Method for preparing iron phosphate from ferrophosphorus slag

Abstract

The present invention provides a method for preparing iron phosphate from ferrophosphorus slag. The method comprises the following steps: (1) pretreating ferrophosphorus slag to obtain a mixture containing aluminum phosphate; (2) mixing the mixture with chloride, roasting to obtain roasted slag, after washing and filtering, mixing the roasted slag with an acid solution, and after reaction, performing solid-liquid separation to obtain a solution A; (3) mixing the solution A with elemental iron, after reaction, carrying out solid-liquid separation to obtain a solution B, and adding an iron source and / or a phosphorus source to adjust a molar ratio of phosphorus to iron to obtain a raw material solution; and (4) mixing the raw material solution with hydrogen peroxide, adjusting the pH value for reaction, carrying out solid-liquid separation to obtain iron phosphate dihydrate, and carrying out sintering treatment to obtain iron phosphate. The method of the present invention can realize deep removal of Al and Cu impurities, thereby preparing high-purity iron phosphate; and the method has a simple process and relatively low costs.

Description

A method for preparing ferric phosphate from ferrophosphorus slag Technical Field

[0001] The present invention belongs to the field of resource recovery and relates to a method for preparing ferric phosphate from ferrophosphorus slag. Background Art

[0002] Currently, lithium iron phosphate (LiFePO4), a regular olivine-like material, is hailed as an ideal cathode material for lithium-ion energy storage batteries and has achieved large-scale production. However, the limited lifespan of lithium-ion batteries will inevitably lead to the retirement of a large number of power lithium-ion batteries. In used LiFePO4 batteries, LiFePO4 accounts for 30%-35% of the battery mass, while copper and aluminum foil account for approximately 10%. The content of the valuable metal elements Li, Fe, Cu, and Al far exceeds their natural mineral content. Indiscriminate disposal of these batteries results in a significant waste of valuable resources, which is inconsistent with the country's green and sustainable development strategy.

[0003] However, Al, Cu, and Fe have similar properties and are difficult to separate. The presence of these impurities can affect the recovery of this type of ferrophosphorus slag to produce battery-grade iron phosphate, affecting the electrochemical performance of the positive electrode material for lithium iron phosphate batteries. Currently, methods for removing aluminum and copper impurities include leaching with alkaline or acidic solutions, but the impurity content in the recovered iron phosphate is still high. Alternatively, aluminum can be removed by resin adsorption, but this is costly, the process is complex, inefficient, and has poor impurity removal results.

[0004] Summary of the Invention

[0005] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0006] The purpose of the present disclosure is to provide a method for preparing ferric phosphate from ferrophosphorus slag. The present disclosure achieves deep removal of Al and Cu impurities by mixing ferrophosphorus slag with chloride, sintering the mixture, and adding iron elemental replacement during the recovery process, thereby producing high-purity ferric phosphate. The method is simple in process and low in cost.

[0007] To achieve this disclosure purpose, the present disclosure adopts the following technical solutions:

[0008] In a first aspect, an embodiment of the present disclosure provides a method for preparing ferric phosphate from ferrophosphorus slag, the method comprising the following steps:

[0009] (1) pre-treating ferrophosphorus slag to obtain a mixed material containing aluminum phosphate;

[0010] (2) mixing a mixture containing aluminum phosphate with a chloride, calcining the mixture to obtain slag, washing and filtering the slag, mixing the slag with an acid solution, reacting the mixture in one step, and performing solid-liquid separation to obtain solution A;

[0011] (3) mixing solution A with elemental iron, reacting in two steps, and performing solid-liquid separation to obtain solution B, and adding an iron source and / or a phosphorus source to adjust the phosphorus-iron molar ratio to obtain a raw material solution;

[0012] (4) mixing the raw material liquid and hydrogen peroxide, adjusting the pH to carry out a three-step reaction, separating the solid and the liquid to obtain ferric phosphate dihydrate, and sintering the mixture to obtain the ferric phosphate.

[0013] The ferrophosphorus slag described in the embodiments of the present disclosure includes but is not limited to the ferrophosphorus slag after lithium extraction from lithium iron phosphate batteries or other ferrophosphate precursors containing aluminum.

