A method for extracting lithium carbonate salt from a lithium fluoride mother liquor

Abstract

This invention discloses a method for extracting and preparing lithium carbonate from lithium fluoride mother liquor, comprising at least the following steps: S1, titanium-based ion sieve adsorption: the lithium fluoride mother liquor is continuously passed into a titanium-based ion sieve adsorption column to adsorb lithium ions in the mother liquor, and then the ion sieve adsorption column is sequentially washed with water and acid to obtain a lithium solution; S2, ultrafiltration: ultrafiltration is used to remove ion sieve debris and / or mechanical impurities and / or colloidal substances from the lithium solution; S3, reverse osmosis: the lithium solution is enriched through a reverse osmosis membrane to obtain a lithium-rich solution; S4, lithium precipitation: a carbonic acid solution is added to the lithium-rich solution to carry out a precipitation reaction, and after drying, a finished lithium carbonate product is obtained. High-purity industrial lithium carbonate is obtained from the lithium fluoride mother liquor, and the entire process achieves a lithium recovery rate of not less than 87% (also referred to as "lithium yield"), more preferably above 91%, making it suitable for mass production and application.

Description

Technical Field

[0001] This invention belongs to the field of new energy materials, specifically relating to a method for extracting and preparing lithium carbonate from lithium fluoride mother liquor. Background Technology

[0002] In recent years, with the rapid development of the new energy industry, the market share of lithium-ion batteries has continued to increase, and the demand for lithium salts has risen year by year. Lithium carbonate (Li2CO3), as a basic lithium salt, is an important raw material for other lithium salts. As a basic lithium salt, it has a wide range of applications and is one of the important raw materials for lithium salt additives. Its current main sources are lithium extraction from ore and lithium extraction from salt lake brine. With the increasing awareness of environmental protection, lithium recycling is also receiving more and more attention.

[0003] In particular, the applicant noted that the production of lithium fluoride salts generates a large amount of lithium fluoride mother liquor, some of which contains as much as 700-800 ppm Li+. Direct discharge of this liquor has a significant impact on the environment and wastes resources.

[0004] For example, the invention patent application CN116724134A, entitled "A Lithium Extraction Device and Method," discloses an electrolytic cell for extracting lithium salts, which uses an electrolytic cell and a lithium ion sieve to extract and separate lithium. Another example is the invention patent application CN118745526A, which discloses a method and device system for directly extracting lithium from salt lake brine, which uses resin adsorption to extract lithium ions. However, the purity of the lithium ion products obtained by these methods is not high. In particular, the raw material used is salt lake brine, which cannot be used as a process route for extracting and preparing lithium carbonate from lithium fluoride mother liquor. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a method for extracting and preparing lithium carbonate from lithium fluoride mother liquor, which yields high-purity industrial lithium carbonate products from lithium fluoride mother liquor, and the entire process achieves a lithium recovery rate of not less than 87% (also referred to as "lithium yield", more preferably 91% or more), suitable for mass production and application.

[0006] The technical solution adopted in this invention is as follows: A method for preparing lithium carbonate from lithium fluoride mother liquor includes at least the following steps: S1. Titanium-based ion sieve adsorption: The lithium fluoride mother liquor is continuously passed into the titanium-based ion sieve adsorption column to adsorb lithium ions in the lithium fluoride mother liquor. Then, the ion sieve adsorption column is washed with water and acid in sequence to obtain a lithium solution. S2. Ultrafiltration: Removing ion sieve debris and / or mechanical impurities and / or colloidal substances from the lithium solution by ultrafiltration; S3, Reverse osmosis: The lithium solution is enriched through a reverse osmosis membrane to obtain a lithium-rich solution; S4. Lithium precipitation: Carbonic acid solution is added to the lithium-rich solution to carry out a precipitation reaction, and the lithium carbonate product is obtained after drying.

[0007] Preferably, in step S1, the titanium-based ion sieve comprises H2TiO3 and H4Ti5O. 12 ; wherein, the H2TiO3 and H4Ti5O 12 The mass ratio range is 1:0.01-0.15.

[0008] Preferably, the titanium-based ion sieve further includes a manganese-based lithium ion sieve, wherein the manganese-based lithium ion sieve is HMn2O4 with a spinel structure; wherein H2TiO3 and H4Ti5O are also present. 12 The sum of their masses and the mass ratio of HMn2O4 is 1:0.05-0.6.

