Method for preparing battery-grade iron phosphate based on titanium dioxide byproduct ferrous sulfate

Abstract

The invention relates to the field of iron phosphate preparation, and provides a method for preparing battery-grade iron phosphate based on titanium dioxide byproduct ferrous sulfate, which comprises the following steps: S1, dissolving the titanium dioxide byproduct ferrous sulfate in deionized water, and retaining free acid in the titanium dioxide byproduct ferrous sulfate to obtain a raw material solution; carrying out first impurity removal treatment on the raw material solution to precipitate heavy metal impurities, carrying out solid-liquid separation, carrying out second impurity removal treatment on the obtained filtrate to complex and remove titanium and aluminum impurities, and separating to obtain a purified solution; s2, adding an oxidizing agent into the purified liquid, adjusting the pH value to 1.0-2.5, and carrying out an oxidation reaction to obtain an oxidized liquid; carrying out purification treatment on the oxidized liquid, and separating to obtain a purified liquid; adding ammonium-containing phosphate and an ammonium-containing crystallization aid into the purified liquid to carry out synthetic reaction to obtain battery-grade iron phosphate; according to the method, the titanium dioxide byproduct ferrous sulfate impurity is effectively removed, the impurity free acid is subjected to resource utilization, and finally the high-quality battery-grade iron phosphate product is obtained.

Description

Technical Field

[0001] This invention relates to the field of iron phosphate preparation technology, and more specifically, to a method for preparing battery-grade iron phosphate based on ferrous sulfate, a byproduct of titanium dioxide production. Background Technology

[0002] In the field of lithium-ion battery cathode materials, battery-grade lithium iron phosphate (LFP) is a key precursor for lithium iron phosphate. Its purity, crystal morphology, and particle size distribution directly affect the energy density, cycle life, and safety performance of the final battery product. With the rapid development of new energy vehicles and energy storage industries, the demand for low-cost, high-performance LFP continues to grow. Utilizing ferrous sulfate, a byproduct of titanium dioxide production, to prepare LFP not only reduces raw material costs but also enables the resource utilization of industrial solid waste. Ferrous sulfate heptahydrate, an important byproduct of titanium dioxide production, has a relatively high yield, making its effective utilization a focus of attention.

[0003] However, the ferrous sulfate byproduct of the titanium dioxide industry has a complex composition. In addition to a high content of free sulfuric acid, it also contains various characteristic metallic impurities such as titanium, manganese, and aluminum, posing a severe challenge to the preparation of battery-grade iron phosphate. Existing production processes have significant shortcomings: First, conventional processes require pre-neutralization of free acid, which not only increases alkali consumption costs but may also introduce harmful impurity ions such as sodium and potassium. Second, it is difficult to effectively remove characteristic impurities such as titanium and manganese with similar radii and chemical properties to iron ions during the impurity removal process, resulting in insufficient purity of the final product. In addition, there is a lack of effective crystallization control methods in the synthesis stage, resulting in problems such as irregular product morphology, excessively wide particle size distribution, and low tap density. Summary of the Invention

[0004] In view of the above-mentioned shortcomings in the existing technology, the core objective of the present invention is to solve the technical problems of difficulty in deep removal of ferrous sulfate impurities from titanium dioxide by-products, difficulty in resource utilization of free acid, and difficulty in controlling the crystallization of ferric phosphate.

[0005] This invention is achieved through the following technical solution: The first objective of this invention is to provide a method for preparing battery-grade iron phosphate based on ferrous sulfate, a byproduct of titanium dioxide production, comprising the following steps: S1. Dissolve ferrous sulfate, a byproduct of titanium dioxide production, in deionized water, retaining the free acid to obtain a raw material solution; firstly, perform a first impurity removal treatment on the raw material solution to precipitate heavy metal impurities, then perform solid-liquid separation, and finally perform a second impurity removal treatment on the obtained filtrate to complex and remove titanium and aluminum impurities, and separate to obtain a purified solution. S2. Add an oxidant to the purified solution, adjust the pH to 1.0-2.5 to carry out the oxidation reaction, and obtain the oxidized solution; purify the oxidized solution and separate to obtain the purified solution; add ammonium phosphate and ammonium crystallization aid to the purified solution to carry out the synthesis reaction, and obtain battery-grade iron phosphate; The first impurity removal treatment uses ammonium-containing sulfides; the second impurity removal treatment uses ammonium-containing fluorides.

