Method for preparing lithium manganese iron phosphate from waste lithium iron phosphate lithium extraction residue

Abstract

The application provides a method for preparing lithium manganese iron phosphate from waste lithium iron phosphate lithium extraction residue, and relates to the technical field of waste battery recycling. The method comprises the following steps: S1: mixing the waste lithium iron phosphate lithium extraction residue with manganese powder and phosphoric acid to obtain a mixture; S2: performing ball milling treatment on the mixture to obtain a reaction solution; performing solid-liquid separation on the reaction solution to obtain a solid residue and a filtrate containing divalent iron and divalent manganese; S3: mixing the filtrate with a lithium source, adjusting the pH, and performing a hydrothermal reaction, so that Li(Fe x ,Mn 1‑x )PO4 solid is obtained after filtration; and S4: mixing the Li(Fe x ,Mn 1‑x )PO4 solid with a carbon source, and performing solid-phase sintering under a protective atmosphere to obtain a carbon-coated lithium manganese iron phosphate material. The method for preparing lithium manganese iron phosphate from waste lithium iron phosphate lithium extraction residue has low reagent consumption, a short process flow, high product uniformity, and is suitable for industrial production.

Description

Technical Field

[0001] This invention relates to the field of waste battery recycling technology, and in particular to a method for recovering and preparing lithium manganese iron phosphate from waste lithium iron phosphate lithium extraction residue. Background Technology

[0002] With the booming development of the new energy vehicle industry, lithium iron phosphate batteries have dominated the power battery market due to their high safety, long cycle life, and low cost. Currently, the industry mainly uses hydrometallurgical processes to recycle waste lithium iron phosphate electrode powder after dismantling. While the mainstream "selective lithium extraction" technology can effectively recover lithium resources, it has led to the long-term neglect of iron and phosphorus resources, which account for more than 70% of the cathode mass. Statistics show that every ton of lithium carbonate recovered generates 4 to 5 tons of iron and phosphorus slag. Although sulfuric acid leaching-alkali precipitation is a conventional method for treating this iron and phosphorus slag, its economic benefits are not ideal due to the high cost of reagents and wastewater treatment.

[0003] In recent years, upgrading and regenerating iron-phosphorus slag into lithium manganese iron phosphate materials has become a research hotspot. However, existing technologies still face significant bottlenecks. For example, the patent with publication number CN 1150902B uses a two-stage sulfuric acid leaching combined with solid-phase sintering process. Although it can synthesize the target product, it faces problems such as complex process, large acid consumption, and poor product uniformity in the solid-phase method. The patent with publication number CN119263249A uses a route of adding manganese source after phosphoric acid leaching and co-precipitating precursor by adjusting pH value before hydrothermal synthesis. However, since the iron in iron-phosphorus slag mainly exists in the insoluble trivalent state, this process not only consumes a huge amount of phosphoric acid, but also requires a large amount of alkali solution in the subsequent neutralization process, resulting in a surge in acid and alkali costs and the generation of a large amount of phosphorus-containing wastewater, making it difficult to achieve green and efficient resource utilization. Summary of the Invention

[0004] To address the technical problems existing in the prior art, this invention provides a method for recovering and preparing lithium manganese iron phosphate from waste lithium iron phosphate residue. This method features low reagent consumption, a short process flow, and high product uniformity. The technical solution is as follows:

[0005] This invention provides a method for recovering lithium iron phosphate residue from waste lithium iron phosphate to prepare lithium manganese iron phosphate, comprising the following steps:

[0006] S1: Mix waste lithium iron phosphate residue with manganese powder and phosphoric acid to obtain a mixture; wherein, the molar ratio of manganese powder to iron in lithium iron phosphate residue is (0.5~2.0):1, and the molar ratio of phosphoric acid to (manganese powder + iron in lithium iron phosphate residue) is (1.0~1.5):1.

[0007] S2: The mixture from step S1 is ball-milled at a speed of 100~500 rpm for 0.5~2 h to obtain a reaction solution; the reaction solution is subjected to solid-liquid separation to obtain a solid residue and a filtrate containing ferrous iron and ferrous manganese.

[0008] S3: Mix the filtrate from step S2 with a lithium source, adjust the pH to 5-11, and carry out a hydrothermal reaction at 180-240℃ for 6-12 hours. After filtration, Li(Fe)2 is obtained. x ,Mn 1-x PO4 solid;

[0009] S4: The Li(Fe) from step S3... x ,Mn 1-x Solid PO4 is mixed with a carbon source and sintered under a protective atmosphere to obtain carbon-coated lithium manganese iron phosphate material.

