Reverse osmosis of ammonium and sodium salt solutions and its model description

The tested models of membrane transport were based on the steric, dielectric (Born and image force effects), and Donnan exclusions. Generally, the models with the concentration-dependent electrolyte permeability described the retention data satisfactorily, irrespectively of the origin of that dependence (dielectric or Donnan effect). Regarding the steric-dielectric exclusion, the same goodness of fit was obtained for many pairs of pore radius and dielectric constant. However, it was not possible to explain the differences in the electrolyte permeabilities, because of the inconsistency of the dielectric constant of a pore solution and/or an effective membrane thickness. Much too high values of that thickness obtained for the pure Donnan exclusion indicated that this type of exclusion was of marginal importance.