A method for recycling waste lithium iron phosphate battery black powder

Abstract

The present application relates to the technical field of resource recycling of waste lithium batteries, and particularly relates to a recovery method of waste lithium iron phosphate battery black powder, which specifically comprises the following steps: S1: first stage leaching; S2: first stage iron and phosphorus precipitation; S3: second stage leaching; S4: second stage iron and phosphorus precipitation; S5: intensified leaching, and recovery of graphite product; S6: separation and recovery of acid; S7: lithium solution is subjected to three times of chemical precipitation and resin deep purification to remove impurities, and three times of impurity removal liquid is obtained; S8: selective extraction; S9: bipolar membrane electrodialysis, in-situ generation of alkali solution and acid solution; and S10: water closed loop, and a byproduct is obtained. The present application is a green black powder recovery process with the characteristics of "closed loop, low consumption and zero emission", realizes the conversion of all components of black powder into high value-added products, and has extremely high industrial application value and environmental and economic benefits.

Description

Technical Field

[0001] This invention relates to the field of waste lithium battery resource recycling technology, and in particular to a method for recycling black powder from waste lithium iron phosphate batteries. Background Technology

[0002] With the global energy structure transformation and the deepening of the "dual-carbon" strategy, the new energy vehicle industry is experiencing explosive growth. Lithium iron phosphate (LiFePO4) batteries, with their advantages of high safety, long cycle life, and low cost, occupy half of the power battery market. It is estimated that by 2030, my country will have over 1.5 million tons of retired lithium iron phosphate batteries per year. The lithium, iron, phosphorus, and graphite contained in these waste batteries are all strategic resources, and their efficient recycling is of great significance for ensuring national resource security, reducing import dependence, and minimizing environmental impact.

[0003] Currently, the mainstream technology for recycling waste lithium iron phosphate black powder is the hydrometallurgical process, whose basic steps include: acid leaching, impurity removal, precipitation / extraction separation, and product preparation. However, existing technologies generally suffer from serious "linear economics" defects, making it difficult to meet the requirements of green manufacturing and a circular economy. 1. Linear consumption of acid and alkali reagents and massive waste salt discharge: The leaching process consumes large amounts of inorganic acids (such as H2SO4), while subsequent impurity removal and precipitation processes consume large amounts of alkalis (such as NaOH and NH3·H2O). These acids and alkalis typically participate in only one reaction, ultimately transforming into low-value, highly soluble inorganic salts (such as Na2SO4 and NaCl), which are discharged with wastewater or evaporated and crystallized into waste salt. Treating every ton of lithium carbonate product often generates 4-6 tons of waste salt, resulting in high disposal costs and significant environmental pressure.

[0004] 2. Low Lithium-Iron-Phosphorus Separation Efficiency: Due to the large specific surface area and adsorption capacity of iron phosphate precipitate (FePO4·xH2O), some lithium ions are adsorbed or encapsulated by the newly formed iron phosphate precipitate during traditional single or double iron-phosphorus precipitation processes, resulting in mechanical entrainment loss of lithium. To achieve high lithium recovery rates, complex washing processes are often required, which not only increases water consumption but also adds to the process difficulty due to the low concentration of lithium in the washing water.

[0005] 3. High water consumption and wastewater generation: The multi-stage leaching, washing, and sedimentation processes generate large amounts of process wastewater containing salt, ammonia nitrogen, or organic matter. Traditional processes lack systematic reuse designs, and large amounts of wastewater are discharged after simple treatment, resulting in water waste.

[0006] 4. Low added value and insufficient full-component recovery: Many processes focus only on lithium recovery, while iron and phosphorus are discarded as solid waste in the form of crude iron phosphate or iron-phosphorus slag, or used only as raw materials for low-end building materials. Graphite slag is often treated as fuel, failing to realize its high-value utilization (such as as a raw material for battery-grade graphite anode materials). The level of comprehensive resource utilization is low.

[0007] CN121294864B relates to a method for one-step chlorination recovery of lithium from waste lithium iron phosphate battery black powder and removal of copper and aluminum from the lithium extraction residue, belonging to the field of waste battery recycling technology. Specifically, in a closed reactor, waste lithium iron phosphate battery black powder is mixed with an acidic deionized water solution, chlorine gas is introduced, and by controlling the initial temperature, maximum temperature rise, reaction pressure, and reaction time, selective lithium extraction and removal of copper and aluminum impurities are achieved through a one-step chlorination reaction. Lithium enters the liquid phase as LiCl through the chlorination reaction, while iron and phosphorus remain in the solid phase as FePO4. Copper and aluminum are removed in the acidic environment and Fe... 3+ After dissolving under the influence of chlorine, it enters the liquid phase. However, this process involves harsh reaction conditions and carries high safety and environmental risks. The method uses highly toxic chlorine gas as a chlorinating agent; even a slight leak in industrial production could lead to a serious safety accident. Furthermore, chlorine gas is extremely corrosive to equipment, significantly increasing equipment investment and maintenance costs.

[0008] Against the backdrop of the "dual carbon" goals and green manufacturing, there is an urgent need to develop a new recycling method that starts from the process design stage. Summary of the Invention

