Measurements of Solid–Liquid Equilibria in the Quaternary Systems LiBr–NaBr–KBr–H2O and LiBr–KBr–SrBr2–H2O at 308.15 K

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.