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

Phase equilibria of the reciprocal quinary system Na+(K+), Mg2+//Cl-,SO₄^2-,B4O72-- H₂O and its subsystems (Including two simple quaternary systems K+//Cl-,SO₄^2-,B4O72--H₂O and Na+//Cl-, SO₄^2-, B4O72--H₂O) at 288K were studied by isothermal solution equilibrium method. Solubilities and densities in the solution of above listed were determined experimentally. According to the experimental data, the equilibrium phase diagrams and density-composition diagrams of the quaternary systems were plotted. The phase diagrams, corresponding water content diagrams and corresponding Mg2+ content diagrams of the quinary systems at 288K ( saturated with MgB4O7·9H₂O ) were also plotted.The quaternary system Na +//Cl-, SO₄^2-, B4O72--H₂O was of simple eutectic type and no double salt or solid solution was found. In the phase diagram, the quaternary system has one invariant point, three univariant curves, and three fields of crystallization NaCl,Na2B4O7·10H₂O and Na2SO4.10H₂O.The quaternary system K+//Cl-, SO₄^2-, B4O72--H₂O was of simple eutectic type and no double salt or solid solution was found. In the phase diagram, the quaternary system has one invariant point, three univariant curves, and three fields of crystallization K2B4O7·4H₂O, K2SO4 and KCl. The experimental results show that KCl had very strong salting-out effect on K2B4O7·4H₂O, and K2SO4.In stable equilibrium phase diagram of the quinary system Na+,Mg2+// Cl-,SO₄^2-,B4O72--H₂O at 288K, there are the double salts Na2SO4·MgSO4·4H₂O , four invariant points, nine univariant curves, and six crystallization fields (saturated with MgB4O7·9H₂O): NaCl , Na2SO4·10H₂O , Na2B4O7·10H₂O , MgCl2·6H₂O ,MgSO4·7H₂O and Na2SO4·MgSO4·4H₂O.The salt MgCl2 had the biggest solubilities and very strong salting-out effect on other salts.In stable equilibrium phase diagram of the quinary system K+,Mg2+,// Cl-,SO₄^2-,B4O72--H₂O at 288K, there are the double salts K2SO4·MgSO4·6H₂O and KCl·MgCl2·6H₂O , five invariant points, eleven univariant curves, and seven crystallization fields (saturated with MgB4O7·9H₂O): KCl,K2SO4,K2B4O7·4H₂O,MgCl2·6H₂O,MgSO4·7H₂O,K2SO4·MgSO4·6H₂O and KCl·MgCl2·6H₂O.The salt MgCl2·6H₂O had the biggest solubilities and very strong salting-out effect on other salts.