Method for recovering all components of lithium iron phosphate black powder

Abstract

The invention relates to the technical field of lithium iron phosphate black powder recovery, in particular to a method for preparing iron phosphate and lithium hydroxide by electrochemically and selectively recovering waste lithium iron phosphate. The method comprises the following steps: separating an anode chamber and a cathode chamber through a cation selective permeable membrane, respectively adding electrolyte into the anode chamber and the cathode chamber, electrolyzing for a period of time to respectively form an acidic environment and an alkaline environment, adding lithium iron phosphate black powder into the anode chamber, selectively leaching lithium into a solution within a proper pH range, and migrating the lithium into the cathode chamber under the action of an electric field, and iron is retained in the solid in the form of iron phosphate, so that lithium-iron separation and lithium ion enrichment can be realized in the leaching process. According to the method, the leaching rate of lithium can reach 99% or above, the leaching rate of iron is kept below 0.01%, the phosphorus iron slag can be restored into an iron phosphate precursor after being calcined, and the enriched lithium liquid is recycled in a high-purity lithium hydroxide form after being evaporated and concentrated. According to the method, electrons are used as a green oxidizing agent, the use of acid and alkali is greatly reduced in the leaching process, and all components are recycled.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium iron phosphate black powder recovery, and in particular relates to a method for recovering all components of lithium iron phosphate black powder. Background Art

[0002] Lithium-ion batteries do not produce toxic or harmful substances during use, but if the discarded lithium-ion batteries are not properly and effectively handled, the electrolyte, heavy metals, plastics and other substances in the discarded lithium batteries will cause serious pollution to the environment. At the same time, discarded lithium batteries contain high levels of metals, which are also valuable resources. Therefore, whether from the perspective of environmental protection or resource utilization, it is necessary to recycle and regenerate discarded lithium batteries.

[0003] The recycling process of waste lithium iron phosphate batteries includes disassembly, crushing and recycling. Disassembly and crushing are used as battery pretreatment. The waste battery shell, electrode sheet and diaphragm are separated by mechanical sorting, and then the electrode sheet is treated by high-temperature incineration to separate the positive electrode material from the battery; recycling is to extract valuable metal elements from the separated positive electrode material by chemical methods. The mainstream chemical methods include pyrometallurgy and hydrometallurgy. Pyrometallurgy recovers valuable metals in the form of alloys through high-temperature calcination. The process is simple but energy-intensive. Hydrometallurgy mainly uses acid and alkali solutions as a medium to dissolve the metal ions in the lithium iron phosphate battery, and further uses precipitation, adsorption, ion exchange and other methods to extract the metal ions in the form of salts, but the process is relatively cumbersome and requires the use of a large amount of chemical reagents. Therefore, the development of efficient, green and short-process recycling processes can occupy a favorable position in the recycling market.

[0004] Jinchuan Group Co., Ltd. disclosed a method for recycling waste lithium iron phosphate positive electrode materials (CN113735087a); the Institute of Process Engineering of the Chinese Academy of Sciences disclosed a method for recovering iron phosphate and lithium carbonate from waste lithium iron phosphate positive electrode materials (CN115611252A); Anhui Tianshuo Lithium Battery New Material Technology Co., Ltd. disclosed a method for recycling lithium iron phosphate batteries to prepare lithium carbonate (CN117416974A); Central South University disclosed a method for full resource recovery of valuable components in waste lithium iron phosphate batteries (CN116002646A). In all cases, excessive acid needs to be added during the leaching process to destroy the LiFePO4 structure, resulting in a large amount of wastewater generated during the lithium extraction process. At the same time, the high concentration of acid causes impurities to be leached out, making the subsequent impurity removal steps cumbersome. In summary, the existing full leaching process of lithium iron black powder is still limited by the large amount of acid and alkali used and the complex process. Therefore, the selective leaching process has gradually become the mainstream of wet recovery. Hunan Brunp Recycling Technology Co., Ltd. has disclosed a method for recovering lithium from lithium iron phosphate waste and its application (CN112678791B), Guangdong Brunp Recycling Technology Co., Ltd. has disclosed a method for preparing lithium iron phosphate positive electrode materials by directional circulation of waste lithium iron phosphate batteries (CN115744857A), and Beijing Chemical Metallurgical Research Institute of Nuclear Industry has disclosed a method for preparing battery-grade iron phosphate using waste lithium iron phosphate battery positive electrode powder (CN116177510A). However, selective leaching requires the use of oxidants, which increases the use of chemical reagents, and the large amount of salt-containing wastewater generated puts great pressure on subsequent water treatment. Therefore, it is of great significance to develop green and efficient wet recovery methods. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides an electrochemical selective leaching method. The method generates the acid required in the leaching process through electrolysis, and does not require the addition of additional acid or alkali. At the same time, electrons are used as green oxidants without the need for external chemical oxidizing agents. The electrodes directly provide redox potential to selectively leach lithium, thereby achieving separation and recovery of lithium iron, effectively reducing the use of acid and alkali, and reducing corrosion to equipment and the difficulty of back-end water treatment.

