A method for preparing iron phosphate by ferrous sulfate circulation

Abstract

This invention belongs to the field of battery inorganic material preparation technology, specifically relating to a method for preparing ferric phosphate by ferrous sulfate recycling. The method includes the following steps: S1, mixing ferrous sulfate solution and phosphoric acid solution, adding a catalyst, reacting, and separating the solid and liquid phases; S2, washing, aging, separating the solid and liquid phases again, and drying the solid obtained in step S1 to obtain the ferric phosphate; S3, adding a reducing agent to the filtrate obtained in step S1, reacting, filtering, obtaining a ferrous sulfate solution, and returning to step S1. This invention prepares ferric phosphate through the oxidation reaction of ferrous sulfate and phosphoric acid at high temperature, eliminating the need for precise pH control with the addition of an alkaline solution, and simplifying the operation. Furthermore, the reaction process does not produce sulfate byproducts, reducing the equipment and investment required for treating sulfate wastewater, and avoiding cost pressures caused by fluctuations in the prices of raw materials such as sulfur and sulfuric acid, thus possessing high economic value.

Description

Technical Field

[0001] This invention belongs to the field of battery inorganic material preparation technology, specifically relating to a method for preparing ferric phosphate by ferrous sulfate recycling. Background Technology

[0002] Lithium iron phosphate (LFP) is an important cathode material for lithium-ion batteries, widely used in power and energy storage fields. Iron phosphate is the most commonly used raw material in the synthesis of LFP, and it has a significant impact on the performance of LFP. Currently, there are many methods for synthesizing iron phosphate, each with its own advantages and disadvantages in terms of product performance and production cost.

[0003] Chinese patent CN116534820A discloses a method using ferrous sulfate as a raw material. After complete oxidation with hydrogen peroxide, monoammonium phosphate is slowly added to the oxidized solution, and under heating conditions, ferric phosphate dihydrate with varying particle sizes is prepared, ultimately yielding high-pressure compacted ferric phosphate. Patent CN116253304A also uses ferrous sulfate as a raw material, rapidly mixing and reacting it with phosphate containing hydrogen peroxide in a small reactor to obtain a slurry containing numerous crystal nuclei. This slurry is then transferred to a large-volume reactor for growth, ultimately yielding ferric phosphate dihydrate with varying particle sizes. Patent CN120229697A uses titanium dioxide and ferrous sulfate as a raw material. After impurity removal, it is first oxidized to obtain an iron source solution, which is then slowly added to a weakly acidic phosphate solution. The resulting slurry is aged with phosphoric acid to obtain ferric phosphate dihydrate. These methods all produce sulfate byproducts during the preparation of ferric phosphate. Depending on the alkaline substance used, they can be classified as ammonium method and sodium method, with ammonium sulfate and sodium sulfate as byproducts, respectively.

[0004] Besides these two mainstream processes, there is another iron-based process, which uses iron powder as raw material to react with phosphoric acid and hydrogen peroxide to prepare ferric phosphate. This process produces no salt byproducts and has relatively low cost, but the reaction of iron powder and phosphoric acid generates a large amount of hydrogen gas, posing a safety hazard. Patent CN118343714A uses titanium dioxide and ferrous sulfate as raw material. After purification, the raw material is first oxidized to prepare ferric hydroxide. The ferric hydroxide is then washed and reacted with phosphoric acid to produce ferric phosphate dihydrate. The mother liquor is then hydrolyzed to prepare polyferric sulfate. This process also produces almost no salt byproducts, but the reaction of ferric hydroxide with phosphoric acid to prepare ferric phosphate dihydrate may result in incomplete reaction of the ferric hydroxide or it becoming trapped within the ferric phosphate dihydrate. Trapped ferric hydroxide, after high-temperature dehydration, will become ferric oxide impurities. Patent CN113955732A is also a process that produces no salt byproducts and does not generate hydrogen gas. It uses ferric chloride as raw material and reacts with phosphoric acid to prepare ferric phosphate. The ferric chloride is recycled, and the pH value is not adjusted during the process. This process is short and has low cost. However, the dihydrate ferric phosphate prepared by this process has a high chloride ion content, which will corrode the equipment during the subsequent decrystallization process, thus having certain limitations.

