Lithium extraction system and method for extracting and separating lithium from alkaline solution

Abstract

The invention discloses a lithium extraction system and a method for extracting and separating lithium from an alkaline solution. The lithium extraction system comprises an extraction agent, the extraction agent comprises a triazole substituted phenolic compound, and the triazole substituted phenolic compound has a structure as shown in the following formula: R1 and R2 are independently selected from a straight chain with 1-12 carbons or alkyl with a branched chain, a halogen atom substituent group or a nitro group. According to the lithium extraction system, lithium can be extracted and separated from a high-alkalinity solution, meanwhile, the lithium extraction system has good tolerance to alkali in an aqueous solution, and the defect that a traditional alkaline extraction system is prone to degradation and damage in a strong alkali environment can be overcome in the application process.

Description

Technical Field

[0001] This invention belongs to the field of lithium extraction and separation technology, specifically relating to a lithium extraction system and a method for extracting and separating lithium from an alkaline solution. Background Technology

[0002] Lithium is the lightest metal in nature and possesses extremely high electrochemical activity. Its metals and compounds are widely used in industries and fields such as glass, ceramics, aluminum smelting, organic chemicals, aerospace, and nuclear fusion as explosives in thermonuclear fusion (hydrogen bombs), high-performance propellant for aircraft, rockets, and missiles, and shielding materials for nuclear reactors. Lithium batteries have 4 to 30 times higher energy storage than ordinary batteries and excellent performance, and have long been used as propulsion for torpedoes, submarines, and spacecraft. Lithium-aluminum and lithium-magnesium alloys are high-strength and lightweight, making them excellent materials for aerospace and rockets, and highly favored by the military and aerospace industries. In the 21st century, with the rising demand for clean energy and the production of low-priced lithium salts, lithium energy is likely to profoundly impact people's lives, thus lithium is called the "energy metal of the 21st century."

[0003] Currently, the main extraction systems for lithium extraction from solution include tributyl phosphate-ferric chloride-kerosene extraction system, tributyl phosphate-amide-ferric chloride extraction system, tributyl phosphate-ionic liquid extraction system, diketone-organophosphorus extraction system, and salicylate extraction system. Among these, phosphate ester extraction systems are typically used for lithium extraction from salt lake brine, but this system has high requirements for chloride ion content, limiting its application range. Diketone-organophosphorus co-extraction systems can extract and separate lithium from alkaline lithium-containing solutions, but diketone compounds are usually expensive, resulting in high production costs and limiting their large-scale application prospects. Salicylate extraction systems can extract and separate lithium from alkaline solutions, but their ester bond structure may undergo hydrolysis reactions when switching between acidic and alkaline environments, thereby destroying the structure and losing its extraction ability. Summary of the Invention

[0004] The main objective of this invention is to provide a lithium extraction system and a method for extracting and separating lithium from an alkaline solution, in order to overcome the shortcomings of the prior art.

[0005] To achieve the aforementioned objectives, the technical solution adopted by this invention includes: This invention provides a lithium extraction system comprising an extractant, wherein the extractant comprises a triazole-substituted phenolic compound having a structure as shown in formula (I):

[0006] Formula (I)

[0007] R1 and R2 are independently selected from alkyl groups, halogen atom substituents, or nitro groups with 1 to 12 carbon atoms in a straight chain or with branches.

[0008] This invention also provides the application of the aforementioned lithium extraction system in the extraction and separation of lithium from alkaline solutions.

[0009] This invention also provides a method for extracting and separating lithium from an alkaline solution, comprising: An alkaline lithium-containing solution is provided as the aqueous phase to be extracted; The aforementioned lithium extraction system is provided as the extraction organic phase; Furthermore, the organic phase to be extracted is mixed with the aqueous phase to be extracted for extraction and back-extraction treatment, thereby achieving the extraction and separation of lithium.

