Modified separation membrane, method for preparing the same, and use thereof

Abstract

The application provides a modified separation membrane and a preparation method and application thereof, wherein the preparation method of the modified separation membrane comprises the following steps: obtaining a mixed system of a mineral material and a polar solvent, subjecting the mixed system to ultrasonic liquid phase stripping to obtain a to-be-treated liquid, and the mass-volume ratio of the mineral material and the polar solvent is 50-100 mg:30-60 ml; centrifugally treating the to-be-treated liquid, collecting supernatant, and obtaining a nanometer suspension; mixing a crosslinking agent with the nanometer suspension to obtain a modified liquid, the modified liquid contains modified nanometer sheets, and the mass of the crosslinking agent is 2%-30% of the mass of the mineral material; filtering the modified liquid through a filter membrane, so that the modified nanometer sheets are uniformly loaded on the surface of the filter membrane, and the modified separation membrane is prepared. The modified separation membrane prepared by the application has the advantages of high separation coefficient, high retention rate and high flux of the modified separation membrane material, and has excellent performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of membrane separation, and particularly relates to a modified separation membrane and a preparation method and application thereof. BACKGROUND

[0002] As an important resource, salt lake brine contains rich lithium, magnesium and other metal ions. With the rapid development of new energy industry, the demand for lithium resources is increasing, and the extraction of lithium from salt lake brine has become one of the important ways to obtain lithium resources. However, salt lake brine usually contains a high concentration of magnesium ions, and magnesium and lithium ions have similar properties. How to realize efficient and selective separation of magnesium and lithium ions has become a key technical problem in the extraction of lithium resources from salt lake brine. In the existing methods for treating salt lake brine, there are many limitations. The traditional chemical precipitation method consumes a large amount of chemical reagents, which not only increases the treatment cost, but also may introduce new impurities and pollute the environment. Although the solvent extraction method has a certain selectivity, the organic solvents used are often toxic, and the extraction process is complex, the equipment investment is large, and the operation cost is high. In the ion exchange method, the adsorption capacity of ion exchange resin is limited, and the regeneration process is complicated, which is difficult to meet the demand of large-scale industrial treatment of salt lake brine.

[0003] Membrane separation technology, as a new separation technology, has attracted widespread attention in the field of salt lake brine treatment due to its advantages of high efficiency, energy saving, no pollution, etc. However, the existing separation membrane materials still have deficiencies in the selective separation of magnesium and lithium ions. The ordinary separation membrane has a poor difference in the retention rate of magnesium and lithium ions, and a low separation coefficient, which cannot realize efficient separation of magnesium and lithium ions.

[0004] Therefore, it is necessary to provide a modified separation membrane material with high separation coefficient, high retention rate and high flux to alleviate or solve the above problems. SUMMARY

[0005] To solve the technical problem that it is difficult to realize effective and selective separation of ions in wastewater such as salt lake brine while maintaining high retention rate and high flux in the above common technologies, the application provides a preparation method of a modified separation membrane, comprising the following steps:

[0006] A mixed system of a mineral material and a polar solvent is obtained, the mixed system is subjected to ultrasonic liquid phase stripping to obtain a to-be-treated liquid, and the mass-volume ratio of the mineral material to the polar solvent is 50-100 mg:30-60 ml;

[0007] The to-be-treated liquid is subjected to centrifugal treatment, and the supernatant is collected to obtain a nanosuspension;

[0008] A crosslinking agent is mixed with the nanosuspension to obtain a modified liquid, the modified liquid contains modified nanosheets, and the mass of the crosslinking agent is 2%-30% of the mass of the mineral material.

[0009] The modified liquid is filtered through a filter membrane, so that the modified nanosheets are uniformly loaded on the surface of the filter membrane to obtain a modified separation membrane.

[0010] Further, the mineral material comprises kaolinite and / or montmorillonite, and the polar solvent comprises one or more of water, ethanol and propylene glycol.

[0011] Further, the cross-linking agent comprises one or more of 1,3-propanediamine, 1,6-hexanediamine, 1,9-nonanediamine and 1,12-diaminododecane.

[0012] Further, the ultrasonic condition in the ultrasonic liquid phase exfoliation process is that the ultrasonic power is 300-500 W, and the exfoliation time is 4-24 h.

[0013] Further, the filtration mode comprises vacuum filtration, and the negative pressure of the vacuum filtration is 0-0.1 MPa.

[0014] Further, the filter membrane comprises a microporous water-based filter membrane, and the pore size of the filter membrane is 0.15-0.3 microns.

[0015] The loading amount of the modified nanosheets on the filter membrane is 0.6-1.4 mg / cm 2 .

[0016] Further, the mass of the cross-linking agent is 2.5%-20% of the mass of the mineral material.

[0017] The application provides a modified separation membrane prepared by the preparation method of the modified separation membrane.

[0018] The application provides application of the modified separation membrane in treatment of salt lake brine.

[0019] Further, the concentration of magnesium ions in the salt lake brine is 0.01-0.5 mol / L, and the concentration of lithium ions in the salt lake brine is 0.01-0.5 mol / L.

