Method for circularly leaching lithium iron phosphate mixed powder from ferric salt and recovering all components

Abstract

The invention discloses a method for circularly leaching lithium iron phosphate mixed powder from ferric salt and recovering all components, and belongs to the field of battery recovery. The method comprises the following steps: leaching mixed powder by adopting an iron salt solution to obtain a lithium-containing leaching solution and leaching residues; ferrous ions in the leachate are regenerated into ferric iron through acidification and oxidation, the ferric iron is cyclically used for leaching the next batch of mixed powder, after the preset cycle number is reached, the leachate is used for re-leaching treatment of multiple batches of leaching residues, and the lithium leaching rate is increased. And finally obtaining enriched liquid containing Li, Fe, Cu and Al and iron phosphate slag containing graphite. And replacing the enriched liquid with iron powder to recover copper, extracting and separating to obtain a high-purity lithium chloride solution, and simultaneously recovering ferric chloride (recycling) and aluminum chloride crystals. And treating the leaching residues with hydrochloric acid to obtain regenerated graphite, and adjusting the pH value with alkali to obtain high-purity iron phosphate. According to the method, all-component recovery is achieved under the mild condition, separation steps are reduced through a leaching-regeneration-leaching circulation mechanism, chemical consumption is reduced, and the method has both environmental and economic benefits.

Description

Technical Field

[0001] The present invention relates to the technical field of efficient recycling of waste lithium iron phosphate batteries, and in particular to a method for recycling lithium iron phosphate mixed powder by leaching with iron salts and recovering all components. Background Art

[0002] Lithium iron phosphate (LFP) batteries are widely used due to their excellent safety, long cycle life, and low cost. However, with the rapid expansion of the new energy vehicle and energy storage markets, and the early widespread adoption of LFP batteries, a large number of batteries are reaching the end of their useful life and entering the first wave of retirements. This has made LFP battery recycling a key focus in the current waste power battery recycling industry. However, waste LFP batteries contain significant amounts of lithium, iron, and phosphorus, posing a high added value. Recycling these materials not only reduces environmental pollution but also enables resource utilization. Therefore, research on efficient recycling of all components of waste LFP batteries is crucial.

[0003] The existing lithium iron phosphate leaching and recovery processes mostly target positive electrode powder. For example, CN115611252B uses acid leaching-oxidation-crystallization technology to recover iron phosphate, and the residual liquid uses triethanolamine to deeply remove impurities to prepare lithium carbonate. However, this method has problems such as the inability to recycle the leaching agent, the low lithium concentration of the leachate, and the high cost caused by the large amount of triethanolamine used. In order to solve the problem of large amount of hydrogen peroxide used in the acid leaching method and the inability to recycle the leaching agent, CN117165770A and CN117163928A disclose a method for recovering waste lithium iron phosphate materials, which uses Fe2(SO4)3 and FeCl3 to recover positive electrode powder, respectively, to achieve the recycling of the leaching agent. However, the leaching agent regeneration process in this method must first undergo more complex separation processes such as oxidation, extraction, and stripping before regeneration can be achieved, and the Li in the leachate is + The concentration is still relatively low. CN110474123A discloses a comprehensive recovery method for waste lithium iron phosphate battery positive electrode materials, which also uses salt solutions such as Fe2(SO4)3 and FeCl3 to leach lithium ions. The leachate is first added with alkali solution and oxidant to obtain iron hydroxide precipitate, which is then dissolved by dilute acid to obtain a regenerated leaching agent for recycling. The regeneration process still requires a relatively cumbersome separation process and consumes a large amount of acid and alkali solution. In addition, the alkaline cations will accumulate during the mother liquor circulation process, resulting in a significant reduction in the effect of the leaching agent, and the subsequent preparation of lithium salt products with low purity.

[0004] However, in practice, the sources of recycled waste batteries are complex and some are severely damaged, making it difficult to effectively separate the positive and negative electrodes. To reduce costs and increase efficiency, the industry typically mixes and crushes the positive and negative electrodes, significantly increasing the copper, aluminum, and carbon content of the mixed black powder. Currently, the recovery of mixed powder still mostly relies on a combination of acid and oxidant for selective lithium extraction. However, the leaching agent in this method cannot be regenerated and recycled, significantly affecting the economic feasibility of the process. For example, CN116553510B discloses a method for recycling waste lithium iron phosphate powder. The method involves first leaching with alkaline leaching to remove fluoride ions, then acid leaching and oxidation to extract lithium, remove aluminum, and produce lithium carbonate. This is followed by high-temperature roasting and hydrothermal phosphorus supplementation to produce iron phosphate. Finally, the recovered lithium carbonate and iron phosphate are calcined to achieve the final lithium iron phosphate recycling cycle. Although this method can achieve closed-loop regeneration of lithium iron phosphate, the graphite roasting and removal process itself has the disadvantages of high energy consumption, high carbon emissions, and severe pollution. Furthermore, the pretreatment defluorination and subsequent aluminum removal steps suffer from high liquid caustic soda consumption and large amounts of waste liquid, significantly weakening the green economy of the process. CN113912033A discloses a method for recovering mixed powder of positive and negative electrodes of waste lithium iron phosphate batteries with a pre-extracted lithium. The method uses processes such as front-end liquid alkali aluminum removal, sulfuric acid and oxidant selective lithium extraction, high-concentration acid leaching of iron phosphate and graphite mixed slag to recover high-concentration iron phosphate dihydrate. However, the front-end liquid alkali aluminum removal process uses an excessive amount of alkali, and the oxidizing acid leaching process for lithium extraction consumes a large amount of oxidant, resulting in high costs. Meanwhile, impurities such as iron and aluminum remaining in the leachate are not effectively removed, which seriously affects the refined quality of lithium carbonate. A large amount of waste acid and alkali solution will be discharged, causing secondary pollution and significantly increasing the economic cost of recycling. CN 113443640B discloses a method for preparing battery-grade lithium carbonate and battery-grade iron phosphate from waste positive and negative electrode powder from lithium iron phosphate batteries. The method uses an inorganic acid, an oxidant, and a regulator (primarily soluble iron, calcium, and magnesium salts) to selectively extract lithium, producing a high-concentration lithium solution. This solution is then subjected to extensive impurity removal with sodium hydroxide to produce battery-grade lithium carbonate. A mixed slag of iron phosphate and graphite is then dissolved in acid and extensively impurity-removed to convert it into battery-grade iron phosphate. However, the extensive impurity removal process with sodium hydroxide not only consumes a large amount of alkali solution, but the high sodium ion concentration in the resulting solution also significantly increases the difficulty of preparing battery-grade lithium carbonate.

