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Water purification remains a challenge across sectors worldwide, especially the efficient removal of specific (toxic or valuable) dissolved ions at low salinity. In this article, shock electrodialysis (SED) is shown for the first time to have this capability, by demonstrating continuous separation of magnesium ions from aqueous mixtures of NaCl and MgCl2. By systematically measuring the composition of all input and output streams, the mechanisms that drive selectivity, current efficiency, and desalination are revealed, as well as strategies to improve performance. For solutions initially rich in sodium, highly selective (> 98%) continuous removal of magnesium can be achieved with only moderate (50–70%) total salt removal. This remarkable selectivity is associated with super‐diffusive ion transport, mediated by charged double layers in a porous glass frit, behind a steady deionization shockwave in cross flow. [ABSTRACT FROM AUTHOR]

Conventional desalination technologies such as distillation and reverse osmosis are well suited for the supply of fresh water at large scale. The expensive infrastructure and high capital, operating, and maintenance costs associated with these technologies, however, limit their application in remote or underdeveloped areas. Here, we show that shock electrodialysis, a recently developed electrokinetic process, can be used to continuously desalinate artificial seawater (3.5 wt. %) for small-scale (≤ 25 m3 day−1 as a long-term goal), decentralized applications. In two steps, 99.8% of the salt fed was rejected, with selectivity for magnesium ions of which > 99.99 % were removed (based on measurements of concentration by mass spectrometry). We also demonstrated for the first time the viability of using and continuously recycling solutions of sodium citrate buffer to simultaneously reduce waste and inhibit precipitation reactions in the electrode streams. As with conventional electrodialysis, the energy consumed by our technology can be significantly reduced by desalinating sources that are less saline than seawater, such as brackish water and various industrial or municipal process streams. Since the design of the system and choice of materials have yet to be optimized, there remain ample opportunities to further reduce the cost of desalination by shock electrodialysis. Unlabelled Image • Shock electrodialysis is used to desalinate artificial seawater, from which 99.8% of the salt fed is continuously rejected. • As a result of inherent ionic selectivity, more than 99.99% of magnesium ions are removed. • Sodium citrate buffer is used under closed-loop operation as a robust electrolyte for the electrode streams. [ABSTRACT FROM AUTHOR]