[0020] The modified separation membrane has a lithium ion retention rate of not less than 90%, a magnesium ion separation rate of not less than 95%, and a separation coefficient greater than 1.5.

[0021] Compared with the prior art, the application at least has the following advantages:

[0022] The present application successfully optimizes the separation performance of the separation membrane by original design of steps and raw materials, cooperates the structural characteristics of the raw materials, ultrasonic peeling, crosslinking modification and filter membrane loading and other technical features, significantly improves the separation effect of lithium and magnesium ions, and prepares a modified separation membrane material with high separation coefficient, high retention rate and high flux, in particular:

[0023] Correlation between raw material structure characteristics and separation performance. Kaolinite and montmorillonite have typical two-dimensional layered structure and high stacking degree. This structure makes the nanosheet formed after subsequent treatment have larger specific surface area and abundant surface active sites. In the separation process, these active sites can interact specifically with lithium and magnesium ions; the larger specific surface area also increases the contact opportunity of ions and the separation membrane, which is beneficial to improve the retention rate and separation coefficient of ions.

[0024] Optimization of separation effect by ultrasonic peeling. Kaolinite and montmorillonite are effectively peeled into single-layer or few-layer nanosheets after ultrasonic treatment. Single-layer or few-layer nanosheets have thinner thickness and greater flexibility, which can be more closely arranged on the filter membrane surface during the preparation of the separation membrane to form more uniform ion channels. For lithium and magnesium ions, due to the differences in ion radius and charge properties, they will be hindered to different degrees when passing through these ion channels, thereby improving the selectivity (separation coefficient) of the separation membrane to lithium and magnesium ions. At the same time, uniform ion channels also help to improve the retention rate of ions and reduce the disordered permeation of ions.

[0025] Significant improvement of separation performance by crosslinking modification. New peaks appear in the infrared spectrum after adding different crosslinking agents, confirming that the crosslinking agent is successfully grafted between the layers. After the grafting of the crosslinking agent, the surface chemical properties and spatial structure of the nanosheet are changed. Firstly, the specific functional groups carried by the crosslinking agent can interact with lithium and magnesium ions, and due to the differences in ion properties, the interaction strength and mode are different, thereby strengthening the selective recognition and separation ability of ions and improving the separation coefficient. Secondly, crosslinking makes the connection between nanosheets more closely, and a more stable separation membrane structure is constructed. This stable structure can effectively block the disordered permeation of ions and improve the retention rate of lithium and magnesium ions.

[0026] Guarantee of separation effect by filter membrane loading. The surface of the microporous water system filter membrane is smooth and has no cross-sectional layered structure, and water molecules and salt ions can freely permeate. After uniformly loading the modified nanosheet on it, the smooth surface reduces the ion transmission resistance, helping the ions to smoothly reach the modified nanosheet layer and fully exert their selective separation function. At the same time, the good permeability of the filter membrane guarantees the ion transmission efficiency and avoids affecting the separation effect due to its own hindrance. This loading method ensures that the modified nanosheet stably exerts the separation performance and continuously improves the high selectivity (separation coefficient), retention rate and flux of the separation membrane to lithium and magnesium ions. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the accompanying drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, the accompanying drawings in the following description only constitute some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained from the structures shown in the drawings without any creative effort.

[0028] Figure 1 (a) is a SEM morphology of kaolinite applied in the embodiment 1 of the present application, Figure 1 (b) is a SEM morphology of montmorillonite applied in the embodiment 5 of the present application.

[0029] Figure 2 (a), Figure 2 (b) and Figure 2 (c) are the morphologies of kaolinite nanosheets after exfoliation in the embodiment 1 of the present application; wherein, Figure 2 (a) is the distribution state of kaolinite nanosheets under 20000 times; Figure 2 (b) is the morphology of kaolinite nanosheets under 10000 times; Figure 2 (c) is the microstructure of kaolinite nanosheets under 100000 times, and the inset in the upper right corner is the corresponding selected area electron diffraction (SAED) pattern.

[0030] Figure 2 (d), Figure 2 (e) and Figure 2 (f) are TEM morphologies of montmorillonite nanosheets after exfoliation in the embodiment 5 of the present application; Figure 2 (d) is the overall distribution of montmorillonite nanosheets under 20000 times; Figure 2 (e) is the image of montmorillonite nanosheets under 10000 times; Figure 2 (f) is the morphology of montmorillonite nanosheets under 100000 times, and the inset in the upper right corner is the corresponding SAED pattern.

[0031] Figure 3 (a) is the infrared spectrogram of the kaolinite modified separation membrane prepared in the embodiments 1-4 of the present application; Figure 3 (b) is the infrared spectrogram of the montmorillonite modified separation membrane in the embodiments 5-8 of the present application.

