Iron phosphate material, method for preparing the same, and use thereof

Abstract

This invention discloses an iron phosphate material, its preparation method, and its applications. The preparation method of this iron phosphate material includes the following steps: mixing iron-based raw materials, phosphoric acid solution, and a complexing stabilizer; undergoing a first reaction and solid-liquid separation to obtain a ferrous dihydrogen phosphate solution; under high-speed shear emulsification conditions, mixing the ferrous dihydrogen phosphate solution, an oxidant, and a crystal form control agent; undergoing a second reaction to obtain an iron phosphate suspension; and aging, washing, and drying the iron phosphate suspension to obtain iron phosphate dihydrate. This invention successfully prepares a high-performance iron phosphate material through a coupling of complexation leaching and shear oxidation crystallization. The method of this invention can directly utilize magnetite or natural magnetite, has low raw material costs, good intermediate product stability, excellent product performance, high process integration, and is environmentally friendly, making it suitable for large-scale industrial production.

Description

Technical Field

[0001] This invention relates to the field of iron phosphate materials technology, and in particular to an iron phosphate material, its preparation method, and its application. Background Technology

[0002] Iron phosphate (FePO4) is a key precursor for the preparation of lithium iron phosphate (LiFePO4) cathode materials, and its purity, morphology, and particle size distribution directly affect the electrochemical performance of lithium-ion batteries. Currently, there are two main industrial processes for preparing iron phosphate: one is the ferrous sulfate-phosphate co-precipitation method, which generates a large amount of wastewater containing ammonium sulfate or sodium sulfate, resulting in high environmental treatment costs; the other is the iron method, which involves reacting pure iron with phosphoric acid to generate a ferrous dihydrogen phosphate solution, which is then oxidized to obtain iron phosphate.

[0003] The iron-based process has significant advantages due to its short process flow and the fact that it does not require an external alkali source. However, existing technologies still face the following technical bottlenecks: (1) High raw material cost: The mainstream process requires the use of high-purity iron blocks or pure iron powder, resulting in raw material costs accounting for more than 40% of the production cost. Although some studies have tried to use cheap iron sources such as iron oxide scale, there are problems such as slow dissolution rate and high impurity content, requiring complex acid ratio control.

[0004] (2) Poor stability of intermediate products: Ferrous dihydrogen phosphate (Fe(H2PO4)2) solution is sensitive to oxygen and is prone to oxidative hydrolysis to generate Fe. 3+ Precipitation leads to an imbalance in the iron-phosphorus ratio during subsequent synthesis.

[0005] (3) The process control is difficult: In the traditional two-step process of "dissolving-filtration-oxidation", the oxidation stage is prone to uneven local supersaturation, resulting in uncontrollable product morphology and poor batch stability.

[0006] Therefore, developing a green preparation method for iron phosphate that can directly utilize low-cost iron tetroxide or natural magnetite as raw materials and integrate the "leaching-purification-oxidation-crystallization" process is of great significance for reducing production costs and improving product quality. Summary of the Invention

[0007] The purpose of this invention is to overcome the above-mentioned technical deficiencies and propose an iron phosphate material, its preparation method and application, thereby solving the technical problems of high raw material cost, unstable intermediate products and difficult process control in the existing iron-based process.

[0008] In a first aspect, the present invention provides a method for preparing an iron phosphate material, comprising the following steps: Iron-based raw materials, phosphoric acid solution and complexing stabilizer are mixed, and after the first reaction and solid-liquid separation, ferrous dihydrogen phosphate solution is obtained; Under high-speed shear emulsification conditions, ferrous dihydrogen phosphate solution, oxidant and crystal form control agent are mixed and subjected to a second reaction to obtain ferric phosphate suspension; Ferric phosphate suspension was aged, washed, and dried to obtain ferric phosphate dihydrate.

[0009] In a second aspect, the present invention provides an iron phosphate material, which is obtained by the preparation method of the iron phosphate material provided in the first aspect of the present invention.

