Method for preparing battery-grade manganese phosphate solution and lithium manganese iron phosphate positive electrode material from feed-grade manganese sulfate

Abstract

The application discloses a method for preparing battery-grade manganese phosphate solution and manganese iron phosphate lithium positive electrode material from feed-grade manganese sulfate, and relates to the technical field of chemical industry.The method comprises the following steps: dissolving feed-grade manganese sulfate crystals in water, and filtering to obtain a manganese sulfate solution; mixing the manganese sulfate solution with a saponified organic phase to perform extraction, and obtaining a manganese-rich organic phase, wherein the saponified organic phase is mainly obtained by mixing an acidic extractant, a diluent and lye; and performing back extraction on the manganese-rich organic phase after washing to obtain the battery-grade manganese phosphate solution and a back-extracted organic phase.The application selects feed-grade manganese sulfate as raw material, so that the cost is lower, and the saponified organic phase is used for extraction, so that the extraction effect is better, the battery-grade manganese phosphate solution obtained by extraction is high in purity, and the manganese iron phosphate lithium positive electrode material prepared has low impurity content.

Description

Technical Field

[0001] This invention relates to the field of chemical technology, and more specifically, to a method for preparing battery-grade manganese phosphate solution and lithium iron phosphate cathode material from feed-grade manganese sulfate. Background Technology

[0002] Manganese is a strategic resource widely used in steel smelting, chemical industry, and non-ferrous metallurgy. It is the most basic element in steel and a crucial alloying element that significantly impacts performance; all steel grades and products contain manganese. With the development of the new energy industry in recent years, manganese is also widely used in the synthesis of ternary cathode materials and lithium manganese iron phosphate, leading to a rapid increase in demand for manganese resources. Currently, the manganese sources used in the industrial synthesis of lithium manganese iron phosphate are mainly elemental manganese, battery-grade manganese sulfate, manganese nitrate, or manganese carbonate. Using these battery-grade manganese sources results in high production costs.

[0003] In view of this, the present invention is proposed. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing battery-grade manganese phosphate solution and lithium iron phosphate cathode material from feed-grade manganese sulfate. This invention uses low-cost feed-grade manganese sulfate crystals as raw material, uses an acidic extractant to separate calcium and magnesium impurities, and adopts a process route of one-stage extraction, one-stage washing, and one-stage back-extraction. The removal rate of calcium and magnesium impurities is higher than 97%. Battery-grade manganese phosphate solution is obtained by back-extraction with phosphoric acid or mixed acid containing phosphoric acid. Lithium iron phosphate cathode material can also be prepared by supplementing iron source, lithium source, etc.

[0005] This invention is implemented as follows:

[0006] In a first aspect, the present invention provides a method for preparing battery-grade manganese phosphate solution from feed-grade manganese sulfate, comprising:

[0007] Dissolve feed-grade manganese sulfate crystals in water and filter to obtain a manganese sulfate solution;

[0008] The manganese sulfate solution is mixed with the saponified organic phase for extraction to obtain a manganese-rich organic phase and raffinate. The saponified organic phase is obtained by mixing an acidic extractant, a diluent, and an alkaline solution. The manganese-rich organic phase is washed and then back-extracted to obtain a battery-grade phosphorus-manganese solution and a back-extracted organic phase.

[0009] In an optional embodiment, the saponified organic phase is obtained by adding a diluent to an acidic extractant to obtain the organic phase, and then adding an alkaline solution to saponify the organic phase.

[0010] Preferably, the acidic extractant includes one or more of C272, P507, and MEHPA;

[0011] Preferably, the molar ratio of the cations in the alkaline solution to the total calcium, magnesium, and manganese ions in the manganese sulfate solution is (2-2.1):1.

[0012] In an optional embodiment, the preparation of the saponified organic phase includes at least one of features (1)-features (4);

[0013] Feature (1): The mass ratio of the manganese sulfate solution to the saponified organic phase is 1:(2-3);

[0014] Feature (2): The mass ratio of the acidic extractant to the diluent is (3-4):(7-6);

[0015] Feature (3): The diluent includes one or more of 260# solvent oil and kerosene;

[0016] Feature (4): The alkaline solution includes any one of ammonia, sodium hydroxide and potassium hydroxide, and the molar ratio of ammonium ions or sodium ions or potassium ions in the alkaline solution to the total calcium, magnesium and manganese ions in the manganese sulfate solution is (2~2.1):1.

[0017] In an optional embodiment, the step of washing the manganese-rich organic phase and then back-extracting it to obtain a battery-grade phosphorus-manganese solution and the back-extracted organic phase includes: washing the manganese-rich organic phase with washing acid to obtain a purified manganese-rich organic phase.

[0018] Preferably, the washing acid is sulfuric acid, and the mass of the sulfuric acid is 15% to 20% of the mass of the manganese-rich organic phase;

[0019] Preferably, the hydrogen ions in the washing acid are 40% to 50% of the total molar amount of calcium, magnesium, and manganese ions in the manganese sulfate solution.

