BET MODEL FOR CALCULATING ACTIVITIES OF SALTS AND WATER, MOLAR ENTHALPIES, MOLAR VOLUMES AND LIQUID-SOLID PHASE-BEHAVIOR IN CONCENTRATED ELECTROLYTE-SOLUTIONS

This paper demonstrates the calculation of the activities of salts and water, excess properties and solid phase equilibria in aqueous media by applying the general properties of solutions to extensions of the Stokes-Robinson application of the Brunauer-Emmett-Teller (BET) adsorption isotherm. Such a comprehensive treatment provides a thermodynamically consistent method of obtaining equilibrium properties of moderately to highly concentrated (up to molten salt regime) aqueous solutions with as few as two parameters, plus a third parameter in the case of molar volumes. The present state of development allows treatment of electrolytes with common anions or common cations, but does not yet include reciprocal salt mixtures. Multicomponent aqueous solutions can be treated as pseudobinary if desired, by invoking the proposed mixing rules. The real advantage of the method lies in the use of a minimal number of parameters to represent a wide variety of thermodynamic properties with reasonable accuracy over relatively wide temperature and concentration ranges. This comprehensive treatment is verified through comparison of predicted results and experimental data on: water vapor pressure-temperature-composition behavior of aqueous LiBr and of (Li, K, Na)NO3 mixtures; partial excess and molar volume-temperature-composition of aqueous LiBr and of (Li, K, Na)NO3 mixtures; partial excess and integral molar enthalpy temperature-composition of aqueous LiBr; phase equilibria of NaOH in aqueous solution.