Lithium extraction agent, lithium extraction system and lithium extraction method

Abstract

The invention discloses a lithium extraction agent, a lithium extraction system and a lithium extraction method, and belongs to the technical field of lithium extraction. The lithium extraction agent has the following structure: # imgabs0 #, wherein R1, R2, R3, R4, R5, R6, R7 and R8 are independently selected from hydrogen, halogen, cyano, nitro or C1-C18 alkyl; the lithium ion chelating agent has a chelating effect on lithium ions in a solution system, lithium is efficiently extracted from a lithium-containing aqueous solution by using a lithium extraction system formed by the lithium ion chelating agent, and particularly the separation of lithium from other alkali metal ions is realized; the method is used for efficiently extracting lithium from neutral or alkaline salt lake brine and geothermal brine with low magnesium and calcium contents, or lithium precipitation mother liquor of lithium carbonate or lithium phosphate and other lithium-containing mother liquor.

Description

Technical Field

[0001] The present invention relates to a lithium extractant, in particular to a lithium extractant with 2-(2'-hydroxy-phenyl)benzotriazole as a parent structure; it also relates to a lithium extraction system, in particular to a lithium extraction system with the lithium extractant as a main component; it also relates to a method for extracting lithium, in particular to a method for extracting lithium from a lithium-containing aqueous solution using the lithium extraction system, and belongs to the technical field of lithium extraction. Background Art

[0002] Lithium is widely used in batteries, glass, alloys, ceramics, lubricants and other fields. With the explosive growth of the demand for lithium salts in the power battery industry, lithium has been hailed as the "energy metal of the 21st century". Lithium mainly exists in solid minerals such as spodumene, lepidolite and lithium clay, and liquid minerals such as salt lake brine, oilfield brine, geothermal water, etc. However, the development of any type of lithium ore inevitably involves the stage of extracting lithium from aqueous solutions containing alkali metals and alkaline earth metals. The development of compounds and combinations that have special selectivity for lithium is a key area for efficient lithium extraction.

[0003] At present, the methods for extracting lithium salts from lithium-containing aqueous solutions at home and abroad mainly include precipitation, adsorption, ion exchange, electrodialysis membrane, nanofiltration membrane, solvent extraction, etc. Solvent extraction has the advantages of high efficiency, strong selectivity, simple process and equipment, continuous operation, and easy automatic control. In addition, the existing extraction technology has been able to achieve magnesium-lithium separation, calcium-lithium separation, and sodium (potassium)-lithium separation, etc., and can extract lithium from lithium-containing old brine and lithium precipitation mother liquor. Common reagents for extracting lithium in the prior art include: tributyl phosphate-ferric chloride composition, β-diketone-neutral phosphine composition, pyrazolone-TBP composition, crown chemicals, and neutral amides. Tributyl phosphate-ferric chloride composition can extract lithium from lithium-containing solutions with high chloride ion concentrations; β-diketone-neutral phosphine composition can extract lithium from alkaline lithium-containing solutions. Tributyl phosphate-ferric chloride composition has strong corrosion to equipment during the extraction process; crown chemicals lack industrial application prospects due to the difficulty of synthesis and high cost. The price of β-diketone compounds used to extract lithium from alkaline lithium-containing solutions is also relatively high, and they dissolve significantly due to their short alkyl chains. The fluorinated diketone compounds that can directly extract lithium from weakly alkaline lithium-containing aqueous solutions have even higher manufacturing costs. Moreover, the fluorinated compounds that dissolve into water bodies have long-lasting stability and cannot be degraded, which has a huge environmental load and has also limited their industrial application to a certain extent.

[0004] Therefore, there is a need to continue to develop new lithium extractants, extraction compositions and extraction processes to meet the economic and efficiency requirements of industrial applications. Summary of the invention

[0005] In view of the defects of the prior art, the first object of the present invention is to provide a lithium extractant having 2-(2'-hydroxy-phenyl)benzotriazole as a parent structure, which has a chelating effect on lithium ions in a solution system and can be used as a lithium extractant.

[0006] The second object of the present invention is to provide a lithium extraction system, which introduces an extractant having 2-(2'-hydroxy-phenyl)benzotriazole as a parent structure, which can increase the lithium extraction capacity, reduce the equilibrium pH value of the raffinate, and reduce the consumption of alkali in the lithium extraction process.

[0007] The third object of the present invention is to provide a method for extracting lithium, which uses an extraction system containing an extractant having 2-(2'-hydroxy-phenyl)benzotriazole as a parent structure to improve the efficiency of lithium extraction from a lithium-containing aqueous solution, especially to achieve the separation of lithium from other alkali metal ions, thereby achieving efficient lithium extraction from neutral or alkaline salt lake brine with low magnesium and calcium content, geothermal brine, or lithium precipitation mother liquor of lithium carbonate or lithium phosphate, mother liquor after preparing lithium hydroxide, and lithium-containing mother liquor after extracting nickel, cobalt, and manganese.

[0008] In order to achieve the above technical objectives, the present invention provides a lithium extractant having a structure of Formula 1:

[0009]

[0010] wherein R1, R2, R3, R4, R5, R6, R7 and R8 are independently selected from hydrogen, halogen substituents, nitro, cyano or C1-C 18 of hydrocarbon groups.

[0011] The lithium extractant of the present invention has the following parent structure:

[0012]

[0013] The phenolic hydroxyl group on the benzene ring has a certain acidity, so that the hydrogen proton is easily ionized, and the formed oxygen anion forms a chelate structure with the electron-rich nitrogen on the triazole. Based on the electronic effect and the steric effect, lithium ions can be selectively chelated, so that it can be used as a lithium extractant. Furthermore, conventional small molecule substituents can be introduced on the benzene ring of benzotriazole and the benzene ring substituted on the 2-nitrogen on the triazole ring. These small molecule groups can adjust the oil solubility of the lithium extractant and affect the chelating ability for lithium ions. For example, the benzene ring of benzotriazole can be substituted with an alkane group, a halogen substituent, a nitro group, a cyano group or an alkoxy group, etc. These substituents mainly affect the oil solubility of the lithium extractant, and have a weaker effect on the chelating ability of the nitrogen atom on the triazole. The benzene ring substituted on the nitrogen at position 2 on the triazole ring can be substituted with an alkane group, a halogen substituent, a nitro group, a cyano group or an alkoxy group, etc. These substituent groups not only affect the oil solubility of the lithium extractant, but more importantly, they can adjust the dissociation ability of the hydrogen protons on the phenolic hydroxyl group, thereby affecting the chelation ability of the phenolic hydroxyl group to lithium ions. For example, strong polar groups such as nitro and cyano on the benzene ring can improve the dissociation ability of the hydrogen protons on the phenolic hydroxyl group by affecting the electron distribution on the benzene ring, thereby being more conducive to the formation of oxygen anions, participating in the chelation of lithium ions, and improving the extraction efficiency of lithium ions. Therefore, it is beneficial to introduce strong polar groups such as nitro on the benzene ring substituted on the nitrogen at position 2 on the triazole ring.

