Method for preparing battery-grade lithium carbonate by defluorinating crude lithium carbonate

Abstract

The invention provides a method for preparing battery-grade lithium carbonate by defluorinating crude lithium carbonate, which comprises the following steps: mixing crude lithium carbonate with water, fully stirring to prepare slurry, and introducing CO2 for hydrogenation to obtain crude hydrogenated liquid containing lithium bicarbonate; adding bismuth oxysulfate into the crude hydrogenated liquid, stirring, keeping a certain temperature for reaction, and performing solid-liquid separation after the reaction to obtain hydrogenated liquid; and performing thermal decomposition on the hydrogenated liquid to obtain lithium carbonate slurry, and performing solid-liquid separation on the lithium carbonate slurry to obtain the battery-grade lithium carbonate. According to the method, bismuth oxysulfate prepared from bismuth oxide is adopted as a precipitator to remove fluorine ions in the crude hydrogenated liquid, the fluorine removal effect is good, the fluorine removal rate is high, the process is simple, the matching degree with an existing process for preparing battery-grade lithium carbonate from industrial-grade lithium carbonate is high, and a battery-grade lithium carbonate product meeting the requirement can be obtained.

Description

Technical Field

[0001] The invention relates to the technical field of battery-grade lithium carbonate production, and in particular to a method for removing fluorine from crude lithium carbonate to prepare battery-grade lithium carbonate. Background Art

[0002] In recent years, with the rapid development of the new energy industry, the demand for lithium products has been rising year by year. Among them, battery-grade lithium carbonate, as the main raw material for synthesizing positive electrode materials for lithium batteries, has attracted widespread attention for its quality. In particular, in the process of extracting lithium from battery waste, there is a problem of lithium hexafluorophosphate in waste batteries contaminating lithium carbonate products. The fluorine content of such regenerated lithium carbonate products is often higher than that of lithium carbonate products obtained from brine and lithium ore.

[0003] With the rapid increase in the amount of retired power batteries, there is an urgent need to effectively remove fluorine from regenerated lithium carbonate. In the process of preparing battery-grade lithium carbonate from industrial crude lithium carbonate using the hydrogenation decomposition method, fluorine impurities are in a low concentration state, and conventional technology is difficult to meet the impurity removal requirements of battery-grade lithium carbonate. At present, the removal of fluoride ions mostly uses the lime method, which can reduce the F content in the solution to about 50ppm. However, this method requires the consumption of excessive lime and cannot deeply remove fluorine, resulting in the fluorine content in the lithium carbonate product often exceeding the standard, which cannot meet the requirements of battery-grade lithium carbonate for fluorine impurities. Therefore, we urgently need to develop a method that can deeply remove fluoride ions from crude lithium carbonate hydrogenation solution to prepare battery-grade lithium carbonate. Summary of the invention

[0004] The object of the present invention is to provide a method for preparing battery-grade lithium carbonate by removing fluorine from crude lithium carbonate. The method adopts bismuth oxysulfate prepared from bismuth oxide as a precipitant to remove fluoride ions in crude hydrogenated liquid, has good defluorination effect, high defluorination rate, simple process, high matching degree with the existing process of preparing battery-grade lithium carbonate from industrial-grade lithium carbonate, and can obtain a battery-grade lithium carbonate product that meets the requirements.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] A method for removing fluorine from crude lithium carbonate to prepare battery-grade lithium carbonate comprises the following steps:

[0007] S1, mix crude lithium carbonate with water, stir thoroughly to make slurry, and introduce CO 2 Carrying out hydrogenation to obtain a crude hydrogenated liquid containing lithium bicarbonate;

[0008] S2, adding bismuth oxysulfate to the crude hydrogenated liquid, stirring and maintaining a certain temperature for reaction, and separating the solid and the liquid after the reaction to obtain a hydrogenated liquid;

[0009] S3, thermally decomposing the hydrogenated liquid to obtain lithium carbonate slurry, and separating the lithium carbonate slurry into a solid and a liquid to obtain battery-grade lithium carbonate.

[0010] In one embodiment of the present application, step S201 is further included, wherein bismuth oxide and concentrated sulfuric acid are mixed, and then heated for reaction. When the bismuth oxide changes from yellow to white precipitate, the heating is stopped, and solid-liquid separation is performed to obtain bismuth oxysulfate.

[0011] In one embodiment of the present application, in step S201, the mass ratio of the bismuth oxide to concentrated sulfuric acid is 1:1-1:3, and the temperature of the heating reaction is 100-200°C.

