Caloric evaporation of the brine in Zangnan Salt Lake

Zangnan Salt Lake on the south of the Tibet is a type of carbonate lake with high concentrations of lithium, boron, and potassium and obviously it differs from seawater in its chemical composition. An experimental simulation of the caloric evaporation of the lake’s brine was conducted by first freezing the brine and then performing isothermal evaporation at 288.15 K. The freezing path and the physicochemical properties of the brine were determined. The crystallization sequence was natron, hydrohalite, halite, sylvite, zabuyelite, trona, aphthitalite, thermonatrite, and borax. Rubidium and cesium salts did not crystallized out but concentrated in the mother solution. The physicochemical properties (density, refractive index, conductivity, and pH) of the liquid phase changed as the evaporation progressed. In the beginning of the evaporation processes, the concentration of potassium ions in the liquid phase gradually increased but later it decreased. A peak value of 55.21 g/L was obtained when the evaporation was 88% complete. When the mineral aphthitalite began to crystallize; the concentrations of B₂O₃, Li⁺, Rb⁺, and Cs⁺ gradually increased as the evaporation progressed. When the evaporation was 98% complete, their concentrations in the mother liquor were 40.77 g/L, 4.838 g/L, 400.17 mg/L and 31.95 mg/L, respectively. This essential fundamental study can provide an important reference for the comprehensive utilization of brines in Zangnan Salt Lake.