A method for comprehensive recovery of lithium carbonate precipitation mother liquor

Abstract

This invention discloses a method for the comprehensive recovery of lithium carbonate precipitation mother liquor. The method involves first selectively recovering lithium from the mother liquor using an adsorbent or extractant; subsequently, the lithium-extracted mother liquor (containing Na) is then... + K + High-salinity wastewater containing lithium carbonate is acidified and aerated. The generated carbon dioxide gas is recovered using sodium hydroxide to produce sodium carbonate as a byproduct. Furthermore, the acidified high-salinity wastewater is processed using a bipolar membrane to produce acid and alkali for system use. Excess high-salinity wastewater is evaporated and crystallized using an MVR (Mechanical Vapor Reduction) system to separate crude sodium sulfate (or sodium chloride). Compared with other processes, this invention achieves comprehensive recovery of lithium carbonate precipitation mother liquor, with high lithium recovery efficiency. The acid and alkali produced from the high-salinity wastewater via the bipolar membrane replaces purchased acid and alkali, reducing production costs and further increasing the company's economic benefits.

Description

Technical Field

[0001] This invention relates to the field of hydrometallurgical technology, specifically to a method for the comprehensive recovery of lithium carbonate precipitation mother liquor. Background Technology

[0002] Lithium is primarily stored in hard rocks and salt lake brines in nature, accounting for over 70% of its composition in these brines. Lithium carbonate is an important intermediate lithium product, typically obtained through precipitation (i.e., lithium precipitation process). However, this process generates a large amount of mother liquor. Due to the solubility of lithium carbonate in water, the lithium concentration in the mother liquor is generally 1-2 g / L. To further improve the overall lithium recovery rate and increase the economic benefits for enterprises, it is necessary to recover the lithium from the mother liquor.

[0003] The traditional method for recovering lithium from lithium precipitation mother liquor is to first acidify the mother liquor with sulfuric acid (or hydrochloric acid, etc.) to remove carbonate ions, and then evaporate and concentrate the acidified mother liquor to precipitate sodium sulfate (or sodium chloride solid), thereby obtaining a mixed solution with a higher lithium concentration (the solution contains only Li). + In addition, it also contains Na + K + (Isocations), and then the mixed solution is returned to the main system to undergo a secondary lithium precipitation reaction with sodium carbonate solution to obtain solid lithium carbonate. In addition, the open circuit problem of lithium precipitation mother liquor is further solved. However, this traditional lithium precipitation mother liquor recovery process has the following disadvantages: (1) the sodium sulfate (or sodium chloride) solid separated by evaporation and concentration will carry lithium, resulting in lithium loss; (2) the Na in the concentrated lithium precipitation mother liquor + K + High concentration will further affect the purity of the prepared lithium carbonate product; (3) The lithium precipitation mother liquor is repeatedly circulated in this process, the direct recovery rate is low, the acid consumption is high, and the production cost is high.

[0004] To address the problems and shortcomings of traditional lithium precipitation mother liquor recovery methods, metallurgists have proposed new processes, such as adsorption, extraction, and precipitation. Among these, Chinese patent application CN112717468A discloses a method for lithium recovery from lithium precipitation mother liquor, which uses a lithium-sodium separation resin to adsorb lithium from the mother liquor. Furthermore, Chinese patent application CN111533146A proposes using a titanium-based adsorbent to adsorb lithium from the mother liquor, followed by desorption with acid to obtain a qualified lithium-containing solution. Additionally, Chinese patent application CN113061750A discloses a method for extracting and recovering lithium from lithium precipitation mother liquor, which uses an alkaline extractant for extraction, followed by CO2 back-extraction, achieving a lithium recovery rate of over 90%. In addition to the above, Chinese patent application CN104925837A discloses a method for preparing lithium salts from battery-grade lithium carbonate precipitation mother liquor. First, phosphoric acid is added to the battery-grade lithium carbonate precipitation mother liquor to adjust the pH to 6-8, then NaOH is added to adjust the pH to 10-12, causing the lithium carbonate in the mother liquor to convert into lithium phosphate precipitate. Then, water or washing solution is used to adjust the slurry, and the pH is adjusted to 8-10, followed by aging for 30-60 minutes. Finally, filtration yields a relatively pure lithium salt solution. Therefore, regardless of whether the lithium precipitation mother liquor is recovered by adsorption, extraction, or precipitation, the lithium recovery rate is high, and the final lithium carbonate product has high purity. However, the disposal of the lithium precipitation mother liquor (i.e., high-salt wastewater) after lithium extraction remains a problem. Storing it would occupy a huge amount of space, while discharging it would cause environmental problems.

