Method for recovering waste lithium iron phosphate battery positive electrode

Abstract

The present application provides a method for recovering a waste lithium iron phosphate battery positive electrode. After roasting and leaching treatments, impurity elements, organic matter and carbon can be substantially removed at the same time, thereby reducing the energy consumption of separately removing organic matter and carbon; a leaching treatment is then performed, such that impurity elements in waste lithium iron phosphate can be effectively removed, Li+ can also be efficiently leached out, and the loss of iron phosphate is also low. Moreover, this process has a simple impurity removal process and low costs, and is environmentally friendly.

Description

A method for recycling the positive electrode of waste lithium iron phosphate batteries

[0001] This application claims priority to Chinese Patent Application No. 202411195172.9, filed on August 29, 2024, entitled "A Method for Removing Impurities from Waste Lithium Iron Phosphate and an Iron Phosphate Product", and Chinese Patent Application No. 202411195173.3, filed on August 29, 2024, entitled "A Method for Recycling the Positive Electrode of Waste Lithium Iron Phosphate Batteries", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of waste battery recycling technology, and in particular to a method for recycling the positive electrode of waste lithium iron phosphate batteries. Background Technology

[0003] With the rapid development of the new energy vehicle industry, a large number of retired lithium iron phosphate batteries have emerged, and the number is showing a rapid growth trend. The hazardous components in retired lithium iron phosphate batteries, once released into the environment, not only cause serious pollution but also pose safety hazards such as fire and explosion. Therefore, the recycling of waste lithium iron phosphate batteries is extremely urgent. This not only solves environmental problems and eliminates safety hazards but also brings certain economic benefits.

[0004] Currently, the main methods for recycling and processing spent lithium iron phosphate batteries include hydrometallurgy, high-temperature solid-phase recovery, bioleaching, and pyrometallurgy. Hydrometallurgy is widely used in recycling spent lithium iron phosphate batteries due to its advantages such as high metal recovery rate, easy process control, low energy consumption, and less pollution. However, it has disadvantages such as difficulty in controlling the selectivity of recovered metals, small batch processing capacity, and large amounts of waste liquid. High-temperature solid-phase recovery has a relatively short process, simple operation, and does not require large amounts of acid and alkali reagents, but it requires high purity of the raw materials, as impurities can reduce the electrochemical performance of the resulting product. Bioleaching, while environmentally friendly and low-cost, has disadvantages such as low leaching rate, high environmental requirements, and long cycle time. Pyrometallurgy has the characteristics of wide application and high recovery rate, but this process is not only energy-intensive but also generates a large amount of waste gas and other pollutants, and it cannot effectively reuse various metals. Therefore, current recycling methods suffer from complex processes and high costs.

[0005] Summary of the Invention

[0006] The purpose of this application is to provide a method for recycling the positive electrode of spent lithium iron phosphate batteries, simplifying the recycling process and reducing recycling costs. The specific technical solution is as follows:

[0007] This application provides a method for recycling the positive electrode of waste lithium iron phosphate batteries, including the following steps: dismantling waste lithium iron phosphate batteries to obtain waste lithium iron phosphate, wherein the waste lithium iron phosphate includes impurity elements, removing impurities from the waste lithium iron phosphate to obtain purified iron phosphate residue;

[0008] The impurity removal process for waste lithium iron phosphate includes:

[0009] (1) Disassemble waste lithium iron phosphate batteries to obtain waste lithium iron phosphate, mix the waste lithium iron phosphate with (NH4)2SO4 and then roast to obtain roasted product.

[0010] (2) The calcined material is mixed with water to obtain a slurry, the slurry is subjected to leaching treatment, filtered to obtain leachate and filter residue, wherein the filter residue is purified ferric phosphate residue.

[0011] In some embodiments of this application, the impurity elements include aluminum and / or calcium.

[0012] In some embodiments of this application, in step (1), the mass ratio X of the waste lithium iron phosphate to (NH4)2SO4 is 1:(0.6 to 1), and the roasting temperature T1 is 250°C to 400°C and the roasting time t1 is 0.5h to 12h.

[0013] In step (2), the pH of the slurry is ≤3.

[0014] In some embodiments of this application, in step (1), the mass ratio X is 1:(0.75 to 0.85).

[0015] In some embodiments of this application, in step (1), the calcination temperature T1 is 300°C to 350°C and the time t1 is 0.5h to 4h.

[0016] In some embodiments of this application, in step (1), oxygen-containing gas, which includes air or oxygen, is continuously introduced into the roasting process.

[0017] In some embodiments of this application, in step (2), the solid-liquid ratio of the calcined material to water is 0.1 g / ml to 0.3 g / ml.

[0018] In some embodiments of this application, in step (2), the pH of the slurry is 2 ≤ pH ≤ 3.

[0019] In some embodiments of this application, in step (2), the leaching treatment temperature T2 is 15°C to 35°C and the time t2 is 0.5h to 10h.

[0020] In some embodiments of this application, in step (2), the leachate contains Li+ and the impurity elements.

[0021] In some embodiments of this application, the aluminum content in the filter residue is ≤500ppm and the calcium content is ≤100ppm.

[0022] In some embodiments of this application, the recovery method further includes: after obtaining the purified ferric phosphate residue, recovering the purified ferric phosphate residue to obtain the product ferric phosphate;

[0023] The process of recovering the purified ferric phosphate slag includes:

[0024] (3) The intermediate product is mixed with phosphoric acid solution and dissolved, then filtered to obtain the first filtrate, wherein the intermediate product is the purified iron phosphate residue;

[0025] (4) The first filtrate is mixed with water to obtain a mixed solution, and then crystallization is performed. Hydrogen peroxide is added during the crystallization process. Then the filter is filtered to obtain a filter residue and a second filtrate. The filter residue is calcined to obtain the product iron phosphate.

[0026] The pH of the mixed solution is between 0.7 and 2.5.

[0027] In some embodiments of this application, in step (3), the concentration C of the phosphoric acid solution is 1 mol / L to 6 mol / L, and the mass ratio Y of the intermediate product to the phosphoric acid solution is 1:(5 to 20).

[0028] In some embodiments of this application, in step (3), the dissolution time t2 is 3h to 12h, and the dissolution temperature T2 is 15 to 35°C.

[0029] In some embodiments of this application, in step (4), the hydrogen peroxide addition rate V is 0.017 mL / min to 0.03 mL / min; preferably, the total amount of hydrogen peroxide added is 1 ml to 2 ml for every 3 g of waste lithium iron phosphate treated; preferably, the hydrogen peroxide is added dropwise.

[0030] In some embodiments of this application, in step (4), the pH of the mixed solution is 0.9 to 1.2.

[0031] In some embodiments of this application, in step (4), the temperature T3 of the crystallization treatment is 70°C to 110°C and the time t3 is 3h to 6h; preferably, in step (4), the calcination temperature T4 is 400°C to 700°C and the time t4 is 1.5h to 6h.

[0032] In some embodiments of this application, the recovery method further includes the following steps: (5) heating the second filtrate to make its volume the same as that of the first filtrate, and then adding it to the first filtrate to continue dissolving the intermediate product.

[0033] In some embodiments of this application, in step (1), the mass ratio X of the waste lithium iron phosphate to (NH4)2SO4 is 1:(0.6 to 1); the roasting temperature T1 is 250°C to 400°C; and oxygen-containing gas, including oxygen or air, is continuously introduced during the roasting.

[0034] In some embodiments of this application, in step (2), the pH of the slurry obtained by mixing the calcined material with water is ≤3; the leachate contains Li + The intermediate product contains impurity elements, including Al and / or Ca; and contains phosphorus and iron.

[0035] In some embodiments of this application, the iron content in the product ferric phosphate is 35.7 wt% to 36.7 wt%, and the phosphorus content is 20.0 wt% to 21.1 wt%.

[0036] The beneficial effects of this application are:

[0037] This application provides a method for recycling the positive electrode of a waste lithium iron phosphate battery, comprising the following steps: dismantling the waste lithium iron phosphate battery to obtain waste lithium iron phosphate, which includes impurity elements; removing impurities from the waste lithium iron phosphate to obtain purified iron phosphate residue. The removal of impurities from the waste lithium iron phosphate includes: (1) dismantling the waste lithium iron phosphate battery to obtain waste lithium iron phosphate; mixing the waste lithium iron phosphate with (NH4)2SO4 and then roasting to obtain roasted material; (2) mixing the roasted material with water to obtain a slurry; leaching the slurry; filtering to obtain leachate and filter residue, the filter residue being purified iron phosphate residue. The recycling method provided in this application, after roasting and leaching, can essentially remove impurity elements (such as Ca, Al, etc.), organic matter, and carbon simultaneously, reducing the energy consumption of separately removing organic matter and carbon at high temperatures, thereby simplifying the recycling process and reducing recycling costs.

[0038] In this application, the roasting process only uses ammonium sulfate, which has reducing properties, to react with waste lithium iron phosphate, thereby removing the Fe... 2+ Transformed into Fe 3+ The intermediate product obtained is ferric phosphate slag (the iron-to-phosphorus ratio at this point does not meet the requirements). Further acid dissolution and crystallization are then carried out. During the crystallization process, hydrogen peroxide, an oxidant, needs to be added to prevent Fe from being released. 3+ Oxidized to Fe 2+ This is beneficial for obtaining products with a suitable iron-to-phosphorus ratio.

[0039] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0040] The accompanying drawings, which are provided to further illustrate this application and form part of this application, illustrate exemplary embodiments of this application and are used to explain this application, but do not constitute an undue limitation of this application.

