Method for efficiently removing fluorine from spent lithium battery

Abstract

Disclosed is a method for efficiently removing fluorine from a spent lithium battery. The method comprises: mixing aluminum and a sodium hydroxide solution for reaction to obtain a sodium metaaluminat

Description

Efficient method for removing fluorine from waste lithium batteries Technical Field

[0001] The invention belongs to the technical field of waste battery recycling, and particularly relates to a method for efficiently removing fluorine from waste lithium batteries. Background Art

[0002] Lithium batteries are a promising clean energy storage technology, currently primarily used in consumer electronics and new energy vehicles. With the booming development of industries such as mobile phones, laptops, digital cameras, electric vehicles, power tools, and new energy vehicles in my country, demand for lithium batteries is expected to increase further. However, lithium batteries have a limited lifespan, typically 5-8 years, with an effective lifespan of 4-6 years. Consequently, the number of discarded lithium batteries is expected to surge, and the recycling and disposal of these discarded lithium batteries has become a pressing issue.

[0003] There are two main recycling methods for used lithium batteries: pyrometallurgy and hydrometallurgy. Currently, the vast majority of used lithium batteries are processed using the hydrometallurgical recycling process. The hydrometallurgical recycling process involves discharging, crushing, sorting, and screening the used lithium batteries to obtain battery powder. The powder is then leached with acid and a reducing agent to extract the nickel, cobalt, manganese, and lithium metals. This is then treated with reagents to remove impurities. After extraction, a refined nickel, cobalt, and manganese sulfate solution is obtained, which is then used to synthesize precursor materials. Because used lithium batteries contain lithium hexafluorophosphate as an electrolyte and sodium fluoride is introduced during impurity removal, the fluorine content in the battery powder leachate ranges from 1 to 3 g / L. The presence of fluorine not only corrodes equipment but also affects the synthesized precursor products. Currently, there are few publicly available reports on methods for defluoridating battery powder leachates, and these methods primarily focus on calcium salt systems. For example, a related art has developed a defluoridation process for used lithium batteries that first removes fluorine by adding calcium oxide to the waste battery leachate. This is followed by a secondary defluoridation process using resin adsorption to reduce the fluorine concentration in the leachate. The addition of calcium oxide to this process for fluoride removal not only causes the precipitation of nickel, cobalt, and manganese, but also introduces calcium ions, necessitating a subsequent calcium removal step. To address these issues with fluoride removal from used lithium batteries, new fluoride removal processes are urgently needed.

[0004] Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art. To this end, the present invention provides a method for efficiently removing fluorine from waste lithium batteries.

[0006] According to one aspect of the present invention, a method for efficiently removing fluorine from waste lithium batteries is proposed, comprising the following steps:

[0007] S1: mixing aluminum with sodium hydroxide solution to react and obtain sodium metaaluminate solution;

[0008] S2: adding sulfuric acid to the sodium aluminate solution and stirring the mixture at a certain temperature to obtain a defluorination agent;

[0009] S3: adding sodium fluoroaluminate seed crystals and the defluoridating agent to the battery powder leachate after impurity removal, and simultaneously introducing sodium carbonate solution, reacting at a certain temperature, and controlling the pH at the reaction end point. After the reaction is completed, solid-liquid separation is performed to obtain a defluoridated liquid and a filter residue. Since a small amount of aluminum ions will be dissolved during the reaction, the role of sodium carbonate can be used to adjust the pH of the solution to ensure that the aluminum ion content in the solution is very low, thereby avoiding the introduction of impurity aluminum during defluoridation;

[0010] S4: adding sodium hydroxide solution to the filter residue to react, and performing solid-liquid separation to obtain a fluorine-aluminum-containing filtrate and an insoluble residue.

[0011] In some embodiments of the present invention, in step S1, the aluminum is recovered from waste lithium batteries to obtain aluminum slag powder. Specifically, the aluminum is obtained by disassembling, crushing, sorting, screening and finely crushing waste lithium batteries to obtain aluminum slag powder. The slag obtained after the aluminum slag powder reacts with sodium hydroxide solution can be added to the acid leaching reaction of the battery powder. The aluminum slag obtained after disassembling and crushing waste lithium batteries is used to prepare a defluoridating agent. The aluminum slag obtained after disassembling and crushing waste lithium batteries is finely crushed and sieved to obtain aluminum slag powder. After adding sodium hydroxide solution to react, it is filtered to obtain sodium aluminate solution, and then sulfuric acid is added to prepare an aluminum-based defluoridating agent, which not only has a good defluoridation effect but also greatly reduces the defluoridation cost.