[0032] Figure 4 are SEMs of the microporous water system filter membranes used in the embodiments and the comparative examples of the present application and the SEMs of the modified separation membranes in the embodiment 1 and the embodiment 7;

[0033] wherein, Figure 4 (a) is the SEM of the front surface (water permeable surface) of the microporous water system filter membrane; Figure 4(b) is a SEM image of the surface of the modified separation membrane in Example 1; Figure 4 (c) is a SEM image of the side (end surface) of the modified separation membrane in Example 1; Figure 4 (d) is a SEM image of the side (end surface) of the microporous water system filter membrane; Figure 4 (e) is a SEM image of the surface of the modified separation membrane in Example 7; Figure 4 (f) is a SEM image of the side (end surface) of the modified separation membrane in Example 7. DETAILED DESCRIPTION

[0034] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0035] In addition, the technical solutions of the various embodiments of the present application can be combined with each other, but it must be based on the fact that a person skilled in the art can realize it. When the combination of technical solutions appears to be contradictory or unachievable, it should be considered that the combination of technical solutions does not exist and is not within the scope of protection required by the present application.

[0036] When the embodiments give numerical ranges, it should be understood that, unless otherwise stated by the present application, both endpoints of each numerical range and any number between the two endpoints can be selected. Unless otherwise defined, all technical and scientific terms used in the present application are used by those skilled in the art in the present technical field and in the description of the present application. Any method, equipment and material of the prior art similar or equivalent to the method, equipment and material of the embodiments of the present application can also be used to realize the present application.

[0037] The present application provides a preparation method of a modified separation membrane, comprising the steps of:

[0038] S1. Obtain a mixed system of mineral materials and a polar solvent, and the mixed system is subjected to ultrasonic liquid phase exfoliation to obtain a to-be-treated liquid.

[0039] In the present application, the mineral materials include kaolinite and / or montmorillonite. Kaolinite and montmorillonite are natural two-dimensional layered clay minerals, and the nanosheet layers are connected by weak interaction forces such as hydrogen bonds or van der Waals forces. Ultrasonic waves are mechanical waves that can propagate in liquids. By causing rapid expansion and collapse of tiny bubbles in the liquid between the nanosheet layers, the mutual separation between the layers is accelerated, the nanosheet is exfoliated, and single-layer or few-layer nanosheet materials are produced. In some embodiments, before mixing the mineral materials with the polar solvent, the mineral materials can be passed through a 200-mesh sieve.

[0040] In the present application, the polar solvent includes one or more of water, ethanol and propylene glycol.

[0041] In the present application, the mass-volume ratio of the mineral material to the polar solvent can be 50-100 mg:30-60 ml; for example, 50-80:30-40, or 60-70:30-50.

[0042] In the present application, the ultrasonic liquid phase exfoliation can be performed in an ultrasonic cleaner. In some embodiments, the ultrasonic conditions in the ultrasonic liquid phase exfoliation process are: ultrasonic power 300-500 W, exfoliation time 4-24 h; more specifically, the ultrasonic power can be 400-500 W, and the exfoliation time can be 16-24 h.

[0043] S2. Centrifuging the mixed system to collect the supernatant to obtain a nanosuspension.

[0044] In the present application, the device for centrifugation can be a centrifuge. In some embodiments, the centrifuge speed in the centrifugation process can be 3500-4000 rpm, and the time can be 2-5 minutes. For example, at a speed of 3500 rpm, the time can be 3 minutes; at a speed of 4000 rpm, the time can be 3 minutes.

[0045] S3. Mixing a crosslinking agent with the nanosuspension to obtain a modified liquid, the modified liquid containing modified nanosheets, the mass of the crosslinking agent being 2%-30% of the mass of the mineral material.

[0046] In the present application, the crosslinking agent can be one or more of 1,3-propanediamine (TN), 1,6-hexanediamine (HDM), 1,9-nonanediamine (NMD) and 1,12-diaminododecane (DMD).

[0047] In some embodiments, the mass of the crosslinking agent can also be 2.5-20% of the mass of the mineral material;

[0048] For example, the mass of the crosslinking agent can also be 2.5-5 wt%, or 2.5-7.5 wt%, or 2.5-10 wt%, or 2.5-15 wt%, or 5-15 wt%, or 5-20 wt%, or 10-20 wt%, or 2.5-20 wt% of the mass of the mineral material.

[0049] For example, the mass of the crosslinking agent can also be 2-3 wt%, or 4-6 wt%, or 7-8 wt%, or 9-11 wt%, or 14-16 wt%, or 19-21 wt% of the mass of the mineral material.

[0050] In some embodiments, the cross-linking agent can be mixed with the suspension and then placed on a magnetic stirring table for mixing to ensure successful cross-linking. In some specific embodiments, the magnetic stirring speed can be 200-400 rpm and the time can be 0.5-2 h.

[0051] The surface Zeta potential of the modified nanosheets changes, the surface Zeta potential of the modified kaolinite nanosheets ranges from -48 mV to -19 mV, the surface Zeta potential of the modified montmorillonite nanosheets ranges from -39 mV to -23 mV, the surface potential of the unmodified kaolinite nanosheets is -52 mV, and the surface potential of the unmodified montmorillonite nanosheets is -42 mV.

