Chemistry and thermodynamics of the distribution of lanthanide and actinide elements between molten LiFBeF 2 and liquid bismuth solutions

Abstract

Distribution coefficients (mole fraction in bismuth phase divided by mole fraction in salt phase) were determined for several lanthanide and actinide elements in molten LiFBeF 2-liquid bismuth systems. Most of the data were obtained at 600°C with LiFBeF 2 (66·7−33·3 mole %) as the salt phase, although some data were obtained in the temperature range 500–700°C and with LiFBeF 2 (56·9−43·1 mole %). At each temperature, the distribution coefficients ( D M ) obeyed the relationship D M = ( D Li n ) K′ M , in which n is the valence of the element in the salt phase. With the possible exceptions of samarium and americium, the valences of the various species were generally those expected. Samarium was divalent over the range of conditions studied. A significant fraction of the americium in the salt phase was found to be in the divalent state at 600°C. Values for log K′ U and log K′ Pu were obtained over the temperature range of 500–700°C. These values, when used in conjunction with other information from the literature, led to the following expressions for the free energies of formation of the respective trifluorides: ΔG UF3 f (kcal/mole) = −374·3 + 71·93( T/10 3), and + ΔG PuF3 f = −394·6 + 73·35( T/10 3).