A method for preparing manganese phosphate from rhodochrosite and manganese phosphate

Abstract

This invention discloses a method for preparing manganese phosphate from rhodochrosite and the manganese phosphate itself. The method for preparing manganese phosphate from rhodochrosite includes the following steps: raw material pretreatment: crushing rhodochrosite and leaching it with acid to obtain manganese phosphate containing Mn. 2+ The leachate; impurity removal: removing impurities from the leachate to obtain a solution containing Mn. 2+ Impurity removal leachate; directional crystallization: towards Mn-containing leachate. 2+ A crystal-directing agent is added to the impurity-removing leaching solution to obtain a precursor; calcination: the precursor is calcined to obtain the manganese phosphate; the crystal-directing agent includes ammonium dihydrogen phosphate and sodium citrate. The method for preparing manganese phosphate from rhodochrosite provided by this invention allows for controllable crystal morphology in the process of preparing manganese phosphate from rhodochrosite, thereby obtaining high-density and high-purity battery-grade manganese phosphate that meets the requirements of lithium-ion battery materials.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of new energy material preparation, and particularly relates to a method for preparing manganese phosphate from rhodochrosite and the manganese phosphate. BACKGROUND

[0002] As a precursor of lithium ion battery cathode material, manganese phosphate (Mn3(PO4)2) has the advantages of high voltage and low cost, but its industrial production faces the following problems: 1. Raw material limitation: The traditional process relies on high-purity manganese salt (such as manganese sulfate), which has high raw material cost and relies on import; 2. Difficulty in impurity control: Fe, Ca, Mg and other impurities in rhodochrosite are difficult to remove deeply, resulting in insufficient product purity (total impurity content > 500 ppm); 3. Process defects: The existing wet process crystallization process is uncontrollable, and the product tap density is low (< 1.0 g / cm 3 ), affecting the performance of lithium ion batteries; 4. Environmental pollution: The ammonia nitrogen content of the acid leaching waste liquid is high, and the treatment cost is expensive. SUMMARY

[0003] In order to solve the above technical problems, the purpose of the present application is to provide a method for preparing manganese phosphate from rhodochrosite and the manganese phosphate, so as to realize controllable crystalline morphology in the process of preparing manganese phosphate from rhodochrosite, thereby preparing high-density and high-purity battery-grade manganese phosphate meeting the demand of lithium ion battery material.

[0004] The application provides a method for preparing manganese phosphate from rhodochrosite, comprising the following steps:

[0005] S1. Raw material pretreatment: crushing rhodochrosite, leaching with acid to obtain a leaching solution containing Mn 2+ ;

[0006] S2. Impurity removal: removing impurities from the leaching solution to obtain an impurity-removed leaching solution containing Mn 2+ ;

[0007] S3. Directional crystallization: adding a crystal form directing agent to the impurity-removed leaching solution containing Mn 2+ to obtain a precursor;

[0008] S4. Calcination: calcining the precursor to obtain the manganese phosphate;

[0009] The crystal form directing agent comprises ammonium dihydrogen phosphate and sodium citrate.

