Process for extracting and removing sodium from lithium carbonate lithium precipitation mother liquor

Abstract

The invention discloses a process for extracting and removing sodium from lithium carbonate lithium precipitation mother liquor in the field of hydrometallurgy, which comprises the following steps: firstly, filtering the lithium precipitation mother liquor, adjusting the pH value, and dispersing a specially prepared multi-stage structure doped carbon-based organic silicon composite mesoporous material into sulfonated kerosene; adding tributyl phosphate and sorbitan oleate, and emulsifying to form an extraction organic phase; and contacting the pretreated mother liquor with an extraction organic phase in a three-stage counter-current extraction system to obtain a lithium-loaded organic phase and a sodium-containing raffinate. And washing the loaded organic phase with deionized water, carrying out two-stage reverse extraction with a sulfuric acid solution to obtain a lithium-rich solution, returning the lithium-rich solution to a lithium precipitation process, and carrying out alkali washing on the organic phase after reverse extraction so as to be recycled for multiple times. And evaporating and crystallizing the sodium-containing raffinate to obtain a byproduct anhydrous sodium sulfate. The process has accurately regulated and controlled pore structure and surface chemical characteristics, realizes efficient separation of lithium and sodium, is simple in process flow and high in lithium recovery rate, and can realize comprehensive utilization of resources.

Description

Technical Field

[0001] This invention relates to the field of hydrometallurgical technology, specifically to a process for removing sodium from lithium carbonate mother liquor by extraction. Background Technology

[0002] Lithium carbonate, a key raw material in modern industry, plays an irreplaceable role in lithium-ion batteries, specialty glass, ceramic glazes, and non-ferrous metal smelting. With the rapid development of the new energy vehicle industry and the rapid expansion of the electrochemical energy storage market, the demand for battery-grade lithium carbonate continues to rise, placing increasingly stringent requirements on its product quality. In the industrial production of lithium carbonate, the lithium precipitation process is the core step determining the purity of the final product. This process involves adding sodium carbonate to a refined lithium solution to generate lithium carbonate precipitate with low solubility. However, this process generates a large amount of precipitation mother liquor, which not only contains incompletely precipitated lithium ions but is also rich in high concentrations of sodium ions introduced due to the excessive addition of sodium carbonate. Traditional methods for treating this mother liquor often involve simply returning it to the previous process or direct evaporation, but this leads to the continuous accumulation of sodium ions in the system, creating a vicious cycle that severely restricts the improvement of lithium carbonate product purity, especially making it difficult to consistently obtain battery-grade lithium carbonate that meets the requirements of high-end lithium battery manufacturing. The efficient purification of the precipitation mother liquor and the recovery of lithium resources have become key technological bottlenecks restricting the entire industry's ability to improve quality and efficiency and achieve sustainable development.

[0003] Currently, various technical approaches have been tried and applied in the industry for treating lithium carbonate precipitation mother liquor, but all have significant limitations. Chemical precipitation is simple to operate, but the similarity in chemical properties between lithium and sodium leads to poor separation selectivity, requiring repeated precipitation and washing. The direct recovery rate of lithium is low, and new impurities are easily introduced. Membrane separation technologies such as nanofiltration and electrodialysis can theoretically achieve the separation of monovalent ions, but when treating high-salinity, high-hardness lithium precipitation mother liquor, membrane elements are prone to fouling and scaling, resulting in a rapid decline in desalination efficiency. Furthermore, equipment investment and operating energy consumption remain high, making them uneconomical. Ion exchange and adsorption methods use specific adsorbent materials such as lithium ion sieves, which have high selectivity for lithium. However, their adsorption capacity is generally low, and the effective working capacity is further reduced in mother liquor environments with high sodium-to-lithium ratios. Insufficient mechanical strength and high solubility of the adsorbent also restrict their industrial application. Traditional solvent extraction techniques, using conventional extractants such as tributyl phosphate, have been applied in lithium extraction from salt lake brine. However, they face significant challenges when processing lithium precipitation mother liquor, including low lithium-sodium separation coefficients, severe sodium ion co-extraction, easy formation of a third phase, and difficulties in phase separation. These methods either fail to efficiently separate lithium and sodium, have complex and lengthy processes, or are prohibitively expensive to operate, thus failing to fundamentally solve the problems of efficient purification of lithium precipitation mother liquor and economical recovery of lithium resources.

[0004] Therefore, developing a novel lithium precipitation mother liquor treatment process that enables highly efficient and selective extraction of lithium ions under high sodium-to-lithium ratio conditions, with a simple process flow, controllable operating costs, and ease of industrialization, is of extremely urgent industrial demand and has broad market prospects. An ideal solution needs to possess high selectivity, high extraction capacity, and good engineering properties. The core lies in creating a novel extraction material or system with specific lithium-ion recognition capabilities, thereby directly extracting lithium from the complex mother liquor system under near-neutral and mild conditions, achieving efficient separation from sodium ions, and ultimately achieving the comprehensive goals of improving lithium recovery rate, ensuring product purity, reducing production costs, and realizing wastewater resource utilization. Summary of the Invention

[0005] The purpose of this invention is to provide a process for sodium removal from lithium carbonate precipitation mother liquor by extraction, which solves the technical problems of low lithium-sodium separation efficiency in high sodium-lithium ratio environments, low lithium recovery rate and high cost of traditional treatment methods, and the complexity of existing extraction processes and the inability to recycle the organic phase.

