A method for preparing ferric phosphate from recycled ferric phosphate waste

Abstract

This invention belongs to the field of waste battery material recycling and reuse technology, and specifically relates to a method for regenerating iron phosphate waste to prepare iron phosphate, including the following steps: (1) mixing iron phosphate waste and iron powder, grinding, adding acid solution to dissolve, filtering, and adding an oxidant to the filtered filtrate to obtain an oxidized liquid containing iron ions; (2) mixing nickel carbonate and phosphoric acid, dissolving and filtering, adding a dispersant to the filtered filtrate, stirring and dispersing to obtain a pre-P solution; (3) mixing the oxidized liquid and the pre-P solution, heating to produce a precipitation reaction, filtering to obtain a solid phase and a filtered liquid, adding water to the solid phase to make a slurry and grinding to obtain iron phosphate seed crystals; (4) mixing the iron phosphate seed crystals and the filtered liquid, heating and keeping warm to produce a precipitation reaction, filtering, adding water to the obtained solid phase to make a slurry and adding phosphoric acid for aging; (5) filtering the aged slurry, taking the solid phase and calcining to prepare anhydrous iron phosphate.

Description

Technical Field

[0001] This invention belongs to the field of waste battery material recycling technology, and specifically relates to a method for regenerating and preparing iron phosphate from waste iron phosphate. Background Technology

[0002] In recent years, with the continuous development of the new energy industry, especially the technological breakthroughs in the electric vehicle field, lithium iron phosphate has gradually become the mainstream in terms of market share. Battery-grade iron phosphate, as a precursor in the production of lithium iron phosphate batteries, plays a decisive role in the performance of lithium iron phosphate batteries.

[0003] Currently, the production process of ferric phosphate generates a large amount of substandard ferric phosphate waste. Direct disposal would lead to resource waste and environmental pollution. Therefore, there is an urgent need for a new process that can quickly and efficiently prepare high-purity ferric phosphate, achieve resource utilization of waste ferric phosphate slag, and eliminate wastewater and waste residue discharge. Summary of the Invention

[0004] This invention aims to at least solve one of the technical problems existing in related technologies. To this end, this invention proposes a method for the regeneration of waste iron phosphate to prepare iron phosphate, which enables the resource-based reuse of waste iron phosphate slag, avoiding waste and environmental pollution.

[0005] The above-mentioned technical objective of the present invention is achieved through the following technical solution:

[0006] A method for preparing ferric phosphate from recycled ferric phosphate waste includes the following steps:

[0007] (1) Mix the iron phosphate waste and iron powder, grind them, add acid to dissolve them, filter them, and add an oxidant to the filtrate to obtain an oxidized liquid containing iron ions.

[0008] (2) Mix nickel carbonate and phosphoric acid, dissolve and filter, add dispersant to the filtrate, stir and disperse to obtain the solution before preparing P;

[0009] (3) The oxidized liquid is mixed with the liquid before P preparation. The Fe / P molar ratio after mixing is 0.9-1.0. Then, the temperature is raised to cause a precipitation reaction. The solid phase and the filtered liquid are obtained by filtration. The solid phase is slurried with water and then ground to obtain iron phosphate seed crystals.

[0010] (4) The iron phosphate seed crystals are mixed with the filtered liquid and heated and kept at a temperature to cause a precipitation reaction. After filtration, the obtained solid phase is slurried with water and then added to phosphoric acid for aging.

[0011] (5) The aged slurry was filtered, and the solid phase was calcined to prepare anhydrous iron phosphate.

[0012] In one embodiment, in step (1), the iron phosphate waste and the iron powder are mixed and ground in a molar ratio of 2:(1-1.5).

[0013] In one embodiment, in step (1), the acid solution is a sulfuric acid solution with a mass concentration of 60%-80%.

[0014] In one embodiment, in step (1), the oxidant is hydrogen peroxide with a mass concentration of 20%-50%.

[0015] In one embodiment, in step (2), the phosphoric acid is a phosphoric acid solution with a mass concentration of >85%.

