Method for preparing high-purity lithium oxalate from disassembled product of lithium ion battery

Abstract

The invention discloses a method for preparing high-purity lithium oxalate from a disassembled product of a lithium ion battery. Relates to the technical field of lithium ion battery recovery. The method for preparing lithium oxalate comprises the following steps: S1, mixing waste lithium battery black powder and calcium salt in an organic solvent, and grinding and filtering to obtain first slag; s2, the first slag is dried at the temperature of 400 DEG C or below, and second slag is obtained; s3, mixing the second slag with carbonate, and performing vacuum roasting to obtain third slag; s4, mixing the third slag, oxalic acid and water, heating for reaction, and filtering to obtain a crude lithium oxalate solution; s5, heating the crude lithium oxalate solution, adding oxalic acid, calcium salt and an alkaline reagent, and filtering to obtain a refined lithium oxalate solution after the reaction is completed; and S6, enabling the refined lithium oxalate solution to pass through an adsorption material, and filtering to obtain the lithium oxalate. The method is short in production flow, simple in equipment and easy in process control, high-purity lithium oxalate can be prepared, and the lithium yield is greater than or equal to 92%.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion battery recycling, in particular to a method for preparing high-purity lithium oxalate from lithium ion battery disassembly products. BACKGROUND

[0002] With the increasing demand for renewable energy and electric vehicles worldwide, lithium ion batteries, especially ternary lithium batteries, have become important energy storage and conversion devices. However, with the large-scale use of ternary lithium batteries, the problem of their retirement and disposal has become increasingly prominent. The treatment and recycling of waste ternary lithium batteries not only concerns resource reuse, but also involves environmental protection and sustainable development.

[0003] The main components of waste ternary lithium batteries include positive electrode materials, negative electrode materials, electrolytes and separators. Among them, the positive electrode material is usually composed of nickel, cobalt, manganese and other metal oxides, and the negative electrode material is mainly graphite. The electrolyte is composed of organic solvents and lithium salts, and the separator is generally made of polyolefin material. With the use of the battery, the active substances in the positive and negative electrode materials gradually degrade, leading to a decrease in battery capacity, and eventually requiring retirement treatment.

[0004] After the end of the service life of waste ternary lithium batteries, a black solid powder called "black powder" is generated during the disassembly process. This black powder is mainly composed of positive electrode materials, negative electrode materials, electrolytes, binders and a small amount of aluminum and copper powder. Specifically, the positive electrode material is usually lithium nickel cobalt manganese oxide, and the negative electrode material is mainly graphite. The electrolyte is composed of organic solvents and lithium salts, and the binder is used to bond the active material with the current collector. During the disassembly process, these materials are crushed and separated, eventually forming a black powder containing multiple components.

[0005] The traditional black powder recycling method mainly uses hydrometallurgical process, i.e. mixing black powder with acidic solution, extracting valuable metals such as lithium, nickel, cobalt, manganese, etc. through leaching reaction. Then, these metals are separated and purified by solvent extraction, precipitation, etc. However, this method has problems such as long production process, complex equipment, difficult process control, lithium recovery rate of only 80-85%, etc. In addition, the products obtained by traditional methods are usually crude lithium salts with low purity, which cannot meet the demand for high-purity lithium salts.

[0006] Lithium oxalate is an important lithium source material, widely used in the synthesis of positive electrode materials for lithium batteries. High-purity lithium oxalate not only improves the performance of the battery, but also reduces production costs, promoting the sustainable development of the lithium battery industry. It is of great significance to recover lithium oxalate from black powder. Black powder contains lithium elements, and its lithium content is relatively low (generally above 3.5%), so through effective recovery methods, lithium elements can be extracted from it to prepare high-purity lithium oxalate.

[0007] However, the existing technology still faces some challenges in recovering lithium oxalate from the black powder. The traditional hydrometallurgical process may produce fluoride waste residues when dealing with fluorine-containing waste, causing environmental pollution. In addition, the existing methods have low lithium recovery rate, low product purity, complex process, high cost, and environmental pollution problems.

