Method for selectively extracting lithium from waste lithium iron phosphate positive electrode material

Abstract

The invention belongs to the technical field of lithium iron phosphate recovery, and relates to a method for selectively extracting lithium from a waste lithium iron phosphate positive electrode material. The invention discloses a method for selectively extracting lithium from a waste lithium iron phosphate positive electrode material. The method comprises the following steps: (1) separately placing positive electrode material powder of a waste lithium iron phosphate battery and concentrated sulfuric acid in the same closed container; (2) roasting the closed container in heating equipment to obtain a roasted product; and (3) leaching the roasted product in water to obtain a solid-liquid mixture, and filtering to obtain iron phosphate-containing filter residues and a lithium-containing solution. The method for selectively extracting the lithium from the waste lithium iron phosphate positive electrode material is short in technological process, low in energy consumption, easy to operate, low in cost and capable of effectively achieving selective lithium extraction.

Description

Technical Field

[0001] The invention 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 materials. Background Art

[0002] Lithium iron phosphate (LiFePO4) is an important lithium-ion battery material and is widely used in electric vehicles and energy storage systems. In order to recycle resources such as lithium metal to achieve sustainable utilization, reduce acquisition costs, promote a circular economy, and reduce heavy metal pollution and chemical waste disposal pressure, battery material recycling is required. 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 recycling lithium iron phosphate. Traditional lithium extraction methods usually involve complex steps and high costs. The current mainstream recovery methods are (1) wet method: divided into ① selective recovery: recover lithium from the leachate and recover iron and phosphorus from the filter residue; ② non-selective recovery: dissolve all the positive electrode materials and recover all metal ions in the leachate. (2) pyrometallurgy: mainly inorganic salt-assisted roasting, which can achieve acid-free recovery and selective recovery. Among them, method (1) is the mainstream recovery method, which can obtain the target metal product with higher 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 the lithium; however, it needs to consume a large amount of acid, alkali and oxidant, the oxidant is expensive, the recovery income is low, and there will be entrained losses in the subsequent purification process. In addition, a large amount of wastewater will be generated during the recovery process, increasing the cost of environmental governance. Method (2) destroys the chemical bonds of lithium iron phosphate through high-temperature oxidation roasting, converts lithium iron phosphate into other forms of metal compounds, and uses the difference in solubility of different metal compounds in solvents to achieve a highly selective recovery method; however, it requires a higher reaction temperature, high recovery energy consumption, and produces harmful gases during the recovery process. In addition, most existing methods require at least two steps, and the recovery process is relatively cumbersome. Summary of the invention

[0003] The purpose of the present invention is to address the above-mentioned problems existing in the prior art and to propose a method for selectively extracting lithium from waste lithium iron phosphate positive electrode materials, which has the advantages of short process flow, low energy consumption, simple operation, low cost and can effectively realize selective lithium extraction.

[0004] The purpose of the present invention can be achieved by the following technical solutions:

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

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

[0007] (2) placing the sealed container in a heating device for calcining to obtain a calcined product;

[0008] (3) placing the roasted product in water for leaching to obtain a solid-liquid mixture, and filtering to obtain a filter residue containing iron phosphate and a lithium-containing solution.

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

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

[0011] More preferably, the molar ratio of the positive electrode material powder to the 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 0.1-10 h.

[0013] More preferably, the calcination temperature in (2) is 290-360° C., and the calcination time is 1-3 h.

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

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

[0016] More 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] More preferably, 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 the ferric phosphate in (3) is ≥85%, and the purity is ≥80%.

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

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

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

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

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

[0025] More preferably, the Li / Fe separation factor in the calcined product of (3) is ≥30.

[0026] More preferably, the Li / Fe separation factor in the calcined 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. The present invention separates the positive electrode material of the waste lithium iron phosphate battery from concentrated sulfuric acid and reacts them through low-temperature roasting. A lithium-containing solution and a filter residue containing iron phosphate can be obtained by water immersion, which greatly simplifies the process flow of selective lithium extraction, improves the recovery efficiency, and reduces the process cost required for lithium extraction.

[0030] 2. The concentrated sulfuric acid of the present invention is used as both an oxidant and a leaching agent, which saves raw material costs and reduces the difficulty of post-processing compared to the traditional acid leaching process that requires the addition of an oxidant.

[0031] 3. The present invention separates the positive electrode material of the waste lithium iron phosphate battery from concentrated sulfuric acid and reacts them through low-temperature roasting. The concentrated sulfuric acid begins to undergo thermal decomposition reaction at 290°C, and the decomposed SO3 reacts with LiFePO4 to generate Li2SO4 and FePO4. During the reaction, the oxidizing property of SO3 oxidizes the divalent iron in LiFePO4 into trivalent iron, and the lithium metal ions in the olivine structure are deintercalated and combined with sulfate to generate lithium sulfate. The lithium iron phosphate after the lithium ions are deintercalated is converted into iron phosphate. The roasted product is then immersed in water, and the solubility difference between Li2SO4 and FePO4 in water is used to separate the two.

