Green separation and extraction process of waste lithium iron phosphate battery cathode material

Abstract

The application discloses a green separation and extraction process for a waste lithium iron phosphate battery cathode material, relates to the technical field of resource utilization and circular economy of waste lithium ion batteries, and comprises the following steps: adding water to waste lithium iron phosphate battery cathode powder material to form a slurry, adding a sodium hydroxide solution to the slurry to perform an alkali leaching reaction under the condition of 60-80 DEG C, selectively leaching phosphate, performing solid-liquid separation after the reaction, and obtaining a dephosphorized solid and a phosphorus-containing leaching mother liquor; and the dephosphorized solid is washed and then enters an oxidation pretreatment procedure; in the application, the reaction activity is strengthened through pretreatment, the phosphate is preferentially separated and recovered as a high-value sodium phosphate product through selective alkali leaching, the iron valence state is stabilized through oxidation pretreatment, the iron is selectively precipitated through acid leaching and pH regulation, and the iron is further calcined into iron oxide, deep impurity removal and selective lithium precipitation ensure efficient extraction and high purity of battery-grade lithium carbonate, and the closed-circuit circulation and shunt desalination mechanism of the washing liquid and the mother liquor in the process reduce reagent consumption and wastewater discharge.

Description

Technical Field

[0001] This application relates to the field of waste lithium-ion battery resource utilization and circular economy technology, and in particular to a green separation and extraction process for waste lithium iron phosphate battery cathode materials. Background Technology

[0002] Currently, the industry generally uses acid leaching to recycle and utilize cathode materials from waste lithium iron phosphate batteries. This method has problems such as high acid consumption, high reagent costs, large amounts of wastewater generation, severe equipment corrosion, and low utilization rate of cathode materials. Moreover, traditional processes mostly only recover lithium elements, resulting in a large loss of valuable resources such as iron and phosphorus, which makes it difficult to meet the industrial development needs of green, low-carbon, and high-value utilization. Summary of the Invention

[0003] To address the aforementioned issues, this application provides a green separation and extraction process for waste lithium iron phosphate battery cathode materials.

[0004] This application provides a green separation and extraction process for waste lithium iron phosphate battery cathode materials, which adopts the following technical solution:

[0005] A green separation and extraction process for waste lithium iron phosphate battery cathode materials includes the following steps:

[0006] S1, add water to the waste lithium iron phosphate battery cathode powder to make a slurry, add sodium hydroxide solution at 60-80℃ to carry out alkaline leaching reaction, selectively leach out phosphate, and then perform solid-liquid separation after the reaction to obtain dephosphorized solid and phosphorus-containing leachate mother liquor.

[0007] After being washed, the dephosphorized solids enter the oxidation pretreatment process, and the washing liquid is returned to the slurry preparation process.

[0008] The phosphorus-containing leaching mother liquor is cooled and crystallized, and then the solid and liquid are separated again. The solid is washed and dried to obtain sodium phosphate product. The separated mother liquor and washing liquid are returned to the slurry preparation process for recycling.

[0009] S2, the dephosphorized solid material after the oxidation pretreatment process is pulped, sulfuric acid is added for acid leaching, after the reaction is complete, the pH of the solution is adjusted to 3.2, so that ferric iron is precipitated in the form of ferric hydroxide, and then solid-liquid separation is performed to obtain ferric hydroxide product and first mother liquor, and the washing liquid is returned to the pulping process;

[0010] S3, add calcium oxide or sodium hydroxide to the first mother liquor obtained from S2, adjust the pH to 5.5-6.5, and after the reaction, perform solid-liquid separation to remove sulfate, residual iron ions and aluminum ions impurities. The resulting solid is the impurity-removed residue, and the washing liquid is returned to the pulping process.

[0011] The second mother liquor obtained after solid-liquid separation is further added with sodium phosphate for deep impurity removal, followed by solid-liquid separation again. The resulting solid is returned to the slurry material in S1 for recycling to obtain purified liquid.

