Method for preparing manganese phosphate from rhodochrosite and manganese phosphate

Abstract

The method for preparing the manganese phosphate from the rhodochrosite comprises the following steps that raw materials are pretreated, specifically, the rhodochrosite is crushed and leached with acid, and leachate containing Mn < 2 + > is obtained; impurity removal: removing impurities from the leaching solution to obtain an impurity-removed leaching solution containing Mn < 2 + >; directional crystallization: adding a crystal form guiding agent into the impurity-removed leachate containing Mn < 2 + > to obtain a precursor; calcining: calcining the precursor to obtain the manganese phosphate, the crystal form directing agent comprises ammonium dihydrogen phosphate and sodium citrate. According to the method for preparing the manganese phosphate from the rhodochrosite, the crystal morphology can be controlled in the process for preparing the manganese phosphate from the rhodochrosite, so that the high-density and high-purity battery-grade manganese phosphate meeting the requirements of a lithium ion battery material is prepared.

Description

Technical Field

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

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

[0003] In order to solve the above technical problems, the purpose of the present invention is to provide a method for preparing manganese phosphate from rhodochrosite and manganese phosphate, so as to achieve controllable crystallization 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.

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

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

[0006] S2. Impurity removal: Removing impurities from the leaching solution to obtain a purified leaching solution containing Mn 2+ ;

[0007] S3. Oriented crystallization: Adding a crystal form guiding agent to the purified leaching solution containing Mn 2+ to obtain a precursor;

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

[0009] The crystal form guiding agent includes ammonium dihydrogen phosphate and sodium citrate.

[0010] The method for preparing manganese phosphate from rhodochrosite provided by the present invention has a controllable crystallization morphology of the precursor during oriented crystallization, so that the prepared manganese phosphate has a spherical or quasi-spherical morphology, with a concentrated particle size distribution and D90 < 20 μm, thereby meeting the requirements of lithium-ion battery materials for high-density manganese phosphate. Specifically, the NH4 provided by ammonium dihydrogen phosphate in the crystal form guiding agent +Interact with phosphate groups (PO4 3- ) and water molecules (H2O) through hydrogen bonds to stabilize the hydrated layer structure in the crystal, promote the regular arrangement of Mn3(PO4)2·3H2O, and prevent the crystal form transformation or structure collapse caused by dehydration; furthermore, the phosphate buffer system (H2PO4 - / HPO4 2- ) provided by ammonium dihydrogen phosphate can prevent the pH value of the solution from being too large, avoid the further oxidation of Mn 2+ in the solution to form Mn(OH)3 after generating Mn(OH)2, improving the recovery rate of Mn in rhodochrosite and the purity of the product manganese phosphate. In addition, the carboxylate (-COO - ) and hydroxyl (-OH) functional groups provided by sodium citrate in the crystal form guiding agent can form stable polydentate complexes with Mn 2+ in the solution. This complexation significantly reduces the concentration of free Mn 2+ , delays the rapid generation of crystal nuclei, creates conditions for the orderly growth of crystals, promotes the formation of more uniform crystal nuclei, so as to obtain manganese phosphate with high crystallinity. At the same time, the Na + provided by sodium citrate reduces the surface energy of the high-energy crystal plane through selective adsorption, drives the evolution of the crystal morphology towards the spherical shape with the minimum interfacial energy, and simultaneously regulates the nucleation and growth kinetics, ultimately realizing the controllable preparation of manganese phosphate microspheres. Ammonium dihydrogen phosphate and sodium citrate, as a composite crystal form guiding agent for the directional crystallization precursor, interact synergistically with each other to achieve controllable crystallization morphology in the process of preparing manganese phosphate from rhodochrosite, thereby improving the tap density of manganese phosphate.

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

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

[0013] In this solution, in the S1, the acid includes sulfuric acid and phosphoric acid. Using a mixed acid system of sulfuric acid and phosphoric acid, the complexation of phosphoric acid inhibits the hydrolysis of Fe 3+ , reduces the leaching of Fe in rhodochrosite, and at the same time can also reduce the leaching rates of harmful metals Pb and Cd, reduce the subsequent impurity removal pressure, and can also increase the leaching rate of Mn, which is beneficial to improving the recovery rate of Mn in rhodochrosite and the purity of the product manganese phosphate.

