Recycling method of lithium iron phosphate waste powder

Abstract

The invention provides a lithium iron phosphate waste powder recycling method, which comprises: at least mixing lithium iron phosphate waste powder with a polyacrylic acid derivative, a first acid solution, an oxidizing agent and a solvent to obtain a lithium iron phosphate slurry, the pH value of the lithium iron phosphate slurry being a first pH value; an alkaline substance is added into the lithium iron phosphate slurry, so that the pH value of the lithium iron phosphate slurry is adjusted to a second pH value, and the second pH value is larger than the first pH value; and carrying out solid-liquid separation operation on the lithium iron phosphate slurry to obtain a lithium-containing solution and filter residues. According to the recycling method of the lithium iron phosphate waste powder, the leaching rate and the leaching selectivity of lithium ions can be improved.

Description

Technical Field

[0001] This application relates to the field of waste battery recycling, and particularly to a method for recycling and utilization of lithium iron phosphate waste powder. Background Art

[0002] With the rapid development of new energy vehicles, the demand and production of lithium iron phosphate batteries have increased year by year, and the number of retired waste lithium iron phosphate batteries is increasing. The lithium content in lithium iron phosphate materials is much higher than that in common lithium resources such as lepidolite, spodumene and salt lakes, and has high recycling value. Recycling and utilization of waste lithium iron phosphate batteries not only have good economic prospects, but also can save energy, reduce emissions and protect the environment.

[0003] In the existing lithium iron phosphate waste powder recycling technology, the leaching rate of lithium is low, and part of the lithium remains in the phosphorus iron slag, resulting in a low lithium recovery rate, which greatly affects the economy of the overall lithium recovery. Summary of the Invention

[0004] To solve the above technical problems, this application provides a method for recycling and utilization of lithium iron phosphate waste powder, which can improve the leaching rate and leaching selectivity of lithium ions.

[0005] This application provides a method for recycling and utilization of lithium iron phosphate waste powder, including the following steps: mixing at least the lithium iron phosphate waste powder with a polyacrylic acid derivative, a first acid solution, an oxidant and a solvent to obtain a lithium iron phosphate slurry, and the pH value of the lithium iron phosphate slurry is a first pH value; adding an alkaline substance to the lithium iron phosphate slurry to adjust the pH value of the lithium iron phosphate slurry to a second pH value, and the second pH value is greater than the first pH value; performing a solid-liquid separation operation on the lithium iron phosphate slurry to obtain a lithium-containing solution and a filter residue.

[0006] In the method for recycling and utilization of lithium iron phosphate waste powder provided by this application, by adding a polyacrylic acid derivative, the wettability of the lithium iron phosphate waste powder in the solvent can be improved and the aggregation of the lithium iron phosphate waste powder in the solvent can be avoided, so that the lithium iron phosphate waste powder is more uniformly dispersed in the solvent, thereby improving the leaching rate of lithium ions. And, by adding the oxidant to oxidize ferrous ions to ferric ions, and by increasing the pH value of the lithium iron phosphate slurry, so that ferric ions combine with phosphate radicals to form ferric phosphate hydrate precipitate, and lithium elements can be separated from phosphorus elements and iron elements by solid-liquid separation, thereby improving the leaching selectivity of lithium ions. Description of the Drawings

[0007] To more clearly illustrate the technical solutions of this application, the following will briefly introduce the drawings required for implementation. Obviously, the drawings in the following description are some embodiments of this application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0008] Figure 1 It is a flowchart of a method for recycling lithium iron phosphate waste powder provided in an embodiment of this application.

[0009] Figure 2 It is a flowchart of a method for recycling lithium iron phosphate waste powder provided in another embodiment of this application. Specific Embodiments

[0010] The following will clearly and completely describe the technical solutions in the embodiments of this application with reference to the drawings in the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, rather than all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of this application.

[0011] In the description of this application, terms such as "first" and "second" are used to distinguish different objects, rather than to describe a specific order. The orientation or positional relationship indicated by terms such as "upper", "lower", and "inner" is only for the convenience of describing this application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to this application.

[0012] Please refer to Figure 1 , Figure 1 It is a flowchart of a method for recycling lithium iron phosphate waste powder provided in an embodiment of this application. As Figure 1 shown, the method for recycling lithium iron phosphate waste powder includes the following steps:

[0013] S101: Mix at least the lithium iron phosphate waste powder with a polyacrylic acid derivative, a first acid solution, an oxidant, and a solvent to obtain a lithium iron phosphate slurry, and the pH value of the lithium iron phosphate slurry is a first pH value.

[0014] S102: Add an alkaline substance to the lithium iron phosphate slurry to adjust the pH value of the lithium iron phosphate slurry to a second pH value, and the second pH value is greater than the first pH value.

[0015] S103: Perform a solid-liquid separation operation on the lithium iron phosphate slurry to obtain a lithium-containing solution and a filter residue.

[0016] Among them, the polyacrylic acid derivative has the structure shown in Formula I, wherein, R1, R2 and R3 are each independently one of a hydrogen atom and a hydrocarbon group. The hydrocarbon group can be an alkyl group, an alkenyl group, an aryl group, etc. For example, the polyacrylic acid derivative can be polyacrylic acid, and its structure is shown in Formula II, Again, for example, the polyacrylic acid derivative can be polymethacrylic acid, and its structure is shown in Formula III, Formula

[0017] A large number of carboxylic acid groups exist in the polyacrylic acid derivative molecule. These carboxylic acid groups can form hydrogen bonds with the solvent and the lithium iron phosphate waste powder, thereby improving the wettability of the lithium iron phosphate waste powder in the solvent. Moreover, the polyacrylic acid derivative has a long-chain polymer structure and has a certain steric hindrance, which can prevent the lithium iron phosphate waste powder from agglomerating in the solvent, increasing the contact area between the lithium iron phosphate waste powder and the solvent, and thus making the lithium iron phosphate waste powder disperse more uniformly in the solvent.

[0018] In some embodiments, the lithium iron phosphate waste powder includes a mixture of lithium iron phosphate and a carbon material. The carbon material includes, for example, graphite, soft carbon, hard carbon, carbon fiber, graphene, etc. The abundant carboxylic acid groups in the polyacrylic acid derivative molecule can form hydrogen bonds with the hydroxyl or carboxyl groups on the surface of the carbon material, lithium iron phosphate and the solvent, thereby improving the wettability of lithium iron phosphate and the carbon material in the solvent. Moreover, the long-chain structure of the polyacrylic acid derivative can prevent agglomeration between lithium iron phosphate particles, between carbon material particles, and between lithium iron phosphate and the carbon material, so that lithium iron phosphate disperses more uniformly in the solvent, increasing the contact area between the lithium iron phosphate waste powder and the solvent, and making the carbon material disperse more uniformly in the solvent. By improving the wettability and dispersion uniformity of lithium iron phosphate, the leaching rate of lithium ions can be increased. Due to the improved dispersion uniformity of the carbon material, more lithium iron phosphate wrapped by the carbon material is released, further increasing the contact area between lithium iron phosphate and the solvent, and thus further increasing the lithium ion leaching rate. In addition, the polyacrylic acid derivative can undergo a lithiation reaction with the lithium ions in lithium iron phosphate, which helps the lithium ions in lithium iron phosphate to escape from the lattice and dissolve in the solvent.

[0019] The recycling method of the lithium iron phosphate waste powder provided by the embodiments of the present application can improve the wettability of the lithium iron phosphate waste powder in the solvent and avoid the aggregation of the lithium iron phosphate waste powder in the solvent by adding a polyacrylic acid derivative, so that the lithium iron phosphate waste powder is more uniformly dispersed in the solvent, thereby increasing the leaching rate of lithium ions. Moreover, by adding the oxidant, ferrous ions are oxidized to ferric ions, and by adjusting the pH value of the lithium iron phosphate slurry, ferric ions combine with phosphate radicals to form ferric phosphate hydrate precipitate, and through solid-liquid separation, lithium elements can be separated from phosphorus elements and iron elements, thereby improving the leaching selectivity of lithium ions.

[0020] In step S101, the lithium iron phosphate waste powder can be first mixed with the polyacrylic acid derivative and the solvent, and then the first acid solution and the oxidant are added.

[0021] First, the lithium iron phosphate waste powder is mixed with the polyacrylic acid derivative and the solvent to make the lithium iron phosphate waste powder uniformly dispersed in the solvent, and then the first acid solution and the oxidant are added, so that the first acid solution and the oxidant can better contact the lithium iron phosphate waste powder, thereby further promoting the leaching of lithium ions and the reaction between ferrous ions and the oxidant.

[0022] In some embodiments, the first pH value is a value in the range of 0.8 - 1.2.

[0023] In this acidic environment, lithium ions in the lithium iron phosphate in the lithium iron phosphate waste powder will escape from the crystal lattice and dissolve in the solution, and a small amount of phosphate radicals and ferrous ions will also dissolve in the solution. At the same time, due to the presence of the oxidant, the oxidant will oxidize the undissolved ferrous phosphate and the ferrous ions dissolved in the solution into ferric phosphate and ferric ions respectively. The ferric phosphate formed by oxidation will not dissolve in the solution but exist in the form of a precipitate.

