Method for synthesizing manganese ferrite magnetic material from waste lithium iron manganese phosphate positive electrode material

Abstract

The invention relates to the technical field of resource recycling and high-value utilization of lithium ion batteries, in particular to a technology for generating, recycling or refining metal through an electrolytic method. The invention discloses a method for synthesizing a manganese ferrite magnetic material from a waste lithium manganese iron phosphate positive electrode material. The method comprises the following steps: preparing waste lithium manganese iron phosphate positive electrode powder, an organic binder and a solvent into slurry, and coating the surface of a titanium mesh with the slurry to obtain a positive plate; constructing an electrolytic tank by taking a blank titanium mesh as a negative electrode and a NaOH aqueous solution as an electrolyte, carrying out electrolytic leaching to obtain Li and P elements, concentrating the electrolyte, supplementing a phosphorus source, and adjusting the pH value to recover lithium phosphate; the method comprises the following steps: ultrasonically separating ferromanganese / graphite remained on a titanium mesh, acidizing and dissolving, filtering to remove graphite, adding citric acid into filtrate for gelation, and subsequently calcining to obtain the manganese ferrite magnetic material. According to the method, efficient leaching of Li and P is achieved through electrochemical treatment, Mn and Fe are synchronously converted into high-crystallinity manganese ferrite in a high-valued mode, and the method has the advantages of being environmentally friendly, low in consumption and capable of achieving all-element closed-loop recovery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of resource recycling and high-value utilization of lithium ion batteries, and the process of electrolytic generation, recovery or refining of metals, in particular to a method for synthesizing manganese ferrite magnetic material from waste lithium manganese iron phosphate positive electrode material. BACKGROUND

[0002] With the rapid development of new energy vehicles and energy storage industry, the annual shipment and retirement volume of lithium ion batteries continue to surge. Lithium iron phosphate batteries are widely used due to their high safety, long cycle life, environmental friendliness and low cost, but due to the defects of low electronic conductivity and lithium ion diffusion coefficient, the industry generally prepares manganese lithium phosphate by doping Mn. The material has high safety, long cycle life of lithium iron phosphate and high energy density of lithium manganese phosphate, and the Mn raw material cost is low, the oxidation-reduction potential is higher than that of Fe, which significantly improves the comprehensive performance and commercial value of the battery, and is known as the "upgraded version of lithium iron phosphate".

[0003] Lithium manganese iron phosphate and lithium iron phosphate belong to the same olivine structure, and also have the advantages of high thermal stability such as needle puncture overcharge non-self-ignition and no explosion risk. At present, it has realized commercial application, and is gradually replacing lithium iron phosphate on a large scale for electric vehicles and energy storage equipment. With the rapid increase of its market penetration rate, the retirement volume of waste lithium manganese iron phosphate positive electrode material will increase explosively in the future. However, the existing recycling technology (high energy consumption of pyrometallurgical process and heavy pollution of hydrometallurgical process) cannot realize efficient recovery and high-value utilization of all elements, so it is of great practical significance to develop green and efficient recycling technology for waste lithium manganese iron phosphate. SUMMARY

[0004] Based on the problems existing in the prior art, the present application provides a method for synthesizing manganese ferrite magnetic material from waste lithium manganese iron phosphate positive electrode material, which aims to overcome the defects of traditional pyrometallurgical (high energy consumption) and hydrometallurgical (high pollution) recycling technologies, and provide a green and efficient resource utilization method for waste lithium manganese iron phosphate positive electrode material. By constructing an alkaline constant current electrochemical system, lithium element selective leaching, phosphorus element recovery, graphite separation and manganese iron element enrichment are realized simultaneously, and then nitric acid acidification, citrate precursor gelation and controllable calcination are carried out to convert manganese iron elements into manganese ferrite magnetic material with excellent magnetic permeability and uniform particle size.

[0005] In order to achieve the purpose of the present application, the following technical solutions are adopted: The method for synthesizing manganese ferrite magnetic material from waste lithium manganese iron phosphate positive electrode material comprises the following steps: Step 1: taking waste old lithium manganese iron phosphate positive electrode powder as raw material; dissolving organic binder in solvent, stirring until completely dissolved; adding waste old lithium manganese iron phosphate positive electrode powder to the binder solution, and uniformly dispersing or stirring for 10-120 min or 1-24 h to prepare a uniform slurry; uniformly coating the slurry on the surface of the titanium mesh, drying at 60-120℃ for 2-12 h to obtain a positive electrode sheet.

