A lithium ion extraction membrane based on a polymeric extractant, preparation and use

Abstract

The application discloses a lithium ion extraction membrane based on a polymer extractant, preparation and application, and comprises the following steps: preparing a phosphonate polymer extractant, mixing a polymer, a phosphite organic matter and a solvent, refluxing, sedimentation, washing, suction filtration and vacuum drying to obtain the phosphonate polymer extractant; and preparing a lithium ion selective extraction membrane, blending the phosphonate polymer extractant, a synergistic extractant, a plasticizer and a weak polar organic solvent, pouring the solution into a flat-bottomed container and volatilizing into a film to obtain the lithium ion extraction membrane. Lithium ions in a solution are extracted and selectively separated through the extraction membrane under an operating voltage. The method has small environmental pollution, high transmission rate, high removal rate and high membrane extraction efficiency, and the membrane phase does not leak, and is a high-stability membrane product with high mass transfer performance for lithium ions and a separation method.

Description

Technical Field

[0001] This invention belongs to the technical fields of materials chemistry, hydrometallurgy and wastewater treatment, and relates to the synthesis of phosphonate ester polymer extractants, the preparation of membrane extraction materials and the method for extracting lithium metal ions by membrane extraction. Background Technology

[0002] In recent years, with the rapid increase in demand for lithium energy, lithium resource extraction technology has developed rapidly. Lithium in nature is mainly stored in liquid deposits and solid minerals. Compared to lithium extraction processes from solid minerals, extracting lithium from liquid lithium resources such as seawater and salt lakes is less costly. my country's salt lake brines contain abundant lithium resources, but due to the high magnesium-to-lithium ratio (200 / 1 or higher) and low lithium concentration, efficient separation technology with high lithium selectivity has become an urgent priority.

[0003] Compared to lithium extraction technologies such as adsorption and membrane separation, liquid-liquid extraction technology enjoys advantages in lithium extraction from salt lake brines due to its high efficiency, speed, and high selectivity. However, with the implementation of the "dual carbon" national policy, lithium extraction technologies face higher requirements in terms of greenness, energy conservation, and emission reduction. Membrane extraction technology, which combines extraction and back-extraction, has attracted much attention in the separation field due to its high selectivity, greenness, and energy efficiency. However, the supporting liquid membrane carrier is prone to leakage and cannot be used for a long time. While polymer-encapsulated liquid membranes require less carrier and can be reused, their stability remains insufficient because the extractant is not effectively immobilized in the membrane material. Furthermore, to increase the carrier content and stability in the membrane, a higher membrane thickness is required, which affects the lithium extraction rate, preventing the industrial application of membrane extraction technology. Currently, there are no reports on immobilizing the carrier in the membrane material. Summary of the Invention

[0004] To address the problems of instability in existing membrane extraction materials, slow mass transfer rates in membrane extraction lithium extraction systems, and easy carrier leakage, this invention aims to provide a method for preparing a highly stable membrane extraction material and a corresponding membrane extraction lithium extraction system. This provides an efficient and highly selective lithium extraction process for the seawater or brine lithium extraction industry. Furthermore, the study of efficient separation of metal ions using external electric field coupled membrane extraction technology has significant theoretical importance and substantial economic value.

[0005] The present invention is achieved through the following technical solution.

[0006] According to one aspect of the present invention, a method for preparing a lithium-ion extraction membrane based on a polymer extractant is provided, comprising the following steps:

[0007] Step 1, Preparation of phosphonate polymer extractant:

[0008] Mix 10%–14% polymer, 26%–42% phosphite organics and 45%–65% solvent according to the mass ratio; reflux homogeneously, cool to room temperature, add anhydrous ethanol to the mixture for precipitation, wash the precipitate repeatedly with anhydrous ethanol, filter, and dry under reduced pressure to obtain phosphonate polymer extractant.

[0009] Step 2, Preparation of lithium-ion selective extraction membrane:

[0010] According to the mass ratio, 2% to 5% of phosphonate polymer extractant is mixed with 0.5% to 4% co-extractant, 0% to 1.8% plasticizer, and 90% to 98% weakly polar organic solvent to form a homogeneous solution. The solution is quantitatively poured into a flat-bottomed container, and after the solvent is evaporated, a lithium-ion selective extraction membrane is obtained.

[0011] According to an exemplary embodiment of the present invention, the polymer is polyvinyl chloride with a molecular weight greater than 72,000 and a degree of polymerization less than 2,500.

[0012] The phosphite esters are trimethyl phosphite, triethyl phosphite, tributyl phosphite, or trioctyl phosphite.

[0013] The solvent is one or a mixture of two or more of N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, and dioxane.

[0014] The co-extractant is N503-FeCl4. - 2-Thiophenecarboxyltrifluoroacetone, di(2-ethylhexyl) phosphate, or trialkylphosphine oxide.

[0015] The plasticizer is dioctyl phthalate or 2-nitrophenyl octyl ether.

[0016] The weakly polar organic solvent is tetrahydrofuran or N,N-dimethylacetamide.

