Method for recycling lithium from waste lithium iron phosphate battery

Abstract

The invention provides a method for recycling lithium from waste lithium iron phosphate batteries. The method comprises the following steps: pretreating the waste lithium iron phosphate battery to obtain positive electrode powder; mixing the positive electrode powder, the buffer leaching agent solution and the lithium salt seed crystal suspension, and carrying out leaching reaction to obtain a lithium-rich leaching solution; and carrying out post-treatment on the lithium-rich lixivium to prepare a lithium salt product. According to the method, the buffer leaching agent solution and the lithium salt seed crystal suspension are adopted to play a synergistic effect, the selective leaching efficiency of lithium can be effectively improved, and the buffer leaching agent not only can destroy the lattice structure of the positive electrode material and promote dissolution of lithium ions, but also can effectively relieve pH fluctuation to avoid generation of impurity colloids; the lithium salt seed crystal suspension can further reduce co-dissolution of transition metal ions and other impurities through the same ion effect, so that the finally prepared lithium salt product is high in purity and high in yield.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of resource recycling, and particularly relates to a method for recovering lithium from waste lithium iron phosphate batteries. BACKGROUND

[0002] Lithium ion batteries have been widely used in portable electronic devices, electric vehicles and energy storage systems due to their high energy density and long cycle life. However, the number of waste lithium ion batteries has increased rapidly, and improper disposal will not only cause serious environmental pollution, but also lead to great waste of valuable resources such as lithium. Therefore, efficient recovery of lithium resources from waste lithium ion batteries is of great significance for alleviating lithium resource shortage, reducing dependence on primary minerals and promoting sustainable development of the battery industry.

[0003] Patent CN103035977A discloses a method for separating and recovering lithium from waste lithium ion batteries. The waste lithium ion batteries are discharged and then disassembled to remove the battery shell. The battery core is crushed. The crushed battery core is leached with inorganic acid and oxidizing agent, filtered to obtain filtrate. The pH value of the filtrate is adjusted to greater than or equal to 8, and impurities and precipitates are removed by filtration to obtain a recovery liquid containing lithium ions. The lithium ions in the recovery liquid are adsorbed by resin. The resin is desorbed to obtain a separated and recovered lithium salt. Patent CN113415814A discloses a method for selectively recovering lithium from waste lithium ion batteries by ultra-low temperature roasting. The method for selectively recovering lithium from waste lithium ion batteries involves a method for selectively recovering lithium from waste lithium ion batteries. The method adds a composite salt to selectively destroy the interlayer structure of lithium and oxygen in the positive plate of the lithium ion battery and form a soluble lithium salt, thereby realizing selective extraction of lithium ions. Patent CN114207161A discloses a method for recovering one or more transition metals and lithium from waste lithium ion batteries or parts thereof. The method comprises the steps of: (a) providing a particulate material containing transition metal compounds and / or transition metals, wherein the transition metals are selected from Ni and Co, and at least a portion of the Ni and / or Co, if present, is in an oxidation state lower than +2, such as in a metallic state; the particulate material further contains a lithium salt; (b) treating the material provided in step (a) with a polar solvent and optionally an alkaline earth metal hydroxide; (c) separating the solid from the liquid, optionally followed by a solid-solid separation step; and (d) treating the solid containing transition metals in a smelting furnace to obtain a metal melt containing Ni and / or Co.

[0004] However, the above-mentioned prior art has the problems of incomplete impurity removal, poor selective extraction of lithium and low purity of lithium recovery, although it has achieved the separation and recovery of lithium and the improvement of purity to some extent.

[0005] Therefore, how to more thoroughly remove impurities, improve the selective extraction capacity of lithium, and thus significantly improve the purity of recovered lithium is a technical problem to be solved. SUMMARY

[0006] In view of the deficiencies of the prior art, the purpose of the present application is to provide a method for recovering lithium from waste lithium iron phosphate batteries. In the method provided by the present application, the synergistic effect of buffer leaching agent solution and lithium salt crystal seed suspension is used to accurately extract lithium components from the positive electrode powder, significantly improving the selective leaching efficiency of lithium. The buffer leaching agent solution not only reduces the binding force of transition metals on lithium ions, destroys the crystal lattice structure of the positive electrode material, and promotes the dissolution of lithium ions, but also effectively alleviates pH fluctuations and avoids the generation of impurity colloids. The lithium salt crystal seed suspension can form a soluble salt with lithium ions through the common ion effect, further reducing the co-dissolution of transition metal ions and other impurities, and reducing lithium loss. The final lithium salt product has high purity and high yield. In summary, the method improves the recovery purity of lithium metal, is suitable for large-scale recovery of lithium, and is especially suitable for scenes with high lithium content and low valence state metals. In addition, the method is simple in process, low in cost, and has a very broad application prospect.