[0009] Preferably, when H2TiO3 and H4Ti5O 12 When the mass ratio of the sum of the masses of the components to that of HMn2O4 is 1:0.3-0.6, the pH during adsorption by the titanium-based ion sieve is 7.5-9.5, the adsorption temperature is controlled at 10-30℃, the concentration of the lithium fluoride mother liquor is 200-700mg / L, the flow rate is controlled at 4-20L / min, and the operating pressure is controlled at 0.5-2.5bar. When H2TiO3, H4Ti5O 12 When the mass ratio of the sum of the masses of the titanium-based ion sieves to the mass of HMn2O4 is 1:0.2-0.3, the pH during adsorption is 8.5-10.5, the adsorption temperature is controlled at 20-40℃, the concentration of lithium fluoride mother liquor is 500-700mg / L, the flow rate is controlled at 35-70L / min, and the operating pressure is controlled at 0.5-2.5bar. When H2TiO3, H4Ti5O 12 When the mass ratio of the sum of the components to HMn2O4 is 1:0.05-0.2, the pH during adsorption by the titanium-based ion sieve is 9.5-11.5, the adsorption temperature is controlled at 30-45℃, the concentration of the lithium fluoride mother liquor is 500-700 mg / L, the flow rate is controlled at 100-120 L / min, and the operating pressure is controlled at 0.5-2.5 bar.

[0010] Preferably, in step S1, the reaction equation includes: H₂TiO₃ (solid adsorbent) + 2Li + (Solution)⇌Li₂TiO₃ (solid adsorbent) + 2H⁺ + (solution); The residual lithium fluoride mother liquor in the adsorbent solid is then removed by water washing, followed by acid washing to obtain a lithium solution. The acid washing process includes the following reaction steps: Li₂TiO₃ (solid adsorbent) + 2HCl ⇌ 2LiCl + H₂TiO₃ (solid adsorbent); LiCl is the lithium solution.

[0011] Preferably, the titanium-based ion sieve further includes a binder for improving the adsorption stability, cycle number, and adsorption capacity of the titanium-based ion sieve; wherein the binder accounts for 1-6% of the mass of the titanium-based ion sieve; and / or the binder is any one or a mixture of several of polyacrylic acid (PAA), polyvinyl chloride (PVC), polyethylene glycol (PEG), and cyanoacrylate (CA).

[0012] Preferably, in step S2, the operating pressure of ultrafiltration is set to 1-2.5 bar; and / or the membrane pore size used in ultrafiltration is 1-100 nanometers.

[0013] Preferably, in step S3, the lithium ion rejection rate of reverse osmosis is not less than 95%; the reverse osmosis includes sequential first-stage reverse osmosis and high-pressure reverse osmosis; wherein the operating pressure of the first-stage reverse osmosis is 0.5-2.5 bar; and the operating pressure of the high-pressure reverse osmosis is 10-30 bar.

[0014] Preferably, in step S4, the carbonic acid solution is a Na2CO3 solution, and the equation for its precipitation reaction is as follows: 2LiCl+ Na2CO3⇌Li2CO3+ 2NaCl.

[0015] Preferably, in step S4, before the precipitation reaction, the lithium-rich solution obtained in step S3 is pretreated with a cation exchange resin to remove calcium and magnesium ions.

[0016] It should be noted that the lithium fluoride mother liquor involved in this application is mainly derived from the lithium fluoride mother liquor raw material generated during the production of lithium fluoride lithium salts. Before implementing this application, the lithium fluoride mother liquor raw material can be subjected to pre-physical filtration treatment to remove suspended solids, colloids, mechanical impurities, etc. These are conventional technical choices for those skilled in the art and are not considered as innovative content of this application. This application will not elaborate on this further.

[0017] This application proposes a process consisting of four steps: titanium-based ion sieve adsorption, ultrafiltration, reverse osmosis, and lithium precipitation, to extract and prepare lithium carbonate from lithium fluoride mother liquor. The final product is a high-purity industrial lithium carbonate (purity of 98% or higher, more preferably 99% or higher). The entire process achieves a lithium recovery rate of no less than 87% (also referred to as "lithium yield"), which is suitable for mass production and application. Attached Figure Description

[0018] Figure 1 This is a flowchart illustrating the steps for extracting and preparing lithium carbonate from lithium fluoride mother liquor according to a specific embodiment of this application. Detailed Implementation

