Method for separating and recycling waste lithium iron phosphate material

Abstract

The present application relates to a kind of separation and recovery method of waste lithium iron phosphate material, belong to waste lithium battery recycling technical field.The recovery method of the present application includes using potassium ferrocyanide leaching solution to the waste lithium iron phosphate material is leached after filtration to obtain precipitate and filtrate, filtrate is separated by electrochemistry method high-purity LiOH, precipitate is removed by fire calcination to obtain iron phosphate after removing carbon-containing substance, iron phosphate is obtained by wet method base leaching iron hydroxide and phosphate salt.The recovery method of the present application can realize the full element recovery of phosphorus, iron, lithium.

Description

Technical Field

[0001] This invention relates to the field of waste lithium battery recycling technology, and in particular to a method for separating and recycling waste lithium iron phosphate materials. Background Technology

[0002] The volume of retired lithium iron phosphate batteries is enormous, and the efficient and green full-component recycling of lithium, iron, and phosphorus is an urgent need for the sustainable development of the industry.

[0003] Current mainstream recycling technologies have significant drawbacks. Pyrometallurgy requires high-temperature roasting above 1000℃, resulting in high energy consumption, emissions of toxic tail gases containing fluorine and phosphorus, and the product is only a mixed oxide of iron, phosphorus, and lithium that is difficult to separate for high-value applications. Hydrometallurgy uses complete leaching with inorganic acids, consuming 4-8 tons of acid and 3-6 tons of alkali per ton of raw material, with reagent costs exceeding 60% and more than 20 processes; it also focuses primarily on lithium extraction, with iron and phosphorus being disposed of as low-purity products at low prices or even landfilled, resulting in a resource utilization rate of less than 60% and generating large amounts of high-salt wastewater and toxic tail gases, causing serious secondary pollution. Electrochemical recovery technology based on ferricyanide redox targeting can selectively remove lithium with a relatively high lithium recovery rate, but the mixed solid phase of iron phosphate and carbon black generated at the anode lacks an effective path for iron and phosphorus separation and high-value utilization, achieving only single-element lithium recovery. Existing attempts at full-element recovery either fail to substantially separate iron and phosphorus, resulting in low added value of the product, or require repeated acid-base adjustments, have lengthy processes, and are not coupled with green delithiation processes.

[0004] In summary, existing technologies generally suffer from low resource utilization, high chemical consumption, heavy secondary pollution, and lengthy processes, and cannot simultaneously achieve high-value recovery of lithium, iron, and phosphorus. There is an urgent need to develop a new low-consumption, green, all-element coupled recovery process. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a process that can achieve the full elemental separation and recovery of lithium iron phosphate materials.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a method for separating and recycling waste lithium iron phosphate materials, comprising the following steps: S1. Add waste lithium iron phosphate powder to the leaching solution and stir to carry out ion exchange reaction. Filter to obtain solution A and precipitate A. S2. Electrolyze solution A to obtain solution B and LiOH solution; S3. After washing and drying, calcining the precipitate A yields FePO4 powder; S4. Mix FePO4 powder with alkaline solution and stir to carry out alkaline leaching reaction, then filter to obtain Fe(OH)3 precipitate and phosphate solution; In step S1, the leaching solution comprises ferricyanide, and the concentration of ferricyanide in the leaching solution is 0.25~2.0 mol / L; the pH value of the leaching solution is 4.0~6.5; and the calcination temperature in step S3 is 500~600℃.