[0052] S4. The modification liquid is filtered through a filter membrane, so that the modified nanosheets are uniformly loaded on the surface of the filter membrane to prepare a modified separation membrane.

[0053] In the present application, the filtration method can be vacuum filtration, and the negative pressure of the vacuum filtration is 0-0.1 MPa. In some specific embodiments, the detailed operation steps of the vacuum filtration method include: placing the filter membrane on the mouth of the filtration bottle, vacuum filtering to a negative pressure of 0.1 MPa in the bottle, and pouring the nanosuspension into the bottle. Under the action of hydrogen bonding and electrostatic interaction force, the modified kaolinite / montmorillonite nanosheets are stacked layer by layer to prepare a layered modified separation membrane with good layered structure.

[0054] In the present application, the filter membrane can be a microporous water-based filter membrane.

[0055] In some embodiments, the pore size of the filter membrane can be 0.15-0.3 μm, such as 0.2-0.25 μm. For example, the pore size can be 0.22 μm.

[0056] In some embodiments, the material of the microporous water-based filter membrane can be mixed cellulose, and the diameter thereof can be 20-80 mm, such as 40-60 mm.

[0057] In some embodiments, the ratio between the mass of the modified nanosheets and the diameter of the microporous water-based filter membrane can satisfy 8-12 mg: 50 mm.

[0058] In some embodiments, the loading amount of the modified nanosheets on the filter membrane can be 0.6-1.4 mg / cm 2 , such as 0.8-1.4 mg / cm 2 , or 0.6-1.2 mg / cm 2 , or 0.8-1.2 mg / cm 2 It should be noted that the definition of the loading amount here is the ratio between the mass of the modified nanosheets and the effective loading area; wherein, the effective loading area is not equal to the area of the microporous water-based filter membrane, and the definition of the effective loading area is the effective filtration area of the mouth of the filtration bottle in the vacuum filtration device.

[0059] In some embodiments, the effective loading area of the modified separation membrane prepared by the method can be 10-20 cm 2 , such as 12-13 cm 2 ; and the mass of the nanosheets in the nanosuspension can be 6-28 mg.

[0060] The microporous water-based filter membrane used in all embodiments of the present application is purchased from Tianjin Keyilong Experimental Equipment Co., Ltd.

[0061] The present application provides a modified separation membrane prepared by the method for preparing the modified separation membrane according to any one of the embodiments.

[0062] In the present application, the modified separation membrane comprises a filter membrane and modified nanosheets loaded thereon.

[0063] In some embodiments, the pore size of the filter membrane can be 0.15-0.3 μm, such as 0.2-0.25 μm. For example, the pore size can be 0.22 μm.

[0064] In some embodiments, the material of the microporous water-based filter membrane can be mixed cellulose, and the diameter thereof can be 20-80 mm, such as 40-60 mm.

[0065] In some embodiments, the ratio between the mass of the modified nanosheets and the diameter of the microporous water-based filter membrane can satisfy 8-12 mg: 50 mm.

[0066] In some embodiments, the loading amount of the modified nanosheets on the filter membrane can be 0.6-1.4 mg / cm 2 , such as 0.8-1.4 mg / cm 2 , or 0.6-1.2 mg / cm 2 , or 0.8-1.2 mg / cm 2 . It should be noted that the loading amount defined herein is the ratio between the mass of the modified nanosheets and the effective loading area; wherein the effective loading area is not equal to the area of the microporous water-based filter membrane, and the effective loading area is defined as the effective membrane forming area of the bottle mouth of the vacuum filtration device.

[0067] In some embodiments, the effective loading area of the modified separation membrane prepared by the method can be 10-20 cm 2 , such as 12-13 cm 2 ; and the mass of the nanosheets in the nanosuspension can be 6-28 mg.

[0068] It should be noted that the filter membrane diameter, pore size, effective microporous water system filter membrane loading area of the modified separation membrane, and nanosheet mass in the above embodiments are only examples of a specific implementation. In actual applications, these parameters are not fixed and can be reasonably adjusted and optimized according to specific separation requirements, raw material characteristics, and actual production conditions. It has been verified in practice that as long as the preparation method of the present application is followed, the modified separation membrane prepared under different parameter combinations can also exhibit excellent separation performance and effectively separate target ions.

[0069] The present application provides the application of the modified separation membrane prepared by the preparation method of the modified separation membrane as described above in the treatment of salt lake brine.

[0070] The present application provides the application of the modified separation membrane as described above in the treatment of salt lake brine.

[0071] In the present application, the salt lake brine can be treated by forward osmosis or reverse osmosis. In practice, both forward / reverse osmosis can be used. However, reverse osmosis has high energy consumption and poor ion retention effect. The modified separation membrane prepared in the present application has good forward osmosis performance; therefore, it is recommended to apply the modified separation membrane in the present application to forward osmosis, i.e., to separate wastewater by forward osmosis.