[0006] Preferably, in step S2, the purification process uses ferric salts, and the mixture is stirred and reacted for 30 to 120 minutes at a temperature of 30 to 80°C and a pH value of 1.5 to 3.0, and then filtered to obtain the purified liquid.

[0007] Preferably, the trivalent iron salt is one or more of ferric chloride, ferric nitrate, and ferric sulfate; Based on the molar amount of residual fluoride ions in the oxidized solution, the amount of ferric salt added is 1.5 to 3.0 times the molar amount of residual fluoride ions.

[0008] More preferably, the trivalent iron salt is ferric sulfate, the reaction temperature is 50-70°C, and the reaction time is 60-90 min.

[0009] More preferably, the amount of the ferric salt added is 1.8 to 2.5 times the molar amount of the residual fluoride ions.

[0010] Preferably, the ammonium-containing sulfide is ammonium sulfide or ammonium hydrosulfide; the ammonium-containing fluoride is ammonium fluoride or ammonium hydrogen fluoride. Based on the total molar amount of heavy metal ions in the raw material solution, the amount of ammonium sulfide added is 1.0 to 1.5 times the total molar amount of heavy metal ions. Based on the total molar amount of titanium ions and aluminum ions in the raw material solution, the amount of ammonium fluoride added is 2.0 to 6.0 times the total molar amount of titanium ions and aluminum ions.

[0011] Preferably, the pH conditions for the first impurity removal treatment are 2.0 to 4.0; and the pH conditions for the second impurity removal treatment are 2.5 to 5.0.

[0012] Preferably, in step S2, the oxidant is hydrogen peroxide; Based on the content of ferrous ions in the purification solution, the molar ratio of hydrogen peroxide to ferrous ions is (1.0~1.2):2.

[0013] Preferably, the ammonium-containing phosphate is one or more of diammonium dihydrogen phosphate, diammonium hydrogen phosphate, and triammonium phosphate.

[0014] Preferably, based on the total iron content in the purified solution, the molar amount of phosphate ions in the added ammonium phosphate is controlled so that the molar ratio of phosphate ions to total iron is 1.0:1 to 1.2:1.

[0015] More preferably, the molar ratio of phosphate ions to total iron is 1.02:1 to 1.05:1.

[0016] Preferably, the ammonium-containing crystallization aid is ammonium pyrophosphate; based on the total iron content in the purified liquid, the molar ratio of ammonium pyrophosphate to total iron is 0.001:1 to 0.01:1.

[0017] More preferably, the molar ratio of ammonium pyrophosphate to total iron is 0.002:1 to 0.005:1.

[0018] A second objective of this invention is to provide a battery-grade iron phosphate, prepared by the above method.

[0019] This invention utilizes ferrous sulfate, a byproduct of titanium dioxide production, as a specific low-quality raw material to prepare battery-grade iron phosphate. Specifically: First, the ferrous sulfate raw material, a byproduct of titanium dioxide production, is purified. This involves a first impurity removal process, conducted in an acidic environment with a pH of 2.0–4.0, utilizing the dissociation of ammonium sulfides into sulfur dioxide. 2- The heavy metals form sulfide precipitates with very low solubility with the heavy metal ions. Based on the difference in solubility product rules, selective separation of heavy metals is achieved. Subsequently, a second impurity removal treatment is performed under conditions of pH 2.5–5.0, utilizing the reaction of fluoride ions with Ti... 4+ Al 3+ Formation of stable fluorine complexes (such as [TiF6)) 2- β6≈10 21 ), while Fe 2+ It hardly participates in coordination, thus efficiently complexing and removing specific impurities such as titanium and aluminum. After two impurity removal processes, a high-purity ferrous solution is provided for subsequent reactions. In particular, the retention of free acid impurities—that is, by retaining the free acid in the system—effectively inhibits the reaction of Fe using its low pH environment. 2+ The hydrolysis and oxidation process ensures the solubility and stability of iron, and more importantly, provides the necessary proton source for subsequent oxidation reactions, allowing hydrogen peroxide to maintain optimal oxidation activity. At the same time, this acid will also serve as a driving resource for subsequent phosphating reactions. Compared with the traditional method of neutralization followed by precipitation and impurity removal, this invention achieves a fundamental transformation from a "processing burden" to a "reaction resource".

