Amorphous ferric phosphate and a method for producing the same, anhydrous ferric phosphate and a method for producing the same

Abstract

The present application provides amorphous ferric phosphate, wherein the X-ray diffraction spectrum of the amorphous ferric phosphate has a first diffraction peak θ1 and a second diffraction peak θ2 at 19-21° and 28-30° respectively, and the ratio of the peak intensity I1 of the first diffraction peak to the peak intensity I2 of the second diffraction peak is 0.8-0.91; the amorphous ferric phosphate is spherical or spheroidal particle. The amorphous ferric phosphate has low content of iron hydroxide, uniform particle size distribution, small primary particle size and low agglomeration degree, which is beneficial to the subsequent preparation of high specific surface area, small primary particle size and low agglomeration ferric phosphate. The present application also provides a preparation method of the amorphous ferric phosphate and anhydrous ferric phosphate prepared based on the amorphous ferric phosphate.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery material technology, specifically relating to the modification of iron phosphate intermediates and anhydrous iron phosphate. Background Technology

[0002] Among lithium-ion battery cathode materials, lithium iron phosphate (LFP) has become a research hotspot due to its advantages such as non-toxicity, low cost, and good safety. With the development of applications such as new energy power generation and storage, and home energy storage, the cost and long-cycle performance advantages of LFP are becoming increasingly prominent, leading to its widespread use in automotive and large-scale energy storage applications. However, the compaction density and electrochemical performance of LFP still need improvement. As the backbone of lithium iron phosphate, the morphology and structure of iron phosphate play a decisive role in its compaction density and electrochemical performance. Therefore, researching LFP preparation processes with controllable particle distribution has high application value and research significance. Summary of the Invention

[0003] To address the aforementioned technical problems, this application provides amorphous ferric phosphate and its preparation method, as well as anhydrous ferric phosphate and its preparation method.

[0004] To achieve the above objectives, this application proposes the following technical solution:

[0005] In a first aspect, an amorphous iron phosphate is provided, wherein the X-ray diffraction pattern of the amorphous iron phosphate has a first diffraction peak θ1 and a second diffraction peak θ2 at 19~21° and 28~30° respectively, and the ratio of the peak intensity I1 of the first diffraction peak to the peak intensity I2 of the second diffraction peak is 0.8~0.91, and the amorphous iron phosphate is spherical or near-spherical particles.

[0006] Furthermore, 95% of the primary particles of the amorphous iron phosphate have a particle size of less than 80 nm.

[0007] Secondly, a method for preparing amorphous iron phosphate is provided, comprising:

[0008] Solution A was prepared using a phosphorus source and a ferrous source. The pH and temperature of solution A were adjusted, and the reaction was carried out to obtain a grayish-white ferrous hydrogen phosphate slurry.

[0009] The grayish-white ferrous hydrogen phosphate slurry was oxidized to obtain a yellow amorphous ferric phosphate slurry. After solid-liquid separation and washing, amorphous ferric phosphate was obtained.

[0010] Further, adjust the pH of solution A to 1.5~3.5.

[0011] Furthermore, the reagent used to adjust the pH of solution A is one or more of ammonia, urea, and sodium hydroxide.

[0012] Furthermore, the temperature of solution A is adjusted to 40-60°C.o C.

[0013] Furthermore, the phosphorus source is one or two of ammonium dihydrogen phosphate, phosphoric acid, diammonium hydrogen phosphate, and ammonium phosphate.

[0014] Furthermore, the ferrous source is one or more of ferrous sulfate, ferrous chloride, ferrous nitrate, iron powder, ferrous oxide, and ferrous oxalate.

[0015] Furthermore, the molar ratio of phosphorus source (calculated as phosphate) to ferrous source (calculated as iron) is 0.95 to 1.2:1.

[0016] Furthermore, the oxidant used in the oxidation process is one or more of hydrogen peroxide, air, oxygen, and ozone.

[0017] Furthermore, the amount of oxidant used is 1.2 to 1.4 times the theoretically required amount.

[0018] Furthermore, in solution A, the mass percentage concentration of phosphorus is 2-5%.

[0019] Furthermore, in solution A, the mass percentage concentration of iron is 3-7%.

[0020] Furthermore, the pH value of solution A is 0.5 < pH < 1.2.

[0021] Furthermore, the raw materials for preparing solution A also include an acidic solution or an alkaline solution; the acidic solution is one or more of sulfuric acid and hydrochloric acid, and the alkaline solution is one or more of ammonia water, urea solution, and sodium hydroxide solution.

[0022] Furthermore, the washing process uses pure water; preferably, the conductivity of the wash water at the end of the washing process is not greater than 20000 μS / cm.

[0023] Thirdly, anhydrous ferric phosphate is provided, the raw material for which is the aforementioned amorphous ferric phosphate or the amorphous ferric phosphate prepared by the aforementioned preparation method is used.

[0024] The anhydrous ferric phosphate has a primary particle size of less than 90 nm, a specific surface area of ​​9~14 m² / g, and a tap density of 0.7~1.0 g / cm³.

[0025] Fourthly, a method for preparing anhydrous ferric phosphate is provided, including:

[0026] The aforementioned amorphous ferric phosphate or the amorphous ferric phosphate prepared by the aforementioned preparation method is mixed with a phosphoric acid solution, heated to crystallize, filtered, washed with water, and calcined to obtain anhydrous ferric phosphate.

