Method for removing aluminum from oriented recycled lithium iron phosphate waste material

Abstract

This application provides a method for removing aluminum from lithium iron phosphate waste through directional recycling. The method includes the following steps: (1) mixing lithium iron phosphate waste, iron salt solution, and reducing agent to form a slurry, and then reacting in one step to obtain a mixed salt solution containing aluminum ions and ferrous ions, and lithium iron phosphate after aluminum removal; (2) adjusting the pH of the mixed salt solution obtained in step (1), and then reacting in two steps to obtain aluminum hydroxide slag and a solution containing ferrous ions through solid-liquid separation; (3) mixing the ferrous ions obtained in step (2) with an oxidizing agent, adjusting the pH, and then reacting in three steps to obtain an iron salt solution, which is used for recycling the iron salt solution from step (1). The aluminum removal method described in this application does not introduce other impurities during leaching, is simple to operate, pollution-free, and the impurity removal agent can be recycled. Furthermore, the iron element can be recovered, resulting in low process cost and good impurity removal effect.

Description

Technical Field

[0001] This application relates to the field of resource recycling technology, such as a method for removing aluminum from lithium iron phosphate waste through directional recycling. Background Technology

[0002] As a major product in the battery market, the production of lithium-ion batteries is increasing year by year. At the same time, the number of discarded lithium-ion batteries each year is also enormous. China's new energy vehicle industry is expected to continue its rapid development, which means that the demand for lithium-ion batteries will continue to expand, and the number of discarded lithium-ion batteries will gradually increase. Among them, a large number of discarded lithium iron phosphate batteries indicate that lithium iron phosphate batteries will account for the majority of discarded batteries in the future. Therefore, it is imperative to recycle discarded lithium iron phosphate batteries. Recycling discarded lithium iron phosphate batteries is not only beneficial to environmental protection, but also to the sustainable development of my country's lithium battery industry.

[0003] Currently, the main methods for treating waste lithium iron phosphate powder are wet and pyrometallurgical processes. Wet processes are further divided into wet full-component leaching and wet selective lithium leaching. The wet full-component leaching method involves the complete recovery of all components from the waste lithium iron phosphate powder, dissolving all the elements in the waste before removing impurities. In wet selective lithium leaching, lithium is immersed in a solution to separate it from elements such as phosphorus and iron. However, this method has limitations for treating waste lithium iron phosphate powder. When the waste lithium iron phosphate powder contains aluminum impurities, these impurities will enter the phosphorus-iron solution, resulting in high impurity levels and low quality in the final iron phosphate product. Furthermore, if impurity removal is carried out in the phosphorus-iron solution, the cost and difficulty of removal are high, and a significant amount of phosphorus and iron is lost.

[0004] CN114784405A discloses a method for recycling and removing aluminum from waste lithium iron phosphate batteries. The steps include: sequentially performing an aluminum removal reaction, solid-liquid separation, i-th washing, and leaching treatment on the positive electrode material powder of the waste lithium iron phosphate batteries; wherein, the j-th washing uses the j+1-th washing solution obtained after the j+1-th washing in the previous batch, and the i-th washing uses pure water; wherein, 2≤i≤6, 1≤j.

[0005] CN116199201A discloses a method for removing aluminum and comprehensively recycling waste lithium iron phosphate electrode powder, belonging to the field of resource recycling technology; specifically, it includes the following steps: 1. Using hydrochloric acid of a certain concentration and an oxidant to leach lithium, iron, phosphorus, and other impurity elements from the waste lithium iron phosphate electrode powder; 2. Adding an extractant to the solution to extract ferric iron from the aqueous solution and introduce it into the organic phase; 3. After shaking separation, adjusting the pH value of the aqueous phase to precipitate aluminum as aluminum hydroxide, and filtering it out; 4. Remixing the inorganic and organic phases, adjusting the pH value to obtain iron phosphate precipitate, and filtering it; 5. Adjusting the pH of the filtrate after filtration, adding phosphate, and obtaining lithium phosphate.

