A method for preparing high-density iron phosphate by using agricultural ammonium purification

Abstract

The application provides a method for preparing high-compaction-type iron phosphate by utilizing agricultural monoammonium phosphate, and the method comprises the following steps: (1) performing controllable oxidative decomposition on organic matters in the agricultural monoammonium phosphate; (2) removing impurities from the agricultural monoammonium phosphate by ammonia, and obtaining a surfactant by utilizing a catalytic reaction of the decomposed organic matters; (3) performing emulsification and foaming on the phosphorus-ammonium clear solution, and obtaining iron phosphate precursors with different particle sizes by using an organic iron salt reaction; (4) aging the iron phosphate precursors to obtain iron phosphate dihydrate; and (5) obtaining anhydrous iron phosphate by high-temperature calcination. Specifically, the method is a method for simultaneously preparing high-compaction-type iron phosphate by utilizing associated organic matters in the agricultural monoammonium phosphate to convert the surfactant. The iron phosphate prepared by using the method has a spherical shape, a wide particle size distribution range, and is suitable for a high-compaction-type iron phosphate lithium preparation process. In addition, the method effectively solves the problem of the treatment of the organic matters in the agricultural monoammonium phosphate, and has good application value and economic value.

Description

Technical Field

[0001] This technical solution mainly relates to the fields of battery manufacturing and environmental engineering, specifically to a method for preparing high-pressure compacted iron phosphate using agricultural monoammonium phosphate purification. Background Technology

[0002] Iron phosphate (FePO4) is an important battery precursor, widely used in the preparation of cathode materials for lithium iron phosphate (LFP) batteries. Currently, the main methods for preparing FePO4 are liquid-phase and solid-phase methods. The liquid-phase method involves mixing soluble iron salts and phosphates and preparing FePO4 by controlling reaction conditions. However, this method typically requires the use of refined phosphoric acid or industrial phosphates, which not only increases the production cost of FePO4 but also generates large amounts of agricultural phosphoric acid and fertilizer-grade phosphate byproducts, increasing raw material costs and production pressure. To address these issues, some researchers have proposed using agricultural monoammonium phosphate (MAP) as a raw material to prepare FePO4. Agricultural MAP is a mixture containing numerous impurities, mainly composed of ammonium dihydrogen phosphate and ammonium sulfate. Patent CN115477293B uses agricultural MAP with ammonia water to adjust the pH to obtain a phosphorus source solution for preparing FePO4, thus achieving the development of a low-cost FePO4 process. This method reduces the cost of FePO4 on the one hand and increases the utilization value of agricultural MAP on the other. However, this method for preparing FePO4 still has some problems. First, agricultural MAP contains many impurity metal ions, which generate many impurity phases during the direct synthesis of FePO4, affecting the purity and performance of FePO4. Secondly, agricultural monoammonium phosphate (MAP) contains organic compounds such as humic acid and polyaliphatic hydrocarbon derivatives, which typically require oxidants to decompose them into H2O, CO2, and small-molecule organic compounds. This method is energy-intensive, consuming large amounts of oxidants, and the small-molecule organic compounds such as amino acids, peptides, and fatty alcohols produced by humic acid hydrolysis still have a certain impact on the subsequent synthesis of ferric phosphate materials. Therefore, how to effectively reduce the difficulty of handling organic compounds in agricultural MAP while ensuring product purity and performance, and at the same time avoiding the impact of residual organic compounds on ferric phosphate synthesis, is a significant challenge currently facing the technology of preparing ferric phosphate using agricultural MAP. Summary of the Invention

[0003] To achieve the above objectives, this invention provides a method for preparing high-pressure compacted lithium iron phosphate using agricultural monoammonium phosphate (MAP). This method achieves purification and impurity removal of MAP and degradation of organic macromolecules. The fatty acyl amino acids produced by humic acid decomposition undergo a quaternization reaction to obtain an amphoteric surfactant. The foaming principle of this surfactant is then used to prepare high-pressure compacted lithium iron phosphate. The prepared lithium iron phosphate exhibits a near-spherical morphology with a wide particle size distribution, making it suitable for high-pressure compacted lithium iron phosphate processes. The preparation method includes the following steps:

[0004] S1. Degreasing reaction: Dissolve powdered agricultural monoammonium phosphate in hot water at 50-80 ℃, filter to obtain clear agricultural monoammonium phosphate solution; add concentrated sulfuric acid with a mass fraction of 95-98% to the clear agricultural monoammonium phosphate solution to adjust the pH of the solution to 1-2; after stirring evenly, add hydrogen peroxide with a mass fraction of 5-10%, stir at 50-70 ℃ for 5-30 min, then add reducing agent, stir at 50-70 ℃ for 30 min to obtain degreasing solution.

