CN119144838A

CN119144838A - Method for recycling target metal in lithium battery anode material

Info

Publication number: CN119144838A
Application number: CN202411671152.4A
Authority: CN
Inventors: 袁伟佳; 司马忠志; 杨诚辉; 杨诗旻
Original assignee: Ganzhou Jirui New Energy Technology Co ltd
Current assignee: Ganzhou Jirui New Energy Technology Co ltd
Priority date: 2024-11-21
Filing date: 2024-11-21
Publication date: 2024-12-17
Anticipated expiration: 2044-11-21
Also published as: CN119144838B

Abstract

The invention discloses a method for recycling target metal in a lithium battery anode material, which comprises the steps of obtaining anode material particles after pretreatment of the lithium battery, adding the particles into a composite solvent consisting of citric acid and diaza-ring ligand, leaching target metal ions to obtain leaching solution, adding a magnetic adsorbent with a surface modified with phosphate groups and/or sulfonic groups to enrich the target metal ions on the adsorbent, and applying a magnetic field to separate the magnetic adsorbent enriched with the target metal ions. The method for recycling the target metal in the lithium battery anode material can enable target metal ions to be leached efficiently by using a composite solvent system consisting of citric acid and organic ligands containing two nitrogen heterocycles, and simultaneously enables target metal ions to be enriched efficiently by using a magnetic adsorbent with surface modified with phosphate groups or sulfonic acid groups, and to be separated rapidly under an external magnetic field.

Description

Method for recycling target metal in lithium battery anode material

Technical Field

The invention belongs to the technical field of waste battery recycling treatment, and particularly relates to a method for recycling target metals in a lithium battery anode material.

Background

In the current recovery process of the lithium ion battery, the recovery of valuable metals (such as cobalt, nickel and manganese) in the anode material of the retired lithium ion battery has important economic value and environmental significance. However, the existing positive electrode material recycling technology has various problems, so that the efficient recycling process faces great challenges.

In the prior art, the leaching efficiency is generally low in the leaching process, particularly when cobalt, nickel and other transition metals are recovered, the traditional method generally adopts inorganic acid (such as sulfuric acid, nitric acid and the like) to carry out metal leaching, and the method has certain dissolving capacity, but the acidic condition often requires higher, so that the leaching process of the material is slow and the efficiency is not ideal. Meanwhile, the use of strong acid has high requirements on equipment and environment, and the operation cost is increased. Many studies have shown that strong acids, while effective in leaching lithium battery cathode materials, are environmentally corrosive and handling complexity that limit the possibilities for large-scale applications.

In addition, the problem of poor selectivity during leaching is also very pronounced. Besides target metals such as cobalt and nickel, the lithium battery anode material also contains impurity metals such as aluminum and iron, and the like, and the lithium battery anode material is leached by purely depending on strong acid or single organic acid, so that multiple metals are often dissolved at the same time, and the selectivity of the target metals is lacked. This not only increases the difficulty in subsequent separation of the leachate, but also reduces the purity of the target metal, resulting in further reduction in recovery efficiency. Particularly under the high-concentration acidic condition, the leaching amount of impurity metals is higher, and the requirements on separation and purification processes in the subsequent purification process are remarkably increased.

Therefore, in view of the above technical problems, it is necessary to provide a new solution.

Disclosure of Invention

The invention aims to provide a method for recycling target metals in a lithium battery anode material, which can solve the problems of low leaching efficiency and poor selectivity of recycling valuable metals in the lithium battery anode material.

In order to achieve the above purpose, the technical scheme provided by the invention is as follows:

The invention provides a method for recycling target metals in a lithium battery positive electrode material, which comprises the steps of preprocessing a lithium battery to obtain positive electrode material particles, adding the positive electrode material particles into a composite solvent, adjusting the pH value to 3.3-5, leaching target metal ions to obtain a leaching solution, adding a magnetic adsorbent into the leaching solution, adjusting the pH value to 1-2.7, enriching the target metal ions on the magnetic adsorbent to form a mixed solution, modifying the surface of the magnetic adsorbent with phosphate groups and/or sulfonate groups, and applying a magnetic field to the mixed solution to separate the magnetic adsorbent enriched with the target metal ions from the mixed solution.

In one or more embodiments, the pretreatment method of the lithium battery comprises the steps of completely discharging the lithium battery, disassembling and separating the positive electrode material, and crushing and screening the positive electrode material to obtain positive electrode material particles with the particle size of less than 100 microns.

In one or more embodiments, the mass ratio of the positive electrode material particles to the composite solvent is 1 (10-20), and/or the concentration of citric acid in the composite solvent is 0.5-1.5 mol/L, and/or the molar ratio of the organic ligand in the composite solvent to the target metal ion is (1-2): 1.

In one or more embodiments, the organic ligand includes at least one of 2,2' -bipyridine and 1, 10-phenanthroline.

In one or more embodiments, the preparation method of the compound solvent comprises the steps of dissolving citric acid in deionized water to obtain a citric acid solution, dissolving an organic ligand in ethanol to obtain an organic ligand solution, and uniformly mixing the citric acid solution and the organic ligand solution to obtain the compound solvent.

In one or more embodiments, the magnetic adsorbent comprises magnetic carbon nanotubes with cobalt and/or nickel nanoparticles attached thereto.

In one or more embodiments, the preparation method of the magnetic carbon nanotube comprises the steps of refluxing the carbon nanotube in mixed acid composed of sulfuric acid and nitric acid for 2-6 hours, conducting acidification treatment, dispersing the acidified carbon nanotube in cobalt and/or nickel metal salt solution, conducting ultrasonic treatment for 3-8 hours to obtain carbon nanotube suspension, adding sodium hydride into the carbon nanotube suspension under the ice bath condition, stirring for reaction, reducing cobalt and/or nickel metal ions into metal nano particles, attaching the metal nano particles on the surface of the carbon nanotube, centrifugally separating and collecting products, washing and drying to obtain the magnetic carbon nanotube.

In one or more embodiments, the magnetic adsorbent comprises magnetic polymer microspheres having magnetic nanoparticles embedded therein.