[0005] Therefore, there is an urgent need to develop a method for preparing iron phosphate that can effectively solve the problems of sulfate byproducts, hydrogen safety hazards, intermediate product inclusions, and chloride ion corrosion of equipment in existing technologies. Summary of the Invention

[0006] To address at least one deficiency in existing technologies, this invention aims to provide a method for the cyclic preparation of ferric phosphate from ferrous sulfate. This method utilizes the oxidation reaction of ferrous sulfate and phosphoric acid at high temperature to produce ferric phosphate, eliminating the need for precise pH control with the addition of an alkaline solution, thus simplifying the operation. Furthermore, by controlling the molar ratio of ferrous sulfate to phosphoric acid, sulfate ions in the system are converted to ferric sulfate, which is then reduced by elemental iron to regenerate ferrous sulfate, enabling recycling. The reaction process does not produce sulfate byproducts, reducing the equipment and investment required for sulfate wastewater treatment and avoiding cost pressures from fluctuations in the prices of raw materials such as sulfur and sulfuric acid, thus possessing high economic value. The preparation process does not generate hydrogen gas or introduce chloride ions, demonstrating strong applicability and safety.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing ferric phosphate by ferrous sulfate recycling, comprising the following steps: S1. Mix ferrous sulfate solution and phosphoric acid solution, add catalyst, react, and separate solid and liquid components; S2. The solid obtained from the solid-liquid separation in step S1 is washed, aged, separated again, and dried to obtain the iron phosphate. S3. Add a reducing agent to the filtrate obtained from the solid-liquid separation in step S1, react, filter, and obtain a ferrous sulfate solution, then return to step S1.

[0008] In one embodiment of the method for preparing ferric phosphate by ferrous sulfate recycling according to the present invention, the ferrous ion concentration in the ferrous sulfate solution is 1.0-2.5 mol / L.

[0009] In one embodiment of the method for preparing ferric phosphate by ferrous sulfate recycling according to the present invention, the phosphoric acid solution content is 50%-85%.

[0010] In the method for preparing ferric phosphate using ferrous sulfate recycling of this invention, by controlling the concentration of ferrous ions in the ferrous sulfate solution within a suitable range, the smooth preparation of ferric phosphate product from the raw material reaction system can be effectively maintained. When the concentration of ferrous ions in the ferrous sulfate solution is too high, it can easily lead to problems in the production of ferrous phosphate product during the reaction process, resulting in a decrease in the purity of the ferric phosphate product. When the concentration of ferrous ions in the ferrous sulfate solution is too low, the yield will decrease, and more water will be introduced.

[0011] In a preferred embodiment of the method for preparing ferric phosphate by ferrous sulfate recycling according to the present invention, the ferrous ion concentration in the ferrous sulfate solution is 1.5-2.0 mol / L.

[0012] In one embodiment of the method for preparing ferric phosphate by ferrous sulfate recycling according to the present invention, the molar ratio of ferrous ions to phosphorus in the phosphoric acid solution is 3:(0.95-1.20).