[0005] In summary, there are currently no specific and feasible methods for the efficient recovery of lithium from lithium precipitation mother liquor and the treatment of high-salinity wastewater after lithium extraction. Therefore, it is necessary to seek a new process for recovering lithium precipitation mother liquor to improve the overall lithium recovery efficiency and solve the problem of treating high-salinity wastewater after lithium extraction, so as to further increase the economic benefits of enterprises. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention aims to provide a method for the comprehensive recovery of lithium carbonate precipitation mother liquor.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for the comprehensive recovery of lithium carbonate precipitation mother liquor includes the following steps:

[0009] S1. Selectively extract lithium from the lithium precipitation mother liquor by adsorption or extraction, and then desorb or back-extract to obtain a lithium-rich solution. The lithium-rich solution is returned to the lithium precipitation process for lithium precipitation. The tail liquid after adsorption or extraction of the lithium precipitation mother liquor, i.e., high-salt wastewater, is transferred to step S2 for treatment.

[0010] S2. The high-salt wastewater obtained in step S1 is acidified and aerated with acid to remove carbonate ions. The generated CO2 gas is absorbed by alkaline solution and used to prepare carbonate by-products. The obtained carbonate by-products are used in the process of precipitating lithium carbonate in the lithium precipitation process.

[0011] S3. A portion of the high-salt wastewater after acidification and aeration in step S2 is subjected to bipolar membrane electrodialysis to produce acid, alkali and low-salt materials. The low-salt materials are concentrated and then subjected to MVR evaporation and crystallization with another portion of the high-salt wastewater after acidification and aeration.

[0012] Furthermore, in step S1, if lithium is selectively extracted from the lithium precipitation mother liquor by adsorption, the adsorbent is one or a combination of titanium-based adsorbents, manganese-based adsorbents, or adsorption resins; if lithium is selectively extracted from the lithium precipitation mother liquor by extraction, the extractant is an alkaline extractant.

[0013] Furthermore, the alkaline extractant includes one or a combination of several of M54-100, Cy923, and N503.

[0014] Furthermore, in step S1, if one or both of titanium-based and manganese-based adsorbents are used as adsorbents in the adsorption process, and acid is used for desorption, the acid consumption is [amount in mol H]. + / mol Li + The concentration of Li is 1-1.5, the desorption temperature is 25-35℃, and the concentration of Li in the lithium-rich solution obtained after desorption is 0.5-4 g / L.

[0015] Furthermore, in step S1, if adsorption resin is used for adsorption, an alkaline solution needs to be added during the adsorption process to control the pH at 6-7 to suppress CO2 overflow; then, acid is used for desorption, consuming an amount of acid in mol H₂. + / molLi + The concentration of Li in the lithium-rich solution obtained after desorption is 10-15 g / L, with a desorption temperature of 5-30℃.

[0016] Furthermore, in step S1, if lithium is selectively extracted from the lithium precipitation mother liquor using an extraction method, and acid is used for back-extraction, the acid consumption is [amount in mol H]. + / mol Li + The concentration of Li in the lithium-rich solution obtained after back-extraction is 1-1.2, the extraction and back-extraction temperatures are 15-25℃, and the Li concentration is 15-20g / L.

[0017] Furthermore, in step S2, the Li in the high-salt wastewater obtained in step S1 + The concentration is 20-100 mg / L, and the acid consumption during acidification aeration is mol H₂. + / (2*mol CO3 2+ +mol HCO3 - The concentration of alkali used to absorb CO2 gas is 1-1.2; the amount of alkali used is molOH. - The CO2 concentration is 2-2.2 per mol.

[0018] Furthermore, in step S3, a portion of the alkali produced by bipolar membrane electrodialysis is used for the absorption of CO2 gas in step S2, and another portion is concentrated by MVR and used for calcium and magnesium impurity removal in the lithium precipitation process; the fresh water produced after the alkali is concentrated by MVR is returned as the receiving liquid for acid and alkali in bipolar membrane electrodialysis.