[0032] 4. The method of selectively extracting lithium from waste lithium iron phosphate positive electrode materials of the present invention reacts in a closed container and produces sulfur trioxide. As the reaction ends, the sulfur trioxide is consumed, and the remaining sulfur trioxide combines with water in the air to change from gas to liquid as the temperature decreases, and will not evaporate into the air to cause pollution.

[0033] 5. The cathode material of the waste lithium iron phosphate battery used in the present invention does not require pre-treatment processes such as alkaline leaching and roasting, which further simplifies the process.

[0034] 6. The method of selectively extracting lithium from waste lithium iron phosphate positive electrode materials of the present invention has the advantages of short process flow, low energy consumption, simple operation, low industrial cost, etc., and effectively realizes selective lithium extraction. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a schematic diagram of a closed container with a partition structure used in the present invention. DETAILED DESCRIPTION

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

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

[0038] The particle size of the positive electrode material powder of the waste lithium iron phosphate battery in the present invention is 0.2-100 μm.

[0039] In this article, the cathode material powder of the waste lithium iron phosphate battery is obtained by discharging the waste lithium iron phosphate battery, disassembling the waste lithium iron phosphate battery, and crushing or pulverizing the cathode material.

[0040] In this article, the positive electrode 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 in FIG. Figure 1 As shown; other devices that can separate the positive electrode material powder (SLFP) of waste lithium iron phosphate batteries from concentrated sulfuric acid can also be used.

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

[0043] In this article, a method for selectively extracting lithium from waste lithium iron phosphate positive electrode materials includes:

[0044] (1) The cathode material powder of the waste lithium iron phosphate battery and concentrated sulfuric acid in a molar ratio of 1: (0.1-10) are separated and placed in the same sealed container;

[0045] (2) placing the sealed container in a heating device for calcination at a temperature of 290 to 400° C. for a time of 0.1 to 10 h to obtain a calcined product;

[0046] (3) placing the roasted product in water for leaching, the liquid-to-solid ratio of water to the roasted product is (20-200):1, the leaching time is 0.1-10 hours, the leaching temperature is 20-80° C., and a solid-liquid mixture is obtained. After filtering, 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 positive electrode 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 positive electrode materials of the present invention has a recovery rate of iron phosphate of ≥86.3% and a purity of ≥84.8%.

[0049] Example 1

[0050] (1) The cathode material powder of the waste lithium iron phosphate battery and concentrated sulfuric acid (98%) with a molar ratio of 2:1 are separated and placed in the same sealed container;

[0051] (2) placing the sealed container in a muffle furnace for calcination at a temperature of 290° C. for 1 h to obtain a calcined product;

[0052] (3) placing the roasted product 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 filtering, a filter residue containing iron phosphate and a lithium-containing solution are obtained.

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

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

[0055] Example 2

[0056] (1) The cathode material powder of the waste lithium iron phosphate battery and concentrated sulfuric acid (98%) in a molar ratio of 1:1 are separated and placed in the same sealed container;

[0057] (2) placing the sealed container in a muffle furnace for calcination at a temperature of 300° C. for 2 h to obtain a calcined product;

[0058] (3) placing the roasted product in water for leaching, with a liquid-to-solid ratio of 200:1, a leaching time of 2 hours, and a leaching temperature of 50° C., to obtain a solid-liquid mixture; after filtering, a filter residue containing iron phosphate and a lithium-containing solution are obtained.

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

[0060] Example 3

[0061] (1) The cathode material powder of the waste lithium iron phosphate battery and concentrated sulfuric acid (98%) in a molar ratio of 1:1 are separated and placed in the same sealed container;

[0062] (2) placing the sealed container in a muffle furnace for calcination at a temperature of 350° C. for 1 h to obtain a calcined product;

[0063] (3) placing the roasted product 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 filtering, a filter residue containing iron phosphate and a lithium-containing solution are obtained.

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

[0065] Example 4

[0066] (1) The cathode material powder of the waste lithium iron phosphate battery and concentrated sulfuric acid (98%) at a molar ratio of 1:2 are separated and placed in the same sealed container;

[0067] (2) placing the sealed container in a muffle furnace for calcination at a temperature of 330° C. for 2 h to obtain a calcined product;

[0068] (3) placing the roasted product 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 filtering, a filter residue containing iron phosphate and a lithium-containing solution are obtained.