[0007] To achieve this purpose, the present application adopts the following technical solutions:

[0008] In a first aspect, the present application provides a method for recovering lithium from waste lithium iron phosphate batteries, comprising the following steps:

[0009] The waste lithium iron phosphate battery is pretreated to obtain a positive electrode powder.

[0010] The positive electrode powder, buffer leaching agent solution and lithium salt crystal seed suspension are mixed to perform leaching reaction to obtain a lithium-rich leaching solution.

[0011] The lithium-rich leaching solution is post-treated to obtain a lithium salt product.

[0012] The method provided by the present application can accurately extract lithium components in the positive electrode powder by using the synergistic effect of the buffer leaching agent solution and the lithium salt crystal seed suspension, and significantly improves the selective leaching efficiency of lithium, wherein the buffer leaching agent solution can not only reduce the binding force of transition metals on lithium ions, destroy the lattice structure of the positive electrode material, and promote the dissolution of lithium ions, but also effectively alleviate the pH fluctuation to avoid the generation of impurity colloids; the lithium salt crystal seed suspension can form a soluble salt with lithium ions by the same ion effect, further reduce the co-dissolution of transition metal ions and other impurities, and reduce the loss of lithium. Finally, the purity and yield of the prepared lithium salt product are high. In summary, the method improves the recovery purity of lithium metal, is suitable for large-scale recovery of lithium, and is especially suitable for scenes with high lithium content and less low-valence metal in raw materials. In addition, the method has simple process and low cost, and has very wide application prospect.

[0013] Preferably, the pretreatment comprises the following steps:

[0014] (a) disassembling and separating the waste lithium iron phosphate battery to obtain a positive electrode sheet.

[0015] (b) performing calcination treatment on the positive electrode sheet to obtain a positive electrode powder.

[0016] Preferably, the temperature of the calcination treatment is 500-600℃, for example, it can be 500℃, 520℃, 540℃, 560℃, 580℃ or 600℃, etc.

[0017] Preferably, the time of the calcination treatment is 2-4h, for example, it can be 2h, 3h or 4h, etc.

[0018] Preferably, the atmosphere of the calcination treatment is an air atmosphere.

[0019] Preferably, the buffer leaching agent solution is a mixed solution of an acid salt and an acid. Preferably, the acid salt comprises an alkali metal dihydrogen phosphate.

[0020] In the present application, the alkali metal dihydrogen phosphate can provide H2PO4 - , H2PO4 - In an aqueous solution, the ionization equilibrium releases H + and PO4 3- When the impurity elements aluminum or iron in the raw material are leached, they will combine with PO4 3- in the system to form precipitates and be removed from the solution, while H + is released to supplement the H + consumed by the leaching of impurity elements, thereby buffering the sharp fluctuation of the solution pH during the leaching process, ensuring the stability of the dissociation equilibrium of H2PO4 - , and avoiding the precipitation of Li⁺ or the intensification of impurity dissolution caused by sudden changes in pH.

[0021] Preferably, the alkali metal dihydrogen phosphate includes any one or a combination of at least two of lithium dihydrogen phosphate, potassium dihydrogen phosphate, sodium dihydrogen phosphate, or ammonium dihydrogen phosphate.

[0022] Preferably, the acid includes citric acid and / or acetic acid.

[0023] In this invention, the aforementioned types of acids can disrupt the crystal structure of the cathode material, thereby promoting the dissolution of lithium ions.

[0024] Preferably, in the mixed solution of the acid salt and the acid, the concentration of the acid salt is 0.5-0.8 mol / L, for example, it can be 0.5 mol / L, 0.6 mol / L, 0.7 mol / L or 0.8 mol / L, etc.

[0025] Preferably, in the mixed solution of the acid salt and the acid, the molar concentration ratio of the acid salt and the acid is (0.5-0.8):(0.3-0.5), wherein the acid salt is selected in the range of "0.5-0.8", for example, 0.5, 0.6, 0.7 or 0.8, and the acid is selected in the range of "0.3-0.5", for example, 0.3, 0.4 or 0.5.

