Method for preparing high-quality iron phosphate in short process

Abstract

The invention discloses a method for preparing high-quality iron phosphate in a short process, and belongs to the field of battery material manufacturing. The method comprises the following steps: dissolving iron powder with phosphoric acid to prepare a ferrous phosphate solution, then transferring the solution into a pressurized reaction kettle, blowing high-speed oxygen to oxidize ferrous phosphate into ferric phosphate, adding ammonia water to control the pH value to be 1.5-2.0, and carrying out solid-liquid separation to obtain the water-containing amorphous ferric phosphate, after washing is finished, a water-containing material is fed into a muffle furnace to be subjected to stepped calcination, dehydration and crystal transformation are completed, and the alpha monoclinic system iron phosphate is obtained. The method provided by the invention is short in process flow and low in energy consumption, the oxidant is easy to obtain and safe, the particle size uniformity of reaction materials is good, and the prepared iron phosphate is uniform in particle size, regular in structure and stable in iron-phosphorus ratio and is a high-quality precursor material.

Description

Technical Field

[0001] The patent of this invention relates to the field of battery material manufacturing, and specifically to a short-process method for preparing high-quality iron phosphate. Background Art

[0002] With the rapid development of new energy vehicles, lithium iron phosphate batteries are favored by the market due to their advantages such as long cycle life, high energy density and high safety. At present, the mainstream process routes for producing lithium iron phosphate include ferrous oxalate process, iron phosphate process, iron red process, etc. Among them, the iron phosphate process route is to mix iron phosphate, carbon source and lithium source by ball milling, and then prepare it by high temperature reduction. This process route is simple and has low energy consumption, but the product performance is heavily dependent on the raw material iron phosphate. The quality of iron phosphate directly determines the electrochemical performance of the product lithium iron phosphate. The preparation processes of ferric phosphate include ammonium method, sodium method, iron powder process, etc. The main differences lie in the raw materials and the types of alkali used to adjust the pH. The main process routes all include raw material removal, oxidation, synthesis reaction, washing, aging, washing calcination, post-treatment and other processes. The oxidant is generally hydrogen peroxide. In the iron solution system, it decomposes violently and the reaction risk is high. The product is easy to agglomerate during the synthesis process, the particle size is difficult to be evenly distributed, and the structure is irregular. Therefore, dissolution and recrystallization, that is, aging, is required. This process is energy-intensive, time-consuming, and has the risk of failure. Since the overall process is relatively long, and many links have an impact on key product indicators such as particle size, structure, and iron-phosphorus ratio, the properties of the commercial ferric phosphate are unstable, affecting downstream use.

[0003] In summary, it is necessary to develop a safe, environmentally friendly, short process and stable product quality iron phosphate preparation process. Summary of the invention

[0004] One of the purposes of the present invention is to utilize a green oxidant for pressurized oxidation, and to prepare iron phosphate with uniform particle size distribution through the strong shear force of high-speed gas, thereby overcoming the danger and agglomeration problems of traditional methods, and having an extremely high reaction efficiency (above 99%). The fluctuation range of the iron-phosphorus ratio of iron phosphate is narrow (±0.001). Compared with the traditional method of controlling the particle size by aging, the present invention realizes accurate control of the particle size at the reaction end, thus creating conditions for calcination and crystal transformation.

[0005] In order to achieve the above invention object, the present invention adopts the following technical solutions:

[0006] A method for preparing high-quality ferric phosphate in a short process comprises the following steps:

[0007] 1) preparing a ferrous phosphate solution using an iron source and a phosphorus source;

[0008] 2) transferring the ferrous phosphate solution to a pressure reactor, and blowing high-speed oxygen into the reactor to oxidize the ferrous phosphate into ferric phosphate, and after the reaction, releasing the pressure and adding ammonia water to adjust the pH;

[0009] 3) Separating and obtaining the hydrous amorphous iron phosphate, washing and performing step-wise calcination and dehydration to obtain α monoclinic iron phosphate.

