Aiming at the composition of underground brines in the Sichuan Basin of China, stable phase equilibria in quaternary systems LiBr−NaBr−SrBr 2 −H 2 O and LiBr−KBr−SrBr 2 −H 2 O 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−SrBr 2 −H 2 O, there are two invariant points, five univariate curves, and four solid crystallization regions, which are LiBr•2H 2 O, NaBr, NaBr•2H 2 O, and SrBr 2 •6H 2 O, respectively, of which LiBr•2H 2 O 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•2H 2 O, KBr, and SrBr 2 •6H 2 O in the quaternary system LiBr−KBr−SrBr 2 −H 2 O, respectively. The experimental results show that the solubilities of salts KBr, NaBr, and SrBr 2 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 SrBr 2 in the solution.
