A Study Of The Metastable Phase Equilibrium For Quinary System Li⁺,Na⁺,K⁺//SO₄^2-,B₄O₇^2--H₂O At 273K

In order to develop the resource in the zabuye saline lake,Tibet, An experimental study on metastable equilibria at 273 K in the quinary system Li⁺, Na⁺, K⁺//SO₄^2-, B₄O₇^2--H₂O and four quaternary and three ternary sub-systems was done by isothermal evaporation method. Metastable equilibrium solubilities and density of the solution were determined. According to the experimental data, the metastable equilibrium phase diagram and the density-composition diagram and the water-content diagram were plotted.The results show that the double salt KLiSO₄ and 3Na₂SO₄·Li₂SO₄·12H₂O are formed in the quinary system Li⁺, Na⁺, K⁺//SO₄^2-, B₄O₇^2--H₂O. The metastable phase diagram has six invariant points, eighteen univariant curves, eight fields of crystallization which are Na₂B₄O₇·10H₂O, Na₂SO₄·10H₂O, Li₂SO₄·H₂O, LiBO₂·8H₂O, K₂SO₄, K₂B₄O₇·4H₂O, KLiSO₄ and 3Na₂SO₄·Li₂SO₄·12H₂O. The crystallization fields of lithium, sodium and potassium borate minerals are larger but the salt Li₂SO₄·H₂O and the double salt 3Na₂SO₄·Li₂SO₄·12H₂O are smaller. This feature is very important to extract lithium and borate from the salt lake brine.The double salt 3Na₂SO₄·Li₂SO₄·12H₂O and KLiSO₄ were also founded in the simple quaternary system Li⁺, Na⁺, K⁺//SO₄^2--H₂O. The simple quaternary system has three invariant points and seven univariant curves. The salt Li₂SO₄·H₂O has the smalle st crystallization field, but the salt Na₂SO₄·10H₂O has the biggest crystallization field. In the Li⁺, Na⁺//SO₄^2- B₄O₇^2--H₂O system, the double salt 3Na₂SO₄·Li₂SO₄·12H₂O was formed. Its metastable phase diagram consists of three invariant points, seven univariant curves and five fields of crystallization. The salt Li₂SO₄·H₂O has the small-est crystallization field, but the salt Na₂B₄O₇·10H₂O has the biggest crystallization field. compared with the phase diagram at 288 K, crystallization field and crystallizat-ion form change obviously, so we make use of phase diagram in the different temperature to get product. The quaternary system Na⁺, K⁺//SO₄^2-, B₄O₇^2--H₂O is of the simple type, it has two invariant points, five univariant curves and four crystallization fields, The salt Na₂B₄O₇·10H₂O has the biggest crystallization field. The salt Na₂B₄O₇·10H₂O and K₂SO₄ are stable salt in the quaternary system at 273 K. The double salt KLiSO₄ was formed in the system Li⁺, K⁺//SO₄^2-, B₄O₇^2--H₂O. The metastable phase diagram consists of three invariant points, seven univariant curves and five crystallization fields, The salt LiBO₂·8H₂O has the biggest crystallization field. The borate salt is very complicated in the solution, the salt Li[B(OH)₄]·6H₂O formation mechanism also need a further research.Pitzer's theory is used in high concentration multicomponent water-salt systems. Using the solubility of the ternary and quaternary systems, the single salt parameters of Na₂SO₄, Na₂B₄O₇, K₂B₄O₇, K₂SO₄, Li₂SO₄ and Li₂B₄O₇, the solid-phase equilibrium constant and the mixing parameters were getted by the multiple linear regression method. Using the Pitzer's equation, the solublities of the quinary system and invariant points of sub-system were calculated. The calculated values are good agreement with experimental results. The borate salt system calculation also need further research and find out the accurate distribution in the solution. this system is a high concentration multicomponent water-salt systems, so using the Pitzer's equation will be difficult.