Two-dimensional montmorillonite film for reinforcing lithium-magnesium separation in the direction of channel normal and preparation method and application thereof

Abstract

The application discloses a two-dimensional montmorillonite film for strengthening lithium-magnesium separation in the direction of channel normal line, comprising a supporting base body and a two-dimensional montmorillonite film with channel normal line direction pore modification arranged on the surface of the supporting base body; wherein the two-dimensional montmorillonite film with channel normal line direction pore modification comprises a self-assembled film formed by end face hydrophilic modification chelate and straight-chain alkyl ammonium salt modified two-dimensional montmorillonite nanosheet and high-valence cations chelated by the self-assembled film. The high-valence cations are stably fixed in the direction of channel normal line of the two-dimensional montmorillonite film, and the hydrophilic modification and strengthening modification are carried out, so that the magnesium ion interception effect is improved, the transmission of lithium ions with low steric hindrance is accelerated, the transportation of lithium ions and water molecules is promoted, and the problems of low lithium extraction efficiency of the traditional modified film and the like are solved, and the applicability is wide.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation and lithium extraction technology, specifically relating to a two-dimensional montmorillonite thin film for enhancing lithium-magnesium separation in the channel normal direction, its preparation method, and its application. Background Technology

[0002] With the rapid development of new energy vehicles, electronic devices, and energy storage technologies, the demand for lithium has surged. More than 70% of the world's lithium resources are found in salt lake brines, making lithium extraction from these brines the primary method for obtaining lithium. However, due to the influence of impurity ions (mainly magnesium ions), separating high-purity lithium salts from salt lake brines remains a significant challenge. Currently, the main technologies for lithium extraction from salt lakes include adsorption, membrane separation, and solvent extraction. Among these, membrane separation has become the mainstream lithium extraction technology from salt lake brines due to its high efficiency and environmental friendliness.

[0003] The core of membrane separation lies in membrane material design. Two-dimensional nanochannel membranes are widely used for lithium extraction from salt lake brine due to their highly precise sub-nanochannel sieving characteristics. Because conventional two-dimensional materials such as graphene oxide and MXene contain abundant functional groups on their surfaces, current research mainly focuses on surface modification of nanosheets to enhance lithium-magnesium separation by functionalizing the membrane channels and surfaces (Zhang T, et al. J. Memb. Sci, 2023, 675: 121573; Xie L, et al. Adv. Funct. Mater, 2023, 33: 2208959). It is noteworthy that the pores along the normal direction of the two-dimensional membrane nanochannels are the entry points for ions into the membrane, but traditional processes have failed to fully utilize these sites to enhance lithium-magnesium separation. Studies have shown that high magnesium ion retention can be achieved by controlling the channel height of two-dimensional membranes and by modifying the surface with positive charge, but problems such as low lithium ion permeability still exist (Lu Z, et al. Angew. Chem. Int. Ed, 2021, 60: 22265-22269; Peng Q, et al. Nat. Commun, 2024, 15: 2505), which results in a low lithium extraction efficiency of the membrane in practical applications. Summary of the Invention

[0004] The main objective of this invention is to address the problems and shortcomings of existing technologies by providing a two-dimensional montmorillonite film that enhances lithium-magnesium separation along the channel normal and its preparation method. This method improves magnesium ion retention while accelerating the permeation of lithium ions with low steric hindrance, promoting the transport of lithium ions and water molecules, and effectively enhancing lithium extraction efficiency.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A two-dimensional montmorillonite film for enhancing lithium-magnesium separation in the channel normal direction includes a supporting substrate and a two-dimensional montmorillonite film with channel normal pore modification disposed on its surface; wherein, the two-dimensional montmorillonite film with channel normal pore modification comprises a self-assembled film formed by end-face hydrophilic modified chelates and two-dimensional montmorillonite nanosheets modified with straight-chain alkylammonium salts, and its chelated high-valence cations.

[0006] In the above scheme, the average porosity of the two-dimensional montmorillonite film with channel normal direction pore modification is 10-25 nm along the normal direction (the straight line direction perpendicular to the film surface).