[0016] In one embodiment, in step (2), the nickel carbonate is industrial nickel carbonate.

[0017] In one embodiment, in step (2), the dispersant is at least one of 1,2-propylene glycol and polyethylene glycol.

[0018] In one embodiment, in step (2), the mass concentration of the dispersant in the pre-P solution is 2%-5%.

[0019] In one embodiment, in step (2), the dispersion and stirring time is 15-50 min.

[0020] In one embodiment, in step (3), the temperature after heating is 40-80°C, the heating rate is 8-15°C / h, and the precipitation reaction time is 3-5h.

[0021] In one embodiment, in step (3), the solid phase is first washed until the conductivity is <500 μS / cm before water is added to form a slurry.

[0022] In one embodiment, in step (3), the solid-liquid ratio of the solid phase slurry preparation with added water is 1 g: (2-8) mL.

[0023] In one embodiment, in step (3), the particle size of the obtained iron phosphate seed crystals is 0.5-1 μm.

[0024] In one embodiment, in step (4), the mixing mass of the iron phosphate seed crystals is 5%-15% of the theoretically generated iron phosphate mass.

[0025] In one embodiment, in step (4), the temperature after heating is 60-90°C, and the heat preservation time is 1-3 hours.

[0026] In one embodiment, in step (4), the filtrate obtained after filtration is extracted to remove impurities, and then evaporated and concentrated to obtain nickel sulfate crystals.

[0027] In one embodiment, in step (4), the solid-liquid ratio of the solid phase slurry preparation with added water is 1 g: (3-8) mL.

[0028] In one embodiment, in step (4), the phosphoric acid is a phosphoric acid solution with a mass concentration of 80%-90%.

[0029] In one embodiment, in step (4), the added phosphoric acid is 5%-20% of the total mass of the solid phase after water addition and pulping.

[0030] In one embodiment, in step (4), the filtrate obtained after filtration can be reused for aging.

[0031] In one embodiment, in step (4), when the Ni content in the filtrate obtained after filtration is greater than 2 g / L, the filtrate can be used to dissolve the nickel carbonate in step (2).

[0032] In one embodiment, in step (4), the aging temperature is 80-100°C and the aging time is 1-5 hours.

[0033] In one embodiment, in step (5), the solid phase is first washed and dried before being calcined.

[0034] In one embodiment, in step (5), the calcination temperature is 600-800°C and the calcination time is 1-3 hours.

[0035] The beneficial effects of this invention are:

[0036] (1) Iron phosphate waste and iron powder are ball-milled. Under mechanical force, iron phosphate generates ferrous phosphate through surface activation and lattice distortion, which solves the safety risk of a large amount of hydrogen gas generated by the reaction of iron powder with sulfuric acid during the addition process.

[0037] (2) The present invention uses the seed crystals generated by the nickel method to adjust the value. After washing, the seed crystals are ground to a small particle size and used as self-produced seed crystals (industry seed crystals are often induced by external iron phosphate seed crystals or are not controlled to form seed crystals, and their seed crystal morphology is compact and unstable). The present invention achieves fine control of seed crystals (the loose seed crystals generated by adjusting the value themselves are looser in morphology after being ground by sand milling, and have lower impurities after washing. The improvement of product impurity index and the precise control of product index are far superior to the ammonia method / sodium method).

[0038] (3) The nickel method is used for adjustment. Compared with the ammonia method, there is no wastewater treatment. Its nickel sulfate products can be used in ternary systems. It has high economic benefits and few environmental problems. Compared with the sodium method, its economic benefits are also high. Its impurity level is much lower than that of the sodium method (the solution impurity is Ni. Ni and Fe have similar atomic radii. They can be better replaced in the process of aging and crystallization to remove impurities. Basically, no lattice defects are formed, and the introduction of impurities is lower).

