Method for producing lithium and co-producing natural soda by closed loop of carbonic type salt lake brine

Abstract

The present application belongs to the technical field of lithium extraction from salt lake brine and comprehensive utilization of salt lake resources, and particularly relates to a method for closed-loop lithium extraction and co-production of natural soda from carbonic acid type salt lake brine. The method concentrates the carbonic acid root-containing materials of the original brine carbonic acid root-rich concentrated water, lithium precipitation mother liquor and carbonization mother liquor, and performs collaborative and directional carbonization, so as to completely utilize the carbonic acid root resources in the multiple materials of the salt lake to prepare sodium bicarbonate / natural soda required for lithium precipitation, without purchasing sodium carbonate, and thus the lithium precipitation cost of the highland salt lake lithium extraction can be reduced. Meanwhile, the introduction of foreign impurities to the highland ecology is completely avoided, the whole process has no high-salt tail water discharge, and thus the development requirements of the ecologically sensitive areas such as Tibet can be met.

Description

Technical Field

[0001] This invention belongs to the technical field of lithium extraction from salt lake brine and comprehensive utilization of salt lake resources. Specifically, it relates to a closed-loop method for lithium extraction and co-production of natural alkali from carbonate-type salt lake brine, which is particularly suitable for the large-scale development of carbonate-type salt lake lithium resources in high-altitude, logistics-restricted, and ecologically sensitive areas such as Tibet. Background Technology

[0002] Lithium is a core strategic resource for the new energy industry. With the explosive growth of the global power battery and energy storage industries, the market demand for lithium salts continues to rise. my country has the world's second largest lithium reserves, with Tibet possessing abundant carbonate-type salt lake lithium resources. Representative salt lakes such as Zabuye Chaka and Bangor Co have prospective lithium carbonate reserves exceeding ten million tons. Moreover, carbonate-type salt lakes have the natural advantage of an extremely low magnesium-to-lithium ratio, making them high-quality raw materials for lithium extraction from brine.

[0003] Currently, the mainstream lithium extraction process from carbonate-type salt lakes in my country adopts the gradient solar pond process, with Zabuye Salt Lake as a representative example. This process has achieved large-scale production capacity, but it suffers from several insurmountable industry pain points: First, the lack of industrial support in high-altitude areas necessitates the long-distance transportation of sodium carbonate (natural alkali) required for the lithium precipitation process from inland areas. Transportation costs account for over 40% of the total cost of lithium precipitation, significantly increasing the production cost of lithium carbonate. Second, purchasing soda ash from external sources introduces a large amount of foreign impurities into the salt lake system, disrupting the fragile ecological balance of the plateau and failing to meet ecological protection requirements. Third, the solar pond process is severely limited by the plateau climate and sunlight conditions, resulting in poor production stability and low lithium recovery rates.

[0004] Adsorption-based lithium extraction has become the mainstream technology for lithium extraction from salt lakes in recent years. For carbonate-type salt lake brines, aluminum-based adsorbents have good lithium adsorption selectivity. However, existing technologies still have significant drawbacks: the adsorbents have poor adaptability to carbonate-type brines, low lithium adsorption capacity, and a simple desorption process that cannot balance high adsorption efficiency and desorption stability. Furthermore, the lithium precipitation mother liquor produced in the lithium precipitation process contains high concentrations of valuable components such as carbonate and sodium ions. Current processes often directly discharge the tail brine or simply produce salt, failing to achieve the synergistic recovery of multiple carbonate-containing materials. The total utilization rate of carbonate is less than 60%, which not only causes serious resource waste but also brings environmental pressure to the treatment of high-salinity wastewater.

[0005] Regarding the resource utilization of lithium extraction tail brine, existing technologies disclose a process for preparing natural alkali via direct carbonation. However, this process only focuses on the preparation of natural alkali itself and has three major shortcomings: First, it does not form a complete closed-loop chain with the lithium precipitation process in salt lake lithium extraction, failing to incorporate residual carbonate ions in the lithium precipitation mother liquor into the resource utilization system, thus failing to fundamentally solve the cost problem of purchasing lithium precipitation agents externally. Second, the lithium-rich liquid concentration process is outdated, resulting in a lithium ion concentration of only 2-3 g / L after concentration, leading to a large volume of the lithium precipitation reaction system, low lithium carbonate precipitation rate (generally below 85%), large mother liquor circulation volume, and high energy consumption. Third, the process parameters are not synergistically optimized for the complex salt system of multiple alkaline materials in carbonate-type salt lakes, resulting in low CO2 utilization and an inability to simultaneously achieve product purity and yield. For example:

[0006] Patent CN117945441A discloses a method for preparing lithium carbonate from lithium brine. The method involves adsorption, concentration, lithium precipitation, and carbonation pyrolysis to prepare lithium carbonate. However, the lithium concentration of the lithium-rich concentrate is only 2-3 g / L, the lithium precipitation efficiency is low, and it does not involve the synergistic recovery and utilization of carbonate ions in the lithium extraction tail brine and the lithium precipitation mother liquor. It still requires the purchase of lithium precipitation agents, resulting in high costs.

[0007] Patent CN118851216A discloses a method for directly extracting lithium from chloride-type salt lake brine, which optimizes the adsorption and membrane concentration process. However, it is designed for chloride-type brine and cannot be adapted to the highly alkaline system of carbonate-type salt lakes. Furthermore, it does not solve the core problems of synergistic recovery of carbonate from multiple materials and self-generation of lithium precipitation agent in a closed loop.

[0008] Existing research on sodium carbonate preparation has only explored the basic parameters of the reaction between NaOH and CO2. It has not developed an industrial carbonization process suitable for multiple alkaline materials in salt lakes, nor has it achieved full-process coupling with lithium extraction processes, thus failing to solve the actual production problems of high-altitude salt lakes.

