Recycling method of waste lithium ion battery

Abstract

The invention provides a waste lithium ion battery recycling method, and relates to the technical field of waste lithium ion battery recycling, and the waste lithium ion battery recycling method comprises the following steps: carrying out fused salt roasting on crushed waste lithium ion batteries to convert lithium in the waste lithium ion batteries into soluble lithium salt to obtain powder; screening the powder to obtain black powder and a high-purity copper aluminum foil product; and the black powder is subjected to size mixing through circulating water and then subjected to flotation, and tailings containing high-purity nickel-cobalt-manganese oxide, concentrate of high-purity graphite and a lithium-rich solution are obtained. According to the method, the molten salt roasting process and the flotation process are coupled, so that the recovery purity of lithium is improved, positive electrode valuable gold and graphite with high additional value are recovered, and efficient, environment-friendly and low-cost recovery of the waste lithium ion battery is realized.

Description

Technical Field

[0001] This application relates to the field of waste lithium-ion battery recycling technology, and in particular to a method for recycling waste lithium-ion batteries. Background Technology

[0002] In related technologies, in order to recover valuable metals from waste lithium-ion batteries, sulfuric acid and hydrogen peroxide are usually used to leach all metal elements from the waste lithium-ion batteries at high temperature at one time. However, this process has the problems of discarding graphite with recycling value as residue and having to use a costly and cumbersome solvent extraction process to separate the valuable metals one by one, which leads to a low recovery rate of the minimum lithium element. Summary of the Invention

[0003] The main objective of this application is to provide a method for recycling waste lithium-ion batteries, aiming to solve the technical problem that related technologies cannot recycle all valuable components in waste lithium-ion batteries in a green and low-cost manner.

[0004] To achieve the above objectives, this application proposes a method for recycling waste lithium-ion batteries, the method comprising: The crushed waste lithium-ion batteries are subjected to molten salt roasting to convert the lithium in the waste lithium-ion batteries into soluble lithium salts to obtain powder. After the powder is sieved, black powder and high-purity copper aluminum foil products are obtained. The black powder is slurried using circulating water and then subjected to flotation to obtain tailings containing high-purity nickel, cobalt, and manganese oxides, high-purity graphite concentrate, and lithium-rich solution.

[0005] In one embodiment, the step of molten salt roasting of the crushed waste lithium-ion batteries to convert the lithium in the waste lithium-ion batteries into soluble lithium salts includes: After adding sodium chloride, molten salt roasting is carried out at a temperature of 500 ℃~700 ℃ under a reducing atmosphere to convert the lithium in the waste lithium-ion battery into soluble lithium salt.

[0006] In one embodiment, the mass ratio of the waste lithium-ion battery to the sodium chloride is 1:1.5 to 1:5.

[0007] In one embodiment, before molten salt roasting at a temperature of 500°C to 700°C under a reducing atmosphere after the addition of sodium chloride, the method for recycling the waste lithium-ion batteries further includes: The crushed waste lithium-ion batteries are roasted at 300 ℃ to 500 ℃ to decompose the binder and electrolyte in the waste lithium-ion batteries.

[0008] In one embodiment, the step of using circulating water to prepare the black powder slurry followed by flotation to obtain tailings containing high-purity nickel, cobalt, and manganese oxides, graphite products, and a lithium-rich solution includes: The black powder was slurryed using circulating water to obtain a mineral slurry; Selective flocculant, collector and foaming agent are added sequentially to the slurry, and then the foam is scraped off to obtain the graphite product; After the foaming process is completed, the material is filtered. The remaining sediment is the tailings containing high-purity nickel, cobalt, and manganese oxides, and the solution obtained by filtration is the lithium-rich solution.

[0009] In one embodiment, the selective flocculant is phosphate-modified starch, and the preparation method of the phosphate-modified starch includes: Starch and phosphate are dispersed in water and the pH is adjusted to acidity to obtain a mixture; wherein the mass ratio of starch to phosphate is 10:0.5~2, and the mass ratio of starch to water is 1:2~5; The mixture was reacted at 45 °C to 65 °C; After the reaction was completed, centrifugation was performed, and the precipitate was washed and dried to obtain phosphate-modified starch.

[0010] In one embodiment, the amount of selective flocculant added is 500 g / t to 1000 g / t.

[0011] In one embodiment, the collector is kerosene or n-dodecane, and the amount of the collector added is 200 g / t to 500 g / t; The foaming agent is methyl isobutyl methanol, and the amount of foaming agent added is 200 g / t to 500 g / t.

[0012] In one embodiment, after the black powder is slurried with circulating water and then subjected to flotation to obtain tailings containing high-purity nickel, cobalt, and manganese oxides, graphite products, and a lithium-rich solution, the method for recycling waste lithium-ion batteries further includes: The lithium-rich solution is used as the circulating water to slurry the black powder; The process is repeated a target number of times until the lithium ion concentration in the lithium-rich solution obtained after flotation reaches 8 g / L to 15 g / L. Then, carbon dioxide is introduced into the lithium-rich solution for evaporation to obtain lithium carbonate precipitate and filtrate.

