Method for enriching < 7 > Li through electrodialysis coupling extraction

Abstract

The invention discloses a method for enriching < 7 > Li through electrodialysis coupling extraction, which comprises the following steps of: connecting a plurality of functional membranes in series and coupling for enriching < 7 > Li through electrodialysis, respectively placing a supply phase and a receiving phase on two sides of the functional membranes, and adjusting the volume ratio of the supply phase to the receiving phase to be (1-100): (1-100) by controlling the flow rates of the supply phase and the receiving phase through PID (Proportion Integration Differentiation), and electrifying the electrodes on the two sides of the plurality of functional membranes which are connected in series, applying voltage with the voltage of-20 to 20V for 3 seconds to 120 minutes, and extracting and separating the Li isotope. According to the method, the Li isotope is subjected to cascade separation through an electrodialysis coupling membrane technology, so that the selectivity of 7Li is increased, the separation and enrichment effect of the 7Li isotope is improved, and the abundance of the 7Li natural stable isotope can be improved from 92.47% to 5N level through 102-level cascade.

Description

Technical Field

[0001] The present invention relates to an extraction and enrichment method. 7 Li method, specifically involving an electrodialysis coupled extraction enrichment 7 Li's method. Background Art

[0002] Li has 6 Li and 7 There are two natural stable isotopes of Li, 7 Li isotopes play an important role in the nuclear industry: 7 Li is an indispensable material for regulating pH value in reactors and is a molten salt coolant material for manufacturing thorium-based molten salt reactors. 7 Li can also be used in thermal neutron capture experiments in nuclear reactors and for generating thermal neutrons. 6 Li and 7 The separation of Li is a technically challenging task because their masses differ very little and their chemical and physical properties are very similar. These factors make their effective separation quite difficult. 7 The purity of Li is required to be above 99.999%.

[0003] The various natural stable isotopes of the same element have the same number of protons in the nucleus and the same number of electrons outside the nucleus, so their chemical properties are very similar and difficult to separate. However, they have different numbers of neutrons in the nucleus, so their atomic weights are different, which causes differences in the thermodynamic properties of isotopes or their molecules. The purpose of separation can be achieved by using the subtle differences in the physical and chemical properties of isotopes.

[0004] At present, isotope separation methods can be divided into four categories: (1) directly utilizing the difference in isotope mass, such as electromagnetic separation and centrifugal separation; (2) utilizing the difference in equilibrium molecular transfer properties, such as diffusion, thermal diffusion, ion migration, and molecular distillation; (3) utilizing the difference in thermodynamic properties (chemical equilibrium and phase equilibrium), such as distillation, chemical exchange, extraction, absorption, adsorption, ion exchange, and crystallization; (4) utilizing the difference in the kinetic properties of isotope chemical reactions, such as electrolysis and photochemical separation (including laser separation). At present, the main methods for isotope separation at home and abroad are magnetic separation and laser separation, but they have the disadvantages of high cost and low separation flux. Therefore, it is necessary to develop a new separation and enrichment process with high throughput and low cost.

[0005] for 7 Li is a natural stable isotope. The traditional separation method is the lithium amalgam method, but the production process requires a large amount of highly toxic mercury. The U.S. Environmental Protection Agency (EPA) has banned the use of the lithium amalgam method to produce lithium isotopes. Summary of the invention

[0006] The purpose of the present invention is to provide an electrodialysis coupled extraction enrichment 7 Li method, using electrodialysis coupled membrane technology to separate Li isotopes in cascade, increasing 7 The selectivity of Li is improved 7 Effect of Li isotope separation and enrichment.

