Method for extracting lithium element from waste batteries

Abstract

The invention belongs to the technical field of lithium battery waste recovery, and particularly relates to a method for extracting a lithium element from a waste battery. According to the method, the waste battery is charged firstly, so that lithium is gathered to the negative electrode graphite, the lithium is embedded into the graphite, then crushing treatment is carried out underwater, heat is absorbed through a large amount of water to isolate oxygen, and the thermal runaway phenomenon caused by electrification in the crushing process is avoided; during crushing, the graphite negative electrode can be desorbed into water from a pole piece, and the graphite negative electrode is separated out and lithium ions embedded in the graphite negative electrode are brought out in a froth flotation manner by utilizing the hydrophobicity of graphite; and subsequently, acid liquor is used for recycling the lithium element through leaching. According to the method disclosed by the invention, most lithium is recovered by adopting a mode of pre-extraction and small part of lithium is subjected to post-extraction, the pure lithium element is preferentially extracted in a simple mode, and the condition of lithium loss caused by post-extraction of lithium is reduced; and the raffinate is recycled, so that the consumption of other materials is reduced while the lithium recovery rate is increased. The method is simple, and the recovery rate of lithium is high.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium battery waste recycling, and in particular relates to a method for extracting lithium elements from waste batteries. Background Art

[0002] At present, the richness of elements in waste ternary batteries makes it difficult to extract high-purity lithium; in addition to valuable elements such as nickel, cobalt, and manganese, the leachate also contains other impurity elements such as copper, aluminum, calcium, and magnesium. The methods for recovering lithium from waste batteries are mainly divided into pre-lithium extraction and post-lithium extraction. The pre-lithium extraction method is to use acid to leach lithium for recovery, but it is inevitable that more impurities will be brought out during the process, resulting in the need for multiple steps of impurity removal later. Although post-lithium extraction can naturally recycle lithium at the end of the process to improve purity when other elements are extracted in the early stage, it is inevitable that some lithium will be lost during the extraction of other elements, reducing the recovery rate. Summary of the invention

[0003] In view of this, the present invention provides a method for extracting lithium from waste batteries. The method provided by the present invention is simple and easy to operate, and has a high recovery rate for lithium.

[0004] In order to solve the above technical problems, the present invention provides a method for extracting lithium from waste batteries, comprising the following steps: The waste lithium-ion batteries are charged and then crushed underwater to obtain slurry; The slurry is subjected to bubble flotation to obtain waste graphite and mixed slurry respectively; The waste graphite is subjected to a first leaching in a first acid solution to obtain a lithium-containing solution; The mixed slurry is calcined and then sieved, and the sieved material is taken to obtain the waste positive electrode material; The waste positive electrode material, the second acid solution and the reducing agent are mixed for second leaching to obtain a leaching solution; The extract is subjected to multi-stage extraction to obtain a raffinate; The raffinate is recycled to the first leaching.

[0005] Preferably, the charging is to charge the waste lithium-ion battery to saturation.

[0006] Preferably, the bubble flotation comprises the following steps: The slurry is placed in a flotation device and stirred for the first time, and then foam is introduced. After entering a flotation cell, the slurry is stirred for the second time and air is introduced.

[0007] Preferably, the first stirring speed is 500~1500rpm, and the first stirring time is 5~30min; After the foam is introduced, the concentration of the foam in the system is 5-20 ppm; The second stirring speed is 500-1500 rpm, and the second stirring time is 5-30 min; The air flow rate is 1~10L / min, and the air supply time is 4~6min.

[0008] Preferably, the molar concentration of hydrogen ions in the first acid solution is 1-4 mol / L, and the mass ratio of the waste graphite to the first acid solution is 1:2-4; The first leaching time is 1-4 hours, the first leaching is accompanied by stirring, and the stirring speed is 100-400 r / min.

[0009] Preferably, the pH value of the raffinate is 4.5-5.0; Reusing the raffinate for the first leaching step further comprises: adjusting the pH value of the raffinate to a pH value required by the first acid solution.

[0010] Preferably, the calcination temperature is 400-800° C., and the calcination holding time is 1-4 hours.

[0011] Preferably, the screening includes multi-stage screening; the particle size of the waste positive electrode material is less than 100 mesh.