[0005] S2, Ammoniation reaction: Alkali solution is introduced into the deoiled solution obtained in S1 to adjust the pH to 8-9. After stirring evenly, the supernatant is obtained by filtration. A catalyst is added to the supernatant, and the reaction is stirred under an inert atmosphere. After the reaction is completed, the purified ammonium phosphate solution is obtained by filtration.

[0006] S3. Oxidation reaction: An organic iron salt solution is used as the iron source, and the purified ammonium phosphate solution obtained in step S2 is used as the phosphorus source. The iron source and phosphorus source solutions are weighed according to the ratio of Fe:P = 1:1.2-1.5. The phosphorus source solution is rapidly stirred using an automatic constant speed stirrer at a speed of 1000 rpm / min and a stirring time of 10 s / cycle, and stirred 40 times at 50-70 ℃. Then, the iron source solution is added dropwise to the stirrer over 30-40 min, and the reaction is carried out at 300-400 rpm for 50-60 min. After standing and separating into layers, the lower layer of iron phosphate slurry is taken, filtered, and washed with water to obtain the iron phosphate precursor. The upper organic solvent is treated and reused for the preparation of the organic iron source.

[0007] S4. Aging reaction: The ferric phosphate precursor in S3 is dispersed in a 4-5‰ dilute phosphoric acid solution, and then reacted at 80-100℃ for 2-3 h to obtain ferric phosphate dihydrate slurry. After filtration and washing with water, ferric phosphate dihydrate is obtained.

[0008] S5, Dehydration reaction: Baking the ferric phosphate dihydrate in S4 at 80-100 ℃ for 4-8 h, crushing it, and then placing it in a quartz crucible and calcining it in a muffle furnace at 550-650 ℃ for 3-4 h to obtain anhydrous ferric phosphate.

[0009] In some embodiments, the hot water can fully dissolve most of the agricultural monoammonium phosphate, increasing solubility, and can also promote the suspension of some oil stains. Furthermore, it can make some insoluble impurities active under this temperature condition and distributed in the oil stains.

[0010] In step S1, the content of agricultural monoammonium phosphate (MAP) P2O5 is 50-70%, and the solid-liquid ratio is 1:2-1:3. Agricultural MAP often contains a large amount of humic acid, insoluble matter, and metal impurities. The amount of hydrogen peroxide used is 10-20% of the total weight of the solution. The reducing agent is one or more of ferrous sulfate, ferrous chloride, or ferrous nitrate, and the amount used is 1-2‰ of the total solution.

[0011] In step S1, humic acid is hydrolyzed under strongly acidic conditions to obtain long-chain amino acids and aliphatic hydrocarbon macromolecules. Hydrogen peroxide is used for controlled decomposition to obtain fatty acyl amino acid molecules with good consistency. Then, the fatty acyl amino acids undergo quaternization to obtain an amphoteric surfactant. The foaming effect of this surfactant is used to obtain an ammonium phosphate solution with good emulsification. In the subsequent dropwise addition of organic iron salt solution, the affinity between the organic bilayer on the surface of the "foam" and the organic iron salt is utilized, making it easy for the organic iron salt to react with phosphate ions on the foam surface. Different sizes of iron phosphate particles are obtained by using different foam sizes.

[0012] In step S2, the alkaline solution is one or more of sodium hydroxide, potassium hydroxide, and ammonia water; the catalyst is one or more of chloroacetic acid, bromoacetic acid, and sodium glycolate; and the reaction temperature is 80-90 ℃.