[0013] In one embodiment, after obtaining the lithium carbonate precipitate and filtrate, the method for recycling the waste lithium-ion batteries further includes: The filtrate was evaporated and crystallized to obtain sodium chloride; The sodium chloride is reused in the molten salt roasting process.

[0014] One or more technical solutions proposed in this application have at least the following technical effects: This application provides a method for recycling waste lithium-ion batteries. The method includes: molten salt roasting of crushed waste lithium-ion batteries to convert lithium into soluble lithium salts, yielding powder; sieving of the powder to obtain black powder and high-purity copper-aluminum foil products; and flotation of the black powder after slurry preparation with circulating water to obtain tailings containing high-purity nickel-cobalt-manganese oxides, high-purity graphite concentrate, and lithium-rich solution. The waste lithium-ion battery recycling method provided in this application first selectively converts the stable lithium in the waste lithium-ion batteries into soluble lithium chloride through molten salt roasting, achieving preferential separation and extraction of lithium. This not only improves the purity of lithium recovery but also shortens the lithium recovery process. Furthermore, by combining this with flotation, high-value-added graphite is simultaneously and efficiently recovered while recovering valuable metals from the cathode. In summary, the waste lithium-ion battery recycling method provided in this application has the advantages of being green, low-cost, having a high resource utilization rate, a short recycling process, and low pollution. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a flowchart illustrating a method for recycling waste lithium-ion batteries according to an embodiment of this application; Figure 2 This is a schematic flowchart of a method for recycling waste lithium-ion batteries according to an embodiment of this application; Figure 3 Fourier transform infrared spectra of the selective flocculants prepared in Examples 1, 2 and Comparative Example 1.

[0017] The purpose, features, and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0018] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0019] It should be noted that if the embodiments of this application involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0020] Furthermore, if the embodiments of this application involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the use of "and / or" or "and / or" throughout the text includes three parallel solutions. For example, "A and / or B" includes solution A, solution B, or a solution that simultaneously satisfies A and B. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed in this application.

[0021] In this application, when numerical intervals (i.e., numerical ranges) are involved, unless otherwise specified, the distribution of selectable numerical values ​​within the numerical interval is considered continuous, and includes the two endpoints of the numerical interval (i.e., the minimum and maximum values), as well as every numerical value between these two endpoints. Unless otherwise specified, when a numerical interval refers only to integers within that numerical interval, it includes the two endpoint integers of the numerical range, as well as every integer between the two endpoints, which is equivalent to directly listing every integer. When multiple numerical ranges are provided to describe features or characteristics, these numerical ranges can be merged. In other words, unless otherwise specified, the numerical ranges disclosed in this application should be understood to include any and all subranges included therein. The "numerical value" in the numerical interval can be any quantitative value, such as a number, percentage, ratio, etc. The term "numerical interval" can be broadly included to include percentage intervals, ratio intervals, proportion intervals, etc.

[0022] This application proposes a method for recycling waste lithium-ion batteries, such as... Figure 1 As shown, the recycling method for waste lithium-ion batteries includes steps S10 to S30: Step S10: Molten salt roasting is performed on the crushed waste lithium-ion batteries to convert the lithium in the waste lithium-ion batteries into soluble lithium salts and obtain powder.

[0023] Understandably, this embodiment uses molten salt roasting to selectively convert the lithium that is stably present in waste lithium-ion batteries into soluble lithium chloride at high temperature. Subsequently, only simple water immersion is needed to preferentially and directionally separate the lithium. This fundamentally avoids lithium getting caught in the subsequent complex separation process, and achieves preferential separation of lithium from all valuable metals, thereby greatly improving the lithium recovery rate.

[0024] In this embodiment, as Figure 2 As shown, crushing is to prevent the electrolyte in waste lithium-ion batteries from leaking, evaporating, or deteriorating. Specifically, the crushing process can be as follows: waste lithium-ion batteries are fed into the crushing device via a belt. In a sealed oxygen-controlled environment filled with inert gas, the waste lithium-ion batteries are crushed while charged to effectively separate their casing, positive and negative electrode plates, and terminal blocks.

[0025] In one embodiment, the crushed waste lithium-ion batteries are subjected to molten salt roasting to convert the lithium in the waste lithium-ion batteries into soluble lithium salts. This includes adding sodium chloride and then performing molten salt roasting at a temperature of 500 ℃ to 700 ℃ under a reducing atmosphere to convert the lithium in the waste lithium-ion batteries into soluble lithium salts.

[0026] In this embodiment, sodium chloride is added during roasting to achieve molten salt roasting. During this process, the sodium chloride melts at high temperature, creating an active chloride ion environment. Under this active chloride ion environment and a reducing atmosphere, lithium stably present in the cathode material of waste lithium-ion batteries can be reduced to water-soluble lithium chloride, achieving efficient and preferential separation and extraction of lithium, thus avoiding the loss of even a minimal amount of lithium in subsequent processing. Furthermore, during molten salt roasting, other valuable metals are converted into water-insoluble oxides in the active chloride ion environment. These oxides enhance the flotation effect, enabling better suppression effects when using the selective flocculant provided in this embodiment. These other valuable metals include lithium, nickel, cobalt, manganese, copper, and aluminum.

