Method for preparing iron phosphate dihydrate containing orthorhombic crystal form by ammonium method and preparation method of anhydrous iron phosphate

Abstract

The invention belongs to the field of chemical processes, and particularly relates to a method for preparing orthorhombic crystal form-containing iron phosphate dehydrate by an ammonium method and a method for preparing anhydrous iron phosphate. The method provided by the invention comprises the following steps: a) adding a monoammonium phosphate solution into a ferrous sulfate solution, and then adjusting the pH value of the system to 1.25-1.6 by using sulfuric acid to obtain mixed slurry; in the step a), the molar ratio of P in the monoammonium phosphate solution to Fe in the ferrous sulfate solution is (2-2.25): 1; the invention discloses a method for preparing iron phosphate dihydrate containing an orthorhombic crystal form, which comprises the following steps: a) preparing a mixed slurry, b) adding hydrogen peroxide into the mixed slurry for oxidation treatment to obtain oxidized slurry, and c) heating the oxidized slurry to 90-95 DEG C, aging for 2-8 hours, filtering, washing and drying to obtain the iron phosphate dihydrate containing the orthorhombic crystal form. The method provided by the invention can be used for preparing the iron phosphate dihydrate containing the orthorhombic crystal form, and is simple in process and good in economical efficiency.

Description

Technical Field

[0001] This invention belongs to the field of chemical processes, and particularly relates to a method for preparing orthorhombic ferric phosphate dihydrate using the ammonium method and a method for preparing anhydrous ferric phosphate. Background Technology

[0002] Lithium iron phosphate (LFP) batteries, thanks to their high thermal stability due to their olivine structure, cobalt-free and low-cost characteristics (raw material costs are only 50% of those of ternary materials), and a cycle life exceeding 3000 cycles, have seen their penetration rate continue to climb in the power battery (especially energy storage electric vehicles) and large-scale energy storage fields. However, the actual mass energy density (approximately 140~160Wh / kg under conventional processes) corresponding to their theoretical specific capacity (170mAh / g) is insufficient to meet the upgrade requirements of new energy vehicles achieving a range exceeding 1200 kilometers and energy storage systems requiring "high capacity + small size," becoming a core bottleneck restricting their ability to capture a share of the high-end market.

[0003] Numerous studies have confirmed that the crystal structure and microstructure of iron phosphate dihydrate directly determine the subsequent electrochemical performance of lithium iron phosphate. Iron phosphate dihydrate (FePO4·2H2O) mainly exists in three crystal forms: amorphous, monoclinic, and orthorhombic. Among them, the amorphous crystal form has poor stability due to its disordered crystal arrangement; although the monoclinic crystal form has better stability than the amorphous crystal form, the lithium-ion migration channels are partially blocked, limiting the rate performance; while the orthorhombic crystal form has a more regular crystal arrangement and wider lithium-ion diffusion channels, resulting in superior electrochemical performance.

[0004] Traditional processes for preparing orthorhombic iron phosphate dihydrate mostly involve iron powder, which is costly, lengthy, and uneconomical. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a method for preparing ferric phosphate dihydrate with orthorhombic crystal form and a method for preparing anhydrous ferric phosphate by ammonium method. The method provided by the present invention can prepare ferric phosphate dihydrate with orthorhombic crystal form, and the process is simple and economical.

[0006] This invention provides a method for preparing iron phosphate dihydrate with orthorhombic crystal form using the ammonium method, comprising the following steps:

[0007] a) Add monoammonium phosphate solution to ferrous sulfate solution, and then adjust the pH of the system to 1.25~1.6 with sulfuric acid to obtain a mixed slurry;

[0008] In step a), the molar ratio of P in the monoammonium phosphate solution to Fe in the ferrous sulfate solution is (2~2.25):1;

[0009] b) Add hydrogen peroxide to the mixed slurry for oxidation treatment to obtain an oxidized slurry;

[0010] c) Heat the oxidized slurry to 90~95℃, age for 2~8h, filter, wash, and dry to obtain ferric phosphate dihydrate containing orthorhombic crystals.

[0011] Preferably, in step a), the concentration of the monoammonium phosphate solution is 0.8~1.2 mol / L.

[0012] Preferably, in step a), the Fe in the ferrous sulfate solution... 2+ The content is 5~8wt%.

[0013] Preferably, in step a), the temperature of the ferrous sulfate solution is 30~40℃.