[0008] To solve the above problems, in recent years, researchers have proposed various improved black powder recovery methods. For example, some studies use a sulfation roasting process to mix black powder with concentrated sulfuric acid and roast at high temperature to leach lithium in ionic form, thereby improving the recovery rate of lithium. In addition, some studies separate the black powder into different components through grading and magnetic separation, and leach them separately to improve the recovery rate of valuable metals. These methods have improved the recovery rate of lithium and the purity of the product to some extent, but still have problems such as complex process, high cost, and environmental pollution.

[0009] Therefore, developing an efficient, environmentally friendly, and low-cost black powder recovery method to prepare high-purity lithium oxalate is still an important research direction in the field of lithium battery recycling. SUMMARY

[0010] The purpose of the present application is to develop an efficient, environmentally friendly, and low-cost method for recycling waste ternary lithium battery black powder to prepare high-purity lithium oxalate.

[0011] The first aspect of the present application is to:

[0012] A method for preparing lithium oxalate is provided.

[0013] The second aspect of the present application is to:

[0014] The application of the method for preparing lithium oxalate.

[0015] The present application also proposes an electrolyte and a lithium supplement.

[0016] Specifically, the technical scheme adopted according to the first aspect of the present application is:

[0017] A method for preparing lithium oxalate, comprising the following steps:

[0018] S1 mixing waste lithium battery black powder and calcium salt in an organic solvent, grinding and filtering to obtain a first residue;

[0019] S2 drying the first residue at a temperature below 400℃ to obtain a second residue;

[0020] S3 mixing the second residue with a carbonate salt and vacuum roasting to obtain a third residue;

[0021] S4 mixing the third residue, oxalic acid, and water, heating and reacting, filtering to obtain a crude lithium oxalate solution;

[0022] S5 heating the crude lithium oxalate solution, adding oxalic acid, calcium salt and alkaline reagent, and after the reaction is completed, filtering to obtain a refined lithium oxalate solution;

[0023] S6 passing the refined lithium oxalate solution through an adsorption material, and filtering to obtain the lithium oxalate.

[0024] According to the embodiments of the present application, one of the technical solutions has at least one of the following advantages or beneficial effects:

[0025] The present application is aimed at waste lithium battery black powder material, which is activated by washing and low-temperature volatilization, and then reduced to lithium carbonate and lithium oxide by using its own carbon source at high temperature in vacuum roasting. Subsequently, the lithium is converted into a crude lithium oxalate solution by using an oxalic acid lithium extraction process, and then refined, adsorbed, filtered and other steps to obtain high-purity lithium oxalate. Compared with the traditional recovery method, the present application has the following advantages: first, the traditional recovery method has a long production process, complex equipment and difficult process control, while the present application has a short production process, simple equipment and easy process control. Second, the lithium yield of the traditional recovery method is only about 80-85%, while the lithium yield of the present application is ≥92%. Finally, the traditional recovery method usually produces crude or industrial-grade lithium salt, while the present application produces high-purity lithium oxalate.

[0026] Specifically:

[0027] In step S1, the organic solvent is used to dissolve the electrolyte and the binder, reducing the interference of impurities in the subsequent steps; the calcium salt reacts with the fluoride ions to form insoluble calcium fluoride, preliminarily fixing the fluorine elements, thereby improving the lithium extraction efficiency and reducing fluorine pollution;

[0028] In step S2, drying below 400℃ can ensure that the organic solvent and other volatile substances in the first filter residue are removed, and in this process, the calcium salt will react with the fluoride ions in the first filter residue to form calcium fluoride to further fix the fluoride ions. In addition, an environment below 400℃ can avoid lithium volatilization caused by high temperature, and activate the carbon powder to enhance the reduction ability, providing a high-activity carbon source for subsequent roasting;

[0029] In step S3, during vacuum roasting, the carbon powder contained in the second residue is used to reduce nickel, cobalt and manganese, while the lithium in the second residue reacts to form lithium carbonate. After step S1 and step S2, the carbon powder contained in the second residue is purified and activated, making the reduction ability and effect of carbon better. Carbonates react to generate carbon dioxide gas during vacuum roasting, which not only makes the reaction more complete, but also makes the second residue and carbonates more loose, which is more conducive to the reaction.

