Process for preparing iron phosphate from pure iron

Abstract

The invention discloses a process for preparing iron phosphate from pure iron, and relates to the technical field of chemical production. The method comprises the following specific steps: firstly, dissolving pure iron blocks in a phosphoric acid solution, and carrying out solid-liquid separation to obtain ferrous phosphate mother liquor; a proper amount of surfactant is added into the ferrous phosphate mother liquor, so that the dispersity and uniformity of particles in subsequent reaction are improved. Mixing the ferrous phosphate mother liquor with hydrogen peroxide, and adjusting with ammonia water to carry out oxidation reaction to obtain an iron phosphate crude product; and washing the crude product with hot water, mixing with water and phosphoric acid, and aging. And after aging, carrying out solid-liquid separation, washing with hot water, and drying to obtain high-purity iron phosphate. The method has the advantages of simple process, mild reaction conditions and stable product quality, and is suitable for industrial production.

Description

Technical Field

[0001] The invention relates to the technical field of chemical production, in particular to a process for preparing ferric phosphate from pure iron. Background Art

[0002] As a compound with excellent performance, iron phosphate (FePO4) is widely used in many fields, especially in lithium-ion battery cathode materials, catalysts, coatings and pigments. In the battery field, iron phosphate is often used as a precursor of lithium iron phosphate (LiFePO4) due to its high thermal stability and good electrochemical performance. Lithium iron phosphate has become one of the mainstream materials used in electric vehicles and energy storage systems due to its low cost, excellent cycle life and safety. Therefore, the quality of iron phosphate is directly related to the performance of battery materials.

[0003] In the prior art, the preparation method of iron phosphate mostly adopts the reaction of iron salt (such as ferrous sulfate, ferrous chloride) with phosphate solution to generate iron phosphate. For example, the patent document: A method for directly synthesizing lithium iron phosphate from ferrous sulfate (patent publication number: CN118026132A) includes the following method steps: S1, preparing ferrous sulfate into a 26-40wt% solution; S2, adding a dispersant to the ferrous sulfate solution; S3, adding a carbon source to the above solution to control the carbon content of the lithium iron phosphate to be 1-5wt%; S4, adding a lithium source to the above solution to control the iron-lithium molar ratio to be 0.98-1.05; S5, adding a phosphorus source to the above solution to control the iron-phosphorus molar ratio to be 0.965-1.02; S6, after mixing the above solution evenly, granulation is performed by spray drying; S7, the granulated product is subjected to curve sintering to obtain a carbon-coated lithium iron phosphate product.

[0004] However, this method has the following shortcomings: Particle agglomeration problem: Due to the rapid precipitation reaction during the reaction process, the generated iron phosphate particles are easy to agglomerate, resulting in uneven particle size distribution of the product, affecting the processability of the material and the performance stability in subsequent applications; Incomplete reaction: During the chemical reaction of iron salt and phosphate, the reaction is often not completely carried out due to the influence of the solution pH value, reaction temperature and reaction time, and unreacted precursors are easily left, which reduces the purity of the iron phosphate product and affects the electrochemical properties and catalytic activity of the final material.

[0005] In response to the above problems, some new technical solutions have been gradually proposed in recent years, such as the process of using pure iron to directly react with phosphoric acid solution to generate ferrous phosphate mother liquor. This method not only reduces the intermediate salt reaction steps, but also effectively avoids the problems of incomplete reaction of iron salts and impurities. By controlling the reaction conditions, such as the concentration of phosphoric acid solution, pH value and the amount of oxidant added, the morphology and purity of the generated iron phosphate particles can be better controlled, and the particle agglomeration phenomenon can be reduced. In addition, combined with the use of surfactants, the dispersibility of iron phosphate can be further improved to ensure that the particles are uniform and have good processability. Compared with traditional methods, this method has the advantages of simple process, strong operability, high product purity and environmental friendliness, and therefore has broad application prospects in industrial production. Summary of the invention