[0020] In an optional embodiment, the step of washing and back-extracting the manganese-rich organic phase to obtain a battery-grade phosphorus-manganese solution and the back-extracted organic phase includes: back-extracting the purified manganese-rich organic phase with a back-extraction acid containing at least phosphoric acid to obtain the battery-grade phosphorus-manganese solution and the back-extracted organic phase.

[0021] Preferably, the back-extraction acid includes phosphoric acid, or a mixed acid formed by phosphoric acid and one or more of sulfuric acid, nitric acid, hydrochloric acid, citric acid, acetic acid, and oxalic acid; the molar amounts of phosphorus ions and hydrogen ions in the back-extraction acid are adjusted according to the required phosphorus ion content and manganese ion content in lithium manganese iron phosphate.

[0022] In an optional embodiment, the mass of the back-extracted acid is 50% to 100% of the mass of the purified manganese-rich organic phase;

[0023] Preferably, the molar ratio of P in the back-extraction acid to Mn in the purified manganese-rich organic phase is 1:(0.5-0.8);

[0024] Preferably, the molar ratio of H ions in the back-extraction acid to Mn in the purified manganese-rich organic phase is (2-2.5):1;

[0025] In an optional embodiment, the method for preparing lithium manganese iron phosphate from feed-grade manganese sulfate further includes: washing the back-extracted organic phase with water to obtain a regenerated organic phase.

[0026] Specifically, the regenerated organic phase is the organic phase before saponification with alkali, that is, the organic phase obtained by mixing acidic extractant and diluent. In other words, the acidic extractant can be recycled in the saponified organic phase.

[0027] In an optional embodiment, the feed-grade manganese sulfate crystals have at least one of features (5) to (8) when dissolved in water;

[0028] Feature (5): The solid-liquid ratio of the feed-grade manganese sulfate crystals to the water is 1:(6-6.5);

[0029] Feature (6): The water is at least one of pure water, deionized water, distilled water and ultrapure water;

[0030] Feature (7): The temperature at which the feed-grade manganese sulfate crystals are dissolved in the water is 20-30℃;

[0031] Feature (8): The manganese sulfate solution contains: Mn 2+ The content is 40-50 g / L, Ca 2+ The content is 100-300 ppm, Mg 2+ The content is 200-400 ppm.

[0032] In an optional embodiment, the battery-grade manganese phosphorus solution contains Mn 2+ The content is 30-40 g / L, Ca 2+ The content is less than 5 ppm, Mg 2+ The content is below 5 ppm.

[0033] In a second aspect, the present invention provides a method for producing a lithium manganese iron phosphate cathode material, comprising:

[0034] The battery-grade manganese phosphorus solution is prepared by the method for preparing battery-grade manganese phosphorus solution from feed-grade manganese sulfate as described in any of the foregoing embodiments;

[0035] An iron source, a lithium source, and a carbon source were added to the battery-grade manganese phosphorus solution to obtain a lithium iron phosphate precursor.

[0036] The lithium manganese iron phosphate precursor was sintered to obtain the lithium manganese iron phosphate cathode material.

[0037] In an optional embodiment, the iron source is ferric nitrate, the lithium source is either lithium hydroxide or lithium carbonate, and the carbon source is either sucrose or glucose.

[0038] The present invention has the following beneficial effects:

[0039] This application provides a method for preparing battery-grade manganese phosphorus solution from feed-grade manganese sulfate. This method selects a specific saponified organic phase for extraction of feed-grade manganese sulfate. The saponified organic phase used in this application differs from conventional extractants. For example, using conventional P204 extractant, due to the metal extraction sequence and the physicochemical properties of the extractant itself, P204 cannot achieve the extraction effect described in this application. This method achieves a better saponification effect, resulting in a better extraction effect, laying the foundation for subsequent washing and back-extraction. The battery-grade manganese phosphorus solution obtained after extraction of feed-grade manganese sulfate has high purity, and the prepared lithium manganese iron phosphate cathode material has a low impurity content (Ca). 2+ ≤5ppm, Mg 2+ (≤5ppm); In this application, the acidic extractant in the saponified organic phase is recycled. In production, stirring power can be provided by an electric motor, and a specific extraction box is used, resulting in low energy consumption; it has a wide range of applications and is easy to operate.

[0040] Furthermore, using feed-grade manganese sulfate as a raw material results in a lower price, offering a significant cost advantage compared to existing technologies that use battery-grade manganese sulfate, industrial-grade manganese carbonate, or electrolytic manganese. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0042] This invention provides a method for preparing battery-grade manganese phosphate solution from feed-grade manganese sulfate, comprising the following steps:

[0043] S1, Dissolve.

[0044] Dissolve feed-grade manganese sulfate crystals in water, filter to obtain manganese sulfate solution and a small amount of calcium residue.

[0045] In this application, the solid-liquid ratio of feed-grade manganese sulfate crystals to water is 1:(6-6.5); the water is at least one of pure water, deionized water, distilled water, and ultrapure water; the temperature at which the feed-grade manganese sulfate crystals are dissolved in water is 20-30℃; the manganese sulfate solution contains: Mn 2+ The content is 40-50 g / L, Ca 2+The content is 100-300 ppm, Mg 2+ The content is 200-400 ppm.

