A process for recovering rare earth elements from low-concentration rare earth solutions

Abstract

This invention discloses a process for recovering rare earth elements from low-concentration rare earth solutions. The process involves disassembling retired lithium-ion batteries after discharge to extract the negative electrode graphite material. This graphite is then heat-treated to remove organic binders, followed by acid leaching to obtain purified graphite. The purified graphite is then oxidized and intercalated to form graphene oxide, which is subsequently modified with sulfonate groups to obtain a sulfonated graphene oxide adsorbent. This adsorbent can selectively adsorb rare earth ions such as lanthanum in a sulfuric acid system containing aluminum impurities, exhibiting high adsorption capacity and selectivity. This invention features low-cost, simple, and environmentally friendly processes, achieving high-value conversion of retired lithium-ion battery negative electrode graphite and providing a low-cost solution for the green enrichment and recovery of low-concentration rare earth ions.

Description

Technical Field

[0001] This invention relates to the fields of resource utilization technology for retired lithium batteries and green recycling technology for rare earth resources, specifically to a process for recovering rare earths from low-concentration rare earth solutions. Background Technology

[0002] During the extraction of rare earth resources, a large amount of wastewater containing low concentrations of rare earth ions is inevitably generated. This not only wastes rare earth resources but also causes water pollution. Therefore, the comprehensive recovery of valuable rare earth elements remaining in rare earth wastewater during rare earth resource development has become an urgent need for the industry. Researchers have developed various technologies for treating low-concentration rare earth wastewater, including chemical precipitation, ion exchange, electrochemical methods, and membrane separation. Among these, adsorption has become an ideal technical approach for treating low-concentration rare earth wastewater due to its significant advantages such as simple operation, low cost, high renewability, and low secondary waste generation. Adsorbents, as the core of adsorption methods, commonly used types include natural zeolites, biochar, clay minerals, and metal-organic frameworks. However, these adsorbents generally suffer from technical shortcomings such as low adsorption capacity, poor selectivity, and difficulty in controlling stability, limiting their large-scale application in low-concentration rare earth recovery.

[0003] my country is the world's largest producer and consumer of lithium-ion batteries, and the number of retired lithium-ion batteries is increasing dramatically every year, resulting in millions of tons of waste graphite anodes that are difficult to utilize effectively. Therefore, developing an adsorbent using retired lithium-ion battery anode graphite as raw material, characterized by low cost, simple process, and scalable preparation, and its targeted application in the enrichment and recovery of low-concentration rare earth ions, can not only solve the problem of recycling retired lithium-ion battery anode graphite but also provide a new pathway for the high-value recovery of low-concentration rare earth resources. This has significant scientific and industrial value in promoting the greening, high-value utilization, and recycling of rare earth resources.

[0004] Graphite, as a highly stable carbon-based material, has broad application prospects in adsorption, new energy, and advanced materials. Graphene oxide, as a core derivative of graphite, exhibits great potential in adsorption and separation due to its unique layered structure and abundant active sites. However, conventional carbon-based materials show poor selectivity in the competitive adsorption of rare earth ions and aluminum ions. Their surface active sites are unable to differentiate between the two hard acid ions, resulting in insufficient selective adsorption capacity and failing to meet the demand for efficient recovery of low-concentration rare earths from aluminum-containing impurity systems. Summary of the Invention

[0005] To address the difficulties in the resource recovery and utilization of decommissioned graphite and the low adsorption capacity and poor cycle stability of graphene oxide adsorbents, this invention provides a rare earth recovery process from a low-concentration rare earth solution. This achieves high-value utilization of decommissioned lithium-ion battery anode graphite and provides a green, low-cost, low-concentration rare earth ion enrichment and recovery scheme, filling a gap in existing technologies.

[0006] To achieve the above objectives, this invention proposes a process for recovering rare earth elements from low-concentration rare earth solutions, comprising the following steps: (1) After the retired lithium battery is discharged, the waste negative electrode graphite is placed in a muffle furnace for heat treatment to obtain precursor graphite. (2) The precursor graphite obtained in step (1) and the oxidant and sulfuric acid solution are placed in an ultrasonic microwave reactor and stirred continuously for 5 to 120 min to obtain an acid-impregnated mixed slurry. The acid-impregnated mixed slurry is then filtered and dried under vacuum at 45 °C for 12 h to obtain impurity-free graphite. (3) The graphite was purified by the Hummers method and then freeze-dried in a freeze dryer for 24 h to obtain graphene oxide; (4) Graphene oxide is dispersed in DMF solution, a certain proportion of sulfonating reagent is added, and then the product is wet-milled in a planetary ball mill. The product is washed multiple times with anhydrous ethanol and ultrapure water, and then freeze-dried for 24 h to obtain sulfonated graphene oxide adsorbent. The sulfonated graphene oxide adsorbent is used to selectively adsorb rare earth ions in a sulfuric acid system containing aluminum impurities, and the adsorption capacity for rare earth ions is 100~400 mg / g, and the adsorption separation coefficient between rare earth ions and aluminum ions is greater than 3000. The initial concentration range of rare earth ions and aluminum ions is 10~100 mg / L.

