Thermodynamic properties of aqueous solutions of single and multiple salts using the Q-electrolattice equation of state

Abstract

Thermodynamic property calculations of solutions containing electrolytes are relevant to design and optimize industrial process, among which water desalination. The conventional way of designing such processes relies on specific models or correlations for vapor pressure, density, osmotic coefficient, and mean ionic activity coefficient. Nonetheless, an equation of state (EOS) for electrolyte solutions enables, in principle, the evaluation of all of them. In previous work, the electrolattice EOS was presented, being composed by three terms: the Mattedi–Tavares–Castier (MTC) lattice-based contribution, the Born contribution, and an explicit mean spherical approximation (MSA) for ions of equal diameters. In the present work, an explicit MSA term suitable for ions of unequal diameters is used instead, along with new water parameters and two adjustable parameters per ion. The new expression for the Helmholtz energy, referred to as Q-electrolattice model, is used to correlate mean ionic activity coefficients and densities in strong 78 single-salt aqueous solutions. Additionally, calculations of vapor pressure, osmotic coefficient, and apparent molar volume of salt are performed. Predictions of thermodynamic properties for aqueous solutions containing multiple salts and seawater are also presented without using any additional adjustable parameter.