Method for preparing manganese tetroxide-doped precursors and lithium manganese oxide from manganese-containing waste residue

Abstract

A method for preparing a manganese tetroxide-doped precursor from manganese-containing waste residue includes the following steps: (1) leaching; (2) calcium removal; (3) adjusting the ratio; (4) modifying the co-precipitate; (5) preparing the manganese tetroxide-doped precursor: adding a certain amount of magnesium fluoride to the manganese tetroxide precipitate after primary doping, ball milling, and calcining to obtain the manganese tetroxide-doped precursor. This invention has a simple and feasible process. After leaching manganese-containing waste residue, only simple calcium removal is required before it can be directly used to prepare manganese tetroxide-doped material. The spinel lithium manganese oxide cathode material produced using manganese tetroxide-doped material achieves comprehensive and efficient resource recycling.

Description

Technical Field

[0001] This invention belongs to the field of clean metallurgical production technology, specifically a method for preparing manganese tetroxide-doped precursors and lithium manganese oxide from manganese-containing waste slag. Background Technology

[0002] In the hydrometallurgical production of electrolytic manganese, manganese dioxide, and manganese sulfate, a large amount of manganese sulfide slag (manganese-containing waste slag) containing manganese, cobalt, and nickel is generated. The main components of this waste slag are sulfides such as MnS, NiS, and CoS, with a manganese content of approximately 10%–15%, nickel 0.5%–1.0%, and cobalt 1.0%–1.8%, along with small amounts of calcium, magnesium, and iron. The cobalt and nickel content in the slag is higher than that in common cobalt and nickel minerals, and the slag volume is large. Since no effective treatment method has yet been found, this slag is currently mainly stored in slag storage facilities. As of March 2022, the cumulative stockpile of manganese sulfide slag in my country exceeded 100 million tons, with an additional 10 million tons added annually. Effective and feasible resource-based value-added treatment solutions are urgently needed to address this waste slag.

[0003] Currently, the main manganese sources for preparing lithium manganese oxide (LiMn2O4) include manganese dioxide, manganese tetroxide, manganese sulfate, manganese acetate, and manganese carbonate. When using manganese dioxide as a manganese source to prepare spinel-type lithium manganese oxide, its application is limited due to high impurity content and unstable morphology. The manganese carbonate method for preparing lithium manganese oxide is currently limited to laboratory research and is difficult to industrialize due to high energy consumption and cost. Furthermore, high-temperature solid-state synthesis inevitably leads to material sintering, making it difficult to achieve the required physical properties of the prepared lithium manganese oxide (LiMn2O4). In contrast, manganese tetroxide has advantages such as stable quality, good process repeatability, and high tap density. Moreover, lithium manganese oxide (LiMn2O4) prepared using manganese tetroxide as a precursor exhibits excellent electrochemical performance and can effectively alleviate the decay of battery charge-discharge specific capacity, making it very suitable for preparing spinel-type lithium manganese oxide.

[0004] We have found the following patents related to the preparation of manganese tetroxide doped from waste residue: 1. Application No.: 202211403289.2, Invention Title: A Method for Preparing High-Bulk-Sounding Cation- and Anion-Doped Manganese Tetraoxide Precursor Materials. This invention mixes manganese chloride monohydrate, EDTA-2Na, and aluminum chloride hexahydrate, and uses a step-by-step feed flow based on particle size, employing a cyclic concentration method to prepare 8μm doped aluminum-manganese tetraoxide particles using 4μm manganese tetraoxide particles as the core. Alternatively, manganese chloride monohydrate and EDTA-2Na are mixed, and sodium fluoride is mixed with liquid alkali, and the feed flow is also stepped-by-step based on particle size, employing a cyclic concentration method to prepare 10μm doped aluminum- and fluorine-doped manganese tetraoxide particles. The prepared doped aluminum- and fluorine-doped manganese tetraoxide particles are dried in an oven and sieved to prepare the desired doped aluminum- and fluorine-doped manganese tetraoxide precursor materials. The high-voltage lithium manganese oxide prepared with doped aluminum- and fluorine-doped manganese tetraoxide exhibits improved initial discharge capacity, good charge-discharge cycle performance, and high-temperature performance. However, this invention does not actually measure the charge-discharge specific capacity and capacity retention rate of the lithium manganese oxide cathode material.