[0010] The method for preparing manganese phosphate from rhodochrosite provided by the application can control the crystalline morphology of the precursor during directional crystallization, so that the prepared manganese phosphate has spherical or spherical-like morphology, the particle size distribution is concentrated, and D90< 20 μm, thereby meeting the demand of lithium ion battery material for high-density manganese phosphate. Specifically, the ammonium dihydrogen phosphate in the crystal form directing agent provides NH4 +Through hydrogen bonds with phosphate (PO4) 3- The interaction between Mn3(PO4)2·3H2O and water molecules (H2O) stabilizes the hydration layer structure in the crystal, promotes the regular arrangement of Mn3(PO4)2·3H2O, and prevents crystal transformation or structural collapse caused by dehydration; furthermore, the phosphate buffer system (H2PO4) provided by ammonium dihydrogen phosphate... - / HPO4 2- This can prevent the pH value of the solution from becoming too high and avoid the presence of Mn in the solution. 2+ After the formation of Mn(OH)2, it is further oxidized to Mn(OH)3, which improves the recovery rate of Mn in rhodochrosite and the purity of the product manganese phosphate. In addition, the sodium citrate in the crystal-directing agent provides carboxylate ions (-COO-). - The hydroxyl (-OH) functional groups can react with Mn in solution. 2+ The formation of stable multidentate complexes significantly reduces the free Mn content. 2+ The concentration of sodium citrate slows down the rapid formation of crystal nuclei, creating conditions for the orderly growth of crystals and promoting the formation of more uniform crystal nuclei, thus enabling the production of highly crystalline manganese phosphate. Simultaneously, sodium citrate provides Na... + By selectively adsorbing to reduce the surface energy of high-energy crystal faces, the crystal morphology is driven to evolve towards a spherical shape with minimal interfacial energy. Simultaneously, nucleation and growth kinetics are controlled, ultimately achieving the controllable preparation of manganese phosphate microspheres. Ammonium dihydrogen phosphate and sodium citrate, as a composite crystal-directing agent for directional crystallization precursors, work synergistically to achieve controllable crystal morphology in the process of preparing manganese phosphate from rhodochrosite, thereby improving the tap density of manganese phosphate.

[0011] Preferably, in S1, the acid includes at least one of sulfuric acid and phosphoric acid.

[0012] More preferably, in S1, the acid includes sulfuric acid and phosphoric acid.

[0013] In S1 of this scheme, the acid includes sulfuric acid and phosphoric acid, using a mixed acid system of sulfuric acid and phosphoric acid. The complexing effect of phosphoric acid inhibits Fe. 3+ Hydrolysis reduces the leaching rate of Fe in rhodochrosite, while also reducing the leaching rates of harmful metals Pb and Cd, thus reducing the pressure of subsequent impurity removal. It also increases the leaching rate of Mn, thereby improving the recovery and utilization rate of Mn in rhodochrosite and increasing the purity of the product manganese phosphate.

[0014] More preferably, in S1, the volume ratio of sulfuric acid to phosphoric acid is 1:(0.5-2), for example, it can be 1:0.5, 1:1, 1:1.5, 1:2, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0015] Preferably, in S1, the mass ratio of rhodochrosite to acid is 1:(4-6), for example, it can be 1:4, 1:5, 1:6, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0016] Preferably, in S1, the leaching reaction time with acid is 2 to 4 hours, for example, 2 hours, 3 hours, or 4 hours, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0017] Preferably, in step S2, the de-dust removal includes gradient de-dust removal, which specifically includes the following steps:

[0018] S21. First stage: Add precipitant A to adjust the pH to 3.5-4.0 to carry out the first stage of precipitation and impurity removal;

[0019] S22. Second stage: Add precipitant B to adjust the pH to 4.5-5.0, and carry out the second stage of precipitation and impurity removal;

[0020] The precipitant A includes at least one of ammonium fluoride, sodium fluoride, and sodium sulfide, and the precipitant B includes at least one of sodium carbonate and sodium oxalate.

[0021] This method employs a gradient purification approach. Specifically, it first removes iron at a deep level by using precipitant A to preferentially precipitate Fe from the solution. 3+ This avoids interference from Fe(OH)3 colloids in subsequent steps, followed by the co-precipitation of calcium and magnesium, i.e., using precipitant B to precipitate Ca. 2+ and Mg 2+ To achieve Ca 2+ and Mg 2+ The synchronous deep removal of impurities avoids the formation of Ca3(PO4)2, which affects the purity of the product. This gradient impurity removal method achieves deep removal of impurities, thereby meeting the demand for high-purity manganese phosphate in lithium-ion battery materials.

[0022] More preferably, the precipitant B comprises sodium carbonate and sodium oxalate.

