Method for preparing magnesium-doped iron phosphate material by wet process

Abstract

The invention provides a method for preparing a magnesium-doped iron phosphate material by a wet process, which comprises the following steps: S1, synthesis reaction: preparing an iron phosphate leaching solution, a magnesium metal oxide suspension or a magnesium metal oxide solid, taking a mixed solution of pure water and a regenerated iron leaching solution or the regenerated iron leaching solution as a base solution, and heating the base solution to obtain yellow slurry A, washing and separating to obtain a synthetic filter cake A; s2, conversion reaction: preparing a phosphoric acid solution, mixing the synthesized filter cake A with pure water to form slurry, heating and adding the phosphoric acid solution, heating and preserving heat to obtain white slurry B, and washing and carrying out solid-liquid separation to obtain a white filter cake B; s3, drying and calcining: drying, calcining and crushing the white filter cake B to obtain a magnesium-doped iron phosphate material; the magnesium-doped iron phosphate material is prepared by adopting a wet method, the problem of high energy consumption caused by a high-temperature solid-phase method is avoided, the whole preparation process is carried out at a relatively low temperature, energy is saved, and the method is easy to operate and control.

Description

Technical Field

[0001] The invention belongs to the technical field of iron phosphate, and specifically relates to a method for preparing magnesium-doped iron phosphate material by a wet process. Background Art

[0002] As a positive electrode material for lithium-ion batteries, iron phosphate materials have been widely used in the field of new energy due to their high safety, environmental friendliness, and low cost. However, traditional iron phosphate materials have problems such as capacity decay and insufficient cycle stability during the charge and discharge cycle. In order to improve the electrochemical properties of iron phosphate materials, researchers have tried a variety of doping modification methods, among which magnesium doping is considered to be an effective modification method.

[0003] At present, magnesium-doped iron phosphate is very rare, and most of them choose to dope magnesium into lithium iron phosphate, but the preparation method mostly adopts high-temperature solid phase method. Although the preparation process of this method is simple, it has the disadvantages of high energy consumption, low product purity, large particle size, etc. Therefore, it is particularly important to develop a preparation method of magnesium-doped iron phosphate material with low energy consumption, high purity and uniform particles.

[0004] Patent CN105355859 B "A method for preparing a magnesium and barium doped lithium iron phosphate positive electrode material for lithium ion batteries" includes mixing lithium hydroxide, ammonium dihydrogen phosphate, barium carbonate, ferrous oxalate, and dysprosium oxide and then ball milling to obtain a nano precursor; then dissolving magnesium propylene oxide and a co-solvent toluene to form a magnesium salt sol to obtain a magnesium salt sol coating liquid; adding the precursor powder to the coating phase acetone to mix, adding the magnesium salt sol coating liquid, and ball milling again; finally sintering in a nitrogen atmosphere, heating to 500°C at a heating rate of 5°C / min, and keeping warm for 6-7h; then heating to 700°C at a heating rate of 10°C / min, and keeping warm for 12h; then cooling to 600°C at a cooling rate of 15°C / min, annealing for 8h, and cooling to room temperature to obtain a lithium iron phosphate positive electrode material doped with magnesium and barium.

[0005] Patent CN116344801A "Doped lithium iron phosphate and its preparation method and application" uses nickel, manganese or further doping with magnesium elements to replace the iron element to form Ni-O bonds and Mn-O bonds or further form Mg-O bonds, thereby playing a synergistic role in doping lithium iron phosphate, giving the doped lithium iron phosphate high capacity and potential difference, and effectively improving the lithium ion diffusion rate. Moreover, the preparation method of doped lithium iron phosphate can ensure that the prepared doped lithium iron phosphate has stable crystal structure and electrochemical properties, and is highly efficient, saving production costs.

