A method for preparing trimanganese tetraoxide by a liquid phase method

Abstract

The application discloses a method for preparing trimanganese tetraoxide by a liquid phase method, which comprises the following steps: adding manganese sulfate solution and lye into a reaction system in parallel flow, controlling the pH value of the reaction system to be 9-10, filtering and washing the reaction precipitate to obtain a manganese hydroxide filter cake; mixing the manganese hydroxide filter cake with deionized water to prepare a suspension, and performing staged oxidation treatment: in the first stage, adding an oxidant hydrogen peroxide into the suspension, and introducing air to accelerate the start of oxidation; in the second stage, stopping adding the hydrogen peroxide, increasing the air introduction amount, controlling the pH value to be 6-8, reducing the oxidation reaction rate, until the precipitate is changed into red black, and a trimanganese tetraoxide suspension is obtained; and performing post-treatment on the trimanganese tetraoxide suspension to obtain a trimanganese tetraoxide product. Through the staged oxidation of hydrogen peroxide and air, the oxidation rate and the particle growth rate are considered, and the particle size concentration and the morphology consistency are improved.

Description

Technical Field

[0001] This invention relates to the field of manganese tetroxide preparation technology, and in particular to a liquid-phase method for preparing manganese tetroxide. Background Technology

[0002] Manganese tetroxide (Mn3O4) is an important functional material widely used in lithium manganese oxide materials, soft magnetic materials, catalysts, and other fields. Mn3O4 is a black tetragonal crystal belonging to the spinel group, with an ionic structure of Mn2O4. 2+ (Mn 3+ )20 4， Divalent and trivalent manganese ions are distributed in two different lattice positions. Oxygen ions are cubically close-packed, divalent manganese ions occupy tetrahedral voids, and trivalent manganese ions occupy octahedral voids.

[0003] Currently, there are several methods for preparing manganese tetroxide, including liquid-phase method, roasting method, reduction method, oxidation method, and electrolysis method. Among them, the liquid-phase method mainly adopts a two-step process of "precipitation separation followed by dissolution and oxidation". That is, manganese sulfate is first reacted with alkaline solution to generate manganese hydroxide precipitate, which is then filtered, washed, and then dissolved and oxidized. Generally, manganese sulfate and alkaline solution are first mixed and added to the reaction system to convert manganese ions into Mn(OH)2 precipitate. Then, the separated Mn(OH)2 is slurried and oxidized with an oxidant to obtain manganese tetroxide.

[0004] In existing technologies, the oxidation process of manganese hydroxide typically involves introducing air or oxygen into an alkaline medium to oxidize the manganese hydroxide suspension into manganese tetroxide. As the reaction proceeds, manganese ions are continuously consumed due to precipitation, while the system volume continuously increases, leading to a decrease in manganese ion concentration and affecting the precipitation environment. This results in inconsistent physical properties of manganese tetroxide. Manganese tetroxide has a wide particle size distribution, uneven particle size, and irregular shape. When used in the preparation of lithium manganese oxide materials, its purity and particle morphology play a crucial role in the performance of lithium manganese oxide materials. Poor consistency of manganese tetroxide will also lead to inconsistent performance of battery cathode materials, affecting the consistency of battery products. Summary of the Invention

[0005] The purpose of this invention is to provide a liquid-phase method for preparing manganese tetroxide, which improves the controllability of the morphology of manganese tetroxide, obtains spherical manganese tetroxide particles with a relatively concentrated particle size, and improves the consistency of the finished manganese tetroxide product.

[0006] To solve the above technical problems, the embodiments of the present invention provide a technical solution as follows: A method for preparing manganese tetroxide by liquid phase, comprising the following steps: S1: Preparation of manganese hydroxide precipitate: Pure water is added to a reaction vessel as a base liquid, and then manganese sulfate solution and alkaline solution are added to the base liquid. The pH value of the reaction system is controlled to be 9-10. Manganese hydroxide precipitate is generated by the reaction. When the average particle size D50 of the precipitate reaches 6-8 μm, the feeding is stopped, and the reaction is continued by stirring for 1-3 hours. After filtration and washing, manganese hydroxide filter cake is obtained; S2: Staged oxidation: The hydrogen and oxygen... Manganese tetroxide filter cake is mixed with deionized water to form a suspension, which is then subjected to a staged oxidation process: Stage 1: Hydrogen peroxide is added to the suspension and air is introduced, the reaction temperature is controlled at 40~50℃, and the pH value is controlled at 9~10 to accelerate the oxidation process; Stage 2: The addition of hydrogen peroxide is stopped, the air flow rate is increased, the reaction temperature is controlled at 50~60℃, and the pH value is controlled at 6~8 to reduce the oxidation reaction rate until the precipitate in the reaction system turns reddish-black, thus obtaining a manganese tetroxide suspension; S3: The manganese tetroxide suspension is post-treated to obtain the finished manganese tetroxide product.

