A method for recycling and processing waste lithium iron phosphate lithium extraction residue and application

Abstract

The application provides a recovery treatment method and application of waste lithium iron phosphate lithium extraction residue, and relates to the technical field of lithium ion battery material recovery. Specifically, the treatment method comprises the following steps: 1) sequentially performing acid leaching treatment and first reduction treatment on the waste lithium iron phosphate lithium extraction residue; 2) adding a second reducing agent and precipitating and removing aluminum, and then adding sulfonated kerosene and extracting and removing aluminum; 3) adding a complexing agent and precipitating and removing copper; 4) adding a sulfidizing agent and precipitating and removing titanium; 5) adding ammonium dihydrogen phosphate, ammonia water and polyvinylpyrrolidone and fully mixing; 6) adding phosphoric acid and a third reducing agent, adjusting to pH 1.5-2.5 and fully reacting; 7) adding a lithium source, a carbon source and a reducing agent, mixing and grinding, and then high-temperature sintering to obtain battery-grade lithium iron phosphate. The application has the advantages of high iron recovery rate, high recovery purity, high recovery utilization efficiency and the like by optimizing the impurity removal method and impurity removal process.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery material recycling technology, and more specifically, to a method and application for recycling and treating waste lithium iron phosphate residue. Background Technology

[0002] Lithium iron phosphate batteries have many advantages such as high energy density, good safety performance, and environmental friendliness, and are widely used in energy storage and new energy vehicles; however, due to their limited cycle life, a large number of waste batteries also face more environmental pressure.

[0003] Currently, the main methods for recycling lithium iron phosphate batteries include high-temperature remediation and hydrometallurgy. However, high-temperature remediation has high recycling costs and the recovered battery materials have low performance; while hydrometallurgical recycling can produce more valuable products, including iron phosphate and lithium carbonate, the content of impurity elements is still high and the resource recovery rate is low. Therefore, impurity removal has become a key point in hydrometallurgical recycling technology.

[0004] Specifically, the current acid leaching process for waste lithium iron phosphate residue uses sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid. Among these, hydrochloric acid and nitric acid leaching result in an Fe / P ratio greater than 1, while sulfuric acid leaching results in an Fe / P ratio lower than 1. Phosphoric acid leaching results in an Fe / P ratio close to 1, but its price is higher than the other three acid solutions. Therefore, finding a suitable acid leaching method is the first step in the recycling of waste lithium iron phosphate.

[0005] Besides acid leaching, the subsequent impurity removal process of lithium iron phosphate (LFP) extraction slag is equally important, mainly because the content of impurity elements can affect the usability of LFP. Currently, methods for copper removal include displacement, acid leaching, and complexation / precipitation; methods for aluminum removal include precipitation, ion exchange resin methods, and alkaline leaching. The order of impurity removal is also crucial; otherwise, iron phosphate precipitation will occur, resulting in a waste of iron phosphate resources. Therefore, optimizing the process for recycling waste LFP extraction slag to produce LFP is essential.

[0006] In view of this, the present invention is hereby proposed. Summary of the Invention

[0007] The primary objective of this invention is to provide a method for recycling and processing waste lithium iron phosphate residue, which addresses the technical deficiency in the recovery of waste lithium iron phosphate batteries via hydrometallurgical recycling, where the content of impurity elements in the recycled products remains high due to poor impurity removal.

[0008] A second objective of this invention is to provide a battery-grade lithium iron phosphate.

[0009] A third objective of this invention is to provide a lithium-ion battery.

[0010] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0011] The recycling and treatment method for waste lithium iron phosphate lithium extraction residue includes the following steps:

[0012] (1) The waste lithium iron phosphate lithium extraction residue is subjected to acid leaching and first reduction treatment in sequence to obtain the first solution;

[0013] (2) Add a second reducing agent to the first solution and precipitate to remove aluminum, then add sulfonated kerosene and extract to remove aluminum, and obtain a second solution after separation;

[0014] (3) Add a complexing agent to the second solution and precipitate to remove copper. After solid-liquid separation, a third solution is obtained.