[0006] Patent CN114335478 A "A magnesium-doped lithium iron phosphate / carbon composite microsphere with high tap density and its preparation method and application": (1) Weigh appropriate amounts of iron source, phosphorus source, lithium source, magnesium hydroxide, PEG-400, and carbon source A, mix them in solid phase to obtain a mixture, then add the mixture into deionized water containing zirconium sand for ball milling, and filter and separate the zirconium sand with a sieve to obtain a slurry after ball milling; (2) The slurry obtained in step (1) is spray-dried to obtain a yellow-brown precursor powder; (3) The yellow-brown precursor powder obtained in step (2) is subjected to high-temperature sintering. The sintering method is: placing the yellow material in a tubular furnace rich in inert gas, and sintering at high temperature for 8 hours under the conditions of the temperature set to 730°C and the gas flow rate of 0.1 mL / s to obtain magnesium-doped lithium iron phosphate / carbon composite microspheres with high tap density.

[0007] However, all of the above technologies use a high-temperature solid-phase method. Although this method has a simple preparation process, it has disadvantages such as high energy consumption, low product purity, large particle size, and uneven distribution of doping elements. Moreover, the raw materials are mixed and ground and then sintered at high temperature. The prepared iron phosphate has large particle size and uneven distribution after mixing, which affects the performance of the battery. The high-temperature sintering time is long, and high-temperature resistant equipment and materials are required, which greatly causes energy waste. Summary of the invention

[0008] In order to solve the above technical problems, the present invention provides a method for preparing magnesium-doped ferric phosphate, which comprises adding magnesium metal oxide at the synthesis end to act as a pH regulator of the reaction system, and doping magnesium into ferric phosphate while participating in the synthesis reaction, thereby obtaining magnesium-doped ferric phosphate, as follows: A method for preparing magnesium-doped iron phosphate material by a wet process comprises the following steps: S1. Synthesis reaction: prepare iron phosphate leachate, magnesium metal oxide suspension or magnesium metal oxide solid respectively, use a mixture of pure water and regenerated iron leachate or regenerated iron leachate as base liquid, heat the base liquid to 60° C., obtain yellow slurry A through synthesis reaction, and wash and separate the yellow slurry A through a centrifuge to obtain synthetic filter cake A; S2, conversion reaction: prepare phosphoric acid solution, mix the synthetic filter cake A with pure water to form a slurry with a solid content of 10-15%, heat the slurry to 40°C, add phosphoric acid solution to obtain yellow slurry B, heat to 80-100°C, and keep warm for 90 minutes. After the end of the insulation, white slurry B is obtained, and the white slurry B is washed by a centrifuge and solid-liquid separation is performed to obtain white filter cake B; S3, drying and calcining: drying the white filter cake B in an oven, calcining it at high temperature in a muffle furnace, and treating it in a crusher to obtain a magnesium-doped iron phosphate material.

[0009] Preferably, in step S1, in the iron phosphate leachate, the molar ratio of iron element to phosphorus element is 0.995-1:1, and the mass proportion of magnesium metal oxide in the magnesium metal oxide suspension does not exceed 15% of the total mass.

[0010] Preferably, in step S1, the magnesium metal oxide is both a source of doping elements and a pH regulator at the wet synthesis end, and participates in the synthesis of the iron phosphate material.

[0011] Preferably, in step S1, the magnesium metal oxide is one of magnesium oxide, magnesium peroxide or magnesium superoxide.

[0012] Preferably, in step S1, in the mixed solution of pure water and regenerated iron leaching solution, the volume ratio of pure water to regenerated iron leaching solution is 1:1.

[0013] Preferably, in step S2, the pH of the slurry is controlled to be 0.9-1.5 after adding the phosphoric acid solution.

[0014] Preferably, in step S1, the pH of the yellow slurry A is ≤2.2.

