四元体系(NaB_(5)O_(8)+KB_(5)O_(8)+RbB_(5)O_(8)+H_(2)O)288.15 K固液相平衡与相图研究

Solid-liquid Phase Equilibrium and Phase Diagram of the Quaternary System(NaB_(5)O_(8)+KB_(5)O_(8)+RbB_(5)O_(8)+H_(2)O)at 288.15 K

我国东台吉乃尔盐湖卤水中锂钾硼含量显著,水盐体系相平衡与相图为盐湖矿物的分离提取提供了理论基础。本文对四元体系(NaB_(5)O_(8)+KB_(5)O_(8)+RbB_(5)O_(8)+H_(2)O)在288.15 K时的相平衡与相图采用等温溶解平衡法研究,实验得出溶解度以及平衡液相的密度和折光率这两个主要物化性质,分析且鉴定出存在的盐湖矿物种类。研究发现:288.15 K时,该体系稳定相图中的共饱点(NaB_(5)O_(8)·5H_(2)O+KB_(5)O_(8)·4H_(2)O+RbB_(5)O_(8)·4H_(2)O)的液相组成为w(NaB_(5)O_(8))=9.02%、w(KB_(5)O_(8))=0.47%、w(RbB_(5)O_(8))=0.21%,且3种盐类矿物(NaB_(5)O_(8)·5H_(2)O、KB_(5)O_(8)·4H_(2)O、RbB_(5)O_(8)·4H_(2)O)的体系没有固溶体或复盐生成。三个矿物中RbB_(5)O_(8)·4H_(2)O的结晶区面积最大,溶解度最小。液相的折光率和密度均随Z(NaB_(5)O_(8))的增加呈规律性变化,密度和折光率均采用经验公式进行相对误差计算,所得计算值与实验值吻合较好。

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(NaB_(5)O_(8)+KB_(5)O_(8)+RbB_(5)O_(8)+H_(2)O)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(NaB_(5)O_(8)·5H_(2)O+KB_(5)O_(8)·4H_(2)O+RbB_(5)O_(8)·4H_(2)O)at 288.15 K is characterized by a liquid phase composition of w(NaB_(5)O_(8))=9.02%,w(KB_(5)O_(8))=0.47%,w(RbB_(5)O_(8))=0.21%.There are three salt minerals,NaB_(5)O_(8)·5H_(2)O,KB_(5)O_(8)·4H_(2)O,and RbB_(5)O_(8)·4H_(2)O,and the system has no solid solution or double salt formation.Among the three minerals,RbB_(5)O_(8)·4H_(2)O 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(NaB_(5)O_(8))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.