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Electrodialysis for Salt Purification

Selective electrodialysis occurs with cation-exchange membranes coated with polyelectrolyte mutilayers.
Nick White
Nick White, a PhD graduate who now works for Wacker, initiated work on coated ion-exchange membranes.

In electrodialysis, an electrical potential drives ions across membranes to effect separations. However, typical ion-exchange membranes show minimal selectivity between monovalent and divalent ions, which is important for applications such as water softening and salt purification. In contrast, we found that polyelectrolyte multilayers adsorbed on ion-exchange give rise to an electrodialysis K+/Mg2+ selectivity >1000 (ACS Appl. Mater. Interfaces 2015, 7, 6620–6628). Recently we showed that these high selectivities occur even with inexpensive aliphatic polyamide membranes from Fujifilm (J. Membr. Sci. 2017, 537, 177-185), and that highly swollen polyelectrolytes give rise to high current efficiencies.  Coated membranes also show high Li+/Co2+ selectivities, which might prove useful in recycling Li batteries.  Current studies are exploring increasing limiting currents and developing membrane with high selectivities for monovalent over divalent anions.  The Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences of the U.S. Department of Energy (DE-FG02-98ER14907) supports our efforts in electrically-driven separations.