[0015] (4) Add a sulfiding agent to the third solution and precipitate to remove titanium. After solid-liquid separation, a fourth solution is obtained.

[0016] (5) Add ammonium dihydrogen phosphate, ammonia and polyvinylpyrrolidone to the fourth solution, and mix thoroughly to obtain a suspension containing ferrous phosphate;

[0017] (6) Add phosphoric acid and a third reducing agent to the suspension, adjust the pH to 1.5-2.5, and after the reaction is complete, separate the solid and liquid to obtain iron phosphate;

[0018] (7) After mixing and grinding the iron phosphate, lithium source, carbon source and reducing agent, high-temperature sintering is carried out to obtain battery-grade lithium iron phosphate.

[0019] A lithium iron phosphate is prepared by the recycling and treatment method described above for waste lithium iron phosphate lithium extraction residue.

[0020] A lithium-ion battery, wherein the positive electrode of the lithium-ion battery is a lithium iron phosphate positive electrode, and the lithium iron phosphate positive electrode is prepared by means of the lithium iron phosphate.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] (1) This invention provides a method for recycling battery-grade lithium iron phosphate, using lithium extraction residue from waste lithium iron phosphate as the raw material for recycling. By optimizing the impurity removal method and process, it has advantages such as high iron recovery rate, high recycling purity, and high recycling efficiency.

[0023] (2) The present invention uses a mixture of phosphoric acid and hydrochloric acid for acid leaching, which has advantages such as price advantage, mature engineering application and great effect on impurity leaching.

[0024] (3) The present invention uses chemical precipitation and extraction to remove aluminum, which can achieve the effect of deep aluminum removal.

[0025] (4) The present invention uses a complexing agent to remove copper, which can form a stable copper-containing compound and avoid the problem of incomplete removal of impurities.

[0026] (5) The present invention uses polyvinylpyrrolidone (PVP) assisted coprecipitation method, which can improve the purity and crystallinity of the product Fe3(PO4)2·8H2O, and at the same time control the morphology and uniformity.

[0027] (6) The present invention adopts a synthesis process that first forms Fe3(PO4)2·8H2O and then forms FePO4·2H2O, which can reduce the amount of washing water used and the content of impurity elements in the precipitation process.

[0028] (7) The present invention uses a high-temperature solid-state method to prepare LiFePO4, which can prepare lithium iron phosphate positive electrode active material with microporous spherical morphology. Detailed Implementation

[0029] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially. In addition, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0030] The first aspect of the present invention is to provide a method for recycling and treating waste lithium iron phosphate lithium extraction residue.

[0031] This invention uses lithium extraction slag from waste lithium iron phosphate as the starting material for the reaction. The source of the lithium extraction slag is as follows: more than 90% of the lithium can be extracted by hydrometallurgical methods to recover lithium iron phosphate batteries, but a large amount of lithium extraction slag will remain. Because the lithium extraction slag contains impurity metals such as Mg, Ca, Cu, and Ni, and the content is much higher than the 50ppm content requirement of the Chinese battery and FePO4 chemical industry standard (HG / T 4701-2014), and the composition is complex, it is difficult to reuse.

[0032] The recycling and treatment method for waste lithium iron phosphate residue includes the following seven steps, and the technical features involved will be explained in detail below.

[0033] (1) The waste lithium iron phosphate residue is subjected to acid leaching and first reduction treatment in sequence to obtain the first solution.

[0034] In a preferred embodiment, the acid used in the acid leaching treatment is a mixture of phosphoric acid and hydrochloric acid.

[0035] In a more preferred embodiment, the concentration of phosphoric acid is 1.3 mol / L to 2 mol / L; and the concentration of hydrochloric acid is 0.25 mol / L to 0.03 mol / L.

[0036] In a more preferred embodiment, the volume ratio of phosphoric acid to hydrochloric acid is (3-6):1, including but not limited to any one or any two of the following: 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, 6:1.