[0006] In order to achieve the above technical objectives, the present invention adopts the following technical solutions: (1) Add electrolyte to the anode and cathode chambers respectively, and perform electrolysis at a certain voltage to make the anode and cathode chambers acidic or alkaline respectively.

[0007] (2) According to the liquid-to-solid ratio, black powder is added to the anode chamber for electrolytic oxidation leaching. After the reaction is completed for 2-4 hours, the material in the anode chamber is separated into solid and liquid to obtain ferrophosphorus slag.

[0008] (3) The filtrate obtained in step (2) can be reused as the electrolyte in the anode chamber, and the filter residue is calcined at 500-800°C to obtain carbon-removed iron phosphate.

[0009] (4) After multiple leaching, the lithium solution obtained by enrichment in the cathode chamber is subjected to impurity removal, evaporation and crystallization to obtain a high-purity lithium hydroxide product.

[0010] The main process flow for recovering all components of lithium iron phosphate black powder provided by the present invention is: electrochemical oxidation leaching, calcination of iron phosphate to remove carbon and remove impurities to recover lithium products. The specific process is 1. Electrochemical leaching first electrolyzes the electrolyte to make the anode chamber acidic, and then the electrode is in contact with the lithium iron phosphate black powder to complete the electron transfer, so that the lithium iron phosphate is oxidized to iron phosphate and accompanied by the leaching of lithium ions. The leached lithium ions migrate to the cathode chamber for enrichment under the action of the electric field. During the leaching process, iron is separated from lithium in the form of iron phosphate slag; 2. The separated iron phosphate slag is calcined to remove carbon to obtain an iron phosphate product; 3. The lithium in the electrolyte is enriched to more than 10 g / L, and the above can be obtained by impurity removal, evaporation and crystallization to obtain a lithium hydroxide product.

[0011] As a preferred solution, the waste lithium iron phosphate black powder has a Li content of 3.58-4.94%, a Fe content of 33.67-36.84%, a P content of 14.33-16.02%, an impurity Al content of 0.11-0.18%, and an impurity Cu content of 0.0020-0.0047%.

[0012] As a preferred solution, the electrolyte in step (1) is one of lithium nitrate, lithium sulfate and lithium chloride, with a concentration of 0.02-0.3 mol / L, a stirring speed of 600-1000 r / min, and a current density of 200-600 mA / cm 2 , the electrolysis time is 0.5-1 h. The pH of the anode chamber is between 1-4 to provide an acidic environment required for oxidative leaching. It is further preferred to achieve a pH of 1.0-2.0 in the anode chamber and a pH of 10.0-12.0 in the cathode chamber.

[0013] As a preferred solution, in step (2), the anode of the electrochemical leaching reaction adopts a high oxygen evolution potential electrode, such as a boron-doped diamond film electrode, a platinum group noble metal anode, a titanium-based coating anode, etc., and the cathode is a conventional inert electrode with a current density of 200-600 mA / cm 2 , the electrolysis time is 2-6 h, the electrolysis temperature is 25-50℃, and the solid-liquid ratio in the anode chamber is 10-100 g / L.