[0012] Preferably, the molar concentration of hydrogen ions in the second acid solution is 1-4 mol / L, and the mass ratio of the waste positive electrode material to the second acid solution is 1:4-10; The reducing agent includes sodium thiosulfate or hydrogen peroxide; the mass ratio of the waste positive electrode material to the reducing agent is 1:0.2-0.5; The temperature of the second leaching is 50-95° C., the time of the second leaching is 2-4 hours, the second leaching is accompanied by stirring, and the stirring speed is 100-400 r / min.

[0013] Preferably, the multi-stage extraction comprises a first extraction, a second extraction, a third extraction and a fourth extraction performed sequentially; The first extraction solvent is P204 extraction solvent, the second extraction solvent is P204 extraction solvent, the third extraction solvent is P507 extraction solvent, and the fourth extraction solvent is P507 extraction solvent.

[0014] The invention provides a method for extracting lithium from waste batteries, comprising the following steps: charging the waste lithium ion batteries and then crushing them underwater to obtain slurry; subjecting the slurry to bubble flotation to obtain waste graphite and mixed slurry respectively; subjecting the waste graphite to a first leaching in a first acid solution to obtain a lithium-containing solution; calcining the mixed slurry and then screening it to obtain waste positive electrode materials; mixing the waste positive electrode materials, a second acid solution and a reducing agent to perform a second leaching to obtain a leaching solution; subjecting the leaching solution to multi-stage extraction to obtain a raffinate; and recycling the raffinate to the first leaching. The present invention first charges the waste battery so that the lithium in the battery gathers in the negative electrode graphite and embeds the lithium into the graphite, and then performs a crushing process underwater, absorbing heat and isolating oxygen through a large amount of water, thereby avoiding the thermal runaway phenomenon caused by charging during the crushing process; the binder of the graphite negative electrode is mainly an aqueous binder such as CMC, so the graphite negative electrode can be desorbed from the pole piece into the water during crushing, and the graphite negative electrode is separated by foam flotation by utilizing the hydrophobicity of the graphite and the embedded lithium ions are taken out at the same time; the lithium element is subsequently recovered by leaching using acid solution. The present invention adopts the method of extracting most of the lithium in advance and extracting a small part of the lithium in the post-extraction mode for recovery, and preferentially extracts pure lithium elements in a simple manner and reduces the loss of lithium caused by post-extraction of lithium. The present invention separates the lithium element while separating the graphite, simplifies the separation and purification steps, eliminates the step of battery discharge, and reduces the demand for equipment during the crushing process; the raffinate is reused, while increasing the lithium recovery rate, reducing the consumption of other materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The present invention provides a schematic flow chart of a method for extracting lithium from waste batteries. DETAILED DESCRIPTION

[0016] The present invention provides a method for extracting lithium from waste batteries, comprising the following steps: The waste lithium-ion batteries are charged and then crushed underwater to obtain slurry; The slurry is subjected to bubble flotation to obtain waste graphite and mixed slurry respectively; The waste graphite is subjected to a first leaching in a first acid solution to obtain a lithium-containing solution; The mixed slurry is calcined and then sieved, and the sieved material is taken to obtain the waste positive electrode material; The waste positive electrode material, the second acid solution and the reducing agent are mixed for second leaching to obtain a leaching solution; The extract is subjected to multi-stage extraction to obtain a raffinate; The raffinate is recycled to the first leaching.

[0017] In the present invention, unless otherwise specified, all materials are conventional commercially available products.

[0018] The present invention charges the waste lithium ion battery and then crushes it underwater to obtain a slurry. As a specific embodiment of the present invention, the charging can be charging the waste lithium ion battery to saturation. The present invention utilizes the principle that lithium elements will be embedded in the graphite negative electrode after the battery is charged, and first charges the waste battery so that the lithium in the battery is gathered in the negative electrode graphite.

[0019] As a specific embodiment of the present invention, the crushing can be carried out in a crusher; the present invention has no special requirements for the underwater crushing, and the conventional method in the art can be used. The present invention can absorb heat and isolate oxygen through a large amount of water during underwater crushing, thereby avoiding thermal runaway caused by electrification during the crushing process; at the same time, the binder of the graphite negative electrode is mainly a water-based binder such as CMC, so the graphite negative electrode can be desorbed from the electrode into the water during crushing.