[0010] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The extractant used in this invention is a triazole-substituted phenolic compound, and the co-extractant is a neutral phosphorus oxide or amide compound, which can achieve selective extraction of lithium ions in alkaline solution; (2) The triazole-substituted phenolic compounds in the lithium extraction system of this invention have a solubility of only 0.01-0.1 mg / L in aqueous solution, and the compounds do not contain elements such as fluorine that are highly toxic to the human body. As an industrial extractant, they pose little harm to the environment. (3) The method proposed in this invention has a simple lithium extraction and separation process, higher selectivity for lithium, and weaker extraction effect on alkali metal ions such as sodium and potassium. It can achieve lithium extraction and separation with short process and high efficiency. (4) The process of this invention is simple, easy to control, and has a wide range of applications. It can be applied to secondary lithium resources such as lithium-containing waste liquid, intermediate liquid and solid waste leachate from different industries, providing a new way for the efficient and comprehensive utilization of lithium resources in my country. Attached Figure Description

[0011] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0012] Figure 1 This is a schematic flowchart of a method for extracting and separating lithium from an alkaline solution in a typical embodiment of the present invention. Detailed Implementation

[0013] In view of the deficiencies of the prior art, the inventors of this case, through long-term research and extensive practice, have proposed the technical solution of this invention. The technical solution of this invention will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0014] Specifically, as one aspect of the technical solution of this invention, a lithium extraction system includes an extractant comprising a triazole-substituted phenolic compound having a structure as shown in formula (I):

[0015] Formula (I)

[0016] R1 and R2 are independently selected from alkyl groups, halogen atom substituents, or nitro groups with 1 to 12 carbon atoms in a straight chain or with branches.

[0017] In some preferred embodiments, the triazole-substituted phenolic compound is a compound having a phenolic hydroxyl group and an ortho-triazole.

[0018] In some preferred embodiments, the triazole-substituted phenolic compound includes any one or more combinations of L-benzotriazolyloctylalkyl P-cresol, benzotriazolyl diisooctyl P-cresol, 2-(2H-3,5-di-tert-butyl-2-hydroxyphenyl)benzotriazole, 2,4-di-tert-butyl-6-(5-chloro-2H-benzo[d][1,2,3]triazol-2-yl)phenol, 2-(tert-butyl)-6-(5-chloro-2H-benzo[d][1,2,3]triazol-2-yl)-4-methylphenol, and 2-allyl-6-(2H-benzo[d][1,2,3]triazol-2-yl)-4-methylphenol, and is not limited thereto.

[0019] In some preferred embodiments, the lithium extraction system further includes a co-extractant and a diluent; the co-extractant includes, but is not limited to, neutral phosphorus oxides and / or neutral amides.

[0020] In some preferred embodiments, the co-extractant is a compound containing P=O and N=O electron-donating groups.

[0021] In some preferred embodiments, the co-extractant includes any one or more combinations of triphenylphosphine oxide, trioctylphosphine oxide, trialkylphosphine oxide, tributyl phosphate, tri(2-chloropropyl) phosphate, phenyl di(2-ethylhexyl) phosphate, trioctyl phosphate, 2-(diethylhexyl)acetamide, and 2-(dimethylheptyl)acetamide, and is not limited thereto.

[0022] In some preferred embodiments, the diluent includes any one or more combinations of sulfonated kerosene, dodecane, ethyl butyrate, chloroform, and toluene, and is not limited thereto.

[0023] In some preferred embodiments, the concentration of the extractant in the lithium extraction system is 0.05~1.67 mol / L.

[0024] In some preferred embodiments, the concentration of the co-extractant in the lithium extraction system is 0.05~1.67 mol / L.

[0025] In some preferred embodiments, the

[0026] In the triazole-substituted phenolic compound extraction system proposed in this invention, the phenolic hydroxyl group can bind with lithium, and the N atom provides a lone pair electron to form a six-membered ring complex with lithium. The mechanism for lithium extraction is shown in the following equation: ; Substituted phenols are neutral after chelating with metal ions. This inner complex salt has very low solubility in the organic phase. If a ligand (S, co-extractant) is present, it can complex with the inner complex salt to form an extractable neutral extract. This ligand is called the co-extractant (S). The mechanism of lithium extraction is shown in the following equation: ; When triazole-substituted phenolic compound extractants are used to extract metal ions, they are usually combined with neutral co-extractants to form a co-extraction system to improve the stability of the complexes formed during the extraction process.

[0027] Another aspect of the present invention provides the application of the aforementioned lithium extraction system in the extraction and separation of lithium from alkaline solutions.

