Preparation method and application of high-selectivity lithium-extraction fluorine-containing copolymer adsorbent

Abstract

The application relates to a preparation method and application of a high-selectivity lithium-extracting fluorine-containing copolymer adsorbent, and relates to a preparation method and application of a lithium-extracting fluorine-containing adsorbent. The application aims to solve the technical problems of low lithium ion adsorption capacity and poor selectivity of the existing adsorbent. The hydrophilic monomer used in the application is methacrylic acid, which has hydrophilicity and can effectively interact with ions in water to improve the adsorption capacity; the hydrophobic functional monomer used is 2-(perfluorohexyl) ethyl methacrylic acid ester, which has a long carbon fluoride chain and can provide a large number of fluorine sites for lithium ions. The high-selectivity lithium-extracting fluorine-containing copolymer adsorbent prepared by the application is applied to selective separation of lithium ions in mixed wastewater containing lithium ions, sodium ions and potassium ions. The application adopts reversible addition fragmentation chain transfer polymerization technology, and has high selectivity and adsorption capacity for lithium ions.

Description

Preparation method and application of a highly selective lithium extraction fluorinated copolymer adsorbent Technical Field

[0001] This invention relates to a method for preparing a fluorine-containing adsorbent for lithium extraction and its application. Background Technology

[0002] In building a lithium resource security system, the recycling of spent lithium-ion batteries has become a key breakthrough. However, existing recycling processes still face significant lithium losses. Due to the chemical equilibrium limitations of the lithium precipitation process, lithium still remains in the mother liquor after lithium carbonate precipitation at a concentration of 0.5–2 g / L. The significant gap in low-concentration lithium enrichment technology makes lithium extraction difficult and costly, forcing companies to directly discharge lithium-containing wastewater. Therefore, there is an urgent need to develop efficient direct lithium extraction technology tailored to the characteristics of low-concentration lithium solutions to achieve full-scale lithium extraction efficiency from lithium-ion batteries.

[0003] Emerging direct lithium extraction (DLE) technologies offer new pathways for the efficient recovery of low-concentration lithium resources through innovative methods such as electrochemical membrane extraction, solvent extraction, and adsorption. Among these, adsorption, with its advantages of simplified processes, environmental friendliness, and tunable targeted design, has become a research focus for overcoming the bottleneck in low-concentration wastewater recovery. Current mainstream lithium adsorption materials include aluminum-based and titanium / manganese-based inorganic ion sieves, as well as organic polymers based on ion imprinting and crown ether structures. Their extraction mechanisms primarily rely on the coordination of oxygen groups (hydroxyl, carboxyl, etc.) and sub-angstrom size sieving effects. However, oxygen groups have limited ability to effectively sieve Li... + The selective coordination ability of lithium is weaker than that of other competing ions, and conventional sieving channels show a significant decrease in selectivity when separating ions with similar radii / hydrated ion radii. This results in a lithium adsorption capacity of less than 10 mg / g and a selectivity close to 1 in practical applications. It is noteworthy that in the post-lithium precipitation solution, the main competing ion is Na+. + , and Na + / Li + The ratio reached 30:1, further improving the adsorption capacity of the adsorbent material for Li. + Requirements for target-specific binding ability.

[0004] Fluorine-containing groups exhibit unique advantages in lithium-specific recognition due to their strong coordination bonds with lithium ions. This characteristic has been validated by the stable coordination of LiPF6 in lithium-ion battery electrolytes and the high selectivity of fluorinated β-diketone ligands in solvent extraction systems. However, the strong self-aggregation effect of fluorine-containing molecules easily leads to the embedding of active sites, severely weakening the adsorption performance of materials. Breakthroughs in reversible addition-fragmentation chain transfer polymerization (RAFT) technology offer a new approach to overcoming this challenge: by precisely controlling the block ratio of fluorine-containing monomers to hydrophilic monomers, polymers possessing both fluorine-recognition domains and hydrophilic transport channels can be constructed, simultaneously improving the exposure of lithium adsorption sites and enhancing mass transfer, thereby achieving high selectivity and high capacity for Li-ion adsorption. + Adsorption extraction. Summary of the Invention

[0005] The present invention aims to solve the technical problems of low adsorption capacity and poor selectivity of existing adsorbents for lithium ions, and provides a method for preparing a fluorinated copolymer adsorbent with high selectivity for lithium extraction and its application.

