Method for recycling lithium from leaching solution of waste lithium ion battery and application thereof

Abstract

The application discloses a method for recycling lithium in leaching solution of waste lithium ion battery and application thereof, and comprises the following steps: removing copper and iron aluminum from the leaching solution of the waste lithium ion battery to obtain a post-removing impurity solution; preparing a calcium sulfate solution; adding sodium fluoride, ammonium fluoride and a dispersing agent into the calcium sulfate solution; heating and reacting the obtained mixed solution; obtaining calcium-doped sodium fluoride crystals after cooling; adding the calcium-doped sodium fluoride crystals into the post-removing impurity solution; performing lithium precipitation under low-speed stirring; and performing solid-liquid separation to obtain lithium fluoride residue and post-lithium precipitation solution. The method uses calcium-doped sodium fluoride solid to precipitate lithium in the leaching solution at one time, so that the lithium in the leaching solution is enriched in the lithium fluoride residue, the recovery rate of the lithium is improved, the content of nickel, cobalt and manganese metals in the lithium fluoride residue is reduced, the difficulty in preparing battery-grade lithium carbonate from the lithium fluoride residue is reduced, and the subsequent treatment process of the nickel, cobalt and manganese metal solution is simplified.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery recycling technology, specifically relating to a method for recycling lithium from leachate of waste lithium-ion batteries and its application. Background Technology

[0002] With the rapid development of the new energy electric vehicle industry, the installed capacity of power lithium-ion batteries is increasing year by year. As a key component of power lithium batteries, the supply of lithium is only increasing. With the increasing installed capacity of power batteries, the number of lithium-ion batteries reaching their end-of-life is also increasing annually. Therefore, it is necessary to develop a low-cost, high-efficiency recycling method to achieve a high recovery rate and high return on investment for this high-value metal.

[0003] Patent CN101942569A discloses a method for recovering lithium from waste lithium-ion batteries and waste electrode sheets, including the following steps: (1) crushing waste lithium-ion batteries or waste electrode sheets with a crusher, and then placing them in a high-temperature furnace for heat treatment to remove the binder and obtain powder; (2) dissolving and removing aluminum from the powder with sodium hydroxide solution, and filtering to obtain low-aluminum filter mud; (3) leaching the low-aluminum filter mud with acid and reducing agent to obtain leachate; (4) removing impurities such as iron, copper, and aluminum from the leachate by chemical method; (5) precipitating lithium in the leachate with fluoride salt to obtain crude lithium fluoride product; (6) washing, filtering, and drying the crude lithium fluoride product to obtain lithium fluoride product. The purity of the LiF product after multiple washing and purification can reach more than 98%, but the lithium recovery rate of a single precipitation using the above method is low, and the recovered lithium fluoride contains too many nickel, cobalt, and manganese metal ions, resulting in the loss of valuable metals in the battery cathode material.

[0004] Using a simple fluoride salt solution to precipitate lithium ions in the leachate often results in incomplete precipitation, requiring multiple concentrations to improve lithium ion recovery. This also leads to an increase in the content of metal ions such as nickel, cobalt, and manganese in the lithium fluoride slag, making the recovery process more complex and increasing the difficulty and cost of subsequent battery-grade lithium carbonate production. Therefore, there is an urgent need to develop a short-process, efficient method for recovering lithium ions from the leachate to reduce the difficulty and cost of subsequent battery-grade lithium carbonate production. Summary of the Invention

[0005] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes a method for recovering lithium from the leachate of spent lithium-ion batteries and its application. This method uses calcium-doped sodium fluoride solid to precipitate lithium in the leachate in a single step, enriching the metallic lithium in the leachate into the lithium fluoride slag, thereby improving the recovery rate of metallic lithium. Simultaneously, it reduces the content of nickel, cobalt, and manganese metals in the lithium fluoride slag, lowers the difficulty in preparing battery-grade lithium carbonate from the lithium fluoride slag, and simplifies the subsequent processing of the nickel, cobalt, and manganese metal liquid.

[0006] According to one aspect of the present invention, a method for recovering lithium from leachate of spent lithium-ion batteries is provided, comprising the following steps:

[0007] S1: The leachate from waste lithium-ion batteries is treated to remove copper, iron and aluminum, resulting in a purified solution.

