Method for synergistically recovering waste lithium batteries by using flue gas of power plant

Abstract

The invention belongs to the technical field of waste lithium battery recovery, and particularly relates to a method for synergistically recovering waste lithium batteries by utilizing power plant flue gas, which comprises the steps of waste lithium battery pretreatment, power plant flue gas pretreatment and gradient pyrolysis, wet leaching and valuable metal recovery and flue gas treatment. Organic matters such as electrolyte and a binding agent contained in the battery are heated and decomposed to generate substances reaching the emission standard, so that harmless treatment is realized; and through waste heat utilization of the pyrolyzing furnace and reutilization of a subsequent wet process procedure of cooled flue gas, components such as SOx, NOx, COx and O2 in the flue gas are reutilized, valuable metal leaching of the waste lithium iron phosphate batteries and the ternary batteries is synergistically achieved, dangerous chemical reagents such as strong acid, strong alkali, a strong oxidizing agent and a strong reducing agent do not need to be additionally added, and the method is environmentally friendly. Harmful components in the flue gas are recycled in the recovery process, waste is turned into wealth, and the flue gas treatment cost and the battery recovery reagent cost are reduced.

Description

Technical Field

[0001] This invention belongs to the field of waste lithium battery recycling technology, and in particular relates to a method for co-recycling waste lithium batteries using power plant flue gas. Background Technology

[0002] With the rapid development of the new energy vehicle industry, the amount of retired lithium batteries has increased dramatically. Improper disposal of these batteries can lead to the seepage of heavy metals such as nickel, cobalt, manganese, and iron, as well as electrolytes, into the soil and water, causing long-term environmental pollution. Furthermore, indiscriminate dismantling can trigger short circuits, fires, and even explosions. Meanwhile, the flue gas emitted from power plants and other industrial facilities contains SO₂. x NO x The presence of harmful components requires significant investment in treatment to meet emission standards, while the low- and medium-temperature waste heat (300-500℃) in the flue gas is not effectively utilized, resulting in resource waste.

[0003] Currently, the main recycling processes for waste lithium batteries are pyrometallurgical and hydrometallurgical methods. Pyrometallurgical methods extract valuable metals through high-temperature roasting, but this requires high-temperature smelting (around 1000℃), resulting in high energy consumption and significant pollution. Hydrometallurgical methods use strong acids, alkalis, oxidants, and reducing agents, leading to large reagent consumption and wastewater discharge. Furthermore, existing technologies do not integrate power plant flue gas treatment with waste battery recycling, failing to achieve synergistic resource utilization. Summary of the Invention

[0004] The purpose of this invention is to provide a method for synergistically recovering waste lithium batteries by utilizing the waste heat and components of low-temperature flue gas in power plants, thereby realizing the resource utilization of waste heat and reducing energy consumption in battery recycling.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for co-recycling spent lithium batteries using power plant flue gas includes the following steps: S1. Pre-treatment of waste lithium batteries: After discharging, crushing and sorting the waste lithium batteries, a mixture of black powder and metal is obtained. S2. Power plant flue gas pretreatment and gradient pyrolysis: Power plant flue gas is fed into a pyrolysis furnace to perform gradient pyrolysis on the black powder obtained in step S1, resulting in pyrolyzed black powder and cooled flue gas. S3. Wet leaching: Cooled flue gas is passed into black powder slurry for reaction, and then the reactants are separated into solid and liquid to obtain leachate and solid product; S4. Valuable Metal Recovery and Flue Gas Treatment: Valuable metals are recovered by separating and purifying the leachate. Unreacted flue gas is treated by a tail gas absorption device to meet emission standards. The absorbent is used to adjust the pH of the leaching system.

[0006] Furthermore, the metal mixture in step S1 consists of copper granules, aluminum granules, and a metal shell, which is used for direct recycling and reuse.

[0007] Furthermore, the waste lithium battery is one or a mixture of two of the following: waste lithium iron phosphate batteries and waste ternary lithium batteries.

[0008] Furthermore, in step S2, the temperature of the power plant flue gas is 300~600℃, and it contains SO₂. x NO x CO x Components such as O2.

