<p>The safe and effective treatment of multivalent radioactive waste is a critical challenge for the sustainable development of nuclear energy. In this study, Ce⁴⁺ was selected as a surrogate for multivalent radionuclides. Silicate glass particles served as the glass former, and walnut shell-derived carbon was used as the reducing agent. Using microwave sintering technology, walnut shell-derived biochar (WSB) and ZnCl₂-activated walnut shell-derived activated carbon (WSA@ZnCl₂) were prepared. The microwave energy conversion and wave-absorption properties of both carbons were systematically compared at different carbonization temperatures, revealing that ZnCl₂ activation enhances the reduction performance of walnut shell-based carbon. Thermodynamic analysis indicated that the complete reduction of CeO₂ to Ce₂O₃ requires a molar ratio&#xa0;n(C):n(CeO₂) &gt; 1:2 or a mass ratio&#xa0;m(C):m(CeO₂) &gt; 0.034:0.966. At a sintering temperature of 1200&#xa0;°C, the phase evolution, microstructure, valence state, and morphology of the cured bodies were examined. The addition of WSA@ZnCl₂-700 demonstrated stronger reducing efficacy than WSB-700, achieving the transformation of 58.22% of Ce⁴⁺ to Ce³⁺. The maximum solid solubility of cerium exceeded 25 wt%, with uniform distribution within the glass network. This study provides a new approach for treating multivalent radioactive waste.</p>