[0023] The precipitant B described in this scheme includes sodium carbonate and sodium oxalate. During the second stage of precipitation and impurity removal, the synergistic removal of calcium by sodium carbonate and sodium oxalate further removes Ca. 2+ This addresses the problem of excessive Ca residue caused by high-calcium minerals.

[0024] Preferably, in step S2, the impurity removal further includes membrane separation; after precipitation impurity removal, the product is subjected to membrane separation to obtain a product containing Mn. 2+The impurity-removing leachate is prepared using a nanofiltration membrane with a molecular weight cutoff of 200–500 Da, and an operating pressure of 1.0–2.5 MPa. The molecular weight cutoff of 200–500 Da can be, for example, 200 Da, 300 Da, 400 Da, or 500 Da, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. The operating pressure of 1.0–2.5 MPa can be, for example, 1.0 MPa, 1.5 MPa, 2.0 MPa, or 2.5 MPa, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0025] In S2 of this scheme, the impurity removal also includes membrane separation. Using the membrane separation method of this scheme, on the one hand, the sieving effect retains colloids and macromolecular complexes, while also retaining organic matter, thus achieving further impurity removal; on the other hand, membrane separation allows Mn... 2+ Free permeability and solution concentration allow for further enrichment of Mn. 2+ This provides a suitable solution environment for subsequent directional crystallization.

[0026] Preferably, the mass ratio of the ammonium dihydrogen phosphate to the sodium citrate is (1:1) to (3.5:1), for example, it can be 1:1, 2:1, 3:1, or 3.5:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0027] The mass ratio of ammonium dihydrogen phosphate to sodium citrate in this scheme is (1:1) to (3.5:1), which can further improve the sphericity of manganese phosphate, make the particle size distribution of manganese phosphate narrower and the particle size more uniform, and also give manganese phosphate a suitable particle size to improve the tap density of manganese phosphate.

[0028] Preferably, the crystal-directing agent and the impurity-removing Mn-containing agent are... 2+ The mass ratio of the leachate is (0.5 to 2.0):100, for example, it can be 0.5:100, 1:100, 1.5:100, 2.0:100, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0029] Preferably, the specific reaction conditions for the directional crystallization include: [the following conditions are specified in the original text, but are not translated here: "towards Mn-containing..."] 2+ A crystal-directing agent is added to the impurity-removing leachate, and the reaction temperature is controlled at 50–80°C and the pH at 6.0–7.5. The controlled reaction temperature of 50–80°C can be, for example, 50°C, 60°C, 70°C, or 80°C, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. The pH of 6.0–7.5 can be, for example, 6.0, 6.5, 7.0, or 7.5, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0030] The specific reaction conditions for directional crystallization described in this scheme include: [the following conditions are specified in the original text, likely related to Mn-containing crystals]. 2+ Adding a crystal-directing agent to the impurity-removing leachate and controlling the reaction temperature at 50–80℃ and the pH at 6.0–7.5 can not only make the particle size distribution of the obtained manganese phosphate narrower and the particle size more uniform, but also give the manganese phosphate a suitable particle size to improve the tap density of manganese phosphate.

[0031] Preferably, the stirring rate during the directional crystallization is 200 to 400 rpm, for example, 200 rpm, 250 rpm, 300 rpm, 350 rpm, or 400 rpm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0032] Preferably, the calcination is a segmented calcination, which includes the following steps:

[0033] S41. First stage: Removal of water of crystallization at 300-400℃;

[0034] S42. Second stage: Crystal transformation is completed at 500-650℃.

[0035] The temperature for removing water of crystallization is 300–400°C, for example, 300°C, 350°C, or 400°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable. The temperature for completing the crystal form transformation is 500–650°C, for example, 500°C, 550°C, 600°C, or 650°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0036] This calcination method employs segmented calcination. In the first stage, at 300–400℃, the water of crystallization is removed. Since water of crystallization is an integral part of the crystal structure, it can be gradually removed at 300–400℃, avoiding structural abrupt changes caused by the rapid escape of water molecules and maintaining the integrity of the crystal framework. Simultaneously, after gradually removing the water of crystallization, the crystal form transformation is completed at 500–650℃, which can promote the continuity of crystal form transformation, complete the formation of the target crystal form, and thus improve the purity and performance of the product.

