A method for removing fluorine and aluminum from the positive and negative electrode powder of waste lithium iron phosphate batteries

Abstract

This invention discloses a method for removing fluoride and aluminum from waste lithium iron phosphate battery positive and negative electrode powder. The method includes the following steps: 1) mixing the waste lithium iron phosphate positive and negative electrode powder with a defluorinating agent (non-oxidizing acid solution), and then calcining it under a protective atmosphere to obtain defluorinated powder; 2) adjusting the defluorinated powder with water into a slurry, and then adding concentrated acid solution for leaching to obtain an acid leaching solution; 3) adding an aluminum precipitant and a fluorine precipitant to the acid leaching solution, and carrying out a precipitation reaction in a non-oxidizing gas atmosphere to obtain a defluorinated and aluminum-removing purified solution. This method, through calcination defluorination combined with precipitation for synergistic defluorination and aluminum removal, can achieve efficient and deep removal of fluoride and aluminum from waste lithium-ion battery positive and negative electrode powder, which is beneficial for obtaining high-purity lithium iron phosphate and lithium carbonate products.

Description

Technical Field

[0001] This invention relates to a method for removing fluorine and aluminum from the positive and negative electrode powder of waste lithium iron phosphate batteries, belonging to the field of waste lithium-ion battery recycling. Background Technology

[0002] Lithium iron phosphate (LFP) batteries are widely used in new energy vehicles, energy storage, and 5G base stations due to their excellent electrochemical performance. The recycling process for waste LFP battery positive and negative electrode powder involves: waste lithium-ion batteries → pretreatment, disassembly, discharge, crushing, screening, and separation of waste positive and negative electrode powder. LFP batteries use aluminum foil as the current collector and lithium hexafluorophosphate as the electrolyte. The screening process cannot completely separate the aluminum foil from the positive and negative electrode powder, inevitably resulting in waste positive and negative electrode powder containing high levels of fluorine and aluminum. Subsequently, during the wet leaching process, large amounts of fluorine and aluminum enter the leachate, causing severe equipment corrosion and significantly affecting the quality of the recycled products. Therefore, removing fluorine and aluminum from waste positive and negative electrode powder is crucial for its resource utilization.

[0003] Chinese patent CN 110643814 B discloses a method for removing aluminum and recycling waste lithium iron phosphate batteries, involving a concentrated sulfuric acid aging process combined with negative pressure / airflow purging for defluorination. This method can effectively remove a large amount of fluorine before the positive and negative electrode powders are leached. However, the concentrated sulfuric acid aging process will cause Fe... 2+ Extensive oxidation increases the consumption of iron powder in subsequent aluminum removal processes. Chinese patent CN 113897490 B discloses a method and application for defluorination of lithium-ion battery cathode material leachate, specifically including carbonate precipitation stage I flocculation defluorination and carbonate + flocculant stage II flocculation defluorination. This method can achieve deep defluorination; however, the flocculant is an aluminum salt compound, and the pH for impurity removal is adjusted to 4-6. At this pH, significant losses of iron, phosphorus, and lithium will occur, making this method unsuitable for waste lithium iron phosphate leachate systems. Chinese patent CN 110994062 A discloses a method for recovering fluoride from the front end of waste lithium-ion batteries, specifically involving mixing fluorine-containing powder with a fluoride-dissolving agent, heating, stirring, and filtering. This method can achieve a defluorination efficiency of over 90%, but the process flow is relatively long, and the defluorination rate needs further improvement. Summary of the Invention

[0004] To address the shortcomings of existing technologies for removing fluorine and aluminum from waste lithium iron phosphate battery positive and negative electrode powders, the present invention aims to provide a method for removing fluorine and aluminum from waste lithium iron phosphate battery positive and negative electrode powders. This method combines calcination defluorination with precipitation for synergistic defluorination and aluminum removal, achieving efficient and deep removal of fluorine and aluminum from waste lithium-ion battery positive and negative electrode powders, which is beneficial for obtaining high-purity iron phosphate and lithium carbonate products.

