四元体系Rb+, Cs+, Mg2+ // SO42- - H2O 298.2 K相平衡研究

采用等温溶解平衡法研究了298.2 K下四元体系Rb⁺, Cs⁺, Mg²⁺ // SO₄^2- - H₂O的相平衡关系，测定了该体系的溶解度、密度以及折射率，并绘制了相应的稳定相图、水图、密度-组成图和折射率-组成图。研究表明：298.2 K下，该四元体系为复杂四元体系，有复盐Cs₂SO₄·MgSO₄·6H₂O和Rb₂SO₄·MgSO₄·6H₂O以及固溶体(Rb, Cs）₂SO₄]生成。其稳定相图由4个四元共饱点、9条单变量曲线以及6个结晶区组成。四元共饱点中E₁、E₂、E₃为相称共饱点，E₄为不相称共饱点。6个结晶相区分别对应3种单盐Rb₂SO₄、MgSO₄·7H₂O、Cs₂SO₄，2种复盐Cs₂SO₄·MgSO₄·6H₂O、Rb₂SO₄·MgSO₄·6H₂O和1种固溶体(Rb,Cs）₂SO₄]。其中，复盐Rb₂SO₄·MgSO₄·6H₂O结晶区最大，表明其在该体系中最易结晶析出；Cs₂SO₄结晶区最小。平衡液相的密度和折射率随着溶液中Cs₂SO₄含量变化呈规律性变化。该体系稳定相图将为硫酸镁亚型盐湖卤水中的铷、铯等资源开发利用提供理论依据。

Phase equilibria for quaternary system Rb+, Cs+, Mg2+ // SO42- - H2O at 298.2 K

Phase equilibria for the quaternary system Rb⁺, Cs⁺, Mg²⁺ // SO₄^2- - H₂O at 298.2 K was studied by an isothermal dissolution equilibrium method. The solubilities, densities, and refractive indices of the system at equilibrium were also determined experimentally. Based on the measured data, the stable phase diagram, and diagrams of density vs composition, refractive index vs composition were plotted. The results show that the quaternary system belongs to a complex type at 298.2 K with the double salts Cs₂SO₄·MgSO₄·6H₂O, Rb₂SO₄·MgSO₄·6H₂O, and solid solution (Rb, Cs)₂SO₄] formed. The phase diagram consists of 4 invariant points, 9 univariant curves, and 6 crystallization zones. Invariant points E₁, E₂, and E₃ belong to commensurate type, while invariant point E₄ belongs to incommensurate type. The crystallization zones corrsepond to 3 single salts Rb₂SO₄, MgSO₄·7H₂O, Cs₂SO₄, 2 double salts Cs₂SO₄·MgSO₄·6H₂O and Rb₂SO₄·MgSO₄·6H₂O, 1 solid solution (Rb, Cs)₂SO₄]. The crystallization zone of double salt Rb₂SO₄·MgSO₄·6H₂O is the largest, while the crystallization zone of single salt Cs₂SO₄ is the smallest, which indicating that Rb₂SO₄·MgSO₄·6H₂O is most easily crystallized. The densities and refractive indices change regularly with the changing of Cs₂SO₄ content of the solution. The stable phase diagram of the system will provide a theoretical basis for the development and utilization of resources such as rubidium and cesium in the magnesium sulfate subtype salt lake brine.