A method for preparing iron phosphate from lithium iron phosphate waste

Abstract

The invention discloses a method for preparing iron phosphate from lithium iron phosphate waste, and relates to the field of battery technology; the method comprises the following steps: S1, using an oxidant and a mixed acid to acid-leach the lithium iron phosphate waste to obtain an acid-leach residue; S2, mixing the acid-leach residue with a phosphoric acid solution, separating the solid and the liquid, and collecting the liquid phase; S3, mixing the liquid phase, iron phosphate, an additive and water, and then crystallizing; after the crystallization is completed, the solid and the liquid are separated, and the solid phase is collected; S4, the solid phase is calcined. The method of the invention uses a mixed acid system of citric acid and sulfuric acid to leach lithium from the waste; and the solubility of iron phosphate is relatively low under low acidity conditions, thereby achieving preliminary impurity removal of lithium iron phosphate waste; then mixing the acid-leach residue with a phosphoric acid solution to leach iron, and realizing iron recovery; and adding additives during the crystallization process can better control the regeneration of iron phosphate.

Description

Technical Field

[0001] The invention belongs to the technical field of batteries, and in particular is a method for preparing iron phosphate from lithium iron phosphate waste. Background Art

[0002] Lithium-ion batteries are widely used in mobile phones, computers, new energy vehicles, energy storage stations and other industries. Lithium iron phosphate lithium-ion batteries are highly praised for their high safety, good thermal stability, low price and low pollution. While lithium iron phosphate is widely used, a large number of lithium iron phosphate batteries are scrapped and eliminated, and the amount of lithium iron phosphate battery waste is growing rapidly.

[0003] Commonly used recycling processes for lithium iron phosphate waste can be divided into solid phase method, liquid phase method, electrochemical method, biological decomposition method, etc. Among them, the electrode material regenerated by the solid phase method has poor electrochemical performance and high energy consumption. The recovery efficiency of the electrochemical method and the biological decomposition method is low, which is not conducive to large-scale industrial application. Summary of the invention

[0004] The object of the present invention is to provide a method for preparing iron phosphate from lithium iron phosphate waste, so as to solve at least one aspect of the problems and defects raised in the above background technology.

[0005] Specifically, the present invention provides a method for preparing iron phosphate from lithium iron phosphate waste, comprising the following steps:

[0006] S1, using an oxidant and mixed acid to acid-leach the lithium iron phosphate waste to obtain acid-leach residue;

[0007] S2, mixing the acid leaching residue and the phosphoric acid solution, separating the solid and the liquid, and collecting the liquid phase;

[0008] S3, mixing the liquid phase, iron phosphate, additives and water and crystallizing; after the crystallization is completed, the solid and liquid are separated and the solid phase is collected;

[0009] S4, calcining the solid phase obtained in step S3;

[0010] The mixed acid is a mixed solution of sulfuric acid and citric acid;

[0011] The additive comprises the following preparation raw materials:

[0012] 10 parts of butyl acrylate, 40 to 50 parts of o-phenylphenoxyethyl acrylate, 40 to 50 parts of hydroxyethyl methacrylate, 50 to 70 parts of ethyl acetate and 0.1 to 5 parts of benzoyl peroxide.

[0013] According to one technical solution of the method of the present invention, at least the following beneficial effects are achieved:

[0014] The method of the present invention uses a mixed acid system of citric acid and sulfuric acid to leach lithium from the waste; and the solubility of iron phosphate is relatively low under low acidity conditions, thereby achieving preliminary impurity removal of lithium iron phosphate waste;

[0015] The acid leaching residue is then mixed with a phosphoric acid solution to leach out the iron, thereby realizing iron recovery. An additive is added during the crystallization process. The additive has a hydrophilic group of a hydroxyl group and a hydrophobic group containing a benzene ring, and the additive is connected by a connecting group through a chemical bond. The hydrophobic group can be adsorbed on the particle surface, and the hydrophilic group is dissolved in the dispersion medium, which has a spatial hindrance effect, thereby better dispersing the reactants and better controlling the regeneration of iron phosphate.

[0016] According to some embodiments of the present invention, the temperature of the acid leaching in step S1 is 80°C to 90°C.