[0007] Preferably, the specific method for discharging in step (1) is to immerse the retired lithium battery in a 10wt% sodium chloride solution for 24 hours to complete the discharge.

[0008] Preferably, in step (1), the heat treatment temperature is 300~900 ℃, the heat treatment time is 1~24 h, and the heat treatment atmosphere is a hydrogen-argon mixture, wherein the hydrogen volume concentration is 5%.

[0009] Preferably, in step (2), the oxidant includes one or more of hydrogen peroxide, nitric acid, sodium chlorate, sodium hypochlorite, and sodium perchlorate, the sulfuric acid concentration is 0.1~2 mol / L, and the solid-liquid ratio of the precursor graphite to the mixed solution of oxidant and sulfuric acid is 1:6~1:100, with the unit corresponding to the solid-liquid ratio being g:mL.

[0010] Preferably, in step (2), the ultrasonic-microwave reaction temperature is 25~80 ℃, the microwave power is 200~900 W, the ultrasonic power is 200~1200 W, and the stirring rate is 200~400 r / min.

[0011] Preferably, the Hummers method in step (3) is as follows: Weigh 1-3 g of sodium nitrate and purified graphite in a mass ratio of 0.5-0.7:1 and place them in a 250 mL flask. Then add 30 mL of concentrated sulfuric acid to the flask and stir for half an hour under ice bath conditions. Continue to add 5 g of potassium permanganate at low temperature, slowly adding it over one hour. After the addition is completed, react the system at 35 °C for two hours. Add 150 mL of ultrapure water to the flask and raise the temperature to 95 °C to react for one hour. Then lower the temperature to 80 °C and add 4-15 mL of 30wt% hydrogen peroxide. Wait for it to cool to room temperature, wash it with hydrochloric acid as the washing solution, centrifuge it at 9000 r / min for 10 minutes and rinse it several times. After testing with barium chloride and finding no precipitate, wash it with ultrapure water until neutral and freeze-dry it in a vacuum freeze dryer for 24 h to obtain graphene oxide adsorbent.

[0012] Preferably, in step (4), the sulfonating agent includes one or more of sulfur trioxide pyridine complex, aminobenzenesulfonic acid, and fuming sulfuric acid, and the mass ratio of the sulfonating agent to graphene oxide is 1:1 to 1:10.

[0013] Preferably, in step (4), the content of oxygen-containing functional groups on the surface of sulfonated graphene oxide is 3~20 mmol / g, of which the content of sulfonic acid groups is 1~20 mmol / g.

[0014] A sulfonated graphene oxide adsorbent is used for the selective adsorption of low concentrations of rare earth elements.

[0015] Preferably, the above-mentioned sulfonated graphene oxide adsorbent is added to a sulfuric acid system solution containing rare earth ions and aluminum ions, and shaken on a shaker at 200 r / min, wherein the solid-liquid ratio of the sulfonated graphene oxide adsorbent to the sulfuric acid system solution containing rare earth ions and aluminum ions is 1 mg: 8 mL.

[0016] Preferably, the adsorption conditions in the sulfuric acid system solution are a temperature of 25 °C, a reaction time of 30 min, and a pH of 5.

[0017] The technical solution adopted in this invention has the following advantages compared with the prior art: 1. The low-concentration rare earth ion adsorbent based on waste graphite anode prepared by this invention uses solid waste decommissioned lithium battery anode graphite as the sole carbon source, realizing resource recycling and high-quality reuse of waste graphite anode.

