The selective removal of trivalent lanthanides and actinides from acidic radioactive waste solutions is important for the treatment of high-level liquid waste. In this work, an amide-podand-functionalized all-silica ZSM-5 zeolite adsorbent, denoted as ZSM-5-DGA, was developed for the efficient adsorption of Eu(Ⅲ), which was selected as a nonradioactive surrogate for trivalent actinides. The adsorbent was prepared by covalently grafting a silyl-functionalized diglycolamide ligand onto the all-silica ZSM-5 framework through a silane coupling strategy. Characterization results confirmed the successful introduction of DGA ligands while the crystalline MFI framework of ZSM-5 was well preserved.
The adsorption performance of ZSM-5-DGA toward Eu(Ⅲ) was systematically investigated under various solution conditions, including acidity, contact time, initial Eu(Ⅲ) concentration, solid-to-liquid ratio, competing ions, ionic strength, and temperature. Compared with pristine ZSM-5, the modified adsorbent exhibited significantly enhanced Eu(Ⅲ) uptake, especially in acidic nitrate media, with a maximum adsorption capacity of 74.79 mg g^-1. This enhanced uptake was mainly attributed to the synergistic coordination of nitrate ions and DGA ligands, which promoted the formation of stable Eu-nitrate-DGA complexes. The effect of solid-to-liquid ratio further clarified the relationship between adsorbent dosage, available coordination sites, and Eu(Ⅲ) removal efficiency. Kinetic studies showed that Eu(Ⅲ) adsorption proceeded rapidly at the initial stage and approached equilibrium within a relatively short time. The adsorption process was better described by the pseudo-second-order kinetic model, suggesting that chemisorption dominated by coordination interactions played a major role. Equilibrium adsorption data fitted well with the Langmuir isotherm model, indicating monolayer adsorption on relatively homogeneous active sites.
The effects of ionic strength and temperature were further evaluated to assess the applicability of ZSM-5-DGA in complex aqueous environments. Competitive adsorption experiments in the presence of Na(I), K(I), Cs(I), Sr(Ⅱ), Cu(Ⅱ), Zn(Ⅱ), Ni(Ⅱ), Fe(Ⅲ), and Zr(Ⅳ) demonstrated the high selectivity of ZSM-5-DGA for Eu(Ⅲ). Fluorescence analysis also supported the formation of Eu–ligand complexes during adsorption. In addition, the adsorbent showed good regeneration performance after multiple adsorption-desorption cycles. These results indicate that amide-podand-functionalized all-silica zeolites are promising solid adsorbents for the selective removal of trivalent radionuclides from acidic radioactive waste streams.
 

All-silica ZSM-5,Diglycolamide,Eu(Ⅲ) adsorption,Acidic nitrate solution