Preparation methods of positively charged nanofiltration membranes, nanofiltration membranes, and their applications.

Abstract

This invention provides a method for preparing a positively charged nanofiltration membrane, the nanofiltration membrane itself, and its applications. The preparation method includes: dissolving an amine-containing organic compound and a metal salt in an organic solvent, adding an organic acid to react and obtain a turbid liquid; performing solid-liquid separation, washing, and drying of the turbid liquid to obtain positively charged active particles with amine groups; dissolving a membrane substrate in an alkylamide compound and adding a pore-forming agent to obtain a casting slurry; subjecting the casting slurry to a phase transition reaction to obtain a base membrane; alkalizing and then acidifying the base membrane to obtain a carboxyl-containing nanofiltration base membrane; laying an organic amine solution on the surface of the nanofiltration base membrane and heating it to obtain a surface-amined nanofiltration base membrane; while still hot, laying an acyl chloride compound solution on the surface of the nanofiltration base membrane and allowing it to stand to obtain a surface-acyl-chlorinated nanofiltration base membrane; and stirring the positively charged active particles with amine groups and the surface-acyl-chlorinated nanofiltration base membrane in water to obtain a positively charged nanofiltration membrane. The prepared nanofiltration membrane has certain positive charge and pore size parameters, and can carry Li... + Effective separation of high-valence heavy metal ions.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery recycling and utilization technology, and in particular to a method for preparing a positively charged nanofiltration membrane, the nanofiltration membrane itself, and its applications. Background Technology

[0002] Since their commercialization, lithium-ion batteries have enjoyed a broad market prospect due to their numerous advantages. While lithium-ion batteries are called "green batteries" because they do not contain highly toxic heavy metals such as mercury, cadmium, and lead, this does not mean they are pollution-free. Improper disposal of used lithium-ion batteries can still impact the environment and human health. For example, heavy metals in the cathode material can raise the pH level of the environment, affecting the ecosystem. Furthermore, heavy metals and lithium in the cathode material are elements with very low natural abundance, relatively high compared to mined minerals. Therefore, conducting research on the recycling and utilization of materials from used lithium-ion batteries can not only mitigate environmental impact but also...

[0003] This can bring certain economic benefits. The environmental pollution caused by waste lithium-ion power batteries and the issue of their rational resource recycling have become common concerns and urgent problems to be solved in the industry.

[0004] Currently, the main materials recycled from spent lithium-ion batteries are the negative electrode current collector (commonly copper foil), the positive electrode current collector (commonly aluminum foil), the positive electrode active material, and the negative electrode active material. Electrode recycling typically involves three main steps: first, discharging the spent battery and disassembling it to remove the electrodes; second, separating the materials in the electrodes from the current collector; and third, recovering and utilizing valuable metals. Specifically, the spent battery is disassembled in a glove box or other moisture-free environment to remove the positive electrode. Mechanical crushing, ultrasonic-assisted separation, or the high-strength acidity / alkalinity of strong acids and alkalis, or organic solvent methods are used to separate the active material in the positive electrode from the current collector to obtain a leachate. This leachate usually contains all the metal elements contained in the positive electrode, such as Ni. 2+ Co 2+ Mn 2+ Li + And doping elements, etc. Traditional metal separation methods generally achieve the separation of various metals by adjusting the pH value of the leachate and using extraction solvents, but this method suffers from low selectivity, introduction of new impurities, poor separation effect, and Li + Limitations such as losses.

[0005] To avoid Li + Loss, before separating heavy metal ions, Li + Separating from high-valence heavy metal ions is particularly important. Summary of the Invention

[0006] To address the aforementioned problems, the present invention aims to provide a method for preparing a positively charged nanofiltration membrane, the nanofiltration membrane itself, and its applications. The nanofiltration membrane prepared using this method possesses a certain positive charge and specific pore size parameters, enabling it to filter Li... + It can effectively separate high-valence heavy metal ions, and the nanofiltration membrane can be recycled.

[0007] To achieve the above objectives, the present invention provides a method for preparing a positively charged nanofiltration membrane, comprising the following steps:

[0008] (1) Preparation of positively charged active particles with amine groups

[0009] An organic compound with an amine group and a metal salt are dissolved in an organic solvent, dispersed by an organic acid, and then heated to react and obtain a turbid liquid. The turbid liquid is then subjected to solid-liquid separation to obtain a solid. The solid is then washed and dried to obtain positively charged active particles with an amine group.

