Method for recovering ferrous oxalate from waste lithium iron phosphate oxalic acid extraction slag
The method of oxalic acid leaching to recover ferrous oxalate from waste lithium iron phosphate extraction residue at ambient temperature and pressure solves the problem of ineffective iron recovery, realizes efficient and low-energy resource recycling, and obtains high-purity ferrous oxalate powder.
Patent Information
- Application Number
- CN202511072585.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-01
- Publication Date
- 2025-11-11
AI Technical Summary
In existing technologies, the iron remaining after the lithium element is recovered from the waste lithium iron phosphate extraction residue cannot be effectively recovered, resulting in a decrease in commercial value. Furthermore, traditional processes require oxidants and highly corrosive acids, which result in high energy consumption and difficulty in separating impurities.
Using oxalic acid as the leaching agent, ferrous oxalate is recovered by acid leaching, omitting the oxidant step. The process is carried out at room temperature and pressure, and combines filtration, vacuum distillation and freeze crystallization techniques to separate and recover ferrous oxalate, simplifying the impurity removal process.
This method enables efficient recovery of ferrous oxalate at room temperature and pressure, reducing energy consumption, simplifying impurity removal steps, obtaining high-purity ferrous oxalate powder, and improving resource utilization.
Smart Images
Figure CN120923338A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of lithium-ion battery resource recycling technology, and more specifically, it is a method for recovering ferrous oxalate from the oxalic acid extraction residue of waste lithium iron phosphate. Background Technology
[0003] Currently, the most studied wet recovery processes mainly involve leaching iron and lithium elements from lithium iron phosphate using inorganic strong acids (such as hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, etc.) in synergistic action with oxidants (such as H2O2, O2, sodium thiosulfate, etc.). Mechanical activation is used to optimize process conditions, including temperature, duration, and pressure. The general idea is to extract lithium elements in the form of Li... + The leaching process involves leaching in the form of ferrous iron, while the oxidation of ferrous iron in the raw material to ferric iron not only disrupts the olivine structure of lithium iron phosphate, thus improving the efficiency of Li... + The leaching and formation of Fe 3+ The easily precipitated ferric salt achieves the separation of lithium and iron. However, in the subsequent synthesis of lithium iron phosphate, the ferric salt needs to be reduced back to ferrous iron. If the reduction is ineffective, the residual ferric salt will also affect the electrochemical performance of lithium iron phosphate. Fe... 3+ Cu 2+ With Al 3+ The three elements exist in the liquid phase in ionic form, and the pH range of the salt precipitates formed by them is relatively close. Separating the three ions remains a challenge industrially. Polyvinylpyrrolidone (PVP) can effectively precipitate aluminum without precipitating iron salts, but it is expensive and impractical for large-scale industrial application. Therefore, we propose a method for leaching lithium iron phosphate waste using oxalic acid as the leaching acid and recycling the resources (Chinese Patent Application No. 2025102623310). The waste residue after lithium extraction contains a large amount of ferrous oxalate, which has not been recycled. Therefore, it is important to pay attention to the waste residue after lithium extraction and to recover the valuable metals therein, which is the focus of this patent. Currently, the main problem with large-scale lithium iron phosphate recycling is that only lithium is recovered, while the remaining large amount of iron is not effectively recovered and is disposed of in landfills, greatly reducing its commercial value. Therefore, effective recovery of iron from lithium extraction waste is essential. Summary of the Invention
[0004] This invention aims to address, at least to some extent, certain technical bottlenecks in related fields. It proposes a method for deep recovery of the waste residue obtained after recovering lithium from lithium iron phosphate powder using oxalic acid, whereby iron can be recovered in the form of ferrous oxalate. This method eliminates the need for adding oxidants in previous processes, avoids the introduction of highly corrosive acids such as sulfuric acid and nitric acid, and features low energy consumption, easy operation, and deep removal of copper and aluminum impurities.
