Bipolar membrane ion rectification coupled carbon dioxide mineralization separation system and application thereof

Abstract

The invention discloses a bipolar membrane ion rectification coupled carbon dioxide mineralization separation system and application thereof. The system comprises a cation rectification device with a bipolar membrane as an end-capped diaphragm, and a carbon dioxide gas nano disperser is arranged in a last-stage cation rectification chamber of the rectification device. When the separation system is used for extracting lithium from the salt lake, on one hand, separation of monovalent and multivalent ions in salt lake brine and production of a strongly alkaline lithium-rich solution are realized through a bipolar membrane ion rectification technology, and on the other hand, the separation system is coupled with a carbon dioxide nano mineralization separation technology; high-selectivity separation of lithium ions and other monovalent impurity cations in the salt lake brine is achieved, and finally the purpose of preparing battery-grade high-purity lithium carbonate from the salt lake brine is achieved. The method disclosed by the invention has the advantages of low energy consumption, high integration level, high product purity, environmental protection and the like, and shows a wide application prospect in the field of special ion separation such as salt lake recycling.

Description

Technical Field

[0001] The invention belongs to the field of electrically driven membrane coupled separation, and in particular relates to a bipolar membrane ion distillation coupled carbon dioxide mineralization separation system. Background Art

[0002] As an important chemical technology, special ion separation plays an important role in salt lake resource utilization, especially in lithium extraction from salt lakes. At present, lithium and its metal compounds have been widely used in lithium batteries, aerospace, lasers, ceramics and other fields due to their excellent physical and chemical properties. However, the ion content in natural salt lakes is complex, especially the sodium ions and potassium ions with the same valence and similar properties as lithium ions are high in content and difficult to separate, which brings difficulties and challenges to lithium extraction from salt lakes.

[0003] Traditional salt lake lithium extraction processes, especially the separation of lithium ions and other cations, include adsorption and multi-stage crystallization. The above-mentioned process methods are based on the functional groups of the separation material itself and the physical properties of the target ions to be separated to separate ions, which can realize the resource utilization of salt lake brine to a certain extent. However, due to the limitations of the process principle, their ability to recover lithium is limited, and the environmental pollution is large, so it is difficult to apply them in actual production at this stage. Among them, the adsorption method achieves the goal of lithium extraction based on the difference in the physical affinity of lithium ions and other cations for functional materials, and mainly extracts lithium from brine with relatively high lithium content. Although the adsorption method has simple process operation and high lithium ion recovery rate, it involves multiple adsorption and desorption processes of functional materials during the operation, which makes it difficult to operate continuously for a long time. After multiple cycles, the structure of the functional separation material will be destroyed, which will lead to a serious reduction in the adsorption capacity of lithium ions, which is not conducive to long-term use; in addition, the desorption regeneration process needs to be carried out under acidic conditions, which poses a challenge to the corrosion resistance of the operating equipment, and it is also necessary to use biochemical, advanced oxidation, pressure-driven membrane and other methods to purify the generated acidic wastewater, which will also bring great difficulties to environmental protection. The multi-stage crystallization principle is based on the solubility difference between lithium salts and other monovalent cation salts, multi-stage operation, and the final purification of experimental lithium products. This method involves phase change processes many times, has a long operation time, high energy consumption, large amount of evaporated water, is environmentally unfriendly, and it is difficult to quickly obtain high-quality products.

