Microwave vitrification of Sr-saturated magnetic AMP@SiO2 for effective strontium removal in radioactive wastewater.

The high mobility and long-lived radiotoxicity of 90Sr pose persistent challenges in radioactive wastewater management. In this study, a closed-loop adsorption-vitrification strategy was developed to integrate Sr2+ capture, magnetic separation, microwave vitrification, and release prediction within a single treatment framework. A magnetic composite adsorbent (AMP@SiO2, denoted as MAS) was prepared by the crystallization of ammonium molybdophosphate (AMP) within a porous SiO2 matrix, followed by Fe3O4 functionalization, enabling rapid and selective Sr2+ uptake. The equilibrium adsorption behavior followed the Langmuir isotherm model, with a maximum adsorption capacity of 38.64 mg g-1, while the adsorption kinetics conformed to the pseudo-second order model, with a high correlation coefficient (R2 = 0.9903). After adsorption, the Sr-loaded adsorbent (Sr-MAS), with B2O3 and NH4H2PO4 introduced as glass-formers, was directly converted in situ into iron-phosphate glass via microwave vitrification. The optimized sample (1300-N40), sintered at 1300 °C for 30 min, doped with 5 wt% B2O3 and 40 wt% NH4H2PO4 and exhibited a dense and homogeneous amorphous structure, accompanied by high density (2.72 g cm-3) and excellent chemical durability (normalized Sr2+ leaching rate of 4.19 × 10-6 g m-2·d-1 after 42 days). In addition, Gaussian Process Regression (GPR) coupled with 200 bootstrap resampling iterations, was employed to model and predict the medium-term Sr2+ release behavior and quantify, the extrapolation uncertainty of the long-term release curves. This study provides a scalable route for the minimization of secondary waste and safe immobilization of radioactive strontium in aqueous radioactive effluents.