A method for recovering oxalic acid from a ferrous oxalate-containing recovery residue

Abstract

The application discloses a method for recovering oxalic acid from a ferrous oxalate-containing recovery residue, and the ferrous oxalate-containing recovery residue is derived from a process of leaching lithium iron phosphate batteries with oxalic acid. The method comprises the following steps: removing iron ions by adjusting pH with sodium hydroxide, obtaining an oxalic acid solution by acidification reaction with hydrochloric acid, and finally obtaining oxalic acid crystals by evaporation concentration and cooling crystallization. The protection scope of the application is all the steps from hydrochloric acid decarburization to evaporation concentration and cooling crystallization. The process steps are reasonable, the operation is simple, impurities are completely removed, oxalic acid can be efficiently recovered, the purity of the finished product is greater than or equal to 99.5%, the recovery rate of oxalic acid can reach more than 90%, the reaction conditions are mild, the equipment investment is low, the method is suitable for industrial large-scale production, resource recycling is realized, and environmental pollution is reduced.

Description

Technical Field

[0001] This invention belongs to the field of lithium iron phosphate battery recycling and chemical resource regeneration technology, specifically relating to a method for recovering oxalic acid from ferrous oxalate-containing recovery residue, wherein the ferrous oxalate-containing recovery residue originates from the process of leaching lithium iron phosphate batteries with oxalic acid. Background Technology

[0002] With the rapid development of the new energy vehicle industry, the amount of scrapped lithium iron phosphate batteries has been increasing year by year, and their recycling has become an important issue in ensuring resource security and reducing environmental pollution. At present, oxalic acid leaching is commonly used in industry to treat scrapped lithium iron phosphate batteries. This method has advantages such as high leaching efficiency, environmental friendliness, and low corrosivity to equipment. It can effectively recover valuable metals such as lithium and iron from the batteries, while generating a large amount of recycling residue containing ferrous oxalate.

[0003] In addition to ferrous oxalate, the ferrous oxalate recovery residue also contains small amounts of copper impurities, carbon powder, and free iron ions. Oxalic acid, acting as a leaching agent, exists in both bound and free forms in the residue and has high recovery value. Directly discarding this residue not only wastes oxalic acid resources but may also pollute soil and water bodies due to the acidity of oxalic acid.

[0004] In existing technologies, the treatment of ferrous oxalate recovery residue mainly focuses on recovering iron, with less attention paid to oxalic acid recovery. A few oxalic acid recovery methods suffer from problems such as complex processes, low oxalic acid recovery rates, low product purity, and high reagent consumption, making industrial application difficult. For example, some methods use solvent extraction to recover oxalic acid, which can obtain oxalic acid with a certain purity, but the extractant is expensive, volatile, and poses a risk of secondary pollution. Other methods use precipitation to recover oxalic acid, requiring the addition of specific precipitants, which makes subsequent separation difficult and results in low oxalic acid recovery rates.

[0005] Therefore, developing a simple, low-cost, high-recovery-rate, and high-purity method for recovering oxalic acid from ferrous oxalate-containing recovery residue is of great significance for realizing resource recycling, reducing environmental pollution, and improving the economic benefits of lithium iron phosphate battery recycling. Summary of the Invention

[0006] The purpose of this invention is to provide a method for recovering oxalic acid from ferrous oxalate recovery residue, solving the problems of complex oxalic acid recovery processes, low recovery rates, and low product purity in existing technologies, and achieving efficient recovery and purification of oxalic acid resources. This method has a simple process, low processing costs, and is easy to industrialize.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for recovering oxalic acid from ferrous oxalate-containing recovery residue, wherein the residue originates from the oxalic acid leaching process of spent lithium iron phosphate batteries and has undergone pre-treatment with ferric chloride to remove copper. This method protects the recovery process after the copper removal treatment and specifically includes the following steps:

[0009] (1) Extraction of oxalate: Add sodium hydroxide solution to the ferrous oxalate recovery residue, adjust the pH value to the preset range, let it stand for a period of time, so that the oxalate exists in the solution in the form of sodium oxalate, while the remaining iron, carbon and impurities remain in the solid phase, and filter to obtain the filtrate.

