Hydroxyferric phosphate and its preparation method and application

Abstract

The present invention discloses a hydroxy ferric phosphate and its preparation method and application. The preparation method of hydroxy ferric phosphate comprises: step 1, uniformly mixing an iron salt and water to obtain a solution A, and uniformly mixing a phosphate salt and water to obtain a solution B; step 2, dropwise adding the solution B to the solution A under stirring conditions and mixing uniformly to obtain a solution C, wherein, in terms of the amount of substance, the ratio of the iron in the solution A to the phosphorus in the solution B is (0.8-1.2):(0.8-1.2); step 3, reacting the solution C at 170-200°C for 10-14 hours, cooling to room temperature, centrifuging, washing, and drying to obtain the hydroxy ferric phosphate. The present invention also discloses a method for preparing a slow-release fertilizer, ammonium ferrous phosphate, from a deactivated catalyst. The hydroxy ferric phosphate facilitates the two-electron reduction of O2 and can generate a large amount of ROS during the EF reaction, which is beneficial to the degradation of organic pollutants. The present invention successfully converts the deactivated hydroxy ferric phosphate into the slow-release fertilizer, ammonium ferrous phosphate, thereby realizing the resource recovery and utilization of the deactivated catalyst.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrochemical treatment of organic pollutant wastewater, and specifically relates to hydroxyferric phosphate and a preparation method and application thereof. Background Art

[0002] In recent decades, water pollution caused by industrialization and daily life has become increasingly serious, posing a serious threat to human health. Electro-Fenton (EF), one of the advanced oxidation technologies, has been widely used in the treatment of organic wastewater due to its advantages, including ease of operation, the absence of additional oxidants, safety, and the generation of a variety of reactive oxygen species (ROS) during the EF process. However, the EF process typically requires the addition of large amounts of catalysts to promote the generation of ROS during the reaction. Transition metal phosphates are one of the commonly used heterogeneous catalysts in EF processes. They are inorganic materials with a metal center bound to a phosphate group, a combination that facilitates the formation of a layered structure with an open framework. Transition metal phosphates have the advantages of low cost, abundant resources, environmental friendliness, high stability, unique physicochemical properties, and strong tunability, making them highly valuable in electrochemical reactions. However, with repeated use, the performance of the catalyst gradually degrades, and currently, there is no recycling of these deactivated catalysts, resulting in resource waste and environmental pollution. Summary of the Invention

[0003] In view of the shortcomings of the prior art, the present invention aims to provide a hydroxy iron phosphate (Fe5(PO4)4(OH)3·2H2O).

[0004] Another object of the present invention is to provide a method for preparing the above-mentioned ferric hydroxyphosphate, wherein the ferric hydroxyphosphate is synthesized from an iron salt and a phosphate by a hydrothermal method.

[0005] Another object of the present invention is to provide the use of the above-mentioned hydroxyferric phosphate as a catalyst in the electro-Fenton degradation of organic pollutants in wastewater, and the hydroxyferric phosphate as a catalyst has good recycling stability in the degradation of wastewater.

[0006] Another object of the present invention is to provide a method for recovering a deactivated catalyst to prepare slow-release fertilizer ammonium ferrous phosphate.

[0007] The purpose of the present invention is achieved through the following technical solutions.

[0008] A method for preparing ferric hydroxyphosphate comprises the following steps:

[0009] Step 1: Mix iron salt and water to obtain solution A, and mix phosphate and water to obtain solution B;

[0010] In step 1, the concentration of iron salt in solution A is 0.25-0.4 mol·L -1 The concentration of phosphate in the B solution is 0.25-0.4 mol·L -1 .

[0011] Step 2: adding the solution B dropwise to the solution A under stirring and mixing uniformly to obtain a solution C, wherein the ratio of iron in the solution A to phosphorus in the solution B is (0.8-1.2): (0.8-1.2) by amount of substance;

[0012] In steps 1 and 2, the uniform mixing is achieved by stirring, the stirring time is 30 to 45 minutes, and the stirring temperature is 20 to 25°C.

