Electrolyte solutions occur in many natural systems and are present in several industrial processes. Aqueous solutions of electrolytes are particularly important for designing water purification and treatment systems, among which water desalination processes. The design of processes with electrolyte solutions may require determining phase equilibrium conditions, and predicting volumetric and calorimetric properties. Equations of state (EOSs) are, in principle, capable of such predictions and, for this reason, a several equations of state (EOS) have been developed considering the ionic interactions in electrolytes solutions. An example is the electrolattice equation of state. This model evaluates the Helmholtz energy as the summation of three contributions: the first considers the short range interactions (by using the Mattedi-Tavares-Castier equation of state (MTC-EOS)); the second, the Born contribution term, accounts the solvation effects; the third, the primitive mean spherical approximation (MSA) term, describes the long range effects. In the electrolattice EOS, the diameters of cations and anions are considered to be equal. In this work, we calculate vapor pressures, mean ionic activity coefficients, osmotic coefficients, and densities of mixtures containing water and a single 2:1 strong electrolyte with a revised version of the electrolattice EOS, which is called Q-electrolattice EOS. The latter preserves the first and the second contributions of the electrolattice EOS, but includes another MSA term, which is an explicit mean spherical approximation under the assumption the ions have unlike diameters. The water molecule is assumed to have a dispersion region, an electron-donor region, and an electron-acceptor region. To reduce the number of adjustable parameters of the model, the ionic diameters are taken from the literature. Also, interactions between the each ion and each of the three regions of the water molecule are assumed to be equal. Finally, short range interactions between ions are neglected. With this set of assumptions, the inclusion of each ion only requires the fitting of one additional parameter. The work compares the performance of the electrolattice and Q-electrolattice models with respect to other equations of state for similar applications.


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