[0004] The latest reported ion distillation technology, such as a bipolar membrane-assisted ion distillation method for preparing battery-grade lithium products from salt lake brine in one step disclosed in patent CN 113559715, treats salt lake brine by ion distillation to obtain battery-grade lithium hydroxide products and hydrochloric acid products. However, the composition of salt lake brine is complex, and the main ions included include free ions such as lithium ions, sodium ions, potassium ions, magnesium ions, calcium ions, chloride ions, sulfate ions, nitrate ions and borate ions, as well as physical impurities such as crystal particles of different sizes. Ion distillation is mainly based on the electrostatic repulsion of a single multivalent ion exchange membrane, which can only achieve the step-by-step separation of monovalent and multivalent ions, and cannot achieve the separation of ions that are all monovalent. Therefore, before passing through the ion distillation system, the method also needs to perform multi-pond evaporation, multi-step crystallization, causticization precipitation and other processes on the salt lake brine to remove monovalent impurity ions such as sodium and potassium, resulting in cumbersome process steps and high cost. And after obtaining lithium hydroxide solution by ion distillation, it needs to be further evaporated to obtain a solid product. At the same time, lithium hydroxide and lithium carbonate are suitable for different battery systems. At present, in order to obtain battery-grade lithium carbonate, it is necessary to causticize lithium hydroxide by adding additional sodium salts such as sodium carbonate, which inevitably introduces new impurities and increases the cost of lithium extraction.

[0005] Therefore, how to quickly and efficiently obtain lithium carbonate from systems such as salt lake brine with complex ion composition is a key issue that needs to be solved urgently at this stage. Summary of the invention

[0006] Based on the problems existing in the above-mentioned prior art, the present invention first provides a carbon dioxide mineralization separation system coupled with bipolar membrane ion distillation, and based on the system, further provides a method for preparing lithium carbonate from carbon dioxide mineralized salt lake brine. On the one hand, the bipolar membrane ion distillation technology is used to achieve the separation of monovalent and polyvalent ions in the salt lake brine and the production of a strong alkaline lithium-rich solution. On the other hand, it is coupled with the carbon dioxide nano-mineralization separation technology. Based on the difference in the solubility of carbonates with different monovalent cations, a highly selective separation of lithium ions and other monovalent impurity cations in the salt lake brine is achieved, and ultimately the purpose of preparing battery-grade high-purity lithium carbonate from the salt lake brine is achieved.

[0007] In order to achieve the purpose, the present invention adopts the following technical scheme:

[0008] The present invention firstly discloses a bipolar membrane ion distillation coupled carbon dioxide mineralization separation system, which is characterized in that it comprises a cation distillation device with a bipolar membrane as a capping diaphragm, the last stage cation distillation chamber of the cation distillation device serves as a product chamber, and a carbon dioxide gas nanodisperser is arranged in the product chamber.

[0009] Furthermore, the specific configuration of the cationic distillation device and other structures that assist the operation of the cationic distillation device (including a solution auxiliary circulation system and a current power supply system) can be referenced to patent CN113663519B. The cation distillation device is composed of at least one group of cation distillation units encapsulated between the anode plate and the cathode plate; the cation distillation unit is a membrane unit composed of one or more anion exchange membranes and one or more special cation selective membranes, which are stacked in sequence according to the principle of "same type on the same side" and then added with a flow channel separator and a sealing gasket; one or more anion retention chambers are formed between adjacent anion exchange membranes; one or more cation distillation chambers are formed between adjacent special cation selective membranes; a liquid chamber is formed between the anion exchange membrane and the special cation selective membrane; a bipolar membrane is arranged as a capping diaphragm between the anode plate, the cathode plate and the cation distillation unit; an anode chamber is formed between the anode plate and the adjacent bipolar membrane, and a cathode chamber is formed between the cathode plate and the adjacent bipolar membrane; an anion retention chamber is formed between the bipolar membrane close to the anode plate and the adjacent anion exchange membrane, and a last stage cation distillation chamber as a product chamber is formed between the bipolar membrane close to the cathode plate and the adjacent special cation selective membrane. The distillation stages of the ion distillation device can be designed according to the system components and product requirements.

