Phase diagrams of the quaternary system Mg2+, NH4+//Cl-, SO42- in water at 25 degrees C and their application

摘要

Based on the requirement of the new technology for producing Mg-N compound fertilizer by the reaction of MgCl2 and (NH4)(2)SO4, the phase equilibrium of the quaternary system Mg2+, NH4+//Cl-, SO42--H2O at 25 degrees C was studied. The solubilities of the quaternary system Mg2+, NH4//Cl-, SO42--H2O were measured using isothermal method, and the phase diagram of this system was investigated. According to the phase diagram, there are nine solid phase crystalline zones, which correspond to MgSO4 center dot 7H(2)O, MgSO4 center dot 6H(2)O, MgSO4 center dot 5H(2)O, MgSO4 center dot 4H(2)O, (NH4)(2)SO4, MgSO4,(NH4)(2)SO4 center dot 6H(2)O, MgCl2 center dot 6H(2)O, NH4Cl and MgCl2 center dot NH4Cl center dot 6H(2)O respectively. MgSO4 center dot(NH4)(2)SO4 center dot 6H(2)O has the largest crystalline zone among these crystalline zones, which indicates that the double salt MgSO4 center dot(NH4)(2)SO4 center dot 6H(2)O is the easiest to crystallize out. Based on the analysis and calculation of the phase diagrams, the suitable conditions for the new technology were determined. The extended Pitzer model was derived and applied to the phase equilibrium calculation of system Mg2+, NH4+//Cl-, SO42-H2O and its sub-systems at 25 degrees C. The results showed that the calculated values were consistent with experimental results well. (C) 2014 Elsevier B.V. All rights reserved.