[0010] (2) Preparation of nanofiltration membranes with carboxyl groups

[0011] Membrane substrate particles are dissolved in alkylamide compounds and a pore-forming agent is added and heated and stirred to obtain a casting slurry. The casting slurry is coated on a plate and immersed in water. The casting slurry undergoes a phase transition reaction to obtain a base membrane. The base membrane is alkalized and then acidified to obtain a nanofiltration base membrane with carboxyl groups.

[0012] (3) Surface amination of nanofiltration membranes

[0013] An organic amine solution is coated on the surface of the nanofiltration membrane with carboxyl groups, and the solution is heated until the solvent in the solution evaporates to obtain ammoniated nanofiltration membrane.

[0014] (4) Surface acyl chloride of nanofiltration membrane

[0015] While still hot, an acyl chloride compound solution is spread on the surface of the surface-amined nanofiltration membrane, and after standing for a certain period of time, a surface-acyl chlorided nanofiltration membrane is obtained.

[0016] (5) Covalent bonding

[0017] The positively charged nanofiltration membrane is obtained by stirring the positively charged active particles with amine groups and the surface acyl chloride nanofiltration membrane in water for a certain period of time.

[0018] The method for preparing the positively charged nanofiltration membrane of this invention utilizes positively charged active particles with amine groups and a surface-acyl chloride-based nanofiltration membrane for reaction. The amine and acyl chloride groups react and covalently bond, thus obtaining a positively charged nanofiltration membrane. This nanofiltration membrane not only possesses a positive charge but also exhibits certain pore size parameters and strength, making it suitable for use in Li... + Effective separation of high-valence heavy metal ions. Details are as follows.

[0019] (1) In the preparation of positively charged active particles with amine groups, organic compounds and metal salts with amine groups are first dissolved in an organic solvent. Under acidic conditions, inorganic and organic compounds are combined to obtain metal-organic framework materials. Introducing inorganic compounds can improve the strength of active particles and even nanofiltration membranes.

[0020] (2) In the preparation of nanofiltration membranes with carboxyl groups, the casting solution contains membrane substrate particles, alkylamide compounds, and pore-forming agents. The membrane substrate particles serve as the main material of the base membrane and even the nanofiltration base membrane. The alkylamide compound is alkalized on the surface of the base membrane to form a carboxylate compound, which is then acid-washed to convert the carboxylate compound into carboxyl groups, thus introducing carboxyl groups onto the surface of the base membrane. The pore-forming agent forms pores during the phase transition reaction or subsequent heating process to give the nanofiltration membrane certain pore size parameters.

[0021] (3) In the surface amination of nanofiltration membrane, organic amines combine with carboxyl groups on the surface of nanofiltration membrane, so that amine groups are fixed on the surface of nanofiltration membrane. Since amine groups themselves carry a positive charge, the surface of nanofiltration membrane after surface amination carries a positive charge due to the introduction of positively charged amine groups.

[0022] (4) In the surface acyl chloride process of nanofiltration membrane, acyl chloride groups can be further introduced into the surface of the amination nanofiltration membrane through instantaneous temperature changes, so as to react with positively charged active particles with amine groups.

[0023] (5) Positively charged active particles with amine groups react with nanofiltration base membranes with surface acyl chloride. The amine groups and acyl chloride groups react, thus forming a nanofiltration layer with a monovalent positive charge on the surface of the base membrane.

[0024] As one technical solution of the present invention, the amine-containing organic compound includes at least one of 2-aminoterephthalic acid, 2-aminoterephthalic acid monomethyl ester and 2-aminoterephthalic acid dimethyl ester.

[0025] As one technical solution of the present invention, the metal salt includes zirconium chloride and / or titanium chloride.

[0026] As one technical solution of the present invention, the organic solvent includes N,N-dimethylamide and / or N,N-dimethylformamide.

[0027] As one technical solution of the present invention, the organic acid is acetic acid.

[0028] As one technical solution of the present invention, the molar ratio of the amine-containing organic compound, the metal salt and the organic acid is 1:1:80 to 120.