[0013] Step 3: hydrothermally reacting the C solution at 170-200° C. for 10-14 hours, cooling to room temperature, centrifuging, washing, and drying to obtain hydroxyferric phosphate.

[0014] In step 3, distilled water and ethanol are used for washing.

[0015] In step 3, the drying temperature is 60-80° C., and the drying time is 10-12 hours.

[0016] The hydroxyferric phosphate obtained by the above preparation method.

[0017] The above-mentioned ferric hydroxyphosphate is used as a catalyst in the electro-Fenton degradation of organic pollutants in wastewater.

[0018] In the above technical solution, the organic pollutant is one or more of sulfamethoxazole (SMX), ciprofloxacin (CIP), tetracycline (TC) and norfloxacin (NRFX).

[0019] In the above technical solution, the pH of the wastewater is 3-9.

[0020] In the above technical solution, the method for degrading wastewater includes: adding a catalyst and an electrolyte into the wastewater, then setting an anode and a cathode in the wastewater, applying an external voltage of 2 to 6V between the anode and the cathode, and introducing oxygen under stirring conditions.

[0021] In the above technical solution, the flow rate of oxygen is 90-120 mL min -1 The time for introducing oxygen is 30 to 150 minutes.

[0022] In the above technical solution, the concentration of electrolyte in the wastewater is 0.04-0.06 mol·L -1 .

[0023] In the above technical solution, the mass of the catalyst added to every 60 mL of the wastewater is 10 to 60 mg.

[0024] A method for preparing slow-release fertilizer ammonium ferrous phosphate by recovering a deactivated catalyst comprises: mixing a deactivated catalyst and concentrated HCl, heating the mixture to 90-100° C., stirring the mixture for 40-60 minutes until uniform, cooling the mixture to room temperature of 20-25° C. to obtain a D solution; mixing L-ascorbic acid with the D solution, stirring the mixture for 25-45 minutes until uniform, adjusting the pH value to 5-7 to obtain a precipitate; washing the precipitate, and drying the precipitate to obtain the slow-release fertilizer ammonium ferrous phosphate. The ratio of the mass fraction of the catalyst, the volume fraction of concentrated HCl, and the mass fraction of L-ascorbic acid is (50-300):50:(10-30), the units of the mass fractions are mg, and the units of the volume fractions are mL. The catalyst is hydroxyferric phosphate.

[0025] In the above technical solution, the pH is adjusted by dripping ammonia water, and the concentration of the ammonia water is 24-28 wt%.

[0026] In the above technical solution, the washing is performed by washing with water and then with ethanol.

[0027] In the above technical solution, the drying temperature is 60-80° C., and the drying time is 10-12 hours.

[0028] In the above technical solution, the mass fraction of HCl in the concentrated HCl is 36-38 wt%.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1. The hydroxyferric phosphate of the present invention is beneficial to the 2-electron reduction of O2, and can generate a large amount of ROS during the EF reaction process, which is beneficial to the degradation of organic pollutants.

[0031] 2. The hydroxyferric phosphate of the present invention is stable and universal as a catalyst.

[0032] 3. The present invention successfully converts the deactivated hydroxyferric phosphate into the slow-release fertilizer ammonium ferrous phosphate, thereby realizing the resource recovery and utilization of the deactivated catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The SEM, X-ray spectrometer (EDS) elemental map and XRD pattern of the hydroxyferric phosphate prepared in Example 1, wherein (a) and (b) are SEM images of hydroxyferric phosphate at different magnifications, (c) is an X-ray spectrometer (EDS) elemental map of hydroxyferric phosphate, and (d) is an XRD pattern of hydroxyferric phosphate;

[0034] Figure 2 This is the FT-IR spectrum of the ferric hydroxyphosphate prepared in Example 1;

[0035] Figure 3 The specific surface area diagram of the ferric hydroxyphosphate prepared in Example 1 and the pore size distribution diagram in the inset are shown;

[0036] Figure 4 This is the high-resolution XPS elemental spectrum of the ferric hydroxyphosphate prepared in Example 1, where (a) is the full spectrum, (b) is Fe 2p, (c) is O1s, and (d) is P 2p;