[0041] Figure 1 is a flowchart of the impurity removal process in Example 1-1;

[0042] Figure 2 shows photographs of the roasted products from Comparative Examples 1-3;

[0043] Figure 3 is a flowchart of the experiment in Example 2-1;

[0044] Figure 4 is a comparison diagram of the mixed solutions in Example 2-1 and Comparative Example 2-3. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention are within the scope of protection of this invention.

[0046] In order to simplify the impurity removal process and reduce the impurity removal cost, this application provides the following technical solution:

[0047] The first aspect of this application provides a method for removing impurities from waste lithium iron phosphate, wherein the waste lithium iron phosphate includes impurity elements, the impurity elements including aluminum and / or calcium; the method includes the following steps:

[0048] (1) The waste lithium iron phosphate is mixed with (NH4)2SO4 and then roasted to obtain the roasted product;

[0049] Wherein, the mass ratio X of the waste lithium iron phosphate to (NH4)2SO4 is 1:(0.6 to 1), and the roasting temperature T1 is 250℃ to 400℃ and the roasting time t1 is 0.5h to 12h;

[0050] (2) The slurry after mixing the roasted material with water is subjected to leaching treatment and filtered to obtain leachate and filter residue, wherein the filter residue is purified ferric phosphate residue;

[0051] The pH of the slurry is ≤3.

[0052] In some embodiments of this application, in step (1), the mass ratio X is 1:(0.75 to 0.85).

[0053] In some embodiments of this application, in step (1), the calcination temperature T1 is 300°C to 350°C and the time t1 is 0.5h to 4h.

[0054] In some embodiments of this application, in step (1), oxygen-containing gas, which includes air or oxygen, is continuously introduced into the roasting process.

[0055] In some embodiments of this application, in step (1), before mixing (NH4)2SO4, it is ground and sieved, and the sieve is 50 to 200 mesh.

[0056] In some embodiments of this application, in step (2), the solid-liquid ratio of the calcined material to water is 0.1 g / ml to 0.3 g / ml.

[0057] In some embodiments of this application, in step (2), the pH of the slurry is 2 ≤ pH ≤ 3.

[0058] In some embodiments of this application, in step (2), the leaching treatment temperature T2 is 15°C to 35°C and the time t2 is 0.5h to 10h.

[0059] In some embodiments of this application, in step (2), the leachate contains Li + and the impurity elements.

[0060] In some embodiments of this application, the aluminum content in the filter residue is ≤500ppm and the calcium content is ≤100ppm.

[0061] A second aspect of this application provides an iron phosphate product, wherein the molar ratio of iron to phosphorus in the iron phosphate product is (0.96 to 1):1; the iron phosphate product is prepared from purified iron phosphate slag obtained by the impurity removal method described in any of the foregoing embodiments.

[0062] The impurity removal scheme is described in detail below:

[0063] This application provides a method for removing impurities from waste lithium iron phosphate, wherein the waste lithium iron phosphate includes impurity elements, including aluminum and / or calcium; the method includes the following steps (1) and (2):

[0064] (1) Mix waste lithium iron phosphate with (NH4)2SO4 and then roast to obtain roasted product;

[0065] The mass ratio X of waste lithium iron phosphate to (NH4)2SO4 is 1:(0.6 to 1), preferably 1:(0.75 to 0.85; for example, the mass ratio X can be 1:0.6, 1:0.65, 1:0.7, 1:0.75, 1:0.8, 1:0.85, 1:0.9, 1:0.95 or 1:1, or any two of the above ratios. The calcination temperature T1 is 250℃ to 400℃ and the time t1 is 0.5h to 12h, preferably 300℃ to 350℃ and 0.5h to 4h. For example, T1 can be 250℃, 260℃, 270℃, 280℃, 290℃, 300℃, 310℃, 320℃, 330℃, 340℃, 350℃, 360℃, 370℃, 380℃, 390℃, or 400℃, or any two of the above numbers. For example, t1 can be 0.5h, 0.6h, 0.7h, 0.8h, 0.9h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, or 12h, or any two of the above numbers. In this process, impurities (Al, Ca, etc.) in waste lithium iron phosphate are removed by roasting with (NH4)2SO4, as well as organic matter and carbon. That is, roasting alone is beneficial for achieving the purpose of Li impregnation and impurity removal in the subsequent process.

[0066] (2) The slurry obtained by mixing the calcined material with water is subjected to leaching treatment, filtered, and a leachate and filter residue are obtained. The filter residue is purified ferric phosphate residue. The pH of the slurry is ≤3, preferably 2≤pH≤3. For example, the pH of the slurry can be 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, or 2.9, or any two of the above values. In this process, Li is achieved by water leaching. + The method for separating impurity elements from iron phosphate is novel and requires less water during immersion.

[0067] This application does not particularly limit the source of waste lithium iron phosphate. For example, waste lithium iron phosphate batteries are disassembled to obtain the positive electrode. The positive electrode current collector and the positive electrode material layer of the disassembled positive electrode are separated. The obtained positive electrode material layer is also the waste lithium iron phosphate. The waste lithium iron phosphate may contain, but is not limited to, lithium iron phosphate, organic matter, carbon, etc. This application does not limit the aforementioned organic matter and carbon. For example, the organic matter may be a binder in the positive electrode material layer, and the carbon may be a conductive agent in the positive electrode material layer.

[0068] The impurity removal method provided in this application involves roasting, where impurity elements in waste lithium iron phosphate react with (NH4)2SO4 to form sulfates of the impurity elements. Iron and lithium elements in the waste lithium iron phosphate also react with (NH4)2SO4 to form iron phosphate and lithium sulfate, respectively. Simultaneously, organic matter and carbon in the waste lithium iron phosphate are removed. Subsequently, the roasted material is leached with water. Since the sulfates of the impurity elements are soluble or slightly soluble in water, while iron phosphate is insoluble, filtration after leaching separates the iron phosphate from the impurity elements. Simultaneously, lithium sulfate is soluble in water, and leaching also separates the lithium element. Therefore, the impurity removal method provided in this application can obtain purified iron phosphate slag through roasting, leaching, and filtration alone. The impurity removal process is simple, and the (NH4)2SO4 used is inexpensive, reducing the cost of impurity removal. Furthermore, the absence of alkali in the impurity removal process further reduces costs, and the water leaching method for lithium leaching and impurity element removal is more environmentally friendly. In other words, the impurity removal method provided in this application is not only simple and inexpensive, but also environmentally friendly.

[0069] In step (1), waste lithium iron phosphate and (NH4)2SO4 are mixed at a mass ratio (waste lithium iron phosphate: (NH4)2SO4 = 1:0.6~1) and then roasted. A mass ratio of waste lithium iron phosphate to (NH4)2SO4 within the range of 1:0.6~1 is beneficial for achieving a high lithium leaching rate and a low iron phosphate loss (lithium leaching rate above 90%, iron phosphate loss within 10wt%), and also ensures the effective leaching of other impurity elements (Al, Ca, etc.).

[0070] More preferably, the waste lithium iron phosphate and (NH4)2SO4 are in a mass ratio of 1:(0.75 to 0.85), which can further achieve a lithium leaching filtration rate of over 99% and an iron phosphate loss of less than 6 wt%.

[0071] In step (1), when the mass ratio X of waste lithium iron phosphate to (NH4)2SO4 is too small, for example less than 1:0.6 (e.g., 1:0.4, 1:0.3, etc.), the lithium leaching rate decreases in step (2). When the mass ratio X of waste lithium iron phosphate to (NH4)2SO4 is too large, for example greater than 1:1 (e.g., 1:1.1, 1:1.2, etc.), the excess (NH4)2SO4 will cause the Fe element in the waste lithium iron phosphate to be converted into Fe2(SO4)3, resulting in an increase in the loss of iron phosphate. Therefore, by controlling the mass ratio X of waste lithium iron phosphate to (NH4)2SO4 within the above range, iron phosphate is less likely to be lost, which is beneficial to obtaining more purified iron phosphate slag, and the lithium leaching rate is high.

[0072] During the roasting process, if the temperature T1 is too high, for example above 400℃, the waste lithium iron phosphate is easily oxidized into iron oxide, resulting in increased iron phosphate loss. More importantly, by controlling the temperature T1 within the above range, (NH4)2SO4 is in a liquid state and has an acidic pH. At temperature T1, it can react with the organic matter and carbon in the waste lithium iron phosphate, thereby removing the organic matter and carbon, avoiding high-temperature roasting for carbon and organic matter removal, and reducing energy consumption. By controlling the roasting temperature T1 within the above range, the waste lithium iron phosphate and (NH4)2SO4 can react fully, which is conducive to the formation of corresponding sulfates by impurity elements and lithium elements, and the formation of iron phosphate by iron elements. Furthermore, iron elements are not easily oxidized into iron oxide, thus achieving effective separation of iron phosphate and impurity elements in step (2), as well as sufficient leaching of lithium elements.

[0073] In step (2), after the calcined material is cooled to room temperature, it is immersed in water for Li leaching (the amount of water should not be too much, pH ≤ 3), and then filtered and dried. If the pH is below 3, aluminum will exist in ionic form; if the pH of the slurry is too high, for example, greater than 3, Al(OH)3 precipitate is easily formed, which will remain in the purified ferric phosphate residue after leaching and filtration, affecting its purity. If the pH of the slurry is too low, ferric phosphate may dissolve again in the liquid phase. By adding water to adjust the pH of the slurry within the above range, aluminum exists in ionic form and, after leaching and filtration, mainly exists in the leachate, achieving effective separation from ferric phosphate and improving the purity of the purified ferric phosphate residue.

