A Study On Stable And Metastable Equilibria In Quinary System Li～+, Na～+, K～+//CO₃～2, B₄O₇～(2-)-H₂O At 288K

In this paper, phase equilibria of quinary reciprocal system Li+, Na% KV/ C032. B4O72~-H2O and its subsystems (nine ternary systems and five quaternary systems) at 288K were studied by isothermal method; An experimental study on metastable equilibria at 288K in the quinary system was done by isothermal evaporation method, also. Solubilities and physico-chemical properties (density, Conductivity, and pH) in the solution of these systems were determined. According to the experimental data, equilibria phase diagrams and physico-chemical property -composition diagrams of ternary systems were plotted; Equilibrium phase diagrams and corresponding water content diagrams of quaternary systems were finished; Stable and metastable phase diagrams, corresponding water content diagrams of the quinary systems at 288K (saturated with Li2CO3) were also plotted.Potassium and Sodium Carbonate double salt NaKCO3 - 6H2O was found in the ternary system Na2CO3-K2CO3-H2O at 288K, comparison with phase diagram at 298K of one, crystallization field of Na2CO3 ?7H2O disappeared at 288K. Other ternary systems all were of simple eutectic type and no double salt or solid solution was found. Potassium borate (K2B4O7) had obviously salting-in effect on Na2B4O7 in the ternary system K-,B4O7-Na2B4O7-H:O at 288K, which was also found in the quaternary system K2B4O7-Na;B4O7-Li2B407-H20 at 28 8K. On the contrary, Potassium carbonate (K2CO3) had strong salting-out effect on other salts in the systems including K2CO3. Double salt NaKCO3 - 6H2O was also found in quaternary system: Li+, Na+, KV/CO32--H:O , Na*, KV/CO32, B4072- -H2O and in the stable and metastable equilibrium quinary system Lf, Na+, KV/CO32~, B4O72 -H2O at 288K.In stable equilibrium phase diagram of quinary system Li+, Na+, KV/CO/', B4O72 -H2O at 288K, there are six crystallization fields (saturated with Li2CO3): K2CO3 -3/2H2O, NajCO, ?10H2O, KjB4PO7 MH2O, NajB4O7- 10H2O, Li2B4O7 -3H2O and NaKCO3 - 6H2O; nine invariant curves; four invariant points.In metastable equilibrium phase diagram of quinary system Li+, Na+, KV/C032", B4O72 -H2O at 288K, there are six crystallization fields (saturated with Li2CO3): K2CO3 -3/2H2O, Na2CO3 MOHjO, NaKCO3 -6H2O, K2B4O7 5H2O, Li,B2O4 -16H2O and Na2B2O4 8H2O. nine univariant curves; four invariant points.Some differences were found between stable phase diagram and metastable one at 288K. The crystallization fields of K,B4O7 ?4HLO, Li,B4O7 - 3H,O and Na2B4O7 -10H2O which were found in the stable phase diagram disappeared in themetastable one and replaced by K2B4O7 - 5H2O, Li2B2O4 - 16H2O and Na2B2O4 - 8H2O, respectively. The crystallization field of Na2CO3 - 10H,O in metastable phase diagram obviously became bigger than in stable one.Using the solubilities data of binary and ternary systems at 288K, the single salt ion-interaction parameters and corresponding ion-interaction mixing parameters for Pitzer's equations were fitted by multiple linear regression method. Equilibrium constant of salts for (liquid +solid) equilibrium at 288 K were evaluated with Pitzer's model. The solubilities of quaternary and quinary system were calculated by Pitzer 's equations. The prediction results were in agreement with the experimental results essentially. Corresponding discussion of prediction results was finished.