[0024] When the lithium iron phosphate waste powder is mixed with the polyacrylic acid derivative, the first acid solution, the oxidant and the solvent, by adjusting the pH value to 0.8 - 1.2, the acidity of the lithium iron phosphate slurry is relatively strong, and lithium ions in the lithium iron phosphate waste powder are more likely to escape from the lithium iron phosphate crystal lattice and dissolve in the solution in a stronger acidic environment, thereby increasing the leaching rate of lithium ions.

[0025] Moreover, within this pH range, the amounts of phosphate radicals and divalent iron ions in the lithium iron phosphate in the lithium iron phosphate waste powder dissolved in the solution are relatively small, that is, the leaching rates of the phosphate radicals and divalent iron ions are relatively low. Among them, the divalent iron ions dissolved in the solution will react with the oxidant and be oxidized to trivalent iron ions. The relatively low leaching rates of phosphorus and iron are beneficial to subsequently increasing the pH value to cause the small amount of dissolved phosphate radicals to combine with the small amount of trivalent iron ions to form iron phosphate hydrate and precipitate out. As a result, the contents of phosphorus and iron elements in the obtained lithium-containing solution after solid-liquid separation are very low, and the purity of the lithium-containing solution is very high, thereby greatly improving the leaching selectivity of lithium ions.

[0026] If the first pH value is less than 0.8, it may cause an increase in the amounts of phosphate radicals and divalent iron ions in the lithium iron phosphate waste powder dissolved in the solution, which is not conducive to subsequently removing the dissolved phosphorus and iron by increasing the pH value, resulting in more phosphorus and iron mixed in the lithium-containing solution and affecting the leaching selectivity of lithium ions. If the first pH value is greater than 1.2, it is not conducive to the dissolution of lithium ions in the lithium iron phosphate waste powder in the solution, which will reduce the leaching rate of lithium ions and thus affect the recovery rate of lithium ions.

[0027] In some embodiments, the second pH value is a value within 1.8 - 2.2.

[0028] When the pH value of the lithium iron phosphate slurry is increased from 0.8 - 1.2 to 1.8 - 2.2, the trivalent iron ions in the solution combine with the phosphate radicals to form iron phosphate hydrate and precipitate out from the solution, while the lithium ions remain dissolved in the solution. The obtained filter residue after solid-liquid separation includes iron phosphate and iron phosphate hydrate, and the lithium ions are present in the filtrate, that is, the lithium-containing solution, thereby realizing the separation of lithium elements from phosphorus and iron elements in the lithium iron phosphate waste powder.

[0029] If the second pH value is less than 1.8, some ferric ions and some phosphates may still be dissolved in the solution, and will not be combined to precipitate in the form of iron phosphate hydrate, that is, the solution of the lithium iron phosphate slurry contains ferric ions, phosphates and lithium ions, resulting in ferric ions and phosphates in the lithium-containing solution, thereby reducing the leaching selectivity of lithium ions; if the second pH value is greater than 2.2, some lithium ions will be combined with phosphates and precipitated in the form of lithium phosphate, resulting in a low leaching rate of lithium ions, and within this pH range, ferric ions are easily reacted with the alkaline substance to form iron hydroxide colloid, which has adsorption properties and will adsorb lithium ions in the solution. After solid-liquid separation operation, lithium ions will be mixed in the filter residue, thereby reducing the extraction rate of lithium ions. Therefore, by raising the pH value of the lithium iron phosphate slurry to 1.8-2.2, the lithium-containing solution with high lithium ion purity and high extraction rate can be obtained, which is conducive to the subsequent acquisition of high-purity lithium-containing salts and the efficient recovery of lithium elements.

[0030] The lithium iron phosphate slurry is first adjusted to a lower pH value so that the lithium ions are in a strong acidic environment, which is conducive to the leaching of lithium ions, and then adjusted to a higher pH value to relatively weaken the acidity so that the dissolved phosphate radicals and trivalent iron ions form lithium iron phosphate hydrate precipitation, thereby not only improving the leaching rate of lithium ions, but also improving the leaching selectivity of lithium ions. As a result, most of the lithium ions in the lithium iron phosphate waste powder exist in the lithium-containing solution, and there are very few impurities in the lithium-containing solution.

[0031] In some embodiments, the alkaline substance includes at least one of lithium hydroxide, sodium hydroxide, sodium carbonate, potassium carbonate, potassium hydroxide, ammonium carbonate and ammonia water.

[0032] In some embodiments, the alkaline substance may be lithium hydroxide. Hydroxyl in the lithium hydroxide will combine with hydrogen ions in the lithium iron phosphate slurry to generate water, thereby avoiding the introduction of impurity ions.

[0033] In some embodiments, the first acid solution includes an inorganic acid and / or an organic acid, the inorganic acid includes at least one of concentrated sulfuric acid, phosphoric acid, hydrochloric acid and nitric acid, and the organic acid may include citric acid and / or oxalic acid.

[0034] In some embodiments, the first acid solution may include concentrated sulfuric acid, i.e., sulfuric acid with a mass fraction of 98 wt%. Compared with hydrochloric acid and nitric acid, concentrated sulfuric acid is less corrosive to equipment. Using phosphoric acid as the first acid solution will result in a relatively large amount of phosphate radicals in the lithium-containing solution. To improve the purity of the lithium-containing salt obtained by performing lithium precipitation on the lithium-containing solution, it is usually necessary to use phosphoric acid or phosphate to perform lithium precipitation on the lithium-containing solution to obtain lithium phosphate, which will limit the application range of the recovered lithium salt. However, using concentrated sulfuric acid as the first acid solution can avoid this problem.

[0035] In some embodiments, the oxidant includes at least one of hydrogen peroxide and hypochlorous acid.

[0036] In some embodiments, the oxidant can be hydrogen peroxide. Hydrogen peroxide is more environmentally friendly and does not produce pollutants.

[0037] Please refer to Figure 2 , which is a flowchart of the method for recycling lithium iron phosphate waste powder provided in another embodiment of the present application. In some embodiments, as Figure 2 shown, the method for recycling lithium iron phosphate waste powder includes the following steps:

[0038] S201: Mix at least the lithium iron phosphate waste powder with a polyacrylic acid derivative, a first acid solution, an oxidant, and a solvent to obtain a lithium iron phosphate slurry, and the pH value of the lithium iron phosphate slurry is the first pH value.

[0039] S202: Add an alkaline substance to the lithium iron phosphate slurry to adjust the pH value of the lithium iron phosphate slurry to a second pH value, and the second pH value is greater than the first pH value.

[0040] S203: Perform a solid-liquid separation operation on the lithium iron phosphate slurry to obtain a lithium-containing solution and a filter residue.

[0041] S204: Wash the filter residue and collect the washing solution.

[0042] Among them, step S201 includes: mixing the lithium iron phosphate waste powder with a polyacrylic acid derivative, a first acid solution, an oxidant, a solvent, and the washing solution to obtain a lithium iron phosphate slurry, and the pH value of the lithium iron phosphate slurry is the first pH value. That is, as Figure 2 shown, the washing solution collected in step S204 is used to return to step S201 and mix with the next lithium iron phosphate waste powder, polyacrylic acid derivative, first acid solution, oxidant, and solvent to obtain the lithium iron phosphate slurry.

[0043] By returning the washing solution to step S201, the lithium ions in the washing solution can be recovered, thereby further improving the recovery rate of lithium ions.

[0044] In some embodiments, in step S204, washing the filter residue includes: washing the filter residue with a mixed solution of a second acid solution and a polyacrylic acid derivative, wherein the polyacrylic acid derivative has the structure shown in the foregoing formula I. The polyacrylic acid derivative in step S204 may be the same as or different from the polyacrylic acid derivative in step S201.

[0045] Among them, the polyacrylic acid derivative can undergo a lithiation reaction with lithium ions to generate lithium polyacrylate salts, and the lithium polyacrylate salts are easily soluble in the mixed solution, so that the lithium ions adsorbed on the surface of the filter residue and the lithium ions located in the voids and pores of the filter residue are separated from the filter residue. The binding force between the polyacrylic acid derivative and lithium ions is greater than the binding force between lithium ions and the filter residue. Therefore, under the action of the polyacrylic acid derivative, lithium ions are easily separated from the filter residue, which can improve the leaching rate of lithium ions in the mixed solution.

[0046] In some embodiments, the polyacrylic acid derivative in the mixed solution is polyacrylic acid, and polyacrylic acid can react with lithium ions to generate LiPAA (lithium polyacrylate) and dissolve in the mixed solution.

[0047] Among them, the pH value of the second acid solution is a value in the range of 1.8 - 2.2. Within this pH value range, the lithium ions adsorbed on the surface of the filter residue and in the internal pores and voids are easily leached into the mixed solution. And within this pH value range, the iron phosphate and iron phosphate hydrate in the filter residue do not dissolve and still exist in the form of a precipitate, so as to avoid the phosphorus and iron elements in the filter residue from entering the washing solution. When using the mixed solution to wash the filter residue, the acidic environment provided by the second acid solution with a pH value of 1.8 - 2.2 and the polyacrylic acid derivative play a synergistic role, which can fully transfer the lithium ions in the filter residue to the mixed solution.