[0014] As a preferred solution, the C1 to C 18 The hydrocarbon groups include C1~C 18 Alkyl, or C2~C 18 A hydrocarbon group containing double bonds and / or triple bonds and / or benzene rings.

[0015] In the structural formula 1 of the lithium extractant of the present invention, the C1 to C 18 The hydrocarbon group may be a saturated hydrocarbon group, such as C 1～18 The alkyl radical of C1-C2 may be a linear alkyl radical or a branched alkyl radical, for example, methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, sec-butyl, isobutyl, tert-butyl, pentyl, isopentyl, neopentyl, hexyl, heptyl, octyl, 2-ethylhexyl, etc. 18 The hydrocarbon group may also be an unsaturated hydrocarbon group, such as C2~C 18 A hydrocarbon group containing double bonds and / or triple bonds and / or a benzene ring, such as at least one alkenyl and / or alkynyl group on the hydrocarbon chain, such as butenyl, 2-pentenyl, propynyl, butynyl, 2-phenyl-butyl, etc., such as an aromatic hydrocarbon group or an aromatic ring on the hydrocarbon chain, the aromatic hydrocarbon group can be phenyl, naphthyl or condensed ring, etc., or a group derived from phenyl, naphthyl or condensed ring, such as a small molecule aliphatic hydrocarbon group on the benzene ring, toluyl, ethylphenyl, etc.

[0016] In the structural formula 1 of the lithium extractant of the present invention, the halogen substituent is, for example, a fluorine substituent, a chlorine substituent, a bromine substituent or an iodine substituent.

[0017] As a preferred solution, in the structure of Formula 1, R1, R2, R3 and R4 are independently selected from C 1～10 Hydrocarbyl, hydrogen, halogen substituent, nitro or C 1～10 Alkoxy, and R5, R6, R7 and R8 are independently selected from hydrogen or C 1～10 Alkyl. C 1～10 The hydrocarbon groups include C 1～10 Alkyl or C 1～10 Unsaturated hydrocarbon group, C 1～10 The unsaturated hydrocarbon group contains at least one of a double bond, a triple bond, and an aromatic ring.

[0018] The preferred lithium extractant of the present invention is, for example, the following chemical structure:

[0019]

[0020] The present invention also provides a lithium extraction system, which comprises the lithium extractant. The lithium extractant having the structure of Formula 1 in the lithium extraction system has a selective chelating ability for lithium ions in the solution system, and can realize efficient extraction of lithium ions in the solution system.

[0021] As a preferred solution, the concentration of the lithium extractant in the lithium extraction system is 0.01 mol / L to 1.0 mol / L. A low concentration of the lithium extractant will result in a low lithium extraction capacity, while a high concentration of the lithium extractant will affect its solubility and dispersibility in the lithium extraction system. Therefore, the concentration of the lithium extractant in the lithium extraction system is further preferably 0.02 to 0.4 mol / L.

[0022] As a preferred solution, the lithium extraction system further comprises a synergist and a diluent. The introduction of the synergist into the lithium extraction system can promote the extraction composition to enter the organic phase by coordinating with the ions to be extracted. The diluent is mainly used to fully dissolve the extractant, improve the phase separation ability, and give full play to the lithium extraction effect of the lithium extractant.

[0023] As a preferred solution, the synergist includes at least one of tributyl phosphate, trioctyl phosphate, tri(2-ethylhexyl) phosphate, trihexyl phosphate, tripentyl phosphate, dibutyl butyl phosphate, dibutyl butyl phosphate, di-sec-octyl methyl phosphate, diisooctyl methyl phosphate, diisooctyl isopropyl phosphate, diisopentyl methyl phosphate, triphenylphosphine oxide, diphenylbenzylphosphine oxide, diphenyl(2-hydroxyphenylmethyl)phosphine oxide, 2,5-dihydroxyphenyl(diphenyl)phosphine oxide, trioctylphosphine oxide, and trialkylphosphine oxide TRPO. The stronger the alkalinity of the synergist, the more significant the synergistic effect it exerts on the lithium extractant, so the preferred neutral phosphine oxide synergist is at least one of tributylphosphine oxide, trioctylphosphine oxide, Cyanex923, and triphenylphosphine oxide.

[0024] As a preferred solution, the diluent includes at least one of kerosene, D80 solvent oil, D60 solvent oil, n-heptane, cyclohexane, octane, dodecane, petroleum ether, xylene, anisole, methyl isobutyl ketone, toluene, octanone, 5-nonanone, isopentanol, n-butanol, and halogenated benzene. The preferred diluent has good solubility in the lithium extractant and strong phase separation ability with water.

[0025] As a preferred solution, the concentration of the synergist in the lithium extraction system is 0.01 mol / L to 2.0 mol / L. As a more preferred solution, the concentration of the synergist in the lithium extraction system is 0.04 to 0.8 mol / L.

[0026] As a preferred solution, the molar ratio of the lithium extractant to the synergist is 3:1 to 0.5:1. The molar ratio of the lithium extractant to the synergist is more preferably 1:1 to 1:2.

[0027] As a preferred solution, the lithium extractant is used alone or in combination with other lithium extractants other than the lithium extractant. The other lithium extractants include at least one of β-diketone extractants, phenol-ketone extractants, and azo extractants. The other lithium extractants involved in the present invention are conventional commercial lithium extractants disclosed in the prior art.

[0028] The present invention also provides a method for extracting lithium, which comprises using the lithium extraction system and a water solution containing lithium ions for mixed extraction to obtain a lithium-carrying organic phase and a raffinate.

[0029] As a preferred solution, the initial pH value of the aqueous solution containing lithium ions is 5-13.

[0030] As a preferred solution, the pH of the aqueous solution containing lithium ions is adjusted by adding an alkaline substance, and the alkaline substance includes at least one of alkali metal hydroxides, alkali metal carbonates, alkali metal phosphates, alkali metal borates, ammonium carbonates, ammonium phosphates, ammonium borates, and ammonia water.

[0031] As a preferred solution, the aqueous solution containing lithium ions comprises at least one of alkaline natural brine, lithium precipitation mother liquor for producing lithium carbonate, and lithium precipitation mother liquor for producing lithium phosphate.

[0032] As a preferred solution, the alkali metal hydroxide includes at least one of sodium hydroxide and potassium hydroxide; the alkali metal carbonate includes at least one of sodium carbonate and potassium carbonate.

[0033] As a preferred solution, the alkali metal phosphate includes at least one of trisodium phosphate, tripotassium phosphate, disodium hydrogen phosphate, and dipotassium hydrogen phosphate.

[0034] As a preferred embodiment, the alkali metal borate includes at least one of sodium metaborate, potassium metaborate, sodium tetraborate and potassium tetraborate.

[0035] As a preferred embodiment, the ammonium carbonate salt includes at least one of ammonium bicarbonate and ammonium carbonate.

