CN112267031B - Method for extracting lithium by using phosphate ionic liquid - Google Patents

Method for extracting lithium by using phosphate ionic liquid Download PDF

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CN112267031B
CN112267031B CN202011075738.6A CN202011075738A CN112267031B CN 112267031 B CN112267031 B CN 112267031B CN 202011075738 A CN202011075738 A CN 202011075738A CN 112267031 B CN112267031 B CN 112267031B
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ionic liquid
phosphate
lithium
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hexafluorophosphate
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CN112267031A (en
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石成龙
秦亚茹
李宏霞
卢娜娜
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Qinghai Nationalities University
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B26/00—Obtaining alkali, alkaline earth metals or magnesium
    • C22B26/10—Obtaining alkali metals
    • C22B26/12—Obtaining lithium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
    • C22B3/20—Treatment or purification of solutions, e.g. obtained by leaching
    • C22B3/26—Treatment or purification of solutions, e.g. obtained by leaching by liquid-liquid extraction using organic compounds
    • C22B3/38—Treatment or purification of solutions, e.g. obtained by leaching by liquid-liquid extraction using organic compounds containing phosphorus
    • C22B3/387—Cyclic or polycyclic compounds
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling

Abstract

The invention discloses a phosphate ionic liquid, a preparation method, application and an extraction method thereof, wherein the preparation method of the ionic liquid comprises the following steps: dropwise adding dialkyl phosphate into bromoalkyl alcohol for reaction, and then diluting, filtering, washing, drying and decompressing to obtain a compound I; mixing the compound I and alkyl imidazole, washing, and drying in vacuum to obtain a compound II; and mixing the compound II with hexafluorophosphate or bis (trifluoromethyl) sulfonyl imide, standing, separating, washing and vacuum drying to obtain the phosphate ionic liquid. The invention also discloses the ionic liquid prepared by the method, application of the ionic liquid in lithium extraction and an extraction method. According to the invention, phosphate groups are introduced into cations of the ionic liquid, hexafluorophosphate groups or bis-trifluoromethyl sulfimide is selected as anions, the ionic liquid is prepared, and lithium ions are extracted and separated, so that the problems of low extraction efficiency, ionic liquid loss and the like in the prior art are effectively solved.

Description

Method for extracting lithium by using phosphate ionic liquid
Technical Field
The invention relates to the technical field of lithium extraction, and particularly relates to a phosphate ionic liquid, and a preparation method, application and an extraction method thereof.
Background
Lithium called 'white gold' in the 21 st century is an alkali metal with the smallest atomic radius and the lightest mass, and because of the unique physicochemical properties, the lithium has wide application in the fields of aerospace, lithium batteries, aluminum lithium alloys, high-speed rails, airplanes, military affairs, oceans and the like, and the lithium salt are regarded as important novel energy and strategic resources. The existing forms of lithium in nature mainly include solid lithium ore and natural water rich in lithium, wherein lithium in salt lake brine is an important source of all economic lithium products. China has rich lithium resources in salt lakes, and is mainly distributed in Qinghai lakes and Tibet lakes. Compared with foreign salt lakes, the lithium resources of the salt lakes in China are characterized in that the mass concentration ratio of magnesium to lithium is relatively high and generally reaches 40-1200. Because lithium and magnesium are located diagonally in the periodic table, the lithium and magnesium are chemically very similar, which makes it very difficult to extract lithium from the brine separately. The solvent extraction method is one of the most effective and easily-realized industrial methods suitable for extracting lithium from salt lake brine with high magnesium-lithium ratio, and has the advantages of convenience in operation, simple process, high efficiency and the like. Wherein the better extraction effect is tributyl phosphate (TBP)/ferric trichloride (FeCl)3) Kerosene system in which FeCl is present3Is added into salt lake brine as a co-extractant to react with Cl existing in the brine-Formation of LiFeCl4Complex, liFeCl4Then reacting with TBP to formThe formed complex enters an organic phase to realize the separation of lithium ions. The extraction system has high extraction efficiency on lithium, but the system needs to extract under a strong acid condition, the equipment corrosion is serious, the solvent loss of an extracting agent is large, and the use of a large amount of volatile organic solvents in the system can cause pollution to the environment.
