Method for preparing lithium iron manganese phosphate by using lithium iron phosphate lithium extraction tailings

Abstract

The invention relates to the technical field of battery positive electrode material processing, in particular to a method for preparing lithium iron manganese phosphate from lithium iron phosphate lithium extraction tailings, which specifically comprises the following steps: dissolving the lithium iron phosphate lithium extraction tailings in a sulfuric acid solution, heating to 60-90 DEG C, continuously stirring for 2-8 hours, adding excessive reduced iron powder until ferric iron is completely reduced, and filtering to obtain phosphorus and ferric acid liquor; the method comprises the following steps: adding phosphorus and iron acid liquor into a reaction kettle together with ammonia water and hydrogen peroxide after supplementing phosphorus, filtering, washing to obtain an amorphous iron phosphate yellow material filter cake, and pulping to obtain iron phosphate slurry; the method comprises the following steps: adding a manganese source into a carbonate solution, filtering, washing to obtain a manganese carbonate filter cake, and dissolving in a phosphoric acid solution to obtain phosphorus and manganese acid liquor; and adding the iron phosphate slurry, phosphorus, a manganic acid solution, LiOH and a carbon source into a reaction kettle, carrying out a hydrothermal reaction, filtering, washing, and carrying out vacuum drying to obtain the lithium iron manganese phosphate. The method provided by the invention is simple, convenient, safe and low in cost, and the obtained lithium manganese iron phosphate has few impurities and good electrochemical performance.

Description

Technical Field

[0001] The invention relates to the technical field of battery positive electrode material processing, and in particular to a method for preparing lithium manganese iron phosphate by utilizing lithium iron phosphate lithium extraction tailings. Background Art

[0002] The rise of new energy vehicles has triggered the problem of incomplete recycling and waste of lithium-ion battery resources. Generally, the life of lithium-ion batteries in new energy vehicles is 3 to 5 years. According to forecasts, the amount of retired power batteries will reach 350,000 tons in 2025, so the recycling of waste lithium-ion batteries is imminent.

[0003] At present, there are some problems in the large-scale recycling of waste lithium-ion batteries: first, most lithium-ion batteries focus on recycling high-value lithium, while ignoring lithium iron phosphate. For example, Chinese patent CN116902998A discloses a method for efficiently recycling lithium in waste lithium iron phosphate batteries, but does not effectively recycle the remaining lithium iron phosphate; second, the large amount of phosphorus and iron elements remaining in lithium-ion batteries are not effectively recycled at high value, and are usually landfilled or made into phosphate fertilizers with low commercial value. For example, Chinese patent CN116924366A discloses a method for recycling lithium battery positive electrode materials, and positive electrode waste is not effectively recycled. Recycled lithium iron phosphate fertilizer; third, even if lithium iron phosphate is recycled as the positive electrode material of lithium-ion batteries, the preparation method is relatively complicated. For example, Chinese patent CN116119638A discloses a method for recycling lithium iron phosphate waste powder to prepare lithium iron manganese phosphate. The lithium iron phosphate waste powder is subjected to the steps of calcination in a reducing atmosphere, leaching in a phosphoric acid solution, solid-liquid separation, hydrogen peroxide oxidation-reduction, spray drying and calcination in a protective atmosphere to finally obtain lithium iron manganese phosphate. The process steps are cumbersome, multiple calcinations consume high energy, and the last calcination needs to be placed in a protective atmosphere. The operating conditions are high and the preparation cost increases. Summary of the invention

[0004] In view of the technical problems in the prior art of using lithium iron phosphate tailings to prepare lithium ferromanganese phosphate, which have complicated process steps and high costs, the present invention provides a method for preparing lithium ferromanganese phosphate using lithium iron phosphate tailings. No high-temperature calcination is required. Lithium ferromanganese phosphate can be obtained by hydrothermal reaction of various raw materials in a certain ratio. The method is simple, safe and low-cost.