[0020] Furthermore, the purified solution is oxidized and deeply purified, that is, an oxidant is added to the purified solution and the pH is controlled to be ≤2.0. Specifically, hydrogen peroxide is used as the oxidant, with highly active H3O2. + Form, through the free radical pathway, Fe 2+ Efficient conversion to Fe 3+ Among them, the acidic environment inhibited Fe 3+Hydrolysis ensures the selectivity and completeness of the oxidation reaction; subsequently, residual F that may be introduced by the preceding fluorination treatment is addressed. - Further utilization of Fe 3+ The precipitate forms a poorly soluble FeF3 precipitate, which deeply removes fluoride ions, ensuring the ultra-high purity of the reaction system before final synthesis and laying the foundation for the preparation of battery-grade iron phosphate. Specifically, under conditions of pH 1.5–3.0 and temperature 30–80℃, this precipitation reaction is fast and selective, and can remove F... - Concentration reduced to below 10 mg / L; Fe 3+ The amount of iron added should be 1.5 to 3.0 times the stoichiometric amount to ensure complete precipitation while avoiding the excessive introduction of iron ions.

[0021] Furthermore, in obtaining high-purity Fe 3+ Based on the solution, the molar ratio of phosphate to iron ions was further controlled (1.0:1-1.2:1) to ensure complete reaction while avoiding the formation of impurity phases due to excess phosphate. Subsequently, ammonium pyrophosphate was introduced as a crystallization aid, whose P2O7... 4- Through a dual mechanism of "selective adsorption inhibition" and "slow-release hydrolysis," the relative growth rate and nucleation supersaturation of crystal faces are precisely controlled at the molecular level, thereby guiding the crystals to form products with regular morphology and uniform particle size; among them, P2O7 4- Selective adsorption on specific crystal planes alters the relative growth rates of different crystal planes, guiding the crystal to grow in a more thermodynamically stable direction; P2O7 4- Slow hydrolysis in an acidic medium provides a stable phosphate ion concentration, controls supersaturation, and promotes uniform nucleation.

[0022] Most importantly, all additives in this invention are introduced in the form of ammonium salts, NH4 + It can decompose into NH3 and escape during subsequent heat treatment, avoiding the release of Na. + K + Residues of harmful alkali metals, etc.

[0023] In summary, this invention utilizes the free acid inherent in the raw materials, preventing the deterioration of ferrous ions and providing readily available reaction conditions for subsequent steps, thus eliminating the cost of adding additional acid. Next, a two-step impurity removal method is employed: first, precise capture and impurity removal is achieved by forming a sparingly soluble precipitate between sulfide ions and heavy metal ions; then, selective separation is achieved by forming a stable complex between fluoride ions and titanium-aluminum ions, yielding a pure ferrous solution. Subsequently, after converting ferrous ions to ferric ions through oxidation, a deep impurity removal process is performed, using ferric ions to form a precipitate with residual fluoride ions to completely remove them, ensuring a highly pure solution. Finally, the raw material ratio is precisely controlled during the synthesis stage, and a special regulator, ammonium pyrophosphate, is added. Through its dual effects of adsorption and slow release, the crystal growth process is finely controlled, resulting in a high-quality iron phosphate product with regular shape and uniform particles. The entire process is tightly integrated, and all raw material selection avoids the introduction of new impurities, ultimately achieving an upgrade and transformation from an industrial byproduct to a battery-grade material.

