ION-EXCHANGE KINETICS - HETEROGENEOUS RESIN-PHASE MODEL

A new approach to cation-exchange kinetics views ion-exchange resin as an aggregate of uniform cylindrical pores. ion exchange occurs at the pore surface. The counterions dissociate only partially from the fixe d sites, and the charge created on the pore surface is balanced by the counterions in the electrical double layer: Thus: any cross section o f a pore consists of an annular double-layer region and a central core region. Electroneutrality prevails in the core region through an infl ux of coions. Diffusion of ions through both regions is considered. Th e complete model incorporating these ideas for, kinetics of monovalent cation exchange was tested with oui experimental data as well as with the reported data. The pore diffusion coefficients used in the model are free ionic diffusion coefficients corrected for the tortuosity fac tor of the pores. Unknown parameters of the model are the degree of di ssociation of counterions from the fixed sites of the pore (f(sigma)), and the film thickness (delta). Both parameters are insensitive to th e type of counterions, solution concentration, and the direction of ex change. Further, f(sigma) appears to be a characteristic property of r esin alone. Superiority of the developed model over the previous model s is established.