[0005] 2. Application No.: 202110872485.3, Invention Title: A Method for Preparing Modified Manganese Tetraoxide, its Products, and Applications. This invention provides a method for preparing modified manganese tetraoxide by doping a soluble salt solution of aluminum with a soluble salt solution of manganese, i.e., modifying manganese tetraoxide by doping with Al, so that Al and Mn elements in the system precipitate uniformly. Then, a mixture of ammonia and oxygen is introduced below the liquid surface of the system to carry out a gas-liquid phase contact reaction. The mixed gas reacts uniformly with the soluble salt of manganese, the reaction is slow and controllable, and the gas and liquid are in full contact, reducing the phenomenon of uneven diffusion of manganese ions. This allows manganese to be rapidly oxidized to manganese tetraoxide after forming manganese hydroxide precipitate, reducing the adsorption of impurities, especially greatly reducing the formation of basic manganese sulfate. The resulting manganese tetraoxide has low impurity content, complete crystal structure, and high crystallinity. This solves the problems of excessive impurity content and imperfect crystal structure in the currently prepared manganese tetroxide, but the invention does not improve the charge-discharge specific capacity and capacity retention of lithium manganese oxide cathode material.

[0006] 3. Application No.: 202311016514.1, Invention Title: A bulk-doped and surface-coated manganese tetroxide material. This invention utilizes the different precipitation sequences of hydroxides of different elements in solution to achieve bulk doping and surface coating in one step during the precursor preparation stage of the co-precipitation method, improving doping uniformity and coating stability. Furthermore, through the combined effect of doping and coating, it effectively solves the problems of capacity decay and interfacial side reactions in lithium manganese oxide. Lithium-ion batteries using lithium manganese oxide cathode materials prepared with this bulk-doped and surface-coated manganese tetroxide material exhibit excellent cycle performance, good rate performance, and high specific capacity. However, the capacity retention rate of the lithium manganese oxide cathode material of this invention still needs improvement.

[0007] 4. Application No.: 201210345734.4, Invention Title: Preparation Method of Ni and Al Co-doped Manganese Tetraoxide and the Doped Manganese Tetraoxide, provides a preparation method of Ni and Al co-doped Manganese Tetraoxide and the doped Manganese Tetraoxide. The method includes the following steps: (1) mixing soluble nickel salt and soluble aluminum salt according to the Ni / Al molar ratio = (1.0 / 2.0) ± 0.01 to prepare a nickel-aluminum mixed solution; (2) passing ammonia gas into the soluble manganese salt solution to control the pH of the soluble manganese salt solution within the range of 7.0 to 7.5; (3) mixing the soluble manganese salt solution and the nickel-aluminum mixed solution according to the (Ni+Al) / Mn3O4 molar ratio of 3%, and then spraying it into the air to carry out a gas-liquid oxidation reaction; and (4) adding ammonia gas to the solution after the gas-liquid oxidation reaction in step (3) to adjust the pH to the range of 7.0 to 7.5, and then repeating the process of spraying the reaction solution - adding ammonia gas to adjust the pH - spraying the reaction solution until the [Mn3O4] in the reaction solution is in the range of 7.0 to 7.5. 2+ The reaction was stopped when the concentration of Ni and Al co-doped Mn3O4 was ≤500 ppm. The resulting product had controllable particle size, narrow particle size distribution, less ultrafine powder, and low impurity content. However, this invention did not improve the charge-discharge specific capacity and capacity retention of the lithium manganese oxide cathode material. Summary of the Invention

[0008] The purpose of this invention is to solve the above-mentioned technical problems and provide a simple and feasible method for preparing doped manganese tetroxide precursors and lithium manganese oxide from manganese-containing waste residue, which can improve the cycle performance of lithium manganese oxide electrode materials.