[0074] In this process, the amount of (NH4)2SO4, the roasting temperature, and the pH of the leaching solution can significantly affect the impurity content in the crystalline lithium iron phosphate, the leaching effect, and the loss of lithium iron phosphate. In summary, the impurity removal method provided in this application, by utilizing ammonium sulfate roasting and water leaching, and controlling the mass ratio X, roasting temperature T1, and slurry pH within the above-mentioned ranges, can effectively remove impurity elements from waste lithium iron phosphate, achieving highly efficient lithium leaching. Furthermore, the impurity removal process is simple, low-cost, and environmentally friendly.

[0075] In some embodiments of this application, in step (1), oxygen-containing gas, including air or oxygen, is continuously introduced during roasting. The aluminum on the surface of waste lithium iron phosphate typically exists in oxide form, and some elemental aluminum may also be present internally. Continuously introducing oxygen-containing gas during roasting converts the internal elemental aluminum into aluminum oxide, which facilitates its reaction with (NH4)2SO4 to form aluminum sulfate. This application does not impose any particular limitation on the flow rate of the oxygen-containing gas, as long as it achieves the purpose of this application. For example, the flow rate of the oxygen-containing gas can be from 24 L / min to 36 L / min. The oxygen volume content in the oxygen-containing gas is greater than or equal to 15%.

[0076] In some embodiments of this application, step (1) includes the following reaction:

[0077] Al2O3+3(NH4)2SO4=Al2(SO4)3+6NH3+3H2O;

[0078] CaO+(NH4)2SO4=CaSO4+2NH3+H2O;

[0079] 4LiFePO4+2(NH4)2SO4+O2=4FePO4+2Li2SO4+4NH3+2H2O.

[0080] Al₂(SO₄)₃ is soluble in water, and after calcination, it can efficiently leach Al from the waste. CaSO₄ is slightly soluble in water, with a solubility of approximately 0.2 g / 100 ml. Since the Ca content in the waste is already low, even though CaSO₄ is slightly soluble in water after the reaction, it can still effectively leach out most of the Ca, ensuring that the Ca content in the resulting iron phosphate slag meets the requirements. Li₂SO₄ is soluble in water, while FePO₄ is insoluble in water. After leaching, impurity elements aluminum and calcium can be separated from iron phosphate, and lithium can also be leached.

[0081] In some embodiments of this application, in step (1), before mixing (NH4)2SO4, it is ground and sieved using a sieve with a mesh size of 50 to 200 mesh. For example, the sieve can be 50 mesh, 60 mesh, 70 mesh, 80 mesh, 100 mesh, 120 mesh, 140 mesh, 170 mesh, or 200 mesh. Grinding and sieving (NH4)2SO4 before mixing it with waste ferric phosphate facilitates thorough mixing of (NH4)2SO4 and waste ferric phosphate, allowing for complete reaction during the roasting process.

[0082] In some embodiments of this application, in step (2), the solid-liquid ratio of the calcined material to water is from 0.1 g / ml to 0.3 g / ml. For example, the solid-liquid ratio Y can be 0.1 g / ml, 0.11 g / ml, 0.12 g / ml, 0.13 g / ml, 0.14 g / ml, 0.15 g / ml, 0.16 g / ml, 0.17 g / ml, 0.18 g / ml, 0.19 g / ml, 0.2 g / ml, 0.21 g / ml, 0.22 g / ml, 0.23 g / ml, 0.24 g / ml, 0.25 g / ml, 0.26 g / ml, 0.27 g / ml, 0.28 g / ml, 0.29 g / ml, or 0.3 g / ml, or any two of the above figures. Al2(SO4)3 has a high solubility in water, while CaSO4 has a lower solubility. By adjusting the solid-liquid ratio Y within the above range, CaSO4 and Al2(SO4)3 can be fully dissolved in water during the leaching process, which is beneficial for the effective separation of ferric phosphate and impurity elements and improves the purity of the purified ferric phosphate residue.

[0083] In some embodiments of this application, in step (2), the leaching treatment temperature T2 is 15°C to 35°C, and the time t2 is 0.5h to 10h. For example, T2 can be 15°C, 16°C, 17°C, 18°C, 19°C, 20°C, 21°C, 22°C, 23°C, 24°C, 25°C, 26°C, 27°C, 28°C, 29°C, 30°C, 31°C, 32°C, 33°C, 34°C, or 35°C, or any two of the above numbers. For example, t2 can be 0.5h, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, or 10h, or any two of the above numbers. By adjusting the leaching temperature T2 and time t2 within the above range, CaSO4 and Al2(SO4)3 can be fully dissolved in water, which is beneficial to the effective separation of ferric phosphate and impurity elements, improves the purity of purified ferric phosphate slag, and reduces energy consumption.

[0084] In some embodiments of this application, in step (2), the leachate contains Li + And impurity elements. Li can be further separated. + With impurities such as Al and Ca, for example, by adjusting the pH with an alkaline solution to precipitate Al and Ca elements, and then reacting them with Li + Separation. This application does not limit the above-mentioned alkaline solution, as long as it can achieve the purpose of this application.

[0085] In some embodiments of this application, the aluminum content W1 in the filter residue is ≤500 ppm, and the calcium content W2 is ≤100 ppm. For example, W1 can be 5 ppm, 10 ppm, 20 ppm, 30 ppm, 50 ppm, 70 ppm, 90 ppm, 100 ppm, 150 ppm, 200 ppm, 250 ppm, 300 ppm, 350 ppm, 400 ppm, 450 ppm, or 500 ppm, or between any two of the above numbers. For example, the calcium content W2 can be 5 ppm, 10 ppm, 20 ppm, 30 ppm, 40 ppm, 50 ppm, 60 ppm, 70 ppm, 80 ppm, 90 ppm, or 100 ppm, or between any two of the above numbers. The aluminum and calcium content in the filter residue being within the above ranges indicates that the impurity element content in the filter residue is very low, resulting in a high purity of the purified ferric phosphate residue.

[0086] In some embodiments of this application, in step (2), the obtained filter residue is further dried to obtain purified ferric phosphate residue. This application does not limit the drying parameters, as long as they can achieve the purpose of this application.

[0087] This application also provides an iron phosphate product, wherein the molar ratio Z of iron to phosphorus in the iron phosphate product is (0.96 to 1):1; for example, the molar ratio Z can be 0.96:1, 0.97:1, 0.98:1, 0.99:1, or 1:1, or any two of the above numbers. The iron phosphate product is prepared from purified iron phosphate slag obtained by the impurity removal method in any of the foregoing embodiments, that is, the molar ratio of iron to phosphorus in the purified iron phosphate slag obtained by the impurity removal method provided in this application is (0.96 to 1):1, which meets the standard and can be used to prepare lithium iron phosphate, the positive electrode material for secondary batteries, thereby realizing the recycling and reuse of waste lithium iron phosphate materials.

[0088] In some embodiments of this application, the preparation steps for producing ferric phosphate products from purified ferric phosphate slag may include, but are not limited to, the following steps: acid dissolution, water mixing, and crystallization of the purified ferric phosphate slag to obtain the ferric phosphate product. This application does not limit the specific steps of acid dissolution, water mixing, and crystallization, as long as the desired ferric phosphate product can be obtained. For example, the acid used for acid dissolution may include, but is not limited to, at least one of phosphoric acid, hydrochloric acid, and sulfuric acid.

[0089] This application provides a method for removing impurities from waste lithium iron phosphate, which includes impurity elements, including aluminum and / or calcium. The method includes the following steps: (1) mixing waste lithium iron phosphate with (NH4)2SO4 and then roasting it, wherein the mass ratio X of waste lithium iron phosphate to (NH4)2SO4 is 1:(0.6 to 1), the roasting temperature T1 is 250℃ to 400℃, and then the slurry after mixing the roasted material with water is leached and filtered to obtain leachate and filter residue, wherein the filter residue is purified iron phosphate residue; wherein the pH of the slurry is ≤3. By using the method for removing impurities provided in this application, through roasting and leaching, and by synergistically controlling the mass ratio X, the roasting temperature T1, and the pH of the slurry within the above range, impurity elements in waste lithium iron phosphate can be effectively removed, and Li can also be removed. + The process is highly efficient in leaching, with low loss of ferric phosphate. Furthermore, the impurity removal process is simple, low-cost, and environmentally friendly.

[0090] This application utilizes (NH4)2SO4 to remove impurities from waste lithium iron phosphate through roasting, which can remove carbon and organic matter, reducing the process of high-temperature roasting to remove carbon and organic matter (after roasting at low temperature of 250°C to 400°C, immersion in water shows that carbon and organic matter have been removed), and reducing the complexity of the impurity removal process.

[0091] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time.

[0092] This application provides a method for recycling the positive electrode of waste lithium iron phosphate batteries, comprising the following steps: dismantling waste lithium iron phosphate batteries to obtain waste lithium iron phosphate, which contains impurity elements; removing impurities from the waste lithium iron phosphate to obtain purified iron phosphate residue. The removal of impurities from the waste lithium iron phosphate includes:

[0093] (1) Dismantle waste lithium iron phosphate batteries to obtain waste lithium iron phosphate, mix the waste lithium iron phosphate with (NH4)2SO4 and then roast to obtain roasted product; In this process, by roasting waste lithium iron phosphate with (NH4)2SO4, impurities (Al, Ca, etc.) in waste lithium iron phosphate are removed as well as organic matter and carbon. That is, by roasting alone, it is beneficial to achieve the purpose of Li impregnation and impurity removal in the subsequent process.

[0094] (2) The calcined material is mixed with water to obtain a slurry. The slurry is then leached and filtered to obtain a leachate and filter residue. The filter residue is purified ferric phosphate residue. In this process, Li is achieved through water leaching. + The method for separating impurity elements from iron phosphate is novel and requires less water during immersion.

