Analysis of Some Electrolyte Models Including Their Ability to Predict the Activity Coefficients of Individual Ions

This work presents a modeling study, with selected models, of the mean ionic activity coefficients of electrolytes in aqueous solutions, where predictions of the activity coefficients of individual ions (ACI) are also considered, as well as an analysis of the various contributions in the models. In this work, we consider one electrolyte equation of state (the electrolyte cubic-plus-association equation of state, e-CPA) and other approaches based on combinations of various versions of the Debye-Huckel (DH) or mean spherical approximation (MSA) and Born terms. The results obtained in this work for ACI and the analysis of terms are discussed in the context of other recent literature studies. The results with the various modeling approaches are not identical but all models show some qualitatively good behavior for the ACI, with the extended version of DH+Born model performing overall better. Moreover, this study shows that, while good results are obtained in many cases, several parameters like the ion radius, Born radius, and relative static permittivity have a significant effect on the results. Finally, in all approaches it appears that the ion-ion (DH or MSA) and ion-solvent (Born) terms have almost equally large opposing contributions to the activity coefficients, indicating that both are equally important. This conclusion is agreement with most literature studies.