Synthesis of high mechanical strength and excellent radiation resistance NaX zeolite microspheres via geopolymer in-situ conversion and their adsorption study of 137Cs and 90Sr

Researchers have prepared zeolites with excellent performance by regulating different geometries shapes (films, flakes and core-shells) and sizes, and considerable progress has been made in the research on the transformation mechanism of zeolites. However, the preparation of zeolites is mainly hydrothermal method, which is harsh and complicated, generating a large amount of organic wastewater. In addition, the zeolites prepared are mostly in powder with low mechanical strength, and easily causes high pressure drop in dynamic adsorption experiments. The spherical materials exhibit good fluidity and low powdering resistance through the dynamic adsorption. At present, spherical zeolites are mainly formed by the binder pelletizing method, leading to pore blockage and performance degradation. Therefore, it is necessary to develop an in-situ growth method for preparing spherical zeolites.

Recently, a team of material scientists led by Kaituo Wang from Guangxi University, China first reported synthesis of high mechanical strength and excellent radiation resistance NaX zeolite microspheres via geopolymer in-situ conversion and their adsorption study of ¹³⁷Cs and ⁹⁰Sr. This research not only provides new insights and prospects for the industrial-scale removal of radionuclides from nuclear wastewater, but also holds great significance for the controllable preparation of high-strength zeolite microsphere adsorbent and further understanding of the adsorption mechanism for Cs⁺ and Sr²⁺.

The team published their work in Journal of Advanced Ceramics on June 29, 2025.

“In this work, we fabricated a kind of high-strength NaX zeolite microspheres with 75-150 μm particle size (GXU-NaXs, compressive strength: 19.21 MPa, Vickers hardness: 216.30) by the in-situ conversion of geopolymer technology under normal pressure at 105 ºC for 12 h, and directly from precisely controlled aluminosilicate precursors and water glass, eliminating the need for extra binders and avoiding pore blockage.” said Dr. Kaituo Wang, the corresponding author of the paper, a professor in the School of Resources, Environment and Materials at Guangxi University in Nanning, China.

“Just like precisely building a micro-purification factory with ‘molecular Lego’,” Dr. Kaituo Wang, made an analogy. “Water is only used as the reaction medium, and energy consumption is reduced by 40%. Meanwhile, GXU-NaXs exhibits exceptional adsorption performance for Cs⁺ and Sr²⁺, reaching equilibrium at 45/30 min with maximum saturated adsorption capacities 138.30 and 153.60 mg·g^-1, respectively, following predominantly monolayer adsorption.

GXU-NaXs maintained >98 % structural stability and adsorption capacity for Cs⁺ and Sr²⁺ after 500 kGy γ-irradiation, which had the potential for excellent stability in the nuclear environment. “This breaks the traditional perception that irradiation causes material disintegration,” Kaituo Wang emphasized.

“It is also possible to qualitatively predict that the optimal adsorption site models and adsorption energies in the Sr²⁺ and Cs⁺ capture are the interior of the cage of GXU-NaXs (E_ads= -3.52 eV) and the surface of the cage of GXU-NaXs (E_ads= -2.43 eV), which reveals that Sr²⁺ is mostly immobilised inside the GXU-NaXs microspheres after adsorption and diffusion, while Cs⁺ is mainly adsorbed on the microsphere surface.” said Kaituo Wang.

Future work should focus on scaling up the synthesis, evaluating long-term stability under continuous radiation and flow conditions, and assessing the economic viability and performance in pilot-scale treatment of real radioactive effluents to fully realize their engineering potential.

This work was supported by the Guangxi Natural Science Fund (Grant No. 2025GXNSFAA069185 and 2025GXNSFBA069338), National Natural Science Foundation of China (Grant No. 12105056) and Innovation Project of Guangxi Graduate Education (Grants No. YCBZ2023010).

About Author

Dr. Kaituo Wang is an associate professor and master's supervisor in the School of Resources, Environment and Materials, Guangxi University. His main research directions are the preparation of new functional nano-adsorption materials and geopolymer-based functional materials, as well as the green development and comprehensive utilization of solid waste.

About Journal of Advanced Ceramics

Journal of Advanced Ceramics (JAC) is an international academic journal that presents the state-of-the-art results of theoretical and experimental studies on the processing, structure, and properties of advanced ceramics and ceramic-based composites. JAC is Fully Open Access, monthly published by Tsinghua University Press, and exclusively available via SciOpen. JAC’s 2024 IF is 16.6, ranking in Top 1 (1/33, Q1) among all journals in “Materials Science, Ceramics” category, and its 2024 CiteScore is 25.9 (5/130) in Scopus database. ResearchGate homepage: https://www.researchgate.net/journal/Journal-of-Advanced-Ceramics-2227-8508