A biochar-supported UiO-66(NH2) composite material, its preparation method and application

Abstract

The present application relates to a kind of biomass charcoal load UiO-66 (NH2) Composite material and its preparation method and application, the preparation method includes the following steps, after limiting oxygen pyrolysis, the agricultural straw biomass raw material is again activated by alkali solution and pretreated biomass charcoal is obtained;The pretreated biomass charcoal is added to the reaction system containing zirconium salt and amino terephthalic acid ligand, under heating condition, the metal organic framework crystal is in situ grown on the surface of pretreated biomass charcoal;After reaction is finished, it is washed with ethanol and dried, and the biomass charcoal load amino functionalized zirconium metal organic framework composite material, i.e. BC@UiO-66 (NH2) Is obtained.The BC@UiO-66 (NH2) Material prepared in the present application shows high selectivity to phosphorus in the competition system of multiple ions coexisting, so as to realize the efficient, low-cost and high-value recovery of phosphorus from waste.

Description

Technical Field

[0001] This invention belongs to the field of energy-saving and environmentally friendly functional materials and resource recycling technology, specifically relating to a biomass char supported UiO-66(NH2) composite material, its preparation method and application. Background Technology

[0002] Phosphorus is an indispensable resource in agricultural production and modern industry. Municipal sludge incineration ash, industrial byproducts, and some wastewater are rich in phosphorus, making these secondary resources a potentially important source of phosphorus. Existing phosphorus recovery technologies mainly include chemical precipitation, solvent extraction, and conventional adsorption. However, these methods have shortcomings in practical applications, such as insufficient selectivity. In systems containing multiple metal ions (iron, aluminum, calcium, magnesium, manganese, etc.) and / or multiple anions (sulfate, nitrate, etc.), there are problems such as severe competitive adsorption, difficulty in selectively separating phosphorus, and low desorption efficiency, resulting in low phosphorus recovery rates and poor recycling rates of adsorbent materials. Furthermore, the added value of recovered phosphorus products is low; typically, only low-purity phosphate salts are obtained, making direct high-value utilization difficult. Therefore, developing an adsorbent material with high selectivity for phosphorus that can operate stably in complex systems, and constructing a matching efficient and low-cost phosphorus recovery process, is of great significance for promoting the recycling of phosphorus resources. Based on this, this invention provides a biochar-supported UiO-66(NH2) composite material, its preparation method, and its application. Summary of the Invention

[0003] The purpose of this invention is to provide a biochar-supported UiO-66(NH2) composite material, its preparation method, and its application in order to solve the above-mentioned problems.

[0004] The present invention achieves the above objectives through the following technical solutions: This invention provides a method for preparing a biochar-supported UiO-66(NH2) composite material, comprising the following steps: Step 1: Agricultural straw biomass raw materials are subjected to oxygen-limited pyrolysis, followed by alkaline solution activation treatment to obtain pretreated biochar; The agricultural straw biomass raw material is at least one of corn straw, wheat straw, and rice straw; Step 2: The pretreated biochar is added to a reaction system containing zirconium salt and amino terephthalic acid ligand, and the reaction is carried out under heating conditions. The zirconium-oxygen clusters form an interfacial coupling structure with the oxygen-containing functional groups on the surface of the biochar, so that the metal-organic framework crystals grow in situ on the surface of the pretreated biochar. Step 3: After the reaction is completed, the mixture is washed with ethanol and dried to obtain the biochar-supported amino-functionalized zirconium-based metal-organic framework composite material BC@UiO-66(NH2).

[0005] As a further optimization of the present invention, in step one, the oxygen-limited pyrolysis is performed at 400-550°C for 1-3 hours under a N2 atmosphere; The alkaline solution activation treatment is performed by activating with a sodium hydroxide solution with a mass concentration of 4-10 wt% for 5-8 hours.

[0006] As a further optimization of the present invention, in step two, the reaction system containing zirconium salt and amino terephthalic acid ligand is obtained by dissolving ZrCl4 and NH2-BDC in N,N-dimethylformamide at a molar ratio of (1-2):(1-2), adjusting the pH to 1.5-3.5 with acetic acid, and stirring for 30-50 min to obtain the precursor solution; In the precursor solution, the concentration of ZrCl4 is 1-5 mmol / L; the concentration of NH2-BDC is 1-5 mmol / L. The amount of pretreated biochar added to the reaction system is 2-5 wt%, and the reaction is carried out at 100-135℃ for 18-30 h.