[0046] S2, Extraction.

[0047] A manganese sulfate solution with a mass ratio of 1:(2-3) was mixed with a saponified organic phase and extracted to obtain a manganese-rich organic phase and raffinate.

[0048] In this application, the saponified organic phase is obtained by mixing an acidic extractant, a diluent, and an alkaline solution. Specifically, the organic phase is obtained by adding a diluent to the acidic extractant and then adding an alkaline solution to saponify the organic phase. The mass ratio of the acidic extractant to the diluent is (3-4):(7-6). The molar ratio of the cations in the alkaline solution to the total calcium, magnesium, and manganese ions in the manganese sulfate solution is (2-2.1):1.

[0049] This application obtains an organic phase by adding a diluent to an acidic extractant, then saponifying the organic phase with an alkaline solution to obtain a saponified organic phase. The saponified organic phase is then used to extract manganese sulfate solution. The saponified organic phase differs from conventional extractants. Specifically, the extractant used in this application is an acidic extractant. When it exchanges with metal ions, the metal ions enter the organic phase, while the extractant releases hydrogen ions. As the reaction proceeds, the acidity of the solution increases, which, according to chemical equilibrium, ultimately hinders the chemical reaction from proceeding to the right. To avoid this trend, this application saponifies the extractant, i.e., reacting it with an alkaline substance. Saponification stabilizes the pH during the extraction process, ensuring extraction efficiency.

[0050] In this application, a better saponification effect is achieved by strictly controlling the molar ratio of cations in the alkaline solution to the total calcium, magnesium, and manganese ions in the manganese sulfate solution. When the saponification rate is too low, the extraction will be incomplete, requiring multiple extractions. When the saponification rate is too high, some saponified organic phase will remain in the purified manganese-rich organic phase after extraction. During the washing process, this saponified organic phase neutralizes some of the hydrogen ions in the washing acid, affecting the washing effect and causing the impurities in the back-extraction solution to fail to meet the standards.

[0051] This application has found that not all acidic extractants are suitable for preparing the saponified organic phase described herein. The acidic extractants used in this application include one or more of C272, P507, and MEHPA. If other acidic extractants (e.g., P204 extractant) are used, the metal extraction sequence and the physicochemical properties of the extractant itself may lead to Ca... 2+ Mg 2+ The impurity content did not meet the standards for battery-grade manganese phosphorus solution, which resulted in the prepared lithium manganese iron phosphate failing to meet performance indicators.

[0052] The diluent includes, but is not limited to, one or more of 260# solvent oil and kerosene; the alkaline solution includes, but is not limited to, any one of ammonia, sodium hydroxide and potassium hydroxide, and the cation in the alkaline solution is specifically ammonium ion, sodium ion or potassium ion.

[0053] S3, Washing.

[0054] Washing acid was added to the manganese-rich organic phase to obtain a washing solution that purified the manganese-rich organic phase and removed calcium and magnesium impurities.

[0055] The washing acid is sulfuric acid, with a mass of 15%–20% of the manganese-rich organic phase. The hydrogen ions in the washing acid account for 40%–50% of the total molar mass of calcium, magnesium, and manganese ions in the manganese sulfate solution. In this application, by precisely controlling the amount of saponified ammonia added, and simultaneously adjusting the H ion content in the washing acid for extraction and washing, a battery-grade phosphorus-manganese solution with acceptable impurities can be obtained without pH control during the extraction process.

[0056] S4, back-extraction.

[0057] Add a back-extraction acid containing at least phosphoric acid to the purified manganese-rich organic phase to obtain a battery-grade phosphorus-manganese solution and a back-extraction organic phase.

[0058] The back-extraction acid includes phosphoric acid, or a mixed acid formed by phosphoric acid and one or more of sulfuric acid, nitric acid, hydrochloric acid, citric acid, acetic acid, and oxalic acid; the molar amounts of phosphorus ions and hydrogen ions in the back-extraction acid are adjusted according to the required phosphorus ion content and manganese ion content in lithium manganese iron phosphate.

[0059] Furthermore, this application allows for the selection of different types of back-extraction acids to obtain lithium manganese iron phosphate precursors in different proportions, resulting in a wider range of applications and simpler operation.

[0060] Specifically, the mass of the back-extraction acid is 50%–100% of the mass of the purified manganese-rich organic phase; the molar ratio of P in the back-extraction acid to Mn in the purified manganese-rich organic phase is 1:(0.5–0.8); the molar ratio of H ions in the back-extraction acid to Mn in the purified manganese-rich organic phase is (2–2.5):1; the battery-grade phosphorus-manganese solution contains: Mn 2+ The content is 30-40 g / L, Ca 2+ The content is ≤5ppm, Mg 2+ The content is ≤5ppm.