[0005] The technical solution of the present invention is as follows: A method for preparing lithium iron manganese phosphate using lithium iron phosphate tailings comprises the following steps: (1) Dissolve the lithium iron phosphate tailings in a sulfuric acid solution, heat to 60-90°C, continue stirring for 2-8 hours, and add excess reduced iron powder during stirring until the trivalent iron is completely reduced, and then filter to obtain phosphorus and iron acid solution; (2) adding phosphorus-supplemented phosphorus and iron acid solution, ammonia water and hydrogen peroxide into a reaction kettle at a molar ratio of P: NH3·H2O: H2O2 of 1: 0.2-0.5: 0.5-0.72, followed by filtering and washing to obtain an amorphous iron phosphate yellow material filter cake, and beating to obtain an iron phosphate slurry; (3) adding a manganese source to a carbonate solution, wherein the molar ratio of the manganese source to the carbonate is 1:1-1.5, filtering and washing to obtain a manganese carbonate filter cake, and then dissolving the cake in a phosphoric acid solution to obtain a phosphorus and manganese acid solution; (4) Adding ferric phosphate slurry, phosphorus and manganese acid solution, LiOH and carbon source into a reactor in a mass ratio of 0.3-1:0.4-4:1-1.05:5-20 for hydrothermal reaction at a reaction temperature of 90-220°C for a reaction time of 12-24h, followed by filtering, washing and vacuum drying to obtain lithium manganese iron phosphate.

[0006] Furthermore, in step (1), the solid-liquid ratio of the lithium iron phosphate tailings to the sulfuric acid solution is 2kg:1L; and the concentration of the sulfuric acid solution is 5mol / L.

[0007] Furthermore, in step (1), the reaction conditions are to raise the temperature to 80° C. and continue stirring for 3 h.

[0008] Furthermore, in step (2), the phosphorus and iron acid solution is supplemented with phosphorus until the iron-phosphorus ratio is 1:1.

[0009] Furthermore, the phosphorus and ferric acid solution in step (2) is added to the reactor with ammonia water and hydrogen peroxide at a molar ratio of P: NH3·H2O: H2O2 of 1:0.3:0.6.

[0010] Furthermore, in step (3), the manganese source is manganese sulfate, manganese oxalate, potassium permanganate or manganese oxide.

[0011] Furthermore, in step (3), the carbonate is sodium carbonate, sodium bicarbonate or ammonium carbonate.

[0012] Furthermore, in step (4), the carbon source is a mixture of sucrose, polyethylene glycol and glucose.

[0013] Furthermore, in step (4), the mass ratio of the ferric phosphate slurry, phosphorus and manganese acid solution, LiOH and carbon source is 0.3-0.4:0.6-0.7:1.02:15.

[0014] Furthermore, in step (4), the hydrothermal reaction temperature is 120° C. and the reaction time is 18 h.

[0015] The beneficial effects of the present invention are: The present invention provides a method for preparing lithium iron manganese phosphate by using tailings of lithium iron phosphate for lithium extraction. The method does not require calcination under a protective atmosphere, and lithium iron manganese phosphate can be prepared by hydrothermal reaction. The method is simple and safe to operate, and has lower cost. The obtained lithium iron manganese phosphate has less impurities, higher compaction density and good electrochemical performance. The compaction density reaches 2.5g / cm 3 The above, 0.1C discharge capacity reaches more than 165mAh / g, 1C discharge capacity reaches more than 155mAh / g, for the waste lithium iron phosphate after the recovery of lithium tailings remaining to provide a high-value recovery method. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0017] Figure 1 This is a process flow chart for preparing lithium iron manganese phosphate using lithium iron phosphate tailings.

[0018] Figure 2 This is the XRD diagram of the amorphous iron phosphate yellow material filter cake of Example 1.

[0019] Figure 3 This is the XRD diagram of the manganese carbonate filter cake in Example 1.

[0020] Figure 4 This is the XRD diagram of lithium manganese iron phosphate in Example 1.

[0021] Figure 5 This is a high-magnification SEM image of the lithium manganese iron phosphate after airflow crushing in Example 1.

[0022] Figure 6 This is a low-magnification SEM image of the lithium manganese iron phosphate after airflow crushing in Example 1. DETAILED DESCRIPTION