[0007] In order to achieve the above object, the present invention provides an electrodialysis coupled extraction enrichment 7 The method comprises: coupling a plurality of functionalized membranes in series for electrodialysis, wherein a supply phase and a receiving phase are located on both sides of the functionalized membrane, and the volume ratio of the supply phase to the receiving phase is (1 to 100): (1 to 100), and energizing the electrodes on both sides of the plurality of functionalized membranes in series, and applying a voltage of -20 to 20 V (at a positive voltage) 7 Li is enriched in the receiving phase; under negative voltage 7 Li is enriched in the supply phase), the time is 3s to 120min, and Li isotope extraction and separation is performed; wherein, the supply phase is a Li ion aqueous salt solution, and the pH of the Li ion aqueous salt solution is 1 to 7, and the pH is adjusted to acidic to improve the selectivity of the extractant for Li isotopes; the receiving phase is a hydrochloric acid solution; the functionalized membrane is an anion exchange membrane and a cation exchange membrane loaded with an extractant; the cation exchange membrane and the anion exchange membrane loaded with the extractant are alternately arranged; the supply phase and the receiving phase are alternately arranged between the cation exchange membrane and the anion exchange membrane loaded with the extractant; the extractant is selected from any one or more of an amide acid and crown ether coupling extractant and a β-diketone-TOPO deep eutectic extractant; the cation exchange membrane is selected from any one or more of an SLM membrane, a PIM membrane and an IIM membrane.

[0008] Preferably, the voltage of the electrodialysis is -5 to 5V.

[0009] Preferably, the electrodialysis time is 5 to 120 min.

[0010] The structure of the β-diketone-TOPO deep eutectic extractant (DES) is as follows:

[0011]

[0012] Deep eutectic extractants are mainly composed of hydrogen bond donors (such as polyols, urea and carboxylic acids) and hydrogen bond acceptors (such as quaternary ammonium salts, choline chloride, etc.), which can form binary or ternary systems; these solvents are characterized by having a lower melting point, similar to ionic liquids. The β-diketone-TOPO deep eutectic extractant of the present invention is a mixture of 2-thenoyltrifluoroacetone and tri-n-octylphosphine oxide, and its preparation method comprises:

[0013] 2-thenoyltrifluoroacetone and tri-n-octylphosphine oxide are mixed for reaction to prepare an extractant; the molar ratio of the 2-thenoyltrifluoroacetone to tri-n-octylphosphine oxide is (3-1):1; the reaction temperature of the extractant is 15-85°C, preferably 40-60°C, and the reaction time is 2-48h, preferably 6-20h.

[0014] Preferably, the molar ratio of 2-thenoyltrifluoroacetone to tri-n-octylphosphine oxide is (2-1):1.

[0015] The present invention uses fuzzy cascade theory to control the flow rate of the supply phase and the receiving phase and the electric field strength of the electrodialysis coupling extraction system through a PID controller (proportional-integral-differential controller), and the enrichment can be obtained through membrane coupled electrodialysis enrichment technology. 7 The solution of Li isotopes can be cascaded through multiple stages. 7 The natural stable isotope abundance of Li is increased to ≥99%.

[0016] Preferably, the amide acid in the amide acid and crown ether coupling extractant is selected from DODGAA and / or D2EHDGAA; and the crown ether is selected from benzene-15-crown-5 crown ether.

[0017] The preparation method of DODGAA comprises: adding diglycolic anhydride to an organic solvent, adding dioctylamine dissolved in the organic solvent, stirring at 500 rpm for 2 to 24 hours at room temperature with a magnetic stirrer to prepare DODGAA; the mass ratio of diglycolic anhydride to dioctylamine is 1:(0.5 to 20); wherein the organic solvent is selected from CH2Cl2, n-dodecane, kerosene, a mixture of kerosene and alcohol, an imidazole solvent, [C 2～16 mim][Tf2N]、[C 2～16 mim][PF6] and [C 2～16 mim][BF4], so as to be able to completely or partially dissolve glycolic anhydride and / or di-n-octylamine.

[0018] Furthermore, the preparation method of the extractant also includes a post-treatment step: washing, adsorbing, and distilling the prepared product to remove the solvent and water. For example, washing with hydrochloric acid, nitric acid, sulfuric acid, water, etc., and also, for example, adsorption with activated carbon. For example, the obtained product is washed 5 times with 0.1-5 mol / L H2SO4 and deionized water in a separation funnel, and excess impurities are adsorbed with activated carbon. Finally, a rotary evaporation device and a drying oven are used to remove the solvent and water.