[0009] In summary, existing technologies have consistently failed to address the following technical challenges in lithium extraction from carbonate-containing salt lakes: first, the high cost and ecological damage of purchased lithium precipitation agents contradict the need for comprehensive utilization of the salt lake's own carbonate resources; second, the low concentration of lithium-rich solutions and poor lithium precipitation efficiency contradict the need for industrial-scale energy consumption control; and third, the dispersed processing of multiple carbonate-containing materials and the low overall carbonate utilization rate contradict the need for low resource utilization. Therefore, there is an urgent need to develop an integrated process that combines lithium extraction, high-concentration lithium-rich solution refining, co-carbonation of lithium precipitation mother liquor and raw brine concentrate, self-production of lithium precipitation agents, and closed-loop recycling throughout the entire process. This process would achieve efficient lithium extraction while simultaneously enabling the full recycling of the salt lake's own carbonate resources, balancing economic benefits, environmental benefits, and ecological protection requirements. Summary of the Invention

[0010] To address the technical challenges of lithium extraction from carbonated brine, including the need for externally purchased sodium carbonate, high transportation costs, introduction of foreign impurities, lithium precipitation mother liquor, carbonate dispersion treatment in carbonate-rich concentrates of the original brine, low overall utilization rate, poor compatibility of existing aluminum-based adsorbents with carbonated brines, low lithium adsorption capacity, limited desorption processes, low CO2 utilization rate in existing direct carbonation processes for tail brine, and the inability to simultaneously achieve both purity and yield of sodium bicarbonate, this invention provides a closed-loop method for lithium extraction and co-production of natural alkali from carbonated brine. This method is suitable for high-altitude salt lake environments, features a closed-loop mother liquor process, is simple in design, has low energy consumption, is adaptable to remote salt lake sites, and improves lithium adsorption efficiency and process adaptability.

[0011] To achieve the above technical objectives, the present invention adopts the following technical solution:

[0012] A closed-loop method for lithium extraction and co-production of natural alkali from carbonated salt lake brine includes the following steps:

[0013] S1: Using carbonated salt lake brine as raw material, after solid-liquid separation and impurity removal, lithium-rich permeate and carbonate-rich concentrate are obtained by separation through alkali-resistant nanofiltration membrane. The carbonate-rich concentrate is then frozen and impurity removed before being combined with the mother liquor of subsequent processes.

[0014] S2: The lithium-rich water obtained from S1 is passed into a modified aluminum-based adsorbent column for dynamic adsorption. After adsorption saturation, reverse desorption is performed using fresh water or dilute acid solution to obtain lithium-rich desorption solution.

[0015] S3: The lithium-rich eluent obtained from S2 is subjected to deep impurity removal through nanofiltration membrane, high-pressure reverse osmosis membrane concentration, and multi-effect evaporation concentration to obtain a refined lithium-rich concentrate.

[0016] S4: The lithium precipitation mother liquor from S6 and the carbonate-rich concentrated water from S1 are mixed to obtain alkaline brine. After membrane pretreatment and concentration, carbonation stock solution is obtained. CO2 gas is continuously introduced into the carbonation stock solution, and carbonation reaction is carried out under temperature and pressure control. After solid-liquid separation, sodium bicarbonate coarse precipitate and carbonation mother liquor are obtained. The carbonation mother liquor is returned to the front end of this process to continue to participate in the carbonation reaction.

[0017] S5: The crude sodium bicarbonate precipitate obtained in S4 is washed countercurrently with sodium bicarbonate solution to remove impurities. After solid-liquid separation, refined sodium bicarbonate solid is obtained. Part of the refined sodium bicarbonate solid is directly used in the subsequent lithium precipitation process, and the remaining part is calcined and decomposed to obtain natural alkali product.

[0018] S6: The refined sodium bicarbonate solid or natural alkali product obtained in S5 is mixed with the refined lithium-rich concentrate obtained in S3 to carry out a temperature-controlled lithium precipitation reaction. After solid-liquid separation, the product is washed and dried to obtain battery-grade lithium carbonate. The lithium precipitation mother liquor is returned to the S4 process for the preparation of carbonization stock solution.

[0019] Furthermore, in step S1, the carbonate-type brine is carbonate-type brine, concentrated brine after lithium extraction, salt production tailwater, or underground associated lithium brine; the alkali-resistant nanofiltration membrane is a sulfonated polyether sulfone-based alkali-resistant composite nanofiltration membrane with a continuous operating pH tolerance range of 3-14, a molecular weight cutoff of 100-1000 Da, and an operating pressure of 2.5-8.0 MPa; the temperature for cryogenic impurity removal is 4-10℃, and the treatment time is 2-4 hours.

[0020] Further, in step S2, the modified aluminum-based adsorbent is a modified adsorbent consisting of activated alumina supported on a lithium chloride-aluminum chloride bicomponent. The preparation method is as follows: activated alumina powder is impregnated in a mixed solution of 10-20 wt% aluminum chloride and 2-5 wt% lithium chloride for 4-6 hours, filtered, dried at 110-130℃ for 1-3 hours, and calcined at 280-320℃ for 2-4 hours. The dynamic adsorption temperature is 5-30℃, and the adsorption flow rate is 1-3 h / min. -1 The dilute acid solution is 1.0 × 10⁻⁶. -3 -1.0×10 -6 For hydrochloric acid or sulfuric acid at mol / L concentrations, the desorption temperature is 10-40℃, and the desorption flow rate is 0.5-1 h. -1 The desorption of fresh water is performed using hot pure water at 10-40℃, with a desorption flow rate of 1-2 hours. -1 .

[0021] Furthermore, in step S3, the nanofiltration membrane for deep impurity removal uses a sulfonated polyether sulfone-based alkali-resistant composite nanofiltration membrane with a molecular weight cutoff of 100-1000 Da, and an operating pressure of 2.5-8.0 MPa; the high-pressure reverse osmosis membrane concentration uses a high-pressure resistant wide-channel reverse osmosis membrane, with an operating pressure of 3.0-12.0 MPa, and a lithium ion concentration ≥8 g / L after concentration; the temperature of the multi-effect evaporation concentration is 100-115℃.

[0022] Furthermore, in step S4, the alkaline brine has a pH of 8-14, a lithium concentration ≥30ppm, and a CO3 concentration of [missing information]. 2- Concentration ≥ 5 g / L; CO3 in the carbonized stock solution obtained after membrane pretreatment concentration 2- The concentration is 40g / L-70g / L; the flow rate of the CO2 gas is ≥800mL / min; the control pressure of the carbonization reaction is ≤0.5MPa; the reaction temperature is 30-50℃; the reaction time is 30-60min; and the reaction endpoint is when the pH of the system drops to 7.0-8.0.