[0007] In the above scheme, the end-face hydrophilic modified chelate contains both an amino group and a hydrophilic chelating group that specifically chelates with high-valent cations.

[0008] In the above scheme, the hydrophilic chelating group for the high-valent cation specific chelation is one or more of the following: carboxyl group, phenolic hydroxyl group, sulfonic acid group, phosphonic acid group, etc.

[0009] Furthermore, the end-face hydrophilic modified chelate is one or more of ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, aminophenol, ethylenediaminetetramethylenephosphonic acid, aminotrimethylenephosphonic acid, aminosulfonic acid, sulfoethylenediamine, etc.

[0010] In the above scheme, the straight-chain alkylammonium salt is one or more of the following: dodecylammonium chloride, tetradecylammonium chloride, hexadecylammonium chloride, octadecylammonium chloride, dodecylammonium bromide, tetradecylammonium bromide, hexadecylammonium bromide, and octadecylammonium bromide.

[0011] In the above scheme, the high-valent metal cation is a trivalent or tetravalent metal cation.

[0012] In the above scheme, the trivalent or tetravalent metal cation is specifically Fe. 3+ Al 3+ La 3+ Sn 4+ Ir 4+ Zr 4+ One or more of the following.

[0013] In the above scheme, the supporting matrix can be selected from matrix materials such as cellulose acetate, polypropylene, polyvinylidene fluoride, and polyethersulfone.

[0014] This invention also provides a method for preparing the above-mentioned two-dimensional montmorillonite thin film with enhanced lithium-magnesium separation in the channel normal direction, the specific steps of which are as follows: 1) The end-face hydrophilic modified chelate dispersion was added to the two-dimensional montmorillonite nanosheet suspension and stirred to obtain the end-face hydrophilic modified two-dimensional montmorillonite nanosheet suspension. 2) The linear alkylammonium salt dispersion was added to the end-face hydrophilic modified two-dimensional montmorillonite nanosheet suspension and stirred to obtain the end-face reinforced modified two-dimensional montmorillonite nanosheet suspension. 3) The end-face reinforced modified two-dimensional montmorillonite nanosheet suspension was self-assembled into a film on a support substrate, and after drying, a two-dimensional montmorillonite film with channel normal direction modified was obtained. 4) The two-dimensional montmorillonite film modified in the channel normal direction was immersed in a high-valence metal cation solution for chelation reaction, washed (water wash), and dried to obtain a two-dimensional montmorillonite film with enhanced lithium-magnesium separation in the channel normal direction.

[0015] In the above scheme, in step 1), the thickness of the two-dimensional montmorillonite nanosheets is 1-20 nm, the average sheet size is 50-600 nm, and the concentration of the two-dimensional montmorillonite nanosheet suspension is 0.1-4 wt%.

[0016] In the above scheme, in step 1), the concentration of the end-face hydrophilic modified chelate dispersion is 0.1-10 wt%.

[0017] In the above scheme, the amount of end-face hydrophilic modified chelate introduced in step 1) is 0.5-20 wt% of the amount of two-dimensional montmorillonite nanosheets, and the stirring reaction time of end-face hydrophilic modified chelate and two-dimensional montmorillonite nanosheets is 0.1-5 h.

[0018] In the above scheme, in step 2), the concentration of the linear alkylammonium salt dispersion is 0.1-3 wt%, the amount of the introduced linear alkylammonium salt is 0.1-4 wt% of the amount of the two-dimensional montmorillonite nanosheets, and the stirring reaction time of the linear alkylammonium salt and the end-face hydrophilic modified two-dimensional montmorillonite nanosheet suspension is 0.1-3 h.

[0019] In the above scheme, in step 3), the average pore size of the support substrate is 20-500 nm.

[0020] In the above scheme, the self-assembly film formation method is one of the following: blade coating, spin coating, and vacuum filtration. The drying temperature is 10-120 ℃, and the drying time is 0.2-20 h.

[0021] In the above scheme, the concentration of the high-valence metal cation solution in step 4) is 0.1-3 mol / L.

[0022] The present invention also provides an application of the above-mentioned two-dimensional montmorillonite membrane for lithium-magnesium separation in the enhanced channel normal direction, specifically, as a separation membrane for lithium-magnesium ion separation in salt lake brine.