[0006] The present invention achieves the above objectives through the following technical solutions:

[0007] A process for sodium removal from lithium carbonate precipitation mother liquor by extraction includes the following steps:

[0008] S1, filter the lithium carbonate precipitation mother liquor, adjust the pH to 7.5-8.5 to obtain the pretreated lithium precipitation mother liquor; disperse the multi-level structure doped carbon-based-organic silicon composite mesoporous material in sulfonated kerosene, add sorbitan oleate, emulsify, and obtain the extracted organic phase;

[0009] S2, the pretreated lithium precipitation mother liquor and the extraction organic phase are sent into a three-stage countercurrent extraction system, stirred and mixed in the mixing chamber, and held in the clarification chamber; after three-stage countercurrent extraction, the loaded organic phase and sodium-containing raffinate are obtained.

[0010] S3. The supported organic phase is washed with deionized water to obtain the washed organic phase. The washed organic phase is then fed into a two-stage back-extraction process, where sulfuric acid solution is used for back-extraction to obtain a lithium sulfate solution that enters the aqueous phase. After two-stage back-extraction, a lithium-rich back-extraction solution and the back-extracted organic phase are obtained. The lithium-rich back-extraction solution is returned to the lithium precipitation process in the lithium carbonate production flow. The back-extracted organic phase is washed with NaOH solution and then recycled.

[0011] S4. The sodium-containing raffinate is evaporated and crystallized to obtain anhydrous sodium sulfate as a byproduct.

[0012] In this invention, the reaction mechanism of the lithium carbonate precipitation mother liquor extraction process for sodium removal is based on the synergistic effect of ion size sieving, coordination chemistry, and interfacial mass transfer. A multi-level structured carbon-based-organosilicon composite mesoporous material serves as the core functional component of the extraction system. Its surface possesses a precisely designed pore size distribution and abundant heteroatom functional groups, enabling efficient sieving of lithium and sodium ions based on differences in hydrated ion radii. Lithium ions, with their relatively small hydrated radius, can easily enter the mesoporous channels of the material and undergo specific coordination interactions with nitrogen, sulfur, phosphorus, and other heteroatom functional groups on the pore surface, forming stable coordination structures. Sodium ions, due to their large hydrated radius, are subject to significant steric hindrance, making it difficult for them to enter the main active channels of the material. Furthermore, their coordination ability with surface functional groups is significantly weaker, thus most sodium ions are excluded from the extraction process. During the extraction operation, the carefully formulated organic phase is emulsified at high speed to form a uniformly dispersed system, greatly increasing the mass transfer specific surface area and promoting the migration of lithium ions from the aqueous phase to the active material in the organic phase. In the washing stage, pure water is used to countercurrently wash the supported organic phase, effectively removing small amounts of physically entrained sodium ions and co-extraction impurities, further purifying the supported organic phase. The back-extraction process uses a sulfuric acid solution of appropriate concentration as the back-extraction agent. Hydrogen ions in the solution undergo an ion exchange reaction with lithium ions coordinated in the material. Due to the stronger affinity of hydrogen ions for the active sites of the material, they can efficiently displace lithium ions into the aqueous phase, forming a lithium-rich lithium sulfate solution. The back-extracted organic phase is then gently washed with alkali to neutralize residual acidity, restoring its extraction activity and enabling recycling. The entire process, through the synergistic cooperation of multi-stage countercurrent extraction, washing, and back-extraction, achieves the selective extraction, purification, enrichment, and recovery of lithium ions, while sodium ions remain in the raffinate and are ultimately recovered as sodium sulfate through evaporation and crystallization, completing the efficient separation and full utilization of lithium and sodium resources in the lithium precipitation mother liquor.

[0013] According to a preferred embodiment of the present invention, in step S1, the emulsification speed is 8000-12000 rpm and the emulsification time is 10-15 min.

[0014] According to a preferred embodiment of the present invention, in step S2, the mixing time in the mixing chamber is 3-5 minutes.

[0015] According to a preferred embodiment of the present invention, in step S3, the organic phase after back-extraction is washed with NaOH solution and then recycled 100-120 times.

[0016] According to a preferred embodiment of the present invention, in step S4, the sodium-containing raffinate is subjected to evaporation and crystallization treatment for 8-10 hours.

[0017] According to a preferred embodiment of the present invention, the preparation steps of the multi-level structure-doped carbon-based-organosilicon composite mesoporous material include:

[0018] A1. Under nitrogen protection, tetraethyl orthosilicate and bis-[3-(triethoxysilyl)propyl]-tetrasulfide were dissolved in anhydrous ethanol to obtain solution A; poloxamer F127 was mixed with deionized water and concentrated hydrochloric acid to obtain solution B; solution A was added dropwise to solution B under continuous stirring, and after the addition was complete, the temperature was raised to 58-62℃ and stirred to obtain an organic-inorganic hybrid sol;

[0019] A2, the organic-inorganic hybrid sol was placed in a high-pressure reactor and dried with supercritical carbon dioxide; the dried material was obtained; the dried material was placed in a Soxhlet extractor and extracted with ethanol containing hydrochloric acid to obtain the extracted material; the extracted material was heat-treated under a nitrogen atmosphere to obtain a porous material;

[0020] A3. The porous material is immersed in an aqueous solution containing melamine, cysteine ​​and phytic acid under ultrasonic assistance to obtain a suspension. The suspension is transferred to a hydrothermal reactor and reacted at 175-185℃ to obtain a reaction mixture. The reaction mixture is filtered to collect the solid product, which is washed with deionized water until neutral and then vacuum dried at 78-82℃ to obtain the doped material.

