A Study On Metastable Equilibria In Quaternary System Li～+, K～+//CO₃～(2-), B₄O₇～(2-)-H₂O And Its Sub-systems At 298K

In accordance with natural condition of Zabuye and the composition of the salinelake brine in Tibet, metastable phase equilibrium and physico-chemical properties inequilibria liquid phase of quaternary reciprocal system Li⁺,K⁺//CO₃^2-, B₄O₇^2-—H₂Oand its sub-systems at 298K were studied by isothermal evaporationmethod, metastable phase diagram and corresponding water content diagram ofquaternary system, the corresponding metastable phase diagrams of ternarysub-systems, physico-chemical property-composition diagrams(density, refractiveindex and pH value) were plotted.Research shows: the systems all were of simple eutectic type and no solidsolution or double salt was found. The metastable equilibrium solid phases existenceforms are consistent with the stable phase diagram, respectively are: Li₂CO₃,K₂CO₃·3/2H₂O, K₂B₄O₇·4H₂O, with the only exception of Li₂B₄O₇·5H₂O. Boratesrepresent a certain metastability that is easily supersaturated. It is a long time for themto reach the liquid-solid metastable equilibrium. The K₂CO₃ solubility is large, whichplays a leading role in the physico-chemical property of the liquid, and has the intensesalting-out effect to other salts.Using Pitzer's parameters and various salts metastable solubility equilibriumconstants with metastable conditions at 298K, the solubility values of metastableequilibrium in the quaternary system were calculated by Pitzer's equation. Theprediction results were in agreement with the experimental results essentially, and theresults which forecast to the theory have made analysis and discussion.These metastable phase diagrams were completed, which can more objectivelyreflect the process of evaporation-crystallization and the liquid-solid phase mutualfunction relations in Zabuye Salt Lake brine. This feature is very important to extractlithium and borate from the salt lake brine.