Effects of Aliphatic Alcohols on Solubility, Physicochemical Properties, and Morphology of Calcium Sulfate Dihydrate (Gypsum) in Aqueous Sodium Chloride Solution at 35 °C

The effect of addition of aliphatic alcohols (methanol, ethanol, and isopropyl alcohol) on the dissolution characteristics of calcium sulfate dihydrate (gypsum, CaSO4·2H2O) in brines has been studied at 35 °C. Addition of alcohols decreased the dissolution of CaSO4·2H2O in aqueous NaCl solutions significantly and also shifted its solubility maximum toward a lower concentration of NaCl. We have also recorded the density (ρ) and speed of sound (u) for the quaternary systems (CaSO4·2H2O + NaCl + alcohols + H2O) at 35 °C. Using primary data, we derived the isentropic compressibility (κS) of the solutions. The experimentally determined physical and derived properties have been correlated using polynomial or linear fits using the method of least-squares. The crystal growth behavior and morphology of gypsum cocrystallized with NaCl crystals from different solutions has also been examined. Alcohol additives seem to be an environmentally friendly, low-cost additive to decrease the solubility of gypsum in aqueous systems with or without NaCl.