A complex extractant and method for selective extraction of impurities from a lithium solution

Abstract

The present application belongs to the field of metal ion separation and purification, and particularly relates to a composite extractant and method for selective extraction and impurity removal of a lithium solution, wherein the composite extractant comprises a molar ratio of 1:1-5 of an extractant of formula 1 and an extractant of formula 2. Researches show that the combination of formula 1 and formula 2 and the combined control of the molar ratio of the two can achieve synergy and efficient selective separation of lithium and impurity elements.

Description

Technical Field

[0001] This invention relates to the field of metal ion separation and purification, and in particular to a method for lithium solution extraction, purification and impurity removal. Background Technology

[0002] With the rapid development of new energy vehicles and energy storage industries, the demand for lithium resources has increased dramatically. Currently, industrial lithium mainly comes from lithium mines, salt lake brine, and recycled waste batteries. However, whether it's the leachate obtained from the wet processing of ore and waste batteries, or the crude lithium solution from the salt lake brine system, it often contains a large amount of metallic impurities such as iron, aluminum, nickel, cobalt, manganese, and calcium. If these impurities are not thoroughly removed, they will not meet the purity requirements of battery-grade lithium salt products, seriously affecting battery performance. Therefore, developing efficient lithium solution purification and impurity removal technologies is of great significance for improving the comprehensive utilization rate of lithium resources.

[0003] For the purification and impurity removal of lithium solutions, current mainstream processes are mostly based on the differences in precipitation properties between impurity elements and lithium. Separation is achieved by adding alkaline reagents or oxidants to induce impurity precipitation. For example, Chinese patent application CN116995327A discloses a technique for adjusting the pH to 8-9 to remove nickel, cobalt, and manganese from lithium sulfate solutions; Chinese patent application CN110451535A discloses a method for simultaneously removing iron, nickel, cobalt, manganese, and fluoride ions using calcium peroxide in conjunction with pH adjustment. Although the above chemical precipitation methods can effectively reduce impurity concentrations, the colloidal substances such as hydroxides generated by the precipitation reaction have strong adsorption and entrainment effects, leading to significant lithium loss with the filter residue. Furthermore, Chinese patent application CN115180639A discloses a strategy for combined impurity removal using a sulfiding agent and an adsorbent, but the introduction of the sulfiding agent inevitably brings potential environmental pollution risks and subsequent treatment challenges.

[0004] To overcome the severe lithium entrainment loss problem in chemical precipitation methods, solvent extraction with higher selectivity has attracted much attention in the field of lithium solution purification. Existing extraction systems mainly include organophosphorus compounds, carboxylic acids, and co-extraction systems. For example, Chinese patent application CN112063847A discloses a method for one-step co-extraction of nickel, cobalt, and manganese and separation of lithium from acid leaching solutions of waste ternary cathode materials using P227 extractant. However, relying solely on P227 cannot completely avoid lithium co-extraction loss. To further improve separation efficiency, Chinese patent application CN111041203A discloses a co-extraction system of monosubstituted alkylphenoxycarboxylic acids and disubstituted phenoxycarboxylic acids. Although this improves the separation effect, the synthesis process of these unconventional extractants is complex, and the cost for industrial application is high. Furthermore, Chinese patent application CN113481367A discloses a co-extraction system composed of organophosphorus compounds and pyridine carboxylates for the separation of lithium and nickel, but its core component, pyridine carboxylates, has poor chemical stability in acidic environments.

[0005] In summary, existing technologies have reported many methods for removing impurities from lithium solutions, but the selectivity for separating lithium and impurities still needs to be further improved. Summary of the Invention

[0006] To address the problems of high lithium loss, high cost, and unsatisfactory purification effects in existing lithium solution purification and impurity removal processes, this invention proposes a composite extractant for selective extraction and impurity removal of lithium solutions. The aim is to provide a method that can directly and selectively extract and separate impurity ions from lithium solutions containing complex multimetallic impurities such as iron, aluminum, nickel, cobalt, manganese, calcium, and magnesium, thereby significantly reducing lithium loss and achieving efficient purification of lithium solutions.

[0007] The second objective of this invention is to provide a method for selectively extracting and removing impurities from lithium solutions using the aforementioned composite extractant.