[0027] Compared with the prior art, one or more of the above technical solutions can achieve at least one of the following beneficial effects:

[0028] This application provides amorphous iron phosphate, wherein the peak intensity ratio of the first diffraction peak to the second diffraction peak at 19~21° and 28~30° is 0.8~0.91, respectively. The amorphous iron phosphate contains low amounts of iron hydroxide, has a uniform primary particle size distribution, small primary particle size, and low degree of agglomeration, which is beneficial for the subsequent preparation of iron phosphate with high specific surface area, small primary particle size, and low agglomeration.

[0029] The method for preparing amorphous iron phosphate provided in this application uses ferrous iron and phosphorus as raw materials. First, a ferrous hydrogen phosphate slurry is generated by reaction, and then an amorphous iron phosphate material with low iron hydroxide content is obtained by oxidation. This amorphous iron phosphate material has low iron hydroxide content, uniform particle size distribution, small primary particle size, and low degree of agglomeration, which is beneficial for the subsequent preparation of iron phosphate with high specific surface area, small primary particle size, and low agglomeration. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 The images show the XRD patterns of amorphous iron phosphate prepared in Example 1, Comparative Example 1, and Comparative Example 2.

[0032] Figure 2 SEM image and particle distribution diagram of the amorphous iron phosphate prepared in Example 1.

[0033] Figure 3 SEM image and particle distribution diagram of anhydrous ferric phosphate prepared in Example 1.

[0034] Figure 4 The image shows the XRD pattern of anhydrous ferric phosphate prepared in Example 1.

[0035] Figure 5 SEM images and particle distribution diagrams of the amorphous iron phosphate prepared for Comparative Example 1.

[0036] Figure 6 SEM image and particle distribution diagram of anhydrous ferric phosphate prepared for Comparative Example 1.

[0037] Figure 7 The XRD pattern of anhydrous ferric phosphate prepared in Comparative Example 1 is shown.

[0038] Figure 8 SEM images and particle distribution diagrams of the amorphous iron phosphate prepared for Comparative Example 2.

[0039] Figure 9 SEM images and particle distribution diagrams of the anhydrous ferric phosphate prepared for Comparative Example 2.

[0040] Figure 10 The XRD pattern of anhydrous iron phosphate prepared in Comparative Example 2 is shown.

[0041] in, Figure 2 , 3 The particle distribution maps in 5, 6, 8, and 9 were obtained by processing and statistically analyzing the SEM images using ImageJ software. Detailed Implementation

[0042] Currently, the main production process for ferric phosphate on the market is a two-step method. First, a neutralization reaction occurs between a phosphorus source and a ferric source to produce amorphous ferric phosphate. Amorphous ferric phosphate has low crystallinity, with particles that are nearly spherical, and contains metal ions such as sulfate, ammonium, and manganese. Then, the amorphous ferric phosphate undergoes a crystal transformation while removing excess impurities to form dihydrate ferric phosphate. Dihydrate ferric phosphate has a relatively high specific surface area, typically around 50 μm. 2 The final dehydration process yields approximately [g] of anhydrous ferric phosphate, with spherical particles and secondary particles forming porous aggregates without a specific morphology. This process typically results in severe material agglomeration, large particles, low specific surface area, and significant difficulty in subsequent crushing. Furthermore, the numerous unfilled pores between particles reduce compaction density, and some particles may overcharge or over-discharge during charge-discharge processes, impacting electrochemical performance. Additionally, the ferric phosphate synthesis process is influenced by numerous factors, and current research on the products of amorphous ferric phosphate processes is limited.

[0043] During the synthesis of anhydrous ferric phosphate, the applicant discovered that synthesizing amorphous ferric phosphate with low ferric hydroxide content is beneficial for improving the particle size distribution of amorphous ferric phosphate and reducing agglomeration and primary particle size. Furthermore, this intermediate amorphous ferric phosphate is subsequently synthesized into anhydrous ferric phosphate through conventional crystallization and dewatering. During the crystallization process, inorganic acid diffuses into the interior of the intermediate amorphous ferric phosphate to react, removing ferric hydroxide and achieving crystallization. Since the intermediate amorphous ferric phosphate is amorphous ferric phosphate with low agglomeration and good dispersibility, the ferric phosphate obtained after crystallization and dewatering can maintain the morphological characteristics of amorphous ferric phosphate, enabling the synthesis of anhydrous ferric phosphate with smaller primary particle size, lower agglomeration, and higher specific surface area. Based on this, the present invention was completed.

[0044] The present invention provides an amorphous iron phosphate, wherein the X-ray diffraction pattern of the amorphous iron phosphate has a first diffraction peak θ1 and a second diffraction peak θ2 at 19~21° and 28~30° respectively, and the ratio of the peak intensity I1 of the first diffraction peak to the peak intensity I2 of the second diffraction peak is 0.8~0.91, and the amorphous iron phosphate is a spherical or near-spherical particle.

[0045] In the above technical solution, the characteristic peaks of 19~21° belong to ferric hydroxide and ferric phosphate, and the characteristic peaks of 28~30° belong to ferric phosphate. Therefore, the ratio of peak intensity I1 / I2 can reflect the content of ferric hydroxide in amorphous ferric phosphate.

[0046] In some preferred embodiments, the ratio of the peak intensity I1 of the first diffraction peak to the peak intensity I2 of the second diffraction peak is 0.82 to 0.905, for example, 0.82, 0.825, 0.83, 0.835, 0.84, 0.845, 0.85, 0.855, 0.86, 0.865, 0.87, 0.875, 0.88, 0.885, 0.89, 0.895, 0.90, 0.905, etc.