[0017] According to some embodiments of the present invention, the pH of the acid leaching in step S1 is 1-2.

[0018] According to some embodiments of the present invention, the acid leaching time in step S1 is 1 h to 2 h.

[0019] According to some embodiments of the present invention, the molar ratio of sulfuric acid to citric acid in the mixed acid is 10:1-2.

[0020] According to some embodiments of the present invention, the mass volume ratio of the lithium iron phosphate waste and the mixed acid is 1 g: 100 mL to 200 mL.

[0021] According to some embodiments of the present invention, the oxidant in step S1 is at least one of chlorate, hypochlorite, peroxide, persulfate and ozone.

[0022] According to some embodiments of the present invention, the chlorate is at least one of sodium chlorate and potassium chlorate.

[0023] According to some embodiments of the present invention, the hypochlorite is at least one of sodium hypochlorite and potassium hypochlorite.

[0024] According to some embodiments of the invention, the peroxide is hydrogen peroxide.

[0025] According to some embodiments of the present invention, the persulfate is at least one of potassium persulfate or sodium persulfate.

[0026] According to some embodiments of the present invention, the molar concentration of the phosphoric acid solution in step S2 is 3 mol / L to 6 mol / L.

[0027] According to some embodiments of the present invention, a liquid-to-solid ratio of the phosphoric acid solution to the acid leaching residue is 5 mL to 10 mL: 1 g.

[0028] According to some embodiments of the present invention, the mixing speed in step S2 is 300 rpm to 500 rpm.

[0029] According to some embodiments of the present invention, the mixing temperature in step S2 is 70°C to 95°C.

[0030] According to some embodiments of the present invention, the mixing time in step S2 is 1 h to 2 h.

[0031] According to some embodiments of the present invention, the mass ratio of the additive to iron phosphate in step S3 is 1:100-200.

[0032] According to some embodiments of the present invention, the mass ratio of the iron phosphate to the iron in the liquid phase is 1 to 5:100.

[0033] According to some embodiments of the present invention, the volume ratio of the liquid phase to water in step S3 is 1:1-4.

[0034] According to some embodiments of the present invention, the crystallization temperature in step S3 is 80°C to 95°C.

[0035] According to some embodiments of the present invention, the crystallization time in step S3 is 3 hours to 8 hours.

[0036] According to some embodiments of the present invention, the stirring speed of the crystallization in step S3 is 150 rpm to 400 rpm.

[0037] According to some embodiments of the present invention, the method for preparing the additive comprises the following steps:

[0038] S01, mixing butyl acrylate, o-phenylphenoxyethyl acrylate, hydroxyethyl methacrylate and ethyl acetate to prepare a first mixture;

[0039] S02, mixing the first mixture and benzoyl peroxide for reaction.

[0040] According to some embodiments of the present invention, the mixing temperature in step S01 is 100°C to 110°C.

[0041] According to some embodiments of the present invention, the mixing time in step S01 is 1 h to 2 h.

[0042] According to some embodiments of the present invention, the reaction temperature in step S02 is 110°C to 125°C.

[0043] According to some embodiments of the present invention, the reaction time in step S02 is 2 h to 3 h.

[0044] According to some embodiments of the present invention, after the reaction in step S02, the pH value is adjusted to neutral to obtain a neutral emulsion.

[0045] According to some embodiments of the present invention, the calcination temperature in step S4 is 500°C to 800°C.

[0046] According to some embodiments of the present invention, the calcination time in step S4 is 2 h to 5 h.

[0047] According to some embodiments of the present invention, the calcination atmosphere in step S4 is a protective atmosphere.

[0048] According to some embodiments of the present invention, the protective atmosphere is nitrogen or argon. DETAILED DESCRIPTION

[0049] The following will be combined with the embodiments to clearly and completely describe the concept of the present invention and the technical effects produced, so as to fully understand the purpose, characteristics and effects of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0050] In the description of the present invention, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0051] If the specific conditions are not specified in the examples, the experiments were carried out under conventional conditions or conditions recommended by the manufacturer. If the manufacturers of the reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0052] Example 1

[0053] This embodiment is a method for preparing iron phosphate from lithium iron phosphate waste, which consists of the following steps:

[0054] S1, adding hydrogen peroxide solution (mass concentration of 20%) and mixed acid (mixed solution of sulfuric acid and citric acid; the molar ratio of sulfuric acid to citric acid is 10:1.5) to lithium iron phosphate waste for acid leaching (the pH of the acid leaching is 1.5, the temperature is 80° C., and the time is 1 h) to obtain leached residue;

[0055] The mass volume ratio of lithium iron phosphate waste and hydrogen peroxide solution is 1g:12mL;

[0056] S2, mixing the leached residue and 6 mol / L phosphoric acid solution (the volume ratio of the leached residue to the phosphoric acid solution is 1 g: 5 mL) (mixing temperature is 90° C., time is 1.5 h, stirring speed is 450 rpm); solid-liquid separation is performed to obtain a solid phase and a liquid phase;

[0057] S3, mixing the liquid phase, iron phosphate, additives and water (the volume ratio of the liquid phase to water is 1:1; the mass ratio of the iron element to iron phosphate in the liquid phase is 100:3; the mass ratio of the additive to iron phosphate is 1:120), then crystallizing (temperature is 95°C, time is 5.5h, rotation speed is 200rpm), separating the solid and the liquid, and collecting the solid phase;

[0058] S4, calcining the solid phase obtained in step S3 (temperature is 500° C., time is 3 hours, atmosphere is nitrogen) to obtain anhydrous iron phosphate.

[0059] In this embodiment, the additives include the following raw materials in parts by weight:

[0060] 10 parts of butyl acrylate, 48 parts of o-phenylphenoxyethyl acrylate, 42 parts of hydroxyethyl methacrylate, 70 parts of ethyl acetate and 4 parts of benzoyl peroxide.

[0061] The preparation method of the additive in this embodiment consists of the following steps:

[0062] S1. Butyl acrylate, o-phenylphenoxyethyl acrylate, hydroxyethyl methacrylate and ethyl acetate are mixed and kept at 110° C. for 1.5 hours to obtain a first mixture.

[0063] S2. Mix 1 / 2 of the formula amount of benzoyl peroxide with the first mixture and keep the mixture at 115° C. for 1.5 hours to obtain a second mixture.

[0064] S3. Mix 1 / 2 of the formula amount of benzoyl peroxide and the second mixture and keep it at 125° C. for 1.5 hours; cool it to room temperature (25° C.), and then add ammonia water (mass fraction of 28%) to adjust the pH to neutral.

[0065] Example 2

[0066] This embodiment is a method for preparing iron phosphate from lithium iron phosphate waste, which consists of the following steps:

[0067] S1, adding hydrogen peroxide solution (mass concentration of 22%) and mixed acid (mixed solution of sulfuric acid and citric acid; the molar ratio of sulfuric acid to citric acid is 10:2) to lithium iron phosphate waste for acid leaching (the pH of the acid leaching is 1.5, the temperature is 80° C., and the time is 1 h) to obtain leached residue;

[0068] The mass volume ratio of lithium iron phosphate waste and hydrogen peroxide solution is 1g:10mL;

[0069] S2, mixing the leached residue and 4 mol / L phosphoric acid solution (the volume ratio of the leached residue to the phosphoric acid solution is 1 g: 6 mL) (mixing temperature is 90° C., time is 1.5 h, stirring speed is 450 rpm); solid-liquid separation is performed to obtain a solid phase and a liquid phase;

[0070] S3, mixing the liquid phase, iron phosphate, additives and water (the volume ratio of the liquid phase to water is 1:2; the mass ratio of the iron element to iron phosphate in the liquid phase is 100:4; the mass ratio of the additive to iron phosphate is 1:110), then crystallizing (temperature is 95°C, time is 5.5h, rotation speed is 200rpm), separating the solid and the liquid, and collecting the solid phase;

[0071] S4, calcining the solid phase obtained in step S3 (temperature is 500° C., time is 3 hours, atmosphere is nitrogen) to obtain anhydrous iron phosphate.

[0072] In this embodiment, the additives include the following raw materials in parts by weight:

[0073] 10 parts of butyl acrylate, 45 parts of o-phenylphenoxyethyl acrylate, 45 parts of hydroxyethyl methacrylate, 70 parts of ethyl acetate and 4 parts of benzoyl peroxide.