[0012] In step S4, sodium hydroxide is added to the purified solution obtained in step S3 to adjust the pH to 10-10.5, and the solution is heated to 80-90℃. Sodium carbonate is then added to precipitate lithium as lithium carbonate. Solid-liquid separation is then performed to obtain lithium carbonate precipitate. The separated lithium precipitate mother liquor is returned to the slurry preparation process in step S1 for recycling.

[0013] As a preferred technical solution of this application, before the alkaline leaching reaction in S1, a pretreatment step is also included: mixing the cathode powder material with sodium hydroxide solution and treating it for 10-30 minutes with the assistance of ultrasound or high-energy ball milling.

[0014] As a preferred technical solution of this application, the oxidation pretreatment process is as follows: in the presence of air or an oxidant, the dephosphorized solid obtained in S1 is stirred at 60-90°C for 0.5-2 hours to convert the iron element in the material into the trivalent state.

[0015] As a preferred technical solution of this application, the iron hydroxide product obtained in S2 is washed, dried, and then calcined at 600-800°C to transform into an iron oxide product.

[0016] As a preferred technical solution of this application, the sodium phosphate product prepared in S1 is purified by recrystallization or ion exchange, and the crystallization conditions are controlled to further prepare one or more of disodium hydrogen phosphate, trisodium phosphate, or sodium polyphosphate.

[0017] As a preferred technical solution of this application, in S4, the lithium carbonate precipitate obtained after solid-liquid separation is post-treated, the post-treatment including: washing with hot water at 80-90°C, drying at 105-120°C, and then calcining at 200-300°C.

[0018] As a preferred technical solution of this application, in S4, before the lithium precipitation mother liquor is returned to S1 for slurry preparation, it first flows through a selective electrodialysis unit or a selective nanofiltration unit to enrich the residual lithium ions in the mother liquor. The resulting lithium-rich liquid is returned to the slurry preparation process, and the effluent from the desalination side is used as process makeup water.

[0019] As a preferred technical solution of this application, it further includes: periodically diverting a portion of the liquid from the mother liquor flow path returning to the slurry preparation channel in S1 or the lithium precipitation mother liquor flow path returning to the slurry preparation channel in S4, and then evaporating, concentrating and crystallizing it to remove the accumulated sodium sulfate impurities.

[0020] In summary, this application includes the following beneficial technical effects:

[0021] This application enhances reaction activity through pretreatment, selectively separates and recovers phosphate ions to high-value sodium phosphate products through alkaline leaching, stabilizes the iron valence state through oxidative pretreatment, selectively precipitates iron through acid leaching and pH adjustment, and further calcines it into iron oxide. Deep impurity removal and selective lithium precipitation ensure efficient extraction and high purity of battery-grade lithium carbonate. The closed-loop circulation and diversion desalination mechanism of washing liquid and mother liquor in the process reduces reagent consumption and wastewater discharge, realizing efficient separation and resource utilization of phosphorus, iron and lithium elements, and meeting the industrial development needs of green, low-carbon and high-value utilization. Attached Figure Description

[0022] Figure 1 This is a flow chart of the green separation and extraction process for waste lithium iron phosphate battery cathode materials in this application. Detailed Implementation

[0023] The following is in conjunction with the appendix Figure 1 This application will be described in further detail.

[0024] See Figure 1 A green separation and extraction process for waste lithium iron phosphate battery cathode materials includes the following steps:

[0025] Pretreatment steps: Mix the cathode powder with sodium hydroxide solution and treat for 10-30 minutes with the assistance of ultrasound or high-energy ball milling;

[0026] The first step of the process is pretreatment, which mainly involves the initial activation and separation of the cathode active material powder (mainly composed of lithium iron phosphate, and may contain conductive agents, binder residues and trace amounts of aluminum foil impurities) obtained after the waste lithium iron phosphate batteries have been crushed and sorted.

