Permeation mechanism and interplay between ions in nanofiltration

Noga Fridman-Bishop, Karen Adie Tankus, Viatcheslav Freger

Research output: Contribution to journalArticlepeer-review

28 Scopus citations


Nanofiltration (NF) is widely used today for water purification, however, governing physical mechanisms are still largely unclear and predictive modeling remains a challenge, especially, for mixed ionic solutions. The current study systematically investigates NF of binary mixtures of NaCl and CaCl2 with the purpose to understand the mechanisms and interplay between different ions in the membrane. Using extensive filtration data and the Nernst-Planck relations, the paper concludes that (a) the standard mean-field models based on an average Donnan potential are unsuitable for describing ion permeation in NF; (b) the observed ranking of ion permeabilities (Na+ > Cl- > Ca2+) points to the solvation (Born) energy rather than interaction with fixed charges as the main factor controlling ion permeation; (c) the fixed charges are largely neutralized by pairing with counter-ions, which reduces their role in ion permeation; (d) saturation of Ca2+ uptake and its competition with Na+ for pairing with fixed charges may explain the unusual decrease of Ca2+ permeability with Ca2+ concentration and its strong effect on Na+ permeability. These conclusions, inconsistent with the commonly used mean-field picture, strongly suggest the need to revise the current approach to NF modeling.

Original languageEnglish
Pages (from-to)449-458
Number of pages10
JournalJournal of Membrane Science
StatePublished - 15 Feb 2018
Externally publishedYes


  • Electrolyte transport
  • Extended Nernst-Planck equation
  • Ionic permeability
  • Multi component nanofiltration

ASJC Scopus subject areas

  • Biochemistry
  • Materials Science (all)
  • Physical and Theoretical Chemistry
  • Filtration and Separation


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