Wettability of coal - a comparative study

A comparative study of the contact angles of air bubbles, hydrocarbon oils (benzene and dodecane - both in the absence and in the presence of water-soluble dodecylamine (laurylamine) chloride), flocculants and coagulants drops on flat polished coal surfaces immersed in water was made. The effect of the hydrocarbon chain length of some n-alkylamine chlorides on the coal-oil-water was also investigated. The relationship of the measured contact angles to the flocculants, coagulants and dodecylamide chloride concentrations and pH was established. Results obtained show that maximum contact angles for the coals studied occur in the alkaline pH range (pH > 7) for the systems investigated. Evidence is also provided to show that benzene and dodecane do not spread spontaneously on wet coal surfaces, even in the presence of a water-soluble cationic surfactant. The results further show that the coal-benzene water contact angles increase with an increase in the hydrocarbon chain length of the surfactant. Coagulants probably affect flotation of coal fines adversely, whereas flocculants; have a remarkable effect on contact angles similar to that of surfactants.