Surface properties of coal and their effects on the selective oil agglomeration process

The heat of immersion of coal in water and various organic liquids provides a useful means for characterizing the surface of the material, while the oil-water-coal, three-phase contact angle provides a characterization of the coal surface as well as the interactions among oil, water, and coal. Such characterizations may provide an indication of how well the coal will respond to cleaning by the froth flotation and oil agglomeration methods which are controlled by the surface properties of the material.; The heat of immersion of two types of coal in water and in several different organic liquids was determined with a microcalorimeter. The effects of particle size and moisture content were also investigated. The heat of immersion was found to depend on the total wetted surface area of the coal including both the external particle surface and a portion of the internal pore surface. For a given coal and a given liquid, the heat of immersion correlated well with particle size.; The suction potential method for measuring the three-phase contact angle was modified and used to determine the oil-water-solid contact angle for particles of graphite and coal. The modification greatly reduced the measurement time and made the method more controllable. The three-phase contact angle was found to vary with coal rank and particle size.; The heat of immersion of coal in water and the three-phase contact angle were used along with the hydrophilicity index calculated from the Fourier Transform Infrared (FTIR) absorption spectrum to characterize the surface properties of raw and oxidized coals. Two coals, highly hydrophobic No.2 Gas Seam coal, and moderately hydrophobic Colchester Seam coal, were oxidized at 150{dollar}spcirc{dollar}C in air for a series of time intervals. When the oxidation time was varied for a given coal, the measured three-phase contact angle for oxidized coal correlated well with the heat of immersion and the hydrophilicity index. The oil agglomeration response of these coals was determined by measuring the agglomeration recovery and relative turbidity change of the coal particle suspension. The agglomeration response correlated well with either the three-phase contact angle, the heat of immersion, or the hydrophilicity index.; The measured contact angle of oil-water-coal systems indicates that agglomerates are held together by oil bridges between coal particles. The more oleophilic the coal surface, the larger the binding force. The presence of air bubbles on a hydrophobic coal surface was found to favor the attachment of oil droplets on the coal surface and promote a higher initial agglomeration rate than that observed in the absence of air bubbles.