[0026] In this invention, under a suitable molar concentration ratio, the acid salt and acid can not only disrupt the crystal structure of the cathode material and promote the dissolution of lithium ions, but also effectively mitigate pH fluctuations and prevent the generation of impurity colloids.

[0027] Preferably, the lithium salt seed suspension includes a lithium phosphate seed suspension.

[0028] In this invention, the lithium phosphate seed suspension can release PO4. 3- PO4 3- It will react with H2PO4 in the solution - The equilibrium system for the formation of phosphate ions (H2PO4) - ⇌H + +HPO4 2- ⇌2H + +PO4 3- ), when PO4 3- As the concentration increases, according to the common ion effect, H2PO4 - Although the dissociation equilibrium is somewhat suppressed, the presence of acid provides sufficient H⁺ to maintain the H₂PO₄ concentration in the system. - The dominant position ensures that Li⁺ preferentially interacts with H₂PO₄. - They combine to form soluble LiH₂PO₄. Simultaneously, PO₄ 3- It forms insoluble phosphate precipitates with transition metal ions, which can further reduce the co-precipitation loss of Li⁺ and impurities.

[0029] Preferably, the content of lithium salt seed crystals in the lithium salt seed crystal suspension is 3-5% based on the mass of the positive electrode powder, for example, it can be 3%, 4% or 5%, etc.

[0030] In the present application, the appropriate amount of lithium salt seed crystals helps to ensure that the seed crystals are in sufficient contact with the leaching system while avoiding particle agglomeration caused by excessive seed crystals or competitive adsorption of H2PO4 - from the leaching agent, and maintaining the selective precipitation balance of PO4 3- and transition metal impurities, thereby further strengthening the impurity removal effect while improving the lithium leaching rate, and forming a precise match with the synergistic effect of the alkali metal dihydrogen phosphate and the acid to ensure the high purity and stability of the lithium-rich leaching solution.

[0031] Preferably, the leaching reaction is a constant temperature process.

[0032] Preferably, the reaction temperature of the leaching reaction is 60-80℃, for example, it can be 60℃, 70℃ or 80℃, etc., and the reaction time is 2-6h, for example, it can be 2h, 3h, 4h, 5h or 6h, etc. In the present application, the appropriate reaction temperature helps to control the dissolution rate of Li⁺, avoid the co-dissolution of impurities, and further ensure the purity and stability of the lithium-rich leaching solution.

[0033] Preferably, the post-treatment includes the following steps:

[0034] (c) mixing the lithium-rich leaching solution and the precipitant to perform an impurity removal reaction, so that the transition metal ions are precipitated, and then solid-liquid separation is performed to obtain a lithium-containing solution after impurity removal.

[0035] (d) adding to the lithium-containing solution after impurity removal to perform a lithium precipitation reaction, and obtaining a lithium phosphate product.

[0036] It should be noted that the sodium phosphate can be, for example, a sodium phosphate solution or a sodium phosphate solid powder, etc.

[0037] Preferably, the precipitant includes flake caustic soda or liquid caustic soda.

[0038] Preferably, the temperature of the impurity removal reaction is 30-50℃, for example, it can be 30℃, 40℃ or 50℃, etc.

[0039] Preferably, during the impurity removal reaction, the pH value of the reaction system is 6-7, for example, it can be 6, 6.2, 6.4, 6.6, 6.8 or 7, etc.

[0040] By adjusting the pH value of the reaction system, the present application can make different transition metal ions completely precipitate, avoiding the influence of impurity residues on the purity of the subsequent lithium salt product.

[0041] Preferably, the pH value of the reaction system during the lithium precipitation reaction is 10.5-11.5, for example, it can be 10.5, 11 or 11.5, etc.

[0042] Preferably, the temperature of the lithium precipitation reaction is 70-90℃, for example, it can be 70℃, 75℃, 80℃, 85℃ or 90℃, etc.

[0043] Preferably, the time of the lithium precipitation reaction is 2-4h, for example, it can be 2h, 3h or 4h, etc.

