Composite extraction system and process for extracting lithium from lithium-containing solution

Abstract

The invention belongs to the technical field of lithium extraction, and particularly relates to a composite extraction system and process for extracting lithium from a lithium-containing solution. The composite extraction system for extracting lithium from the lithium-containing solution comprises the following components: 0.1 mol / L to 1 mol / L of N-containing diketone compounds as shown in a formula 1A, 0.2 mol / L to 0.8 mol / L of tertiary amide compounds as shown in a formula 1B, 0.5 mol / L to 2 mol / L of phosphatide compounds as shown in a formula 1C, 0.05 mol / L to 0.2 mol / L of 2, 4, 5, 6-tetraaminopyrimidine and a diluent. The composite extractant system applicable to the wide pH range and the extraction process provided by the invention have the advantages of capability of extracting lithium in a water phase under the weakly alkaline condition that the pH is greater than or equal to 9, high selectivity, no alkali consumption, fast phase splitting and no emulsification, and are suitable for large-scale industrial lithium extraction.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium extraction, and in particular relates to a composite extraction system and process for extracting lithium from a lithium-containing solution. Background Art

[0002] The source of lithium in my country is mainly lithium-containing ores, such as spodumene and lithium mica. With the rise of new energy vehicles, lithium resources have gradually become insufficient and prices have risen. Finding new lithium sources is of great significance to the further development of the new energy industry. my country has abundant salt lake brine resources, and my country's brine lithium resources are rich, which is an important resource for the subsequent development of the lithium industry. At present, solvent extraction is used to selectively separate Li and Na, K, Mg, Ca, etc., which is an emerging method with development potential. β-diketone compounds have the characteristics of selective extraction of lithium, mainly acetylacetone, dipivaloyl acetone, benzoyl acetone, benzoyl trifluoroacetone, thenoyl trifluoroacetone, etc., among which fluoroacetone has the best effect. However, a problem faced by diketone extractants, especially fluorodiketones, is that the pH application range is narrow, and higher pH conditions are required for successful extraction. It takes a lot of alkali to adjust the pH of lithium-containing aqueous solutions, and highly alkaline solutions need to be neutralized before they can be discharged; and under strong alkaline conditions, the loss of extractants is large, and the loss of organic phase is large, which will greatly increase the cost. Therefore, developing a system that can effectively extract lithium in a wide pH range is particularly important in the current environment that emphasizes green environmental protection.

[0003] CN118241039A discloses an extractant for extracting lithium from an alkaline lithium-containing solution, comprising: a main extractant, a reinforcing agent and a co-extractant; the main extractant is an alkyl diketone compound, the reinforcing agent is a fluorine-based diketone compound, and the co-extractant is a phosphine oxide compound. The alkyl diketone compound and the fluorine-based diketone compound combine their respective advantages, cooperate with each other, and obtain an excellent comprehensive effect. The pH of the aqueous phase after extraction and stripping is nearly neutral.

[0004] CN116904765A discloses a method for selectively extracting and precipitating lithium from a lithium-containing alkaline aqueous solution, comprising the following steps: (1) weighing a certain mass of a cyclopentane acid compound, an alkylphenoxycarboxylic acid derivative, or a mixture of the two in a certain mass ratio, adding the mixture to the lithium-containing alkaline aqueous solution, stirring and mixing the mixture at room temperature for 5 minutes to 1 hour to obtain a liquid-solid two-phase mixture; (2) diluting the liquid-solid two-phase mixture obtained in step (1) by 20 to 50 times with water, adding a flocculant, stirring, standing the mixture for a period of time, and then filtering the mixture. or centrifugation to obtain a solid; (3) washing the solid obtained in step (2) with deionized water until the filtrate is neutral, then adding a stripping agent aqueous solution at a certain mass ratio, stirring and mixing at a temperature of 20 to 80° C. for 5 minutes to 1 hour, and cooling to room temperature to obtain a liquid-liquid two-phase mixture or a liquid-solid two-phase mixture; (4) centrifuging the liquid-liquid two-phase mixture obtained in step (3), washing the obtained upper liquid phase with deionized water until neutral, returning to step (1) and adding it to the lithium-containing alkaline aqueous solution to repeat steps (1) to (4) for use. Further, or filtering or centrifuging the liquid-solid two-phase mixture obtained in step (3), washing the obtained solid with deionized water until the filtrate is neutral, returning to step (1) and adding it to the lithium-containing alkaline aqueous solution to repeat steps (1) to (4) for use.