[0005] To achieve the above-mentioned technical objectives, the present invention provides a method for removing fluorine and aluminum from the positive and negative electrode powder of waste lithium iron phosphate batteries, the method comprising the following steps:

[0006] 1) The defluorinating agent is mixed with waste lithium iron phosphate positive and negative electrode powders and then calcined under a protective atmosphere to obtain defluorinated powder; the defluorinating agent is a non-oxidizing acid solution;

[0007] 2) After the defluorination powder is mixed with water to form a slurry, concentrated acid solution is added for leaching to obtain an acid leaching solution;

[0008] 3) Add aluminum precipitant and fluorine precipitant to the acid leaching solution and carry out the precipitation reaction in a non-oxidizing atmosphere to obtain a defluorinated and aluminum-removing purification solution.

[0009] The key to this invention lies in the integration of a high-temperature calcination defluorination process with a precipitation method for the synergistic removal of fluorine and aluminum from acid leaching solutions. This achieves highly efficient and deep removal of fluorine and aluminum from waste lithium iron phosphate positive and negative electrodes, laying the foundation for the recycling of battery-grade lithium iron phosphate and lithium carbonate. More specifically, the fluorine and aluminum removal process from waste lithium iron phosphate battery positive and negative electrode powders comprises the following three processes: The first process is a calcination defluorination process, in which the lithium iron phosphate positive and negative electrode powders are first mixed with a defluorinating agent and then calcined in a non-oxidizing atmosphere. This process disrupts the spatial structure of LiPF6 through a high-temperature acidic environment, making it easier to remove fluorine and aluminum. - It is converted into hydrogen fluoride gas and discharged; the introduction of non-oxidizing gas during calcination can effectively prevent Fe from being discharged. 2+ Oxidized to Fe 3+ To avoid making iron leaching difficult and leading to iron loss, the second process involves acid leaching of the defluorinated powder. The strongly acidic environment breaks the chemical bonds of LiFePO4 / C and a few other compounds, transferring Li, Fe, P, Al, F, etc., in ionic form into the leaching solution, based on AlF... n (3-n) The stability of the complexes is crucial; most of the F in the leachate exists as stable fluorine-aluminum complex ions. The third process involves the synergistic removal of fluorine and aluminum from the leachate through precipitation, via Al... 3+ As the precipitation process continues, the fluorine (F) in the fluorine-aluminum complex is gradually released, which then reacts with the fluoride ion precipitant to form fluoride precipitates, achieving a synergistic effect of aluminum removal and deep defluorination.

[0010] As a preferred embodiment, the liquid-to-solid ratio of the defluorinating agent to the waste lithium iron phosphate positive and negative electrode powder is (0.1-6) L:15 kg. A further preferred liquid-to-solid ratio is (0.3-3) L:15 kg.

[0011] As a preferred embodiment, the defluorinating agent is a sulfuric acid solution and / or a hydrochloric acid solution with a hydrogen ion concentration of 6–30 mol / L, more preferably 8–20 mol / L. The defluorinating agent primarily provides hydrogen ions to volatilize the fluorine in the waste lithium iron phosphate positive and negative electrode powders in the form of hydrogen fluoride.

[0012] As a preferred embodiment, the calcination conditions are: a protective gas flow rate ≥ 1.6 L / min, a temperature of 400–850 °C, and a time of 2.0–9.0 h. The calcination temperature is further preferably 500–750 °C, and the calcination time is further preferably 3.0–7.0 h. Under these preferred calcination conditions, most of the fluorine can be converted into hydrogen fluoride gaseous form for volatilization and removal, achieving a fluorine removal efficiency of over 99%. The optimal removal of most of the fluorine is beneficial for subsequent fluoropolymer-aluminum synergistic deep removal. The introduction of the protective gas can prevent the oxidation of ferrous iron during high-temperature calcination and also serve as a carrier gas, improving the fluorine volatilization and removal efficiency.

[0013] As a preferred embodiment, the protective gas includes at least one selected from nitrogen, carbon dioxide, carbon monoxide, and argon. Nitrogen is further preferred as the protective gas.

