The Phase Diagram and the Application for the Quaternary System K+, NH4+//Cl−, SO42-–H2O at 80.0 °C

The solubilities in the quaternary system K + , NH 4 + //Cl − , SO 4 2 - – H 2 O and its two ternary subsystems NH 4 Cl–KCl–H 2 O, (NH 4 ) 2 SO 4 –K 2 SO 4 –H 2 O at 80.0 °C were measured using the isothermal dissolution equilibrium method under atmospheric pressure, and the corresponding phase diagrams were plotted. In the phase diagram of the NH 4 Cl–KCl–H 2 O system, there are three crystalline zones, which correspond to (K 1− m ,(NH 4 ) m )Cl, ((NH 4 ) n ,K 1− n )Cl and the co-existence zone of (K 1− m ,(NH 4 ) m )Cl and ((NH 4 ) n ,K 1− n )Cl, respectively. In the phase diagram of the (NH 4 ) 2 SO 4 –K 2 SO 4 –H 2 O system, there is only one crystalline zone for (K 1− t , (NH 4 ) t ) 2 SO 4 . In the phase diagram of the K + , NH 4 + //Cl − , SO 4 2 - – H 2 O system, there are three crystal zones, which correspond to (K 1− t ,(NH 4 ) t ) 2 SO 4 , (K 1− m ,(NH 4 ) m )Cl and ((NH 4 ) n ,K 1− n )Cl, respectively. According to the analysis and the calculations for the phase diagrams of the K + , NH 4 + //Cl − , SO 4 2 - – H 2 O system at 80.0 °C and 50.0 °C, this paper proposes a technological process. In the process, the (K 1− t ,(NH 4 ) t ) 2 SO 4 can be prepared at 80.0 °C and the ((NH 4 ) n ,K 1− n )Cl can crystallize out at 50.0 °C. The mass fraction of K 2 SO 4 in product L 1 (K 1− t ,(NH 4 ) t ) 2 SO 4 ( t = 0.1465) is 88.48%. The composition of solid solutions in the K + , NH 4 + //Cl − , SO 4 2 - – H 2 O system was experimentally determined and then theoretical calculations about the process can be carried out.