[0010] Thirdly, the present invention provides an application of an iron phosphate material, which is used as a precursor for lithium iron phosphate cathode materials.

[0011] Compared with the prior art, the beneficial effects of the present invention include: This invention successfully prepared high-performance iron phosphate materials through a coupled complexation leaching and shear oxidation crystallization method. The Fe / P molar ratio of the prepared iron phosphate dihydrate material is 0.95-0.99, and the BET specific surface area is 20-45 m². 2 / g, D50 particle size 2-10μm; tap density of anhydrous iron phosphate material ≥0.98g / cm³ 3 The iron phosphate material of this invention exhibits excellent electrochemical performance when used as a precursor for lithium iron phosphate. The method of this invention enables the direct utilization of iron tetroxide or natural magnetite, resulting in low raw material costs, good intermediate product stability, excellent product performance, high process integration, and environmental friendliness, making it suitable for large-scale industrial production. Attached Figure Description

[0012] Figure 1 This is the XRD pattern of the iron phosphate dihydrate material prepared in Example 1 of this invention; Figure 2 This is a SEM image of the iron phosphate dihydrate material prepared in Example 1 of this invention. Detailed Implementation

[0013] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0014] In a first aspect, the present invention provides a method for preparing an iron phosphate material, comprising the following steps: S1. Complexation leaching: Iron-based raw materials, phosphoric acid solution and complexation stabilizer are mixed, and after the first reaction and solid-liquid separation, ferrous dihydrogen phosphate solution is obtained. S2, Shear Oxidation Crystallization: Under high-speed shear emulsification conditions, ferrous dihydrogen phosphate solution, oxidant and crystal form control agent are mixed and subjected to a second reaction to obtain ferric phosphate suspension; S3. Post-treatment: The ferric phosphate suspension is aged, washed, and dried to obtain ferric phosphate dihydrate.

[0015] In this invention, a mixed slurry containing ferrous dihydrogen phosphate is obtained by mixing iron-based raw materials, phosphoric acid solution, and a complexing stabilizer, followed by a first reaction; wherein, the complexing stabilizer functions to: 1. affect the Fe... 2+ It has selective complexation properties and can achieve Fe 2+ The process involves two main steps: 1) selective extraction to separate ferrous dihydrogen phosphate from impurities in situ; 2) improving the stability of the intermediate product ferrous dihydrogen phosphate; 3) solid-liquid separation of the mixed slurry containing ferrous dihydrogen phosphate to remove leaching residues and impurity precipitates, yielding a ferrous dihydrogen phosphate solution; 4) mixing the ferrous dihydrogen phosphate solution, oxidant, and crystal form control agent under high-speed shear emulsification conditions, followed by a second reaction to allow Fe... 2+ Oxidation and FePO4 crystallization occur simultaneously to obtain a ferric phosphate suspension; the ferric phosphate suspension is then aged, washed, and dried to obtain ferric phosphate dihydrate.

[0016] In this invention, in step S1, the iron-based raw material is at least one of magnetite (Fe3O4), natural magnetite (whose main component is magnetite), and elemental iron. Compared with elemental iron, this invention, by using magnetite and natural magnetite as iron-based raw materials, is more conducive to reducing production costs.

[0017] In some specific embodiments of the present invention, the natural magnetite contains ≥50% TFe by mass percentage, preferably ≥60%, and more preferably ≥68.5%.

[0018] In some more specific embodiments of the present invention, the main components of natural magnetite, by mass percentage, are: TFe 60%-75%, SiO2 0.1%-5%, Al2O3 0.1%-3%, and MgO 0.1%-3%.

[0019] In this invention, in step S1, the particle size of the iron-based raw material is ≤100μm.

[0020] In this invention, in step S1, the mass fraction of the phosphoric acid solution is 10%-30%, including but not limited to 10%, 15%, 20%, 25%, 30%, etc.

