Method for recycling iron phosphate and graphite from residues obtained after valuable metal is extracted from waste lithium battery black powder

Abstract

The invention discloses a method for recycling iron phosphate and graphite from residues obtained after valuable metal is extracted from waste lithium battery black powder. The method comprises the following steps: carrying out alkali solution reaction on ferrophosphorus residues obtained after lithium is extracted from lithium iron phosphate black powder, so that elements such as phosphorus, aluminum and titanium are all dissolved in a liquid phase, and the iron element generates ferric hydroxide which is left in alkali-soluble residues; the alkali-soluble residues are soaked in an ammonia complexing solution to remove impurities such as copper and nickel, and then are neutralized by an acid solution with relatively low concentration to obtain an iron salt solution and graphite carbon residues; oxidizing roasting, flotation, purification and drying are carried out on graphite carbon residues, negative electrode carbon residues obtained after valuable metal is extracted from waste ternary lithium battery black powder after optional preliminary purification, and graphite carbon residues obtained after lithium and ferrophosphorus are extracted from current lithium iron phosphate black powder, so that graphite can be recycled; and acid is added into the alkali dissolution filtrate to adjust the pH value to 6.0-9.0, and then the temperature is raised to hydrolyze impurity salts such as aluminum, titanium and chromium dissolved out of the phosphate solution to form hydroxides and metatitanic acid precipitates to be removed, so that finally, the quality of the iron phosphate prepared by the method disclosed by the invention is ensured to reach related standards.

Description

Technical Field

[0001] This invention relates to the field of waste lithium battery resource utilization technology, and in particular to a method for recovering iron phosphate and graphite from the residue after extracting valuable metals from waste lithium battery black powder. Background Technology

[0002] Lithium-ion batteries are widely used in new energy vehicles and energy storage due to their advantages such as high specific capacity, good safety, and long cycle life. However, lithium-ion batteries have a limited lifespan, and as their service life increases, they will inevitably be retired, resulting in a large number of scrapped lithium-ion batteries. Based on the type of cathode material, lithium-ion batteries are mainly divided into lithium iron phosphate batteries (LiFePO4) and nickel-cobalt-manganese ternary lithium-ion batteries (LiNi). 1-x-y Co x Mn y O2), and its negative electrode material is usually graphite. At present, the industrial pretreatment of these two types of waste lithium batteries adopts pretreatment processes such as discharge, crushing and physical sorting to obtain a mixture of metal particles such as iron, copper and aluminum and positive and negative electrode materials—waste lithium battery black powder (referred to as lithium iron phosphate black powder and ternary lithium battery black powder, respectively).

[0003] In actual industrial production, lithium iron phosphate (LFP) black powder is leached with inorganic acids or organic acids + oxidants to extract high-value lithium. After lithium extraction, a large amount of iron phosphate residue is generated, whose main components are iron phosphate, graphite, conductive carbon black, organic adhesives, and small amounts of metal salt impurities. Ternary lithium battery black powder is first treated with inorganic acids + reducing agents, and then valuable metals such as nickel, cobalt, manganese, and lithium are extracted through wet leaching and extraction methods, producing a certain amount of negative electrode carbon residue, whose main components are graphite, conductive carbon black, organic adhesives, and small amounts of nickel-cobalt-manganese sulfates. It is evident that both types of residue contain graphite, conductive carbon black, and their surface-coated organic adhesives. The iron phosphate residue also contains a large amount of iron phosphate. Currently, neither of these types of residue has been effectively treated or utilized for resource recovery. Most companies temporarily store ferric phosphate residue as waste, while a few use it as a raw material for phosphorus and iron, adding sulfuric acid and iron powder to resynthesize ferric phosphate through dissolution leaching. However, this method suffers from drawbacks such as complex processes, large amounts of sodium sulfate as a byproduct (with limited market capacity), and high production costs. Furthermore, some quality indicators of the recycled ferric phosphate products fail to meet the requirements of the "Ferric Phosphate for Batteries" standard (HG / T4701-2021). The key to preparing battery-grade ferric phosphate from ferric phosphate residue lies in controlling production costs and effectively removing impurities such as aluminum, titanium, and copper to meet product quality requirements. To achieve this, existing technologies use a low-volume sodium hydroxide solution to leach the lithium-extracted ferric phosphate residue to remove aluminum impurities; only a small portion of the iron is leached out during this stage. The leaching residue is then treated with a high-concentration inorganic acid to dissolve most of the remaining ferric phosphate, resulting in an acidic filtrate containing a large amount of ferric salts. Reducing salts such as sodium sulfide or sodium thiosulfate are added to the acidic filtrate to remove copper, titanium, and other impurities, ultimately synthesizing ferric phosphate. However, the high concentration of Fe... 3+ It exhibits strong oxidizing properties in acidic solutions and rapidly reacts with reducing agents such as sulfur. 2- The reaction is thus rapidly consumed, making it difficult to guarantee its impurity removal efficiency and ensuring that the regenerated iron phosphate product meets the quality standards for battery iron phosphate. Furthermore, the graphite carbon residue remaining after extracting valuable metals (lithium, nickel, cobalt, manganese) or iron phosphate from waste lithium battery black powder still contains a high proportion of ultrafine conductive carbon black, PVDF adhesive, and a small amount of magnetic metal impurities. Due to the oleophilic nature of the ultrafine conductive carbon black surface and its adsorption of larger graphite particles, it is difficult to separate high-purity graphite directly using flotation methods. Simultaneously, a small amount of metal impurity ions remain on the graphite surface and between its crystalline layers, making it difficult to meet the application requirements of graphite-based anode materials for batteries and other fields.

[0004] Therefore, there is an urgent need to provide a method for recovering iron phosphate and graphite from the residue after extracting valuable metals from waste lithium battery black powder, in order to solve the technical problems of the difficulty in meeting the quality index of iron phosphate recovered from lithium iron phosphate black powder to meet the "Iron Phosphate for Batteries" standard, the high production cost, and the difficulty and low purity of graphite recovery from the graphite carbon residue after extracting valuable metals or iron phosphate from waste lithium battery black powder. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned technical deficiencies and propose a method for recovering iron phosphate and graphite from the residue after extracting valuable metals from waste lithium battery black powder. This method solves the technical problems in the prior art, such as the difficulty in meeting the "Iron Phosphate for Batteries" standard for the quality indicators of iron phosphate recovered from the lithium extraction residue of lithium iron phosphate black powder, high production costs, and the difficulty and low purity of graphite recovery from the graphite carbon residue after extracting valuable metals or iron phosphate from waste lithium battery black powder.

[0006] In a first aspect, the present invention provides a method for recovering iron phosphate from the residue after extracting valuable metals from waste lithium battery black powder, comprising the following steps: S1. Alkali dissolution: The phosphorus iron residue after lithium extraction from lithium iron phosphate black powder is mixed and reacted with the first alkaline solution. After solid-liquid separation, alkaline dissolution residue and alkaline dissolution filtrate are obtained; wherein, the alkaline dissolution filtrate is an alkaline crude sodium phosphate solution. S2, Ammonia Complexation: The alkaline-soluble residue is soaked in an ammonia complexation solution to remove impurities, and then separated into solid and liquid components to obtain ammonia complexation filter residue and ammonia complexation filtrate. S3, Acid Dissolution: The ammonia complex filter residue is neutralized by the first acid solution. After solid-liquid separation, acid-dissolved residue and acid-dissolved filtrate are obtained. The acid-dissolved residue is graphite carbon residue, and the acid-dissolved filtrate is an iron salt solution. S4. Neutralization and impurity removal: Adjust the pH of the alkaline solution filtrate to 6.0~9.0, and then heat it, let it stand to settle and separate the solid and liquid to obtain acid neutralization precipitate and acid neutralization filtrate; wherein, the acid neutralization precipitate is a precipitate containing aluminum hydroxide, chromium hydroxide and metatitanic acid, and the acid neutralization filtrate is a sodium dihydrogen phosphate solution. S5. Iron phosphate for battery synthesis: The pH of the acid neutralization filtrate is adjusted to 10-13, and then mixed with the acid-soluble filtrate for precipitation reaction. After aging and solid-liquid separation, iron phosphate dihydrate is obtained.

