Forward osmosis system based on macroporous polyamide membrane and large-structure draw solution, preparation method and application of forward osmosis system in extraction of lithium from salt lake brine

Abstract

The invention provides a forward osmosis system based on a macroporous polyamide membrane and a large-structure draw solution, a preparation method and application of the forward osmosis system in lithium extraction of salt lake brine, and relates to the field of lithium extraction of salt lakes. According to the method, a positively charged macroporous polyamide forward osmosis membrane is adopted as a membrane of a forward osmosis system, a large-structure draw solution is adopted as a draw solution, and lithium in the lake brine is extracted. According to the application of the forward osmosis system based on the macroporous polyamide membrane and the large-structure draw solution to extraction of lithium from salt lake brine, external pressure is not needed, the anti-pollution capacity is high, the osmotic pressure difference of the solution serves as driving force, and the high lithium recovery rate is achieved through the forward osmosis integrated process. Compared with a traditional membrane process for extracting lithium, the phenomenon that the separation efficiency is reduced due to salting-out and salt polarization effects in a nanofiltration process does not occur when the forward osmosis system treats the solution with the high magnesium-lithium ratio, and a new thought and a new technical direction are provided for effectively extracting lithium from the salt lake brine with the high magnesium-lithium ratio.

Description

Technical Field

[0001] The present invention relates to the field of lithium extraction from salt lakes, and in particular to a forward osmosis system based on a macroporous polyamide membrane and a large-structure draw solution, a preparation method thereof, and an application in lithium extraction from salt lake brine. Background Art

[0002] The rapid development of new energy technologies such as new energy vehicles, electronic products, and energy storage systems has led to an increasing demand for metallic lithium. Approximately 60 - 80% of lithium resources come from salt lake brine. Therefore, related technologies for lithium extraction from salt lakes have become a current research hotspot. Magnesium-lithium separation is one of the key links in lithium extraction from salt lakes. However, due to the similar properties of magnesium and lithium and the characteristic of high magnesium-lithium ratio in salt lake brine, the separation of the two has become the main challenge in lithium extraction from salt lakes.

[0003] Nanofiltration has advantages such as simple operation, small chemical consumption, and easy large-scale application. However, the pressure-driven nanofiltration process has extremely high energy consumption and serious membrane fouling problems, which have become the technical bottleneck for the nanofiltration process to achieve lithium extraction from salt lakes. The inventor believes that different from nanofiltration, the osmotic pressure-driven forward osmosis separation technology has characteristics such as low energy consumption, strong anti-fouling ability, and high environmental friendliness. These advantages have attracted extensive attention to the forward osmosis separation technology in the field of water treatment. Therefore, applying the forward osmosis separation technology to magnesium-lithium separation is expected to break through the current technical bottleneck.

[0004] However, the inventor found through experimental research that the two core elements of the forward osmosis separation process, namely the forward osmosis membrane that plays a separation role and the draw solution that provides the driving force, cannot be applied to the effective separation of magnesium and lithium in salt lake brine with a high magnesium-lithium ratio. After analysis by the inventor, this is mainly because the traditional forward osmosis semi-permeable membrane only allows water molecules to pass through and does not have ion selectivity; it cannot effectively form an ion-selective forward osmosis system with the existing draw solution. Therefore, providing a forward osmosis system based on a macroporous polyamide membrane and a large-structure draw solution, a preparation method thereof, and an application in lithium extraction from salt lake brine has important technical significance and research value. Summary of the Invention

[0005] To solve the technical problems existing in the prior art, the present invention provides a forward osmosis system based on a macroporous polyamide membrane and a large-structure draw solution, which can, aiming at the magnesium-lithium separation characteristics of salt lake brine with a high magnesium-lithium ratio, through the effective cooperation of the macroporous polyamide forward osmosis membrane and the large-structure draw solution, construct an ion-selective forward osmosis system to achieve the efficient selective separation of lithium in salt lake brine with a high magnesium-lithium ratio; the present invention also provides a preparation method of a forward osmosis system based on a macroporous polyamide membrane and a large-structure draw solution; the present invention also provides an application of the forward osmosis system based on a macroporous polyamide membrane and a large-structure draw solution in lithium extraction from salt lake brine.

[0006] To solve the above technical problems, the technical solutions adopted by the present invention are as follows: A preparation method of a forward osmosis system based on a macroporous polyamide membrane and a large-structure draw solution, comprising the steps of: preparing a positively charged macroporous polyamide forward osmosis membrane and preparing a large-structure draw solution; The preparation of the positively charged macroporous polyamide forward osmosis membrane includes the following steps: preparing a casting solution, preparing a support layer substrate membrane, and preparing a positively charged macroporous membrane; In the preparation of the positively charged macroporous membrane, iron ions are coordinated with the surface carboxyl groups of the support layer substrate membrane to obtain a positively charged macroporous polyamide forward osmosis membrane; The preparation of the large-structure draw solution is to dissolve the zinc complex formed by coordinating zinc ions with betaine. Specifically, after mixing a zinc ion solution with betaine, the zinc complex is formed by coordinating zinc ions with betaine, and then after purification and drying, it is dissolved to obtain the large-structure draw solution.

