Preparation method of battery-grade iron phosphate and battery-grade iron phosphate

Abstract

The invention discloses a preparation method of battery-grade iron phosphate. The method comprises the following steps: S1, preparing an iron source solution from titanium dioxide slag; s2, mixing a phosphate solution with an oxidizing agent to obtain a phosphorus source solution; s3, adding pure water, a surfactant, the iron phosphate dihydrate seed crystal, the iron source solution and the phosphorus source solution into the reaction kettle to generate iron phosphate crystals; s4, adding phosphoric acid into the reaction kettle for high-temperature aging, and filtering; and S5, washing and drying the filter residues to obtain a battery-grade iron phosphate finished product. Through combination of impurity removal of the iron source solution, seed crystal induced crystallization and high-temperature aging, one-step synthesis of the iron phosphate and synergistic effects among steps, heavy metal impurities in the iron phosphate are controlled to meet the battery grade standard, the process route is shortened, and the quality of the iron phosphate can be ensured to meet the battery grade standard while the production cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of precursors for cathode materials of lithium-ion batteries, and particularly to a preparation method of battery-grade iron phosphate and battery-grade iron phosphate. Background Art

[0002] Lithium-ion batteries have been fully applied in many fields such as consumer electronics, power tools, transportation, and energy storage. At present, the cathode materials of lithium-ion batteries that can be reversibly cycled in the market include lithium cobaltate, lithium nickelate, lithium manganate, lithium iron phosphate, and a series of ternary derivatives.

[0003] Due to its outstanding advantages in safety performance, cycle life, and cost control, the penetration of lithium iron phosphate batteries into various fields will enter the fast lane.

[0004] At present, the production processes of battery-grade iron phosphate are divided into the ammonium method, the sodium method, the iron powder method, and the iron oxide method. The iron powder method and the iron oxide method require the iron source to have sufficient purity, which leads to too high a price of the iron source and thus a relatively high production cost of iron phosphate. The ammonium method uses ammonia water to adjust the pH, and the sodium method uses sodium hydroxide to adjust the pH. However, the iron sources required by both the ammonium method and the sodium method also face the problem of impurity removal. The common method for removing lead is to use sulfide to remove lead, but lead sulfide and other sulfides generated are hazardous wastes, and the treatment process is troublesome, resulting in too high a production cost.

[0005] The preparation methods of battery-grade iron phosphate in the prior art have at least the following defects: In the prior art, the production cost of preparing battery-grade iron phosphate is relatively high, the solid waste generated by impurity removal is difficult to treat, and the separation is difficult during the production process. Summary of the Invention

[0006] The present invention discloses a preparation method of battery-grade iron phosphate and battery-grade iron phosphate to solve the technical problems of high cost and difficult waste treatment caused by using sulfide to remove lead when producing battery-grade iron phosphate in the prior art.

[0007] To solve the above problems, the present invention adopts the following technical solutions: In a first aspect, the present application provides a preparation method of battery-grade iron phosphate, which is characterized by comprising the following steps: S1. Adjust the pH of the ferrous sulfate solution prepared from titanium white waste residue to 5.0 - 6.0, control the temperature at 35 - 55 °C, remove titanium and aluminum simultaneously through hydrolysis, filter to obtain a ferrous sulfate solution from which titanium and aluminum have been removed; add ammonium fluoride to the ferrous sulfate solution from which titanium and aluminum have been removed, filter after the reaction is completed to obtain a refined ferrous sulfate solution; adjust the pH of the refined ferrous sulfate solution to 1.8 - 2.2 to obtain an iron source solution; S2. Mix a phosphate solution and an oxidant to obtain a phosphorus source solution; S3. Add pure water and surfactant into the reaction kettle, start stirring and keep it at low speed; mix the pure water and surfactant evenly and heat up to 45 - 55 °C; continuously control the temperature at 45 - 55 °C, and add iron phosphate dihydrate seeds into the reaction kettle; then add the iron source solution and phosphorus source solution into the reaction kettle. After adding the iron source solution and phosphorus source solution, add ammonia water to adjust the pH to 2 - 3, and react to form iron phosphate dihydrate crystals. Then continue stirring and reacting for 0.5 - 1 h until no more crystals are formed; S4. Add phosphoric acid into the reaction kettle and stir evenly, carry out high - temperature aging, and after completion, carry out solid - liquid separation to obtain a filtrate and a filter residue; S5. Wash and dry the filter residue to obtain the battery - grade iron phosphate finished product.

[0008] In the second aspect, the present application provides a battery - grade iron phosphate prepared by the above - mentioned preparation method.

[0009] During the preparation process of the iron source solution in the present application, the removal principles of titanium, aluminum, calcium, and magnesium are as follows: ① Removal principle of titanium and aluminum: When the temperature is 35 - 55 °C and pH ≥ 4.7, Al 3+ and Ti 4+ will be completely hydrolyzed and precipitated, respectively forming titanium hydroxide and aluminum hydroxide precipitates. The reaction equations are shown as the following formulas (Ⅰ) and (Ⅱ): Al 3+ + 3OH - → Al(OH)3↓ (Ⅰ); Ti 4+ + 4OH - → Ti(OH)4↓ (Ⅱ).

[0010] ② Removal principle of calcium and magnesium: After ammonium fluoride dissolves in the solution, it will dissociate into fluoride ions (F - ) and ammonium ions (NH4 + ). The fluoride ions react with calcium and magnesium ions in the wastewater to form calcium fluoride (CaF2) and magnesium fluoride (MgF2) precipitates that are insoluble in water. The reaction equations are shown as the following formulas (Ⅲ) and (Ⅳ): Ca 2+ + 2F - → CaF2↓ (Ⅲ); Mg 2+ + 2F - → MgF2↓ (Ⅳ).

