Solid-liquid Phase Equilibrium and Phase Diagram of the Quaternary System(NaB5O8+KB5O8+RbB5O8+H2O)at 288.15 K
There are abundant reserves of lithium,potassium,and boron in many salt lake brines on the East Taijinaier salt lake,and the phase equilibrium of the water and salt system and the phase diagram provide a research basis and theoretical support for the separation and extraction of salt lake minerals.In this study,the phase equilibrium diagram of the quaternary system(NaB5O8+KB5O8+RbB5O8+H2O)at 288.15 K was explored by the isothermal solution equilibrium method.Solubility and two principal physicochemical properties of the system,equilibrium liquid phase density and refractive index,were obtained by experiments,and the existing mineral species of the salt lake were analyzed and identified.The results showed that the saturation point in the stable phase diagram of the system(NaB5O8·5H2O+KB5O8·4H2O+RbB5O8·4H2O)at 288.15 K is characterized by a liquid phase composition of w(NaB5O8)=9.02％,w(KB5O8)=0.47％,w(RbB5O8)=0.21％.There are three salt minerals,NaB5O8·5H2O,KB5O8·4H2O,and RbB5O8·4H2O,and the system has no solid solution or double salt formation.Among the three minerals,RbB5O8·4H2O has the largest crystal area and the smallest solubility.The refractive index and density of the liquid phase changes regularly with the increase of the dry base mass fraction Z(NaB5O8)in the solution.The relative errors of density and refractive index were calculated by empirical formula,and the calculated values agree well with the experimental ones.
water-salt systemsolid-liquid equilibrium and phase diagramsalt mineralssolubilitypentaborate
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