[0048] Moreover, setting the pH value of the second acid solution to 1.8 - 2.2 can avoid the dissolution of iron phosphate and iron phosphate hydrate in the filter residue caused by too low pH value (too strong acidity), thus avoiding the mixing of phosphorus and iron elements into the washing solution; it can also avoid the formation of lithium phosphate precipitate due to too high pH value, thus avoiding affecting the recovery rate of lithium ions. Therefore, using the mixed solution obtained by mixing the second acid solution with a pH value of 1.8 - 2.2 and the polyacrylic acid derivative to wash the filter residue can obtain a washing solution with a relatively high lithium ion purity and extraction rate, which is beneficial to avoiding the mixing of impurities into the lithium iron phosphate slurry and can improve the recovery rate of lithium elements.

[0049] Among them, the acidity of the polyacrylic acid derivative is very weak, and mixing the polyacrylic acid derivative with the second acid solution has little effect on the pH value of the second acid solution. The pH value of the mixed solution of the second acid solution and the polyacrylic acid derivative is approximately 1.8 - 2.2.

[0050] After the first washing operation of the filter residue using the mixed solution, pure water can also be used to perform a second washing operation on the filter residue. The washing solutions generated from the first washing operation and the second washing operation are collected and returned to step S201. Among them, the first washing operation can be carried out once or multiple times, and the second washing operation can be carried out once or multiple times.

[0051] Among them, the second acid solution can be a solution of an inorganic acid and / or an organic acid dissolved in water. The inorganic acid can include at least one of sulfuric acid, phosphoric acid, hydrochloric acid, and nitric acid. The organic acid can include citric acid and / or oxalic acid.

[0052] Among them, the type of acid in the second acid solution can be the same as or different from the type of acid in the first acid solution.

[0053] In some embodiments, the type of inorganic acid in the second acid solution is the same as the type of inorganic acid in the first acid solution, which can avoid introducing other impurity elements. In some embodiments, the second acid solution includes dilute sulfuric acid.

[0054] In some embodiments, the mass ratio of the second acid solution to the lithium iron phosphate waste powder is (3 - 5):1, that is, the mass ratio of the second acid solution to the lithium iron phosphate waste powder in step S201 is (3 - 5):1.

[0055] By controlling the mass ratio of the second acid solution to the lithium iron phosphate waste powder to be (3 - 5):1, the lithium ions in the filter residue can be fully transferred into the washing solution, and the economic applicability can be improved, the cost can be reduced, and the pollution can be reduced.

[0056] Among them, the second acid solution with a mass ratio to the mass of the lithium iron phosphate waste powder of (3 - 5):1 can wash the filter residue in multiple times, which can improve the lithium ion transfer efficiency.

[0057] In some embodiments, the mass ratio of the polyacrylic acid derivative in the mixed solution to the lithium iron phosphate waste powder is greater than 0 and less than or equal to 0.5:100, that is, the mass ratio of the polyacrylic acid derivative in the mixed solution of the aforementioned second acid solution and the polyacrylic acid derivative to the lithium iron phosphate waste powder in step S201 is greater than 0 and less than or equal to 0.5:100. This can avoid introducing impurities due to excessive content of the polyacrylic acid derivative in the washing solution.

[0058] In some embodiments, the mass ratio of the polyacrylic acid derivative in the mixed solution to the lithium iron phosphate waste powder is (0.01 - 0.5):100, that is, the mass ratio of the polyacrylic acid derivative in the mixed solution of the aforementioned second acid solution and the polyacrylic acid derivative to the lithium iron phosphate waste powder in step S201 is (0.01 - 0.5):100.

[0059] By controlling the mass ratio of the polyacrylic acid derivative in the mixed solution to the lithium iron phosphate waste powder to be (0.01 - 0.5):100, the lithiation reaction of the polyacrylic acid derivative with the lithium ions in the filter residue can be effectively promoted, which is beneficial for the lithium ions in the filter residue to enter the washing solution along with the polyacrylic acid derivative.

[0060] In some embodiments, in step S101 and step S201, the mass ratio of the polyacrylic acid derivative to the lithium iron phosphate waste powder is greater than 0 and less than or equal to 0.5:100, so as to avoid introducing impurities into the lithium-containing solution due to excessive content of the polyacrylic acid derivative.

[0061] In some embodiments, in step S101 and step S201, the mass ratio of the polyacrylic acid derivative to the lithium iron phosphate waste powder is (0.01 - 0.5):100. By controlling the mass ratio of the polyacrylic acid derivative to the lithium iron phosphate waste powder to be (0.01 - 0.5):100, the surface performance of the lithium iron phosphate waste powder can be better improved, so that the lithium iron phosphate waste powder has better wettability.

[0062] In some embodiments, in step S101 and step S201, the molar ratio of the oxidant to the lithium element in the lithium iron phosphate waste powder is (0.5 - 2):1. By controlling the molar ratio of the oxidant to the lithium element in the lithium iron phosphate waste powder to be (0.5 - 2):1, it is beneficial for the oxidant to completely oxidize the dissolved divalent iron ions into trivalent iron ions, thereby improving the leaching selectivity of lithium ions. Among them, before performing the aforementioned steps S101 and S201, ICP-OES (Inductively Coupled Plasma Optical Emission Spectrometer) can be used to perform elemental analysis and testing on the lithium iron phosphate waste powder to test the content of the lithium element in the lithium iron phosphate waste powder, and then determine the addition amount of the oxidant.

[0063] In some embodiments, the liquid-solid ratio of the lithium iron phosphate slurry is (3-10):1. Within this liquid-solid ratio range, both the leaching efficiency of lithium ions and the reaction efficiency of ferrous ions with the oxidant are relatively high. It can avoid the low leaching efficiency of lithium ions and the low conversion efficiency of ferrous ions to ferric ions caused by a low liquid-solid ratio, and can also avoid the problem of waste of the first acid solution, the oxidant and the solvent caused by a high liquid-solid ratio. Moreover, a high liquid-solid ratio will affect the lithium precipitation efficiency during subsequent lithium precipitation operations. If the lithium-containing solution needs to be concentrated to improve the lithium precipitation efficiency, this will increase the concentration cost and further increase the recovery cost. By controlling the liquid-solid ratio to (3-10):1, not only as described above, the leaching efficiency of lithium ions and the conversion efficiency of ferrous ions to ferric ions can be relatively high, but also the waste of the first acid solution, the oxidant and the solvent can be avoided, and the recovery cost can be relatively low.

[0064] In some embodiments, in step S101 and step S201, the step of at least mixing the lithium iron phosphate waste powder with a polyacrylic acid derivative, a first acid solution, an oxidant and a solvent to obtain a lithium iron phosphate slurry includes: at least mixing the lithium iron phosphate waste powder with the polyacrylic acid derivative, the first acid solution, the oxidant and the solvent and heating to 40°C - 80°C, and stirring at a stirring speed of 200 rpm - 700 rpm for at least 2 h to obtain the lithium iron phosphate slurry.

[0065] Heating to 40°C - 80°C helps to promote the reaction of ferrous ions with the oxidant, and is beneficial for lithium ions in the lithium iron phosphate waste powder to escape from the crystal lattice and dissolve into the solution.

[0066] Stirring at a stirring speed of 200 rpm - 700 rpm can avoid agglomeration of the lithium iron phosphate waste powder caused by too slow a rotation speed, and can also avoid the adverse effect of too fast a rotation speed on the leaching of lithium ions and the oxidation reaction of ferrous ions with the oxidant.

[0067] Controlling the stirring duration to be at least 2 h can enable sufficient leaching of lithium ions in the lithium iron phosphate waste powder, and enable the dissolved ferrous ions to have sufficient time to undergo an oxidation reaction with the oxidant, improving the conversion rate of ferrous ions to ferric ions, so that the dissolved iron and phosphorus can be precipitated in the form of iron phosphate hydrate as much as possible, thereby improving the leaching selectivity of lithium ions.

[0068] In some embodiments, the stirring duration is controlled to be 2 h - 6 h. By controlling the stirring duration to be less than or equal to 6 h, it is beneficial to improve production efficiency.

[0069] The solvent may include water.

[0070] In some embodiments, after obtaining the lithium-containing solution, the method for recycling the lithium iron phosphate waste powder further includes the step of performing a lithium precipitation operation on the lithium-containing solution to obtain a lithium salt. Specifically, it may include mixing the lithium-containing solution with at least one of a carbonate, phosphoric acid, and phosphate to obtain the lithium salt.

[0071] The carbonate may be, for example, sodium carbonate, and the phosphate may be, for example, sodium dihydrogen phosphate, disodium hydrogen phosphate, etc. The lithium salt may include lithium carbonate and / or lithium phosphate.