[0007] Furthermore, in step S1, the concentration of the manganese sulfate solution is 2-4 mol / L; the alkaline solution is a mixture of ammonia and sodium hydroxide solution, and the pH value of the alkaline solution is 13.4-13.7.

[0008] Furthermore, the alkaline solution is a mixed solution of 2-5 mol / L ammonia and 2 mol / L sodium hydroxide in a volume ratio of 3:1, or a mixed solution of 8 wt% ammonia and 2 mol / L sodium hydroxide in a volume ratio of 3:1.

[0009] Furthermore, in step S1, the temperature of the reaction system is controlled at 20~30℃; after stopping the feeding, the reaction is continued for no less than 2 hours.

[0010] Furthermore, step S1 also includes the simultaneous addition of an auxiliary agent to the reaction system; the auxiliary agent includes sodium dodecylbenzenesulfonate at a relative mass ratio of 0.1% to 0.2% of the alkali solution and ethylene glycol at a relative mass ratio of 5% to 8% of the alkali solution.

[0011] Furthermore, in step S2, the suspension is prepared according to a mass ratio of manganese hydroxide filter cake to deionized water of 1:5, and stirred in a reaction vessel to form a uniform suspension.

[0012] Furthermore, in the first stage of step S2, the amount of hydrogen peroxide added is 1 to 1.3 times the total molar amount of manganese ions in the reaction system, and the feeding time is 20 to 60 minutes; and air is introduced into the reactor at a rate of 6% to 10% of the reactor volume per minute, and the duration of the first stage is 20 to 60 minutes.

[0013] Furthermore, in the second stage of step S2, the air flow rate is increased to 40% to 50% of the reactor volume per minute, and the second stage lasts for 3 to 5 hours.

[0014] Furthermore, in step S3, the post-processing of the manganese tetroxide suspension includes: filtration of the manganese tetroxide suspension, collection of the filter cake, repeated washing with deionized water, and microwave drying of the washed filter cake to obtain the finished manganese tetroxide product.

[0015] The present invention also provides a technical solution, a manganese tetroxide, prepared by the method described in any one of the above-mentioned methods, wherein the particle morphology is quasi-spherical and the particle size distribution satisfies: D10 is 4.5~6.0μm, D50 is 6.5~8.0μm, and D90 is 9.0~11.5μm.

[0016] The present invention provides a liquid-phase method for preparing manganese tetroxide, which, compared with the prior art, involves the staged oxidation of manganese hydroxide suspension. In the initial stage of the reaction, the strong oxidizing effect of hydrogen peroxide is used to quickly initiate the oxidation reaction, thereby increasing the reaction rate and reducing the reaction time. In the later stage of the reaction, the oxidation rate is slowed down by a single supply of air and the air flow rate is controlled, thereby increasing the controllability of the morphology of manganese tetroxide, obtaining spherical manganese tetroxide particles with a more concentrated particle size, and improving the consistency of the finished manganese tetroxide product. Attached Figure Description

[0017] One or more embodiments are illustrated by way of example with reference to the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Elements with the same reference numerals in the drawings represent similar elements. Unless otherwise stated, the figures in the drawings do not constitute a limitation on scale.

[0018] Figure 1 This is a flowchart of a method for preparing manganese tetroxide by liquid phase in an embodiment of the present invention; Figure 2 The image shows the particle morphology of manganese tetroxide prepared in the embodiments of the present invention as observed by a scanning electron microscope. Figure 3 These are particle morphology images of manganese tetroxide prepared in the embodiments of the present invention, observed under different magnifications using a scanning electron microscope. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the various embodiments of this invention will be described in detail below with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details have been provided in the various embodiments of this invention to facilitate a better understanding of this application. However, the technical solutions claimed in the claims of this application can be implemented even without these technical details and various variations and modifications based on the following embodiments. The terms "comprising," "including," and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that comprises a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or apparatuses.