[0007] This invention achieves the separation and recovery of all elements (phosphorus, iron, and lithium) in lithium iron phosphate materials through a highly efficient coupling of "electrochemical-pyrometallurgical-hydrometallurgical" processes. A weakly acidic environment is beneficial for improving the leaching efficiency of Li. Leaching is first performed in a weakly acidic ferricyanide solution. Taking advantage of the greater stability of ferric phosphate than ferricyanide ions, the iron in lithium iron phosphate is dissolved in the leaching solution, separating the ferric phosphate precipitate. The exchanged ferrous ions react with cyanide ions to form ferrocyanide ions, which remain in the solution along with Li ions. The chemical reactions that occur are as follows: LiFePO4+[Fe(CN)6] 3- →[Fe(CN)6] 4- +FePO4+Li + Secondly, ferrocyanide ions are oxidized to ferricyanide ions through electrochemical oxidation. During the energizing process, Li ions are enriched in another electrode chamber through the cation exchange membrane to obtain LiOH, thus achieving the separation of Li element. The electrochemical reactions occurring in the electrolytic cell are as follows: Anode: [Fe(CN)6] 4- - e - → [Fe(CN)6] 3- Cathode: 4Li + + 2H2O +O2 + 4e - → 4LiOH The separated ferric phosphate precipitate contained a large amount of carbon black, PVDF, and other carbonaceous impurities. These impurities were removed by high-temperature calcination to obtain high-purity FePO4 solid, which was then subjected to alkaline leaching, utilizing the reaction of Fe and OH- under alkaline conditions. - The precipitation reaction separates iron and phosphorus elements, yielding Fe(OH)3 and PO4. 3- Ultimately, the complete recycling of waste lithium iron phosphate materials is achieved, and the following chemical reactions occur: FePO4 + 3KOH → Fe(OH)3 + K3PO4 As a preferred embodiment of the separation and recycling method for waste lithium iron phosphate materials of the present invention, the preparation method of the leachate includes the following steps: preparing an aqueous solution of ferricyanide, adjusting the pH value, filtering to remove impurities, and obtaining a ferricyanide solution; the ferricyanide includes one or more of potassium ferricyanide and sodium ferricyanide.

[0008] In a preferred embodiment of the separation and recycling method for waste lithium iron phosphate materials of the present invention, in step S1, the solid-liquid ratio of waste lithium iron phosphate powder to leachate is 50~200 g / L; the reaction temperature of ion exchange is 25~70℃, the reaction time is 2~8 h; and the stirring speed is 200~800 rpm.

[0009] In a preferred embodiment of the separation and recycling method for waste lithium iron phosphate materials according to the present invention, the electrolysis in step S2 includes the following steps: S21. The solution A is pumped into the anode chamber for circulation, and pure water is pumped into the cathode chamber for circulation. The anode chamber and the cathode chamber are separated by a cation exchange membrane. S22. Aerate the cathode chamber; S23. Electrolysis is performed by energizing the electrolytic cell, resulting in solution B in the anode chamber and LiOH solution in the cathode chamber.

[0010] In a preferred embodiment of the separation and recycling method for waste lithium iron phosphate materials of the present invention, in step S21, the circulation flow rate of the pumped solution A is 0.5~5 L / min, and the circulation flow rate of the pumped pure water is 0.5~5 L / min; in step S22, the aeration gas includes one or more of oxygen and air, and the flow rate is 0.1~2 L / min; in step S23, the electrolysis voltage is 1.5~2.5 V.

[0011] As a preferred embodiment of the separation and recycling method for waste lithium iron phosphate materials of the present invention, the method further includes recycling the solution B and using it as the leaching solution in step S1.

[0012] In a preferred embodiment of the separation and recycling method for waste lithium iron phosphate materials of the present invention, in step S3, the washing includes washing with deionized water until the conductivity of the washing liquid is ≤100 μS / cm; the FePO4 powder has a mesh size of 200~400 mesh, and the calcination time in step S3 is 5~7 h.

[0013] In a preferred embodiment of the separation and recycling method for waste lithium iron phosphate materials of the present invention, in step S4, the solid-liquid ratio of FePO4 powder to alkaline solution is 50~150 g / L; the alkaline solution includes one or more of potassium hydroxide solution and sodium hydroxide solution; the molar ratio of alkali to FePO4 powder in the alkaline solution is (3~7):1; the alkaline leaching reaction temperature is 40~90℃, and the time is 5~7 h.

[0014] As a preferred embodiment of the separation and recycling method for waste lithium iron phosphate materials of the present invention, the method further includes converting the phosphate solution into dihydrogen phosphate, comprising the following steps: A1. Add phosphoric acid to the phosphate solution until the pH of the solution is 4-5, stir and filter to obtain solution C; A2. Concentrate solution C under reduced pressure, crystallize, wash, and dry to obtain dihydrogen phosphate; In step A1, the stirring time is 30-60 min; in step A2, the supersaturation of the solution C after vacuum concentration is 1.1-1.3, the drying temperature is 60-80℃, and the drying time is 4-8 h.

[0015] This conversion method can transform phosphates into high-value dihydrogen phosphates, enabling the high-value application of waste lithium iron phosphate materials.

[0016] Secondly, the present invention provides a separation and recycling apparatus for the above-mentioned separation and recycling method of waste lithium iron phosphate materials, comprising at least the following units: leaching and electrochemical unit, calcination unit, and alkaline leaching unit; The leaching and electrochemical unit includes a dissolving tank, a storage tank, an electrolytic cell, and a liquid pump; the calcination unit includes a washing tank, a first solid-liquid separation device, an aeration calcination device, a cooling device, and a grinding device; the alkaline leaching unit includes a solution preparation tank, an alkaline leaching reaction vessel, a second solid-liquid separation device, and a concentration detector.