[0007] The present invention also provides a biochar-supported UiO-66(NH2) composite material, which is prepared by the preparation method described above.

[0008] This invention also provides an application of biochar-supported UiO-66(NH2) composite material in phosphorus recovery, the specific steps of which are as follows: (1) Biochar-supported UiO-66(NH2) composite material was directly added to a phosphorus-containing acid leaching solution containing multiple ions and reacted at room temperature with stirring. After adsorption was completed, phosphorus-supported BC@UiO-66(NH2) was obtained by solid-liquid separation. (2) The phosphorus-loaded BC@UiO-66(NH2) is placed in a desorption solution and a desorption reaction is carried out at room temperature and under stirring conditions. The phosphate ions adsorbed on the surface of BC@UiO-66(NH2) are effectively released, forming a phosphorus-enriched recovery solution. At the same time, the adsorbent material BC@UiO-66(NH2) is regenerated and can be reused. (3) Combine the recovered solutions of phosphorus enrichment from multiple recovery, add ferrous salt to them, control the molar ratio of iron to phosphorus, adjust the pH to neutral conditions, and phosphorus will precipitate out in the form of ferrous phosphate hydrate. The precipitate obtained is the phosphorus mineralization recovery product.

[0009] As a further optimization of the present invention, in step (1), the phosphorus-containing acid leaching solution is sludge incineration ash acid leaching solution or industrial wastewater leachate, and the phosphorus-containing acid leaching solution contains phosphate and at least one metal ion selected from iron, aluminum, calcium, magnesium and manganese ions and / or at least one anion selected from sulfate and nitrate ions; The biochar-supported UiO-66(NH2) composite material is added to a phosphorus-containing acid leaching solution at a dosage of 1-4 g / L.

[0010] As a further optimization of the present invention, in step (2), the desorption solution is a sodium hydroxide solution with a mass concentration of 3-5 wt%, and the desorption reaction time is 0.5-2 h.

[0011] As a further optimization of the present invention, in step (3), the molar ratio of iron to phosphorus is 1.4-1.7.

[0012] The beneficial effects of this invention are as follows: 1) In this invention, the hierarchical porous structure of biochar provides a rapid mass transfer channel for phosphate. The zirconium metal nodes in UiO-66(NH2) form stable Zr-OP coordination bonds with phosphate. The surface amino groups further capture phosphate in a directional manner through hydrogen bonding and electrostatic interactions. The synergistic effect of these three factors enables BC@UiO-66(NH2) material to exhibit high selectivity for phosphorus in a competitive system with multiple coexisting ions, thereby achieving efficient and low-cost phosphorus recovery. The phosphorus recovery product has a high added value, and biochar as a carrier can significantly improve structural stability, allowing BC@UiO-66(NH2) material to be reused multiple times, reducing production costs. It is suitable for the recovery of phosphorus resources from sludge incineration ash and industrial wastewater, and has good engineering application prospects.

[0013] 2) In this invention, agricultural straw biomass raw materials are used. Biochar loaded with UiO-66(NH2) is obtained by activation treatment with sodium hydroxide solution to obtain BC@UiO-66(NH2) material. The BC@UiO-66(NH2) material can achieve a high phosphorus recovery rate under high and / or low concentration of metal ions and / or anions interference conditions, indicating that it has high phosphorus selectivity and is suitable for phosphorus recovery in sludge incineration ash leachate, industrial wastewater and complex systems containing multiple metal ions and coexisting anions. Attached Figure Description

[0014] Figure 1 This is a flowchart illustrating the preparation process of the biochar-supported amino-functionalized zirconium-based metal-organic framework composite material of the present invention.

[0015] Figure 2 These are Fourier transform infrared (a) and scanning electron microscope (b) images of the biochar-supported amino-functionalized zirconium-based metal-organic framework composite material (BC@UiO-66(NH2)) prepared in Example 3 of this invention.

[0016] Figure 3This is a flowchart of phosphorus recovery using the biochar-supported amino-functionalized zirconium-based metal-organic framework composite material (BC@UiO-66(NH2)) prepared in Example 3 of this invention.

