Method for recycling waste lithium iron phosphate battery

Abstract

The application belongs to the technical field of chemical products, and particularly relates to a method for recycling waste lithium iron phosphate batteries. The method comprises the following steps: firstly, a saturated solution of beta-cyclodextrin is prepared by using a sodium hydroxide solution; a beta-cyclodextrin / NaOH inclusion compound is prepared for standby; a waste lithium iron phosphate battery is sequentially discharged, disassembled, crushed and sieved to obtain waste lithium iron phosphate recovery powder; the prepared waste lithium iron phosphate recovery powder is taken, acid liquor and a reducing agent are added to the waste lithium iron phosphate recovery powder, acid immersion treatment is performed, and ion-rich filtrate B is obtained by filtration; the prepared beta-cyclodextrin / NaOH inclusion compound is added to the obtained ion-rich filtrate B, stirring is continuously performed, the pH value of the filtrate is adjusted to 1.5-5.5, Cu 2+ and Al 3+ impurities are precipitated, and filtrate C is obtained by filtration; a phosphate ion supplement is added to the filtrate C, an oxidizing agent is simultaneously added, the pH value of the solution is adjusted to 1-3, FePO4 is precipitated, a lithium ion precipitant is added to the filtrate, and Li2CO3 is obtained. The process flow of the method is short, the production process is safe and reliable, and the product has high purity.

Description

Technical Field

[0001] This invention belongs to the field of chemical products technology, specifically relating to a method for recycling and reusing waste lithium iron phosphate batteries. Background Technology

[0002] In recent years, with the rapid development of the new energy industry and the large-scale popularization of new energy applications, the demand for green, sustainable, circular, and efficient energy has become the focus and goal of future development. Since the first batch of new energy vehicles were put into use, a portion of lithium-ion batteries are now reaching their peak retirement period. With the current rise in the price of lithium iron phosphate (LFP) batteries, the recycling of used LFP batteries is also increasing. Currently, the recycling of LFP batteries mainly relies on direct pyrometallurgical repair and hydrometallurgical recycling. Pyrometallurgical recycling has the advantage of simple processes and short recycling flow, but it has stringent requirements for recycled materials and high requirements for recycling equipment, resulting in high energy consumption. While hydrometallurgical recycling can achieve the recycling of multiple components, the recycling process is long, and the amount of wastewater generated during recycling is large. Both pyrometallurgical and hydrometallurgical recycling currently face a major challenge: the removal of valuable metal impurities from used LFP cathode materials.

[0003] Due to the difficulties in large-scale industrial production, most companies currently use the following process for recycling waste lithium iron phosphate batteries: 1) Discharging; 2) Crushing; 3) High-temperature calcination to remove electrolyte binder and separator; 4) Sieving to remove copper-aluminum mixed powder, obtaining carbon-based lithium iron phosphate mixed powder; 5) Acid leaching of the carbon-based lithium iron phosphate mixed powder for valuable component recovery. The carbon-based lithium iron phosphate mixed powder obtained by the above method contains copper and aluminum impurities far exceeding recycling standards. To recover iron phosphate, a precipitation method is needed to remove copper and aluminum impurities beforehand. However, the problem is that iron and aluminum ions have similar properties, and the precipitation conditions for ferrous phosphate, iron phosphate, and aluminum phosphate are very similar. Adjusting the pH by adding sodium hydroxide or ammonia not only fails to remove aluminum but also causes iron and aluminum to co-precipitate due to locally high pH during pH adjustment, making them difficult to clean and distinguish, resulting in resource waste.

