Pretreatment methods for waste electrolyte after lithium-ion battery dismantling and methods for the complete recovery of lithium, fluorine and phosphorus.

Abstract

This application relates to the field of material recycling technology after lithium-ion battery dismantling, and in particular to a pretreatment method for waste electrolyte after lithium-ion battery dismantling and a method for the complete recovery of lithium, fluorine, and phosphorus from it. The pretreatment method includes step S1: mixing the recovered electrolyte with a first reducing iron source, a first inorganic acid, and pure water, and reacting the mixture. After the reaction, solid-liquid separation is performed to obtain a first liquid, wherein the electrolyte in the first liquid includes lithium hexafluorophosphate. Step S2: adjusting the pH of the first liquid to 1.5–2.0, and removing H2PO2 from the first liquid... ‑ Oxidized to PO4 3‑ The electrolyte precipitates as a solid, and after the reaction, solid-liquid separation is performed to obtain a second liquid and a solid precipitate. This pretreatment method can effectively separate lithium and fluorine from phosphorus in waste electrolyte, thereby improving the product yield and purity of subsequent recovery steps, and the entire process causes almost no environmental pollution.

Description

Technical Field

[0001] This application relates to the field of material recycling technology after lithium-ion battery dismantling, and in particular to a pretreatment method for waste electrolyte after lithium-ion battery dismantling and a method for the complete recovery of lithium, fluorine and phosphorus therein. Background Technology

[0002] Lithium-ion batteries possess advantages such as high specific capacity, no memory effect, and environmental friendliness, leading to their widespread application in energy storage, electronic communications, and new energy vehicles. In recent years, with the increase in lithium-ion battery production capacity, the number of waste lithium-ion batteries has also increased significantly. Therefore, the recycling and utilization of lithium-ion battery materials has considerable economic and environmental benefits. Current research mainly focuses on the recycling of positive and negative electrode materials, while research on electrolyte recycling is relatively limited. This may be due to the complex composition of electrolytes, making it difficult for traditional technologies to achieve the required recycling efficiency and product purity for practical applications. Lithium-ion batteries are disassembled to collect the electrolyte. Typically, battery disassembly involves steps such as discharging, primary crushing, membrane separation, magnetic separation of the steel casing, shearing and crushing, and vibratory sieving, resulting in battery material fragments and the electrolyte.

[0003] Electrolyte, as a major component of lithium-ion batteries, accounts for only about 12% of the battery cost in manufacturing, but its recycling profit can reach as high as 40%. Electrolyte comprises organic solvents and electrolytes, and electrolyte recycling typically refers to the recycling and reuse of the electrolyte. The electrolyte mainly includes lithium hexafluorophosphate (LiPF6), in which lithium, phosphorus, and fluorine are essential elements for synthesizing lithium-ion battery materials; therefore, the recycling of lithium, phosphorus, and fluorine has certain application prospects. Traditional technology achieves lithium-ion battery recovery by adding chlorides with large cation radii to the electrolyte. + With PF6 - The traditional method involves pre-separation and preparation of the recovered product lithium carbonate (Li₂CO₃). However, because the generated hexafluorophosphate partially dissolves in water, the pre-separated lithium, fluorine, and phosphorus elements mix again, resulting in low Li₂CO₃ yield and purity. In other words, the low recovery rate and product purity of traditional technologies are mainly due to the inability to effectively separate lithium, phosphorus, and fluorine elements from the electrolyte. Therefore, providing a pretreatment method for lithium, phosphorus, and fluorine elements in dismantled waste electrolytes has become an urgent problem to be solved. Summary of the Invention

[0004] Based on this, this application provides a pretreatment method for recycling waste electrolyte from dismantled lithium-ion batteries, a method for recovering lithium and fluorine from waste electrolyte using the above pretreatment method, and a method for recovering phosphorus from waste electrolyte using the above pretreatment method. The pretreatment method of this application can effectively separate lithium and fluorine from phosphorus in waste electrolyte, thereby improving the product yield and purity of subsequent recovery steps, and the entire process causes almost no environmental pollution.

[0005] In a first aspect, a pretreatment method for recycling waste electrolyte from dismantled lithium-ion batteries is provided, comprising the following steps:

[0006] Step S1: The recovered electrolyte is mixed with a first reducing iron source, a first inorganic acid and pure water and reacted. After the reaction, solid-liquid separation is performed to obtain a first liquid, wherein the electrolyte of the electrolyte includes lithium hexafluorophosphate.

[0007] Step S2: Adjust the pH of the first liquid to 1.5-2.0, and remove the H2PO2 from the first liquid. - Oxidized to PO4 3- It precipitates out as a precipitate, and after the reaction, solid-liquid separation is performed to obtain a second liquid and a solid precipitate.

[0008] The separation of lithium, fluorine, and phosphorus elements in waste electrolyte was achieved through pretreatment. The addition of the first reducing iron source not only promotes the separation of PF6 - Hydrolysis, and can promote the reaction of H2PO2 in step S2. - Oxidized to PO4 3- This process forms a poorly soluble solid precipitate, achieving efficient separation of phosphorus. Furthermore, due to the strong oxidizing properties of the reaction system, organic matter in the electrolyte can be oxidized to an inorganic state, thereby releasing Li₂ complexed with the organic matter. + This increased the Li content in the second liquid. + The content of lithium is conducive to the full recovery of lithium.

[0009] In some embodiments, the first reducing iron source includes at least one of elemental iron and a ferrous salt, and the first inorganic acid includes at least one of hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid. Optionally, the elemental iron is provided in at least one of iron powder, iron bars, and iron blocks, and the ferrous salt includes at least one of ferrous chloride, ferrous chloride hydrate, ferrous sulfate, ferrous sulfate hydrate, ferrous nitrate, ferrous nitrate hydrate, ferrous oxalate, and ferrous oxalate hydrate.

[0010] In some embodiments, in step S1, the mass ratio of iron in the first reducing iron source to the electrolyte is (0.05–0.3):1, the mass ratio of inorganic acid to the electrolyte is (0.05–0.4):1, and the mass ratio of pure water to the electrolyte is (0.2–0.5):1. Optionally, the reaction temperature in step S1 is 60–100°C, and the reaction time is 3–10 h.

