The underground brines in the Sichuan basin of China are rich in many valuable components, such as Li+, K+, Sr2+, Br–, and others. In view of comprehensive utilization of the underground brines, the stable solid–liquid equilibria of the quaternary systems LiBr–NaBr–KBr–H2O and LiBr–KBr–SrBr2–H2O at 308.15 K were measured by the isothermal dissolution equilibrium method. The results show that both phase diagrams of the quaternary systems listed above are hydrate-type. Both equilibrium phase diagrams are composed of two invariant points, five univariant curves and four crystallization fields. The equilibrium solid phases in the first quaternary system are LiBr·2H2O, NaBr·2H2O, NaBr, and KBr, respectively, and those in the second quaternary system are LiBr·2H2O, SrBr2·6H2O, SrBr2·2H2O, and KBr. In both phase diagrams, the crystallization field of KBr is the largest, while that of LiBr·2H2O is the smallest. The results indicate that KBr is the easiest to be separated from the saturated solution in the two quaternary systems. Furthermore, the comparison of phase equilibria of the quaternary systems and its ternary subsystems at different temperatures is presented and discussed in detail.
Xing-Xing Zeng,Shi-Hua Sang,Xiao-Yun Qi,Xiao-Feng Guo,Rui-Zhi Cui
Aiming at the composition of underground brines in the Sichuan Basin of China, stable phase equilibria in quaternary systems LiBr–NaBr–SrBr2–H2O and LiBr–KBr–SrBr2–H2O at 288.15 K are studied using the isothermal dissolution equilibrium method. The solubilities of salts in the quaternary systems listed above are measured, and the corresponding equilibrium solid phases are identified using X-ray powder diffraction. As a result, the corresponding phase diagrams of the two quaternary systems are plotted, respectively. In the two stable phase diagrams, there is no solid solution or complex salt at 288.15 K. For the quaternary system LiBr–NaBr–SrBr2–H2O, there are two invariant points, five univariate curves, and four solid crystallization regions, which are LiBr·2H2O, NaBr, NaBr·2H2O, and SrBr2·6H2O, respectively, of which LiBr·2H2O has the smallest crystallization field, indicating that its solubility is the largest and it is the hardest to be precipitated from the saturated solution. There are one invariant point, three univariate curves, and three solid crystallization fields, corresponding to LiBr·2H2O, KBr, and SrBr2·6H2O in the quaternary system LiBr–KBr–SrBr2–H2O, respectively. The experimental results show that the solubilities of salts KBr, NaBr, and SrBr2 in the saturated solution decrease with the increasing concentration of LiBr, which indicates that LiBr has a strong salting out effect on KBr, NaBr, and SrBr2 in the solution.
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