[0020] After obtaining the slurry, the present invention performs bubble flotation on the slurry to obtain waste graphite and mixed slurry respectively. As a specific embodiment of the present invention, the bubble flotation may include the following steps: placing the slurry in a flotation device, stirring it for the first time, then introducing foam, and stirring it for the second time after entering the flotation tank, and introducing air. As a specific embodiment of the present invention, the rotation speed of the first stirring can be 500-1500rpm, can also be 800-1300rpm, and can further be 1000-1200rpm; the time of the first stirring can be 5-30min, can also be 10-20min, and can further be 15-18min; the concentration of foam in the system after the foam is introduced can be 5-20ppm, and can also be 10-15ppm; the rotation speed of the second stirring can be 500-1500rpm, can also be 800-1300rpm, and can further be 1000-1200rpm; the time of the second stirring can be 5-30min, can also be 10-20min, and can further be 15-18min; the flow rate of air introduced can be 1-10L / min, can also be 3-8L / min, and can further be 5-7L / min; the time of air introduction can be 4-6min, and can specifically be 4min, 5min or 6min.

[0021] In the present invention, waste graphite is located in the upper liquid layer after bubble flotation, and the lower liquid layer is a mixed slurry, which mainly contains black powder.

[0022] After obtaining the waste graphite, the present invention performs a first leaching on the waste graphite in a first acid solution to obtain a lithium-containing solution. As a specific embodiment of the present invention, the first leaching process may further include: washing the waste graphite with water. As a specific embodiment of the present invention, the first acid solution may be an aqueous sulfuric acid solution or an aqueous hydrochloric acid solution; the molar concentration of hydrogen ions in the first acid solution may be 1-4 mol / L, or 2-3 mol / L; the mass ratio of the waste graphite to the first acid solution may be 1:2-4, or specifically 1:2, 1:3 or 1:4. As a specific embodiment of the present invention, the time of the first leaching may be 1-4 hours, or 2-3 hours; the first leaching may be accompanied by stirring, and the stirring speed may be 100-400 r / min, or 200-300 r / min. As a specific embodiment of the present invention, the pH value of the system during the first leaching may be 0-1.5, and the present invention may adjust the pH value of the system during the first leaching by adjusting the amount of the first acid solution added.

[0023] After obtaining the mixed slurry, the present invention calcines the mixed slurry and then screens it, takes the sieve, and obtains the waste positive electrode material. As a specific embodiment of the present invention, the calcination may also include: filtering the mixed slurry and removing the filtrate. As a specific embodiment of the present invention, the calcination temperature may be 400-800°C, specifically 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C or 800°C; the calcination insulation time may be 1-4h, specifically 1h, 2h, 3h or 4h.

[0024] The present invention can remove organic matter such as binders and plastics in the mixed slurry by pyrolysis after roasting. As a specific embodiment of the present invention, the screening can include multi-stage screening; the particle size of the waste positive electrode material is less than 100 meshes, and the present invention has no special requirements for the aperture of the screen used for the multi-stage screening, as long as the waste positive electrode material with a particle size less than 100 meshes can be obtained.

[0025] After obtaining the waste positive electrode material, the present invention mixes the waste positive electrode material, the second acid solution and the reducing agent for a second leaching to obtain a leaching solution. As a specific embodiment of the present invention, the second acid solution can be a sulfuric acid aqueous solution or a hydrochloric acid aqueous solution; the molar concentration of hydrogen ions in the second acid solution can be 1-4 mol / L, or 2-3 mol / L; the mass ratio of the waste positive electrode material and the second acid solution can be 1:4-10, and can be specifically 1:4, 1:5, 1:6, 1:7, 1:8, 1:9 or 1:10. As a specific embodiment of the present invention, the reducing agent can include sodium thiosulfate or hydrogen peroxide; the mass ratio of the waste positive electrode material and the reducing agent can be 1:0.2-0.5, and can be specifically 1:0.2, 1:0.3, 1:0.4 or 1:0.5. The present invention has no special requirements for the way of mixing the waste positive electrode material, the second acid solution and the reducing agent, as long as they can be mixed evenly. As a specific embodiment of the present invention, the temperature of the second extraction can be 50~95°C, or 60~80°C; the time of the second extraction can be 2~4h, or 2.5~3h; the second extraction can be accompanied by stirring, and the stirring speed can be 100~400r / min, or 200~300r / min.