[0047] In some preferred embodiments, 95% of the primary particles of the amorphous iron phosphate have a particle size of less than 80 nm, more preferably between 20 and 80 nm, and even more preferably between 20 and 70 nm, such as 20-70 nm, 20-60 nm, etc. The primary particles of the amorphous iron phosphate have a small particle size and uniform particle size distribution.

[0048] This invention provides a method for preparing amorphous iron phosphate, comprising:

[0049] Solution A was prepared using a phosphorus source and a ferrous source. The pH and temperature of solution A were adjusted, and the reaction was carried out to obtain a grayish-white ferrous hydrogen phosphate slurry.

[0050] The grayish-white ferrous hydrogen phosphate slurry was oxidized to obtain a yellow amorphous ferric phosphate slurry. After solid-liquid separation and washing, amorphous ferric phosphate was obtained.

[0051] The applicant's research revealed that by first neutralizing ferrous hydrogen phosphate (Fe2+) and phosphorus (Fe3+) sources (through pH adjustment), and then forming a ferrous hydrogen phosphate precipitate through homogeneous nucleation, followed by further oxidation of the precipitate slurry, amorphous iron phosphate material with low iron hydroxide content can be obtained. This amorphous iron phosphate material exhibits uniform particle size distribution, low agglomeration, and small particle size. The applicant's research also found that the iron hydroxide content affects the particle uniformity, agglomeration degree, and primary particle size of the amorphous iron phosphate material. A lower iron hydroxide content in the prepared amorphous iron phosphate material is beneficial for improving the uniformity of particle size distribution, reducing agglomeration, and decreasing the primary particle size. Analysis showed that in this preparation method, because the ferrous hydrogen phosphate precipitate is preferentially synthesized, the formation of iron hydroxide crystal nuclei is suppressed. The resulting ferrous hydrogen phosphate solid can serve as a template, and oxidation yields amorphous iron phosphate with uniform particle distribution. Conversely, if oxidation is used first, iron hydroxide crystal nuclei are easily formed preferentially, and phosphoric acid and iron ions grow rapidly on their surface, agglomerating in a small area to form iron phosphate particles. The resulting amorphous iron phosphate particles are very large and unevenly distributed.

[0052] In the above preparation method, solution A containing phosphorus source and ferrous source can be prepared in various ways, as long as the phosphorus source and ferrous source in solution A do not undergo precipitation reaction. For example, a phosphorus source solution can be prepared separately using the phosphorus source, and a solution can be prepared using the ferrous source as a raw material. The ferrous source can be a water-soluble or water-insoluble raw material. When using a water-insoluble raw material, the water-insoluble ferrous source can be dissolved in acid to obtain a ferrous-containing solution, and then the two solutions can be mixed to obtain solution A. Alternatively, phosphorus source and ferrous source can be used as raw materials, and solution A can be prepared while ensuring that the phosphorus source and ferrous source do not undergo precipitation reaction. Specifically, this can be achieved by adjusting and controlling the pH of the solution. The pH adjuster can be an acidic solution or an alkaline solution. The acidic solution can be sulfuric acid, hydrochloric acid, etc., and the alkaline solution can be ammonia, urea, sodium hydroxide, etc.

[0053] In some preferred embodiments, the pH value of solution A is adjusted to 1.5~3.5, for example, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, etc.

[0054] In some embodiments, the reagent used to adjust the pH of solution A is one or more of ammonia, urea, and sodium hydroxide.

[0055] In some preferred embodiments, the temperature of solution A is adjusted to 40-60°C. o C, for example, 40℃, 45℃, 50℃, 55℃, 60℃, etc.

[0056] In some preferred embodiments, the phosphorus source is one or more of ammonium dihydrogen phosphate, phosphoric acid, and diammonium hydrogen phosphate;

[0057] In some preferred embodiments, the ferrous source is one or more of ferrous sulfate, ferrous chloride, ferrous nitrate, ferrous oxalate, iron powder, and ferrous oxide;

[0058] In some preferred embodiments, the molar ratio of phosphorus in the phosphorus source to iron in the iron source is 0.95 to 1.2:1.

[0059] In some preferred embodiments, the oxidant used in the oxidation is one or more of hydrogen peroxide, air, oxygen, and ozone.

[0060] Research has shown that the method for preparing amorphous iron phosphate provided by this invention requires a lower amount of oxidant than existing methods, which typically require more than 1.4 times the theoretically required amount. In some preferred embodiments, the amount of oxidant is 1.2 to 1.4 times the theoretically required amount, for example, 1.2, 1.3, or 1.4 times.

[0061] In some preferred embodiments, the mass percentage concentration of phosphorus in solution A is 2% to 5%, such as 2%, 3%, 4%, 5%, etc.

[0062] In some preferred embodiments, the iron concentration in solution A is 3% to 7% by mass, for example, 3%, 4%, 5%, 6%, 7%, etc.

[0063] In some preferred embodiments, the pH value of solution A is 0.5 < pH < 1.2, such as 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, etc. By keeping solution A within the above pH range, it is ensured that the phosphorus source and ferrous source do not undergo precipitation reaction.

[0064] In some preferred embodiments, the washing is performed using pure water; the conductivity of the wash water at the end of the washing process is not greater than 20000 μs / cm.

