A method for recovering phosphorus from livestock and poultry manure by pre-oxidation and hydrothermal carbonization to prepare iron phosphate

Abstract

The application discloses a method for recovering phosphorus from livestock and poultry manure and preparing iron phosphate by pre-oxidation and synergistic hydrothermal carbonization, and belongs to the technical field of livestock and poultry manure treatment and phosphorus resource recovery. The method realizes efficient recovery and directional conversion of phosphorus in livestock and poultry manure and prepares high-value iron phosphate products by using a Fe(II) / peroxide advanced oxidation pretreatment and synergistic hydrothermal carbonization coupling process. In the pre-oxidation process, strong oxidizing free radicals are generated to effectively break down the structure of organic matter in the livestock and poultry manure and promote the sufficient release of combined state phosphorus; in the hydrothermal carbonization process, the released phosphorus is combined with iron ions in the system in situ, and the enrichment and conversion of the phosphorus are simultaneously realized. The method has simple process operation and mild conditions, and provides an overall technical scheme for resource utilization of livestock and poultry manure and recovery of phosphorus resources.

Description

Technical Field

[0001] This invention belongs to the field of livestock and poultry manure treatment and phosphorus resource recovery technology, and particularly relates to a method for recovering phosphorus from livestock and poultry manure and preparing ferric phosphate through pre-oxidation synergistic hydrothermal carbonization. Background Technology

[0002] Phosphorus is an essential nutrient for plant growth and a non-renewable strategic resource. Global phosphate rock reserves are limited and unevenly distributed. With the continuous expansion of livestock farming, the amount of livestock manure produced has increased dramatically. Currently, the main treatment methods for livestock manure include composting, anaerobic digestion, and direct application to the fields, all of which suffer from long treatment cycles, low phosphorus recovery efficiency, and low added value. Of particular note is that phosphorus in livestock manure is mostly in the form of organic phosphorus or bound to organic matter, making it difficult to effectively recover and utilize.

[0003] Hydrothermal carbonization is an emerging method for treating organic waste, converting biomass into hydrothermal char, process liquid, and a small amount of gas under subcritical water conditions. This technology requires no pre-drying and is particularly suitable for treating livestock and poultry manure with high moisture content. However, in traditional hydrothermal carbonization, although phosphorus is mainly enriched in the solid phase of the hydrothermal char, some phosphorus remains tightly bound to organic matter, making it difficult to fully release and convert, thus limiting the resource utilization efficiency of phosphorus. Advanced oxidation technologies generate strong oxidizing free radicals (such as sulfate radicals SO4· ... - Hydroxyl radicals (·OH) can effectively break down organic matter in sludge or biomass, promoting the release of intracellular substances. Therefore, combining advanced oxidation as a pretreatment method with hydrothermal carbonization is expected to overcome the technical limitations of hydrothermal carbonization alone in phosphorus recovery from livestock and poultry manure.

[0004] Iron phosphate (FePO4) is an important phosphorus chemical product, serving both as a slow-release carrier for phosphate fertilizers and as a precursor for lithium iron phosphate (LiFePO4), a cathode material in lithium-ion batteries, thus possessing high economic value. Currently, the preparation of iron phosphate mainly employs chemical precipitation, using chemical reagents as raw materials, which is costly. If phosphorus could be recovered from livestock and poultry manure and used to produce iron phosphate, it would offer both significant economic and environmental benefits. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a method for recovering phosphorus from livestock and poultry manure and preparing ferric phosphate through pre-oxidation synergistic hydrothermal carbonization.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A method for recovering phosphorus from livestock and poultry manure and preparing ferric phosphate via pre-oxidation synergistic hydrothermal carbonization includes the following steps: Step 1) Mix ammonium sulfate and sulfuric acid to prepare an electrolyte. Electrolyze the electrolyte in an electrolytic cell with platinum as the anode and graphite as the cathode. After electrolysis, obtain solid peroxide by filtration, cooling and crystallization, centrifugation and drying. Step 2) After degreasing the iron filings with alkaline solution and washing them with water, they are added to dilute sulfuric acid and reacted until completely dissolved. After filtration, acidification, cooling and crystallization, centrifugation and drying, ferrous salt crystals are obtained. Step 3) Mix the ferrous salt crystals obtained in Step 2) with the solid peroxide obtained in Step 1), add the mixture to the livestock and poultry manure mixture, and stir and react at room temperature to obtain a pretreated mixture; the molar ratio of the ferrous salt crystals to the solid peroxide is (1~4):1; the dosage of the solid peroxide is 0.5~4.5 mmol / g based on the dry weight of the livestock and poultry manure. Step 4) Transfer the pretreated mixture obtained in Step 3) to a closed reactor for hydrothermal carbonization reaction. After the reaction is completed, allow it to cool naturally to room temperature. Open the reactor and obtain the solid product by filtration, washing, drying and grinding. Step 5) Extract the solid product obtained in step 4) by shaking with sulfuric acid solution, centrifuge, heat to react, cool to precipitate, wash, dry and calcine to obtain the iron phosphate product.