[0007] Secondly, this invention provides a method for recovering graphite from the residue after extracting valuable metals from waste lithium battery black powder, comprising the following steps: A1. The graphite carbon residue is oxidized and roasted to obtain the roasted material; A2. The roasted material is separated by flotation to obtain concentrate and tailings; wherein the concentrate is crude graphite and the tailings are industrial waste residue. A3. The concentrate is deeply purified and dried to obtain recycled graphite; The graphite carbon residue includes the acid-soluble residue provided in the first aspect of the present invention, and optionally at least one of the graphite carbon residue after lithium and iron phosphate are extracted from conventional lithium iron phosphate black powder, and the negative electrode carbon residue after valuable metals are extracted from ternary lithium battery black powder.

[0008] Thirdly, this invention provides an apparatus for recovering ferric phosphate and graphite from the residue after extracting valuable metals from waste lithium battery black powder, comprising an alkaline dissolution kettle, a first filter, an ammonia leaching filter, an acid dissolution kettle, a second filter, a neutralization precipitator, a third filter, a modulator, a synthesis reactor, a fourth filter, a calcination furnace, a flotation machine, and a purification dryer; wherein... The discharge port of the alkali dissolving kettle is connected to the first filter, the filter residue outlet of the first filter is connected to the ammonia leaching filter, and the filtrate outlet of the first filter is connected to the neutralization precipitator. The filter residue outlet of the ammonia leaching filter is connected to the acid dissolution kettle, the discharge port of the acid dissolution kettle is connected to the second filter, and the filtrate outlet of the second filter is connected to the synthesis reaction kettle. The upper clear liquid outlet of the neutralization precipitator is connected to the modulator, the lower mud outlet of the neutralization precipitator is connected to the third filter, the filtrate outlet of the third filter is connected to the modulator, and the discharge port of the modulator is connected to the synthesis reactor. The outlet of the synthesis reactor is connected to the fourth filter. The filter residue outlet of the second filter press is connected to the roasting furnace, the discharge port of the roasting furnace is connected to the flotation machine, and the concentrate outlet of the flotation machine is connected to the purification dryer.

[0009] Compared with the prior art, the beneficial effects of the present invention include: This invention involves reacting the phosphorus-iron residue after lithium extraction from lithium iron phosphate black powder with a high-concentration alkaline solution, causing elements such as phosphorus, aluminum, and titanium to dissolve in the liquid phase. The iron element forms ferric hydroxide and remains in the alkaline residue. After soaking the alkaline residue in an ammonia complex solution to remove impurities such as copper and nickel, it is neutralized with a low-concentration acid solution to obtain an iron salt solution and graphite carbon residue. The graphite carbon residue, along with the negative electrode carbon residue after extracting valuable metals from waste ternary lithium battery black powder (optionally pre-purified) and the graphite carbon residue after lithium and phosphorus extraction from existing lithium iron phosphate black powder, undergo oxidative roasting, flotation, purification, and drying to recover graphite. The alkaline filtrate is first acidified to adjust the pH to 6.0-9.0 and then heated to decompose impurities such as aluminum, titanium, and chromium dissolved in the phosphate solution, forming hydroxides and metatitanic acid precipitates for removal. Ultimately, this ensures that the quality of the iron phosphate prepared by this invention meets relevant standards. Attached Figure Description

[0010] Figure 1 This is a process flow diagram of one embodiment of the method for recovering iron phosphate from the residue after extracting valuable metals from waste lithium battery black powder provided by the present invention. Figure 2This is a process flow diagram of one embodiment of the method for recovering graphite from the residue after extracting valuable metals from waste lithium battery black powder provided by the present invention. Figure 3 This is a schematic diagram of one embodiment of the apparatus for recovering iron phosphate and graphite from the residue after extracting valuable metals from waste lithium battery black powder provided by the present invention. Figure 4 This is an optical photograph of the alkali-soluble residue in Example 1 of the present invention; Figure 5 These are scanning electron microscope images of concentrate graphite (a) and tailings slag (b) in Embodiment 1 of the present invention; Figure 6 This is the XRD pattern of the recycled graphite in Embodiment 1 of the present invention; Figure 7 These are the electrochemical performance test results of the recycled graphite in Example 1 of this invention; Figure 3 The components are as follows: 1. Alkali dissolving kettle, 2. First filter, 3. Ammonia immersion filter, 4. Acid dissolving kettle, 5. Second filter, 6. Neutralization precipitator, 7. Third filter, 8. Modulator, 9. Synthesis reactor, 10. Fourth filter, 11. Roasting furnace, 12. Flotation machine, 13. Purification dryer, 14. Water washing filter. Detailed Implementation

[0011] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0012] Please see Figure 1 In a first aspect, the present invention provides a method for recovering iron phosphate from the residue after extracting valuable metals from waste lithium battery black powder, comprising the following steps: S1. Alkali dissolution: The phosphorus iron residue after lithium extraction from lithium iron phosphate black powder is mixed and reacted with the first alkaline solution. After solid-liquid separation, alkaline dissolution residue and alkaline dissolution filtrate are obtained; wherein, the alkaline dissolution filtrate is an alkaline crude sodium phosphate solution.

[0013] In this step, the phosphorus-iron residue after lithium extraction from lithium iron phosphate black powder is mixed with the first alkaline solution for reaction, causing phosphorus, aluminum, titanium, chromium, and zinc to dissolve and exist in the alkaline crude sodium phosphate solution. The dissolution rate of phosphorus, aluminum, titanium, chromium, and zinc is greater than 98%; while iron and other metallic elements form hydroxides and exist in the alkaline residue. The main chemical reactions are as follows: FePO4+ 3NaOH = Na3PO4+ Fe(OH)3↓ Al₂O₃ + 2NaOH = 2NaAlO₂ + H₂O TiO2 + 2NaOH = Na2TiO3 + H2O Cr₂O₃ + 2NaOH = 2NaCrO₂ + H₂O ZnO + 2NaOH = Na2ZnO2 + H2O.

[0014] S2, Ammonia Complexation: The alkaline-soluble residue is soaked in an ammonia complexation solution to remove impurities. After solid-liquid separation, ammonia complexation filter residue and ammonia complexation filtrate are obtained.

[0015] In this step, the alkaline-dissolved residue is soaked in an ammonia complex solution to remove impurities. This allows magnetic impurities such as copper and nickel to enter the liquid phase through a complexation reaction, thus removing them and significantly reducing the impurity content in the iron salt solution obtained in the subsequent acid dissolution step. The principle of the impurity removal reaction is as follows: Cu(OH)2+ 4NH3·H2O = Cu(NH3)4(OH)2+ 4H2O Ni(OH)2+ 6NH3·H2O = Ni(NH3)6(OH)2+ 6H2O.

[0016] S3, Acid Dissolution: The ammonia complex filter residue is neutralized by the first acid solution. After solid-liquid separation, acid-dissolved residue and acid-dissolved filtrate are obtained. The acid-dissolved residue is graphite carbon residue, and the acid-dissolved filtrate is an iron salt solution.

[0017] In this step, the ammonia complex filter residue is neutralized with a first acid solution, causing iron to dissolve at a rate greater than 99%, yielding an iron salt solution and graphite carbon residue. The main reaction equation between the ammonia complex filter residue and the first acid solution (using hydrochloric acid as an example) is as follows: Fe(OH)3+ 3HCl = FeCl3+ 3H2O.

[0018] S4. Neutralization and impurity removal: Adjust the pH of the alkaline filtrate to 6.0~9.0, and then heat, allow it to settle and separate solids and liquids to obtain acid neutralization precipitate and acid neutralization filtrate; wherein, the acid neutralization precipitate is a precipitate of aluminum hydroxide, chromium hydroxide and metatitanic acid, etc., and the acid neutralization filtrate is a sodium dihydrogen phosphate solution.