[0039] (4) Phosphoric acid is added during the aging stage to make its crystal surface structure loose, which is conducive to the precipitation of impurities and reduces the product impurity index. At the same time, phosphoric acid aging can be recycled in a closed loop. When the enriched impurity index is too high, it can be used to dissolve nickel carbonate at the front end. The whole system produces no waste acid liquid, thus maximizing the utilization of phosphoric acid.

[0040] (5) Addition of dispersants such as polyethylene glycol / 1,2-propylene glycol / low-temperature precipitation at 60℃. This ensures small particle size and good uniformity, preventing product agglomeration and resulting in excellent performance of the prepared lithium iron phosphate. Attached Figure Description

[0041] Figure 1 This is a flowchart illustrating Embodiment 1 of the present invention;

[0042] Figure 2 This is one of the SEM images (scale bar is 10 μm) of the iron phosphate prepared in Example 1 of the present invention;

[0043] Figure 3 This is the second SEM image (scale bar is 3 μm) of the iron phosphate prepared in Example 1 of the present invention;

[0044] Figure 4 The XRD pattern of the iron phosphate prepared in Example 1 of this invention;

[0045] Figure 5 This is one of the SEM images (scale bar is 10 μm) of the iron phosphate prepared in Comparative Example 1 of this invention;

[0046] Figure 6 This is the second SEM image of the iron phosphate prepared in Comparative Example 1 of this invention (scale bar is 3 μm). Detailed Implementation

[0047] The present invention will be further described below with reference to specific embodiments.

[0048] Example 1:

[0049] A method for preparing ferric phosphate from recycled ferric phosphate waste, such as Figure 1 As shown, the specific steps include the following:

[0050] (1) The iron phosphate waste and iron powder were ball-milled at a material molar ratio of 2:1 to obtain the ground material;

[0051] (2) Add 60% sulfuric acid to the ground material to dissolve it, and filter to obtain ferrous sulfate solution;

[0052] (3) Add 20% hydrogen peroxide to the ferrous sulfate solution obtained in step (2) to ensure that the ferrous ions are completely oxidized to ferric ions to obtain the oxidized solution.

[0053] (4) Take industrial nickel carbonate and add phosphoric acid (mass fraction of 90%) until the nickel carbonate no longer dissolves. Filter to obtain a solution. Add 1,2-propanediol to the solution and stir for 15 min to obtain the solution before preparing P. The mass concentration of 1,2-propanediol in the solution before preparing P is 2%.

[0054] (5) Mix the pre-P solution in step (4) with the post-oxidation solution in step (3) and stir well. The Fe / P molar ratio after mixing is 0.9. Heat to 40℃ at a rate of 10℃ / h and stir for 30 min to induce precipitation reaction. The precipitation reaction time is 4 h. Then filter to obtain solid phase and filtrate. Wash the solid phase with water until the conductivity is <500us / cm. Add water at a solid-liquid ratio of 1g:3mL to make a slurry and grind it in a sand mill to obtain iron phosphate seed crystals with a particle size of 0.5um.

[0055] (6) The iron phosphate seed obtained by grinding in step (5) is mixed with the filtered liquid in step (5), wherein the mixed mass of iron phosphate seed is 5% of the theoretical mass of iron phosphate generated. Then the temperature is raised to 60°C to carry out the iron phosphate precipitation reaction. The temperature is kept at 60°C for 3 hours. Then the solid phase and filtrate are obtained by filtration. The obtained filtrate is a nickel sulfate solution. The filtrate is extracted to remove impurities and then evaporated and concentrated to obtain nickel sulfate crystals.

[0056] (7) Mix the solid phase obtained by filtration in step (6) with water at a solid-liquid ratio of 1g:3mL to make pulp. Add 90% phosphoric acid at 5% of the total mass after pulping. After aging at 80℃ for 5 hours, filter. The filtrate can be repeatedly aged. When the Ni in the filtrate is greater than 2g / L, the filtrate can be used in step (4) to dissolve industrial nickel carbonate. Add fresh phosphoric acid in the pulping and aging stage for subsequent aging. Repeat step (7).