[0023] Furthermore, when this invention is applied as a separation membrane for the separation of lithium and magnesium ions in salt lake brine, a magnesium ion rejection rate of 98-100%, a lithium ion permeability of 100-125%, and a water flux of 9-13 L·m⁻¹ can be achieved. -2 ·h -1 ·bar -1 Furthermore, it uses a wide range of brine.

[0024] This invention fixes high-valence cations in the normal direction of the two-dimensional montmorillonite film channel and performs hydrophilic modification and enhancement, effectively enhancing magnesium ion retention while promoting lithium ion permeation, thus solving the problem of low lithium extraction efficiency of conventional modified films. The specific working principle is as follows: The amine groups on the end-face hydrophilic modified chelate used in this invention can undergo hydrogen bonding crosslinking with the aluminum hydroxyl groups on the end-face of two-dimensional montmorillonite nanosheets. After assembly into a film, it can be modified at the pores in the normal direction of the film channel, providing sites for the crosslinking of linear alkylammonium salts and the chelation of metal ions. Utilizing the hydrogen bonding crosslinking between the amine groups in the linear alkylammonium salt and the chelating groups in the end-face hydrophilic modified chelate, the linear alkylammonium salt can be further fixed at the end-face of the nanosheets. Combined with its long-chain structure, this promotes increased porosity between the end-faces of the nanosheets after assembly, thereby improving water flux and lithium ion permeability. The chelating effect of the end-face hydrophilic modified chelate can also chelate and fix high-valence metal cations at the pores in the normal direction of the film. High-valence metal cations have a stronger binding ability to the chelate than magnesium ions, and can stably repel magnesium ions at the entrance of the pores in the normal direction of the film. Furthermore, the pairing effect of high-valence cations is stronger with magnesium ions and anions than that of magnesium ions, inducing the transport of anions in the feed brine within the membrane. The charge balance effect also accelerates the permeation of lithium ions with low steric hindrance. Simultaneously, the hydrophilic environment provided by the hydrophilic groups of the end-face modified chelates further accelerates the entry of lithium ions and water molecules into the membrane. The combined effect of these mechanisms allows for high magnesium ion retention while simultaneously achieving high lithium ion permeation and water flux, significantly improving lithium extraction efficiency.

[0025] Compared with the prior art, the beneficial effects of the present invention include: 1. The present invention performs lithium-magnesium separation enhancement modification and alteration at the pores in the normal direction of the two-dimensional membrane channel, thereby achieving efficient retention of magnesium ions and permeation of lithium ions from the entrance of the ion into the membrane, significantly improving lithium extraction efficiency.

[0026] 2. The end-face hydrophilic modified chelate introduced in this invention can stably chelate high-valence metal cations at the pores in the normal direction of the two-dimensional membrane channel to exclude magnesium ions from entering the film, thereby achieving efficient retention of magnesium ions; at the same time, the alkylammonium cross-linked at the end face of the nanosheet can promote the increase of the pores in the normal direction of the two-dimensional membrane channel, thereby simultaneously increasing the water flux and lithium ion permeability.

[0027] 3. This invention utilizes the sites of aluminum hydroxyl groups on the end face of montmorillonite to stably chelate high-valence cations (different from traditional ion exchange), and utilizes the stronger ion pairing effect between high-valence cations and anions to induce the transport of anions in brine within the membrane. In turn, due to the charge balance effect, it promotes the permeation of lithium ions with low steric hindrance, thereby enhancing the lithium ion permeability.

[0028] 4. The hydrophilic groups of the end-face hydrophilic modified chelate introduced in this invention are beneficial to strengthening the water environment at the ion inlet of the pores in the normal direction of the film channel, which can promote the speed of lithium ions and water molecules entering the film, further enhance the lithium ion permeability and water flux, and improve the lithium extraction efficiency. Attached Figure Description

[0029] Figure 1 A schematic diagram illustrating the structural design and working principle of a two-dimensional montmorillonite thin film designed to enhance lithium-magnesium separation along the channel normal.