[0037] Figure 5 is the O2 adsorption-desorption equilibrium ( Figure 5 SMX degradation efficiency change trend chart within 120 minutes from 0 minute;

[0038] Figure 6 (a) SMX degradation efficiency change trend diagram and (b) pseudo-first-order chemical kinetic constant within 120 minutes from O2 adsorption-desorption equilibrium in Examples 4 to 7;

[0039] Figure 7 The figure shows the trend of SMX degradation efficiency within 120 minutes from the O adsorption-desorption equilibrium in Examples 6, 8, and 9, wherein (a) is the SMX degradation efficiency and (b) is the pseudo-first-order chemical kinetic constant curve;

[0040] Figure 8 The SMX degradation efficiency change trend diagram in Examples 6 and 10-11 within 120 minutes from the O2 adsorption-desorption equilibrium;

[0041] Figure 9 This is a universality test diagram of the ferric hydroxyphosphate prepared in Example 1;

[0042] Figure 10 This is a stability test chart of the ferric hydroxyphosphate prepared in Example 1;

[0043] Figure 11 The SEM and EDS elemental maps of the slow-release fertilizer ammonium ferrous phosphate prepared in Example 12, wherein (a) is the SEM, and (b) is the EDS elemental map;

[0044] Figure 12 (a) XRD pattern and (b) FT-IR spectrum of the slow-release ammonium ferrous phosphate fertilizer prepared in Example 12;

[0045] Figure 13 This is the germination and growth of the seeds in Example 13. DETAILED DESCRIPTION

[0046] The technical solution of the present invention is further described below with reference to specific embodiments.

[0047] The purity and purchasing manufacturers of the drugs involved in the following examples are as follows:

[0048]

[0049] The models and manufacturers of the instruments involved in the following embodiments are as follows:

[0050]

[0051] In the following examples, water is distilled water.

[0052] In the following examples, the solvent used to simulate wastewater containing organic pollutants is water.

[0053] Example 1

[0054] A method for preparing ferric hydroxyphosphate comprises the following steps:

[0055] Step 1: Mix ferric chloride (FeCl3·6H2O) and water, stir at room temperature of 20-25°C for 30 min until the mixture is uniform, to obtain solution A; mix sodium ammonium hydrogen phosphate (NaNH4HPO4·4H2O) and water, stir at room temperature of 20-25°C for 30 min until the mixture is uniform, to obtain solution B. The concentration of ferric chloride in solution A is 0.3 mol·L -1 The concentration of sodium ammonium phosphate in solution B is 0.3 mol·L -1 ;

[0056] Step 2: Add solution B dropwise to solution A under stirring, and stir at room temperature of 20-25° C. for 45 minutes until the mixture is uniformly mixed to obtain solution C, wherein the ratio of iron in solution A to phosphorus in solution B is 1:1, based on the amount of substance;

[0057] Step 3: Transfer solution C to a 100 mL reactor, carry out hydrothermal reaction at 180° C. for 12 h under sealed conditions, cool naturally to room temperature (20-25° C.), centrifuge, wash with water and ethanol in sequence, and vacuum dry at 60° C. for 12 h to obtain hydroxyferric phosphate (Fe5(PO4)4(OH)3·2H2O).

[0058] Figure 1 Figures (a) and (b) show SEM images of the ferric hydroxyphosphate prepared in Example 1 at different magnifications. The ferric hydroxyphosphate is spherical in shape, with a relatively rough surface and numerous pores. The rough surface and porous structure expose more active sites on the ferric hydroxyphosphate, facilitating the attachment of active substances. Figure 1(c) is the EDS elemental map of hydroxyferric phosphate, from which it can be seen that the Fe, O and P elements are evenly distributed on the spherical hydroxyferric phosphate.