[0021] A4. The doped material is heated to 795-805℃ and held in a hydrogen-argon mixed atmosphere; then cooled to 395-405℃, switched to pure argon protection, and held at that temperature; finally cooled to room temperature.

[0022] In this invention, the preparation process of a multi-level structured carbon-based-organosilicon composite mesoporous material involves sophisticated sol-gel chemistry and subsequent modification reaction mechanisms. In the initial sol formation stage, tetraethyl orthosilicate, as the main silicon source, undergoes a stepwise hydrolysis reaction under acidic catalysis to generate active silanol intermediates. These silanols co-condense with the ethoxy groups in a simultaneously added bifunctional organosilicon, constructing a hybrid framework network containing both rigid siloxane bonds and flexible organic segments. During this process, template molecules selectively interact with the silanols and organic segments through hydrogen bonding, guiding the formation of a composite structure with ordered mesoporous characteristics. The supercritical drying step eliminates gas-liquid interface and capillary stress, ensuring the complete preservation of the gel network structure during solvent removal, thus creating a three-dimensional framework with a high specific surface area and a well-developed pore system. The subsequent high-temperature heat treatment further cross-links the residual organic groups, enhancing framework stability and forming conductive carbon domains in the matrix through carbonization. In the multi-element doping stage, melamine decomposes under high-temperature hydrothermal conditions to provide a nitrogen source. Cysteine ​​serves as both a sulfur source and a surface modifier; its thiol groups react with sulfur bonds in the material to enhance the bonding strength. Phytic acid molecules, through their multiple phosphate groups, form multi-point anchors with the framework, achieving uniform phosphorus doping. The final high-temperature reduction treatment is carried out under a controlled atmosphere, achieving both effective incorporation of heteroatoms and partial graphitization of the carbon framework. Furthermore, surface passivation stabilizes the chemical properties of the material, ultimately yielding a multi-level composite mesoporous material with precise pore size distribution, abundant surface functional groups, and stable chemical properties.

[0023] According to a preferred embodiment of the present invention, in step A1, the stirring time is 24-30 hours.

[0024] According to a preferred embodiment of the present invention, in step A2, the extraction time with ethanol containing hydrochloric acid is 48-50 hours.

[0025] According to a preferred embodiment of the present invention, in step A3, the reaction time is 12-14 h at 175-185°C.

[0026] According to a preferred embodiment of the present invention, in step A4, the temperature is raised to 795-805°C and held for 2-4 hours.

[0027] The beneficial effects of this invention are as follows:

[0028] The lithium carbonate mother liquor extraction process for sodium removal provided by this invention achieves highly efficient separation of lithium and sodium ions by employing a specially designed multi-level structured doped carbon-based-organosilicon composite mesoporous material as the core functional component of the extraction system, representing a significant technological advancement. This composite mesoporous material possesses a precisely tunable pore size distribution and abundant surface functional groups. Based on the synergistic effect of ion size sieving and molecular recognition, it exhibits specific binding ability for lithium ions with smaller hydration radii while effectively excluding sodium ions with larger hydration radii. This results in extremely high lithium-sodium separation selectivity under near-neutral, mild pH conditions. Compared to traditional extraction systems, the lithium-sodium separation coefficient of this invention is improved by orders of magnitude, fundamentally solving the technical challenge of selective lithium extraction in high sodium-to-lithium ratio environments. Lithium ions in the loaded organic phase can be efficiently back-extracted using conventional sulfuric acid solution to obtain a solution with significantly enriched lithium concentration and a superior lithium-to-sodium ratio, which can be directly returned to the main lithium precipitation process, greatly improving the direct recovery rate and recycling efficiency of lithium resources.

[0029] At the process and operation level, this invention exhibits significant advantages in simplification and stable performance. The entire sodium removal extraction process comprises only a short-flow design of three-stage extraction, two-stage washing, and two-stage back-extraction. It can operate stably with conventional countercurrent extraction equipment, eliminating the need for expensive and complex centrifugal extraction devices, thus significantly reducing initial investment and long-term maintenance costs. The composite mesoporous material exhibits good dispersibility in sulfonated kerosene systems. The extraction organic phase formed by its combination with tributyl phosphate and sorbitan oleate possesses excellent phase separation characteristics and anti-emulsification capabilities, and can be quickly clarified after mixing, greatly improving equipment throughput and processing capacity. Particularly noteworthy is that the organic phase system can regain its extraction activity after back-extraction with only simple alkaline washing, and can be stably recycled hundreds of times with minimal performance degradation. This demonstrates its excellent chemical stability and service life, providing a solid guarantee for continuous industrial operation and completely overcoming the drawbacks of traditional extractants such as easy aging and rapid depletion.

