Resourceful treatment method for aluminum-containing iron phosphate slag and waste lithium iron phosphate material

Abstract

The invention relates to a resourceful treatment method for aluminum-containing iron phosphate and waste lithium iron phosphate materials, which comprises the following steps: sequentially or simultaneously carrying out oxidation treatment and ferric salt leaching treatment on the waste lithium iron phosphate materials to be treated, and then carrying out solid-liquid separation to obtain leachate and aluminum-containing iron phosphate slag; after the aluminum-containing iron phosphate slag is leached in an acid solution, solid-liquid separation is conducted, and a coarse graphite phase and a mixed solution containing iron, phosphorus and aluminum are obtained; and adjusting the molar ratio of iron to phosphorus of the mixed solution, adjusting the pH value of the mixed solution to 1.0-3.5, carrying out hydrothermal reaction, and carrying out solid-liquid separation, acid pickling and dehydration to obtain the aluminum-doped iron phosphate. According to the method, the traditional treatment thinking set is broken, the aluminum impurity is considered from the perspective of taking the iron phosphate material as the lithium iron phosphate precursor, the waste lithium iron phosphate material is taken as the raw material to control the content and the form of the impurity Al in the phosphorus iron slag, the aluminum-doped iron phosphate is prepared, the material performance is optimized while the impurity removal difficulty is reduced, and the product quality is improved. The electrochemical performance of subsequently synthesized lithium iron phosphate can be further improved.

Description

TECHNICAL FIELD

[0001] The present application relates to a resource processing method of aluminum-containing iron phosphate slag and waste lithium iron phosphate material, and belongs to the field of resource recycling and utilization of solid waste. BACKGROUND

[0002] Lithium iron phosphate battery has the characteristics of high theoretical capacity, high safety, low cost, long service life, good thermal stability and environmental friendliness. To further improve the energy density and cycle performance of lithium iron phosphate battery, the mainstream method is to improve the particle size, tap density and compacted density through process improvement during material preparation, or to directly improve the crystal structure of the material itself. For example, small particle size lithium iron phosphate material can be prepared, which can improve the tap density and compacted density, and thus improve the energy density, but this method will increase the specific surface area, which is not conducive to the processing of battery electrodes. For another example, the lithium iron phosphate crystal structure is improved, which directly changes its properties and obtains the required material. This method is mainly realized by doping metal ions.

[0003] Doping Al 3+ is one of the common methods to improve the crystal structure of lithium iron phosphate and thus improve its performance. The valence of Al 3+ is equivalent to that of Fe 3+ , and it is not easy to be reduced to Al 2+ . Thus, in the preparation of lithium iron phosphate, the position of iron in LiFePO4 forms a mixed state of Fe 2+ / Fe 3+ -Al 3+ , which improves the conductivity and reduces the resistance, and thus improves the energy density. In addition, appropriate low concentration doping will not destroy the olivine structure of lithium iron phosphate, and can maintain its high stability, thereby improving the cycle performance. Moreover, aluminum is cheap and will not increase the cost. Therefore, doping aluminum in lithium iron phosphate is a good choice.

[0004] Chinese patent application specification CN113979420A discloses a preparation method of high-compact long-cycle aluminum-doped lithium iron phosphate positive electrode material. A precursor solution is prepared by proportioning soluble lithium source, iron source, phosphorus source, aluminum source and carbon source, and then aluminum-doped lithium iron phosphate material is hydrothermally synthesized in a high-temperature inert gas atmosphere. The aluminum source is one or more of nano-sized aluminum oxide, aluminum chloride, aluminum sulfate, aluminum nitrate and aluminum hydroxide, which finally realizes the optimization and modification of lithium iron phosphate material and improves its electrochemical performance and safety performance.

[0005] However, with the widespread use of lithium iron phosphate batteries and the resulting battery disposal, more and more recycled lithium iron phosphate is entering the lithium iron phosphate battery manufacturing process. Currently, waste lithium iron phosphate materials often contain aluminum impurities that have not been thoroughly separated through beneficiation. The current industrial recycling process often adopts a method similar to that described in CN112811404A for recycling waste lithium iron phosphate cathode powder: only lithium elements and crude iron phosphate are recovered. If it is desired to further purify the lithium-extracted iron phosphate slag into battery-grade iron phosphate, special selective precipitants are often required to selectively precipitate aluminum using chemical precipitation, or ion exchange resins with special functional groups are used to selectively remove aluminum using ion exchange. Furthermore, to achieve complete separation of aluminum impurities, complex impurity removal methods or lengthy process flows are often required; alternatively, other aluminum removal processes may be used.

[0006] For example, Chinese invention patent application CN113880063A discloses a method for removing aluminum from ferrophosphate slag after lithium extraction from waste lithium iron phosphate and a method for preparing battery-grade ferrophosphate. This method uses one of pyridine carboxylic acid compounds, quinoline carboxylic acid compounds, and isoquinoline-3-carboxylic acid compounds as an aluminum remover. Under inert gas protection, it selectively reduces and leaches Fe and P elements while precipitating Al impurities, thereby obtaining a pure ferrous phosphate solution for the preparation of battery-grade ferrophosphate. This aluminum removal method introduces organic reagents for complexation and impurity removal, leading to an increase in the organic content of the solution system, which adversely affects the morphology and electrochemical performance of the synthesized ferrophosphate, and also increases wastewater treatment costs.

[0007] Chinese invention patent application CN202310285978.6 discloses a method for recycling and reusing waste lithium iron phosphate batteries. This method uses a prepared β-cyclodextrin / NaOH inclusion complex as a selective precipitant to selectively remove the main impurity elements Al and Cu. While the process is relatively short, the preparation of the β-cyclodextrin / NaOH inclusion complex requires spray drying facilities, and the impurity removal process requires nitrogen protection throughout. This results in high reagent costs, preparation costs, equipment investment, and operational requirements. Furthermore, the final purity of the recovered Li₂CO₃ and FePO₄ is 98.13% and 99.87%, respectively, which does not meet the relevant standards for battery-grade products, thus limiting its practical application value.

[0008] Chinese invention patent application CN114920226A discloses a method for removing aluminum and copper impurities from the iron-phosphate slag after lithium extraction from lithium iron phosphate batteries. The method employs fluoride salt roasting and selective acid leaching to remove Al and Cu impurities, thus achieving the removal of aluminum impurities from the iron-phosphate slag. The remaining iron-phosphate material can then be used to prepare battery-grade iron phosphate. However, this aluminum removal method requires fluoride salt roasting, which severely corrodes the roasting equipment, and the generated fluorine-containing gases are not properly treated, posing serious environmental problems.