[0005] In order to solve the problems of high oxidant consumption and difficulty in recycling leaching agents in the acid leaching method, CN119220819B discloses a recovery method for extracting lithium, copper and aluminum from waste lithium iron phosphate batteries, using iron sulfate solution to leach positive and negative electrode sheets. In the pretreatment section of waste batteries, this method uses manual fine disassembly instead of mechanical crushing process, and directly screens the positive and negative electrode sheets as wet leaching raw materials, which can effectively reduce the copper and aluminum content in the raw materials. However, manual disassembly is inefficient and costly, and the material separation accuracy in large-scale production is insufficient, which is significantly restricted in large-scale continuous production. At the same time, the leaching agent iron sulfate regeneration process must first cooperate with LiOH and the oxidant to form an iron hydroxide precipitate, which is then dissolved by a large amount of acid before it can be recycled. The regeneration steps are cumbersome, not only lengthening the overall process, but also significantly increasing the recovery cost due to the repeated consumption of a large amount of acid and alkali reagents.

[0006] In addition to the aforementioned wet recovery methods, CN118291779B discloses a method for recovering lithium from lithium iron phosphate black powder. This involves adding auxiliary materials, mixing with the lithium iron phosphate black powder, calcining, acid dissolving, adjusting the pH with alkali, and then separating the solid and liquid to produce a lithium feed solution and iron phosphate slag. Although this process is short, the high-temperature calcination and oxidation of the lithium iron phosphate and decomposition of carbon powder pose challenges such as high energy consumption, low iron phosphate product purity, high carbon emissions, and environmental pollution. CN117954728B discloses a comprehensive method for recovering lithium, iron, and graphite from waste lithium iron phosphate battery black powder. The waste battery black powder is mixed with alkali, smelted at high temperatures, and then water-leached to produce a water-leached slag rich in iron and graphite and a water-leached solution rich in lithium and phosphorus. The water-leached slag is further acid-dissolved to separate the iron-containing solution and regenerated graphite, achieving integrated recovery of lithium, iron, and graphite from waste lithium iron phosphate battery black powder. However, the high-temperature smelting process consumes a lot of energy and lacks effective impurity separation between the water-leached solution and the iron-containing solution. The aqueous solution is mainly a mixture of sodium pyrophosphate and lithium hydroxide, and impurities such as copper and aluminum in the iron-containing solution are not effectively removed.

[0007] In summary, while research on the efficient recovery of spent lithium iron phosphate cathode and cathode mixed powders has achieved some success, existing processes generally face challenges with the difficulty of regenerating and recycling the leaching agent or the cumbersome and complex regeneration steps. Furthermore, there are deficiencies in leaching efficiency and the recovery of all battery components. Therefore, there is an urgent need to develop a leaching agent that is easily recyclable to achieve efficient recovery of all components of spent lithium iron phosphate cathode and cathode mixed powders. Summary of the Invention

[0008] The purpose of the present invention is to overcome the shortcomings of the existing technology and provide a method for cyclic leaching of lithium iron phosphate mixed powder with iron salts and recovery of all components. The present invention uses ferric chloride or ferric sulfate solution as a leaching agent to effectively recover all components, including Li, Fe, P, Cu, Al, and graphite, from the mixed powder of used lithium iron phosphate batteries under milder reaction conditions. By constructing a new and efficient "leaching-regeneration-leaching" cycle mechanism, the intermediate separation steps are significantly reduced and the process is simplified. The leaching efficiency of lithium ions is effectively improved by re-leaching the previously accumulated leaching residue, which has good environmental and economic benefits and overcomes the shortcomings of the existing technology.

[0009] The present invention solves the above-mentioned problem with the following technical solution: a method for recycling leaching of lithium iron phosphate mixed powder with iron salt and recovering all components, the method comprising the following steps:

[0010] S1. Using an iron salt solution as a leaching agent, the iron salt solution is fully mixed with the waste lithium iron phosphate positive and negative electrode mixed powders to perform a leaching reaction to obtain a leachate and a leach residue; the iron salt is ferric chloride or ferric sulfate;

[0011] S2, the leachate is regenerated by acidification and oxidation; the resulting regenerated leaching agent is returned to S1 to carry out leaching reaction on the next batch of positive and negative electrode mixed powders, and the acidification, oxidation, regeneration and leaching are repeated until the regenerated leaching agent reaches a predetermined regeneration number;

[0012] S3, combining the leaching residues obtained from S1 and S2 into several groups, and sequentially performing re-leaching reaction with the regenerated leaching agent after S2 reaches a predetermined regeneration number to obtain the final leachate and final leaching residue;

[0013] S4, adding iron powder to the final leachate to replace copper ions to obtain crude copper and a lithium-containing mother liquor; adding acid to the crude copper, performing solid-liquid separation to obtain industrial-grade copper powder and a ferrous ion solution; oxidizing the ferrous ion solution, and then performing vacuum distillation to obtain an iron salt solution as a leaching agent;

[0014] S5, adding an extractant to the lithium-containing mother liquor of S4, and selectively extracting iron and aluminum in multiple stages to obtain an extraction phase loaded with iron ions, an extraction phase loaded with aluminum ions, and an extraction phase containing Li + The two types of extract phases are stripped and post-treated to recover iron and aluminum;

[0015] S6. Acid is added to the final leaching residue of S3 to dissolve the ferric phosphate, and solid-liquid separation is performed to obtain crude graphite and ferric phosphate acid solution; the crude graphite is washed and calcined to obtain regenerated graphite; a phosphorus source or an iron source is added to the ferric phosphate acid solution to adjust the iron-phosphorus material ratio, and then hydrogen peroxide is added to oxidize the ferrous ions therein, and then an alkali solution is added to fully react to obtain crude ferric phosphate; the crude ferric phosphate is washed, aged, crystallized, and calcined to prepare anhydrous ferric phosphate.

[0016] Preferably, when the leaching agent is ferric chloride, the acid used in the subsequent steps is hydrochloric acid; when the leaching agent is ferric sulfate, the acid used in the subsequent steps is sulfuric acid.

[0017] The present invention provides a method for circulating leaching of lithium iron phosphate mixed powder with iron salts and recovery of all components. The method utilizes the isostructural induction effect of FeCl3 or Fe2(SO4)3 to rapidly leach the lithium iron phosphate material, and obtains FePO4 leaching residue containing graphite and lithium chloride leachate containing iron, copper and aluminum through solid-liquid separation.

[0018] The leachate is directly acidified, oxidized, and regenerated. Through multiple cycles of leaching and subsequent leaching of the leached residue, a concentrated solution containing lithium, iron, copper, and aluminum, and a graphite-containing iron phosphate leaching residue, is ultimately obtained. The final leachate is first replaced with iron powder to produce industrial-grade copper powder. The iron and aluminum are then extracted using P204 in a multi-stage, step-by-step extraction process. Multi-stage stripping then achieves efficient separation of the iron and aluminum, resulting in a highly concentrated lithium solution.