[0006] The preparation method of the highly selective lithium extraction fluorinated copolymer adsorbent of the present invention is carried out according to the following steps:

[0007] 1. Dissolve 4-cyano-4-[[(dodecylthio)thionylmethyl]thio]valeric acid in solvent A, then add methacrylic acid and 2-(perfluorohexyl)ethyl methacrylate, disperse evenly, and quickly transfer the resulting mixed solution to a solvent storage bottle;

[0008] Azobisisobutyronitrile (AIBN) was prepared into a solution using solvent A and then added to the solvent storage bottle mentioned above.

[0009] 2. After the product from step one is subjected to 3 to 4 cycles of freeze-thaw and nitrogen deoxygenation, it is placed in an oil bath for reaction to obtain a turbid yellow product solution.

[0010] 3. ① Add the turbid yellow product solution obtained in step 2 dropwise to deionized water for sedimentation, then filter the water and retain the solid part; the deionized water is placed in an ice-water mixture environment;

[0011] ② Place the solid portion obtained in ① into methanol, stir and wash, then filter and retain the solid portion;

[0012] ③ Place the solid portion obtained in ② into anhydrous ethanol, stir and wash, then filter and retain the solid portion;

[0013] Fourth, place the solid part obtained in step three into a vacuum drying oven, dry it at a constant temperature in a vacuum environment, and then grind it after cooling to room temperature to obtain the lithium extraction adsorbent TTC-P (MAA-Alt-PFH) material.

[0014] The highly selective lithium extraction fluorinated copolymer adsorbent prepared in this invention is used for the selective separation of lithium ions in mixed wastewater containing lithium, sodium, and potassium ions.

[0015] The polymerization method used in this invention is reversible addition-fragmentation chain transfer polymerization (RAFT), and the RAFT reagent used is 4-cyano-4-[[(dodecylthio)thiononemethyl]thio]valerate (TTC-acid).

[0016] The hydrophilic monomer used in this invention is methacrylic acid (MAA). MAA's hydrophilicity allows it to effectively interact with ions in water, enhancing its adsorption capacity. The hydrophobic functional monomer used is 2-(perfluorohexyl)ethyl methacrylate (PFHEMA). PFHEMA's long carbon fluorine chain provides numerous fluorine sites that interact with lithium ions.

[0017] Advantages of this invention:

[0018] 1. The hydrophobic functional monomer 2-(perfluorohexyl)ethyl methacrylate (PFHEMA) used in this invention has a long carbon fluorine chain that provides a large number of fluorine sites to act on lithium ions, and preferentially binds to lithium, thus exhibiting lithium selectivity, thereby improving the adsorption capacity and selectivity of the material for lithium ions. At the same time, the hydrophilicity of methacrylate (MAA) can effectively improve the hydrophobicity of the material, making it more suitable for operation in aqueous solutions and increasing the effective binding of fluorine sites to lithium;

[0019] 2. This invention employs reversible addition-fragmentation chain transfer polymerization technology, resulting in a simple and low-cost preparation method with high selectivity and adsorption capacity for lithium ions. The adsorbent prepared by this invention can adsorb lithium ions in monovalent metal mixed solutions with high adsorption capacity and selectivity, achieving a maximum adsorption capacity of 82 mg / g. In practical low-concentration, highly competitive lithium-containing wastewater, Li... + / Na + The selectivity is greater than 6000. Attached Figure Description