[0012] In one embodiment of the present application, in step S2, the ratio of the added mass of the bismuth oxysulfate to the volume of the crude hydrogenated liquid is 1:100-1:150, the unit of the added mass of the bismuth oxysulfate is kilogram, and the unit of the volume of the crude hydrogenated liquid is liter.

[0013] In one embodiment of the present application, in step S2, the reaction temperature is 30-60° C., and the reaction time is 30-90 min.

[0014] In one embodiment of the present application, in step S2, precipitated residue is obtained after solid-liquid separation;

[0015] The method further includes step S202, mixing the precipitated residue with concentrated sulfuric acid, heating and reacting the mixture to obtain bismuth oxide and hydrogen fluoride gas, wherein the hydrogen fluoride gas is condensed and recovered, and the bismuth oxide is recovered and used in step S201.

[0016] In one embodiment of the present application, in step S202, the mass ratio of the precipitated residue to the concentrated sulfuric acid is 1:1 to 1:4;

[0017] The heating reaction temperature is 60~90℃, and the reaction time is 30~60min.

[0018] In one embodiment of the present application, in step S1, the mass ratio of the crude lithium carbonate to water is 1:15-1:30.

[0019] In one embodiment of the present application, in step S3, the temperature at which the hydrogenated liquid is thermally decomposed is 90-100°C.

[0020] In one embodiment of the present application, in step S3, the lithium carbonate slurry is subjected to solid-liquid separation to obtain a mother liquor, and the mother liquor is recycled and used for mixing with crude lithium carbonate to prepare slurry in step S1.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The present invention uses bismuth oxysulfate prepared from bismuth oxide as a precipitant to remove fluoride ions in the crude hydrogenated liquid. The present invention has good defluorination effect, high defluorination rate, simple process, mild reaction conditions, and a high degree of matching with the existing process of preparing battery-grade lithium carbonate from industrial-grade lithium carbonate. A battery-grade lithium carbonate product that meets the requirements can be obtained, and the fluorine content is ≤15ppm.

[0023] 2. The precipitant used in the present invention can be recycled after simple treatment after defluorination, with small amount of reagent used, low cost and simple operation.

[0024] 3. The present invention introduces less impurities, and the mother liquor produced after preparing battery-grade lithium carbonate can be recycled and reused, which can effectively reduce the loss of lithium. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0026] Figure 1 The present invention is a flow chart of the method for removing fluorine from crude lithium carbonate to prepare battery-grade lithium carbonate in the present application.

[0027] Figure 2 This is a process flow chart for removing fluorine from crude lithium carbonate to prepare battery-grade lithium carbonate in Example 1 of the present application.

[0028] Figure 3 This is a process flow chart for removing fluorine from crude lithium carbonate to prepare battery-grade lithium carbonate in Example 2 of the present application. DETAILED DESCRIPTION

[0029] In the following, only some exemplary embodiments are briefly described. As those skilled in the art will appreciate, the described embodiments may be modified in various ways without departing from the spirit or scope of the present invention. Therefore, the drawings and descriptions are considered to be exemplary and non-restrictive in nature.

[0030] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0031] like Figures 1 to 3 As shown, an embodiment of the present invention provides a method for removing fluorine from crude lithium carbonate to prepare battery-grade lithium carbonate, the method comprising the following steps:

[0032] Step S1, slurry preparation and hydrogenation: crude lithium carbonate and water are mixed in a certain mass ratio, stirred and slurried to obtain a uniformly dispersed suspension, and CO is introduced. 2The gas is subjected to hydrogenation operation to obtain a crude hydrogenated liquid containing lithium bicarbonate.

[0033] Step S2, purification and defluorination: add bismuth oxysulfate or activated residue of bismuth oxide activated by concentrated sulfuric acid to the crude hydrogenated liquid obtained in step S1, maintain stirring and keep a certain temperature for reaction, perform solid-liquid separation after a certain reaction time, and obtain hydrogenated liquid.

[0034] Step S3, thermal decomposition: the hydrogenated liquid obtained in step S2 is sent to the thermal decomposition section for thermal decomposition, and lithium carbonate slurry is obtained after thermal decomposition. The lithium carbonate slurry is subjected to solid-liquid separation to obtain battery-grade lithium carbonate wet material, and a battery-grade lithium carbonate product is obtained after drying.