[0010] In some specific embodiments, the iron source in step 1) is iron powder, the phosphorus source is phosphoric acid, and the iron powder is dissolved in phosphoric acid to prepare a ferrous phosphate solution.

[0011] In some preferred embodiments, iron powder is added to phosphoric acid for dissolution, and then the reaction solution is filtered to prepare a ferrous phosphate solution, wherein the mass concentration of the ferrous phosphate is 10% to 17%, for example, 11%, 12%, 13%, 14%, 15%, 16%, 17%, etc.;

[0012] Preferably, the reaction temperature is 30-60°C, for example 35°C, 40°C, 45°C, 50°C, 55°C, etc., and the reaction time is 1-5h, for example 1h, 2h, 3h, 4h, 4h, etc.

[0013] In some preferred embodiments, the pH of the system is controlled at 0.5 to 1.2, such as 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, etc., by adjusting the amount of phosphoric acid;

[0014] Preferably, the reaction solution is filtered by suction filtration, and the suction filtration accuracy is 0.5 to 2 μm, such as 1 μm, 1.5 μm, 2 μm, etc.

[0015] In some specific embodiments, a gas distributor is provided at the bottom of the reactor in step 2), and the high-speed oxygen enters the reactor through the gas distributor.

[0016] In some specific embodiments, the reaction pressure in the pressurized reactor is 3-10 MPa, for example, 4 MPa, 5 MPa, 6 MPa, 7 MPa, 8 MPa, 9 MPa, etc., the reaction temperature is 30-75°C, for example, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, etc., and the reaction time is 0.5-2h, for example, 1h, 1.5h, 2h, etc.

[0017] In some specific embodiments, the flow rate of the high-speed oxygen in step 2) is 6 to 14 m / s, for example, 7 m / s, 8 m / s, 9 m / s, 10 m / s, 11 m / s, 12 m / s, 13 m / s, 14 m / s, etc.

[0018] In some specific embodiments, in step 2), aqueous ammonia is added to adjust the pH to 1.5-2.0, such as 1.6, 1.7, 1.8, 1.9, etc.

[0019] In some specific embodiments, the solid product is washed with hot water in step 3) until the conductivity of the washed water is less than 50 ms / cm, such as 49 ms / cm, 45 ms / cm, 40 ms / cm, 35 ms / cm, 30 ms / cm, 25 ms / cm, 20 ms / cm, 15 ms / cm, 10 ms / cm, 5 ms / cm, etc.;

[0020] Preferably, the hot water is desalted water, and the temperature is 60-90°C, for example, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, etc.

[0021] In some specific embodiments, the calcination in step 3) is carried out at a high temperature in an air atmosphere, the purpose of the calcination is dehydration and crystal transformation, the calcination temperature is 200-775°C, for example, 250°C, 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, etc., and the residence time is 3-9h, for example, 4h, 5h, 6h, 7h, 8h, 9h, etc.;

[0022] Preferably, the mixture is first calcined at 200-300° C. for 2-5 hours to complete dehydration, and then the temperature is raised to 550-775° C. to complete crystal transformation and calcined for 1-4 hours.

[0023] Compared with the prior art, the present invention can bring the following effects:

[0024] (1) The present invention uses a green oxidant for pressurized oxidation and produces iron phosphate with uniform particle size distribution through the strong shear force of high-speed gas, thus overcoming the danger and agglomeration problems of the traditional method. The mass transfer efficiency is high, resulting in extremely high reaction efficiency (more than 99%), and a more stable iron-phosphorus ratio of the product (fluctuation range is between ±0.001). Compared with the traditional method of controlling the particle size by aging, the present invention realizes accurate control of the particle size at the reaction end, creating conditions for calcination and crystal transformation;

[0025] (2) The present invention uses step-by-step calcination to complete material dehydration and crystal transformation, skips the aging step of the traditional method, improves continuous constant high temperature calcination, greatly shortens the process flow, reduces energy consumption, and prepares high-quality iron phosphate with stable performance;

[0026] (3) The process route of the present invention is simple, requires little investment, and has stable finished product quality, and is an extremely excellent iron phosphate preparation route. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to make the advantages, features and uniqueness of this invention patent more obvious, the process and equipment diagram of the method are fully displayed through the accompanying drawings.