[0009] Existing technologies also include methods for directly preparing doped iron phosphate products from waste iron phosphate batteries. For example, Chinese invention patent application CN 111977628 A discloses a method for recovering and preparing lithium iron phosphate from lithium-ion batteries. This method involves air-classifying and leaching waste lithium iron phosphate material to prepare aluminum-containing iron phosphate as a precursor for synthesizing lithium iron phosphate materials. However, this process cannot handle waste battery materials with many impurities and lacks methods for removing other impurity metals. Typically, lithium-ion batteries are slightly contaminated by impurity elements during conventional salt discharge, and subsequent drying is required before air-classification. Domestic and international air-classification technologies cannot completely separate waste lithium iron phosphate from graphite and aluminum foil, especially for retired batteries with excessive cycle counts or severely corroded battery cathodes. Generally, after air-classification and sieving, the Al impurity content is >0.2%. In this patent case, after subsequent phosphoric acid treatment to synthesize iron phosphate, aluminum will also be converted to aluminum phosphate. The scheme has no special aluminum removal steps other than air-classification, and the final aluminum impurity content in the iron phosphate is approximately 3%. It is evident that air-classification and sieving cannot reduce the main impurities to a low level. If the waste material itself contains a large number of impurities, it is impossible to reduce them to battery-grade levels simply through air classification, which will significantly impact the performance of subsequent lithium iron phosphate materials. Therefore, this patent is more suitable for high-purity, easily peelable waste cathode materials, and is not feasible for production of battery waste with high impurity content.

[0010] Furthermore, while existing technologies for the initial recycling of spent lithium iron phosphate batteries involve co-extraction of lithium through oxidation and acid leaching—for example, Chinese invention patent application CN 114644326 A discloses a catalytic recycling method for spent lithium-ion battery black powder—this process, in order to completely remove other metal ions during the catalytic recycling of lithium-ion battery black powder, results in Al-free iron phosphate as the solid material. During the recycling process, other metal elements such as Al enter the leachate, thus preventing the value-added utilization of Al metal. The resulting iron phosphate lacks Al-doped characteristics. Moreover, additional impurity removal steps are required during the subsequent lithium extraction from the leachate.

[0011] Chinese invention patent application CN 110459828A discloses a comprehensive recycling method for waste lithium iron phosphate battery cathode materials, comprising: (1) placing the pulverized waste lithium iron phosphate battery cathode material into a small amount of trivalent iron salt solution, stirring and reacting, then adding an oxidant to continue the reaction, filtering after the reaction is completed to obtain a first filtrate and a first filter cake; (2) adding alkali to the first filtrate, reacting and filtering to obtain a second filtrate and a second filter cake; (3) adding a lithium salt precipitant to the second filtrate, reacting and filtering to obtain a third filtrate and crude lithium salt. In this recycling process, the first filter cake contains iron hydroxide and iron phosphate, which requires further acid washing to obtain iron phosphate products, which easily leads to the loss of iron phosphate; in addition, it removes iron from the first filtrate by adding alkali precipitation, without considering the high-value recycling treatment of this part of iron. Summary of the Invention

[0012] In view of the shortcomings of the prior art, the purpose of this invention is to provide a resource-based treatment method for waste lithium iron phosphate materials to improve treatment efficiency; a second purpose of this invention is to provide a resource-based treatment method for aluminum-containing iron phosphate slag to achieve high-value treatment of aluminum-containing iron phosphate slag.

[0013] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0014] The resource recovery method for waste lithium iron phosphate materials includes the following steps:

[0015] S1. After the waste lithium iron phosphate material to be treated is subjected to oxidation treatment and iron salt leaching treatment in sequence or simultaneously, solid-liquid separation is performed to obtain leachate and aluminum-containing iron phosphate slag.

[0016] Among these methods, iron salt leaching is carried out under acidic conditions; during the iron salt leaching process, the Fe content in the reaction system is controlled. 3+ The initial concentration is 0.1-5 mol / L, preferably 1-2 mol / L, and more preferably, H + The initial molar amount is 0.8-1.2 times that of LiFePO4 in the waste lithium iron phosphate material to be treated; preferably, the initial liquid-solid ratio of the reaction system is 0.8:1 to 2:1, more preferably 0.9:1 to 1.5:1, and even more preferably 1:1 to 1.3:1;

[0017] S2. After leaching the aluminum-containing ferric phosphate slag in an acid solution, solid-liquid separation is performed to obtain a coarse graphite phase and a mixed solution containing iron, phosphorus, and aluminum. The iron-phosphorus molar ratio of the mixed solution is adjusted and the pH value of the mixed solution is adjusted to 1.0-3.5. Then, a hydrothermal reaction is carried out, followed by solid-liquid separation, washing, and dehydration to obtain aluminum-doped ferric phosphate. During the hydrothermal reaction, the pH value is maintained at 1.0-3.5.

[0018] Thus, oxidation treatment can oxidize the ferrous iron in waste lithium iron phosphate materials to ferric iron, facilitating lithium leaching. 3+ Under leaching conditions, AlPO4 or Al2O3 in the solid phase can be leached by Fe. 3+ Displaced and entered the liquid phase, while Fe 3+ The addition of [a specific ingredient] also effectively promoted the reaction between Li and PO4. 3- Separation, through specific Fe 3+ H + Iron salt co-leaching was carried out under certain concentration or content conditions, and the resulting leachate contained Li. + Al 3+ Fe 3+ The resulting aluminum-containing iron phosphate slag contains a small amount of aluminum and has a low lithium content, enabling efficient lithium leaching. Subsequently, the aluminum-containing iron phosphate slag is acid-dissolved to separate the graphite phase from iron, phosphorus, and aluminum. The iron-phosphorus molar ratio is then adjusted, and a hydrothermal reaction is carried out under specific conditions, causing the iron, phosphorus, and aluminum in the mixed solution to precipitate as aluminum-doped iron phosphate dihydrate. After acid washing and dehydration, crystallized aluminum-doped iron phosphate is obtained, which can be used as a precursor for the preparation of aluminum-doped lithium iron phosphate. Therefore, this invention breaks away from the traditional approach of directly recovering iron and phosphorus as pure phosphorus-containing substances such as iron phosphate and removing aluminum as an impurity in the treatment of lithium iron phosphate waste. Through oxidation treatment and iron salt leaching under specific conditions, a small amount of aluminum is retained in the leached iron phosphate slag, achieving a very high lithium leaching rate while reducing the leaching requirements for aluminum. This prepares the material for the subsequent direct preparation of aluminum-doped iron phosphate from the resulting iron phosphate slag, facilitating the separation and recovery of valuable elements such as lithium, phosphorus, and iron, and improving overall treatment efficiency.