[0013] In the method for preparing ferric phosphate by ferrous sulfate recycling of this invention, by controlling the molar ratio of ferrous ions in the ferrous sulfate solution and phosphorus in the phosphoric acid solution within a suitable range, the raw material reaction system of this invention can be kept in an appropriate pH environment, thereby effectively promoting the formation of ferric phosphate product. When the molar ratio of phosphorus in the phosphoric acid solution is too high, the initial acidity of the ferrous sulfate and phosphoric acid mixture is too high, resulting in difficulty in the ionization of orthophosphate and making it difficult to synthesize ferric phosphate. When the molar ratio of phosphorus in the phosphoric acid solution is too low, it cannot fully react with the ferrous ions in the system to form ferric phosphate precipitate, and a large amount of ferrous ions will remain in the mother liquor, causing waste of iron resources and a significant reduction in product yield. At the same time, when the phosphorus ratio is too low and the acidity is relatively insufficient, as the reaction proceeds, ferrous ions tend to hydrolyze to form ferrous hydroxide, and after oxidation, they are converted into impurity phases such as ferric hydroxide or basic ferric phosphate. These non-target products mixed into the final product will seriously reduce the phase purity and crystallinity of ferric phosphate.

[0014] In a preferred embodiment of the method for preparing ferric phosphate by ferrous sulfate recycling according to the present invention, the molar ratio of ferrous ions to phosphorus in the phosphoric acid solution is 3:(1.0-1.05).

[0015] In one embodiment of the method for preparing ferric phosphate by ferrous sulfate recycling according to the present invention, the amount of catalyst added is 0.05%-0.3% of the total mass of ferrous sulfate solution and phosphoric acid solution.

[0016] In one embodiment of the method for preparing ferrous phosphate by ferrous sulfate recycling according to the present invention, the catalyst includes at least one of nitric acid, nitrous acid, nitrate, and nitrite.

[0017] In one embodiment of the method for preparing ferric phosphate by ferrous sulfate recycling according to the present invention, in step S1, the reaction temperature is 110-130℃ and the reaction time is 2-4h.

[0018] In one embodiment of the method for preparing ferric phosphate by ferrous sulfate recycling according to the present invention, in step S1, oxygen is introduced during the reaction process, and the pressure during the reaction process is 0.1-0.3 MPa.

[0019] In one embodiment of the method for preparing ferric phosphate by ferrous sulfate recycling according to the present invention, the washing process involves: a first washing with pure water, followed by a second washing after filtration.

[0020] In one embodiment of the method for preparing ferric phosphate by ferrous sulfate recycling according to the present invention, the conductivity of the filtrate obtained by the second washing is less than 800 μs / cm.

[0021] In the method for preparing ferric phosphate by ferrous sulfate recycling of the present invention, the solid obtained by solid-liquid separation in step S1 is washed twice, and the conductivity of the filtrate obtained by the second pure water washing is controlled to be less than 800 μs / cm. This can effectively remove ions entrained in the solid, ensure that the impurity content in the final ferric phosphate product is within the required range, and ensure that a high purity ferric phosphate product can be obtained.

[0022] In one embodiment of the method for preparing ferric phosphate by ferrous sulfate recycling according to the present invention, the aging temperature is 60-90℃ and the aging time is 2-5h.

[0023] In one embodiment of the method for preparing ferric phosphate by ferrous sulfate recycling according to the present invention, the solvent for aging includes a phosphoric acid solution; the concentration of the phosphoric acid solution is 0.2-0.5 mol / L.

[0024] In the method for preparing ferric phosphate by ferrous sulfate recycling of the present invention, by using phosphoric acid solution as the solvent in the aging process, the iron-to-phosphorus ratio of ferric phosphate can be effectively adjusted, thereby ensuring that the ferric phosphate product obtained subsequently can meet the actual requirements.

[0025] As one embodiment of the method for preparing ferric phosphate by ferrous sulfate recycling according to the present invention, the drying is as follows: first drying at 100~110℃ for 10-60 min, and then drying at 500~600℃ for 1~3 h.

[0026] In one embodiment of the method for preparing ferric phosphate by ferrous sulfate recycling according to the present invention, the reducing agent is elemental iron.

[0027] As one embodiment of the method for preparing ferric phosphate by ferrous sulfate recycling according to the present invention, the elemental iron includes one or more of iron powder, iron filings, and iron blocks.

