Method for preparing battery-grade manganese phosphate

Abstract

The invention relates to a method for preparing battery-grade manganese phosphate, which comprises the following steps: S1, reacting manganous oxide with phosphoric acid to prepare a manganous phosphate solution, and S2, adding an oxidizing agent with equivalent molar weight or more to react, generating precipitate in the reaction solution, and separating the precipitate to obtain manganese phosphate monohydrate, wherein the ratio of phosphorus to manganese is 3: 1-20: 1, and the oxidizing agent is ozone or potassium permanganate. Manganese phosphate obtained by the method can be used as a raw material for preparing lithium iron manganese phosphate. According to the method, the raw material manganous oxide with lower cost can be used as the manganese source, the production cost is reduced, the pressure of wastewater treatment is greatly reduced, and as the ozone or potassium permanganate is used as the oxidizing agent to prepare manganese phosphate, impurities can be effectively prevented from being brought in, and the battery-grade application requirement is met.

Description

[0001] This application claims the priority of a prior application with application number 202311659619.9, filed with the State Intellectual Property Office on December 6, 2023, and invention name “A method for preparing battery-grade manganese phosphate”. The full text of the prior application is incorporated into this application. Technical Field

[0002] The invention belongs to the technical field of preparation of inorganic materials and lithium battery materials, and specifically relates to the preparation of manganese phosphate and / or lithium iron manganese phosphate. Background Art

[0003] Manganese phosphate is a widely used chemical raw material. It is mainly used as a phosphating agent for steel products, especially for the phosphating treatment of large mechanical equipment. It can prevent rust and can also be used as a lubricant and protective agent in the defense industry. In recent years, manganese phosphate has important application value as a high-quality raw material for lithium iron manganese phosphate, a positive electrode material for lithium-ion batteries.

[0004] The existing preparation methods are mainly:

[0005] 1) Oxidation-precipitation method, such as the method disclosed in CN101673819A and CN105609765A, is to prepare a manganese phosphate product in an acidic system with a soluble divalent manganese source and a phosphorus source as raw materials, and add an oxidant. This type of method has a problem that it will introduce elements other than manganese and phosphorus. For example, if manganous sulfate, manganous chloride, and manganous nitrate are used as raw materials, other impurity ions will be introduced and the yield is low, resulting in low purity of the prepared product, especially difficult to meet the requirements of lithium-ion battery materials, or more purification post-processing steps are required, and too much wastewater, waste gas and waste residue will be generated during the production process. In addition, in the above reaction process, only HNO 3 The oxidation of divalent Mn to trivalent Mn can only occur in the presence of hydrogen peroxide, and hydrogen peroxide alone cannot achieve the above purpose.

[0006] 2) Solvothermal synthesis method, such as the paper titled "Solvothermal Synthesis and Characterization of New Titanium Phosphate and Manganese Phosphate Crystals" [D]. Jilin University, 2003, using various organic amines as structure-directing agents in a n-butanol system, a layered manganese phosphate formed by manganese oxide octahedrons and phosphorus oxides was prepared. When preparing manganese phosphate by the solvothermal synthesis method, the reaction system is complex, the composition and structure of the manganese phosphate product are complex, and it is not easy to scale up production.

[0007] 3) CN112142028B uses potassium permanganate to react with concentrated phosphoric acid to generate manganese phosphate. The reaction equation is: 3KMnO 4 +4H 3 PO 4 =3MnPO 4 ·H 2O+K 3 PO 4 +3H 2 O+3O 2 ↑. The drawback of this method is that it is not economical in terms of molecule and will produce potassium phosphate byproducts and oxygen. The production of potassium phosphate byproducts will lead to wastewater and byproducts that need to be treated, which will increase the cost when it is put into practical use.

[0008] The industry is in urgent need of a new method for preparing manganese phosphate, especially a method for preparing battery-grade manganese phosphate. Summary of the invention

[0009] The invention uses relatively cheap reaction raw materials such as manganous oxide, ozone or potassium permanganate to prepare manganese phosphate.