[0037] More preferably, the segmented calcination includes the following steps:

[0038] First stage: Keep at 300-400℃ for 1-2 hours to remove water of crystallization;

[0039] Second stage: Hold at 500-650℃ for 2-3 hours to complete the crystal transformation.

[0040] The heat treatment time for removing water of crystallization is 1 to 2 hours, for example, 1 hour, 1.5 hours, or 2 hours, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable. The heat treatment time for completing the crystal form transformation is 2 to 3 hours, for example, 2 hours, 2.5 hours, or 3 hours, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0041] Preferably, the calcination is carried out under an inert gas atmosphere.

[0042] Preferably, the calcination includes heating to the required calcination temperature at a heating rate of 2 to 5 °C / min. The heating rate is 2 to 5 °C / min, for example, it can be 2 °C / min, 3 °C / min, 4 °C / min, or 5 °C / min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0043] The present invention also provides manganese phosphate prepared by the method for preparing manganese phosphate from rhodochrosite. Detailed Implementation

[0044] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0045] Example 1

[0046] S1. Raw material pretreatment: Take 1 kg of rhodochrosite and crush it until D90 < 85 μm. Add 5 L of mixed acid (98% sulfuric acid and 85% phosphoric acid in a volume ratio of 1:1), react at 80℃ for 3 h, and filter to obtain Mn-containing material. 2+ The leachate;

[0047] S2. Impurity Removal: First stage, removing impurities containing Mn. 2+ The leachate was treated with ammonium fluoride solution (0.15 mol / L, water) to adjust the pH to 3.8 for the first stage of precipitation and impurity removal. In the second stage, sodium carbonate solution (0.3 mol / L, water) and sodium oxalate solution (0.05 mol / L, water) were added in a volume ratio of 4:1. The pH was adjusted to 4.8 for the second stage of precipitation and impurity removal. After filtration, the solution was concentrated using a nanofiltration membrane with a molecular weight cutoff of 200 Da (operating pressure 2.0 MPa) to obtain a solution containing Mn. 2+ The impurity-removing leachate;

[0048] S3. Directed crystallization: crystallizing towards Mn-containing... 2+ Add a crystal-directing agent (the crystal-directing agent and Mn-containing leachate) to the impurity removal leachate. 2+The mass ratio of the impurity removal leachate was 1.2:100. The crystal-directing agent was composed of ammonium dihydrogen phosphate and sodium citrate (mass ratio of ammonium dihydrogen phosphate to sodium citrate was 2:1). The temperature was controlled at 65℃ and the pH was 7.0. The reaction was carried out at a stirring rate of 300 rpm for 4 hours to generate a monodisperse spherical Mn3(PO4)2·3H2O precursor.

[0049] S4. Dynamic calcination: The Mn3(PO4)2·3H2O precursor was placed in a rotary tube furnace and calcined in stages under N2 atmosphere: First stage: 350℃ for 1.5h to remove water of crystallization; Second stage: 600℃ for 2.5h to form highly crystalline Mn3(PO4)2, thus obtaining battery-grade manganese phosphate.

[0050] Example 2

[0051] The method for preparing manganese phosphate from rhodochrosite in this embodiment is the same as in Example 1, except that the mass ratio of ammonium dihydrogen phosphate to sodium citrate is 4:1.

[0052] Example 3

[0053] The method for preparing manganese phosphate from rhodochrosite in this embodiment is the same as in Example 1, except that sodium oxalate solution is not added in step S2, and only sodium carbonate solution is added to adjust the pH to 4.8.