The ionic liquid as a novel green solvent is completely composed of positive and negative ions, has the characteristics of high stability, good solubility, extremely low vapor pressure, designability and the like, and is expected to replace the traditional volatile organic solvent. In the prior art, imidazole hexafluorophosphate or imidazole diimine ionic liquid is used as a co-extraction agent to separate lithium ions from salt lake brine. However, the used imidazolium hexafluorophosphate or imidazolium bisimide ionic liquid does not have the function of extracting lithium, but improves the extraction rate of lithium in a system by a cation exchange mode. This results in the imidazole cations of the ionic liquid being exchanged into the aqueous brine solution during extraction, resulting in loss of the ionic liquid. Therefore, it is urgently needed to design a novel ionic liquid which can be used as an extractant of lithium and avoid the loss caused by cation exchange.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a phosphate ionic liquid, and a preparation method, application and an extraction method thereof, wherein phosphate groups with strong extraction performance on lithium are introduced into cations of the ionic liquid, hexafluorophosphate groups or bis (trifluoromethyl) sulfimide are simultaneously selected as anions to prepare the phosphate ionic liquid, and the phosphate ionic liquid is used as an extracting agent to extract and separate lithium ions in salt lake brine, so that the problems of low extraction efficiency, ionic liquid loss and the like in the prior art are effectively solved.
In order to achieve the purpose, the technical scheme adopted by the invention for solving the technical problem is as follows: the preparation method of the phosphate ionic liquid comprises the following steps:
(1) Dropwise adding dialkyl phosphate into bromoalkyl alcohol under the conditions of 10-15 ℃ ice water bath and alkalinity, removing the ice water bath, reacting for 3-5h at room temperature, and then sequentially diluting, filtering, washing, drying and decompressing to obtain a compound I; the mol ratio of dialkyl phosphate and alkyl bromide is 1:1-1.5;
(2) Mixing the compound I obtained in the step (1) with alkyl imidazole, stirring at room temperature for 36-60h, washing and purifying with ethyl acetate, and drying in vacuum to obtain a compound II; the molar ratio of the compound I to the alkyl imidazole is 1:1-2;
(3) Mixing the compound II obtained in the step (2) with hexafluorophosphate or bis (trifluoromethyl) sulfonyl imide, stirring and reacting for 20-28h at room temperature, and then sequentially standing, separating, washing and vacuum drying to obtain phosphate ionic liquid; the molar ratio of the compound II to the hexafluorophosphate or bis-trifluoromethylsulfonyl imide salt is 1:1-2.
Further, in the step (1), the mixture is diluted and filtered by dichloromethane, and then washed by 2vt percent dilute hydrochloric acid for 2 to 4 times, washed by deionized water for 2 to 4 times, dried by anhydrous sodium sulfate, and decompressed to remove carbon tetrachloride and dichloromethane.
Further, the dialkyl phosphate has the structural formula:
Figure BDA0002716652430000031
the structural formula of the bromoalkyl alcohol is as follows:
Figure BDA0002716652430000032
the alkyl imidazole has the structural formula:
Figure BDA0002716652430000033
wherein R is1And R2Is C2-C8 linear or branched alkyl, R3Is C1-C8 straight chain or straight chain alkyl, and n is an integer between 0 and 8.
Further, the hexafluorophosphate is at least one of lithium hexafluorophosphate, sodium hexafluorophosphate and potassium hexafluorophosphate; the bis-trifluoromethyl sulfonyl imide salt is at least one of bis-trifluoromethyl sulfonyl imide lithium, bis-trifluoromethyl sulfonyl imide sodium and bis-trifluoromethyl sulfonyl imide potassium.