[0019] The graphite-containing FePO4 leached residue is first dissolved in dilute acid to produce regenerated graphite. The pH of the ferric phosphate solution is then adjusted with alkali. After washing, aging, and calcination, high-purity regenerated anhydrous ferric phosphate is obtained. Under milder reaction conditions, the full recovery of Li, Fe, P, Cu, Al, and graphite from the mixed powder of used lithium iron phosphate batteries is achieved.

[0020] The beneficial effects of the present invention are:

[0021] (1) The present invention proposes a new and efficient "leaching-regeneration-leaching" cycle system. Compared with the traditional "leaching-separation-regeneration-leaching" process, its core advantage is that it significantly reduces the reliance on and number of intermediate separation steps. This innovative design not only greatly simplifies the process flow, effectively reduces operational complexity and system energy consumption, but also brings significant economic and environmental benefits: the consumption of hydrogen peroxide and acid can be saved by 30%-40%, and the industrial water consumption can be saved by 40%-50%. At the same time, the amount of wastewater is also greatly reduced, thereby significantly reducing the total operating cost and recovery cost. After leaching with iron salt solution, the single leaching rate of lithium ions is 98.12%. The ferrous ions in the lithium-containing solution are directly acidified and oxidized to achieve leaching agent regeneration, and continuous leaching can be achieved for 10 times, with the tenth leaching rate still being 87.94%.

[0022] (2) The present invention proposes to re-acidify and oxidize the leachate after a predetermined number of cycles of leaching, and then re-leach the accumulated leaching residue, which can significantly improve the lithium ion leaching efficiency. Before re-leaching, the total lithium ion leaching rate after ten cycles was 93.77%; after re-leaching, the total leaching rate can be further increased to 99.21%.

[0023] (3) In the key impurity removal link, the present invention can not only efficiently remove impurity ions in the system, but also the separated impurity ions can be recycled and converted into valuable target products. The "iron powder replacement-dilute acid washing" process is used to obtain recycled copper powder with a purity of 99.8% (recovery rate of 97%). The filtrate after dilute acid washing of crude copper contains a high concentration of ferrous solution, which can be used for the cyclic leaching of mixed powder after acidification, oxidation, and vacuum distillation. Using P204 multi-stage selective extraction, a relatively pure lithium ion solution can be obtained; the extraction phase is subjected to multi-stage back extraction to obtain iron salt, aluminum salt solution and an empty organic phase respectively; the iron salt solution is subjected to vacuum distillation and can be recycled for the leaching of mixed powder; the aluminum salt solution is evaporated and crystallized to obtain aluminum chloride hexahydrate crystals or aluminum sulfate crystals containing crystal water; the empty organic phase can be recycled for extraction. Compared with the direct chemical precipitation method, it can significantly avoid the problem of large-scale consumption of alkali solution in the traditional process, significantly reduce the wastewater treatment load, thereby greatly reducing production costs and improving the green environmental protection level of the process.

[0024] (4) This invention has developed a high-value-added, environmentally friendly, full-component recycling technology for waste lithium iron phosphate battery mixed powder. This technology successfully regenerates iron phosphate (96% recovery rate, 98% purity) and graphite, and recovers valuable elements including Li, Fe, P, Cu, and Al, greatly optimizing resource utilization efficiency and significantly reducing operating costs. This fully demonstrates the huge industrial application prospects of this invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The figure is a flow chart of the cyclic leaching step in the method of the present invention.

[0026] Figure 2 The figure is a flow chart of the final leachate separation and purification step in the method of the present invention.

[0027] Figure 3 The figure is a flow chart of the final leach residue separation and regeneration steps in the method of the present invention.

[0028] Figure 4 This is a diagram showing the influence of the number of leaching times on the leaching effects of lithium and copper in Example 1.

[0029] Figure 5 This is a diagram showing the influence of the number of leaching times on the leaching effects of lithium and copper in Example 2.

[0030] Figure 6 This is a diagram showing the influence of the number of leaching times on the lithium leaching effect in Example 3. DETAILED DESCRIPTION

[0031] The technical solution of the present invention will be further described below with reference to the accompanying drawings and through specific implementation methods.

[0032] The examples given are only used to explain the present invention and are not used to limit the scope of the present invention. The technical features of each embodiment of the present invention can be combined accordingly without conflict.

[0033] All embodiments obtained based on the embodiments of the present invention without making any creative achievements shall fall within the scope of protection of the present invention.

[0034] The metal concentrations in the solution were detected using a flame atomic absorption spectrometer (FAAS, Thermo Fisher) and an inductively coupled plasma optical emission spectrometer (ICP-OES, Agilent 5800). The leaching rate of valuable metal elements was calculated as follows:

[0035]

[0036] Among them C i is the concentration of element i in the leachate; V is the volume of the leachate; m is the mass of the mixed powder; w i is the mass proportion of element i in the mixed powder.

[0037] The main reaction equations of the leaching process and the oxidation regeneration of the leaching agent are:

[0038] ;

[0039] .

[0040] The method for recycling leaching of lithium iron phosphate mixed powder by iron salt and recovering all components of the present invention mainly comprises three steps: recycling leaching step, final leachate separation and purification step, and final leach residue separation and regeneration step; Figures 1 to 3 The flowcharts of the three steps are shown respectively.

[0041] like Figure 1 As shown, the cyclic leaching steps mainly include:

[0042] S1. A leaching reaction is performed by thoroughly mixing an iron salt solution with waste lithium iron phosphate positive and negative electrode mixed powders using an iron salt solution as a leaching agent, stirring the mixture to obtain a leachate and a leaching residue; the iron salt is ferric chloride or ferric sulfate. The waste lithium iron phosphate positive and negative electrode mixed powders described in S1 are obtained from waste lithium iron phosphate batteries through pretreatment such as discharge and mechanical disassembly. In addition to the primary positive electrode material, lithium iron phosphate, and the negative electrode material, graphite, the mixed powders may contain one or more of a binder, a current collector, and an electrolyte.

[0043] Preferably, the waste lithium iron phosphate positive and negative electrode mixed powder is allowed to contain one or more impurities in the positive and negative electrode aluminum foil and copper foil, and among the impurities, the Cu element is ≤15wt.%, and the Al element is ≤10wt.%.

[0044] Preferably, in step S1, the ferric chloride and the Li in the lithium iron phosphate positive and negative electrode powders + The molar ratio is 1.0-2.0; the solid-liquid ratio of lithium iron phosphate positive and negative electrode powders to the leaching agent solution is 100-600 g / L, the reaction temperature is 20-60°C, and the reaction time is 20-60 minutes.

