A graphite recovery method based on leached residue from waste lithium batteries

Abstract

The present invention belongs to the technical field of lithium battery resource recovery, and in particular, relates to a graphite recovery method based on waste lithium battery leaching residue. The present invention provides a graphite recovery method based on waste lithium battery leaching residue, comprising the following steps: pre-treating the lithium battery to obtain an electrolyte; subjecting the electrolyte to a first hydrolysis reaction, mixing the leaching residue containing graphite with the solution after the first hydrolysis reaction, and then removing impurities to obtain a mixed slurry; subjecting the mixed slurry to a second hydrolysis reaction, and subjecting the mixed slurry after the second hydrolysis reaction to flotation treatment to obtain a flotation product and a first residual solution; and post-treating the flotation product to obtain graphite. Through the graphite recovery method provided by the present invention, the electrolyte of waste lithium batteries can be recycled and reused for the recovery of graphite in the leaching residue, effectively solving the problems of difficulty in recovering electrolyte and graphite, complex process and high cost, low purity of the recovered graphite and failure to meet the grade of raw materials for battery production.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium battery resource recovery, and in particular relates to a graphite recovery method based on leached residues of waste lithium batteries. Background Art

[0002] With the development of the new energy industry, the technology in the field of battery recycling has been continuously updated. In the field of battery recycling technology, traditional technology mainly uses hydrometallurgical processes, focusing on the recovery of high-value metals such as nickel, cobalt, manganese, and lithium.

[0003] The electrolyte produced during battery recycling is usually treated by direct incineration or collected by evaporation and condensation because it is rich in organic solvents, has a complex recycling process, is difficult to recycle and has low recycling profits. The collected electrolyte contains a variety of cyclic carbonates and chain carbonates with complex components and is difficult to separate from each other. It requires high-temperature cracking treatment, which will cause a lot of energy consumption and greatly increase the processing cost.

[0004] In the traditional recycling process, the negative electrode graphite produced in battery recycling often crushes the positive electrode and the negative electrode together; the positive electrode powder, negative electrode powder, copper foil or aluminum foil fragments are mixed into battery powder. After the leaching treatment, the metal substances in the leached slag are dissolved by acid, but the graphite in the leached slag cannot be dissolved by acid, so the recovery rate is low. In addition, the graphite used for battery production is flake graphite, and the graphite obtained by this method cannot meet the graphite raw material grade for battery manufacturing. At the same time, the leached slag contains a large amount of impurities and cannot be directly recycled and applied to battery production. It can only be landfilled or used as a reducing agent in the blast furnace of the smelter, which cannot give full play to the value of the negative electrode graphite itself in the leached slag.

[0005] Finding a suitable recycling process for graphite and electrolyte in waste lithium batteries will create additional economic value. The recycling process of waste lithium batteries in the existing technology has the following problems:

[0006] 1. The recycling process of electrolyte is complicated and costly, and the reuse of electrolyte in the recycling process of waste lithium batteries has not been explored;

[0007] 2. The graphite recovered from the leaching residue contains more metal impurities, which makes the recovery difficult and the recovery rate low. In addition, the recovered graphite cannot meet the raw material grade required for battery manufacturing.

[0008] In view of the above, a new recycling method is urgently needed to treat waste lithium batteries in order to recycle the electrolyte and recover the graphite. Summary of the invention

[0009] The present invention aims at solving the problems existing in the prior art and provides a method for recovering graphite based on leaching residue of waste lithium batteries, aiming to solve the problems in the prior art that the electrolyte recovery process is complicated and costly, the reuse of the electrolyte recovery process has not been explored, and the graphite recovered from the leaching residue contains more metal impurities, resulting in difficulty in graphite recovery, low recovery rate, and the recovered graphite cannot meet the raw material grade required for battery manufacturing.

[0010] The present invention provides a graphite recovery method based on waste lithium battery leaching residue, comprising the following steps:

[0011] S1, pre-treating the lithium battery to obtain an electrolyte;

[0012] S2, subjecting the electrolyte to a first hydrolysis reaction, mixing the leached residue containing graphite with the solution after the first hydrolysis reaction, and then performing an impurity removal treatment to obtain a mixed slurry;

[0013] S3, performing a second hydrolysis reaction on the mixed slurry, and performing flotation treatment on the mixed slurry after the second hydrolysis reaction to obtain a flotation product and a first residual solution;

[0014] S4. Post-processing the flotation product to obtain graphite.

[0015] In the optional scheme of the present application, by designing a graphite recovery method, the electrolyte is subjected to a first hydrolysis reaction, so that the lithium hexafluorophosphate in the electrolyte is hydrolyzed to generate hydrofluoric acid and lithium fluoride salt; the graphite-containing leaching residue is mixed with the solution after the first hydrolysis reaction and then subjected to impurity removal treatment, and the residual metal impurities in the leaching residue of the waste lithium battery can be removed by utilizing the corrosiveness of the fluorine-containing solution to the metal, and then the calcium powder and fluoride ions are used to generate calcium fluoride precipitation to remove the fluoride ions to obtain a mixed slurry, thereby solving the problem that the leaching residue contains more metal impurities and is not conducive to graphite recovery.