[0006] The aluminum removal method described above is prone to causing the loss of other elements during the aluminum removal process and is also prone to introducing impurities, which increases the cost of impurity removal. Summary of the Invention

[0007] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of the claims.

[0008] This application provides a method for removing aluminum from lithium iron phosphate waste through directional recycling. The aluminum removal method described in this application does not introduce other impurities during leaching, is simple to operate, pollution-free, and the impurity removal agent can be recycled. Furthermore, the iron element can be recovered, resulting in low process cost and good impurity removal effect.

[0009] In a first aspect, this application provides a method for removing aluminum from lithium iron phosphate waste through targeted recycling, the method comprising the following steps:

[0010] (1) Mix lithium iron phosphate waste, iron salt solution and reducing agent to make slurry, and then react in one step to obtain a mixed salt solution containing aluminum ions and ferrous ions and lithium iron phosphate after aluminum removal.

[0011] (2) Adjust the pH of the mixed salt solution obtained in step (1), and after two-step reaction, solid-liquid separation is performed to obtain aluminum hydroxide slag and a solution containing ferrous iron.

[0012] (3) The ferrous solution obtained in step (2) is mixed with an oxidant, the pH is adjusted, and an iron salt solution is obtained through a three-step reaction. The iron salt solution is used for recycling of the iron salt solution in step (1).

[0013] This application leaches aluminum by adding waste lithium iron phosphate powder to an iron salt solution and a reducing agent to control the oxidation potential, while preventing the leaching of lithium from the lithium iron phosphate. The aluminum in the waste lithium iron phosphate powder is then leached out as Al. 3+ It enters the aluminum-containing solution in the form of Fe, and the solution also contains Fe. 2+ Al containing aluminum solution 3+ Aluminum slag is generated by adjusting the pH value, and then Fe in the solution is removed. 2+ Oxidized to Fe 3+ As an iron salt, it can be recycled. The process does not result in any loss of iron, thus reducing iron loss and lowering the cost of impurity removal. The process conditions are environmentally friendly.

[0014] The equation for iron salt alumina is as follows:

[0015] 3Fe 3+ +Al=Al 3+ +3Fe 2+

[0016] At the same time, a reducing agent is added to maintain the potential. Since Al is lower than the leaching potential of lithium, aluminum is separated from lithium iron phosphate waste, thus avoiding the problem of difficult removal of impurity aluminum.

[0017] In one embodiment, the iron salt solution in step (1) includes any one or a combination of at least two of ferric sulfate solution, ferric chloride solution, or ferric nitrate solution.

[0018] In one embodiment, the concentration of ferric ions in the iron salt solution is 2 to 20 g / L, for example: 2 g / L, 5 g / L, 10 g / L, 15 g / L or 20 g / L.

[0019] In one embodiment, the reducing agent includes any one or a combination of at least two of ferrous sulfate, ferrous nitrate, or ferrous chloride.

[0020] In one embodiment, the liquid-to-solid ratio of the lithium iron phosphate waste slurry prepared in step (1) is (2-10):1mL / g, for example: 2:1mL / g, 4:1mL / g, 5:1mL / g, 8:1mL / g or 10:1mL / g, etc.

[0021] In one embodiment, the potential of the one-step reaction in step (1) is -2.0 to -1.0V, for example: -2.0V, -1.8V, -1.5V, -1.2V or -1.0V, etc.

[0022] In one embodiment, the temperature of the one-step reaction is 30 to 80°C, for example: 30°C, 40°C, 50°C, 60°C or 80°C.

[0023] In one embodiment, the reaction time for the first step is 2 to 8 hours, for example: 2 hours, 3 hours, 5 hours, 6 hours, or 8 hours.

[0024] In one embodiment, the pH of the one-step reaction is 2 to 4, for example: 2, 2.5, 3, 3.5 or 4, etc.

[0025] In one embodiment, the pH adjuster in step (2) includes any one or a combination of at least two of sodium hydroxide, sodium carbonate, or ammonia.

