Abstract
ABSTRACT: The Pitzer thermodynamic model for solid–liquid equilibria in the quinary system
LiCl–NaCl–KCl–SrCl2–H2O at 298.15 K was constructed by selecting the proper parameters for the
substystems in the literature. The solubility data of the systems NaCl–SrCl2–H2O, KCl–SrCl2–H2O,
LiCl–SrCl2–H2O, and NaCl–KCl–SrCl2–H2O were used to evaluate the model. Good agreement
between the experimental and calculated solubilities shows that the model is reliable. The Pitzer model for the quinary 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 from
Nanyishan district in the Qaidam Basin. The evaporation-crystallization path and sequence of salt
precipitation, change in concentration and precipitation of lithium, sodium, potassium, and strontium,
and water activities during the evaporation process were demonstrated. The salts precipitated from the brine in the order : KCl, NaCl, SrCl2·6H2O, SrCl2·2H2O, and LiCl·H2O. The entire evaporation process may be divided into 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.
Keywords: Pitzer thermodynamic model; solid–liquid equilibrium; Strontium chloride; Computer
simulation of isothermal evaporation; Oilfield brine system