[0061] In this application, the phosphoric acid in the back-extraction acid mainly provides phosphorus and hydrogen ions. In actual production, the phosphoric acid in the back-extraction acid is prepared according to the required proportion of lithium manganese iron phosphate. If the phosphoric acid does not provide enough hydrogen ions, other acids (such as nitric acid or sulfuric acid) are added to provide hydrogen ions. By directly introducing phosphoric acid as the back-extraction acid in this application, phosphorus ions can be directly introduced. In the subsequent preparation of lithium manganese iron phosphate cathode materials, there is no need to supplement the phosphorus source again. At the same time, the addition of phosphoric acid also provides most of the hydrogen ions, which helps to reduce the amount of other acids used, thereby saving costs and optimizing the process route.

[0062] Research has shown that when the amount of phosphoric acid used in the back-extraction acid exceeds the range specified in this application, it will lead to excessive use of phosphoric acid, resulting in increased costs. Conversely, when the amount of phosphoric acid used in the back-extraction acid is too small, the phosphoric acid will not ionize to produce enough hydrogen ions, failing to completely back-extract manganese and causing unnecessary loss of manganese, thus affecting the manganese recovery rate. Therefore, controlling the amount of back-extraction acid used in this application within the above-mentioned appropriate range can ensure complete back-extraction, reduce the amount of other acids used, and thus save costs.

[0063] S5. Wash the back-extracted organic phase with water to obtain a regenerated organic phase.

[0064] In this application, by washing the back-extracted organic phase, the impurities physically entrained in the extractant can be cleaned with pure water, thereby enabling the extractant to be recycled in subsequent processes.

[0065] Furthermore, the present invention also provides a method for producing a lithium manganese iron phosphate cathode material, comprising:

[0066] The battery-grade manganese phosphate solution was prepared using the above-described method for preparing battery-grade manganese phosphate solution from feed-grade manganese sulfate.

[0067] A lithium manganese phosphate precursor is obtained by mixing an iron source, a lithium source, and a carbon source in a battery-grade manganese phosphorus solution. The iron source includes, but is not limited to, iron nitrate; the lithium source includes, but is not limited to, any one of lithium hydroxide and lithium carbonate; and the carbon source includes, but is not limited to, any one of sucrose and glucose.

[0068] The lithium manganese iron phosphate precursor is sintered to obtain the lithium manganese iron phosphate cathode material. The sintering temperature and time can be handled according to conventional sintering parameters.

[0069] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0070] Example 1

[0071] A method for preparing lithium manganese iron phosphate from feed-grade manganese sulfate includes the following steps:

[0072] (1) Take 50g of manganese sulfate crystals and dissolve them in 325g of pure water at room temperature (25℃) for 1 hour. Filter to obtain filter residue and manganese sulfate solution.

[0073] (2) Prepare 400g of organic phase with C272 extractant and 260# solvent oil in a mass ratio of 3:7. Use 25% ammonia water and control the molar ratio of ammonium ions in ammonia water to the total calcium, magnesium and manganese ions in manganese sulfate solution to be 2:1. Saponify the organic phase to obtain saponified organic phase. Take 200g of manganese sulfate solution obtained in step (1) and add it to C272 saponified organic phase for extraction to obtain manganese-rich organic phase and raffinate.

[0074] (3) Add sulfuric acid to the manganese-rich organic phase obtained in step (2). The mass of sulfuric acid is 15% of the mass of the manganese-rich organic phase. Control the hydrogen ions in the washing acid to be 45% of the total molar amount of calcium, magnesium and manganese ions in the manganese sulfate solution. A washing solution containing purified manganese-rich organic phase and calcium and magnesium impurities is obtained.

[0075] (4) Weigh phosphoric acid, the mass of which is 50% of the mass of the purified manganese-rich organic phase, and control the molar ratio of phosphorus in phosphoric acid to manganese ions in the purified manganese-rich organic phase to be 1:0.5. Back-extract the manganese-rich organic phase to obtain battery-grade phosphorus-manganese solution and organic phase.

[0076] (5) The organic phase obtained in step (4) is washed with pure water to obtain a recyclable organic phase.

[0077] (6) Take the phosphorus-manganese solution obtained in step (4), weigh lithium hydroxide, ferric nitrate and sucrose according to Li:Mn:Fe:P = 1:0.5:0.5:1 and add them to the phosphorus-manganese solution to mix and obtain lithium manganese iron phosphate precursor. Sinter the lithium manganese iron phosphate precursor to obtain lithium manganese iron phosphate.

[0078] Example 2

[0079] A method for preparing lithium manganese iron phosphate from feed-grade manganese sulfate includes the following steps:

[0080] (1) Take 20g of manganese sulfate crystals and add 130g of pure water to dissolve for 1 hour at room temperature (25℃). Filter to obtain filter residue and manganese sulfate solution.

[0081] (2) Prepare 200g of organic phase by using C272 extractant and 260# solvent oil in a mass ratio of 3:7. Use 25% ammonia water and control the molar ratio of ammonium ions in ammonia water to the total calcium, magnesium and manganese ions in manganese sulfate solution to be 2.1:1. Saponify the organic phase to obtain saponified organic phase. Take 100g of manganese sulfate solution obtained in step (1) and add it to C272 saponified organic phase for extraction to obtain manganese-rich organic phase and raffinate.