[0014] Preferably, in step b), the Fe in the mixed slurry 2+ The molar ratio of H2O2 in the hydrogen peroxide to H2O2 in the hydrogen peroxide solution is 2: (1.1~1.3).

[0015] Preferably, in step b), the oxidation treatment temperature is 30~40℃.

[0016] Preferably, in step b), the oxidation treatment time is 60-70 minutes.

[0017] This invention provides a method for preparing anhydrous ferric phosphate, comprising the following steps:

[0018] Ferric phosphate dihydrate is prepared according to the method described in the above technical solution;

[0019] The ferric phosphate dihydrate was calcined to obtain anhydrous ferric phosphate.

[0020] Preferably, the calcination temperature is 550~620℃.

[0021] Preferably, the calcination time is 2 to 4 hours.

[0022] Compared with existing technologies, this invention provides a method for preparing orthorhombic ferric phosphate dihydrate and anhydrous ferric phosphate using the ammonium method. The method provided by this invention includes the following steps: a) adding monoammonium phosphate solution to ferrous sulfate solution, then adjusting the pH of the system to 1.25-1.6 with sulfuric acid to obtain a mixed slurry; in step a), the molar ratio of P in the monoammonium phosphate solution to Fe in the ferrous sulfate solution is (2-2.25):1; b) adding hydrogen peroxide to the mixed slurry for oxidation treatment to obtain an oxidized slurry; c) heating the oxidized slurry to 90-95℃, aging for 2-8 hours, filtering, washing, and drying to obtain orthorhombic ferric phosphate dihydrate. This invention uses ferrous sulfate solution as the base solution, and by adding monoammonium phosphate solution, sulfuric acid, and hydrogen peroxide, and strictly controlling the nP / Fe ratio, slurry pH, aging temperature, and time, directly induces the directional growth of orthorhombic FePO4·2H2O. The method provided by this invention has a simple process, and the obtained iron phosphate dihydrate is mostly orthorhombic. The morphology of the iron phosphate dihydrate is polygonal block particles. The anhydrous iron phosphate obtained after subsequent calcination can maintain the above morphological characteristics, which is beneficial for preparing lithium iron phosphate with high electrochemical performance. Attached Figure Description

[0023] 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 only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0024] Figure 1 This is the XRD pattern of ferric phosphate dihydrate provided in Embodiment 1 of the present invention;

[0025] Figure 2 This is a SEM image of ferric phosphate dihydrate provided in Embodiment 1 of the present invention;

[0026] Figure 3 This is a SEM image of anhydrous ferric phosphate provided in Embodiment 1 of the present invention;

[0027] Figure 4 This is the XRD pattern of ferric phosphate dihydrate provided in Embodiment 2 of the present invention;

[0028] Figure 5 This is a SEM image of ferric phosphate dihydrate provided in Embodiment 2 of the present invention;

[0029] Figure 6 This is a SEM image of ferric phosphate dihydrate provided in Embodiment 3 of the present invention;

[0030] Figure 7This is the XRD pattern of ferric phosphate dihydrate provided in Embodiment 4 of the present invention;

[0031] Figure 8 This is a SEM image of ferric phosphate dihydrate provided in Example 4 of the present invention;

[0032] Figure 9 This is the XRD pattern of ferric phosphate dihydrate provided in Comparative Example 1 of this invention;

[0033] Figure 10 This is a SEM image of ferric phosphate dihydrate provided in Comparative Example 1 of this invention;

[0034] Figure 11 This is a SEM image of anhydrous ferric phosphate provided in Comparative Example 1 of this invention. Detailed Implementation

[0035] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] This invention provides a method for preparing iron phosphate dihydrate with orthorhombic crystal form using the ammonium method, comprising the following steps:

[0037] a) Add monoammonium phosphate solution to ferrous sulfate solution, and then adjust the pH of the system to 1.25~1.6 with sulfuric acid to obtain a mixed slurry;

[0038] b) Add hydrogen peroxide to the mixed slurry for oxidation treatment to obtain an oxidized slurry;

[0039] c) Heat the oxidized slurry to 90~95℃, age for 2~8h, filter, wash, and dry to obtain ferric phosphate dihydrate containing orthorhombic crystals.

