Sodium-lithium exchange on synthetic zeolite 4A in water-dioxane mixtures

Abstract Sodium-lithium exchange on the synthetic zeolite 4 A from 0·01 isomolal NaCl + LiCl solutions in water, 20, 45 and 82 wt% dioxane has been investigated. Two exchange processes have been established: one at n Li z n Li z > 0·35, temperature dependent. Thermodynamic functions of the ion exchange equilibria were calculated from the isotherms obtained at 5°, 25°, 45° and 65°C. ΔG° for the overall process is positive for the exchange of sodium in the zeolite by lithium and increases slightly with increasing dioxane concentration. ΔH° is positive and constant up to high dioxane concentrations, when it decreases rapidly, becoming zero for the exchange in 82 wt% dioxane. ΔS° varies from +1·6 e.u. for exchange in water to −5·6 e.u. for exchange in 82 wt% dioxane. An attempt has been made to correlate these data with some properties of the liquid phase.