[0024] The technical solutions of the embodiments of the present invention have at least the following advantages and beneficial effects: (1) By retaining free acid impurities, the present invention not only avoids the problems of reagent consumption and impurity introduction in traditional neutralization processes, but also transforms free acid into favorable conditions for subsequent reactions, significantly reducing production costs.

[0025] (2) The present invention adopts a graded targeted impurity removal method. By precisely controlling the reaction conditions, it effectively solves the problem that existing processes are difficult to deeply remove characteristic impurities such as titanium and manganese, ensuring the high purity of the iron source and laying the foundation for subsequent synthesis of high-quality products.

[0026] (3) In this invention, ammonium pyrophosphate is introduced as a crystallization regulator. Through its unique mechanism of action, it achieves precise control over crystal morphology and particle size distribution, thereby significantly improving the tap density and quality uniformity of the product.

[0027] (4) The entire process of this invention adopts the "ammonia-ammonium" closed-loop system, which fundamentally avoids the introduction of harmful impurities such as sodium and potassium, and ensures the purity and electrochemical performance of the final product. Detailed Implementation

[0028] Example 1 This embodiment provides a method for preparing battery-grade iron phosphate based on ferrous sulfate, a byproduct of titanium dioxide production, including the following steps: S1. Raw material purification process Raw material preparation: 100.0 g of ferrous sulfate heptahydrate, a byproduct of the sulfuric acid process for titanium dioxide production, was taken. Analysis showed that it contained 850 ppm Ti, 520 ppm Mn, 420 ppm Al, 35 ppm Pb, 28 ppm Cd, and approximately 5% free sulfuric acid (calculated as H2SO4). It was dissolved in 200 mL of deionized water and stirred until completely dissolved to obtain the raw material solution. The Fe content in the raw material solution was measured. 2+ The concentration is approximately 0.9 mol / L.

[0029] First impurity removal treatment: Ammonium sulfide solution is added to the feed solution. This is based on the heavy metal ion content (Pb) in the feed solution. 2+ Cd 2+ Add an equimolar amount of ammonium sulfide solution containing S2-, based on 1.0 times the total molar amount (approximately 0.045 mmol). Maintain the pH of the reaction system at 2.0 and stir the reaction mixture at room temperature for 60 minutes. After the reaction is complete, filter the mixture using a Buchner funnel and collect the filtrate.

[0030] Second impurity removal treatment: Add solid ammonium fluoride to the filtrate from the previous step. Based on the Ti content in the feed solution... 4+ Al 3+ Ammonium fluoride was added at 2.0 times the total molar amount (approximately 1.25 mmol). The pH of the reaction system was controlled at 2.5, and the reaction was stirred at 50 °C for 120 minutes. After the reaction was completed, the solution was filtered again to obtain the purified solution. ICP-MS analysis showed that the contents of Ti and Al in the purified solution were both below 2 ppm.

[0031] S2, Iron Phosphate Synthesis Stage Oxidation reaction: Slowly add 30% hydrogen peroxide to the purified solution. Based on the ferrous ion content in the purified solution (approximately 90 mmol), add approximately 1.5 mL of hydrogen peroxide at a molar ratio of (1.0):2 for hydrogen peroxide to ferrous ions. Control the pH of the reaction system at 1.0 and stir the reaction at 45°C. Monitor the oxidation-reduction potential with an ORP meter. Once the oxidation-reduction potential stabilizes at approximately +480 mV, the oxidation is considered complete, and the oxidized solution is obtained.

[0032] Purification treatment: Add ferric sulfate crystals to the solution after the previous oxidation step. This is based on the residual F in the solution after oxidation. - Approximately 6 mg of ferric sulfate was added, based on 1.5 times the molar amount (approximately 0.015 mmol). The reaction system was maintained at pH 1.5 and temperature 30°C, and stirred for 120 minutes. After the reaction was complete, the mixture was filtered to obtain a purified solution. The concentration of F in the purified solution was measured. - Concentration <8mg / L.