[0028] Another aspect of the present invention provides a method for extracting and separating lithium from an alkaline solution, comprising: An alkaline lithium-containing solution is provided as the aqueous phase to be extracted; The aforementioned lithium extraction system is provided as the extraction organic phase; Furthermore, the organic phase to be extracted is mixed with the aqueous phase to be extracted for extraction and back-extraction treatment, thereby achieving the extraction and separation of lithium.

[0029] In some preferred embodiments, the pH value of the alkaline lithium-containing solution is 7 to 14, but not 7.

[0030] In some preferred embodiments, the concentration of hydroxide ions in the alkaline lithium-containing solution is 0.05~6 mol / L.

[0031] In some preferred embodiments, the mass concentration of lithium ions in the alkaline lithium-containing solution is 0.05~20 g / L.

[0032] In some preferred embodiments, the mass concentration of sodium ions in the alkaline lithium-containing solution is 10~120 g / L.

[0033] In some preferred embodiments, the alkaline lithium-containing solution also includes calcium ions and magnesium ions, and the total content of calcium ions and magnesium ions is ≤0.1 g / L.

[0034] In some preferred embodiments, the anions in the alkaline lithium-containing solution are selected from Cl... - SO4 2- CO3 2- NO 3- Any one or more combinations thereof, but not limited to.

[0035] In some preferred embodiments, the method specifically includes: The organic phase to be extracted is mixed with the aqueous phase to be extracted by shaking to obtain the loaded organic phase and the raffinate; wherein the extraction time is 5~60 min and the shaking speed during extraction is 100~300 rpm; Furthermore, the loaded organic phase is mixed with the back-extraction solution by shaking and back-extraction to achieve the extraction and separation of lithium; wherein the back-extraction time is 2-60 min, and the shaking and mixing rate during back-extraction is 100-300 rpm.

[0036] Furthermore, the volume ratio of the extracted organic phase to the extracted aqueous phase is 1:20-20:1.

[0037] Furthermore, the extraction is countercurrent extraction, and the number of stages of the countercurrent extraction is 2 to 10.

[0038] Furthermore, the volume ratio of the supported organic phase to the back-extraction solution is 1:1 to 20:1.

[0039] Furthermore, the back-extraction solution includes, but is not limited to, inorganic acids.

[0040] Furthermore, the concentration of the inorganic acid is 0.05~6 mol / L.

[0041] Furthermore, the inorganic acid includes, but is not limited to, hydrochloric acid.

[0042] In some more specific embodiments, the method for extracting and separating lithium from an alkaline solution includes: A lithium extraction system is provided: the extraction system consists of an extractant, a co-extractant, and a diluent, wherein the extractant is L-benzotriazolyloctylalkyl P-cresol, benzotriazolyl diisooctyl P-cresol, 2-(2H-3,5-di-tert-butyl-2-hydroxyphenyl)benzotriazole, 2,4-di-tert-butyl-6-(5-chloro-2H-benzo[d][1,2,3]triazol-2-yl)phenol, or 2-(tert-butyl)-6-(5-chloro-2H-benzo[d]) [1,2,3]triazol-2-yl)-4-methylphenol, 2-allyl-6-(2H-benzo[d][1,2,3]triazol-2-yl)-4-methylphenol and other compounds with phenolic hydroxyl groups and ortho-triazoles, co-extracting compounds are triphenylphosphine oxide, trioctylphosphine oxide, trialkylphosphine oxide, tributyl phosphate, tri(2-chloropropyl) phosphate, phenyl di(2-ethylhexyl) phosphate, trioctyl phosphate, 2-(diethylhexyl)acetamide, 2-(dimethylheptyl)acetamide and other compounds containing P=O, N=O electron-donating groups, and diluents are sulfonated kerosene, dodecane, ethyl butyrate, chloroform, toluene and other common industrial diluents.