[0008] S2: Prepare a calcium sulfate solution by adding sodium fluoride, ammonium fluoride and a dispersant to the calcium sulfate solution, heating the resulting mixed solution, and then separating the solid and liquid after cooling to obtain calcium-doped sodium fluoride crystals.

[0009] S3: The calcium-doped sodium fluoride crystals are added to the purified liquid, and a lithium precipitation reaction is carried out under low-speed stirring. Solid-liquid separation is performed to obtain lithium fluoride slag and lithium precipitation liquid.

[0010] In some embodiments of the present invention, in step S1, the leachate is prepared by the following process: pulping the positive electrode powder obtained after crushing and screening waste lithium-ion batteries, adding acid and a reducing agent to leach the positive electrode powder, and separating the solid and liquid phases to obtain the leachate. Further, the acid is at least one selected from sulfuric acid, hydrochloric acid, phosphoric acid, citric acid, ascorbic acid, or oxalic acid; the reducing agent is at least one selected from hydrogen peroxide, sodium sulfite, sodium thiosulfate, or ammonium chloride.

[0011] In some embodiments of the present invention, in step S1, the waste lithium-ion battery is at least one of the following: ternary lithium nickel cobalt manganese oxide battery, ternary lithium nickel cobalt aluminum oxide battery, lithium cobalt oxide battery, lithium manganese oxide battery, quaternary lithium nickel cobalt manganese aluminum oxide battery, lithium iron phosphate battery, or lithium manganese iron phosphate battery.

[0012] In some embodiments of the present invention, in step S1, the copper, iron, and aluminum removal process is as follows: metal powder is added to the leaching solution to conduct a displacement reaction; solid-liquid separation is performed to obtain sponge copper and filtrate; alkali is added to the filtrate to adjust the pH to precipitate iron and aluminum; solid-liquid separation is performed to obtain iron-aluminum slag and the purified liquid. Further, the metal powder is at least one of iron powder, nickel powder, or manganese powder. The alkali is at least one of soda ash or sodium hydroxide.

[0013] In some embodiments of the present invention, in step S1, the content of nickel in the purified liquid is 35-60 g / L, the content of cobalt is 15-35 g / L, the content of manganese is 10-30 g / L, the content of lithium is 6-18 g / L, the content of iron is 0-15 mg / L, the content of aluminum is 0-20 mg / L, the content of copper is 0-15 mg / L, the content of calcium is 5-135 mg / L, and the content of magnesium is 8-100 mg / L.

[0014] In some embodiments of the present invention, in step S2, the calcium sulfate solution is prepared from a calcium salt, sulfuric acid, and an EDTA chelating agent, wherein the calcium salt is at least one of calcium sulfate or calcium fluoride. Adding sulfuric acid and EDTA during the preparation of the calcium sulfate solution can accelerate the dissolution of calcium sulfate and reduce the uneven distribution of Ca in the sodium fluoride crystals caused by the low solubility of calcium sulfate.

[0015] In some embodiments of the present invention, in step S2, the molar ratio of the calcium salt, sulfuric acid and EDTA chelating agent is 1:(0.3-0.6):(0.1-0.4).

[0016] In some embodiments of the present invention, in step S2, the molar ratio of sodium fluoride, ammonium fluoride and dispersant is 1:(0.1-0.4):(0.05-0.15).

[0017] In some embodiments of the present invention, in step S2, the molar ratio of calcium sulfate to sodium fluoride in the calcium sulfate solution is (0.05-0.15):1.

[0018] In some embodiments of the present invention, in step S2, the amount of calcium doping in the calcium-doped sodium fluoride crystal is 5 mol%-15 mol.

[0019] In some embodiments of the present invention, in step S2, the heating reaction is carried out by microwave heating at a temperature of 120-180°C for a reaction time of 2-6 hours. Microwave heating can raise the solution temperature to a high temperature in a short time, resulting in a uniform temperature rise in the solution and near-dissolution of the substances in the solution. Compared with the conventional hydrothermal method, microwave heating produces smaller crystals with better results, and also yields higher output.

[0020] In some embodiments of the present invention, in step S2, the dispersant is sodium citrate.

