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Retention measurements of nanofiltration membranes with electrolyte solutions

Authors
Journal
Journal of Membrane Science
0376-7388
Publisher
Elsevier
Publication Date
Volume
145
Issue
2
Identifiers
DOI: 10.1016/s0376-7388(98)00079-9
Keywords
  • Nanofiltration
  • Salt Retention
  • Extended Nernst–Planck Equation

Abstract

Abstract Retention measurements with single salt solutions of CaCl 2, NaCl and Na 2SO 4 revealed that the rejection mechanism of commercial polymeric nanofiltration membranes investigated in this study may be divided into two categories: 1. Membranes for which Donnan exclusion seems to play an important role. 2. Membranes for which retention is determined by both Donnan exclusion and size effects. In category 1 both positively and negatively charged membranes were found. Ceramic γ-Al 2O 3 ultrafiltration membranes with a pore size of 3 nm showed a same type of salt retention behavior as the positively charged polymeric membranes. The extended Nernst–Planck equation in combination with the Donnan equilibrium has been used to model the flux-retention experiments for the salt solutions. The numerical calculations resulted in a good agreement with experimental data and acceptable values for the fixed charge densities have been determined. The effective membrane thicknesses calculated were higher than those observed by scanning electron microscopy.

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