Extraction system and extraction method capable of efficiently extracting lithium from lithium-containing solution

Abstract

The invention discloses an extraction system and an extraction method capable of efficiently extracting lithium from a lithium-containing solution, dibenzoylmethane and tributyl phosphate are creatively compounded to serve as main extraction functional components, on one hand, the lithium extraction efficiency can be remarkably improved, the dosage of a composite extraction agent is greatly reduced, and corrosion of the extraction agent to extraction equipment is reduced; on the other hand, the organic phase after reverse extraction does not need to be regenerated and can be directly recycled, the extraction process is greatly shortened, and consumption of excessive acid and alkali and loss of the extraction agent are avoided; and on the other hand, the extraction system is low in cost and wide in applicability, lithium ions in lithium-containing solutions with different lithium ion concentrations and different sources can be extracted, the lithium extraction rate is high, the selectivity is good, and interference of hetero-ions can be well shielded.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion extraction technology, and particularly relates to an extraction system and extraction method for efficiently extracting lithium from lithium-containing solutions. Background Technology

[0002] Lithium extraction requires multiple purification steps. Classic processes typically involve evaporation and concentration, separation and impurity removal, and deep removal of calcium and magnesium ions to obtain a high-purity lithium-containing solution. This solution is then precipitated to obtain lithium carbonate. This process is complex, resulting in low Li recovery rates, high impurity content, and high costs. Solvent extraction, on the other hand, offers significant advantages due to its high metal ion separation coefficient, high selectivity, simple operation, low energy consumption, low cost, and large throughput. The extraction system used for lithium extraction is usually a TBP (tributyl phosphate) + FeCl3 system. During extraction, a certain acidity needs to be maintained to prevent iron hydrolysis. Back-extraction requires a higher concentration of acid to back-extract the metal ions, but this high concentration can break the phosphine-oxygen bonds in TBP, causing TBP degradation. Furthermore, this extraction system requires the addition of FeCl3 to promote lithium extraction, making it only suitable for acidic, high-chlorine conditions. However, the mother liquor for lithium precipitation is often a typical high-sodium, low-lithium alkaline brine system.

[0003] Besides these, common existing extractants also include β-diketone solvent systems (such as DBM), which generally achieve lithium recovery rates of over 90% and separation factors in the thousands, making them preferred extractants for lithium extraction from alkaline brines (including lithium precipitation mother liquor). β-diketones need to form a composite system with synergistic extractants (such as TOPO) to achieve optimal performance, because H... + It has a higher affinity for extractants than Li. + The β-diketone system requires saponification pretreatment (OH) - Attacking DBM completes deprotonation and loads Na. + To establish lithium selectivity. However, DBM is a solid at room temperature, and when used with organophosphorus oxides, it is prone to precipitate from the extraction system, and phase separation is also quite difficult due to the high viscosity of DBM.

[0004] Therefore, there is an urgent need to find an extraction system with good lithium selectivity, a clear phase separation interface, and the ability to mitigate extractant loss. Furthermore, solvent extraction methods often require highly acidic or alkaline environments for extraction and back-extraction, causing significant corrosion to equipment and shortening its service life. Therefore, it is also necessary to find suitable methods to reduce equipment corrosion and lower costs. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides an extraction system and method for efficiently extracting lithium from lithium-containing solutions. It creatively combines dibenzoylmethane and tributyl phosphate as the main extraction active ingredients. This significantly enhances lithium extraction efficiency, drastically reduces the amount of composite extractant used, and minimizes corrosion of the extraction equipment. Furthermore, the organic phase after back-extraction does not require regeneration and can be directly recycled, greatly shortening the extraction process and avoiding excessive consumption of acid and alkali, as well as extractant loss. Moreover, the extraction system is low-cost, widely applicable, and can extract lithium ions from lithium-containing solutions of different concentrations and sources, exhibiting high extraction rate and good selectivity, while effectively shielding against interference from impurities.

[0006] The present invention proposes an extraction system for efficient lithium extraction from lithium-containing solutions, the extraction system comprising: an extractant, a co-extractant, a phase modifier, and a diluent;

[0007] The extractant is dibenzoylmethane, and the co-extractant is tributyl phosphate.