[0005] CN115433830A discloses an extraction system for extracting lithium from an alkaline lithium-containing solution, comprising a mixed solution containing an extractant and a synergist; wherein the extractant is selected from any one or more of isooctyl salicylate, n-octyl salicylate, butyl salicylate, propyl salicylate, hexyl salicylate and isopentyl salicylate, and the synergist is selected from any one or more of triphenylphosphine oxide, trioctylphosphine oxide, trialkylphosphine oxide, tributyl phosphate, phenyl di(2-ethylhexyl) phosphate, trioctyl phosphate, 2-(diethylhexyl) acetamide and 2-(dimethylheptyl) acetamide.

[0006] The above patents disclose methods for extracting lithium from alkaline solutions, but the initial aqueous phase needs to be at a relatively high pH for extraction. Developing a system that can effectively extract lithium in a wide pH range, especially a system with excellent extraction performance at pH ≥ 9, is of great significance and commercial value.

[0007] CN110777266A discloses an extraction system for separating calcium and extracting lithium from calcium-containing brine using a secondary amide / alkane composite solvent. The extraction system contains two types of substances, A and B; wherein the type A substance is a secondary amide composed of a single compound or a mixture of two or more, and the type B substance is an alkane. It has excellent extraction performance in the extraction of high calcium-to-lithium ratio oilfield brine. However, the single-stage extraction efficiency of Li is very low, and it is only applicable to high calcium systems, not to high sodium systems. Summary of the invention

[0008] In view of the shortcomings of the prior art that the extraction system for extracting lithium from lithium-containing solutions requires higher pH conditions, has high organic solvent loss, and long extraction time, which is not conducive to industrial production, the present invention provides a composite extractant system and extraction process suitable for a wide pH range. The composite extraction system of the present invention includes N-diketone compounds, tertiary amide compounds, phospholipid compounds, 2,4,5,6-tetraaminopyrimidine and a diluent. The composite extractant system of the present invention has the advantages of high selectivity, no alkali consumption, fast phase separation, and no emulsification, and is very suitable for large-scale industrial lithium extraction. To achieve this purpose, the present invention adopts the following technical scheme: A composite extraction system for extracting lithium from a lithium-containing solution, comprising the following components: 0.1-1 mol / L of an N-containing diketone compound of formula 1A, 0.2-0.8 mol / L of a tertiary amide compound of formula 1B, 0.5-2 mol / L of a phosphoester compound of formula 1C, 0.05-0.2 mol / L of 2,4,5,6-tetraaminopyrimidine, and a diluent; 1A Among them, R 1 , R 2 , R 3 , R 4 Independently selected from C1-10 alkyl, C1-10 alkoxy, C6-20 aryl or C5-15 heteroaryl; the C5-15 heteroaryl contains 1-3 heteroatoms including O, S, N, P; 1B Among them, R 5 is a C6-C20 aromatic group, R 6 , R 7 independently selected from C1-C10 alkyl groups; 1C Among them, R 8 , R 9 , R 10 are independently selected from C1-10 alkyl, C1-10 alkoxy, C6-20 aryl, C5-15 heteroaryl, wherein R 8 , R 9 , R 10 At least one of them is a C1-10 alkoxy group; The chemical formula of 2,4,5,6-tetraaminopyrimidine is as follows: .

[0009] Furthermore, the composite extraction system for extracting lithium from a lithium-containing solution provided by the present invention comprises the following components: 0.3-0.7 mol / L of an N-containing diketone compound represented by formula 1A, 0.25-0.5 mol / L of a tertiary amide compound represented by formula 1B, 1-1.5 mol / L of a phosphite compound represented by formula 1C, 0.05-0.1 mol / L of 2,4,5,6-tetraaminopyrimidine, and a diluent.