[0026] In one embodiment, the pH is 3.5 to 5.5, for example: 3.5, 4, 4.5, 5 or 5.5, etc.

[0027] In one embodiment, the temperature of the two-step reaction in step (2) is 30 to 90°C, for example: 30°C, 40°C, 50°C, 60°C or 90°C.

[0028] In one embodiment, the two-step reaction takes 3 to 10 hours, for example: 3 hours, 4 hours, 5 hours, 8 hours, or 10 hours.

[0029] In one embodiment, the oxidant in step (3) includes any one or a combination of at least two of hydrogen peroxide, oxygen, or hypochlorous acid.

[0030] In one embodiment, the molar ratio of the oxidant to the ferrous ions in the ferrous solution is (1-5):1, for example: 1:1, 2:1, 3:1, 4:1 or 5:1, etc.

[0031] In one embodiment, the pH adjuster in step (3) includes any one or a combination of at least two of sulfuric acid, nitric acid, or hydrochloric acid.

[0032] In one embodiment, the pH is 0.1 to 2, for example: 0.1, 0.5, 1, 1.5 or 2, etc.

[0033] In one embodiment, the temperature of the three-step reaction in step (3) is 20 to 60°C, for example: 20°C, 30°C, 40°C, 50°C or 60°C.

[0034] In one embodiment, the three-step reaction time is 0.5 to 3 hours, for example: 0.5 hours, 1 hour, 1.5 hours, 2 hours, or 3 hours.

[0035] As an optional solution to this application, the method includes the following steps:

[0036] (1) Mix lithium iron phosphate waste, iron salt solution with iron concentration of 2-20 g / L and reducing agent with liquid-solid ratio of (2-10):1 mL / g to form a slurry, and react at a potential of -2.0--1.0 V and 30-80 °C for 2-8 h to obtain a mixed salt solution containing aluminum ions and ferrous ions and lithium iron phosphate after aluminum removal.

[0037] (2) Adjust the pH of the mixed salt solution obtained in step (1) to 3.5-5.5 by adding alkali, react at 30-90℃ for 3-10h, and separate the solid and liquid to obtain aluminum hydroxide slag and a solution containing ferrous iron.

[0038] (3) The ferrous solution obtained in step (2) is mixed with the oxidant at a molar ratio of 1:(1~5), the pH is adjusted to 0.1~2 with acid, and the mixture is reacted at 20~60℃ for 0.5~3h to obtain an iron salt solution. The iron salt solution is used for recycling of the iron salt solution in step (1).

[0039] Compared with related technologies, this application has the following advantages:

[0040] (1) This application utilizes the fact that trivalent iron will form a corrosion cell with aluminum under acidic conditions to increase the solubility of aluminum. At the same time, a reducing agent is added to maintain the reduction potential so that lithium will not dissolve, thereby achieving the purpose of separating impurity aluminum from lithium iron phosphate in lithium iron phosphate waste.

[0041] (2) The iron salt solution in the aluminum removal method described in this application can be recycled, and will not introduce other impurity ions to increase the cost of impurity removal. The impurity removal effect is good, the reaction conditions are mild, and the harm to the environment is reduced.

[0042] (3) The lithium iron phosphate recovered by the aluminum removal method described in this application can have a lithium content of more than 3.64%, an aluminum content of less than 0.02%, a phosphorus content of more than 12.93%, and an iron content of more than 26.35%, thus achieving aluminum removal while avoiding lithium leaching.

[0043] After reading and understanding the accompanying diagrams and detailed descriptions, the other aspects can be understood. Attached Figure Description

[0044] The accompanying drawings are used to provide a further understanding of the technical solutions in this paper and form part of the specification. They are used together with the embodiments of this application to explain the technical solutions in this paper and do not constitute a limitation on the technical solutions in this paper.

[0045] Figure 1 This is a process flow diagram of the aluminum removal method described in one embodiment of this application. Detailed Implementation

[0046] The technical solution of this application will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely to help understand this application and should not be regarded as specific limitations on this application.