[0095] By controlling the roasting process, carbon and organic matter in waste lithium iron phosphate can be removed. This process also facilitates the formation of corresponding sulfates from impurity elements and lithium, and the formation of iron phosphate from iron. Furthermore, iron is less easily oxidized to iron oxide, thus achieving effective separation of iron sulfate and impurity elements in step (2), as well as sufficient leaching of lithium. It also reduces the need for separate high-temperature roasting to remove carbon and organic matter, simplifying the recycling method. The roasted material is then leached. Aluminum exists in ionic form and, after leaching and filtration, is mainly present in the leachate, enabling effective separation from iron phosphate and reducing the content of impurity elements in the intermediate product. Therefore, in this process, lithium is effectively separated from iron phosphate through water leaching. + The method for separating impurity elements from iron phosphate is novel and requires less water during immersion. In the recycling process, removing impurities from waste lithium iron phosphate through the above steps (1) and (2) is more conducive to obtaining the product iron phosphate later.

[0096] Furthermore, current high-temperature solid-phase recycling methods primarily repair the composition and structure by adding lithium salts and carbon sources. Hydrometallurgy mainly uses acid solutions to leach lithium from waste lithium iron phosphate cathode powder into the liquid phase, then obtains lithium carbonate, lithium phosphate, or lithium chloride products through impurity removal, precipitation, and evaporation. The remaining lithium iron phosphate is discarded as residue. For example, lithium, iron, and phosphorus can be recovered using the sulfate melt permeation-oxidation coordinated control principle, but the final product's iron-phosphorus molar ratio is not within the range of (0.96 to 1:1), failing to meet the requirements of iron phosphate in the secondary battery field, thus limiting the application scope of the recycled products.

[0097] This application also provides a method for recycling the positive electrode of waste lithium iron phosphate batteries, including the following steps:

[0098] (1) Disassemble waste lithium iron phosphate batteries to obtain waste lithium iron phosphate, mix the waste lithium iron phosphate with (NH4)2SO4 and then roast to obtain roasted product.

[0099] (2) The roasted material is mixed with water and leached, and then filtered to obtain the leachate and the solid intermediate product;

[0100] (3) The intermediate product is mixed with phosphoric acid solution and dissolved, then filtered to obtain the first filtrate;

[0101] (4) The first filtrate is mixed with water to obtain a mixed solution, and then crystallization is performed. Hydrogen peroxide is added during the crystallization process. Then the solution is filtered to obtain a filter residue and a second filtrate. The filter residue is calcined to obtain the product iron phosphate. The pH of the mixed solution is 0.7 to 2.5.

[0102] In some embodiments of this application, in step (3), the concentration C of the phosphoric acid solution is 1 mol / L to 6 mol / L, and the mass ratio Y of the intermediate product to the phosphoric acid solution is 1:(5 to 20).

[0103] In some embodiments of this application, in step (3), the dissolution time t2 is 3h to 12h, and the dissolution temperature T2 is 15 to 35°C.

[0104] In some embodiments of this application, in step (4), the hydrogen peroxide addition rate V is 0.017 mL / min to 0.03 mL / min; preferably, the total amount of hydrogen peroxide added is 1 ml to 2 ml for every 3 g of waste lithium iron phosphate treated; preferably, the hydrogen peroxide is added dropwise.

[0105] In some embodiments of this application, the pH of the mixed solution is from 0.9 to 1.2.

[0106] In some embodiments of this application, in step (4), the temperature T3 of the crystallization treatment is 70°C to 110°C and the time t3 is 3h to 6h.

[0107] In some embodiments of this application, in step (4), the calcination temperature T4 is 400°C to 700°C and the time t4 is 1.5h to 6h.

[0108] In some embodiments of this application, the recovery method further includes the following steps: (5) heating the second filtrate to make its volume the same as that of the first filtrate, and then adding it to the first filtrate to continue dissolving the intermediate product.

[0109] In some embodiments of this application, in step (1), the mass ratio X of the waste lithium iron phosphate to (NH4)2SO4 is 1:(0.6 to 1); the roasting temperature T1 is 250°C to 400°C; and oxygen-containing gas, including oxygen or air, is continuously introduced during the roasting.

[0110] In some embodiments of this application, in step (2), the pH of the slurry obtained by mixing the calcined material with water is ≤3; the leachate contains Li + The intermediate product contains impurity elements, including Al and / or Ca; the intermediate product contains phosphorus and iron. In this application, slurry is also referred to as paste.

[0111] In some embodiments of this application, the iron content in the product ferric phosphate is 35.7 wt% to 36.7 wt%, and the phosphorus content is 20.0 wt% to 21.1 wt%.

[0112] The overall recycling plan is described in detail below:

[0113] Includes the following steps:

[0114] (1) Disassemble waste lithium iron phosphate batteries to obtain waste lithium iron phosphate, mix the waste lithium iron phosphate with (NH4)2SO4 and then roast to obtain roasted product.

[0115] (2) The roasted material is mixed with water for leaching treatment, and then filtered to obtain the leachate and solid intermediate product;

[0116] (3) The intermediate product was mixed with phosphoric acid solution and dissolved, then filtered to obtain the first filtrate;

[0117] (4) The first filtrate is mixed with water to obtain a mixed solution, which is then subjected to crystallization treatment. Hydrogen peroxide is added during the crystallization treatment. The solution is then filtered to obtain a filter residue and a second filtrate. The filter residue is calcined to obtain the product ferric phosphate. The pH of the mixed solution is between 0.7 and 2.5. For example, the pH of the mixed solution can be 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4 or 2.5, or between any two of the above numbers.

[0118] In this application, the solid intermediate product (i.e. filter residue) is sometimes referred to as purified ferric phosphate residue.

[0119] This application does not particularly limit the method of obtaining waste lithium iron phosphate. Exemplarily, waste lithium iron phosphate batteries are disassembled to obtain the positive electrode. The positive electrode current collector and the positive electrode material layer of the disassembled positive electrode are separated. The obtained positive electrode material layer is also the waste lithium iron phosphate. The waste lithium iron phosphate may contain, but is not limited to, lithium iron phosphate, organic matter, carbon, etc. This application does not limit the aforementioned organic matter and carbon. Exemplarily, the organic matter can be a binder in the positive electrode material layer, and the carbon can be a conductive agent in the positive electrode material layer.

[0120] The impurity removal method provided in this application involves roasting. Impurity elements in waste lithium iron phosphate react with (NH4)2SO4 to form sulfates of these impurity elements (CaSO4 and Al2(SO4)3). Iron and lithium elements in the waste lithium iron phosphate react with (NH4)2SO4 to form iron phosphate and lithium sulfate, respectively. Simultaneously, organic matter and carbon are removed from the waste lithium iron phosphate. Subsequently, the roasted product is leached with water. Since the sulfates of the impurity elements are soluble or slightly soluble in water, while iron phosphate is insoluble, filtration after leaching separates the iron phosphate from the impurity elements. Simultaneously, lithium sulfate is soluble in water, and leaching also removes lithium. Then, the intermediate product is mixed with a phosphoric acid solution. This not only fully dissolves the intermediate product, facilitating subsequent recrystallization, but more importantly, phosphoric acid provides phosphorus supplementation. A single recrystallization step yields a product with the required iron-to-phosphorus ratio, eliminating the need for further phosphorus supplementation and simplifying the process. Finally, the first filtrate obtained from dissolution and filtration is pH-adjusted with water and then subjected to crystallization. Hydrogen peroxide is added during the crystallization process to reduce the Fe content in the mixed solution. 3+ It will be converted into Fe 2+ The probability of reducing Fe 2+ The generation of phosphoric acid compounds results in the crystallization of iron phosphate, which further reduces impurity elements in iron phosphate. After crystallization, the mixture is filtered, and the resulting filter residue is calcined to obtain the product iron phosphate. The iron-to-phosphorus molar ratio is in the range of (0.96 to 1):1, which meets the requirements of iron phosphate in the field of secondary batteries.

[0121] In step (4), if the pH of the mixed solution is too low, for example below 0.7, ferric phosphate will not precipitate or the amount of precipitation will be too low during the crystallization process; if the pH is too high, for example above 2.5, white precipitate Fe(OH)3 will easily form during the crystallization process, making it impossible to obtain a product with the required iron-to-phosphorus ratio. Therefore, by adjusting the pH of the mixed solution within the above range, it is beneficial to obtain a product with the required iron-to-phosphorus ratio.

[0122] Furthermore, in this process, the pH of the mixed solution is adjusted to 0.9 to 1.2, which not only yields ferric phosphate products with a satisfactory iron-to-phosphorus ratio, but also increases the recovery rate of ferric phosphate to over 90%. Moreover, the amount of water used to adjust the pH during the recovery process is moderate, avoiding the use of large amounts of water, thereby reducing energy consumption in the subsequent evaporation and crystallization process.

[0123] Therefore, the impurity removal method provided in this application can basically remove impurity elements, organic matter and carbon simultaneously after roasting and leaching treatment, reducing the energy consumption of removing organic matter and carbon separately. In the crystallization process, only water is used to adjust the pH, avoiding the use of alkali, which is more environmentally friendly and lower in cost. At the same time, the desired iron-phosphorus molar ratio of the product iron phosphate is obtained by crystallization, which reduces the use of acid compared with the traditional method of using a large amount of acid, further reducing recycling costs and increasing the added value of waste lithium iron phosphate products.

