Method for recycling waste lithium iron phosphate material

Abstract

The application provides a recycling method of waste lithium iron phosphate material, and relates to the technical field of lithium iron phosphate material recycling.The recycling method of the waste lithium iron phosphate material comprises the following steps: mixing lithium iron phosphate black powder, a hydrogen sulfate aqueous solution and an oxidizing agent to perform a hydrothermal reaction, performing solid-liquid separation on obtained hydrothermal liquid to obtain filtrate A and filter residue A; adding a phosphate into the filtrate A to perform first impurity removal to obtain filtrate B; adding a first strong base into the filtrate B to adjust the pH to be less than or equal to 6 to perform second impurity removal to obtain filtrate C; concentrating the filtrate C to a Li + content of not less than 2 g / L, adding a second strong base to adjust the pH to be 10-12, adding a carbonate to perform a lithium precipitation reaction at a temperature of 80-100 DEG C, and performing hot filtration to obtain lithium carbonate.The recycling method is relatively mild, and can efficiently recycle lithium carbonate and iron phosphate.

Description

Technical Field

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

[0002] The recycling of waste lithium iron phosphate cathode materials plays an important role and is of great significance to the development of lithium-ion batteries. Lithium salts (such as lithium carbonate), iron phosphate, and other resources can be recovered from waste lithium iron phosphate cathode material powder (commonly known as lithium iron phosphate black powder). It is even possible to directly recycle and react it to obtain fresh lithium iron phosphate cathode material.

[0003] Strong alkaline and acidic conditions are commonly used treatment methods for recycling lithium iron phosphate (LFP) black powder, which can effectively destroy the structure of LFP, but also generate significant environmental pressure. Developing milder LFP recycling technologies is a major trend in the industry. Chinese patent CN118867456A discloses a method of leaching LFP black powder using a mixture of a pH-buffered leaching agent, an oxidant, and water. Carbonate is then added to the leachate for co-precipitation to obtain lithium carbonate. However, the leachate still contains metal ions such as iron and aluminum ions. Directly adding carbonate to the leachate for co-precipitation will result in lithium carbonate containing impurities such as iron carbonate, iron hydroxide, and aluminum hydroxide.

[0004] Therefore, existing lithium iron phosphate black powder recycling technologies still need further improvement. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for recycling waste lithium iron phosphate materials.

[0006] The technical solution of the present invention is as follows: A method for recycling waste lithium iron phosphate materials, comprising the following steps: S1, lithium iron phosphate black powder, hydrogen sulfate aqueous solution and oxidant are mixed and then subjected to hydrothermal reaction. The resulting hydrothermal liquid is subjected to solid-liquid separation to obtain filtrate A and filter residue A. S2. Phosphate is added to the filtrate A in step S1 for the first impurity removal to obtain filtrate B; A first strong base is added to filtrate B to adjust the pH to ≤ 6 for a second impurity removal process, resulting in filtrate C. S3, The filtrate C described in step S2 is concentrated to Li + The content is not less than 2g / L. A second strong alkali is added to adjust the pH to 10-12. Then, carbonate is added and lithium precipitation reaction is carried out at 80-100℃. The mixture is filtered while hot to obtain lithium carbonate.

[0007] Preferably, the concentration of the hydrogen sulfate aqueous solution in step S1 is 0.3-2 mol / L, and the hydrogen sulfate is selected from one or more of sodium bisulfate, ammonium bisulfate, and potassium bisulfate; The oxidant is selected from hydrogen peroxide, with a concentration of 1-10 wt%.

[0008] Preferably, the volume ratio of the hydrogen sulfate aqueous solution to the oxidant in step S1 is 1-4:1; The solid-liquid ratio in the hydrothermal reaction is 80-120g:1000mL.

[0009] Preferably, the hydrothermal reaction in step S1 is carried out at 200-250°C for 5-60 minutes.

[0010] Preferably, the phosphate in step S2 is selected from one or more of ammonium monohydrogen phosphate, sodium monohydrogen phosphate, potassium monohydrogen phosphate, sodium dihydrogen phosphate, ammonium dihydrogen phosphate, sodium phosphate, and potassium phosphate; The pH of the filtrate A after the addition of phosphate is 2.5-5.