[0023] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0024] Example 1 A method for preparing lithium iron manganese phosphate using lithium iron phosphate tailings, the process is as follows Figure 1As shown, the specific steps include: (1) Add 2 kg of lithium iron phosphate tailings into 1 L of 5 mol / L sulfuric acid solution, stir and dissolve, heat to 80 ° C, continue stirring for 3 h, and add excess reduced iron powder during stirring until the trivalent iron is completely reduced, and then filter to obtain phosphorus and iron acid solution; (2) Phosphorus and ferric acid solution was supplemented with phosphorus to an iron-phosphorus ratio of 1:1 and then diluted to 1 mol / L. Phosphorus and ferric acid solution, ammonia water and hydrogen peroxide were added to the reactor at a molar ratio of P: NH3·H2O: H2O2 of 1:0.3:0.6, and then filtered and washed to obtain an amorphous iron phosphate yellow material filter cake (XRD as Figure 2 As shown), after beating, iron phosphate slurry is obtained, and the iron phosphate slurry is diluted with water to 1 mol / L for later use; The iron-phosphorus ratio of 1:1 can improve the recovery rate of iron in the acid leaching solution of lithium iron phosphate tailings; (3) adding 1 L, 1 mol / L manganese sulfate to 1 L, 1.1 mol / L sodium carbonate solution, filtering and washing to obtain a manganese carbonate filter cake, and dissolving the manganese carbonate filter cake in 1.2 mol phosphoric acid solution to obtain phosphorus and manganese acid solution; Manganese ions react with carbonate ions to form manganese carbonate, which can remove sulfate and significantly reduce the sulfur content in the product. The XRD pattern of manganese carbonate filter cake is as follows: Figure 3 As shown, it has high crystallinity and no impurity phase; Dissolving and dispersing manganese carbonate with phosphoric acid can discharge carbonate ions as carbon dioxide, reducing the impact of anions on product performance; (4) Add ferric phosphate slurry, phosphorus and manganese acid solution, LiOH and carbon source (sucrose, polyethylene glycol and glucose mixed in a mass ratio of 1:1:1) in a mass ratio of 0.4:0.6:1.02:15 into a stainless steel reactor lined with polytetrafluoroethylene and hydrothermally react at 120°C for 18 hours. After the reaction, filter, wash and vacuum dry to obtain lithium manganese iron phosphate. XRD results are as follows: Figure 4 As shown, lithium manganese iron phosphate exists in the form of a solid solution and has good dispersion.

[0025] Example 2 A method for preparing lithium iron manganese phosphate using lithium iron phosphate tailings, specifically comprising the following steps: (1) Add 2 kg of lithium iron phosphate tailings into 1 L of 5 mol / L sulfuric acid solution, stir and dissolve, heat to 80 ° C, continue stirring for 3 h, and add excess reduced iron powder during stirring until the trivalent iron is completely reduced, and then filter to obtain phosphorus and iron acid solution; (2) Phosphorus is added to the phosphorus and iron acid solution until the iron-phosphorus ratio is 1:1 and then diluted to 1 mol / L. Phosphorus and iron acid solution, ammonia water and hydrogen peroxide are added to the reactor at a molar ratio of P: NH3·H2O: H2O2 of 1:0.3:0.6, followed by filtration and washing to obtain an amorphous iron phosphate yellow material filter cake, and iron phosphate slurry is obtained after pulping. The iron phosphate slurry is diluted to 1 mol / L with water for later use; (3) adding 1 L, 1 mol / L manganese sulfate to 1 L, 1.1 mol / L sodium carbonate solution, filtering and washing to obtain a manganese carbonate filter cake, and dissolving the manganese carbonate filter cake in 1.2 mol phosphoric acid solution to obtain phosphorus and manganese acid solution; (4) Add ferric phosphate slurry, phosphorus and manganese acid solution, LiOH and carbon source (sucrose, polyethylene glycol and glucose mixed in a mass ratio of 1:1:1) in a mass ratio of 0.3:0.7:1.02:15 into a stainless steel reactor lined with polytetrafluoroethylene, and carry out hydrothermal reaction at 120°C for 18 hours. After the reaction, filter, wash and vacuum dry to obtain lithium manganese iron phosphate.

[0026] In short, the difference between Example 2 and Example 1 is that in step (4), the mass ratio of ferric phosphate slurry, phosphorus and manganese acid solution, LiOH and carbon source is 0.3:0.7:1.02:15.