[0015] Preferably, in step S4, the molar ratio of phosphorus in the added phosphoric acid solution to phosphorus in the iron phosphate leaching solution should be controlled to be n(P):n(Fe)=0.25~0.35:1.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention can complete the preparation of magnesium-doped iron phosphate material by providing magnesium metal oxide through the wet end to participate in the synthesis reaction process. The principle is: pure water and part of the regenerated iron leachate are used as the base liquid or all the regenerated iron leachate is used as the base liquid, magnesium oxide suspension and the remaining regenerated iron phosphate leachate are used as the feed liquid or magnesium oxide solid is added alone, and the magnesium element is doped into the iron phosphate lattice by controlling the synthetic feeding method and feeding rate, and a small amount of phosphoric acid solution is continuously added to obtain the magnesium-doped iron phosphate material.

[0017] 2. The present invention adopts a wet method to prepare magnesium-doped iron phosphate material, avoiding the high energy consumption problem caused by the high-temperature solid-phase method. The entire preparation process is carried out at a lower temperature, which not only saves energy but also is easy to operate and control, thereby improving the purity of the product.

[0018] 3. The present invention not only achieves the doping of magnesium element by directly adding magnesium metal oxide at the synthesis end, but also acts as a pH regulator for the reaction system, making the reaction more stable and controllable. The prepared magnesium-doped iron phosphate material has higher purity, and the distribution of magnesium element in the material is more uniform, thereby improving the electrochemical properties of the material.

[0019] 4. The present invention proposes a method for preparing magnesium-doped iron phosphate materials by a wet process. By controlling the synthesis reaction conditions, uniform doping of magnesium elements is achieved, thereby improving the electrochemical properties of the iron phosphate materials.

[0020] 5. The preparation method of the present invention can obtain magnesium-doped iron phosphate materials with fine and uniform particles. The fine particle size is conducive to shortening the diffusion path of lithium ions and improving the charge and discharge performance of the material. At the same time, the doping of magnesium elements can also improve the structural stability of the material and extend the cycle life of the battery.

[0021] 6. The present invention uses a mixture of pure water and regenerated iron leaching solution as the base liquid, which can not only reduce production costs but also achieve resource recycling.

[0022] 7. The preparation method provided by the present invention effectively improves the charge and discharge platform and cycle stability of the iron phosphate material by magnesium doping, thereby improving the performance of the lithium-ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The XRD patterns of the iron phosphate dihydrate of Examples 4 and 5 are compared with the XRD patterns of normal iron phosphate dihydrate; Figure 2 The XRD patterns of the iron phosphate dihydrate of Comparative Examples 1 and 2 are compared with the XRD patterns of normal iron phosphate dihydrate; Figure 3 The scanning electron microscope image of the anhydrous ferric phosphate prepared in Example 4 is shown in the figure; Figure 4 The scanning electron microscope image of the anhydrous ferric phosphate prepared in Example 5 is shown in the figure; Figure 5 The scanning electron microscope image of the anhydrous ferric phosphate prepared in Comparative Example 1 is shown in the figure; Figure 6 The scanning electron microscope image of the anhydrous ferric phosphate prepared in Comparative Example 2 is shown in the figure. DETAILED DESCRIPTION

[0024] Example 1 A method for preparing magnesium-doped iron phosphate material by a wet process comprises the following steps: S1. Synthesis reaction: prepare iron phosphate leaching solution, magnesium metal oxide suspension or magnesium metal oxide solid respectively, use a mixture of pure water and regenerated iron leaching solution as the base liquid, heat the base liquid to 60° C., obtain yellow slurry A through synthesis reaction, and wash and separate the yellow slurry A through a centrifuge to obtain synthetic filter cake A; S2, conversion reaction: prepare phosphoric acid solution, mix the synthetic filter cake A with pure water to form a slurry with a solid content of 15%, heat the slurry to 40°C, add phosphoric acid solution to obtain yellow slurry B, heat to 90°C, and keep warm for 90 minutes. After the end of the insulation, white slurry B is obtained, and the white slurry B is washed by a centrifuge and solid-liquid separation is performed to obtain white filter cake B; S3, drying and calcining: drying the white filter cake B in an oven, calcining it at high temperature in a muffle furnace, and treating it in a crusher to obtain a magnesium-doped iron phosphate material.