[0074] The preparation method of the additive in this example is carried out by referring to Example 1.

[0075] Example 3

[0076] This embodiment is a method for preparing iron phosphate from lithium iron phosphate waste, which consists of the following steps:

[0077] S1, adding hydrogen peroxide solution (mass concentration of 20%) and mixed acid (mixed solution of sulfuric acid and citric acid; the molar ratio of sulfuric acid to citric acid is 10:1.1) to lithium iron phosphate waste for acid leaching (the pH of the acid leaching is 1.5, the temperature is 80° C., and the time is 1 h) to obtain leached residue;

[0078] The mass volume ratio of lithium iron phosphate waste and hydrogen peroxide solution is 1g:14mL;

[0079] S2, mixing the leached residue and 4.5 mol / L phosphoric acid solution (the volume ratio of the leached residue to the phosphoric acid solution is 1 g: 10 mL) (mixing temperature is 90° C., time is 1.5 h, stirring speed is 450 rpm); solid-liquid separation is performed to obtain a solid phase and a liquid phase;

[0080] S3, mixing the liquid phase, iron phosphate, additives and water (the volume ratio of the liquid phase to water is 1:4; the mass ratio of the iron element to iron phosphate in the liquid phase is 100:5; the mass ratio of the additive to iron phosphate is 1:100), then crystallizing (temperature is 95°C, time is 5.5h, rotation speed is 200rpm), separating the solid and the liquid, and collecting the solid phase;

[0081] S4, calcining the solid phase obtained in step S3 (temperature is 500° C., time is 3 hours, atmosphere is nitrogen) to obtain anhydrous iron phosphate.

[0082] In this embodiment, the additives include the following raw materials in parts by weight:

[0083] 10 parts of butyl acrylate, 46 parts of o-phenylphenoxyethyl acrylate, 43 parts of hydroxyethyl methacrylate, 70 parts of ethyl acetate and 4 parts of benzoyl peroxide.

[0084] The preparation method of the additive in this example is carried out by referring to Example 1.

[0085] Example 4

[0086] This embodiment is a method for preparing iron phosphate from lithium iron phosphate waste, which consists of the following steps:

[0087] S1, adding hydrogen peroxide solution (mass concentration of 20%) and mixed acid (mixed solution of sulfuric acid and citric acid; the molar ratio of sulfuric acid to citric acid is 10:1.8) to lithium iron phosphate waste for acid leaching (the pH of the acid leaching is 1.5, the temperature is 80° C., and the time is 1 h) to obtain leached residue;

[0088] The mass volume ratio of lithium iron phosphate waste and hydrogen peroxide solution is 1g:15mL;

[0089] S2, mixing the leached residue and 4 mol / L phosphoric acid solution (the volume ratio of the leached residue to the phosphoric acid solution is 1 g: 8 mL) (mixing temperature is 90° C., time is 1.5 h, stirring speed is 450 rpm); solid-liquid separation is performed to obtain a solid phase and a liquid phase;

[0090] S3, mixing the liquid phase, iron phosphate, additives and water (the volume ratio of the liquid phase to water is 1:2; the mass ratio of the iron element to iron phosphate in the liquid phase is 100:3; the mass ratio of the additive to iron phosphate is 1:200), then crystallizing (temperature is 95°C, time is 5.5h, rotation speed is 200rpm), separating the solid and the liquid, and collecting the solid phase;

[0091] S4, calcining the solid phase obtained in step S3 (temperature is 500° C., time is 3 hours, atmosphere is nitrogen) to obtain anhydrous iron phosphate.

[0092] In this embodiment, the additives include the following raw materials in parts by weight:

[0093] 10 parts of butyl acrylate, 41 parts of o-phenylphenoxyethyl acrylate, 50 parts of hydroxyethyl methacrylate, 70 parts of ethyl acetate and 4 parts of benzoyl peroxide.

[0094] The preparation method of the additive in this example is carried out by referring to Example 1.