[0012] In some embodiments of the present invention, in step S1, the solid-liquid ratio of the aluminum to the sodium hydroxide solution is 1:(2-5) g / ml, and the mass concentration of the sodium hydroxide is 10-30%.

[0013] In some embodiments of the present invention, in step S1, the reaction temperature is 50-80° C., and the reaction time is 30-60 min.

[0014] In some embodiments of the present invention, in step S2, the reaction temperature is 80-95° C., and the stirring rate is 150-300 rpm.

[0015] In some embodiments of the present invention, in step S2, the mass concentration of the sulfuric acid is 10-20%, and the flow rate of the sulfuric acid is 1.0-2.5 mL / min.

[0016] In some embodiments of the present invention, in step S2, an appropriate amount of water is evaporated during the reaction to concentrate the reaction solution until the concentration of aluminum ions in the reaction solution is controlled at 0.8-1.5 g / L and the pH at the end of the reaction is controlled at 2.0-3.0.

[0017] In some embodiments of the present invention, in step S3, the battery powder leachate after impurities removal is prepared by the following process: waste battery powder is added with water to prepare pulp, leached with sulfuric acid and hydrogen peroxide, and then the impurities are removed.

[0018] In some embodiments of the present invention, in step S3, the amount of sodium fluoroaluminate seed crystals added is 1-3 g / L; preferably, the amount of defluoridating agent added is such that the molar ratio of aluminum in the defluoridating agent to fluorine in the battery powder leachate is (1-1.5):6.

[0019] In some embodiments of the present invention, in step S3, the mass concentration of the sodium carbonate solution is 10-15%, and the flow rate of the sodium carbonate solution is 0.5-2.0 mL / min.

[0020] In some embodiments of the present invention, in step S3, the reaction temperature is 40-60° C., the reaction time is 60-90 min, and the pH at the end of the reaction is controlled at 5.0-5.5.

[0021] In some embodiments of the present invention, step S4 further includes preparing sodium fluoroaluminate from the fluorine-aluminum-containing filtrate by adding dilute sulfuric acid to the fluorine-aluminum-containing filtrate, stirring the reaction at a certain temperature, and controlling the pH at the reaction endpoint. After the pH of the solution stabilizes, stirring is stopped, the solution is aged for a period of time, and then filtered, the filter residue is washed with water, and sodium fluoroaluminate is obtained after drying. Further preferably, the mass concentration of the dilute sulfuric acid introduced is 5-12%, the flow rate of the dilute sulfuric acid is 0.5-2.0 mL / min, the reaction temperature is 40-60° C., the stirring rate is 150-200 rpm, the pH at the reaction endpoint is 6.0-6.5, and the aging time is 12-18 h.

[0022] In some embodiments of the present invention, in step S4, the mass concentration of the sodium hydroxide solution is 20-30%, the sodium hydroxide solution is added to the filter residue and the reaction temperature is 80-90° C., the reaction time is 20-40 minutes, and the reaction is carried out under stirring at a stirring rate of 200-400 rpm.

[0023] In some embodiments of the present invention, in step S4, the insoluble slag may be added to the leaching reaction of the battery powder.

[0024] According to a preferred embodiment of the present invention, there are at least the following beneficial effects:

[0025] The defluorination process of the present invention achieves excellent defluorination results, reducing fluoride to below 20 mg / L. The aluminum ion concentration introduced into the defluorinated solution is less than 1 mg / L. After nickel, cobalt, manganese, and lithium are recovered from the defluorinated solution, no further defluorination is required after it is pumped into the wastewater treatment plant. The fluoride removal rate is as high as 99%. The defluorinated residue can be purified to produce sodium fluoroaluminate with a purity exceeding 97%. This sodium fluoroaluminate can be used in the electrolytic aluminum industry as a solvent, pesticide for crops, and as a flux and opalescent agent for enamels, with great potential for recovery.

[0026] 2. The present invention utilizes the addition of sodium fluoroaluminate seed crystals to induce fluoride removal. During fluoride removal, sodium fluoroaluminate seed crystals are first added to the battery leachate. The induction of the seed crystals not only accelerates the combination of fluorine and aluminum in the solution to form sodium hexafluoroaluminate, shortening the reaction time and improving fluoride removal efficiency, but also reduces the fluoride content in the solution to below 20 mg / L, thereby achieving deep fluoride removal.