[0004] A typical Chinese patent application, publication number "CN 113737018 A", discloses a "method for recycling positive electrode materials from waste batteries". This method includes the following steps: Step 1: Discharging, disassembling, roasting, peeling, and crushing the waste batteries to separate the waste lithium iron phosphate battery positive electrode powder; Step 2: Slurrying the lithium iron phosphate positive electrode powder with water and then leaching it with sulfuric acid. After leaching, solid-liquid separation is performed to obtain leachate and leachate residue; Step 3: Adjusting the pH of the leachate with alkali and adding iron powder to remove copper, resulting in a purified solution; Step 4: Adding sodium phosphate to the purified solution according to the iron and phosphorus ratio. The purified lithium iron phosphate leachate, alkali, and oxidizing agent hydrogen peroxide are added simultaneously in a certain proportion. During this process, the pH of the solution is adjusted to 1.5-3.5 to precipitate iron phosphate. After solid-liquid separation, iron phosphate precipitate is obtained; Step 5: The filtrate is a lithium-containing solution. Carbon dioxide is passed through the filtrate to obtain precipitated lithium. The above invention has a typical problem: when removing aluminum impurities by adding an alkaline solution, the alkaline solution used is a sodium hydroxide solution; if a high concentration of sodium hydroxide solution is added, it will cause a momentary local OH- ionization in the solution. - Excessive concentration causes iron and aluminum to precipitate simultaneously, resulting in resource waste; if a lower concentration of sodium hydroxide solution is used, not only will the amount of wastewater treated increase, but the yield will also decrease, and the production cost will increase significantly.

[0005] Cyclodextrin (CD) is a green, biodegradable, and cost-effective cyclic oligosaccharide compound. Based on the number of glucose units, it can be classified into α-CD, β-CD, and γ-CD. Among them, β-CD is the most widely used, possessing a hydrophilic edge and a moderately hydrophobic molecular cavity, providing hydrophobic binding sites for inorganic ions. β-Cyclodextrin is compounded with sodium hydroxide to prepare a β-Cyclodextrin / NaOH inclusion complex. In the recycling of spent lithium iron phosphate batteries, the β-Cyclodextrin / NaOH inclusion complex is used to adjust the pH of the solution, allowing for stable pH control and more precise separation and removal of aluminum impurities. This effectively improves product purity and increases the recovery rate of valuable metals.

[0006] In view of the above situation, this invention is proposed. Summary of the Invention

[0007] The present invention aims to solve the above-mentioned technical problems and provide a method for recycling and reusing waste lithium iron phosphate batteries. The method has a simple process flow, safe and reliable production process, high stability, and can effectively improve product purity and increase the recovery rate of valuable metals.

[0008] The technical solution of the present invention is as follows: A method for recycling and reusing waste lithium iron phosphate batteries, the method comprising the following steps:

[0009] (1) Add sodium hydroxide particles to deionized water to prepare sodium hydroxide solution;

[0010] (2) Add β-cyclodextrin to deionized water and heat to 90°C to prepare a saturated β-cyclodextrin solution;

[0011] (3) Add the saturated β-cyclodextrin solution prepared in step (2) to the reaction vessel, and add the sodium hydroxide solution prepared in step (1) to it. Heat to 60°C and keep warm, stir continuously for 4 hours, and then cool to room temperature to obtain β-cyclodextrin / NaOH inclusion complex solution A.

[0012] (4) Spray dry the β-cyclodextrin / NaOH inclusion complex solution A prepared in step (3) and pass it through a 100-mesh sieve to obtain the β-cyclodextrin / NaOH inclusion complex for later use;

[0013] (5) Waste lithium iron phosphate batteries are discharged, disassembled, crushed and screened in sequence to obtain waste lithium iron phosphate recycled powder;

[0014] (6) Take the waste lithium iron phosphate recycling powder prepared in step (5), add acid and reducing agent to it, stir continuously, carry out acid leaching treatment, and filter to obtain ion-rich filtrate B.

[0015] (7) Add the β-cyclodextrin / NaOH inclusion complex prepared in step (4) to the ion-rich filtrate B obtained in step (6), stir continuously, adjust the pH of the filtrate to between 1.5 and 5.5, and precipitate Cu. 2+ And Al 3+ After filtering to remove impurities, filtrate C was obtained.

[0016] (8) Add phosphate ion supplement to the filtrate C obtained in step (7), add oxidant and adjust the pH of the solution to between 1 and 3 to precipitate FePO4, and then add lithium ion precipitant to the filtrate to obtain Li2CO3.

[0017] Preferably, in step (1), the concentration of the sodium hydroxide solution is 1.0-3.5 mol / L.

[0018] Preferably, in step (6), the acid solution is one or a combination of hydrochloric acid, sulfuric acid, nitric acid and citric acid.

[0019] Preferably, in step (6), the reducing agent is iron powder.