[0019] This embodiment proposes a method for preparing lithium carbonate from lithium fluoride mother liquor, which includes at least the following steps: S1. Titanium-based ion sieve adsorption: The lithium fluoride mother liquor is continuously passed into a titanium-based ion sieve adsorption column to adsorb lithium ions in the mother liquor. The ion sieve adsorption column is then sequentially washed with water and acid to obtain a lithium solution. Preferably, in step S1, the titanium-based ion sieve includes H2TiO3 and H4Ti5O. 12 Among them, H2TiO3 and H4Ti5O 12 The mass ratio range is 1:0.01-0.15; more preferably, in this embodiment, the titanium-based ion sieve also includes a manganese-based lithium ion sieve, wherein the manganese-based lithium ion sieve is HMn2O4 with a spinel structure; wherein H2TiO3 and H4Ti5O 12 The sum of their masses and the mass ratio of HMn2O4 is 1:0.05-0.6; more preferably, in this embodiment, the titanium-based ion sieve further includes a binder to improve the adsorption stability, cycle number and adsorption capacity of the titanium-based ion sieve; wherein the binder accounts for 1-6% of the mass of the titanium-based ion sieve; and / or the binder is any one or a mixture of several of polyacrylic acid PAA, polyvinyl chloride PVC, polyethylene glycol PEG, and cyanoacrylate CA; Preferably, to further improve the adsorption effect of step S1, in this embodiment, when H2TiO3 and H4Ti5O... 12 When the mass ratio of the sum of the masses of the components to that of HMn2O4 is 1:0.3-0.6, the pH during adsorption by the titanium-based ion sieve is 7.5-9.5, the adsorption temperature is controlled at 10-30℃, the concentration of the lithium fluoride mother liquor is 200-700mg / L, the flow rate is controlled at 4-20L / min, and the operating pressure is controlled at 0.5-2.5bar. When H2TiO3, H4Ti5O 12When the mass ratio of the sum of the masses of the titanium ion sieves to HMn2O4 is 1:0.2-0.3, the pH during adsorption is 8.5-10.5, the adsorption temperature is controlled at 20-40℃, the concentration of lithium fluoride mother liquor is 500-700mg / L, the flow rate is controlled at 35-70L / min, and the operating pressure is controlled at 0.5-2.5bar. When H2TiO3, H4Ti5O 12 When the mass ratio of the sum of the masses of the components to that of HMn2O4 is 1:0.05-0.2, the pH during adsorption by the titanium-based ion sieve is 9.5-11.5, the adsorption temperature is controlled at 30-45℃, the concentration of the lithium fluoride mother liquor is 500-700 mg / L, the flow rate is controlled at 100-120 L / min, and the operating pressure is controlled at 0.5-2.5 bar. Those skilled in the art can make specific choices during actual implementation. It should be specifically noted that, based on the results of a large-scale control group (50 groups selected) in this application, the use of "H2TiO3, H4Ti5O" is appropriate. 12 The highest lithium yield is achieved in the following implementation scheme: when the mass ratio of the sum of H2TiO3 and HMn2O4 is 1:0.3-0.6, the pH during adsorption by the titanium ion sieve is 7.5-9.5, the adsorption temperature is controlled at 10-30℃, the concentration of the lithium fluoride mother liquor is 200-700 mg / L, the flow rate is controlled at 4-20 L / min, and the operating pressure is controlled at 0.5-2.5 bar. This scheme guarantees a lithium yield of at least 91%, with most achieving a yield of over 95% and a purity of over 99%. The other two implementation schemes achieve lower lithium yields. Specifically, the scheme where "when H2TiO3 and H4Ti5O4 are in a mass ratio of 1:0.3-0.6, the lithium yield is higher than that achieved by using H2TiO3 and H4Ti5O4" is higher. 12 When the mass ratio of the sum of H2TiO3 and HMn2O4 is 1:0.2-0.3, the pH during adsorption by the titanium-based ion sieve is 8.5-10.5, the adsorption temperature is controlled at 20-40℃, the concentration of the lithium fluoride mother liquor is 500-700 mg / L, the flow rate is controlled at 35-70 L / min, and the operating pressure is controlled at 0.5-2.5 bar, the achieved lithium yield is approximately 89%. 12 When the mass ratio of the sum of the masses of the components to HMn2O4 is 1:0.05-0.2, the pH during adsorption by the titanium-based ion sieve is 9.5-11.5, the adsorption temperature is controlled at 30-45℃, the concentration of the lithium fluoride mother liquor is 500-700 mg / L, the flow rate is controlled at 100-120 L / min, and the operating pressure is controlled at 0.5-2.5 bar, the lithium yield achieved in this implementation scheme is approximately 87%. Therefore, these two implementation schemes are not recommended as preferred embodiments.

