Permeation selectivity in the electro-dialysis of mono- and divalent cations using supported liquid membranes

Zexin Qian*, Henk Miedema, Louis C.P.M. de Smet, Ernst J.R. Sudhölter

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

6 Citations (Scopus)
55 Downloads (Pure)

Abstract

We investigated in detail the permeation selectivity in the electro-dialysis of Na+, K+, Mg2+ and Ca2+ in both binary and quaternary mixtures using a supported liquid membrane (SLM). The SLM consisted of the organic liquid 2-nitrophenyl octyl ether (NPOE) containing a lipophilic anion, i.e. tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, as the cation-exchanging site, which was used to fill the pores of the supporting membrane AccurelR. We first determined the electro-phoretic mobilities of the migrating cations in single salt solutions, yielding: Na+ > K+ > Mg2+ > Ca2+. This order reflects the different size of the migrating cations. The monovalent cations Na+ and K+ migrate in the dehydrated state and the divalent cations Ca2+ and Mg2+ migrate in a (partly) hydrated state, a conclusion was supported by Karl Fisher titrations. Both binary and quaternary salt experiments showed a permeation selectivity in the following order: K+ > Na+ > Ca2+ > Mg2+. Since this order does not correlate with the order of electro-phoretic mobilities, we have determined the ion-exchange selectivity constant (Kex) and found: K+ > Ca2+ > Mg2+ ≈ Na+. We conclude that the overall permeation selectivity is determined by the combination of ion-exchange selectivity and electro-phoretic mobility of the cations present in the membrane.

Original languageEnglish
Article number115398
Number of pages11
JournalDesalination
Volume521
DOIs
Publication statusPublished - 2022

Keywords

  • Electro-dialysis
  • Ion dehydration
  • Ion electro-phoretic mobility
  • Ion exchange
  • Ion selectivity
  • Supported liquid membrane

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