Multicomponent ion exchange in zeolites. Part 3.—Equilibrium properties of the sodium/potassium/cadmium–zeolite X system

Abstract

A study is reported on the ternary exchange equilibrium involving the cations sodium, potassium and cadmium in zeolite X. This system is an apt one on which to test recently developed prediction procedures since it is possible, in principle, to convert zeolite X to the 100%-exchanged homoionic forms of each of these three cations, thus avoiding the normalisation problems reported previously (K. R. Franklin and R. P. Townsend, J. Chem. Soc., Faraday Trans. 1, 1985, 81, 3127; K. R. Franklin and R. P. Townsend, J. Chem. Soc., Faraday Trans. 1, 1985, 81, 1071). In addition, cadmium salts in solution show markedly non-ideal behaviour even in dilute solution, and therefore the procedures developed for allowing for this non-ideality can be tested adequately. Data are given not only for the ternary system but also for the three conjugate binaries, for which the thermodynamic closure rule (‘triangle rule’) is shown to hold. In general, successful prediction of exchange equilibria for different external solution concentrations is shown to be possible, although systematic errors develop at the highest concentration examined.