[0047] The elemental contents of lithium iron phosphate waste used in the embodiments and comparative examples of this application are as follows:

[0048] Table 1

[0049] element Li Al P Fe content(%) 3.72 0.58 13.65 28.20

[0050] Example 1

[0051] This embodiment provides a method for removing aluminum from lithium iron phosphate waste through directional recycling. The process flow diagram of the method is shown below. Figure 1 As shown, the method includes the following steps:

[0052] (1) Mix 100g of lithium iron phosphate waste with Fe 3+A 15 g / L ferric sulfate solution was mixed and prepared into a slurry at a liquid-solid ratio of 3:1 mL / g. Ferrous sulfate was added and the potential was controlled at -1.0 V. The mixture was reacted at 50 °C for 5 h to obtain a mixed salt solution containing aluminum ions and ferrous ions, and lithium iron phosphate after aluminum removal.

[0053] (2) Heat the mixed salt solution obtained in step (1) to 80°C, add sodium hydroxide to adjust the pH to 4, react for 3 hours, filter, and obtain aluminum hydroxide slag and ferrous solution;

[0054] (3) The ferrous sulfate solution obtained in step (2) was mixed with hydrogen peroxide solution at a molar ratio of 1:3 to oxidize all the ferrous sulfate in the solution after aluminum removal to ferric sulfate. Sulfuric acid was added to adjust the pH to 1.5, and the mixture was reacted at 25°C for 1 hour to obtain Fe. 3+ A ferric salt solution with a concentration ≥15 g / L can be directly recycled; otherwise, ferric sulfate needs to be added to maintain the Fe concentration. 3+ Once the concentration reaches 15g / L, it can be recycled.

[0055] Example 2

[0056] This embodiment provides a method for removing aluminum from lithium iron phosphate waste through directional recycling. The process flow diagram of the method is shown below. Figure 1 As shown, the method includes the following steps:

[0057] (1) Mix 100g of lithium iron phosphate waste with Fe 3+ A 10 g / L ferric chloride solution was mixed with a liquid-solid ratio of 10:1 mL / g to form a slurry. Ferrous chloride was added and the potential was controlled at -1.5 V. The mixture was reacted at 30 °C for 8 h to obtain a mixed salt solution containing aluminum ions and ferrous ions, and lithium iron phosphate after aluminum removal.

[0058] (2) Heat the mixed salt solution obtained in step (1) to 45°C, add sodium hydroxide to adjust the pH to 4, react for 10 h, filter, and obtain aluminum hydroxide slag and ferrous solution.

[0059] (3) The ferrous chloride solution obtained in step (2) was mixed with the hypochlorous acid solution at a molar ratio of 1:1 to oxidize all the ferrous chloride in the aluminum-removed solution to ferric chloride. Hydrochloric acid was added to adjust the pH to 1.5, and the mixture was reacted at 30°C for 1 hour to obtain Fe. 3+ Ferrous salt solutions with a concentration ≥10 g / L can be directly recycled; otherwise, ferric chloride needs to be added to maintain the Fe concentration. 3+ Once the concentration reaches 10g / L, it can be recycled.

[0060] Example 3

[0061] This embodiment provides a method for removing aluminum from lithium iron phosphate waste through directional recycling. The process flow diagram of the method is shown below. Figure 1 As shown, the method includes the following steps:

[0062] (1) Mix 100g of lithium iron phosphate waste with Fe 3+ A 18 g / L ferric nitrate solution was mixed with a liquid-solid ratio of 2:1 mL / g to form a slurry. Ferrous nitrate was added and the potential was controlled at -2.0 V. The mixture was reacted at 80 °C for 2 h to obtain a mixed salt solution containing aluminum ions and ferrous ions, and lithium iron phosphate after aluminum removal.

[0063] (2) Heat the mixed salt solution obtained in step (1) to 80°C, add sodium hydroxide to adjust the pH to 5.5, react for 3 hours, filter, and obtain aluminum hydroxide slag and a solution containing ferrous iron.

