Study On The Stable Equilibria In Quinary System Li⁺, K⁺, Mg²⁺//So₄^2-, B₄O₇^2- – H₂O At 273 K

In this paper, phase equilibria in three ternary systems (Li2B4O7-MgB4O7-H2O; K2B4O7-MgB4O7-H2O; Li2B4O7-K2B4O7-H2O) and three quaternary systems (one simple quaternary system Li+, K+, Mg2+//B4O72--H2O; two reciprocal quaternary systems Li+, K+//SO42-, B4O72--H2O and Li+, Mg2+//SO42-, B4O72-H2O) at 273 K were studied using isothermal solution equilibrium method. Furthermore, phase equilibria of the reciprocal quinary system Li+, K+, Mg2+//SO42-, B4O72--H2O at 273 K was studied by isothermal solution equilibrium method. The densities and solubilities of the components in these systems listed above were measured experimentally. Based on the determined experimental data, the corresponding equilibrium phase diagrams, density-composition diagrams and water content diagrams of the systems listed above were shown, respectively. The corresponding Li+ content diagram of the quinary system at 273 K (saturated with Li2B4O7·3H2O) was also plotted.The results show that all the three ternary systems at 273 K are simple total saturated type that there is no complex salt or solid solution found. Besides, the phase diagrams of the three ternary systems are all constituted of one eutectic point, two univariant solubility curves and two solid crystalline phase regions. The two equilibrium solid phases corresponding to the eutectic point in the Li2B4O7 MgB4O7-H2O ternary system are Li2B4O7·3H2O and MgB4O7·9H2O. In the K2B4O7-MgB4O7-H2O ternary system K2B4O7·4H2O and MgB4O7·9H2O are the two equilibrium solid phases relevant to the eutectic point. In the ternary system Li2B4O7-K2B4O7-H2O the two equilibrium solid phases relevant to the eutectic point are Li2B4O7·3H2O and K2B4O7·4H2O.The simple quaternary system Li+, K+, Mg2+//B4O72--H2O belongs to simple eutectic type and no double salt or solid solution is found. There are one invariant point, three univariant curves and three fields of crystallization (Li2B4O7·3H2O, K2B4O7·4H2O and MgB4O7·9H2O) in the phase diagram. The three equilibrium solid phases relevant to the eutectic point are K2B4O7·4H2O, MgB4O7·9H2O, and Li2B4O7·3H2O.The reciprocal quaternary system Li+, Mg2+//SO42-, B4O72--H2O is simple eutectic type and no double salt or solid solution is found. In the phase diagram, there are two invariant points, five univariant curves and four fields of crystallization Li2B4O7·3H2O, Li2SO4H·2O, MgB4O7·9H2O and MgSO4·7H2O. Invariant point F1 is saturated with salts MgSO4·7H2O, Li2SO4H·2O and MgB4O7·9H2O. Invariant point F2 is saturated with salts Li2B4O7·3H2O, Li2SO4H·2O and MgB4O7·9H2O.Double salt KLiSO4 was found in the reciprocal quaternary system Li+, K+// SO42-, B4O72--H2O at 273 K. The quaternary system has three invariant points, seven univariant curves and five fields of crystallization. The five crystallization regions correspond to Li2B4O7·3H2O, Li2SO4H·2O, K2B4O7·4H2O, K2SO4 and KLiSO4, respectively. Invariant point F1 is saturated with salts K2SO4, K2B4O7·4H2O and Li2B4O7·3H2O. Invariant point F2 is saturated with salts K2SO4, KLiSO4 and Li2B4O7·3H2O. Invariant point F3 is saturated with salts Li2SO4H·2O, KLiSO4 and Li2B4O7·3H2O.The double salt KLiSO4 was found in the reciprocal quinary system Li+, K+ Mg2+//SO42-, B4O72--H2O at 273 K (saturated with Li2B4O7·3H2O). The quinary system has three invariant points, seven univariant curves and five fields of crystallization (K2B4O7·4H2O, MgB4O7·9H2O, Li2SO4H·2O, K2SO4 and KLiSO4). Invariant point F1 is saturated with salts K2SO4, K2B4O7·4H2O, MgB4O7·9H2O and Li2B4O7·3H2O. Invariant point F2 is saturated with salts K2SO4, KLiSO4, MgB4O7·9H2O and Li2B4O7·3H2O. Invariant point F3 is saturated with salts Li2SO4H·2O, KLiSO4, MgB4O7·9H2O and Li2B4O7·3H2O.The experimental results show that Li2SO4H·2O has a strong salting-out effect on other salts in the systems.