Method for preparing iron phosphate based on deep copper removal of waste lithium iron phosphate battery powder

Abstract

The invention discloses a method for preparing iron phosphate based on deep copper removal of waste lithium iron phosphate battery powder. The method comprises the following steps: firstly, mixing the waste lithium iron phosphate battery powder with an amino acid solution, and carrying out complex reaction to remove copper; and then on the basis of copper removal, the iron phosphate is prepared through the procedures of acid leaching, impurity removal, oxidation, aging and calcination. According to the copper removal method, the copper element in the waste lithium iron phosphate battery powder can be fully removed, and meanwhile the loss of other elements is reduced; the iron phosphate prepared on the basis of the method is not only low in copper content, but also more uniform in particle and high in conductivity.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparing iron phosphate from recycled waste lithium iron phosphate, and particularly relates to a method for preparing iron phosphate based on deep copper removal from waste lithium iron phosphate battery powder. Background Art

[0002] Lithium iron phosphate batteries have the advantages of safe performance, long cycle life, environmental friendliness, etc., and have obvious advantages in the fields of energy storage, new energy vehicles, etc., and their supply is increasing year by year. With the increasing number of retired batteries year by year, it has become extremely urgent to recycle retired LiFePO4 batteries, and at the same time, challenges also exist. The LiFePO4 cathode material accounts for about 40% of the battery production cost. Recycling the cathode material with high added value has important economic significance. Currently, the recycling process of waste power batteries generally includes pretreatment, separation, recovery, impurity removal and reuse. Waste LiFePO4 batteries are first discharged and disassembled to separate components such as battery cases, anode materials, cathode materials and diaphragms, and then recovered separately. Among them, the cathode material is separated from the active substance by heat treatment, alkali leaching or organic solvent method, and then the valuable metals in it are recovered by high-temperature direct regeneration or wet process.

[0003] Since the inherent values of P and Fe in the recycled cathode material are relatively low, and it is difficult to remove impurities such as Al and Cu in the lithium extraction slag, only Li with high economic value is often recovered during the wet metallurgy recycling of the cathode material. This results in a large amount of lithium iron phosphate lithium extraction slag that cannot be recycled in the existing lithium iron phosphate recycling system. The lithium extraction slag produced after lithium extraction is mostly used as a raw material for building materials, and iron and phosphorus cannot be efficiently utilized. Facing the current dilemma of lithium battery recycling, to improve the economic and social benefits of lithium battery recycling, it is necessary to study a method that can not only recover lithium from lithium iron phosphate, but also fully recover the iron and phosphorus components and prepare them into battery-grade iron phosphate for reuse. Currently, wet metallurgy is the mainstream recycling process for LiFePO4 cathode materials. Usually, the LiFePO4 cathode material is acid-leached and Li salts and FePO4 are obtained by stepwise precipitation. However, the corrosion of the current collector caused by overcharging and over-discharging of LiFePO4 batteries, as well as the mixing of materials caused by unrolling and screening, will all cause different amounts of current collector Cu powder to be mixed in the LiFePO4 cathode powder. During the wet recycling process, Cu impurities will inevitably enter the acid leaching solution with other components, resulting in the problem that the FePO4 prepared by recycling generally has an excessive Cu content, reducing the product added value and recycling economic value. Therefore, deep Cu removal is one of the important processes for the recycling and utilization of waste LiFePO4 cathode materials.

[0004] At present, the existing copper removal methods mainly include iron powder or metal chelating agent copper removal. For example, in the technical solution of the Chinese invention patent application with publication number CN111009660A, a certain amount of iron powder is added to the acid leaching solution and reacted at 30-80°C to achieve copper removal. However, the copper removal effect of iron powder is general. At the same time, the introduction of Fe source will destroy the iron-phosphorus ratio (Fe / P) of FePO4 in the acid solution, and the reaction activity and usage of Fe powder are difficult to control. Subsequently, phosphorus source needs to be supplemented for adjustment, which increases the complexity of the process and reduces the stability of the Cu removal effect.