[0045] S2, the leachate is regenerated by acidification and oxidation; the regenerated leaching agent is returned to S1 to carry out leaching reaction on the next batch of positive and negative electrode mixed powders, and the acidification, oxidation, regeneration and leaching are repeated until the regenerated leaching agent reaches the predetermined regeneration times. The acid used for acidification in step S2 is hydrochloric acid or sulfuric acid, and its hydrogen ion molarity is the Fe 2+ The oxidant used for oxidation is hydrogen peroxide, the mass concentration of hydrogen peroxide is 10%-30%, and the amount is Fe in the solution. 2+ 0.5-1.0 times of the molar amount, oxidation time 5-30 min, oxidation temperature 20-40℃.

[0046] S3: The leached residues obtained by combining S1 and S2 are divided into several groups. The leached residues of each group are sequentially subjected to a re-leaching reaction with the regenerated leaching agent after reaching a predetermined regeneration number in S2 to obtain a final leachate and a final leached residue. The regenerated leaching agent in S3 is sequentially and continuously subjected to a re-leaching reaction on each group of leached residues without reoxidizing the leachate. The solid-liquid ratio of each group of re-leaching reaction is 100-600g / L, the reaction temperature is 20-60°C, and the reaction time is 20-60 minutes.

[0047] like Figure 2 As shown, the final leachate separation and purification steps mainly include:

[0048] S4, adding iron powder to the final leachate to replace copper ions to obtain crude copper and lithium-containing mother liquor; adding acid to the crude copper, performing solid-liquid separation to obtain industrial-grade copper powder and ferrous ion solution; oxidizing the ferrous ion solution, and then obtaining an iron salt solution as a leaching agent by vacuum distillation; the amount of iron powder in S4 is 1.0-2.0 times the copper ion content in the solution; the hydrogen ion concentration in the acid is 0.5-5.0 mol / L; the oxidant used for oxidizing the ferrous ion solution is hydrogen peroxide with a mass concentration of 10%-30%, and the amount used is the Fe content in the solution. 2+ 0.5-1.0 times of the molar amount, oxidation time 5-30 min, oxidation temperature 20-40℃.

[0049] S5, adding an extractant to the lithium-containing mother liquor of S4, and selectively extracting iron and aluminum in multiple stages to obtain an extraction phase loaded with iron ions, an extraction phase loaded with aluminum ions, and an extraction phase containing Li + The two types of extract phases are stripped and post-treated to recover iron and aluminum;

[0050] The pH value of the mother liquor containing lithium is less than 1, and an extractant is added thereto to obtain an extraction phase loaded with iron ions and a raffinate phase containing aluminum salts and lithium salts; for the treatment of the raffinate phase containing aluminum salts and lithium salts, a LiOH solution is first added to the extractant for saponification treatment, and the saponification degree is controlled to be 40%-80%; the saponified extractant and the raffinate phase containing aluminum salts and lithium salts are subjected to multi-stage extraction to obtain an extraction phase loaded with aluminum ions and a raffinate phase containing lithium ions. + Raffinate solution;

[0051] The extractants are all di(2-ethylhexyl) phosphate diluted with kerosene, and the volume fraction of di(2-ethylhexyl) phosphate in the extractant is 20%-40%; in each stage of extraction, the volume ratio of the organic phase to the aqueous phase is (1-3):1.

[0052] In S5, the two types of extract phases are stripped and post-treated to recover iron and aluminum, respectively, including:

[0053] The iron ion-loaded extraction phase is subjected to multi-stage acid stripping to obtain an empty organic phase and an aqueous phase containing iron ions. The empty organic phase is recycled as an extractant for cyclic extraction of iron, and the aqueous phase is subjected to reduced pressure distillation to obtain an iron salt leaching agent.

[0054] The aluminum ion-loaded extract phase is subjected to multi-stage acid stripping to obtain an empty organic phase and an aluminum ion-containing aqueous phase. The empty organic phase is recycled as an extractant for cyclic extraction of aluminum, and the aqueous phase is evaporated and crystallized to obtain aluminum salt crystals.

[0055] The acid used in all stripping processes is hydrochloric acid or sulfuric acid, and the hydrogen ion concentration in the acid is in the range of 2-8 mol / L; during the stripping process, the volume ratio of the organic phase to the aqueous phase is 1:(1-3).

[0056] like Figure 3 As shown, the final leaching residue separation and regeneration steps mainly include:

[0057] S6. Adding acid to the final leaching residue obtained in the cyclic leaching step to dissolve the ferric phosphate, and performing solid-liquid separation to obtain crude graphite and ferric phosphate acid solution; washing the crude graphite with a small amount of acid multiple times, and then calcining at a high temperature under a nitrogen atmosphere to remove binder PVDF and other substances to obtain relatively pure regenerated graphite; supplementing the ferric phosphate acid solution with a phosphorus source or an iron source, adjusting the iron-phosphorus material ratio, and then adding hydrogen peroxide to oxidize the ferrous ions therein, and then adding alkaline solution to fully react to obtain crude ferric phosphate; the crude ferric phosphate is washed, aged, crystallized, and calcined to prepare anhydrous ferric phosphate.

[0058] The phosphorus source is one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and phosphoric acid, with an iron-to-phosphorus molar ratio of 0.9-1.2. The iron source is ferric chloride or ferric sulfate. The alkali solution is one or more of potassium hydroxide, sodium hydroxide, and ammonia water, with a concentration of 1.0-3.0 mol / L. The pH is adjusted to 1.0-4.0 using the alkali solution. The reaction temperature is 50°C-80°C, and the reaction time is 2-4 hours. After acid washing, the crude graphite is calcined in a nitrogen atmosphere at a temperature of 450°C-700°C for 1-3 hours. The crude iron phosphate is washed with deionized water and aged and crystallized in dilute phosphoric acid at a concentration of 0.1-1.0 mol / L for 2-10 hours. The iron phosphate is calcined at a temperature of 300°C-600°C for 1-3 hours.

[0059] The overall method is described in detail below with reference to several specific embodiments.

[0060] Example 1

[0061] (1) Circulating leaching

[0062] Prepare FeCl3 solution as a leaching agent, mix it with the positive and negative electrode mixed powder of waste lithium iron phosphate battery (main components and content by mass percentage: Li 3.05%, Fe 24.97%, Cu 7.54%, Al 1.24%, P 14.14%, C 13.68%), and stir it thoroughly to complete the leaching reaction.

[0063] The molar ratio of lithium in FeCl3 and mixed powder is 1.50, and the solid-liquid ratio is 200 g·L -1 Under the conditions of reaction temperature of 40 ℃ and reaction time of 30 min, the single leaching rate of Li was 98.13%, and lithium-containing leachate and leach residue were obtained by solid-liquid separation.