[0014] More preferably, in the S1, the volume ratio of the sulfuric acid to the 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, and other unlisted values within the numerical range are equally applicable.

[0015] Preferably, in the step S1, the mass ratio of the rhodochrosite to the 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 numerical range are equally applicable.

[0016] Preferably, in the step S1, the leaching reaction time for acid leaching is 2-4 h. For example, it can be 2 h, 3 h, 4 h, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0017] Preferably, in the step S2, the impurity removal includes gradient impurity removal, and the gradient impurity removal specifically includes the following steps:

[0018] S21. The first stage: adding a precipitant A to adjust the pH to 3.5-4.0 for the first-stage precipitation impurity removal;

[0019] S22. The second stage: adding a precipitant B to adjust the pH to 4.5-5.0 for the second-stage precipitation 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] The impurity removal in this solution adopts the method of gradient impurity removal. Specifically, the iron is deeply removed first, that is, using the precipitant A to preferentially precipitate Fe in the solution 3+ , avoiding the interference of Fe(OH)3 colloid in the subsequent steps. Subsequently, calcium and magnesium are co-precipitated, that is, using the precipitant B to precipitate Ca 2+ and Mg 2+ , realizing the synchronous deep removal of Ca 2+ and Mg 2+ , avoiding the generation of Ca3(PO4)2 and affecting the purity of the product. This gradient impurity removal method realizes the deep removal of impurities, thus meeting the requirements of lithium-ion battery materials for high-purity manganese phosphate.

[0022] Further preferably, the precipitant B includes sodium carbonate and sodium oxalate.

[0023] In this solution, the precipitant B includes sodium carbonate and sodium oxalate. When performing the second-stage precipitation impurity removal, calcium is co-removed by sodium carbonate and sodium oxalate, which can further remove Ca 2+ , solving the problem of excessive Ca residue caused by high-calcium ore.

[0024] Preferably, in the step S2, the impurity removal further includes membrane separation. After precipitation impurity removal, through membrane separation, a solution containing Mn 2+The impurity-removing leaching solution, the membrane separation uses a nanofiltration membrane with a molecular weight cut-off of 200-500 Da, and the operating pressure is 1.0-2.5 MPa. The molecular weight cut-off is 200-500 Da, for example, it can be 200 Da, 300 Da, 400 Da, 500 Da, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable. The operating pressure is 1.0-2.5 MPa, for example, it can be 1.0 MPa, 1.5 MPa, 2.0 MPa, 2.5 MPa, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0025] In this solution, in the S2, the impurity removal also includes membrane separation. Using the membrane separation method of this solution, on the one hand, the sieving effect intercepts colloids and macromolecular complexes, and at the same time can also intercept organic substances, which can achieve the purpose of further impurity removal; on the other hand, the membrane separation allows Mn 2+ to freely pass through, and the solution is concentrated, which can further enrich Mn 2+ and provide a suitable solution environment for subsequent directional crystallization.

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

[0027] The mass ratio of ammonium dihydrogen phosphate to sodium citrate in this solution is (1:1)-(3.5:1), which can not only further improve the sphericity of manganese phosphate, but also make the particle size distribution of manganese phosphate narrower, the particle size uniform, and also enable manganese phosphate to have a suitable particle size to improve the tap density of manganese phosphate.

[0028] Preferably, the mass ratio of the crystal form guiding agent to the impurity-removing Mn 2+ leaching solution is (0.5-2.0):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, and other unlisted values within the numerical range are equally applicable.