[0017] Figure 4 The images show scanning electron microscope (SEM) (a) and elemental analysis (b) images of the phosphorus recovery product obtained by recovering phosphorus using the biochar-supported amino-functionalized zirconium-based metal-organic framework composite material (BC@UiO-66(NH2)) prepared in Example 3 of this invention. Detailed Implementation

[0018] The present application will now be described in further detail with reference to the accompanying drawings. It should be noted that the following specific embodiments are only used to further illustrate the present application and should not be construed as limiting the scope of protection of the present application. Those skilled in the art can make some non-essential improvements and adjustments to the present application based on the above application content.

[0019] I. Materials 1. Agricultural straw biomass raw materials: at least one of corn straw, wheat straw, and rice straw; 2. Phosphorus-containing acid leaching solutions: acid leaching solutions from sludge incineration ash or industrial wastewater leachates; 3. NH2-BDC: 2-Amino-terephthalic acid (McLean brand), analytical grade, purchased from the market; 4. Zirconium chloride (ZrCl4): Purchased from the market, brand Maclean's zirconium chloride, analytical grade.

[0020] Unless otherwise specified, all methods used in this application are conventional methods known to those skilled in the art, and all reagents and materials used are commercially available products unless otherwise specified.

[0021] II. Methods In this embodiment, as Figure 1 As shown, this invention provides a method for obtaining a biochar-supported amino-functionalized zirconium-based metal-organic framework composite material (BC@UiO-66(NH2)), the specific steps of which are as follows: 1) Agricultural straw biomass raw materials are subjected to oxygen-limited pyrolysis at 450℃ for 2 hours (under N2 atmosphere), followed by alkaline activation treatment (using 6wt% sodium hydroxide solution for 6 hours) to obtain pretreated biochar with a hierarchical porous structure and hydroxyl / carboxyl functional groups on its surface; 2) The pretreated biochar was added to a reaction system containing zirconium salt and aminoterephthalic acid ligand (ZrCl4 and NH2-BDC were dissolved in N,N-dimethylformamide at a molar ratio of 1:1, the pH was adjusted to 2 with acetic acid, and the mixture was stirred for 35 min to obtain a precursor solution, in which the concentration of ZrCl4 was 2 mmol / L and the concentration of NH2-BDC was 2 mmol / L). The amount of pretreated biochar added to the reaction system was 2-5 wt% (3.5 wt% in this invention), and the reaction was carried out under solvent heating conditions (120℃ for 24 h) to allow metal-organic framework crystals to grow in situ on the surface of the pretreated biochar. 3) After the reaction was completed, the biochar-supported amino-functionalized zirconium-based metal-organic framework composite material (BC@UiO-66(NH2)) was obtained by washing and drying with ethanol.

[0022] like Figure 2 (a) As shown in the sample of Example 3, the successful synthesis of BC@UiO-66(NH2) was confirmed by the analysis of the characteristic peaks of the Fourier transform infrared spectrum. Figure 2 (b) Scanning electron microscopy images further demonstrate that the metal-organic framework structure UiO-66(NH2) has been successfully loaded onto the biochar support.