[0016] Furthermore, by subjecting the mixed slurry to a second hydrolysis reaction, cyclic carbonates such as ethylene carbonate and propylene carbonate in the mixed slurry are further hydrolyzed into diols and polyglycols. Such alcohol substances containing hydrophilic groups and hydrophobic groups can be used as frothers for graphite flotation. At the same time, the chain carbonates in the mixed slurry after the second hydrolysis reaction are non-polar collectors and can be used as collectors for graphite flotation to enhance the hydrophobicity of graphite particles. By subjecting the mixed slurry after the second hydrolysis reaction to flotation treatment, the diols, Polyglycol and chain carbonate are recycled and reused as frothers and collectors in flotation treatment. Flotation treatment obtains flotation products and a first residual solution, and a recovery rate of more than 98% of flotation products can be achieved. Graphite can be obtained by post-processing the flotation products. The obtained graphite product can retain a fine flaky morphology structure, and the graphite recovery rate can reach more than 85%, and the recovered graphite metal residue is below the ppm level. At the same time, the first residual solution can be recycled and used as a supplementary aqueous solution in the aforementioned hydrolysis reactions or flotation treatments to reduce waste liquid discharge and reduce costs.

[0017] In the preferred scheme of the present application, a second hydrolysis reaction is performed on the mixed slurry, and an adjusting agent is added to the mixed slurry after the second hydrolysis reaction for flotation treatment, which specifically includes: firstly adding a catalyst to the mixed slurry for the second hydrolysis reaction to improve the efficiency of the second hydrolysis reaction; then, after the mixed slurry after the second hydrolysis reaction is subjected to concentration adjustment treatment and aeration and stirring treatment, an adjusting agent is added for flotation treatment.

[0018] In the preferred scheme of the present application, in the concentration adjustment treatment, the concentration of the mixed slurry after the second hydrolysis reaction is adjusted to 25wt%~40wt%; in the aeration and stirring treatment, the aeration rate is 400~600L / h, and the aeration time is 10~30min; the catalyst includes at least one of alkali metals, alkaline earth metal salts, organic amines, anion exchange resins, supported metal oxides, organic silanes, and quaternary ammonium salts; the regulator includes at least one of sodium hexametaphosphate and calcium powder.

[0019] In the preferred solution of the present application, during the flotation treatment, the foaming agent is selected from at least one of the diol and polyglycol contained in the mixed slurry component after the second hydrolysis reaction; the collector is selected from the chain carbonate contained in the mixed slurry component after the second hydrolysis reaction. By using the diol and / or polyglycol obtained by hydrolysis of the electrolyte as the foaming agent and the chain carbonate as the collector, the reuse of the waste battery electrolyte in the flotation of graphite from the leached residue is achieved, and there is no need to perform complex recycling treatment on the electrolyte in the subsequent recycling process.

[0020] In the preferred solution of the present application, the flotation treatment adopts batch scraping to obtain the flotation product, the interval between each batch is 20s to 40s, the scraping time is 2 to 4min, and the scraping times are 5 to 8 times.

[0021] In the preferred scheme of the present application, the impurity removal treatment includes: mixing the leached residue containing graphite with the solution after the first hydrolysis reaction, supplementing the acid solution for dissolution reaction to remove metal impurities to obtain a dissolved solution, and the supplementing acid solution can further promote the dissolution of insoluble metal impurities to remove or further recover the metal impurities, thereby promoting the reduction of the impurity content of the final graphite; adding calcium powder to the dissolved solution to adjust the pH, and performing fluoride precipitation treatment to combine the fluoride ions generated by the first hydrolysis reaction of the electrolyte with calcium ions to form calcium fluoride precipitates to achieve the removal of fluoride ions.

[0022] In a preferred solution of the present application, the electrolyte undergoes a first hydrolysis reaction in a container lined with polytetrafluoroethylene material, and the container lined with polytetrafluoroethylene material can prevent the hydrofluoric acid generated by electrolysis from corroding the reaction container; and / or the mass ratio of the electrolyte to water in the first hydrolysis reaction is controlled to be (0.5-5):1000.

[0023] In a preferred embodiment of the present application, the solution components after the first hydrolysis reaction include at least one of hydrofluoric acid and lithium fluoride salt; and / or the acid solution includes at least one of sulfuric acid solution and hydrochloric acid solution; and / or the calcium powder includes at least one of calcium oxide, calcium hydroxide and calcium carbonate.

[0024] In the preferred embodiment of the present application, the graphite extraction method further includes: filtering the first residual solution to obtain a filtered solution; adding carbonate to the filtered solution to perform a lithium precipitation reaction, and obtaining lithium carbonate and a second residual solution after filtering and washing.

[0025] In the preferred solution of the present application, the temperature of the lithium precipitation reaction is controlled at 70°C to 90°C, and the carbonate is preferably sodium carbonate.

[0026] In the preferred scheme of the present application, the second residual solution is returned to the flotation treatment for recycling; and / or the second residual solution is returned to the first hydrolysis reaction for recycling; and / or the second residual solution is returned to the second hydrolysis reaction for recycling; the first residual solution can be directly recycled as a supplementary solvent in the first hydrolysis reaction, the second hydrolysis reaction and the flotation treatment, or the high-value lithium element can be further extracted to obtain the second residual solution which is then recycled as a supplementary solvent in the first hydrolysis reaction, the second hydrolysis reaction and the flotation treatment, thereby reducing waste liquid discharge and facilitating the effective recovery of all battery components.

[0027] In the preferred scheme of the present application, the mass ratio of the leaching residue to the solution after the first hydrolysis reaction is controlled to be 1: (3-5); and / or the time of the dissolution reaction is controlled to be 1h-4h to fully dissolve the insoluble metal impurities in the leaching residue; and / or the pH of the fluorine precipitation treatment is controlled to be 6-8 to promote the precipitation of fluoride ions, and the reaction time is controlled to be 2h-4h; and / or the temperature of the second hydrolysis reaction is controlled to be 60°C-80°C.