[0020] Preferably, in step S1, the reaction equation includes: H₂TiO₃ (solid adsorbent) + 2Li + (Solution)⇌Li₂TiO₃ (solid adsorbent) + 2H⁺ + (solution); The residual lithium fluoride mother liquor in the adsorbent solid is then removed by water washing, followed by acid washing to obtain a lithium solution. The acid washing process includes the following reaction steps: Li₂TiO₃ (solid adsorbent) + 2HCl ⇌ 2LiCl + H₂TiO₃ (solid adsorbent); LiCl is a lithium solution; S2, Ultrafiltration: Removing ion-sieve debris and / or mechanical impurities and / or colloids from the lithium solution by ultrafiltration; preferably, in step S2, the operating pressure of ultrafiltration is set to 1-2.5 bar; and / or preferably, in step S2, the membrane pore size used for ultrafiltration is 1-100 nanometers; it should be further noted that, in specific implementation, known ultrafiltration membranes and ultrafiltration processes in the prior art can be used, and this application does not have any particular limitations in this regard; S3. Reverse osmosis: Enriching the lithium solution through a reverse osmosis membrane to obtain a lithium-rich solution; preferably, in this step S3, the lithium ion rejection rate of reverse osmosis is not less than 95%; reverse osmosis includes sequential first-stage reverse osmosis and high-pressure reverse osmosis; wherein, the operating pressure of the first-stage reverse osmosis is 0.5-2.5 bar; the operating pressure of the high-pressure reverse osmosis is 10-30 bar; it should be further noted that, in specific implementation, known reverse osmosis and reverse osmosis processes (including high-pressure reverse osmosis processes) in the prior art can be used, and this application does not have any particular limitations in this regard; S4, Lithium precipitation: A carbonic acid solution is added to the lithium-rich solution to carry out a precipitation reaction, and the product is obtained after drying. Preferably, in step S4, the carbonic acid solution is a Na2CO3 solution, and the equation for the precipitation reaction is as follows: 2LiCl+ Na2CO3⇌Li2CO3+ 2NaCl; Preferably, in step S4 of this embodiment, before the precipitation reaction, the lithium-rich solution obtained in step S3 is pretreated with a cation exchange resin to remove calcium and magnesium ions; preferably, in this embodiment, a sodium-type strong acid cation exchange resin is used as the cation exchange resin.

[0021] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions in the embodiments of this invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0022] Based on the above-described implementation schemes, this application further proposes the following specific embodiments: First, it should be noted that the reagent raw materials used in the following specific embodiments and comparative examples of the present invention are sourced from the following sources: Unless otherwise specified, all raw materials are ordinary commercially available products; The lithium fluoride mother liquor is a raw material produced during the production of lithium fluoride lithium salt. The raw material of lithium fluoride mother liquor has been filtered and tested. The concentration of lithium fluoride mother liquor is 500-700 mg / L. It should be understood that the following specific embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0023] Example 1: Preparation of a titanium-based ion sieve adsorption column, wherein, in this Example 1, the titanium-based ion sieve is composed of H2TiO3 and H4Ti5O 12 It is composed of HMn2O4 and polyacrylic acid PAA; wherein, H2TiO3:H4Ti5O 12 The mass ratio of HMn2O4 to polyacrylic acid (PAA) is 1:0.08:0.4:0.06. The lithium fluoride mother liquor was continuously fed into the titanium-based ion sieve adsorption column at a flow rate of 10 L / min. The pH during adsorption was 8-8.5, the adsorption temperature was controlled at 20℃, and the operating pressure was controlled at 1.5 bar. Then, the titanium-based ion sieve adsorption column was washed with water and then with hydrochloric acid to obtain a lithium solution. The lithium solution was subjected to ultrafiltration at an operating pressure of 2 bar using a ZeeWeed® series hollow fiber membrane. The lithium solution was then enriched using a reverse osmosis membrane, which consisted of a first-stage reverse osmosis (operating pressure 2 bar) and a high-pressure reverse osmosis (operating pressure 18 bar) process. The reverse osmosis membrane used was a DuPont BW30-400, resulting in a lithium-rich solution. Na2CO3 solution was added to a lithium-rich solution to induce a precipitation reaction and obtain Li2CO3 precipitate. The Li2CO3 precipitate was dried to obtain lithium carbonate product. The purity of the lithium carbonate product was tested and found to be 99.2%, with a lithium yield of 95.3%.