[0023] Furthermore, in step S5, the sodium bicarbonate solution is a saturated sodium bicarbonate solution, the countercurrent washing is performed 2-3 times, and the washing temperature is 20-30℃; the calcination decomposition temperature is 160-250℃, the calcination time is 1-3 hours, and the calcination equipment is any one of a rotary kiln, a pot furnace, or a rotary bed furnace; the purity of the natural alkali product is ≥99.6%.

[0024] Furthermore, in step S6, the temperature of the controlled lithium precipitation reaction is 90-95℃, the reaction time is 45-60 min, and the final pH of the reaction system is 10.5-12.5; the purity of the battery-grade lithium carbonate product is ≥99.5%.

[0025] Furthermore, in step S4, the carbonization mother liquor is recycled and carbonized to CO3. 2- After the concentration is ≤10g / L, sodium chloride is obtained by evaporation and desalination. The condensate is returned to the S1 process for brine dilution. All mother liquors in the whole process are recycled in a closed loop, and there is no discharge of high-salt tailwater, forming a closed loop of internal circulation of all components of salt lake resources.

[0026] Furthermore, the lithium ion concentration of the refined lithium-rich concentrate is 10.0~30.0 g / L.

[0027] Furthermore, the lithium ion concentration of the lithium-rich solution is 0.4~1.5 g / L.

[0028] A closed-loop method for lithium extraction and co-production of natural alkali from carbonated brine is disclosed. The core process logic is as follows: Raw brine from the carbonated brine undergoes pretreatment and alkali-resistant nanofiltration separation to obtain lithium-rich permeate and carbonate-rich concentrate. The lithium-rich permeate is selectively purified for lithium using a modified aluminum-based adsorbent to obtain a lithium-rich eluent. This eluent undergoes a three-stage purification process: nanofiltration membrane impurity removal, high-pressure reverse osmosis concentration, and multi-effect evaporation concentration, to obtain a high-concentration refined lithium-rich concentrate with a lithium ion concentration of 10.0-30.0 g / L. The carbonate-containing materials—raw brine carbonate concentrate, lithium precipitation mother liquor, and carbonation mother liquor—are mixed and concentrated using a ceramic membrane, followed by pressure-controlled directional carbonation to obtain sodium bicarbonate precipitate. After washing and purification, a portion is directly used in the lithium precipitation reaction to prepare lithium carbonate, while the other portion is calcined to obtain high-quality natural alkali. The lithium precipitation mother liquor and carbonation mother liquor are all recycled in a closed loop, forming a complete internal circulation loop of all components of the salt lake resources.

[0029] The specific process steps are as follows:

[0030] S1 Brine Pretreatment: Using carbonated salt lake brine as raw material, suspended solids, silt, and other mechanical impurities are first removed by plate and frame filter press or clarification tank. Then, the brine is fed into a nanofiltration unit, where an alkali-resistant nanofiltration membrane is used for nanofiltration separation. The permeate is lithium-rich permeate, and the concentrate is carbonate-rich concentrate, rich in carbonate and sulfate. The carbonate-rich concentrate is frozen at 4-10℃ for 2-4 hours to allow sulfate crystallization. After filtration to remove impurities, the concentrate is combined with the mother liquor from subsequent processes. The frozen filtrate is used in the subsequent carbonation process. The alkali-resistant nanofiltration membrane is a sulfonated polyethersulfone-based alkali-resistant composite nanofiltration membrane with a continuous operating pH tolerance range of 3-14, a molecular weight cutoff of 100-1000 Da, and an operating pressure of 2.5-8.0 MPa.

[0031] S2 Selective adsorption for lithium extraction: The lithium-rich permeate obtained from S1 is passed through an adsorption column packed with a modified aluminum-based adsorbent at 5-30℃ and a flow rate of 1-3 h / min. -1 Under these conditions, dynamic adsorption occurs, and lithium ions in the brine are selectively captured by the adsorbent. Adsorption stops when the lithium ion concentration in the effluent reaches the breakthrough point, and reverse desorption is performed using either fresh water or dilute acid solution, depending on the brine quality. When using dilute acid desorption, a 1.0 × 10⁻⁶ solution is used. -3 -1.0×10 -6 A solution of hydrochloric acid, sulfuric acid, or a mixed acid solution with hydrogen ion concentrations within their respective ranges (mol / L) is prepared at 10-40°C and a flow rate of 0.5-1 h. -1 Desorption occurs under specific conditions; when using fresh water for desorption, use hot pure water at 10-40℃ at a flow rate of 1-2 h / min. -1 Desorption is performed under specific conditions; after desorption, a lithium-rich solution is obtained and sent to the subsequent refining and concentration process.

[0032] The modified aluminum-based adsorbent is a modified adsorbent consisting of lithium chloride and aluminum chloride supported on activated alumina. The preparation method is as follows: activated alumina powder is impregnated in a mixed solution of 10-20 wt% aluminum chloride and 2-5 wt% lithium chloride for 4-6 hours, filtered, dried at 120°C for 2 hours, and calcined at 300°C for 3 hours. Compared with ordinary activated alumina, the lithium adsorption capacity is increased by more than 30%, and the adaptability to carbonate-type high-alkaline brine is stronger.

[0033] S3 Lithium-Rich Solution Refining and Concentration: The lithium-rich eluent obtained from S2 is first sent to a nanofiltration unit for deep impurity removal to remove residual divalent impurity ions such as calcium, magnesium, and sulfate. The nanofiltration membrane used for deep impurity removal is a sulfonated polyethersulfone-based alkali-resistant composite nanofiltration membrane with a molecular weight cutoff of 100-1000 Da, and the operating pressure is 2.5-8.0 MPa. The nanofiltration permeate is sent to a high-pressure reverse osmosis membrane unit for pre-concentration at an operating pressure of 3.0-12.0 MPa to increase the lithium ion concentration to above 8 g / L. The reverse osmosis concentrate is sent to a multi-effect evaporator for evaporation and concentration at 100-115℃ to finally obtain a refined lithium-rich concentrate with a lithium ion concentration of 10.0-30.0 g / L, which is then sent to the subsequent lithium precipitation process.