[0030] In step S3, most of lithium is converted into lithium carbonate and a small amount of lithium oxide by vacuum roasting. In step S4, oxalic acid converts lithium carbonate and lithium oxide into lithium oxalate after the reaction is completed by heating. Through step S3, selective extraction of lithium is achieved, and high-value metals Ni, Co, and Mn are separated at the same time.

[0031] In step S4, oxalic acid converts lithium carbonate and lithium oxide into lithium oxalate, simplifying the lithium extraction process and avoiding multi-step separation operations.

[0032] In step S5, oxalic acid precipitates residual metal cations, and calcium salt is added to further remove fluoride ions. Adding an alkaline reagent adjusts the pH of the solution to weakly acidic or neutral, allowing the reaction to proceed faster and neutralizing free acid in the solution, thereby significantly improving the purity of lithium oxalate.

[0033] In step S6, the refined lithium oxalate solution is passed through an adsorption material to remove boric acid, pigments, and oil in the solution. The decolorized refined lithium oxalate solution is filtered to remove solid particles, obtaining the high-purity lithium oxalate.

[0034] According to an embodiment of the present application, the calcium salt includes at least one of calcium oxalate, calcium hydroxide, and calcium sulfate. Preferably, the calcium salt includes calcium oxalate, which is added to solidify fluorine during subsequent low-temperature volatilization and high-temperature roasting, ensuring that fluorine is not dissolved by water and oxalic acid.

[0035] According to an embodiment of the present application, the mass ratio of fluorine ions in the fluorine-containing substance in the waste lithium battery black powder to the mass of the calcium salt is 1-1.2:3-5.

[0036] According to an embodiment of the present application, in step S1, the following steps are further included: mixing the waste lithium battery black powder and the calcium salt in the organic solvent at a temperature of 25-50°C.

[0037] According to an embodiment of the present application, in step S1, the following steps are further included: the liquid-solid ratio of the waste lithium battery black powder to the organic solvent is 3-4:1-1.2.

[0038] According to an embodiment of the present application, the organic solvent includes at least one of dehydrogenated coal oil and an alcohol compound. This method uses an organic solvent to grind and wash to remove residual electrolyte and binder, reducing the extraction of lithium and increasing the yield of lithium.

[0039] Preferably, the organic solvent includes dehydrogenated coal oil, which is used for grinding and washing. The advantage is that it can dissolve electrolyte, binder, and other substances in the black powder into coal oil during grinding, thereby better separating the black powder.

[0040] According to an embodiment of the present application, in step S1, the grinding time is 30-60 minutes.

[0041] According to an embodiment of the present application, in step S1, after grinding, a washing step is further included.

[0042] According to an embodiment of the present application, in step S2, the temperature is below 400°C, preferably 180-320°C.

[0043] According to an embodiment of the present application, in step S2, the drying time is 60-90 minutes.

[0044] According to an embodiment of the present application, in step S2, when the calcium salt is calcium oxalate, the calcium oxalate has the following reaction during drying: 2F - + CaC2O4 = CaF2 + C2O4 2- Through the reaction, the calcium oxalate solidifies the fluorine, ensuring that the fluorine is not dissolved by other substances.

[0045] According to an embodiment of the present application, in step S2, a step of recycling the organic solvent volatilized during drying is further included, so as to be recycled and added to step S1 during recycling.

[0046] According to an embodiment of the present application, in step S3, the carbonate salt includes at least one of ammonium carbonate and sodium carbonate.

[0047] According to an embodiment of the present application, in step S3, the mass ratio of the second slag to the carbonate salt is 1-1.2:0.05-0.2.

[0048] According to an embodiment of the present application, in step S3, the vacuum roasting temperature is 700-820°C.

[0049] According to an embodiment of the present application, in step S3, the vacuum roasting time is 60-180 minutes.