[0011] The technical solution adopted by the present invention can achieve the following beneficial effects: (1)The preparation method of battery-grade iron phosphate provided by this application uses titanium white waste residue as a raw material to prepare an iron source solution. During the preparation of the iron source solution, titanium and aluminum are removed simultaneously by hydrolysis. When the temperature is 35 - 55 °C and pH ≥ 4.7, Al 3+ and Ti 4+ will be completely hydrolyzed and precipitated, while the pH for Fe 2+ to precipitate is 6.5 - 7.5. Therefore, Al 3+ and Ti 4+ are removed simultaneously by controlling the temperature and adjusting the pH; further, by adding ammonium fluoride, calcium fluoride precipitate and magnesium fluoride precipitate are generated to further remove Ca 2+ and Mg 2+ . Before adding the iron source and phosphorus source, the iron phosphate dihydrate crystal seeds are added to the reaction kettle and evenly distributed in the reaction kettle. When the iron source and phosphorus source are continuously added to the reaction kettle at a stable rate, the previously added iron phosphate dihydrate crystal seeds can serve as crystal nuclei and quickly enter the crystal growth stage, enabling the grown iron phosphate crystals to be more uniform, dense, and not easily agglomerated to wrap impurities. Therefore, impurities are not easily incorporated into the iron phosphate crystals. Then phosphoric acid is added for high-temperature aging. Through the in-situ purification mechanism and using the Ostwald ripening effect, small crystals dissolve due to their higher surface energy, and the solute redeposits on more stable crystal seeds or large crystals. During this process, after the small crystals containing impurities dissolve, the impurities are released back into the solution, while the pure solute continues to deposit on the crystal seeds, thereby further improving the crystal purity. The crystal particle size of the iron phosphate crystals generated by this method is D50 = 2 - 5 μm and D99 < 20 μm, which are very small crystals. Therefore, during the high-temperature aging process of iron phosphate, continuous dissolution and crystallization will fully exclude impurities and further improve the product quality; this application combines impurity removal of the iron source solution, crystal seed-induced crystallization, and high-temperature aging to synthesize iron phosphate in one step. The steps have a synergistic effect, controlling the heavy metal impurities in iron phosphate to meet the battery-grade standard, shortening the process route, reducing the production cost, and ensuring that the quality of iron phosphate meets the battery-grade standard at the same time.

[0012] (2)The preparation method of battery-grade iron phosphate provided by this application uses titanium white waste residue as a raw material to prepare an iron source solution, which realizes the resource utilization of the waste residue and reduces the production cost of battery-grade iron phosphate; and in the preparation method of this application, the method of using sulfide to remove lead is avoided, thereby also avoiding the generation and treatment of sulfide hazardous waste, shortening the process route, and reducing the production cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can also be obtained based on these drawings.

[0014] Figure 1 is the scanning electron microscope image of the iron phosphate prepared in Comparative Example 1 at 4 µm; Figure 2 is the scanning electron microscope image of the iron phosphate prepared in Comparative Example 1 at 400 nm; Figure 3 is the scanning electron microscope image of the iron phosphate prepared in Example 1 at 4 µm; Figure 4 is the scanning electron microscope image of the iron phosphate prepared in Example 1 at 400 nm. Detailed Embodiments

[0015] To make the objectives, technical solutions, and advantages of the present invention clearer, the following will describe the technical solutions of the present invention in detail. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope protected by the present invention.