[0005] For another example, the technical solution of the Chinese invention patent application with publication number CN112811404A discloses that lithium iron phosphate material is reacted with a metal complexing agent under the action of an inorganic acid to remove impurity metals such as aluminum and copper, wherein the metal complexing agent is selected from at least one of EDTA, PMA, PAA and HEDP, but these metal complexing agents, especially EDTA, are not effective under acidic conditions.

[0006] For example, in the technical solution of the Chinese invention patent application with publication number CN114180545A, copper is removed by adding a quaternary ammonium surfactant to the acid leaching solution, but the copper content in the finally prepared iron phosphate is still 200 ppm, which does not meet the conventional copper impurity index requirement of iron phosphate.

[0007] Since the existing copper removal schemes all have the problem of poor copper removal effect, based on this, a method for deeply removing copper from waste lithium iron phosphate battery powder and preparing iron phosphate based on it is now studied. Summary of the invention

[0008] Purpose of the invention: The technical problem to be solved by the present invention is to provide a method for preparing iron phosphate based on deep copper removal of waste lithium iron phosphate battery powder, which can remove copper impurities to the greatest extent, improve the purity of the prepared iron phosphate, and at the same time improve the uniformity and conductivity of the prepared iron phosphate.

[0009] Technical solution: The method for preparing iron phosphate based on deep copper removal of waste lithium iron phosphate battery powder comprises the following steps:

[0010] (1) mixing waste lithium iron phosphate battery powder with an amino acid solution according to a solid content of 5-30%, adjusting the pH value thereof to 7-11, and performing a complexation reaction at 50-80° C. under stirring for 0.5-2 h, and filtering to obtain a filter cake;

[0011] (2) dissolving the filter cake in water, adding an inorganic acid to adjust the pH value of the system to 0-1.0, performing an acid leaching reaction, and filtering to obtain an acid leaching solution;

[0012] (3) Adjust the pH value of the acid leaching solution to 1.5 - 2.5 to precipitate impurities and obtain a filtrate after impurity removal;

[0013] (4) Add an oxidant to the filtrate, adjust the pH to 1.5 - 2.5, and age for 2 - 4 h at 70 - 90 °C to obtain an iron phosphate precipitate. Finally, the precipitate is filtered, washed, dried, and calcined to obtain iron phosphate.

[0014] In the present invention, an amino acid solution is used as a copper complexing agent and mixed with waste lithium iron phosphate battery powder. Under alkaline conditions, heating is carried out to promote the complexation reaction between copper and the amino acid complexing agent. This complexing agent has good leaching selectivity for copper and low affinity for other metal ions. Therefore, it can effectively avoid the leaching of other metal ions, resulting in very small losses of lithium, iron, and phosphorus contents in the battery powder. At the same time, based on the complexing agent remaining in the filter cake after copper removal, when further using acid leaching to prepare iron and phosphorus to obtain iron phosphate, the amino acid complexing agent contains amino and carboxyl functional groups, which can form complexes with iron ions in the acid leaching solution, prevent their agglomeration or precipitation during the synthesis process, improve the stability and dispersion of iron ions, and thus control the growth of particles. And the formed complex is oxidized, and the divalent iron ions on the complex are oxidized to trivalent iron ions, and can be detached from the complex and combined with phosphorus to deposit and form iron phosphate, ultimately improving the uniformity and conductivity of the prepared iron phosphate.

[0015] Furthermore, in step (1) of the preparation method of the present invention, the concentration of the amino acid solution is 0.1 - 2 mol / L, and the amino acid is glycine, alanine, valine, leucine, isoleucine, methionine, proline, tryptophan, serine, tyrosine, cysteine, phenylalanine, asparagine, glutamine, threonine, aspartic acid, glutamic acid, lysine, arginine, or histidine.

[0016] Furthermore, in step (1) of the preparation method of the present invention, the rotation speed of the stirring is 100 - 400 rpm.

[0017] Furthermore, in step (2) of the preparation method of the present invention, the inorganic acid is hydrochloric acid, sulfuric acid, oxalic acid, or citric acid.

