Surface chemistry aspects of coal flotation in bore water

Several theories have been proposed to explain enhancement of coal flotation in salt solutions. In this paper, surface chemistry aspects of coal flotation in bore (hypersaline) water were examined using bubble-particle attachment time experiments, zeta potential measurements, cyclic measurements of contact angle and Atomic Force Microscopy (AFM). The attachment time experiments showed that the bubble-particle attachment in deionized water was instantaneous and independent of the particle size. The attachment in bore water required longer time, which increased with increasing particle size. The cyclic measurements of contact angle on a flat coal surface showed that the coal hydrophobicity as measured by the advancing (maximum) and receding (minimum) contact angle did not change in the presence of salt ions. The zeta potential measurements show that both the coal particles and air bubbles were negatively charged in bore water. The AFM studies showed that bore water reduced repulsive surface forces between the coal particles and air bubbles but had little effect on the force of adhesion. The overall results suggest that enhancement of coal flotation in hypersaline water is not entirely attributed to the surface chemistry aspects as previously proposed.