In one or more embodiments, the magnetic polymer microsphere is prepared by dispersing magnetic nanoparticles in ethanol solution, adding polyvinyl alcohol, performing ultrasonic dispersion for 30min to obtain a magnetic nanoparticle suspension, uniformly mixing styrene, methacrylic acid and divinylbenzene monomers according to a proportion to obtain a monomer mixed solution, adding the monomer mixed solution into the magnetic nanoparticle suspension, stirring uniformly, adding an initiator, stirring and reacting for 6-8 h at 65-75 ℃ under inert protective atmosphere to polymerize the styrene, methacrylic acid and divinylbenzene monomers on the surfaces of the magnetic nanoparticles, performing centrifugal separation and collection, washing and drying to obtain the magnetic polymer microsphere.

In one or more embodiments, the method further comprises washing the separated magnetic adsorbent enriched in target metal ions, adding the washed magnetic adsorbent to an ethylenediamine tetraacetic acid solution to dissociate the target metal ions enriched on the magnetic adsorbent to obtain a dissociation solution, and applying a magnetic field to the dissociation solution to separate the magnetic adsorbent from the dissociation solution.

Compared with the prior art, the method for recycling the target metal in the lithium battery anode material has the advantages that the target metal ions are efficiently leached out under the proper acidic condition by using a composite solvent system consisting of citric acid and organic ligands containing two nitrogen heterocycles, wherein the citric acid provides a stable acidic environment, the selective complexing of cobalt, nickel and manganese is enhanced by the double nitrogen heterocycles, meanwhile, the target metal ions are efficiently enriched by adopting the magnetic adsorbent with the surface modified with phosphate groups and/or sulfonic groups through pH adjustment, the rapid separation is realized under an external magnetic field, and the recovery rate and the recovery purity of the method are both higher.

Drawings

In order to more clearly illustrate the technical solution of the embodiments of the present invention, the drawings that are needed in the description of the embodiments will be briefly described. It is obvious that the drawings in the following description are only some embodiments described in the present invention, and that other drawings may be obtained from these drawings without inventive effort for a person of ordinary skill in the art.

Fig. 1 is a flowchart of a method for recovering a target metal in a positive electrode material of a lithium battery according to an embodiment of the invention.

Detailed Description

In order to make the technical solution of the present invention better understood by those skilled in the art, the technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present invention without making any inventive effort, shall fall within the scope of the present invention.

It is noted that all numbers expressing feature sizes, amounts, and physical properties used in the specification and claims are to be understood as being modified in all instances by the term "about" unless otherwise indicated. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can be varied appropriately by those skilled in the art utilizing the desired properties sought to be obtained by the teachings disclosed herein. The use of numerical ranges by endpoints includes all numbers subsumed within that range and any range within that range, e.g., 1 to 5 includes 1, 1.2, 1.4, 1.55, 2, 2.75, 3, 3.80, 4,5, and the like.

The recovery method is based on deep analysis of the existing lithium battery anode material recovery technology. When the existing technology is used for treating the anode material of the retired lithium ion battery, the problems of low efficiency, high requirements on energy consumption and equipment due to the fact that the existing method depends on strong acid solvents frequently in the leaching process, poor selectivity, complicated subsequent purification steps due to the fact that most solvents cannot effectively distinguish target metals and impurity metals in the leaching process, and high environmental protection pressure due to the fact that the existing method depends on strong acid solvents are solved. Accordingly, the present invention addresses these problems by providing a recovery method that integrates high efficiency, selectivity, and simplicity.

The technology of the invention realizes the idea that the efficient and selective leaching effect is achieved by a composite solvent system, and the separation and enrichment of metal ions are completed by assisting a magnetic adsorbent and an external magnetic field. In the leaching stage, a specific compound solvent system is utilized, and the dissolution and complexation efficiency of target metal ions is improved by matching proper acidity and organic ligands, so that a relatively stable complex is formed, and the metal can be leached effectively under mild conditions. Meanwhile, through selective complexation, the dissolution of impurity metals is reduced, thereby realizing selective leaching. In the metal enrichment stage, the complex is dissociated into target metal ions by adjusting the solution conditions, and the ions are selectively adsorbed on the magnetic adsorbent. The external magnetic field can further assist in realizing rapid separation of the adsorbent, and the process flow is simplified.

The realization thinking improves the leaching efficiency through the design of the composite solvent, realizes high-purity recovery through selective complexation and magnetic separation, and improves the operation simplicity and environmental protection of the whole process through simplifying the separation step. The recycling scheme of the invention has remarkable advantages in the aspects of economy and environmental protection, and provides an improved path for efficiently recycling the anode material of the retired lithium battery.

Referring to fig. 1, a flowchart of a method for recovering a target metal in a positive electrode material of a lithium battery according to an embodiment of the invention is shown. The method for recycling target metals in the lithium battery anode material comprises the following steps:

and S101, preprocessing the lithium battery to obtain positive electrode material particles.

The implementation of step S101 specifically includes performing discharge treatment, disassembly, separation of the positive electrode material, pulverization, and sieving on the lithium battery. The main aim is to ensure the safe and efficient recovery of the positive electrode material and increase the specific surface area of the positive electrode material, thereby providing a good physical basis for the subsequent leaching process of metal ions.

In an exemplary embodiment, the pretreatment method for the lithium battery specifically comprises the steps of completely discharging the lithium battery, disassembling and separating the positive electrode material, and crushing and screening the positive electrode material to obtain positive electrode material particles with the particle size of less than 100 microns.

The pretreatment process mainly comprises two core steps of disassembling and separating the positive electrode material after completely discharging the lithium battery, and crushing and screening the positive electrode material to obtain positive electrode material particles with the particle size of less than 100 mu m.

The lithium battery usually still keeps partial electric quantity when retired, and direct disassembly may cause danger such as short circuit, spark and even burning. Accordingly, these safety risks can be significantly reduced by discharging the residual amount of electricity in the battery through the discharge process.

The discharge method generally includes a solution discharge and a load resistance discharge. In solution discharge, a lithium battery can be placed in an electrolyte solution, and the charge in the battery is released by ion conduction, so that the battery gradually reaches a state with zero voltage. Another method is to connect the battery to the resistive load by switching in the appropriate resistive load and monitor the battery voltage using a voltage monitoring device, when the voltage drops to 0V, the discharging process is completed.