[0019] The extractant used in the present invention is stable at room temperature, in acidic / alkaline solutions and in electric fields.

[0020] Preferably, the extractant structure contains any one of the functional groups of hydroxyl, carboxyl, amino and nitro.

[0021] Preferably, the Li ion aqueous salt solution is selected from any one or more of Li ion chloride, nitrate, sulfate and organic acid salt; or / and, the purity of the Li ion aqueous salt is 3-6N grade; or / and, the concentration of the Li ion aqueous salt is 5-60ppm.

[0022] More preferably, the concentration of the Li ion water-soluble salt is 10 to 30 ppm.

[0023] Preferably, the preparation of the Li ion aqueous salt solution comprises: dissolving the Li ion aqueous salt in water, adding hydrochloric acid, and adjusting the pH to 6.02 using ammonia water (adjusting the pH to acidity can improve the selectivity of the extractant for Li isotopes), to obtain the supply phase.

[0024] Preferably, the ionic liquid of the SLM membrane is selected from [C n mim][Tf2N]、[C m mim][PF6] and [C p mim][BF4]; wherein n, m and p are each independently selected from 2 to 16.

[0025] Preferably, an SLM membrane is selected for the cation exchange membrane, and the preparation of the functionalized membrane comprises: immersing a polyvinylidene fluoride membrane in the ionic liquid solution, sealing and standing, taking it out and lightly wiping off the residual organic phase on the membrane surface with filter paper to prepare an ionic liquid supported liquid membrane.

[0026] Preferably, an IIM membrane is selected for the cation exchange membrane, and the extractant is an amic acid and a crown ether coupling extractant. The preparation of the functionalized membrane comprises:

[0027] The organic phase is dichloromethane dissolved with amide acid and crown ether coupling extractant, the aqueous phase is a high-purity lithium solution, wherein the amount of Li relative to the extractant is 2.5 to 3.5 times in excess, and dilute hydrochloric acid is added to the aqueous phase to make the pH value 1.5; the organic phase and the aqueous phase are mixed and oscillated, and the volume ratio of the aqueous phase to the organic phase is 1:1; wherein the concentration of the high-purity lithium solution is 10 to 30 ppm; after the oscillation is completed, centrifugation is performed, and then the organic phase is taken and stirred at room temperature to dissolve the casting solution, wherein the casting solution accounts for 50wt% of the total mass; then, a customized glass cup is placed on the glass plate, the glass cup has good sealing performance, a smooth cross-section, and fits tightly with the glass plate to prevent leakage; a micropipette is used to absorb the casting solution and drip it into the glass cup; wherein the amount of the casting solution is determined according to the required film thickness; the casting solution is selected from at least one of triacetylcellulose and polyvinylidene fluoride; then, the glass cup is covered with filter paper to evaporate the solvent slowly; finally, the Li ion imprint is eluted and then washed with ultrapure water.

[0028] Preferably, the purity of the Li ion water-soluble salt is 3-6N level.

[0029] Preferably, the concentration of the Li ion water-soluble salt is 5 to 60 ppm.

[0030] Preferably, the volume ratio of the supply phase and the receiving phase is controlled to be 1:(5-10); or / and, the volume ratio of the supply phase and the receiving phase is adjusted by PID control of the flow rate of the supply phase and the receiving phase; or / and, the electrodialysis voltage is 5-15V; or / and, the electrodialysis time is 30-120min.

[0031] More preferably, the flow rates of the donating and receiving phases are controlled by PID.

[0032] Preferably, the anion exchange membrane adopts the commercial ORION anion exchange membrane CMX-40-20.

[0033] Preferably, the concentration of the hydrochloric acid solution in the receiving phase is 0.05-1M.

[0034] More preferably, the concentration of the hydrochloric acid solution in the receiving phase is 0.1M.