[0095] Example 5

[0096] This embodiment is a method for preparing iron phosphate from lithium iron phosphate waste, which consists of the following steps:

[0097] S1, adding hydrogen peroxide solution (mass concentration of 23%) and mixed acid (mixed solution of sulfuric acid and citric acid; the molar ratio of sulfuric acid to citric acid is 10:1) to lithium iron phosphate waste for acid leaching (the pH of the acid leaching is 1.5, the temperature is 80° C., and the time is 1 h) to obtain leached residue;

[0098] The mass volume ratio of lithium iron phosphate waste and hydrogen peroxide solution is 1g:10mL;

[0099] S2, mixing the leached residue and 5 mol / L phosphoric acid solution (the volume ratio of the leached residue to the phosphoric acid solution is 1 g: 5 mL) (mixing temperature is 90° C., time is 1.5 h, stirring speed is 450 rpm); solid-liquid separation is performed to obtain a solid phase and a liquid phase;

[0100] S3, mixing the liquid phase, iron phosphate, additives and water (the volume ratio of the liquid phase to water is 1:2; the mass ratio of the iron element to iron phosphate in the liquid phase is 100:5; the mass ratio of the additive to iron phosphate is 1:100), followed by crystallization (temperature of 95°C, time of 5.5h, rotation speed of 200rpm), solid-liquid separation, and collecting the solid phase;

[0101] S4, calcining the solid phase obtained in step S3 (temperature is 500° C., time is 3 hours, atmosphere is nitrogen) to obtain anhydrous iron phosphate.

[0102] In this embodiment, the additives include the following raw materials in parts by weight:

[0103] 10 parts of butyl acrylate, 40 parts of o-phenylphenoxyethyl acrylate, 40 parts of hydroxyethyl methacrylate, 70 parts of ethyl acetate and 4 parts of benzoyl peroxide.

[0104] The preparation method of the additive in this example is carried out by referring to Example 1.

[0105] Comparative Example 1

[0106] This comparative example is a method for preparing iron phosphate from lithium iron phosphate waste, which consists of the following steps:

[0107] S1, adding hydrogen peroxide solution (mass concentration of 23%) and mixed acid (mixed solution of sulfuric acid and citric acid; the molar ratio of sulfuric acid to citric acid is 10:1) to lithium iron phosphate waste for acid leaching (the pH of the acid leaching is 1.5, the temperature is 80° C., and the time is 1 h) to obtain leached residue;

[0108] The mass volume ratio of lithium iron phosphate waste and hydrogen peroxide solution is 1g:10mL;

[0109] S2, mixing the leached residue and 5 mol / L phosphoric acid solution (the volume ratio of the leached residue to the phosphoric acid solution is 1 g: 5 mL) (mixing temperature is 90° C., time is 1.5 h, stirring speed is 450 rpm); solid-liquid separation is performed to obtain a solid phase and a liquid phase;

[0110] S3, mixing the liquid phase, iron phosphate and water (the volume ratio of the liquid phase to water is 1:2; the mass ratio of the iron element to the iron phosphate in the liquid phase is 100:5; the mass ratio of the additive to the iron phosphate is 1:100), then crystallizing (temperature is 95°C, time is 5.5h, rotation speed is 200rpm), separating the solid and the liquid, and collecting the solid phase;

[0111] S4, calcining the solid phase obtained in step S3 (temperature is 500° C., time is 3 hours, atmosphere is nitrogen) to obtain anhydrous iron phosphate.

[0112] Comparative Example 2

[0113] This comparative example is a method for preparing iron phosphate from lithium iron phosphate waste, which consists of the following steps:

[0114] S1, adding hydrogen peroxide solution (mass concentration of 23%) and mixed acid (mixed solution of sulfuric acid and citric acid; the molar ratio of sulfuric acid to citric acid is 10:1) to lithium iron phosphate waste for acid leaching (the pH of the acid leaching is 1.5, the temperature is 80° C., and the time is 1 h) to obtain leached residue;

[0115] The mass volume ratio of lithium iron phosphate waste and hydrogen peroxide solution is 1g:10mL;

[0116] S2, mixing the leached residue and 5 mol / L phosphoric acid solution (the volume ratio of the leached residue to the phosphoric acid solution is 1 g: 5 mL) (mixing temperature is 90° C., time is 1.5 h, stirring speed is 450 rpm); solid-liquid separation is performed to obtain a solid phase and a liquid phase;

[0117] S3, mixing the liquid phase, iron phosphate, additives and water (the volume ratio of the liquid phase to water is 1:2; the mass ratio of the iron element to iron phosphate in the liquid phase is 100:5; the mass ratio of the additive to iron phosphate is 1:100), followed by crystallization (temperature of 95°C, time of 5.5h, rotation speed of 200rpm), solid-liquid separation, and collecting the solid phase;

[0118] S4, calcining the solid phase obtained in step S3 (temperature is 500° C., time is 3 hours, atmosphere is nitrogen) to obtain anhydrous iron phosphate.