[0009] Furthermore, the gradient pyrolysis in step S2 specifically involves three stages of pyrolysis: a low-temperature stage (200-300℃), a medium-temperature stage (300-400℃), and a high-temperature stage (400-600℃) along the material's heating direction. The distribution of these three stages is rationally selected based on the flue gas temperature and the raw materials being processed. The medium-temperature and high-temperature stages are optimized settings, selected as appropriate for energy saving and adapting to production conditions. If the flue gas temperature is low, the residence time can be extended to remove organic impurities. The pyrolysis temperature is distributed along the material feeding direction, gradually decomposing residual electrolytes, binders, and other organic matter in the crushed material. The decomposition products are gases that meet emission standards (such as CO2 and H2O), achieving harmless treatment. In the low-temperature stage, the electrolyte (such as dimethyl carbonate and lithium hexafluorophosphate) in the material undergoes preliminary volatilization and decomposition, generating CO2, H2O, and HF. (Adsorbed by the alkaline tail gas absorption device of the kiln); in the medium temperature section, the binder (such as PVDF, CMC) is decomposed into small molecule organic matter, which is further oxidized into CO2 and H2O; in the high temperature section, the residual organic matter is rapidly and completely decomposed to ensure that there are no organic impurities in the black powder.

[0010] Furthermore, in step S2, the temperature of the cooled flue gas is not higher than 80°C. After the medium-low temperature flue gas passes through the pyrolysis furnace for heat exchange, the residual heat is fully utilized, and the flue gas temperature is cooled to below 80°C. The cooled flue gas is then introduced into the subsequent wet leaching system to avoid the high temperature flue gas affecting the stability of the leaching reaction.

[0011] Furthermore, in step S3, the black powder slurry is prepared by mixing water and pyrolyzed black powder at a liquid-to-solid mass ratio of 1~20:1, with a reaction temperature of 40~80℃ and a reaction time of 1~12h.

[0012] Furthermore, in step S3, the black powder is either lithium iron phosphate black powder or ternary black powder. When the black powder is lithium iron phosphate black powder, the synergistic effect during leaching is as follows: SO2 and CO2 in the flue gas provide an acidic environment, lowering the pH of the system and promoting the dissolution and leaching of lithium iron phosphate (LiFePO4); SO3 has both acidic and strong oxidizing properties, providing an acidic environment on the one hand, and reducing the Fe in lithium iron phosphate on the other hand. 2+ Oxidized to Fe 3+ Promote Li +Separation from FePO4; O2, NO, and NO2 enhance oxidation, synergistically promoting lithium leaching to obtain a lithium-containing leachate, FePO4-containing solid, and graphite; when the black powder is ternary black powder, the synergistic effect during leaching is: SO3 and CO2 in the flue gas provide an acidic environment, promoting the leaching of ternary cathode materials (such as LiNi). x Co y Mn 1-x-y The dissolution of O2, with its acidic and strong reducing properties, reduces the Ni content in the ternary material. 3+ Co 3+ Reduced to Ni 2+ Co 2+ , Mn 4+ Restored to Mn 2+ This process promotes the simultaneous leaching of lithium, nickel, cobalt, and manganese, while NO and NO2 assist in reduction, synergistically achieving the simultaneous leaching of lithium, nickel, cobalt, and manganese to obtain a lithium-containing mixed leachate and graphite.

[0013] Furthermore, when the leachate in step S4 is a lithium-containing leachate, its separation, purification, and recovery process is as follows: the pH value of the lithium-containing leachate is adjusted sequentially, with the first pH being 5.5~8.0 for impurity removal, and the second pH being 9~13 for impurity removal and filtration. Then, it undergoes a lithium precipitation reaction with a sodium carbonate solution, and solid-liquid separation is performed to obtain solid lithium carbonate. The lithium precipitation mother liquor is recycled for the slurry preparation process of the black powder slurry in step S3. After carbonization, purification with ion exchange resin, and heating to precipitate, battery-grade lithium carbonate is obtained.