[0017] The leaching and electrochemical unit includes a dissolving tank, a storage tank, an electrolytic cell, and a liquid pump; the calcination unit includes a washing tank, a first solid-liquid separation device, an aeration calcination device, a cooling device, and a grinding device; the alkaline leaching unit includes a solution preparation tank, an alkaline leaching reaction vessel, a second solid-liquid separation device, and a concentration detector.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention is the first to achieve the simultaneous and efficient recovery of the three core elements lithium, iron and phosphorus from waste lithium iron phosphate, solving the problem of low-cost disposal of iron and phosphorus elements and resource waste caused by existing technologies.

[0019] The redox-targeted electrochemical system of this invention uses lithium ferricyanide as the only electron transfer medium and can be recycled in a closed loop. The subsequent wet alkaline leaching process consumes little alkali, does not require the use of large amounts of harmful reagents, has no wastewater discharge, and generates no harmful gases. The separation process is continuous and automated, with high process safety, and is suitable for industrial safety production requirements. Detailed Implementation

[0020] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0021] Unless otherwise specified, all other materials and reagents used in the examples are commercially available.

[0022] The apparatus used in the following embodiments is as follows: (1) Leaching and Electrochemical Unit Dissolving tank: The dissolving tank is made of polytetrafluoroethylene and equipped with a stirring device such as a magnetic stirrer to dissolve and mix potassium ferricyanide raw material evenly.

[0023] Storage tank: A corrosion-resistant storage tank is installed to temporarily store the prepared potassium ferricyanide and deionized water. The tank is equipped with a level gauge and an outlet valve for easy control of the raw material output. A polypropylene membrane filter is connected between the dissolving tank and the storage tank to perform preliminary filtration of the potassium ferricyanide solution, removing solid impurities.

[0024] Electrolyzer: The electrolyzer is made of corrosion-resistant materials such as nylon. The electrolyzer structure is sealed, with a cation exchange membrane separating the anode and cathode chambers to ensure that the solutions in the anode and cathode chambers do not communicate. The electrolyzer size is designed according to production scale. The anode uses inert and corrosion-resistant titanium alloy or graphite felt electrodes, and the cathode can also use graphite felt electrodes. The electrodes are fixed to the anode and cathode chambers by a distributor, and the electrodes are sealed to the electrolyzer using fluororubber sealing rings. The power supply is an adjustable DC power supply with an output voltage range of 1-6V and stable voltage output. The positive and negative terminals of the power supply are connected to the anode and cathode respectively via wires, and the connection points between the wires and the electrodes are insulated and corrosion-resistant.

[0025] Liquid pump: A fluoroplastic centrifugal pump and polytetrafluoroethylene pipe are installed between the raw material storage tank and the anode and cathode chambers of the electrolytic cell to pump the leachate into the anode chamber and the deionized water into the cathode chamber. Flow control valves and flow meters are installed on the pipes to accurately control the liquid flow rate.

[0026] (2) Calcination unit Washing tank: A multi-stage countercurrent washing tank with a stirring device is used for multi-stage countercurrent water washing of solid materials. The stirring process ensures that the materials and washing water are fully mixed and in contact, effectively removing soluble impurities adsorbed on the solid surface.

[0027] The first solid-liquid separation equipment adopts a diaphragm filter press with a filtration accuracy of ≤5μm. It is used for solid-liquid separation and deep dehydration of washed materials to achieve efficient separation of solid materials and washing waste liquid.

[0028] Aeration calcination equipment: A programmable temperature box-type muffle furnace is selected, equipped with an atmosphere control system, a programmable temperature control system and a waste heat recovery device. The calcination temperature can be controlled within the range of 300-1000℃. Air or pure oxygen atmosphere can be introduced to achieve gradient heating and aerobic calcination of materials.

[0029] Cooling equipment: A closed-loop water-cooled cooler is used for rapid cooling of high-temperature materials after calcination. The closed structure can effectively isolate the ambient moisture and prevent the calcined products from absorbing moisture and deteriorating.

[0030] Grinding equipment: A ball mill is selected for crushing and particle size control of calcined products, so that the particle size of the material meets the requirements of subsequent processes and ensures the uniformity of subsequent alkali leaching reaction.