[0019] Furthermore, in step S3, a portion of the acid produced by bipolar membrane electrodialysis is returned to step S1 for desorption or back-extraction, and another portion is returned for acidification of the high-salt wastewater in step S2.

[0020] Furthermore, the lithium precipitation mother liquor is a chloride-type or sulfate-type lithium precipitation mother liquor.

[0021] The beneficial effects of this invention are as follows:

[0022] 1) This invention uses adsorption or extraction processes to extract lithium from lithium carbonate mother liquor. Compared with traditional lithium recovery processes from lithium carbonate mother liquor, it avoids lithium loss caused by crystalline salt entrainment, resulting in high lithium recovery efficiency and low impurity ion concentration in lithium-rich solutions, which can be used to prepare battery-grade lithium carbonate products.

[0023] 2) The lithium precipitation mother liquor after lithium extraction is acidified and aerated, and CO2 gas is received by a bipolar membrane self-produced alkali solution to obtain sodium carbonate solution, which can be used in the lithium precipitation process, thereby reducing production costs.

[0024] 3) After high-salt wastewater is concentrated into low-salt material through bipolar membrane electrodialysis, it is mixed with the remaining high-salt wastewater and returned to the MVR for evaporation and crystallization. The desalinated water produced in the MVR process is used as the receiving liquid in the acid and alkali chambers of the bipolar membrane. Therefore, the combined bipolar membrane and MVR process can achieve open-circuit treatment of high-salt wastewater. In addition, the acid and alkali produced by the bipolar membrane can replace purchased acid and alkali and be returned to the system for use, realizing comprehensive recovery of lithium precipitation mother liquor and reducing production costs, thereby further increasing the company's economic benefits. Attached Figure Description

[0025] Figure 1 This is a process flow diagram of various embodiments of the present invention. Detailed Implementation

[0026] The present invention will be further described below with reference to the accompanying drawings. It should be noted that this embodiment is based on the present technical solution and provides detailed implementation methods and specific operation processes, but the protection scope of the present invention is not limited to this embodiment.

[0027] Example 1

[0028] This embodiment provides a method for the comprehensive recovery of lithium and high-salinity wastewater from lithium carbonate precipitation mother liquor using a titanium-based adsorbent. Figure 1 As shown, the specific process is as follows:

[0029] (1) Lithium recovery from lithium precipitation mother liquor:

[0030] Using titanium-based adsorbents to treat lithium precipitation mother liquor I (Li + 1.25 g / L, Na + 95g / L, K + 6.5g / L, CO3 2- 18g / L, Cl - Lithium was extracted from a sample containing 152.2 g / L of lithium. Specifically, a titanium-based adsorbent was packed into a column (1 BV = 150 L). Then, at room temperature, 6 BV of lithium precipitation mother liquor was passed into an adsorption column (with an insulating jacket) packed with activated titanium-based adsorbent at a flow rate of 9 BV / h. After all the lithium precipitation mother liquor had been passed through, it was washed with 2 BV of fresh water, and the mother liquor and wash water were collected to determine the Li content. Subsequently, desorption was performed at 35℃ using 1.4 BV of 0.3 mol / L hydrochloric acid at a flow rate of 24 BV / h. During this process, 2 mol / L of hydrochloric acid was added to maintain the pH at approximately 1.5. Once the pH of the desorption solution remained constant (acid consumption was mol / L), the desorption was continued. + / mol Li + Approximately 1.5 g of the solution was washed with 2 BV of fresh water, and the desorption solution and wash water were collected to determine the Li content. The Li content in the post-adsorption solution was detected. + The concentration was 62.5 mg / L, and it was treated as high-salinity wastewater for subsequent processing. The Li in the desorption solution... + Concentration 3.6 g / L, Na + The concentration was 527 mg / L, and it was returned to the lithium precipitation process as a lithium-rich solution. Calculations showed that the lithium recovery rate was approximately 95%.