[0010] Existing technologies use FePO4 in iron-phosphate slag because the iron exists in the form of ferric iron (Fe3+), which combines with phosphate to form FePO4, a highly stable crystal structure with extremely low solubility in water. Therefore, to dissolve solid FePO4 into the solution, a high concentration of H2O is required. + Using excessive inorganic acid to drive dissolution not only results in huge acid consumption but also generates a large amount of saline wastewater in the subsequent neutralization process, leading to high environmental costs. In contrast, this application employs a ball milling-assisted manganese powder reduction leaching method with low phosphoric acid dosage, which significantly enhances the in-situ reduction reaction between manganese powder and iron-phosphorus slag. This avoids the loss of reducing capacity due to the reaction of large amounts of manganese powder with phosphoric acid. The introduced metallic manganese powder serves as both a manganese source and an in-situ reducing agent, efficiently reducing the poorly soluble ferric iron to the easily soluble ferrous iron. Thus, efficient leaching of iron and manganese is achieved without introducing impurities and with extremely low acid consumption.

[0011] Optionally, the lithium source is one or more of lithium hydroxide, lithium sulfate, lithium chloride, lithium nitrate, or organic lithium salts.

[0012] Optionally, the carbon source is glucose.

[0013] Optionally, in step S2, the mass ratio of the balls is (5~50):1.

[0014] Optionally, in step S3, the molar ratio of lithium in the solution to (manganese and iron in the solution) is (1~2):1.

[0015] Optionally, in step S4, the solid-state sintering temperature is 500~800℃ and the sintering time is 2~8h.

[0016] The beneficial effects of the technical solutions provided in the embodiments of the present invention include at least the following:

[0017] This invention discloses a method for recovering and preparing lithium manganese iron phosphate from waste lithium iron phosphate residue. Through mechanochemical assistance and in-situ reduction with metallic manganese powder, it achieves efficient reduction of trivalent iron and simultaneous deep dissolution of iron and manganese elements from the waste lithium iron phosphate residue under mild conditions with low phosphoric acid dosage. This not only significantly reduces reagent consumption and the risk of impurity introduction, but also allows for direct hydrothermal synthesis of the resulting leachate with a lithium source. Utilizing a high-temperature homogeneous environment, it achieves molecular-level uniform mixing of all elements, effectively overcoming the uneven mixing defects of traditional solid-phase methods. This constructs a high-value utilization scheme for waste lithium iron phosphate residue that integrates low reagent consumption, short process flow, and high product uniformity. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is the XRD pattern of the iron-phosphorus slag after lithium extraction in an embodiment of the present invention;

[0020] Figure 2 This is a scanning electron microscope (SEM) image of the iron-phosphorus slag after lithium extraction in an embodiment of the present invention.

[0021] Figure 3 This is the XRD pattern of the solid slag in Example 1 of the present invention;

[0022] Figure 4 This is a scanning electron microscope (SEM) image of the solid slag in Example 1 of this invention;

[0023] Figure 5 This is the XRD pattern of lithium manganese iron phosphate synthesized in Example 1 of the present invention. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0025] Example 1

[0026] A method for recovering lithium iron phosphate residue from waste lithium iron phosphate to prepare lithium manganese iron phosphate includes the following steps:

[0027] S1: Mix waste lithium iron phosphate residue with manganese powder and phosphoric acid solution to obtain a mixture; the molar ratio of manganese powder to iron in lithium iron phosphate residue is 0.5:1, and the molar ratio of phosphoric acid to (manganese powder + iron in lithium iron phosphate residue) is 1.2:1.

[0028] S2: The mixture from step S1 was ball-milled at 300 rpm for 1 hour with a ball-to-material ratio of 20:1 to obtain a reaction solution; the reaction solution was subjected to solid-liquid separation to obtain a solid residue and a filtrate containing ferrous iron and ferrous manganese; wherein the leaching rates of iron and manganese were 98.6% and 99.2%, respectively.