[0029] Preferably, the specific reaction conditions for the directional crystallization include: adding a crystal form guiding agent to the impurity-removing leaching solution containing Mn 2+ , and controlling the reaction temperature to be 50-80°C and the pH to be 6.0-7.5. The controlled reaction temperature is 50-80°C, for example, it can be 50°C, 60°C, 70°C, 80°C, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable. The pH is 6.0-7.5, for example, it can be 6.0, 6.5, 7.0, 7.5, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0030] The specific reaction conditions of the directional crystallization described in this solution include: adding a crystal form guiding agent to the impurity-removing leaching solution containing Mn 2+ , controlling the reaction temperature to be 50-80°C and the pH to be 6.0-7.5, which can not only make the particle size distribution of the prepared manganese phosphate narrower and the particle sizes more uniform, but also enable manganese phosphate to have a suitable particle diameter to improve the tap density of manganese phosphate.

[0031] Preferably, the stirring rate in the directional crystallization is 200-400 rpm. For example, it can be 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0032] Preferably, the calcination is carried out in stages, and the staged calcination includes the following steps:

[0033] S41. The first stage: removing crystal water at 300-400°C;

[0034] S42. The second stage: completing crystal form transformation at 500-650°C.

[0035] The temperature for removing crystal water is 300-400°C. For example, it can be 300°C, 350°C, 400°C, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable; the temperature for completing crystal form transformation is 500-650°C. For example, it can be 500°C, 550°C, 600°C, 650°C, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0036] In this solution, the calcination is carried out in stages. In the first stage, crystal water is removed at 300-400°C. Crystal water is a component of the crystal structure. At 300-400°C, crystal water can be gradually removed, avoiding structural mutations caused by the rapid escape of water molecules and maintaining the integrity of the crystal framework. At the same time, after gradually removing crystal water and then completing crystal form transformation at 500-650°C, the continuity of crystal form transformation can be promoted, the formation of the target crystal form can be completed, thereby improving the product purity and performance.

[0037] Further preferably, the staged calcination includes the following steps:

[0038] The first stage: keeping the temperature at 300-400°C for 1-2 h to remove crystal water;

[0039] The second stage: keeping the temperature at 500-650°C for 2-3 h to complete crystal form transformation.

[0040] The heat preservation time for removing crystal water is 1-2h. For example, it can be 1h, 1.5h, 2h, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable; the heat preservation time for completing crystal form transformation is 2-3h. For example, it can be 2h, 2.5h, 3h, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

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

[0042] Preferably, the calcination includes heating to the required calcination temperature at a heating rate of 2-5°C / min. The heating rate is 2-5°C / min. For example, it can be 2°C / min, 3°C / min, 4°C / min, 5°C / min, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

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

[0044] In order to enable those skilled in the art to better understand the solution of 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 a part of the embodiments of the present invention, rather than all the embodiments.

[0045] Example 1

[0046] S1. Raw material pretreatment: Take 1 kg of rhodochrosite and crush it to D90 < 85 μm, add 5 L of mixed acid (the volume ratio of 98% sulfuric acid to 85% phosphoric acid is 1:1), react at 80°C for 3 h, and filter to obtain a leaching solution containing Mn 2+ ;

[0047] S2. Impurity removal: In the first stage, add ammonium fluoride solution (concentration 0.15 mol / L, solvent water) to the leaching solution containing Mn 2+ to adjust the pH to 3.8 for impurity removal by precipitation in the first stage; in the second stage, add sodium carbonate solution (concentration 0.3 mol / L, solvent water) and sodium oxalate solution (concentration 0.05 mol / L, solvent water), the volume ratio of sodium carbonate solution to sodium oxalate solution is 4:1, adjust the pH to 4.8 for impurity removal by precipitation in the second stage. After filtration, concentrate using a nanofiltration membrane with a molecular weight cut-off of 200 Da (operating pressure 2.0 MPa) to obtain a purified leaching solution containing Mn 2+ ;

[0048] S3. Oriented crystallization: Add a crystal form guiding agent to the purified leaching solution containing Mn 2+ (the crystal form guiding agent and the leaching solution containing Mn 2+The mass ratio of the impurity-removing leaching solution is 1.2:100. The crystal form guiding agent consists of ammonium dihydrogen phosphate and sodium citrate, and the mass ratio of ammonium dihydrogen phosphate to sodium citrate is 2:1). The temperature is controlled at 65 °C and the pH is 7.0, and the reaction is carried out at a stirring rate of 300 rpm for 4 h to generate a monodisperse spherical Mn3(PO4)2·3H2O precursor;