[0050] According to an embodiment of the present application, in step S3, when the carbonate salt is ammonium carbonate, the reaction involved includes:

[0051] Li(Ni x Co y Mn 1-x-y )O2 + (1+2x+2y) / 4C = 1 / 2Li2O + xNi + yCo + (1-x-y)MnO + (1+2x+2

[0052] y) / 4CO2↑;

[0053] (NH4)2CO3 = NH3↑ + CO2↑ + H2O;

[0054] Li2O + CO2 = Li2CO3.

[0055] According to an embodiment of the present application, when the calcium salt is calcium oxalate, the calcium oxalate that is not completely reacted in step S2 is completely reacted in step S3 to convert fluorine into calcium fluoride, and the reaction involved includes 2F - + CaC2O4 = CaF2 + C2O4 2- .

[0056] According to an embodiment of the present application, in step S4, the following step is further included: first ball-milling the third residue, and then mixing the third residue, oxalic acid and water.

[0057] According to an embodiment of the present application, in step S4, the liquid-solid ratio of the third residue and water is 3-4:1-1.2.

[0058] According to an embodiment of the present application, in step S4, the temperature of the heating reaction is 50-70°C.

[0059] According to an embodiment of the present application, in step S4, the time of the heating reaction is 60-120 minutes.

[0060] According to an embodiment of the present application, in step S4, the pH value of the mixture of the third residue, oxalic acid and water is 3-4. Through pH control, the dissolution of other metals is inhibited, and the conversion of lithium carbonate and lithium oxide into lithium oxalate by oxalic acid is further promoted.

[0061] According to an embodiment of the present application, in step S4, the conversion of lithium carbonate and lithium oxide into lithium oxalate by oxalic acid involves the following reaction:

[0062] Li2O + H2C2O4 = Li2C2O4 + H2O;

[0063] Li2CO3 + H2C2O4 = Li2C2O4 + H2O + CO2↑.

[0064] According to an embodiment of the present application, in step S5, the temperature of the heating is 85-95°C.

[0065] According to an embodiment of the present application, in step S5, the amount of oxalic acid added is 2-10 kg of oxalic acid per cubic volume of the crude lithium oxalate solution.

[0066] According to an embodiment of the present application, in step S5, the amount of calcium salt added is 10-15 times the calcium salt based on the weight fraction of fluorine ions in the crude lithium oxalate solution.

[0067] According to an embodiment of the present application, in step S5, the calcium salt comprises at least one of calcium hydroxide, calcium sulfate and calcium oxalate. Preferably, the calcium salt comprises calcium oxalate. The solubility product constant Ksp of calcium oxalate is 4.0 x 10 sp The solubility product constant Ksp of calcium fluoride is 3.95 x 10 -8 The solubility product constant Ksp of calcium fluoride is 3.95 x 10 sp The solubility product constant Ksp of calcium fluoride is 3.95 x 10 -11 The addition of calcium oxalate can generate calcium fluoride from the fluorine ions in the crude lithium oxalate solution, which is more difficult to dissolve.

[0068] According to an embodiment of the present application, in step S5, the method further comprises the following step: after the addition of the calcium salt and oxalic acid into the crude lithium oxalate solution, the reaction is allowed to proceed for 60-120 minutes, and then the alkaline reagent is added.

[0069] According to an embodiment of the present application, in step S5, the alkaline reagent comprises sodium hydroxide, sodium carbonate, calcium hydroxide, potassium hydroxide and lithium hydroxide. Preferably, the alkaline reagent comprises lithium hydroxide.

[0070] According to an embodiment of the present application, in step S5, the method further comprises the following step: the pH value of the mixed solution of the crude lithium oxalate solution, the calcium salt and the oxalic acid is adjusted to 6.5-7.0 by adding the alkaline reagent.

[0071] According to an embodiment of the present application, in step S6, the adsorption material comprises activated carbon and / or decolorizing resin.

[0072] According to an embodiment of the present application, in step S6, the filtration comprises the following step: the refined lithium oxalate solution is passed through a filter to remove the solid particles therein.