[0031] (2) Acidification Aeration Process

[0032] Add 2 mol / L hydrochloric acid to the lithium precipitation mother liquor (high-salt wastewater) after lithium extraction. The amount of acid used is 1.2 times the molar amounts of carbonate and bicarbonate ions in the solution, i.e., mol H₂. + / (2*mol CO3 2+ +mol HCO3 - Approximately 1.2. Aeration was then carried out, and CO2 gas was received using a 2 mol / L sodium hydroxide solution, yielding a sodium carbonate solution with a mass concentration of approximately 10%. In the high-salinity wastewater after acidification and aeration, Li... + 51.13 mg / L, Na +77.72 g / L, K + 5.32 g / L.

[0033] (3) Bipolar membrane electrolysis and MVR evaporation concentration process

[0034] A portion of the high-salinity wastewater after acidification and aeration was subjected to bipolar membrane electrodialysis to prepare acid and alkali. The energy consumption of bipolar membrane electrodialysis was 1900 kWh / t NaOH. After the acid and alkali preparation was completed, 2 mol / L hydrochloric acid and sodium hydroxide solutions were obtained, respectively. The resulting low-salinity materials contained Na... + The concentration was approximately 18 g / L. The low-salt material was then concentrated using RO (reverse osmosis). The concentrate (containing Na...) + The wastewater (concentration approximately 36 g / L) is returned to the MVR system for evaporation and crystallization, while the freshwater is returned to the bipolar membrane system. Additionally, another portion of the acidified, aerated, high-salt wastewater is subjected to evaporation and crystallization. The MVR energy consumption is 50 kWh / m³. 3 Water. After evaporation, the freshwater recovery efficiency is approximately 90%, the NaCl solid content is approximately 109.5 kg, and the crystallization mother liquor (containing Na...) + The concentration of approximately 125 g / L was returned to the MVR system for further evaporation.

[0035] Example 2

[0036] This embodiment provides a method for recovering lithium and high-salinity wastewater from lithium carbonate precipitation mother liquor using a titanium-based adsorbent, such as... Figure 1 As shown, the specific process is as follows:

[0037] (1) Lithium recovery process from lithium precipitation mother liquor

[0038] Using titanium-based adsorbents to precipitate lithium mother liquor II (Li + 2.5 g / L, Na + 79g / L, K + 0.05 g / L, CO3 2- 28g / L, SO4 2- Lithium was extracted from a sample containing 152.2 g / L of lithium. The specific process was as follows: A titanium-based adsorbent was packed into a column (1 BV = 150 L). Then, at room temperature, 3 BV of lithium precipitation mother liquor was passed into an adsorption column (with an insulating jacket) packed with activated titanium-based adsorbent at a flow rate of 9 BV / h. After all the lithium precipitation mother liquor had been passed through, it was washed with 2 BV of fresh water, and the mother liquor and wash water were collected to determine the Li content. Subsequently, desorption was performed at 35℃ using 1.4 BV of 0.15 mol / L sulfuric acid at a flow rate of 24 BV / h. During this process, 1 mol / L of sulfuric acid was added to maintain the pH at approximately 1.5. Once the pH of the desorption solution remained constant (acid consumption was mol H₂), the desorption was continued. + / mol Li +Approximately 1.5 g of the solution was washed with 2 BV of fresh water, and the desorption solution and wash water were collected to determine the Li content. The Li content in the post-adsorption solution was detected. + The concentration was 57.5 mg / L, and it was treated as high-salinity wastewater for subsequent processing. The Li in the desorption solution... + Concentration 3.53 g / L, Na + The concentration was 468 mg / L, and it was returned to the lithium precipitation process as a lithium-rich solution. Calculations showed that the lithium recovery rate was approximately 95%.

[0039] (2) Acidification Aeration Process

[0040] Add 1 mol / L sulfuric acid to the lithium precipitation mother liquor (high-salt wastewater) after lithium extraction. The amount of acid used is 1.2 times the molar amounts of carbonate and bicarbonate ions in the solution, i.e., mol H₂. + / (2*mol CO3 2+ +mol HCO3 - Approximately 1.2. Aeration was then carried out, and CO2 gas was received using a 2 mol / L sodium hydroxide solution to obtain a sodium carbonate solution with a mass concentration of approximately 10%. Furthermore, in the high-salinity wastewater after acidification and aeration, Li... + 44.5 mg / L, Na + 60.85g / L, K + 0.035g / L.