[0072] The following uses Examples 1-23 and Comparative Examples 1-4 to illustrate the present application in detail. The following examples are only used to illustrate and explain the present application, and the protection scope of the present application is not limited by the following examples.

[0073] Example 1

[0074] Mix 1 kg of lithium iron phosphate waste powder with 1 g of polyacrylic acid, concentrated sulfuric acid, 0.35 L of hydrogen peroxide, and 4 L of water, and heat to 60 °C, stir evenly to obtain a lithium iron phosphate slurry. Among them, during the addition of concentrated sulfuric acid, by controlling the addition amount of concentrated sulfuric acid, the first pH value of the lithium iron phosphate slurry is controlled to be 1.2. After stirring for 4 h, add ammonia water to the lithium iron phosphate slurry to adjust the pH value of the lithium iron phosphate slurry to 2.0, that is, the second pH value is 2.0. Let the lithium iron phosphate slurry stand, and after 1 h, perform solid-liquid separation to obtain a lithium-containing solution and a filter residue. Mix dilute sulfuric acid with a pH value of 2.0 and 1 g of polyacrylic acid to form a mixed solution, use this mixed solution to wash the filter residue, and after solid-liquid separation, wash the filter residue with pure water again, and collect the washing liquid obtained when washing the filter residue with the mixed solution and pure water. Among them, the structure of the polyacrylic acid is as shown in Formula II above.

[0075] Example 2

[0076] Mix 1 kg of lithium iron phosphate waste powder with 0.5 g of polyacrylic acid, concentrated sulfuric acid, 0.35 L of hydrogen peroxide, and 4 L of water, and heat to 60 °C, stir evenly to obtain a lithium iron phosphate slurry. Among them, during the addition of concentrated sulfuric acid, by controlling the addition amount of concentrated sulfuric acid, the first pH value of the lithium iron phosphate slurry is controlled to be 1.2. After stirring for 4 h, add ammonia water to the lithium iron phosphate slurry to adjust the pH value of the lithium iron phosphate slurry to 2.0, that is, the second pH value is 2.0. Let the lithium iron phosphate slurry stand, and after 1 h, perform solid-liquid separation to obtain a lithium-containing solution and a filter residue. Mix dilute sulfuric acid with a pH value of 2.0 and 1 g of polyacrylic acid to form a mixed solution, use this mixed solution to wash the filter residue, and after solid-liquid separation, wash the filter residue with pure water again, and collect the washing liquid obtained when washing the filter residue with the mixed solution and pure water.

[0077] The difference between Example 2 and Example 1 is that the mass of polyacrylic acid is 0.5 g.

[0078] Example 3 of implementation

[0079] Mix 1 kg of lithium iron phosphate waste powder with 5 g of polyacrylic acid, concentrated sulfuric acid, 0.35 L of hydrogen peroxide and 4 L of water, and heat to 60 °C, stir evenly to obtain lithium iron phosphate slurry. Among them, during the addition of concentrated sulfuric acid, by controlling the addition amount of concentrated sulfuric acid, the first pH value of the lithium iron phosphate slurry is controlled to be 1.2. After stirring for 4 h, add ammonia water to the lithium iron phosphate slurry to adjust the pH value of the lithium iron phosphate slurry to 2.0, that is, the second pH value is 2.0. Let the lithium iron phosphate slurry stand, and after 1 h, carry out solid-liquid separation to obtain a lithium-containing solution and filter residue. Mix dilute sulfuric acid with a pH value of 2.0 and 1 g of polyacrylic acid to form a mixed solution, use this mixed solution to wash the filter residue, after solid-liquid separation, wash the filter residue with pure water again, and collect the washing liquid obtained when washing the filter residue with the mixed solution and pure water.

[0080] The difference between Example 3 of implementation and Example 1 of implementation is that the mass of polyacrylic acid is 5 g.

[0081] Example 4 of implementation

[0082] Mix 1 kg of lithium iron phosphate waste powder with 10 g of polyacrylic acid derivative, concentrated sulfuric acid, 0.35 L of hydrogen peroxide and 4 L of water, and heat to 60 °C, stir evenly to obtain lithium iron phosphate slurry. Among them, during the addition of concentrated sulfuric acid, by controlling the addition amount of concentrated sulfuric acid, the first pH value of the lithium iron phosphate slurry is controlled to be 1.2. After stirring for 4 h, add ammonia water to the lithium iron phosphate slurry to adjust the pH value of the lithium iron phosphate slurry to 2.0, that is, the second pH value is 2.0. Let the lithium iron phosphate slurry stand, and after 1 h, carry out solid-liquid separation to obtain a lithium-containing solution and filter residue. Mix dilute sulfuric acid with a pH value of 2.0 and 1 g of polyacrylic acid to form a mixed solution, use this mixed solution to wash the filter residue, after solid-liquid separation, wash the filter residue with pure water again, and collect the washing liquid obtained when washing the filter residue with the mixed solution and pure water.

[0083] The difference between Example 4 of implementation and Example 1 of implementation is that the mass of polyacrylic acid is 10 g.

[0084] Example 5 of implementation

[0085] Mix 1 kg of lithium iron phosphate waste powder with 1 g of polyacrylic acid, concentrated sulfuric acid, 0.35 L of hydrogen peroxide and 4 L of water, and heat to 60 °C. Stir evenly to obtain a lithium iron phosphate slurry. Among them, during the addition of concentrated sulfuric acid, by controlling the addition amount of concentrated sulfuric acid, the first pH value of the lithium iron phosphate slurry is controlled to be 1.0. After stirring for 4 h, add ammonia water to the lithium iron phosphate slurry to adjust the pH value of the lithium iron phosphate slurry to 2.0, that is, the second pH value is 2.0. Let the lithium iron phosphate slurry stand, and after 1 h, carry out solid-liquid separation to obtain a lithium-containing solution and a filter residue. Mix dilute sulfuric acid with a pH value of 2.0 and 1 g of polyacrylic acid to form a mixed solution. Use this mixed solution to wash the filter residue. After solid-liquid separation, wash the filter residue with pure water again, and collect the washing liquid obtained when washing the filter residue with the mixed solution and pure water.

[0086] Example 5 is different from Example 1 in that the first pH value is 1.0.

[0087] Example 6

[0088] Mix 1 kg of lithium iron phosphate waste powder with 1 g of polyacrylic acid, concentrated sulfuric acid, 0.35 L of hydrogen peroxide and 4 L of water, and heat to 60 °C. Stir evenly to obtain a lithium iron phosphate slurry. Among them, during the addition of concentrated sulfuric acid, by controlling the addition amount of concentrated sulfuric acid, the first pH value of the lithium iron phosphate slurry is controlled to be 0.6. After stirring for 4 h, add ammonia water to the lithium iron phosphate slurry to adjust the pH value of the lithium iron phosphate slurry to 2.0, that is, the second pH value is 2.0. Let the lithium iron phosphate slurry stand, and after 1 h, carry out solid-liquid separation to obtain a lithium-containing solution and a filter residue. Mix dilute sulfuric acid with a pH value of 2.0 and 1 g of polyacrylic acid to form a mixed solution. Use this mixed solution to wash the filter residue. After solid-liquid separation, wash the filter residue with pure water again, and collect the washing liquid obtained when washing the filter residue with the mixed solution and pure water.

[0089] Example 6 is different from Example 1 in that the first pH value is 0.6.

[0090] Example 7

[0091] Mix 1 kg of lithium iron phosphate waste powder with 1 g of polyacrylic acid, concentrated sulfuric acid, 0.35 L of hydrogen peroxide and 4 L of water, and heat to 60 °C. Stir evenly to obtain a lithium iron phosphate slurry. Among them, during the addition of concentrated sulfuric acid, by controlling the addition amount of concentrated sulfuric acid, the first pH value of the lithium iron phosphate slurry is controlled to be 1.5. After stirring for 4 h, add ammonia water to the lithium iron phosphate slurry to adjust the pH value of the lithium iron phosphate slurry to 2.0, that is, the second pH value is 2.0. Let the lithium iron phosphate slurry stand, and after 1 h, carry out solid-liquid separation to obtain a lithium-containing solution and a filter residue. Mix dilute sulfuric acid with a pH value of 2.0 and 1 g of polyacrylic acid to form a mixed solution. Use this mixed solution to wash the filter residue. After solid-liquid separation, wash the filter residue with pure water again, and collect the washing liquid obtained when washing the filter residue with the mixed solution and pure water.

[0092] Example 7 is different from Example 1 in that the first pH value is 1.5.

[0093] Example 8

[0094] 1 kg of lithium iron phosphate waste powder is mixed with 1 g of polyacrylic acid, concentrated sulfuric acid, 0.35 L of hydrogen peroxide and 4 L of water and heated to 60 °C, and stirred evenly to obtain a lithium iron phosphate slurry. Among them, during the addition of concentrated sulfuric acid, the addition amount of concentrated sulfuric acid is controlled to control the first pH value of the lithium iron phosphate slurry to be 1.2. After stirring for 4 h, ammonia water is added to the lithium iron phosphate slurry to adjust the pH value of the lithium iron phosphate slurry to 1.8, that is, the second pH value is 1.8. The lithium iron phosphate slurry is allowed to stand, and after 1 h, solid-liquid separation is carried out to obtain a lithium-containing solution and a filter residue. Dilute sulfuric acid with a pH value of 2.0 is mixed with 1 g of polyacrylic acid to form a mixed solution, and the filter residue is washed with the mixed solution. After solid-liquid separation, the filter residue is washed with pure water, and the washing solutions obtained when washing the filter residue with the mixed solution and pure water are collected.