[0007] Further, in the preparation of the casting solution, polyethersulfone, polyethylene glycol, N-methyl-2-pyrrolidone, and deionized water are mixed and then thermally polymerized to obtain the casting solution; In the preparation of the support layer substrate membrane, the casting solution is blade-coated to a predetermined thickness and then phase-inverted to obtain a support layer substrate membrane with a thickness of 100-150 μm; In the preparation of the positively charged macroporous membrane, an interfacial polymerization reaction is carried out on the support layer substrate membrane using an aqueous monomer piperazine and an oil-phase monomer trimesoyl chloride to obtain a membrane after interfacial polymerization; the membrane after interfacial polymerization is placed in an iron ion solution for secondary modification to obtain a positively charged macroporous polyamide forward osmosis membrane. Specifically, the support layer substrate membrane is immersed in an aqueous monomer piperazine solution and then immersed in an oil-phase monomer trimesoyl chloride solution to obtain a membrane after interfacial polymerization; then the membrane after interfacial polymerization is placed in an iron ion solution for secondary modification to obtain a positively charged macroporous polyamide forward osmosis membrane.

[0008] Preferably, in the preparation of the casting solution, the mass ratio of polyethersulfone, polyethylene glycol, N-methyl-2-pyrrolidone, and water is 20.4%: 38.8%: 38.8%: 2.0%.

[0009] Preferably, in the preparation of the casting solution, the thermal polymerization temperature is 60-70 °C and the thermal polymerization time is 12-16 h.

[0010] Preferably, in the preparation of the positively charged macroporous membrane, the concentration of the aqueous monomer piperazine solution used is 1 wt%; the concentration of the oil-phase monomer trimesoyl chloride solution is 0.15 wt%; The iron ion concentration in the iron ion solution is 5-9 wt%; the secondary modification time is 10-50 min.

[0011] Preferably, in the preparation of the large-structure draw solution, the molar ratio of zinc ions to betaine in the zinc ion solution used is 1:4-5; The complexation reaction temperature of zinc ions and betaine is 70 - 75 °C, and the complexation reaction time is 6 - 8 h.

[0012] A forward osmosis system based on a macroporous polyamide membrane and a large - structure draw solution, comprising: a positively charged macroporous polyamide forward osmosis membrane, a large - structure draw solution; prepared by the aforementioned preparation method.

[0013] An application of the aforementioned forward osmosis system based on a macroporous polyamide membrane and a large - structure draw solution in extracting lithium from salt lake brine, using a positively charged macroporous polyamide forward osmosis membrane as the membrane of the forward osmosis system; using a large - structure draw solution with a zinc complex concentration of 0.35 - 0.45 mol / L as the draw solution; extracting lithium in the feed liquid into the draw solution, and then using anhydrous ethanol to precipitate and recover the zinc complex in the draw solution to complete the extraction of lithium in the lake brine; The feed liquid is salt lake brine, and the molar ratio of magnesium to lithium in the salt lake brine is 1 - 1000:1; especially salt lake brine with a molar ratio of magnesium to lithium of 20 - 1000:1 and a salt concentration of 2000 - 10000 g / L.

[0014] Furthermore, the feed liquid can also be a pre - regulated feed liquid; The preparation method of the pre - regulated feed liquid is to add aminotrimethylenephosphonic acid to the salt lake brine. After aminotrimethylenephosphonic acid coordinates with magnesium ions in the salt lake brine, the pre - regulated feed liquid is obtained. Specifically, aminotrimethylenephosphonic acid is added to the salt lake brine, and after aminotrimethylenephosphonic acid coordinates with magnesium ions in the salt lake brine, the pre - regulated feed liquid is obtained.

[0015] Preferably, the molar addition amount of aminotrimethylenephosphonic acid is equal to the molar amount of magnesium ions in the salt lake brine; The temperature for the coordination of aminotrimethylenephosphonic acid and magnesium ions in the salt lake brine is room temperature, and the time is 20 - 24 h.

[0016] Compared with the prior art, the beneficial effects of the present invention are: (1) In view of the magnesium-lithium separation characteristics of high-magnesium-lithium ratio salt lake brine, the present invention constructs a positively osmotic system with ion selectivity through the effective cooperation of a macroporous polyamide forward osmosis membrane and a large-structure draw solution. Specifically, a positively charged macroporous polyamide forward osmosis membrane is used as the membrane of the forward osmosis system, and a large-structure draw solution is used as the draw solution to extract lithium from the lake brine. The application of the forward osmosis system based on the macroporous polyamide membrane and the large-structure draw solution in the extraction of lithium from salt lake brine does not require an external pressure, has strong anti-pollution ability, and relies on the osmotic pressure difference of the solution as the driving force. For the first time, the forward osmosis integrated process is used to achieve efficient and selective separation of lithium in high-magnesium-lithium ratio salt lake brine, and a high lithium recovery rate is obtained. Compared with the traditional membrane process for lithium extraction, the forward osmosis system does not show the phenomenon of reduced separation efficiency caused by salting out and salt polarization effects in the nanofiltration process when treating high-magnesium-lithium ratio solutions.