[0021] In this invention, in step S1, the iron-based raw material is iron(II,III) oxide and / or natural magnetite, and the molar ratio of divalent iron in the iron-based raw material to phosphorus in the phosphoric acid solution is 1:(2-2.5), including but not limited to 1:2, 1:2.1, 1:2.2, 1:2.3, 1:2.4, 1:2.5, etc.

[0022] In this invention, in step S1, the iron-based raw material is elemental iron, and the molar ratio of iron in the iron-based raw material to phosphorus in the phosphoric acid solution is 1:(2-2.5), including but not limited to 1:2, 1:2.1, 1:2.2, 1:2.3, 1:2.4, 1:2.5, etc.

[0023] In this invention, in step S1, the complexing stabilizer is at least one of citric acid, ascorbic acid, ethylenediaminetetraacetic acid (EDTA), aminotrimethylphosphonic acid (ATMP), and gluconic acid.

[0024] In this invention, in step S1, the amount of complexing stabilizer added is 0.5%-10% of the mass of the iron-based raw material, including but not limited to 0.5%, 1%, 1.5%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc. If the amount of complexing stabilizer added is too low, it will lead to low extraction efficiency of divalent iron; if the amount of complexing stabilizer added is too high, it will lead to increased production costs and waste.

[0025] In this invention, the first reaction in step S1 is a pressure leaching reaction. By employing pressure leaching, this invention can more effectively improve the leaching effect of divalent iron in iron-based raw materials.

[0026] In this invention, during step S1, the temperature during the first reaction is 60-130℃, including but not limited to 60℃, 70℃, 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, etc., the pressure is 0.1-0.6MPa, including but not limited to 0.1MPa, 0.2MPa, 0.3MPa, 0.4MPa, 0.5MPa, 0.6MPa, etc., the stirring rate is 100-200rpm, including but not limited to 100rpm, 120rpm, 140rpm, 160rpm, 180rpm, 200rpm, etc., and the time is 2-6h, including but not limited to 2h, 3h, 4h, 5h, 6h, etc.

[0027] In this invention, in step S1, the first reaction is carried out under a protective atmosphere and with ultrasonic assistance. By carrying out the first reaction under a protective atmosphere, this invention can avoid Fe... 2+ Oxidation; This invention improves the leaching effect by conducting the first reaction under ultrasonic assistance. This invention does not limit the type of protective atmosphere; those skilled in the art can select it according to the actual situation. For example, the protective atmosphere can be nitrogen or argon.

[0028] Preferably, the ultrasonic frequency is 10-30kHz, including but not limited to 10kHz, 15kHz, 20kHz, 25kHz, 30kHz, etc., and the ultrasonic power is 100-800W, including but not limited to 100W, 200W, 300W, 400W, 500W, 600W, 700W, 800W, etc. If the ultrasonic power is too low, the cavitation effect will be insufficient, resulting in poor leaching effect; if the ultrasonic power is too high, it will lead to excessive energy consumption and increased production costs.

[0029] In this invention, during step S2, the rotor linear velocity during high-speed shear emulsification is 20-35 m / s, including but not limited to 20 m / s, 22 m / s, 25 m / s, 28 m / s, 30 m / s, 32 m / s, and 35 m / s. If the shear linear velocity is too low, the system will be unevenly mixed, resulting in large product particle size and low tap density; if the shear linear velocity is too high, although finer particles and higher specific surface area can be obtained, the tap density will decrease.

[0030] In this invention, in step S2, the oxidant is at least one of hydrogen peroxide, ammonium persulfate, sodium chlorate, and oxygen.

[0031] In this invention, in step S2, the amount of oxidant added is such that Fe 2+ Completely oxidized to Fe 3+ 1 to 1.2 times the theoretical molar amount, including but not limited to 1, 1.05, 1, 1.1, 1, 1.15, 1, 1.2, etc.

