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 (MNO 3, where M = Na, K, and NH 4 ) on the solubility behavior of calcium sulfate dihydrate (gypsum, CaSO 4 ·2H 2 O) in aqueous NaCl solutions has been examined at 308.15 K. The addition of nitrate salts in an aqueous NaCl system increased the CaSO 4 ·2H 2 O solubility significantly, and the increase was higher at lower salinities. The order of increase in CaSO 4 ·2H 2 O solubility with addition of different salts was NH 4 NO 3 > NaNO 3 > KNO 3 . The maximum solubility of CaSO 4 ·2H 2 O 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 CaSO 4 ·2H 2 O, NaCl, nitrate salts, and H 2 O at 308.15 K. Measurements of speed of sound and density have been used to determine solution isentropic compressibility (κ S ). Empirical equations describing the solubility, density, speed of sound, and isentropic compressibility in these systems are presented.