[0008] A composite extractant for selective extraction and impurity removal from lithium solution, comprising extractant of formula 1 and extractant of formula 2 in a molar ratio of 1:1 to 5;

[0009] Formula 1;

[0010] Formula 2;

[0011] Among them, R1 and R2 are individually C4~C 14 alkyl or olefinic groups;

[0012] R3 and R4 are C individually. 6~ C 14 alkyl or C 6~ C 14 The alkoxy group; M is H, Na, K or NH4.

[0013] To address the problem of unsatisfactory extraction selectivity of lithium and impurity elements, and to minimize the accompanying extraction loss of lithium while improving the extraction of impurity elements, this invention innovatively demonstrates that combining Formula 1 and Formula 2, along with the joint control of their molar ratio, can achieve synergy and enable highly efficient and selective separation of lithium and impurity elements.

[0014] In this invention, the molar ratio of the extractant of Formula 1 to the extractant of Formula 2 is 1:1.5~4; preferably 1:1.5~3; more preferably 1:1.8~2.2. At the preferred ratio, the separation selectivity of impurities and Li can be further improved.

[0015] In this invention, the composite extractant also includes a hydrophobic diluent; for example, it can be at least one of aviation kerosene, sulfonated kerosene, No. 260 solvent oil, GV-18A, Escaid 110, and C8~13 high carbon alcohols.

[0016] Preferably, the concentration of the extractant of Formula 1 in the composite extractant is 0.1~0.4M; more preferably 0.15~0.35M; and even more preferably 0.2~0.3M. Research in this invention shows that at this concentration, the accompanying extraction of lithium during impurity removal can be avoided, which helps to further improve its impurity removal selectivity.

[0017] The present invention also provides a method for selective extraction and impurity removal of lithium solution, wherein a lithium solution containing impurity ions and lithium ions to be treated is mixed with the composite extractant for extraction to obtain a loaded organic phase enriched with impurity ions and a purified lithium raffinate.

[0018] The impurity ions include at least one of iron, aluminum, nickel, cobalt, manganese, calcium, and magnesium.

[0019] The present invention demonstrates that, thanks to the combination of Formula 1 and Formula 2 in the specific ratio, a synergistic effect can be achieved, thereby enhancing the extraction selectivity of lithium and impurity elements.

[0020] In this invention, the lithium solution is at least one of lithium sulfate solution, lithium chloride solution, and lithium nitrate solution containing the impurity ions;

[0021] Preferably, the lithium concentration in the lithium solution is 2~30 g / L, and the impurity concentration is ≤5 g / L.

[0022] In this invention, the equilibrium pH of the aqueous phase during extraction is 2.0–5.5; preferably 3–4.5; and more preferably 3.5–4.5. Research in this invention shows that at this preferred pH, lithium extraction during impurity removal can be avoided, which helps to further improve the selectivity for impurity removal.

[0023] The pH value of the aqueous phase during the extraction process is controlled by saponifying the organic phase; the alkaline solution used in the saponification process is at least one of sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium carbonate, potassium carbonate, and ammonia water; the saponification rate of the organic phase is 10% to 90%, preferably 20% to 80%.

[0024] The number of extraction stages is 1 to 10; when the number of extraction stages is greater than or equal to 2, the extraction method is countercurrent extraction; the volume flow rate ratio of the organic phase to the aqueous phase during the extraction process is 1:10 to 10:1.

[0025] The supported organic phase is back-extracted to enrich impurity ions and regenerate the composite extractant;

[0026] Preferably, the supported organic phase needs to be washed before back-extraction; the washing process uses an aqueous solution of an inorganic acid as the washing agent, wherein the inorganic acid is at least one of sulfuric acid, hydrochloric acid, or nitric acid, and its H+ content is... +The concentration is 0.1~5 mol / L; the number of washing stages is 1~10; when the number of washing stages is greater than or equal to 2, the washing method is countercurrent washing; the volume flow ratio of organic phase to aqueous phase during the washing process is 1:1~30:1;

[0027] Preferably, the washed organic phase is subjected to single-stage or multi-stage countercurrent back-extraction using an aqueous solution of an inorganic acid; the inorganic acid is at least one of sulfuric acid, hydrochloric acid, or nitric acid, and its H+ content is... + The concentration is 0.1~5 mol / L; the number of back-extraction stages is 1~5, and the volume flow ratio of the organic phase to the aqueous phase during back-extraction is 1:1~15:1.

[0028] The present invention provides an example of a method for selectively extracting impurities from a lithium solution, comprising the following steps:

[0029] The first step is extraction: the organic phase containing the composite extractant is contacted with the lithium solution containing impurities for extraction. The impurities preferentially enter the organic phase, resulting in an organic phase loaded with impurities and a lithium solution without impurities, thus achieving the separation of lithium from impurities.