[0028] Figure 1 The figure is a schematic diagram of a short-process method for preparing high-quality iron phosphate according to the present invention. DETAILED DESCRIPTION

[0029] The following is a more detailed explanation of the content of the present invention in conjunction with specific preferred implementation cases. It should be clear that the preferred implementation cases are intended to help practitioners in this field better understand the content of the invention and fully convey the technology. Any experimental form that can realize the present invention belongs to the content protected by the invention and should not be limited by the preferred implementation cases.

[0030] like Figure 1 As shown, a short-process method for preparing high-quality iron phosphate includes four steps: raw material dissolution, pressure oxidation, washing, and calcination and crystal transformation, wherein high-speed oxygen is introduced into the pressure oxidation step.

[0031] In a specific scheme, a short-process method for preparing high-quality iron phosphate is provided, wherein the iron source used is iron powder and the phosphorus source is phosphoric acid. Phosphoric acid is used to dissolve iron powder to prepare a ferrous phosphate solution, which is then transferred to a pressurized reactor. A gas distributor is provided at the bottom of the reactor, and high-speed oxygen is blown in to oxidize the ferrous phosphate into ferric phosphate. Due to the strong shear force of the high-speed gas, the agglomeration of the generated iron phosphate crystal nuclei is greatly slowed down. After the reaction is completed, ammonia water is added to obtain hydrous amorphous iron phosphate after solid-liquid separation. After washing, the hydrous material is sent to a muffle furnace for step-by-step calcination, dehydration and crystallization. During the calcination process, the iron phosphate is transformed from amorphous to a regular α monoclinic system. The prepared iron phosphate has uniform particle size, regular structure and stable iron-phosphorus ratio.

[0032] More specifically, the method for preparing the high-quality iron phosphate comprises the following steps:

[0033] S1: Dissolution of raw materials: 100-150g of iron powder is added to 5.7-10wt% phosphoric acid for dissolution, the reaction temperature is 30-60°C, after the reaction for 1-5h, the reaction liquid is filtered by suction, the filter paper precision is 0.5-2μm, and a dark green ferrous phosphate solution is prepared, and the ferrous phosphate concentration is 10%-17%.

[0034] S2: Synthesis reaction: The prepared ferrous phosphate solution is transferred to the reactor. The reaction temperature is 30-75°C. Oxygen is blown into the bottom of the reactor through a gas distributor. The reaction pressure is 3-10 MPa. The oxygen flow rate is 6-14 m / s. The high flow rate is beneficial to slow down the agglomeration of the generated ferrous phosphate crystal nuclei, making the particle size smaller and more uniform. At the same time, the mass transfer is enhanced, which greatly improves the reaction efficiency. As the reaction proceeds, a light yellow precipitate appears in the solution. After 0.5-2h of reaction, the pressure is released and ammonia water is added. According to the online pH indicator, the pH of the reaction slurry is controlled at 1.5-2.0. Within this pH range, the solubility of ferric phosphate is low, which ensures the solid phase yield. After adding ammonia water, stirring is continued for 15min-45min to terminate the reaction.

[0035] S3: Washing of crude product: The reaction product is filtered to separate the solid and the liquid. After the filtration, the filter cake is transferred to a pulping kettle, 1000-5000g of 60-90℃ hot desalted water is added, and the solid product is washed with hot water until the conductivity of the washing water is less than 50ms / cm.