[0027] To effectively convert lithium in spent lithium-ion batteries into soluble lithium salts, the preferred molten salt roasting temperature is 600℃~700℃. It should also be noted that if the molten salt roasting temperature in this embodiment is below 500℃, the stable lithium in the spent lithium-ion batteries will not be able to be converted into soluble lithium salts.

[0028] The reducing atmosphere can be nitrogen, argon, an argon-hydrogen mixture, or a mixture of hydrogen and an inert gas. Furthermore, in this embodiment, lithium in the waste lithium-ion batteries needs to be reduced to water-soluble lithium chloride. Therefore, oxygen is required during the molten salt roasting process; that is, the reducing atmosphere also includes oxygen, with an oxygen content of 2% to 5%.

[0029] Since a subsequent flotation process is required to recover all valuable components, this embodiment uses sodium chloride for molten salt roasting instead of calcium chloride, zinc chloride, copper chloride, barium chloride, or potassium chloride to avoid affecting the recovery effect of the subsequent flotation. For example, if calcium chloride is used, it will precipitate with water in the lithium-rich solution, thus preventing the direct acquisition of high-purity lithium carbonate precipitate. All valuable components include high-purity nickel-cobalt-manganese oxides, high-purity graphite, and elemental lithium.

[0030] In this embodiment, the molten salt roasting time is 1 h to 2 h.

[0031] In one embodiment, the mass ratio of waste lithium-ion batteries to sodium chloride is 1:1.5 to 1:5.

[0032] In this embodiment, if the mass ratio of sodium chloride is greater than 5, it will result in the inability to achieve uniform molten salt roasting, which will lead to incomplete selective conversion of lithium that is stable in waste lithium-ion batteries, and thus greatly reduce the lithium recovery rate.

[0033] To avoid the complex components such as binders and electrolytes in waste lithium-ion batteries affecting preferential lithium extraction and ultimately leading to low lithium recovery rates, in one embodiment, before molten salt roasting at 500 ℃~700 ℃ under a reducing atmosphere after adding sodium chloride, the waste lithium-ion battery recycling method further includes roasting the crushed waste lithium-ion batteries at 300 ℃~500 ℃ to decompose the binders and electrolytes in the waste lithium-ion batteries.

[0034] In this embodiment, roasting at 300℃~500℃ decomposes the binder and electrolyte of the waste lithium-ion battery, removing them from the battery materials and exposing the intrinsic surface properties of the ternary cathode material and the graphite anode material, thus improving the subsequent flotation effect. Simultaneously, it carbonizes the separator in the waste lithium-ion battery and burns the current collector into particles, separating the active material from the current collector. Therefore, subsequent step S20 only requires sieving to separate the two. It should be noted that if undecomposed binder and electrolyte remain after roasting, further decomposition can be achieved through molten salt roasting at higher temperatures.

[0035] Specifically, the calcination time is 1 hour. The powder obtained by calcination and molten salt calcination is a mixture of active material and current collector. The current collector is copper foil and aluminum foil. The active material includes negative electrode graphite material and positive electrode ternary material.

[0036] In one embodiment, the equipment used for molten salt roasting and roasting to decompose the binder and electrolyte can be a baking oven, and further, the baking oven is a multi-stage split heating oven.

[0037] In step S20, after the powder is sieved, black powder and high-purity copper aluminum foil products are obtained.

[0038] In one example, a linear sieve can be used to separate the black powder from the high-purity copper aluminum foil product.

[0039] Specifically, after the powder is cooled to 30℃~60℃, it is conveyed through a closed system to a linear sieve (100 mesh) for sieving. The undersize product is black powder, and the oversize product is high-purity copper-aluminum foil with a mesh size greater than 100. To further separate the copper and aluminum foils, the resulting high-purity copper-aluminum foil is subjected to gravity separation, yielding high-purity copper foil and high-purity aluminum foil. In one example, the gravity separation equipment can be a gravity separator.

[0040] In one embodiment, dust and volatile gases generated during crushing, roasting, molten salt roasting, sieving, and gravity separation are collected and introduced into a tail gas treatment system, where they are purified to ensure compliance with emission standards before being discharged. Among these volatile gases is fluorine gas generated from the decomposition of the electrolyte.

[0041] In step S30, the black powder is slurried with circulating water and then floated to obtain tailings containing high-purity nickel, cobalt and manganese oxides, high-purity graphite concentrate and lithium-rich solution.

[0042] In this embodiment, by coupling molten salt roasting and flotation, the flotation process can be greatly reduced, thereby lowering the equipment investment and operating costs of flotation, so as to achieve green and low-cost recycling.

[0043] The waste lithium-ion battery recycling method provided in this embodiment first uses molten salt roasting to selectively convert the stable lithium in the waste lithium-ion batteries into soluble lithium chloride, achieving preferential separation and extraction of lithium. This not only improves the purity of the recovered lithium but also shortens the lithium recycling process. Then, by combining this with a flotation process, valuable metals such as nickel, cobalt, and manganese from the cathode are recovered simultaneously and efficiently, along with high-value-added graphite. In summary, the waste lithium-ion battery recycling method provided in this application has the advantages of being green, low-cost, having a high resource utilization rate, a short recycling process, and low pollution.