[0072] In some embodiments, the forward osmosis method can be carried out by the following steps: injecting raw material liquid on one side of the U-shaped tube and injecting driving liquid on the other end. The modified separation membrane is placed in the middle membrane to separate it, the raw material liquid contacts one side of the modified separation membrane, and the other side of the modified separation membrane contacts the driving liquid. During the contact process, the osmotic pressure of the raw material liquid is lower than that of the driving liquid, and water molecules penetrate the modified separation membrane under the push of the osmotic pressure difference, but the interlayer structure of the membrane has different blocking effects on ions of different sizes / charge intensities, which provides a basis for the selective separation of ions in wastewater.

[0073] In the present application, the concentration of magnesium ions in the salt lake brine can be 0.01-0.5 mol / L, such as 0.01-0.3 mol / L or 0.01-0.4 mol / L or 0.1-0.5 mol / L; the concentration of lithium ions in the salt lake brine can be 0.01-0.5 mol / L, such as 0.01-0.3 mol / L or 0.01-0.4 mol / L or 0.1-0.5 mol / L.

[0074] Compared with seawater desalination, there is no need to specially treat magnesium and lithium ions in the salt lake brine, there is no need to optimize the separation coefficient, and there is no technical problem to be solved in the present application, and the specific reasons are as follows:

[0075] The difference in ion concentration is huge: the molar concentration of magnesium ions in seawater is usually not more than 50 mmol / L, and the molar concentration of lithium ions is usually not more than 0.01 mmol / L. The concentration of magnesium ions in salt lake brine is 0.01-0.5 mol / L, and the concentration of lithium ions is 0.01-0.5 mol / L. It can be seen that the concentration of lithium and magnesium ions in seawater is much lower than that in salt lake brine. In the process of seawater desalination, the main goal of which is to remove a large amount of salt to obtain fresh water, the content of lithium and magnesium ions in the numerous ions is extremely small, and even if the magnesium and lithium ions are not specially treated, the impact on the yield and quality of fresh water is minimal. However, the concentration of magnesium and lithium ions in salt lake brine is relatively high, and the separation of magnesium and lithium is the key to obtaining valuable lithium resources, so special treatment is required.

[0076] The core goal of seawater desalination is different: the core goal of seawater desalination is to significantly reduce the salt content (sodium chloride content) in seawater to meet the salinity, hardness and other indicators of fresh water. Magnesium and lithium ions are not the key focus of seawater desalination, and there is no problem of not being able to meet the fresh water production standards due to the mutual influence of magnesium and lithium ions. However, in the field of lithium extraction from salt lake brine, due to the similar properties of magnesium and lithium ions, the presence of magnesium ions can seriously interfere with the extraction efficiency and purity of lithium in the process of extracting lithium, so it is necessary to optimize the separation coefficient of magnesium and lithium to solve this problem, which is one of the key technical problems to be solved by the present application.

[0077] In the present application, the modified separation membrane has a retention rate for lithium ions of not less than 90%, a separation rate for magnesium ions of not less than 95%, and a separation coefficient greater than 1.5. The present application optimizes the separation coefficient of magnesium and lithium, which can on the one hand improve the extraction efficiency of lithium resources: in lithium-containing resource systems such as salt lake brine, magnesium and lithium ions often coexist and have similar properties, making separation difficult. Increasing the separation coefficient means that lithium ions can be more effectively separated from the magnesium-lithium mixed system, reducing the loss of lithium ions in the separation process, and allowing more lithium ions to enter the product phase, thereby improving the extraction efficiency of lithium resources and increasing the yield of lithium.

[0078] On the other hand, it can significantly improve the purity of lithium products: magnesium ions are one of the main impurity ions that affect the purity of lithium products. After the separation coefficient is increased, magnesium ions and lithium ions can be more completely separated, significantly reducing the content of magnesium ions in lithium products, meeting the strict requirements of high-end lithium products for high purity, and improving the application performance and market competitiveness of lithium products in the fields of batteries, medicine, etc.

[0079] It should be noted that the separation coefficient is usually used to measure the separation ability of the separation process for two different components, and the more it deviates from 1, the better the separation effect of the two components. In the present application, the separation coefficient is , and the calculation formula is: That is, for lithium ions and magnesium ions, if the retention rate of the membrane to magnesium ions is higher than that to lithium ions, it means that the relative content of lithium ions will increase and the relative content of magnesium ions will decrease on the permeation side, so will be greater than , and the separation coefficient will be greater than 1.

[0080] In order to facilitate those skilled in the art to further understand the present application, examples are given as follows:

[0081] Example 1

[0082] Preparation of modified separation membrane:

[0083] S1. 80 mg of kaolinite was added to 40 ml of water to obtain a mixed system; wherein the kaolinite was previously ground with a three-head grinder and passed through a 200-mesh fine sieve. The SEM morphology of the kaolinite is shown in Figure 1 (a), which has a significant laminar stacking structure.

[0084] The mixed system was subjected to ultrasonic liquid phase exfoliation to obtain a treated liquid; the ultrasonic power was set to 450 W, the exfoliation time was 20 h, and the uniform shaking interval was 2 h.

