The Pitzer thermodynamic model for liquid-solid equilibrium in the quinary system LiCl-NaCl-KCl-SrCl 2 -H 2 O at 298.15 K was constructed by selecting the proper parameters and standard chemical potential. The solubility data and water activity data of the systems SrCl 2 -H 2 O, NaCl-SrCl 2 -H 2 O, KCl-SrCl 2 -H 2 O, LiCl-SrCl 2 -H 2 O, and NaCl-KCl-SrCl 2 -H 2 O were used to evaluate the model. Good agreement between the calculated and experimental solubility data indicates that the model is reliable. The Pitzer model for the above system at 298.15 K was then used to calculate the component solubilities and conduct computer simulation of isothermal evaporation of the mother liquor for the oilfield brine in Nanyishan region of Qaidam Basin (China). The evaporation-crystallization route and order of salt precipitation, changes in concentration and precipitation of lithium, sodium, potassium, and strontium, and water activities during the evaporation process were demonstrated. The salts crystallized from the brine in the order : KCl, NaCl, SrCl 2 ·6H 2 O, SrCl 2 ·2H 2 O, and LiCl·H 2 O. The whole evaporation-crystallization process may consist of six stages. In each stage the variation trends for the relationships between ion concentrations or water activities and the evaporation ratio are different. This result of the simulation of brines can be used as a theoretical reference for comprehensive exploitation and utilization of this type of brine resources.

The metastable solubility of the reciprocal quaternary system containing sodium, potassium, chloride, and borate ions and the physicochemical properties corresponding to density, viscosity, pH value, and refractive index at 308.15 K have been studied with the isothermal evaporation method. According to the experimental data, the metastable equilibrium phase diagrams of dry salt and the water phase diagram of the system were plotted. In the dry-salt phase diagram, there are two invariant points, five univariant curves, and four crystallizing regions corresponding to sodium chloride, potassium chloride, borax (Na 2 B 4 O 7 · 10H 2 O), and potassium tetraborate tetrahydrate (K 2 B 4 O 7 · 4H 2 O). The crystallized region of borax is the largest, while the phase region of NaCl is the smallest with the highest concentration and a strong salting-out effect to borax. There are neither double salts nor solid solutions formed in the metastable system. When compared with the stable phase diagram at 298.15 K of the system, the areas of both metastable phase regions of borax and potassium chloride are enlarged, while other metastable phase regions are decreased. The calculated values of densities and refractive index in the metastable quaternary system with the empirical equations are in good agreement with the experimental values.

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