[0073] According to an embodiment of the present application, the filter has a filtration accuracy of 0.01-0.05 μm.

[0074] Another aspect of the present application provides an electrolyte comprising the high-purity lithium oxalate prepared by the method according to the above-mentioned embodiments of the first aspect. Since the application employs all the technical solutions of the above-mentioned method, it at least has all the beneficial effects brought by the technical solutions of the above-mentioned embodiments.

[0075] Another aspect of the present application provides a lithium supplement agent comprising the high-purity lithium oxalate prepared by the method according to the above-mentioned embodiments of the first aspect. Since the application employs all the technical solutions of the above-mentioned method, it at least has all the beneficial effects brought by the technical solutions of the above-mentioned embodiments.

[0076] Other features and advantages of the present application will be set forth in the following description, and in part will become apparent to those skilled in the art upon examination of the following or can be learned by practice of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0077] The above and / or additional aspects and advantages of the present application will become apparent and be readily appreciated from the description of the embodiments, given in conjunction with the accompanying drawings, in which:

[0078] Figure 1 Flow chart of the method for preparing lithium oxalate for Examples 1-4. DETAILED DESCRIPTION

[0079] In the description of the present application, if there is description to first, second, etc. is only for the purpose of distinguishing technical features, and can not be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features or the sequence of the indicated technical features.

[0080] The words "preferably", "more preferably", and the like, in the present application, refer to embodiments of the present application which can provide certain benefits under certain circumstances. However, other embodiments can also be preferred under the same or other circumstances. In addition, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful, and is not intended to exclude other embodiments from the scope of the present application.

[0081] When a numerical range is disclosed herein, the range is to be construed as continuous, and to include each and every value and sub-range within the range. Further, when ranges are given, the range includes the minimum and maximum values, and each integer within the range. Additionally, where multiple ranges are provided, the ranges can be combined. In other words, unless otherwise indicated, all ranges disclosed herein are to be understood as being inclusive of the endpoints, and individually to each and every value and sub-range within the range.

[0082] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the scope of the present application.

[0083] The reagents, methods and equipment used in the present application are conventional reagents, methods and equipment in the technical field, unless otherwise specified.

[0084] Example 1

[0085] A method for preparing lithium oxalate, the flow chart is shown as Figure 1 Specifically, the method comprises the following steps:

[0086] S1 In the grinding machine, 200 g of waste lithium battery black powder and 25 g of calcium oxalate were mixed in 800 g of dehydrogenated kerosene, the temperature was controlled at 25 ℃, and grinding and washing were performed for 30 minutes. After grinding was completed, filtration was performed to obtain a first residue;

[0087] S2 The first residue was placed in a blast circulating oven, the temperature was controlled at 200 ℃, and drying was performed for 60 minutes to obtain a second residue;

[0088] S3 The second residue was mixed with 10 g of ammonium carbonate, and was added into a vacuum furnace, and was heated to 700 ℃, and was kept at the temperature for roasting for 60 minutes. The material was broken to obtain a third residue;

[0089] S4 The third residue and 600 mL of pure water were mixed, stirring was performed at a temperature of 50 ℃, oxalic acid (35.5 g of oxalic acid was added) was added to adjust the pH value to 3, and the pH value was kept for reaction for 60 minutes. Filtration was performed to obtain a crude lithium oxalate solution of 577 mL, and the fluorine content was 0.083 g / L. The filter residue obtained after drying was 187.5 g, and the content in the filter residue was 0.17%;

[0090] S5 The crude lithium oxalate solution was heated to 85 ℃, 3.5 g of oxalic acid was added, and the reaction was kept for 30 minutes. After the time was reached, 0.5 g of calcium oxalate was added for continuous reaction for 60 minutes. After the time was reached, lithium hydroxide was added to adjust the pH value to 6.5. A total of 5.7 g of lithium hydroxide was added. Filtration was performed to obtain a refined lithium oxalate solution of 570 mL. It was determined that the fluorine content in the refined lithium oxalate solution was 0.0073 g / L, the COD was 0.012 g / L, and the B content was 0.033 g / L. The filter residue after drying was 2.3 g, and the lithium content was 0.11%;

