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

Abstract

The present application relates to the technical field of lithium ion battery resource recycling and high value utilization, specifically relates to the process of generating, recycling or refining metal by electrolysis method, and discloses a method for synthesizing manganese ferrite magnetic material from waste manganese iron phosphate lithium positive electrode material: first, waste manganese iron phosphate lithium positive electrode powder is mixed with organic binder and solvent to form slurry, and then the slurry is coated on the surface of titanium mesh to obtain a positive electrode sheet; a blank titanium mesh is used as a negative electrode, and NaOH aqueous solution is used as an electrolyte to construct an electrolytic cell, and Li and P elements are leached by electrolysis; the electrolyte is concentrated, supplemented with phosphorus source, and adjusted in pH to recover lithium phosphate; the manganese iron / graphite remaining on the titanium mesh is separated by ultrasonic, and then acidized and dissolved; the graphite is removed by filtration; the filtrate is gelled with citric acid; and the manganese ferrite magnetic material is obtained by subsequent calcination. The method realizes efficient leaching of Li and P through electrochemical treatment, and simultaneously converts Mn and Fe into high-crystallinity manganese ferrite, which has the advantages of green low consumption and full-element closed-loop recycling.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery resource recycling and high-value utilization technology, as well as the process of generating, recycling or refining metals by electrolysis, specifically to a method for synthesizing manganese ferrite magnetic materials from waste lithium manganese iron phosphate cathode materials. Background Technology

[0002] With the rapid development of new energy vehicles and energy storage industries, the annual shipments and retirement volumes of lithium-ion batteries have continued to surge. Lithium iron phosphate (LFP) batteries are widely used due to their high safety, long cycle life, environmental friendliness, and low cost. However, limited by their low electronic conductivity and lithium-ion diffusion coefficient, the industry generally prepares lithium manganese iron phosphate (Mn) through Mn doping modification. This material combines the high safety and long cycle life of LFP with the high energy density of Mn phosphate. Furthermore, Mn raw materials are inexpensive and have a higher redox potential than Fe, significantly improving the overall battery performance and commercial value, and is hailed as an "upgraded version of lithium iron phosphate."

[0003] Lithium manganese iron phosphate (LMP) shares the same olivine-type structure as lithium iron phosphate (LFP) and possesses advantages such as high thermal stability (no spontaneous combustion upon overcharging and no explosion risk). It has already achieved commercial application and is gradually replacing LFP in electric vehicles and energy storage devices on a large scale. With its rapid market penetration, the amount of retired waste LMP cathode materials will experience explosive growth in the future. However, existing recycling technologies (high energy consumption of pyrometallurgical processes and heavy pollution of wet processes) are insufficient to achieve efficient recovery and high-value utilization of all elements. Therefore, developing green and efficient waste LMP recycling technologies is of significant practical importance. Summary of the Invention

[0004] Based on the problems existing in the prior art, this invention provides a method for synthesizing manganese ferrite magnetic materials from waste lithium manganese iron phosphate cathode materials. This method aims to overcome the shortcomings of traditional pyrometallurgical (high energy consumption) and wet (high pollution) recycling technologies, providing a green and efficient method for the resource utilization of waste lithium manganese iron phosphate cathode materials. By constructing an alkaline constant current electrochemical system, selective leaching of lithium, recovery of phosphorus, graphite separation, and synergistic enrichment of manganese and iron elements are simultaneously achieved. Following nitric acid acidification, citrate precursor gelation, and controlled calcination, the high-value manganese and iron elements are transformed into manganese ferrite magnetic materials with excellent magnetic permeability and uniform particle size.

[0005] To achieve its objectives, the present invention employs the following technical solution:

[0006] A method for synthesizing manganese ferrite magnetic materials from waste lithium manganese iron phosphate cathode materials includes the following steps:

[0007] Step 1: Using waste lithium manganese iron phosphate cathode powder as raw material; dissolve the organic binder in the solvent and stir until completely dissolved; add the waste lithium manganese iron phosphate cathode powder to the binder solution, and prepare a uniform slurry by ultrasonic dispersion for 10~120min or stirring for 1~24h; uniformly coat the slurry onto the surface of the titanium mesh and dry it at 60~120℃ for 2~12h to obtain the cathode sheet.

