The purpose of this study was to illucidate the thermodynamics of the adsorption process of a hydrophobic polymeric flocculant, poly(2-ethylhexyl methacrylate), on hydrophobic colloidal coal particles leading to the determination of the Gibbs free energy change and whether the hydrophobic effect is the main driving force for adsorption. Thus, from the adsorption isotherms, DELTA-G-degrees-ads was determined. In addition, contributions to DELTA-G-degrees-ads from electrostatic forces, DELTA-G-degrees-el, and the "specific" adsorption, DELTA-G-degrees-sp, were determined. To determine the nature of the "specific" adsorption forces, the free energy changes due to hydrophobic association, DELTA-G-degrees-H, and van der Waals forces, DELTA-G-degrees-vdw, were calculated and compared. The results indicated that adsorption of the hydrophobic polymeric flocculant on coal is influenced by coal type and pH, but the main driving force for adsorption appears to be the hydrophobic effect.