[0044] In one embodiment, step S30 includes steps S31 to S33: Step S31: Use circulating water to adjust the black powder into a slurry to obtain a mineral slurry.

[0045] In this embodiment, after the black powder is slurry prepared, the mass concentration of the slurry is 5% to 15% to facilitate subsequent flotation.

[0046] In one embodiment, after step S31 and before step S32, the method for recycling waste lithium-ion batteries further includes: adjusting the pH of the slurry to obtain a slurry with a pH of 7 to 10.

[0047] In this embodiment, the slurry pH is adjusted to alkaline to provide the necessary conditions for the selective flocculant to flocculate. Furthermore, after adjusting the slurry pH, it is stirred for 5 to 10 minutes to ensure that lithium chloride is fully dissolved in the slurry, preventing lithium from being carried over to the sediment and thus reducing the lithium recovery rate. After stirring for 5 to 10 minutes, 99.4% or more of the lithium chloride dissolves in the slurry, meaning the lithium leaching rate can reach 99.4% or more.

[0048] In this embodiment, since lithium is preferentially extracted and selectively converted into soluble lithium salts before this step, the soluble lithium chloride can be completely dissolved in water during the stirring process. That is, lithium can be preferentially and directionally separated by simple water immersion. The water separated from the slurry will not affect the lithium recovery rate in subsequent flotation and other processes. Finally, the lithium-rich solution can be obtained by filtration in step S33.

[0049] Step S32: Selective flocculant, collector and foaming agent are added to the slurry in sequence, and then the foam is scraped to obtain graphite product.

[0050] In this embodiment, a selective flocculant is first added to the slurry and stirred for 2-4 minutes. Then, a collector is added and stirred for 2-4 minutes, followed by the addition of a frother and stirring for another 2-4 minutes. The mixture is then skimmed to obtain the graphite product. It should also be noted that the three agents must be added in a specific order. If the selective flocculant, collector, and frother are added simultaneously, effective separation of nickel-cobalt-manganese oxides and graphite cannot be achieved.

[0051] The following examples provide two selective flocculants obtained using specific preparation methods. In one embodiment, the selective flocculant is phosphate-modified starch, and the preparation method of phosphate-modified starch includes: Starch and phosphate were dispersed in water and the pH was adjusted to acidic to obtain a mixture. The mass ratio of starch to phosphate was 10:0.5~2, and the mass ratio of starch to water was 1:2~5. The mixture was reacted at 45 ℃~65 ℃. After the reaction was completed, the mixture was centrifuged, and the precipitate was washed and dried to obtain phosphate-modified starch.

[0052] Specifically, the pH of the mixture is 4-6, the reaction time of the mixture is 3-5 h at 45 ℃-65 ℃, the cleaning solvent is 75%-90% ethanol solution, and the drying can be carried out by vacuum drying at 40 ℃-60 ℃.

[0053] The phosphate-modified starch provided in this embodiment is prepared using the specific preparation method described above. Specifically, the selective flocculant obtained using this preparation method is added to the slurry and stirred for 2 to 4 minutes. During this stirring process, the selective flocculant utilizes the strong metal chelating effect of its phosphate groups to adsorb onto the surface of nickel-cobalt-manganese oxides in the black powder (i.e., a mixture of nickel-cobalt-manganese oxides and graphite). The phosphate groups form stable coordination bonds with the transition metal ions dissolved from the surface of the nickel-cobalt-manganese oxides, thereby achieving the specific capture of the ternary cathode material in the black powder. Subsequently, at a specific slurry pH (7 to 10), the specifically captured ternary cathode material separates from the black powder, resulting in selective flocculation and sedimentation of the ternary cathode material. This achieves efficient separation of the ternary cathode material and graphite from the black powder, thereby not only improving the recovery rate of nickel-cobalt-manganese oxides but also increasing the purity of graphite.

[0054] In another embodiment, the selective flocculant is phosphate-carboxymethyl dual-modified starch. The preparation method of phosphate-carboxymethyl dual-modified starch includes: dispersing starch and phosphate in water and adjusting the pH to acidic to obtain a mixture; wherein the mass ratio of starch to phosphate is 10:0.5~2, and the mass ratio of starch to water is 1:2~5; reacting the mixture at 45 ℃~65 ℃; after the reaction is completed, centrifuging is performed, and the precipitate is taken, washed, and dried to obtain phosphate-modified starch; mixing phosphate-modified starch with ethanol, adding a solvent containing sodium hydroxide for activation, then adding chloroacetic acid and reacting at 40 ℃~60 ℃; after the reaction is completed, taking the precipitate, washing, and drying to obtain phosphate-carboxymethyl dual-modified starch.

[0055] Specifically, the pH of the mixture is 4-6, the reaction time of the mixture is 3-5 h at 45 ℃-65 ℃, the cleaning solvent is 75%-90% ethanol solution, and the drying can be carried out by vacuum drying at 40 ℃-60 ℃.