[0021] In some embodiments of the present invention, in step S3, the calcium-doped sodium fluoride crystal is added at a molar ratio of fluoride ions in the calcium-doped sodium fluoride crystal to lithium ions in the purified solution of (1.1-1.3):1.

[0022] In some embodiments of the present invention, in step S3, the stirring speed is 50-200 r / min, and the temperature of the lithium precipitation reaction is 50-90°C. Further, the lithium precipitation reaction time is 4-8 h.

[0023] In some embodiments of the present invention, in step S3, the lithium fluoride slag contains 70%-85% lithium fluoride by mass, 6%-14% calcium ions by mass, 1%-2% magnesium ions by mass, and ≤3% total nickel, cobalt, and manganese ions by mass.

[0024] In some embodiments of the present invention, in step S3, the total concentration of nickel, cobalt, and manganese in the lithium precipitation solution is 60-85 g / L, and the concentration of lithium ions is ≤0.3 g / L.

[0025] In some embodiments of the present invention, step S3 further includes: extracting and purifying the lithium-precipitated liquid with an extractant to obtain a nickel-cobalt-manganese extract and a calcium- and magnesium-containing raffinate; then back-extracting the nickel-cobalt-manganese extract with acid to obtain a nickel-cobalt-manganese salt solution. Further, the extractant is at least one of P204, P507, or a carboxylic acid extractant BC196. Further, the acid used for back-extraction is sulfuric acid or hydrochloric acid. The pH of the lithium-precipitated liquid is 3.5-5.0, at which pH essentially no extraction of Ca, Mg, and Li metals is achieved.

[0026] This invention also provides the application of the lithium fluoride slag obtained by the method in the preparation of battery-grade lithium carbonate. It should be noted that lithium fluoride produced by precipitation with fluoride salt solution using traditional methods also contains calcium impurities. In the subsequent preparation of battery-grade lithium carbonate from lithium fluoride, soda ash is generally added for calcium removal, which is relatively easy. Therefore, even if calcium is introduced into the lithium fluoride slag by this invention, the increased calcium content will not bring additional impurity removal pressure to the downstream processes.

[0027] According to a preferred embodiment of the present invention, at least the following beneficial effects are achieved:

[0028] 1. This invention first synthesizes calcium-doped sodium fluoride crystals, which are then directly added in solid form to the leachate of purified waste batteries. Under low-speed stirring, lithium ions in the leachate are precipitated. Because calcium sulfate in the calcium-doped sodium fluoride crystal structure has low solubility, while sodium fluoride is readily soluble, the fluoride ions released from the dissolving sodium fluoride can react with Li ions in the solution to form a precipitate, preferentially precipitating within the calcium sulfate crystal framework. This forms a lithium fluoride slag encapsulated by a calcium sulfate (or calcium fluoride) framework. This reduces the contact area between lithium fluoride and the solution while maintaining the crystal framework, thereby reducing the Li concentration in the solution. This invention can reduce the lithium ion concentration in the leachate solution to below 0.3 g / L, simplifying the subsequent purification process of nickel-cobalt-manganese salt solutions. Furthermore, controlling the low stirring speed reduces the dissolution rate of the calcium-doped sodium fluoride solid and controls the diffusion rate of fluoride ions formed by the dissolution of sodium fluoride. This allows Li ions to diffuse in the liquid phase to the surface of the calcium-doped sodium fluoride solid and react with F to form LiF, which then deposits within the calcium-doped sodium fluoride solid, further reducing the lithium ion concentration in the solution.

[0029] 2. During the preparation of calcium-doped sodium fluoride crystals, some calcium fluoride is generated. During the cooling process, sodium fluoride, calcium sulfate, and calcium fluoride crystals will grow on the tiny crystal nuclei to form precipitates and co-doped crystals.

[0030] 2. By using calcium-doped sodium fluoride crystals to precipitate lithium in the leaching solution, the content of nickel, cobalt, and manganese metals in lithium fluoride slag can be reduced to below 3%, thereby reducing the amount of nickel, cobalt, and manganese metals precipitated during the lithium precipitation stage and reducing subsequent recycling costs.

