Preparation method of positively charged nanofiltration membrane, nanofiltration membrane and application

Abstract

The invention provides a preparation method of a positively charged nanofiltration membrane, the nanofiltration membrane and application. The preparation method comprises the following steps: dissolving an amino-containing organic matter and a metal salt in an organic solvent, adding an organic acid for reaction to obtain a turbid solution, and carrying out solid-liquid separation, cleaning and drying on the turbid solution to obtain amino-containing electropositive active particles; the preparation method comprises the following steps: dissolving a membrane base material in an alkyl amide compound, adding a pore-forming agent to obtain membrane casting slurry, carrying out phase transformation reaction on the membrane casting slurry to obtain a base membrane, alkalifying the base membrane, and acidifying to obtain a nanofiltration base membrane with carboxyl; laying an organic amine solution on the surface of the nanofiltration base membrane, and heating to obtain a surface aminated nanofiltration base membrane; laying an acyl chloride compound solution on the surface of the nanofiltration base membrane while the nanofiltration base membrane is hot, and standing to obtain a nanofiltration base membrane of which the surface is subjected to acylating chlorination; and stirring the amido-containing electropositive active particles and the surface-acylated nanofiltration base membrane in water to obtain the electropositive nanofiltration membrane. The prepared nanofiltration membrane has certain positive charges and aperture parameters, and Li < + > and high-valence heavy metal ions can be effectively separated.

Description

Technical Field

[0001] The present invention relates to the technical field of recycling and utilization of lithium ion batteries, and in particular to a preparation method and application of a positively charged nanofiltration membrane. Background Art

[0002] Since the commercialization of lithium-ion batteries, they have a broad market prospect due to their many advantages. Although lithium-ion batteries are called green batteries because they do not contain heavy metal elements with high toxicity such as mercury, cadmium, and lead, it does not mean that they are pollution-free products. If waste lithium-ion batteries are not handled properly, they can still have an impact on the environment and human health. For example, the heavy metals contained in the positive electrode materials can increase the pH value of the environment and affect the ecological environment. In addition, the heavy metals and lithium in the positive electrode materials are elements with very small reserves in nature. Their content is higher than that in mined minerals. Carrying out research on the recycling and utilization of materials in waste lithium-ion batteries can not only reduce the impact on the environment, but also bring

[0003] The environmental pollution problem and the reasonable resource recycling and utilization of waste lithium-ion power batteries have become a common concern in the industry and a difficult problem that needs to be solved urgently.

[0004] At present, the main materials recycled from waste lithium-ion batteries are negative electrode current collectors (commonly copper foil), positive electrode current collectors (commonly aluminum foil), positive electrode active materials and negative electrode active materials. There are usually three main steps in the recycling of pole pieces: first, the waste batteries are discharged and the pole pieces are disassembled; second, the materials in the pole pieces are separated from the current collectors; third, the recovery and utilization of valuable metals. Specifically, the waste batteries are disassembled in a glove box or other environment isolated from water vapor to take out the positive electrode pieces, and mechanical crushing, ultrasonic-assisted separation, or high-strength acidity and alkalinity of strong acids and alkalis, or organic solvents are used to separate the active substances 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 piece, such as Ni 2+ 、Co 2+ 、Mn 2+ 、Li + The traditional method of metal separation is to adjust the pH value of the leaching solution and use extractants to separate the metals. However, this method has the disadvantages of low selectivity, introduction of new impurities, poor separation effect and Li + Limitations such as losses.

[0005] In order to avoid Li + Loss, before heavy metal ion separation, Li + It is particularly important to separate high-valent heavy metal ions. Summary of the Invention

[0006] Based on the above problems, the purpose of the present invention is to provide a method for preparing a positively charged nanofiltration membrane and a nanofiltration membrane, and its application. The nanofiltration membrane prepared by this preparation method has a certain positive charge and a certain pore size parameter, which can + It can effectively separate high-valent heavy metal ions and the nanofiltration membrane can be recycled.

