer repulsive force between quartz particles reached the minimum. These findings might be reasons of the aggregation of quart particles and therefore reduce the quartz entrainment in fine coal flotation.