[0029] As a technical solution of the present invention, the heating temperature in step (1) is 100-150°C and the time is 18-30h.

[0030] As one technical solution of the present invention, the membrane substrate particles include polyacrylonitrile particles and / or polypropylene particles.

[0031] As one technical solution of the present invention, the number average molecular weight of the polymer in the membrane substrate particles is 100,000 to 200,000.

[0032] As one technical solution of the present invention, the mass percentage of the membrane substrate particles in the alkylamide compound is 10-20%.

[0033] As one technical solution of the present invention, the alkylamide compound includes N,N-dimethylamide and / or N,N-dimethylformamide.

[0034] As one technical solution of the present invention, the pore-forming agent is polyethylene glycol or polyvinyl alcohol with a molecular weight of 300 to 500.

[0035] As a technical solution of the present invention, the heating temperature in step (2) is 50-80°C and the heating time is 10-18h.

[0036] As one technical solution of the present invention, the solution used for alkalization is a 0.8-1.5 mol / L sodium hydroxide aqueous solution or a 0.8-1.5 mol / L potassium hydroxide aqueous solution.

[0037] As one technical solution of the present invention, the temperature of the alkalization reaction is 50-100°C, and the time of the alkalization reaction is 2-5 hours.

[0038] As one technical solution of the present invention, the acidification solution is a hydrochloric acid aqueous solution of 0.8 to 1.5 mol / L or a nitric acid aqueous solution of 0.8 to 1.5 mol / L.

[0039] As a technical solution of the present invention, the acidification reaction is carried out at room temperature and the acidification reaction takes 10 to 18 hours.

[0040] As one technical solution of the present invention, the organic amine solution includes a polyethyleneimine solution or a poly(N-vinyl o-phenylimine) solution with a mass fraction of 1-5%.

[0041] As one technical solution of the present invention, the mass fraction of the acyl chloride compound in the acyl chloride compound solution is 0.1-3.0%.

[0042] As a technical solution of the present invention, the acyl chloride compound includes at least one of 1,3,5-tristoyl chloride, phthaloyl chloride, isophthaloyl chloride, terephthaloyl chloride, biphenyl dicarboxylate chloride, and benzene disulfonyl chloride.

[0043] As a technical solution of the present invention, the certain time mentioned in step (4) is 0.5 to 1.5 hours.

[0044] As a technical solution of the present invention, the certain time mentioned in step (5) is 5 to 10 hours.

[0045] The second aspect of this invention provides a method for preparing a positively charged nanofiltration membrane. The positively charged nanofiltration membrane prepared has a pore size of 5.5–6.5 nm and a Zeta potential of 4–10 mV at pH 7. Nanofiltration membranes with these parameters can be used in Li… + Effective separation of high-valence heavy metal ions.

[0046] A third aspect of the present invention provides a method for separating lithium ions and metal ions in a positive electrode, comprising:

[0047] (1) The positive electrode sheet removed from the battery is processed to obtain leachate;

[0048] (2) The positively charged nanofiltration membrane prepared by the aforementioned positively charged nanofiltration membrane preparation method or the aforementioned positively charged nanofiltration membrane is loaded into the nanofiltration system, and the leachate is sent into the nanofiltration system for filtration treatment.

[0049] In the separation method of this invention, the leachate is fed into a nanofiltration system for filtration. The nanofiltration membrane, with its monovalent positively charged amine groups, has a strong repulsive ability for positively charged metal ions, thus removing heavy metal ions (such as Ni) from the leachate. 2+ Co 2+ Mn 2+ Fe 2+ (etc.) and Li + It will be repelled by the positively charged nanofiltration membrane. However, in comparison, Ni with a positive divalent charge... 2+ Co 2+ Mn 2+ Fe 2+ The electrostatic repulsion force experienced by Li is higher. + The electrostatic repulsion force experienced is lower (due to the Donnan effect). Therefore, Ni, which experiences higher repulsion, 2+ Co 2+ Mn 2+ Fe 2+ Heavy metal ions are blocked outside the nanofiltration membrane, while Li, which has a lower repulsive force, is blocked. + Under liquid pressure, it will pass through the filter pores and permeate the nanofiltration membrane, resulting in Li with a higher concentration and purity. + The filtrate is separated from the leachate.