[0041] (3) MVR evaporation concentration and bipolar membrane electrolysis process

[0042] A portion of the high-salinity wastewater after acidification and aeration was subjected to bipolar membrane electrodialysis to prepare acid and alkali. The energy consumption of bipolar membrane electrodialysis was 1900 kWh / t NaOH. After the acid and alkali preparation was completed, 1 mol / L sulfuric acid and 2 mol / L sodium hydroxide solutions were obtained, respectively. The resulting low-salinity materials contained Na... + The concentration was approximately 18 g / L. The low-salt material was then concentrated using RO (reverse osmosis), and the concentrate (containing Na...) + The wastewater (concentration approximately 36 g / L) is returned to the MVR system for evaporation and crystallization, while the freshwater is returned to the bipolar membrane electrodialysis system. Additionally, another portion of the acidified, aerated, high-salt wastewater is subjected to evaporation and crystallization. The MVR energy consumption is 50 kWh / m³. 3 Water. After evaporation, the freshwater recovery efficiency is approximately 90%, with about 42 kg of Na₂SO₄ solid and crystallization mother liquor (containing Na₂SO₄). + (Concentration approximately 125 g / L) is returned to the MVR system for further evaporation and crystallization.

[0043] Example 3

[0044] This embodiment provides a method for recovering lithium and high-salt wastewater from lithium carbonate precipitation mother liquor using adsorption resin, such as... Figure 1As shown, the specific process is as follows:

[0045] (1) Lithium recovery process from lithium precipitation mother liquor

[0046] Using adsorption resin to treat lithium precipitation mother liquor (Li + 1.25 g / L, Na + 95g / L, K + 6.5g / L, CO3 2- 18g / L, Cl - Lithium was extracted from a sample containing 152.2 g / L. The specific process was as follows: 900 L of lithium precipitation mother liquor was mixed with adsorption resin (density 0.75 kg / L) at a liquid-to-solid ratio (L / kg) of 8. The stirring speed was 250 rpm, the adsorption time was 40 min, and the adsorption temperature was room temperature. During adsorption, 2 mol / L sodium hydroxide solution was added to control the pH of the feed solution at the outlet to approximately 6. After adsorption, the solution was filtered, and the filtered adsorption resin was washed with fresh water. The mother liquor and wash water were collected separately to determine the Li content. Subsequently, pre-desorption (to remove adsorbed sodium ions) was performed at room temperature using 2 mol / L hydrochloric acid and the loaded adsorption resin at a liquid-to-solid ratio of 2.73, with stirring at 250 rpm for 10 min. After pre-desorption, the mixture was filtered, and the collected pre-desorbed solution was mixed with the adsorption solution. Then, desorption was performed again using 2 mol / L hydrochloric acid and the pre-desorbed adsorption resin at a liquid-to-solid ratio (L / kg) of 1.37, with stirring at 250 rpm for 10 min. After desorption, the mixture was filtered, and the filtered adsorption resin was washed with fresh water. The desorbed solution and desorption wash water were collected, and the Li content was determined. The analysis showed that the Li content in the adsorption solution was... + The concentration was 55.8 mg / L, and it was treated as high-salinity wastewater; the Li in the desorption solution was... + Concentration 6.92 g / L, Na + The concentration was 477 mg / L, and it was returned to the lithium precipitation process as a lithium-rich solution. Calculations showed that the lithium recovery rate was approximately 95%.

[0047] (2) Acidification Aeration Process

[0048] Add 2 mol / L hydrochloric acid to the lithium precipitation mother liquor (high-salt wastewater) after lithium extraction. The amount of acid used is 1.2 times the molar amounts of carbonate and bicarbonate ions in the solution, i.e., mol H₂. + / (2*mol CO3 2+ +mol HCO3 - Approximately 1.2. Aeration was then carried out, and CO2 gas was received using a 2 mol / L sodium hydroxide solution to obtain a sodium carbonate solution with a mass concentration of approximately 10%. Furthermore, in the high-salinity wastewater after acidification and aeration, Li... + 54.9 mg / L, Na +63.43 g / L, K + 4.3g / L.

