Method and device for extracting lithium carbonate from salt lake

Abstract

The invention belongs to the technical field of new energy, and particularly relates to a method and a device for extracting lithium carbonate from a salt lake. The method comprises the following steps: S1, performing selective electrodialysis on the salt lake brine to obtain treated brine; s2, collecting the treated brine, adjusting the pH value, and performing ultrafiltration to obtain filtrate; s3, collecting the filtrate, and adsorbing and desorbing the filtrate by adopting same-valence separation resin to obtain a desorption solution; s4, collecting the desorption solution, performing high-pressure reverse osmosis treatment and bipolar membrane treatment to obtain lithium hydroxide, and reacting the lithium hydroxide with carbon dioxide to obtain lithium carbonate; high-pressure reverse osmosis treatment and bipolar membrane treatment cooperate with each other, so that complete recovery of lithium and pure water in a desorption solution is realized, and reutilization and zero emission of water resources are realized; carbon dioxide released by the carbon dioxide capturing and releasing unit reacts with lithium ions, so that sodium ion impurities are prevented from being introduced into a product by adopting sodium carbonate, carbon dioxide in the atmosphere is directly utilized, the cost is reduced, and energy conservation and emission reduction are realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy, and particularly relates to a method and device for extracting lithium carbonate from salt lakes. Background Art

[0002] Lithium carbonate is an important component of lithium-ion batteries. Due to its high energy density and long cycle life, it is usually used in electronic devices, such as new energy vehicles and energy storage systems. The existing lithium carbonate preparation processes mainly include extracting lithium from spodumene, extracting lithium from lepidolite, extracting lithium from salt lakes, and extracting lithium from waste batteries.

[0003] Among them, there are many processes for extracting lithium ore from salt lakes. For salt lake brines or old salt lake bitterns with a pH in the neutral or near-neutral and slightly acidic range, aluminum-based adsorbents are mostly used to extract lithium ore resources. The extraction process includes passing the brine through a resin column filled with the adsorbent. After adsorbing lithium, water (usually fresh brine, with a neutral or slightly acidic pH) is used for desorption. The liquid product of desorption sequentially passes through a nanofiltration membrane to remove magnesium impurities, through a RO membrane to concentrate lithium ions and remove boron impurities, electro-dialysis to remove boron impurities not completely removed by the RO membrane and further concentrate lithium ions in the system, and resin adsorption method to finely remove boron impurities again. Then, MVR evaporation is used to concentrate the lithium ion concentration in the system to more than 10 g / L, and a precipitant sodium carbonate is added to precipitate lithium in the concentrated solution to obtain lithium carbonate. After centrifugation, washing, demagnetization, and drying, battery-grade lithium carbonate is obtained. However, this method has the following disadvantages: 1. The mother liquor separated by centrifugation after lithium precipitation still contains lithium ions, and due to the high sodium ion concentration, it cannot be recycled, resulting in a low lithium recovery rate; 2. The precipitant sodium carbonate generally uses a saturated solution, which will cause the product lithium carbonate to wrap sodium, introducing new impurities and resulting in unstable purity of battery-grade lithium carbonate; 3. In the lithium precipitation stage, due to the use of sodium carbonate, the cost is relatively high, and due to the excessive addition of sodium carbonate, carbon emissions increase, causing environmental pollution; 4. As the adsorption progresses, carbonates enter the adsorbent and occupy the sites, causing the adsorption capacity of the aluminum-based adsorbent to decline. In order to maintain the adsorption of the adsorbent, the aluminum-based adsorbent needs to be continuously replaced, restricting the industrial exploitation of carbonate-type salt lakes; 5. It is only applicable to salt lake brines with a pH in the neutral or near-neutral and slightly acidic range or the old bitterns after potassium extraction in salt lake potash production, and cannot be industrially exploited for alkaline salt lakes or low-salinity salt lakes. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the above defects of the prior art, and thus provide a method and device for extracting lithium carbonate from salt lakes.

[0005] To this end, the present invention provides the following technical solutions:

[0006] The first aspect of the present invention protects a method for extracting lithium carbonate from a salt lake, wherein the method includes the following steps:

[0007] S1. Perform selective electrodialysis on the salt lake brine to obtain the treated brine;

[0008] S2. Collect the treated brine, adjust the pH, and perform ultrafiltration to obtain the filtrate;

[0009] S3. Collect the filtrate, adsorb it with a same-valence separation resin, and desorb to obtain the desorbed solution;

[0010] S4. Collect the desorbed solution, perform high-pressure reverse osmosis treatment, and perform bipolar membrane treatment to obtain lithium hydroxide. React lithium hydroxide with carbon dioxide to obtain lithium carbonate.

[0011] According to the present invention, the selective electrodialysis comprises 2 - 5 electrodialysis modules connected in series.

[0012] According to the present invention, in the selective electrodialysis, the flow directions of the brine and the electrodialysis product water are opposite.

[0013] In the present invention, the selective electrodialysis separates most of the monovalent cations from the divalent and higher-valent cations. And as the separation progresses, ions of the same valence state in different regions aggregate, and concentration is also achieved synchronously; a solution containing monovalent cations such as sodium ions, lithium ions, potassium ions, rubidium ions, and cesium ions and a solution containing anions such as chloride ions, carbonate ions, sulfate ions, and borate ions are obtained; after the selective electrodialysis, the treated brine and the electrodialysis product water are obtained; the concentration of monovalent cations in the treated brine is 5000 - 100000 mg / L; optionally, the concentration of monovalent cations is 5000 - 20000 mg / L; the characteristic of the selective electrodialysis in the present invention is that there is no need to screen and separate different anions, and the concentration of monovalent cations in the brine can meet the above range, reducing the production cost.

[0014] In the present invention, the detection methods for sodium ion concentration can be selected as: atomic absorption spectrophotometry, inductively coupled plasma mass spectrometry, flame photometry; the detection methods for lithium ion concentration can be selected as: atomic absorption spectrophotometry, inductively coupled plasma mass spectrometry; the detection methods for potassium ion concentration can be selected as: atomic absorption spectrophotometry, inductively coupled plasma mass spectrometry, flame photometry; the detection methods for calcium ion and magnesium ion concentrations can be selected as: inductively coupled plasma mass spectrometry, EDTA titration method. In the present invention, lithium ions are tested by atomic absorption spectrophotometry, sodium ions are tested by flame photometry, potassium ions are tested by flame photometry, calcium ions are tested by inductively coupled plasma mass spectrometry, and magnesium ions are tested by inductively coupled plasma mass spectrometry.

[0015] In the present invention, the detection method for the concentration of carbonate ions is: the national standard titration method, and the specific process can be found in GB / T 11064.12-2013 "Methods for chemical analysis of lithium carbonate, lithium hydroxide monohydrate and lithium chloride - Part 12: Determination of carbonate content - Acid-base titration method"; the detection method for the concentration of sulfate ions is: the barium sulfate precipitation method, and the specific process can be found in GB / T 11064.9-2023 "Methods for chemical analysis of lithium carbonate, lithium hydroxide monohydrate and lithium chloride - Part 9: Determination of sulfate content - Barium sulfate turbidimetry".

