Describing chlorophenol sorption on variable-charge soil using the triple-layer model.

The sorption of 2,4-dichlorophenol, 2,4,6-trichlorophenol, and pentachlorophenol by a variable-charge soil from southern Chile was studied in a series of batch experiments. The chlorophenol sorption behavior was evaluated as a function of pH (pH range 4-8) at two different ionic strengths, 0.01 and 0.1 M KCl (25 degrees C). Chlorophenol sorption depended on pH and a downward shift in the soil PZC was observed with increasing chlorophenol concentration. Chlorophenol sorption decreased with increasing pH, suggesting that the undissociated species is sorbed more readily and that electrostatic repulsion may inhibit partitioning as pH increases. Data from the sorption experiments were fitted 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.