Ind. Eng. Chem. Res. 1999, 38, 1723-1728
1723
Activity Coefficients of Actinide and Rare-Earth Chlorides in Molten LiCl/KCl Eutectic Salt Tom B. Bechtel*,† and Truman S. Storvick Department of Chemical Engineering, University of MissourisColumbia, Columbia, Missouri 65211
Using a numerical Gibbs free-energy minimization technique, the activity coefficients of actinide and rare-earth chlorides in molten LiCl/KCl eutectic at 450 °C have been calculated. Laboratory tests of an electrochemical process for separating actinide metals from rare-earth metals in LiCl/ KCl solvent at 450 °C provided experimental concentration and cathode potential data. 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. The Wohl parameters for the activity coefficient expansions were obtained by minimizing the total Gibbs free energy expressed in terms of the experimental mole fractions. This thermodynamic model will be valuable for process design and scale-up calculations. Introduction The Japanese electric power industries have a plan to remove essentially all of the uranium and transuranic metals from spent nuclear fuel. This reduces the time required to manage the long-lived radiological hazardous materials from about 1 million to about 300 years. The PUREX process is used to recycle the uranium and plutonium fuel values. The PUREX waste containing the fission products, some uranium, and the higher actinides will be denitrified and chlorinated and will have essentially all of the actinides removed using a “dry” electrochemical pyropartitioning process.1-3 In this paper, the activity coefficients of the metal chlorides in molten salt are computed. This thermodynamic representation of the molten salt solutions is necessary for process design calculations. Experimental Apparatus and Procedures All experiments were carried out at a constant temperature of 450 °C in a thermal well which extended from the floor of an argon glovebox (