[0010] The solvent system for extracting lithium of the present invention, the N-containing diketone compound shown in Formula 1A, adds N atoms on the basis of conventional diketone compounds, and gives the composite extraction system good selectivity for extracting lithium without the need for fluorinated substituents, and is not easy to emulsify. The coordination of the tertiary amide compound shown in Formula 1B and 2,4,5,6-tetraaminopyrimidine can be that the composite extraction system of the present invention can have excellent extraction performance in a wide pH range, and can effectively and selectively extract lithium under weak alkaline conditions (pH ≥ 9), completing the conventional extractant needs to have good extraction performance in a high alkaline environment of pH ≥ 12. The inventor also tried its polyamino compounds, such as chain polyamines such as diethylenetriamine and triethylenetetramine, or aromatic polyamino compounds such as tetra-(4-amino-(1,1-biphenyl))ethylene, 3,3'-diaminobenzidine, and 3,3',4,4'-tetraaminodiphenyl ether. However, only 2,4,5,6-tetraaminopyrimidine can simultaneously improve the extraction performance, phase separation time and pH range of the extraction system, and the concentration of 2,4,5,6-tetraaminopyrimidine in the composite extraction system needs to be controlled within the range of 0.05-0.2 mol / L, preferably within the range of 0.05-0.1 mol / L to improve the extraction system.

[0011] Furthermore, R 1 , R 2 , R 3 , R 4 , R 8 , R 9 , R 10 R is independently selected from C1-6 alkyl, C1-6 alkoxy, C6-12 aryl, C5-15 heteroaryl; 8 , R 9 , R 10 At least one of them is a C1-6 alkoxy group; R 5 is a C6-C12 aryl group; R 6 , R 7 Independently selected from C1-6 alkyl.

[0012] Furthermore, the C1-6 alkyl is selected from methyl, ethyl, propyl, butyl, pentyl, and hexyl; the C1-6 alkoxy is selected from methoxy, ethoxy, propoxy, butoxy, pentyloxy, and hexyl; the C6-12 aryl is selected from phenyl, biphenyl, naphthyl, and anthracenyl; the C5-15 heteroaryl is selected from pyrrolyl, pyrazolyl, pyridyl, and thienyl; the H atoms in the above-mentioned alkyl, alkoxy, aryl, and heteroaryl are optionally substituted by substituents, and the substituents are selected from at least one of methyl, ethyl, isopropyl, trifluoromethyl, nitro, hydroxyl, amino, and thiol.

[0013] Furthermore, R 2 With R 3 The ring may contain nitrogen, oxygen, or sulfur atoms. 2 With R 3 The linker is pyrazolone, 2H-pyrrol-2-one, imidazolone, thiazolidinone, pyridone or oxazolidinone.

[0014] In a preferred technical solution of the present invention, compound 1A is selected from at least one of N,N-di(2-ethylhexyl)-3-butanone acetamide, N,N-dihexyl-3-butanone acetamide, N,N-diisopropyl-3-butanone acetamide, 2-ethyl-N,N-dimethyl-3-oxohexanamide, 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone, and 1-(4-trifluoromethylphenyl)-3-methyl-4-benzoyl-5-pyrazolone; Compound 1B is selected from at least one of N,N-dimethyl-4-methylbenzamide, N,N-diethyl-4-methylbenzamide, N,N-diisopropyl-4-methylbenzamide, N,N-dihexyl-4-methylbenzamide, and N,N-dibutyl-4-methylbenzamide; Compound 1C is selected from at least one of trioctyl phosphate, tributyl phosphate, trihexyl phosphate, triheptyl phosphate, tripentyl phosphate, diisooctyl methylphosphonate, and triphenoxyphosphine oxide.