[0014] As a preferred solution, in step (3), the filtrate is recycled as the electrolyte after adjusting the electrolyte concentration, the filter residue is dried at 80-120°C for 10-12 h, and then calcined in a muffle furnace at 500-800°C for 3-5 h to remove carbon and repair the crystal structure.

[0015] As a preferred solution, in step (4), after the cathode electrolyte is recycled, the lithium content is 10-25 g / L and the pH is 10-12. After filtration and separation, a pure lithium hydroxide solution is obtained, and after evaporation and crystallization, a high-purity lithium hydroxide product is obtained.

[0016] Compared with the prior art, the present invention has the following technical effects: (1) The present invention relates to a method for recovering all components of waste lithium iron phosphate black powder. The method separates lithium iron by electrochemical selective leaching, and then recovers all components of iron phosphate and lithium. The present invention converts waste lithium iron phosphate batteries from solid waste into metal resources. The full component recovery realizes the recycling of resources, reduces environmental pressure and creates economic value.

[0017] (2) Compared with the traditional full leaching process, the present invention reduces the use of a large amount of acid and alkali. Compared with the conventional selective leaching process, no additional chemical oxidant is added, which reduces the introduction of impurity ions. Compared with other electrochemical leaching methods, it does not need to make black powder into electrodes, and the process is simple. Replacing traditional oxidants with electrons can accurately control the pH and redox potential during the leaching process, which can be adjusted at any time according to different raw materials, and has extremely high flexibility and applicability.

[0018] (3) In the present invention, lithium ions are enriched by recycling the electrolyte, which reduces the energy consumption of evaporation and concentration. The use of a cation exchange membrane in the electrolytic cell reduces anionic impurities. At the same time, cationic impurities are immediately precipitated and separated at a high pH value, and a pure lithium product can be obtained without multi-step impurity removal of the lithium-rich solution. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is the XRD diagram of iron phosphate calcined at different temperatures in Example 1.

[0020] Figure 2 Schematic diagram of the device, 1 is the anode, 2 is the cathode, 3 is the cation exchange membrane, and 4 is the electrolyte.

[0021] Figure 3 It is a process flow chart. DETAILED DESCRIPTION

[0022] The technical solution provided by the present invention will be described in detail below in conjunction with specific embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, and other embodiments obtained by relevant personnel in the field without making creative improvements and labor are all within the scope of protection of the present invention.

[0023] Table 1. Black powder component content

[0024] Example 1 Step 1: Electrochemical oxidation leaching 1. Add electrolytes to the cathode and anode chambers respectively. Add 0.1 M lithium sulfate solution as electrolyte to the anode chamber and 0.1 M lithium hydroxide as electrolyte to the cathode chamber. Keep 200 mA / cm in the solution at room temperature. 2 Electrolysis was performed at a current density of 0.5 h to make the anode and cathode chambers continuously acidic and alkaline, respectively, with the pH of the anode chamber at 2.6 and the pH of the cathode chamber at 10.2. The hydrogen ions in the anode chamber created the acidic environment required for oxidative leaching.

[0025] 2. Solid-liquid ratio 30 g / L, add black powder into the anode chamber, use boron-doped diamond electrode as anode, ruthenium-titanium electrode as cathode, maintain 200 mA / cm in the solution at room temperature 2 The current density was 2 hours for leaching reaction. The boron-doped diamond electrode is a high oxygen evolution potential electrode, which inhibits the occurrence of oxygen evolution side reaction and can produce strong oxidizing substances for indirect oxidation, greatly improving the oxidation capacity. Driven by the electric field, lithium ions are enriched in the cathode chamber. Under this operating condition, the lithium leaching rate reaches 99.76% and the iron leaching rate is 0.004%. After the reaction, the electrolyte and ferrophosphorus slag in the anode chamber are separated by filtration.

[0026] Step 2: Calcination of iron phosphate to remove carbon After the ferrophosphorus slag was dried at 120 °C for 8 h, the same mass of ferrophosphate was calcined in an air atmosphere muffle furnace at 500, 600, 700 and 800 °C for 3 h respectively to remove the negative electrode carbon powder and organic carbon PVDF.