[0050] The separation method of the present invention separates Li through membrane filtration. + Separation from heavy metal ions and realization of Li+ The purification process simplifies the steps and avoids the problems associated with adjusting pH and using extractants in traditional processes, which can lead to the degradation of Li. + The losses increased Li + The nanofiltration membrane of this invention also has regenerative properties. The nanofiltration membrane can be removed from the nanofiltration system, and after removing the filter cake, rinsing, and reactivating (ammoniation), it can be reused, thus exhibiting reusability.

[0051] Furthermore, compared to traditional nanofiltration technology (which mainly separates metal ions of different particle sizes through pore size), the separation method of this invention, based on pore size sieving, introduces a positively charged nanofiltration layer on the surface of the nanofiltration base membrane. This enhances the charge repulsion effect, thereby separating Li... + The separation from other heavy metal ions is the result of a combination of pore size sieving and charge repulsion. This results in better separation efficiency and yields Li-containing ions. + 的 It has higher purity. Detailed Implementation

[0052] This invention utilizes a nanofiltration system to remove Li from the leachate. + Separation from high-valence heavy metal ions. The separation steps include: (1) processing the positive electrode sheet removed from the battery to obtain a leachate; (2) installing a nanofiltration membrane into a nanofiltration system and sending the leachate into the nanofiltration system for filtration. The leachate can be prepared using conventional methods, such as first crushing the positive electrode sheet using mechanical crushing, and then using strong acid or strong alkali to dissolve and separate the Li-containing particles. + Leachate containing high-valence heavy metal ions.

[0053] The nanofiltration membrane of this invention is not a conventional nanofiltration membrane that is sieved by pore size. It not only has a specific pore size but also a certain positive charge and strength. Furthermore, the pore size is 5.5–6.5 nm, and the Zeta potential is 4–10 mV at pH 7. Therefore, the nanofiltration membrane of this invention uses the combined effect of pore size sieving and charge repulsion to remove Li from the filtrate. + It can separate high-valence heavy metal ions, and the nanofiltration membrane can be reused.

[0054] The method for preparing the positively charged nanofiltration membrane of the present invention includes the following steps.

[0055] (1) Preparation of positively charged active particles with amine groups

[0056] An organic compound with an amine group and a metal salt are dissolved in an organic solvent, dispersed by an organic acid, and then heated to react and obtain a turbid liquid. The turbid liquid is then separated into a solid and a liquid to obtain a solid. The solid is then washed and dried to obtain positively charged active particles with an amine group.

[0057] (2) Preparation of nanofiltration membranes with carboxyl groups

[0058] Membrane substrate particles are dissolved in alkylamide compounds and a pore-forming agent is added. The mixture is heated and stirred to obtain a casting slurry. The casting slurry is coated onto a substrate and immersed in water. The casting slurry undergoes a phase transition reaction to obtain a base membrane. The base membrane is alkalized and then acidified to obtain a nanofiltration base membrane with carboxyl groups.

[0059] (3) Surface amination of nanofiltration membranes

[0060] An organic amine solution is applied to the surface of a nanofiltration membrane with carboxyl groups, and the solution is heated until the solvent in the solution evaporates to obtain a surface-amined nanofiltration membrane.

[0061] (4) Surface acyl chloride of nanofiltration membrane

[0062] While the nanofiltration membrane is still hot, an acyl chloride compound solution is applied to the surface of the surface-amined nanofiltration membrane, and the membrane is left to stand for a certain period of time to obtain a surface-acyl chlorided nanofiltration membrane.

[0063] (5) Covalent bonding

[0064] Positively charged nanofiltration membranes are obtained by stirring positively charged active particles with amine groups and surface-acyl chloride nanofiltration membranes in water for a certain period of time.

