Diffusional and conductive membrane permeabilities in the cation exchange membrane-aqueous electrolyte system

Abstract

An electrochemical study, using a cation exchange membrane-aqueous calcium chloride system, has been presented as an experimental verification of the preceding theory for ion transport through membranes [1]. In this theory, the cross terms for the phenomenological coefficients are explicitly accounted for on the basis of nonequilibrium thermodynamics. The membrane permeability to ion α, P α, estimated from the potential and conductance data was greater than the membrane permeability, P α 0, estimated from the potential and salt flux data at zero electric current. This discrepancy can be explained in terms of the elements of a permeability matrix and of a conductance matrix estimated from both the electrochemical and salt flux data. Pα and P α 0 were proportional to the mobility and diffusion coefficient of ion α, respectively. The proportionality factor was expressed as the partition coefficient of ion α divided by a membrane thickness. The membrane permeability, P α *, estimated from the tracer flux was close to P α 0. The diffusion coefficients of a calcium ion across the solution—membrane interface are proportional to the activity of the external calcium ion. This can be explained in terms of an energy barrier theory.