[0030] Figure 2 This is a graph showing the binding energy data of the end-face hydrophilic modified chelate with high-valence cations and magnesium ions in Example 1. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0032] Example 1 A two-dimensional montmorillonite thin film for enhancing lithium-magnesium separation along the channel normal direction is illustrated in the schematic diagram of its structural design and working principle. Figure 1 The specific preparation method includes the following steps: (1) A solution of diethylenetriaminepentaacetic acid (DTA) was added to a suspension of two-dimensional montmorillonite nanosheets with an average sheet thickness of 3 nm and an average sheet diameter of 600 nm (the DTA introduced accounted for 10 wt% of the amount of the two-dimensional montmorillonite nanosheets) and stirred for 5 h to obtain a suspension of two-dimensional montmorillonite nanosheets with hydrophilic modification of the end face. The concentration of the DTA solution was 3 wt% and the concentration of the two-dimensional montmorillonite nanosheet suspension was 0.1 wt%. (2) Add dodecyltrimethylammonium chloride solution to the obtained end-face hydrophilic modified two-dimensional montmorillonite nanosheet suspension (the introduced dodecyltrimethylammonium chloride accounts for 2wt% of the amount of two-dimensional montmorillonite nanosheets) and stir for 0.1 h to react, to obtain end-face reinforced modified two-dimensional montmorillonite nanosheet suspension, wherein the concentration of dodecyltrimethylammonium chloride solution is 1.5wt%; (3) The obtained end-face reinforced two-dimensional montmorillonite nanosheet suspension was spin-coated on a support film (polypropylene matrix) with an average pore size of 500 nm and dried at 10 °C for 20 h to obtain a channel normal modified two-dimensional montmorillonite film with an average pore size of 10 nm in the normal direction of the film. (4) The obtained two-dimensional montmorillonite film with modified channel normal direction was immersed in 0.1 mol / L Fe solution. 3+ After chelation reaction in solution for 6 h, followed by washing with water and drying, a two-dimensional montmorillonite film with enhanced lithium-magnesium separation along the channel normal was obtained.

[0033] Figure 2 The figure shows the binding energy of the end-face hydrophilic modified chelate with high-valence cations and magnesium ions in this embodiment. It can be seen that the binding energy of high-valence cations is significantly higher than that of magnesium ions, indicating that high-valence cations can stably chelate at the normal pores of the film and repel magnesium ions.

[0034] This invention was applied as a separation membrane to separate lithium and magnesium ions in raw brine from salt lakes in Qinghai Province. Calculations showed that the magnesium ion rejection rate was 99%, the lithium ion permeability was 115%, and the water flux was 9 L·m⁻¹. -2 ·h -1 ·bar -1 The present invention was applied as a separation membrane to separate lithium and magnesium ions in old brine from salt lakes in Qinghai Province. Calculations showed that the magnesium ion rejection rate was 99%, the lithium ion permeability was 105%, and the water flux was 9 L·m⁻¹. -2 ·h -1 ·bar -1 The present invention was applied as a separation membrane to separate lithium and magnesium ions in the brine of lithium extraction adsorbent desorption solution from salt lakes in Qinghai Province. Calculations showed that the magnesium ion rejection rate was 100%, the lithium ion permeability was 110%, and the water flux was 11 L·m⁻¹. -2 ·h -1 ·bar -1 .

