Ion exchange treatment processes are designated as best available technology for removal of several contaminants in drinking water, including uranium (VI). For users of private drinking water wells, ion exchange units provide a commercially available solution to address water quality concerns. Common co-solutes in ground and surface water with elevated uranium concentrations include carbonate, hydroxide, and phosphate anions. These constituents simultaneously react and persist in soluble complexes with the uranyl cation and demonstrate preferential affinity over uranium species for ion exchange resins. Abundant dissolved natural organic matter in solution forms large, highly soluble, and negatively charged uranium species. Furthermore, uranium is the largest naturally occurring element, and the uranyl cation is strongly hydrated. This combination of physiochemical characteristics limits the treatment of uranium in drinking water. To elucidate the function of ion exchange affinity on uranium removal, we have developed a suite of functionalized electrospun polymeric sorbent materials to understand the influence of uranyl speciation in the presence of model organic ligands and inorganic anions on ion exchange processes. Polymeric materials functionalized with quaternary ammonium salts Aliquat-336 and tetra-<i>n</i>-butyl ammonium bromide display weak electrostatic affinity for elevated and environmentally relevant concentrations of dissolved uranyl citrate and uranyl oxalate and do not release respective counter-anions chloride or bromide with uptake. For the model inorganic anion nitrate, complete removal and counter-anion exchange is demonstrated with these novel membrane materials. Because mixtures of multiple cationic, anionic, and neutral uranium species exist in groundwater, electrostatic interactions ultimately govern the extent of coordination of soluble uranium with ion exchange membranes and resins. Improved ion exchange unit processes, especially for consumer devices, should move towards employing multi-step treatment to effectively remove large, reactive uranyl complexes in source water.

Effects of affinity and aqueous speciation on uranium(VI) removal by ion exchange drinking water treatment processes

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.