[0049] S4. Dynamic calcination: Place the Mn3(PO4)2·3H2O precursor in a rotary tube furnace and calcine it in stages under a N2 atmosphere: The first stage: Keep it at 350 °C for 1.5 h to remove the crystal water; The second stage: Keep it at 600 °C for 2.5 h to form highly crystalline Mn3(PO4)2 and obtain battery-grade manganese phosphate.

[0050] Example 2

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

[0052] Example 3

[0053] In this example, the method for preparing manganese phosphate from rhodochrosite is the same as that in Example 1 except that in step S2, no sodium oxalate solution is added and only sodium carbonate solution is added to adjust the pH to 4.8.

[0054] Example 4

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

[0056] Dynamic calcination: Place the Mn3(PO4)2·3H2O precursor in a rotary tube furnace and calcine it in stages under a N2 atmosphere: The first stage: Keep it at 350 °C for 1.5 h to remove the crystal water; The second stage: Keep it at 450 °C for 2.5 h to form highly crystalline Mn3(PO4)2 and obtain battery-grade manganese phosphate.

[0057] Comparative Example 1

[0058] In this comparative example, the method for preparing manganese phosphate from rhodochrosite is the same as that in Example 1 except that the crystal form guiding agent omits ammonium dihydrogen phosphate, and the mass ratio of the sodium citrate used to the impurity-removing leaching solution containing Mn 2+ is 1.2:100.

[0059] Comparative Example 2

[0060] In this comparative example, the method for preparing manganese phosphate from rhodochrosite is the same as that in Example 1 except that the crystal form guiding agent omits sodium citrate, and the mass ratio of the ammonium dihydrogen phosphate used to the impurity-removing leaching solution containing Mn 2+ is 1.2:100.

[0061] Comparative Example 3

[0062] The method for preparing manganese phosphate from rhodochrosite in this comparative example is the same as that in Example 1, except that the crystal structure 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 Test

[0064] (1) Tap density

[0065] According to GB / T 31057.2-2018 (Measurement of tap density of particulate matter), the tap density of the manganese phosphate prepared in the examples and comparative examples was measured.

[0066] (2) Manganese content

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

[0068] (3) Recovery rate of manganese

[0069] Recovery rate of manganese = (mass of manganese element in product / mass of manganese element in input raw material) × 100%.

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

[0071] The specific surface area was measured according to GB / T 11107-2018 (Determination of specific surface area and particle size of metal and its compound powders - Air permeability method), and the specific surface area of the manganese phosphate prepared in the examples and comparative examples was measured.

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

[0073] Table 1

[0074]

[0075]

[0076] As can be seen from Table 1:

[0077] The methods for preparing manganese phosphate from rhodochrosite in Examples 1 to 4 all fall within the scope of the preparation methods protected by the technical solution of the present invention. The battery-grade manganese phosphate prepared by the preparation methods in Examples 1 to 4 showed good test results in the performance tests of tap density, manganese content, manganese yield, and specific surface area. That is, the method for preparing manganese phosphate from rhodochrosite provided by the present invention can achieve controllable crystal morphology, thereby preparing high-density and high-purity battery-grade manganese phosphate that meets the requirements of lithium-ion battery materials, and at the same time can also improve the manganese yield. However, the preparation methods of manganese phosphate in Comparative Examples 1 to 3 do not fall within the scope of the preparation methods protected by the technical solution of the present invention. The manganese phosphate prepared by the preparation methods in Comparative Examples 1 to 3 showed significant deterioration in at least one of the performance tests of tap density, manganese content, manganese yield, and specific surface area. That is, the preparation methods in Comparative Examples 1 to 3 cannot both increase the manganese yield and prepare high-density and high-purity battery-grade manganese phosphate.