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

[0070] Example 5

[0071] (1) The cathode material powder of the waste lithium iron phosphate battery and concentrated sulfuric acid (98%) with a molar ratio of 2:3 are separated and placed in the same sealed container;

[0072] (2) placing the sealed container in a muffle furnace for calcination at a temperature of 340° C. for 3 h to obtain a calcined product;

[0073] (3) placing the roasted product 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 filtering, a filter residue containing iron phosphate and a lithium-containing solution are obtained.

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

[0075] Example 6

[0076] (1) The cathode material powder of the waste lithium iron phosphate battery and concentrated sulfuric acid (98%) at a molar ratio of 1:5 are separated and placed in a sealed container;

[0077] (2) placing the sealed container in a muffle furnace for calcination at a temperature of 330° C. for 2 h to obtain a calcined product;

[0078] (3) placing the roasted product 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 filtering, a filter residue containing iron phosphate and a lithium-containing solution are obtained.

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

[0080] Example 7

[0081] (1) The cathode material powder of the waste lithium iron phosphate battery and concentrated sulfuric acid (98%) at a molar ratio of 1:2 are separated and placed in the same sealed container;

[0082] (2) placing the sealed container in a muffle furnace for calcination at a temperature of 420° C. for 2 h to obtain a calcined product;

[0083] (3) placing the roasted product 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 filtering, a filter residue containing iron phosphate and a lithium-containing solution are obtained.

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

[0085] Example 8

[0086] (1) The cathode material powder of waste lithium iron phosphate batteries and sulfuric acid (85%) at a molar ratio of 1:2 are separated and placed in the same sealed container;

[0087] (2) placing the sealed container in a muffle furnace for calcination at a temperature of 330° C. for 6 h to obtain a calcined product;

[0088] (3) placing the roasted product 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 filtering, a filter residue containing iron phosphate and a lithium-containing solution are obtained.

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

[0090] In this embodiment, sulfuric acid (85%) is used, which leads to a lower boiling point, which is not conducive to the formation of sulfur trioxide, thereby reducing the reaction speed and increasing the roasting time; if the roasting time continues to be shortened, it will lead to incomplete reaction.

[0091] Comparative Example 1

[0092] (1) The cathode material powder of the waste lithium iron phosphate battery and concentrated sulfuric acid (98%) at a molar ratio of 1:12 are separated and placed in the same sealed container;

[0093] (2) placing the sealed container in a muffle furnace for calcination at a temperature of 330° C. for 2 h to obtain a calcined product;

[0094] (3) placing the roasted product 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 filtering, a filter residue containing iron phosphate and a lithium-containing solution are obtained.

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

[0096] In this comparative example, excessive concentrated sulfuric acid was added, resulting in increased leaching rates of iron and phosphorus and reduced leaching selectivity of lithium.

[0097] In summary, the present invention separates the positive electrode material of the waste lithium iron phosphate battery from concentrated sulfuric acid and reacts them through low-temperature roasting, and obtains lithium-containing leaching solution and iron phosphate residue through water immersion, which greatly simplifies the process flow of selective lithium extraction, improves the recovery efficiency, and reduces the process cost required for lithium extraction.

[0098] The specific embodiments described herein are merely examples of the spirit of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in similar ways, but they will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

Claims

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

2. The method for selectively extracting lithium from waste lithium iron phosphate positive electrode material according to claim 1, characterized in that: The molar ratio of the positive electrode material powder to the concentrated sulfuric acid in (1) is 1:(0.1-10).

3. The method for selectively extracting lithium from waste lithium iron phosphate positive electrode material according to claim 1, characterized in that: The molar ratio of the positive electrode material powder to the concentrated sulfuric acid in (1) is 1:(0.2-5).

4. The method for selectively extracting lithium from waste lithium iron phosphate positive electrode material according to claim 1, characterized in that: In the step (2), the calcination temperature is 290-400° C. and the calcination time is 0.1-10 h.

5. The method for selectively extracting lithium from waste lithium iron phosphate positive electrode material according to claim 1, characterized in that: In the step (2), the calcination temperature is 290 to 360° C. and the calcination time is 1 to 3 hours.

6. The method for selectively extracting lithium from waste lithium iron phosphate positive electrode material according to claim 1, characterized in that: The liquid-to-solid ratio of water to the calcined product in (3) is (20-200):

1.

7. The method for selectively extracting lithium from waste lithium iron phosphate positive electrode material according to claim 1, characterized in that: In the step (3), the leaching time is 0.1 to 10 hours, and the leaching temperature is 20 to 80°C.

8. The method for selectively extracting lithium from waste lithium iron phosphate positive electrode material according to claim 1, characterized in that: The leaching time in (3) is 0.5 to 4 hours.

9. The method for selectively extracting lithium from waste lithium iron phosphate positive electrode material according to claim 1, characterized in that: 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.

10. The method for selectively extracting lithium from waste lithium iron phosphate positive electrode material according to claim 1, characterized in that: The lithium-containing solution in (3) is purified to prepare lithium sulfate.

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