Enhanced adsorption removal of fluoride by multifunctional polymer-based hydrated neodymium oxide: Capacity...

The serious fluorine (F-) pollution has been triggered by the rapid development of chemical industry, and there is an urgent need to seek the efficient and stable adsorbent for F- removal. Although majority of hydrated metal oxides possess certain defluorination capability, problems of metal ion leaching, narrow pH, and difficult powder recovery are common in engineering applications. Herein, a novel nanocomposite (HNO@D201) was fabricated by confining hydrated neodymium oxide (HNO) nanoparticles within anionic resin (D201) pores. Batch experiments revealed that HNO@D201 could effectively adsorb F- under a wide pH range (5-10), and reached a maximum adsorption capacity of 34.17 mg F-/g at pH 6. Notably, its F- removal capability was much higher than that of common D201-based hydrated metal (Al, Mn, Fe, and Ce) oxides. Moreover, HNO@D201 demonstrated excellent stability, as evidenced by the Nd leaching concentration remaining below 5 mg/L at pH 5. Based on the systematic characterization analysis, the synergistic "electrostatic enrichment-ion exchange-ligand immobilization" adsorption mechanism was proposed. These results aligned best with the pseudo-second-order kinetic model and the Sips adsorption isotherm, where the adsorption process combined monolayer chemisorption with multilayer physisorption. Besides, its defluorination efficiency was still as high as 26.35 mg F-/g after ten cycles and regeneration. Higher concentrations of coexisting anions and natural organic matters did not markedly affect the adsorption efficiency of HNO@D201 for F-. Finally, in the long-term continuous flow test, the treatment capacity of HNO@D201 reached 702 BV and 442 BV in the simulated and actual wastewater, respectively, after three cycles. These findings suggest the potential application of HNO@D201 for removing F- from wastewater.