A method for efficiently and selectively extracting uranium from seawater by using a hydrophobic deep eutectic solvent

Abstract

Uranium ions (UO2 2+ ) in seawater are abundant, but their extremely low concentration severely restricts the extraction efficiency. In this study, two novel hydrophobic deep eutectic solvents (HDESs) were synthesized with tributyl phosphate (TBP) as a hydrogen bond acceptor and octanoic acid (OA) and 2-thiophenecarbonyl trifluoroacetone (HTTA) as hydrogen bond donors, respectively, for the selective extraction of UO2 2+ + from seawater. The single-stage extraction efficiencies of both HDESs were over 99% at low dosages and short contact times, and they exhibited selectivity in the presence of various coexisting ions. Efficient back-extraction of UO2 2+ + and regeneration of the HDESs were achieved by sulfuric acid and ammonium sulfate, respectively. The overall performance of [TBP][HTTA] was the best after multiple cycles. This extraction system is simple to prepare, cost-controllable, and recyclable, and it has good economic and environmental benefits. It has application potential in the field of uranium extraction from seawater.

Description

Technical Field

[0001] This invention belongs to the field of extraction chemistry and chemical separation and purification technology, specifically relating to a method for the efficient and selective extraction of uranium from seawater using a hydrophobic eutectic solvent. Background Technology

[0002] Nuclear energy, as a low-carbon and efficient non-fossil energy source, holds significant strategic importance for alleviating the global energy crisis and reducing greenhouse gas emissions. However, terrestrial uranium resources are limited, estimated to last only 80 to 120 years. In contrast, seawater uranium reserves total approximately 4.5 billion tons, exceeding terrestrial reserves by more than three orders of magnitude. If advanced marine extraction technology can be used to efficiently recover uranium from seawater, it will not only overcome the constraint of uneven geographical distribution of uranium resources but also provide a fuel guarantee for nuclear energy for thousands of years, possessing significant strategic value for ensuring long-term energy security. Therefore, seawater uranium extraction is considered one of the most promising chemical separation technologies, expected to have a profound impact on the future energy landscape.

[0003] Currently, various methods for uranium recovery have been developed, mainly including chemical precipitation, membrane separation, adsorption, and ion exchange. However, ion exchange suffers from frequent equipment maintenance and difficulties in material regeneration; precipitation easily generates large amounts of sludge, causing secondary pollution; and reduction methods are highly dependent on chemical reagents, increasing operating costs and environmental burden. Overall, these methods still face many challenges in terms of operational efficiency, large-scale application, and economic feasibility. In contrast, solvent extraction, due to its high extraction efficiency and good selectivity, has attracted widespread attention in the field of uranium separation and recovery.

[0004] Eutectic solvents, first reported by Abbott et al. in 2003, are a novel class of "green solvents" formed by mixing hydrogen bond acceptors and hydrogen bond donors in a specific stoichiometric ratio. They possess advantages such as tunable physicochemical properties, high thermal stability, and low volatility. However, the high water solubility of traditional eutectic solvents limits their application in aqueous extraction systems. To address this issue, researchers have developed hydrophobic eutectic solvents, expanding their application range in aqueous systems. Currently, hydrophobic eutectic solvents show broad application prospects in the selective extraction and separation of radioactive elements, rare elements, and high-value elements. Tributyl phosphate (TBP), due to its high electron cloud density and strong coordination ability of the P=O group, exhibits excellent extraction performance for metal ions. β-diketones and carboxylic acids can act as hydrogen bond donors, forming hydrophobic eutectic solvents with a synergistic extraction effect with TBP. Based on the above ideas, this invention aims to develop a novel hydrophobic eutectic solvent extraction system with TBP as the hydrogen bond acceptor and β-diketone or carboxylic acid as the hydrogen bond donor, for the efficient and highly selective extraction of uranyl ions in seawater, which has important research significance and practical application value. Summary of the Invention

