Electrochemical partitioning of actinides and rare earths in molten salt and cadmium solvents: Activity coefficients and equilibrium simulation

The activity coefficients of actinide and rare earth chlorides in molten LiCl/KCl eutectic and of the reduced metals in molten cadmium have been calculated using a numerical method to minimize the Gibbs free energy. The generalized expansion by Wohl was used to express the concentration dependence of the excess Gibbs free energy. The activity coefficients were expressed in terms of the Wohl volume and interaction energy parameters. Laboratory tests of an electrochemical process for separating actinide metals from rare earth metals provide the experimental data. The Wohl parameters for the activity coefficients were obtained by minimizing the total Gibbs free energy.; A computer model was developed to simulate and predict results of laboratory electrorefining experiments. This model uses the activity coefficient expressions determined by free energy minimization in the equations for equilibrium to predict electrode potentials and solution concentrations in the process. Good agreement with experimental data has been found. The thermodynamic model will be useful for process design and scale-up calculations for separation processes.