[0016] I. Raw Materials Titanium white residue: Taking HG / T 4701-2021 "Iron Phosphate for Batteries" as the detection standard, the impurity content of the titanium white residue used in the examples and comparative examples was detected, and the detection results are shown in Table 1 below: Table 1 Impurity Content of Titanium White Residue (Unit: ppm) II. Examples: Item <![CDATA[Fe 2+ > Na Mg Al K Ca Ti Cr Mn Co Cu Zn Pb Titanium white residue 20%-25% 883 13386 2546 224 13824 7027 46 7027 35 0.8 132 9.75 Example 1: A preparation method of battery-grade iron phosphate includes the following steps: S1. Preparation of iron source solution S11. Dissolve the titanium white residue in pure water, and the mass ratio of the titanium white residue to pure water is 1:3.6; then stir at a temperature of 50 °C for 1.0 h, with a stirring speed of 300 rpm. After stirring, filter to obtain the first ferrous sulfate solution, and the mass percentage content of total iron in the first ferrous sulfate solution is 6.5%; S12. Add ammonia water to the first ferrous sulfate solution protected by nitrogen until the pH reaches 5.5, control the temperature at 45 °C, continue stirring for 1 h at a stirring speed of 300 rpm, remove titanium and aluminum simultaneously through hydrolysis, and perform filtration after stirring is completed to obtain the second ferrous sulfate solution with titanium and aluminum removed; S13. Add the second ferrous sulfate solution to the reaction kettle, start stirring at a stirring speed of 300 rpm, and add ammonium fluoride under the condition of nitrogen protection. The ammonium fluoride is added in a ratio of 1:2 based on the sum of the molar amounts of Ca 2+ and Mg 2+ to the molar amount of ammonium fluoride. React at 45 °C for 1 h to form calcium fluoride precipitate and magnesium fluoride precipitate. After the reaction is completed, perform filtration to obtain the refined ferrous sulfate solution with calcium and magnesium removed; adjust the pH of this refined ferrous sulfate solution to 2.0 to obtain the iron source solution; S2. Preparation of the phosphorus source solution S21. Dissolve ammonium dihydrogen phosphate in pure water with a mass ratio of ammonium dihydrogen phosphate to pure water of 150:500, and then adjust the pH to 6.5 with ammonia water to prepare a phosphate solution; S22. Mix the phosphate solution prepared in step S21 and hydrogen peroxide, and mix them in a molar ratio of PO4 3- in the phosphate solution to hydrogen peroxide of 1:0.6, which is the phosphorus source solution; S3. Crystal formation S31. Add pure water and cetyltrimethylammonium bromide to the reaction kettle, start stirring at a stirring speed of 300 rpm; mix the pure water and cetyltrimethylammonium bromide evenly and heat up to 50 °C; The addition amount of pure water is 50% of the mass of the iron source solution added in the subsequent step S33; The addition amount of cetyltrimethylammonium bromide is 0.5% of the mass of FePO4·2H2O theoretically generated calculated based on the iron content of the ferrous sulfate solution prepared from titanium white waste residue in step S1; S32. Keep the stirring speed at 300 rpm, continuously control the temperature at 50 °C, and add ferric phosphate dihydrate crystal seeds to the reaction kettle. The addition amount of ferric phosphate dihydrate crystal seeds is 7.5% of the mass of FePO4·2H2O theoretically generated calculated based on the iron content of the ferrous sulfate solution prepared from titanium white waste residue in step S1; S33. Keep the stirring speed at 300 rpm, and then add the iron source solution and the phosphorus source solution to the reaction kettle through a peristaltic pump. The iron source solution is added to the reaction kettle at a flow rate of 1.0 L / min, and the phosphorus source solution is added to the reaction kettle at a flow rate of 1.0 L / min; the addition amounts of the iron source solution and the phosphorus source solution are based on PO4 3- in the phosphorus source solution and Fe 2+Added in a molar ratio of 1.15:1; after the addition of the iron source solution and the phosphorus source solution, ammonia water was added to adjust the pH to 2.5, and iron phosphate dihydrate crystals were formed by reaction. Then, the reaction was continued with stirring for 1 h until no more crystals were formed; S4. Crystal aging Maintain the stirring speed at 300 rpm, add 85% industrial phosphoric acid to the reaction kettle and stir evenly. The addition amount of industrial phosphoric acid was added according to the concentration of phosphoric acid after addition being 3%; then aged at 90 °C for 2 h. After completion, plate and frame filtration was used for solid-liquid separation to obtain filtrate and filter residue; S5. Post-treatment The filter residue obtained in step S4 was washed by pulping with pure water three times. The washing included: First washing: The filter residue and pure water were mixed in a mass ratio of 1:7 and pulped for 20 min, and then plate and frame filtration was used for solid-liquid separation to obtain filter residue A; Second washing: Filter residue A and pure water were mixed in a mass ratio of 1:7 and pulped for 20 min, and then plate and frame filtration was used for solid-liquid separation to obtain filter residue B; Third washing: Filter residue B and pure water were mixed in a mass ratio of 1:7 and pulped for 20 min, and then plate and frame filtration was used for solid-liquid separation to obtain filter residue C; Finally, filter residue C was dried in a constant temperature drying oven at 110 °C for 8 h to obtain the finished product of iron phosphate dihydrate.

[0017] Example 2: A preparation method of battery-grade iron phosphate, comprising the following steps: S1. Preparation of iron source solution S11. Dissolve titanium white waste residue in pure water, and the mass ratio of titanium white waste residue to pure water is 1:2.5; then stir at 55 °C for 1.5 h with a stirring speed of 200 rpm. After stirring, filter to obtain the first ferrous sulfate solution, and the mass percentage content of total iron in the first ferrous sulfate solution is 6.7%; S12. Add ammonia water to the first ferrous sulfate solution to adjust the pH to 6.0, control the temperature at 55 °C, continue to stir for 1 h with a stirring speed of 200 rpm, remove titanium and aluminum by hydrolysis at the same time. After stirring, filter to obtain the second ferrous sulfate solution from which titanium and aluminum are removed; S13. Add the second ferrous sulfate solution to the reaction kettle, start stirring, with a stirring speed of 200 rpm, and add ammonium fluoride under the condition of nitrogen protection. Ammonium fluoride is in the form of Ca 2+ and Mg 2+The ratio of the sum of the molar amounts to the molar amount of ammonium fluoride is added at 1:2, and the reaction is carried out at a temperature of 55 °C for 0.5 h to form calcium fluoride precipitate and magnesium fluoride precipitate. After the reaction is completed, filtration is carried out to obtain a refined ferrous sulfate solution with calcium and magnesium removed; the pH of the refined ferrous sulfate solution is adjusted to 2.2 to obtain an iron source solution; Preparation of S2, phosphorus source solution S21. Dissolve diammonium hydrogen phosphate in pure water, and the mass ratio of phosphate to pure water is 100:400. Then adjust the pH to 7 with ammonia water to make a phosphate solution S22. Mix the phosphate solution and hydrogen peroxide, and mix them in a molar ratio of PO4 in the phosphate solution 3- and hydrogen peroxide of 1:0.7 to obtain a phosphorus source solution; S3. Generate crystals S31. Add pure water and sodium dodecyl sulfate to the reaction kettle, start stirring, and the stirring speed is 200 rpm; mix the pure water and sodium dodecyl sulfate evenly and heat up to 55 °C; The addition amount of pure water is added at 65% of the mass of the iron source solution added in the subsequent step S33; The addition amount of sodium dodecyl sulfate is added at 1% of the mass of FePO4·2H2O theoretically generated calculated based on the iron content of the ferrous sulfate solution prepared from titanium dioxide residue in step S1; S32. Keep the stirring speed at 200 rpm, continuously control the temperature at 55 °C, and add ferric phosphate dihydrate crystal seeds to the reaction kettle. The addition amount of ferric phosphate dihydrate crystal seeds is added at 10% of the mass of FePO4·2H2O theoretically generated calculated based on the iron content of the ferrous sulfate solution prepared from titanium dioxide residue in step S1; S33. Keep the stirring speed at 200 rpm, and then add the iron source solution and the phosphorus source solution to the reaction kettle through a peristaltic pump. The iron source solution is added to the reaction kettle at a flow rate of 1.5 L / min, and the phosphorus source solution is added to the reaction kettle at a flow rate of 1.5 L / min; the addition amounts of the phosphorus source solution and the phosphorus source solution are based on PO4 in the phosphorus source solution 3- and Fe in the iron source solution 2+ The molar ratio of is added at 1.25:1; after the iron source solution and the phosphorus source solution are added, add ammonia water to adjust the pH to 3, and react to form ferric phosphate dihydrate crystals, and then continue to stir and react for 0.5 h until no more crystals are formed; S4. Crystal aging Keep the stirring speed at 200 rpm, add 85% industrial phosphoric acid to the reaction kettle and stir evenly. The addition amount of industrial phosphoric acid is added according to the concentration of phosphoric acid after addition being 1%; then age at 95 °C for 2.5 h, and after completion, carry out solid-liquid separation by plate and frame pressure filtration to obtain a filtrate and a filter residue; S5. Post-treatment The filter residue obtained in step S4 is washed by beating with pure water three times. The washing includes: First washing: The filter residue and pure water are mixed and beaten in a mass ratio of 1:5 for 30 min, and then plate-and-frame filtration is used for solid-liquid separation to obtain filter residue A; Second washing: Filter residue A and pure water are mixed and beaten in a mass ratio of 1:5 for 30 min, and then plate-and-frame filtration is used for solid-liquid separation to obtain filter residue B; Third washing: Filter residue B and pure water are mixed and beaten in a mass ratio of 1:9 for 30 min, and then plate-and-frame filtration is used for solid-liquid separation to obtain filter residue C; Finally, filter residue C is dried in a constant-temperature drying oven at a temperature of 100 °C for 10 h to obtain the finished product of iron phosphate dihydrate.

