Effect of Al‐F Complexation on Advanced Fluoride Removal by Zirconium Oxide Nanocomposite: Performance, Mechanism, and Mitigation Strategy

Conventional fluoride removal strategies predominantly target free F − adsorption, while the impact of aluminum‐fluoride (Al‐F) complexation from residual aluminum ions (Al 3+ ) in coagulation effluents is an often‐overlooked factor compromising treatment efficiency. This study investigates how Al‐F speciation regulates the performance of nano‐hydrous zirconium oxide embedded in anion exchange resin (HZO‐201), revealing adsorption inhibition by Al 3+ and establishing mitigation strategies. The adsorbent achieved a dynamic adsorption capacity of 2000 bed volumes at pH 3.5 but failed completely with coexisting Al 3+ (Al 3+ = 6.4 mg/L, F/Al = 1:1) due to dual inhibition mechanisms: electrostatic repulsion of positively charged Al‐F complexes ([AlF] 2+ and [AlF 2 ] + ) by quaternary ammonium groups on D201 and competitive site occupation. Thermodynamic and experimental analyses showed pH and F/Al ratio‐controlled speciation: cationic [AlF] + dominated at F/Al ≤ 1 and pH 3.5, while neutral/anionic species ([AlF], [AlF] − ) prevailed at F/Al ≥ 2 and pH ≥ 5, enabling effective adsorption. EDS mapping confirmed pore‐confined nano‐HZO as active sites with ligand‐exchange dominating under sulfate‐shielded conditions. XPS resolved distinct F1s signatures (683~686 eV for F − , 688 eV for Al‐F complexes) and Zr3d perturbation differences (Δ1.0 vs. 0.7 eV), confirming coordination‐dependent adsorption pathways. This study bridges molecular‐level Al‐F coordination chemistry to process optimization, providing mechanistic insights into the role of Al‐F charge states in defluoridation and advancing from singular fluoride targeting to multispecies cooperative regulation paradigms.