Method for resource utilization of retired lithium iron phosphate battery black powder

Abstract

The present application relates to the technical field of resource recycling and heavy metal pollution control of waste lithium ion batteries, and particularly relates to a method for resource utilization of retired lithium iron phosphate battery black powder. The retired lithium iron phosphate battery black powder is mixed with water, the pH is adjusted, hydrogen peroxide is added, electrolysis is carried out, solid-liquid separation is carried out after electrolysis, lithium extraction residue and lithium-containing filtrate are obtained; the lithium-containing filtrate is mixed with carbonate, a precipitation reaction is carried out, lithium carbonate is obtained; the lithium extraction residue, inorganic alkali and water are mixed, a hydrothermal reaction is carried out, phosphorus-containing filtrate and iron-graphite mixture are obtained; the pH value of the phosphorus-containing filtrate is adjusted to 4-4.5, recrystallization is carried out, potassium dihydrogen phosphate is obtained; the iron-graphite mixture is dried, an iron-graphite-based soil conditioner is obtained; the present application realizes high-value utilization of all components of retired lithium iron phosphate battery black powder through two-step coupling, the process is simple, reagent consumption is low, and there is no secondary waste residue, which overcomes the defects that the existing technology must be calcined or separated from graphite.

Description

Technical Field

[0001] This invention relates to the field of resource recycling and heavy metal pollution control of waste lithium-ion batteries, and in particular to a method for resource utilization of black powder from retired lithium iron phosphate batteries. Background Technology

[0002] With the explosive growth of the new energy vehicle industry, lithium iron phosphate (LFP) batteries have become the mainstream product in my country's power battery market due to their high safety, long cycle life, and low cost. According to industry statistics, the first batch of commercially used LFP batteries in my country have entered their retirement phase, and the amount of retired LFP batteries is expected to exceed 3 million tons by 2030. Retired LFP batteries contain valuable resources such as lithium, iron, phosphorus, and graphite. Improper disposal will not only cause serious resource waste, but the heavy metals and organic electrolytes they contain will also cause irreversible pollution to soil, water bodies, and the ecological environment. Therefore, developing efficient, green, and comprehensive recycling technologies for retired LFP batteries has become an urgent need for the sustainable development of my country's new energy industry.

[0003] Currently, recycling technologies for retired lithium iron phosphate batteries are mainly divided into three categories: pyrometallurgical processes, hydrometallurgical processes, and biological processes. Pyrometallurgical processes decompose battery materials through high-temperature roasting. While the process is simple, it suffers from drawbacks such as high energy consumption, large carbon emissions, low lithium recovery rates (typically below 80%), and the generation of toxic and harmful fumes. Furthermore, iron, phosphorus, and graphite components are mostly discarded as slag, resulting in extremely low resource utilization. Traditional hydrometallurgical processes use strong acids (sulfuric acid, hydrochloric acid) or strong alkalis to leach lithium. Although this improves lithium recovery rates, it suffers from high reagent consumption, severe equipment corrosion, and the generation of large amounts of acidic / alkaline wastewater and slag. Moreover, most processes only focus on lithium recovery, disposing of iron-phosphorus slag and graphite slag as hazardous waste through landfills, which not only increases environmental risks but also results in a significant waste of iron and phosphorus resources.

[0004] In recent years, electrolysis has gradually gained attention as a green recycling technology. It utilizes electrochemical oxidation to selectively leach lithium, reducing the use of chemical reagents. However, most existing electrolysis processes use diaphragm electrolyzers, which suffer from high diaphragm costs, easy clogging, complex maintenance, and low current efficiency, hindering large-scale industrial application. Furthermore, the lithium extraction slag produced by existing electrolysis processes is still mainly composed of iron phosphate and graphite, lacking efficient separation and high-value utilization technologies for iron, phosphorus, and graphite, thus failing to achieve full-component resource recovery. To address these issues, those skilled in the art have conducted extensive research, but an ideal solution has yet to be found. For example, one technology discloses a comprehensive utilization method for waste lithium iron phosphate slag, using potassium hydroxide as an additive for aerobic calcination to recover phosphorus; however, the graphite carbon is directly burned during the calcination stage, failing to achieve resource recovery of graphite. Another example is a method for preparing potassium phosphate from waste lithium iron phosphate slag, which uses a calcination process that not only burns away graphite carbon but also requires the iron phase to undergo complex calcination transformation before it can be utilized.

