Method for recovering iron phosphate from waste lithium iron phosphate material

Abstract

The invention relates to a method for recovering iron phosphate from a waste lithium iron phosphate active substance, which comprises the following steps: placing the waste lithium iron phosphate active substance subjected to oxidizing roasting in an acid solution leaching system, leaching, and carrying out solid-liquid separation to obtain hydrated iron phosphate and a lithium-rich solution; in the acid solution leaching system, the initial molar weight of phosphoric acid is 1.8-2.5 times of the sum of the molar weights of Li and Fe in the active substances of the waste lithium iron phosphate; or the sum of the initial molar weight of the phosphoric acid and the initial molar weight of H < + > contained in the strong acid is 1.5-2.5 times of the sum of the molar weights of Li and Fe in the waste lithium iron phosphate active substance; or, the sum of the initial concentrations of the phosphate radicals, the monohydrogen phosphate radicals and the dihydrogen phosphate radicals is larger than or equal to 0.8 mol / L, and the initial molar weight of H < + > contained in the strong acid is 1.2-2.0 times of the sum of the molar weights of Li and Fe in the waste lithium iron phosphate active substance. The method is short in process and high in selectivity, leaching separation of iron, phosphorus, lithium and the like can be achieved through one-step leaching, the purity of the obtained hydrated iron phosphate product can reach the battery grade, and the comprehensive treatment benefit is high.

Description

Technical Field

[0001] This invention relates to a method for recovering iron phosphate from waste lithium iron phosphate materials, belonging to the field of waste battery resource utilization. Background Technology

[0002] The booming development of the lithium-ion battery market has triggered changes in people's consumption and lifestyles. Lithium iron phosphate batteries, due to their high safety and good charge-discharge stability, have been widely used in electric vehicles and energy storage devices. However, without appropriate technological measures, the large-scale disposal of lithium iron phosphate batteries will cause serious environmental damage and resource waste.

[0003] Direct regeneration, as a non-destructive recycling technology, has achieved widespread success in laboratory-scale recycling of waste lithium iron phosphate materials. However, this method is only suitable for cathode materials that have been completely separated from organic binders and solvents, have low impurity content, and whose crystal structure has not undergone severe irreversible phase transitions. Currently, the recycled lithium iron phosphate waste often comes from the crushing and dismantling after brine discharge. During the complex physicochemical dismantling and separation process, the cathode materials often undergo irreversible crystal structure changes and chemical reactions. Therefore, direct regeneration technology has poor raw material adaptability and cannot be well applied industrially.

[0004] Wet recycling remains the mainstream technology for the industrial recycling of lithium iron phosphate materials. However, current mainstream wet recycling of spent cathode materials from retired lithium iron phosphate batteries mainly focuses on lithium recovery, while iron and phosphorus elements are not effectively recovered, resulting in a waste of iron and phosphorus resources. Existing publicly available regeneration technologies for recovering iron and phosphorus often suffer from problems such as lengthy recycling steps, high consumption of acid and alkali reagents, large amounts of high-salt wastewater, or low purity of the produced iron phosphate product, resulting in low economic value and low industrialization feasibility.

[0005] Chinese invention patent application CN108110357B discloses a method for recovering valuable metals from waste lithium iron phosphate battery cathode materials. The core technology of this patent is oxidative roasting and selective lithium leaching with a weak acid. It utilizes the physical property that Fe2O3 and FePO4 in the roasted mixture are poorly soluble in dilute acid, and achieves solid-liquid separation of Fe2O3, FePO4, and Li3PO4 in the roasted mixture by controlling the pH value of the acid leaching solution. However, this patent only achieves selective leaching of lithium; iron and phosphorus elements cannot be recovered, and the residual iron and phosphorus slag after leaching has a complex composition, making effective recycling and reuse impossible.

[0006] Chinese invention patent application CN117756075A discloses a method for preparing battery-grade iron phosphate from lithium iron phosphate powder. The method uses alkaline washing to remove residual aluminum from lithium iron phosphate cathode powder, followed by conventional wet oxidation selective leaching of lithium, acid dissolution to remove insoluble carbon, and then alkaline precipitation to recover iron phosphate. This process has limited separation effect during alkaline pretreatment to remove aluminum, which can cause lithium element damage and aluminum impurity residue. The subsequent consumption of acid and alkali reagents is large, and the high-salt wastewater needs to be treated.

[0007] Chinese invention patent application CN109626350A discloses a method for preparing battery-grade iron phosphate from waste lithium iron phosphate battery cathode sheets. This method employs low-temperature roasting to remove aluminum, followed by phosphoric acid and oxidant leaching to achieve lithium leaching and iron phosphate preparation. However, the low-temperature roasting process fails to completely separate the cathode material from organic matter, requiring subsequent washing and drying with organic reagents. These reagents are costly, and the waste liquid is difficult to treat, posing a potential environmental hazard. Furthermore, low-temperature roasting cannot oxidize the ferrous iron in the lithium iron phosphate material, necessitating the addition of oxidants for selective leaching, resulting in high reagent costs. Since phosphoric acid is a weak acid, the leaching step requires the addition of excess phosphoric acid to achieve leaching, and after completion, ferric iron must be added to precipitate the excess phosphoric acid and prepare iron phosphate. This leads to high phosphoric acid reagent consumption and high reagent costs.

[0008] Chinese invention patent application CN113880064A discloses a method for treating high-impurity lithium iron phosphate waste powder with low-consumption phosphoric acid. This method involves roasting in a protective atmosphere to remove organic matter, but the gaseous reagents are expensive, and subsequent addition of oxidants is required for selective leaching, further increasing reagent costs. The patent uses LiOH alkaline leaching to remove aluminum, which leads to the loss of valuable lithium elements, resulting in high impurity removal reagent costs. Furthermore, the patent's impurity removal principle indicates that it can only remove elemental aluminum and copper, but in reality, aluminum in high-impurity lithium iron phosphate also exists in the form of aluminum phosphate, which the wet phosphoric acid leaching process cannot remove.

[0009] Chinese invention patent specification CN106450547B discloses a method for recovering iron phosphate and lithium carbonate from lithium iron phosphate waste. The method is achieved through the following steps: (1) Oxidative roasting: The waste lithium iron phosphate positive electrode is placed in a roasting furnace and roasted at 400-500℃ for 3-4 hours to obtain positive electrode roasting material containing lithium iron phosphate active material and current collector aluminum foil; (2) Electrode cleaning: After the roasted positive electrode is cooled to 25℃, it is placed in an ultrasonic cleaning tank. After ultrasonic cleaning, the aluminum foil is taken out and recycled. The lithium iron phosphate active material in the filtering solution is used for later use, and the filtrate is recycled as the cleaning solution for the next batch of material; (3) Activation by ball milling with added phosphoric acid: 85-95% concentrated phosphoric acid is added to the filtered lithium iron phosphate active material. Stir the acid evenly, put it into a ball mill jar and seal it. Place the ball mill jar on a ball mill and ball mill at 500-600 r / min for 30-60 min. Then separate the ball material to obtain a mixture of FePO4 and Li3Fe2(PO4)3. The solid-liquid ratio of lithium iron phosphate active material and concentrated phosphoric acid is 5:1-6:1. (4) Acid washing to separate FePO4: Add dilute sulfuric acid solution to the obtained mixture of FePO4 and Li3Fe2(PO4)3, stir and wash at room temperature, and then filter to separate FePO4 and filtrate. The solid-liquid ratio of FePO4 and Li3Fe2(PO4)3 mixture and dilute sulfuric acid solution is 1:2-1:3. (5) Finally, precipitate lithium in the filtrate to obtain lithium carbonate. This patent uses ball milling activation with added phosphoric acid to convert iron oxide into iron phosphate. This requires mechanical operations such as ball milling and sieving, which involves complex equipment, high energy consumption, and material loss, making it unsuitable for industrial application. In addition, the material activated by ball milling needs to be acid-leached to separate iron phosphate and lithium, making the process still relatively long.

[0010] Therefore, it is necessary to develop a short-process, highly selective process for recovering valuable elements such as iron, phosphorus, and lithium from waste lithium iron phosphate materials. Summary of the Invention

[0011] To address the shortcomings of existing technologies, the present invention aims to provide a method for recovering iron phosphate from waste lithium iron phosphate materials with a shorter process.

[0012] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0013] A method for recovering iron phosphate from waste lithium iron phosphate active materials includes the following steps:

[0014] S1. Provides active materials from waste lithium iron phosphate after oxidative roasting;

[0015] S2. Place the waste lithium iron phosphate active material described in S1 into an acid solution leaching system. After leaching, the solid and liquid are separated to obtain hydrated iron phosphate and a lithium-rich solution.