[0091] S6 The refined lithium oxalate solution was subjected to decolorization and oil removal through an activated carbon column to obtain a solution of 570 mL. The fluorine content in the solution was 0.0051 g / L, the B content was 0.005 g / L, and the COD was 0.004 g / L. The solution was further filtered through two layers of qualitative filter paper (slow speed). There was yellow filter residue on the filter paper, which could not be weighed due to the small amount. The refined lithium oxalate solution was directly evaporated to dryness to obtain lithium oxalate.

[0092] Among them, the mass percentage of elements in 200 g of waste lithium battery black powder is shown in Table 1.

[0093] Table 1

[0094] Li F C Ni Co Mn 2.28％ 3.67％ 31.82％ 11.17％ 5.33％ 8.26％

[0095] Among them, the mass percentage of elements in the lithium oxalate obtained by evaporation to dryness in step S6 is shown in Table 2.

[0096] Table 2

[0097]

[0098]

[0099] The calculated lithium yield is: 100% - [(2.3 x 0.11% + 187.5 x 0.17%) ÷ (200 x 2.28%)] x 100% = 92.95%.

[0100] Example 2

[0101] A method for preparing lithium oxalate, a flow chart is shown as Figure 1 Specifically, the method comprises the following steps:

[0102] S1 In a grinder, mix 200 g of waste lithium battery black powder and 25 g of calcium oxalate in 800 g of dehydrogenated kerosene, control the temperature at 25°C, and grind and wash for 60 minutes. After grinding is completed, filter to obtain a first residue;

[0103] S2 Place the first residue in a blast circulating oven, control the temperature at 320°C, and dry for 90 minutes to obtain a second residue;

[0104] S3 Mix the second residue with 20 g of ammonium carbonate, and add into a vacuum furnace. Heat to 750°C, and keep the temperature for roasting for 180 minutes. Crush the material to obtain a third residue;

[0105] S4 Mix the third residue with 600 mL of pure water, control the temperature at 70°C, and stir. Add oxalic acid (30.8 g of oxalic acid is added) to adjust the pH value to 3.5, and keep the pH value for 120 minutes of reaction. Filter to obtain a crude lithium oxalate solution of 591 mL, and the fluorine content is 0.17 g / L. Dry the filter residue obtained by filtering to obtain 189.3 g of filter residue, and the content of the filter residue is 0.14%;

[0106] S5 Heat the crude lithium oxalate solution to 95°C, add 5.9 g of oxalic acid, and keep the temperature for 60 minutes of reaction. After the time is reached, add 1.5 g of calcium oxalate to continue the reaction for 120 minutes. After the time is reached, add lithium hydroxide to adjust the pH value to 7.0. A total of 7.4 g of lithium hydroxide is added. Filter to obtain 590 mL of refined lithium oxalate solution. The fluorine content is 0.0099 g / L, the COD is 0.009 g / L, and the B content is 0.017 g / L. Dry the filter residue obtained after filtering to obtain 3.6 g of filter residue, and the lithium content is 0.13%;

[0107] S6 The refined lithium oxalate solution is subjected to decolorization and oil removal through an activated carbon column to obtain 590 mL of solution, wherein the fluorine content is 0.0062 g / L, the B content is 0.003 g / L, and the COD is 0.001 g / L. Then, the solution is filtered through two layers of qualitative filter paper (slow speed). There is yellow filter residue on the filter paper, which cannot be weighed due to small amount. The refined lithium oxalate solution is directly evaporated to dryness to obtain lithium oxalate.

[0108] The mass percentage of elements in the 200 g waste lithium battery black powder is shown in Table 3.

[0109] Table 3

[0110] Li F C Ni Co Mn 1.98％ 2.44％ 36.91％ 9.89％ 4.12％ 10.48％

[0111] The lithium oxalate obtained by evaporation in step S6 is shown in Table 4.

