An excess Gibbs free energy model composed of a short range term, expressed by the nonelectrolyte UNIQUAC-NRF model, and a long range contribution based on the Pitzer-Debye-Hückel equation is implemented for strong aqueous electrolyte solutions. The present model is applied for calculations of mean activity coefficient and osmotic coefficient of aqueous electrolyte solutions using two approaches: salt parameter model and ion specific parameter model. In salt parameter scheme, the present model has two adjustable parameters per each aqueous salt that are salt-water and water-salt energy parameters. In ion specific approach, the interaction energy parameters of each species with the other species are obtained. The experimental activity coefficients of aqueous electrolyte solutions are used to determine the energy parameters. The surface and volume parameters of ions are calculated using their radius. The results of the models are in good agreements with the experimental data. The extensions of the two approaches for prediction of solubility and osmotic coefficients of some mixed-salt systems have been carried out.

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