Solid-liquid phase equilibrium determination and correlation of ternary systems NH4Cl+AlCl3+H2O, MgCl2+AlCl3+H2O and SrCl2+AlCl3+H2O at 298 K

An original technology named HNO3 pressure leaching has been proposed by our team to leach Al from coal gangue and fly ash. Although the preliminary separation of Al and Fe had been achieved during leaching, a small amount of Fe impurity was still unavoidably dissolved into the leach liquor. To obtain pure Al2O3 during subsequent pyrolysis, it is imperative to synchronously remove Fe3+ during the crystallization of Al(NO3)3·9H2O. Herein, the phase equilibria of the Al(NO3)3–Fe(NO3)3–H2O(−HNO3) system at 25–40 °C and 0–8.12 mol kg–1 of HNO3 molality were investigated. The results indicated that the ternary system was a simple cosaturated type consisting of an immutable point, two univariate curves, and two crystallization regions. Notably, the solubility and crystallization region of Al(NO3)3·9H2O were barely impacted by acidity, while the opposite was true for Fe(NO3)3·9H2O. This finding was instructive for the crystallization of Fe(NO3)3·9H2O from the liquor with high Fe and low Al. Moreover, a high crystallization yield could be obtained at low temperatures. Finally, an appropriate crystallization procedure was provided. This study is expected to provide basic data and theoretical support for the crystallization and separation of mixed nitrates containing Al and Fe.

Section: Methodsmentioning

confidence: 99%

Phase Diagram of the Al(NO₃)₃–Fe(NO₃)₃–H₂O(−HNO₃) System and Its Application in the Separation of Al³⁺ and Fe³⁺

Shi

Shao

et al. 2023

“…Until now, there have been some experimental and theoretical studies which relate to the hexacomponent system NH 4 Cl–MgCl 2 –CaCl 2 –SrCl 2 –AlCl 3 –H 2 O, as described below: binary systems of SrCl 2 –H 2 O at 252.2–524.2 K, CaCl 2 –H 2 O at 239.2–523.2 K, and MgCl 2 –H 2 O at 223.2–503.2 K; ternary systems of MgCl 2 –CaCl 2 –H 2 O at 273.2–368.2 K, − CaCl 2 –SrCl 2 –H 2 O at 288.2–387.2 K, − MgCl 2 –SrCl 2 –H 2 O at 288.2–373.2 K, − NH 4 Cl–CaCl 2 –H 2 O at 273.2–348.2 K, − AlCl 3 –CaCl 2 –H 2 O at 278.2–363.2 K, , NH 4 Cl–MgCl 2 –H 2 O at 273.2–308.2 K, − AlCl 3 –SrCl 2 –H 2 O, NH 4 Cl–AlCl 3 –H 2 O, MgCl 2 –AlCl 3 –H 2 O at 298.2 K; quaternary systems of NH 4 Cl–CaCl 2 –AlCl 3 –H 2 O at 283.2–353.2 K, , MgCl 2 –SrCl 2 –AlCl 3 –H 2 O at 298.2 K, and NH 4 Cl–MgCl 2 –SrCl 2 –H 2 O at 298.2 K . The results show that (1) the solid solutions [(Ca, Sr)Cl 2 ]·6H 2 O and [(Sr, Ca)Cl 2 ]·6H 2 O are formed in the chloride-type system with the coexistence of strontium and calcium; (2) when magnesium chloride coexists with calcium or ammonium, it is easy to form double salts 2MgCl 2 ·CaCl 2 ·12H 2 O and NH 4 Cl·MgCl 2 ·6H 2 O; (3) strontium chloride can form into various hydrated salts at different temperatures, such as SrCl 2 ·6H 2 O, SrCl 2 ·2H 2 O, and SrCl 2 ·H 2 O; (4) the crystallization form of strontium chloride is also related to the coexisting ions, when MgCl 2 salt coexists with SrCl 2 ·6H 2 O at 298.2 K, both SrCl 2 ·6H 2 O and SrCl 2 ·2H 2 O exist in the systems of MgCl 2 –SrCl 2 –H 2 O and SrCl 2 –NH 4 Cl–MgCl 2 –H 2 O at 298.2 K. As for the quaternary systems NH 4 Cl–SrCl 2 –AlCl 3 –H 2 O and NH 4 Cl–MgCl 2 –AlCl 3 –H 2 O, they are the basic subsystems of the hexacomponent system NH 4 Cl–MgCl 2 –CaCl 2 –SrCl 2 –AlCl 3 –H 2 O, and the ternary subsystems NH 4 Cl–SrCl 2 –H 2 O, NH 4 Cl–MgCl 2 –H 2 O, AlCl 3 –SrCl 2 –H 2 O, NH 4 Cl–AlCl 3 –H 2 O, and MgCl 2 –AlCl 3 –H 2 O of these two quaternary systems at 298.2 K have been done by our previous works, while there is scarcely any literature about the phase equilibria of these two quaternary systems. Consequently, the solid–liquid phase equilibria of the quaternary systems NH 4 Cl–SrCl 2 –AlCl 3 –H 2 O and NH 4 Cl–MgCl 2 –AlCl 3 –H 2 O were experimentally determined based on the ternary subsystems.…”