[0008] In this invention, tributyl phosphate (TBP), which also has a P=O functional group, is used instead of organophosphorus oxides. The low cost of TBP (1 / 5 to 1 / 3 of the cost of TOPO) and the synergistic use of non-fluorinated dibenzoylmethane (DBM) significantly reduce the cost of the extractant. Operation at room temperature and pressure avoids the high energy consumption of wet processes. Regarding the process flow, the low viscosity of TBP alleviates the difficulty of phase separation in the DBM system, shortening the phase separation time to about 5 minutes. Furthermore, the integrated "extraction-washing-back-extraction" process replaces the multi-stage precipitation of wet processes, significantly improving efficiency and shortening the steps. In terms of lithium selectivity, the synergistic coordination of P=O and β-diketone enhances the extraction of Li. + High lithium recovery rates (≥99.8%) can be achieved through at least three stages of countercurrent extraction, while suppressing Na+ degradation. + The DBM system, which avoids the toxicity risks of fluorinated solvents, utilizes TBP's low toxicity to reduce occupational exposure hazards, and employs a closed-loop extractant recycling system to minimize waste, demonstrating high environmental friendliness. Unlike the traditional DBM-TOPO / TRPO system, which requires a highly alkaline pH ≥ 12, the DBM-TBP system only needs to maintain a pH ≥ 10.5 to achieve high-efficiency lithium extraction. This significantly reduces equipment corrosion and wear while minimizing alkali input, further lowering costs and enhancing industrial feasibility. In conclusion, the TBP+DBM system provides a low-cost, highly selective, and green new lithium extraction pathway for lithium precipitation mother liquor, and its large-scale application is expected to drive the low-carbon transformation of lithium resource extraction technology.

[0009] Preferably, the phase modifier is a C4-C10 alcohol compound and / or a phosphate ester compound;

[0010] Preferably, the phase modifier is at least one of n-octanol, n-butanol, or di(2-ethylhexyl) phosphate.

[0011] Preferably, the diluent is at least one of alcohols, ketones, ethers, and esters that have polar hydrophobic properties;

[0012] Preferably, the diluent is at least one of sulfonated kerosene, 120# solvent oil, 260# solvent oil, 2-octanone, 1-octanol, methyl isobutyl ketone, or methyl tert-butyl ether.

[0013] Preferably, the extractant further includes: a fortifying agent;

[0014] The reinforcing agent is a geminiamide surfactant, which is obtained by amidation of propylene diamine and chloroacetyl chloride, followed by quaternization of triethylamine.

[0015] The structural formulas of the above-mentioned geminiamide surfactants are shown below:

[0016]

[0017] In this invention, the gesiniamide surfactant can form a complex with TBP to ensure that TBP achieves a high extraction rate at a low concentration, and can also interact with lithium to reduce interference from other ions, thereby improving the extraction selectivity of lithium ions and further enhancing the extraction efficiency.

[0018] This invention also proposes an efficient extraction method for lithium extraction from lithium-containing solutions, comprising the following steps:

[0019] S1. After adjusting the lithium-containing solution to alkaline, the above extraction system is used for extraction to transfer lithium ions from the aqueous phase to the organic phase, resulting in a loaded organic phase and a raffinate phase.

[0020] S2. After back-extraction of the supported organic phase, lithium-rich aqueous phase and organic phase are obtained. The organic phase is returned to step S1 for recycling.

[0021] Preferably, the extraction system is obtained by mixing the co-extractant, phase modifier, and diluent, and then adding the extractant to dissolve them completely.

[0022] Preferably, the co-extractant, phase modifier, and diluent are used as a whole, with the co-extractant having a volume percentage of 25% vol-60% vol, the phase modifier having a volume percentage of 2% vol-8% vol, and the diluent having the remainder.

[0023] Preferably, the concentration of the extractant relative to the extraction system is 0.2-0.5 mol / L.

[0024] Preferably, adjusting the lithium-containing solution to alkaline is specifically achieved by adding alkali to the lithium-containing solution, stirring and mixing, and adjusting the pH value to 10-13.

[0025] Preferably, the lithium-containing solution is salt lake brine, lithium precipitation mother liquor, ore leachate, or battery leachate;

[0026] Preferably, the alkali is at least one selected from sodium hydroxide, potassium hydroxide, ammonia, sodium carbonate, or potassium carbonate.