[0018] Furthermore, in step (2) of the preparation method of the present invention, the temperature of the acid leaching reaction is 40 - 80 °C, and the acid leaching reaction time is 1 - 4 h.

[0019] Furthermore, in step (3) of the preparation method of the present invention, after adjusting the pH value of the acid leaching solution to 1.5 - 2.5, react at 40 - 80 °C for 1 - 2 h to precipitate impurities.

[0020] Furthermore, in step (4) of the preparation method of the present invention, the oxidant is hydrogen peroxide, potassium permanganate, sodium chlorate or potassium persulfate.

[0021] Furthermore, in step (4) of the preparation method of the present invention, the drying temperature is 100 - 12 °C, the calcination temperature is 400 - 600 °C, and the calcination time is 1 - 4 h.

[0022] Beneficial effects: Compared with the prior art, the significant advantages of the present invention are as follows: This copper removal method can fully remove copper elements in waste lithium iron phosphate battery powder and simultaneously reduce the loss of other elements; moreover, the lithium iron phosphate prepared based on this method has low copper content, excellent particle uniformity, and strong conductivity. Description of the Drawings

[0023] Figure 1 It is the scanning electron microscope image of the lithium iron phosphate prepared in Example 2 of the present invention;

[0024] Figure 2 It is the scanning electron microscope image of the lithium iron phosphate prepared in Comparative Example 3 of the present invention;

[0025] Figure 3 It is the scanning electron microscope image of the lithium iron phosphate prepared in Example 3 of the present invention;

[0026] Figure 4 It is the scanning electron microscope image of the lithium iron phosphate prepared in Comparative Example 4 of the present invention. Detailed Embodiments

[0027] The technical solutions of the present invention will be further described in detail below in conjunction with the embodiments.

[0028] It should be noted that the solvent used in the amino acid solution of the present invention can be pure water.

[0029] The main element compositions of the waste lithium iron phosphate battery powder used in the following embodiments and comparative examples of the present invention are shown in Table 1 below.

[0030] Table 1 Element Compositions of Waste Lithium Iron Phosphate Battery Powder

[0031] Elements in battery powder Li Fe P Cu Al Content / % 1.98 10.89 6.42 0.5 0.3

[0032] Example 1

[0033] The method for preparing lithium iron phosphate based on the deep copper removal of waste lithium iron phosphate battery powder in this Example 1 includes the following steps:

[0034] (1) Take 100 g of waste lithium iron phosphate battery powder, place it in a beaker, add 900 g of glycine solution with a concentration of 2 mol / L, adjust the pH to 9.5 with ammonia water, heat it in a water bath to 60 °C, and react for 2 h under the condition of a stirring rate of 200 rpm to form a copper glycine complex. Filter to obtain a filter cake.

[0035] (2) Take the above filter cake, add 233 g of pure water, adjust the pH to 0.7 with sulfuric acid, and carry out an acid leaching reaction at 60 °C for 2 h. After the reaction, filter to obtain an acid leaching solution.

[0036] (3) Add ammonia water to the above acid leaching solution, adjust the pH of the solution to 2.5, and react at 60 °C for 1 h to precipitate impurities and obtain a purified filtrate.

[0037] (4) Add hydrogen peroxide to the above filtrate to oxidize the ferrous ions therein. Based on the standard that the solution makes potassium ferricyanide colorless, the addition amount is 20 g. Then adjust the pH of the solution to 2.0 with ammonia water and age at 90 °C for 3 h to allow the iron phosphate to settle fully.

[0038] (5) Finally, filter, wash the filter cake until the conductivity < 500 μm / cm to obtain iron phosphate dihydrate. After drying the iron phosphate dihydrate at 110 °C, calcine it in a muffle furnace at 550 °C for 2 h to prepare iron phosphate.

[0039] Comparative Example 1

[0040] The basic steps are the same as those in Example 1, except that copper is not removed first. The specific steps are as follows:

[0041] (1) Take 100 g of waste lithium iron phosphate battery powder, add 233 g of pure water, adjust the pH to 0.7 with sulfuric acid, and carry out an acid leaching reaction at 60 °C for 2 h. After the reaction, filter to obtain an acid leaching solution.

