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The solubilities in the quaternary system K+, NH4+//Cl−, SO42--H2O and its two ternary subsystems NH4Cl-KCl-H2O, (NH4)2SO4-K2SO4-H2O 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 NH4Cl-KCl-H2O system, there are three crystalline zones, which correspond to (K1−m,(NH4)m)Cl, ((NH4)n,K1−n)Cl and the co-existence zone of (K1−m,(NH4)m)Cl and ((NH4)n,K1−n)Cl, respectively. In the phase diagram of the (NH4)2SO4-K2SO4-H2O system, there is only one crystalline zone for (K1−t,(NH4)t)2SO4. In the phase diagram of the K+, NH4+//Cl−, SO42--H2O system, there are three crystal zones, which correspond to (K1−t,(NH4)t)2SO4, (K1−m,(NH4)m)Cl and ((NH4)n,K1−n)Cl, respectively. According to the analysis and the calculations for the phase diagrams of the K+, NH4+//Cl−, SO42--H2O system at 80.0 °C and 50.0 °C, this paper proposes a technological process. In the process, the (K1−t,(NH4)t)2SO4 can be prepared at 80.0 °C and the ((NH4)n,K1−n)Cl can crystallize out at 50.0 °C. The mass fraction of K2SO4 in product L1 (K1−t,(NH4)t)2SO4 (t = 0.1465) is 88.48%. The composition of solid solutions in the K+, NH4+//Cl−, SO42--H2O system was experimentally determined and then theoretical calculations about the process can be carried out. [ABSTRACT FROM AUTHOR]

Based on the requirement for the comprehensive exploitation and utilization of the salt lake resources magnesium chloride and potassium chloride, a new technology to produce KCl and ammonium carnallite (NHCl·MgCl·6HO) by using NHCl as salting-out agent to separate carnallite is proposed. The solubilities of quaternary system KCl-MgCl-NHCl-HO were measured by the isothermal method at t = 60.00 °C and the corresponding phase diagram was plotted and analyzed. The analysis of this phase diagram shows that there are seven saturation points and eight regions of crystallization. These eight regions of crystallization represent salts corresponding to KCl, NHCl, MgCl·6HO, (K(NH))Cl, ((NH)K)Cl, (K(NH))Cl·MgCl·6HO, KCl·MgCl·6HO and NHCl·MgCl·6HO. According to the phase diagram analysis and calculations, ammonium carnallite (NHCl·MgCl·6HO) and KCl can be obtained using carnallite as raw materials and ammonium chloride as salting-out agent at t = 60.00 °C. The new technology shows the advantages of being easy to operate and having low energy consumption. The research on this quaternary phase diagram is the foundation for reasonable development of carnallite resources and comprehensive utilization of the salt lake brines. [ABSTRACT FROM AUTHOR]

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]

Thesolubilities of the ternary system MgSO4–(NH4)2SO4–H2O and thequaternary system Na2SO4–MgSO4–(NH4)2SO4–H2O at 0 °C were measured, and the phase diagrams of these twosystems wereplotted. On the basis of the phase diagrams obtained, we analyzedeach saturation point and crystalline region. It indicated thatammonium sulfate as the salting-out agent can form double salt MgSO4·(NH4)2SO4·6H2O with magnesium sulfate, realizing better separation of sodiumsulfate and magnesium sulfate. On the basis of the Pitzer model ofelectrolyte solution theory, the ionic strength function was introducedto express the interaction parameters between two kinds of electrolyteat 0 °C. The interaction parameters were regressed from the experimentaldata of the ternary systems, and the solubilities of Na2SO4–MgSO4–(NH4)2SO4–H2O system at 0 °C werecalculated. The results showed that the calculated values werewell consistent with experimental results. [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]