[0010] Further, the carbon dioxide gas nano-disperser is connected to the carbon dioxide gas cylinder. The carbon dioxide gas nano-disperser can disperse and reduce the volume of carbon dioxide bubbles in the solution and increase the contact area between carbon dioxide and alkaline lithium-rich solution. The dispersion effect of carbon dioxide can be adjusted according to the pore size of the carbon dioxide gas nano-disperser. The carbon dioxide gas cylinder and the carbon dioxide gas nano-disperser can be connected by a connecting pipe, and a pressure valve is set at the gas outlet of the carbon dioxide gas cylinder to control the flow rate of the gas.

[0011] Furthermore, the solution in the product chamber circulates independently and is not connected to other membrane stack chambers to ensure a strong alkaline environment in the product chamber.

[0012] The present invention also discloses the application of the bipolar membrane ion distillation coupled carbon dioxide mineralization separation system, which is characterized in that: it is used to process the raw salt, so that the required cations in the raw salt enter the product chamber through step-by-step distillation, and first react with OH generated by the bipolar membrane in the product chamber. - Combined with CO2, and then further combined with CO2 uniformly dispersed by the carbon dioxide gas nanodispersor to form the corresponding carbonate. Furthermore, based on the solubility difference of different carbonates, the recovery of low-solubility carbonates can be achieved in the form of precipitation.

[0013] Based on the above application, the present invention provides a method for preparing lithium carbonate from salt lake brine by mineralizing carbon dioxide, which is characterized in that: the above bipolar membrane ion distillation coupled carbon dioxide mineralization separation system is used to add the salt lake brine to be treated into the feed liquid chamber, so that lithium ions and other monovalent cations are driven by the electric field to pass through the special cation selective membrane (using a multivalent cation selective membrane) from the feed liquid chamber step by step into the product chamber, and the multivalent cations are selectively blocked step by step from the feed liquid chamber by the special cation selective membrane, so as to achieve the separation of monovalent cations and multivalent cations; the monovalent cations are firstly reacted with OH generated by the bipolar membrane in the product chamber; - It is combined with CO2 evenly dispersed by a carbon dioxide gas nanodispersor to form carbonates of monovalent cations. At the same time, based on the solubility differences of carbonates of different monovalent cations, the separation of lithium ions from other monovalent cations is achieved in the form of nanoscale lithium carbonate precipitation.

[0014] Furthermore, the salt lake brine is ultrafiltered to remove impurities such as crystal particles, and diluted to improve the fluidity of the brine before being introduced into the cation distillation device. Lithium hydroxide can be used as the initial solution in the product chamber, hydrochloric acid can be used as the initial solution in the anion retention chamber, lithium chloride can be used as the initial solution in the cation distillation chamber, and sodium sulfate can be used as the initial solution in the electrode chamber.

[0015] Furthermore, when the concentration of lithium ions in the product chamber rises to 0.8 mol / L or above, carbon dioxide gas is introduced into the product chamber to ensure that the lithium ion content is much greater than its solubility, thereby generating lithium carbonate precipitation.

[0016] Furthermore, the carbon dioxide flow rate and the pore size of the carbon dioxide gas nanodispersor are adjusted according to the product chamber volume and the lithium ion concentration to improve the carbon dioxide utilization efficiency and the precipitation effect of lithium carbonate.

