Phase equilibrium of CaSO4-Ca(OH)2-H2O system
(1. School of Metallurgical Science and Engineering, Central South University, Changsha 410083, China;
2. Environmental Monitoring Central Station of Hunan Province, Changsha 410014, China)
2. Environmental Monitoring Central Station of Hunan Province, Changsha 410014, China)
Abstract: In order to provide the theoretical guidance for applying the neutralization method to treatment of heavy metals wastewater with high concentration of sulfate, and to better understand the mechanism of calcium sulfate scale formation, the equilibrium solubility data of CaSO4-Ca(OH)2-H2O system at 298.15 K were theoretically calculated via the Pitzer semi-empirical ion-interaction theory, and determined experimentally by the optical method combining with X-ray diffractometry, and the calculated and determined phase diagrams of CaSO4-Ca(OH)2-H2O system were plotted and compared. Physical definition of each area was studied, and the physical law of characteristic point and line was explained in detail. Adjusting the pH value of neutralization-hydrolysis solution depended on the SO42- concentration in the system. And interaction characteristics between the solubilities of CaSO4(s) and Ca(OH)2(s) were found out.
Key words: CaSO4-Ca(OH)2-H2O system; phase equilibrium; phase diagram; wastewater