[0027] 3. Defluorination residue can be made into high-purity sodium fluoroaluminate. The residue obtained after defluorination is a mixture of sodium fluoroaluminate and nickel, cobalt and manganese carbonate. Sodium fluoroaluminate is dissolved by adding sodium hydroxide solution, while nickel, cobalt and manganese carbonate remain insoluble. After filtration, filtrate and residue are obtained. The residue can be returned to the acid leaching step of battery powder for dissolution. The filtrate is reacted by adding sulfuric acid to adjust the pH. After aging, filtration, washing and drying, high-purity sodium fluoroaluminate is obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0029] FIG1 is a process flow chart of Example 1 of the present invention. DETAILED DESCRIPTION

[0030] The following will clearly and completely describe the concept and technical effects of the present invention in conjunction with the embodiments to fully understand the purpose, features and effects of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0031] Example 1

[0032] A method for efficiently removing fluorine from waste lithium batteries and recovering fluorine, the specific process is as follows:

[0033] (1) Pretreatment: Dismantle, crush, sort and screen the used lithium batteries after discharge to obtain battery powder and aluminum slag;

[0034] (2) Preparation of aluminum-based defluoridant: After the aluminum slag is finely crushed, it is passed through a 100-mesh sieve to obtain aluminum slag powder, which is mixed with 10% sodium hydroxide solution at a solid-liquid ratio of 1:5 g / ml, and stirred at 80°C for 60 minutes. After the reaction, the solution is filtered to obtain insoluble slag and sodium aluminate solution. The insoluble slag is transferred to (3) for acid leaching and dissolution. A peristaltic pump is used to add 10% sulfuric acid at a flow rate of 2.5 mL / min to the sodium aluminate solution. The reaction temperature is 90°C, the stirring rate is 150 rpm, and an appropriate amount of water is evaporated to concentrate the solution until the aluminum ion concentration in the solution is concentrated to 0.8 g / L and the pH is stabilized at 3.0. After the solution becomes clear, stirring is stopped to obtain an aluminum ion-containing defluoridant;

[0035] (3) Leaching and removing impurities from battery powder: The battery powder obtained in step (1) is slurried with pure water, and then leached with sulfuric acid and hydrogen peroxide. After impurities are removed, a fluorine-containing purified liquid is obtained. The composition content is shown in Table 1:

[0036] Table 1 Content of fluorine-containing purification fluid components (g / L)

[0037] Ni 2+ Co 2+ Mn 2+ Li + Na + F - 35.458.5410.712.6320.352.32

[0038] (4) Adding sodium fluoroaluminate seeds to induce defluorination: taking 0.5 L of fluorine-containing purified liquid, first adding 1 g / L of sodium fluoroaluminate seeds, and then adding the defluorinating agent of step (3), the defluorinating agent is added in an amount such that the molar ratio of aluminum in the defluorinating agent to fluorine in the fluorine-containing purified liquid is 1.1:6. Under the conditions of a stirring rate of 100 rpm and a temperature of 40°C, a 10% sodium carbonate solution is pumped into the solution at a flow rate of 1 mL / min through a peristaltic pump. The reaction is carried out for 90 minutes, and the pH value at the reaction end point is controlled at 5.5. After the reaction, the solution is filtered to obtain a defluorinated liquid and a filter residue. The filter residue is washed twice with pure water, and the washing water is combined with the defluorinated liquid to obtain a total of 0.725 L of defluorinated liquid.

[0039] (5) Residue recovery to prepare high-purity sodium fluoroaluminate: The filter residue of step (4) is slurried with pure water, and then 20% sodium hydroxide solution is added to adjust the pH to 12 under the conditions of a stirring rate of 200 rpm and a temperature of 80°C. The mixture is reacted for 40 minutes. After the reaction, the solution is filtered to obtain a filtrate and an insoluble residue. The insoluble residue is transferred to the acid leaching and dissolution in (3). The filtrate is added with 12% sulfuric acid by mass at a flow rate of 0.5 mL / min using a peristaltic pump. The mixture is reacted at a stirring rate of 150 rpm and a temperature of 40°C until the pH of the solution stabilizes at 6.5. The stirring is then stopped, the solution is aged for 12 hours, and then filtered. The filter residue is washed with pure water three times and dried to obtain high-purity sodium fluoroaluminate.

