Yu Zhangfa, Zeng Ying, Sun Hongbo, Li Longgang, He Wanghai, Huang Peng, Yu Xudong
CITIC Guoan Industrial Group Co., Ltd., Beijing 100004, P. R. China.
Sulfate-type Salt Lake Utilization Key Lab of Qinghai Province, Golmud 816000, P. R. China.
ACS Omega. 2024 May 7;9(20):22196-22202. doi: 10.1021/acsomega.4c00636. eCollection 2024 May 21.
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, Mg//SO-HO were studied by the isothermal dissolution method at = 298.2 K and = 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 RbSO, LiSO·HO, and MgSO·7HO, as well as double salts 3LiSO·RbSO·2HO, LiSO·RbSO, and RbSO·MgSO·6HO. 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 Mg and SO 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 3LiSO·RbSO·2HO changes to 3LiSO·RbSO at 308.2 K and the crystallization area of LiSO·RbSO gradually decreases, while the crystallization area of RbSO·MgSO·6HO generally exhibits an increasing trend.
本研究的目的是获取298.2 K下锂-铷-硫酸镁体系中离子相互作用与盐类结晶模式之间的关系。采用等温溶解法在T = 298.2 K、p = 94.77 kPa条件下研究了Li、Rb、Mg//SO-H₂O四元水体系的相平衡。测定了平衡溶液的密度、折射率和组成，并据此绘制了固液相图以及密度/折射率与组成关系图。相图由四个四元不变点和六个结晶区域组成，分别对应单盐Rb₂SO₄、Li₂SO₄·H₂O和MgSO₄·7H₂O以及复盐3Li₂SO₄·Rb₂SO₄·2H₂O、Li₂SO₄·Rb₂SO₄和Rb₂SO₄·MgSO₄·6H₂O的结晶区域。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和SO₄之间的相互作用较为复杂，导致形成并析出了各种含锂和铷的复盐，这在盐田太阳能蒸发过程中阻碍了锂和铷的有效浓度。此外，对273.2、298.2和308.2 K下的固液相图进行多温度比较发现，温度也是影响固相类型和结晶区域的重要因素。例如，复盐3Li₂SO₄·Rb₂SO₄·2H₂O在308.2 K时结晶形式变为3Li₂SO₄·Rb₂SO₄，Li₂SO₄·Rb₂SO₄的结晶区域逐渐减小，而Rb₂SO₄·MgSO₄·6H₂O的结晶区域总体呈增加趋势。