[0044] Preferably, the method comprises the following steps:

[0045] (1) After the waste lithium iron phosphate battery is disassembled and crushed, the ferromagnetic substances are separated by magnetic separation, and then calcination treatment is carried out in an air atmosphere at 500-600℃ for 2-4h, followed by screening separation to obtain positive electrode powder; wherein the particle size D50 of the positive electrode powder is 70-200μm (for example, it can be 70μm, 100μm, 150μm or 200μm, etc., and the particle size is too small to be easily dusted, and the subsequent leaching is not complete after being too large).

[0046] (2) The positive electrode powder and water are mixed according to the solid-liquid ratio of 1mg:(4-10)mL (for example, it can be 1mg:4mL, 1mg:5mL, 1mg:6mL, 1mg:7mL, 1mg:8mL, 1mg:9mL or 1mg:10mL, etc.), then a buffer leaching agent solution is added, mixed uniformly, then a lithium salt crystal seed suspension is added and mixed, stirred uniformly, and leaching reaction is carried out to obtain a lithium-rich leaching solution.

[0047] Wherein, the volume ratio of the obtained slurry to the buffer leaching agent solution is 1:(1-2) (for example, it can be 1:1, 1:1.5 or 1:2, etc.); the buffer leaching agent solution is a mixed solution of acid salt and acid, the concentration of acid salt is 0.5-0.8mol / L, and the molar concentration ratio of acid salt to acid is (0.5-0.8):(0.3-0.5); the lithium salt crystal seed suspension includes lithium phosphate crystal seed suspension; the content of lithium salt crystal seed in the lithium salt crystal seed suspension is 3-5% based on the mass of the positive electrode powder; the leaching reaction process is a constant temperature process; the reaction temperature of the leaching reaction is 60-80℃, and the reaction time is 2-6h.

[0048] (3) Under stirring conditions, the lithium-rich leaching solution and a precipitant are mixed to carry out impurity removal reaction at a temperature of 30-50℃, so that the transition metal ions are completely precipitated, then solid-liquid separation is carried out to obtain a lithium-containing solution after impurity removal; wherein, the pH value of the reaction system during the impurity removal reaction is 6-7.

[0049] (4) adding a sodium phosphate solution or a sodium phosphate solid to the lithium-containing solution after the impurities are removed, controlling the molar ratio of P element to Li element in the mixed solution to be 1.1-1.3 (for example, it can be 1.1, 1.2 or 1.3, etc.), and adjusting the pH value of the reaction system to 10.5-11.5 by liquid alkali, and performing a lithium precipitation reaction at a temperature of 70-90℃ for 2-4h to obtain a lithium phosphate precipitate.

[0050] (5) filtering, washing and drying the lithium phosphate precipitate to obtain a lithium phosphate product.

[0051] The numerical ranges described herein also include any and all point values and sub-ranges contained therein. Merely listing the numerical values and ranges herein is not a disclaimer of any other value or range. The mere fact that a numerical value or range is stated does not bar the inclusion of other, different, and / or intervening numerical values and / or ranges, even if such other, different, and / or intervening numerical values and / or ranges are not explicitly listed. The numerical ranges mentioned herein are therefore to be interpreted as merely stating the broadest values and sub-ranges that may fall within the ambit of the disclosure.

[0052] Compared with the prior art, the present application has the following beneficial effects:

[0053] In the method provided by the present application, the buffer leaching agent solution and the lithium salt crystal seed suspension are used to exert a synergistic effect, which can accurately extract the lithium component in the positive electrode powder, and significantly improve the selective leaching efficiency of lithium. The buffer leaching agent solution can not only reduce the binding force of transition metals to lithium ions, destroy the crystal lattice structure of the positive electrode material, and promote the dissolution of lithium ions, but also effectively alleviate the pH fluctuation to avoid the generation of impurity colloids. The lithium salt crystal seed suspension can form a soluble salt with lithium ions through the common ion effect, further reduce the co-dissolution of transition metal ions and other impurities, and reduce the loss of lithium. Finally, the lithium salt product prepared has high purity and high yield. In summary, the method improves the recovery purity of lithium metal, is suitable for large-scale recovery of lithium, and is especially suitable for scenes with high lithium content and less low-valence metal in raw materials. In addition, the method is simple in process and low in cost, and has a very broad application prospect. DETAILED DESCRIPTION

[0054] The technical solutions of the present application will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only to help understand the present application and should not be regarded as a specific limitation on the present application.

[0055] It should be noted that the waste lithium iron phosphate batteries used in the following embodiments are of the same batch, and after being disassembled and crushed, the ferromagnetic substances are separated by magnetic separation to obtain lithium iron phosphate waste.

