Separations

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13 pages, 4706 KiB

Open AccessArticle

Preparation of Lithium Carbonate from Manganese-Containing Desorption Solution from Salt Lakes via an Organophosphoric Acid Extraction System

by Shaolei Xie, Yuze Zhang, Xiaowu Peng, Yong Niu, Hailong Lu, Fugen Song, Dong Shi and Lijuan Li

Separations 2025, 12(4), 98; https://doi.org/10.3390/separations12040098 - 15 Apr 2025

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Abstract

Adsorption is a popular method for the recovery of low-grade lithium. It is a low-cost and highly efficient way to treat solutions with low lithium concentrations. The impurity content determines the industrial application. This study investigated a novel strategy to remove divalent cations [...] Read more.

Adsorption is a popular method for the recovery of low-grade lithium. It is a low-cost and highly efficient way to treat solutions with low lithium concentrations. The impurity content determines the industrial application. This study investigated a novel strategy to remove divalent cations from a desorption solution containing Mg²⁺, Ca²⁺, and Mn²⁺, generated by a manganese absorbent using an organophosphoric acid, followed by precipitation of lithium carbonate from the concentrated raffinate by evaporation. Di(2-ethylhexyl)phosphoric acid (P204) was selected as the preferred extractant. The saponification method and degree of saponification were determined, and the extraction parameters (pH, extractant concentration, and phase ratio) were investigated. A three-stage countercurrent extraction process was tested. Removal efficiencies of Mg²⁺, Ca²⁺, and Mn²⁺ from the manganese-containing desorption solution exceeded 99%, leaving <1.0 mg/L divalent cations in the raffinate. The raffinate was evaporated and concentrated to >23 g/L lithium. The total concentration of divalent cations in the lithium-rich solution was approximately 10.0 mg/L. Further conversion with sodium carbonate was carried out to prepare a battery-grade lithium carbonate product with a purity of 99.83%. The present work may provide a novel means of lithium recovery from a manganese-containing desorption solution. Full article

(This article belongs to the Special Issue Green and Efficient Separation and Extraction of Salt Lake Resources)

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21 pages, 13811 KiB

Open AccessArticle

Experimental Study on Brine Storage for Overwintering by Using Salinity-Gradient Solar Pond in Zabuye Salt Lake, Tibet

by Qian Wu, Yunsheng Wang, Jintao Zhang, Ke Zhang, Juntao Li, Zhikui He, Lingzhong Bu, Jiangjiang Yu and Zhen Nie

Separations 2025, 12(2), 54; https://doi.org/10.3390/separations12020054 - 19 Feb 2025

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Abstract

Known as the “white oil”, lithium is a key raw material to support strategic emerging industries and future industrial development. Zabuye Salt Lake is the only one in Tibet, China that has so far realized the industrialization of lithium extraction from the salt [...] Read more.

Known as the “white oil”, lithium is a key raw material to support strategic emerging industries and future industrial development. Zabuye Salt Lake is the only one in Tibet, China that has so far realized the industrialization of lithium extraction from the salt lake brine. The green and low-cost lithium extraction technology by using the salinity-gradient solar pond (SGSP) adopted has always been paid much attention by lithium-related practitioners and researchers. In order to improve the lithium yield and grade of a single crystallization pond, the cross-year brine mixing method can be used to increase the initial temperature and CO₃²⁻ concentration of the raw brine for making the SGSP. The premise is to ensure that the summer brine with low Li⁺ and high CO₃²⁻ prepared in the previous year could be stored safely for overwintering with a minimal change in brine composition, for use in brine mixing in February and March of the next year, which can be realized by using the SGSP. In this paper, two experiments of brine storage for overwintering were carried out in the Zabuye mining area, Tibet in 2020 and 2021 by using the large-scale SGSP with an area of nearly 4000 m². The results show that during the operation of the SGSP in winter, the brine temperature in the lower convective zone (LCZ) can still rise to more than 20 °C and remain relatively stable, indicating that the coverage of surface ice layer not only has an effect of heat preservation and insulation on the SGSP, but also plays a positive role in the thermal storage capacity of the SGSP. The vertical distributions of brine temperature, density and salinity in the pond showed the ideal gradient curves increasing from top to bottom, and the concentrations of Li⁺ and CO₃²⁻ in the brine only decreased slightly. The structure of the salinity-gradient layer tended to stabilize faster when the brine filling depth was larger, but the boundary between the upper convective zone (UCZ) and the non-convective zone (NCZ) was relatively blurred. It is completely feasible to store the brine for overwintering by using the SGSP in the Zabuye mining area, and the experimental results could be directly scalable to larger industrial applications. It can not only provide high-quality raw brine for cross-year brine mixing, but also reduce the pressure of brine production, and a small amount of lithium mixed salt collected is helpful to increase the output of a single crystallization pond. Additionally, the potential challenges of maintaining the SGSP system during extreme winter conditions are described, and effective measures and suggestions are proposed to make the technology feasible in diverse climates. Full article