[0040] Example 2

[0041] A method for efficiently removing fluorine from waste lithium batteries and recovering fluorine, the specific process is as follows:

[0042] (1) Pretreatment: Dismantle, crush, sort and screen the used lithium batteries after discharge to obtain battery powder and aluminum slag;

[0043] (2) Preparation of aluminum-based defluoridant: After the aluminum slag is finely crushed, it is passed through a 100-mesh sieve to obtain aluminum slag powder, which is mixed with 10% sodium hydroxide solution at a solid-liquid ratio of 1:2 g / ml, and stirred at 50°C for 40 minutes. After the reaction, the solution is filtered to obtain insoluble slag and sodium aluminate solution. The insoluble slag is transferred to (3) for acid leaching and dissolution. A peristaltic pump is used to add 20% sulfuric acid at a flow rate of 1.0 L / min to the sodium aluminate solution. The reaction temperature is 80°C, the stirring rate is 200 rpm, and an appropriate amount of water is evaporated to concentrate the solution until the aluminum ion concentration in the solution is concentrated to 1.5 g / L and the pH is stabilized at 2.0. After the solution becomes clear, stirring is stopped to obtain an aluminum ion-containing defluoridant;

[0044] (3) Leaching and removing impurities from battery powder: The battery powder obtained in step (1) is slurried with pure water, and then leached with sulfuric acid and hydrogen peroxide. After impurities are removed, a fluorine-containing purified liquid is obtained. The composition content is shown in Table 2:

[0045] Table 2 Content of fluorine-containing purification fluid components (g / L)

[0046] Ni 2+ Co 2+ Mn 2+ Li + Na + F - 25.4710.4514.282.4419.362.41

[0047] (4) Adding sodium fluoroaluminate seeds to induce defluorination: taking 0.8 L of fluorine-containing purified liquid, first adding 3 g / L of sodium fluoroaluminate seeds, and then adding the defluorinating agent of step (3), the defluorinating agent is added in an amount such that the molar ratio of aluminum in the defluorinating agent to fluorine in the fluorine-containing purified liquid is 1.3:6. Under the conditions of a stirring rate of 50 rpm and a temperature of 60°C, a 15% sodium carbonate solution is pumped in at a flow rate of 0.5 mL / min through a peristaltic pump. The reaction is carried out for 60 minutes, and the pH value at the reaction end point is controlled at 5.5. After the reaction, the solution is filtered to obtain a defluorinated liquid and a filter residue. The filter residue is washed twice with pure water, and the washing water is combined with the defluorinated liquid to obtain a total of 1.6 L of defluorinated liquid.

[0048] (5) Residue recovery to prepare high-purity sodium fluoroaluminate: The filter residue of step (4) is slurried with pure water, and then 30% sodium hydroxide solution is added to adjust the pH to 14 under the conditions of a stirring rate of 400 rpm and a temperature of 90°C. The mixture is reacted for 20 minutes. After the reaction, the solution is filtered to obtain a filtrate and an insoluble residue. The insoluble residue is transferred to (3) for acid leaching and dissolution. The filtrate is added with 10% sulfuric acid at a flow rate of 1.0 mL / min using a peristaltic pump. The mixture is reacted at a stirring rate of 200 rpm and a temperature of 60°C until the pH of the solution stabilizes at 6.0. The stirring is then stopped, the solution is aged for 18 hours, and then filtered. The filter residue is washed with pure water three times and dried to obtain high-purity sodium fluoroaluminate.

[0049] Example 3

[0050] A method for efficiently removing fluorine from waste lithium batteries and recovering fluorine, the specific process is as follows:

[0051] (1) Pretreatment: Dismantle, crush, sort and screen the used lithium batteries after discharge to obtain battery powder and aluminum slag;

[0052] (2) Preparation of aluminum-based defluoridant: After the aluminum slag is finely crushed, it is passed through a 100-mesh sieve to obtain aluminum slag powder, which is mixed with a 20% sodium hydroxide solution at a solid-liquid ratio of 1:3 g / ml, and stirred at 65°C for 50 minutes. After the reaction, the solution is filtered to obtain an insoluble slag and a sodium aluminate solution. The insoluble slag is transferred to (3) for acid leaching and dissolution. A peristaltic pump is used to add 15% sulfuric acid at a flow rate of 1.5 mL / min to the sodium aluminate solution. The reaction temperature is 85°C, the stirring rate is 250 rpm, and an appropriate amount of water is evaporated to concentrate the solution until the aluminum ion concentration in the solution is concentrated to 1.0 g / L and the pH is stabilized at 2.5. After the solution becomes clear, stirring is stopped to obtain an aluminum ion-containing defluoridant.