[0042] (2) Add ammonia water to the above acid leaching solution, adjust the pH of the solution to 2.5, and react at 60 °C for 1 h to precipitate impurities and obtain a purified filtrate.

[0043] (3) Add hydrogen peroxide to the above filtrate to oxidize the ferrous ions therein. Based on the standard that the solution makes potassium ferricyanide colorless, the addition amount is 20 g. Then adjust the pH of the solution to 2.0 with ammonia water and age at 90 °C for 3 h to allow the iron phosphate to settle fully.

[0044] (4) Finally, filter, wash the filter cake until the conductivity < 500 μm / cm to obtain iron phosphate dihydrate. After drying the iron phosphate dihydrate at 110 °C, calcine it in a muffle furnace at 550 °C for 2 h to prepare iron phosphate.

[0045] Comparative Example 2

[0046] The basic steps are the same as those in Example 1, except that iron powder is used to remove copper, and the specific steps are as follows:

[0047] (1) Take 100 g of waste lithium iron phosphate battery powder, add 233 g of pure water, adjust the pH to 0.7 with sulfuric acid, and carry out acid leaching reaction at 60 °C for 2 h. After the reaction, filter to obtain the acid leaching solution;

[0048] (2) Add ammonia water to the above acid leaching solution to adjust the pH of the solution to 2.5, add 0.7 g of iron powder, and react at 60 °C for 1 h to precipitate impurities and obtain the purified filtrate;

[0049] (3) Add hydrogen peroxide to the above filtrate to oxidize the ferrous ions therein. Based on the standard that potassium ferricyanide shows colorless in the solution, the addition amount is 20 g. Then adjust the pH of the solution to 2.0 with ammonia water and age at 90 °C for 3 h to make the iron phosphate fully settle;

[0050] (4) Finally, filter, wash the filter cake until the conductivity < 500 μm / cm to obtain iron phosphate dihydrate. After drying the iron phosphate dihydrate at 110 °C, calcine it in a muffle furnace at 550 °C for 2 h to prepare iron phosphate.

[0051] Measure the loss rate of main elements and the removal rate of impurity elements in step (1) of Example 1, and the obtained results are shown in Table 2.

[0052] Table 2 Loss rate of main elements and removal rate of impurity elements in step (1) of Example 1

[0053] Elements in iron phosphate Li Fe P Cu Example 1 0.8％ 0.2％ 0.13％ 98％

[0054] Measure the content of main elements and impurity content in the iron phosphate prepared in Example 1 and the comparative examples, and the results are shown in Table 3.

[0055] Table 3 Content of main elements in the iron phosphate prepared in Example 1, Comparative Example 1 and Comparative Example 2

[0056]

[0057]

[0058] Combined with Table 2 and Table 3, it can be seen that by using the recycling and re-preparation process of the present invention, copper in the waste lithium iron phosphate battery powder can be effectively removed and the loss of other metal ions can be reduced, and the content of copper in the prepared iron phosphate is low and the purity of the iron phosphate is high.

[0059] Example 2

[0060] A method for preparing iron phosphate based on the deep removal of copper from waste lithium iron phosphate battery powder in this Example 2 includes the following steps:

[0061] (1) Take 100 g of waste lithium iron phosphate battery powder, place it in a beaker, add 500 g of glycine solution with a concentration of 1 mol / L, adjust the pH to 7 with ammonia water, heat it in a water bath to 70 °C, and react for 1 h under the condition of a stirring rate of 300 rpm to form a copper glycine complex. After filtration, a filter cake is obtained.

[0062] (2) Take the above filter cake, add 233 g of pure water, adjust the pH to 0.5 with sulfuric acid, and carry out an acid leaching reaction at 60 °C for 2 h. After the reaction, filter to obtain an acid leaching solution.