[0005] In summary, existing technologies for recycling retired lithium iron phosphate batteries generally suffer from technical bottlenecks such as graphite resource waste, complex processes, high energy consumption, and low added value of products. Of particular note is that most existing technologies focus on the precise separation of graphite and iron phases in lithium extraction slag, or on the resource recovery of phosphorus and iron by calcining to destroy the graphite structure. They fail to propose a technical approach for the direct high-value utilization of the iron phase and graphite as a mixture, thus failing to achieve high-value utilization of all components: lithium, iron, phosphorus, and graphite. Therefore, developing a green process that is simple in its flow, consumes fewer reagents, produces no secondary waste, and recovers all components is of great significance for promoting the healthy development of the retired lithium iron phosphate battery resource recovery industry. Summary of the Invention

[0006] The purpose of this invention is to provide a method for the resource utilization of retired lithium iron phosphate battery black powder. Using retired lithium iron phosphate battery black powder as raw material, the method achieves the resource utilization of all components, including lithium, phosphorus, iron and graphite, through a membraneless slurry electrolysis-alkaline hydrothermal separation coupling process.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution: One of the technical solutions of this invention provides a method for the resource utilization of black powder from retired lithium iron phosphate batteries, comprising the following steps: (1) After mixing the black powder from retired lithium iron phosphate batteries with water, adjust the pH to 1.4~2, add hydrogen peroxide, carry out electrolysis reaction, and after electrolysis, separate the solid and liquid to obtain lithium extraction residue and lithium-containing filtrate. (2) The lithium-containing filtrate and carbonate are mixed and a precipitation reaction is carried out to obtain lithium carbonate; (3) Mix lithium extraction residue, inorganic alkali and water, and carry out hydrothermal reaction to obtain phosphorus-containing filtrate and iron-graphite mixture; (4) Adjust the pH of the phosphorus-containing filtrate to 4-4.5 and recrystallize it to obtain potassium dihydrogen phosphate; (5) The iron-graphite mixture is dried to obtain an iron-graphite-based soil conditioner; There is no requirement for the order of steps (2) and (3), and there is no requirement for the order of steps (4) and (5).

[0008] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention uses a membraneless slurry electrolysis method to treat the black powder of retired lithium iron phosphate batteries. It utilizes anodic oxidation in conjunction with hydrogen peroxide to selectively leach lithium. The electrolyte is recycled in a closed loop. The lithium-containing filtrate is precipitated and washed to obtain battery-grade lithium carbonate. The process is simple and the reagent consumption is low, avoiding the problem of large-scale discharge of waste acid and alkali in traditional wet processes.

[0009] (2) In this invention, lithium extraction slag is directly reacted with potassium hydroxide in a hydrothermal reaction without prior calcination or separation. This achieves efficient separation of phosphorus and iron-graphite phase in one step. The phosphorus-containing filtrate is adjusted to pH and recrystallized to obtain potassium dihydrogen phosphate. The iron-graphite mixture is dried at low temperature to obtain soil conditioner. This realizes the full utilization of lithium extraction slag and no secondary waste is generated.

[0010] (3) This invention uses iron-graphite mixture directly as a soil conditioner for the remediation of heavy metal pollution, which overturns the traditional path of separating graphite from iron phase or calcining graphite. It utilizes the synergistic effect of amorphous iron oxide and graphite to passivate heavy metals such as cadmium and lead, opening up a new direction for the resource utilization of retired battery black powder. Attached Figure Description

[0011] Figure 1 This is a process flow diagram of the present invention.

[0012] Figure 2 The XRD patterns of the products prepared in Example 1 of the present invention are shown, wherein (a) is a mixture of iron phosphate and graphite; and (b) is a mixture of iron and graphite. Figure 3 The XRD pattern of the product prepared in Example 1 of the present invention is shown, wherein (a) is lithium carbonate and (b) is potassium dihydrogen phosphate. Figure 4 Iron-graphite based modifier for Cd 2+ Pb 2+ The adsorption kinetics fitting curve is shown. Detailed Implementation

[0013] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0014] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0015] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0016] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This application specification and embodiments are merely exemplary.