[0018] 2. The low-concentration rare earth ion adsorbent based on waste graphite anode prepared in this invention is specifically applied to the enrichment and recovery of low-concentration rare earth ions. Addressing the problem of poor rare earth selectivity in sulfuric acid systems containing aluminum impurities, sulfonation modification is used to covalently graft sulfonic acid groups onto the surface of graphene oxide, directionally introducing hard base groups with preferential coordination ability for hard acid rare earth ions. Simultaneously, ball milling further expands the graphene sheets, increasing the interlayer spacing and specific surface area. This results in a maximum adsorption capacity of rare earth ions greater than 100 mg / g, and an adsorption separation coefficient between rare earth ions and aluminum ions greater than 3000, significantly higher than that of unmodified impurity-removing graphite and graphene oxide adsorbents.

[0019] 3. The low-concentration rare earth ion adsorbent based on waste graphite negative electrode prepared by this invention retains its complete morphology after adsorption. Attached Figure Description

[0020] Figure 1 This is a SEM image of the sulfonated graphene oxide adsorbent in Example 1.

[0021] Figure 2 This is a SEM image of the sulfonated graphene oxide adsorbent after adsorption in a sulfuric acid system containing rare earth ions and aluminum impurities in Example 1.

[0022] Figure 3 The image shows the FT-IR spectrum of the sulfonated graphene oxide adsorbent in Example 1.

[0023] Figure 4 The graph shows the concentrations of sulfonated graphene oxide adsorbent in a sulfuric acid system containing rare earth ions and aluminum impurities in Example 4. The horizontal axis represents the concentration of rare earth ions in the sulfuric acid system containing rare earth ions and aluminum impurities, and the vertical axis represents the amount of rare earth adsorption.

[0024] Figure 5 The graph shows the different concentrations of the graphite adsorbent used in Comparative Example 2 in a sulfuric acid system containing rare earth ions and aluminum impurities. The horizontal axis represents the concentration of rare earth ions in the sulfuric acid system containing rare earth ions and aluminum impurities, and the vertical axis represents the amount of rare earth adsorption. Detailed Implementation

[0025] In all embodiments and comparative examples of this invention, the adsorption performance test was conducted under the same standard conditions: the competitive adsorption system was a sulfuric acid system of rare earth ions and aluminum ions, with the initial concentration range of the two ions being 10~100 mg / L; 5 mg of adsorbent was added to 40 mL of the above mixed solution, the pH of the solution was adjusted to 5, and the solution was placed in a constant temperature shaker at 25 ℃ and shaken at 200 r / min for 30 min for adsorption.

[0026] Example 1 The specific steps for preparing rare earth ion adsorbents are as follows: (1) The retired lithium battery was soaked in a 10wt% sodium chloride solution for 24 h to complete the discharge. The waste negative electrode graphite was placed in a muffle furnace and pretreated at 500 °C for 5 h with a hydrogen-argon mixture in the heat treatment atmosphere to obtain the precursor graphite. The hydrogen volume concentration was 5%. (2) Take 1.2 g of the precursor graphite obtained in step (1), mix it with 20 mL of 30 wt% hydrogen peroxide and 100 mL of 2 mol / L sulfuric acid solution, and transfer it to an ultrasonic microwave reactor. Under the conditions of temperature control at 35 ℃ and stirring rate at 300 r / min, turn on the ultrasonic and microwave simultaneously, set the microwave power to 600 W and the ultrasonic power to 700 W, and continue stirring for 120 min. After the reaction is completed, filter the resulting acid-impregnated mixed slurry and dry it under vacuum at 45 ℃ for 12 h to obtain impurity-free graphite. (3) The Hummers method was used to remove impurities from the graphite. 0.75 g of sodium nitrate and 1.25 g of graphite were placed in a 250 mL flask. Then, 30 mL of concentrated sulfuric acid was added to the flask and stirred for half an hour under ice bath conditions. 5 g of potassium permanganate was added slowly over an hour at low temperature. After the addition was completed, the system was reacted at 35 °C for two hours. 150 mL of ultrapure water was added to the flask, and the temperature was raised to 95 °C and reacted for one hour. Then, the temperature was lowered to 80 °C and 4-15 mL of 30 wt% hydrogen peroxide was added. After cooling to room temperature, the system was washed with hydrochloric acid and centrifuged at 9000 r / min for 10 minutes. After rinsing several times, barium chloride was used to detect the absence of precipitate. The system was then washed with ultrapure water until neutral and freeze-dried in a vacuum freeze dryer for 24 h to obtain graphene oxide adsorbent. (4) 1 g of graphene oxide was dispersed in 100 mL of DMF solution, 0.1 g of sulfur trioxide pyridine complex was added, and the product was then placed in a planetary ball mill for wet milling for 4 h. The product was washed multiple times with anhydrous ethanol and ultrapure water, and then freeze-dried for 24 h to obtain sulfonated graphene oxide. The sulfonated graphene oxide adsorbent prepared in this embodiment has a uniform distribution of carbon, oxygen, and sulfur. Scanning electron micrographs before and after rare earth adsorption are shown below. Figure 1 , Figure 2 As shown, the materials are all uniformly sized, worm-like porous structures with a particle size of about 20 μm. The three-dimensional structure after adsorption does not show significant differences from the morphology before adsorption, indicating that the structure is intact and has the potential for regeneration; the Fourier transform infrared spectrum is shown below. Figure 3 As shown, 1062, 1240 cm -1 The absorption peak at 634 cm⁻¹ is attributed to the asymmetric stretching vibration of the S=O bond in the sulfonic acid group. -1The absorption peak at the point is attributed to the stretching vibration of the CS bond. The newly added characteristic peaks of the S=O bond and the CS bond prove that the sulfonic acid group was successfully grafted onto the graphene oxide. The maximum rare earth adsorption capacity of the sulfonated graphene oxide adsorbent under the competitive adsorption conditions of aluminum and rare earths reached 300.4 mg / g, and the adsorption separation coefficient between rare earth ions and aluminum ions reached 3134, which proves its excellent rare earth adsorption capacity and selectivity.

