Process for the preparation of basic ammonium iron phosphate

Abstract

The application relates to a preparation method of basic ammonium iron phosphate, which comprises the following steps: dropping a phosphorus salt solution with a N:P molar ratio of 0.95-1.5 and containing an oxidant into a ferrous sulfate solution above 93 DEG C, generating a precipitate while dropping and oxidizing, rapidly performing crystal transformation on the generated amorphous basic ammonium iron phosphate, generating the first crystal as a crystal seed, inducing the subsequent amorphous crystal to perform crystal transformation, and obtaining the basic ammonium iron phosphate. In the application, a part of particle crystal transformation is first allowed, the subsequent particle crystal transformation is induced as a crystal seed, the nucleation and growth of the crystal are in a stable state in the whole process, the ordered growth of the particles is facilitated, the basic ammonium iron phosphate product with uniform particle, good sphericity and pure phase is easily obtained, the whole process is simple, easy to operate, high in efficiency and low in cost.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium batteries and relates to a method for efficiently preparing basic ammonium ferric phosphate. Background Art

[0002] Lithium iron phosphate (LIFP), an important cathode material for lithium-ion batteries, offers advantages such as low cost, high safety, and excellent cycle performance. A variety of LFP cathode material preparation processes exist. Among them, LFP prepared via a carbothermal reduction reaction using ferric phosphate as a precursor has been widely used in the production of LiFePO4 / C materials. As a key LFP precursor, the quality of ferric phosphate significantly impacts its performance. The current mainstream process uses anhydrous ferric phosphate (AFP) as a precursor by drying and calcining ferric phosphate dihydrate. However, this anhydrous AFP easily aggregates and melts during the drying and calcining process, resulting in a low specific surface area and large particle size. This makes grinding and dispersion difficult during LFP preparation, and the resulting LFP particles are generally larger. Some processes use basic ammonium ferric phosphate (AFP) as a precursor. During the high-temperature LFP preparation process, it decomposes to produce water vapor and ammonia, which act as pores. The slightly positive pressure generated by these gases inhibits particle growth and aggregation, resulting in smaller LFP particles and improved conductivity. The invention provides a method for efficiently preparing basic ammonium phosphate. The method has the advantages of simple process, low cost, high crystallinity, small and uniform particle size, and nanometer primary particles.

[0003] Patent International Publication No. WO2022 / 127322 Al, the preparation process is to first dissolve the iron phosphate waste with acid to obtain trivalent iron and phosphorus-containing solution, and then adjust the pH value with alkali to obtain amorphous iron phosphate yellow filter cake. After rinsing, aging, pulping, heating, adding phosphoric acid and alkali solution to react, washing, filtering and drying, basic ammonium ferric phosphate is obtained. This process provides a way to treat waste. Iron and phosphorus are in the same state. Adding alkali solution will cause a large amount of nucleation and growth, and the particle size is difficult to control. At the same time, the two-step method is used, the process is cumbersome and the cost is high.

[0004] Patent CN114772571 A uses two rinses and two-step aging or multi-step aging to prepare basic ammonium ferric phosphate, which has a long and complicated process and high cost.

[0005] Patents CN 109860530 A and CN 102167305 B mix an iron source, a titanium source, a phosphorus source, an oxidant, and a precipitant to obtain a mixed solution, and adjust the pH to obtain precipitation. This will cause a large amount of nucleation and growth, and the particles are prone to agglomeration and growth. In addition, the precipitation pH is high, which easily generates iron hydroxide impurities, which decompose into magnetic substances in the later iron-lithium preparation process, increasing safety risks.

[0006] Patent CN 11348638 A uses iron blocks and sulfuric acid to produce a ferrous sulfate solution. Ammonia and hydrazine hydrate are added to adjust the pH to 8-9.5, followed by phosphoric acid to adjust the pH to 6.8-7.2. The resulting slurry is washed, phosphoric acid is added to adjust the pH to 2-3, and the temperature is raised while air is introduced before washing to produce basic ammonium ferric phosphate. This process is lengthy, requiring two washes and consuming large amounts of water. The addition of large amounts of ammonia and phosphoric acid for repeated pH adjustment and the use of iron blocks as an iron source result in very high raw material costs. The ferrous hydroxide colloidal particles produced in the initial step are small and difficult to wash, and the subsequent introduction of air as an oxidant makes it difficult to ensure complete oxidation, resulting in the inevitable formation of ferrous phosphate precipitation in the product.

