This paper analyzes the separation properties of monovalent-anion-permselective membranes, manufactured and commercialized for edible salt production from seawater. Experimental data from the separation of SO42- from Cl- ions are used to verify the reliability of a new theory based on kinetic concepts, and compared with those of a previously studied separation (C2O42-/Cl-). In both cases, the proposed model fits data satisfactorily, contrary to the classical solution-diffusion model (based on thermodynamic principles), which cannot account for the strong dependency of the measured separation factors on the electric current density applied; the new proposed model may be thus regarded as a good tool for process design purposes.