Equilibrium distribution of actinide and lanthanide elements between molten fluoride salts and liquid bismuth solutions

Abstract

The equilibrium distributions of several actinide and lanthanide elements between liquid bismuth solutions and a variety of LiF-containing molten fluoride salts were determined between 500 and 700°C. At each temperature, the distribution coefficients (mole fraction in bismuth phase divided by mole fraction in salt) obeyed the relationship D = ( D Li n ) K′, in which n is the valence of the element in the salt phase. Over the range of conditions investigated, Th, Pa, and Zr existed as tetravalent species in the salt; U, Np, Pu, Am, Cm, Cf, La, and Nd were trivalent; and, Eu was divalent. The distribution behavior of each element was affected by salt composition and temperature. Values of log K′ increased regularly with decreasing temperature. With LiFBeF 2ThF 4 (72-16-12 mole %) as the salt phase, the values of log K′ at 600°C for the trivalent actinide elements varied systematically with atomic number, and passed through a minimum near Z = 96(Cm).