[0006] Based on the above technical background, the present invention has developed a new process using pure iron blocks as raw materials, which is simple to operate, has strong reaction controllability, and can effectively improve the purity and uniformity of particle size distribution of iron phosphate. This process can not only solve the above problems in the prior art, but also further improve the application performance of iron phosphate in the fields of battery materials and catalysts, and has important research and application value.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] A process for preparing ferric phosphate from pure iron, characterized in that it comprises the following steps:

[0009] 10 to 20 parts by weight of a pure iron block is dissolved in 100 to 120 parts by weight of a phosphoric acid solution at a dissolution temperature of 70 to 90° C., and a ferrous phosphate mother liquor is obtained after solid-liquid separation; a surfactant is added to the ferrous phosphate mother liquor, and after being stirred evenly, it is mixed with 10 to 15 parts by weight of hydrogen peroxide, and ammonia water is used to adjust the pH value, and an oxidation reaction is carried out to obtain a crude ferric phosphate product; the crude ferric phosphate product is washed 2 to 5 times with hot water at 60 to 80° C.; the washed crude ferric phosphate product is mixed with water and 5 to 10 parts by weight of phosphoric acid, and aged for 4 to 6 hours; after aging, the solid-liquid is separated, and the product is washed again with hot water at 60 to 80° C., and dried to obtain a finished ferric phosphate product.

[0010] In some embodiments, the phosphoric acid solution has a concentration of 10% to 30%.

[0011] In some embodiments, the surfactant is added in an amount of 0.1 to 2 wt % of the pure iron block.

[0012] In some embodiments, the preparation method of the surfactant is:

[0013] By weight, 17-34 parts of trimethylvinyl ammonium bromide, CAS number: 10603-92-6; 0.02-0.5 parts of 4-methylacrylamidosalicylic acid, CAS number: 50512-48-6; 3-8 parts of 11-ferrocenyl-1-undecanethiol, CAS number: 127087-36-9; 0.8-2 parts of benzoyl peroxide and 300-400 parts of toluene are added into a reaction kettle, stirred at 70-90° C. for 100-160 minutes, and toluene is removed by distillation to obtain a surfactant.

[0014] In some embodiments, the concentration of the hydrogen peroxide is 5% to 10%.

[0015] In some embodiments, the pH value of the ammonia water is adjusted to 1.3-1.6.

[0016] In some embodiments, the oxidation reaction temperature is 20 to 40° C., and the reaction time is 1 to 3 hours.

[0017] In some embodiments, the aging temperature is 50 to 70°C.

[0018] In some embodiments, the drying temperature is 100-120°C.

[0019] Preparation mechanism of the above surfactants:

[0020] 1) Click chemistry reaction:

[0021] The trimethylvinyl ammonium bromide and the thiol group of 11-ferrocenyl-1-undecanethiol form a new chemical bond through a click chemistry reaction.

[0022] 2) Formation of surfactant:

[0023] The product generated by the click chemistry reaction further reacts with 4-methacrylamidosalicylic acid to finally form a surfactant grafted with salicylic acid, ferrocenyl and polytrimethylammonium bromide. This surfactant combines multiple functional groups, including salicylic acid groups, ferrocenyl groups and quaternary ammonium salt cationic groups, which give the surfactant unique physical and chemical properties.

[0024] The surfactant has the following effects:

[0025] 1) Promote the formation of spherical iron phosphate:

[0026] Surfactants can significantly improve the growth process of iron phosphate crystals. By adjusting the concentration and type of surfactants, the morphology of iron phosphate crystals can be controlled so that they tend to form a spherical structure. Spherical iron phosphate has a higher packing density and better fluidity than other forms of iron phosphate, which is of great significance in practical applications.

[0027] 2) Improve the morphology of iron phosphate:

[0028] Surfactants can reduce the surface energy of iron phosphate crystals, thereby affecting their growth habits. By introducing specific surfactants, iron phosphate crystals can be made to grow in a specific direction, thereby improving their morphology.

[0029] 3) Improve the performance of iron phosphate:

[0030] Surfactants can not only improve the morphology of iron phosphate, but also improve its electrochemical performance. For example, the reversible transformation of surfactants between the reduced state and the oxidized state can be achieved through electrochemical methods, thereby regulating the electrochemical behavior of iron phosphate. Surfactants can also enhance the stability and dispersibility of iron phosphate, making it more stable and reliable during application.

