Solubility Behavior of Calcium Sulfate Dihydrate (Gypsum) in an Aqueous Sodium Chloride System in the Presence of Hydroxyalkyl Ammonium Acetate Ionic Liquids Additives: Morphology Changes and Physicochemical Solution Properties at 35 °C

Abstract

Dissolution characteristics of calcium sulfate dihydrate (gypsum, CaSO4·2H2O) in brines have been investigated in the presence of hydroxyalkyl ammonium acetate ionic liquids (ILs): hydroxyethylammonium acetate (HEAA), dihydroxyethylammonium acetate (DHEAA), or trihydroxyethylammonium acetate (THEAA) at 35 °C. The addition of ILs increased solubility significantly following the order: HEAA > DHEAA > THEAA. Solubility maximum of CaSO4·2H2O shifted toward a lower concentration of NaCl in solution with the addition of ILs. Mean ionic activity coefficients γ± of CaSO4·2H2O have been estimated as a function of solution ionic strength using the extended Debye–Huckel law with quadratic terms. The solubility product was calculated using a solubility equilibrium of CaSO4·2H2O. Density (ρ) and speed of sound (u) of (CaSO4·2H2O + NaCl + ILs + H2O) system have been recorded at 35 °C. Primary data on u and ρ were used to derive solution isentropic compressibility (κS). Polynomial equations have been used to fit the mea...