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DOE OSTI · 1868530

Highly selective ion separations based on counter-flow electromigration in nanoporous membranes

Tang, Chao·Bondarenko, Mykola P.·Yaroshchuk, Andriy·Bruening, Merlin L.
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Abstract

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.

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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRYcurrent densityelectromigrationion separationsnanoporous membranesselectivity

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Tang, Chao, Bondarenko, Mykola P., Yaroshchuk, Andriy, Bruening, Merlin L.. 2021-08-05. Highly selective ion separations based on counter-flow electromigration in nanoporous membranes. https://doi.org/10.1016/j.memsci.2021.119684

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