[0035] The electrodialysis coupled extraction enrichment of the present invention 7 Li's method has the following advantages:

[0036] (1) The present invention develops a new method for high-throughput enrichment and separation of natural stable isotopes of Li. Through an electrodialysis cascade device with a specific functionalized membrane, Li isotope ions will combine with the extractant to form a complex. Under the action of an external electric field, the difference in the electromigration properties between different complexes can increase 7 The separation factor of Li is improved 7The effect of Li isotope separation and enrichment is achieved by adjusting the process conditions under the premise of using the same device. 7 The natural stable isotopes of Li can be separated and enriched, greatly shortening the time required to reach extraction equilibrium. 7 Li isotopes were separated and enriched by 10 2 The cascade level can 7 The abundance of natural stable isotopes of Li increased from 92.47% to 5N level;

[0037] (2) The present invention uses a hydrometallurgical method, uses an amic acid and a crown ether coupling extractant, a β-diketone structure deep eutectic extractant, and a membrane coupled electrodialysis 7 Li natural stable isotope separation and enrichment, the invention has the advantages of being advanced, green and economical, and there is no report on the use of a method similar to or the same as the present invention;

[0038] (3) The present invention reduces the amount of extractant used and improves the efficiency of extractant use through electrodialysis coupled membrane technology, thereby achieving green and environmentally friendly cleaning requirements. This method can achieve Li isotope enrichment at ultra-low and ultra-high concentrations;

[0039] (4) The present invention adopts a deep eutectic extractant with a β-diketone structure, which has a separation effect on Li isotopes. 6 Li is selective for 7 Li has a separation effect, and the extractant is simple to prepare and low in cost, and can be used for enrichment and separation 7 Li isotopes;

[0040] (5) The extractant of the present invention has multiple active sites, which can improve the selectivity of isotope separation by specifically combining functional groups with Li isotopes, and is more environmentally friendly than traditional acidic proton exchangers. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is the infrared spectrum of DES in Example 1.

[0042] Figure 2 This is the hydrogen nuclear magnetic resonance spectrum of DES in Example 1.

[0043] Figure 3 (a) is the P2p XPS spectrum of the DES extractant (molar ratio: HTTA / TOPO=2 / 1). Figure 3 (b) is the O1s XPS spectrum of the DES extractant.

[0044] Figure 4 It is the PVDF blank membrane in Example 2.

[0045] Figure 5 The SLM membrane immersed in DES in Example 3 was extracted at different times and the voltages of 5V, 10V and 15V in the supply phase and the receiving phase were 6 Li, 7 Changes in Li isotope concentration; (a) 5V 6 Li concentration variation curve; (b) 5V 7 Li concentration change curve; (c) 10V 6 Li concentration change curve; (d) 10V 7 Li concentration change curve; (e) 15V 6 Li concentration variation curve; (f) 15V 7 Li concentration variation curve.

[0046] Figure 6 The electrodialysis extraction separation at 1V for 3h in Example 4 7 Changes of Li concentration and separation factor over time.

[0047] Figure 7 This is an example diagram of the eb-electrodialysis coupled extraction cascade process in Example 5.

[0048] Figure 8 In Example 5, the controller controls the flow rates of the supply phase and the receiving phase to adjust the extraction enrichment. 7 Separation factor of Li isotopes. DETAILED DESCRIPTION

[0049] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0050] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0051] According to the present invention, the synthesis of DES extractant, characterization test of various properties and its effect on 7 The adsorption of Li isotopes is specifically implemented as follows:

[0052] Example 1 Synthesis of Extractant DES

[0053] 1. Synthesis method of the extractant DES of the present invention

[0054] The specific implementation steps are as follows:

[0055] In a round-bottom flask, 5.06 g of 2-thenoyltrifluoroacetone (HTTA, 140.06 g / mol, 0.04 mol) and 7.7326 g of tri-n-octylphosphine oxide (TOPO, 386.63 g / mol, 0.02 mol) were added and stirred at 500 rpm with a magnetic stirrer. The mixture was stirred at 40-60°C for 1 h. The resulting solution was filtered and the product was the extractant DES, which was a golden viscous liquid.

