MODIFIED DIFFUSION TECHNIQUE FOR STUDYING NONLINEAR AND KINETIC SORPTION AND DESORPTION PROCESSES

A new method is presented to interpret data on diffusion-sorption proc esses obtained from through-diffusion experiments. Both sorption and d esorption are modeled as kinetically controlled processes by incorpora ting nonlinear isotherms. The diffusion-sorption equation was solved n umerically and the resulting algorithm was integrated into a nonlinear regression code to test various models. The through-diffusion techniq ue was modified such as to obtain sorption and desorption data from a single experiment. Data are presented for the diffusion of cesium thro ugh a Eutric Cambisol soil pellet. Various sorption models were tested . The best fit to the experimental data was obtained assuming first-or der kinetics with a Freundlich isotherm. Desorption shows a marked hys teresis.