[0032] In this invention, in step S2, the crystal form control agent is at least one of ammonium sulfate, ammonium phosphate, polyethylene glycol (including but not limited to polyethylene glycol 400), hexadecyltrimethylammonium bromide, and polyvinylpyrrolidone (including but not limited to K30, etc.).

[0033] In this invention, in step S2, the amount of crystal form control agent added is 0.05%-1.5% of the mass of the ferrous dihydrogen phosphate solution, including but not limited to 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.7%, 0.9%, 1.1%, 1.3%, and 1.5%. If the amount of crystal form control agent added is too low, it will result in excessively fine particle size and uneven morphology; if the amount of crystal form control agent added is too high, it will increase production costs.

[0034] In this invention, step S2, mixing the ferrous dihydrogen phosphate solution, oxidant, and crystal form control agent includes: simultaneously and slowly adding the oxidant and crystal form control agent to the ferrous dihydrogen phosphate solution at a temperature of 40-90°C, including but not limited to 40°C, 50°C, 60°C, 70°C, 80°C, and 90°C, and at a time of 30-60 minutes, including but not limited to 30 minutes, 40 minutes, 50 minutes, and 60 minutes.

[0035] In this invention, the oxidant and crystal form control agent can be prepared into a solution or added directly, and those skilled in the art can choose according to the actual situation.

[0036] In this invention, in step S2, the temperature of the second reaction is 40-90℃, including but not limited to 40℃, 50℃, 60℃, 70℃, 80℃, 90℃, etc., and the time of the second reaction is 30-240min, including but not limited to 30min, 60min, 90min, 120min, 150min, 180min, 210min, 240min, etc.

[0037] In this invention, in step S3, the aging reaction temperature is 80-90℃, including but not limited to 80℃, 82℃, 84℃, 86℃, 88℃, 90℃, etc., and the aging reaction time is 1-3h, including but not limited to 1h, 1.5h, 2h, 2.5h, 3h, etc., and the aging reaction is carried out under stirring conditions.

[0038] Preferably, the stirring speed is 300-400 r / min, including but not limited to 300 r / min, 320 r / min, 340 r / min, 360 r / min, 380 r / min, 400 r / min, etc.

[0039] In this invention, the preparation method of the above-mentioned iron phosphate material further includes: S4. Calcining ferric phosphate dihydrate yields anhydrous ferric phosphate.

[0040] Preferably, in step S4, the calcination temperature is 500-800℃, including but not limited to 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, etc., and the calcination time is 2-8h, including but not limited to 2h, 3h, 4h, 5h, 6h, 7h, 8h, etc., and the calcination atmosphere is air.

[0041] More preferably, the heating rate is 2-10℃ / min, including but not limited to 2℃ / min, 4℃ / min, 6℃ / min, 8℃ / min, 10℃ / min, etc.

[0042] In a second aspect, the present invention provides an iron phosphate material, which is obtained by the preparation method of the iron phosphate material provided in the first aspect of the present invention.

[0043] In this invention, the Fe / P molar ratio of the iron phosphate dihydrate material is 0.95-0.99, and the BET specific surface area is 20-45 m². 2 / g, D50 particle size 2-10μm, further 3-10μm; tap density of anhydrous iron phosphate material ≥0.98g / cm³ 3 .

[0044] Thirdly, the present invention provides an application of an iron phosphate material, which is used as a precursor for lithium iron phosphate cathode materials.