[0063] (3) Add ammonia water to the above acid leaching solution, adjust the pH of the solution to 2, and react at 60 °C for 1 h to precipitate impurities and obtain a filtrate after impurity removal.

[0064] (4) Add hydrogen peroxide to the above filtrate to oxidize the ferrous ions therein. Taking the solution making potassium ferricyanide colorless as the standard, the addition amount is 20 g. Then adjust the pH of the solution to 2.5 with ammonia water and age at 80 °C for 3 h to make the iron phosphate fully settle.

[0065] (5) Finally, carry out filtration, wash the filter cake until the conductivity < 500 μm / cm to obtain iron phosphate dihydrate. After drying the iron phosphate dihydrate at 100 °C, place it in a muffle furnace and calcine at 500 °C for 2 h to prepare iron phosphate.

[0066] Comparative Example 3

[0067] The basic steps are the same as those in Example 2. The difference is that after the filter cake obtained in step (1), it is washed to remove the residual amino acids and then iron phosphate is prepared. The specific steps are as follows:

[0068] (1) Take 100 g of waste lithium iron phosphate battery powder, place it in a beaker, add 500 g of glycine solution with a concentration of 1 mol / L, adjust the pH to 8 with ammonia water, heat it in a water bath to 70 °C, and react for 1 h under the condition of a stirring rate of 300 rpm to form a copper glycine complex. After filtration and washing, a filter cake is obtained.

[0069] (2) Take the above filter cake, add 233 g of pure water, adjust the pH to 0.5 with sulfuric acid, and carry out an acid leaching reaction at 60 °C for 2 h. After the reaction, filter to obtain an acid leaching solution.

[0070] (3) Add ammonia water to the above acid leaching solution, adjust the pH of the solution to 2, and react at 60 °C for 1 h to precipitate impurities and obtain a filtrate after impurity removal.

[0071] (4) Add hydrogen peroxide to the above filtrate to oxidize the ferrous ions therein. Based on the standard that the solution makes potassium ferricyanide colorless, the addition amount is 20 g. Then adjust the pH of the solution to 2.5 with ammonia water, and age for 3 h at 80 °C to allow the iron phosphate to settle sufficiently.

[0072] (5) Finally, filter, wash the filter cake until the conductivity < 500 μm / cm to obtain iron phosphate dihydrate. After drying the iron phosphate dihydrate at 100 °C, calcine it in a muffle furnace at 500 °C for 2 h to prepare iron phosphate.

[0073] Example 3

[0074] The method for preparing iron phosphate based on the deep copper removal from waste lithium iron phosphate battery powder in Example 3 includes the following steps:

[0075] (1) Take 100 g of waste lithium iron phosphate battery powder, place it in a beaker, add 400 g of glycine solution with a concentration of 0.5 mol / L, adjust the pH to 11 with ammonia water, heat it in a water bath to 50 °C, and react for 1 h under the condition of a stirring rate of 400 rpm to form a glycine copper complex, and obtain a filter cake through filtration.

[0076] (2) Take the above filter cake, add 233 g of pure water, adjust the pH to 0 with sulfuric acid, and carry out an acid leaching reaction at 60 °C for 2 h. After the reaction, filter to obtain an acid leaching solution.

[0077] (3) Add ammonia water to the above acid leaching solution, adjust the pH of the solution to 1.5, and react at 60 °C for 1 h to precipitate impurities and obtain a purified filtrate.

[0078] (4) Add hydrogen peroxide to the above filtrate to oxidize the ferrous ions therein. Based on the standard that the solution makes potassium ferricyanide colorless, the addition amount is 20 g. Then adjust the pH of the solution to 1.5 with ammonia water, and age for 3 h at 70 °C to allow the iron phosphate to settle sufficiently.

[0079] (5) Finally, filter, wash the filter cake until the conductivity < 500 μm / cm to obtain iron phosphate dihydrate. After drying the iron phosphate dihydrate at 120 °C, calcine it in a muffle furnace at 400 °C for 2 h to prepare iron phosphate.