[0010] (2) Oxalic acid recovery: Add hydrochloric acid to the filtrate obtained in step (1) to carry out an acidification reaction, so that the oxalate ions in the solution are converted into oxalic acid; the solution is evaporated and concentrated, cooled and crystallized, and crude oxalic acid and crystallization mother liquor are obtained by filtering using the significant difference in solubility of oxalic acid and sodium chloride in water.

[0011] (3) Recrystallization purification: Dissolve the crude oxalic acid obtained in step (2) in deionized water, heat to dissolve, cool and recrystallize, filter, wash and dry to obtain high-purity oxalic acid product.

[0012] Further, in step (1), the concentration of the sodium hydroxide solution is 2~5 mol / L, the pH of the solution is adjusted to 2.5~3.5, and the standing time is 20~40 min; the filtration is carried out by precision filtration, and the pore size of the filter membrane is 0.22~0.45 μm; the ratio of the ferrous oxalate recovery residue to sodium hydroxide is 1:2 g / mL.

[0013] Further, in step (2), the concentration of the hydrochloric acid solution is 3~8 mol / L, the temperature of the acidification reaction is 25~40℃, the stirring speed is 150~250 r / min, the reaction time is 15~30 min, and the pH value of the solution is adjusted to 1.0~2.0.

[0014] Furthermore, the evaporation and concentration in step (2) is carried out under reduced pressure evaporation, with an evaporation temperature of 60~80 ℃ and a vacuum degree of 0.06~0.08 MPa; the final temperature of the cooling crystallization is 0~15 ℃ and the cooling time is 4~8 h.

[0015] Further, in step (3), the solid-liquid ratio of crude oxalic acid to deionized water is 1:2~1:5 (g / mL), the heating temperature during dissolution is 60~80 ℃, the cooling crystallization temperature is 5~10 ℃, and the cooling time is 3~6 h; the washing is performed with deionized water 2~3 times, the drying temperature is 50~60 ℃, and the drying time is 2~4 h.

[0016] Furthermore, high-purity oxalic acid was prepared using the above method, with a purity of ≥99.5% and an oxalic acid recovery rate of ≥92%.

[0017] The recovery method provided by this invention has the following principle and effect: In step (1), sodium hydroxide solution is used to adjust the pH. Under this condition, oxalate ions can combine with sodium ions to form sodium oxalate, which is easily soluble in water. Iron, carbon and other impurities have extremely low solubility in this pH range and can remain stably in the solid phase, providing a pure raw material solution for subsequent oxalic acid recovery. In step (2), hydrochloric acid is used to adjust the pH to 1.0~2.0. At this time, oxalate ions in the solution combine with hydrogen ions to convert into oxalic acid. Vacuum evaporation can be used to quickly concentrate the solution at a lower temperature to avoid high-temperature decomposition of oxalic acid. Then the solution is cooled, and the significant difference in solubility between oxalic acid and sodium chloride in water is used to make oxalic acid crystallize out preferentially. After filtration, crude oxalic acid is obtained. In step (3), crude oxalic acid is dissolved in deionized water and heated to dissolve, so that trace impurities in the crude product are fully dissolved. Then it is cooled for recrystallization. The surface-adsorbed impurities are removed by deionized water, and finally high-purity oxalic acid product is obtained. The whole process conditions are mild and the separation efficiency is high, which is suitable for large-scale application.

[0018] Compared with existing technologies, this invention has the following significant advantages: The process is simple and easy to operate, requiring only conventional reagents such as hydrochloric acid and sodium hydroxide, eliminating the need for complex and expensive equipment, resulting in low processing costs and suitability for large-scale industrial production. Simultaneously, it effectively removes impurities through iron removal purification with sodium hydroxide, and utilizes the solubility difference between oxalic acid and sodium chloride for crystallization purification, achieving an oxalic acid recovery rate of up to 92.8% and a product purity of 99.7%, meeting industrial-grade requirements. Furthermore, this process achieves resource recycling, treating the residue generated from oxalic acid leaching of lithium iron phosphate batteries in a resource-efficient manner. While recovering oxalic acid resources and reducing waste, it also avoids environmental pollution, aligning with green environmental protection principles. Attached Figure Description

[0019] Figure 1 The image shows the XRD pattern of the oxalic acid crystals prepared in Example 3. Detailed Implementation

[0020] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0021] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, are also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0022] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar to or equivalent to those described herein may be used in the implementation or testing of this invention.