(This article belongs to the Special Issue Green and Efficient Separation and Extraction of Salt Lake Resources)

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13 pages, 3850 KiB

Open AccessArticle

Electromigration Separation of Lithium Isotopes with the Benzo-12-Crown-4-Ether (B12C4) System

by Zhiyu Zhao, Lianjing Mao, Tianyu Zheng, Xiao Li, Chunsen Ye, Pengrui Zhang, Huifang Li, Wei Sun and Jinhe Sun

Separations 2025, 12(2), 27; https://doi.org/10.3390/separations12020027 - 26 Jan 2025

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Abstract

Enriched lithium isotopes (⁶Li and ⁷Li) are essential in the nuclear energy industry, where ⁶Li is bombarded with neutrons to produce tritium for fusion reactions, while ⁷Li is used as a core coolant and pH regulator. Separation of [...] Read more.

Enriched lithium isotopes (⁶Li and ⁷Li) are essential in the nuclear energy industry, where ⁶Li is bombarded with neutrons to produce tritium for fusion reactions, while ⁷Li is used as a core coolant and pH regulator. Separation of ⁶Li and ⁷Li by electromigration is a promising method for producing enriched lithium isotopes that fulfill industrial needs. In this work, based on a previously proposed biphasic system electromigration routine, a three-stage system of ‘LiCl aqueous solution (anolyte)|B12C4-[EMIm][NTf₂] organic solution|NH₄Cl aqueous solution (catholyte)’ was constructed and the rules of lithium isotope separation and lithium-ion migration investigated. It was shown that the isotope enrichment effect of the catholyte was greatly affected by the experimental conditions, while that of the organic solution was less affected. As the B12C4 concentration increased, enhancement of ⁷Li enrichment in the catholyte and ⁶Li enrichment in the organic solution was observed, and α(C/O) and α(O/A) reached 0.975 and 1.018 at B12C4 of 0.5 mol/L. With the increase in current, migration time, and LiCl concentration, the isotope that was enriched in the catholyte trended from ⁷Li to ⁶Li (about 6 mA, 12 h or LiCl of 5 mol/L). Taking lithium-ion transport efficiency and lithium isotope separation effect into consideration together, a current of at least 6 mA, duration of at least 12 h, LiCl concentration of at least 1 mol/L and B12C4 concentration of 0.2 mol/L are suggested for the electromigration process. The work provides an important reference for system construction and experimental design of a biphasic electromigration separation method, which is expected to be an industrial alternative because of its environmental protection and high efficiency. Full article

(This article belongs to the Special Issue Green and Efficient Separation and Extraction of Salt Lake Resources)

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16 pages, 3550 KiB

Open AccessArticle

Phase Equilibrium of CO₂ Hydrate with Rubidium Chloride Aqueous Solution

by Ryonosuke Kasai, Leo Kamiya and Ryo Ohmura

Separations 2025, 12(1), 13; https://doi.org/10.3390/separations12010013 - 11 Jan 2025

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Abstract

Salt lakes are a rich source of metals used in various fields. Rubidium is found in small amounts in salt lakes, but extraction technology on an industrial scale has not been developed completely. Clathrate hydrates are crystalline compounds formed by the encapsulation of [...] Read more.