[0011] Preferably, in step S2, the first strong base is selected from one or both of sodium hydroxide and potassium hydroxide.

[0012] Preferably, in step S2, the second strong base is selected from one or two of sodium hydroxide and potassium hydroxide, and the carbonate is selected from one or more of sodium carbonate, ammonium carbonate and potassium carbonate. Li in filtrate C + The molar ratio with carbonate is 2:1-1.1.

[0013] Preferably, in step S1, an aqueous solution of phosphoric acid is added to the filter residue A to adjust the molar ratio of Fe to P to 1:0.98-1.03, the reaction is carried out at 60-90℃, and the residue is filtered, washed with water, and dried to obtain filter residue B. The filter residue B is calcined at high temperature to obtain iron phosphate.

[0014] More preferably, the solid-liquid ratio of the filter residue A and the phosphoric acid aqueous solution is 80-140g:1000ml; The high-temperature calcination is performed at 600-650℃ for 5-7 hours under an inert gas atmosphere.

[0015] The beneficial effects of this invention are: (1) This invention uses acidic salts as a synergistic oxidant to treat lithium iron phosphate black powder, which can directly obtain Li-containing products. + The leachate (filtrate A) and the filter residue A containing Fe / P are used. The leachate, after two simple impurity removal processes, can be co-precipitated with carbonates to obtain high-purity lithium carbonate. The filter residue A can be reacted with phosphoric acid to directly obtain high-purity iron phosphate.

[0016] (2) The recycling method of the present invention is simple and can achieve a recovery rate of 97% or more for Li and Fe in lithium iron phosphate. Detailed Implementation

[0017] The technical solution of the present invention will be further explained and described below through specific embodiments.

[0018] This invention proposes a method for recycling waste lithium iron phosphate materials, the steps of which include: S1, lithium iron phosphate black powder, hydrogen sulfate aqueous solution and oxidant are mixed and then subjected to hydrothermal reaction. The resulting hydrothermal liquid is subjected to solid-liquid separation to obtain filtrate A and filter residue A. S2. In step S1, phosphate is added to filtrate A for the first impurity removal to obtain filtrate B. Add a strong base to filtrate B to adjust the pH to ≤ 6 for a second impurity removal process, and obtain filtrate C. S3, Concentrate filtrate C from step S2 to Li + The content is not less than 2g / L. A second strong alkali is added to adjust the pH to 10-12. Then, carbonate is added and lithium precipitation reaction is carried out at 80-100℃. The mixture is filtered while hot to obtain lithium carbonate.

[0019] To address the issue of trace metallic impurities in the leachate (filtrate A, pH typically 2-4) after lithium iron phosphate black powder treatment, this invention employs a two-stage impurity removal process. The first step involves adding phosphate to precipitate iron and aluminum ions (forming phosphate precipitates) to remove most of the impurity metal ions in filtrate A (primarily iron and aluminum ions). Then, alkali is added to adjust the pH, allowing the remaining trace amounts of iron and aluminum ions to precipitate a second time (forming hydroxide precipitates). The resulting filtrate C contains very low levels of iron and aluminum ions; the iron and aluminum ion content in filtrate C does not exceed 100 ppm, and the only cations present in filtrate C are Li. + Other cations are water-soluble components (such as sodium ions), so after adding carbonate, a lithium precipitation reaction is carried out (to form lithium carbonate), and after hot filtration, lithium carbonate with high purity can be obtained with a high recovery rate.

[0020] The recovery method of the present invention is simple and can achieve a recovery rate of Li in lithium iron phosphate (calculated as lithium carbonate) of 97% or more, and the purity of the obtained lithium carbonate can reach 99% or higher.

[0021] In some embodiments, the concentration of the hydrogen sulfate aqueous solution in step S1 is 0.3-2 mol / L, and the hydrogen sulfate is selected from one or more of sodium bisulfate, ammonium bisulfate, and potassium bisulfate; The oxidant is selected from hydrogen peroxide, with a concentration of 1-10 wt%.