[0057] (8) The filtered liquid from step (7) was washed and dried to obtain ferric phosphate dihydrate. The ferric phosphate dihydrate was calcined at 600℃ for 3 hours to obtain anhydrous ferric phosphate. The SEM image of the prepared anhydrous ferric phosphate is shown below. Figure 2-3 As shown, by Figure 2-3 It can be seen that the prepared anhydrous iron phosphate has a small particle size and a loose and porous morphology, which corresponds to the low impurity index in Table 1. The XRD pattern is shown in the figure. Figure 4 As shown, by Figure 4 It can be seen that its XRD has no impurity peaks, indicating that it is anhydrous iron phosphate crystal form, which meets the requirements.

[0058] Example 2:

[0059] A method for preparing ferric phosphate from recycled ferric phosphate waste includes the following specific steps:

[0060] (1) The iron phosphate waste and iron powder were ball-milled at a material molar ratio of 2:1.5 to obtain the ground material;

[0061] (2) Add sulfuric acid with a mass concentration of 80% to the grinding material to dissolve it, and filter to obtain ferrous sulfate solution;

[0062] (3) Add 50% hydrogen peroxide to the ferrous sulfate solution obtained in step (2) to ensure that the ferrous ions are completely oxidized to ferric ions to obtain the oxidized solution.

[0063] (4) Take industrial nickel carbonate and add phosphoric acid (mass fraction of 90%) until the nickel carbonate no longer dissolves. Filter to obtain a solution. Add polyethylene glycol to the solution and stir for 50 min to obtain the solution before preparing P. The mass concentration of polyethylene glycol in the solution before preparing P is 3%.

[0064] (5) Mix the pre-P solution in step (4) with the post-oxidation solution in step (3) and stir well. The Fe / P molar ratio after mixing is 1.0. Heat to 80℃ at a rate of 10℃ / h and stir for 30 min to induce precipitation reaction. The precipitation reaction time is 4 h. Then filter to obtain solid phase and filtrate. Wash the solid phase with water until the conductivity is <500us / cm. Add water at a solid-liquid ratio of 1g:8mL to make a slurry and grind it in a sand mill to obtain iron phosphate seed crystals with a particle size of 0.6um.

[0065] (6) The iron phosphate seed obtained by grinding in step (5) is mixed with the filtered liquid in step (5), wherein the mixed mass of iron phosphate seed is 15% of the theoretical mass of iron phosphate generated. Then the temperature is raised to 90°C to carry out the iron phosphate precipitation reaction. The mixture is kept at 90°C for 1 hour. Then the solid phase and filtrate are obtained by filtration. The filtrate is a nickel sulfate solution. The filtrate is extracted to remove impurities and then evaporated and concentrated to obtain nickel sulfate crystals.

[0066] (7) Mix the solid phase obtained by filtration in step (6) with water at a solid-liquid ratio of 1g:8mL to make pulp. Add 20% of the total mass of the pulp with 80% phosphoric acid. After aging at 100℃ for 1 hour, filter. The filtrate can be aged repeatedly. When the Ni in the filtrate is greater than 2g / L, the filtrate can be used in step (4) to dissolve industrial nickel carbonate. Add fresh phosphoric acid to the pulp aging section for subsequent aging. Repeat step (7).

[0067] (8) Wash and dry the filtered liquid from step (7) to obtain ferric phosphate dihydrate. Calcine the ferric phosphate dihydrate at 800℃ for 1 hour to obtain anhydrous ferric phosphate.

[0068] Example 3:

[0069] A method for preparing ferric phosphate from recycled ferric phosphate waste includes the following specific steps:

[0070] (1) The iron phosphate waste and iron powder were ball-milled at a material molar ratio of 2:1.2 to obtain the ground material;

[0071] (2) Add 70% sulfuric acid to the ground material to dissolve it, and filter to obtain ferrous sulfate solution;

[0072] (3) Add 30% hydrogen peroxide to the ferrous sulfate solution obtained in step (2) to ensure that the ferrous ions are completely oxidized to ferric ions to obtain the oxidized solution.

