Non-hydrothermal synthesis of robust and radiation-resistant sodalite microspheres for effective removal and in-situ immobilization of Cs + and Sr 2+

Abstract The safe management of radioactive 137Cs and 90Sr from nuclear wastewater requires not only efficient capture but also permanent immobilization, yet current strategies often treat these as separate processes, leading to incompatibility and complex operations. Herein, non-hydrothermal method based on geopolymer technology was developed to fabricate robust sodalite zeolite microspheres (GXU-SODs) for the integrated adsorption-immobilization of Cs+ and Sr2+. The synthesized GXU-SODs exhibited well-defined crystalline structure and spherical morphology with compressive strength of 13.88 MPa. Batch adsorption experiments revealed the maximum adsorption capacities (Qm) of GXU-SODs were 56.67 and 59.64 mg·g-1 for Sr2+ and Cs+ with rapid kinetics of 1.21 and 0.94 g·mg-1·min-1, respectively. The adsorption process followed pseudo-second order and Langmuir models, indicating monolayer homogeneous chemisorption. Meanwhile, GXU-SODs exhibited excellent radiation resistance, retaining >96 % structural integrity and adsorption performance after 500 kGy. Dynamic adsorption column tests confirmed excellent breakthrough performance and practical applicability in real seawater. The adsorbed GXU-SODs could permanently immobilize radionuclides via simple thermal treatment at 1100 ºC without secondary additives, achieving 28-day leaching rates significantly below regulatory standard. Combining XRD, XPS, FT-IR, SEM-EDS and DFT calculations revealed the ion exchange, chemisorption and lattice incorporation within the sodalite cages were the primary mechanisms for the effective adsorption and long-term immobilization of Sr2+ and Cs+. This work presents a novel, scalable, and energy-efficient synthesis route for advanced sodalite-based materials and establishes an integrated adsorption-immobilization strategy for the treatment and safe disposal of radioactive wastes.