[0085] The TEM morphology of the kaolinite nanosheets after exfoliation is shown in Figure 2 (a), Figure 2 (b), and Figure 2 (c). Among them, Figure 2 (a) shows the distribution state of kaolinite nanosheets at a lower magnification, and a large number of nanosheets can be observed scattered in the field of view, showing irregular flaky morphology with certain size differences; Figure 2 (b) is the morphology of a single kaolinite nanosheet at a higher magnification, and the outline of the nanosheet can be clearly seen, with slightly irregular edges and a certain texture on the surface, indicating that the kaolinite has been successfully exfoliated into single-layer or few-layer nanosheets. Figure 2 (c) further magnifies the microstructure of the kaolinite nanosheet, and the inset in the upper right corner is the selected area electron diffraction (SAED) pattern, which presents regular diffraction spots, confirming that the kaolinite nanosheet has a good crystal structure and the exfoliation process has not seriously damaged its crystal integrity.

[0086] S2. The treated liquid was centrifuged using a freeze-drying centrifuge, with a speed setting of 3500 rpm for 3 minutes, and the residual on the tube wall was discarded. The upper layer of nanosuspension with obvious Tyndall effect was taken and the mass concentration was calibrated using a UV spectrophotometer to establish a concentration-absorbance standard curve.

[0087] S4. 1,3-propanediamine (TN) was added to the nanosheet suspension, and placed on a magnetic stirrer for magnetic stirring for 1 h to ensure successful crosslinking, obtaining a modified liquid, and the mass of the modified nanosheet in the modified liquid was 12 mg.

[0088] Experimental groups with crosslinking reagent dosages of 2.5 wt%, 5 wt%, 7.5 wt% and 10 wt% of kaolinite were set respectively, and the application effects of the modified separation membranes prepared in each group were as shown in Table 1.

[0089] S5. The modified liquid was filtered through a filter membrane by vacuum filtration, and the modified nanosheets were uniformly loaded on the circular microporous water-based filter membrane, obtaining a modified separation membrane.

[0090] The base membrane material was mixed cellulose, with a diameter of 50 mm and a pore size of 0.22 μm, purchased from Tianjin Keyilong Experimental Equipment Co., Ltd., and the effective loading area of the membrane was 12.56 cm 2 , and the loading amount of the modified nanosheet on the filter membrane was about 12 mg.

[0091] Application of the modified separation membrane:

[0092] The prepared modified separation membrane was subjected to a 4h forward osmosis experiment in a U-tube, and the water flux and the rejection rate of Li ＋ , Mg 2+ ions were measured, and the separation coefficient was calculated: wherein one side of the modified separation membrane was 100 ml of 0.1 mol / L LiCl and MgCl2 mixed solution (simulating salt lake brine) of the same concentration, and the other side was 100 mL of deionized water.

[0093] The modified separation membrane under the same preparation conditions was taken, and 100 mL of deionized water was filtered through the modified separation membrane from top to bottom under the condition of vacuum pump filtration, and the filtration flux of the modified separation membrane for water was measured, wherein the negative pressure in the bottle was 0.1 MPa.

[0094] Table 1 Ion rejection and water flux performance table of the modified separation membrane prepared under different crosslinking reagent dosages

[0095]

[0096] Example 2

[0097] In this example, only 1,3-propanediamine (TN) was replaced by 1,6-hexanediamine (HDM), and other conditions remained unchanged. The test results corresponding to different concentrations of 1,6-hexanediamine (HDM) in this example are shown in the following table:

[0098] Table 2 Ion rejection and water flux performance table of the modified separation membrane prepared under different crosslinking reagent dosages

[0099]

[0100] Example 3

[0101] In this example, only 1,3-propanediamine (TN) was replaced by 1,9-nonanediamine (NMD) compared with Example 1, and other conditions remained unchanged. The corresponding test results of different concentrations of 1,9-nonanediamine (NMD) in this example are shown in the following table:

[0102] Table 3 Ion rejection and water flux performance table of modified separation membranes prepared under different amounts of cross-linking reagents

[0103]

[0104] Example 4

[0105] In this example, only 1,3-propanediamine (TN) was replaced by 1,12-diaminododecane (DMD) compared with Example 1, and other conditions remained unchanged. The corresponding test results of different concentrations of 1,12-diaminododecane (DMD) in this example are shown in the following table:

[0106] Table 4 Ion rejection and water flux performance table of modified separation membranes prepared under different amounts of cross-linking reagents

[0107]

[0108] The infrared spectrum images of kaolinite modified separation membranes of Examples 1-4 are shown in Figure 3 (a).