[0016] In the present invention, after selective electrodialysis, trace divalent and higher-valent cations such as calcium ions, magnesium ions, and ferric ions still exist in the obtained brine. The total concentration of divalent cations such as calcium ions and magnesium ions in the solution does not exceed 100 mg / L; however, in order not to be affected by divalent ions during subsequent lithium ion adsorption, it is necessary to further remove divalent and higher-valent cations. An alkaline solution is added to adjust the pH value of the brine to above 11.8, optionally, the pH value is 12-12.8. After adding the alkaline solution, magnesium ions form magnesium hydroxide precipitation with hydroxide ions; calcium ions combine with carbonate ions from the electrodialysis product water in step S1 under high alkaline conditions to form calcium carbonate, making use of divalent and higher-valent anions in the electrodialysis product water in step S1 and reducing production costs; these precipitates are removed through an ultrafiltration unit to ensure that after ultrafiltration, the concentration of divalent cations in the solution ≤ 1 ppm, and further, the total concentration of divalent and higher-valent cations ≤ 1 ppm; the ultrafiltration material is a conventional material in the art. Typically and non-limitingly, the specific membrane materials used for ultrafiltration include at least one of SiC, ceramics, and organic materials; the organic materials include at least one of cellulose acetate (CA), polystyrene (PS), polyvinylidene fluoride (PVDF), polycarbonate (PC), polyacrylonitrile (PAN), polyethersulfone (PES), and nylon (PA).

[0017] In the present invention, step S2 can be repeated until the concentration of divalent and higher-valent cations in the filtrate satisfies < 1 ppm.

[0018] In the present invention, in the resin adsorption unit, a same-valence separation resin is used for adsorption to obtain a desorbed solution. The same-valence separation resin uses the material in Example 1 of CN108421539B; in the present invention, an acid solution is added for desorption, and the concentration of the acid solution is 1.5-3 mol / L; the acid solution includes a combination of hydrochloric acid solution and sulfuric acid solution, or one of hydrochloric acid solutions. When the acid solution is a combination of hydrochloric acid solution and sulfuric acid solution, the mass ratio of hydrochloric acid in the hydrochloric acid solution to sulfuric acid in the sulfuric acid solution is determined according to the mass ratio of chloride ions to sulfate ions in the filtrate and kept consistent.

[0019] According to the present invention, the concentration of lithium ions in the desorbing solution is > 6 g / L, and the concentration of sodium ions is < 3 g / L.

[0020] In the present invention, the pressure during the high-pressure reverse osmosis treatment is 5 - 9 MPa, and can be optionally 6 - 8 MPa; the concentration of lithium ions after the high-pressure reverse osmosis treatment is > 12 g / L, optionally, the concentration of lithium ions is > 20 g / L, and the concentration of sodium ions is ≤ 10 g / L; the water generated after the high-pressure reverse osmosis treatment can be used as one of the sources for replenishing water in the acid chamber and the alkali chamber of the bipolar membrane; the concentration of the acid solution obtained after the bipolar membrane treatment is 1 - 5 mol / L, and can be optionally 1.5 - 3 mol / L; the concentration of the alkali solution obtained after the bipolar membrane treatment is 1 - 5 mol / L, and can be optionally 1.5 - 3 mol / L.

[0021] In the present invention, the obtained acid solution is a mixture of hydrochloric acid solution and sulfuric acid solution, and the detection method for the concentration is the potentiometric method. The specific process is to use an automatic potentiometric titrator for automatic titration. Take 1 mL of the sample to be tested and put it into the automatic potentiometric titrator for automatic titration.

[0022] According to the present invention, in the bipolar membrane treatment, the single-time migration rate of lithium ions is ≥ 60%; the single-time migration rate is the ratio of the amount of salt consumed for migrating and preparing acids and bases within a unit time to the total amount of salt entering the bipolar membrane system within a unit time. The larger the ratio, the higher the migration conversion and the better the efficiency; among them, the detection method for the amount of salt consumed for migrating and preparing acids and bases within a unit time can be: atomic absorption spectrophotometry, inductively coupled plasma mass spectrometry or flame photometry. In the present invention, the specific test method is to detect the lithium ion concentration at the mother liquor inlet and the discharge port of the first bipolar membrane using an atomic absorption spectrometer (atomic absorption spectroscopy) at a wavelength of 670.8 nm. The lithium ion concentration at the mother liquor inlet minus the lithium ion concentration at the discharge port is the concentration of the salt consumed for migrating and preparing acids and bases.

[0023] The second aspect of the present invention protects a device for extracting lithium carbonate from a salt lake. Among them, the device includes a selectively electrodialysis unit, an ultrafiltration unit, a resin adsorption unit, a high-pressure reverse osmosis unit, a first bipolar membrane unit, a carbon dioxide capture and release unit, and a reaction unit that are connected in sequence.

[0024] According to the present invention, the selectively electrodialysis unit is provided with a mother liquor inlet, a discharge port, and a waste port;

[0025] The ultrafiltration unit is provided with a mother liquor inlet and a discharge port, and the mother liquor inlet of the ultrafiltration unit is connected to the discharge port of the selectively electrodialysis unit;

[0026] The resin adsorption unit is provided with a mother liquor inlet and a discharge port, and the mother liquor inlet of the resin adsorption unit is connected to the discharge port of the ultrafiltration unit;

[0027] The high-pressure reverse osmosis unit is provided with a mother liquor inlet and a discharge outlet, and the mother liquor inlet of the high-pressure reverse osmosis unit is connected to the discharge outlet of the resin adsorption unit;

[0028] The first bipolar membrane unit is provided with a mother liquor inlet and an alkali material outlet, and the mother liquor inlet of the first bipolar membrane unit is connected to the discharge outlet of the high-pressure reverse osmosis unit;

[0029] The reaction unit is provided with a mother liquor inlet, an air inlet, a discharge outlet, and a water outlet, and the mother liquor inlet of the reaction unit is connected to the alkali material outlet of the first bipolar membrane unit;

[0030] The carbon dioxide capture and release unit is provided with an air inlet and an air outlet, and the air outlet of the carbon dioxide capture and release unit is connected to the air inlet of the reaction unit.

[0031] According to the present invention, the device further includes a second bipolar membrane unit, which is arranged between the resin adsorption unit and the high-pressure reverse osmosis unit. The second bipolar membrane unit is provided with a feed inlet, an alkali material outlet, an acid material outlet, and a water outlet.

[0032] According to the present invention, the ultrafiltration unit further includes an alkali material inlet and a water outlet.

[0033] According to the present invention, the resin adsorption unit further includes an acid material inlet and a bottom liquid outlet.