[0019] Generally, commercially available or self-made waste lithium iron phosphate materials mainly contain aluminum foil and graphite as impurities, and have a low aluminum content. Therefore, in high-concentration, high-temperature Fe... 3+ Under leaching conditions, AlPO4 or Al2O3 in the solid phase can be leached by Fe. 3+ Displaced and entered the liquid phase, while Fe 3+ The addition of [a substance] can also effectively promote the reaction between Li and PO4 through displacement reaction. 3- The separation of the lithium and the synergistic leaching of the lithium with the acid are achieved.

[0020] Optionally, the waste lithium iron phosphate material contains 2-5% Li, 20-40% Fe, 14-30% P, and 0.05-2% Al.

[0021] Furthermore, the waste lithium iron phosphate material contains 2.5-4% Li, 25-35% Fe, 16-28% P, and 0.1-1.5% Al.

[0022] Furthermore, the waste lithium iron phosphate material contains 2.8-3.8% Li, 28-33% Fe, 18-25% P, and 0.2-1.3% Al.

[0023] Optionally, the aluminum content in the aluminum-containing ferric phosphate slag is 0.05-1 wt%, and more specifically 0.1-0.8 wt%.

[0024] Preferably, the aluminum content in the aluminum-containing ferric phosphate slag is 0.4-0.6 wt%.

[0025] Furthermore, in S1, the waste lithium iron phosphate material to be treated is subjected to oxidative roasting and iron salt leaching treatment in sequence; or, the waste lithium iron phosphate material to be treated is subjected to oxidative leaching and iron salt leaching treatment simultaneously.

[0026] Preferably, the oxidation and calcination are carried out at 550-650℃ for 1-10 hours; more preferably, the oxidation and calcination are carried out at 580-620℃ for 3-6 hours.

[0027] Optionally, the waste lithium iron phosphate material is in powder form;

[0028] Optionally, the waste lithium iron phosphate material is placed in a rotary kiln under air, oxygen-enriched atmosphere, or oxygen atmosphere for oxidative roasting treatment. Using a rotary kiln allows for continuous feeding and discharging, improving processing efficiency. The oxygen volume content in the oxygen-enriched atmosphere is 25% or more, preferably 50% or more, more preferably 75% or more, and most preferably 90% or more.

[0029] Preferably, after oxidative roasting, the Fe content in the resulting roasted material is... 2+ Content less than 0.5%;

[0030] Preferably, the oxidant used in the oxidative leaching process includes one or more of H2O2, NaClO3, NaClO, O2, and O3;

[0031] Preferably, the amount of oxidant used in the oxidative leaching process is such that the Fe content in the waste lithium iron phosphate material to be treated is reduced. 2+ Completely oxidized to Fe 3+ 1.1 to 2 times the theoretical amount required.

[0032] Furthermore, in S1, during the iron salt leaching process, the leaching temperature is controlled at 85-100℃.

[0033] Furthermore, in S1, the leaching time is 0.5-5h, even further 1-4h, and still further 1.5-3h, preferably 2-2.5h.

[0034] Furthermore, in S1, iron salt leaching treatment is carried out in an acidic solution of water-soluble iron salt;

[0035] Preferably, the water-soluble iron salt includes one or more of ferric chloride, ferric sulfate, and ferric nitrate;

[0036] Preferably, the acid is one or more of hydrochloric acid, nitric acid, and sulfuric acid.

[0037] Furthermore, some or all of the leachate is used to treat the iron salts of the next batch of waste lithium iron phosphate material;

[0038] Preferably, when Al in the leachate 3+ When the concentration reaches 5-10 g / L, the pH of the leachate is adjusted to 6-8. After co-precipitation, solid-liquid separation is performed to obtain polyaluminum iron hydroxide and a lithium-rich solution. Then, the polyaluminum iron hydroxide is dehydrated to obtain a composite aluminum iron flocculant. In this way, aluminum and iron in the system are precipitated, which prepares the initial stage for subsequent lithium precipitation. At the same time, the produced composite aluminum iron flocculant is a commonly used water treatment agent on the market with large market demand and can be sold as a by-product to further improve treatment efficiency.

[0039] Preferably, after purifying and removing impurities from the lithium-rich solution, lithium is precipitated to obtain a lithium salt product that can reach battery grade.

[0040] Preferably, the dehydration treatment is carried out at 105-150℃.

[0041] The leachate mainly contains leached Li + Al 3+ and excessive Fe 3+ The solution, due to the high concentration of Fe 3+ The primary approach is to promote displacement from a thermodynamic perspective. In reality, very little is consumed in the reaction, and the substances can be recycled, thus controlling the amount of Fe. 3+ The concentration can be set at the target concentration, and the required acid can be replenished in each cycle according to the amount of newly processed lithium iron phosphate material.

[0042] Optionally, the pH of the leachate is adjusted to 6-8 by adding alkali. Optionally, the alkali is one or more of sodium hydroxide, potassium hydroxide, ammonia, and sodium oxide.

[0043] Optionally, water-soluble carbonates are added to precipitate lithium. Optionally, the lithium salt product is a lithium carbonate product.

[0044] Furthermore, in S2, during leaching, the H in the reaction system is controlled. + The initial molar amount is 1.0-1.8 times the molar amount of Fe, preferably 1.2-1.6 times.

[0045] Furthermore, in S2, when the hydrothermal reaction is carried out, the reaction is carried out at 60-130℃ for 2-16 hours, preferably at 80-120℃ for 4-12 hours;

[0046] Preferably, when adjusting the pH value of the mixed solution, the rate of change of pH value is controlled to be 0.1-0.2 / s;

[0047] Preferably, the acid solution includes one or more of hydrochloric acid, sulfuric acid, and nitric acid;

[0048] Preferably, the iron-phosphorus molar ratio of the mixed solution is adjusted by one or more of phosphoric acid, water-soluble phosphate, water-soluble ferric salt, ferric hydroxide, ferrous hydroxide, water-soluble ferrous salt, and oxidant, so that the ratio of the total molar amount of Fe and Al to the molar amount of P in the mixed solution reaches the target value; more preferably, the water-soluble phosphate is one or more of Na3PO4, NaH2PO4, Na2HPO4, K3PO4, KH2PO4, and K2HPO4; the water-soluble ferrous salt is one or more of ferrous sulfate, ferrous chloride, and ferrous nitrate; and the oxidant is one or more of H2O2, Na2O2, NaClO, NaClO3, O2, and O3.

[0049] Preferably, the ratio of the total molar amount of Fe and Al to the molar amount of P in the mixed solution is controlled to be 0.97-1:1;

[0050] Preferably, OH is used. - Adjust the pH of the mixed solution with an alkaline solution of concentration <2 mol / L;

[0051] Preferably, the pH of the mixed solution is adjusted to 1.2-2.5; the pH is maintained at 1.2-2.5 during the reaction.

