Dual-functional ionic liquid as well as preparation method and application thereof

Abstract

The invention discloses a bifunctional ionic liquid as well as a preparation method and application thereof, and belongs to the technical field of lithium resource extraction and hydrometallurgy. According to the invention, the dual-functional ionic liquid is prepared, and the dual-functional ionic liquid can be used for synchronously realizing efficient extraction of lithium ions from the lepidolite acid leaching solution and synergic deep removal of fluorine and chlorine, so that the limitation and defects of a traditional solvent extraction agent are effectively overcome; the problems that an existing lepidolite lithium extraction technology is long in process, low in separation efficiency and serious in equipment corrosion can be solved.

Description

Technical Field

[0001] This invention belongs to the field of lithium resource extraction and hydrometallurgical technology, and relates to a bifunctional ionic liquid, its preparation method and application. Specifically, it relates to a green separation method that uses a bifunctional ionic liquid to simultaneously extract lithium and synergistically remove fluorine and chlorine from acidic leaching solution of lepidolite. Background Technology

[0002] After calcination with sulfuric acid and leaching with water, the resulting acidic leachate from lepidolite contains high concentrations of fluoride ions (2000-5000 mg / L), chloride ions (1000-3000 mg / L), and numerous metallic impurities. Among these, fluoride ions form stable complexes with aluminum (such as AlF2). ＋ AlF4 － This significantly inhibits defluorination efficiency, while chloride ions cause severe corrosion of equipment under high temperature and acidic conditions, leading to scaling and blockage in the evaporation and crystallization section.

[0003] Current mainstream industrial technologies have significant limitations: chemical precipitation requires the stepwise addition of calcium chloride for fluoride removal and silver nitrate for chlorine removal, resulting in high reagent costs and the introduction of silver ion pollution; adsorption methods have low fluoride adsorption capacity, with a regeneration process loss rate exceeding 20%; membrane separation methods suffer from AlF... x Colloidal substances clog membrane pores, causing a significant decrease in flux after a short period of operation; distillation methods are extremely energy-intensive and economically unfeasible; none of the above treatment processes can achieve simultaneous deep removal of fluorine and chlorine.

[0004] Traditional solvent extractants (such as the TBP / FeCl3 system) can extract lithium, but they are not selective enough for lithium ions. More than six stages of extraction are required to obtain a qualified lithium-rich solution. Furthermore, due to the complete lack of fluorine and chlorine removal capabilities, subsequent processes require the addition of independent impurity removal units, which is lengthy and reduces the lithium recovery rate to below 85%.

[0005] In view of this, developing a synergistic extraction process that can simultaneously complete lithium extraction and deep removal of fluorine and chlorine in acidic leachate is a key breakthrough direction for solving the pain points of lithium extraction from lepidolite, such as long process, high cost and severe equipment corrosion. Summary of the Invention

[0006] To address the problems mentioned in the background technology, this invention prepares a bifunctional ionic liquid. Based on the fact that this ionic liquid can simultaneously achieve efficient extraction of lithium ions from acidic lepidolite leachate and synergistic deep removal of fluorine and chlorine, it solves the problems of lengthy process, low separation efficiency and severe equipment corrosion in existing lepidolite lithium extraction technology.

[0007] To achieve the above objectives, the present invention specifically adopts the following technical solution: This invention provides a method for preparing a bifunctional ionic liquid, comprising the following steps: S1. Slowly add 3-bromopropylboronic acid pinacol ester to 1-methylimidazole, heat under reflux and react. After the reaction is complete, distill under reduced pressure to obtain a viscous oil. S2. Add acetone to the obtained oily substance, sonicate to crystallize, filter, wash and dry to obtain a white powdery intermediate. S3. The obtained intermediate was mixed with potassium carbonate and heated to activate it. Then 4'-chloromethylbenzo-12-crown-4 was added to continue the reaction. The mixture was filtered and washed. The filtrate was poured into ice-cold ether, and a viscous oily substance precipitated out. The supernatant was discarded, and the oily substance was washed to obtain the crude product. S4. Slowly add LiTf2N aqueous solution to the crude product aqueous solution. A white precipitate is produced. The mixture is allowed to stand and separate into phases. The lower organic phase is collected, washed and dried to obtain a pale yellow viscous liquid or waxy solid, which is the bifunctional ionic liquid (DFIL).

