Slow Sorption Kinetics of Pentachlorophenol on Soil: Concentration Effects

We investigated the sorption kinetics of pentachlorophenol (PCP) on soil at a pH of 4.1 using batch techniques. A multiple spiking methodology was employed to circumvent the solubility limitation of PCP. The ratio of sorbed PCP to solution-phase PCP (S/C) after 2-4 days of equilibration was concentration dependent. It decreased from 90 to 60 L/kg with a 4-fold increase in the total PCP concentration, from 5 to 20 mg/L. Increasing residence times resulted in slow increases in sorption. The onset of the slow sorption kinetics was also concentration dependent. At higher PCP concentrations, the slow sorption kinetics were much more pronounced. However, there was not a clear definable trend in which concentration could be correlated to S/C. A 2-day desorption study demonstrated that the extent of desorption was also concentration dependent. At higher PCP concentrations, a smaller percent of the sorbed PCP was available for desorption.