[0010] The present invention discloses a method for preparing manganese phosphate, which comprises:

[0011] Step S1, reacting manganous oxide with phosphoric acid to prepare a manganous phosphate solution,

[0012] Step S2, adding an equivalent molar amount or more of an oxidant to react, generating a precipitate in the reaction solution, and separating the precipitate to obtain manganese phosphate monohydrate;

[0013] Among them, the ratio of the amount of phosphoric acid to manganous oxide (phosphorus to manganese ratio) is 2.5:1-20:1, preferably 2.9:1-8:1, for example 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1, 7.6:1, 7.7:1, 7.8:1, 7.9:1, etc., and the oxidant is ozone or potassium permanganate, preferably ozone.

[0014] Preferably, before step S2, a solid-liquid separation step is added to remove unreacted solids and reduce impurities.

[0015] The equivalent molar amount is the molar amount that can achieve complete reaction according to the valence state change of redox. For example, in the equivalent reaction, the molar ratio of ozone to manganous oxide is 1:2, and the molar ratio of potassium permanganate to manganous oxide is 1:4. Taking into account the dissipation loss of ozone during the ozone reaction, ozone can be appropriately excessive when used as an oxidant, for example, at least 50% excessive, which can be 2 times, 3 times, 4 times, 5 times, 6 times or even 20 times the equivalent amount. For potassium permanganate, the theoretical amount of potassium permanganate is 0.25 times the molar amount of manganous oxide. Too much potassium permanganate is not good and will introduce too much K element. The amount of the oxidant, calculated based on manganous oxide, is 0.05-20 times the mole of manganous oxide, preferably 0.2-6 times, for example, 0.3 times, 0.5 times, 1 times, 1.5 times, 2 times, 2.5 times, 3 times, 3.5 times, 4 times, 4.5 times, 5 times, 5.5 times, 5.6 times, 5.7 times, 5.8 times, 5.9 times, etc.

[0016] As in the above method, after the reaction of step S2 is completed, the product (precipitate) is obtained by solid-liquid separation, and the mother liquor is separated and returned to the reaction process of manganese oxide and phosphoric acid in step S1. According to the value of the phosphorus-manganese ratio, it is determined whether phosphoric acid needs to be supplemented or not in the reused mother liquor. However, when the oxidant is potassium permanganate, the enrichment of K ions needs to be considered, and the mother liquor with excessive K ion concentration does not need to be recycled.

[0017] Furthermore, the mother liquor can be evaporated to reduce the water content and increase the phosphoric acid concentration in the mother liquor to meet the phosphorus-manganese ratio requirement in step S1.

[0018] When the oxidant is ozone, after the ozone gas passes through the reaction liquid, the unreacted gas can be recycled and introduced into the reaction liquid in step S2 again, thereby improving the utilization rate of ozone and reducing environmental damage.

[0019] The concentration of phosphoric acid is not limited. Considering the low solubility of manganese phosphate, a phosphoric acid concentration of 5%-85% can achieve the purpose of the present invention.

[0020] As a preferred embodiment, the inventors found that the concentration of phosphoric acid is between 2M and 9M, preferably between 2.9M and 6M, for example: 2.95M, 3M, 3.5M, 4M, 4.5M, 5M, 5.5M, 5.95M, 5.99M, etc., and the reaction temperature of step S2 is between room temperature and 100°C, preferably between 25°C and 75°C, for example 26°C, 27°C, 28°C, 29°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 71°C, 72°C, 73°C, 74°C, etc., the reaction yield of the present invention is relatively high.

[0021] Terminology explanation:

[0022] Phosphorus-manganese ratio: refers to the ratio of the amount of phosphorus to manganese in the present invention, such as the ratio of the amount of phosphorus source and manganese source in the reaction raw material system. Low phosphorus-manganese ratio means lower phosphoric acid dosage, and reducing the phosphorus-manganese ratio will effectively reduce production costs, but low phosphorus-manganese ratio will lead to a reduced reaction rate and even the possibility of non-reaction. On the contrary, high phosphorus-manganese ratio, such as 10:1 or even 20:1 phosphorus-manganese ratio, can still achieve the purpose of the present invention, but will lead to excessive phosphoric acid, high cost, and difficult post-processing (high concentration phosphoric acid wastewater treatment, etc.). The present invention limits the phosphorus-manganese ratio to 3:1-20:1, such as 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, etc.

[0023] Manganous oxide: also known as manganese monoxide, with the molecular formula MnO.