[0013] Adjusting the pH to 8-9 here can achieve complete precipitation of metal ions such as Fe, Mg, and Al in agricultural monoammonium phosphate, and also provide the necessary alkaline environment for the subsequent quaternization reaction of fatty acyl amino acids.

[0014] In step S3, the organic iron source is one or more of ferric phenylacetate, ferric benzoate, or ferric stearate.

[0015] The use of an organic iron source here can promote Fe 3+ Better with PO4 in the organic bilayer on the foam surface 3- By contacting and reacting, and utilizing the fusion and separation between bubbles of different sizes, the nucleation and growth of iron phosphate particles are promoted, thereby obtaining iron phosphate particles of different sizes. This iron phosphate material with a wide particle size distribution is suitable for high-pressure compaction lithium iron phosphate process.

[0016] In step S3, the upper organic solvent is simply filtered and then mixed with 0.1-0.5 mol·L⁻¹. -1 The solution is oxidized with potassium permanganate, then extracted and separated using deionized water, and used again for the preparation of organic iron sources.

[0017] The heating rate in step S5 is 5-10 ℃ / min.

[0018] The method for preparing high-pressure compacted ferric phosphate by purifying monoammonium phosphate in agriculture has the following advantages:

[0019] 1) This invention utilizes the hydrolysis reaction of humic acid under strongly acidic conditions to obtain long-chain amino acids and aliphatic hydrocarbon macromolecules. Controllable decomposition with hydrogen peroxide yields homogeneous fatty acyl amino acid molecules. Quaternization of these fatty acyl amino acids then produces an amphoteric surfactant. The foaming effect of this surfactant produces a phosphorus ammonium solution with good emulsifying properties. During the subsequent addition of an organic iron salt solution, the Fe in the organic iron source... 3+ PO4 in the organic bilayer on the foam surface 3- The reaction involves the fusion and separation of bubbles of different sizes, promoting the nucleation and growth of iron phosphate particles, thus yielding iron phosphate particles of varying sizes. The material synthesized using this method exhibits a near-spherical morphology with a wide range of iron phosphate particle size distributions (D90 of 10–20 μm), and can be used to synthesize high-compact lithium iron phosphate (compact density of 2.55–2.65 g·cm³). -1 ).

[0020] 2) The organic components in agricultural monoammonium phosphate are decomposed by controlled oxidation reaction to obtain multi-amino acid molecules for preparing surfactants. The foaming of the surfactant is used to obtain an emulsification reaction system. The "like dissolves like" principle is used to prepare iron phosphate in different sizes. This method has low economic cost and good practical and economic value. Attached Figure Description

[0021] Figure 1 SEM images of the iron phosphate prepared in Example 1 (left) and Comparative Example 1 (right).

[0022] Figure 2 The XRD patterns are those of the iron phosphate prepared in Example 1 and Comparative Example 1.

[0023] Figure 3 A schematic diagram of the growth mechanism of iron phosphate particles of different sizes. Detailed Implementation

[0024] To avoid repetition, the present invention will be further described below with reference to the accompanying drawings and specific embodiments, which is not intended to limit the scope of protection thereof.

[0025] The agricultural monoammonium phosphate used in this invention is a byproduct of the production of industrial-grade monoammonium phosphate by a phosphate chemical enterprise in Hubei Province. Specific indicators are shown in the table below:

[0026]

[0027] The method for preparing purified ammonium phosphate by removing impurities from agricultural monoammonium phosphate provided by the present invention includes the following steps:

[0028] S1. Degreasing reaction: Dissolve powdered agricultural monoammonium phosphate in hot water, filter to obtain clear agricultural monoammonium phosphate solution; add concentrated sulfuric acid to the obtained clear agricultural monoammonium phosphate solution to adjust the pH of the solution, stir evenly, add hydrogen peroxide, stir at high temperature, add reducing agent, stir at high temperature to obtain degreasing solution.

[0029] S2, Ammoniation reaction: Alkali solution is introduced into the deoiling solution obtained in S1 to adjust the pH, and after stirring evenly, the supernatant is obtained by filtration; a catalyst is added to the supernatant, and the reaction is stirred under an inert atmosphere. After the reaction is completed, the solution is filtered to obtain a purified ammonium phosphate solution.