Section: Introductionmentioning

confidence: 99%

Phase Equilibria of Quaternary Systems Containing the Chlorides of Ammonium, Strontium(Magnesium), and Aluminum at 298.2 K

Ren

Zheng

et al. 2022

Self Cite

The phase equilibria of the quaternary systems NH 4 Cl−SrCl 2 −AlCl 3 −H 2 O and NH 4 Cl−MgCl 2 −AlCl 3 −H 2 O at 298.2 K were investigated by using the isothermal dissolution method. The solubility, density, and refractive index of the systems were measured experimentally, and the related phase diagrams, density/refractive index versus composition diagrams, are plotted. There is one quaternary invariant point and three crystallization regions corresponding to single salts NH 4 Cl, AlCl 3 •6H 2 O, and SrCl 2 •6H 2 O in the phase diagram of the system NH 4 Cl−SrCl 2 −AlCl 3 −H 2 O at 298.2 K, which belongs to a simple system. In addition to the single salts NH 4 Cl, AlCl 3 •6H 2 O, and MgCl 2 •6H 2 O, the double salt NH 4 Cl•MgCl 2 •6H 2 O is formed in the quaternary system NH 4 Cl−MgCl 2 −AlCl 3 −H 2 O at 298.2 K, which indicates that the addition of magnesium makes the interaction relationship between Al 3+ , NH 4+ , and Mg 2+ more complex and increases the difficulty of separation of magnesium. The crystallization region of NH 4 Cl is the largest in both the systems, which indicates that NH 4 Cl is much easier to separate than the other salts from the two systems.

“…Until now, the phase equilibria of aqueous salts containing ammonium at multiple temperatures have been reported. For example, there are only two crystallization regions of NH 4 Cl and LiCl·2H 2 O at 273.2 K in the ternary system LiCl + NH 4 Cl + H 2 O, while the crystallization region of the solid solution (NH 4 Cl) x (LiCl·H 2 O) 1– x is formed at 298.2 and 323.2 K. , The solid solutions (NH 4 Cl) x (KCl) 1– x and (NH 4 Cl) 1– x (KCl) x are formed in the system KCl + NH 4 Cl + H 2 O at 273.2, 283.2, 298.2, and 308.2 K. − The quaternary system NH 4 Cl + SrCl 2 + AlCl 3 + H 2 O and its ternary subsystems NH 4 Cl + SrCl 2 + H 2 O and NH 4 Cl + AlCl 3 + H 2 O at 298.2 K are simple types, neither a double salt nor a solid solution formed. − The quaternary system NaCl + KCl + NH 4 Cl + H 2 O at 323.2 K formed the solid solutions (NH 4 Cl) x (KCl) 1– x and (NH 4 Cl) 1– x (KCl) x . For the quaternary system NaCl + NH 4 Cl + MgCl 2 + H 2 O at 273.2, 298.2, 333.2, and 348.2 K, − the crystallization region of the double salt NH 4 Cl·MgCl 2 ·6H 2 O exists.…”

Section: Introductionmentioning

confidence: 99%

Phase Equilibria of Aqueous Ternary Systems NH₄Cl + CaCl₂ + H₂O and NH₄Cl + MgCl₂ + H₂O at 308.2 K: Measurement and Calculation

Zhao

et al. 2022

Self Cite

The phase equilibria of aqueous ternary systems NH4Cl + CaCl2 + H2O and NH4Cl + MgCl2 + H2O at 308.2 K were measured by the isothermal dissolution method, and the solubility, density, and refractive index were determined experimentally. The stable phase diagrams and the diagrams of density/refractive index versus composition of these two ternary systems are plotted. The results show that both these systems at 308.2 K are complex systems, with the formation of double salts 2NH4Cl·CaCl2·3H2O and NH4Cl·MgCl2·6H2O, respectively. The multitemperature phase diagrams of the ternary systems NH4Cl + CaCl2 + H2O at (273.2, 298.2, 308.2, 323.2, and 348.2 K) and NH4Cl + MgCl2 + H2O at (273.2, 298.2, 308.2, and 323.2 K) are compared, respectively. The results show that within the temperature range discussed, the double salt NH4Cl·MgCl2·6H2O is formed, and the double salt 2NH4Cl·CaCl2·3H2O is only formed at 308.2, 323.2, and 348.2 K. The crystallization areas of 2NH4Cl·CaCl2·3H2O and NH4Cl·MgCl2·6H2O gradually increase with increasing temperature. Thus, the increasing temperature is conducive to the separation of calcium or magnesium from these two systems in the form of 2NH4Cl·CaCl2·3H2O or NH4Cl·MgCl2·6H2O. The interaction relationship between the ions of the system NH4Cl + CaCl2 + H2O becomes simpler at 273.2–298.2 K, which is more beneficial to the precipitation of single salts. When the temperature reaches 323.2 K, NH4Cl·MgCl2·6H2O precipitates into a more stable salt of commensurate type. Meanwhile, the thermodynamic calculations of these two systems at 308.2 K were fitted by the Pitzer–Simonson–Clegg model, and the predicted values agree well with the experimental values.