[0059] Figure 1 (d) is the XRD pattern of the ferric hydroxyphosphate prepared in Example 1, wherein the peaks at 2θ are 226.67°, 27.86°, 34.58°, 39.47°, 44.23°, 44.67°, 48.68°, 49.73°, 52.13°, 55.11°, 57.36° and 57.68°, respectively corresponding to the (320), (330), (400), (421), (520), (480), (362), (1140), (2140), (4120), (522) and (482) crystal planes of ferric hydroxyphosphate (PDF#45-1436). There are no other impurity peaks in the XRD diffraction pattern, indicating that the ferric hydroxyphosphate is of high purity and free of other impurities. The ferric hydroxyphosphate obtained by the above method has sharp diffraction peaks, proving that the ferric hydroxyphosphate has good crystallinity.

[0060] FT-IR spectroscopy is commonly used to detect various functional groups in synthetic products. Figure 2 This is the FT-IR spectrum of the ferric hydroxyphosphate prepared in Example 1. -1 and 3450cm -1 The characteristic peak of OH can be observed at 1062cm, which includes the OH functional group of hydroxyferric phosphate itself and the bending vibration of crystal water HOH. -1 The broadband is asymmetric PO4 3- Stretching vibration, which is directly related to the phosphate group in the ferric hydroxyphosphate. 1003cm -1 and 710cm -1 The peak at can be considered as the stretching vibration of Fe-O in hydroxyferric phosphate, which proves that PO4 3- O and Fe in 3+ The characteristic peaks of FT-IR spectrum fully prove the successful synthesis of ferric hydroxyphosphate. The results obtained from FT-IR spectrum analysis are consistent with the above XRD results.

[0061] The BET surface area and pore size distribution of the ferric hydroxyphosphate prepared in Example 1 were studied by N2 adsorption-desorption isotherms. Figure 3 The specific surface area diagram of the ferric hydroxyphosphate prepared in Example 1 and the pore size distribution diagram in the illustration are shown. Figure 3 As shown in Figure 2, hydroxyferric phosphate exhibits a typical IV type isotherm and H3 type hysteresis loop. The main pore size distribution of hydroxyferric phosphate is 4-15 nm, the average pore size is 9.98 nm, and the specific surface area is 27.72 m 2 ·g-1 In the degradation experiment, the porous microspheres with a larger specific surface area provide more active sites for adsorbing pollutants, thereby effectively degrading the pollutants.

[0062] The surface element composition and corresponding chemical valence of the ferric hydroxyphosphate prepared in Example 1 were detected by XPS. Figure 4 This is the high-resolution XPS elemental spectrum of the ferric hydroxyphosphate prepared in Example 1, where (a) is the full spectrum, (b) is Fe 2p, (c) is O1s, and (d) is P 2p. Figure 4 As shown in (a)-(d), the XPS full spectrum scan of hydroxyferric phosphate clearly shows Fe, O, P and C elements from the outside on the surface of hydroxyferric phosphate, which indicates the successful synthesis of hydroxyferric phosphate. The high-resolution Fe 2p photoelectron spectrum was fitted, and the fitted spectrum showed that Fe2p 3 / 2 (712.5eV), satellite peak (715.0eV) and Fe2p 1 / 2 (726.2eV) three signal peaks. These three signal peaks are mainly caused by the presence of Fe in the lattice structure of the compound. 3+ However, in the EF process, due to the presence of external voltage, Fe 3+ Easily reduced to Fe 2+ The O1s peak is fitted into three peaks with peak centers at 532.5eV, 531.5eV and 531.2eV respectively. These O1s peaks are caused by HOH in H2O, OH in hydroxyl and PO4 3- The peak of P 2p is at 133.09eV, which is PO4 3- The results of XPS analysis are consistent with those of elemental analysis. Among them, the iron ions on the surface of hydroxyferric phosphate can undergo valence transformation in the EF reaction to promote the reaction of H2O2 to generate ·OH and ·O 2- , producing a variety of ROS for the degradation of the antibiotic sulfamethoxazole (SMX), achieving the effect of sewage purification.

[0063] Simulate the configuration of organic pollutant wastewater: the electrolyte (Na2SO4) concentration is 0.05mol·L -1 The Na2SO4 aqueous solution was used as the electrolyte solution to prepare sulfamethoxazole (SMX) with a concentration of 50 mg·L -1 simulated organic pollutant wastewater.