[0014] As a preferred embodiment, the leaching conditions are as follows: leaching temperature of 20–90℃, leaching time of 0.5–4.0 h, concentrated acid dosage of 0.8–1.5 times the theoretical amount, and liquid-to-solid ratio of (1.0–4.0) L:1 kg; where the theoretical amount is the theoretical molar amount of concentrated acid required to leach all metal ions from the waste lithium iron phosphate powder. The leaching temperature is further preferably 50–80℃. The concentrated acid dosage is 0.9–1.3 times the theoretical amount. The leaching time is further preferably 1.0–3.0 h. The theoretical dosage of concentrated acid is calculated based on the total amount required for the waste lithium iron phosphate powder to react chemically with the acid. The chemical reaction includes the reaction between the acid and lithium iron phosphate and the reaction between the acid and compounds such as metals (Al, Cu, Mn, Ti, Ni, Co). Under these preferred leaching conditions, the useful metal ions in the waste lithium iron phosphate powder can be efficiently leached, improving the metal ion recovery efficiency.

[0015] As a preferred embodiment, the concentrated acid solution is concentrated sulfuric acid and / or concentrated hydrochloric acid.

[0016] As a preferred embodiment, the aluminum precipitant comprises at least one selected from elemental iron, elemental zinc, sodium hydroxide, ammonia, urea, ammonium phosphate, and sodium phosphate. More preferably, the aluminum precipitant comprises at least one selected from elemental iron, sodium hydroxide, ammonia, urea, ammonium phosphate, and sodium phosphate.

[0017] As a preferred embodiment, the fluorine precipitant comprises a calcium-containing compound and / or a magnesium-containing compound; more preferably, it comprises at least one of CaO, Ca(OH)2, CaCO3, CaCl2, MgCl2, MgO, Mg(OH)2, MgCO3, etc.

[0018] As a preferred embodiment, the amount of aluminum precipitant added to the acid leaching solution is 5–500 g / L. More preferably, the amount of aluminum precipitant added to the acid leaching solution is 20–150 g / L.

[0019] As a preferred embodiment, the amount of fluorine precipitant added to the acid leaching solution is 0.1–200 g / L. More preferably, the amount of fluorine precipitant added to the acid leaching solution is 1–60 g / L.

[0020] As a preferred embodiment, the precipitation reaction conditions are: a reaction temperature of 50–95°C and a reaction time of 1.5–5.0 h. The reaction temperature is further preferably 70–90°C, and the reaction time is further preferably 2.5–3.5 h. At the preferred reaction temperature, the precipitation reaction rate can be increased and the precipitation reaction time shortened. The precipitation reaction of this invention, in conjunction with an aluminum precipitant and a fluorine precipitant, can effectively destroy AlF₂. n (3-n) The structure of the complex allows the aluminum and fluoride ions to be fully converted into precipitates.

[0021] The method for removing fluorine and aluminum from the positive and negative electrode powder of waste lithium iron phosphate batteries of the present invention includes the following specific steps:

[0022] (1) Calcination of waste iron phosphate positive and negative electrode powder: Add defluorinating agent to waste lithium iron phosphate positive and negative electrode powder according to liquid-solid ratio (0.1~6) L:15kg, mix well, and calcine in an inert atmosphere at 400~850℃ for 2.0~9.0h. Cool to room temperature to obtain defluorinated powder.

[0023] (2) Leaching of defluorinated powder: Mix the defluorinated powder with deionized water at a liquid-to-solid ratio of (1.0-4.0) L:1kg, then add 0.8-1.5 times the theoretical amount of concentrated acid solution, stir at 20-90℃ for 0.5-4.0h, and the acid leaching solution is obtained by liquid-solid separation;

[0024] (3) Deep purification of acid leaching solution: Add aluminum precipitant at a liquid-to-solid ratio of 1L:(5~500)g and fluorine precipitant at a liquid-to-solid ratio of 1L:(0.1~200)g respectively. Then isolate the air and stir the reaction at 50~95℃ for 1.5~5.0h. The liquid and solid are separated to obtain the deep purified solution.