[0030] The second step is washing: The organic phase loaded with impurities obtained in the first step is brought into contact with a detergent for washing, resulting in a washed organic phase and a washing solution.

[0031] The third step is back-extraction: The washed or supported organic phase obtained in the second step is contacted with the back-extraction agent for back-extraction, yielding a back-extraction organic phase and a back-extraction solution containing a high concentration of impurity salts. The back-extraction organic phase can be returned to the first step extraction cycle directly or after saponification.

[0032] Beneficial effects

[0033] 1) This invention uses a synergistic extraction system to selectively remove impurities from lithium solutions, which can significantly reduce lithium entrainment loss compared to traditional chemical precipitation methods. Compared with a single extractant, the synergistic system of this invention has a higher separation coefficient and effectively avoids lithium co-extraction.

[0034] 2) The synergistic extraction system provided by this invention, with its excellent selectivity, can directly and efficiently extract various impurity metal ions such as iron, aluminum, nickel, cobalt, manganese, and calcium from lithium solution. The process is short, the chemical reagent consumption is low, the product quality is high, and it is easy to realize industrial application. Attached Figure Description

[0035] Figure 1 The mass spectrum of Equation 1a is shown below.

[0036] Figure 2 The NMR spectrum of Equation 1a is shown below. Detailed Implementation

[0037] To better understand the present invention, specific embodiments are described below, but the listed embodiments do not limit the scope of protection of the present invention.

[0038] In the embodiments, the distribution ratio D, separation coefficient β, and extraction rate E (%) are calculated according to equations (1) to (3), respectively:

[0039] D = C O / C R (1)

[0040] βM / Li=DM / DLi (2)

[0041] E=(C F ×V F -C R ×V R ) / (C F ×V F )×100% (3)

[0042] In equation (1), C O C R β represents the concentration of ions in the supported organic phase and the raffinate, respectively; in equation (2), β M / Li D represents the separation factor between the impurity metal and lithium. M D Li The numbers represent the distribution ratio of the impurity metal and lithium, respectively; in equation (3), C F C R V represents the concentration of metal ions in the feed solution and the raffinate, respectively. F V R These represent the volumes of the feed liquid and the raffinate, respectively.

[0043] Formula 1 of the present invention can be prepared by the following conventional substitution reaction:

[0044] X can be Cl; during the substitution reaction, an acid-binding agent is also added, which can be an alkaline component such as sodium hydroxide or TEA.

[0045] For example, a typical synthesis of formula 1a is as follows: Compound a is subjected to a substitution reaction with 1.2 eqv of compound b and 3 eqv of sodium hydroxide, yielding formula 1a; its mass spectrum is shown below. Figure 1 The hydrogen spectrum is shown below. Figure 2 .

[0046] .

[0047] Example 1

[0048] Aqueous phase: lithium sulfate solution containing 3.06 g / L nickel and 4.03 g / L lithium.

[0049] Organic phase: 1# organic phase is 0.75 mol / L formula 1a (compound 1) + sulfonated kerosene;

[0050] Organic phase #2 is 0.75 mol / L formula 2a ( Compound 2) + sulfonated kerosene;

[0051] The organic phase #3 is: 0.25 mol / L Formula 1a (compound 1) + 0.5 mol / L Formula 2a (compound 2) + sulfonated kerosene.

[0052] Extraction conditions: The above three organic phases were contacted with the aqueous phase solution for single-stage extraction, and the experiment numbers were 1#, 2# and 3# respectively. Saponification was performed using 10 mol / L sodium hydroxide solution, the equilibrium pH was controlled at 4.0, the O / A ratio was 1:1, the time was 10 min, and the temperature was 40°C.

[0053]

[0054] As shown in Table 1, when using Formula 1a alone for extraction, nickel and lithium are hardly extracted, with extraction rates of less than 1%; when using Formula 2a alone for extraction, the extraction rates of nickel and lithium are 89.87% and 25.06%, respectively, with separation coefficients β... Ni / Li The extraction efficiency was 26.52; when using the mixed organic phases of Formula 1a and Formula 2a in the stated proportions for extraction, the extraction rate of nickel reached 98.98%, while the extraction rate of lithium was only 1.48%, and the separation coefficient β... Ni / Li With a value as high as 6465.12, the separation effect between nickel and lithium is significantly improved, and the removal of nickel impurities in lithium solution has been achieved.