[0028] In the preferred solution of the present application, the pre-treatment includes disassembling the lithium battery and then using evaporation condensation treatment or centrifugal separation treatment to collect the electrolyte from the lithium battery.

[0029] In the preferred scheme of the present application, the post-treatment includes washing treatment, filtering treatment, drying treatment and sintering treatment; by washing and filtering the flotation product, soluble metal impurities and excess organic solvents can be filtered out, and after drying treatment, the flotation product is subjected to high-temperature graphitization sintering treatment to obtain graphite.

[0030] In a preferred embodiment of the present application, the washing solvent of the washing treatment includes at least one of an aqueous solution and a hydrochloric acid solution; and / or the sintering treatment is carried out under an inert gas atmosphere to prevent the carbon in the graphite from generating other carbides, and the sintering temperature is controlled at 2500°C to 3000°C, wherein the inert gas is selected from at least one of argon, nitrogen and helium.

[0031] The graphite recovery method based on waste lithium battery leaching residue provided by the present invention has the following beneficial effects compared with the prior art:

[0032] The graphite recovery method provided by the present invention can realize the recovery and reuse of all components of the organic solvent of the electrolyte, simplify the recovery process of the electrolyte, and reduce the subsequent treatment cost of the electrolyte; by mixing the electrolyte hydrolysis product with the leaching residue, the metal impurities contained in the leaching residue can be separated and recovered, and the organic components in the hydrolysis product are used as a foaming agent and a collector for graphite flotation, so that the graphite recovery is more efficient, the recovery rate is greatly improved, and the recovered graphite can meet the raw material grade required for battery manufacturing; the present invention optimizes the recovery process of the electrolyte and graphite by recycling the electrolyte of the waste lithium battery for the graphite recovery in the leaching residue, reduces the recovery cost of the waste lithium battery, solves the two difficult problems of electrolyte and graphite recovery at one stroke, and has important guiding significance for the recovery of all components of the waste lithium battery.

[0033] Other advantages and features of the present invention will be further described in the specific implementation manner. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0035] Figure 1 A schematic diagram of the steps of a graphite recovery method exemplarily provided by the present invention;

[0036] Figure 2 A schematic diagram of a flow chart of a graphite recovery method exemplarily provided in the present invention. DETAILED DESCRIPTION

[0037] In order to make the above and other features and advantages of the present invention more clear, the present invention is further described below in conjunction with the accompanying drawings. It should be understood that the specific embodiments given herein are for the purpose of explaining to those skilled in the art and are only exemplary and not restrictive.

[0038] [Overall Inventive Concept]

[0039] The general inventive concept of the present invention provides a graphite recovery method based on the leached residue of waste lithium batteries. Aiming at the problems existing in the recycling process of waste lithium batteries in the above-mentioned prior art, a graphite recovery method is designed. Considering that the electrolyte in the prior art contains lithium hexafluorophosphate and a large amount of organic solvents, such as cyclic carbonates and chain carbonates, the recovery is difficult, the process is complicated and the profit is low when it is recovered through conventional recovery processes, which is not conducive to reducing the recovery cost. The present invention reuses the electrolyte in the waste lithium battery for graphite recovery in the leached residue, utilizes the corrosiveness of the fluorine-containing solution after the hydrolysis of lithium hexafluorophosphate in the electrolyte to the metal, mixes the solution after the first hydrolysis reaction of the electrolyte with the leached residue for reaction, and can dissolve the metal impurities in the leached residue and then recover, solving the problem of high metal impurity content in the leached residue when graphite is recovered; for the fluorine ions introduced after the hydrolysis of the electrolyte, calcium powder can be added to the solution after the hydrolysis to remove them.

[0040] As mentioned above, the electrolyte solution after the first hydrolysis treatment is mixed with the leached residue to form a mixed slurry. At this time, the mixed slurry contains chain carbonate and cyclic carbonate. The mixed slurry can be subjected to a second hydrolysis reaction, so that the cyclic carbonate is further hydrolyzed into diol and polyglycol. The present invention adopts a flotation process to recover graphite in the leached residue. The chain carbonate is a non-polar collector and can be used as a collector for graphite flotation treatment. The diol and polyglycol contain hydrophilic groups and hydrophobic groups, which can meet the requirements of the frother in the flotation treatment and are used as frothers for graphite flotation. After the second hydrolysis reaction, By adding an appropriate adjusting agent to the mixed slurry for flotation treatment, a flotation product with a high graphite content and a first residual solution can be obtained. The flotation product can be recovered to obtain fine flaky graphite after post-treatment such as washing, filtering, drying and sintering. The first residual solution after flotation treatment can be further recovered with lithium precipitation process to obtain a second residual solution containing residual organic matter. The second residual solution can continue to be recycled as a frother and collector in flotation treatment, or continue to be recycled as a supplementary solvent for the first hydrolysis reaction and the second hydrolysis reaction, thereby avoiding sewage discharge and saving recovery costs.

[0041] Through the graphite recovery method provided by the present invention, the recovered graphite still retains a flaky structure, which can meet the raw material grade required for battery manufacturing, and the graphite recovery rate can reach more than 98%, the graphite purity is high, and the metal residue is below the ppm level.

[0042] It should be noted that "waste lithium batteries" in this application can be lithium iron phosphate batteries, ternary lithium batteries, lithium cobalt oxide batteries, etc., and the types of lithium batteries are not limited; "leached slag" in this application refers to waste lithium batteries, such as lithium iron phosphate batteries, which are produced after the leaching process during the recycling process, and contain graphite and impurities such as phosphorus, iron, and lithium. "ppm" refers to parts per million, and 1ppm is one part per million.