[0037] In a more preferred embodiment, the liquid-to-solid ratio of the acid used in the acid leaching treatment to the lithium extraction slag is 10 mg / L to 40 mg / L, including but not limited to any one or any two of the following values: 10, 12, 15, 18, 20, 22, 24, 25, 28, 30, 32, 35, 38, and 40 (mg / L).

[0038] In a preferred embodiment, the acid leaching temperature is 10℃~80℃, and the acid leaching time is 1h~4h.

[0039] In this invention, ferric ions are reduced to ferrous ions by a first reduction treatment; as a preferred embodiment, the reducing agent for the first reduction treatment includes at least one of methanol, iron powder or sodium sulfite.

[0040] In a preferred embodiment, the reaction temperature of the first reduction treatment is 50°C to 60°C.

[0041] In a preferred embodiment, the endpoint of the first reduction treatment is determined by electrolysis. The electrolysis method includes the following steps: inserting electrodes into the reaction solution of the first reduction treatment and connecting them to a constant voltage DC power supply to carry out the electrolysis reaction. When hydrogen evolution begins at the cathode, it is proven that the iron ions have been completely reduced, and the first reduction treatment has reached the reaction endpoint.

[0042] (2) Add a second reducing agent to the first solution and precipitate to remove aluminum, then add sulfonated kerosene and extract to remove aluminum, and obtain a second solution after separation.

[0043] In a preferred embodiment, the second reducing agent includes at least one of sodium fluoride, hydrogen fluoride, lithium fluoride, or iron powder. The reaction equation for the precipitation in this step is:

[0044] Al 3+ +3F- —AlF3; or, 2Al 3+ +3Fe——2Al+3Fe 2+ .

[0045] In a preferred embodiment, the molar ratio of the amount of the second reducing agent to the amount of aluminum in the second reduction treatment is (6-8):1.

[0046] In a preferred embodiment, the sulfonated kerosene is P204-sulfonated kerosene.

[0047] In a preferred embodiment, the volume concentration of the sulfonated kerosene is 30% to 50%, and the solvent for the sulfonated kerosene is sulfuric acid. The sulfonated kerosene used in this invention is obtained by reacting concentrated sulfuric acid with kerosene as a sulfiding agent. In some optional embodiments, the volume ratio of the raw material kerosene to concentrated sulfuric acid is 5:1.

[0048] In a preferred embodiment, the volume ratio of the sulfonated kerosene to the reaction liquid is (1-2):1.

[0049] (3) Add a complexing agent to the second solution and precipitate to remove copper. After solid-liquid separation, a third solution is obtained.

[0050] In a preferred embodiment, the complexing agent includes at least one of ammonia, ammonia water, or ethylenediamine. Taking ammonia as an example, the reaction equation for complexation is as follows:

[0051] Cu 2+ +4NH3——[Cu(NH3)4] 2+ .

[0052] In a preferred embodiment, the amount of the complexing agent is 4 to 5 times the Cu content, in molar ratio.

[0053] In a preferred embodiment, after adding the complexing agent, the mixture is allowed to stand until precipitation is complete before performing the solid-liquid separation.

[0054] (4) Add a sulfiding agent to the third solution and precipitate to remove titanium. After solid-liquid separation, a fourth solution is obtained.

[0055] In a preferred embodiment, the sulfiding agent includes at least one of potassium sulfide, sodium sulfide, or ammonium sulfide. Taking sodium sulfide as an example, the reaction equation for precipitation is as follows:

[0056] 2Na2S+Ti 4+ ——4Na 2+ +TiS2.

[0057] In a preferred embodiment, the amount of the vulcanizing agent is 2 to 3 times the Ti content, in molar ratio.

[0058] (5) Add ammonium dihydrogen phosphate, ammonia and polyvinylpyrrolidone to the fourth solution, and mix thoroughly to obtain a suspension containing ferrous phosphate.

[0059] As a preferred embodiment, the processing steps (2) to (5) are all carried out in a normal temperature environment.

