Hybrid Anion Exchange Fibers with Dual Binding Sites: Simultaneous and Reversible Sorption of Perchlorate and Arsenate

When multiple trace contaminants of significantly different chemical properties are present in a single source of contaminated water, designing an engineered sorbent for their simultaneous removal poses a major challenge. Physical-chemical properties of the sorption sites need to be tailored and expanded for preferential binding of more than one contaminant in such cases. The scientific challenge becomes increasingly complex when the sorbent requires to be reusable through intermittent regenerations. In this study, hydrated Fe(III) oxide or HFO nanoparticles were dispersed within an ion exchange fiber containing covalently attached quaternary ammonium functional groups. The resulting hybrid anion exchange fiber (HADG-F) showed very high sorption affinity for both perchlorate and arsenate in the presence of orders of magnitude greater concentrations of competing sulfate and chloride anions. A series of experimental studies validated that relatively hydrophobic perchlorate was selectively bound to quaternary ammonium functional groups while arsenate uptake took place onto HFO surfaces through ligand exchange. The most significant finding of the study was that perchlorate and arsenate could be desorbed efficiently but separately from each other in a simple-to-operate two-step regeneration using conventional regenerants, namely, sodium hydroxide and sodium chloride solutions. In contrast, spherical anion exchange resins are not amenable to such high regeneration efficiency for perchlorate due to significantly longer diffusion path lengths. The unique sorption and desorption behaviors of HAIX-F can be easily extended to other applications where hydrophobic or polyvalent anions [e.g., pentachlorophenate, uranium(VI) oxyanion, ben-zenesulfonate] are simultaneously present with environmentally significant ligands, such as phosphate, oxalate, vanadate.