[0035] Bismuth oxysulfate is used as a precipitant to remove fluoride ions in the crude hydrogenated liquid. The impurity removal effect is good, the impurity removal process is simple, and the degree of matching with the existing process of preparing battery-grade lithium carbonate from industrial-grade lithium carbonate is high, so that a battery-grade lithium carbonate product that meets the requirements can be obtained.

[0036] Preferably, bismuth oxysulfate is prepared by activating bismuth oxide with concentrated sulfuric acid, so the method also includes step S201, concentrated sulfuric acid activation: taking bismuth oxide and concentrated sulfuric acid in a certain mass ratio and stirring and mixing them evenly, then heating and reacting for a certain time, stopping heating when the bismuth oxide changes from yellow to white precipitate, performing solid-liquid separation, and obtaining activated slag after activation, i.e., bismuth oxysulfate.

[0037] In step S201, the mass ratio of bismuth oxide to concentrated sulfuric acid is preferably controlled to be 1:1-1:3, and the heating reaction temperature is controlled to be 100-200° C. during concentrated sulfuric acid activation, and the heating reaction time is usually 10-60 min.

[0038] In step S2, when bismuth oxysulfate or activated slag is added to the crude hydrogenated liquid, the ratio of the added mass (kg) of bismuth oxysulfate or activated slag to the volume (L) of the crude hydrogenated liquid is preferably controlled to be 1:100-150, wherein the mass unit of bismuth oxysulfate or activated slag is kilogram (kg), and the volume unit of the crude hydrogenated liquid is liter (L). Controlling the added amount of the precipitant (bismuth oxysulfate or activated slag) to the volume of the crude hydrogenated liquid within this ratio range can ensure that the fluoride ions in the crude hydrogenated liquid are fully removed, so that the fluorine concentration in the obtained battery-grade lithium carbonate meets the requirements, and reduce the waste of the precipitant and the introduction of impurities.

[0039] In step S2, the defluorination reaction is preferably carried out at a temperature of 30-60°C and a reaction time of 30-90 min.

[0040] In step S2, solid-liquid separation is performed after the fluorine removal reaction, and in addition to obtaining hydrogenated liquid, precipitated residue is also obtained.

[0041] The method further includes step S202, regenerating the precipitant: recovering the precipitated residue obtained in step S2, mixing it with concentrated sulfuric acid at a certain mass ratio, stirring and heating it to react, and obtaining bismuth oxide and hydrogen fluoride (HF) gas. The hydrogen fluoride gas is recovered by condensation, and the bismuth oxide is recovered and used as a raw material in the above step S201, so as to be recovered for preparing the precipitant (bismuth oxysulfate or activated residue).

[0042] In step S202, when the precipitated residue is recovered, the mass ratio of the precipitated residue to concentrated sulfuric acid is controlled to be 1:1-1:4; the temperature of the stirring and heating reaction is controlled to be 60-90°C, and the reaction time is 30-60 minutes. Bismuth oxide can be fully recovered and defluorination is completed.

[0043] In step S3, the temperature of the hydrogenated liquid for thermal decomposition is preferably controlled to be 90-100° C., and lithium carbonate slurry is obtained after thermal decomposition, and battery-grade lithium carbonate is obtained by solid-liquid separation. Controlling the thermal decomposition temperature within this range can ensure that the lithium carbonate obtained by crystallization has high purity and low impurity content.

[0044] In step S3, after solid-liquid separation of the lithium carbonate slurry, in addition to battery-grade lithium carbonate, a mother liquor is obtained. The mother liquor can be recycled and used in step S1 for mixing with the crude lithium carbonate raw material for slurry preparation, which can effectively reduce water consumption, reduce lithium loss, and improve lithium yield.

[0045] Preferably, in step S1, crude lithium carbonate and water are mixed and slurried in a mass ratio of 1:15 to 1:30; when the mother liquor is recovered for recycling, the amount of water added can be appropriately reduced.

[0046] When the purity of the crude lithium carbonate raw material is ≥98.5 wt%, the fluorine content is ≥100 ppm, and the chlorine content is <1000 ppm, the fluorine content of the battery-grade lithium carbonate prepared by the above method is ≤15 ppm.

[0047] In summary, the present application uses bismuth oxysulfate prepared from bismuth oxide as a precipitant to remove fluoride ions in the crude hydrogenated liquid, and the impurity removal effect is good, the impurity removal process is simple, and the process matching degree with the existing industrial-grade lithium carbonate to prepare battery-grade lithium carbonate is high, and a battery-grade lithium carbonate product that meets the requirements can be obtained; the precipitant used in the present application can be recycled after simple treatment after fluorine removal, the reagent usage is small, the cost is low, and the operation is simple; and the impurities introduced are small, and the mother liquor generated after the preparation of battery-grade lithium carbonate can be recycled and reused, which can effectively reduce water consumption and reduce lithium loss.