[0030] The method for preparing ferric phosphate provided by the present invention includes the following steps:

[0031] S3. Oxidation reaction: An organic iron salt solution is used as the iron source, and the purified ammonium phosphate solution obtained in step S2 is used as the phosphorus source. The iron source and phosphorus source solutions are weighed according to the ratio of Fe:P = 1:1.2-1.5. An automatic constant speed stirrer is used to foam the phosphorus source, and then the iron source solution is slowly added dropwise to the stirrer. After the addition is completed, the mixture is allowed to stand and separate into layers. The lower layer of iron phosphate slurry is taken out, filtered, and washed with water to obtain the iron phosphate precursor. The upper organic solvent is treated and reused for the preparation of the organic iron source.

[0032] S4. Aging reaction: The ferric phosphate precursor in S3 is dispersed in a dilute phosphoric acid solution, and then aged under high temperature conditions to obtain ferric phosphate dihydrate slurry. After filtration and washing with water, ferric phosphate dihydrate is obtained.

[0033] S5, Dehydration reaction: The ferric phosphate dihydrate in S4 is baked at high temperature, crushed and placed in a quartz crucible, and calcined in a muffle furnace to obtain anhydrous ferric phosphate.

[0034] The method for preparing high-pressure lithium iron phosphate provided by the present invention includes the following steps:

[0035] S6. Mix the iron phosphate obtained in steps S3 to S5 with a lithium source and a carbon source, and spray dry to obtain a lithium iron phosphate precursor.

[0036] S7. The lithium iron phosphate precursor is sintered under an inert atmosphere to obtain high-pressure compact lithium iron phosphate.

[0037] Example 1

[0038] A1: Dissolve 800 g of agricultural monoammonium phosphate in 2000 g of hot water, stir well, and filter to obtain a clear agricultural monoammonium phosphate solution; add 17 g of concentrated sulfuric acid to the clear agricultural monoammonium phosphate solution to adjust the pH of the solution to 1.8; then add 25% hydrogen peroxide and stir at 70℃ for 10 min; then add 5 g of FeSO4 solid and stir at 70℃ for 30 min, and filter to obtain the supernatant.

[0039] A2: Ammonia water is bubbled into the clear liquid obtained in A1 to adjust the pH to 8.5. After stirring evenly, the supernatant is obtained by filtration. 5 g of chloroacetic acid is added to the supernatant and stirred under nitrogen atmosphere. After the reaction is completed, the solution is filtered to obtain purified ammonium phosphate solution.

[0040] A3: Using ferric benzoate as the iron source and the purified ammonium phosphate solution obtained in step A2 as the phosphorus source, the iron source and phosphorus source solutions were weighed according to the ratio of Fe:P = 1:1.2. The phosphorus source solution was rapidly stirred using an automatic constant-speed stirrer at a speed of 1000 rpm / min for 10 s / cycle, and stirred 40 times at 60 ℃. Subsequently, the iron source solution was added dropwise to the stirrer over 30 min, and the reaction was carried out at 300 rpm for 50 min. After standing and separating into layers, the lower layer of ferric phosphate slurry was taken, filtered, and washed with water to obtain the ferric phosphate precursor. The upper organic solvent was treated and reused for the preparation of the organic iron source.

[0041] A4: The ferric phosphate precursor in A3 was dispersed in 2000 g of dilute phosphoric acid solution with a mass fraction of 5‰, and then reacted at 90 °C for 3 h to obtain ferric phosphate dihydrate slurry. After filtration, it was washed with pure water to obtain ferric phosphate dihydrate.

[0042] A5: The ferric phosphate dihydrate in A4 was dried at 100 °C for 8 h, pulverized, and then placed in a quartz crucible and calcined at 650 °C for 4 h to obtain anhydrous ferric phosphate.