[0009] To achieve the above objectives, the technical solution of the present invention is as follows: A method for preparing a manganese tetroxide-doped precursor from manganese-containing waste residue includes the following steps: (1) Leaching: Manganese-containing waste residue is mixed with a sulfuric acid solution of a certain concentration, heated and leached to obtain leachate; (2) Calcium removal: Add ammonia to the leachate, adjust the pH to weakly acidic, heat, then add sodium fluoride and react for a period of time, then add flocculant, let stand and separate, and obtain the calcium-removed filtrate. (3) Adjusting the ratio: Add cobalt salt, nickel salt and iron salt to the filtrate respectively, and adjust the filtrate to the set manganese-cobalt-nickel-iron molar ratio to obtain a manganese-cobalt-nickel-iron solution; (4) Modification coprecipitation: Add ammonia-ammonium chloride buffer solution to the reaction vessel, heat, then add the modifier, stir to dissolve, slowly add manganese cobalt nickel iron solution and sodium hydroxide solution, and at the same time bleed oxygen into the solution to carry out precipitation reaction. After the manganese cobalt nickel iron solution is added, keep warm for a period of time, then stop bleed oxygen, and then age and separate and dry to obtain manganese tetroxide precipitate after one doping. In this step, the manganese in manganese sulfate is first alkalized to obtain Mn2(OH)2SO4. Part of Mn2(OH)2SO4 is oxidized to obtain Mn3O4, and the other part is further alkalized to obtain Mn(OH)2. Finally, all of Mn(OH)2 is oxidized to obtain Mn3O4.

[0010]

[0011] Cobalt, nickel, and iron elements are also incorporated into the manganese tetroxide precipitate in oxide form.

[0012] (5) Preparation of manganese tetroxide precursor: Add a certain amount of magnesium fluoride to the manganese tetroxide precipitate after primary doping, ball mill, and calcine to obtain manganese tetroxide precursor.

[0013] As a further technical solution, in step (1) above, the liquid-solid ratio of the sulfuric acid solution to the manganese-containing waste residue is (5ml~8ml):1g, the concentration of the sulfuric acid solution is 80g / L~150g / L, the temperature of the heating leaching is 50~90℃, and the leaching time is 60~180min.

[0014] As a further technical solution, in step (2) above, the pH value of the leachate is adjusted to 4.0-6.0 with ammonia water, the heating temperature is 70-95℃, the amount of sodium fluoride is 1.5-3.0 times the theoretical mass of calcium in the leachate, the reaction time after adding sodium fluoride is 60-120 min, the flocculant is aluminum sulfate, the amount of aluminum sulfate is 0.3-0.6 g / L leachate, and the standing time is 2-3 h.

[0015] As a further technical solution, the above-mentioned manganese-cobalt-nickel-iron molar ratio is (1.90~1.95):(0.01~0.04):(0.01~0.04):(0.01~0.04).

[0016] As a further technical solution, the cobalt salt mentioned above is one or a mixture of several of cobalt sulfate, cobalt chloride, cobalt acetate, and cobalt nitrate; the nickel salt is one or a mixture of several of nickel sulfate, nickel chloride, nickel acetate, and nickel nitrate; and the iron salt is one or a mixture of several of ferric sulfate, ferric chloride, cobalt acetate, and ferric nitrate.

[0017] As a further technical solution, the above-mentioned modifier is any one or a mixture of two of hexadecyltrimethylammonium bromide and hexadecyltrimethylammonium chloride.

[0018] As a further technical solution, in step (4) above, the pH value of the ammonia-ammonium chloride buffer solution is 8.0-10.0, the heating temperature is 50-75℃, the amount of the modifier is 3-6 g / L of the total mixed solution, and the total mixed solution is a mixture of ammonia-ammonium chloride buffer solution, manganese cobalt nickel iron solution and sodium hydroxide solution; the concentration of manganese in the manganese cobalt nickel iron solution is 0.5-1.5 mol / L, the volume ratio of sodium hydroxide solution to manganese cobalt nickel iron solution is (1-1.5):1, the mass concentration of sodium hydroxide solution is 2-5%, the oxygen flow rate is 1-5 L / min, the heat preservation time is 30-60 min, and the aging time is 60-120 min.

[0019] As a further technical solution, the magnesium fluoride and the primary doped manganese tetroxide precipitate mentioned above are in the following molar ratio of manganese, cobalt, nickel, iron, magnesium and fluorine: (1.90~1.95):(0.01~0.04):(0.01~0.04):(0.01~0.04):(0.01~0.02):(0.01~0.02).

[0020] As a further technical solution, the ball milling speed is 300-500 r / min, and the ball milling time is 3-6 h.

[0021] A method for preparing lithium manganese oxide involves mixing lithium carbonate and a doped manganese tetroxide precursor as described above, followed by ball milling and high-temperature calcination to obtain a lithium manganese oxide cathode material. The molar ratio of the doped manganese tetroxide precursor to lithium carbonate is 0.95–1.1:2. The ball milling speed is 300–500 r / min, and the ball milling time is 3–6 h. The high-temperature calcination temperature is 750–900 °C, and the calcination time is 12–20 h.

