Effect of Coal Surface Wettability on Aggregation of Fine Coal Particles

Abstract

Fine coal aggregation in concentrated coal-water suspensions was studied through steady-state rheological measurements. The wettability of coal particles was modified by dry oxidation of a bituminous coal. The degree of hydrophobicity was monitored using film flotation. The rheological measurements revealed that hydrophobic coal particles aggregate in aqueous suspensions over a wide pH range, and produce slurries with high yield stresses. As the degree of coal oxidation increases, the coal particles become more hydrophilic and such suspensions exhibit lower yield stress values. The yield stress values for suspensions prepared from oxidized/hydrophilic coal become a strong function of pH and correlate well with the surface charge as determined through electroacoustic measurements. For the suspensions prepared from the samples with intermediate degree of oxidation the effect of coal surface heterogeneity becomes very important. These results indicate that the coal particle aggregation, and thus the yield stress of aqueous suspensions of coal, is strongly affected by wettability of coal particles.