[0065] In some embodiments, the mass fraction of water in the amorphous ferric phosphate is 25-40%, such as 25%, 28%, 30%, 32%, 35%, 38%, 40%, etc.

[0066] This invention also provides a method for preparing anhydrous ferric phosphate, comprising:

[0067] The aforementioned amorphous ferric phosphate or the amorphous ferric phosphate prepared by the aforementioned preparation method is mixed with a phosphoric acid solution, heated to crystallize, filtered, washed with water, and calcined to obtain anhydrous ferric phosphate.

[0068] In the above technical solution, since the amorphous iron phosphate prepared above is used as a template, the amorphous iron phosphate has a low iron hydroxide content, resulting in uniform particle size distribution, low agglomeration, and small particle size. Consequently, after crystallization and calcination, the grain size and agglomeration of the amorphous iron phosphate are well maintained, thus obtaining anhydrous iron phosphate with small particle size, low agglomeration, and high specific surface area. 95% of the primary particles of the anhydrous iron phosphate have a particle size below 90 nm, preferably 30 nm. The specific surface area is 90 nm, more preferably 40~90 nm, and the specific surface area is 9~14 m² / g, such as 9 m² / g, 10 m² / g, 11 m² / g, 12 m² / g, 13 m² / g, 14 m² / g, etc. The tap density is 0.7~1.0 g / cm³, such as 0.7 g / cm³, 0.75 g / cm³, 0.8 g / cm³, 0.85 g / cm³, 0.9 g / cm³, 0.95 g / cm³, 1.0 g / cm³, etc.

[0069] The secondary particles of the anhydrous ferric phosphate have a D100 of less than 90 μm, more preferably 35-90 μm, such as 40 μm, 45 μm, 40 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, and 90 μm; a D99 of less than 50 μm, more preferably 20-50 μm, such as 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, and 50 μm; a D90 of less than 7.5 μm, more preferably 4-7.5 μm, such as 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, and 7.5 μm; and a D50 of 2-4 μm, such as 2 μm, 2.5 μm, 3 μm, 3.5 μm, and 4 μm.

[0070] In the preparation method of anhydrous ferric phosphate, the molar ratio of phosphoric acid to amorphous ferric phosphate in the phosphoric acid solution can be conventionally controlled, as long as the crystallization of amorphous ferric phosphate can be achieved. In some embodiments, this ratio can be 0.02~0.2∶1, for example 0.02∶1, 0.03∶1, 0.04∶1, 0.05∶1, 0.08∶1, 0.1∶1, 0.12∶1, 0.15∶1, 0.18∶1, 0.20∶1, etc.

[0071] In the preparation method of anhydrous ferric phosphate, the crystallization temperature corresponding to the heating crystallization is a conventional crystallization temperature in the art; in some embodiments, this temperature is 70~100°C. o C, for example, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃, 100℃, etc.

[0072] In the preparation method of anhydrous ferric phosphate, pure water can be used for washing; the conductivity of the wash water at the end of the washing process should not exceed 1000 μS / cm.

[0073] In the preparation method of anhydrous ferric phosphate, the purpose of calcination is dehydration, and conventional dehydration temperatures in the art can be used; in some embodiments, the calcination temperature is 500~650℃. o C, for example, 500℃, 520℃, 550℃, 580℃, 600℃, 620℃, 650℃, etc.

[0074] The present invention also provides anhydrous ferric phosphate, which is prepared using the aforementioned preparation method.

[0075] To facilitate understanding of the present invention, the invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0076] The tap density test methods for the products in the following embodiments and comparative examples are as follows:

[0077] Take approximately 100g of the sample to be tested and place it into a 250mL graduated cylinder. Tap the cylinder 10, 500, and 1250 times, recording the corresponding volumes V10, V500, and V1250, accurate to the smallest graduation. If the difference between V500 and V1250 is less than 2mL, take V1250 as the tapped volume; otherwise, increase the number of taps until the difference between two consecutive volume records is less than 2mL. Calculate the tapped density using the formula m / V, where m is the sample mass and V is the tapped volume.

[0078] The test method for the specific surface area of ​​the product is as follows:

[0079] Referring to GB / T 13390-2008 Determination of specific surface area of ​​metal powders - Nitrogen adsorption method, the specific surface area was measured using a specific surface area analyzer.

[0080] The test method for particle size distribution of the product is as follows:

[0081] Referencing HG / T 4701, the method for determining the particle size of iron phosphate for batteries (5.11); mix the sample thoroughly, weigh 0.1g of the sample, place it in a 100mL clean beaker containing 50mL of water, sonicate for 15min, and then use a Bettersize2600 laser particle size analyzer wet method system for detection.

[0082] The method for detecting the particle size distribution of 95% of primary particles in the product is as follows:

[0083] Import the SEM image into ImageJ software to obtain particle distribution statistics. The particle statistics are then fitted with the statistical distribution using Origin software to obtain the data distribution results. a±b represents the 95% primary particle size range, where a and b are the mean and standard deviation, respectively.

