Phase diagrams of Na2SO4–MgSO4–CO(NH2)2–H2O system at 60 °C and their application.

The solubilities of ternary system Na 2 SO 4 –CO(NH 2 ) 2 –H 2 O and MgSO 4 –CO(NH 2 ) 2 –H 2 O and quaternary system Na 2 SO 4 –MgSO 4 –CO(NH 2 ) 2 –H 2 O at 60 °C were measured by isothermal method, and the corresponding phase diagrams were studied. There are five crystalline fields in the quaternary system Na 2 SO 4 –MgSO 4 –CO(NH 2 ) 2 –H 2 O at 60 °C, which correspond to MgSO 4 ·6H 2 O, Na 2 SO 4 ·MgSO 4 ·4H 2 O, Na 2 SO 4 , CO(NH 2 ) 2 and MgSO 4 ·CO(NH 2 ) 2 ·4H 2 O respectively. On the basis of the analyses of the phase diagram of the quaternary system Na 2 SO 4 –MgSO 4 –CO(NH 2 ) 2 –H 2 O at 60 °C and 25 °C, Na 2 SO 4 and Mg–N compound fertilizers can be produced using CO(NH 2 ) 2 as salting-out agent directly. On the basis of the extended Pitzer model of electrolyte solution theory, the solubilities of Na 2 SO 4 –MgSO 4 –CO(NH 2 ) 2 –H 2 O system at 60 °C were calculated. The results showed that calculated values were well consistent with experimental results. [ABSTRACT FROM AUTHOR]