[0007] Therefore, how to efficiently prepare basic ammonium ferric phosphate is a technical problem that needs to be solved. Summary of the Invention

[0008] In order to solve the problems existing in the above-mentioned prior art, the present invention provides a preparation method of basic ammonium ferric phosphate product with high efficiency, low cost, easy operation and easy acquisition of uniform particles, good sphericity and pure phase.

[0009] The present invention is achieved through the following technical solutions:

[0010] The above-mentioned preparation method of basic ammonium ferric phosphate is to dropwise add a phosphate solution containing an oxidant and having an N:P molar ratio of 0.95-1.5 to a ferrous sulfate solution above 93°C, generate a precipitate while adding oxidation, and the generated amorphous basic ammonium ferric phosphate rapidly undergoes crystal transformation. The first generated crystals serve as crystal seeds to induce subsequent amorphous crystals to undergo crystal transformation, thereby producing basic ammonium ferric phosphate.

[0011] The preparation method of basic ammonium ferric phosphate comprises the following steps: after the dropwise addition is completed, the slurry is kept warm at above 93°C until the color of the slurry changes from yellow to off-white, and the heat is continued until the pH of the solution is 0.9-1.3 after the heat preservation is completed, and the solution is rinsed, squeezed and dried to obtain basic ammonium ferric phosphate with a moisture content of less than 1%.

[0012] The preparation method of basic ammonium ferric phosphate comprises the following specific steps:

[0013] 1) Prepare ferrous sulfate solution;

[0014] 2) Prepare a phosphate solution with an N:P molar ratio of 0.95-1.5;

[0015] 3) Measure the ferrous sulfate solution and phosphate solution according to Fe:P=1.14~1.33, add the measured ferrous sulfate solution into the stainless steel reactor at one time, heat it to above 93℃, and then add the measured phosphate solution dropwise to the reactor at a uniform speed. After the addition is completed, heat it to above 93℃ and keep it warm until the color of the slurry changes from yellow to off-white. Continue to keep it warm for 1h-2h. After the insulation is completed, the pH of the solution is 0.9-1.3;

[0016] 4) Rinse and filter press;

[0017] 5) Pressing to obtain a filter cake with a moisture content of about 35-40%;

[0018] 6) Drying to obtain basic ammonium ferric phosphate with a moisture content of less than 1%.

[0019] The preparation method of basic ammonium ferric phosphate, wherein: the preparation of the ferrous sulfate solution is to dissolve solid ferrous sulfate in water at 60°C, add iron powder or iron sheet after it is fully dissolved, heat to 85-90°C, react until the pH value reaches 3.5-4.5, and then filter through a plate and frame filter press to obtain a clear ferrous sulfate solution with an iron concentration of 1 mol / L.

[0020] The preparation method of basic ammonium ferric phosphate, wherein: the preparation of the phosphate salt solution is based on one or more of monoammonium phosphate, diammonium phosphate, and phosphoric acid as the phosphorus source, ammonia water as the alkali solution, and hydrogen peroxide as the oxidant, wherein the phosphorus concentration is 1.5 mol / L and the hydrogen peroxide concentration is 0.9-1 mol / L.

[0021] The preparation method of basic ammonium ferric phosphate, wherein: the rinsing and filtration uses a plate and frame filter press, and the water washing is carried out until the end point conductivity is 400us / cm.

[0022] The preparation method of basic ammonium ferric phosphate, wherein: the pressing is to pulp and disperse the rinsed filter cake, and after dispersing for about 50 minutes, pump it into a pressing filter press with a pressing pressure of 4-5MPa.

