Phase Equilibrium Of The Tenary K₂CO₃-Na₂CO₃-H₂O And KHCO₃-NaHCO₃-H₂O:An Experimental Study

The study is a part of the project Technology of Extracting K2CO3 from Insoluble Potassium, the filtered liquid of the process is a NaHCO3-KHCO3-H2O system. The Na2CO3-K2CO3-H2O and KHCO3-NaHO3-H2O system at 25 ℃have been studied by dissolution-equilibrium method, and the KHCO3-NaHO3-H2O system has been studied by evaporation-equilibrium method. The study can be referred to the 'Technology of Extracting K2CO3 from Insoluble Potassium'. After the studying of the Na2CO3-K2CO3-H2O system, we have drawn the following conclusion: with the adding of K2CO3, the liquid refractive index, density, conductance and pH value of this liquid phase rise steadily until keep invariableness after reaching equilibrium. On the other hand, as to the solid phase, according to the XRD analysis of the selected points based on the result of content of K+,Na+, we can draw the conclusion that K2CO3 has a intense salting effect to Na2CO3 , with K2CO3 adding to pure Na2CO3. Adding K2CO3 to pure Na2CO3 in this solid system, NaKCO3·6H2O comes into being. Keeping adding K2CO3, the mainly new forming matter is K2CO3·1.5H2O. After studying the phase equilibrium and the chemical-physical properties of contents in KHCO3-NaHO3-H2O system by dissolution-equilibrium method, we have drawn the following conclusion: with the adding of KHCO3, the density and refractive index of liquid phase rise linearly, then keeps invariable after reaching equilibrium. Conductance rises steadily but falls little after reaching the balance for the ion concentration. The pH value rises steadily till reaches its maximum when equilibrium and falls from then on. Correspondingly, by means of XRD according to the selected points, it is can been found that with the adding of KHCO3, The main solid content is NaHCO3 at the beginning and it changes to KHCO3 with the adding of KHCO3 incessantly till the WKHCO3/WNaHCO3 ≥40/11 in this system. The KHCO3-NaHO3-H2O system has been studied by evaporation-equilibrium method. The solid and the liquid phase have been analyzed their chemical-physical properties separately after they have been separated. We could find that the liquid density , conductance and refractive index rises with the augment of K/Na and keep invariableness after reaching given proportion.some point.