After the discharge is completed, the battery can be disassembled and separated, and the process comprises the disassembly of the battery shell and the extraction of electrode materials. In the disassembly process, the shell, the diaphragm, the electrolyte and the anode and cathode materials of the battery are required to be separated to obtain the anode material rich in valuable metals. Disassembly typically includes mechanical disruption, shelling, and separation steps. For example, the battery may be cut by a mechanical cutter, the casing removed, and the positive electrode material separated from other components by centrifugal separation or sieving techniques.

The disassembled battery can release materials with different components including a positive electrode, a negative electrode, a diaphragm, electrolyte and the like, wherein the positive electrode material is a recycling key point, and the positive electrode material is rich in valuable metals such as cobalt, nickel, manganese and the like.

After the positive electrode material is separated, it is required to be crushed and sieved. The main purpose of the crushing is to crush the anode material to a proper particle size so as to increase the specific surface area of the anode material, thereby improving the chemical reaction efficiency in the subsequent leaching process.

In the pulverization, a ball mill, a high-pressure crusher, or the like, which can control the particle diameter of the positive electrode material to 100 μm or less, may be used. The smaller particles have larger specific surface area, so that the leaching agent and the material can be fully contacted, and the leaching agent can enter the particles to be contacted with metal ions more quickly, thereby improving the leaching speed and the overall efficiency of the metal ions.

After crushing, the positive electrode material can be screened, so that the obtained positive electrode material particles have uniform particle size distribution. Through the screen cloth that uses certain aperture, sieving out the granule of suitable size can effectively get rid of large granule and the partial impurity that produces in the crushing process to promote the homogeneity and the purity of anodal material. The uniformity of the screening contributes to the stability of the leaching process, since too large or too small particles can lead to non-uniformity of the reaction, which in turn affects the leaching efficiency of the metal ions.

S102, adding the positive electrode material particles into a composite solvent, adjusting the pH to 3.3-5, and leaching target metal ions to obtain a leaching solution, wherein the composite solvent comprises citric acid and an organic ligand containing two nitrogen heterocycles.

The core of step S102 is to utilize a specific composite solvent system to leach out target metal ions (such as cobalt, nickel and manganese) in the pretreated positive electrode material particles efficiently, so as to obtain a leaching solution rich in metal ions. The specific process of the step comprises the steps of adding positive electrode material particles into a composite solvent, regulating the pH value of the solution to 3.3-5, and effectively promoting the dissolution and selective complexation of metal ions through components (comprising citric acid and organic ligands containing two nitrogen heterocycles) in a composite solvent system. By controlling the precise proportioning and pH conditions of the solvent system, step S102 can realize efficient dissolution and selective extraction of metal ions. The leaching solution can be obtained by filtration, centrifugation and other separation modes.

In a specific embodiment, the pretreated positive electrode material particles are first added to a pre-formulated composite solvent. The main components of the composite solvent comprise citric acid and an organic ligand with two nitrogen heterocycles. Citric acid, an environmentally friendly and biodegradable organic acid, can provide H ⁺ in solution and form a preliminary complex with metal ions through its carboxyl (-COOH) and hydroxyl (-OH) groups. The complexation can increase the solubility of the target metal ions, thereby increasing the leaching efficiency. At the same time, the acidity of citric acid helps the solution maintain a moderate pH range, providing a favorable environment for dissolution of the target metal ions. In addition, the citric acid is selected instead of strong acid (such as sulfuric acid, hydrochloric acid, nitric acid and the like), so that the corrosive influence on equipment can be effectively reduced, and the operation safety risk and the treatment cost are reduced.

Citric acid can provide enough H ⁺ within the pH range of 3.3-5 to promote the dissolution of metal oxides, and can avoid excessive dissolution of non-target metals (such as iron and aluminum) caused by too low pH. Thus, such acidity adjustment helps to limit the dissolution of the impurity metals, ensuring selective leaching of the target metals.

Another key component in the complex solvent is an organic ligand (e.g., 2' -bipyridine or 1, 10-phenanthroline) containing two nitrogen heterocycles. The nitrogen atoms in the ligand molecular structure have lone pair electrons, and can form stable chelate with transition metal ions such as cobalt, nickel and the like. Through selective complexation, the ligand has higher affinity to target metal ions, which is helpful for improving the selectivity of metal leaching.

Because the target metal ions (e.g., co ²⁺、Ni²⁺) have a higher affinity for the ligand's complexation reaction, they preferentially bind to the ligand to form a stable complex. The selective complexing characteristic reduces the leaching amount of non-target metal ions, so that the leaching rate of target metals such as cobalt, nickel, manganese and the like is greatly improved.

For example, two nitrogen atoms of bipyridine molecules can form stable chelate with metal ions such as Co ²⁺, the free state concentration of the bipyridine molecules is obviously reduced in the solution, and the complexing selectivity of the solution is enhanced. The process not only improves the recovery purity of target metals such as cobalt, nickel and the like, but also inhibits the dissolution of impurity metals (such as aluminum and iron), thereby simplifying the subsequent separation process and improving the quality of the leaching solution.

After the ligand forms a stable complex with the target metal ion, the free energy of the target metal ion is reduced, and the solubility of the target metal ion in the solution is increased. For non-target metals (such as aluminum, iron, etc.), the selective dissolution of the target metal oxide/salt is achieved because the ligand has lower stability with the complex formed thereby, and is more difficult to dissolve.

The citric acid and the organic ligand have synergistic effect, the citric acid and the target metal ion form a primary complex, the solubility of the target metal ion is improved, the organic ligand and the target metal ion further form a more stable complex, and the leaching effect of the target metal ion in the solution is enhanced.

The acidic environment of citric acid can accelerate the dissolution reaction of the metal oxide, so that target metal ions enter the solution. Meanwhile, the carboxyl and hydroxyl of the citric acid have stronger complexing action on target metal ions to form a preliminary complex. The addition of the bifunctional organic ligand containing two nitrogen heterocycles further forms a stable complex of the target metal ion with the ligand, thereby maintaining a lower free metal ion concentration in the solution. This dynamic equilibrium mechanism allows more target metal oxide/salt to be dissolved, increasing the overall leaching rate.