In the preparation of phosphate ionic liquid, in the first step, dialkyl phosphate and alkyl bromide are subjected to alkaline conditions to obtain a compound I (alkyl bromide phosphate), wherein the reaction formula is as follows:
Figure BDA0002716652430000034
and secondly, reacting the compound I with alkyl imidazole to obtain a compound II (bromoimidazole ionic liquid), wherein the reaction formula is as follows:
Figure BDA0002716652430000041
thirdly, reacting the compound II with hexafluorophosphate or bis (trifluoromethyl) sulfonyl imide salt to obtain a target product phosphate ionic liquid (a compound III or a compound IV), wherein the reaction formula is as follows:
Figure BDA0002716652430000042
the phosphate ionic liquid prepared by the preparation method of the phosphate ionic liquid.
The phosphate ionic liquid is applied to extraction of lithium.
A method for extracting lithium by using phosphate ionic liquid comprises the following steps:
(1) Drying the phosphate ionic liquid, and mixing the dried phosphate ionic liquid with a diluent according to the volume ratio of 1-4:1 to obtain an extracted organic phase;
(2) Mixing the extracted organic phase obtained in the step (1) with a raw material liquid according to a volume ratio of 0.1-3:1, performing oscillation extraction at a temperature of 10-70 ℃ for 5-360min, and centrifuging to obtain a raffinate and a loaded organic phase;
(3) And (3) carrying out back extraction on the loaded organic phase obtained in the step (2) and 0.01-12mol/L of stripping agent according to the volume ratio of 1-10 at the temperature of 10-70 ℃, and centrifuging to obtain a purified lithium solution.
Further, the diluent is at least one of anisole, chloroform, kerosene, dichloromethane, 1,2-dichloroethane, n-hexane, n-heptane, carbon tetrachloride, tetrachloroethylene, toluene, xylene, diethylbenzene, bromobenzene, nitrobenzene, petroleum ether, tributyl phosphate, trioctyl phosphate and trialkylphosphine oxide.
Further, in the step (2), the raw material solution is lithium-containing salt lake brine, the concentration of lithium ions is 0.05-10g/L, and the mass ratio of magnesium to lithium is 1-100.
Further, in the step (3), the stripping agent is hydrochloric acid solution or sulfuric acid solution.
In summary, the invention has the following advantages:
1. according to the invention, phosphate groups with strong extraction performance on lithium are introduced into cations of the ionic liquid, and hexafluorophosphate groups or bis-trifluoromethylsulfonyl imide is selected as anions to prepare the phosphate ionic liquid, and the phosphate ionic liquid is used as an extractant to extract and separate lithium ions in salt lake brine, so that equipment cannot be corroded, environmental pollution cannot be caused, loss caused by ionic liquid cation exchange or anion exchange can be avoided, and the problems of low extraction efficiency, ionic liquid loss and the like in the prior art are effectively solved.
2. Phosphate ionic liquid utilizes the advantage of designability of the ionic liquid, functional groups capable of complexing with lithium are introduced into cations of the ionic liquid, the aim of separating and purifying lithium from a lithium-containing solution is fulfilled, and the phosphate ionic liquid has better extraction performance; meanwhile, the phosphate ionic liquid is composed of ions and hardly volatilizes, so that the use proportion of the traditional volatile organic solvent is reduced, the advantage of environmental protection of the ionic liquid is ensured, and the extraction performance is higher.
3. When the phosphate ionic liquid is applied to extracting lithium ions from salt lake brine, a co-extractant of ferric trichloride is not required to be added in the extraction process, acid is not required to be added to adjust the pH value, the extraction cost is reduced, the process operation is simple, and the application prospect is good.
