Phase Diagrams of the Quaternary System NaCl–MgCl2–NH4Cl in Water at 0 and 25 °C and Their Application

• Published in: Journal of chemical and engineering data 2016-01, Vol.61 (1), p.450-457
• Main Authors: Dou, Shuai-Yong, Guo, Hong-Fei, Zhao, Bin, Xue, Chun-Yan, Cao, Ji-Lin
• Format: Article
• Language: English
• ISSN: 0021-9568; 1520-5134
• DOI: 10.1021/acs.jced.5b00639

On the basis of the comprehensive utilization of the Na–Mg salt deposit, a new process to produce NaCl and ammonium carnallite (MgCl2·NH4Cl·6H2O) by using NH4Cl and the solution left after the preparation of potassium salt as raw materials was proposed. For this, the phase equilibrium of the quaternary system NaCl–MgCl2–NH4Cl–H2O at 25 and 0 °C was studied. The solubilities of the quaternary system NaCl–MgCl2–NH4Cl–H2O were measured by an isothermal method, and the corresponding phase diagrams were drawn out. From the phase diagrams: there are four solid phase crystalline zones, which correspond to NaCl, MgCl2·6H2O, NH4Cl, and MgCl2·NH4Cl·6H2O respectively. NaCl and MgCl2·NH4Cl·6H2O have larger crystalline zones at 25 °C than at 0 °C, and NH4Cl has a smaller crystalline zone at 25 °C than at 0 °C. It indicates that NaCl and MgCl2·NH4Cl·6H2O are easy to crystallize out. On the basis of the analysis and calculation of the phase diagrams, the appropriate conditions for the process were identified. In the process, the NaCl could be prepared at 25 °C, and the ammonium carnallite could crystallize out at 0 °C when NH4Cl was added into the remaining solution. The solubilities of the studied system were calculated based on the extended Pitzer model, and the results showed that the calculated values were closed to the experimental results.