[0014] The disclosed embodiment achieves phase transformation of aluminum impurities in the ferrophosphorus slag by calcining ferrophosphorus slag and chloride at high temperature, converting the aluminum impurities into aluminum chloride and forming volatilization gas. The obtained calcined slag is washed and filtered to remove excess chloride, and the washed slag is reacted with acid. After solid-liquid separation, a leachate containing iron and phosphorus ions is obtained. The leachate is then replaced by iron to remove copper, thereby achieving deep removal of Al and Cu impurities. The phosphorus-iron ratio is adjusted by adding an iron source or a phosphorus source to obtain a synthetic stock solution with a certain phosphorus-iron ratio. Hydrogen peroxide is added and the pH is adjusted to obtain an iron phosphate precursor precipitate. The process is simple and the production cost is low.

[0015] In one embodiment, the pretreatment in step (1) includes:

[0016] The ferrophosphorus slag is mixed with a solvent, a phosphoric acid solution is added, the pH value is controlled to react, and the mixture is dried to obtain a mixed material containing aluminum phosphate.

[0017] In one embodiment, the solvent comprises water.

[0018] In one embodiment, the mass concentration of the phosphoric acid solution is 50% to 85%, for example, 50%, 60%, 70% or 80%.

[0019] In one embodiment, the pH is 1.8 to 3.5, for example, 1.8, 2, 2.5, 3 or 3.5.

[0020] In one embodiment, the reaction temperature is 50-90°C, for example, 50°C, 60°C, 70°C, 80°C or 90°C.

[0021] In one embodiment, the reaction time is 1 to 2 hours, for example, 1 hour, 1.2 hours, 1.5 hours, 1.8 hours or 2 hours.

[0022] In one embodiment, the chloride in step (2) includes sodium chloride, potassium chloride and ferric chloride.

[0023] In one embodiment, based on the mass of the chloride being 100%, the mass fraction of the sodium chloride is 15-30%, for example, 15%, 18%, 20%, 25% or 30%.

[0024] In one embodiment, the mass fraction of potassium chloride is 15% to 25%, for example, 15%, 18%, 20%, 22% or 25%.

[0025] In one embodiment, the mass fraction of the ferric chloride is 55% to 75%, for example, 55%, 60%, 65%, 70% or 75%.

[0026] The disclosed embodiments can reduce the melting point of the eutectic salt to below 200° C. by controlling the composition and ratio of the chlorides. The molten chloride can react better with aluminum phosphate. After calcination, washing is performed to prevent the generated aluminum oxide from remaining in the molten chloride. Aluminum phosphate is reformed during acid dissolution, further reducing the aluminum content in the target product. The method is simple and highly efficient.

[0027] In one embodiment, the mass ratio of the mixed material to the chloride in step (2) is 1:(0.2-0.6), for example: 1:0.2, 1:0.3, 1:0.4, 1:0.5 or 1:0.6, etc.

[0028] The calcination reaction equation of the mixed material and chloride described in the embodiment of the present disclosure is as follows (taking sodium chloride as an example): AlPO4+3NaCl=AlCl3↑+Na3PO4.

[0029] In one embodiment, the calcination temperature in step (2) is 185-270°C, for example, 185°C, 200°C, 220°C, 250°C or 270°C.

[0030] In one embodiment, the atmosphere of the calcination treatment in step (2) includes air.

[0031] In one embodiment, the calcination time in step (2) is 1 to 2 hours, for example, 1 hour, 1.2 hours, 1.5 hours, 1.8 hours or 2 hours.

[0032] In one embodiment, the acid solution in step (2) includes sulfuric acid and / or phosphoric acid.

[0033] The ionic equation of the mixture of the roasted slag and the sulfuric acid solution in the embodiment of the present disclosure is as follows: 2FePO4+6H + +3SO4 2- =2Fe 3+ +3SO4 2- +2H2PO4 - +2HPO42- .

[0034] The ionic equation of the mixture of the roasted slag and the phosphoric acid solution in the embodiment of the present disclosure is as follows: FePO4+3H + +PO4 3- =Fe 3+ +H2PO4 - +HPO4 2- .

[0035] In one embodiment, the concentration of the acid solution in step (2) is 0.8 to 1.2 mol / L, for example, 0.8 mol / L, 0.9 mol / L, 1 mol / L, 1.1 mol / L or 1.2 mol / L.

[0036] In one embodiment, the mass volume ratio of the calcined slag and the acid solution in step (2) is 1g:(5-10)mL, for example: 1g:5mL, 1g:6mL, 1g:7mL, 1g:8mL or 1g:10mL, etc.