[0008] In a preferred embodiment, the molar ratio of 1-methylimidazole to pinacol 3-bromopropylboronic acid in S1 is 1:1, the dropping time is controlled at 1 h, the heating temperature is 80 °C, and the reflux reaction time is 24 h.

[0009] In a preferred embodiment, the molar ratio of the intermediate to potassium carbonate in S3 is 1:2, and the heating activation temperature is 70°C for 30 min.

[0010] In a preferred embodiment, the molar ratio of the intermediate in S3 to 4'-chloromethylbenzo-12-crown-4 is 1:1, the reaction temperature is 70°C, and the reaction time is 48 h.

[0011] In a preferred embodiment, the amount of LiTf2N added in S4 is 1-2 times the molar amount of the intermediate in S3.

[0012] As a preferred embodiment, the bifunctionalized ionic liquid structure in S4 is: [B(OH)2-C3H6-mim-C1H2-Benzo-12-C-4] ＋ [Tf2N] － .

[0013] The present invention also provides a bifunctional ionic liquid obtained by the above preparation method.

[0014] This invention also provides the application of the above-mentioned bifunctionalized ionic liquid in the simultaneous extraction of lithium and synergistic removal of fluorine and chlorine from acidic leaching solutions of lepidolite, comprising the following steps: Using lepidolite leachate as the aqueous phase, the bifunctionalized ionic liquid was dissolved in a diluent as the organic phase. The two were stirred and mixed in proportion, and then separated to obtain an aqueous phase and a supported organic phase.

[0015] In a preferred embodiment, the lepidolite leachate needs to be adjusted to pH 2.5-3.5; the diluent is composed of sulfonated kerosene and n-octanol in a volume ratio of (8-9):(2-1), preferably 9:1, and the concentration of the organic phase after dilution is 0.15-0.35 mol / L.

[0016] The aqueous leachate after calcining lepidolite with sulfuric acid was filtered to remove insoluble matter and suspended particles. The pH was then adjusted to the range of 2.5-3.5. This pH range effectively inhibits the precipitation of easily hydrolyzed metal ions such as aluminum and iron while ensuring that the various functional groups in the DFIL are in their optimal active state. The pretreated leachate (aqueous phase) was mixed with the organic phase at an oil-to-water ratio of 1:(3-5) and thoroughly stirred at 25-45°C. After mixing, the mixture was allowed to stand for phase separation. The loaded organic phase was enriched with lithium ions, fluoride ions, and chloride ions, while the content of these ions in the raffinate was significantly reduced, allowing it to be directly returned or further processed.

[0017] As a preferred embodiment, the method further includes stepwise back-extraction of the supported organic phase and DFIL regeneration: hydrochloric acid (0.8-1.5 mol / L) is added to the supported organic phase for back-extraction, and the phases are separated by standing to obtain an aqueous lithium chloride phase; the back-extracted organic phase is mixed with sodium hydroxide solution (1.0-2.0 mol / L), shaken, and allowed to separate by standing, and the aqueous phase is discarded to obtain a regenerated organic phase.

[0018] Hydrogen ions in hydrochloric acid can competitively exchange with lithium ions bound to crown ethers, allowing the lithium ions to enter the aqueous phase and yielding a pure lithium chloride solution. Strong base hydroxide ions can disrupt the covalent / hydrogen bonds between DFIL and fluoride ions, causing fluoride and chloride ions to enter the aqueous phase as NaF / NaCl and be removed. Simultaneously, DFIL is restored to its initial form, achieving regeneration and recycling.

[0019] Compared with the prior art, the beneficial effects of the present invention are: 1. Minimal steric hindrance: Two functional groups are mounted on the same cation through a flexible connecting chain, but there is enough space between them so that they do not interfere with each other and can work simultaneously.