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

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

[0009] dissolving an organic substance with an amino group and a metal salt in an organic solvent, adding an organic acid for dispersion, and then heating to react to obtain a turbid liquid, performing solid-liquid separation on the turbid liquid to obtain a solid, and washing and drying the solid to obtain positively electroactive particles with an amino group;

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

[0011] Dissolving membrane substrate particles in an alkylamide compound and adding a pore-forming agent, heating and stirring to obtain a casting slurry, coating the casting slurry on a plate and immersing the plate in water, the casting slurry undergoes a phase transition reaction to obtain a base membrane, and alkalizing and then acidifying the base membrane to obtain a nanofiltration base membrane with carboxyl groups;

[0012] (3) Surface amination of nanofiltration membrane

[0013] Laying an organic amine solution on the surface of the nanofiltration base membrane with carboxyl groups, and heating the solution until the solvent in the solution evaporates to obtain a surface-aminated nanofiltration base membrane;

[0014] (4) Surface chlorination of nanofiltration membrane

[0015] while still hot, laying an acyl chloride compound solution on the surface of the surface-aminated nanofiltration base membrane, and allowing it to stand for a certain period of time to obtain a surface-acylchlorinated nanofiltration base membrane;

[0016] (5) Covalent binding

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

[0018] The preparation method of the positively charged nanofiltration membrane of the present invention utilizes positively active particles with amino groups to react with nanofiltration base membrane with acyl chloride on the surface, and the amino groups and acyl chloride groups react to form a covalent bond, thereby obtaining a positively charged nanofiltration membrane. This nanofiltration membrane not only has a positive charge but also has certain pore size parameters and strength, and can be used for Li + and effective separation of high-valent heavy metal ions. The details are as follows.

[0019] (1) In the preparation of positively charged active particles with amino groups, the organic matter with amino groups and the metal salt are first dissolved in an organic solvent. Under acidic conditions, the inorganic and organic materials are combined to produce a metal-organic framework material. The introduction of inorganic materials can improve the strength of the active particles and even the nanofiltration membrane.

[0020] (2) In the preparation of a nanofiltration base membrane with carboxyl groups, the casting solution contains membrane substrate particles, an alkylamide compound, and a pore-forming agent. 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, thereby introducing carboxyl groups on the surface of the base membrane. The pore-forming agent forms pores during the phase transition reaction or the subsequent heating process, so that the nanofiltration membrane has a certain pore size parameter.

[0021] (3) During the surface amination of the nanofiltration base membrane, the organic amine combines with the carboxyl groups on the surface of the nanofiltration base membrane, fixing the amine groups on the surface of the nanofiltration base membrane. Since the amine groups themselves carry a monovalent positive charge, the surface of the nanofiltration base membrane after surface amination carries a monovalent positive charge due to the introduction of positively charged amine groups.

[0022] (4) During the surface chlorination of the nanofiltration membrane, acyl chloride groups can be further introduced onto the surface of the aminated nanofiltration membrane through instantaneous temperature changes, so as to prepare for the reaction with the positively electroactive particles with amino groups.

[0023] (5) The positively charged particles with amino groups react with the nanofiltration base membrane with acyl chloride on the surface. The amino groups react with the acyl chloride groups, so that a nanofiltration layer with monovalent positive charge is formed on the surface of the base membrane.

[0024] As a technical solution of the present invention, the organic matter with an amino group includes at least one of 2-aminoterephthalic acid, 2-aminoterephthalic acid monomethyl ester and 2-aminoterephthalic acid dimethyl ester.

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

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

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

[0028] As a technical solution of the present invention, the molar ratio of the organic compound with an amino group, the metal salt and the organic acid is 1:1:80-120.

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

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

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

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

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

[0034] As a 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 to 80° C. and the heating time is 10 to 18 hours.

[0036] As a 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 a 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 a technical solution of the present invention, the solution used for the acidification is a 0.8-1.5 mol / L hydrochloric acid aqueous solution or a 0.8-1.5 mol / L nitric acid aqueous solution.

