PREFERENTIAL ION TRANSPORT THROUGH ION EXCHANGE MEMBRANES BY ELECTRODIALYSIS

Abstract

The preferential transport of a certain ionic species to others through an ion exchange membrane has been investigated. It was found from some experimental data that the preferential ion transport, S^B_A, should be closely related to an operating parameter ξ, where S^K+_NA+ for example, is defined as the ratio of the Sherwood number concerning the transfer rate of K⁺ to that of Na⁺, and E is defined as (∧Δφ/₂FDV). The Stanton number St=(l/F)/C¹⁰V defined as the ratio of the total ionic flux in the direction to the membrane to that in the direction of the bulk flow, was also a function of ξ. These factors, ∧, Δφ, F, D, V, I, and C¹⁰ are the equivalent conductivity, the effective applied voltage to a single desalting compartment, the Faraday constant, the channel thickness, the linear flow velocity, the current density and the total equivalent concentration, respectively.
Under the operating condition of ξ> IO^-3, no ion exchange membrane will serve to transport a certain ion preferentially. If ξ∧1O^-4, however, the membrane will fully reveal its own ability for selecting a certain ionic species, because the concentration ratio of two ionic species at the membrane surface will approach that in the equilibrium state.