[0017] Furthermore, the produced lithium carbonate precipitate is collected by filtration, and washed several times to further remove the soluble sodium carbonate and potassium carbonate attached to the surface of the precipitate. Finally, the precipitate is dried to obtain a battery-grade high-purity lithium carbonate product.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] Based on the separation of multi-ion complex systems, especially the problem of lithium extraction in salt lakes, the present invention starts from the aspects of intensive chemical production, economic production process and efficient operation process, and synergistically couples bipolar membrane ion distillation and carbon dioxide nano-mineralization technology, and proposes a bipolar membrane ion distillation coupled carbon dioxide mineralization separation system and its application method in salt lake lithium extraction production. First, relying on ion distillation technology, bipolar membranes are used to seal on both sides of the membrane stack of the ion distillation device, and monovalent cations are enriched and concentrated in the product chamber through the step-by-step separation of multivalent cations, and a strong alkaline lithium-rich solution is obtained in the product chamber based on the in-situ acid-base performance of the bipolar membrane; then, facing the separation of monovalent cation systems with the same physical and chemical properties, carbon dioxide nano-mineralization technology is introduced, and carbon dioxide bubbles are refined through carbon dioxide gas nano-dispersors to promote the absorption of carbon dioxide by alkaline solutions. Based on the solubility differences between different carbonates, the separation of lithium ions and other monovalent impurity ions (such as sodium ions and potassium ions) in the process of salt lake resource utilization is realized, and high-purity lithium carbonate products are directly and quickly obtained. The present invention combines the advantages of ion distillation and concentration and carbon dioxide nano-mineralization technology, and takes complex salt lake brine as an example to achieve lithium ion concentration and efficient separation from other impurity ions, thereby quickly preparing high-purity battery-grade lithium carbonate products at low cost. The method of the present invention has the advantages of low energy consumption, high integration, high product purity, and environmental protection, and shows broad application prospects in the field of special ion separation such as salt lake resource utilization. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A technical route for treating simulated brine using a carbon dioxide mineralization separation system coupled with bipolar membrane ion distillation;

[0021] Figure 2 This is a schematic diagram of the arrangement of the carbon dioxide gas nanodisperser used in the embodiment of the present invention in the product room;

[0022] Figure 3 The curve of the change of the hydroxide concentration in the product chamber over time in Example 3;

[0023] Figure 4 The curve of the change of cation concentration in the product chamber over time in Example 3;

[0024] Figure 5 The XRD patterns of the lithium carbonate products in Examples 1 to 3 are as follows;

[0025] Figure 6 This is an optical photograph of the lithium carbonate product in Example 3; DETAILED DESCRIPTION

[0026] The specific implementation of the present invention is described in detail below in conjunction with the examples. The following content is only an example and explanation of the concept of the present invention. The technicians in this technical field can make various modifications or supplements to the specific implementation cases described or replace them in a similar manner. As long as they do not deviate from the concept of the invention or exceed the scope defined by the claims, they should all belong to the protection scope of the present invention.

[0027] Example 1

[0028] This embodiment uses a bipolar membrane ion distillation coupled carbon dioxide mineralization separation system to treat simulated brine, which mainly converts into lithium ions, magnesium ions, and chloride ions, and the concentration of cations (lithium ions, magnesium ions) is 0.1 mol / L.

[0029] The bipolar membrane ion distillation coupled carbon dioxide mineralization separation system of this embodiment includes a cation distillation device with a bipolar membrane as a capping diaphragm, the last stage cation distillation chamber of the cation distillation device is used as a product chamber, and a carbon dioxide gas nanodisperser is arranged in the product chamber. Figure 2 As shown, the carbon dioxide gas nanodisperser is connected to the carbon dioxide gas cylinder through a connecting pipe, and a pressure regulating valve is arranged at the gas outlet of the carbon dioxide gas cylinder to control the flow rate of the gas.

[0030] The cation distillation device used in this embodiment is a four-stage asymmetric structure, and the number of cation distillation units is 1. The cation distillation device of this embodiment is composed of 1 anion exchange membrane, 4 special monovalent selective cation exchange membranes and 2 bipolar membranes (as end-capping diaphragms). Among them, 2 ruthenium iridium electrodes are installed on both sides of the cation distillation device as end plates and current collectors, and 2 bipolar membranes are placed near the anode and cathode sides as end-capping diaphragms, 4 special monovalent selective cation exchange membranes are repeatedly stacked at one end near the cathode side, and the anion exchange membrane is installed at one end near the anode side. This embodiment adopts the membrane stack arrangement of asymmetric bipolar membrane cation distillation. The effective area of ​​a single membrane and a ruthenium iridium electrode is 21cm 2 The special monovalent and multivalent selective cation exchange membrane, anion exchange membrane and bipolar membrane adopt the ion exchange membrane products CIMS, AMX and BP-1E of Japan ASTOM Company respectively.