[0065] Further, in step (1), the amine-containing organic matter includes at least one of 2-aminoterephthalic acid, monomethyl 2-aminoterephthalate, and dimethyl 2-aminoterephthalate, and the amine-containing organic matter is an organic matter particle with a large specific surface area. The metal salt includes zirconium chloride and / or titanium chloride, preferably zirconium chloride. The addition of the metal salt can enhance the strength of the nanofiltration membrane and improve its stability. The organic solvent includes N,N-dimethylamide and / or N,N-dimethylformamide, and the organic solvent needs to be able to dissolve or disperse the amine-containing organic matter and the metal salt particles. The organic acid is acetic acid. The molar ratio of the amine-containing organic matter, the metal salt, and the organic acid is 1:1:80 to 120. The mixing of the amine-containing organic matter, the metal salt, the organic acid, and the organic solvent can be carried out in a high-speed mixer to accelerate uniform dispersion. The heating temperature is 100 to 150°C, and the heating time is 18 to 30 hours. For solid-liquid separation, a centrifuge can be used for separation, and the solid can be cleaned with water or alcohol.

[0066] In step (2), the membrane substrate particles include polyacrylonitrile particles and / or polypropylene particles, with a number-average molecular weight of 100,000 to 200,000, preferably polyacrylonitrile particles. The mass percentage of the membrane substrate particles in the alkylamide compound is 10% to 20%. The alkylamide compound includes N,N-dimethylamide and / or N,N-dimethylformamide. The alkylamide compound serves as the main raw material for the nanofiltration layer, undergoing subsequent acidification, alkalization, amination, and acyl chloride reactions at least on its surface. The pore-forming agent is polyethylene glycol or polyvinyl alcohol with a molecular weight of 300 to 500. The alkalization solution is a 0.8 to 1.5 mol / L sodium hydroxide aqueous solution or a 0.8 to 1.5 mol / L potassium hydroxide aqueous solution. The acidification solution is a 0.8 to 1.5 mol / L hydrochloric acid aqueous solution or a 0.8 to 1.5 mol / L nitric acid aqueous solution. The heating temperature during the preparation of the casting slurry is 50 to 80°C, and the mixture is stirred continuously for 10 to 18 hours. The casting slurry can be coated onto the substrate using a coating machine, with a coating thickness of 100–200 μm. The alkalization reaction temperature is 50–100 °C, and the alkalization reaction time is 2–5 h. The acidification reaction temperature is room temperature, and the acidification reaction time is 10–18 h. Through acidification and alkalization, carboxyl groups are introduced onto the alkylamide compound.

[0067] In step (3), the organic amine solution includes a polyethyleneimine solution or a poly(N-vinyl o-phenylimine) solution with a mass fraction of 1-5%. The organic amine solution is spread on the surface, and then the liquid on the film surface is evaporated at 50-80°C, thus completing the amination of the base film surface.

[0068] In step (4), the acyl chloride compound solution is laid while still hot after evaporation in step (3). Acyl chloride is achieved on the surface of the base membrane through a transient temperature change. The mass fraction of the acyl chloride compound in the solution is 0.1–3.0%. The acyl chloride compound includes at least one of 1,3,5-tribenzoyl chloride, phthaloyl chloride, isophthaloyl chloride, terephthaloyl chloride, biphenyl dicarboxylate chloride, and benzene disulfonyl chloride. After laying and standing for 0.5–1.5 h, a nanofiltration base membrane with surface acyl chloride is obtained.

[0069] In step (5), positively charged active particles with amine groups and nanofiltration membranes with surface acyl chloride are stirred in water for 5 to 10 hours to obtain a positively charged nanofiltration membrane.

[0070] To better illustrate the purpose, technical solution, and beneficial effects of this invention, the invention will be further described below with reference to specific embodiments. It should be noted that the methods described below are further explanations of this invention and should not be construed as limiting it.

[0071] Example 1

[0072] This embodiment describes a method for preparing a positively charged nanofiltration membrane, which includes the following steps.

[0073] (1) Preparation of positively charged active particles with amine groups

[0074] 2-Aminoterephthalic acid and zirconium chloride were dissolved in N,N-dimethylamide, and acetic acid (the molar ratio of 2-aminoterephthalic acid, zirconium chloride, and acetic acid was 1:1:100) was added. The mixture was dispersed at high speed for 2 hours to obtain a clear liquid. The clear liquid was placed in a high-temperature reactor and reacted at 130°C for 25 hours to obtain a turbid liquid. The turbid liquid was centrifuged to obtain a solid. The solid was washed with water and industrial alcohol and then dried to obtain positively charged active particles with amine groups.

