Kinetic and thermodynamic study of chlorophenol sorption in an allophanic soil.

The sorption of 2,4-dichlorophenol, 2,4,6-trichlorophenol, and pentachlorophenol by a allophanic soil was studied in a series of batch experiments. Chlorophenol sorption behavior was evaluated as a function of reaction time (0-96h) and input concentration at a fixed ionic strength (0.1mol L(-1) KCl) at 25, 35, and 45 degrees C. Sorption results for the various reaction temperatures were used in calculating thermodynamic parameters. Chlorophenol sorption increased with temperature, suggesting an endothermic process. The Elovich equation was used to describe the kinetic data. Data from the isotherm experiments were described by the Triple-Layer Model in which monodentate outer- and inner-sphere complexes were formed between deprotonated organic molecules and active sites on the variable-charge soil. The calculated thermodynamic parameters suggest that chlorophenol sorption is a spontaneous (DeltaG<0), endothermic (DeltaH>0) and entropy-driven reaction (DeltaS>0).