A method for selectively extracting lithium from waste lithium iron phosphate cathode material

Abstract

The application belongs to the technical field of lithium iron phosphate recovery, and relates to a method for selectively extracting lithium from waste lithium iron phosphate positive electrode material. The application discloses a method for selectively extracting lithium from waste lithium iron phosphate positive electrode material, which comprises the following steps: (1) placing the positive electrode material powder of the waste lithium iron phosphate battery and concentrated sulfuric acid in the same airtight container in a separated manner; (2) placing the airtight container in a heating device to perform roasting, so as to obtain a roasting product; and (3) placing the roasting product in water to perform leaching, so as to obtain a solid-liquid mixture, and then performing filtration to obtain a filter residue containing iron phosphate and a lithium-containing solution. The application provides a method for selectively extracting lithium from waste lithium iron phosphate positive electrode material, which has the advantages of short process flow, low energy consumption, simple operation, low cost and effective selective lithium extraction.

Description

Technical Field

[0001] This invention belongs to the field of lithium iron phosphate recycling technology, and relates to a method for selectively extracting lithium from waste lithium iron phosphate cathode materials. Background Technology

[0002] Lithium iron phosphate (LiFePO4) is an important lithium-ion battery material widely used in electric vehicles and energy storage systems. In order to recover resources such as lithium metal to achieve sustainable utilization, reduce acquisition costs, promote the circular economy, and at the same time reduce heavy metal pollution and reduce the pressure of chemical waste disposal, it is necessary to recycle battery materials. The most valuable metal element in lithium iron phosphate is lithium, so how to selectively separate lithium from it is the main research direction for lithium iron phosphate recycling. Traditional lithium extraction methods usually involve complex steps and high costs. The mainstream recycling methods at present are (1) wet process: divided into ① selective recycling: recovering lithium from the leachate and recovering iron and phosphorus from the filter residue; ② non-selective recycling: dissolving all the cathode material and recovering all metal ions in the leachate. (2) pyrometallurgical process: mainly inorganic salt assisted roasting, which can achieve acid-free recycling and selective recycling. Method (1) is the mainstream recycling method, which can obtain target metal products with high purity. Its principle is to first use an oxidant to destroy or weaken the lithium-oxygen bond, and then use a leaching agent to extract lithium. However, it requires a large amount of acid, alkali and oxidant. The oxidant is expensive, the recycling benefit is low, and there will be entrainment losses in the subsequent purification process. Moreover, a large amount of wastewater will be generated in the recycling process, increasing the cost of environmental treatment. Method (2) destroys the chemical bond of lithium iron phosphate by high-temperature oxidation roasting, converting lithium iron phosphate into other forms of metal compounds. It uses the difference in solubility of different metal compounds in solvents to achieve a highly selective recycling method. However, it requires a high reaction temperature, has high energy consumption for recycling, and generates harmful gases in the recycling process. In addition, existing methods mostly require at least two steps, and the recycling process is relatively cumbersome. Summary of the Invention

[0003] The purpose of this invention is to address the aforementioned problems in the existing technology by proposing a method for selectively extracting lithium from waste lithium iron phosphate cathode materials that features a short process flow, low energy consumption, simple operation, low cost, and effective selective lithium extraction.

[0004] The objective of this invention can be achieved through the following technical solutions:

[0005] A method for selectively extracting lithium from waste lithium iron phosphate cathode materials, the method comprising:

[0006] (1) Separate the positive electrode material powder of waste lithium iron phosphate batteries from concentrated sulfuric acid and place them in the same sealed container;

[0007] (2) Place the sealed container in a heating device for roasting to obtain the roasted product;

[0008] (3) The roasted product is placed in water for leaching to obtain a solid-liquid mixture. After filtration, a filter residue containing iron phosphate and a lithium-containing solution are obtained.

[0009] Preferably, the molar ratio of the positive electrode material powder to concentrated sulfuric acid in (1) is 1:(0.1-10).

[0010] Further preferred, the molar ratio of the positive electrode material powder and concentrated sulfuric acid in (1) is 1:(0.2-5).

[0011] More preferably, the molar ratio of the positive electrode material powder and concentrated sulfuric acid in (1) is 1:(0.5-2).

[0012] Preferably, the calcination temperature in (2) is 290-400°C and the calcination time is 0.1-10h.

