The phase equilibria of the ternary system NaCl–SrCl2–H2O at 273 and 308 K and quaternary system LiCl–NaCl–SrCl2–H2O at 308 K were measured by the isothermal dissolution equilibrium method. The phase diagrams of the ternary system at two temperatures both contain one invariant point, two univariant curves, and two crystallization fields (SrCl2·6H2O and NaCl). The phase equilibria of this ternary system were also compared and discussed at different temperatures. The phase diagram of the quaternary system LiCl–NaCl–SrCl2–H2O at 308 K consists of two invariant points, five univariant curves, and four crystallization fields (which are corresponding to SrCl2·6H2O, SrCl2·2H2O, LiCl·H2O, and NaCl). The Pitzer model known as an ion-interaction model has been successfully used to calculate the solubilities of salts in water–salt systems with an experimental accuracy. Based on the Pitzer model parameters from the literatures, the Pitzer model was used to predict the solubilities of salts in the ternary system NaCl–SrCl2–H2O at 273 and 308 K. The comparisons show that the calculated results are in good agreement with those of experiment.

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Stable phase equilibria of the quaternary system LiBr–KBr–SrBr2–H2O and ternary system LiBr–NaBr–H2O at 323 K were studied by an isothermal dissolution equilibrium method. The solubilities of salts in the two systems were measured experimentally. The equilibrium solid phases at invariant points in these two systems were also identified using X-ray powder diffraction and the Schreinemakers rule. According to the experimental results, the isothermal phase diagrams of the corresponding systems were drawn in detail. The experimental results show that the isothermal phase diagram of the ternary system LiBr–NaBr–H2O at 323 K has two invariant points, three univariate curves, and three single-salt solid-phase crystallization regions, corresponding to LiBr·H2O, NaBr, and NaBr·2H2O. The quaternary system LiBr–KBr–SrBr2–H2O has no double salts and solid solutions. The phase diagram of the quaternary system LiBr–KBr–SrBr2–H2O at 323 K has two invariant points, five univariate curves, and four solid-phase crystallization regions, which are LiBr·H2O, KBr, SrBr2·2H2O, and SrBr2·6H2O. The crystallization region of KBr is larger than those of LiBr·H2O, SrBr2·2H2O, and SrBr2·6H2O, which indicates that KBr has the smallest solubility and is the easiest to be precipitated from the saturated solution. In addition, a comparison of phase equilibria of some similar systems at different temperatures is presented and discussed in detail.

The solid–liquid equilibria in the ternary system LiBr–SrBr2–H2O at 273.15, 308.15, and 323.15 K were studied by isothermal dissolution equilibrium method in this work. At three different temperatures, the ternary system LiBr–SrBr2–H2O belongs to hydrate type I saturation. The phase diagram at 273.15 K includes one cosaturation point, two univariant curves, and two crystallization zones corresponding to LiBr·2H2O and SrBr2·6H2O. The other two phase diagrams contain two cosaturation points, three univariant curves, and three crystallization fields corresponding to LiBr·2H2O, SrBr2·2H2O, and SrBr2·6H2O at 308.15 K and LiBr·H2O, SrBr2·2H2O, and SrBr2·6H2O at 323.15 K, respectively. Lithium bromide has an obvious salting-out effect on strontium bromide. The crystallization area of lithium bromide hydrate is the smallest, and lithium bromide is difficult to crystallize out of the solution at different temperatures.

The solid−liquid equilibria relationship in the two ternary systems sodium chloride−zinc chloride−water and magnesium chloride−zinc chloride−water at 298 K were investigated based on the isothermal dissolution equilibrium method, integrated with the methods of humid residue, X-ray powder crystal diffraction, and density bottle. According to the determined solubility data combined with the humid residue composition and equilibrium solid phase, the phase diagrams of the two systems were depicted. It is concluded that the two isothermal phase diagrams are categorized as a complex type due to the precipitation of double salt between the two inorganic salt components rather than solid solution. Both of them can be divided into three single solid phase crystalline regions and an unsaturated region. Three solid crystalline phase regions in the ternary system NaCl−ZnCl 2 −H 2 O at 298 K were saturated with NaCl, ZnCl 2 , and 2NaCl•ZnCl 2 •2H 2 O, and those for the ternary system MgCl 2 −ZnCl 2 −H 2 O at 298 K were deposited for MgCl 2 •6H 2 O, MgCl 2 •ZnCl 2 •5H 2 O, and ZnCl 2 . The densities in the equilibrated liquid phase were determined experimentally and simulated by the Laliberte model. As a result, the model can basically describe the density of two electrolytes in an aqueous solution at normal temperature.