[0019] The ferric phosphate residue obtained after lithium extraction from lithium iron phosphate black powder undergoes alkali dissolution, ammonia complexation, and acid dissolution treatment to produce an acidic iron salt solution and an alkaline crude sodium phosphate solution, which can be used as raw materials for subsequent preparation of ferric phosphate. However, due to the high impurity content in the alkaline crude sodium phosphate solution, it needs to be refined to remove impurities. In this step, the pH of the alkaline crude sodium phosphate solution is adjusted to 6.0-9.0, causing amphoteric oxide elements (aluminum, chromium, etc.) to form hydroxide precipitates for removal. Since phosphate ions in the solution have a certain inhibitory effect on the hydrolysis of aluminum and chromium salts, increasing the temperature accelerates their hydrolysis rate and promotes the formation of hydroxide precipitates. Simultaneously, as the solution pH decreases to neutral, sodium metatitanate in the solution also undergoes hydrolysis, gradually and slowly precipitating metatitanic acid precipitate. When the temperature of the solution system gradually increases, the above reaction rate is significantly accelerated, and the formation of hydroxide precipitates can act as a coagulation and trapping agent for the simultaneously precipitated metatitanic acid suspension, which helps to remove impurities and ensures that the ferric phosphate finally prepared by this invention meets the relevant standards. The main reactions are as follows: NaAlO2+ HCl + H2O = Al(OH)3↓+ NaCl NaCrO2+ HCl + H2O = Cr(OH)3↓+ NaCl Na2TiO3+ 2HCI = H2TiO3↓+ 2NaCl.

[0020] S5. Iron phosphate for battery synthesis: The pH of the acid neutralization filtrate is adjusted to 10-13, and then mixed with the acid-soluble filtrate for precipitation reaction. After aging and solid-liquid separation, iron phosphate dihydrate is obtained. The acidic mother liquor containing sodium chloride is neutralized and concentrated to precipitate sodium chloride, and the water is reused.

[0021] In this step, the acid neutralization filtrate and the acidic iron salt solution undergo precipitation reaction, aging, and solid-liquid separation to obtain iron phosphate dihydrate for batteries.

[0022] In this embodiment, in step S1, the first alkaline solution is a sodium hydroxide solution.

[0023] In this embodiment, in step S1, the mass fraction of sodium hydroxide in the first alkaline solution is 8wt%~15wt%.

[0024] In this embodiment, in step S1, the molar amount of sodium hydroxide in the first alkaline solution is 3.0 to 3.3 times the molar amount of iron in the ferrophosphate residue.

[0025] In this embodiment, in step S1, during the mixing and reaction of the phosphorus iron residue after lithium extraction from lithium iron phosphate black powder and the first alkaline solution, the reaction temperature is 80~100℃, the reaction time is 30~180 minutes, and the mixing reaction is carried out under stirring conditions.

[0026] In this invention, in the above-mentioned alkali dissolution step, the alkali dissolution residue is returned to the alkali dissolution step for secondary alkali dissolution, thereby improving the recovery rate of the target element; the secondary alkali dissolution filtrate is reused in the alkali dissolution step to improve the utilization rate of alkali.

[0027] In this embodiment, in step S2, the ammonia complex solution is ammonia water or a mixture of ammonia water and an ammonium salt. The ammonium salt is at least one selected from ammonium acetate, ammonium formate, ammonium chloride, and ammonium nitrate. This invention, by combining ammonia water with an ammonium salt, can maintain pH stability and reduce iron loss.

[0028] In this embodiment, the concentration of NH3 in the ammonia complex solution is 0.1wt%~5.0wt%, and the concentrations of NH3 and NH4 are... + The molar ratio is 1:(0~1); the solid-liquid mass ratio of the alkali-soluble residue to the ammonia complex is 1:(1~2).

[0029] In this embodiment, in step S2, during the process of soaking and removing impurities from the alkali-soluble residue using an ammonia complex solution, the soaking temperature is 10~50℃ and the soaking time is 20~120 minutes.

[0030] In this embodiment, in step S3, the first acid solution is hydrochloric acid.

[0031] In this embodiment, in step S3, the mass fraction of the first acid solution is 5wt%~15wt%, and the molar amount of hydrochloric acid is 2.7~3.25 times the molar amount of iron in the ammonia complex filter residue.

[0032] In this embodiment, during step S3, when the ammonia complex filter residue is neutralized with the first acid solution, the reaction temperature is 10~60℃ and the reaction time is 2.0~8.0 hours.

[0033] In this embodiment, in step S4, the pH value of the alkaline filtrate is adjusted to 6.0~9.0, and further to 7.0~8.0, using a second acid solution.

[0034] Preferably, the second acid solution is hydrochloric acid.

[0035] Preferably, the mass fraction of the second acid solution is 1.0 wt% to 10 wt%.

[0036] In this embodiment, in step S4, the temperature is raised to 50~70℃, and further to 50~60℃, and the settling time is 0.5~4 hours.

[0037] In this embodiment, step S4 includes: adjusting the pH value of the alkali-dissolved filtrate to 6.0~9.0 using a second acid solution, then heating it to 50~70°C, and then allowing it to settle and filter to obtain acid neutralization precipitate and acid neutralization filtrate; in this process, the neutral supernatant and the filtrate obtained by filtration are sodium dihydrogen phosphate solution, and the filter residue is a precipitate containing impurities such as aluminum, chromium and titanium.

[0038] In this embodiment, in step S5, the pH value of the acid-neutralized filtrate is adjusted to 10-13, and further to 11-12, using a second alkaline solution.

[0039] The second alkaline solution is a sodium hydroxide solution.

[0040] The mass fraction of the second alkaline solution is 1.0 wt% to 10 wt%.

[0041] In this embodiment, in step S5, the pH value of the acid neutralization filtrate is adjusted to 10~13, and then mixed with the acid-soluble filtrate to carry out the precipitation reaction. During this process, the molar ratio of phosphorus to iron in the acid neutralization filtrate and the acid-soluble filtrate is controlled to be (1~1.05):1.

[0042] In this embodiment, in step S5, the precipitation reaction temperature is 65~100℃, the precipitation reaction time is 1~4 hours, and the precipitation reaction is carried out under stirring conditions; the aging temperature is 60~80℃, the aging time is 6~10 hours, and the aging is carried out under standing conditions; the pH value of the reaction system is controlled to be 1.5~2.5, and further to 2.0~2.5, by adjusting the pH value of the acid neutralization filtrate.

[0043] In this embodiment, step S5 includes: adjusting the pH value of the acid neutralization filtrate to 10-13, then adding it to the reaction vessel in parallel with the acid-dissolving filtrate to carry out a precipitation reaction, followed by aging and solid-liquid separation to obtain ferric phosphate dihydrate.

[0044] In this embodiment, step S5 further includes: calcining ferric phosphate dihydrate to obtain anhydrous ferric phosphate. Preferably, the calcination temperature is 500~550℃, the calcination time is 1~3h, and the calcination atmosphere is air.

[0045] Please see Figure 2 Secondly, the present invention provides a method for recovering graphite from the residue after extracting valuable metals from waste lithium battery black powder, comprising the following steps: A1. The graphite carbon residue is oxidized and roasted to obtain the roasted material; A2. The roasted material is separated by flotation to obtain concentrate and tailings; wherein the concentrate is crude graphite and the tailings are industrial waste residue. A3. The concentrate is deeply purified and dried to obtain recycled graphite; The graphite carbon residue includes the acid-soluble residue provided in the first aspect of the present invention, and optionally at least one of the graphite carbon residue after lithium and iron phosphate are extracted from conventional lithium iron phosphate black powder, and the negative electrode carbon residue after valuable metals are extracted from ternary lithium battery black powder.

[0046] In this invention, the iron-phosphorus residue after lithium extraction from lithium iron phosphate black powder, obtained through steps S1-S3 (alkali dissolution, ammonia complexation, acid dissolution) in the first aspect of this invention, the graphite carbon residue after lithium and iron-phosphorus extraction from existing lithium iron phosphate black powder, and the graphite anode residue after extraction of valuable metals from ternary lithium battery black powder, contain very low levels of metal elements such as iron, nickel, and cobalt. They are mainly composed of inorganic substances such as graphite, conductive carbon black, organic adhesives, and dust particles. Because some graphite particles are still coated or adsorbed with impurities such as ultrafine conductive carbon black, their particle surfaces are oleophilic, making direct separation by flotation difficult. This invention fully utilizes the characteristics of graphite, such as its slow oxidation rate below 500℃ and its inherent antioxidant properties, to oxidize and roast graphite carbon residue. This process completely oxidizes and decomposes carbon materials and organic matter, including ultrafine conductive carbon black and adhesives, eliminating interference with subsequent flotation separation. Simultaneously, the oxidation and decomposition of impurities like conductive carbon black and adhesives, along with the resulting CO2 and CO, reduces the oxygen content in the furnace atmosphere, further inhibiting the oxidation rate of graphite and thus preserving the graphite crystal particles intact. Subsequently... Utilizing the difference in hydrophobicity between graphite and other residual impurities, flotation is performed to separate graphite from other impurities. The concentrate obtained by flotation separation is a crude graphite product, which contains trace amounts of metallic element impurities adsorbed on its surface and between crystal layers. The crude graphite is then soaked in H2O2 solution and EDTA chelating agent solution to oxidize the trace magnetic elemental substances in the crude graphite product into ionic states. Furthermore, taking advantage of the strong chelating ability of EDTA for divalent or trivalent metal ions, the trace amounts of metallic ion impurities remaining on the graphite surface and between its layers are thoroughly removed to obtain high-purity graphite.