[0016] Wherein: the acid solution leaching system contains phosphoric acid, and is referred to as the phosphoric acid leaching system, wherein the initial molar amount of phosphoric acid is 1.8-2.5 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1;

[0017] Alternatively, the acid leaching system contains phosphoric acid and a strong acid, denoted as the phosphoric acid and strong acid leaching system, wherein the initial concentration of phosphoric acid is ≥1.0 mol / L, and the initial molar amount of phosphoric acid and the H+ content of the strong acid are... + The initial sum of molar amounts is 1.3-2.5 times the sum of molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1, wherein the strong acid contains H + The initial molar amount is lower than the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1.

[0018] Alternatively, the acid leaching system contains phosphate and a strong acid, denoted as the phosphate-strong acid leaching system, wherein the sum of the initial concentrations of phosphate, monohydrogen phosphate, and dihydrogen phosphate provided by the phosphate is ≥0.8 mol / L, and the H+ content of the strong acid is ≥0.8 mol / L. + The initial molar amount is 1.2-2.0 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1;

[0019] Alternatively, the acid leaching system contains phosphate, phosphoric acid, and a strong acid, and is denoted as the phosphate, phosphoric acid, and strong acid leaching system, wherein the sum of the initial concentrations of phosphate, monohydrogen phosphate, and dihydrogen phosphate provided by phosphoric acid and phosphate is ≥0.8 mol / L, and the initial molar amount of phosphoric acid and the H+ content of the strong acid are ≥0.8 mol / L. + The sum of the initial molar amounts is 1.2-2.5 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1, and the initial molar amounts of phosphoric acid and the H content of the strong acid are also 1.2-2.5 times the sum of the initial molar amounts of phosphoric acid and the H content of the strong acid. + The ratio of the sum of the initial molar amounts of the components to the initial molar amount of the phosphate is 2.5 to 6.0.

[0020] Thus, in the oxidative roasting of waste lithium iron phosphate active materials, ferrous iron has been oxidized to ferric iron, and the electrolytes, binders, solvents, and other organic matter, as well as acetylene black and conductive carbon contained in the waste lithium iron phosphate, have been oxidized and removed. This lays a good foundation for subsequent selective leaching through an acid solution leaching system to simultaneously generate high-purity hydrated iron phosphate. Subsequently, through the leaching treatment of the acid solution leaching system of this invention, Li in Li3Fe2(PO4)3 in the waste lithium iron phosphate active materials can enter the liquid phase, and Fe can be converted into hydrated iron phosphate solid. Fe in Fe2O3 can also be converted into hydrated iron phosphate solid. After leaching, solid-liquid separation can be achieved, thus separating hydrated iron phosphate from the lithium-rich solution. Therefore, this invention can separate Fe and phosphate from lithium in waste lithium iron phosphate active materials through a one-step selective leaching process and obtain high-purity hydrated iron phosphate product. Compared with existing processes for separating and recovering iron, phosphorus, and lithium from waste lithium iron phosphate materials, the process is simpler and more compact, and has greater industrial application value and prospects. Subsequently, the obtained hydrated iron phosphate is further washed to obtain battery-grade hydrated iron phosphate; the lithium-rich solution is purified and the pH value is adjusted to generate lithium phosphate.

[0021] The following chemical reactions may occur during the leaching process of S2 in this invention:

[0022] 2Li3Fe2(PO4)3+6H + =6Li + +2H3PO4+4FePO4↓

[0023] Fe2O3+6H + =2Fe 3+ +3H2O

[0024] 2Fe 3+ +2PO4 3- +nH2O=2FePO4·nH2O↓.

[0025] Optionally, in S1, the method for preparing the waste lithium iron phosphate active material after oxidation roasting includes the following steps: after oxidizing and roasting the waste lithium iron phosphate positive electrode sheet, separating it to obtain the waste lithium iron phosphate active material and aluminum foil.

[0026] Preferably, the oxidative calcination temperature is 550-800℃, more preferably 600-750℃, and even more preferably 650-700℃;

[0027] Preferably, the oxidative calcination time is 1-10 hours, more preferably 2-8 hours, and even more preferably 4-5 hours;

[0028] Preferably, oxidative roasting is carried out in an oxygen and / or air atmosphere; oxidative roasting can completely oxidize the divalent iron in lithium iron phosphate to trivalent iron, and can also oxidize and remove organic solvents, binders and conductive carbon in the positive electrode sheet, thereby completely separating the positive electrode active material from the current collector aluminum foil, solving the problem of incomplete separation between the positive electrode active material and the current collector, and also providing a high oxidation-reduction potential as a basis for subsequent selective leaching, laying the foundation for obtaining battery-grade iron phosphate and lithium phosphate products directly without the need for impurity removal.

[0029] Preferably, separation is achieved by one or more of gravity separation, air separation, and sieving.

[0030] Preferably, the aluminum foil has a purity of ≥99wt%. Aluminum foil of this purity also has economic value and can be further recycled or sold.

[0031] Optionally, in S2, the leaching temperature is >60°C, preferably ≥65°C, preferably ≥70°C, more preferably ≥75°C, even more preferably ≥85°C, even more preferably 90-200°C, and even more preferably 95-180°C;

[0032] Preferably, the leaching time is ≥0.5h, more preferably 1-4h, and even more preferably 1.5-2h;

[0033] Furthermore, in S1, the content of Al in the waste lithium iron phosphate active material is <0.05wt%, preferably <0.03wt%, and more preferably ≤0.005wt%. By controlling the aluminum content, it helps to avoid the aluminum removal steps that may be needed later. The content of divalent iron is <1wt%, and more preferably ≤0.1wt%.

[0034] Preferably, the content of Ca is <2wt% and the content of Mg is <1wt%.

[0035] Preferably, the content of Li is 0.5-6 wt%, the content of Fe is 25-40 wt%, and the content of P is 10-20 wt%.

[0036] The reaction formula for oxidative roasting is as follows:

[0037] 6LiFePO4+1.5O2=2Li3Fe2(PO4)3+Fe2O3.

[0038] Generally, the main components of waste lithium iron phosphate active materials are Fe2O3 and Li3Fe2(PO4)3.

[0039] Optionally, in S2, in the phosphoric acid and strong acid leaching system, the initial molar amount of phosphoric acid is 0.7-1.8 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1. Optionally, the strong acid contains H... +The sum of the initial molar amounts is 0.5-0.8 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1.

[0040] Optionally, in S2, the initial molar amount of phosphoric acid in the phosphoric acid leaching system is 1.8-2.4 times, preferably 1.8-2.1 times, the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1.

[0041] Alternatively, in the phosphoric acid and strong acid leaching system, the initial concentration of phosphoric acid is 1.1-6 mol / L, preferably 1.2-5 mol / L, and the initial molar amount of phosphoric acid and the H content of the strong acid are... + The sum of the initial molar amounts is 1.4-2.4 times, preferably 1.5-2.3 times, the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1.

[0042] Alternatively, in the phosphate and strong acid leaching system, the sum of the initial concentrations of phosphate, monohydrogen phosphate, and dihydrogen phosphate is 0.9-1.5 mol / L, preferably 1-1.4 mol / L, and even more preferably 1.1-1.3 mol / L, and the strong acid contains H+. + The initial molar amount is 1.2-1.9 times, preferably 1.2-1.6 times, and even more preferably 1.2-1.4 times, the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1.

[0043] Alternatively, in the phosphate, phosphoric acid, and strong acid leaching system, the initial concentration of phosphate ions provided by phosphoric acid and phosphate is 1.0-1.4 mol / L, preferably 1.1-1.3 mol / L, and the initial molar amount of phosphoric acid and the H content of the strong acid are... + The sum of the initial molar amounts is 1.3-1.7 times, preferably 1.3-1.5 times, the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1, and the initial molar amounts of phosphoric acid and the H content of the strong acid are also present. + The ratio of the sum of the initial molar amounts of the strong acid to the initial molar amount of the phosphate is 2.7–5.5, preferably 3.0–5.0. Optionally, the H+ contained in the strong acid... + The initial molar amount is not higher than 2.0 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1, and more preferably not higher than 1.5 times; preferably, the phosphate is a dihydrogen phosphate.

[0044] Preferably, the strong acid includes one or more of hydrochloric acid, sulfuric acid, and nitric acid;

[0045] Preferably, the phosphate includes one or more of sodium phosphate, sodium monohydrogen phosphate, sodium dihydrogen phosphate, potassium phosphate, potassium monohydrogen phosphate, and potassium dihydrogen phosphate.