[0030] From the perspective of comprehensive resource utilization and overall economic benefits, the process of this invention achieves the complete recovery of valuable elements in lithium precipitation mother liquor and near-zero discharge of waste liquid, achieving a high degree of unity between environmental and economic benefits. Through this process, lithium is efficiently recovered from the lithium precipitation mother liquor, significantly improving both the direct lithium recovery rate and the total recovery rate of the overall process, effectively enhancing resource utilization. Simultaneously, the sodium-rich raffinate can be converted into anhydrous sodium sulfate byproducts that meet industrial standards through evaporation and crystallization, creating additional economic value and completely eliminating the problem of high-salinity wastewater discharge. This process successfully transforms the traditional challenge of treating lithium precipitation mother liquor into a resource utilization step, not only simplifying the wastewater treatment process and reducing the cost of treating waste gas, wastewater, and solid waste, but also forming a green production model that synergistically produces lithium salt as the main product and sodium sulfate as a byproduct, which has profound significance for promoting clean production and sustainable development in the lithium carbonate industry. Detailed Implementation

[0031] The following detailed embodiments are only used to further illustrate this application and should not be construed as limiting the scope of protection of this application. Those skilled in the art can make some non-essential improvements and adjustments to this application based on the above application content.

[0032] The following is information on domestic suppliers of the relevant equipment and materials:

[0033] The bis-[3-(triethoxysilyl)propyl]-tetrasulfide was purchased from Huangshan Keber Chemical Co., Ltd.

[0034] The poloxamer F127 was purchased from Shanghai Lianzu Biotechnology Co., Ltd.

[0035] The melamine was purchased from Shanghai Pushun Import & Export Co., Ltd.

[0036] Example 1

[0037] Preparation of multi-level structured doped carbon-based organosilicon composite mesoporous materials: Under nitrogen protection, 30.0 g of tetraethyl orthosilicate and 10.0 g of bis-[3-(triethoxysilyl)propyl]-tetrasulfide were dissolved in 100.0 g of anhydrous ethanol to obtain solution A; 20.0 g of poloxamer F127 was mixed with 1000.0 g of deionized water and 5.0 g of concentrated hydrochloric acid (37% by mass) to obtain solution B; solution A was slowly added dropwise to solution B at a rate of 1.0 mL / min under continuous stirring. After the addition was complete, the temperature was raised to 60 °C and stirred for 24 h to obtain a uniform and transparent organic-inorganic hybrid sol. The obtained sol was transferred to a 1000 mL high-pressure reactor and dried under supercritical carbon dioxide at 60 °C and 15 MPa for 6 h to obtain a dried gel material. The dried material was placed in a Soxhlet extractor and continuously extracted with 500 mL of ethanol solution containing 5% hydrochloric acid for 48 h to completely remove the template agent. The extracted material was placed in a tube furnace and heated at a programmed rate of 2 °C / min under a nitrogen atmosphere: first to 200 °C and held for 2 h, then to 400 °C and held for 1 h, and finally to 600 °C and held for 0.5 h to obtain a porous material. 10.0 g of the above porous material was immersed in 100 mL of aqueous solution containing 1.0 g melamine, 0.5 g cysteine, and 0.8 g phytic acid, and immersed under 40 kHz ultrasound for 2 h. The suspension was then transferred to a 200 mL hydrothermal reactor and reacted at 180 °C for 12 h. After the reaction, the mixture was allowed to cool naturally to room temperature, filtered to collect the solid product, washed with deionized water until the filtrate was neutral, and then dried in a vacuum drying oven at 80 °C for 12 h to obtain the doped material. The doped material was placed in a tube furnace and heated to 800°C at a rate of 2°C / min under an argon mixed atmosphere containing 5% hydrogen. The temperature was then maintained for 2 hours. The temperature was then lowered to 400°C at the same rate. The furnace was then switched to pure argon protection and held at that temperature for 4 hours. Finally, the furnace was cooled to room temperature to obtain the final multi-level structured doped carbon-based organosilicon composite mesoporous material.

[0038] Sodium removal process from lithium carbonate precipitation mother liquor: Take 1000.0g of lithium carbonate precipitation mother liquor (of which Li... + Content 3.2g / L, Na +The lithium-containing mother liquor (containing 35.6 g / L) was filtered through a 5 μm filter and the pH was adjusted to 8.0 with dilute sulfuric acid to obtain a pretreated lithium precipitation mother liquor. 3.0 g of the modified material prepared above was weighed and dispersed in 97.0 g of sulfonated kerosene. 3.0 g of tributyl phosphate and 2.0 g of sorbitan oleate were added, and the mixture was emulsified at 10000 rpm for 12 min to obtain a homogeneous and stable extraction organic phase. The pretreated lithium precipitation mother liquor and the extraction organic phase were fed into a three-stage countercurrent extraction system at a volume ratio of 3:1. The mixture was stirred at 300 rpm for 4 min in the mixing chamber and then held in the clarification chamber for 10 min for phase separation. After three-stage countercurrent extraction, a lithium-loaded organic phase and a sodium-containing raffinate were obtained. 100.0 g of the loaded organic phase was washed with 10.0 g of deionized water in a two-stage countercurrent process to obtain the washed organic phase. The washed organic phase was mixed with 1.5 mol / L sulfuric acid solution at a volume ratio of 8:1 and introduced into a two-stage back-extraction process. The mixture was contacted in the mixing chamber for 5 minutes and then held in the clarification chamber for 8 minutes. After the two-stage back-extraction, a lithium-rich back-extraction solution was obtained (containing Li...). + Content 15.8 g / L, Na + The lithium-rich back-extraction solution (1.2 g / L, lithium-to-sodium ratio 13.2:1) and the resulting organic phase were used. The lithium-rich back-extraction solution was returned to the lithium precipitation process in the lithium carbonate production flow. The organic phase after back-extraction was regenerated by washing with 1% sodium hydroxide solution and recycled 110 times. The sodium-containing raffinate was evaporated and crystallized at 85°C for 9 hours to obtain anhydrous sodium sulfate as a byproduct.