[0036] S4: Calcination treatment: The washed crude product is placed in a crucible, put into a muffle furnace, and calcined in an air atmosphere in a step-by-step manner. The purpose of calcination is to dehydrate and transform the crystals. First, calcine at 200-300°C for 2-5 hours to complete dehydration, and then raise the temperature to 550-775°C for 1-4 hours to convert the amorphous iron phosphate into α monoclinic system. After the calcination, a light yellow product iron phosphate is obtained.

[0037] The present invention utilizes pressurized high-speed oxygen for oxidation, and the agglomeration of the generated iron phosphate crystal nuclei is greatly slowed down. The reactant particle size is fine and evenly distributed, and the quality of the iron phosphate after aging in the traditional process is achieved (still amorphous). Then, dehydration and high-temperature crystallization are completed through step-by-step calcination (the traditional method is aging crystallization). The method has a short process flow, and has good stability in particle size, structure, iron-phosphorus ratio, etc., and finally obtains high-quality iron phosphate.

[0038] The present invention is further described below by more specific examples, but does not constitute any limitation.

[0039] The main raw materials used in the following examples are from the following sources:

[0040] Iron powder (purity 99.9%) comes from Aladdin, phosphoric acid and ammonia water come from Inokite, and oxygen comes from Air Liquide.

[0041] The test methods involved in the following embodiments are as follows:

[0042] The particle size test was performed using a Malvern laser particle size analyzer, the crystal form test was performed using XRD, and the iron and phosphorus test was performed using titration.

[0043] Example 1

[0044] S1: Dissolution of raw materials: 100g of iron powder was added to 2269g of 10wt% phosphoric acid for dissolution, the reaction temperature was 60°C, after the reaction for 4h, the reaction solution was filtered by suction, the filter paper precision was 2μm, and a dark green ferrous phosphate solution was prepared, and the ferrous phosphate concentration was 17%.

[0045] S2: Synthesis reaction: The prepared ferrous phosphate solution was transferred to a reactor. The reaction temperature was 65°C. Oxygen was blown into the bottom of the reactor through a gas distributor. The reaction pressure was 10 MPa and the oxygen flow rate was 13 m / s. The high flow rate was beneficial to slow down the agglomeration of ferrous phosphate crystal nuclei and make the particle size smaller and more uniform. As the reaction proceeded, a light yellow precipitate appeared in the solution. After reacting for 1 hour, the pressure was released and ammonia water was added. According to the online pH indicator, the pH of the reaction slurry was controlled at 2.0. Within this pH range, the solubility of ferrous phosphate was low, ensuring the solid phase yield. After adding ammonia water, stirring was continued for 15 minutes to terminate the reaction.

[0046] S3: Washing of crude product: The reaction product is filtered to separate the solid and the liquid. After the filtration, the filter cake is transferred to a pulping kettle, 3000 g of 70°C hot desalted water is added, and the solid product is washed with hot water until the conductivity of the washing water is less than 50 ms / cm.

[0047] S4: Calcination treatment: The washed crude product is placed in a crucible, put into a muffle furnace, and calcined in an air atmosphere in a step-by-step manner. The purpose of calcination is to dehydrate and transform the crystals. First, calcine at 300°C for 2 hours to complete dehydration, and then increase the temperature to 675°C and calcine for 3 hours. The amorphous iron phosphate is converted into α monoclinic system. After the calcination, a light yellow product iron phosphate is obtained.

[0048] Example 2

[0049] S1: Dissolution of raw materials: 125g of iron powder was added to 3451g of 8.2wt% phosphoric acid for dissolution. The reaction temperature was 45°C. After reacting for 2.5h, the reaction solution was filtered by suction. The filter paper precision was 0.5μm. A dark green ferrous phosphate solution was prepared. The ferrous phosphate concentration was 14%.