In a complex solvent system, the target metal ion forms a complex with the ligand rapidly, thereby reducing the possibility of hydrolysis or precipitation. Once the target metal ions are complexed, the target metal ions can be kept in a stable state in the solution, and the loss of the target metal caused by hydrolysis is avoided. In addition, the stable complex reduces the probability of reverse precipitation, and ensures that the target metal ions can be dissolved from the positive electrode material efficiently and continuously.

The pH value is always kept in a range favorable for metal dissolution and complexation due to the acidity regulation and the selective complexation of the organic ligand in the composite solvent system. The influence of extremely acidic or alkaline conditions on equipment and reaction processes is avoided, and the consumption of energy and cost is reduced, so that higher leaching efficiency is realized under mild conditions.

In the absence of citric acid, the dissolution rate of the target metal oxide/salt will be significantly reduced, resulting in a decrease in the efficiency of target metal ions entering the solution. In addition, the primary complexing action of the citric acid and the target metal ions helps to prevent the target metal ions from being hydrolyzed and precipitated, and once the citric acid is lack, the stability of the target metal ions in the solution is reduced, insoluble precipitates are easily formed under the condition of higher pH value, and the leaching efficiency is further reduced.

The organic ligand contains two nitrogen heterocycles, and the structure can form highly stable chelate with target transition metal ions such as cobalt, nickel, manganese and the like, so that the organic ligand has higher complexing selectivity. The existence of the organic ligand can reduce the activity of target metal ions, promote more target metal ions to be dissolved out of the anode material, improve the leaching efficiency, and simultaneously, the organic ligand inhibits the dissolution of impurity metal ions by selective complexation, thereby improving the leaching efficiency of target metal.

If the organic ligand is absent, the solution lacks a selectivity factor capable of selectively complexing target metals such as cobalt, nickel, manganese and the like, which causes impurity metals (such as aluminum and iron) to also enter the leaching solution, thereby reducing the selectivity of the target metals. In addition, the lack of selective complexation of the target metal by the organic ligand results in faster saturation of the target metal ions in the solution, and difficulty in promoting further metal dissolution, resulting in reduced leaching efficiency.

The citric acid and the difunctional organic ligand are mutually complemented in the composite solvent system, so that the acidic condition and the selective complexation are respectively ensured, and the target metal ions can be efficiently dissolved and kept in the solution under the mild condition. The acidity and preliminary complexation provided by citric acid reduce the difficulty of dissolution of the target metal oxide/salt, while the selective complexation characteristics of the bifunctional ligands improve the selective dissolution of the target metal and prevent interference of impurities.

In the pH range of 3.3-5, the acidity of the solution is moderate, and the citric acid can effectively release H ⁺ to promote the dissolution of target metal oxides/salts (such as cobalt, nickel and manganese oxides). The acidic environment can break the oxide crystal structure to enable target metal ions to enter the solution, and meanwhile, the corrosive influence of strong acidity on the solution and high impurity dissolution are avoided. In the pH range, the nitrogen atom on the organic ligand is not completely protonated, the lone pair electrons are reserved, coordination bonds can be effectively formed with transition metal ions, and the complexing capability with target metals is maintained. This combination promotes dissolution of the target metal oxide/salt and selective release of the target metal ions, ensuring a higher leaching efficiency.

Under the over-strong acid environment with the pH value lower than 3.3, impurity metals such as aluminum, iron and the like are easily dissolved into the solution, and the selective recovery of target metals is affected. The aza ring sites of the organic ligands are easily protonated, reducing the ability to complex with the target metal. This will result in reduced stability of the target metal ions in solution, difficulty in forming stable complexes, affecting leaching selectivity and efficiency. Under the condition that the pH value is higher than 5, the acidity is insufficient to break the crystal structure of the metal oxide, so that the release of target metal ions is limited, and the leaching efficiency of the metal ions is reduced.

In an exemplary embodiment, the mass ratio of the positive electrode material particles to the composite solvent is 1 (10-20), and/or the concentration of citric acid in the composite solvent is 0.5-1.5 mol/L, and/or the molar ratio of the organic ligand in the composite solvent to the target metal ion is (1-2): 1.

The mass ratio of the positive electrode material particles to the composite solvent is 1 (10-20), namely, the composite solvent with the mass of 10-20 units is needed for each 1 unit mass of positive electrode material. This ratio ensures that the composite solvent is able to sufficiently saturate the surface of the particles of the positive electrode material, forming a sufficient reaction interface for the citric acid and organic ligand to effectively contact each particle. If the solvent is used in too small an amount, the surface of the particles cannot be completely covered, so that the reaction rate in the leaching process is reduced, the leaching is incomplete, and the extraction efficiency of the metal is reduced. On the other hand, excessive solvent not only wastes resources, but also increases the difficulty and cost of subsequent treatments.

The concentration of the citric acid is controlled to be 0.5-1.5 mol/L, and the concentration range provides moderate acidity for the composite solvent so as to ensure the effective dissolution of the metal oxide in the leaching process. If the concentration of citric acid is lower than 0.5mol/L, the acidity is insufficient, the dissolution rate is reduced, resulting in a decrease in leaching efficiency, whereas if the concentration is higher than 1.5mol/L, unnecessary excess acidity may be brought, increasing the dissolution of impurity metals, but rather decreasing the selectivity effect.

The molar ratio of the organic ligand to the target metal ion is (1-2): 1, so that the organic ligand can effectively complex and stabilize the target metal ion in the solution. When the molar ratio of the organic ligand to the target metal ions is 1:1, single-molecule complexing can be realized, and the target metal can be effectively complexed, while when the molar ratio is 2:1, the multi-molecule complexing is beneficial to improving the complexing stability, and the dissolution and the stability of the target metal are further enhanced in an acidic solution. If the molar ratio is less than 1:1, insufficient complexation may result, the degree of dissociation of metal ions increases, and the selectivity decreases, and if it is more than 2:1, the ligand consumption increases, the cost increases, and the effect is not significantly improved.

