Isothermal Evaporation Process Simulation Using the Pitzer Model for the Quinary System LiCl–NaCl–KCl–SrCl₂–H₂O at 298.15 K

The Pitzer thermodynamic model for liquid–solid equilibrium in the quinary system LiCl–NaCl–KCl–SrCl₂–H₂O 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 SrCl₂–H₂O, NaCl–SrCl₂–H₂O, KCl–SrCl₂–H₂O, LiCl–SrCl₂–H₂O, and NaCl–KCl–SrCl₂–H₂O 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, SrCl₂·6H₂O, SrCl₂·2H₂O, and LiCl·H₂O. The entire 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.