[0031] (3) The apparatus involved in the alkaline leaching unit Liquid preparation tank: The liquid preparation tank is made of a material resistant to strong alkali corrosion. It is equipped with a stirring device and a level gauge. It is used to prepare potassium hydroxide leaching solution of a set concentration to achieve uniform mixing of the leaching solution and real-time monitoring of the liquid level in the tank.

[0032] Alkali leaching reactor: It adopts a single-reactor intermittent structure. The main body is a jacketed constant temperature reactor. The parts of the reactor body that come into contact with the material are lined with polytetrafluoroethylene. The temperature control range is room temperature to 100℃. It is equipped with a variable frequency stirring device, feed port, discharge port and thermometer interface. It is used for constant temperature alkali leaching reaction of materials to ensure that the reaction process temperature is controllable and the materials are mixed evenly.

[0033] The second solid-liquid separation equipment uses a precision filter press with a built-in corrosion-resistant filter membrane with a pore size ≤0.22μm. It is used for high-precision solid-liquid separation of materials after alkaline leaching reaction, and achieves efficient separation of alkaline leaching filtrate and solid residue.

[0034] Concentration monitor: Installed at the filtrate outlet of the four-stage solid-liquid separation equipment, it can monitor the concentration of phosphorus and iron in the filtrate in real time, and is used to accurately determine and control the endpoint of the alkaline leaching reaction.

[0035] Example 1 One embodiment of the present invention provides a method for separating and recycling waste lithium iron phosphate materials. The method for separating and recycling waste lithium iron phosphate materials described in this embodiment is as follows: S1. Prepare 500 mL of a 0.5 mol / L potassium ferricyanide aqueous solution as the leaching solution, and adjust the pH to 4.6 using phosphoric acid. Add 25 g of waste lithium iron phosphate cathode powder to the leaching solution at a solid-liquid ratio of 50 g / L and stir at 500 rpm for 6 h. Filter to obtain solution A and precipitate A.

[0036] S2. The above solution A is pumped into the anode chamber for circulation using a liquid pump, and 100 mL of deionized water is pumped into the cathode chamber for circulation. Oxygen is introduced into the cathode chamber. The circulation flow rate of solution A is 1 L / min, the circulation flow rate of deionized water is 1 L / min, and the oxygen flow rate is 0.5 L / min. Constant voltage electrolysis is performed using a voltage of 2.2 V for 12 h. Solution B is obtained in the anode chamber, and LiOH solution is obtained in the cathode chamber. Solution B can be recycled and used as the leaching solution in step S1.

[0037] S3. Precipitate A was washed with deionized water in a three-stage countercurrent process until the conductivity of the washing solution was ≤100μS / cm. After washing, it was dehydrated using a diaphragm filter press to obtain a filter cake with a moisture content of 30%. The filter cake was vacuum dried at 105℃ and then sent to an atmosphere calcination device. Air was introduced for calcination, and the temperature was increased to 500℃ at 5℃ / min for 6 hours. After calcination, it was sent to a closed cooling device to cool to room temperature. After cooling, it was ground to 300 mesh to obtain 4.86 g of purified iron phosphate powder.

[0038] S4. Prepare a 1.5 mol / L potassium hydroxide solution, measure 97.2 mL and add it to the alkaline leaching reactor. Heat the reactor to 60℃ and add the above 4.86 g of ferric phosphate powder. At this time, the solid-liquid ratio is 50 g / L and the molar ratio of potassium hydroxide to ferric phosphate is 4.43:1. Stir the reaction for 6 h. After the reaction is completed, send the mixture to a solid-liquid separation device for pressure filtration to obtain ferric hydroxide filter cake and potassium phosphate filtrate.

[0039] S5. Add potassium phosphate to the reaction vessel and stir. Add phosphoric acid until the pH value is 4 and stir for 45 min. Filter the solution after reaction to remove trace amounts of insoluble impurities. Concentrate under reduced pressure until the supersaturation value is 1.2. Cool to crystallize. After crystallization, centrifuge to obtain potassium dihydrogen phosphate crystals. Dry at 70℃ for 6 h to obtain potassium dihydrogen phosphate powder.

[0040] Example 2 The only difference from Example 1 is the molar ratio of potassium hydroxide to ferric phosphate, which is 3.73:1. The remaining steps and parameters are the same as in Example 1.

[0041] Example 3 The only difference from Example 1 is the molar ratio of potassium hydroxide to ferric phosphate, which is 4.43:1. The remaining steps and parameters are the same as in Example 1.