In an exemplary embodiment, the organic ligand includes at least one of 2,2' -bipyridine and 1, 10-phenanthroline. Both 2,2' -bipyridine (C ₁₀H₈N₂) and 1, 10-phenanthroline (C ₁₂H₈N₂) contain two nitrogen heterocycles in the molecule. The nitrogen atom of these nitrogen heterocycles has a lone pair electron, and can be bonded to a transition metal ion through a coordination bond to form a stable complex. By means of the double-tooth coordination effect, the ligands have extremely high selectivity, and complexes formed by the ligands and metal ions such as cobalt, nickel and the like have higher stability than impurity metals such as aluminum, iron and the like. The selectivity reduces the solubility of impurity metal ions, so that high-purity target metal is obtained in the leaching solution, and the complexity of subsequent separation and purification is avoided.

Under a specific reaction environment, nitrogen atoms of the 2,2' -bipyridine and the 1, 10-phenanthroline cannot be easily protonated, so that the nitrogen atoms can be still effectively complexed with target metals under weak acidic conditions (pH 3.3-5), and efficient leaching is realized under mild conditions. The high selectivity comes from the geometric structure and electron distribution characteristics of the ligand, and can be matched with the electron structure and empty d orbit of transition metals such as cobalt, nickel and the like, so that the complexing effect is strong and stable.

In an exemplary embodiment, the compound solvent is prepared by dissolving citric acid in deionized water to obtain a citric acid solution, dissolving an organic ligand in ethanol to obtain an organic ligand solution, and uniformly mixing the citric acid solution and the organic ligand solution to obtain the compound solvent.

S103, adding a magnetic adsorbent into the leaching solution, adjusting the pH to 1-2.7, and enriching target metal ions on the magnetic adsorbent to form a mixed solution, wherein the surface of the magnetic adsorbent is modified with phosphate groups and/or sulfonic acid groups.

It should be noted that, under the condition that the pH is 1 to 2.7, the organic ligand (such as 2,2' -bipyridine or 1, 10-phenanthroline) is protonated, and loses the ability to form a stable complex with the target metal ion (such as cobalt, nickel, manganese). This protonation breaks the coordination bond between the ligand and the metal ion, allowing the metal ion to dissociate from the ligand and release into solution. This process ensures that the target metal ions previously bound to the ligand can be in a free state again and can bind to phosphate and/or sulfonate groups on the adsorbent surface.

The phosphate group (-PO ₄H₂) and the sulfonate group (-SO ₃ H) have very high electronegativity in a low pH environment, SO that the phosphate group (-PO ₄H₂) and the sulfonate group (-SO ₃ H) can effectively adsorb positively charged metal ions. The surfaces of the phosphate groups and the sulfonate groups are provided with lone pair electrons and polarized oxygen atoms, and the characteristics lead the phosphate groups and the sulfonate groups to have strong affinity to transition metal ions such as cobalt, nickel, manganese and the like. Because these functional groups exist stably in a strongly acidic environment, they can efficiently enrich target metal ions on the surface of the adsorbent, and selective adsorption is achieved.

In an exemplary embodiment, the magnetic adsorbent comprises magnetic carbon nanotubes with cobalt and/or nickel nanoparticles attached thereto. The preparation method of the magnetic carbon nanotube comprises the steps of refluxing the carbon nanotube in mixed acid composed of sulfuric acid and nitric acid for 2-6 hours, conducting acidification treatment, dispersing the acidified carbon nanotube in cobalt and/or nickel metal salt solution, conducting ultrasonic treatment for 3-8 hours to obtain carbon nanotube suspension, adding sodium hydride into the carbon nanotube suspension under the ice bath condition, conducting stirring reaction, enabling cobalt and/or nickel metal ions to be reduced into metal nanoparticles, attaching the metal nanoparticles on the surface of the carbon nanotube, conducting centrifugal separation, collecting products, washing and drying to obtain the magnetic carbon nanotube.

The first step in preparing the magnetic carbon nanotubes is to carry out reflux acidification treatment on the carbon nanotubes in a mixed acid of sulfuric acid and nitric acid, and the reflux acidification treatment is usually carried out for 2-6 hours. The purpose of the acidification process is to introduce carboxyl (-COOH) and hydroxyl (-OH) oxygen-containing functional groups on the surface of the carbon nano tube, so that the surface of the carbon nano tube has stronger hydrophilicity and activity, thereby providing binding sites for the loading of metal nano particles. The combination of sulfuric acid and nitric acid can effectively remove impurities on the surface of the carbon nanotube and defects in a carbon atom chain, improve the purity and the surface area of the carbon nanotube, and create surface conditions for metal loading in the subsequent step.

The acidified carbon nanotubes are dispersed in a cobalt or nickel metal salt solution (such as cobalt nitrate or nickel nitrate) and treated for 3-8 hours under ultrasonic treatment to ensure that metal ions can be uniformly adsorbed on the surfaces of the carbon nanotubes. The core of the process is that the carbon nano tube can be fully contacted with metal ions in the metal salt solution through the action of ultrasonic waves. The carbon nano tube can be fully dispersed in the solution under the action of ultrasonic wave, so that agglomeration is avoided, and meanwhile, metal ions and the surface of the carbon nano tube form preliminary electrostatic adsorption through mechanical oscillation, so that uniform distribution of the metal ions is achieved.

After the adsorption step is completed, the carbon nanotube suspension is placed under ice bath conditions (low temperature environment near 0 ℃), and a reducing agent (e.g., sodium hydride NaH) is added and stirred for reaction. The low temperature environment of the ice bath helps to control the rate of the reduction reaction and prevents agglomeration of the metal particles due to too fast a reaction. Sodium hydride is used as a strong reducing agent, and cobalt or nickel ions in the solution can be effectively reduced to a metal state, so that nano particles are formed on the surface of the carbon nano tube and firmly attached. And after the reduction is finished, removing residual reducing agent and other byproducts through centrifugal separation, washing with deionized water and ethanol for multiple times to ensure the purity of the adsorbent, and finally drying in a vacuum drying oven to obtain the final magnetic carbon nanotube.

The magnetic carbon nanotube as an adsorbent exhibits excellent magnetic properties due to cobalt or nickel metal nanoparticles supported on the surface thereof. The magnetic property enables the adsorbent to be rapidly recovered through an externally applied magnetic field after the adsorption process is completed, and the complexity of the traditional filtering and centrifuging operation is avoided.