[0017] (2) The application method of the forward osmosis system based on the macroporous polyamide membrane and the large-structure draw solution in the extraction of lithium from salt lake brine of the present invention achieves stable separation performance in the 24-hour separation test, and there are no obvious changes in the water flux and the magnesium-lithium separation factor, showing good magnesium-lithium separation effect and stable water treatment efficiency.

[0018] (3) The application method of the forward osmosis system based on the macroporous polyamide membrane and the large-structure draw solution in the extraction of lithium from salt lake brine of the present invention has high magnesium-lithium selectivity for raw material liquids with different magnesium-lithium ratios and different salt concentrations, can effectively adapt to the different magnesium-lithium ratio characteristics of salt lake brines in different regions, effectively extract lithium from salt lake brines with different magnesium-lithium ratios, has strong adaptability, and can achieve stable separation of magnesium and lithium.

[0019] (4) The application method of the forward osmosis system based on the macroporous polyamide membrane and the large-structure draw solution in the extraction of lithium from salt lake brine of the present invention treats raw material liquids with different high magnesium-lithium ratios and high salt concentrations through multi-stage forward osmosis. The multi-stage forward osmosis system has a lithium recovery rate ≥ 83%, and can effectively recover lithium from high-salt solutions with high magnesium-lithium ratios through multi-stage forward osmosis integration technology.

[0020] (5) The application method of the forward osmosis system based on the macroporous polyamide membrane and the large-structure draw solution in the extraction of lithium from salt lake brine of the present invention has good ion selectivity, high separation efficiency, strong anti-pollution ability compared with the traditional nanofiltration process, and the water flux recovery performance after three cycles is significantly better than that of nanofiltration.

[0021] (6)The application method of the forward osmosis system based on macroporous polyamide membrane and large-structure draw solution of the present invention in extracting lithium from salt lake brine, in combination with the strategy of coordinating ligand aminotrimethylphosphonic acid with magnesium ions in the salt lake brine to change the existence form of magnesium ions in the salt lake brine and further improve the magnesium retention performance of the forward osmosis system; through experiments, the retention rate of magnesium in the feed liquid with different magnesium-lithium ratios and different salt concentrations is nearly 100%, effectively improving the retention of magnesium ions by the forward osmosis system and achieving a higher magnesium-lithium separation efficiency.

[0022] (7)The application method of the forward osmosis system based on macroporous polyamide membrane and large-structure draw solution of the present invention in extracting lithium from salt lake brine, using the forward osmosis system driven by the solution osmotic pressure difference for magnesium-lithium separation in extracting lithium from salt lake brine. By preparing a forward osmosis membrane with separation performance and a draw solution suitable for the ion-selective membrane system, and further separating magnesium and lithium through a forward osmosis integrated process or single-stage forward osmosis, a stable and high lithium recovery rate is achieved, providing new ideas and technical directions for the development of extracting lithium from salt lakes with a high magnesium-lithium ratio. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the synthesis process of the positively charged macroporous polyamide forward osmosis membrane of the present invention.

[0024] Figure 2 It is a schematic diagram of the synthesis process of the large-structure zinc complex [Zn(Bet)4](NO3)2 of the present invention.

[0025] Figure 3 It is a graph of the long-term separation test results of the forward osmosis system in Example 2.

[0026] Figure 4 It is a graph of the test results of the forward osmosis system in Example 2 for separating feed liquids with different magnesium-lithium ratios.

[0027] Figure 5 It is a graph of the test results of the forward osmosis system in Example 2 for separating feed liquids with different salt concentrations.

[0028] Figure 6 It is a graph of the test results of the multi-stage forward osmosis system in Example 2 for separating feed liquids with a high magnesium-lithium ratio.

[0029] Figure 7 It is a graph of the test results of the separation behavior of forward osmosis and nanofiltration in Example 3.

[0030] Figure 8 It is a graph of the test results of forward osmosis and nanofiltration membrane fouling in Example 3.

[0031] Figure 9 It is a scanning electron microscope photograph of the membrane surface after the forward osmosis and nanofiltration membrane fouling test in Example 3.