[0084] Example 1

[0085] An aqueous solution containing 0.345 mol of ammonium dihydrogen phosphate was added to an aqueous solution containing 0.3 mol of ferrous sulfate. Sulfuric acid was added to adjust the pH of the mixed solution to 1.0, resulting in a phosphorus-to-iron ratio of 1.15. The mixed solution contained 6.0% iron and 3.5% phosphorus by mass. The mixed solution was heated to 50°C. o C. Add ammonia to adjust the pH to 2.66 to form a grayish-white ferrous hydrogen phosphate slurry;

[0086] The above slurry was oxidized by adding hydrogen peroxide containing 0.21 mol of hydrogen peroxide, followed by filtration and washing until the conductivity of the wash water was no greater than 20000 μS / cm, yielding ferric phosphate yellow. X-ray diffraction analysis was performed on the obtained ferric phosphate yellow, and the results are shown in the figure below. Figure 1 As shown, from Figure 1 It can be seen that the peak intensity ratio between the characteristic peak at 19~21° and the characteristic peak at approximately 28~30° is 0.852; the SEM image and particle distribution diagram of the obtained amorphous iron phosphate yellow are shown below. Figure 2 As shown in the figure, the particles are evenly distributed, and the particle size of 95% of the amorphous iron phosphate particles is 32.7±4.5nm.

[0087] The ferric phosphate slurry and phosphoric acid were mixed and reacted at 95°C for 3 hours. The molar ratio of phosphoric acid to ferric phosphate was 0.03. The mixture was filtered and washed with pure water until the conductivity of the wash water was no more than 1000 μS / cm.

[0088] The filtered and washed product was dried and then heated at 550°C. o Anhydrous ferric phosphate was obtained by sintering at C for 2 hours. SEM images and particle size distribution diagrams of the anhydrous ferric phosphate are shown below. Figure 3 As shown in the figure, the primary particle size of the obtained anhydrous ferric phosphate is 57.8 ± 14.9 nm, and the particle size is consistent. The specific surface area is measured to be 12.3 m². 2 / g, tap density 0.85g / cm³ 3 The particle aggregation is minimal. The X-ray diffraction pattern of the obtained anhydrous ferric phosphate is shown below. Figure 4 As shown in Table 2, the particle size of the secondary particles is shown in Table 2.

[0089] Comparative Example 1

[0090] The raw materials and amounts used in this comparative example are exactly the same as those in Example 1, the only difference being the preparation method. The preparation method specifically includes:

[0091] A solution containing 0.345 mol ammonium dihydrogen phosphate, hydrogen peroxide containing 0.21 mol hydrogen peroxide, and ammonia water were added concurrently to an acidic aqueous solution containing 0.3 mol ferrous sulfate, with stirring. The phosphorus-to-ferrous ratio was 1.15. The pH of the reaction system was controlled at 2.2, and the reaction temperature was 50℃. A yellow precipitate was obtained, filtered, and washed until the conductivity of the wash water was no greater than 20000 μS / cm, yielding ferric phosphate yellow. X-ray diffraction analysis of the obtained ferric phosphate yellow was performed, and the results are shown in the figure below. Figure 1 As shown, from Figure 1 It can be seen that the peak intensity ratio of the characteristic peaks at 19~21° and 28~30° is 0.917; the SEM images and particle distribution diagrams of the obtained amorphous iron phosphate yellow are as follows. Figure 5 As shown in the figure, the particle distribution is good. The particle size of 95% of the amorphous iron phosphate particles is 133.98±27.8nm, the particle distribution is relatively wide, and some agglomeration occurs.

[0092] The ferric phosphate slurry and phosphoric acid were mixed and reacted at 95°C for 3 hours. The molar ratio of phosphoric acid to ferric phosphate was 0.03. The mixture was filtered and washed with pure water until the conductivity of the wash water was no more than 1000 μS / cm.

[0093] The filtered and washed product was dried and then sintered at 550℃ for 2 hours to obtain anhydrous ferric phosphate. SEM images and particle size distribution diagrams of anhydrous ferric phosphate are shown below. Figure 6 As shown in the figure, the 95% primary particle size of the obtained anhydrous ferric phosphate is 84.3 ± 19.9 nm, and the specific surface area is measured to be 8.2 m². 2 / g, tap density is 0.95g / cm³ 3 Slight aggregation was observed. The X-ray diffraction pattern of the obtained anhydrous ferric phosphate is shown below. Figure 7 As shown in Table 2, the particle size of the secondary particles is shown in Table 2.

[0094] In this comparative example, both the obtained ferric phosphate yellow material and anhydrous ferric phosphate exhibited slight agglomeration. Analysis suggests that the slight agglomeration may be due to the following: when ferrous phosphate, phosphorus, ammonia, and hydrogen peroxide are mixed, the formation of ferrous hydrogen phosphate and the oxidation of ferrous phosphate occur simultaneously, creating a competitive relationship. This can alleviate the formation of ferric hydroxide crystal nuclei and the growth of large yellow material particles to some extent. However, due to the oxidation of some ferrous ions to ferric ions, a certain amount of ferric hydroxide is generated. Phosphoric acid and ferric ions grow rapidly on the surface of ferric hydroxide, agglomerating in a small area to form ferric phosphate particles, thus resulting in slight agglomeration. During subsequent crystallization, the inorganic acid can diffuse into the interior of the yellow material to remove impurities such as ferric hydroxide. The morphology of the slightly agglomerated yellow material particles does not change significantly after crystallization, thus the anhydrous ferric phosphate also exhibits slight agglomeration.

[0095] Comparative Example 2

[0096] The raw materials and amounts used in this comparative example are exactly the same as those in Example 1, the only difference being the preparation method. The preparation method specifically includes:

[0097] Ferrous sulfate solution is obtained by adding hydrogen peroxide containing 0.21 mol hydrogen peroxide to an acidic aqueous solution containing 0.3 mol ferrous sulfate.

