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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]

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]

Abstract: In order to develop a new process for concentrating and separating sodium sulfate (Na2SO4) and magnesium sulfate (MgSO4) of the bloedite by gas hydrate, the equilibrium of the ternary system H2O–Na2SO4–C3H8, H2O–MgSO4–C3H8 and the quaternary system H2O–Na2SO4–MgSO4–C3H8 with tetrahydrofuran (THF) additive were studied at 0°C. It showed that the mass percentage of Na2SO4 (MgSO4) in equilibrium liquid was higher than in feed. It proved that gas hydrate could be used to the concentration and separation of Na2SO4 and MgSO4. The solubility of the propane was calculated based on the Krichevsky–Kasarnovsky equation. The extended Pitzer model of electrolyte–electrolyte–nonelectrolyte–water system was derived and applied into H2O–Na2SO4–MgSO4–C3H8 system and its sub-systems. The necessary thermodynamic parameters had been derived from a least-squares optimization program. The model calculation value was in good agreement with experimental solubility for ternary and quaternary mixtures, which indicated that the Pitzer model could be successfully used to predict the phase equilibrium of the electrolyte–electrolyte–nonelectrolyte–water systems containing gas hydrate. [Copyright &y& Elsevier]

In order to develop a new processfor concentrating and separatingsodium sulfate (Na2SO4) and magnesium sulfate(MgSO4) of the bloedite based on tetrahydrofuran (THF)hydrate method, the equilibrium of the ternary systems THF–Na2SO4–H2O and THF–MgSO4–H2O and the quaternary system THF–Na2SO4–MgSO4–H2O were measured at 5 °C, and the phase digrams of these threesystems were investigated. It showed that the mass percentage of Na2SO4(MgSO4) in equilibrium liquid washigher than in feed and we could obtain Na2SO4·10H2O and MgSO4·7H2Oin turn. It proved that THF hydrate could be used to the concentrationand separation of Na2SO4and MgSO4. The extended Pitzer model of the electrolyte–electrolyte–nonelectrolyte–watersystem was derived and applied into THF–Na2SO4–MgSO4–H2O system andits subsystems. The necessary thermodynamic parameters had been derivedfrom a least-squares optimization program. The model calculation valuewas in good agreement with experimental solubility for ternary andquaternary mixtures, which indicated that the Pitzer model could besuccessfully used to predict the phase equilibrium of the electrolyte–electrolyte–nonelectrolyte–watersystems containning THF hydrate. [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]

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 solubilities of the quaternary system K 2 SO 4 –MgSO 4 –(NH 4 ) 2 SO 4 –H 2 O were measured by isothermal method at 25 °C and their dry salt phase diagrams were plotted. The results indicated that, at 25 °C, the solubility phase diagram of this quaternary system consists of seven crystallization regions, those are single-salt crystallization region MgSO 4 ·7H 2 O, (NH 4 ) 2 SO 4 , and K 2 SO 4, complex salt crystallization region MgSO 4 ·(NH 4 ) 2 SO 4 ·6H 2 O, MgSO 4 ·K 2 SO 4 ·6H 2 O, solid solution crystallization region (K 1−n , NH 4n ) 2 SO 4 (n:0.143–0.893) and (K 1−n , NH 4n ) 2 SO 4 ·MgSO 4 ·6H 2 O (n:0.552–0.973), respectively. The extended Pitzer model was derived and applied to the phase equilibrium calculation of system K 2 SO 4 –MgSO 4 –(NH 4 ) 2 SO 4 –H 2 O and its sub-systems at 25 °C. The results showed that the calculated values were consistent with experimental results well. The study on the quaternary system K 2 SO 4 –MgSO 4 –(NH 4 ) 2 SO 4 –H 2 O provides a foundation for the N–Mg–K–S compound fertilizers preparation. [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]

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]