[0034] According to the present invention, the alkali material inlet of the ultrafiltration unit is connected to the alkali material outlet of the second bipolar membrane unit.

[0035] According to the present invention, the acid material inlet of the resin adsorption unit is connected to the acid material outlet of the second bipolar membrane unit.

[0036] According to the present invention, the feed inlet of the second bipolar membrane unit is connected to the bottom material outlet of the resin adsorption unit.

[0037] According to the present invention, the high-pressure reverse osmosis unit further includes a circulating liquid inlet and a water outlet.

[0038] According to the present invention, the first bipolar membrane unit further includes an acid material outlet, a water outlet, and an alkali material inlet.

[0039] In the present invention, the first bipolar membrane unit and the second bipolar membrane unit are conventional bipolar membrane units in the art and have the same structure. Specifically, the bipolar membrane unit includes a first bipolar membrane, an anion exchange membrane, a cation exchange membrane, and a second bipolar membrane arranged in sequence. An acid chamber is formed between the first bipolar membrane and the anion exchange membrane. The acid chamber is respectively provided with an acid feed inlet and an acid feed outlet, and the produced acid feed leaves the system from the acid feed outlet. A salt chamber is formed between the anion exchange membrane and the cation exchange membrane. The salt chamber is respectively provided with a mother liquor inlet and a salt feed outlet, and the produced salt feed leaves the system from the salt feed outlet. An alkali chamber is formed between the cation exchange membrane and the second bipolar membrane. The alkali chamber is respectively provided with an alkali feed inlet and an alkali feed outlet, and the produced alkali feed leaves the system from the alkali feed outlet.

[0040] According to the present invention, the acid feed inlet of the resin adsorption unit is also connected to the acid feed outlet of the first bipolar membrane unit.

[0041] According to the present invention, the circulating liquid inlet of the high-pressure reverse osmosis unit is connected to the water outlet of the first bipolar membrane unit.

[0042] According to the present invention, the mother liquor inlet of the first bipolar membrane unit is connected to the water outlet of the high-pressure reverse osmosis unit.

[0043] According to the present invention, the feed inlet of the second bipolar membrane unit is connected to the water outlet of the high-pressure reverse osmosis unit.

[0044] According to the present invention, the water outlet of the reaction unit is connected to the alkali feed inlet of the first bipolar membrane unit.

[0045] According to the present invention, the water outlet of the reaction unit is connected to the mother liquor inlet of the ultrafiltration unit.

[0046] According to the present invention, the selective electrodialysis unit is composed of 2-5 electrodialysis modules connected in series. The arrangement of each electrodialysis cell from the anode to the cathode is a monovalent selective cation exchange membrane and an anion exchange membrane.

[0047] In the present invention, lithium hydroxide reacts with carbon dioxide in the reaction unit, and lithium carbonate is obtained after centrifugal filtration. A part of the reacted liquid returns to the alkali feed inlet of the first bipolar membrane unit to participate in the reaction again; another part is continuously concentrated. When the sodium concentration accumulates to more than 70 g / L, it returns to the alkali feed inlet of the ultrafiltration unit to participate in pH adjustment, and at the same time, lithium is recovered to improve the resource utilization efficiency.

[0048] During the test process, the inventors unexpectedly found that when the high-pressure reverse osmosis unit is connected to the first bipolar membrane unit in the present invention, there is a synergistic effect between the two units, which can realize the complete recovery of lithium and pure water in the desorbing liquid, thus bringing about the reuse of water resources and zero discharge.

[0049] The technical solution of the present invention has the following advantages:

[0050] 1. The present invention provides a method for extracting lithium carbonate from salt lakes. The method includes the following steps: S1, subjecting salt lake brine to selective electrodialysis to obtain treated brine; S2, collecting the treated brine, adjusting the pH, and performing ultrafiltration to obtain a filtrate; S3, collecting the filtrate, adsorbing it using a same-valence separation resin, and desorbing to obtain a desorbing solution; S4, collecting the desorbing solution, performing high-pressure reverse osmosis treatment and bipolar membrane treatment to obtain lithium hydroxide, and reacting the lithium hydroxide with carbon dioxide to obtain lithium carbonate. First, the present invention performs selective electrodialysis to separate most monovalent cations from divalent and higher-valent cations. As the separation progresses, ions of the same valence state accumulate in different regions, and concentration is also achieved synchronously. Then, the pH is adjusted to precipitate the divalent cations that were not completely separated in step S1, and ultrafiltration is performed to separate magnesium ions in the form of magnesium hydroxide precipitate and calcium ions in the form of calcium carbonate precipitate. The obtained filtrate is adsorbed using a same-valence separation resin to adsorb lithium ions onto the resin, while sodium ions are separated in the form of a solution. The sodium ion concentration in the desorbing solution after desorption is < 3 g / L. Then, high-pressure reverse osmosis and bipolar membrane treatment are performed, and their synergistic effect can achieve complete recovery of lithium and pure water in the lithium-rich concentrate, thus bringing about the reuse of water resources and zero emissions. In the present invention, carbon dioxide reacts with the lithium hydroxide obtained from the bipolar membrane without the need to additionally add raw materials, and carbon dioxide emissions can be reduced, which is beneficial to environmental protection. Because of the three steps of selective electrodialysis, ultrafiltration, and extraction using a same-valence separation resin for the brine, and the synergistic effect of these three steps, this method is applicable to lithium extraction from all system salt lakes. Because of the synergistic effect of the two steps of bipolar membrane treatment and direct reaction with carbon dioxide, the lithium recovery rate in the lithium carbonate reaction stage can be greatly improved (from 85% to 98%).

[0051] 2. The present invention provides an apparatus for extracting lithium carbonate from salt lakes. The apparatus includes a selectively electrodialyzing unit, an ultrafiltration unit, a resin adsorption unit, a high-pressure reverse osmosis unit, a first bipolar membrane unit, a carbon dioxide capture and release unit, and a reaction unit that are connected in sequence. The high-pressure reverse osmosis unit is connected to the first bipolar membrane unit, and their synergistic effect can achieve complete recovery of lithium and pure water in the lithium-rich concentrate, thus bringing about the reuse of water resources and zero emissions. The carbon dioxide capture and release unit in the present invention releases carbon dioxide to react with lithium ions, avoiding the introduction of sodium ion impurities into the product due to the use of sodium carbonate, and directly using carbon dioxide in the atmosphere, reducing costs and achieving green chemistry.

[0052] 3. In the present invention, the feed inlet of the second bipolar membrane unit is connected to the bottom material outlet of the resin adsorption unit; the alkali feed inlet of the ultrafiltration unit is connected to the alkali feed outlet of the second bipolar membrane unit; the acid feed inlet of the resin adsorption unit is connected to the acid feed outlet of the second bipolar membrane unit; the waste bottom material generated in the resin adsorption unit is collected and treated by the second bipolar membrane unit, reducing the waste liquid discharge, which is environmentally friendly; and the acid and alkali generated after the bipolar membrane treatment are returned to the previous unit to participate in the reaction, reducing the production cost and improving the resource utilization rate.