[0047] In this embodiment, in step A1, the graphite carbon residue after lithium and iron phosphate extraction from conventional lithium iron phosphate black powder and / or the negative electrode carbon residue after valuable metal extraction from ternary lithium battery black powder are pre-treated by washing and desalting before oxidation and roasting. This washing and desalting treatment removes residual metal salt impurities from the surface of the graphite particles, achieving a preliminary purification effect.

[0048] Preferably, the washing and desalination treatment method includes: soaking and washing the graphite carbon residue after lithium and iron phosphate extraction from existing lithium iron phosphate black powder and / or the negative electrode carbon residue after valuable metal extraction from ternary lithium battery black powder to remove impurities.

[0049] The solid-liquid mass ratio of graphite carbon residue after lithium and ferrophosphate extraction from lithium iron phosphate black powder and / or negative electrode carbon residue after valuable metal extraction from ternary lithium battery black powder to water is 1:(1~2).

[0050] The soaking and washing process involves immersing the product at a temperature of 10-30℃ for 20-60 minutes.

[0051] In this embodiment, in step A1, the oxidation calcination temperature is 380~500℃, the oxidation calcination time is 20~120 minutes, and the oxidation calcination atmosphere is air.

[0052] In this embodiment, in step A2, the flotation reagent includes a graphite collector and a frother; wherein the graphite collector includes at least one of industrial kerosene, fatty acids, and sodium fatty acids, and the frother includes at least one of polyols and polyhydric alcohols; the mass ratio of graphite collector to frother is 1:(0.01~0.2), further being 1:(0.1~0.2), and the mass of the flotation reagent is 1.0wt%~5.0wt% of the roasted material.

[0053] In this embodiment, in step A2, positive flotation is used, and the number of positive flotation cycles is 1 to 2.

[0054] In this embodiment, the deep purification process in step A3 includes: sequentially soaking the concentrate in hydrogen peroxide and then in EDTA (ethylenediaminetetraacetic acid) solution.

[0055] Preferably, the mass fraction of hydrogen peroxide is 0.2 wt% to 2.0 wt%; the solid-liquid mass ratio of concentrate to hydrogen peroxide is 1:(0.5~2).

[0056] Preferably, during the hydrogen peroxide soaking treatment, the soaking temperature is 10~40℃ and the soaking time is 5~30 minutes.

[0057] Preferably, the mass fraction of the EDTA solution is 0.1 wt% to 5.0 wt%, more preferably 0.5 wt% to 1 wt%; the solid-liquid mass ratio of the concentrate to the EDTA solution is 1:(0.5~2).

[0058] Preferably, during the EDTA solution soaking process, the soaking temperature is 10~50℃ and the soaking time is 10~40 minutes.

[0059] Preferably, during the EDTA solution soaking process, the pH needs to be adjusted to 5.0~8.0, and further to 6.0~8.0, using ammonia water.

[0060] Specifically, the mass fraction of ammonia water is 0.5wt% to 5wt%, preferably 1wt% to 2wt%.

[0061] In this embodiment, the drying method is at least one of ordinary drying and microwave radiation drying. This invention does not limit the ordinary drying method; those skilled in the art can choose according to the actual situation, for example, room temperature drying, hot air drying, etc.

[0062] In this invention, it should be noted that solid-liquid separation includes filtration and optional washing, which can be selected by those skilled in the art according to the actual situation.

[0063] Please see Figure 3 Thirdly, the present invention provides an apparatus for recovering ferric phosphate and graphite from the residue after extracting valuable metals from waste lithium battery black powder, comprising an alkaline dissolution kettle 1, a first filter 2, an ammonia leaching filter 3, an acid dissolution kettle 4, a second filter 5, a neutralization precipitator 6, a third filter 7, a modulator 8, a synthesis reaction kettle 9, a fourth filter 10, a calcination furnace 11, a flotation machine 12, and a purification dryer 13; wherein, The outlet of the alkali dissolving kettle 1 is connected to the first filter 2, the filter residue outlet of the first filter 2 is connected to the ammonia leaching filter 3, and the filtrate outlet of the first filter 2 is connected to the neutralization precipitator 6. The filter residue outlet of the ammonia leaching filter 3 is connected to the acid dissolution vessel 4, the discharge port of the acid dissolution vessel 4 is connected to the second filter 5, and the filtrate outlet of the second filter 5 is connected to the synthesis reaction vessel 9. The upper clear liquid outlet of the neutralization precipitator 6 is connected to the modulator 8, the lower mud outlet of the neutralization precipitator 6 is connected to the third filter 7, the filtrate outlet of the third filter 7 is connected to the modulator 8, and the discharge port of the modulator 8 is connected to the synthesis reactor 9. The discharge port of the synthesis reactor 9 is connected to the fourth filter 10; The filter residue outlet of the second filter press 5 is connected to the roasting furnace 11, the discharge port of the roasting furnace 11 is connected to the flotation machine 12, and the concentrate outlet of the flotation machine 12 is connected to the purification dryer 13.

[0064] Based on the above apparatus, the process route of the present invention is as follows: The phosphorus-iron residue after lithium extraction from lithium iron phosphate black powder is fed into an alkaline dissolution vessel 1, and a first alkaline solution is added. The mixture is heated and reacted. After solid-liquid separation by a first filter 2, alkaline dissolution residue and alkaline dissolution filtrate are obtained. The alkaline dissolution filtrate is an alkaline crude sodium phosphate solution. The alkaline dissolution residue is sent to an ammonia leaching filter 3 for complexation leaching with an ammonia complexing solution. Copper and a small amount of other impurities are introduced into the liquid phase through the complexation reaction. The ammonia complexing filtrate (i.e., copper-containing ammonia water) obtained after filtration and washing is collected and recycled. The ammonia complexing filtrate is sent to an acid dissolution vessel 4, where a first acid solution is added for acid dissolution. After solid-liquid separation by a second filter 5, acid dissolution residue (i.e., graphite carbon residue) and acid dissolution filtrate (i.e., iron salt solution) are obtained. The acid dissolution filtrate is sent to a synthesis reaction vessel 9. The alkaline filtrate is sent to the neutralization precipitator 6, where the pH is first adjusted to 6-9 with a second acid solution. Then, it is heated, allowed to settle, and filtered (using a third filter 7). The acid neutralization precipitate contains aluminum hydroxide, chromium hydroxide, and metatitanic acid. The neutral supernatant and filtrate (collectively referred to as acid neutralization filtrate) are NaH2PO4 solution and sent to the modulator 8, where the pH is adjusted to 10-13 with a second alkaline solution. Then, it is added to the synthesis reactor 9 in parallel with the acid filtrate for precipitation and aging. After filtration and washing by the fourth filter 10, ferric phosphate dihydrate and acidic mother liquor are obtained. The acidic mother liquor is neutralized, concentrated, and sodium chloride is precipitated.

[0065] The acid-soluble residue is sent to the roasting furnace 11 for oxidative roasting to obtain roasted material; the roasted material is sent to the flotation machine 12 and flotation reagents are added for positive flotation treatment to obtain concentrate (i.e., graphite crude product) and tailings (i.e., industrial waste residue); the concentrate is subjected to deep purification and drying treatment in the purification dryer 13 to obtain graphite.