[0011] In some embodiments, in step S2, hydrogen peroxide is added to the first liquid to remove H2PO2 from the first liquid. - Oxidized to PO4 3- The mass ratio of hydrogen peroxide to electrolyte is (0.03–0.1):1. Optionally, the reaction temperature in step S2 is 20–50°C, and the reaction time is 0.5–10 h. Further, the pH value is adjusted to 1.5–2.0 by adding at least one of ammonia, ammonium carbonate, and ammonium bicarbonate to the first liquid.

[0012] In a second aspect, a method for recovering lithium and fluorine from waste electrolyte after dismantling lithium-ion batteries is provided, comprising the pretreatment method described in the first aspect, wherein the method for recovering lithium and fluorine further comprises the following steps:

[0013] Step S3: Adjust the pH of the second liquid to 3.0–7.0, so that the Li in the second liquid… + It precipitates out as a precipitate, yielding a compound containing lithium and fluorine.

[0014] In some embodiments, the reaction temperature of step S3 is 50–100°C, and the reaction time is 1–5 h. Optionally, the pH value is adjusted to 3.0–7.0 by adding at least one of sodium hydroxide, sodium carbonate, and sodium bicarbonate to the second liquid. Further optionally, step S3 also includes a first post-treatment step of the lithium- and fluorine-containing compound, the first post-treatment including filtration, evaporation concentration, and solid-liquid separation.

[0015] The reaction in step S3 causes lithium and fluorine in the second liquid to form compounds with a purity greater than 99%, achieving efficient recovery of lithium and fluorine. The recovered product is one of the raw materials for the preparation of LiPF6, thus possessing high recovery value.

[0016] Thirdly, a method for recovering phosphorus from waste electrolyte after dismantling lithium-ion batteries is provided, comprising the pretreatment method described in the first aspect, wherein the phosphorus recovery method further comprises the following steps:

[0017] Step S4: Mix the solid precipitate with the second reducing iron source, the second inorganic acid and pure water and react them. After the reaction, perform solid-liquid separation to obtain the third liquid and filter residue containing insoluble impurities.

[0018] Step S5: Adjust the pH of the third liquid to 1.5-2.0, and perform solid-liquid separation after the reaction to obtain phosphorus-containing compounds.

[0019] In some embodiments, in step S4, the second reducing iron source comprises elemental iron, and the second inorganic acid comprises at least one selected from hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid. Optionally, the mass ratio of iron to electrolyte in the second reducing iron source is (0.02–0.15):1, the mass ratio of inorganic acid to electrolyte is (0.1–0.3):1, and the mass ratio of pure water to electrolyte is (0.3–0.8):1. Further optionally, the reaction temperature in step S4 is 40–80°C, and the reaction time is 2–10 h. Still further optionally, the elemental iron is provided in the form of at least one selected from iron powder, iron bars, and iron blocks.

[0020] In some embodiments, in step S5, hydrogen peroxide is added to the third liquid to make Fe... 2+ Oxidized to Fe 3+ Optionally, the mass ratio of hydrogen peroxide to electrolyte is (0.05–0.3):1. Further optionally, the reaction temperature in step S5 is 60–100°C, and the reaction time is 4–10 h.

[0021] In some embodiments, in step S5, the pH value is adjusted to 1.5–2.0 by adding at least one of ammonia, ammonium carbonate, and ammonium bicarbonate to the third liquid. Optionally, step S5 further includes a second post-treatment step of the phosphorus-containing compound, which may include washing and drying.

[0022] Phosphorus in the solid precipitate was purified through steps S4 and S5, yielding phosphorus-containing compounds with a purity greater than 99%. The second reducing iron source not only promotes the purification of Fe in the solid precipitate... 3+ Reduced to Fe 2+ It dissolves and prevents the dissolution of other impurity ions, thus purifying the third liquid. Subsequently, Fe... 2+ Oxidized to Fe 3+ It precipitates out in the form of phosphorus-containing compounds. These phosphorus-containing compounds are raw materials for preparing lithium iron phosphate cathode materials, and therefore have high recycling value.

[0023] Furthermore, the recycling method described in this application can recover lithium, fluorine, and phosphorus elements from waste electrolyte in a single process, reducing resource waste and improving atom economy. Moreover, the aforementioned recycling method has advantages such as simple operation, low equipment investment, environmental friendliness, controllable quality, and ease of industrialization, generating significant economic and social benefits and possessing broad application prospects. Attached Figure Description

[0024] Figure 1The XRD pattern of lithium fluoride recovered in one embodiment of this application is shown.

[0025] Figure 2 The image shows the XRD pattern of ferric phosphate dihydrate recovered in one embodiment of this application. Detailed Implementation

[0026] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application are described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0027] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items. The term "more" as used herein includes two or more items. The term "above a certain number" as used herein should be understood as a number and a range greater than a certain number.

[0029] Electrolyte accounts for 12% to 15% of the mass of a lithium-ion battery. Recycling and reusing it could generate significant economic and environmental benefits. However, traditional technologies have not achieved substantial commercial success in electrolyte recycling. The challenges in recycling waste electrolyte from lithium-ion batteries lie in the high cost and risk, as well as the low yield and purity of the recovered products. Electrolyte comprises an electrolyte (e.g., lithium hexafluorophosphate, LiPF6), an organic solvent (e.g., ethylene carbonate), and functional additives. Lithium, phosphorus, and fluorine in LiPF6 are essential for synthesizing lithium-ion battery materials. For example, LiF, composed of lithium and fluorine, is a raw material for synthesizing LiPF6, while FePO4, composed of phosphorus, is a raw material for synthesizing lithium iron phosphate cathode materials. Therefore, the recovery of lithium, phosphorus, and fluorine to obtain high-purity, high-value recycled products holds considerable application potential.

