Solid–Liquid Phase Equilibria Determination of Quaternary System NH₄⁺, Mg²⁺, Ca²⁺//Cl^––H₂O at T = 298.2 and 323.2 K and p = 94.77 kPa

Abstract

Solid–liquid phase equilibria of quaternary system NH4 +, Mg2+, Ca2+//Cl––H2O are investigated at T = 298.2 and 323.2 K and p = 94.77 kPa by the isothermal dissolution equilibrium method, and the corresponding stable phase diagram, density vs composition, and water content diagram are plotted at 298.2 and 323.2 K. Results show that when the temperature is 298.2 K, there are three quaternary invariant points and five crystallization fields corresponding to two double salts (2MgCl2·CaCl2·12H2O, NH4Cl·MgCl2·6H2O), two hydrate salts (MgCl2·6H2O, CaCl2·6H2O), and one single salt (NH4Cl) in the phase diagram. When the temperature is 323.2 K, the phase diagram structure of the system and the crystalline form of the salt have changed, and there are four quaternary invariant points and six crystallization regions including the four crystallization forms existing at 298.2 K. The salt change is mainly reflected when CaCl2·6H2O is dehydrated into CaCl2·2H2O at 323.2 K and a new double salt (2NH4Cl·CaCl2·3H2O) is formed at 323.2 K. The composition of double salt 2NH4Cl·CaCl2·3H2O is determined by chemical analysis and thermogravimetric analysis.

Solid–Liquid Phase Equilibria of the Pb2+, Ca2+, Mg2+//Cl––H2O Quaternary System and Its Subsystems at 303.2 K

“…The compositions of B (PbCl 2 , MgCl 2 , CaCl 2 , H 2 O) are expressed in Table as the mass fractions w B and the Janecke’s exponent J B (g/100 g dry salt). The Janecke index of J B can be defined as eqs – , w s = w false( P b C l 2 false) + w false( C a C l 2 false) + w ( normalM normalg normalC normall 2 false) J false( PbCl 2 false) = w false( PbCl 2 false) w normals × 100 J false( CaCl 2 false) = w false( CaCl 2 false) w normals × 100 J false( MgCl 2 false) = w false( MgCl 2 false) w normals × 100 …”

“…The compositions of B (PbCl 2 , MgCl 2 , CaCl 2 , H 2 O) are expressed in Table 4 as the mass fractions w B and the Janecke’s exponent J B (g/100 g dry salt). The Janecke index of J B can be defined as eqs 1 – 4 27 , 33 …”

“…The isothermal dissolution method was used to analyze the equilibrium liquid phase density of the systems of Pb 2+ , Ca 2+ //Cl – –H 2 O, Pb 2+ , Mg 2+ //Cl – –H 2 O, and Mg 2+ , Ca 2+ //Cl – –H 2 O as well as the quaternary system of Pb 2+ , Mg 2+ , Ca 2+ //Cl – –H 2 O at 303.2 K. Initially, a mixed solution was prepared by combining substances which constitute the eutectic. Subsequently, another new salt was introduced and gradually added to the mixed solution covering different mass fractions ranging from 0 to saturation. − All samples were then placed in a constant-temperature bath and stirred for a minimum of 2 weeks. The mixed solution system was considered to reach equilibrium when the adjacent sampling analyses of the same sample were within 0.3%.…”

“…Subsequently, another new salt was introduced and gradually added to the mixed solution covering different mass fractions ranging from 0 to saturation. 25 − 27 All samples were then placed in a constant-temperature bath and stirred for a minimum of 2 weeks. The mixed solution system was considered to reach equilibrium when the adjacent sampling analyses of the same sample were within 0.3%.…”

Solid–Liquid Phase Equilibria of Potassium–Ammonium–Magnesium Chloride System at 323.2 and 348.2 K

“…The analysis of existing phase equilibrium studies shows that the ternary system KCl + CaCl 2 + H 2 O is a simple system at 273.2–308.2 K, while the crystallization region of double-salt KCl·CaCl 2 formed at 323.2 and 348.2 K. − In the ternary system KCl + MgCl 2 + H 2 O, the double salt carnallite (KCl·MgCl 2 ·6H 2 O) forms at 298.2–348.2 K. − Similarly, the ternary systems LiCl + MgCl 2 + H 2 O, RbCl + MgCl 2 + H 2 O, and CsCl + MgCl 2 + H 2 O, all exhibit carnallite-type double salts formation, namely LiCl·MgCl 2 ·7H 2 O, RbCl·MgCl 2 ·6H 2 O, and CsCl·MgCl 2 ·6H 2 O, respectively. − For the ammonium-containing water–salt system, the ternary system LiCl + NH 4 Cl + H 2 O is a simple ternary system at 273.2 K, while the solid solution (NH 4 Cl) x (LiCl·H 2 O) 1– x is formed at 298.2 and 323.2 K. , As for the ternary system KCl + NH 4 Cl + H 2 O, the solid solutions (KCl) x (NH 4 Cl) 1– x and (NH 4 Cl) x (KCl) 1– x are formed at 273.2–373.2 K. − Ammonium carnallite (NH 4 Cl·MgCl 2 ·6H 2 O) is formed in the ternary system NH 4 Cl + MgCl 2 + H 2 O at 273.2–323.2 K. − In the ternary system NH 4 Cl + CaCl 2 + H 2 O, there is no double salt formation at 273.2 and 298.2 K and the ammonium calcium double salt(2NH 4 Cl·CaCl 2 ·3H 2 O) is formed at 308.2–348.2 K, indicating that the formation of ammonium calcium double salt was related to temperature. − The phase equilibrium of the quaternary system KCl + NH 4 Cl + MgCl 2 + H 2 O at 273.2 and 298.2 K have been reported. The results show that in addition to the formation of carnallite (KCl·MgCl 2 ·6H 2 O), ammonium carnallite (NH 4 Cl·MgCl 2 ·6H 2 O), and solid solutions (KCl) x (NH 4 Cl) 1– x and (NH 4 Cl) x (KCl) 1– x , a solid solution-type double salt ((NH 4 )K 2 Mg 3 Cl 9 ·18H 2 O) is also found in the system. , In summary, it can be seen that NH 4 + has a great influence on the crystalline form of coexisting ions and is easy to form double salts or solid solutions with alkali (soil) metal ions, resulting in the loss of valuable elements in the brine.…”