[0020] Preferably, step (7) is completed entirely in a protective atmosphere, and the protective gas used in step (7) is one of N2, Ar and He, and the purity of the protective gas is above 99.96%.

[0021] Preferably, in step (8), the phosphate ion supplement is one of sodium phosphate and phosphoric acid; the oxidant is one of oxygen, hydrogen peroxide, peracetic acid and sodium dichromate; and the lithium ion precipitant is one of sodium carbonate, sodium bicarbonate and CO2.

[0022] Due to the adoption of the above technical solution, the beneficial effects of the present invention are as follows:

[0023] This invention provides high-purity iron phosphate and lithium carbonate products from recycled waste lithium iron phosphate batteries, with a high recovery rate of valuable metals. Specifically, this invention represents a breakthrough improvement on existing waste lithium iron phosphate battery recycling processes. When using alkaline solution to adjust the pH and remove aluminum impurities, a self-made β-cyclodextrin / NaOH inclusion complex is used. Utilizing the slow and stable release of hydroxide ions by the β-cyclodextrin / NaOH inclusion complex, the pH of the solution is kept consistent, effectively preventing instantaneous localized high hydroxide ion concentrations and the co-precipitation of aluminum impurities and iron. This efficiently removes aluminum impurities, improving the recovery rate of iron phosphate and increasing product purity. Furthermore, copper impurities are also efficiently removed. Specifically, the excess reducing agent iron not only reduces ferrous ions to ferrous ions but also displaces copper ions in the solution. The remaining small amount of copper ions can be further removed by the stable and precise pH adjustment using the β-cyclodextrin / NaOH inclusion complex. This efficient removal of copper impurities also effectively improves product purity.

[0024] The process of this invention is concise, safe, reliable, and highly stable. Specifically, the recycling and reuse of waste lithium iron phosphate batteries involves not only the preparation of β-cyclodextrin / NaOH inclusion complexes but also the recycling of iron phosphate and lithium carbonate products. The entire production process is controlled under normal pressure and non-high temperature (not exceeding 100°C) conditions, ensuring safety, reliability, and high stability. Detailed Implementation

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Example 1

[0027] A method for recycling and reusing waste lithium iron phosphate batteries, the method comprising the following steps:

[0028] First, prepare the β-cyclodextrin / NaOH inclusion complex for later use. The specific steps are as follows:

[0029] (1) Add sodium hydroxide particles to deionized water to prepare a sodium hydroxide solution with a concentration of 1 mol / L;

[0030] (2) Add β-cyclodextrin to deionized water and heat to 90°C to prepare a saturated β-cyclodextrin solution;

[0031] (3) Add the saturated β-cyclodextrin solution prepared in step (2) to the reaction vessel, and add the same volume of sodium hydroxide solution prepared in step (1) to it. Heat to 60°C and keep warm, stir continuously for 4 hours, and then cool to room temperature to obtain β-cyclodextrin / NaOH inclusion complex solution A.

[0032] (4) Spray dry the β-cyclodextrin / NaOH inclusion complex solution A prepared in step (3) and pass it through a 100-mesh sieve to obtain the β-cyclodextrin / NaOH inclusion complex for later use;

[0033] Then, iron phosphate and lithium carbonate products are recovered from the spent lithium iron phosphate batteries. The specific steps are as follows:

[0034] (5) Waste lithium iron phosphate batteries are sequentially discharged, disassembled, crushed, and screened to obtain waste lithium iron phosphate recycling powder. Waste lithium iron phosphate batteries refer to waste battery packs or waste single cells;

[0035] (6) Take 100g of the waste lithium iron phosphate recovery powder prepared in step (5). The main element content of the waste lithium iron phosphate recovery powder is shown in Table 1. Add 300ml of sulfuric acid with a volume concentration of 30% and 10g of reducing agent iron powder to it. Stir continuously and carry out acid leaching treatment. Filter to obtain ion-rich filtrate B. In this step, the addition of reducing agent can reduce iron ions to ferrous ions. Because ferrous ions have a higher pH value when precipitating compared to iron ions, the precipitation loss of iron in the solution can be avoided in the subsequent process of adjusting the pH value to remove impurity aluminum. At the same time, the reducing agent can also replace the impurity copper in the solution.

