Synthesis of P−Type Zeolite and Analcime via Recrystallization of Natural Mordenite and Their Adsorption Performance for Typical Simulated Nuclides

Natural mordenite exhibits poor adsorption performance for radionuclides in aqueous environments due to its high Si/Al ratio and low specific surface area. To improve its adsorption capacity, natural mordenite was hydrothermally modified at temperatures ranging from 80 to 140 °C, resulting in the formation of zeolite phases with lower Si/Al ratios and higher specific surface areas. In this study, natural mordenite was used as a precursor and subjected to hydrothermal treatment. The composition, morphology, and structural characteristics of the pristine and modified samples were investigated by X−ray diffraction (XRD), Fourier−transform infrared spectroscopy (FTIR), X−ray fluorescence (XRF), scanning electron microscopy coupled with energy−dispersive X−ray spectroscopy (SEM−EDS), N₂ adsorption−desorption analysis, and laser particle size analysis. The adsorption performance of the modified materials was evaluated using Sr²⁺, Co²⁺, and Mn²⁺ as simulated radionuclides. The results show that hydrothermal treatment at 100 °C and 140 °C converts natural mordenite into zeolite P and analcime, respectively. The Si/Al ratio decreases from 4.47 for natural mordenite to 2.69 and 2.50 after hydrothermal treatment at 100 °C and 140 °C, respectively. Meanwhile, the specific surface area increases from 17 m²/g to 23 m²/g and 29 m²/g, respectively. Natural mordenite exhibits low adsorption capacities of 15, 6, and 5 mg/g for Sr²⁺, Co²⁺, and Mn²⁺, respectively. Compared with natural mordenite, the adsorption capacities of the samples obtained at 100 °C increase by 4.0, 4.2, and 5.3 times for Sr²⁺, Co²⁺, and Mn²⁺, respectively, while those of the samples obtained at 140 °C increase by 3.4, 5.2, and 2.8 times, respectively. In complex systems containing K⁺, Na⁺, Ca²⁺, and Mg²⁺, the hydrothermally modified samples exhibit significantly improved selective adsorption performance compared with natural mordenite. The selectivity coefficients of Sr²⁺, Co²⁺, and Mn²⁺ over K⁺ and Mg²⁺ are all greater than 1, ranging from 1.05 to 24.22. The sample obtained at 140 °C exhibits higher selective adsorption ability for the three target ions than the sample obtained at 100 °C, whereas the latter shows higher adsorption capacity. The adsorption performance of hydrothermally modified mordenite is closely related to its Si/Al ratio, specific surface area, and framework structure. Overall, the sample obtained by hydrothermal treatment at 100 °C exhibits superior adsorption capacity, indicating its potential for the efficient utilization of natural mordenite in radionuclide removal applications.