[0124] In some embodiments of this application, in step (3), the concentration C of the phosphoric acid solution is from 1 mol / L to 6 mol / L, and the mass ratio Y of the intermediate product to the phosphoric acid solution is 1:(5 to 20). For example, the concentration C of the phosphoric acid solution can be 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, 5 mol / L, 5.5 mol / L, or 6 mol / L, or any two of the above numbers. For example, the mass ratio Y can be 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, or 1:20, or any two of the above numbers. By adjusting the concentration C and the mass ratio Y within the above range, it is beneficial for the intermediate product to dissolve fully, so as to obtain the desired iron-phosphorus molar ratio product iron phosphate in the subsequent crystallization process.

[0125] In some embodiments of this application, in step (3), the dissolution time t2 is 3h to 12h, and the dissolution temperature T2 is 15 to 35°C. For example, the dissolution time t2 can be 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, or 12h, or any two of the above numbers. For example, the dissolution temperature T2 can be 15°C, 16°C, 17°C, 18°C, 19°C, 20°C, 21°C, 22°C, 23°C, 24°C, 25°C, 26°C, 27°C, 28°C, 29°C, 30°C, 31°C, 32°C, 33°C, 34°C, or 35°C, or any two of the above numbers. By controlling the dissolution temperature T2 and time t2 within the above ranges, it is beneficial for the intermediate product to dissolve fully, so as to obtain the desired iron-phosphorus molar ratio product iron phosphate in the subsequent crystallization process.

[0126] In some embodiments of this application, in step (4), the pH of the first filtrate is adjusted with water to make the pH of the resulting mixed solution range from 0.7 to 2.5, and then crystallization is carried out. During the crystallization process, H2O2 needs to be continuously added to reduce the Fe content in the mixed solution. 3+ It will be converted into Fe2+ The probability. If H2O2 is added too quickly, the pH of the mixed solution is difficult to control, and some H2O2 may not have enough time to inhibit Fe. 3+ Converted to Fe 2+ It has already decomposed under heat (because the crystallization process takes place at high temperatures), and the decomposition of H2O2 under heat produces oxygen, which affects the crystallization of ferric phosphate, thus affecting the yield of ferric phosphate; if the H2O2 is added too slowly, H2O2 is mainly used to inhibit the crystallization of Fe. 3+ Converted to Fe 2+ While H2O2 does not decompose to produce large amounts of oxygen that would affect crystallization, it can lead to the precipitation of a large number of crystals, causing the iron phosphate crystals to agglomerate and become larger in size. Excessively large particle size may negatively impact the electrochemical performance of the subsequently synthesized lithium iron phosphate. Therefore, it is necessary to control the rate and amount of H2O2 addition and select an appropriate addition method to obtain the desired iron-phosphorus molar ratio and particle size of the product iron phosphate, and to improve the final recovery rate.

[0127] In some embodiments of this application, in step (4), the addition rate V of hydrogen peroxide is from 0.017 mL / min to 0.03 mL / min. For example, the addition rate V can be 0.017 mL / min, 0.018 mL / min, 0.019 mL / min, 0.02 mL / min, 0.021 mL / min, 0.022 mL / min, 0.023 mL / min, 0.024 mL / min, 0.025 mL / min, 0.026 mL / min, 0.027 mL / min, 0.028 mL / min, 0.029 mL / min, or 0.03 mL / min, or any two of the above values. By controlling the addition rate V of hydrogen peroxide within the above range, the partial thermal decomposition of H2O2 to produce oxygen can inhibit the crystallization of iron phosphate to a certain extent, while another part of H2O2 is used to inhibit Fe 3+ Converted to Fe 2+ This facilitates obtaining the desired iron-phosphorus molar ratio and particle size of the product iron phosphate, and improves the final recovery rate.

[0128] In this process, H2O2 needs to be added slowly and continuously during the regeneration and crystallization of ferric phosphate to prevent Fe from rising in the solution. 3+ Converted to Fe 2+ This ensures that no Fe is generated during the crystallization process. 2+ The phosphoric acid compound ensures that the product meets the iron-phosphorus ratio requirements, and by further controlling the addition rate, not only is a high yield of iron phosphate guaranteed, but also an iron phosphate product with a grain size that meets the requirements is obtained.

[0129] In some embodiments of this application, the total amount of hydrogen peroxide added is 1 ml to 2 ml per 3 g of waste lithium iron phosphate processed. For example, the amount of hydrogen peroxide added can be 1 ml, 1.1 ml, 1.2 ml, 1.3 ml, 1.4 ml, 1.5 ml, 1.6 ml, 1.7 ml, 1.8 ml, 1.9 ml, or 2 ml, or any two of the above figures. By controlling the total amount of hydrogen peroxide added within the above range, it is beneficial to obtain the desired iron-phosphorus molar ratio and particle size of the product iron phosphate, and to improve the final recovery rate.

[0130] In some embodiments of this application, hydrogen peroxide is added dropwise, which is highly operable and controllable, and also facilitates large-scale recycling and treatment.

[0131] In some embodiments of this application, in step (4), the crystallization treatment temperature T3 is 70°C to 110°C, and the time t3 is 3h to 6h. For example, the crystallization treatment temperature T3 can be 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, or 105°C, 110°C, or any two of the above numbers. For example, the crystallization treatment time t3 can be 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, or 6h, or any two of the above numbers. By controlling the crystallization treatment temperature T3 and time t3 within the above ranges, it is beneficial to achieve sufficient crystallization of ferric phosphate and improve the recovery rate of ferric phosphate.

[0132] In some embodiments of this application, in step (4), the calcination temperature T4 is 400°C to 700°C, and the time t4 is 1.5h to 6h. For example, the calcination temperature T4 can be 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, or any two of the above numbers. For example, the calcination time t4 can be 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, or 6h, or any two of the above numbers. By controlling the calcination temperature T4 and time t4 within the above ranges, it is beneficial to remove the water of crystallization from ferric phosphate and improve the purity of the ferric phosphate product.

[0133] In some embodiments of this application, the recovery method further includes the following step: (5) heating the second filtrate to make its volume the same as that of the first filtrate, and then adding it to the first filtrate to continue dissolving the intermediate product. The residual ferric phosphate in the first filtrate can be recovered again to improve the final ferric phosphate recovery rate.

[0134] In some embodiments of this application, in step (1), the mass ratio X of waste lithium iron phosphate to (NH4)2SO4 is 1:(0.6 to 1); in some embodiments of this application, in step (1), the mass ratio X is 1:(0.75 to 0.85). For example, the mass ratio X can be 1:0.6, 1:0.65, 1:0.7, 1:0.75, 1:0.8, 1:0.85, 1:0.9, 1:0.95 or 1:1, or between any two of the above ratios. Oxygen-containing gas, including oxygen or air, is continuously introduced during roasting. By adjusting the mass ratio X of waste lithium iron phosphate to (NH4)2SO4 within the above range, it is less likely to lose iron phosphate, which is beneficial to obtain more intermediate products, and the leaching rate of lithium element is high, and a better impurity removal effect can also be obtained. The roasting temperature T1 is between 250°C and 400°C; for example, T1 can be 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, 310°C, 320°C, 330°C, 340°C, 350°C, 360°C, 370°C, 380°C, 390°C, or 400°C, or any two of the above numbers. By adjusting the temperature T1 within the above range, (NH4)2SO4 is in a liquid state and has an acidic pH, and at temperature T1 it can react with the organic matter and carbon in the waste lithium iron phosphate, thereby removing the organic matter and carbon. By adjusting the temperature T1 and time t1 during roasting within the above range, waste lithium iron phosphate and (NH4)2SO4 can react fully, which is conducive to the formation of corresponding sulfates by impurity elements and lithium elements, the formation of iron phosphate by iron elements, and the iron elements are not easily oxidized to iron oxide. Thus, in step (2), the effective separation of iron sulfate and impurity elements is achieved, as well as the full leaching of lithium elements.

[0135] This application does not impose any particular limitation on the flow rate of the oxygen-containing gas, as long as the purpose of this application is achieved. For example, the flow rate of the oxygen-containing gas can be from 24 L / min to 36 L / min. The oxygen content in the oxygen-containing gas is greater than or equal to 15% by volume.

[0136] In some embodiments of this application, in step (1), the calcination time t1 is 0.5h to 12h.

[0137] In some embodiments of this application, in step (1), the roasting temperature T1 is 300°C to 350°C and the roasting time t1 is 0.5h to 4h. By adjusting the roasting temperature T1 and time t1 within the above range, the waste lithium iron phosphate and (NH4)2SO4 can react more fully, which is conducive to the formation of corresponding sulfates by impurity elements and lithium elements, the formation of iron phosphate by iron elements, and the iron elements are not easily oxidized to iron oxide. Thus, in step (2), the effective separation of iron phosphate and impurity elements is achieved, as well as the full leaching of lithium elements, and finally, the desired iron-phosphorus molar ratio of the product iron phosphate is obtained.

[0138] The following reactions occur during the roasting process:

[0139] Al2O3+3(NH4)2SO4=Al2(SO4)3+6NH3+3H2O;

[0140] CaO+(NH4)2SO4=CaSO4+2NH3+H2O;

[0141] 4LiFePO4+2(NH4)2SO4+O2=4FePO4+2Li2SO4+4NH3+2H2O.

[0142] Al₂(SO₄)₃ is soluble in water, and after calcination, it can efficiently leach Al from the waste. CaSO₄ is slightly soluble in water, with a solubility of approximately 0.2 g / 100 ml. Since the Ca content in the waste is already low, even though CaSO₄ is slightly soluble in water after the reaction, it can still effectively leach out most of the Ca, ensuring that the Ca content in the resulting iron phosphate slag meets the requirements. Li₂SO₄ is soluble in water, while FePO₄ is insoluble in water. After leaching, impurity elements aluminum and calcium can be separated from iron phosphate, and lithium can also be leached.

