Abstract:Based on surface thermodynamics and XDLVO theory, free energy changes induced by hydrophobic interactions (GH), free energy changes originated from electrostatic force (GEL) and the total free energy changes in the adsorption of P. putida and B. subtilis on kaolinite and montmorillonite were obtained. The negative values of GH and the positive values of GEL suggested that the hydrophobic force favors, and the electrostatic force unfavors the bacterial adsorption on kaolinite and montmorillonite. The absolute values of GH were much larger than those of GEL, indicating that hydrophobic interactions play a role more important than electrostatic force does in bacterial adsorption. The negative total free energy changes (G) suggested that the sorption of bacteria on clay minerals is a thermodynamically spontaneous process. Greater G values for bacterial adsorption on kaolinite than on montmorillonite indicated higher affinity of the bacteria for kaolinite than for montmorillonite.