Effect of Nitrate Salts on Solubility Behavior of Calcium Sulfate Dihydrate (Gypsum) in the Aqueous Sodium Chloride System and Physicochemical Solution Properties at 308.15 K

Abstract

The effect of addition of nitrate salts (MNO3, where M = Na, K, and NH4) on the solubility behavior of calcium sulfate dihydrate (gypsum, CaSO4·2H2O) in aqueous NaCl solutions has been examined at 308.15 K. The addition of nitrate salts in an aqueous NaCl system increased the CaSO4·2H2O solubility significantly, and the increase was higher at lower salinities. The order of increase in CaSO4·2H2O solubility with addition of different salts was NH4NO3 > NaNO3 > KNO3. The maximum solubility of CaSO4·2H2O in aqueous NaCl solutions with the addition of nitrate salts was found to shift toward the lower salinities. We also measured accurate density (ρ) and speed of sound (u) for the quaternary systems containing CaSO4·2H2O, NaCl, nitrate salts, and H2O at 308.15 K. Measurements of speed of sound and density have been used to determine solution isentropic compressibility (κS). Empirical equations describing the solubility, density, speed of sound, and isentropic compressibility in these systems are presented.