[0043] Based on the above general inventive concept, a graphite recovery method is designed, which includes the following steps:

[0044] S1, pre-treating the lithium battery to obtain an electrolyte;

[0045] S2, subjecting the electrolyte to a first hydrolysis reaction, mixing the leached residue containing graphite with the solution after the first hydrolysis reaction, and then performing an impurity removal treatment to obtain a mixed slurry;

[0046] S3, performing a second hydrolysis reaction on the mixed slurry, and performing flotation treatment on the mixed slurry after the second hydrolysis reaction to obtain a flotation product and a first residual solution;

[0047] S4. Post-processing the flotation product to obtain graphite.

[0048] It can be understood that the solution after the first hydrolysis reaction in step S2 is a fluorine-containing solution after the hydrolysis of lithium hexafluorophosphate in the electrolyte, and the main purpose of the impurity removal treatment is to dissolve the metal impurities in the leached residue and remove the fluoride ions; the mixed slurry components after the second hydrolysis reaction in step S3 are mainly graphite, diols and polyglycols after the hydrolysis of chain carbonates and cyclic carbonates, wherein the diols and polyglycols are used as frothers, and the chain carbonates are used as collectors. The mixed slurry after the second hydrolysis reaction is added with a regulator for flotation treatment to obtain a flotation product and the first residue. The flotation product is graphite concentrate; in step S4, the flotation product is washed, filtered, dried and subjected to high-temperature graphitization sintering and other post-treatments to obtain graphite; the first residual solution obtained in step S3 can be directly used as a supplementary solvent in the first hydrolysis reaction, the second hydrolysis reaction or the flotation treatment and is continuously recycled, or the first residual solution can be subjected to a lithium precipitation reaction to obtain lithium carbonate and a second residual solution, and the second residual solution can be used as a supplementary solvent in the first hydrolysis reaction, the second hydrolysis reaction or the flotation treatment and is continuously recycled to reduce waste liquid discharge.

[0049] Based on the above, through the graphite recovery method provided by the present invention, the electrolyte in the waste lithium battery is directly reused for graphite recovery of the leached residue after hydrolysis, which optimizes the electrolyte recovery process, so that the electrolyte can be directly used in the graphite recovery process, reducing the subsequent treatment cost of the electrolyte; at the same time, the recovery of graphite in the leached residue is more efficient, the purity of the recovered graphite is improved, and the fine flaky structure can be retained to meet the raw material grade required for battery manufacturing.

[0050] It should be noted that the description of graphite meeting the raw material grade required for battery manufacturing in this application means that the graphite can meet the national standard of Grade III or above in GB / T 24533-2019.

[0051] The invention is further described below through specific embodiments.

[0052] [Example 1]

[0053] The recycled lithium battery is disassembled and collected by evaporation and condensation to obtain an electrolyte; the electrolyte and water are mixed and stirred in a sealed container wrapped with a polytetrafluoroethylene lining material to perform a first hydrolysis reaction, wherein the mass ratio of the electrolyte to water is 0.5:1000, so that lithium hexafluorophosphate is hydrolyzed to generate hydrofluoric acid and lithium fluoride salt, and a fluorine-containing solution containing hydrofluoric acid and lithium fluoride salt is obtained; the sealed container wrapped with a polytetrafluoroethylene lining material is used as a reaction container for the first hydrolysis reaction to prevent the hydrofluoric acid generated by the first hydrolysis reaction from corroding the reaction container;

[0054] The leached residue is mixed with the solution obtained by the first hydrolysis reaction, and hydrochloric acid is added to perform a dissolution reaction under stirring, the mass ratio of the leached residue to the solution obtained by the first hydrolysis reaction is 1:3, and the dissolution reaction time is 3 hours; the strong oxidizing property of hydrofluoric acid is used to dissolve the insoluble metal oxides, elemental copper, etc. in the leached residue; after the dissolution reaction is complete, calcium hydroxide is added to adjust the pH value of the solution system to 7, so as to promote the production of calcium fluoride precipitation by fluoride ions, and obtain a mixed slurry;

[0055] Adding magnesium chloride as a catalyst to the mixed slurry adjusted to pH 7, stirring and heating to 80°C, and performing a second hydrolysis reaction, so that the cyclic carbonate in the electrolyte is hydrolyzed to generate diols and polyglycols; adjusting the concentration of the mixed slurry after the second hydrolysis reaction to 25wt%, aerating and stirring, controlling the aeration rate to 600L / h, and the aeration time to 10min, adding calcium powder as a regulator after aeration to perform flotation treatment; wherein the frother in the flotation treatment is the diols and polyglycols generated by the second hydrolysis reaction of the cyclic carbonate in the electrolyte, and the collector is the chain carbonate in the electrolyte; the flotation treatment is performed in a batch scraping mode, the time interval for generating the flotation product is 30s, and the scraping is 3min, to obtain 6 groups of flotation products and a first residual solution;

[0056] After merging the six groups of flotation products, they were washed with pure water and filtered to remove soluble metal impurities and excess organic solvents in the flotation products, and then dried to remove excess water. After drying, they were subjected to high-temperature graphitization sintering under nitrogen protection, and the sintering temperature was controlled to be 2800°C to obtain graphite 1. The first residual solution was filtered to remove the flotation tailings, and sodium carbonate solution was added. The temperature was raised to 85°C with stirring to precipitate lithium, and then filtered and washed to obtain a lithium carbonate product and a second residual solution. The second residual solution was used as a supplementary solution for the first hydrolysis reaction and recycled.

