Sorption of Pentachlorophenol to HDTMA-Clay as a Function of Ionic Strength and pH.

We investigated the sorption of pentachlorophenol (PCP) to a surfactant-modified clay and the solubility of PCP as a function of pH and ionic strength. Pentachlorophenol is a hydrophobic ionizable organic compound; therefore, it can exist as either a protonated or adeprotonated species. The objectives of this study were to determine differences in the sorption and solubility of the two species and to model the sorption as a function of pH. We developed a model that described the sorption across the experimental pH range (4-8.5). The model represented the sorption of the deprotonated species by a Langmuir-type isotherm and the sorption of the protonated species by a linear isotherm. Between pH 4 and pH8.5, the sorptiondecreases by three times and the solubility increases by 3 orders of magnitude as the dominant aqueous species changes from the protonated to the deprotonated form.