[0064] (3) In step (2), oxygen was introduced into the ferrous solution at a molar ratio of 1:3 to oxidize all the ferrous nitrate in the aluminum-removed solution to ferric nitrate. Nitric acid was added to adjust the pH to 1.5, and the reaction was carried out at 25°C for 3 hours to obtain Fe. 3+ Ferrous salt solutions with a concentration ≥18 g / L can be directly recycled; otherwise, ferric nitrate needs to be added to maintain the Fe concentration. 3+ Once the concentration reaches 18g / L, it can be recycled.

[0065] Example 4

[0066] The only difference between this embodiment and Embodiment 1 is that in step (1), the reaction potential is adjusted to -2.5V, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0067] Example 5

[0068] The only difference between this embodiment and Embodiment 1 is that in step (1), the reaction potential is adjusted to -0.5V, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0069] Example 6

[0070] The only difference between this embodiment and Example 1 is that the pH of the reaction in step (1) is 4, while the other conditions and parameters are exactly the same as in Example 1.

[0071] Example 7

[0072] The only difference between this embodiment and Example 1 is that the pH of the reaction in step (1) is 1, while the other conditions and parameters are exactly the same as in Example 1.

[0073] Comparative Example 1

[0074] The only difference between this comparative example and Example 1 is that no reducing agent is added; all other conditions and parameters are exactly the same as in Example 1.

[0075] Comparative Example 2

[0076] The only difference between this comparative example and Example 1 is that the iron salt solution is replaced with water; all other conditions and parameters are exactly the same as in Example 1.

[0077] Performance testing:

[0078] The content of each component of lithium iron phosphate after aluminum removal was tested in the above examples and comparative examples. The test results are shown in Table 2.

[0079] Table 2

[0080]

[0081]

[0082] As can be seen from Table 2, as obtained from Examples 1-3, the lithium iron phosphate recovered by the aluminum removal method described in this application can have a lithium content of more than 3.64%, an aluminum content of less than 0.07%, a phosphorus content of more than 12.93%, and an iron content of more than 26.35%, thus achieving aluminum removal while avoiding lithium leaching.

[0083] Comparing Examples 1 and 4-5, it can be seen that in the aluminum removal method described in this application, adjusting the reaction potential value in step (1) will affect the aluminum removal and lithium iron phosphate recovery effect. Controlling the reaction potential between -2.0 and -1.0V will result in better aluminum removal. If the potential is too low (potential < -2.0V), aluminum will not dissolve. If the potential is too high (potential > -1.0V), lithium and aluminum will dissolve simultaneously.

[0084] Comparing Examples 1 and 6-7, it can be seen that in the aluminum removal method described in this application, the pH of the reaction in step (3) affects the effect of aluminum removal and lithium iron phosphate recovery. Controlling the pH of the reaction at 2-4 yields better results. If the pH is too high, neither aluminum nor lithium will dissolve. If the pH is too low, lithium and aluminum will dissolve simultaneously.

[0085] As can be seen from the comparison between Example 1 and Comparative Example 1, when no reducing agent is added to adjust the potential, the iron salt solution, as a leaching agent, leaches both Li and Al, making it difficult to separate the impurity Al. The method provided in this application controls the pH value while maintaining a certain potential, ensuring that Al is leached while Li is not leached, thereby achieving the purpose of aluminum removal.

[0086] As can be seen from the comparison between Example 1 and Comparative Example 2, this application, by adding a ferric salt solution, completely oxidizes Al in waste lithium iron phosphate to Al. 3+ If a ferric salt solution is not added, although waste lithium iron phosphate contains a small amount of ferric iron, it is not enough to completely oxidize Al, and therefore cannot achieve the effect of removing aluminum.

[0087] The applicant declares that the above description is only a specific implementation of this application, but the protection scope of this application is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application fall within the protection and disclosure scope of this application.