In an exemplary embodiment, the magnetic adsorbent comprises magnetic polymer microspheres having magnetic nanoparticles embedded therein. The preparation method of the magnetic polymer microsphere comprises the steps of dispersing magnetic nanoparticles in an ethanol solution, adding polyvinyl alcohol, conducting ultrasonic dispersion for 30min to obtain a magnetic nanoparticle suspension, uniformly mixing styrene, methacrylic acid and divinylbenzene monomers according to a proportion to obtain a monomer mixed solution, adding the monomer mixed solution into the magnetic nanoparticle suspension, stirring uniformly, adding an initiator, stirring and reacting for 6-8 h under the condition of 65-75 ℃ and inert protective atmosphere to enable styrene, methacrylic acid and divinylbenzene monomers to polymerize on the surfaces of the magnetic nanoparticles, conducting centrifugal separation to collect products, washing and drying to obtain the magnetic polymer microsphere.

The first step of the preparation method of the magnetic polymer microsphere is to disperse magnetic nano particles (such as Fe ₃O₄ particles) in ethanol solution, add polyvinyl alcohol (PVA), and obtain uniform magnetic nano particle suspension by ultrasonic dispersion for 30 min. The effect of this step is to ensure uniform dispersion of the nanoparticles, since nanoparticles have extremely high surface areas and surface energies, and agglomeration is easy to occur. Ethanol is used as a solvent, so that the mutual attraction between particles can be effectively reduced, and polyvinyl alcohol is used as a stabilizer to form a protective layer on the surfaces of nano particles so as to prevent the particles from aggregating in a solution.

Styrene, methacrylic acid and divinylbenzene monomers are mixed in proportion to obtain monomer mixed solution. Styrene can form a firm polymer skeleton after polymerization to provide mechanical strength and stability of the microsphere, methacrylic acid is introduced to increase hydrophilicity and active sites on the surface of the microsphere, thereby facilitating subsequent adsorption of target metal ions, and divinylbenzene is used as a cross-linking agent to form a cross-linking structure among polymer molecules to improve the stability and chemical resistance of the polymer.

And adding the monomer mixed solution into the magnetic nanoparticle suspension, uniformly stirring, adding an initiator, and reacting for 6-8 hours in an inert atmosphere (usually under the protection of nitrogen) at 65-75 ℃. Under the action of the temperature and the initiator, the styrene, the methacrylic acid and the divinylbenzene start free radical polymerization reaction, and gradually polymerize and coat the surfaces of the magnetic nano particles. Due to the existence of inert atmosphere, the polymerization process can be stably carried out, and the interference of oxygen is avoided, so that the magnetic nano particles can be uniformly embedded into the structure of the polymer microsphere, and are not only simply attached to the surface of the microsphere. The microsphere embedded with the magnetic nano particles maintains the high specific surface area of the microsphere and endows the microsphere with good magnetic response.

After the polymerization reaction is completed, the product is centrifugally separated to remove unreacted monomers, solvent and other byproducts. The microspheres were then washed with deionized water and ethanol multiple times to ensure their purity and dried under vacuum to give the final magnetic polymer microspheres. The microsphere has an embedded magnetic structure, and the magnetic nano particles in the microsphere endow the microsphere with the capability of rapidly responding to an external magnetic field, so that the microsphere can be conveniently and rapidly separated by utilizing the magnetic field after the metal adsorption process is completed. The magnetic polymer microsphere embedded magnetic nano particles provide magnetic response, and meanwhile, the magnetic nano particles cannot be dissolved or agglomerated due to direct contact with the outside, so that the stability of the adsorbent is ensured.

Phosphate groups can be introduced on the surface of the magnetic adsorbent by reaction with phosphoric acid or a phosphate ester. Specifically, 3-phosphoric acid oxypropyl trimethoxy silane (PPTS) can be used as a modifying agent, so that a stable phosphate base layer can be formed on the surface of the nanoparticle, and the adsorption capacity can be enhanced. The magnetic adsorbent may be sulphonated using concentrated sulphuric acid, introducing sulphonic acid groups.

And S104, applying a magnetic field to the mixed solution to separate the magnetic adsorbent enriched with the target metal ions from the mixed solution.

The adsorbent with the magnetic nano particles is quickly gathered on one side of the solution by externally applying magnetic force, so that the recovery, filtration and washing are convenient, and the separation of target metal ions is effectively realized. The separation method utilizes the magnetic response characteristic of the magnetic adsorbent, so that the separation process of the target metal is more efficient and simple, and complicated operation and equipment requirements in the traditional centrifugation or filtration process are avoided.

The basic principle of applying a magnetic field to separate the adsorbent is that the magnetic adsorbent generates a magnetic aggregation effect under the action of the applied magnetic field. The magnetic adsorbent contains magnetic nano particles (such as cobalt, iron or nickel nano particles) inside, and when an external magnetic field is applied, the particles can be rapidly gathered under the action of the magnetic field force, so that the whole adsorbent is driven to move together. Because these magnetic nanoparticles are embedded or encapsulated in the adsorbent structure, the effect of the magnetic field can directly affect the entire adsorbent, enabling it to be rapidly separated from solution. Compared with the traditional centrifugal separation method, the magnetic field separation method is simple and rapid to operate, can complete the complete recovery of the adsorbent in a few minutes, and is suitable for large-scale continuous separation.

In an exemplary embodiment, the separated magnetic adsorbent enriched in target metal ions can be washed, the washed magnetic adsorbent is added into an ethylenediamine tetraacetic acid solution to dissociate the target metal ions enriched on the magnetic adsorbent to obtain a dissociation solution, and a magnetic field is applied to the dissociation solution to separate the magnetic adsorbent from the dissociation solution.

The magnetic adsorbent which is obtained by separation and is enriched with target metal ions is washed, and the main purpose is to remove residual impurities or solution possibly existing on the surface of the adsorbent so as to ensure that the dissociation effect is not influenced by impurity interference in the dissociation process. Typically, washing is performed with deionized water or an ethanol solution to avoid the effect of ion or solvent residues on the dissociation reaction.