[0025] Compared with the prior art, the technical solution of the present invention has the following technical advantages:

[0026] (1) The technical solution of the present invention removes fluorine and aluminum by combining calcination defluorination with precipitation, which can efficiently remove fluorine and aluminum from the positive and negative electrode powders of waste lithium-ion batteries, laying the foundation for obtaining high-value-added high-purity iron phosphate and lithium carbonate.

[0027] (2) The preferred technical solution of the present invention removes more than 99% of the fluorine in the powder through the calcination process, which will significantly reduce the AlF in the acid leaching solution. n (3-n) The concentration of complex ions is beneficial for the precipitation and removal of aluminum ions. 3+ AlF is continuously released during the precipitation process. n (3-n) The F in the complex facilitates the reaction of fluoride ions with Ca. 2+ / Mg 2+ Precipitation occurs, and the aluminum and fluorine removal rate is further improved through synergistic defluorination and aluminum removal technology. Detailed Implementation

[0028] The following examples are intended to further illustrate the present invention, but not to limit the scope of protection of the claims. The composition of waste lithium iron phosphate cathode powder (hereinafter referred to as black powder) is shown in Table 1.

[0029] Table 1. Elemental composition of waste lithium iron phosphate cathode powder

[0030]

[0031] Example 1

[0032] Calcination and defluorination: Weigh 120g of black powder into a crucible, add 9mL of defluorination agent (6mol / L sulfuric acid solution), mix thoroughly, then transfer to a box furnace, purge the air with nitrogen, adjust the nitrogen flow rate to 1.7L / min, heat to 700℃ and start timing, calcine for 5.0h, and cool to room temperature to obtain defluorinated powder.

[0033] Leaching: Add the defluorinated powder to 385 mL of deionized water, stir well, then add 35 mL of concentrated sulfuric acid. Continue stirring at 50 °C for 3.0 h, and separate the liquid and solid. The filtrate is the acid leaching solution. The composition of the acid leaching solution is listed in Table 1. The fluorine leaching rate is calculated based on the ratio of the fluorine content in the leaching solution to the fluorine content of the black powder before defluorination.

[0034] Deep purification: Measure 200mL of acid leaching solution and pour it into the reactor. Add 100mL of deionized water and stir evenly. Then add 4.2g of calcium oxide emulsion and stir at room temperature for 30min. Then add 10.2g of iron powder, seal the reactor, heat to 80℃ and continue stirring for 3.0h. Then separate the liquid and solid. The filtrate is the deep purification solution, and its composition is listed in Table 2.

[0035] Example 2

[0036] Calcination defluorination: Weigh 120g of black powder into a crucible, add 9mL of defluorination agent (8mol / L sulfuric acid solution), mix thoroughly, then transfer to a box furnace, introduce carbon dioxide to purge the air, adjust the carbon dioxide flow rate to 1.9L / min, raise the temperature to 600℃ and start timing, calcine for 7.0h, and cool to room temperature to obtain defluorinated powder.

[0037] Leaching: Add the defluorinated powder to 350 mL of deionized water, stir well, then add 70 mL of concentrated hydrochloric acid. Continue stirring at 90 °C for 4.0 h, and separate the liquid and solid. The filtrate is the acid leaching solution. The composition of the acid leaching solution is listed in Table 1.

[0038] Deep purification: The experimental procedure was the same as in Example 1, except that calcium oxide was replaced with calcium chloride, the amount was adjusted to 12.0 g, the amount of iron powder was adjusted to 11.8 g, and the reaction temperature was 70°C. The components of the deep purification solution are listed in Table 2.

[0039] Example 3

[0040] Calcination and defluorination: Argon was used instead of inert gas, and other experimental parameters and operations were the same as in Example 2.

[0041] Leaching: Add the defluorinated powder to 375 mL of deionized water, stir well, then add 28 mL of concentrated sulfuric acid. Continue stirring at 80 °C for 5.0 h. Separate the liquid and solid, and the filtrate is the acid leaching solution. The composition of the acid leaching solution is listed in Table 1.