[0066] In this embodiment, the device of the present invention further includes a water washing filter 14, the filter residue outlet of which is connected to the roasting furnace 11, so that the graphite carbon residue after lithium and iron phosphate black powder is extracted and / or the negative electrode residue after valuable metal is extracted from ternary lithium battery black powder is treated by water soaking, washing and desalting, and then filtered and mixed with the above-mentioned graphite carbon residue or separately sent to the roasting furnace 11 for oxidation roasting to obtain roasted material.

[0067] This invention does not limit the types of filters; those skilled in the art can select according to actual conditions. For example, the filter can be at least one of the following types of industrial filters: gravity filter, plate and frame filter press, vacuum filter, etc.

[0068] This invention does not limit the type of roasting furnace, and those skilled in the art can select one according to the actual situation. For example, the roasting furnace can be at least one of box-type roasting furnace, rotary kiln, tunnel kiln, etc., and the heating source can be at least one of electricity, natural gas, methanol, light hydrocarbons, liquefied petroleum gas, etc.

[0069] The present invention does not limit the concentration method of the acidic mother liquor. Those skilled in the art can choose according to the actual situation, such as at least one of reverse osmosis membrane concentration, evaporation concentration, etc.

[0070] Example 1 The mass percentages of phosphorus and iron elements and other impurity elements in the phosphorus residue after lithium extraction from lithium iron phosphate black powder used in this embodiment are as follows:

[0071] Note: This residue comes from a waste lithium battery recycling company that separates the waste lithium iron phosphate pretreatment production line from the waste ternary lithium battery pretreatment production line.

[0072] (1) The phosphorus-iron residue after lithium extraction from lithium iron phosphate black powder was put into alkaline dissolution kettle 1, and a sodium hydroxide solution with a mass fraction of 10 wt% was added. The molar amount of sodium hydroxide was 3.2 times the molar amount of iron in the phosphorus-iron residue. The mixture was stirred and heated to 85℃ for 2.0 hours. The phosphorus dissolution rate was over 98%. After solid-liquid separation by filter 2, alkaline dissolution residue and alkaline dissolution filtrate were obtained. The state and appearance of the alkaline dissolution residue are shown in the figure. Figure 4 The alkali-dissolved filtrate is an alkaline crude sodium phosphate solution, which is sent to neutralization precipitator 6.

[0073] (2) Place the alkali-soluble residue in the ammonia leaching filter 3, add ammonia complex solution (NH3 mass fraction of 0.5 wt%, ammonium acetate mass fraction of 0.3 wt%), solid-liquid mass ratio of 1:1.5, complex leaching for 30 minutes at room temperature, filter and wash to obtain filter residue, and collect the ammonia complex waste liquid containing copper and other impurities for recycling; put the ammonia complex filter residue into the acid dissolution kettle 4, add hydrochloric acid solution with mass fraction of 10 wt%, the molar amount of hydrochloric acid is 3.05 times the molar amount of iron in the ammonia complex filter residue, the reaction temperature is 30℃, the reaction time is 4 hours, and the iron dissolution rate is greater than 99%; filter through filter 5 and wash with water to obtain acid dissolution filtrate (ferric chloride solution), send the acid dissolution filtrate to the synthesis reaction kettle 9, and the acid dissolution filter residue is graphite carbon residue.

[0074] (3) The graphite carbon residue is fed into the rotary kiln 11 for oxidation roasting in air atmosphere. The constant temperature roasting temperature is 450℃ and the constant temperature roasting time is 35 minutes. After the roasting operation is completed, it is naturally cooled to room temperature to obtain roasted material.

[0075] (4) The roasted material is fed into the SF-type flotation machine 12. Based on 100% of the roasted material's mass, a flotation reagent mixture of 2wt% kerosene and 0.2wt% MIBC (4-methyl-2-pentanol) is added. Two positive flotation separation operations are performed. The float concentrate is graphite crude, and the tailings are industrial waste. The microstructures of the graphite concentrate and the tailings are as follows: Figure 5 As shown, (a) is a SEM image of the graphite concentrate, and (b) is a SEM image of the tailings residue. The results indicate that the concentrate obtained by flotation separation in this invention accounts for a large proportion, while the tailings residue accounts for a small proportion, and the tailings residue still contains a small amount of graphite; scanning electron microscopy characterization revealed that, as... Figure 5 As shown, the tailings slag particles are very small, mostly cryptocrystalline graphite with poor flotation properties, while the concentrate graphite particles are relatively large and belong to crystalline graphite with good flotation properties. Those skilled in the art know that crystalline graphite has a wide range of applications and is more suitable as a negative electrode material for lithium batteries.

[0076] (5) After washing and drying the crude graphite, place it in a purification desiccator 13. Under normal temperature conditions, first add a 1.0 wt% H2O2 solution and stir for 5 minutes, with a solid-liquid mass ratio of 1:1. Then add a 0.5 wt% EDTA solution, with a solid-liquid mass ratio of 1:1.2. Adjust the pH value to approximately 8.0 with 1.0 wt% ammonia water. Chelate for 25 minutes, then filter, wash, and dry to obtain recovered graphite. Collect the chelation solution for recycling. The XRD pattern of the recovered graphite is shown below. Figure 6 As shown; the electrochemical performance test results of recycled graphite as a negative electrode material are as follows. Figure 7 As shown. Figures 6-7 As shown, recycled graphite possesses a complete graphite crystal structure, and the half-cell made using it as the negative electrode material exhibits excellent electrochemical performance. The steps for preparing the half-cell using recycled graphite as the negative electrode material are as follows: Graphite, binder (a dispersion of 50% SBR and 2% CMC at a mass ratio of 3:2), and acetylene black conductive agent at a mass ratio of 92:5:3 are mixed uniformly in N-methyl-2-pyrrolidone solvent to form a paste, which is then coated onto copper foil to a wet film thickness of 200 μm. After drying, a graphite electrode sheet is fabricated. In an argon-atmospheric glove box, using lithium metal as the counter electrode, Celgard 2400 as the separator, and a 1.0 mol / L LiPF6 EC / DMC / EMC (1:1:1, v / v / v) solution as the electrolyte, a half-cell is assembled. The test conditions are as follows: The Land BT2000 system was used for testing, the cyclic voltammetry scan rate was 0.1 mV / s, and the constant current charge-discharge test voltage range was 0.001V~2.0V.

[0077] (6) First, add 7wt% hydrochloric acid solution to the alkaline crude sodium phosphate solution in neutralization precipitator 6 to adjust the pH value to 7.0. Then heat it to 50°C to promote the hydrolysis reaction of impurities such as aluminum and titanium in the solution. Then let it stand for precipitation for 1.5 hours. The bottom sediment is extracted and filtered to collect the aluminum and titanium sediment. The neutral upper clear liquid and filtrate are all sent to the modulator 8 and the pH is adjusted to about 12 with 5wt% sodium hydroxide solution for later use.

[0078] (7) In the modulator 8, the sodium dihydrogen phosphate solution and the ferric chloride solution after pH adjustment are fed into the synthesis reactor 9 in parallel. The molar ratio of phosphorus to iron in the system is controlled to be 1:(1~1.05) by the P / Fe ratio of the two feeds. The pH of the reaction system is controlled to be 2.0~2.5 by adjusting the pH of the feed sodium dihydrogen phosphate solution. The reaction temperature is 80℃ and the reaction time is 2.0 hours. Then, it is aged at 60℃ for 8 hours. After filtration and washing, the ferric phosphate dihydrate product is obtained. The reaction mother liquor containing sodium chloride is neutralized, concentrated by reverse osmosis and evaporated to precipitate sodium chloride. The water is reused.

[0079] Example 2 (1) The phosphorus-iron residue (main components are the same as in Example 1) after lithium extraction from lithium iron phosphate black powder is put into alkaline dissolution kettle 1, and a sodium hydroxide solution with a mass fraction of 12wt% is added. The molar amount of sodium hydroxide is 3.0 times the molar amount of iron in the phosphorus-iron residue. The mixture is stirred and heated to 80°C for 1.5 hours. After solid-liquid separation by filter 2, the primary alkaline dissolution residue and the primary alkaline dissolution filtrate are obtained. The primary alkaline dissolution filtrate is an alkaline crude sodium phosphate solution and is sent to neutralization precipitator 6. The primary alkaline dissolution residue is put back into alkaline dissolution kettle 1, and a sodium hydroxide solution with a mass fraction of 12wt% is added at 5% of the amount of the first alkali. The mixture is stirred and heated to 80°C for a second alkaline dissolution reaction for 1.0 hour. The residue is filtered to obtain a second alkaline dissolution residue. The second alkaline dissolution filtrate is used as raw material for the next batch of alkaline dissolution operation. The total phosphorus dissolution rate of the two alkaline dissolutions is over 99%.