[0020] like Figure 1 As shown, one embodiment of the present invention relates to a method for preparing manganese tetroxide by liquid phase method, comprising the following steps: S1: Preparation of manganese hydroxide precipitate: Add pure water to the reaction vessel as the base liquid, and then add manganese sulfate solution and alkaline solution in parallel to the base liquid. Control the pH value of the reaction system to 9~10. The reaction generates manganese hydroxide precipitate. When the average particle size D50 of the precipitate reaches 6~8μm, stop feeding and continue stirring the reaction for 1-3 hours. After filtration and washing, manganese hydroxide filter cake is obtained. The concentration of the prepared manganese sulfate solution is 2-4 mol / L; the pH of the alkaline solution is 13.4-13.7. The alkaline solution is a mixture of 2-5 mol / L ammonia and 2 mol / L sodium hydroxide in a volume ratio of 3:1, or it can be a mixture of 8 wt% ammonia and 2 mol / L sodium hydroxide in a volume ratio of 3:1. Pure water is added to the reactor as the base liquid, and then the prepared manganese sulfate solution and alkaline solution are added to the base liquid simultaneously. The pH of the reaction system is maintained between 9 and 10 by controlling the flow rates of the manganese sulfate solution and the alkaline solution. After the reaction forms a turbid liquid, a sample is taken from the turbid liquid. When the average particle size distribution D50 of the manganese hydroxide obtained from the sample is 6-8 μm, the feeding is stopped, and the reaction is continued to be stirred for more than 2 hours. Then the precipitate obtained from the reaction is filtered and washed to obtain a manganese hydroxide filter cake. Preferably, the temperature of the reaction process is maintained at 20-30℃; the washing is performed with pure water at least twice. Preferably, an auxiliary agent is added to the reaction system simultaneously. In one example, the auxiliary agent includes sodium dodecylbenzenesulfonate at a relative mass ratio of 0.1% to 0.2% of the alkali solution and ethylene glycol at a relative mass ratio of 5-8% of the alkali solution. Sodium dodecylbenzenesulfonate acts as a dispersant to regulate the morphology of the precipitated manganese hydroxide, while ethylene glycol acts as a dispersant to effectively improve the low-temperature dispersion performance of manganese hydroxide, prevent the agglomeration of manganese hydroxide, and contribute to the uniformity of the subsequent oxidation reaction and the consistency of the morphology of the oxidized manganese tetroxide.

[0021] S2: Staged oxidation: The manganese hydroxide filter cake obtained in step S1 is mixed with deionized water to form a suspension for staged oxidation treatment: Preferably, the manganese hydroxide filter cake and deionized water are mixed at a mass ratio of 1:(4-6), placed in an oxidation reactor, and stirred to form a uniform suspension.

[0022] The phased oxidation process includes: The first stage involves adding hydrogen peroxide as an oxidant to the suspension and purging with air. The reaction temperature is controlled at 40-50°C, and the pH value at 9-10. The strong oxidizing properties of hydrogen peroxide rapidly initiate oxidation. In one example, 5% hydrogen peroxide (by mass) is added dropwise to the suspension. The total amount of hydrogen peroxide added is 1-1.3 times the total molar amount of manganese ions in the reaction system. The feeding time is 20-60 minutes to ensure the Mn²⁺ content is within a certain range. + Fully oxidized to Mn³ + To prevent excessive oxidation, air is introduced into the reactor at a rate of 6%–10% of its volume per minute to maintain a stable reaction temperature of 45°C. During the process, a 10% sodium hydroxide solution is added dropwise to precisely control the pH of the reaction system between 9.0 and 9.5, and the reaction continues for 20–60 minutes. Preferably, the air pressure introduced into the reactor is 0.01–0.05 MPa to improve mass transfer efficiency.

[0023] The second stage: Stop adding hydrogen peroxide, increase the air flow rate into the reactor, control the reaction temperature at 50-60℃ and the pH at 6-8, and reduce the oxidation rate until the precipitate turns reddish-black, obtaining a manganese tetroxide suspension. In one example, after the first stage, after stopping the addition of hydrogen peroxide, increase the air flow rate to 40%-50% of the reactor volume per minute, while simultaneously raising the reaction temperature to 55℃ and maintaining the pH between 6 and 8. By adjusting the air flow rate, the oxidation rate is slowed down to ensure the uniformity of the morphology of the oxidized manganese tetroxide particles. Continue the reaction for 3-5 hours; when the precipitate in the reaction system is observed to have uniformly turned reddish-black, stop the reaction to obtain a manganese tetroxide suspension.