[0017] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0018] All raw materials used in this invention can be obtained commercially or prepared using existing technologies.

[0019] The room temperature mentioned in this invention is calculated as 20~30℃.

[0020] To address the common problems of incomplete component separation, low resource utilization, and secondary waste pollution in existing recycling technologies, this invention employs a slurry electrolysis-hydrothermal separation coupled process to achieve the synergistic recovery of all components, including lithium, iron, phosphorus, and graphite. Black powder is prepared into an H2SO4-H2O2 suspension electrolyte, which is electrolyzed in a diaphragm-free slurry electrolyzer. Anodizing is used in conjunction with H2O2 to selectively leach lithium, while ferrous iron is oxidized to ferric iron and retained in the slag as FePO4. The electrolyte is circulated in a closed loop, achieving a lithium leaching rate of ≥98%. The lithium-containing filtrate is precipitated with sodium carbonate and washed with hot water to obtain battery-grade lithium carbonate with a purity of ≥99.5%. The lithium extraction slag is directly reacted with KOH via hydrothermal reaction to achieve phosphorus and iron-graphite separation. The phosphorus-containing filtrate is adjusted to pH and recrystallized to obtain KH2PO4, achieving a phosphorus recovery rate of ≥90%. The hydrothermal residual iron-graphite mixture was directly dried at 60 °C to obtain an iron-graphite-based soil conditioner composed of amorphous Fe3O4 / FeOOH and graphite, which is used for the remediation of heavy metal pollution. This invention achieves high-value utilization of all components of decommissioned lithium iron phosphate black powder through a two-step coupling process. The process is simple, consumes few reagents, and produces no secondary waste residue, overcoming the shortcomings of existing technologies that require calcination or separation of graphite.

[0021] Specifically, this invention provides a method for the resource utilization of black powder from retired lithium iron phosphate batteries, comprising the following steps: (1) After mixing the black powder from retired lithium iron phosphate batteries with water, adjust the pH to 1.4~2, add hydrogen peroxide, carry out electrolysis reaction, and after electrolysis, separate the solid and liquid to obtain lithium extraction residue and lithium-containing filtrate. (2) The lithium-containing filtrate and carbonate are mixed and a precipitation reaction is carried out to obtain lithium carbonate; (3) Mix lithium extraction residue, inorganic alkali and water, and carry out hydrothermal reaction to obtain phosphorus-containing filtrate and iron-graphite mixture; (4) Adjust the pH of the phosphorus-containing filtrate to 4-4.5 and recrystallize it to obtain potassium dihydrogen phosphate; (5) The iron-graphite mixture is dried to obtain an iron-graphite-based soil conditioner; There is no requirement for the order of steps (2) and (3), and there is no requirement for the order of steps (4) and (5).

[0022] Step (1) of this invention involves mixing retired lithium iron phosphate battery black powder with water, adjusting the pH to 1.4-2 (e.g., 1.4, 1.45, 1.5, 1.6, 1.7, 1.8, 1.9, or 2), adding hydrogen peroxide, and preparing the retired lithium iron phosphate battery black powder into an H2SO4-H2O2 system suspension electrolyte. This electrolyte is then placed in a membrane-free slurry electrolytic cell for electrolysis. Utilizing the synergistic oxidation effect of anodic oxidation and hydrogen peroxide, the ferrous iron in the black powder is oxidized to ferric iron and retained in the leaching residue in the form of FePO4. Simultaneously, highly selective lithium leaching is achieved, with a lithium leaching rate of over 98%. After electrolysis, solid-liquid separation yields lithium extraction residue and lithium-containing filtrate. The electrolyte can be recycled back to the slurry electrolysis process in a closed loop.

[0023] In this invention, the solid-liquid ratio of the retired lithium iron phosphate battery black powder and water is 15~50 g / L, for example, it can be 15 g / L, 20 g / L, 25 g / L, 30 g / L, 35 g / L, 40 g / L, 45 g / L or 50 g / L, etc.

[0024] In this invention, the molar ratio of lithium in the hydrogen peroxide and the retired lithium iron phosphate battery black powder is 1.1 to 4:1, for example, it can be 1.1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1 or 4:1, etc.

