Ion exchange in molten salts. I. The ion-exchange properties of sodium zeolite A in molten NaNO₃; exchange reactions with alkali metal, thallium, and silver cations

Cation-exchange equilibria between sodium zeolite A and molten mixtures of sodium nitrate and those of lithium, potassium, cesium, silver, or thallium were studied over substantial ranges of compositions of the exchanger at 330° (350° for the potassium exchanges). In those cases (lithium, sodium, silver) where occlusion of nitrate in the α cage of the zeolite occurs, all of the cations can be exchanged, but in the other cases limited exchange only occurs. When extrapolated to trace concentrations in the sodium zeolite-sodium nitrate system, the selectivity order is Cs > Tl > Ag > K > Li > Na, but the positions of Cs, Tl, and K are transposed to the right as their loading increases. The standard free energy change for complete exchange from sodium to silver zeolite in equilibrium with the pure molten salts at 330° is ΔG° = -3230 cal/mol.