[0027] Table 2. Phosphorus and iron content of calcined iron phosphate at different temperatures

[0028] Step 3: Lithium product recovery The filtrate from the anode chamber is reused to supplement the electrolyte, and the electrolyte from the cathode chamber is recycled without treatment. When the lithium ion concentration is enriched to 20 g / L, since the electrolyte in the cathode chamber is alkaline, the trace amount of leached iron migrates to the cathode chamber and precipitates immediately. The cathode chamber electrolyte is filtered to obtain a pure lithium hydroxide solution, which is concentrated and crystallized to obtain the lithium hydroxide product, with a recovery rate of 98.27% and a product purity of 99.66%.

[0029] Example 2 Step 1: Electrochemical oxidation leaching 1. Add electrolytes to the cathode and anode chambers respectively. Add 0.2 M lithium chloride solution as electrolyte to the anode chamber and 0.1 M lithium hydroxide as electrolyte to the cathode chamber. Keep 250 mA / cm in the solution at room temperature. 2Electrolysis was carried out for 1 h at a current density of , so that the anode and cathode chambers continued to be acidic and alkaline, respectively, with the pH of the anode chamber at 1.6 and the pH of the cathode chamber at 11.5. The hydrogen ions obtained by electrolysis in the anode chamber created the acidic environment required for oxidative leaching.

[0030] 2. Solid-liquid ratio 30 g / L, add black powder into the anode chamber, use tin dioxide electrode as anode, ruthenium titanium electrode as cathode, maintain 250 mA / cm in the solution at room temperature 2 The current density was 2 hours for leaching reaction. The tin dioxide electrode is also a high oxygen evolution potential electrode. Driven by the electric field, lithium ions are enriched in the cathode chamber. Under this operating condition, the lithium leaching rate reached 99.64% and the iron leaching rate was 0.003%. After the reaction, the electrolyte and ferrophosphorus slag in the anode chamber were separated by filtration.

[0031] Step 2: Calcination of iron phosphate to remove carbon The ferrophosphorus slag was dried at 120 °C for 8 h and then calcined in an air atmosphere muffle furnace at 700 °C for 3 h to remove negative electrode carbon powder and organic carbon PVDF.

[0032] Step 3: Lithium product recovery The filtrate from the anode chamber is reused to supplement the electrolyte, and the electrolyte from the cathode chamber is recycled without treatment. When the lithium ion concentration is enriched to 20 g / L, the electrolyte from the cathode chamber is filtered to obtain a pure lithium hydroxide solution, which is concentrated and crystallized to obtain the lithium hydroxide product, with a recovery rate of 98.65% and a product purity of 99.73%.

[0033] Example 3 Step 1: Electrochemical oxidation leaching 1. Add electrolytes to the cathode and anode chambers respectively. Add 0.2 M lithium chloride solution as electrolyte to the anode chamber and 0.1 M lithium hydroxide as electrolyte to the cathode chamber. Keep 200 mA / cm in the solution at room temperature. 2 Electrolysis was carried out for 1 h at a current density of , so that the anode and cathode chambers continued to be acidic and alkaline, respectively, with the pH of the anode chamber at 1.8 and the pH of the cathode chamber at 11.1. The hydrogen ions obtained by electrolysis in the anode chamber created the acidic environment required for oxidative leaching.

[0034] 2. Solid-liquid ratio of 30 g / L, add black powder into the anode chamber, use CNT-PbO2 electrode as anode, ruthenium titanium electrode as cathode, maintain 200 mA / cm in the solution at room temperature 2 The current density was 2 h, and the leaching reaction was carried out. The CNT-PbO2 electrode is also a high oxygen evolution potential electrode, and can generate hydrogen peroxide to indirectly oxidize LFP, while reacting with a small amount of Fe 2+Fenton reaction occurs, which greatly enhances the oxidation capacity of the anode chamber. Lithium ions are enriched in the cathode chamber under the drive of the electric field. Under this operating condition, the lithium leaching rate reaches 99.88% and the iron leaching rate is 0.004%. After the reaction is completed, the electrolyte and ferrophosphorus slag in the anode chamber are separated by filtration.