[0006] Step 2: connecting the positive electrode sheet prepared in step 1 to the positive electrode of an adjustable direct current electrolytic cell, connecting a blank titanium mesh to the negative electrode, using a sodium hydroxide aqueous solution with a concentration of 0.1-2 mol / L and a pH value of 10-14 as the electrolyte, applying a constant current field of 1-200 mA to the two electrodes, and electrolyzing for 1-600 min.

[0007] Step 3: taking out the positive electrode sheet after electrolysis, washing with deionized water, and drying at 60-100℃ to obtain an electrolysis product; adding the electrolysis product to deionized water, and ultrasonic dispersing at a power of 100-500 W for 1-600 min to disperse the agglomerates of manganese iron product and graphite, and then filtering to collect the solid mixture, which is a mixture of manganese iron product and graphite.

[0008] Step 4: evaporating and concentrating the remaining electrolyte from step 2 at 100-150℃, supplementing a phosphorus source to the concentrated solution, adjusting the pH value of the system to 10-13 to precipitate lithium, and filtering to obtain lithium phosphate.

[0009] Step 5: dissolving the mixture of manganese iron product and graphite collected in step 3 in a nitric acid solution with a concentration of 1-3 mol / L, stirring until the manganese iron product is completely dissolved (graphite is insoluble in nitric acid), and filtering to remove undissolved graphite; adding citric acid at a molar ratio of 1:0.1-1 to the total molar amount of manganese iron elements in the manganese iron product, stirring and mixing for 60-600 min, and then evaporating water from the obtained solution at 60-120℃ to obtain a viscous gel.

[0010] Step 6: placing the viscous gel obtained in step 5 in an air or oxygen atmosphere, calcining at 400-700℃ for 60-300 min to decompose the citric acid; grinding the calcined product, washing with deionized water until the pH is neutral, and drying to obtain a manganese ferrite magnetic material.

[0011] Further, in step 1, the content of lithium manganese iron phosphate in the positive electrode powder is 95-99.9 wt%, and the content of carbon is 0.1-5 wt%, based on the total mass of the waste old lithium manganese iron phosphate positive electrode powder.

[0012] Further, in step 1, the organic binder is a polyvinylidene fluoride or Nafion solution, and the mass ratio of the organic binder to the waste old lithium manganese iron phosphate positive electrode powder is 1:10-100.

[0013] Further, in step 4, the phosphorus source is one or more of trisodium phosphate, sodium dihydrogen phosphate, tripotassium phosphate, dipotassium hydrogen phosphate, and phosphoric acid.

[0014] Further, in step 4, the reagent used to adjust the pH of the system is one or more of ammonia, sodium hydroxide, disodium hydrogen phosphate, and dipotassium hydrogen phosphate.

[0015] The present application constructs an integrated technical path of "electrochemical selective leaching - multi-element staged recovery - high-value material synthesis", which has the following outstanding advantages compared with traditional pyrometallurgy and hydrometallurgy: 1. By precisely controlling the key parameters of the electrolyte concentration, electrolysis current and time of the alkaline electrolysis system, efficient selective leaching of Li and P elements in waste and old manganese iron lithium phosphate is realized, while Mn and Fe elements are retained in the solid product. Subsequently, through steps such as nitric acid dissolution, graphite separation, gelation and calcination, directional conversion of Mn and Fe elements into high-value ferrite is realized, and ultimately full recovery and resource utilization of Li, Mn, Fe and P four core elements are achieved, without resource waste, solving the problem of low element recovery rate and serious resource loss in traditional technology.

[0016] 2. The present application breaks through the limitation of traditional recovery technology which only recovers single metal salt, and co-converts Mn and Fe elements into manganese ferrite magnetic material with excellent magnetic performance (saturation magnetization ≥ 70 emu / g, uniform particle size), recovers Li and P elements into high-purity lithium phosphate (purity ≥ 98%), and the separated graphite conductive agent can be recycled, and the economic value of the recovered products is significantly improved compared with traditional methods.

[0017] 3. The present application uses an alkaline electrochemical leaching system, avoids the use of large amounts of strong acid reagents in hydrometallurgy, reduces acid waste pollution; the electrolysis process is carried out at normal temperature and pressure, and the subsequent calcination temperature is only 400-700℃ (much lower than the high temperature of 800℃ or more in pyrometallurgy), the overall energy consumption is reduced; there is no harmful gas emission, and the washing wastewater can be recycled after simple treatment, the environmental load is significantly reduced.