[0057] [Example 2]

[0058] The recovered lithium battery is disassembled, centrifuged and filtered to obtain an electrolyte; the electrolyte and water are mixed and stirred in a sealed container wrapped with a polytetrafluoroethylene lining material to perform a first hydrolysis reaction, wherein the mass ratio of the electrolyte to water is 5:1000, so that lithium hexafluorophosphate is hydrolyzed to generate hydrofluoric acid and lithium fluoride salt, and a fluorine-containing solution containing hydrofluoric acid and lithium fluoride salt is obtained; the sealed container wrapped with a polytetrafluoroethylene lining material is used as a reaction container for the first hydrolysis reaction to prevent the hydrofluoric acid generated by the first hydrolysis reaction from corroding the reaction container;

[0059] The leached residue is mixed with the solution obtained by the first hydrolysis reaction, and hydrochloric acid is added to perform a dissolution reaction under stirring, wherein the mass ratio of the leached residue to the solution obtained by the first hydrolysis reaction is 1:5, and the dissolution reaction time is 2 hours; the insoluble metal oxides, elemental copper, etc. in the leached residue are dissolved by utilizing the strong oxidizing property of hydrofluoric acid; after the dissolution reaction is complete, calcium hydroxide is added to adjust the pH value of the solution system to 6, so as to promote the production of calcium fluoride precipitation by fluoride ions, and obtain a mixed slurry;

[0060] Porous alumina is added as a catalyst to the mixed slurry adjusted to pH 6, and the mixture is stirred and heated to 80°C to perform a second hydrolysis reaction, so that the cyclic carbonate in the electrolyte is hydrolyzed to generate diols and polyglycols; the concentration of the mixed slurry after the second hydrolysis reaction is adjusted to 35%, and aeration and stirring are performed, the aeration rate is controlled to be 400L / h, the aeration time is 30min, and calcium powder is added as a regulator after aeration to perform flotation treatment; wherein the frother in the flotation treatment is the diols and polyglycols generated by the second hydrolysis reaction of the cyclic carbonate in the electrolyte, and the collector is the chain carbonate in the electrolyte; the flotation treatment is performed in a batch scraping mode, the time interval for generating the flotation product is 20s, the scraping is 2min, and 8 groups of flotation products and a first residual solution are obtained;

[0061] After merging the 8 groups of flotation products, they were washed and filtered with 1% mass concentration of dilute hydrochloric acid to wash and filter the soluble metal impurities and organic solvents in the flotation products, and then dried to remove excess water. After drying, they were subjected to high-temperature graphitization sintering treatment under nitrogen protection, and the sintering temperature was controlled to be 3000°C to obtain graphite 2; the first residual solution was filtered to remove the flotation tailings, sodium carbonate solution was added, the temperature was raised and stirred to 70°C for lithium precipitation, and then filtered and washed to obtain a lithium carbonate product and a second residual solution, and the second residual solution was used as a supplementary solution for the second hydrolysis reaction for recycling.

[0062] [Example 3]

[0063] The recovered lithium battery is disassembled, centrifuged and filtered to obtain an electrolyte; the electrolyte and water are mixed and stirred in a sealed container wrapped with a polytetrafluoroethylene lining material to perform a first hydrolysis reaction, wherein the mass ratio of the electrolyte to water is 2.5:1000, so that lithium hexafluorophosphate is hydrolyzed to generate hydrofluoric acid and lithium fluoride salt, and a fluorine-containing solution containing hydrofluoric acid and lithium fluoride salt is obtained; the sealed container wrapped with a polytetrafluoroethylene lining material is used as a reaction container for the first hydrolysis reaction to prevent the hydrofluoric acid generated in the first hydrolysis reaction from corroding the reaction container;

[0064] The leached residue is mixed with the solution obtained by the first hydrolysis reaction, and hydrochloric acid is added to perform a dissolution reaction under stirring, the mass ratio of the leached residue to the solution obtained by the first hydrolysis reaction is 1:4, and the dissolution reaction time is 2 hours; the strong oxidizing property of hydrofluoric acid is used to dissolve the insoluble metal oxides, elemental copper, etc. in the leached residue; after the dissolution reaction is complete, calcium hydroxide is added to adjust the pH value of the solution system to 6, so as to promote the production of calcium fluoride precipitation by fluoride ions, and obtain a mixed slurry;

[0065] Calcium chloride and porous alumina are added as catalysts to the mixed slurry adjusted to pH 6, and the mixture is stirred and heated to 70°C to perform a second hydrolysis reaction, so that the cyclic carbonate in the electrolyte is hydrolyzed to generate diols and polyglycols; the concentration of the mixed slurry after the second hydrolysis reaction is adjusted to 30%, and aeration and stirring are performed, the aeration rate is controlled to be 500L / h, the aeration time is 20min, and calcium powder is added as a regulator after aeration to perform flotation treatment; wherein the frother in the flotation treatment is the diols and polyglycols generated by the second hydrolysis reaction of the cyclic carbonate in the electrolyte, and the collector is the chain carbonate in the electrolyte; the flotation treatment is performed in a batch scraping mode, the time interval for generating the flotation product is 30s, the scraping is 3min, and 6 groups of flotation products and a first residual solution are obtained;

[0066] After merging the six groups of flotation products, they were washed and filtered with 1% mass concentration of acetic acid to wash and filter the soluble metal impurities and excess organic solvents in the flotation products, and then dried to remove excess water. After drying, they were subjected to high-temperature graphitization sintering treatment under nitrogen protection, and the sintering temperature was controlled to be 3000°C to obtain graphite 3; the first residual solution was filtered to remove the flotation tailings, sodium carbonate solution was added, the temperature was raised and stirred to 90°C for lithium precipitation, and then filtered and washed to obtain a lithium carbonate product and a second residual solution, and the second residual solution was used as a supplementary solution for flotation treatment and recycled.