[0040] In the method provided by the present invention, in step a), the concentration of the monoammonium phosphate solution is preferably 0.8~1.2 mol / L, specifically 0.8 mol / L, 0.85 mol / L, 0.9 mol / L, 0.95 mol / L, 1 mol / L, 1.05 mol / L, 1.1 mol / L, 1.15 mol / L or 1.2 mol / L, and most preferably 1 mol / L.

[0041] In the method provided by this invention, in step a), the Fe of the ferrous sulfate solution... 2+ The preferred content is 5 to 8 wt%, specifically 5 wt%, 5.5 wt%, 6 wt%, 6.5 wt%, 7 wt%, 7.5 wt%, or 8 wt%, with 6 wt% being the most preferred.

[0042] In the method provided by the present invention, in step a), the molar ratio of P in the monoammonium phosphate solution to Fe in the ferrous sulfate solution is (2~2.25):1, specifically 2:1, 2.05:1, 2.1:1, 2.15:1, 2.2:1 or 2.25:1, with 2:1 being the most preferred.

[0043] In the method provided by the present invention, in step a), the temperature of the ferrous sulfate solution is preferably 30~40℃, specifically 30℃, 31℃, 32℃, 33℃, 34℃, 35℃, 36℃, 37℃, 38℃, 39℃ or 40℃.

[0044] In the method provided by the present invention, in step a), the pH value of the system can be specifically adjusted to 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, 1.55 or 1.6, with 1.5 being the most preferred.

[0045] In the method provided by the present invention, in step a), during the process of adding to the ferrous sulfate solution and adjusting the pH value of the system with sulfuric acid, it is preferable to stir the mixed system, and the stirring speed is preferably 100~500 rpm, specifically 100 rpm, 150 rpm, 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, 450 rpm or 500 rpm.

[0046] In the method provided by this invention, in step b), the Fe in the mixed slurry 2+ The preferred molar ratio of hydrogen peroxide to H2O2 in hydrogen peroxide is 2:(1.1~1.3), meaning the actual amount of hydrogen peroxide used is equal to the amount of Fe oxidized. 2+ The dosage is 1.1 to 1.3 times the theoretical dosage, specifically 2:1.1, 2:1.15, 2:1.2, 2:1.25 or 2:1.3, with 2:1.2 being the most preferred.

[0047] In the method provided by the present invention, in step b), the temperature of the oxidation treatment is preferably 30~40℃, specifically 30℃, 31℃, 32℃, 33℃, 34℃, 35℃, 36℃, 37℃, 38℃, 39℃ or 40℃; the time of the oxidation treatment is preferably 60~70min, specifically 60min, 61min, 62min, 63min, 64min, 65min, 66min, 67min, 68min, 69min or 70min.

[0048] In the method provided by the present invention, in step c), the oxidized slurry can be heated to 90°C, 91°C, 92°C, 93°C, 94°C or 95°C.

[0049] In the method provided by the present invention, in step c), the aging time can be 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h or 8h, with 4h being the most preferred.

[0050] In the method provided by the present invention, in step c), the detergent used for washing is preferably water.

[0051] In the method provided by the present invention, in step c), the drying temperature is preferably 100~130℃, specifically 100℃, 105℃, 110℃, 115℃, 120℃, 125℃ or 130℃; the drying time is preferably 12~48h, specifically 12h, 16h, 20h, 24h, 28h, 32h, 36h, 40h, 44h or 48h.

[0052] This invention also provides a method for preparing anhydrous ferric phosphate, comprising the following steps:

[0053] Ferric phosphate dihydrate (i.e., ferric phosphate precursor) is prepared according to the method described in the above technical solution.

[0054] The iron phosphate precursor was calcined to obtain anhydrous iron phosphate.

[0055] In the preparation method provided by the present invention, the calcination temperature is preferably 550~620℃, specifically 550℃, 560℃, 570℃, 580℃, 590℃, 600℃, 610℃ or 620℃; the calcination time is preferably 2~4h, specifically 2h, 2.5h, 3h, 3.5h or 4h.

[0056] For clarity, the following examples and comparative models will be used to provide a detailed description.

[0057] Example 1

[0058] (1) Using ferrous sulfate heptahydrate, prepare Fe 2+ An aqueous solution with a content of 6 wt% was used as the iron source.

[0059] (2) Use monoammonium phosphate to prepare an aqueous solution with a concentration of 1 mol / L as a phosphorus source.