[0050] S2: Synthesis reaction: The prepared ferrous phosphate solution was transferred to a reactor. The reaction temperature was 50°C. Oxygen was bubbled into the bottom of the reactor through a gas distributor. The reaction pressure was 6 MPa and the oxygen flow rate was 9 m / s. The high flow rate was beneficial to slow down the agglomeration of ferrous phosphate crystal nuclei and make the particle size smaller and more uniform. As the reaction proceeded, a light yellow precipitate appeared in the solution. After 2 hours of reaction, the pressure was released and ammonia water was added. According to the online pH indicator, the pH of the reaction slurry was controlled at 1.8. Within this pH range, the solubility of ferrous phosphate was low, ensuring the solid phase yield. After adding ammonia water, stirring was continued for 30 minutes to terminate the reaction.

[0051] S3: Washing of crude product: The reaction product is filtered to separate the solid and the liquid. After the filtration, the filter cake is transferred to a pulping kettle, 4000 g of 60°C hot desalted water is added, and the solid product is washed with hot water until the conductivity of the washing water is less than 50 ms / cm.

[0052] S4: Calcination treatment: The washed crude product is placed in a crucible, put into a muffle furnace, and calcined in an air atmosphere in a step-by-step manner. The purpose of calcination is dehydration and crystal transformation. First, calcine at 260°C for 3.5 hours to complete dehydration, and then increase the temperature to 750°C and calcine for 2 hours. The amorphous iron phosphate is converted into α monoclinic system. After the calcination, a light yellow product iron phosphate is obtained.

[0053] Example 3

[0054] S1: Dissolution of raw materials: 150g of iron powder was added to 5944g of 5.7wt% phosphoric acid for dissolution. The reaction temperature was 32°C. After the reaction for 1h, the reaction solution was filtered by suction. The filter paper precision was 1μm. A dark green ferrous phosphate solution was prepared. The ferrous phosphate concentration was 10%.

[0055] S2: Synthesis reaction: The prepared ferrous phosphate solution was transferred to a reactor. The reaction temperature was 30°C. Oxygen was bubbled into the bottom of the reactor through a gas distributor. The reaction pressure was 3MPa and the oxygen flow rate was 6m / s. The high flow rate was beneficial to slow down the agglomeration of ferrous phosphate crystal nuclei and make the particle size smaller and more uniform. As the reaction proceeded, a light yellow precipitate appeared in the solution. After 0.5h of reaction, the pressure was released and ammonia water was added. According to the online pH indicator, the pH of the reaction slurry was controlled at 1.5. Within this pH range, the solubility of ferric phosphate was low, ensuring the solid phase yield. After adding ammonia water, stirring was continued for 45min to terminate the reaction.

[0056] S3: Washing of crude product: The reaction product is filtered to separate the solid and the liquid. After the filtration, the filter cake is transferred to a pulping kettle, 1000 g of 90°C hot desalted water is added, and the solid product is washed with hot water until the conductivity of the washing water is less than 50 ms / cm.

[0057] S4: Calcination treatment: The washed crude product is placed in a crucible, put into a muffle furnace, and calcined in an air atmosphere in a step-by-step manner. The purpose of calcination is to dehydrate and transform the crystals. First, calcine at 200°C for 5 hours to complete dehydration, and then increase the temperature to 550°C and calcine for 4 hours. The amorphous iron phosphate is converted into α monoclinic system. After the calcination, a light yellow product iron phosphate is obtained.

[0058] Comparative Example 1

[0059] S1: Dissolution of raw materials: 150g of iron powder was added to 5944g of 5.7wt% phosphoric acid for dissolution. The reaction temperature was 32°C. After the reaction for 1h, the reaction solution was filtered by suction. The filter paper precision was 1μm. A dark green ferrous phosphate solution was prepared. The ferrous phosphate concentration was 10%.

[0060] S2: Synthesis reaction: The prepared ferrous phosphate solution was transferred to a reactor, the reaction temperature was 30°C, 165g of 27.5% hydrogen peroxide was added for oxidation, and as the reaction proceeded, a light yellow precipitate appeared in the solution. After 0.5h of reaction, ammonia water was added, and the pH of the reaction slurry was controlled at 1.5 according to the online pH indicator. Within this pH range, the solubility of ferrous phosphate was low, ensuring the solid phase yield. After adding ammonia water, stirring was continued for 45min to terminate the reaction. The particle size of the reactant was 30-40μm.