[0029] S3: Add the filtrate from step S2 to a high-pressure reactor, then add lithium hydroxide to the reactor to make the molar ratio of lithium to (manganese + iron) in the solution 1.5:1. Adjust the pH to 7, and carry out a hydrothermal reaction at 200℃ for 4 hours. After filtration, washing with ethanol, and drying, Li(Fe) is obtained. x ,Mn 1-x PO4 cathode material;

[0030] S4: The Li(Fe) from step S3... x ,Mn 1-x PO4 cathode material was mixed with 10 wt.% glucose and sintered in solid state at 650℃ for 5 h in an argon atmosphere to obtain carbon-coated lithium manganese iron phosphate material. The lithium manganese iron phosphate material had an initial discharge specific capacity of 155.4 mAh / g at a current density of 0.1C, a coulombic efficiency of 99.7%, and a capacity retention rate of 95.6% after 100 charge-discharge cycles at 0.5C.

[0031] Example 2

[0032] A method for recovering lithium iron phosphate residue from waste lithium iron phosphate to prepare lithium manganese iron phosphate, the steps of which are the same as in Example 1, except that:

[0033] In step S1, the molar ratio of phosphoric acid to (manganese powder + iron from lithium iron phosphate residue) is 1:1; after step S2, the leaching rates of iron and manganese are 97.1% and 98.3%, respectively.

[0034] In step S3, the hydrothermal reaction temperature is 180℃ and the reaction time is 4h;

[0035] The lithium manganese iron phosphate material obtained after step S4 has an initial discharge specific capacity of 149.3 mAh / g at a current density of 0.1C, a coulombic efficiency of 95.2%, and a capacity retention rate of 92.3% after 100 charge-discharge cycles at 0.5C.

[0036] Example 3

[0037] A method for recovering lithium iron phosphate residue from waste lithium iron phosphate to prepare lithium manganese iron phosphate, the steps of which are the same as in Example 1, except that:

[0038] In step S1, the molar ratio of phosphoric acid to (manganese powder + iron from lithium iron phosphate residue) is 1.4:1; after step S2, the leaching rates of iron and manganese are 99.2% and 99.5%, respectively.

[0039] In step S3, the hydrothermal reaction temperature is 220℃ and the reaction time is 4h;

[0040] The lithium manganese iron phosphate material obtained after step S4 has an initial discharge specific capacity of 153.6 mAh / g at a current density of 0.1C, a coulombic efficiency of 98.5%, and a capacity retention rate of 94.1% after 100 charge-discharge cycles at 0.5C.

[0041] Example 4

[0042] A method for recovering lithium iron phosphate residue from waste lithium iron phosphate to prepare lithium manganese iron phosphate, the steps of which are the same as in Example 1, except that:

[0043] In step S1, the molar ratio of phosphoric acid to (manganese powder + iron from lithium iron phosphate residue) is 1.3:1; after step S2, the leaching rates of iron and manganese are 99.0% and 99.2%, respectively.

[0044] In step S3, the hydrothermal reaction temperature is 190℃ and the reaction time is 5h;

[0045] The lithium manganese iron phosphate material obtained after step S4 has an initial discharge specific capacity of 153.2 mAh / g at a current density of 0.1C, a coulombic efficiency of 98.2%, and a capacity retention rate of 92.7% after 100 charge-discharge cycles at 0.5C.

[0046] Comparative Example 1

[0047] A method for recovering lithium iron phosphate residue from waste lithium iron phosphate to prepare lithium manganese iron phosphate, the steps of which are the same as in Example 1, except that:

[0048] In step S1, the manganese powder was replaced with manganese sulfate. Since manganese sulfate lacks reducing power, effective iron leaching is difficult to achieve using only phosphoric acid and mechanical ball milling, resulting in an extremely low iron leaching rate of only 9.2% in the iron-phosphorus slag.

[0049] Comparative Example 2

[0050] A method for recovering lithium iron phosphate residue from waste lithium iron phosphate to prepare lithium manganese iron phosphate, the steps of which are the same as in Example 1, except that:

[0051] In step S1, the manganese powder was replaced with manganese dioxide. Since manganese dioxide lacks reducing power, effective leaching of iron is difficult to achieve using only phosphoric acid and mechanical ball milling, resulting in extremely low leaching rates of both iron and manganese in the system, at 8.3% and 0.4%, respectively.

[0052] Comparative Example 3

[0053] A method for recovering lithium iron phosphate residue from waste lithium iron phosphate to prepare lithium manganese iron phosphate, the steps of which are the same as in Example 1, except that:

[0054] The manganese powder in step S1 was replaced with carbon powder. This is because the iron-phosphorus slag after lithium extraction already contains carbon, and carbon powder has a very weak reducing ability at room temperature, resulting in a final iron leaching rate of only 5.8%.