[0053] 4. The first bipolar membrane unit of the present invention further includes an acid feed outlet, and the acid feed inlet of the resin adsorption unit is also connected to the acid feed outlet of the first bipolar membrane unit, so that the acid feed generated by the first bipolar membrane unit is no longer used as waste, but returned to the previous unit as a raw material to participate in the reaction, optimizing the process flow.

[0054] 5. The high-pressure reverse osmosis unit of the present invention further includes a circulating liquid inlet, and the circulating liquid inlet of the high-pressure reverse osmosis unit is connected to the water outlet of the first bipolar membrane unit, reducing the discharge of brine wastewater and realizing the reuse of water resources; the mother liquid inlet of the first bipolar membrane unit is connected to the water outlet of the high-pressure reverse osmosis unit; the feed inlet of the second bipolar membrane unit is connected to the water outlet of the high-pressure reverse osmosis unit; the used water of the high-pressure reverse osmosis unit is collected and re-entered into the first bipolar membrane unit and the second bipolar membrane unit, realizing the reuse of water resources and reducing the waste liquid discharge. Description of the Drawings

[0055] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0056] Figure 1 It is a schematic structural diagram of the device adopted in Example 1;

[0057] Figure 2 It is a schematic structural diagram of the device adopted in Example 2;

[0058] Figure 3 It is a schematic structural diagram of the device adopted in the comparative example;

[0059] Description of the reference numerals: 1 - Selective electrodialysis unit; 2 - Ultrafiltration unit; 3 - Resin adsorption unit; 4 - High-pressure reverse osmosis unit; 5 - First bipolar membrane unit; 6 - Reaction unit; 7 - Carbon dioxide capture and release unit; 8 - Second bipolar membrane unit; 9 - Nanofiltration membrane unit; 10 - Electrodialysis unit; 11 - Resin impurity removal unit; 12 - MVR unit; 13 - Second reaction unit. Detailed implementation manners

[0060] The following embodiments are provided to better further understand the present invention. They are not limited to the described optimal implementation manners, and do not constitute a limitation to the content and protection scope of the present invention. Any product that is the same as or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with those of other existing technologies falls within the protection scope of the present invention.

[0061] For those embodiments where specific experimental steps or conditions are not indicated, the operations or conditions of the conventional experimental steps described in the literature in this field can be followed. For reagents or instruments whose manufacturers are not indicated, they are all conventional reagent products that can be obtained through commercial purchase.

[0062] Solid amine adsorbent material: The purchasing company is Xi'an Lanchang New Materials Co., Ltd., and the product number is LXQ-80;

[0063] ICP multi-element standard solution IV: The purchasing company is Supelco, UNSPSC code: 41116107;

[0064] The specific method for testing ion concentration by atomic absorption spectrophotometry is the conventional atomic absorption spectrophotometry in this field. Taking lithium ions as an example, the specific process is as follows: Using ICP multi-element standard solution IV, diluting with ultrapure water to prepare 5 standard solutions with lithium ion concentrations of 1 mg / L, 3 mg / L, 5 mg / L, 7 mg / L, and 10 mg / L, with each standard solution having a volume of 20 mL. Detecting using an atomic absorption spectrometer (atomic absorption spectrophotometry), the detection wavelength of lithium ions is 670.8 nm, obtaining the lithium ion standard curve, and then using the atomic absorption spectrometer to test the sample, substituting back into the lithium ion standard curve formula to calculate the concentration of lithium ions in the sample; the concentrations of the standard solutions of other ions also tested by atomic absorption spectrophotometry are determined according to the actual situation.

[0065] The specific method for testing ion concentration by flame photometry is the conventional flame photometry in this field. Taking sodium ions as an example, the specific process is as follows: Using ICP multi-element standard solution IV, diluting with ultrapure water to prepare 5 standard solutions with sodium ion concentrations of 1 mg / L, 5 mg / L, 10 mg / L, 15 mg / L, and 20 mg / L, with each standard solution having a volume of 20 mL. Testing using flame photometry, the detection wavelength of sodium ions is 589.0 nm, obtaining the sodium ion standard curve, and then using flame photometry to test the sample, substituting back into the sodium ion standard curve formula to calculate the concentration of sodium ions in the sample; the concentrations of the standard solutions of other ions also tested by flame photometry are determined according to the actual situation.

[0066] The specific method for testing ion concentration by inductively coupled plasma mass spectrometry is the conventional inductively coupled plasma mass spectrometry in this field. Taking calcium ions as an example, the specific process is as follows: Using ICP multi-element standard solution IV, it is fixed volume with ultrapure water to prepare 5 standard solutions with calcium ion concentrations of 1mg / L, 2mg / L, 3mg / L, 4mg / L, and 5mg / L. The volume of each standard solution is 20mL. It is tested by inductively coupled plasma mass spectrometry. The detection wavelength of calcium ions is 393.366nm to obtain the calcium ion standard curve. Then, the sample is tested by inductively coupled plasma mass spectrometry, bringing back the calcium ion standard curve formula to calculate the concentration of calcium ions in the sample; the concentration of the standard solution of other ions also tested by inductively coupled plasma mass spectrometry is determined according to the actual situation;

[0067] The detection method for carbonate ion concentration is: national standard titration method. The specific process can be seen in GB / T11064.12 - 2013 "Chemical analysis methods for lithium carbonate, lithium hydroxide monohydrate and lithium chloride - Part 12: Determination of carbonate content - Acid - base titration method"; the detection method for sulfate ion concentration is: barium sulfate precipitation method. The specific process can be seen in GB / T 11064.9 - 2023 "Chemical analysis methods for lithium carbonate, lithium hydroxide monohydrate and lithium chloride - Part 9: Determination of sulfate content - Barium sulfate turbidimetry".