[0026] The present invention can leach out metal elements in waste positive electrode materials through the second leaching; the metal elements may include manganese, cobalt, nickel and lithium.

[0027] After obtaining the leaching solution, the present invention performs multi-stage extraction on the leaching solution to obtain a raffinate. As a specific embodiment of the present invention, the multi-stage extraction may include a first extraction, a second extraction, a third extraction and a fourth extraction performed in sequence; the first extraction agent may be a P204 extraction agent, the second extraction agent may be a P204 extraction agent, the third extraction agent may be a P507 extraction agent, and the fourth extraction agent may be a P507 extraction agent. The present invention can remove impurities in the leaching solution through the first extraction, and the impurities include one or more of Fe, Zn, Ca, Al and Cu; the present invention can separate the manganese element in the leaching solution through the second extraction; the present invention can separate the cobalt element in the leaching solution through the third extraction; the present invention can separate the nickel element in the leaching solution through the fourth extraction; the raffinate contains a small amount of lithium. The present invention uses P204 to preferentially extract impurity ions and then extracts manganese ions through multi-stage extraction, and then uses P507 to extract cobalt and then nickel. When the target ion concentration reaches the requirement, it enters the next extraction stage, thereby realizing the graded extraction of different elements.

[0028] After obtaining the raffinate, the present invention reuses the raffinate for the first leaching. As a specific embodiment of the present invention, the pH value of the raffinate may be 4.5-5.0; and reusing the raffinate before the first leaching may further include: adjusting the pH value of the raffinate to the pH value required by the first acid solution.

[0029] Figure 1 The present invention provides a schematic flow chart of a method for extracting lithium from waste batteries.

[0030] In order to further illustrate the present invention, the technical solutions provided by the present invention are described in detail below in conjunction with embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0031] Example 1 Step 1: Charge the used lithium-ion battery at 1C constant current and constant voltage until the current is less than 0.1C; Step 2: Put the used batteries charged in step 1 into a crusher and crush them underwater to obtain slurry; Step 3: Put the slurry crushed in step 2 into the bubble flotation device, stir and mix at 1000 rpm for 10 minutes, then fill with foam with a concentration of 10 ppm, continue to stir and mix at 1000 rpm for 10 minutes after entering the flotation cell, and then continuously inject air at a flow rate of 3 L / min for 5 minutes; Step 4: Separate the upper layer of liquid after bubble flotation to obtain waste graphite, and the lower layer of liquid after bubble flotation is a mixed slurry of black powder; Step 5: washing the waste graphite and then leaching it in a sulfuric acid solution with a hydrogen ion concentration of 2 mol / L at a mass ratio of 1:2 (accompanied by stirring at 200 r / min) for 3 hours to obtain a lithium-containing solution; Step 6: Filter the mixed slurry obtained in step 4 and then perform high-temperature pyrolysis (calcination) at 700°C for 2 hours to remove organic matter such as binders and plastics; Step 7: The powder after calcination in step 6 is subjected to multi-stage screening to obtain waste positive electrode materials with a particle size of less than 100 mesh; Step 8: Mix the waste positive electrode materials sorted in step 7, a sulfuric acid solution with a hydrogen ion concentration of 4 mol / s and sodium thiosulfate, and perform leaching at 60° C. and 200 r / min for 2 h to obtain a leaching solution; wherein the mass ratio of the waste positive electrode materials to the sulfuric acid solution is 1:4, and the mass ratio of the waste positive electrode materials to the sodium thiosulfate is 1:0.4; Step nine: subjecting the leaching solution obtained in step eight to multi-stage extraction, using P204 extractant for the first extraction to remove impurities, using P204 extractant for the second extraction to remove manganese; using P507 extractant for the third extraction to remove cobalt, using P507 extractant for the fourth extraction to remove nickel, to obtain a raffinate containing a small amount of residual lithium element; adjusting the pH value of the obtained raffinate and then returning it to step five as a lithium leaching solution.