[0034] S4 Nanofiltration concentrate directional carbonization for sodium bicarbonate co-production: The lithium precipitation mother liquor from S6, the carbonate-rich concentrate from S1, and the carbonation mother liquor are mixed to obtain a solution with pH 8-14, lithium concentration ≥50ppm, and CO32-. 2- For alkaline brine with a concentration ≥5 g / L, the carbonized stock solution obtained after pretreatment and concentration using the ceramic membrane contains CO3. 2⁻ The concentration is 40g / L-70g / L; the carbonation stock solution is sent into the carbonation reactor, and CO2 gas is continuously introduced. The CO2 flow rate is controlled at ≥800ml / min (laboratory scale) or the gas-liquid volume ratio is ≥15:1 (industrial scale). The reaction pressure is ≤0.5MPa, the reaction temperature is 30-50℃, and the carbonation reaction is carried out for 30-60min. The reaction is stopped when the pH of the system drops to 7.0-8.0. At this time, the sodium carbonate in the solution reacts with CO2 to generate sodium bicarbonate and precipitates out as supersaturated. After solid-liquid separation by filtration, the crude sodium bicarbonate precipitate and carbonation mother liquor are obtained. The carbonation mother liquor is returned to the front end of this process to continue to participate in the carbonation reaction, so as to realize the gradient recovery of carbonate ions.

[0035] S5 Precipitation Washing and Product Preparation: The crude sodium bicarbonate precipitate obtained in S4 is subjected to 2-3 countercurrent washes using a saturated sodium bicarbonate solution. The washing temperature is controlled at 20-30℃. The common ion effect is used to suppress the dissolution loss of sodium bicarbonate, while removing impurities such as sodium chloride and sodium sulfate entrained in the precipitate. After filtration, refined sodium bicarbonate solid is obtained. 50%-80% of the refined sodium bicarbonate solid is directly fed into the subsequent lithium precipitation process, and the remaining part is sent to a calcination device and calcined at 160-250℃ for 1-3 hours to completely decompose the sodium bicarbonate into sodium carbonate. After cooling, a high-grade natural alkali product is obtained, which can be sold or kept for later use. The calcination device can be any one of a rotary kiln, a pot furnace, or a rotary bed furnace. The purity of the high-grade natural alkali product is ≥99.6%, which meets the GB / T 210.1-2022 high-grade standard.

[0036] S6 Closed-loop lithium precipitation for lithium carbonate preparation: The refined sodium bicarbonate solid or natural alkali product obtained in S5 is mixed with the refined lithium-rich concentrate obtained in S3 at a stoichiometric ratio. The mixture is stirred at 90-95℃ for 45-60 minutes to induce a lithium precipitation reaction. The final pH of the reaction is controlled at 10.5-12.5 to ensure complete conversion of lithium ions into lithium carbonate precipitate. After the reaction is complete, the mixture is kept warm and filtered to obtain crude lithium carbonate. This crude lithium carbonate is washed 2-3 times with hot water above 90℃ and then vacuum dried at 120℃ to obtain battery-grade lithium carbonate. The lithium precipitation mother liquor contains unreacted carbonate ions, which are returned to process S4 for preparing the carbonation stock solution, achieving resource recycling. The purity of the battery-grade lithium carbonate product is ≥99.5%, conforming to the GB / T 11075-2013 battery-grade standard.

[0037] Furthermore, in step S4, the carbonization mother liquor is carbonized to CO3 through multiple cycles. 2- After the concentration is ≤10g / L, sodium chloride is obtained as a by-product by multi-effect evaporation and desalination. The condensate is returned to the S1 process for brine dilution. All mother liquors in the entire process are recycled in a closed loop, and there is no discharge of high-salt tailwater, forming a closed loop of internal circulation of all components of salt lake resources.

[0038] Beneficial effects

[0039] The method described in this invention enables a fully closed-loop internal resource recycling system, eliminating the introduction of foreign impurities and offering both economic and ecological benefits. This invention is the first to achieve a complete closed-loop industrial chain encompassing lithium extraction from salt lake brine, lithium precipitation mother liquor, synergistic carbonization of concentrated brine, and self-production and reuse of the lithium precipitation agent. It fully utilizes the carbonate resources within the salt lake's various materials to prepare the sodium bicarbonate / natural alkali required for lithium precipitation, eliminating the need to purchase sodium carbonate externally. This reduces the cost of lithium precipitation from high-altitude salt lakes by over 40%. Simultaneously, it completely avoids the introduction of foreign impurities that could damage the high-altitude ecosystem, with no high-salinity wastewater discharged throughout the entire process, meeting the development requirements of ecologically sensitive areas such as Tibet.

[0040] The synergistic carbonation of multiple carbonate-containing materials significantly improves the overall utilization rate of carbonate. This invention centrally processes three carbonate-containing materials—raw brine rich in carbonate concentrate, lithium precipitation mother liquor, and carbonation mother liquor—and performs synergistic and directional carbonation. Compared to the existing technology of processing single materials separately, the overall utilization rate of carbonate increases from less than 60% to over 90%, and the CO2 utilization rate remains stable at over 90%, achieving full recovery of valuable components from salt lakes.

[0041] This invention targets complex salt systems with mixed materials in carbonate-type salt lakes. Through synergistic optimization of parameters—ceramic membrane pre-concentration to control carbonate concentration, pressure and flow rate control during carbonation, and common ion washing for impurity removal—it overcomes the technical bias in existing technologies where direct carbonation of complex salt systems cannot simultaneously achieve both purity and yield. The prepared natural alkali has a purity ≥99.6%, meeting the superior grade standard of GB / T 210.1-2022, and the total carbon yield is consistently above 30%, representing a yield increase of over 50% compared to conventional carbonation processes. It can be directly used in lithium precipitation processes without additional refining, while simultaneously achieving a significant improvement in product purity and yield.

[0042] The modified aluminum-based adsorbent optimized in this invention improves lithium adsorption capacity by more than 30% for carbonated high-alkaline brine, achieving a lithium adsorption selectivity of ≥98% and a total lithium recovery rate of ≥90%, far exceeding the 60% recovery rate of traditional solar pond processes. Simultaneously, it innovatively designs a dilute acid / freshwater dual-mode desorption process, which can be flexibly selected according to the water quality and operating conditions at the salt lake site, making it far more adaptable than existing single desorption processes. The entire process is not limited by high-altitude climate or sunlight conditions, significantly improving lithium extraction efficiency and having a wide range of applications, enabling continuous and stable production, and is suitable for on-site industrial construction in remote salt lakes such as Tibet.

