Solid–Liquid Phase Equilibria of the Aqueous Quaternary System Rb<sup>+</sup>, Cs<sup>+</sup>, Mg<sup>2+</sup>//SO<sub>4</sub><sup>2−</sup> - H<sub>2</sub>O at <i>T</i> = 323.2 K
Sulfate-type salt lakes constitute over half of the total salt lakes in China and are rich in rare elements, such as rubidium and cesium. However, the complex interactions between ions make the separation and extraction process quite challenging. To address this, phase equilibrium studies were condu...
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| Main Authors: | , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
MDPI AG
2024-10-01
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| Series: | Separations |
| Subjects: | |
| Online Access: | https://www.mdpi.com/2297-8739/11/11/309 |
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| Summary: | Sulfate-type salt lakes constitute over half of the total salt lakes in China and are rich in rare elements, such as rubidium and cesium. However, the complex interactions between ions make the separation and extraction process quite challenging. To address this, phase equilibrium studies were conducted on the sulfate system containing rubidium, cesium, and magnesium. Specifically, the phase equilibria of the aqueous quaternary system Rb<sup>+</sup>, Cs<sup>+</sup>, Mg<sup>2+</sup>//SO<sub>4</sub><sup>2−</sup> - H<sub>2</sub>O at 323.2 K were investigated using the isothermal dissolution method. The solubility, density, and refractive index of the system were experimentally measured. The results indicate that the system at 323.2 K belongs to a complex type with the formation of one solid solution (Rb, Cs)<sub>2</sub>SO<sub>4</sub> and two double salts (Rb<sub>2</sub>SO<sub>4</sub>·MgSO<sub>4</sub>·6H<sub>2</sub>O, Cs<sub>2</sub>SO<sub>4</sub>·MgSO<sub>4</sub>·6H<sub>2</sub>O). The corresponding phase diagram consists of four quaternary invariant points, nine univariate curves, and six crystallization regions. Among these, the crystalline region for Cs<sub>2</sub>SO<sub>4</sub>·MgSO<sub>4</sub>·6H<sub>2</sub>O is the largest, while that for the single salt Cs<sub>2</sub>SO<sub>4</sub> is the smallest. Moreover, the crystalline regions for the double salt and solid solutions are significantly larger than those for the single salt, highlighting the difficulty in separation of valuable single salts. A comparison of multi-temperature phase diagrams from 298.2 K to 323.2 K reveals that the crystalline form of MgSO<sub>4</sub> changes from MgSO<sub>4</sub>·7H<sub>2</sub>O (298.2 K) to MgSO<sub>4</sub>·6H<sub>2</sub>O (323.2 K). As the temperature increases, the phase regions for Rb<sub>2</sub>SO<sub>4</sub>, Cs<sub>2</sub>SO<sub>4</sub>, (Rb, Cs)<sub>2</sub>SO<sub>4</sub>, and Cs<sub>2</sub>SO<sub>4</sub>·MgSO<sub>4</sub>·6H<sub>2</sub>O expand, while the phase region of Rb<sub>2</sub>SO<sub>4</sub>·MgSO<sub>4</sub>·6H<sub>2</sub>O contracts, indicating that the single salts (Rb<sub>2</sub>SO<sub>4</sub>, Cs<sub>2</sub>SO<sub>4</sub>) are more readily precipitated at higher temperature, which provides theoretical guidance for the future production and separation of Rb, Cs, and Mg from sulfate-type salt lakes. |
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| ISSN: | 2297-8739 |