[0037] In one embodiment, the reaction time of step (2) is 0.5 to 2.5 h, for example, 0.5 h, 1 h, 1.5 h, 2 h or 2.5 h.

[0038] In one embodiment, the iron element in step (3) comprises iron powder.

[0039] In one embodiment, the solution A in step (3) contains impurities Cu 2+ .

[0040] In one embodiment, the iron element in step (3) and the impurity Cu in solution A 2+ The molar ratio is (1-2):1, for example: 1:1, 1.2:1, 1.5:1, 1.8:1 or 2:1, etc.

[0041] The iron element and the impurity Cu in the solution of the embodiment disclosed in the present invention 2+ The reaction ion equation is as follows: Fe+Cu 2+ =Fe 2+ +Cu.

[0042] In one embodiment, the time of the two-step reaction in step (3) is 0.5 to 2.5 h, for example, 0.5 h, 1 h, 1.5 h, 2 h or 2.5 h.

[0043] In one embodiment, the iron source in step (3) includes any one of ferric sulfate, ferric chloride or ferric nitrate, or a combination of at least two thereof.

[0044] In one embodiment, the phosphorus source in step (3) includes any one of ammonium dihydrogen phosphate, sodium phosphate, ammonium phosphate or ammonium monohydrogen phosphate, or a combination of at least two thereof.

[0045] In one embodiment, the phosphorus-iron molar ratio in step (3) is (1-1.1):1, for example: 1:1, 1.02:1, 1.05:1, 1.08:1 or 1.1:1, etc.

[0046] In one embodiment, the molar ratio of the hydrogen peroxide in step (4) to the iron in the raw material solution is (1-1.5):1, for example: 1:1, 1.1:1, 1.2:1, 1.4:1 or 1.5:1, etc.

[0047] In one embodiment, the pH regulator in step (4) comprises aqueous ammonia.

[0048] In one embodiment, the pH in step (4) is 1.6 to 2.2, for example, 1.6, 1.8, 2, 2.1 or 2.2.

[0049] In one embodiment, the temperature of the three-step reaction in step (4) is 50-95°C.

[0050] In one embodiment, the three-step reaction time in step (4) is 1 to 2 hours, for example, 1 hour, 1.2 hours, 1.5 hours, 1.8 hours or 2 hours.

[0051] In one embodiment, the temperature of the sintering treatment in step (4) is 350-650°C, for example, 350°C, 400°C, 450°C, 500°C or 650°C.

[0052] In one embodiment, the sintering treatment time in step (4) is 3 to 6 hours, for example, 3 hours, 3.5 hours, 4 hours, 5 hours or 6 hours.

[0053] As an optional solution of the embodiment of the present disclosure, the method includes the following steps:

[0054] (1) mixing ferrophosphorus slag with water, adding a phosphoric acid solution with a mass concentration of 50% to 85%, controlling the pH to 1.8 to 3.5, reacting at 50 to 90° C. for 1 to 2 hours, and filtering to obtain a mixed material containing aluminum phosphate;

[0055] (2) mixing a mixture containing aluminum phosphate with a chloride in a mass ratio of 1:(0.2-0.6), calcining the mixture at 185-270° C. for 1-2 h to obtain a calcined residue, washing and filtering the calcined residue, and then mixing the calcined residue with an acid solution in a mass volume ratio of 1 g:(5-10) mL, reacting the mixture in one step for 0.5-2.5 h, and then performing solid-liquid separation to obtain a solution A;

[0056] (3) mixing solution A with iron powder, reacting in the second step for 0.5 to 2.5 hours, and then performing solid-liquid separation to obtain solution B, and adding an iron source and / or a phosphorus source to adjust the phosphorus-iron molar ratio to (1 to 1.1):1 to obtain a raw material solution;

[0057] (4) mixing the raw material liquid and hydrogen peroxide, adding ammonia water to adjust the pH to 1.6-2.2, and carrying out a three-step reaction for 1-2 hours, solid-liquid separation to obtain dihydrated iron phosphate, and sintering at 350-650° C. for 3-6 hours to obtain the iron phosphate.

[0058] The present disclosure has the following beneficial effects:

[0059] (1) The present invention discloses a method of mixing ferrophosphorus slag with chloride, sintering the mixture, and adding iron elemental substitution during the recovery process to achieve deep removal of Al and Cu impurities, thereby producing high-purity ferrophosphate. The method is simple in process and low in cost.

