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 HSO-4 (aq). 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 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+, SO2-4 , and HSO-4 ions.