[0025] Moreover, in step S1, in the iron phosphate leaching solution, the molar ratio of iron element to phosphorus element is 1:1, and the mass proportion of magnesium metal oxide in the magnesium metal oxide suspension does not exceed 15% of the total mass.

[0026] Moreover, in step S1, the magnesium metal oxide is one of magnesium oxide, magnesium peroxide or magnesium superoxide.

[0027] Moreover, in step S1, in the mixed solution of pure water and regenerated iron leaching solution, the volume ratio of pure water to regenerated iron leaching solution is 1:1.

[0028] Furthermore, in step S2, the pH of the slurry is controlled to be 1.5 after the phosphoric acid solution is added.

[0029] Moreover, in step S1, the pH of the yellow slurry A is ≤2.2.

[0030] Moreover, in step S4, the molar ratio of phosphorus in the added phosphoric acid solution to phosphorus in the iron phosphate leaching solution should be controlled to be n(P):n(Fe)=0.25:1.

[0031] Example 2 A method for preparing magnesium-doped iron phosphate material by a wet process comprises the following steps: S1. Synthesis reaction: prepare iron phosphate leaching solution, magnesium metal oxide suspension or magnesium metal oxide solid respectively, use regenerated iron leaching solution as base liquid, heat the base liquid to 60° C., obtain yellow slurry A through synthesis reaction, and wash and separate the yellow slurry A through centrifuge to obtain synthetic filter cake A; S2, conversion reaction: prepare phosphoric acid solution, mix the synthetic filter cake A with pure water to form a slurry with a solid content of 10%, heat the slurry to 40°C, add phosphoric acid solution to obtain yellow slurry B, heat to 100°C, and keep warm for 90 minutes. After the end of the insulation, white slurry B is obtained, and the white slurry B is washed by a centrifuge and solid-liquid separation is performed to obtain white filter cake B; S3, drying and calcining: drying the white filter cake B in an oven, calcining it at high temperature in a muffle furnace, and treating it in a crusher to obtain a magnesium-doped iron phosphate material.

[0032] Moreover, in step S1, in the iron phosphate leaching solution, the molar ratio of iron element to phosphorus element is 0.995:1, and the mass proportion of magnesium metal oxide in the magnesium metal oxide suspension does not exceed 15% of the total mass.

[0033] Moreover, in step S1, the magnesium metal oxide is magnesium oxide.

[0034] Furthermore, in step S2, the pH of the slurry is controlled to be 0.9 after the phosphoric acid solution is added.

[0035] Moreover, in step S1, the pH of the yellow slurry A is ≤2.2.

[0036] Moreover, in step S4, the molar ratio of phosphorus in the added phosphoric acid solution to phosphorus in the iron phosphate leaching solution should be controlled to be n(P):n(Fe)=0.35:1.

[0037] Example 3 A method for preparing magnesium-doped iron phosphate material by a wet process comprises the following steps: S1. Synthesis reaction: prepare iron phosphate leachate, magnesium metal oxide suspension or magnesium metal oxide solid respectively, use a mixture of pure water and regenerated iron leachate or regenerated iron leachate as base liquid, heat the base liquid to 60° C., obtain yellow slurry A through synthesis reaction, and wash and separate the yellow slurry A through a centrifuge to obtain synthetic filter cake A; S2, conversion reaction: prepare phosphoric acid solution, mix the synthetic filter cake A with pure water to form a slurry with a solid content of 12%, heat the slurry to 40°C, add phosphoric acid solution to obtain yellow slurry B, heat to 90°C, and keep warm for 90 minutes. After the end of the insulation, white slurry B is obtained, and the white slurry B is washed by a centrifuge and solid-liquid separation is performed to obtain white filter cake B; S3, drying and calcining: drying the white filter cake B in an oven, calcining it at high temperature in a muffle furnace, and treating it in a crusher to obtain a magnesium-doped iron phosphate material.