[0042] Deep purification: The experimental procedure was the same as in Example 1, except that calcium oxide was replaced with calcium carbonate, the amount was adjusted to 15.0g, the amount of iron powder was adjusted to 7.0g, and 4.5g of urea was added. The reaction temperature was 85℃. The components of the deep purification solution are listed in Table 2.

[0043] Example 4

[0044] Calcination defluorination: Weigh 120g of black powder into a crucible, add 10mL of defluorination agent (5mL of 10mol / L hydrochloric acid solution + 5mL of 10mol / L sulfuric acid), mix thoroughly, and then transfer to a box furnace. Purge the air with a mixture of 20% carbon monoxide, 30% carbon dioxide and 50% nitrogen. Adjust the carbon dioxide flow rate to 1.6L / min, raise the temperature to 550℃ and start timing. Calcinate for 7.0h, and cool to room temperature to obtain defluorinated powder.

[0045] Leaching: Add the defluorinated powder to 440 mL of deionized water, stir well, then add 42 mL of concentrated sulfuric acid. Continue stirring at 80 °C for 3.0 h. Separate the liquid and solid, and the filtrate is the acid leaching solution. The composition of the acid leaching solution is listed in Table 1.

[0046] Deep purification: Measure 200mL of acid leaching solution and pour it into the reactor. Adjust the pH to 1.7 with 15% dilute ammonia water. After stirring evenly, add 8.5g of calcium oxide emulsion and stir at room temperature for 30min. Then add 8.3g of iron powder, seal the reactor, raise the temperature to 80℃ and continue stirring for 3.0h. Then separate the liquid and solid. The filtrate is the deep purification solution, and its composition is listed in Table 2.

[0047] Comparative Example 1 (as opposed to Example 1)

[0048] Calcination and defluorination were carried out according to the process in Example 1.

[0049] Deep purification: Only aluminum precipitant and 11.0g of iron powder were added, without adding any fluorine precipitant. Other operations and reagent additions were the same as in Example 1. The final deep purification liquid composition is listed in Table 2.

[0050] Comparative Example 2 (as a comparison with Example 1)

[0051] Calcination and defluorination were carried out according to the process in Example 1.

[0052] Deep purification: Only 6.0g of fluorine precipitant calcium oxide emulsion was added, without adding any aluminum precipitant. All other operations and reagent additions were the same as in Example 1. The final deep purification liquid composition is listed in Table 2.

[0053] Comparative Example 3

[0054] Leaching: 120.0g of uncalcined defluorinated black powder was directly weighed as raw material for leaching, and the operation process was the same as in Example 1. The composition of the acid leaching solution is listed in Table 1.

[0055] Deep purification: Measure 200mL of acid leaching solution and pour it into the reactor, then add 100mL of deionized water and stir evenly. Add 10.0g of aluminum precipitant iron powder and 50.0g of fluorine precipitant calcium oxide. Seal the reaction device, heat to 90℃ and react for 4.0h. Then separate the liquid and solid. The filtrate is the deep purification solution, and its components are listed in Table 2.

[0056] Comparative Example 4 (as opposed to Example 1)

[0057] Calcination defluorination: No defluorinating agent was added, and other experimental parameters and operations were the same as in Example 1. The results are listed in Table 1.

[0058] Leaching: The leaching process was carried out according to the parameters and procedures of Example 1.

[0059] Deep purification: The amount of calcium oxide emulsion was adjusted to 42g, the amount of iron powder was adjusted to 15g, and other experimental parameters and operations were the same as in Example 1. The results are listed in Table 2.

[0060] Table 1. Defluorination effect during calcination

[0061]

[0062] Table 2. Aluminum and Fluorine Removal Efficiency During the Purification Process

[0063]

[0064] According to the data analysis in Table 1, by introducing a defluorinating agent, creating an oxygen-free atmosphere, adjusting the gas flow rate, and calcining at an appropriate temperature, the fluorine removal rate reaches over 99%, and the residual fluorine in the leachate is as low as less than 1%.