[0082] (3) Add sulfuric acid to the manganese-rich organic phase obtained in step (2). The mass of sulfuric acid is 20% of the mass of the manganese-rich organic phase. Control the hydrogen ions in the washing acid to be 50% of the total molar amount of calcium, magnesium and manganese ions in the manganese sulfate solution. A washing solution containing purified manganese-rich organic phase and calcium and magnesium impurities is obtained.

[0083] (4) Weigh out the mixed acid (a mixture of phosphoric acid and sulfuric acid), the mass of the mixed acid is 50% of the mass of the purified manganese-rich organic phase, and control the molar ratio of phosphorus in the mixed acid to manganese ions in the purified manganese-rich organic phase to be 1:0.7; the molar ratio of free hydrogen ions in the mixed acid to manganese ions in the purified manganese-rich organic phase to be 2.2:1, and perform back-extraction to obtain battery-grade phosphorus-manganese solution and organic phase.

[0084] (5) The organic phase obtained in step (4) is washed with pure water to obtain a regenerated organic phase.

[0085] (6) Take the phosphorus-manganese solution obtained in step (4), weigh lithium carbonate and iron nitrate according to Li:Mn:Fe:P = 1:0.7:0.3:1 and add them to the phosphorus-manganese solution to mix and obtain lithium manganese iron phosphate precursor. Then, sinter the lithium manganese iron phosphate precursor to obtain lithium manganese iron phosphate.

[0086] Example 3

[0087] A method for preparing lithium manganese iron phosphate from feed-grade manganese sulfate includes the following steps:

[0088] (1) Take 50g of manganese sulfate crystals and add 325g of pure water to dissolve for 1 hour at room temperature (25℃). Filter to obtain filter residue and manganese sulfate solution.

[0089] (2) Prepare 400g of organic phase with C272 extractant and 260# solvent oil in a mass ratio of 4:6. Use 25% ammonia water and control the molar ratio of ammonium ions in ammonia water to the total calcium, magnesium and manganese ions in manganese sulfate solution to be 2:1. Saponify the organic phase to obtain saponified organic phase. Take 200g of manganese sulfate solution obtained in step (1) and add it to C272 saponified organic phase for extraction to obtain manganese-rich organic phase and raffinate.

[0090] (3) Add sulfuric acid to the manganese-rich organic phase obtained in step (2). The mass of sulfuric acid is 15% of the mass of the manganese-rich organic phase. Control the hydrogen ions in the washing acid to be 48% of the total molar amount of calcium, magnesium and manganese ions in the manganese sulfate solution. A washing solution containing purified manganese-rich organic phase and calcium and magnesium impurities is obtained.

[0091] (4) Weigh out the mixed acid (a mixture of phosphoric acid and nitric acid), the mass of the mixed acid is 50% of the mass of the purified manganese-rich organic phase, and control the molar ratio of phosphorus in the mixed acid to manganese ions in the purified manganese-rich organic phase to be 1:0.8; the molar ratio of free hydrogen ions in the mixed acid to manganese ions in the purified manganese-rich organic phase to be 2.5:1, and perform back-extraction to obtain battery-grade phosphorus-manganese solution and organic phase.

[0092] (5) The organic phase obtained in step (4) is washed with pure water to obtain a regenerated organic phase.

[0093] (6) Take the phosphorus-containing manganese solution obtained in step (4), weigh lithium hydroxide, ferric nitrate and glucose according to Li:Mn:Fe:P = 1:0.8:0.2:1 and add them to the phosphorus-manganese solution to mix and obtain lithium manganese iron phosphate precursor. Sinter the lithium manganese iron phosphate precursor to obtain lithium manganese iron phosphate.

[0094] Example 4

[0095] A method for preparing lithium manganese iron phosphate from feed-grade manganese sulfate includes the following steps:

[0096] (1) Take 50g of manganese sulfate crystals, add 300g of deionized water and dissolve at 30℃ for 1h, filter, and obtain filter residue and manganese sulfate solution;

[0097] (2) Prepare 400g of compound organic phase according to the mass ratio of P507 extractant, MEHPA extractant and 260# solvent oil of 1:2:7, and use 25% ammonia water, and control the molar ratio of ammonium ions in ammonia water to the total calcium, magnesium and manganese ions in manganese sulfate solution to be 2:1. Saponify the organic phase to obtain saponified organic phase. Take 200g of manganese sulfate solution obtained in step (1) and add it to the compound saponified organic phase for extraction to obtain manganese-rich organic phase and raffinate.

[0098] (3) Add sulfuric acid to the manganese-rich organic phase obtained in step (2). The mass of sulfuric acid is 15% of the mass of the manganese-rich organic phase. Control the hydrogen ions in the washing acid to be 48% of the total molar amount of calcium, magnesium and manganese ions in the manganese sulfate solution. A washing solution containing purified manganese-rich organic phase and calcium and magnesium impurities is obtained.

[0099] (4) Weigh out a mixed acid (a mixture of phosphoric acid, sulfuric acid and nitric acid), the mass of which is 50% of the mass of the purified manganese-rich organic phase, and control the molar ratio of phosphorus in the mixed acid to manganese ions in the purified manganese-rich organic phase to be 1:0.8; the molar ratio of free hydrogen ions in the mixed acid to manganese ions in the purified manganese-rich organic phase to be 2.5:1. Perform back-extraction to obtain a battery-grade phosphorus-manganese solution and an organic phase.