[0013] Further preferred, the calcination temperature in (2) is 290-360℃ and the calcination time is 1-3h.

[0014] Preferably, the liquid-to-solid ratio of water to calcined product in (3) is (20-200):1.

[0015] Preferably, the leaching time in (3) is 0.1 to 10 hours and the leaching temperature is 20 to 80°C.

[0016] Further preferably, the leaching time in (3) is 0.5 to 4 hours.

[0017] Preferably, the mass ratio of the filter residue containing iron phosphate in (3) to the positive electrode material powder in (1) is (8-9.6):10.

[0018] Further preferred, the mass ratio of the filter residue containing iron phosphate in (3) to the positive electrode material powder in (1) is (9.4-9.6):10.

[0019] Preferably, the recovery rate of ferric phosphate in (3) is ≥85%, and the purity is ≥80%.

[0020] Further preferred, the recovery rate of ferric phosphate in (3) is ≥95%, and the purity is ≥95%.

[0021] Preferably, the lithium leaching rate in the calcined product of (3) is 95-99.9%, the iron leaching rate is 1-12%, and the phosphorus leaching rate is 1-13%.

[0022] Further preferably, the lithium leaching rate in the calcined product of (3) is 95-99.9%, the iron leaching rate is 1-5%, and the phosphorus leaching rate is 1-8%.

[0023] More preferably, the lithium leaching rate in the calcined product of (3) is 97-99.9%, the iron leaching rate is 1-3%, and the phosphorus leaching rate is 1-5%.

[0024] Preferably, the Li / Fe separation factor in the calcined product of (3) is ≥20.

[0025] Further preferred, the Li / Fe separation factor in the calcination product of (3) is ≥30.

[0026] More preferably, the Li / Fe separation factor in the calcination product of (3) is ≥50.

[0027] Preferably, the lithium-containing solution in (3) is purified to prepare lithium sulfate.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. This invention separates the positive electrode material of waste lithium iron phosphate batteries from concentrated sulfuric acid and reacts them by low-temperature roasting. The lithium-containing solution and iron phosphate-containing filter residue can be obtained by water immersion, which greatly simplifies the selective lithium extraction process, improves the recycling efficiency, and reduces the process cost required for lithium extraction.

[0030] 2. The concentrated sulfuric acid of the present invention serves as both an oxidant and a leaching agent. Compared with the traditional acid leaching process that requires the addition of an oxidant later, it saves raw material costs and reduces the difficulty of post-processing.

[0031] 3. In this invention, the positive electrode material of waste lithium iron phosphate batteries is placed separately from concentrated sulfuric acid and reacted by low-temperature roasting. The concentrated sulfuric acid begins to undergo thermal decomposition at 290°C. The SO3 produced by the decomposition reacts with LiFePO4 to generate Li2SO4 and FePO4. During the reaction, the oxidizing property of SO3 oxidizes the divalent iron in LiFePO4 to trivalent iron, causing lithium metal ions in the olivine structure to be intercalated and deintercalated, and combine with sulfate to generate lithium sulfate. The lithium iron phosphate after the lithium ion intercalation and deintercalation is converted into iron phosphate. Then, the roasted product is soaked in water, and the two are separated by the difference in solubility of Li2SO4 and FePO4 in water.

[0032] 4. The method for selectively extracting lithium from waste lithium iron phosphate cathode material of the present invention involves a reaction in a closed container, which produces sulfur trioxide. As the reaction ends, the sulfur trioxide is consumed, and the remaining sulfur trioxide combines with water in the air as the temperature decreases, changing from a gaseous state to a liquid state, and will not volatilize into the air and cause pollution.

[0033] 5. The cathode material of the waste lithium iron phosphate battery used in this invention does not require pretreatment processes such as alkaline leaching and roasting, further simplifying the process.

[0034] 6. The method for selectively extracting lithium from waste lithium iron phosphate cathode materials of the present invention has the advantages of short process flow, low energy consumption, simple operation, and low industrialization cost, and effectively achieves selective lithium extraction. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of a sealed container with a partition structure used in this invention. Detailed Implementation

[0036] The following are specific embodiments of the present invention, which further describe the technical solution of the present invention, but the present invention is not limited to these embodiments.

[0037] Unless otherwise specified, the materials used in this invention are commercially available products, and the methods used are conventional technical means.

