SURFACE TENSION EFFECTS IN THE SEDIMENTATION OF COAL PARTICLES IN VARIOUS LIQUID MIXTURES

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Abstract
The sedimentation volume, V sed, of coal particles in mixtures of pairs of non-polar and more polar organic liquid combinations as well as in aqueous solutions was determined at 20°C. The liquid combinations were chosen such that the surface tension, γSV, of the coal particles fell between the surface tensions, γLV, of the two liquids. A constant mass of a given coal sample was suspended in constant volumes of liquid mixtures of different concentrations. It was found that the sedimentation volume changed with varying composition of the liquid mixtures, as did the surface tension. A maximum or a minimum occurred in V sed when the surface tension of the suspending liquid was equal to that of the coal particles, i.e. when γLV = γSV. Maxima occurred in more polar and minima in the non-polar or less polar liquid mixtures. The position of the extrema, and hence the surface tension, γsv, of the particles, was found to change with particle size, in agreement with findings from other independent techniques. It was found that the surface tension of coal, γsv, depends on the surrounding liquid, i.e. coal is hydrophobic in organic and hydrophilic in aqueous media, again in agreement with the results from other techniques.