[0048] Example 1

[0049] (1) Slurry preparation and hydrogenation: Mix crude lithium carbonate and water in a mass ratio of about 1:25, stir and slurry thoroughly to obtain a uniformly dispersed suspension, and introduce CO 2The gas is subjected to hydrogenation operation to obtain a crude hydrogenated liquid containing lithium bicarbonate.

[0050] (2) Activation with concentrated sulfuric acid: bismuth oxide and concentrated sulfuric acid are mixed in a mass ratio of 1:2 and stirred evenly, and then heated to 180°C for reaction. When the bismuth oxide changes from yellow to white precipitate, heating is stopped. The heating reaction time is about 10 minutes. After the reaction, solid-liquid separation is performed to obtain activated slag, i.e., bismuth oxysulfate.

[0051] (3) Purification and defluorination: Add the activated slag / bismuth oxysulfate obtained to the crude hydrogenated liquid prepared above, and control the ratio of the amount of activated slag / bismuth oxysulfate added (kg) to the volume (L) of the crude hydrogenated liquid to be 1:120; maintain stirring and keep the temperature at about 30°C. After reacting for 60 minutes, perform solid-liquid separation to obtain hydrogenated liquid and precipitated slag.

[0052] (4) Regeneration of precipitant: The precipitated residue obtained by purification and defluorination is mixed with concentrated sulfuric acid in a mass ratio of 1:2, heated to 60°C under stirring, and reacted for about 45 minutes to obtain bismuth oxide and hydrogen fluoride gas. The hydrogen fluoride gas is recovered by condensation to achieve the removal and recovery of fluorine; the bismuth oxide is used as a raw material to enter the above-mentioned concentrated sulfuric acid activation step to prepare the precipitant (i.e., activated residue / bismuth oxysulfate), thereby achieving the recovery and recycling of the precipitant.

[0053] (5) Thermal decomposition: The hydrogenated liquid obtained in the purification and defluorination step is thermally decomposed at 90-100°C to obtain lithium carbonate slurry, and the lithium carbonate slurry is subjected to solid-liquid separation to obtain mother liquor and battery-grade lithium carbonate wet material. The mother liquor is returned to the slurry preparation and hydrogenation step to be mixed with crude lithium carbonate for slurry preparation. The battery-grade lithium carbonate wet material is washed, dried, and crushed to obtain a battery-grade lithium carbonate product. The fluorine content of the battery-grade lithium carbonate product is found to be 12 ppm.

[0054] Example 2

[0055] The operation is basically the same as that of Example 1, except that in step (2) of concentrated sulfuric acid activation, bismuth oxide and concentrated sulfuric acid are stirred and mixed in a mass ratio of 1:3; and the fluorine content of the battery-grade lithium carbonate product finally obtained is 10 ppm.

[0056] Example 3

[0057] The operation is basically the same as that of Example 1, except that in step (2) concentrated sulfuric acid activation, bismuth oxide and concentrated sulfuric acid are stirred and mixed in a mass ratio of 1:4; and the fluorine content of the battery-grade lithium carbonate product finally obtained is 9 ppm.

[0058] Example 4

[0059] The operation is basically the same as that of Example 2, except that in step (2) of concentrated sulfuric acid activation, the bismuth oxide and concentrated sulfuric acid are stirred and mixed and then heated to 200° C. for reaction; the fluorine content of the battery-grade lithium carbonate product finally obtained is 10 ppm.

[0060] Example 5

[0061] The operation is basically the same as that of Example 2, except that in step (2) of concentrated sulfuric acid activation, the bismuth oxide and concentrated sulfuric acid are stirred and mixed and then heated to 250° C. for reaction; the fluorine content of the battery-grade lithium carbonate product finally obtained is 9 ppm.

[0062] Example 6

[0063] The operation is basically the same as that of Example 5, except that in the purification and defluorination in step (3), the ratio of the amount of precipitant (activated slag / bismuth oxysulfate) added (kg) to the volume (L) of the crude hydrogenated liquid is 1:100; the fluorine content of the battery-grade lithium carbonate product finally obtained is 8 ppm.

