Ion-Selective Ion Exchange Membranes for the Specific Recovery of Phosphorous and Lithium

Abstract: Specific ion selectivity is a highly desirable feature for the next generation of membrane-based separations. However, existing membranes rely on differences in charge, size, and hydration energy, which limits their ability to target individual ion species. Here, we demonstrate an approach towards achieving specific ion selectivity using nanocomposite ion exchange membrane materials that enable a reverse-selective transport mechanism. We demonstrate this transport mechanism with phosphate ions selectively transporting across negatively charged cation exchange membranes (CEM). Selective transport is enabled by the in-situ growth of hydrous manganese oxide (HMO) nanoparticles (NPs) throughout a CEM that provide a specific diffusion pathway via phosphate-specific, reversible outer-sphere interactions. Upon incorporating the HMO NPs, the membrane’s phosphate flux increased by a factor of 27 over an unmodified CEM, and the selectivity of phosphorous over sulfate, nitrate, and chloride reaches 47, 100 and 20, respectively. By pairing ion-specific outer-sphere interactions between target ions and appropriate NPs, these nanocomposite ion exchange materials can in principle achieve selective transport for a range of ions. In another application, we demonstrate this reverse selectivity using a nano composite anion exchange membrane capable of selectively transporting lithium over other cations (Ca, Mg, Na), with exceptionally high selectivity (Li/Ca, Mg > 1,000 and Li/Na > 10). In addition to material development, we explore the integration of these reverse-selective membranes into conventional electrodialysis stacks.

Bio: David Jassby is a professor in the Department of Civil and Environmental Engineering at UCLA. He received his Ph.D. in Civil and Environmental Engineering from Duke University (2011), an M.S. in Civil and Environmental Engineering from UC Davis (2005), and a B.Sc. in Biology from Hebrew University (2002). David’s research is primarily concerned with membrane separations, environmental electrochemistry, and water treatment technologies. His lab is currently engaged in research concerning membrane development, specific ion separations, desalination, wastewater treatment, CO₂ capture and sequestration, green cement manufacturing, and the electrochemical treatment of contaminated water. He holds multiple patents on electroactive membranes and CO₂ capture and sequestration, and has published more than 100 peer-reviewed manuscripts in peer-reviewed journals.

 
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