Sodium-lithium exchange on synthetic zeolite 4A in water-dimethyl sulphoxide (DMSO) mixtures

Abstract Sodium-lithium exchange on synthetic 4A zeolite from 0·1 and 0·01 isomolal solutions of NaCl + LiCl in water-DMSO mixtures has been investigated. Ion-exchange isotherms are identical for the solutions of the two ionic strengths. They are of a complex type, indicating two successive processes. 4A zeolite shows a higher selectivity for sodium, which increases with increasing DMSO content of the mixture. Thermodynamic values ΔG 0 , ΔH 0 and ΔS 0 were obtained. Between 5 and 45° the exchange is practically temperature independent in mixtures with more than 20 wt.% DMSO. The data are compared with those of water and water-dioxane systems obtained earlier, and are discussed with respect to the dielectric constant and solvating ability of the solvents.