[0014] Furthermore, when the leachate in step S4 is a lithium-containing mixed leachate, its separation, purification and recovery process is as follows: nickel, cobalt and manganese ions in the lithium-containing mixed leachate are separated sequentially using extraction separation technology to obtain the corresponding metal salts or oxides, and the remaining lithium-containing solution is recovered as battery-grade lithium carbonate according to the lithium-containing leachate separation, purification and recovery process.

[0015] mechanism: Waste lithium iron phosphate battery recycling: Waste lithium iron phosphate black powder is mixed with water to form a slurry, which is then passed through cooled flue gas. The components in the flue gas react with the lithium iron phosphate. Specifically: SO2 and CO2 in the flue gas act as acids when passed into water, promoting the leaching of lithium iron phosphate; SO3 acts as both an acid and a strong oxidant, promoting the oxidation of ferrous ions in lithium iron phosphate to ferric ions, and simultaneously promoting lithium leaching; O2, NO, and NO2 all act as oxidants, promoting the oxidation of ferrous ions in lithium iron phosphate to ferric ions, and simultaneously promoting lithium leaching. Under the combined action of these various flue gases, lithium iron phosphate can be effectively leached, yielding a lithium-containing leachate and solid iron phosphate. At the same time, the residual heat from the gradient pyrolysis of the flue gas can heat the reaction solution, accelerating the reaction rate.

[0016] Waste ternary lithium battery recycling: Waste ternary lithium battery black powder is mixed with water to form a slurry, which is then passed through cooled flue gas. The components in the flue gas react with the ternary cathode material. Specifically: SO3 and CO2 in the flue gas act as acids when passed into water, promoting the leaching of the ternary cathode material; SO2 acts as both an acid and a strong reducer, promoting the reduction of nickel, cobalt, and manganese ions in the ternary cathode material to lower valence states, thus achieving the leaching of lithium, nickel, cobalt, and manganese; NO and NO2 also act as reducers, promoting the reduction of nickel, cobalt, and manganese ions in the ternary cathode material to lower valence states, thus achieving the leaching of lithium, nickel, cobalt, and manganese. Under the combined action of these various flue gases, the leaching of lithium, nickel, cobalt, and manganese in the ternary cathode material can be effectively achieved, yielding a leachate. At the same time, the residual heat after the gradient pyrolysis of the flue gas can heat the reaction solution, accelerating the reaction rate.

[0017] The advantages of this invention are: 1. Lower energy consumption: The waste heat from power plant flue gas is used to complete the pyrolysis and leaching temperature maintenance, and the energy consumption is only 1 / 5 to 1 / 3 of that of the traditional pyrometallurgical process, with no additional heating costs; 2. More cost-effective: Utilizing SO₂ in flue gas x NO x CO x Components such as O2 work together to achieve the leaching of valuable metals from waste lithium iron phosphate batteries and ternary batteries without the need for strong acids, strong alkalis, oxidants, or reducing agents, reducing reagent costs by 40% to 60%; at the same time, it reduces the cost of flue gas desulfurization and denitrification in power plants, achieving "waste treatment with waste". 3. More environmentally friendly: Wastewater discharge is reduced by more than 70% (mother liquor recycling), exhaust gas meets emission standards, and acid and alkali pollution and heavy metal leakage are avoided; 4. Higher efficiency: The synergistic effect of multiple components in the flue gas results in lithium leaching efficiency ≥98% (lithium iron phosphate) and nickel-cobalt-manganese leaching efficiency ≥98% (ternary), which is superior to traditional wet processes; 5. Wider compatibility: Wide liquid-to-solid ratio adapts to two battery types, without the need to replace core equipment, and can flexibly meet different waste battery recycling needs. Detailed Implementation