[0100] (5) The organic phase obtained in step (4) is washed with pure water to obtain a regenerated organic phase.

[0101] (6) Take the phosphorus-containing manganese solution obtained in step (4), weigh lithium hydroxide, ferric nitrate and glucose according to Li:Mn:Fe:P = 1:0.8:0.2:1 and add them to the phosphorus-manganese solution to mix and obtain lithium manganese iron phosphate precursor. Sinter the lithium manganese iron phosphate precursor to obtain lithium manganese iron phosphate.

[0102] Comparative Example 1

[0103] This comparative example is essentially the same as Example 1, except that the acidic extractant used in this comparative example is P204 extractant. Specifically, this comparative example provides a method for preparing a lithium manganese iron phosphate precursor, comprising the following steps:

[0104] (1) Take 50g of manganese sulfate crystals and add 325g of pure water to dissolve for 1 hour at room temperature (25℃). Filter to obtain filter residue and manganese sulfate solution.

[0105] (2) Prepare 400g of organic phase with a mass ratio of P204 extractant to 260# solvent oil of 3:7, and use 25% ammonia water, and control the molar ratio of ammonium ions in ammonia water to the total calcium, magnesium and manganese ions in manganese sulfate solution to be 2:1. Saponify the organic phase to obtain saponified organic phase. Take 200g of manganese sulfate solution obtained in step (1) and add it to the P204 saponified organic phase for extraction to obtain manganese-rich organic phase and raffinate.

[0106] (3) Add sulfuric acid to the manganese-rich organic phase obtained in step (2). The mass of sulfuric acid is 15% of the mass of the manganese-rich organic phase. Control the hydrogen ions in the washing acid to be 45% of the total molar amount of calcium, magnesium and manganese ions in the manganese sulfate solution.

[0107] (4) Weigh phosphoric acid, the mass of which is 50% of the mass of the purified manganese-rich organic phase, and control the molar ratio of phosphorus in phosphoric acid to manganese ions in the purified manganese-rich organic phase to be 1:0.5. Back-extract the manganese-rich organic phase to obtain battery-grade phosphorus-manganese solution and organic phase.

[0108] (5) Take the phosphorus-manganese solution obtained in step (4), weigh lithium hydroxide, ferric nitrate and sucrose according to Li:Mn:Fe:P = 1:0.5:0.5:1 and add them to the phosphorus-manganese solution to mix and obtain lithium manganese iron phosphate precursor. Sinter the lithium manganese iron phosphate precursor to obtain lithium manganese iron phosphate.

[0109] Comparative Example 2

[0110] This comparative example is essentially the same as Example 1, except that the molar ratio of ammonium ions in ammonia water to the total calcium, magnesium, and manganese ions in manganese sulfate solution is 2.3:1. Specifically, this comparative example provides a method for preparing a lithium manganese iron phosphate precursor, comprising the following steps:

[0111] (1) Take 50g of manganese sulfate crystals and dissolve them in 325g of pure water at room temperature for 1 hour. Filter the solution to obtain the filter residue and manganese sulfate solution.

[0112] (2) Prepare 400g of organic phase with C272 extractant and 260# solvent oil in a mass ratio of 3:7. Use 25% ammonia water and control the molar ratio of ammonium ions in ammonia water to the total calcium, magnesium and manganese ions in manganese sulfate solution to be 2.3:1. Saponify the organic phase to obtain saponified organic phase. Take 200g of manganese sulfate solution obtained in step (1) and add it to C272 saponified organic phase for extraction to obtain manganese-rich organic phase and raffinate.

[0113] (3) Add sulfuric acid to the manganese-rich organic phase obtained in step (2). The mass of sulfuric acid is 15% of the mass of the manganese-rich organic phase. Control the hydrogen ions in the washing acid to be 45% of the total molar amount of calcium, magnesium and manganese ions in the manganese sulfate solution.

[0114] (4) Weigh phosphoric acid, the mass of which is 50% of the mass of the purified manganese-rich organic phase, and control the molar ratio of phosphorus in phosphoric acid to manganese ions in the purified manganese-rich organic phase to be 1:0.5. Back-extract the manganese-rich organic phase to obtain battery-grade phosphorus-manganese solution and organic phase.

[0115] (5) Take the phosphorus-manganese solution obtained in step (4), weigh lithium hydroxide, ferric nitrate and sucrose according to Li:Mn:Fe:P = 1:0.5:0.5:1 and add them to the phosphorus-manganese solution to mix and obtain lithium manganese iron phosphate precursor. Sinter the lithium manganese iron phosphate precursor to obtain lithium manganese iron phosphate.

[0116] Comparative Example 3

[0117] This comparative example is basically the same as Example 1, except that: the mass of the washing acid used in this comparative example is 10% of the mass of the manganese-rich organic phase, and the hydrogen ions in the washing acid are 30% of the total molar amount of calcium, magnesium and manganese ions in the manganese sulfate solution.