[0060] (3) Heat the iron source to 30~40℃, add the phosphorus source to the iron source according to n P / Fe=2.0, use constant speed electric stirring for the iron source, stirring speed 300rpm, and then use sulfuric acid solution to adjust the pH value of the slurry to 1.50±0.1.

[0061] (4) Add 1.2 times the amount of hydrogen peroxide (i.e., Fe in the slurry) to the slurry. 2+The slurry was oxidized with hydrogen peroxide (H2O2 in a molar ratio of 2:1.2) for 65 minutes. After oxidation, the slurry was heated to 90-95℃.

[0062] (5) After the slurry is aged at 90~95℃ for 4 hours, it is filtered and separated. The resulting filter cake is washed with pure water and filtered again to obtain the iron phosphate precursor.

[0063] (6) The ferric phosphate precursor was placed in an oven at 110°C for 24 hours to dry and remove free water, thus obtaining a sample of ferric phosphate dihydrate containing orthorhombic crystals.

[0064] (7) The ferric phosphate dihydrate sample was placed in a muffle furnace and calcined at 580°C for 3 hours to obtain anhydrous ferric phosphate.

[0065] X-ray diffraction (XRD) analysis was performed on the ferric phosphate dihydrate prepared in this embodiment, and the results are as follows: Figure 1 As shown, Figure 1 This is the XRD pattern of ferric phosphate dihydrate provided in Embodiment 1 of the present invention. (The text abruptly ends here.) Figure 1 It can be seen that the sample is iron phosphate dihydrate containing orthorhombic crystal form (PDF#33-0667), and also contains monoclinic crystal form (PDF-72-0471).

[0066] The dihydrate ferric phosphate and anhydrous ferric phosphate prepared in this embodiment were observed by scanning electron microscopy (SEM), and the results are as follows: Figures 2-3 As shown, Figure 2 This is a SEM image of ferric phosphate dihydrate provided in Example 1 of this invention. Figure 3 This is a SEM image of anhydrous ferric phosphate provided in Embodiment 1 of the present invention. (The image is obtained through...) Figures 2-3 It can be seen that the morphology of the sample did not change much after calcination, and the polygonal block particles of the dried sample were maintained.

[0067] Example 2

[0068] (1) Using ferrous sulfate heptahydrate, prepare Fe 2+ An aqueous solution with a content of 6 wt% was used as the iron source.

[0069] (2) Use monoammonium phosphate to prepare an aqueous solution with a concentration of 1 mol / L as a phosphorus source.

[0070] (3) Heat the iron source to 30~40℃, add the phosphorus source to the iron source according to n P / Fe=2.0, use constant speed electric stirring for the iron source, stirring speed 300rpm, and then use sulfuric acid solution to adjust the pH value of the slurry to 1.50±0.1.

[0071] (4) Add 1.2 times the amount of hydrogen peroxide to the slurry for oxidation treatment. After oxidation treatment for 65 minutes, heat the slurry to 90~95℃.

[0072] (5) After the slurry is aged at 90~95℃ for 2 hours, it is filtered and separated. The resulting filter cake is washed with pure water and filtered again to obtain the iron phosphate precursor.

[0073] (6) The ferric phosphate precursor was placed in an oven at 110°C for 24 hours to dry and remove free water, thus obtaining a sample of ferric phosphate dihydrate containing orthorhombic crystals.

[0074] (7) The ferric phosphate dihydrate sample was placed in a muffle furnace and calcined at 580°C for 3 hours to obtain anhydrous ferric phosphate.

[0075] X-ray diffraction (XRD) analysis was performed on the ferric phosphate dihydrate prepared in this embodiment, and the results are as follows: Figure 4 As shown, Figure 4 This is the XRD pattern of ferric phosphate dihydrate provided in Embodiment 2 of the present invention. (The text abruptly ends here.) Figure 4 It can be seen that the sample is iron phosphate dihydrate containing orthorhombic crystal form (PDF#33-0667), and also contains monoclinic crystal form (PDF-72-0471).

[0076] The ferric phosphate dihydrate prepared in this embodiment was observed by scanning electron microscopy (SEM), and the results are as follows: Figure 5 As shown, Figure 5 This is a SEM image of ferric phosphate dihydrate provided in Embodiment 2 of the present invention. (The image is obtained through...) Figure 5 As can be seen, compared with Example 1, the sample of Example 2 contains more flaky particles.

