ADSORPTION OF PENTACHLOROPHENOL BY NATURAL SOILS

The adsorption of pentachlorophenol, a listed hazardous substance, by natural soils was investigated at pH values of 4, 7, and 10 using various soils collected from the surface horizon. The effects of soil properties, such as organic carbon and fines content, were also studied and were found to have a significant positive correlation with the amount of solute adsorbed. Although soil properties strongly influence the process, the pH of the soil-water system was found to be a primary factor which determines the affinity of solute for the soil particle surface. Pentachlorophenol, a weak organic acid, is transformed to pentachlorophenate ion at pH higher than pK(a) and adsorption is reduced. The anionic form of the molecule was found to be much more hydrophilic than the neutral form resulting in a two orders of magnitude reduction of the adsorption capacity as the pH was elevated from 4 to 10. The presence of cosolvents had a negative effect on the process leading to substantial reductions in the adsorption capacity of the soils. The data obtained from the batch experiments were fitted to both linear and nonlinear models and it was concluded that the Freundlich model adequately describes the process, whereas the linear partition model consistently underestimates the degree of adsorption.