ABSTRACT Radioactive spent silica gel is a type of secondary waste generated during the decontamination and purification processes of spent fuel reprocessing. This work reports borosilicate glass containing zircon mineral phases to achieve the immobilization of such waste. The physical phase evolution, microstructure, and immobilization mechanism were systematically investigated. The XRD and refinement results confirmed the lattice substitution of uranium in zircon crystals. The XPS and UV‐vis‐DRS results demonstrated that the uranium mainly showed quadrivalent and pentavalent states in the ZrSiO 4 crystal. The FT‐IR results demonstrated that the microcrystal glass became more structurally intact and polymerized as the uranium content in the crystal increased. EPR analysis and theoretical calculations revealed that the entry of uranium into the ZrSiO 4 structure adjusted the amount of oxygen vacancy defects in the material. The electron density difference analysis showed that the electrons produced by the vacancy defects were concentrated on the surrounding oxygen atoms. Ultimately, these behaviors enhanced the chemical stability of the material. This work provides a good strategy for the disposal of this waste and a new perspective on the entry of uranium atoms into the zircon structure in the field of radioactive waste disposal.
Qiu et al. (Tue,) studied this question.