[0031] Before applying current: simulated brine is passed into the feed liquid chamber. A lithium chloride solution with a concentration of 0.1 mol / L is circulated in the first cation distillation chamber; similarly, a lithium chloride solution with a concentration of 0.1 mol / L is circulated in the second cation distillation chamber; similarly, a lithium chloride solution with a concentration of 0.1 mol / L is circulated in the third cation distillation chamber; a lithium hydroxide solution with a concentration of 0.01 mol / L is circulated in the fourth cation distillation chamber (i.e., the product chamber). A 0.01 mol / L sulfuric acid solution is circulated in the anion retention chamber, and a 0.3 mol / L lithium sulfate solution is circulated in the anode chamber and the cathode chamber as an auxiliary electrolyte.

[0032] The solution in each membrane stack chamber circulates in the ion distillation storage tank for 10 minutes. When the liquid level in the ion distillation storage tank remains constant and the device is running stably, 5 mA / cm is applied to the cationic distillation device. 2 A constant current is applied, and a power supply is used to detect the current and voltage changes during the operation of the cation distillation device online. A conductivity meter is used to detect the conductivity changes in each chamber during the operation. During the operation, samples are taken from each cation distillation chamber at regular intervals, and an inductively coupled plasma optical emission spectrometer (ICP-OES) is used to detect and analyze the ion concentration in the final product chamber of the bipolar membrane ion distillation device.

[0033] Utilizing the carbon dioxide gas nanodisperser fixed in the product chamber, after the device operation is completed, carbon dioxide gas at a suitable flow rate of 2L / min is introduced into the product chamber for 5 minutes to achieve efficient mineralization of carbon dioxide and quickly obtain nano-scale carbonate particles in the product chamber.

[0034] Finally, the precipitate is filtered, washed and dried to obtain a high-purity lithium carbonate product. A portion of the lithium carbonate product is taken, acid leached and dissolved, and the composition of the lithium carbonate product obtained in this embodiment is detected by inductively coupled plasma optical emission spectrometry (ICP-OES). The mass fractions of cations in the product chamber solution of the ion distillation device and the lithium carbonate product before carbon dioxide mineralization are shown in Table 1.

[0035] Table 1

[0036] chemical composition Lithium carbonate product (ppm) Product room liquid before mineralization (ppm) <![CDATA[Li + ]]> 72.65 65.4 <![CDATA[Mg 2+ ]]> 0.102 0.142 <![CDATA[Purity of Li2CO3]]> 99.96％ /

[0037] Example 2

[0038] This embodiment uses the same bipolar membrane ion distillation coupled carbon dioxide mineralization analysis system as in Example 1 to treat simulated brine (the concentrations of lithium ions, sodium ions, and potassium ions in the simulated brine are all 0.1 mol / L, and the concentration of chloride ions is 0.3 mol / L). The mass fractions of cations in the product chamber solution of the ion distillation device and the lithium carbonate product before carbon dioxide mineralization are shown in Table 2.

[0039] Table 2

[0040] chemical composition Lithium carbonate product (ppm) Product room liquid before mineralization (ppm) <![CDATA[Li + ]]> 104.43 26.26 <![CDATA[Na + ]]> 0.956 115.62 <![CDATA[K + ]]> 1.259 264.25 <![CDATA[Purity of Li2CO3]]> 99.51％ /

[0041] Example 3

[0042] This embodiment uses the same bipolar membrane ion distillation coupled carbon dioxide mineralization analysis system as in Example 1 to process real salt lake brine. The salt lake brine mainly becomes lithium ions, sodium ions, potassium ions, calcium ions, magnesium ions, chloride ions, and sulfate ions. The cationic components in the solution are shown in Table 3.