[0056] The mass ratio of phosphate-modified starch to chloroacetic acid is 1:0.3~1, and the acid-base ratio of chloroacetic acid to sodium hydroxide is 1:1.5~2.5. The activation temperature is 40 ℃~55 ℃, the activation time is 0.5 h~2 h, and the solvent used for sodium hydroxide is a 75%~90% ethanol solution. After adding chloroacetic acid, the reaction time is 3 h~5 h at 40 ℃~60 ℃. The solvent used for washing is a 75%~90% ethanol solution, and drying can be carried out by vacuum drying at a temperature of 40 ℃~60 ℃.

[0057] The phosphate-carboxymethyl dual-modified starch provided in this embodiment is prepared by the specific preparation method described above. When the selective flocculant obtained by this preparation method is added to the slurry and stirred for 2-4 minutes, the synergistic effect of its bifunctional groups allows the positive electrode ternary material (particulate) in the black powder (i.e., the positive and negative electrode mixture) to be selectively flocculated, thereby achieving efficient separation of the positive electrode ternary material and graphite from the black powder.

[0058] It should be noted that the bifunctional groups refer to phosphate groups and carboxymethyl groups. The synergistic effect of the bifunctional groups means that the selective flocculant uses the strong metal chelating effect of its phosphate groups to adsorb onto the surface of the ternary cathode material in the black powder (i.e., the mixture of positive and negative electrodes). On the one hand, the phosphate groups form stable coordination bonds with the transition metal ions dissolved from the surface of the cathode material, thereby achieving the specific capture of the ternary cathode material in the black powder. On the other hand, the ionization of the carboxymethyl groups on the surface of the cathode material in the black powder generates a negative charge, and then the carboxymethyl groups form a negatively charged interface layer on the surface of the ternary cathode material (particulate), thereby enhancing the electrostatic repulsion between the ternary cathode material and graphite, effectively overcoming the hydrophobic flocculation tendency of graphite, realizing the dispersion of the graphite negative electrode material, and thus avoiding the mechanical entrainment of the ternary cathode material when the graphite negative electrode material floats.

[0059] The synergistic adsorption performance of the bifunctional groups was further optimized at a specific slurry pH (pH 7-10). Specifically, at the specific slurry pH, the specifically captured cathode material was separated from the waste lithium battery black powder, resulting in selective flocculation and sedimentation of the cathode material. The dispersed graphite particles were then floated to the surface by bubble flotation, thereby achieving efficient separation of the cathode material and the graphite anode material from the waste lithium battery black powder.

[0060] In one embodiment, the amount of selective flocculant added is 500 g / t to 1000 g / t. Specifically, 500 g / t to 1000 g / t means adding 500 g to 1000 g of selective flocculant per ton of black powder.

[0061] In one embodiment, the collector is kerosene or n-dodecane, and the amount of collector added is 200 g / t to 500 g / t.

[0062] Specifically, after adding a selective flocculant to the slurry and stirring for 2 to 4 minutes, a collector is added and stirred for another 2 to 4 minutes. During the 2 to 4 minutes of stirring, the collector is adsorbed onto the surface of the dispersed graphite to further enhance the hydrophobicity of the graphite, thereby better separating the graphite from nickel, cobalt, and manganese oxides and improving the recovery rate and purity of the graphite.

[0063] In one embodiment, the foaming agent is methyl isobutyl methanol, and the amount of foaming agent added is 200 g / t to 500 g / t.

[0064] Specifically, after adding the foaming agent, the mixture is stirred for 2 to 4 minutes. During this stirring process, because the phosphate-carboxymethyl dual-modified starch had already been added before stirring to selectively flocculate the nickel, cobalt, and manganese oxides in the black powder (positive and negative electrode mixture), and the subsequently added collector specifically and selectively adsorbs onto the graphite surface to significantly enhance the hydrophobicity of the dispersed graphite, the foaming agent generates bubbles during this stirring process. The high-purity graphite, whose hydrophobicity has been effectively enhanced, floats to the surface attached to these bubbles, thereby achieving effective separation of high-purity nickel, cobalt, and manganese oxides and high-purity graphite.

[0065] Step S33: After the bubble is scraped off, the material is filtered. The remaining sediment is tailings containing high-purity nickel, cobalt and manganese oxides. The solution obtained by filtration is a lithium-rich solution.

[0066] Specifically, the scraping time is 3 to 5 minutes.

[0067] Because this embodiment uses a selective flocculant with monofunctional or difunctional groups, high-purity graphite, high-purity nickel-cobalt-manganese oxides, and lithium-rich solutions can be obtained in a single flotation step. Furthermore, since lithium extraction is preferentially achieved in step S10, a significant number of flotation processes are reduced, lowering equipment investment and operating costs. In summary, this embodiment, by coupling molten salt roasting and flotation, greatly reduces the flotation process, lowers equipment investment and operating costs, and achieves green, low-cost recycling.