[0095] Example 8 is different from Example 1 in that the second pH value is 1.8.

[0096] Example 9

[0097] 1 kg of lithium iron phosphate waste powder is mixed with 1 g of polyacrylic acid, concentrated sulfuric acid, 0.35 L of hydrogen peroxide and 4 L of water and heated to 60 °C, and stirred evenly to obtain a lithium iron phosphate slurry. Among them, during the addition of concentrated sulfuric acid, the addition amount of concentrated sulfuric acid is controlled to control the first pH value of the lithium iron phosphate slurry to be 1.2. After stirring for 4 h, ammonia water is added to the lithium iron phosphate slurry to adjust the pH value of the lithium iron phosphate slurry to 2.2, that is, the second pH value is 2.2. The lithium iron phosphate slurry is allowed to stand, and after 1 h, solid-liquid separation is carried out to obtain a lithium-containing solution and a filter residue. Dilute sulfuric acid with a pH value of 2.0 is mixed with 1 g of polyacrylic acid to form a mixed solution, and the filter residue is washed with the mixed solution. After solid-liquid separation, the filter residue is washed with pure water, and the washing solutions obtained when washing the filter residue with the mixed solution and pure water are collected.

[0098] Example 9 is different from Example 1 in that the second pH value is 2.2.

[0099] Example 10

[0100] Mix 1 kg of lithium iron phosphate waste powder with 1 g of polyacrylic acid, concentrated sulfuric acid, 0.35 L of hydrogen peroxide and 4 L of water, and heat to 60 °C. Stir evenly to obtain a lithium iron phosphate slurry. Among them, during the addition of concentrated sulfuric acid, by controlling the addition amount of concentrated sulfuric acid, the first pH value of the lithium iron phosphate slurry is controlled to be 1.2. After stirring for 4 h, add ammonia water to the lithium iron phosphate slurry to adjust the pH value of the lithium iron phosphate slurry to 1.5, that is, the second pH value is 1.5. Let the lithium iron phosphate slurry stand, and after 1 h, perform solid-liquid separation to obtain a lithium-containing solution and filter residue. Mix dilute sulfuric acid with a pH value of 2.0 and 1 g of polyacrylic acid to form a mixed solution. Use this mixed solution to wash the filter residue. After solid-liquid separation, wash the filter residue with pure water again, and collect the washing liquid obtained when washing the filter residue with the mixed solution and pure water.

[0101] Example 10 is different from Example 1 in that the second pH value is 1.5.

[0102] Example 11

[0103] Mix 1 kg of lithium iron phosphate waste powder with 1 g of polyacrylic acid, concentrated sulfuric acid, 0.35 L of hydrogen peroxide and 4 L of water, and heat to 60 °C. Stir evenly to obtain a lithium iron phosphate slurry. Among them, during the addition of concentrated sulfuric acid, by controlling the addition amount of concentrated sulfuric acid, the first pH value of the lithium iron phosphate slurry is controlled to be 1.2. After stirring for 4 h, add ammonia water to the lithium iron phosphate slurry to adjust the pH value of the lithium iron phosphate slurry to 2.5, that is, the second pH value is 2.5. Let the lithium iron phosphate slurry stand, and after 1 h, perform solid-liquid separation to obtain a lithium-containing solution and filter residue. Mix dilute sulfuric acid with a pH value of 2.0 and 1 g of polyacrylic acid to form a mixed solution. Use this mixed solution to wash the filter residue. After solid-liquid separation, wash the filter residue with pure water again, and collect the washing liquid obtained when washing the filter residue with the mixed solution and pure water.

[0104] Example 11 is different from Example 1 in that the second pH value is 2.5.

[0105] Example 12

[0106] Mix 1 kg of lithium iron phosphate waste powder with 1 g of polyacrylic acid, concentrated sulfuric acid, 0.35 L of hydrogen peroxide and 4 L of water, and heat to 60 °C. Stir evenly to obtain a lithium iron phosphate slurry. Among them, during the addition of concentrated sulfuric acid, by controlling the addition amount of concentrated sulfuric acid, the first pH value of the lithium iron phosphate slurry is controlled to be 1.2. After stirring for 4 h, add ammonia water to the lithium iron phosphate slurry to adjust the pH value of the lithium iron phosphate slurry to 2.0, that is, the second pH value is 2.0. Let the lithium iron phosphate slurry stand, and after 1 h, perform solid-liquid separation to obtain a lithium-containing solution and filter residue. Mix dilute sulfuric acid with a pH value of 1.8 and 1 g of polyacrylic acid to form a mixed solution. Use this mixed solution to wash the filter residue. After solid-liquid separation, wash the filter residue with pure water again, and collect the washing liquid obtained when washing the filter residue with the mixed solution and pure water.

[0107] Example 12 is different from Example 1 in that the pH value of the second acid solution is 1.8.

[0108] Example 13

[0109] 1 kg of lithium iron phosphate waste powder is mixed with 1 g of polyacrylic acid, concentrated sulfuric acid, 0.35 L of hydrogen peroxide and 4 L of water and heated to 60 °C, and stirred evenly to obtain a lithium iron phosphate slurry. Among them, during the addition of concentrated sulfuric acid, the addition amount of concentrated sulfuric acid is controlled to control the first pH value of the lithium iron phosphate slurry to be 1.2. After stirring for 4 h, ammonia water is added to the lithium iron phosphate slurry to adjust the pH value of the lithium iron phosphate slurry to 2.0, that is, the second pH value is 2.0. The lithium iron phosphate slurry is allowed to stand, and after 1 h, solid-liquid separation is carried out to obtain a lithium-containing solution and a filter residue. Dilute sulfuric acid with a pH value of 2.2 is mixed with 1 g of polyacrylic acid to form a mixed solution, and the filter residue is washed with the mixed solution. After solid-liquid separation, the filter residue is washed with pure water, and the washing solutions obtained when washing the filter residue with the mixed solution and pure water are collected.

[0110] Example 13 is different from Example 1 in that the pH value of the second acid solution is 2.2.

[0111] Example 14

[0112] 1 kg of lithium iron phosphate waste powder is mixed with 1 g of polyacrylic acid, concentrated sulfuric acid, 0.35 L of hydrogen peroxide and 4 L of water and heated to 60 °C, and stirred evenly to obtain a lithium iron phosphate slurry. Among them, during the addition of concentrated sulfuric acid, the addition amount of concentrated sulfuric acid is controlled to control the first pH value of the lithium iron phosphate slurry to be 1.2. After stirring for 4 h, ammonia water is added to the lithium iron phosphate slurry to adjust the pH value of the lithium iron phosphate slurry to 2.0, that is, the second pH value is 2.0. The lithium iron phosphate slurry is allowed to stand, and after 1 h, solid-liquid separation is carried out to obtain a lithium-containing solution and a filter residue. Dilute sulfuric acid with a pH value of 1.5 is mixed with 1 g of polyacrylic acid to form a mixed solution, and the filter residue is washed with the mixed solution. After solid-liquid separation, the filter residue is washed with pure water, and the washing solutions obtained when washing the filter residue with the mixed solution and pure water are collected.

[0113] Example 14 is different from Example 1 in that the pH value of the second acid solution is 1.5.

[0114] Example 15

[0115] Mix 1 kg of lithium iron phosphate waste powder with 1 g of polyacrylic acid, concentrated sulfuric acid, 0.35 L of hydrogen peroxide and 4 L of water, and heat to 60 °C, stir evenly to obtain lithium iron phosphate slurry. Among them, during the addition of concentrated sulfuric acid, the addition amount of concentrated sulfuric acid is controlled to control the first pH value of the lithium iron phosphate slurry to be 1.2. After stirring for 4 h, add ammonia water to the lithium iron phosphate slurry to adjust the pH value of the lithium iron phosphate slurry to 2.0, that is, the second pH value is 2.0. Let the lithium iron phosphate slurry stand, and after 1 h, carry out solid-liquid separation to obtain a lithium-containing solution and filter residue. Mix dilute sulfuric acid with a pH value of 2.5 and 1 g of polyacrylic acid to form a mixed solution, use this mixed solution to wash the filter residue, after solid-liquid separation, wash the filter residue with pure water again, and collect the washing liquid obtained when washing the filter residue with the mixed solution and pure water.

[0116] Example 15 is different from Example 1 in that the pH value of the second acid solution is 2.5.