[0143] In some embodiments of this application, in step (2), the pH of the slurry obtained by mixing the calcined material with water is ≤3; in some embodiments of this application, in step (2), the pH of the slurry is 2 ≤ pH ≤ 3; the leachate contains Li + The intermediate product contains phosphorus and iron (ferric phosphate slag). For example, the pH of the slurry can be 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, or 3, or any two of the above values. This process controls the amount of water added; excessive water usage should be avoided. By adjusting the pH of the slurry within the above range, aluminum exists in ionic form and, after leaching and filtration, is mainly present in the leachate, effectively separating it from ferric phosphate and reducing the content of impurities in the intermediate product. If too much water is added, causing the slurry pH to be too high (e.g., greater than 3), Al(OH)3 precipitate is easily formed, affecting the purity of the intermediate product. In this process, Li is achieved through water leaching. + The method for separating impurity elements from iron phosphate is novel and requires less water during immersion.

[0144] In some embodiments of this application, the leachate in step (2) can be further separated from Li+ and impurities Al and Ca elements, for example, by adjusting the pH with an alkaline solution to precipitate Al and Ca elements and separate them from Li+. This application does not limit the alkaline solution mentioned above, as long as it can achieve the purpose of this application.

[0145] In some embodiments of this application, in step (2), the solid-liquid ratio Z of the calcined material to water is from 0.1 g / ml to 0.3 g / ml. For example, the solid-liquid ratio Z can be 0.1 g / ml, 0.11 g / ml, 0.12 g / ml, 0.13 g / ml, 0.14 g / ml, 0.15 g / ml, 0.16 g / ml, 0.17 g / ml, 0.18 g / ml, 0.19 g / ml, 0.2 g / ml, 0.21 g / ml, 0.22 g / ml, 0.23 g / ml, 0.24 g / ml, 0.25 g / ml, 0.26 g / ml, 0.27 g / ml, 0.28 g / ml, 0.29 g / ml, or 0.3 g / ml, or any two of the above figures. Al2(SO4)3 has high solubility in water, while CaSO4 has lower solubility, being only slightly soluble (approximately 0.2 g / 100 ml). Since the waste contains less Ca than Al, even with its slight solubility in water, CaSO4 can effectively leach out most of the Ca elements after the reaction. By controlling the solid-liquid ratio Z within the aforementioned range, both CaSO4 and Al2(SO4)3 can fully dissolve in water during the leaching process. This facilitates the effective separation of ferric phosphate and impurities, improving the purity of the purified ferric phosphate slag.

[0146] In some embodiments of this application, in step (2), the leaching temperature T5 is between 15°C and 35°C, and the time t5 is between 0.5h and 10h. For example, T5 can be 15°C, 16°C, 17°C, 18°C, 19°C, 20°C, 21°C, 22°C, 23°C, 24°C, 25°C, 26°C, 27°C, 28°C, 29°C, 30°C, 31°C, 32°C, 33°C, 34°C, or 35°C, or any two of the above numbers. For example, t5 can be 0.5h, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, or 10h, or any two of the above numbers. By adjusting the leaching temperature T5 and time t5 within the above ranges, CaSO4 and Al2(SO4)3 can be fully dissolved in water, thereby facilitating the effective separation of ferric phosphate and impurity elements, improving the purity of the purified ferric phosphate slag, and reducing energy consumption.

[0147] In some embodiments of this application, the intermediate product obtained in step (2) is further dried. This application does not limit the drying parameters, as long as they can achieve the purpose of this application.

[0148] In some embodiments of this application, the aluminum content in the intermediate product is ≤500ppm and the calcium content is ≤100ppm. The aluminum and calcium content in the intermediate product being within these ranges indicates that the content of impurity elements in the intermediate product is very low, resulting in a high purity intermediate product, which is beneficial for obtaining a high-purity product, iron phosphate.

[0149] In some embodiments of this application, the iron content W1 in the product ferric phosphate is 35.7 wt% to 36.7 wt%, and the phosphorus content W2 is 20.0 wt% to 21.1 wt%. For example, the iron content W1 can be 35.7 wt%, 35.8 wt%, 35.9 wt%, 36.0 wt%, 36.1 wt%, 36.2 wt%, 36.3 wt%, 36.4 wt%, 36.5 wt%, 36.6 wt%, or 36.7 wt%, or between any two of the above figures. For example, the phosphorus content W2 can be 20.0 wt%, 20.1 wt%, 20.1 wt%, 20.3 wt%, 20.4 wt%, 20.5 wt%, 20.6 wt%, 20.7 wt%, 20.8 wt%, 20.9 wt%, 21.0 wt%, or 21.1 wt%, or between any two of the above figures. The iron content in the product is 35.7wt% to 36.7wt%, and the phosphorus content is 20.0wt% to 21.1wt%, which meets the requirements for battery-grade iron phosphate.

[0150] In some embodiments of this application, the molar ratio of iron to phosphorus in the product iron phosphate is (0.96 to 1):1. For example, the molar ratio Z can be 0.96:1, 0.97:1, 0.98:1, 0.99:1, or 1:1, or any two of the above figures. The molar ratio of iron to phosphorus in the product iron phosphate (0.96 to 1:1) meets the standard and can be used to prepare lithium iron phosphate, the positive electrode material for secondary batteries, thereby realizing the recycling and reuse of waste lithium iron phosphate materials.

[0151] This application provides a method for recycling the positive electrode of a waste lithium iron phosphate battery, comprising the following steps: (1) dismantling the waste lithium iron phosphate battery to obtain waste lithium iron phosphate, mixing the waste lithium iron phosphate with (NH4)2SO4 and then roasting to obtain roasted material; (2) mixing the roasted material with water for leaching treatment, and then filtering to obtain leaching liquid and solid intermediate product; (3) mixing the intermediate product with phosphoric acid solution for dissolution, filtering to obtain a first filtrate; (4) mixing the first filtrate with water to obtain a mixed solution, then performing crystallization treatment, adding hydrogen peroxide during the crystallization treatment, and then filtering to obtain filter residue and a second filtrate, and calcining the filter residue to obtain product iron phosphate; wherein, the pH of the mixed solution is 0.7 to 2.5. The recycling method provided in this application can basically remove impurity elements (such as Ca, Al, etc.), organic matter, and carbon simultaneously after roasting and leaching treatment, reducing the energy consumption of removing organic matter and carbon separately at high temperatures. In the crystallization process, water is first used to adjust the pH of the first filtrate, avoiding the use of alkali, which is more environmentally friendly and lower in cost. At the same time, the desired iron-phosphorus molar ratio of the product iron phosphate is obtained by crystallization, which not only meets the national standard requirements, but also reduces the use of acid compared to the traditional method that uses a large amount of acid, further reducing recycling costs and increasing the added value of waste lithium iron phosphate products.

[0152] In this application, the intermediate product is dissolved using phosphoric acid, and only one crystallization process is required to obtain ferric phosphate with the required iron-to-phosphorus ratio. This is because phosphoric acid has the effect of supplementing phosphorus, ensuring that the content of P element in the crystallization system is appropriate and simplifying the process.

[0153] In this application, the roasting process only uses ammonium sulfate, which has reducing properties, to react with waste lithium iron phosphate, thereby removing the Fe... 2+ Transformed into Fe 3+ The intermediate product obtained is ferric phosphate slag (the iron-to-phosphorus ratio at this point does not meet the requirements). Further acid dissolution and crystallization are then carried out. During the crystallization process, hydrogen peroxide, an oxidant, needs to be added to prevent Fe from being released. 3+ Oxidized to Fe 2+ This is beneficial for obtaining products with a suitable iron-to-phosphorus ratio.

[0154] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time.

[0155] Example

[0156] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0157] Example 1-1 (The mass ratio of waste lithium iron phosphate to ammonium sulfate is 1:0.8)

[0158] Figure 1 is a flowchart of the experiment in Example 1-1. The specific steps are as follows:

[0159] 3g of waste lithium iron phosphate and 2.4g of ammonium sulfate (mass ratio 1:0.8) were mixed. Before mixing, the ammonium sulfate was ground and passed through a 200-mesh sieve. After mixing, the mixture was roasted at T1 = 300℃ with continuous air circulation for t1 = 0.5h. After roasting, the roasted material was placed in water at a solid-liquid ratio of 0.3g / ml. The pH of the mixed slurry was 2.2, and then leaching treatment was performed, i.e., Li leaching and impurity removal. The leaching temperature T2 was 25℃, and the time t2 was 0.5h. After completion, the mixture was filtered to obtain leachate and filter residue. After drying, 2.85g of filter residue was obtained (with a 5wt% loss of iron phosphate). Inductively coupled plasma mass spectrometry (ICP) analysis of the filter residue showed that the Li leaching rate was 99.8%. After lithium leaching, the Al content in the filter residue was 300ppm and the Ca content was 80ppm.

[0160] During the lithium leaching process after roasting, no carbon powder was found to float on the water surface, indicating that the carbon in the waste lithium iron phosphate was removed, and the roasted material was completely wetted with water, indicating that the organic matter in the waste lithium iron phosphate was removed.

[0161] Wherein, the loss of iron phosphate = (1 - mass of filter residue / waste lithium iron phosphate) × 100%; the leaching rate of Li = lithium content in the leachate / lithium content in waste lithium iron phosphate × 100% (the same applies to other examples).

[0162] Table 1. Content of various elements in waste lithium iron phosphate (before impurity removal)

[0163] As shown in the table above, waste lithium iron phosphate contains high levels of Al and Ca impurities. Using it in product preparation will result in an excessively high impurity content in the final product, failing to meet product requirements. Therefore, impurity removal is necessary for waste lithium iron phosphate. When waste lithium iron phosphate is roasted with ammonium sulfate, the Ca impurities are converted into calcium sulfate. Based on the solubility of calcium sulfate, it can be completely dissolved during leaching. The Al impurities are ultimately converted into aluminum sulfate, which will be completely dissolved if the pH of the leaching solution is not higher than 3, thus achieving the separation of iron phosphate from impurity elements.