[0109] Example 5

[0110] In this example, only kaolinite was replaced by montmorillonite compared with Example 1, and the reagent system was adjusted, and other conditions remained unchanged. The SEM morphology of montmorillonite is shown in Figure 1 (b), and the TEM morphology of montmorillonite nanosheet after exfoliation is shown in Figure 2 (d), Figure 2 (e), Figure 2 (f). Figure 2 (d) shows the overall distribution of montmorillonite nanosheet at a relatively low magnification, and it can be seen that the nanosheet is uniformly dispersed, and the morphology is also irregular sheet. Figure 2 (e) is an image of a single montmorillonite nanosheet at a higher magnification, and the detailed features of the nanosheet can be observed. The surface is relatively flat, but there are some slight undulations, reflecting the structural characteristics of the montmorillonite nanosheet. Figure 2(f) is the morphology of the montmorillonite nanosheet at a higher magnification, the inset in the upper right corner is the corresponding SAED pattern, the diffraction spots are clear and distinguishable, indicating that the exfoliated montmorillonite nanosheet still maintains a good crystal structure, and the exfoliation to a single-layer or few-layer nanosheet is successfully realized.

[0111] In this embodiment, different concentrations of 1,3-propanediamine (TN) are used, and the corresponding test results are shown in the following table:

[0112] Table 5 Ion rejection and water flux performance table of modified separation membranes prepared under different cross-linking agent dosages

[0113]

[0114] Example 6

[0115] In this embodiment, 1,3-propanediamine (TN) is replaced by 1,6-hexanediamine (HDM) compared with Example 5, and other conditions remain unchanged.

[0116] In this embodiment, different concentrations of 1,6-hexanediamine (HDM) are used, and the corresponding test results are shown in the following table:

[0117] Table 6 Ion rejection and water flux performance table of modified separation membranes prepared under different cross-linking agent dosages

[0118]

[0119] Example 7

[0120] In this embodiment, 1,3-propanediamine (TN) is replaced by 1,9-nonanediamine (NMD) compared with Example 5, and other conditions remain unchanged. In this embodiment, different concentrations of 1,9-nonanediamine (NMD) are used, and the corresponding test results are shown in the following table:

[0121] Table 7 Ion rejection and water flux performance table of modified separation membranes prepared under different cross-linking agent dosages

[0122]

[0123] Example 8

[0124] In this embodiment, 1,3-propanediamine (TN) is replaced by 1,12-diaminododecane (DMD) compared with Example 5, and other conditions remain unchanged. In this embodiment, different concentrations of 1,12-diaminododecane (DMD) are used, and the corresponding test results are shown in the following table:

[0125] Table 8 Ion rejection and water flux performance table of modified separation membranes prepared under different cross-linking agent dosages

[0126]

[0127] Infrared spectral images of the montmorillonite-modified separation membranes in Examples 5-8 are shown below. Figure 3 As shown in (b).

[0128] Comparative Example 1

[0129] Compared to Example 1, this comparative example did not prepare a modified separation membrane (steps 1-4 were omitted), and the modified separation membrane was replaced with a microporous aqueous filter membrane, while other conditions remained unchanged.

[0130] The experimental results for the microporous aqueous filter membrane in this comparative example are shown in the table below:

[0131] Table 9. Ion Retention and Water Flux Performance of Microporous Aqueous Filter Membranes

[0132]

[0133] Comparative Example 2

[0134] Compared to Example 1, no crosslinking agent was added in step 4 of this comparative example, while other conditions remained the same.

[0135] The experimental results for the pure kaolinite film in this comparative example are shown in the table below:

[0136] Table 10. Ion Retention and Water Flux Performance of Pure Kaolinite Membranes

[0137]

[0138] Comparative Example 3

[0139] Compared to Example 5, no crosslinking agent was added in step 4 of this comparative example, while other conditions remained the same.

[0140] The experimental results for the pure montmorillonite membrane in this comparative example are shown in the table below:

[0141] Table 11 Ion Retention and Water Flux Performance of Pure Montmorillonite Membranes

[0142]

[0143] Comparative Example 4

[0144] Compared to Example 1, this comparative example differs only in that the crosslinking agent 1,3-propanediamine (TN) added in step 4 is replaced with polyethyleneimine (PEI), while all other conditions remain unchanged. The experimental results for different concentrations of polyethyleneimine (PEI) in this comparative example are shown in the table below:

[0145] Table 12. Ion rejection and water flux performance of modified separation membranes prepared with different PEI dosages.

[0146]

[0147] Comparative Example 5

[0148] Compared to Example 5, this comparative example differs only in that the crosslinking agent 1,3-propanediamine (TN) added in step 4 is replaced with polyethyleneimine (PEI), while all other conditions remain unchanged. The experimental results for different concentrations of polyethyleneimine (PEI) in this comparative example are shown in the table below:

[0149] Table 13. Ion rejection and water flux performance of modified separation membranes prepared with different PEI dosages.

[0150]

[0151] Analysis example 1

[0152] pass Figure 1 It can be seen that kaolinite and montmorillonite have typical two-dimensional layered structures and a high degree of stacking.

[0153] pass Figure 2 It can be seen that after ultrasound, kaolinite and montmorillonite are effectively exfoliated to obtain single-layer or few-layer nanosheets.

[0154] pass Figure 3 It can be seen that the addition of different crosslinking agents resulted in new peaks appearing on the infrared spectrum, indicating that the crosslinking agents were successfully grafted onto the interlayer, and the modified separation membrane was successfully prepared.