[0038] Moreover, in step S1, in the iron phosphate leaching solution, the molar ratio of iron element to phosphorus element is 0.998:1, and the mass proportion of magnesium metal oxide in the magnesium metal oxide suspension does not exceed 15% of the total mass.

[0039] Moreover, in step S1, the magnesium metal oxide is one of magnesium oxide, magnesium peroxide or magnesium superoxide.

[0040] Moreover, in step S1, in the mixed solution of pure water and regenerated iron leaching solution, the volume ratio of pure water to regenerated iron leaching solution is 1:1.

[0041] Furthermore, in step S2, the pH of the slurry is controlled to be 1.2 after the phosphoric acid solution is added.

[0042] Moreover, in step S1, the pH of the yellow slurry A is ≤2.2.

[0043] Moreover, in step S4, the molar ratio of phosphorus in the added phosphoric acid solution to phosphorus in the iron phosphate leaching solution should be controlled to be n(P):n(Fe)=0.3:1.

[0044] Example 4 A method for preparing magnesium-doped iron phosphate material by a wet process comprises the following steps: (1) Take 4 L of regenerated iron phosphate leaching solution; (2) Weigh 140 g of magnesium oxide solid and add water to prepare a suspension; (3) Take 1.5L of pure water as the base solution; (4) Pour 1L of regenerated iron leaching solution into the bottoming pure water, then heat it to 60°C, and add the magnesium oxide suspension and the remaining regenerated iron phosphate leaching solution into the reactor at a certain rate while stirring to obtain yellow slurry A; (5) After the synthetic slurry is washed and dried by a centrifuge, pure water is added for 20 minutes, and then phosphoric acid solution is added to obtain yellow slurry B; (6) Pour the yellow slurry B into the reactor, raise the temperature to 90°C, and keep it warm for 90 minutes after the yellow slurry turns white; (7) Dehydrating, washing and drying the whitened material using a centrifuge to obtain ferric phosphate dihydrate; (8) The obtained dihydrate iron phosphate is calcined at high temperature in a muffle furnace and then cooled to obtain anhydrous iron phosphate.

[0045] Example 5 A method for preparing magnesium-doped iron phosphate material by wet process, Example 5 is similar to Example 4, except that the base solution is all regenerated iron leaching solution and magnesium oxide solid is directly added to the reaction system during the feeding process. The method comprises the following steps: (1) Take 4 L of regenerated iron phosphate leaching solution; (2) Weigh 140 g of magnesium oxide solid; (3) Pour all 4L of regenerated iron leaching solution into the reactor, then heat it to 60°C, and add magnesium oxide solid into the reactor at a certain rate while stirring to obtain yellow slurry A; (5) After the synthetic slurry is washed and dried by a centrifuge, pure water is added for 20 minutes, and then phosphoric acid solution is added to obtain yellow slurry B; (6) Pour the yellow slurry B into the reactor, raise the temperature to 90°C, and keep it warm for 90 minutes after the yellow slurry turns white; (7) Dehydrating, washing and drying the whitened material using a centrifuge to obtain ferric phosphate dihydrate; (8) The obtained dihydrate iron phosphate is calcined at high temperature in a muffle furnace and then cooled to obtain anhydrous iron phosphate.

[0046] Comparative Example 1 Comparative Example 1 of the present invention is a method for preparing ferric phosphate, which is similar to the steps of Examples 4 and 5, except that magnesium oxide is replaced with magnesium sulfate, magnesium sulfate is configured into a solution, and the materials are added in the same proportion. The specific steps are as follows: (1) Take 4 L of regenerated iron phosphate leaching solution; (2) Weigh 140 g of magnesium sulfate solid and add pure water to prepare a magnesium sulfate solution; (3) Take 1.5L of pure water as the base solution; (4) Pour 1L of regenerated iron leaching solution into the bottoming pure water, then heat it to 60°C, and add the magnesium sulfate solution and the remaining regenerated iron phosphate leaching solution into the reactor at a certain rate while stirring to obtain yellow slurry A; (5) After the synthetic slurry is washed and dried by a centrifuge, pure water is added for 20 minutes, and then a phosphoric acid solution is added to obtain a white slurry B; (6) Pour the white slurry B into the reactor, raise the temperature to 90°C, and keep it warm for 90 minutes after the yellow slurry turns white; (7) Dehydrating, washing and drying the whitened material using a centrifuge to obtain ferric phosphate dihydrate; (8) The obtained dihydrate iron phosphate is calcined at high temperature in a muffle furnace and then cooled to obtain anhydrous iron phosphate.