[0164] Examples 1-2 (mass ratio of waste lithium iron phosphate to ammonium sulfate is 1:0.6)

[0165] The only difference from Example 1-1 is the adjustment of the mass ratio of waste lithium iron phosphate to ammonium sulfate; the rest is the same as in Example 1-1, as detailed below:

[0166] Mix 3g of waste lithium iron phosphate with 1.8g of ammonium sulfate.

[0167] In this embodiment, the Li leaching rate was 90.6%. After leaching, filtration, and drying, 2.83g of filter residue was obtained (with a ferric phosphate loss of 5.6wt%). The Al content in the filter residue was 400ppm and the Ca content was 90ppm.

[0168] A comparison of Examples 1-2 and 1-1 shows that adjusting the mass ratio of waste lithium iron phosphate to ammonium sulfate from 1:0.6 to 1:0.8 has little effect on the loss of iron phosphate and the content of impurities Al and Ca in the filter residue, but can improve the lithium leaching rate.

[0169] Examples 1-3 (The mass ratio of waste lithium iron phosphate to ammonium sulfate is 1:1)

[0170] The only difference from Example 1-1 is the adjustment of the mass ratio of waste lithium iron phosphate to ammonium sulfate; the rest is the same as in Example 1-1, as detailed below:

[0171] Mix 3g of waste lithium iron phosphate with 3g of ammonium sulfate.

[0172] In this embodiment, the Li leaching rate was 99.0%. After leaching, filtration, and drying, 2.76g of filter residue was obtained (with a ferric phosphate loss of 8wt%). The Al content in the filter residue was 450ppm and the Ca content was 50ppm.

[0173] A comparison of Examples 1-3 and Example 1-1 shows that adjusting the mass ratio of waste lithium iron phosphate to ammonium sulfate from 1:1 to 1:0.8 has little effect on the lithium leaching rate and the content of impurities Al and Ca in the filter residue, but can reduce the loss of iron phosphate.

[0174] Examples 1-4 to Examples 1-7

[0175] The parameter changes are shown in Table 2, and the rest are the same as in Example 1-1.

[0176] Examples 1-4 are similar to Examples 1-1, except that the calcination temperature is adjusted to 350℃. The experimental results show that the effect is similar to that of Example 1, indicating that a calcination temperature of 300℃ to 350℃ can achieve a better impurity removal effect and a high lithium leaching rate, while the loss of iron phosphate is low.

[0177] Examples 1-5 adjusted the calcination time and the solid-liquid ratio of water added after calcination based on Examples 1-4. It can be seen that when the calcination time is from 0.5h to 4h and the solid-liquid ratio is from 0.1g / ml to 0.3g / ml, good impurity removal effect and high lithium leaching rate can be obtained, and the loss of iron phosphate is also low.

[0178] Examples 1-6 are similar to Examples 1-1, except that the roasting temperature is further increased to 400°C. In Examples 1-6, due to the higher roasting temperature, the ammonium sulfate volatilizes faster and does not have enough time to react with the waste lithium iron phosphate. Therefore, the lithium leaching effect and impurity removal effect are worse than those in Examples 1-1. As for the loss of iron phosphate, since the filter residue still contains a small amount of unreacted waste lithium iron phosphate, it will affect the calculation of the loss of iron phosphate.

[0179] Examples 1-7 are similar to Examples 1-1, except that the calcination time is increased (12h) and the solid-liquid ratio of water added after calcination is adjusted to 0.2g / ml. They still achieve good impurity removal effect and high lithium leaching rate, and the loss of iron phosphate is low.

[0180] Comparative Example 1-1 (The mass ratio of waste lithium iron phosphate to ammonium sulfate is 1:0.4)

[0181] The only difference from Example 1-1 is that 3g of waste lithium iron phosphate and 1.2g of ammonium sulfate (mass ratio of 1:0.4) are mixed together, and the rest is the same as in Example 1-1.

[0182] 2.80 g of filter residue was obtained, with a ferric phosphate loss of 6.7 wt%. ICP analysis of the filter residue showed a Li leaching rate of 71%.

[0183] As can be seen, compared with Example 1-1, when the mass ratio of lithium iron phosphate to ammonium sulfate is 1:0.4, the loss of iron phosphate is less affected, but the leaching rate of Li is more affected, decreasing to 71.0%.

[0184] Comparative Examples 1-2 (the mass ratio of waste lithium iron phosphate to ammonium sulfate is 1:1.1)

[0185] The only difference from Example 1-1 is that 3g of waste lithium iron phosphate and 3.3g of ammonium sulfate (mass ratio of 1:1.1) are mixed together, and the rest is the same as in Example 1-1.

[0186] 2.7g of filter residue was obtained, with a ferric phosphate loss of 10wt%. ICP analysis of the filter residue showed that the Li leaching rate was 99%.

[0187] When there is an excess of ammonium sulfate, it reacts with ferric phosphate as follows:

[0188] 2FePO4+3(NH4)2SO4=Fe2(SO4)3+2(NH4)3PO4.

[0189] It can be seen that, compared with Example 1-1, the excess (NH4)2SO4 in Comparative Examples 1-2 leads to the conversion of Fe elements in LFP into Fe2(SO4)3, increases the loss of ferric phosphate, and has little effect on the Li leaching rate.

[0190] Comparative Examples 1-3 (if the roasting temperature is too high, such as 500℃, LFP will be oxidized into red iron oxide).

[0191] The difference from Example 1-1 is that the calcination temperature was 500℃, otherwise it was the same as Example 1-1. After calcination, it was found that some lithium iron phosphate was oxidized into red iron oxide, as shown in Figure 2, making subsequent operations impossible.

[0192] Comparative Examples 1-4

[0193] The difference from Example 1-1 is that the solid-liquid ratio of water added after calcination is 0.05 g / ml, the pH of the mixed slurry is 3.1, and a white precipitate Al(OH)3 is found to be generated during the water addition process, which will affect the purity of solid-phase iron phosphate and result in low impurity removal efficiency.

[0194] The preparation parameters and performance tests for each embodiment and comparative example are shown in Table 2.

[0195] Table 2

[0196] Note: " / " in Table 2 indicates that the corresponding parameter or performance does not exist; the Li leaching rate in Comparative Example 1-1 was too low, and the iron phosphate loss in Comparative Example 1-2 was too large, so the final impurity content was not tested; subsequent operations could not be performed in Comparative Example 1-3, so the iron phosphate loss, Li leaching rate, and impurity content could not be tested; other precipitates were generated in Comparative Example 1-4, so the iron phosphate loss, Li leaching rate, and impurity content were not tested.

[0197] Example 2-1

[0198] Figure 3 is a flowchart of the experiment in Example 2-1. The specific steps are as follows:

[0199] 3g of waste lithium iron phosphate and 2.4g of ammonium sulfate were mixed. After mixing, the mixture was roasted for 2 hours with air continuously introduced at T1 = 300℃. After roasting, the roasted material was placed in water with a solid-liquid ratio Z of 0.3g / ml. The pH of the resulting slurry was 2.1. Then, leaching was performed at a temperature of T5 = 25℃ and a time of t5 = 2 hours. After leaching, the mixture was filtered. The iron phosphate residue (i.e., the intermediate product) obtained from the filtration was dried. ICP testing showed that the iron-phosphorus molar ratio was not within the range of (0.96 to 1):1, and therefore did not meet the requirements.

[0200] Next, the dried ferric phosphate residue was added to a 6 mol / L phosphoric acid solution, with a mass ratio of intermediate product to phosphoric acid solution Y of 1:20. The mixture was stirred and dissolved at room temperature (T2 = 25℃) for t2 = 12 hours. The solution was then filtered, and the first filtrate was collected. Water was added to the first filtrate to obtain a mixed solution with a pH of 0.7. After this process, the mixed solution was regenerated and crystallized at T3 = 90℃. During crystallization, H2O2 was continuously added at a rate V = 0.03 mL / min for 1 hour, with a total addition of 1.8 mL. Crystallization was carried out at T3 = 90℃ for t3 = 6 hours. The resulting residue was filtered to obtain a filter residue and a second filtrate. The filter residue was dried and calcined at T4 = 550℃ for t4 = 3.5 hours to remove the water of crystallization, yielding 1.5 g of ferric phosphate. The Fe content was 35.8%, and the P content was 20.2%, meeting the requirements. The second filtrate is evaporated to remove the added water until it reaches the same volume as the first filtrate, and then added back to the first filtrate for reuse.

[0201] In Example 2-1, ICP testing showed that the Al content in the waste lithium iron phosphate was 2288 ppm and the Ca content was 156.62 ppm. ICP elemental analysis of the intermediate product, iron phosphate residue, obtained in Example 2-1 showed that the Al content was 300 ppm and the Ca content was 80 ppm, which met the requirements for impurity content. It can be seen that the roasting process of this method has a good impurity removal effect, and the impurity content in the obtained iron phosphate residue meets the requirements, allowing for the next step of dissolution and crystallization.

[0202] The particle size D50 of the dried ferric phosphate residue obtained in Example 2-1 was 16.3 micrometers, and the particle size D50 of the ferric phosphate product was 2.8 micrometers. It can be seen that after crystallization treatment, not only did the iron-phosphorus ratio in the ferric phosphate product meet the requirements, but the particle size of the product also met the requirements.

