Study On The Equilibria In Quinary And Its Partial Sub-system Li⁺,Mg²⁺//Cl^-,SO₄^2-,B₄O₇^2--H₂O At 273K

In this paper,the phase equilibria of the quinary system Li⁺,Mg²⁺ // Cl^–,SO₄^2–,B₄O₇^2––H₂O and its partial sub-systems at 273 K were studied.The stable phase equilibria of ternary system Mg B₄O₇–Mg SO₄–H₂O,quaternary systems Li⁺ // Cl^–,SO₄^2–,B₄O₇^2––H₂O,Li⁺,Mg²⁺ // Cl^–,B₄O₇^2––H₂O,and quinary system Li⁺,Mg²⁺ // Cl^–,SO₄^2–,B₄O₇^2––H₂O were studied by isothermal solution equilibrium method.Meanwhile,the metastable phase equilibria of the ternary subsystems Mg B₄O₇–Mg SO₄–H₂O,K₂B₄O₇–K₂SO₄–H₂O,K₂B₄O₇–KCl^–H₂O,and Li₂B₄O₇–Li Cl^–H₂O were studied by isothermal evaporation crystallization method.The solubilities and densities of equilibrium liquid phase in different systems were determined.Based on the experimental data and the corresponding equilibrium solid phase,the phase diagrams and density versus composition diagrams of those systems were plotted,respectively.The corresponding water content diagrams for the quaternary and quinary systems were plotted,and the Mg²⁺ content diagram of the quinary system at 273 K（saturated with Mg B₄O₇·9H₂O）was also plotted.The components of saturated salt were identified by X-ray powder diffraction,and the corresponding XRD patterns were obtained.Both the stable and metastable phase equilibria of Mg B₄O₇–Mg SO₄–H₂O belong to hydrate I type.The solubility curves of the hydrate salts are existed in the system,and no double salt or solid solution is found.Stable and metastable phase diagrams are constituted of one invariant point,two univariant solubility curves,and two solid phase crystalline regions corresponding to Mg SO₄?7H₂O and Mg B₄O₇?9H₂O.It is found that the densities gradually increased with the increasing of the concentration of magnesium sulfate in the solution,and they become the largest one at the invariant point.Compared with the stable phase diagram,the solubilities of the Mg B₄O₇ and Mg SO₄ are bigger in the metastable phase diagram.Cmparison with the stable phase diagram of 298 K,the crystalline form of the salt has not been changed.The metastable phase equilibria of K₂B₄O₇–K₂SO₄–H₂O and K₂B₄O₇–KCl^–H₂O belong to simple cosaturated type,and there is no double salt or solid solution.The phase diagrams are constituted of one invariant point,two univariant solubility curves,and two solid phase crystalline regions.The equilibrium solid phases correspond to K₂SO₄ and K₂B₄O₇?4H₂O for K₂SO₄–K₂B₄O₇–H₂O.And,the equilibrium solid phases correspond to KCl and K₂B₄O₇?4H₂O for KCl^–K₂B₄O₇–H₂O,respectively.The metastable phase equilibrium of Li₂B₄O₇–Li Cl^–H₂O belongs to hydrate I type and there is no complex salt or solid solution.The phase diagram is constituted of one invariant point,two univariant solubility curves,and two solid phase crystalline regions corresponding to Li BO₂·8H₂O and Li Cl·H₂O.Compared with the stable phase diagram,the crystalline form of Li₂B₄O₇ in the metastable phase diagram is Li BO₂?8H₂O.However,the crystalline form is Li₂B₄O₇?3H₂O in the stable phase diagram.The stable phase equilibrium of simple quaternary system Li⁺ // Cl^–,SO₄^2–,B₄O₇^2––H₂O belongs to hydrate I type,and there is no complex salt or solid solution.The phase diagram is constituted of one invariant point,three univariant solubility curves,and three solid phase crystalline regions: Li Cl·H₂O,Li₂SO₄·H₂O and Li₂B₄O₇·3H₂O.The experimental results show that Li Cl has a strong salting-out effect on Li₂SO₄ in the system.The stable phase equilibrium of reciprocal quaternary system Li⁺,Mg²⁺ // Cl^–,B₄O₇^2––H₂O belongs to complex type,and the double salt of lithium carnallite（Li Cl·Mg Cl₂·7H₂O）is found.There are three invariant points,seven univariant solubility curves,and five solid phase crystalline regions: Mg Cl₂·6H₂O,Mg B₄O₇·9H₂O,Li Cl·Mg Cl₂·7H₂O,Li Cl·H₂O,Li₂B₄O₇·3H₂O.The double salt Li Cl·Mg Cl₂·7H₂O is found in the stable phase equilibrium of reciprocal quinary system Li⁺,Mg²⁺ // Cl^–,SO₄^2–,B₄O₇^2––H₂O（saturated with Mg B₄O₇·9H₂O）,it belongs to complex type.The phase diagram is constituted of four eutectic points,nine univariant solubility curves,and six solid phase crystalline regions: Mg Cl₂·6H₂O,Li₂SO₄·H₂O,Li Cl·Mg Cl₂·7H₂O,Li Cl·H₂O,Li₂B₄O₇·3H₂O,Mg SO₄·7H₂O.