[0043] The extractant concentration ranges from 0.05 mol / L to 1.67 mol / L, the co-extractant concentration ranges from 0.05 mol / L to 1.67 mol / L, and the remainder is a diluent. The aqueous phase to be extracted is an alkaline lithium-containing solution. The pH of the feed solution is 7-14 or the hydroxide concentration is 0.05-6 mol / L. In the feed solution, Li... + The mass concentration is 0.05 g / L~20 g / L, the sodium ion concentration is 10~120 g / L, and the total calcium and magnesium ion content is not higher than 0.1 g / L. The anions in the feed solution are selected from Cl. - SO4 2- CO3 2- NO3 - At least one of them; Lithium extraction procedure: The organic phase to be extracted (lithium extraction system) is shaken and mixed with the aqueous phase to be extracted at a volume ratio of O / A of 20 / 1 to 1 / 20. The extraction (retention) time is 5 to 60 minutes, and the shaking speed should be 100 to 300 rpm. In addition, the number of countercurrent extraction stages is 2 to 10.

[0044] Lithium back-extraction step: The lithium-loaded organic phase and the back acid solution are mixed by shaking, with a volume ratio of O / A of 1 / 1 to 20 / 1, an acid concentration of 0.05 mol / L to 6 mol / L, a back-extraction time of 2 to 60 min, and a shaking rate of 100 to 300 rpm.

[0045] A schematic flowchart of the method for extracting and separating lithium from an alkaline solution in this invention is shown below. Figure 1 As shown.

[0046] The technical solution of the present invention will be further described in detail below with reference to several preferred embodiments and accompanying drawings. This embodiment is implemented on the premise of the technical solution of the invention, and provides detailed implementation methods and specific operation processes. However, the protection scope of the present invention is not limited to the following embodiments.

[0047] Unless otherwise specified, the experimental materials used in the examples below can be purchased from conventional biochemical reagent companies.

[0048] Example 1: The composition of the intermediate feed liquid in the production process of a lithium mining company is shown in Table 1 below: Table 1 Composition of Leachate

[0049] Using this feed solution as raw material, and 0.4 mol / L benzotriazolyldodecyl p-cresol + 0.5 mol / L TOPO (trioctylphosphine oxide) as extractant, lithium was extracted using a three-stage countercurrent extraction under a ratio O / A = 1:1. The supported organic phase was washed with 1.0 mol / L hydrochloric acid at a ratio O / A = 20 / 1, and the washed organic phase was then subjected to a two-stage countercurrent back-extraction using 3 mol / L hydrochloric acid at a ratio O / A = 20 / 1. The final results are shown in Table 2 below. Table 2 Extraction Experiment Results

[0050] The lithium extraction rate reached 95.8%, the lithium concentration in the lithium enrichment solution reached 20 g / L, and the content of other metal ions was less than 1.0 g / L, achieving efficient separation of lithium from other metal ions.

[0051] Example 2: The composition of the leachate from the solid by-products produced by a lithium mining company is shown in Table 3 below: Table 3 Composition of Leachate

[0052] Using this feed solution as raw material, and 0.6 mol / L benzotriazolyl octylalkyl P-cresol + 0.5 mol / L TOPO (trioctylphosphine oxide) as extractant, lithium was extracted using a four-stage countercurrent extraction at a ratio O / A = 2:1. The supported organic phase was washed with 1.0 mol / L hydrochloric acid in a three-stage countercurrent wash at a ratio O / A = 20 / 1. The washed organic phase was then back-extracted with 5 mol / L hydrochloric acid in a three-stage countercurrent stripping at a ratio O / A = 20 / 1. The final results are shown in Table 4 below. Table 4 Extraction Experiment Results

[0053] The lithium extraction rate reached 98.3%, the lithium concentration in the lithium enrichment solution reached 30 g / L, and the content of other metal ions was less than 1.5 g / L, achieving efficient separation of lithium from other metal ions.

[0054] Example 3: The composition of the circulating feed liquid of a lithium mining enterprise is shown in Table 5 below: Table 5 Composition of Leachate

[0055] Using this feed solution as raw material, and 0.6 mol / L benzotriazolyl diisooctyl P-cresol + 0.6 mol / L TOPO (trioctylphosphine oxide) as extractant, lithium was extracted using a four-stage countercurrent extraction at a ratio O / A = 5:1. The supported organic phase was washed with 1.0 mol / L hydrochloric acid in a three-stage countercurrent wash at a ratio O / A = 20 / 1. The washed organic phase was then back-extracted with 5 mol / L hydrochloric acid in a three-stage countercurrent stripping at a ratio O / A = 20 / 1. The final results are shown in Table 6 below. Table 6 Extraction Experiment Results

[0056] The lithium extraction rate reached 98.8%, the lithium concentration in the lithium enrichment solution reached 31.6 g / L, and the content of other metal ions was less than 1.5 g / L, achieving efficient separation of lithium from other metal ions.

