SORPTION AND DESORPTION RATES OF CARBON-TETRACHLORIDE AND 1,2-DICHLOROBENZENE TO 3 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 var ying alkyl-chain length were quantified. The effects of solute structu re, 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. Th e experimental data were simulated using a two-site model and a model incorporating a continuous distribution of mass-transfer rate coeffici ents. Based on a statistical analysis of the model simulations, the fo llowing conclusions were made: (1) the rate of 1,2-DCB sorption to the organobentonites was significantly faster than the rate of 1,2-DCB so rption 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-ch ain lengths of the organobentonites did not affect the rate of mass-tr ansfer during sorption; however, the rate of 1,2-DCB desorption decrea sed as the length of the organobentonite alkyl-chain increased. (4) Th e rate of solute desorption was slower than the rate of solute uptake for two of the three organobentonites. (5) For most environmental appl ications using the organobentonites studied here, a local equilibrium assumption will satisfactorily describe CCl4 and 1,2-DCB sorption and desorption.