[0043] Table 3

[0044] chemical composition Salt lake brine components (ppm) <![CDATA[Li + ]]> 3380 <![CDATA[Na + ]]> 125 <![CDATA[K + ]]> 414 <![CDATA[Ca 2+ ]]> 1520 <![CDATA[Mg 2+ ]]> 106740

[0045] The mass fractions of cations in the product chamber solution of the ion distillation device and the lithium carbonate product before carbon dioxide mineralization are shown in Table 4.

[0046] Table 4

[0047] chemical composition Lithium carbonate product (ppm) Product room liquid before mineralization (ppm) <![CDATA[Li + ]]> 114.43 6751 <![CDATA[Na + ]]> 1.056 3753 <![CDATA[K + ]]> 0.559 2338 <![CDATA[Mg 2+ ]]> 0.106 5.05 <![CDATA[Purity of Li2CO3]]> 99.60％ /

[0048] It can be seen from Tables 1, 2 and 4 that the carbon dioxide nano-mineralization technology can obtain battery-grade high-purity lithium carbonate products by utilizing the difference in solubility of different carbonates on the basis of bipolar membrane ion distillation and concentration to remove multivalent ions, and further realize the efficient separation of lithium ions and other cations, especially monovalent cations.

[0049] from Figure 3 , Figure 4 It can be seen that when the four-stage ion distillation device is used to treat real salt lake brine, the cation concentration in the product chamber gradually increases with time. Due to the multi-stage screening effect of the special monovalent cation selective exchange membrane for magnesium ions, a good separation effect can be achieved for magnesium ions. However, the special monovalent cation selective exchange membrane has no selectivity between different monovalent ions, resulting in the gradual enrichment of sodium ions and potassium ions in the product chamber, just like lithium ions. At the same time, due to the use of bipolar membranes as ion distillation end-capping membranes, the hydroxide ion concentration in the product chamber also gradually increases, which provides strong alkaline conditions for the efficient mineralization of carbon dioxide. From Table 4 and Figure 5 It can be seen that the carbon dioxide nano-mineralization technology can realize the separation of sodium ions and potassium ions in the strongly alkaline lithium-rich solution in the product chamber, so that after multiple filtration and washing, the lithium extraction operation can be efficiently realized to obtain a battery-grade lithium carbonate product with a purity of 99.60%, and no phase other than lithium carbonate is found in the XRD spectrum.

[0050] From Example 1, Example 2 and Example 3, it can be concluded that when facing different complex ion systems, the technical route of the present invention can further achieve the separation of lithium ions and impurity ions, especially other monovalent ions, on the basis of ion distillation separation of monovalent and polyvalent ions. The use of bipolar membrane as an ion distillation end-capping diaphragm provides a strong alkaline environment for carbon dioxide nano-mineralization technology, and then based on the solubility difference of different carbonates, effectively achieves the purpose of lithium extraction from salt lakes, and can directly obtain battery-grade high-purity lithium carbonate products.

[0051] The present invention adopts a coupling process of bipolar membrane ion distillation and carbon dioxide mineralization technology, and prepares a lithium-rich solution with a lithium-magnesium selectivity of up to 10000-100000 in a one-step method for high magnesium-lithium ratio salt lake brine, and combines carbon dioxide mineralization technology to achieve efficient separation of monovalent cations. By adopting a coupling process, the efficient separation of lithium ions and magnesium ions, sodium ions, and potassium ions is effectively achieved, which greatly simplifies the lithium extraction process of salt lake brine, shortens the ion separation process, reduces production costs, and realizes the refined screening of complex component ions in salt lake brine, and can directly obtain high-purity lithium carbonate products. At the same time, the cation distillation system and the carbon dioxide mineralization process do not need to introduce additional chemical reagents, are environmentally friendly, and effectively avoid the problems of pollution to the natural environment in the traditional salt lake lithium extraction process.