[0031] Technical effects:

[0032] The preparation method of the present invention can effectively improve the dispersibility and uniformity of iron phosphate particles and avoid particle agglomeration. At the same time, by strictly controlling the pH and temperature conditions of the oxidation reaction, the purity and quality stability of iron phosphate can be guaranteed. The method is simple in process, easy to operate, and suitable for large-scale industrial production. DETAILED DESCRIPTION

[0033] The embodiments of the present application will be described in detail below in conjunction with specific examples, but it will be appreciated by those skilled in the art that the following examples are only used to illustrate the present application and should not be considered as limiting the scope of the present application. If specific conditions are not specified in the examples, they are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0034] The test method involved in the present invention is as follows:

[0035] 1. Particle size distribution test: Use a laser particle size analyzer to measure the particle size distribution of the iron phosphate sample. Take an appropriate amount of dried iron phosphate sample, disperse it in deionized water, use ultrasonic vibration for 1 minute to ensure that the particles are fully dispersed, and then perform a particle size test. Record the average particle size and particle size distribution curve of the sample.

[0036] 2. Product purity test: Use inductively coupled plasma optical emission spectrometer (ICP-OES) to analyze the main components and impurities in the iron phosphate sample. Take an appropriate amount of sample for acid dissolution, dilute after dissolution, and determine the iron and phosphorus content in the sample after calibration with a standard solution. Determine the purity of the product by calculating the molar ratio of iron to phosphorus and detecting the impurity content.

[0037] Example 1

[0038] A process for preparing ferric phosphate from pure iron, characterized in that it comprises the following steps:

[0039] 10 g of a pure iron block is dissolved in 100 g of a phosphoric acid solution at a dissolution temperature of 70°C, and a ferrous phosphate mother liquor is obtained after solid-liquid separation; a surfactant is added to the ferrous phosphate mother liquor, and the mixture is mixed with 10 g of hydrogen peroxide after uniform stirring, and the pH is adjusted with ammonia water to perform an oxidation reaction to obtain a crude ferric phosphate product; the crude ferric phosphate product is washed twice with hot water at 60°C; the washed crude ferric phosphate product is mixed with water and 5 g of phosphoric acid, and aged for 4 hours; after aging, the solid-liquid is separated, and the mixture is washed again with hot water at 60°C, and the finished ferric phosphate product is obtained after drying.

[0040] The concentration of the phosphoric acid solution is 10%.

[0041] The surfactant is added in an amount of 0.5 wt % of the pure iron block.

[0042] The preparation method of the surfactant is:

[0043] Add 17 g of trimethylvinyl ammonium bromide, CAS No.: 10603-92-6; 0.02 g of 4-methylacrylamidosalicylic acid, CAS No.: 50512-48-6; 3 g of 11-ferrocenyl-1-undecanethiol, CAS No.: 127087-36-9; 0.8 g of benzoyl peroxide and 300 g of toluene into a reaction kettle, stir at 70° C. for 100 minutes, and distill off toluene to obtain a surfactant.

[0044] The concentration of the hydrogen peroxide is 5%.

[0045] The pH value of the ammonia water is adjusted to 1.3.

[0046] The oxidation reaction temperature is 20° C. and the reaction time is 1 h.

[0047] The aging temperature is 50°C

[0048] The drying temperature is 100°C.

[0049] Example 2

[0050] A process for preparing ferric phosphate from pure iron, characterized in that it comprises the following steps:

[0051] 15 g of a pure iron block is dissolved in 110 g of a phosphoric acid solution at a dissolution temperature of 80° C., and a ferrous phosphate mother liquor is obtained after solid-liquid separation; a surfactant is added to the ferrous phosphate mother liquor, and the mixture is mixed with 12 g of hydrogen peroxide after uniform stirring, and the pH is adjusted with ammonia water to perform an oxidation reaction to obtain a crude ferric phosphate product; the crude ferric phosphate product is washed three times with hot water at 70° C.; the washed crude ferric phosphate product is mixed with water and 7 g of phosphoric acid, and aged for 5 hours; after aging, the solid-liquid is separated, and the product is washed again with hot water at 70° C., and dried to obtain a finished ferric phosphate product.