[0064] The amount of ferrous ions in the lithium-containing leachate was determined by potassium dichromate titration. 2+ Hydrochloric acid with a molar ratio of 1.0 and Fe 2+ The leaching agent regeneration rate is close to 100%, and the regenerated leaching agent FeCl3 containing lithium is obtained. The next batch of materials (mixed positive and negative electrode powders of waste lithium iron phosphate battery) is leached. The above steps are repeated continuously. In this embodiment, a total of ten batches of materials are leached. The Li leaching rate of 87.94% is still maintained during the tenth leaching. The specific influence of the number of leaching times on the lithium and copper leaching effects is shown in the figure. Figure 4 shown.

[0065] After ten rounds of leaching, the tenth leachate L 10The ten batches of leaching residue were combined into four groups: the first, second, and third batches, the fourth, fifth, and sixth batches, the seventh and eighth batches, and the ninth and tenth batches. The purpose of grouping the leaching residue is to control the solid-liquid ratio in the re-leaching reaction to an appropriate level (100-600 g / L), avoiding the problem of limited lithium re-leaching from the leaching residue due to an excessively high solid-liquid ratio.

[0066] The tenth leaching solution L was obtained by acidification oxidation. 10 The four groups of leaching residues were leached sequentially, without further oxidation, at a leaching temperature of 40°C and a leaching time of 30 minutes. Leaching and washing were completed, increasing the Li leaching rate to 99.21% and the total Cu leaching rate to 78.36%. The final lithium-rich leachate and final leaching residue were separated by filtration. The total Li concentration in the lithium-rich leachate was 3.5 mol / L (based on 100 mL). The final leaching residue was a mixture of iron phosphate and graphite.

[0067] (2) Separation and purification of the final leachate

[0068] The composition and content of the final leachate were detected using inductively coupled plasma optical emission spectrometry, as shown in Table 1.

[0069] Table 1 - Composition and content of the final leachate

[0070]

[0071] At room temperature, the final leachate was added according to the ratio of n(Fe):n(Cu 2+ )=1.05 molar ratio was added to reduce iron powder, and mechanical stirring was continued for 30 min to complete the replacement reaction. After solid-liquid separation, the mother liquor containing lithium was detected and analyzed. M The copper ions in the crude copper were completely removed (replacement rate 100%). The crude copper was then pickled with 2 mol / L hydrochloric acid at a solid-to-liquid ratio of 100 g / L, with mechanical stirring at room temperature for 1 hour to remove excess iron powder. After this treatment process, copper powder with a purity of 99.8% was obtained, with a recovery rate of 96.9%.

[0072] Inductively coupled plasma emission spectrometry was used to detect the lithium-containing mother liquor after copper removal. M The mass concentration of each ion in the solution is shown in Table 2. The pH of the solution was tested using a pH meter and was 0.6.

[0073] Table 2 - Lithium-containing mother liquor L F Ingredients and content

[0074]

[0075] Prepare the extractant, which is di(2-ethylhexyl) phosphate (P204) diluted with kerosene, where the volume fraction of P204 is 40%. At room temperature, the extractant is mixed with the lithium-containing mother liquor L diluted with water. F The mixture (controlling the O / A ratio to be 1:1, and the lithium-containing mother liquor can be left undiluted) is then extracted in a water bath with a constant temperature oscillator for 30 minutes. This yields an iron-loaded extract phase and a mixed solution of aluminum chloride and lithium chloride (the raffinate phase). The iron ion extraction rate reaches over 99%. The P2O4 extraction process is very sensitive to pH. At lower pH, iron ions have a stronger complexing capacity than aluminum ions and are more easily extracted by P2O4. Therefore, under these pH conditions (pH < 1), aluminum ions are virtually not extracted.

[0076] At room temperature, the iron-laden extract phase is mixed with 6 mol / L hydrochloric acid (O / A = 1:1) and stripped in a water bath in a thermostatic oscillator for 30 minutes. After three stages of stripping, an empty organic phase and an iron-enriched aqueous phase are obtained. The empty organic phase can be used as an extractant to extract iron again. The iron-enriched aqueous phase, primarily composed of ferric chloride and hydrochloric acid, is distilled under reduced pressure to yield FeCl3, which is then recycled as the leaching agent in the leaching step.

[0077] The extractant was re-prepared, remaining unchanged: di(2-ethylhexyl) phosphate (P204) diluted with kerosene, with a P204 volume fraction of 40%. A 0.5 mol / L LiOH solution was then added to the extractant for saponification, resulting in a saponification degree of 40%. The saponified extractant was mixed with equal volumes of the raffinate (a mixture of aluminum chloride and lithium chloride) diluted with water at room temperature and extracted in a thermostatically controlled water bath for 30 minutes. After three extraction steps, the aluminum-loaded extract and a relatively pure lithium chloride solution (raffinate) were obtained.

[0078] At room temperature, the aluminum-laden extract phase is mixed with 6 mol / L hydrochloric acid (O / A = 1:1) and stripped in a water bath in a thermostatic oscillator for 30 minutes. After multiple stripping steps, an empty organic phase and an aluminum-enriched aqueous phase are obtained. The empty organic phase can be used again to extract aluminum; the aluminum-enriched aqueous phase, primarily composed of aluminum chloride and hydrochloric acid, is evaporated and crystallized to yield aluminum chloride hexahydrate crystals.

[0079] (3) Final leaching residue separation and regeneration

[0080] Add 2 mol / L dilute hydrochloric acid solution to the final leaching residue with a solid-liquid ratio of 200 g / L and react at 60°C for 1.5 h. Solid-liquid separation is performed to obtain crude graphite and ferric phosphate solution L A The crude graphite was washed several times with 0.1 mol / L dilute hydrochloric acid in small amounts, and then calcined at 600°C in a nitrogen atmosphere to remove the binder PVDF and other substances, thereby obtaining relatively pure regenerated graphite.

[0081] The above washing liquid and ferric phosphate solution L A Mix, use potassium dichromate titration method to detect the amount of ferrous ions in the lithium-containing leachate, add Fe 2+ The molar ratio of hydrogen peroxide was 0.6, and the reaction was carried out at room temperature for 20 min to convert it into Fe 3+ The iron-phosphorus molar ratio was then adjusted to 1.0 using phosphoric acid.

[0082] Subsequently, a 2 mol / L potassium hydroxide solution was added dropwise, and the pH of the system was precisely controlled to 2.0. The reaction was then continued at 80°C for 2 hours. After the reaction was completed, crude ferric phosphate was obtained through solid-liquid separation. The surface potassium chloride crystals were then washed off with deionized water in small amounts multiple times to obtain amorphous ferric phosphate. This was then placed in a 0.5 mol / L phosphoric acid solution and aged at 80°C for 4 hours to crystallize, thereby preparing high-purity ferric phosphate dihydrate. Finally, calcination at 600°C for 2 hours converted the product into anhydrous ferric phosphate crystals with a purity of 98% and a recovery rate of 96%.