[0007] This invention utilizes a pre-oxidation synergistic hydrothermal carbonization coupling process to efficiently recover phosphorus from livestock and poultry manure and prepare ferric phosphate products, simultaneously achieving the resource utilization and harmless treatment of livestock and poultry manure. The ferric phosphate products prepared by this invention have high purity and good crystallinity, and have promising prospects for resource utilization applications.

[0008] Further, in step 1), the concentration of ammonium sulfate in the electrolyte is 30-40 wt%; the concentration of sulfuric acid in the electrolyte is 10-20 wt%; and the conditions during the electrolysis process are: a current density of 0.5-1 A / cm². 2 The electrolysis voltage is 4~8V and the electrolysis time is 4~6h.

[0009] Further, in step 1), the specific operation steps for cooling crystallization are as follows: first place the sample in an ice-water bath for 2-4 hours, and then place it in a vacuum drying oven at 30-40°C for 4-6 hours.

[0010] Further, in step 2), the concentration of the alkaline solution is 5-10 wt%; the degreasing treatment time is 10-30 min; the concentration of the dilute sulfuric acid is 10-20 wt%; and the reaction time is 1-3 h.

[0011] Further, in step 2), the acidification is to adjust the pH to 1-6 with sulfuric acid; the specific operation steps of the cooling crystallization are as follows: first, place the sample in an ice-water bath and let it stand for 2-4 hours, and then place it in a vacuum drying oven at 30-40℃ for 2-4 hours.

[0012] Further, in step 3), the solid-liquid ratio in the livestock and poultry manure mixture is 1g:(5-15)mL; the stirring reaction is carried out by mechanical stirring at a speed of 300-600rpm for a duration of 0.5-2h.

[0013] Further, in step 4), the temperature of the hydrothermal carbonization reaction is 100~220℃, and the reaction time is 1~4h; the washing is rinsing with deionized water 3~5 times; and the drying is drying in a 60℃ oven for 12h.

[0014] Further, in step 5), the concentration of the acid solution is 0.1~0.5mol / L; the solid-liquid ratio of the solid product and the acid solution is 1g:(10~30)mL.

[0015] Further, in step 5), the oscillation rate of the oscillation extraction is 150~250 rpm, and the oscillation time is 2~6 h.

[0016] Further, in step 5), the heating reaction temperature is 70~90℃, and the reaction time is 1~3h; the cooling is natural cooling at room temperature; the washing is washing 2~3 times each with deionized water and anhydrous ethanol; the drying is drying in a 60℃ oven for 12h; the calcination temperature is 600~800℃, and the calcination time is 2~6h.

[0017] Compared with the prior art, the present invention has the following advantages and technical effects: 1. This invention employs a pre-oxidation synergistic hydrothermal carbonization coupling process, which can efficiently release phosphorus in livestock and poultry manure and achieve its directional conversion, transforming low-value livestock and poultry manure into high-value-added iron phosphate products, thereby simultaneously realizing the resource recovery and high-value utilization of phosphorus.

[0018] 2. This invention employs hydrothermal carbonization technology, which provides mild reaction conditions and eliminates the need for pre-drying of livestock and poultry manure, making it particularly suitable for processing raw materials with high moisture content. This process is energy-efficient, easy to operate, and readily applicable for industrial application.