[0080] (2) Place the alkali-soluble residue in the ammonia leaching filter 3, add ammonia complex solution (NH3 and ammonium acetate are both 1.0wt%), the solid-liquid mass ratio is 1:1.2, and complex leaching is carried out at 20℃ for 30 minutes. After filtration and washing, filter residue is obtained, and the ammonia complex waste liquid containing copper and other impurities is collected for recycling. The ammonia complex filter residue is put into the acid dissolution kettle 4, and 8wt% hydrochloric acid solution is added. The molar amount of hydrochloric acid is 3.00 times the molar amount of iron in the ammonia complex filter residue. The reaction temperature is 20℃ and the reaction time is 6 hours. The iron dissolution rate is more than 99.5%. After filtration by the filter 5 and washing with water, acid dissolution filtrate (ferric chloride solution) is obtained. The acid dissolution filtrate is sent to the synthesis reaction kettle 9. The acid dissolution filter residue is graphite carbon residue.

[0081] (3) The negative electrode carbon residue after extracting valuable metals from ternary lithium battery black powder is placed in a water washing filter 14 and clean water is added. It is soaked and washed for 25 minutes at 20°C with a solid-liquid mass ratio of 1:1.5. After filtration, it is mixed with the above graphite carbon residue at a mass ratio of 1:2 and sent to a rotary kiln 11 for oxidation roasting in air atmosphere. The constant temperature roasting temperature is 420°C and the constant temperature roasting time is 45 minutes. After the roasting operation is completed, it is naturally cooled to room temperature to obtain roasted material.

[0082] In this embodiment, the graphite content in the negative electrode residue after extracting valuable metals from ternary lithium battery black powder is 67.13%, with the remainder being carbon, adhesive, and small amounts of impurities such as sulfates of elements like copper, nickel, cobalt, and manganese.

[0083] (4) The roasted material is fed into the BF type flotation machine 12. Based on the mass of the roasted material as 100%, 1.5% kerosene, 0.5% oleic acid and 0.2% MIBC mixed flotation reagents are added to carry out two positive flotation separation operations. The float concentrate is graphite crude product and the tailings are industrial waste residue.

[0084] (5) After washing and drying the crude graphite, place it in the purification dryer 13. Under normal temperature conditions, first add 0.25wt% H2O2 solution and stir for 10 minutes. The solid-liquid mass ratio is 1:2. Then add 1.0wt% EDTA solution. The solid-liquid mass ratio is 1:1. Adjust the pH value to about 7.5 with 1wt% ammonia water. Chelate for 20 minutes. After filtration, washing and drying, the recovered graphite is obtained. Collect the chelation liquid for recycling.

[0085] (6) First, add 5 wt% hydrochloric acid solution to the alkaline crude sodium phosphate solution in the neutralization precipitator 6 to adjust the pH value to 7.5. Then heat it to 55°C to promote the hydrolysis reaction of impurities such as aluminum and titanium in the solution. Then let it stand for 1 hour to precipitate. The bottom sediment is extracted and filtered to collect the aluminum and titanium sediment. The neutral upper clear liquid and filtrate are all sent to the modulator 8 and the pH value is adjusted to about 12.5 with 5.0 wt% sodium hydroxide solution.

[0086] (7) In the modulator 8, the sodium dihydrogen phosphate solution and the ferric chloride solution after pH adjustment are fed into the synthesis reactor 9 in parallel. The molar ratio of phosphorus to iron in the system is controlled to be 1:(1~1.02) by the P / Fe ratio of the two feeds. The pH of the reaction system is controlled to be 2.0~2.5 by adjusting the pH of the feed sodium dihydrogen phosphate solution. The reaction temperature is 85℃ and the reaction time is 1.5 hours. Then, it is aged at 70℃ for 6 hours. After filtration and washing, the dihydrate ferric phosphate product is obtained. Then, it is calcined in a rotary kiln at 530℃ for 1.5 hours in an air atmosphere to obtain the anhydrous ferric phosphate product for batteries.

[0087] Example 3 (1) The graphite carbon residue after preparing iron phosphate from ferric phosphorus residue through the current steps of sulfuric acid and iron powder reduction, and the negative electrode residue after extracting valuable metals from ternary lithium battery black powder are placed in water washing filter 14, and water is added. They are soaked and washed at 20°C for 20 minutes with a solid-liquid mass ratio of 1:2. After filtration, they are dried. Then, the graphite carbon residue prepared by the method of Example 1 of this invention, the graphite carbon residue after preparing iron phosphate from ferric phosphorus residue through the current steps of sulfuric acid and iron powder reduction, and the negative electrode residue after extracting valuable metals from ternary lithium battery black powder are mixed in a mass ratio of 1:1:1 for later use.

[0088] In this embodiment, the graphite carbon residue after preparing ferric phosphate using the existing steps of sulfuric acid and iron powder reduction has a graphite content of 64.5%, with the remainder being impurities such as carbon black, adhesive, and miscellaneous salts; the negative electrode carbon residue after extracting valuable metals from ternary lithium battery black powder has a graphite content of 67.13%, with the remainder being impurities such as carbon black and adhesive.

[0089] (2) The mixture of the three residues is fed into the rotary kiln 11 and oxidized and roasted in an air atmosphere. The constant temperature roasting temperature is 480℃ and the constant temperature roasting time is 25 minutes. After the roasting operation is completed, it is naturally cooled to room temperature to obtain roasted material.

[0090] (3) The roasted material is fed into the SF type flotation machine 12. Based on the mass of the roasted material as 100%, 2% kerosene and 0.3% MIBC mixed flotation reagent are added to carry out two positive flotation separation operations. The float concentrate is graphite crude product and the tailings are industrial waste residue.

[0091] (4) After washing and drying the crude graphite, place it in the purification dryer 13. Under normal temperature conditions, first add 0.5wt% H2O2 solution and stir for 8 minutes, with a solid-liquid mass ratio of 1:1. Then add 0.8wt% EDTA solution, with a solid-liquid mass ratio of 1:0.8. Adjust the pH value to 6.5 with 1.5wt% ammonia water. Chelate for 30 minutes, filter, wash and dry to obtain recycled graphite. Collect the chelation solution for recycling.

[0092] Comparative Example 1 The only difference between this comparative example and Example 1 is that the concentration of the sodium hydroxide solution added in step (1) is adjusted from "10wt%" to "5wt%", and the volume of the solution remains unchanged (i.e., the molar amount of sodium hydroxide is halved).

[0093] Comparative Example 2 The only difference between this comparative example and Example 1 is that in step (2), the alkali-soluble residue was not purified by the ammonia immersion filter 3 and was directly put into the acid dissolution kettle 4.

[0094] Comparative Example 3 The only difference between this comparative example and Example 2 is that the constant temperature calcination temperature in step (3) is adjusted from 420°C to 300°C.

[0095] Comparative Example 4 The only difference between this comparative example and Example 1 is that the constant temperature calcination temperature in step (3) is adjusted from 450°C to 600°C.

[0096] Comparative Example 5 The only difference between this comparative example and Example 1 is that the step (5) of “treating metal ion chelation with 0.5wt% EDTA solution” is changed to “washing with 2wt% nitric acid solution”.

[0097] Comparative Example 6 The only difference between this comparative example and Example 1 is that in step (5), instead of first stirring with a 1.0wt% H2O2 solution for 5 minutes, a 0.5wt% EDTA solution was directly added.

[0098] Comparative Example 7 The only difference between this comparative example and Example 1 is that in step (6), the alkaline crude sodium phosphate solution was adjusted to pH 7.0 by adding a 7wt% hydrochloric acid solution and then heated to 20°C instead of being heated.

