Phase Equilibrium Of The Carbonated System Li⁺,Na⁺//Cl^-,HCO₃^-,SO₄^2--CO₂-H₂O At 298.15 K

China has rich salt lake lithium resources,and brine lithium extraction products have outstanding resource advantages,and the application of salt lake lithium extraction products in the future will also become the key target of China’s lithium product supply side upgrade.In the process of enrichment and refining,the mother liquor of lithium precipitation is easy to be affected by multiple ions,which is not conducive to the purification and precipitation of lithium.In this paper,on the basis of the original equilibrium reaction kettle,a new type of carbonation phase equilibrium reaction device was designed and optimized by stable temperature control,precise pressure control,and sampling under pressure.On the basis of the isothermal dissolution method,a certain pressure of CO₂ was introduced to explore the changes of the system before and after carbonization.The lithium carbonate salt was converted into bicarbonate,and the phase equilibrium study of the related systems were completed.With the improved carbonation apparatus,the phase equilibria of the systems Li Cl-CO₂-H₂O,Li⁺//Cl^-,HCO₃^--CO₂-H₂O,Na⁺//Cl^-,HCO₃^--CO₂-H₂O,Na⁺//Cl^-,HCO₃^-,SO₄^2--H₂O,Li⁺,Na⁺//Cl^-,HCO₃^--H₂O and Li⁺,Na⁺//Cl^-,HCO₃^-,SO₄^2--H₂O were studied at298.15 K with the pressure 0.3 MPa for CO₂ using the isothermal dissolution method.There is an invariant point in the systems Li⁺//Cl^-,HCO₃^--CO₂-H₂O and Na⁺//Cl^-,HCO₃^--CO₂-H₂O.No double salt and solid solution forms.The solubility of Li HCO₃ and Na HCO₃ is affected by the salting out of Li Cl and Na Cl,respectively.The area of crystallization zone for bicarbonate is small and it is easier to be saturated.On the basis of Pitzer electrolyte theory,a model was constructed by combining Pitzer parameters and dissolution product constants to predict the solubilities in systems Li Cl-CO₂-H₂O,Na⁺//Cl^-,HCO₃^--CO₂-H₂O,and Na⁺//Cl^-,HCO₃^-,SO₄^2--CO₂-H₂O.The agreement between the calculated and experimental data shows that the experimental data and improved apparatus are reliable.The phase diagrams for the system Na⁺//Cl^-,HCO₃^-,SO₄^2--H₂O are nearly the same as that after carbonization.The area for the crystallization zones are nearly unchanged.The phase diagram in the system Li⁺,Na⁺//Cl^?,HCO₃^?-CO₂-H₂O consists of two invariant points and four crystallization regions.After carbonization,the carbonate system is transformed into bicarbonate system.The presence of Li⁺and Cl^-has a great influence on the solubility in the system.The phase diagram in the system Li⁺,Na⁺//Cl^-,HCO₃^-,SO₄^2--H₂O consists of five invariant points and seven crystallization regions with Na Cl saturation.The areas of Na HCO₃and Li Cl phase regions are the largest and smallest among the six crystallization zones.The double salts Db1（Li₂SO₄·3Na₂SO₄·12H₂O）and Db2（Li₂SO₄·Na₂SO₄）forms in the system.The J（H₂O）and J(Na₂²⁺)change regularly with the concentration changing,which can be used to judge the changes of water content and concentration in the system.Through the determination of the physicochemical properties of the above system,the p H values and refractive indices change regularly as the concentration changing.Through the variation of refractive index,the invariant point range of the systems can be roughly judged.In the systems containing Li Cl,the p H decreases with the increase of Li Cl concentration.The refractive index is generally the highest at the invariant point.