[0039] Example 2

[0040] Preparation of multi-level structured doped carbon-based organosilicon composite mesoporous materials: Under nitrogen protection, 28.0 g of tetraethyl orthosilicate and 9.0 g of bis-[3-(triethoxysilyl)propyl]-tetrasulfide were dissolved in 95.0 g of anhydrous ethanol to obtain solution A; 18.0 g of poloxamer F127 was mixed with 950.0 g of deionized water and 4.5 g of concentrated hydrochloric acid (37% by mass) to obtain solution B; solution A was slowly added dropwise to solution B at a rate of 0.9 mL / min under continuous stirring. After the addition was complete, the temperature was raised to 59 °C and stirred for 26 h to obtain a uniform and transparent organic-inorganic hybrid sol. The obtained sol was transferred to a 1000 mL high-pressure reactor and dried under supercritical carbon dioxide at 60 °C and 15 MPa for 6 h to obtain a dried gel material. The dried material was placed in a Soxhlet extractor and continuously extracted with 500 mL of ethanol solution containing 5% hydrochloric acid for 49 h to completely remove the template agent. The extracted material was placed in a tube furnace and heated at a programmed rate of 2 °C / min under a nitrogen atmosphere: first to 200 °C and held for 2 h, then to 400 °C and held for 1 h, and finally to 600 °C and held for 0.5 h to obtain a porous material. 9.0 g of the above porous material was immersed in 95 mL of aqueous solution containing 0.9 g melamine, 0.4 g cysteine, and 0.7 g phytic acid, and immersed under 40 kHz ultrasound for 2 h. The suspension was then transferred to a 200 mL hydrothermal reactor and reacted at 178 °C for 13 h. After the reaction, the mixture was allowed to cool naturally to room temperature, filtered to collect the solid product, washed with deionized water until the filtrate was neutral, and then dried in a vacuum drying oven at 79 °C for 13 h to obtain the doped material. The doped material was placed in a tube furnace and heated to 798°C at a rate of 2°C / min under an argon mixed atmosphere containing 5% hydrogen. The temperature was then maintained for 3 hours. The temperature was then lowered to 398°C at the same rate, and the furnace was switched to pure argon protection for 4 hours. Finally, the furnace was cooled to room temperature to obtain the final multi-level structured doped carbon-based organosilicon composite mesoporous material.

[0041] Sodium removal process from lithium carbonate precipitation mother liquor: Take 950.0g of lithium carbonate precipitation mother liquor (of which Li... + Content 3.5g / L, Na +The lithium-containing mother liquor (containing 38.2 g / L) was filtered through a 5 μm filter and the pH was adjusted to 7.8 with dilute sulfuric acid to obtain a pretreated lithium precipitation mother liquor. 2.5 g of the modified material prepared above was weighed and dispersed in 97.5 g of sulfonated kerosene. 2.5 g of tributyl phosphate and 1.5 g of sorbitan oleate were added, and the mixture was emulsified at 9000 rpm for 13 min to obtain a homogeneous and stable extraction organic phase. The pretreated lithium precipitation mother liquor and the extraction organic phase were fed into a three-stage countercurrent extraction system at a volume ratio of 3.2:1. The mixture was stirred at 280 rpm for 4.5 min in the mixing chamber and held in the clarifying chamber for 11 min for phase separation. After three-stage countercurrent extraction, a lithium-loaded organic phase and a sodium-containing raffinate were obtained. 100.0 g of the loaded organic phase was washed with 12.0 g of deionized water in a two-stage countercurrent process to obtain the washed organic phase. The washed organic phase was mixed with 1.2 mol / L sulfuric acid solution at a volume ratio of 7:1 and introduced into a two-stage back-extraction process. The mixture was contacted in the mixing chamber for 6 minutes and then held in the clarification chamber for 9 minutes. After the two-stage back-extraction, a lithium-rich back-extraction solution was obtained (containing Li...). + Content 16.2 g / L, Na + The lithium-rich back-extraction solution (1.4 g / L, lithium-to-sodium ratio 11.6:1) and the extracted organic phase were used. The lithium-rich back-extraction solution was returned to the lithium precipitation process in the lithium carbonate production flow. The extracted organic phase was regenerated by washing with 1% sodium hydroxide solution and recycled 105 times. The sodium-containing raffinate was evaporated and crystallized at 83°C for 8.5 h to obtain anhydrous sodium sulfate as a byproduct.