[0056] Example 1

[0057] The present embodiment provides a method for recovering lithium from waste lithium iron phosphate batteries, which comprises the following steps:

[0058] (1) The lithium iron phosphate waste material is calcined in an air atmosphere at 550°C for 3h, and then separated by sieving to obtain a positive electrode powder; wherein the particle size D50 of the positive electrode powder is 150μm.

[0059] (2) The positive electrode powder and water are mixed according to a solid-liquid ratio of 1mg:8mL to obtain a slurry, then a buffer leaching agent solution is added according to a volume ratio of 1:1.5, and after uniform mixing, a lithium phosphate seed crystal suspension is added and mixed, stirred uniformly, and subjected to leaching reaction to obtain a lithium-rich leaching solution.

[0060] The buffer leaching agent solution is a mixed solution of potassium dihydrogen phosphate and citric acid, the concentration of potassium dihydrogen phosphate is 0.65mol / L, and the molar concentration ratio of potassium dihydrogen phosphate to citric acid is 0.65:0.4; the content of lithium phosphate seed crystals in the lithium phosphate seed crystal suspension is 4% based on the mass of the positive electrode powder; the reaction temperature of the leaching process is 70°C, and the reaction time is 4h.

[0061] (3) The lithium-rich leaching solution and liquid alkali are mixed under stirring conditions, and a decontamination reaction is carried out at a temperature of 40°C to make transition metal ions completely precipitate, and then solid-liquid separation is carried out to obtain a lithium-containing solution after decontamination; wherein the pH value of the reaction system during the decontamination reaction is 7.

[0062] (4) A saturated sodium phosphate solution is added to the lithium-containing solution after decontamination, the molar ratio of P element to Li element in the mixed solution is controlled to be 1.15, the pH value of the reaction system is adjusted to 11 by liquid alkali, and a lithium precipitation reaction is carried out at a temperature of 85°C for 3h to obtain lithium phosphate precipitate.

[0063] (5) The lithium phosphate precipitate is filtered, washed and dried to obtain lithium phosphate product.

[0064] Example 2

[0065] The present embodiment provides a method for recovering lithium from waste lithium iron phosphate batteries, which comprises the following steps:

[0066] (1) The lithium iron phosphate waste material is calcined in an air atmosphere at 550°C for 3h, and then separated by sieving to obtain a positive electrode powder; wherein the particle size D50 of the positive electrode powder is 150μm.

[0067] (2) The positive electrode powder and water are mixed according to a solid-liquid ratio of 1mg:5mL to obtain a slurry, then a buffer leaching agent solution is added according to a volume ratio of 1:1, and after uniform mixing, a lithium phosphate seed crystal suspension is added and mixed, stirred uniformly, and subjected to leaching reaction to obtain a lithium-rich leaching solution.

[0068] The buffer leaching agent solution is a mixed solution of sodium dihydrogen phosphate and citric acid, the concentration of sodium dihydrogen phosphate is 0.5 mol / L, and the molar concentration ratio of sodium dihydrogen phosphate to citric acid is 0.5:0.5; the content of lithium phosphate seed in the lithium phosphate seed suspension is 3% based on the mass of the positive electrode powder; the leaching reaction is a constant temperature process, the reaction temperature is 60°C, and the reaction time is 6h.

[0069] (3) The lithium-rich leaching solution and liquid alkali are mixed under stirring to perform a decontamination reaction at a temperature of 40°C, so that transition metal ions are completely precipitated, and then solid-liquid separation is performed to obtain a lithium-containing solution after decontamination; wherein, in the decontamination reaction, the pH value of the reaction system is 7.

[0070] (4) A saturated sodium phosphate solution is added to the lithium-containing solution after decontamination, the molar ratio of P element to Li element in the mixed solution is controlled to be 1.1, the pH value of the reaction system is adjusted to 10.5 through liquid alkali, and a lithium precipitation reaction is performed at a temperature of 70°C for 4h to obtain lithium phosphate precipitate.

[0071] (5) The lithium phosphate precipitate is filtered, washed and dried to obtain lithium phosphate product.

[0072] Example 3

[0073] The embodiment provides a method for recovering lithium from waste lithium iron phosphate batteries, and the method comprises the following steps:

[0074] (1) The lithium iron phosphate waste is calcined in an air atmosphere at 550°C for 3h, and then screened and separated to obtain a positive electrode powder; wherein, the particle size D50 of the positive electrode powder is 120μm.