[0043] This invention allows for flexible adjustment of the ratio of sodium bicarbonate used for lithium precipitation to externally sold natural alkali based on lithium carbonate market conditions. When lithium salt prices are low, it can expand the production capacity of natural alkali for external sales, thereby enhancing the project's risk resistance and overall economic benefits, and possesses strong industrialization and promotion value. Attached Figure Description

[0044] Figure 1 This is a process flow diagram of lithium extraction in the closed-loop lithium extraction and co-production of natural alkali from carbonated salt lake brine according to the present invention.

[0045] Figure 2 This is a process flow diagram for preparing natural alkali in the closed-loop lithium extraction and co-production of natural alkali from carbonated salt lake brine according to the present invention. Detailed Implementation

[0046] The present invention will be further described in detail below with reference to specific embodiments and comparative examples. This embodiment is implemented based on the technical solution of the present invention, and provides detailed implementation methods and specific operating procedures. The scope of protection of the present invention is not limited to the following embodiments.

[0047] In the following examples and comparative examples, the raw materials used were raw brine, old brine, and salt production tailwater from a carbonate-type salt lake in Tibet. The core water quality indicators are shown in the table below. Product testing standards: the purity of natural alkali refers to GB / T 210.1-2022, the purity of lithium carbonate refers to GB / T 11075-2013, the total carbon yield is calculated based on the initial total carbonate in the brine, the CO2 utilization rate is calculated as the ratio of actual carbonate reacted to theoretically consumed CO2, and the total carbonate utilization rate is the ratio of carbonate recovered throughout the process to the total carbonate in the raw materials.

[0048]

[0049] Example 1

[0050] This embodiment uses raw brine from a carbonate-type salt lake in Tibet as the raw material. The specific process steps are as follows:

[0051] S1 Brine Pretreatment: Take 10L of raw brine from the salt lake, remove suspended solids by plate and frame filter press, and then send it to a nanofiltration device. Use a sulfonated polyethersulfone-based alkali-resistant nanofiltration membrane (molecular weight cutoff 300 Da, pH tolerance 3-14) for nanofiltration separation at an operating pressure of 4.0 MPa to obtain 8L of lithium-rich permeate and 2L of carbonate-rich concentrate. Freeze the carbonate-rich concentrate at 5℃ for 3 hours, filter to remove precipitated sodium sulfate crystals, and keep the frozen filtrate for later use.

[0052] S2 Selective Adsorption for Lithium Extraction: Lithium-rich permeate is passed through an adsorption column packed with a modified aluminum-based adsorbent. The column has an inner diameter of 50 mm and an adsorbent packing height of 1000 mm. The process is carried out at 25°C and a flow rate of 2 h / min. -1 Dynamic adsorption was carried out under the specified conditions; after adsorption was completed, a 1.0×10⁻⁶ m³ / h filter was used. -5 A mol / L hydrochloric acid solution was prepared at 25°C with a flow rate of 0.8 h⁻¹. -1 Under the condition of reverse desorption, 1 L of lithium-rich eluent was obtained with a lithium ion concentration of 0.75 g / L.

[0053] S3 Lithium-Rich Solution Refining and Concentration: The lithium-rich eluent is fed into a nanofiltration unit (molecular weight cutoff 200 Da) for deep impurity removal at a pressure of 3.0 MPa; the permeate is fed into a high-pressure reverse osmosis membrane unit and concentrated to a lithium-ion concentration of 8.1 g / L at an operating pressure of 8.0 MPa; then it is concentrated by multi-effect evaporation at 105 °C to finally obtain 0.15 L of refined lithium-rich concentrate with a lithium-ion concentration of 15.0 g / L.

[0054] S4 nanofiltration concentrate directional carbonization co-production of sodium bicarbonate: The lithium precipitation mother liquor from the previous cycle and the carbonate-rich concentrate from S1 are mixed to obtain a solution with pH 10.0, lithium concentration 32 ppm, and CO32. 2- Alkaline brine with a concentration of 16 g / L was concentrated via membrane pretreatment to obtain CO3. 2-5L of carbonization stock solution with a concentration of 52g / L was added to the carbonization reactor. CO2 gas was continuously introduced at a flow rate of 900ml / min, the reaction pressure was 0.2MPa, the reaction temperature was 45℃, and the carbonization reaction was carried out for 45min. The reaction was stopped when the pH of the system dropped to 7.5. The mixture was filtered to obtain crude sodium bicarbonate precipitate and carbonization mother liquor. The carbonization mother liquor was returned to the front end of this process for recycling carbonization.

[0055] S5 Precipitation Washing and Product Preparation: The coarse precipitate was washed twice countercurrently with a saturated sodium bicarbonate solution at a washing temperature of 25°C. The precipitate was filtered to obtain refined sodium bicarbonate solid with a purity of 99.52%. 70% of the refined sodium bicarbonate solid was used for the lithium precipitation process, and the remaining 30% was calcined at 200°C for 2 hours to obtain the natural alkali product with a purity of 99.81%.

[0056] S6 Closed-loop lithium precipitation to prepare lithium carbonate: Refined sodium bicarbonate solid is mixed with refined lithium-rich concentrate, stirred and reacted at 95℃ for 50 min, the final pH is controlled at 11.0, filtered after heat preservation, washed twice with 90℃ hot water, and vacuum dried at 120℃ to obtain battery-grade lithium carbonate product with a purity of 99.65%; the lithium precipitation mother liquor is returned to the S4 process for reuse.

[0057] According to the test results, the total lithium recovery rate of this embodiment is 90.3%, the total carbon recovery rate is 31.5%, the CO2 utilization rate is 91.2%, the total carbonate utilization rate is 92.7%, the lithium carbonate precipitation rate is 96.1%, the purity of natural alkali meets the national standard for superior grade, and the lithium carbonate meets the battery grade standard.

[0058] Example 2

[0059] This embodiment uses old brine from a carbonate-type salt lake in Tibet as raw material. The specific process steps are as follows:

[0060] S1 Brine Pretreatment: Take 10L of old brine from the salt lake, remove suspended solids in a clarifier, and then send it to an alkali-resistant nanofiltration device for nanofiltration separation at an operating pressure of 5.2MPa to obtain 7.5L of lithium-rich permeate and 2.5L of carbonate-rich concentrate. Place the carbonate-rich concentrate at 8℃ for 4 hours, filter to remove impurities, and then use it for later use.