[0015] Further, the diluent includes C4-C 14 Alkanes, C4-C 14 Ester compounds, C4-C 14 Alcohol compounds, C4-C 14 any one or a combination of at least two of ketone compounds and aromatic hydrocarbon compounds; preferably, the diluent is kerosene, sulfonated kerosene, D80, 260# solvent oil, Escaid 110, butyl benzoate, heptyl acetate, octanol, dodecanol, 4-methyl-2-pentanone, diisobutyl ketone, S150, toluene, one or a combination of two or more that can be miscible in any volume ratio.

[0016] The second object of the present invention is to provide a method for extracting lithium, comprising the following steps: (S1) adding the N-containing diketone compound of formula 1A, the tertiary amide compound of formula 1B, the phospholipid compound of formula 1C, and 2,4,5,6-tetraaminopyrimidine to a diluent, and mixing them uniformly to obtain an organic phase; (S2) adjusting the pH value of the lithium-containing aqueous solution to 9-10 to obtain an aqueous phase; (S3) mixing the organic phase with the aqueous phase and performing countercurrent extraction to obtain an organic phase enriched with lithium; (S4) The lithium-enriched organic phase is sequentially subjected to acid countercurrent washing and acid countercurrent stripping to obtain a stripped organic phase and a lithium-enriched aqueous phase, and the stripped organic phase is returned to the initial extraction device for recycling.

[0017] In step (2), if the initial aqueous phase pH is ≥ 9, there is no need to add alkali solution for adjustment. If the alkalinity is insufficient, one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, ammonia water, etc. can be added to adjust the pH to a weak alkaline, such as pH = 9-11.

[0018] The extraction equipment in step (3) can use a mixing and settling tank, an extraction tower or a centrifugal extractor, and the extraction stage number is 1-30, preferably 5-20, and the volume ratio of the organic phase to the aqueous phase is 1:60-60:1, preferably 1:1-5.

[0019] The acid in the acid solution in step (4) is at least one of hydrochloric acid, sulfuric acid and nitric acid. The acid concentration during countercurrent washing is 0.01-0.5 mol / L, preferably 0.1-0.3 mol / L. During countercurrent stripping of the acid solution, the acid concentration is 0.5-3 mol / L, preferably 1-2 mol / L. During countercurrent washing and countercurrent stripping of the acid solution, the volume ratio of the organic phase to the aqueous phase is 5-30:1, such as 10-20:1.

[0020] Compared with the prior art, the present invention has the following beneficial effects: The composite extraction system provided by the present invention can be applied in a wide range of pH, especially in weakly alkaline conditions, such as a good extraction effect under weakly alkaline conditions of pH=9-10. In addition, the composite extraction system of the present invention is not suitable for emulsification during extraction, the organic phase loss is small, and the phase separation time is fast. The selective extraction of lithium in the weakly alkaline lithium-containing aqueous phase can be completed quickly and efficiently at low cost. The pH of the residual liquid is close to neutral and can be discharged after simple treatment. In addition, the composite extraction system of the present invention has little loss after extraction, can be recycled and reused, and the extraction performance is basically not reduced. The high-purity lithium-containing solution obtained after extraction can be used to prepare high-purity lithium carbonate with a purity greater than 99.7%, realizing the short-process preparation of battery-grade lithium carbonate. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1is the XRD pattern of battery-grade lithium carbonate obtained in Example 1; Figure 2 This is a photograph of the first phase separation over time of Example 1; Figure 3 This is a photograph of the first phase of Example 1 over time. DETAILED DESCRIPTION

[0022] The technical solution of the present invention is further illustrated below through specific implementation methods.

[0023] Example 1 The composition of the composite extractant is 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone (content 0.5 mol / L), N, N-dihexyl-4-methylbenzamide (content 0.4 mol / L), trioctyl phosphate (content 1 mol / L), 2,4,5,6-tetraaminopyrimidine (content 0.07 mol / L), and the diluent is a mixture of D80 and diisobutyl ketone (v / v=8:1). The components of the composite extractant are mixed evenly to obtain an organic phase. The aqueous phase to be treated contains 2.6 g / L lithium, 67.7 g / L sodium, 12.3 g / L potassium, 3.5 g / L magnesium, and pH=9.