[0027] Preferably, the extraction is achieved using multi-stage countercurrent extraction;

[0028] Preferably, the volume ratio of the extraction system to the lithium-containing solution is O / A = 1 / (0.5-4), the single-stage extraction temperature is 10℃-50℃, the stirring speed is 200rpm-550rpm, and the extraction time is 2min-10min.

[0029] Preferably, the number of extraction stages is 1 to 5, and the settling time for each stage is 1 min to 10 min.

[0030] Preferably, the Li in the supported organic phase + Concentration ≥1.8 g / L, Li in the raffinate phase + Concentration ≤ 0.15 g / L.

[0031] Preferably, the back-extraction is achieved using an acid solution or by introducing CO2;

[0032] Preferably, the acid solution is hydrochloric acid or sulfuric acid, with a concentration of 0.5 mol / L to 2.0 mol / L;

[0033] Preferably, the CO2 flow rate is 15-80 L / (h·L supported organic phase);

[0034] Preferably, in the back-extraction, the volume ratio of the supported organic phase to the aqueous phase is O / A = (4-10):1, and the back-extraction time is 5 min-10 min.

[0035] Compared with the prior art, the present invention has the following technical effects:

[0036] 1. Optimization of process efficiency

[0037] The extraction system of this invention effectively alleviates the phase separation problem of the traditional DBM system by utilizing the low viscosity characteristics of TBP, reducing the phase separation time to a minimum of only 1 minute, greatly improving operational efficiency and simplifying the process.

[0038] 2. Breakthrough in cost control

[0039] By using TBP (costing only 1 / 5 to 1 / 3 of TOPO) in combination with fluorine-free DBM, the overall cost of the extractant is reduced by 60-80%; the pH requirement of the system is reduced from ≥12 to ≥10.5, alkali consumption is reduced by more than 15%, and the operation at normal temperature and pressure avoids the energy consumption of high temperature and high pressure, resulting in an overall energy saving of 30%-40%; in addition, it has less corrosiveness to the equipment, further extending the equipment life and reducing maintenance costs. Attached Figure Description

[0040] Figure 1 This is a flowchart illustrating the method for efficiently extracting lithium from lithium-containing solutions according to an embodiment of the present invention. Detailed Implementation

[0041] The present invention will now be described in detail through specific embodiments. However, these embodiments are clearly provided for illustrative purposes and are not intended to limit the scope of the present invention.

[0042] Example 1

[0043] Reference Figure 1 This embodiment proposes an efficient lithium extraction method for lithium-containing solutions, which includes:

[0044] (1) Extraction system: 30% vol of tributyl phosphate (TBP) and 5% vol of n-octanol were dissolved in 65% vol of sulfonated kerosene according to the volume ratio. After stirring and mixing evenly, dibenzoylmethane (DBM) was added. After dissolving completely by stirring with gentle heat, the concentration of DBM was 0.3 mol / L, and the extraction system was obtained.

[0045] (2) Lithium extraction: Sodium hydroxide was added to the lithium precipitation mother liquor with a lithium content of 2.5 g / L and stirred until the pH value reached 11.5. The extraction system and the lithium precipitation mother liquor after alkalization were subjected to three-stage countercurrent extraction. The volume ratio of the extraction system to the lithium-containing solution was O / A = 1:2. The single-stage extraction temperature was 30℃, the stirring speed was 400 rpm, the extraction time was 3 min, and the phases were separated after standing for 3 min to allow lithium ions to transfer from the aqueous phase to the organic phase, resulting in a loaded organic phase and a raffinate phase. The residual lithium ion concentration in the raffinate phase was 0.14 g / L, and the lithium ion extraction rate was calculated to be 94.4%.

[0046] (3) Back-extraction and regeneration: The supported organic phase was back-extracted with a sulfuric acid solution with a concentration of 1.0 mol / L. The volume ratio of the supported organic phase to the aqueous phase was O / A = 5:1. The back-extraction time was 8 min, resulting in a lithium-rich aqueous phase and an organic phase. The lithium-rich aqueous phase was enriched with a lithium ion concentration of 22.4 g / L. The calculated back-extraction rate was 95.0%, and the total yield was approximately 90.0%.

