A solid phase of natural zeolite was transformed to Na-zeolite P (NaP zeolite) by a “top-down approach” hydrothermal reaction using 3 M of NaOH solution in a 96 °C oven. Time-dependent X-ray diffraction (XRD), Fourier-transform infrared (FT-IR), XRF, and scanning electron microscopy (SEM) analysis as well as kinetic, isotherm, and cation exchange capacity experiments were performed to understand the mechanism of mineral transition from natural zeolite to NaP zeolite. The XRD crystal peaks of the natural zeolite decreased (decrystallization phase) first, and then the NaP zeolite XRD crystal peaks increased gradually (recrystallization phase). From the XRF results, the dissolution rate of Si was slow in the recrystallization phase, while it was rapid in the decrystallization phase. The specific surface area measured by BET analysis was higher in NaP zeolite (95.95 m²/g) compared to that of natural zeolite (31.35 m²/g). Furthermore, pore structure analysis confirmed that NaP zeolites have more micropores than natural zeolite. In the kinetic experiment, the results showed that the natural zeolite and NaP zeolite were well matched with a pseudo-second-order kinetic model, and reached equilibrium within 24 h. The isotherm experiment results confirmed that both zeolites were well matched with the Langmuir isotherm, and the maximum removal capacity (Q_max) values of Sr and Ni were highly increased in NaP zeolite. In addition, the cation exchange capacity (CEC) experiment showed that NaP zeolite has an enhanced CEC of 310.89 cmol/kg compared to natural zeolite (CEC = 119.19 cmol/kg). In the actual batch sorption test, NaP zeolite (35.3 mg/g) still showed high Cs removal efficiency though it was slightly lower than the natural zeolite (39.0 mg/g). However, in case of Sr and Ni, NaP zeolite (27.9 and 27.8 mg/g, respectively) showed a much higher removal efficiency than natural zeolite (4.9 and 5.5 mg/g for Sr and Ni, respectively). This suggests that NaP zeolite, synthesized by a top-down desilication method, is more practical to remove mixed radionuclides from a waste solution.

中文翻译：

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从天然沸石自上而下合成NaP沸石可提高Cs，Sr和Ni的去除效率

天然沸石的固相通过在96°C的烘箱中使用3 M NaOH溶液通过“自上而下的方法”水热反应转化为Na-沸石P（NaP沸石）。进行了时变X射线衍射（XRD），傅立叶变换红外（FT-IR），XRF和扫描电子显微镜（SEM）分析以及动力学，等温线和阳离子交换容量实验，以了解其机理。从天然沸石到NaP沸石的矿物过渡。天然沸石的XRD晶体峰先降低（去结晶阶段），然后NaP沸石的XRD晶体峰逐渐增加（再结晶阶段）。根据XRF的结果，Si在再结晶阶段的溶解速度缓慢，而在再结晶阶段则迅速。² / g）与天然沸石（31.35 m ² / g）相比。此外，孔结构分析证实，NaP沸石比天然沸石具有更多的微孔。在动力学实验中，结果表明天然沸石和NaP沸石与拟二级动力学模型很好地匹配，并在24 h内达到平衡。等温线实验结果证实，两种沸石均与Langmuir等温线匹配良好，并且最大去除量（Q _maxNaP沸石中Sr和Ni的值大大提高。此外，阳离子交换容量（CEC）实验表明，与天然沸石（CEC = 119.19 cmol / kg）相比，NaP沸石的CEC增强了310.89 cmol / kg。在实际的批次吸附测试中，NaP沸石（35.3 mg / g）仍显示出较高的Cs去除效率，尽管它稍低于天然沸石（39.0 mg / g）。然而，在Sr和Ni的情况下，NaP沸石（分别为27.9和27.8 mg / g）显示出比天然沸石（分别为Sr和Ni分别为4.9和5.5 mg / g）更高的去除效率。这表明通过自上而下的脱硅方法合成的NaP沸石从废液中去除混合的放射性核素更为实用。