Reaction Mechanism of Uranium Metal and Cadmium Chloride in LiCl-KCl Eutectic Molten Salt

The synthesis of high-concentration uranium trichloride (UCl₃) was investigated through the reaction of cadmium chloride (CdCl₂) with metallic uranium (U) in a LiCl-KCl eutectic molten salt system. This process is particularly relevant to nuclear fuel reprocessing, as the production of UCl₃ is essential for efficient uranium electrorefining. The study aims to investigate the thermodynamic feasibility, reaction dynamics, and synthesis mechanism of UCl₃ in LiCl-KCl molten salt system. Thermodynamic calculations were performed to predict the likely reaction pathways and the equilibrium conditions. Electrochemical monitoring and in-situ absorption spectroscopy were employed to observe the concentration changes of uranium and cadmium species during the reaction. The experimental results demonstrate that CdCl₂ is capable of oxidizing metallic uranium to U³⁺, leading to the formation of UCl₃. Metallic cadmium (Cd) is produced as a byproduct. As the reaction proceeded, the concentration of UCl₃ in the molten salt increases steadily, while the concentration of Cd²⁺ decreases over time. The process reaches equilibrium after a certain period. Thermodynamic calculations confirm that the reaction is energetically favorable for the formation of UCl₃. No higher-valent uranium compounds, such as UCl₄ or UCl₅, are observed in the reaction, which is consistent with the experimental data. The electrochemical analysis reveals a clear transition in the oxidation states of uranium, from U to U³⁺, as the reaction progressed. In addition, in-situ absorption spectroscopy was used to monitor the formation of UCl₃ in real-time. The results confirm that UCl₃ is the dominant product formed during the reaction. No significant formation of U⁴⁺ or U⁵⁺ is detected, further validating the thermodynamic predictions. The formation of UCl₃ is accompanied by a gradual decrease in the concentration of Cd²⁺, which is reduced to metallic Cd and deposited at the bottom of the reaction vessel. The high concentration of UCl₃ (50.86%) is successfully achieved, and the LiCl-KCl-UCl₃ molten salt system is subsequently used as the initial electrolyte for uranium electrorefining experiments. The results of this study demonstrate that synthesizing UCl₃ using CdCl₂ and metallic uranium is both thermodynamically and electrochemically feasible. This provides important technical support for the preparation of molten salt electrolytes in uranium electrorefining. The study also highlights the potential for recycling cadmium by reducing Cd²⁺ to metallic cadmium, thereby enhancing the sustainability of the process. Overall, the findings of this research contribute to the advancement of molten salt electrorefining technology for nuclear fuel reprocessing and offer valuable insights for future industrial applications.