[0046] Optionally, in step S2, after leaching, the pH of the leaching system is adjusted to 1.8-2.5, aged for 0-5 hours, and then solid-liquid separation is performed. Preferably, after leaching, the pH of the leaching system is adjusted to 1.9-2.4, aged for 0.5-2 hours, and then solid-liquid separation is performed. Preferably, a first alkaline reagent is used to adjust the pH of the leaching system, which includes one or more of ammonia, sodium hydroxide, and potassium hydroxide. Aging and alkalinity adjustment can reduce the loss of iron and phosphorus elements in the leachate, further improving the iron and phosphorus recovery rate.

[0047] Optionally, in S2, after solid-liquid separation, the obtained solid phase is washed to obtain hydrated iron phosphate; washing can remove other substances adhering to the surface of hydrated iron phosphate, further improving the purity of the hydrated iron phosphate product and helping to obtain battery-grade hydrated iron phosphate (purity >99.95%).

[0048] Preferably, the obtained solid phase is washed with water 3-8 times, more preferably 4-6 times; more preferably, each time the solid phase is washed, the solid phase is mixed with water at a solid-liquid mass ratio of 1:3-8, and stirred at a rate of ≥150 rpm for 10-60 min under conditions of ≥60°C, and then the solid and liquid are separated; even more preferably, each time the solid phase is washed, the solid phase is mixed with water at a solid-liquid mass ratio of 1:5-7, and stirred at a rate of 200-300 rpm for 20-30 min under conditions of 70-80°C, and then the solid and liquid are separated.

[0049] Optionally, after S2, the pH of the lithium-rich solution is adjusted to 6.8-8.5, followed by solid-liquid separation to obtain a purified lithium-rich solution; preferably, the pH of the lithium-rich solution is adjusted to 7-7.5. Preferably, a second alkaline reagent is used to adjust the pH of the lithium-rich solution, and the second alkaline reagent includes one or more of ammonia, sodium hydroxide, and potassium hydroxide. By adjusting the pH, small amounts of impurities such as Al, Ca, and Mg contained in the lithium-rich solution can be converted into precipitates, which can then be removed by solid-liquid separation, further preparing for the preparation of high-purity ferric phosphate.

[0050] Optionally, some or all of the lithium-rich purified solution can be returned to S2 for use in constructing an acid leaching system. This allows for the reuse of water, excess phosphate, hydrogen ions, etc., avoiding reagent waste and helping to further reduce processing costs. Generally, when constructing an acid leaching system, relevant substances from strong acid, phosphoric acid, and phosphate can be added as needed.

[0051] Optionally, the pH value of part or all of the lithium-rich purification solution is adjusted to 10-12, and after reacting for 20-120 minutes, solid-liquid separation is performed to obtain lithium phosphate product; preferably, the purity of the lithium phosphate product can reach more than 99.5 wt%.

[0052] Preferably, the pH value of the lithium-rich purification solution is adjusted to 11-12, and after reacting for 30-60 minutes, solid-liquid separation is performed.

[0053] Preferably, the method further includes a step of washing the lithium phosphate product; more preferably, during washing, the lithium phosphate product is mixed with water at a solid-liquid mass ratio of 1:3-8, and the mixture is stirred and washed 2-5 times at a speed of ≥150 rpm under conditions of ≥50°C, followed by solid-liquid separation; even more preferably, during washing, the lithium phosphate product is mixed with water at a solid-liquid mass ratio of 1:4-5, and the mixture is stirred and washed 3-4 times at a speed of ≥150 rpm under conditions of 60-90°C, followed by solid-liquid separation.

[0054] The leaching system of this invention is strongly acidic, which dissolves the iron oxide in the oxidized and roasted waste lithium iron phosphate active material and converts ferric iron into lithium iron phosphate. Simultaneously, the leaching system contains a high concentration of phosphate, which inhibits the dissolution of ferric phosphate, effectively reducing iron-phosphorus leaching losses and thus achieving selective lithium leaching, allowing ferric phosphate to remain in the slag phase. Furthermore, a certain temperature can be controlled during the leaching process to promote the dissolution of iron oxide and its conversion into hydrated ferric phosphate, while simultaneously completing the crystallization of hydrated ferric phosphate, facilitating the one-step production of crystallized hydrated ferric phosphate products. Moreover, by controlling the leaching temperature, the solubility of lithium phosphate in the leaching system can be effectively increased, and the iron leaching rate can be reduced, resulting in a more thorough separation of ferric phosphate and lithium.

[0055] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0056] (1) The method of this invention has a short process and high selectivity. It can achieve the leaching, separation and recovery of valuable elements such as iron, phosphorus and lithium in one step to obtain high-purity hydrated iron phosphate and other products. The purity of the hydrated iron phosphate product can reach the battery grade. It has high comprehensive processing efficiency and greater development prospects and industrialization potential. More specifically, this invention achieves selective leaching of lithium in an acidic phosphoric acid / phosphate leaching environment. The phosphate atmosphere completely converts all trivalent iron phases into hydrated iron phosphate, and the leaching process can be carried out at high temperature. While replacing and synthesizing iron phosphate, the crystallization of iron phosphate is also completed, and Li is retained in the liquid phase. Thus, after leaching, battery-grade crystallized hydrated iron phosphate product and lithium-rich solution can be directly produced. Selective lithium leaching and battery-grade iron phosphate product production can be achieved in one step. Selective lithium extraction, iron phosphate product synthesis and iron phosphate product crystallization and concentration are concentrated in one process step, which greatly shortens the recovery process steps, reduces reagent consumption and loss of valuable elements in the process steps, and reduces recovery costs.

[0057] (2) The method of the present invention does not require high-energy ball milling and other processes, has lower energy consumption, and mainly uses wet metallurgical equipment, which is simpler and easier to operate, and helps to further reduce processing costs.

[0058] (3) The method of the present invention can realize the recycling of all elements such as aluminum foil, iron, phosphorus and lithium in waste lithium iron phosphate cathode sheets, avoiding the waste of valuable elements, and the recycled products have high purity. For example, the purity of lithium phosphate products is >99.5% and the purity of battery-grade hydrated iron phosphate is >99.95%. The process route has considerable economic benefits and strong industrialization feasibility.

[0059] (4) The method of the present invention does not require the use of oxidant during the leaching process, resulting in lower reagent costs. It also eliminates concerns about the accuracy of the oxidant addition, which could affect the leaching effect and helps to reduce the difficulty of process control. Attached Figure Description

[0060] Figure 1 This is a process flow diagram of the present invention for recovering battery-grade iron phosphate and lithium salts from waste lithium iron phosphate materials.

[0061] Figure 2 This is a digital photograph of hydrated ferric phosphate from Example 1.

[0062] Figure 3 This is a digital photograph of the solid phase obtained in S2 of Comparative Example 1.

[0063] Figure 4 a is a digital photograph of the reaction system sample after the S2 leaching reaction in Comparative Example 2.

[0064] Figure 4 b is a digital photograph of the solid-liquid separation (vacuum filtration) of the reaction system sample after the S2 leaching reaction in Comparative Example 2.

[0065] Figure 5 This is a digital photograph of the solid phase obtained in S2 of Comparative Example 3.

[0066] Figure 6 This is a digital photograph of the solid phase obtained in S2 of Comparative Example 6.

[0067] Figure 7 This is the XRD pattern of hydrated iron phosphate obtained in Example 1.

[0068] Figure 8 This is the XRD pattern of the solid obtained from S2 in Comparative Example 1.

[0069] Figure 9 This is the XRD pattern of the solid obtained from S2 in Comparative Example 6. Detailed Implementation

[0070] The present invention will be described in detail below with reference to embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be combined with each other. Unless otherwise specified, the relevant percentages refer to mass percentages.

[0071] Example 1

[0072] See Figure 1 A method for recovering iron phosphate from waste lithium iron phosphate active materials includes the following steps:

[0073] S1. After oxidizing and roasting the waste lithium iron phosphate positive electrode sheet to be treated, separate it to obtain waste lithium iron phosphate active material and aluminum foil.

[0074] The oxidation roasting temperature was 600℃ and the oxidation roasting time was 3h; the oxidation roasting was carried out in an air atmosphere; separation was performed by sieving; the waste lithium iron phosphate active material contained 4.111% Li, 32.049% Fe, 0.0022% Al, 16.867% P, and 0.053% ferrous iron.