[0035] Step 2: Calcination of iron phosphate to remove carbon After the ferrophosphorus slag was dried at 120 °C for 8 h, it was heated in a muffle furnace at 700 °C in air atmosphere. o C was calcined for 3 h to remove negative electrode carbon powder and organic carbon PVDF, etc.

[0036] Step 3: Lithium product recovery The filtrate from the anode chamber is reused to supplement the electrolyte, and the electrolyte from the cathode chamber is recycled without treatment. When the lithium ion concentration is enriched to 25g / L, the electrolyte from the cathode chamber is filtered to obtain a pure lithium hydroxide solution, which is concentrated and crystallized to obtain the lithium hydroxide product. The recovery rate is 97.91% and the product purity is 99.83%.

[0037] Example 4 Step 1: Electrochemical oxidation leaching 1. Add electrolytes to the cathode and anode chambers respectively. Add 0.1 M lithium sulfate solution as electrolyte to the anode chamber and 0.1 M lithium hydroxide as electrolyte to the cathode chamber. Keep 200 mA / cm in the solution at room temperature. 2 Electrolysis was performed at a current density of 0.5 h to make the anode and cathode chambers continuously acidic and alkaline, respectively, with the pH of the anode chamber at 2.0 and the pH of the cathode chamber at 10.8. The hydrogen ions in the anode chamber created the acidic environment required for oxidative leaching.

[0038] 2. Solid-liquid ratio 30 g / L, add black powder into the anode chamber, use stainless steel electrode as anode, ruthenium titanium electrode as cathode, maintain 200 mA / cm in the solution at room temperature 2 The current density was 2 h, and the leaching reaction was carried out. Lithium ions were enriched in the cathode chamber under the drive of the electric field. Under this operating condition, the lithium leaching rate reached 90.21% and the iron leaching rate was 0.005%. After the reaction, the electrolyte and ferrophosphorus slag in the anode chamber were separated by filtration.

[0039] Step 2: Calcination of iron phosphate to remove carbon After the ferrophosphorus slag was dried at 120 °C for 8 h, it was heated in a muffle furnace at 700 °C in air atmosphere. o C was calcined for 3 h to remove negative electrode carbon powder and organic carbon PVDF, etc.

[0040] Step 3: Lithium product recovery The filtrate from the anode chamber is reused to supplement the electrolyte, and the electrolyte from the cathode chamber is recycled without treatment. When the lithium ion concentration is enriched to 20 g / L, the electrolyte from the cathode chamber is filtered to obtain a pure lithium hydroxide solution, which is concentrated and crystallized to obtain the lithium hydroxide product. The recovery rate is 89.15% and the product purity is 99.82%.

[0041] Example 5 Step 1: Electrochemical oxidation leaching 1. Add 0.1 M lithium sulfate solution as electrolyte to the electrolytic cell. Keep 200 mA / cm in the solution at room temperature. 2 The electrolysis was carried out at a current density of 0.5 h.

[0042] 2. Solid-liquid ratio 30 g / L, add black powder into the electrolytic cell, use boron-doped diamond electrode as anode, ruthenium-titanium electrode as cathode, maintain 200 mA / cm in the solution at room temperature 2 The current density was 2 hours for leaching reaction. The boron-doped diamond electrode is a high oxygen evolution potential electrode, which inhibits the occurrence of oxygen evolution side reaction and can produce strong oxidizing substances for indirect oxidation, greatly improving the oxidation capacity. Under this operating condition, the lithium leaching rate reached 84.37% and the iron leaching rate was 0.02%. After the reaction, the electrolyte and ferrophosphorus slag were separated by filtration.

[0043] Step 2: Calcination of iron phosphate to remove carbon The ferrophosphorus slag was dried at 120 °C for 8 h and then calcined in an air atmosphere muffle furnace at 700 °C for 3 h to remove negative electrode carbon powder and organic carbon PVDF.