[0023] In this embodiment, as Figure 3 As shown, an application of the above-described biochar-supported amino-functionalized zirconium-based metal-organic framework composite material (BC@UiO-66(NH2)) for phosphorus recovery in a phosphorus-containing acid leaching solution (using sludge incineration ash as the target material, which contains at least one metal ion from iron, aluminum, calcium, magnesium, and manganese, and / or at least one anion from sulfate and nitrate, in addition to phosphate) is also provided. The specific steps are as follows: 1) The sludge incineration ash is leached with an acid solution to obtain a phosphorus-containing acid leachate; 2) Without any pre-treatment to remove impurities from the phosphorus-containing acid leaching solution, the BC@UiO-66(NH2) composite material was directly added to the solution. The dosage of the BC@UiO-66(NH2) composite material in the phosphorus-containing acid leaching solution is 1-4 g / L (3 g / L in this invention); 3) The reaction is carried out at room temperature with stirring, so that phosphate ions are preferentially captured by the adsorbent material; 4) After adsorption is complete, phosphorus-loaded BC@UiO-66(NH2) is obtained by solid-liquid separation; 5) The phosphorus-loaded BC@UiO-66(NH2) as described above is placed in an alkaline desorption solution (3-5 wt% NaOH solution, 4 wt% NaOH solution is used in this application) and the desorption reaction is carried out at room temperature and under stirring conditions for 1 hour. The phosphate ions adsorbed on the surface of BC@UiO-66(NH2) are effectively released, forming a phosphorus-enriched alkaline recovery solution. At the same time, the adsorbent material BC@UiO-66(NH2) is regenerated and can be reused in subsequent adsorption processes. 6) Combine the phosphorus-enriched alkaline recovery solutions obtained from multiple desorption processes, add ferrous salt to maintain the molar ratio of iron to phosphorus in the solution between 1.4 and 1.7 (1.5:1 in this application), and adjust the pH of the solution to neutral conditions. Under these conditions, phosphorus precipitates out as ferrous phosphate hydrate, and the resulting precipitate is the phosphorus mineralization recovery product, such as... Figure 4 As shown in a; Experimental analysis: such as Figure 4 As shown in b, the elemental composition analysis of the samples in Example 3 showed that the molar ratio of iron to phosphorus in the precipitate was approximately 1.54:1, which is highly consistent with the theoretical stoichiometric ratio. This indicates that the recovered phosphorus mainly exists in the form of the target mineral, with low impurity content and high added value of the phosphorus recovery product.

[0024] (1) In order to compare the effects of different biomass raw materials and biochar obtained by different alkaline solution activation treatments on the phosphorus recovery effect of the final adsorbent material BC@UiO-66(NH2) in phosphorus-containing acid leaching solutions with high and / or low concentrations of metal ions and / or anions, this application designed the experimental schemes of Examples 1-7 and Comparative Examples 1-3 as shown in Table 1 below, as detailed below: Table 1. Experimental design of Examples 1-7 and Comparative Examples 1-3

[0025] Note: When using two biomass raw materials, their mass ratio is 1:1; when using three biomass raw materials, their mass ratio is 1:1:1.

[0026] Phosphorus-containing acid leaching solution with high concentrations of metal ions: The acid leaching solution of sludge incineration ash is used as the object to be treated. In addition to phosphate, the acid leaching solution also contains a variety of metal ions such as iron, aluminum, calcium, magnesium, and manganese. The phosphorus-containing acid leaching solution contains 280 mg / L of phosphate, 80 mg / L of iron, 65 mg / L of aluminum, 128 mg / L of calcium, 25 mg / L of magnesium, and 6 mg / L of manganese.

[0027] Acid leaching solution containing low concentrations of metal ions: Acid leaching solution containing sludge incineration ash was used as the object to be treated. In addition to phosphate, the acid leaching solution also contained a variety of metal ions such as iron, aluminum, calcium, magnesium, and manganese. The concentrations of phosphate, iron, aluminum, calcium, magnesium, and manganese in the phosphorus-containing acid leaching solution were 280 mg / L, iron 35 mg / L, aluminum 23 mg / L, calcium 58 mg / L, magnesium 12 mg / L, and manganese 3.5 mg / L.

[0028] High-concentration anion-containing acid leaching solution: The acid leaching solution of sludge incineration ash is used as the object to be treated. In addition to phosphate, the acid leaching solution also contains a variety of metal ions such as iron, aluminum, calcium, magnesium, and manganese, as well as anions such as sulfate and nitrate. The concentrations of phosphate, iron, aluminum, calcium, magnesium, manganese, sulfate, and nitrate in the phosphorus-containing acid leaching solution are 280 mg / L, iron 35 mg / L, aluminum 23 mg / L, calcium 58 mg / L, magnesium 12 mg / L, manganese 3.5 mg / L, sulfate 260 mg / L, and nitrate 220 mg / L.