[0052] The concentration of the phosphoric acid solution is 20%.

[0053] The surfactant is added in an amount of 1 wt % of the pure iron block.

[0054] The preparation method of the surfactant is:

[0055] Add 23g trimethylvinyl ammonium bromide, CAS No.: 10603-92-6; 0.2g 4-methylacrylamidosalicylic acid, CAS No.: 50512-48-6; 5g 11-ferrocenyl-1-undecanethiol, CAS No.: 127087-36-9; 1.4g benzoyl peroxide and 350g toluene into a reaction kettle, stir at 80°C for 135 minutes, distill off toluene, and obtain a surfactant.

[0056] The concentration of the hydrogen peroxide is 7%.

[0057] The pH value of the ammonia water is adjusted to 1.4.

[0058] The oxidation reaction temperature is 30° C. and the reaction time is 2 h.

[0059] The aging temperature is 60°C

[0060] The drying temperature is 110°C.

[0061] Example 3

[0062] A process for preparing ferric phosphate from pure iron, characterized in that it comprises the following steps:

[0063] 15 g of a pure iron block is dissolved in 110 g of a phosphoric acid solution at a dissolution temperature of 80° C., and a ferrous phosphate mother liquor is obtained after solid-liquid separation; a surfactant is added to the ferrous phosphate mother liquor, and the mixture is mixed with 14 g of hydrogen peroxide after uniform stirring, and the pH is adjusted with ammonia water to perform an oxidation reaction to obtain a crude ferric phosphate product; the crude ferric phosphate product is washed with hot water at 70° C. for 4 times; the washed crude ferric phosphate product is mixed with water and 9 g of phosphoric acid, and aged for 5 hours; after aging, the solid-liquid is separated, and the product is washed with hot water at 70° C. again, and dried to obtain a finished ferric phosphate product.

[0064] The concentration of the phosphoric acid solution is 20%.

[0065] The surfactant is added in an amount of 1.5 wt % of the pure iron block.

[0066] The preparation method of the surfactant is:

[0067] Add 28g of trimethylvinyl ammonium bromide, CAS No.: 10603-92-6; 0.4g of 4-methylacrylamidosalicylic acid, CAS No.: 50512-48-6; 7g of 11-ferrocenyl-1-undecanethiol, CAS No.: 127087-36-9; 1.8g of benzoyl peroxide and 350g of toluene into a reaction kettle, stir at 80°C for 150 minutes, and distill off toluene to obtain a surfactant.

[0068] The concentration of the hydrogen peroxide is 9%.

[0069] The pH value of the ammonia water is adjusted to 1.5.

[0070] The oxidation reaction temperature is 30° C. and the reaction time is 2 h.

[0071] The aging temperature is 60°C

[0072] The drying temperature is 110°C.

[0073] Example 4

[0074] A process for preparing ferric phosphate from pure iron, characterized in that it comprises the following steps:

[0075] 20 g of a pure iron block is dissolved in 120 g of a phosphoric acid solution at a dissolution temperature of 90° C., and a ferrous phosphate mother liquor is obtained after solid-liquid separation; a surfactant is added to the ferrous phosphate mother liquor, and the mixture is mixed with 15 g of hydrogen peroxide after being stirred evenly, and the pH is adjusted with ammonia water to perform an oxidation reaction to obtain a crude ferric phosphate product; the crude ferric phosphate product is washed with 80° C. hot water for 5 times; the washed crude ferric phosphate product is mixed with water and 10 g of phosphoric acid, and aged for 6 hours; after aging, the solid-liquid is separated, and the mixture is washed again with 80° C. hot water, and dried to obtain a finished ferric phosphate product.

[0076] The concentration of the phosphoric acid solution is 30%.

[0077] The surfactant is added in an amount of 2 wt % of the pure iron block.

[0078] The preparation method of the surfactant is:

[0079] Add 34g trimethylvinyl ammonium bromide, CAS No.: 10603-92-6; 0.5g 4-methylacrylamidosalicylic acid, CAS No.: 50512-48-6; 8g 11-ferrocenyl-1-undecanethiol, CAS No.: 127087-36-9; 2g benzoyl peroxide and 400g toluene into a reaction kettle, stir at 90°C for 160 minutes, and distill off toluene to obtain a surfactant.