[0028] In one embodiment of the method for preparing ferric phosphate by ferrous sulfate recycling according to the present invention, the amount of reducing agent added is 40-60% of the total iron mass in the filtrate.

[0029] In this invention, total iron refers to the sum of ferric and ferrous iron in the filtrate.

[0030] In one embodiment of the method for preparing ferric phosphate by ferrous sulfate recycling according to the present invention, in step S3, the reaction is carried out by stirring at 60~80℃ for 1~3 hours.

[0031] Compared with the prior art, the present invention has the following beneficial effects: (1) The method for preparing ferric phosphate by recycling ferrous sulfate in this invention prepares ferric phosphate by oxidizing ferrous sulfate and phosphoric acid at high temperature. It does not require the addition of alkaline solution to accurately control the pH value and is simple to operate. At the same time, by controlling the molar ratio of ferrous sulfate and phosphoric acid, the sulfate ions in the system are converted into ferric sulfate, and then reduced by elemental iron to generate ferrous sulfate, so as to achieve recycling. No sulfate byproducts are generated during the reaction, which reduces the equipment and investment required for treating sulfate wastewater. It can also avoid the cost pressure caused by the price fluctuations of raw materials such as sulfur and sulfuric acid, and has high economic value.

[0032] (2) The method for preparing ferric phosphate by ferrous sulfate recycling of the present invention does not produce hydrogen gas or introduce chloride ion problems, and has strong applicability and safety. Attached Figure Description

[0033] Figure 1 This is a flowchart illustrating the preparation process of iron phosphate according to an embodiment of the present invention.

[0034] Figure 2 This is a SEM image of the iron phosphate prepared according to an embodiment of the present invention. Detailed Implementation

[0035] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0036] Unless otherwise specified, the experimental methods used in the examples and comparative examples are conventional methods, and the materials and reagents used are commercially available unless otherwise specified.

[0037] The reactions involved in the ferrous sulfate recycling method for preparing ferric phosphate in this embodiment of the invention mainly include: The synthesis process of iron phosphate: 12FeSO4 + 4H3PO4 + 3O2 + 2H2O = 4FePO4·2H2O + 4Fe2(SO4)3 Mother liquor circulation process: Fe2(SO4)3 + Fe = 3FeSO4 Example 1: A method for preparing ferric phosphate by ferrous sulfate recycling S1. Weigh 2000.0 mL of ferrous sulfate solution and mix it with phosphoric acid solution. Add the catalyst and stir (600 rpm) to react. After the reaction is complete, separate the solid and liquid. S2. The solid obtained from the solid-liquid separation in step S1 is washed, aged, separated again, and dried to obtain the iron phosphate. S3. Add a reducing agent to the filtrate obtained from the solid-liquid separation in step S1, stir and react at 60°C for 2 hours, filter to obtain a ferrous sulfate solution, and return to step S1.

[0038] The ferrous sulfate solution contains 1.5 mol / L of ferrous ions.

[0039] The phosphoric acid solution has a content of 75%.

[0040] The molar ratio of ferrous ions to phosphorus in the phosphoric acid solution is 3:1.00.

[0041] The catalyst was added at a rate of 0.1% of the total mass of the ferrous sulfate solution and the phosphoric acid solution. The catalyst is sodium nitrite.

[0042] The reaction temperature was 120℃, and the reaction time was 3 hours. Oxygen is introduced during the reaction process, and the pressure during the reaction is 0.2 MPa.

[0043] The washing process involves a first wash with pure water, followed by filtration and a second wash; the conductivity of the filtrate obtained after the second wash is less than 800 μS / cm. The aging temperature is 80℃ and the aging time is 4 hours; The solvent used for aging is a phosphoric acid solution; the concentration of the phosphoric acid solution is 0.3 mol / L; the mass ratio of the solid after washing and filtration to phosphoric acid is 1:4.

[0044] The drying process involves drying the solid after solid-liquid separation and washing at 105°C for 60 minutes to remove free water, and then drying it at 550°C for 1 hour to remove water of crystallization, thus obtaining ferric phosphate.