[0119] The additives in this comparative example include the following preparation raw materials in parts by weight:

[0120] 10 parts of butyl acrylate, 40 parts of hydroxyethyl methacrylate, 70 parts of ethyl acetate and 4 parts of benzoyl peroxide.

[0121] The preparation method of the additive in this comparative example consists of the following steps:

[0122] S1. Butyl acrylate, hydroxyethyl methacrylate and ethyl acetate are mixed and kept at 110° C. for 1.5 hours to obtain a first mixture.

[0123] S2. Mix 1 / 2 of the formula amount of benzoyl peroxide with the first mixture and keep the mixture at 115° C. for 1.5 hours to obtain a second mixture.

[0124] S3. Mix 1 / 2 of the formula amount of benzoyl peroxide and the second mixture and keep it at 125° C. for 1.5 hours; cool it to room temperature (25° C.), and then add ammonia water (mass fraction of 28%) to adjust the pH to neutral.

[0125] Comparative Example 3

[0126] This comparative example is a method for preparing iron phosphate from lithium iron phosphate waste, which consists of the following steps:

[0127] S1, adding hydrogen peroxide solution (mass concentration of 20%) and mixed acid (mixed solution of sulfuric acid and citric acid; the molar ratio of sulfuric acid to citric acid is 10:1) to lithium iron phosphate waste for acid leaching (the pH of the acid leaching is 1.5, the temperature is 80° C., and the time is 1 h) to obtain leached residue;

[0128] The mass volume ratio of lithium iron phosphate waste and hydrogen peroxide solution is 1g:10mL;

[0129] S2, mixing the leached residue and 5 mol / L phosphoric acid solution (the volume ratio of the leached residue to the phosphoric acid solution is 1 g: 5 mL) (mixing temperature is 90° C., time is 1.5 h, stirring speed is 450 rpm); solid-liquid separation is performed to obtain a solid phase and a liquid phase;

[0130] S3, mixing the liquid phase, iron phosphate, additives and water (the volume ratio of the liquid phase to water is 1:2; the mass ratio of the iron element to iron phosphate in the liquid phase is 100:5; the mass ratio of the additive to iron phosphate is 1:100), followed by crystallization (temperature of 95°C, time of 5.5h, rotation speed of 200rpm), solid-liquid separation, and collecting the solid phase;

[0131] S4, calcining the solid phase obtained in step S3 (temperature is 500° C., time is 3 hours, atmosphere is nitrogen) to obtain anhydrous iron phosphate.

[0132] The additives in this comparative example include the following preparation raw materials in parts by weight:

[0133] 10 parts of butyl acrylate, 40 parts of o-phenylphenoxyethyl acrylate, 70 parts of ethyl acetate and 4 parts of benzoyl peroxide.

[0134] The preparation method of the additive in this comparative example consists of the following steps:

[0135] S1. Butyl acrylate, o-phenylphenoxyethyl acrylate and ethyl acetate are mixed and kept at 110° C. for 1.5 hours to obtain a first mixture.

[0136] S2. Mix 1 / 2 of the formula amount of benzoyl peroxide with the first mixture and keep the mixture at 115° C. for 1.5 hours to obtain a second mixture.

[0137] S3. Mix 1 / 2 of the formula amount of benzoyl peroxide and the second mixture and keep it at 125° C. for 1.5 hours; cool it to room temperature (25° C.), and then add ammonia water (mass fraction of 28%) to adjust the pH to neutral.