[0030] In electrolytes, LiPF6 is usually in the form of Li+ and PF6 - LiPF6 exists in the form of phosphorus, but due to its poor thermal and chemical stability, it will deteriorate when the battery temperature exceeds 80°C or when a small amount of water is present in the electrolyte. - Inevitably, it will decompose to form F. - and H2PO2 - These two byproduct ions cannot be recovered using conventional techniques; therefore, traditional techniques typically remove F... - and H2PO2 - Direct discharge as waste not only reduces the recovery rate of phosphorus and fluorine, but more importantly, it causes environmental pollution. In other words, traditional technologies usually cannot achieve the complete recovery of lithium, phosphorus, and fluorine. Furthermore, traditional technologies typically only recover lithium, or lithium and phosphorus, but cannot recover all three elements (lithium, phosphorus, and fluorine) at once.

[0031] Studies have found that the low yield and purity of traditional recycling technologies are mainly due to their inability to effectively separate lithium, phosphorus, and fluorine. For example, in a traditional recycling process, lithium is recovered by adding chlorides with large cationic radii to the electrolyte. + With PF6 - The pre-separation and preparation of the recovered product lithium carbonate (Li2CO3) were carried out, but because the generated hexafluorophosphate partially dissolved in water, the lithium, fluorine and phosphorus elements after pre-separation were mixed together again, resulting in low yield and purity of Li2CO3.

[0032] To overcome the above problems, one embodiment of this application provides a pretreatment method for recycling waste electrolyte from dismantled lithium-ion batteries. This method effectively separates lithium and fluorine elements from phosphorus elements in the waste electrolyte, thereby improving the product yield and purity of subsequent recycling steps, and the entire process causes almost no environmental pollution. The method includes the following steps:

[0033] Step S1: The recovered electrolyte is mixed with a first reducing iron source, a first inorganic acid and pure water and reacted. After the reaction, solid-liquid separation is performed to obtain a first liquid, wherein the electrolyte of the electrolyte includes lithium hexafluorophosphate.

[0034] Step S2: Adjust the pH of the first liquid to 1.5-2.0, and remove the H2PO2 from the first liquid. - Oxidized to PO4 3- It precipitates out as a precipitate, and after the reaction, solid-liquid separation is performed to obtain a second liquid and a solid precipitate.

[0035] Understandably, lithium hexafluorophosphate dissociates in organic solvents to form Li + and PF6 -Therefore, the reaction in step S1 mainly causes PF6 to... - Hydrolysis of PF6. Furthermore, PF6... - Converted to H2PO2 - HF and trace amounts of F - Simultaneously, the first reducing iron source dissolves to form Fe. 2+ During this process, Fe 2+ Able to promote PF6 - Hydrolysis. After solid-liquid separation, all the above ions are retained in the first liquid. Insoluble impurities in the waste electrolyte are removed as filter residue. It should be noted that F... - Under the action of the first inorganic acid, most of it is converted into HF. Since HF is easily soluble in water but does not easily ionize, it mainly exists in the first liquid in the form of molecules.

[0036] The reaction system in step S2 has strong oxidizing properties and can react with H2PO2. - Oxidized to PO4 3- Furthermore, the organic solvent is oxidized to an inorganic state, thus achieving the degradation of the organic solvent. Further, since the pH of the first liquid is 1.5–2.0, specifically, the pH value of the first liquid can be 1.5, 1.6, 1.7, 1.8, 1.9, or 2, the generated PO4... 3- Able to interact with Fe 3+ The substances combine and precipitate as insoluble precipitates, but the resulting solid precipitate contains many impurities and has low purity, which may not meet the requirements of practical applications. Furthermore, when the system pH is higher than 2.0, the purity of the subsequently obtained recovered products is low. After solid-liquid separation, Li in the first liquid... + HF and trace amounts of F - The phosphorus element remains in the second liquid, while it precipitates out. It should be noted that the waste electrolyte in this application refers to the electrolyte obtained by dismantling used and discarded lithium-ion batteries, and the electrolyte in the aforementioned electrolyte includes lithium hexafluorophosphate. Understandably, the aforementioned electrolyte may also contain other electrolytes or functional additives, which this application does not limit. Furthermore, pure water is water containing a small amount of impurity ions, with a purity greater than or equal to 99%. For example, pure water can be deionized water.

[0037] The separation of lithium, fluorine, and phosphorus elements from waste electrolytes was achieved through pretreatment. The addition of the first reducing iron source not only promotes the separation of electrolyte and PF6 in step S1, but also... - Hydrolysis of H2PO2 in the system can enhance the oxidizing power of the reaction system, thereby reducing the H2PO2 content in the system. - Convert to PO4 3-This process forms a poorly soluble solid precipitate, achieving efficient separation of phosphorus. Furthermore, due to the strong oxidizing properties of the reaction system, organic solvents (such as ethylene carbonate) in the electrolyte can be oxidized to inorganic forms, which is beneficial for increasing the concentration of Li in the second liquid. + The content is reduced to achieve the effect of fully recovering lithium.

[0038] In one specific example, the first reducing iron source includes at least one of elemental iron and a ferrous salt, and the first inorganic acid includes at least one of hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid. Optionally, the elemental iron is provided in the form of iron powder, iron bars, or iron blocks, and the ferrous salt includes at least one of ferrous chloride, ferrous chloride hydrate, ferrous sulfate, ferrous sulfate hydrate, ferrous nitrate, ferrous nitrate hydrate, ferrous oxalate, and ferrous oxalate hydrate.

[0039] The first iron source can form Fe 2+ This promotes the hydrolysis of electrolytes and enhances the oxidation capacity of the system. It should be noted that all of the above-mentioned inorganic acids are commercially available, and this application does not have specific requirements regarding their concentration.

[0040] In a specific example, the mass ratio of iron to electrolyte in the first reducing iron source in step S1 is (0.05–0.3):1, specifically 0.05:1, 0.1:1, 0.15:1, 0.2:1, 0.25:1, or 0.3:1. The mass ratio of inorganic acid to electrolyte is (0.05–0.4):1, specifically 0.05:1, 0.1:1, 0.15:1, 0.2:1, 0.25:1, 0.3:1, 0.35:1, or 0.4:1. The mass ratio of pure water to electrolyte is (0.2–0.5):1, specifically 0.2:1, 0.25:1, 0.3:1, 0.35:1, 0.4:1, 0.45:1, or 0.5:1.

[0041] In a specific example, the reaction temperature in step S1 is 60–100°C, and the reaction time is 3–10 h. Specifically, the reaction temperature can be 60°C, 70°C, 80°C, 90°C, or 100°C, and the reaction time can be 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, or 10 h.