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

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

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

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

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

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

[0045] The second aspect of the present invention provides a method for preparing a positively charged nanofiltration membrane. The positively charged nanofiltration membrane prepared has a pore size of 5.5 to 6.5 nm and a Zeta potential of 4 to 10 eV at pH 7. The nanofiltration membrane with these parameters can be used for Li + and effective separation of high-valent 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 sheet, comprising:

[0047] (1) treating the positive electrode sheet disassembled from the battery to obtain a leachate;

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

[0049] In the separation method of the present invention, the leachate is sent to the nanofiltration system for filtration treatment. The nanofiltration membrane with a monovalent positively charged amine group has a strong repulsive ability to positively charged metal ions. The heavy metal ions (such as Ni 2+ 、Co 2+ 、Mn 2+ 、Fe 2+ etc.) and Li + Will be rejected by the positively charged nanofiltration membrane. But in contrast, the positively charged Ni 2+ 、Co 2+ 、Mn 2+ 、Fe 2+ The electrostatic repulsion is higher, Li + The electrostatic repulsion is lower (Donnan effect). 2+ 、Co 2+ 、Mn 2+ 、Fe 2+ Heavy metal ions such as Li+ will be blocked outside the nanofiltration membrane, while Li+ with lower repulsive force will be blocked outside the nanofiltration membrane. + It will pass through the filter pores under the pressure of the liquid flow and pass through the nanofiltration membrane to obtain Li + The filtrate is separated from the leachate.

[0050] The separation method of the present invention separates Li + Separate from heavy metal ions and realize Li+ The purification of Li ions simplifies the process steps and avoids the use of pH adjustment and extraction agents in traditional processes. + The loss increased Li + The nanofiltration membrane of the present invention also has the characteristic of regeneration. The nanofiltration membrane of the nanofiltration system can be taken out, the filter residue is removed from the nanofiltration membrane, and the membrane is rinsed and reactivated (aminated) before it can be used again, thus having the characteristic of repeated use.

[0051] In addition, based on the comparison with the traditional nanofiltration technology (which mainly separates metal ions of different particle sizes by pore size), the separation method of the present invention is based on pore size screening, by introducing a positively charged nanofiltration layer on the surface of the nanofiltration base membrane, by enhancing the charge repulsion effect, Li + Separation from other heavy metal ions is the result of the combined effect of pore size screening and charge repulsion. The separation effect is better, and the Li-containing + 的 Higher purity. DETAILED DESCRIPTION

[0052] The present invention utilizes nanofiltration system to extract Li + The separation steps include: (1) treating the positive electrode sheets 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 by conventional methods, such as first crushing the positive electrode sheets by mechanical crushing, and then using a strong acid or strong base to dissolve the particles and separate the Li-containing + and leachate of high-valent heavy metal ions.

[0053] The nanofiltration membrane of the present invention is not a conventional nanofiltration membrane that is screened by pore size. It not only has a certain pore size, but also has a certain positive charge and strength. Furthermore, the pore size is 5.5-6.5 nm, and the Zeta potential is 4-10 eV at pH 7. Therefore, the nanofiltration membrane of the present invention uses pore size screening and charge repulsion to remove Li in the filtrate. + It can separate high-valent heavy metal ions and the nanofiltration membrane can be used repeatedly.

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

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

[0056] An organic substance with an amino group and a metal salt are dissolved in an organic solvent, an organic acid is added for dispersion, and then heated to react to obtain a turbid liquid, the turbid liquid is subjected to solid-liquid separation to obtain a solid, and the solid is washed and dried to obtain positively electroactive particles with an amino group.

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

[0058] The membrane substrate particles are dissolved in an alkylamide compound 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.

[0059] (3) Surface amination of nanofiltration membrane

[0060] The surface of the nanofiltration base membrane with carboxyl groups is covered with an organic amine solution, and the solution is heated until the solvent in the solution is evaporated to obtain the nanofiltration base membrane with surface amination.

[0061] (4) Surface chlorination of nanofiltration membrane

[0062] The acyl chloride compound solution is laid on the surface of the surface aminated nanofiltration base membrane while it is still hot, and the solution is allowed to stand for a certain period of time to obtain the surface acylchlorinated nanofiltration base membrane.

[0063] (5) Covalent binding

[0064] Positively charged nanofiltration membrane is obtained by stirring positively charged active particles with amino groups and nanofiltration base membrane with surface chlorination in water for a certain period of time.