[0067] [Example 4]

[0068] The recycled lithium battery is disassembled and collected by evaporation and condensation to obtain an electrolyte; the electrolyte and water are mixed and stirred in a sealed container wrapped with a polytetrafluoroethylene lining material to perform a first hydrolysis reaction, wherein the mass ratio of the electrolyte to water is 2.5:1000, so that lithium hexafluorophosphate is hydrolyzed to generate hydrofluoric acid and lithium fluoride salt, and a fluorine-containing solution containing hydrofluoric acid and lithium fluoride salt is obtained; the sealed container wrapped with a polytetrafluoroethylene lining material is used as a reaction container for the first hydrolysis reaction to prevent the hydrofluoric acid generated by the first hydrolysis reaction from corroding the reaction container;

[0069] The leached residue is mixed with the solution obtained by the first hydrolysis reaction, and sulfuric acid is added to perform a dissolution reaction under stirring, the mass ratio of the leached residue to the solution obtained by the first hydrolysis reaction is 1:4, and the dissolution reaction time is 4 hours; the insoluble metal oxides, elemental copper, etc. in the leached residue are dissolved by utilizing the strong oxidizing property of hydrofluoric acid; after the dissolution reaction is complete, calcium hydroxide is added to adjust the pH value of the solution system to 8, so as to promote the production of calcium fluoride precipitation by fluoride ions, and obtain a mixed slurry;

[0070] Adding porous alumina as a catalyst to the mixed slurry adjusted to pH 8, stirring and heating to 80° C., and performing a second hydrolysis reaction to hydrolyze the cyclic carbonate in the electrolyte to generate diols and polyglycols;

[0071] The concentration of the mixed slurry after the second hydrolysis reaction is adjusted to 40%, and aeration and stirring are performed. The aeration rate is controlled to be 500L / h, and the aeration time is 20min. After aeration, calcium powder and sodium hexametaphosphate are added as adjusting agents for flotation treatment; wherein the frother in the flotation treatment is the diol and polyglycol generated by the second hydrolysis reaction of the cyclic carbonate in the electrolyte, and the collector is the chain carbonate in the electrolyte; the flotation treatment is performed in a batch scraping mode, the time interval for generating the flotation product is 40s, the scraping is 4min, and 6 groups of flotation products and the first residual solution are obtained;

[0072] After merging the six groups of flotation products, they were washed with pure water and filtered to remove soluble metal impurities and excess organic solvents in the flotation products, and then dried to remove excess water. After drying, they were subjected to high-temperature graphitization sintering under nitrogen protection, and the sintering temperature was controlled to be 2800°C to obtain graphite 4. The first residual solution was filtered to remove the flotation tailings, and sodium carbonate solution was added. The temperature was raised and stirred to 90°C for lithium precipitation, and then filtered and washed to obtain a lithium carbonate product and a second residual solution. The second residual solution was cyclically used as a supplementary solution for the first hydrolysis reaction.

[0073] The carbon content, impurity content and recovery rate of graphites 1 to 4 obtained in the above embodiments 1 to 4 were statistically analyzed, and the statistical data are shown in Appendix 1. The structure and electrical properties of graphites 1 to 4 obtained in the above embodiments 1 to 4 were tested, and the data are shown in Appendix 2.

[0074] Appendix 1 Statistics of carbon content, impurity content and recovery rate

[0075]

[0076] Note: ppm means parts per million.

[0077] Appendix 2 Characterization structure and electrical performance test statistics

[0078]

[0079]

[0080] Note: D50 refers to median particle size, TD refers to tap density, and BET refers to specific surface area.

[0081] It can be seen from Appendix 1 that, through the graphite recovery method provided in the embodiment of the present invention, the recovery rate of graphites 1 to 4 recovered can reach more than 85%, the carbon content can be as high as 98.5%, and the metal impurities such as Co, Ni, Li, Fe, Cu, B, Al, As, Mg in the graphite products do not exceed 1ppm, and the purity of graphite 1, graphite 2 and graphite 3 are all maintained at a high level; It can be seen from Appendix 2 that the median particle size D50 of the graphite product can be maintained at 27μm to 30μm, and the tap density is 1.0g / cm 3 ~1.15g / cm 3 , with a specific surface area of ​​2.3m 3 / g~2.5m 3 / g, and the graphite morphology is fine flake, which can meet the graphite raw material grade requirements for battery manufacturing; after the electrical performance test of graphite, the first charge and discharge efficiency of graphite 1 to 3 is above 92%, and the 0.1C discharge capacity is 325mAh g -1 ~340mAh g -1, which can maintain the electrical properties of battery-grade graphite.

[0082] Therefore, in Examples 1 to 4 of the present invention, each graphite product obtained can achieve a relatively high recovery rate, with an impurity content at the parts per million level, which is extremely low. Each graphite can retain a fine flaky structure and has excellent electrical properties, which can meet the graphite raw material grade required for battery manufacturing.

[0083] In order to evaluate the effect of the hydrolysis product of the electrolyte on the graphite recovery rate in the graphite recovery method provided by the present invention, two groups of comparative examples are provided below.