[0027] Example 2 The specific steps for preparing rare earth ion adsorbents are as follows: (1) The retired lithium battery was soaked in a 10wt% sodium chloride solution for 24 h to complete the discharge. The waste negative electrode graphite was placed in a muffle furnace and pretreated at 900 °C for 1 h with a hydrogen-argon mixture in the heat treatment atmosphere to obtain the precursor graphite. The hydrogen volume concentration was 5%. (2) Take 1 g of the precursor graphite obtained in step (1), mix it with 20 mL of nitric acid and 20 mL of 1 mol / L sulfuric acid solution, and transfer it to an ultrasonic microwave reactor. Under the conditions of temperature control at 60 ℃ and stirring rate at 350 r / min, turn on the ultrasonic and microwave simultaneously, set the microwave power to 500 W and the ultrasonic power to 800 W, and continue stirring for 30 min. After the reaction is completed, filter the resulting acid-impregnated mixed slurry and dry it under vacuum at 45 ℃ for 12 h to obtain impurity-free graphite. (3) The Hummers method was used to remove impurities from the graphite. 1 g of sodium nitrate and 1.66 g of graphite were placed in a 250 mL flask. Then, 30 mL of concentrated sulfuric acid was added to the flask and stirred for half an hour under ice bath conditions. 5 g of potassium permanganate was added slowly over an hour at low temperature. After the addition was completed, the system was reacted at 35 °C for two hours. 150 mL of ultrapure water was added to the flask, and the temperature was raised to 95 °C and reacted for one hour. Then, the temperature was lowered to 80 °C and 4-15 mL of 30 wt% hydrogen peroxide was added. After cooling to room temperature, the system was washed with hydrochloric acid and centrifuged at 9000 r / min for 10 minutes. After rinsing several times, barium chloride was used to detect the absence of precipitate. The system was then washed with ultrapure water until neutral and freeze-dried in a vacuum freeze dryer for 24 h to obtain graphene oxide adsorbent. (4) 1 g of graphene oxide was dispersed in 100 mL of DMF solution, 0.2 g of aminobenzenesulfonic acid was added, and the product was then placed in a planetary ball mill for wet milling for 4 h. The product was washed multiple times with anhydrous ethanol and ultrapure water, and then freeze-dried for 24 h in a freeze dryer to obtain sulfonated graphene oxide. The sulfonated graphene oxide adsorbent prepared in this embodiment has a uniform distribution of carbon, oxygen, sulfur, and nitrogen, resulting in a worm-like porous structure with a uniform particle size of approximately 30 μm. Under competitive adsorption conditions between aluminum and rare earth elements, the sulfonated graphene oxide adsorbent achieved a maximum rare earth adsorption capacity of 287.2 mg / g, and an adsorption separation coefficient of 3004 between rare earth ions and aluminum ions, demonstrating its excellent rare earth adsorption capacity and selectivity.

