Occlusion and ion exchange in the molten (lithium chloride+potassium chloride+alkaline-earth chloride) salt+zeolite 4A system with alkaline-earth chlorides of calcium and strontium and in the molten (lithium chloride+potassium chloride+actinide chloride) salt+zeolite 4A system with the actinide chloride of uranium

Abstract

The interaction between molten salts of the type LiCl-KCl-MeCl n (Me=Ca, Sr, U; \(x_{MeCl_n } \)= to 0.45; and x KCl/x LiCl=0.69) and zeolite 4A have been studied at 823 K. The main interactions between these salts and zeolite are molten salt occlusion to form salt-loaded zeolite and ion exchange between the molten salt and salt-loaded zeolite. An irreversible chemical reaction has been observed in the LiCl-KCl-UCl3+zeolite system. The extent of occlusion is a function of the concentration of MeCl n in the zeolite and is equal to 10±1 Cl− per zeolite unit cell, (AlSiO4)12, at infinite MeCl n dilution. The ion-exchange mole-fraction equilibrium constants (separation factors) with respect to Li are decreasing functions of the concentration of SrCl2 and UCl3, but an increasing function of the concentration of CaCl2 in the zeolite. At infinite MeCl n dilution, they are equal to 0.9, 11.9, and 13 for CaCl2, SrCl2, and UCl3, respectively. The standard ion-exchange chemical potentials are equal to −50.0, −84, and −101.1 kJ·mol−1 for Ca2+, Sr2+, and U3+, respectively.