[0018] Example 1: Recycling of Waste Lithium Iron Phosphate Batteries (1) After discharging the waste lithium iron phosphate batteries, crush and sort them to obtain lithium iron phosphate black powder; (2) Power plant flue gas at 300℃ is introduced into a pyrolysis furnace, and lithium iron phosphate black powder is placed in the furnace for gradient pyrolysis. Since the flue gas temperature is only 300℃, the gradient pyrolysis is as follows: ethylene carbonate (EC) has an initial decomposition temperature of 198.15℃, binder PVDF has an initial decomposition temperature of 200℃, and diethyl carbonate (DEC) and dimethyl carbonate (DMC) have an initial decomposition temperature of 250℃. The organic matter is completely decomposed by appropriately extending the pyrolysis time. (3) Mix lithium iron phosphate black powder and water at a liquid-solid ratio of 1:1, introduce cooled flue gas, control the reaction temperature at 70℃, and stir the reaction for 1 hour. (4) Solid-liquid separation yielded a lithium-containing leachate and a FePO4-containing solid and graphite, with a lithium leaching efficiency of 90.0%; (5) The lithium-containing leachate is subjected to two pH adjustments in sequence. The first adjustment is to pH 5.5 to remove impurities, and the second adjustment is to pH 9 to remove impurities and filter. Then it is subjected to lithium precipitation reaction with sodium carbonate solution. Solid lithium carbonate is obtained by solid-liquid separation. The lithium precipitation mother liquor can be recycled for the slurry preparation process. After carbonization, purification with ion exchange resin, and heating precipitation, battery-grade lithium carbonate (purity ≥ 99.5%) is obtained.

[0019] Example 2: Recycling of Waste Lithium Iron Phosphate Batteries (1) After discharging the waste lithium iron phosphate batteries, crush and sort them to obtain lithium iron phosphate black powder; (2) Power plant flue gas at 450℃ is introduced into a pyrolysis furnace, and lithium iron phosphate black powder is placed in the furnace for gradient pyrolysis. The gradient pyrolysis is divided into a low temperature section of 200℃, a medium temperature section of 300℃ and a high temperature section of 400℃, and the organic matter is completely decomposed. (3) Mix lithium iron phosphate black powder with water at a liquid-solid ratio of 10:1, introduce cooled flue gas, control the reaction temperature at 50℃, and stir the reaction for 6 hours. (4) Solid-liquid separation yielded a lithium-containing leachate and a FePO4-containing solid, with a lithium leaching efficiency of 95.0%; (5) The lithium-containing leachate is subjected to two pH adjustments in sequence. The first adjustment is to pH 7.0 to remove impurities, and the second adjustment is to pH 11 to remove impurities and filter. Then it is subjected to a lithium precipitation reaction with sodium carbonate solution. Solid lithium carbonate is obtained by solid-liquid separation. The lithium precipitation mother liquor can be recycled for the slurry preparation process. After carbonization, purification with ion exchange resin, and heating to precipitate, battery-grade lithium carbonate (purity ≥ 99.5%) is obtained.

[0020] Example 3: Recycling of Waste Lithium Iron Phosphate Batteries (1) After discharging the waste lithium iron phosphate batteries, crush and sort them to obtain lithium iron phosphate black powder; (2) Power plant flue gas at 600℃ is introduced into a pyrolysis furnace, and lithium iron phosphate black powder is placed in the furnace for gradient pyrolysis. The gradient pyrolysis is divided into a low temperature section of 250℃, a medium temperature section of 350℃ and a high temperature section of 450℃, and the organic matter is completely decomposed. (3) Mix lithium iron phosphate black powder with water at a liquid-solid ratio of 20:1, introduce cooled flue gas, control the reaction temperature at 30℃, and stir the reaction for 12 hours. (4) Solid-liquid separation yielded a lithium-containing leachate and a FePO4-containing solid and graphite, with a lithium leaching efficiency of 99.5%; (5) The lithium-containing leachate is subjected to two pH adjustments in sequence. The first adjustment is to pH 8.0 to remove impurities, and the second adjustment is to pH 13 to remove impurities and filter. Then it is subjected to lithium precipitation reaction with sodium carbonate solution. Solid lithium carbonate is obtained by solid-liquid separation. The lithium precipitation mother liquor can be recycled for the slurry preparation process. After carbonization, purification with ion exchange resin, and heating to precipitate, battery-grade lithium carbonate (purity ≥ 99.5%) is obtained.

