Modeling of the diffusion-kinetics-controlled adsorption of cations on a sorbent surface

A mathematical model for describing the sorption of two kinds of cations from dilute immobile liquid solutions on a flat sorbent surface was proposed. A criterion of the transition from the kinetics-controlled sorption mode, in which the selectivity of the sorbent is governed by the ratio between the rate constants of the reactions of the different cations from the solution and adsorption sites on the sorbent surface, to the diffusion-controlled mode, in which the selectivity is determined by the difference between the diffusion coefficient for the migration of the cations to the sorbent surface, was proposed. Formulas were obtained for calculating the surface concentration of adsorbed cations as a function of the time. The calculation results are in a reasonable agreement with the experimental data.