[0060] (2) The Al content in the ferrophosphorus raw material liquid obtained by the method disclosed in the present invention can reach less than 0.0039%, the Cu content can reach less than 0.003%, the P content can reach more than 12.04%, and the Fe content can reach more than 25.33%. The iron content in the recovered ferrophosphate can reach more than 29.35%, the phosphorus element can reach more than 16.32%, the impurity Al ion content can reach less than 0.004%, and the impurity copper ion content can reach less than 0.003%. DETAILED DESCRIPTION

[0061] The technical solution of the present disclosure is further described below through specific implementation methods. Those skilled in the art should understand that the embodiments are only used to help understand the present disclosure and should not be regarded as specific limitations of the present disclosure.

[0062] The main elements of the ferrophosphorus slag used in the embodiments and comparative examples of the present disclosure are as follows:

[0063] Al: 0.50%, Cu: 0.32%, P: 8.11%, Fe: 15.34%. The proportions or percentages in the embodiments and comparative examples of the present disclosure are all mass ratios unless otherwise specified.

[0064] The chloride compositions used in the examples and comparative examples of the present disclosure are as follows:

[0065] Sodium chloride: 20%, potassium chloride: 20%, ferric chloride: 60%.

[0066] Example 1

[0067] This embodiment provides a method for preparing ferric phosphate from ferrophosphorus slag, the method comprising the following steps:

[0068] (1) The ferrophosphorus slag after lithium extraction from the lithium iron phosphate battery was dispersed in an aqueous solution at a liquid-solid mass ratio of 2:1, a 70% phosphoric acid solution was added to control the pH to 2.5, and the mixture was reacted at a temperature of 70°C for 1.5 hours. After the reaction was completed, the mixture was filtered and dried at 100°C to obtain a mixed material;

[0069] (2) Weigh 100 g of the mixture and 40 g of the chloride, mix thoroughly, place in a muffle furnace, and calcine at 250°C for 1.5 h in an air atmosphere to obtain slag. After washing and filtering, the slag is reacted in a 1 mol / L sulfuric acid solution with a solid-liquid ratio of 1 g:7.5 mL for 1.5 h, and then solid-liquid separation is performed to obtain solution A.

[0070] (3) adding iron powder to solution A in an amount of 1.5 times the molar amount of copper in the solution, and reacting for 1.5 h. After the reaction, solid-liquid separation is performed to obtain solution B. In solution B, an iron source or a phosphorus source is added to adjust the phosphorus-iron molar ratio in the system to 1:1.05 according to Fe:P=, thereby supplementing phosphorus and iron to obtain a raw material solution, wherein the iron supplementing agent is ferric sulfate and the phosphorus supplementing agent is ammonium dihydrogen phosphate;

[0071] (4) The raw material liquid and hydrogen peroxide were mixed at a molar ratio of hydrogen peroxide to iron of 1.2:1, and ammonia was added to adjust the pH to 1.9 for coprecipitation reaction. The reaction temperature was 70°C and the reaction time was 1.5 hours. After the reaction, solid-liquid separation was performed to obtain dihydrated iron phosphate precipitate, which was calcined at 500°C in a muffle furnace for 4 hours to obtain iron phosphate.

[0072] Example 2

[0073] This embodiment provides a method for preparing ferric phosphate from ferrophosphorus slag, the method comprising the following steps:

[0074] (1) The ferrophosphorus slag after lithium extraction from the lithium iron phosphate battery was dispersed in an aqueous solution at a liquid-solid mass ratio of 2:1, and an 85% phosphoric acid solution was added to control the pH to 1.8. The mixture was reacted at a temperature of 50°C for 1 hour. After the reaction was completed, the mixture was filtered and dried at 100°C to obtain a mixed material;

[0075] (2) Weigh 100 g of the mixture and 60 g of the chlorine compound, mix thoroughly, place in a muffle furnace, and calcine at 270°C for 2 h in an air atmosphere to obtain slag. After washing and filtering, the slag is reacted in a 0.8 mol / L sulfuric acid solution with a solid-liquid ratio of 1 g:10 mL for 2 h, and then solid-liquid separation is performed to obtain solution A.