[0027] Comparative Example 1 A method for preparing lithium iron manganese phosphate using lithium iron phosphate tailings, specifically comprising the following steps: (1) Add 2 kg of lithium iron phosphate tailings into 1 L of 5 mol / L sulfuric acid solution, stir and dissolve, heat to 80 ° C, continue stirring for 3 h, and add excess reduced iron powder during stirring until the trivalent iron is completely reduced, and then filter to obtain phosphorus and iron acid solution; (2) Phosphorus is added to the phosphorus and iron acid solution until the iron-phosphorus ratio is 1:1 and then diluted to 1 mol / L. Phosphorus and iron acid solution, ammonia water and hydrogen peroxide are added to the reactor at a molar ratio of P: NH3·H2O: H2O2 of 1:0.3:0.6, followed by filtration and washing to obtain an amorphous iron phosphate yellow material filter cake, and iron phosphate slurry is obtained after pulping. The iron phosphate slurry is diluted to 1 mol / L with water for later use; (3) adding 1L, 1.5mol / L manganese sulfate to 1L, 1.1mol / L sodium carbonate solution, filtering and washing to obtain a manganese carbonate filter cake, and dissolving the manganese carbonate filter cake in 1.2mol phosphoric acid solution to obtain phosphorus and manganese acid solution; (4) Add ferric phosphate slurry, phosphorus and manganese acid solution, LiOH and carbon source (sucrose, polyethylene glycol and glucose mixed in a mass ratio of 1:1:1) in a mass ratio of 0.4:0.6:1.02:15 into a stainless steel reactor lined with polytetrafluoroethylene, and carry out hydrothermal reaction at 120°C for 18 hours. After the reaction, filter, wash and vacuum dry to obtain lithium iron manganese phosphate.

[0028] In short, the difference between Comparative Example 1 and Example 1 is that the manganese sulfate used in step (3) is 1 L and 1.5 mol / L.

[0029] Comparative Example 2 A method for preparing lithium iron manganese phosphate using lithium iron phosphate tailings, specifically comprising the following steps: (1) Add 2 kg of lithium iron phosphate tailings into 1 L of 5 mol / L sulfuric acid solution, stir and dissolve, heat to 80 ° C, continue stirring for 3 h, and add excess reduced iron powder during stirring until the trivalent iron is completely reduced, and then filter to obtain phosphorus and iron acid solution; (2) Phosphorus is added to the phosphorus and iron acid solution until the iron-phosphorus ratio is 1:1 and then diluted to 1 mol / L. Phosphorus and iron acid solution, ammonia water and hydrogen peroxide are added to the reactor at a molar ratio of P: NH3·H2O: H2O2 of 1:0.3:0.6, followed by filtration and washing to obtain an amorphous iron phosphate yellow material filter cake, and iron phosphate slurry is obtained after pulping. The iron phosphate slurry is diluted to 1 mol / L with water for later use; (3) adding 1 L, 1 mol / L manganese sulfate to 1 L, 1.1 mol / L sodium carbonate solution, filtering and washing to obtain a manganese carbonate filter cake, and dissolving the manganese carbonate filter cake in 1.2 mol phosphoric acid solution to obtain phosphorus and manganese acid solution; (4) Add ferric phosphate slurry, phosphorus and manganese acid solution, LiOH and carbon source (sucrose, polyethylene glycol and glucose mixed in a mass ratio of 1:1:1) in a mass ratio of 0.3:0.7:1.02:20 into a stainless steel reactor lined with polytetrafluoroethylene, and carry out hydrothermal reaction at 120°C for 18 hours. After the reaction, filter, wash and vacuum dry to obtain lithium manganese iron phosphate.

[0030] In short, the difference between Comparative Example 2 and Example 1 is that in step (4), the mass ratio of ferric phosphate slurry, phosphorus and manganese acid solution, LiOH and carbon source is 0.3:0.7:1.02:20.

[0031] Comparative Example 3 A method for preparing lithium iron manganese phosphate using lithium iron phosphate tailings, specifically comprising the following steps: (1) Add 2 kg of lithium iron phosphate tailings into 1 L of 5 mol / L sulfuric acid solution, stir and dissolve, heat to 80 ° C, continue stirring for 3 h, and add excess reduced iron powder during stirring until the trivalent iron is completely reduced, and then filter to obtain phosphorus and iron acid solution; (2) Phosphorus is added to the phosphorus and iron acid solution until the iron-phosphorus ratio is 1:1 and then diluted to 1 mol / L. Phosphorus and iron acid solution, ammonia water and hydrogen peroxide are added to the reactor at a molar ratio of P: NH3·H2O: H2O2 of 1:0.3:0.6, followed by filtration and washing to obtain an amorphous iron phosphate yellow material filter cake, and iron phosphate slurry is obtained after pulping. The iron phosphate slurry is diluted to 1 mol / L with water for later use; (3) adding 1 L, 1 mol / L manganese sulfate to 1 L, 1.1 mol / L sodium carbonate solution, filtering and washing to obtain a manganese carbonate filter cake, and dissolving the manganese carbonate filter cake in 1.2 mol phosphoric acid solution to obtain phosphorus and manganese acid solution; (4) Add ferric phosphate slurry, phosphorus and manganese acid solution, LiOH and carbon source (sucrose, polyethylene glycol and glucose mixed in a mass ratio of 1:1:1) in a mass ratio of 0.3:0.7:1.02:10 into a stainless steel reactor lined with polytetrafluoroethylene, and carry out hydrothermal reaction at 120°C for 18 hours. After the reaction, filter, wash and vacuum dry to obtain lithium iron manganese phosphate.

