Phase Equilibrium Of The Quarternary Systeym (Li⁺, Mg²⁺//SO₄^2-, B₄O₇^2--H₂O) And Its Ternary Subsystem At323.15K

In this dissertation, the phase equilibrium of the quaternary system (Li⁺, Mg²⁺//SO₄^2-,B₄O₇^2--H₂O) and its ternary subsystem （Li₂SO₄-MgSO₄-H₂O） at323.15K werestudied by isothermal equilibrium method. Solubilities and physicochemicalproperties in the solutions were measured, and the equilibrium phase diagram of theternary system, and the dry-salt phase diagram and the water-phase diagram of thequaternary system as well as the physicochemical properties versus compositiondiagrams were plotted based on those experimental data.The experimental phase diagram shows that there is one invariant point, twounivariant curves and two crystallization fields corresponding to MgSO₄·6H₂O andLi₂SO₄·H₂O in the ternary system （Li₂SO₄-MgSO₄-H₂O） at323.15K, and it belongsto the hydrate type I of ternary system obviously. Compared with the stable andmetastable diagram at the same temperatures of323.15K, although it shows that thecrystallization fields are the same, the crystallized area of MgSO₄·6H₂O of the stablediagram is larger than that of the metastable diagram whereas the crystallized area ofLi₂SO₄·H₂O is nearly the same. As to the physicochemical properties versuscomposition diagram, it can be found that the density and pH of the aqueous solutionsin the ternary system change regularly with the content change of MgSO₄, and there isa singularity point in the invariant point. Based on the experiential equation of densityreported in the literature, the densities of the ternary system at323.15K have beencalculated, and the results show that the experimental and calculated values agreewell.In the equlibium phase diagram of the quaternary system (Li⁺, Mg²⁺//SO₄^2-,B₄O₇^2--H₂O) at323.15K, there is five univariant curvest, two invariant poin and fourcrystallization fields corresponding to Li₂B₄O₇·3H₂O, Li₂SO₄·H₂O, MgSO₄·6H₂O andMgB₄O₇·9H₂O. A comparison of the equilibrium phase diagrams for the system at（323.15and298.15） K shows that the crystallized zone of MgSO₄·7H₂O in the stableequilibrium at298.15K is insteaded by MgSO₄·6H₂O in the stable equilibrium at323.15K; the crystallized area of Li₂B₄O₇·3H₂O at323.15K is smaller than that at298.15K, and the crystallized area of Li₂SO₄·H₂O at323.15K is larger than that at298.15K. As to the physicochemical properties versus composition diagram, it can be found that the aqueous solutions in the quaternary system change regularly with thecontent change of solutions. Based on the experiential equation of density reported inliterature, the densities in the quaternary system at323.15K have been calculated, andthe results show that the experimental and calculated values agree well.On the basis of the Pitzer model and its extended HW model, the predictivestable solubilities and the phase diagrams of the quaternary system (Li⁺, Mg²⁺//SO₄^2-,B₄O₇^2--H₂O) at323.15K were done through the Fortran Program in our laboratory.The predictive stable phase diagram agrees well with the experimental stable phasediagram.