[0036] (7) Add the β-cyclodextrin / NaOH inclusion complex prepared in step (4) to the ion-rich filtrate B obtained in step (6), stir continuously, adjust the pH of the filtrate to 1.5, and precipitate Cu. 2+ And Al 3+ After removing impurities, filter to obtain filtrate C; step (7) is carried out under nitrogen protection throughout;

[0037] (8) Add sodium phosphate as a phosphate ion supplement to the filtrate C obtained in step (7), and add 50 ml of hydrogen peroxide at the same time. Adjust the pH of the solution to 2 by β-cyclodextrin / NaOH inclusion complex to precipitate FePO4. Then add sodium carbonate precipitant to the filtrate to obtain Li2CO3.

[0038] The collected FePO4 and Li2CO3 were dried and weighed, and the purity of the product was analyzed. Filtrate C was also taken, and the element Cu in filtrate C was analyzed. 2+ And Al 3+ Content (measurement of element Cu in filtrate C) 2+ And Al 3+ The content was measured using an ICP spectrometer.

[0039] The analytical results are as follows: the purity of FePO4 product reached 99.87%, and the recovery rate of valuable metal Fe reached 99.90%; the purity of Li2CO3 product reached 98.13%, and the recovery rate of valuable metal Li reached 99.90%; the element Cu in filtrate C... 2+ And Al 3+ The contents were 3 ppm and 184 ppm, respectively; after step (7), the impurity Cu 2+ And Al 3+ The removal rates of the contained substances reached 99.99% and 99.98%, respectively.

[0040] Table 1. Element content in recycled lithium iron phosphate powder

[0041] element Fe Li Al Cu content(%) 35.62 4.32 1.17 0.02

[0042] Example 2

[0043] First, prepare NaOH solution A for later use. The specific method is as follows: Add sodium hydroxide particles to deionized water to prepare sodium hydroxide solution A with a concentration of 1 mol / L for later use.

[0044] Then, iron phosphate and lithium carbonate products are recovered from the spent lithium iron phosphate batteries. The specific steps are as follows:

[0045] (1) Waste lithium iron phosphate batteries are sequentially discharged, disassembled, crushed, and screened to obtain waste lithium iron phosphate recycling powder. Waste lithium iron phosphate batteries refer to waste battery packs or waste single cells;

[0046] (2) Take 100g of the waste lithium iron phosphate recovery powder prepared in step (1). The main element content of the waste lithium iron phosphate recovery powder is shown in Table 1. Add 300ml of sulfuric acid with a volume concentration of 30% and 10g of reducing agent iron powder to it. Stir continuously and carry out acid leaching treatment. Filter to obtain ion-rich filtrate B. In this step, the addition of reducing agent can reduce iron ions to ferrous ions. Because ferrous ions have a higher pH value when precipitating compared to iron ions, the precipitation loss of iron in the solution can be avoided in the subsequent process of adjusting the pH value to remove impurity aluminum. At the same time, the reducing agent can also replace the impurity copper in the solution.

[0047] (3) Add the prepared sodium hydroxide solution A to the ion-rich filtrate B obtained in step (2), stir continuously, adjust the pH of the filtrate to 1.5, and precipitate Cu. 2+ And Al 3+ After removing impurities, filtrate C was obtained by filtration; step (3) was carried out under nitrogen protection throughout.

[0048] (4) Add sodium phosphate to the filtrate C obtained in step (3) as a phosphate ion supplement, and add 50 ml of hydrogen peroxide and adjust the pH of the solution to 2 by sodium hydroxide solution A to precipitate FePO4. Then add sodium carbonate precipitant to the filtrate to obtain Li2CO3.

[0049] The collected FePO4 and Li2CO3 were dried and weighed, and the purity of the product was analyzed. Filtrate C was also taken, and the element Cu in filtrate C was analyzed. 2+ And Al 3+ Content (measurement of element Cu in filtrate C) 2+ And Al 3+ The content was measured using an ICP spectrometer.