[0022] The chemical reaction formula for preparing lithium manganese oxide using a doped manganese tetroxide precursor and lithium carbonate is as follows:

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The process of this invention is simple and feasible. After leaching manganese-containing waste residue, it can be directly used to prepare doped manganese tetroxide after only simple calcium removal. The spinel lithium manganese oxide cathode material produced by doping manganese tetroxide achieves comprehensive recycling and efficient utilization of resources.

[0024] 2. This invention fully utilizes impurities such as Mn, Ni, Co, and Fe from manganese-containing waste residue, with manganese serving as the manganese source for lithium manganese oxide. Fe, Mg, and Co doping enhances the average valence state of Mn, inhibits Mn dissolution, and suppresses the Jahn-Teller effect. Co doping improves the electronic conductivity of the electrode, enhancing its rate performance. Ni doping increases the capacity of the cathode material. F increases the specific capacity, achieving a relatively ideal doped manganese tetroxide precursor. The bulk-phase doped manganese tetroxide precursor obtained according to the molar ratio of manganese, cobalt, nickel, iron, magnesium, and fluorine of this invention is used to manufacture spinel lithium manganese oxide cathode materials, effectively improving the cycle performance of the lithium manganese oxide cathode material. The capacity retention rate reaches over 98.9% after 50 cycles and over 98.0% after 100 cycles.

[0025] 3. In this invention, a surfactant is used to adjust the microstructure of manganese tetroxide during doping and coprecipitation, so that manganese tetroxide maintains a spinel structure. Therefore, when using manganese tetroxide to prepare lithium manganese oxide materials, there will be no drastic structural changes, doping and surface modification, so that the prepared lithium manganese oxide has better electrochemical performance. Attached Figure Description

[0026] Figure 1 This is an electron microscope image of the manganese tetroxide-doped precursor of Example 1 of the present invention; Figure 2 This is an electron microscope image of the manganese tetroxide-doped precursor in Example 2 of the present invention; Figure 3 This is an electron micrograph of the manganese tetroxide precursor in Comparative Example 1. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to the embodiments, but the implementation of the present invention is not limited to the scope shown in the embodiments.

[0028] The manganese sulfide slag of this invention comes from a manganese processing enterprise in Guangxi. The main components of the manganese sulfide slag are shown in Table 1.

[0029] Table 1

[0030] Example 1: 700 mL of 150 g / L sulfuric acid solution was added to a reaction vessel and heated to 90 °C. 100 g of manganese-containing waste residue was added with stirring, and the mixture was leached for 180 min. The leachate was then filtered, washed, and centrifuged to obtain the leachate. The pH of the leachate was adjusted to 5.5 with ammonia water, and the mixture was heated to 90 °C. 0.05 g of sodium fluoride was added with continuous stirring for 80 min. 0.21 g of aluminum sulfate flocculant was added, and stirring continued. The mixture was allowed to stand for 2 h, filtered, washed, and centrifuged to obtain the calcium-removed filtrate. Cobalt / nickel / iron sulfate was added to the calcium-removed filtrate to adjust the manganese-cobalt-nickel-iron molar ratio to 1.90:0.03:0.02:0.01. After stirring and dissolving, a manganese-cobalt-nickel-iron solution was obtained for later use. Add 500 mL of ammonia-ammonium chloride buffer solution with pH=10.0 to the reactor, heat to 65 °C, add 6 g of cetyltrimethylammonium bromide modifier, stir to dissolve, and then slowly add a prepared manganese cobalt nickel iron solution and a 4% sodium hydroxide solution dropwise at a volume ratio of 1:1. At the same time, oxygen is introduced into the solution at a flow rate of 5 L / min. After the solution is added, continue to keep warm and stir for 120 min, stop the oxygen introduction, age for 100 min, filter, wash, centrifuge, and dry the obtained precipitate at 105 °C for 6 h to obtain the first-doped manganese tetroxide precipitate. Magnesium fluoride was added to the manganese tetroxide precipitate after one doping at a molar ratio of manganese, cobalt, nickel, iron, magnesium, and fluorine of 1.90:0.03:0.02:0.01:0.02:0.02. The mixture was ball-milled at 500 rpm for 4 hours and then calcined in a muffle furnace at 350℃ for 10 hours to obtain 16.2 g of doped manganese tetroxide precursor. Electron microscopy results are shown below. Figure 1 As shown.