[0032] Figure 10 Figure 4 is the test result graph of the magnesium-lithium separation performance after pre-regulation pretreatment by ATMP chelation treatment in Example 4; in the figure, Figure a is the test result graph of forward osmosis lithium extraction for raw material solutions with different salt concentrations; Figure b is the test result graph of forward osmosis lithium extraction for raw material solutions with different magnesium-lithium molar ratios; Figure c is the test result graph of long-term forward osmosis lithium extraction. Detailed implementation manners

[0033] In order to have a clearer understanding of the technical features, objectives, and effects of the present invention, the specific implementation manners of the present invention will now be described. It should be noted that the following detailed descriptions are all exemplary and are intended to provide further explanations of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0034] It should be noted that the terms used here are only for describing specific implementation manners and are not intended to limit the exemplary embodiments according to the present invention. As used here, "first", "second", etc. are used to distinguish similar objects and are not used to describe a specific order or sequence. In addition, it should also be understood that when the terms "include" and / or "comprise" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0035] The present invention will be further described below in conjunction with some specific embodiments.

[0036] Example 1 This example provides a forward osmosis system based on a macroporous polyamide membrane and a large-structure draw solution, including: a macroporous polyamide membrane and a large-structure draw solution.

[0037] Among them, the macroporous polyamide membrane is a positively charged macroporous polyamide forward osmosis membrane.

[0038] The large-structure draw solution is a large-structure zinc complex draw solution; the large structure is a macromolecular complex that can form a three-dimensional network structure in an aqueous solution.

[0039] This example also provides a preparation method for the forward osmosis system based on the macroporous polyamide membrane and the large-structure draw solution. The specific steps are as follows: 1. Preparation of the positively charged macroporous polyamide forward osmosis membrane 1) Prepare the casting solution: Mix polyethersulfone, polyethylene glycol, N-methyl-2-pyrrolidone, and water in a three-necked flask in a ratio of 20.4%: 38.8%: 38.8%: 2.0%. Then, heat and stir the reaction in a constant temperature water bath at 70 °C for 12 h, and obtain a mixed reaction solution through thermal polymerization. After that, the mixed reaction solution is naturally cooled to room temperature and left standing for 24 h to obtain the casting solution for preparing the support layer.

[0040] 2) Preparation of the support layer base membrane: Use a clean glass plate, pour an appropriate amount of casting solution onto the glass plate, and evenly scrape it from above the glass plate with a precision scraper to form a transparent liquid film. Then, completely immerse the glass plate with the casting solution liquid film in a pure water water bath. After phase inversion, a polyethersulfone support layer base membrane with a thickness of 100 μm is obtained. After standing for 12 h, it is used for subsequent steps.

[0041] 3) Preparation of the positively charged macroporous membrane: Prepare an aqueous monomer piperazine solution with a concentration of 1 wt%. After completely immersing the polyethersulfone support layer base membrane in the piperazine solution for 2 min, remove the residual liquid on the surface. Prepare an organic phase monomer trimesoyl chloride solution with a concentration of 0.15 wt%. After completely immersing the polyethersulfone support layer base membrane infiltrated with the piperazine solution in the trimesoyl chloride solution for 1 min, pour out the excess liquid, and rinse the surface of the infiltrated membrane with an organic solvent to remove unreacted organic monomers, obtaining a membrane after interfacial polymerization. Then, perform secondary modification on the membrane after interfacial polymerization. Specifically, completely immerse the membrane after interfacial polymerization in a ferric nitrate solution with a ferric ion concentration of 7 wt% for 30 min, controlling the coordination of ferric ions with the carboxyl groups on the surface of the macroporous forward osmosis membrane. Then, let it stand at room temperature for 5 min. After rinsing with deionized water, a positively charged macroporous polyamide forward osmosis membrane is obtained. Place the positively charged macroporous polyamide forward osmosis membrane in deionized water and store it for 12 h for use. The specific reaction mechanism is as Figure 1 shown.

[0042] 2. Preparation of the large-structure draw solution 1) Preparation of zinc complex [Zn(Bet)4](NO3)2 Dissolve 17.82 g of zinc nitrate hexahydrate in 10 mL of deionized water and add it to 10 mL of deionized water containing 28.08 g of betaine. Stir under reflux at 75 °C for 6 h to form a large-structure zinc complex [Zn(Bet)4](NO3)2 through the coordination of zinc ions and betaine. Then, add ethanol to precipitate the crude product. After filtering the crude product to remove impurities, wash it 3 times with an ethanol aqueous solution and dry it under vacuum to obtain a high-purity white solid powder of the large-structure zinc complex [Zn(Bet)4](NO3)2 with a yield > 99%. The reaction mechanism is shown in Figure 2.

[0043] 2) Preparation of the draw solution Put the large-structure zinc complex [Zn(Bet)4](NO3)2 into deionized water to prepare a large-structure draw solution with a concentration of 0.4 mol / L that has a separation performance for lithium for use.

[0044] This example also provides the application of the forward osmosis system based on the macroporous polyamide membrane and the large-structure draw solution in the extraction of lithium from salt lake brine, specifically as follows: A positively charged macroporous polyamide forward osmosis membrane is used as the membrane of the forward osmosis system; a large-structured draw liquid is used as the draw liquid; lithium in the raw liquid (i.e., salt lake brine) is extracted into the draw liquid, and then, utilizing the different solubilities of the zinc complex [Zn(Bet)4](NO3)2 and lithium salt in ethanol in the draw liquid, anhydrous ethanol is used to precipitate and recover the zinc complex [Zn(Bet)4](NO3)2, thereby achieving the separation of the zinc complex [Zn(Bet)4](NO3)2 and lithium in the draw liquid, and completing the extraction of lithium from the salt lake brine.