[0052] Preferably, during the reaction, the stirring rate is controlled at ≥200 rpm, more preferably ≥300 rpm;

[0053] Preferably, an acid pickling solution with a pH of 0.1 to 2.0 is used for washing; more preferably, the acid pickling solution includes one or more of phosphoric acid, hydrochloric acid, sulfuric acid, and nitric acid.

[0054] Preferably, the pickling temperature is ≥80℃, the number of pickling cycles is ≥3, and the pickling time is ≥20min / cycle;

[0055] More preferably, the water is dehydrated at 550-650℃ for 1-8 hours; even more preferably, the water is dehydrated at 580-620℃ for 3-5 hours; optionally, the dehydration method is roasting.

[0056] A method for the resource-based treatment of aluminum-containing ferric phosphate slag involves leaching the slag in an acid solution, followed by solid-liquid separation to obtain a coarse graphite phase and a mixed solution containing iron, phosphorus, and aluminum. The iron-phosphorus molar ratio of the mixed solution is adjusted, and the pH value is adjusted to 1.0-3.5. A hydrothermal reaction is then carried out, followed by solid-liquid separation, acid washing, and dehydration to obtain aluminum-doped ferric phosphate. During the hydrothermal reaction, the pH value is maintained at 1.0-3.5.

[0057] Furthermore, when carrying out the hydrothermal reaction, the reaction is carried out at 60-130℃ for 2-16 hours, preferably at 80-120℃ for 4-12 hours;

[0058] Preferably, when adjusting the pH value of the mixed solution, the rate of change of pH value is controlled to be 0.1-0.2 / s;

[0059] Preferably, the acid solution includes one or more of hydrochloric acid, sulfuric acid, and nitric acid;

[0060] Preferably, the iron-phosphorus molar ratio of the mixed solution is adjusted by one or more of phosphoric acid, water-soluble phosphate, water-soluble ferric salt, ferric hydroxide, ferrous hydroxide, water-soluble ferrous salt, and oxidant; more preferably, the water-soluble phosphate is one or more of Na3PO4, NaH2PO4, Na2HPO4, K3PO4, KH2PO4, and K2HPO4; the water-soluble ferrous salt is one or more of ferrous sulfate, ferrous chloride, and ferrous nitrate; and the oxidant is one or more of H2O2, Na2O2, NaClO, NaClO3, O2, and O3.

[0061] Preferably, the ratio of the total molar amount of Fe and Al to the molar amount of P in the mixed solution is controlled to be 0.97-1:1;

[0062] Furthermore, using OH - Adjust the pH of the mixed solution with an alkaline solution of concentration <2 mol / L;

[0063] Preferably, the pH of the mixed solution is adjusted to 1.2-2.5; the pH is maintained at 1.2-2.5 during the reaction.

[0064] Preferably, during the reaction, the stirring rate is controlled at ≥200 rpm, more preferably ≥300 rpm;

[0065] Preferably, the reaction is carried out at 80-120℃ for 4-12 hours;

[0066] Preferably, an acid pickling solution with a pH of 0.1 to 2.0 is used for washing; more preferably, the acid pickling solution includes one or more of phosphoric acid, hydrochloric acid, sulfuric acid, and nitric acid.

[0067] Preferably, the pickling temperature is ≥80℃, the number of pickling cycles is ≥3, and the pickling time is ≥20min / cycle;

[0068] More preferably, the water is dehydrated at 550-650℃ for 1-8 hours; even more preferably, the water is dehydrated at 580-620℃ for 3-5 hours; optionally, the dehydration method is roasting.

[0069] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0070] (1) This invention uses high-concentration iron salts to leach oxidized lithium iron phosphate material under acidic conditions. This can promote the selective leaching of lithium (lithium <0.001% in the leaching residue) and, from a thermodynamic perspective, promote the selective leaching of aluminum, thereby increasing the lithium leaching rate and maximizing the purity of the iron phosphate phase. However, this method cannot completely remove AlPO4 impurities. This invention follows this approach by controlling the concentration of the iron solution used in the synergistic leaching to prepare lithium iron phosphate material with the target Al content. The Al content in the iron phosphate residue is controllable. After completely dissolving and separating the graphite insoluble matter with acid, a stable iron-phosphate solution with the target Al content is obtained. Then, crystallized aluminum-doped iron phosphate dihydrate is synthesized by high-temperature hydrothermal synthesis and slow alkali adjustment. After washing and dehydration of the residue, an aluminum-doped anhydrous iron phosphate product with the target aluminum content can be prepared as a precursor for lithium iron phosphate.

[0071] (2) This invention breaks with traditional thinking by considering aluminum impurities from the perspective of using iron phosphate materials as precursors for lithium iron phosphate. It transforms aluminum impurities into a valuable precursor for modified iron phosphate materials, laying the groundwork for subsequent optimization and modification of lithium iron phosphate materials. This invention uses waste lithium iron phosphate materials as raw materials to control the content and morphology of Al impurities in the iron phosphate slag, preparing aluminum-doped iron phosphate. This reduces the difficulty of impurity removal while optimizing material performance, further enhancing the electrochemical performance of subsequent lithium iron phosphate synthesis.

[0072] (3) This invention uses aluminum-doped iron phosphate as a precursor for modified lithium iron phosphate. From the perspective of the difficulty in separating Al impurities during the recycling of waste iron phosphate materials and crude iron phosphate materials, it considers turning waste aluminum into treasure, converting aluminum into crystalline aluminum compounds and dispersing them evenly in iron phosphate, converting waste into aluminum-doped iron phosphate for recycling, and using aluminum-doped iron phosphate as a precursor for lithium iron phosphate. Then, optimized modified lithium iron phosphate materials can be prepared by carbothermal reduction, which reduces the processing difficulty and improves the processing efficiency.

[0073] (4) The present invention uses aluminum iron phosphate as raw material and performs high-temperature hydrothermal synthesis under specific conditions. The phosphorus, iron and aluminum in aluminum iron phosphate can be recovered in the form of aluminum iron phosphate. The resulting aluminum iron phosphate is a high-performance lithium iron phosphate precursor and can be used to prepare high-performance aluminum iron phosphate materials by conventional methods. Attached Figure Description

[0074] Figure 1 This is a flowchart of a method for the resource utilization of waste lithium iron phosphate material according to the present invention.

[0075] Figure 2 This is the XRD pattern of aluminum-doped iron phosphate obtained in Example 1 of the present invention.

[0076] Figure 3 This is a SEM image of aluminum-doped iron phosphate obtained in Example 1 of the present invention. Detailed Implementation

[0077] The present invention will be described in detail below with reference to embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be combined with each other. Unless otherwise specified, the relevant percentages refer to mass percentages.