[0031] Example 2: Add 600 mL of 120 g / L sulfuric acid solution to a reaction vessel, heat to 80 °C, add 100 g of manganese-containing waste residue while stirring, leach for 150 min, filter, wash, and centrifuge to obtain the leachate. Adjust the pH of the leachate to 4.5 with ammonia water, heat to 95 °C, add 0.05 g of sodium fluoride while stirring continuously, stir for 120 min, add 0.28 g of aluminum sulfate flocculant, continue stirring, let stand for 2 h, filter, wash, and centrifuge to obtain the calcium-removed filtrate. Add cobalt / nickel / iron sulfate to the calcium-removed filtrate to adjust the molar ratio of manganese, cobalt, nickel, and iron to 1.93:0.02:0.02:0.01, stir to dissolve, and obtain a manganese-cobalt-nickel-iron solution for later use. Add 500 mL of ammonia-ammonium chloride buffer solution with pH=9 to the reactor, heat to 60 °C, add 5 g of hexadecyltrimethylammonium chloride modifier, stir to dissolve, and then slowly add a prepared manganese cobalt nickel iron solution and a 3% sodium hydroxide solution dropwise at a volume ratio of 1:1. At the same time, oxygen is introduced into the solution at a flow rate of 4 L / min. After the solution is added, continue to keep warm and stir for 90 min, then stop the oxygen introduction, age for 90 min, filter, wash, centrifuge, and dry the obtained precipitate at 105 °C for 6 h to obtain the first-doped manganese tetroxide precipitate. Magnesium fluoride was added to the manganese tetroxide precipitate after one doping at a molar ratio of manganese, cobalt, nickel, iron, magnesium, and fluorine of 1.93:0.02:0.02:0.01:0.01:0.01. The mixture was ball-milled at 400 rpm for 3 hours and then calcined in a muffle furnace at 350°C for 6 hours to obtain 15.8 g of doped manganese tetroxide precursor. Electron microscopy results are shown below. Figure 2 As shown.

[0032] Example 3: Add 500 mL of 100 g / L sulfuric acid solution to a reaction vessel, heat to 50 °C, add 100 g of manganese-containing waste residue while stirring, leach for 60 min, filter, wash, and centrifuge to obtain the leachate. Adjust the pH of the leachate to 6.5 with ammonia water, heat to 80 °C, add 0.06 g of sodium fluoride while stirring continuously, stir for 100 min, add 0.35 g of aluminum sulfate flocculant, continue stirring, let stand for 2 h, filter, wash, and centrifuge to obtain the calcium-removed filtrate. Add cobalt / nickel / iron sulfate to the calcium-removed filtrate to adjust the molar ratio of manganese, cobalt, nickel, and iron to 1.92:0.02:0.02:0.02, stir to dissolve, and obtain a manganese-cobalt-nickel-iron solution for later use. Add 500 mL of ammonia-ammonium chloride buffer solution with pH=8.0 to the reactor, heat to 50 °C, add 3 g of hexadecyltrimethylammonium bromide modifier, stir to dissolve, and then slowly add a prepared manganese cobalt nickel iron solution and a 2% sodium hydroxide solution dropwise at a volume ratio of 1:1. At the same time, oxygen is introduced into the solution at a flow rate of 1 L / min. After the solution is completely added, continue to keep warm and stir for 60 min, stop the oxygen introduction, age for 100 min, filter, wash, centrifuge, and dry the obtained precipitate at 105 °C for 6 h to obtain the first-doped manganese tetroxide precipitate. Magnesium fluoride was added to the manganese tetroxide precipitate after one doping at a molar ratio of manganese, cobalt, nickel, iron, magnesium, and fluorine of 1.92:0.02:0.02:0.02:0.01:0.01. The mixture was ball-milled at 300 r / min for 5 h and then calcined in a muffle furnace at 350 °C for 8 h to obtain 15.2 g of doped manganese tetroxide precursor.