[0075] S2. The waste lithium iron phosphate active material described in S1 is placed in an acid leaching system and leached at 95°C for 1.5 hours. After adjusting the pH of the leaching system to 2.3, it is aged at 95°C for 1.5 hours. Solid-liquid separation is performed to obtain a solid phase and a lithium-rich solution. In this embodiment, the lithium leaching rate is 100%. The solid phase is washed to obtain battery-grade hydrated lithium iron phosphate (see actual image). Figure 2 (It is a pure white substance).

[0076] The acid leaching system is a pure phosphoric acid leaching system, wherein the initial molar amount of phosphoric acid is 1.9 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1. The pH value of the leaching system is adjusted using a first alkaline reagent, which is ammonia. The obtained solid phase is washed with water six times; during each wash, the solid phase and water are mixed at a solid-liquid mass ratio of 1:4, stirred at 200 rpm for 20 minutes at 70°C, and then the solid and liquid phases are separated.

[0077] S3. After adjusting the pH value of the lithium-rich solution to 7.0, solid-liquid separation is performed to obtain a lithium-rich purified solution.

[0078] The pH value of the lithium-rich solution is adjusted using a second alkaline reagent, which is ammonia.

[0079] S4. Adjust the pH value of the lithium-rich purification solution to 11.6, react for 60 minutes, then separate the solid and liquid, wash, and obtain a high-purity lithium phosphate product.

[0080] During the washing process, lithium phosphate product is mixed with water at a solid-liquid mass ratio of 1:5, and washed four times at 60°C to separate the solid and liquid components.

[0081] Testing revealed that the purity of the battery-grade hydrated iron phosphate was 99.97%, the purity of the lithium phosphate product was 99.71%, the yield of Fe (calculated as hydrated iron phosphate) was 99.14%, and the yield of Li (calculated as lithium phosphate) was 97.74%.

[0082] Example 2

[0083] Repeat Example 1, except that:

[0084] S2. The waste lithium iron phosphate active material described in S1 is placed in an acid solution leaching system and leached at 110°C for 2 hours. After adjusting the pH value of the leaching system to 1.95, it is aged at 95°C for 1 hour. Solid-liquid separation is performed to obtain a solid phase and a lithium-rich solution. In this embodiment, the lithium leaching rate is 100%. The solid phase is washed to obtain battery-grade hydrated iron phosphate.

[0085] The acid leaching system is a pure phosphoric acid leaching system, wherein the initial molar amount of phosphoric acid is 1.8 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1. The pH value of the leaching system is adjusted using a first alkaline reagent, which is ammonia. The obtained solid phase is washed with water six times; during each wash, the solid phase and water are mixed at a solid-liquid mass ratio of 1:4, stirred at 200 rpm for 20 minutes at 70°C, and then the solid and liquid phases are separated.

[0086] S3. After adjusting the pH value of the lithium-rich solution to 7.0, solid-liquid separation is performed to obtain a lithium-rich purified solution.

[0087] The pH value of the lithium-rich solution is adjusted using a second alkaline reagent, which is ammonia.

[0088] S4. Adjust the pH value of the lithium-rich purification solution to 11.0, react for 60 minutes, then separate the solid and liquid, wash, and obtain a high-purity lithium phosphate product.

[0089] During the washing process, lithium phosphate product is mixed with water at a solid-liquid mass ratio of 1:5, and washed three times at 60°C to separate the solid and liquid components.

[0090] Testing revealed that the purity of the battery-grade hydrated iron phosphate was 99.96%, the purity of the lithium phosphate product was 99.38%, the yield of Fe (calculated as hydrated iron phosphate) was 98.78%, and the yield of Li (calculated as lithium phosphate) was 97.03%.

[0091] Example 3

[0092] Repeat Example 1, except that:

[0093] S2. The waste lithium iron phosphate active material described in S1 is placed in an acid solution leaching system and leached at 90°C for 3.5 hours. After adjusting the pH value of the leaching system to 1.8, it is aged at 95°C for 1.5 hours. Solid-liquid separation is performed to obtain a solid phase and a lithium-rich solution. In this embodiment, the lithium leaching rate is 100%. The solid phase is washed to obtain battery-grade hydrated iron phosphate.

[0094] The acid leaching system is a pure phosphoric acid leaching system, wherein the initial molar amount of phosphoric acid is 2.5 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1. The pH value of the leaching system is adjusted using a first alkaline reagent, which is ammonia. The obtained solid phase is washed with water six times; during each wash, the solid phase and water are mixed at a solid-liquid mass ratio of 1:4, stirred at 200 rpm for 20 minutes at 70°C, and then the solid and liquid phases are separated.

[0095] S3. After adjusting the pH value of the lithium-rich solution to 7.0, solid-liquid separation is performed to obtain a lithium-rich purified solution.

[0096] The pH value of the lithium-rich solution is adjusted using a second alkaline reagent, which is ammonia.

[0097] S4. Adjust the pH value of the lithium-rich purification solution to 12.0, react for 60 minutes, then separate the solid and liquid, wash, and obtain a high-purity lithium phosphate product.

[0098] During the washing process, lithium phosphate product is mixed with water at a solid-liquid mass ratio of 1:5, and washed five times at 60°C to separate the solid and liquid components.

[0099] Testing revealed that the purity of the battery-grade hydrated iron phosphate was 99.95%, the purity of the lithium phosphate product was 99.13%, the yield of Fe (calculated as hydrated iron phosphate) was 98.29%, and the yield of Li (calculated as lithium phosphate) was 97.89%.

[0100] Comparative Example 1

[0101] Example 1 is repeated, except that in S2, the initial molar amount of phosphoric acid is 1.7 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1; and the leaching time is 2 hours.

[0102] The results showed that the precipitate obtained from S2 was a pink mixture of Fe2O3 and FePO4 (see [reference]). Figure 3 Therefore, it is impossible to obtain battery-grade hydrated iron phosphate products.

[0103] Comparative Example 2

[0104] Example 1 is repeated, except that in S2, the initial molar amount of phosphoric acid is 3.0 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1; and the leaching time is 2 hours.

[0105] The results showed that after leaching in S2, the solid phase was almost completely dissolved, with lithium leaching rate of 100% and iron leaching rate of 89.71% (see [reference]). Figure 4 Afterwards, a large amount of alkali needs to be added to adjust the pH value in order to precipitate ferric phosphate.

[0106] Example 4

[0107] A method for recovering iron phosphate from waste lithium iron phosphate active materials includes the following steps:

[0108] S1. After oxidizing and roasting the waste lithium iron phosphate positive electrode sheet to be treated, separate it to obtain waste lithium iron phosphate active material and aluminum foil.

[0109] The oxidation roasting temperature was 620℃, and the oxidation roasting time was 3h; the oxidation roasting was carried out in an air atmosphere; separation was performed by sieving; the waste lithium iron phosphate active material contained 4.109% Li, 33.347% total Fe, 0.0024% Al, 16.689% P, and 0.041% ferrous iron.

[0110] S2. The waste lithium iron phosphate active material described in S1 is placed in an acid solution leaching system and leached at 90°C for 5 hours. After adjusting the pH value of the leaching system to 1.95, it is aged at 98°C for 1 hour. Solid-liquid separation is performed to obtain a solid phase and a lithium-rich solution. In this embodiment, the lithium leaching rate is 100%. The solid phase is washed to obtain battery-grade hydrated iron phosphate.

[0111] The acid leaching system is a mixed acid leaching system of strong acid (hydrochloric acid) and phosphoric acid, wherein the initial concentration of phosphoric acid is 3.0 mol / L, and the initial molar amount of phosphoric acid and the H content of the strong acid are... + The initial molar sum of the amounts is 1.7 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1 (wherein, the initial molar amount of phosphoric acid is 1.2 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material, and the H content of the strong acid is...). + The initial molar amount is 0.5 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1. The pH value of the leaching system is adjusted using a first alkaline reagent, which is sodium hydroxide. The obtained solid phase is washed with water four times; during each wash, the solid phase and water are mixed at a solid-liquid mass ratio of 1:5, stirred at 250 rpm for 25 min at 80°C, and then the solid and liquid are separated.

[0112] S3. After adjusting the pH value of the lithium-rich solution to 7.2, solid-liquid separation is performed to obtain a lithium-rich purified solution.

[0113] In this process, a second alkaline reagent is used to adjust the pH value of the lithium-rich solution. The second alkaline reagent is sodium hydroxide.