[0061] S2 Selective adsorption for lithium extraction: Lithium-rich permeate is passed through a modified aluminum-based adsorbent column and subjected to an adsorption process at 28°C and a flow rate of 1.5 h⁻¹. -1 Dynamic adsorption was performed under specific conditions; after adsorption was complete, hot pure water at 35℃ was used at a flow rate of 1.5 h⁻¹. -1 Under the condition of reverse desorption, 1 L of lithium-rich eluent was obtained with a lithium ion concentration of 0.52 g / L.

[0062] S3 Lithium-rich solution refining and concentration: The lithium-rich solution is subjected to nanofiltration for deep impurity removal and high-pressure reverse osmosis concentration to a lithium ion concentration of 11.8 g / L. Then, it is concentrated by multi-effect evaporation at 110℃ to obtain 0.12 L of refined lithium-rich concentrate with a lithium ion concentration of 25.0 g / L.

[0063] S4 nanofiltration concentrate directional carbonization co-production of sodium bicarbonate: The lithium precipitation mother liquor from the previous cycle, the carbonate-rich concentrate from S1, and the carbonization mother liquor are mixed to obtain a solution with pH 11.8, lithium concentration 41 ppm, and CO32-. 2- Alkaline brine with a concentration of 24 g / L; after membrane concentration, CO3 is obtained. 2- 5 L of carbonization stock solution with a concentration of 48 g / L was used; CO2 gas was introduced, with a flow rate of 850 ml / min, a reaction pressure of 0.3 MPa, a reaction temperature of 50 °C, and the carbonization reaction was carried out for 50 min. The reaction was stopped when the pH of the system dropped to 7.2. The crude sodium bicarbonate precipitate was obtained by filtration, and the carbonization mother liquor was recycled.

[0064] S5 Precipitation Washing and Product Preparation: The coarse precipitate was washed three times countercurrently with a saturated sodium bicarbonate solution at a washing temperature of 25°C to obtain refined sodium bicarbonate solid with a purity of 99.48%. 75% was used for the lithium precipitation process, and the remaining 25% was calcined at 220°C for 1.5 hours to obtain natural alkali product with a purity of 99.63%.

[0065] S6 Closed-loop lithium precipitation to prepare lithium carbonate: Refined sodium bicarbonate is mixed with refined lithium-rich concentrate and reacted at 92°C for 60 min. The final pH is 11.8. After heat preservation, filtration, washing and drying, battery-grade lithium carbonate with a purity of 99.68% is obtained. The lithium precipitation mother liquor is returned to the S4 process for reuse.

[0066] According to the test results, the total lithium recovery rate in this embodiment is 89.7%, the total carbon recovery rate is 30.8%, the CO2 utilization rate is 90.5%, the total carbonate utilization rate is 91.8%, the lithium carbonate precipitation rate is 95.7%, the purity of natural alkali meets the national standard for superior grade, and the lithium carbonate meets the battery grade standard.

[0067] Example 3

[0068] This embodiment uses the tail brine from lithium extraction in a salt production process as raw material. The specific process steps are as follows:

[0069] S1 Brine Pretreatment: Take 10L of salt production tailwater, remove impurities by vacuum filtration, and send it to an alkali-resistant nanofiltration device for nanofiltration separation at an operating pressure of 5.5MPa to obtain 9L of lithium-rich permeate and 1L of carbonate-rich concentrate. Place the carbonate-rich concentrate at 10℃ for 2 hours for freezing treatment, filter to remove impurities, and then use it for later use.

[0070] S2 Selective adsorption for lithium extraction: Lithium-rich permeate is passed through a modified aluminum-based adsorbent column and subjected to an adsorption process at 30°C and a flow rate of 3 h / min. -1Dynamic adsorption under specific conditions; after adsorption is complete, a 1.0×10⁻⁶ m³ / h filter is used. -4 A sulfuric acid solution of mol / L was prepared at 30°C and a flow rate of 1 h. -1 Under the condition of reverse desorption, 0.5 L of lithium-rich eluent was obtained with a lithium ion concentration of 0.58 g / L.

[0071] S3 Lithium-rich solution refining and concentration: The lithium-rich solution is subjected to nanofiltration for deep impurity removal, high-pressure reverse osmosis concentration, and 115℃ multi-effect evaporation concentration to obtain 8 mL of refined lithium-rich concentrate with a lithium ion concentration of 10.0 g / L.

[0072] S4 nanofiltration concentrate directional carbonation co-production of sodium bicarbonate: The carbonate-rich concentrate from S1 is mixed with the lithium precipitation mother liquor to obtain a solution with pH 10 and CO32-. 2- Alkaline brine with a concentration of 25 g / L; after membrane pretreatment and concentration, CO3 is obtained. 2- 5L of carbonization stock solution with a concentration of 50g / L was used; CO2 gas was introduced and the flow rate was controlled at 1000ml / min. The reaction was carried out at atmospheric pressure and 40℃ for 60min. The reaction was stopped when the pH of the system dropped to 7.8. The crude precipitate of sodium bicarbonate was obtained by filtration.

[0073] S5 Precipitation washing and product preparation: The coarse precipitate was washed twice countercurrently with a saturated sodium bicarbonate solution at a washing temperature of 30℃ to obtain refined sodium bicarbonate solid with a purity of 99.50%; all of it was calcined at 180℃ for 3 hours to obtain natural alkali product with a purity of 99.70%.

[0074] According to the test results, the total carbon yield of this embodiment is 30.3%, the CO2 utilization rate is 89.8%, the total carbonate utilization rate is 90.5%, and the purity of the natural alkali meets the national standard for superior grade products.

[0075] Comparative Example 1

[0076] The only difference between this comparative example and Example 1 is that in step S4, the alkaline brine was not concentrated using a high-pressure reverse osmosis membrane; instead, the original alkaline brine (CO3) was used directly. 2- The carbonization stock solution was prepared at a concentration of 26 g / L, and the remaining process parameters were completely consistent with those in Example 1.