[0073] (4) Take industrial nickel carbonate and add phosphoric acid (mass fraction of 90%) until the nickel carbonate no longer dissolves. Filter to obtain a solution. Add 1,2-propanediol to the solution and stir for 30 min to obtain the solution before preparing P. The mass concentration of 1,2-propanediol in the solution before preparing P is 4%.

[0074] (5) Mix the pre-P solution in step (4) with the post-oxidation solution in step (3) until the Fe / P molar ratio is 0.95. Heat to 50℃ at a rate of 10℃ / h and stir for 30 min to induce precipitation. The precipitation reaction takes 4 h. Then filter to obtain solid phase and filtrate. Wash the solid phase with water until the conductivity is <500us / cm. Add water at a solid-liquid ratio of 1g:5mL to make a slurry and grind it in a sand mill to obtain iron phosphate seed crystals with a particle size of 0.6um.

[0075] (6) The iron phosphate seed obtained by grinding in step (5) is mixed with the filtered liquid in step (5), wherein the mixed mass of iron phosphate seed is 10% of the theoretical mass of iron phosphate generated. Then the temperature is raised to 70°C to carry out the iron phosphate precipitation reaction. The mixture is kept at 70°C for 2 hours. Then the solid phase and filtrate are obtained by filtration. The filtrate is a nickel sulfate solution. The filtrate is extracted to remove impurities and then evaporated and concentrated to obtain nickel sulfate crystals.

[0076] (7) Mix the solid phase obtained by filtration in step (6) with water at a solid-liquid ratio of 1g:4mL to make pulp. Add 10% of the total mass of the pulp with 85% phosphoric acid. After aging at 90℃ for 2 hours, filter. The filtrate can be aged repeatedly. When the Ni in the filtrate is greater than 2g / L, the filtrate can be used in step (4) to dissolve industrial nickel carbonate. Add fresh phosphoric acid to the pulp aging section for subsequent aging. Repeat step (7).

[0077] (8) Wash and dry the filtered liquid from step (7) to obtain ferric phosphate dihydrate. Calcine the ferric phosphate dihydrate at 650°C for 2 hours to obtain anhydrous ferric phosphate.

[0078] Example 4:

[0079] A method for preparing ferric phosphate from recycled ferric phosphate waste includes the following specific steps:

[0080] (1) The iron phosphate waste and iron powder were ball-milled at a material molar ratio of 2:1.2 to obtain the ground material;

[0081] (2) Add 70% sulfuric acid to the ground material to dissolve it, and filter to obtain ferrous sulfate solution;

[0082] (3) Add 30% hydrogen peroxide to the ferrous sulfate solution obtained in step (2) to ensure that the ferrous ions are completely oxidized to ferric ions to obtain the oxidized solution.

[0083] (4) Take industrial nickel carbonate and add phosphoric acid (mass fraction of 90%) until the nickel carbonate no longer dissolves. Filter to obtain a solution. Add polyethylene glycol (molecular weight of 500) to the solution and disperse and stir for 30 min to obtain the solution before preparing P. The mass concentration of polyethylene glycol in the solution before preparing P is 2%.

[0084] (5) Mix the pre-P solution in step (4) with the post-oxidation solution in step (3) and stir well. The Fe / P molar ratio after mixing is 0.95. Heat to 50℃ at a rate of 10℃ / h and stir for 30 min to induce precipitation reaction. The precipitation reaction time is 4 h. Then filter to obtain solid phase and filtrate. Wash the solid phase with water until the conductivity is <500us / cm. Add water at a solid-liquid ratio of 1g:5mL to make a slurry and grind it in a sand mill to obtain iron phosphate seed crystals with a particle size of 1um.

