Volumetric Properties Modeling in Unsaturated Solutions of the Ternary Na2SO4 – H2SO4 – H2O and MgSO4 – H2SO4 – H2O Systems from 298.15 to 318.15 K and at 101.3 kPa Using the Pitzer Equations

Abstract

This work presents a modeling approach to describe the volumetric properties in unsaturated solutions of the ternary Na₂SO₄ – H₂SO₄ – H₂O and MgSO₄ – H₂SO₄ – H₂O systems from 298.15 to 318.15 K and at 101.3 kPa using the Pitzer equations, incorporating the partial dissociation of ${\text{HSO}}_4^{--}$${\text{HSO}}_4^{--}$. These systems contain two salts that form part of the electrolytic environment found in salt lakes brines in the north of Chile, which are used to produce lithium compounds.The densities measured in this study for ternary systems exhibited trends consistent with changes in concentration and temperature, with Na₂SO₄(aq) and MgSO₄(aq) having a greater impact on densities compared to H₂SO₄(aq).New volumetric parameters for the H₂SO₄ – H₂O system was obtained and their volumetric interaction coefficients in ternary mixtures with Na₂SO₄(aq) and MgSO₄(aq) in water were determined at 298.15, 308.15, and 318.15 K, incorporating the partial dissociation of ${\text{HSO}}_4^{--}$${\text{HSO}}_4^{--}$(aq), thereby expanding the existing database. The resulting standard deviations were low (below 1%), demonstrating the model robustness in predicting volumetric properties for complex multi–component systems.The analysis of the volume of mixing in the ternary systems suggests that interactions between aqueous species and water can induce structural changes in the total volume of solutions, associated directly with solvation effects. The ternary systems containing H₂SO₄(aq), Na₂SO₄(aq) promote an increase in the system volume, while MgSO₄(aq) strongly contracts it. This behavior is primarily attributed to the stronger solvation effect of Mg²⁺ ions compared to Na⁺, ${\text{SO}}_4^{2--}$${\text{SO}}_4^{2--}$, and ${\text{HSO}}_4^{--}$${\text{HSO}}_4^{--}$ ions.