[0020] Figure 1 is a schematic diagram of the synthesis reaction of FHP adsorbent in Experiment 1;

[0021] Figure 2 shows the 1H NMR spectrum of the FHP adsorbent prepared in Experiment 1;

[0022] Figure 3 is a transmission electron microscope image of the FHP adsorbent prepared in Experiment 1;

[0023] Figure 4 shows the isothermal adsorption curves in Experiment 2;

[0024] Figure 5 shows the kinetic adsorption curves for Experiment 3;

[0025] Figure 6 shows the selective adsorption data from Experiment 4. Detailed Implementation

[0026] Specific Implementation Method 1: This implementation method is a preparation method of a highly selective lithium extraction fluorinated copolymer adsorbent, specifically carried out according to the following steps:

[0027] 1. Dissolve 4-cyano-4-[[(dodecylthio)thionylmethyl]thio]valeric acid in solvent A, then add methacrylic acid and 2-(perfluorohexyl)ethyl methacrylate, disperse evenly, and quickly transfer the resulting mixed solution to a solvent storage bottle;

[0028] Azobisisobutyronitrile (AIBN) was prepared into a solution using solvent A and then added to the solvent storage bottle mentioned above.

[0029] 2. After the product from step one is subjected to 3 to 4 cycles of freeze-thaw and nitrogen deoxygenation, it is placed in an oil bath for reaction to obtain a turbid yellow product solution.

[0030] 3. ① Add the turbid yellow product solution obtained in step 2 dropwise to deionized water for sedimentation, then filter the water and retain the solid part; the deionized water is placed in an ice-water mixture environment;

[0031] ② Place the solid portion obtained in ① into methanol, stir and wash, then filter and retain the solid portion;

[0032] ③ Place the solid portion obtained in ② into anhydrous ethanol, stir and wash, then filter and retain the solid portion;

[0033] Fourth, place the solid part obtained in step three into a vacuum drying oven, dry it at a constant temperature in a vacuum environment, and then grind it after cooling to room temperature to obtain the lithium extraction adsorbent TTC-P (MAA-Alt-PFH) material.

[0034] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the molar ratio of 4-cyano-4-[[(dodecylthio)thiononemethyl]thio]valeric acid to methacrylic acid in step one is 1:(50~70). Everything else is the same as in Specific Implementation Method One.

[0035] Specific Implementation Method 3: This implementation method differs from Specific Implementation Method 1 or 2 in that the molar ratio of 4-cyano-4-[[(dodecylthio)thionylmethyl]thio]valeric acid to 2-(perfluorohexyl)ethyl methacrylate in step 1 is 1:(50~70). Everything else is the same as in Specific Implementation Method 1 or 2.

[0036] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the molar ratio of azobisisobutyronitrile to 4-cyano-4-[[(dodecylthio)thiononemethyl]thio]valerate in step one is (0.25~0.3):1. Everything else is the same as in Specific Implementation Methods One to Three.

[0037] Specific Implementation Method Five: This implementation method differs from Specific Implementation Method Four in that solvent A mentioned in step one is tetrahydrofuran. Everything else is the same as in Specific Implementation Method Four.

[0038] Specific Implementation Method Six: This implementation method differs from Specific Implementation Method Five in that the freeze-thaw nitrogen deoxygenation cycle process described in step two is as follows: After sealing the solvent storage bottle from step one and connecting it to the double-row tube, quickly immerse it in a liquid nitrogen bath, ensuring the liquid level is completely below the liquid nitrogen level, until the mixed solution in the solvent storage bottle is completely frozen into a solid; while the sample remains completely frozen, start the vacuum pump to evacuate the system; maintain the vacuum state for 10 minutes; then turn off the vacuum pump, remove the solvent storage bottle from the liquid nitrogen bath, and immerse it in a room temperature water bath to completely thaw the frozen sample into a liquid state. After the sample is completely dissolved, open the N2 gas valve to allow N2 gas to smoothly backfill the container to atmospheric pressure. Everything else is the same as in Specific Implementation Method Five.