[0118] Experimental Example

[0119] The battery-grade phosphorus-manganese solutions obtained after back-extraction using the methods provided in Examples 1-4 and Comparative Examples 1-3 were tested, and the test results are shown in Table 1.

[0120] Table 1. Statistical Table of Metal Element Content in Raw Materials and Battery-Grade Phosphorus-Manganese Solution

[0121]

[0122] As can be seen from the table above, the phosphorus-manganese solution obtained by the method provided in Examples 1-4 of this application contains Ca... 2+ Mg 2+ The impurity content can reach the standard of battery-grade phosphorus and manganese solution, resulting in lithium manganese iron phosphate with excellent performance.

[0123] The data from Comparative Example 1 show that the phosphorus-manganese solution obtained after the above P204 extraction, washing, and back-extraction processes contains Ca... 2 + Mg 2+ Impurity content failing to meet battery-grade manganese phosphorus solution standards will result in substandard performance of the prepared lithium manganese iron phosphate. The reason for this is that the metal extraction order of P204 is Ca > Mn > Mg. With a constant amount of washing acid, the washing process prioritizes Mg > Mn > Ca in the aqueous phase, leading to greater Mn loss during washing compared to C272, and also affecting the Ca content. 2+ Incomplete washing ultimately affects the Ca content in the back-extraction solution. 2+ Impurities do not meet standards.

[0124] The data from Comparative Example 2 show that the phosphorus-manganese solution obtained after extraction, washing, and back-extraction using the above method contains Ca... 2 + Mg 2+ If the impurity content does not meet the battery-grade manganese phosphate solution standard, the performance indicators of the prepared lithium manganese iron phosphate will fail to meet the requirements. Analysis shows that the molar ratio of ammonium ions in the ammonia solution to the total calcium, magnesium, and manganese ions in the manganese sulfate solution is 2.3:1. At this point, there is excess ammonia, leading to an excessively high saponification rate. Even after the extraction stage, the purified manganese-rich organic phase still contains some saponified organic phase. During the washing process, this saponified organic phase neutralizes some of the hydrogen ions in the washing acid, affecting the washing effect and resulting in substandard impurities in the back-extraction solution.

[0125] As can be seen from the data in Comparative Example 3, in our study on the amount of washing acid, we found that when the amount of washing acid is less than the range specified in this application, it leads to incomplete washing of impurities, ultimately resulting in excessive calcium and magnesium content in the back-extraction acid. Furthermore, when the amount of washing acid is greater than that specified in this application, it causes a significant loss of manganese (>25%), necessitating further experiments.

[0126] In summary, the method for preparing battery-grade manganese phosphate solution from feed-grade manganese sulfate provided in this application involves selecting a specific saponified organic phase for extraction of feed-grade manganese sulfate. The saponified organic phase used in this application differs from conventional extractants. Taking conventional P204 extractant as an example, due to the metal extraction sequence and the physicochemical properties of the extractant itself, P204 cannot achieve the extraction effect described in this application. This application achieves better saponification and thus better extraction by strictly controlling the selection of the acidic extractant in the saponified organic phase and the molar ratio of cations in the alkaline solution to the total calcium, magnesium, and manganese ions in the manganese sulfate solution. This lays the foundation for subsequent washing and back-extraction. The manganese-containing solution obtained after extraction of feed-grade manganese sulfate has high purity, and the prepared lithium manganese iron phosphate has low impurity content (Ca). 2+ ≤5ppm, Mg 2+(≤5ppm); In this application, the acidic extractant in the saponified organic phase is recycled. In production, stirring power is provided by an electric motor, and a specific extraction tank is used, resulting in low energy consumption. Furthermore, this application allows for the selection of different types of back-extraction acids to obtain different battery-grade manganese phosphorus solutions (e.g., battery-grade manganese phosphate, phosphorus-manganese mixed solution), which are used to prepare lithium iron phosphate precursors with different proportions, thus expanding the application range and simplifying the operation. Further, feed-grade manganese sulfate is used as a raw material, which has a lower raw material cost than other battery-grade manganese sources, offering a certain cost advantage.

[0127] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing battery-grade manganese phosphate solution from feed-grade manganese sulfate, characterized in that, Includes the following steps: Dissolve feed-grade manganese sulfate crystals in water and filter to obtain a manganese sulfate solution; The manganese sulfate solution is mixed with the saponified organic phase for extraction to obtain a manganese-rich organic phase and raffinate; wherein the saponified organic phase is mainly obtained by mixing an acidic extractant, a diluent and an alkaline solution, and the acidic extractant includes one or more of C272, P507 and MEHPA; After washing the manganese-rich organic phase, a purified manganese-rich organic phase is obtained; the purified manganese-rich organic phase is back-extracted using a back-extraction acid containing at least phosphoric acid to obtain a battery-grade phosphorus-manganese solution and a back-extracted organic phase, wherein the back-extraction acid includes phosphoric acid, or a mixed acid formed by phosphoric acid and one or more of sulfuric acid, nitric acid, hydrochloric acid, citric acid, acetic acid, and oxalic acid. The battery-grade phosphorus-manganese solution is used to prepare lithium iron phosphate cathode material.