[0075] (2) The positive electrode powder and water are mixed according to a solid-liquid ratio of 1mg:10mL to obtain a slurry, then a buffer leaching agent solution is added according to a volume ratio of 1:2, the mixture is uniformly mixed, a lithium phosphate seed suspension is added, stirred uniformly, and a leaching reaction is performed to obtain a lithium-rich leaching solution.

[0076] The buffer leaching agent solution is a mixed solution of potassium dihydrogen phosphate and acetic acid, the concentration of potassium dihydrogen phosphate is 0.8 mol / L, and the molar concentration ratio of potassium dihydrogen phosphate to acetic acid is 0.8:0.3; the content of lithium phosphate seed in the lithium phosphate seed suspension is 5% based on the mass of the positive electrode powder; the leaching reaction is a constant temperature process, the reaction temperature is 80°C, and the reaction time is 2h.

[0077] (3) mixing the lithium-rich leaching solution and liquid alkali under stirring, and carrying out a decontamination reaction at a temperature of 40°C to make transition metal ions completely precipitate, and then carrying out solid-liquid separation to obtain a lithium-containing solution after decontamination; wherein, in the decontamination reaction, the pH value of the reaction system is 7.

[0078] (4) adding a saturated sodium phosphate solution to the lithium-containing solution after decontamination, controlling the molar ratio of P element to Li element in the mixed solution to be 1.3, adjusting the pH value of the reaction system to 11.5 through liquid alkali, and carrying out a lithium precipitation reaction at a temperature of 90°C for 2h to obtain lithium phosphate precipitate.

[0079] (5) filtering, washing and drying the lithium phosphate precipitate to obtain lithium phosphate product.

[0080] Example 4

[0081] The difference between this example and Example 1 is that in the buffer leaching agent solution of step (2), the acetic acid is replaced by an equimolar amount of potassium dihydrogen phosphate.

[0082] The rest of the methods and parameters remain the same as in Example 1.

[0083] Example 5

[0084] The difference between this example and Example 1 is that in the buffer leaching agent solution of step (2), the potassium dihydrogen phosphate is replaced by an equimolar amount of acetic acid.

[0085] The rest of the methods and parameters remain the same as in Example 1.

[0086] Example 6

[0087] The difference between this example and Example 1 is that in the mixed solution of potassium dihydrogen phosphate and acetic acid of step (2), the molar concentration ratio of potassium dihydrogen phosphate to acetic acid is 0.5:0.8.

[0088] The rest of the methods and parameters remain the same as in Example 1.

[0089] Example 7

[0090] The difference between this example and Example 1 is that in the mixed solution of potassium dihydrogen phosphate and acetic acid of step (2), the molar concentration ratio of potassium dihydrogen phosphate to acetic acid is 1:0.3.

[0091] The rest of the methods and parameters remain the same as in Example 1.

[0092] Example 8

[0093] The difference between this example and Example 1 is that the content of lithium phosphate seed in the lithium phosphate seed suspension is 1% based on the mass of the positive electrode powder.

[0094] The rest of the method and parameters are consistent with Example 1.

[0095] Example 9

[0096] The difference between this example and Example 1 is that the content of lithium phosphate seed crystals in the lithium phosphate seed crystal suspension is 8% based on the mass of the positive electrode powder.

[0097] The rest of the method and parameters are consistent with Example 1.

[0098] Comparative Example 1

[0099] The difference between this example and Example 1 is that no lithium phosphate seed crystal suspension is added in step (2).

[0100] The rest of the method and parameters are consistent with Example 1.

[0101] Comparative Example 2

[0102] The difference between this example and Example 1 is that no buffer leaching agent solution is added in step (2).

[0103] The rest of the method and parameters are consistent with Example 1.

[0104] Performance test

[0105] The purity of the lithium phosphate product obtained by the method provided in the above examples and comparative examples is tested by ICP-OES method, and the lithium recovery rate is calculated (recovery rate = mass of lithium in product / mass of lithium in positive electrode powder x 100%).

[0106] The test results are shown in Table 1.