[0023] The preparation method of basic ammonium ferric phosphate, wherein: the drying is to soften the filter cake through a forced feeder and enter the flash drying, and the temperature of the mixing chamber is controlled at 130-160°C.

[0024] Beneficial effects:

[0025] The present invention drips a phosphate solution containing an oxidant and having a certain N:P molar ratio into a high-temperature ferrous sulfate solution, and generates a precipitate while the oxidation is being added. Due to the high reaction temperature, the generated amorphous basic ammonium ferric phosphate rapidly undergoes crystal transformation. The first generated crystals serve as crystal seeds to induce subsequent amorphous crystals to undergo crystal transformation, which is conducive to the rapid progress of the reaction. There is no need to first synthesize the amorphous basic ammonium ferric phosphate, rinse and pulp, add phosphoric acid again to increase the temperature for crystal transformation, and then rinse again as described in other patents. The entire process is simple and easy to operate, and the power cost, raw material cost, labor cost, equipment depreciation cost, etc. are relatively low.

[0026] Since a portion of the particle crystals are transformed first and serve as seed crystals to induce subsequent particle transformation, the nucleation and growth of the crystals are in a stable state during the entire process, which is conducive to the orderly growth of the particles and makes it easy to obtain basic ammonium ferric phosphate products with uniform particles, good sphericity and pure physical phase.

[0027] After rinsing, it is pressed in a filter press to greatly reduce the moisture content of the filter cake. It then enters a flash dryer through a forced feeder for drying, which is highly efficient and uses less natural gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a SEM image of basic ammonium ferric phosphate prepared in Example 1 of the present invention;

[0029] Figure 2 This is a SEM image of basic ammonium ferric phosphate prepared in Example 2 of the present invention;

[0030] Figure 3 This is a SEM image of basic ammonium ferric phosphate prepared in Example 3 of the present invention;

[0031] Figure 4 This is a SEM image of basic ammonium ferric phosphate prepared in Example 4 of the present invention;

[0032] Figure 5 This is a SEM image of basic ammonium ferric phosphate prepared in Example 5 of the present invention;

[0033] Figure 6 This is the phase analysis of the examples and comparative examples of the present invention. DETAILED DESCRIPTION

[0034] The preparation method of basic ammonium ferric phosphate of the present invention comprises the following steps: dropwise adding a phosphate solution containing an oxidant and having an N:P molar ratio of 0.95-1.5 to a ferrous sulfate solution at a temperature above 93°C, generating a precipitate while adding the oxidant, and rapidly transforming the generated amorphous basic ammonium ferric phosphate into a crystal. The first generated crystal serves as a crystal seed to induce subsequent amorphous crystals to undergo a crystal transformation. After the dropwise addition is completed, the solution is kept warm at a temperature above 93°C until the color of the slurry changes from yellow to off-white, and the temperature is continued to be maintained until the pH of the solution reaches 0.9-1.3 after the temperature is maintained. The solution is rinsed, squeezed, and dried to obtain basic ammonium ferric phosphate having a moisture content of less than 1%.

[0035] The preparation method of the above-mentioned basic ammonium ferric phosphate comprises the following specific steps:

[0036] 1. Dissolve solid ferrous sulfate in water at 60°C. After fully dissolved, add iron powder or iron sheet, heat to 85-90°C, react until the pH value reaches 3.5-4.5, and filter through a plate and frame filter press to obtain a clear ferrous sulfate solution with an iron concentration of 1 mol / L.

[0037] 2. Using one or more of monoammonium phosphate, diammonium phosphate, and phosphoric acid as the phosphorus source, ammonia water as the alkali solution, and hydrogen peroxide as the oxidant, a phosphate solution is prepared, wherein: the N:P molar ratio is 0.95-1.5, the phosphorus concentration is 1.5 mol / L, and the hydrogen peroxide concentration is 0.9-1 mol / L;