[0042] By adjusting the feed ratio, reaction temperature, and reaction time in step S1, the electrolyte and PF6 in the waste electrolyte are made more uniform. - It can be effectively hydrolyzed, thus separating from insoluble impurities, ensuring a high yield and purity of product in subsequent steps. If the mass ratio of the first reducing iron source added is less than 0.05, H2PO2 - It may not be able to be completely converted into PO4 3-This results in lower yields of iron and phosphorus compounds, and lower purity of lithium compounds. Furthermore, adding a first reducing iron source at a mass ratio higher than 0.3 leads to lower yields of lithium compounds. If the reaction temperature or reaction time is below the range specified in this application, H2PO2... - Incomplete conversion may occur, resulting in lower yields of iron and phosphorus compounds and lower purity of lithium compounds. While exceeding the application range in reaction temperature or time will not further improve yield and purity, it will increase production costs.

[0043] In a specific example, in step S2, hydrogen peroxide is added to the first liquid to remove H2PO2 from the first liquid. - Oxidized to PO4 3- Optionally, the mass ratio of hydrogen peroxide to electrolyte is (0.03 to 0.1):1, specifically 0.03:1, 0.04:1, 0.05:1, 0.06:1, 0.07:1, 0.08:1, 0.09:1 or 0.1:1.

[0044] Due to hydrogen peroxide and Fe in the first liquid 2+ The coexistence of these elements enables the system to convert H2PO2. - Oxidized to PO4 3- At the same time, it oxidizes organic solvents into inorganic states, thus achieving the degradation of organic solvents.

[0045] In a specific example, the reaction temperature in step S2 is 20–50°C, and the reaction time is 0.5–10 h. Specifically, the reaction temperature can be 20°C, 30°C, 40°C, or 50°C, and the reaction time can be 0.5 h, 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, or 10 h.

[0046] In one specific example, the pH value is adjusted to 1.5–2.0 by adding at least one of ammonia, ammonium carbonate, and ammonium bicarbonate to the first liquid.

[0047] Adjusting the amount of hydrogen peroxide added, the reaction temperature, and the reaction time in step S2 is beneficial for obtaining products with higher yields and purity. If the system pH, reaction temperature, reaction time, or oxidant dosage is below the range specified in this application, the fixed precipitate cannot be completely precipitated, resulting in lower yields of iron and phosphorus compounds and lower purity of lithium compounds. Conversely, exceeding the range specified in this application for reaction temperature, reaction time, or oxidant dosage will not further improve the yield and purity but will increase production costs.

[0048] Furthermore, another embodiment of this application provides a method for recovering lithium and fluorine from waste electrolyte after dismantling lithium-ion batteries, including any of the above-mentioned pretreatment methods, wherein the method for recovering lithium and fluorine further includes the following steps:

[0049] Step S3: Adjust the pH of the second liquid to 3.0–7.0, so that the Li in the second liquid… + It precipitates out as a precipitate, yielding a compound containing lithium and fluorine.

[0050] Step S3 involves the recovery of lithium and fluorine from the second liquid. In step S3, the pH of the second liquid is adjusted to 3.0–7.0, specifically, it can be 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, or 7.0. Under these conditions, HF and Li in the second liquid... + The reaction forms a compound containing lithium and fluorine.

[0051] In a specific example, the reaction temperature in step S3 is 50–100°C, and the reaction time is 1–5 h. Specifically, the reaction temperature can be 50°C, 60°C, 70°C, 80°C, 90°C, or 100°C, and the reaction time can be 1 h, 2 h, 3 h, 4 h, or 5 h. By adjusting the reaction temperature, reaction time, and pH value in step S3, the HF and Li in the second liquid are controlled. + and F - It can fully analyze and improve the yield and purity of the recovered products.

[0052] In one specific example, the pH value is adjusted by adding at least one of sodium hydroxide, sodium carbonate, and sodium bicarbonate to the second liquid.

[0053] In a specific example, step S3 further includes a first post-treatment step of the lithium-containing compound, which optionally includes filtration, evaporation concentration, and solid-liquid separation. Understandably, in this embodiment, a high-purity recovered product is obtained by post-treating the lithium- and fluorine-containing compound. Specifically, the lithium- and fluorine-containing compound yields LiF after the first post-treatment.

[0054] By adjusting the pH value in step S3, the Li in the second liquid is reduced. + and F - A compound with a purity greater than 99% was formed, achieving efficient recovery of lithium and fluorine. The recovered product is one of the raw materials for the preparation of LiPF6, thus possessing high recovery value.

[0055] Furthermore, another embodiment of this application provides a method for recovering phosphorus from waste electrolyte after dismantling lithium-ion batteries, including any of the above-mentioned pretreatment methods, and the phosphorus recovery method further includes the following steps:

[0056] Step S4: Mix the solid precipitate with the second reducing iron source, the second inorganic acid and pure water and react them. After the reaction, perform solid-liquid separation to obtain the third liquid and filter residue containing insoluble impurities.

[0057] Step S5: Adjust the pH of the third liquid to 1.5-2.0, and perform solid-liquid separation after the reaction to obtain phosphorus-containing compounds.

[0058] It should be noted that step S3 is for the recovery of lithium and fluorine from the second liquid, while steps S4 and S5 are for the recovery of phosphorus. Furthermore, steps S3, S4, and S5 are for the recovery of different products and do not interfere with each other. Therefore, the recovery steps S3, S4, and S5 can be performed simultaneously or sequentially, and this application does not impose any restrictions on this.

[0059] In step S4, the addition of a second reducing iron source reduces the Fe content in the solid precipitate. 3+ Reduced to Fe 2+ The Fe is dissolved into the reaction solution, while the insoluble impurities in the solid precipitate that cannot react with the second iron source are removed as filter residue. This ensures that the third liquid contains as much Fe as possible. 2+ Understandably, step S5 is equivalent to the recrystallization process of the solid precipitate, in which Fe... 2+ Converted to Fe 3+ and with PO4 in the system 3- The reaction produces insoluble iron and phosphorus compounds. The pH of the third liquid is between 1.5 and 2.0, specifically, it can be 1.5, 1.6, 1.7, 1.8, 1.9, or 2. Furthermore, because the reaction system in step S5 has strong oxidizing properties, it can eliminate any small amounts of H₂PO₂ that may be present in the system. - Oxidized to PO4 3- This further improved the phosphorus recovery rate.