[0022] In this invention, bisulfate is used as the leaching agent for lithium iron phosphate black powder. This reduces the oxidation energy barrier of lithium iron phosphate and can even disrupt its crystal structure. The oxidant acts as an auxiliary agent, oxidizing the lithium iron phosphate and leaching the lithium into the leachate. Bisulfate has good salt solubility, and the introduced hydrogen ions do not form precipitates with phosphate or hydroxide ions, thus avoiding increased difficulty in precipitation. Simultaneously, reducing the amount of precipitate formed during the first and second impurity removal processes also reduces the entrainment effect of the precipitate on lithium ions, minimizing lithium ion loss.

[0023] For example, the concentration of hydrogen sulfate aqueous solution can be 0.3 mol / L, 0.5 mol / L, 0.7 mol / L, 1 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, 2 mol / L, etc., and the concentration of hydrogen peroxide can be 1 wt%, 3 wt%, 5 wt%, 6 wt%, 8 wt%, 10 wt%, etc.

[0024] In some embodiments, the volume ratio of the hydrogen sulfate aqueous solution to the oxidant in step S1 is 1-4:1; The solid-liquid ratio in the hydrothermal reaction is 80-120g:1000mL.

[0025] For example, the volume ratio of hydrogen sulfate aqueous solution to oxidant can be 1:1, 2:1, 3:1, 4:1, etc., and the solid-liquid ratio in hydrothermal reaction can be 80g:1000mL, 90g:1000mL, 100g:1000mL, 110g:1000mL, 120g:1000mL, etc.

[0026] In some embodiments, the hydrothermal reaction in step S1 is carried out at 200-250°C for 5-60 minutes. For example, the hydrothermal reaction can be carried out at 200°C for 60 minutes, 200°C for 30 minutes, 220°C for 20 minutes, 250°C for 10 minutes, 250°C for 5 minutes, etc. The hydrothermal reaction enhances reaction kinetics through high-temperature, high-pressure fluid, thereby increasing the dissolution efficiency and degree of metal ions while reducing the amount of acidic substances (hydrogen sulfate) and lowering the pressure of post-treatment.

[0027] In some embodiments, the phosphate in step S2 is selected from one or more of diammonium hydrogen phosphate, disodium hydrogen phosphate, dipotassium hydrogen phosphate, sodium dihydrogen phosphate, ammonium dihydrogen phosphate, sodium phosphate, and potassium phosphate. The pH of filtrate A after adding phosphate is 2.5-5.

[0028] Phosphate is added to filtrate A to form phosphate precipitates with iron and aluminum ions in filtrate A. Maintaining the pH at 2.5-5 helps prevent the formation of lithium phosphate precipitates, such as water-soluble dilithium hydrogen phosphate and / or lithium dihydrogen phosphate. Alternatively, the amount of added phosphate can preferentially precipitate with iron and aluminum ions (the solubility product constant of lithium phosphate is much lower than that of iron phosphate and aluminum phosphate). Furthermore, the phosphate can be disodium hydrogen phosphate, dipotassium hydrogen phosphate, sodium dihydrogen phosphate, or ammonium dihydrogen phosphate, etc. The formation of phosphate ions releases hydrogen ions while maintaining the pH of filtrate A at 2.5-5.

[0029] In some embodiments, the first strong base in step S2 is selected from one or both of sodium hydroxide and potassium hydroxide.

[0030] In some embodiments, the second strong base in step S2 is selected from one or two of sodium hydroxide and potassium hydroxide, and the carbonate is selected from one or more of sodium carbonate, ammonium carbonate and potassium carbonate. Li in filtrate C + The molar ratio with carbonate is 2:1-1.1.

[0031] After filtrate C is concentrated, a second strong base is added to adjust the pH to alkaline. This prevents the added carbonate from reacting with the acid to produce carbon dioxide and also reduces the amount of carbonate used. 2 Li + To form a lithium carbonate precipitate by combining with one carbonate ion, the carbonate needs to be relatively close to the Li. + Sufficient amount or slightly excess. Excess carbonate has good solubility and can remain in the solution. For example, Li in filtrate C + The molar ratio with carbonate can be 2:1, 2:1.02, 2:1.05, 2:1.06, 2:1.08, 2:1.1, etc.