[0045] Example 2 A forward osmosis separation test was conducted using the forward osmosis system based on the macroporous polyamide membrane and the macrostructured draw solution and the application method thereof in lithium extraction from salt lake brine of Example 1.

[0046] Specifically, a laboratory-scale forward osmosis system was used to evaluate its magnesium-lithium separation performance. The specific test method was as follows: salt lake brine with different magnesium-lithium ratios and different salt concentrations was used as the raw material liquid, and a pre-regulated raw material liquid was obtained through pre-regulation; a large-structured draw liquid with a concentration of 0.4 mol / L was used as the draw liquid; the positively charged macroporous polyamide forward osmosis membrane was used as the membrane of the forward osmosis system (membrane area of 4.5 cm 2 ), the separation test was carried out at 25℃ for 30min, and the test was repeated 3 times with three new membranes under the same conditions, and the average value was taken.

[0047] The membrane assembly is connected to the feed solution and the draw solution, respectively. Driven by a peristaltic pump, these flow through flexible hoses in the membrane tank at a cross-flow rate of 0.014 L / min. The draw solution is connected to an electronic analytical balance, which records the change in draw solution mass every 5 seconds during the test. The peristaltic pump is turned off at the end of the test. The change in draw solution mass before and after the test is used to calculate the water flux, and the magnesium-lithium separation factor is calculated by measuring the lithium and magnesium ion concentrations in the feed and draw solutions.

[0048] The concentrations of magnesium ions and lithium ions were determined by inductively coupled plasma optical emission spectrometry (ICP-OES), and the magnesium-lithium separation factor was calculated according to formula (1); (1) In formula (1), C p,Li + 、C p,Mg 2+ 、C f,Li + 、C f,Mg 2+ are Mg in the extraction solution and the raw material solution, respectively. 2+ He Li + concentration.

[0049] The water flux, J, of the membrane separation process w (LMH), is obtained by calculation according to formula (2): (2) In formula (2), ∆V(L) is the volume of the permeate within ∆t (h), and A is the membrane area (m 2 ).

[0050] The specific experiments are as follows: 1. Using a mixed salt solution with a salt concentration of 2000 g / L and a molar ratio of magnesium to lithium of 20:1 as the feed solution, a long-term separation experiment of the forward osmosis system is carried out; the concentration of the large-structure draw solution is 0.4 mol / L, the continuous operation time is 24 h, and the test temperature is 25 °C. The results are as Figure 3 shown. It can be seen that after 24 h of long separation time, neither the water flux nor the magnesium-lithium separation factor shows obvious changes, indicating that the forward osmosis system based on the macroporous polyamide membrane and the large-structure draw solution in Example 1 and its application method in extracting lithium from salt lake brine have good magnesium-lithium separation effects and stable water treatment efficiencies.

[0051] 2. Keeping the salt concentration of the feed solution at 2000 g / L, using mixed salt solutions with molar ratios of magnesium to lithium of 1:1, 10:1, 20:1, 50:1, 80:1, and 135:1 as the feed solutions, the concentration of the large-structure draw solution is 0.4 mol / L, the test process is 30 min, and the applicability of the forward osmosis system and application method in Example 1 for magnesium-lithium separation is tested. According to the magnesium-lithium concentrations of the feed solution and the draw solution, the magnesium-lithium selectivity of the forward osmosis system is calculated. The results are as Figure 4 shown. It can be seen that the forward osmosis system and application method in Example 1 have high magnesium-lithium selectivity for feed solutions with different magnesium-lithium ratios, can effectively adapt to the different magnesium-lithium ratio characteristics of salt lake brines in different regions, and can effectively extract lithium from salt lake brines with different magnesium-lithium ratios, with strong adaptability.

[0052] 3. Keeping the molar ratio of magnesium to lithium in the feed solution at 20:1, using mixed salt solutions with salt concentrations of 2000 g / L and 10000 g / L as the feed solutions, the concentration of the large-structure draw solution is 0.4 mol / L, the test process is 30 min, and the applicability of the forward osmosis system for magnesium-lithium separation is tested. According to the magnesium-lithium concentrations of the feed solution and the draw solution, the magnesium-lithium selectivity of the forward osmosis system is calculated. The results are as Figure 5 shown. It can be seen that the forward osmosis system and application method in Example 1 have high magnesium-lithium selectivity for feed solutions with different salt concentrations, can effectively adapt to the different salt concentration characteristics of salt lake brines in different regions, and can effectively extract lithium from salt lake brines with different salt concentrations, with strong adaptability.

