Highly selective ion separations based on counter-flow electromigration in nanoporous membranes
- Univ. of Notre Dame, IN (United States); University of Notre Dame
- National Academy of Sciences of Ukraine (NASU), Kyiv (Ukraine)
- Polytechnic University of Catalonia, Barcelona (Spain); ICREA, Barcelona (Spain)
- Univ. of Notre Dame, IN (United States)
Highly selective ion separations are vital for recovering important salts, and membrane-based techniques may enable environmentally friendly ion separations that operate continuously. This study demonstrates that simply opposing convective flow with electromigration in track-etched membranes leads to remarkable selectivities among monovalent ions. Because the membrane-pore diameters are orders of magnitude larger than the ion diameters, advection moves all ions at the same velocity, whereas electrophoretic velocities are proportional to ion mobilities. Thus during counter-flow cation electromigration, less mobile cations have lower electromigration velocity components and pass through porous membranes more rapidly than more mobile cations. Using membranes with 400 nm pores, counter-flow electromigration gives Li+/K+ selectivities of 100 and Li+/Na+ selectivities around 30 in mixed-salt studies. In this work, numerical simulations based on the extended Nernst-Planck equation agree with trends in experimental data and highlight the importance of high Péclet numbers, high current-to-flow ratios, and uniform current distributions for achieving high selectivities. Importantly, experimental separations give high selectivities at 0.3 M ionic strength and low Li+/K+ ratios, which suggest these methods may also work in brine solutions. Nevertheless, energy costs for such separations are high.
- Research Organization:
- Univ. of Notre Dame, IN (United States)
- Sponsoring Organization:
- Spanish Ministry of Economy and Competitiveness; The National Research Foundation of Ukraine (NRFU); USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences & Biosciences Division
- Grant/Contract Number:
- SC0017618
- OSTI ID:
- 1868530
- Journal Information:
- Journal of Membrane Science, Journal Name: Journal of Membrane Science Vol. 638; ISSN 0376-7388
- Publisher:
- ElsevierCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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