[0029] After repeating the process five times (acid leaching with phosphorus-containing acid leaching solution - desorption treatment with alkaline desorption solution - phosphorus mineralization recovery), the phosphorus recovery efficiency of BC@UiO-66(NH2) in each group was tested. The test was repeated three times, and the average value was recorded in Tables 2 and 3 to evaluate the cycle stability. The test results are shown in Tables 2 and 3. Table 2. Data Recording Sheet for Phosphorus Recovery Rate Test

[0030] Experimental conclusion: Using a specific combination of corn stalks and rice straw as biomass raw materials, and activating the biochar with sodium hydroxide solution to load UiO-66(NH2), BC@UiO-66(NH2) material was obtained. The synergistic effect between the hierarchical porous structure, zirconium metal nodes, and amino functional groups of this biochar enabled the prepared BC@UiO-66(NH2) material to achieve a high phosphorus recovery rate under both high and low concentrations of metal ion interference conditions. This indicates that BC@UiO-66(NH2) has high phosphorus selectivity and is easy to recycle and reuse. Among them, the BC@UiO-66(NH2) group in Example 3 showed a small difference in phosphorus recovery rate under high and low concentration metal ion interference conditions. After 5 cycles, the average phosphorus recovery rate remained at a high level, indicating the best performance. This shows that the BC@UiO-66(NH2) group in Example 3 has stronger stability.

[0031] Table 3. Data Recording Sheet for Phosphorus Recovery Rate Test

[0032] Experimental conclusions: In a phosphorus-containing acid leaching solution with high concentrations of anions, the phosphorus recovery rate of BC@UiO-66(NH2) in Example 3 group remained high. After 5 cycles, the average phosphorus recovery rate remained above 87%. Compared with other example groups and comparative groups, it exhibited the lowest decrease in phosphorus recovery rate and average phosphorus recovery rate after 5 cycles in a multi-element ion (metal ion and anion coexistence) system, indicating strong anti-interference ability, minimal performance degradation, and high stability. This demonstrates that BC@UiO-66(NH2) prepared by this invention has a wide range of applications and can selectively adsorb phosphorus in systems containing multiple metal ions such as iron, aluminum, calcium, magnesium, and manganese, and / or coexisting anions such as sulfate and nitrate, thereby achieving efficient phosphorus removal.

[0033] (2) To compare the effects of different adsorbents on phosphorus recovery in phosphorus-containing acid leaching solutions with high concentrations of metal ions, this application designed experimental schemes for comparative examples 4-6 as shown below: Comparative Example 4 In this comparative example, the difference from Example 3 is that an equal mass of pretreated biochar was directly added to a phosphorus-containing acid leaching solution with a high concentration of metal ions for acid leaching treatment, alkaline solution desorption treatment, and phosphorus mineralization recovery. Using the same detection method as described above, it was found that the phosphorus recovery rate in the phosphorus-containing acid leaching solution with a high concentration of metal ions was less than 5%, which indicates that the phosphorus selectivity of this material is too low and the application effect is very poor.

[0034] Comparative Example 5 In this comparative example, the difference from Example 3 is that an equal mass of pure UiO-66(NH2) powder was directly added to a phosphorus-containing acid leaching solution with a high concentration of metal ions for acid leaching treatment followed by alkaline solution desorption treatment. The phosphorus desorption rates were 91.2% and 90.3%, respectively. However, the dispersibility and solid-liquid separation performance of the pure UiO-66(NH2) powder were significantly poor. Therefore, it was difficult to carry out subsequent phosphorus mineralization recovery and recycling processes, resulting in high recovery difficulty and hindering industrial application.

[0035] Comparative Example 6 In this comparative example, the present invention provides a method for obtaining a biochar-supported zirconium-based metal-organic framework composite material (BC@UiO-66), the specific steps of which are as follows: 1) Agricultural straw biomass raw materials (corn straw and rice straw) are subjected to oxygen-limited pyrolysis at 450℃ for 2 hours (under N2 atmosphere), followed by alkaline activation treatment (6 wt% sodium hydroxide solution for 6 hours) to obtain pretreated biochar with a hierarchical porous structure and hydroxyl / carboxyl functional groups on its surface; 2) The pretreated biochar was added to a reaction system containing zirconium salt and terephthalic acid ligand (ZrCl4 and BDC were dissolved in N,N-dimethylformamide at a molar ratio of 1:1, the pH was adjusted to 2 with acetic acid, and the mixture was stirred for 35 min to obtain a precursor solution, in which the concentration of ZrCl4 was 2 mmol / L and the concentration of BDC was 2 mmol / L). The amount of pretreated biochar added to the reaction system was 3.5 wt%, and the reaction was carried out under solvent heating conditions (120 °C for 24 h) to allow metal-organic framework crystals to grow in situ on the surface of the pretreated biochar. 3) After the reaction is completed, the material is washed with ethanol and dried to obtain a biochar-supported zirconium-based metal-organic framework composite material (BC@UiO-66), which is a composite phosphorus selective adsorbent material BC@UiO-66.