[0005] The present invention adopts the following technical solution: A method for recovering ferrous oxalate from the oxalic acid extraction residue of spent lithium iron phosphate includes the following steps: Step 1: After the waste lithium iron phosphate is crushed and sorted, lithium iron phosphate black powder is obtained; after the lithium element is recovered by oxalic acid leaching, the slag sample contains carbon powder, PVDF, ferrous oxalate and copper and aluminum impurities, and is named coarse iron slag. Step 2: The coarse iron slag is acid-leached to separate carbon powder and PVDF from the slag. The acid leaching solution contains iron, aluminum, copper and oxalate. Step 3: Add excess iron powder to the acid leaching solution, and remove the copper element from the acid leaching solution by filtration to obtain a solution containing ferrous oxalate. Step four: The solution containing ferrous oxalate is distilled under reduced pressure to recover hydrochloric acid from the gas phase and recycled to the leaching section. Step 5: The liquid phase is frozen to recover ferrous oxalate crystals, and the mother liquor is recycled to the vacuum distillation section for further processing after multiple cycles.
[0006] The acidic substances in the acid leaching process include one or more of nitrate ions and hydrochloride ions.
[0007] The solid-to-crude iron slag ratio of the acid leaching solution is (3~8):1.
[0008] The pH range of the acid leaching is between 0.5 and 2, and the acid leaching time is between 30 min and 180 min.
[0009] In step three, iron powder is added to the filtrate after acid leaching, the pH value is adjusted to a range of 1 to 3, and the reaction time is a range of 30 to 60 minutes. Filtration can remove copper impurities from the acid leaching solution.
[0010] In step five, the temperature range for freezing and recovering ferrous oxalate crystals is -10 to 5°C.
[0011] Compared with previous technologies, the advantages of this invention are: acid leaching can be carried out under normal temperature and pressure conditions without the need for oxidants, thus reducing energy consumption. Previous technologies often used sulfuric acid and nitric acid as leaching acids, requiring subsequent impurity removal operations to remove sulfate and nitrate ions. Oxalic acid, however, is easily oxidized and thermally decomposed into carbon dioxide gas, making impurity removal a simpler process. Simultaneously, by sequentially performing impurity removal, dissolution, and pH adjustment operations on the leaching residue, high-purity ferrous oxalate powder can be recovered. Attached Figure Description
[0012] Figure 1 The diagram shows the overall process flow for recovering iron from lithium iron phosphate powder.
[0013] Figure 2The diagram shows a flowchart illustrating the acid leaching process for lithium extraction powder from waste lithium iron phosphate.
[0014] Figure 3 The diagram shows a flowchart illustrating the process of removing copper impurities using an acid leaching solution.
[0015] Figure 4 The diagram shows a flowchart illustrating the vacuum distillation process of iron- and aluminum-containing solutions.
[0016] Figure 5 The flowchart shown illustrates the recovery of ferrous oxalate from iron-containing mother liquor by cryogenic crystallization. Detailed Implementation
[0017] 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.
[0018] 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.
[0019] 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.
[0020] 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.
[0021] Example 1 The method for recovering ferrous oxalate from the oxalic acid extraction residue of waste lithium iron phosphate according to the present invention includes the following steps (Example 1): (1) After crushing the waste material from lithium iron phosphate oxalic acid extraction, weigh 10g of coarse iron slag powder and 100ml of 2.5mol / L hydrochloric acid solution for acid leaching. The temperature is controlled at 25℃ and the reaction time is 120min.
[0022] (2) After the reaction is completed, filter to obtain filter residue containing carbon powder and PVDF and filtrate containing iron, copper and aluminum. Add iron powder to the filtrate to adjust the pH to 1.5 and the reaction time is 60 min.
[0023] (3) Filtering the pre-reaction liquid in step (2) can remove excess iron powder and copper after displacement, thus achieving the purpose of removing copper.
[0024] (4) The filtrate obtained in step (3) can be subjected to vacuum distillation to recover hydrochloric acid from the distillation vapor phase and can be recycled to the leaching section for use.
