Water solubility in molten-salt mixtures. A theory for selective ionic hydration

Abstract

A statistical thermodynamic treatment based on the quasi-lattice model of molten salts is developed to explain the non-linear dependence of the enthalpy of transfer of water from liquid water to an infinitely dilute solution of water in a binary molten-salt mixture on the molar composition of the mixture. The derived equation is used to fit previously determined data for the enthalpy of transfer of water from liquid water to (undercooled) liquid LiNO₃+ NH₄NO₃ mixtures in the whole composition range; a satisfactory fit is obtained for a reasonable choice of the values for the quasi-lattice coordination numbers of LiNO₃ and NH₄NO₃. Literature data for the enthalpy of dissolution of water in molten LiNO₃+ NaNO₃ and LiNO₃+ KNO₃ mixtures are in qualitative agreement with the predictions of the present theory.