[0064] Example 2

[0065] Take 60mL of simulated organic pollutant wastewater and store it in a cylindrical glass container. -1The pH value was adjusted to 3 by adding NaOH aqueous solution and H2SO4 aqueous solution, 30 mg of hydroxyferric phosphate prepared in Example 1 was evenly dispersed in the simulated organic pollutant wastewater, and a CF (3×4×0.5 cm) was immersed in the simulated organic pollutant wastewater and stirred at 100 mL·min -1 Oxygen was continuously introduced at a flow rate of 30 min to achieve O2 adsorption-desorption equilibrium. After the reaction started, oxygen was continuously introduced for 120 min for physical adsorption.

[0066] Example 3

[0067] Take 60mL of simulated organic pollutant wastewater and store it in a cylindrical glass container. -1 The pH value of the solution was adjusted to 3 by adding NaOH aqueous solution and H2SO4 aqueous solution. A platinum sheet (1×2 cm) was used as the anode and a CF (3×4×0.5 cm) was used as the cathode. The anode and cathode were immersed in the simulated organic pollutant wastewater. Before the reaction started, the solution was stirred at 100 mL min -1 Oxygen was continuously introduced at a flow rate of 100 μg / min for 30 min to achieve the adsorption-desorption equilibrium of O2. After the reaction started, oxygen was continuously introduced for 120 min, and the external voltage was adjusted to 4 V for electrosorption.

[0068] Examples 4 to 9

[0069] Take 60mL of simulated organic pollutant wastewater and store it in a cylindrical glass container. -1 The pH value was adjusted by using NaOH aqueous solution and H2SO4 aqueous solution. Platinum sheet (1×2 cm) and CF (3×4×0.5 cm) were used as the anode and cathode of the EF device, respectively. The hydroxy ferric phosphate prepared in Example 1 was uniformly dispersed in the simulated organic pollutant wastewater. Before the reaction started, the ferric hydroxy phosphate was heated at 100 mL·min -1 Oxygen was continuously introduced at a flow rate of 100 μg / min for 30 minutes to achieve O2 adsorption-desorption equilibrium. The applied voltage connected to the EF device was then adjusted to 4 V, and the SMX degradation experiment began under continuous O2 infusion. The mass of ferric hydroxyphosphate input and the adjusted pH are shown in Table 1.

[0070] Table 1

[0071] Example pH Amount of hydroxyferric phosphate added (unit: mg) Example 4 3 10 Example 5 3 20 Example 6 3 30 Example 7 3 40 Example 8 6 30 Example 9 9 30

[0072] Examples 2, 3 and 6 show the effects of different degradation processes on the degradation efficiency of SMX. Figure 5As shown. Example 6 is an EF process, in which the applied voltage is 4V and the amount of hydroxy ferric phosphate added is 30mg; Example 2 is a physical adsorption process, in which no voltage is applied and the amount of hydroxy ferric phosphate added is 30mg; Example 3 is an electrosorption process, in which only a voltage of 4V is applied and no catalyst is added. Figure 5 As shown, in Example 2, the SMX degradation efficiency of hydroxyferric phosphate within 120 minutes was 0.2%, and SMX was almost not degraded. In Example 3, the SMX degradation efficiency of hydroxyferric phosphate within 120 minutes was 68.9%, which was improved compared with Example 2. In Example 6, the SMX degradation efficiency of hydroxyferric phosphate within 120 minutes was significantly improved, and the SMX degradation efficiency was 94.5%, which proved the superiority of the EF process in degrading organic pollutant wastewater.