[0017] According to an exemplary embodiment of the present invention, in step 1, the solvent is mixed and subjected to homogeneous reflux reaction at 100-160°C for 12-30 hours.

[0018] In step 2, the thickness of the membrane material is 50–150 μm.

[0019] According to another aspect of the present invention, a lithium-ion extraction membrane based on a polymer extractant prepared by the method is provided.

[0020] According to another aspect of the present invention, an application of lithium-ion extraction membrane for separating and extracting lithium ions is provided, comprising:

[0021] A lithium-ion extraction membrane is installed in a membrane extraction device to separate the lithium-ion-containing liquid phase from the precipitate phase, and the material composition in the two solutions remains homogeneous.

[0022] Control the ion concentration and pH of the feed liquid solution and the concentration of the eluent solution;

[0023] An external electric field coupled membrane extraction process is used, in which the anode platinum wire is placed in the feed liquid phase and the cathode platinum wire is placed in the eluent phase, or the feed liquid phase and the eluent phase are continuously stirred under no power conditions to carry out mass transfer reaction.

[0024] According to an exemplary embodiment of the present invention, the liquid phase exists in the form of a lithium ion solution with a lithium ion concentration of 15-500 mg / L.

[0025] According to an exemplary embodiment of the present invention, when a lithium-ion extraction membrane prepared with 2-thiophenecarboxyltrifluoroacetone, di(2-ethylhexyl) phosphate or trialkylphosphine oxide as the co-extractant is used, the pH of the feed liquid phase is maintained between 10 and 12, and the eluent phase is neutral water or 0.5 to 1 mol / L hydrochloric acid solution.

[0026] According to an exemplary embodiment of the present invention, when the co-extraction agent is N503-FeCl4 - When preparing the lithium-ion extraction membrane, the pH of the feed liquid phase is maintained between 6 and 8, and the eluent phase is 0.5-1 mol / L hydrochloric acid + 1-2 mol / L sodium chloride solution.

[0027] According to an exemplary embodiment of the present invention, the stirring speed in the two-phase solution is 300-500 rpm and remains constant; the continuous stirring reaction time is 9-72 h.

[0028] According to an exemplary embodiment of the present invention, the operating voltage in the external electric field coupled membrane extraction process is 10-40V. After continuous extraction for 12-72h, the removal rate of Li(Ⅰ) in the feed liquid phase reaches 75%-99%, and the recovery rate of Li(Ⅰ) in the eluent phase reaches 70%-92%.

[0029] This polymer extractant is produced by reacting phosphite compounds with polyvinyl chloride via a nucleophilic substitution reaction to generate polyvinyl chloride dialkylphosphonate. This polyvinyl chloride dialkylphosphonate is then formulated with a specific co-extractant to prepare a lithium-ion selective extraction membrane, which can be applied to the selective separation, extraction, and enrichment of lithium in lithium-containing solutions.

[0030] The present invention, by adopting the above technical solution, has the following beneficial effects:

[0031] 1. This invention prepares a phosphonate polymer extractant (polyvinyl chloride dialkyl phosphonate) using a homogeneous reflux reaction. The synthesis process requires minimal equipment, is simple to operate, and is inexpensive. Furthermore, it provides a new approach for the extraction and separation of alkali metal lithium.

[0032] 2. The four polymer membrane materials provided by this invention, along with the techniques and methods for the removal, extraction, or separation of lithium ions, exhibit excellent mass transfer performance. The preparation of the membrane products and the membrane extraction operation are simple and easy to perform, requiring minimal reagents, causing minimal environmental pollution, and achieving high transfer rates, thus meeting the requirements of high efficiency, energy saving, and environmental protection.

[0033] 3. The present invention provides a method for membrane extraction using a polymer membrane coupled with an external electric field, which can accelerate the extraction process through an electric field. It has good application potential in environmental protection and hydrometallurgy. Attached Figure Description

[0034] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, do not constitute an undue limitation of the invention. In the drawings:

[0035] Figure 1 This is the infrared spectrum of the extraction membrane prepared in Example 1 of the present invention;

[0036] Figure 2 This is the infrared spectrum of the extraction membrane prepared in Example 3 of the present invention;

[0037] Figure 3 This is a graph showing the concentration changes of the two phases of lithium extracted by the extraction membrane prepared in Example 5 of this invention under an external electric field coupled membrane.

[0038] Figure 4 The figure shows the concentration change and mass transfer kinetics of the two phases extracted by the extraction membrane prepared in Example 7 of this invention. Detailed Implementation

[0039] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The illustrative embodiments and descriptions of the present invention are used to explain the present invention, but are not intended to limit the present invention.

