Interaction characteristics between diesel and coal with different hydrophilicity: Kinetic and force effects

Abstract

Collector adhesion and spreading on the surface of coal plays a critical role in increasing the floatability and flotation efficiency of coal. In this work, the interaction characteristics, including kinetic and force effects, between the collector and coal surface with different hydrophilicity was comprehensively investigated using collector adsorption tests, induction time measurements, the atomic force microscope (AFM) colloidal probe technique, and molecular dynamics simulation (MDS). The results showed that the process of diesel adsorption on the coal surface conformed to the pseudo first-order kinetic model. As coal hydrophilicity increased, the maximum capacity exhibited a non-linear exponential decrease while the rate exhibited a linear decrease, in accordance with the induction time of coal particle-oil bubble. Force effects results showed that the adhesion force and acting distance between model diesel and coal decreased as coal hydrophilicity increased. MDS results further showed that hydrocarbon collectors were adsorbed on the hydrophobic sites of coal, but not on the hydrophilic sites. Therefore, the number of hydrophobic sites for non-polar diesel adsorption and the adhesion force between diesel and coal particles decrease as hydrophilicity increases, which in turn causes a reduction in the collector adsorption rate and maximum adsorption capacity. Furthermore, flotation tests were conducted to validate the kinetic and force effects and to indicate that both the combustible matter recovery and clean coal ash content of coal samples significantly decrease from 98.49% to 58.44% and from 3.02% to 2.65%, respectively, with increasing coal hydrophilicity.