Phenomenological analysis of transport of mono- and divalent ions in nanofiltration

Sarit Bason, Viatcheslav Freger

Research output: Contribution to journalArticlepeer-review

43 Scopus citations

Abstract

A phenomenological approach was used to deduce concentration-dependent permeabilities of salts containing divalent ions (CaCl2, MgCl2 and Na2SO4) for NF200 membrane and compare them with results for monovalent salts and predictions of the steric-dielectric-Donnan (electric) (SDE) model. As a part of this effort the importance of the correction for concentration polarization was demonstrated and the error associated with the use of single average values of mass transfer coefficients and permeate concentration was analyzed. The dependence of permeability on salt concentration was found incompatible with the standard SDE picture for all salts. The discrepancy was more drastic for divalent cations, which showed a permeability decreasing with concentration in the whole analyzed range, in opposite to the standard model. It may be suggested that, a localized binding or association of counter-ions with fixed charges accompanied by charge reversal for divalent cations may be responsible for the observed behavior, provided the bound ions may retain osmotic activity. Such association may be promoted by the low dielectric constant of the membrane hence a large Bjerrum length commensurate with spacing of fixed charges.

Original languageEnglish
Pages (from-to)389-396
Number of pages8
JournalJournal of Membrane Science
Volume360
Issue number1-2
DOIs
StatePublished - 1 Sep 2010

Keywords

  • Ion exclusion mechanism
  • Modeling
  • Mono- and divalent ions
  • Nanofiltration
  • Phenomenological transport coefficients
  • Salt partitioning

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