Directional recycling method for removing aluminum from lithium iron phosphate waste

Abstract

A directional recycling method for removing aluminum from lithium iron phosphate waste, comprising the following steps: (1) mixing lithium iron phosphate waste, an iron salt solution and a reducing agent for pulping, and carrying out one-step reaction to obtain a mixed salt solution containing aluminum ions and ferrous ions and aluminum-removed lithium iron phosphate; (2) adjusting the pH of the mixed salt solution obtained in step (1), carrying out two-step reaction, and then carrying out solid-liquid separation to obtain aluminum hydroxide slag and a ferrous-containing solution; and (3) mixing the ferrous-containing solution obtained in step (2) with an oxidizing agent, adjusting the pH, and carrying out three-step reaction to obtain an iron salt solution, wherein the iron salt solution is used for recycling the iron salt solution in step (1). According to the aluminum removal method, no other impurities are introduced during leaching, the operation is simple, pollution is avoided, an impurity removal agent can be recycled, iron elements can be recycled, the process costs are low, and the impurity removal effect is good.

Description

A method for removing aluminum from directional circulating lithium iron phosphate waste Technical Field

[0001] The present application relates to the field of resource recovery technology, for example, a method for removing aluminum from lithium iron phosphate waste in a directional circulation. Background Art

[0002] As the main product in the battery market, the output of lithium-ion batteries is increasing year by year. At the same time, the number of discarded lithium-ion batteries each year is also very huge. China's new energy vehicles are expected to continue to develop rapidly, which means that the demand for lithium-ion batteries will continue to expand, and thus the number of scrapped lithium-ion batteries will gradually increase. Among them, there are a large number of waste lithium iron phosphate batteries, which means that lithium iron phosphate batteries will account for the majority of scrapped batteries in the future. Therefore, it is urgent to recycle waste lithium iron phosphate batteries. Recycling waste lithium iron phosphate batteries is beneficial to protecting the environment and is also conducive to the sustainable development of my country's lithium battery industry.

[0003] At present, the methods for treating waste lithium iron phosphate powder are mainly divided into wet method and fire method, and the wet method is further divided into wet method full component leaching and wet method selective lithium leaching. The wet method full component treatment method is to recover all components of waste lithium iron phosphate powder, dissolve all component elements in the waste material and then remove impurities; when wet method selectively leaching lithium, lithium is immersed in the solution to separate it from elements such as phosphorus and iron, but this method has limitations for the treatment of waste lithium iron phosphate powder. When the waste lithium iron phosphate powder contains aluminum impurities, the aluminum impurities will enter the ferrophosphorus liquid, resulting in the final output of the ferrophosphate product with high impurities and low quality. In addition, if impurities are removed in the ferrophosphorus liquid, the cost of impurity removal is high, the difficulty is great, and the loss of ferrophosphorus is relatively high.

[0004] CN114784405A discloses a method for recycling and removing aluminum from waste lithium iron phosphate batteries, comprising the following steps: sequentially subjecting the positive electrode material powder of the waste lithium iron phosphate batteries to aluminum removal reaction, solid-liquid separation, i-th washing, and leaching treatment; wherein the j-th washing uses the j+1-th washing liquid 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 from waste lithium iron phosphate pole piece powder and comprehensively recovering it, which belongs to the field of resource recovery and utilization technology; the method specifically comprises the following steps: 1. using a certain concentration of hydrochloric acid and an oxidant to leach lithium, iron, phosphorus and other impurity elements from the waste lithium iron phosphate pole piece black powder; 2. adding an extractant to the solution to extract trivalent iron from the aqueous solution into an organic phase; 3. after shock separation, adjusting the pH value of the aqueous phase to precipitate the aluminum element in the form of aluminum hydroxide, which is then filtered out; 4. re-mixing the inorganic phase with the organic phase, adjusting the pH value to obtain an iron phosphate precipitate, which is then filtered; 5. adjusting the pH of the filtered filtrate, adding phosphate to obtain lithium phosphate.

[0006] The aluminum removal method described in the above scheme is likely to cause loss of other elements during the aluminum removal process, and is likely to introduce impurity elements, thereby increasing the cost of impurity removal.

[0007] Summary of the Invention

[0008] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0009] The present application provides a method for removing aluminum from lithium iron phosphate waste in a directional cycle. The aluminum removal method described in the present application does not introduce other impurities during leaching, is simple to operate, is pollution-free, and the impurity remover can be recycled, and the iron element can also be recovered. The process cost is low and the impurity removal effect is good.

