Phase Equilibrium And Thermodynamic Model Of The Quinary System LiCl-Li₂SO₄-LiBO₂-Li₂B₄O₇-H₂O At 323.15 K

The brine of salt lake and underground oil field was rich in lithium,boron and other resources.The study of brine of salt lake and underground oil field can provide theoretical basis for the development of lithium borate in China.In this dissertation,The isopiestic equilibrium,solid and liquid phase equilibrium,distribution of boron species and Pitzer model of brine systems containing lithium borate were studied.The isopiestic equilibrium concentration and water activity of the ternary system LiB(OH)₄-Li₂B₄O₅(OH)₄-H₂O have been measured.The single salt parameters?⁽⁰⁾,?⁽¹⁾and C^((?))as well as the mixing parameters?and?of the ternary system have been fitted according to the Pitzer chemical model.Compared with the experimental water activity,the calculated water activity has a small difference.The phase equilibrium of LiCl-LiBO₂-Li₂B₄O₇-H₂O and Li₂SO₄-LiBO₂-Li₂B₄O₇-H₂O were studied by isothermal dissolution method.The quaternary LiCl-LiBO₂-Li₂B₄O₇-H₂O and Li₂SO₄-LiBO₂-Li₂B₄O₇-H₂O have no double salt and solid solution at 323.15 K,and belong to the simple system.At 323.15 K,the phase diagrams of the two quaternary systems have a invariant point(LiCl·H₂O+Li₂B₄O₇·3H₂O+LiBO₂·2H₂O)and(Li₂SO₄·H₂O+Li₂B₄O₇·3H₂O+LiBO₂·2H₂O),respectively.In addition,there are three univariate curves and three crystal regions in the two quaternary systems.The physicochemical properties such as refractive index and p H value of the liquid phase of the two quaternary systems change regularly with the solubility of LiBO₂.The theoretical refractices index calculated by semi-empirical formula are in good agreement with the experimental values,indicating that the experimental data of the two systems are accurate and reliable.Finally,according to Pitzer parameters,the chemical model of quaternary system LiCl-LiBO₂-Li₂B₄O₇-H₂O was established,and the solubilities of the quaternary system were calculated.The calculated solubilities show remarkable deviation with the experimental data.The main reason is that the lakcing Pitzer parameters for different boron species are not considered in solubility calculation.The phase diagram of the quinary system LiCl-Li₂SO₄-LiBO₂-Li₂B₄O₇-H₂O contains an invariant point(LiCl·H₂O+Li₂SO₄·H₂O+Li₂B₄O₇·3H₂O+LiBO₂·2H₂O)at323.15 K.There are four univariate dissolution curves and four solid phase crystallization regions.In addition,the physical and chemical properties of the system,such as refractive index and p H value,show regular changes with the change of J(?)necke dry-salt index of LiBO₂.The distribution of boron species in five ternary systems,two quaternary systems and one quinary system containing lithium borate at 323.15 K was calculated by p H value and equilibrium constant between boron species.The results showed that LiCl had a greater effect on the distribution of boron species than Li₂SO₄ when LiCl and Li₂SO₄ existed in the solution.The existence of LiCl in the solution changed the p H value of the solution and then affected the total boron concentration of the solution,resulting in a series of polymerization hydrolysis reactions between boron species.The results indicates that p H value and total boron concentration can affect the distribution of multi-boron species.