[0099] Performance testing The phosphorus dissolution rate, ferric phosphate dihydrate recovery rate, and graphite content were tested in different embodiments and comparative examples. The results are shown in Table 1. Phosphorus leaching rate: The percentage of phosphorus in the alkali filtrate obtained after alkali dissolution and the phosphorus residue in the lithium iron phosphate black powder after lithium extraction is determined by the phosphomolybdic acid colorimetric method (GB5009.87-2016). Iron phosphate dihydrate yield: The percentage of iron in the iron phosphate dihydrate product and the iron in the iron phosphate residue after lithium extraction from lithium iron phosphate black powder; Graphite yield: The percentage of the amount of recovered graphite obtained after purification and drying to the amount of residue after extracting valuable metals from waste lithium battery black powder (Example 1: phosphorus iron residue; Example 2: acid dissolution filter residue + negative electrode carbon residue; Example 3: acid dissolution filter residue + negative electrode carbon residue + graphite carbon residue from the current process). Impurity content of iron phosphate products: Refer to the test methods in the standard "Iron Phosphate for Batteries" (HG / T4701-2021); Electrochemical performance of recycled graphite: The determination methods of relevant indicators in "Graphite Anode Materials for Lithium-ion Batteries" (GB / T 24533-2019) shall be followed.

[0100] Table 1

[0101] Please refer to Table 1. As can be seen from Table 1, the iron phosphate dihydrate prepared by the method of this embodiment meets the requirements of "Iron Phosphate for Batteries" (HG / T4701-2021), and the recycled graphite meets the requirements of "Graphite Anode Materials for Lithium-ion Batteries" (GB / T24533-2019).

[0102] Compared with Example 1, the concentration of the alkaline solution used in the alkaline dissolution process of the phosphate residue in Comparative Example 1 was too low and the amount was insufficient. The dissolution strength of phosphate in the phosphate residue was insufficient, resulting in a significant decrease in the phosphorus dissolution rate, which affected the subsequent phosphate quality and yield, as well as the graphite flotation separation.

[0103] Compared with Example 1, the alkali-soluble residue in Comparative Example 2 was not treated with ammonia leaching, and the trace amounts of impurities such as copper hydroxide could not be removed, resulting in the copper content of the ferric phosphate product exceeding the standard.

[0104] Compared with Example 2, when the calcination temperature of the graphite carbon residue in Comparative Example 3 was 300°C, the adhesive and carbon conductive agent in the graphite carbon residue and negative electrode carbon residue could not be fully oxidized and decomposed. The difference in oleophilic or hydrophilic properties of the material particles was not obvious, and the subsequent flotation separation could not be effectively operated. The graphite product obtained by flotation contained a large amount of impurities such as ultrafine carbon black, and it was impossible to obtain a product of the corresponding quality.

[0105] Compared with Example 1, the calcination temperature of the graphite carbon residue in Comparative Example 4 was 600°C. Under the higher oxidative calcination temperature, impurities such as adhesives and carbon conductive agents in the graphite carbon residue were burned off, and some of the graphite was oxidized and lost. Therefore, the graphite yield was significantly reduced.

[0106] Compared with Example 1, the crude graphite obtained by flotation in Comparative Example 5 was not treated with EDTA solution for metal ion chelation, but was soaked and washed with dilute nitric acid solution. Since dilute nitric acid has no complexing ability for impurity metal ions and its chemical bonding force is insufficient, a small amount of metal impurity ions on the surface of graphite particles and between their crystal layers cannot be completely removed, resulting in excessive content of copper and iron ions and magnetic substances in the graphite product.

[0107] Compared with Example 1, the crude graphite obtained by flotation in Comparative Example 6 was not treated with 1.0% H2O2 solution, which failed to oxidize the tiny magnetic elemental metals adsorbed on the graphite surface and convert them into ionic states so that they could be chelated by the chelating agent. As a result, the magnetic material content in the graphite product exceeded the standard.

[0108] Compared with Example 1, in Comparative Example 7, the alkaline crude sodium phosphate solution was adjusted to pH value but not heated. Due to the low temperature, the hydrolysis reaction of sodium metatitanate was very slow, and metatitanate precipitate could not be precipitated in time. At the same time, the sodium aluminate in it did not completely form aluminum hydroxide precipitate, and some aluminum impurities remained, which affected the quality of the subsequently synthesized iron phosphate.

[0109] Compared with the prior art, the beneficial effects of the present invention include: (1) In this invention, the phosphorus iron residue after lithium extraction from lithium iron phosphate black powder is reacted with a high concentration of alkaline solution, so that elements such as phosphorus, aluminum and titanium are dissolved in the liquid phase, and the iron element is generated as iron hydroxide and remains in the alkaline residue. After the alkaline residue is soaked in ammonia complex solution to remove impurities such as copper and nickel, it is neutralized by a low concentration of acid solution to obtain iron salt solution and graphite carbon residue. The graphite carbon residue, the negative electrode carbon residue after the extraction of valuable metals from waste ternary lithium battery black powder (optionally pre-purified), and the graphite carbon residue after the extraction of lithium and phosphorus iron from existing lithium iron phosphate black powder are oxidized, roasted, floated, purified and dried to recycle graphite. Furthermore, the graphite recovered by flotation is mostly crystalline graphite, suitable for use as a negative electrode material for lithium batteries or for other industrial graphite applications; after the alkali-soluble residue is treated with ammonia complexation immersion, magnetic substances such as copper and nickel can be removed, and the impurity content of the iron salt solution obtained after acid dissolution is greatly reduced; the pH value of the alkali-soluble filtrate is first adjusted to 6.0~9.0 with acid and then heated to decompose the impurities such as aluminum, titanium, and chromium dissolved in the phosphate solution into hydroxides and metatitanic acid precipitates for removal, ultimately ensuring that the quality of the iron phosphate prepared by this invention meets the relevant standards.

[0110] (2) The main raw materials used in this invention are common alkalis and acids, which are inexpensive and readily available. The synthesis reaction mother liquor produced in the entire process is sodium chloride solution with very low impurity content. The by-product sodium chloride can be used as a raw material for ion-exchange membrane caustic soda chemical industry. It is suitable to form a closed-loop cycle of upstream and downstream products and raw materials with caustic soda and hydrochloric acid produced by chlor-alkali chemical enterprises, avoiding the problems of large amounts of other sodium salts that cannot be consumed or high-concentration saline wastewater discharge generated by other phosphorus iron slag resource utilization methods.

[0111] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for recovering iron phosphate from a waste lithium battery black powder after valuable metal recovery, characterized in that, The method comprises the following steps: S1, alkali dissolution: mixing and reacting the phosphorus-iron residue after lithium extraction from lithium iron phosphate black powder with a first alkali solution, and performing solid-liquid separation to obtain an alkali dissolution residue and an alkali dissolution filtrate; wherein the alkali dissolution filtrate is a crude sodium phosphate solution with alkalinity; S2, ammonia complexation: immersing and impurity-removing the alkali dissolution residue with an ammonia complexing solution, and performing solid-liquid separation to obtain an ammonia complexation residue and an ammonia complexation filtrate; S3, acid dissolution: neutralizing the ammonia complexation residue with a first acid solution, and performing solid-liquid separation to obtain an acid dissolution residue and an acid dissolution filtrate; wherein the acid dissolution residue is a graphite carbon residue, and the acid dissolution filtrate is an iron salt solution; S4, impurity-removing neutralization: adjusting the pH value of the alkali dissolution filtrate to 6.0-9.0, and then performing temperature rising, standing and settling, and solid-liquid separation to obtain an acid neutralization precipitate and an acid neutralization filtrate; wherein the acid neutralization precipitate is a precipitate containing aluminum hydroxide, chromium hydroxide and metatitanic acid, and the acid neutralization filtrate is a sodium dihydrogen phosphate solution; S5, synthesizing battery iron phosphate: adjusting the pH value of the acid neutralization filtrate to 10-13, and then performing a precipitation reaction with the acid dissolution filtrate, and then performing aging and solid-liquid separation to obtain iron phosphate dihydrate.

2. The method according to claim 1, wherein the method for recovering iron phosphate from the waste lithium battery black powder after recovering valuable metals, characterized in that, In step S1, the first alkali solution is a sodium hydroxide solution; and / or, In the first alkali solution, the mass fraction of sodium hydroxide is 8wt%-15wt%; and / or, In the first alkali solution, the molar amount of sodium hydroxide is 3.0-3.3 times the molar amount of iron in the phosphorus-iron residue; and / or, In the process of mixing and reacting the phosphorus-iron residue after lithium extraction from lithium iron phosphate black powder with the first alkali solution, the reaction temperature is 80-100℃, the reaction time is 30-180 minutes, and the mixing reaction is performed under stirring.