[0047] Comparative Example 2 Comparative Example 2 of the present invention is a method for preparing ferric phosphate. The steps of Comparative Example 2 are similar to those of Examples 4 and 5, except that the magnesium oxide suspension or magnesium oxide solid is replaced with pure water, and the materials are added in the same proportion. The specific steps are as follows: (1) Take 4 L of regenerated iron phosphate leaching solution; (2) Weigh 800g of pure water; (3) Take 1.5L of pure water as the base solution; (4) Pour 1L of regenerated iron leaching solution into the bottoming pure water, then heat it to 60°C, and add the ammonia solution and the remaining regenerated iron phosphate leaching solution into the reactor at a certain rate while stirring to obtain yellow slurry A; (5) After the synthetic slurry is washed and dried by a centrifuge, pure water is added for 20 minutes, and then a phosphoric acid solution is added to obtain a white slurry B; (6) Pour the white slurry B into the reactor, raise the temperature to 90°C, and keep it warm for 90 minutes after the yellow slurry turns white; (7) Dehydrating, washing and drying the whitened material using a centrifuge to obtain ferric phosphate dihydrate; (8) The obtained dihydrate iron phosphate is calcined at high temperature in a muffle furnace and then cooled to obtain anhydrous iron phosphate.

[0048] Figure 1 The XRD patterns of the iron phosphate dihydrate prepared in Examples 4 and 5 of the present invention are compared with the XRD patterns of normal iron phosphate dihydrate. It can be seen from the figure that the iron phosphate phase of Examples 4 and 5 is shifted to the left compared with the normal iron phosphate dihydrate, indicating that the magnesium element is successfully doped into the iron phosphate material.

[0049] Figure 2 The XRD patterns of the iron phosphate dihydrate prepared in Comparative Examples 1 and 2 of the present invention are compared with the XRD patterns of normal iron phosphate dihydrate. It can be seen from the figure that the iron phosphates in Comparative Examples 1 and 2 are not offset relative to the normal iron phosphate dihydrate phase, indicating that the magnesium element has not been doped into the iron phosphate material.

[0050] The results of ICP testing showed that the magnesium content in the anhydrous iron phosphate of Example 4 was 690.5 ppm, and the magnesium content in the anhydrous iron phosphate of Example 5 was 710.5 ppm, indicating that the magnesium element was successfully doped into the iron phosphate lattice. The magnesium content in the anhydrous iron phosphate of Comparative Example 1 was 6.50 ppm, and the magnesium content in the anhydrous iron phosphate of Comparative Example 2 was 4.68 ppm, indicating that there was no magnesium element in the iron phosphate material.

[0051] The scanning electron microscope images of anhydrous ferric phosphate prepared in Examples 4 and 5 of the present invention and Comparative Examples 1 and 2 are as follows: Figure 3-6 As shown in the figure, it can be seen that the anhydrous ferric phosphate particles prepared in Examples 4 and 5 are full, round, evenly distributed, and the particles do not stick together; while the anhydrous ferric phosphate particles prepared in Comparative Examples 1 and 2 are severely fused, the particles are small and unclear, and the morphology is poorly developed.

[0052] The physical and chemical indicators of the anhydrous ferric phosphate prepared in Examples 4 and 5 of the present invention and Comparative Examples 1 and 2 are shown in Table 1.