[0078] Example 1

[0079] The resource recovery method for waste lithium iron phosphate material in this embodiment includes the following steps:

[0080] S1. Waste lithium iron phosphate material with a Li content of 3.473%, Fe content of 31.78%, P content of 21.82%, and Al content of 0.93% was oxidized and roasted at 600℃ for 4 hours, and then subjected to iron salt leaching treatment with an iron salt leaching solution, wherein the iron salt leaching solution is a mixed solution of ferric chloride and hydrochloric acid, and the leaching temperature is 95℃. The Fe content in the reaction system is... 3+ The initial concentration was 1 mol / L, H + The initial molar amount of the waste lithium iron phosphate material to be treated was 1.1 times that of LiFePO4, and the initial liquid-solid ratio was 1 mL: 1 g. After leaching for 2 h, solid-liquid separation was performed to obtain leachate (the leaching rate of lithium was 99.9%) and aluminum-containing iron phosphate slag (containing 0.006% Li and 0.394% Al).

[0081] S2. The aluminum-containing ferric phosphate slag is leached in a sulfuric acid solution, where H2O is present in the sulfuric acid solution. +The initial molar amount was 1.1 times the molar amount of Fe in the corresponding aluminum-containing ferric phosphate slag. After the reaction, solid-liquid separation was performed to obtain a crude graphite phase and a mixed solution containing iron, phosphorus, and aluminum. Ferric chloride was then used to adjust the ratio of the total molar amount of Fe and Al to the molar amount of P in the mixed solution to 1:1. The pH of the mixed solution was adjusted to 1.6 ± 0.1 using 0.5 mol / L NH3·H2O solution, with the pH change rate controlled within the range of 0.1-0.2 / s. The reaction was then carried out at 110℃ and 500 rpm for 8 hours, maintaining a pH of 1.6 ± 0.1 during the reaction. Solid-liquid separation was performed, and washing was carried out with hydrochloric acid solution of pH = 0.2 at 85℃ for 5 times, with a washing time of 20 min / wash, to obtain aluminum-doped ferric phosphate dihydrate. Finally, it was calcined at 600℃ for 3 hours to dehydrate, obtaining aluminum-doped ferric phosphate (containing 36.643% Fe, 21.56% P, and 0.5% Al). 0.487%);

[0082] S3. Use part or all of the leachate for iron salt treatment of the next batch of waste lithium iron phosphate material; when the Al in the leachate... 3+ When the concentration reaches 6 g / L, the pH of the leachate is adjusted to 6.5 with NH3·H2O. After co-precipitation, solid-liquid separation is performed to obtain polyaluminum iron hydroxide and lithium-rich solution. Then, the polyaluminum iron hydroxide is dehydrated at 110℃ to obtain composite aluminum iron flocculant. After purification and impurity removal of the lithium-rich solution, lithium is precipitated to obtain lithium salt product.

[0083] Preparation of lithium iron phosphate by ball milling and calcination (hereinafter the same): Battery-grade aluminum-doped iron phosphate obtained in S2 and battery-grade lithium carbonate were weighed at a ratio of n(Li):n(Fe) = 1.05:1. Then, 7.5 wt.% glucose (based on the total amount of aluminum-doped iron phosphate and battery-grade lithium carbonate) was added to obtain a mixture. The mixture was then placed in a planetary ball mill with agate balls (ball-to-material ratio of 4:1) and milled at 200 rpm for 2 hours to obtain a final mixture. The mixture was placed in a tube furnace under a nitrogen atmosphere, pre-calcined at 450℃ for 5 hours, then calcined at 700℃ for 10 hours, and finally cooled to room temperature to obtain Al-doped lithium iron phosphate cathode material.

[0084] The coin cell manufacturing process (hereinafter the same) is as follows: Lithium iron phosphate cathode material, conductive carbon black, and polyvinylidene fluoride are weighed in a mass ratio of 8:1:1. A certain amount of N-methylpyrrolidone is added and stirred until the slurry is uniform. The electrode slurry is uniformly coated on aluminum foil and dried in a vacuum drying oven at 120°C for 4 hours. Then, it is punched into a cathode sheet with a radius of 12 mm. In a glove box under a high-purity argon atmosphere, a CR2025 coin cell is assembled using a 150*1 mm lithium metal sheet as the negative electrode, 1 mol / L LiPF6 dissolved in a mixed solvent (DMC, EMC, and EC in a volume ratio of 1:1:1) as the electrolyte, and polyethylene (Celgard 2400) as the separator.

[0085] Figure 2 The XRD pattern of the obtained aluminum-doped iron phosphate shows that the aluminum-doped iron phosphate is crystallized aluminum-doped iron phosphate. In addition to the main characteristic peak of iron phosphate, there are also characteristic peaks of aluminum element due to aluminum doping. Figure 3 The SEM image of the obtained aluminum-doped iron phosphate shows that the material surface is uniform and smooth, the nanoparticles are obvious, and the morphology is excellent.

[0086] Example 2

[0087] The resource recovery method for waste lithium iron phosphate material in this embodiment includes the following steps:

[0088] S1. Waste lithium iron phosphate material with a Li content of 3.473%, Fe content of 31.78%, P content of 21.82%, and Al content of 0.93% is simultaneously subjected to oxidation treatment and iron salt leaching treatment. The iron salt leaching solution is a mixed solution of ferric sulfate and sulfuric acid. The Fe content in the reaction system is controlled. 3+ The initial concentration was 5 mol / L, H + The initial molar amount of the leaching agent was 1.1 times that of LiFePO4 in the waste lithium iron phosphate material to be treated, the initial liquid-to-solid ratio was 1 mL:1 g, and the leaching temperature was 95 °C. During iron salt leaching, H2O2 was added for simultaneous oxidative leaching. The amount of H2O2 used in the oxidative leaching process was such that the Fe content in the waste lithium iron phosphate material to be treated was reduced. 2+ Completely oxidized to Fe 3+ The required amount was 1.8 times the theoretical amount; after 2 hours of reaction, solid-liquid separation was performed to obtain leachate (lithium leaching rate of 99.9%) and aluminum-containing iron phosphate slag (containing 0.001% Li and 0.068% Al);

[0089] S2. The aluminum-containing ferric phosphate slag is leached in hydrochloric acid solution, and the hydrochloric acid solution contains H... +The initial molar amount of Fe was 1.1 times that of Fe in the corresponding aluminum-containing ferric phosphate slag. After the reaction, solid and liquid were separated to obtain a crude graphite phase and a mixed solution containing iron, phosphorus, and aluminum. Then, the ratio of the total molar amount of Fe and Al to the molar amount of P in the mixed solution was adjusted to 1:1 using ferric sulfate. The pH of the mixed solution was then adjusted to 1.7±0.1 using 0.2 mol / L NaOH solution, with the pH change rate controlled within the range of 0.1-0.2 / s. The reaction was then carried out at 110℃ and 500 rpm for 10 h, maintaining the pH at 1.7±0.1 during the reaction. Solid and liquid were then separated, and aluminum-doped ferric phosphate dihydrate was obtained by washing. The washing was performed using a mixed acid solution of phosphoric acid and hydrochloric acid with pH=0.15 at 90℃, 5 times, and 20 min per wash. Finally, it was calcined at 580℃ for 4 hours to remove water, and aluminum-doped iron phosphate (containing 36.6% Fe, 21.01% P, and 0.08% Al) was obtained.