[0005] To address the technical challenges posed by existing extraction methods, such as the large dosage of traditional extractants, extremely low uranium content in seawater, numerous and varied coexisting interfering ions, and the economic feasibility of uranium extraction from seawater in complex marine environments, this invention provides a method for selectively extracting uranyl ions from seawater using a hydrophobic eutectic solvent. This method uses a hydrophobic eutectic solvent formed by tributyl phosphate with octanoic acid and 2-thiophenecarboxylic acid trifluoroacetone as the extractant, achieving highly efficient and selective extraction of trace uranyl ions from seawater.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: 1. A method for selectively extracting uranium from seawater using a hydrophobic eutectic solvent, characterized by comprising the following steps; (1) One-step synthesis of extractant: The extractant is composed of two hydrophobic eutectic solvents, which are composed of hydrogen bond acceptor and hydrogen bond donor respectively; wherein, the hydrogen bond acceptor is tributyl phosphate, and the hydrogen bond donor is octanoic acid and 2-thiophenecarboxyltrifluoroacetone; (2) Preparation of simulated seawater: A simulated solution of Yellow Sea seawater containing sodium, calcium, magnesium, potassium, copper, iron, nickel, zinc and uranyl ions is prepared as the aqueous phase; (3) Optimization of extraction process conditions: The effects of temperature, extraction time, phase ratio and pH value on extraction performance are investigated; (4) Extraction equilibrium study: Metal extraction equilibrium experiment is carried out using a constant temperature water ring liquid-liquid phase equilibrium vessel. The metal residual concentration in the raffinate phase is determined by inductively coupled plasma mass spectrometry, and the extraction efficiency and selectivity of each metal ion are calculated according to the law of conservation of mass; (5) Back-extraction and recovery: A suitable back-extraction solvent is selected to realize the back-extraction of uranyl ions and the recovery and reuse of hydrophobic eutectic solvent.

[0007] As another preferred embodiment of the method of the present invention, the extractant is characterized in that: the extractant is composed of two hydrophobic eutectic solvents consisting of tributyl phosphate, octanoic acid and 2-thiophenecarboxylic acid trifluoroacetone in a molar ratio of 1:1.

[0008] As another preferred embodiment of the method of the present invention, the hydrophobic eutectic solvent is synthesized under the following conditions: a hydrogen bond donor to hydrogen bond acceptor molar ratio of 1:1, a synthesis temperature of 80°C, and a synthesis time of 30 min.

[0009] As another preferred embodiment of the method of the present invention, the pH value of the aqueous phase in the extraction process is 4-8.

[0010] As another preferred embodiment of the method of the present invention, the extraction temperature is 20-40℃.

[0011] As another preferred embodiment of the method of the present invention, the extraction time is 2-20 min.

[0012] As another preferred embodiment of the method of the present invention, the ratio of the extractant to the aqueous phase is 1:1, 1:4, 1:5, 1:90000, or 1:100000.

[0013] As another preferred embodiment of the method of the present invention, the concentrations of metal ions in the simulated seawater are: Na + (NaCl, 10800 mg·L) -1 ), Ca 2+ (CaCl2·2H2O, 413 mg·L -1 ) Mg 2+ (MgCl2·6H2O, 1290 mg·L -1 ), K + (KCl, 400 mg·L -1 ), UO2 2+ (UO2(CH3COO)2·2H2O, 3.30μg·L -1 Cu 2+ (CuSO4·5H2O, 1.00 μg·L -1 ), Fe 3+ (FeCl3·6H2O, 3.40 μg·L -1 ), Ni 2+ (NiCl2·6H2O, 6.60 μg·L -1 ) and Zn 2+ (Zn(NO3)2·6H2O, 5.00 μg·L -1 Under the optimal process conditions of each extraction system, the method is effective for UO2. 2+ It exhibits excellent selectivity.

[0014] As another preferred embodiment of the method of the present invention, the method is characterized in that: in the back-extraction process conditions, the sulfuric acid concentration is 4-6 mol / L, the ammonium sulfate concentration is 1-3 mol / L, and the ratio of the hydrophobic eutectic solvent phase loaded with uranyl ions to the back-extractant is 1:1.

[0015] The present invention also provides the application of the above-mentioned hydrophobic eutectic solvent or the above-mentioned method in the field of uranium extraction from seawater.

