Occlusion and ion exchange in the molten (lithium chloride-potassium chloride-alkali metal chloride) salt plus zeolite 4A system with alkali metal chlorides of sodium, rubidium, and cesium

Interaction between molten salts of the type LiCl-KCl-MeCl (Me = Na, Rb, Cs , x(MeCl) = 0 to 0.5, x(KCl)/x(LiCl) = 0.69) and zeolite 4A have been studi ed at 823 K. The main interactions between these salts and zeolite are molt en salt occlusion to form salt-loaded zeolite and ion exchange between the molten salt and salt-loaded zeolite. No chemical reaction has been observed . The extent of occlusion is a function of the concentration of MeCl in the zeolite and is equal to 11 +/- 1 Cl- per zeolite unit cell, (AlSiO4)(12), at infinite MeCl dilution. The ion-exchange mole fraction equilibrium const ants (separation factors) with respect to Li are decreasing functions of co ncentration of MeCl in the zeolite. At infinite MeCl dilution, they are equ al to 0.84, 0.87, and 2.31 for NaCl, RbCl, and CsCl, respectively, and incr ease in the order Na < Rb < Cs at identical MeCl concentrations. The standa rd ion-exchange chemical potentials are equal to -(0.0 +/- 0.5) kJ.mol(-1), -(0.4 +/- 0.3) kJ.mol(-1), and -(6.5 +/- 0.5) kJ.mol(-1) for Na+, Rb+, and Cs+, respectively.