The aim of this study was to obtain the relationship between ion interactions and the crystallization patterns of salt species in the lithium–rubidium–magnesium sulfate system at 298.2 K. The phase equilibria of the aqueous quaternary system Li⁺, Rb⁺, Mg²⁺//SO₄^2–-H₂O were studied by the isothermal dissolution method at T = 298.2 K and p = 94.77 kPa. The density, refractive index, and composition of equilibrium solution were determined, on the basis of which solid–liquid phase diagrams and density/refractive index vs composition diagrams were drawn. The phase diagram consists of four quaternary invariant points and six crystallization regions, corresponding to the crystallization areas of single salts Rb₂SO₄, Li₂SO₄·H₂O, and MgSO₄·7H₂O, as well as double salts 3Li₂SO₄·Rb₂SO₄·2H₂O, Li₂SO₄·Rb₂SO₄, and Rb₂SO₄·MgSO₄·6H₂O. Notably, rubidium-containing double salts occupy more than 50% of the entire phase diagram area. The results indicate that the interactions between Li⁺ and Rb⁺ with coexisting Mg²⁺ and SO₄^2– are complex, leading to the formation and precipitation of various lithium- and rubidium-bearing double salts, which hinder the effective concentrations of lithium and rubidium during the solar evaporation process in salt pans. Additionally, a multitemperature comparison of the solid–liquid phase diagrams at 273.2, 298.2, and 308.2 K reveals that temperature is also a significant factor influencing the solid-phase types and crystallization areas. For instance, the crystallization form of the double salt 3Li₂SO₄·Rb₂SO₄·2H₂O changes to 3Li₂SO₄·Rb₂SO₄ at 308.2 K and the crystallization area of Li₂SO₄·Rb₂SO₄ gradually decreases, while the crystallization area of Rb₂SO₄·MgSO₄·6H₂O generally exhibits an increasing trend.

中文翻译：

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含锂、铷和镁的季硫酸盐型体系在 298.2 K 时的固液相平衡


本研究的目的是获得 298.2 K 下锂-铷-镁硫酸盐体系中离子相互作用与盐物种结晶模式之间的关系。水性四元体系 Li ⁺ 的相平衡， Rb ⁺ , Mg ²⁺ //SO ₄ ^2– -H ₂ O等温溶解研究方法在 T = 298.2 K 和 p = 94.77 kPa 时进行。测定平衡溶液的密度、折射率和成分，并在此基础上绘制固-液相图和密度/折射率与成分图。相图由四个四元不变点和六个结晶区组成，分别对应单盐Rb ₂ SO ₄ 、 Li ₂ SO ₄ ·H ₂ O 和 MgSO ₄ ·7H ₂ O，以及复盐 3Li ₂ SO ₄ ·Rb ₂ SO ₄ ·2H ₂ O、Li ₂ SO ₄ ·Rb ₂ SO ₄ 和 Rb ₂ SO ₄ ·MgSO ₄ ·6H ₂ O.值得注意的是，含铷复盐占据了整个相图面积的50%以上。结果表明，Li ⁺ 和 Rb ⁺ 与共存的 Mg ²⁺ 和 SO ₄ ^2– 之间存在相互作用。其结构复杂，导致各种含锂、铷复盐的形成和沉淀，阻碍了盐田太阳蒸发过程中锂、铷的有效浓度。此外，还对 273.2、298.2 和 308 处的固液相图进行了多温度比较。2 K表明温度也是影响固相类型和结晶区域的重要因素。例如，复盐的结晶形式 3Li ₂ SO ₄ ·Rb ₂ SO ₄ ·2H ₂ SO ₄ ·Rb ₂ SO ₄ 以及Li ₂ SO ₄ ·Rb ₂ SO ₄ 逐渐减小，而 Rb ₂ SO ₄ ·6H ₂ O总体呈增加趋势。