[0009] This invention provides a method for recycling black powder from waste lithium iron phosphate batteries, comprising the following steps: S1: Mix black powder with water to form a slurry, add reagent A and reagent B for the first stage of leaching, and separate the solid and liquid to obtain a first-stage leachate (first leaching solution) and a first-stage leach residue (first leaching residue); In step S1, under acidic and oxidizing atmosphere, the olivine structure of lithium iron phosphate is destroyed, and Li⁺ is released from the crystal lattice into the solution. At the same time, Fe²⁺ is oxidized to Fe³⁺, which combines with PO₄³⁻ in the solution to form FePO₄ precipitate in situ. The goal of this step is to achieve "lithium preferential leaching and iron-phosphorus co-precipitation", avoiding a large amount of iron and phosphorus entering the solution and reducing the burden on subsequent lithium purification; S2: Add reagent B and reagent C to the first leaching solution (first leaching solution), and adjust the pH value with reagent D to carry out the first stage of iron and phosphorus precipitation. Solid-liquid separation is obtained to obtain a first purified solution (first leaching iron and phosphorus precipitation solution) and a first iron and phosphorus slag (first leaching iron and phosphorus slag). A small amount of Fe²⁺ and PO₄³⁻ remain in the leaching solution of step S1. By adding an iron source, the stoichiometric ratio is precisely controlled to ensure that the final FePO₄ precipitate has a complete crystal form and good filterability. Precise pH control (1.0-2.5) is the optimal range for FePO₄ precipitation, and at the same time, it can avoid the hydrolysis precipitation or co-precipitation of Li⁺ to the greatest extent. This step is called "stepwise iron and phosphorus precipitation". Its core concept is to remove iron and phosphorus from the solution to an extremely low level step by step and precisely. S3: The first-stage leaching residue (first-stage leaching residue) and the first-stage iron-phosphorus residue (first-stage leaching iron-phosphorus residue) are combined, and reagents A and B are added for a second-stage leaching. Solid-liquid separation yields a second-stage leaching solution (second-stage leaching solution) and a second-stage leaching residue (iron-phosphorus residue). Li⁺ physically or chemically adsorbed / entrained on the surface of the first-stage FePO4 precipitate is displaced by a high concentration of H⁺ under these conditions and enters the second-stage leaching solution. This significantly improves the overall lithium recovery rate. The second-stage leaching residue mainly consists of purer FePO4. S4: Add reagent B and reagent C to the second-stage leachate (second-stage leachate), adjust the pH value with reagent D to precipitate iron phosphorus, and separate the solid and liquid to obtain the first-stage iron phosphorus precipitate solution (first-stage iron phosphorus precipitate solution) and the first-stage iron phosphorus precipitate slag (first-stage iron phosphorus precipitate slag). Add reagent D to the first-stage iron phosphorus precipitate solution (first-stage iron phosphorus precipitate solution) again, and perform second-stage iron phosphorus precipitate filtration to obtain the second-stage purified solution (second-stage iron phosphorus precipitate solution) and the second-stage iron phosphorus precipitate slag. S5: The first-stage leaching iron-phosphorus slag (first-stage leaching iron-phosphorus slag), the second-stage leaching slag (iron-phosphorus slag), and the second-stage leaching iron-phosphorus slag are mixed and subjected to enhanced leaching with reagent A, followed by solid-liquid separation to obtain ferrophosphorus leaching solution (iron-phosphorus solution) and carbon slag. The carbon slag is washed to obtain graphite products, and the washing water is returned to S1 and S3 for use as pulping water. High-concentration acid can completely dissolve FePO4 to generate Fe³⁺ and H3PO4, forming ferrophosphorus leaching solution. This solution can be directly used as a high-quality raw material for producing battery-grade FePO4 precursors. The insoluble carbon-rich slag is washed in multiple stages of countercurrent (washing water is reused) to obtain high-purity graphite products. S6: The ferric phosphorus leaching solution (iron-phosphorus solution) obtained in step S5 is sent to an electrodialysis system to separate and recover the acid. The recovered acid is returned to S1, S3, and S5 as leaching acid, and the deacidified solution enters the subsequent ferric phosphorus preparation system. The ferric phosphorus leaching solution contains high concentrations of Fe³⁺ and PO₄³⁻, as well as free H₂SO₄. Electrodialysis can selectively separate and recover the free acid to obtain dilute sulfuric acid, which can be directly reused in S1, S3, and S5. The deacidified solution mainly consists of Fe₂(SO₄)₃ and H₃PO₄, which is an ideal raw material for preparing battery-grade FePO₄ without the need for additional pH adjustment. S7: The first stage purification solution (first stage iron and phosphorus precipitation solution) and the second stage purification solution (second stage iron and phosphorus precipitation solution) are combined to obtain a lithium solution. The lithium solution is subjected to three chemical precipitation impurity removals and resin deep purification impurity removals to obtain a three-stage impurity removal solution. S8: The three-stage purification solution obtained in step S7 is subjected to lithium-selective extraction using an extractant to obtain a loaded organic phase and raffinate. The loaded organic phase is back-extracted with carbon dioxide gas to obtain a carbonized solution. Compared with traditional acid back-extraction, this process does not introduce Cl⁻ or other anions, and directly obtains a high-purity LiHCO3 solution, which can be pyrolyzed to prepare battery-grade Li₂CO₃ without further conversion. CO₂ can be recycled. S9: The organic phase after carbon dioxide gas back-extraction in step S8 is acid-back-extracted and regenerated for reuse. The lithium-enriched solution obtained after acid back-extraction is sent to a bipolar membrane electrodialysis system to generate an alkaline solution and an acid solution in situ under a DC electric field. The alkaline solution is returned to S2 and S4 for use as precipitating iron phosphate, and the acid solution is returned to S1, S3 and S5 for use as leaching acid, thereby realizing a double closed loop of acid and alkali. S10: The raffinate obtained in step S8 is de-oiled and adsorbed by activated carbon before being sent to the MVR system for evaporation and crystallization. The condensate is returned to the front-end pulping to achieve water closed loop. The crystals are sodium sulfate by-products.

[0010] Further, in steps S1 and S3, reagent A is at least one of sulfuric acid and citric acid; reagent B is 27.5wt% hydrogen peroxide; the leaching conditions are: pH 0.6-1.2, temperature 50-90℃, time 1-2h, liquid-solid ratio (3-7):1. Hydrogen peroxide and sulfuric acid work together to ensure that iron exists in the form of Fe³⁺, which immediately combines with PO₄³⁻ to form FePO₄ precipitate, preventing Fe²⁺ from circulating in the solution and avoiding re-encapsulation of lithium.