[0112] Table 4

[0113]

[0114] The calculated lithium yield is: 100%-[(3.6x0.13%+189.3x0.14%) / (200x1.98%)]x100%=93.19%.

[0115] Example 3

[0116] A method for preparing lithium oxalate is shown in the flow chart Figure 1 Specifically, the method comprises the following steps:

[0117] S1 In a grinding machine, mix 200 g of waste lithium battery black powder and 15 g of calcium oxalate, add 600 g of dehydrogenated kerosene, control the temperature at 45℃, and grind and wash for 45 minutes. After grinding, filter to obtain a first residue;

[0118] S2 The first residue is placed in a blast circulating oven, the temperature is controlled at 180℃, and the residue is dried for 90 minutes to obtain a second residue;

[0119] S3 Mix the second residue with 40 g of ammonium carbonate, and add it into a vacuum furnace, heat to 820℃, and keep the temperature for roasting for 120 minutes. Crush the material to obtain a third residue;

[0120] S4 Mix the third residue with 800 mL of pure water, control the temperature at 70℃, and stir. Add oxalic acid (43.7 g) to adjust the pH value to 4, and keep the pH value for 60 minutes. Filter to obtain a crude lithium oxalate solution of 793 mL, and the fluorine content is 0.17 g / L. After drying, the filter residue is 186.3 g, and the content of the filter residue after filtration is 0.18%;

[0121] S5 heating the crude lithium oxalate solution to 90℃, adding 7.5g oxalic acid, and reacting for 60 minutes, then adding 2.0g calcium oxalate and continuing to react for 120 minutes, then adding lithium hydroxide to adjust the pH value to 7.0, a total of 6.6g lithium hydroxide is added, and 790mL of refined lithium oxalate solution is obtained, wherein the fluorine content is: 0.0059g / L, the COD is: 0.010g / L, and the B content is: 0.09g / L; the filter residue obtained after filtration is dried to obtain 7.3g, and the lithium content is 0.081%;

[0122] S6 The refined lithium oxalate solution is subjected to decolorization and oil removal by passing through an activated carbon column to obtain 790mL of solution, wherein the fluorine content is: 0.0033g / L, the B content is: 0.005g / L, and the COD is: 0.0027g / L, and then filtered through two layers of qualitative filter paper (slow speed), and the filter paper has yellow filter residue which cannot be weighed due to small amount, and the refined lithium oxalate solution is directly evaporated to dryness to obtain lithium oxalate.

[0123] The mass percentage of elements in the 200g waste lithium battery black powder is shown in Table 5.

[0124] Table 5

[0125] Li F C Ni Co Mn 2.53％ 1.55％ 25.13％ 12.80％ 5.98％ 10.43％

[0126] The lithium oxalate obtained by evaporation in step S6 has the mass percentage of elements shown in Table 6.

[0127] Table 6

[0128]

[0129] The calculated lithium yield is: 100%-[(7.3x0.081%+186.3x0.18%) / (200x2.53%)]x100%=93.26%.

[0130] Example 4

[0131] A method for preparing lithium oxalate, the flow chart is shown in Figure 1 Specifically, the method comprises the following steps:

[0132] S1 In a grinder, mix 200g waste lithium battery black powder and 20g calcium oxalate, add 800g dehydrogenated kerosene, control the temperature to 50℃, and grind and wash for 60 minutes, then filter to obtain a first residue;

[0133] S2 Place the first residue in a blast circulating oven, control the temperature to 250℃, and dry for 90 minutes to obtain a second residue;

[0134] S3: The second residue was mixed with 40 g of ammonium carbonate, and then was added into a vacuum furnace and was baked at 820 ℃ for 180 min. The material was crushed to obtain a third residue;

[0135] S4: The third residue and 600 mL of pure water were mixed and stirred at 70 ℃. Oxalic acid (50.9 g) was added to adjust the pH value to 3, and the reaction was maintained for 120 min. The lithium oxalate solution was filtered to obtain 589 mL of a crude lithium oxalate solution, and the fluorine content was 0.22 g / L. The filter residue was dried to obtain 195.9 g of a filter residue, and the lithium content was 0.12%.