[0040] This invention provides a method for preparing a lithium-ion selective extraction membrane using a polymer extractant, comprising the following steps:

[0041] Step 1, Preparation of phosphonate polymer extractant:

[0042] Mix 10%–14% polymer, 26%–42% phosphite, and 45%–65% solvent according to the mass ratio, with the total amount of the above raw materials being 100%. After homogeneous reflux reaction at 100–160°C for 12–30 h, cool to room temperature, add anhydrous ethanol to the mixture for precipitation, wash the precipitate repeatedly with anhydrous ethanol to remove excess phosphite, filter, and dry under reduced pressure to obtain phosphonate polymer extractant (polyvinyl chloride dialkyl phosphonate).

[0043] The polymer mentioned above is polyvinyl chloride with a molecular weight greater than 72,000 and a degree of polymerization less than 2,500.

[0044] The aforementioned phosphites include, but are not limited to, some low-level alkyl phosphite small molecule compounds such as trimethyl phosphite, triethyl phosphite, tributyl phosphite, and trioctyl phosphite.

[0045] The solvents mentioned above are one or a mixture of two or more polar or weakly polar organic solvents such as N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone and dioxane.

[0046] Step 2, Preparation of lithium-ion selective extraction membrane:

[0047] According to the mass ratio, 2%–5% of phosphonate polymer extractant is mixed with 0.5%–4% co-extractant, 0%–1.8% plasticizer, and 90%–98% weakly polar organic solvent, with the total amount of the above raw materials being 100%. After being mixed and dissolved at room temperature to form a homogeneous solution, the solution is quantitatively poured into a flat-bottomed container made of glass or polytetrafluoroethylene. After the solvent is evaporated and removed, a lithium-ion selective extraction membrane with a membrane material thickness of 50–150 μm is obtained.

[0048] In the above-mentioned lithium selective extraction membrane, the co-extractant includes, but is not limited to: N5O3-FeCl4 - 2-Thiophenecarboxyltrifluoroacetone, di(2-ethylhexyl) phosphate, or trialkylphosphine oxide, etc.

[0049] The aforementioned plasticizers include, but are not limited to, high-boiling-point, low-water-soluble organic compounds such as dioctyl phthalate and 2-nitrophenyl octyl ether.

[0050] The aforementioned weakly polar organic solvents include, but are not limited to, tetrahydrofuran and N,N-dimethylacetamide.

[0051] This invention also provides an application of lithium ion separation and extraction using a polymer-based lithium ion extraction membrane.

[0052] One method for separating and extracting lithium ions using membrane extraction is without the application of electricity, and includes the following steps:

[0053] The obtained lithium-ion extraction membrane was installed in a membrane extraction device to separate the feed phase and the eluent phase. This ensured that the liquid ions in the separated feed and eluent phases could only transfer mass across the membrane through the membrane interface. During the separation process, an electric stirring device was used to maintain homogeneity of the material composition in both phases. The stirring speed in both phases was 300–500 rpm and remained consistent. The stirring reaction was continued for 9–72 hours until the concentration of lithium-containing ions in the feed solution showed no significant change, at which point the mass transfer was terminated. During the mass transfer process, 0.5 mL samples were taken from both the feed and eluent phases every 2–4 hours, and 0.5 mL of the corresponding acid-base buffer solution was added to each phase to maintain material equilibrium. The ion concentrations in both phases during the mass transfer process were detected using inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0054] Furthermore, the liquid phase exists in the form of a lithium-ion solution with a lithium-ion concentration of 15–500 mg / L.

[0055] Furthermore, when the co-extractant in the preparation of the lithium-ion extraction membrane is 2-thiophenecarboxyltrifluoroacetone, di(2-ethylhexyl) phosphate, or trialkylphosphine oxide, the pH of the feed liquid phase is maintained between 10 and 12, and the eluent phase is neutral water or 0.5–1 mol / L hydrochloric acid solution.

[0056] Furthermore, in the preparation of the lithium-ion extraction membrane, the co-extractant is N5O3-FeCl4. - At that time, the pH of the feed liquid phase was maintained between 6 and 8, and the eluent phase was 0.5-1 mol / L hydrochloric acid + 1-2 mol / L sodium chloride solution.

[0057] Another method for separating and extracting lithium ions using membrane extraction is to couple the membrane extraction process with an external electric field.

[0058] The membrane extraction process is the same as the electrostatic method described above. In the external electric field coupled membrane extraction process, the anode platinum wire is placed in the feed phase, and the cathode platinum wire is placed in the desorption phase. The electric field is provided by a DC regulated power supply. Extraction is performed continuously for 12–72 hours at a voltage of 10–40V. The voltage and terminal current density I are obtained using a programmable adjustable regulated power supply (HSPY-60-02, Beijing Hansheng Puyuan Technology). Sampling and detection operations are the same as the method without electricity.

[0059] After continuous extraction, the removal rate of Li(Ⅰ) in the feed liquid phase reached 75%–99%, and the recovery rate of Li(Ⅰ) in the eluent phase reached 70%–92%.

[0060] The present invention will be further illustrated below through different embodiments.

[0061] One implementation method involves the synergistic extraction of Li(Ⅰ) using a phosphonate polymer extractant and a ketone extractant.