[0023] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0024] Example 1:

[0025] A method for recovering oxalic acid from ferrous oxalate recovery residue, comprising the following specific steps:

[0026] 1. Oxalate extraction: Take 100 g of ferrous oxalate recovery residue, add 200 mL of 3 mol / L sodium hydroxide solution, stir at room temperature and 250 r / min, adjust the pH of the solution to 3.0, let stand for 30 min, and then filter precisely using a 0.3 μm filter membrane to obtain filtrate and residue containing sodium oxalate.

[0027] 2. Hydrochloric acid acidification reaction: Slowly add 5 mol / L hydrochloric acid to the filtrate obtained in step 1, stir the reaction at 30℃ and 200 r / min for 20 min, adjust the pH of the solution to 1.5, and complete the acidification reaction;

[0028] 3. Crystallization separation: The acidified solution was placed in a vacuum evaporator and evaporated and concentrated at 70℃ and 0.07 MPa until a crystal film appeared in the solution. Then it was cooled to 10℃, allowed to stand for 6 hours, and filtered to obtain crude oxalic acid and crystallization mother liquor.

[0029] 4. Recrystallization purification: Add crude oxalic acid to deionized water at a solid-liquid ratio of 1:2 (g / mL), heat to 70 ℃ and stir until completely dissolved, then cool to 8 ℃, let stand for 4 h, filter, wash twice with deionized water, and then dry at 55 ℃ for 3 h to obtain high-purity oxalic acid product.

[0030] The oxalic acid recovery rate in this experimental example was 92.5%, and the product purity was 99.6%.

[0031] Experiment Example 2

[0032] A method for recovering oxalic acid from ferrous oxalate recovery residue, comprising the following specific steps:

[0033] 1. Oxalate extraction: Take 100 g of ferrous oxalate recovery residue, add 200 mL of 2 mol / L sodium hydroxide solution, stir at room temperature and 200 r / min, adjust the pH of the solution to 2.5, let stand for 20 min, and then filter precisely using a 0.22 μm filter membrane to obtain filtrate and residue containing sodium oxalate.

[0034] 2. Hydrochloric acid acidification reaction: Slowly add 3 mol / L hydrochloric acid to the filtrate obtained in step 1, stir the reaction at 25℃ and 150 r / min for 15 min, adjust the pH of the solution to 1.0, and complete the acidification reaction;

[0035] 3. Crystallization separation: The acidified solution was placed in a vacuum evaporator and evaporated and concentrated at 60℃ and 0.06 MPa until a crystal film appeared in the solution. Then it was cooled to 0℃, allowed to stand for 8 h, and filtered to obtain crude oxalic acid and crystallization mother liquor.

[0036] 4. Recrystallization purification: Add crude oxalic acid to deionized water at a solid-liquid ratio of 1:5 (g / mL), heat to 60 ℃ and stir until completely dissolved, then cool to 5 ℃, let stand for 6 h, filter, wash 3 times with deionized water, and then dry at 50 ℃ for 4 h to obtain high-purity oxalic acid product.

[0037] The oxalic acid recovery rate in this experimental example was 92.1%, and the product purity was 99.5%.

[0038] Experimental Example 3

[0039] A method for recovering oxalic acid from ferrous oxalate recovery residue, comprising the following specific steps:

[0040] 1. Oxalate extraction: Take 100 g of ferrous oxalate recovery residue, add 200 mL of 5 mol / L sodium hydroxide solution, stir at room temperature and 300 r / min, adjust the pH of the solution to 3.5, let stand for 40 min, and then filter precisely using a 0.45 μm filter membrane to obtain filtrate and residue containing sodium oxalate.