[0018] Example 3: A preparation method of battery-grade iron phosphate includes the following steps: S1. Preparation of iron source solution S11. Dissolve titanium white waste residue in pure water, and the mass ratio of titanium white waste residue to pure water is 1:2; then stir at a temperature of 45 °C for 0.5 h, the stirring speed is 200 rpm, and after stirring is completed, filter to obtain the first ferrous sulfate solution, and the mass percentage content of total iron in the first ferrous sulfate solution is 7.0%; S12. Add ammonia water to the first ferrous sulfate solution to adjust the pH to 6.0, control the temperature at 35 °C, continue to stir for 1 h, the stirring speed is 200 rpm, remove titanium and aluminum by hydrolysis at the same time, and filter after stirring is completed to obtain the second ferrous sulfate solution from which titanium and aluminum are removed; S13. Add the second ferrous sulfate solution to the reaction kettle, start stirring, the stirring speed is 200 rpm, and add ammonium fluoride under the condition of nitrogen protection. The molar ratio of the sum of the molar amounts of Ca 2+ and Mg 2+ to the molar amount of ammonium fluoride is 1:2, react at a temperature of 35 °C for 1 h to form calcium fluoride precipitate and magnesium fluoride precipitate, filter after the reaction is completed to obtain the refined ferrous sulfate solution from which calcium and magnesium are removed; adjust the pH of the refined ferrous sulfate solution to 2.2 to obtain the iron source solution; S2. Preparation of phosphorus source solution S21. Dissolve ammonium phosphate in pure water, and the mass ratio of phosphate to pure water is 200:600, and then adjust the pH to 6 with ammonia water to prepare a phosphate solution; S22. Mix the phosphate solution and hydrogen peroxide, and mix them in a molar ratio of PO4 3- in the phosphate solution to hydrogen peroxide of 1:0.5, which is the phosphorus source solution; S3. Crystal formation S31. Add pure water and polyethylene glycol into the reaction kettle, start stirring at a speed of 200 rpm; mix the pure water and polyethylene glycol evenly and heat up to 45 °C; The addition amount of pure water is 35% of the mass of the iron source solution added in the subsequent step S33; The addition amount of polyethylene glycol is 0.5% of the mass of FePO4·2H2O theoretically generated calculated based on the iron content of the ferrous sulfate solution prepared from titanium white waste residue in step S1; S32. Keep the stirring speed at 200 rpm, continuously control the temperature at 45 °C, and add ferric phosphate dihydrate seeds into the reaction kettle according to the theoretical output of ferric phosphate calculated based on the iron content of the ferrous sulfate solution prepared from titanium white waste residue in step S1. The addition amount of ferric phosphate dihydrate seeds is 5% of the mass of FePO4·2H2O theoretically generated calculated based on the iron content of the ferrous sulfate solution prepared from titanium white waste residue in step S1; S33. Keep the stirring speed at 200 rpm, and then add the iron source solution and the phosphorus source solution into the reaction kettle by a peristaltic pump. The iron source solution is added into the reaction kettle at a flow rate of 0.8 L / min, and the phosphorus source solution is added into the reaction kettle at a flow rate of 0.8 L / min; the addition amounts of the phosphorus source solution and the phosphorus source solution are added according to the molar ratio of PO4 3- in the phosphorus source solution to Fe 2+ in the iron source solution of 1.05:1; after the iron source solution and the phosphorus source solution are added, add ammonia water to adjust the pH to 2, react to form ferric phosphate dihydrate crystals, and then continue to stir and react for 1 h until no more crystals are formed; S4. Crystal aging Keep the stirring speed at 200 rpm, add 85% industrial phosphoric acid into the reaction kettle and stir evenly. The addition amount of industrial phosphoric acid is added according to the concentration of phosphoric acid after addition being 5%; then age at 85 °C for 1.5 h, and after completion, carry out solid-liquid separation by plate-and-frame filtration to obtain filtrate and filter residue; S5. Post-treatment Slurry-wash the filter residue obtained in step S4 three times with pure water. The washing includes: First washing: Mix the filter residue and pure water in a mass ratio of 1:9, slurry for 25 min, and then carry out solid-liquid separation by plate-and-frame filtration to obtain filter residue A; Second washing: Mix filter residue A and pure water in a mass ratio of 1:9, slurry for 25 min, and then carry out solid-liquid separation by plate-and-frame filtration to obtain filter residue B; Third washing: Mix filter residue B and pure water in a mass ratio of 1:5, slurry for 25 min, and then carry out solid-liquid separation by plate-and-frame filtration to obtain filter residue C; Finally, dry filter residue C in a constant-temperature drying oven at 120 °C for 6 h to obtain the finished product of ferric phosphate dihydrate.

