Thermodynamic properties for rare earths and americium in pyropartitioningprocess solvents

The design of a molten metal-molten salt based chemical and electrochemical process for separation of actinides from plutonium-uranium extraction wast e requires a consistent set of thermodynamic properties for the actinides a nd rare earths present in nuclear waste. Standard potential data for Y, La, Ce, Pr, and Gd in molten LiCl-KCl were obtained. Americium data obtained w ere standard potentials in molten LiCl-KCl and activity coefficients for Cd and Bi. Data were obtained between 400 and 500 degrees C. Results for the rare earth chlorides using an-improved experimental technique were consiste nt with theory, with standard free energy of formation values somewhat more negative than those found in the literature. Special attention was given t o Am in the LiCl-KCl/Cd system because it can exist as the +2 and/or +3 ion in this system. Americium ions existed only as the +3 ion in LiCl-KCl/Bi. Standard electrochemical potentials for Am/Am+2 in LiCl-KCl eutectic at 400 , 450, and 500 degrees C were -2.893, -2.853, and -2.838 V,respectively, re lative to Cl-2/Cl-. Standard electrochemical potentials vs. Cl-2/Cl- for Am /Am+3 in LiCl-KCl eutectic were -2.838 V at 450 degrees C and -2.78 V at 50 0 degrees C. Activity coefficients for Am in molten Cd were 1 x 10(-5) and 8 x 10(-5) at 450 and 500 degrees C. Activity coefficients for Am in molten Bi were 2 x 10(-11) and 2 x 10(-10) at 450 and 500 degrees C. (C) 1999 The Electrochemical Society. S0013-4651(98)12-098-0. All rights reserved.