[0056] Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance ( 1 HNMR) analysis of the synthesized DES extractant, characterization spectrum such as Figure 1 and Figure 2 As shown in Figure 2, the FT-IR analysis results are consistent with the compound structure. Figure 2 As shown, the δ value is the chemical shift. After the formation of DES containing HTTA and TOPO, a sharp peak appeared between 14.4ppm and 14.6ppm. This is due to the formation of intermolecular hydrogen bonds between HTTA and TOPO in the DES extractant. Through the above comparison of HTTA and DES (2:1), the formation of intermolecular hydrogen bonds in HTTA and DES (2:1) can be predicted. In the case of intermolecular hydrogen bonds, HTTA and DES (2:1) extractants can effectively separate 6 Li and 7 Li.

[0057] 2. Experiment on the extraction effect of the extractant DES of the present invention

[0058] The adjusted high-purity Li solution and the organic phase (extractant DES) were mixed in a test tube at a volume ratio of 2:1 between the aqueous phase and the organic phase, and the mixed test tube was shaken at a constant temperature of 313K for 6 hours in a full-temperature oscillating incubator (ZQPW-70, Tianjin Laboterui Instrument Equipment Co., Ltd.). In order to ensure that the aqueous phase and the organic phase can be evenly mixed, the shaking speed was adjusted to 250rpm. After shaking, the test tube with the evenly mixed aqueous phase and organic phase was centrifuged in a centrifuge (CTK80, Xiangyi Centrifuge Co., Ltd.) with a set speed of 3000rpm and a time of 3min, and the aqueous phase was extracted from the centrifuged test tube and placed in a new test tube. This process required the use of a filter head and a syringe to complete. The extracted water phase in the new test tube was tested by an inductively coupled plasma emission spectrometer (JY-Horiba ICP-OES Ultima2, Agilent Technologies, France) to determine the concentration of lithium ions in the water phase; the concentrations of lithium-6 and lithium-7 in the water phase before and after extraction were measured using an inductively coupled plasma emission spectrometer (JY-Horiba ICP-MS 8800, Agilent Technologies, France).

[0059] At the equilibrium point of pH=6.02, the energy barrier of hydrogen bonds between molecules in the deep eutectic solvent extractant makes the separation effect optimal. The separation factor (β (7Li / 6Li) ) can reach a maximum value of 1.068. Figure 3 In (a), the XPS spectra before and after extraction show that P 2p The orbital has not changed. In the extraction system, HTTA plays a major role in the extraction of Li ions. Figure 3 In (b), the XPS spectra before and after extraction show that the OH bond is converted into an O-Li bond, and its binding energy decreases by 0.82 eV. This change is consistent with the theory that a decrease in electron binding energy indicates an increase in electron cloud density. + Replace H + , the OH bond is converted into an O-Li bond. In short, the Li ions are ion-exchanged with the proton hydrogen ions of HTTA.

[0060] Example 2 Preparation of ionic liquid supported liquid membrane (SLM)

[0061] A method for preparing an ionic liquid supported liquid membrane (SLM), the specific steps are as follows:

[0062] The PVDF membrane (product model HVHP04700, pore size 0.45 μm, diameter 47 mm, thickness 125 μm, electron microscope image see Figure 4 ) was immersed in 0.5 mL of the extractant DES solution prepared in Example 1, sealed and allowed to stand for 12 h, and then taken out and lightly wiped with filter paper to remove the residual organic phase on the membrane surface to prepare an ionic liquid supported liquid membrane (SLM).

[0063] The SLM prepared by the present invention is a dense membrane with fewer and larger pores. This is due to the structure of DES. DES enters the pores of PVDF and adheres to the pore walls. 6 Li is then selectively extracted by complexation. 7 Li ions are transported through the membrane. In addition, the membrane impregnated with ionic liquid has a rougher surface compared to the blank membrane with PVDF. The presence of DES will minimize the intermolecular interaction forces in the PVDF scaffold, resulting in higher membrane permeability.