[0053] (3) Leaching and removing impurities from battery powder: The battery powder obtained in step (1) is slurried with pure water, and then leached with sulfuric acid and hydrogen peroxide. After impurities are removed, a fluorine-containing purified liquid is obtained. The composition content is shown in Table 3:

[0054] Table 3 Content of fluorine-containing purification liquid components (g / L)

[0055] Ni 2+ Co 2+ Mn 2+ Li + Na + F - 10.3232.458.432.5418.872.35

[0056] (4) Adding sodium fluoroaluminate seeds to induce defluorination: taking 1.0 L of fluorine-containing purified liquid, first adding 2 g / L of sodium fluoroaluminate seeds, and then adding the defluorinating agent of step (3), the defluorinating agent is added in an amount such that the molar ratio of aluminum in the defluorinating agent to fluorine in the fluorine-containing purified liquid is 1.2:6. Under the conditions of a stirring rate of 80 rpm and a temperature of 50°C, a 12% sodium carbonate solution is pumped into the solution at a flow rate of 1.5 mL / min through a peristaltic pump. The reaction is carried out for 70 minutes, and the pH value at the reaction end point is controlled at 5.5. After the reaction, the solution is filtered to obtain a defluorinated liquid and a filter residue. The filter residue is washed twice with pure water, and the washing water is combined with the defluorinated liquid to obtain a total of 1.56 L of defluorinated liquid.

[0057] (5) Residue recovery to prepare high-purity sodium fluoroaluminate: The filter residue of step (4) is slurried with pure water, and then 25% sodium hydroxide solution is added to adjust the pH to 12 under the conditions of a stirring rate of 300 rpm and a temperature of 85°C. The mixture is reacted for 30 minutes. After the reaction, the solution is filtered to obtain a filtrate and an insoluble residue. The insoluble residue is transferred to the acid leaching and dissolution in step (3). The filtrate is added with 5% sulfuric acid at a flow rate of 2.0 mL / min using a peristaltic pump. The mixture is reacted at a stirring rate of 180 rpm and a temperature of 50°C until the pH of the solution stabilizes at 6.5. The stirring is then stopped, the solution is aged for 15 hours, and then filtered. The filter residue is washed with pure water three times and dried to obtain high-purity sodium fluoroaluminate.

[0058] Comparative Example 1

[0059] A method for removing fluorine from waste lithium battery leachate and recovering the fluorine, the specific process is as follows:

[0060] (1) Pretreatment: Dismantle, crush, sort and screen the used lithium batteries after discharge to obtain battery powder;

[0061] (2) Leaching and removing impurities from battery powder: The battery powder obtained in step (1) was slurried with pure water, and then leached with sulfuric acid and hydrogen peroxide. After impurities were removed, a fluorine-containing purified liquid was obtained, the composition of which is shown in Table 4.

[0062] Table 4 Content of fluorine-containing purification liquid components (g / L)

[0063] Ni 2+ Co 2+ Mn2+ Li + Na + F - 33.2910.2812.562.4519.552.39

[0064] (3) Adding calcium hydroxide to remove fluorine: Take 0.5L of fluorine-containing purified liquid, add 3.0 times the theoretical amount of calcium hydroxide required for the reaction with fluorine, and stir the reaction at 60°C for 90 minutes. During the reaction, 15% sulfuric acid is added to maintain the pH of the solution at 5.5. After the reaction is completed, filter to obtain defluorinated residue and defluorinated liquid, obtain defluorinated liquid and filter residue, wash the filter residue twice with pure water, and combine the washing water with the defluorinated liquid to obtain 2.3L of defluorinated liquid in total;

[0065] (4) Purification of defluorination residue: The defluorination residue from step (3) was added with pure water to prepare a pulp. Under the conditions of a stirring rate of 300 rpm and a temperature of 85° C., 20% sulfuric acid was added to adjust the pH to 1.5. The mixture was reacted for 40 minutes. After the reaction, the solution was filtered to obtain a filtrate and an insoluble residue. The insoluble residue was washed three times with pure water. The washing water was combined with the filtrate. The filtrate was transferred to step (2) for preparing a pulp for battery powder. The insoluble residue was washed and dried to obtain purified calcium fluoride.

