Characteristics of Coal Slurry Aggregate Induced by Inorganic Salts

Abstract

The impact of coagulant type and dosage on the clarity, zeta potential, floc size, and floc structure of a coal slurry suspension was investigated. The results showed that the critical coagulation concentrations of trivalent ions are 0.81 mM and 0.018 mM for coal–coal and coal–kaolinite, respectively, which are lower than those of divalent ions. The initial settling was more affected by AlCl3 and FeCl3 than MgCl2 and CaCl2, while the supernatant turbidity was significantly decreased at a lower dosage (0.06 mM) for trivalent ions, consistent with the classical Derjaguin–Landau–Verwey–Overbeek theory, zeta potential results, and adsorption behaviors of quartz crystal microbalance with dissipation. The floc size and settling rate induced by AlCl3 and FeCl3 were greater than those of divalent ions at lower concentrations and tended to have an irregular and porous structure, enhancing the coagulation effect. The findings highlight the differences in the physical characteristics of floc size and structure in optimizing the coagulation process produced by electrical neutralization and sweep-floc coagulation of amorphous metal hydroxide precipitates.