[0020] 2. Charge balance: DFIL itself is electrically neutral, but when it combines with a Li ＋ Subsequently, the positive charge of the cation increases, and in order to maintain overall electroneutrality, it strongly requires the adsorption of an anion to balance the charge; conversely, when it binds an F-ion through a boronic acid group... － Afterwards, it will also enhance the attraction to cations.

[0021] 3. Co-migration of "ion pairs": DFIL forms neutral complexes with the target ion, such as [(DFIL ＋ )-Li＋ ...[B-F3] － Or with Cl － The combined structure is similar; this neutral ion exhibits enhanced hydrophobicity and readily migrates from the aqueous phase to the organic phase, thereby achieving Li ＋ F － Cl － Simultaneous extraction. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with embodiments. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0024] Example 1 A green separation method for simultaneously extracting lithium and synergistically removing fluorine and chlorine from acidic lepidolite leachate using bifunctionalized ionic liquids includes the following steps: 1. Weigh 8.21 g of 0.1 mol / L 1-methylimidazole into a dry 250 mL three-necked flask, add 50 mL of anhydrous acetonitrile, and stir to dissolve under nitrogen protection. Cool to 0-5℃ in an ice-water bath, weigh 26.5 g of 0.1 mol / L 3-bromopropylboronic acid pinacol ester, dissolve in 30 mL of acetonitrile, and then slowly add it dropwise to the reaction flask, completing the addition within 1 h. Remove the ice bath, heat to 80℃ and reflux for 24 h. After the reaction is complete, remove most of the solvent by rotary evaporation under reduced pressure to obtain a viscous oily substance; add 50 mL of acetone to crystallize, filter, wash three times with 20 mL of cold acetone, and dry under vacuum to obtain a white solid intermediate.

[0025] 2. Dissolve 3.0 g of the obtained intermediate (10.1 mmol) in 20 mL of anhydrous DMP, add 2.80 g of potassium carbonate (20.2 mmol), and activate by stirring at 70 °C for 30 min. Add 3.23 g of 4'-chloromethylbenzo-12-crown-4, and continue the reaction at 70 °C for 48 h. After cooling, filter to remove inorganic salts. Pour the filtrate into 200 mL of ice-cold diethyl ether, and a pale yellow viscous substance precipitates. Discard the supernatant, and wash the oily substance three times with 20 mL of diethyl ether to obtain the crude product.

[0026] 3. Dissolve the crude product in 20 mL of deionized water, then weigh 4.33 g of 15.1 mmol LiTf₂N and dissolve it in 15 mL of deionized water. Slowly add the LiTf₂N aqueous solution to the crude product solution; a white precipitate will immediately form. Continue stirring for 2 h. Transfer the solution to a separatory funnel, collect the organic phase, and wash repeatedly with deionized water until no Br is detected by 0.1 M AgNO₃ solution. － The product was placed in a vacuum drying oven at 50°C for 24 hours to obtain a pale yellow viscous liquid, namely DFIL.

[0027] 4. Dissolve an appropriate amount of DFIL in a diluent (sulfonated kerosene and n-octanol in a volume ratio of 9:1) to prepare a 0.15 mol / L organic phase. Take a lithium mica leachate (lithium ion content 2500 mg / L, aluminum ion content 5000 mg / L, fluoride ion content 3500 mg / L, chloride ion content 2500 mg / L), adjust the pH to 3.0, and filter. Measure 40 mL of the leachate into a 100 mL stoppered conical flask and add 10 mL of the organic phase. Place the flask in a constant temperature water bath shaker and shake at 250 rpm for 10 min at 30℃. Transfer the mixture to a separatory funnel, allow it to stand for 15 min to fully separate the phases, and collect the lower aqueous phase for analysis.

[0028] 5. Take 10 mL of the loaded organic phase, add 10 mL of 1.0 mol / L HCl solution, and shake at 30℃ for 15 min. Allow to stand and separate the phases, collect the aqueous phase and analyze the lithium ion concentration. Mix the back-extracted organic phase with 10 mL of 1.5 mol / L NaOH solution, shake at 30℃ for 20 min, allow to stand and separate the phases, discard the aqueous phase, and the regenerated organic phase can be reused.