[0008] 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 a sodium hydroxide aqueous solution with a concentration of 0.1~2mol / L and a pH value of 10~14 as the electrolyte, apply a constant current electric field of 1~200mA to the two electrodes, and electrolyze for 1~600min.

[0009] Step 3: Take out the positive electrode after electrolysis, wash it with deionized water, and dry it at 60-100℃ to obtain the electrolysis product; add the electrolysis product to deionized water and ultrasonically disperse it at 100-500W power for 1-600min to break up the agglomerates of manganese iron product and graphite, and then filter and collect the solid mixture, which is the mixture of manganese iron product and graphite.

[0010] Step 4: Evaporate and concentrate the remaining electrolyte from Step 2 at 100~150℃, add phosphorus source to the concentrate, adjust the pH of the system to 10~13, so that lithium element precipitates, and obtain lithium phosphate after filtration.

[0011] Step 5: Dissolve 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, stir until the manganese-iron product is completely dissolved (graphite is insoluble in nitric acid), filter to remove undissolved graphite; add citric acid at a molar ratio of 1:0.1~1 to the total molar amount of manganese-iron element in the manganese-iron product, stir and mix for 60~600 min, then stir and evaporate the resulting solution at 60~120℃ to remove water, and obtain a viscous gel.

[0012] Step 6: Place the viscous gel obtained in Step 5 in an air or oxygen atmosphere and calcine it at 400~700℃ for 60~300min to decompose the citric acid; after grinding, the calcined product is washed with deionized water until the pH is neutral, and then dried to obtain manganese ferrite magnetic material.

[0013] Furthermore, 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%.

[0014] Further, 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.

[0015] Further, in step 4, the phosphorus source is one or more of trisodium phosphate, sodium dihydrogen phosphate, tripotassium phosphate, potassium dihydrogen phosphate, and phosphoric acid.

[0016] Furthermore, 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.

[0017] This invention constructs an integrated technical path of "electrochemical selective leaching—multi-element graded recovery—synthesis of high-value materials," which has the following outstanding advantages compared with traditional pyrometallurgy and hydrometallurgy:

[0018] 1. By precisely controlling key parameters such as electrolyte concentration, electrolysis current, and time in the alkaline electrolysis system, efficient and selective leaching of Li and P elements in waste lithium manganese phosphate is achieved, while Mn and Fe elements are retained in the solid product. Subsequently, through steps such as nitric acid dissolution, graphite separation, gelation, and calcination, the Mn and Fe elements are directionally converted into high-value-added manganese ferrite, ultimately achieving full recovery and resource utilization of the four core elements of Li, Mn, Fe, and P, with no resource waste, solving the problems of low element recovery rate and serious resource loss in traditional technologies.

[0019] 2. This invention breaks through the limitation of traditional recycling technology that only recovers single metal salts. It synergistically converts Mn and Fe elements into manganese ferrite magnetic materials with excellent magnetic properties (saturation magnetization ≥70 emu / g, uniform particle size), recovers Li and P elements into high-purity lithium phosphate (purity ≥98%), and the graphite conductive agent can be recycled after separation. The economic value of the recovered products is significantly improved compared with traditional methods.

[0020] 3. This invention adopts an alkaline electrochemical leaching system, which avoids the large-scale use of strong acid reagents in hydrometallurgy and reduces acidic wastewater pollution; the electrolysis process is carried out at room temperature and pressure, and the subsequent calcination temperature is only 400-700℃ (far lower than the high temperature of 800℃ or above in pyrometallurgy), thus reducing overall energy consumption; there is no harmful gas emission in the process, and the washing wastewater can be recycled after simple treatment, significantly reducing the environmental impact.