[0098] Ferric sulfate solution and an aqueous solution containing 0.345 mol of ammonium dihydrogen phosphate were mixed (iron-to-phosphorus ratio 1.15). No precipitate formed. Ammonia water was then added dropwise to adjust the pH to 2.1. The reaction was continued at 50°C. The mixture was filtered and washed until the conductivity of the wash water was no greater than 20,000 μS / cm, yielding ferric phosphate yellow. X-ray diffraction analysis of the obtained ferric phosphate yellow was performed, and the results are shown in the figure below. Figure 1 As shown, from Figure 1 It can be seen that the peak intensity ratio of the characteristic peaks at 19~21° and 28~30° is 0.951; the SEM images and particle distribution diagrams of the obtained amorphous iron phosphate yellow are as follows. Figure 8 As shown in the figure, the particles are severely agglomerated, and the particle size of 95% of the amorphous iron phosphate particles is above 165.8±51.2 nm.

[0099] The ferric phosphate slurry and phosphoric acid were mixed and reacted at 95°C for 3 hours. The molar ratio of phosphoric acid to ferric phosphate was 0.03. The mixture was filtered and washed with pure water until the conductivity of the wash water was no more than 1000 μS / cm.

[0100] The filtered and washed product was dried and then sintered at 550°C for 2 hours to obtain the ferric phosphate. SEM images and particle size distribution diagrams of the ferric phosphate are shown below. Figure 9 As shown, from Figure 9 It can be seen that the 95% primary particle size of the obtained anhydrous iron phosphate is 166.3 ± 62.1 nm. Figure 9 The specific surface area was measured to be 5.3 m². 2 / g, tap density is 0.98g / cm³ 3 The aggregation was severe. The X-ray diffraction pattern of the obtained anhydrous ferric phosphate is shown below. Figure 10 As shown in Table 2, the particle size of the secondary particles is shown in Table 2.

[0101] In this comparative example, both the obtained ferric phosphate yellow and anhydrous ferric phosphate exhibited severe agglomeration. Analysis suggests this may be because during the ammonia addition process, ferric iron precipitates to form ferric hydroxide, and ferric iron reacts with the phosphorus source to form ferric phosphate. However, due to the rapid nucleation rate of ferric hydroxide crystals, phosphate and iron ions grow rapidly on their surface, agglomerating in small areas to form ferric phosphate particles. The resulting ferric phosphate yellow has a large particle size and uneven particle distribution. During subsequent crystallization, inorganic acids can diffuse into the interior of the yellow to remove impurities such as ferric hydroxide. Therefore, the morphology of the severely agglomerated yellow does not change significantly after crystallization, resulting in severe agglomeration of the obtained anhydrous ferric phosphate.

[0102] Example 2

[0103] Add 0.315 mol of phosphoric acid to an aqueous solution containing 0.3 mol of ferrous sulfate, adjust the pH of the solution to 1.0 with ammonia, and the phosphorus-to-iron ratio is 1.05. The iron content is 6% by mass and the phosphorus content is 3.5% by mass.

[0104] Heat the mixture to 50°C. o C. Add ammonia to adjust the pH to 2.8 to form a grayish-white ferrous hydrogen phosphate slurry;

[0105] The above slurry was oxidized by adding hydrogen peroxide containing 0.21 mol of hydrogen peroxide, then filtered and washed until the conductivity of the wash water was no greater than 20000 μS / cm, to obtain iron phosphate yellow. X-ray diffraction analysis of the obtained amorphous iron phosphate yellow showed a peak intensity ratio of 0.881 for the characteristic peaks at approximately 19–21° and 28–30°, and the 95% primary particle size of the amorphous iron phosphate was 40.5 ± 6.6 nm.

[0106] Mix ferric phosphate slurry and phosphoric acid, 85 o The reaction proceeds for 3 hours at C, with a molar ratio of phosphoric acid to iron phosphate of 0.03. The mixture is then filtered and washed with pure water until the conductivity of the wash water is no greater than 1000 μS / cm.

[0107] The filtered and washed product was dried and then heated at 550°C. o The iron phosphate was obtained by sintering at C for 2 hours. Analysis showed that 95% of the primary particles of the obtained iron phosphate were distributed at 64.2 ± 15.6 nm, with a specific surface area of ​​10.2 m². 2 / g, tap density is 0.81g / cm³ 3 The particles showed minimal agglomeration. The secondary particle size of the obtained anhydrous ferric phosphate is shown in Table 2.

[0108] Example 3

[0109] An aqueous solution containing 0.303 mol of ammonium dihydrogen phosphate was added to an aqueous solution containing 0.3 mol of ferrous sulfate. Sulfuric acid was added to adjust the pH of the solution to 1.1. The iron content was 5% by mass, and the phosphorus content was 2.8% by mass; the phosphorus-iron ratio was 1.01. The above solution was heated to 50°C. o C. Add sodium hydroxide to adjust the pH to 2.0 to form a grayish-white ferrous hydrogen phosphate slurry;

[0110] The above slurry was oxidized by adding hydrogen peroxide containing 0.18 mol of hydrogen peroxide, followed by filtration and washing until the conductivity of the wash water was no greater than 20000 μS / cm, thus obtaining ferric phosphate yellow. X-ray diffraction analysis of the obtained amorphous ferric phosphate yellow showed a peak intensity ratio of 0.892 for the characteristic peaks at approximately 19–21° and 28–30°, and the 95% primary particle size of the amorphous ferric phosphate was 52.5 ± 7.2 nm.