[0203] Example 2-2 (pH adjusted to 1.0)

[0204] The only difference from Example 2-1 is that the pH of the mixed solution was adjusted to 1.0 using water; otherwise, it was the same as Example 2-1. 2.8 g of ferric phosphate was obtained, with a high yield. The Fe content was 36.1%, and the P content was 20.6%, meeting the requirements.

[0205] The impurity content of the ferric phosphate residue in Example 2-2 is the same as that in Example 2-1.

[0206] The particle size D50 of the product ferric phosphate is 2.6 micrometers.

[0207] Examples 2-3 (dropping rate 0.04 mL / min)

[0208] The only difference from Example 2-1 is that the dropping rate and time of H2O2 were adjusted. The dropping rate V was 0.04 mL / min, the dropping time was 45 min, and the total dropping volume was 1.8 mL. Everything else was the same as in Example 2-1. 1.3 g of ferric phosphate was obtained, with an Fe content of 35.9% and a P content of 20.2%, meeting the requirements.

[0209] It is evident that a rapid dropping rate of H2O2 will cause a significant amount of H2O2 to decompose due to heat before it can participate in the reaction. This decomposition produces oxygen, and the resulting bubbles will affect the crystallization process, preventing the effective formation of crystals and reducing the yield of iron phosphate.

[0210] The impurity content of the ferric phosphate residue in Examples 2-3 is the same as that in Example 2-1.

[0211] Examples 2-4 (dropping rate 0.015 mL / min)

[0212] The only difference from Example 2-1 is that the dropping rate and time of H2O2 were adjusted. The dropping rate V was 0.015 mL / min, the dropping time was 120 min, and the total dropping volume was 1.8 mL. Everything else was the same as in Example 2-1. 1.5 g of ferric phosphate was obtained, with an Fe content of 35.9% and a P content of 20.3%, meeting the requirements.

[0213] Compared to Example 2-1, it was found during the experiment that more ferric phosphate precipitated in a shorter time in Example 2-4. This was because the dropping speed was slower, and hydrogen peroxide was mainly used to inhibit the oxidation of ferric ions in the solution. It did not decompose in large quantities to produce oxygen and affect crystallization, resulting in a large amount of crystal precipitation. The rapid precipitation of ferric phosphate caused the ferric phosphate crystals to agglomerate and the particle size to increase. In this example, the particle size D50 was 11.2 micrometers, and subsequent ball milling was required to obtain a product with a qualified particle size.

[0214] The impurity content of the ferric phosphate residue in Examples 2-4 is the same as that in Example 2-1.

[0215] Examples 2-5 (pH adjusted to 1.5)

[0216] The only difference from Example 2-2 is that the pH of the mixed solution was adjusted to 1.5 using water; the crystallization temperature T3 = 105℃, and the crystallization time t3 = 3h; the H2O2 dropping rate V = 0.02mL / min, the dropping time 100min, and the total dropping volume 2ml; and the calcination temperature T4 = 700℃, and the calcination time t4 = 2h. The rest was the same as in Example 2-1. Approximately 2.8g of ferric phosphate was obtained, with an Fe content of 36.1% and a P content of 20.9%, meeting the requirements.

[0217] In this embodiment, the process of adjusting the pH of the filtrate with water yields a product of ferric phosphate with a similar mass to that in Example 2-2. However, this requires more water, approximately twice that of Example 2-2, and subsequent evaporation consumes more energy.

[0218] The impurity content of the ferric phosphate residue in Examples 2-5 is the same as that in Example 2-2.

[0219] Comparative Example 2-1 (pH too low, 0.5)

[0220] The only difference from Example 2-1 is that the pH of the mixed solution was adjusted to 0.5 using water; otherwise, the process was the same as in Example 2-1. 0.3 g of ferric phosphate was obtained, with an Fe content of 35.9% and a P content of 20.1%, meeting the required iron-to-phosphorus ratio. This indicates that a large amount of ferric phosphate did not crystallize out.

[0221] Comparative Example 2-2 (pH 3 if too high)

[0222] The only difference from Example 2-1 is that the pH of the mixed solution was adjusted to 3 using water; otherwise, it was the same as Example 2-1. A large amount of white precipitate was generated during the crystallization process, making further processing impossible.

[0223] Comparative Examples 2-3 (without H2O2)

[0224] The only difference from Example 2-1 is that H2O2 is not added during the crystallization process. As shown in Figure 4, the right side shows the mixed solution from Comparative Example 2-3, which is colorless and transparent; the left side shows the mixed solution from Example 2-1.

[0225] The mixed solution in Example 2-1 exhibits Fe 3+ The yellow color indicates that the iron in the mixed solution is mainly in the form of Fe. 3+ It exists in form.

[0226] In Comparative Examples 2-3, the Fe content in the iron phosphate product was 38.5% and the P content was 20.2%, which did not meet the requirements.

[0227] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for recycling the positive electrode of a waste lithium iron phosphate battery, comprising the following steps: Dismantling waste lithium iron phosphate batteries yields waste lithium iron phosphate, which includes impurity elements. The waste lithium iron phosphate is then purified to obtain purified iron phosphate residue. The impurity removal process for waste lithium iron phosphate includes: (1) Disassemble waste lithium iron phosphate batteries to obtain waste lithium iron phosphate, mix the waste lithium iron phosphate with (NH4)2SO4 and then roast to obtain roasted product. (2) The roasted material is mixed with water to obtain a slurry, the slurry is subjected to leaching treatment, filtered to obtain leachate and filter residue, wherein the filter residue is purified ferric phosphate residue.

2. The recycling method according to claim 1, wherein, The impurity elements include aluminum and / or calcium.

3. The recycling method according to claim 1, wherein, In step (1), the mass ratio X of the waste lithium iron phosphate to (NH4)2SO4 is 1:(0.6 to 1), and the roasting temperature T1 is 250℃ to 400℃ and the roasting time t1 is 0.5h to 12h. In step (2), the pH of the slurry is ≤3.

4. The recycling method according to claim 3, wherein, In step (1), the mass ratio X is 1:(0.75 to 0.85).

5. The recycling method according to claim 3, wherein, In step (1), the calcination temperature T1 is 300℃ to 350℃ and the time t1 is 0.5h to 4h.

6. The recycling method according to claim 3, wherein, In step (1), oxygen-containing gas is continuously introduced into the roasting process, and the oxygen-containing gas includes air or oxygen.

7. The recycling method according to claim 3, wherein, In step (2), the solid-liquid ratio of the calcined material to water is 0.1 g / ml to 0.3 g / ml.

8. The recycling method according to claim 3, wherein, In step (2), the pH of the slurry is 2 ≤ pH ≤ 3.

9. The recycling method according to claim 3, wherein, In step (2), the leaching treatment temperature T2 is 15°C to 35°C, and the time t2 is 0.5h to 10h.

10. The recycling method according to claim 3, wherein, In step (2), the leachate contains Li + and the impurity elements.

11. The recycling method according to claim 3, wherein, The filter residue contains ≤500ppm aluminum and ≤100ppm calcium.

12. The recycling method according to claim 1, wherein, It also includes: after obtaining the purified ferric phosphate residue, recovering the purified ferric phosphate residue to obtain the product ferric phosphate; The process of recovering the purified ferric phosphate slag includes: (3) The intermediate product is mixed with phosphoric acid solution and dissolved, then filtered to obtain the first filtrate. The purified ferric phosphate residue; (4) The first filtrate is mixed with water to obtain a mixed solution, and then crystallization is performed. Hydrogen peroxide is added during the crystallization process. Then the filter is filtered to obtain a filter residue and a second filtrate. The filter residue is calcined to obtain the product iron phosphate. The pH of the mixed solution is between 0.7 and 2.

5.

13. The recycling method according to claim 12, wherein, In step (3), the concentration C of the phosphoric acid solution is 1 mol / L to 6 mol / L, and the mass ratio Y of the intermediate product to the phosphoric acid solution is 1:(5 to 20).

14. The recycling method according to claim 12, wherein, In step (3), the dissolution time t2 is 3h to 12h, and the dissolution temperature T2 is 15 to 35℃.

15. The recycling method according to claim 12, wherein, In step (4), the hydrogen peroxide addition rate V is from 0.017 mL / min to 0.03 mL / min; Preferably, the total amount of hydrogen peroxide added is: 1 ml to 2 ml of hydrogen peroxide for every 3 g of waste lithium iron phosphate treated; Preferably, the hydrogen peroxide is added dropwise.

16. The recycling method according to claim 12, wherein, In step (4), the pH of the mixed solution is 0.9 to 1.

2.

17. The recycling method according to claim 12, wherein, In step (4), the temperature T3 of the crystallization treatment is 70°C to 110°C and the time t3 is 3h to 6h; Preferably, in step (4), the calcination temperature T4 is 400°C to 700°C and the time t4 is 1.5h to 6h.

18. The recycling method according to claim 12, wherein, It also includes the following steps: (5) Heat the second filtrate to make its volume the same as that of the first filtrate, and then add it to the first filtrate to continue dissolving the intermediate product.

19. The recycling method according to claim 12, wherein, In step (1), the mass ratio X of the waste lithium iron phosphate to (NH4)2SO4 is 1:(0.6 to 1); The roasting temperature T1 is 250°C to 400°C; During the roasting process, oxygen-containing gas, including oxygen or air, is continuously introduced.

20. The recycling method according to claim 12, wherein, In step (2), the pH of the slurry obtained by mixing the calcined material with water is ≤3; The leachate contains Li + and impurity elements, said impurity elements including Al and / or Ca; The intermediate product contains phosphorus and iron.

21. The recycling method according to claim 12, wherein, The iron content in the product, ferric phosphate, is 35.7 wt% to 36.7 wt%, and the phosphorus content is 20.0 wt% to 21.1 wt%.

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