[0117] Example 16

[0118] Mix 1 kg of lithium iron phosphate waste powder with 1 g of polyacrylic acid, concentrated sulfuric acid, 0.35 L of hydrogen peroxide and 4 L of water, and heat to 60 °C, stir evenly to obtain lithium iron phosphate slurry. Among them, during the addition of concentrated sulfuric acid, the addition amount of concentrated sulfuric acid is controlled to control the first pH value of the lithium iron phosphate slurry to be 1.2. After stirring for 4 h, add ammonia water to the lithium iron phosphate slurry to adjust the pH value of the lithium iron phosphate slurry to 2.0, that is, the second pH value is 2.0. Let the lithium iron phosphate slurry stand, and after 1 h, carry out solid-liquid separation to obtain a lithium-containing solution and filter residue. Mix dilute sulfuric acid with a pH value of 2.0 and 0.5 g of polyacrylic acid to form a mixed solution, use this mixed solution to wash the filter residue, after solid-liquid separation, wash the filter residue with pure water again, and collect the washing liquid obtained when washing the filter residue with the mixed solution and pure water.

[0119] Example 16 is different from Example 1 in that the mass ratio of polyacrylic acid to lithium iron phosphate waste powder in the mixed solution in Example 16 is 0.05:100, and the mass ratio of polyacrylic acid to lithium iron phosphate waste powder in the mixed solution in Example 1 is 0.1:100.

[0120] Example 17

[0121] Mix 1 kg of lithium iron phosphate waste powder with 1 g of polyacrylic acid, concentrated sulfuric acid, 0.35 L of hydrogen peroxide and 4 L of water, and heat to 60 °C. Stir evenly to obtain a lithium iron phosphate slurry. Among them, during the addition of concentrated sulfuric acid, the addition amount of concentrated sulfuric acid is controlled to control the first pH value of the lithium iron phosphate slurry to be 1.2. After stirring for 4 h, add ammonia water to the lithium iron phosphate slurry to adjust the pH value of the lithium iron phosphate slurry to 2.0, that is, the second pH value is 2.0. Let the lithium iron phosphate slurry stand, and after 1 h, carry out solid-liquid separation to obtain a lithium-containing solution and a filter residue. Mix dilute sulfuric acid with a pH value of 2.0 and 5 g of polyacrylic acid to form a mixed solution. Use this mixed solution to wash the filter residue. After solid-liquid separation, wash the filter residue with pure water again, and collect the washing liquid obtained when washing the filter residue with the mixed solution and pure water.

[0122] The difference between Example 17 and Example 1 is that in Example 16, the mass ratio of polyacrylic acid to lithium iron phosphate waste powder in the mixed solution is 0.5:100, and in Example 1, the mass ratio of polyacrylic acid to lithium iron phosphate waste powder in the mixed solution is 0.1:100.

[0123] Example 18

[0124] Mix 1 kg of lithium iron phosphate waste powder with 1 g of polyacrylic acid, concentrated sulfuric acid, 0.35 L of hydrogen peroxide and 4 L of water, and heat to 60 °C. Stir evenly to obtain a lithium iron phosphate slurry. Among them, during the addition of concentrated sulfuric acid, the addition amount of concentrated sulfuric acid is controlled to control the first pH value of the lithium iron phosphate slurry to be 1.2. After stirring for 4 h, add ammonia water to the lithium iron phosphate slurry to adjust the pH value of the lithium iron phosphate slurry to 2.0, that is, the second pH value is 2.0. Let the lithium iron phosphate slurry stand, and after 1 h, carry out solid-liquid separation to obtain a lithium-containing solution and a filter residue. Mix dilute sulfuric acid with a pH value of 2.0 and 10 g of polyacrylic acid to form a mixed solution. Use this mixed solution to wash the filter residue. After solid-liquid separation, wash the filter residue with pure water again, and collect the washing liquid obtained when washing the filter residue with the mixed solution and pure water.

[0125] The difference between Example 18 and Example 1 is that in Example 16, the mass ratio of polyacrylic acid to lithium iron phosphate waste powder in the mixed solution is 1:100, and in Example 1, the mass ratio of polyacrylic acid to lithium iron phosphate waste powder in the mixed solution is 0.1:100.

[0126] Example 19

[0127] Mix 1 kg of lithium iron phosphate waste powder with 1 g of polyacrylic acid, concentrated sulfuric acid, 0.35 L of hydrogen peroxide and 4 L of water, and heat to 60 °C, stir evenly to obtain a lithium iron phosphate slurry. Among them, during the addition of concentrated sulfuric acid, by controlling the addition amount of concentrated sulfuric acid, the first pH value of the lithium iron phosphate slurry is controlled to be 1.2. After stirring for 4 h, add ammonia water to the lithium iron phosphate slurry to adjust the pH value of the lithium iron phosphate slurry to 2.0, that is, the second pH value is 2.0. Let the lithium iron phosphate slurry stand, and after 1 h, carry out solid-liquid separation to obtain a lithium-containing solution and a filter residue. Wash the filter residue with dilute sulfuric acid with a pH value of 2.0, and then wash the filter residue with pure water after solid-liquid separation. Collect the washing liquid obtained when washing the filter residue with the mixed liquid and pure water.

[0128] The difference between Example 19 and Example 1 is that in Example 19, polyacrylic acid is not used to wash the filter residue.

[0129] Example 20

[0130] Mix 1 kg of lithium iron phosphate waste powder with 1 g of polyacrylic acid, concentrated sulfuric acid, 0.35 L of hydrogen peroxide and 4 L of water, and heat to 60 °C, stir evenly to obtain a lithium iron phosphate slurry. Among them, during the addition of concentrated sulfuric acid, by controlling the addition amount of concentrated sulfuric acid, the first pH value of the lithium iron phosphate slurry is controlled to be 1.2. After stirring for 4 h, add ammonia water to the lithium iron phosphate slurry to adjust the pH value of the lithium iron phosphate slurry to 1.8, that is, the second pH value is 1.8. Let the lithium iron phosphate slurry stand, and after 1 h, carry out solid-liquid separation to obtain a lithium-containing solution and a filter residue. Mix dilute sulfuric acid with a pH value of 1.8 and 1 g of polyacrylic acid to form a mixed liquid, use the mixed liquid to wash the filter residue, and then wash the filter residue with pure water after solid-liquid separation. Collect the washing liquid obtained when washing the filter residue with the mixed liquid and pure water.

[0131] The difference between Example 20 and Example 1 is that the second pH value is 1.8, and the pH value of the second acid solution is 1.8.

[0132] Example 21

[0133] Mix 1 kg of lithium iron phosphate waste powder with 1 g of polyacrylic acid, concentrated sulfuric acid, 0.35 L of hydrogen peroxide and 4 L of water, and heat to 60 °C, stir evenly to obtain a lithium iron phosphate slurry. Among them, during the addition of concentrated sulfuric acid, by controlling the addition amount of concentrated sulfuric acid, the first pH value of the lithium iron phosphate slurry is controlled to be 1.2. After stirring for 4 h, add ammonia water to the lithium iron phosphate slurry to adjust the pH value of the lithium iron phosphate slurry to 2.2, that is, the second pH value is 2.2. Let the lithium iron phosphate slurry stand, and after 1 h, carry out solid-liquid separation to obtain a lithium-containing solution and a filter residue. Mix dilute sulfuric acid with a pH value of 2.2 and 1 g of polyacrylic acid to form a mixed liquid, use the mixed liquid to wash the filter residue, and then wash the filter residue with pure water after solid-liquid separation. Collect the washing liquid obtained when washing the filter residue with the mixed liquid and pure water.

[0134] Implementation Example 21 is different from Implementation Example 1 in that the second pH value is 2.2, and the pH value of the second acid solution is 2.2.

[0135] Implementation Example 22

[0136] 1kg of lithium iron phosphate waste powder was mixed with 1g of polyacrylic acid, concentrated sulfuric acid, 0.7L of hydrogen peroxide and 4L of water and heated to 60°C, and stirred evenly to obtain lithium iron phosphate slurry. In the process of adding concentrated sulfuric acid, the amount of concentrated sulfuric acid added was controlled to control the first pH value of the lithium iron phosphate slurry to 1.2. After stirring for 4 hours, ammonia water was added to the lithium iron phosphate slurry to adjust the pH value of the lithium iron phosphate slurry to 2.0, that is, the second pH value was 2.0. The lithium iron phosphate slurry was allowed to stand, and solid-liquid separation was performed after 1 hour to obtain a lithium-containing solution and a filter residue. Dilute sulfuric acid with a pH value of 2.0 was mixed with 1g of polyacrylic acid to form a mixed solution, and the filter residue was washed with the mixed solution. After solid-liquid separation, the filter residue was washed with pure water, and the washing liquid obtained when the filter residue was washed with the mixed solution and pure water was collected.

[0137] The difference between Implementation Example 22 and Implementation Example 1 is that in Implementation Example 1, the molar ratio of hydrogen peroxide to lithium element in waste lithium iron phosphate powder is 0.8:1, and in Implementation Example 22, the molar ratio of hydrogen peroxide to lithium element in waste lithium iron phosphate powder is 1.6:1.