[0019] 3. This invention utilizes iron introduced in the pre-oxidation stage as a phosphorus precipitant, which undergoes an in-situ fixation reaction with the released phosphate ions during hydrothermal carbonization, simplifying the process and reducing reagent costs. Attached Figure Description

[0020] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 The images show the SEM images of chicken manure before and after pretreatment in Example 1 of this invention. Figure 2 The image shows the three-dimensional fluorescence spectra of chicken manure before and after pretreatment in Example 1 of this invention. Figure 3 This is a comparison chart of the total phosphorus content of hydrothermal carbon obtained in Example 1 and Comparative Example 1 of the present invention; Figure 4 This is a comparison chart of the hydrothermal carbon yields obtained in Example 1 and Comparative Example 1 of the present invention; Figure 5 The XRD pattern of the iron phosphate product obtained in Example 1 of this invention; Figure 6 The image shows the SEM-EDS spectrum of the iron phosphate product obtained in Example 1 of this invention. Figure 7 The changes in total phosphorus content in hydrothermal carbon after treatment in Examples 1, 2-5 are shown. Figure 8 The changes in total phosphorus content in hydrothermal carbon after treatment in Examples 1, 6-9 are shown. Detailed Implementation

[0021] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0022] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0023] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0024] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0025] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0026] This invention provides a method for recovering phosphorus from livestock and poultry manure and preparing ferric phosphate via pre-oxidation synergistic hydrothermal carbonization, comprising the following steps: Step 1) Prepare an electrolyte by mixing ammonium sulfate with a concentration of 30-40 wt% (e.g., 35 wt%) and sulfuric acid with a concentration of 10-20 wt% (e.g., 15 wt%). Electrolyze the electrolyte in an electrolytic cell using platinum as the anode and graphite as the cathode. The electrolysis conditions are: current density 0.5-1 A / cm². 2 (e.g., 0.8A / cm) 2 The electrolysis voltage is 4~8V (e.g., 6V), and the electrolysis time is 4~6h (e.g., 4h). After electrolysis, the product is filtered, cooled and crystallized in an ice-water bath for 2~4h (e.g., 3h), centrifuged, and then dried in a vacuum drying oven at 30~40℃ (e.g., 35℃) for 4~6h (e.g., 5h) to obtain solid peroxide. Step 2) Soak the iron filings in an alkaline solution with a concentration of 5-10 wt% (e.g., 8 wt%) to remove oil for 10-30 min (e.g., 20 min). After washing with water, add the iron filings to a dilute sulfuric acid solution with a concentration of 10-20 wt% (e.g., 15 wt%) and react for 1-3 h (e.g., 2 h) until completely dissolved. After filtration, adjust the pH of the filtrate to 1-2 (e.g., pH=1.5) with sulfuric acid for acidification. Then place the solution in an ice-water bath to cool and crystallize for 2-4 h (e.g., 3 h). Centrifuge the solution and then dry it in a vacuum drying oven at 30-40℃ (e.g., 35℃) for 2-4 h (e.g., 3 h) to obtain ferrous salt crystals. Step 3) Mix the ferrous salt crystals obtained in Step 2) with the solid peroxide obtained in Step 1) at a molar ratio of (1~4):1 (e.g., 1:1, 2:1, 3:1 or 4:1). The amount of solid peroxide added is 0.5~4.5 mmol / g (e.g., 0.5 mmol / g, 1.5 mmol / g, 2.5 mmol / g, 3.5 mmol / g or 4.5 mmol / g) based on the dry weight of livestock and poultry manure. Add the ferrous salt crystals and solid peroxide to the livestock and poultry manure mixture and mechanically stir at a rate of 300~600 rpm (e.g., 400 rpm) at room temperature for 0.5~2h (e.g., 1h) to obtain a pretreated mixture. The solid-liquid ratio of the livestock and poultry manure mixture is 1g:(5~15)mL (e.g., 1g:10mL). Step 4) Transfer the pretreated mixture obtained in Step 3) to a closed reactor and perform hydrothermal carbonization reaction at 100~220℃ (e.g., 180℃) for 1~4h (e.g., 1h). After the reaction is completed, allow it to cool naturally to room temperature, open the reactor, filter it, wash it with deionized water 3~5 times (e.g., 4 times), and dry it in a 60℃ oven for 12h to obtain a solid product. Step 5) Add the solid product obtained in step 4) to an acid solution with a concentration of 0.1-0.5 mol / L (e.g., 0.2 mol / L) at a solid-liquid ratio of 1 g: (10-30) mL (e.g., 1 g: 20 mL). Extract by shaking at 150-250 rpm (e.g., 200 rpm) for 2-6 h (e.g., 4 h). Heat the mixture at 70-90℃ (e.g., 80℃) for 1-3 h (e.g., 2 h). Allow the precipitate to cool naturally at room temperature. Wash the precipitate 2-3 times (e.g., 3 times) with deionized water and anhydrous ethanol. Dry the precipitate in a 60℃ oven for 12 h. Finally, calcine the precipitate at 600-800℃ (e.g., 700℃) for 2-6 h (e.g., 4 h) to obtain the iron phosphate product.