[0010] In a first aspect, the present application provides a method for removing aluminum from lithium iron phosphate waste in a directional circulation process, the method comprising the following steps:

[0011] (1) mixing lithium iron phosphate waste, an iron salt solution and a reducing agent to prepare a pulp, and obtaining a mixed salt solution containing aluminum ions and ferrous ions and lithium iron phosphate after aluminum removal through a one-step reaction;

[0012] (2) adjusting the pH of the mixed salt solution obtained in step (1), and after a two-step reaction, performing solid-liquid separation to obtain aluminum hydroxide slag and a solution containing ferrous iron;

[0013] (3) The ferrous solution obtained in step (2) is mixed with an oxidant, the pH is adjusted, and a three-step reaction is performed to obtain an iron salt solution, which is used for recycling the iron salt solution in step (1).

[0014] The present invention adds waste lithium iron phosphate powder to an iron salt solution and a reducing agent to control the oxidation potential to leach aluminum. At the same time, the lithium in the lithium iron phosphate will not be leached. The Al element in the waste lithium iron phosphate powder is converted to Al 3+ In the form of aluminum solution, the solution also contains Fe 2+ . The Al containing aluminum solution 3+ Aluminum slag is generated by adjusting the pH value, and then the Fe 2+ Oxidized to Fe 3+ It can be recycled as an iron salt. There will be no iron loss in the process, which reduces the loss of iron and the cost of impurity removal. The process conditions are environmentally friendly.

[0015] The formula for iron salt alumina is as follows: 3Fe 3+ +Al=Al 3+ +3Fe 2+

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

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

[0018] In one embodiment, the concentration of trivalent iron 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 of ferrous sulfate, ferrous nitrate or ferrous chloride, or a combination of at least two thereof.

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

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

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

[0023] In one embodiment, the one-step reaction time 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.

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

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

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

[0028] In one embodiment, the two-step reaction time is 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) comprises any one of hydrogen peroxide, oxygen or hypochlorous acid, or a combination of at least two thereof.

[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.

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

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

[0033] In one embodiment, the temperature of the three-step reaction in step (3) is 20-60°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 h, for example, 0.5 h, 1 h, 1.5 h, 2 h or 3 h.

[0035] As an optional solution of the present application, the method comprises the following steps:

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

[0037] (2) adding alkali to adjust the pH of the mixed salt solution obtained in step (1) to 3.5-5.5, reacting at 30-90° C. for 3-10 hours, and performing solid-liquid separation to obtain aluminum hydroxide slag and a solution containing ferrous iron;

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

[0039] Compared with the related art, this application has the following beneficial effects:

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

[0041] (2) The iron salt solution in the aluminum removal method described in the present application can be recycled, and other impurity ions will not be introduced 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 aluminum removal method described in the present application can recover lithium iron phosphate with 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%. While achieving aluminum removal, lithium dissolution is avoided.

[0043] Still other aspects will become apparent upon reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The accompanying drawings are used to provide a further understanding of the technical solution of this article and constitute a part of the specification. Together with the embodiments of this application, they are used to explain the technical solution of this article and do not constitute a limitation on the technical solution of this article.

[0045] FIG1 is a process flow chart of the aluminum removal method according to an embodiment of the present application. DETAILED DESCRIPTION

[0046] The technical solution of the present application is further described below through specific implementation methods. Those skilled in the art should understand that the embodiments are only used to help understand the present application and should not be regarded as specific limitations of the present application.

[0047] The content of each element in the lithium iron phosphate waste used in the examples and comparative examples of the present application is as follows:

[0048] Table 1

[0049] Example 1

[0050] This embodiment provides a method for removing aluminum from lithium iron phosphate waste by directional circulation. The process flow chart of the method is shown in FIG1 . The method comprises the following steps:

[0051] (1) 100g of lithium iron phosphate waste and Fe 3+ A 15 g / L ferric sulfate solution was mixed with a liquid-solid ratio of 3:1 mL / g to prepare a slurry, ferrous sulfate was added, the potential was controlled at -1.0 V, and the mixture was reacted at 50°C for 5 hours to obtain a mixed salt solution containing aluminum ions and ferrous ions and lithium iron phosphate after aluminum removal;

[0052] (2) heating the mixed salt solution obtained in step (1) to 80° C., adding sodium hydroxide to adjust the pH to 4, reacting for 3 h, and filtering to obtain aluminum hydroxide slag and a solution containing ferrous iron;

[0053] (3) The ferrous sulfate solution obtained in step (2) was mixed with hydrogen peroxide solution in 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+ ≥15g / L iron salt solution, it can be directly recycled, otherwise it is necessary to add ferric sulfate to make Fe 3+ =15g / L, it can be recycled.