[0038] 3. Measure the ferrous sulfate solution and phosphate solution to ensure that Fe:P=1.14~1.33. Add the measured ferrous sulfate solution into the stainless steel reactor at one time. After heating to above 93°C, add the measured phosphate solution to the reactor at a uniform speed for 60-90 minutes through a peristaltic pump. After the addition is completed, heat to above 93°C and keep warm until the color of the slurry changes from yellow to off-white. Continue to keep warm for 1h-2h. After the insulation is completed, the pH of the solution is 0.9-1.3;

[0039] 4. Rinse and filter through a plate and frame filter press, washing with water until the end conductivity is 400us / cm;

[0040] 5. Beat and disperse the rinsed filter cake. After about 50 minutes of dispersion, pump it into the filter press at a pressing pressure of 4-5 MPa to obtain a filter cake with a moisture content of about 35-40%;

[0041] 6. The filter cake is softened by a forced feeder and then flash dried. The temperature of the mixing chamber is controlled at 130-160°C to obtain basic ammonium ferric phosphate with a moisture content of less than 1%.

[0042] The present invention is further described below with reference to specific embodiments.

[0043] Example 1

[0044] Preparation of ferrous sulfate solution: solid ferrous sulfate is dissolved in water at 60℃, after fully dissolved, add enough iron skin, increase temperature to 85℃, react until PH value is 4, then filter through plate frame filter press, prepare clear ferrous sulfate solution with iron concentration of 1 mol / L;

[0045] Preparation of phosphorus salt: dissolve monammonium phosphate in water, add phosphoric acid and hydrogen peroxide to the dissolved monammonium phosphate solution, wherein: N:P molar ratio is 0.95, phosphorus concentration is 1.5 mol / L, and hydrogen peroxide concentration is 0.9 mol / L;

[0046] Measure 1L of ferrous sulfate solution and 0.76L of phosphorus salt solution, ensure Fe:P = 1.14, add the measured ferrous sulfate solution into the stainless steel reaction kettle at one time, increase the temperature to above 93℃, then add the measured phosphorus salt solution into the reaction kettle at a constant speed through peristaltic pump for 60 minutes, increase the temperature to 93℃ after the addition is completed, continue to keep warm until the color of the slurry changes from yellow to gray white, and keep warm for 1h, and the solution PH is 0.95 after keeping warm;

[0047] The above slurry is rinsed and filtered through a plate frame filter press, and washed with water until the final point conductivity is 400us / cm;

[0048] The rinsed filter cake is dispersed by beating, and pumped into a press filter after dispersion for about 50 minutes, and a filter cake with a water content of about 40% is obtained under a pressing pressure of 4MPa;

[0049] The filter cake is softened by a forced feeder and enters flash drying, and the temperature of the mixing chamber is controlled at 140℃, and ammonium ferric phosphate hydroxide with a water content of 0.71% is prepared.

[0050] The SEM of ammonium ferric phosphate hydroxide prepared in Example 1 is shown in Figure 1 .

[0051] Example 2

[0052] Preparation of ferrous sulfate solution: solid ferrous sulfate is dissolved in water at 60℃, after fully dissolved, add enough iron skin, increase temperature to 88℃, react until PH value is 4.5, then filter through plate frame filter press, prepare clear ferrous sulfate solution with iron concentration of 1 mol / L;

[0053] Preparation of phosphorus salt: dissolve diammonium phosphate in water, add phosphoric acid and hydrogen peroxide to the dissolved diammonium phosphate solution, wherein: N:P molar ratio is 1.2, phosphorus concentration is 1.5 mol / L, and hydrogen peroxide concentration is 1 mol / L;

[0054] FeSO4 solution 1L, phosphorus salt solution 0.85L, ensure Fe:P = 1.275, the metering good ferrous sulfate solution is added to the stainless steel reactor, heated to 95℃ or more, after the metering good phosphorus salt solution is added to the reactor by peristaltic pump at a constant speed for 75 minutes, after the completion of the drop, the temperature is raised to 95℃, until the slurry color has yellow to gray white continue to keep 1.5h, the solution PH is 1.1 after the completion of the heat preservation;

[0055] (4) through the plate and frame filter press rinse filter, washing to the end point conductance is 400us / cm;

[0056] (5) the filter cake is rinsed and dispersed, and pumped into a press filter after dispersion for about 50 minutes, and a filter cake with a water content of about 36% is obtained under a pressing pressure of 5MPa;

[0057] (6) the filter cake is softened by a forced feeder and enters flash drying, and the temperature of the mixing chamber is controlled at 160℃, and ammonium ferric phosphate hydroxide with a water content of 0.54% is prepared.