[0027] The specific operation is as follows: a certain mass of cathode powder material is mixed with a sodium hydroxide solution with a concentration of 1-5 mol / L at a liquid-to-solid ratio (L / S) of 5:1 to 15:1 mL / g, and placed in an alkali-resistant container. Subsequently, auxiliary treatment is carried out in an ultrasonic cleaner or a high-energy planetary ball mill. The treatment time is controlled between 10 and 30 minutes. This pretreatment process can partially dissolve aluminum impurities in a short time and initially destroy the crystal structure of lithium iron phosphate, making the subsequent alkaline leaching reaction (S1) easier to carry out, improving the reaction rate and selective leaching efficiency. The pretreated slurry can directly enter the slurry preparation process of S1 without solid-liquid separation, realizing a compact connection of the process.

[0028] S1, add water to the waste lithium iron phosphate battery cathode powder to make a slurry, add sodium hydroxide solution at 60-80℃ to carry out alkaline leaching reaction, selectively leach out phosphate, and then perform solid-liquid separation after the reaction to obtain dephosphorized solid and phosphorus-containing leachate mother liquor.

[0029] After being washed, the dephosphorized solids enter the oxidation pretreatment process, while the washing liquid is returned to the slurry preparation process.

[0030] The phosphorus-containing leaching mother liquor is cooled and crystallized, followed by solid-liquid separation. The solid is washed and dried to obtain sodium phosphate product. The separated mother liquor and washing liquid are returned to the slurry preparation process for recycling. The sodium phosphate product prepared in S1 is purified by recrystallization or ion exchange, and the crystallization conditions are controlled to further prepare one or more of disodium hydrogen phosphate, trisodium phosphate, or sodium polyphosphate. The oxidation pretreatment process is as follows: in the presence of air or an oxidant, the dephosphorized solid obtained in S1 is stirred at 60-90℃ for 0.5-2 hours to convert the iron element in the material into the trivalent state.

[0031] This step involves selective alkaline leaching to separate phosphate ions from the cathode material and recover them as sodium phosphate. First, the pretreated slurry or directly used cathode powder is mixed with the washing liquid, mother liquor, and replenished clean water (deionized water) from the process cycle in an alkali-resistant reactor equipped with stirring and heating. The liquid-to-solid ratio of the slurry is controlled between 8:1 and 20:1 mL / g. The slurry temperature is raised and maintained within the optimized range of 60-80℃. While stirring continuously, a sodium hydroxide solution with a concentration of 4-8 mol / L is slowly added. The amount of sodium hydroxide added is 1.2-2.0 times the theoretically required molar amount to ensure that the phosphate ions in lithium iron phosphate are fully converted into soluble sodium phosphate. The alkaline leaching reaction continues for 1-3 hours.

[0032] Under these conditions, lithium iron phosphate reacts with sodium hydroxide, and phosphate ions enter the solution in the form of sodium phosphate, while elements such as iron and lithium remain in the solid phase. After the reaction is completed, solid-liquid separation is immediately carried out by plate and frame filter press, vacuum filtration device or centrifuge to obtain a solid phase (i.e., "dephosphorized solid", mainly composed of amorphous lithium iron phosphate compounds, carbon, etc.) and a liquid phase (i.e., "phosphorus-containing leaching mother liquor", mainly containing sodium phosphate, excess sodium hydroxide and a small amount of impurities such as silicon and aluminum). The dephosphorized solid needs to be washed with hot water at 60-80℃ under stirring conditions in a countercurrent or by multiple decantation until the washing liquid is close to neutral to fully remove the entrained alkali and soluble salts. The washing liquid is collected and returned to the initial slurry preparation process of this step.

[0033] The phosphorus-containing leaching mother liquor is transferred to a crystallization kettle and slowly cooled to 10-25°C by water cooling or freezing. It is then left to stand and age for 2-6 hours to allow sodium phosphate dodecahydrate (Na3PO4·12H2O) or other forms of sodium phosphate to crystallize out completely. Solid-liquid separation is performed again, and the obtained crystals are washed with a small amount of ice water or low-temperature ethanol to remove the surface mother liquor. Then, they are dried at 80-100°C to obtain crude sodium phosphate. The mother liquor and crystal washing liquid after separation and crystallization are returned to the slurry preparation process for recycling to improve reagent utilization.