[0076] (3) adding iron powder to solution A in an amount twice the molar amount of copper in the solution, reacting for 2 h, and performing solid-liquid separation after the reaction to obtain solution B, and adding an iron source or a phosphorus source to solution B according to Fe:P= to adjust the phosphorus-iron molar ratio in the system to 1:1.1 to supplement phosphorus and iron, thereby obtaining a raw material solution, wherein the iron supplementing agent is ferric sulfate, and the phosphorus supplementing agent is ammonium dihydrogen phosphate;

[0077] (4) The raw material liquid and hydrogen peroxide were mixed at a molar ratio of hydrogen peroxide to iron of 1.5:1, and ammonia was added to adjust the pH to 2.2 for coprecipitation reaction. The reaction temperature was 95°C and the reaction time was 1 hour. After the reaction, solid-liquid separation was performed to obtain dihydrated iron phosphate precipitate, which was calcined at 650°C in a muffle furnace for 3 hours to obtain iron phosphate.

[0078] Example 3

[0079] This embodiment provides a method for preparing ferric phosphate from ferrophosphorus slag, the method comprising the following steps:

[0080] (1) The ferrophosphorus slag after lithium extraction from the lithium iron phosphate battery was dispersed in an aqueous solution at a liquid-solid mass ratio of 2:1, a 70% phosphoric acid solution was added to control the pH to 3.5, and the mixture was reacted at a temperature of 90°C for 2 hours. After the reaction was completed, the mixture was filtered and dried at 100°C to obtain a mixed material;

[0081] (2) Weigh 100 g of the mixture and 20 g of the chloride, mix thoroughly, place in a muffle furnace, and calcine at 185°C for 1 h in an air atmosphere to obtain slag. After washing and filtering, the slag is reacted in a 1.2 mol / L sulfuric acid solution with a solid-liquid ratio of 1 g:5 mL for 0.5 h, and then solid-liquid separation is performed to obtain solution A.

[0082] (3) adding iron powder to solution A in an amount equal to 1 times the molar amount of copper in the solution, and reacting for 0.5 h. After the reaction, solid-liquid separation is performed to obtain solution B. An iron source or a phosphorus source is added to solution B according to Fe:P= to adjust the phosphorus-iron molar ratio in the system to 1:1 to supplement phosphorus and iron, thereby obtaining a raw material solution. The iron supplementing agent is ferric sulfate, and the phosphorus supplementing agent is ammonium dihydrogen phosphate.

[0083] (4) The raw material liquid and hydrogen peroxide were mixed in a molar ratio of hydrogen peroxide to iron of 1:1, and ammonia was added to adjust the pH to 1.6 for co-precipitation reaction. The reaction temperature was 50°C and the reaction time was 2 hours. After the reaction, solid-liquid separation was performed to obtain dihydrated iron phosphate precipitate, which was calcined in a muffle furnace at 350°C for 6 hours to obtain iron phosphate.

[0084] Example 4

[0085] The only difference between this embodiment and embodiment 1 is that the mass of sodium chloride is 10 g, and other conditions and parameters are exactly the same as those in embodiment 1.

[0086] Example 5

[0087] The only difference between this embodiment and embodiment 1 is that the mass of sodium chloride is 70g, and other conditions and parameters are exactly the same as those in embodiment 1.

[0088] Example 6

[0089] The only difference between this embodiment and embodiment 1 is that the calcination temperature in step (2) is 170° C., and the other conditions and parameters are exactly the same as those in embodiment 1.

[0090] Example 7

[0091] The only difference between this embodiment and embodiment 1 is that the calcination temperature in step (2) is 300° C., and the other conditions and parameters are exactly the same as those in embodiment 1.

[0092] Comparative Example 1

[0093] This comparative example provides a method for preparing ferric phosphate from ferrophosphorus slag, the method comprising the following steps:

[0094] (1) The ferrophosphorus slag after lithium extraction from the lithium iron phosphate battery was reacted in a 1 mol / L sulfuric acid solution at a solid-liquid ratio of 1 g:7.5 mL for 1.5 h, and then solid-liquid separation was performed to obtain solution A;

[0095] (2) adding iron powder to solution A in an amount of 1.5 times the molar amount of iron in the solution, reacting for 1.5 h, and performing solid-liquid separation after the reaction to obtain solution B;

[0096] (3) Adding an iron source or a phosphorus source to solution B according to Fe:P to adjust the molar ratio of phosphorus to iron in the system to 1:1.05 to supplement phosphorus and iron. The iron supplement reagent is ferric sulfate, and the phosphorus supplement reagent is ammonium dihydrogen phosphate;

[0097] (4) Hydrogen peroxide was added to solution B in a molar amount of 1.2 times the molar amount of iron in the solution. Ammonia was added to adjust the pH to 1.9 for coprecipitation reaction. The reaction temperature was 70°C and the reaction time was 1.5 h. After the reaction, solid-liquid separation was performed to obtain dihydrated iron phosphate precipitate, which was calcined in a muffle furnace at 500°C for 4 h to obtain iron phosphate.