[0038] In this invention, the particle size of the positive electrode material powder from waste lithium iron phosphate batteries is 0.2–100 μm.

[0039] In this paper, the positive electrode material powder of waste lithium iron phosphate batteries is obtained by discharging, dismantling, and crushing or pulverizing the positive electrode material of waste lithium iron phosphate batteries.

[0040] In this paper, the cathode material powder of waste lithium iron phosphate batteries can also be obtained by other existing methods.

[0041] In this article, a schematic diagram of a closed container with a partition structure is shown as follows: Figure 1 As shown; other devices that can separate the cathode material powder (SLFP) from the concentrated sulfuric acid can also be used.

[0042] In this paper, the concentration of concentrated sulfuric acid is ≥12 mol / L, preferably ≥18 mol / L.

[0043] This paper describes a method for selectively extracting lithium from spent lithium iron phosphate cathode materials, including:

[0044] (1) Place the positive electrode material powder of waste lithium iron phosphate batteries with a molar ratio of 1:(0.1~10) separately from concentrated sulfuric acid in the same sealed container;

[0045] (2) Place the sealed container in a heating device for roasting at a temperature of 290-400℃ for 0.1-10h to obtain the roasted product;

[0046] (3) The roasted product is placed in water for leaching. The liquid-solid ratio of water to roasted product is (20-200):1. The leaching time is 0.1-10h and the leaching temperature is 20-80℃. A solid-liquid mixture is obtained. After filtration, a filter residue containing iron phosphate and a lithium-containing solution are obtained.

[0047] The method for selectively extracting lithium from waste lithium iron phosphate cathode materials of the present invention can achieve a lithium leaching rate of 95-99%, an iron leaching rate of 1-11.3%, and a phosphorus leaching rate of 1-12.5%.

[0048] The method for selectively extracting lithium from waste lithium iron phosphate cathode materials of the present invention achieves a recovery rate of ≥86.3% and a purity of ≥84.8% for the obtained iron phosphate.

[0049] Example 1

[0050] (1) Place the positive electrode material powder of waste lithium iron phosphate batteries with a molar ratio of 2:1 and concentrated sulfuric acid (98%) separately in the same sealed container;

[0051] (2) The sealed container was placed in a muffle furnace for roasting at a temperature of 290°C for 1 hour to obtain the roasted product.

[0052] (3) The roasted product was placed in water for leaching, with a liquid-to-solid ratio of 50:1, a leaching time of 0.5 h, and a leaching temperature of 30 °C, to obtain a solid-liquid mixture; after filtration, a filter residue containing iron phosphate and a lithium-containing solution were obtained.

[0053] In this embodiment, the leaching rate of lithium was 97.6%, the leaching rate of iron was 1.8%, and the leaching rate of phosphorus was 1.1%; the recovery rate of iron phosphate was 93.6%, and the purity was 97.3%.

[0054] In this embodiment, the Li / Fe separation factor, which is the ratio of lithium leaching rate to iron leaching rate, is 54.2.

[0055] Example 2

[0056] (1) Place the positive electrode material powder of waste lithium iron phosphate batteries with a molar ratio of 1:1 and concentrated sulfuric acid (98%) separately in the same sealed container;

[0057] (2) The sealed container was placed in a muffle furnace for roasting at a temperature of 300°C for 2 hours to obtain the roasted product.

[0058] (3) The roasted product was placed in water for leaching. The liquid-to-solid ratio was 200:1, the leaching time was 2 hours, and the leaching temperature was 50°C to obtain a solid-liquid mixture. After filtration, filter residue containing iron phosphate and lithium-containing solution were obtained.

[0059] In this embodiment, the leaching rate of lithium was 98.6%, the leaching rate of iron was 4.2%, and the leaching rate of phosphorus was 5.3%; the recovery rate of iron phosphate was 92.4%, and the purity was 98.1%.

[0060] Example 3

[0061] (1) Place the positive electrode material powder of waste lithium iron phosphate batteries with a molar ratio of 1:1 and concentrated sulfuric acid (98%) separately in the same sealed container;

[0062] (2) The sealed container was placed in a muffle furnace for roasting at a temperature of 350°C for 1 hour to obtain the roasted product.