[0060] As a preferred embodiment, the polyvinylpyrrolidone is usually in solid form (such as powder). Before step (5), the polyvinylpyrrolidone is vigorously stirred with water until homogeneous. After it is completely dissolved and allowed to stand to remove bubbles, the solution of the polyvinylpyrrolidone is used.

[0061] In a preferred embodiment, the thorough mixing time is 30 min to 60 min; in a more preferred embodiment, the thorough mixing is carried out by stirring at a frequency of 100 rpm to 300 rpm.

[0062] In a preferred embodiment, the polyvinylpyrrolidone plays an auxiliary co-precipitation role, and the amount of polyvinylpyrrolidone added is 20% to 30% of the volume of the fourth solution.

[0063] In a preferred embodiment, the amount of ammonium dihydrogen phosphate added should be in a molar ratio of 3:2 to the iron content in the solution.

[0064] In a preferred embodiment, the amount of ammonia added is such that the pH of the mixed reaction solution in step (5) is adjusted to 6 to 6.5; in a preferred embodiment, the pH of the reaction solution in step (5) should not be higher than 7.

[0065] In a preferred embodiment, after step (5), distilled water is added for washing until the conductivity of the reaction solution is 1400 uS / cm to 1600 uS / cm. Unreacted raw material impurities in the solution are removed by washing with distilled water to obtain a higher purity iron phosphate product.

[0066] (6) Add phosphoric acid and a third reducing agent to the suspension and adjust the pH to 1.5-2.5. After the reaction is complete, separate the solid and liquid to obtain iron phosphate.

[0067] In a preferred embodiment, the third reducing agent is hydrogen peroxide; in this step, hydrogen peroxide undergoes a redox reaction under specific pH conditions to convert ferrous phosphate in the solution into ferric phosphate; the main chemical reactions involved include:

[0068] 3Fe2+ +3PO4 3- +8H2O—Fe3(PO4)2·8H2O;

[0069] 2[Fe3(PO4)2·8H2O]+2PO4 3- +3H₂O₂ + 6H₂ + —6[FePO4·2H2O]+10H2O.

[0070] In a preferred embodiment, the concentration of phosphoric acid is 1.5 mol / L to 2.5 mol / L.

[0071] In a preferred embodiment, the temperature for the full reaction is 80°C to 95°C, and the reaction time is 1.5h to 3h.

[0072] As a preferred embodiment, the iron phosphate obtained by precipitation in step (6) usually carries water of crystallization. Therefore, after step (6), the obtained product is dried and calcined to remove the water of crystallization, so as to avoid affecting the subsequent synthesis of positive electrode active material.

[0073] In a more preferred embodiment, the calcination temperature is 500℃~600℃, and the reaction time is 1.5h~2.5h.

[0074] (7) The iron phosphate, lithium source, carbon source, and reducing agent are mixed and ground, then sintered at high temperature to obtain battery-grade lithium iron phosphate. The main chemical reactions involved in this step are:

[0075] 24FePO4+C6H 12 O6+12Li2CO3—24LiFePO4+18CO2+6H2O.

[0076] In a preferred embodiment, the lithium source includes at least one of lithium carbonate, lithium hydroxide, and lithium acetate; the carbon source includes at least one of glucose, sucrose, phenolic resin, or carbon black; and the reducing agent includes at least one of ascorbic acid or stearic acid.

[0077] In a preferred embodiment, the grinding is carried out by wet grinding, in which water is added to a mixture of solid raw materials to form a solution, and then high-speed ball milling is performed in a ball mill.

[0078] In a more preferred embodiment, the ball milling speed is 250 rpm to 300 rpm.

[0079] In a more preferred embodiment, the wet grinding process further includes a spray drying process of the raw material mixture, wherein the inlet temperature of the spray dryer is 180℃~240℃ and the peristaltic pump speed is 20rpm~30rpm.

[0080] In a preferred embodiment, the high-temperature sintering temperature is 650℃~750℃, and the high-temperature sintering time is 8h~12h.