[0045] Example 1 (1) Take 100 kg of natural magnetite concentrate (passed through a 325-mesh sieve, with the following composition: TFe 68.5%, Fe 2+ Content 22.8%, Fe 3+ The content was 45.7%, and the impurities were: SiO2 2.8%, Al2O3 0.9%, MgO 0.6%. The mixture was placed in a high-pressure reactor; a 16% phosphoric acid solution was prepared; and the Fe content was adjusted by molar ratio. 2+ With a ratio of P=1:2.1, phosphoric acid solution was added to a high-pressure reactor, followed by 2.0 kg of citric acid (2% of the mass of natural magnetite concentrate) as a complexing stabilizer. Nitrogen gas was introduced to replace the air in the high-pressure reactor, and an ultrasonic generator (400 W power, 20 kHz frequency) was turned on. The temperature was raised to 95 °C, the pressure was controlled at 0.25 MPa, the stirring speed was 120 rpm, and the reaction was carried out for 4 hours to obtain a mixed slurry containing ferrous dihydrogen phosphate.

[0046] (2) The mixed slurry containing ferrous dihydrogen phosphate was cooled to 50°C, and then filtered by plate and frame filter press to remove leaching residue and impurities, yielding a light green, clear ferrous dihydrogen phosphate solution (tested to contain Fe). 2+ Content 4.1%, pH=2.1, Si≤15ppm, Al≤12ppm, Mg≤8ppm).

[0047] (3) Transfer the above ferrous dihydrogen phosphate solution to a reaction vessel equipped with a high-shear emulsifier, heat it to 65°C, turn on the high-speed shear emulsifier, adjust the rotor linear speed to 22 m / s, and under emulsification conditions, slowly add 30% hydrogen peroxide (as an oxidant, the amount added is 1.05 times the theoretical amount required for oxidation) and polyethylene glycol 400 (as a crystal form control agent, the amount added is 0.3% of the mass of the ferrous dihydrogen phosphate solution) through a metering pump for 40 min. After the addition is completed, continue the emulsification reaction for 2 hours. The system gradually turns milky white, and ferric phosphate suspension is obtained.

[0048] (4) Transfer the ferric phosphate suspension to an aging kettle and age it at 85°C for 2 hours, controlling the stirring speed at 350 r / min. Then, centrifuge and wash it with pure water until the conductivity of the wash water is ≤150 μS / cm. Then, dry it at 120°C for 5 hours to obtain ferric phosphate dihydrate. Place the ferric phosphate dihydrate in a rotary kiln and heat it to 680°C at a heating rate of 5°C / min. Calcinate it at 680°C for 4 hours in an air atmosphere. Finally, pulverize it with airflow to obtain anhydrous ferric phosphate.

[0049] Example 2 Compared with Example 1, the only difference is that in step (1), the complexing stabilizer is replaced with aminotrimethylphosphonic acid (ATMP, added at 1.5% of the mass of natural magnetite concentrate), and the reaction time is adjusted to 3.5 hours; in step (2), ferrous dihydrogen phosphate solution is obtained by plate and frame filtration (and Fe is detected to be...). 2+ Content 4.1%, Si≤10ppm, Al≤8ppm, Mg≤5ppm).

[0050] Steps (3) and (4) are the same as in Example 1.

[0051] Example 3 Compared with Example 1, the only difference is that in step (3), the linear velocity of high-speed shear emulsification is adjusted to 35 m / s.

[0052] Example 4 Compared with Example 1, the only difference is that step (3) is as follows: Take the ferrous dihydrogen phosphate solution obtained in step (2) of Example 1 and transfer it to a reaction vessel equipped with a high-shear emulsifier. Heat it to 70°C, turn on the high-shear emulsifier, and adjust the rotor linear speed to 22 m / s. Under emulsification conditions, slowly add 30% ammonium persulfate solution (as an oxidant, the amount added is 1.1 times the theoretical amount required for oxidation) and polyvinylpyrrolidone K30 (as a crystal form control agent, the amount added is 0.2% of the mass of the ferrous dihydrogen phosphate solution) through a metering pump. The addition time is 40 min. After the addition is completed, continue the emulsification reaction for 2.5 hours to obtain ferric phosphate suspension.

[0053] Step (4) is the same as in Example 1.