[0033] Synthesis reaction: The total iron concentration in the purified solution was determined to be approximately 0.85 mol / L (total volume approximately 120 mL, total iron content approximately 100 mmol). Based on this, the amount of diammonium hydrogen phosphate added (approximately 13.2 g) was controlled to achieve a molar ratio of phosphate ions to total iron of 1.0:1. Simultaneously, based on the total iron content, approximately 34 mg of ammonium pyrophosphate was added at a molar ratio of ammonium pyrophosphate to total iron of 0.001:1. The pH of the mixture was adjusted to 2.0, the temperature was raised to 70°C, and the reaction was stirred at 250 rpm for 4 hours. After the reaction was completed, the mixture was filtered, washed three times with deionized water, and dried at 105°C for 12 hours to obtain approximately 23.5 g of a white powdery battery-grade iron phosphate product.

[0034] Example 2 This embodiment provides a method for preparing battery-grade iron phosphate based on ferrous sulfate, a byproduct of titanium dioxide production, including the following steps: S1. Raw material purification process Raw material preparation: Take 100.0 g of ferrous sulfate heptahydrate, a byproduct of the sulfuric acid process for titanium dioxide production, with the same composition as in Example 1. Dissolve it in 200 mL of deionized water and stir until completely dissolved to obtain the raw material solution. The Fe content in the raw material solution was measured. 2+ The concentration is approximately 0.9 mol / L.

[0035] First impurity removal treatment: Add ammonium hydrosulfide solution to the feed solution. Based on 1.3 times the total molar amount of heavy metal ions in the feed solution (approximately 0.045 mmol), add an equimolar amount of S... 2- An ammonium hydrosulfide solution was prepared. The pH of the reaction system was controlled at 3.0, and the reaction was stirred at room temperature for 45 minutes. After the reaction was completed, the mixture was filtered using a Buchner funnel, and the filtrate was collected. Second impurity removal treatment: solid ammonium hydrofluoride was added to the filtrate from the previous step. Based on the Ti content in the feed solution... 4+ Al 3+ Ammonium bifluoride was added at 4.0 times the total molar amount (approximately 1.25 mmol). The pH of the reaction system was controlled at 3.5, and the mixture was stirred at 60°C for 90 minutes. After the reaction was completed, the mixture was filtered again to obtain a purified solution. ICP-MS analysis showed that the contents of Ti and Al in the purified solution were both less than 1 ppm.

[0036] S2, Iron Phosphate Synthesis Stage Oxidation reaction: Slowly add 30% hydrogen peroxide to the purified solution. Based on the ferrous ion content in the purified solution (approximately 90 mmol), add approximately 1.65 mL of hydrogen peroxide at a molar ratio of (1.1):2 for hydrogen peroxide to ferrous ions. Control the pH of the reaction system at 1.5 and stir the reaction at 45°C. Monitor the oxidation-reduction potential with an ORP meter. Once the oxidation-reduction potential stabilizes at approximately +500 mV, the oxidation is considered complete, and the oxidized solution is obtained.

[0037] Purification treatment: Add ferric chloride crystals to the solution after the previous oxidation step. This is based on the residual F in the solution after oxidation. - Approximately 5 mg of ferric chloride was added, based on 2.0 times the molar amount (approximately 0.015 mmol). The reaction system was maintained at pH 2.0 and temperature 50°C, and stirred for 90 minutes. After the reaction was complete, the mixture was filtered to obtain a purified solution. The concentration of F in the purified solution was measured. - Concentration <5mg / L.