[0060] In a specific example, in step S4, the second reducing iron source comprises elemental iron, and the second inorganic acid comprises at least one selected from hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid. Specifically, the elemental iron is provided in the form of at least one selected from iron powder, iron bars, and iron blocks. The second reducing iron source is capable of reacting with Fe in the solid precipitate. 3+ A redox reaction occurs, causing Fe to... 3+ Reduced to readily soluble Fe 2+ Promoted Fe 3+ Dissolution.

[0061] In a specific example, the mass ratio of iron to electrolyte in the second reducing iron source is (0.02–0.15):1, specifically 0.02:1, 0.04:1, 0.06:1, 0.08:1, 0.1:1, 0.12:1, 0.14:1, or 0.15:1. The mass ratio of inorganic acid to electrolyte is (0.1–0.3):1, specifically 0.1:1, 0.15:1, 0.2:1, 0.25:1, or 0.3:1. The mass ratio of pure water to electrolyte is (0.3–0.8):1, specifically 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, or 0.8:1.

[0062] In a specific example, the reaction temperature in step S4 is 40–80°C, and the reaction time is 2–10 h. Specifically, the reaction temperature can be 40°C, 50°C, 60°C, 70°C, or 80°C, and the reaction time can be 2 h, 4 h, 6 h, 8 h, or 10 h.

[0063] By controlling the feed ratio, reaction temperature, and reaction time in step S4, iron in the solid precipitate is fully extracted, ensuring the yield and purity of the product in subsequent steps. If the mass ratio of the second reducing iron source is less than 0.02, the yield and purity of the iron and phosphorus compounds will be low. Conversely, if the mass ratio of the second reducing iron source is greater than 0.15, the yield and purity will be further improved, but the production cost will increase.

[0064] In a specific example, in step S5, hydrogen peroxide is added to the third liquid to make Fe... 2+ Oxidized to Fe 3 + The mass ratio of hydrogen peroxide to electrolyte is (0.05–0.3):1, specifically 0.05:1, 0.1:1, 0.15:1, 0.2:1, 0.25:1, or 0.3:1.

[0065] In a specific example, the reaction temperature in step S5 is 60–100°C, and the reaction time is 4–10 h. Specifically, the reaction temperature can be 60°C, 70°C, 80°C, 90°C, or 100°C, and the reaction time can be 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, or 10 h.

[0066] In one specific example, the pH value is adjusted by adding at least one of ammonia, ammonium carbonate, and ammonium bicarbonate to the third liquid.

[0067] By adjusting the amount of the second reducing iron source added in step S5, the reaction temperature, reaction time, and pH value, the Fe in the third liquid is reduced. 2+ Sufficient oxidation and precipitation improve the yield and purity of the recovered products.

[0068] In a specific example, step S5 further includes a second post-processing step of the phosphorus-containing compound, optionally including washing and drying. Understandably, in this embodiment, a high-purity recovered product is obtained by performing the appropriate post-processing on the phosphorus-containing compound. Specifically, the phosphorus-containing compound, after the second post-processing, yields FePO4·2H2O. Since FePO4·2H2O is a raw material for preparing lithium iron phosphate cathode materials, it has high recovery value.

[0069] To make the objectives and advantages of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of this application.

[0070] The materials used in the following examples are all commercially available.

[0071] Since the electrolyte content in the waste electrolyte may vary slightly in different lithium-ion batteries, the recycling method of this application is applicable to various waste electrolytes. For ease of description and comparison of test results, the following examples and comparative examples all use waste electrolytes with a mass percentage of 10% electrolyte (mainly LiPF6) and a mass percentage of 90% organic solvent, hereinafter referred to as electrolytes.

[0072] Example 1

[0073] (1) Preprocessing

[0074] 400g of electrolyte, 20g of iron powder, 80g of sulfuric acid, and 80g of pure water were mixed and reacted at 100℃ for 3.0h. After the reaction, solid-liquid separation was performed to obtain a first liquid and filter residue. The first liquid was mixed with 40g of hydrogen peroxide, and the pH was adjusted to 2.0 with ammonia water. The mixture was reacted at 50℃ for 0.5h. After the reaction, solid-liquid separation was performed to obtain a second liquid and a solid precipitate.

[0075] (2) Recovery of lithium and fluorine compounds

[0076] The pH of the second liquid was adjusted to 6.0 using sodium hydroxide, and the reaction was carried out at 80°C for 3.0 h. After the reaction, the solution was filtered, and the filtrate was successively evaporated and concentrated, followed by solid-liquid separation to obtain LiF.

[0077] (3) Recovery of phosphorus-containing compounds

[0078] The solid precipitate was mixed with 15g iron strip, 40g phosphoric acid, 60g sulfuric acid, and 120g pure water, and reacted at 40℃ for 3.0h. After the reaction, solid-liquid separation was performed to obtain a third liquid and filter residue. The third liquid was mixed with 50g hydrogen peroxide, and the pH was adjusted to 1.5 with ammonia water. The reaction temperature was controlled at 100℃, and the reaction time was 6.0h. After the reaction, solid-liquid separation was performed to obtain a crude solid product. The crude solid product was washed and dried sequentially to obtain FePO4·2H2O.

[0079] Example 2

[0080] (1) Preprocessing

[0081] 1000g of electrolyte, 814.3g of ferrous sulfate, 350g of hydrochloric acid, and 500g of pure water were mixed and reacted at 70℃ for 10.0h. After the reaction, solid-liquid separation was performed to obtain a first liquid and a filter residue. The first liquid was mixed with 70g of hydrogen peroxide, and the pH was adjusted to 2.0 using ammonium bicarbonate. The mixture was reacted at 45℃ for 1.5h. After the reaction, solid-liquid separation was performed to obtain a second liquid and a solid precipitate.