[0025] In this invention, the voltage of the electrolysis reaction is 0~5V, for example, it can be 1V, 2V, 3V, 4V or 5V, etc., the electrolysis time is 30~180 min, for example, it can be 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 120 min, 140 min, 160 min or 180 min, etc., and the electrolysis temperature is room temperature.

[0026] Step (2) of this invention is to add lithium-containing filtrate to carbonate for precipitation reaction to obtain crude lithium carbonate precipitate, and after washing and refining with hot water, obtain battery-grade lithium carbonate product with a purity ≥99.5%, which meets the YS / T 582-2023 standard; In this invention, the carbonate includes sodium carbonate, preferably saturated sodium carbonate; the amount of carbonate added is based on the total molar number of lithium ions in the lithium-containing filtrate, according to the reaction... The molar ratio is calculated to be 1.05 to 1.2 times the theoretical value, for example, it can be 1.05 times, 1.1 times, 1.15 times or 1.2 times, etc.

[0027] In this invention, the temperature of the precipitation reaction is 60~90 ℃, for example, 60 ℃, 70 ℃, 80 ℃ or 90 ℃, and the time is 40~90 min, for example, 40 min, 50 min, 60 min, 70 min, 80 min or 90 min.

[0028] In this invention, the temperature of the hot water washing is 80~100 ℃, and the number of washing cycles is 2~3.

[0029] In a preferred embodiment of the present invention, in step (2), the lithium-containing filtrate is first concentrated, and then lithium carbonate is added to carry out a precipitation reaction; the concentration is to concentrate the lithium-containing filtrate to 1 / 3 to 1 / 4 of its original volume, preferably 3 / 1.

[0030] Step (3) of the present invention is to mix lithium extraction slag with inorganic alkali and then carry out hydrothermal reaction. No pre-separation or calcination treatment is required to achieve efficient separation of phosphorus and iron-graphite phase. After the reaction is completed, solid-liquid separation is carried out to obtain phosphorus-containing filtrate and iron-graphite mixture.

[0031] In this invention, the inorganic alkali includes potassium hydroxide; the mass ratio of the inorganic alkali to the lithium extraction slag is 0.4~0.55:1, for example, it can be 0.4:1, 0.42:1, 0.45:1, 0.47:1, 0.5:1, 0.52:1 or 0.55:1, etc.

[0032] In this invention, the total mass of the lithium extraction residue and inorganic alkali is 40 g / L as the solid-liquid ratio of water.

[0033] Step (4) of this invention involves adjusting the pH of the phosphorus-containing filtrate to 4-4.5 with phosphoric acid (e.g., 4, 4.1, 4.2, 4.3, 4.4 or 4.5, etc.) and recrystallizing it. The resulting potassium dihydrogen phosphate product has a purity of over 94%, meeting the quality requirements for fertilizer-grade potassium dihydrogen phosphate (HG / T 2321-2016), and the phosphorus recovery rate is over 90%.

[0034] In this invention, the recrystallization temperature is 20~30℃, for example, it can be 20℃, 25℃ or 30℃, etc., and the time is 4~12 h, for example, it can be 4 h, 6 h, 8 h, 10 h or 12 h, etc.

[0035] In a preferred embodiment of the present invention, in step (4), the phosphorus-containing filtrate is first concentrated and then the pH is adjusted; the concentration is to concentrate the phosphorus-containing filtrate to 1 / 2 to 1 / 3 of its original volume, preferably 3 / 1.

[0036] Step (5) of the present invention is to dry the iron-graphite mixture to obtain an iron-graphite-based soil conditioner composed of amorphous iron tetroxide / ferric hydroxide and graphite.

[0037] In this invention, the drying temperature is 60 °C and the drying time is 12 h.

[0038] In this invention, the iron-graphite-based soil conditioner is used for passivation remediation of heavy metal contaminated soil.

[0039] In a preferred embodiment of the present invention, the iron-graphite-based soil conditioner is used for passivation remediation of soil contaminated with heavy metals such as cadmium and lead. Adsorption kinetics experiments have verified that it has a good stabilization effect on heavy metals.

[0040] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0041] The retired lithium iron phosphate battery black powder used in all embodiments of this invention is mainly composed of lithium iron phosphate and graphite. The specific elemental content of the retired lithium iron phosphate battery black powder by mass percentage is shown in the table below: Table 1. Composition of black powder from retired lithium iron phosphate batteries

[0042] Example 1 This embodiment employs a slurry electrolysis-hydrothermal separation coupled process to achieve the resource recovery of all components, including lithium, iron, phosphorus, and graphite. The process is as follows: Figure 1 As shown.