[0028] Example 3 The specific steps for preparing rare earth ion adsorbents are as follows: (1) The retired lithium battery was soaked in a 10wt% sodium chloride solution for 24 h to complete the discharge. The waste negative electrode graphite was placed in a muffle furnace and pretreated at 300 °C for 24 h with a hydrogen-argon mixture in the heat treatment atmosphere to obtain the precursor graphite. The hydrogen volume concentration was 5%. (2) Take 2 g of the precursor graphite obtained in step (1), mix it with 2 mL of sodium chlorate and 10 mL of 2 mol / L sulfuric acid solution, and transfer it to an ultrasonic microwave reactor. Under the conditions of temperature control of 50 ℃ and stirring rate of 200 r / min, turn on the ultrasonic and microwave at the same time, set the microwave power to 900 W and the ultrasonic power to 1200 W, and continue stirring for 5 min. After the reaction is completed, filter the obtained acid-impregnated mixed slurry and dry it under vacuum at 45 ℃ for 12 h to obtain impurity-free graphite. (3) The Hummers method was used to remove impurities from the graphite. 0.9 g of sodium nitrate and 1.5 g of graphite were placed in a 250 mL flask. Then, 30 mL of concentrated sulfuric acid was added to the flask and stirred for half an hour under ice bath conditions. 5 g of potassium permanganate was added slowly over an hour at low temperature. After the addition was completed, the system was reacted at 35 °C for two hours. 150 mL of ultrapure water was added to the flask, and the temperature was raised to 95 °C and reacted for one hour. Then, the temperature was lowered to 80 °C and 4-15 mL of 30 wt% hydrogen peroxide was added. After cooling to room temperature, the system was washed with hydrochloric acid and centrifuged at 9000 r / min for 10 minutes. After rinsing several times, barium chloride was used to detect the absence of precipitate. The system was then washed with ultrapure water until neutral and freeze-dried in a vacuum freeze dryer for 24 h to obtain graphene oxide adsorbent. (4) 1 g of graphene oxide was dispersed in 100 mL of DMF solution, 1 g of fuming sulfuric acid was added, and the product was then placed in a planetary ball mill and wet-milled for 4 h. The product was washed multiple times with anhydrous ethanol and ultrapure water, and then freeze-dried for 24 h in a freeze dryer to obtain sulfonated graphene oxide. The sulfonated graphene oxide adsorbent prepared in this embodiment has a uniform distribution of carbon, oxygen, and sulfur, resulting in a uniformly sized sheet-like structure with a particle size of approximately 20 μm. Under competitive adsorption conditions between aluminum and rare earth elements, the sulfonated graphene oxide adsorbent achieved a maximum rare earth adsorption capacity of 101.8 mg / g, and an adsorption separation coefficient of 3198 between rare earth ions and aluminum ions, demonstrating its excellent rare earth adsorption capacity and selectivity.

[0029] Example 4 The specific steps for preparing rare earth ion adsorbents are as follows: (1) The retired lithium battery was soaked in a 10wt% sodium chloride solution for 24 h to complete the discharge. The waste negative electrode graphite was placed in a muffle furnace and pretreated at 600 °C for 3 h with a hydrogen-argon mixture in the heat treatment atmosphere to obtain the precursor graphite. The hydrogen volume concentration was 5%. (2) Take 3 g of the precursor graphite obtained in step (1), mix it with 2 mL of sodium hypochlorite and 40 mL of 1.5 mol / L sulfuric acid solution, and transfer it to an ultrasonic microwave reactor. Under the conditions of temperature control at 80 ℃ and stirring rate at 300 r / min, turn on the ultrasonic and microwave simultaneously, set the microwave power to 500 W and the ultrasonic power to 800 W, and continue stirring for 90 min. After the reaction is completed, filter the resulting acid-impregnated mixed slurry and dry it under vacuum at 45 ℃ for 12 h to obtain impurity-free graphite. (3) The Hummers method was used to remove impurities from the graphite. 0.8 g of sodium nitrate and 1.33 g of graphite were placed in a 250 mL flask. Then, 30 mL of concentrated sulfuric acid was added to the flask and stirred for half an hour under ice bath conditions. 5 g of potassium permanganate was added slowly over an hour at low temperature. After the addition was completed, the system was reacted at 35 °C for two hours. 150 mL of ultrapure water was added to the flask and the temperature was raised to 95 °C for one hour. Then, the temperature was lowered to 80 °C and 4-15 mL of 30 wt% hydrogen peroxide was added. After cooling to room temperature, the system was washed with hydrochloric acid and centrifuged at 9000 r / min for 10 minutes. After rinsing several times, barium chloride was used to detect the absence of precipitate. The system was then washed with ultrapure water until neutral and freeze-dried in a vacuum freeze dryer for 24 h to obtain graphene oxide adsorbent. (4) 1 g of graphene oxide was dispersed in 100 mL of DMF solution, 0.04 g of sulfur trioxide pyridine complex and 0.16 g of aminobenzenesulfonic acid were added, and the product was then placed in a planetary ball mill for wet milling for 4 h. The product was washed multiple times with anhydrous ethanol and ultrapure water, and then freeze-dried for 24 h to obtain sulfonated graphene oxide. The sulfonated graphene oxide adsorbent prepared in this embodiment has a uniform distribution of carbon, oxygen, sulfur, and nitrogen, resulting in a worm-like porous structure with a uniform particle size of approximately 15 μm. The graph shows the sulfonated graphene oxide adsorbent at different concentrations in a sulfuric acid system containing rare earth ions and aluminum impurities. Figure 4 As shown, the adsorption capacity of the adsorbent for rare earth ions increases linearly with the increase of the initial concentration. When the concentration increases to 100 mg / L, the adsorption capacity still does not reach saturation, reaching an extremely high value of 399.6 mg / g. The adsorption separation coefficient between rare earth ions and aluminum ions reaches 3065, which proves its excellent rare earth adsorption capacity and selectivity.