[0063] (3) The roasted product was placed in water for leaching, with a liquid-to-solid ratio of 100:1, a leaching time of 4 hours, and a leaching temperature of 40°C, to obtain a solid-liquid mixture; after filtration, filter residue containing iron phosphate and lithium-containing solution were obtained.

[0064] In this embodiment, the leaching rate of lithium was 97.9%, the leaching rate of iron was 3.8%, and the leaching rate of phosphorus was 2.1%; the recovery rate of iron phosphate was 94.7%, and the purity was 99.5%.

[0065] Example 4

[0066] (1) Place the positive electrode material powder of waste lithium iron phosphate batteries with a molar ratio of 1:2 and concentrated sulfuric acid (98%) separately in the same sealed container;

[0067] (2) The sealed container was placed in a muffle furnace for roasting at a temperature of 330°C for 2 hours to obtain the roasted product.

[0068] (3) The roasted product was placed in water for leaching, with a liquid-to-solid ratio of 200:1, a leaching time of 3 hours, and a leaching temperature of 20°C, to obtain a solid-liquid mixture; after filtration, filter residue containing iron phosphate and lithium-containing solution were obtained.

[0069] In this embodiment, the leaching rate of lithium was 99.6%, the leaching rate of iron was 4.6%, and the leaching rate of phosphorus was 7.3%; the recovery rate of iron phosphate was 99.5%, and the purity was 98.6%.

[0070] Example 5

[0071] (1) Place the positive electrode material powder of waste lithium iron phosphate batteries with a molar ratio of 2:3 and concentrated sulfuric acid (98%) separately in the same sealed container;

[0072] (2) The sealed container was placed in a muffle furnace for roasting at a temperature of 340°C for 3 hours to obtain the roasted product.

[0073] (3) The roasted product was placed in water for leaching, with a liquid-to-solid ratio of 100:1, a leaching time of 0.5 h, and a leaching temperature of 80 °C, to obtain a solid-liquid mixture; after filtration, filter residue containing iron phosphate and lithium-containing solution were obtained.

[0074] In this embodiment, the leaching rate of lithium was 97.6%, the leaching rate of iron was 2.7%, and the leaching rate of phosphorus was 3.9%; the recovery rate of iron phosphate was 96.2%, and the purity was 96.7%.

[0075] Example 6

[0076] (1) Place the positive electrode material powder of waste lithium iron phosphate batteries with a molar ratio of 1:5 and concentrated sulfuric acid (98%) separately in a sealed container;

[0077] (2) The sealed container was placed in a muffle furnace for roasting at a temperature of 330°C for 2 hours to obtain the roasted product.

[0078] (3) The roasted product was placed in water for leaching, with a liquid-to-solid ratio of 200:1, a leaching time of 3 hours, and a leaching temperature of 20°C, to obtain a solid-liquid mixture; after filtration, filter residue containing iron phosphate and lithium-containing solution were obtained.

[0079] In this embodiment, the leaching rate of lithium was 95.6%, the leaching rate of iron was 11.3%, and the leaching rate of phosphorus was 12.5%; the recovery rate of iron phosphate was 86.3%, and the purity was 84.8%.

[0080] Example 7

[0081] (1) Place the positive electrode material powder of waste lithium iron phosphate batteries with a molar ratio of 1:2 and concentrated sulfuric acid (98%) separately in the same sealed container;

[0082] (2) The sealed container was placed in a muffle furnace for roasting at a temperature of 420°C for 2 hours to obtain the roasted product.

[0083] (3) The roasted product was placed in water for leaching, with a liquid-to-solid ratio of 200:1, a leaching time of 3 hours, and a leaching temperature of 20°C, to obtain a solid-liquid mixture; after filtration, filter residue containing iron phosphate and lithium-containing solution were obtained.

[0084] In this embodiment, the leaching rate of lithium was 93.3%, the leaching rate of iron was 5.8%, and the leaching rate of phosphorus was 4.6%; the recovery rate of iron phosphate was 90.6%, and the purity was 88.5%.

[0085] Example 8

[0086] (1) Place the positive electrode material powder of waste lithium iron phosphate batteries with a molar ratio of 1:2 and sulfuric acid (85%) separately in the same sealed container;

[0087] (2) The sealed container was placed in a muffle furnace for roasting at a temperature of 330°C for 6 hours to obtain the roasted product.