[0081] In a preferred embodiment, the high-temperature sintering is carried out in a protective gas environment.

[0082] A second aspect of the present invention is to provide a lithium iron phosphate. The lithium iron phosphate is prepared by the aforementioned method for recycling and treating waste lithium iron phosphate extraction residue. The lithium iron phosphate has a battery-grade purity; that is, the lithium iron phosphate content is approximately 95% to 97%, and it can be directly used in the preparation of lithium iron phosphate batteries.

[0083] A third aspect of the present invention is to provide a lithium-ion battery. The positive electrode of the lithium-ion battery is a lithium iron phosphate positive electrode, and the lithium iron phosphate positive electrode is prepared from the lithium iron phosphate. In conventional manufacturing processes, the lithium iron phosphate is compounded with a conductive agent and a binder to a current collector and then sintered to obtain the lithium iron phosphate positive electrode. This positive electrode is then assembled with a negative electrode, a separator, an electrolyte, and other necessary structural components to obtain the lithium-ion battery. In this invention, no limitations are placed on the types of negative electrode, separator, or electrolyte; any device that provides battery functionality is considered an embodiment of the present invention.

[0084] Example 1

[0085] Step S1: Prepare 150g of lithium extraction residue from waste lithium iron phosphate; first, use 200mL of a mixed solution of 1.5mol / L phosphoric acid and 0.25mol / L hydrochloric acid (volume ratio of 5:1) for acid leaching at 50℃ for 3h to obtain lithium extraction residue acid leaching solution A.

[0086] Step S2: Add 20g of iron powder to the lithium residue acid leaching solution A and heat it to 50℃. Insert the electrode under constant temperature conditions and connect it to a constant voltage DC power supply (voltage = 2V) to carry out the electrolysis reaction. When hydrogen ions begin to be generated at the cathode, it can be proved that the iron ions have been completely reduced. Stop the electrolysis and obtain solution B.

[0087] Step S3: Add 9.2g of sodium fluoride to solution B for preliminary chemical precipitation to remove aluminum, and then add 200mL of P204-sulfonated kerosene extractant (30% volume concentration, concentrated sulfuric acid as solvent) for further Al removal. After separation, solution C is obtained.

[0088] Step S4: Add 50 mL of ammonia to solution C to remove Cu, and filter to obtain solution D;

[0089] Step S5: Add 15g of sodium sulfide to solution D to remove Ti, and filter to obtain solution E;

[0090] Step S6: Prepare 30g of polyvinylpyrrolidone and 70mL of water, mix vigorously for 30min, and set aside after complete dissolution; add 40g of ammonium dihydrogen phosphate, 35mL of 25% ammonia solution and polyvinylpyrrolidone solution to solution E, stir to obtain a blue-white suspension; wash with distilled water until the conductivity is 1500uS / cm, which is solution F;

[0091] Step S7: Add 320 mL of 2 mol / L phosphoric acid solution to solution F under stirring; then slowly add 75 mL of hydrogen peroxide to the mixed solution; adjust the pH of the mixed solution to 2.0 with ammonia; stir the slurry mixture at 90 °C for 2 h, filter and wash, then dry at 105 °C for 15 h to obtain FePO4·2H2O, and then calcine at 550 °C for 2 h to obtain FePO4;

[0092] Step S8: Mix 20g of FePO4 and 19.57g of Li2CO3 with water, then add 15wt.% glucose and 3wt.% ascorbic acid to form a mixed solution. Transfer the solution to a ball mill for ball milling at 300rpm, and then spray dry it under ultrasonic treatment.

[0093] Step S9: Transfer the spray-dried mixture into a tube furnace and calcine it at high temperature under a nitrogen protective atmosphere. Calcination at 700°C for 10 hours will yield lithium iron phosphate of this embodiment.

[0094] Example 2

[0095] Same as Example 1, except that:

[0096] Step S1: The volume ratio of phosphoric acid to hydrochloric acid is 3:1; the acid leaching temperature is 20℃, and the leaching time is 4 hours;

[0097] Step S3: Replace 9.2g of sodium fluoride with 4.4g of hydrogen fluoride;

[0098] Step S5: Replace 15g of sodium sulfide with 21g of potassium sulfide.