[0062] Example 1: Polyvinyl chloride diethylphosphonate + 2-thiophenecarboxylic acid trifluoroacetone system

[0063] Step 1, Preparation of phosphonate polymer extractant:

[0064] 14% polyvinyl chloride, 36.74% triethyl phosphite, and 49.26% N,N-dimethylacetamide were mixed according to the mass ratio, heated to reflux at 100°C, and reacted homogeneously for 30 hours. After cooling to room temperature, anhydrous ethanol was added to the mixture for precipitation. The precipitate was repeatedly washed with anhydrous ethanol to remove excess triethyl phosphite. The mixture was then filtered and dried to obtain the product polyvinyl chloride diethylphosphonate.

[0065] Step 2, Preparation of lithium-ion extraction membrane:

[0066] The following mixtures were prepared by mass ratio: 1.93% polyvinyl chloride diethylphosphonate, 1.72% 2-thiophenecarboxyltrifluoroacetone, 0.64% dioctyl phthalate, and 95.71% tetrahydrofuran. The mixture was dissolved at room temperature to form a homogeneous solution. The solution was then horizontally placed in a flat-bottomed dish and allowed to evaporate completely at 30°C and ambient pressure, solidifying into a smooth, homogeneous, transparent, and uniformly thick extraction membrane with a thickness of 50 μm. The infrared spectrum of the extraction membrane is shown below. Figure 1 As shown.

[0067] Membrane extraction method for separating and extracting lithium ions: an electro-assisted extraction method.

[0068] The prepared polymer membrane was sealed using hollow clamps, polytetrafluoroethylene gaskets, screws, etc., and then assembled with two 250 mL liquid pools. The effective mass transfer area of ​​the membrane was 26.4 cm² for each pool. 2 .

[0069] 250 mL of 500 mg / L lithium chloride solution was placed in the feed phase, and the pH of the feed phase was adjusted to 12. The eluent phase was 250 mL of 1 mol / L hydrochloric acid solution. The anode platinum wire was placed in the feed phase, and the cathode platinum wire was placed in the eluent phase. The magnetic stirring devices in both tanks were turned on to start mass transfer. The stirring speed was 300 rpm. After continuous extraction for 72 h at 40 V, the removal rate of Li(Ⅰ) in the feed phase was 88.40%, and the recovery rate of Li(Ⅰ) in the eluent phase reached 87.65%.

[0070] Example 2: Polyvinyl chloride dibutylphosphonate + 2-thiophenecarboxylic acid trifluoroacetone system

[0071] Step 1, Preparation of phosphonate polymer extractant:

[0072] 10.32% polyvinyl chloride, 41.33% tributyl phosphite, and 48.35% N,N-dimethylformamide were mixed according to the mass ratio, heated to reflux at 160°C, and reacted homogeneously for 12 hours. After cooling to room temperature, anhydrous ethanol was added to the mixture for precipitation. The precipitate was repeatedly washed with anhydrous ethanol to remove excess tributyl phosphite. The mixture was then filtered and dried to obtain the product polyvinyl chloride dibutylphosphonate.

[0073] Step 2, Preparation of lithium-ion extraction membrane:

[0074] 4.40% polyvinyl chloride dibutylphosphonate, 3.44% 2-thiophenecarboxylic acid trifluoroacetone, 1.72% 2-nitrophenyl octyl ether, and 90.44% tetrahydrofuran were mixed according to the mass ratio and dissolved into a homogeneous solution at room temperature. The solution was then placed horizontally in a flat-bottomed vessel and allowed to evaporate completely at 30°C and normal pressure, solidifying into a flat, homogeneous, transparent, and uniformly thick extraction membrane with a membrane thickness of 100 μm.

[0075] Membrane extraction method for separating and extracting lithium ions: an electro-assisted extraction method.

[0076] The prepared polymer membrane was sealed using hollow clamps, polytetrafluoroethylene gaskets, screws, etc., and then assembled with two 250 mL liquid pools. The effective mass transfer area of ​​the membrane was 26.4 cm² for each pool. 2 .

[0077] 250 mL of 100 mg / L lithium chloride solution was placed in the feed phase, and the pH of the feed phase was adjusted to 10. The eluent phase was 250 mL of 0.08 mol / L hydrochloric acid solution. The anode platinum wire was placed in the feed phase, and the cathode platinum wire was placed in the eluent phase. The magnetic stirring devices in both tanks were turned on to start mass transfer. The stirring speed was 500 rpm. After continuous extraction for 32 h at 30 V, the removal rate of Li(Ⅰ) in the feed phase was 85.23%, and the recovery rate of Li(Ⅰ) in the eluent phase reached 82.95%.

[0078] One implementation involves the synergistic extraction of Li(Ⅰ) using a phosphonate polymer extractant and a phosphonic oxide extractant.