[0077] Example 3

[0078] (1) Using ferrous sulfate heptahydrate, prepare Fe 2+ A 6% aqueous solution was used as the iron source.

[0079] (2) Use monoammonium phosphate to prepare an aqueous solution with a concentration of 1 mol / L as a phosphorus source.

[0080] (3) Heat the iron source to 30~40℃, add the phosphorus source to the iron source according to n P / Fe=2.0, use constant speed electric stirring for the iron source, stirring speed 300rpm, and then use sulfuric acid solution to adjust the pH value of the slurry to 1.25±0.1.

[0081] (4) Add 1.2 times the amount of hydrogen peroxide to the slurry for oxidation treatment. After oxidation treatment for 65 minutes, heat the slurry to 90~95℃.

[0082] (5) After the slurry is aged at 90~95℃ for 6 hours, it is filtered and separated. The resulting filter cake is washed with pure water and filtered again to obtain the iron phosphate precursor.

[0083] (6) The ferric phosphate precursor was placed in an oven at 110°C for 24 hours to dry and remove free water, thus obtaining a sample of ferric phosphate dihydrate containing orthorhombic crystals.

[0084] (7) The ferric phosphate dihydrate sample was placed in a muffle furnace and calcined at 580°C for 3 hours to obtain anhydrous ferric phosphate.

[0085] X-ray diffraction (XRD) analysis of the ferric phosphate dihydrate prepared in this embodiment showed that the sample contained an orthorhombic crystal form (PDF#33-0667) and also contained a monoclinic crystal form (PDF-72-0471).

[0086] The ferric phosphate dihydrate prepared in this embodiment was observed by scanning electron microscopy (SEM), and the results are as follows: Figure 6 As shown, Figure 6 This is a SEM image of ferric phosphate dihydrate provided in Embodiment 3 of the present invention. (The image is obtained through...) Figure 6 As can be seen, compared with Example 1, the sample morphology uniformity of Example 3 is slightly worse, consisting of polygonal block-shaped particles, sheet-like particles, and small particles attached to the block-shaped particles.

[0087] Example 4

[0088] (1) Using ferrous sulfate heptahydrate, prepare Fe 2+ A 6% aqueous solution was used as the iron source.

[0089] (2) Use monoammonium phosphate to prepare an aqueous solution with a concentration of 1 mol / L as a phosphorus source.

[0090] (3) Heat the iron source to 30~40℃, add the phosphorus source to the iron source according to nP / Fe=2.25, use constant speed electric stirring for the iron source, stirring speed 300rpm, and then use sulfuric acid solution to adjust the pH value of the slurry to 1.50±0.1.

[0091] (4) Add 1.2 times the amount of hydrogen peroxide to the slurry for oxidation treatment. After oxidation treatment for 65 minutes, heat the slurry to 90~95℃.

[0092] (5) After the slurry is aged at 90~95℃ for 4 hours, it is filtered and separated. The resulting filter cake is washed with pure water and filtered again to obtain the iron phosphate precursor.

[0093] (6) The ferric phosphate precursor was placed in an oven at 110°C for 24 hours to dry and remove free water, thus obtaining a sample of ferric phosphate dihydrate containing orthorhombic crystals.

[0094] (7) The ferric phosphate dihydrate sample was placed in a muffle furnace and calcined at 580°C for 3 hours to obtain anhydrous ferric phosphate.

[0095] X-ray diffraction (XRD) analysis was performed on the ferric phosphate dihydrate prepared in this embodiment, and the results are as follows: Figure 7 As shown, Figure 7 This is the XRD pattern of ferric phosphate dihydrate provided in Embodiment 4 of the present invention. (The last sentence appears to be incomplete and possibly refers to a different XRD pattern.) Figure 7 It can be seen that the sample is ferric phosphate dihydrate containing orthorhombic crystal form (PDF#33-0667), and also contains basic ferric phosphate (PDF#82-1165) and acidic ferric phosphate (PDF#43-0102).

[0096] The ferric phosphate dihydrate prepared in this embodiment was observed by scanning electron microscopy (SEM), and the results are as follows: Figure 8 As shown, Figure 8 This is a SEM image of ferric phosphate dihydrate provided in Embodiment 4 of the present invention. (The image is obtained through...) Figure 8 It can be seen that the sample morphology of Example 4 is polygonal block and fragmented particles.

