Effect of MgCl2 on the Solubility of CaSO4·2H2O in the Aqueous NaCl System and Physicochemical Solution Properties at 35 °C

The solubility of CaSO4·2H2O was determined in aqueous NaCl solutions up to very high salinities and at constant MgCl2 concentrations at 35 °C. The addition of MgCl2 into the aqueous NaCl system enhances the solubility of CaSO4·2H2O significantly at lower NaCl concentrations. The solubility maximum of CaSO4·2H2O also shifts slightly toward the lower salinities with the addition of MgCl2. We also measured accurate density (ρ) and speed of sound (u) for the quaternary system CaSO4·2H2O + NaCl + MgCl2 + H2O at 35 °C. Measurements of the speed of sound and density have been used to determine solution isentropic compressibility (κS) and ion-hydration characteristics. Empirical equations describing the solubility, density, speed of sound, and isentropic compressibility in these systems are presented.