[0054] Example 5 Compared with Example 1, the only difference is that step (1) is as follows: Take 23.15 kg of reduced iron powder (passed through a 200-mesh sieve, TFe≥98.5%) and place it in a high-pressure reactor; prepare a 16% phosphoric acid solution; add the phosphoric acid solution to the high-pressure reactor at a molar ratio of Fe:P=1:2.1, followed by 2 kg of citric acid as a complexing stabilizer; purge the air in the high-pressure reactor with nitrogen, turn on the ultrasonic generator (power 400W, frequency 20kHz), raise the temperature to 85℃, control the pressure at 0.15MPa, stir at 120rpm, and react for 2 hours to obtain a mixed slurry containing ferrous dihydrogen phosphate.

[0055] In step (2), a ferrous dihydrogen phosphate solution was obtained by plate and frame filtration (and Fe was detected). 2+ Content 4.1%, Si≤0.13ppm, Al≤1ppm, Mg≤0.07ppm.

[0056] Steps (3) and (4) are the same as in Example 1.

[0057] Comparative Example 1 Comparative Example 1 uses a conventional two-step method, without shear emulsification or crystal form control agents. The specific steps are as follows: (1) A high-purity iron block (purity 98.75%) was reacted with dilute phosphoric acid with a mass fraction of 16%. The Fe:P molar ratio was controlled at 1:2.1. Under nitrogen protection, the reaction was stirred at 90°C until the iron block was completely dissolved. The stirring speed was controlled at 300 r / min. After filtration, a ferrous dihydrogen phosphate solution was obtained. (2) Transfer the ferrous dihydrogen phosphate solution to a regular anchor-type stirred tank, heat it to 60°C, control the stirring speed to 350 r / min, and slowly add 30% hydrogen peroxide (as an oxidant, the amount added is 1.05 times the theoretical amount required for oxidation) dropwise through a metering pump for 40 min; after the addition is completed, continue stirring the reaction for 2 hours to obtain ferric phosphate suspension; (3) Transfer the ferric phosphate suspension to an aging kettle and age it at 85°C for 2 hours, controlling the stirring speed at 350 r / min. Then, centrifuge and wash it with pure water until the conductivity of the wash water is ≤150 μS / cm. Then, dry it at 120°C for 5 hours to obtain ferric phosphate dihydrate. Place the ferric phosphate dihydrate in a rotary kiln and heat it to 680°C at a heating rate of 5°C / min. Calcinate it at 680°C for 4 hours in an air atmosphere. Finally, pulverize it with airflow to obtain anhydrous ferric phosphate.

[0058] Comparative Example 2 Compared with Example 1, the only difference is that no complexing stabilizer was added in step (1), the slurry gradually turned yellow-green during the reaction, and filtration was difficult; in step (2), the solution obtained by plate and frame filtration was turbid, and a yellow precipitate (Fe) appeared after standing. 3+Hydrolysis products), upon testing, showed Fe 2+ The content is only 2.8%, and the contents of Si and Al impurities are 85ppm and 62ppm, respectively.

[0059] Since Fe has appeared in the solution 3+ Precipitation occurred, making it impossible to prepare qualified iron phosphate. Therefore, subsequent steps (3) and (4) were not performed.

[0060] Comparative Example 3 Compared with Example 1, the only difference is that in step (3), the linear velocity of high-speed shear emulsification is adjusted to 8 m / s.

[0061] Performance testing (1) Fe / P: The phosphorus content was determined by the gravimetric method of quinoline phosphomolybdate, and the iron content was determined by the potentiometric titration method. The Fe / P molar ratio was then calculated. (2) BET specific surface area: tested using a fully automated specific surface area and pore size analyzer; (3) D50: Tested using a laser particle size analyzer; (4) Tap density: Tested using a tap density meter.

[0062] Table 1. Reaction conditions and product performance test results for each embodiment and comparative example.