[0042] Example 4 The only difference from Example 1 is the molar ratio of potassium hydroxide to ferric phosphate, which is 5.23:1. The remaining steps and parameters are the same as in Example 1.

[0043] Example 5 The only difference from Example 1 is the molar ratio of potassium hydroxide to ferric phosphate, which is 5.96:1. The remaining steps and parameters are the same as in Example 1.

[0044] Example 6 The only difference from Example 1 is the molar ratio of potassium hydroxide to ferric phosphate, which is 6.65:1. The remaining steps and parameters are the same as in Example 1.

[0045] Example 7 The only difference from Example 1 is that the concentration of the potassium ferricyanide aqueous solution is 0.25 mol / L; the rest of the steps and parameters are the same as in Example 1.

[0046] Example 8 The only difference from Example 1 is that the concentration of the potassium ferricyanide aqueous solution is 0.75 mol / L; the rest of the steps and parameters are the same as in Example 1.

[0047] Example 9 The only difference from Example 1 is that the concentration of the potassium ferricyanide aqueous solution is 1 mol / L; the rest of the steps and parameters are the same as in Example 1.

[0048] Example 10 The only difference from Example 1 is that the potassium ferricyanide aqueous solution leaching time is 4 hours; the remaining steps and parameters are the same as in Example 1. Comparative Example 1 The only difference from Example 1 is that the calcination in step S3 is not used; the remaining steps and parameters are the same as in Example 1.

[0049] Comparative Example 2 The only difference from Example 1 is that the calcination temperature in step S3 is 400°C, while the other steps and parameters are the same as in Example 1.

[0050] Comparative Example 3 The only difference from Example 1 is that the calcination temperature in step S3 is 300°C, while the other steps and parameters are the same as in Example 1.

[0051] Comparative Example 4 The only difference from Example 1 is that the pH value of the extract in step S1 is 9; the other steps and parameters are the same as in Example 1.

[0052] Comparative Example 5 The only difference from Example 1 is that the concentration of the potassium ferricyanide aqueous solution is 0.1 mol / L; the rest of the steps and parameters are the same as in Example 1.

[0053] Example of effect 1 This example examines the phosphorus recovery effect of the separation and recycling method for waste lithium iron phosphate materials of the present invention. The specific results are shown in Table 1.

[0054] Table 1 As can be seen from Table 1, calcination at excessively low temperatures or without calcination can affect the efficiency of subsequent alkaline leaching. Therefore, the calcination step plays a crucial role in the system of this invention. During alkaline leaching, a high phosphorus recovery rate can be achieved when the amount of alkali used is within the range specified in this invention. In Comparative Example 1, the calcination step was not performed, resulting in the decomposition of PVDF contained in the electrode powder under alkaline conditions. This introduced impurities into the solution, leading to a higher impurity content in the subsequently obtained potassium dihydrogen phosphate, resulting in a higher phosphorus recovery rate that deviated from the normal value.

[0055] Example 2 This example investigated the effects of the concentration and acidity / alkalinity of the potassium ferricyanide solution on the lithium leaching rate of the present invention. The specific results are shown in Table 2.

[0056] Table 2 As shown in Table 2, a low concentration of potassium ferricyanide aqueous solution significantly affects the lithium leaching rate during lithium leaching. When the leaching solution is alkaline, the selective oxidation ability of ferricyanide is reduced under alkaline conditions, thus significantly impacting the lithium leaching rate.

[0057] Example 3 This example investigated the concentration of recovered products in the lithium iron phosphate recovery method of this invention. First, the obtained LiOH was further recovered. The specific steps are as follows: The prepared LiOH-KOH mixed alkaline solution was pumped into a glass-lined stirred carbonization reactor with a steam jacket. The jacket steam was turned on to raise the temperature and maintain the liquid temperature in the reactor at a constant 90°C. CO2 gas was continuously introduced through the aeration distribution pipe at the bottom of the reactor for a constant aeration time of 30 min. During the aeration stage, white LiCO3 solid suspension precipitated gradually from the uniform transparent alkaline solution in the reactor. This example specifically investigated the purity of the recovered products Li2CO3, KH2PO4, and Fe(OH)3 in Example 10, as shown in Table 3.