[0019] Example 4: A preparation method of battery-grade iron phosphate includes the following steps: S1. Preparation of iron source solution S11. Dissolve titanium white residue in pure water, and the mass ratio of titanium white residue to pure water is 1:3; then stir at 53°C for 0.8 h with a stirring speed of 250 rpm, and filter after stirring to obtain the first ferrous sulfate solution, and the mass percentage of total iron in the first ferrous sulfate solution is 7.1%; S12. Add ammonia water to the first ferrous sulfate solution to adjust the pH to 5.8, control the temperature at 50°C, continue to stir for 0.8 h with a stirring speed of 250 rpm, remove titanium and aluminum by hydrolysis at the same time, and filter after stirring to obtain the second ferrous sulfate solution from which titanium and aluminum are removed; S13. Add the second ferrous sulfate solution to the reaction kettle, start stirring with a stirring speed of 250 rpm, and add ammonium fluoride under the protection of nitrogen. The ammonium fluoride is added in a ratio of 1:2 based on the sum of the molar amounts of Ca 2+ and Mg 2+ to the molar amount of ammonium fluoride, react at 50°C for 0.6 h to form calcium fluoride precipitate and magnesium fluoride precipitate, filter after the reaction is completed to obtain a refined ferrous sulfate solution from which calcium and magnesium are removed; adjust the pH of the refined ferrous sulfate solution to 2.1 to obtain the iron source solution; S2. Preparation of phosphorus source solution S21. Dilute 85% industrial phosphoric acid into 30% dilute phosphoric acid, and adjust the pH to 6.5 with ammonia water to obtain a phosphate solution; S22. Mix the phosphate solution and hydrogen peroxide, and mix them in a molar ratio of 1:0.6 of PO4 3- in the phosphate solution to hydrogen peroxide to obtain the phosphorus source solution; S3. Crystal formation S31. Add pure water and sodium dodecylbenzenesulfonate to the reaction kettle, start stirring with a stirring speed of 250 rpm; mix the pure water and sodium dodecylbenzenesulfonate evenly and heat up to 55°C; The addition amount of pure water is 60% of the mass of the iron source solution added in the subsequent step S33; The addition amount of sodium dodecylbenzenesulfonate is 0.9% of the mass of FePO4·2H2O theoretically generated calculated based on the iron content of the ferrous sulfate solution prepared from titanium white residue in step S1; S32. Keep the stirring speed at 250 rpm, continuously control the temperature at 50 °C, and add ferrous phosphate dihydrate seeds to the reaction kettle according to the theoretical yield of iron phosphate calculated from the iron content of the ferrous sulfate solution prepared from the titanium dioxide residue in step S1. The addition amount of the ferrous phosphate dihydrate seeds is 9% of the mass of FePO4·2H2O theoretically generated calculated from the iron content of the ferrous sulfate solution prepared from the titanium dioxide residue in step S1. S33. Keep the stirring speed at 250 rpm, and then add the iron source solution and the phosphorus source solution to the reaction kettle by a peristaltic pump. The iron source solution is added to the reaction kettle at a flow rate of 1.2 L / min, and the phosphorus source solution is added to the reaction kettle at a flow rate of 1.2 L / min. The addition amounts of the phosphorus source solution and the phosphorus source solution are added according to the molar ratio of PO4 3- in the phosphorus source solution to Fe 2+ in the iron source solution of 1.05:1. After the iron source solution and the phosphorus source solution are added, add ammonia water to adjust the pH to 3, react to form ferrous phosphate dihydrate crystals, and then continue to stir and react for 1 h until no more crystals are formed. S4. Crystal aging Keep the stirring speed at 250 rpm, add 85% industrial phosphoric acid to the reaction kettle and stir evenly. The addition amount of the industrial phosphoric acid is added according to the concentration of phosphoric acid after addition being 3.5%. Then age at 90 °C for 2.5 h. After completion, perform solid-liquid separation by plate-and-frame filtration to obtain a filtrate and a filter residue. S5. Post-treatment The filter residue obtained in step S4 is washed by pulping with pure water three times. The washing includes: First washing: Mix the filter residue and pure water at a mass ratio of 1:9, pulp for 15 min, and then perform solid-liquid separation by plate-and-frame filtration to obtain filter residue A. Second washing: Mix filter residue A and pure water at a mass ratio of 1:9, pulp for 15 min, and then perform solid-liquid separation by plate-and-frame filtration to obtain filter residue B. Third washing: Mix filter residue B and pure water at a mass ratio of 1:9, pulp for 15 min, and then perform solid-liquid separation by plate-and-frame filtration to obtain filter residue C. Finally, dry filter residue C in a constant-temperature drying oven at 1.5 °C for 9 h to obtain the finished product of ferrous phosphate dihydrate.