Detailed Description
Example 1
A preparation method of phosphate ionic liquid comprises the following steps:
(1) Adding a 25wt% sodium hydroxide aqueous solution (35 mL), 3-bromopropanol (20.85 g), carbon tetrachloride (30 mL), dichloromethane (30 mL) and tetrabutylammonium bromide (TBAB, 0.39 g) into a four-neck flask provided with a stirrer, a constant pressure dropping funnel, a thermometer and an air guide tube in sequence, slowly dropping a mixed solution of di-n-butyl phosphite (36.38 g) and carbon tetrachloride (35 mL) into the system through the constant pressure dropping funnel under the condition of an ice-water bath at 10-15 ℃, removing the ice-water bath, reacting for 4h at room temperature, diluting and filtering with dichloromethane (25 mL), washing for 3 times with 2vt% diluted hydrochloric acid (25 mL) in sequence, washing for 3 times with deionized water (25 mL), drying with anhydrous sodium sulfate, and removing carbon tetrachloride and dichloromethane under reduced pressure to obtain a compound I (bromopropyl-di-n-butyl phosphate); the reaction process is as follows:
Figure BDA0002716652430000061
(2) Mixing 4.97g of the compound I obtained in the step (1) with 1.23g N-methylimidazole, stirring at room temperature for 48h, washing and purifying with ethyl acetate, and drying in vacuum for 24h to obtain a compound II (1- (di-n-butyl-n-propyl phosphate) -3-methylimidazolium bromide); the reaction process is as follows:
Figure BDA0002716652430000062
(3) And (3) dissolving 6.20g of the compound II obtained in the step (2) in 30mL of deionized water, mixing with 2.76g of an aqueous solution of potassium hexafluorophosphate (30 mL of deionized water), stirring at room temperature for reaction for 24 hours, standing for layering, separating an organic phase, washing until no bromide ion exists in an aqueous phase, and drying in vacuum to obtain the phosphate ionic liquid (target ionic liquid). The reaction process is as follows:
Figure BDA0002716652430000063
the phosphate ionic liquid prepared by the method is applied to lithium extraction, and the extraction method comprises the following steps:
(1) Drying the phosphate ionic liquid, and mixing the dried phosphate ionic liquid with a diluent dichloroethane according to a volume ratio of 1:1 to obtain an extracted organic phase;
(2) Mixing the extracted organic phase obtained in the step (1) with a raw material liquid according to a volume ratio of 2:1, performing oscillation extraction at the temperature of 20 ℃ for 30min, and centrifuging to obtain a raffinate and a loaded organic phase; the raw material liquid is lithium-containing salt lake brine, the concentration of lithium ions is 2.0g/L, and the concentration of magnesium ions is 90g/L;
(3) And (3) carrying out back extraction on the loaded organic phase obtained in the step (2) and 1mol/L hydrochloric acid solution according to the volume ratio of 1:1 for 30min at the temperature of 20 ℃, and centrifuging to obtain a purified lithium solution.
Example 2
A preparation method of phosphate ionic liquid comprises the following steps:
(1) Adding 25wt% of sodium hydroxide aqueous solution (35 mL), 4-bromobutanol (22.95 g), carbon tetrachloride (30 mL), dichloromethane (30 mL) and tetrabutylammonium bromide (TBAB, 0.39 g) into a four-neck flask provided with a stirrer, a constant pressure dropping funnel, a thermometer and an air guide tube in sequence, slowly dropping a mixed solution of diisoamyl phosphate (44.44 g) and carbon tetrachloride (35 mL) into the system through the constant pressure dropping funnel under the condition of an ice-water bath at 10-15 ℃, removing the ice-water bath, reacting at room temperature for 4 hours, diluting and filtering with dichloromethane (25 mL), washing with 2vt% of dilute hydrochloric acid (25 mL) for 3 times in sequence, washing with deionized water (25 mL) for 3 times, drying with anhydrous sodium sulfate, and removing carbon tetrachloride and dichloromethane under reduced pressure to obtain a compound I (bromo-butyl-diisoamyl phosphate); the reaction process is as follows:
Figure BDA0002716652430000071
(2) Mixing the compound I (5.60 g) obtained in the step (1) with N-methylimidazole (1.23 g), stirring at room temperature for 48h, washing and purifying with ethyl acetate, and drying in vacuum for 24h to obtain a compound II; the reaction process is as follows:
Figure BDA0002716652430000081
(3) Will go to stepCompound II (6.83 g) obtained in step (2) and lithium bistrifluoromethylsulfonimide (Li (CF)3SO2)2N) (4.31 g), stirring and reacting for 24 hours at room temperature, then standing and layering, separating an organic phase, washing until no bromide ion exists in a water phase, and drying in vacuum to obtain phosphate ionic liquid (target ionic liquid); the reaction process is as follows:
Figure BDA0002716652430000082
the phosphate ionic liquid prepared by the method is applied to extracting lithium, and the extraction method comprises the following steps:
(1) Drying the phosphate ionic liquid, and mixing the dried phosphate ionic liquid with diluent tributyl phosphate according to the volume ratio of 1:1 to obtain an extracted organic phase;
(2) Mixing the extracted organic phase obtained in the step (1) with a raw material solution according to a volume ratio of 3:1, oscillating and extracting for 30min at the temperature of 20 ℃, and centrifuging to obtain raffinate and a loaded organic phase; the raw material liquid is lithium-containing salt lake brine, the concentration of lithium ions is 2.0g/L, and the concentration of magnesium ions is 90g/L;
(3) And (3) carrying out back extraction on the loaded organic phase obtained in the step (2) and 1mol/L hydrochloric acid solution according to the volume ratio of 1:1 for 30min at the temperature of 20 ℃, and centrifuging to obtain a purified lithium solution.
Example 3
A preparation method of phosphate ionic liquid comprises the following steps:
(1) Adding 25wt% of sodium hydroxide aqueous solution (35 mL), 4-bromobutanol (22.95 g), carbon tetrachloride (30 mL), dichloromethane (30 mL) and tetrabutylammonium bromide (TBAB, 0.39 g) into a four-neck flask provided with a stirrer, a constant-pressure dropping funnel, a thermometer and an air guide tube in sequence, slowly dropping a mixed solution of dibutyl phosphite (36.38 g) and carbon tetrachloride (35 mL) into the system through the constant-pressure dropping funnel under the condition of an ice-water bath at 10-15 ℃, removing the ice-water bath, reacting at room temperature for 4 hours, diluting and filtering with dichloromethane (25 mL), washing with 2vt% of dilute hydrochloric acid (25 mL) for 3 times in sequence, washing with deionized water (25 mL) for 3 times, drying with anhydrous sodium sulfate, and removing the carbon tetrachloride and the dichloromethane under reduced pressure to obtain a compound I (bromobutyl-di-n-butyl phosphate); the reaction process is as follows:
Figure BDA0002716652430000091
(2) Mixing the compound I (5.18 g) obtained in the step (1) with N-butylimidazole (1.86 g), stirring at room temperature for 48h, washing with ethyl acetate, purifying, and vacuum-drying to obtain a compound II; the reaction process is as follows:
Figure BDA0002716652430000092
(3) And (3) mixing the compound II (7.04 g) obtained in the step (2) with sodium bistrifluoromethylsulfonyl imide (4.55 g), stirring and reacting at room temperature for 24h, then sequentially standing and layering, separating an organic phase, washing until no bromide ion exists in an aqueous phase, and drying in vacuum to obtain the phosphate ionic liquid (target ionic liquid). The reaction process is as follows:
Figure BDA0002716652430000101
the phosphate ionic liquid prepared by the method is applied to extracting lithium, and the extraction method comprises the following steps:
(1) Drying the phosphate ionic liquid, and mixing the dried phosphate ionic liquid with diluent n-hexane according to the volume ratio of 1:1 to obtain an extracted organic phase;
(2) Mixing the extracted organic phase obtained in the step (1) with a raw material liquid according to a volume ratio of 2:1, performing oscillation extraction at the temperature of 20 ℃ for 30min, and centrifuging to obtain a raffinate and a loaded organic phase; the raw material liquid is lithium-containing salt lake brine, the concentration of lithium ions is 2.0g/L, and the concentration of magnesium ions is 90g/L;
(3) And (3) carrying out back extraction on the loaded organic phase obtained in the step (2) and 1mol/L hydrochloric acid solution according to the volume ratio of 1:1 for 30min at the temperature of 20 ℃, and centrifuging to obtain a purified lithium solution.