[0083] Example 2

[0084] (1) Circulating leaching

[0085] Prepare FeCl3 solution as a leaching agent, mix it with the mixed positive and negative electrode powders of waste lithium iron phosphate batteries (the main components are the same as those in Example 1), and stir it thoroughly to complete the leaching reaction.

[0086] The molar ratio of lithium in FeCl3 and mixed powder is 1.30, and the solid-liquid ratio is 200 g·L -1 Under the conditions of reaction temperature of 40℃ and reaction time of 30min, the single leaching rate of Li was 98.03%, and lithium-containing leachate and leach residue were obtained by solid-liquid separation.

[0087] The amount of ferrous ions in the lithium-containing leachate was determined by potassium dichromate titration. 2+ Hydrochloric acid with a molar ratio of 1.0 and Fe 2+ The molar ratio of hydrogen peroxide is 0.6, and the oxidation reaction is carried out at room temperature for 20 minutes. The regeneration rate of the leaching agent is close to 100%, and the regenerated leaching agent FeCl3 containing lithium is obtained to leach the next batch of materials. The above steps are repeated continuously, and a total of four batches of materials are leached. The Li leaching rate in the fourth leaching is 89.28%. The influence of the specific number of leaching times on the lithium leaching effect is shown in the figure. Figure 5 shown.

[0088] After four rounds of leaching, the fourth leachate L4 and four batches of leached residue were collected. These four batches were combined into two groups: the first and second batches, and the third and fourth batches. This step aims to control the appropriate solid-liquid ratio (100-600 g / L) to avoid the problem of limited lithium re-leaching from the leached residue due to an excessively high solid-liquid ratio.

[0089] The fourth leachate, L4, was used for acidification and oxidation, and the two groups of leached residues were leached sequentially without further oxidation. Leaching and washing were completed at a leaching temperature of 40°C and a leaching time of 30 minutes. The Li leaching yield increased to 99.16%, and the total Cu leaching yield was 92.28%. The final lithium-rich leachate and final leach residue were separated by filtration. The total Li concentration in the lithium-rich leachate was 1.4 mol / L (based on 100 mL). The final leach residue was a mixture of iron phosphate and graphite.

[0090] (2) Separation and purification of the final leachate

[0091] At room temperature, the final leachate was added according to the ratio of n(Fe):n(Cu 2+ )=1.1 molar ratio, and then the reduced iron powder was added and mechanical stirring was continued for 30 min to complete the replacement reaction. After solid-liquid separation, the test showed that the lithium-containing mother liquor L M The copper ions were completely removed (replacement rate 100%). The crude copper was then pickled with 2 mol / L hydrochloric acid at a solid-to-liquid ratio of 100 g / L, with mechanical stirring at room temperature for 1 hour to remove excess iron powder. After this treatment process, copper powder with a purity of 98.8% was obtained, with a recovery rate of 99%.

[0092] Inductively coupled plasma emission spectrometry was used to detect the lithium-containing mother liquor after copper removal. M The mass concentration of each ion in the solution was measured using a pH meter and the pH of the solution was 0.6.

[0093] Prepare the extractant, which is di(2-ethylhexyl) phosphate (P204) diluted with kerosene, where the volume fraction of P204 is 30%. At room temperature, the extractant is mixed with the lithium-containing mother liquor L diluted with water. M After mixing (O / A=1:1) and extracting in a water bath constant temperature oscillator for 30 min, an iron-loaded extraction phase and a mixed solution of aluminum chloride and lithium chloride (raffinate phase) can be obtained. At this time, the iron ion extraction rate is more than 99%.

[0094] At room temperature, the iron-laden extract is mixed with 6 mol / L hydrochloric acid (O / A = 1:1) and stripped in a water bath oscillator at 50°C for 30 minutes. After three stripping steps, an empty organic phase and an iron-enriched aqueous phase are obtained. The empty organic phase can be reused for iron extraction; the iron-enriched aqueous phase, primarily composed of ferric chloride and hydrochloric acid, is distilled under reduced pressure to yield FeCl₃, which is then recycled as the leaching agent in the leaching step.

[0095] The extractant was prepared again, remaining unchanged: di(2-ethylhexyl) phosphate (P204) diluted with kerosene, with a P204 volume fraction of 30%. A 0.5 mol / L LiOH solution was then added to the extractant for saponification, resulting in a saponification degree of 40%. The saponified extractant was mixed with equal volumes of the raffinate (a mixture of aluminum chloride and lithium chloride) diluted with water at room temperature and extracted in a thermostatically controlled water bath for 30 minutes. After three extraction steps, an aluminum-loaded extract phase and a relatively pure lithium chloride solution (raffinate phase) were obtained.

[0096] At room temperature, the aluminum-enriched extract is mixed with 6 mol / L hydrochloric acid (O / A = 1:1) and stripped in a water bath oscillator at 50°C for 30 minutes. After multiple stripping steps, an empty organic phase and an aluminum-enriched aqueous phase are obtained. The empty organic phase can be used again to extract aluminum; the aluminum-enriched aqueous phase, primarily composed of aluminum chloride and hydrochloric acid, is evaporated and crystallized to yield aluminum chloride hexahydrate crystals.

[0097] (3) Final leaching residue separation and regeneration

[0098] Add 3 mol / L dilute hydrochloric acid solution to the final leaching residue with a solid-liquid ratio of 100 g / L and react at 60°C for 2 h. Solid-liquid separation is performed to obtain crude graphite and ferric phosphate solution L A The crude graphite was washed several times with 0.1 mol / L dilute hydrochloric acid in small amounts, and then calcined at 700°C under a nitrogen atmosphere to remove the binder PVDF and other substances, thereby obtaining relatively pure regenerated graphite.

[0099] The above washing liquid and ferric phosphate solution L A Mix, use potassium dichromate titration method to detect the amount of ferrous ions in the lithium-containing leachate, add Fe 2+ The molar ratio of hydrogen peroxide was 0.6, and the reaction was carried out at room temperature for 20 min to convert it into Fe 3+ The iron-phosphorus material ratio was then adjusted to 1.0 using phosphoric acid.

[0100] Subsequently, a 2 mol / L potassium hydroxide solution was added dropwise, and the pH of the system was precisely controlled to 3.0. The reaction was then continued at 80°C for 2 hours. After the reaction was complete, solid-liquid separation was performed to obtain crude ferric phosphate. The surface potassium chloride crystals were then washed off with deionized water in small amounts multiple times to obtain amorphous ferric phosphate. The amorphous ferric phosphate was then placed in a 0.5 mol / L phosphoric acid solution and aged at 80°C for 5 hours to crystallize, thereby preparing high-purity ferric phosphate dihydrate. Finally, calcination at 600°C for 2 hours converted the product into anhydrous ferric phosphate crystals with a purity of 96% and a recovery rate of 97%.