[0054] Example 2

[0055] This embodiment provides a method for removing aluminum from lithium iron phosphate waste by directional circulation. The process flow chart of the method is shown in FIG1 . The method comprises the following steps:

[0056] (1) 100g of lithium iron phosphate waste and Fe 3+ A 10 g / L ferric chloride solution was mixed with a liquid-solid ratio of 10:1 mL / g to prepare a slurry, ferrous chloride was added, the potential was controlled at -1.5 V, and the mixture was reacted at 30°C for 8 hours to obtain a mixed salt solution containing aluminum ions and ferrous ions and lithium iron phosphate after aluminum removal;

[0057] (2) heating the mixed salt solution obtained in step (1) to 45° C., adding sodium hydroxide to adjust the pH to 4, reacting for 10 hours, and filtering to obtain aluminum hydroxide slag and a solution containing ferrous iron;

[0058] (3) The ferrous solution obtained in step (2) was mixed with a hypochlorous acid solution in a molar ratio of 1:1 to oxidize all the ferrous chloride in the solution after aluminum removal 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+ ≥10g / L iron salt solution, it can be directly recycled, otherwise it is necessary to add ferric chloride to make Fe 3+ =10g / L, it can be recycled.

[0059] Example 3

[0060] This embodiment provides a method for removing aluminum from lithium iron phosphate waste by directional circulation. The process flow chart of the method is shown in FIG1 . The method comprises the following steps:

[0061] (1) 100g of lithium iron phosphate waste and Fe 3+An 18 g / L ferric nitrate solution was mixed with a liquid-solid ratio of 2:1 mL / g to prepare a slurry, ferrous nitrate was added, the potential was controlled at -2.0 V, and 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;

[0062] (2) heating the mixed salt solution obtained in step (1) to 80° C., adding sodium hydroxide to adjust the pH to 5.5, reacting for 3 h, and filtering to obtain aluminum hydroxide slag and a solution containing ferrous iron;

[0063] (3) The ferrous solution obtained in step (2) was introduced with oxygen at a molar ratio of 1:3 to oxidize all the ferrous nitrate in the solution after aluminum removal 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+ ≥18g / L iron salt solution, it can be directly recycled, otherwise it is necessary to add ferric nitrate to make Fe 3+ =18g / L, it can be recycled.

[0064] Example 4

[0065] The only difference between this embodiment and embodiment 1 is that the reaction potential in step (1) is adjusted to -2.5 V, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0066] Example 5

[0067] The only difference between this embodiment and embodiment 1 is that the reaction potential in step (1) is adjusted to -0.5 V, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0068] Example 6

[0069] The only difference between this embodiment and embodiment 1 is that the pH of the reaction in step (1) is 4, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0070] Example 7

[0071] The only difference between this embodiment and embodiment 1 is that the pH of the reaction in step (1) is 1, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0072] Comparative Example 1

[0073] The only difference between this comparative example and Example 1 is that no reducing agent is added, and other conditions and parameters are exactly the same as those in Example 1.

[0074] Comparative Example 2

[0075] The only difference between this comparative example and Example 1 is that the iron salt solution is replaced with water, and the other conditions and parameters are exactly the same as those in Example 1.

[0076] Performance testing:

[0077] The lithium iron phosphate obtained after aluminum removal from the above examples and comparative examples was tested for the content of each component. The test results are shown in Table 2:

[0078] Table 2

[0079] As can be seen from Table 2, from Examples 1-3, the aluminum removal method described in the present application can recover lithium iron phosphate with 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%. While achieving aluminum removal, lithium dissolution is avoided.

[0080] By comparing Example 1 with Examples 4-5, it can be seen that in the aluminum removal method described in the present application, adjusting the potential value of the reaction in step (1) will affect the effect of aluminum removal and recovery of lithium iron phosphate. When the reaction potential is controlled at -2.0 to -1.0 V, the aluminum removal effect is better. If the potential is too low (potential < -2.0 V), aluminum will not be dissolved. If the potential is too high (potential > -1.0 V), lithium and aluminum will be dissolved simultaneously.

[0081] By comparing Example 1 with Examples 6-7, it can be seen that in the aluminum removal method described in the present application, the pH of the reaction in step (3) will affect the effect of aluminum removal and recovery of lithium iron phosphate. The effect is better when the pH of the reaction is controlled at 2 to 4. If the pH is too high, neither aluminum nor lithium will be dissolved. If the pH is too low, lithium and aluminum will be dissolved simultaneously.

[0082] By comparing Example 1 and Comparative Example 1, it can be seen that when no reducing agent is added to adjust the potential, the iron salt solution acts as a leaching agent to leach Li and Al at the same time, making it difficult to separate the impurity Al. The method provided in the present application controls the pH value while maintaining a certain potential, thereby ensuring that Al is leached while Li is not leached, thereby achieving the purpose of aluminum removal.