[0020] Example 5: A preparation method of battery-grade iron phosphate, comprising the following steps: S1. Preparation of the iron source solution S11. Dissolve the titanium dioxide residue in pure water with a mass ratio of titanium dioxide residue to pure water of 1:3.2. Then stir at 48°C for 1.2 h at a stirring speed of 100 rpm. After stirring, filter to obtain the first ferrous sulfate solution, and the mass percentage of total iron in the first ferrous sulfate solution is 6.8%. S12. Add ammonia water to the first ferrous sulfate solution to adjust the pH to 6.0, control the temperature at 40°C, continue to stir for 1 h at a stirring speed of 100 rpm, remove titanium and aluminum simultaneously by hydrolysis, and filter after stirring to obtain the second ferrous sulfate solution with titanium and aluminum removed. S13. Add the second ferrous sulfate solution to the reaction kettle, start stirring at a stirring speed of 100 rpm, and add ammonium fluoride under the protection of nitrogen. The ammonium fluoride is added in a ratio of the sum of the molar amounts of Ca 2+ and Mg 2+ to the molar amount of ammonium fluoride of 1:2, react at 40°C for 1 h to form calcium fluoride precipitate and magnesium fluoride precipitate, filter after the reaction is completed to obtain the refined ferrous sulfate solution with calcium and magnesium removed. Adjust the pH of the refined ferrous sulfate solution to 1.8 to obtain the iron source solution. S2. Preparation of the phosphorus source solution S21. The method for preparing the phosphate solution is to dilute 85% industrial phosphoric acid into 20% dilute phosphoric acid and adjust the pH to 7 with ammonia water to obtain the phosphate solution. S22. Mix the phosphate solution and hydrogen peroxide, and mix them in a molar ratio of PO4 3- in the phosphate solution to hydrogen peroxide of 1:0.55 to obtain the phosphorus source solution. S3. Generating crystals S31. Add pure water and cetyltrimethylammonium bromide to the reaction kettle, start stirring at a stirring speed of 100 rpm. Mix the pure water and cetyltrimethylammonium bromide evenly and heat up to 55°C. The addition amount of pure water is added according to 45% of the mass of the iron source solution added in the subsequent step S33. The addition amount of cetyltrimethylammonium bromide is added at 0.8% of the mass of FePO4·2H2O theoretically generated calculated based on the iron content of the ferrous sulfate solution prepared from the titanium dioxide residue in step S1. S32. Keep the stirring speed at 100 rpm, continuously control the temperature at 50°C, and add ferric phosphate dihydrate crystal seeds to the reaction kettle according to the theoretically calculated ferric phosphate output based on the iron content of the ferrous sulfate solution prepared from the titanium dioxide residue in step S1. The addition amount of ferric phosphate dihydrate crystal seeds is added at 6% of the mass of FePO4·2H2O theoretically generated calculated based on the iron content of the ferrous sulfate solution prepared from the titanium dioxide residue in step S1. S33. Maintain the stirring speed at 100 rpm, and then add the iron source solution and the phosphorus source solution to the reaction kettle by means of a peristaltic pump. The iron source solution is added to the reaction kettle at a flow rate of 0.8 L / min, and the phosphorus source solution is added to the reaction kettle at a flow rate of 0.8 L / min; the addition amounts of the phosphorus source solution and the phosphorus source solution are added according to the molar ratio of PO4 3- in the phosphorus source solution to Fe 2+ in the iron source solution being 1.2:1; after the iron source solution and the phosphorus source solution are added, add ammonia water to adjust the pH to 2.2, and ferric phosphate dihydrate crystals are formed by reaction. Then continue to stir and react for 0.8 h until no more crystals are formed; S4. Crystal aging Maintain the stirring speed at 100 rpm, add 85% industrial phosphoric acid to the reaction kettle and stir evenly. The addition amount of the industrial phosphoric acid is added according to the concentration of phosphoric acid being 2.5% after addition; then age at 90 °C for 2 h. After completion, perform solid-liquid separation by plate-and-frame filtration to obtain a filtrate and a filter residue; S5. Post-treatment The filter residue obtained in step S4 is washed by pulping with pure water three times. The washing includes: First washing: Mix the filter residue and pure water at a mass ratio of 1:9, pulp for 15 min, and then perform solid-liquid separation by plate-and-frame filtration to obtain filter residue A; Second washing: Mix filter residue A and pure water at a mass ratio of 1:5, pulp for 30 min, and then perform solid-liquid separation by plate-and-frame filtration to obtain filter residue B; Third washing: Mix filter residue B and pure water at a mass ratio of 1:7, pulp for 20 min, and then perform solid-liquid separation by plate-and-frame filtration to obtain filter residue C; Finally, dry filter residue C in a constant-temperature drying oven at 110 °C for 8 h to obtain the finished product of ferric phosphate dihydrate.

[0021] II. Comparative example: Comparative example 1: Compared with Example 1: In step S3, no ferric phosphate dihydrate crystal seeds are added; other conditions are the same as in Example 1 to obtain the finished product of ferric phosphate dihydrate.

[0022] III. Experimental example 1. Taking Example 1 as an example, detect the impurity contents in the second ferrous sulfate solution and the refined ferrous sulfate solution in the example.

[0023] 1.1 The detection of the impurity contents in the second ferrous sulfate solution and the refined ferrous sulfate solution is carried out by performing a total element analysis of the solution according to icp-ms (inductively coupled plasma mass spectrometry).

[0024] 1.2 The detection results are shown in Table 2 below.

[0025] Table 2 Impurity content of the process solution in Example 1 (unit: ppm) Item <![CDATA[Fe 2+ > Na Mg Al K Ca Ti Cr Mn Co Cu Zn Pb Second ferrous sulfate solution 6.3% 2250 222 1.3 17 95 1.6 1.8 160 2.7 0.15 27 6 Refined ferrous sulfate solution 6.2% 2320 45 1.0 16 15 0.8 1.5 153 2.4 0.13 30 5 As can be seen from Table 2, in this application, titanium and aluminum are first removed simultaneously by hydrolysis, and then calcium fluoride precipitate and magnesium fluoride precipitate are formed by adding ammonium fluoride to further remove Ca 2+ and Mg 2+ , with good impurity removal effect, providing a favorable basis for the subsequent production of battery-grade iron phosphate.