[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention constructs two hydrophobic eutectic solvents, which are effective against uranyl ions (UO2). 2+It exhibits excellent selective extraction capabilities, enabling efficient enrichment of trace uranium from complex seawater systems containing multiple competing ions.

[0017] (2) The hydrophobic eutectic solvent used in the method is an extractant, which has the advantages of simple synthesis process, convenient operation and low cost. At the same time, the extractant has extremely low solubility in the aqueous phase, and there is almost no loss during the extraction process, thus avoiding secondary pollution of the aqueous phase by organic solvents.

[0018] (3) The hydrophobic eutectic solvent raw material selected in this invention is relatively inexpensive, and the solvent can be recovered and recycled after extraction through back extraction, which significantly reduces production costs, improves the efficiency of comprehensive resource utilization, and has good economic and environmental benefits. Attached Figure Description

[0019] Figure 1 This is a process flow diagram of the present invention for the efficient and selective extraction of uranium from seawater using a hydrophobic eutectic solvent. Detailed Implementation

[0020] Example 1: Preparation and preliminary extraction performance evaluation of hydrophobic eutectic solvent Using tributyl phosphate (TBP) as the hydrogen bond acceptor and octanoic acid (OA) and 2-thiophenecarboxylic acid trifluoroacetone (HTTA) as hydrogen bond donors, the hydrogen bond acceptor and donors were mixed at a molar ratio of 1:1 and stirred in a magnetic stirrer at 80°C for 30 min until a homogeneous and transparent liquid was formed. After natural cooling, two hydrophobic eutectic solvents were obtained, denoted as [TBP][OA] and [TBP][HTTA], respectively. Simulated seawater was prepared as the aqueous phase, with the following composition: Na... + (NaCl, 10800 mg·L) -1 ), Ca 2+ (CaCl2·2H2O, 413 mg·L -1 ) Mg 2+ (MgCl2·6H2O, 1290 mg·L -1 ), K + (KCl, 400 mg·L) -1 ), UO2 2+ (UO2(CH3COO)2·2H2O, 3.30 μg·L -1 Cu 2+ (CuSO4·5H2O, 1.00 μg·L -1 ), Fe 3+ (FeCl3·6H2O, 3.40 μg·L -1 ), Ni 2+(NiCl2·6H2O, 6.60 μg·L -1 ) and Zn 2+ (Zn(NO3)2·6H2O, 5.00 μg·L -1 Two hydrophobic eutectic solvents were used as the organic phase and mixed with simulated seawater at a ratio of O / A = 1:1. Extraction was performed at room temperature with shaking for 10 min. After extraction, the phases were separated by centrifugation, and the lower aqueous phase was collected. The residual concentrations of each metal ion were determined by inductively coupled plasma mass spectrometry (ICP-MS), and the extraction efficiency was calculated based on the law of conservation of mass. The results showed that, under unoptimized conditions, the two extractants were effective for UO2. 2+ The single-stage extraction efficiency reached over 96%, demonstrating excellent extraction capability.

[0021] Example 2: Optimization of extraction process conditions Using the two hydrophobic eutectic solvents prepared in Example 1, and simulating seawater as the aqueous phase, the effects of extraction time, phase ratio, pH value, and other conditions on UO2 were investigated. 2+ The effect of extraction efficiency was investigated to determine the optimal process parameters for each extraction system. For the [TBP][OA] extraction system, under the conditions of extraction time 3 min, O / A = 1:4, aqueous phase pH = 4-8, and room temperature, UO2 2+ The single-stage extraction efficiency reached over 99%. For the [TBP][HTTA] extraction system, under the conditions of 10 min extraction time, O / A = 1:90000, aqueous phase pH = 4-8, and room temperature, UO2... 2+ The single-stage extraction efficiency reached over 99%. These results demonstrate that by optimizing the extraction conditions, both hydrophobic eutectic solvents can effectively extract trace amounts of UO2 from simulated seawater. 2+ Highly efficient extraction.