[0029] The test results of this embodiment are shown in Table 1.

[0030] Table 1

[0031] Example 2 A green separation method for simultaneously extracting lithium and synergistically removing fluorine and chlorine from acidic lepidolite leachate using bifunctionalized ionic liquids includes the following steps: 1. Weigh 8.21 g of 0.1 mol / L 1-methylimidazole into a dry 250 mL three-necked flask, add 50 mL of anhydrous acetonitrile, and stir to dissolve under nitrogen protection. Cool to 0-5℃ in an ice-water bath, weigh 26.5 g of 0.1 mol / L 3-bromopropylboronic acid pinacol ester, dissolve in 30 mL of acetonitrile, and then slowly add it dropwise to the reaction flask, completing the addition within 1 h. Remove the ice bath, heat to 80℃ and reflux for 24 h. After the reaction is complete, remove most of the solvent by rotary evaporation under reduced pressure to obtain a viscous oily substance; add 50 mL of acetone to crystallize, filter, wash three times with 20 mL of cold acetone, and dry under vacuum to obtain a white solid intermediate.

[0032] 2. Dissolve 3.0 g of the obtained intermediate (10.1 mmol) in 20 mL of anhydrous DMP, add 2.80 g of potassium carbonate (20.2 mmol), and activate by stirring at 70 °C for 30 min. Add 3.23 g of 4'-chloromethylbenzo-12-crown-4, and continue the reaction at 70 °C for 48 h. After cooling, filter to remove inorganic salts. Pour the filtrate into 200 mL of ice-cold diethyl ether, and a pale yellow viscous substance precipitates. Discard the supernatant, and wash the oily substance three times with 20 mL of diethyl ether to obtain the crude product.

[0033] 3. Dissolve the crude product in 20 mL of deionized water, then weigh 4.33 g of 15.1 mmol LiTf₂N and dissolve it in 15 mL of deionized water. Slowly add the LiTf₂N aqueous solution to the crude product solution; a white precipitate will immediately form. Continue stirring for 2 h. Transfer the solution to a separatory funnel, collect the organic phase, and wash repeatedly with deionized water until no Br is detected by 0.1 M AgNO₃ solution. － The product was placed in a vacuum drying oven at 50°C for 24 hours to obtain a pale yellow viscous liquid, namely DFIL.

[0034] 4. Dissolve an appropriate amount of DFIL in a diluent (sulfonated kerosene and n-octanol in a volume ratio of 9:1) to prepare a 0.25 mol / L organic phase. Take a lithium mica leachate (lithium ion content 2200 mg / L, aluminum ion content 6000 mg / L, fluoride ion content 6000 mg / L, chloride ion content 2000 mg / L), adjust the pH to 3.0, and filter. Measure 40 mL of the leachate into a 100 mL stoppered conical flask and add 10 mL of the organic phase. Place the flask in a constant temperature water bath shaker and shake at 250 rpm for 10 min at 30℃. Transfer the mixture to a separatory funnel, allow it to stand for 15 min to fully separate the phases, and collect the lower aqueous phase for analysis.

[0035] 5. Take 10 mL of the loaded organic phase, add 10 mL of 1.0 mol / L HCl solution, and shake at 30℃ for 15 min. Allow to stand and separate the phases, collect the aqueous phase and analyze the lithium ion concentration. Mix the back-extracted organic phase with 10 mL of 1.5 mol / L NaOH solution, shake at 30℃ for 20 min, allow to stand and separate the phases, discard the aqueous phase, and the regenerated organic phase can be reused.

[0036] The test results of this embodiment are shown in Table 2.

[0037] Table 2

[0038] Comparative Example 1 Comparison with traditional extractant TBP Prepare 0.15 mol / L TBP-sulfonated kerosene as the organic phase instead of the ionic liquid of the present invention; conduct comparative extraction experiments using the same leachate and extraction conditions as in Example 1.