[0064] Example 7

[0065] The operation is basically the same as that of Example 5, except that in step (3) of purification and defluorination, the ratio of the amount of precipitant (activated slag / bismuth oxysulfate) added (kg) to the volume (L) of the crude hydrogenated liquid is 1:150; the fluorine content of the battery-grade lithium carbonate product finally obtained is 14 ppm.

[0066] Example 8

[0067] The operation is basically the same as that of Example 5, except that in step (3) of purification and defluorination, the precipitant (activated slag / bismuth oxysulfate) and the crude hydrogenation liquid are stirred and mixed, and the temperature is maintained at 40°C for reaction; the fluorine content of the battery-grade lithium carbonate product finally obtained is 10 ppm.

[0068] Example 9

[0069] The operation is basically the same as that of Example 5, except that in step (3) of purification and defluorination, the precipitant (activated slag / bismuth oxysulfate) and the crude hydrogenation liquid are stirred and mixed, and the temperature is maintained at 50°C for reaction; the fluorine content of the battery-grade lithium carbonate product finally obtained is 9 ppm.

[0070] Example 10

[0071] The operation is basically the same as that of Example 5, except that in step (3) of purification and defluorination, the precipitant (activated slag / bismuth oxysulfate) and the crude hydrogenation liquid are stirred and mixed, and the temperature is maintained at 60°C for reaction; the fluorine content of the battery-grade lithium carbonate product finally obtained is 8 ppm.

[0072] Embodiment 11

[0073] The operation is basically the same as that of Example 9, except that in step (3) of purification and defluorination, the precipitant (activated slag / bismuth oxysulfate) and the crude hydrogenation liquid are stirred and mixed, and the temperature is maintained at 50°C for reaction for 30 minutes; the fluorine content of the battery-grade lithium carbonate product finally obtained is 13 ppm.

[0074] Example 12

[0075] The operation is basically the same as that of Example 9, except that in step (3) of purification and defluorination, the precipitant (activated slag / bismuth oxysulfate) and the crude hydrogenated liquid are stirred and mixed, and the temperature is maintained at 50°C for reaction for 90 minutes; the fluorine content of the battery-grade lithium carbonate product finally obtained is 8 ppm.

[0076] Embodiment 13

[0077] The operation is basically the same as that of Example 9, except that in step (4) of regenerating the precipitant, the precipitated residue recovered from the purification and defluorination step is mixed with concentrated sulfuric acid in a mass ratio of 1:3; the fluorine content of the battery-grade lithium carbonate product finally obtained is 9 ppm.

[0078] Embodiment 14

[0079] The operation is basically the same as that of Example 1, except that in step (3) of purification and defluorination, the precipitant (activated slag / bismuth oxysulfate) and the crude hydrogenation liquid are stirred and mixed, and the temperature is maintained at 50°C for reaction; in step (4) of precipitant regeneration, the precipitated slag recovered from the purification and defluorination step is mixed with concentrated sulfuric acid in a mass ratio of 1:4; and the fluorine content of the battery-grade lithium carbonate product finally obtained is 9 ppm.

[0080] Embodiment 15

[0081] The operation is basically the same as that of Example 1, except that, in step (2) concentrated sulfuric acid activation, bismuth oxide and concentrated sulfuric acid are stirred and mixed and then heated to 250° C. for reaction; in step (3) purification and defluorination, the precipitant (activated slag / bismuth oxysulfate) and the crude hydrogenated liquid are stirred and mixed and then kept at 50° C. for reaction; in step (4) precipitant regeneration, the precipitated slag recovered from the purification and defluorination step is mixed with concentrated sulfuric acid at a mass ratio of 1:5; the fluorine content of the battery-grade lithium carbonate product finally obtained is 8 ppm.

[0082] Example 16

[0083] The operation is basically the same as that of Example 1, except that, in step (2) concentrated sulfuric acid activation, bismuth oxide and concentrated sulfuric acid are stirred and mixed at a mass ratio of 1:4, and the bismuth oxide and concentrated sulfuric acid are stirred and mixed and then heated to 250° C. for reaction; in step (3) purification and defluorination, the ratio of the amount of precipitant (activated slag / bismuth oxysulfate) added (kg) to the volume (L) of the crude hydrogenated liquid is 1:100, and after the precipitant (activated slag / bismuth oxysulfate) and the crude hydrogenated liquid are stirred and mixed, the temperature is maintained at 60° C. for reaction, and the reaction time is 90 min; in step (4) precipitant regeneration, the precipitated slag recovered in the purification and defluorination step is mixed with concentrated sulfuric acid at a mass ratio of 1:4; the fluorine content of the battery-grade lithium carbonate product finally obtained is 5 ppm.