[0075] (2) Preparation of nanofiltration membranes with carboxyl groups

[0076] Polyacrylonitrile particles with a number-average molecular weight of approximately 150,000 were dissolved in N,N-dimethylamide at a mass fraction of 15%. Polyethylene glycol with a number-average molecular weight of approximately 400 was added, and the mixture was stirred continuously at 70°C for 12 hours to obtain a casting slurry. The casting slurry was coated onto a substrate with a thickness of 150±2 μm using a coating machine, and then immersed in water to undergo a phase transition reaction to obtain a base film. The base film was placed in 1.2 mol / L NaOH and reacted at 80°C for 3 hours. It was then placed in 1.0 mol / L hydrochloric acid and reacted for 15 hours, followed by washing with water.

[0077] (3) Surface amination of nanofiltration membranes

[0078] A 3% (w / w) aqueous solution of polyethyleneimine was applied to the surface of a nanofiltration membrane with carboxyl groups. The solution was then heated at 75°C until the water in the solution evaporated to obtain a surface-amined nanofiltration membrane.

[0079] (4) Surface acyl chloride of nanofiltration membrane

[0080] While still hot, a 1.0% (w / w) solution of 1,3,5-tribenzoyl chloride was applied to the surface of the surface-amined nanofiltration membrane, and the membrane was allowed to stand for 1 hour to obtain a surface-acyl-chlorinated nanofiltration membrane.

[0081] (5) Covalent bonding

[0082] Positively charged nanofiltration membranes were obtained by stirring positively charged active particles with amine groups and surface-acyl chloride nanofiltration membranes in water for 8 hours.

[0083] The prepared nanofiltration membrane was subjected to performance testing. Its pore size was measured to be approximately 6.0 nm using a pore size analyzer, and its zeta potential was 6 mV at pH 7.

[0084] Example 2

[0085] This embodiment describes a method for preparing a positively charged nanofiltration membrane, which includes the following steps.

[0086] (1) Preparation of positively charged active particles with amine groups

[0087] Dimethyl 2-aminoterephthalate and titanium chloride were dissolved in N,N-dimethylformamide, and acetic acid (the molar ratio of dimethyl 2-aminoterephthalate, yttrium chloride, and acetic acid was 1:1:110) was added. The mixture was then dispersed at high speed for 3 hours to obtain a clear liquid. The clear liquid was placed in a high-temperature reactor and reacted at 130°C for 25 hours to obtain a turbid liquid. The turbid liquid was centrifuged to obtain a solid. The solid was washed with water and industrial alcohol and then dried to obtain positively charged active particles with amine groups.

[0088] (2) Preparation of nanofiltration membranes with carboxyl groups

[0089] Polypropylene particles with a number-average molecular weight of approximately 120,000 were dissolved in N,N-dimethylformamide at a mass fraction of 18%. Polyvinyl alcohol with a number-average molecular weight of approximately 450 was added, and the mixture was stirred continuously at 70°C for 15 hours to obtain a casting slurry. The casting slurry was coated onto a substrate using a coating machine to a thickness of 150±2 μm, and then immersed in water to undergo a phase transition reaction to obtain a base film. The base film was placed in 1.2 mol / L NaOH and reacted at 80°C for 3 hours. It was then placed in 1.0 mol / L hydrochloric acid and reacted for 15 hours, followed by washing with water.

[0090] (3) Surface amination of nanofiltration membranes

[0091] A 5% (w / w) aqueous solution of poly(N-vinyl o-phenylimine) was applied to the surface of a nanofiltration membrane with carboxyl groups, and the solution was heated at 75°C until the water in the solution evaporated to obtain a surface-amined nanofiltration membrane.

[0092] (4) Surface acyl chloride of nanofiltration membrane

[0093] While still hot, a 1.0% (w / w) solution of 1,3,5-tribenzoyl chloride was applied to the surface of the surface-amined nanofiltration membrane, and the membrane was allowed to stand for 0.5 h to obtain a surface-acyl-chlorinated nanofiltration membrane.

[0094] (5) Covalent bonding

[0095] Positively charged nanofiltration membranes were obtained by stirring positively charged active particles with amine groups and surface-acyl chloride nanofiltration membranes in water for 10 hours.