[0111] Mix ferric phosphate slurry and phosphoric acid, react at 85℃ for 3 hours, with a molar ratio of phosphoric acid to ferric phosphate of 0.03, filter and wash with pure water until the conductivity of the wash water is no greater than 1000 μS / cm.

[0112] The filtered and washed product was dried and then heated at 550°C. o Sintering at C for 2 hours yielded the ferric phosphate. Analysis showed that 95% of the primary ferric phosphate particles were distributed at 65.4 ± 14.5 nm, with a specific surface area of ​​9.3 m². 2 / g, tap density is 0.92g / cm³ 3 The particles showed minimal agglomeration. The secondary particle size of the obtained anhydrous ferric phosphate is shown in Table 2.

[0113] Example 4

[0114] An aqueous solution containing 0.345 mol of ammonium dihydrogen phosphate was added to an aqueous solution containing 0.3 mol of ferrous sulfate. Sulfuric acid was added to adjust the pH of the solution to 0.6. The iron mass fraction was 5.5%, the phosphorus mass fraction was 3.5%, and the phosphorus-iron ratio was 1.15. The mixed solution was heated to 50°C. o C. Add ammonia to adjust the pH to 2.66 to form a grayish-white ferrous hydrogen phosphate slurry;

[0115] Oxygen was introduced into the above slurry for oxidation at a flow rate of 900 mL / h for 2 hours until complete oxidation. The slurry was then filtered and washed with pure water until the conductivity of the wash water was no greater than 20000 μS / cm, yielding ferric phosphate yellow. X-ray diffraction analysis of the obtained ferric phosphate yellow showed a peak intensity ratio of 0.871 between the characteristic peaks at 19–21° and approximately 28–30°. The particle distribution was uniform, with 95% of the primary particles of amorphous ferric phosphate having a particle size of 28.5 ± 5.8 nm, exhibiting minimal agglomeration.

[0116] The ferric phosphate slurry and phosphoric acid were mixed and reacted at 95°C for 3 hours. The molar ratio of phosphoric acid to ferric phosphate was 0.15. The mixture was filtered and washed with pure water until the conductivity of the wash water was no more than 1000 μS / cm.

[0117] The filtered and washed product was dried and then heated at 550°C. o Anhydrous ferric phosphate was obtained by sintering at C for 2 hours. 95% of the primary ferric phosphate particles had a particle size distribution of 61.5 ± 13.8 nm, and the specific surface area was measured to be 10.7 m². 2 / g, tap density is 0.88g / cm³ 3 The particles showed minimal agglomeration. The secondary particle size of the obtained anhydrous ferric phosphate is shown in Table 2.

[0118] Example 5

[0119] An aqueous solution containing 0.285 mol of ammonium dihydrogen phosphate was added to an aqueous solution containing 0.3 mol of ferrous sulfate. Sulfuric acid was added to adjust the pH of the solution to 0.6. The iron content was 3.8% by mass, the phosphorus content was 2% by mass, and the phosphorus-iron ratio was 0.95. The mixed solution was heated to 40°C. o C. Add ammonia to adjust the pH to 1.6 to form a grayish-white ferrous hydrogen phosphate solution;

[0120] The above slurry was oxidized by adding hydrogen peroxide containing 0.21 mol of hydrogen peroxide, followed by filtration and washing until the conductivity of the wash water was no greater than 20000 μS / cm, thus obtaining iron phosphate yellow. X-ray diffraction analysis of the obtained amorphous iron phosphate yellow showed a peak intensity ratio of 0.863 for the characteristic peaks at approximately 19–21° and 28–30°, and the 95% particle size of the amorphous iron phosphate was 41.8 ± 6.2 nm.

[0121] The ferric phosphate slurry and phosphoric acid were mixed and reacted at 95°C for 3 hours. The molar ratio of phosphoric acid to ferric phosphate was 0.15. The mixture was filtered and washed with pure water until the conductivity of the wash water was no more than 1000 μS / cm.

[0122] The filtered and washed product was dried and then heated at 550°C. o Anhydrous ferric phosphate was obtained by sintering at C for 2 hours. The 95% primary particle size of the obtained anhydrous ferric phosphate was 58.5 ± 14.5 nm, and the specific surface area was measured to be 10.5 m². 2 / g, tap density is 0.93g / cm³ 3 The particles showed minimal agglomeration. The secondary particle size of the obtained anhydrous ferric phosphate is shown in Table 2.

[0123] Example 6

[0124] An aqueous solution containing 0.348 mol of ammonium dihydrogen phosphate was added to an aqueous solution containing 0.3 mol of ferrous sulfate. Hydrochloric acid was added to adjust the pH of the solution to 1.1. The iron content was 7% by mass, the phosphorus content was 4.5% by mass, and the phosphorus-iron ratio was 1.16. The mixed solution was heated to 60°C. o C. Add ammonia to adjust the pH to 3.3 to form a grayish-white ferrous hydrogen phosphate solution;

[0125] The above slurry was oxidized by adding hydrogen peroxide containing 0.21 mol of hydrogen peroxide, followed by filtration and washing until the conductivity of the wash water was no greater than 20000 μS / cm, thus obtaining iron phosphate yellow. X-ray diffraction analysis of the obtained amorphous iron phosphate yellow showed a peak intensity ratio of 0.876 for the characteristic peaks at approximately 19–21° and 28–30°, and the 95% particle size of the obtained amorphous iron phosphate yellow was 31.5 ± 5.6 nm.