3. The method according to claim 1, wherein the method for recovering iron phosphate from the waste lithium battery black powder after recovering valuable metals is characterized by, In step S2, the ammonia complexing solution is ammonia water or a mixed solution composed of ammonia water and an ammonium salt; the ammonium salt is at least one of ammonium acetate, ammonium formate, ammonium chloride and ammonium nitrate; and / or, The concentration of NH3 in the ammonia complexing solution is 0.1wt% to 5.0wt%, the molar ratio of NH3 to NH4 + + is 1:(0~1); and / or, The solid-liquid mass ratio of the alkali dissolution residue to the ammonia complexing solution is 1:(1-2); and / or, In the process of immersing and impurity-removing the alkali dissolution residue with the ammonia complexing solution, the immersion temperature is 10-50℃, and the immersion time is 20-120 minutes.

4. The method for recovering iron phosphate from the residue after valuable metals are extracted from the black powder of waste lithium batteries according to claim 1, characterized in that, In step S3, the first acid solution is hydrochloric acid; the mass fraction of the hydrochloric acid is 5wt%-15wt%; the molar amount of the hydrochloric acid is 2.7-3.25 times the molar amount of iron in the ammonia complexation residue; and / or, In the process of neutralizing the ammonia complexation residue with the first acid solution, the reaction temperature is 10-60℃, and the reaction time is 2.0-8.0 hours.

5. The method for recovering iron phosphate from the residue after valuable metals are extracted from the waste lithium battery black powder according to claim 1, characterized in that, In step S4, a second acid solution is used to adjust the pH value of the alkali dissolution filtrate to 6.0-9.0; the second acid solution is an acid solution, which is hydrochloric acid; the mass fraction of the second acid solution is 1.0wt%-10wt%; and / or, The temperature is raised to 50-70℃, and the standing and settling time is 0.5-4 hours.

6. The method for recovering iron phosphate from the valuable metal-extracted residue of waste lithium battery black powder according to claim 1, characterized in that, In step S5, the pH value of the acid neutralization filtrate is adjusted to 10-13 by using a second alkali solution; the second alkali solution is a sodium hydroxide solution; the mass fraction of the second alkali solution is 1.0wt%-10wt%; And / or, In the process of adjusting the pH value of the acid neutralization filtrate to 10-13 and then mixing with the acid-dissolved filtrate to perform the precipitation reaction, the molar ratio of phosphorus element to iron element in the acid neutralization filtrate and the acid-dissolved filtrate is controlled to be (1-1.05):1; and / or, The temperature of the precipitation reaction is 65-100℃, the time of the precipitation reaction is 1-4 hours, and the precipitation reaction is performed under stirring; and / or, The temperature of the aging is 60-80℃, the time of the aging is 6-10 hours, and the aging is performed under static state; and / or, The pH value of the reaction system is controlled to be 1.5-2.5 by adjusting the pH value of the acid neutralization filtrate; and / or, Step S5 further comprises: the iron phosphate dihydrate is calcined to obtain iron phosphate anhydride.

7. A method for recovering graphite from a waste lithium battery black powder after valuable metal recovery, characterized by, Comprise the following steps: A1, graphite carbon residue is oxidized and roasted to obtain roasted material; A2, the roasted material is subjected to flotation separation to obtain concentrate and tailings; wherein, the concentrate is a crude graphite product, and the tailings are industrial waste residue; A3, the concentrate is subjected to deep purification and drying to obtain recovered graphite; Wherein, the graphite carbon residue comprises the acid-dissolved residue in any one of claims 1-6 and at least one of the graphite carbon residue after extracting lithium and phosphorus iron from the existing lithium phosphate iron black powder and the negative electrode carbon residue after extracting valuable metals from the ternary lithium battery black powder.

8. The method according to claim 7, wherein the graphite is recovered from the residue after the recovery of the valuable metals from the spent lithium battery black powder. In step A1, the graphite carbon residue after extracting lithium and phosphorus iron from the existing lithium phosphate iron black powder and / or the negative electrode carbon residue after extracting valuable metals from the ternary lithium battery black powder is subjected to washing and desalting treatment before oxidation roasting; The washing and desalting treatment method comprises: immersing and washing the graphite carbon residue after extracting lithium and phosphorus iron from the existing lithium phosphate iron black powder and / or the negative electrode carbon residue after extracting valuable metals from the ternary lithium battery black powder with water to remove impurities; wherein, the solid-liquid mass ratio of the graphite carbon residue after extracting lithium and phosphorus iron from the existing lithium phosphate iron black powder and / or the negative electrode carbon residue after extracting valuable metals from the ternary lithium battery black powder to water is 1:(1-2); the temperature of the immersion and washing is 10-30℃, and the time of the immersion and washing is 20-60 minutes; and / or, In step A1, the temperature of the oxidation roasting is 380-500℃, the time of the oxidation roasting is 20-120 minutes, and the atmosphere of the oxidation roasting is air; and / or, In step A2, the flotation reagent comprises a graphite collector and a foaming agent; wherein, the graphite collector comprises at least one of industrial kerosene, fatty acid, and sodium fatty acid; the foaming agent comprises at least one of a multi-carbon alcohol and a polyol; the mass ratio of the graphite collector to the foaming agent is 1:(0.01-0.2); the mass of the flotation reagent is 1.0wt%-5.0wt% of the roasted material; and / or, In step A2, the positive flotation is performed for 1-2 times.

9. The method according to claim 7, wherein the graphite is recovered from the residue after the valuable metals are extracted from the waste lithium battery black powder. In step A3, the deep purification process includes: sequentially treating the concentrate with hydrogen peroxide and then with EDTA solution; wherein, The hydrogen peroxide has a mass fraction of 0.2 wt% to 2.0 wt%; and / or, The solid-liquid mass ratio of the concentrate to hydrogen peroxide is 1:(0.5~2); and / or, During the hydrogen peroxide immersion treatment, the immersion temperature is 10~40℃, and the immersion time is 5~30 minutes; and / or, The EDTA solution has a mass fraction of 0.1 wt% to 5.0 wt%; and / or, The solid-liquid mass ratio of the concentrate to the EDTA solution is 1:(0.5~2); and / or, During the EDTA solution immersion treatment, the immersion temperature is 10~50℃, and the immersion time is 10~40 minutes; and / or, During the EDTA solution soaking process, the pH needs to be adjusted to 5.0-8.0 using ammonia water with a mass fraction of 0.5wt% to 5wt%.

10. An apparatus for recovering ferric phosphate and graphite from the residue after extracting valuable metals from waste lithium battery black powder, characterized in that, It includes an alkali dissolving kettle, a first filter, an ammonia leaching filter, an acid dissolving kettle, a second filter, a neutralization precipitator, a third filter, a modulator, a synthesis reactor, a fourth filter, a calcining furnace, a flotation machine, and a purification dryer; among which, The outlet of the alkali dissolving kettle is connected to the first filter, the filter residue outlet of the first filter is connected to the ammonia leaching filter, and the filtrate outlet of the first filter is connected to the neutralization precipitator. The filter residue outlet of the ammonia leaching filter is connected to the acid dissolution vessel, the discharge port of the acid dissolution vessel is connected to the second filter, and the filtrate outlet of the second filter is connected to the synthesis reaction vessel. The upper clear liquid outlet of the neutralization precipitator is connected to the modulator, the lower mud outlet of the neutralization precipitator is connected to the third filter, the filtrate outlet of the third filter is connected to the modulator, and the discharge port of the modulator is connected to the synthesis reactor. The outlet of the synthesis reactor is connected to the fourth filter. The filter residue outlet of the second filter press is connected to the roasting furnace, the discharge port of the roasting furnace is connected to the flotation machine, and the concentrate outlet of the flotation machine is connected to the purification dryer. The apparatus for recovering ferric phosphate and graphite from the residue after extracting valuable metals from waste lithium battery black powder is used to perform the method for recovering ferric phosphate from the residue after extracting valuable metals from waste lithium battery black powder as described in claim 1 and / or the method for recovering graphite from the residue after extracting valuable metals from waste lithium battery black powder as described in claim 7.

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