[0031] 3. Calcium sulfate is used to prepare calcium-doped sodium fluoride crystals. Calcium sulfate has low solubility, which can better maintain the overall framework structure of the calcium-doped sodium fluoride solid, which is beneficial to the deep lithium deposition effect. At the same time, it can reduce the introduction of other anions (chloride ions) and reduce the difficulty of subsequent treatment of the leaching solution.

[0032] 4. Adding NH4F during the synthesis of calcium-doped sodium fluoride crystals can control the crystal growth direction, making the crystal structure appear as a long rod. Because it is not a short and thick shape, the path for sodium fluoride to dissolve and diffuse into the solution is shorter, making it easier to form lithium fluoride. Therefore, the long rod structure can improve the utilization efficiency of sodium fluoride. Adding a dispersant is beneficial to controlling the uniform distribution of Ca ions during the reaction.

[0033] 5. The nickel-cobalt-manganese metal liquid after lithium precipitation has a low lithium ion content, so it can be directly extracted and purified by an extractant. This can achieve the goal of basically not extracting Ca, Mg, and Li metals. The purified nickel-cobalt-manganese salt solution can be used for the synthesis of ternary precursors, reducing the cost increase of the purification process caused by excessive Li content in the extraction stage. Attached Figure Description

[0034] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein:

[0035] Figure 1 This is a process flow diagram of Embodiment 1 of the present invention;

[0036] Figure 2 This is a SEM image of the calcium-doped sodium fluoride crystal obtained in Example 2 of the present invention;

[0037] Figure 3 This is a SEM image of the calcium-doped sodium fluoride crystal obtained in Comparative Example 2 of this invention. Detailed Implementation

[0038] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0039] Example 1

[0040] A method for recovering lithium from leachate of spent lithium batteries using calcium-doped sodium fluoride crystals, referring to... Figure 1 The specific process is as follows:

[0041] (1) Take 1 kg of ternary powder obtained after crushing and screening waste nickel-cobalt-manganese lithium batteries, add 3 L of water to make slurry, add 0.43 L of concentrated sulfuric acid and 0.13 L of 30% hydrogen peroxide to leach the ternary powder, and filter and separate the powder after fully acid leaching out the metal to obtain leachate.

[0042] (2) Use 6g of iron powder to remove copper from the leaching solution. After filtration, sponge copper and filtrate are obtained. Then, use soda ash to control the pH of the filtrate to 3.8-4.0 to remove iron and aluminum. After filtration, iron and aluminum slag and impurity-removed liquid are obtained.

[0043] Table 1. Concentrations of various ions in the purified solution

[0044]

[0045] (3) Prepare a calcium sulfate solution by mixing 0.1 mol calcium sulfate, 0.03 mol 98% concentrated sulfuric acid, 0.03 mol EDTA chelating agent and 10 L water. Add a mixture of 2 mol sodium fluoride, 0.2 mol ammonium fluoride and 0.1 mol sodium citrate to the calcium sulfate solution and stir to form a mixed solution.

[0046] (4) The above mixed solution was microwave heated to a high temperature under closed conditions, kept at 180°C for 2 hours, and then slowly cooled and filtered and washed to obtain calcium-doped sodium fluoride crystals with a calcium molar content of 5%.

[0047] (5) The calcium-doped sodium fluoride crystals prepared above are directly added to the purified liquid obtained in step (2) at a fluoride ion: lithium ion molar ratio of 1.1:1 to carry out the lithium precipitation reaction. The reaction temperature is 50℃, the solution stirring speed is 200r / min, and the precipitation reaction time is 4h. After filtration, lithium fluoride slag and lithium precipitation liquid are obtained. The lithium fluoride slag is subjected to leaching, calcium removal, lithium precipitation and other treatments to prepare battery-grade lithium carbonate.

[0048] (6) The above lithium precipitation liquid was extracted with carboxylic acid extractant BC196 to obtain nickel cobalt manganese extract and calcium and magnesium raffinate. The nickel cobalt manganese extract was back-extracted with sulfuric acid to obtain nickel cobalt manganese sulfate solution.

[0049] Example 2

[0050] A method for recovering lithium from leachate of spent lithium batteries using calcium-doped sodium fluoride crystals, the specific process of which is as follows:

[0051] Steps (1) and (2) are the same as in Example 1;

[0052] (3) Prepare a calcium sulfate solution by mixing 0.1 mol calcium sulfate, 0.05 mol 98% concentrated sulfuric acid, 0.03 mol EDTA chelating agent and 10 L water. Add a mixture of 1 mol sodium fluoride, 0.2 mol ammonium fluoride and 0.1 mol sodium citrate to the calcium sulfate solution and stir to form a mixed solution.