[0030] Example 5 The specific steps for preparing rare earth ion adsorbents are as follows: (1) The retired lithium battery was soaked in a 10wt% sodium chloride solution for 24 h to complete the discharge. The waste negative electrode graphite was placed in a muffle furnace and pretreated at 600 °C for 4 h with a hydrogen-argon mixture in the heat treatment atmosphere to obtain the precursor graphite. The hydrogen volume concentration was 5%. (2) Take 1.8 g of the precursor graphite obtained in step (1), mix it with 2 mL of sodium perchlorate and 98 mL of 0.5 mol / L sulfuric acid solution, and transfer it to an ultrasonic microwave reactor. Under the conditions of temperature control at 25 ℃ and stirring rate at 400 r / min, turn on the ultrasonic and microwave simultaneously, set the microwave power to 200 W and the ultrasonic power to 200 W, and continue stirring for 120 min. After the reaction is completed, filter the resulting acid-impregnated mixed slurry and dry it under vacuum at 45 ℃ for 12 h to obtain impurity-free graphite. (3) The Hummers method was used to remove impurities from the graphite. 0.5 g of sodium nitrate and 0.83 g of graphite were placed in a 250 mL flask. Then, 30 mL of concentrated sulfuric acid was added to the flask and stirred for half an hour under ice bath conditions. 5 g of potassium permanganate was added slowly over an hour at low temperature. After the addition was completed, the system was reacted at 35 °C for two hours. 150 mL of ultrapure water was added to the flask and the temperature was raised to 95 °C for one hour. Then, the temperature was lowered to 80 °C and 4-15 mL of 30 wt% hydrogen peroxide was added. After cooling to room temperature, the system was washed with hydrochloric acid and centrifuged at 9000 r / min for 10 minutes. After rinsing several times, barium chloride was used to detect the absence of precipitate. The system was then washed with ultrapure water until neutral and freeze-dried in a vacuum freeze dryer for 24 h to obtain graphene oxide adsorbent. (4) 1 g of graphene oxide was dispersed in 100 mL of DMF solution, 0.5 g of fuming sulfuric acid and 0.2 g of aminobenzenesulfonic acid were added, and the product was then placed in a planetary ball mill for wet milling for 4 h. The product was washed multiple times with anhydrous ethanol and ultrapure water, and then freeze-dried for 24 h in a freeze dryer to obtain sulfonated graphene oxide. The sulfonated graphene oxide adsorbent prepared in this embodiment has a uniform distribution of carbon, oxygen, sulfur, and nitrogen, resulting in a layered structure with a uniform particle size of approximately 20 μm. Under competitive adsorption conditions between aluminum and rare earth elements, the sulfonated graphene oxide adsorbent achieved a maximum rare earth adsorption capacity of 155.4 mg / g, and an adsorption separation coefficient of 3054 between rare earth ions and aluminum ions, demonstrating its excellent rare earth adsorption capacity and selectivity.