[0068] Example 1

[0069] The old brine from the salt lake with a pH value of 5.2 (the original brine is treated through a sodium salt pond and a potassium salt pond), the concentration of lithium ions in the old brine is 150 - 240mg / L, the concentration of magnesium ions is 118000 - 120000mg / L, and the concentration of sodium ions is 1100 - 2600mg / L;

[0070] This example provides a device for extracting lithium carbonate from a salt lake. The structural schematic diagram is as Figure 1 shown as follows:

[0071] The device includes a selective electrodialysis unit 1, an ultrafiltration unit 2, a resin adsorption unit 3, a high - pressure reverse osmosis unit 4, a first bipolar membrane unit 5, a reaction unit 6, and a carbon dioxide capture and release unit 7;

[0072] The selective electrodialysis unit 1 is provided with a mother liquor inlet, a discharge port, and a waste port;

[0073] The ultrafiltration unit 2 is provided with a mother liquor inlet and a discharge port. The mother liquor inlet of the ultrafiltration unit 2 is connected to the discharge port of the selective electrodialysis unit 1;

[0074] The resin adsorption unit 3 is provided with a mother liquor inlet and a discharge port. The mother liquor inlet of the resin adsorption unit 3 is connected to the discharge port of the ultrafiltration unit 2;

[0075] The high-pressure reverse osmosis unit 4 is provided with a mother liquor inlet and a discharge port, and the mother liquor inlet of the high-pressure reverse osmosis unit 4 is connected to the discharge port of the resin adsorption unit 3;

[0076] The first bipolar membrane unit 5 is provided with a mother liquor inlet and an alkali material outlet, and the mother liquor inlet of the first bipolar membrane unit 5 is connected to the discharge port of the high-pressure reverse osmosis unit 4;

[0077] The reaction unit 6 is provided with a mother liquor inlet, an air inlet, a discharge port, and a water outlet, and the mother liquor inlet of the reaction unit 6 is connected to the alkali material outlet of the first bipolar membrane unit 5;

[0078] The carbon dioxide capture and release unit 7 is provided with an air inlet and an air outlet, and the air outlet of the carbon dioxide capture and release unit 7 is connected to the air inlet of the reaction unit 6;

[0079] A method for extracting lithium carbonate from a salt lake includes the following steps:

[0080] S1. Perform selective electrodialysis on the old brine of the salt lake, including two electrodialysis modules connected in series. In the selective electrodialysis, the flow directions of the brine and the electrodialysis product water are opposite to preliminarily separate monovalent ions from divalent ions, collect the monovalent ions to obtain the treated brine. The concentration of magnesium ions in the treated brine has been greatly reduced compared to the brine in the salt lake. The concentration of monovalent cations in the treated brine is 5000 mg / L, and the concentration of divalent and higher-valent cations is 1500 mg / L;

[0081] S2. Add 2.5 mol / L sodium hydroxide to the collected treated brine to adjust the pH to 12.0, and perform ultrafiltration using a ceramic membrane. Repeat the steps of adjusting the pH and ultrafiltration once to obtain a filtrate, and the concentration of divalent and higher-valent cations ≤ 1 ppm;

[0082] S3. Collect the filtrate and adsorb it using the same-valence separation resin defined in Example 1 of CN108421539B, and add a mixed acid with a concentration of 2.5 mol / L (2.5 mol / L hydrochloric acid and 2.5 mol / L sulfuric acid) for desorption to obtain a desorbed solution. The concentration of lithium ions in the desorbed solution is 6.5 g / L, and the concentration of sodium ions is 2.1 g / L;

[0083] S4. Collect the desorbed solution and perform high-pressure reverse osmosis treatment using a polyvinyl acetate fiber membrane. The pressure of the high-pressure reverse osmosis is 6.2 MPa; after treatment, the concentration of lithium ions in the system is 20.4 g / L, perform bipolar membrane treatment, and the single migration rate of lithium ions reaches 70%. The lithium concentration at the outlet of the bipolar membrane is 6.1 g / L to ensure the migration rate. Obtain lithium hydroxide and the solid amine adsorbent material from the carbon dioxide capture and release unit The carbon dioxide reaction treated by LXQ-80 can successfully separate lithium ions from other ions in the salt lake to obtain products. The specific components of the products are shown in Table 1. The carbon dioxide capture and release unit releases carbon dioxide to react with lithium ions, avoiding the introduction of excessive sodium ion impurities into the products due to the use of sodium carbonate precipitation (based on the mass of the product, the concentration of sodium ions ≤ 0.02%). Moreover, the yield of battery-grade lithium carbonate is significantly increased (the yield of lithium carbonate is calculated as the ion concentration in the product / the lithium ion concentration at the inlet of the reaction unit × 100% and is 98%). In addition, directly using carbon dioxide in the atmosphere reduces production costs and realizes green chemistry.

[0084] Table 1 Concentrations of Li2CO3-D1 standard in battery-grade lithium carbonate YS / T 582-2023 and the products prepared in this example

[0085]

[0086] Example 2

[0087] The salt lake brine with a pH value of 9.65 has a lithium ion concentration of 120-145 mg / L, a magnesium ion concentration of 600-1100 mg / L, and a sodium ion concentration of 75000-90000 mg / L.

[0088] This example provides a device for extracting lithium carbonate from a salt lake. The structural schematic diagram is as Figure 2 shown as follows:

[0089] The device includes a selective electrodialysis unit 1, an ultrafiltration unit 2, a resin adsorption unit 3, a high-pressure reverse osmosis unit 4, a first bipolar membrane unit 5, a reaction unit 6, a carbon dioxide capture and release unit 7, and a second bipolar membrane unit 8;

[0090] The selective electrodialysis unit 1 is provided with a mother liquor inlet, a discharge port, and a waste port;

[0091] The ultrafiltration unit 2 is provided with a mother liquor inlet, a discharge port, an alkali feed inlet, and a water outlet. The mother liquor inlet of the ultrafiltration unit 2 is connected to the discharge port of the selective electrodialysis unit 1;

[0092] The resin adsorption unit 3 is provided with a mother liquor inlet, a discharge port, an acid feed inlet, and a bottom liquid outlet. The mother liquor inlet of the resin adsorption unit 3 is connected to the discharge port of the ultrafiltration unit 2;

[0093] The high-pressure reverse osmosis unit 4 is provided with a mother liquor inlet, a discharge port, a circulating liquid inlet, and a water outlet. The mother liquor inlet of the high-pressure reverse osmosis unit 4 is connected to the discharge port of the resin adsorption unit 3;

[0094] The first bipolar membrane unit 5 is provided with a mother liquor inlet, an alkali material outlet, an acid material outlet, a water outlet, and an alkali material inlet. The mother liquor inlet of the first bipolar membrane unit 5 is connected to the discharge port of the high-pressure reverse osmosis unit 4;

[0095] The reaction unit 6 is provided with a mother liquor inlet, an air inlet, a discharge port, and a water outlet. The mother liquor inlet of the reaction unit 6 is connected to the alkali material outlet of the first bipolar membrane unit 5; the water outlet of the reaction unit 6 is connected to the alkali material inlet of the first bipolar membrane unit 5, and the water outlet of the reaction unit 6 is connected to the alkali material inlet of the ultrafiltration unit 2; after the reaction in the reaction unit, the remaining liquid product can return to the system to participate in the reaction, reducing the discharge of waste materials and realizing the reuse of resources;

[0096] The carbon dioxide capture and release unit 7 is provided with an air inlet and an air outlet. The air outlet of the carbon dioxide capture and release unit 7 is connected to the air inlet of the reaction unit 6;