[0073] The results of the EF process degradation of SMX in Examples 4 to 7 are as follows: Figure 6 shown. Figure 6 (a) shows that as the amount of ferric hydroxyphosphate added increases, the degradation efficiency of the antibiotic SMX first increases and then decreases. When the amount of ferric hydroxyphosphate added is 10 mg, the degradation efficiency of SMX is 84.9%. When the amount of ferric hydroxyphosphate added is 20 mg, the degradation efficiency of SMX is 88.8%. When the amount of ferric hydroxyphosphate added is 30 mg, the catalytic degradation of SMX by ferric hydroxyphosphate in the EF system reaches a maximum value of 94.5%. As the amount of ferric hydroxyphosphate increases, the degradation efficiency of SMX begins to decrease. When the amount of ferric hydroxyphosphate added is 40 mg, the degradation efficiency of the antibiotic SMX is 91.6%. Figure 6 (b) is a trend diagram of the pseudo-first-order chemical kinetic constants of the EF process of Examples 4 to 7. When the amount of hydroxyferric phosphate added increases from 10 mg to 30 mg, the pseudo-first-order chemical kinetic constant k gradually increases, which are 0.0162 min -1 、0.0179min -1 and 0.0241min -1 However, when the addition amount of hydroxyferric phosphate is 40 mg, the pseudo-first-order chemical kinetic constant k becomes smaller to 0.0236 min -1 . Figure 6 It shows that when the EF system degrades SMX, the more hydroxyferric phosphate is added, the better it is. It is necessary to find a suitable addition amount. This is because as the catalyst content increases, the pores of CF will be blocked, thereby reducing the degradation efficiency of SMX.

[0074] Examples 6, 8 and 9 are experiments to determine the degradation effect of ferric hydroxyphosphate on SMX in simulated organic pollutant wastewater at different pH values. The results are as follows: Figure 7 As shown. Figure 7As shown in (a), when pH = 3, the degradation efficiency of SMX in the EF system is 94.5% at 120 minutes from the O2 adsorption-desorption equilibrium. However, as the pH value increases, the degradation efficiency of SMX decreases. The degradation efficiencies of SMX at pH values ​​of 6 and 9 are 81.1% and 73.8% at 120 minutes from the adsorption-desorption equilibrium, respectively. The trend diagram of the pseudo-first-order chemical kinetic constants of the degradation of SMX by EF at different pH values ​​is shown in Figure 2. Figure 7 As shown in (b), when the pH values ​​are 3, 6 and 9, the corresponding pseudo-first-order chemical kinetic constants k are 0.0241, 0.0136 and 0.00996 min, respectively. -1 Under acidic conditions, the electrons of O2 and H + Combined with H2O2, which is more likely to generate ROS, and acidic conditions are more conducive to the catalyst to produce favorable Fe 3+ Used in redox reactions.

[0075] Examples 10-11

[0076] This embodiment is basically the same as embodiment 6, the only difference being the applied voltage.

[0077] Table 2

[0078]

[0079] In Examples 10 and 11, voltages of 2 V and 6 V were applied to the EF device, respectively. The SMX degradation efficiencies of Examples 6 and 10 to 11 are shown in FIG. Figure 8 As shown in the figure, the degradation efficiency of SMX increases with the increase of the applied voltage. The degradation efficiency of SMX is 77.9% at an applied voltage of 2V 120 minutes after the O2 adsorption-desorption equilibrium; the degradation efficiency of SMX is 94.5% 120 minutes after the adsorption-desorption equilibrium reaction when the applied voltage is 4V; when the applied voltage is 6V, the degradation efficiency of SMX reaches 95.8% 120 minutes after the adsorption-desorption equilibrium reaction. A higher applied voltage can promote O2 to obtain electrons to produce H2O2, which further reacts with the catalyst to generate ROS. In addition, as the applied voltage increases, the electron transfer can be promoted to make Fe 3+ Rapidly converted to Fe 2+ , thereby accelerating the reaction of H2O2 and Fe 3+ / Fe 2+ Oxidation-reduction reaction occurs, forming more OH and O 2- .