[0047] Example 2

[0048] Reference Figure 1 This embodiment proposes an efficient lithium extraction method for lithium-containing solutions, which includes:

[0049] (1) Extraction system: 45% vol of tributyl phosphate (TBP) and 2% vol of di(2-ethylhexyl) phosphate were dissolved in 53% vol of 260# solvent oil according to the volume ratio. After stirring and mixing evenly, dibenzoylmethane (DBM) was added. After complete dissolution by stirring with gentle heat, the concentration of DBM was 0.4 mol / L, and the extraction system was obtained.

[0050] (2) Extraction of lithium: Sodium hydroxide was added to the leachate of waste batteries with a lithium content of 1.8 g / L. After stirring and mixing evenly, the pH value reached 10.5. During the pH adjustment process, precipitation occurred in the solution, mainly Fe(OH)3 and other impurities. After filtering the precipitate in the leachate, the extraction system and the alkaline-adjusted waste battery leachate were subjected to four-stage countercurrent extraction. The volume ratio of the extraction system to the lithium-containing solution was O / A = 1:1.8. The single-stage extraction temperature was 40℃, the stirring speed was 350 rpm, the extraction time was 4 min, and the phases were separated after standing for 2 min, so that lithium ions were transferred from the aqueous phase to the organic phase, and the loaded organic phase and the raffinate phase were obtained. The residual lithium ion concentration in the raffinate phase was 0.08 g / L. The lithium ion extraction rate was calculated to be 95.6%.

[0051] (3) Back-extraction and regeneration: The supported organic phase was back-extracted by passing CO2 gas through it. The volume ratio of the supported organic phase to pure water was O / A = 8:1. The CO2 flow rate was 50 L / (h·L supported organic phase), and the back-extraction time was 5 min. A lithium-rich aqueous phase and an organic phase were obtained. The lithium-rich aqueous phase was enriched with a lithium ion concentration of 23.8 g / L. The calculated back-extraction rate was 96.1%, and the total yield was approximately 91.9%.

[0052] Example 3

[0053] Reference Figure 1 This embodiment proposes an efficient lithium extraction method for lithium-containing solutions, which includes:

[0054] (1) Extraction system: 50% vol of tributyl phosphate (TBP) and 6% vol of n-octanol were dissolved in 44% vol of 120# solvent oil according to the volume ratio. After stirring and mixing evenly, dibenzoylmethane (DBM) was added. After dissolving completely by stirring with gentle heat, the concentration of DBM was 0.25 mol / L, and the extraction system was obtained.

[0055] (2) Extraction of lithium: Sodium carbonate was added to the brine with a lithium content of 0.8 g / L and stirred until the pH value reached 11.0. The extraction system and the alkaline-adjusted brine were subjected to three-stage countercurrent extraction. The volume ratio of the extraction system to the lithium-containing solution was O / A = 1:4. The single-stage extraction temperature was 25℃, the stirring speed was 300 rpm, the extraction time was 5 min, and the phases were separated after standing for 3 min to allow lithium ions to transfer from the aqueous phase to the organic phase, resulting in a loaded organic phase and a raffinate phase. The residual lithium ion concentration in the raffinate phase was 0.05 g / L, and the lithium ion extraction rate was calculated to be 93.7%.

[0056] (3) Back-extraction and regeneration: The supported organic phase is back-extracted by passing CO2 gas through it. The volume ratio of the supported organic phase to pure water is O / A = 6:1. The CO2 flow rate is 60 L / (h·L supported organic phase). The back-extraction time is 6 min. A lithium-rich aqueous phase and an organic phase are obtained. The lithium-rich aqueous phase is enriched with lithium ion concentration of 17.4 g / L. The calculated back-extraction rate is 96.6%, and the total yield is about 90.5%.

[0057] Example 4

[0058] Reference Figure 1 This embodiment proposes an efficient lithium extraction method for lithium-containing solutions, which includes:

[0059] (1) Extraction system: 25% vol of tributyl phosphate (TBP), 5% vol of n-octanol and 5% vol of geminiamide surfactant were dissolved in 65% vol of sulfonated kerosene according to the volume ratio. After stirring and mixing evenly, dibenzoylmethane (DBM) was added. After complete dissolution by stirring with gentle heat, the concentration of DBM was 0.3 mol / L, and the extraction system was obtained.