Comparative example 1
A method for extracting lithium, which comprises the following steps:
(1) Preparing an extraction organic phase: mixing conventional ionic liquid 1-butyl-3-methylimidazole bistrifluoromethylsulfonyl imide salt ([ C ]4mim][NTf2]) And uniformly mixing the extract with a diluent n-hexane according to a volume ratio of 1:1 to prepare an extracted organic phase.
(2) And (3) extraction: lithium-containing salt lake brine is used as a raw material liquid, wherein the concentration of lithium ions is 2.0g/L, and the concentration of magnesium ions is 90g/L. And (2) putting the extracted organic phase obtained in the step (1) and the raw material liquid into a separating funnel according to the volume ratio of 2:1, and performing shaking extraction for 30min at the room temperature of 20 ℃. And after extraction, centrifugally separating the mixed solution to obtain raffinate and a loaded organic phase.
(3) And (3) carrying out back extraction on the loaded organic phase by adopting a 2mol/L hydrochloric acid solution as a back extractant, wherein the volume ratio of the loaded organic phase to the back extractant is 1:1, and the back extraction time is 30min at the room temperature of 20 ℃. And (4) centrifugally separating the mixed solution after the back extraction is finished to recover lithium.
Comparative example 2
A method for extracting lithium, which comprises the following steps:
(1) Preparing an extraction organic phase: mixing ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([ C ]4mim][PF6]) Uniformly mixing the extract with tributyl phosphate (TBP) according to the volume ratio of 1:1 to prepare an extracted organic phase.
(2) And (3) extraction: lithium-containing salt lake brine is used as a raw material liquid, wherein the concentration of lithium ions is 2.0g/L, and the concentration of magnesium ions is 90g/L. Adding co-extractant ferric trichloride (FeCl) into the raw material liquid3) While at the same time for preventing Fe3+Adjusting the pH of the raw material solution to 1.5. And (2) putting the extracted organic phase obtained in the step (1) and the raw material liquid into a separating funnel according to the volume ratio of 2:1, and performing shaking extraction for 30min at the room temperature of 20 ℃. And after extraction, centrifugally separating the mixed solution to obtain raffinate and a loaded organic phase.
(3) And (3) carrying out back extraction on the loaded organic phase by adopting a 2mol/L hydrochloric acid solution as a back extractant, wherein the volume ratio of the loaded organic phase to the back extractant is 1:1, and the back extraction time is 30min at the room temperature of 20 ℃. And (4) centrifugally separating the mixed solution after the back extraction is finished to recover lithium.
Centrifuging raffinate obtained in the extraction of the examples 1-3 and the comparative examples 1-2 at the rotating speed of 6000r/min for 10min, and measuring the concentration of lithium ions in the raffinate to obtain the extraction efficiency of the lithium ions; and meanwhile, centrifuging the recovered lithium solution for 10min at the rotating speed of 8000r/min, separating to obtain the lithium solution and an extraction organic phase, and measuring the concentration of lithium ions in the lithium solution to obtain the lithium ion back-extraction efficiency, wherein the result is shown in table 1.
TABLE 1 lithium ion extraction efficiency and stripping efficiency
Figure BDA0002716652430000111
Figure BDA0002716652430000121
As can be seen from table 1, the extraction efficiency and the back-extraction efficiency of the present invention are both high, because the present invention introduces phosphate groups having a strong extraction performance for lithium into cations of the ionic liquid, and selects hexafluorophosphate groups or bis-trifluoromethylsulfonyl imide as anions to prepare phosphate ionic liquids, and functional groups capable of complexing with lithium exist in the ionic liquids, which can improve the extraction efficiency.
While the present invention has been described in detail with reference to the specific embodiments thereof, it should not be construed as limited by the scope of the present patent. Various modifications and changes may be made by those skilled in the art without inventive step within the scope of the appended claims.