[0034] To further enhance product value, crude sodium phosphate can be dissolved in hot water and purified by recrystallization under controlled crystallization conditions such as cooling rate, pH, and additives. Alternatively, it can be passed through a column packed with selective ion exchange resin to remove impurity ions. By regulating the crystallization process (such as controlling pH, temperature, and concentration), the purified sodium phosphate solution can be further converted into disodium hydrogen phosphate (Na2HPO4), trisodium phosphate (Na3PO4), or polyphosphate products of different specifications can be prepared through polymerization reactions.

[0035] The purpose of the oxidation pretreatment step is to completely oxidize the ferrous ions (Fe²⁺) in the dephosphorized solids obtained from S1 to ferric ions (Fe³⁺), creating crucial conditions for subsequent acid leaching and efficient selective precipitation of iron. The washed dephosphorized solids are transferred to a reactor equipped with heating, stirring, and aeration (or a sealable pressurized system). Water or returned washing liquid is added for slurry preparation, controlling the solid content at 10-30%. The slurry temperature is raised to a suitable range of 60-90℃, and under continuous stirring, the iron is precipitated into… Air is introduced into the system, or an appropriate amount of oxidant (such as hydrogen peroxide H2O2, sodium hypochlorite NaClO, or a mixture of air and a small amount of ozone) is added. If hydrogen peroxide is used, it can be added slowly dropwise at 1.05-1.2 times the stoichiometric amount required for the theoretical oxidation of ferrous iron. The oxidation treatment time is controlled between 0.5 and 2 hours. During this process, the oxygen in the air or the added oxidant will oxidize the unstable Fe²⁺ in the material to the more stable Fe³⁺, which is then converted into ferric hydroxide or ferric oxide hydrate.

[0036] To ensure complete oxidation, the oxidation-reduction potential (ORP) of the slurry can be sampled and tested to reach a stable plateau, or the o-phenanthroline spectrophotometric method can be used to confirm that Fe²⁺ has basically disappeared. Oxidation pretreatment can not only stabilize the valence state of iron and prevent it from generating divalent iron interference in subsequent acid leaching, but also further destroy residual organic matter. After treatment, the slurry can be directly used for the next step of S2 acid leaching, or it can be cooled down slightly for later use.

[0037] S2 involves slurrying the dephosphorized solid material after the oxidation pretreatment process, adding sulfuric acid for acid leaching, and adjusting the pH of the solution to 3.2 after the reaction is complete, causing ferric iron to precipitate as ferric hydroxide. Solid-liquid separation is then performed to obtain ferric hydroxide product and the first mother liquor. The washing liquid is returned to the slurrying process. The ferric hydroxide product obtained in S2 is washed, dried, and then calcined at 600-800℃ to convert it into ferric oxide product.

[0038] The purpose of this step is to dissolve elements such as iron and lithium in the solid after oxidation pretreatment and to preferentially separate and recover iron. The slurry after oxidation pretreatment is pumped into an acid-resistant reactor, and the temperature is maintained at 50-70℃. Under stirring conditions, industrial sulfuric acid diluted to a concentration of 1:1 to 1:3 is slowly added. The amount of sulfuric acid added is calculated based on the total amount of metals such as iron and lithium in the solid. Usually, the final pH is controlled to be below 1.0 to ensure that iron and lithium are fully leached out. The acid leaching reaction lasts for 1-2 hours. After the reaction is complete, dilute sodium hydroxide solution, sodium carbonate or calcium oxide suspension is slowly added to the leachate under stirring to adjust the pH of the solution to 3.2±0.1. At this pH, the ferric ions (Fe³⁺) in the solution are almost completely hydrolyzed and precipitated as ferric hydroxide [Fe(OH)3], while lithium ions (Li⁺) remain stable in the solution.