[0096] The prepared nanofiltration membrane was subjected to performance testing. Its pore size was measured to be approximately 5.8 nm using a pore size analyzer, and its zeta potential was 5 mV at pH 7.

[0097] Example 3

[0098] This embodiment describes a method for preparing a positively charged nanofiltration membrane, which includes the following steps.

[0099] (1) Preparation of positively charged active particles with amine groups

[0100] 2-Aminoterephthalic acid and zirconium chloride were dissolved in N,N-dimethylamide, and acetic acid (the molar ratio of 2-aminoterephthalic acid, zirconium chloride, and acetic acid was 1:1:120) was added. The mixture was dispersed at high speed for 2 hours to obtain a clear liquid. The clear liquid was placed in a high-temperature reactor and reacted at 150°C for 20 hours to obtain a turbid liquid. The turbid liquid was centrifuged to obtain a solid. The solid was washed with water and industrial alcohol and then dried to obtain positively charged active particles with amine groups.

[0101] (2) Preparation of nanofiltration membranes with carboxyl groups

[0102] Polyacrylonitrile particles with a number-average molecular weight of approximately 150,000 were dissolved in N,N-dimethylamide at a mass fraction of 15%. Polyethylene glycol with a number-average molecular weight of approximately 400 was added, and the mixture was stirred continuously at 80°C for 15 hours to obtain a casting slurry. The casting slurry was coated onto a substrate with a thickness of 150±2 μm using a coating machine, and then immersed in water to undergo a phase transition reaction to obtain a base film. The base film was placed in 1.0 mol / L NaOH and reacted at 100°C for 2 hours. It was then placed in 1.2 mol / L hydrochloric acid and reacted for 12 hours, followed by washing with water.

[0103] (3) Surface amination of nanofiltration membranes

[0104] A 3% (w / w) aqueous solution of polyethyleneimine was applied to the surface of a nanofiltration membrane with carboxyl groups. The solution was then heated at 80°C until the water in the solution evaporated to obtain a surface-amined nanofiltration membrane.

[0105] (4) Surface acyl chloride of nanofiltration membrane

[0106] While still hot, a 2.0% isophthaloyl chloride solution was applied to the surface of the surface-amined nanofiltration membrane, and the membrane was allowed to stand for 1.5 hours to obtain a surface-acyl-chlorinated nanofiltration membrane.

[0107] (5) Covalent bonding

[0108] Positively charged nanofiltration membranes were obtained by stirring positively charged active particles with amine groups and surface-acyl chloride nanofiltration membranes in water for 8 hours.

[0109] The prepared nanofiltration membrane was subjected to performance testing. Its pore size was measured to be approximately 6.1 nm using a pore size analyzer, and its zeta potential was 7 mV at pH 7.

[0110] The nickel-cobalt-manganese positive electrode sheet disassembled from a nickel-cobalt-manganese ternary battery was mechanically crushed, then soaked in NMP and subjected to ultrasonic vibration for 8 hours before filtration to obtain the filtrate. The nanofiltration membranes prepared in Examples 1-3 were placed in a nanofiltration system, and the filtrates were filtered separately. The Li after filtration was calculated for each filtrate.+ Recovery rate and purity. In Example 1, Li... + The recovery rate was 87.6%, and the purity was 97.8%. In Example 2, Li... + The recovery rate was 86.7%, and the purity was 96.9%. In Example 3, Li... + The recovery rate was 85.6%, and the purity was 96.2%.

[0111] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, it is not limited to those listed in the embodiments. Those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a positively charged nanofiltration membrane, characterized in that, Including the following steps: (1) Preparation of positively charged active particles with amine groups An organic compound with an amine group and a metal salt are dissolved in an organic solvent, dispersed by an organic acid, and then heated to react and obtain a turbid liquid. The turbid liquid is then subjected to solid-liquid separation to obtain a solid. The solid is then washed and dried to obtain positively charged active particles with an amine group. (2) Preparation of nanofiltration membranes with carboxyl groups Membrane substrate particles are dissolved in alkylamide compounds and a pore-forming agent is added and heated and stirred to obtain a casting slurry. The casting slurry is coated on a plate and immersed in water. The casting slurry undergoes a phase transition reaction to obtain a base membrane. The base membrane is alkalized and then acidified to obtain a nanofiltration base membrane with carboxyl groups. (3) Surface amination of nanofiltration membranes An organic amine solution is coated on the surface of the nanofiltration membrane with carboxyl groups, and the solution is heated until the solvent in the solution evaporates to obtain ammoniated nanofiltration membrane. (4) Surface acyl chloride of nanofiltration membrane While still hot, an acyl chloride compound solution is spread on the surface of the surface-amined nanofiltration membrane, and after standing for a certain period of time, a surface-acyl chlorided nanofiltration membrane is obtained. (5) Covalent bonding The positively charged nanofiltration membrane is obtained by stirring the positively charged active particles with amine groups and the surface acyl chloride nanofiltration membrane in water for a certain period of time.