[0053] 4. A three-stage forward osmosis system is used to separate the brine of salt lakes with high salt concentration and high magnesium-lithium ratio. The salt concentration of the initial raw material liquid is 10,000 g / L, and the magnesium-lithium molar ratios are 1000:1, 100:1, and 20:1. The concentration of the large-structure draw solution is 0.4 mol / L. The test time for each stage of the forward osmosis process is 30 min. According to the magnesium-lithium concentrations of the raw material liquid and the draw solution, the magnesium-lithium selectivity of the forward osmosis system is calculated, and the results are as Figure 6 shown. It can be seen that for the high-salt raw material liquids with different high magnesium-lithium ratios, after separation by the three-stage forward osmosis system of the forward osmosis system and application method in Example 1, the magnesium-lithium ratio drops to less than 0.4; it shows that the forward osmosis system and application method in Example 1 can effectively recover lithium from the high-salt solution with a high magnesium-lithium ratio through the multi-stage forward osmosis integration technology. Example 3

[0054] The forward osmosis system based on the macroporous polyamide membrane and the large-structure draw solution in Example 1 and its application method for extracting lithium from brine of salt lakes are used to conduct separation behavior tests of forward osmosis and nanofiltration: 1. Keep the salt concentration of the raw material liquid at 2000 g / L, and the magnesium-lithium molar ratios are 10:1, 20:1, 50:1, and 80:1. Using the positively charged macroporous polyamide membrane in Example 1 as the separation membrane, test its separation behavior in the forward osmosis mode and the nanofiltration mode: For the forward osmosis test, use the experimental equipment in Example 2, the concentration of the large-structure draw solution is 0.4 mol / L, and the test process is 30 min.

[0055] The nanofiltration experiment is carried out in a cross-flow filtration device with an effective membrane area of 3.14 cm 2 . Before the separation performance test of the nanofiltration system, it is first stabilized at 25 ± 0.5 °C and 6 bar for 0.5 h, and then data is collected. The results are as Figure 7 shown.

[0056] It can be seen that under the condition of the raw material liquid with the same magnesium-lithium ratio, the ion selectivity of forward osmosis is better than that of nanofiltration. It shows that the forward osmosis system and application method in Example 1 have higher separation efficiency compared with the nanofiltration mode. After analysis, due to the different driving force methods, the nanofiltration process that requires an external pressure is more likely to generate concentration polarization on the membrane surface, thereby reducing the selectivity of the membrane.

[0057] 2. Sodium alginate, which is common in water, was used as a pollutant to separately test the fouling conditions of the membrane in forward osmosis and nanofiltration. Before the membrane fouling experiment, deionized water was used as the feed solution to test the pure water flux Jw1 of the membrane. After 6 hours of the membrane fouling experiment, the membrane system was physically cleaned with deionized water for 30 minutes. Subsequently, the pure water flux of the cleaned membrane was tested and denoted as Jw2. This process was used as the first cycle, and a total of three cycles were performed. The water flux recovery rate (FRR) was used to evaluate the membrane fouling condition. The calculation formula for the water flux recovery rate (FRR) is shown in the following formula (3): (3) The test results of forward osmosis and nanofiltration membrane fouling are as Figure 8 shown; it can be seen that after 18 hours of the fouling experiment, the water flux in the nanofiltration mode decreased by 24%. After two alternating fouling and cleaning experiments, the water flux recovery rates were 85% and 78%; in contrast, the water flux in the forward osmosis mode only decreased by 12% after 18 hours, and the water flux recovery rates reached 95% and 90% after two alternating fouling and cleaning experiments.

[0058] Scanning electron microscope photos of the membrane surface after forward osmosis and nanofiltration membrane fouling tests are as Figure 9 shown; it can be seen that in the nanofiltration mode, pollutants were significantly attached to the membrane surface (forming a "cake layer" in the membrane micropores); the membrane surface could remain relatively smooth in the forward osmosis mode; it shows that compared with the nanofiltration mode, the forward osmosis mode has better anti-fouling performance.

[0059] It can be seen that in the present invention, a macroporous forward osmosis membrane was constructed by chemical coordination of a traditional semi-aromatic polyamide membrane with iron ions, and a zinc complex draw solution was designed and synthesized by a one-step reaction of betaine with zinc ions to construct a new forward osmosis system, which was used for lithium extraction from salt lake brine with a high magnesium-lithium ratio for the first time. The macroporous structure of the forward osmosis membrane significantly improves the water treatment efficiency compared with traditional forward osmosis membranes, while the large structure of the zinc complex draw solution makes the solute loss in forward osmosis separation negligible. For the treatment of a salt solution with a Mg 2+ / Li + molar ratio of 20:1, its Mg 2+ / Li + separation effect and water treatment efficiency are comparable to those of a pressure-driven nanofiltration magnesium-lithium separation system. For the recovery of Li 2+ / Li + from a solution with a higher ratio by multi-stage forward osmosis, after three-stage forward osmosis separation, the recovery rate of Li + is as high as over 83%, and the recovery rate of Li + is much higher than that of the reported nanofiltration magnesium-lithium separation system, proving that the multi-stage forward osmosis technology can effectively recover Li + from a salt solution with a high magnesium-lithium ratio. + . Example 4