[0044] Step 3: Lithium product recovery The filtrate is still reused as electrolyte. When the lithium ion concentration is enriched to above 5 g / L, the pH is adjusted to 8, and the reaction is carried out for 1 h to remove impurities. After impurities are removed, the colorless and transparent filtrate is separated by suction. Then, according to Li:PO4 3- Solid Na3PO4 was added at a molar ratio of 3:1.1 and reacted at 90 °C for 1 h to obtain a white precipitate, which was placed in an oven at 80 °C for 12 h. The recovery rate was calculated by weighing and was 79.64%, and the product purity was 99.33%.

[0045] Example 6 Step 1: Electrochemical oxidation leaching Electrolytes were added to the cathode and anode chambers respectively. 0.1 M lithium sulfate solution was added to the anode chamber as electrolyte, and 0.1 M lithium hydroxide was added to the cathode chamber as electrolyte. The solid-liquid ratio was 30 g / L. Black powder was added to the anode chamber. A boron-doped diamond electrode was used as the anode and a stainless steel electrode was used as the cathode. At room temperature, the solution was maintained at 200 mA / cm 2The current density was 2 hours, and the leaching reaction lasted for 2 hours. Lithium ions were enriched in the cathode chamber under the drive of the electric field. Under this operating condition, the lithium leaching rate reached 83.61%, and the iron leaching rate was 0.003%. After the reaction, the electrolyte and ferrophosphorus slag in the anode chamber were separated by filtration.

[0046] Step 2: Calcination of iron phosphate to remove carbon The ferrophosphorus slag was dried at 120 °C for 8 h and then calcined in an air atmosphere muffle furnace at 700 °C for 3 h to remove negative electrode carbon powder and organic carbon PVDF.

[0047] Step 3: Lithium product recovery The filtrate from the anode chamber is reused to supplement the electrolyte, and the electrolyte from the cathode chamber is recycled without treatment. When the lithium ion concentration is enriched to 20 g / L, the electrolyte from the cathode chamber is filtered to obtain a pure lithium hydroxide solution, which is then concentrated and crystallized to obtain the lithium hydroxide product, with a recovery rate of 80.17% and a product purity of 99.58%.

[0048] It can be seen from Example 4 that when the anode does not use a high oxygen evolution potential electrode, the anode oxygen evolution side reaction is serious, and the bubbles hinder the contact between LFP and the anode, and the oxidation of LFP is limited. At the same time, the oxidizing ability of oxygen is lower than the free radical oxidizing substances produced by the high oxygen evolution potential electrode, resulting in a decrease in the leaching rate of LFP. Comparative Examples 1, 2, and 3 show that the use of a high oxygen evolution potential electrode can enhance the oxidizing ability of the electrolysis process, and the use of a cation exchange membrane to separate the electrode chamber can enhance the chance of contact between LFP and the anode, and the anode chamber is always in an acidic environment, without the need for additional acid leaching. At the same time, it can be seen from Examples 1 and 4 that the more ions in the solution, the stronger the current density, and the stronger the acidity and alkalinity in the electrode chamber. It can be seen from Examples 2 and 3 that the larger the current density is, the more violent the electrolysis reaction is, which can also lead to stronger acidity and alkalinity. And within a certain pH, the acidity is due to the characteristics of the cation exchange membrane, and the reactions are all carried out at room temperature. At the same time, it can be seen from Example 5 that without using a cation exchange membrane, the pH of the electrolyte is maintained between 3-5, which is insufficient to destroy the surface structure of LFP, resulting in diffusion restriction of lithium ion leaching. At the same time, if the anode and cathode chambers are not separated, the contact opportunity between LFP and the anode is reduced, while the contact opportunity with the cathode is increased, so that the same leaching time cannot achieve a high lithium leaching rate. It can be seen from Example 6 that even if the anode and cathode chambers are separated and the contact between LFP and the anode is strengthened, the leaching rate is still not high, indicating that in this electrolysis process, if the electrolyte is not electrolyzed first, hydrogen ions accumulate in the anode chamber, and leaching is only performed through oxidizing substances, resulting in a greatly extended leaching time.

[0049] Through the decarbonization calcination of ferrophosphorus slag at different temperatures in Example 1, it can be seen that when calcined at 500-600 ℃, there are still impurity peaks, and when the temperature reaches 700 ℃, the impurity peaks disappear, and the peak intensity at 800 ℃ does not increase significantly. The characteristic peaks are sharp, and the phosphorus-iron ratio is normal, indicating that the crystal recovery and regeneration of iron phosphate can be achieved through calcination and decarbonization.

