Journal
JOURNAL OF MEMBRANE SCIENCE
Volume 535, Issue -, Pages 132-142Publisher
ELSEVIER
DOI: 10.1016/j.memsci.2017.04.007
Keywords
Divalent ions; Ion exchange polymers; Donnan exclusion; Donnan-Manning model
Categories
Funding
- NSF CBET Program [CBET-1160128]
- Australian-American Fulbright Commission of the U.S. Fulbright Distinguished Chair in Science, Technology and Innovation - Commonwealth Scientific and Industrial Research Organization (CSIRO)
- Div Of Chem, Bioeng, Env, & Transp Sys
- Directorate For Engineering [1160128] Funding Source: National Science Foundation
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Many fundamentals of ion sorption in ion exchange membranes (IEMs) are not fully understood, and few modern studies focus on multivalent ion sorption, despite the importance of divalent ion transport properties in water purification applications. Here, MgCl2 and CaCl2 sorption in a commercial cross-linked, styrene-divinylbenzene cation exchange membrane (CEM) with fixed sulfonate groups was measured and compared with NaCl, LiCl and KCl sorption in the same material. The data were correlated with counter-ion size and valence, as well as membrane water content. Divalent salts had higher sorption coefficients than monovalent salts, even though membrane water content significantly decreased in the presence of divalent counter-ions. The Donnan potential is weaker in the presence of multivalent counter-ions, which increases co-ion sorption, contributing to the observed increase in salt sorption coefficients for divalent salts. Ion activity coefficients in the membrane were calculated and compared to predictions of the recently proposed Manning-Donnan model. This model showed much better agreement with the experimental data than the ideal Donnan model, suggesting that ion nonideality in the membrane is important when analyzing ion sorption and transport in IEMs.
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