Thermodynamic properties of trivalent lanthanide and actinide ions in molten mixtures of LiCl and KCl

The thermodynamic stability of Ln(III) (Ln: La, Ce, Pr, Tb, and Er) and U(III) complexes in LiCl–KCl system at 923 K was studied by electrochemical techniques. The Gibbs free energy change of the Ln3+/Ln0 and U3+/U0 redox reactions, Δ G 3 / 0 ∘ ′ , was investigated under various mole fraction of KCl, χK = 0–0.65. In general, Δ G 3 / 0 ∘ ′ increased linearly with the decrease of χK due to the distortion of octahedral symmetry of LnCl 6 3 - and UCl 6 3 - , but a few exceptions were found for lighter Ln elements, e.g., La and Ce, at smaller χK of 0–0.2. The discrepancy suggests an increase of the number of Cl− ions around La3+ and Ce3+.