[0038] Synthesis reaction: The total iron concentration in the purified solution was determined to be approximately 0.85 mol / L (total volume approximately 120 mL, total iron content approximately 100 mmol). Based on this, the amount of the mixture of ammonium dihydrogen phosphate and diammonium hydrogen phosphate (approximately 14.5 g) was controlled to achieve a molar ratio of phosphate ions to total iron of 1.1:1. Simultaneously, based on the total iron content, approximately 170 mg of ammonium pyrophosphate was added at a molar ratio of ammonium pyrophosphate to total iron of 0.005:1. The pH of the mixture was adjusted to 2.2, the temperature was raised to 85°C, and the reaction was stirred at 250 rpm for 3 hours. After the reaction was completed, the mixture was filtered, washed three times with deionized water, and dried at 105°C for 12 hours to obtain approximately 24.2 g of a white powdery battery-grade iron phosphate product.

[0039] Example 3 This embodiment provides a method for preparing battery-grade iron phosphate based on ferrous sulfate, a byproduct of titanium dioxide production, including the following steps: S1. Raw material purification process Raw material preparation: Take 100.0 g of ferrous sulfate heptahydrate, a byproduct of the sulfuric acid process for titanium dioxide production, with the same composition as in Example 1. Dissolve it in 200 mL of deionized water and stir until completely dissolved to obtain the raw material solution. The Fe content in the raw material solution was measured. 2+ The concentration is approximately 0.9 mol / L.

[0040] First impurity removal treatment: Add ammonium sulfide solution to the feed solution. Based on 1.5 times the total molar amount of heavy metal ions in the feed solution (approximately 0.045 mmol), add an equimolar amount of S... 2- An ammonium sulfide solution was prepared. The pH of the reaction system was controlled at 4.0, and the reaction was stirred at room temperature for 30 minutes. After the reaction was completed, the mixture was filtered through a Buchner funnel, and the filtrate was collected.

[0041] Second impurity removal treatment: Add solid ammonium fluoride to the filtrate from the previous step. Based on the Ti content in the feed solution... 4+ Al 3+ Ammonium fluoride was added at 6.0 times the total molar amount (approximately 1.25 mmol). The pH of the reaction system was controlled at 5.0, and the reaction was stirred at 70°C for 60 minutes. After the reaction was completed, the solution was filtered again to obtain the purified solution. ICP-MS analysis showed that the contents of Ti and Al in the purified solution were both below 0.5 ppm.

[0042] S2, Iron Phosphate Synthesis Stage Oxidation reaction: Slowly add 30% hydrogen peroxide to the purified solution. Based on the ferrous ion content in the purified solution (approximately 90 mmol), add approximately 1.8 mL of hydrogen peroxide at a molar ratio of (1.2):2 for hydrogen peroxide to ferrous ions. Control the pH of the reaction system at 2.5 and stir the reaction at 45°C. Monitor the oxidation-reduction potential with an ORP meter. Once the oxidation-reduction potential stabilizes at approximately +520 mV, the oxidation is considered complete, and the oxidized solution is obtained.

[0043] Purification treatment: Add ferric nitrate crystals to the solution after the previous oxidation step. This is based on the residual F in the solution after oxidation. - Approximately 9 mg of ferric nitrate was added, based on 3.0 times the molar amount (approximately 0.015 mmol). The reaction system was maintained at pH 3.0 and temperature 80°C, and stirred for 30 minutes. After the reaction was complete, the mixture was filtered to obtain a purified solution. The concentration of F in the purified solution was measured. - Concentration <3mg / L.

[0044] Synthesis reaction: The total iron concentration in the purified solution was determined to be approximately 0.85 mol / L (total volume approximately 120 mL, total iron content approximately 100 mmol). Based on this, the amount of triammonium phosphate added (approximately 15.8 g) was controlled to achieve a molar ratio of phosphate ions to total iron of 1.2:1. Simultaneously, based on the total iron content, approximately 340 mg of ammonium pyrophosphate was added at a molar ratio of ammonium pyrophosphate to total iron of 0.01:1. The pH of the mixture was adjusted to 2.5, the temperature was raised to 95℃, and the reaction was stirred at 250 rpm for 2 hours. After the reaction was completed, the mixture was filtered, washed three times with deionized water, and dried at 105℃ for 12 hours to obtain approximately 24.8 g of a white powdery battery-grade iron phosphate product.