[0039] The results of this comparative test are shown in Table 3.

[0040] Table 3

[0041] In summary, the traditional extractant TBP has an extremely low lithium ion extraction rate in high-concentration fluorinated chlorine mica leachate systems and can hardly remove fluoride and chloride ions; while the synergistic extraction effect of the DFIL of this invention is far superior to the traditional process, with extremely significant advantages.

[0042] The embodiments described above are merely preferred embodiments of the present invention, and while the descriptions are specific and detailed, they are not intended to limit the present invention. It should be noted that various changes and modifications can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the concept and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a bifunctional ionic liquid, characterized in that, Includes the following steps: S1. Slowly add 3-bromopropylboronic acid pinacol ester to 1-methylimidazole, heat under reflux and react. After the reaction is complete, distill under reduced pressure to obtain a viscous oil. S2. Add acetone to the obtained oily substance, sonicate to crystallize, filter, wash and dry to obtain a white powdery intermediate. S3. The obtained intermediate was mixed with potassium carbonate and heated to activate it. Then 4'-chloromethylbenzo-12-crown-4 was added to continue the reaction. The mixture was filtered and washed. The filtrate was poured into ice-cold ether, and a viscous oily substance precipitated out. The supernatant was discarded, and the oily substance was washed to obtain the crude product. S4. Slowly add LiTf2N aqueous solution to the crude product aqueous solution. A white precipitate is produced. The mixture is allowed to stand and separate into phases. The lower organic phase is collected, washed and dried to obtain a pale yellow viscous liquid or waxy solid, which is the bifunctional ionic liquid.

2. The method for preparing the bifunctional ionic liquid according to claim 1, characterized in that, In S1, the molar ratio of 1-methylimidazole to 3-bromopropylboronic acid pinacol ester is 1:1, the dropping time is controlled at 1 h, the heating temperature is 80℃, and the reflux reaction time is 24 h.

3. The method for preparing the bifunctional ionic liquid according to claim 1, characterized in that, The molar ratio of the intermediate to potassium carbonate in S3 is 1:2, and the heating activation temperature is 70℃ for 30 min.

4. The method for preparing the bifunctional ionic liquid according to claim 1, characterized in that, The intermediate described in S3 is in a molar ratio of 1:1 to 4'-chloromethylbenzo-12-crown-4, and the reaction temperature is 70°C for 48 h.

5. The method for preparing the bifunctional ionic liquid according to claim 1, characterized in that, The amount of LiTf2N added in S4 is 1-2 times the molar amount of the intermediate in S3.

6. The method for preparing the bifunctional ionic liquid according to claim 1, characterized in that, The bifunctionalized ionic liquid structure described in S4 is: [B(OH)2-C3H6-mim-C1H2-Benzo-12-C-4] ＋ [Tf2N] － .

7. The bifunctionalized ionic liquid obtained by the preparation method according to any one of claims 1-6.

8. The application of the bifunctionalized ionic liquid of claim 7 in the simultaneous extraction of lithium and synergistic removal of fluorine and chlorine from acidic leaching solution of lepidolite, characterized in that, Includes the following steps: Using lepidolite leachate as the aqueous phase, the bifunctionalized ionic liquid was dissolved in a diluent as the organic phase. The two were stirred and mixed in proportion, and then separated to obtain an aqueous phase and a supported organic phase.

9. The application according to claim 8, characterized in that, The lepidolite leachate needs to be adjusted to pH 2.5-3.5; the diluent is composed of sulfonated kerosene and n-octanol in a volume ratio of (8-9):(2-1).

10. The application according to claim 8, characterized in that, It also includes stepwise back-extraction and regeneration of the supported organic phase: hydrochloric acid is added to the supported organic phase for back-extraction, and the phases are separated by standing to obtain an aqueous phase of lithium chloride; the back-extracted organic phase is mixed with sodium hydroxide solution, shaken, and allowed to separate by standing, and the aqueous phase is discarded to obtain a regenerated organic phase.

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