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

Abstract

The solubility of CaSO 4 ·2H 2 O was determined in aqueous NaCl solutions up to very high salinities and at constant MgCl 2 concentrations at 35 °C. The addition of MgCl 2 into the aqueous NaCl system enhances the solubility of CaSO 4 ·2H 2 O significantly at lower NaCl concentrations. The solubility maximum of CaSO 4 ·2H 2 O also shifts slightly toward the lower salinities with the addition of MgCl 2 . We also measured accurate density (ρ) and speed of sound ( u ) for the quaternary system CaSO 4 ·2H 2 O + NaCl + MgCl 2 + H 2 O at 35 °C. Measurements of the speed of sound and density have been used to determine solution isentropic compressibility (κ S ) and ion-hydration characteristics. Empirical equations describing the solubility, density, speed of sound, and isentropic compressibility in these systems are presented.