2. The method for preparing a positively charged nanofiltration membrane according to claim 1, characterized in that, The amine-containing organic compound includes at least one of 2-aminoterephthalic acid, monomethyl 2-aminoterephthalate, and dimethyl 2-aminoterephthalate; the metal salt includes zirconium chloride and / or titanium chloride; the organic solvent includes N,N-dimethylamide and / or N,N-dimethylformamide; the organic acid is acetic acid; and the molar ratio of the amine-containing organic compound, the metal salt, and the organic acid is 1:1:80 to 120.

3. The method for preparing a positively charged nanofiltration membrane according to claim 1, characterized in that, The heating temperature in step (1) is 100-150°C and the heating time is 18-30 hours.

4. The method for preparing a positively charged nanofiltration membrane according to claim 1, characterized in that, The membrane substrate particles include polyacrylonitrile particles and / or polypropylene particles, the number average molecular weight of the polymer in the membrane substrate particles is 100,000 to 200,000, the mass percentage of the membrane substrate particles in the alkylamide compound is 10 to 20%, the alkylamide compound includes N,N-dimethylamide and / or N,N-dimethylformamide, and the pore-forming agent is polyethylene glycol or polyvinyl alcohol with a molecular weight of 300 to 500.

5. The method for preparing a positively charged nanofiltration membrane according to claim 1, characterized in that, The heating temperature in step (2) is 50-80℃ and the heating time is 10-18h.

6. The method for preparing a positively charged nanofiltration membrane according to claim 1, characterized in that, The alkalization solution is a 0.8–1.5 mol / L sodium hydroxide aqueous solution or a 0.8–1.5 mol / L potassium hydroxide aqueous solution. The alkalization reaction temperature is 50–100°C, and the alkalization reaction time is 2–5 h. The acidification solution is a 0.8–1.5 mol / L hydrochloric acid aqueous solution or a 0.8–1.5 mol / L nitric acid aqueous solution. The acidification reaction temperature is room temperature, and the acidification reaction time is 10–18 h.

7. The method for preparing a positively charged nanofiltration membrane according to claim 1, characterized in that, The organic amine solution comprises a polyethyleneimine solution or a poly(N-vinyl o-phenylimine) solution with a mass fraction of 1-5%, and the acyl chloride compound solution comprises an acyl chloride compound with a mass fraction of 0.1-3.0%, wherein the acyl chloride compound comprises at least one selected from 1,3,5-tribenzoyl chloride, phthaloyl chloride, isophthaloyl chloride, terephthaloyl chloride, biphenyl dicarboxylate chloride, and benzene disulfonyl chloride.

8. The method for preparing a positively charged nanofiltration membrane according to claim 1, characterized in that, The certain time mentioned in step (4) is 0.5 to 1.5 hours, and the certain time mentioned in step (5) is 5 to 10 hours.

9. The positively charged nanofiltration membrane prepared by the method for preparing a positively charged nanofiltration membrane according to any one of claims 1 to 8, characterized in that, The pore size is 5.5–6.5 nm, and the zeta potential is 4–10 mV at pH 7.

10. A method for separating lithium ions and metal ions in a positive electrode, characterized in that, include: (1) The positive electrode sheet removed from the battery is processed to obtain leachate; (2) The positively charged nanofiltration membrane prepared by the method of preparing the positively charged nanofiltration membrane according to any one of claims 1 to 8 or the positively charged nanofiltration membrane according to claim 9 is loaded into the nanofiltration system, and the leachate is sent into the nanofiltration system for filtration treatment.