[0065] Based on the data analysis in Table 2, we can conclude that:

[0066] (1) In Comparative Example 1, the removal rates of aluminum and fluorine were 67.6% and 11.5% respectively, with the addition of aluminum precipitant but without the addition of aluminum precipitant; in Comparative Example 2, the removal rates of aluminum and fluorine were 17.9% and 61.7% respectively, with the addition of fluorine precipitant but without the addition of aluminum precipitant. Based on the experimental results of Examples 1 to 4, the simultaneous addition of defluorinating agent and aluminum removal agent has a synergistic effect on the deep purification of fluorine and aluminum in the leachate.

[0067] (2) Comparative Example 3, without solid-phase defluorination, aimed at one-step defluorination and aluminum removal in the liquid phase. Even with the addition of fluorine precipitant and aluminum precipitant, the removal rates of aluminum and fluorine were 26.7% and 22.8%, respectively. Combining the experimental results of Examples 1 to 4, even with the simultaneous intervention of fluorine and aluminum purifiers in the leachate, the effect of defluorination by liquid phase in the leachate alone without a solid-phase defluorination process is very poor.

[0068] (3) Comparative Example 4: No defluorinating agent was added during the calcination process. The fluorine removal rate during the calcination process was only 87.9%, and the fluorine content in the leachate was as high as 0.82 g / L. Further liquid phase aluminum / fluorine removal was not ideal.

Claims

1. A method for removing fluorine and aluminum from the positive and negative electrode powder of waste lithium iron phosphate batteries, characterized in that: Includes the following steps: 1) The defluorinating agent is mixed with waste lithium iron phosphate positive and negative electrode powders and then calcined under a protective atmosphere to obtain defluorinated powder; the defluorinating agent is a non-oxidizing acid solution; 2) After the defluorination powder is mixed with water to form a slurry, concentrated acid solution is added for leaching to obtain an acid leaching solution; 3) Add aluminum precipitant and fluorine precipitant to the acid leaching solution and carry out the precipitation reaction in a non-oxidizing gas atmosphere to obtain a defluorinated and aluminum-removing purification solution. The aluminum precipitant includes at least one of elemental iron, elemental zinc, sodium hydroxide, ammonia, urea, ammonium phosphate, and sodium phosphate. The fluorine precipitant includes calcium-containing compounds and / or magnesium-containing compounds; The amount of aluminum precipitant added to the acid leaching solution is 5~500g / L; The amount of fluoride precipitant added to the acid leaching solution is 0.1~200 g / L; The precipitation reaction conditions are: reaction temperature of 50~95℃ and reaction time of 1.5~5.0h.

2. The method for removing fluorine and aluminum from the positive and negative electrode powder of waste lithium iron phosphate batteries according to claim 1, characterized in that: The liquid-to-solid ratio of the defluorinating agent to the waste lithium iron phosphate positive and negative electrode powder is (0.1~6) L:15kg; The defluorinating agent is a sulfuric acid solution and / or a hydrochloric acid solution with a hydrogen ion concentration of 6~30 mol / L.

3. A method for removing fluorine and aluminum from the positive and negative electrode powder of waste lithium iron phosphate batteries according to claim 1 or 2, characterized in that: The calcination conditions are: protective gas flow rate ≥ 1.6 L / min, temperature 400~850 ℃, and time 2.0~9.0 h.

4. The method for removing fluorine and aluminum from the positive and negative electrode powder of waste lithium iron phosphate batteries according to claim 3, characterized in that: The protective gas includes at least one of nitrogen, carbon dioxide, carbon monoxide, and argon.

5. The method for removing fluorine and aluminum from the positive and negative electrode powder of waste lithium iron phosphate batteries according to claim 1, characterized in that: The leaching conditions are as follows: leaching temperature is 20~90℃, leaching time is 0.5~4.0h, the amount of concentrated acid solution is 0.8~1.5 times the theoretical amount, and the liquid-solid ratio is (1.0~4.0)L:1kg; wherein, the theoretical amount is the theoretical molar amount of concentrated acid solution required to leach out all metal ions from waste lithium iron phosphate powder.

6. The method for removing fluorine and aluminum from the positive and negative electrode powder of waste lithium iron phosphate batteries according to claim 5, characterized in that: The concentrated acid solution is concentrated sulfuric acid and / or concentrated hydrochloric acid.

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