[0079] Example 3: Polyvinyl chloride diethylphosphonate + trialkylphosphine oxide system

[0080] Step 1, Preparation of phosphonate polymer extractant:

[0081] 11.97% polyvinyl chloride, 31.88% triethyl phosphite, and 56.15% dimethyl sulfoxide were mixed according to the mass ratio, heated to reflux at 140°C, and reacted homogeneously for 26 hours. After cooling to room temperature, anhydrous ethanol was added to the mixture for precipitation. The precipitate was repeatedly washed with anhydrous ethanol to remove excess triethyl phosphite. The mixture was then filtered and dried to obtain the product polyvinyl chloride diethyl phosphite.

[0082] Step 2, Preparation of lithium-ion extraction membrane:

[0083] 3.14% polyvinyl chloride diethylphosphonate, 2.96% trialkylphosphine oxide (Cyanex 923), and 93.90% tetrahydrofuran were mixed according to the mass ratio and dissolved at room temperature to form a homogeneous solution. The solution was then horizontally placed in a flat-bottomed vessel and allowed to evaporate completely at 30°C and normal pressure, solidifying into a flat, homogeneous, transparent, and uniformly thick extraction membrane with a thickness of 150 μm. The infrared spectrum of the extraction membrane is shown below. Figure 2 As shown.

[0084] Membrane extraction method for separating and extracting lithium ions: an extraction method without applying electricity.

[0085] The prepared polymer membrane was sealed using hollow clamps, PTFE gaskets, screws, etc., and then assembled with two 250 mL liquid pools. The effective mass transfer area of ​​the membrane was 26.4 cm² for each pool. 2 .

[0086] 250 mL of 25 mg / L lithium chloride solution was placed in the feed phase, and the pH of the feed phase was adjusted to 11. The eluent phase was 250 mL of 0.07 mol / L hydrochloric acid solution. The magnetic stirrers in both tanks were turned on to start mass transfer at a stirring speed of 400 rpm. After 24 hours of continuous extraction under stirring, the removal rate of Li(Ⅰ) in the feed phase was 92.08%, and the recovery rate of Li(Ⅰ) in the eluent phase reached 84.54%.

[0087] Example 4: Polyvinyl chloride dimethylphosphonate + trialkylphosphine oxide system

[0088] Step 1, Preparation of phosphonate polymer extractant:

[0089] 9.50% polyvinyl chloride, 25.87% trimethyl phosphite, and 64.63% N-methylpyrrolidone were mixed according to the mass ratio, heated to reflux at 110°C, and reacted homogeneously for 20 hours. After cooling to room temperature, anhydrous ethanol was added to the mixture for precipitation. The precipitate was repeatedly washed with anhydrous ethanol to remove excess trimethyl phosphite. The mixture was then filtered and dried to obtain the product polyvinyl chloride dimethyl phosphonate.

[0090] Step 2, Preparation of lithium-ion extraction membrane:

[0091] 2.21% polyvinyl chloride dimethyl phosphonate, 1.48% trialkylphosphine oxide (Cyanex 923), and 96.31% tetrahydrofuran were mixed according to the mass ratio and dissolved into a homogeneous solution at room temperature. The solution was then placed horizontally in a flat-bottomed container and allowed to evaporate completely at 30°C and normal pressure, thus curing a flat, homogeneous, transparent polymer film with a uniform thickness of 80 μm.

[0092] Membrane extraction method for separating and extracting lithium ions: an electro-assisted extraction method.

[0093] The prepared polymer membrane was sealed using hollow clamps, polytetrafluoroethylene gaskets, screws, etc., and then assembled with two 250 mL liquid pools. The effective mass transfer area of ​​the membrane was 26.4 cm² for each pool. 2 .

[0094] 250 mL of 15 mg / L lithium chloride solution was placed in the feed phase, and the pH of the feed phase was adjusted to 10. The eluent phase was 250 mL of neutral water. The anode platinum wire was placed in the feed phase, and the cathode platinum wire was placed in the eluent phase. The magnetic stirring devices in both tanks were turned on to start mass transfer. The stirring speed was 350 rpm. After continuous extraction at 40 V for 48 h, the removal rate of Li(Ⅰ) in the feed phase was 79.02%, and the recovery rate of Li(Ⅰ) in the eluent phase reached 70.95%.

[0095] One implementation method involves the synergistic extraction of Li(Ⅰ) using a phosphonate polymer extractant and an ester extractant.

[0096] Example 5: Polyvinyl chloride diethylphosphonate + di(2-ethylhexyl)phosphate system

[0097] 9.50% polyvinyl chloride, 41.33% trioctyl phosphonite, and 49.17% N,N-dimethylacetamide + dioxane were mixed according to the mass ratio, heated to reflux at 150°C, and reacted homogeneously for 12 hours. After cooling to room temperature, anhydrous ethanol was added to the mixture for precipitation. The precipitate was repeatedly washed with anhydrous ethanol to remove excess trioctyl phosphonite. The mixture was then filtered and dried to obtain the product polyvinyl chloride diethylphosphonate.