[0036] As a preferred solution, the ammonium phosphate salt includes at least one of ammonium hydrogen phosphate and ammonium dihydrogen phosphate.

[0037] As a preferred solution, the ammonium borate salt includes at least one of ammonium metaborate and ammonium tetraborate.

[0038] As a preferred solution, when the initial pH value of the aqueous solution containing lithium ions is 5 to 8, the lithium extraction system is subjected to saponification pretreatment; when the initial pH value of the aqueous solution containing lithium ions is greater than 8, the lithium extraction system does not need to be subjected to saponification pretreatment.

[0039] As a preferred solution, the saponification pretreatment uses at least one alkali solution selected from the group consisting of sodium hydroxide solution, potassium hydroxide solution, sodium carbonate solution, potassium carbonate solution, sodium bicarbonate solution, and potassium bicarbonate aqueous solution.

[0040] As a preferred solution, the extraction conditions are: one-stage or multi-stage extraction, phase volume ratio O / W=30:1-1:30, extraction time 3-30min. The extraction phase volume ratio O / W is more preferably 20:1-1:8, and the extraction time is more preferably 5-10min.

[0041] As a preferred solution, the lithium concentration in the aqueous solution containing lithium ions is 0.01 mol / L to 2.0 mol / L, and / or contains sodium ions. The lithium extraction system of the present invention has a high separation coefficient for lithium ions and sodium ions, and can achieve highly selective extraction and separation of lithium ions in a solution system where sodium ions and lithium ions coexist. The lithium concentration in the aqueous solution containing lithium ions is further preferably 0.02 mol / L to 0.5 mol / L.

[0042] As a preferred solution, the lithium-loaded organic phase is stripped with acid solution to obtain a lithium-rich solution.

[0043] As a preferred solution, the acid solution includes at least one of a carbonic acid solution, a sulfuric acid solution, a sulfurous acid solution, a hydrochloric acid solution, a nitric acid solution, and a phosphoric acid solution; and / or the concentration of hydrogen ions in the acid solution is 0.05 mol / L to 6 mol / L. The concentration of hydrogen ions in the acid solution is further preferably 0.5 mol / L to 5 mol / L.

[0044] As a preferred solution, the stripping conditions are: one or more stages of stripping, a phase volume ratio W / O=1:1-1:50, and a stripping time of 3-30 min. The phase volume ratio W / O of the stripping is more preferably 1:3-1:20. The stripping time is more preferably 5-10 min.

[0045] As a preferred solution, the extraction is carried out in a mixing and settling tank, a centrifugal extractor or an extraction tower; and / or the stripping is carried out in a mixing and settling tank, a centrifugal extractor or an extraction tower.

[0046] As a preferred solution, in the multi-stage stripping process, after the acid solution is stripped in the first stage, concentrated acid is added for stripping in the next stage; the concentrated acid is 6-12 mol / L hydrochloric acid, 6-18 mol / L sulfuric acid, 6-14 mol / L nitric acid or 6-15 mol / L phosphoric acid. By continuously adding concentrated acid for stripping, the lithium ion concentration in the lithium-rich solution can be greatly increased, which is beneficial for subsequent further recovery and treatment.

[0047] Compared with the prior art, the technical solution of the present invention has the following beneficial technical effects:

[0048] The lithium extractant provided by the invention has 2-(2'-hydroxy-phenyl)benzotriazole as a parent structure, has a chelating effect on lithium ions in a solution system, and can be used as a lithium extractant.

[0049] The lithium extraction system provided by the present invention utilizes a lithium extraction agent having 2-(2'-hydroxy-phenyl)benzotriazole as a parent structure as a main extraction agent, and can improve the lithium extraction capacity, reduce the equilibrium pH value of the raffinate, and reduce the consumption of alkali in the lithium extraction process by matching other lithium extraction agents, synergists and diluents.

[0050] The method for extracting lithium provided by the present invention utilizes an extraction system comprising a lithium extractant having 2-(2'-hydroxy-phenyl)benzotriazole as a parent structure, which can improve the efficiency of extracting lithium from a lithium-containing aqueous solution, and in particular can achieve the separation of lithium from other alkali metal ions, and can achieve efficient lithium extraction from neutral or alkaline salt lake brine with low magnesium and calcium content, geothermal brine, or lithium precipitation mother liquor of lithium carbonate or lithium phosphate, mother liquor after preparing lithium hydroxide, and lithium-containing mother liquor after extracting nickel, cobalt, and manganese. DETAILED DESCRIPTION

[0051] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the embodiments of the present invention are clearly and completely described below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be understood as limiting the present invention. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should belong to the scope of protection of the present invention.

[0052] The present invention may be implemented in other specific forms without departing from the basic attributes of the present invention. It should be understood that, without conflict, any and all embodiments of the present invention may be combined with the technical features in any other embodiment or multiple other embodiments to obtain other embodiments. The present invention includes other embodiments obtained by such combination.

[0053] All publications and patents mentioned in the present invention are hereby incorporated into the present invention by reference in their entirety. If the purposes or terms used in any publications and patents incorporated by reference conflict with the purposes or terms used in the present invention, then the purposes and terms of the present invention shall prevail.

[0054] The section headings used in this Summary are for organizational purposes only and are not to be construed as limiting the subject matter described.

[0055] Unless otherwise specified, all technical and scientific terms used in the present invention have the common meaning in the field to which the claimed subject matter belongs. If there are multiple definitions for a term, the definition herein shall prevail.

[0056] Except in the working examples or otherwise indicated, all numbers of quantitative properties such as dosage stated in the specification and claims should be understood to be modified by the term "about" in all cases. It should also be understood that any numerical range recited in the present invention is intended to include all subranges within the range and any combination of the respective endpoints of the range or subrange.

[0057] The words "include", "contain" or "comprises" and the like used in the present invention mean that the elements preceding the word include the elements listed after the word and their equivalents, without excluding unrecorded elements. The terms "contain" or "includes (comprising)" used in the present invention may be open, semi-closed and closed. In other words, the term also includes "essentially consisting of" or "consisting of".

[0058] The term "optionally" in the context of the present invention means that the described situation may or may not be present. For example, a composition comprising an optional diluent means that the composition may or may not include the diluent.

[0059] The term "extractant" in the present invention refers to a substance that reacts with the metal to be extracted (such as lithium, sodium, potassium, etc.) to form an extractant that is extracted into the organic phase through a coordination chemical reaction, and can also extract the extracted metal from the organic phase to the aqueous phase through a certain chemical reaction, thereby achieving the purification or enrichment of the metal. For example, a lithium extractant is used to achieve the purification or enrichment of lithium through extraction.

[0060] The term "hydrocarbon group" in the context of the present invention refers to a group containing only carbon and hydrogen, including saturated carbon and hydrogen groups and unsaturated carbon and hydrogen groups, saturated carbon and hydrogen groups such as alkyl groups, unsaturated carbon and hydrogen groups such as carbon and hydrogen groups containing double bonds, triple bonds or benzene rings. Groups containing double bonds include but are not limited to vinyl, propenyl, butenyl, cyclohexenyl, etc., and carbon and hydrogen groups containing triple bonds include but are not limited to ethynyl, 2-butynyl, etc. Carbon and hydrogen groups containing benzene rings include but are not limited to benzyl, p-methylphenyl, p-ethylphenyl, etc.