[0024] Example 2: The remaining technical solutions of Example 2 are the same as those of Example 1, except that in Example 2, the titanium-based ion sieve is composed of H2TiO3 and H4Ti5O. 12 It is composed of HMn2O4 and polyacrylic acid PAA; wherein, H2TiO3:H4Ti5O 12 The mass ratio of HMn2O4 to polyacrylic acid (PAA) is 1:0.08:0.45:0.07. Purity testing showed that the purity of the finished lithium carbonate product was 99.4%, and the lithium yield reached 95.4%.

[0025] Example 3: The remaining technical solutions of Example 3 are the same as those of Example 1, except that in Example 3, the titanium-based ion sieve is composed of H2TiO3 and H4Ti5O. 12 And composed of HMn2O4; wherein, H2TiO3:H4Ti5O 12 The mass ratio of HMn2O4 is 1:0.08:0.4; Purity testing showed that the purity of the finished lithium carbonate product was 98.3%, and the lithium yield reached 92.4%. Furthermore, in this Example 3, three parallel control groups were tested, and significant differences in stability were found.

[0026] Example 4: The remaining technical solutions of Example 4 are the same as those of Example 1, except that in Example 4, the titanium-based ion sieve is composed of H2TiO3 and H4Ti5O. 12 And composed of polyacrylic acid (PAA); wherein, H2TiO3:H4Ti5O 12 The mass ratio of polyacrylic acid (PAA) to polyacrylate (PAA) is 1:0.08:0.06. Purity testing revealed that the finished lithium carbonate product had a purity of 98.8% and a lithium yield of less than 85%.

[0027] Example 5: The remaining technical solutions of Example 5 are the same as those of Example 1, except that in Example 5, the titanium-based ion sieve is composed of H2TiO3, HMn2O4 and polyacrylic acid PAA; wherein the mass ratio of H2TiO3:HMn2O4:polyacrylic acid PAA is 1:0.4:0.06. Purity testing showed that the finished lithium carbonate product had a purity of 98.2% and a lithium yield of approximately 86%.

[0028] Example 6: The remaining technical solutions of Example 6 are the same as those of Example 1, except that in step S4 of Example 6, before the precipitation reaction, the lithium-rich solution obtained in step S3 is pretreated with sodium-type strong acid cation exchange resin to further remove calcium and magnesium ions from the lithium-rich solution. Purity testing showed that the lithium carbonate product had a purity of 99.5% and a lithium yield of 95.1%.

[0029] Comparative Example 1: The rest of the technical solutions of Comparative Example 1 are the same as those of Example 1, except that in Comparative Example 1, a manganese ion sieve is used instead of a titanium ion sieve in Example 1. The manganese ion sieve is composed of HMn2O4 and polyacrylic acid PAA, wherein the mass ratio of HMn2O4 to polyacrylic acid PAA is 1:0.06. Purity testing showed that the purity of the finished lithium carbonate product was approximately 96%, and the lithium yield was approximately 80%.

[0030] Comparative Example 2: The rest of the technical solutions of Comparative Example 2 are the same as those of Example 1, except that in Comparative Example 2, step S1: titanium ion sieve adsorption in Example 1 is removed, and the lithium fluoride mother liquor is directly subjected to step S2. Purity testing revealed that the purity of the finished lithium carbonate product was less than 85%, and the lithium yield was less than 70%.

[0031] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0032] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing lithium carbonate from lithium fluoride mother liquor, characterized in that, It should include at least the following steps: S1. Titanium-based ion sieve adsorption: The lithium fluoride mother liquor is continuously passed into the titanium-based ion sieve adsorption column to adsorb lithium ions in the lithium fluoride mother liquor. Then, the ion sieve adsorption column is washed with water and acid in sequence to obtain a lithium solution. S2. Ultrafiltration: Removing ion sieve debris and / or mechanical impurities and / or colloidal substances from the lithium solution by ultrafiltration; S3, Reverse osmosis: The lithium solution is enriched through a reverse osmosis membrane to obtain a lithium-rich solution; S4. Lithium precipitation: Carbonic acid solution is added to the lithium-rich solution to carry out a precipitation reaction, and the lithium carbonate product is obtained after drying.