[0024] Manganese phosphate: The manganese phosphate described in the present invention is MnPO 3 , Mn is a trivalent ion. In the present invention, monohydrated manganese phosphate MnPO 4 ·H 2 The method for preparing manganese phosphate in the present invention often refers to the method for preparing manganese phosphate monohydrate or monohydrated manganese phosphate.

[0025] Equivalent, in the present invention, refers to the amount of substance or mass ratio (theoretical calculation) required for complete reaction between reactants according to the reaction equation, the equivalent molar amount is calculated by mole, and the equivalent mass number is calculated by mass. The amount of oxidant or supplementary oxidant used in the present invention is the equivalent mole number, which refers to the amount of the corresponding substance of the oxidant or supplementary oxidant calculated according to the stoichiometric ratio required to completely oxidize the reducing agent (set as 1 mole).

[0026] Room temperature: refers to the indoor temperature. In the present invention, the room temperature is between 15-25°C, a temperature that does not require heating.

[0027] Gauge pressure: refers to the amount by which the total absolute pressure exceeds the surrounding atmospheric pressure or the pressure at a certain point in the liquid that is higher than the atmospheric pressure. In the present invention, gauge pressure refers to the pressure value higher than the atmospheric pressure. When converted to absolute pressure, the atmospheric pressure value should be added. In the present invention, if not specifically indicated, the pressure is absolute pressure.

[0028] min: indicates minutes.

[0029] H: indicates hours

[0030] M: molar concentration, mol / L

[0031] Beneficial Effects

[0032] The method for preparing manganese phosphate of the present invention has the following effects:

[0033] 1. Use lower-cost raw material manganous oxide as a manganese source to reduce production costs and greatly reduce the pressure on wastewater treatment.

[0034] 2. Using ozone or potassium permanganate as an oxidant to prepare manganese phosphate can effectively avoid the introduction of unnecessary impurities and meet the needs of battery-level applications.

[0035] 3. The present invention explores a method for efficiently preparing manganese phosphate and obtains the relationship between the appropriate phosphoric acid concentration, phosphorus-manganese ratio and reaction temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is the XRD diagram of the product in Example 2.

[0037] Figure 2 This is the SEM image of the product in Example 5. DETAILED DESCRIPTION

[0038] The present invention is further described below in conjunction with the examples. It should be noted that the examples cannot be used as a limitation on the protection scope of the present invention, and those skilled in the art understand that any improvements and changes made on the basis of the present invention are within the protection scope of the present invention.

[0039] The conventional reagents used in the following examples are all commercially available.

[0040] The ozone generator used in the embodiment of the present invention is purchased from Beijing Tonglin Technology Co., Ltd., model 3S-T10, gas production, air source ≤4.5g / h, oxygen source ≤10g / h. The air source is used in the present invention.

[0041] Example 1: 100 ml system (Mn:P=1:1)

[0042] Experimental steps and results

[0043] 1. Weigh 7.094 g (0.1 mole) of MnO,

[0044] 2. Prepare 1M HO 3 PO 4 100mL solution (6.9ml 85% H 3 PO 4 +93.1ml H 2 O)

[0045] 3. Add MnO to the phosphoric acid solution and stir at room temperature for 1 hour. When it is first added, the solution is green and the heat release is not obvious. It then turns white and precipitates white after standing. The supernatant is colorless. Continue the reaction, and the phenomenon does not change. The system still appears white.

[0046] The experiment failed and the target product, manganese phosphate, was not obtained.

[0047] Example 2 100 ml system (Mn:P=1:3)

[0048] Experimental steps and results

[0049] 1. Weigh 7.094 g (0.1 mole) of MnO,

[0050] 2. Preparation of 3M H 3 PO 4 100mL solution (20.7ml 85% H 3 PO 4 +79.3ml H 2 O)

[0051] 3. Add MnO to the phosphoric acid solution in portions and stir at room temperature. The solution is green when it is first added and quickly turns purple. Stop stirring after 1 hour.

[0052] 4. Filter by suction, the unreacted residue weighs 0.3053g. The filtrate is light pink, and the filtrate is transferred to a beaker.