2. The method for preparing battery-grade manganese phosphate solution from feed-grade manganese sulfate according to claim 1, characterized in that, The saponified organic phase is obtained by adding the diluent to the acidic extractant to obtain the organic phase, and then adding the alkali solution to saponify the organic phase.

3. The method for preparing battery-grade manganese phosphate solution from feed-grade manganese sulfate according to claim 1, characterized in that, The molar ratio of the cations in the alkaline solution to the total calcium, magnesium and manganese ions in the manganese sulfate solution is (2~2.1):

1.

4. The method for preparing battery-grade manganese phosphate solution from feed-grade manganese sulfate according to claim 1, characterized in that, The process of mixing the manganese sulfate solution with the saponified organic phase for extraction includes at least one of features (1) to features (4); Feature (1): The mass ratio of the manganese sulfate solution to the saponified organic phase is 1:(2~3); Feature (2): The mass ratio of the acidic extractant to the diluent is (3~4):(7~6); Feature (3): The diluent includes at least one of 260# solvent oil and kerosene; Feature (4): The alkaline solution includes any one of ammonia, sodium hydroxide and potassium hydroxide, and the molar ratio of ammonium ions or sodium ions or potassium ions in the alkaline solution to the total calcium, magnesium and manganese ions in the manganese sulfate solution is (2~2.1):

1.

5. The method for preparing battery-grade manganese phosphate solution from feed-grade manganese sulfate according to claim 1, characterized in that, The step of washing the manganese-rich organic phase and then back-extracting it to obtain a battery-grade phosphorus-manganese solution and a back-extracted organic phase includes: washing the manganese-rich organic phase with washing acid to obtain a purified manganese-rich organic phase.

6. The method for preparing battery-grade manganese phosphate solution from feed-grade manganese sulfate according to claim 5, characterized in that, The washing acid is sulfuric acid, and the mass of the sulfuric acid is 15% to 20% of the mass of the manganese-rich organic phase.

7. The method for preparing battery-grade manganese phosphate solution from feed-grade manganese sulfate according to claim 5, characterized in that, The hydrogen ions in the washing acid are 40% to 50% of the total molar amount of calcium, magnesium, and manganese ions in the manganese sulfate solution.

8. The method for preparing battery-grade manganese phosphate solution from feed-grade manganese sulfate according to claim 1, characterized in that, The molar amounts of phosphorus and hydrogen ions in the back-extracting acid are adjusted according to the required phosphorus and manganese ion content in the lithium manganese iron phosphate.

9. The method for preparing battery-grade manganese phosphate solution from feed-grade manganese sulfate according to claim 1, characterized in that, The mass of the back-extracting acid is 50% to 100% of the mass of the purified manganese-rich organic phase.

10. The method for preparing battery-grade manganese phosphate solution from feed-grade manganese sulfate according to claim 1, characterized in that, The molar ratio of P in the back-extraction acid to Mn in the purified manganese-rich organic phase is 1:(0.5~0.8).

11. The method for preparing battery-grade manganese phosphate solution from feed-grade manganese sulfate according to claim 1, characterized in that, The molar ratio of H ions in the back-extracting acid to Mn in the purified manganese-rich organic phase is (2~2.5):

1.

12. The method for preparing battery-grade manganese phosphate solution from feed-grade manganese sulfate according to any one of claims 1 to 11, characterized in that, The method for preparing battery-grade manganese phosphate solution from feed-grade manganese sulfate further includes: washing the back-extracted organic phase with water to obtain a regenerated organic phase.

13. The method for preparing battery-grade manganese phosphate solution from feed-grade manganese sulfate according to claim 1, characterized in that, When the feed-grade manganese sulfate crystals are dissolved in water, they have at least one of the characteristics (5) to (8); Feature (5): The solid-liquid ratio of the feed-grade manganese sulfate crystals to the water is 1:(6~6.5); Feature (6): The water is at least one of pure water, deionized water, distilled water and ultrapure water; Feature (7): The temperature at which the feed-grade manganese sulfate crystals are dissolved in the water is 20-30℃; Feature (8): The manganese sulfate solution contains: Mn 2+ The content is 40~50g / L, Ca 2+ The content is 100~300ppm, Mg 2+ The content is 200~400ppm.

14. The method for preparing battery-grade manganese phosphate solution from feed-grade manganese sulfate according to claim 1, characterized in that, In the battery-grade phosphorus-manganese solution, Mn 2+ The content is 30~40g / L, Ca 2+ The content is less than 5 ppm, Mg 2+ The content is below 5 ppm.

15. A method for preparing a lithium iron phosphate cathode material, characterized in that, It includes: The method for preparing battery-grade manganese phosphorus solution according to any one of claims 1 to 14 is used to prepare battery-grade manganese phosphorus solution; An iron source, a lithium source, and a carbon source were added to the battery-grade manganese phosphorus solution to obtain a lithium iron phosphate precursor. The lithium manganese iron phosphate precursor was sintered to obtain the lithium manganese iron phosphate cathode material.

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