[0027] Unless otherwise specified, "room temperature" in this invention refers to 25±2℃.

[0028] All raw materials used in this invention were purchased from the market.

[0029] The technical solution of the present invention will be further illustrated by the following embodiments.

[0030] Example 1 A method for recovering phosphorus from livestock and poultry manure and preparing ferric phosphate via pre-oxidation synergistic hydrothermal carbonization includes the following steps: Step 1) Prepare an electrolyte by mixing 35 wt% ammonium sulfate and 15 wt% sulfuric acid. Electrolyze the solution in an electrolytic cell using platinum as the anode and graphite as the cathode under the following conditions: current density 0.8 A / cm². 2 The electrolysis voltage was 6V and the electrolysis time was 4h. After electrolysis, the solid peroxide was obtained by filtration, cooling and crystallizing in an ice-water bath for 3h, centrifugation, and then drying in a vacuum drying oven at 35℃ for 5h. Step 2) Soak the iron filings in an 8 wt% alkaline solution (sodium hydroxide solution) for 20 min to remove oil. After washing with water, add them to a 15 wt% dilute sulfuric acid solution and react for 2 h until completely dissolved. After filtration, adjust the pH of the filtrate to 1.5 with sulfuric acid for acidification. Then place it in an ice-water bath to cool and crystallize for 3 h. Centrifuge to separate the crystals and then dry them in a vacuum drying oven at 35 ℃ for 3 h to obtain ferrous salt crystals. Step 3) Mix the ferrous salt crystals obtained in Step 2) with the solid peroxide obtained in Step 1) at a molar ratio of 1:1. The amount of ammonium persulfate crystals added is 1.5 mmol / g based on the dry weight of livestock and poultry manure (chicken manure). Add the mixture to 5g of livestock and poultry manure mixture. The solid-liquid ratio of the livestock and poultry manure mixture is 1g:10mL. Stir mechanically at 400rpm for 1h at room temperature to obtain the pretreated mixture. Step 4) Transfer the pretreated mixture obtained in Step 3) to a 100 mL sealed reactor and perform hydrothermal carbonization reaction at 180 °C for 1 h. After the reaction is completed, allow it to cool naturally to room temperature, open the reactor, filter it, wash it 4 times with deionized water, and dry it in a 60 °C oven for 12 h to obtain a solid product (hydrothermal carbon). Step 5) Add the solid product obtained in step 4) to 20 mL of 0.2 mol / L acid solution (sulfuric acid solution) at a solid-liquid ratio of 1 g: 20 mL. Extract by shaking at 200 rpm for 4 h, heat at 80 °C for 2 h, cool naturally at room temperature to precipitate, wash three times each with deionized water and anhydrous ethanol, dry in an oven at 60 °C for 12 h, and finally calcine at 700 °C for 4 h to obtain the iron phosphate product.

[0031] Comparative Example 1 Same as Example 1, except that in step 3), no solid peroxide and ferrous salt crystals are added, resulting in a solid product obtained by direct hydrothermal carbonization without pretreatment.

[0032] The surface morphology of chicken manure before and after pretreatment in Example 1 was measured, and the results are as follows: Figure 1 As shown in the figure, the results indicate that after pre-oxidation treatment, the structure of chicken manure was destroyed, the surface became rough, and a loose structure formed by the accumulation of fine particles was formed. This shows that pre-oxidation treatment can effectively destroy the dense structure of chicken manure, promote the degradation of organic matter, and create favorable conditions for the full release of phosphorus.

[0033] The soluble organic matter content of chicken manure before and after pretreatment in Example 1 was measured, and the results are as follows: Figure 2 As shown in the figure. The results indicate that the fluorescence intensity of dissolved organic matter in chicken manure decreased significantly after pre-oxidation treatment, suggesting that pre-oxidation treatment can effectively decompose organic matter, destroy its macromolecular structure, and convert it into small molecules, thereby facilitating the release of phosphorus from the bound state of organic matter.