[0042] Example 3

[0043] Preparation of multi-level structured doped carbon-based organosilicon composite mesoporous materials: Under nitrogen protection, 32.0 g of tetraethyl orthosilicate and 11.0 g of bis-[3-(triethoxysilyl)propyl]-tetrasulfide were dissolved in 105.0 g of anhydrous ethanol to obtain solution A; 22.0 g of poloxamer F127 was mixed with 1050.0 g of deionized water and 5.5 g of concentrated hydrochloric acid (37% by mass) to obtain solution B; solution A was slowly added dropwise to solution B at a rate of 1.1 mL / min under continuous stirring. After the addition was complete, the temperature was raised to 61 °C and stirred for 28 h to obtain a uniform and transparent organic-inorganic hybrid sol. The obtained sol was transferred to a 1000 mL high-pressure reactor and dried under supercritical carbon dioxide at 60 °C and 15 MPa for 6 h to obtain a dried gel material. The dried material was placed in a Soxhlet extractor and continuously extracted with 500 mL of ethanol solution containing 5% hydrochloric acid for 50 h to completely remove the template agent. The extracted material was placed in a tube furnace and heated at a programmed rate of 2 °C / min under a nitrogen atmosphere: first to 200 °C and held for 2 h, then to 400 °C and held for 1 h, and finally to 600 °C and held for 0.5 h to obtain a porous material. 11.0 g of the above porous material was immersed in 105 mL of aqueous solution containing 1.1 g melamine, 0.6 g cysteine ​​and 0.9 g phytic acid, and immersed under 40 kHz ultrasound for 2 h. The suspension was then transferred to a 200 mL hydrothermal reactor and reacted at 182 °C for 13 h. After the reaction, the mixture was allowed to cool naturally to room temperature, filtered to collect the solid product, washed with deionized water until the filtrate was neutral, and then dried in a vacuum drying oven at 81 °C for 13 h to obtain the doped material. The doped material was placed in a tube furnace and heated to 802°C at a rate of 2°C / min under an argon mixed atmosphere containing 5% hydrogen. The temperature was then maintained for 3 hours. The temperature was then lowered to 402°C at the same rate. The furnace was then switched to pure argon protection and held for 4 hours. Finally, the furnace was cooled to room temperature to obtain the final multi-level structured doped carbon-based organosilicon composite mesoporous material.

[0044] Sodium removal process from lithium carbonate precipitation mother liquor: Take 1050.0g of lithium carbonate precipitation mother liquor (of which Li... + Content 2.9g / L, Na +The lithium-containing mother liquor (containing 32.8 g / L) was filtered through a 5 μm filter and the pH was adjusted to 8.2 with dilute sulfuric acid to obtain a pretreated lithium precipitation mother liquor. 3.5 g of the modified material prepared above was weighed and dispersed in 96.5 g of sulfonated kerosene. 3.5 g of tributyl phosphate and 2.5 g of sorbitan oleate were added, and the mixture was emulsified at 11000 rpm for 14 min to obtain a homogeneous and stable extraction organic phase. The pretreated lithium precipitation mother liquor and the extraction organic phase were fed into a three-stage countercurrent extraction system at a volume ratio of 2.8:1. The mixture was stirred at 320 rpm for 3.5 min in the mixing chamber and held in the clarifying chamber for 9 min for phase separation. After three-stage countercurrent extraction, a lithium-loaded organic phase and a sodium-containing raffinate were obtained. 100.0 g of the loaded organic phase was washed with 8.0 g of deionized water in a two-stage countercurrent process to obtain the washed organic phase. The washed organic phase was mixed with 1.8 mol / L sulfuric acid solution at a volume ratio of 9:1 and introduced into a two-stage back-extraction process. The mixture was contacted in the mixing chamber for 4 minutes and then held in the clarification chamber for 7 minutes. After the two-stage back-extraction, a lithium-rich back-extraction solution was obtained (containing Li...). + Content 14.9 g / L, Na + The lithium-rich back-extraction solution (1.1 g / L, lithium-to-sodium ratio 13.5:1) and the resulting organic phase were used. The lithium-rich back-extraction solution was returned to the lithium precipitation process in the lithium carbonate production flow. The organic phase after back-extraction was regenerated by washing with 1% sodium hydroxide solution and recycled 115 times. The sodium-containing residue was evaporated and crystallized at 87°C for 9.5 h to obtain anhydrous sodium sulfate as a byproduct.

[0045] Comparative Example 1

[0046] The specific implementation method is the same as in Example 1, except that bis-[3-(triethoxysilyl)propyl]-tetrasulfide is not added. Material preparation: Under nitrogen protection, 40.0 g of tetraethyl orthosilicate was dissolved in 100.0 g of anhydrous ethanol to obtain solution A; 20.0 g of poloxamer F127 was mixed with 1000.0 g of deionized water and 5.0 g of concentrated hydrochloric acid to obtain solution B; subsequent preparation conditions were exactly the same as in Example 1. The sodium removal process conditions for lithium carbonate precipitation mother liquor extraction were exactly the same as in Example 1.

[0047] Comparative Example 2

[0048] The specific implementation method is the same as in Example 1, except that sorbitan oleate is not added. Sodium removal process from lithium carbonate precipitation mother liquor: 1000.0g of lithium carbonate precipitation mother liquor was filtered, and the pH was adjusted to 8.0 to obtain the pretreated precipitation mother liquor; 3.0g of multi-level structured doped carbon-based organosilicon composite mesoporous material was dispersed in 97.0g of sulfonated kerosene, and 3.0g of tributyl phosphate was added. The mixture was emulsified at 10000rpm for 12min to obtain the extracted organic phase. Other process conditions were exactly the same as in Example 1.

[0049] Comparative Example 3

[0050] The specific implementation method is the same as in Example 1, except that the element doping step is not performed. Material preparation: Under nitrogen protection, 30.0 g of tetraethyl orthosilicate and 10.0 g of bis-[3-(triethoxysilyl)propyl]-tetrasulfide were dissolved in 100.0 g of anhydrous ethanol to obtain solution A; 20.0 g of poloxamer F127 was mixed with 1000.0 g of deionized water and 5.0 g of concentrated hydrochloric acid to obtain solution B; solution A was added dropwise to solution B under continuous stirring, and after the addition was complete, the temperature was raised to 60°C and stirred for 24 h. The resulting sol was subjected to supercritical drying, Soxhlet extraction and programmed temperature heat treatment (conditions are the same as in Example 1) to obtain the final material. The sodium removal process conditions for lithium carbonate precipitation mother liquor extraction are exactly the same as in Example 1.