[0049] (3) MVR evaporation concentration and bipolar membrane electrolysis process

[0050] A portion of the high-salinity wastewater after acidification and aeration was subjected to bipolar membrane electrodialysis to prepare acid and alkali. The energy consumption of bipolar membrane electrodialysis was 1900 kWh / t NaOH. After the acid and alkali preparation was completed, 2 mol / L hydrochloric acid and sodium hydroxide solutions were obtained, respectively. The resulting low-salinity materials contained Na... + The concentration was approximately 18 g / L. The low-salt material was then concentrated using RO (reverse osmosis). The concentrate (containing Na...) + The wastewater (concentration approximately 36 g / L) is returned to the MVR system for evaporation and crystallization, while the freshwater is returned to the bipolar membrane system. Additionally, another portion of the acidified, aerated, high-salt wastewater is subjected to evaporation and crystallization. The MVR energy consumption is 50 kWh / m³. 3 Water. After evaporation, the freshwater recovery efficiency is approximately 90%, with about 115 kg of NaCl solid and crystallization mother liquor (containing Na...) + The concentration of approximately 125 g / L was returned to the MVR system for further evaporation.

[0051] Example 4

[0052] This embodiment provides a method for recovering lithium and high-salt wastewater from lithium carbonate precipitation mother liquor using an extractant, such as... Figure 1 As shown, the specific process is as follows:

[0053] (1) Lithium recovery from lithium precipitation mother liquor:

[0054] Using an extractant to treat lithium precipitation mother liquor (Li + 1.25 g / L, Na + 95g / L, K + 6.5g / L, CO3 2- 18g / L, Cl - Lithium was extracted from a sample containing 152.2 g / L. The experimental procedure was as follows: M54-100 was used as the main extractant, and Cy923 was used as a co-extractant to form a composite extraction system. Sulfonated kerosene was used as the diluent, the M54-100 / Cy923 mixing volume ratio was 0.5, the extractant concentration was 30%, the extraction ratio (O / A) was 1, the temperature was room temperature, the extraction time was 5 min, and the single-stage extraction rate of lithium was 70%. After four stages of countercurrent extraction, the Li content in the raffinate was determined. + At a concentration of 37.5 mg / L, the lithium extraction rate can reach over 95%. Finally, back-extraction is performed using 2 mol / L hydrochloric acid, with an O / A ratio of 10 and a shaking time of 10 min; the single-stage back-extraction rate of lithium can reach over 75%. After three stages of countercurrent back-extraction, the lithium concentration in the back-extraction solution is 11.4 g / L, and the acid consumption is [amount missing - likely mol H+].+ / mol Li + With a concentration of 1.2, the lithium back-extraction rate can reach approximately 95%. The raffinate is treated as high-salt wastewater for further processing, while the back-extraction solution is returned to the lithium precipitation process as a lithium-rich solution for lithium precipitation.

[0055] (2) Acidification Aeration Process

[0056] Add 2 mol / L hydrochloric acid to the lithium precipitation mother liquor (high-salt wastewater) after lithium extraction. The amount of acid used is 1.2 times the molar amounts of carbonate and bicarbonate ions in the solution, i.e., mol H₂. + / (2*mol CO3 2+ +mol HCO3 - Approximately 1.1. Aeration was then carried out, and CO2 gas was received using a 2 mol / L sodium hydroxide solution to obtain a sodium carbonate solution with a mass concentration of approximately 10%. Furthermore, the mother liquor after acidification aeration, i.e., the high-salt wastewater, contains Li... + 31.25 mg / L, Na + 79.2 g / L, K + 5.42 g / L.

[0057] (3) MVR evaporation concentration and bipolar membrane electrolysis process

[0058] A portion of the high-salinity wastewater after acidification and aeration was subjected to bipolar membrane electrodialysis to prepare acid and alkali. The energy consumption of bipolar membrane electrodialysis was 1900 kWh / t NaOH. After the acid and alkali preparation was completed, 2 mol / L hydrochloric acid and sodium hydroxide solutions were obtained, respectively, and the low-salinity Na... + The concentration was approximately 18 g / L. The low-salt material was then concentrated using RO (reverse osmosis). The concentrate (containing Na...) + The wastewater (concentration approximately 36 g / L) is returned to the MVR system for evaporation and crystallization, while the freshwater is returned to the bipolar membrane system. Additionally, another portion of the acidified, aerated, high-salt wastewater is subjected to evaporation and crystallization. The MVR energy consumption is 50 kWh / m³. 3 Water. After evaporation, the freshwater recovery efficiency is approximately 90%, with about 113 kg of NaCl solid and the crystallization mother liquor (containing Na...) + (Concentration approximately 125 g / L) is returned to the MVR system for further evaporation and crystallization.