[0060] The geminiamide surfactant was prepared by the following method: chloroacetyl chloride was dissolved in dichloromethane, and 0.5 equivalents of 1,3-propanediamine of chloroacetyl chloride were added dropwise under an ice-water bath. After the addition was complete, the mixture was stirred in a water bath at 35°C for 4 hours. After removing the dichloromethane by rotary evaporation, the resulting product was dissolved in ethyl acetate, and 0.5 equivalents of triethylamine of chloroacetyl chloride were added. The mixture was stirred at room temperature for 6 hours, and after removing the solvent by vacuum distillation, the resulting product was recrystallized twice with ethyl acetate to obtain the geminiamide surfactant.

[0061] (2) Lithium extraction: Sodium hydroxide was added to the lithium precipitation mother liquor with a lithium content of 2.5 g / L and stirred until the pH value reached 11.5. The extraction system and the lithium precipitation mother liquor after alkalization were subjected to three-stage countercurrent extraction. The volume ratio of the extraction system to the lithium-containing solution was O / A = 1:2. The single-stage extraction temperature was 30℃, the stirring speed was 400 rpm, the extraction time was 3 min, and the phases were separated after standing for 3 min to allow lithium ions to transfer from the aqueous phase to the organic phase, resulting in a loaded organic phase and a raffinate phase. The residual lithium ion concentration in the raffinate phase was 0.04 g / L, and the lithium ion extraction rate was calculated to be 98.4%.

[0062] (3) Back-extraction and regeneration: The supported organic phase was back-extracted with a sulfuric acid solution with a concentration of 1.0 mol / L. The volume ratio of the supported organic phase to the aqueous phase was O / A = 5:1. The back-extraction time was 8 min, resulting in a lithium-rich aqueous phase and an organic phase. The lithium-rich aqueous phase was enriched with a lithium ion concentration of 23.6 g / L. The calculated back-extraction rate was 96.0%, and the total yield was approximately 94.4%.

[0063] Comparative Example 1

[0064] Reference Figure 1 This comparative example proposes an efficient extraction method for lithium extraction from lithium-containing solutions, comprising:

[0065] (1) Extraction system: 25% vol of tributyl phosphate (TBP), 5% vol of n-octanol and 5% vol of N,N-dioctylacetamide were dissolved in 65% vol of sulfonated kerosene according to the volume ratio. After stirring and mixing evenly, dibenzoylmethane (DBM) was added. After complete dissolution by stirring with gentle heat, the concentration of DBM was 0.3 mol / L, and the extraction system was obtained.

[0066] (2) Extraction of lithium: Sodium hydroxide was added to the lithium precipitation mother liquor with a lithium content of 2.5 g / L and stirred until the pH value reached 11.5. The extraction system and the lithium precipitation mother liquor after alkalization were subjected to three-stage countercurrent extraction. The volume ratio of the extraction system to the lithium-containing solution was O / A = 1:2. The single-stage extraction temperature was 30℃, the stirring speed was 400 rpm, the extraction time was 3 min, and the phases were separated after standing for 3 min to allow lithium ions to transfer from the aqueous phase to the organic phase, resulting in a loaded organic phase and a raffinate phase. The residual lithium ion concentration in the raffinate phase was 0.15 g / L, and the lithium ion extraction rate was calculated to be 94.0%.

[0067] (3) Back-extraction and regeneration: The supported organic phase was back-extracted with a sulfuric acid solution with a concentration of 1.0 mol / L. The volume ratio of the supported organic phase to the aqueous phase was O / A = 5:1. The back-extraction time was 8 min, resulting in a lithium-rich aqueous phase and an organic phase. The lithium-rich aqueous phase was enriched with a lithium ion concentration of 22.2 g / L. The calculated back-extraction rate was 94.5%, and the total yield was approximately 88.8%.

[0068] As can be seen from the above, the extraction system involved in this invention can significantly improve lithium extraction efficiency, greatly reduce the amount of extraction system used, and reduce the corrosion of extraction equipment by the extractant. This extraction system exhibits good phase separation, with no emulsification or third phase formation, greatly reducing the solubility loss of the extractant in the mixed aqueous phase and its degradation under acidic and alkaline environments. Furthermore, compared to general amide compounds, the introduction of gemini amide-type surfactants can further improve the extraction selectivity of lithium ions, thereby further enhancing the extraction effect.