[0058] The SEM of ammonium ferric phosphate hydroxide prepared in Example 2 is shown in Figure 2 .

[0059] Example 3

[0060] Preparation of ferrous sulfate solution: solid ferrous sulfate is dissolved in water at 60℃, after sufficient dissolution, sufficient iron skin is added, the temperature is raised to 90℃, and the reaction is carried out until the PH value is 3.5, and then filtered by a plate and frame filter press, and a clear ferrous sulfate solution with a concentration of 1mol / L is prepared;

[0061] Preparation of phosphorus salt: phosphoric acid and ammonia are added to a reactor with dilution water, and hydrogen peroxide is added when the temperature drops to below 50℃, wherein the molar ratio of N:P is 1.4, the concentration of phosphorus is 1.5mol / L, and the concentration of hydrogen peroxide is 1mol / L;

[0062] FeSO4 solution 1L, phosphorus salt solution 0.88L, ensure Fe:P = 1.32, the metering good ferrous sulfate solution is added to the stainless steel reactor, heated to 98℃ or more, after the metering good phosphorus salt solution is added to the reactor by peristaltic pump at a constant speed for 90 minutes, after the completion of the drop, the temperature is raised to 98℃, until the slurry color has yellow to gray white continue to keep 2h, the solution PH is 1.28 after the completion of the heat preservation;

[0063] The above slurry is rinsed and filtered by a plate and frame filter press, and washed to an end point conductance of 400us / cm;

[0064] The filter cake is rinsed and dispersed, and pumped into a press filter after dispersion for about 50 minutes, and a filter cake with a water content of about 39% is obtained under a pressing pressure of 4.5MPa;

[0065] The filter cake was softened by a forced feeder and then entered into a flash drying process. The temperature of the mixing chamber was controlled at 130°C to obtain basic ammonium ferric phosphate with a moisture content of 0.82%.

[0066] The SEM of the basic ammonium ferric phosphate prepared in Example 3 is as follows: Figure 3 shown.

[0067] Example 4

[0068] Preparation of ferrous sulfate solution: Dissolve solid ferrous sulfate in 60°C water. Once fully dissolved, add sufficient iron powder and heat to 86°C. React until the pH reaches 3.8, then filter through a plate and frame filter press to obtain a clear ferrous sulfate solution with an iron concentration of 1 mol / L.

[0069] Preparation of phosphate salt: Dissolve diammonium phosphate in water, add phosphoric acid and hydrogen peroxide into a reactor containing dilution water, wherein: N:P molar ratio is 1.5, phosphorus concentration is 1.5 mol / L, and hydrogen peroxide concentration is 1.0 mol / L;

[0070] Measure 1L of ferrous sulfate solution and 0.887L of phosphate solution to ensure that Fe:P=1.33. Add the measured ferrous sulfate solution into a stainless steel reactor at once. After heating to above 99°C, add the measured phosphate solution to the reactor at a uniform speed for 80 minutes using a peristaltic pump. After the addition is completed, heat to 99°C and keep warm until the slurry color changes from yellow to off-white. Continue to keep warm for 2 hours. After the insulation is completed, the pH of the solution is 1.32.

[0071] The slurry was rinsed and filtered through a plate and frame filter press, and washed with water until the end point conductivity was 400 μs / cm;

[0072] The rinsed filter cake was beaten and dispersed, and after about 50 minutes of dispersion, it was pumped into the filter press with a pressing pressure of 4.3 MPa to obtain a filter cake with a moisture content of about 37%;

[0073] The filter cake was softened by a forced feeder and then flash dried. The temperature of the mixing chamber was controlled at 140°C to obtain basic ammonium ferric phosphate with a moisture content of 0.62%.