[0065] Furthermore, in step (1), the organic compound with an amino group comprises at least one of 2-aminoterephthalic acid, 2-aminoterephthalic acid monomethyl ester, and 2-aminoterephthalic acid dimethyl ester, and the organic compound with an amino group is an organic compound particle with a large specific surface area. The metal salt comprises zirconium chloride and / or titanium chloride, preferably zirconium chloride. The addition of the metal salt can enhance the strength and stability of the nanofiltration membrane. The organic solvent comprises N,N-dimethylamide and / or N,N-dimethylformamide, and the organic solvent needs to be able to dissolve or disperse the organic compound with an amino group and the metal salt particles. The organic acid is acetic acid. The molar ratio of the organic compound with an amino group, the metal salt, and the organic acid is 1:1:80-120. The mixing of the organic compound with an amino group, 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 100-150° C., and the heating time is 18-30 hours. A centrifuge can be used for solid-liquid separation, and the solid can be washed with water or alcohol.

[0066] In step (2), 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, 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 is the main raw material of the nanofiltration layer, and it undergoes subsequent acidification, alkalization, amination, chlorination and other reactions at least on the surface. The pore-forming agent is polyethylene glycol or polyvinyl alcohol with a molecular weight of 300 to 500. The solution used for alkalization 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 solution used for acidification 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. During the preparation of the casting slurry, the heating temperature is 50 to 80°C and stirring is continuous for 10 to 18 hours. The casting slurry can be applied to the plate using a coating apparatus to a thickness of 100-200 μm. The alkalization reaction temperature is 50-100°C for 2-5 hours. The acidification reaction temperature is room temperature for 10-18 hours. Through acidification and alkalization, carboxyl groups are introduced into the alkylamide compound.

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

[0068] In step (4), after evaporation in step (3), the acyl chloride compound solution is laid while hot. Acid chloride is carried out on the surface of the base membrane by transient temperature change. The mass fraction of the acyl chloride compound in the acyl chloride compound solution is 0.1 to 3.0%. The acyl chloride compound includes at least one of 1,3,5-tribenzoyl chloride, phthaloyl chloride, isophthaloyl chloride, terephthaloyl chloride, biphenyl dichloride and benzene disulfonyl chloride. After laying, the base membrane is left to stand for 0.5 to 1.5 hours to obtain a nanofiltration base membrane with surface chlorination.

[0069] In step (5), the positively charged nanofiltration membrane is obtained by stirring the positively charged active particles with amino groups and the nanofiltration base membrane with surface chlorination in water for 5 to 10 hours.

[0070] In order to better illustrate the purpose, technical solutions and beneficial effects of the present invention, the present invention will be further described below in conjunction with specific embodiments. It should be noted that the following implementation method is a further explanation of the present invention and should not be used as a limitation of the present invention.

[0071] Example 1

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

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

[0074] 2-Aminoterephthalic acid and zirconium chloride were dissolved in N,N-dimethylamide, and acetic acid was added (the molar ratio of 2-aminoterephthalic acid, zirconium chloride, and acetic acid was 1:1:100). The mixture was then dispersed at high speed for 2 hours to obtain a clear solution. The clear solution was placed in a high-temperature reactor and reacted at 130°C for 25 hours to obtain a turbid solution. The turbid solution was centrifuged to obtain a solid, which was then washed with water and denatured alcohol and dried to obtain positively electroactive particles with amino 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 produce a casting slurry. The casting slurry was applied to a plate with a thickness of 150±2μm using a coating apparatus. The plate was then immersed in water to undergo a phase transition reaction to produce a base film. The base film was then placed in 1.2mol / L NaOH and reacted at 80°C for 3 hours. It was then placed in 1.0mol / L hydrochloric acid for 15 hours, followed by washing with water.

[0077] (3) Surface amination of nanofiltration membrane

[0078] A 3% by mass polyethyleneimine aqueous solution is laid on the surface of a nanofiltration base membrane with carboxyl groups, and the solution is heated at 75° C. until the water in the solution is evaporated to obtain a surface-aminated nanofiltration base membrane.