[0061] The term "alkyl" in the context of the present invention refers to a branched and straight chain monovalent hydrocarbon group having n carbon atoms and 2n+1 hydrogen atoms. Typical alkyl groups include, but are not limited to, methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, sec-butyl, isobutyl, tert-butyl, pentyl, isopentyl, neopentyl, hexyl, heptyl, octyl, 2-ethylhexyl, nonyl, decyl, dodecyl, hexadecyl, etc.

[0062] The term "alkoxy" in the context of the present invention refers to an alkyl group as defined above that is connected to the parent structure through oxygen. Typical alkoxy groups include, but are not limited to, methoxy, ethoxy, propoxy, isopropoxy, n-butoxy, isobutoxy, sec-butoxy, isobutoxy, tert-butoxy, pentyloxy, isopentyloxy, neopentyloxy, hexyloxy, heptyloxy, octyloxy, 2-ethylhexyloxy, nonyloxy, decyloxy, dodecyloxy, hexadecyloxy, etc.

[0063] The term "cycloalkyl" in the context of the present invention refers to a monocyclic or polycyclic group containing only carbon and hydrogen, which may be saturated or partially unsaturated. In some embodiments, the cycloalkyl is a C3 to C6 cycloalkyl. Illustrative examples of cycloalkyl include, but are not limited to, the following groups: cyclopropyl, cyclobutyl, cyclopentyl, cyclopentenyl, cyclohexyl, cyclohexenyl, etc. In some preferred embodiments, the cycloalkyl is cyclopentyl or cyclohexyl.

[0064] The term "nitro" in the context of the present invention refers to a -NO2 group.

[0065] The term "benzyloxy" in the context of the present invention refers to the monovalent group PhCH2O- remaining after benzyl alcohol loses the hydrogen atom on the hydroxyl group.

[0066] The term "halo" or "halogen" in the context of the present invention refers to a fluorine substituent, a chlorine substituent, a bromine substituent or an iodine substituent. In some embodiments, "halo" or "halogen" is a chlorine substituent or a bromine substituent. In other embodiments, "halo" or "halogen" is a fluorine substituent.

[0067] The term "synergist" in the context of the present invention refers to an agent that can increase the partition ratio after adding it to the extractant. Synergist can be used interchangeably with co-extraction agent in the context of the present invention.

[0068] The term "diluent" in the context of the present invention refers to an agent that improves the physical properties of the extracted organic phase, such as an organic solvent as an extractant, increasing the solubility of the extractant in the organic phase, reducing the viscosity of the extractant and increasing its fluidity, and changing the density of the organic phase.

[0069] The present invention aims to provide a class of lithium extractants with stable properties and low cost, which can selectively extract lithium from lithium-containing aqueous solutions and a lithium extraction system composed thereof. In particular, the present invention provides a lithium extractant for extracting lithium from liquid lithium resources such as low-magnesium and calcium lithium-containing brine, alkaline natural lithium-containing brine, and lithium carbonate / lithium phosphate lithium precipitation mother liquor, so as to replace the β-diketone and salicylate lithium extractants known in the prior art, and overcome the defects of the existing extraction technology for lithium, such as the difficulty in synthesizing the extractant, the high price, and the high dissolution rate.

[0070] The compounds with the structure of Formula 1 involved in the present invention are all conventional commercially available products (except those containing nitro substituents), and the compounds with the structure of Formula 1 containing nitro substituents are prepared by conventional nitration reaction of commercially available compounds with the structure of Formula 1 without nitro substituents.

[0071] The basic concept of the present invention is derived from the understanding and discovery of the following basic principles:

[0072]

[0073] The compound with the above parent structure has the chemical name: 2-(2'-hydroxy-phenyl)benzotriazole. Its phenolic hydroxyl group has a certain acidity and will be deprotonated in an alkaline solution. It is easy to form a chelate reaction with its adjacent electron-rich nitrogen to chelate and coordinate lithium ions. Especially under the action of a phosphine-containing synergist, this chelate reaction is relatively stable and has a high selectivity. The chelate reaction formula is as follows:

[0074]

[0075] Thereby, the lithium ions in the aqueous phase (aq) are extracted into the organic phase (org).

[0076] Among them, the lithium extractant and the synergist can be purchased in bulk on the market, or obtained by further processing of bulk reagents.

[0077] The present invention introduces a conventional small molecule substituent group on the benzene ring of the parent structure 2-(2'-hydroxy-phenyl)benzotriazole, and further finds that this type of compound has similar properties and has the ability to separate lithium ions from aqueous solution. It has the following structure 1:

[0078]

[0079] wherein R1, R2, R3, R4, R5, R6, R7 and R8 are independently selected from hydrogen, halogen, cyano, nitro, C1-C 18 of hydrocarbon groups.

[0080] The substituents on the benzene ring of benzotriazole mainly affect the oil solubility of the lithium extractant, but have little effect on the chelating ability of lithium ions. The present invention is based on comprehensive consideration of the preparation economy of the lithium extractant, the availability of raw materials, and the atomic economy of synthesis, and mainly optimizes the group types of R1 to R4. Based on the fact that the acidity of the phenolic hydroxyl group is greatly affected by the steric effect and steric effect of the substituents on the benzene ring, the preferred more specific lithium extractants of the present invention include but are not limited to:

[0081]

[0082] In a specific embodiment of the present invention, R1, R2, R3 and R4 can be independently selected to be the same or different substituent groups. The introduction of benzyl or alkyl groups on the benzene ring can increase the oil solubility of the lithium extractant and reduce its water solubility. In a preferred embodiment, at least one of R1, R2, R4 and R4 is a nitro group, mainly based on the fact that the introduction of the electron-withdrawing group nitro group in the benzene ring can increase the acidity of the phenolic hydroxyl group, especially the ortho- and / or para-substituted nitro groups of the phenolic hydroxyl group, which significantly improves the acidity of the phenolic hydroxyl group. In the most preferred embodiment, at least one of R2 or R4 is a nitro group, so that its pKa is significantly lower than that of the unsubstituted H-type structure, so that it can be used to extract lithium ions from weakly alkaline aqueous solutions.

[0083] The present invention also provides an extraction system, more specifically an organic phase containing a lithium extractant, which comprises: one or more lithium extractants of formula 1, a synergist and a diluent. In some embodiments, the lithium extractant of formula 1 can also be used in combination with other lithium extractants disclosed in the prior art.