[0098] Comparative Example 2

[0099] The only difference between this comparative example and Example 1 is that iron powder is not added in step (3), and the other conditions and parameters are exactly the same as those in Example 1.

[0100] Performance testing:

[0101] (1) The mass concentrations of the main elements in solution B were obtained by ICP testing the examples and comparative examples. The test results are shown in Table 1:

[0102] Table 1

[0103] (2) The mass fractions of the various components in the ferric phosphate prepared in the test examples and comparative examples were obtained. The test results are shown in Table 2:

[0104] Table 2

[0105] As can be seen from Table 1-2 and Examples 1-3, the Al content in the ferrophosphorus raw material liquid obtained by the method described in the present disclosure can reach less than 0.0039%, the Cu content can reach less than 0.003%, the P content can reach more than 12.04%, and the Fe content can reach more than 25.33%. The iron content in the recovered ferrophosphate can reach more than 29.35%, the phosphorus element can reach more than 16.32%, the impurity Al ion content can reach less than 0.004%, and the impurity copper ion content can reach less than 0.003%.

[0106] By comparing Example 1 with Examples 4-5, it can be seen that in the method disclosed herein, the amount of chloride added affects the recovery effect. The recovery effect is better when the mass ratio of the mixed material to the chloride is controlled at 1: (0.2-0.6). If the amount of chloride added is too large, it will lead to waste of chloride salt and easily introduce new impurities. If the amount of chloride added is too small, the reaction cannot be fully carried out, resulting in a high content of aluminum impurities in the ferrophosphorus slag after roasting.

[0107] By comparing Example 1 with Examples 5-6, it can be seen that in the method disclosed herein, the roasting temperature in step (2) affects the recovery effect. When the roasting temperature is controlled at 185-270°C, the recovery effect is better. If the roasting temperature is too high, ferric chloride is generated and volatilized, resulting in iron loss. If the roasting temperature is too low, the boiling point of aluminum chloride cannot be reached, which affects the removal of aluminum impurities in the ferrophosphorus slag.

[0108] By comparing Example 1 with Comparative Examples 1-2, it can be seen that the present disclosure achieves phase transformation of aluminum impurities in the ferrophosphorus slag by calcining ferrophosphorus slag and chloride salt at high temperature, so that the aluminum impurities are converted into aluminum chloride and form gas volatilization, and then the slag obtained after roasting is reacted with acid, and after solid-liquid separation, an iron-phosphorus ion-containing leachate is obtained, and then copper is removed by adding iron displacement, which can achieve deep removal of Al and Cu impurities. By adding an iron source or a phosphorus source to adjust the phosphorus-iron ratio, a synthetic stock solution with a certain phosphorus-iron ratio is obtained, hydrogen peroxide and ammonia water are added, and the pH is adjusted to obtain an iron phosphate precursor precipitate. The process is simple and the production cost is low.

Claims

1. A method for preparing ferric phosphate from ferrophosphorus slag, the method comprising the following steps: (1) pretreating ferrophosphorus slag to obtain a mixed material containing aluminum phosphate; (2) mixing a mixed material containing aluminum phosphate with a chloride, calcining the mixture to obtain calcined residue, washing and filtering the calcined residue, mixing the calcined residue with an acid solution, reacting the mixture in one step, and performing solid-liquid separation to obtain a solution A; (3) mixing solution A with elemental iron, reacting in two steps, performing solid-liquid separation to obtain solution B, and adding an iron source and / or a phosphorus source to adjust the phosphorus-iron molar ratio to obtain a raw material solution; (4) The raw material liquid and hydrogen peroxide are mixed, the pH is adjusted to carry out a three-step reaction, solid-liquid separation is performed to obtain dihydrated iron phosphate, and sintering treatment is performed to obtain the iron phosphate.

2. The method of claim 1, wherein: The pretreatment in step (1) comprises: The ferrophosphorus slag is mixed with a solvent, a phosphoric acid solution is added, the pH value is controlled to react, and the mixture is dried to obtain a mixed material containing aluminum phosphate; Optionally, the solvent comprises water; Optionally, the mass concentration of the phosphoric acid solution is 50% to 85%; Optionally, the pH is 1.8 to 3.5; Optionally, the reaction temperature is 50-90°C; Optionally, the reaction time is 1 to 2 hours.