[0063] Please see Figure 1 ,pass Figure 1 It can be seen that the iron phosphate dihydrate material prepared in Example 1 of the present invention has good crystallinity and no impurity phase exists.

[0064] Please see Figure 2 ,pass Figure 2 As can be seen, the iron phosphate dihydrate material prepared in Example 1 of the present invention exhibits a spherical morphology composed of interlaced thin sheets.

[0065] Please refer to Table 1. As can be seen from Table 1, in Examples 1-5 of this invention, iron phosphate materials were successfully prepared using natural magnetite concentrate or reduced iron powder as raw materials. The Fe / P ratio of the iron phosphate dihydrate material prepared by this invention is 0.95-0.99, and the BET specific surface area is 20-45 m². 2 The anhydrous iron phosphate material prepared in this invention has a D50 particle size of 2-10 μm and good morphological uniformity; the tap density is ≥0.98 g / cm³. 3 .

[0066] Compared with Example 1, Example 2 uses aminotrimethylphosphonic acid as a complexing stabilizer, which has a stronger chelating ability for metal ions, a better impurity removal effect, and a slightly higher specific surface area of ​​the iron phosphate material.

[0067] Compared with Example 1, the shearing linear velocity of Example 3 and Comparative Example 3 is higher or lower, respectively, which will have a significant impact on product performance, and 20-35 m / s is the preferred range.

[0068] Compared with Example 1, Example 4 uses ammonium persulfate as an oxidant, which can also achieve complete oxidation and obtain iron phosphate material that meets the index requirements, but it will introduce sulfur and ammonium impurities.

[0069] Compared with Example 1, Example 5 uses reduced iron powder as raw material, which has high activity and more vigorous reaction. It also produces hydrogen gas, so the temperature and pressure cannot be too high and the reaction time should be shortened. At the same time, since the pure iron powder raw material has low impurity content, the product purity is higher and the tap density is also slightly better, but the raw material cost increases by about 35%.

[0070] Compared with Example 1, Comparative Example 1 uses a conventional two-step method, and the tap density of the prepared iron phosphate material is lower.

[0071] Compared to Example 1, no complexing stabilizer was added in Comparative Example 2, and the impurities in the natural magnetite concentrate catalyzed Fe. 2+ Oxidation, and Fe 3+ The ferrous dihydrogen phosphate solution is easily hydrolyzed and precipitated, making it impossible to obtain a pure and stable solution, indicating that the complexing stabilizer plays a crucial role.

[0072] In summary, the present invention has the following advantages: (1) Low raw material cost: For the first time, the direct utilization of iron oxide or natural magnetite is realized. Through the selective complexation effect of the complexing stabilizer, Fe is achieved in the leaching stage. 2+ The efficient extraction and in-situ separation of impurities eliminate the need for pre-purification of iron tetroxide or natural magnetite, reducing raw material costs by more than 30%.

[0073] (2) High process integration: The traditional leaching, purification, oxidation and crystallization processes that require multiple steps are coupled into an integrated process, shortening the production cycle by more than 40% and reducing equipment investment.

[0074] (3) Excellent product performance: Under high-speed shear emulsification conditions, the oxidant is instantly and uniformly dispersed, overcoming the problem of uneven local supersaturation in traditional oxidation processes. The D50 particle size of the dihydrate ferric phosphate material is 2-10μm, and the tap density of the anhydrous ferric phosphate material is ≥0.98g / cm³. 3 When used as a precursor for lithium iron phosphate, its 0.1C discharge specific capacity can reach over 160 mAh / g.

[0075] (4) Environmentally friendly: No external alkali source is added throughout the process. In particular, when hydrogen peroxide is used as an oxidant, no waste salt containing sulfate or chloride is produced. The wastewater is mainly washing water containing a small amount of phosphate, which is easy to recycle and treat.