[0080] Comparative Example 4

[0081] The basic steps are the same as those in Example 3. The difference is that after obtaining the filter cake in step (1), wash it to remove the residual amino acids, and then prepare iron phosphate. The specific steps are as follows:

[0082] (1) Take 100 g of waste lithium iron phosphate battery powder and place it in a beaker. Add 400 g of glycine solution with a concentration of 0.5 mol / L. Adjust the pH to 11 using ammonia water, heat it in a water bath to 50 °C, and react for 1 h under a stirring rate of 400 rpm to form a copper glycine complex. After filtration and washing, obtain the filter cake;

[0083] (2) Take the above filter cake, add 233 g of pure water, adjust the pH to 0 using sulfuric acid, and carry out an acid leaching reaction at 60 °C for 2 h. After the reaction, filter to obtain the acid leaching solution;

[0084] (3) Add ammonia water to the above acid leaching solution, adjust the pH of the solution to 1.5, and react at 60 °C for 1 h to precipitate impurities and obtain the purified filtrate;

[0085] (4) Add hydrogen peroxide to the above filtrate to oxidize the ferrous ions therein. Based on the standard that the solution makes potassium ferricyanide colorless, the addition amount is 20 g. Then adjust the pH of the solution to 1.5 using ammonia water and age at 70 °C for 3 h to allow the iron phosphate to settle sufficiently;

[0086] (5) Finally, carry out filtration, wash the filter cake until the conductivity < 500 μm / cm to obtain iron phosphate dihydrate. After drying the iron phosphate dihydrate at 120 °C, place it in a muffle furnace and calcine at 400 °C for 2 h to prepare iron phosphate.

[0087] Determine the main element content and impurity content in the iron phosphate prepared in the examples and comparative examples. The results are shown in Table 4.

[0088] Table 4 Main element content in the iron phosphate prepared in Examples 2 - 3 and Comparative Examples 3 - 4

[0089] Elements in iron phosphate Li Fe P Cu Example 2 0.00006％ 36.33％ 20.88％ 0.004％ Comparative Example 3 0.00004％ 36.29％ 20.76％ 0.0025％ Example 3 0.00005％ 36.39％ 20.73％ 0.0003％ Comparative Example 4 0.00007％ 36.30％ 20.78％ 0.00034％

[0090] As can be seen from Table 4, for the two groups of Example 2 and Comparative Example 3, and Example 3 and Comparative Example 4, after forming the copper glycine complex in step (1), the difference lies in whether to wash the filter cake. By detecting the main element content in the prepared iron phosphate, it is found that the difference is not significant. Thus, it can be known that the addition of the complex in step (1) has been able to remove copper sufficiently.

[0091] At the same time, conduct structural characterization on the iron phosphate prepared in Example 2 and Comparative Example 3, and Example 3 and Comparative Example 4. The obtained results are as Figures 1 to 4 It can be seen that there is little difference in the removal of copper elements by whether to wash the filter cake, verifying that after the complexation reaction and filtration, it can be removed sufficiently, but the uniformity of the finally prepared iron phosphate is relatively obvious. Combining Figure 1 and Figure 3 , with Figure 2 and Figure 4By comparison, it can be seen that the iron phosphate prepared in Examples 2 and 3 without washing is relatively uniformly dispersed and no agglomeration is formed, while the iron phosphate prepared in Comparative Examples 3 and 4 after washing has relatively poor uniformity and agglomeration is formed. This is because amino acids are soluble in water themselves. After washing the filter cake prepared in step (1), the remaining amino acids are washed away by water, and thus the function of stabilizing and dispersing iron ions cannot be achieved, resulting in poor dispersibility of the finally prepared iron phosphate.

[0092] In addition to the above examples, the preparation process of the present invention and the defined process parameter ranges can all achieve the technical effects claimed by the present invention, and thus no further experiments are needed for verification one by one. For example, in step (1) of the preparation method of the present invention, the solid contents of the waste iron phosphate lithium battery powder and the amino acid solution can also be 5-30%, and the amino acids used can also be alanine, valine, leucine, isoleucine, methionine, proline, tryptophan, serine, tyrosine, cysteine, phenylalanine, asparagine, glutamine, threonine, aspartic acid, glutamic acid, lysine, arginine or histidine. The rotation speed of stirring and complexing can also be 100-400 rpm, and the complexing reaction time can also be 0.5-2 h.