[0055] Example 2

[0056] Aqueous phase: lithium sulfate solution containing 0.38 g / L nickel, 0.28 g / L cobalt, 0.35 g / L manganese, 0.11 g / L calcium, and 20.05 g / L lithium.

[0057] Organic phase: The organic phase is 0.125 mol / L Formula 1b ( ) + 0.25 mol / L Formula 2a + sulfonated kerosene.

[0058] Extraction conditions: The organic phase and aqueous phase were contacted for three-stage countercurrent extraction. The equilibrium pH was adjusted to 2.0, 2.5, 3.0, 3.5, 4.0, 4.5 and 5.0 with concentrated ammonia. The O / A ratio was 1:1. The extraction time was 10 min and the temperature was 40°C. The experimental results are shown in Figure 2.

[0059]

[0060] Table 2 shows that during the extraction process, the extraction rates of impurities such as nickel, cobalt, manganese, and calcium, as well as lithium, increased synchronously with the increase of the aqueous phase equilibrium pH. The results indicate that the aqueous phase equilibrium pH is a key factor affecting the separation efficiency of impurities and lithium in this extraction system. When the aqueous phase equilibrium pH is controlled at 3.5, the removal rates of nickel, cobalt, and manganese reach 99.47%, 98.21%, and 98.28%, respectively, while the calcium removal rate is 59.09%, and the lithium co-extraction loss rate is only 0.69%. When the pH is increased to 4.0, the removal rates of nickel, cobalt, and manganese all exceed 99%, the calcium removal rate significantly increases to 96.36%, and the lithium co-extraction loss rate remains at a low level of 0.99%. However, when the pH continues to rise to 5.0, the lithium co-extraction loss rate surges to 6.03%. Therefore, to ensure a high lithium recovery rate, the aqueous phase equilibrium pH during the extraction process should not exceed 4.5.

[0061] Example 3

[0062] Aqueous phase: lithium chloride solution containing 1.67 g / L nickel, 0.23 g / L cobalt, 0.36 g / L calcium, and 15.69 g / L lithium.

[0063] Organic phase: Formula 1c ( (Compound 1) + Formula 2a (Compound 2) + sulfonated kerosene, controlling the total concentration of Compound 1 and Compound 2 to be 0.6 mol / L, and the ratio of Compound 1 to Compound 2 to be 1:1, 1:2, 1:3, 1:4, and 1:5, respectively.

[0064] Extraction conditions: The organic phase and aqueous phase were contacted for four-stage countercurrent extraction. The outlet equilibrium pH was controlled at 3.5, the O / A ratio was 1:1, the time was 10 min, and the temperature was 40°C. The experimental results are shown in Figure 3.

[0065]

[0066] Table 3 shows that during the extraction process, as the proportion of compound 2 increases, the extraction rates of nickel, cobalt, calcium impurities, and lithium increase simultaneously. However, excessively high proportions of compound 2 lead to co-extraction of more lithium, while low proportions result in insufficient calcium removal. When the ratio of compound 1 to compound 2 is 1:1, the removal rates of nickel and cobalt reach 99.82% and 99.13%, respectively, but the calcium removal rate is only 93.30%. When the ratio of compound 1 to compound 2 is 1:4, the removal rates of nickel, cobalt, and calcium reach 89.82%, 89.56%, and 98.86%, respectively, with a lithium co-extraction rate of 5.54%. Although the calcium removal rate is high, the removal rates of nickel and cobalt are insufficient, and lithium loss is significant. When the ratio of compound 1 to compound 2 is 1:3, the removal rates of nickel, cobalt, and calcium reach 99.52%, 98.69%, and 98.58%, respectively, with a lithium co-extraction rate of only 0.95%, and a separation coefficient β.Ni / Li β Ca / Li The values ​​are as high as 21522.90 and 7209.34. Therefore, in order to ensure a high lithium recovery rate while removing impurities, the ratio of compound 1 to compound 2 is very important, and the molar ratio of compound 1 to compound 2 needs to be controlled at 1:2 to 1:3.

[0067] Example 4

[0068] Aqueous phase: Lithium chloride solution containing 0.53 g / L iron, 0.42 g / L aluminum, 0.18 g / L nickel, and 3.84 g / L lithium.

[0069] Organic phase: The organic phase is 0.125 mol / L Formula 1c (compound 1) + 0.25 mol / L Formula 2b ( ) + No. 260 solvent oil.