Salt lakes are a rich source of metals used in various fields. Rubidium is found in small amounts in salt lakes, but extraction technology on an industrial scale has not been developed completely. Clathrate hydrates are crystalline compounds formed by the encapsulation of guest molecules in cage-like structures made of water molecules. One of the most important properties for engineering practices of hydrate-based technologies is the comprehension of the phase equilibrium conditions. Phase equilibrium conditions of CO₂ hydrate in rubidium chloride aqueous solution with mass fractions of 0.05, 0.10, 0.15 and 0.20 were experimentally investigated in the pressure range from 1.27 MPa to 3.53 MPa, and the temperature was from 268.7 K to 280.6 K. The measured equilibrium temperature in this study decreased roughly in proportion to the concentration of the RbCl solution from the pure water system. This depression is due to the lowering of the chemical potential of water in the liquid phase by the dissolution of RbCl. Experimental results compared with other salt solution + CO₂ hydrate systems showed that the equilibrium temperatures decreased to a similar degree for similar mole fractions. Full article

(This article belongs to the Special Issue Green and Efficient Separation and Extraction of Salt Lake Resources)

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22 pages, 5851 KiB

Open AccessArticle

Ion Activity Coefficient of Sodium Halides in Anion-Exchange Polymers: Empirical Model Based on Manning’s Counterion Condensation Theory

by Guiming Liu and Dandan Gao

Separations 2024, 11(12), 360; https://doi.org/10.3390/separations11120360 - 23 Dec 2024

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Abstract

The theory of electrolyte solution provides a precise description of the thermodynamic state and non-ideality of electrolyte solutions, allowing for the accurate prediction of the crystallization separation process of Salt Lake brine. Analogously, we attempt to describe the non-ideality of ions in ion-exchange [...] Read more.

The theory of electrolyte solution provides a precise description of the thermodynamic state and non-ideality of electrolyte solutions, allowing for the accurate prediction of the crystallization separation process of Salt Lake brine. Analogously, we attempt to describe the non-ideality of ions in ion-exchange polymers based on Manning’s Counterion Condensation Theory, which was originally used to describe the thermodynamics of polyelectrolyte solutions, has amply proven the potential to extend to ion-exchange polymers. In this article, equilibrium solvent and solute concentrations in aminated cross-linked polystyrene AEM were determined experimentally as a function of external NaCl concentration, and ion activity coefficients in the membranes were obtained via a thermodynamic treatment. With the recombination and empirical parameters added to Manning’s model, the ion activity coefficient of NaCl and NaBr in the aminated cross-linked polystyrene AEM can be accurately described in concentration ranges of 0.01 mol·kg⁻¹~3 mol·kg⁻¹. Compared with the original model, the Coefficient of Determination between the improved model and the experimental data was increased from 0.65 to 0.95. The Residual Sum of Squares is reduced by about one order of magnitude, significantly improving the Manning model’s adaptability when applied to AEM. Full article

(This article belongs to the Special Issue Green and Efficient Separation and Extraction of Salt Lake Resources)

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10 pages, 2330 KiB

Open AccessArticle

The 288.2 K Isothermal Evaporation Experiment of Potassium Precipitation Brine in West Taijinair Salt Lake

by Yousheng Yang, Xiaowang Wu, Xudong Yu, Jiazheng Qin, Jianjun Su, Caixiong Quan and Pan Xu

Separations 2024, 11(12), 348; https://doi.org/10.3390/separations11120348 - 9 Dec 2024

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Abstract

Rubidium and cesium are important strategic resources, and West Taijinar Salt Lake is rich in rubidium and cesium reserves, while the concentration is low and the relationship with coexisting potassium and magnesium ions is complex. In order to understand the evaporative enrichment and [...] Read more.