[0031] Comparative Example 1 The specific steps for preparing rare earth ion adsorbents are as follows: (1) The retired lithium battery was soaked in a 10wt% sodium chloride solution for 24 h to complete the discharge. The waste negative electrode graphite was placed in a muffle furnace and pretreated at 500 °C for 5 h with a hydrogen-argon mixture in the heat treatment atmosphere to obtain the precursor graphite. The hydrogen volume concentration was 5%. (2) Take 1.5 g of the precursor graphite obtained in step (1), mix it with 8 mL of hydrogen peroxide, 2 mL of sodium perchlorate and 140 mL of 2 mol / L sulfuric acid solution, and transfer it to an ultrasonic microwave reactor. Under the conditions of temperature control at 35 ℃ and stirring rate at 350 r / min, turn on the ultrasonic and microwave simultaneously, set the microwave power to 600 W and the ultrasonic power to 600 W, and continue stirring for 80 min. After the reaction is completed, filter the resulting acid-impregnated mixed slurry and dry it under vacuum at 45 ℃ for 12 h to obtain impurity-free graphite. (3) The Hummers method was used to remove impurities from the graphite. 0.7 g of sodium nitrate and 1.17 g of graphite were placed in a 250 mL flask. Then, 30 mL of concentrated sulfuric acid was added to the flask and stirred for half an hour under ice bath conditions. 5 g of potassium permanganate was added slowly over an hour at low temperature. After the addition was completed, the system was reacted at 35 °C for two hours. 150 mL of ultrapure water was added to the flask, and the temperature was raised to 95 °C and reacted for one hour. Then, the temperature was lowered to 80 °C and 4-15 mL of 30 wt% hydrogen peroxide was added. After cooling to room temperature, the system was washed with hydrochloric acid and centrifuged at 9000 r / min for 10 minutes. After rinsing several times, barium chloride was used to detect the absence of precipitate. The system was then washed with ultrapure water until neutral and freeze-dried in a vacuum freeze dryer for 24 h to obtain graphene oxide adsorbent. The graphene oxide adsorbent prepared in this comparative example has a uniform distribution of carbon and oxygen elements, resulting in a worm-like porous structure with a uniform particle size of approximately 5 μm. Under competitive adsorption conditions between aluminum and rare earth elements, the maximum rare earth adsorption capacity of the graphene oxide adsorbent reached 72.8 mg / g, and the adsorption separation coefficient between rare earth ions and aluminum ions was 5.92, demonstrating that its adsorption capacity and selectivity are significantly lower than those of the sulfonated graphene oxide adsorbent.

[0032] Comparative Example 2 The specific steps for preparing rare earth ion adsorbents are as follows: (1) The retired lithium battery was soaked in a 10wt% sodium chloride solution for 24 h to complete the discharge. The waste negative electrode graphite was placed in a muffle furnace and pretreated at 500 °C for 5 h with a hydrogen-argon mixture in the heat treatment atmosphere to obtain the precursor graphite. The hydrogen volume concentration was 5%. (2) Take 1.8 g of the precursor graphite obtained in step (1), mix it evenly with 180 mL of 2 mol / L sulfuric acid solution, and transfer it to an ultrasonic microwave reactor; under the conditions of temperature control at 35 ℃ and stirring rate at 400 r / min, turn on the ultrasonic and microwave simultaneously, set the microwave power to 700 W and the ultrasonic power to 600 W, and continue stirring for 120 min; after the reaction is completed, filter the obtained acid-impregnated mixed slurry, and dry it under vacuum at 45 ℃ for 12 h to obtain impurity-free graphite; The graphite adsorbent prepared in this comparative example exhibits a uniform distribution of carbon and oxygen elements, resulting in a layered structure with a uniform particle size of approximately 10 μm. The graphs show the graphite adsorbent at different concentrations in a sulfuric acid system containing rare earth ions and aluminum impurities. Figure 5 As shown, unmodified graphite exhibits extremely poor adsorption performance for rare earth ions, with a maximum adsorption capacity of only 3.33 mg / g at a rare earth ion concentration of 30 mg / L, and an adsorption separation coefficient of 7.53 between rare earth ions and aluminum ions. This is because the surface of unmodified graphite has almost no active adsorption sites, relying solely on weak physical adsorption to adsorb rare earth ions. This comparative result demonstrates that the adsorption capacity and selectivity of the graphite adsorbent are far lower than those of the sulfonated graphene oxide adsorbent.