[0077] The purity of the natural alkali prepared in this comparative example was 98.11%, which only meets the industrial grade standard. The total carbon recovery rate was 20.3%, the CO2 utilization rate was 72.4%, the total carbonate utilization rate was 68.2%, and the total lithium recovery rate was 90.1%.

[0078] Comparative Example 2

[0079] The only difference between this comparative example and Example 1 is that the carbonization reaction in step S4 was carried out under normal pressure without applying pressure; the other process parameters were completely consistent with those in Example 1.

[0080] The purity of the natural alkali prepared in this comparative example was 98.20%, which only meets the industrial grade standard. The total carbon recovery rate was 22.1%, the CO2 utilization rate was 75.6%, the total carbonate utilization rate was 70.5%, and the total lithium recovery rate was 90.2%.

[0081] Comparative Example 3

[0082] The only difference between this comparative example and Example 1 is that in step S4, only the carbonate-rich concentrated water from S1 is used as the carbonation raw material, and no lithium precipitation mother liquor or carbonization mother liquor is added. The remaining process parameters are completely consistent with those of Example 1.

[0083] According to the test results, the total carbon recovery rate of this comparative example was 18.5%, the CO2 utilization rate was 89.7%, the total carbonate utilization rate was 58.3%, the total lithium recovery rate was 90.0%, and a large amount of carbonate resources were recovered with the lithium mother liquor.

[0084] Comparative Example 4

[0085] The only difference between this comparative example and Example 1 is that the CO2 gas flow rate is controlled at 500 mL / min in step S4, while the other process parameters are completely consistent with those of Example 1.

[0086] Testing revealed that the purity of the natural alkali prepared in this comparative example was 98.30%, which only met the industrial grade standard. The total carbon recovery rate was 24.2%, the CO2 utilization rate was 68.7%, the total carbonate utilization rate was 72.4%, and the total lithium recovery rate was 89.9%.

[0087] Comparative Example 5

[0088] The only difference between this comparative example and Example 1 is that pure water is used to wash the coarse sodium bicarbonate precipitate in step S5, while the other process parameters are completely consistent with those of Example 1.

[0089] Testing revealed that the purity of the natural alkali prepared in this comparative example was 98.52%, the total carbon yield was 18.7%, the CO2 utilization rate was 90.8%, and the total carbonate utilization rate was 65.7%. The product suffered severe dissolution loss, resulting in a significant decrease in yield.

[0090] Comparative Example 6

[0091] This comparative example uses the conventional solar pond process of existing technology. Specifically, the raw brine of the salt lake is directly frozen and precipitated for lithium using the solar pond process. Sodium carbonate is purchased externally as the lithium precipitation agent, and the other raw materials are the same as in Example 1.

[0092] Testing showed that the total lithium recovery rate in this comparative example was 61.2%, the lithium carbonate purity was 98.50%, which only met the industrial grade standard, no natural alkali products were produced, the cost of lithium carbonate precipitation agent per ton was 42% higher than that in Example 1, 10L of high-salt tailwater was generated, and the total utilization rate of carbonate ions was 0%.

[0093] Analysis of Experimental Results

[0094] The core performance indicators of Examples 1-3 and Comparative Examples 1-6 are shown in the table below:

[0095]

[0096] The following conclusions can be clearly drawn from the data in the table above:

[0097] The natural alkali prepared in Examples 1-3 of this invention has a purity of ≥99.6%, meeting the superior grade standard of GB / T 210.1-2022. The total carbon yield is consistently above 30%, the CO2 utilization rate is ≥89.8%, the total lithium recovery rate is ≥89.7%, the lithium carbonate precipitation rate is ≥95.7%, and the total carbonate utilization rate is ≥90.5%, which are all superior to the comparative examples and have achieved significant technical effects.

[0098] Comparative Example 1 lacked pre-concentration, Comparative Example 2 lacked pressure control, and Comparative Example 5 had insufficient CO2 flow rate. All of these resulted in product purity dropping to industrial grade, total carbon yield decreasing by 25%-53%, and CO2 utilization and total carbonate utilization significantly decreasing. This fully demonstrates that the conditional carbonization stock solution CO3 of the present invention... 2- A concentration of 40-70 g / L, a CO2 flow rate of ≥800 ml / min, and a reaction pressure of ≤0.5 MPa exhibit a significant synergistic effect and are essential conditions for achieving both high purity and high yield. None of these conditions can be omitted, and they are not conventional parameter adjustments in this field.

[0099] Comparative Example 3, which did not include lithium precipitation mother liquor and adsorbed tail brine for synergistic carbonation, resulted in a sharp drop in the total carbonate utilization rate from 92.7% to 58.3%, with a large amount of carbonate resources lost. This fully demonstrates that the synergistic carbonation process of multiple carbonate-containing materials in this invention is the core innovation for achieving full recovery of salt lake resources.

[0100] Comparative Example 5 used pure water for washing, which resulted in a large amount of sodium bicarbonate dissolution and loss, and the total carbon yield plummeted to 18.7%. This proves that the countercurrent washing process with saturated sodium bicarbonate solution used in this invention effectively inhibits product dissolution through the common ion effect, which is a key technical feature to ensure high yield.

[0101] Comparative Example 6 uses existing conventional solar cell technology, with a total lithium recovery rate of only 61.2%, which is far lower than that of the present invention. In addition, it requires the purchase of lithium precipitation agents, which is costly and generates a large amount of tailwater, resulting in a complete waste of carbonate resources. This fully demonstrates that the closed-loop process of the present invention fundamentally solves the core technical problems of the prior art and has outstanding creativity and practicality.