[0032] In some embodiments, in step S1, an aqueous solution of phosphoric acid is added to filter residue A to adjust the molar ratio of Fe to P to 1:0.98-1.03, and the reaction is carried out at 60-90°C. After filtration, washing with water, and drying, filter residue B is obtained. Filter residue B is calcined at high temperature to obtain iron phosphate.

[0033] When lithium iron phosphate black powder is reacted with an aqueous solution of bisulfate and an oxidant via hydrothermal reaction, the resulting filter residue A is mainly composed of iron phosphate. However, the proportion of iron phosphate is unbalanced, with iron being more abundant than phosphate. Therefore, an aqueous solution of phosphoric acid is added to filter residue A to adjust the molar ratio of Fe to P to 1:0.98-1.03. After further heating and reaction, a high-purity filter residue B—iron phosphate—is obtained, with a purity of 99% or higher.

[0034] In this invention, the recovery rate of terephosphate in lithium iron phosphate black powder is high, reaching 97% or more.

[0035] In some embodiments, the solid-liquid ratio of filter residue A and phosphoric acid aqueous solution is 80-140g:1000ml; High-temperature calcination is performed at 600-650℃ for 5-7 hours under inert gas.

[0036] For example, the solid-liquid ratio of filter residue A and phosphoric acid aqueous solution can be 80g:1000ml, 90g:1000ml, 100g:1000ml, 110g:1000ml, 120g:1000ml, 130g:1000ml, 140g:1000ml, etc.

[0037] The iron phosphate obtained after the reaction can be calcined at high temperature to obtain iron phosphate that meets the requirements of "Iron Phosphate for Batteries" (HG / T 4701-2021).

[0038] The technical solution of the present invention will be further described and illustrated below with reference to various embodiments. Unless otherwise specified, the parts mentioned in the following embodiments are parts by weight.

[0039] Example 1 The lithium iron phosphate black powder obtained after mechanical crushing was added to a hydrothermal tank, along with sodium bisulfate aqueous solution (concentration of 0.5 mol / L) and hydrogen peroxide solution (concentration of 5 wt%). The volume ratio of sodium bisulfate aqueous solution to hydrogen peroxide solution was 2:1, and the solid-liquid ratio was 80 g: 1000 mL. The hydrothermal tank was heated to 250°C and maintained for 10 minutes. The reaction was then stopped and cooled to room temperature. The mixture was filtered to obtain filtrate A and filter residue A. Testing showed that over 99% of the lithium iron phosphate powder was leached into filtrate A.

[0040] Diammonium hydrogen phosphate was added to filtrate A, with the molar amount of diammonium hydrogen phosphate equal to the molar amounts of iron and aluminum ions in filtrate A. After stirring for 10 minutes, the pH of the solution was 4.5. The solution was then filtered to obtain filtrate B. A 5 wt% sodium hydroxide aqueous solution was added to filtrate B to adjust the pH to 5.5. After stirring for 5 minutes, the solution was filtered to obtain filtrate C. Analysis showed that filtrate C contained 82 ppm of iron ions and 57 ppm of aluminum ions.

[0041] The above filtrate C was evaporated and concentrated to Li. + The concentration was 10 g / L. A 3 wt% sodium hydroxide aqueous solution was added to adjust the pH to 10.5, followed by the addition of a 15 wt% sodium carbonate aqueous solution. The sodium carbonate and Li... +The molar ratio of lithium iron phosphate to lithium carbonate was 1:2. The mixture was heated to 80°C and held at that temperature for 90 minutes. The precipitate was obtained by hot filtration, washed three times with deionized water, and dried overnight at 60°C to obtain lithium carbonate. The precipitation efficiency of lithium carbonate was measured to be 97.9% (precipitation efficiency = weight of lithium in lithium carbonate / weight of lithium in solution C), and the purity of the obtained lithium carbonate was 99.4%. Based on the recovered Li in the lithium carbonate, the Li recovery rate in lithium iron phosphate reached 97.1%.