[0041] 2. Hydrochloric acid acidification reaction: Slowly add 8 mol / L hydrochloric acid to the filtrate obtained in step 1, stir the reaction at 40℃ and 250 r / min for 30 min, adjust the pH of the solution to 2.0, and complete the acidification reaction;

[0042] 3. Crystallization separation: The acidified solution was placed in a vacuum evaporator and evaporated and concentrated at 80℃ and 0.08 MPa until a crystal film appeared in the solution. Then it was cooled to 15℃, allowed to stand for 4 h, and filtered to obtain crude oxalic acid and crystallization mother liquor.

[0043] 4. Recrystallization purification: Add crude oxalic acid to deionized water at a solid-liquid ratio of 1:3 (g / mL), heat to 80 ℃ and stir until completely dissolved, then cool to 10 ℃, let stand for 3 h, filter, wash twice with deionized water, and then dry at 60 ℃ for 2 h to obtain high-purity oxalic acid product.

[0044] The oxalic acid recovery rate in this experimental example was 92.8%, and the product purity was 99.7%. Figure 1 The image shows the XRD pattern of the oxalic acid crystals prepared in Example 3. According to the XRD pattern analysis, the main diffraction peaks of the sample completely match those of the oxalic acid standard card (PDF#04-009-3739), indicating that its main phase is well-crystallized oxalic acid. The sharp diffraction peaks and stable baselines indicate high sample purity, complete crystallinity, and the absence of obvious impurity peaks, suggesting a single oxalic acid phase.

[0045] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A method for recovering oxalic acid from ferrous oxalate recovery residue, characterized in that, The process includes the following steps: (1) Extraction of oxalate: Add sodium hydroxide solution to the ferrous oxalate recovery residue, adjust the pH value, let stand for a period of time, so that the oxalate exists in the solution in the form of sodium oxalate, and the remaining iron, carbon and impurities remain in the solid phase, and filter to obtain filtrate; (2) Oxalic acid recovery: Add hydrochloric acid to the filtrate obtained in step (1) to carry out an acidification reaction, so that the oxalate ions in the solution are converted into oxalic acid; evaporate and concentrate the solution, cool and crystallize, and use the significant difference in solubility of oxalic acid and sodium chloride in water to filter to obtain crude oxalic acid and crystallization mother liquor; (3) Recrystallization purification: Dissolve, cool and crystallize, filter, wash and dry the crude oxalic acid obtained in step (2) to obtain high-purity oxalic acid product.

2. The method according to claim 1, characterized in that, In step (1), the concentration of the sodium hydroxide solution is 2~5 mol / L, the pH value of the solution is adjusted to 2.5~3.5, and the standing time is 20~40 min; the filtration adopts precision filtration, and the pore size of the filter membrane is 0.22~0.45 μm.

3. The method according to claim 1, characterized in that, In step (1), the ratio of the ferrous oxalate recovery residue to sodium hydroxide is 1:2 g / mL.

4. The method according to claim 1, characterized in that, In step (2), the concentration of hydrochloric acid is 3~8 mol / L, the temperature of the acidification reaction is 25~40 ℃, the stirring speed of the acidification is 150~250 r / min, the reaction time is 15~30 min, and the pH value of the solution is adjusted to 1.0~2.

0.

5. The method according to claim 1, characterized in that, In step (2), the evaporation and concentration are carried out by vacuum evaporation, with an evaporation temperature of 60~80 ℃ and a vacuum degree of 0.06~0.08 MPa; the cooling crystallization temperature is 0~15 ℃ and the cooling time is 4~8 h.

6. The method according to claim 1, characterized in that, In step (3), the solid-liquid ratio of crude oxalic acid to deionized water is 1:2~1:5 g / mL, the heating temperature during dissolution is 60~80 ℃, the cooling crystallization temperature is 5~10 ℃, the cooling time is 3~6h, the washing is performed with deionized water 2~3 times, the drying temperature is 50~60 ℃, and the drying time is 2~4h.

7. A high-purity oxalic acid, characterized in that, It is prepared using the method described in any one of claims 1-6.

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