Study On Equilibria In Quinary System Na⁺, Mg²⁺, K⁺//SO₄^2-, B₄O₇^2--H₂O At 288K

Phase equilibria of reciprocal quinary system Na⁺,Mg²⁺,K⁺//SO₄^2-,B₄O₇^2--H₂O and its subsystems (one ternary system and four quaternary systems) at 288K were studied by isothermal solution equilibrium method. Solubilities and densities in the solution of these systems were determined experimentally. According to the experimental data, the equilibria phase diagram and density-composition diagram of the ternary 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 Mg²⁺ content diagram of the quinary system at 288K ( saturated with MgB₄O₇·9H₂O) were also plotted.The experimental results show that the ternary systems Na₂B₄O₇-MgB₄O₇-H₂O at 288K was of simple eutectic type and no double salt or solid solution was found. In the phase diagram, the ternary system has one invariant points, two univariant curves, two fields of crystallization [Na₂B₄O₇·10H₂O and MgB₄O₇·9H₂O].The quaternary system Na₂B₄O₇-MgB₄O₇-K₂B₄O₇-H₂O was of simple eutectic type and no double salt or solid solution was found also. In the phase diagram, the quaternary system has one invariant points, three univariant curves, three fields of crystallization [Na₂B₄O₇·10H₂O, MgB₄O₇·9H₂O and K₂B₄O₇·4H₂O].The double salt Na₂SO₄·3K₂SO₄ forms in the quaternary system Na⁺,K⁺//SO₄²⁺,B₄O₇²⁺-H2O at 288K. 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, Na₂SO₄·3K₂SO₄].The experimental results show that the double salt Na₂SO₄·MgSO₄·4H₂O forms in the quaternary system Na⁺,Mg²⁺//SO₄^2-,B₄O₇^2--H₂O at 288K. The quaternary system has three invariant points, seven univariant curves, five fields of crystallization[Na₂SO₄·MgSO₄·4H₂O,Na₂B₄O₇·10H₂O,Na₂SO₄·10H₂O, MgSO₄·7H₂O MgB₄O₇·9H₂O].The double salt K₂SO₄·MgSO₄·6H₂O was found in the quaternary system Mg²⁺,K⁺//SO₄^2-,B₄O₇^2--H₂O at 288K. The quaternary system has three invariant points, seven univariant curves, five fields of crystallization [MgB₄O₇·9H₂O, MgSO₄·7H₂O, K₂B₄O₇·4H₂O, K₂SO₄, K₂SO₄·MgSO₄·6H₂O]. In stable equilibrium phase diagram of quinary system Na⁺,Mg²⁺,K⁺//SO₄^2-,B₄O₇^2--H₂O at 288K, there are fourteen uninvariant curves, serven invariant points, eight crystallization fields (saturated with MgB₄O₇·9H₂O): Na₂B₄O₇·10H₂O,Na₂SO₄·MgSO₄·4H₂O,Na₂SO₄·3K₂SO₄,K₂SO₄·MgSO₄·6H₂O, K₂SO₄,Na₂SO₄·10H₂O, K₂B₄O₇·4H₂O, MgSO₄·7H₂O.