[0033] Example 4: Add 800 mL of 80 g / L sulfuric acid solution to a reaction vessel, heat to 70 °C, add 100 g of manganese-containing waste residue while stirring, leach for 120 min, filter, wash, and centrifuge to obtain the leachate. Adjust the pH of the leachate to 5 with ammonia water, heat to 70 °C, add 0.07 g of sodium fluoride while stirring continuously, stir for 60 min, add 0.42 g of aluminum sulfate flocculant, continue stirring, let stand for 2 h, filter, wash, and centrifuge to obtain the calcium-removed filtrate. Add cobalt / nickel / iron sulfate to the calcium-removed filtrate to adjust the molar ratio of manganese, cobalt, nickel, and iron to 1.94:0.02:0.01:0.01, stir to dissolve, and obtain a manganese-cobalt-nickel-iron solution for later use. Add 500 mL of ammonia-ammonium chloride buffer solution with pH=9.5 to the reactor, heat to 75 °C, add 4.5 g of cetyltrimethylammonium bromide modifier, stir to dissolve, and then slowly add a prepared manganese cobalt nickel iron solution and a 5% sodium hydroxide solution dropwise at a volume ratio of 1:1. At the same time, oxygen is introduced into the solution at a flow rate of 3 L / min. After the solution is added, continue to keep warm and stir for 100 min, then stop the oxygen introduction, age for 60 min, filter, wash, centrifuge, and dry the obtained precipitate at 105 °C for 6 h to obtain the first-doped manganese tetroxide precipitate. Magnesium fluoride was added to the manganese tetroxide precipitate after one doping at a molar ratio of manganese, cobalt, nickel, iron, magnesium, and fluorine of 1.94:0.02:0.01:0.01:0.01:0.01. The mixture was ball-milled at 400 r / min for 5 h and then calcined in a muffle furnace at 350 °C for 12 h to obtain 15.5 g of doped manganese tetroxide precursor.

[0034] Comparative experiment Comparative Example 1: No modifier was added; all other steps were the same as in Example 1. Electron microscopy results are as follows: Figure 3 As shown.

[0035] from Figures 1-3 It can be seen that the product particles produced by the method of the present invention are uniform and maintain a better spinel structure.

[0036] Next, the present invention uses the doped manganese tetroxide precursor prepared in Examples 1-4 to prepare lithium manganese oxide cathode material. The molar ratio of the doped manganese tetroxide precursor to lithium carbonate is 0.95:2. After mixing, the mixture is ball-milled and calcined at high temperature to obtain the lithium manganese oxide cathode material. The ball milling speed is 300 r / min and the ball milling time is 4 h. The high temperature calcination temperature is 800 °C and the calcination time is 16 h.

[0037] Comparative Example 2: Preparation of lithium manganese oxide cathode material without doping: The molar ratio of commercially available manganese tetroxide and lithium carbonate was 0.95:2. After mixing, the mixture was ball-milled and calcined at high temperature to obtain lithium manganese oxide cathode material. The ball milling speed was 300 r / min and the ball milling time was 4 h. The high temperature calcination temperature was 800 ℃ and the calcination time was 16 h.

[0038] Table 2

[0039] As shown in Table 2, the lithium manganese oxide cathode material prepared by the present invention using the manganese tetroxide precursor can achieve a first charge-discharge specific capacity of over 125 mAh / g, and a capacity retention rate of over 98.9% after 50 weeks and over 98.0% after 100 weeks, demonstrating good cycle performance.

[0040] The above embodiments are merely specific examples to further illustrate the purpose, technical solution, and beneficial effects of the present invention, and the present invention is not limited thereto. Any modifications, equivalent substitutions, improvements, etc., made within the scope of the disclosure of the present invention are included within the protection scope of the present invention.