[0050] The analytical results are as follows: the purity of FePO4 product reached 95.31%, and the recovery rate of valuable metal Fe reached 93.97%; the purity of Li2CO3 product reached 92.44%, and the recovery rate of valuable metal Li reached 94.11%; the element Cu in filtrate C... 2+ And Al 3+ The contents were 13 ppm and 986 ppm, respectively; after step (3), the impurity Cu 2+ And Al 3+ The removal rates of the contained substances reached 99.94% and 99.92%, respectively.

[0051] Comparative Example 1

[0052] The difference between this comparative example and Example 2 is that the concentration of NaOH solution A is different. In this example, the concentration of NaOH solution A is 3 mol / L.

[0053] The analytical results are as follows: the purity of FePO4 product reached 93.15%, and the recovery rate of valuable metal Fe reached 91.24%; the purity of Li2CO3 product reached 91.33%, and the recovery rate of valuable metal Li reached 93.54%; the element Cu in filtrate C... 2+ And Al 3+ The contents were 5 ppm and 813 ppm, respectively; after step (3), the impurity Cu 2+ And Al 3+ The removal rates of the contained substances reached 99.98% and 99.93%, respectively.

[0054] The above description is a detailed description of the preferred embodiments of the present invention. However, the embodiments are not intended to limit the scope of the patent application of the present invention. All equivalent changes or modifications made under the technical spirit of the present invention should fall within the patent scope covered by the present invention.

Claims

1. A method for recycling and reusing waste lithium iron phosphate batteries, characterized in that: The method includes the following steps: (1) Add sodium hydroxide particles to deionized water to prepare sodium hydroxide solution; (2) Add β-cyclodextrin to deionized water and heat to 90°C to prepare a saturated β-cyclodextrin solution; (3) Add the saturated β-cyclodextrin solution prepared in step (2) to the reaction vessel, and add the sodium hydroxide solution prepared in step (1) to it. Heat to 60°C and keep warm, stir continuously for 4 hours, and then cool to room temperature to obtain β-cyclodextrin / NaOH inclusion complex solution A. (4) Spray dry the β-cyclodextrin / NaOH inclusion complex solution A prepared in step (3) and pass it through a 100-mesh sieve to obtain the β-cyclodextrin / NaOH inclusion complex for later use; (5) Waste lithium iron phosphate batteries are discharged, disassembled, crushed and screened in sequence to obtain waste lithium iron phosphate recycled powder; (6) Take the waste lithium iron phosphate recycling powder prepared in step (5), add acid and reducing agent to it, stir continuously, carry out acid leaching treatment, and filter to obtain ion-rich filtrate B. (7) Add the β-cyclodextrin / NaOH inclusion complex prepared in step (4) to the ion-rich filtrate B obtained in step (6), stir continuously, adjust the pH of the filtrate to between 1.5 and 5.5, and precipitate Cu. 2+ And Al 3+ After filtering to remove impurities, filtrate C was obtained. (8) Add phosphate ion supplement to the filtrate C obtained in step (7), add oxidant and adjust the pH of the solution to between 1 and 3 to precipitate FePO4, and then add lithium ion precipitant to the filtrate to obtain Li2CO3.

2. The method for synthesizing and preparing iron phosphate according to claim 1, characterized in that: In step (1), the concentration of the sodium hydroxide solution is 1.0-3.5 mol / L.

3. The method for recycling and reusing waste lithium iron phosphate batteries according to claim 1, characterized in that: In step (6), the acid solution is one or a combination of hydrochloric acid, sulfuric acid, nitric acid and citric acid.

4. The method for recycling and reusing waste lithium iron phosphate batteries according to claim 1, characterized in that: In step (6), the reducing agent is iron powder.

5. The method for recycling and reusing waste lithium iron phosphate batteries according to claim 1, characterized in that: Step (7) is completed entirely in a protective atmosphere, and the protective gas used in step (7) is one of N2, Ar and He, with a purity of 99.96% or higher.

6. The method for recycling and reusing waste lithium iron phosphate batteries according to claim 1, characterized in that: In step (8), the phosphate ion supplement is one of sodium phosphate and phosphoric acid; the oxidant is one of oxygen, hydrogen peroxide, peracetic acid and sodium dichromate; and the lithium ion precipitant is one of sodium carbonate, sodium bicarbonate and CO2.