[0080] Degradation of ciprofloxacin (CIP), tetracycline (TC) and norfloxacin (NRFX) in the EF process using ferric hydroxyphosphate: basically the same as Example 6, the only difference is that sulfamethoxazole (SMX) in the simulated organic pollutant wastewater in Example 6 is replaced by "ciprofloxacin (CIP), tetracycline (TC) or norfloxacin (NRFX)". Figure 9 This is a universality test diagram of the ferric hydroxyphosphate prepared in Example 1, wherein: Figure 9 TC is the degradation efficiency of tetracycline (TC) by ferric hydroxyphosphate at 120 minutes from the O2 adsorption-desorption equilibrium. Figure 9 CIP is the degradation efficiency of ciprofloxacin by ferric hydroxyphosphate at 120 minutes from the O2 adsorption-desorption equilibrium. Figure 9 NRFX is the degradation efficiency of norfloxacin (NRFX) by ferric hydroxyphosphate at 120 minutes from the O2 adsorption-desorption equilibrium. Figure 9 Where SMX represents the degradation efficiency of Example 6 at 120 min from the O2 adsorption-desorption equilibrium. Figure 9 As shown in the figure, after 120 minutes of EF reaction starting from the O2 adsorption-desorption equilibrium, it can be found that ferric hydroxyphosphate has a good effect on the EF-catalytic degradation of the above-mentioned organic pollutants, indicating the universality of ferric hydroxyphosphate in the EF process.

[0081] The recyclability of ferric hydroxyphosphate is an important indicator of the stability of ferric hydroxyphosphate as a catalyst. A recycling experiment was conducted on the degradation of SMX according to the reaction conditions of Example 6. The results of the recycling experiment are shown in Figure 2. Figure 10 As shown in the figure, after 10 cycles, the catalytic degradation efficiency of hydroxyferric phosphate on SMX can still reach 90.6% at 120 minutes from the adsorption-desorption equilibrium, and it can be seen that the degradation efficiency of hydroxyferric phosphate on SMX is almost the same at different numbers of cycles during the cycle process, indicating that hydroxyferric phosphate has good cyclic stability.

[0082] Example 12

[0083] The hydroxy ferric phosphate that was inactivated after multiple cycles of reaction in Example 6 (deactivation was defined as a significant decrease in the degradation effect of the catalyst) was recovered. The hydroxy ferric phosphate after the reaction was adsorbed on CF (3×4×0.5 cm). Therefore, 5 pieces of CF with 150 mg of hydroxy ferric phosphate adsorbed thereon after the reaction were dissolved in 50 mL of concentrated HCl, wherein the mass fraction of HCl in the concentrated HCl was 37 wt %. The mixture was heated to 90° C. and stirred for 45 min until the hydroxy ferric phosphate was completely dissolved. The mixture was cooled to room temperature of 25° C. to obtain a solution D. 10 mg of L-ascorbic acid was mixed with the solution D and stirred for 30 min until uniform. Ammonia water (ammonia water concentration was 25 wt %) was added dropwise to adjust the pH to 6 to obtain a precipitate. The precipitate was centrifuged and washed with distilled water and ethanol, respectively. The mixture was dried in vacuo at 60° C. for 12 h to obtain a slow-release fertilizer, ammonium ferrous phosphate. The conversion rate of the slow-release fertilizer, ammonium ferrous phosphate, was 85.6%.

[0084] Figure 11 (a) and (b) are the SEM image and EDS element mapping of the slow-release fertilizer ammonium ferrous phosphate, respectively. Figure 11 (a) shows that the slow-release fertilizer ammonium ferrous phosphate recovered in Example 12 is in irregular flakes. Figure 11 (b) shows that N, Fe, P and O on the slow-release fertilizer ammonium ferrous phosphate are evenly distributed, indicating that the slow-release fertilizer ammonium ferrous phosphate obtained in Example 12 has the elements necessary to promote plant growth.

[0085] The slow-release fertilizer ammonium ferrous phosphate obtained in Example 12 was characterized by XRD and FT-IR. Figure 12 As shown, Figure 12 In (a), NH4FePO4·H2O is the slow-release fertilizer ammonium ferrous phosphate obtained in Example 12. Figure 12 (a) It can be found that the slow-release fertilizer ammonium ferrous phosphate prepared by recycling the deactivated catalyst has a sharp XRD diffraction peak, and its characteristic peak is similar to that of commercially available FeNH4PO4·H2O( Figure 12 The NH4FePO4·H2O standard in the test sample is exactly the same. Figure 12 (b) is the FT-IR spectrum of the slow-release fertilizer ammonium ferrous phosphate obtained in Example 12, Figure 12 In (b), PO peak, NH peak, Fe-O peak and OH peak can be clearly observed, which further confirms that the failed hydroxyferric phosphate is converted into slow-release fertilizer ammonium ferrous phosphate.

