Equilibrium Solubility Of Rubidium/Cesium Salt-Mixed Solvent System And Its Phase Relationship

In recent years, salt-mixed solvent system has become a very important system. And with the development of studies on rare alkali metal rubidium and cesium, it is significant to study the rubidium / cesium salt-mixed solvent system. This thesis includes a review and a research section.In the review, the basic knowledge of the aqueous two-phase systems, rubidium, cesium and their compounds were introduced firstly. And the importance was paid on the systems of alkali metal and alkali earth metal salts-polyethylene glycol(PEG)-H2O. The equilibrium solubility and physico-chemical properties of these systems can provide not only basic thermodynamic data for solution chemistry, but also new purification methods for inorganic salts and the partition of biomaterials.The research section introduced the method and the results of the experiment. In the research section, we have used a semimicro installation to study phase diagrams of Cs₂SO₄-PEG(1000, 4000, 10 000)-H₂O ternary systems at 25 ℃ and Rb₂SO₄/Rb₂CO₃/ CsCl-PEG(1000, 4000, 10 000)-H₂O system at (25, 35 and 45) ℃. The solutions of these systems have appeared two phases: organic (light) phase and water (heavy) phase. With the increasement of temperature and the molecular weight of PEG, the two-phase area increased. Samples of the equilibrium solid phase in Rb₂SO₄-PEG4000-H₂O system at 25 ℃ analyzed by TGA showed that they consisted of anhydrous salt. Six zones were observed in the complete phase diagram. They are L, L+L, L+S(two), 2L+S and L+2S, respectively. The binodal curves were given using a four-parameter equation y = a + bx^0.5+cx+dx². The tie lines were correlated by the Othmer-Tobias and Bancroft equations.We have also studied the solubility and refractive index for the ternary systems CsNO₃-PEG(1000, 4000)-H₂O and RbNO₃-ROH(R=N-C₃H₇, i-C₃H₇-,t-C₄H₉-)-H₂O at (25, 35 and 45) ℃. The two ternary systems did not appear two phases and only one solubility limit was observed. It could be observed that at a fixed temperature the solubility of the salt decreased with the addition of PEG or aliphatic alcohol, the solubility and refractive index of the solution were correlated to the PEG or aliphatic alcohol content according to the four-parameter equation In Y = A₀ +A₁X +A₂x²+A₃x³Liquid-liquid and solid-liquid equilibria of the PEG 10 000-H2O-RbNC>3 system was also presented. And we get the lower critical solution temperature of this system.In this thesis, a series of phase equilibrium data of rubidium/cesium salt mixed solvent system were given out, the experimental results provided not only basic thermodynamic data for solution chemistry, but also new purification methods for inorganic salts and the partition of biomaterials.