[0107] Table 1

[0108]

[0109] Analysis:

[0110] As can be seen from Table 1, in the method provided by the application, the synergistic effect of the buffer leaching agent solution and the lithium salt crystal seed suspension is adopted to accurately extract the lithium component in the positive electrode powder, and the selective leaching efficiency of lithium is significantly improved. The buffer leaching agent solution can not only reduce the binding force of transition metals on lithium ions, destroy the crystal lattice structure of the positive electrode material, and promote the dissolution of lithium ions, but also effectively alleviate the pH fluctuation to avoid the generation of impurity colloids; the lithium salt crystal seed suspension can form a soluble salt with lithium ions by the common ion effect, further reduce the co-dissolution of transition metal ions and other impurities, and reduce the loss of lithium. The purity of the finally prepared lithium salt product can reach more than 99.5%, and the comprehensive yield can reach more than 97%. In summary, the method improves the recovery purity of lithium metal, is suitable for large-scale recovery of lithium, and is especially suitable for scenes with high lithium content and less low-valence metal in raw materials.

[0111] As can be seen from the comparison of Example 1 and Examples 4-5, if only the acid salt is used as the buffer leaching agent solution, the Li+ dissolution efficiency is reduced due to the lack of sufficient H+ to destroy the positive electrode material lattice; if only the acid is used as the buffer leaching agent solution, Li+ is easily dissolved together with transition metal ions, and the adsorption loss of lithium increases and the lithium recovery rate decreases due to the co-precipitation of impurity elements in the form of colloids in the impurity removal process.

[0112] As can be seen from the comparison of Example 1 and Examples 6-7, if the molar concentration ratio of potassium dihydrogen phosphate to acetic acid in the buffer leaching agent solution is too small, excessive H+ will inhibit the dissolution of Li+ and H2PO4 - and combine with Li+ to form LiH2PO4, which is easily adsorbed on the surface of the residue again, and may also increase the dissolution of transition metal ions, increasing the difficulty of subsequent impurity removal; if the molar concentration ratio of potassium dihydrogen phosphate to acetic acid in the buffer leaching agent solution is too large, H+ is insufficient to effectively destroy the positive electrode material lattice, resulting in a slow Li+ dissolution rate and a decreased leaching efficiency.

[0113] As can be seen from the comparison of Example 1 and Examples 8-9, if the amount of lithium phosphate crystal seeds in the lithium phosphate crystal seed suspension is too small, the lattice matching effect and selective adsorption cannot be fully exerted, and the precipitation inhibition effect on transition metal ions is weakened, thereby reducing the lithium recovery rate and the purity of lithium phosphate; if the amount of lithium phosphate crystal seeds in the lithium phosphate crystal seed suspension is too large, the lithium recovery efficiency is reduced.

[0114] As can be seen from the comparison of Example 1 and Comparative Example 1, if the lithium phosphate crystal seed suspension is not added, the lithium leaching rate in the battery powder is relatively reduced, and the comprehensive lithium recovery rate is reduced.

[0115] It can be seen from the comparison between Example 1 and Comparative Example 2 that if the buffer leaching agent solution is not added, the lithium in the positive electrode powder cannot be fully dissolved, the preparation of the subsequent lithium-rich leaching solution and the production of the lithium phosphate product cannot be realized, the lithium recovery process is interrupted, and the recovery rate is extremely low.

[0116] It should be noted that the process of the present application is illustrated by the above examples, but the present application is not limited to the above examples, i.e. it does not mean that the present application must rely on the above examples to be implemented. Those skilled in the art should understand that any improvement of the present application, equivalent replacement of each raw material of the product of the present application, addition of auxiliary ingredients, selection of specific methods, etc. fall within the protection scope and disclosure scope of the present application.

Claims

1. A method for recovering lithium from a spent lithium iron phosphate battery, characterized by, The method includes the following steps: Waste lithium iron phosphate batteries are pretreated to obtain positive electrode powder; The positive electrode powder, buffer leaching agent solution and lithium salt seed crystal suspension are mixed and leaching reaction is carried out to obtain lithium-rich leaching solution; The lithium-rich leachate is post-treated to obtain lithium salt products.

2. The method of claim 1, wherein, The preprocessing includes the following steps: (a) Dismantling and separating waste lithium iron phosphate batteries to obtain positive electrode sheets; (b) The positive electrode sheet is calcined to obtain positive electrode powder; Preferably, the calcination temperature is 500-600℃; Preferably, the calcination treatment time is 2-4 hours; Preferably, the calcination treatment is performed in an air atmosphere.