[0018] 4. The present application solves three key technical problems in the recovery of waste and old manganese iron lithium phosphate: first, green and efficient extraction of lithium element, avoiding high pollution and low selectivity of traditional methods; second, efficient separation of graphite and metal oxides, using the property of graphite insoluble in nitric acid to realize precise separation; third, co-conversion of Mn and Fe elements into high-value materials, through citrate precursor method and controllable calcination, realizing one-step conversion from waste electrode material to functional magnetic material.

[0019] 5、The lithium extraction, dephosphorization, graphite separation, lithium phosphate preparation, and manganese ferrite synthesis are integrated in several core steps, the process is simple and controllable, and complex equipment is not needed; the reaction conditions of each step are mild (normal temperature electrolysis and medium temperature calcination), and the parameters are easy to control, and the actual production demand can be enlarged, thus providing a feasible technical scheme for large-scale treatment of waste manganese iron lithium phosphate positive electrode materials. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is an X-ray diffraction (XRD) diagram of the manganese ferrite magnetic material obtained in Example 1 of the present application.

[0021] Figure 2 is a high-resolution transmission electron microscope (HRTEM) photo of the manganese ferrite magnetic material obtained in Example 1 of the present application.

[0022] Figure 3 is an element proportion diagram of the manganese ferrite magnetic material obtained in Example 1 of the present application.

[0023] Figure 4 is a vibrating sample magnetometer (VSM) hysteresis loop diagram of the manganese ferrite magnetic material obtained in Example 1 of the present application.

[0024] Figure 5 is a Zeta potential distribution diagram of the manganese ferrite magnetic material obtained in Example 1 of the present application.

[0025] Figure 6 is a particle size distribution diagram of the manganese ferrite magnetic material obtained in Example 1 of the present application.

[0026] Figure 7 is a vibrating sample magnetometer (VSM) hysteresis loop diagram of the manganese ferrite magnetic material obtained in Example 2 of the present application.

[0027] Figure 8 is a vibrating sample magnetometer (VSM) hysteresis loop diagram of the manganese ferrite magnetic material obtained in Example 3 of the present application. DETAILED DESCRIPTION

[0028] The embodiments of the present application are described in detail below, and the embodiments are implemented on the premise of the technical scheme of the present application, and detailed implementation modes and specific operation processes are given, but the protection scope of the present application is not limited to the following embodiments.

[0029] Example 1 The method for synthesizing the manganese ferrite magnetic material from the waste manganese iron lithium phosphate positive electrode material is as follows: Step 1: Using waste lithium manganese iron phosphate cathode powder as raw material (containing 98.54 wt% lithium manganese iron phosphate and 1.46 wt% carbon), 0.03 g of PVDF was dissolved in 4 mL of N-methylpyrrolidone (NMP) and stirred for 30 min until completely dissolved to obtain a binder solution. 3 g of waste lithium manganese iron phosphate cathode powder was added to the binder solution and stirred for 8 h to prepare a uniform slurry. The slurry was uniformly coated onto a 4 cm × 5 cm titanium mesh and dried in an oven at 80℃ for 6 h to obtain the cathode sheet.

[0030] Step 2: Connect the positive electrode sheet prepared in Step 1 to the positive electrode of the adjustable DC electrolytic cell, connect the blank titanium mesh to the negative electrode, use 1 mol / L sodium hydroxide aqueous solution (pH=14) as electrolyte, and apply a constant current electric field of 100 mA to the two electrodes for 240 min for electrolysis.

[0031] Step 3: Take out the positive electrode after electrolysis, wash it 3 times with deionized water, and dry it at 80℃ for 4 hours to obtain the electrolysis product; add the electrolysis product to 50mL of deionized water, and ultrasonically disperse it at 300W power for 60min to break up the agglomerates of manganese iron product and graphite. Then filter and collect the solid mixture to obtain 1.708g of the mixture of manganese iron product and graphite.

[0032] Step 4: Evaporate and concentrate the remaining electrolyte from Step 2 to one-tenth of its original volume at 120°C. After cooling to 90°C, add 0.2 g of trisodium phosphate (phosphorus source) to the concentrate. Adjust the pH of the system to 12 with ammonia. Stir for 30 min, filter, and dry at 80°C to obtain lithium phosphate product (0.742 g, purity 98.8%, lithium recovery rate 99.2%).