[0045] The reducing agent is elemental iron; the elemental iron is selected from iron powder.

[0046] The amount of reducing agent added is 50% of the total iron mass in the filtrate.

[0047] SEM image of the iron phosphate prepared in Example 1 is shown below. Figure 2 As shown, iron phosphate consists of near-spherical particles with a primary particle size of 50-200 nm. This morphology of the precursor is suitable for preparing high-performance lithium iron phosphate cathode materials.

[0048] Example 2: A method for preparing ferric phosphate by ferrous sulfate recycling S1. Weigh 2000.0 mL of ferrous sulfate solution and mix it with phosphoric acid solution. Add the catalyst and stir (600 rpm) to react. After the reaction is complete, separate the solid and liquid. S2. The solid obtained from the solid-liquid separation in step S1 is washed, aged, separated again, and dried to obtain the iron phosphate. S3. Add a reducing agent to the filtrate obtained from the solid-liquid separation in step S1, stir and react at 70°C for 2 hours, filter to obtain ferrous sulfate solution, and return to step S1.

[0049] The ferrous ion concentration in the ferrous sulfate solution is 1.0 mol / L.

[0050] The phosphoric acid solution has a content of 50%.

[0051] The molar ratio of ferrous ions to phosphorus in the phosphoric acid solution is 3:0.95.

[0052] The amount of catalyst added is 0.05% of the total mass of the ferrous sulfate solution and the phosphoric acid solution; The catalyst is nitric acid.

[0053] The reaction temperature was 130℃, and the reaction time was 2 hours. Oxygen is introduced during the reaction process, and the pressure during the reaction is 0.2 MPa.

[0054] The washing process involves a first wash with pure water, followed by filtration and a second wash; the conductivity of the filtrate obtained after the second wash is less than 800 μS / cm. The aging temperature is 60℃ and the aging time is 5 hours; The aging solvent includes a phosphoric acid solution; the concentration of the phosphoric acid solution is 0.2 mol / L.

[0055] The drying process involves drying the solid after solid-liquid separation and washing at 105°C for 60 minutes to remove free water, and then drying it at 550°C for 1 hour to remove water of crystallization, thus obtaining ferric phosphate.

[0056] The reducing agent is elemental iron; the elemental iron is iron filings.

[0057] The amount of reducing agent added is 40% of the total iron mass in the filtrate.

[0058] Example 3: A method for preparing ferric phosphate by ferrous sulfate recycling S1. Weigh 2000.0 mL of ferrous sulfate solution and mix it with phosphoric acid solution. Add the catalyst and stir (600 rpm) to react. After the reaction is complete, separate the solid and liquid. S2. The solid obtained from the solid-liquid separation in step S1 is washed, aged, separated again, and dried to obtain the iron phosphate. S3. Add a reducing agent to the filtrate obtained from the solid-liquid separation in step S1, stir and react at 80°C for 1 hour, filter to obtain a ferrous sulfate solution, and return to step S1.

[0059] The ferrous ion concentration in the ferrous sulfate solution is 2.5 mol / L.

[0060] The phosphoric acid solution has a content of 85%.

[0061] The molar ratio of ferrous ions to phosphorus in the phosphoric acid solution is 3:1.20.

[0062] The amount of catalyst added is 0.3% of the total mass of the ferrous sulfate solution and the phosphoric acid solution; The catalyst is nitrous acid.

[0063] The reaction temperature was 110℃, and the reaction time was 4 hours. Oxygen is introduced during the reaction, and the pressure during the reaction is 0.3 MPa.

[0064] The washing process involves a first wash with pure water, followed by filtration and a second wash; the conductivity of the filtrate obtained after the second wash is less than 800 μS / cm. The aging temperature is 90℃ and the aging time is 2 hours; The aging solvent includes a phosphoric acid solution; the concentration of the phosphoric acid solution is 0.5 mol / L.

