An equation of state for electrolyte solutions by a combination of low-density expansion of non-primitive mean spherical approximation and statistical associating fluid theory

A two-parameter equation of state (EOS) for electrolyte solutions is developed. The equation is in terms of Helmholtz free energy and incorporated with our previous results of the low-density expansion of non-primitive mean spherical approximation (MSA). The concentration dependent dielectric constant is thus inherently included in the model. The statistical associating fluid theory (SAFT) is introduced to represent the association interactions, including the solvent–solvent and ion–solvent. The EOS is tested for 15 aqueous alkali halide solutions at ambient condition. The equation can represent simultaneously the mean ionic activity coefficients, the osmotic coefficients and densities in a good accuracy up to saturated concentration. The comparisons with EOSs published earlier in the literature are carried out. The limitations of the model are also discussed.