[0025] (5) After the distillation and concentration process in step (4), the iron-containing mother liquor can be subjected to low-temperature freezing treatment. The temperature is controlled at -10℃ and the freezing crystallization time is controlled at 1h. Ferrous oxalate crystals can be recovered, filtered, washed and dried, and the mother liquor is recycled back to the distillation section.
[0026] Example 2 The method for recovering ferrous oxalate from the oxalic acid extraction residue of waste lithium iron phosphate according to the present invention includes the following steps (Example 2): (1) After crushing the waste material from lithium iron phosphate oxalic acid extraction, weigh 15g of coarse iron slag powder and 100ml of 3mol / L hydrochloric acid solution for acid leaching. The temperature is controlled at 25℃ and the reaction time is 90min.
[0027] (2) After the reaction is completed, filter to obtain filter residue containing carbon powder and PVDF and filtrate containing iron, copper and aluminum. Add iron powder to the filtrate to adjust the pH to 1.8 and the reaction time is 45 min.
[0028] (3) Filtering the pre-reaction liquid in step (2) can remove excess iron powder and copper after displacement, thus achieving the purpose of removing copper.
[0029] (4) The filtrate obtained in step (3) can be subjected to vacuum distillation to recover hydrochloric acid from the distillation vapor phase and can be recycled to the leaching section for use.
[0030] (5) After the distillation and concentration process in step (4), the iron-containing mother liquor can be subjected to low-temperature freezing treatment. The temperature is controlled at -5℃ and the freezing crystallization time is controlled at 1.5h. Ferrous oxalate crystals can be recovered, filtered, washed and dried, and the mother liquor is recycled back to the distillation section.
[0031] Example 3 The method for recovering ferrous oxalate from the oxalic acid extraction residue of waste lithium iron phosphate according to the present invention includes the following steps (Example 3): (1) After crushing the waste material from lithium iron phosphate oxalic acid extraction, weigh 12g of coarse iron slag powder and 100ml of 3.5mol / L hydrochloric acid solution for acid leaching. The temperature is controlled at 25℃ and the reaction time is 60min.
[0032] (2) After the reaction is completed, filter to obtain filter residue containing carbon powder and PVDF and filtrate containing iron, copper and aluminum. Add iron powder to the filtrate to adjust the pH to 1.9 and the reaction time is 60 min.
[0033] (3) Filtering the pre-reaction liquid in step (2) can remove excess iron powder and copper after displacement, thus achieving the purpose of removing copper.
[0034] (4) The filtrate obtained in step (3) can be subjected to vacuum distillation to recover hydrochloric acid from the distillation vapor phase and can be recycled to the leaching section for use.
[0035] (5) After the distillation and concentration process in step (4), the iron-containing mother liquor can be subjected to low-temperature freezing treatment. The temperature is controlled at 0°C and the freezing crystallization time is controlled at 2h. Ferrous oxalate crystals can be recovered, filtered, washed and dried, and the mother liquor is recycled back to the distillation section.
[0036] Example 4 The method for recovering ferrous oxalate from the oxalic acid extraction residue of waste lithium iron phosphate according to the present invention includes the following steps (Example 4): (1) After crushing the waste material from lithium iron phosphate oxalic acid extraction, weigh 18g of coarse iron slag powder and 100ml of 5mol / L hydrochloric acid solution for acid leaching. The temperature is controlled at 25℃ and the reaction time is 100min.
[0037] (2) After the reaction is completed, filter to obtain filter residue containing carbon powder and PVDF and filtrate containing iron, copper and aluminum. Add iron powder to the filtrate to adjust the pH to 2 and the reaction time is 90 min.
[0038] (3) Filtering the pre-reaction liquid in step (2) can remove excess iron powder and copper after displacement, thus achieving the purpose of removing copper.
[0039] (4) The filtrate obtained in step (3) can be subjected to vacuum distillation to recover hydrochloric acid from the distillation vapor phase and can be recycled to the leaching section for use.