[0039] Subsequently, solid-liquid separation is immediately performed by pressure filtration or centrifugation to obtain a reddish-brown ferric hydroxide filter cake and a first mother liquor containing lithium, excess sulfate, and a small amount of impurities. The ferric hydroxide filter cake is thoroughly washed with hot water to remove entrained lithium salts and sulfates. The washing liquid is returned to the initial slurrying process of this step. The washed wet ferric hydroxide filter cake is placed in an oven and dried to constant weight at 105-120℃. To further enhance the added value of the iron product, the dried ferric hydroxide can be placed in a muffle furnace or rotary kiln and calcined in an air atmosphere at 600-800℃ for 2-4 hours to completely dehydrate it and convert it into high-purity red iron oxide (Fe2O3) powder, which can be used as a pigment or magnetic material raw material.

[0040] S3, add calcium oxide or sodium hydroxide to the first mother liquor obtained from S2, adjust the pH to 5.5-6.5, and after the reaction, perform solid-liquid separation to remove sulfate, residual iron ions and aluminum ions impurities. The resulting solid is the impurity-removed residue, and the washing liquid is returned to the pulping process.

[0041] The second mother liquor obtained after solid-liquid separation is further added with sodium phosphate for deep impurity removal, followed by solid-liquid separation again. The resulting solid is returned to the slurry material in S1 for recycling to obtain purified liquid.

[0042] The first mother liquor obtained from S2 is transferred to another stirred reactor. First, at room temperature or with moderate heating (<60℃), lime milk (calcium oxide suspension) or sodium hydroxide solution is added to the first mother liquor, and the pH is slowly adjusted to 5.5-6.5. Within this pH range, the residual trace amounts of Fe³⁺ and Al³⁺ will form hydroxide precipitates. At the same time, most of the sulfate ions (SO₄²⁻) in the solution will react with calcium ions (from calcium oxide or the material itself) to form slightly soluble calcium sulfate (CaSO₄·2H₂O) co-precipitates. After the reaction matures for 0.5-1 hour, solid-liquid separation is performed. The obtained solid is a "removed residue" containing calcium sulfate, iron hydroxide, aluminum hydroxide, etc., which can be safely landfilled or specifically recycled.

[0043] The separated second mother liquor mainly contains lithium ions, sodium ions, and a small amount of residual sulfate and phosphate ions. For further purification, the second mother liquor is heated to 50-70℃, and sodium phosphate solid or concentrated solution prepared in step S1 is added under stirring. The addition of phosphate ions will form phosphate precipitates with smaller solubility products with residual calcium, magnesium, iron, aluminum and other impurity ions in the solution. After the reaction is complete, solid-liquid separation is performed again. The resulting solid is rich in phosphate impurities and can be returned to the initial slurry material in step S1 for recycling to recover the trace amounts of lithium encapsulated therein and achieve internal circulation of phosphorus. After these two steps of precipitation and impurity removal, the purity and concentration of lithium in the obtained "purified liquid" have been improved, and the content of major impurities such as calcium, magnesium, iron, aluminum and sulfate ions has been reduced to the ppm level, meeting the requirements for lithium precipitation.

[0044] In S4, the purified solution obtained in S3 is adjusted to pH 10-10.5 with sodium hydroxide, heated to 80-90℃, and then sodium carbonate is added to precipitate lithium as lithium carbonate. Solid-liquid separation is then performed to obtain lithium carbonate precipitate. The separated lithium-precipitated mother liquor is returned to the slurry preparation process in S1 for recycling. In S4, the lithium carbonate precipitate obtained after solid-liquid separation undergoes post-treatment, including washing with hot water at 80-90℃, drying at 105-120℃, and then calcining at 200-300℃. Before returning to the slurry preparation process in S1, the lithium-precipitated mother liquor is first passed through a selective electrodialysis unit or a selective nanofiltration unit to enrich the residual lithium ions in the mother liquor. The resulting lithium-rich solution is returned to the slurry preparation process, and the effluent from the desalination side is used as process makeup water.

[0045] It also includes: periodically diverting a portion of the liquid from the mother liquor flow path that returns to the slurry preparation from S1 or the lithium precipitation mother liquor flow path that returns to the slurry preparation from S4, and then evaporating, concentrating, and crystallizing it to remove the accumulated sodium sulfate impurities.