[0114] S4. Adjust the pH value of the lithium-rich purification solution to 11.5, react for 30 minutes, then separate the solid and liquid, wash, and obtain a high-purity lithium phosphate product.

[0115] During the washing process, lithium phosphate product is mixed with water at a solid-liquid mass ratio of 1:4, and washed three times at 80°C to separate the solid and liquid components.

[0116] Testing revealed that the purity of the battery-grade hydrated iron phosphate was 99.95%, the purity of the lithium phosphate product was 99.60%, the yield of Fe (calculated as hydrated iron phosphate) was 98.69%, and the yield of Li (calculated as lithium phosphate) was 97.81%.

[0117] Example 5

[0118] Example 4 is repeated, except that in S2, the waste lithium iron phosphate active material described in S1 is placed in an acid leaching system and leached at 98°C for 1.5 hours. After adjusting the pH of the leaching system to 2.03, it is aged at 98°C for 0.5 hours. Solid-liquid separation is performed to obtain a solid phase and a lithium-rich solution. In this example, the lithium leaching rate is 100%. The solid phase is washed to obtain battery-grade hydrated iron phosphate.

[0119] The acid leaching system is a mixed acid leaching system of strong acid (hydrochloric acid) and phosphoric acid, wherein the initial concentration of phosphoric acid is 3.8 mol / L, and the initial molar amount of phosphoric acid and the H content of the strong acid are... + The initial molar sum of the amounts is 2.0 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1 (wherein, the initial molar amount of phosphoric acid is 1.5 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material, and the H content of the strong acid is...). + The initial molar amount is 0.5 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1.

[0120] The purity of the obtained battery-grade hydrated iron phosphate was 99.96%, the purity of the lithium phosphate product was 99.38%, the yield of Fe based on hydrated iron phosphate was 98.77%, and the yield of Li based on lithium phosphate was 97.61%.

[0121] Example 6

[0122] Example 4 is repeated, except that in S2, the waste lithium iron phosphate active material described in S1 is placed in an acid leaching system and leached at 95°C for 1.5 hours. After adjusting the pH of the leaching system to 1.95, it is aged at 98°C for 1 hour. Solid-liquid separation is performed to obtain a solid phase and a lithium-rich solution. In this example, the lithium leaching rate is 100%. The solid phase is washed to obtain battery-grade hydrated iron phosphate.

[0123] The acid leaching system is a mixed acid leaching system of strong acid (hydrochloric acid) and phosphoric acid, wherein the initial concentration of phosphoric acid is 4.1 mol / L, and the initial molar amount of phosphoric acid and the H content of the strong acid are... + The initial molar sum of the amounts is 2.5 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1 (wherein, the initial molar amount of phosphoric acid is 1.7 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material, and the H content of the strong acid is...). + The initial molar amount is 0.8 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1.

[0124] The purity of the obtained battery-grade hydrated iron phosphate was 99.96%, the purity of the lithium phosphate product was 99.27%, the yield of Fe based on hydrated iron phosphate was 98.54%, and the yield of Li based on lithium phosphate was 97.84%.

[0125] Example 7

[0126] Example 4 is repeated, except that in S2, the waste lithium iron phosphate active material described in S1 is placed in an acid leaching system and leached at 98°C for 1.5 hours. After adjusting the pH of the leaching system to 2.17, it is aged at 98°C for 0.5 hours. Solid-liquid separation is performed to obtain a solid phase and a lithium-rich solution. In this example, the lithium leaching rate is 100%. The solid phase is washed to obtain battery-grade hydrated iron phosphate.

[0127] The acid leaching system is a mixed acid leaching system of strong acid (sulfuric acid) and phosphoric acid, wherein the initial concentration of phosphoric acid is 3.8 mol / L, and the initial molar amount of phosphoric acid and the H content of the strong acid are... + The initial molar sum of the amounts is 2.0 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1 (wherein, the initial molar amount of phosphoric acid is 1.5 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material, and the H content of the strong acid is...). + The initial molar amount is 0.5 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1.

[0128] The purity of the obtained battery-grade hydrated iron phosphate was 99.95%, the purity of the lithium phosphate product was 99.35%, the yield of Fe based on hydrated iron phosphate was 98.83%, and the yield of Li based on lithium phosphate was 97.59%.

[0129] Example 8

[0130] Example 4 is repeated, except that in S2, the waste lithium iron phosphate active material described in S1 is placed in an acid solution leaching system and leached at 98°C for 2 hours. After adjusting the pH value of the leaching system to 1.95, it is aged at 98°C for 1.0 hour. Solid-liquid separation is performed to obtain a solid phase and a lithium-rich solution, wherein the lithium leaching rate is 100%. The solid phase is washed to obtain battery-grade hydrated iron phosphate.

[0131] The acid leaching system is a mixed acid leaching system of strong acid (hydrochloric acid) and phosphoric acid, wherein the initial concentration of phosphoric acid is 1.27 mol / L, and the initial molar amount of phosphoric acid and the H content of the strong acid are... + The initial molar sum of the amounts is 1.3 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1 (wherein, the initial molar amount of phosphoric acid is 0.7 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material, and the H content of the strong acid is...). + The initial molar amount is 0.6 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1.

[0132] The purity of the obtained battery-grade hydrated iron phosphate was 99.95%, the purity of the lithium phosphate product was 99.33%, the yield of Fe based on hydrated iron phosphate was 98.32%, and the yield of Li based on lithium phosphate was 96.42%.

[0133] Comparative Example 3

[0134] Example 4 is repeated, except that in S2, the waste lithium iron phosphate active material described in S1 is placed in an acid solution leaching system and leached at 98°C for 1.5 hours. Then, solid-liquid separation is performed to obtain a solid phase.

[0135] The acid leaching system is a mixed acid leaching system of strong acid (hydrochloric acid) and phosphoric acid, wherein the initial concentration of phosphoric acid is 1 mol / L, and the initial molar amount of phosphoric acid and the H content of the strong acid are... + The initial molar sum of the amounts is 1.1 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1 (wherein, the initial molar amount of phosphoric acid is 0.4 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material, and the H content of the strong acid is...). +The initial molar amount is 0.7 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1.

[0136] Upon testing, the obtained solid precipitate was also pink (see...). Figure 5 Therefore, it is evident that battery-grade hydrated iron phosphate products cannot be obtained at this time.

[0137] Comparative Example 4

[0138] Example 4 was repeated, except that in S2, the waste lithium iron phosphate active material described in S1 was placed in an acid leaching system and leached at 98°C for 1.5 hours. In this comparative example S2, the solid phase was almost completely dissolved, with all lithium leached out and the iron leaching rate being 93.762%.

[0139] The acid leaching system is a mixed acid leaching system of strong acid (hydrochloric acid) and phosphoric acid, wherein the initial concentration of phosphoric acid is 1.5 mol / L, and the initial molar amount of phosphoric acid and the H content of the strong acid are... + The initial molar sum of the amounts is 2.6 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1 (wherein, the initial molar amount of phosphoric acid is 0.6 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material, and the H content of the strong acid is...). + The initial molar amount is 2.0 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1.

[0140] Example 9

[0141] A method for recovering iron phosphate from waste lithium iron phosphate active materials includes the following steps:

[0142] S1. After oxidizing and roasting the waste lithium iron phosphate positive electrode sheet to be treated, separate it to obtain waste lithium iron phosphate active material and aluminum foil.

[0143] The oxidation roasting temperature was 580℃, and the oxidation roasting time was 5h; the oxidation roasting was carried out in an air atmosphere; separation was performed by sieving; the waste lithium iron phosphate active material contained 4.116% Li, 33.178% total Fe, 0.0013% Al, 16.735% P, and 0.0489% ferrous iron.

[0144] S2. The waste lithium iron phosphate active material described in S1 is placed in an acid solution leaching system and leached at 98°C for 2 hours. The pH at the leaching endpoint is 1.8. Solid-liquid separation is performed to obtain a solid phase and a lithium-rich solution. In this embodiment, the lithium leaching rate is 99.62%. The solid phase is washed to obtain battery-grade hydrated iron phosphate.

[0145] The acid leaching system is a mixed acid leaching system of strong acid (hydrochloric acid) and phosphate (sodium dihydrogen phosphate). In this system, the initial concentration of dihydrogen phosphate provided by the phosphate is 0.8 mol / L, and the strong acid contains H₂... + The initial molar amount was 1.2 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1. The obtained solid phase was washed with water four times; each time, the solid phase and water were mixed at a solid-liquid mass ratio of 1:6, stirred at 200 rpm for 20 min at 85°C, and then the solid and liquid were separated.