[0053] 5. Add 50 ml of water (as base liquid) to the three-necked flask and heat it to 30°C; start pumping the filtrate (pumping rate: 2 ml / min) and ozone (ozone rate: 400 ml / min) into the flask at the same time. After the pumping is completed (50 min), continue to pass ozone for 4 hours; the estimated ozone input is about 2.3 g / h. A total of 11.1 g (0.232 mol) of ozone was introduced in the experiment.

[0054] 6. After cooling, filter and wash the collected green precipitate several times until the pH value of the filtrate reaches neutral. Then put the precipitate in a vacuum drying oven and dry it at 70°C. XRD confirmed that it is MnPO 4 ·H 2 O, XRD pattern see Figure 1 .

[0055] Finally, 15.0960 g of product was obtained, and the calculated total yield was: 0.0899 mole / 0.1 mole=89.9%.

[0056] Example 3 100 ml system (Mn:P=1:3)

[0057] Experimental steps and results

[0058] 1. Weigh 7.094 g (0.1 mole) of MnO.

[0059] 2. Preparation of 3M H 3 PO 4 100mL solution (20.7ml 85% H 3 PO 4 +79.3ml H 2 O).

[0060] 3. Add MnO to the phosphoric acid solution and stir at room temperature for 1 hour. The solution is green when it is first added, and quickly turns purple. After 10 minutes, it turns brown and the system becomes turbid.

[0061] 4. Filter by suction, the unreacted residue weighs 0.0084g. The filtrate is light pink, and the filtrate is transferred to a beaker.

[0062] 5. Add 50 ml of water (as base liquid) to the three-necked flask and heat it to 60°C; start pumping the filtrate (pumping rate: 2 ml / min) and ozone (ozone rate: 400 ml / min) into the flask at the same time. After the pumping is completed (50 min), continue to pass ozone for 4 hours; the estimated ozone input is about 2.3 g / h. A total of 11.1 g (0.232 mol) of ozone was introduced in the experiment.

[0063] 6. After cooling, filter and wash the collected green precipitate several times until the pH value of the filtrate reaches neutral. Then put the precipitate in a vacuum drying oven and dry it at 70°C. XRD confirmed that it is MnPO 4 ·H 2 O.

[0064] Finally, 16.2547 g of product was obtained, and the calculated total yield was: 0.0968 mole / 0.1 mole=96.8%.

[0065] Example 4 100 ml system (Mn:P=1:3)

[0066] Experimental steps and results

[0067] 1. Weigh 7.094 g (0.1 mole) of MnO.

[0068] 2. Preparation of 3M H 3 PO 4 100mL solution (20.7ml 85% H 3 PO 4 +79.3ml H 2 O).

[0069] 3. Add MnO to the phosphoric acid solution and stir at room temperature for 1 hour. The solution is green when it is first added, and quickly turns purple. After 10 minutes, it turns brown and the system becomes turbid.

[0070] 4. Filter by suction, the unreacted residue weighs 0.0162g. The filtrate is light pink, and the filtrate is transferred to a beaker.

[0071] 5. Add 50 ml of water (as base liquid) to the three-necked flask and heat it to 90°C; start pumping the filtrate (pumping rate: 2 ml / min) and ozone (ozone rate: 400 ml / min) into the flask at the same time. After the pumping is completed (50 min), continue to pass ozone for 4 hours; the estimated ozone input is about 2.3 g / h. A total of 11.1 g (0.232 mol) of ozone was introduced in the experiment.

[0072] 6. After cooling, filter and wash the collected green precipitate several times until the pH value of the filtrate reaches neutral. Then put the precipitate in a vacuum drying oven and dry it at 70°C. XRD confirmed that it is MnPO 4 ·H 2 O.

[0073] Finally, 13.8030 g of product was obtained, and the calculated total yield was: 0.0822 mole / 0.1 mole=82.2%.

[0074] Example 5 100 ml system (Mn:P=1:5)

[0075] Experimental steps and results

[0076] 1. Weigh 7.094 g (0.1 mole) of MnO.

[0077] 2. Preparation of 5 MH 3 PO 4 100mL solution (34.5ml 85% H 3 PO 4 +65.5ml H 2 O).

[0078] 3. Add MnO to the phosphoric acid solution and stir at room temperature for 1 hour. The solution is green when it is first added, and quickly turns purple. After 10 minutes, it turns brown and the system becomes turbid.