[0097] The second bipolar membrane unit 8 is provided with a feed inlet, an alkali material outlet, an acid material outlet, and a water outlet. The alkali material inlet of the ultrafiltration unit 2 is connected to the alkali material outlet of the second bipolar membrane unit 8; the acid material inlet of the resin adsorption unit 3 is connected to the acid material outlet of the second bipolar membrane unit 8; the waste bottom material generated in the resin adsorption unit is collected and processed by the second bipolar membrane unit, reducing the discharge of waste liquid and being environmentally friendly; and the processed bottom material returns to the previous unit to participate in the reaction in the form of acid material and alkali material, reducing the production cost and improving the resource utilization rate;

[0098] The acid material inlet of the resin adsorption unit 3 is also connected to the acid material outlet of the first bipolar membrane unit 5; so that the acid material generated by the first bipolar membrane unit no longer serves as waste, but returns to the previous unit to participate in the reaction as a raw material, optimizing the process flow;

[0099] The circulating liquid inlet of the high-pressure reverse osmosis unit 4 is connected to the water outlet of the first bipolar membrane unit 5. After the reaction, the mother liquor returns to the high-pressure reverse osmosis unit, reducing the discharge of brine wastewater and realizing the reuse of water resources;

[0100] The mother liquor inlet of the first bipolar membrane unit 5 is connected to the water outlet of the high-pressure reverse osmosis unit 4; the feed inlet of the second bipolar membrane unit 8 is connected to the water outlet of the high-pressure reverse osmosis unit 4; the used water of the high-pressure reverse osmosis unit is collected and re-enters the first bipolar membrane unit and the second bipolar membrane unit, realizing the reuse of water resources and reducing the discharge of waste liquid.

[0101] A method for extracting lithium carbonate from a salt lake, comprising the following steps:

[0102] S1. Perform selective electrodialysis on the salt lake brine, including two electrodialysis modules connected in series. In the selective electrodialysis, the flow directions of the brine and the electrodialysis product water are opposite to preliminarily separate monovalent ions from divalent ions, collect the monovalent ions to obtain the treated brine. The concentration of magnesium ions in the treated brine has been greatly reduced compared to the brine in the salt lake. The concentration of monovalent cations in the treated brine is 69000 mg / L.

[0103] S2. Add sodium hydroxide with a concentration of 1.5 mol / L to the collected treated brine, adjust the pH to 12.2, and perform ultrafiltration using a polyvinylidene fluoride membrane. Repeat the steps of adjusting the pH and ultrafiltration for 3 times to obtain the filtrate.

[0104] S3. Collect the filtrate and adsorb it using the same-valence separation resin defined in Example 1 of CN108421539B, and perform desorption by adding hydrochloric acid with a concentration of 1.5 mol / L to obtain the desorbed solution. The concentration of lithium ions in the desorbed solution is 6.0 g / L, and the concentration of sodium ions is 2.9 g / L.

[0105] S4. Collect the desorbed solution and perform high-pressure reverse osmosis treatment using a cellulose acetate membrane. After the high-pressure reverse osmosis treatment at a pressure of 6.5 MPa, the concentration of lithium ions in the system is 12.1 g / L, the lithium concentration at the outlet of the bipolar membrane is 4.23 g / L, and the single-pass mobility of lithium ions reaches 65%. Perform bipolar membrane treatment to react lithium hydroxide with carbon dioxide treated by the solid amine adsorbent material LXQ-80 in the carbon dioxide capture and release unit, which can successfully separate lithium ions from other ions in the salt lake to obtain the product. The specific components of the product are shown in Table 2. Calculate the lithium carbonate yield based on (ion concentration in the product / lithium ion concentration at the inlet of the reaction unit) × 100%. The lithium carbonate yield is 98%.

[0106] Table 2 Concentrations of Li2CO3-D1 standard in battery-grade lithium carbonate YS / T 582-2023 and the product prepared in this example

[0107]

[0108]

[0109] Comparative Example 1

[0110] The salt lake brine with a pH value of 5.3 is treated through a sodium salt pond and a potassium salt pond to obtain the old brine. The concentration of lithium ions in the old brine is 2400 - 3500 mg / L, the concentration of magnesium ions is 118000 - 120000 mg / L, the concentration of calcium ions is 8000 - 10000 mg / L, and the concentration of boron ions is 80 - 600 mg / L.

[0111] The device includes a nanofiltration membrane unit 9, an electrodialysis unit 10, a resin impurity removal unit 11, an MVR unit 12, and a second reaction unit 13. The structural schematic diagram is as shown in Figure 3 shown;

[0112] The nanofiltration membrane unit 9 is provided with a mother liquor inlet, a discharge port, and a waste port;

[0113] The electrodialysis unit 10 is provided with a mother liquor inlet, a discharge port, and a waste port. The mother liquor inlet of the electrodialysis unit 10 is connected to the discharge port of the nanofiltration membrane unit 9;

[0114] The resin impurity removal unit 11 is provided with a mother liquor inlet, a discharge port, and a waste port. The mother liquor inlet of the resin impurity removal unit 11 is connected to the discharge port of the electrodialysis unit 10;

[0115] The MVR unit 12 is provided with a mother liquor inlet, a discharge port, and a water outlet. The mother liquor inlet of the MVR unit 12 is connected to the discharge port of the resin impurity removal unit 11;

[0116] The second reaction unit 13 is provided with a mother liquor inlet, a sodium carbonate inlet, a discharge port, and a water outlet. The mother liquor inlet of the reaction unit 5 is connected to the discharge port of the MVR unit 12;

[0117] A method for extracting lithium carbonate from a salt lake includes the following steps:

[0118] S1. Perform nanofiltration membrane separation on the old brine to preliminarily separate monovalent ions from divalent ions and ions with a valence of two or more, and collect the monovalent ions to obtain the treated brine. The concentration of magnesium ions in the treated brine has been greatly reduced compared to the brine in the salt lake, and the magnesium ion concentration < 10 mg / L;

[0119] S2. Perform electrodialysis concentration on the collected treated brine, adjust the system pH to 5, and use electrodialysis for concentration. The concentration of lithium ions in the concentrated solution is 10 g / L;

[0120] S3. Collect the concentrated solution and use ion exchange resin to remove calcium ions, magnesium ions, and boron ions. After treatment, the magnesium ion concentration in the impurity removal solution < 1 mg / L, the calcium ion concentration < 1 mg / L, and the boron ion concentration < 1 mg / L;

[0121] S4. Collect the impurity removal solution and use double-effect concentrated evaporation (MVR) for concentration. After treatment, the lithium ion concentration in the system is 28 g / L. Lithium chloride reacts with sodium carbonate to obtain crude lithium carbonate, which is centrifuged, washed, demagnetized, and dried to obtain the product. The specific components of the product are shown in Table 3. Calculate the lithium carbonate yield by taking the ion concentration in the product / the lithium ion concentration at the inlet of the reaction unit × 100%. The lithium carbonate yield is 85%;