[0021] 4. This invention solves three key technical problems in the recycling of waste lithium manganese iron phosphate: first, green and efficient extraction of lithium, avoiding the high pollution and low selectivity of traditional methods; second, efficient separation of graphite and metal oxides, utilizing the characteristic that graphite is insoluble in nitric acid to achieve precise separation; and third, synergistic high-value conversion of Mn and Fe elements, achieving one-step conversion from waste electrode materials to functional magnetic materials through the citrate precursor method and controlled calcination.

[0022] 5. This invention integrates lithium extraction, phosphorus removal, graphite separation, lithium phosphate preparation, and manganese ferrite synthesis into several core steps. The process is simple, the operation is controllable, and no complex equipment is required. The reaction conditions of each step are mild (room temperature electrolysis, medium temperature calcination), and the parameters are easy to control. It can be scaled up according to actual production needs, providing a practical and feasible technical solution for the large-scale treatment of waste manganese iron lithium cathode materials. Attached Figure Description

[0023] Figure 1 This is the X-ray diffraction (XRD) pattern of the manganese ferrite magnetic material obtained in Example 1 of the present invention.

[0024] Figure 2 This is a high-resolution transmission electron microscope (HRTEM) image of the manganese ferrite magnetic material obtained in Example 1 of this invention.

[0025] Figure 3 This is a diagram showing the elemental composition of the manganese ferrite magnetic material obtained in Example 1 of this invention.

[0026] Figure 4 This is a hysteresis loop diagram of the vibrating sample magnetometer (VSM) of the manganese ferrite magnetic material obtained in Example 1 of the present invention.

[0027] Figure 5 This is a Zeta potential distribution diagram of the manganese ferrite magnetic material obtained in Example 1 of the present invention.

[0028] Figure 6 This is a particle size distribution diagram of the manganese ferrite magnetic material obtained in Example 1 of the present invention.

[0029] Figure 7 This is a hysteresis loop diagram of the vibrating sample magnetometer (VSM) of the manganese ferrite magnetic material obtained in Example 2 of the present invention.

[0030] Figure 8 This is a hysteresis loop diagram of the vibrating sample magnetometer (VSM) of the manganese ferrite magnetic material obtained in Example 3 of the present invention. Detailed Implementation

[0031] The embodiments of the present invention are described in detail below. These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments.

[0032] Example 1

[0033] The method for synthesizing manganese ferrite magnetic material from waste lithium manganese iron phosphate cathode material in this embodiment is as follows:

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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%).

[0038] 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.

[0039] 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%).

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] Example 2

[0047] The method for synthesizing manganese ferrite magnetic material from waste lithium manganese iron phosphate cathode material in this embodiment is as follows:

[0048] 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 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.

[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 (0.738 g, purity 98.6%, lithium recovery rate 99.1%).

[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 0.0435 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.

[0053] 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%).

[0054] 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.

[0055] Example 3

[0056] The method for synthesizing manganese ferrite magnetic materials using waste lithium manganese iron phosphate cathode materials in this embodiment is as follows:

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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%).

[0061] 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.

[0062] 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%).

[0063] 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.

[0064] 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 prepared in Step 1 to the positive electrode of the adjustable DC electrolytic cell, connect the blank titanium mesh to the negative electrode, use a sodium hydroxide aqueous solution with a concentration of 0.1~2 mol / L and a pH value of 10~14 as the electrolyte, apply a constant current electric field to the two electrodes for electrolysis, the electrolysis current is 1~200 mA, and the electrolysis time is 1~600 min; 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; the molar ratio of citric acid to the total molar amount of manganese-iron element in the manganese-iron product is 1:0.1~1. Step 6: Calcine the viscous gel obtained in Step 5 at 400~700℃ for 60~300 min to decompose the citric acid; after grinding and washing the calcined product until the pH is neutral and drying, manganese ferrite magnetic material is obtained.

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 3, the ultrasonic dispersion power is 100~500 W, and the ultrasonic time is 1~600 min.

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 4, the phosphorus source is one or more of trisodium phosphate, sodium dihydrogen phosphate, tripotassium phosphate, potassium dihydrogen phosphate, and phosphoric acid.

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 4, the evaporation and concentration temperature is 100~150℃.

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