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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]

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]

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]