[0069] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. An extraction system for efficiently extracting lithium from lithium-containing solutions, characterized in that, The extraction system includes: an extractant, a co-extractant, a phase modifier, and a diluent; The extractant is dibenzoylmethane, and the co-extractant is tributyl phosphate.

2. The extraction system for efficiently extracting lithium from lithium-containing solutions according to claim 1, characterized in that, The phase modifier is a C4-C10 alcohol compound and / or a phosphate ester compound; Preferably, the phase modifier is at least one of n-octanol, n-butanol, or di(2-ethylhexyl) phosphate.

3. The extraction system for efficiently extracting lithium from lithium-containing solutions according to claim 1 or 2, characterized in that, The diluent is at least one of alcohols, ketones, ethers, and esters that have polar hydrophobic properties; Preferably, the diluent is at least one of sulfonated kerosene, 120# solvent oil, 260# solvent oil, 2-octanone, 1-octanol, methyl isobutyl ketone, or methyl tert-butyl ether.

4. The extraction system for efficiently extracting lithium from lithium-containing solutions according to any one of claims 1-3, characterized in that, The extractant also includes: a fortifying agent; The reinforcing agent is a geminiamide surfactant, which is obtained by amidation of propylene diamine and chloroacetyl chloride, followed by quaternization of triethylamine.

5. An extraction method for efficiently extracting lithium from lithium-containing solutions, characterized in that, Includes the following steps: S1. After adjusting the lithium-containing solution to alkaline, extraction is performed using the extraction system described in any one of claims 1-4, so that lithium ions are transferred from the aqueous phase to the organic phase, and a loaded organic phase and a raffinate phase are obtained. S2. After back-extraction of the supported organic phase, lithium-rich aqueous phase and organic phase are obtained. The organic phase is returned to step S1 for recycling.

6. The extraction method for efficiently extracting lithium from lithium-containing solutions according to claim 5, characterized in that, The extraction system is obtained by mixing the co-extractant, phase modifier and diluent, and then adding the extractant to dissolve them completely. Preferably, the co-extractant, phase modifier, and diluent are used as a whole, with the co-extractant having a volume percentage of 25% vol-60% vol, the phase modifier having a volume percentage of 2% vol-8% vol, and the diluent having the remainder. Preferably, the concentration of the extractant relative to the extraction system is 0.2-0.5 mol / L.

7. The extraction method for efficiently extracting lithium from lithium-containing solutions according to claim 5 or 6, characterized in that, The process of adjusting the lithium-containing solution to alkaline is specifically achieved by adding alkali to the lithium-containing solution, stirring and mixing, and adjusting the pH value to 10-13. Preferably, the lithium-containing solution is salt lake brine, lithium precipitation mother liquor, ore leachate, or battery leachate; Preferably, the alkali is at least one selected from sodium hydroxide, potassium hydroxide, ammonia, sodium carbonate, or potassium carbonate.

8. The extraction method for efficiently extracting lithium from lithium-containing solutions according to any one of claims 5-7, characterized in that, The extraction is achieved using multi-stage countercurrent extraction. Preferably, the volume ratio of the extraction system to the lithium-containing solution is O / A = 1 / (0.5-4), the single-stage extraction temperature is 10℃-50℃, the stirring speed is 200rpm-550rpm, and the extraction time is 2min-10min. Preferably, the number of extraction stages is 1 to 5, and the settling time for each stage is 1 min to 10 min.

9. The extraction method for efficiently extracting lithium from lithium-containing solutions according to any one of claims 5-8, characterized in that, Li in the supported organic phase + Concentration ≥1.8 g / L, Li in the raffinate phase + Concentration ≤ 0.15 g / L.

10. The extraction method for efficiently extracting lithium from a lithium-containing solution according to any one of claims 5-9, characterized in that, The back-extraction is achieved using an acid solution or by introducing CO2. Preferably, the acid solution is hydrochloric acid or sulfuric acid, with a concentration of 0.5 mol / L to 2.0 mol / L; Preferably, the CO2 flow rate is 15-80 L / (h·L supported organic phase); Preferably, the volume ratio of the supported organic phase to the aqueous phase is O / A = (4-10):1, and the back-extraction time is 5 min-10 min.

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