[0078] Compared with the mass ratio of ammonium dihydrogen phosphate to sodium citrate as the crystal form guiding agent in the method for preparing manganese phosphate from rhodochrosite in Example 1 being 2:1, the mass ratio of ammonium dihydrogen phosphate to sodium citrate as the crystal form guiding agent in Example 2 was 4:1. That is, the mass ratio of ammonium dihydrogen phosphate to sodium citrate as the crystal form guiding agent in Example 2 was not within the further preferred range of (1:1) to (3.5:1). The test results of the battery-grade manganese phosphate prepared by the preparation method in Example 2 were worse than those in Example 1 in terms of tap density and manganese yield. This shows that in the method for preparing manganese phosphate from rhodochrosite in the present invention, when the mass ratio of ammonium dihydrogen phosphate to sodium citrate as the crystal form guiding agent is (1:1) to (3.5:1), the prepared battery-grade manganese phosphate can have a more suitable particle size, which can further increase the tap density of manganese phosphate and at the same time further improve the manganese yield.

[0079] Compared with using sodium carbonate and sodium oxalate together as the precipitant in the second stage of gradient impurity removal in the method for preparing manganese phosphate from rhodochrosite in Example 1, Example 3 only used sodium carbonate as the precipitant in the second stage of gradient impurity removal. That is, the second-stage precipitant used in Example 3 was not within the further preferred range of using sodium carbonate and sodium oxalate together as a composite precipitant. The test results of the battery-grade manganese phosphate prepared by the preparation method in Example 3 were worse than those in Example 1 in terms of manganese content and manganese yield. This shows that in the method for preparing manganese phosphate from rhodochrosite in the present invention, when performing precipitation impurity removal in the second stage of gradient impurity removal, the synergistic calcium removal by sodium carbonate and sodium oxalate can further remove Ca 2+ , thereby further improving the purity of manganese phosphate and the manganese yield.

[0080] Compared with Example 1 where the temperature for the completion of crystal form transformation in the second stage of staged calcination in the method for preparing manganese phosphate from rhodochrosite is 600 °C, the temperature for the completion of crystal form transformation in the second stage of staged calcination in Example 4 is 450 °C. That is, the temperature for the completion of crystal form transformation in the second stage of staged calcination in Example 4 is not within the further preferred range of 500 - 650 °C. The test effect of the battery-grade manganese phosphate prepared by the preparation method of Example 4 in terms of tap density is worse than that of Example 1. Thus, it is shown that in the method for preparing manganese phosphate from rhodochrosite in the present invention, the completion of crystal form transformation under the condition of 500 - 650 °C can promote the continuity of crystal form transformation of crystals, complete the formation of the target crystal form, thereby improving the tap density and purity of manganese phosphate.

[0081] Compared with Example 1 where the crystal form guiding agent used in the method for preparing manganese phosphate from rhodochrosite is ammonium dihydrogen phosphate and sodium citrate, the crystal form guiding agent used in Comparative Example 1 is only sodium citrate. That is, the crystal form guiding agent adopted in the preparation method of Comparative Example 1 is not ammonium dihydrogen phosphate and sodium citrate included in the technical solution of the present invention. Compared with Example 1, the test effects of the manganese phosphate prepared by the preparation method of Comparative Example 1 in terms of tap density, manganese content, and manganese yield are significantly deteriorated. The reason is that in the process of directional crystallization, omitting the crystal form guiding agent ammonium dihydrogen phosphate will form too many fine crystals resulting in agglomeration, significantly reducing the density. At the same time, manganese ions precipitate in other forms rather than manganese phosphate, significantly reducing the manganese yield.

[0082] Compared with Example 1 where the crystal form guiding agent used in the method for preparing manganese phosphate from rhodochrosite is ammonium dihydrogen phosphate and sodium citrate, the crystal form guiding agent used in Comparative Example 2 is only ammonium dihydrogen phosphate. That is, the crystal form guiding agent adopted in the preparation method of Comparative Example 2 is not ammonium dihydrogen phosphate and sodium citrate included in the technical solution of the present invention. Compared with Example 1, the test effect of the manganese phosphate prepared by the preparation method of Comparative Example 2 in terms of tap density is significantly deteriorated. The reason is that in the process of directional crystallization, omitting the crystal form guiding agent sodium citrate will lead to poor crystallinity and significantly reduce the tap density.