Claims

1. A process for recovering rare earth elements from a low-concentration rare earth solution, characterized in that, Includes the following steps: (1) After the retired lithium battery is discharged, the waste negative electrode graphite is placed in a muffle furnace for heat treatment to obtain precursor graphite. (2) The precursor graphite obtained in step (1) and the oxidant and sulfuric acid solution are placed in an ultrasonic microwave reactor and stirred continuously for 5 to 120 min to obtain an acid-impregnated mixed slurry. The acid-impregnated mixed slurry is then filtered and dried under vacuum at 45 °C for 12 h to obtain impurity-free graphite. (3) The graphite was purified by the Hummers method and then freeze-dried in a freeze dryer for 24 h to obtain graphene oxide; (4) Graphene oxide is dispersed in DMF solution, a certain proportion of sulfonating reagent is added, and then the product is wet-milled in a planetary ball mill. The product is washed multiple times with anhydrous ethanol and ultrapure water, and then freeze-dried for 24 h to obtain sulfonated graphene oxide adsorbent. The sulfonated graphene oxide adsorbent is used to selectively adsorb rare earth ions in a sulfuric acid system containing aluminum impurities, and the adsorption capacity for rare earth ions is 100~400 mg / g, and the adsorption separation coefficient between rare earth ions and aluminum ions is greater than 3000. The initial concentration range of rare earth ions and aluminum ions is 10~100 mg / L.

2. The process as described in claim 1, characterized in that, The specific method for discharging in step (1) is as follows: immerse the retired lithium battery in a 10wt% sodium chloride solution for 24 hours to complete the discharge.

3. The process according to claim 1, characterized in that, In step (1), the heat treatment temperature is 300~900 ℃, the heat treatment time is 1~24 h, and the heat treatment atmosphere is a hydrogen-argon mixture, wherein the hydrogen volume concentration is 5%.

4. The process according to claim 1, characterized in that, In step (2), the oxidant includes one or more of hydrogen peroxide, nitric acid, sodium chlorate, sodium hypochlorite, and sodium perchlorate, the sulfuric acid concentration is 0.1~2 mol / L, and the solid-liquid ratio of the precursor graphite to the mixed solution of oxidant and sulfuric acid is 1:6~1:100, with the unit corresponding to the solid-liquid ratio being g:mL.

5. The process according to claim 1, characterized in that, In step (2), the ultrasonic-microwave reaction temperature is 25~80 ℃, the microwave power is 200~900 W, the ultrasonic power is 200~1200 W, and the stirring rate is 200~400 r / min.

6. The process as described in claim 1, characterized in that, The Hummers method described in step (3) includes the following steps: Weigh out 1-3 g of sodium nitrate and purified graphite at a mass ratio of 0.5-0.7:1 and place them in a 250 mL flask. Then add 30 mL of concentrated sulfuric acid to the flask and stir for half an hour under ice bath conditions. Continue to add 5 g of potassium permanganate slowly over one hour at low temperature. After the addition is complete, react the system at 35 °C for two hours. Add 150 mL of ultrapure water to the flask and raise the temperature to 95 °C to react for one hour. Then lower the temperature to 80 °C and add 4-15 mL of 30 wt% hydrogen peroxide. After cooling to room temperature, wash with hydrochloric acid as the washing solution, centrifuge at 9000 r / min for 10 minutes and rinse several times. After testing with barium chloride and finding no precipitate, wash with ultrapure water until neutral and freeze-dry in a vacuum freeze dryer for 24 hours to obtain graphene oxide adsorbent.

7. The process as described in claim 1, characterized in that, In step (4), the sulfonating agent includes one or more of sulfur trioxide pyridine complex, aminobenzenesulfonic acid, and fuming sulfuric acid, and the mass ratio of the sulfonating agent to graphene oxide is 1:1 to 1:

10.

8. The process as described in claim 1, characterized in that, In step (4), the surface oxygen-containing functional group content of sulfonated graphene oxide is 3~20 mmol / g, of which the sulfonic acid group content is 1~20 mmol / g.

9. The process as described in claim 1, characterized in that, Sulfonated graphene oxide adsorbent was added to a sulfuric acid system solution containing rare earth ions and aluminum ions, and shaken at 200 r / min. The solid-liquid ratio of the sulfonated graphene oxide adsorbent to the sulfuric acid system solution containing rare earth ions and aluminum ions was 1 mg: 8 mL.

10. The process as described in claim 9, characterized in that, The adsorption conditions in the sulfuric acid system solution were a temperature of 25°C, a reaction time of 30 min, and a pH of 5.

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