[0045] Comparative Example 1 The difference between this comparative example and Example 1 lies in the pretreatment method and impurity removal strategy of the raw material solution. Specifically, in step S1, the free acid in the raw material is not retained, but the pH of the system is pre-neutralized to 6.0 using sodium hydroxide solution; and, instead of using staged targeted impurity removal, sodium sulfide and sodium fluoride are added to the raw material solution simultaneously for a one-time impurity removal reaction.

[0046] Comparative Example 2 The difference between this comparative example and Example 1 is that the deep purification treatment step is omitted. Specifically, in step S2, after the oxidation reaction is completed and the oxidized liquid is obtained, the purification treatment of residual fluoride ions by precipitating with ferric salt is not carried out. Instead, ammonium phosphate and ammonium pyrophosphate are directly added to the oxidized liquid to carry out the synthesis reaction.

[0047] Comparative Example 3 The difference between this comparative example and Example 1 lies in the crystallization aid used in the synthesis reaction. Specifically, in the synthesis reaction of step S2, two groups were used for comparison. Group A did not add any crystallization aid, while Group B used an equimolar amount of ammonium citrate instead of ammonium pyrophosphate as the crystallization aid.

[0048] Comparative Example 4 The difference between this comparative example and Example 1 lies in the selection of key reagents. Specifically, sodium sulfide is used instead of ammonium sulfide in the first impurity removal treatment of step S1, and sodium fluoride is used instead of ammonium fluoride in the second impurity removal treatment; sodium dihydrogen phosphate is used instead of diammonium hydrogen phosphate in the synthesis reaction of step S2, and no ammonium pyrophosphate crystallization aid is added.

[0049] Experimental Example 1 The products prepared in Examples 1-3 and Comparative Examples 1-4 were used as samples for multiple performance tests. The test methods referenced the following standards: the tap density of the products was determined according to GB / T5162-2021; the particle size distribution D50 was determined according to GB / T19077-2016; the electrochemical performance was tested by assembling CR2032 coin cells, referring to the relevant test methods in GB / T42260-2022 "Electrochemical Performance Test and Cycle Life Test Method for Cathode Materials of Lithium-ion Batteries". The test results are shown in the table below: Table 1 Performance Test Results

[0050] Analysis of the data in Table 1 shows that the iron phosphate materials prepared in all examples are significantly superior to those in the comparative examples in terms of both physical properties and electrochemical performance, and exhibit a clear optimization trend. Specifically, through specific impurity removal steps and crystallization control, the tap density in the examples (0.85 to 0.96 g / cm³) was improved. 3The median particle size D50 (4.8 to 1.8 μm) gradually increased, effectively reducing and concentrating its distribution. These physical properties directly translated into excellent electrochemical performance, with systematic improvements in initial discharge specific capacity (152 to 158 mAh / g), initial charge-discharge efficiency (95.5% to 96.8%), rate performance (94.3% to 96.8%), and long cycle life (capacity retention of 91.5% to 95.5% after 500 cycles). In contrast, the comparative examples suffered from defects in key process steps, such as: comparative example Comparative Example 1 suffered a comprehensive deterioration in physicochemical properties due to pre-neutralization and one-time impurity removal; Comparative Example 2 experienced a significant decrease in cycle life (84.5%) due to the omission of deep purification; Comparative Examples 3A (without additives) and 3B (organic additives) had shortcomings in tap density and long-term cycle stability, respectively; Comparative Example 4 suffered from poor overall performance due to the introduction of sodium impurities. These examples further fully verified the key role and synergistic effect of the retention of free acid, graded targeted impurity removal, deep purification, and "ammonia-ammonium" closed-loop crystallization control scheme used in the examples for obtaining high-performance battery-grade iron phosphate materials.

