Rate-Limited Sorption and Desorption of 1,2-Dichlorobenzene to a Natural Sand Soil Column

Abstract

The rate of sorption of 1,2-dichlorobenzene (DCB) onto a natural sandy soil in water-saturated soil columns was measured. Desorption rates were also measured after allowing the solute-sorbent system to equilibrate during a no-flow period, ranging from 3 to 49 d. Two-site equilibrium/kinetic and Γ-distributed rate sorption models were then used to determine a single set of sorption parameters that could describe both the uptake and desorption of 1,2-DCB from these columns. Ninety-five percent confidence regions for the mass transfer rates and the two-site parameters were generated. Both the Γ-distribution model and the two-site model could describe uptake and desorption with a single set of parameters, although the Γ-distribution model was better at the 95% confidence level in three of five experiments. There was no statistically significant change in the sorption parameters between 3 and 49 d of no-flow. Allowing the Γ-distributions of rates to differ between uptake and desorption improved the ability to fit the observed data, and for some experiments it could be concluded with 95% confidence that the rate of desorption is different than the rate of uptake.