[0011] Further, in steps S2 and S4, reagent C is at least one of ferrous sulfate and ferric chloride, used to adjust the iron-phosphorus molar ratio in the system to 1:1; reagent D is an alkali, with the target pH range for pH adjustment being 1.0-2.5, the reaction temperature being 50-90℃, and the time being 0.5-1.5 h. The alkali is the alkali produced in step S9, or a sodium hydroxide solution, or a lithium hydroxide solution. Only when the molar ratio of Fe and P is strictly 1:1 can the simultaneous and complete precipitation of both be guaranteed, avoiding any excess leading to product impurity or incomplete iron-phosphorus precipitation. Excess Fe³⁺ will hydrolyze to produce ferric hydroxide colloid, while excess P will lead to excessive phosphorus in subsequent lithium products.

[0012] Furthermore, in step S6, the acid recovery rate of the electrodialysis system is not less than 95%, and the concentrated acid can be reused in the leaching section.

[0013] Further, in step S8, the extractant is pyrrole trifluoromethyl-β-diketone or a quaternary synergistic extraction system; the carbon dioxide back-extraction pressure is 0.1-0.5 MPa, and the temperature is 20-40℃; the lithium bicarbonate solution generated by back-extraction can be directly used to prepare lithium carbonate products; the carbon dioxide gas can be recycled; the quaternary synergistic extraction system is a quaternary synergistic extraction system of dibenzoylmethane, tributyl phosphate, trioctylphosphine oxide, and n-octanol-sulfonated kerosene composite diluent; the volume concentration of dibenzoylmethane is 5-15%, serving as the main extractant for selectively chelating Li⁺ to form hydrophobic complexes; the volume concentration of tributyl phosphate is 2-8%, serving as the first co-extractant. To reduce the viscosity and melting point of the system and enhance the coordination ability of Li⁺ through intermolecular hydrogen bonds, the volume concentration of trioctylphosphine oxide is 1-5%, which acts as a second co-extractant to form a "sandwich" coordination structure with dibenzoylmethane, further improving the selective coordination ability of Li⁺. The composite diluent is 70-92%, which is composed of sulfonated kerosene and n-octanol in a volume ratio of (5-10):1. Among them, n-octanol acts as a surfactant to reduce the interfacial tension between the two phases, thereby shortening the phase separation time and preventing the formation of microemulsion phase. The quaternary system of the present invention achieves “three synergistic” enhancement: (1) dual synergistic extraction - the P=O functional groups of trioctylphosphine oxide and tributyl phosphate form a dual coordination enhancement effect with the enol anion of dibenzoylmethane through different spatial configurations, which greatly improves the partition coefficient of Li⁺ in the organic phase; (2) phase modification synergistic - n-octanol reduces interfacial tension and prevents the formation of reverse microemulsion, which greatly shortens the phase separation time; (3) stability synergistic - tributyl phosphate and n-octanol jointly inhibit the precipitation and crystallization of dibenzoylmethane.

[0014] Further, a pre-oxidation treatment is added before step S1. This process involves mixing black powder and potassium persulfate at a mass ratio of 100:(3-8) and performing a mechanochemical activation pre-oxidation treatment to obtain pre-oxidized black powder. The mixing method involves placing the black powder and potassium persulfate in a planetary ball mill at a milling speed of 300-600 r / min, a ball-to-material ratio of (10-20):1, and a milling time of 1-3 hours. Under the mechanical force of the ball mill, potassium persulfate acts as a solid-phase oxidant and undergoes a mechanochemical solid-phase oxidation reaction with LiFePO4. The mechanical force induces a decrease in LiFePO4 particle size and an increase in specific surface area, and also acts as a driving force for the oxidation reaction, causing Li⁺ to migrate out of the olivine structure, and Fe... 2+ Oxidized to Fe 3+ The crystal structure of LiFePO4, after mechanical solid-phase oxidation treatment, has been destroyed in advance, creating extremely favorable conditions for subsequent water leaching lithium extraction, and the water leaching rate of lithium is further improved.

[0015] Furthermore, in step S9, the bipolar membrane electrodialysis system is composed of alternating cation exchange membranes, anion exchange membranes, and bipolar membranes. Under the action of a DC electric field, it decomposes lithium-containing aqueous solutions into acid solutions and alkaline solutions, with an acid conversion rate of not less than 75% and an alkaline conversion rate of not less than 79%.

[0016] Furthermore, the alkaline solution produced in step S9 is returned to S2 and S4 for use, and the acid solution produced is combined with the acid recovered in step S6 and returned to S1, S3 and S5 for use. The self-sufficiency rate of acid and alkali in the system is significantly improved, and the amount of reagents used is greatly reduced.

[0017] Furthermore, the recycling method provided by this invention forms a complete material cycle: lithium is ultimately recovered as lithium bicarbonate / lithium carbonate products, iron and phosphorus are recovered as iron phosphate precursors, carbon is recovered as graphite products, sodium is recovered as sodium sulfate byproducts, water is recycled within the system, and acids and alkalis are regenerated in situ through a membrane system.

[0018] Furthermore, the recycling method of the present invention achieves a comprehensive lithium recovery rate of ≥95%, an iron recovery rate of ≥92%, a phosphorus recovery rate of ≥93%, and a graphite recovery rate of ≥90% throughout the entire process. The amount of waste salt discharged from the process is significantly reduced compared to the traditional acid and alkali process that purchases all its own salt, and the amount of fresh water replenished is also significantly reduced.