[0084] The above examples used 4 batches of crude lithium carbonate raw materials from the same manufacturer. The composition and impurity content of the crude lithium carbonate raw materials, as well as the fluorine content of the battery-grade lithium carbonate products obtained in each example are shown in Table 1.

[0085] As can be seen from Table 1, Examples 1, 5, 9, 13, Examples 2, 6, 10, 14, Examples 3, 7, 11, 15 and Examples 4, 8, 12, 16 respectively used a batch of crude lithium carbonate raw materials. The fluorine (F) contents in the four batches of crude lithium carbonate raw materials were quite different, namely 125 ppm, 312 ppm, 824 ppm and 154 ppm, respectively. However, after defluorination treatment using the method of the present application, the fluorine contents were all lower than 15 ppm, indicating that the defluorination effect of the method of the present application is good.

Claims

1. A method for removing fluorine from crude lithium carbonate to prepare battery-grade lithium carbonate, characterized in that: The following steps are involved: S1, mixing crude lithium carbonate with water, fully stirring to make slurry, introducing CO2 to hydrogenate, and obtaining a crude hydrogenated liquid containing lithium bicarbonate; S2, adding bismuth oxysulfate to the crude hydrogenated liquid, stirring and maintaining a certain temperature for reaction, and separating the solid and the liquid after the reaction to obtain a hydrogenated liquid; S3, thermally decomposing the hydrogenated liquid to obtain lithium carbonate slurry, and separating the lithium carbonate slurry into a solid and a liquid to obtain battery-grade lithium carbonate.

2. The method for preparing battery-grade lithium carbonate by removing fluorine from crude lithium carbonate according to claim 1, characterized in that: The method further includes step S201, mixing bismuth oxide and concentrated sulfuric acid, and then heating for reaction, stopping heating when the bismuth oxide changes from yellow to white precipitate, and performing solid-liquid separation to obtain bismuth oxysulfate.

3. The method for preparing battery-grade lithium carbonate by removing fluorine from crude lithium carbonate according to claim 2, characterized in that: In step S201, the mass ratio of the bismuth oxide to concentrated sulfuric acid is 1:1-1:3, and the temperature of the heating reaction is 100-200°C.

4. The method for preparing battery-grade lithium carbonate by removing fluorine from crude lithium carbonate according to claim 1 or 3, characterized in that: In step S2, the ratio of the added mass of bismuth oxysulfate to the volume of the crude hydrogenated liquid is 1:100-1:150, the unit of the added mass of bismuth oxysulfate is kilogram, and the unit of the volume of the crude hydrogenated liquid is liter.

5. The method for preparing battery-grade lithium carbonate by removing fluorine from crude lithium carbonate according to claim 4, characterized in that: In step S2, the reaction temperature is 30-60°C, and the reaction time is 30-90 min.

6. The method for preparing battery-grade lithium carbonate by removing fluorine from crude lithium carbonate according to claim 2, characterized in that: In step S2, after solid-liquid separation, precipitated residue is obtained; The method further includes step S202, mixing the precipitated residue with concentrated sulfuric acid, heating and reacting the mixture to obtain bismuth oxide and hydrogen fluoride gas, wherein the hydrogen fluoride gas is condensed and recovered, and the bismuth oxide is recovered and used in step S201.

7. The method for preparing battery-grade lithium carbonate by removing fluorine from crude lithium carbonate according to claim 6, characterized in that: In step S202, the mass ratio of the precipitated residue to concentrated sulfuric acid is 1:1 to 1:4; The heating reaction temperature is 60~90℃, and the reaction time is 30~60min.

8. The method for preparing battery-grade lithium carbonate by removing fluorine from crude lithium carbonate according to claim 1, characterized in that: In step S1, the mass ratio of the crude lithium carbonate to water is 1:15-1:

30.

9. The method for preparing battery-grade lithium carbonate by removing fluorine from crude lithium carbonate according to claim 1, characterized in that: In step S3, the temperature of thermal decomposition of the hydrogenated liquid is 90-100°C.

10. The method for preparing battery-grade lithium carbonate by removing fluorine from crude lithium carbonate according to claim 1 or 9, characterized in that: In step S3, the lithium carbonate slurry is subjected to solid-liquid separation to obtain a mother liquor, and the mother liquor is recycled and used for mixing with crude lithium carbonate to prepare slurry in step S1.

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