[0076] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing an iron phosphate material, characterized in that, Includes the following steps: Iron-based raw materials, phosphoric acid solution and complexing stabilizer are mixed, and after the first reaction and solid-liquid separation, ferrous dihydrogen phosphate solution is obtained; Under high-speed shear emulsification conditions, the ferrous dihydrogen phosphate solution, oxidant, and crystal form control agent are mixed and subjected to a second reaction to obtain a ferric phosphate suspension. The ferric phosphate suspension was subjected to aging, washing, and drying to obtain ferric phosphate dihydrate.

2. The method for preparing the iron phosphate material according to claim 1, characterized in that, The iron-based raw material is at least one of iron(III) oxide, natural magnetite, and elemental iron; and / or... The particle size of the iron-based raw material is ≤100μm.

3. The method for preparing the iron phosphate material according to claim 1, characterized in that, The phosphoric acid solution has a mass fraction of 10%-30%; and / or, The iron-based raw material is iron(III) oxide and / or natural magnetite, wherein the molar ratio of divalent iron to phosphorus in the phosphoric acid solution is 1:(2-2.5); and / or, The iron-based raw material is elemental iron, and the molar ratio of iron to phosphorus in the phosphoric acid solution is 1:(2-2.5); and / or, The complexing stabilizer is at least one selected from citric acid, ascorbic acid, ethylenediaminetetraacetic acid, aminotrimethylphosphonic acid, and gluconic acid; and / or, The amount of the complexing stabilizer added is 0.5%-10% of the mass of the iron-based raw material.

4. The method for preparing the iron phosphate material according to claim 1, characterized in that, The first reaction is a pressure leaching reaction; and / or, During the first reaction, the temperature is 60-130℃, the pressure is 0.1-0.6MPa, the stirring rate is 100-200rpm, and the time is 2-6h; and / or, The first reaction was carried out under a protective atmosphere and with ultrasonic assistance; the ultrasonic frequency was 10-30kHz and the ultrasonic power was 100-800W.

5. The method for preparing the iron phosphate material according to claim 1, characterized in that, During the high-speed shear emulsification process, the rotor linear velocity is 20-35 m / s.

6. The method for preparing the iron phosphate material according to claim 1, characterized in that, The oxidant is at least one selected from hydrogen peroxide, ammonium persulfate, sodium chlorate, and oxygen; and / or, The amount of oxidant added is such that Fe 2+ Completely oxidized to Fe 3+ 1-1.2 times the theoretical molar amount; and / or, The crystal form control agent is at least one selected from ammonium sulfate, ammonium phosphate, polyethylene glycol, hexadecyltrimethylammonium bromide, and polyvinylpyrrolidone; and / or, The amount of the crystal form control agent added is 0.05%-1.5% of the mass of the ferrous dihydrogen phosphate solution.

7. The method for preparing the iron phosphate material according to claim 1, characterized in that, The mixing of ferrous dihydrogen phosphate solution, oxidant, and crystal form control agent includes: simultaneously and slowly adding the oxidant and crystal form control agent to the ferrous dihydrogen phosphate solution at a temperature of 40-90°C for 30-60 minutes; and / or, The temperature of the second reaction is 40-90℃, and the reaction time is 30-240 min; and / or, The aging reaction is carried out at a temperature of 80-90℃ for 1-3 hours, under stirring conditions, and the stirring speed is 300-400 r / min.

8. The method for preparing the iron phosphate material according to claim 1, characterized in that, Also includes: The ferric phosphate dihydrate was calcined to obtain anhydrous ferric phosphate; wherein... The calcination temperature is 500-800℃, the calcination time is 2-8 hours, and the calcination atmosphere is air; and / or, During the calcination process, the heating rate is 2-10℃ / min.

9. A ferric phosphate material, characterized in that, The iron phosphate material is obtained by the preparation method of the iron phosphate material according to any one of claims 1-8.

10. An application of the iron phosphate material as described in claim 9, characterized in that, The iron phosphate material is used as a precursor for lithium iron phosphate cathode materials.

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