[0060] On the basis of Example 1, this example also provides an application of a forward osmosis system based on macroporous polyamide membrane and large-structure draw solution in extracting lithium from salt lake brine, specifically as follows: a. Pre-regulation Add aminotrimethylenephosphonic acid (ATMP) to the feed solution (i.e., salt lake brine), stir at room temperature for 20 - 24 h. By coordinating the ligand aminotrimethylenephosphonic acid with magnesium ions in the salt lake brine, change the existing form of magnesium ions in the salt lake brine, and further improve the rejection of magnesium by the forward osmosis system. Then, after adjusting the pH with LiOH, obtain the pre-regulated feed solution.

[0061] Among them, the molar addition amount of aminotrimethylenephosphonic acid is equal to the molar amount of Mg 2+ in the salt lake brine.

[0062] b. Forward osmosis separation Use a positively charged macroporous polyamide forward osmosis membrane as the membrane of the forward osmosis system; use a large-structure draw solution as the draw solution; extract lithium in the pre-regulated feed solution into the draw solution, and then utilize the characteristic that the solubility of zinc complex [Zn(Bet)4](NO3)2 and lithium salt in ethanol is different, and precipitate and recover zinc complex [Zn(Bet)4](NO3)2 with absolute ethanol to achieve the separation of zinc complex [Zn(Bet)4](NO3)2 and lithium in the draw solution, and complete the extraction of lithium from the salt lake brine.

[0063] Use a laboratory-scale forward osmosis system FO to evaluate the magnesium-lithium separation performance of the application method described in Example 4. The specific test method is as follows: use a positively charged macroporous polyamide forward osmosis membrane as the membrane of the forward osmosis system; use a large-structure draw solution as the draw solution; use salt lake brines with different salt concentrations and different magnesium-lithium ratios as the feed solutions respectively. After obtaining the pre-regulated feed solutions through pre-regulation, conduct forward osmosis system separation and lithium extraction respectively. Among them, the salt concentrations of the feed solutions are 2000 g / L, 4000 g / L, 6000 g / L, 8000 g / L, and 10000 g / L respectively; the magnesium-lithium molar ratios of the feed solutions are 20:1, 100:1, 500:1, and 1000:1 respectively; the concentration of the large-structure draw solution is 0.4 mol / L, and the test process is 30 min. The forward osmosis FO lithium extraction performance of salt lake brines with different salt concentrations is as shown in Figure 10 Figure a therein, and the forward osmosis FO lithium extraction performance of salt lake brines with different magnesium-lithium molar ratios is as shown in Figure 10 Figure b therein.

[0064] Furthermore, a laboratory-scale forward osmosis (FO) system was used to evaluate the long-term magnesium-lithium separation performance of the application method in Example 4. The specific test method was as follows: a positively charged macroporous polyamide forward osmosis membrane was used as the membrane of the forward osmosis system; a large-structure draw solution was used as the draw solution; and brine from a salt lake with a salt concentration of 2000 g / L and a magnesium-lithium molar ratio of 20:1 was used as the feed solution. After pre-regulation to obtain a pre-regulated feed solution, lithium was separated by the forward osmosis system. Among them, the concentration of the large-structure draw solution was 0.4 mol / L, and the test process was 24 h. The results are as Figure 10 shown in Figure c of

[0065] It can be seen that in the forward osmosis system and application method of Example 4, after the ligand aminotrimethylenephosphonic acid coordinates with magnesium ions in the salt lake brine to form a stable [Mg-ATMP] complex, the magnesium-lithium separation factor of the single-stage forward osmosis system continuously maintains at a relatively high level (90.6 - 110.9%), showing good separation selectivity. Compared with the application method of Example 1, after single-stage forward osmosis treatment, the magnesium-lithium molar ratio of the feed solution with a magnesium-lithium molar ratio of 20:1 is significantly reduced to 1.6; while in the ATMP-assisted forward osmosis separation process of Example 4, after single-stage ATMP-assisted forward osmosis separation treatment of the feed solution with a magnesium-lithium molar ratio of 20:1, the magnesium-lithium molar ratio is reduced to 0.22. It can be seen that the introduction of ATMP can effectively improve the retention of magnesium ions by the forward osmosis system, achieving a higher magnesium-lithium separation efficiency. At the same time, after forward osmosis treatment, zinc complexes and Li can be effectively separated by solvent precipitation + . The above test results show that the forward osmosis system of the present invention using a positively charged macroporous membrane as the separation membrane and a zinc complex as the draw solution provides a simple and efficient magnesium-lithium separation strategy for the treatment of high-magnesium-lithium salt lake brine, and provides new ideas and technical directions for the development of lithium extraction from salt lakes with a high magnesium-lithium ratio.

[0066] Unless otherwise specified, the percentages used in the present invention are all mass percentages.