[0054] Example 4

[0055] The method for preparing manganese phosphate from rhodochrosite in this embodiment is the same as in Example 1, except for the calcination method in step S4. The specific method for calcination in step S4 of this embodiment is as follows:

[0056] Dynamic calcination: The Mn3(PO4)2·3H2O precursor was placed in a rotary tube furnace and calcined in stages under N2 atmosphere: First stage: 350℃ for 1.5h to remove water of crystallization; Second stage: 450℃ for 2.5h to form highly crystalline Mn3(PO4)2, thus obtaining battery-grade manganese phosphate.

[0057] Comparative Example 1

[0058] This comparative example uses a method for preparing manganese phosphate from rhodochrosite, omitting ammonium dihydrogen phosphate as a crystal-directing agent, and using sodium citrate and Mn-containing... 2+ The mass ratio of the impurity-removing leachate was 1.2:100, and the rest was the same as in Example 1.

[0059] Comparative Example 2

[0060] This comparative example uses a method for preparing manganese phosphate from rhodochrosite, omitting sodium citrate as a crystal-directing agent. It also uses ammonium dihydrogen phosphate containing Mn. 2+ The mass ratio of the impurity-removing leachate was 1.2:100, and the rest was the same as in Example 1.

[0061] Comparative Example 3

[0062] The method for preparing manganese phosphate from rhodochrosite in this comparative example is the same as in Example 1, except that the crystal-directing agent used is composed of sodium dihydrogen phosphate and ammonium citrate, and the mass ratio of sodium dihydrogen phosphate to ammonium citrate is 2:1.

[0063] Performance testing

[0064] (1) Tap density

[0065] The tap density of manganese phosphate prepared in the examples and comparative examples was determined in accordance with GB / T 31057.2-2018 (Measurement of tap density of particulate matter).

[0066] (2) Manganese content

[0067] The manganese content (mass percentage) in the manganese phosphate prepared in the examples and comparative examples was determined.

[0068] (3) Manganese yield

[0069] Manganese yield = (mass of manganese in the product / mass of manganese in the raw materials) × 100%.

[0070] (4) Specific surface area of ​​manganese phosphate

[0071] The specific surface area was determined according to GB / T 11107-2018 (Determination of specific surface area and particle size of metals and their compounds by air permeation method) for manganese phosphate prepared in the examples and comparative examples.

[0072] The manganese phosphate prepared in the examples and comparative examples was subjected to the above-mentioned performance tests, and the test results are shown in Table 1 below:

[0073] Table 1

[0074]

[0075]

[0076] As shown in Table 1:

[0077] The methods for preparing manganese phosphate from rhodochrosite in Examples 1-4 all fall within the scope of preparation methods protected by this invention. The battery-grade manganese phosphate prepared by the methods in Examples 1-4 exhibits good performance in tests of tap density, manganese content, manganese yield, and specific surface area. That is, the method for preparing manganese phosphate from rhodochrosite provided by this invention allows for controllable crystal morphology, thereby producing high-density and high-purity battery-grade manganese phosphate that meets the requirements of lithium-ion battery materials, while also improving manganese yield. However, the methods for preparing manganese phosphate in Comparative Examples 1-3 do not fall within the scope of preparation methods protected by this invention. The manganese phosphate prepared by the methods in Comparative Examples 1-3 shows significant deterioration in at least one of the performance tests for tap density, manganese content, manganese yield, and specific surface area. That is, the methods in Comparative Examples 1-3 cannot both improve manganese yield and produce high-density and high-purity battery-grade manganese phosphate.

[0078] Compared to Example 1, which used a 2:1 mass ratio of ammonium dihydrogen phosphate to sodium citrate as a crystal-directing agent in the method for preparing manganese phosphate from rhodochrosite, Example 2 used a 4:1 mass ratio of ammonium dihydrogen phosphate to sodium citrate. This means that the mass ratio of ammonium dihydrogen phosphate to sodium citrate used in Example 2 is not within the further preferred range of (1:1) to (3.5:1). The battery-grade manganese phosphate prepared by the method in Example 2 showed inferior performance in terms of tap density and manganese yield compared to Example 1. This indicates that in the method for preparing manganese phosphate from rhodochrosite of the present invention, using a mass ratio of ammonium dihydrogen phosphate to sodium citrate of (1:1) to (3.5:1) allows the prepared battery-grade manganese phosphate to have a more suitable particle size, further improving the tap density of manganese phosphate and also further increasing the manganese yield.