[0070] Extraction conditions: The organic phase and aqueous phase feed solution were subjected to three-stage countercurrent extraction, and saponification was performed using 5 mol / L potassium hydroxide solution. The outlet equilibrium pH was controlled at 3.5, the extraction ratio O / A was 1:1, the extraction time was 10 min, and the temperature was 40°C. The extracted loaded organic phase was washed in one stage with 0.1 mol / L hydrochloric acid, with a washing ratio O / A of 10:1. The aqueous phase generated from the washing was incorporated into the extraction feed solution. The washed organic phase was then subjected to two-stage countercurrent back-extraction with 1 mol / L hydrochloric acid, with a back-extraction ratio O / A of 10:1. After back-extraction, the organic phase was saponified with 2 mol / L potassium hydroxide solution and then returned to the extraction cycle for reuse.

[0071] Once the system reached stable equilibrium, the analysis data showed that the raffinate contained 0.00025 g / L iron, 0.00045 g / L aluminum, 0.00031 g / L nickel, and 3.52 g / L lithium; the back-extraction solution contained 5.46 g / L iron, 4.31 g / L aluminum, 1.82 g / L nickel, and 0.020 g / L lithium. The extraction removal rates of iron, aluminum, and nickel were 99.95%, 99.89%, and 99.82%, respectively, while the lithium loss rate was only 0.052%, indicating that deep removal of iron, aluminum, and nickel impurities from lithium chloride solution can be achieved with extremely low lithium loss.

[0072] Example 5

[0073] Aqueous phase: Lithium sulfate solution containing 0.11 g / L copper, 0.08 g / L aluminum, 1.09 g / L manganese, and 16.28 g / L lithium.

[0074] Organic phase: The organic phase is 0.25 mol / L formula 1a + 0.5 mol / L formula 2c ( (Compound 2) + Escaid110.

[0075] Extraction conditions: The organic phase and aqueous phase feed solution were subjected to three-stage countercurrent extraction. Saponification was performed using 10 mol / L sodium hydroxide solution at a saponification rate of 40%, with an extraction ratio of O / A of 1:2, a time of 10 min, a temperature of 40°C, and an outlet equilibrium pH of 4.0. The extracted loaded organic phase was subjected to two-stage countercurrent washing with 0.1 mol / L sulfuric acid, with a washing ratio of O / A of 10:1. The aqueous phase generated during washing was incorporated into the extraction feed solution. The washed organic phase was subjected to three-stage countercurrent back-extraction with 1 mol / L sulfuric acid, with a back-extraction ratio of O / A of 10:1. The back-extracted organic phase was then saponified with 10 mol / L sodium hydroxide solution and returned to the extraction cycle for reuse.

[0076] After the system reached stable equilibrium, the analysis data showed that the raffinate contained 0.00053 g / L copper, 0.0011 g / L aluminum, 0.0013 g / L manganese, and 15.91 g / L lithium; the back-extraction solution contained 2.43 g / L copper, 1.81 g / L aluminum, 22.19 g / L manganese, and 0.096 g / L lithium. The extraction removal rates of copper, aluminum, and manganese were 99.52%, 98.62%, and 99.88%, respectively, while the lithium loss rate was only 0.029%, indicating that deep removal of copper, aluminum, and manganese impurities from lithium sulfate solution can be achieved with extremely low lithium loss.

[0077] Example 6

[0078] Aqueous phase: lithium nitrate solution containing 4.31 g / L nickel, 4.48 g / L cobalt, and 2.12 g / L lithium, with a pH of 4.05.

[0079] Organic phase: The organic phase is 0.25 mol / L Formula 1a + 0.5 mol / L Formula 2b + aviation kerosene.

[0080] Extraction conditions: The organic phase and aqueous phase feed solution were subjected to 5-stage countercurrent extraction. Saponification was performed using 10 mol / L sodium hydroxide solution at an 80% saponification rate. The extraction ratio O / A was 2:1, the extraction time was 10 min, the temperature was 40°C, and the outlet equilibrium pH was controlled at 3.5. The extracted loaded organic phase was washed with 0.2 mol / L nitric acid in 3-stage countercurrent washing with an O / A ratio of 10:1. The aqueous phase generated from washing was incorporated into the extraction feed solution. The washed organic phase was then subjected to 4-stage countercurrent back-extraction with 1.5 mol / L nitric acid with an O / A ratio of 10:1. After back-extraction, the organic phase was saponified with 10 mol / L sodium hydroxide solution and then returned to the extraction cycle for reuse.