[0084] [Comparative Example 1]

[0085] Compared with Examples 1 to 4, the electrolyte in the mixed slurry in Comparative Example 1 did not undergo the second hydrolysis reaction, and the specific steps were as follows:

[0086] The recycled lithium battery is disassembled and collected by evaporation and condensation to obtain an electrolyte; the electrolyte and water are mixed and stirred in a sealed container wrapped with a polytetrafluoroethylene lining material to perform a first hydrolysis reaction, wherein the mass ratio of the electrolyte to water is 2.5:1000, so that lithium hexafluorophosphate is hydrolyzed to generate hydrofluoric acid and lithium fluoride salt, and a fluorine-containing solution containing hydrofluoric acid and lithium fluoride salt is obtained; the sealed container wrapped with a polytetrafluoroethylene lining material is used as a reaction container for the first hydrolysis reaction to prevent the hydrofluoric acid generated by the first hydrolysis reaction from corroding the reaction container;

[0087] The leached residue is mixed with the solution obtained by the first hydrolysis reaction, and sulfuric acid is added to perform a dissolution reaction under stirring, the mass ratio of the leached residue to the solution obtained by the first hydrolysis reaction is 1:4, and the dissolution reaction time is 4 hours; the insoluble metal oxides, elemental copper, etc. in the leached residue are dissolved by utilizing the strong oxidizing property of hydrofluoric acid; after the dissolution reaction is complete, calcium hydroxide is added to adjust the pH value of the solution system to 8, so as to promote the production of calcium fluoride precipitation by fluoride ions, and obtain a mixed slurry;

[0088] The concentration of the mixed slurry was adjusted to 40%, and aeration and stirring were performed. The aeration rate was controlled to be 500 L / h, and the aeration time was 20 min. After aeration, sodium hexametaphosphate was added as a regulator for flotation treatment. The flotation treatment was performed in batches by scraping bubbles. The time interval for producing flotation products was 40 s, and the scraping bubbles were 4 min. Six groups of flotation products and the first residual solution were obtained.

[0089] After merging the six groups of flotation products, they were washed with pure water and filtered to remove soluble metal impurities and excess organic solvents in the flotation products, and then dried to remove excess water. After drying, they were subjected to high-temperature graphitization sintering under nitrogen protection, and the sintering temperature was controlled to be 2800°C to obtain graphite 5. The first residual solution was filtered to remove the flotation tailings, and sodium carbonate solution was added. The temperature was raised to 90°C and stirred for lithium precipitation, and then filtered and washed to obtain a lithium carbonate product and a second residual solution. The second residual solution was used as a supplementary solution for the first hydrolysis reaction and recycled.

[0090] [Comparative Example 2]

[0091] Compared with Examples 1 to 4, the flotation treatment in Comparative Example 2 uses kerosene as a frother and fusel alcohol as a collector, and the specific steps are as follows:

[0092] The recycled lithium battery is disassembled and collected by evaporation and condensation to obtain an electrolyte; the electrolyte and water are mixed and stirred in a sealed container wrapped with a polytetrafluoroethylene lining material to perform a first hydrolysis reaction, wherein the mass ratio of the electrolyte to water is 2.5:1000, so that lithium hexafluorophosphate is hydrolyzed to generate hydrofluoric acid and lithium fluoride salt, and a fluorine-containing solution containing hydrofluoric acid and lithium fluoride salt is obtained; the sealed container wrapped with a polytetrafluoroethylene lining material is used as a reaction container for the first hydrolysis reaction to prevent the hydrofluoric acid generated by the first hydrolysis reaction from corroding the reaction container;

[0093] The leached residue is mixed with the solution obtained by the first hydrolysis reaction, and sulfuric acid is added to perform a dissolution reaction under stirring, the mass ratio of the leached residue to the solution obtained by the first hydrolysis reaction is 1:4, and the dissolution reaction time is 4 hours; the insoluble metal oxides, elemental copper, etc. in the leached residue are dissolved by utilizing the strong oxidizing property of hydrofluoric acid; after the dissolution reaction is complete, calcium hydroxide is added to adjust the pH value of the solution system to 8, so as to promote the production of calcium fluoride precipitation by fluoride ions, and obtain a mixed slurry;

[0094] The concentration of the mixed slurry was adjusted to 40%, and aeration and stirring were performed. The aeration rate was controlled to be 500 L / h, and the aeration time was 20 min. After aeration, sodium hexametaphosphate was added as a regulator, kerosene as a frother, and fusel alcohol as a collector, and flotation treatment was performed. The flotation treatment was performed in batches by scraping bubbles, and the time interval for generating flotation products was 40 s. The scraping bubbles were 4 min, and 6 groups of flotation products and the first residual solution were obtained.

[0095] After merging the six groups of flotation products, they were washed with pure water and filtered to remove soluble metal impurities and excess organic solvents in the flotation products, and then dried to remove excess water. After drying, they were subjected to high-temperature graphitization sintering under nitrogen protection, and the sintering temperature was controlled to be 2800°C to obtain graphite 6. The first residual solution was filtered to remove the flotation tailings, and sodium carbonate solution was added. The temperature was raised and stirred to 90°C for lithium precipitation, and then filtered and washed to obtain a lithium carbonate product and a second residual solution. The second residual solution was cyclically used as a supplementary solution for the first hydrolysis reaction.

[0096] The graphite recovery rates of the above Comparative Examples 1 and 2 were tested and statistically analyzed, and summarized together with Examples 1 to 4 in the following Appendix 3 for the convenience of comparison.

[0097] Appendix 3 Graphite recovery test statistics

[0098]

[0099] It can be seen from the above Appendix 3 that the electrolyte in Comparative Example 1 has not undergone the second hydrolysis reaction, that is, the cyclic carbonate therein is not hydrolyzed into diols and polyglycols, resulting in a lack of frothers in the subsequent flotation treatment, resulting in the graphite recovery rate of the obtained graphite 5 being only 30%, which is significantly lower than that of Examples 1 to 4; In Comparative Example 2, kerosene is used as a frother and fusel alcohol is used as a collector for flotation treatment, and its flotation effect is worse than that of the polyglycols and diols obtained by hydrolysis of the electrolyte as frothers and chain carbonates as collectors, resulting in the graphite recovery rate of the recovered graphite 6 being only 40%, which is significantly lower than that of Examples 1 to 4.