[0064] Example 3 Separation of lithium isotope enrichment 7 Li's Method

[0065] A method for separating lithium isotope enrichment 7 Li's method, the specific steps are as follows:

[0066] (1) Preparation of supply phase

[0067] Take lithium chloride as raw material (purity 99.99%), add ultrapure water to slowly dissolve, filter, then add ammonium chloride, use ammonia water to adjust the pH to 6.02, the ammonium chloride concentration is 0.1M, the lithium ion concentration is 25ppm, and the volume of the supply phase solution is 35mL;

[0068] (2) Preparation of receiving phase

[0069] Prepare 0.1M hydrochloric acid, the volume of the receiving phase solution is 35mL;

[0070] (3) Membrane-coupled electrodialysis enrichment process

[0071] The SLM film prepared in Example 2 was used, and the supply phase and the receiving phase were placed on both sides of the SLM film, respectively, with a volume ratio of the supply phase to the receiving phase of 1:1, and different voltages (5V, 10V, 15V) were applied to the receiving phase. 7 Li isotope enrichment, electrodialysis extraction separation 3h, 6 Li, 7 The results of the Li concentration change over time are shown in Figure 5 shown.

[0072] Before and after 3 h of electrodialysis coupled extraction, ICP-MS was used to analyze the Li isotopes in the donor and receiver phases ( 6 Li, 7 Li) content was tested, such as Figure 5 As shown, after 30 minutes of extraction, the phases before and after extraction 7 Li concentration / 6 Li concentration = 1.173, 7 The single-stage fractionation efficiency of Li isotopes reached 1.173, and the separation coefficient of Li isotopes reached its maximum value. 7 The separation coefficient of Li is higher than 1.068 of the DES liquid-liquid extraction method, which means that the extraction efficiency of Li isotopes in the present invention is better than that of the electrodialysis-free coupled extraction system.

[0073] The present invention uses PVDF as a carrier to prepare a SLM membrane containing an extractant, and couples the extraction to the electrodialysis 7 Li isotope specific adsorption, experiments show that the present invention 7 It has great practical potential in Li enrichment and separation.

[0074] Example 4

[0075] A method for separating lithium isotope enrichment 7 Li's method, the specific steps are as follows:

[0076] (1) Preparation of supply phase

[0077] Take lithium chloride as raw material (99.99%), add ultrapure water to slowly dissolve, filter, then add ammonium chloride and L-aspartic acid, use hydrochloric acid to adjust the pH to 1.5, the ammonium chloride concentration is 0.1M, the L-aspartic acid concentration is 1M, the Li ion concentration is 25ppm, and the volume of the supply phase solution is 35mL.

[0078] (2) Preparation of receiving phase

[0079] Prepare 0.1 M hydrochloric acid and 0.05 M diglycolic acid, and the volume of the receiving phase solution is 35 mL.

[0080] (3) Preparation of IIM membrane

[0081] The organic phase is dichloromethane dissolved with 25mM D2EHDGAA and benzene-15-crown-5 crown ether, and the aqueous phase is a high-purity Li solution (30ppm), in which the amount of Li relative to the amount of the extractant is about 3 times the amount of the substance, and dilute hydrochloric acid is added to the aqueous phase to make the pH = 1.5. The organic phase and the aqueous phase are mixed and shaken for 12 hours, the volume ratio of the aqueous phase to the organic phase is 1:1, and centrifuged for 5 minutes. Then the organic phase is taken to dissolve triacetate (polymer CTA), wherein the polymer CTA accounts for 50wt% of the total mass ratio, and is stirred and dissolved on a magnetic stirrer at room temperature. Subsequently, a specially customized glass cup (with an inner diameter of 60mm, good sealing performance, smooth cross-section, and close fit with the glass plate to prevent leakage) is placed on the glass plate, and the casting solution is sucked with a micropipette and dripped into the glass cup. Among them, the amount of the casting solution (organic phase with triacetate dissolved) needs to be determined according to the thickness of the required film. Then cover the glass cup with filter paper to evaporate the solvent slowly. Finally, the Li ion imprint was eluted using 1 M HCl and 0.05 M diglycolic acid, followed by washing with ultrapure water.