Claims

1. A method for removing aluminum from lithium iron phosphate waste through directional recycling, comprising the following steps: (1) Lithium iron phosphate waste, iron salt solution and reducing agent are mixed and pulped, and a mixed salt solution containing aluminum ions and ferrous ions and lithium iron phosphate after aluminum removal are obtained by one-step reaction; the potential of the one-step reaction is -2.0~-1.0V; (2) Adjust the pH of the mixed salt solution obtained in step (1), and after two-step reaction, solid-liquid separation is performed to obtain aluminum hydroxide slag and a solution containing ferrous iron. (3) The ferrous solution obtained in step (2) is mixed with an oxidant, the pH is adjusted, and an iron salt solution is obtained through a three-step reaction. The iron salt solution is used for recycling of the iron salt solution in step (1).

2. The method as described in claim 1, characterized in that, The iron salt solution in step (1) includes any one or a combination of at least two of the following: ferric sulfate solution, ferric chloride solution, or ferric nitrate solution.

3. The method as described in claim 1, characterized in that, The concentration of ferric ions in the iron salt solution is 2~20 g / L.

4. The method as described in claim 1, characterized in that, The reducing agent includes any one or a combination of at least two of ferrous sulfate, ferrous nitrate, or ferrous chloride.

5. The method as described in claim 1, characterized in that, The liquid-to-solid ratio of the lithium iron phosphate waste slurry in step (1) is (2~10):1 mL / g.

6. The method as described in claim 1, characterized in that, The temperature of the first-step reaction is 30~80℃.

7. The method as described in claim 1, characterized in that, The reaction time for this step is 2 to 8 hours.

8. The method as described in claim 1, characterized in that, The pH of the one-step reaction is 2-4.

9. The method as described in claim 1, characterized in that, The pH adjuster in step (2) includes any one or a combination of at least two of sodium hydroxide, sodium carbonate, or ammonia.

10. The method as described in claim 1, characterized in that, The pH value in step (2) is 3.5 to 5.

5.

11. The method as described in claim 1, characterized in that, The temperature of the two-step reaction in step (2) is 30~90℃.

12. The method as described in claim 1, characterized in that, The reaction time for the two steps in step (2) is 3 to 10 hours.

13. The method as described in claim 1, characterized in that, The oxidant in step (3) includes any one or a combination of at least two of hydrogen peroxide, oxygen, or hypochlorous acid.

14. The method as described in claim 1, characterized in that, In step (3), the molar ratio of the oxidant and the ferrous ions in the ferrous solution is (1~5):

1.

15. The method as described in claim 1, characterized in that, The pH adjuster in step (3) includes any one or a combination of at least two of sulfuric acid, nitric acid, or hydrochloric acid.

16. The method as described in claim 1, characterized in that, The pH in step (3) is 0.1~2.

17. The method as described in claim 1, characterized in that, The temperature of the three-step reaction in step (3) is 20~60℃.

18. The method as described in claim 1, characterized in that, The three-step reaction takes 0.5 to 3 hours.

19. The method of claim 1, further comprising the following steps: (1) Mix lithium iron phosphate waste, iron salt solution with iron concentration of 2~20g / L and reducing agent with liquid-solid ratio of (2~10):1 to form a slurry, and react at a potential of -2.0~-1.0V and 30~80℃ for 2~8h to obtain a mixed salt solution containing aluminum ions and ferrous ions and lithium iron phosphate after aluminum removal. (2) Adjust the pH of the mixed salt solution obtained in step (1) to 3.5~5.5 by adding alkali. React at 30~90℃ for 3~10h, and separate the solid and liquid to obtain aluminum hydroxide slag and a solution containing ferrous iron. (3) The ferrous solution obtained in step (2) is mixed with the oxidant at a molar ratio of 1:(1~5), the pH is adjusted to 0.1~2 with acid, and the reaction is carried out at 20~60℃ for 0.5~3h to obtain an iron salt solution. The iron salt solution is used for recycling of the iron salt solution in step (1).

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