Claims (7)

1. A method for extracting lithium by using phosphate ionic liquid is characterized by comprising the following steps:
(1) Drying the phosphate ionic liquid, and mixing the dried phosphate ionic liquid with a diluent according to the volume ratio of 1-4:1 to obtain an extracted organic phase;
(2) Mixing the extracted organic phase obtained in the step (1) with a raw material liquid according to a volume ratio of 0.1-3:1, performing oscillation extraction at a temperature of 10-70 ℃ for 5-360min, and centrifuging to obtain a raffinate and a loaded organic phase;
(3) Carrying out back extraction on the loaded organic phase obtained in the step (2) and 0.01-12mol/L of stripping agent according to a volume ratio of 1-10;
the preparation method of the phosphate ionic liquid comprises the following steps:
(1.1) dropwise adding dialkyl phosphate into bromoalkyl alcohol in an ice-water bath at the temperature of 10-15 ℃ and under an alkaline condition, removing the ice-water bath, reacting at room temperature for 3-5h, and then sequentially diluting, filtering, washing, drying and decompressing to obtain a compound I; the mole ratio of the dialkyl phosphate to the alkyl bromide is 1:1-1.5;
(1.2) mixing the compound I obtained in the step (1.1) with alkyl imidazole, stirring at room temperature for 36-60h, washing with ethyl acetate, purifying, and drying in vacuum to obtain a compound II; the molar ratio of the compound I to the alkyl imidazole is 1:1-2;
(1.3) mixing the compound II obtained in the step (1.2) with hexafluorophosphate or bis (trifluoromethyl) sulfonyl imide, stirring and reacting for 20-28h at room temperature, and then sequentially standing, separating, washing and vacuum drying to obtain phosphate ionic liquid; the molar ratio of the compound II to the hexafluorophosphate or bis-trifluoromethylsulfonyl imide salt is 1:1-2.
2. The method for extracting lithium using phosphate-based ionic liquid according to claim 1, wherein in the step (1.1), the solution is diluted and filtered with dichloromethane, and then washed with 2vt% diluted hydrochloric acid for 2 to 4 times, washed with deionized water for 2 to 4 times, dried with anhydrous sodium sulfate, and then carbon tetrachloride and dichloromethane are removed under reduced pressure.
3. The method for extracting lithium by using phosphate ionic liquid as claimed in claim 1, wherein the dialkyl phosphate has a structural formula:
Figure FDA0003846778230000021
the structural formula of the bromoalkyl alcohol is as follows:
Figure FDA0003846778230000022
the alkyl imidazole has a structural formula:
Figure FDA0003846778230000023
wherein R is1And R2Is C2-C8 linear or branched alkyl, R3Is C1-C8 straight chain or alkyl with straight chain, and n is an integer between 0 and 8.
4. The method for extracting lithium using phosphate-based ionic liquid according to claim 1, wherein the hexafluorophosphate is at least one of lithium hexafluorophosphate, sodium hexafluorophosphate and potassium hexafluorophosphate; the bis-trifluoromethyl sulfonyl imide salt is at least one of bis-trifluoromethyl sulfonyl imide lithium, bis-trifluoromethyl sulfonyl imide sodium and bis-trifluoromethyl sulfonyl imide potassium.
5. The method for extracting lithium using phosphate-based ionic liquid according to claim 1, wherein the diluent is at least one of anisole, chloroform, kerosene, methylene chloride, 1,2-dichloroethane, n-hexane, n-heptane, carbon tetrachloride, tetrachloroethylene, toluene, xylene, diethylbenzene, bromobenzene, nitrobenzene, petroleum ether, tributyl phosphate, trioctyl phosphate, and trialkylphosphine oxide.
6. The method for extracting lithium by using phosphate ionic liquid according to claim 1, wherein in the step (2), the raw material liquid is lithium-containing salt lake brine, the lithium ion concentration is 0.05-10g/L, and the mass ratio of magnesium to lithium is 1-100.
7. The method for extracting lithium by using phosphate ionic liquid according to claim 1, wherein in the step (3), the stripping agent is hydrochloric acid solution or sulfuric acid solution.
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