[0084] The lithium extractant of formula 1 provided in the present invention, together with other lithium extractants, synergists and diluents, constitutes a lithium extraction system for extracting lithium from a lithium-containing aqueous solution, i.e., an extraction composition. The other lithium extractants include, but are not limited to, β-diketone extractants, phenol ketone extractants, azo extractants, etc.; the synergist is, for example, a neutral phosphine oxide, specifically: tributyl phosphate, trioctyl phosphate, tri(2-ethylhexyl) phosphate, trihexyl phosphate, tripentyl phosphate, dibutyl butyl phosphate, dibutyl butyl phosphate, di-sec-octyl methyl phosphate, diisooctyl methyl phosphate, dimethylheptyl methyl phosphate, diisooctyl isopropyl phosphate, diisopentyl methyl phosphate, triphenylphosphine oxide, diphenylbenzyl oxide Phosphine, diphenyl (2-hydroxyphenylmethyl) phosphine oxide, 2,5-dihydroxyphenyl (diphenyl) phosphine oxide, trioctyl phosphine oxide (or Cyanex921), trialkyl phosphine oxide TRPO (or Cyanex923) one or more; the diluent is kerosene, D80 solvent oil, D60 solvent oil, n-heptane, cyclohexane, octane, dodecane, petroleum ether, xylene, anisole, methyl isobutyl ketone, toluene, octanone, 5-nonanone, isopentanol, n-butanol, one or more of halogenated benzene.

[0085] By introducing the lithium extractant of formula 1 into the extraction system, on the one hand, the capacity of the extractant can be increased, and on the other hand, the equilibrium pH value of the raffinate can be reduced, thereby reducing the consumption of alkali in the lithium extraction process.

[0086] The addition of the synergist can enhance the acidity by forming hydrogen bonds with the extraction system, and can also enhance the chemical stability of the formed extraction composition under the action of alkaline solution and air. The stronger the alkalinity of the synergist, the more significant the above effect, so the preferred neutral phosphine oxide synergists are tributylphosphine oxide, trioctylphosphine oxide, Cyanex923 and triphenylphosphine oxide.

[0087] The extraction system provided by the present invention can be used to extract lithium from a lithium-containing aqueous solution. The lithium-containing aqueous solution is a lithium precipitation mother liquor of neutral or alkaline salt lake brine with low magnesium and calcium content, geothermal brine, lithium carbonate or lithium phosphate, a mother liquor after preparing lithium hydroxide, and a lithium-containing mother liquor after extracting nickel, cobalt and manganese. When performing the extraction and lithium extraction operation, the concentration of the lithium extractant of formula 1 or the mixture of the lithium extractant of formula 1 and other lithium extractants in the lithium extraction system is 0.01 mol / L to 1.0 mol / L, and the preferred concentration is 0.02 to 0.4 mol / L. The concentration of the synergist in the extraction system is 0.01 mol / L to 2.0 mol / L, and the preferred concentration is 0.02 to 0.4 mol / L. The molar ratio of the lithium extractant of formula 1 to the synergist is 3:1 to 0.5:1, and the preferred molar ratio is 1.5:1 to 0.8:1. The pH value of the aqueous solution containing lithium ions is 5 to 14, and the preferred pH value is 8 to 12.5. For alkaline natural brine, it can be directly reacted with an organic solution containing an extractant to allow the lithium ions in the brine to enter the organic solution containing the extractant; for lithium-containing aqueous solutions with a pH value less than 8, the pH and alkalinity can be adjusted to 8 to 12.5 by adding alkaline compounds, such as alkali metal hydroxides, alkali metal carbonates, alkali metal phosphates, alkali metal borates, ammonia water, ammonium carbonates, ammonium phosphates, and ammonium borates; it is also possible to use an extractant saponified with sodium or / and potassium ions to directly react with the lithium-containing aqueous solution with a pH value less than 8, and through the exchange of sodium or / and potassium ions with lithium ions, the lithium ions in the brine can enter the organic solution containing the extractant.

[0088] The alkali metal hydroxide used to adjust the pH and alkalinity of the lithium-containing aqueous solution or to saponify the lithium extractant is one or more of sodium hydroxide and potassium hydroxide; and / or, the alkali metal carbonate or ammonium carbonate is one or more of sodium carbonate and potassium carbonate, ammonium carbonate, and ammonium bicarbonate; and / or, the alkali metal phosphate or ammonium phosphate is at least one of trisodium phosphate, tripotassium phosphate, triammonium phosphate, disodium hydrogen phosphate, dipotassium hydrogen phosphate and diammonium hydrogen phosphate; and / or, the alkali metal borate or ammonium phosphate is at least one of sodium metaborate, potassium metaborate, ammonium metaborate, sodium tetraborate, potassium tetraborate and ammonium tetraborate.

[0089] In the operation of extracting lithium ions, the volume ratio of the aqueous solution containing lithium ions to the lithium extractant is 30:1 to 1:30, and a further preferred extraction volume ratio is 20:1 to 1:20; the lithium concentration in the aqueous solution containing lithium ions is 0.01 mol / L to 3.0 mol / L, and a further preferred lithium concentration is 0.02 mol / L to 1 mol / L; the extraction operation temperature is -5°C to 40°C, and a further preferred extraction temperature is 15°C to 30°C.

[0090] The extraction process reaches equilibrium within 3 to 30 minutes, and the preferred equilibrium time is 5 to 10 minutes. After that, liquid-liquid stratification is performed by standing or centrifugation, and the remaining aqueous solution after extraction is discharged, and the lithium-loaded organic phase is obtained at the same time.

[0091] Further, the lithium-carrying organic phase is stripped with a stripping agent, so that lithium ions enter the stripping solution, and at the same time, the lithium extraction system has the ability to extract lithium from the lithium-containing aqueous solution again; the stripping agent is an acid solution, and the preferred acid solution is at least one of a carbonate solution, a sulfuric acid solution, a sulfurous acid solution, a hydrochloric acid solution, a nitric acid solution and a phosphoric acid solution. In the acid solution, the concentration of hydrogen ions is 0.05mol / L to 6mol / L, and the further preferred hydrogen ion concentration is 0.1mol / L to 3mol / L. The acid solution can be added once or in steps; the volume ratio of the acid solution to the lithium-carrying organic phase is 1:1 to 1:50, and the further preferred volume ratio is 1:3 to 1:20. After reaching the stripping equilibrium, the lithium concentration in the stripping solution is 0.05mol / L to 10mol / L, and the further preferred lithium concentration is 0.5mol / L to 5mol / L. The action time between the lithium-carrying organic phase and the stripping agent is 3 to 30 minutes, and the further preferred time is 3 to 10 minutes.

[0092] The reaction between the extractant and the lithium-containing aqueous solution and / or the lithium ion removal agent is carried out in a mixing and settling tank, a centrifugal extractor or an extraction tower, and lithium extraction, separation of lithium from sodium, potassium, etc., and concentration of lithium can be achieved through multi-stage extraction, washing, and stripping.