[0126] The ferric phosphate slurry and phosphoric acid were mixed and reacted at 95°C for 3 hours. The molar ratio of phosphoric acid to ferric phosphate was 0.15. The mixture was filtered and washed with pure water until the conductivity of the wash water was no more than 1000 μS / cm.

[0127] The filtered and washed product was dried and then heated at 550°C. o Anhydrous ferric phosphate was obtained by sintering at C for 2 hours. The primary particle size of the obtained anhydrous ferric phosphate was 95.4 ± 12.5 nm, and the specific surface area was measured to be 10.7 m². 2 / g, tap density is 0.78g / cm³ 3 The particles showed minimal agglomeration. The secondary particle size of the obtained anhydrous ferric phosphate is shown in Table 2.

[0128] The ratio of the peak intensity I1 of the characteristic peak at 19–21° to the peak intensity I2 of the characteristic peak at approximately 28–30°, the particle size of the primary particles of amorphous iron phosphate, the particle size of the primary particles of anhydrous iron phosphate, and the specific surface area of ​​anhydrous iron phosphate are shown in Table 1.

[0129] As can be seen from Table 1, compared with the amorphous iron phosphate prepared in each comparative example, the ratio of the characteristic peak intensity I1 at 19~21° and the characteristic peak intensity I2 at 28~30° of the X-ray diffraction pattern of the amorphous iron phosphate prepared in each example is lower (i.e., the iron hydroxide content is lower), and the primary particle size of the amorphous iron phosphate in each example is smaller and the particle size distribution is more uniform.

[0130] As can be seen from Table 1, compared with the anhydrous ferric phosphate prepared in each comparative example, the anhydrous ferric phosphate prepared in each example has a relatively higher specific surface area, a relatively narrower primary particle size distribution, a more uniform particle size distribution, and a smaller primary particle size; it can be seen that anhydrous ferric phosphate inherits the characteristics of the primary particles of amorphous ferric phosphate.

[0131] Table 1. Peak intensity ratio of amorphous iron phosphate and physical property parameters of anhydrous iron phosphate.

[0132]

[0133] As can be seen from Table 2, compared with the anhydrous ferric phosphate prepared in each comparative example, the secondary particle size of the anhydrous ferric phosphate prepared in each example is smaller, indicating that the anhydrous ferric phosphate agglomerates obtained in each example are relatively small.

[0134] Table 2 Characterization of secondary particle physical properties of anhydrous ferric phosphate

[0135]

[0136] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing amorphous iron phosphate, characterized in that, The X-ray diffraction pattern of the amorphous iron phosphate has a first diffraction peak θ1 and a second diffraction peak θ2 at 19~21° and 28~30°, respectively, and the ratio of the peak intensity I1 of the first diffraction peak to the peak intensity I2 of the second diffraction peak is 0.8~0.91; the amorphous iron phosphate is spherical or near-spherical particles; 95% of the primary particles of the amorphous iron phosphate have a particle size of less than 80 nm; the preparation method includes: Solution A was prepared using phosphorus and ferrous sources. The pH and temperature of solution A were adjusted, and the reaction proceeded to obtain a grayish-white ferrous hydrogen phosphate slurry. The pH of solution A was adjusted to 2.5–3, and the temperature of solution A was adjusted to 40–50°C. o C; the molar ratio of phosphorus source (calculated as phosphate) to ferrous source (calculated as iron) is 1.15~1.2:1; the mass percentage concentration of phosphorus in solution A is 3~5%; the mass percentage concentration of iron in solution A is 5~7%; The grayish-white ferrous hydrogen phosphate slurry is oxidized to obtain a yellow amorphous ferric phosphate slurry. Solid-liquid separation and washing are performed to obtain amorphous ferric phosphate. The oxidant used in the oxidation is one or more of hydrogen peroxide, air, oxygen, and ozone.

2. The method for preparing amorphous iron phosphate as described in claim 1, characterized in that, The reagent used to adjust the pH of solution A is one or more of ammonia, urea, and sodium hydroxide.

3. The method for preparing amorphous iron phosphate as described in claim 1, characterized in that, The phosphorus source is one or more selected from ammonium dihydrogen phosphate, phosphoric acid, diammonium hydrogen phosphate, and ammonium phosphate; and / or, The ferrous source is one or more of ferrous sulfate, ferrous chloride, ferrous nitrate, iron powder, ferrous oxide, and ferrous oxalate.

4. The method for preparing amorphous iron phosphate as described in claim 1, characterized in that, The amount of oxidant used is 1.2 to 1.4 times the theoretically required amount.

5. The method for preparing amorphous iron phosphate as described in claim 1, characterized in that, The pH value of solution A is 0.5 < pH < 1.2; The raw materials for preparing solution A also include an acidic solution or an alkaline solution; the acidic solution is one or more of sulfuric acid and hydrochloric acid, and the alkaline solution is one or more of ammonia water, urea solution, and sodium hydroxide solution.

6. The method for preparing amorphous iron phosphate as described in claim 1, characterized in that, The washing process uses pure water; the conductivity of the wash water at the end of the washing process is no greater than 20000 μS / cm.

7. A method for preparing anhydrous ferric phosphate, characterized in that, include: The amorphous ferric phosphate prepared by the method according to any one of claims 1 to 6 is mixed with a phosphoric acid solution, heated to crystallize, filtered, and washed with water. Calcination yields anhydrous ferric phosphate.

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