Solubilities of the quaternary system CO(NH 2 ) 2 -MgSO 4 -(NH 4 ) 2 SO 4 -H 2 O at 0 °C and 25 °C were studied by isothermal solution saturation method. Under the experimental data, phase diagrams were constructed. This quaternary system at 25 °C contains five crystallization regions corresponding to MgSO 4 ·7H 2 O, MgSO 4 ·(NH 4 ) 2 SO 4 ·6H 2 O, CO(NH 2 ) 2 , (NH 4 ) 2 SO 4 and MgSO 4 ·CO(NH 2 ) 2 ·2H 2 O. Compared with the phase diagram at 25 °C, there was no crystallization region of MgSO 4 ·CO(NH 2 ) 2 ·2H 2 O in the phase diagram at 0 °C·MgSO 4 ·(NH 4 ) 2 SO 4 ·6H 2 O has the largest crystallization area among the salts, indicating MgSO 4 ·(NH 4 ) 2 SO 4 ·6H 2 O is the easiest to crystallize out. Based on the characteristic of the phase diagrams, a new technology to separate (NH 4 ) 2 SO 4 and CO(NH 2 ) 2 from urea waste water is proposed. This process shows the advantages of recovering desirable substances and making urea waste water discharged up to standard. [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]

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]

The stable phase equilibrium data of Mg2+, NH 4 +//Cl−, SO 4 2−−H 2 O quaternary interaction system and its four ternary subsystems at 363.15 K were determined by isothermal dissolution equilibrium method, and the corresponding stable phase diagrams of the above systems were plotted. According to the phase diagram, there are seven solid phase crystalline regions, which correspond to MgSO 4 ·(NH 4) 2 SO 4 ·6H 2 O, MgSO 4 ·6H 2 O, MgSO 4 ·4H 2 O, MgCl 2 ·6H 2 O, (NH 4) 2 SO 4 , MgCl 2 ·NH 4 Cl·6H 2 O and NH 4 Cl, respectively. MgSO 4 ·(NH 4) 2 SO 4 ·6H 2 O has the largest crystalline region among these crystalline regions, 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 extended Pitzer model, the solubility data of the ternary subsystems and the quaternary system were calculated. The results showed that the calculated values were close to the experimental values. According to the comparison between the stable phase diagram of the quaternary system at 298.15 K and 363.15 K, a new process of preparing N–Mg compound fertilizer (MgSO 4 ·(NH 4) 2 SO 4 ·6H 2 O) at 298.15 K and crystallizing NH 4 Cl at 363.15 K by using ammonium sulfate and magnesium chloride as raw materials was designed in this paper and the process route was verified by experiment. [ABSTRACT FROM AUTHOR]

• Solubilities of NaCl-MgCl 2 -NH 4 Cl-H 2 O and its ternary subsystem NaCl-MgCl 2 -H 2 O were investigated. • The extended Pitzer model was applied to the phase equilibrium calculation. • The ion interaction parameters θ and ψ were correlated. • A technological process to produce ammonium carnallite and NaCl via mixed solution after extracting potassium chloride. Based on the requirement of the new technology for producing ammonium carnallite and NaCl via the solution left after the preparation of potassium salt as raw materials, the solubilities of the quaternary system NaCl-MgCl 2 -NH 4 Cl-H 2 O and ternary subsystem NaCl-MgCl 2 -H 2 O at 333.15 K were measured using the isothermal dissolution method, and the corresponding phase diagrams were plotted. The phase diagram of the ternary system consists of three fields of crystallization, which correspond to NaCl, MgCl 2 ·6H 2 O and their co-existing fields respectively. There are four fields of crystallization in the quaternary system, which correspond to MgCl 2 ·6H 2 O, NH 4 Cl, NaCl and the double salt MgCl 2 ·NH 4 Cl·6H 2 O respectively. By analyzing and calculating the phase diagrams, a technological route was proposed, which indicated that the Na-Mg resources were fully utilized. The extended Pitzer model was applied to the phase equilibrium calculation and the results showed that the calculated data were consistent with experimental values well. [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]