[0101] Example 3

[0102] (1) Circulating leaching

[0103] Prepare Fe2(SO4)3 solution as a leaching agent, mix it with the positive and negative electrode mixed powder of waste lithium iron phosphate battery (main components and content are the same as those in Example 1), stir it thoroughly, and complete the leaching reaction.

[0104] The molar ratio of lithium in Fe2(SO4)3 and mixed powder is 0.6, and the solid-liquid ratio is 100 g·L -1 Under the conditions of reaction temperature of 40 ℃ and reaction time of 40 min, the single leaching rate of Li was 95.87%, and lithium-containing leachate and leach residue were obtained by solid-liquid separation.

[0105] The amount of ferrous ions in the lithium-containing leachate was determined by potassium dichromate titration. 2+ Sulfuric acid with a molar ratio of 0.5 and Fe 2+ The molar ratio of hydrogen peroxide is 0.6, and the oxidation reaction is carried out at room temperature for 30 minutes. The regeneration rate of the leaching agent is close to 100%, and the regenerated leaching agent Fe2(SO4)3 containing lithium is obtained to leach the next batch of materials. The above steps are repeated continuously, and a total of three batches of materials are leached. The Li leaching rate in the third leaching is 74.31%. The influence of the specific leaching times on the lithium and copper leaching effects is shown in the figure. Figure 6 shown.

[0106] After three rounds of leaching, the third leachate L3 and three batches of leaching residue were collected. The three batches of leaching residue were combined into one group. After acidification and oxidation of the third leachate L3, the above-mentioned group of leaching residues were leached. Leaching and washing were completed under the conditions of leaching temperature of 40°C and leaching time of 40 minutes, and the lithium leaching rate increased to 98.26%. The final lithium-rich leachate and final leaching residue were obtained by filtration and separation. The total lithium concentration in the lithium-rich leachate was 1.0 mol / L (based on 100 mL). The final leaching residue was a mixture of iron phosphate and graphite.

[0107] (2) Separation and purification of the final leachate

[0108] The composition and content of the final leachate were detected by inductively coupled plasma emission spectrometry. 2+ )=1.05 molar ratio was added to reduce iron powder, and mechanical stirring was continued for 30 min to complete the replacement reaction. After solid-liquid separation, the mother liquor containing lithium was detected and analyzed. M The copper ions in the crude copper were completely removed (replacement rate 100%). The crude copper was then pickled with 1 mol / L sulfuric acid at a solid-to-liquid ratio of 100 g / L, with mechanical stirring at room temperature for 1 hour to remove excess iron powder. After this treatment process, copper powder with a purity of 99.7% was obtained, with a recovery rate of 96.1%.

[0109] Inductively coupled plasma emission spectrometry was used to detect the lithium-containing mother liquor after copper removal. M The mass concentration of each ion in the solution was measured using a pH meter and the pH of the solution was 0.6.

[0110] Prepare the extractant, which is di(2-ethylhexyl) phosphate (P204) diluted with kerosene, where the volume fraction of P204 is 40%. At room temperature, the extractant is mixed with the lithium-containing mother liquor L diluted with water. F After mixing (O / A=1:1) and extracting in a water bath constant temperature oscillator for 30 min, an iron-loaded extraction phase and a mixed solution of aluminum sulfate and lithium sulfate (raffinate phase) can be obtained. At this time, the iron ion extraction rate is more than 99%.

[0111] The iron-laden extract is mixed with 1.5 mol / L sulfuric acid (O / A = 1:1) at room temperature and stripped in a water bath in a thermostatic oscillator for 30 minutes. After three stripping steps, an empty organic phase and an iron-enriched aqueous phase are obtained. The empty organic phase can be reused for iron extraction; the iron-enriched aqueous phase, primarily composed of ferric sulfate, is recycled as the leaching agent in the leaching step.

[0112] The extractant was re-prepared, remaining unchanged: di(2-ethylhexyl) phosphate (P204) diluted with kerosene, with a P204 volume fraction of 40%. A 0.5 mol / L LiOH solution was then added to the extractant for saponification, resulting in a saponification degree of 40%. The saponified organic phase was mixed with the water-diluted raffinate (a mixed solution of aluminum sulfate and lithium sulfate) in equal volumes at room temperature and extracted in a thermostatically controlled water bath for 30 minutes. After three extraction steps, the aluminum-loaded extract phase and a relatively pure lithium sulfate solution (raffinate phase) were obtained.

[0113] At room temperature, the aluminum-laden extract is mixed with 1.5 mol / L sulfuric acid (O / A = 1:1) and stripped in a water bath oscillator for 30 minutes. After multiple stripping steps, an empty organic phase and an aluminum-enriched aqueous phase are obtained. The empty organic phase can be used again to extract aluminum; the aluminum-enriched aqueous phase, primarily composed of aluminum sulfate and sulfuric acid, is evaporated and crystallized to yield aluminum sulfate crystals with water of crystallization.

[0114] (3) Final leaching residue separation and regeneration

[0115] Add 1.5 mol / L dilute sulfuric acid solution to the final leaching residue with a solid-liquid ratio of 200 g / L and react at 60°C for 2 h. Solid-liquid separation is performed to obtain crude graphite and ferric phosphate solution L A The crude graphite was washed several times with 0.05 mol / L dilute sulfuric acid in small amounts, and then calcined at 600°C in a nitrogen atmosphere to remove the binder PVDF and other substances, thereby obtaining relatively pure regenerated graphite.

[0116] The above washing liquid and ferric phosphate solution L A Mix, use potassium dichromate titration method to detect the amount of ferrous ions in the lithium-containing leachate, add Fe 2+ The molar ratio of hydrogen peroxide was 0.6, and the reaction was carried out at room temperature for 20 min to convert it into Fe 3+ The iron-phosphorus molar ratio was then adjusted to 1.0 using phosphoric acid.

[0117] Subsequently, a 2 mol / L potassium hydroxide solution was added dropwise, and the pH of the system was precisely controlled to 2.0. The reaction was then continued at 80°C for 2 hours. After the reaction was completed, crude ferric phosphate was obtained through solid-liquid separation. The surface potassium sulfate crystals were then washed off with deionized water in small amounts multiple times to obtain amorphous ferric phosphate. The phosphate was then placed in a 0.5 mol / L phosphoric acid solution and aged at 80°C for 4 hours to crystallize, thereby preparing high-purity ferric phosphate dihydrate. Finally, calcination at 600°C for 2 hours converted the phosphate into anhydrous ferric phosphate crystals with a purity of 98% and a recovery rate of 96%.

[0118] The above-described embodiments merely illustrate several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. Persons skilled in the art will readily appreciate that variations and modifications may be made without departing from the scope of the present invention, all of which fall within the scope of protection of the present invention.

