We have established a theoretical description of the co-ion and counter-ion fluxes through an ion-exchange membrane (IEM) used in a bi-ionic system. This study is based on the modified Nernst-Planck equation applied to three parallel homogenous phases: two diffusion boundary layers (DBLs) and an IEM. The role of the IEM and of the DBLs in the control of the interdiffusion process is discussed. The influence of the common concentration, the co-ion and counter-ion diffusion coefficients in the membrane, the membrane selectivity and affinity, the concentration of functional sites and the convection velocity are evaluated. [References: 22]
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