[0122] Table 3 Concentrations of Li2CO3-D1 and Li2CO3-D3 in YS / T 582-2023 for battery-grade lithium carbonate and the product prepared in this comparative example

[0123]

[0124] Comparative Example 2

[0125] This comparative example provides a device for extracting lithium carbonate from a salt lake. In the same manner as in Example 1, the difference is that the device does not include the selective electrodialysis unit 1 and the reaction unit 6:

[0126] A method for extracting lithium carbonate from a salt lake includes the following steps:

[0127] Salt lake brine with a pH value of 9.65, in which the concentration of lithium ions is 120 - 145 mg / L, the concentration of magnesium ions is 600 - 1100 mg / L, and the concentration of sodium ions is 75000 - 90000 mg / L;

[0128] S1. Add sodium hydroxide with a concentration of 2.0 mol / L to the salt lake brine, adjust the pH to 12.5, and perform ultrafiltration using a polyvinylidene fluoride membrane. Repeat the steps of adjusting the pH and ultrafiltration 3 times to obtain a filtrate;

[0129] S2. Collect the filtrate and adsorb it using the same-valence separation resin defined in Example 1 of CN108421539B, and add hydrochloric acid with a concentration of 2.0 mol / L for desorption. The desorbed solution is obtained, and the concentration of lithium ions in the desorbed solution is 6.0 g / L, and the concentration of sodium ions is 3.0 g / L;

[0130] S3. Collect the desorbed solution and perform high-pressure reverse osmosis treatment using a cellulose acetate membrane. The pressure of the high-pressure reverse osmosis is 6.5 MPa. After treatment, the concentration of lithium ions in the system is 11.8 g / L. Use MVR to treat until the concentration of lithium ions in the concentrated solution is 28 g / L. React the obtained concentrated solution with sodium carbonate. The molar ratio of lithium ions in the concentrated solution to carbonate ions in sodium carbonate is 1:0.55 to obtain crude lithium carbonate. After centrifugation, washing, demagnetization, and drying, the product is obtained. The specific components of the product are shown in Table 4; Calculate the yield of lithium carbonate as 86% based on (ion concentration in the product / lithium ion concentration in the concentrated solution) × 100%.

[0131] Table 4 Concentrations of Li2CO3-D1 and Li2CO3-D3 in YS / T 582-2023 for battery-grade lithium carbonate and the product prepared in this comparative example

[0132]

[0133]

[0134] Comparative Example 3

[0135] This comparative example provides a device for extracting lithium carbonate from a salt lake. In the same manner as in Example 1, the difference is that the device does not include the ultrafiltration unit 2, the resin adsorption unit 3, and the reaction unit 6. The outlet of the selective electrodialysis unit 1 is connected to the mother liquor inlet of the high-pressure reverse osmosis unit 4;

[0136] A method for extracting lithium carbonate from a salt lake includes the following steps:

[0137] Salt lake brine with a pH value of 5.5, in which the concentration of lithium ions is 3120 - 3545 mg / L, the concentration of magnesium ions is 90000 - 120000 mg / L, the concentration of calcium ions is 12000 - 15000 g / L, the concentration of sodium ions is 1000 - 5000 mg / L, and the concentration of potassium ions is 4000 - 8000 g / L;

[0138] S1, in the same manner as S1 in Example 1, to obtain the treated brine;

[0139] S2, collect the treated brine and perform high-pressure reverse osmosis treatment using a polyacetate fiber membrane. The pressure of the high-pressure reverse osmosis is 7.8 MPa; the concentration of lithium ions in the treated system is 6.8 g / L. Then, use the chemical precipitation method to add solid sodium hydroxide (the molar ratio of hydroxide ions in sodium hydroxide to magnesium ions in the system is 1:2.05) and solid sodium carbonate (the molar ratio of carbonate ions in sodium carbonate to calcium ions is 1:1.01) to remove calcium ions and magnesium ions. After treatment, the concentration of magnesium ions < 5 mg / L and the concentration of calcium ions < 5 mg / L. Use MVR to treat until the concentration of lithium ions in the concentrated liquid is 23 g / L. React the obtained concentrated liquid with sodium carbonate. The molar ratio of lithium ions in the concentrated liquid to carbonate ions in sodium carbonate is 1:0.55 to obtain crude lithium carbonate. After centrifugation, washing, demagnetization, and drying, the product is obtained. The specific components of the product are shown in Table 5; calculate the yield of lithium carbonate as 85% based on (ion concentration in the product / lithium ion concentration in the concentrated liquid) × 100%.

[0140] Table 5 Concentrations of Li2CO3-D1 and Li2CO3-D3 in battery-grade lithium carbonate YS / T 582 - 2023 and the product prepared in this comparative example

[0141]

[0142] Comparative Example 4

[0143] This comparative example provides a device for extracting lithium carbonate from a salt lake. In the same manner as in Example 1, the difference is that the device does not include the first bipolar membrane unit 5, the reaction unit 6, and the carbon dioxide capture and release unit 7; the mother liquor inlet of the MVR unit 12 in the device is connected to the outlet of the high-pressure reverse osmosis unit 4;

[0144] In step S4, after high-pressure reverse osmosis treatment, the lithium ion concentration in the system is 12.4 g / L, and it is treated by MVR until the lithium ion concentration in the concentrated solution reaches 27.6 g / L; the obtained concentrated solution reacts with sodium carbonate, and the molar ratio of lithium ions in the concentrated solution to carbonate ions in sodium carbonate is 1:0.55 to obtain crude lithium carbonate, which is centrifuged, washed, demagnetized, and dried to obtain the product; the specific components of the product are shown in Table 6, and lithium carbonate is prepared; taking the ion concentration in the product / concentration of lithium ions in the concentrated solution × 100%, the yield of lithium carbonate is calculated to be 88%.

[0145] Table 6 Concentrations of Li2CO3-D1 and Li2CO3-D3 in the battery-grade lithium carbonate YS / T 582-2023 and the product prepared in this comparative example

[0146]

[0147] Lithium is extracted from acidic salt lakes in Example 1 and from alkaline salt lakes in Example 2. From the data in Table 1 and Table 2, it can be seen that the lithium extraction method of the present invention is applicable to all types of salt lakes and has better industrial value.

[0148] By comparing Examples 1 and 2 with Comparative Example 1, it can be seen that the products prepared in Examples 1 and 2 can meet the standard of Li2CO3-D1 in YS / T 582-2023, while the product prepared in Comparative Example 1 does not meet the standard of Li2CO3-D1 in YS / T 582-2023 and can only meet the standard of Li2CO3-D3 in YS / T 582-2023. The method for extracting lithium carbonate from salt lakes of the present invention can prepare high-quality lithium carbonate, thereby preparing high-quality lithium-ion batteries;

[0149] By comparing Examples 1, Comparative Examples 2 and 3, it can be seen that there is a synergistic effect among the three steps of selective electrodialysis, ultrafiltration, and extraction using a resin with the same valence state separation, which is applicable to all types of salt lakes and can improve the recovery rate and purity of lithium extraction from salt lakes; the lithium carbonate prepared therefrom can meet the production requirements of high-quality lithium-ion batteries;

[0150] By comparing Example 1 with Comparative Example 4, it can be seen that the synergy of the two steps of bipolar membrane treatment and direct reaction with carbon dioxide can greatly improve the lithium recovery rate and increase the purity. The lithium carbonate prepared in this way has the performance to meet the production requirements of high-quality lithium-ion batteries.

