Phase diagrams of the quaternary system NaCl-MgCl2-NH4Cl-H2O at 333.15 K and their application

• Published in: The Journal of chemical thermodynamics 2020-01, Vol.140, p.105872, Article 105872
• Main Authors: Li, Cheng, Wang, Dong-Yan, Guo, Hong-Fei, Zhao, Bin, Liu, Xiu-Wu, Fan, Shuan-Shi, Cao, Ji-Lin
• Format: Article
• Language: English
• Subjects: Ammonium carnallite; Phase equilibrium; Pitzer thermodynamic model; Solubility
• ISSN: 0021-9614; 1096-3626
• DOI: 10.1016/j.jct.2019.07.014

•Solubilities of NaCl-MgCl2-NH4Cl-H2O and its ternary subsystem NaCl-MgCl2-H2O were investigated.•The extended Pitzer model was applied to the phase equilibrium calculation.•The ion interaction parameters θ and ψ were correlated.•A technological process to produce ammonium carnallite and NaCl via mixed solution after extracting potassium chloride. Based on the requirement of the new technology for producing ammonium carnallite and NaCl via the solution left after the preparation of potassium salt as raw materials, the solubilities of the quaternary system NaCl-MgCl2-NH4Cl-H2O and ternary subsystem NaCl-MgCl2-H2O at 333.15 K were measured using the isothermal dissolution method, and the corresponding phase diagrams were plotted. The phase diagram of the ternary system consists of three fields of crystallization, which correspond to NaCl, MgCl2·6H2O and their co-existing fields respectively. There are four fields of crystallization in the quaternary system, which correspond to MgCl2·6H2O, NH4Cl, NaCl and the double salt MgCl2·NH4Cl·6H2O respectively. By analyzing and calculating the phase diagrams, a technological route was proposed, which indicated that the Na-Mg resources were fully utilized. The extended Pitzer model was applied to the phase equilibrium calculation and the results showed that the calculated data were consistent with experimental values well.