Dissolution of zirconium–cerium oxide solid solution in an aqueous system

The solid-solution aqueous-solution (SSAS) system often involves dissolution/precipitation and redox reactions simultaneously. Comprehensive understanding of the SSAS system requires mechanistic insights into the dissolution mechanism of the solid solution based on reliable characterisation of the solid phases. Given this background, this study investigates the dissolution behaviour of zirconium-cerium oxide solid solution ((Zr,Ce)O₂/(Ce,Zr)O₂), which contains the redox-active metal Ce (Ce(III/IV)) and is of particular importance in the nuclear industry. The solid phases of the solid solution were comprehensively characterised by powder X-ray diffraction (PXRD) with Rietveld analysis and X-ray absorption spectroscopy (XAS) with factor analysis, indicating that the solid solution was primarily composed of tetragonal-(Zr,Ce)O₂ and cubic-(Ce,Zr)O₂. Water immersion of the solid solution leads to the dissolution of the solid phase at the solid-liquid interface. The addition of a reductant to the system reduces Ce(IV) in the solid solution to -(III) at the surface, promoting the dissolution of Ce from the solid-solution phase. The release of Ce from the solid solution also enriches the Zr content in the remaining solid-solution phase at the surface, which makes it more insoluble. This results in the formation of a protective layer at the solid surface, retarding further dissolution of the solid-solution phase.