[0079] 4. Filter by suction, the unreacted residue weighs 0.5165g. The filtrate is light pink, and the filtrate is transferred to a beaker.

[0080] 5. Add 50 ml of water (as base liquid) to the three-necked flask and heat it to 30°C; start pumping the filtrate (pumping rate: 2 ml / min) and ozone (ozone rate: 400 ml / min) into the flask at the same time. After the pumping is completed (50 min), continue to pass ozone for 4 hours; the estimated ozone input is about 2.3 g / h. A total of 11.1 g (0.232 mol) of ozone was introduced in the experiment.

[0081] 6. After cooling, filter and wash the collected green precipitate several times until the pH value of the filtrate reaches neutral. Then put the precipitate in a vacuum drying oven and dry it at 70°C. XRD confirmed that it is MnPO 4 ·H 2 O.

[0082] Finally, 16.1203 g of product was obtained, and the total yield was calculated to be: 0.096 mole / 0.1 mole = 96.0%. The SEM image of the product is shown in Figure 2 From the figure, it can be seen that the manganese phosphate prepared in the experiment is a dense spherical structure, the primary particles are about 200-300nm, and the secondary particles are spherical with a size of about 10μm.

[0083] Example 6 100 ml system (Mn:P=1:5)

[0084] Experimental steps and results

[0085] 1. Weigh 7.094 g (0.1 mole) of MnO.

[0086] 2. Preparation of 5 MH 3 PO 4 100mL solution (34.5ml 85% H 3 PO 4 +65.5ml H 2 O)

[0087] 3. Add MnO to the phosphoric acid solution and stir at room temperature for 1 hour. The solution is green when it is first added, and quickly turns purple. After 10 minutes, it turns brown and the system becomes turbid.

[0088] 4. Filter by suction, the unreacted residue weighs 0.0122g. The filtrate is light pink, and the filtrate is transferred to a beaker.

[0089] 5. Add 50 ml of water (as base liquid) to the three-necked flask and heat it to 60°C; start pumping the filtrate (pumping rate: 2 ml / min) and ozone (ozone rate: 400 ml / min) into the flask at the same time. After the pumping is completed (50 min), continue to pass ozone for 4 hours; the estimated ozone input is about 2.3 g / h. A total of 11.1 g (0.232 mol) of ozone was introduced in the experiment.

[0090] 6. After cooling, filter and wash the collected green precipitate several times until the pH value of the filtrate reaches neutral. Then put the precipitate in a vacuum drying oven and dry it at 70°C. XRD confirmed that it is MnPO 4 ·H 2 O.

[0091] Finally, 15.8348 g of product was obtained, and the calculated total yield was: 0.0943 mole / 0.1 mole=94.3%.

[0092] Example 7 100 ml system (Mn:P=1:5)

[0093] Experimental steps and results

[0094] 1. Weigh 7.094 g (0.1 mole) of MnO.

[0095] 2. Preparation of 5 MH 3 PO 4 100mL solution (34.5ml 85% H 3 PO 4 +65.5ml H 2 O)

[0096] 3. Add MnO to the phosphoric acid solution and stir at room temperature for 1 hour. The solution is green when it is first added, and quickly turns purple. After 10 minutes, it turns brown and the system becomes turbid.

[0097] 4. Filter by suction, the unreacted residue weighs 0.4461 g. The filtrate is light pink, and the filtrate is transferred to a beaker.

[0098] 5. Add 50 ml of water (as base liquid) to the three-necked flask and heat it to 90°C; start pumping the filtrate (pumping rate: 2 ml / min) and ozone (ozone rate: 400 ml / min) into the flask at the same time. After the pumping is completed (50 min), continue to pass ozone for 4 hours; the estimated ozone input is about 2.3 g / h. A total of 11.1 g (0.232 mol) of ozone was introduced in the experiment.

[0099] 6. After cooling, filter and wash the collected green precipitate several times until the pH value of the filtrate reaches neutral. Then put the precipitate in a vacuum drying oven and dry it at 70°C. XRD confirmed that it is MnPO 4 ·H 2 O.

[0100] Finally, 14.4576 g of product was obtained, and the calculated total yield was: 0.0861 mole / 0.1 mole=86.1%.