[0024] S3: Post-process the manganese tetroxide suspension to obtain the finished manganese tetroxide product. The manganese tetroxide suspension from step S2 is filtered, the filter cake is collected, and repeatedly washed with deionized water until the pH of the washing solution reaches 7.0-7.5. The washed filter cake is then microwave-dried to obtain the finished manganese tetroxide product. Preferably, the reaction precipitate is washed with pure water at least twice, and the washed precipitate is then microwave-dried. This microwave internal heating method avoids the "hard outside, wet inside" problem of traditional oven drying, reduces particle surface cracking and agglomeration, preserves the near-spherical morphology, and shortens the drying time by more than 50% compared to traditional oven drying.

[0025] The preparation and performance testing of manganese tetroxide using the above-described liquid-phase method are as follows: Preparation of manganese hydroxide precipitate: Pure water is added to the reactor as the base liquid, and then 2-4 mol / L manganese sulfate solution and alkali solution with pH 13.4-13.7 are added to the base liquid in parallel flow. The volume ratio of manganese sulfate solution to alkali solution is 1:(1-1.2). The alkali solution is a mixture of 8 wt% ammonia water and 2 mol / L sodium hydroxide in a volume ratio of 3:1. Pure water is added to the reactor as the base liquid, and then the prepared manganese sulfate solution and alkali solution are added to the base liquid simultaneously. The volume ratio of manganese sulfate solution to alkali solution to the base liquid is 1:(0.2-0.5). The pH value of the reaction system is controlled to be 9-10. Manganese hydroxide precipitate is generated by the reaction. When the average particle size D50 of the precipitate reaches 6-8 μm, the feeding is stopped, and the reaction is continued to be stirred for 1-3 hours. After filtration and washing, manganese hydroxide filter cake is obtained. The preparation of manganese tetroxide by staged oxidation: A 5L reactor was used as the reaction vessel. Manganese hydroxide filter cake and deionized water were mixed at a mass ratio of 1:(4-6) and placed in the oxidation reactor, and stirred to form a uniform suspension. In the first stage, hydrogen peroxide was added to the suspension as an oxidant, and air was introduced. The reaction temperature was controlled at 40-50℃ and the pH value was 9-10. In the second stage, the addition of hydrogen peroxide was stopped, the air flow rate was increased, the reaction temperature was controlled at 50-60℃, the pH value was controlled at 6-8, and the oxidation reaction rate was reduced until the precipitate in the reaction system turned reddish-black, thus obtaining a manganese tetroxide suspension. Table 1 shows some of the process parameters for the staged oxidation process in Examples 1-6.

[0026] Table 1. Staged oxidation process parameters The manganese tetroxide suspension prepared in the above embodiments was filtered, washed with pure water, and dried by microwave to obtain the finished manganese tetroxide product.

[0027] The particle size distribution of the above-mentioned manganese tetroxide product was sampled and tested. The test results are shown in Table 2, which is the sample particle size distribution test record table.

[0028] Table 2 Sample Particle Size Distribution Detection Record The particle size measurements of the manganese tetroxide prepared above are D10: 4.5~6.0 μm; D50: 6.5~8.0 μm; D90: 9.0~11.5 μm, with a concentrated particle size distribution; such as Figure 2-3 The image shows the morphology of manganese tetroxide under an electron microscope. The particles are nearly spherical, with relatively uniform size and high consistency. Using manganese tetroxide prepared by the method provided in this invention as a precursor for lithium manganese oxide cathode materials can significantly improve the consistency and performance of lithium manganese oxide materials, meeting the market demand for high-performance lithium battery fabrication.

[0029] The present invention provides a liquid-phase method for preparing manganese tetroxide, which involves the staged oxidation of manganese hydroxide suspension. In the initial stage of the reaction, the strong oxidizing effect of hydrogen peroxide is used to quickly initiate the oxidation reaction, thereby increasing the reaction rate and reducing the reaction time. In the later stage of the reaction, the oxidation efficiency is slowed down by using a single supply of air and controlling the air flow rate. This increases the controllability of the morphology of manganese tetroxide, resulting in spherical manganese tetroxide particles with a relatively concentrated particle size, thus improving the consistency of the finished manganese tetroxide product.