[0021] Example 4: Recycling of used ternary lithium batteries (NCM523) (1) After discharging the waste NCM523 ternary batteries, crush and sort them to obtain NCM523 positive electrode black powder; (2) Power plant flue gas at 300°C is introduced into a pyrolysis furnace, and NCM523 black powder is placed in the furnace for gradient pyrolysis. The gradient pyrolysis operation is the same as in Example 1, and the organic matter is completely decomposed. (3) Mix NCM523 black powder with water at a liquid-solid ratio of 1:1, introduce cooled flue gas, control the reaction temperature at 65℃, and stir the reaction for 1 hour. (4) Solid-liquid separation yielded a mixed leachate containing lithium, nickel, cobalt, and manganese, and graphite. The leaching efficiencies of lithium, nickel, cobalt, and manganese were 92.1%, 92.5%, 93.2%, and 91.0%, respectively. (5) The mixed leachate was extracted and separated to obtain nickel sulfate, cobalt sulfate and manganese sulfate in sequence. The remaining lithium-containing solution was processed according to the lithium precipitation process in Example 2 to obtain battery-grade lithium carbonate (purity ≥99.5%).

[0022] Example 5: Recycling of Waste Ternary Lithium Batteries (NCM523) (1) After discharging the waste NCM523 ternary batteries, crush and sort them to obtain NCM523 positive electrode black powder; (2) Power plant flue gas at 450°C was introduced into a pyrolysis furnace, and NCM523 black powder was placed in the furnace for gradient pyrolysis. The gradient pyrolysis operation was the same as in Example 2, and the organic matter was completely decomposed. (3) Mix NCM523 black powder with water at a liquid-solid ratio of 10:1, introduce cooled flue gas, control the reaction temperature at 45℃, and stir for 6 hours. (4) Solid-liquid separation yielded a mixed leachate containing lithium, nickel, cobalt, and manganese, and graphite. The leaching efficiencies of lithium, nickel, cobalt, and manganese were 96.5%, 95.0%, 95.8%, and 94.2%, respectively. (5) The mixed leachate was extracted and separated to obtain nickel sulfate, cobalt sulfate and manganese sulfate in sequence. The remaining lithium-containing solution was processed according to the lithium precipitation process in Example 2 to obtain battery-grade lithium carbonate (purity ≥99.5%).

[0023] Example 6: Recycling of Waste Ternary Lithium Batteries (NCM523) (1) After discharging the waste NCM523 ternary batteries, crush and sort them to obtain NCM523 positive electrode black powder; (2) Power plant flue gas at 600℃ is introduced into a pyrolysis furnace, and NCM523 black powder is placed in the furnace for gradient pyrolysis. The gradient pyrolysis operation is the same as in Example 3, and the organic matter is completely decomposed. (3) Mix NCM523 black powder with water at a liquid-solid ratio of 20:1, introduce cooled flue gas, control the reaction temperature at 25℃, and stir the reaction for 12 hours. (4) Solid-liquid separation yielded a mixed leachate containing lithium, nickel, cobalt, and manganese, and graphite. The leaching efficiencies of lithium, nickel, cobalt, and manganese were 99.1%, 98.55%, 99.2%, and 98.0%, respectively. (5) The mixed leachate was extracted and separated to obtain nickel sulfate, cobalt sulfate and manganese sulfate in sequence. The remaining lithium-containing solution was processed according to the lithium precipitation process in Example 2 to obtain battery-grade lithium carbonate (purity ≥99.5%).

[0024] Example 7: Mixed recycling of waste lithium iron phosphate and ternary batteries (1) The waste lithium iron phosphate battery and NCM523 ternary battery were mixed at a mass ratio of 1:1, discharged, crushed and sorted to obtain mixed positive electrode black powder. (2) Power plant flue gas at 450°C is introduced into a pyrolysis furnace, and mixed positive electrode black powder is placed in the furnace for gradient pyrolysis. The gradient pyrolysis operation is the same as in Example 3, and the organic matter is completely decomposed. (3) Mix the positive electrode black powder and water at a liquid-solid ratio of 10:1, introduce cooled flue gas, control the reaction temperature at 35℃, and stir the reaction for 5 hours; (4) Solid-liquid separation yielded a mixed leachate containing lithium, nickel, cobalt, and manganese, a solid containing FePO4, and graphite. The lithium leaching efficiency was 99.5%, the leaching efficiencies of nickel, cobalt, and manganese were all ≥98%, and the FePO4 recovery rate was ≥98%. (5) The FePO4 solid is directly recovered, and the mixed leachate is extracted to separate nickel, cobalt and manganese. The lithium-containing solution is precipitated to obtain battery-grade lithium carbonate, and the lithium precipitation mother liquor is recycled for slurry preparation.