[0138] Electrical performance test

[0139] The lithium iron phosphate material was prepared using the iron phosphate recovered from Examples 1 to 5 and Comparative Examples 1 to 3. The specific raw materials and methods for preparation are as follows:

[0140] Lithium carbonate and iron phosphate (the molar ratio of lithium carbonate to iron phosphate is 1:2) are ground and mixed, sintered at 700° C. for 10 hours, cooled to room temperature, and taken out to obtain lithium iron phosphate positive electrode material.

[0141] The lithium iron phosphate materials prepared by the above method are respectively used as positive electrode active materials, and are mixed at a mass ratio of lithium iron phosphate: acetylene black: PVDF binder = 90:5:5 at room temperature (25°C) and normal pressure to form a slurry, which is evenly coated on a substrate with aluminum foil as a current collector to make a pole piece. The obtained film has a thickness of 5μm to 30μm and is used as a positive electrode.

[0142] Using metallic lithium as the negative electrode, 1 mol of LiPF6 was dissolved in 1 L of a mixed solvent of EC and DEC (volume ratio 1:1) as the electrolyte, and the positive and negative electrodes, separators, and electrolyte were prepared into a C2032 model battery in a nitrogen-protected glove box.

[0143] The battery was charged at 0.1C, 2.5-3.8V, and discharged at 0.1C, 2.5-3.8V for 50 cycles. The test results are shown in Table 1.

[0144] Table 1 Performance test results of iron phosphate corresponding to Examples 1 to 5 of the present invention and Comparative Examples 1 to 3

[0145]

[0146] In summary, the method of the present invention uses a mixed acid system of citric acid and sulfuric acid to leach lithium from waste materials; and the solubility of iron phosphate is relatively low under low acidity conditions, thereby achieving preliminary impurity removal of lithium iron phosphate waste materials; the acid leaching residue is then mixed with a phosphoric acid solution to leach iron, thereby achieving iron recovery; and an additive is added during the crystallization process, the additive having a hydrophilic group of a hydroxyl group and a hydrophobic group containing a benzene ring, and the additive is connected by a connecting group through a chemical bond, the hydrophobic group can be adsorbed on the particle surface, and the hydrophilic group is dissolved in the dispersion medium, which has a steric hindrance effect, thereby better dispersing the reactants and better controlling the regeneration of iron phosphate.

[0147] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing iron phosphate from lithium iron phosphate waste, characterized in that: The following steps are involved: S1, using an oxidant and mixed acid to acid-leach the lithium iron phosphate waste to obtain acid-leach residue; S2, mixing the acid leaching residue and the phosphoric acid solution, separating the solid and the liquid, and collecting the liquid phase; S3, mixing the liquid phase, iron phosphate, additives and water and crystallizing them; After the crystallization is completed, the solid and liquid are separated and the solid phase is collected; S4, calcining the solid phase obtained in step S3; The mixed acid is a mixed solution of sulfuric acid and citric acid; The additive comprises the following preparation raw materials: 10 parts of butyl acrylate, 40 to 50 parts of o-phenylphenoxyethyl acrylate, 40 to 50 parts of hydroxyethyl methacrylate, 50 to 70 parts of ethyl acetate and 0.1 to 5 parts of benzoyl peroxide; The pH of the acid leaching in step S1 is 1-2; The oxidant in step S1 is at least one of chlorate, hypochlorite, peroxide, persulfate and ozone; The preparation method of the additive comprises the following steps: S01, mixing butyl acrylate, o-phenylphenoxyethyl acrylate, hydroxyethyl methacrylate and ethyl acetate to prepare a first mixture; S02, mixing the first mixture and benzoyl peroxide for reaction.

2. The method according to claim 1, characterized in that The acid leaching temperature in step S1 is 80°C to 90°C.

3. The method according to claim 1, characterized in that The molar concentration of the phosphoric acid solution in step S2 is 3 mol / L to 6 mol / L.

4. The method according to claim 1, characterized in that: The mixing temperature in step S2 is 70°C to 95°C.

5. The method according to claim 1, characterized in that The mixing time in step S2 is 1 h to 2 h.

6. The method according to claim 1, characterized in that The mass ratio of the additive to iron phosphate in step S3 is 1:100-200.

7. The method according to claim 1, characterized in that The crystallization temperature in step S3 is 80°C to 95°C.

8. The method according to claim 1, characterized in that The calcination temperature in step S4 is 500°C to 800°C.

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