[0024] The organic phase and the aqueous phase were subjected to three-stage continuous countercurrent extraction in a mixing and settling tank at a volume ratio of 1:1 to obtain an organic phase enriched in lithium. The organic phase was washed with 0.3 mol / L hydrochloric acid in two stages, wherein the volume ratio of the organic phase to the aqueous phase was 10:1, and the organic phase was then separated in two stages with 4 mol / L hydrochloric acid. The volume ratio of the organic phase to the aqueous phase was 15:1, and the LiCl concentration in the aqueous phase of the stripping solution was 30.1 g / L, and the lithium recovery rate reached 97.5%. The organic phase after stripping was returned to the extraction equipment for continued recycling. Sodium carbonate was added to the lithium chloride solution to precipitate to obtain battery-grade lithium carbonate with a purity of >99.9%.

[0025] Figure 1 This is the XRD diagram of the battery-grade lithium carbonate obtained in Example 1.

[0026] Table 1 is the elemental composition of the battery-grade lithium carbonate obtained in Example 1.

[0027] Table 1 Elemental composition of lithium carbonate .

[0028] Example 2 The other conditions are the same as those in Example 1, except that the composition of the organic phase composite extractant is 1-(4-trifluoromethylphenyl)-3-methyl-4-benzoyl-5-pyrazolone (content is 0.6 mol / L), N,N-dibutyl-4-methylbenzamide (content is 0.4 mol / L), the organophosphorus compound is tributyl phosphate (content is 1.3 mol / L), 2,4,5,6-tetraaminopyrimidine (content is 0.05 mol / L), and the diluent is a mixture of heptyl acetate and octanol (v / v=4:1).

[0029] Example 3 The other conditions are the same as those in Example 1, except that the composition of the organic phase composite extractant is N, N-dihexyl-3-butanoneacetamide (content is 0.4 mol / L), N, N-diisopropyl-4-methylbenzamide (content is 0.8 mol / L), the organophosphorus compound is tributyl phosphate (content is 1.2 mol / L), 2,4,5,6-tetraaminopyrimidine (content is 0.04 mol / L), and the diluent is a mixture of 260# solvent oil and S150 (v / v=1:1).

[0030] Example 4 The other conditions are the same as those in Example 1, except that the composition of the organic phase composite extractant is N, N-diisopropyl-3-butanoneacetamide (content 0.7 mol / L), N, N-dibutyl-4-methylbenzamide (content 0.3 mol / L), the organophosphorus compound is trioctyl phosphate (content 1.1 mol / L), 2,4,5,6-tetraaminopyrimidine (content 0.1 mol / L), and the diluent is a mixture of sulfonated kerosene and octanol (v / v = 5:1).

[0031] Example 5 The other conditions are the same as those in Example 1, except that the composition of the organic phase composite extractant is N, N-di(2-ethylhexyl)-3-butanoneacetamide (content 0.2 mol / L), N, N-dihexyl-4-methylbenzamide (content 0.5 mol / L), the organophosphorus compound is trioctyl phosphate (content 1.5 mol / L), 2,4,5,6-tetraaminopyrimidine (content 0.2 mol / L), and the diluent is a mixture of S150 and 4-methyl-2-pentanone (v / v=10:1).

[0032] Example 6 The other conditions were the same as those in Example 1, except that the pH of the aqueous phase to be treated was 11.7.

[0033] Comparative Example 1 The other conditions were the same as those in Example 1, except that the extractant was a commercial lithium extractant Lix54-P113 composite system.

[0034] Comparative Example 2 The other conditions were the same as those in Comparative Example 1, except that the pH of the aqueous phase to be treated was 11.7.

[0035] Comparative Example 3 The other conditions were the same as those in Example 1, except that in the organic phase composite extractant, 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone was replaced with thenoyltrifluoroacetone in an equimolar concentration.

[0036] Comparative Example 4 The other conditions were the same as those in Example 1, except that 2,4,5,6-tetraaminopyrimidine was not added to the organic phase composite extractant.