[0057] Example 4: The composition of the tailings liquid discharged by a lithium mining company is shown in Table 7 below: Table 7 Composition of Leachate

[0058] Using this feed solution as raw material, the pH of the feed solution was first adjusted to 0.3 mol / L with alkali. 0.2 mol / L benzotriazolylbutyloctyl p-cresol + 0.2 mol / L TOPO (trioctylphosphine oxide) were used as the extractant. Lithium was extracted using a three-stage countercurrent extraction under a ratio O / A = 1:1. The supported organic phase was washed with 1.0 mol / L hydrochloric acid under a ratio O / A = 20 / 1 using a three-stage countercurrent extraction method. The washed organic phase was then back-extracted with 2 mol / L hydrochloric acid under a ratio O / A = 20 / 1 using a three-stage countercurrent extraction method. The final results are shown in Table 8 below. Table 8 Extraction Experiment Results

[0059] The lithium extraction rate reached 96%, the lithium concentration in the lithium enrichment solution reached 9.5 g / L, and the content of other metal ions was less than 0.6 g / L, achieving efficient separation of lithium from other metal ions.

[0060] Comparative Example 1: The composition of the circulating feed liquid of a lithium mining enterprise is shown in Table 9 below: Table 9 Composition of Leachate

[0061] Using this feed solution as raw material, and 0.6 mol / L isooctyl salicylate + 0.6 mol / L TOPO (trioctylphosphine oxide) as extractant, lithium was extracted using a four-stage countercurrent extraction at a ratio O / A = 5:1. The supported organic phase was washed with 1.0 mol / L hydrochloric acid in a three-stage countercurrent wash at a ratio O / A = 20 / 1. The washed organic phase was then back-extracted with 5 mol / L hydrochloric acid in a three-stage countercurrent stripping at a ratio O / A = 20 / 1. The final results are shown in Table 10 below. Table 10 Extraction Experiment Results

[0062] The lithium extraction rate was approximately 81.3%, the lithium concentration in the lithium enrichment solution reached 23.6 g / L, and the content of other metal ions was approximately 3.0 g / L. This initially achieved efficient separation of lithium from other metal ions. However, under the same conditions, the lithium enrichment solution had a high impurity content, and the lithium extraction rate was only 81.3%.

[0063] Comparative Example 2: The composition of the circulating feed liquid of a lithium mining enterprise is shown in Table 11 below: Table 11 Composition of Leachate

[0064] Using this feed solution as raw material, lithium was extracted using 0.6 mol / L benzoyltrifluoroacetone + 0.6 mol / L TOPO (trioctylphosphine oxide) as the extractant under a ratio O / A = 5:1, with four-stage countercurrent extraction. The supported organic phase was washed with 1.0 mol / L hydrochloric acid under a ratio O / A = 20 / 1, with three-stage countercurrent back-extraction. The washed organic phase was then back-extracted with 5 mol / L hydrochloric acid under a ratio O / A = 20 / 1. The final results are shown in Table 12 below. Table 12 Extraction Experiment Results

[0065] The lithium extraction rate was approximately 87.5%, the lithium concentration in the lithium enrichment solution reached 26.6 g / L, and the content of other metal ions was approximately 3.0 g / L. This initially achieved efficient separation of lithium from other metal ions. However, under the same conditions, the lithium enrichment solution had a high impurity content, and the lithium extraction rate was only 87.5%. In addition, the phase separation time after extraction was as long as 20 min, and the formation of a third phase by the extractant molecules in the alkaline solution was not conducive to the smooth progress of the process.

[0066] In addition, the inventors of this case also conducted experiments with other raw materials, process operations, and process conditions described in this specification, referring to the aforementioned embodiments, and obtained relatively ideal results in all cases.

[0067] It should be understood that the technical solutions of the present invention are not limited to the specific embodiments described above. Any technical modifications made to the technical solutions of the present invention without departing from the spirit and scope of the claims are within the scope of protection of the present invention.