[0079] (4) Surface chlorination of nanofiltration membrane

[0080] While hot, a 1.0% mass fraction of 1,3,5-tribenzoyl chloride solution was laid on the surface of the surface aminated nanofiltration base membrane, and the solution was allowed to stand for 1 hour to obtain a surface chlorinated nanofiltration base membrane.

[0081] (5) Covalent binding

[0082] Positively charged nanofiltration membranes were obtained by stirring positively charged active particles with amino groups and surface chlorinated nanofiltration base membranes in water for 8 hours.

[0083] The prepared nanofiltration membrane was subjected to a performance test, and its pore size was measured to be about 6.0 nm using a pore size tester, and its Zeta potential was 6 eV at a pH of 7.

[0084] Example 2

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

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

[0087] Dimethyl 2-aminoterephthalate and titanium chloride were dissolved in N,N-dimethylformamide. Acetic acid (the molar ratio of dimethyl 2-aminoterephthalate, yttrium chloride, and acetic acid was 1:1:110) was added and dispersed at high speed for 3 hours to obtain a clear solution. The clear solution was placed in a high-temperature reactor and reacted at 130°C for 25 hours to obtain a turbid solution. The turbid solution was centrifuged to obtain a solid. The solid was washed with water and denatured alcohol and then dried to obtain positively electroactive particles with amino 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 produce a casting slurry. The casting slurry was applied to a sheet material using a coating apparatus to a thickness of 150±2μm. The sheet material was immersed in water to undergo a phase transition reaction to produce a base film. The base film was then placed in 1.2mol / L NaOH and reacted at 80°C for 3 hours. The base film was then placed in 1.0mol / L hydrochloric acid for 15 hours, followed by washing with water.

[0090] (3) Surface amination of nanofiltration membrane

[0091] A 5% by mass poly(N-vinyl o-phenylimine) aqueous solution is laid on the surface of a nanofiltration base membrane with carboxyl groups, and the solution is heated at 75° C. until the water in the solution is evaporated to obtain a surface aminated nanofiltration base membrane.

[0092] (4) Surface chlorination of nanofiltration membrane

[0093] While hot, a 1.0% by mass 1,3,5-tribenzoyl chloride solution was laid on the surface of the surface-aminated nanofiltration base membrane, and the solution was allowed to stand for 0.5 h to obtain a surface-chlorinated nanofiltration base membrane.

[0094] (5) Covalent binding

[0095] Positively charged nanofiltration membranes were obtained by stirring positively charged active particles with amino groups and surface chlorinated nanofiltration base membranes in water for 10 hours.

[0096] The prepared nanofiltration membrane was subjected to a performance test, and its pore size was measured to be about 5.8 nm using a pore size tester, and its Zeta potential was 5 eV at a pH of 7.

[0097] Example 3

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

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

[0100] 2-Aminoterephthalic acid and zirconium chloride were dissolved in N,N-dimethylamide, and acetic acid was added (the molar ratio of 2-aminoterephthalic acid, zirconium chloride, and acetic acid was 1:1:120). The mixture was dispersed at high speed for 2 hours to obtain a clear solution. The clear solution was placed in a high-temperature reactor and reacted at 150°C for 20 hours to obtain a turbid solution. The turbid solution was centrifuged to obtain a solid, which was then washed with water and denatured alcohol and dried to obtain positively electroactive particles with amino 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-dimethylformamide 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 produce a casting slurry. The casting slurry was applied to a plate with a thickness of 150±2μm using a coating apparatus. The plate was then immersed in water to undergo a phase transition reaction to produce a base film. The base film was then placed in 1.0 mol / L NaOH and reacted at 100°C for 2 hours. The plate was then placed in 1.2 mol / L hydrochloric acid for 12 hours, followed by rinsing with water.

[0103] (3) Surface amination of nanofiltration membrane

[0104] A 3% by mass polyethyleneimine aqueous solution is laid on the surface of a nanofiltration base membrane with carboxyl groups, and the solution is heated at 80° C. until the water in the solution is evaporated to obtain a surface-aminated nanofiltration base membrane.