[0033] Step 5: Add the solid mixture collected in Step 3 to 30 mL of 3 mol / L nitric acid solution and stir for 30 min until the manganese-iron product is completely dissolved. Then filter to remove undissolved graphite (about 0.0436 g, recovery rate 99.5%). Add citric acid at a molar ratio of 1:0.33 to the total molar amount of manganese-iron elements, stir and mix for 60 min, and then stir and evaporate the resulting solution at 90 °C for 4 h to remove water and obtain a viscous gel.

[0034] Step 6: Place the viscous gel obtained in Step 5 in an air atmosphere and calcine it at 400℃ for 120 min to decompose the citric acid; after grinding, the calcined product is washed with deionized water until pH=7 and dried at 60℃ to obtain manganese ferrite magnetic material (2.252g, purity 99.6%).

[0035] Figure 1The XRD pattern of the manganese ferrite magnetic material obtained in Example 1 shows that its diffraction peaks completely match the characteristic peaks of the manganese ferrite standard card (JCPDS No. 38-0430). The peaks are sharp and there are no impurity peaks, indicating that the manganese ferrite synthesized by this method has high crystallinity and excellent phase purity.

[0036] Figure 2 The image shows an HRTEM image of the manganese ferrite magnetic material obtained in Example 1. It can be seen that the manganese ferrite particles prepared by the citrate precursor method have a particle size concentrated in the range of 15~20nm, with uniform particle morphology, good dispersibility, and no obvious agglomeration.

[0037] Figure 3 The elemental composition diagram of the manganese ferrite magnetic material obtained in Example 1 shows that the atomic percentages of Mn, Fe, and O are 15.1%, 29.8%, and 54.6%, respectively, corresponding to a molar ratio of Mn:Fe:O ≈ 1:2:3.6, which is basically consistent with the theoretical stoichiometric ratio (1:2:4) of the target product MnFe2O4 (the error is within a reasonable range), further verifying the phase composition of the product.

[0038] Figure 4 The VSM hysteresis loop diagram of the manganese ferrite magnetic material obtained in Example 1 shows typical characteristics of soft magnetic materials: the magnetization rapidly saturates with increasing magnetic field strength, and the coercivity is extremely low. The saturation magnetization of this material reaches 58.2 emu / g, exhibiting excellent magnetic properties that perfectly match the soft magnetic properties of manganese ferrite. It can meet the application requirements of magnetic materials in fields such as magnetic sensors and microwave absorbing materials, and has good prospects for industrialization.

[0039] Figure 5 The zeta potential distribution of the manganese ferrite magnetic material obtained in Example 1 is shown in the spectrum. The spectrum shows a single sharp peak with the peak center located at -25 mV. The peak width at half maximum (FWHM) is narrow and the total count is high. At the same time, the |Zeta| potential is greater than 20 mV, indicating that the surface charge distribution of the manganese ferrite particles is uniform and the stability is excellent.

[0040] Figure 6 The particle size distribution of the manganese ferrite magnetic material obtained in Example 1 is shown in the spectrum. The spectrum shows a sharp single-peak narrow distribution characteristic, with the peak value concentrated in a specific particle size range, indicating that the manganese ferrite particles have uniform particle size and good dispersion.

[0041] Example 2 The method for synthesizing manganese ferrite magnetic material from waste lithium manganese iron phosphate cathode material in this embodiment is as follows: Step 1: Using waste lithium manganese iron phosphate cathode powder as raw material (containing 98.54 wt% lithium manganese iron phosphate and 1.46 wt% carbon), dissolve 0.03 g PVDF in 4 mL NMP and stir for 30 min until completely dissolved to obtain a binder solution. Add 3 g of waste lithium manganese iron phosphate cathode powder to the binder solution and stir for 8 h to prepare a uniform slurry. Coat the slurry uniformly onto a 4 cm × 5 cm titanium mesh and dry in an oven at 80℃ for 6 h to obtain the cathode sheet.

[0042] Step 2: Connect the positive electrode sheet prepared in Step 1 to the positive electrode of the adjustable DC electrolytic cell, connect the blank titanium mesh to the negative electrode, use 1 mol / L sodium hydroxide aqueous solution (pH=14) as electrolyte, and apply a constant current electric field of 100 mA to the two electrodes for 240 min for electrolysis.

[0043] Step 3: Take out the positive electrode after electrolysis, wash it 3 times with deionized water, and dry it at 80℃ for 4 hours to obtain the electrolysis product; add the electrolysis product to 50mL of deionized water, and ultrasonically disperse it at 300W power for 60min to break up the aggregates of manganese iron product and graphite. Then filter and collect the solid mixture to obtain 1.686g of the mixture of manganese iron product and graphite.