[0019] This invention provides a circular recycling method for waste lithium iron phosphate battery black powder. Through a "tiered oxidation acid leaching-stepwise precise iron and phosphorus precipitation" technology, it significantly improves the separation efficiency of lithium from iron and phosphorus, ensuring a high recovery rate. Using a "electrodialysis-bipolar membrane electrodialysis" dual-membrane coupling system, it achieves for the first time a "double closed loop" for leaching acid and iron and phosphorus precipitation alkali, greatly reducing the consumption of purchased chemicals and waste salt emissions. Through a systematic water reuse design, it achieves a closed-loop aqueous phase. This invention innovates the traditional "open-loop, high-consumption, high-emission" process into a "closed-loop, low-consumption, zero-emission" green process, realizing the transformation of all components of the black powder into high-value-added products. It has extremely high industrial application value and environmental and economic benefits, meeting the urgent national needs for a circular economy and "dual-carbon" goals. Attached Figure Description

[0020] Figure 1 This is a schematic flowchart illustrating the method for recycling black powder from waste lithium iron phosphate batteries according to the present invention. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0022] In the examples below, each waste lithium iron phosphate black powder was 1000g, dry basis, with lithium 2.83%, iron 18.15%, and phosphorus 10.46%, and was slurried with pure water at a liquid-to-solid ratio of 5:1. Example

[0023] A method for recycling black powder from waste lithium iron phosphate batteries includes the following steps: S1: Mix black powder with water to make a pulp, add reagent A and reagent B to carry out the first stage of leaching, and separate the solid and liquid to obtain a leaching solution and a leaching residue. S2: Add agent B and agent C to the first leaching solution, adjust the pH value with agent D to carry out the first stage of iron phosphorus precipitation, and separate the solid and liquid to obtain a first leaching iron phosphorus precipitation solution and a first leaching iron phosphorus precipitation residue. S3: Combine the first leaching residue with the first leached iron-phosphorus residue, add reagent A and reagent B for a second leaching stage, and separate the solid and liquid to obtain the second leaching solution and iron-phosphorus residue. S4: Add reagent B and reagent C to the second immersion solution, adjust the pH value with reagent D to precipitate iron phosphorus, and separate the solid and liquid to obtain a first-stage iron phosphorus precipitate solution and a first-stage iron phosphorus precipitate slag. Add reagent D to the first-stage iron phosphorus precipitate solution again and perform second-stage iron phosphorus precipitate filtration to obtain a second-stage iron phosphorus precipitate solution and a second-stage iron phosphorus precipitate slag. S5: Mix the first stage iron-phosphorus slag, the iron-phosphorus slag and the second stage iron-phosphorus slag, and perform enhanced leaching with reagent A, followed by solid-liquid separation to obtain iron-phosphorus liquid and carbon slag. The carbon slag is washed to obtain graphite products, and the washing water is returned to S1 and S3 for use as pulping water. S6: The iron-phosphorus solution described in step S5 is sent to an electrodialysis system to separate and recover acid. The recovered acid is returned to S1, S3, and S5 as leaching acid, and the deacidified solution is sent to the subsequent iron phosphate preparation system. S7: The first-stage iron-phosphorus precipitation solution and the second-stage iron-phosphorus precipitation solution are combined to obtain a lithium solution. The lithium solution is then subjected to three chemical precipitation impurity removals and resin deep purification impurity removals to obtain a three-stage impurity removal solution. S8: The three impurity removal solutions obtained in step S7 are subjected to lithium selective extraction using an extractant to obtain a loaded organic phase and raffinate. The loaded organic phase is back-extracted with carbon dioxide gas to obtain a carbonized solution. S9: The organic phase after carbon dioxide gas back-extraction in step S8 is acid-back-extracted and regenerated for reuse. The lithium-enriched solution obtained after acid back-extraction is sent to a bipolar membrane electrodialysis system to generate an alkaline solution and an acid solution in situ under a DC electric field. The alkaline solution is returned to S2 and S4 for use as precipitating iron phosphate, and the acid solution is returned to S1, S3 and S5 for use as leaching acid, thereby realizing a double closed loop of acid and alkali. S10: The raffinate obtained in step S8 is de-oiled and adsorbed by activated carbon before being sent to the MVR system for evaporation and crystallization. The condensate is returned to the front-end pulping to achieve water closed loop. The crystals are sodium sulfate by-products.

[0024] In steps S1 and S3, reagent A is 15wt% sulfuric acid; reagent B is 27.5wt% hydrogen peroxide; the leaching conditions are: pH 0.9-1.1, temperature 60-65℃, time 2h, and liquid-solid ratio 5:1.

[0025] In steps S2 and S4, reagent C is ferrous sulfate, used to adjust the iron-phosphorus molar ratio in the system to 1:1; reagent D is a base, the target pH range of which is 1.6-1.8, the reaction temperature is 60-65℃, the reaction time is 1h, and the base is the base produced in step S9.

[0026] In step S6, the acid recovery rate of the electrodialysis system is 95.3%, and the concentrated acid can be reused in the leaching section.

[0027] In step S8, the extractant is pyrrole trifluoromethyl-β-dione, the carbon dioxide back-extraction pressure is 0.2 MPa, the temperature is 25-30℃, the lithium bicarbonate solution generated by back-extraction can be directly used to prepare lithium carbonate products, and the carbon dioxide gas can be recycled.

[0028] In step S9, the bipolar membrane electrodialysis system is composed of alternating cation exchange membranes, anion exchange membranes, and bipolar membranes. Under the action of a DC electric field, it decomposes lithium-containing aqueous solution into acid solution and alkaline solution, with an acid conversion rate of 76.2% and an alkaline conversion rate of 79.3%.

[0029] The alkaline solution produced in step S9 is returned to S2 and S4 for use, and the acid solution produced is combined with the acid recovered in step S6 and returned to S1, S3 and S5 for use. The self-sufficiency rate of acid and alkali in the system is significantly improved, and the amount of reagents used is greatly reduced.