[0079] Compared to Example 1, which uses both sodium carbonate and sodium oxalate as precipitants in the second stage of gradient purification for preparing manganese phosphate from rhodochrosite, Example 3 uses only sodium carbonate as the precipitant in the second stage of gradient purification. This means that the precipitant used in Example 3 is not within the range of further preferred composite precipitants of sodium carbonate and sodium oxalate. The battery-grade manganese phosphate prepared by the method in Example 3 shows inferior results in terms of manganese content and yield compared to Example 1. This indicates that in the method of preparing manganese phosphate from rhodochrosite of the present invention, during the precipitation purification in the second stage of gradient purification, the synergistic removal of calcium by sodium carbonate and sodium oxalate can further remove Ca. 2+ This can further improve the purity of manganese phosphate and the yield of manganese.

[0080] Compared to Example 1, where the temperature for completing the crystal transformation in the second stage of segmented calcination in the method for preparing manganese phosphate from rhodochrosite was 600°C, the temperature for completing the crystal transformation in the second stage of segmented calcination in Example 4 was 450°C. This means that the temperature for completing the crystal transformation in the second stage of segmented calcination in Example 4 is not within the further preferred range of 500–650°C. Therefore, the battery-grade manganese phosphate prepared by the method of Example 4 showed worse tap density performance than that of Example 1. This indicates that in the method for preparing manganese phosphate from rhodochrosite of the present invention, completing the crystal transformation at 500–650°C can promote the continuity of crystal transformation, complete the formation of the target crystal form, and thus improve the tap density and purity of manganese phosphate.

[0081] Compared with Example 1, which uses ammonium dihydrogen phosphate and sodium citrate as crystal-directing agents in the method for preparing manganese phosphate from rhodochrosite, Comparative Example 1 uses only sodium citrate as a crystal-directing agent. That is, the crystal-directing agent used in the preparation method of Comparative Example 1 is not the ammonium dihydrogen phosphate and sodium citrate included in the technical solution of this invention. Compared with Example 1, the manganese phosphate prepared by the method of Comparative Example 1 shows significantly worse test results in terms of tap density, manganese content, and manganese yield. The reason is that, during the directional crystallization process, the crystal-directing agent ammonium dihydrogen phosphate is omitted, which will form too many fine crystals and cause agglomeration, resulting in a significant decrease in density. At the same time, manganese ions precipitate in other forms than manganese phosphate, which significantly reduces the manganese yield.

[0082] Compared with Example 1, which uses ammonium dihydrogen phosphate and sodium citrate as crystal-directing agents in the method for preparing manganese phosphate from rhodochrosite, Comparative Example 2 uses only ammonium dihydrogen phosphate as a crystal-directing agent. That is, the crystal-directing agent used in the preparation method of Comparative Example 2 is not the ammonium dihydrogen phosphate and sodium citrate included in the technical solution of this invention. Compared with Example 1, the manganese phosphate prepared by the preparation method of Comparative Example 2 has significantly deteriorated in terms of tap density. The reason is that the crystal-directing agent sodium citrate is omitted in the directional crystallization process, which leads to poor crystallinity and a significant decrease in tap density.

