This study used red mud and metakaolin as the main raw material, with sodium silicate as the alkali activator. Red mud-metakaolin based geopolymer microspheres (RM-MGMs) with good sphericity and high mechanical strength are prepared via dispersion-suspension-solidification method. By investigating the adsorption performance of RM-MGMs calcined at different temperatures for Cu²⁺ and Pb²⁺, the uncalcined RM-MGMs exhibit excellent heavy metal cation adsorption due to their abundant surface hydroxyl groups and high ion exchange capacity. The optimal adsorption conditions for Cu²⁺/Pb²⁺ were adsorbent dosages of 1.5/0.3 g/L, pH of 5.3-5.6/5.0, respectively. Cu²⁺ adsorption reached equilibrium at 960 min. Pb²⁺ showed faster adsorption rate due to its smaller hydrated ionic radius and reached equilibrium at 60 min. Kinetic results indicated that the pseudo-second-order model better describes the adsorption process of RM-MGMs for Cu²⁺/Pb²⁺. Adsorption isotherm models showed that increasing temperature favors the adsorption of Cu²⁺/Pb²⁺ by RM-MGMs. At 318 K, the adsorption capacities of RM-MGMs for Cu²⁺/Pb²⁺ reach 0.86/1.43 mmol/g, respectively. In competitive experiments, the removal rates of Cu²⁺/Pb²⁺ by RM-MGMs both exceed 80%. RM-MGMs achieve adsorption of Cu²⁺/Pb²⁺ through synergistic mechanisms including ion exchange, electrostatic attraction and complexation.

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 (Q_m) 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.

For the remediation of radionuclides (e.g., ¹³⁷Cs and ⁹⁰Sr) in nuclear wastewater, conventional materials struggle to simultaneously exhibit excellent adsorption performance, high mechanical strength, and good irradiation resistance. Herein, high-strength NaX zeolite microspheres from Guangxi university (GXU-NaXs, compressive strength: 19.21 MPa, Vickers hardness: 216.30) with 75–150 μm particle sizes were prepared for the first time via in situ conversion via geopolymer technology under normal pressure at 105 °C for 12 h. The results revealed that GXU-NaXs achieved removal efficiencies exceeding 90% for Cs⁺ and Sr²⁺ within 20 min at a dosage of 0.8 g·L⁻¹, following pseudo-second-order and Langmuir models with maximum saturated adsorption capacities of 138.30 and 153.60 mg·g⁻¹ at 45 and 30 min, respectively. Moreover, GXU-NaXs maintained > 98% structural stability and adsorption capacity after 500 kGy γ-irradiation, which has the potential for excellent stability in the nuclear environment. GXU-NaXs also exhibited good dynamic adsorption effects at a flow rate of 6 mL·min⁻¹, and the removal efficiency after three cycles remained 97.89% and 56.39% for Cs⁺ and Sr²⁺, respectively, demonstrating that GXU-NaXs have good feasibility for industrial applications. GXU-NaXs showed good removal capacity and selectivity in complex seawater matrices for Cs⁺ and Sr²⁺. Density functional theory (DFT) calculations revealed adsorption energies of −2.43 (Cs⁺) and −3.52 eV (Sr²⁺), whereas scanning electron microscopy (SEM)/energy dispersive spectrometry (EDS), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FT-IR) methods confirmed that the adsorption mechanism was ion exchange and chemisorption. This study pioneers advanced synthesis technology for nuclear adsorbents, offering a promising direction for radioactive wastewater remediation.