[0052] The above are merely exemplary embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A bipolar membrane ion distillation coupled carbon dioxide mineralization separation system, characterized in that: The invention comprises a cation rectification device with a bipolar membrane as an end-capping diaphragm, wherein the last-stage cation rectification chamber of the cation rectification device serves as a product chamber, and a carbon dioxide gas nanodisperser is arranged in the product chamber.

2. The bipolar membrane ion distillation coupled carbon dioxide mineralization separation system according to claim 1 is characterized in that: The cation rectification device is composed of at least one group of cation rectification units encapsulated between the anode plate and the cathode plate; the cation rectification unit is a membrane unit composed of one or more anion exchange membranes and one or more special cation selective membranes, which are sequentially stacked according to the "same type, same side" principle and then added with a flow channel spacer and a sealing gasket; One or more anion retention chambers are formed between adjacent anion exchange membranes; one or more cation rectification chambers are formed between adjacent special cation selective membranes; and a feed liquid chamber is formed between the anion exchange membrane and the special cation selective membrane; A bipolar membrane is arranged between the anode plate, the cathode plate and the cation distillation unit as a capping diaphragm; an anode chamber is formed between the anode plate and the adjacent bipolar membrane, and a cathode chamber is formed between the cathode plate and the adjacent bipolar membrane; an anion retention chamber is formed between the bipolar membrane close to the anode plate and the adjacent anion exchange membrane, and a final cation distillation chamber as a product chamber is formed between the bipolar membrane close to the cathode plate and the adjacent special cation selective membrane.

3. The bipolar membrane ion distillation coupled carbon dioxide mineralization separation system according to claim 1, characterized in that: The carbon dioxide gas nano-disperser is connected to the carbon dioxide gas cylinder.

4. The bipolar membrane ion distillation coupled carbon dioxide mineralization separation system according to claim 2, characterized in that: The solution in the product chamber circulates independently and is not connected to other membrane stack chambers.

5. An application of the bipolar membrane ion distillation coupled carbon dioxide mineralization separation system according to any one of claims 1 to 4, characterized in that: It is used to process the raw salt so that the required cations in the raw salt enter the product chamber through step-by-step distillation and react with the OH produced by the bipolar membrane in the product chamber. - Combined with the CO2 uniformly dispersed by the carbon dioxide gas nanodispersor to form the corresponding carbonate.

6. The use according to claim 5, characterized in that: Based on the difference in solubility of different carbonates, the recovery of low-solubility carbonates is achieved in the form of precipitation.

7. A method for preparing lithium carbonate from salt lake brine by mineralization of carbon dioxide, characterized in that: The carbon dioxide mineralization separation system coupled with bipolar membrane ion distillation according to any one of claims 1 to 4 is used to add salt lake brine into the feed liquid chamber, so that lithium ions and other monovalent cations are driven by the electric field to gradually pass through the special cation selective membrane from the feed liquid chamber into the product chamber, and multivalent cations are selectively blocked step by step from the feed liquid chamber by the special cation selective membrane, thereby realizing the separation of monovalent cations and multivalent cations; the monovalent cations are firstly reacted with OH generated by the bipolar membrane in the product chamber, and then the OH generated by the bipolar membrane is reacted with the OH generated by the bipolar membrane. - It is combined with CO2 evenly dispersed by a carbon dioxide gas nanodispersor to form carbonates of monovalent cations. At the same time, based on the solubility differences of carbonates of different monovalent cations, the separation of lithium ions from other monovalent cations is achieved in the form of nanoscale lithium carbonate precipitation.

8. The method according to claim 6, characterized in that: The carbon dioxide flow rate and the pore size of the carbon dioxide gas nanodisperser are adjusted according to the product chamber volume and lithium ion concentration.

9. The method according to claim 6, characterized in that: The produced lithium carbonate precipitate is collected by filtration, washed several times to further remove soluble sodium carbonate and potassium carbonate, and finally the precipitate is dried to obtain a battery-grade high-purity lithium carbonate product.

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