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

ABSTRACT

Dissolution trend and solubility data of calcium sulfate dihydrate (CaSO4*2H2O gypsum) in aqueous Na, Ca, Mg, and Al chloride salt solutions have been studied at 278.15 K to 308.15 K. The concentration ranges were up to 4.5 mol*L-1 for NaCl, 3.0 mol*L-1 for MgCl2, 2.0 mol*L-1 for CaCl2, and 1.6 mol*L-1 for AlCl3, respectively. Measurement results show that except for CaCl2, the other three salts allow the solubility of gypsum to rise a lot first and then descend smoothly after attaining the maximum. Because of common ions effect, the solubility of CaSO4*2H2O drops sharply in CaCl2 solution at low concentration and continues to fall almost linearly as concentration exceeds 0.2 mol kg-1 . Impacts of Na, Mg, Al chloride salts on solubility of CaSO4*2H2O are explained on the basis of dissolution and thermodynamic equilibrium. The solubility of CaSO4*2H2O in AlCl3 solution is highest compared with that in NaCl and MgCl2 solution because two sulfur-bearing chemical complex Al(SO4)2 -(aq) and AlSO4 + (aq) are expected to be formed in solution. Besides, a number of H+ ions produced in AlCl3 solution further promote the dissolution of CaSO4*2H2O. In addition, it is demonstrated that CaSO4*2H2O is fairly stable in the above chloride salts solution of high concentration (4.5 mol*L-1 for NaCl, 3.0 mol*L-1 for MgCl2, 2.0 mol*L-1 for CaCl2 and 1.6 mol*L-1 for AlCl3) for 2 weeks at 308.15 K by the evidence that no new peaks emerged in X-ray power diffraction results.