Study On Metastable In Equilibria System Of Li～+, Na～+//CO₃～(2-), SO₄～(2-), B₄O₇～(2-)-H₂O At 273K

An experimental study on metastable equilibria at 273 K in the quinary system Li⁺, Na⁺//CO₃^2-, SO₄^2-, B₄O₇^2- -H₂O was done by isothermal evaporation method. The metastable equilibria for quaternary systems Li⁺, Na⁺//CO₃^2-, SO₄^2- -H₂O, Li⁺, Na⁺//CO₃^2-, B₄O₇^2- -H₂O and Li⁺, Na⁺, K⁺//SO₄^2- -H₂O at 273 K were studied by isothermal evaporation method. Metastable equilibrium solubilities and densities of the solution were determined experimentally. According to the experimental data, the metastable equilibrium phase diagrams were plotted.The experimental results of the metastable equilibria show that the double salt 2Na₂SO₄·Na₂CO₃ and Na₃Li(SO₄)₂^·-6H₂O form in the quinary system Li⁺, Na⁺//CO₃^2-, SO₄^2-, B₄O₇^2- -H₂O at 273.15 K. In the metastable phase diagram, the quinary system has five invariant points, eleven univariant curves, seven fields of crystallization [Na₂B₄O₇·10H₂O and Na₂CO₃·10H₂O, Na₂B₄O₇·10H₂O and Na₂SO₄·10H₂O, Na₂B₄O₇·10H₂O and Li₂CO₃, Na₂B₄O₇·10H₂O and Li₂SO₄·H₂O, Na₂B₄O₇·10H₂O and Li₂B₂O₄·16H₂O, Na₂B₄O₇·10H₂O and Na₃Li(SO₄)₂·6H₂O, Na₂B₄O₇·10H₂O and 2Na₂SO₄·Na₂CO₃].The metastable phase diagram of system Li⁺, Na⁺//CO₃^2-, B₄O₇^2- -H₂O is simple common saturation type. In the metastable phase diagram, the quaternary system has two invariant points, five univariant curves, four fields of crystallization The double salt Na₃Li(SO₄)₂·6H₂O and 2Na₂SO₄·Na₂CO₃ form in the quaternary system Li⁺, Na⁺//CO₃^2-, SO₄^2- -H₂O at 273.15 K. In the metastable phase diagram, the quaternary system has four invariant points, nine univariant curves, six fields of crystallization. The experimental results of the metastable equilibria show that the double salt Li₂SO₄·K₂SO₄ and Na₃Li(SO₄)₂·6H₂O form in the quinary system Li⁺, Na⁺, K⁺//SO₄^2- -H₂O at 273.15 K. In the metastable phase diagam, the quaternary system has three invariant points, seven univariant curves, five fields of crystallization.According to the experimental solubility data of the quaternary systems Li⁺, Na⁺//CO₃^2-, SO₄^2- -H₂O and Li⁺, Na⁺//CO₃^2-, B₄O₇^2- -H₂O, the Pitzer parameters caculated. As follow:β_? =0.2034,β_?=-0.2138, C_Li2CO3^φ=0.00041,β_?=-2.075 C_Li2SO4^φ=0.0084,θ_Li,Na=0.0428,θ_CO3,B4O7=0.0573,θ_SO4,B4O7=0.12,ψ_Li,Na,CO3=0.63, ψ_Li,Na,SO4=0.004,ψ_Li,Na,B4O7=-0.0221,ψ_CO3,SO4,Li=-0.246,ψ_CO3,B4O7,Li=0.0326,ψ_CO3,B4O7,Na=-0.2894,ψ_SO4,B4O7,Li=-0.0572,ψ_SO4,B4O7,Na=-0.3021, and the solution equilibrium constant of Li₂CO₃, Li₂SO₄, Li₂B₄O₇, Na₂CO₃, Na₂SO₄, Na₂B₄O₇. On basis of equilibrium constant of deliquescence, the solubility values on metastable equilibria of the system Li⁺, Na⁺//CO₃^2-, SO₄^2-, B₄O₇^2- -H₂O at 273K were caculated by Pitzer model. Relatively fit together with the experimental data.