[0098] Step 2, Preparation of lithium-ion extraction membrane:

[0099] 1.94% polyvinyl chloride diethylphosphonate, 0.5% di(2-ethylhexyl) phosphate, 0.03% dioctyl phthalate, and 97.53% tetrahydrofuran were mixed according to the mass ratio and dissolved at room temperature to form a homogeneous solution. The solution was then placed horizontally in a flat-bottomed container and allowed to evaporate completely at 30°C and normal pressure, solidifying into a flat, homogeneous, transparent, and uniformly thick extraction membrane with a membrane thickness of 150 μm.

[0100] Membrane extraction method for separating and extracting lithium ions: an electro-assisted extraction method.

[0101] The prepared polymer membrane was sealed using hollow clamps, polytetrafluoroethylene gaskets, screws, etc., and then assembled with two 250 mL liquid pools. The effective mass transfer area of ​​the membrane was 26.4 cm² for each pool. 2 .

[0102] 250 mL of 25 mg / L lithium chloride solution was placed in the feed phase, and the pH of the feed phase was adjusted to 12. The eluent phase was 250 mL of 0.05 mol / L hydrochloric acid solution. The anode platinum wire was placed in the feed phase, and the cathode platinum wire was placed in the eluent phase. The magnetic stirring devices in both tanks were turned on to start mass transfer. The stirring speed was 300 rpm. After 12 hours of continuous extraction at 20 V, the removal rate of Li(Ⅰ) in the feed phase was 99.05%, and the recovery rate of Li(Ⅰ) in the eluent phase reached 91.15%.

[0103] The graph showing the concentration change of lithium in the two phases after extraction by the external electric field coupling membrane is shown below. Figure 3 As shown.

[0104] Example 6: Polyvinyl chloride dibutylphosphonate + di(2-ethylhexyl)phosphate system

[0105] Step 1, Preparation of phosphonate polymer extractant:

[0106] 10.32% polyvinyl chloride, 38.02% tributyl phosphite, and 51.66% N,N-dimethylacetamide were mixed according to the mass ratio, heated to reflux at 160°C, and reacted homogeneously for 18 hours. After cooling to room temperature, anhydrous ethanol was added to the mixture for precipitation. The precipitate was repeatedly washed with anhydrous ethanol to remove excess tributyl phosphite. The mixture was then filtered and dried to obtain the product polyvinyl chloride dibutylphosphonate.

[0107] Step 2, Preparation of lithium-ion extraction membrane:

[0108] The following mixtures were prepared by mass ratio: 1.94% polyvinyl chloride dibutylphosphonate, 1.48% di(2-ethylhexyl) phosphate, 0.44% 2-nitrophenyl octyl ether, and 96.14% tetrahydrofuran. The mixture was dissolved at room temperature to form a homogeneous solution. The solution was then placed horizontally in a flat-bottomed dish and allowed to evaporate completely at 30°C and normal pressure. The solution was then solidified into a flat, homogeneous, transparent, and uniformly thick extraction membrane with a thickness of 120 μm.

[0109] Membrane extraction method for separating and extracting lithium ions: an electro-assisted extraction method.

[0110] The prepared polymer membrane was sealed using hollow clamps, PTFE gaskets, screws, etc., and then assembled with two 250 mL liquid pools. The effective mass transfer area of ​​the membrane was 26.4 cm² for each pool.2 .

[0111] 250 mL of 15 mg / L lithium chloride solution was placed in the feed phase, and the pH of the feed phase was adjusted to 11. The eluent phase was 250 mL of 0.1 mol / L hydrochloric acid solution. The anode platinum wire was placed in the feed phase, and the cathode platinum wire was placed in the eluent phase. The magnetic stirring devices in both tanks were turned on to start mass transfer. The stirring speed was 500 rpm. After 9 hours of continuous extraction at 10 V, the removal rate of Li(Ⅰ) in the feed phase was 93.88%, and the recovery rate of Li(Ⅰ) in the eluent phase reached 87.45%.

[0112] One implementation method involves the synergistic extraction of Li(Ⅰ) using a phosphonate polymer extractant and an amide extractant.

[0113] Example 7: Polyvinyl chloride diethylphosphonate + N503-FeCl4 - system

[0114] Step 1, Preparation of phosphonate polymer extractant:

[0115] 12.97% polyvinyl chloride, 41.33% triethyl phosphite, and 45.70% N,N-dimethylacetamide were mixed according to the mass ratio, heated to reflux at 140°C, and reacted homogeneously for 20 hours. After cooling to room temperature, anhydrous ethanol was added to the mixture for precipitation. The precipitate was repeatedly washed with anhydrous ethanol to remove excess triethyl phosphite. The mixture was then filtered and dried to obtain the product polyvinyl chloride diethylphosphonate.

[0116] Step 2, using a volume ratio of 20% N,N-bis(1-methylheptyl)acetamide (N503), 30% sulfonated kerosene, and 50% 300 mg·L⁻¹ acetamide. -1 Ferric chloride solution + 5 mol·L -1 Hydrochloric acid solution, the total amount of the above raw materials is 100%; extraction for 30 min, recovery of organic phase, to obtain extractant N503-FeCl4. - .

