Study On Equilibria In Quinary System Na⁺, K⁺//Cl^-, SO₄^2-, B₄O₇^2--H₂O

Phase equilibria of reciprocal quinary system Na⁺,K⁺// Cl-,SO₄^2-,B₄O₇^2--H₂O and its subsystems which included two simple eutectic type systems: K₂B₄O₇ - K₂SO₄ - KCl - H₂O and Na₂B₄O₇ - Na₂SO₄ - NaCl - H₂O at 298K, Na⁺,K⁺//SO₄^2-,B₄O₇^2--H₂O at 298K and 323K, were studied by isothermal solution equilibrium method. The solubilities and densities of listed above at a specifically temperature were mensurated. According to the experimental data, the equilibria phase diagrams and density-composition diagrams of the relevant system were plotted. Equilibrium phase diagrams and corresponding water content diagrams of quaternary systems were finished. The phase diagram, corresponding water content diagram and corresponding Na⁺ content diagram of the quinary system at 298K ( saturated with NaCl) were also plotted.The experimental results show that the quaternary system K₂B₄O₇ - K₂SO₄ - KCl - H₂O at 298K was of simple eutectic type and no double salt or solid solution was found . In the phase diagram, the quaternary system has one invariant points, three univariant curves, three fields of crystallization [KCl, K₂B₄O₇·4H₂O and K₂SO₄]. The experimental results show KCl had the salting-out effect on K₂B₄O₇·4H₂O and K₂SO₄ .There is no double salt in the quaternary system Na₂B₄O₇ - Na₂SO₄ - NaCl - H₂O at 298K. Hydration salt Na₂B₄O₇·10H₂O and Na₂SO₄·10H₂O were found. In the phase diagram, the quaternary system has two invariant points, five univariant curves, four fields of crystallization [Na₂B₄O₇·10H₂O, Na₂SO₄, Na₂SO₄·10H₂O and NaCl].The double salt Na₂SO₄·3K₂SO₄ forms in the quaternary system Na⁺,K⁺//SO₄^2-,B4O72--H₂O at 298K. In the phase diagram, this quaternary system has three invariant points, seven univariant curves, five fields of crystallization [Na₂B₄O₇·10H₂O, K₂B₄O₇·4H₂O, Na₂SO₄·10H₂O, K₂SO₄ and Na₂SO₄·3K₂SO₄].The quaternary system Na⁺,K⁺//SO₄^2-,B₄O₇^2--H₂O was found the double salt Na₂SO₄·3K₂SO₄ at 323K. In the phase diagram, this quaternary system has three invariant points, seven univariant curves, five fields of crystallization [Na₂B₄O₇·10H₂O, K₂B₄O₇·4H₂O, Na₂SO₄, K₂SO₄ and Na₂SO₄·3K₂SO₄].Comparing to the different temperature at 298K and 323K, Change of temperature has great affect on Na₂B₄O₇·10H₂O , and that high temperature also made the water of the crystal (Na₂SO₄·10H₂O) disappeared.In stable equilibrium phase diagram of quinary system Na⁺,K⁺// Cl-,SO₄^2-,B₄O₇^2--H₂O at 298K, there are the double salt Na₂SO₄·3K₂SO₄ ,nine uninvariant curves, four invariant points, six crystallization fields (saturated with NaCl): [Na₂SO₄, Na₂B₄O₇·10H₂O, Na₂SO₄·3K₂SO₄(Gla), K₂SO₄, K₂B₄O₇·4H₂O and KCl].