[0151] Obviously, the above embodiments are merely examples for clear illustration and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation manners here. And the obvious changes or modifications derived therefrom still fall within the protection scope of the present invention.

Claims

1. A method for extracting lithium carbonate from a salt lake, characterized in that: The method comprises the following steps: S1, subjecting the salt lake brine to selective electrodialysis to obtain treated brine; S2, collecting the treated brine, adjusting the pH, and performing ultrafiltration to obtain a filtrate; S3, collecting the filtrate, using the same valence separation resin for adsorption, and desorbing to obtain a desorbed liquid; S4, collecting the desorption liquid for high-pressure reverse osmosis treatment, and performing bipolar membrane treatment to obtain lithium hydroxide, and the lithium hydroxide reacts with carbon dioxide to obtain lithium carbonate.

2. The method according to claim 1, characterized in that: The selective electrodialysis comprises 2-5 electrodialysis modules connected in series; and / or, the brine in the selective electrodialysis flows in opposite directions to the electrodialysis product water; And / or, the concentration of monovalent cations in the treated brine is 5000-100000 mg / L, optionally 5000-20000 mg / L.

3. The method according to claim 1 or 2, characterized in that: In step S2, the pH value is adjusted to be greater than or equal to 11.8, and may be 12-12.8; And / or, the concentration of divalent and higher cations in the filtrate is ≤1 ppm.

4. The method according to any one of claims 1 to 3, characterized in that: In step S3, an acid solution is added for desorption; Optionally, the concentration of the acid solution is 1.5-3 mol / L; Optionally, the acid solution includes a combination of a hydrochloric acid solution and a sulfuric acid solution, or a hydrochloric acid solution; And / or, the concentration of lithium ions in the desorption solution is >6 g / L, and the concentration of sodium ions is <3 g / L.

5. The method according to any one of claims 1 to 4, characterized in that: The pressure of the high-pressure reverse osmosis is 5-9MPa, and can be 6-8MPa; And / or, the concentration of lithium ions after the high-pressure reverse osmosis treatment is greater than 12 g / L, optionally, the concentration of lithium ions is greater than 20 g / L, and the concentration of sodium ions is ≤10 g / L; And / or, the water generated after the high-pressure reverse osmosis treatment can be used as one of the sources of water replenishment for the acid chamber and the alkaline chamber of the bipolar membrane; And / or, the concentration of the acid solution obtained after the bipolar membrane treatment is 1-5 mol / L, optionally 1.5-3 mol / L; And / or, the concentration of the alkaline solution obtained after the bipolar membrane treatment is 1-5 mol / L, optionally 1.5-3 mol / L; And / or, in the bipolar membrane treatment, the single mobility of lithium ions is ≥ 60%.

6. A device for extracting lithium carbonate from a salt lake, characterized in that: The device comprises a selective electrodialysis unit, an ultrafiltration unit, a resin adsorption unit, a high-pressure reverse osmosis unit, a first bipolar membrane unit, a carbon dioxide capture and release unit, and a reaction unit which are connected in sequence.

7. The device according to claim 6, characterized in that The selective electrodialysis unit is provided with a mother liquid inlet, a discharge port, and a waste port; And / or, the ultrafiltration unit is provided with a mother liquid inlet and a discharge port, and the mother liquid inlet of the ultrafiltration unit is connected to the discharge port of the selective electrodialysis unit; And / or, the resin adsorption unit is provided with a mother liquid inlet and a discharge port, and the mother liquid inlet of the resin adsorption unit is connected to the discharge port of the ultrafiltration unit; And / or, the high-pressure reverse osmosis unit is provided with a mother liquid inlet and a discharge port, and the mother liquid inlet of the high-pressure reverse osmosis unit is connected to the discharge port of the resin adsorption unit; And / or, the first bipolar membrane unit is provided with a mother liquor inlet and an alkali material outlet, and the mother liquor inlet of the first bipolar membrane unit is connected to the outlet of the high-pressure reverse osmosis unit; And / or, the reaction unit is provided with a mother liquor inlet, an air inlet, a material outlet, and a water outlet, and the mother liquor inlet of the reaction unit is connected to the alkali material outlet of the first bipolar membrane unit; And / or, the carbon dioxide capture and release unit is provided with an air inlet and an air outlet, and the air outlet of the carbon dioxide capture and release unit is connected to the air inlet of the reaction unit; And / or, the device further comprises a second bipolar membrane unit, which is arranged at the rear end of the resin adsorption unit, and the second bipolar membrane unit is provided with a feed inlet, an alkali material outlet, an acid material outlet, and a water outlet; And / or, the ultrafiltration unit further comprises an alkali material inlet and a water outlet; And / or, the resin adsorption unit further comprises an acid material inlet and a bottom liquid outlet; And / or, the alkali material inlet of the ultrafiltration unit is connected to the alkali material outlet of the second bipolar membrane unit; And / or, the acid material inlet of the resin adsorption unit is connected to the acid material outlet of the second bipolar membrane unit; And / or, the feed inlet of the second bipolar membrane unit is connected to the bottom material outlet of the resin adsorption unit; And / or, the high-pressure reverse osmosis unit further includes a circulating liquid inlet and a water outlet.

8. The device according to claim 7, characterized in that The first bipolar membrane unit also includes an acid material outlet, a water outlet, and an alkali material inlet; Optionally, the acid material inlet of the resin adsorption unit is also connected to the acid material outlet of the first bipolar membrane unit; and / or, the circulating liquid inlet of the high-pressure reverse osmosis unit is connected to the water outlet of the first bipolar membrane unit; And / or, the mother liquid inlet of the first bipolar membrane unit is connected to the water outlet of the high-pressure reverse osmosis unit; And / or, the feed inlet of the second bipolar membrane unit is connected to the water outlet of the high-pressure reverse osmosis unit.

9. The device according to claim 8, characterized in that The water outlet of the reaction unit is connected to the alkali material inlet of the first bipolar membrane unit; And / or, the water outlet of the reaction unit is connected to the alkali material inlet of the ultrafiltration unit.

10. The device according to any one of claims 6 to 9, characterized in that: The selective electrodialysis unit comprises 2-5 electrodialysis modules connected in series, and each electrodialysis cell is arranged from the anode to the cathode with a monovalent selective cation exchange membrane and anion exchange membrane.

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