2. The method for preparing lithium carbonate from lithium fluoride mother liquor according to claim 1, characterized in that, In step S1, the titanium-based ion sieve comprises H2TiO3 and H4Ti5O 12 ; wherein, the H2TiO3 and H4Ti5O 12 The mass ratio range is 1:0.01-0.

15.

3. The method for extracting and preparing lithium carbonate from lithium fluoride mother liquor according to claim 2, characterized in that, The titanium-based ion sieve also includes a manganese-based lithium ion sieve, wherein the manganese-based lithium ion sieve is HMn2O4 with a spinel structure; wherein H2TiO3 and H4Ti5O are present. 12 The sum of their masses and the mass ratio of HMn2O4 is 1:0.05-0.

6.

4. The method for extracting and preparing lithium carbonate from lithium fluoride mother liquor according to claim 3, characterized in that, When H2TiO3, H4Ti5O 12 When the mass ratio of the sum of the masses of the components to that of HMn2O4 is 1:0.3-0.6, the pH during adsorption by the titanium-based ion sieve is 7.5-9.5, the adsorption temperature is controlled at 10-30℃, the concentration of the lithium fluoride mother liquor is 200-700mg / L, the flow rate is controlled at 4-20L / min, and the operating pressure is controlled at 0.5-2.5bar. When H2TiO3, H4Ti5O 12 When the mass ratio of the sum of the masses of the titanium-based ion sieves to the mass of HMn2O4 is 1:0.2-0.3, the pH during adsorption is 8.5-10.5, the adsorption temperature is controlled at 20-40℃, the concentration of lithium fluoride mother liquor is 500-700mg / L, the flow rate is controlled at 35-70L / min, and the operating pressure is controlled at 0.5-2.5bar. When H2TiO3, H4Ti5O 12 When the mass ratio of the sum of the components to HMn2O4 is 1:0.05-0.2, the pH during adsorption by the titanium-based ion sieve is 9.5-11.5, the adsorption temperature is controlled at 30-45℃, the concentration of the lithium fluoride mother liquor is 500-700 mg / L, the flow rate is controlled at 100-120 L / min, and the operating pressure is controlled at 0.5-2.5 bar.

5. The method for preparing lithium carbonate from lithium fluoride mother liquor according to claim 2, 3, or 4, characterized in that, In step S1, the reaction equation includes: H₂TiO₃ (solid adsorbent) + 2Li + (Solution)⇌Li₂TiO₃ (solid adsorbent) + 2H⁺ + (solution); The residual lithium fluoride mother liquor in the adsorbent solid is then removed by water washing, followed by acid washing to obtain a lithium solution. The acid washing process includes the following reaction steps: Li₂TiO₃ (solid adsorbent) + 2HCl ⇌ 2LiCl + H₂TiO₃ (solid adsorbent); LiCl is the lithium solution.

6. The method for preparing lithium carbonate from lithium fluoride mother liquor according to claim 3 or 4, characterized in that, The titanium-based ion sieve further includes a binder for improving the adsorption stability, cycle number, and adsorption capacity of the titanium-based ion sieve; wherein the binder accounts for 1-6% of the mass of the titanium-based ion sieve; and / or the binder is any one or a mixture of several of polyacrylic acid (PAA), polyvinyl chloride (PVC), polyethylene glycol (PEG), and cyanoacrylate (CA).

7. The method for preparing lithium carbonate from lithium fluoride mother liquor according to claim 1, characterized in that, In step S2, the operating pressure of ultrafiltration is set to 1-2.5 bar; and / or the membrane pore size used in ultrafiltration is 1-100 nanometers.

8. The method for preparing lithium carbonate from lithium fluoride mother liquor according to claim 1, characterized in that, In step S3, the lithium ion rejection rate of reverse osmosis is not less than 95%; the reverse osmosis includes sequential first-stage reverse osmosis and high-pressure reverse osmosis; wherein the operating pressure of the first-stage reverse osmosis is 0.5-2.5 bar; and the operating pressure of the high-pressure reverse osmosis is 10-30 bar.

9. The method for preparing lithium carbonate from lithium fluoride mother liquor according to claim 1, characterized in that, In step S4, the carbonic acid solution is a Na2CO3 solution, and the equation for its precipitation reaction is as follows: 2LiCl+ Na2CO3⇌Li2CO3+ 2NaCl.

10. The method for preparing lithium carbonate from lithium fluoride mother liquor according to claim 1 or 9, characterized in that, In step S4, before the precipitation reaction, the lithium-rich solution obtained in step S3 is pretreated with a cation exchange resin to remove calcium and magnesium ions.

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