[0051] Performance testing

[0052] The sodium removal process of lithium carbonate mother liquor extraction prepared in Examples 1-3 and Comparative Examples 1-3 was tested according to the following method, which included the following steps:

[0053] Accurately weigh 10.0 g of the sample to be tested and place it in a 250 mL Erlenmeyer flask. Add 100.0 mL of deionized water and incubate in a constant temperature water bath at 25 ± 0.5 °C with shaking at 200 rpm for 60 min until solid-liquid equilibrium is reached. Let it stand for 30 min. Filter the supernatant through a 0.45 μm microporous membrane. Use an inductively coupled plasma atomic emission spectrometer equipped with an autosampler to determine the concentrations of lithium and sodium ions in the filtrate. The instrument operating parameters are set as follows: plasma power 1.2 kW, nebulizer pressure 200 kPa, auxiliary gas flow rate 1.0 L / min, and pump speed 50 rpm. Prepare three replicates for each sample, and take the average value of three measurements for each replicate.

[0054] The extraction rate is calculated by measuring the ratio of the target ion concentration in the organic phase to the initial aqueous phase concentration of that ion. The formula is: Extraction rate = (Corg × Vorg) / (Caq0 × Vaq0) × 100%, where Corg is the ion concentration in the organic phase, Vorg is the volume of the organic phase, Caq0 is the initial aqueous phase ion concentration, and Vaq0 is the initial aqueous phase volume. The back-extraction rate is calculated by measuring the ratio of the total amount of the target ion in the aqueous phase after back-extraction to the total amount of that ion in the organic phase before back-extraction. The formula is: Back-extraction rate = (Caq1 × Vaq1) / (Corg × Vorg) × 100%, where Caq1 is the ion concentration in the aqueous phase after back-extraction, and Vaq1 is the volume of the aqueous phase after back-extraction.

[0055] The lithium-sodium separation coefficient was calculated as the ratio of the lithium-sodium concentration in the organic phase to that in the aqueous phase, using the formula: Separation coefficient = (CLi,org / CNa,org) / (CLi,aq / CNa,aq). The organic phase cycling stability test was conducted under standard conditions. Each cycle included 30 min of extraction, 20 min of back-extraction, and 15 min of regeneration. The number of cycles required for the extraction performance to decline to 90% of its initial value was recorded.

[0056] The phase separation time test was performed using a high-definition video recording method. The homogeneous two-phase system was transferred to a 100mL stoppered graduated cylinder and allowed to stand at a constant temperature of 25±0.5℃. The time interval from when stirring was stopped to when the two-phase interface was completely clear and there was no emulsion layer at the interface was recorded.

[0057] The specific surface area and pore size distribution of the material were determined by a static volumetric nitrogen adsorption instrument at 77 K. The sample was degassed under vacuum at 150 °C for 6 h before analysis. The specific surface area was calculated using the BET equation within a relative pressure range of 0.05-0.30, and the pore size distribution was calculated from the adsorption branches using the BJH model.

[0058] Test results:

[0059] Table 1: Test results of each embodiment and comparative example

[0060] Test Project Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Lithium extraction rate / % 98.5 97.8 98.2 85.0 88.0 90.0 Sodium co-extraction rate / % 0.8 1.1 0.9 12.5 8.0 7.2 Lithium-sodium separation coefficient 425 312 385 80 95 95 Back-extraction rate / % 99.2 98.7 99.0 92.5 94.0 95.5 Product liquid lithium sodium ratio 13.2:1 11.6:1 13.5:1 2.5:1 3.8:1 4.2:1 Phase separation time / min 0.8 1.0 0.9 3.5 8.0 2.2 Organic phase cycle times 110 105 115 35 45 50 Specific surface area (m² / g) 1250 1180 1220 850 1230 1050 Average pore size / nm 2.5 2.3 2.6 3.8 2.5 3.2

[0061] As shown in Table 1, Examples 1-3 successfully solved three major technical challenges in the treatment of lithium carbonate mother liquor by employing an innovative design using a multi-level structured carbon-based-organosilicon composite mesoporous material. Regarding lithium-sodium separation efficiency, Example 1 achieved a lithium-sodium separation coefficient of 425, more than four times higher than Comparative Example 1's 80. This is mainly attributed to the synergistic effect of bis-[3-(triethoxysilyl)propyl]-tetrasulfide and multi-element doping in the material, creating a precise pore size and surface chemical environment suitable for lithium-ion transport. Comparative Example 1, lacking organosilicon, resulted in an excessively wide pore size distribution and decreased selectivity; Comparative Example 3, lacking elemental doping, lacked specific recognition sites. Both examples demonstrate the necessity of a complete material structure for achieving efficient separation.

[0062] Regarding lithium recovery rate and cost control, Example 1 achieved a lithium extraction rate as high as 98.5%, and the organic phase could be stably recycled 110 times, far superior to the 85% extraction rate and 35-cycle life of Comparative Example 1. This significant improvement stems from the stable hybrid framework and surface functional groups of the material, which ensures the extractant maintains stable performance during repeated use, greatly reducing operating costs. Furthermore, the product liquid lithium-to-sodium ratio of Example 1 reached 13.2:1, allowing it to be directly returned to the lithium precipitation process, while Comparative Example 1 only had a ratio of 2.5:1, requiring further purification treatment, demonstrating that the present invention effectively simplifies subsequent processes.

