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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2024-10-01
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| author | Zhangfa Yu Ying Zeng Xuequn Li Hongbo Sun Longgang Li Wanghai He Peijun Chen Xudong Yu |
| author_facet | Zhangfa Yu Ying Zeng Xuequn Li Hongbo Sun Longgang Li Wanghai He Peijun Chen Xudong Yu |
| author_sort | Zhangfa Yu |
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| description | 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. |
| format | Article |
| id | doaj-art-2f1dc764ae22431795ada4befc87f51b |
| institution | OA Journals |
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| language | English |
| publishDate | 2024-10-01 |
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| spelling | doaj-art-2f1dc764ae22431795ada4befc87f51b2025-08-20T01:53:56ZengMDPI AGSeparations2297-87392024-10-01111130910.3390/separations11110309Solid–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 KZhangfa Yu0Ying Zeng1Xuequn Li2Hongbo Sun3Longgang Li4Wanghai He5Peijun Chen6Xudong Yu7CITIC Guoan Industrial Group Co., Ltd., Beijing 100004, ChinaSulfate-Type Salt Lake Utilization Key Lab of Qinghai Province, Golmud 816099, ChinaCITIC Guoan Industrial Group Co., Ltd., Beijing 100004, ChinaSulfate-Type Salt Lake Utilization Key Lab of Qinghai Province, Golmud 816099, ChinaSulfate-Type Salt Lake Utilization Key Lab of Qinghai Province, Golmud 816099, ChinaSulfate-Type Salt Lake Utilization Key Lab of Qinghai Province, Golmud 816099, ChinaCollege of Materials and Chemistry & Chemical Engineering, Chengdu University of Technology, Chengdu 610059, ChinaSulfate-Type Salt Lake Utilization Key Lab of Qinghai Province, Golmud 816099, ChinaSulfate-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.https://www.mdpi.com/2297-8739/11/11/309phase equilibriarubidiumcesiumsolid solutiondouble salt |
| spellingShingle | Zhangfa Yu Ying Zeng Xuequn Li Hongbo Sun Longgang Li Wanghai He Peijun Chen Xudong Yu 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 Separations phase equilibria rubidium cesium solid solution double salt |
| title | 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 |
| title_full | 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 |
| title_fullStr | 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 |
| title_full_unstemmed | 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 |
| title_short | 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 |
| title_sort | 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 |
| topic | phase equilibria rubidium cesium solid solution double salt |
| url | https://www.mdpi.com/2297-8739/11/11/309 |
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