[0061] S3: Washing of crude product: The reaction product is filtered to separate the solid and liquid. After the filtration, the filter cake is transferred to a pulping kettle, 1000 g of 90°C hot desalted water is added, and the solid product is washed with hot water until the conductivity of the washing water is less than 50 ms / cm. 3030 g of desalted water is added to prepare a 10 wt% solid content slurry.

[0062] S4: Aging: The above slurry is placed in an aging kettle for aging, 46g of 85% phosphoric acid is added, the aging temperature is 85°C, the aging time is 4h, after the aging is completed, the crude product is placed in a crucible, put into a muffle furnace, and calcined at high temperature in an air atmosphere at a calcination temperature of 550°C for 4h to obtain a light yellow product iron phosphate after the calcination is completed.

[0063] Comparative Example 2

[0064] S1: Dissolution of raw materials: 100g of iron powder was added to 2269g of 10wt% phosphoric acid for dissolution, the reaction temperature was 60°C, after the reaction for 4h, the reaction solution was filtered by suction, the filter paper precision was 2μm, and a dark green ferrous phosphate solution was prepared, and the ferrous phosphate concentration was 17%.

[0065] S2: Synthesis reaction: The prepared ferrous phosphate solution was transferred to a reactor, the reaction temperature was 65°C, 110 g of 27.5% hydrogen peroxide was added for oxidation, and as the reaction proceeded, a light yellow precipitate appeared in the solution. After 1 hour of reaction, ammonia water was added, and the pH of the reaction slurry was controlled at 2 according to the online pH indicator. Within this pH range, the solubility of ferrous phosphate was low, ensuring the solid phase yield. After adding ammonia water, stirring was continued for 15 minutes to terminate the reaction. The particle size of the reactant was 25 to 50 μm.

[0066] S3: Washing of crude product: The reaction product is filtered to separate the solid and the liquid. After the filtration, the filter cake is transferred to a pulping kettle, 3000 g of 70°C hot desalted water is added, and the solid product is washed with hot water until the conductivity of the washing water is less than 50 ms / cm. 2025 g of desalted water is added to prepare a 10 wt% solid content slurry.

[0067] S4: Aging: The slurry is placed in an aging kettle for aging, 31 g of 85% phosphoric acid is added, the aging temperature is 85°C, the aging time is 4 hours, after the aging is completed, the crude product is placed in a crucible, put into a muffle furnace, and calcined at high temperature in an air atmosphere at a calcination temperature of 675°C for 3 hours, and a light yellow product iron phosphate is obtained after the calcination is completed.

[0068] Comparative Example 3

[0069] S1: Preparation of ferrous sulfate solution: Dissolve 160g of ferrous sulfate in deionized water and make up to 500ml. Add 57ml of concentrated sulfuric acid and make up to 1L, and stir thoroughly.

[0070] S2: Preparation of dilute phosphoric acid: Take 77 ml of industrial grade concentrated phosphoric acid, dilute to 1 L, and stir thoroughly.

[0071] S3: Synthesis reaction: Add ferrous solution and phosphoric acid solution into a 3L reactor and stir. Set the reaction temperature to 90°C. Introduce oxygen micro-nano bubbles into the reactor through a micro-nano bubble device. Adjust the pH of the system with ammonia water. Continue the reaction for 3 hours after the feeding is completed.

[0072] S4: Dehydration and calcination treatment: The crude product is washed and dried at 100°C for 8 hours. After the free water is dried, it is calcined at 650°C for 2 hours. After the calcination, a light yellow product, iron phosphate, is obtained.