[0046] The purified liquid obtained from S3 is pumped into a precipitation reactor equipped with heating and stirring. First, the pH value of the purified liquid is adjusted to 10-10.5 with sodium hydroxide solution. Then, the solution is heated to 80-90℃, and under continuous heating and strong stirring, saturated sodium carbonate (Na2CO3) solution or solid powder is slowly and evenly added. The amount of sodium carbonate added is 1.05-1.15 times the molar amount of lithium in the solution. Under these high temperature and strong alkaline conditions, lithium ions react with carbonate ions to form lithium carbonate (Li2CO3) precipitate with very low solubility. After the addition is completed, the solution is kept at 80-90℃ for 1-2 hours to allow the precipitate to age and crystals to grow completely, which is convenient for subsequent filtration. After aging, solid-liquid separation is performed while hot using a vacuum filtration device or a filter press to obtain a white lithium carbonate wet filter cake and lithium precipitation mother liquor.

[0047] The lithium carbonate filter cake is immediately washed repeatedly with hot pure water at 80-90℃ to thoroughly remove impurities such as sodium salts adsorbed on the surface. The washed wet filter cake is placed in an oven and dried at 105-120℃ for 4-8 hours. To further improve product purity and reduce weight loss on ignition, the dried lithium carbonate powder can be calcined at 200-300℃ for 2-3 hours to obtain high-purity lithium carbonate product.

[0048] The separated lithium-precipitated mother liquor (mainly containing sodium carbonate, sodium hydroxide, and a small amount of residual lithium) needs to undergo special treatment before returning to the S1 slurry preparation process to recover residual lithium and control impurity accumulation: The mother liquor first flows through a selective electrodialysis unit or a selective nanofiltration unit. In electrodialysis, a selective ion exchange membrane is used to selectively migrate lithium ions to the concentration chamber under the action of a DC electric field, resulting in a "lithium-rich liquor" with a significantly increased lithium concentration. Returning to the S1 slurry preparation process, in nanofiltration, a membrane with nanoscale pores is used to retain multivalent ions and some monovalent lithium ions, reducing the lithium concentration in the permeate and separating the mother liquor into "…". The lithium-rich solution and the desalination solution are used. The lithium-rich solution is returned to S1 for slurry preparation, while the desalination solution (mainly containing sodium salts) can be used as process makeup water. In addition, in order to control the balance of impurity ions such as sodium sulfate in the system, a portion (e.g., 5-10%) of liquid needs to be diverted from the mother liquor flow path returned from S1 for slurry preparation or the lithium precipitation mother liquor flow path returned from S4 for slurry preparation periodically. This diverted liquid is concentrated by multi-effect evaporation or MVR evaporation. After cooling, mixed salt impurities such as sodium sulfate decahydrate (sodium sulfate) are crystallized out and removed from the system. The crystallization mother liquor can be returned to evaporation or discharged after careful treatment, thereby ensuring the long-term stable operation of the entire water-salt system.

[0049] This application enhances reaction activity through pretreatment, selectively separates and recovers phosphate ions to high-value sodium phosphate products through selective alkaline leaching, stabilizes the iron valence state through oxidative pretreatment, selectively precipitates iron through acid leaching and pH adjustment, and further calcines it into iron oxide. Deep impurity removal and selective lithium precipitation ensure efficient extraction and high purity of battery-grade lithium carbonate. The closed-loop circulation and diversion desalination mechanism of washing liquid and mother liquor in the process reduces reagent consumption and wastewater discharge, and realizes efficient separation and resource utilization of phosphorus, iron and lithium elements.