[0082] (2) Recovery of lithium and fluorine compounds

[0083] The pH of the second liquid was adjusted to 7.0 using sodium carbonate, and the reaction was carried out at 100°C for 1.0 h. After the reaction, the solution was filtered, and the filtrate was successively evaporated and concentrated, followed by solid-liquid separation to obtain LiF.

[0084] (3) Recovery of phosphorus-containing compounds

[0085] The solid precipitate was mixed with 150g iron bar, 200g sulfuric acid, and 800g pure water, and reacted at 70℃ for 3.5h. After the reaction, solid-liquid separation was performed to obtain a third liquid and filter residue. The third liquid was mixed with 300g hydrogen peroxide, and the pH was adjusted to 1.5 using ammonium carbonate. The reaction temperature was controlled at 60℃, and the reaction time was 6.0h. After the reaction, solid-liquid separation was performed to obtain a crude solid product. The crude solid product was washed and dried sequentially to obtain FePO4·2H2O.

[0086] Example 3

[0087] (1) Preprocessing

[0088] 800g of electrolyte, 317.5g of ferrous chloride, 320g of hydrochloric acid, and 350g of pure water were mixed and reacted at 60℃ for 6.0h. After the reaction, solid-liquid separation was performed to obtain a first liquid and a filter residue. The first liquid was mixed with 24g of hydrogen peroxide, and the pH was adjusted to 1.5 using ammonium carbonate. The mixture was reacted at 20℃ for 2.0h. After the reaction, solid-liquid separation was performed to obtain a second liquid and a solid precipitate.

[0089] (2) Recovery of lithium and fluorine compounds

[0090] The pH of the second liquid was adjusted to 3.0 using sodium carbonate, and the reaction was carried out at 90°C for 5.0 h. After the reaction, the solution was filtered, and the filtrate was subsequently evaporated and concentrated, followed by solid-liquid separation to obtain LiF.

[0091] (3) Recovery of phosphorus-containing compounds

[0092] The solid precipitate was mixed with 20g iron strip, 100g sulfuric acid, 60g hydrochloric acid, and 500g pure water, and reacted at 80℃ for 5.5h. After the reaction, solid-liquid separation was performed to obtain a third liquid and filter residue. The third liquid was mixed with 40g hydrogen peroxide, and the pH was adjusted to 1.8 with ammonia water. The reaction temperature was controlled at 80℃, and the reaction time was 8.0h. After the reaction, solid-liquid separation was performed to obtain a crude solid product. The crude solid product was washed and dried sequentially to obtain FePO4·2H2O.

[0093] Example 4

[0094] (1) Preprocessing

[0095] 2500g of electrolyte, 1092.9g of ferrous nitrate, 125g of nitric acid, and 350g of pure water were mixed and reacted at 80℃ for 5.5h. After the reaction, solid-liquid separation was performed to obtain a first liquid and filter residue. The first liquid was mixed with 130g of hydrogen peroxide, and the pH was adjusted to 1.8 using ammonium carbonate. The mixture was reacted at 50℃ for 4.0h. After the reaction, solid-liquid separation was performed to obtain a second liquid and a solid precipitate.

[0096] (2) Recovery of lithium and fluorine compounds

[0097] The pH of the second liquid was adjusted to 7.0 using sodium hydroxide, and the reaction was carried out at 50°C for 4.0 h. After the reaction, the solution was filtered, and the filtrate was successively evaporated and concentrated, followed by solid-liquid separation to obtain LiF.

[0098] (3) Recovery of phosphorus-containing compounds

[0099] The solid precipitate was mixed with 60g iron strip, 200g phosphoric acid, 100g hydrochloric acid, and 1500g pure water, and reacted at 80℃ for 6.5h. After the reaction, solid-liquid separation was performed to obtain a third liquid and filter residue. The third liquid was mixed with 200g hydrogen peroxide, and the pH was adjusted to 2.0 with ammonia water. The reaction temperature was controlled at 80℃, and the reaction time was 8.0h. After the reaction, solid-liquid separation was performed to obtain a crude solid product. The crude solid product was washed and dried sequentially to obtain FePO4·2H2O.

[0100] Comparative Example 1

[0101] It is basically the same as Example 1, except that the iron source in (1) is ferric chloride and the amount added is 58g. Other operations are the same as in Example 1.

[0102] Comparative Example 2

[0103] It is basically the same as Example 1, except that the amount of iron powder added in (1) is 10g, and the other operations are the same as in Example 1.

[0104] Comparative Example 3

[0105] It is basically the same as Example 1, except that the reaction time of the first liquid with hydrogen peroxide in (1) is 10 minutes.

[0106] Comparative Example 4

[0107] It is basically the same as Example 1, except that the reaction temperature of the first liquid with hydrogen peroxide in (1) is 10°C.

[0108] Comparative Example 5

[0109] It is basically the same as Example 1, except that hydrogen peroxide is not added to the first liquid in (1).

[0110] Comparative Example 6

[0111] It is basically the same as Example 1, except that no iron bar is added to the third liquid in (3).

[0112] Comparative Example 7

[0113] The waste electrolyte is pretreated according to an existing waste electrolyte recycling process (CN11908438 A), as follows:

[0114] (1) Preprocessing

[0115] Take 150g of waste electrolyte, add 0.1mol of sodium fluoride, and sinter at 700℃ for 1.5h, then collect the ash.

[0116] The above ash was dissolved in 40 mL of 30% nitric acid, and then 24 g of ferric nitrate was added. Ammonia was added to adjust the pH of the solution to 2. The mixture was heated at 76 °C for 2 h and then filtered to obtain filter residue and lithium-containing filtrate (i.e., the first liquid).

[0117] The subsequent recovery of LiF and FePO4·2H2O was carried out using the same process as in Example 1.

[0118] Comparative Example 8

[0119] Based on an existing waste electrolyte recovery process (CN11908438 A), the waste electrolyte is pretreated and FePO4 is recovered using a traditional process, as detailed below:

[0120] (1) Preprocessing

[0121] Take 150g of waste electrolyte, add 0.1mol of sodium fluoride, and sinter at 700℃ for 1.5h, then collect the ash.