[0039] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Method Six in that the reaction conditions in the oil bath described in step two are: a reaction at a temperature of 70℃~75℃ for 20h~24h. Everything else is the same as in Specific Implementation Method Six.

[0040] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Method Seven in that the drying conditions in step four are: constant temperature drying in a vacuum environment at 40℃~45℃ for 10h~12h. Everything else is the same as in Specific Implementation Method Seven.

[0041] Specific Implementation Method Nine: This implementation method is an application of the highly selective lithium-extraction fluorinated copolymer adsorbent from Specific Implementation Method One, applied to the extraction of lithium-containing compounds. + Na + and K + Selective separation of lithium ions in mixed wastewater. Other aspects are the same as in specific implementation method eight.

[0042] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Method Nine in that: the Li-containing... + Na + and K + Li in mixed wastewater + The concentration of Na is 80 mmol / L~90 mmol / L. + The concentration was 2400 mmol / L~2500 mmol / L, K+ The concentration is 50 mmol / L to 55 mmol / L; the pH of the mixed wastewater is 6 to 8; the adsorption time is 24 to 36 hours; and the temperature is 25°C to 45°C. Other parameters are the same as in Specific Implementation Method Nine.

[0043] The invention was verified using the following experiments:

[0044] Experiment 1: This experiment demonstrates a method for preparing a highly selective lithium-extraction fluorinated copolymer adsorbent, specifically carried out according to the following steps:

[0045] 1. Dissolve 64.9 mg of 4-cyano-4-[[(dodecylthio)thionylmethyl]thio]valeric acid in 17.972 mL of tetrahydrofuran solvent, then add 0.818 mL of methacrylic acid and 2.787 mL of 2-(perfluorohexyl)ethyl methacrylate, disperse evenly, and quickly transfer the resulting mixed solution to a solvent storage bottle;

[0046] Prepare a solution of 15 mg of azobisisobutyronitrile using 3 mL of tetrahydrofuran, and then weigh 2.6 mL of the solution and add it to the solvent storage bottle mentioned above.

[0047] 2. After the product from step one is subjected to four freeze-thaw cycles with nitrogen and oxygen removal, it is placed in an oil bath for reaction, resulting in a turbid yellow product solution.

[0048] The freeze-thaw nitrogen deoxygenation cycle process is as follows: After sealing the solvent storage bottle in step one and connecting it to the double-row tube, quickly immerse it in the liquid nitrogen bath, ensuring that the liquid level is completely lower than the liquid nitrogen level, until the mixed solution in the solvent storage bottle is completely frozen into a solid; while the sample is kept completely frozen, start the vacuum pump to evacuate the system; maintain the vacuum state for 15 minutes; then turn off the vacuum pump, remove the solvent storage bottle from the liquid nitrogen bath, and immerse it in a room temperature water bath to completely thaw the frozen sample into a liquid state; after the sample is completely dissolved, open the N2 gas valve to allow N2 gas to be smoothly backfilled into the container to atmospheric pressure;

[0049] The reaction conditions in the oil bath are: reaction at 70°C for 24 hours;

[0050] 3. ① Add the turbid yellow product solution obtained in step 2 dropwise to 250 mL of deionized water to allow it to settle, then filter the water and retain the solid portion; the deionized water is placed in an ice-water mixture environment;

[0051] ② Place the solid portion obtained in ① into 50 mL of methanol and stir and wash for 5 min, then filter and retain the solid portion;

[0052] ③ Place the solid portion obtained in ② into 50 mL of anhydrous ethanol and stir and wash for 5 min, then filter and retain the solid portion;

[0053] 4. Place the solid part obtained in step 3 into a vacuum drying oven and dry it at a constant temperature in a vacuum environment. Then cool it to room temperature and grind it to obtain the lithium extraction adsorbent material, denoted as FHP. The drying conditions are: constant temperature drying in a vacuum environment at 45℃ for 12 hours.