[0044] Step 4: Evaporate and concentrate the remaining electrolyte from Step 2 to one-tenth of its original volume at 120°C. After cooling to 90°C, add 0.2 g of trisodium phosphate (phosphorus source) to the concentrate, adjust the pH of the system to 12 with ammonia, stir for 30 min, filter, and dry at 80°C to obtain lithium phosphate product (0.738 g, purity 98.6%, lithium recovery rate 99.1%).

[0045] Step 5: Add the solid mixture collected in Step 3 to 30 mL of 3 mol / L nitric acid solution and stir for 30 min until the manganese-iron product is completely dissolved. Then filter to remove undissolved graphite (about 0.0435 g, recovery rate 99.4%). Add citric acid at a molar ratio of 1:0.33 to the total molar amount of manganese-iron elements, stir and mix for 60 min, and then stir and evaporate the resulting solution at 90 °C for 4 h to remove water and obtain a viscous gel.

[0046] Step 6: Place the viscous gel obtained in Step 5 in an air atmosphere and calcine it at 500℃ for 120 min to decompose the citric acid; after grinding, the calcined product is washed with deionized water until pH=7 and dried at 60℃ to obtain manganese ferrite magnetic material (2.248g, purity 99.8%).

[0047] Figure 7The image shows the VSM hysteresis loop of the manganese ferrite magnetic material obtained in Example 2. The curve exhibits typical characteristics of soft magnetic materials: the magnetization rapidly saturates with increasing magnetic field strength, and the coercivity is extremely low. The saturation magnetization of this material reaches 62.1 emu / g, demonstrating excellent magnetic properties that perfectly match the soft magnetic properties of manganese ferrite.

[0048] Example 3 The method for synthesizing manganese ferrite magnetic materials using waste lithium manganese iron phosphate cathode materials in this embodiment is as follows: Step 1: Using waste lithium manganese iron phosphate cathode powder as raw material (containing 98.54 wt% lithium manganese iron phosphate and 1.46 wt% carbon), dissolve 0.03 g PVDF in 4 mL NMP and stir for 30 min until completely dissolved to obtain a binder solution. Add 3 g of waste lithium manganese iron phosphate cathode powder to the binder solution and stir for 8 h to prepare a uniform slurry. Coat the slurry uniformly onto a 4 cm × 5 cm titanium mesh and dry in an oven at 80℃ for 6 h to obtain the cathode sheet.

[0049] Step 2: Connect the positive electrode sheet prepared in Step 1 to the positive electrode of the adjustable DC electrolytic cell, connect the blank titanium mesh to the negative electrode, use 1 mol / L sodium hydroxide aqueous solution (pH=14) as electrolyte, and apply a constant current electric field of 100 mA to the two electrodes for 240 min for electrolysis.

[0050] Step 3: Take out the positive electrode after electrolysis, wash it 3 times with deionized water, and dry it at 80℃ for 4 hours to obtain the electrolysis product; add the electrolysis product to 50mL of deionized water, and ultrasonically disperse it at 300W power for 60min to break up the agglomerates of manganese iron product and graphite. Then filter and collect the solid mixture to obtain a mixture of 1.704g of manganese iron product and graphite.

[0051] Step 4: Evaporate and concentrate the remaining electrolyte from Step 2 to one-tenth of its original volume at 120°C. After cooling to 90°C, add 0.2 g of trisodium phosphate (phosphorus source) to the concentrate, adjust the pH of the system to 12 with ammonia, stir for 30 min, filter, and dry at 80°C to obtain lithium phosphate product (0.744 g, purity 99%, lithium recovery rate 99.5%).

[0052] Step 5: Add the solid mixture collected in Step 3 to 30 mL of 3 mol / L nitric acid solution and stir for 30 min until the manganese-iron product is completely dissolved. Then filter to remove undissolved graphite (about 0.0436 g, recovery rate 99.5%). Add citric acid at a molar ratio of 1:0.33 to the total molar amount of manganese-iron elements, stir and mix for 60 min, and then stir and evaporate the resulting solution at 90 °C for 4 h to remove water and obtain a viscous gel.

[0053] Step 6: Place the viscous gel obtained in Step 5 in an air atmosphere and calcine it at 600℃ for 120 min to decompose the citric acid; after grinding, the calcined product is washed with deionized water until pH=7 and dried at 60℃ to obtain manganese ferrite magnetic material (2.25g, purity 99.6%).