[0105] (4) Surface chlorination of nanofiltration membrane

[0106] While still hot, a 2.0% by mass isophthaloyl chloride solution was laid on the surface of the surface-aminated nanofiltration base membrane, and the solution was allowed to stand for 1.5 hours to obtain a surface-chlorinated nanofiltration base membrane.

[0107] (5) Covalent binding

[0108] Positively charged nanofiltration membranes were obtained by stirring positively charged active particles with amino groups and surface chlorinated nanofiltration base membranes in water for 8 hours.

[0109] The prepared nanofiltration membrane was subjected to a performance test, and its pore size was measured to be about 6.1 nm using a pore size tester, and its Zeta potential was 7 eV at a pH of 7.

[0110] The nickel-cobalt-manganese cathode sheet disassembled from the nickel-cobalt-manganese ternary battery was mechanically crushed, soaked in NMP and subjected to ultrasonic vibration for 8 hours, and then filtered to obtain the filtrate. The nanofiltration membranes prepared in Examples 1 to 3 were placed in the nanofiltration system, and the filtrates were filtered and treated respectively. The Li+ The recovery rate and purity of Li in Example 1 + The recovery rate is 87.6% and the purity is 97.8%. + The recovery rate is 86.7% and the purity is 96.9%. + 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 rather than to limit the scope of protection of the present invention. Although the present invention is described in detail with reference to the preferred embodiments, it is not limited to those listed in the embodiments. Those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents 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: Includes steps: (1) Preparation of positively electroactive particles with amine groups Dissolving an organic substance with an amine group and a metal salt in an organic solvent, adding an organic acid for dispersion and then heating for reaction to obtain a turbid liquid, performing solid-liquid separation on the turbid liquid to obtain a solid, and washing and drying the solid to obtain positively electroactive particles with an amine group; (2) Preparation of nanofiltration membranes with carboxyl groups Dissolving membrane substrate particles in an alkylamide compound and adding a pore-forming agent, heating and stirring to obtain a casting slurry, coating the casting slurry on a plate and immersing it in water, the casting slurry undergoes a phase transition reaction to obtain a base membrane, and alkalizing and then acidifying the base membrane to obtain a nanofiltration base membrane with a carboxyl group; (3) Surface amination of nanofiltration membrane Laying an organic amine solution on the surface of the nanofiltration base membrane with carboxyl groups, and heating until the solvent in the solution evaporates to obtain a nanofiltration base membrane with aminated surface; (4) Surface chlorination of nanofiltration membrane while hot, laying an acyl chloride compound solution on the surface of the surface aminated nanofiltration base membrane, and leaving it to stand for a certain period of time to obtain a surface acylchlorinated nanofiltration base membrane; (5) Covalent binding The positively charged nanofiltration membrane is obtained by stirring the positively charged active particles with amine groups and the surface chlorinated nanofiltration base 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 organic matter with amino groups includes at least one of 2-aminoterephthalic acid, 2-aminoterephthalic acid monomethyl ester and 2-aminoterephthalic acid dimethyl ester, 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 organic matter with amino groups, the metal salt and the organic acid is 1:1:80-120.

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 film substrate particles include polyacrylonitrile particles and / or polypropylene particles, the number average molecular weight of the polymer in the film substrate particles is 100,000 to 200,000, the mass percentage of the film 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° C. and the heating time is 10-18 hours.

6. The method for preparing a positively charged nanofiltration membrane according to claim 1, characterized in that: The solution used for the 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, the temperature of the alkalization reaction is 50-100°C, and the time of the alkalization reaction is 2-5 hours. The solution used for the acidification 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 temperature of the acidification reaction is room temperature, and the time of the acidification reaction is 10-18 hours.

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

8. The method for preparing a positively charged nanofiltration membrane according to claim 1, characterized in that: The certain time in step (4) is 0.5 to 1.5 hours, and the certain time 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 eV at pH 7.

10. A method for separating lithium ions and metal ions in a positive electrode sheet, characterized in that: include: (1) treating the positive electrode sheet removed from the battery to obtain a leachate; (2) 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 or the positively charged nanofiltration membrane according to claim 9 is installed in a nanofiltration system, and the leachate is sent into the nanofiltration system for filtration treatment.