[0050] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A green separation and extraction process for waste lithium iron phosphate battery cathode materials, characterized in that, Includes the following steps: S1, add water to the waste lithium iron phosphate battery cathode powder to make a slurry, add sodium hydroxide solution at 60-80℃ to carry out alkaline leaching reaction, selectively leach out phosphate, and then perform solid-liquid separation after the reaction to obtain dephosphorized solid and phosphorus-containing leachate mother liquor. After being washed, the dephosphorized solids enter the oxidation pretreatment process, and the washing liquid is returned to the slurry preparation process. The phosphorus-containing leaching mother liquor is cooled and crystallized, and then the solid and liquid are separated again. The solid is washed and dried to obtain sodium phosphate product. The separated mother liquor and washing liquid are returned to the slurry preparation process for recycling. S2, the dephosphorized solid material after the oxidation pretreatment process is pulped, sulfuric acid is added for acid leaching, after the reaction is complete, the pH of the solution is adjusted to 3.2, so that ferric iron is precipitated in the form of ferric hydroxide, and then solid-liquid separation is performed to obtain ferric hydroxide product and first mother liquor, and the washing liquid is returned to the pulping process; S3, add calcium oxide or sodium hydroxide to the first mother liquor obtained from S2, adjust the pH to 5.5-6.5, and after the reaction, perform solid-liquid separation to remove sulfate, residual iron ions and aluminum ions impurities. The resulting solid is the impurity-removed residue, and the washing liquid is returned to the pulping process. The second mother liquor obtained after solid-liquid separation is further added with sodium phosphate for deep impurity removal, followed by solid-liquid separation again. The resulting solid is returned to the slurry material in S1 for recycling to obtain purified liquid. In step S4, sodium hydroxide is added to the purified solution obtained in step S3 to adjust the pH to 10-10.5, and the solution is heated to 80-90℃. Sodium carbonate is then added to precipitate lithium as lithium carbonate. Solid-liquid separation is then performed to obtain lithium carbonate precipitate. The separated lithium precipitate mother liquor is returned to the slurry preparation process in step S1 for recycling.

2. The green separation and extraction process for waste lithium iron phosphate battery cathode materials according to claim 1, characterized in that, Before the alkaline leaching reaction in S1, a pretreatment step is also included: mixing the cathode powder material with a sodium hydroxide solution and treating it for 10-30 minutes with the assistance of ultrasound or high-energy ball milling.

3. The green separation and extraction process for waste lithium iron phosphate battery cathode materials according to claim 1, characterized in that, The oxidation pretreatment process is as follows: in the presence of air or an oxidant, the dephosphorized solid obtained in S1 is stirred at 60-90°C for 0.5-2 hours to convert the iron element in the material into the trivalent state.

4. The green separation and extraction process for waste lithium iron phosphate battery cathode materials according to claim 1, characterized in that, The ferric hydroxide product obtained in S2 is washed, dried, and then calcined at 600-800°C to transform into an ferric oxide product.

5. The green separation and extraction process for waste lithium iron phosphate battery cathode materials according to claim 1, characterized in that, The sodium phosphate product prepared in S1 is purified by recrystallization or ion exchange, and the crystallization conditions are controlled to further prepare one or more of disodium hydrogen phosphate, trisodium phosphate, or sodium polyphosphate.

6. The green separation and extraction process for waste lithium iron phosphate battery cathode materials according to claim 1, characterized in that, In S4, the lithium carbonate precipitate obtained after solid-liquid separation is post-treated, which includes washing with hot water at 80-90°C, drying at 105-120°C, and then calcining at 200-300°C.

7. The green separation and extraction process for waste lithium iron phosphate battery cathode materials according to claim 1, characterized in that, In S4, before returning to S1 for slurry preparation, the lithium precipitation mother liquor first flows through a selective electrodialysis unit or a selective nanofiltration unit to enrich the residual lithium ions in the mother liquor. The resulting lithium-rich liquid is returned to the slurry preparation process, and the effluent from the desalination side is used as process makeup water.

8. The green separation and extraction process for waste lithium iron phosphate battery cathode materials according to claim 1, characterized in that, Also includes: A portion of the liquid is periodically diverted from the mother liquor flow path returning to the slurry preparation channel via S1 or the lithium precipitation mother liquor flow path returning to the slurry preparation channel via S4. After evaporation, concentration, and crystallization, the accumulated sodium sulfate impurities are removed.

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