[0059] For those skilled in the art, various corresponding changes and modifications can be made based on the above technical solutions and concepts, and all such changes and modifications should be included within the protection scope of the claims of this invention.

Claims

1. A method for comprehensive recovery of lithium carbonate precipitation mother liquor, characterized in that, Includes the following steps: S1. Selectively extract lithium from the lithium precipitation mother liquor by adsorption or extraction, and then desorb or back-extract to obtain a lithium-rich solution. The lithium-rich solution is returned to the lithium precipitation process for lithium precipitation. The tail liquid after adsorption or extraction of the lithium precipitation mother liquor, i.e., high-salt wastewater, is transferred to step S2 for treatment. S2. The high-salt wastewater obtained in step S1 is acidified and aerated with acid to remove carbonate ions. The generated CO2 gas is absorbed by alkaline solution and used to prepare carbonate by-products. The obtained carbonate by-products are used in the process of precipitating lithium carbonate in the lithium precipitation process. S3. A portion of the high-salt wastewater after acidification and aeration in step S2 is subjected to bipolar membrane electrodialysis to produce acid, alkali, and low-salt materials. The low-salt materials are concentrated and then subjected to MVR evaporation and crystallization with another portion of the high-salt wastewater after acidification and aeration. A portion of the acid produced by bipolar membrane electrodialysis is returned to step S1 for desorption or back-extraction, and another portion is returned for acidification of the high-salt wastewater in step S2. A portion of the alkali produced by bipolar membrane electrodialysis is used for CO2 gas absorption in step S2, and another portion is concentrated by MVR and used for calcium and magnesium impurity removal in the lithium precipitation process. The fresh water produced by MVR concentration of alkali and the fresh water produced by MVR evaporation and crystallization are returned as the receiving liquid for acid and alkali in bipolar membrane electrodialysis.

2. The method according to claim 1, characterized in that, In step S1, if lithium is selectively extracted from the lithium precipitation mother liquor by adsorption, the adsorbent is one or a combination of titanium-based adsorbents, manganese-based adsorbents, or adsorption resins; if lithium is selectively extracted from the lithium precipitation mother liquor by extraction, the extractant is an alkaline extractant.

3. The method according to claim 2, characterized in that, The alkaline extractant includes one or a combination of several of M54-100, Cy923, and N503.

4. The method according to claim 2, characterized in that, In step S1, if one or both of titanium-based and manganese-based adsorbents are used as adsorbents in the adsorption process, and acid is used for desorption, the acid consumption is [amount in mol H]. + / mol Li + The concentration of Li is 1-1.5, the desorption temperature is 25-35℃, and the concentration of Li in the lithium-rich solution obtained after desorption is 0.5-4 g / L.

5. The method according to claim 2, characterized in that, In step S1, if adsorption resin is used for adsorption, an alkaline solution needs to be added during the adsorption process to control the pH at 6-7 to suppress CO2 overflow; then, acid is used for desorption, consuming an amount of acid in mol H₂. + / mol Li + The concentration of Li in the lithium-rich solution obtained after desorption is 10-15 g / L, with a desorption temperature of 5-30℃.

6. The method according to claim 1 or 3, characterized in that, In step S1, if lithium is selectively extracted from the lithium precipitation mother liquor using extraction methods, and acid is used for back-extraction, the acid consumption is [amount in mol H]. + / mol Li + The concentration of Li in the lithium-rich solution obtained after back-extraction is 1-1.2, the extraction and back-extraction temperatures are 15-25℃, and the Li concentration is 15-20g / L.

7. The method according to claim 1, characterized in that, In step S2, the Li in the high-salt wastewater obtained in step S1 + The concentration is 20-100 mg / L, and the acid consumption during acidification aeration is mol H₂. + / (2*mol CO3 2- +mol HCO3 - The value is 1-1.2; the amount of alkali used to absorb CO2 gas is mol OH. - The CO2 concentration is 2-2.2 per mol.

8. The method according to claim 1, characterized in that, The lithium precipitation mother liquor is either chloride-type or sulfate-type lithium precipitation mother liquor.

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