[0097] Comparative Example 1

[0098] (1) Using ferrous sulfate heptahydrate, prepare Fe 2+ A 6% aqueous solution was used as the iron source.

[0099] (2) Use monoammonium phosphate to prepare an aqueous solution with a concentration of 1 mol / L as a phosphorus source.

[0100] (3) Heat the iron source to 30~40℃, add the phosphorus source to the iron source according to n P / Fe=1.5, use constant speed electric stirring for the iron source, stirring speed 300rpm, and then use sulfuric acid solution to adjust the pH value of the slurry to 1.50±0.1.

[0101] (4) Add 1.2 times the amount of hydrogen peroxide to the slurry for oxidation treatment. After oxidation treatment for 65 minutes, heat the slurry to 90~95℃.

[0102] (5) After the slurry is aged at 90~95℃ for 4 hours, it is filtered and separated. The resulting filter cake is washed with pure water and filtered again to obtain the iron phosphate precursor.

[0103] (6) The ferric phosphate precursor was placed in an oven at 110°C for 24 hours to dry and remove free water, thus obtaining the ferric phosphate dihydrate sample.

[0104] (7) The ferric phosphate dihydrate sample was placed in a muffle furnace and calcined at 580°C for 3 hours to obtain anhydrous ferric phosphate.

[0105] X-ray diffraction (XRD) analysis was performed on the iron phosphate dihydrate prepared in this comparative example, and the results are as follows: Figure 9 As shown, Figure 9 This is the XRD pattern of ferric phosphate dihydrate provided in Comparative Example 1 of this invention. (The last sentence appears to be incomplete and possibly refers to a different XRD pattern.) Figure 9It can be seen that the crystal form of Comparative Example 1 is monoclinic iron phosphate dihydrate.

[0106] The dihydrate ferric phosphate and anhydrous ferric phosphate prepared in this comparative example were observed by scanning electron microscopy (SEM), and the results are as follows: Figures 10-11 As shown, Figure 10 This is a SEM image of ferric phosphate dihydrate provided in Comparative Example 1 of this invention. Figure 11 This is a SEM image of anhydrous ferric phosphate provided in Comparative Example 1 of this invention. (The image is obtained through...) Figures 10-11 It can be seen that the sample of Comparative Example 1 consists of flaky agglomerated particles composed of small particles, which become porous and cohesive network particles after calcination.

[0107] 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 ferric phosphate dihydrate containing orthorhombic crystals using the ammonium method, characterized in that, Includes the following steps: a) Add monoammonium phosphate solution to ferrous sulfate solution, and then adjust the pH of the system to 1.25~1.6 with sulfuric acid to obtain a mixed slurry; In step a), the molar ratio of P in the monoammonium phosphate solution to Fe in the ferrous sulfate solution is (2~2.25):1; b) Add hydrogen peroxide to the mixed slurry for oxidation treatment to obtain an oxidized slurry; c) Heat the oxidized slurry to 90~95℃, age for 2~8h, filter, wash, and dry to obtain ferric phosphate dihydrate containing orthorhombic crystals.

2. The method according to claim 1, characterized in that, In step a), the concentration of the monoammonium phosphate solution is 0.8~1.2 mol / L.

3. The method according to claim 1, characterized in that, In step a), the Fe in the ferrous sulfate solution 2+ The content is 5~8wt%.

4. The method according to claim 1, characterized in that, In step a), the temperature of the ferrous sulfate solution is 30~40℃.

5. The method according to claim 1, characterized in that, In step b), the Fe in the mixed slurry 2+ The molar ratio of H2O2 in the hydrogen peroxide to H2O2 in the hydrogen peroxide solution is 2: (1.1~1.3).

6. The method according to claim 1, characterized in that, In step b), the oxidation treatment temperature is 30~40℃.

7. The method according to claim 1, characterized in that, In step b), the oxidation treatment time is 60-70 minutes.

8. A method for preparing anhydrous ferric phosphate, characterized in that, Includes the following steps: Ferric phosphate dihydrate is prepared according to any one of claims 1 to 7; The ferric phosphate dihydrate was calcined to obtain anhydrous ferric phosphate.

9. The preparation method according to claim 8, characterized in that, The calcination temperature is 550~620℃.

10. The preparation method according to claim 8, characterized in that, The calcination time is 2-4 hours.

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