[0036] In this comparative example, the specific operation of applying the composite phosphorus selective adsorbent BC@UiO-66 in phosphorus recovery was consistent with that in Example 3. The detection results obtained by using the same detection method were as described above. The phosphorus recovery rates in phosphorus-containing acid leaching solutions with high and low concentrations of metal ions / anions were 46.3% (high concentration of metal ions), 47.8% (low concentration of metal ions), and 41.3% (high concentration of anions). This indicates that compared with BC@UiO-66(NH2), the phosphorus selectivity of this material is significantly reduced, and its application prospects in industry are poor.

[0037] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. Use of a biomass char-supported UiO-66-NH2 composite material in phosphorus recovery, characterized in that: The preparation method of the biochar-supported UiO-66-NH2 composite material includes the following steps: Step 1: Pyrolyze corn stalks and rice straw in a mass ratio of 1:1 at 400-550℃ for 1-3 hours under N2 atmosphere, and then activate them with sodium hydroxide solution with a mass concentration of 4-10wt% for 5-8 hours to obtain pretreated biochar. Step 2: The pretreated biochar is added to a reaction system containing zirconium salt and amino terephthalic acid ligand, and the reaction is carried out under heating conditions, and metal-organic framework crystals grow in situ on the surface of the pretreated biochar. Step 3: After the reaction is completed, the mixture is washed with ethanol and dried to obtain a biochar-supported amino-functionalized zirconium-based metal-organic framework composite material, namely biochar-supported UiO-66-NH2. The method for recovering phosphorus from the biochar-supported UiO-66-NH2 composite material comprises the following steps: (1) Biochar-supported UiO-66-NH2 composite material was directly added to a phosphorus-containing acid leaching solution containing multiple ions and reacted at room temperature with stirring. After adsorption was completed, phosphorus-loaded biochar-supported UiO-66-NH2 was obtained by solid-liquid separation. (2) The phosphorus-loaded biochar-loaded UiO-66-NH2 is placed in a desorption solution and desorption reaction is carried out at room temperature and under stirring conditions. The phosphate adsorbed on the surface of the biochar-loaded UiO-66-NH2 is effectively released, forming a phosphorus-enriched recovery solution. At the same time, the adsorbent material biochar-loaded UiO-66-NH2 is regenerated and can be reused. (3) Combine the recovered phosphorus-enriched liquids from multiple recovery processes, add ferrous salt to them, control the molar ratio of iron to phosphorus, adjust the pH to neutral conditions, and phosphorus will precipitate out in the form of ferrous phosphate hydrate. The resulting precipitate is the phosphorus mineralization recovery product.

2. Use according to claim 1, characterized in that: In step two, the reaction system containing zirconium salt and amino terephthalic acid ligand is obtained by dissolving ZrCl4 and NH2-BDC in N,N-dimethylformamide at a molar ratio of (1-2):(1-2), adjusting the pH to 1.5-3.5 with acetic acid, and stirring for 30-50 min to obtain the precursor solution. In the precursor solution, the concentration of ZrCl4 is 1-5 mmol / L; the concentration of NH2-BDC is 1-5 mmol / L. The amount of pretreated biochar added to the reaction system is 2-5 wt%, and the reaction is carried out at 100-135℃ for 18-30 h.

3. The application according to claim 1, characterized in that: In step (1), the phosphorus-containing acid leaching solution is sludge incineration ash acid leaching solution or industrial wastewater leaching solution. The phosphorus-containing acid leaching solution contains phosphate and at least one metal ion selected from iron, aluminum, calcium, magnesium and manganese ions and / or at least one anion selected from sulfate and nitrate ions. The biochar-supported UiO-66-NH2 composite material is added at a dosage of 1-4 g / L in a phosphorus-containing acid leaching solution.

4. The application according to claim 1, characterized in that: In step (2), the desorption solution is a sodium hydroxide solution with a mass concentration of 3-5 wt%, and the desorption reaction time is 0.5-2 h.

5. The application according to claim 1, characterized in that: In step (3), the molar ratio of iron to phosphorus is 1.4-1.7.

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