[0073] Comparative Example 4

[0074] S1: Dissolution of raw materials: 150g of iron powder was added to 5944g of 5.7wt% phosphoric acid for dissolution. The reaction temperature was 32°C. After the reaction for 1h, the reaction solution was filtered by suction. The filter paper precision was 1μm. A dark green ferrous phosphate solution was prepared. The ferrous phosphate concentration was 10%.

[0075] S2: Synthesis reaction: The prepared ferrous phosphate solution was transferred to a reactor. The reaction temperature was 30°C. Oxygen was bubbled into the reactor through a gas distributor. The reaction was carried out at normal pressure. The oxygen flow rate was 6 m / s. The high flow rate was beneficial to slow down the agglomeration of ferrous phosphate crystal nuclei and make the particle size smaller and more uniform. As the reaction proceeded, a light yellow precipitate appeared in the solution. After 0.5 h of reaction, ammonia water was added. According to the online pH indicator, the pH of the reaction slurry was controlled at 1.5. Within this pH range, the solubility of ferrous phosphate was low, ensuring the solid phase yield. After adding ammonia water, stirring was continued for 45 min to terminate the reaction.

[0076] S3: Washing of crude product: The reaction product is filtered to separate the solid and the liquid. After the filtration, the filter cake is transferred to a pulping kettle, 1000 g of 90°C hot desalted water is added, and the solid product is washed with hot water until the conductivity of the washing water is less than 50 ms / cm.

[0077] S4: Calcination treatment: The washed crude product is placed in a crucible, put into a muffle furnace, and calcined in an air atmosphere in a step-by-step manner. The purpose of calcination is to dehydrate and transform the crystals. First, calcine at 200°C for 5 hours to complete dehydration, and then increase the temperature to 550°C and calcine for 4 hours. The amorphous iron phosphate is converted into α monoclinic system. After the calcination, a light yellow product iron phosphate is obtained.

[0078] Comparative Example 5

[0079] S1: Dissolution of raw materials: 125g of iron powder was added to 3451g of 8.2wt% phosphoric acid for dissolution. The reaction temperature was 45°C. After reacting for 2.5h, the reaction solution was filtered by suction. The filter paper precision was 0.5μm. A dark green ferrous phosphate solution was prepared. The ferrous phosphate concentration was 14%.

[0080] S2: Synthesis reaction: The prepared ferrous phosphate solution is transferred to the reactor. The reaction temperature is 50°C. Oxygen is bubbled into the reactor through a gas distributor. The reaction pressure is 6MPa and the oxygen flow rate is 9m / s. The high flow rate is beneficial to slow down the agglomeration of ferrous phosphate crystal nuclei and make the particle size smaller and more uniform. As the reaction proceeds, a light yellow precipitate appears in the solution. After 2h of reaction, the pressure is released and ammonia water is added. According to the online pH indicator, the pH of the reaction slurry is controlled at 1.8. Within this pH range, the solubility of ferric phosphate is low, which ensures the solid phase yield. After adding ammonia water, stirring is continued for 30min to terminate the reaction.

[0081] S3: Washing of crude product: The reaction product is filtered to separate the solid and the liquid. After the filtration, the filter cake is transferred to a pulping kettle, 4000 g of 60°C hot desalted water is added, and the solid product is washed with hot water until the conductivity of the washing water is less than 50 ms / cm.

[0082] S4: Drying treatment: The washed crude product is placed in a crucible, put into a muffle furnace, and dried at 260°C in an air atmosphere for 3.5 hours to complete dehydration.

[0083] Examples 1 to 3 are ferric phosphates prepared by the method of the present invention, and Comparative Examples 1 to 5 are ferric phosphates prepared by conventional methods. Eight samples were randomly taken from each batch for testing, and the average value was calculated. The corresponding product particle size, structure and iron-phosphorus ratio data are shown in Table 1.

