Stable Phase Equilibria For Aqueous Quinary Systems Focused On The Xitaijinaier Old Brine Contained With Lithium

In accordance with the composition of the West Taijinaier salt lake brine, the stable phase equilibria of the quinary system Li+, Mg²⁺ // Cl^-, SO₄^2-, borate- H2 O and its five quaternary subsystems, seven ternary subsystems were studied at 308 K using an isothermal dissolution equilibrium method. The physicochemical properties（refractive indices and densities） of the solution and the composition of solid phase and liquid phase at equilibrium in the above systems were also determined. Based on the measured data, the phase diagrams and the diagrams of physicochemical properties（densities and refractive indices） vs composition in the ternary systems were all plotted; the stable phase diagrams, the diagrams of water content vs composition, and the physicochemical properties（densities and refractive indices） vs composition diagrams in the quaternary and quinary（saturated with Mg B4O7） systems were all constructed.The stable phase diagrams of the six ternary systems Li+, Mg²⁺ // SO₄^2-- H2 O, Li+, Mg²⁺ // borate- H2 O, Li+ // Cl^-, SO₄^2-- H2 O, Li+ // Cl^-, borate- H2 O, Mg²⁺ // Cl^-, borate- H2 O, Mg²⁺ // SO₄^2-, borate- H2 O at 308 K belong to simple eutectic type, without solid solution or double salt formed. The ternary system Li+, Mg²⁺ // Cl^-- H2 O is of a complex type with the double salt lithium carnallite（Li Cl·Mg Cl2·7H₂O） formed at 308 K. Results show that salt Li Cl has strong salting out effect on Li2B4O7 and Li2SO4.Comparisons between the stable phase diagrams of the five ternary systems Li+, Mg²⁺ // Cl^- H₂O、Li+, Mg²⁺ // SO₄^2-- H₂O、Li+ // Cl^-, SO₄^2-- H₂O、Mg²⁺ // Cl^-, borate- H₂O、Mg²⁺ // SO₄^2-, borate- H2 O 298 K and 308 K show that the crystallization forms of the salts are the same, whereas the crystallization zones have slight changes. Comparisons between the stable phase diagrams of the ternary system Li+, Mg²⁺ // borate- H2 O at 308 K and 323 K show that the crystallization zones of Mg B4O5（OH）4·7H₂O decreased, Li2B4O7·3H₂O enlarged along with the temperature decreases. Comparisons between the stable phase diagrams of the ternary system Li+ // Cl^-, borate- H2 O at 273 K, 308 K and 323 K show that the crystallization form Li Cl changed with the temperature changes, the crystallization form is Li Cl·2H₂O at 273 K, while at 308 K and 323 K, the form is Li Cl·H₂O.The quaternary system Li+ // Cl^-, SO₄^2-, borate- H2 O and Li+, Mg²⁺ // SO₄^2-, borate-H2 O belong to simple eutectic type, without solid solution or double salt formed at 308 K. Comparisons between the stable phase diagrams of the quaternary system Li+ // Cl^-, SO₄^2-, borate- H2 O at 273 K, 288 K and 308 K show that the crystallization form of Li Cl and Li2SO4 have not changed, while the crystallization form of Li2B4O7 changed with the change of temperature, the crystallization form is Li BO2·8H₂O at 273 K, while the form is Li2B4O7·3H₂O at 308 K and 323 K. Comparisons between the stable phase diagrams of the quaternary system Li+, Mg²⁺ // SO₄^2-, borate- H2 O at 298 K and 308 K show that only the size of the crystallization zones of the salts is changed, with the crystallization zones of salts Mg B4O7·9H₂O and Li2SO4·H₂O enlarging, Li2B4O7·3H₂O and Mg SO4·7H₂O decreasing at 308 K, while the crystallization forms of the salts are not changed. The invariant point F1 is of an incommensurate invariant point, whereas point E1 is of a commensurate invariant point.There are many crystallization form of magnesium sulfate in the quaternary system Mg²⁺ // Cl^-, SO₄^2-, borate- H2 O at 308 K. Results show that in this quaternary system, the crystallization form of magnesium sulfate at 308 K is Mg SO4·4H₂O, Mg SO4·6H₂O, and Mg SO4·7H₂O. The solubilities of the magnesium sulfate decrease in the order of Mg SO4·4H₂O > Mg SO4·6H₂O > Mg SO4·7H₂O.The reciprocal quaternary system Li+, Mg²⁺ // Cl^-, SO₄^2-- H2 O and Li+, Mg²⁺ // Cl^-, borate- H2 O belong to complex type with the double salt lithium carnallite（Li Cl·Mg Cl2·7H₂O） formed at 308 K. The stable phase diagram of Li+, Mg²⁺ // Cl^-, SO₄^2-- H2 O consists of two commensurate invariant points, three incommensurate invariant points, seven crystallization zones, eleven univariant curves. The solubilities of the salts in the system decrease in the order of Li Cl·H₂O > Li Cl·Mg Cl2·7H₂O > Mg Cl2·6H₂O > Mg SO4·4H₂O > Mg SO4·6H₂O > Mg SO4·7H₂O > Li2SO4·H₂O. The stable phase diagram of Li+, Mg²⁺ // Cl^-, borate- H2 O consists of three invariant points（including two commensurate invariant points and one incommensurate invariant point）, five crystallization zones, and seven univariant curves. The solubilities of the salts in the system increase in the order of Mg B4O5（OH）4·7H₂O < Li2B4O7·3H₂O < Mg Cl2·6H₂O < Li Cl·Mg Cl2·7H₂O < Li Cl·H₂O.The reciprocal quinary system Li+, Mg²⁺ // Cl^-, SO₄^2-, borate- H2 O is of a complex type with the double salt lithium carnallite（Li Cl·Mg Cl2·7H₂O） formed at 308 K. The planar projection diagram（saturated with salt Mg B4O7） consists of six invariant points（including two commensurate invariant points and four incommensurate invariant points）, nine crystallization zones, thirteen univariant curves. Under the condition of Mg B4O7 saturated, the scope of crystallization areas of salts is such that Li2SO4·H₂O > Li2B4O7·3H₂O > Mg SO4·7H₂O > Mg SO4·6H₂O > Mg SO4·4H₂O > Mg Cl2·6H₂O > Li Cl·Mg Cl2·7H₂O > Li Cl·H₂O, which indicate that the solubilities of salts decrease in the order of Li Cl·H₂O > Li Cl·Mg Cl2·7H₂O > Mg Cl2·6H₂O > KCl·Mg Cl2·6H₂O > Mg SO4·4H₂O > Mg SO4·6H₂O > Mg SO4·7H₂O > Li2B4O7·3H₂O > Li2SO4·H₂O.