[0082] (4) Membrane-coupled electrodialysis enrichment process

[0083] The supply phase and the receiving phase were placed on both sides of the IIM membrane, with a volume ratio of 1:1. A voltage of 1 V was applied and the receiving phase was 7 Li isotope enrichment.

[0084] 1V electrodialysis extraction separation 3h 7 The results of Li concentration and separation coefficient change with time are shown in Figure 6 shown.

[0085] Example 5eb (flat membrane)-electrodialysis coupled extraction cascade process

[0086] An EB-electrodialysis coupled extraction cascade process, such as Figure 7As shown in the figure (P represents a pump), it is an eb-electrodialysis coupled extraction cascade process diagram, the system used is assembled from a supply phase, a receiving phase and an electrodialysis device, the ionic liquid supported liquid membrane SLM prepared in Example 2 is mounted on the basis of the electrodialysis device as a cation exchange membrane, and the anion permeation membrane adopts a commercial ORION anion exchange membrane CMX-40-20, and several ionic liquid supported liquid membranes SLM prepared in Example 2 are alternately coupled in series with the anion permeation membrane, and under the condition of an external electric field of 15V, the potential difference is used as the driving force, and different positively charged 6 Li and 7 The migration properties of Li isotope complex ions on the DES impregnated membrane are different. 7 Li migrates through the cation exchange membrane to the receiving phase (R) for separation and enrichment. By coupling the electric field, the 6 Li and 7 Separation factor of Li isotopes.

[0087] The flow rates of the supply and receiving phases are controlled by PID controllers to adjust the extraction enrichment 7 The separation factor of Li isotopes is Figure 8 As shown in Figure 2, the volume ratio of the supply phase to the receiving phase is 1:10, 1:5, and 1:1. Before and after 3 h of electrodialysis coupled extraction, ICP-MS was used to analyze the Li isotopes in the supply phase and the receiving phase ( 6 Li, 7 After 30 minutes of extraction, the volume ratio of the supply phase to the receiving phase was 1:10. 7 The single-stage fractionation efficiency of Li isotopes reaches 1.173.

[0088] eb-electrodialysis coupled extraction cascade device, through electrodialysis coupling resin cascade 7 The enrichment effect of Li isotopes is shown in Table 1. 7 The abundance of the natural stable isotope of Li is increased from 92.47% to 5N level (99.999%).

[0089] Table 1 Electrodialysis coupled moving bed / fixed bed cascade pairs 7 Li isotope enrichment

[0090]

[0091] Note: A single supply phase, receiving phase, selective permeable membrane and resin column is called a primary stage.

[0092] The present invention uses eb-electrodialysis coupled extraction cascade device to 7 Li natural stable isotope specific adsorption, experiments show that the present invention 7Li has great practical potential in the enrichment and separation of natural stable isotopes.

[0093] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be appreciated that the above description should not be considered as a limitation of the present invention. After reading the above content, it will be apparent to those skilled in the art that various modifications and substitutions of the present invention will occur. Therefore, the protection scope of the present invention should be limited by the appended claims.

Claims

1. An electrodialysis coupled extraction enrichment 7 Li's method, characterized in that The method includes: A plurality of functionalized membranes are coupled in series for electrodialysis, wherein the supply phase and the receiving phase are located on both sides of the functionalized membrane, and the volume ratio of the supply phase to the receiving phase is (1-100):(1-100), and the electrodes on both sides of the plurality of functionalized membranes connected in series are energized, and a voltage of -20 to 20 V is applied for a time of 3 s to 120 min to extract and separate Li isotopes; Wherein, the supply phase is a Li ion aqueous salt solution, and the pH of the Li ion aqueous salt solution is 1 to 7; The receiving phase is a hydrochloric acid solution; The functionalized membrane is an anion exchange membrane and a cation exchange membrane loaded with an extractant; the cation exchange membrane loaded with an extractant and the anion exchange membrane are alternately arranged; the supply phase and the receiving phase are alternately arranged between the cation exchange membrane loaded with an extractant and the anion exchange membrane; The extractant is selected from any one or more of an amic acid and crown ether coupling extractant and a β-diketone-TOPO deep eutectic extractant; The cation exchange membrane is selected from any one or more of a SLM membrane, a PIM membrane and an IIM membrane.