[0084] Table 1

[0085] sample Reaction efficiency Particle size structure Iron to Phosphorus Ratio (Fe / P) Example 1 99.5％ 4~5μm All conform to the standard diffraction spectrum 0.964～0.965 Example 2 99.4％ 4~5.1μm All conform to the standard diffraction spectrum 0.964～0.965 Example 3 99.5％ 4~5.2μm All conform to the standard diffraction spectrum 0.964～0.965 Comparative Example 1 96％ 5~10μm 75% of the samples conform to the standard diffraction pattern 0.954～0.976 Comparative Example 2 98％ 6~14μm 87% of the samples conform to the standard diffraction spectrum 0.958～0.982 Comparative Example 3 97％ 3~8μm All conform to the standard diffraction spectrum 0.97～1.00 Comparative Example 4 96％ 4~6μm 87% of the samples conform to the standard diffraction spectrum 0.961～0.993 Comparative Example 5 99.4％ 5~8μm None of them meet the standard diffraction pattern 0.964～0.965

[0086] It can be seen from Table 1 that the iron phosphate prepared by the method of the present invention has uniform particle size, regular structure, and stable iron-phosphorus ratio, which has obvious advantages over conventional methods.

[0087] The above describes in detail the specific implementation cases of the present invention. It should be clear that the above cases are only examples and are not exhaustive. For professionals in this field, any adjustment / modification to the above implementation cases or replacement of equivalent solutions without departing from the principles of the present invention is obvious. Any solution that falls within the spirit of this patent should be within the scope of this patent.

Claims

1. A method for preparing high-quality ferric phosphate in a short process, characterized in that: The following steps are involved: 1) preparing a ferrous phosphate solution using an iron source and a phosphorus source; 2) transferring the ferrous phosphate solution to a pressure reactor, and blowing high-speed oxygen into the reactor to oxidize the ferrous phosphate into ferric phosphate, and after the reaction, releasing the pressure and adding ammonia water to adjust the pH; 3) Separating and obtaining the hydrous amorphous iron phosphate, washing and then performing step-wise calcination and dehydration to obtain α monoclinic iron phosphate.

2. The method according to claim 1, characterized in that In step 1), the iron source is iron powder, the phosphorus source is phosphoric acid, and the iron powder is dissolved by phosphoric acid to prepare a ferrous phosphate solution.

3. The method according to claim 2, characterized in that The iron powder is added into phosphoric acid to be dissolved, and then the reaction solution is filtered to prepare a ferrous phosphate solution, wherein the mass concentration of the ferrous phosphate is 10% to 17%; Preferably, the reaction temperature is 30-60° C., and the reaction time is 1-5 h.

4. The method according to claim 3, characterized in that The pH of the system was controlled at 0.5-1.2 by adjusting the amount of phosphoric acid; Preferably, the reaction solution is filtered by suction filtration with a filtration accuracy of 0.5 to 2 μm.

5. The method according to claim 1, characterized in that In step 2), a gas distributor is provided at the bottom of the reactor, and the high-speed oxygen enters the reactor through the gas distributor.

6. The method according to claim 1 or 5, characterized in that: The reaction pressure in the pressure reactor is 3-10 MPa, the reaction temperature is 30-75° C., and the reaction time is 0.5-2 h.

7. The method according to claim 6, characterized in that The flow rate of the high-speed oxygen in step 2) is 6 to 14 m / s.

8. The method according to claim 6, characterized in that In step 2), ammonia water is added to adjust the pH to 1.5-2.

0.

9. The method according to claim 1, characterized in that: In step 3), the solid product is washed with hot water until the conductivity of the washed water is less than 50 ms / cm; Preferably, the hot water is desalted water with a temperature of 60-90°C.

10. The method according to claim 9, characterized in that The calcination in step 3) is carried out at a high temperature in an air atmosphere. The purpose of the calcination is dehydration and crystal transformation. The calcination temperature is 200 to 775° C. and the residence time is 3 to 9 hours. Preferably, the calcination is first performed at 200-300° C. for 2-5 hours to complete dehydration, and then the temperature is raised to 550-775° C. to complete crystal transformation.

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