[0136] S5: The crude lithium oxalate solution was heated to 95 ℃, and 5.5 g of oxalic acid was added. The reaction was maintained for 60 min. Then, 1.9 g of calcium oxalate was added, and the reaction was maintained for 120 min. Then, lithium hydroxide was added to adjust the pH value to 7.0. A total of 7.4 g of lithium hydroxide was added. The lithium oxalate solution was filtered to obtain 585 mL of a refined lithium oxalate solution, and the fluorine content was 0.015 g / L, the COD was 0.011 g / L, and the B content was 0.086 g / L. The filter residue was dried to obtain 10.5 g of a filter residue, and the lithium content was 0.15%.

[0137] S6: The refined lithium oxalate solution was subjected to decolorization and oil removal through an activated carbon column to obtain 585 mL of a solution, and the fluorine content was 0.01 g / L, the B content was 0.005 g / L, and the COD was 0.0055 g / L. The solution was filtered through two layers of qualitative filter paper (slow speed), and the filter paper had a small amount of yellow filter residue that could not be weighed. The refined lithium oxalate solution was directly evaporated to obtain lithium oxalate.

[0138] The mass percentage of the elements in the 200 g of waste lithium battery black powder is shown in Table 7.

[0139] Table 7

[0140] Li F C Ni Co Mn Figure 1 Li Ni Co Mn 1.59％ 3.29％ 38.20％ 7.99％ 4.54％ 11.41％

[0141] The lithium oxalate obtained by evaporation in step S6 is shown in Table 8.

[0142] Table 8

[0143]

[0144] The lithium yield was calculated to be 100%-[(10.5×0.15%+195.9×0.12%) / (200×1.59%)]×100%=92.11%.

[0145] The above merely illustrates the embodiments of the present application, and does not limit the patent scope of the present application, and any equivalent transformation or direct or indirect application in the related technical field based on the content of the present application is also included in the patent protection scope of the present application.

Claims

1. A method of preparing lithium oxalate, characterized by: The method comprises the following steps: S1: mixing waste lithium battery black powder and calcium salt in an organic solvent, grinding and filtering to obtain a first residue; S2: drying the first residue at a temperature below 400℃ to obtain a second residue; S3: mixing the second residue with carbonate, and vacuum roasting to obtain a third residue; S4: mixing the third residue, oxalic acid and water, heating and reacting, filtering to obtain a crude lithium oxalate solution; S5: heating the crude lithium oxalate solution, adding oxalic acid, calcium salt and alkaline reagent, and filtering to obtain a refined lithium oxalate solution after the reaction is completed; S6: filtering the refined lithium oxalate solution through an adsorption material to obtain the lithium oxalate.

2. The method of claim 1, wherein: The calcium salt comprises at least one of calcium oxalate, calcium hydroxide and calcium sulfate.

3. The method of claim 1, wherein: In the step S3, the carbonate comprises at least one of ammonium carbonate and sodium carbonate.

4. The method of claim 1, wherein: In the step S3, the temperature of the vacuum roasting is 700-820℃.

5. The method of claim 1, wherein: In the step S4, the mixture of the third residue, oxalic acid and water has a pH value of 3-4.

6. The method of claim 1, wherein: In the step S5, the calcium salt comprises at least one of calcium hydroxide, calcium sulfate and calcium oxalate.

7. The method of claim 1, wherein: In the step S5, the following step is further included: after adding oxalic acid and calcium salt into the crude lithium oxalate solution, the alkaline reagent is added after 60-120 minutes of reaction.

8. The method of claim 1, wherein: In the step S5, the following step is further included: the pH value of the mixture solution of the crude lithium oxalate solution, oxalic acid and calcium salt is adjusted to 6.5-7.0 by adding the alkaline reagent.

9. The method of claim 1, wherein: In the step S6, the adsorption material comprises activated carbon and / or decolorizing resin.

10. An electrolyte characterized by: The lithium oxalate is prepared by the method according to any one of claims 1 to 9.

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