[0030] The above-mentioned recycling method recovers lithium as lithium bicarbonate / lithium carbonate products, iron and phosphorus as iron phosphate precursors, carbon as graphite products, and sodium as sodium sulfate byproducts. Water is recycled within the system, and acids and alkalis are regenerated in situ through a membrane system. The overall recovery rate of lithium is 95.2%, iron is 92.3%, phosphorus is 93.5%, and graphite is 91.2%. The amount of waste salt discharged from the process is significantly reduced compared to the traditional process of purchasing acid and alkalis entirely externally, and the amount of fresh water replenishment is also significantly reduced. Example

[0031] A method for recycling black powder from waste lithium iron phosphate batteries includes the following steps: S1: Mix black powder with water to make a pulp, add reagent A and reagent B to carry out the first stage of leaching, and separate the solid and liquid to obtain a leaching solution and a leaching residue. S2: Add agent B and agent C to the first leaching solution, adjust the pH value with agent D to carry out the first stage of iron phosphorus precipitation, and separate the solid and liquid to obtain a first leaching iron phosphorus precipitation solution and a first leaching iron phosphorus precipitation residue. S3: Combine the first leaching residue with the first leached iron-phosphorus residue, add reagent A and reagent B for a second leaching stage, and separate the solid and liquid to obtain the second leaching solution and iron-phosphorus residue. S4: Add reagent B and reagent C to the second immersion solution, adjust the pH value with reagent D to precipitate iron phosphorus, and separate the solid and liquid to obtain a first-stage iron phosphorus precipitate solution and a first-stage iron phosphorus precipitate slag. Add reagent D to the first-stage iron phosphorus precipitate solution again and perform second-stage iron phosphorus precipitate filtration to obtain a second-stage iron phosphorus precipitate solution and a second-stage iron phosphorus precipitate slag. S5: Mix the first stage iron-phosphorus slag, the iron-phosphorus slag and the second stage iron-phosphorus slag, and perform enhanced leaching with reagent A, followed by solid-liquid separation to obtain iron-phosphorus liquid and carbon slag. The carbon slag is washed to obtain graphite products, and the washing water is returned to S1 and S3 for use as pulping water. S6: The iron-phosphorus solution described in step S5 is sent to an electrodialysis system to separate and recover acid. The recovered acid is returned to S1, S3, and S5 as leaching acid, and the deacidified solution is sent to the subsequent iron phosphate preparation system. S7: The first-stage iron-phosphorus precipitation solution and the second-stage iron-phosphorus precipitation solution are combined to obtain a lithium solution. The lithium solution is then subjected to three chemical precipitation impurity removals and resin deep purification impurity removals to obtain a three-stage impurity removal solution. S8: The three impurity removal solutions obtained in step S7 are subjected to lithium selective extraction using an extractant to obtain a loaded organic phase and raffinate. The loaded organic phase is back-extracted with carbon dioxide gas to obtain a carbonized solution. S9: The organic phase after carbon dioxide gas back-extraction in step S8 is acid-back-extracted and regenerated for reuse. The lithium-enriched solution obtained after acid back-extraction is sent to a bipolar membrane electrodialysis system to generate an alkaline solution and an acid solution in situ under a DC electric field. The alkaline solution is returned to S2 and S4 for use as precipitating iron phosphate, and the acid solution is returned to S1, S3 and S5 for use as leaching acid, thereby realizing a double closed loop of acid and alkali. S10: The raffinate obtained in step S8 is de-oiled and adsorbed by activated carbon before being sent to the MVR system for evaporation and crystallization. The condensate is returned to the front-end pulping to achieve water closed loop. The crystals are sodium sulfate by-products.

[0032] In steps S1 and S3, reagent A is a mixture of 15wt% sulfuric acid and 5wt% citric acid; reagent B is 27.5wt% hydrogen peroxide; the leaching conditions are: pH 0.9-1.1, temperature 60-65℃, time 2h, and liquid-solid ratio 5:1.

[0033] In steps S2 and S4, reagent C is ferric chloride, used to adjust the iron-phosphorus molar ratio in the system to 1:1; reagent D is a base, the target pH range of which is 1.6-1.8, the reaction temperature is 60-65℃, the reaction time is 1h, and the base is sodium hydroxide solution.

[0034] In step S6, the acid recovery rate of the electrodialysis system is 95.2%, and the concentrated acid can be reused in the leaching section.

[0035] In step S8, the extractant is pyrrole trifluoromethyl-β-dione, the carbon dioxide back-extraction pressure is 0.2 MPa, the temperature is 25-30℃, the lithium bicarbonate solution generated by back-extraction can be directly used to prepare lithium carbonate products, and the carbon dioxide gas can be recycled.

[0036] In step S9, the bipolar membrane electrodialysis system is composed of alternating cation exchange membranes, anion exchange membranes and bipolar membranes. Under the action of a DC electric field, it decomposes lithium-containing aqueous solution into acid solution and alkaline solution, with an acid conversion rate of 76.3% and an alkaline conversion rate of 79.5%.

[0037] The alkaline solution produced in step S9 is returned to S2 and S4 for use, and the acid solution produced is combined with the acid recovered in step S6 and returned to S1, S3 and S5 for use. The self-sufficiency rate of acid and alkali in the system is significantly improved, and the amount of reagents used is greatly reduced.

[0038] The above-mentioned recycling method recovers lithium as lithium bicarbonate / lithium carbonate products, iron and phosphorus as iron phosphate precursors, carbon as graphite products, and sodium as sodium sulfate byproducts. Water is recycled within the system, and acids and alkalis are regenerated in situ through a membrane system. The overall recovery rate of lithium is 95.6%, iron is 92.5%, phosphorus is 93.8%, and graphite is 91.1%. The amount of waste salt discharged from the process is significantly reduced compared to traditional acid and alkali processes that rely entirely on external purchases, and the amount of fresh water replenishment is also significantly reduced. Example