[0093] In order to increase the concentration of lithium ions in the stripping agent, reduce the investment in subsequent concentration equipment and reduce production costs, concentrated acid can be added to the stripping solution multiple times and then used as a stripping agent again to react with the lithium-carrying organic phase to achieve multiple enrichment of lithium ions in the stripping agent; the preferred concentrated acid is 6-12 mol / L hydrochloric acid, 6-18 mol / L sulfuric acid, 6-14 mol / L nitric acid, or 6-15 mol / L phosphoric acid.

[0094] Furthermore, the lithium is concentrated by evaporating the water in the lithium-containing extracting agent, and then sodium carbonate, ammonium carbonate, etc. are added to precipitate lithium carbonate. Moreover, the mother liquor after the lithium carbonate is precipitated can be used again to extract lithium using the extracting agent of the present invention.

[0095] Example:

[0096] The following examples are provided to further illustrate the present invention. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the claims of the present invention. If no specific techniques or conditions are specified in the examples, the techniques or conditions described in the literature in this field or the product instructions are used. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be obtained commercially.

[0097] Example 1

[0098] Extraction agent organic phase configuration: 0.01 mol 2-(2′-hydroxy-5′-methylphenyl)benzotriazole (structure ) and 0.01 mol trioctylphosphine oxide were added to 100 mL diethylbenzene solvent oil, placed in a separatory funnel, and shaken to completely dissolve the solid to form an extractant organic phase. 100 mL of the following lithium-containing aqueous solution of composition B1 was added, shaken at 25° C. for 10 min, and then allowed to stand for phase separation, and the remaining aqueous phase R1 at the bottom was discharged. The concentration of the raffinate was analyzed by an inductively coupled plasma spectrometer (ICP) (the detection method of the subsequent examples is the same), and the results are shown in the following table.

[0099] <![CDATA[c Li / (g / L)]]> <![CDATA[c Na / (g / L)]]> <![CDATA[c K / (g / L)]]> pH Lithium solution B1 0.25 62 none 13.1 Remaining aqueous phase R1 0.10 61.5 none 12.2

[0100] The extraction rate of lithium and sodium ions (E = (c B1 -c R1 ) / c B1 × 100%, the same below) are 60% and 0.82% respectively, and the lithium / sodium separation factor (β Li / Na =(((c Li ) B1 -(c Li ) R1 ) / ((c Na ) B1 -(c Na ) R1 )) / (c Li / c Na ) R1 , the same below) is 184.5.

[0101] Then 100 mL of organic phase was stripped with 5 mL of 0.7 M sulfuric acid solution for 3 minutes at 25 degrees Celsius. The composition of the stripping solution was analyzed as follows: Li + :2.98g / L;Na + :9.9g / L. It can be seen that more than 99% of lithium and sodium can be stripped out, and the organic phase after stripping can be returned for lithium extraction.

[0102] Example 2

[0103] Extraction agent organic phase configuration: 0.01 mol 2-(2'-hydroxy-5'-tert-octylphenyl)benzotriazole (structure ) and 0.01 mol trialkylphosphine oxide were added to an appropriate amount of D80 solvent oil, placed in a separatory funnel, and shaken to completely dissolve the solid to form 100 mL of an extractant organic phase. 100 mL of the following lithium-containing aqueous solution of composition B1 was added, shaken at 18°C ​​for 10 minutes, and then allowed to stand for phase separation, and the remaining aqueous phase R1 at the bottom was discharged. The analysis results are shown in the following table.

[0104]

[0105]

[0106] The extraction rates of lithium and sodium ions were 56% and 0.48%, respectively, and the lithium / sodium separation factor was 261.

[0107] Then 100 mL of organic phase was stripped with 5 mL of 0.7 M sulfuric acid solution for 3 minutes at 25 degrees Celsius. The composition of the stripping solution was analyzed as follows: Li + :2.79g / L;Na + :5.95g / L. It can be seen that more than 99% of lithium and sodium can be stripped out, and the organic phase after stripping can be returned for lithium extraction.

[0108] Example 3

[0109] Extraction agent organic phase configuration: 0.01 mol 2-(2'-hydroxy-3'-nitro-5'-tert-octylphenyl)benzotriazole (structure ) and 0.01 mol trialkylphosphine oxide were added to 100 mL cyclohexane solvent, placed in a separatory funnel, and shaken to completely dissolve the solid to form an extractant organic phase. 100 mL of the lithium-containing aqueous solution of the following composition B1 was added, shaken at 25°C for 10 minutes, and then allowed to stand for phase separation, and the remaining aqueous phase R1 at the bottom was discharged. The analysis results are shown in the following table.

[0110] <![CDATA[c Li / (g / L)]]> <![CDATA[c Na / (g / L)]]> <![CDATA[c K / (g / L)]]> pH Lithium solution B1 0.25 62 none 13.1 Remaining aqueous phase R1 0.0125 56.5 none 10.5

[0111] The extraction rates of lithium and sodium ions were 95% and 8.8%, respectively, and the lithium / sodium separation factor was 195. It can be seen that the extraction rate of lithium was greatly improved and the extraction equilibrium pH was greatly reduced due to the introduction of nitro groups on the benzene ring.

[0112] Example 4

[0113] Extraction agent organic phase configuration: 0.004 mol 2-(2'-hydroxy-3'-nitro-5'-tert-octylphenyl)benzotriazole (structure ), 0.01 mol 2-hydroxy-4-n-octyloxy-5-nitrobenzophenone and 0.014 mol trialkylphosphine oxide were added to 100 mL D80 solvent oil, placed in a separatory funnel, and shaken to completely dissolve the solid to form an extractant organic phase. 100 mL of the following lithium-containing aqueous solution of composition B1 was added, shaken at 25°C for 10 minutes, and then allowed to stand for phase separation, and the remaining aqueous phase R1 at the bottom was discharged. The analysis results are shown in the following table.

[0114] <![CDATA[c Li / (g / L)]]> <![CDATA[c Na / (g / L)]]> <![CDATA[c K / (g / L)]]> pH Lithium solution B1 0.25 62 none 10.72 Remaining aqueous phase R1 0.03 60.03 none 8.95

[0115] The extraction rates for lithium and sodium ions were 88% and 3.2%, respectively, and the lithium / sodium separation factor was 223.

[0116] Example 5

[0117] Extraction agent organic phase configuration: 0.004 mol 2-(2'-hydroxy-3'-nitro-5'-tert-octylphenyl)benzotriazole (structure ), 0.01mol Lix54 and 0.014mol trialkylphosphine oxide were added to 100mL kerosene, placed in a separatory funnel, and shaken to completely dissolve the solid to form an extractant organic phase. 100mL of the lithium-containing aqueous solution with the following composition B1 was added, shaken at 25℃ for 10min, and then allowed to stand for phase separation, and the remaining aqueous phase R1 at the bottom was discharged. The analysis results are shown in the following table.

[0118] <![CDATA[c Li / (g / L)]]> <![CDATA[c Na / (g / L)]]> <![CDATA[c K / (g / L)]]> pH Lithium solution B1 0.25 62 none 12.09 Remaining aqueous phase R1 0.05 61.1 none 9.98

[0119] The extraction rates for lithium and sodium ions were 80% and 1.4%, respectively, and the lithium / sodium separation factor was 270.