[0026] 2. Observe the microscopic morphology of the iron phosphate dihydrate prepared in Example 1 and Comparative Example 1 2.1. Conduct a scanning electron microscopy experiment.

[0027] 2.2. The results of the scanning electron microscopy observation are as Figure 1 - Figure 4 shown.

[0028] Compare Figure 1 , Figure 2 with Figure 3 , Figure 4 . Figure 1 and Figure 2 are SEM pictures of the iron phosphate prepared without adding iron phosphate seeds in Comparative Example 1; Figure 3 and Figure 4 are SEM pictures of the iron phosphate prepared by adding seeds in Example 1, which has a lamellar structure and better crystallinity. It can be shown that during the high-temperature purification process, impurities are released back into the solution, while the pure solute continues to deposit on the seeds, thereby improving the crystal purity.

[0029] 3. Detect the impurity content of the iron phosphate dihydrate finished products obtained in the examples and comparative examples 3.1 Detection standard: Taking HG / T 4701-2021 "Iron Phosphate for Batteries" as the detection standard, detect the impurity content of the iron phosphate dihydrate finished products obtained in the examples and comparative examples.

[0030] 3.2 The detection results are shown in Table 3 below.

[0031] Table 3 Detection results of iron phosphate dihydrate in the examples and comparative examples Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example 1 Iron, w / % 29.6 29.3 29.4 29.5 29.8 29.6 Phosphorus, w / % 16.3 16.6 16.4 16.5 16.4 16.3 Iron to phosphorus ratio 1.0 0.978 0.994 0.991 1.007 1.007 Calcium, ppm 23 24 16 35 18 36 Magnesium, ppm 2.1 3.5 7.4 8.1 12 15 Sodium, ppm 2.5 3.4 1.5 3.7 4.2 1.6 Potassium, ppm 6.2 3.5 14 18 16 7.9 Copper, ppm 0.4 0.2 0.1 0.1 0.2 0.2 Zinc, ppm 1.3 0.6 0.98 1.5 1.3 0.7 Manganese, ppm 16 23 18 17 20 16 Aluminum, ppm 3.1 3.5 1.9 5.6 7.4 5.6 Titanium, ppm 3.5 2.3 1.6 7.4 8.9 6.4 Cobalt, ppm 0.2 0.5 0.6 0.1 0.8 1.1 Lead, ppm 5.6 4.3 5.7 2.4 6.1 67 Chromium, ppm 10 8.3 4.2 5.6 9.3 3.5 As can be seen from Table 3: (1) The iron phosphate dihydrate prepared in Examples 1-5 of this application all meet the standards of battery-grade iron phosphate, indicating that this application combines impurity removal of the iron source solution, seed-induced crystallization, and high-temperature aging to synthesize iron phosphate in one step, with synergistic effects between steps to control the heavy metal impurities in iron phosphate to meet the battery-grade standards.

[0032] (2) The iron phosphate dihydrate seeds added in Examples 1-5 can serve as crystal nuclei, which can quickly enter the crystal growth stage, making the grown iron phosphate crystals more uniform and dense, and not easily agglomerating and wrapping impurities. Impurities are not easily introduced into the iron phosphate crystals. In Comparative Example 1, no iron phosphate dihydrate seeds were added, and impurities were more likely to enter the iron phosphate crystals. Especially for the removal of lead, in this application, lead can be removed without adding sulfides, and the effect of removing lead by adding iron phosphate dihydrate seeds is particularly obvious. For example, the lead content in Examples 1-5 is all lower than 6.1 ppm, while the lead content in Comparative Example 1 is as high as 67 ppm.

[0033] It should be noted that in this text, the term "including", "comprising" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or further includes elements inherent to such process, method, article or device. Without more limitations, an element defined by the statement "including one..." does not exclude the existence of additional identical elements in the process, method, article or device including that element.

[0034] In addition, it should be pointed out that the scope of the methods and devices in the embodiments of this application is not limited to performing functions in the order shown or discussed. It may also include performing functions in a substantially simultaneous manner or in the reverse order according to the functions involved. For example, the described methods may be performed in a different order than described, and various steps may be added, omitted, or combined. Additionally, the features described with reference to certain examples may be combined in other examples.

[0035] As mentioned above, the above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should all be covered within the protection scope of the present invention.

Claims

1. A preparation method of battery-grade iron phosphate dihydrate, characterized in that, It includes the following steps: S1. Adjust the pH of the ferrous sulfate solution prepared from titanium white waste residue to 4.5 - 5.5, control the temperature at 35 - 55 °C, remove titanium and aluminum simultaneously through hydrolysis, and filter to obtain a ferrous sulfate solution from which titanium and aluminum are removed; add ammonium fluoride to the ferrous sulfate solution from which titanium and aluminum are removed, filter after the reaction is completed to obtain a refined ferrous sulfate solution; adjust the pH of the refined ferrous sulfate solution to 1.8 - 2.2 to obtain an iron source solution. S2. Mix the phosphate solution and the oxidant to obtain a phosphorus source solution. S3. Add pure water and a surfactant to the reaction kettle, start stirring and maintain low-speed stirring; mix the pure water and the surfactant evenly and heat up to 45 - 55 °C; continuously control the temperature at 45 - 55 °C, add ferric phosphate dihydrate seeds to the reaction kettle; then add the iron source solution and the phosphorus source solution to the reaction kettle. After adding the iron source solution and the phosphorus source solution, add ammonia water to adjust the pH to 2 - 3, react to form ferric phosphate dihydrate crystals, and continue to stir and react for 0.5 - 1 h until no more crystals are formed. S4. Add phosphoric acid to the reaction kettle and stir evenly, carry out high-temperature aging, and after completion, carry out solid-liquid separation to obtain a filtrate and a filter residue. S5. Wash and dry the filter residue to obtain a battery-grade ferric phosphate dihydrate finished product.