[0146] S3. After adjusting the pH value of the lithium-rich solution to 6.8, solid-liquid separation is performed to obtain a lithium-rich purified solution.

[0147] In this process, a second alkaline reagent is used to adjust the pH value of the lithium-rich solution. The second alkaline reagent is sodium hydroxide.

[0148] S4. Adjust the pH value of the lithium-rich purification solution to 11.8, react for 60 minutes, then separate the solid and liquid, wash, and obtain a high-purity lithium phosphate product.

[0149] During the washing process, lithium phosphate product is mixed with water at a solid-liquid mass ratio of 1:4, and washed three times at 80°C to separate the solid and liquid components.

[0150] Testing revealed that the purity of the battery-grade hydrated iron phosphate was 99.95%, the purity of the lithium phosphate product was 99.37%, the yield of Fe (calculated as hydrated iron phosphate) was 98.02%, and the yield of Li (calculated as lithium phosphate) was 97.68%.

[0151] Example 10

[0152] Example 9 was repeated, except that in S2, the waste lithium iron phosphate active material described in S1 was placed in an acid solution leaching system and leached at 180°C for 0.5 hours. The pH value at the leaching endpoint was 2.31. Solid-liquid separation was performed to obtain a solid phase and a lithium-rich solution. The lithium leaching rate in this example was 99.64%.

[0153] The acid leaching system is a mixed acid leaching system of strong acid (hydrochloric acid) and phosphate (sodium dihydrogen phosphate). In this system, the initial concentration of dihydrogen phosphate provided by the phosphate is 1.18 mol / L, and the strong acid contains H₂... + The initial molar amount is 1.5 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1.

[0154] The purity of the obtained battery-grade hydrated iron phosphate was 99.97%, the purity of the lithium phosphate product was 99.77%, the yield of Fe based on hydrated iron phosphate was 98.97%, and the yield of Li based on lithium phosphate was 98.14%.

[0155] Example 11

[0156] Example 9 was repeated, except that in S2, the waste lithium iron phosphate active material described in S1 was placed in an acid leaching system and leached at 95°C for 2 hours. After the pH value at the leaching endpoint was 2.23, solid-liquid separation was performed to obtain a solid phase and a lithium-rich solution. In this example, the lithium leaching rate was 99.42%.

[0157] The acid leaching system is a mixed acid leaching system of strong acid (hydrochloric acid) and phosphate (sodium dihydrogen phosphate). In this system, the initial concentration of dihydrogen phosphate provided by the phosphate is 1.5 mol / L, and the strong acid contains H₂... + The initial molar amount is 2.0 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1.

[0158] The purity of the obtained battery-grade hydrated iron phosphate was 99.95%, the purity of the lithium phosphate product was 99.19%, the yield of Fe based on hydrated iron phosphate was 98.66%, and the yield of Li based on lithium phosphate was 97.93%.

[0159] Example 12

[0160] Example 9 was repeated, except that in S2, the waste lithium iron phosphate active material described in S1 was placed in an acid leaching system and leached at 180°C for 0.5 hours. The pH at the leaching endpoint was 2.4. Solid-liquid separation was performed to obtain a solid phase and a lithium-rich solution. In this example, the lithium leaching rate was 99.37%.

[0161] The acid leaching system is a mixed acid leaching system of strong acid (sulfuric acid) and phosphate (sodium dihydrogen phosphate). In this system, the initial concentration of dihydrogen phosphate provided by the phosphate is 1.18 mol / L, and the H+ content of the strong acid is... + The initial molar amount is 1.5 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1.

[0162] The purity of the obtained battery-grade hydrated iron phosphate was 99.96%, the purity of the lithium phosphate product was 99.84%, the yield of Fe based on hydrated iron phosphate was 99.02%, and the yield of Li based on lithium phosphate was 98.22%.

[0163] Comparative Example 5

[0164] Example 9 is repeated, except that in S2, the waste lithium iron phosphate active material described in S1 is placed in an acid solution leaching system and leached at 98°C for 2 hours. After solid-liquid separation, a pink solid phase is obtained, that is, the solid product contains a non-hydrated iron phosphate impurity phase.

[0165] The acid leaching system is a mixed acid leaching system of strong acid (hydrochloric acid) and phosphate (sodium dihydrogen phosphate). In this system, the initial concentration of dihydrogen phosphate provided by the phosphate is 0.65 mol / L, and the strong acid contains H₂... + The initial molar amount is 1.2 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1.

[0166] Comparative Example 6

[0167] Example 9 is repeated, except that in S2, the waste lithium iron phosphate active material described in S1 is placed in an acid leaching system and leached at 98°C for 2 hours, followed by solid-liquid separation to obtain a brown solid phase (see Example 9). Figure 6 This means that the solid product contains a non-hydrated iron phosphate impurity phase.

[0168] The acid leaching system is a mixed acid leaching system of strong acid (hydrochloric acid) and phosphate (sodium dihydrogen phosphate). In this system, the initial concentration of dihydrogen phosphate provided by the phosphate is 0.8 mol / L, and the strong acid contains H₂... + The initial molar amount is 1.0 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1.

[0169] XRD analysis results of brown solids are as follows Figure 9 As shown, the main phase composition is ferric hydroxide and hydrated ferric phosphate. A possible reason is that sodium dihydrogen phosphate is a strong base-weak acid salt; when the amount of hydrochloric acid is insufficient, the system becomes too alkaline, and the dissolved iron preferentially reacts to form ferric hydroxide.

[0170] Comparative Example 7

[0171] Example 9 was repeated, except that in S2, the waste lithium iron phosphate active material described in S1 was placed in an acid leaching system and leached at 98°C for 3 hours. It was found that the solid phase was almost dissolved, with a lithium leaching rate of 100% and an iron leaching rate of 93.53%. A large amount of alkali was required to adjust the pH value to achieve the precipitation of iron phosphate.

[0172] The acid leaching system is a mixed acid leaching system of strong acid (hydrochloric acid) and phosphate (sodium dihydrogen phosphate). In this system, the initial concentration of dihydrogen phosphate provided by the phosphate is 0.8 mol / L, and the strong acid contains H₂...+ The initial molar amount is 2.1 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1.

[0173] Example 13

[0174] A method for recovering iron phosphate from waste lithium iron phosphate active materials includes the following steps:

[0175] S1. After oxidizing and roasting the waste lithium iron phosphate positive electrode sheet to be treated, separate it to obtain waste lithium iron phosphate active material and aluminum foil.

[0176] The oxidation roasting temperature was 600℃ and the oxidation roasting time was 3h; the oxidation roasting was carried out in an air atmosphere; separation was performed by sieving; the waste lithium iron phosphate active material contained 4.111% Li, 32.049% Fe, 0.0022% Al, 16.867% P, and 0.053% ferrous iron.

[0177] S2. The waste lithium iron phosphate active material described in S1 is placed in an acid solution leaching system and leached at 98°C for 2 hours. The pH at the leaching endpoint is 1.8. Solid-liquid separation is performed to obtain a solid phase and a lithium-rich solution. In this embodiment, the lithium leaching rate is 100%. The solid phase is washed to obtain battery-grade hydrated iron phosphate.

[0178] The acid leaching system is a mixed acid leaching system of strong acid (hydrochloric acid) and phosphate (sodium dihydrogen phosphate). In this system, the initial concentration of dihydrogen phosphate provided by the phosphate is 0.8 mol / L, and the strong acid contains H₂... + The initial molar amount is 1.2 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1. The obtained solid phase is washed with water three times; each time, the solid phase and water are mixed at a solid-liquid mass ratio of 1:5, stirred at 250 rpm for 25 min at 80°C, and then the solid and liquid are separated.

[0179] The purity of the battery-grade hydrated iron phosphate was found to be 99.95% upon testing.

[0180] Example 14

[0181] A method for recovering iron phosphate from waste lithium iron phosphate active materials includes the following steps:

[0182] S1. After oxidizing and roasting the waste lithium iron phosphate positive electrode sheet to be treated, separate it to obtain waste lithium iron phosphate active material and aluminum foil.

[0183] The oxidation roasting temperature was 600℃ and the oxidation roasting time was 3h; the oxidation roasting was carried out in an air atmosphere; separation was performed by sieving; the waste lithium iron phosphate active material contained 4.111% Li, 32.049% Fe, 0.0022% Al, 16.867% P, and 0.053% ferrous iron.

[0184] S2. The waste lithium iron phosphate active material described in S1 is placed in an acid solution leaching system and leached at 80°C for 2 hours. The pH value at the leaching endpoint is 1.8. Solid-liquid separation is performed to obtain a solid phase and a lithium-rich solution. The solid phase is washed to obtain battery-grade hydrated iron phosphate.

