The wetting behaviour of several organic liquids in water on coal surfaces

Several organic liquids were used to probe the surface chemical characteristics of five coal types ranging in rank from brown to low-volatile bituminous in the presence of water. The liquids were hexane, cyclohexane, diiodomethane, toluene, o-xylene, chloroform, dichloromethane, oleic acid, chloroform and hexan-1-ol. The advancing and receding contact angles formed at the coal-water-liquid junction were measured and it was found that a critical interfacial tension existed, below which the organic liquid wetting properties were equivalent. Above the critical interfacial tension, the wettability of the coal by the organic liquid increased as the polarity of the liquid increased, giving a measure of the efficiency with which the water wetting film could be expelled from the coal surface. At a fixed interfacial tension, the advancing and receding contact angles decreased as the rank of the coal increased.