[0043] (1) Take 10 g of retired lithium iron phosphate battery black powder and prepare a suspension with a solid-liquid ratio of 20 g / L with deionized water. Adjust the pH to 1.5 with concentrated sulfuric acid. Add 30% hydrogen peroxide at a volume ratio of 2.5:1 to the lithium molar ratio in the retired lithium iron phosphate battery black powder to obtain a slurry. Electrolyze the slurry in a membrane-free slurry electrolytic cell at 3 V voltage and room temperature for 90 min. After electrolysis, solid and liquid are separated to obtain lithium extraction residue and lithium-containing filtrate. The lithium leaching rate is 98.5%. The electrolyte is recycled. (2) Heat the lithium-containing filtrate to 100℃ and concentrate it to 1 / 3 of its original volume. Add saturated sodium carbonate and allow it to precipitate at 75℃ for 60 minutes. The amount of saturated sodium carbonate added is based on the total number of moles of lithium ions in the lithium-containing filtrate, according to the reaction... The molar ratio was calculated to be 1.1 times the theoretical value. The crude product was washed three times with hot water at 90°C to obtain lithium carbonate. After testing, the purity of the obtained lithium carbonate was 99.52%, which meets the requirements for battery-grade lithium carbonate. (3) Mix the above lithium extraction residue with potassium hydroxide at a mass ratio of 1:0.5, add water to adjust the solid-liquid ratio to 40 g / L, and hydrothermally react at 180℃ for 12 h. After the reaction is completed, separate the solid and liquid to obtain phosphorus-containing filtrate and iron-graphite mixture. (4) The phosphorus-containing filtrate was first evaporated and concentrated to 1 / 3 of the original filtrate volume, then the pH was adjusted to 4.2 with phosphoric acid, and recrystallized at room temperature for 8 h to obtain potassium dihydrogen phosphate. The purity of the obtained potassium dihydrogen phosphate was 94.5%, and the product met the requirements of fertilizer-grade potassium dihydrogen phosphate. The phosphorus recovery rate was 91.5%. (5) The iron-graphite mixture was dried at 60°C for 12 h to obtain an iron-graphite-based soil conditioner composed of amorphous iron tetroxide / ferric hydroxide and graphite.

[0044] Example 2 (1) Take 10 g of retired lithium iron phosphate battery black powder and prepare a suspension with a solid-liquid ratio of 15 g / L with deionized water. Adjust the pH to 1.8 with concentrated sulfuric acid. Add 30% hydrogen peroxide by volume at a hydrogen peroxide to lithium molar ratio of 1.5:1 in the retired lithium iron phosphate battery black powder to obtain a slurry. Electrolyze the slurry in a membrane-free slurry electrolytic cell at 4 V voltage and room temperature for 120 min. After electrolysis, solid and liquid are separated to obtain lithium extraction residue and lithium-containing filtrate. The lithium leaching rate is 98.2%. The electrolyte is recycled. (2) Heat the lithium-containing filtrate to 100℃ and concentrate it to 1 / 4 of its original volume. Add saturated sodium carbonate and allow it to precipitate at 80℃ for 90 min. The amount of saturated sodium carbonate added is based on the total number of moles of lithium ions in the lithium-containing filtrate, according to the reaction... The molar ratio was calculated to be 1.2 times the theoretical value. The crude product was washed twice with hot water at 85℃ to obtain lithium carbonate. After testing, the purity of the obtained lithium carbonate was 99.55%, which meets the requirements for battery-grade lithium carbonate. (3) The above lithium extraction residue was mixed with potassium hydroxide at a mass ratio of 1:0.45, and water was added to adjust the solid-liquid ratio to 40 g / L. The mixture was then subjected to hydrothermal reaction at 160℃ for 16 h. After the reaction was completed, the solid and liquid were separated to obtain phosphorus-containing filtrate and iron-graphite mixture. (4) The phosphorus-containing filtrate was first evaporated and concentrated to 1 / 3 of the original filtrate volume, then the pH was adjusted to 4.0 with phosphoric acid, and recrystallized at room temperature for 6 h to obtain potassium dihydrogen phosphate. The purity of the obtained potassium dihydrogen phosphate was 94.2%, and the product met the requirements of fertilizer-grade potassium dihydrogen phosphate. The phosphorus recovery rate was 90.8%. (5) The iron-graphite mixture was dried at 60°C for 12 h to obtain an iron-graphite-based soil conditioner composed of amorphous iron tetroxide / ferric hydroxide and graphite.