[0068] It should also be noted that this single-stage flotation refers to a process that does not require further slurry preparation and flotation reagent addition for further flotation, or that does not require the three complex processes of roughing, scavenging, and cleaning, which are difficult to operate and control and have high operating costs.

[0069] To reduce energy consumption, in one embodiment, after using circulating water to slurry the black powder and then performing flotation to obtain tailings containing high-purity nickel, cobalt, and manganese oxides, graphite products, and a lithium-rich solution, the method for recycling waste lithium-ion batteries further includes: using the lithium-rich solution as circulating water to slurry the black powder; circulating a target number of times until the lithium-ion concentration in the lithium-rich solution obtained after flotation is enriched to 8 g / L~15 g / L, then introducing carbon dioxide into the lithium-rich solution for evaporation to obtain lithium carbonate precipitate and filtrate.

[0070] Specifically, in the initial flotation, the circulating water can be water. In subsequent flotation cycles, the circulating water is a lithium-rich solution. The target number of cycles can be 20 to 40. That is, when the lithium-rich solution is returned as circulating water to prepare the pulp with black powder about 20 to 40 times, the lithium ion concentration in the lithium-rich solution is enriched to 8 g / L to 15 g / L, and lithium products can be recovered. The recovery process includes: evaporating carbon dioxide into the lithium-rich solution to concentrate it to 30%-50% of the original volume, obtaining lithium carbonate precipitate, washing the lithium carbonate precipitate with pure water 2 to 4 times, and finally obtaining the lithium carbonate precipitate product. All the solutions obtained from washing are used as filtrate.

[0071] It should be noted that if the lithium-rich solution is not circulated and is directly evaporated and crystallized to obtain lithium carbonate precipitate, the evaporation and crystallization time is longer due to the high water content in the uncirculated lithium-rich solution, resulting in a more energy-intensive evaporation and crystallization process.

[0072] To further achieve green and economical results, in one embodiment, when the sodium ion concentration in the recycled filtrate is greater than or equal to 100 g / L, after obtaining the lithium carbonate precipitate and the filtrate, the recycling method for waste lithium-ion batteries further includes: evaporating and crystallizing the filtrate to obtain sodium chloride; and reusing the sodium chloride in the molten salt roasting process.

[0073] The waste lithium-ion battery recycling method provided in this embodiment, through the coupling of molten salt roasting for preferential lithium extraction and flotation, ultimately yields five high-value-added products: high-purity copper foil, high-purity aluminum foil, high-purity graphite products, tailings containing high-purity nickel-cobalt-manganese oxides, and lithium carbonate precipitate. This achieves efficient, green, and high-value recycling of five major products: lithium, graphite, nickel-cobalt-manganese oxides, copper, and aluminum. Furthermore, the recycling of lithium-rich solutions and the reuse of sodium chloride create a complete closed-loop process, making the waste lithium-ion battery recycling method provided in this embodiment even greener and lower in cost.

[0074] The technical features of the technical solution provided in this application will be described more clearly and completely below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application. Where specific technologies or conditions are not specified in the embodiments, they shall be performed in accordance with the technologies or conditions described in the literature in the art or in accordance with the product instructions. Reagents or instruments used without specified manufacturers are all conventional products that can be obtained commercially.

[0075] Example 1 The crushed waste lithium-ion batteries are roasted at 500 °C to decompose the binder and electrolyte in the waste lithium-ion batteries. Then, sodium chloride is added (the mass ratio of waste lithium-ion batteries to sodium chloride is 1:4), and molten salt roasting is carried out at 700 °C under a reducing atmosphere to convert the lithium in the waste lithium-ion batteries into soluble lithium salts. After the molten salt roasting is completed, powder is obtained.

[0076] After the powder is cooled to 60 ℃, it is conveyed through a closed system to a linear sieve (100 mesh) for sieving. The product under the sieve is black powder, and the product over the sieve is high-purity copper and aluminum foil with a mesh size greater than 100. In order to further separate the copper foil and aluminum foil, the obtained high-purity copper and aluminum foil products are subjected to gravity separation. After separation, high-purity copper foil and high-purity aluminum foil can be obtained.

[0077] After mixing the black powder with circulating water, the slurry concentration was adjusted to 5%, and the pH was adjusted to 8.5. The slurry was stirred for 5 minutes to ensure that lithium chloride was fully dissolved in the water, achieving a lithium leaching rate of 99.4%. After stirring, the slurry was added to the flotation cell of the flotation machine. The stirring speed was 1800 rpm, and the aeration rate for flotation was 0.2 m³ / s. 3 / (min·m 2 Then, phosphate-carboxymethyl double-modified starch (PS-CMS), kerosene, and methyl isobutyl methanol are added in sequence. The flotation machine is started to stir the slurry and skim off the bubbles. The dosages of phosphate-carboxymethyl double-modified starch (PS-CMS), kerosene, and methyl isobutyl methanol are 1000 g / t, 300 g / t, and 200 g / t, respectively.