[0042] A 5wt% phosphoric acid aqueous solution was added to the above filter residue A to adjust the molar ratio of Fe to P to 1:1. The mixture was heated to 90℃ for 120 minutes, filtered, and the resulting filter residue B was washed three times with deionized water, dried overnight at 60℃, milled, and then calcined at 600℃ for 6.5 hours under a nitrogen atmosphere at a heating rate of 5℃ / min. After cooling, iron phosphate was obtained. The purity of the obtained iron phosphate reached 99.1%, and the iron-to-phosphorus ratio was 1:1, which meets the requirements of the standard "Iron Phosphate for Batteries". Based on the Fe content in the iron phosphate, the recovery rate of iron phosphate in lithium iron phosphate reached 97.3%.

[0043] Example 2 The difference between this embodiment and Embodiment 1 is that in Embodiment 1, when lithium carbonate aqueous solution is added, lithium carbonate and Li + The molar ratio was adjusted from 1:2 to 1.05:2. The remaining steps remained unchanged. The precipitation efficiency of lithium carbonate was measured to be 99.2%, the purity of the obtained lithium carbonate was 99.1%, and the recovery rate of Li in lithium iron phosphate reached 98.4%.

[0044] Example 3 The lithium iron phosphate black powder obtained after mechanical crushing was added to a hydrothermal tank, along with sodium bisulfate aqueous solution (concentration of 0.8 mol / L) and hydrogen peroxide solution (concentration of 10 wt%). The volume ratio of sodium bisulfate aqueous solution to hydrogen peroxide solution was 4:1, and the solid-liquid ratio was 120 g: 1000 mL. The hydrothermal tank was heated to 230°C and maintained for 20 minutes. The reaction was then stopped and cooled to room temperature. The mixture was filtered to obtain filtrate A and filter residue A. Testing showed that over 99% of the lithium iron phosphate powder was leached into filtrate A.

[0045] Disodium hydrogen phosphate was added to filtrate A, with the molar amount of disodium hydrogen phosphate equal to the molar amounts of iron and aluminum ions in filtrate A. After stirring for 10 minutes, the pH of the solution was 4.5. The solution was then filtered to obtain filtrate B. A 5 wt% sodium hydroxide aqueous solution was added to filtrate B to adjust the pH to 6.0. After stirring for 5 minutes, the solution was filtered to obtain filtrate C. Analysis showed that filtrate C contained 65 ppm of iron ions and 43 ppm of aluminum ions.

[0046] The above filtrate C was evaporated and concentrated to Li. +The concentration was 2 g / L. A 5 wt% sodium hydroxide aqueous solution was added to adjust the pH to 12, followed by a 10 wt% potassium carbonate aqueous solution. The potassium carbonate and Li... + The molar ratio was 1.03:2. The mixture was heated to 60℃ and held at that temperature for 120 minutes. The precipitate was obtained by hot filtration, washed three times with deionized water, and dried overnight at 60℃ to obtain lithium carbonate. The precipitation efficiency of lithium carbonate was measured to be 98.4%, and the purity of the obtained lithium carbonate was 99.2%. Based on the Li recovered in the lithium carbonate, the Li recovery rate in lithium iron phosphate reached 97.7%.

[0047] A 10wt% phosphoric acid aqueous solution was added to the above filter residue A to adjust the molar ratio of Fe to P to 1:1.01. The mixture was heated to 90℃ for 120 minutes, filtered, and the resulting filter residue B was washed three times with deionized water, dried overnight at 60℃, milled, and then calcined at 650℃ for 5 hours under a nitrogen atmosphere at a heating rate of 5℃ / min. After cooling, iron phosphate was obtained. The purity of the obtained iron phosphate reached 99.4%, and the iron-to-phosphorus ratio was 0.99:1, which meets the requirements of the standard "Iron Phosphate for Batteries". Based on the Fe content in the iron phosphate, the recovery rate of iron phosphate in lithium iron phosphate reached 97.1%.

[0048] Example 4 The difference between this embodiment and Embodiment 3 is that in Embodiment 3, disodium hydrogen phosphate was replaced with an equimolar amount of sodium dihydrogen phosphate, and the pH of the solution was 2.5 after stirring for 10 minutes. The remaining steps remained unchanged.