[0053] (4) The above mixed solution was microwave-heated to a high temperature under sealed conditions, maintained at 160°C for 4 hours, and then slowly cooled before filtration and washing to obtain calcium-doped sodium fluoride crystals with a calcium molar content of 10%, the morphology of which is as follows. Figure 2 As shown in the figure, the crystal structure is long rod-shaped;

[0054] (5) The calcium-doped sodium fluoride crystals prepared above are directly added to the purified liquid obtained in step (2) at a fluoride ion: lithium ion molar ratio of 1.2:1 to carry out the lithium precipitation reaction. The reaction temperature is 70℃, the solution stirring speed is 100r / min, and the precipitation reaction time is 6h. After filtration, lithium fluoride slag and lithium precipitation liquid are obtained. The lithium fluoride slag is leached, calcium removed, and lithium precipitated to prepare battery-grade lithium carbonate.

[0055] (6) The above lithium precipitation liquid was extracted with carboxylic acid extractant BC196 to obtain nickel cobalt manganese extract and calcium and magnesium raffinate. The nickel cobalt manganese extract was back-extracted with sulfuric acid to obtain nickel cobalt manganese sulfate solution.

[0056] Example 3

[0057] A method for recovering lithium from leachate of spent lithium batteries using calcium-doped sodium fluoride crystals, the specific process of which is as follows:

[0058] Steps (1) and (2) are the same as in Example 1;

[0059] (3) Prepare a calcium sulfate solution by mixing 0.1 mol calcium sulfate, 0.06 mol 98% concentrated sulfuric acid, 0.04 mol EDTA chelating agent and 10 L water. Add a mixture of 0.67 mol sodium fluoride, 0.27 mol ammonium fluoride and 0.1 mol sodium citrate to the calcium sulfate solution and stir to form a mixed solution.

[0060] (4) The above mixed solution was microwave heated to a high temperature under closed conditions, kept at 160°C for 4 hours, and then slowly cooled and filtered and washed to obtain calcium-doped sodium fluoride crystals with a calcium molar content of 15%.

[0061] (5) The calcium-doped sodium fluoride crystals prepared above are directly added to the purified liquid obtained in step (2) at a fluoride ion: lithium ion molar ratio of 1.3:1 to carry out the lithium precipitation reaction. The reaction temperature is 90℃, the solution stirring speed is 50r / min, the precipitation reaction time is 4h, and after filtration, lithium fluoride slag and lithium precipitation liquid are obtained. The lithium fluoride slag is leached, calcium removed, and lithium precipitated to prepare battery-grade lithium carbonate.

[0062] (6) The above lithium precipitation liquid was extracted with carboxylic acid extractant BC196 to obtain nickel cobalt manganese extract and calcium and magnesium raffinate. The nickel cobalt manganese extract was back-extracted with sulfuric acid to obtain nickel cobalt manganese sulfate solution.

[0063] Comparative Example 1

[0064] A method for recycling lithium from leachate of spent lithium batteries differs from Example 1 in that it does not prepare calcium-doped sodium fluoride crystals, but instead adds ordinary sodium fluoride to precipitate lithium. The specific process is as follows:

[0065] Steps (1) and (2) are the same as in Example 1;

[0066] (3) According to the fluoride ion: lithium ion molar ratio of 1.1:1, the untreated sodium fluoride solid was directly added to the impurity-removed liquid obtained in step (2) to carry out the lithium precipitation reaction. The reaction temperature was 50℃, the solution stirring speed was 200r / min, and the precipitation reaction time was 4h. After filtration, lithium fluoride slag and lithium precipitation liquid were obtained. The lithium fluoride slag was leached, calcium removed, and lithium precipitated to prepare battery-grade lithium carbonate.

[0067] (4) The above lithium precipitation liquid was extracted with carboxylic acid extractant BC196 to obtain nickel cobalt manganese extract and calcium and magnesium raffinate. The nickel cobalt manganese extract was back-extracted with sulfuric acid to obtain nickel cobalt manganese sulfate solution.