2. The electrodialysis coupled extraction enrichment according to claim 1 7 Li's method, characterized in that The amic acid in the amic acid and crown ether coupling extractant is selected from DODGAA and / or D2EHDGAA; and the crown ether is selected from benzene-15-crown-5 crown ether.

3. The electrodialysis coupled extraction enrichment according to claim 1 7 Li's method, characterized in that The Li ion aqueous salt solution is selected from any one or more of Li ion chloride, nitrate, sulfate and organic acid salt; Or / and, the purity of the Li ion water-soluble salt is 3-6N grade; Or / and, the concentration of the Li ion water-soluble salt is 5 to 60 ppm.

4. The electrodialysis coupled extraction enrichment according to claim 1 7 Li's method, characterized in that The preparation of the Li ion aqueous salt solution comprises: The Li ion water-soluble salt is dissolved in water, hydrochloric acid is added, and ammonia water is used to adjust the pH to obtain the supply phase.

5. The electrodialysis coupled extraction enrichment according to claim 1 7 Li's method, characterized in that The ionic liquid of the SLM membrane is selected from [C n mim][Tf2N]、[C m mim][PF6] and [C p mim][BF4]; wherein n, m and p are each independently selected from 2 to 16.

6. The electrodialysis coupled extraction enrichment according to claim 1 7 Li's method, characterized in that The SLM membrane is selected for the cation exchange membrane, and the preparation of the functionalized membrane comprises: The polyvinylidene fluoride membrane is immersed in the extractant, sealed and allowed to stand, and then taken out and lightly wiped with filter paper to remove the residual organic phase on the membrane surface, thereby preparing an ionic liquid supported liquid membrane.

7. The electrodialysis coupled extraction enrichment according to claim 1 7 Li's method, characterized in that The IIM membrane is selected for the cation exchange membrane, the extractant is an amic acid and a crown ether coupling extractant, and the preparation of the functionalized membrane comprises: The organic phase is dichloromethane dissolved with amic acid and crown ether coupling extractant, the aqueous phase is a high-purity lithium solution, wherein the amount of lithium relative to the extractant is 2.5 to 3.5 times in excess, and dilute hydrochloric acid is added to the aqueous phase to make the pH = 1.5; the organic phase and the aqueous phase are mixed and shaken, and the volume ratio of the aqueous phase to the organic phase is 1:1; wherein the concentration of the high-purity lithium solution is 10 to 30 ppm; After the shaking is completed, centrifuge, then take the organic phase and stir at room temperature to dissolve the casting solution, wherein the casting solution accounts for 50wt% of the total mass; Subsequently, a customized glass cup is placed on the glass plate, wherein the glass cup has good sealing performance, a smooth cross section, and fits tightly with the glass plate to prevent leakage; a casting solution is sucked with a micropipette and dripped into the glass cup; wherein the amount of the casting solution is determined according to the required film thickness; and the casting solution is selected from at least one of triacetylcellulose and polyvinylidene fluoride; Then, cover the glass with filter paper to allow the solvent to evaporate slowly; finally, elute the Li ion imprint and wash with ultrapure water.

8. The electrodialysis coupled extraction enrichment according to claim 1 7 Li's method, characterized in that By controlling the volume ratio of the supply phase to the receiving phase to be 1:(5-10); or / and, adjusting the volume ratio of the supply phase to the receiving phase by controlling the flow rates of the supply phase and the receiving phase by PID; Or / and, the electrodialysis voltage is 5 to 15V; Or / and, the electrodialysis time is 30 to 120 minutes.

9. The electrodialysis coupled extraction enrichment according to claim 1 7 Li's method, characterized in that The anion exchange membrane adopts the commercial ORION anion exchange membrane CMX-40-20.

10. The electrodialysis coupled extraction enrichment according to claim 1 7 Li's method, characterized in that The concentration of the hydrochloric acid solution in the receiving phase is 0.05-1M.

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