[0086] Example 13

[0087] The application of slow-release fertilizer ammonium ferrous phosphate in the seed germination and growth process was prepared. Two portions of soil with 50 seeds buried were prepared. The slow-release fertilizer ammonium ferrous phosphate obtained in Example 12 was applied to one portion of the soil with 50 seeds buried: 20 mL of water was poured into the soil every two days and 30 mg of slow-release fertilizer ammonium ferrous phosphate was applied; no slow-release fertilizer was applied to the other portion of soil with 50 seeds buried, and 20 mL of water was poured into the soil every two days.

[0088] Observe and record the growth of seeds in the two soils on days 0, 3, and 6. Figure 13 As shown, it is shown that the slow-release fertilizer ammonium ferrous phosphate obtained in Example 12 has a promoting effect on seed germination and growth.

[0089] The above is an exemplary description of the present invention. It should be noted that, without departing from the core of the present invention, any simple deformation, modification or other equivalent replacement that can be made by other skilled in the art without expending creative labor falls within the scope of protection of the present invention.

Claims

1. A method for recovering deactivated catalyst to prepare slow-release fertilizer ammonium ferrous phosphate, characterized in that: include: The deactivated catalyst and concentrated HCl are mixed and heated to 90-100° C., stirred until uniform, and cooled to room temperature of 20-25° C. to obtain a D solution, L-ascorbic acid is mixed with the D solution, stirred until uniform, and the pH is adjusted to 5-7 to obtain a precipitate, and the precipitate is washed and dried to obtain a slow-release fertilizer ammonium ferrous phosphate, wherein the ratio of the mass fraction of the catalyst, the volume fraction of concentrated HCl, and the mass fraction of L-ascorbic acid is (50-300):50:(10-30), the unit of the mass fraction is mg, the unit of the volume fraction is mL, and the catalyst is hydroxy ferric phosphate; The preparation method of the hydroxyferric phosphate comprises the following steps: Step 1: Mix iron salt and water to obtain solution A, and mix phosphate and water to obtain solution B; Step 2: adding the solution B dropwise to the solution A under stirring and mixing uniformly to obtain a solution C, wherein the ratio of iron in the solution A to phosphorus in the solution B is (0.8-1.2): (0.8-1.2) by amount of substance; Step 3: hydrothermally reacting the C solution at 170-200° C. for 10-14 hours, cooling to room temperature, centrifuging, washing, and drying to obtain hydroxyferric phosphate.

2. The method according to claim 1, characterized in that In step 1, the concentration of iron salt in solution A is 0.25-0.4 mol·L -1 The concentration of phosphate in the B solution is 0.25-0.4 mol·L -1 .

3. The method according to claim 1, characterized in that In steps 1 and 2, the uniform mixing is achieved by stirring, the stirring time is 30 to 45 minutes, and the stirring temperature is 20 to 25°C.

4. The method according to claim 1, wherein In step 3, distilled water and ethanol are used for washing.

5. The method according to claim 1, wherein In step 3, the drying temperature is 60-80° C., and the drying time is 10-12 hours.

6. The method according to claim 1, characterized in that The deactivated catalyst and concentrated HCl were mixed and heated to 90-100°C, and stirred for 40-60 minutes until homogeneous.

7. The method according to claim 1, characterized in that Mix L-ascorbic acid and the D solution, and stir for 25 to 45 minutes until the mixture is homogeneous.

8. The method according to claim 1, characterized in that The mass fraction of HCl in the concentrated HCl is 36-38 wt %.

9. The method according to claim 1, characterized in that The pH is adjusted by adding aqueous ammonia.

10. The method according to claim 9, characterized in that The concentration of the ammonia water is 24-28 wt%.

11. The method according to claim 1, wherein The precipitate is washed and dried: the washing step is performed by washing with water and then with ethanol in sequence, the drying temperature is 60-80° C., and the drying time is 10-12 h.

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