[0055] Comparative Example 4

[0056] A method for recovering lithium iron phosphate residue from waste lithium iron phosphate to prepare lithium manganese iron phosphate, the steps of which are the same as in Example 1, except that:

[0057] In step S2, without ball milling, phosphoric acid reacts first with the more reactive manganese powder, resulting in almost no iron leaching, with a leaching rate of only 0.6% and a manganese leaching rate of 84.0%.

[0058] Comparative Example 5

[0059] A method for recovering lithium iron phosphate residue from waste lithium iron phosphate to prepare lithium manganese iron phosphate, the steps of which are the same as in Example 1, except that:

[0060] The molar ratio of phosphoric acid to (manganese powder + iron from lithium iron phosphate residue) in step S1 is 0.5:1. The decrease in phosphoric acid content leads to a decrease in the leaching rates of both iron and manganese in the system, to 41.5% and 43.2%, respectively.

[0061] Comparative Example 6

[0062] A method for recovering lithium iron phosphate residue from waste lithium iron phosphate to prepare lithium manganese iron phosphate, the steps of which are the same as in Example 1, except that:

[0063] The molar ratio of phosphoric acid to (manganese powder + iron from lithium iron phosphate extraction residue) in step S1 is 3:1. Both iron and manganese leaching rates can reach over 99%, but the excessive amount of phosphate is detrimental to the subsequent hydrothermal synthesis of lithium iron phosphate materials.

[0064] The lithium manganese iron phosphate materials prepared in the above embodiments and comparative examples were subjected to systematic electrochemical performance and physicochemical index testing under the same test conditions. Specific performance test results are shown in Table 1. The elemental composition of the iron-phosphate slag after lithium extraction is shown in Table 2.

[0065] Table 1

[0066] Phosphoric acid dosage Ball mill speed manganese source Iron leaching rate Manganese leaching rate 0.1C initial discharge specific capacity / mAh / g Capacity retention rate after 100 charge-discharge cycles at 0.5C Coulomb efficiency Example 1 1.2 300 manganese powder 98.6% 99.2% 155.4 95.6% 99.7% Example 2 1.0 300 manganese powder 97.1% 98.3% 149.3 92.3% 95.2% Example 3 1.4 300 manganese powder 99.2% 99.5% 153.6 94.1% 98.5% Example 4 1.3 300 manganese powder 99.0% 99.2% 153.2 92.7% 98.2% Comparative Example 1 1.2 300 manganese sulfate 9.2% \ \ \ \ Comparative Example 2 1.2 300 Manganese dioxide 8.3% 0.4% \ \ \ Comparative Example 3 1.2 300 toner 5.8% \ \ \ \ Comparative Example 4 1.2 0 manganese powder 0.6% 84.0% \ \ \ Comparative Example 5 0.5 300 manganese powder 41.5% 43.2% \ \ \ Comparative Example 6 3 300 manganese powder 99.4% 99.7% \ \ \

[0067] Table 2

[0068] element Fe P Li Al Cu C Content (wt%) 29.6 23.17 0.18 0.47 0.04 46.54

[0069] Comparing Examples 1-4 of this invention with Comparative Examples 1, 2, and 3, it can be seen that when manganese sulfate, manganese dioxide, or carbon powder with extremely weak reducing ability at room temperature are used to replace manganese powder, the leaching rate of iron in iron-phosphorus slag is extremely low (less than 10%). This fully demonstrates that in a low-phosphoric acid system, manganese powder can effectively drive the dissolution of ferric iron through in-situ redox reactions.

[0070] The data from Comparative Example 4 show that if the high-energy ball milling step is omitted, the leaching rate of iron will plummet to below 1% if only conventional stirring or simple mixing is used. This reveals the necessity of mechanical ball milling to enhance the reduction of manganese powder.

[0071] Comparative Example 5 significantly reduced the amount of phosphoric acid (phosphoric acid: total molar ratio of manganese and iron in the system = 0.5:1), but the insufficient acidity led to a decrease in the activity of the reaction system, and the leaching rates of both iron and manganese decreased significantly, making it difficult to meet the recovery requirements. Although Comparative Example 6 achieved a higher leaching rate of manganese and iron by significantly increasing the amount of phosphoric acid (phosphoric acid: total molar ratio of manganese and iron in the system = 3:1), the excessive amount of phosphate not only caused reagent waste, but also led to an imbalance of ion concentration in the subsequent hydrothermal synthesis system, increasing the difficulty of synthesis and the environmental burden.