[0022] Example 3: Back-extraction and extractant regeneration experiment UO2 extracted in Example 2 2+ The two hydrophobic eutectic solvents were mixed with the back-extraction agent at a 1:1 ratio and placed in a constant-temperature water bath shaker for back-extraction experiments. After back-extraction, the mixtures were allowed to stand and separate into two phases. The aqueous phase was diluted and the UO2 was determined by ICP-MS. 2+ Concentration and calculation of back-extraction efficiency. The back-extraction conditions and results are as follows: For the [TBP][OA] system, using 1-3 mol / L ammonium sulfate as the back-extraction agent, the single-wash back-extraction efficiency can reach 99%; for the [TBP][HTTA] system, using 4-6 mol / L sulfuric acid as the back-extraction agent, the single-wash back-extraction efficiency can reach 97%. Experimental results show that both hydrophobic eutectic solvents can achieve UO2 extraction using suitable back-extraction agents. 2+It features highly efficient back-extraction, and the extractant can be regenerated and recycled.

Claims

1. A method for efficiently and selectively extracting uranyl ions from seawater using a hydrophobic eutectic solvent, characterized in that, Including the following steps: (1) Tributyl phosphate was mixed with octanoic acid or 2-thiophenecarboxylic acid trifluoroacetone and heated to prepare two hydrophobic eutectic solvents; (2) Preparation of Na + Ca 2+ Mg 2+ K + Cu 2+ Fe 3+ Ni 2+ Zn 2+ and UO2 2+ The simulated seawater solution was used as the aqueous phase; (3) The hydrophobic eutectic solvent obtained in step (1) is mixed with the aqueous phase obtained in step (2), and liquid-liquid extraction is performed under the conditions of set pH, extraction temperature, extraction time and phase separation to obtain the hydrophobic eutectic solvent phase loaded with uranyl ions and the raffinate aqueous phase. (4) The hydrophobic eutectic solvent phase loaded with uranyl ions obtained in step (3) is mixed with the back-extractant for back-extraction. After phase separation, the back-extracted aqueous phase containing uranyl ions and the recovered hydrophobic eutectic solvent phase are obtained.

2. The method according to claim 1, characterized in that, In step (1), the molar ratio of tributyl phosphate to octanoic acid or 2-thiophenecarboxylic acid trifluoroacetone is 1:

1. The mixture is heated at 80°C for 30 min to obtain two hydrophobic eutectic solvents.

3. The method according to claim 1, characterized in that, The pH of the aqueous phase in step (3) is 4-8.

4. The method according to claim 1, characterized in that, The extraction temperature in step (3) is 20-40℃.

5. The method according to claim 1, characterized in that, The extraction time in step (3) is 3-20 min.

6. The method according to claim 1, characterized in that, The volume ratio of the hydrophobic eutectic solvent to the aqueous phase in step (3) is 1:1, 1:4, 1:5, 1:90000, and 1:100000.

7. The method according to claim 1, characterized in that, The concentrations of each metal ion in the simulated seawater solution mentioned in step (2) are as follows: Na + (NaCl, 10800 mg·L) -1 ), Ca 2+ (CaCl2·2H2O, 413 mg·L -1 ) Mg 2+ (MgCl2·6H2O, 1290 mg·L -1 ), K + (KCl, 400 mg·L -1 ), UO2 2+ (UO2(CH3COO)2·2H2O, 3.30μg·L -1 Cu 2+ (CuSO4·5H2O, 1.00 μg·L -1 ), Fe 3+ (FeCl3·6H2O, 3.40 μg·L -1 ), Ni 2+ (NiCl2·6H2O, 6.60 μg·L -1 ) and Zn 2+ (Zn(NO3)2·6H2O, 5.00 μg·L -1 ).

8. The method according to claim 1, characterized in that, The back-extraction agent in step (4) is an aqueous solution containing 4-6 mol / L sulfuric acid and 1-3 mol / L ammonium sulfate. The volume ratio of the hydrophobic eutectic solvent phase loaded with uranyl ions to the back-extraction agent is 1:

1. The back-extraction temperature is 25℃ and the back-extraction time is 10 min.

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