[0085] (6) The iron phosphate seed obtained by grinding in step (5) is mixed with the filtered liquid in step (5), wherein the mixed mass of iron phosphate seed is 10% of the theoretical mass of iron phosphate generated. Then the temperature is raised to 60°C to carry out the iron phosphate precipitation reaction. The mixture is kept at 60°C for 2 hours. Then the solid phase and filtrate are obtained by filtration. The filtrate is a nickel sulfate solution. The filtrate is extracted to remove impurities and then evaporated and concentrated to obtain nickel sulfate crystals.

[0086] (7) Mix the solid phase obtained by filtration in step (6) with water at a solid-liquid ratio of 1g:4mL to make pulp. Add 10% of the total mass of the pulp with 85% phosphoric acid. After aging at 90℃ for 2 hours, filter. The filtrate can be aged repeatedly. When the Ni in the filtrate is greater than 2g / L, the filtrate can be used in step (4) to dissolve industrial nickel carbonate. Add fresh phosphoric acid to the pulp aging section for subsequent aging. Repeat step (7).

[0087] (8) Wash and dry the filtered liquid from step (7) to obtain ferric phosphate dihydrate. Calcine the ferric phosphate dihydrate at 650°C for 2 hours to obtain anhydrous ferric phosphate.

[0088] Comparative Example 1: (The only difference from Example 4 is that iron phosphate seeds were not prepared or added)

[0089] A method for preparing ferric phosphate from recycled ferric phosphate waste includes the following specific steps:

[0090] (1) The iron phosphate waste and iron powder were ball-milled at a material molar ratio of 2:1.2 to obtain the ground material;

[0091] (2) Add 70% sulfuric acid to the ground material to dissolve it, and filter to obtain ferrous sulfate solution;

[0092] (3) Add 30% hydrogen peroxide to the ferrous sulfate solution obtained in step (2) to ensure that the ferrous ions are completely oxidized to ferric ions to obtain the oxidized solution.

[0093] (4) Take industrial nickel carbonate and add phosphoric acid (mass fraction of 90%) until the nickel carbonate no longer dissolves. Filter to obtain a solution. Add polyethylene glycol to the solution and disperse and stir for 30 min to obtain the solution before preparing P. The mass concentration of polyethylene glycol in the solution before preparing P is 2%.

[0094] (5) Mix the pre-P solution in step (4) with the post-oxidation solution in step (3) and stir well. The Fe / P molar ratio after mixing is 0.95. Heat to 60℃ to carry out the phosphate precipitation reaction. Keep warm at 60℃ for 2 hours. Then filter to obtain solid phase and filtrate. The filtrate is nickel sulfate solution. After extraction to remove impurities, evaporate and concentrate to obtain nickel sulfate crystals.

[0095] (6) Mix the solid phase obtained by filtration in step (5) with water at a solid-liquid ratio of 1g:4mL to make pulp. Add 10% of the total mass of the pulp with 85% phosphoric acid. After aging at 90℃ for 2 hours, filter. The filtrate can be aged repeatedly. When the Ni in the filtrate is greater than 2g / L, the filtrate can be used in step (4) to dissolve industrial nickel carbonate. Add fresh phosphoric acid to the pulp aging stage for subsequent aging. Repeat step (6).

[0096] (7) The filtered liquid from step (6) was washed and dried to obtain ferric phosphate dihydrate. The ferric phosphate dihydrate was calcined at 650℃ for 2 hours to obtain anhydrous ferric phosphate. The SEM image of the prepared anhydrous ferric phosphate is shown below. Figure 5-6 As shown, by Figure 5-6 It can be seen that the prepared ferric phosphate has a compact morphology and large particle size, which corresponds to the high impurity level in Table 1.

[0097] Experimental example:

[0098] The specific surface area, D50, tap density and elemental content of the anhydrous ferric phosphate prepared in Examples 1-4 and Comparative Example 1 were tested respectively. The test results are shown in Table 1.

[0099] Table 1.