[0083] From the comparison between Example 1 and Comparative Example 2, it can be seen that the present invention oxidizes all Al in the waste lithium iron phosphate into Al by adding trivalent iron salt solution. 3+ If the trivalent iron salt solution is not added, although the waste lithium iron phosphate also contains a small amount of trivalent iron, it is not enough to completely oxidize the Al, so it cannot achieve the effect of removing aluminum.

[0084] The applicant declares that the above is only a specific implementation method of the present application, but the protection scope of the present application is not limited thereto. Technical personnel in the relevant technical field should understand that any changes or substitutions that can be easily thought of by technical personnel in the relevant technical field within the technical scope disclosed in this application fall within the protection scope and disclosure scope of this application.

Claims

1. A method for removing aluminum from oriented circulating lithium iron phosphate waste, comprising the following steps: (1) Mix lithium iron phosphate waste, an iron salt solution, and a reducing agent to make a pulp, and obtain a mixed salt solution containing aluminum ions and ferrous ions and aluminum-removed lithium iron phosphate through a one-step reaction; (2) Adjust the pH of the mixed salt solution obtained in step (1), and after a two-step reaction, perform solid-liquid separation to obtain aluminum hydroxide slag and a solution containing ferrous ions; (3) Mix the solution containing ferrous ions obtained in step (2) with an oxidizing agent, adjust the pH, and after a three-step reaction, obtain an iron salt solution, and the iron salt solution is used for recycling the iron salt solution in step (1).

2. The method according to claim 1, wherein 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.

3. The method according to claim 1 or 2, wherein The concentration of ferric ions in the iron salt solution is 2-20 g / L.

4. The method according to any one of claims 1 to 3, wherein, The reducing agent includes any one or a combination of at least two of ferrous sulfate, ferrous nitrate, or ferrous chloride.

5. The method according to any one of claims 1 to 4, wherein The liquid-solid ratio of the lithium iron phosphate waste pulping in step (1) is (2-10):1 mL / g.

6. The method according to any one of claims 1-5, wherein, The potential of the one-step reaction in step (1) is -2.0 to -1.0 V.

7. The method according to any one of claims 1 to 6, wherein, The temperature of the one-step reaction is 30-80 °C; Optionally, the time of the one-step reaction is 2-8 h.

8. The method according to any one of claims 1-7, wherein, The pH of the one-step reaction is 2-4.

9. The method according to any one of claims 1-8, wherein The pH regulator in step (2) includes any one or a combination of at least two of sodium hydroxide, sodium carbonate, or ammonia water.

10. The method according to any one of claims 1-9, wherein The pH in step (2) is 3.5-5.

5.

11. The method according to any one of claims 1-10, wherein, The temperature of the two-step reaction in step (2) is 30-90 °C; Optionally, the time of the two-step reaction is 3-10 h.

12. The method according to any one of claims 1-11, wherein, The oxidizing agent in step (3) includes any one or a combination of at least two of hydrogen peroxide, oxygen, or hypochlorous acid; Optionally, the molar ratio of the oxidizing agent to ferrous ions in the solution containing ferrous ions is (1-5):

1.

13. The method according to any one of claims 1 to 12, wherein, The pH regulator in step (3) includes any one or a combination of at least two of sulfuric acid, nitric acid, or hydrochloric acid.

14. The method according to any one of claims 1-13, wherein, The pH in step (3) is 0.1-2.

15. The method according to any one of claims 1-14, wherein, The temperature of the three-step reaction in step (3) is 20-60 °C; Optionally, the time of the three-step reaction is 0.5-3 h.

16. The method according to any one of claims 1-15, comprising the following steps: (1) Mix lithium iron phosphate waste, an iron salt solution with an iron concentration of 2-20 g / L, and a reducing agent according to a liquid-solid ratio of (2-10):1 to make a pulp, and react at a potential of -2.0 to -1.0 V and 30-80 °C for 2-8 h to obtain a mixed salt solution containing aluminum ions and ferrous ions and aluminum-removed lithium iron phosphate; (2) Add an alkali to adjust the pH of the mixed salt solution obtained in step (1) to 3.5-5.5, and react at 30-90 °C for 3-10 h, and perform solid-liquid separation to obtain aluminum hydroxide slag and a solution containing ferrous ions; (3) Mix the solution containing ferrous ions obtained in step (2) with an oxidizing agent according to a molar ratio of 1:(1-5), add an acid to adjust the pH to 0.1-2, and react at 20-60 °C for 0.5-3 h to obtain an iron salt solution, and the iron salt solution is used for recycling the iron salt solution in step (1).

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