ELECTROTRANSPORT OF PROTON AND DIVALENT-CATIONS THROUGH MODIFIED CATION-EXCHANGE MEMBRANES

Separation of divalent cations from binary electrolyte solutions with protons was achieved by electrotransport through modified cation-excha nge membranes (CEMs). The CEM modification was carried out by adsorpti on of polyethyleneimine on the membrane surface. Without any applied d riving force, both modified and non-modified membranes exhibited a hig her affinity for divalent cations. Under an electrical field, the tran sport number of the divalent cation decreased significantly. The appar ent rate constants of the penetration of the divalent cations into the membrane were calculated on the basis of unidirectional fluxes and co ncentration profiles of cations within the anodic unstirred layer. The unidirectional fluxes were measured by means of the radiotracer techn ique. The concentration profiles were determined by numerical resoluti on of the Nernst-Planck electrodiffusion equations coupled with the Po isson equation for current densities lower than the limiting value.