[0088] (3) The roasted product was placed in water for leaching, with a liquid-to-solid ratio of 200:1, a leaching time of 3 hours, and a leaching temperature of 20°C, to obtain a solid-liquid mixture; after filtration, filter residue containing iron phosphate and lithium-containing solution were obtained.

[0089] In this embodiment, the leaching rate of lithium was 94.4%, the leaching rate of iron was 5.6%, and the leaching rate of phosphorus was 7.2%; the recovery rate of iron phosphate was 91.8%, and the purity was 92.7%.

[0090] In this embodiment, sulfuric acid (85%) is used, which lowers the boiling point and is not conducive to the formation of sulfur trioxide, thereby reducing the reaction rate and increasing the roasting time. If the roasting time is continuously shortened, the reaction will be incomplete.

[0091] Comparative Example 1

[0092] (1) Place the positive electrode material powder of waste lithium iron phosphate batteries with a molar ratio of 1:12 and concentrated sulfuric acid (98%) separately in the same sealed container;

[0093] (2) The sealed container was placed in a muffle furnace for roasting at a temperature of 330°C for 2 hours to obtain the roasted product.

[0094] (3) The roasted product was placed in water for leaching, with a liquid-to-solid ratio of 200:1, a leaching time of 3 hours, and a leaching temperature of 20°C, to obtain a solid-liquid mixture; after filtration, filter residue containing iron phosphate and lithium-containing solution were obtained.

[0095] In this comparative example, the leaching rate of lithium was 96.4%, the leaching rate of iron was 25.2%, and the leaching rate of phosphorus was 33.4%; the recovery rate of iron phosphate was 68.8%, and the purity was 92.3%.

[0096] The addition of excessive concentrated sulfuric acid in this comparative example resulted in increased leaching rates of iron and phosphorus, and decreased leaching selectivity of lithium.

[0097] In summary, this invention separates the positive electrode material of waste lithium iron phosphate batteries from concentrated sulfuric acid and reacts them by low-temperature roasting. The resulting lithium-containing leachate and iron phosphate filter residue can be obtained by water leaching, which greatly simplifies the selective lithium extraction process, improves recycling efficiency, and reduces the process cost required for lithium extraction.

[0098] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A method for selectively extracting lithium from a spent lithium iron phosphate cathode material, characterized in that, The method comprises: (1) placing the positive electrode material powder of the waste lithium iron phosphate battery and concentrated sulfuric acid in the same closed container separately; (2) placing the closed container in a heating device for roasting to obtain a roasted product; (3) placing the roasted product in water for leaching to obtain a solid-liquid mixture, filtering to obtain a filter residue containing iron phosphate and a lithium-containing solution.

2. The method of selectively extracting lithium from spent lithium iron phosphate cathode material of claim 1, wherein, In the (1), the molar ratio of the positive electrode material powder to the concentrated sulfuric acid is 1:(0.1-10).

3. The method of selectively extracting lithium from spent lithium iron phosphate cathode material of claim 1, wherein, In the (1), the molar ratio of the positive electrode material powder to the concentrated sulfuric acid is 1:(0.2-5).

4. The method of selectively extracting lithium from spent lithium iron phosphate cathode material of claim 1, wherein, In the (2), the roasting temperature is 290-400℃, and the roasting time is 0.1-10h.

5. The method of selectively extracting lithium from spent lithium iron phosphate cathode material of claim 1, wherein, In the (2), the roasting temperature is 290-360℃, and the roasting time is 1-3h.

6. The method of selectively extracting lithium from spent lithium iron phosphate cathode material of claim 1, wherein, In the (3), the liquid-solid ratio of water to the roasted product is (20-200):

1.

7. The method of selectively extracting lithium from spent lithium iron phosphate cathode material of claim 1, wherein, In the (3), the leaching time is 0.1-10h, and the leaching temperature is 20-80℃.

8. The method of selectively extracting lithium from spent lithium iron phosphate cathode material of claim 1, wherein, In the (3), the leaching time is 0.5-4h.

9. The method of selectively extracting lithium from spent lithium iron phosphate cathode material of claim 1, wherein, In the (3), the mass ratio of the filter residue containing iron phosphate to the positive electrode material powder in the (1) is (8-9.6):

10.

10. The method of selectively extracting lithium from spent lithium iron phosphate cathode material of claim 1, wherein, In the (3), the lithium-containing solution is purified to prepare lithium sulfate.

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