[0030] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications and improvements without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be defined by the claims.

Claims

1. A method for preparing manganese tetroxide by liquid phase, characterized in that, Includes the following steps: S1: Preparation of manganese hydroxide precipitate: Add pure water to the reaction vessel as the base liquid, and then add manganese sulfate solution and alkaline solution in parallel to the base liquid. Control the pH value of the reaction system to 9~10. The reaction generates manganese hydroxide precipitate. When the average particle size D50 of the precipitate reaches 6~8μm, stop feeding and continue stirring the reaction for 1-3 hours. After filtration and washing, manganese hydroxide filter cake is obtained. S2: Staged oxidation: The manganese hydroxide filter cake is mixed with deionized water to form a suspension, and then subjected to staged oxidation treatment. First stage: Add hydrogen peroxide to the suspension and introduce air, control the reaction temperature at 40~50℃ and the pH value at 9~10 to accelerate the oxidation process; Second stage: Stop adding hydrogen peroxide, increase the air flow rate, control the reaction temperature at 50~60℃, control the pH value at 6~8, reduce the oxidation reaction rate until the precipitate in the reaction system turns reddish-black, and obtain manganese tetroxide suspension. S3: The manganese tetroxide suspension is post-processed to obtain the finished manganese tetroxide product.

2. The method for preparing manganese tetroxide by liquid phase method according to claim 1, characterized in that, In step S1, the concentration of the manganese sulfate solution is 2-4 mol / L; the alkaline solution is a mixture of ammonia and sodium hydroxide solution, and the pH value of the alkaline solution is 13.4-13.

7.

3. The method for preparing manganese tetroxide by liquid phase according to claim 2, characterized in that, The alkaline solution is a mixture of 2-5 mol / L ammonia and 2 mol / L sodium hydroxide in a volume ratio of 3:1, or a mixture of 8 wt% ammonia and 2 mol / L sodium hydroxide in a volume ratio of 3:

1.

4. The method for preparing manganese tetroxide by liquid phase method according to claim 1, characterized in that, In step S1, the temperature of the reaction system is controlled at 20~30℃; after stopping the feeding, the reaction is continued for no less than 2 hours.

5. The method for preparing manganese tetroxide by liquid phase according to claim 1, characterized in that, Step S1 further includes the simultaneous addition of an auxiliary agent to the reaction system; the auxiliary agent includes sodium dodecylbenzenesulfonate at a relative mass ratio of 0.1% to 0.2% of the alkali solution and ethylene glycol at a relative mass ratio of 5% to 8% of the alkali solution.

6. The method for preparing manganese tetroxide by liquid phase method according to claim 1, characterized in that, In step S2, the suspension is prepared according to the mass ratio of manganese hydroxide filter cake to deionized water of 1:5, and stirred in a reaction vessel to form a uniform suspension.

7. The method for preparing manganese tetroxide by liquid phase method according to claim 1, characterized in that, In the first stage of step S2, the amount of hydrogen peroxide added is 1 to 1.3 times the total molar amount of manganese ions in the reaction system, and the feeding time is 20 to 60 minutes; and air is introduced into the reactor at a rate of 6% to 10% of the reactor volume per minute, and the duration of the first stage is 20 to 60 minutes.

8. The method for preparing manganese tetroxide by liquid phase method according to claim 1, characterized in that, In the second stage of step S2, the air flow rate is increased to 40% to 50% of the reactor volume per minute, and the second stage lasts for 3 to 5 hours.

9. The method for preparing manganese tetroxide by liquid phase method according to claim 1, characterized in that, In step S3, the post-processing of the manganese tetroxide suspension includes: filtration of the manganese tetroxide suspension, collection of the filter cake, repeated washing with deionized water, and microwave drying of the washed filter cake to obtain the finished manganese tetroxide product.

10. A manganese tetroxide prepared by the method according to any one of claims 1-9, characterized in that, Its particle morphology is spherical, and the particle size distribution satisfies: D10 is 4.5~6.0μm, D50 is 6.5~8.0μm, and D90 is 9.0~11.5μm.

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