[0039] A method for recycling black powder from waste lithium iron phosphate batteries includes the following steps: S1: Mix black powder with water to make a pulp, add reagent A and reagent B to carry out the first stage of leaching, and separate the solid and liquid to obtain a leaching solution and a leaching residue. S2: Add agent B and agent C to the first leaching solution, adjust the pH value with agent D to carry out the first stage of iron phosphorus precipitation, and separate the solid and liquid to obtain a first leaching iron phosphorus precipitation solution and a first leaching iron phosphorus precipitation residue. S3: Combine the first leaching residue with the first leached iron-phosphorus residue, add reagent A and reagent B for a second leaching stage, and separate the solid and liquid to obtain the second leaching solution and iron-phosphorus residue. S4: Add reagent B and reagent C to the second immersion solution, adjust the pH value with reagent D to precipitate iron phosphorus, and separate the solid and liquid to obtain a first-stage iron phosphorus precipitate solution and a first-stage iron phosphorus precipitate slag. Add reagent D to the first-stage iron phosphorus precipitate solution again and perform second-stage iron phosphorus precipitate filtration to obtain a second-stage iron phosphorus precipitate solution and a second-stage iron phosphorus precipitate slag. S5: Mix the first stage iron-phosphorus slag, the iron-phosphorus slag and the second stage iron-phosphorus slag, and perform enhanced leaching with reagent A, followed by solid-liquid separation to obtain iron-phosphorus liquid and carbon slag. The carbon slag is washed to obtain graphite products, and the washing water is returned to S1 and S3 for use as pulping water. S6: The iron-phosphorus solution described in step S5 is sent to an electrodialysis system to separate and recover acid. The recovered acid is returned to S1, S3, and S5 as leaching acid, and the deacidified solution is sent to the subsequent iron phosphate preparation system. S7: The first-stage iron-phosphorus precipitation solution and the second-stage iron-phosphorus precipitation solution are combined to obtain a lithium solution. The lithium solution is then subjected to three chemical precipitation impurity removals and resin deep purification impurity removals to obtain a three-stage impurity removal solution. S8: The three impurity removal solutions obtained in step S7 are subjected to lithium selective extraction using an extractant to obtain a loaded organic phase and raffinate. The loaded organic phase is back-extracted with carbon dioxide gas to obtain a carbonized solution. S9: The organic phase after carbon dioxide gas back-extraction in step S8 is acid-back-extracted and regenerated for reuse. The lithium-enriched solution obtained after acid back-extraction is sent to a bipolar membrane electrodialysis system to generate an alkaline solution and an acid solution in situ under a DC electric field. The alkaline solution is returned to S2 and S4 for use as precipitating iron phosphate, and the acid solution is returned to S1, S3 and S5 for use as leaching acid, thereby realizing a double closed loop of acid and alkali. S10: The raffinate obtained in step S8 is de-oiled and adsorbed by activated carbon before being sent to the MVR system for evaporation and crystallization. The condensate is returned to the front-end pulping to achieve water closed loop. The crystals are sodium sulfate by-products.

[0040] In steps S1 and S3, reagent A is 15wt% sulfuric acid; reagent B is 27.5wt% hydrogen peroxide; the leaching conditions are: pH 0.9-1.1, temperature 60-65℃, time 2h, and liquid-solid ratio 5:1.

[0041] In steps S2 and S4, reagent C is ferrous sulfate, used to adjust the iron-phosphorus molar ratio in the system to 1:1; reagent D is a base, the target pH range of which is 1.6-1.8, the reaction temperature is 60-65℃, the reaction time is 1h, and the base is the base produced in step S9.

[0042] In step S6, the acid recovery rate of the electrodialysis system is 95.2%, and the concentrated acid can be reused in the leaching section.

[0043] In step S8, the extractant is a quaternary synergistic extraction system. The carbon dioxide back-extraction pressure is 0.2 MPa, and the temperature is 25-30℃. The lithium bicarbonate solution generated by back-extraction can be directly used to prepare lithium carbonate products, and the carbon dioxide gas can be recycled. The quaternary synergistic extraction system is a quaternary synergistic extraction system of dibenzoylmethane, tributyl phosphate, trioctylphosphine oxide, and n-octanol-sulfonated kerosene composite diluent. The volume concentration of dibenzoylmethane is 10%, the volume concentration of tributyl phosphate is 5%, the volume concentration of trioctylphosphine oxide is 3%, and the volume concentration of the composite diluent is 82%. The composite diluent is composed of sulfonated kerosene and n-octanol in a volume ratio of 6:1.

[0044] In step S9, the bipolar membrane electrodialysis system is composed of alternating cation exchange membranes, anion exchange membranes and bipolar membranes. Under the action of a DC electric field, it decomposes lithium-containing aqueous solution into acid solution and alkaline solution, with an acid conversion rate of 76.8% and an alkaline conversion rate of 79.4%.

[0045] The alkaline solution produced in step S9 is returned to S2 and S4 for use, and the acid solution produced is combined with the acid recovered in step S6 and returned to S1, S3 and S5 for use. The self-sufficiency rate of acid and alkali in the system is significantly improved, and the amount of reagents used is greatly reduced.

[0046] The above-mentioned recycling method recovers lithium as lithium bicarbonate / lithium carbonate products, iron and phosphorus as iron phosphate precursors, carbon as graphite products, and sodium as sodium sulfate byproducts. Water is recycled within the system, and acids and alkalis are regenerated in situ through a membrane system. The overall recovery rate of lithium is 96.3%, iron is 92.7%, phosphorus is 93.9%, and graphite is 91.3%. The amount of waste salt discharged from the process is significantly reduced compared to traditional acid and alkali processes that rely entirely on external purchases, and the amount of fresh water replenishment is also significantly reduced. Example