[0099] Example 3

[0100] Same as Example 1, except that:

[0101] Step S1: The volume ratio of phosphoric acid to hydrochloric acid is 6:1; the acid leaching temperature is 80℃, and the leaching time is 1 hour;

[0102] Step S3: Replace 9.2g of sodium fluoride with 12.3g of iron powder;

[0103] Step S6: Replace the mass of polyvinylpyrrolidone with 20g.

[0104] Example 4

[0105] Same as Example 1, except that:

[0106] Step S2: Replace 20g of iron powder with 45g of sodium sulfite and heat to 60℃;

[0107] Step S4: Replace 50 mL of ammonia with 12.5 mL of ethylenediamine;

[0108] Step S6: Wash with distilled water until the conductivity is 1600 uS / cm.

[0109] Example 5

[0110] Same as Example 1, except that:

[0111] Step S7: Stir the slurry mixture at 80℃ for 3 hours, filter and wash it, dry it at 105℃ for 15 hours to obtain FePO4·2H2O, and then calcine it at 500℃ for 2.5 hours to obtain FePO4.

[0112] Step S9: Calcine at 650℃ for 12 hours.

[0113] Example 6

[0114] Same as Example 1, except that:

[0115] Step S7: Stir the slurry mixture at 95℃ for 1.5h, filter and wash it, dry it at 105℃ for 15h to obtain FePO4·2H2O, and then calcine it at 600℃ for 1.5h to obtain FePO4.

[0116] Step S9: Calcine at 750℃ for 12 hours.

[0117] Experimental Example 1

[0118] The iron recovery rate and iron phosphate purity of the iron phosphate products obtained in step S7 of each embodiment of the present invention were calculated, and the results are shown in Table 1 below.

[0119] Among them, iron recovery rate refers to the ratio of the mass of iron in the obtained iron phosphate product to the mass of iron in the lithium extraction residue of waste lithium iron phosphate; iron phosphate purity refers to the ratio of the mass of iron phosphate to the total mass of the product.

[0120] Table 1

[0121] Iron recovery rate (%) Iron phosphate purity (%) Example 1 98.95％ 99.79％ Example 2 98.05％ 99.00％ Example 3 98.32％ 99.20％ Example 4 97.34％ 99.05％ Example 5 98.51％ 99.34％ Example 6 98.38％ 99.10％

[0122] Experimental Example 2

[0123] The method for preparing a positive electrode sheet from the lithium iron phosphate obtained in step S9 of various embodiments of the present invention includes:

[0124] Step 1: Slurry preparation: Mix lithium iron phosphate, conductive agent acetylene black (AB), and binder polytetrafluoroethylene (PTFE) in a mass ratio of 8:1:1, add to N-methylpyrrolidone (NMP) and stir for 5 hours until the slurry reaches a viscous consistency.

[0125] Step 2: Coating: Use a doctor blade and a casting coating machine to evenly coat the positive electrode slurry onto the aluminum foil of the positive electrode current collector;

[0126] Step 3: Drying: The coated aluminum foil is first dried by a forced-air drying process to remove the solvent NMP and the moisture contained therein, with the temperature set at 120℃; then it is dried by vacuum drying, with the vacuum level drawn to 0.1MPa, the temperature set at 120℃, and the time set at 6 hours.

[0127] Step 4: Pressing and cutting: Pressing is performed using a roller press, and the average thickness of the coating is 40μm; then the electrode is placed on a stamping machine to cut into conventional positive electrode sheets.

[0128] The positive electrode plates corresponding to each embodiment are tested, and the methods include:

[0129] The results are shown in Table 2 below.