Claims

1. A method for preparing a manganese tetroxide-doped precursor from manganese-containing waste residue, characterized in that, Includes the following steps: (1) Leaching: Manganese-containing waste residue is mixed with a sulfuric acid solution of a certain concentration, heated and leached to obtain leachate; (2) Calcium removal: Add ammonia to the leachate, adjust the pH to weakly acidic, heat, then add sodium fluoride and react for a period of time, then add flocculant, let stand and separate, and obtain the calcium-removed filtrate. (3) Adjusting the ratio: Add cobalt salt, nickel salt and iron salt to the filtrate respectively, and adjust the filtrate to the set manganese-cobalt-nickel-iron molar ratio to obtain a manganese-cobalt-nickel-iron solution; the set manganese-cobalt-nickel-iron molar ratio is (1.90~1.95):(0.01~0.04):(0.01~0.04):(0.01~0.04); (4) Modification of coprecipitation: Add ammonia-ammonium chloride buffer solution to the reactor, heat, then add the modifier, stir to dissolve, and slowly add manganese cobalt nickel iron solution and sodium hydroxide solution, while simultaneously bubbling oxygen into the solution to carry out the precipitation reaction. After the manganese cobalt nickel iron solution is added, keep warm for a period of time, then stop bubbling oxygen, and then age, separate and dry to obtain manganese tetroxide precipitate after one doping; the modifier is any one or a mixture of two of hexadecyltrimethylammonium bromide and hexadecyltrimethylammonium chloride; (5) Preparation of doped manganese tetroxide precursor: A certain amount of magnesium fluoride is added to the first-doped manganese tetroxide precipitate, ball milled and calcined to obtain the doped manganese tetroxide precursor; the magnesium fluoride and the first-doped manganese tetroxide precipitate are in the molar ratio of manganese, cobalt, nickel, iron, magnesium and fluorine as (1.90~1.95):(0.01~0.04):(0.01~0.04):(0.01~0.04):(0.01~0.02):(0.01~0.02).

2. The method for preparing manganese tetroxide-doped precursors from manganese-containing waste slag according to claim 1, characterized in that: In step (1), the liquid-to-solid ratio of the sulfuric acid solution to the manganese-containing waste residue is (5ml~8ml):1g, the concentration of the sulfuric acid solution is 80g / L~150g / L, the leaching temperature is 50~90℃, and the leaching time is 60~180min.

3. The method for preparing manganese tetroxide-doped precursors from manganese-containing waste slag according to claim 1, characterized in that: In step (2), the pH of the leachate is adjusted to 4.0-6.0 with ammonia water, the heating temperature is 70-95℃, the amount of sodium fluoride used is 1.5-3.0 times the theoretical amount of sodium fluoride required to convert all calcium in the leachate into calcium fluoride precipitate, and the reaction time after adding sodium fluoride is 60-120 min; the flocculant is aluminum sulfate, the amount of aluminum sulfate used is 0.3-0.6 g / L·leachate, and the standing time is 2-3 h.

4. The method for preparing manganese tetroxide-doped precursors from manganese-containing waste slag according to claim 1, characterized in that: The cobalt salt is one or a mixture of several of cobalt sulfate, cobalt chloride, cobalt acetate, and cobalt nitrate; the nickel salt is one or a mixture of several of nickel sulfate, nickel chloride, nickel acetate, and nickel nitrate; and the iron salt is one or a mixture of several of ferric sulfate, ferric chloride, cobalt acetate, and ferric nitrate.

5. The method for preparing manganese tetroxide-doped precursors from manganese-containing waste slag according to claim 1, characterized in that: In step (4), the pH value of the ammonia-ammonium chloride buffer solution is 8.0-10.0, the heating temperature is 50-75℃, the amount of the modifier is 3-6 g / L of the total mixed solution, and the total mixed solution is a mixture of ammonia-ammonium chloride buffer solution, manganese cobalt nickel iron solution and sodium hydroxide solution; the concentration of manganese in the manganese cobalt nickel iron solution is 0.5-1.5 mol / L, the volume ratio of sodium hydroxide solution to manganese cobalt nickel iron solution is (1-1.5):1, the mass concentration of sodium hydroxide solution is 2-5%, the oxygen flow rate is 1-5 L / min, the heat preservation time is 30-60 min, and the aging time is 60-120 min.

6. The method for preparing manganese tetroxide-doped precursors from manganese-containing waste slag according to claim 1, characterized in that: The ball milling speed is 300-500 r / min, and the ball milling time is 3-6 h.

7. A method for preparing lithium manganese oxide, characterized in that: The lithium carbonate and the manganese tetroxide precursor doped as described in any one of claims 1 to 6 are mixed and then subjected to ball milling and high-temperature calcination to obtain a lithium manganese oxide cathode material; the molar ratio of the manganese tetroxide precursor to lithium carbonate is 0.95 to 1.1:2; the ball milling speed is 300 to 500 r / min and the ball milling time is 3 to 6 h; the high-temperature calcination temperature is 750 to 900 °C and the calcination time is 12 to 20 h.

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