[0074] The SEM of the basic ammonium ferric phosphate prepared in Example 4 is as follows: Figure 4 shown.

[0075] Example 5

[0076] Preparation of ferrous sulfate solution: Dissolve solid ferrous sulfate in 60°C water. Once fully dissolved, add sufficient iron sheet. Heat to 90°C. React until the pH reaches 4.2. Filter through a plate and frame filter press to obtain a clear ferrous sulfate solution with an iron concentration of 1 mol / L.

[0077] Preparation of phosphorus salt: phosphoric acid, ammonia and dilution water were added into a reaction kettle, and hydrogen peroxide was added when the temperature dropped to below 50 DEG C, wherein the molar ratio of N:P was 1.1, the concentration of phosphorus was 1.5 mol / L, and the concentration of hydrogen peroxide was 0.95 mol / L;

[0078] The ferrous sulfate solution was measured to be 1L, the phosphorus salt solution was measured to be 0.88L, and the Fe:P was ensured to be 1.21. The measured ferrous sulfate solution was added into a stainless steel reaction kettle at one time, and the temperature was raised to above 98 DEG C. Then the measured phosphorus salt solution was uniformly added into the reaction kettle through a peristaltic pump at a speed of 70 minutes. After the addition was completed, the temperature was raised to 98 DEG C for preservation. When the color of the slurry changed from yellow to gray white, the preservation was continued for 1.8h. After the preservation was completed, the PH of the solution was 1.03.

[0079] The above slurry was rinsed and filtered through a plate and frame filter press, and washed with water until the final point conductivity was 400us / cm.

[0080] The rinsed filter cake was dispersed by beating, and pumped into a press filter after dispersion for about 50 minutes. The press pressure was 4.8MPa, and the filter cake with a water content of about 38% was obtained.

[0081] The filter cake was softened by a forced feeder and entered flash drying, and the temperature of the mixing chamber was controlled at 150 DEG C. The basic ammonium iron phosphate with a water content of 0.57 was prepared.

[0082] The SEM of the basic ammonium iron phosphate prepared in Example 5 is shown in Figure 5 .

[0083] Comparative Example 1

[0084] Step: compared with Example 1, the temperature in step (3) was changed from 93 DEG C to 80 DEG C.

[0085] Comparative Example 2

[0086] Step: compared with Example 1, the temperature in step (3) was changed from 93 DEG C to 88 DEG C.

[0087] Comparative Example 3

[0088] Step: compared with Example 1, the molar ratio of N:P in step (2) was changed to 0.75, and the PH after preservation in step (3) was 0.85.

[0089] The detection results of the examples and comparative examples are shown in Table 1.

[0090] Table 1: detection results of examples and comparative examples

[0091] Serial number D0 (μm) D10 (μm) D50 (μm) D90 (μm) D100 (μm) Specific surface area (m2 / g) phase of matter Morphology attached Example 1 0.313 0.73 1.63 3.37 5.70 62.95 <![CDATA[NH4Fe2(OH)(PO4)2·2H2O]]> Figure 1 Example 2 0.313 0.77 1.74 3.64 6.32 61.5 [NH4Fe2(OH)(PO4)2.2H2O] Figure 2 Example 3 0.314 1.83 2.90 4.96 8.82 58.9 [NH4Fe2(OH)(PO4)2.2H2O] Figure 3 Example 4 0.350 1.61 3.12 5.05 10.32 56 <![CDATA[NH4Fe2(OH)(PO4)2·2H2O]]> Figure 4 Example 5 0.324 0.76 1.70 3.55 6.0 62.31 [NH4Fe2(OH)(PO4)2.2H2O] Figure 5 Comparative Example 1 amorphous Comparative Example 2 <![CDATA[Fe(PO4)·2H2O]]> Comparative Example 3 <![CDATA[Fe(PO4)·2H2O]]>

[0092] The phase analysis of the examples and comparative examples is shown in Figure 6 .