[0049] In this embodiment, the iron ion content in filtrate C is 92 ppm, and the aluminum ion content is 85 ppm. The precipitation efficiency of lithium carbonate is 98.6%, and the purity of the obtained lithium carbonate is 99.0%. Based on the Li recovered in the lithium carbonate, the Li recovery rate in lithium iron phosphate reaches 97.8%.

[0050] As described above, the basic principles, main features, and advantages of the present invention have been shown and described. Those skilled in the art should understand that the present invention is not limited to the above embodiments, which are merely preferred embodiments and should not be construed as limiting the scope of the invention. All equivalent changes and modifications made in accordance with the scope of the patent and the description should still fall within the scope of the present invention. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for recycling waste lithium iron phosphate materials, characterized in that the steps include: include: S1, lithium iron phosphate black powder, hydrogen sulfate aqueous solution and oxidant are mixed and then subjected to hydrothermal reaction. The resulting hydrothermal liquid is subjected to solid-liquid separation to obtain filtrate A and filter residue A. S2. Phosphate is added to the filtrate A in step S1 for the first impurity removal to obtain filtrate B; A first strong base is added to filtrate B to adjust the pH to ≤ 6 for a second impurity removal process, resulting in filtrate C. S3, The filtrate C described in step S2 is concentrated to Li + The content is not less than 2g / L. A second strong alkali is added to adjust the pH to 10-12. Then, carbonate is added and lithium precipitation reaction is carried out at 80-100℃. The mixture is filtered while hot to obtain lithium carbonate.

2. The method for recycling waste lithium iron phosphate materials according to claim 1, characterized in that, The concentration of the hydrogen sulfate aqueous solution in step S1 is 0.3-2 mol / L, and the hydrogen sulfate is selected from one or more of sodium bisulfate, ammonium bisulfate, and potassium bisulfate; The oxidant is selected from hydrogen peroxide, with a concentration of 1-10 wt%.

3. The method for recycling waste lithium iron phosphate materials according to claim 1, characterized in that, The volume ratio of the hydrogen sulfate aqueous solution and the oxidant in step S1 is 1-4:1; The solid-liquid ratio in the hydrothermal reaction is 80-120g:1000mL.

4. The method for recycling waste lithium iron phosphate materials according to claim 1, characterized in that, The hydrothermal reaction described in step S1 is carried out at 200-250℃ for 5-60 minutes.

5. The method for recycling waste lithium iron phosphate materials according to claim 1, characterized in that, The phosphate mentioned in step S2 is selected from one or more of the following: ammonium monohydrogen phosphate, sodium monohydrogen phosphate, potassium monohydrogen phosphate, sodium dihydrogen phosphate, ammonium dihydrogen phosphate, sodium phosphate, and potassium phosphate. The pH of the filtrate A after the addition of phosphate is 2.5-5.

6. The method for recycling waste lithium iron phosphate materials according to claim 1, characterized in that, In step S2, the first strong base is selected from one or both of sodium hydroxide and potassium hydroxide.

7. The method for recycling waste lithium iron phosphate materials according to claim 1, characterized in that, In step S2, the second strong base is selected from one or two of sodium hydroxide and potassium hydroxide, and the carbonate is selected from one or more of sodium carbonate, ammonium carbonate and potassium carbonate. Li in filtrate C + The molar ratio with carbonate is 2:1-1.

1.

8. The method for recycling waste lithium iron phosphate materials according to claim 1, characterized in that, In step S1, an aqueous solution of phosphoric acid is added to filter residue A to adjust the molar ratio of Fe to P to 1:0.98-1.

03. The reaction is carried out at 60-90℃, followed by filtration, washing with water, and drying to obtain filter residue B. The filter residue B is calcined at high temperature to obtain iron phosphate.

9. The method for recycling waste lithium iron phosphate materials according to claim 8, characterized in that, The solid-liquid ratio of the filter residue A and the phosphoric acid aqueous solution is 80-140g:1000ml; The high-temperature calcination is performed at 600-650℃ for 5-7 hours under an inert gas atmosphere.