[0043] A6: Add the ferric phosphate obtained in steps A1-A5 to a stirred tank, add lithium carbonate, graphite black and glucose, wherein the molar ratio of FePO4:Li2CO3 is 1:0.6, and graphite black and glucose are added at 5% and 10% of the mass of ferric phosphate, respectively; use deionized water as the dispersion medium, stir for 1 h and then spray dry to obtain the lithium iron phosphate precursor;

[0044] A6. The lithium iron phosphate precursor was calcined at 800 °C for 12 h under a nitrogen atmosphere and then naturally cooled to room temperature to obtain lithium iron phosphate.

[0045] like Figure 1 As shown in (a), the iron phosphate particles in Example 1 are spherical with a particle size of 100 nm-4 μm and are staggered among each other, resulting in high space utilization.

[0046] Example 2-3

[0047] Examples 2-3 involved changing the mass of FeSO4 solid in step A1, while all other conditions remained the same as in Example 1. In Example 2, the mass of FeSO4 solid was 0 g; in Example 3, the mass of FeSO4 solid was 20 g. Under the same conditions (same as Example 1), the reaction yielded a supernatant, which was then used in subsequent steps to obtain anhydrous ferric phosphate.

[0048] Examples 4-5

[0049] Examples 4 and 5 involve changing the pH condition in step A1, while all other conditions remain the same as in Example 1. In Example 4, the pH was adjusted to 1.0; in Example 5, the pH was adjusted to 2.5. Under the same conditions (same as Example 1), the reaction yielded a supernatant, which was then used in subsequent steps to obtain anhydrous ferric phosphate.

[0050] Examples 6-7

[0051] Examples 6-7 involve changing the type of catalyst in step A2, while all other conditions remain the same as in Example 1. Bromoacetic acid was used in Example 6; sodium glycolate was used in Example 7. Under the same conditions (same as Example 1), a clear ammonium phosphate solution was obtained, which was then followed by subsequent steps to obtain anhydrous ferric phosphate.

[0052] Examples 8-9

[0053] Examples 8-9 involve changing the type of iron source in step A3, while all other conditions remain the same as in Example 1. Example 8 uses Fe2(SO4)3 solution; Example 9 uses ferric stearate solution. Under the same conditions (same as Example 1), a reaction slurry is obtained, which is then processed into anhydrous ferric phosphate through subsequent steps.

[0054] Comparative Example 1

[0055] Comparative Example 1 differed from Example 1 in that the type of agricultural monoammonium phosphate used in step A1 was changed, while all other conditions remained the same. Analytical grade monoammonium phosphate was used directly as the phosphorus source in Comparative Example 1. Under the same conditions (same as Example 1), the reaction yielded a supernatant, which was then used in subsequent steps to obtain anhydrous ferric phosphate.

[0056] like Figure 1 As shown in (b), the iron phosphate particles in Comparative Example 1 are nearly spherical, with a particle size of 100 nm-200 nm, and are uniform in size. Figure 3 As shown, the agricultural monoammonium phosphate solution after foaming treatment contains a lot of foam with varying bubble sizes and a large amount of PO4 on the surface. 3- Due to the unique organic bilayer characteristics of the bubble surface, Fe in the organic iron source... 3+ Easily reacts with PO4 on foam surfaces 3- The reaction occurs, and the fusion and separation of bubbles of different sizes promote the nucleation and growth of iron phosphate particles, thereby obtaining iron phosphate particles of different sizes.

[0057] Table 1 shows the effect data of the examples and comparative examples.

[0058] .

Claims

1. A method for preparing high-pressure compacted ferric phosphate using agricultural monoammonium phosphate purification, characterized in that, The method for preparing high-pressure compacted ferric phosphate by purifying agricultural monoammonium phosphate includes the following steps: S1. Degreasing reaction: Dissolve powdered agricultural monoammonium in water and filter to obtain clear agricultural monoammonium solution; add concentrated sulfuric acid to the obtained clear agricultural monoammonium solution to adjust the pH of the solution, stir evenly and then add hydrogen peroxide, stir at high temperature and then add reducing agent, stir at high temperature and then obtain degreasing solution. S2, Ammoniation reaction: Alkali solution is introduced into the deoiling solution obtained in S1 to adjust the pH, and after stirring evenly, the supernatant is obtained by filtration; a catalyst is added to the supernatant, and the reaction is stirred under an inert atmosphere. After the reaction is completed, the solution is filtered to obtain a purified ammonium phosphate solution. S3. Oxidation reaction: An organic iron salt solution is used as the iron source, and the purified ammonium phosphate solution obtained in step S2 is used as the phosphorus source. The iron source and phosphorus source solutions are weighed according to the ratio of Fe:P = 1:1.2-1.