[0083] Compared with Example 1 where the crystal form guiding agent used in the method for preparing manganese phosphate from rhodochrosite is ammonium dihydrogen phosphate and sodium citrate, the crystal form guiding agent used in Comparative Example 3 is sodium dihydrogen phosphate and ammonium citrate. That is, the crystal form guiding agent adopted in the preparation method of Comparative Example 3 is not ammonium dihydrogen phosphate and sodium citrate included in the technical solution of the present invention. Compared with Example 1, the test effects of the manganese phosphate prepared by the preparation method of Comparative Example 3 in terms of tap density, manganese content, and manganese yield are significantly deteriorated. Thus, it is shown that although both the composite crystal form guiding agents used in Example 1 and Comparative Example 3 can provide a phosphate buffer system (H2PO4 - / HPO4 2- ), NH4 + , carboxylate (-COO -), hydroxyl group (-OH), and sodium ion (Na + ), however, due to the use of different compounds, there are significant differences in the effects of the prepared manganese phosphate in terms of tap density, manganese content, and manganese yield. It can be thus explained that in the method for preparing manganese phosphate from rhodochrosite according to the present invention, it is necessary to use the specific crystal form guiding agent of the present invention to achieve controllable crystallization morphology, thereby preparing high-density and high-purity battery-grade manganese phosphate that meets the requirements of lithium-ion battery materials, and at the same time, the yield of manganese can be increased.

[0084] The above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced, but these modifications or replacements are all within the protection scope of the present invention.

Claims

1. A method for preparing manganese phosphate from rhodochrosite, characterized in that, It includes the following steps: S1. Pretreatment of raw materials: The rhodochrosite is crushed and leached with acid to obtain a leaching solution containing Mn 2+ . S2. Impurity removal: Remove impurities from the leaching solution to obtain a leaching solution after impurity removal containing Mn 2+ ; S3. Directional crystallization: Add a crystal form directing agent to the impurity-removed leaching solution containing Mn 2+ to obtain a precursor; S4. Calcination: Calcining the precursor to obtain the manganese phosphate; The crystal form 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 the step 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 the step S2, the impurity removal includes gradient impurity removal, and the gradient impurity removal specifically includes the following steps: S21. The first stage: Adding a precipitant A to adjust the pH to 3.5 - 4.0 for the first-stage precipitation impurity removal; S22. The second stage: Adding a precipitant B to adjust the pH to 4.5 - 5.0 for the second-stage precipitation 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 the step S2, the impurity removal further includes membrane separation. After impurity removal by precipitation, the impurity-removed leaching solution containing Mn is obtained through membrane separation. 2+ The membrane separation uses a nanofiltration membrane with a molecular weight cut-off of 200-500 Da, and the operating pressure is 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) - (3.5:1).

6. The method for preparing manganese phosphate from rhodochrosite according to claim 1, characterized in that, The crystal form guiding agent and the Mn-containing impurity removal 2+ leaching solution have a mass ratio of (0.5 to 2.0):

100.

7. The method for preparing manganese phosphate from rhodochrosite according to claim 1, wherein, The specific reaction conditions for the directional crystallization include: adding a crystal form guiding agent to the impurity removal leaching solution containing Mn 2+ , controlling the reaction temperature to be 50-80°C and the pH to be 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 in the directional crystallization is 200 - 400 rpm.

9. The method for preparing manganese phosphate from rhodochrosite according to claim 1, wherein The calcination is carried out in stages, and the staged calcination includes the following steps: S41. The first stage: Removing crystal water at 300 - 400 °C; S42. The second stage: Completing crystal form transformation at 500 - 650 °C.

10. A manganese phosphate obtained by the method for preparing manganese phosphate from rhodochrosite according to any one of claims 1 - 9.

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