Surface properties of coal and their role in fine coal processing

This investigation was conducted to identify and characterize those properties of coal that determine its wetting characteristics and its behavior in surface-based coal cleaning processes. Emphasis has been given to the surface oxidation of coal and its role in wetting behavior and the flotation response of coal.;A correlation was observed among the interfacial properties of as-received Cambria ;The distribution of critical wetting surface tension of coal particles in an assemblage can be determined by the film flotation technique using aqueous methanol solutions of various compositions to regulate the liquid surface tension. A method has been developed to estimate the contact angles of particles and the distribution of hydrophobic and hydrophilic sites on coal particles from film flotation data. This new approach has been verified by comparing the calculated mean contact angles from film flotation results with the measured values on the flat surface for a number of pure materials and coal samples.;Thermal oxidation of coal in air affects the properties of coals significantly. When a coal is oxidized, its zeta potential decreases and its IEP shifts to a lower pH value. Lower rank coals were found to be more susceptible to oxidation than a high-rank coal, namely anthracite.;Oxidation has a deleterious effect on the behavior of coal particles in fine coal processing. When coals are oxidized, the water retention capacity of the filter cake increases and the flotation recovery of the coals decreases. The results show that the hydrophilic oxygen functional groups produced on the coal surface during oxidation increase the interaction of water molecules with coal, thereby increasing the water retention capacity and decreasing flotation recovery. (Abstract shortened with permission of author.).