[0078] The preparation method of phosphate-carboxymethyl double-modified starch includes: 50 g of corn starch and 5 g of sodium tripolyphosphate were mixed and dispersed in 150 mL of water. The pH was adjusted to 5 with 5% phosphoric acid, and the mixture was reacted in a 60 °C water bath for 3 h to obtain a mixed solution. The mixture was centrifuged to collect the precipitate, which was washed at least three times with deionized water and ethanol, and then dried in a vacuum oven at 40 °C for 48 h to obtain phosphorylated starch. 10 g of phosphorylated starch was mixed with 10 mL of ethanol and added to 40 mL of 85% ethanol solution containing 4.76 g of sodium hydroxide. The mixture was activated in a 40 °C water bath for 0.5 h, and then 5 g of chloroacetic acid was added. The reaction was continued at 45 °C for 3 h. The mixture was centrifuged to collect the precipitate, which was washed at least three times with 85% ethanol, and then dried in a vacuum oven at 40 °C for 48 h to obtain phosphate-carboxymethyl bis-modified starch (PS-CMS).

[0079] The concentrate obtained by flotation is high-purity graphite, and the tailings product is tailings containing high-purity nickel, cobalt and manganese oxides. The solution obtained by filtration is a lithium-rich solution. The grade of the tailings containing high-purity nickel, cobalt and manganese oxides is 95.74%, and the recovery rate is 97.27%; the grade of high-purity graphite is 97.86%, and the recovery rate is 98.76%.

[0080] When the lithium-rich solution is returned as circulating water to prepare slurry with black powder 20 times, the lithium ion concentration in the lithium-rich solution is enriched to 8 g / L. At this point, lithium products are recovered. Carbon dioxide is introduced into the lithium-rich solution to evaporate it and concentrate it to 40% of the original volume, resulting in lithium carbonate precipitate. The lithium carbonate precipitate is washed with pure water 2-4 times to finally obtain the lithium carbonate precipitate product. All the solutions obtained from washing are used as filtrate. The filtrate is evaporated and crystallized to obtain sodium chloride, which can be reused in the molten salt roasting process.

[0081] Example 2 The difference between this embodiment and Embodiment 1 is that the selective flocculant is changed from phosphate-carboxymethyl double-modified starch (PS-CMS) to phosphate-modified starch (PS).

[0082] Methods for preparing phosphate-modified starch (PS) include: 50 g of corn starch and 5 g of sodium tripolyphosphate were mixed and dispersed in 150 mL of water. The pH was adjusted to 5 with 5% phosphoric acid and reacted in a water bath at 60 °C for 3 h. The mixture was centrifuged to collect the precipitate. The precipitate was washed with deionized water and ethanol at least 3 times and then dried in a vacuum oven at 40 °C for 48 h to obtain phosphate-modified starch (PS).

[0083] After mixing the black powder with circulating water, the pulp concentration was adjusted to 5%, and the pH was adjusted to 8.5. The pulp was stirred for 5 minutes and then added to the flotation cell of the flotation machine. The stirring speed was 1800 rpm, and the aeration rate for flotation was 0.2 m³ / min. 3 / (min·m 2 Then, phosphate-modified starch (PS), n-dodecane, and methyl isobutyl methanol are added in sequence. The flotation machine is started to stir the slurry and skim off the bubbles. The dosages of phosphate-modified starch (PS), n-dodecane, and methyl isobutyl methanol are 1000 g / t, 300 g / t, and 200 g / t, respectively.

[0084] The concentrate obtained by flotation is high-purity graphite, and the tailings product is tailings containing high-purity nickel, cobalt and manganese oxides. The solution obtained by filtration is a lithium-rich solution. The grade of the tailings containing high-purity nickel, cobalt and manganese oxides is 81.05%, and the recovery rate is 79.32%; the grade of high-purity graphite is 76.88%, and the recovery rate is 65.44%.

[0085] Comparative Example 1 The only difference from Example 1 is that the selective flocculant was replaced with corn starch (a soluble starch). The final tailings containing high-purity nickel, cobalt and manganese oxides had a grade of 62.37% and a recovery rate of 58.45%; the high-purity graphite had a grade of 78.21% and a recovery rate of 76.89%.

[0086] The Fourier transform infrared spectra of the selective flocculants prepared in Examples 1, 2, and Comparative Example 1 are shown below. Figure 3 As shown in the figure, the 3000~4000cm -1 The broad peak at 2930 cm⁻¹ is the -OH stretching vibration peak. -1 The peak of the stretching vibration of CH is 1650 cm⁻¹. -1 The nearby peaks are formed by intramolecular hydrogen bonds; for phosphate groups, υPO is at 1150–1185 cm⁻¹. -1 Between; in the Ph-CMS infrared spectrum at 1600 cm⁻¹ -1 A strong absorption peak for the asymmetric stretching vibration of carboxylate -COO- appeared at 1432 cm⁻¹. -1 A weak absorption peak of symmetric stretching vibration of carboxylate -COO- appeared at the position.