[0047] A method for recycling black powder from waste lithium iron phosphate batteries includes the following steps: S1: Mix black powder with water to make a pulp, add reagent A and reagent B to carry out the first stage of leaching, and separate the solid and liquid to obtain a leaching solution and a leaching residue. S2: Add agent B and agent C to the first leaching solution, adjust the pH value with agent D to carry out the first stage of iron phosphorus precipitation, and separate the solid and liquid to obtain a first leaching iron phosphorus precipitation solution and a first leaching iron phosphorus precipitation residue. S3: Combine the first leaching residue with the first leached iron-phosphorus residue, add reagent A and reagent B for a second leaching stage, and separate the solid and liquid to obtain the second leaching solution and iron-phosphorus residue. S4: Add reagent B and reagent C to the second immersion solution, adjust the pH value with reagent D to precipitate iron phosphorus, and separate the solid and liquid to obtain a first-stage iron phosphorus precipitate solution and a first-stage iron phosphorus precipitate slag. Add reagent D to the first-stage iron phosphorus precipitate solution again and perform second-stage iron phosphorus precipitate filtration to obtain a second-stage iron phosphorus precipitate solution and a second-stage iron phosphorus precipitate slag. S5: Mix the first stage iron-phosphorus slag, the iron-phosphorus slag and the second stage iron-phosphorus slag, and perform enhanced leaching with reagent A, followed by solid-liquid separation to obtain iron-phosphorus liquid and carbon slag. The carbon slag is washed to obtain graphite products, and the washing water is returned to S1 and S3 for use as pulping water. S6: The iron-phosphorus solution described in step S5 is sent to an electrodialysis system to separate and recover acid. The recovered acid is returned to S1, S3, and S5 as leaching acid, and the deacidified solution is sent to the subsequent iron phosphate preparation system. S7: The first-stage iron-phosphorus precipitation solution and the second-stage iron-phosphorus precipitation solution are combined to obtain a lithium solution. The lithium solution is then subjected to three chemical precipitation impurity removals and resin deep purification impurity removals to obtain a three-stage impurity removal solution. S8: The three impurity removal solutions obtained in step S7 are subjected to lithium selective extraction using an extractant to obtain a loaded organic phase and raffinate. The loaded organic phase is back-extracted with carbon dioxide gas to obtain a carbonized solution. S9: The organic phase after carbon dioxide gas back-extraction in step S8 is acid-back-extracted and regenerated for reuse. The lithium-enriched solution obtained after acid back-extraction is sent to a bipolar membrane electrodialysis system to generate an alkaline solution and an acid solution in situ under a DC electric field. The alkaline solution is returned to S2 and S4 for use as precipitating iron phosphate, and the acid solution is returned to S1, S3 and S5 for use as leaching acid, thereby realizing a double closed loop of acid and alkali. S10: The raffinate obtained in step S8 is de-oiled and adsorbed by activated carbon before being sent to the MVR system for evaporation and crystallization. The condensate is returned to the front-end pulping to achieve water closed loop. The crystals are sodium sulfate by-products.

[0048] Before step S1, a pre-oxidation treatment is added. The process involves mixing black powder and potassium persulfate at a mass ratio of 100:3 and performing a mechanochemical activation pre-oxidation treatment to obtain pre-oxidized black powder. The mixing method is to carry out the black powder and potassium persulfate in a planetary ball mill with a ball milling speed of 400 r / min, a ball-to-material ratio of 15:1, and a ball milling time of 2 hours.

[0049] In steps S1 and S3, reagent A is 15wt% sulfuric acid; reagent B is 27.5wt% hydrogen peroxide; the leaching conditions are: pH 0.9-1.1, temperature 60-65℃, time 2h, and liquid-solid ratio 5:1.

[0050] In steps S2 and S4, reagent C is ferrous sulfate, used to adjust the iron-phosphorus molar ratio in the system to 1:1; reagent D is a base, the target pH range of which is 1.6-1.8, the reaction temperature is 60-65℃, the reaction time is 1h, and the base is the base produced in step S9.

[0051] In step S6, the acid recovery rate of the electrodialysis system is 95.3%, and the concentrated acid can be reused in the leaching section.

[0052] In step S8, the extractant is pyrrole trifluoromethyl-β-dione, the carbon dioxide back-extraction pressure is 0.2 MPa, the temperature is 25-30℃, the lithium bicarbonate solution generated by back-extraction can be directly used to prepare lithium carbonate products, and the carbon dioxide gas can be recycled.

[0053] In step S9, the bipolar membrane electrodialysis system is composed of alternating cation exchange membranes, anion exchange membranes and bipolar membranes. Under the action of a DC electric field, it decomposes lithium-containing aqueous solution into acid solution and alkaline solution, with an acid conversion rate of 76.3% and an alkaline conversion rate of 79.4%.

[0054] The alkaline solution produced in step S9 is returned to S2 and S4 for use, and the acid solution produced is combined with the acid recovered in step S6 and returned to S1, S3 and S5 for use. The self-sufficiency rate of acid and alkali in the system is significantly improved, and the amount of reagents used is greatly reduced.

[0055] The above-mentioned recycling method recovers lithium as lithium bicarbonate / lithium carbonate products, iron and phosphorus as iron phosphate precursors, carbon as graphite products, and sodium as sodium sulfate byproducts. Water is recycled within the system, and acids and alkalis are regenerated in situ through a membrane system. The overall recovery rate of lithium is 96.1%, iron is 93.6%, phosphorus is 94.1%, and graphite is 91.2%. The amount of waste salt discharged from the process is significantly reduced compared to the traditional process of purchasing acid and alkalis entirely externally, and the amount of fresh water replenishment is also significantly reduced.

[0056] The data comparison of the above embodiments shows that adding citric acid slightly increases the recovery rates of lithium, iron, and phosphorus. The quaternary synergistic extraction system can significantly improve the recovery rates of lithium, iron, and phosphorus. Pre-oxidation treatment can also improve the recovery rates of lithium, iron, and phosphorus.