Claims

1. A method for co-recycling spent lithium batteries using power plant flue gas, characterized in that, Includes the following steps: S1. Pre-treatment of waste lithium batteries: After discharging, crushing and sorting the waste lithium batteries, a mixture of black powder and metal is obtained. S2. Power plant flue gas pretreatment and gradient pyrolysis: Power plant flue gas is fed into a pyrolysis furnace to perform gradient pyrolysis on the black powder obtained in step S1, resulting in pyrolyzed black powder and cooled flue gas. S3. Wet leaching: Cooled flue gas is passed into black powder slurry for reaction, and then the reactants are separated into solid and liquid to obtain leachate and solid product; S4. Valuable Metal Recovery and Flue Gas Treatment: Valuable metals are recovered by separating and purifying the leachate. Unreacted flue gas is treated by a tail gas absorption device to meet emission standards. The absorbent is used to adjust the pH of the leaching system.

2. The method for co-recycling spent lithium batteries using power plant flue gas as described in claim 1, characterized in that: The metal mixture in step S1 consists of copper granules, aluminum granules, and a metal shell, which is used for direct recycling and reuse.

3. The method for co-recycling spent lithium batteries using power plant flue gas as described in claim 1, characterized in that: The waste lithium batteries are one or a mixture of two of the following: waste lithium iron phosphate batteries and waste ternary lithium batteries.

4. The method for co-recycling spent lithium batteries using power plant flue gas as described in claim 1, characterized in that: In step S2, the temperature of the flue gas from the power plant is 300~600℃.

5. The method for co-recycling spent lithium batteries using power plant flue gas as described in claim 1, characterized in that: The gradient pyrolysis in step S2 specifically involves three stages of pyrolysis: 200-300℃ is the low-temperature stage, 300-400℃ is the medium-temperature stage, and 400-600℃ is the high-temperature stage.

6. The method for co-recycling spent lithium batteries using power plant flue gas as described in claim 1, characterized in that: In step S2, the temperature of the cooled flue gas is not higher than 80°C.

7. The method for co-recycling spent lithium batteries using power plant flue gas as described in claim 1, characterized in that: In step S3, the black powder slurry is prepared by mixing water and pyrolyzed black powder at a liquid-to-solid mass ratio of 1 to 20:1, with a reaction temperature of room temperature to 80°C and a reaction time of 1 to 12 hours.

8. The method for co-recycling spent lithium batteries using power plant flue gas as described in claim 1, characterized in that: In step S3, the black powder is lithium iron phosphate black powder or ternary black powder, the leaching solution is lithium-containing leaching solution or lithium-containing mixed leaching solution, and the solid products are FePO4 and graphite.

9. The method for co-recycling spent lithium batteries using power plant flue gas as described in claim 8, characterized in that: When the leachate in step S4 is a lithium-containing leachate, its separation, purification and recovery process is as follows: the pH value of the lithium-containing leachate is adjusted sequentially, the first pH is 5.5~8.0 to remove impurities, the second pH is 9~13 to remove impurities and filter, and then it is reacted with sodium carbonate solution to precipitate lithium. Solid lithium carbonate is obtained by solid-liquid separation. The lithium precipitation mother liquor is recycled for the slurry preparation process of black powder slurry in step S3. The lithium carbonate solid is carbonized, purified by ion exchange resin, and heated to precipitate to obtain battery-grade lithium carbonate.

10. The method for co-recycling spent lithium batteries using power plant flue gas as described in claim 8, characterized in that: When the leachate in step S4 is a lithium-containing mixed leachate, its separation, purification and recovery process is as follows: manganese, cobalt and nickel ions in the lithium-containing mixed leachate are separated sequentially using extraction separation technology to obtain the corresponding metal salts, and the remaining lithium-containing solution is recovered as battery-grade lithium carbonate according to the lithium precipitation process of claim 9.