An equation of state for systems containing aqueous solutions of strong electrolytes

A semi-empirical equation of state (EOS) for strong electrolyte solutions is derived from an expression of Helmholtz free energy containing a nonelectrolyte term (Peng-Robinson EOS) and terms specific to ion-ion (explicit MSA) and ion-water interactions.; Two models A and B are proposed in the present work. Model A accounts for the nonelectrolyte and ion-ion interactions. In Model B, the hydration effect is accounted for in addition to the interactions in Model A. The parameters in the model are the cation diameter, the binary cation-water interaction parameter and the relative hydration number. The first two parameters are common for both the models whereas the relative hydration number is specific to Model B. The osmotic coefficient calculations using these models gave deviation less than 4% for most salts.; Model A and B are extended to mixed electrolyte solutions. Mixing rules are proposed to calculate the effective cation diameter and the equivalent cation-water interaction parameter for common cation electrolyte solution. Model A gave better representation of mixed electrolyte solutions compared to Model B. The EOS for electrolytes is applied in the prediction of carbon dioxide gas hydrate formation conditions.