WETTABILITY MEASUREMENTS ON COAL PARTICLES BY MEANS OF THE SOLIDIFICATION FRONT TECHNIQUE

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Abstract
Reliable methods for the characterization of the surface properties and the wettability of small particles have not been available in the past. A novel technique, based on the behaviour of the lest particles at the solidification front of certain well defined solidifying melts (matrix materials) has been developed recently in our laboratory. This method was used to determine contact angles and surface tensions of coal particles in the range of 20-250 μm. Two types of bituminous and one type of subbituminous coal were tested using thymol, biphenyl, napthalene, salol and 2-phenyl phenol as matrix materials. The results show that contact angles on small particles can be determined to within ± 2°, i.e. to the same degree of accuracy that is typically reported for extended smooth surface by means of conventional techniques. The measurements also show that within one and the same coal sample the larger particles are somewhat more hydrophilic than the smaller ones. Surface tensions and contact angles of coal particles are of great interest in connection with coal beneficiation processes such as froth flotation and oil agglomeration.