[0045] Example 3 (1) Take 10 g of retired lithium iron phosphate battery black powder and prepare a suspension with a solid-liquid ratio of 40 g / L with deionized water. Adjust the pH to 1.4 with concentrated sulfuric acid. Add 30% hydrogen peroxide at a volume fraction of 3.2:1 (the molar ratio of hydrogen peroxide to lithium in the retired lithium iron phosphate battery black powder) to obtain a slurry. Electrolyze the slurry in a membrane-free slurry electrolytic cell at 2 V voltage and room temperature for 60 min. After electrolysis, solid and liquid are separated to obtain lithium extraction residue and lithium-containing filtrate. The lithium leaching rate is 98.8%. The electrolyte is recycled. (2) Heat the lithium-containing filtrate to 100℃ and concentrate it to 1 / 3 of its original volume. Add saturated sodium carbonate and allow it to precipitate at 70℃ for 40 minutes. The amount of saturated sodium carbonate added is based on the total number of moles of lithium ions in the lithium-containing filtrate, according to the reaction... The molar ratio was calculated to be 1.05 times the theoretical value. The crude product was washed twice with hot water at 100℃ to obtain lithium carbonate. After testing, the purity of the obtained lithium carbonate was 99.63%, which meets the requirements for battery-grade lithium carbonate. (3) The above lithium extraction residue was mixed with potassium hydroxide at a mass ratio of 1:0.55, and water was added to adjust the solid-liquid ratio to 40 g / L. The mixture was then subjected to hydrothermal reaction at 200℃ for 8 h. After the reaction was completed, the solid and liquid were separated to obtain phosphorus-containing filtrate and iron-graphite mixture. (4) The phosphorus-containing filtrate was first evaporated and concentrated to 1 / 3 of the original filtrate volume, then the pH was adjusted to 4.5 with phosphoric acid, and recrystallized at 25℃ for 10 h to obtain potassium dihydrogen phosphate. The purity of the obtained potassium dihydrogen phosphate was 94.8%, and the product met the requirements of fertilizer-grade potassium dihydrogen phosphate. The phosphorus recovery rate was 92.1%. (5) The iron-graphite mixture was dried at 60°C for 12 h to obtain an iron-graphite-based soil conditioner composed of amorphous iron tetroxide / ferric hydroxide and graphite.

[0046] Example 4 (1) Take 10 g of retired lithium iron phosphate battery black powder and prepare a suspension with a solid-liquid ratio of 50 g / L with deionized water. Adjust the pH to 2.0 with concentrated sulfuric acid. Add 30% hydrogen peroxide by volume at a hydrogen peroxide to lithium molar ratio of 1.2:1 in the retired lithium iron phosphate battery black powder to obtain a slurry. Electrolyze the slurry in a membrane-free slurry electrolytic cell at 5 V voltage and room temperature for 30 min. After electrolysis, solid and liquid are separated to obtain lithium extraction residue and lithium-containing filtrate. The lithium leaching rate is 98.0%. The electrolyte is recycled. (2) Heat the lithium-containing filtrate to 100℃ and concentrate it to 1 / 3 of its original volume. Add saturated sodium carbonate and allow it to precipitate at 80℃ for 80 minutes. The amount of saturated sodium carbonate added is based on the total number of moles of lithium ions in the lithium-containing filtrate, according to the reaction... The molar ratio was calculated to be 1.15 times the theoretical value. The crude product was washed three times with hot water at 80°C to obtain lithium carbonate. After testing, the purity of the obtained lithium carbonate was 99.51%, which meets the requirements for battery-grade lithium carbonate. (3) The above lithium extraction residue was mixed with potassium hydroxide at a mass ratio of 1:0.4, and water was added to adjust the solid-liquid ratio to 40 g / L. The mixture was then subjected to hydrothermal reaction at 150℃ for 24 h. After the reaction was completed, the solid and liquid were separated to obtain phosphorus-containing filtrate and iron-graphite mixture. (4) The phosphorus-containing filtrate was first evaporated and concentrated to 1 / 3 of the original filtrate volume, then the pH was adjusted to 4.3 with phosphoric acid, and recrystallized at 25℃ for 12 h to obtain potassium dihydrogen phosphate. The purity of the obtained potassium dihydrogen phosphate was 94.0%, and the product met the requirements of fertilizer-grade potassium dihydrogen phosphate. The phosphorus recovery rate was 90.5%. (5) The iron-graphite mixture was dried at 60°C for 12 h to obtain an iron-graphite-based soil conditioner composed of amorphous iron tetroxide / ferric hydroxide and graphite.