[0117] Mix 1.95% polyvinyl chloride diethyl phosphonate and 1.73% N5O3-FeCl4 by weight. - A mixture of 96.32% organic solvent tetrahydrofuran was dissolved at room temperature to form a homogeneous solution. The solution was then placed horizontally in a flat-bottomed vessel and allowed to evaporate completely at 30°C and normal pressure, solidifying into a flat, homogeneous, transparent, and uniformly thick extraction membrane with a membrane material thickness of 90 μm.

[0118] Membrane extraction method for separating and extracting lithium ions: an electro-assisted extraction method.

[0119] The prepared polymer membrane was sealed using hollow clamps, polytetrafluoroethylene gaskets, screws, etc., and then assembled with two 250 mL liquid pools. The effective mass transfer area of ​​the membrane was 26.4 cm² for each pool. 2 .

[0120] A 25 mg / L lithium chloride solution was placed in the feed phase, and the pH of the feed phase was adjusted to 6. The eluent phase was 250 mL of a 1 mol / L hydrochloric acid + 1 mol / L sodium chloride solution. The anode platinum wire was placed in the feed phase, and the cathode platinum wire was placed in the eluent phase. The magnetic stirring devices in both tanks were started to begin mass transfer at a stirring speed of 400 rpm. After 24 hours of continuous extraction at 25 V, the removal rate of Li(Ⅰ) in the feed phase was 90.64%, and the recovery rate of Li(Ⅰ) in the eluent phase was 88.99%.

[0121] The graphs showing the concentration changes and mass transfer kinetics of lithium in the two phases coupled by the external electric field of the extraction membrane are shown below. Figure 4 As shown.

[0122] Example 8: Polyvinyl chloride dimethylphosphonate + N503-FeCl4 - system

[0123] Step 1, Preparation of phosphonate polymer extractant:

[0124] 9.50% polyvinyl chloride, 41.33% trimethyl phosphite, and 49.17% N,N-dimethylacetamide were mixed according to the mass ratio, heated to reflux at 100°C, and reacted homogeneously for 15 hours. After cooling to room temperature, anhydrous ethanol was added to the mixture for precipitation. The precipitate was repeatedly washed with anhydrous ethanol to remove excess trimethyl phosphite. The mixture was then filtered and dried to obtain the product polyvinyl chloride dimethyl phosphonate.

[0125] Step 2, using a volume ratio of 20% N,N-bis(1-methylheptyl)acetamide (N503), 30% sulfonated kerosene, and 50% 300 mg·L⁻¹ acetamide. -1 Ferric chloride solution + 5 mol·L -1 Hydrochloric acid solution, the total amount of the above raw materials is 100%; extraction for 30 min, recovery of organic phase, to obtain extractant N503-FeCl4. - .

[0126] Step 3, Preparation of lithium-ion extraction membrane:

[0127] According to the mass ratio, 4.40% polyvinyl chloride dimethylphosphonate and 3.91% N5O3-FeCl4 were mixed. - A mixture of 91.69% organic solvent tetrahydrofuran was dissolved at room temperature to form a homogeneous solution. The solution was then placed horizontally in a flat-bottomed container and allowed to evaporate completely at 30°C and normal pressure, resulting in a smooth, homogeneous, transparent polymer film with a uniform thickness of 140 μm.

[0128] Membrane extraction method for separating and extracting lithium ions: an electro-assisted extraction method.

[0129] The prepared polymer membrane was sealed using hollow clamps, polytetrafluoroethylene gaskets, screws, etc., and then assembled with two 250 mL liquid pools. The effective mass transfer area of ​​the membrane was 26.4 cm² for each pool. 2 .

[0130] A lithium chloride solution containing 50 mg / L was placed in the feed phase, and the pH of the feed phase was adjusted to 8. The eluent phase consisted of 250 mL of a 1 mol / L hydrochloric acid + 2 mol / L sodium chloride solution. The anode platinum wire was placed in the feed phase, and the cathode platinum wire was placed in the eluent phase. Mass transfer was initiated by magnetic stirring in both tanks at a stirring speed of 300 rpm. After 48 hours of continuous extraction at 40 V, the removal rate of Li(Ⅰ) in the feed phase was 94.24%, and the recovery rate of Li(Ⅰ) in the eluent phase reached 90.53%.

[0131] Comparative Example 1:

[0132] A comparative example is provided to illustrate the superior performance of the polymer-based lithium-ion extraction membrane, with the comparative example being a conventional polymer-encapsulated membrane, as detailed in Table 1.

[0133] Table 1 Comparison of extraction effects of the present invention and comparative examples.

[0134]

[0135] As can be seen from Table 1, compared with the comparative example, the lithium-ion extraction membrane proposed in this invention has a significant improvement in lithium removal rate and recovery rate, and also exhibits high stability.