Claims

1. A lithium extraction system, characterized in that: The lithium extraction system includes an extractant comprising a triazole-substituted phenolic compound having a structure as shown in formula (I): ； Formula (I); R1 and R2 are independently selected from alkyl groups, halogen atom substituents, or nitro groups with 1 to 12 carbon atoms in a straight chain or with branches.

2. The lithium extraction system according to claim 1, characterized in that: The triazole-substituted phenolic compounds include any one or more combinations of L-benzotriazolyloctylalkyl P-cresol, benzotriazolyldiisooctyl P-cresol, 2-(2H-3,5-di-tert-butyl-2-hydroxyphenyl)benzotriazole, 2,4-di-tert-butyl-6-(5-chloro-2H-benzo[d][1,2,3]triazol-2-yl)phenol, 2-(tert-butyl)-6-(5-chloro-2H-benzo[d][1,2,3]triazol-2-yl)-4-methylphenol, and 2-allyl-6-(2H-benzo[d][1,2,3]triazol-2-yl)-4-methylphenol.

3. The lithium extraction system according to claim 1, characterized in that: The lithium extraction system further includes a co-extractant and a diluent; the co-extractant includes neutral phosphorus oxides and / or neutral amides. And / or, the co-extractant comprises any one or more combinations of triphenylphosphine oxide, trioctylphosphine oxide, trialkylphosphine oxide, tributyl phosphate, tri(2-chloropropyl) phosphate, phenyl di(2-ethylhexyl) phosphate, trioctyl phosphate, 2-(diethylhexyl)acetamide, and 2-(dimethylheptyl)acetamide; And / or, the diluent includes any one or more combinations of sulfonated kerosene, dodecane, ethyl butyrate, chloroform, and toluene.

4. The lithium extraction system according to claim 3, characterized in that: The concentration of the extractant in the lithium extraction system is 0.05~1.67 mol / L; And / or, the concentration of the co-extractant in the lithium extraction system is 0.05~1.67 mol / L.

5. The application of the lithium extraction system according to any one of claims 1-4 in the extraction and separation of lithium from alkaline solutions.

6. A method for extracting and separating lithium from an alkaline solution, characterized in that, include: An alkaline lithium-containing solution is provided as the aqueous phase to be extracted; The lithium extraction system according to any one of claims 1-4 is provided as the extraction organic phase; Furthermore, the organic phase to be extracted is mixed with the aqueous phase to be extracted for extraction and back-extraction treatment, thereby achieving the extraction and separation of lithium.

7. The method according to claim 6, characterized in that: The pH value of the alkaline lithium-containing solution is 7~14; And / or, the concentration of hydroxide ions in the alkaline lithium-containing solution is 0.05~6 mol / L; And / or, the mass concentration of lithium ions in the alkaline lithium-containing solution is 0.05~20 g / L; And / or, the mass concentration of sodium ions in the alkaline lithium-containing solution is 10~120 g / L; And / or, the alkaline lithium-containing solution further includes calcium ions and magnesium ions, and the total content of calcium ions and magnesium ions is ≤0.1g / L; And / or, the anions in the alkaline lithium-containing solution are selected from Cl... - SO4 2- CO3 2- NO 3- Any one or more combinations thereof.

8. The method according to claim 6, characterized in that, Specifically, it includes: The organic phase to be extracted is mixed with the aqueous phase to be extracted by shaking to obtain the loaded organic phase and the raffinate; wherein the extraction time is 5~60 min and the shaking speed during extraction is 100~300 rpm; Furthermore, the loaded organic phase is mixed with the back-extraction solution by shaking and back-extraction to achieve the extraction and separation of lithium; wherein the back-extraction time is 2-60 min, and the shaking and mixing rate during back-extraction is 100-300 rpm.

9. The method according to claim 8, characterized in that: The volume ratio of the extracted organic phase to the extracted aqueous phase is 1:20-20:1; And / or, the extraction is countercurrent extraction, and the number of stages of the countercurrent extraction is 2 to 10.

10. The method according to claim 8, characterized in that: The volume ratio of the supported organic phase to the back-extraction solution is 1:1 to 20:1; And / or, the back-extraction solution includes an inorganic acid; preferably, the concentration of the inorganic acid is 0.05~6 mol / L; preferably, the inorganic acid includes hydrochloric acid.

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