2. The preparation method of battery-grade iron phosphate dihydrate according to claim 1, characterized in that, In the step S1, the method for preparing the ferrous sulfate solution from titanium white waste residue is to dissolve the titanium white waste residue in pure water, and the mass ratio of the titanium white waste residue to pure water is 1:2 - 3.6; then stir at a temperature of 45 - 55 °C for 0.5 - 1.5 h, and filter to obtain the ferrous sulfate solution. And / or, in the step S1, ammonium fluoride is added in a ratio of the sum of the molar amounts of Ca 2+ and Mg 2+ to the molar amount of ammonium fluoride of 1:2 - 2.1; And / or, in the step S2, the method for preparing the phosphate solution is to dilute 85% industrial phosphoric acid into 20% - 30% dilute phosphoric acid, then mix it with ammonia water, and adjust the pH to 6 - 7 to obtain the phosphate solution. And / or, in the step S2, the method for preparing the phosphate solution is to dissolve the phosphate in pure water to form a phosphate solution, and adjust the pH to 6 - 7 to obtain the phosphate solution. And / or, in the step S2, the oxidant includes hydrogen peroxide. and / or, in the step S2, the molar ratio of PO4 in the phosphate solution 3- to the oxidant is 1:0.5 - 0.

7.

3. The preparation method of battery-grade iron phosphate according to claim 1, wherein In the step S1, ammonium fluoride is added in a ratio of 1:2 based on the sum of the molar amounts of Ca 2+ and Mg 2+ to the molar amount of ammonium fluoride; And / or, in the step S2, when using phosphoric acid to prepare the phosphate solution, the molar ratio of the phosphoric acid to ammonia water is 1:1 - 3. And / or, in the step S2, when using phosphate to prepare the phosphate solution, the phosphate includes any one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and ammonium phosphate.

4. The preparation method of battery-grade iron phosphate according to claim 1, wherein In the step S3, the addition amount of the surfactant is added at 0.5% - 1% of the mass of FePO₄·2H₂O theoretically generated calculated based on the iron content of the ferrous sulfate solution prepared from titanium white waste residue in the step S1. And / or, in the step S3, the surfactant includes any one of cationic surfactants, anionic surfactants, and non-ionic surfactants. And / or, in the step S3, the addition amount of the ferric phosphate dihydrate seeds is 5% - 10% of the mass of FePO₄·2H₂O theoretically generated calculated based on the iron content of the ferrous sulfate solution prepared from titanium white waste residue in the step S1. And / or, in the step S3, the addition amount of the phosphorus source solution is based on the molar ratio of PO4 3- to Fe 2+ being 1.05 - 1.25:1; And / or, in step S3, the flow rate of adding the iron source solution into the reaction kettle is 0.8 - 1.5 L / min; And / or, in step S3, the flow rate of adding the phosphorus source solution into the reaction kettle is 0.8 - 1.5 L / min.

5. The preparation method of battery-grade iron phosphate according to claim 4, characterized in that, In step S3, the addition amount of the surfactant is added at 0.6% - 0.9% of the theoretically generated mass of FePO₄·2H₂O; And / or, in step S3, the surfactant includes any one of cetyltrimethylammonium bromide, sodium dodecyl sulfate, polyethylene glycol, and sodium dodecylbenzoate; And / or, in step S3, the addition amount of the ferric phosphate dihydrate seed crystal is 8% - 10% of the theoretically generated mass of FePO₄·2H₂O; And / or, in the step S3, the addition amount of the phosphorus source solution is added according to the molar ratio of PO4 3- to Fe 2+ being 1.1 - 1.2:1; And / or, in step S3, the flow rate of adding the iron source solution into the reaction kettle is 0.9 - 1.2 L / min; And / or, in step S3, the flow rate of adding the phosphorus source solution into the reaction kettle is 0.9 - 1.2 L / min.

6. The preparation method of battery-grade iron phosphate according to claim 1, characterized in that, In step S4, the addition amount of the phosphoric acid is added according to the concentration of the phosphoric acid after addition being 15% - 20%; And / or, in step S4, the high-temperature aging is carried out at a temperature of 85 - 95 °C for 1.5 - 2.5 h; And / or, in step S4, the solid-liquid separation is carried out by plate-and-frame pressure filtration.

7. The preparation method of battery-grade iron phosphate according to claim 6, characterized in that, In step S4, the phosphoric acid is diluted from 85% industrial phosphoric acid to a concentration of 18% - 20%; And / or, in step S4, the high-temperature aging is carried out at a temperature of 88 - 92 °C for 1.8 - 2.2 h.

8. The preparation method of battery-grade iron phosphate according to claim 1, characterized in that, In step S5, the washing is carried out by washing with pure water in multiple batches; And / or, in step S5, the drying is carried out at a temperature of 100 °C - 120 °C for 6 h - 10 h.

9. The preparation method of battery-grade iron phosphate according to claim 8, wherein In step S5, the washing includes: First washing: Mix the filter residue and pure water at a mass ratio of 1:5 - 9, beat them into a slurry for 15 - 30 min, and then carry out solid-liquid separation by plate-and-frame pressure filtration to obtain filter residue A; Second washing: Mix filter residue A and pure water at a mass ratio of 1:5 - 9, beat them into a slurry for 15 - 30 min, and then carry out solid-liquid separation by plate-and-frame pressure filtration to obtain filter residue B; Third washing: Mix filter residue B and pure water at a mass ratio of 1:5 - 9, beat them into a slurry for 15 - 30 min, and then carry out solid-liquid separation by plate-and-frame pressure filtration to obtain filter residue C; And / or, in step S5, the drying is carried out at a temperature of 105 °C - 115 °C for 7 h - 9 h.

10. Battery-grade ferric phosphate prepared by the preparation method according to any one of claims 1 - 9.

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