[0130] Table 2

[0131] 0.1C charging specific capacity mAh / g 0.1C discharge specific capacity mAh / g First-time efficiency % Example 1 154.3 145.3 94.2 Example 2 160.4 146.8 91.4 Example 3 153.1 141.3 92.3 Example 4 157.3 146.5 93.1 Example 5 161.0 146.9 90.4 Example 6 157.4 143.1 90.2

[0132] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A method for recycling and treating waste lithium iron phosphate lithium extraction residue, characterized in that, The processing method includes the following steps: (1) The waste lithium iron phosphate residue is subjected to acid leaching and first reduction treatment in sequence to obtain a first solution; the acid used in the acid leaching treatment is a mixture of phosphoric acid and hydrochloric acid, and the volume ratio of phosphoric acid to hydrochloric acid is (3~6):1; the reducing agent in the first reduction treatment includes at least one of methanol, iron powder or sodium sulfite. (2) Add a second reducing agent to the first solution and precipitate to remove aluminum, then add sulfonated kerosene and extract to remove aluminum, and obtain a second solution after separation; (3) Add a complexing agent to the second solution and precipitate to remove copper. After solid-liquid separation, a third solution is obtained. (4) Add a sulfiding agent to the third solution and precipitate to remove titanium. After solid-liquid separation, a fourth solution is obtained. (5) Add ammonium dihydrogen phosphate, ammonia and polyvinylpyrrolidone to the fourth solution, and mix thoroughly to obtain a suspension containing ferrous phosphate; (6) Add phosphoric acid and a third reducing agent to the suspension, adjust the pH to 1.5~2.5, and after the reaction is complete, separate the solid and liquid to obtain iron phosphate; (7) After mixing and grinding the iron phosphate, lithium source, carbon source and reducing agent, high-temperature sintering is carried out to obtain battery-grade lithium iron phosphate.

2. The method for recycling and treating waste lithium iron phosphate residue according to claim 1, characterized in that, In step (1), the temperature of the acid leaching treatment is 10℃~80℃, and the time of the acid leaching treatment is 1h~4h.

3. The method for recycling and treating waste lithium iron phosphate residue according to claim 1, characterized in that, In step (1), the reaction temperature of the first reduction treatment is 50℃~60℃.

4. The method for recycling and treating waste lithium iron phosphate residue according to claim 1, characterized in that, In step (2), the second reducing agent includes at least one of sodium fluoride, hydrogen fluoride, lithium fluoride, or iron powder.

5. The method for recycling and treating waste lithium iron phosphate residue according to claim 1, characterized in that, In step (3), the complexing agent includes at least one of ammonia, ammonia water, or ethylenediamine.

6. The method for recycling and treating waste lithium iron phosphate residue according to claim 1, characterized in that, In step (4), the sulfiding agent includes at least one of potassium sulfide, sodium sulfide or ammonium sulfide.

7. The method for recycling and treating waste lithium iron phosphate residue according to claim 1, characterized in that, In step (5), the amount of polyvinylpyrrolidone added is 20% to 30% of the volume of the fourth solution.

8. The method for recycling and treating waste lithium iron phosphate residue according to claim 1, characterized in that, After step (5), add distilled water to wash until the conductivity of the reaction solution is 1400 uS / cm~1600 uS / cm.

9. The method for recycling and treating waste lithium iron phosphate residue according to claim 1, characterized in that, In step (6), the third reducing agent includes hydrogen peroxide.

10. The method for recycling and treating waste lithium iron phosphate residue according to claim 1, characterized in that, The temperature for the full reaction in step (6) is 80℃~95℃, and the reaction time is 1.5h~3h.

11. The method for recycling and treating waste lithium iron phosphate residue according to claim 1, characterized in that, In step (7), the high-temperature sintering temperature is 650℃~750℃, and the high-temperature sintering time is 8h~12h.

12. The method for recycling and treating waste lithium iron phosphate residue according to claim 1, characterized in that, The lithium source includes at least one of lithium carbonate, lithium hydroxide, and lithium acetate; the carbon source includes at least one of glucose, sucrose, phenolic resin, or carbon black; and the reducing agent includes at least one of ascorbic acid or stearic acid.