[0065] The drying process involves drying the solid after solid-liquid separation and washing at 105°C for 60 minutes to remove free water, and then drying it at 550°C for 1 hour to remove water of crystallization, thus obtaining ferric phosphate.

[0066] The reducing agent is elemental iron; the elemental iron is an iron block.

[0067] The amount of reducing agent added is 60% of the total iron mass in the filtrate.

[0068] Example 4: A method for preparing ferric phosphate by ferrous sulfate recycling S1. Weigh 2000.0 mL of ferrous sulfate solution and mix it with phosphoric acid solution. Add the catalyst and stir (600 rpm) to react. After the reaction is complete, separate the solid and liquid. S2. The solid obtained from the solid-liquid separation in step S1 is washed, aged, separated again, and dried to obtain the iron phosphate. S3. Add a reducing agent to the filtrate obtained from the solid-liquid separation in step S1, stir and react at 60°C for 2 hours, filter to obtain a ferrous sulfate solution, and return to step S1.

[0069] The ferrous ion concentration in the ferrous sulfate solution is 2.5 mol / L.

[0070] The phosphoric acid solution has a content of 75%.

[0071] The molar ratio of ferrous ions to phosphorus in the phosphoric acid solution is 3:1.00.

[0072] The catalyst was added at a rate of 0.1% of the total mass of the ferrous sulfate solution and the phosphoric acid solution. The catalyst is sodium nitrite.

[0073] The reaction temperature was 120℃, and the reaction time was 3 hours. Oxygen is introduced during the reaction process, and the pressure during the reaction is 0.2 MPa.

[0074] The washing process involves a first wash with pure water, followed by filtration and a second wash; the conductivity of the filtrate obtained after the second wash is less than 800 μS / cm. The aging temperature is 80℃ and the aging time is 4 hours; The solvent used for aging is a phosphoric acid solution; the concentration of the phosphoric acid solution is 0.3 mol / L; the mass ratio of the solid after washing and filtration to phosphoric acid is 1:4.

[0075] The drying process involves drying the solid after solid-liquid separation and washing at 105°C for 60 minutes to remove free water, and then drying it at 550°C for 1 hour to remove water of crystallization, thus obtaining ferric phosphate.

[0076] The reducing agent is elemental iron; the elemental iron is selected from iron powder.

[0077] The amount of reducing agent added is 50% of the total iron mass in the filtrate.

[0078] Compared with Example 1, the only difference in this example is that the ferrous ion concentration in the ferrous sulfate solution is 2.5 mol / L.

[0079] Comparative Example 1 Compared with Example 1, the only difference in this comparative example is that the ferrous ion concentration in the ferrous sulfate solution is 3.0 mol / L.

[0080] The preparation method is the same as in Example 1.

[0081] Comparative Example 2 Compared with Example 1, the only difference in this comparative example is that the molar ratio of ferrous ions in the ferrous sulfate solution to phosphorus in the phosphoric acid solution is 1:1.00.

[0082] The preparation method is the same as in Example 1.

[0083] Comparative Example 3 Compared with Example 1, the only difference in this comparative example is that the reaction temperature in step S1 is 90°C.

[0084] The preparation method is the same as in Example 1.

[0085] Comparative Example 4 Compared with Example 1, the only difference in this example is that the reaction temperature in step S1 is 150°C.

[0086] The preparation method is the same as in Example 1.

[0087] Experimental Example 1: Test of Ferric Phosphate Yield and Impurity Content The yields of the ferric phosphate products prepared in the examples and comparative examples were measured, and the impurity content of the ferric phosphate was determined by ICP. The corresponding experimental results are shown in Table 1.