[0100] In summary, the graphite recovery method provided by the embodiment of the present invention can realize the full component reuse of lithium salts and organic solvents in the electrolyte without generating sewage discharge. After the waste electrolyte is treated, the graphite in the battery material leaching residue can be extracted, which simplifies the electrolyte recovery process and reduces the subsequent treatment cost of the electrolyte. By mixing the electrolyte hydrolysis product with the leaching residue, the metal impurities contained in the leaching residue can be separated and recovered, and the organic components in the hydrolysis product are used as foaming agents and collectors for graphite flotation, so that the graphite recovery is more efficient, the recovery rate is greatly improved, and the recovered graphite can meet the raw material grade required for battery manufacturing. The present invention optimizes the recovery process of the electrolyte and graphite by recycling the electrolyte of the waste lithium battery for the graphite recovery in the leaching residue, reduces the recovery cost of the waste lithium battery, and solves the two difficult problems of electrolyte and graphite recovery at one stroke, which has important guiding significance for the full component recovery of the waste lithium battery.

[0101] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A graphite recovery method based on waste lithium battery leaching residue, characterized in that: The following steps are involved: Pre-treating the lithium battery to obtain an electrolyte; The electrolyte is subjected to a first hydrolysis reaction, and the leached residue containing graphite is mixed with the solution after the first hydrolysis reaction and then subjected to an impurity removal treatment to obtain a mixed slurry; Performing a second hydrolysis reaction on the mixed slurry, and performing a flotation treatment on the mixed slurry after the second hydrolysis reaction to obtain a flotation product and a first residual solution; Post-processing the flotation product to obtain graphite; During the flotation treatment, a frother and a collector are added; the frother is selected from at least one of the diols and polyglycols contained in the mixed slurry component after the second hydrolysis reaction; the collector is selected from the chain carbonate contained in the mixed slurry component after the second hydrolysis reaction.

2. The graphite recovery method according to claim 1, characterized in that: The mixed slurry is subjected to a second hydrolysis reaction, and the mixed slurry after the second hydrolysis reaction is subjected to flotation treatment specifically includes: First, a catalyst is added to the mixed slurry to perform a second hydrolysis reaction to improve the efficiency of the second hydrolysis reaction; After the mixed slurry after the second hydrolysis reaction is subjected to concentration adjustment treatment and aeration and stirring treatment, a regulator is added to perform flotation treatment.

3. The graphite recovery method according to claim 2, characterized in that: In the concentration adjustment process, the concentration of the mixed slurry after the second hydrolysis reaction is adjusted to 25wt%~40wt%; During the aeration and stirring treatment, the aeration rate is 400-600 L / h and the aeration time is 10-30 min; The catalyst comprises at least one of alkali metal, alkaline earth metal salt, organic amine, anion exchange resin, supported metal oxide, organic silane, and quaternary ammonium salt; The adjusting agent includes at least one of sodium hexametaphosphate and calcium powder.

4. The graphite recovery method according to claim 2, characterized in that: The flotation treatment adopts batch scraping to obtain the flotation product, the interval time of each batch is 20s~40s, the scraping time is 2~4min, and the scraping times are 5~8 times.

5. The graphite recovery method according to claim 1, characterized in that: The impurity removal process comprises: After mixing the leached residue containing graphite with the solution after the first hydrolysis reaction, an acid solution is added to carry out a dissolution reaction to remove metal impurities, thereby obtaining a dissolved solution; Calcium powder is added to the dissolving solution to adjust the pH and perform fluorine precipitation treatment.

6. The graphite recovery method according to claim 5, characterized in that: The electrolyte undergoes a first hydrolysis reaction in a container lined with polytetrafluoroethylene; and / or The mass ratio of the electrolyte to water in the first hydrolysis reaction is controlled to be (0.5~5):1000.

7. The graphite recovery method according to claim 5, characterized in that: The solution components after the first hydrolysis reaction include at least one of hydrofluoric acid and lithium fluoride salt; and / or The acid solution comprises at least one of a sulfuric acid solution and a hydrochloric acid solution; and / or The calcium powder includes at least one of calcium oxide, calcium hydroxide and calcium carbonate.

8. The graphite recovery method according to claim 1, characterized in that: Also includes: filtering the first residual solution to obtain a filtered solution; Adding carbonate to the filtered solution to perform lithium precipitation reaction, obtaining lithium carbonate and a second residual solution after filtering and washing, wherein the temperature of the lithium precipitation reaction is controlled to be 70° C. to 90° C., and the carbonate is sodium carbonate; returning the second residual solution to the flotation process for recycling; Returning the second residual solution to the first hydrolysis reaction for recycling; The second residual solution is returned to the second hydrolysis reaction for recycling.

9. The graphite recovery method according to claim 5, characterized in that: The mass ratio of the leaching residue to the solution after the first hydrolysis reaction is controlled to be 1:(3-5); and / or The dissolution reaction time is controlled to be 1h~4h; and / or The pH of the fluorine precipitation treatment is controlled to be 6-8, and the reaction time is controlled to be 2h-4h; and / or The temperature of the second hydrolysis reaction is controlled at 60°C to 80°C.

10. The graphite recovery method according to any one of claims 1 to 9, characterized in that: The pre-treatment includes disassembling the lithium battery and then performing evaporation condensation treatment or centrifugal separation treatment; The post-treatment includes washing treatment, filtering treatment, drying treatment and sintering treatment.

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