[0032] In short, the difference between Comparative Example 3 and Example 1 is that in step (4), the mass ratio of ferric phosphate slurry, phosphorus and manganese acid solution, LiOH and carbon source is 0.3:0.7:1.02:10.

[0033] Comparative Example 4 A method for preparing lithium iron manganese phosphate using lithium iron phosphate tailings, specifically comprising the following steps: (1) Add 2 kg of lithium iron phosphate tailings into 1 L of 5 mol / L sulfuric acid solution, stir and dissolve, heat to 80 ° C, continue stirring for 3 h, and add excess reduced iron powder during stirring until the trivalent iron is completely reduced, and then filter to obtain phosphorus and iron acid solution; (2) Phosphorus is added to the phosphorus and iron acid solution until the iron-phosphorus ratio is 1:1 and then diluted to 1 mol / L. Phosphorus and iron acid solution, ammonia water and hydrogen peroxide are added to the reactor at a molar ratio of P: NH3·H2O: H2O2 of 1:0.3:0.6, followed by filtration and washing to obtain an amorphous iron phosphate yellow material filter cake, and iron phosphate slurry is obtained after pulping. The iron phosphate slurry is diluted to 1 mol / L with water for later use; (3) adding 1 L, 1 mol / L manganese sulfate to 1 L, 1.1 mol / L sodium carbonate solution, filtering and washing to obtain a manganese carbonate filter cake, and dissolving the manganese carbonate filter cake in 1.2 mol phosphoric acid solution to obtain phosphorus and manganese acid solution; (4) Add ferric phosphate slurry, phosphorus and manganese acid solution, LiOH and carbon source (sucrose, polyethylene glycol and glucose mixed in a mass ratio of 1:1:1) in a mass ratio of 0.4:0.6:1.02:15 into a stainless steel reactor lined with polytetrafluoroethylene, and perform hydrothermal reaction at 80°C for 10 hours. After the reaction, filter, wash and vacuum dry to obtain lithium iron manganese phosphate.

[0034] In short, the difference between Comparative Example 4 and Example 1 is that the hydrothermal reaction conditions of the ferric phosphate slurry, phosphorus and manganese acid solution, LiOH and carbon source in step (4) are 80° C. for 10 h.

[0035] Experimental Example 1 The lithium manganese iron phosphate prepared in Example 1-2 and Comparative Example 1-4 was tested for impurities using an inductively coupled plasma mass spectrometer (ICP). The test results are shown in Table 1 below: Table 1 Data on the content of metal impurity elements in products of the embodiments and comparative examples

[0036] It can be seen from Table 1 that the total amount of impurity elements in Examples 1-2 is lower than that in Comparative Examples 1-4, among which the contents of Na, Ni, K, Al and S are significantly lower than those in Comparative Examples 1-4, indicating that the impurity content of lithium manganese iron phosphate obtained by the preparation method of the present invention is low.

[0037] Experimental Example 2 The lithium manganese iron phosphate prepared in Example 1-2 and Comparative Example 1-4 was crushed by air flow and used as the positive electrode active material. The positive electrode active material: SP (superconducting carbon black): PVDF (polyvinylidene fluoride) was homogenized in a mass ratio of 90:5:5, coated on a 20μm thick aluminum foil, and then dried, rolled, die-cut, and punched into positive electrode sheets. A lithium sheet was used as the negative electrode, a PE material diaphragm was used, and 80μmL of electrolyte was added dropwise. The electrochemical performance tests of the batteries prepared above were carried out respectively, specifically: the button batteries prepared above were tested using a blue electric tester, and the prepared button batteries were placed in an incubator at 25°C for charge and discharge tests, the voltage range was 2.0-4.2V, 0.1C charge and discharge activation for one cycle, and then charged and discharged at 0.1C and 1C constant current and constant voltage, and the results are shown in Table 2.

[0038] The high and low magnification SEM images of lithium manganese iron phosphate after air flow crushing are shown in Figure 5 , Figure 6 From the figure, we can see that the particles after gas crushing are diamond-shaped with a smooth surface, and the carbon coating is uniform.