And adding the washed magnetic adsorbent into an ethylenediamine tetraacetic acid (EDTA) solution to dissociate target metal ions. EDTA is a chelating agent having four carboxyl groups and two amino groups, and can form a chelate compound of high stability in solution. The molecular structure can form firm coordination bond with target metal ions (such as cobalt, nickel, manganese and the like), and the stability of the molecular structure is far higher than that of the combination of the target metal ions and phosphate groups or sulfonic acid groups. By introducing the EDTA solution, target metal ions adsorbed on the surface of the adsorbent can be chelated with EDTA by competitive complexation to generate EDTA-metal complexes dissolved in the dissociation solution. At this time, the concentration and pH of the EDTA solution are controlled to be neutral or weakly alkaline to ensure that the coordination reaction between EDTA and metal ions proceeds smoothly. The EDTA serving as the dissociating agent has the advantages that the EDTA can dissociate target metal ions with high efficiency, and the stable coordination form of the target metal ions is maintained, so that the EDTA is convenient for subsequent recovery and treatment.

After dissociation of the target metal ions, the magnetic adsorbent is separated from the dissociation solution by application of a magnetic field. The effect of this step is to rapidly separate the adsorbent from the dissociated solution by magnetic separation means to facilitate collection of the target metal ions in the solution. The magnetic adsorbent can be rapidly aggregated when a magnetic field is applied, and EDTA-metal complexes in the dissociation solution can not be influenced by the magnetic field, so that the separation can be smoothly carried out. At this point, the EDTA dissociation solution enriched in the target metal may be further processed to recover the metal, while the magnetic adsorbent may be recovered for the next round of adsorption operation.

The invention will be further illustrated with reference to specific examples.

Example 1

(1) Pretreatment of

And (3) disassembling the waste lithium ion battery after the waste lithium ion battery is completely discharged, and separating out the positive electrode material. The positive electrode material sample was dried and then pulverized to 100 μm or less.

(2) Leaching out

The positive electrode material particles obtained by pretreatment are added into a composite solvent (the mass ratio of the positive electrode material particles to the composite solvent is 1:15), and the composite solvent is composed of citric acid (the concentration is 1 mol/L) and 2,2' -bipyridine ligand (the mol ratio of the positive electrode material particles to target metal ions is 1.3:1). The pH of the solution is adjusted to 3.5 to achieve the preferred leaching conditions for the target metal ions. After agitation leaching for 3 hours at 60 ℃, a leachate containing target metal ions is obtained by filtration, and solid residues are removed.

(3) Enriching target metal ions

Adding magnetic polymer microspheres with phosphate groups modified on the surfaces as magnetic adsorbents into the leaching solution, and adjusting the pH value of the solution to 1.5 so as to promote dissociation of metal ions complexed by the organic ligands and enhance the enrichment effect of the metal ions of the phosphate groups and the sulfonate groups. After stirring for 1h, the target metal ions in the solution are enriched on the adsorbent to obtain a mixed solution. Under stirring conditions, the target metal ions dissociate from the complex and become enriched on the phosphate and sulfonate groups on the surface of the magnetic adsorbent.

(4) Magnetic field separation

The mixed solution is placed beside an electromagnet, and the magnetic adsorbent enriched with the target metal is separated from the solution by applying a magnetic field. The adsorbent is rapidly aggregated under the action of a magnetic field to form solid-liquid separation. The supernatant was poured off, leaving the magnetic adsorbent for subsequent treatment.

(5) Dissociation and metal recovery

And washing the separated magnetic adsorbent enriched with the target metal with deionized water to remove surface impurities. The washed adsorbent is added into 0.1M EDTA solution, and the pH is adjusted to 7 so as to promote the chelating reaction of EDTA and target metal ions on the surface of the adsorbent. The multi-tooth structure of EDTA can effectively dissociate target metal ions on the surface of the adsorbent to generate stable EDTA-metal complex.

After stirring for 30min, a magnetic field was applied to separate the magnetic adsorbent from the dissociation solution. At this time, the dissociation solution contains EDTA-metal complexes enriched in the target metal ions. And collecting the dissociation solution, regulating the pH value to 1-2, and adding a sodium carbonate solution with the concentration of 6.5mol/L to precipitate nickel cobalt manganese to obtain the nickel cobalt manganese coprecipitate.

Example 2

The difference compared to example 1 is that the pH of the solution was adjusted to 5 during the leaching in this example, and the remaining steps and conditions were identical to those of example 1.

Example 3

The difference from example 1 is that the pH of the solution in the process of enriching the target metal ions in this example was adjusted to 2.7, and the remaining steps and conditions were the same as in example 1.

Example 4

The difference compared with example 1 is that the organic ligand in the complex solvent of this example is 1, 10-phenanthroline, and the rest of the steps and conditions are the same as those of example 1.

Example 5

The difference from example 1 is that the magnetic adsorbent in this example is a magnetic carbon nanotube having a phosphate group modified on the surface, and the other preparation methods and conditions are the same as those in example 1.

Example 6

The difference from example 1 is that the magnetic adsorbent in this example is a magnetic polymer microsphere having a sulfonic acid group modified on the surface, and the other preparation methods and conditions are the same as in example 1.

Comparative example 1

The difference compared to example 1 is that the pH of the solution was adjusted to 3 during the leaching of this comparative example, and the remaining steps and conditions were identical to those of example 1.

Comparative example 2

The difference compared to example 1 is that the pH of the solution was adjusted to 5.5 during the leaching of this comparative example, and the remaining steps and conditions were identical to those of example 1.

Comparative example 3

The difference compared with example 1 is that the pH value of the solution in the process of enriching the target metal ions in this comparative example is adjusted to 3, and the rest steps and conditions are the same as those in example 1.

Comparative example 4

The difference compared to example 1 is that the solvent used for leaching in this comparative example is citric acid without organic ligand, and the rest of the steps and conditions are the same as in example 1.

Comparative example 5

The difference compared to example 1 is that the organic ligand in the complex solvent used for leaching in this comparative example is replaced with pyridine, and the remaining steps and conditions are the same as in example 1.