[0080] The concentration of the hydrogen peroxide is 10%.

[0081] The pH value of the ammonia water is adjusted to 1.6.

[0082] The oxidation reaction temperature is 40° C. and the reaction time is 3 h.

[0083] The aging temperature is 70°C

[0084] The drying temperature is 120°C.

[0085] Comparative Example 1

[0086] In this comparative example, no surfactant was added during the preparation of ferric phosphate for comparison, and the remaining steps and processes were consistent with those in Example 1.

[0087] Comparative Example 2

[0088] In this comparative example, 11-ferrocenyl-1-undecanethiol was not added during the preparation of the surfactant for comparison, and the remaining steps and processes were the same as those in Example 1.

[0089] Comparative Example 3

[0090] In this comparative example, 4-methylacrylamidosalicylic acid was not added during the preparation of the surfactant for comparison, and the remaining steps and processes were the same as those in Example 1.

[0091] Test results:

[0092]

[0093] Through the above tests, it can be concluded that the embodiment significantly improves the dispersibility and purity of iron phosphate particles by adding surfactants and controlling the pH and temperature of the oxidation reaction. The particle size is uniform and there is no agglomeration phenomenon, and the purity is more than 99.5%. Compared with the comparative example, the product quality stability of the embodiment is higher and it is suitable for the field of lithium-ion battery positive electrode materials.

[0094] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A process for preparing ferric phosphate from pure iron, characterized in that: The following steps are involved: 10 to 20 parts by weight of a pure iron block is dissolved in 100 to 120 parts by weight of a phosphoric acid solution at a dissolution temperature of 70 to 90° C., and a ferrous phosphate mother liquor is obtained after solid-liquid separation; a surfactant is added to the ferrous phosphate mother liquor, and after being stirred evenly, it is mixed with 10 to 15 parts by weight of hydrogen peroxide, and ammonia water is used to adjust the pH value, and an oxidation reaction is carried out to obtain a crude ferric phosphate product; the crude ferric phosphate product is washed 2 to 5 times with hot water at 60 to 80° C.; the washed crude ferric phosphate product is mixed with water and 5 to 10 parts by weight of phosphoric acid, and aged for 4 to 6 hours; after aging, the solid-liquid is separated, and the product is washed again with hot water at 60 to 80° C., and dried to obtain a finished ferric phosphate product.

2. The process for preparing ferric phosphate from pure iron according to claim 1, characterized in that: The concentration of the phosphoric acid solution is 10% to 30%.

3. The process for preparing ferric phosphate from pure iron according to claim 1, characterized in that: The surfactant is added in an amount of 0.1-2 wt % of the pure iron block.

4. The process for preparing ferric phosphate from pure iron according to claim 1, characterized in that: The preparation method of the surfactant is: According to weight, 17-34 parts of trimethylvinyl ammonium bromide, 0.02-0.5 parts of 4-methylacrylamidosalicylic acid, 3-8 parts of 11-ferrocenyl-1-undecanethiol, 0.8-2 parts of benzoyl peroxide and 300-400 parts of toluene are added into a reaction kettle, stirred at 70-90° C. for 100-160 minutes, and toluene is removed by distillation to obtain a surfactant.

5. The process for preparing ferric phosphate from pure iron according to claim 1, characterized in that: The concentration of the hydrogen peroxide is 5% to 10%.

6. The process for preparing ferric phosphate from pure iron according to claim 1, characterized in that: The pH value of the ammonia water is adjusted to 1.3-1.

6.

7. The process for preparing ferric phosphate from pure iron according to claim 1, characterized in that: The oxidation reaction temperature is 20-40° C., and the reaction time is 1-3 hours.

8. The process for preparing ferric phosphate from pure iron according to claim 1, characterized in that: The aging temperature is 50-70°C.

9. The process for preparing ferric phosphate from pure iron according to claim 1, characterized in that: The drying temperature is 100-120°C.

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