[0122] The above ash was dissolved in 40 mL of 30% nitric acid, and then 24 g of ferric nitrate was added. Ammonia was added to adjust the pH of the solution to 2. The mixture was heated at 76 °C for 2 h and then filtered to obtain filter residue and lithium-containing filtrate (i.e., the first liquid).

[0123] (2) Recovery of FePO4·2H2O

[0124] High-purity ferric phosphate (99.95% purity, with impurity ion content of only 15 ppm) was obtained by washing the solid precipitate three times with water using a shear emulsification pump. The process is as follows: The solid precipitate was mixed with water to form a slurry, which was then placed in the feed pipe of the shear emulsification pump. The pressure difference between the feed pipe and the working chamber containing the rotor of the shear emulsification pump was controlled at 0.2 MPa. Under the pressure difference, the slurry was drawn into the working chamber containing the rotor and homogenized at a rotor speed of 2900 rpm. The homogenized material was filtered, and the solids were collected. The above operation was repeated twice to obtain ferric phosphate dihydrate.

[0125] Performance testing

[0126] XRD tests were performed on the LiF and FePO4·2H2O recovered in Example 1, and the results are as follows: Figure 1 and Figure 2 As shown. By Figure 1 and Figure 2 It can be seen that the LiF and FePO4·2H2O recovered in Example 1 both have good crystal form and high crystallinity.

[0127] Impurity content was tested in each sample using atomic emission spectrometry (ICP) and chemical analysis. Specifically, the concentrations of fluorine, lithium, sodium, potassium, calcium, barium, copper, manganese, cobalt, and nickel in ferric phosphate were tested; the concentrations of potassium, calcium, iron, barium, copper, manganese, cobalt, nickel, and phosphorus in lithium fluoride were tested; the concentration of phosphorus in the second liquid was tested; and the concentrations of lithium and fluorine in the solid precipitate were tested.

[0128] The chemical oxygen demand (COD) of the second liquid in each sample, as well as the total organic carbon (TOC) of LiF, FePO4·2H2O and solid precipitate, were determined by the potassium dichromate colorimetric method.

[0129] The yield of the recovered products for each sample was obtained using the following formula:

[0130] According to the formula: ferric phosphate dihydrate yield = (actual recovered product weight × lithium hexafluorophosphate molecular weight) × 100% / (electrolyte mass × electrolyte mass ratio × ferric phosphate dihydrate molecular weight);

[0131] Lithium fluoride yield = (actual recovered product weight × lithium hexafluorophosphate molecular weight) × 100% / (electrolyte mass × electrolyte mass percentage × lithium fluoride molecular weight).

[0132] The test results for each embodiment are shown in Table 1, and the test results for each comparative example are shown in Table 2.

[0133] Table 1

[0134]

[0135] Table 1 shows that the LiF yield in Examples 1-4 was above 95%, the FePO4·2H2O yield was above 98%, and the impurity content was low. The phosphorus concentration in the second liquid and the lithium and fluorine concentrations in the solid precipitate were both low, indicating that the pretreatment step effectively separated phosphorus, lithium, and fluorine, thereby improving the purity of the product. The low COD in the second liquid indicates the presence of reducing H2PO2. - The reduced amount of H2PO2 in the electrolyte indirectly proves that the pretreatment step can remove the difficult-to-remove H2PO2. - Convert to PO4 3- The low TOC of the solid precipitate, LiF, and FePO4·2H2O indicates a low organic carbon content, suggesting that the pretreatment step effectively removes organic solvents from the electrolyte. Therefore, the purity of the recovered LiF can reach over 99.95%, and the purity of FePO4·2H2O can reach over 99.9%.

[0136] Table 2

[0137]

[0138] Please refer to Tables 1 and 2. Based on the test results of Example 1 and Comparative Example 1, it can be seen that in Comparative Example 1, the pretreatment step using trivalent iron as the first iron source resulted in a significant decrease in the yield of ferric phosphate dihydrate and lithium fluoride, and the product had high impurity content and low purity. Based on the test results of Example 1 and Comparative Example 2, it can be seen that in Comparative Example 2, the amount of iron powder added in the pretreatment step was 10g, resulting in a significant decrease in the yield of ferric phosphate dihydrate and lithium fluoride, and low purity. Based on the test results of Example 1 and Comparative Example 3, it can be seen that in Comparative Example 3, the reaction time of the first liquid with hydrogen peroxide in the pretreatment step was 10 minutes, leading to a slight decrease in the yield of ferric phosphate dihydrate and lithium fluoride, and low purity. Based on the test results of Example 1 and Comparative Example 4, it can be seen that in Comparative Example 4, the reaction temperature of the first liquid with hydrogen peroxide in the pretreatment step was 10℃, resulting in a significant decrease in the yield of ferric phosphate dihydrate and lithium fluoride, and poor product purity. According to the test results of Example 1 and Comparative Example 5, in the first liquid of Comparative Example 5, without the addition of an oxidant, the yields of ferric phosphate dihydrate and lithium fluoride decreased significantly, and the product purity was low. According to the test results of Example 1 and Comparative Example 6, in the second liquid of Comparative Example 6, without the addition of elemental iron, the yields of ferric phosphate dihydrate and lithium fluoride remained basically unchanged, but the purity of ferric phosphate was low.

[0139] Based on the test results of Example 1 and Comparative Example 7, it can be seen that Comparative Example 7 adopted an existing waste electrolyte recovery process. The pretreatment step involved sintering with a stabilizer (sodium fluoride or potassium fluoride), while the subsequent separate recovery steps of ferric phosphate dihydrate and lithium fluoride followed the scheme of this application. The results showed that even though the subsequent separate recovery methods for ferric phosphate dihydrate and lithium fluoride were the same as those of this application, the final yields of ferric phosphate dihydrate and lithium fluoride were significantly reduced, and the purity of lithium fluoride was low. Based on the test results of Example 1 and Comparative Example 8, it can be seen that Comparative Example 8 adopted a complete scheme for recovering ferric phosphate dihydrate from waste electrolyte. The pretreatment involved sintering with a stabilizer (sodium fluoride or potassium fluoride), followed by acid dissolution. After precipitation of crude ferric phosphate dihydrate, ferric phosphate dihydrate was obtained through an emulsification pump. Although the purity of ferric phosphate dihydrate was good, the yield was low.