[0072] In contrast, this invention, through the strategy of "mechanical ball milling-assisted reduction of metallic manganese powder", successfully achieved efficient simultaneous leaching of iron and manganese elements with low acid dosage. This not only avoids the high cost and high pollution problems of traditional processes, but also synthesizes high-purity, high-performance lithium manganese iron phosphate materials.

[0073] Figure 1 and Figure 2 Characterization results show that the lithium-extracted iron-phosphate slag exhibits a typical iron phosphate crystal structure and morphology. Specifically, Figure 1 The X-ray diffraction pattern showed multiple sharp and high-intensity diffraction peaks, with the main characteristic peaks matching the standard card for FePO4, indicating that the main phase is iron phosphate. Furthermore, the carbon characteristic peaks in the pattern indicate that the sample contains residual carbon components derived from waste electrode materials. Figure 2 Scanning electron microscopy images show that the raw material particles are densely aggregated with a wide particle size distribution, and carbon blocks of varying sizes are randomly distributed next to the FePO4 spherical particles.

[0074] From a structural perspective, in comparison Figure 1 and Figure 3 The X-ray diffraction pattern shows that the diffraction peaks that originally belonged to iron phosphate are now... Figure 3 The iron in the slag has largely disappeared, leaving only a distinct carbon peak. This indicates that, under the synergistic effect of ball milling and the reducing agent, most of the iron in the slag has entered the solution. From a morphological perspective, compared to... Figure 2 and Figure 4 Scanning electron microscopy images show that after leaching, the solid residue consists only of blocky carbon, and the original dense spherical structure of ferric phosphate is completely destroyed. This series of changes indicates that the process can efficiently dissolve iron, ensuring its complete and deep extraction in the solid phase.

[0075] Figure 5 The X-ray diffraction pattern showed sharp and symmetrical peaks without obvious impurities, indicating that olivine-type lithium manganese iron phosphate with high crystallinity and pure phase was successfully synthesized using the recovered iron and manganese-containing solution. This result not only demonstrates the excellent effect of the front-end leaching process, but also confirms that the composition and purity of the obtained solution fully meet the requirements of subsequent hydrothermal synthesis, providing a reliable guarantee for obtaining high-quality lithium manganese iron phosphate products.

[0076] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for recovering lithium iron phosphate residue from waste lithium iron phosphate to prepare lithium manganese iron phosphate, characterized in that, Includes the following steps: S1: Mix waste lithium iron phosphate residue with manganese powder and phosphoric acid to obtain a mixture; wherein, the molar ratio of manganese powder to iron in lithium iron phosphate residue is (0.5~2.0):1, and the molar ratio of phosphoric acid to (manganese powder + iron in lithium iron phosphate residue) is (1.0~1.5):

1. S2: The mixture from step S1 is ball-milled at 100-500 rpm for 0.5-2 hours to obtain a reaction solution; the reaction solution is then subjected to solid-liquid separation to obtain a solid residue and a filtrate containing ferrous iron and ferrous manganese. S3: Mix the filtrate from step S2 with a lithium source, adjust the pH to 5-11, and carry out a hydrothermal reaction at 180-240℃ for 6-12 hours. After filtration, Li(Fe)2 is obtained. x ,Mn 1-x PO4 solid; S4: The Li(Fe) from step S3... x ,Mn 1-x Solid PO4 is mixed with a carbon source and sintered under a protective atmosphere to obtain carbon-coated lithium manganese iron phosphate material.

2. The method for recovering and preparing lithium manganese iron phosphate from waste lithium iron phosphate residue according to claim 1, characterized in that, The lithium source is one or more of lithium hydroxide, lithium sulfate, lithium chloride, lithium nitrate, or organic lithium salts.

3. The method for recovering and preparing lithium manganese iron phosphate from waste lithium iron phosphate residue according to claim 1, characterized in that, The carbon source is glucose.

4. The method for recovering and preparing lithium manganese iron phosphate from waste lithium iron phosphate residue according to claim 1, characterized in that, In step S2, the mass ratio of the balls is (5~50):

1.

5. The method for recovering and preparing lithium manganese iron phosphate from waste lithium iron phosphate residue according to claim 1, characterized in that, In step S3, the molar ratio of lithium in the solution to (manganese and iron in the solution) is (1~2):

1.

6. The method for recovering and preparing lithium manganese iron phosphate from waste lithium iron phosphate residue according to claim 1, characterized in that, In step S4, the solid-state sintering temperature is 500~800℃ and the sintering time is 2~8h.

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