Claims

1. A method for closed-loop lithium extraction and co-production of natural alkali from carbonated salt lake brine, characterized in that, Includes the following steps: S1: Using carbonated salt lake brine as raw material, after solid-liquid separation and impurity removal, lithium-rich permeate and carbonate-rich concentrate are obtained by separation through alkali-resistant nanofiltration membrane. The carbonate-rich concentrate is then frozen and impurity removed before being combined with the mother liquor of subsequent processes. S2: The lithium-rich water obtained from S1 is passed into a modified aluminum-based adsorbent column for dynamic adsorption. After adsorption saturation, reverse desorption is performed using fresh water or dilute acid solution to obtain lithium-rich desorption solution. S3: The lithium-rich eluent obtained from S2 is subjected to deep impurity removal through nanofiltration membrane, high-pressure reverse osmosis membrane concentration, and multi-effect evaporation concentration to obtain a refined lithium-rich concentrate. S4: The lithium precipitation mother liquor from S6 and the carbonate-rich concentrated water from S1 are mixed to obtain alkaline brine. After membrane pretreatment and concentration, carbonation stock solution is obtained. CO2 gas is continuously introduced into the carbonation stock solution, and carbonation reaction is carried out under temperature and pressure control. After solid-liquid separation, sodium bicarbonate coarse precipitate and carbonation mother liquor are obtained. The carbonation mother liquor is returned to the front end of this process to continue to participate in the carbonation reaction. S5: The crude sodium bicarbonate precipitate obtained in S4 is washed countercurrently with sodium bicarbonate solution to remove impurities. After solid-liquid separation, refined sodium bicarbonate solid is obtained. Part of the refined sodium bicarbonate solid is directly used in the subsequent lithium precipitation process, and the remaining part is calcined and decomposed to obtain natural alkali product. S6: The refined sodium bicarbonate solid or natural alkali product obtained in S5 is mixed with the refined lithium-rich concentrate obtained in S3 to carry out a temperature-controlled lithium precipitation reaction. After solid-liquid separation, the product is washed and dried to obtain battery-grade lithium carbonate. The lithium precipitation mother liquor is returned to the S4 process for the preparation of carbonization stock solution.

2. The method for closed-loop lithium extraction and co-production of natural alkali from carbonated salt lake brine according to claim 1, characterized in that, In step S1, the carbonate-type brine is carbonate-type brine, concentrated brine after lithium extraction, salt production tailwater, or underground associated lithium brine; the alkali-resistant nanofiltration membrane is a sulfonated polyether sulfone-based alkali-resistant composite nanofiltration membrane with a continuous operating pH tolerance range of 3-14, a molecular weight cutoff of 100-1000 Da, and an operating pressure of 2.5-8.0 MPa; the freezing purification temperature is 4-10℃, and the treatment time is 2-4 hours.

3. The method for closed-loop lithium extraction and co-production of natural alkali from carbonated salt lake brine according to claim 1, characterized in that, In step S2, the modified aluminum-based adsorbent is a modified adsorbent consisting of activated alumina supported on a lithium chloride-aluminum chloride bicomponent. The preparation method is as follows: activated alumina powder is impregnated in a mixed solution of 10-20 wt% aluminum chloride and 2-5 wt% lithium chloride for 4-6 hours, filtered, dried at 110-130℃ for 1-3 hours, and calcined at 280-320℃ for 2-4 hours. The dynamic adsorption temperature is 5-30℃, and the adsorption flow rate is 1-3 h / min. -1 The dilute acid solution is 1.0 × 10⁻⁶. -3 -1.0×10 -6 For hydrochloric acid or sulfuric acid at mol / L concentrations, the desorption temperature is 10-40℃, and the desorption flow rate is 0.5-1 h. -1 The desorption of fresh water is performed using hot pure water at 10-40℃, with a desorption flow rate of 1-2 hours. -1 .

4. The method for closed-loop lithium extraction and co-production of natural alkali from carbonated salt lake brine according to claim 1, characterized in that, In step S3, the nanofiltration membrane for deep impurity removal uses a sulfonated polyether sulfone-based alkali-resistant composite nanofiltration membrane with a molecular weight cutoff of 100-1000 Da and an operating pressure of 2.5-8.0 MPa; the high-pressure reverse osmosis membrane concentration uses a high-pressure resistant wide-channel reverse osmosis membrane with an operating pressure of 3.0-12.0 MPa, and the lithium ion concentration after concentration is ≥8 g / L; the temperature of the multi-effect evaporation concentration is 100-115℃.

5. The method for closed-loop lithium extraction and co-production of natural alkali from carbonated salt lake brine according to claim 1, characterized in that, In step S4, the alkaline brine has a pH of 8-14, a lithium concentration ≥30ppm, and a CO3 concentration of [missing information]. 2- Concentration ≥ 5 g / L; CO3 in the carbonized stock solution obtained after membrane pretreatment concentration 2- The concentration is 40g / L-70g / L; the flow rate of the CO2 gas is ≥800mL / min; the control pressure of the carbonization reaction is ≤0.5MPa; the reaction temperature is 30-50℃; the reaction time is 30-60min; and the reaction endpoint is when the pH of the system drops to 7.0-8.

0.

6. The method for closed-loop lithium extraction and co-production of natural alkali from carbonated salt lake brine according to claim 1, characterized in that, In step S5, the sodium bicarbonate solution is a saturated sodium bicarbonate solution, the countercurrent washing is performed 2-3 times, and the washing temperature is 20-30℃; the calcination decomposition temperature is 160-250℃, the calcination time is 1-3 hours, and the calcination equipment is any one of a rotary kiln, a pot furnace, or a rotary bed furnace; the purity of the natural alkali product is ≥99.6%.

7. The method for closed-loop lithium extraction and co-production of natural alkali from carbonated salt lake brine according to claim 1, characterized in that, In step S6, the temperature of the controlled lithium precipitation reaction is 90-95℃, the reaction time is 45-60 min, and the final pH of the reaction system is 10.5-12.5; the purity of the battery-grade lithium carbonate product is ≥99.5%.

8. The method for closed-loop lithium extraction and co-production of natural alkali from carbonated salt lake brine according to claim 1, characterized in that, In step S4, the carbonization mother liquor is recycled and carbonized to CO3. 2- After the concentration is ≤10g / L, sodium chloride is obtained by evaporation and desalination. The condensate is returned to the S1 process for brine dilution. All mother liquors in the whole process are recycled in a closed loop, and there is no discharge of high-salt tailwater, forming a closed loop of internal circulation of all components of salt lake resources.

9. The method for closed-loop lithium extraction and co-production of natural alkali from carbonated salt lake brine according to claim 1, characterized in that, The lithium ion concentration of the refined lithium-rich concentrate is 10.0~30.0 g / L.

10. The method for closed-loop lithium extraction and co-production of natural alkali from carbonated salt lake brine according to claim 1, characterized in that, The lithium-rich solution has a lithium ion concentration of 0.4~1.5 g / L.

Images