[0155] pass Figure 4 It can be seen that the surface of the microporous water filter membrane is very smooth, the pore size is about 0.22 μm, and there is no layered structure in the cross-section. Water molecules and salt ions can pass through unimpeded. By depositing 12 mg of nanosheets on the base membrane, kaolinite and montmorillonite membranes with a diameter of 5.2 μm and 7.9 μm can be obtained, respectively. Figure 4 SEM images of the microporous aqueous filter membranes used in the various embodiments and comparative examples of this invention, as well as SEM images of the modified separation membranes in Examples 1 and 7;

[0156] in, Figure 4 (a) is a SEM image of the front (water-permeable) side of the microporous water filter membrane; Figure 4 (d) is a SEM image of the side (end face) of the microporous aqueous filter membrane; (b) is a SEM image of the surface of the modified separation membrane in Example 1. Figure 4 (c) is a SEM image of the side (end face) of the modified separation membrane in Example 1; Figure 4 (e) is a SEM image of the surface of the modified separation membrane in Example 7; Figure 4 (f) is a SEM image of the side (end face) of the modified separation membrane in Example 7.

[0157] Based on the experimental data in Examples 1-8 and compared with the data in Comparative Examples 1-5, it can be seen that:

[0158] The flux, rejection rate, and separation coefficient of the kaolinite / montmorillonite modified separation membrane differed from those of the microporous aqueous filter membrane and the pure mineral membrane after the addition of different types and amounts of crosslinking agents. Specifically, the flux of the modified separation membrane with the addition of 1,3-propanediamine (TN) and 1,6-hexanediamine (HDM), two highly hydrophilic crosslinking agents, was significantly increased; while the flux of the modified separation membrane with the addition of 1,9-nonanediamine (NMD) and 1,12-diaminododecane (DMD), two crosslinking agents with longer carbon chains, was somewhat inhibited. All modified separation membranes exhibited ion rejection rates exceeding 90%, demonstrating good retention performance and a significant improvement over the control group. The separation coefficients varied considerably in the examples, particularly with the kaolinite-modified separation membrane. The maximum value was 2.17, and the minimum value was 1.66; montmorillonite-modified separation membrane. The maximum value was 3.91 and the minimum value was 2.29. The separation coefficient was significantly increased compared with the comparative example, indicating that lithium and magnesium ions could be separated efficiently.

[0159] The above technical solutions of the present invention are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made under the technical concept of the present invention using the contents of the present invention specification and drawings, or direct / indirect applications in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A method for preparing a modified separation membrane, characterized in that, Including the following steps: A mixture of mineral and polar solvent is obtained, and the mixture is subjected to ultrasonic liquid-phase exfoliation to obtain a liquid to be treated. The mass-to-volume ratio of the mineral to the polar solvent is 50-100 mg: 30-60 ml; the mineral is montmorillonite. The liquid to be treated is centrifuged, and the supernatant is collected to obtain a nano suspension; the crosslinking agent is mixed with the nano suspension to obtain a modified liquid, wherein the modified liquid contains modified nanosheets; The crosslinking agent is 1,6-hexanediamine, and the mass of the crosslinking agent is 15wt%-20wt% of the mass of the ore; or, the crosslinking agent is 1,9-nonanediamine, and the mass of the crosslinking agent is 14-16% of the mass of the ore; or, the crosslinking agent is 1,12-diaminododecane, and the mass of the crosslinking agent is 9-11% of the mass of the ore. The modified liquid is filtered through a filter membrane to uniformly load the modified nanosheets onto the surface of the filter membrane, thereby obtaining a modified separation membrane.

2. The method for preparing the modified separation membrane according to claim 1, characterized in that, The polar solvent includes one or more of water, ethanol, and propylene glycol.

3. The method for preparing the modified separation membrane according to claim 1, characterized in that, The ultrasonic conditions during the ultrasonic liquid phase stripping process are: ultrasonic power 300-500W, stripping time 4-24h.

4. The method for preparing the modified separation membrane according to claim 1, characterized in that, The filtration method includes vacuum filtration, with a negative pressure of 0-0.1 MPa.

5. The method for preparing the modified separation membrane according to claim 1, characterized in that, The filter membrane includes a microporous aqueous filter membrane; the pore size of the filter membrane is 0.15-0.3 micrometers; The modified nanosheets were loaded onto the filter membrane at a rate of 0.6-1.4 mg / cm³. 2 .

6. A modified separation membrane, characterized in that, It is prepared by the method for preparing the modified separation membrane as described in any one of claims 1-5.

7. The application of the modified separation membrane as described in claim 6 in the treatment of salt lake brine.

8. The application of the modified separation membrane according to claim 7 in the treatment of salt lake brine, characterized in that, The concentration of magnesium ions in the salt lake brine is 0.01-0.5 mol / L, and the concentration of lithium ions in the salt lake brine is 0.01-0.5 mol / L. The modified separation membrane has a lithium ion rejection rate of not less than 90%, a magnesium ion separation rate of not less than 95%, and a separation coefficient greater than 1.5.

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