[0101] Example 8 100ml system (Mn:P=1:5) / potassium permanganate as oxidant

[0102] Experimental steps and results

[0103] 1. Weigh 7.094 g (0.1 mole) of MnO.

[0104] 2. Preparation of 5 MH 3 PO 4 100mL solution (34.5ml 85% H 3 PO 4 +65.5ml H 2 O); prepare 0.5M potassium permanganate solution (0.025mol KMnO 4 Dissolve in 50ml water).

[0105] 3. Add MnO to the phosphoric acid solution and stir at room temperature for 1 hour. The solution is green when it is first added, and quickly turns purple. After 10 minutes, it turns brown and the system becomes turbid.

[0106] 4. Filter by suction, the unreacted residue weighs 0.2919 g. The filtrate is light pink, and the filtrate is transferred to a beaker.

[0107] 5. Transfer the filtrate to a three-necked flask, heat it to 90°C, and pump potassium permanganate solution into it. After the pumping is completed, react for 4 hours to end the reaction. 2+ +Mn 7+ →5Mn 3+ Calculation, 0.1 mole Mn 2+ 0.025 mole KMnO is required 4 , i.e. 3.95 g KMnO 4 .

[0108] 6. Filter and wash the collected green precipitate several times until the pH value of the filtrate reaches neutral, then place the precipitate in a vacuum drying oven and dry it at 70°C. XRD confirmed that it is MnPO 4 ·H 2 O.

[0109] Finally, 17.9180 g of product was obtained, and the calculated total yield was: 0.1067 mole / 0.125 mole=85.4%.

[0110] The final generated MnPO 4 ·H 2 O digestion was performed for full element ICP. The ICP data showed that potassium permanganate as an oxidant would cause residual K in the product, but the K content was low and had almost no effect on the product quality.

[0111] According to the test results of Examples 1-6 above, phosphoric acid concentration and reaction temperature have a significant effect on the yield. For example, in a system with a phosphoric acid concentration of 3M, the yield is highest when the reaction temperature is 60°C, and the yield is lowest at 90°C. In a system with a phosphoric acid concentration of 5M, there is no big difference in yield between the reaction temperatures of 30°C (96%) and 60°C (94.3%), but the yield is lowest at 90°C, indicating that the reaction temperature is too high. If the reaction temperature reaches 90°C, it is not conducive to the MnPO 4 Production.

[0112] The above is an explanation of the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing manganese phosphate, characterized in that: The method comprises: Step S1, reacting manganous oxide with phosphoric acid to prepare a manganous phosphate solution, Step S2, adding an equivalent molar amount or more of an oxidant to react, generating a precipitate in the reaction solution, and separating the precipitate to obtain manganese phosphate monohydrate; The phosphorus-manganese ratio is 2.5:1-20:1, and the oxidant is ozone or potassium permanganate.

2. The method according to claim 1, characterized in that The oxidant is ozone.

3. The method according to claim 1, characterized in that The phosphorus to manganese ratio is 2.9:1-8:

1.

4. The method according to any one of claims 1 to 3, characterized in that: The concentration of phosphoric acid is between 2M and 9M, preferably between 2.9M and 6M. The reaction temperature of step S2 is between room temperature and 100°C, preferably between 25°C and 75°C.

5. The method according to any one of claims 1 to 4, characterized in that: Before step S2, a solid-liquid separation step is added to remove unreacted solids and reduce impurities.

6. The method according to any one of claims 1 to 4, characterized in that: The amount of the oxidant used is 0.05-20 times the molar number of manganous oxide.

7. The method according to claim 6, characterized in that The amount of the oxidant used is 0.2-6 times the molar number of manganous oxide.

8. The method according to any one of claims 1 to 7, characterized in that: After the reaction in step S2 is completed, the product is obtained by solid-liquid separation, and the mother liquor is separated and returned to step S1.

9. The method according to claim 8, characterized in that The mother liquor reduces water content by evaporation, thereby increasing the phosphoric acid concentration in the mother liquor to meet the phosphorus-manganese ratio requirement of step S1.

10. The method according to any one of claims 1 to 9, characterized in that: When the oxidant is ozone, after the ozone gas passes through the reaction liquid, the unreacted gas is circulated back and introduced into the reaction liquid in step S2 again.

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