[0138] Implementation Example 23

[0139] 1kg of lithium iron phosphate waste powder was mixed with 1g of polymethacrylic acid, concentrated sulfuric acid, 0.35L of hydrogen peroxide and 4L of water and heated to 60°C, and stirred evenly to obtain lithium iron phosphate slurry. In the process of adding concentrated sulfuric acid, the amount of concentrated sulfuric acid added was controlled to control the first pH value of the lithium iron phosphate slurry to 1.2. After stirring for 4 hours, ammonia water was added to the lithium iron phosphate slurry to adjust the pH value of the lithium iron phosphate slurry to 2.0, that is, the second pH value was 2.0. The lithium iron phosphate slurry was allowed to stand, and solid-liquid separation was performed after 1 hour to obtain a lithium-containing solution and a filter residue. Dilute sulfuric acid with a pH value of 2.0 was mixed with 1g of polymethacrylic acid to form a mixed solution, and the mixed solution was used to wash the filter residue. After solid-liquid separation, the filter residue was washed with pure water, and the washing liquid obtained when the filter residue was washed with the mixed solution and pure water was collected. In which, the structure of the polymethacrylic acid is shown in Formula III above.

[0140] The difference between Implementation Example 23 and Implementation Example 1 is that the polyacrylic acid derivative used in Implementation Example 1 is polyacrylic acid, and the polyacrylic acid derivative used in Implementation Example 23 is polymethacrylic acid.

[0141] Comparative Example 1

[0142] Mix 1 kg of lithium iron phosphate waste powder with concentrated sulfuric acid, 0.35 L of hydrogen peroxide, and 4 L of water, and heat the mixture to 60 °C. Stir evenly to obtain a lithium iron phosphate slurry. Among them, during the addition of concentrated sulfuric acid, control the addition amount of concentrated sulfuric acid to control the first pH value of the lithium iron phosphate slurry to be 1.2. After stirring for 4 h, add ammonia water to the lithium iron phosphate slurry to adjust the pH value of the lithium iron phosphate slurry to 2.0, that is, the second pH value is 2.0. Let the lithium iron phosphate slurry stand, and after 1 h, perform solid-liquid separation to obtain a lithium-containing solution and a filter residue. Mix dilute sulfuric acid with a pH value of 2.0 with 1 g of polyacrylic acid to form a mixed solution. Use this mixed solution to wash the filter residue. After solid-liquid separation, wash the filter residue with pure water again, and collect the washing liquid obtained when washing the filter residue with the mixed solution and pure water.

[0143] The difference between Comparative Example 1 and Example 1 is that in Comparative Example 1, when mixing the lithium iron phosphate waste powder with the first acid solution, the oxidant, and the solvent, polyacrylic acid is not added.

[0144] Comparative Example 2

[0145] Mix 1 kg of lithium iron phosphate waste powder with 1 g of polyacrylic acid, concentrated sulfuric acid, 0.35 L of hydrogen peroxide, and 4 L of water, and heat the mixture to 60 °C. Stir evenly to obtain a lithium iron phosphate slurry. Among them, during the addition of concentrated sulfuric acid, control the addition amount of concentrated sulfuric acid to control the first pH value of the lithium iron phosphate slurry to be 2.0. After stirring for 4 h, let the lithium iron phosphate slurry stand, and after 1 h, perform solid-liquid separation to obtain a lithium-containing solution and a filter residue. Mix dilute sulfuric acid with a pH value of 2.0 with 1 g of polyacrylic acid to form a mixed solution. Use this mixed solution to wash the filter residue. After solid-liquid separation, wash the filter residue with pure water again, and collect the washing liquid obtained when washing the filter residue with the mixed solution and pure water.

[0146] The difference between Comparative Example 2 and Example 1 is that the first pH value is 2.0 and ammonia water is not added.

[0147] Comparative Example 3

[0148] Mix 1 kg of lithium iron phosphate waste powder with 1 g of polyacrylic acid, concentrated sulfuric acid, 0.35 L of hydrogen peroxide, and 4 L of water, and heat the mixture to 60 °C. Stir evenly to obtain a lithium iron phosphate slurry. Among them, during the addition of concentrated sulfuric acid, control the addition amount of concentrated sulfuric acid to control the first pH value of the lithium iron phosphate slurry to be 1.0. After stirring for 4 h, let the lithium iron phosphate slurry stand, and after 1 h, perform solid-liquid separation to obtain a lithium-containing solution and a filter residue. Mix dilute sulfuric acid with a pH value of 2.0 with 1 g of polyacrylic acid to form a mixed solution. Use this mixed solution to wash the filter residue. After solid-liquid separation, wash the filter residue with pure water again, and collect the washing liquid obtained when washing the filter residue with the mixed solution and pure water.

[0149] The difference between Comparative Example 3 and Example 5 is that in Comparative Example 3, the pH value of the lithium iron phosphate slurry is not adjusted to the second pH value, but a solid-liquid separation operation is performed on the lithium iron phosphate slurry at the first pH value.

[0150] Comparative Example 4

[0151] 1 kg of lithium iron phosphate waste powder was mixed with concentrated sulfuric acid, 0.35 L of hydrogen peroxide and 4 L of water and heated to 60 °C, and stirred evenly to obtain a lithium iron phosphate slurry. Among them, during the addition of concentrated sulfuric acid, the addition amount of concentrated sulfuric acid was controlled to control the first pH value of the lithium iron phosphate slurry to be 1.2. After stirring for 4 h, ammonia water was added to the lithium iron phosphate slurry to adjust the pH value of the lithium iron phosphate slurry to 2.0, that is, the second pH value was 2.0. The lithium iron phosphate slurry was allowed to stand, and after 1 h, solid-liquid separation was carried out to obtain a lithium-containing solution and a filter residue. The filter residue was washed with dilute sulfuric acid with a pH value of 2.0, and after solid-liquid separation, the filter residue was washed with pure water, and the washing solutions obtained when washing the filter residue with the mixed solution and pure water were collected.

[0152] The difference between Comparative Example 4 and Example 1 is that in Comparative Example 4, polyacrylic acid is not added when the lithium iron phosphate waste powder is mixed with the first acid solution, the oxidant and the solvent, and polyacrylic acid is not added when washing the filter residue.

[0153] Elemental analysis was performed on the lithium-containing solutions, filter residues and washing solutions prepared in Examples 1-23 and Comparative Examples 1-4, and the lithium element content and iron element content in the lithium-containing solutions, filter residues and washing solutions were tested. Among them, the lithium element content in the lithium-containing solution is C_Li_1, the iron element content is C_Fe_1, the lithium element content in the filter residue is C_Li_2, the iron element content is C_Fe_2, the lithium element content in the washing solution is C_Li_3, and the iron element content is C_Fe_3. Among them, ICP-OES can be used for elemental analysis.

[0154] The lithium leaching rate, iron leaching rate and lithium leaching selectivity were calculated according to the tested lithium element content and iron element content. Among them, the lithium leaching rate is represented by K_Li, the iron leaching rate is represented by K_Fe, and the lithium leaching selectivity is represented by S. K_Li = (C_Li_1 + C_Li_3) / (C_Li_1 + C_Li_2 + C_Li_3), K_Fe = (C_Fe_1 + C_Fe_3) / (C_Fe_1 + C_Fe_2 + C_Fe_3), S = K_Li / (K_Li + K_Fe).

[0155] In Step S201 of Examples 1-23 and Comparative Examples 1-4, the mass ratio of the polyacrylic acid derivative to the lithium iron phosphate waste powder, the molar ratio of hydrogen peroxide to lithium element in the lithium iron phosphate waste powder, the first pH value, the second pH value, the mass ratio of the polyacrylic acid derivative to the lithium iron phosphate waste powder in S204, and the pH value of the second acid solution are recorded in Table 1 below. Among them, the mass ratio of the polyacrylic acid derivative to the lithium iron phosphate waste powder in Step S201 is represented by Ratio1, and the mass ratio of the polyacrylic acid derivative to the lithium iron phosphate waste powder in the mixed solution is represented by Ratio2. The lithium leaching rate, iron leaching rate, and lithium leaching selectivity of Examples 1-23 and Comparative Examples 1-4 are recorded in Table 2 below.

[0156] Table 1

[0157]

[0158] Table 2

[0159] Lithium leaching rate (%) Iron leaching rate (%) Lithium leaching selectivity (%) Example 1 99.71 0.61 99.39 Example 2 99.86 0.63 99.37 Example 3 99.89 1.13 98.88 Example 4 98.58 0.6 99.40 Example 5 99.86 0.63 99.37 Example 6 99.89 1.13 98.88 Example 7 98.58 0.6 99.40 Example 8 99.74 0.73 99.27 Example 9 99.53 0.6 99.40 Example 10 99.84 0.97 99.04 Example 11 99.31 0.58 99.42 Example 12 99.75 0.63 99.37 Example 13 99.59 0.6 99.40 Example 14 99.79 0.68 99.32 Example 15 99.56 0.59 99.41 Example 16 99.61 0.6 99.40 Example 17 99.83 0.68 99.32 Example 18 99.48 0.73 99.27 Example 19 99.34 0.61 99.39 Example 20 99.78 0.94 99.07 Example 21 99.64 0.32 99.68 Example 22 99.83 0.22 99.78 Example 23 99.69 0.63 99.37 Comparative Example 1 97.78 0.84 99.15 Comparative Example 2 97.78 0.84 99.15 Comparative Example 3 99.52 32.08 75.62 Comparative Example 4 95.74 0.52 99.46

[0160] As can be seen from Examples 1-4 and Comparative Example 1 in Table 1 and Table 2, when the lithium iron phosphate waste powder is mixed with the first acid solution, the oxidant, and the solvent, adding polyacrylic acid can significantly increase the lithium leaching rate.