[0185] The acid leaching system is a mixed acid leaching system of strong acid (hydrochloric acid) and phosphate (sodium dihydrogen phosphate). In this system, the initial concentration of dihydrogen phosphate provided by the phosphate is 0.8 mol / L, and the strong acid contains H₂... + The initial molar amount is 1.2 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1. The obtained solid phase is washed with water three times; each time, the solid phase and water are mixed at a solid-liquid mass ratio of 1:5, stirred at 250 rpm for 25 min at 80°C, and then the solid and liquid are separated.

[0186] S3. After adjusting the pH value of the lithium-rich solution to 6.8, solid-liquid separation is performed to obtain a lithium-rich purified solution.

[0187] In this process, a second alkaline reagent is used to adjust the pH value of the lithium-rich solution. The second alkaline reagent is sodium hydroxide.

[0188] S4. Adjust the pH value of the lithium-rich purification solution to 11.8, react for 60 minutes, then separate the solid and liquid, wash, and obtain a high-purity lithium phosphate product.

[0189] During the washing process, lithium phosphate product is mixed with water at a solid-liquid mass ratio of 1:4, and washed three times at 80°C to separate the solid and liquid components.

[0190] Testing revealed that the purity of the battery-grade hydrated iron phosphate was 99.96%, the purity of the lithium phosphate product was 99.44%, the yield of Fe (calculated as hydrated iron phosphate) was 96.82%, and the yield of Li (calculated as lithium phosphate) was 95.13%.

[0191] Example 15

[0192] Example 14 was repeated, except that in S2, the leaching temperature was 70°C.

[0193] Testing revealed that the purity of the battery-grade hydrated iron phosphate was 99.95%, the purity of the lithium phosphate product was 99.45%, the yield of Fe (calculated as hydrated iron phosphate) was 95.84%, and the yield of Li (calculated as lithium phosphate) was 92.82%.

[0194] Comparative Example 8

[0195] Example 14 was repeated, except that in S2, the leaching temperature was 60°C.

[0196] Testing revealed that the purity of the hydrated ferric phosphate obtained from S2 was 99.57%, and the Fe yield, calculated based on hydrated ferric phosphate, was 55.88%. The lithium leaching rate in S2 was only 62.32%.

[0197] The comparison shows that controlling the leaching temperature can help to further improve leaching efficiency and achieve more thorough separation and recovery of iron and lithium.

[0198] Example 16

[0199] A method for recovering iron phosphate from waste lithium iron phosphate active materials includes the following steps:

[0200] S1. After oxidizing and roasting the waste lithium iron phosphate positive electrode sheet to be treated, separate it to obtain waste lithium iron phosphate active material and aluminum foil.

[0201] The oxidation roasting temperature was 580℃, and the oxidation roasting time was 5h; the oxidation roasting was carried out in an air atmosphere; separation was performed by sieving; the waste lithium iron phosphate active material contained 4.116% Li, 33.178% total Fe, 0.0013% Al, 16.735% P, and 0.0489% ferrous iron.

[0202] S2. The waste lithium iron phosphate active material described in S1 is placed in an acid solution leaching system and leached at 108°C for 2 hours. The pH at the leaching endpoint is 1.83. Solid-liquid separation is performed to obtain a solid phase and a lithium-rich solution. In this embodiment, the lithium leaching rate is 99.79%. The solid phase is washed to obtain battery-grade hydrated iron phosphate.

[0203] The acid leaching system is a mixed acid leaching system of phosphoric acid, strong acid (hydrochloric acid), and phosphate (sodium dihydrogen phosphate). In this system, the initial concentration of phosphate is 0.7 mol / L, and the sum of the initial concentrations of phosphate, monohydrogen phosphate, and dihydrogen phosphate provided by the phosphoric acid and phosphate is 1.2 mol / L. The initial molar amount of phosphoric acid is 0.2 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1. The strong acid contains H... +The initial molar amount is 1.0 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1; the initial molar amount of phosphoric acid and the H content of the strong acid + The sum of the initial molar amounts of the components was 4.1 times the initial molar amount of the phosphate. The resulting solid was washed three times with water. During each wash, the solid was mixed with water at a solid-liquid mass ratio of 1:8 and stirred at 200 rpm for 30 min at 85 °C, followed by solid-liquid separation.

[0204] S3. After adjusting the pH value of the lithium-rich solution to 6.8, solid-liquid separation is performed to obtain a lithium-rich purified solution.

[0205] In this process, a second alkaline reagent is used to adjust the pH value of the lithium-rich solution. The second alkaline reagent is sodium hydroxide.

[0206] S4. Adjust the pH value of the lithium-rich purification solution to 11.8, react for 60 minutes, then separate the solid and liquid, wash, and obtain a high-purity lithium phosphate product.

[0207] During the washing process, lithium phosphate product is mixed with water at a solid-liquid mass ratio of 1:4, and washed three times at 80°C to separate the solid and liquid components.

[0208] Testing revealed that the purity of the battery-grade hydrated iron phosphate was 99.95%, the purity of the lithium phosphate product was 99.56%, the yield of Fe (calculated as hydrated iron phosphate) was 98.73%, and the yield of Li (calculated as lithium phosphate) was 97.85%.

[0209] Example 17

[0210] A method for recovering iron phosphate from waste lithium iron phosphate active materials includes the following steps:

[0211] S1. After oxidizing and roasting the waste lithium iron phosphate positive electrode sheet to be treated, separate it to obtain waste lithium iron phosphate active material and aluminum foil.

[0212] The oxidation roasting temperature was 580℃, and the oxidation roasting time was 5h; the oxidation roasting was carried out in an air atmosphere; separation was performed by sieving; the waste lithium iron phosphate active material contained 4.116% Li, 33.178% total Fe, 0.0013% Al, 16.735% P, and 0.0489% ferrous iron.

[0213] S2. The waste lithium iron phosphate active material described in S1 is placed in an acid solution leaching system and leached at 95°C for 2 hours. After adjusting the pH of the system to 1.95 with sodium hydroxide, it is aged at 98°C for 1 hour. Solid-liquid separation is performed to obtain a solid phase and a lithium-rich solution. In this embodiment, the lithium leaching rate is 100%. The solid phase is washed to obtain battery-grade hydrated iron phosphate.

[0214] The acid leaching system is a mixed acid leaching system of phosphoric acid, strong acid (hydrochloric acid), and phosphate (sodium dihydrogen phosphate). In this system, the initial concentration of phosphate is 1 mol / L, and the sum of the initial concentrations of phosphate, monohydrogen phosphate, and dihydrogen phosphate provided by the phosphoric acid and phosphate is 5.3 mol / L. The initial molar amount of phosphoric acid is 1.8 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1. The strong acid contains H... + The initial molar amount is 0.5 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1; the initial molar amount of phosphoric acid and the H content of the strong acid + The sum of the initial molar amounts of the components was 5.5 times the initial molar amount of the phosphate. The resulting solid was washed with water 6 times; each time, the solid was mixed with water at a solid-liquid mass ratio of 1:8, stirred at 200 rpm for 30 min at 85 °C, and then the solid and liquid were separated.

[0215] S3. After adjusting the pH value of the lithium-rich solution to 6.8, solid-liquid separation is performed to obtain a lithium-rich purified solution.

[0216] In this process, a second alkaline reagent is used to adjust the pH value of the lithium-rich solution. The second alkaline reagent is sodium hydroxide.

[0217] S4. Adjust the pH value of the lithium-rich purification solution to 11.8, react for 60 minutes, then separate the solid and liquid, wash, and obtain a high-purity lithium phosphate product.

[0218] During the washing process, lithium phosphate product is mixed with water at a solid-liquid mass ratio of 1:4, and washed three times at 80°C to separate the solid and liquid components.

[0219] Testing revealed that the purity of the battery-grade hydrated iron phosphate was 99.97%, the purity of the lithium phosphate product was 99.21%, the yield of Fe (calculated as hydrated iron phosphate) was 98.43%, and the yield of Li (calculated as lithium phosphate) was 97.67%.

[0220] The above embodiments should be understood as being used only to illustrate the present invention more clearly, and not to limit the scope of the present invention. After reading the present invention, any modifications of the present invention in various equivalent forms by those skilled in the art fall within the scope defined by the appended claims.

