Phase equilibrium of the quaternary system K2SO4–MgSO4–(NH4)2SO4–H2O at 25 °C

• Published in: Fluid phase equilibria 2016-01, Vol.408, p.115-122
• Main Authors: Xue, Chun-Yan, Zhao, Bin, Guo, Hong-Fei, Dou, Shuai-Yong, Cao, Ji-Lin
• Format: Article
• Language: English
• Subjects: Ammonium sulfate; Magnesium sulfate; N–Mg–K–S compound fertilizers; Phase equilibrium; Pitzer model; Potassium sulfate
• ISSN: 0378-3812; 1879-0224
• DOI: 10.1016/j.fluid.2015.08.019

The solubilities of the quaternary system K2SO4–MgSO4–(NH4)2SO4–H2O were measured by isothermal method at 25 °C and their dry salt phase diagrams were plotted. The results indicated that, at 25 °C, the solubility phase diagram of this quaternary system consists of seven crystallization regions, those are single-salt crystallization region MgSO4·7H2O, (NH4)2SO4, and K2SO4, complex salt crystallization region MgSO4·(NH4)2SO4·6H2O, MgSO4·K2SO4·6H2O, solid solution crystallization region (K1−n, NH4n)2SO4 (n:0.143–0.893) and (K1−n, NH4n)2SO4·MgSO4·6H2O (n:0.552–0.973), respectively. The extended Pitzer model was derived and applied to the phase equilibrium calculation of system K2SO4–MgSO4–(NH4)2SO4–H2O and its sub-systems at 25 °C. The results showed that the calculated values were consistent with experimental results well. The study on the quaternary system K2SO4–MgSO4–(NH4)2SO4–H2O provides a foundation for the N–Mg–K–S compound fertilizers preparation. •Determination of the phase equilibrium of K2SO4–MgSO4–(NH4)2SO4–H2O system at 25 °C.•Dry salt phase diagram of this system was investigated and analyzed.•A new K–Mg–N compound fertilizers was generated.•Calculation of the phase equilibrium of the above system by Pitzer model.•The calculated results are consistent with the experimental data well.