[0050] In summary, the results of the embodiments show that the electrochemical selective recovery method using a high oxygen evolution potential electrode and a cation exchange membrane under optimized conditions can realize the recovery of all components of lithium iron phosphate, and it can be seen from the embodiments that the high oxygen evolution potential electrode can realize efficient and selective leaching of LFP, and the use of a cation exchange membrane can realize an acidic leaching environment, and realize the extraction and enrichment of lithium solution during the leaching process. And it can be seen from the embodiments that a suitable acidic environment is essential during the leaching process. At the same time, lithium salt is used as an electrolyte, which greatly reduces the pressure of impurity removal in the step of recovering lithium products. Therefore, the electrochemical-electrodialysis method is used to selectively leach LFP to reduce the use of chemical oxidants.

Claims

1. A method for recovering all components of lithium iron phosphate black powder, characterized in that: The method comprises the following steps: (1) Add electrolyte to the cathode and anode chambers respectively, and perform electrolysis at a certain current density to make the cathode and anode chambers acidic and alkaline respectively; (2) According to the liquid-solid ratio, waste lithium iron phosphate battery black powder is added to the anode chamber for electrolytic oxidation leaching. After the reaction is completed for 2-6 hours, the anode chamber material is separated into solid and liquid to obtain ferrophosphorus slag and filtrate; (3) The filtrate obtained in step (2) is further reused as the electrolyte in the anode chamber, and the filter residue is calcined to obtain carbon-removed iron phosphate; (4) After multiple leaching, the lithium solution obtained by enriching the cathode chamber is subjected to impurity removal, evaporation and crystallization to obtain a lithium hydroxide product.

2. The method for recovering all components of lithium iron phosphate black powder according to claim 1, characterized in that: The waste lithium iron phosphate battery black powder has a Li content of 3.58-4.94%, a Fe content of 33.67-36.84%, a P content of 14.33-16.02%, an impurity Al content of 0.11-0.18%, and an impurity Cu content of 0.0020-0.0047%.

3. The method for recovering all components of lithium iron phosphate black powder according to claim 1, characterized in that: The electrolyte in step (1) is one or more of lithium nitrate, lithium sulfate, and lithium chloride, with a concentration of 0.02-0.3 mol / L, a stirring speed of 600-1000 r / min, and a current density of 200-600 mA / cm 2 , the electrolysis time is 0.5-1 h.

4. The method for recovering all components of lithium iron phosphate black powder according to claim 1, characterized in that: In steps (1) and (2), the anode of the electrochemical leaching reaction adopts a high oxygen evolution potential electrode, including a boron-doped diamond film electrode, a platinum group noble metal anode, and a titanium-based coating anode, and the cathode is a conventional inert electrode.

5. The method for recovering all components of lithium iron phosphate black powder according to claim 1, characterized in that: In step (1), the pH of the anode chamber is 1.0-4.0; the pH of the cathode chamber is 10.0-12.

0.

6. The method for recovering all components of lithium iron phosphate black powder according to claim 1, characterized in that: In step (2), the current density is 200-600 mA / cm 2 , electrolysis time is 2-6 h, electrolysis temperature is 25-50 ℃, and the solid-liquid ratio in the anode chamber is 10-100 g / L.

7. The method for recovering all components of lithium iron phosphate black powder according to claim 1, characterized in that: In step (3), the filtrate is recycled as the electrolyte after adjusting the electrolyte concentration, and the filter residue is dried at 80-120° C. for 10-12 h and then calcined in a muffle furnace at 500-800° C. for 3-5 h.

8. The method for recovering all components of lithium iron phosphate black powder according to claim 1, characterized in that: In step (4), after the cathode chamber electrolyte is recycled, the lithium content is 10-25 g / L and the pH is 10-12. After filtration and separation, a pure lithium hydroxide solution is obtained, and after evaporation and crystallization, a high-purity lithium hydroxide product is obtained.

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