5. An automatic constant speed stirrer is used to foam the phosphorus source, and then the iron source solution is slowly added dropwise to the stirrer. After the addition is completed, the mixture is allowed to stand and separate into layers. The lower layer of iron phosphate slurry is taken out, filtered, and washed with water to obtain the iron phosphate precursor. The upper organic solvent is treated and reused for the preparation of the organic iron source. S4. Aging reaction: The ferric phosphate precursor in S3 is dispersed in a dilute phosphoric acid solution, and then aged under high temperature conditions to obtain ferric phosphate dihydrate slurry. After filtration and washing with water, ferric phosphate dihydrate is obtained. S5, Dehydration reaction: The ferric phosphate dihydrate in S4 is baked at high temperature, crushed and placed in a quartz crucible, and calcined in a muffle furnace to obtain anhydrous ferric phosphate.

2. The method for preparing high-pressure compacted ferric phosphate using agricultural monoammonium phosphate purification according to claim 1, characterized in that, In step S1, the P2O5 content in the agricultural monoammonium phosphate is 50-70%, the water temperature is 50-80 ℃, and the solid-liquid ratio is 1:2-1:

3.

3. The method for preparing high-pressure compacted ferric phosphate using agricultural monoammonium phosphate purification according to claim 1, characterized in that, In step S1, the concentration of concentrated sulfuric acid is 95-98%, and the pH range is 1-2; the mass fraction of hydrogen peroxide is 5-10%, and the amount used is 10-20% of the total solution; the reducing agent is one or more of ferrous sulfate, ferrous chloride, or ferrous nitrate, and the amount used is 1-2‰ of the total solution.

4. The method for preparing high-pressure compacted ferric phosphate using agricultural monoammonium phosphate purification according to claim 1, characterized in that, In step S2, the alkaline solution is one or more of sodium hydroxide, potassium hydroxide, and ammonia water, and the endpoint pH is 8-9; the catalyst is one or more of chloroacetic acid, bromoacetic acid, and sodium glycolate, and the reaction temperature is 80-90 ℃.

5. The method for preparing high-pressure compacted ferric phosphate using agricultural monoammonium phosphate purification according to claim 1, characterized in that, The organic iron source in step S3 is one or more of ferric phenylacetate, ferric benzoate, or ferric stearate.

6. The method for preparing high-pressure compacted ferric phosphate using agricultural monoammonium phosphate purification according to claim 1, characterized in that, The automatic constant speed stirrer mentioned in step S3 is a commercially available device. The reaction temperature is 50-70 ℃, the stirring speed is 1000 rpm / min, the stirring time is 10 s / time, and the number of stirring times is 40. After the addition is completed, the stirring speed is 300-400 rpm, and the reaction time is 50-60 min.

7. The method for preparing high-pressure compacted ferric phosphate using agricultural monoammonium phosphate purification according to claim 1, characterized in that, In step S3, the upper organic solvent is simply filtered and then subjected to a solution of 0.1-0.5 mol·L⁻¹. -1 The solution is oxidized with potassium permanganate, then extracted and separated using deionized water, and used again for the preparation of organic iron sources.

8. A method for preparing high-pressure compacted ferric phosphate using agricultural monoammonium phosphate purification according to claim 1, characterized in that, In step S4, the concentration of phosphoric acid solution is 4-5‰, the stirring speed is 300-400 rpm, the reaction temperature is 80-100 ℃, and the reaction time is 2-3 h.

9. A method for preparing high-pressure compacted ferric phosphate using agricultural monoammonium phosphate purification according to claim 1, characterized in that, In step S5, the drying temperature is 80-100 ℃ and the drying time is 4-8 h; the calcination temperature is 550-650 ℃, the heating rate is 5-10 ℃ / min, and the holding time is 3-4 h.

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