[0034] The total phosphorus content and yield of the hydrothermal carbon obtained in Example 1 and Comparative Example 1 were determined, and the results are as follows: Figure 3 , Figure 4As shown in the figure. The results show that the total phosphorus content in the pre-oxidized hydrothermal carbon of the present invention is increased by 30.4% and 17.7% compared with the blank group and the comparative example 1 group, respectively, and the hydrothermal carbon yield is increased by 7.0% compared with the comparative example 1 group, indicating that the method of Example 1 of the present invention can simultaneously enhance phosphorus enrichment and improve the yield of hydrothermal carbon.

[0035] The crystal structure, surface morphology, and elemental composition of the iron phosphate product prepared in Example 1 were determined, and the results are as follows: Figure 5 , Figure 6 As shown in the figure. The results show that the iron phosphate product prepared in Example 1 of the present invention has good crystallinity, the characteristic XRD diffraction peaks are consistent with the standard card, and there are no impurity peaks; the SEM image shows that the product is an irregular spherical particle, and the EDS shows that the Fe, P and O elements are uniformly distributed, indicating that the present invention has successfully prepared the iron phosphate product.

[0036] Example 2 Same as Example 1, except that in step 3), no ferrous salt crystals are added, that is, the molar ratio of ferrous salt crystals to solid peroxide is 0:1.

[0037] Example 3 Same as Example 1, except that in step 3), the molar ratio of ferrous salt crystals to solid peroxide is 2:1.

[0038] Example 4 Same as Example 1, except that in step 3), the molar ratio of ferrous salt crystals to solid peroxide is 3:1.

[0039] Example 5 Same as Example 1, except that in step 3), the molar ratio of ferrous salt crystals to solid peroxide is 4:1.

[0040] The total phosphorus content of the pretreated hydrothermal carbon from Examples 1-5 was determined, and the results are as follows: Figure 7 As shown in the figure, the total phosphorus content of hydrothermal carbon initially increases and then decreases with increasing molar ratio of ferrous salt crystals to solid peroxide. This is because a lower dosage of ferrous salt crystals is insufficient to fully activate the solid peroxide and generate enough free radicals, resulting in inadequate phosphorus release. Conversely, excessive ferrous salt crystals consume free radicals, reducing the system's oxidation capacity and hindering phosphorus release.

[0041] Example 6 Same as Example 1, except that in step 3), the amount of solid peroxide added is 0.5 mmol / g.

[0042] Example 7 Same as Example 1, except that in step 3), the amount of solid peroxide added is 2.5 mmol / g.

[0043] Example 8 Same as Example 1, except that in step 3), the amount of solid peroxide added is 3.5 mmol / g.

[0044] Example 9 Same as Example 1, except that in step 3), the amount of solid peroxide added is 4.5 mmol / g.

[0045] The total phosphorus content of the pretreated hydrothermal carbon in Examples 1, 6-9 was determined, and the results are as follows: Figure 8 As shown in the figure, the total phosphorus content of hydrothermal char initially increases and then decreases with increasing peroxide dosage. This is because an appropriate amount of peroxide can generate sufficient free radicals to promote phosphorus release, but excessively high peroxide concentrations can trigger free radical self-quenching, leading to the consumption of free radicals, thereby reducing oxidation efficiency and inhibiting phosphorus release.

[0046] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for recovering phosphorus from livestock and poultry manure and preparing ferric phosphate via pre-oxidation synergistic hydrothermal carbonization, characterized in that, Includes the following steps: Step 1) Mix ammonium sulfate and sulfuric acid to prepare an electrolyte. Electrolyze the electrolyte in an electrolytic cell with platinum as the anode and graphite as the cathode. After electrolysis, obtain solid peroxide by filtration, cooling and crystallization, centrifugation and drying. Step 2) After degreasing the iron filings with alkaline solution and washing them with water, they are added to dilute sulfuric acid and reacted until completely dissolved. After filtration, acidification, cooling and crystallization, centrifugation and drying, ferrous salt crystals are obtained. Step 3) Mix the ferrous salt crystals obtained in Step 2) with the solid peroxide obtained in Step 1), add the mixture to the livestock and poultry manure mixture, and stir and react at room temperature to obtain a pretreated mixture; the molar ratio of the ferrous salt crystals to the solid peroxide is (1~4):1; the dosage of the solid peroxide is 0.5~4.5 mmol / g based on the dry weight of the livestock and poultry manure. Step 4) Transfer the pretreated mixture obtained in Step 3) to a closed reactor for hydrothermal carbonization reaction. After the reaction is completed, allow it to cool naturally to room temperature. Open the reactor and obtain the solid product by filtration, washing, drying and grinding. Step 5) Extract the solid product obtained in step 4) by acid oscillation, centrifuge, heat to react, cool to precipitate, wash, dry and calcinate to obtain iron phosphate.