[0040] (5) After the distillation and concentration process in step (4), the iron-containing mother liquor can be subjected to low-temperature freezing treatment. The temperature is controlled at 5°C and the freezing crystallization time is controlled at 2.5h. Ferrous oxalate crystals can be recovered, filtered, washed and dried, and the mother liquor is recycled back to the distillation section.
[0041] Example 5 The method for recovering ferrous oxalate from the oxalic acid extraction residue of waste lithium iron phosphate according to the present invention includes the following steps (Example 5): (1) After crushing the waste material from lithium iron phosphate oxalic acid extraction, weigh 10g of coarse iron slag powder and 100ml of 4.5mol / L hydrochloric acid solution for acid leaching. The temperature is controlled at 25℃ and the reaction time is 60min.
[0042] (2) After the reaction is completed, filter to obtain filter residue containing carbon powder and PVDF and filtrate containing iron, copper and aluminum. Add iron powder to the filtrate to adjust the pH to 1.8 and the reaction time is 40 min.
[0043] (3) Filtering the pre-reaction liquid in step (2) can remove excess iron powder and copper after displacement, thus achieving the purpose of removing copper.
[0044] (4) The filtrate obtained in step (3) can be subjected to vacuum distillation to recover hydrochloric acid from the distillation vapor phase and can be recycled to the leaching section for use.
[0045] (5) After the distillation and concentration process in step (4), the iron-containing mother liquor can be subjected to low-temperature freezing treatment. The temperature is controlled at -10℃ and the freezing crystallization time is controlled at 0.5h. Ferrous oxalate crystals can be recovered, filtered, washed and dried, and the mother liquor is recycled back to the distillation section.
[0046] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A method for recovering ferrous oxalate from the oxalic acid extraction residue of waste lithium iron phosphate, characterized in that, Includes the following steps: Step 1: After the waste lithium iron phosphate is crushed and sorted, lithium iron phosphate black powder is obtained; the slag sample after oxalic acid leaching to recover lithium contains carbon powder, PVDF, ferrous oxalate, and copper and aluminum impurities, and is named coarse iron slag. Step 2: The coarse iron slag is acid-leached to separate carbon powder and PVDF from the slag. The acid leaching solution contains iron, aluminum, copper and oxalate. Step 3: Add excess iron powder to the acid leaching solution, and remove the copper element from the acid leaching solution by filtration to obtain a solution containing ferrous oxalate. Step four: The solution containing ferrous oxalate is distilled under reduced pressure to recover hydrochloric acid from the gas phase and recycled to the leaching section. Step 5: The liquid phase is frozen to recover ferrous oxalate crystals, and the mother liquor is recycled to the vacuum distillation section for further processing after multiple cycles.
2. The method for recovering ferrous oxalate from the oxalic acid extraction residue of waste lithium iron phosphate according to claim 1, characterized in that: The acidic substances in the acid leaching process include one or more of nitrate ions and hydrochloride ions.
3. The method for recovering ferrous oxalate from the oxalic acid extraction residue of waste lithium iron phosphate according to claim 1, characterized in that: The solid-to-crude iron slag ratio is (3~8):
1.
4. The method for recovering ferrous oxalate from the oxalic acid extraction residue of waste lithium iron phosphate according to claim 1, characterized in that: The pH range of the acid leaching is between 0.5 and 2, and the acid leaching time is between 30 min and 180 min.
5. The method for recovering ferrous oxalate from the oxalic acid extraction residue of waste lithium iron phosphate according to claim 1, characterized in that: In step three, iron powder is added to the filtrate after acid leaching, the pH value is adjusted to a range of 1 to 3, and the reaction time is a range of 30 to 60 minutes. Filtration can remove copper impurities from the acid leaching solution.
6. The method for recovering ferrous oxalate from the oxalic acid extraction residue of waste lithium iron phosphate according to claim 1, characterized in that: The temperature range for freezing and recovering ferrous oxalate crystals in step five is -10 to 5°C.