Rubidium and cesium are important strategic resources, and West Taijinar Salt Lake is rich in rubidium and cesium reserves, while the concentration is low and the relationship with coexisting potassium and magnesium ions is complex. In order to understand the evaporative enrichment and salt precipitation patterns of rare elements such as lithium, rubidium, cesium, and boron of the brine after potassium precipitation in West Taijinar Salt Lake, the 288.2 K isothermal evaporation experiment was carried out. The experimental results show that during the evaporation process at 288.2 K, the following salts precipitate from the brine after potassium crystallization: halite (NaCl), bischofite (MgCl₂·6H₂O), carnallite (KCl·MgCl₂·6H₂O), hexahydrite (MgSO₄·6H₂O), epsomite (MgSO₄·7H₂O), boric acid (H₃BO₃), and lithium sulfate monohydrate (Li₂SO₄·H₂O). The concentrations of lithium and boron are significantly enriched, the content of Li⁺ was enriched from 1.7 g/L to 5.63 g/L, and the B₂O₃ content was enriched from 6.72 g/L to 50.78 g/L. The isomorphism phenomenon of Rb⁺, Cs⁺, and K⁺ makes Rb⁺ and Cs⁺ enter potassium ore to form solid solution-type carnallite ((K, Rb)MgCl₃·6H₂O, (K, Cs)MgCl₃·6H₂O)) and reduce the content of brine. This study provides data support for the development and comprehensive utilization of lithium, boron, rubidium, and cesium resources in West Taijinar Salt Lake. Full article

(This article belongs to the Special Issue Green and Efficient Separation and Extraction of Salt Lake Resources)

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11 pages, 2615 KiB

Open AccessArticle

Solid–Liquid Phase Equilibria of the Aqueous Quaternary System Rb⁺, Cs⁺, Mg²⁺//SO₄²⁻ - H₂O at T = 323.2 K

by Zhangfa Yu, Ying Zeng, Xuequn Li, Hongbo Sun, Longgang Li, Wanghai He, Peijun Chen and Xudong Yu

Separations 2024, 11(11), 309; https://doi.org/10.3390/separations11110309 - 27 Oct 2024

Cited by 1 | Viewed by 880

Abstract

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 [...] Read more.

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⁺, Cs⁺, Mg²⁺//SO₄²⁻ - H₂O 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)₂SO₄ and two double salts (Rb₂SO₄·MgSO₄·6H₂O, Cs₂SO₄·MgSO₄·6H₂O). The corresponding phase diagram consists of four quaternary invariant points, nine univariate curves, and six crystallization regions. Among these, the crystalline region for Cs₂SO₄·MgSO₄·6H₂O is the largest, while that for the single salt Cs₂SO₄ 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 MgSO₄ changes from MgSO₄·7H₂O (298.2 K) to MgSO₄·6H₂O (323.2 K). As the temperature increases, the phase regions for Rb₂SO₄, Cs₂SO₄, (Rb, Cs)₂SO₄, and Cs₂SO₄·MgSO₄·6H₂O expand, while the phase region of Rb₂SO₄·MgSO₄·6H₂O contracts, indicating that the single salts (Rb₂SO₄, Cs₂SO₄) 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. Full article

(This article belongs to the Special Issue Green and Efficient Separation and Extraction of Salt Lake Resources)

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13 pages, 5851 KiB

Open AccessArticle

High-Efficiency Selective Adsorption of Rubidium and Cesium from Simulated Brine Using a Magnesium Ammonium Phosphate Adsorbent

by Haining Liu, Yanping Wang, Qiongyuan Zhang, Wenjie Han, Huifang Zhang and Xiushen Ye

Separations 2024, 11(9), 277; https://doi.org/10.3390/separations11090277 - 23 Sep 2024

Cited by 1 | Viewed by 1062

Abstract

Rubidium and cesium are critical strategic elements, and their development and utilization are of great significance. In this study, a magnesium ammonium phosphate (MAP) adsorbent was prepared and characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area analysis, and [...] Read more.

Rubidium and cesium are critical strategic elements, and their development and utilization are of great significance. In this study, a magnesium ammonium phosphate (MAP) adsorbent was prepared and characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area analysis, and Fourier transform infrared spectroscopy (FTIR). The adsorption performance of the adsorbent for Rb⁺ and Cs⁺ in solution was investigated. The results showed that the adsorbent exhibited high adsorption capacities of 2.83 mol/g for Rb⁺ and 4.37 mol/g for Cs⁺. In simulated brine, the adsorbent demonstrated excellent selectivity for Cs⁺. Kinetic and thermodynamic studies indicated that the adsorption process followed a pseudo-second order kinetic model and Langmuir isotherm model. The primary adsorption mechanism was an ion exchange. The development of this adsorbent holds significant promise for the extraction of rubidium and cesium from liquid resources. Full article

(This article belongs to the Special Issue Green and Efficient Separation and Extraction of Salt Lake Resources)

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