[0066] Test example

[0067] Table 5 compares the fluorine removal performance of Examples 1-3 and Comparative Example 1. The specific data are obtained by testing with a fluorine ion selective electrode and ICP-AES equipment.

[0068] Table 5 Comparison of fluorine removal performance of defluoridation agents in Examples and Comparative Examples

[0069]

[0070] Among them, the fluorine removal rate (C1 and V1 are the fluorine concentration and volume of the fluorine-containing purification liquid, respectively; C2 and V2 are the fluorine concentration and volume of the liquid after defluorination, respectively).

[0071] As shown in Table 5, the fluorine concentration of the defluorinated solution in this example is less than 0.02 g / L, the aluminum ion introduced after defluorination is less than 0.001 g / L, and the fluorine removal rate reaches 99%. Furthermore, the defluorinated residue can be purified to produce sodium fluoroaluminate with a purity of up to 97%, significantly improving the defluorination performance compared to the comparative example. The purified residue (i.e., calcium fluoride) in Comparative Example 1 in the table has a lower purity. This is because the use of calcium hydroxide for defluorination generates not only calcium fluoride but also calcium sulfate, resulting in a lower purity of the resulting calcium fluoride.

[0072] While the embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to the embodiments described above. Various modifications may be made within the scope of knowledge possessed by a person skilled in the art without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof may be combined with one another unless there is a conflict.

Claims

1. A method for efficiently removing fluorine from waste lithium batteries, characterized in that, it includes the following steps: S1: Mix aluminum with sodium hydroxide solution for reaction to obtain sodium aluminate solution; S2: Pass sulfuric acid into the sodium aluminate solution, stir and react at a certain temperature to obtain a defluorinating agent; S3: Add cryolite seeds and the defluorinating agent to the leachate of battery powder after impurity removal, and at the same time pass sodium carbonate solution, react at a certain temperature, and control the pH at the end point of the reaction. After the reaction is completed, solid-liquid separation is carried out to obtain defluorinated liquid and filter residue; S4: Add sodium hydroxide solution to the filter residue for reaction, and solid-liquid separation is carried out to obtain a filtrate containing fluorine and aluminum and an insoluble residue.

2. The method according to claim 1, characterized in that, in step S1, the aluminum is aluminum slag powder recovered from waste lithium batteries.

3. The method according to claim 1, characterized in that, in step S2, the reaction temperature is 80-95 °C, preferably, the stirring rate is 150-300 rpm.

4. The method according to claim 1, characterized in that, in step S2, during the reaction, an appropriate amount of water is evaporated to concentrate the reaction solution until the concentration of aluminum ions in the reaction solution is controlled at 0.8-1.5 g / L, and the pH at the end point of the reaction is controlled at 2.0-3.

0.

5. The method according to claim 1, characterized in that, in step S3, the leachate of battery powder after impurity removal is prepared by the following process: adding water to waste battery powder to make a slurry, leaching with sulfuric acid and hydrogen peroxide, and obtaining it after impurity removal.

6. The method according to claim 1, characterized in that, in step S3, the addition amount of the cryolite seeds is 1-3 g / L; preferably, the addition amount of the defluorinating agent is added according to the molar ratio of aluminum in the defluorinating agent to fluorine in the leachate of battery powder being (1-1.5):

6.

7. The method according to claim 1, characterized in that, in step S3, the mass concentration of the sodium carbonate solution is 10-15%, preferably, the feeding flow rate of the sodium carbonate solution is 0.5-2.0 mL / min.

8. The method according to claim 1, characterized in that, in step S3, the reaction temperature is 40-60 °C, preferably, the reaction time is 60-90 min; preferably, the pH at the end point of the reaction is controlled at 5.0-5.

5.

9. The method according to claim 1, characterized in that, in step S4, it further includes making the filtrate containing fluorine and aluminum into cryolite: passing dilute sulfuric acid into the filtrate containing fluorine and aluminum, stirring and reacting at a certain temperature, and controlling the pH at the end point of the reaction. After the pH of the solution is stable, stop stirring, age the solution for a period of time, then filter, wash the filter residue with water, and dry it to obtain cryolite.

10. The method according to claim 1, characterized in that, in step S4, the mass concentration of the sodium hydroxide solution is 20-30%; preferably, the temperature for adding sodium hydroxide solution to the filter residue for reaction is 80-90 °C, and the reaction time is 20-40 min.

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