[0037] Comparative Example 5 The other conditions were the same as those in Example 1, except that in the organic phase composite extractant, 2,4,5,6-tetraaminopyrimidine was replaced by triethylenetetramine in an equimolar concentration.

[0038] Comparative Example 6 The other conditions were the same as those in Example 1, except that in the organic phase composite extractant, 2,4,5,6-tetraaminopyrimidine was replaced by 3,3',4,4'-tetraaminodiphenyl ether in an equimolar concentration.

[0039] Application Example 1 The extraction systems of the above embodiments and comparative examples were evaluated, and the results are shown in Table 2 below.

[0040] Figure 2 This is a photograph of the first phase separation over time in Example 1. The phase separation time is determined by observing whether the phase separation is completed every 10 seconds.

[0041] Figure 3 This is a photograph of the first phase separation over time of comparative example 1. The phase separation time was determined by observing whether the phase separation was completed every minute.

[0042] It can be seen that in Comparative Example 1, a commercial extractant is used, and the extraction rate is very low under the condition of pH = 9, which basically cannot meet the needs of lithium extraction. When the pH is close to 12, the single-stage extraction rate of commercial extractants for Li can reach a level comparable to that of the present invention; but the selection is not good, and the phase separation time is long, requiring about 2 hours to achieve the required degree of extraction and separation. On the one hand, the composite extraction system of the present invention can complete the extraction under lower pH conditions, has a high single-stage extraction rate for Li, good selectivity for Li, and can be completely phase-separated within 80 seconds, showing great practical value in industry.

[0043] Table 2 Performance test of composite extraction system .

[0044] It can be seen from the data in Table 2 that the composite extraction system of the present invention can quickly and efficiently complete the extraction of lithium in the aqueous phase under relatively low pH conditions (pH=9), with high extraction efficiency, good selectivity, and fast phase separation time. Commercial extractants cannot be extracted smoothly under pH=9 conditions, and the pH value needs to be increased, and the selectivity for Li is not as good as the composite extraction system of the present invention. The composite extraction system of the present invention can have excellent extraction performance under relatively low pH conditions, thanks to the reasonable compounding of the components, especially 2,4,5,6-tetraaminopyrimidine, but its concentration needs to be reasonably controlled, otherwise it will be detrimental to the selective extraction of lithium.

[0045] Application Example 2 The composite extraction system of Example 1 was repeatedly used 10 times, and the results are shown in Table 3 below.

[0046] Table 3 Extraction performance test after the extraction system of Example 1 was repeatedly cycled 10 times .

[0047] The composite extraction system provided by the present invention not only has excellent extraction performance, but also can be recycled for multiple times without substantially decreasing the extraction performance.

Claims

1. A composite extraction system for extracting lithium from a lithium-containing solution, characterized in that: Includes the following components: 0.1-1 mol / L of an N-containing diketone compound of formula 1A, 0.2-0.8 mol / L of a tertiary amide compound of formula 1B, 0.5-2 mol / L of a phosphoester compound of formula 1C, 0.05-0.2 mol / L of 2,4,5,6-tetraaminopyrimidine, and a diluent; 1A Among them, R 1 , R 2 , R 3 , R 4 Independently selected from C1-10 alkyl, C1-10 alkoxy, C6-20 aryl or C5-15 heteroaryl; the C5-15 heteroaryl contains 1-3 heteroatoms including O, S, N, P; 1B Among them, R 5 is a C6-C20 aromatic group, R 6 , R 7 independently selected from C1-C10 alkyl groups; 1C Among them, R 8 , R 9 , R 10 are independently selected from C1-10 alkyl, C1-10 alkoxy, C6-20 aryl, C5-15 heteroaryl, wherein R 8 , R 9 , R 10 At least one of them is a C1-10 alkoxy group; The chemical formula of 2,4,5,6-tetraaminopyrimidine is as follows: .

