A Simple G-Excess Model for Concentrated Aqueous Electrolyte Solutions

Abstract

A simple yet accurate thermodynamic model was developed here to represent the nonideal behavior of single electrolytes in water at very high molalities and within a wide temperature range. The present model was obtained from an analytical expression of the excess Gibbs free energy (G-excess) which comprises three major contributions; in this context, a chemical term in the model handles the most predominant short-range ion− solvent interactions by means of a chemical equilibrium approach based on a stepwise ion solvation, whereas another term in the model of physical nature also contributes in describing the aforementioned interactions by incorporating a simple Margules equation, and last, a continuum-solvent term given by the explicit mean-spherical-approximation (MSA) expression serves to account for long-range ion−ion forces. The resulting G-excess model was applied to the representation of experimental mean ionic activity coefficients and osmotic coefficients of various representative aqueous electrolyte solutions: AgNO 3 , CaCl 2 , HCl, HClO 4 , HF, HNO 3 , KF, KOH, LiBr, LiCl, LiNO 3 , NaCNS, NaOH, NH 4 NO 3 , ZnBr 2 , and ZnCl 2 salts in water at 25 °C (and from 0 up to 300 °C only in the case of KOH) and at high concentrations (up to 83.263 M). The results indicated a very good agreement between the experimental data and those calculated using the present G-excess model for the majority of the electrolyte solutions considered here.

Modeling the Hydrate Dissociation Pressure of Light Hydrocarbons in the Presence of Single NaCl, KCl, and CaCl2 Aqueous Solutions Using a Modified Equation of State for Aqueous Electrolyte Solutions with Partial Ionization

“…Accordingly, we have investigated this issue with a chemical term. This term handles the ion–solvent interactions by means of a chemical equilibrium approach based on a stepwise ion solvation . It is important to highlight that all the studied systems in this work, inhibited with aqueous electrolyte solutions, show that the Born contribution is dominant in the AES-PI EoS under different conditions of the deepwater ambient.…”