Sorption and desorption rates of carbon tetrachloride and 1,2-dichlorobenzene to three organobentonites and a natural peat soil

The sorption and desorption rates of carbon tetrachloride (CCl4) and 1,2-dichiorobenzene (1,2-DCB) to and from three organobentonites of varying alkyl-chain length were quantified. The effects of solute structure, organobentonite structure, and solute-sorbent contact time on the rates of solute mass-transfer were investigated. For each solute, the rate of sorption was compared to the rate of desorption. In addition, the rate of 1,2-DCB sorption to a natural peat soil was quantified. The experimental data were simulated using a two-site model and a model incorporating a continuous distribution of mass-transfer rate coefficients. Based on a statistical analysis of the model simulations, the following conclusions were made: (1) the rate of 1,2-DCB sorption to the organobentonites was significantly faster than the rate of 1,2-DCB sorption to the peat soil. (2) The rate of mass-transfer during sorption and desorption was greater for CCl4 than for 12-DCB. (3) The alkyl-chain lengths of the organobentonites did not affect the rate of mass-transfer during sorption; however, the rate of 1,2-DCB desorption decreased as the length of the organobentonite alkyl-chain increased. (4) The rate of solute desorption was slower than the rate of solute uptake for two of the three organobentonites. (5) For most environmental applications using the organobentonites studied here, a local equilibrium assumption will satisfactorily describe CCl4 and 1,2-DCB sorption and desorption.