Search

Highlights: [•] Determination of phase equilibrium of Na2SO4–MgSO4–(NH4)2SO4–H2O system at 25°C. [•] Phase diagram of this system was investigated and analyzed. [•] A new technology to produce Mg–N compound fertilizers was proposed. [•] The advantage of recycling mother liquid, steady production and energy saving. [ABSTRACT FROM AUTHOR]

Based on the requirement of the new technology for producing Mg–N compound fertilizer by the reaction of MgCl 2 and (NH 4 ) 2 SO 4 , the phase equilibrium of the quaternary system Mg 2+ , NH 4 + //Cl − , SO 4 2− –H 2 O at 25 °C was studied. The solubilities of the quaternary system Mg 2+ , NH 4 + //Cl − , SO 4 2− –H 2 O 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 MgSO 4 ·7H 2 O, MgSO 4 ·6H 2 O, MgSO 4 ·5H 2 O, MgSO 4 ·4H 2 O, (NH 4 ) 2 SO 4 , MgSO 4 ·(NH 4 ) 2 SO 4 ·6H 2 O, MgCl 2 ·6H 2 O, NH 4 Cl and MgCl 2 ·NH 4 Cl·6H 2 O respectively. MgSO 4 ·(NH 4 ) 2 SO 4 ·6H 2 O has the largest crystalline zone among these crystalline zones, which indicates that the double salt MgSO 4 ·(NH 4 ) 2 SO 4 ·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 Mg 2+ , NH 4+ //Cl − , SO 4 2 –H 2 O and its sub-systems at 25 °C. The results showed that the calculated values were consistent with experimental results well. [ABSTRACT FROM AUTHOR]

Highlights • Solubilities of the K+, NH 4 +//Cl−, SO 4 2− - H 2 O system were measured by isothermal method. • Completed determination of solid solution composition based on the linear rule. • A technological process to produce chlorine-free K-N compound fertilizers and by-product potassium ammonium chloride. • The proposed process was verified by experiments. Abstract In order to produce chloride-free K-N compound fertilizers by the reaction of KCl (carnallite) and (NH 4) 2 SO 4 as raw materials, the phase equilibrium of the mutual quaternary system K+, NH 4 +//Cl−, SO 4 2− - H 2 O and its two ternary subsystems KCl-NH 4 Cl-H 2 O, K 2 SO 4 -(NH 4) 2 SO 4 -H 2 O were measured by isothermal method at 273.15 K. And the corresponding phase diagrams were plotted and analysed. The equilibrium phase diagram of the quaternary system K+, NH 4 +//Cl−, SO 4 2− - H 2 O shows that there is one saturation point and three solid phase fields of crystallization. Three fields of crystallization represent solid solution salts corresponding 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. The phase analysis shows that field of (K 1−t , (NH 4) t) 2 SO 4 is larger than other crystalline fields, and there is no crystalline field of pure potassium sulfate, which indicates that the K 1-t, (NH 4) t) 2 SO 4 is easy to crystallize out from solution. By analysing and calculating the phase diagrams of K+, NH 4 +//Cl−, SO 4 2− - H 2 O at 273.15 K and 323.15 K, chloride-free K-N compound fertilizers (K 1−t, (NH 4) t) 2 SO 4) can be obtained using KCl and (NH 4) 2 SO 4 as raw materials at 273.15 K, and ((NH 4) t , K 1−t)Cl can crystallize out at 323.15 K. The new technology shows the advantages of effective utilization of carnallite resources. The research on this quaternary phase diagram is the foundation of the chloride-free potash production by the reaction of carnallite and ammonium sulfate. [ABSTRACT FROM AUTHOR]

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]

• Solubilities of quaternary system NaCl-MgCl 2 -NH 4 Cl-H 2 O at 348.15 K. • The extended Pitzer model was used to predict the phase equilibrium data. • The ion interaction parameters θ and ψ at 348.15 K were regressed and calculated. • An optimized process to produce ammonium carnallite. Based on the requirement of the new technology to achieve comprehensive utilization of sodium and magnesium resources by using the mother solution from the preparation of potassium salt as raw material, the phase equilibrium data of the quaternary system NH 4 Cl-MgCl 2 -NaCl-H 2 O as well as its ternary subsystems MgCl 2 -NH 4 Cl-H 2 O and NaCl-NH 4 Cl-H 2 O were investigated by an isothermal equilibrium method under atmospheric pressure at 348.15 K, and the dry-salt phase diagram and water-phase diagram were drawn. Two invariant points and four crystallization fields including two single salts NH 4 Cl and NaCl, one hydrate salt MgCl 2 ·6H 2 O, and one double salt MgCl 2 ·NH 4 Cl·6H 2 O were determined in this quaternary system. Combining our results with available experimental data in the literature, an optimized process to produce ammonium carnallite and NaCl was proposed. Using the Pitzer electrolyte solution model, the experimental results were regressed and calculated. The calculated values agree well with the experimental values. [ABSTRACT FROM AUTHOR]

Based on the requirement of the new technology for producing chloride-free potassium fertilizers by the reaction of KCl·MgCl 2 ·6H 2 O and (NH 4) 2 SO 4 , the phase equilibrium of the mutual quinary system K+, NH 4 +, Mg2+//SO 4 2−, Cl−- H 2 O at 273.15 K and 298.15 K were studied using the isothermal dissolution equilibrium method under atmospheric pressure, and the corresponding phase diagrams were plotted. According to the diagrams, there are seven saturation points and eight solid phase crystalline fields. Fields of K 2 SO 4 ·MgSO 4 ·6H 2 O and (NH 4u ,K 1-u) 2 SO 4 ·MgSO 4 ·6H 2 O are larger than other crystalline fields, which indicates that these two salts can crystallize out from solution easily. By analyzing and calculating the phase diagrams at 273.15 K and 298.15 K, chloride-free compound fertilizers can be produced via KCl·MgCl 2 ·6H 2 O and (NH 4) 2 SO 4 as raw materials, and the by-product NH 4 Cl can crystallize out. Image 1 • Solubilities of the quinary system K+, NH 4 +, Mg2+//SO 4 2−, Cl−- H 2 O were measured by isothermal method. • A technological process to produce chloride-free compound fertilizers and by-product ammonium chloride. • The proposed process was calculated theoretically and verified by experiment. [ABSTRACT FROM AUTHOR]