[0081] Once the system reached stable equilibrium, the analysis data showed that the raffinate contained 0.0035 g / L nickel, 0.0041 g / L cobalt, and 2.03 g / L lithium; the stripping solution contained 22.63 g / L nickel, 23.74 g / L cobalt, and 0.083 g / L lithium. The extraction removal rates of nickel and cobalt were 99.92% and 98.91%, respectively, while the lithium loss rate was only 0.78%, indicating that high concentrations of nickel and cobalt can be deeply removed from lithium nitrate solution with minimal lithium loss.

Claims

1. A composite extractant for selective extraction and impurity removal from lithium solution, characterized in that, This includes extractants of Formula 1 and Formula 2 with a molar ratio of 1:1 to 5; Formula 1; Formula 2; Among them, R1 and R2 are C on their own. 4~ C 14 alkyl or olefinic groups; R3 and R4 are C individually. 6~ C 14 alkyl or C 6~ C 14 The alkoxy group; M is H, Na, K or NH4.

2. The composite extractant for selective extraction and impurity removal of lithium solution as described in claim 1, characterized in that, The molar ratio of the extractant of Formula 1 to the extractant of Formula 2 is 1:1.5~4; preferably 1:1.5~3; more preferably 1:1.8~2.

2.

3. The composite extractant for selective extraction and impurity removal of lithium solution as described in any one of claims 1 to 3, characterized in that, The composite extractant also contains a hydrophobic diluent.

4. The composite extractant for selective extraction and impurity removal of lithium solution as described in claim 3, characterized in that, In the composite extractant, the concentration of the extractant of Formula 1 in the composite extractant is 0.1~0.4M; preferably 0.15~0.35M; more preferably 0.2~0.3M.

5. A method for selective extraction and impurity removal from lithium solution, characterized in that, The lithium solution containing impurity ions and lithium ions to be treated is mixed with the composite extractant according to any one of claims 1 to 4 for extraction to obtain a loaded organic phase enriched with impurity ions and a lithium raffinate after impurity removal. The impurity ions include at least one of iron, aluminum, nickel, cobalt, manganese, calcium, and magnesium.

6. The method for selective extraction and impurity removal from lithium solution as described in claim 5, characterized in that, The lithium solution is at least one of lithium sulfate solution, lithium chloride solution, and lithium nitrate solution containing the impurity ions; Preferably, the lithium concentration in the lithium solution is 2~30 g / L, and the impurity concentration is ≤5 g / L.

7. The method as described in claim 5, characterized in that, The equilibrium pH of the aqueous phase during extraction is 2.0~5.5; preferably 3~4.

5.

8. The method as described in claim 5, characterized in that, The number of extraction stages is 1 to 10; when the number of extraction stages is greater than or equal to 2, the extraction method is countercurrent extraction; the volume flow rate ratio of the organic phase to the aqueous phase during the extraction process is 1:10 to 10:

1.

9. The method as described in claim 8, characterized in that, The pH value of the aqueous phase during the extraction process is controlled by saponifying the organic phase; the alkaline solution used in the saponification process is at least one of sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium carbonate, potassium carbonate, and ammonia water; the saponification rate of the organic phase is 10% to 90%, preferably 20% to 80%.

10. The method according to any one of claims 5 to 9, characterized in that, The supported organic phase is back-extracted to enrich impurity ions and regenerate the composite extractant; Preferably, the supported organic phase needs to be washed before back-extraction; the washing process uses an aqueous solution of an inorganic acid as the washing agent, wherein the inorganic acid is at least one of sulfuric acid, hydrochloric acid, or nitric acid, and its H+ content is... + The concentration is 0.1~5 mol / L; the number of washing stages is 1~10; when the number of washing stages is greater than or equal to 2, the washing method is countercurrent washing; the volume flow ratio of organic phase to aqueous phase during the washing process is 1:1~30:1; Preferably, the washed organic phase is subjected to single-stage or multi-stage countercurrent back-extraction using an aqueous solution of an inorganic acid; the inorganic acid is at least one of sulfuric acid, hydrochloric acid, or nitric acid, and its H+ content is... + The concentration is 0.1~5 mol / L; the number of back-extraction stages is 1~5, and the volume flow ratio of the organic phase to the aqueous phase during back-extraction is 1:1~15:1.

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