Comparative example 6

The difference compared to example 1 is that the citric acid in the complex solvent used for leaching in this comparative example is replaced by sulfuric acid, and the rest of the steps and conditions are identical to those of example 1.

Comparative example 7

The difference compared with example 1 is that the magnetic adsorbent in this comparative example is unmodified phosphate-based and sulfonate-based magnetic polymer microsphere, and the rest of the steps and conditions are the same as those in example 1.

Recovery effect evaluation

The nickel-cobalt-manganese coprecipitates obtained by recovering examples 1 to 6 and comparative examples 1 to 7 were subjected to chemical component detection, and the recovery effects of each example and comparative example were analyzed. The results are shown in Table 1:

TABLE 1 recovery Effect detection results

In summary, the method for recycling the target metal in the lithium battery anode material provided by the invention enables target metal ions to be leached efficiently under a proper acidic condition by using a composite solvent system consisting of citric acid and organic ligands containing two nitrogen heterocycles, wherein the citric acid provides a stable acidic environment, the nitrogen heterocycles ligands enhance selective complexation of cobalt, nickel and manganese, and meanwhile, the magnetic adsorbent with phosphate groups and/or sulfonic groups modified on the surface is adopted, so that the target metal ions are enriched efficiently through pH adjustment and are separated rapidly under an external magnetic field, and the recovery rate and recovery purity of the method are high.

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned.

Furthermore, it should be understood that although the present disclosure describes embodiments, not every embodiment is provided with a separate embodiment, and that this description is provided for clarity only, and that the disclosure is not limited to the embodiments described in detail below, and that the embodiments described in the examples may be combined as appropriate to form other embodiments that will be apparent to those skilled in the art.

Claims

1. A method for recovering a target metal in a positive electrode material of a lithium battery, the target metal comprising cobalt, nickel, and manganese, the method comprising:

pretreating a lithium battery to obtain positive electrode material particles;

Adding the positive electrode material particles into a composite solvent, regulating the pH to 3.3-5, and leaching target metal ions to obtain a leaching solution, wherein the composite solvent comprises citric acid and an organic ligand containing two nitrogen heterocycles;

Adding a magnetic adsorbent into the leaching solution, and adjusting the pH to 1-2.7 to enrich target metal ions on the magnetic adsorbent to form a mixed solution, wherein the surface of the magnetic adsorbent is modified with phosphate groups and/or sulfonic acid groups;

And applying a magnetic field to the mixed solution to separate the magnetic adsorbent enriched with the target metal ions from the mixed solution.

2. The method for recovering a target metal from a positive electrode material of a lithium battery according to claim 1, wherein the pretreatment of the lithium battery comprises:

After the lithium battery is completely discharged, disassembling and separating out the anode material;

the positive electrode material is crushed and sieved to obtain positive electrode material particles with the particle diameter of less than 100 mu m.

3. The method for recovering a target metal from a positive electrode material for a lithium battery according to claim 1, wherein the mass ratio of the positive electrode material particles to the composite solvent is 1 (10-20), and/or

The concentration of the citric acid in the composite solvent is 0.5-1.5 mol/L, and/or

The molar ratio of the organic ligand to the target metal ion in the composite solvent is (1-2): 1.

4. The method for recovering a target metal in a positive electrode material of a lithium battery according to claim 1, wherein the organic ligand comprises at least one of 2,2' -bipyridine and 1, 10-phenanthroline.

5. The method for recovering a target metal from a positive electrode material of a lithium battery according to claim 1, wherein the preparation method of the composite solvent comprises the following steps:

dissolving citric acid in deionized water to obtain a citric acid solution;

dissolving an organic ligand in ethanol to obtain an organic ligand solution;

And uniformly mixing the citric acid solution and the organic ligand solution to obtain the composite solvent.

6. The method of claim 1, wherein the magnetic adsorbent comprises magnetic carbon nanotubes with cobalt and/or nickel nanoparticles attached thereto.

7. The method for recycling target metal in positive electrode material of lithium battery according to claim 6, wherein the preparation method of the magnetic carbon nanotube comprises:

Refluxing the carbon nano tube in mixed acid consisting of sulfuric acid and nitric acid for 2-6 hours, and performing acidification treatment;

dispersing the acidified carbon nano tube in cobalt and/or nickel metal salt solution, and carrying out ultrasonic treatment for 3-8 hours to obtain carbon nano tube suspension;

Adding sodium hydride into the carbon nano tube suspension under ice bath condition, stirring and reacting to reduce cobalt and/or nickel metal ions into metal nano particles, and attaching the metal nano particles on the surface of the carbon nano tube;

And centrifugally separating and collecting a product, washing and drying to obtain the magnetic carbon nano tube.

8. The method for recovering a target metal in a positive electrode material of a lithium battery according to claim 1, the magnetic adsorbent comprises magnetic polymer microspheres, wherein magnetic nanoparticles are embedded in the magnetic polymer microspheres.

9. The method for recycling a target metal in a positive electrode material of a lithium battery according to claim 8, wherein the preparation method of the magnetic polymer microsphere comprises the following steps:

dispersing the magnetic nano particles in an ethanol solution, adding polyvinyl alcohol, and performing ultrasonic dispersion for 30min to obtain a magnetic nano particle suspension;

Uniformly mixing styrene, methacrylic acid and divinylbenzene monomers according to a proportion to obtain a monomer mixed solution;

Adding the monomer mixed solution into the magnetic nanoparticle suspension, uniformly stirring, and adding an initiator;

Stirring and reacting for 6-8 hours at 65-75 ℃ in an inert protective atmosphere to polymerize styrene, methacrylic acid and divinylbenzene monomers on the surfaces of the magnetic nanoparticles;

and centrifugally separating and collecting a product, washing and drying to obtain the magnetic polymer microsphere.

10. The method of recovering a target metal in a lithium battery positive electrode material according to claim 1, further comprising:

washing the separated magnetic adsorbent enriched with target metal ions;

adding the washed magnetic adsorbent into an ethylenediamine tetraacetic acid solution to dissociate target metal ions enriched on the magnetic adsorbent, thereby obtaining a dissociated solution;

Applying a magnetic field to the dissociation solution to separate the magnetic adsorbent from the dissociation solution.