[0100]

[0101] As shown in Table 1, the Fe / P ratio (mass fraction of Fe divided by mass fraction of P) of the iron phosphate prepared by this invention can reach 0.975 or higher, while the Na content is no greater than 0.0013, the S content is no greater than 0.0039, the Cr content is no greater than 0.0003, the Cu content is no greater than 0.0001, and the Ni content is no greater than 0.0022, meeting the requirements for battery-grade iron phosphate. Furthermore, the particle size distribution coefficient of the iron phosphate is no greater than 1.12, and the specific surface area can reach 7.0 m². 2 / g and above, D50 between 6.1-8.7μm, and tap density between 1.02-1.1g / cm³ 3 .

[0102] Comparing Example 1 and Comparative Example 1, it can be seen that when iron phosphate seed crystals are not prepared and added during the preparation of iron phosphate, the S content in the final iron phosphate reaches 0.0231 and the Ni content reaches 0.0098, resulting in excessively high impurity content in the iron phosphate, which fails to meet the requirements for battery-grade iron phosphate. Simultaneously, the particle size distribution coefficient of the iron phosphate increases to 1.58, and the specific surface area decreases to 4.98 μm. 2 / g, D50 increases to 15.65 micrometers, which in turn affects its performance.

Claims

1. A method for preparing ferric phosphate from recycled ferric phosphate waste, characterized in that: Includes the following steps: (1) After mixing and grinding the iron phosphate waste and iron powder, add acid solution to dissolve and filter. Add oxidant to the filtered filtrate to ensure that the ferrous ions are completely oxidized to ferric ions to obtain an oxidized liquid containing iron ions. The iron phosphate waste and the iron powder are mixed and ground in a molar ratio of 2:(1-1.5). (2) Mix nickel carbonate and phosphoric acid until the nickel carbonate no longer dissolves. After dissolving, filter and add a dispersant to the filtrate. Stir and disperse to obtain the solution before preparing P. (3) The oxidized liquid is mixed with the liquid before P preparation. The Fe / P molar ratio after mixing is 0.9-1.

0. Then the temperature is raised to cause a precipitation reaction. The solid phase and the filtered liquid are obtained by filtration. The solid phase is slurried with water and then ground to obtain iron phosphate seed crystals. The temperature after heating is 40-80℃ and the precipitation reaction time is 3-5h. (4) The iron phosphate seed crystals are mixed with the filtered liquid and heated and kept at a certain temperature to cause a precipitation reaction. After filtration, the obtained solid phase is mixed with water to form a slurry and then added to phosphoric acid for aging. The heating temperature is 60-90℃ and the holding time is 1-3h. The aging temperature is 80-100℃ and the aging time is 1-5h. (5) The aged slurry was filtered, and the solid phase was calcined to prepare anhydrous ferric phosphate.

2. The method for preparing ferric phosphate from recycled ferric phosphate waste according to claim 1, characterized in that: In step (1), the acid solution is a sulfuric acid solution with a mass concentration of 60%-80%.

3. The method for preparing ferric phosphate from recycled ferric phosphate waste according to claim 1, characterized in that: In step (1), the oxidant is hydrogen peroxide with a mass concentration of 20%-50%.

4. The method for preparing ferric phosphate from recycled ferric phosphate waste according to claim 1, characterized in that: In step (2), the dispersant is at least one of 1,2-propylene glycol and polyethylene glycol.

5. The method for preparing ferric phosphate from recycled ferric phosphate waste according to claim 1, characterized in that: In step (2), the mass concentration of the dispersant in the pre-P solution is 2%-5%.

6. The method for preparing ferric phosphate from recycled ferric phosphate waste according to claim 1, characterized in that: In step (3), the heating rate is 8-15℃ / h.

7. The method for preparing ferric phosphate from recycled ferric phosphate waste according to claim 1, characterized in that: In step (3), the obtained iron phosphate seed crystals have a particle size of 0.5-1 μm.

8. The method for preparing ferric phosphate from recycled ferric phosphate waste according to claim 1, characterized in that: In step (5), the calcination temperature is 600-800℃ and the calcination time is 1-3h.

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