Electromotive force studies of cellulose acetate membranes. Binding of divalent cations and membrane potentials of KCl–KF mixtures

Abstract

Cellulose acetate (CA) membranes cast in our laboratory were characterised electrochemically by EMF measurements. Henderson and Schlögl integrations are used for calculating the membrane potential. Experiments with divalent ions (BaCl₂, MgCl₂ in HCl) have been performed, and it is shown that the divalent ions bind strongly to the glucuronic acid groups in the CA membrane, transforming the cation exchanger into an anion exchanger. It takes more than one month for the bound divalent cations to dissociate fully from the glucuronic acid groups at 25 °C. The four-ion system KCl–KF–HCl is studied, and it is shown that the F^– ion has a lower diffusion coefficient in the membrane than the Cl^– ion. The differences between Schlögl and Henderson integration are less than the experimental uncertainty for the KCl–KF–HCl measurements. The membrane concentration profiles and fluxes of ions are calculated for the system KCl–KF–HCl.