[0136] In summary, the polymer extractant and its membrane extraction application for lithium extraction provided by this invention achieve a removal rate of over 85% except when using neutral water as the eluent phase. Furthermore, it maintains stable operation under prolonged mass transfer, and the permeability coefficient shows no significant change after four cycles (12 hours each). The lithium-ion extraction membrane constructed with phosphonate ester polymer extractants is a novel membrane extraction material. It is simple to prepare, low in cost, exhibits excellent lithium transport capabilities, minimizes environmental pollution during lithium-ion removal, extraction, or separation, has a fast transport rate, high removal rate and membrane extraction efficiency, and does not leak the membrane phase. It also possesses good selectivity and stability. This invention represents a highly stable membrane product with high mass transfer performance for lithium ions and its separation method.

[0137] This invention is not limited to the above embodiments. Based on the technical solutions disclosed in this invention, those skilled in the art can make some substitutions and modifications to some of the technical features without creative effort, and all such substitutions and modifications are within the protection scope of this invention.

Claims

1. A method for preparing a lithium-ion extraction membrane based on a polymer extractant, characterized in that, Includes the following steps: Step 1, Preparation of phosphonate polymer extractant: Mix 10%–14% polymer, 26%–42% phosphite organics and 45%–65% solvent according to the mass ratio; reflux homogeneously, cool to room temperature, add anhydrous ethanol to the mixture for precipitation, wash the precipitate repeatedly with anhydrous ethanol, filter, and dry under reduced pressure to obtain phosphonate polymer extractant. Step 2, Preparation of lithium-ion selective extraction membrane: According to the mass ratio, 2% to 5% of phosphonate polymer extractant is mixed with 0.5% to 4% co-extractant, 0% to 1.8% plasticizer, and 90% to 98% weakly polar organic solvent to form a homogeneous solution. The solution is quantitatively poured into a flat-bottomed container, and after the solvent is evaporated and removed, a lithium-ion selective extraction membrane is obtained. The polymer is polyvinyl chloride with a molecular weight greater than 72,000 and a degree of polymerization less than 2,500. The phosphite ester organic compounds are trimethyl phosphite, triethyl phosphite, tributyl phosphite, or trioctyl phosphite; The solvent is one or a mixture of two or more of N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone and dioxane; The co-extractant is N503-FeCl4. - 2-Thiophenecarboxyltrifluoroacetone, di(2-ethylhexyl) phosphate, or trialkylphosphine oxide; The plasticizer is dioctyl phthalate or 2-nitrophenyl octyl ether; The weakly polar organic solvent is tetrahydrofuran or N,N-dimethylacetamide; In step 1, the solvents are mixed and refluxed homogeneously at 100–160°C for 12–30 h; In step 2, the thickness of the lithium-ion selective extraction membrane is 50–150 μm.

2. A lithium-ion extraction membrane based on a polymer extractant prepared by the method described in claim 1.

3. An application of a lithium-ion extraction membrane based on a polymer extractant prepared by the method described in claim 1, characterized in that, include: A lithium-ion extraction membrane is installed in a membrane extraction device to separate the lithium-ion-containing liquid phase from the precipitate phase, and the material composition in the two solutions remains homogeneous. Control the ion concentration and pH of the feed liquid solution and the concentration of the eluent solution; An external electric field coupled membrane extraction process is used, in which the anode platinum wire is placed in the feed liquid phase and the cathode platinum wire is placed in the eluent phase, or the feed liquid phase and the eluent phase are continuously stirred separately without the application of electricity to carry out mass transfer.

4. The application of the lithium-ion extraction membrane based on the polymer extractant according to claim 3, characterized in that, The liquid phase exists in the form of a lithium-ion solution with a lithium-ion concentration of 15–500 mg / L.

5. The application of the lithium-ion extraction membrane based on the polymer extractant according to claim 3, characterized in that, When using lithium-ion extraction membranes prepared with 2-thiophenecarboxyltrifluoroacetone, di(2-ethylhexyl) phosphate, or trialkylphosphine oxide as co-extractants, the pH of the feed phase is maintained between 10 and 12, and the eluent phase is neutral water or a 0.5–1 mol / L hydrochloric acid solution.

6. The application of the lithium-ion extraction membrane based on the polymer extractant according to claim 3, characterized in that, When the co-extraction agent is N503-FeCl4 - When preparing the lithium-ion extraction membrane, the pH of the feed liquid phase is maintained between 6 and 8, and the eluent phase is 0.5-1 mol / L hydrochloric acid + 1-2 mol / L sodium chloride solution.

7. The application of the lithium-ion extraction membrane based on the polymer extractant according to claim 3, characterized in that, The stirring speed in the two-phase solution is 300-500 rpm and remains constant; the continuous stirring reaction time is 9-72 h.

8. The application of the lithium-ion extraction membrane based on the polymer extractant according to claim 3, characterized in that, In the external electric field coupled membrane extraction process, the operating voltage is 10-40V. After continuous extraction for 12-72h, the removal rate of Li(Ⅰ) in the liquid phase reaches 75%-99%, and the recovery rate of Li(Ⅰ) in the eluent phase reaches 70%-92%.

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