2. The composite extraction system according to claim 1, characterized in that: The invention comprises the following components: 0.3-0.7 mol / L of an N-containing diketone compound represented by formula 1A, 0.25-0.5 mol / L of a tertiary amide compound represented by formula 1B, 1-1.5 mol / L of a phosphoester compound represented by formula 1C, 0.05-0.1 mol / L of 2,4,5,6-tetraaminopyrimidine, and a diluent.

3. The composite extraction system according to claim 1, characterized in that: R 1 , R 2 , R 3 , R 4 , R 8 , R 9 , R 10 R is independently selected from C1-6 alkyl, C1-6 alkoxy, C6-12 aryl, C5-15 heteroaryl; 8 , R 9 , R 10 At least one of them is a C1-6 alkoxy group; R 5 is a C6-C12 aryl group; R 6 , R 7 Independently selected from C1-6 alkyl.

4. The composite extraction system according to claim 3, characterized in that: The C1-6 alkyl group is selected from methyl, ethyl, propyl, butyl, pentyl and hexyl; the C1-6 alkoxy group is selected from methoxy, ethoxy, propoxy, butoxy, pentyl and hexyl; the C6-12 aryl group is selected from phenyl, biphenyl, naphthyl and anthracenyl; the C5-15 heteroaryl group is selected from pyrrolyl, pyrazolyl, pyridyl and thienyl.

5. The composite extraction system according to claim 1, characterized in that: The H atoms in the alkyl, alkoxy, aryl and heteroaryl groups are optionally substituted by substituents, and the substituents are selected from at least one of methyl, ethyl, isopropyl, trifluoromethyl, nitro, hydroxyl, amino and mercapto groups.

6. The composite extraction system according to claim 1, characterized in that: R 2 With R 3 It is connected to a cycloalkane or a N-containing heterocyclic ring, and the ring may contain nitrogen, oxygen, or sulfur atoms.

7. The composite extraction system according to claim 6, characterized in that: R 2 With R 3 The linker is pyrazolone, 2H-pyrrol-2-one, imidazolone, thiazolidinone, pyridone or oxazolidinone.

8. The composite extraction system according to claim 1, characterized in that: Compound 1A is at least one selected from N,N-di(2-ethylhexyl)-3-butanone acetamide, N,N-dihexyl-3-butanone acetamide, N,N-diisopropyl-3-butanone acetamide, 2-ethyl-N,N-dimethyl-3-oxohexanamide, 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone, 1-(4-trifluoromethylphenyl)-3-methyl-4-benzoyl-5-pyrazolone; and / or Compound 1B is at least one selected from N,N-dimethyl-4-methylbenzamide, N,N-diethyl-4-methylbenzamide, N,N-diisopropyl-4-methylbenzamide, N,N-dihexyl-4-methylbenzamide, and N,N-dibutyl-4-methylbenzamide; and / or Compound 1C is at least one selected from trioctyl phosphate, tributyl phosphate, trihexyl phosphate, triheptyl phosphate, tripentyl phosphate, diisooctyl methylphosphonate, and triphenoxyphosphine oxide.

9. The composite extraction system according to claim 1, characterized in that: The diluent includes C4-C 14 Alkanes, C4-C 14 Ester compounds, C4-C 14 Alcohol compounds, C4-C 14 Any one of ketone compounds and aromatic hydrocarbon compounds or a combination of at least two of them.

10. A method for extracting lithium, characterized in that: The steps include: (S1) adding the N-containing diketone compound of formula 1A, the tertiary amide compound of formula 1B, the phospholipid compound of formula 1C, and 2,4,5,6-tetraaminopyrimidine to a diluent, and mixing them uniformly to obtain the composite extraction system according to any one of claims 1 to 9; (S2) adjusting the pH value of the lithium-containing aqueous solution to 9-10 to obtain an aqueous phase; (S3) mixing the organic phase with the aqueous phase and performing countercurrent extraction to obtain an organic phase enriched with lithium; (S4) The lithium-enriched organic phase is sequentially subjected to acid countercurrent washing and acid countercurrent stripping to obtain a stripped organic phase and a lithium-enriched aqueous phase, and the stripped organic phase is returned to the initial extraction device for recycling.

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