[0090] S3. Use part or all of the leachate to treat the iron salts of the next batch of waste lithium iron phosphate material.

[0091] When Al in the leachate 3+ When the concentration reaches 10 g / L, the pH of the leachate is adjusted to 7.5 with NaOH. After co-precipitation, solid-liquid separation is performed to obtain polyaluminum iron hydroxide and lithium-rich solution. Then, the polyaluminum iron hydroxide is dehydrated at 140℃ to obtain composite aluminum iron flocculant. After purification and impurity removal of the lithium-rich solution, lithium is precipitated to obtain lithium salt product.

[0092] Comparative Example 1

[0093] The resource recovery method for waste lithium iron phosphate material in this comparative example includes the following steps:

[0094] S1. Waste lithium iron phosphate material with a Li content of 3.473%, Fe content of 31.78%, P content of 21.82%, and Al content of 0.93% is subjected to simultaneous oxidation and leaching treatment with an iron-free salt solution. The iron-free salt solution is a hydrochloric acid solution. During iron-free salt leaching, the Fe content in the reaction system is controlled. 3+ The initial concentration was 0 mol / L (i.e., no iron salt was added), H + The initial molar amount is 1.1 times the sum of 3 times the molar amounts of Li, Fe, and Al in the waste lithium iron phosphate material to be treated; during the oxidation treatment, H2O2 is added, and the amount of H2O2 used in the oxidation leaching process is such that the Fe content in the waste lithium iron phosphate material to be treated is reduced to a certain level. 2+ Completely oxidized to Fe 3+The required amount is 1.8 times the theoretical amount; the leaching temperature is 95℃, and after leaching for 2 hours, solid-liquid separation is performed to obtain leachate (lithium leaching rate is 98.29%) and leaching residue (containing 0.053% Li and 0.89% Al);

[0095] S2. Adjust the pH of the leachate to 2.0, add 3 mol / L phosphoric acid solution to allow iron and aluminum in the leachate to fully precipitate, then separate the solid and liquid, and calcine at 600℃ for 3 hours to obtain aluminum-doped iron phosphate (containing 34.56% Fe, 20.08% P, and 0.96% Al).

[0096] The comparison shows that adding iron salts for synergistic leaching helps to promote the positive equilibrium of the Li and Al leaching reaction, and the leaching rates of both Li and Al are improved.

[0097] Comparative Example 2

[0098] Example 1 was repeated, except that undoped battery-grade iron phosphate was used when preparing lithium iron phosphate by ball milling and calcination.

[0099] Comparative Example 3

[0100] Using the aluminum-doped iron phosphate prepared in Comparative Example 1, the process of preparing lithium iron phosphate and coin cell as described in Example 1 was repeated, and the relevant electrochemical performance was characterized.

[0101] Comparative Example 4

[0102] Example 1 was repeated, except that in S2, the pH of the mixed solution was adjusted to 3.8 ± 0.1 using a 0.5 mol / L NH3·H2O solution, and then the reaction was carried out at 110°C and 500 rpm for 9 hours, maintaining the pH at 3.8 ± 0.1 during the reaction. The obtained aluminum-doped iron phosphate contained 36.62% Fe, 21.39% P, and 0.494% Al.

[0103] Comparative Example 5

[0104] Example 1 was repeated, except that in S2, the pH of the mixed solution was adjusted to 1.6 ± 0.1 using a 0.5 mol / L NH3·H2O solution, and then the reaction was carried out at 110°C and 100 rpm for 9 hours, maintaining the pH at 1.6 ± 0.1 during the reaction. The obtained aluminum-doped iron phosphate contained 36.58% Fe, 21.46% P, and 0.501% Al.

[0105] The relevant performance of the button cells obtained in each embodiment and comparative example is shown in Table 1.

[0106] Table 1

[0107]

[0108] After testing, the Al-doped lithium iron phosphate cathode material provided in Example 1, under charge-discharge testing at a rate of 0.1C between 2.5 and 4.2V, showed an initial charge-discharge specific capacity of 164 mAh g⁻¹. -1 With 160mAh g -1 The initial charge / discharge efficiency is 97%, the discharge specific capacity at 1C is 88% of the discharge specific capacity at 0.1C, and the reversible discharge specific capacity after 100 cycles at 1C is 140mAh g. -1 .

[0109] The lithium iron phosphate cathode material provided in Example 2 was tested at a charge / discharge rate of 0.1C between 2.5 and 4.2V, and the initial charge / discharge specific capacity was 157 mAh g. -1 With 150mAh g -1 The initial charge / discharge efficiency is 95%, the discharge specific capacity at 1C is 74% of the discharge specific capacity at 0.1C, and the reversible discharge specific capacity after 100 cycles at 1C is 111 mAh g. -1 .

[0110] The Al-doped lithium iron phosphate cathode material provided in Comparative Example 3 showed an initial charge-discharge specific capacity of 158 mAh g⁻¹ during a charge-discharge test at a 0.1C rate. -1 With 152mAh g -1 The initial charge / discharge efficiency is 96.8%, and the reversible discharge specific capacity after 100 cycles at 1C is 120mAh g. -1 .

[0111] Comparisons of Examples 1, 4, and 5 show that modifying the pH or reaction speed in S2 outside the specific range of this invention, although the elemental composition of the resulting aluminum-doped iron phosphate does not change significantly, the electrochemical performance indicators of the resulting coin cells, such as the initial charge-discharge specific capacity, initial charge-discharge efficiency, and capacity retention, are significantly degraded. This may be because the crystal structure, morphology, or purity of the resulting aluminum-doped iron phosphate changes. This indicates that controlling specific pH ranges and reaction speeds during high-temperature hydrothermal synthesis helps obtain aluminum-doped iron phosphate with superior performance. Possible reasons include: excessively high pH in S2 may lead to the formation of iron hydroxide in the product, affecting the electrochemical performance of the resulting Al-doped lithium iron phosphate cathode material; excessively low stirring speed in S2 may result in uneven or excessively large particle sizes in the product, adversely affecting the electrochemical properties of the resulting Al-doped lithium iron phosphate cathode material.