[0047] Example 5 (1) Take 10 g of retired lithium iron phosphate battery black powder and prepare a suspension with a solid-liquid ratio of 25 g / L with deionized water. Adjust the pH to 1.6 with concentrated sulfuric acid. Add 30% hydrogen peroxide at a volume fraction of 3.9:1 (3.9:1) to obtain a slurry. Electrolyze the slurry in a membrane-free slurry electrolytic cell at 1 V voltage and room temperature for 180 min. After electrolysis, solid and liquid are separated to obtain lithium extraction residue and lithium-containing filtrate. The lithium leaching rate is 98.9%. The electrolyte is recycled. (2) Heat the lithium-containing filtrate to 100℃ and concentrate it to 1 / 3 of its original volume. Add saturated sodium carbonate and allow it to precipitate at 75℃ for 50 minutes. The amount of saturated sodium carbonate added is based on the total number of moles of lithium ions in the lithium-containing filtrate, according to the reaction... The molar ratio was calculated to be 1.08 times the theoretical value. The crude product was washed three times with hot water at 95°C to obtain lithium carbonate. After testing, the purity of the obtained lithium carbonate was 99.58%, which meets the requirements for battery-grade lithium carbonate. (3) The above lithium extraction residue was mixed with potassium hydroxide at a mass ratio of 1:0.52, and water was added to adjust the solid-liquid ratio to 40 g / L. The mixture was then subjected to hydrothermal reaction at 190℃ for 6 h. After the reaction was completed, the solid and liquid were separated to obtain phosphorus-containing filtrate and iron-graphite mixture. (4) The phosphorus-containing filtrate was first evaporated and concentrated to 1 / 3 of the original filtrate volume, then the pH was adjusted to 4.1 with phosphoric acid, and recrystallized at 30℃ for 5 h to obtain potassium dihydrogen phosphate. The purity of the obtained potassium dihydrogen phosphate was 94.6%, and the product met the requirements of fertilizer-grade potassium dihydrogen phosphate. The phosphorus recovery rate was 91.8%. (5) The iron-graphite mixture was dried at 60°C for 12 h to obtain an iron-graphite-based soil conditioner composed of amorphous iron tetroxide / ferric hydroxide and graphite.

[0048] Test case The iron-graphite-based soil conditioner prepared according to this invention (obtained in Example 1) was used to conduct Cd tests at room temperature. 2+ Pb2+ Mixed metal adsorption kinetics experiment: Preparation of Cd at a set concentration 2+ Pb 2+ Equal amounts of iron-graphite-based soil conditioner were weighed and added to the heavy metal solution system, and the adsorption reaction was carried out by constant temperature shaking. Samples were taken at 5 min, 10 min, 30 min, 60 min, 120 min, 240 min, 480 min, 960 min, 1200 min, and 1400 min, respectively. The supernatant was separated by filtration membrane, and the concentration of residual heavy metal ions was determined by inductively coupled plasma atomic emission spectrometry. The adsorption capacity of the material for heavy metals at different time points was calculated based on the concentration difference. The adsorption data were fitted using pseudo-first-order and pseudo-second-order kinetic models, respectively, to obtain the kinetic parameters and correlation coefficients R. 2 The dynamic fitting formula is as follows: Quasi-first-order dynamic model: ( Quasi-second-order dynamic model: + In the formula: To balance the adsorption capacity (mg / g); for t Adsorption capacity at any given time (mg / g); k 1 The quasi-first-order rate constant (min) -1 ); k 2 The pseudo-second-order rate constant (g·mg) -1 ·min -1 ); t Adsorption time (min).

