(607c) Co-Transport of Lithium, Sodium, and Potassium Ions in Pegylated Sulfonated Polysulfones

Lithium (Li⁺) is among the most valuable ions for energy storage devices. Li⁺-rich geothermal brines are recognized as eco-friendly sources of lithium. However, the composition of these brines makes Li⁺ recovery difficult. Electromembrane processes could contribute significantly as a component of a broader separation scheme to isolate Li⁺ from complex solutions containing other ions. A major challenge facing this approach is to separate Li⁺ from other monovalent ions, and Na⁺ and K⁺ are two prime examples. Sulfonated polysulfone (sPSf) is a promising material for cation exchange membranes with favorable thermal and mechanical properties. Poly(ethylene glycol) (PEG), a linear polymer containing ether oxygen, produces a strong dipole moment toward cations that hydrate strongly, suggesting favorable interactions with Li⁺. Engineering Li⁺ selective PEGylated sPSf by combining both of these materials, to leverage their favorable properties, could address challenges facing electromembrane-based monovalent ion separations. Ion transport properties were measured using both single salt measurements (i.e., LiCl, NaCl, or KCl) and measurements where mixtures of the cations were exposed to the membrane. The results inform both the Li⁺ selectivity of the modified sPSf material with respect to Na⁺ and K⁺ and phenomena that occur when the membrane is challenged with mixtures of ions.