[0068] Comparative Example 2

[0069] A method for recovering lithium from the leachate of waste lithium batteries using calcium-doped sodium fluoride crystals differs from Example 2 in that step (3) does not involve the addition of ammonium fluoride. The specific process of step (3) is as follows: 0.1 mol of calcium sulfate, 0.05 mol of 98% concentrated sulfuric acid, 0.03 mol of EDTA chelating agent, and 10 L of water are mixed to form a calcium sulfate solution. A mixture of 1 mol of sodium fluoride and 0.1 mol of sodium citrate is added to the calcium sulfate solution, and the mixture is stirred to form a mixed solution. The other steps of Comparative Example (2) are the same as those in Example (2).

[0070] The morphology of the calcium-doped sodium fluoride crystals prepared in this comparative example is as follows: Figure 3 As shown in the figure, the crystal structure is short and thick.

[0071] Table 2. Concentrations of various ions in the lithium precipitation solution

[0072]

[0073] Table 3. Mass percentage of each ion in lithium fluoride dry base slag

[0074]

[0075] As can be seen from Tables 2 and 3, the lithium ion content in the lithium precipitation liquid of Comparative Example 1 is significantly higher than that of Example 1, while the metal content is significantly lower than that of Example 1. Furthermore, the nickel, cobalt, and manganese contents in the lithium fluoride dry slag of Comparative Example 1 are significantly higher than those of Example 1, indicating that the lithium recovery rate of Comparative Example 1 using ordinary sodium fluoride precipitation is not high, and there is a significant loss of valuable metals such as nickel, cobalt, and manganese.

[0076] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments, and various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A method for recovering lithium from a spent lithium-ion battery leachate, the method comprising: The method comprises the following steps: ​ S1: removing copper, iron and aluminum from the leaching solution of waste lithium ion battery to obtain a post-removing impurity solution; S2: preparing a calcium sulfate solution, adding sodium fluoride, ammonium fluoride and a dispersing agent into the calcium sulfate solution, and performing a heating reaction on the obtained mixed solution, and then performing solid-liquid separation after cooling to obtain calcium-doped sodium fluoride crystals; S3: adding the calcium-doped sodium fluoride crystals into the post-removing impurity solution, performing a lithium precipitation reaction under low-speed stirring, and performing solid-liquid separation to obtain lithium fluoride residue and a post-lithium precipitation solution.

2. The method of claim 1, wherein, In step S1, the process of removing copper, iron and aluminum is as follows: adding metal powder into the leaching solution to perform a displacement reaction, performing solid-liquid separation to obtain sponge copper and a filtrate, adding alkali into the filtrate to adjust pH to precipitate iron and aluminum, and performing solid-liquid separation to obtain iron and aluminum residue and the post-removing impurity solution.

3. The method of claim 1, wherein, In step S2, the calcium sulfate solution is prepared from a calcium salt, sulfuric acid and an EDTA chelating agent, and the calcium salt is at least one of calcium sulfate or calcium fluoride.

4. The method of claim 3, wherein, In step S2, the molar ratio of the calcium salt, sulfuric acid and EDTA chelating agent is 1:(0.3-0.6):(0.1-0.4).

5. The method of claim 1, wherein, In step S2, the molar ratio of the sodium fluoride, ammonium fluoride and dispersing agent is 1:(0.1-0.4):(0.05-0.15).

6. The method of claim 1, wherein, In step S2, the ratio of the molar amount of calcium sulfate in the calcium sulfate solution to the molar amount of sodium fluoride is (0.05-0.15):

1.

7. The method of claim 1, wherein, In step S2, the heating reaction is performed by microwave heating, the heating temperature is 120-180℃, and the reaction time is 2-6h.

8. The method of claim 1, wherein, In step S3, the molar ratio of fluoride ions in the calcium-doped sodium fluoride crystals to lithium ions in the post-removing impurity solution is (1.1-1.3):

1.

9. The method of claim 1, wherein, In step S3, the stirring speed is 50-200r / min, and the temperature of the lithium precipitation reaction is 50-90℃.

10. Use of the lithium fluoride residue prepared by the method of any one of claims 1-9 in the preparation of battery-grade lithium carbonate.

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