[0054] Figure 1 is a schematic diagram of the synthesis reaction of FHP adsorbent in Experiment 1.

[0055] Figure 2 shows the 1H NMR spectrum of the FHP adsorbent prepared in Experiment 1. The presence of characteristic chains a, b, and c proves that the material was successfully prepared.

[0056] Figure 3 shows a transmission electron microscope image of the FHP adsorbent prepared in Experiment 1, which shows that the materials all exhibit a microsphere state.

[0057] Experiment 2: Preparation of Li at concentrations of 10 mg / L, 20 mg / L, 50 mg / L, 100 mg / L, 150 mg / L, 200 mg / L, 250 mg / L, 300 mg / L, 350 mg / L, 400 mg / L, 450 mg / L, and 500 mg / L. + Aqueous solutions were prepared, and the FHP adsorbent prepared in Experiment 1 was added to the above solutions for isothermal adsorption experiments. The adsorbent dosage was 1 mg / mL. The parameters of the isothermal shaker were set as follows: temperature 25℃, rotation speed 180 rpm, and time 24 h. The solutions before and after adsorption were collected, and the Li content in the solutions was determined using atomic absorption spectrometry (AAS). + The concentration.

[0058] Figure 4 shows the isothermal adsorption curves in Experiment 2. The maximum adsorption capacity of FHP was measured to be 82 mg / g, and the data can be successfully fitted to the Langmuir adsorption isotherm model.

[0059] Experiment 3: Preparation of 500 mg / L Li + In an aqueous solution, the FHP adsorbent prepared in Experiment 1 was added to the above solution for adsorption kinetics experiments. The amount of adsorbent added was 1 mg / mL. Samples were taken at 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10 h, and the lithium ion concentration in the solution was determined using an atomic absorption spectrometer (AAS).

[0060] Figure 5 shows the kinetic adsorption curves of Experiment 3. The saturation adsorption time of FHP was measured to be approximately 5-6 hours, and the data can be successfully fitted to the pseudo-second-order kinetic model.

[0061] Experiment 4: Preparation of Li in simulated lithium precipitation solution + Na + and K + A mixed aqueous solution in which Li +The concentration was 89.5 mmol / L, Na + The concentration was 2491.5 mmol / L, K + The concentration was 51.4 mmol / L. The FHP adsorbent prepared in Experiment 1 was added to the above solution for a competitive adsorption experiment. The adsorbent dosage was 1 mg / mL. The parameters of the isothermal shaker were set as follows: temperature 25℃, rotation speed 180 rpm, and time 24 h. The solutions before and after adsorption were collected, and the Li content in the solution was determined using atomic absorption spectrometry (AAS). + Na + and K + The concentration.

[0062] Figure 6 shows the selective adsorption data from Experiment 4, including the measured Li content of FHP. + / Na + The selectivity is 6469.72, which is greater than 6000, indicating that the adsorbent has high selectivity.

Claims

1. A method for preparing a highly selective lithium-extraction fluorinated copolymer adsorbent, characterized in that... The preparation method of the highly selective lithium extraction fluorinated copolymer adsorbent is carried out according to the following steps:

1. Dissolve 4-cyano-4-[[(dodecylthio)thionylmethyl]thio]valeric acid in solvent A, then add methacrylic acid and 2-(perfluorohexyl)ethyl methacrylate, disperse evenly, and quickly transfer the resulting mixed solution to a solvent storage bottle; prepare a solution of azobisisobutyronitrile with solvent A, and then add it to the above solvent storage bottle; 2. After the product of step 1 is subjected to 3 to 4 freeze-thaw cycles with nitrogen deoxygenation, it is placed in an oil bath for reaction to obtain a turbid yellow product solution; 3. ① The turbid yellow product solution obtained in step 2 is added dropwise to deionized water for sedimentation, then the water is filtered and the solid portion is retained; the deionized water is placed in an ice-water mixture environment; ②, the solid portion obtained in step 1 is placed in methanol and stirred for washing, then filtered and the solid portion is retained; ③, the solid portion obtained in step 2 is placed in anhydrous ethanol and stirred for washing, then filtered and the solid portion is retained; ④, the solid portion obtained in step 3 is placed in a vacuum drying oven and dried at a constant temperature in a vacuum environment, then cooled to room temperature and ground to obtain the lithium extraction adsorbent TTC-P (MAA-Alt-PFH) material.

2. The method for preparing a highly selective lithium-extraction fluorinated copolymer adsorbent according to claim 1, characterized in that... The molar ratio of 4-cyano-4-[[(dodecylthio)thionylmethyl]thio]valeric acid to methacrylic acid in step one is 1:(50~70).

3. The method for preparing a highly selective lithium-extraction fluorinated copolymer adsorbent according to claim 1, characterized in that... The molar ratio of 4-cyano-4-[[(dodecylthio)thionylmethyl]thio]valeric acid to 2-(perfluorohexyl)ethyl methacrylate in step one is 1:(50~70).

4. The method for preparing a highly selective lithium-extraction fluorinated copolymer adsorbent according to claim 1, characterized in that... The molar ratio of azobisisobutyronitrile to 4-cyano-4-[[(dodecylthio)thiononemethyl]thio]valerate in step one is (0.25~0.3):

1.

5. The method for preparing a highly selective lithium-extraction fluorinated copolymer adsorbent according to claim 1, characterized in that... Solvent A mentioned in step one is tetrahydrofuran.

6. The method for preparing a highly selective lithium-extraction fluorinated copolymer adsorbent according to claim 1, characterized in that... The freeze-thaw nitrogen deoxygenation cycle process described in step two is as follows: After sealing the solvent storage bottle from step one and connecting it to the double-row tube, quickly immerse it in the liquid nitrogen bath, ensuring that the liquid level is completely below the liquid nitrogen level, until the mixed solution in the solvent storage bottle is completely frozen into a solid; while the sample remains completely frozen, start the vacuum pump to evacuate the system; maintain the vacuum state for 10 minutes; then turn off the vacuum pump, remove the solvent storage bottle from the liquid nitrogen bath, and immerse it in a room temperature water bath to completely thaw the frozen sample into a liquid state; after the sample is completely dissolved, open the N2 gas valve to allow N2 gas to smoothly backfill the container to atmospheric pressure.

7. The method for preparing a highly selective lithium-extraction fluorinated copolymer adsorbent according to claim 1, characterized in that... The reaction conditions in the oil bath mentioned in step two are: reacting at a temperature of 70℃~75℃ for 20h~24h.

8. The method for preparing a highly selective lithium-extraction fluorinated copolymer adsorbent according to claim 1, characterized in that... The drying conditions in step four are: constant temperature drying in a vacuum environment at 40℃~45℃ for 10h~12h.

9. The application of a highly selective lithium-extraction fluorinated copolymer adsorbent prepared by the preparation method according to claim 1, characterized in that... Highly selective lithium extraction fluorinated copolymer adsorbents are used for the extraction of lithium-containing compounds. + Na + and K + Selective separation of lithium ions in mixed wastewater.

10. The application of the highly selective lithium extraction fluorinated copolymer adsorbent according to claim 9, characterized in that... The Li-containing + Na + and K + Li in mixed wastewater + The concentration of Na is 80 mmol / L~90 mmol / L. + The concentration was 2400 mmol / L~2500 mmol / L, K + The concentration was 50 mmol / L to 55 mmol / L; the pH of the mixed wastewater was 6 to 8; the adsorption time was 24 to 36 hours; and the temperature was 25°C to 45°C.

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