[0120] Example 6

[0121] Extraction agent organic phase configuration: 0.01 mol 2-(2'-hydroxy-3'-nitro-5'-tert-octylphenyl)benzotriazole (structure ) and 0.01 mol trialkylphosphine oxide were added to 100 mL cyclohexane solvent, placed in a separatory funnel, and shaken to completely dissolve the solid to form an extractant organic phase. 100 mL of the lithium-containing aqueous solution of the following composition B1 was added, shaken at 25°C for 10 minutes, and then allowed to stand for phase separation, and the remaining aqueous phase R1 at the bottom was discharged. The analysis results are shown in the following table.

[0122] <![CDATA[c Li / (g / L)]]> <![CDATA[c Na / (g / L)]]> <![CDATA[c K / (g / L)]]> pH Lithium solution B1 0.25 62 none 9.0 Remaining aqueous phase R1 0.05 60.8 none 7.8

[0123] The extraction rates of lithium and sodium ions are 80% and 1.9% respectively, and the lithium / sodium separation factor is 202. It can be seen that due to the introduction of nitro group on the benzene ring, a high lithium extraction rate can still be maintained under weak alkaline conditions.

[0124] Example 7

[0125] Extraction agent organic phase configuration: 0.02 mol 2-(2'-hydroxy-5'-tert-octylphenyl)benzotriazole (structure ) and 0.02 mol of trialkylphosphine oxide were added to an appropriate amount of D80 solvent oil, placed in a separatory funnel, and shaken to completely dissolve the solid to form 100 mL of an extractant organic phase. 6 mL of the following lithium-containing aqueous solution of composition B1 was added, shaken at 30°C for 10 minutes, and then allowed to stand for phase separation, and the remaining aqueous phase R1 at the bottom was discharged. The analysis results are shown in the following table.

[0126] <![CDATA[c Li / (g / L)]]> <![CDATA[c Na / (g / L)]]> <![CDATA[c K / (g / L)]]> <![CDATA[c OH -(g / L)]]> Lithium solution B1 23.2 68 15 85 Remaining aqueous phase R1 0.49 46.6 13.8 -

[0127] The extraction rates of lithium, sodium and potassium ions were 97.9%, 31.5% and 8%, respectively.

[0128] Then 100 mL of organic phase was stripped with 6 mL of 2.5 M sulfuric acid solution for 3 minutes at 25 degrees Celsius. The composition of the stripping solution was analyzed as follows: Li + :22.7g / L,Na + :21.3g / L,K + :1.2g / L. It can be seen that after extraction and stripping, the content of sodium, especially potassium, in the lithium-containing liquid is greatly reduced.

[0129] Comparative Example 1: (Compare with Example 1)

[0130] Extraction agent organic phase configuration: 0.01 mol 2-(2′-hydroxy-5′-methylphenyl)benzotriazole (structure ) was added to 100 mL of diethylbenzene solvent oil, placed in a separatory funnel, and shaken to completely dissolve the solid to form an extractant organic phase. 100 mL of the lithium-containing aqueous solution of the following composition B1 was added, shaken at 25° C. for 10 min, and then allowed to stand for phase separation, and the remaining aqueous phase R1 at the bottom was discharged. The concentration of the raffinate was analyzed by an inductively coupled plasma spectrometer (the detection method of the subsequent examples is the same), and the results are shown in the following table.

[0131] <![CDATA[c Li / (g / L)]]> <![CDATA[c Na / (g / L)]]> <![CDATA[c K / (g / L)]]> pH Lithium solution B1 0.25 62 none 13.1 Remaining aqueous phase R1 0.24 61.9 none 13.0

[0132] The extraction rates of lithium and sodium ions are 4% and 0.2%, respectively. Compared with Example 1, when no synergist (such as TRPO) is added, under the same conditions, the lithium extraction performance of 2-(2'-hydroxy-5'-methylphenyl)benzotriazole is significantly reduced. On the contrary, the addition of the synergist can enhance the lithium extraction performance of the novel extractant of the present invention to a certain extent.

[0133] Comparative Example 2: (Compare with Example 4)

[0134] Extraction agent organic phase configuration: 0.01mol 2-hydroxy-4-n-octyloxy-5-nitrobenzophenone and 0.01mol trialkylphosphine oxide were added to 100mL D80 solvent oil, placed in a separatory funnel, and shaken to form an extraction agent organic phase. 100mL of the lithium-containing aqueous solution of the following composition B1 was added, shaken at 25°C for 10min, and then allowed to stand for phase separation, and the remaining aqueous phase R1 at the bottom was discharged. The analysis results are shown in the following table.

[0135] <![CDATA[c Li / (g / L)]]> <![CDATA[c Na / (g / L)]]> pH Lithium solution B1 0.25 62 10.72 Remaining aqueous phase R1 0.087 61.5 9.29

[0136] The extraction rates of lithium and sodium ions were 64.78% and 0.81% respectively, and the lithium / sodium separation factor was 230.4. Compared with Example 4, it can be seen that when 2-(2'-hydroxy-3'-nitro-5'-tert-octylphenyl)benzotriazole was not added in this example, the lithium extraction rate decreased significantly, whereas the addition of 2-(2'-hydroxy-3'-nitro-5'-tert-octylphenyl)benzotriazole could significantly improve the lithium extraction rate of 2-hydroxy-4-n-octyloxy-5-nitrobenzophenone.

[0137] Comparative Example 3 (Compare with Example 5)

[0138] Preparation of extractant organic phase: 0.01 mol Lix54 and 0.01 mol trialkylphosphine oxide were added to 100 mL kerosene, placed in a separatory funnel, and shaken to form an extractant organic phase. 100 mL of lithium-containing aqueous solution with the following composition B1 was added, shaken at 25°C for 10 minutes, and then allowed to stand for phase separation, and the remaining aqueous phase R1 at the bottom was discharged. The analysis results are shown in the following table.

[0139] <![CDATA[c Li / (g / L)]]> <![CDATA[c Na / (g / L)]]> <![CDATA[c K / (g / L)]]> pH Lithium solution B1 0.25 62 none 12.09 Remaining aqueous phase R1 0.11 61.72 none 10.33

[0140] The extraction rates of lithium and sodium ions were 56% and 0.5%, respectively, and the lithium / sodium separation factor was 280. Compared with Example 5, it can be seen that when 2-(2'-hydroxy-3'-nitro-5'-tert-octylphenyl)benzotriazole was not added in this example, the lithium extraction rate decreased significantly. On the contrary, the addition of 2-(2'-hydroxy-3'-nitro-5'-tert-octylphenyl)benzotriazole can significantly improve the lithium extraction of Lix54 and reduce the alkali consumption of lithium extraction.

Claims

1. A lithium extractant, characterized in that: It has the structure of formula 1: wherein R1, R2, R3, R4, R5, R6, R7 and R8 are independently selected from hydrogen, halogen substituents, nitro, cyano or C1-C 18 of hydrocarbon groups.