Claims

1. A method for recycling leaching of lithium iron phosphate mixed powder by iron salt and recovery of all components, characterized in that: The following steps are involved: S1. Using an iron salt solution as a leaching agent, the iron salt solution is fully mixed with the waste lithium iron phosphate positive and negative electrode mixed powders to perform a leaching reaction to obtain a leachate and a leach residue; the iron salt is ferric chloride or ferric sulfate; S2, the leachate is regenerated by acidification and oxidation; the resulting regenerated leaching agent is returned to S1 to carry out leaching reaction on the next batch of positive and negative electrode mixed powders, and the acidification, oxidation, regeneration and leaching are repeated until the regenerated leaching agent reaches a predetermined regeneration number; S3, combining the leaching residues obtained from S1 and S2 into several groups, and sequentially performing re-leaching reaction with the regenerated leaching agent after S2 reaches a predetermined regeneration number to obtain the final leachate and final leaching residue; S4, adding iron powder to the final leachate to replace copper ions to obtain crude copper and a lithium-containing mother liquor; adding acid to the crude copper, performing solid-liquid separation to obtain industrial-grade copper powder and a ferrous ion solution; oxidizing the ferrous ion solution, and then performing vacuum distillation to obtain an iron salt solution as a leaching agent; S5, adding an extractant to the lithium-containing mother liquor of S4, and selectively extracting iron and aluminum in multiple stages to obtain an extraction phase loaded with iron ions, an extraction phase loaded with aluminum ions, and an extraction phase containing Li + The two types of extract phases are stripped and post-treated to recover iron and aluminum; S6. Acid is added to the final leaching residue of S3 to dissolve the ferric phosphate, and solid-liquid separation is performed to obtain crude graphite and ferric phosphate acid solution; the crude graphite is washed and calcined to obtain regenerated graphite; a phosphorus source or an iron source is added to the ferric phosphate acid solution to adjust the iron-phosphorus material ratio, and then hydrogen peroxide is added to oxidize the ferrous ions therein, and then an alkali solution is added to fully react to obtain crude ferric phosphate; the crude ferric phosphate is washed, aged, crystallized, and calcined to prepare anhydrous ferric phosphate.

2. The method according to claim 1, wherein: The waste lithium iron phosphate positive and negative electrode mixed powder is obtained by discharging and mechanically disassembling waste lithium iron phosphate batteries. In addition to the positive electrode material lithium iron phosphate and the negative electrode material graphite, it is allowed to contain one or more of a binder, a current collector, and an electrolyte.

3. The method according to claim 1, wherein: In step S1, the iron ions in the leaching agent and the Li + The molar ratio is 1.0-2.0; the solid-liquid ratio of lithium iron phosphate positive and negative electrode powders to the leaching agent solution is 100-600 g / L, the reaction temperature is 20-60°C, and the reaction time is 20-60 min.

4. The method according to claim 1, wherein: The acid used for acidification in step S2 is hydrochloric acid or sulfuric acid, and the molar amount of hydrogen ions is equal to the Fe 2+ The oxidant used for oxidation is hydrogen peroxide, the mass concentration of hydrogen peroxide is 10%-30%, and the amount is Fe in the solution. 2+ 0.5-1.0 times of the molar amount, oxidation time 5-30 min, oxidation temperature 20-40℃.

5. The method according to claim 1, wherein: In step S3, the regenerated leaching agent is sequentially and continuously subjected to re-leaching reaction on each group of leached residues, during which the leachate is not reoxidized. The solid-liquid ratio of each group of re-leaching reaction is 100-600 g / L, the reaction temperature is 20-60°C, and the reaction time is 20-60 min.

6. The method according to claim 1, wherein: The amount of iron powder in step S4 is 1.0-2.0 times the copper ion content in the solution; the hydrogen ion concentration in the acid is 0.5-5.0 mol / L; the oxidant used in the ferrous oxide solution is hydrogen peroxide with a mass concentration of 10%-30%, and the amount used is the Fe content in the solution. 2+ 0.5-1.0 times of the molar amount, oxidation time 5-30 min, oxidation temperature 20-40℃.

7. The method according to claim 1, wherein: In step S5, the pH of the lithium-containing mother liquor is less than 1, and an extractant is added thereto to obtain an extract phase loaded with iron ions and a raffinate phase containing aluminum salt and lithium salt; For the treatment of the raffinate phase containing aluminum salts and lithium salts, LiOH solution is first added to the extractant for saponification treatment, with a saponification degree of 40%-80%. The saponified extractant and the raffinate phase containing aluminum salts and lithium salts are subjected to multi-stage extraction to obtain an extract phase loaded with aluminum ions and a Li-containing extract phase. + raffinate solution; The extractants are all di(2-ethylhexyl) phosphate diluted with kerosene, and the volume fraction of di(2-ethylhexyl) phosphate in the extractant is 20%-40%; in each stage of extraction, the volume ratio of the organic phase to the aqueous phase is (1-3):

1.

8. The method according to claim 1, wherein: In step S5, the two types of extract phases are stripped and post-treated to recover iron and aluminum, respectively, specifically comprising: The iron ion-loaded extraction phase is subjected to multi-stage acid stripping to obtain an empty organic phase and an aqueous phase containing iron ions. The empty organic phase is recycled as an extractant for cyclic extraction of iron, and the aqueous phase is subjected to reduced pressure distillation to obtain an iron salt leaching agent. The aluminum ion-loaded extract phase is subjected to multi-stage acid stripping to obtain an empty organic phase and an aluminum ion-containing aqueous phase. The empty organic phase is recycled as an extractant for cyclic extraction of aluminum, and the aqueous phase is evaporated and crystallized to obtain aluminum salt crystals. The acid used in all stripping processes is hydrochloric acid or sulfuric acid, and the hydrogen ion concentration in the acid is in the range of 2-8 mol / L; during the stripping process, the volume ratio of the organic phase to the aqueous phase is 1:(1-3).

9. The method according to claim 1, wherein: In step S6, the phosphorus source is one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and phosphoric acid, with an iron-phosphorus molar ratio of 0.9-1.2; the iron source is ferric chloride or ferric sulfate; the alkali solution is one or more of potassium hydroxide, sodium hydroxide, and ammonia water, with a concentration of 1.0-3.0 mol / L, and the pH is adjusted to 1.0-4.0 with the alkali solution. The reaction temperature is 50°C-80°C, and the reaction time is 2-4 h.

10. The method according to claim 1, wherein: In step S6, the crude graphite after acid washing is calcined in a nitrogen atmosphere, the calcination temperature is 450 ℃ -700 ℃, the calcination time is 1-3 h; The crude ferric phosphate is washed with deionized water and aged and crystallized with dilute phosphoric acid, the concentration of which is 0.1-1.0 mol / L, and the aging time is 2-10 h; the calcination temperature of the ferric phosphate is 300° C.-600° C., and the calcination time is 1-3 h.

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