3. The method according to claim 1 or 2, wherein: The chloride in step (2) includes sodium chloride, potassium chloride and ferric chloride; Optionally, based on the mass of the chloride being 100%, the mass fraction of the sodium chloride is 15% to 30%; Optionally, the mass fraction of potassium chloride is 15% to 25%; Optionally, the mass fraction of the ferric chloride is 55% to 75%.

4. The method according to any one of claims 1 to 3, wherein: The mass ratio of the mixed material to the chloride in step (2) is 1:(0.2-0.6).

5. The method according to any one of claims 1 to 4, wherein: The temperature of the calcination treatment in step (2) is 185-270° C. Optionally, the atmosphere for the calcination treatment in step (2) includes air; Optionally, the calcination treatment time in step (2) is 1 to 2 hours.

6. The method according to any one of claims 1 to 5, wherein: The acid solution in step (2) includes sulfuric acid and / or phosphoric acid; Optionally, the concentration of the acid solution in step (2) is 0.8 to 1.2 mol / L.

7. The method according to any one of claims 1 to 6, wherein: The mass volume ratio of the calcined slag and the acid solution in step (2) is 1 g: (5-10) mL; Optionally, the one-step reaction time in step (2) is 0.5 to 2.5 h.

8. The method according to any one of claims 1 to 7, wherein: The iron element in step (3) includes iron powder.

9. The method according to any one of claims 1 to 8, wherein: Step (3) The solution A contains impurities Cu 2+ ; Optionally, the iron element and the impurity Cu in solution A in step (3) 2+ The molar ratio is (1-2):1; Optionally, the time of the two-step reaction in step (3) is 0.5 to 2.5 hours.

10. The method according to any one of claims 1 to 9, wherein: The iron source in step (3) includes any one of ferric sulfate, ferric chloride or ferric nitrate, or a combination of at least two of them.

11. The method according to any one of claims 1 to 10, wherein: The phosphorus source in step (3) includes any one of diammonium phosphate, sodium phosphate, ammonium phosphate or monoammonium hydrogen phosphate, or a combination of at least two thereof.

12. The method according to any one of claims 1 to 11, wherein: The phosphorus-iron molar ratio in step (3) is (1-1.1):

1.

13. The method according to any one of claims 1 to 12, wherein: The molar ratio of the hydrogen peroxide in step (4) to the iron in the raw material solution is (1-1.5):1; Optionally, the pH regulator in step (4) includes aqueous ammonia; Optionally, the pH in step (4) is 1.6 to 2.2; Optionally, the temperature of the three-step reaction in step (4) is 50-95° C.; Optionally, the three-step reaction time in step (4) is 1 to 2 hours.

14. The method according to any one of claims 1 to 13, wherein: The sintering temperature in step (4) is 350-650° C. Optionally, the sintering time in step (4) is 3 to 6 hours.

15. The method according to any one of claims 1 to 14, wherein: The method comprises the following steps: (1) mixing ferrophosphorus slag with water, adding a phosphoric acid solution with a mass concentration of 50% to 85%, controlling the pH value to be 1.8 to 3.5, reacting at 50 to 90° C. for 1 to 2 hours, and filtering to obtain a mixed material containing aluminum phosphate; (2) mixing a mixture containing aluminum phosphate and a chloride in a mass ratio of 1:(0.2-0.6), calcining at 185-270° C. for 1-2 h to obtain calcined slag, washing and filtering, mixing the calcined slag with an acid solution in a mass volume ratio of 1 g:(5-10) mL, reacting in one step for 0.5-2.5 h, and obtaining a solution A by solid-liquid separation; (3) mixing solution A with iron powder, reacting in the second step for 0.5 to 2.5 hours, and obtaining solution B by solid-liquid separation, and adding an iron source and / or a phosphorus source to adjust the phosphorus-iron molar ratio to (1 to 1.1):1 to obtain a raw material solution; (4) The raw material liquid and hydrogen peroxide are mixed, and ammonia water is added to adjust the pH to 1.6-2.2 to carry out a three-step reaction for 1-2 hours, solid-liquid separation is performed to obtain dihydrated iron phosphate, and sintering treatment is performed at 350-650° C. for 3-6 hours to obtain the iron phosphate.

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