[0161] As can be seen from Examples 1, 5-7 and Comparative Example 2, when the first pH value is 0.8-1.2, both the lithium leaching rate and the lithium leaching selectivity are relatively high. And within this pH value range, as the acidity increases, the lithium leaching rate gradually increases, but the lithium leaching selectivity gradually decreases. Therefore, when adjusting the first pH value, it can be adjusted according to the above characteristics to achieve a higher lithium leaching rate and a higher lithium leaching selectivity. If the first pH value is less than 0.8, since the acidity is stronger than that of 0.8-1.2, the leaching rates of lithium, phosphorus, and iron increase, and the lithium leaching selectivity decreases. If the first pH value is greater than 1.2, since the acidity is weaker than that of 0.8-1.2, the lithium leaching amount decreases and the lithium leaching rate decreases. Especially when the first pH value is within 1.8-2.2 and no alkaline substance is added to increase the pH value (Comparative Example 2), it can be understood that in Comparative Example 2, the first pH value is equal to the second pH value and is 1.8-2.2, that is, the pH value of the lithium iron phosphate slurry is not first adjusted to a lower pH value to promote the leaching of lithium ions but directly adjusted to 1.8-2.2, resulting in a significant decrease in the lithium leaching rate and a decrease in the lithium leaching selectivity.

[0162] As can be seen from Examples 1, 8 - 11, when the second pH value is 1.8 - 2.2, both the lithium leaching rate and the lithium leaching selectivity are relatively high. And within this pH value range, as the acidity increases, the lithium leaching rate gradually increases, but the lithium leaching selectivity gradually decreases. Therefore, when adjusting the second pH value, it can be adjusted according to the above characteristics to achieve a higher lithium leaching rate and a higher lithium leaching selectivity. If the second pH value is less than 1.8, since the acidity is stronger compared to 1.8 - 2.2, it will affect the combination of phosphate ions and ferric ions, thereby reducing the lithium leaching selectivity. If the second pH value is greater than 2.2, since the acidity is weaker compared to 1.8 - 2.2, some dissolved lithium ions will combine with phosphate ions to form iron phosphate precipitates, or ferric ions will combine with hydroxide ions to form iron hydroxide colloids, thereby reducing the lithium leaching rate.

[0163] As can be seen from Examples 1, 12 - 15, when the pH value of the second acid solution is 1.8 - 2.2, both the lithium leaching rate and the leaching selectivity are relatively high. And within this pH value range, as the acidity increases, the lithium leaching rate gradually increases, but the lithium leaching selectivity gradually decreases. Therefore, when using the second acid solution to wash the filter residue, the second acid solution with an appropriate pH value can be selected to achieve a higher lithium leaching rate and a higher lithium leaching selectivity. If the pH value of the second acid solution is less than 1.8, since the acidity is stronger compared to 1.8 - 2.2, the leaching rates of phosphorus and iron in the mixed solution increase, while the lithium leaching selectivity decreases. If the pH value of the second acid solution is greater than 2.2, since the acidity weakens compared to 1.8 - 2.2, the leaching rates of phosphorus and iron slightly decrease, while the lithium leaching selectivity slightly increases. However, at the same time, due to the weakened acidity, the amount of lithium leached decreases and the lithium leaching rate decreases.

[0164] As can be seen from Examples 1, 16 - 18 and Example 19, when washing the filter residue, adding polyacrylic acid can increase the lithium leaching rate.

[0165] As can be seen from Example 5 and Comparative Example 3, if the pH value is not adjusted from the first pH value to the second pH value, the lithium leaching selectivity decreases significantly.

[0166] As can be seen from Examples 1, 20 and 21, when the second pH value is within the range of 1.8 - 2.2 and the pH value of the second acid solution is within the range of 1.8 - 2.2, as the second pH value decreases and the pH value of the second acid solution decreases, the lithium leaching rate gradually increases, but the lithium leaching selectivity gradually decreases. Therefore, when adjusting the second pH value and the pH value of the second acid solution, the balance between the lithium leaching rate and the lithium leaching selectivity should be taken into account.

[0167] As can be seen from Example 1 and 22, increasing the molar ratio of hydrogen peroxide to lithium in the lithium iron phosphate waste powder can increase the lithium leaching rate and the lithium leaching selectivity.

[0168] As can be seen from Example 1 and Comparative Example 4, when mixing the lithium iron phosphate waste powder with the first acid solution and the oxidant, no polyacrylic acid derivative is added, and no polyacrylic acid derivative is added when washing the filter residue, resulting in a very obvious decrease in the lithium leaching rate.

[0169] The above is the implementation manner of the embodiments of the present application. It should be noted that for those of ordinary skill in the art, without departing from the principle of the embodiments of the present application, several improvements and refinements can be made, and these improvements and refinements are also regarded as the protection scope of the present application.

Claims

1. A method for recycling lithium iron phosphate waste powder, characterized in that, The method includes: S1: Mix at least the lithium iron phosphate waste powder with a polyacrylic acid derivative, a first acid solution, an oxidant, and a solvent to obtain a lithium iron phosphate slurry, and the pH value of the lithium iron phosphate slurry is a first pH value; S2: Add an alkaline substance to the lithium iron phosphate slurry to adjust the pH value of the lithium iron phosphate slurry to a second pH value, and the second pH value is greater than the first pH value; S3: Perform a solid-liquid separation operation on the lithium iron phosphate slurry to obtain a lithium-containing solution and a filter residue; Wherein, the polyacrylic acid derivative has the structure shown in Formula I, Among them, R1, R2, and R3 are each independently one of a hydrogen atom and a hydrocarbon group.

2. The recycling method of lithium iron phosphate waste powder according to claim 1, characterized in that The first pH value is a value in the range of 0.8 - 1.

2.

3. The recycling method of lithium iron phosphate waste powder according to claim 1, characterized in that The second pH value is a value in the range of 1.8 - 2.

2.

4. The recycling method of lithium iron phosphate waste powder according to claim 1, wherein The method further includes: S4: Wash the filter residue and collect the washing solution; S1 includes: Mix the lithium iron phosphate waste powder with a polyacrylic acid derivative, a first acid solution, an oxidant, a solvent, and the washing solution to obtain a lithium iron phosphate slurry, and the pH value of the lithium iron phosphate slurry is the first pH value.

5. The recycling method of lithium iron phosphate waste powder according to claim 4, characterized in that, The washing of the filter residue includes: Wash the filter residue with a mixed solution of a second acid solution and a polyacrylic acid derivative, and the polyacrylic acid derivative has the structure shown in Formula I.

6. The recycling method of lithium iron phosphate waste powder according to claim 5, characterized in that, The pH value of the second acid solution is a value in the range of 1.8 - 2.

2.

7. The method for recycling lithium iron phosphate waste powder according to claim 5, characterized in that, The mass ratio of the second acid solution to the lithium iron phosphate waste powder is (3 - 5):1, and the mass ratio of the polyacrylic acid derivative in the mixed solution to the lithium iron phosphate waste powder is (0.01 - 0.5):

100.

8. The recycling method of lithium iron phosphate waste powder according to claim 5, characterized in that, The second acid solution includes at least one of sulfuric acid, phosphoric acid, hydrochloric acid, and nitric acid.

9. The method for recycling waste lithium iron phosphate powder according to claim 1, characterized in that, The mass ratio of the polyacrylic acid derivative to the lithium iron phosphate waste powder is (0.01 - 0.5):100, and the molar ratio of the oxidant to the lithium element in the lithium iron phosphate waste powder is (0.5 - 2):

1.

10. The method for recycling lithium iron phosphate waste powder according to claim 1, wherein, The at least mixing the lithium iron phosphate waste powder with a polyacrylic acid derivative, a first acid solution, an oxidant, and a solvent to obtain a lithium iron phosphate slurry includes: At least mix the lithium iron phosphate waste powder with the polyacrylic acid derivative, the first acid solution, the oxidant, and the solvent and heat to 40°C - 80°C, and stir at a stirring speed of 200 rpm - 700 rpm for at least 2 h to obtain the lithium iron phosphate slurry.

11. The method for recycling lithium iron phosphate waste powder according to claim 1, characterized in that, The alkaline substance includes at least one of lithium hydroxide, sodium hydroxide, sodium carbonate, and ammonia water, the first acid solution includes at least one of sulfuric acid, phosphoric acid, hydrochloric acid, and nitric acid, and the oxidant includes at least one of hydrogen peroxide and hypochlorous acid.

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