[0032] Example 2 Step 1: Charge the used lithium-ion battery at 1C constant current and constant voltage until the current is less than 0.1C; Step 2: Put the used batteries charged in step 1 into a crusher and crush them underwater to obtain slurry; Step 3: Put the slurry crushed in step 2 into the bubble flotation device, stir and mix at 500 rpm for 15 minutes, then fill with foam with a concentration of 8 ppm, continue to stir and mix at 500 rpm for 5 minutes after entering the flotation cell, and then continuously inject air at a flow rate of 4 L / min for 5 minutes; Step 4: Separate the upper layer of liquid after bubble flotation to obtain waste graphite, and the lower layer of liquid after bubble flotation is a mixed slurry of black powder; Step 5: washing the waste graphite and then leaching it in a hydrochloric acid solution with a hydrogen ion concentration of 3 mol / L at a mass ratio of 1:3 (accompanied by stirring at 100 r / min) for 3 hours to obtain a lithium-containing solution; Step 6: Filter the mixed slurry obtained in step 4 and then perform high-temperature pyrolysis (calcination) at 700°C for 2 hours to remove organic matter such as binders and plastics; Step 7: The powder after calcination in step 6 is subjected to multi-stage screening to obtain waste positive electrode materials with a particle size of less than 100 mesh; Step eight: The waste cathode material selected in step seven, a hydrochloric acid solution having a hydrogen ion concentration of 3 mol / mol and hydrogen peroxide were mixed, and leached for 2 h at 65 ° C and 100 r / min to obtain an extract; wherein the mass ratio of the waste cathode material to the hydrochloric acid solution was 1:5, and the mass ratio of the waste cathode material to the hydrogen peroxide was 1:0.4; Step nine: subjecting the leaching solution obtained in step eight to multi-stage extraction, using P204 extractant for the first extraction to remove impurities, using P204 extractant for the second extraction to remove manganese; using P507 extractant for the third extraction to remove cobalt, using P507 extractant for the fourth extraction to remove nickel, to obtain a raffinate containing a small amount of residual lithium element; adjusting the pH value of the obtained raffinate and then returning it to step five as a lithium leaching solution.

[0033] Example 3 Step 1: Charge the used lithium-ion battery at 1C constant current and constant voltage until the current is less than 0.05C; Step 2: Put the used batteries charged in step 1 into a crusher and crush them underwater to obtain slurry; Step 3: Put the slurry crushed in step 2 into the bubble flotation device, stir and mix at 1000 rpm for 5 minutes, then fill with foam with a concentration of 10 ppm, continue to stir and mix at 1000 rpm for 5 minutes after entering the flotation cell, and then continuously inject air at a flow rate of 2 L / min for 10 minutes; Step 4: Separate the upper layer of liquid after bubble flotation to obtain waste graphite, and the lower layer of liquid after bubble flotation is a mixed slurry of black powder; Step 5: After washing the waste graphite, leaching it in a hydrochloric acid solution with a hydrogen ion concentration of 2 mol / L at a mass ratio of 1:3 (accompanied by stirring at 300 r / min) for 2 h to obtain a lithium-containing solution; Step 6: Filter the mixed slurry obtained in step 4 and then perform high-temperature pyrolysis (calcination) at 700°C for 2 hours to remove organic matter such as binders and plastics; Step 7: The powder after calcination in step 6 is subjected to multi-stage screening to obtain waste positive electrode materials with a particle size of less than 100 mesh; Step 8: Mix the waste positive electrode materials sorted in step 7, a hydrochloric acid solution with a hydrogen ion concentration of 4 mol / s and hydrogen peroxide, and perform leaching at 70°C and 300 r / min for 3 hours to obtain a leaching solution; wherein the mass ratio of the waste positive electrode materials to the hydrochloric acid solution is 1:4, and the mass ratio of the waste positive electrode materials to the hydrogen peroxide is 1:0.4; Step nine: subjecting the leaching solution obtained in step eight to multi-stage extraction, using P204 extractant for the first extraction to remove impurities, using P204 extractant for the second extraction to remove manganese; using P507 extractant for the third extraction to remove cobalt, using P507 extractant for the fourth extraction to remove nickel, to obtain a raffinate containing a small amount of residual lithium element; adjusting the pH value of the obtained raffinate and then returning it to step five as a lithium leaching solution.