[0054] Figure 8 The image shows the VSM hysteresis loop of the manganese ferrite magnetic material obtained in Example 3. The curve exhibits typical characteristics of soft magnetic materials: the magnetization rapidly saturates with increasing magnetic field strength, and the coercivity is extremely low. The saturation magnetization of this material reaches 70.8 emu / g, demonstrating excellent magnetic properties that perfectly match the soft magnetic properties of manganese ferrite.

[0055] The above description is merely an exemplary embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for synthesizing manganese ferrite magnetic materials from waste lithium manganese iron phosphate cathode materials, characterized in that, Includes the following steps: Step 1: Dissolve the organic binder in a solvent, then add waste lithium manganese iron phosphate cathode powder, and prepare a uniform slurry by ultrasonic dispersion or stirring; then coat the slurry evenly on the surface of a titanium mesh, and obtain the cathode sheet after drying; Step 2: Connect the positive electrode sheet made in Step 1 to the positive electrode of the adjustable DC electrolytic cell, connect the blank titanium mesh to the negative electrode, use sodium hydroxide aqueous solution as electrolyte, and apply a constant current electric field to the two electrodes for electrolysis. Step 3: Remove the positive electrode sheet after electrolysis, wash and dry it to obtain the electrolysis products; The electrolysis products were ultrasonically dispersed and then filtered to obtain a mixture of manganese-iron products and graphite. Step 4: Evaporate and concentrate the remaining electrolyte from Step 2, add phosphorus source to the concentrate, adjust the pH value of the system to precipitate lithium, and obtain lithium phosphate after filtration. Step 5: Dissolve the mixture of manganese-iron product and graphite collected in Step 3 in nitric acid solution, stir until the manganese-iron product is completely dissolved, filter to remove undissolved graphite; then add citric acid, mix well, stir and evaporate the resulting solution to remove water, and obtain a viscous gel. Step 6: Calcine the viscous gel obtained in Step 5 to decompose the citric acid; grind and wash the calcined product until the pH is neutral and then dry it to obtain manganese ferrite magnetic material.

2. The method for synthesizing manganese ferrite magnetic material from waste lithium manganese iron phosphate cathode material according to claim 1, characterized in that: In step 1, based on the total mass of the waste lithium manganese iron phosphate cathode powder, the lithium manganese iron phosphate content in the cathode powder is 95~99.9 wt%, and the carbon content is 0.1~5 wt%.

3. The method for synthesizing manganese ferrite magnetic material from waste lithium manganese iron phosphate cathode material according to claim 1, characterized in that: In step 1, the organic binder is polyvinylidene fluoride or Nafion solution, and the mass ratio of the organic binder to the waste lithium manganese iron phosphate cathode powder is 1:10~100.

4. The method for synthesizing manganese ferrite magnetic material from waste lithium manganese iron phosphate cathode material according to claim 1, characterized in that: In step 2, the sodium hydroxide aqueous solution used as the electrolyte has a concentration of 0.1~2 mol / L and a pH value of 10~14.

5. The method for synthesizing manganese ferrite magnetic material from waste lithium manganese iron phosphate cathode material according to claim 1, characterized in that: In step 2, the electrolysis current is 1~200 mA and the electrolysis time is 1~600 min.

6. The method for synthesizing manganese ferrite magnetic material from waste lithium manganese iron phosphate cathode material according to claim 1, characterized in that: In step 3, the ultrasonic dispersion power is 100~500 W, and the ultrasonic time is 1~600 min.

7. The method for synthesizing manganese ferrite magnetic material from waste lithium manganese iron phosphate cathode material according to claim 1, characterized in that: In step 4, the phosphorus source is one or more of trisodium phosphate, sodium dihydrogen phosphate, tripotassium phosphate, potassium dihydrogen phosphate, and phosphoric acid.

8. The method for synthesizing manganese ferrite magnetic material from waste lithium manganese iron phosphate cathode material according to claim 1, characterized in that: In step 4, the evaporation and concentration temperature is 100~150℃.

9. The method for synthesizing manganese ferrite magnetic material from waste lithium manganese iron phosphate cathode material according to claim 1, characterized in that: In step 5, the molar ratio of citric acid to the total molar amount of manganese and iron in the manganese-iron product is 1:0.1~1.

10. The method for synthesizing manganese ferrite magnetic material from waste lithium manganese iron phosphate cathode material according to claim 1, characterized in that: In step 6, the calcination temperature is 400~700℃ and the calcination time is 60~300 min.

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