[0063] Regarding process simplification and organic phase recycling, Example 1 achieved a phase separation time of only 0.8 minutes with no emulsification, while Comparative Example 2, lacking sorbitan oleate, experienced a phase separation time extended to 8 minutes and severe emulsification. This highlights the synergistic stabilizing effect of the surfactant and the material system, ensuring continuous and stable process operation. Furthermore, the organic phases in Examples 1-3 were recycled more than 100 times with performance degradation of less than 5%, while Comparative Examples 1-3 were recycled less than 50 times with performance degradation exceeding 35%. This fully demonstrates the excellent stability and economy of the material system of this invention, completely solving the technical bottleneck of rapid organic phase loss and frequent replacement in traditional extraction processes.

[0064] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A process for sodium removal from lithium carbonate precipitation mother liquor by extraction, characterized in that, Includes the following steps: S1, filter the lithium carbonate precipitation mother liquor, adjust the pH to 7.5-8.5 to obtain the pretreated lithium precipitation mother liquor; disperse the multi-level structure doped carbon-based-organic silicon composite mesoporous material in sulfonated kerosene, add tributyl phosphate and sorbitan oleate, emulsify to obtain the extracted organic phase; S2, the pretreated lithium precipitation mother liquor and the extraction organic phase are sent into a three-stage countercurrent extraction system, stirred and mixed in the mixing chamber, and held in the clarification chamber; after three-stage countercurrent extraction, the loaded organic phase and sodium-containing raffinate are obtained. S3. The supported organic phase is washed with deionized water to obtain the washed organic phase. The washed organic phase is then fed into a two-stage back-extraction process, where sulfuric acid solution is used for back-extraction to obtain a lithium sulfate solution that enters the aqueous phase. After two-stage back-extraction, a lithium-rich back-extraction solution and the back-extracted organic phase are obtained. The lithium-rich back-extraction solution is returned to the lithium precipitation process in the lithium carbonate production flow. The back-extracted organic phase is washed with NaOH solution and then recycled. S4. The sodium-containing raffinate is evaporated and crystallized to obtain anhydrous sodium sulfate as a byproduct.

2. The process for removing sodium from lithium carbonate mother liquor by extraction according to claim 1, characterized in that, In step S1, the emulsification speed is 8000-12000 rpm and the emulsification time is 10-15 min.

3. The process for removing sodium from lithium carbonate mother liquor by extraction according to claim 1, characterized in that, In step S2, the mixing time in the mixing chamber is 3-5 minutes.

4. The process for removing sodium from lithium carbonate mother liquor by extraction according to claim 1, characterized in that, In step S3, the organic phase after back-extraction is washed with NaOH solution and recycled 100-120 times.

5. The process for removing sodium from lithium carbonate precipitation mother liquor by extraction according to claim 1, characterized in that, In step S4, the sodium-containing raffinate is treated by evaporation and crystallization for 8-10 hours.

6. The process for sodium removal from lithium carbonate mother liquor by extraction according to any one of claims 1-5, characterized in that, The preparation steps of the multi-level structure doped carbon-based-organosilicon composite mesoporous material include: A1. Under nitrogen protection, tetraethyl orthosilicate and bis-[3-(triethoxysilyl)propyl]-tetrasulfide were dissolved in anhydrous ethanol to obtain solution A; poloxamer F127 was mixed with deionized water and concentrated hydrochloric acid to obtain solution B; solution A was added dropwise to solution B under continuous stirring, and after the addition was complete, the temperature was raised to 58-62℃ and stirred to obtain an organic-inorganic hybrid sol; A2, place the organic-inorganic hybrid sol in a high-pressure reactor and dry it with supercritical carbon dioxide; obtain the dried material; place the dried material in a Soxhlet extractor and extract it with ethanol containing hydrochloric acid to obtain the extracted material; heat treat the extracted material under a nitrogen atmosphere to obtain a porous material; A3. The porous material is immersed in an aqueous solution containing melamine, cysteine ​​and phytic acid under ultrasonic assistance to obtain a suspension. The suspension is transferred to a hydrothermal reactor and reacted at 175-185℃ to obtain a reaction mixture. The reaction mixture is filtered to collect the solid product, which is washed with deionized water until neutral and then vacuum dried at 78-82℃ to obtain the doped material. A4. The doped material is heated to 795-805℃ and held in a hydrogen-argon mixed atmosphere; then cooled to 395-405℃, switched to pure argon protection, and held at that temperature; finally cooled to room temperature.

7. The process for removing sodium from lithium carbonate mother liquor by extraction according to claim 6, characterized in that, In step A1, the stirring time is 24-30 hours.

8. The process for removing sodium from lithium carbonate mother liquor by extraction according to claim 6, characterized in that, In step A2, the extraction time with ethanol containing hydrochloric acid is 48-50 hours.

9. The process for removing sodium from lithium carbonate mother liquor by extraction according to claim 6, characterized in that, In step A3, the reaction time is 12-14 hours at 175-185℃.

10. The process for removing sodium from lithium carbonate mother liquor by extraction according to claim 6, characterized in that, In step A4, the temperature is raised to 795-805℃ and held for 2-4 hours.