Interaction of Uranium Trichloride with Lithium Oxide in the Eutectic LiCl–KCl Melt

The interaction between uranium trichloride and molten LiCl–Li₂O in the eutectic LiCl–KCl melt at 773, 823, and 873 K is investigated using potentiometry in order to check the completion of UCl₃ precipitation reaction. Measuring the equilibrium U³⁺/U couple potential is found to allow the precipitation of UCl₃ to be checked in real time. Quantitative precipitation is observed at a UCl₃ : Li₂O molar ratio of 1 : 2; in this case, the uranium electrode potential shifts to the negative region by more than 300 mV relatively to equilibrium. Using the obtained experimental data, the apparent standard potentials of the U³⁺/U couple are determined, and the activity coefficients of UCl₃ in the eutectic LiCl–KCl melt are calculated. The activity coefficients of UCl₃ at 773, 823, and 873 K are 5.4 × 10^–4, 9.1 × 10^–4, and 4.8 × 10^–3, respectively.