[0140] In summary, the recycling method of this application achieves thorough pre-separation of lithium, fluorine, and phosphorus in the waste electrolyte through a pretreatment step, and efficiently removes organic impurities from the waste electrolyte. Furthermore, no external impurity elements are introduced, and impurities are completely separated from the target recoverable materials such as lithium, fluorine, and phosphorus. Subsequently, high-yield and high-purity recovered products are obtained through separate recovery steps using LiF and FePO4·2H2O. In addition, the recycling method of this application has a simple process flow, virtually no emissions of waste gas, wastewater, or solid waste, and is environmentally friendly.

[0141] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0142] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims, and the specification and drawings can be used to interpret the content of the claims.

Claims

1. A pretreatment method for waste electrolyte after dismantling lithium-ion batteries, characterized in that, Includes the following steps: Step S1: The recovered electrolyte is mixed with a first reducing iron source, a first inorganic acid and pure water and reacted. After the reaction, solid-liquid separation is performed to obtain a first liquid. The electrolyte in the electrolyte includes lithium hexafluorophosphate. Step S2: Adjust the pH of the first liquid to 1.5~2.0, and remove the H2PO2 from the first liquid. - Oxidized to PO4 3- It precipitates out as a precipitate, and after the reaction, solid-liquid separation is performed to obtain a second liquid and a solid precipitate. In step S1, the mass ratio of iron in the first reducing iron source to the electrolyte is (0.05~0.3):1, the reaction temperature in step S1 is 60~100 ℃, and the reaction time is 3~10 h.

2. The pretreatment method according to claim 1, characterized in that, The first reducing iron source includes at least one of elemental iron and ferrous salts, and the first inorganic acid includes at least one of hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid.

3. The pretreatment method according to claim 2, characterized in that, The elemental iron is provided in at least one of the following forms: iron powder, iron bar, and iron block, and the divalent iron salt includes at least one of the following: ferrous chloride, ferrous chloride hydrate, ferrous sulfate, ferrous sulfate hydrate, ferrous nitrate, ferrous nitrate hydrate, ferrous oxalate, and ferrous oxalate hydrate.

4. The pretreatment method according to claim 1, characterized in that, In step S1, the mass ratio of the first inorganic acid to the electrolyte is (0.05~0.4):1, and the mass ratio of the pure water to the electrolyte is (0.2~0.5):

1.

5. The pretreatment method according to any one of claims 1 to 4, characterized in that, In step S2, hydrogen peroxide is added to the first liquid to remove H2PO2 from the first liquid. - Oxidized to PO4 3- The mass ratio of hydrogen peroxide to electrolyte is (0.03~0.1):

1.

6. The pretreatment method according to claim 5, characterized in that, The reaction temperature in step S2 is 20~50 ℃, and the reaction time is 0.5~10 h.

7. The pretreatment method according to claim 5, characterized in that, The pH value is adjusted to 1.5-2.0 by adding at least one of ammonia, ammonium carbonate, and ammonium bicarbonate to the first liquid.

8. A method for recovering lithium and fluorine from waste electrolyte after dismantling lithium-ion batteries, characterized in that, The method for recovering lithium and fluorine, comprising the pretreatment method according to any one of claims 1 to 7, further comprises the following steps: Step S3: Adjust the pH of the second liquid to 3.0~7.0, so that the Li in the second liquid... + It precipitates out as a precipitate, yielding a compound containing lithium and fluorine.

9. The method for recovering lithium and fluorine according to claim 8, characterized in that, The reaction temperature in step S3 is 50~100℃, and the reaction time is 1~5 h.

10. The method for recovering lithium and fluorine according to claim 8, characterized in that, The pH value is adjusted to 3.0-7.0 by adding at least one of sodium hydroxide, sodium carbonate, and sodium bicarbonate to the second liquid.

11. The method for recovering lithium and fluorine according to claim 8, characterized in that, Step S3 further includes a first post-treatment step of the lithium- and fluorine-containing compound, the first post-treatment including filtration, evaporation concentration and solid-liquid separation.

12. A method for recovering phosphorus from waste electrolyte after dismantling lithium-ion batteries, characterized in that, The pretreatment method according to any one of claims 1 to 7, the method for recovering phosphorus further includes the following steps: Step S4: Mix the solid precipitate with the second reducing iron source, the second inorganic acid and pure water and react them. After the reaction, perform solid-liquid separation treatment to obtain the third liquid and filter residue containing insoluble impurities. Step S5: Adjust the pH of the third liquid to 1.5~2.0, and perform solid-liquid separation after the reaction to obtain a phosphorus-containing compound.

13. The method for recovering phosphorus according to claim 12, characterized in that, In step S4, the second reducing iron source includes elemental iron, and the second inorganic acid includes at least one of hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid, wherein the elemental iron is provided in the form of at least one of iron powder, iron bar, and iron block.

14. The method for recovering phosphorus according to claim 12, characterized in that, The mass ratio of iron in the second reducing iron source to the electrolyte is (0.02~0.15):1, the mass ratio of the second inorganic acid to the electrolyte is (0.1~0.3):1, and the mass ratio of pure water to the electrolyte is (0.3~0.8):

1.

15. The method for recovering phosphorus according to claim 12, characterized in that, The reaction temperature in step S4 is 40~80℃, and the reaction time is 2~10 h.

16. The method for recovering phosphorus according to claim 12, characterized in that, In step S5, hydrogen peroxide is added to the third liquid to make Fe... 2+ Oxidized to Fe 3+ .

17. The method for recovering phosphorus according to claim 16, characterized in that, The mass ratio of hydrogen peroxide to the electrolyte is (0.05~0.3):

1.

18. The method for recovering phosphorus according to claim 12, characterized in that, The reaction temperature in step S5 is 60~100℃, and the reaction time is 4~10 h.

19. The method for recovering phosphorus according to claim 12, characterized in that, In step S5, the pH value is adjusted to 1.5-2.0 by adding at least one of ammonia, ammonium carbonate and ammonium bicarbonate to the third liquid.

20. The method for recovering phosphorus according to claim 12, characterized in that, Step S5 further includes a second post-treatment step of the phosphorus-containing compound, the second post-treatment including washing and drying.

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