2. A lithium extractant according to claim 1, characterized in that: C1~C 18 The hydrocarbon groups include C1~C 18 Alkyl, or C2~C 18 A hydrocarbon group containing double bonds and / or triple bonds and / or benzene rings.

3. A lithium extractant according to claim 1 or 2, characterized in that: R1, R2, R3 and R4 are independently selected from C 1～10 Hydrocarbyl, hydrogen, halogen substituent, nitro or C 1～6 Alkoxy, and R5, R6, R7 and R8 are independently selected from hydrogen or C 1～10 Alkyl.

4. A lithium extraction system, characterized in that: The lithium extractant comprises the lithium extractant according to any one of claims 1 to 3.

5. A lithium extraction system according to claim 4, characterized in that: The concentration of the lithium extractant in the lithium extraction system is 0.01 mol / L to 1.0 mol / L.

6. A lithium extraction system according to claim 4, characterized in that: Synergists and diluents are also included.

7. A lithium extraction system according to claim 6, characterized in that: The synergist comprises at least one of tributyl phosphate, trioctyl phosphate, tri(2-ethylhexyl) phosphate, trihexyl phosphate, tripentyl phosphate, dibutyl butyl phosphate, dibutyl butyl phosphate, di-sec-octyl methyl phosphate, diisooctyl methyl phosphate, diisooctyl isopropyl phosphate, diisopentyl methyl phosphate, triphenyl phosphine oxide, diphenyl benzyl phosphine oxide, diphenyl (2-hydroxyphenylmethyl) phosphine oxide, 2,5-dihydroxyphenyl (diphenyl) phosphine oxide, trioctyl phosphine oxide, and trialkyl phosphine oxide TRPO.

8. A lithium extraction system according to claim 6, characterized in that: The diluent includes at least one of kerosene, D80 solvent oil, D60 solvent oil, n-heptane, cyclohexane, octane, dodecane, petroleum ether, xylene, anisole, methyl isobutyl ketone, toluene, octanone, 5-nonanone, isopentanol, n-butanol, and halogenated benzene.

9. A lithium extraction system according to any one of claims 4 to 8, characterized in that: The concentration of the synergist in the lithium extraction system is 0.01 mol / L to 2.0 mol / L.

10. A lithium extraction system according to any one of claims 4 to 8, characterized in that: The molar ratio of the lithium extractant to the synergist is 3:1 to 0.5:

1.

11. A lithium extraction system according to claim 4, characterized in that: The lithium extractant is used alone or in combination with other lithium extractants except the lithium extractant; the other lithium extractants include at least one of beta diketone extractants, phenol ketone extractants and azo extractants.

12. A method for extracting lithium, characterized in that: The lithium extraction system according to any one of claims 4 to 11 is mixed with an aqueous solution containing lithium ions for extraction to obtain a lithium-loaded organic phase and a raffinate.

13. A method for extracting lithium according to claim 12, characterized in that: The initial pH value of the aqueous solution containing lithium ions is 5-14.

14. A method for extracting lithium according to claim 12, characterized in that: The aqueous solution containing lithium ions is adjusted in pH by adding an alkaline substance, wherein the alkaline substance comprises at least one of alkali metal hydroxides, alkali metal carbonates, alkali metal phosphates, alkali metal borates, ammonium carbonates, ammonium phosphates, ammonium borates, and ammonia water.

15. A method for extracting lithium according to claim 12, 13 or 14, characterized in that: The aqueous solution containing lithium ions comprises at least one of alkaline natural brine, lithium precipitation mother liquor for producing lithium carbonate, lithium precipitation mother liquor for producing lithium phosphate, mother liquor after preparing lithium hydroxide, and lithium-containing mother liquor after extracting nickel, cobalt and manganese.

16. A method for extracting lithium according to claim 14, characterized in that: The alkali metal hydroxide includes at least one of sodium hydroxide and potassium hydroxide; The alkali metal carbonate includes at least one of sodium carbonate and potassium carbonate; The alkali metal phosphate includes at least one of trisodium phosphate, tripotassium phosphate, disodium hydrogen phosphate, and dipotassium hydrogen phosphate; The alkali metal borate includes at least one of sodium metaborate, potassium metaborate, sodium tetraborate and potassium tetraborate; The ammonium carbonate salt includes at least one of ammonium bicarbonate and ammonium carbonate; The ammonium phosphate salt includes at least one of ammonium hydrogen phosphate and ammonium dihydrogen phosphate; The ammonium borate salt includes at least one of ammonium metaborate and ammonium tetraborate.

17. A method for extracting lithium according to claim 12 or 13, characterized in that: When the initial pH value of the aqueous solution containing lithium ions is 5 to 8, the lithium extraction system undergoes saponification pretreatment; when the initial pH value of the aqueous solution containing lithium ions is greater than 8, the lithium extraction system does not need to undergo saponification pretreatment.

18. A method for extracting lithium according to claim 17, characterized in that: The saponification pretreatment uses at least one alkali solution selected from the group consisting of sodium hydroxide solution, potassium hydroxide solution, sodium carbonate solution, potassium carbonate solution, sodium bicarbonate solution and potassium bicarbonate aqueous solution.

19. The method for extracting lithium according to claim 12, characterized in that: The extraction conditions are: one-stage or multi-stage extraction method, phase volume ratio O / W=30:1-1:30, and extraction time is 3-30 minutes.

20. A method for extracting lithium according to claim 12 or 13, characterized in that: The lithium concentration in the aqueous solution containing lithium ions is 0.01 mol / L to 4.0 mol / L.

21. A method for extracting lithium according to claim 12, characterized in that: The lithium-loaded organic phase is stripped with acid solution to obtain a lithium-rich solution.

22. A method for extracting lithium according to claim 21, characterized in that: The acid solution includes at least one of a carbonic acid solution, a sulfuric acid solution, a sulfurous acid solution, a hydrochloric acid solution, a nitric acid solution, and a phosphoric acid solution; and / or the concentration of hydrogen ions in the acid solution is 0.05 mol / L to 6 mol / L.

23. The method for extracting lithium according to claim 21, characterized in that: The stripping conditions are: one-stage or multi-stage stripping method, phase volume ratio W / O=1:1-1:50, and stripping time is 3-30 minutes.

24. A method for extracting lithium according to claim 12 or 21, characterized in that: The extraction is carried out in a mixing and settling tank, a centrifugal extractor or an extraction tower; and / or the stripping is carried out in a mixing and settling tank, a centrifugal extractor or an extraction tower.

25. The method for extracting lithium according to claim 23, characterized in that: In the multi-stage stripping process, after the acid solution is stripped in one stage, concentrated acid is added for the next stage of stripping; the concentrated acid is 6-12 mol / L hydrochloric acid, 6-18 mol / L sulfuric acid, 6-14 mol / L nitric acid or 6-15 mol / L phosphoric acid.

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