2. The method for recovering phosphorus from livestock and poultry manure to prepare ferric phosphate by pre-oxidation synergistic hydrothermal carbonization according to claim 1, characterized in that, In step 1), the concentration of ammonium sulfate in the electrolyte is 30-40 wt%; the concentration of sulfuric acid in the electrolyte is 10-20 wt%; and the conditions during the electrolysis process are: current density of 0.5-1 A / cm². 2 The electrolysis voltage is 4~8V and the electrolysis time is 4~6h.

3. The method for recovering phosphorus from livestock and poultry manure to prepare iron phosphate by pre-oxidation synergistic hydrothermal carbonization according to claim 1, characterized in that, In step 1), the specific steps for cooling crystallization are as follows: first, place the sample in an ice-water bath for 2-4 hours; then, dry it in a vacuum drying oven at 30-40°C for 4-6 hours.

4. The method for recovering phosphorus from livestock and poultry manure to prepare ferric phosphate by pre-oxidation synergistic hydrothermal carbonization according to claim 1, characterized in that, In step 2), the concentration of the alkaline solution is 5-10 wt%; the degreasing treatment time is 10-30 min; the concentration of the dilute sulfuric acid is 10-20 wt%; and the reaction time is 1-3 h.

5. The method for recovering phosphorus from livestock and poultry manure to prepare ferric phosphate by pre-oxidation synergistic hydrothermal carbonization according to claim 1, characterized in that, In step 2), the acidification is to adjust the pH to 1-6 with sulfuric acid; the specific steps of the cooling crystallization are: first place the sample in an ice-water bath and let it stand for 2-4 hours; the drying is to place it in a vacuum drying oven at 30-40℃ and dry it for 2-4 hours.

6. The method for recovering phosphorus from livestock and poultry manure to prepare iron phosphate by pre-oxidation synergistic hydrothermal carbonization according to claim 1, characterized in that, In step 3), the solid-liquid ratio of the livestock and poultry manure mixture is 1g:(5~15)mL; the stirring reaction is carried out by mechanical stirring at a speed of 300~600rpm for a duration of 0.5~2h.

7. The method for recovering phosphorus from livestock and poultry manure to prepare ferric phosphate by pre-oxidation synergistic hydrothermal carbonization according to claim 1, characterized in that, In step 4), the temperature of the hydrothermal carbonization reaction is 100~220℃, and the reaction time is 1~4h; the washing is rinsing with deionized water 3~5 times; and the drying is drying in a 60℃ oven for 12h.

8. The method for recovering phosphorus from livestock and poultry manure to prepare iron phosphate by pre-oxidation synergistic hydrothermal carbonization according to claim 1, characterized in that, In step 5), the concentration of the acid solution is 0.1~0.5mol / L; the solid-liquid ratio of the solid product and the acid solution is 1g:(10~30)mL.

9. The method for recovering phosphorus from livestock and poultry manure to prepare ferric phosphate by pre-oxidation synergistic hydrothermal carbonization according to claim 1, characterized in that, In step 5), the oscillation rate of the oscillation extraction is 150~250 rpm, and the oscillation time is 2~6 h.

10. The method for recovering phosphorus from livestock and poultry manure to prepare iron phosphate by pre-oxidation synergistic hydrothermal carbonization according to claim 1, characterized in that, In step 5), the heating reaction temperature is 70~90℃ and the reaction time is 1~3h; the cooling is natural cooling at room temperature; the washing is washing 2~3 times each with deionized water and anhydrous ethanol; the drying is drying in a 60℃ oven for 12h; the calcination temperature is 600~800℃ and the calcination time is 2~6h.

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