Thermodynamics Research Center / ThermoML | Journal of Chemical and Engineering Data

ABSTRACT

Solubility behavior of calcium sulfate dihydrate (gypsum, CaSO4!P2H2O) in aqueous NaCl solutions in presence of hydroxyalkyl ammonium acetate based ionic liquids (ILs); hydroxyethylammonium acetate (HEAA), dihydroxyethylammonium acetate (DHEAA) or trihydroxyethylammonium acetate (THEAA) at 35oC has been investigated. The addition of ILs increased solubility significantly following the order: HEAA greater than DHEAA greater than THEAA. Solubility maximum of CaSO4!P2H2O shifted towards lower concentration of NaCl in solution with the addition of ILs. Mean ionic activity coefficients b * of CaSO4!P2H2O 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 solubility equilibrium of CaSO4!P2H2O. Solution properties such as density (poundsl) and speed of sound (u) have been measured for the quaternary systems (CaSO4!P2H2O+NaCl+ILs+H2O) at 35centsXC. Primary data on u and poundsl was used to derive solution isentropic compressibility (poundseS). Physical and derived properties have been fitted with suitable polynomial equations. Dissolution kinetics of gypsum in aqueous ILs solution have been measured using in-situ IR analysis and the morphology of gypsum crystals obtained from various conditions have been examined by recording SEM images. SEM images show both classical and non-classical crystallization behaviour of gypsum depending upon nature of IL.