Claims

1. A method for recovering iron phosphate from waste lithium iron phosphate active materials, characterized in that, Includes the following steps: S1. Provides active materials from waste lithium iron phosphate after oxidative roasting; S2. Place the waste lithium iron phosphate active material described in S1 into an acid solution leaching system. After leaching, the solid and liquid are separated to obtain hydrated iron phosphate and a lithium-rich solution. Wherein: the acid solution leaching system contains phosphoric acid, and is referred to as the phosphoric acid leaching system, wherein the initial molar amount of phosphoric acid is 1.8-2.5 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1; Alternatively, the acid leaching system contains phosphoric acid and a strong acid, denoted as the phosphoric acid and strong acid leaching system, wherein the initial concentration of phosphoric acid is ≥1.0 mol / L, and the initial molar amount of phosphoric acid and the H+ content of the strong acid are... + The initial sum of molar amounts is 1.3-2.5 times the sum of molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1, wherein the strong acid contains H + The initial molar amount is lower than the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1. Alternatively, the acid leaching system contains phosphate and a strong acid, denoted as the phosphate-strong acid leaching system, wherein the sum of the initial concentrations of phosphate, monohydrogen phosphate, and dihydrogen phosphate provided by the phosphate is ≥0.8 mol / L, and the H+ content of the strong acid is ≥0.8 mol / L. + The initial molar amount is 1.2-2.0 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1; Alternatively, the acid leaching system contains phosphate, phosphoric acid, and a strong acid, and is denoted as the phosphate, phosphoric acid, and strong acid leaching system, wherein the sum of the initial concentrations of phosphate, monohydrogen phosphate, and dihydrogen phosphate provided by phosphoric acid and phosphate is ≥0.8 mol / L, and the initial molar amount of phosphoric acid and the H+ content of the strong acid are ≥0.8 mol / L. + The sum of the initial molar amounts is 1.2-2.5 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1, and the initial molar amounts of phosphoric acid and the H content of the strong acid are also 1.2-2.5 times the sum of the initial molar amounts of phosphoric acid and the H content of the strong acid. + The ratio of the sum of the initial molar amounts of the components to the initial molar amount of the phosphate is 2.5-6.

0.

2. The method according to claim 1, characterized in that, In S1, the preparation method of the waste lithium iron phosphate active material after oxidation roasting includes the following steps: after oxidizing and roasting the waste lithium iron phosphate positive electrode sheet, it is separated to obtain the waste lithium iron phosphate active material and aluminum foil. Preferably, the oxidative calcination temperature is 550-800℃, more preferably 600-750℃, and even more preferably 650-700℃; Preferably, the oxidative calcination time is 1-10 hours, more preferably 2-8 hours, and even more preferably 4-5 hours; Preferably, the oxidative roasting is carried out in an oxygen and / or air atmosphere; Preferably, separation is achieved by one or more of gravity separation, air separation, and sieving; Preferably, the purity of the aluminum foil is ≥99wt%; Preferably, in the waste lithium iron phosphate active material, the content of Al is <0.05wt%, preferably ≤0.005wt%; the content of divalent iron is <1wt%, preferably ≤0.1wt%. Preferably, the content of Ca in the waste lithium iron phosphate active material is <2wt%, and the content of Mg is <1wt%. Preferably, the active material of waste lithium iron phosphate contains 0.5-6 wt% Li, 25-40 wt% Fe, and 10-20 wt% P.

3. The method according to claim 1, characterized in that, In S2, the leaching temperature is >60℃, preferably ≥65℃, more preferably ≥75℃, even more preferably ≥85℃, even more preferably 90-200℃, and even more preferably 95-180℃; Preferably, the leaching time is ≥0.5h, more preferably 1-4h, and even more preferably 1.5-2h.

4. The method according to claim 1, characterized in that, In S2, the initial molar amount of phosphoric acid in the phosphoric acid and strong acid leaching system is 0.7-1.8 times the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1.

5. The method according to claim 1, characterized in that, In S2, the initial molar amount of phosphoric acid in the phosphoric acid leaching system is 1.8-2.4 times, preferably 1.8-2.1 times, the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1. Alternatively, in the phosphoric acid and strong acid leaching system, the initial concentration of phosphoric acid is 1.1-6 mol / L, preferably 1.2-5 mol / L, and the initial molar amount of phosphoric acid and the H content of the strong acid are... + The sum of the initial molar amounts is 1.4-2.4 times, preferably 1.5-2.3 times, the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1. Alternatively, in the phosphate and strong acid leaching system, the sum of the initial concentrations of phosphate, monohydrogen phosphate, and dihydrogen phosphate is 0.9-1.5 mol / L, preferably 1-1.4 mol / L, and even more preferably 1.1-1.3 mol / L, and the strong acid contains H+. + The initial molar amount is 1.2-1.9 times, preferably 1.2-1.6 times, and even more preferably 1.2-1.4 times, the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1. Alternatively, in the phosphate, phosphoric acid, and strong acid leaching system, the initial concentration of phosphate ions provided by phosphoric acid and phosphate is 1.0-1.4 mol / L, preferably 1.1-1.3 mol / L, and the initial molar amount of phosphoric acid and the H content of the strong acid are... + The sum of the initial molar amounts is 1.3-1.7 times, preferably 1.3-1.5 times, the sum of the molar amounts of Li and Fe in the waste lithium iron phosphate active material described in S1, and the initial molar amounts of phosphoric acid and the H content of the strong acid are also present. + The ratio of the sum of the initial molar amounts of the components to the initial molar amount of the phosphate is 2.7 to 5.5, preferably 3.0 to 5.0; Preferably, the strong acid includes one or more of hydrochloric acid, sulfuric acid, and nitric acid; Preferably, the phosphate includes one or more of sodium phosphate, sodium monohydrogen phosphate, sodium dihydrogen phosphate, potassium phosphate, potassium monohydrogen phosphate, and potassium dihydrogen phosphate.

6. The method according to any one of claims 1-5, characterized in that, In S2, after leaching, the pH of the leaching system is adjusted to 1.8-2.5, aged for 0-5 hours, and then solid-liquid separation is performed; preferably, after leaching, the pH of the leaching system is adjusted to 1.9-2.4, aged for 0.5-2 hours, and then solid-liquid separation is performed. Preferably, the pH value of the leaching system is adjusted using a first alkaline reagent, which includes one or more of ammonia, sodium hydroxide, and potassium hydroxide.

7. The method according to any one of claims 1-5, characterized in that, In S2, after solid-liquid separation, the obtained solid phase is washed to obtain hydrated iron phosphate; Preferably, the obtained solid phase is washed with water 3-8 times, more preferably 4-6 times; more preferably, each time the solid phase is washed, the solid phase is mixed with water at a solid-liquid mass ratio of 1:3-8, and stirred at a rate of ≥150 rpm for 10-60 min under conditions of ≥60°C, and then the solid and liquid are separated; even more preferably, each time the solid phase is washed, the solid phase is mixed with water at a solid-liquid mass ratio of 1:5-7, and stirred at a rate of 200-300 rpm for 20-30 min under conditions of 70-80°C, and then the solid and liquid are separated.

8. The method according to any one of claims 1-5, characterized in that, After S2, the pH value of the lithium-rich solution is adjusted to 6.8-8.5, followed by solid-liquid separation to obtain a lithium-rich purified solution; preferably, the pH value of the lithium-rich solution is adjusted to 7-7.5; preferably, a second alkaline reagent is used to adjust the pH value of the lithium-rich solution, wherein the second alkaline reagent includes one or more of ammonia, sodium hydroxide, and potassium hydroxide.

9. The method according to claim 8, characterized in that, Part or all of the lithium-rich purification solution is returned to S2 to construct an acid solution leaching system.

10. The method according to claim 8, characterized in that, Adjust the pH of part or all of the lithium-rich purification solution to 10-12. After reacting for 20-120 minutes, solid-liquid separation was performed to obtain lithium phosphate product. Preferably, the pH value of the lithium-rich purification solution is adjusted to 11-12, and after reacting for 30-60 minutes, solid-liquid separation is performed. Preferably, the method further includes a step of washing the lithium phosphate product; more preferably, during washing, the lithium phosphate product is mixed with water at a solid-liquid mass ratio of 1:3-8, and the mixture is stirred and washed 2-5 times at a speed of ≥150 rpm under conditions of ≥50°C, followed by solid-liquid separation; even more preferably, during washing, the lithium phosphate product is mixed with water at a solid-liquid mass ratio of 1:4-5, and the mixture is stirred and washed 3-4 times at a speed of ≥150 rpm under conditions of 60-90°C, followed by solid-liquid separation.

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