[0112] Comparative Example 6

[0113] Example 1 is repeated, except that in S1, during the iron salt leaching treatment, the Fe content in the reaction system is controlled. 3+ The initial concentration was 0 mol / L.

[0114] As a result, the lithium leaching rate was 97.6%; the aluminum-containing ferric phosphate slag contained 0.086% Li and 0.955% Al. The obtained aluminum-doped ferric phosphate contained 36.02% Fe, 21.08% P, and 1.121% Al.

[0115] Example 3

[0116] Example 1 is repeated, except that in S1, during the iron salt leaching treatment, the Fe content in the reaction system is controlled. 3+ The initial concentration was 2 mol / L.

[0117] As a result, the lithium leaching rate was 99.9%; the aluminum-containing ferric phosphate slag contained 0.003% Li and 0.189% Al. The obtained aluminum-doped ferric phosphate contained 36.54% Fe, 21.04% P, and 0.209% Al.

[0118] Example 4

[0119] Example 1 is repeated, except that in S1, during the iron salt leaching treatment, the Fe content in the reaction system is controlled. 3+ The initial concentration was 3 mol / L.

[0120] As a result, the lithium leaching rate was 99.9%; the aluminum-containing iron phosphate slag contained 0.001% Li and 0.121% Al. The obtained aluminum-doped iron phosphate contained 36.34% Fe, 20.7% P, and 0.140% Al.

[0121] Example 5

[0122] Example 1 is repeated, except that in S1, during the iron salt leaching treatment, the Fe content in the reaction system is controlled. 3+ The initial concentration was 4 mol / L.

[0123] As a result, the lithium leaching rate was 99.9%; the aluminum-containing ferric phosphate slag contained 0.001% Li and 0.089% Al. The obtained aluminum-doped ferric phosphate contained 36.84% Fe, 21.07% P, and 0.103% Al.

[0124] The relevant performance of the button cells obtained in Comparative Example 6 and Examples 3-5 is shown in Table 2.

[0125] Table 2

[0126]

[0127] The comparison shows that using iron salt synergistic leaching and controlling the initial concentration of iron ions is beneficial to lithium leaching and promotes aluminum leaching. This makes the degree of aluminum leaching more controllable, and thus makes the aluminum content in the slag more controllable. This helps to obtain aluminum-doped iron phosphate materials with the target aluminum doping amount, thereby better meeting the needs of downstream customers and effectively improving the application value of the obtained aluminum-doped iron phosphate.

[0128] Comparative Example 7

[0129] Example 1 is repeated, except that in S1, during the iron salt leaching treatment, the H in the reaction system is controlled. + The initial molar amount is 0.6 times that of LiFePO4 in the waste lithium iron phosphate material to be treated, and the acid is sulfuric acid.

[0130] As a result, the lithium leaching rate was 61.7%; the aluminum phosphate slag contained 1.458% Li and 0.944% Al.

[0131] Comparative Example 8

[0132] Example 1 is repeated, except that in S1, during the iron salt leaching treatment, the H in the reaction system is controlled. + The initial molar amount is 0.8 times that of LiFePO4 in the waste lithium iron phosphate material to be treated, and the acid is nitric acid.

[0133] As a result, the lithium leaching rate was 83.9%; the aluminum phosphate slag contained 0.611% Li and 0.948% Al.

[0134] The comparison shows that a low initial acid concentration in S1 will lead to a significant decrease in the lithium leaching rate.

[0135] Comparative Example 9

[0136] Example 1 is repeated, except that in S1, during the iron salt leaching treatment, the H in the reaction system is controlled. + The initial molar amount is 2.0 times that of LiFePO4 in the waste lithium iron phosphate material to be treated.

[0137] As a result, the lithium leaching rate was 99.9%; the aluminum phosphate slag contained 0.004% Li and 0.610% Al. Furthermore, based on the iron and phosphorus content in the leachate, the iron loss rate was 76.45%, and the phosphorus loss rate was 73.77%.

[0138] Comparative Example 10

[0139] Example 1 is repeated, except that in S1, during the iron salt leaching treatment, the H in the reaction system is controlled. +The initial molar amount is 3.0 times that of LiFePO4 in the waste lithium iron phosphate material to be treated.

[0140] As a result, the lithium leaching rate was 99.9%; the aluminum phosphate slag contained 0.016% Li and 0.249% Al. Furthermore, based on the iron and phosphorus content in the leachate, the iron loss rate reached 86.66%, and the phosphorus loss rate reached 87.36%.

[0141] The comparison shows that the initial acid concentration in S1 is too high. Although a high lithium leaching rate can be obtained, it will lead to a large amount of iron and phosphorus dissolution and loss.

[0142] The above embodiments should be understood as being used only to illustrate the present invention more clearly, and not to limit the scope of the present invention. After reading the present invention, any modifications of the present invention in various equivalent forms by those skilled in the art fall within the scope defined by the appended claims.

Claims

1. A method for the resource-based treatment of waste lithium iron phosphate materials, characterized in that, Includes the following steps: S1. After the waste lithium iron phosphate material to be treated is subjected to oxidation treatment and iron salt leaching treatment in sequence or simultaneously, solid-liquid separation is performed to obtain leachate and aluminum-containing iron phosphate slag. Among these methods, iron salt leaching is carried out under acidic conditions; during the iron salt leaching process, the Fe content in the reaction system is controlled. 3+ The initial concentration is 0.1-5 mol / L; S2. After leaching the aluminum-containing ferric phosphate slag in an acid solution, solid-liquid separation is performed to obtain a crude graphite phase and a mixed solution containing iron, phosphorus, and aluminum. The iron-phosphorus molar ratio of the mixed solution is adjusted and the pH value is adjusted to 1.0-3.

5. Then, a hydrothermal reaction is carried out, followed by solid-liquid separation, washing, and dehydration to obtain aluminum-doped ferric phosphate. During the hydrothermal reaction, the pH value is maintained at 1.0-3.

5.

2. The resource recovery method according to claim 1, characterized in that, In S1, the waste lithium iron phosphate material to be treated is subjected to oxidative roasting and iron salt leaching treatment in sequence; or, the waste lithium iron phosphate material to be treated is subjected to oxidative leaching and iron salt leaching treatment simultaneously. Preferably, the oxidation and calcination are carried out at 550-650℃ for 1-10 hours; more preferably, the oxidation and calcination are carried out at 580-620℃ for 3-6 hours. Preferably, after oxidative roasting, the Fe content in the resulting roasted material is... 2+ Content less than 0.5%; Preferably, the oxidant used in the oxidative leaching process includes one or more of H2O2, NaClO3, NaClO, O2, and O3; Preferably, the amount of oxidant used in the oxidative leaching process is such that the Fe content in the waste lithium iron phosphate material to be treated is reduced. 2+ Completely oxidized to Fe 3+ 1.1 to 2 times the theoretical amount required.