[0083] Compared to Example 1, which used ammonium dihydrogen phosphate and sodium citrate as crystal-directing agents to prepare manganese phosphate from rhodochrosite, Comparative Example 3 used sodium dihydrogen phosphate and ammonium citrate as crystal-directing agents. That is, the crystal-directing agents used in Comparative Example 3 are not the ammonium dihydrogen phosphate and sodium citrate included in the technical solution of this invention. Compared to Example 1, the manganese phosphate prepared by the method of Comparative Example 3 showed significantly worse test results in terms of tap density, manganese content, and manganese yield. This indicates that although both Example 1 and Comparative Example 3 use composite crystal-directing agents that can provide a phosphate buffer system (H2PO4), the results are not ideal. - / HPO4 2- ), NH4 + Carboxylate (-COO) -), hydroxyl group (-OH), and sodium ion (Na) + However, due to the different compounds used, the manganese phosphate produced has significant differences in tap density, manganese content, and manganese yield. This indicates that in the method of preparing manganese phosphate from rhodochrosite in this invention, the specific crystal form guide of this invention is required to achieve controllable crystal morphology, thereby producing high-density and high-purity battery-grade manganese phosphate that meets the requirements of lithium-ion battery materials, while also improving the manganese yield.

[0084] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention, but such modifications or substitutions are all within the scope of protection of the present invention.

Claims

1. A method for preparing manganese phosphate from rhodochrosite, characterized in that, Includes the following steps: S1. Raw material pretreatment: Rhodochrosite is crushed and leached with acid to obtain Mn-containing material. 2+ The leachate; S2. Impurity removal: Remove impurities from the leachate to obtain a solution containing Mn. 2+ The impurity-removing leachate; S3. Directed crystallization: crystallizing towards Mn-containing... 2+ A crystal-directing agent is added to the impurity-removing leachate to obtain the precursor; S4. Calcination: The precursor is calcined to obtain the manganese phosphate; The crystal-directing agent includes ammonium dihydrogen phosphate and sodium citrate.

2. The method for preparing manganese phosphate from rhodochrosite according to claim 1, characterized in that, In S1, the acid includes at least one of sulfuric acid and phosphoric acid.

3. The method for preparing manganese phosphate from rhodochrosite according to claim 1, characterized in that, In step S2, the de-duplication includes gradient de-duplication, which specifically includes the following steps: S21. First stage: Add precipitant A to adjust the pH to 3.5-4.0 to carry out the first stage of precipitation and impurity removal; S22. Second stage: Add precipitant B to adjust the pH to 4.5-5.0, and carry out the second stage of precipitation and impurity removal; The precipitant A includes at least one of ammonium fluoride, sodium fluoride, and sodium sulfide, and the precipitant B includes at least one of sodium carbonate and sodium oxalate.

4. The method for preparing manganese phosphate from rhodochrosite according to claim 3, characterized in that, In step S2, the impurity removal also includes membrane separation; after precipitation impurity removal, the product is subjected to membrane separation to obtain a product containing Mn. 2+ The impurity-removing leachate is obtained by membrane separation using a nanofiltration membrane with a molecular weight cutoff of 200–500 Da and an operating pressure of 1.0–2.5 MPa.

5. The method for preparing manganese phosphate from rhodochrosite according to claim 1, characterized in that, The mass ratio of the ammonium dihydrogen phosphate to the sodium citrate is (1:1) to (3.5:1).

6. The method for preparing manganese phosphate from rhodochrosite according to claim 1, characterized in that, The crystal-directing agent and the impurity removal agent containing Mn 2+ The mass ratio of the leachate is (0.5~2.0):

100.

7. The method for preparing manganese phosphate from rhodochrosite according to claim 1, characterized in that, The specific reaction conditions for the directional crystallization include: crystallization into Mn-containing... 2+ A crystal-directing agent is added to the impurity-removing leachate, and the reaction temperature is controlled at 50–80℃ and the pH at 6.0–7.

5.

8. The method for preparing manganese phosphate from rhodochrosite according to claim 1 or 7, characterized in that, The stirring rate during the directional crystallization is 200–400 rpm.

9. The method for preparing manganese phosphate from rhodochrosite according to claim 1, characterized in that, The calcination is a segmented calcination, which includes the following steps: S41. First stage: Removal of water of crystallization at 300-400℃; S42. Second stage: Crystal transformation is completed at 500-650℃.

10. Manganese phosphate prepared by the method for preparing manganese phosphate from rhodochrosite as described in any one of claims 1 to 9.

Images