Claims

1. A method for recycling black powder from waste lithium iron phosphate batteries, characterized in that, Includes the following steps: S1: Mix black powder with water to make a pulp, add reagent A and reagent B to carry out the first stage of leaching, and separate the solid and liquid to obtain a leaching solution and a leaching residue. S2: Add agent B and agent C to the first leaching solution, adjust the pH value with agent D to carry out the first stage of iron phosphorus precipitation, and separate the solid and liquid to obtain a first leaching iron phosphorus precipitation solution and a first leaching iron phosphorus precipitation residue. S3: Combine the first leaching residue with the first leached iron-phosphorus residue, add reagent A and reagent B for a second leaching stage, and separate the solid and liquid to obtain the second leaching solution and iron-phosphorus residue. S4: Add reagent B and reagent C to the second immersion solution, adjust the pH value with reagent D to precipitate iron phosphorus, and separate the solid and liquid to obtain a first-stage iron phosphorus precipitate solution and a first-stage iron phosphorus precipitate slag. Add reagent D to the first-stage iron phosphorus precipitate solution again and perform second-stage iron phosphorus precipitate filtration to obtain a second-stage iron phosphorus precipitate solution and a second-stage iron phosphorus precipitate slag. S5: Mix the first stage iron-phosphorus slag, the iron-phosphorus slag and the second stage iron-phosphorus slag, and perform enhanced leaching with reagent A, followed by solid-liquid separation to obtain iron-phosphorus liquid and carbon slag. The carbon slag is washed to obtain graphite products, and the washing water is returned to S1 and S3 for use as pulping water. S6: The iron-phosphorus solution described in step S5 is sent to an electrodialysis system to separate and recover acid. The recovered acid is returned to S1, S3, and S5 as leaching acid, and the deacidified solution is sent to the subsequent iron phosphate preparation system. S7: The first-stage iron-phosphorus precipitation solution and the second-stage iron-phosphorus precipitation solution are combined to obtain a lithium solution. The lithium solution is then subjected to three chemical precipitation impurity removals and resin deep purification impurity removals to obtain a three-stage impurity removal solution. S8: The three impurity removal solutions obtained in step S7 are subjected to lithium selective extraction using an extractant to obtain a loaded organic phase and raffinate. The loaded organic phase is back-extracted with carbon dioxide gas to obtain a carbonized solution. S9: The organic phase after carbon dioxide gas back-extraction in step S8 is acid-back-extracted and regenerated for reuse. The lithium-enriched solution obtained after acid back-extraction is sent to a bipolar membrane electrodialysis system to generate an alkaline solution and an acid solution in situ under a DC electric field. The alkaline solution is returned to S2 and S4 for use as precipitating iron phosphate, and the acid solution is returned to S1, S3 and S5 for use as leaching acid, thereby realizing a double closed loop of acid and alkali. S10: The raffinate obtained in step S8 is de-oiled and adsorbed by activated carbon before being sent to the MVR system for evaporation and crystallization. The condensate is returned to the front-end pulping to achieve water closed loop. The crystals are sodium sulfate by-products.

2. The recycling method according to claim 1, characterized in that, In steps S1 and S3, reagent A is at least one of sulfuric acid and citric acid; reagent B is 27.5wt% hydrogen peroxide; the leaching conditions are: pH value 0.6-1.2, temperature 50-90℃, time 1-2h, and liquid-solid ratio (3-7):

1.

3. The recycling method according to claim 1, characterized in that, In steps S2 and S4, reagent C is at least one of ferrous sulfate and ferric chloride, to adjust the iron-phosphorus molar ratio in the system to 1:1; reagent D is an alkali, the target pH range of which is 1.0-2.5, the reaction temperature is 50-90℃, and the time is 0.5-1.5h. The alkali is the alkali produced in step S9 or a sodium hydroxide solution or a lithium hydroxide solution.

4. The recycling method according to claim 1, characterized in that, In step S6, the acid recovery rate of the electrodialysis system is not less than 95%, and the concentrated acid can be reused in the leaching section.

5. The recycling method according to claim 1, characterized in that, In step S8, the extractant is pyrrole trifluoromethyl-β-diketone or a quaternary synergistic extraction system. The pressure of the carbon dioxide back-extraction is 0.1-0.5 MPa, and the temperature is 20-40℃. The lithium bicarbonate solution generated by back-extraction can be directly used to prepare lithium carbonate products. The carbon dioxide gas can be recycled. The quaternary synergistic extraction system is a quaternary synergistic extraction system of dibenzoylmethane, tributyl phosphate, trioctylphosphine oxide, and n-octanol-sulfonated kerosene composite diluent. The volume concentration of dibenzoylmethane is 5-15%, the volume concentration of tributyl phosphate is 2-8%, the volume concentration of trioctylphosphine oxide is 1-5%, and the volume concentration of the composite diluent is 70-92%. The composite diluent is composed of sulfonated kerosene and n-octanol in a volume ratio of (5-10):

1.

6. The recycling method according to claim 1, characterized in that, Before step S1, a pre-oxidation treatment is added. The process is to mix black powder and potassium persulfate at a mass ratio of 100:(3-8) and carry out mechanical and chemical activation pre-oxidation treatment to obtain pre-oxidized black powder. The mixing method is to carry out the black powder and potassium persulfate in a planetary ball mill with a ball milling speed of 300-600 r / min, a ball-to-material ratio of (10-20):1, and a ball milling time of 1-3 hours.

7. The recycling method according to claim 1, characterized in that, In step S9, the bipolar membrane electrodialysis system is composed of alternating cation exchange membranes, anion exchange membranes and bipolar membranes. Under the action of a DC electric field, it decomposes lithium-containing aqueous solution into acid solution and alkaline solution, with an acid conversion rate of not less than 75% and an alkaline conversion rate of not less than 79%.

8. The recycling method according to claim 1, characterized in that, The alkaline solution produced in step S9 is returned to S2 and S4 for use, and the acid solution produced is combined with the acid recovered in step S6 and returned to S1, S3 and S5 for use. The self-sufficiency rate of acid and alkali in the system is significantly improved, and the amount of reagents used is greatly reduced.

9. The recycling method according to any one of claims 1 to 8, characterized in that, This method forms a complete material cycle: lithium is ultimately recovered as lithium bicarbonate / lithium carbonate products, iron and phosphorus are recovered as iron phosphate precursors, carbon is recovered as graphite products, sodium is recovered as sodium sulfate byproducts, water is recycled within the system, and acids and alkalis are regenerated in situ through a membrane system.

10. The recycling method according to claim 9, characterized in that, The overall lithium recovery rate is ≥95%, iron recovery rate is ≥92%, phosphorus recovery rate is ≥93%, and graphite recovery rate is ≥90%. The amount of waste salt discharged from the process is significantly reduced compared to the traditional acid and alkali process that purchases all its own salts, and the amount of fresh water replenishment is also significantly reduced.

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