[0093] In step (2) of the preparation method of the present invention, the inorganic acid added to adjust the pH value of the system can also be 0-1.0, and the inorganic acid can also be hydrochloric acid, sulfuric acid, oxalic acid or citric acid. The temperature of the acid leaching reaction can also be 40-80 °C, and the acid leaching reaction time can also be 1-4 h.

[0094] In step (3) of the preparation method of the present invention, the reaction temperature for precipitating impurities can also be 40-80 °C.

[0095] In step (4) of the preparation method of the present invention, the oxidant used can also be potassium permanganate, sodium chlorate or potassium persulfate. The aging reaction time can also be 2-4 h. The calcination temperature can also be 400-600 °C, and the calcination time can also be 1-4 h.

Claims

1. A method for preparing iron phosphate based on deep copper removal of waste lithium iron phosphate battery powder, characterized in that: The steps include: (1) mixing waste lithium iron phosphate battery powder with an amino acid solution according to a solid content of 5-30%, adjusting the pH value thereof to 7-11, and performing a complexation reaction at 50-80° C. under stirring for 0.5-2 h, and filtering to obtain a filter cake; (2) dissolving the filter cake in water, adding an inorganic acid to adjust the pH value of the system to 0-1.0, performing an acid leaching reaction, and filtering to obtain an acid leaching solution; (3) adjusting the pH value of the acid leaching solution to 1.5-2.5 to precipitate impurities and obtain a filtrate after impurity removal; (4) adding an oxidant to the filtrate, adjusting the pH to 1.5-2.5, aging at 70-90° C. for 2-4 hours to obtain an iron phosphate precipitate, and finally filtering, washing, drying, and calcining the precipitate to obtain iron phosphate.

2. The method for preparing iron phosphate based on deep copper removal of waste lithium iron phosphate battery powder according to claim 1, characterized in that: In step (1), the concentration of the amino acid solution is 0.1-2 mol / L, and the amino acid is glycine, alanine, valine, leucine, isoleucine, methionine, proline, tryptophan, serine, tyrosine, cysteine, phenylalanine, asparagine, glutamine, threonine, aspartic acid, glutamic acid, lysine, arginine or histidine.

3. The method for preparing iron phosphate based on deep copper removal of waste lithium iron phosphate battery powder according to claim 1, characterized in that: In step (1), the stirring speed is 100-400 rpm.

4. The method for preparing iron phosphate based on deep copper removal of waste lithium iron phosphate battery powder according to claim 1, characterized in that: In step (2), the inorganic acid is hydrochloric acid, sulfuric acid, oxalic acid or citric acid.

5. The method for preparing iron phosphate based on deep copper removal of waste lithium iron phosphate battery powder according to claim 1, characterized in that: In step (2), the temperature of the acid leaching reaction is 40-80° C., and the acid leaching reaction time is 1-4 hours.

6. The method for preparing iron phosphate based on deep copper removal of waste lithium iron phosphate battery powder according to claim 1, characterized in that: In step (3), after adjusting the pH value of the acid leaching solution to 1.5-2.5, the solution is reacted at 40-80° C. for 1-2 hours to precipitate impurities.

7. The method for preparing iron phosphate based on deep copper removal of waste lithium iron phosphate battery powder according to claim 1, characterized in that: In step (4), the oxidant is hydrogen peroxide, potassium permanganate, sodium chlorate or potassium persulfate, and the amount added is based on the standard that the solution makes potassium ferrocyanide appear colorless.

8. The method for preparing iron phosphate based on deep copper removal of waste lithium iron phosphate battery powder according to claim 1, characterized in that: In step (4), the drying temperature is 100-120° C., the calcination temperature is 400-600° C., and the calcination time is 1-4 hours.

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