[0058] Table 3 As can be seen from Table 3, the products obtained by the recovery method of the present invention have high purity. Among them, Fe(OH)3 has relatively low purity due to its high content of water of crystallization. The presence of water of crystallization does not affect the subsequent use of Fe element.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for separating and recycling waste lithium iron phosphate materials, characterized in that, Includes the following steps: S1. Add waste lithium iron phosphate powder to the leaching solution and stir to carry out ion exchange reaction. Filter to obtain solution A and precipitate A. S2. Electrolyze solution A to obtain solution B and LiOH solution; S3. After washing and drying, calcining the precipitate A yields FePO4 powder; S4. Mix FePO4 powder with alkaline solution and stir to carry out alkaline leaching reaction, then filter to obtain Fe(OH)3 precipitate and phosphate solution; In step S1, the leaching solution comprises ferricyanide, and the concentration of ferricyanide in the leaching solution is 0.25~2.0 mol / L; the pH value of the leaching solution is 4.0~6.5; and the calcination temperature in step S3 is 500~600℃.

2. The method for separating and recycling waste lithium iron phosphate materials as described in claim 1, characterized in that, The preparation method of the leaching solution includes the following steps: preparing an aqueous solution of ferricyanide, adjusting the pH, filtering to remove impurities, and obtaining a ferricyanide solution; the ferricyanide includes one or more of potassium ferricyanide and sodium ferricyanide.

3. The method for separating and recycling waste lithium iron phosphate materials as described in claim 1, characterized in that, In step S1, the solid-liquid ratio of waste lithium iron phosphate powder to leachate is 50~200 g / L; the reaction temperature of ion exchange is 25~70℃, and the reaction time is 2~8 h; the stirring speed is 200~800 rpm.

4. The method for separating and recycling waste lithium iron phosphate materials as described in claim 1, characterized in that, The electrolysis in step S2 includes the following steps: S21. The solution A is pumped into the anode chamber for circulation, and pure water is pumped into the cathode chamber for circulation. The anode chamber and the cathode chamber are separated by a cation exchange membrane. S22. Aerate the cathode chamber; S23. Electrolysis is performed by energizing the electrolytic cell, resulting in solution B in the anode chamber and LiOH solution in the cathode chamber.

5. The method for separating and recycling waste lithium iron phosphate materials as described in claim 4, characterized in that, In step S21, the circulation flow rate of solution A pumped in is 0.5~5 L / min, and the circulation flow rate of pure water pumped in is 0.5~5 L / min; in step S22, the aeration gas includes oxygen and one or more of the air, and the flow rate is 0.1~2 L / min; in step S23, the electrolysis voltage is 1.5~2.5 V.

6. The method for separating and recycling waste lithium iron phosphate materials as described in claim 1, characterized in that, It also includes recycling the solution B and using it as the leaching solution in step S1.

7. The method for separating and recycling waste lithium iron phosphate materials as described in claim 1, characterized in that, In step S3, the washing includes washing with deionized water until the conductivity of the washing solution is ≤100 μS / cm; the FePO4 powder has a mesh size of 200~400 mesh; and the calcination time is 5~7 h.

8. The method for separating and recycling waste lithium iron phosphate materials as described in claim 1, characterized in that, In step S4, the solid-liquid ratio of FePO4 powder to alkaline solution is 50~150 g / L; the alkaline solution includes one or more of potassium hydroxide solution and sodium hydroxide solution; the molar ratio of alkali to FePO4 powder in the alkaline solution is (3~7):1; the alkaline leaching reaction temperature is 40~90℃ and the time is 5~7 h.

9. The method for separating and recycling waste lithium iron phosphate materials as described in claim 1, characterized in that, It also includes converting the phosphate solution into dihydrogen phosphate, comprising the following steps: A1. Add phosphoric acid to the phosphate solution until the pH of the solution is 4-5, stir and filter to obtain solution C; A2. Concentrate solution C under reduced pressure, crystallize, wash, and dry to obtain dihydrogen phosphate; In step A1, the stirring time is 30-60 min; in step A2, the supersaturation of the solution C after vacuum concentration is 1.1-1.3, the drying temperature is 60-80℃, and the drying time is 4-8 h.

10. A separation and recycling apparatus for the separation and recycling method of waste lithium iron phosphate material according to any one of claims 1 to 9, characterized in that, It should include at least the following units: leaching and electrochemical unit, calcination unit, and alkaline leaching unit; The leaching and electrochemical unit includes a dissolving tank, a storage tank, an electrolytic cell, and a liquid pump; the calcination unit includes a washing tank, a first solid-liquid separation device, an aeration calcination device, a cooling device, and a grinding device; the alkaline leaching unit includes a solution preparation tank, an alkaline leaching reaction vessel, a second solid-liquid separation device, and a concentration detector.

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