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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]

In order to improve the technology for producing Mg–N compound fertilizer and NH 4 Cl based upon the analysis of phase diagram of Mg 2+ , NH 4 + //Cl − , SO 4 2 − –H 2 O system at 25 °C, the phase equilibrium of this quaternary system at 0 °C was studied. The solubilities of the quaternary system Mg 2+ , NH 4 + //Cl − , SO 4 2 − –H 2 O at 0 °C were measured by isothermal method, and the corresponding phase diagram was plotted. In this phase diagram, there are six solid phase crystalline zones, which correspond to MgCl 2 ·6H 2 O, NH 4 Cl, MgCl 2 ·NH 4 Cl·6H 2 O (NH 4 ) 2 SO 4 , MgSO 4 ·7H 2 O and MgSO 4 ·(NH 4 ) 2 SO 4 ·6H 2 O respectively. The crystalline zones of MgSO 4 ·(NH 4 ) 2 SO 4 ·6H 2 O and NH 4 Cl are larger than the others, which indicates that MgSO 4 ·(NH 4 ) 2 SO 4 ·6H 2 O and NH 4 Cl can crystallize out easily. According to the analysis and calculation of the phase diagrams of Mg 2+ , NH 4 + //Cl − , SO 4 2 − –H 2 O system at 0 °C and 25 °C, the appropriate conditions for this technology were obtained. In the process, the Mg–N compound fertilizer can be prepared at 0 °C and the NH 4 Cl can crystallize out at 25 °C. The solubilities of the studied system were calculated on the basis of the extended Pitzer model, and the results showed that the calculated values agrees well with the experimental results. [ABSTRACT FROM AUTHOR]