[0088] Table 1. Ferric phosphate yield and product impurity content for each group

[0089] As can be seen from the experimental data in Table 1, the ferrous sulfate recycling method for preparing ferric phosphate in this embodiment of the invention can produce ferric phosphate products without adding alkaline solution to accurately control the pH value, and achieves a high ferric phosphate yield. At the same time, the impurity content in the obtained ferric phosphate products can be kept at a low level, which meets the actual application requirements.

[0090] Compared to Example 1, in Comparative Example 1, the ferrous ion concentration in the ferrous sulfate solution was too high, easily leading to the formation of ferrous phosphate during the preparation process, resulting in an impure final product. In Comparative Example 2, the molar ratio of ferrous ions in the ferrous sulfate solution to phosphorus in the phosphoric acid solution was 1:1.00, resulting in an excessively high initial acidity of the mixture, making it difficult for orthophosphate ions to ionize and synthesize ferric phosphate, thus significantly reducing the yield of the final ferric phosphate product. In Comparative Example 3, the reaction temperature was too low, significantly slowing down the oxidation rate of ferrous ions, resulting in a significant reduction in the amount of ferric phosphate produced. In Comparative Example 4, the reaction temperature was too high, resulting in a high partial pressure of water vapor, making it difficult for oxygen to enter the reaction system, leading to a decrease in the yield of the final ferric phosphate product.

[0091] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for preparing ferric phosphate by ferrous sulfate recycling, characterized in that, Includes the following steps: S1. Mix ferrous sulfate solution and phosphoric acid solution, add catalyst, react, and separate solid and liquid components; S2. The solid obtained from the solid-liquid separation in step S1 is washed, aged, separated again, and dried to obtain the iron phosphate. S3. Add a reducing agent to the filtrate obtained from the solid-liquid separation in step S1, react, filter, and obtain a ferrous sulfate solution, then return to step S1.

2. The method for preparing ferric phosphate by ferrous sulfate recycling as described in claim 1, characterized in that, The ferrous sulfate solution has a ferrous ion concentration of 1.0-2.5 mol / L; the phosphoric acid solution has a content of 50%-85%.

3. The method for preparing ferric phosphate by ferrous sulfate recycling as described in claim 2, characterized in that, The molar ratio of ferrous ions to phosphorus in the phosphoric acid solution is 3:(0.95-1.20).

4. The method for preparing ferric phosphate by ferrous sulfate recycling as described in claim 1, characterized in that, The amount of catalyst added is 0.05%-0.3% of the total mass of the ferrous sulfate solution and the phosphoric acid solution; The catalyst includes at least one of nitric acid, nitrite, nitrate, and nitrite.

5. The method for preparing ferric phosphate by ferrous sulfate recycling as described in claim 1, characterized in that, In step S1, the reaction temperature is 110-130℃ and the reaction time is 2-4 hours. In step S1, oxygen is introduced during the reaction process, and the pressure during the reaction process is 0.1-0.3 MPa.

6. The method for preparing ferric phosphate by ferrous sulfate recycling as described in claim 1, characterized in that, The washing process involves a first wash with pure water, followed by filtration and a second wash; the conductivity of the filtrate obtained from the second wash is less than 800 μS / cm. The aging temperature is 60-90℃, and the aging time is 2-5 hours; The aging solvent includes a phosphoric acid solution; the concentration of the phosphoric acid solution is 0.2-0.5 mol / L.

7. The method for preparing ferric phosphate by ferrous sulfate recycling as described in claim 1, characterized in that, The drying process involves first drying at 100-110℃ for 10-60 minutes, followed by drying at 500-600℃ for 1-3 hours.

8. The method for preparing ferric phosphate by ferrous sulfate recycling as described in claim 1, characterized in that, The reducing agent is elemental iron; the elemental iron includes one or more of iron powder, iron filings, and iron blocks; The amount of reducing agent added is 40-60% of the total iron mass in the filtrate.

9. The method for preparing ferric phosphate by recycling ferrous sulfate as described in claim 1, characterized in that, In step S3, the reaction is carried out by stirring at 60~80℃ for 1~3 hours.

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