[0053] Table 1 Physical and chemical indicators of Examples 4 and 5

[0054] As can be seen from Table 1, the anhydrous iron phosphate prepared in Examples 4 and 5 has a moderate iron-to-phosphorus ratio, indicating that the composition of the iron phosphate is relatively ideal; the D50 is high, and the iron phosphate grows well; the magnesium content is 690.5ppm and 710.5ppm, respectively, indicating that magnesium is successfully doped into the iron phosphate through the technical solution of the present invention; while the physical and chemical indicators of the anhydrous iron phosphate prepared in Comparative Examples 1 and 2 are lower than the target requirements, and the magnesium element is not successfully doped.

[0055] The iron phosphate materials prepared in Examples 4 and 5 and Comparative Examples 1 and 2 were made into lithium iron phosphate batteries, and their electrochemical properties and compaction densities were tested. The results are shown in Table 2.

[0056] Table 2 Indices of lithium iron phosphate prepared in Examples and Comparative Examples

[0057] Obviously, the anhydrous iron phosphate prepared in Examples 4 and 5 has high electrochemical performance and sintering compaction after being made into lithium iron phosphate batteries, and the sintering compaction is 2.466 and 2.472 g / cm 3 , 0.1C charge and discharge capacities are both greater than 160 mAh / g, indicating good electrochemical performance, and 1C discharge is greater than 140 mAh / g, indicating better instantaneous charge and discharge performance; while the sintering compaction and electrochemical performance indicators of Comparative Examples 1 and 2 are far lower than those of Examples 4 and 5, and the charge and discharge performance is poor.

Claims

1. A method for preparing magnesium-doped iron phosphate material by a wet process, characterized in that: The following steps are involved: S1. Synthesis reaction: prepare iron phosphate leachate, magnesium metal oxide suspension or magnesium metal oxide solid respectively, use a mixture of pure water and regenerated iron leachate or regenerated iron leachate as base liquid, heat the base liquid to 60° C., obtain yellow slurry A through synthesis reaction, and obtain synthetic filter cake A through washing and separation of yellow slurry A; S2, conversion reaction: prepare phosphoric acid solution, mix the synthetic filter cake A with pure water to form a slurry with a solid content of 10-15%, heat the slurry to 40°C, add phosphoric acid solution to obtain yellow slurry B, heat to 80-100°C, and keep warm for 90 minutes. After the end of the insulation, white slurry B is obtained, and the white slurry B is washed and solid-liquid separated to obtain white filter cake B; S3, drying and calcining: drying, calcining and crushing the white filter cake B to obtain the magnesium-doped iron phosphate material.

2. The method for preparing magnesium-doped iron phosphate material by wet process according to claim 1, characterized in that: In step S1, in the iron phosphate leaching solution, the molar ratio of iron element to phosphorus element is 0.995-1:1, and the mass proportion of magnesium metal oxide in the magnesium metal oxide suspension does not exceed 15% of the total mass.

3. The method for preparing magnesium-doped iron phosphate material by wet process according to claim 1, characterized in that: In step S1, the magnesium metal oxide is one of magnesium oxide, magnesium peroxide or magnesium superoxide.

4. The method for preparing magnesium-doped iron phosphate material by wet process according to claim 1, characterized in that: In step S1, in the mixed solution of pure water and regenerated iron leaching solution, the volume ratio of pure water to regenerated iron leaching solution is 1:

1.

5. The method for preparing magnesium-doped iron phosphate material by wet process according to claim 1, characterized in that: In step S2, after adding the phosphoric acid solution, the pH of the slurry is controlled to be 0.9-1.

5.

6. The method for preparing magnesium-doped iron phosphate material by wet process according to claim 1, characterized in that: In step S1, the pH of the yellow slurry A is ≤2.

2.

7. The method for preparing magnesium-doped iron phosphate material by wet process according to claim 1, characterized in that: In step S4, the molar ratio of phosphorus in the added phosphoric acid solution to phosphorus in the iron phosphate leaching solution should be controlled to be n(P):n(Fe)=0.25~0.35:1.

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