[0049] The adsorption kinetics experiments at room temperature show that the adsorption process of Cd and Pb heavy metals by the iron-graphite-based modifier prepared in this invention conforms to a pseudo-second-order kinetic model, and the fitting correlation coefficient R0 is satisfactory. 2 The adsorption capacity reached 0.9998, with chemical complexation and precipitation mechanisms being the main adsorption mechanisms. The measured equilibrium adsorption capacity of the material for Pb and Cd reached 858.73 mg / g and 143.32 mg / g, respectively. It showed better adsorption and stabilization effect for lead ions and could efficiently passivate cadmium and lead heavy metals in soil, demonstrating excellent potential for soil remediation applications.

[0050] Figure 4 Iron-graphite based modifier for Cd 2+ Pb 2+The adsorption kinetics fitting curves; the left figure is for Cd. 2+ Adsorption kinetics, right figure shows Pb 2+ Adsorption kinetics, with built-in small plots showing the pseudo-second-order kinetic linear fitting curves, and the attached table showing the pseudo-first-order and pseudo-second-order kinetic fitting parameters.

[0051] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for the resource utilization of black powder from retired lithium iron phosphate batteries, characterized in that, Includes the following steps: (1) After mixing retired lithium iron phosphate battery black powder with water, adjust the pH to 1.4~2, add hydrogen peroxide, carry out electrolysis reaction, and after electrolysis, separate solid and liquid to obtain lithium extraction residue and lithium-containing filtrate. (2) The lithium-containing filtrate and carbonate are mixed and a precipitation reaction is carried out to obtain lithium carbonate; (3) Mix lithium extraction residue, inorganic alkali and water, and carry out hydrothermal reaction to obtain phosphorus-containing filtrate and iron-graphite mixture; (4) Adjust the pH of the phosphorus-containing filtrate to 4-4.5 and recrystallize it to obtain potassium dihydrogen phosphate; (5) The iron-graphite mixture is dried to obtain an iron-graphite-based soil conditioner; There is no requirement for the order of steps (2) and (3), and there is no requirement for the order of steps (4) and (5).

2. The method for resource utilization of black powder from decommissioned lithium iron phosphate batteries according to claim 1, characterized in that, The solid-liquid ratio of the retired lithium iron phosphate battery black powder and water is 15~50 g / L.

3. The method for resource utilization of black powder from decommissioned lithium iron phosphate batteries according to claim 2, characterized in that, The molar ratio of lithium in the hydrogen peroxide and the decommissioned lithium iron phosphate battery black powder is 1.1~4:

1.

4. The method for resource utilization of black powder from decommissioned lithium iron phosphate batteries according to claim 1, characterized in that, The voltage of the electrolysis reaction is 0~5 V, the electrolysis time is 30~180 min, and the electrolysis temperature is room temperature.

5. The method for resource utilization of black powder from decommissioned lithium iron phosphate batteries according to claim 1, characterized in that, The carbonate includes sodium carbonate; the amount of carbonate added is based on the total molar number of lithium ions in the lithium-containing filtrate, according to the reaction... The molar ratio is 1.05 to 1.2 times the theoretical value calculated from the molar ratio.

6. The method for resource utilization of black powder from decommissioned lithium iron phosphate batteries according to claim 1, characterized in that, The precipitation reaction is carried out at a temperature of 60-90 °C for a time of 40-90 min.

7. The method for resource utilization of black powder from decommissioned lithium iron phosphate batteries according to claim 1, characterized in that, The inorganic alkali includes potassium hydroxide; the mass ratio of the inorganic alkali to the lithium extraction slag is 0.4~0.55:

1.

8. The method for resource utilization of black powder from decommissioned lithium iron phosphate batteries according to claim 7, characterized in that, The total mass of the lithium extraction residue and inorganic alkali, and the solid-liquid ratio of water, is 40 g / L.

9. The method for resource utilization of black powder from decommissioned lithium iron phosphate batteries according to claim 1, characterized in that, The recrystallization temperature is 20~30 ℃, and the time is 4~12 h.

10. The method for resource utilization of black powder from decommissioned lithium iron phosphate batteries according to claim 1, characterized in that, The iron-graphite-based soil conditioner is used for the passivation and remediation of heavy metal contaminated soil.

Images