Claims

1. A method for preparing battery grade iron phosphate based on titanium dioxide by-product ferrous sulfate, characterized by, The method comprises the following steps: S1, dissolving ferrous sulfate in titanium white by-product in deionized water, retaining free acid therein to obtain a raw material solution; first impurity removal treatment is performed on the raw material solution to precipitate heavy metal impurities, then solid-liquid separation is performed, and then second impurity removal treatment is performed on the obtained filtrate to remove titanium and aluminum impurities by complexation, so as to separate a purified solution; S2, adding an oxidizing agent to the purified solution, adjusting the pH value to 1.0-2.5 to perform oxidation reaction, to obtain an oxidized solution; performing purification treatment on the oxidized solution to separate a purified solution; adding ammonium-containing phosphate and ammonium-containing crystallization aids to the purified solution to perform synthesis reaction, to obtain battery-grade iron phosphate; In the first impurity removal treatment, an ammonium-containing sulfide is used; in the second impurity removal treatment, an ammonium-containing fluoride is used.

2. The process for the preparation of battery grade iron phosphate based on titanium dioxide by-product ferrous sulfate according to claim 1, characterized in that, In step S2, the purification treatment uses a ferric salt, and the ferric salt is stirred for 30-120 min under the condition that the temperature is 30-80 DEG C and the pH value is 1.5-3.0, and then the purified solution is separated by filtration.

3. The process for the preparation of battery grade iron phosphate based on titanium dioxide by-product ferrous sulfate according to claim 2, characterized by, The ferric salt is one or more of ferric chloride, ferric nitrate and ferric sulfate; Based on the molar amount of residual fluoride ions in the oxidized solution, the addition amount of the ferric salt is 1.5-3.0 times the molar amount of the residual fluoride ions.

4. The process for the preparation of battery grade iron phosphate based on titanium dioxide by-product ferrous sulfate according to claim 2, characterized by, The ammonium-containing sulfide is ammonium sulfide or ammonium hydrosulfide; the ammonium-containing fluoride is ammonium fluoride or ammonium bifluoride; Based on the total molar amount of heavy metal ions in the raw material solution, the addition amount of the ammonium-containing sulfide is 1.0-1.5 times the total molar amount of the heavy metal ions; Based on the total molar amount of titanium ions and aluminum ions in the raw material solution, the addition amount of the ammonium-containing fluoride is 2.0-6.0 times the total molar amount of the titanium ions and aluminum ions.

5. The process for the preparation of battery grade iron phosphate based on titanium dioxide by-product ferrous sulphate as claimed in claim 2, wherein, The pH condition of the first impurity removal treatment is 2.0-4.0; the pH condition of the second impurity removal treatment is 2.5-5.

0.

6. The process for the preparation of battery grade iron phosphate based on titanium dioxide by-product ferrous sulphate as claimed in claim 2, wherein, In step S2, the oxidizing agent is hydrogen peroxide; Based on the content of ferrous ions in the purified solution, the molar ratio of hydrogen peroxide to ferrous ions is (1.0-1.2):

2.

7. The process for the preparation of battery grade iron phosphate based on titanium dioxide by-product ferrous sulfate according to claim 2, characterized by, The ammonium-containing phosphate is one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate and ammonium phosphate. 8.The method for preparing battery-grade iron phosphate based on titanium dioxide by-product ferrous sulfate according to claim 7, characterized in that, Based on the total iron element content in the purified solution, the molar amount of phosphate ions in the added ammonium-containing phosphate is controlled, so that the molar ratio of phosphate ions to total iron elements is 1.0:1-1.2:

1.

9. The process for the preparation of battery grade iron phosphate based on titanium dioxide by-product ferrous sulphate as claimed in claim 2, wherein, The ammonium-containing crystallization aid is ammonium pyrophosphate; Based on the total iron element content in the purified solution, the molar ratio of ammonium pyrophosphate to total iron elements is 0.001:1-0.01:

1.

10. A battery grade iron phosphate characterized in that, The battery-grade iron phosphate is prepared by the method in any one of claims 1-9.

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