[0035] Example 2 A two-dimensional montmorillonite thin film for enhancing lithium-magnesium separation along the channel normal direction is prepared by the following steps: (1) An ethylenediaminetetramethylenephosphonic acid solution was added to a two-dimensional montmorillonite nanosheet suspension with an average sheet thickness of 20 nm and an average sheet diameter of 500 nm (the ethylenediaminetetramethylenephosphonic acid introduced accounted for 20 wt% of the amount of two-dimensional montmorillonite nanosheets) and stirred for 0.1 h to obtain a two-dimensional montmorillonite nanosheet suspension with hydrophilic modification of the end face, wherein the concentration of the ethylenediaminetetramethylenephosphonic acid solution was 10 wt% and the concentration of the two-dimensional montmorillonite nanosheet suspension was 2 wt%. (2) An octadecyltrimethylammonium bromide solution was added to a suspension of end-face hydrophilic modified two-dimensional montmorillonite nanosheets (the introduced octadecyltrimethylammonium bromide accounted for 4 wt% of the amount of two-dimensional montmorillonite nanosheets) and stirred for 3 h to obtain an end-face reinforced modified two-dimensional montmorillonite nanosheet suspension, wherein the concentration of the octadecyltrimethylammonium bromide solution was 3 wt%. (3) The end-face reinforced two-dimensional montmorillonite nanosheet suspension was coated onto a support film (cellulose acetate matrix) with an average pore size of 300 nm and dried at 120 °C for 0.2 h to obtain a channel normal modified two-dimensional montmorillonite film with an average pore size of 25 nm in the normal direction of the film. (4) The two-dimensional montmorillonite film modified in the channel normal direction was immersed in 3 mol / L Al 3+ The chelation reaction in solution was carried out for 0.1 h, and after washing with water and drying, a two-dimensional montmorillonite film with enhanced lithium-magnesium separation in the channel normal direction was obtained.

[0036] When this invention was applied as a separation membrane to separate lithium and magnesium ions in raw brine of a salt lake, calculations showed that the magnesium ion rejection rate was 98%, the lithium ion permeability was 125%, and the water flux was 10 L·m⁻¹. -2 ·h -1 ·bar -1 When this invention was applied as a separation membrane to separate lithium and magnesium ions in old brine from a salt lake, calculations showed that the magnesium ion rejection rate was 99%, the lithium ion permeability was 120%, and the water flux was 11 L·m⁻¹. -2 ·h -1 ·bar -1 The present invention was applied as a separation membrane to separate lithium and magnesium ions in the brine of the lithium extraction adsorbent desorption solution in salt lakes. Calculations showed that the magnesium ion rejection rate was 99%, the lithium ion permeability was 115%, and the water flux was 13 L·m⁻¹. -2 ·h -1 ·bar -1 .

[0037] Example 3 A two-dimensional montmorillonite thin film for enhancing lithium-magnesium separation along the channel normal direction is prepared by the following steps: (1) An aminophenol solution was added to a two-dimensional montmorillonite nanosheet suspension with an average sheet thickness of 10 nm and an average sheet diameter of 200 nm (the introduced aminophenol accounted for 0.5 wt% of the amount of two-dimensional montmorillonite nanosheets) and stirred for 3 h to obtain a two-dimensional montmorillonite nanosheet suspension with hydrophilic modification of the end face, wherein the concentration of the aminophenol solution was 0.1 wt% and the concentration of the two-dimensional montmorillonite nanosheet suspension was 4 wt%; (2) A hexadecyltrimethylammonium chloride solution was added to a suspension of end-face hydrophilic modified two-dimensional montmorillonite nanosheets (the amount of hexadecyltrimethylammonium chloride introduced was 0.1 wt% of the amount of two-dimensional montmorillonite nanosheets) and stirred for 1.5 h to obtain an end-face reinforced modified two-dimensional montmorillonite nanosheet suspension, wherein the concentration of the hexadecyltrimethylammonium chloride solution was 0.1 wt%. (3) The two-dimensional montmorillonite nanosheet suspension with end face reinforcement was vacuum filtered on a support membrane (polyethersulfone matrix) with an average pore size of 100 nm and dried at 60 °C for 5 h to obtain a two-dimensional montmorillonite film with channel normal direction modification and an average pore size of 15 nm in the normal direction of the film. (4) The two-dimensional montmorillonite film modified in the channel normal direction was immersed in 0.5 mol / L Sn. 4+ The chelation reaction in solution was carried out for 3 h, and after washing with water and drying, a two-dimensional montmorillonite film with enhanced lithium-magnesium separation in the channel normal direction was obtained.

[0038] When this invention was applied as a separation membrane to separate lithium and magnesium ions in raw brine of a salt lake, calculations showed that the magnesium ion rejection rate was 99%, the lithium ion permeability was 120%, and the water flux was 9 L·m⁻¹. -2 ·h -1 ·bar -1 The present invention was applied as a separation membrane to separate lithium and magnesium ions in old brine of a salt lake. Calculations showed that the magnesium ion rejection rate was 100%, the lithium ion permeability was 110%, and the water flux was 10 L·m⁻¹. -2 ·h -1 ·bar -1 The present invention was applied as a separation membrane to separate lithium and magnesium ions in the brine of the lithium extraction adsorbent desorption solution in salt lakes. Calculations showed that the magnesium ion rejection rate was 100%, the lithium ion permeability was 110%, and the water flux was 12 L·m⁻¹. -2 ·h -1 ·bar -1 .

