Fluoride-tolerant polyamine-amide adsorbent with multidentate O, N chelation for high-capacity U(VI) recovery

Uranium-235 enrichment generates highly alkaline effluents rich in fluoride and uranyl species, which pose significant challenges to conventional treatment technologies. Herein, we report a polyamine-amide adsorbent (MF-PAA) obtained by densely grafting amide units and multi-level amine groups onto a fluoride-inert, macroporous MA-DVB scaffold, creating a surface rich in O, N multidentate binding sites. MF-PAA exhibits an exceptional adsorption capacity 1.43 × 10 3  mg·g −1 for U(VI), and retains 625 mg·g −1 capacity even under 8000 ppm F − . Even in 0.50 mol·L −1 competing anions, the material removes 80–90% of U(VI) and achieves a distribution coefficient of 5.0 × 10 5  mL·g −1 under cationic competition conditions, confirming outstanding anion tolerance and selectivity. Mechanistic studies combining spectroscopy and density functional theory (DFT) calculations reveal the most stable uranyl-MF-PAA complex (ΔG = −115.66 kJ/mol), in which uranyl coordinates with O and N atoms of two amide groups in adjacent chains, forming six coordination bonds with mixed ionic-covalent character dominated by U 5f/6d, N 2p, and O 2s/2p orbital interactions. In column operation with a continuous 8000 ppm F − influent, MF-PAA recovered 94% of U(VI), and its capacity maintained after 15 days of high-fluoride exposure, confirming its long-term engineering viability. These results underscore MF-PAA as a robust, renewable, and high-capacity adsorbent with strong potential for uranium recovery from fluoride-rich wastewater.