This work describes the solid−liquid phase equilibria in the ternary system SrCl 2 −SrBr 2 −H 2 O at T = 273, 298, and 323 K based on the method of isothermal dissolution equilibrium. Since saturated liquid phases and humid residue compositions for a series of synthetic brines were determined simultaneously, the measured equilibrium tie lines were constructed. At the same time, the corresponding equilibrium solid phases were identified by using the Schreinemakers' method supplemented with X-ray powder diffraction. The experimental phase diagrams of the system SrCl 2 −SrBr 2 −H 2 O at T = 273, 298, and 323 K were established according to the theory of phase diagram for water salt system. It is found that the type of the system is classified as completely solid solution type due to formation of solid solution Sr(Cl, Br) 2 •6H 2 O. The phase diagrams of the ternary system SrCl 2 −SrBr 2 −H 2 O at 273, 298, and 323 K are constituted of one univariant solubility curve and one solid crystalline phase region corresponding to Sr(Cl, Br) 2 •6H 2 O, without any invariant point. The Pitzer equation was selected to calculate the solubility data in the ternary system SrCl 2 −SrBr 2 −H 2 O at T = 273, 298, and 323 K. The solubility modeling approach achieved good agreement with experimental solubility data.

The stable phase equilibria of the ternary system MgBr2 + SrBr2 + H2O at 288 and 308 K were studied with the isothermal dissolution equilibrium method. The compositions of solutions and solid phases have been determined and the equilibrium solid phases at the invariant points were identified with the aid of the X-ray diffraction method. The phase diagrams of this system at 288 and 308 K were both constructed in terms of experimental results. Two stable phase diagrams show that this system is hydrate type I at two temperatures without formation of a solid solution or complex salt. Both the phase diagrams are composed of one invariant point, two univariate curves, and two crystallization regions (SrBr2·6H2O and MgBr2·6H2O). The equilibrium solid phases of the invariant point at 288 and 308 K are both SrBr2·6H2O and MgBr2·6H2O, respectively. Combining the Pitzer single-salt parameters of MgBr2 and SrBr2 reported in the literatures, the unreported mixing ion-interaction parameters θMg,Sr and ΨMg,Sr,Br at 288 and 308 K were fitted with the measured values in this study using the Pitzer equations. The agreement between the experimental values and calculated results in the ternary system MgBr2 + SrBr2 + H2O at 288 and 308 K shows that the parameters fitted with solubilities are reliable.

The stable phase equilibrium of the two ternary systems LiCl−MgCl 2 −H 2 O and SrCl 2 −MgCl 2 −H 2 O at 333 K were researched by using the isothermal dissolution equilibrium method. The solubilities of salts in the equilibrium solution were determined, and the equilibrium solids were also investigated by using the Schreinemaker method. In the ternary system LiCl− MgCl 2 −H 2 O at 333 K, the phase diagram of the system is composed of two invariant points, three univariate curves, and three crystallization regions corresponding to MgCl 2 •6H 2 O, LiCl• H 2 O, and double salt LiCl•MgCl 2 •7H 2 O, no solid solution was found in the phase diagram. In the ternary system SrCl 2 −MgCl 2 − H 2 O at 333 K, there are two invariant points, three univariate solubility curves, and three crystallization areas corresponding to SrCl 2 •6H 2 O, SrCl 2 •2H 2 O, and MgCl 2 •6H 2 O; this system belongs to hydrate type II, and neither double salts nor solid solutions were formed.