[0093] The above tables and figures show that the basic ammonium ferric phosphate prepared using this method exhibits small particle size, narrow particle distribution, pure phase, small, spherical primary particles, and a large specific surface area, making it suitable for the preparation of high-performance lithium iron phosphate. As the N:P ratio increases, the particle size and specific surface area increase, and the particles become more densely packed together. This is likely due to the elevated pH and low supersaturation during the synthesis process, which limits the formation of large nuclei and favors particle growth.

[0094] The invention adopts a one-step preparation process of controlling the molar concentration of N:P in the phosphate salt solution and high-temperature synthesis and crystallization. During the high-temperature synthesis process, amorphous basic ammonium ferric phosphate is quickly converted into a crystalline state. The first crystallized state serves as a seed crystal, which is conducive to the rapid progress of subsequent reactions and the uniform growth of particles, thereby obtaining basic ammonium ferric phosphate with uniform sphericity and particle size.

Claims

1. A method for preparing basic ammonium ferric phosphate, characterized in that: Including steps: A phosphate solution containing an oxidant and having an N:P molar ratio of 0.95-1.5 is added dropwise to a ferrous sulfate solution above 93° C. to obtain a slurry, and then the slurry is kept warm until the color of the slurry changes from yellow to off-white and the slurry is kept warm until the pH of the slurry after the insulation is completed is 0.9-1.

3. The slurry is rinsed, squeezed, and dried to obtain basic ammonium ferric phosphate with a moisture content of less than 1%. The phosphate solution is prepared by using one or more of monoammonium phosphate, diammonium phosphate, and phosphoric acid as the phosphorus source, ammonia water as the alkali solution, and hydrogen peroxide as the oxidant, wherein the phosphorus concentration is 1.5 mol / L and the hydrogen peroxide concentration is 0.9-1 mol / L; The specific steps are as follows: 1) Prepare ferrous sulfate solution; 2) Prepare a phosphate solution with an N:P molar ratio of 0.95-1.5; 3) Measure the ferrous sulfate solution and phosphate solution according to Fe:P=1.14~1.33, add the measured ferrous sulfate solution into the stainless steel reactor at one time, heat it to above 93℃, and then add the measured phosphate solution dropwise to the reactor at a uniform rate. After the addition is completed, heat it to above 93℃ and keep it warm until the color of the slurry changes from yellow to off-white. Continue to keep it warm for 1h-2h. After the insulation is completed, the pH of the solution is 0.9-1.3; 4) Rinse and filter press; 5) Pressing to obtain a filter cake with a moisture content of 35-40%; 6) Drying to obtain basic ammonium ferric phosphate with a moisture content of less than 1%; The obtained basic ammonium ferric phosphate particles are uniform and have good sphericity; In step 3), while the oxidation is added dropwise, a precipitate is generated, and the amorphous basic ammonium ferric phosphate undergoes a rapid crystal transformation. The first generated crystals serve as seeds to induce the subsequent amorphous crystals to undergo a crystal transformation.

2. The method for preparing basic ammonium ferric phosphate according to claim 1, wherein: The ferrous sulfate solution is prepared by dissolving solid ferrous sulfate in water at 60° C., adding iron powder or iron sheet after the solution is fully dissolved, heating to 85-90° C., reacting until the pH value reaches 3.5-4.5, and then filtering through a plate and frame filter press to obtain a clear ferrous sulfate solution with an iron concentration of 1 mol / L.

3. The method for preparing basic ammonium ferric phosphate according to claim 2, wherein: The rinsing and filtration was performed using a plate and frame filter press, and the filter was washed with water until the end point conductivity was 400 μs / cm.

4. The method for preparing basic ammonium ferric phosphate according to claim 2, wherein: The pressing is to beat and disperse the rinsed filter cake, and after dispersing for 50 minutes, pump it into a filter press with a pressing pressure of 4-5 MPa.

5. The method for preparing basic ammonium ferric phosphate according to claim 2, wherein: The drying is to soften the filter cake through a forced feeder and then enter the flash drying, and the temperature of the mixing chamber is controlled at 130-160°C.

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