3. The resource recovery method according to claim 1, characterized in that, In S1, during the iron salt leaching process, the leaching temperature is controlled at 85-100℃.

4. The resource recovery method according to claim 1, characterized in that, In S1, during the iron salt leaching treatment, the H in the reaction system is controlled. + The initial molar amount is 0.8-1.2 times that of LiFePO4 in the waste lithium iron phosphate material to be treated, and the initial liquid-solid ratio is 0.8:1 to 2:1; Preferably, the iron salt leaching treatment is carried out in an acidic solution of water-soluble iron salts; Preferably, the water-soluble iron salt includes one or more of ferric chloride, ferric sulfate, and ferric nitrate; Preferably, the acid is one or more of hydrochloric acid, nitric acid, and sulfuric acid.

5. The resource recovery method according to claim 1, characterized in that, Part or all of the leachate may be used to treat the iron salts of the next batch of waste lithium iron phosphate material; Preferably, when Al in the leachate 3+ When the concentration reaches 5-10 g / L, the pH of the leachate is adjusted to 6-8. After co-precipitation reaction, solid-liquid separation is performed to obtain polyaluminum iron hydroxide and lithium-rich solution. Then, the polyaluminum iron hydroxide is dehydrated to obtain composite aluminum iron flocculant. Preferably, after purifying and removing impurities from the lithium-rich solution, lithium is precipitated to obtain a lithium salt product; Preferably, the dehydration treatment is carried out at 105-150℃.

6. The resource recovery method according to claim 1, characterized in that, In S2, when the hydrothermal reaction is carried out, the reaction is carried out at 60-130℃ for 2-16 hours, preferably at 80-120℃ for 4-12 hours; Preferably, when adjusting the pH value of the mixed solution, the rate of change of pH value is controlled to be 0.1-0.2 / s; Preferably, during leaching, the H in the reaction system is controlled. + The initial molar amount is 1.0-1.8 times that of Fe, more preferably 1.2-1.6 times; Preferably, the acid solution includes one or more of hydrochloric acid, sulfuric acid, and nitric acid; Preferably, the iron-phosphorus molar ratio of the mixed solution is adjusted by one or more of phosphoric acid, water-soluble phosphate, water-soluble ferric salt, ferric hydroxide, ferrous hydroxide, water-soluble ferrous salt, and oxidant. More preferably, the water-soluble phosphate is one or more of Na3PO4, NaH2PO4, Na2HPO4, K3PO4, KH2PO4, and K2HPO4; the water-soluble ferrous salt is one or more of ferrous sulfate, ferrous chloride, and ferrous nitrate; and the oxidant is one or more of H2O2, Na2O2, NaClO, NaClO3, O2, and O3. Preferably, the ratio of the total molar amount of Fe and Al to the molar amount of P in the mixed solution is controlled to be 0.97-1:1; Preferably, OH is used. - Adjust the pH of the mixed solution with an alkaline solution of concentration <2 mol / L; Preferably, the pH of the mixed solution is adjusted to 1.2-2.5; the pH is maintained at 1.2-2.5 during the reaction. Preferably, during the reaction, the stirring rate is controlled at ≥200 rpm, more preferably ≥300 rpm.

7. The resource recovery method according to claim 1, characterized in that, In S2, an acidic washing solution with a pH of 0.1 to 2.0 is used for washing; Preferably, the pickling solution includes one or more of phosphoric acid, hydrochloric acid, sulfuric acid, and nitric acid; Preferably, the pickling temperature is ≥80℃, the number of pickling cycles is ≥3, and the pickling time is ≥20min / cycle; More preferably, the dehydration is carried out at 550-650℃ for 1-8 hours, and even more preferably, the dehydration is carried out at 580-620℃ for 3-5 hours.

8. A method for the resource-based treatment of aluminum-containing ferric phosphate slag, characterized in that, After leaching the aluminum-containing ferric phosphate slag to be treated in an acid solution, solid-liquid separation was performed to obtain a crude graphite phase and a mixed solution containing iron, phosphorus, and aluminum. After adjusting the iron-phosphorus molar ratio of the mixed solution and adjusting the pH value of the mixed solution to 1.0-3.5, a hydrothermal reaction is carried out, followed by solid-liquid separation, washing, and dehydration to obtain aluminum-doped iron phosphate. During the hydrothermal reaction, the pH value is maintained at 1.0-3.

5.

9. The resource recovery method according to claim 8, characterized in that, When carrying out the hydrothermal reaction, the reaction is carried out at 60-130℃ for 2-16 hours, preferably at 80-120℃ for 4-12 hours; Preferably, when adjusting the pH value of the mixed solution, the rate of change of pH value is controlled to be 0.1-0.2 / s; Preferably, the acid solution includes one or more of hydrochloric acid, sulfuric acid, and nitric acid; Preferably, the iron-phosphorus molar ratio of the mixed solution is adjusted by one or more of phosphoric acid, water-soluble phosphate, water-soluble ferric salt, ferric hydroxide, ferrous hydroxide, water-soluble ferrous salt, and oxidant. More preferably, the water-soluble phosphate is one or more of Na3PO4, NaH2PO4, Na2HPO4, K3PO4, KH2PO4, and K2HPO4; the water-soluble ferrous salt is one or more of ferrous sulfate, ferrous chloride, and ferrous nitrate; and the oxidant is one or more of H2O2, Na2O2, NaClO, NaClO3, O2, and O3. Preferably, the ratio of the total molar amount of Fe and Al to the molar amount of P in the mixed solution is controlled to be 0.97-1:

1.

10. The resource recovery method according to claim 8, characterized in that, Using OH - Adjust the pH of the mixed solution with an alkaline solution of concentration <2 mol / L; Preferably, the pH of the mixed solution is adjusted to 1.2-2.5; the pH is maintained at 1.2-2.5 during the reaction. Preferably, during the reaction, the stirring rate is controlled at ≥200 rpm, more preferably ≥300 rpm; Preferably, the reaction is carried out at 80-120℃ for 4-12 hours; Preferably, an acid pickling solution with a pH of 0.1 to 2.0 is used for washing; more preferably, the acid pickling solution includes one or more of phosphoric acid, hydrochloric acid, sulfuric acid, and nitric acid. Preferably, the pickling temperature is ≥80℃, the number of pickling cycles is ≥3, and the pickling time is ≥20min / cycle; More preferably, the dehydration is carried out at 550-650℃ for 1-8 hours, and even more preferably, the dehydration is carried out at 580-620℃ for 3-5 hours.

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