Extending Zavitsas’ hydration model to the thermodynamics of solute mixtures in water

While Zavitsas’ hydration model has been used to determine the activity of water in electrolyte solutions, it has not previously been demonstrated to model the activities of solutes. The present study derives the equations for the activity of solutes in aqueous electrolyte solution mixtures for Zavitsas’ hydration model. The derived equations are tested by predicting the solubility of sodium nitrite (NaNO2) in aqueous sodium chloride (NaCl) and sodium hydroxide (NaOH) solutions, electrolytes of interest to nuclear waste processing. The solubility of NaCl in aqueous NaNO2 solutions was also modeled. The solubility of NaNO2 and NaCl were accurately calculated in these systems, even though no solubility data from those mixtures was used in model parametrization. These results demonstrate that Zavitsas’ hydration model can be used to model the activities and solubilities of solutes in electrolyte solutions, in addition to the activity of water.