3. The method according to claim 1 or 2, characterized in that, The buffer leaching agent solution is a mixed solution of acid salt and acid; Preferably, the acid salt comprises an alkali metal dihydrogen phosphate; Preferably, the alkali metal dihydrogen phosphate includes any one or a combination of two of lithium dihydrogen phosphate, potassium dihydrogen phosphate, sodium dihydrogen phosphate, or ammonium dihydrogen phosphate; Preferably, the acid includes citric acid and / or acetic acid.

4. The method of claim 3, wherein, In the mixed solution of the acid salt and the acid, the concentration of the acid salt is 0.5-0.8 mol / L; Preferably, in the mixed solution of the acid salt and the acid, the molar concentration ratio of the acid salt to the acid is (0.5-0.8):(0.3-0.5).

5. The method according to any one of claims 1 to 4, characterized in that, The lithium salt seed suspension includes a lithium phosphate seed suspension; Preferably, based on the mass of the positive electrode powder, the content of lithium salt seeds in the lithium salt seed suspension is 3-5%.

6. The method according to any one of claims 1 to 5, characterized in that, The leaching reaction process is a constant temperature process; Preferably, the leaching reaction is carried out at a temperature of 60-80°C for 2-6 hours.

7. The method according to any one of claims 1 to 6, characterized in that, The post-processing includes the following steps: (c) Mix the lithium-rich leachate and the precipitant to carry out a purification reaction, so that the transition metal ions are precipitated, and then the solid and liquid are separated to obtain a lithium-containing solution after purification; (d) Sodium phosphate is added to the lithium-containing solution after impurity removal to carry out a lithium precipitation reaction and obtain lithium phosphate product.

8. The method of claim 7, wherein, The precipitant includes caustic soda flakes or liquid caustic soda; Preferably, the temperature of the impurity removal reaction is 30-50°C; Preferably, during the impurity removal reaction, the pH value of the reaction system is 6-7.

9. The method according to claim 7 or 8, characterized in that, During the lithium precipitation reaction, the pH value of the reaction system is 10.5-11.5; Preferably, the temperature of the lithium precipitation reaction is 70-90°C; Preferably, the lithium precipitation reaction takes 2-4 hours.

10. The method according to any one of claims 1 to 9, characterized in that, The method includes the following steps: (1) After dismantling and crushing the waste lithium iron phosphate battery, the ferromagnetic material is separated by magnetic separation, and then calcined in an air atmosphere at 500-600℃ for 2-4 hours. After sieving, the positive electrode powder is obtained; wherein the particle size D50 of the positive electrode powder is 70-200μm. (2) The positive electrode powder and water are mixed at a solid-liquid ratio of 1 mg:(4-10) mL, then a buffer leaching agent solution is added, and after mixing evenly, a lithium salt seed suspension is added and mixed evenly to carry out the leaching reaction to obtain a lithium-rich leaching solution. The volume ratio of the obtained slurry to the buffer leaching agent solution is 1:(1-2); the buffer leaching agent solution is a mixed solution of acid salt and acid, the concentration of the acid salt is 0.5-0.8 mol / L, and the molar concentration ratio of the acid salt to the acid is (0.5-0.8):(0.3-0.5); the lithium salt crystal seed suspension includes a lithium phosphate crystal seed suspension; the content of the lithium salt crystal seed in the lithium salt crystal seed suspension is 3-5% based on the mass of the positive electrode powder; the leaching reaction is a constant temperature process; the reaction temperature of the leaching reaction is 60-80 DEG C, and the reaction time is 2-6 h; (3) under stirring, the lithium-rich leaching solution and a precipitant are mixed to perform a decontamination reaction at a temperature of 30-50 DEG C, so that transition metal ions are completely precipitated, then solid-liquid separation is performed, and a lithium-containing solution after decontamination is obtained; in the decontamination reaction, the pH value of the reaction system is 6-7; (4) a sodium phosphate solution is added to the lithium-containing solution after decontamination, the molar ratio of P element to Li element in the mixed solution is controlled to be 1.1-1.3, the pH value of the reaction system is adjusted to 10.5-11.5 by liquid alkali, a lithium precipitation reaction is performed at a temperature of 70-90 DEG C for 2-4 h, and lithium phosphate precipitate is obtained; (5) the lithium phosphate precipitate is filtered, washed and dried, and lithium phosphate product is obtained.

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