Phase Equilibria of the Aqueous Quaternary System Li⁺, Rb⁺, Cs⁺//SO₄^2–-H₂O at T = 273.2 K

Abstract

The phase equilibria of the quaternary system Li + , Rb + , Cs + //SO 4 2− -H 2 O at T = 273.2 K was investigated by the isothermal dissolution method. The solubility and density of the system were measured and the related phase diagram, water content diagram, and density vs composition diagram were plotted. The solid phase of the quaternary invariant point was identified by the Xray diffraction method and the solid solution morphology was analyzed by scanning electron microscopy. Results show that the stable phase diagram consists of 6 invariant points, 13 uninvariant curves, and 8 crystallization regions (corresponding to single salts Li 2 SO 4 •H 2 O, Rb 2 SO 4 , and Cs 2 SO 4 ; double salts 3Li 2 SO 4 •Rb 2 SO 4 •2H 2 O, 3Li 2 SO 4 •Cs 2 SO 4 •2H 2 O, Li 2 SO 4 •Rb 2 SO 4 , and Li 2 SO 4 • Cs 2 SO 4 ; and solid solution [(Rb, Cs) 2 SO 4 ]). Also, the crystallization region of double salt 3Li 2 SO 4 •Rb 2 SO 4 •2H 2 O is the largest, which means that it is easiest to precipitate from this system. Meanwhile, rubidium and cesium easily form a solid solution in the sulfate system, which increases the difficulty of separating the two elements. Comparing the stable phase diagram of the ternary subsystems at T = 273.2 K and T = 298.2 K, it is found that the crystallization regions of Rb 2 SO 4 , Cs 2 SO 4 , [(Rb, Cs) 2 SO 4 ], and 3Li 2 SO 4 •Cs 2 SO 4 •2H 2 O increase with the decrease of temperature, indicating that cooling is conducive to the crystallization of Rb 2 SO 4 , Cs 2 SO 4 , [(Rb, Cs) 2 SO 4 ], and 3Li 2 SO 4 •Cs 2 SO 4 •2H 2 O.

Solid–Liquid Phase Equilibria Determination of the Quaternary System Na+, K+, Ca2+//Cl––H2O at 348.2 and 363.2 K

“…The liquid phase was taken out of the solution periodically to determine and analyze the concentrations of ions. When both the ions' concentrations remained constant, the equilibrium was reached 20 (the equilibrium time was about 4 weeks). After achieving equilibrium, it is transferred to the appropriate temperature-controlled incubator, which maintains a precise temperature of 348.2 or 363.2 K. The sample collection procedure is performed within the precise temperaturecontrolled incubator, which is able to effectively mitigate the effects of temperature fluctuations on the sample; the liquid phase was analyzed for its ion content, while the solid phase was studied through X-ray powder diffraction (XRD).…”