[0087] As can be seen from Example 2, the selective flocculant used in the flotation method provided in Example 2 has a certain positive electrode capture ability, but the negative electrode graphite material is severely entrained, resulting in a significant decrease in its recovery rate to 65.44% and a grade of only 77.88%. Compared with Example 2, the dual-modified starch used in Example 1 exhibits excellent selective capture ability of metal ions, and the synergistic effect of bifunctional groups under weakly alkaline conditions, specifically, the specific recognition of transition metals by phosphate groups and the selective modification of graphite surface by carboxymethyl groups, ultimately resulted in a recovery rate of 97.27% for the positive electrode ternary material and a grade of 95.72%. In contrast, the unmodified corn starch in Comparative Example 3 performed the worst, with the recovery rate and grade of both the positive electrode ternary material and the negative electrode graphite material being only between 60% and 80%, reflecting that the separation process lacks selectivity and is difficult to achieve effective separation under the condition of no specific functional groups.

[0088] The above description is only a part of the embodiments of this application and does not limit the scope of protection of this application. All equivalent structural transformations made under the technical concept of this application and using the content of this application specification and drawings, or direct / indirect applications in other related technical fields, are included in the scope of protection of this application.

Claims

1. A method for recycling waste lithium-ion batteries, characterized in that, The recycling method for the waste lithium-ion batteries includes: The crushed waste lithium-ion batteries are subjected to molten salt roasting to convert the lithium in the waste lithium-ion batteries into soluble lithium salts to obtain powder. After the powder is sieved, black powder and high-purity copper aluminum foil products are obtained. The black powder is slurried using circulating water and then subjected to flotation to obtain tailings containing high-purity nickel, cobalt, and manganese oxides, high-purity graphite concentrate, and lithium-rich solution.

2. The method for recycling waste lithium-ion batteries as described in claim 1, characterized in that, The step of molten salt roasting of the crushed waste lithium-ion batteries to convert the lithium in the waste lithium-ion batteries into soluble lithium salts includes: After adding sodium chloride, molten salt roasting is carried out at a temperature of 500 ℃~700 ℃ under a reducing atmosphere to convert the lithium in the waste lithium-ion battery into soluble lithium salt.

3. The method for recycling waste lithium-ion batteries as described in claim 2, characterized in that, The mass ratio of the waste lithium-ion battery to the sodium chloride is 1:1.5 to 1:

5.

4. The method for recycling waste lithium-ion batteries as described in claim 2, characterized in that, Before molten salt roasting at 500℃~700℃ under a reducing atmosphere after adding sodium chloride, the recycling method for waste lithium-ion batteries further includes: The crushed waste lithium-ion batteries are roasted at 300 ℃ to 500 ℃ to decompose the binder and electrolyte in the waste lithium-ion batteries.

5. The method for recycling waste lithium-ion batteries as described in claim 1, characterized in that, The process involves using circulating water to prepare the black powder slurry, followed by flotation to obtain tailings containing high-purity nickel, cobalt, and manganese oxides, graphite products, and a lithium-rich solution, including: The black powder was slurryed using circulating water to obtain a mineral slurry; Selective flocculant, collector and foaming agent are added sequentially to the slurry, and then the foam is scraped off to obtain the graphite product; After the foaming process is completed, the material is filtered. The remaining sediment is the tailings containing high-purity nickel, cobalt, and manganese oxides, and the solution obtained by filtration is the lithium-rich solution.

6. The method for recycling waste lithium-ion batteries as described in claim 5, characterized in that, The selective flocculant is phosphate-modified starch, and the preparation method of the phosphate-modified starch includes: Starch and phosphate are dispersed in water and the pH is adjusted to acidity to obtain a mixture; wherein the mass ratio of starch to phosphate is 10:0.5~2, and the mass ratio of starch to water is 1:2~5; The mixture was reacted at 45 °C to 65 °C; After the reaction was completed, centrifugation was performed, and the precipitate was washed and dried to obtain phosphate-modified starch.

7. The method for recycling waste lithium-ion batteries as described in claim 5 or 6, characterized in that, The amount of selective flocculant added is 500 g / t to 1000 g / t.

8. The method for recycling waste lithium-ion batteries as described in claim 5, characterized in that, The collector is kerosene or n-dodecane, and the amount of the collector added is 200 g / t to 500 g / t. The foaming agent is methyl isobutyl methanol, and the amount of foaming agent added is 200 g / t to 500 g / t.

9. The method for recycling waste lithium-ion batteries as described in claim 1 or 5, characterized in that, The method for recycling waste lithium-ion batteries further includes the following steps: After using circulating water to prepare the black powder slurry and then performing flotation to obtain tailings containing high-purity nickel, cobalt, and manganese oxides, graphite products, and a lithium-rich solution. The lithium-rich solution is used as the circulating water to slurry the black powder; The process is repeated a target number of times until the lithium ion concentration in the lithium-rich solution obtained after flotation reaches 8 g / L to 15 g / L. Then, carbon dioxide is introduced into the lithium-rich solution for evaporation to obtain lithium carbonate precipitate and filtrate.

10. The method for recycling waste lithium-ion batteries as described in claim 9, characterized in that, After obtaining the lithium carbonate precipitate and filtrate, the method for recycling waste lithium-ion batteries further includes: The filtrate was evaporated and crystallized to obtain sodium chloride; The sodium chloride is reused in the molten salt roasting process.

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