[0039] Table 2 Basic physical and chemical data of products in Examples and Comparative Examples

[0040] As can be seen from Table 2, compared with Comparative Examples 1-4, the compaction density and capacitance performance of the lithium manganese iron phosphate prepared in Example 1-2 are improved, with higher compaction density and specific capacity, and the compaction density reaches 2.5 g / cm 3The 0.1C discharge capacity reaches more than 165mAh / g, and the 1C discharge capacity reaches more than 155mAh / g.

[0041] Although the present invention has been described in detail with reference to the accompanying drawings and in combination with the preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, a person of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and these modifications or substitutions shall be within the scope of the present invention. Any person of ordinary skill in the art may easily think of changes or substitutions within the technical scope disclosed by the present invention, and these shall be within the scope of protection of the present invention.

Claims

1. A method for preparing lithium iron manganese phosphate using lithium iron phosphate tailings, characterized in that: The steps include: (1) Dissolve the lithium iron phosphate tailings in a sulfuric acid solution, heat to 60-90°C, continue stirring for 2-8 hours, and add excess reduced iron powder during stirring until the trivalent iron is completely reduced, and then filter to obtain phosphorus and iron acid solution; (2) adding phosphorus-supplemented phosphorus and iron acid solution, ammonia water and hydrogen peroxide into a reaction kettle at a molar ratio of P: NH3·H2O: H2O2 of 1: 0.2-0.5: 0.5-0.72, followed by filtering and washing to obtain an amorphous iron phosphate yellow material filter cake, and beating to obtain an iron phosphate slurry; (3) adding a manganese source to a carbonate solution, wherein the molar ratio of the manganese source to the carbonate is 1:1-1.5, filtering and washing to obtain a manganese carbonate filter cake, and then dissolving the cake in a phosphoric acid solution to obtain a phosphorus and manganese acid solution; (4) Adding ferric phosphate slurry, phosphorus and manganese acid solution, LiOH and carbon source into a reactor in a mass ratio of 0.3-1:0.4-4:1-1.05:5-20 for hydrothermal reaction at a reaction temperature of 90-220°C for a reaction time of 12-24h, followed by filtering, washing and vacuum drying to obtain lithium manganese iron phosphate.

2. The method for preparing lithium iron manganese phosphate using lithium iron phosphate tailings as claimed in claim 1, characterized in that: In step (1), the solid-liquid ratio of lithium iron phosphate tailings to sulfuric acid solution is 2kg:1L; the concentration of sulfuric acid solution is 5mol / L.

3. The method for preparing lithium iron manganese phosphate using lithium iron phosphate tailings as claimed in claim 1, characterized in that: The reaction conditions in step (1) are to heat the mixture to 80°C and continue stirring for 3 h.

4. The method for preparing lithium iron manganese phosphate using lithium iron phosphate tailings as claimed in claim 1, characterized in that: In step (2), phosphorus is added to the ferric acid solution until the iron-phosphorus ratio is 1:

1.

5. The method for preparing lithium iron manganese phosphate using lithium iron phosphate tailings as claimed in claim 1, characterized in that: In step (2), the phosphorus and ferric acid solution is added to the reactor with ammonia water and hydrogen peroxide in a molar ratio of P: NH3·H2O: H2O2 of 1:0.3:0.6 after phosphorus supplementation.

6. The method for preparing lithium iron manganese phosphate using lithium iron phosphate tailings as claimed in claim 1, characterized in that: In step (3), the manganese source is manganese sulfate, manganese oxalate, potassium permanganate or manganese oxide.

7. The method for preparing lithium iron manganese phosphate using lithium iron phosphate tailings as claimed in claim 1, characterized in that: In step (3), the carbonate is sodium carbonate, sodium bicarbonate or ammonium carbonate.

8. The method for preparing lithium iron manganese phosphate using lithium iron phosphate tailings as claimed in claim 1, characterized in that: In step (4), the carbon source is a mixture of sucrose, polyethylene glycol and glucose.

9. The method for preparing lithium iron manganese phosphate using lithium iron phosphate tailings as claimed in claim 1, characterized in that: In step (4), the mass ratio of ferric phosphate slurry, phosphorus and manganese acid solution, LiOH and carbon source is 0.3-0.4:0.6-0.7:1.02:

15.

10. The method for preparing lithium iron manganese phosphate using lithium iron phosphate tailings as claimed in claim 1, characterized in that: In step (4), the hydrothermal reaction temperature is 120° C. and the reaction time is 18 h.

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