[0067] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a forward osmosis system based on a macroporous polyamide membrane and a large-structure draw solution, characterized in that, It includes the steps of: preparation of a positively charged macroporous polyamide forward osmosis membrane, and preparation of a large-structure draw solution; The preparation of the positively charged macroporous polyamide forward osmosis membrane includes the following steps: preparation of a casting solution, preparation of a support layer substrate membrane, and preparation of a positively charged macroporous membrane; In the preparation of the positively charged macroporous membrane, iron ions coordinate with the surface carboxyl groups of the support layer substrate membrane to obtain a positively charged macroporous polyamide forward osmosis membrane; In the preparation of the large-structure draw solution, zinc ions are coordinated with betaine to form a zinc complex and then dissolved to obtain a large-structure draw solution.

2. The preparation method of the forward osmosis system based on the macroporous polyamide membrane and the large-structure draw solution according to claim 1, characterized in that, In the preparation of the casting solution, polyethersulfone, polyethylene glycol, N-methyl-2-pyrrolidone, and deionized water are mixed and then thermally polymerized to obtain a casting solution; In the preparation of the support layer substrate membrane, the casting solution is blade-coated to a predetermined thickness and then phase-transformed to obtain a support layer substrate membrane with a thickness of 100 - 150 μm; In the preparation of the positively charged macroporous membrane, an interfacial polymerization reaction is carried out on the support layer substrate membrane using an aqueous monomer piperazine and an oil-phase monomer trimesoyl chloride to obtain a membrane after interfacial polymerization; the membrane after interfacial polymerization is placed in an iron ion solution for secondary modification to obtain a positively charged macroporous polyamide forward osmosis membrane.

3. The preparation method of the forward osmosis system based on the macroporous polyamide membrane and the large-structure draw solution according to claim 2, characterized in that, In the preparation of the casting solution, the mass ratio of polyethersulfone, polyethylene glycol, N-methyl-2-pyrrolidone, and water is 20.4%:38.8%:38.8%:2.0%.

4. The preparation method of the forward osmosis system based on the macroporous polyamide membrane and the large-structure draw solution according to claim 2, characterized in that, In the preparation of the casting solution, the temperature of thermal polymerization is 60 - 70 °C, and the time of thermal polymerization is 12 - 16 h.

5. The preparation method of the forward osmosis system based on the macroporous polyamide membrane and the large-structure draw solution according to claim 2, wherein In the preparation of the positively charged macroporous membrane, the concentration of the aqueous monomer piperazine solution used is 1 wt%; the concentration of the oil-phase monomer trimesoyl chloride solution is 0.15 wt%; The iron ion concentration in the iron ion solution is 5 - 9 wt%; the time of secondary modification is 10 - 50 min.

6. The preparation method of the forward osmosis system based on a macroporous polyamide membrane and a large-structure draw solution according to claim 1, characterized in that, In the preparation of the large-structure draw solution, the molar ratio of zinc ions to betaine in the zinc ion solution used is 1:4 - 5; The temperature of the complexation reaction of zinc ions with betaine is 70 - 75 °C, and the time of the complexation reaction is 6 - 8 h.

7. A forward osmosis system based on a macroporous polyamide membrane and a large-structure draw solution, characterized in that, It includes: a positively charged macroporous polyamide forward osmosis membrane, and a large-structure draw solution; It is prepared by using the preparation method described in any one of claims 1 - 6.

8. Use of a forward osmosis system based on a macroporous polyamide membrane and a large-structure draw solution as described in claim 7 in the extraction of lithium from salt lake brine, characterized in that, Using the positively charged macroporous polyamide forward osmosis membrane as the membrane of the forward osmosis system; using a large-structure draw solution with a zinc complex concentration of 0.35 - 0.45 mol / L as the draw solution; extracting lithium in the feed liquid into the draw solution, and then using anhydrous ethanol to precipitate and recover the zinc complex in the draw solution to complete the extraction of lithium from the lake brine; The feed liquid is lake brine, and the magnesium / lithium molar ratio in the lake brine is 1 - 1000:

1.

9. The application of the forward osmosis system based on macroporous polyamide membrane and large-structure draw solution in lithium extraction from salt lake brine according to claim 8, characterized in that, The feed liquid can also be a pre-regulated feed liquid; The preparation method of the pre-regulated feed liquid is to add aminotrimethylenephosphonic acid to the lake brine. After aminotrimethylenephosphonic acid coordinates with magnesium ions in the lake brine, a pre-regulated feed liquid is obtained.

10. The application of the forward osmosis system based on macroporous polyamide membrane and large-structure draw solution in lithium extraction from salt lake brine according to claim 9, characterized in that, The molar addition amount of aminotrimethylenephosphonic acid is equal to the molar amount of magnesium ions in the lake brine; The temperature of the coordination of aminotrimethylenephosphonic acid with magnesium ions in the lake brine is room temperature, and the time is 20 - 24 h.

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