[0034] The concentration of each element in the lithium-containing solution obtained in step 5 during the purification and separation process of Examples 1 to 3 was detected by inductively coupled plasma optical emission spectrometry (ICP-OES), and the results are listed in Table 1.

[0035] Table 1 Concentration of each element in the lithium-containing solution obtained in step 5 of Examples 1 to 3

[0036] The contents of each element in the lithium-containing solution of step 5 and the extraction solution obtained in step 9 in Examples 1 to 3 were measured by ICP-OES, and the leaching rates of lithium, nickel, cobalt and manganese in the waste lithium batteries after purification and separation were calculated. The results are listed in Table 2.

[0037] Table 2 Leaching rate of each element in waste batteries after treatment in Examples 1 to 3

[0038] It can be seen from the results in Table 1 and Table 2 that the method provided by the present invention can leach most of the metal elements in waste batteries, and the recovery rate is relatively high, all above 95%.

[0039] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention, not all of the embodiments. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for extracting lithium from waste batteries, characterized in that: The following steps are involved: The waste lithium-ion batteries are charged and then crushed underwater to obtain slurry; The slurry is subjected to bubble flotation to obtain waste graphite and mixed slurry respectively; The waste graphite is subjected to a first leaching in a first acid solution to obtain a lithium-containing solution; The mixed slurry is calcined and then sieved, and the sieved material is taken to obtain the waste positive electrode material; The waste positive electrode material, the second acid solution and the reducing agent are mixed for second leaching to obtain a leaching solution; The extract is subjected to multi-stage extraction to obtain a raffinate; The raffinate is recycled to the first leaching.

2. The method for extracting lithium from waste batteries according to claim 1, characterized in that: The charging is to charge the waste lithium-ion battery to saturation.

3. The method for extracting lithium from waste batteries according to claim 1, characterized in that: The bubble flotation comprises the following steps: The slurry is placed in a flotation device and stirred for the first time, and then foam is introduced. After entering a flotation cell, the slurry is stirred for the second time and air is introduced.

4. The method for extracting lithium from waste batteries according to claim 3, characterized in that: The first stirring speed is 500~1500rpm, and the first stirring time is 5~30min; After the foam is introduced, the concentration of the foam in the system is 5-20 ppm; The second stirring speed is 500-1500 rpm, and the second stirring time is 5-30 min; The air flow rate is 1~10L / min, and the air supply time is 4~6min.

5. The method for extracting lithium from waste batteries according to claim 1, characterized in that: The molar concentration of hydrogen ions in the first acid solution is 1-4 mol / L, and the mass ratio of the waste graphite to the first acid solution is 1:2-4; The first leaching time is 1-4 hours, the first leaching is accompanied by stirring, and the stirring speed is 100-400 r / min.

6. The method for extracting lithium from waste batteries according to claim 1 or 5, characterized in that: The pH value of the raffinate is 4.5-5.0; Reusing the raffinate for the first leaching step further comprises: adjusting the pH value of the raffinate to a pH value required by the first acid solution.

7. The method for extracting lithium from waste batteries according to claim 1, characterized in that: The calcination temperature is 400-800° C., and the calcination holding time is 1-4 hours.

8. The method for extracting lithium from waste batteries according to claim 1, characterized in that: The screening includes multi-stage screening; the particle size of the waste positive electrode material is less than 100 mesh.

9. The method for extracting lithium from waste batteries according to claim 1, characterized in that: The molar concentration of hydrogen ions in the second acid solution is 1-4 mol / L, and the mass ratio of the waste positive electrode material to the second acid solution is 1:4-10; The reducing agent includes sodium thiosulfate or hydrogen peroxide; the mass ratio of the waste positive electrode material to the reducing agent is 1:0.2-0.5; The temperature of the second leaching is 50-95° C., the time of the second leaching is 2-4 hours, the second leaching is accompanied by stirring, and the stirring speed is 100-400 r / min.

10. The method for extracting lithium from waste batteries according to claim 1, characterized in that: The multi-stage extraction includes a first extraction, a second extraction, a third extraction and a fourth extraction performed sequentially; The first extraction solvent is P204 extraction solvent, the second extraction solvent is P204 extraction solvent, the third extraction solvent is P507 extraction solvent, and the fourth extraction solvent is P507 extraction solvent.

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