[0039] Example 4 A two-dimensional montmorillonite thin film for enhancing lithium-magnesium separation along the channel normal direction is prepared by the following steps: (1) A sulfamic acid solution was added to a two-dimensional montmorillonite nanosheet suspension with an average sheet thickness of 1 nm and an average sheet diameter of 50 nm (the introduced sulfamic acid accounted for 5 wt% of the amount of two-dimensional montmorillonite nanosheets) and stirred for 2 h to obtain a two-dimensional montmorillonite nanosheet suspension with hydrophilic modification of the end face, wherein the concentration of the sulfamic acid solution was 2 wt% and the concentration of the two-dimensional montmorillonite nanosheet suspension was 3 wt%; (2) A tetradecyltrimethylammonium bromide solution was added to a suspension of end-face hydrophilic modified two-dimensional montmorillonite nanosheets (the introduced tetradecyltrimethylammonium bromide accounted for 1 wt% of the amount of two-dimensional montmorillonite nanosheets) and stirred for 1 h to obtain an end-face reinforced modified two-dimensional montmorillonite nanosheet suspension, wherein the concentration of the tetradecyltrimethylammonium bromide solution was 0.8 wt%; (3) The end-face reinforced two-dimensional montmorillonite nanosheet suspension was coated onto a support film (polyvinylidene fluoride vinyl body) with an average pore size of 20 nm and dried at 80 °C for 3 h to obtain a channel normal modified two-dimensional montmorillonite film with an average pore size of 12 nm in the normal direction of the film. (4) The two-dimensional montmorillonite film modified in the channel normal direction was immersed in 1 mol / L Ir 4+ After chelation reaction in solution for 1 h, followed by washing with water and drying, a two-dimensional montmorillonite film with enhanced lithium-magnesium separation along the channel normal was obtained.

[0040] When this invention was applied as a separation membrane to separate lithium and magnesium ions in raw brine of a salt lake, calculations showed that the magnesium ion rejection rate was 98%, the lithium ion permeability was 105%, and the water flux was 10 L·m⁻¹. -2 ·h -1 ·bar -1 The present invention was applied as a separation membrane to separate lithium and magnesium ions in old brine of a salt lake. Calculations showed that the magnesium ion rejection rate was 99%, the lithium ion permeability was 105%, and the water flux was 11 L·m⁻¹. -2 ·h -1 ·bar -1 The present invention was applied as a separation membrane to separate lithium and magnesium ions in the brine of the lithium extraction adsorbent desorption solution in salt lakes. Calculations showed that the magnesium ion rejection rate was 99%, the lithium ion permeability was 100%, and the water flux was 13 L·m⁻¹. -2 ·h -1 ·bar -1 .

[0041] Comparative Example 1 A two-dimensional montmorillonite thin film is prepared by means of the following steps: (1) A sulfamic acid solution was added to a two-dimensional montmorillonite nanosheet suspension with an average sheet thickness of 1 nm and an average sheet diameter of 50 nm (the introduced sulfamic acid accounted for 5 wt% of the amount of two-dimensional montmorillonite nanosheets) and stirred for 2 h to obtain a two-dimensional montmorillonite nanosheet suspension with hydrophilic modification of the end face, wherein the concentration of the sulfamic acid solution was 2 wt% and the concentration of the two-dimensional montmorillonite nanosheet suspension was 3 wt%; (2) The obtained end-face hydrophilic modified two-dimensional montmorillonite nanosheet suspension was coated onto a support film (polyvinylidene fluoride vinyl body) with an average pore size of 20 nm and dried at 80 °C for 3 h to obtain a channel normal modified two-dimensional montmorillonite film with an average pore size of 8 nm in the normal direction of the film. (3) The two-dimensional montmorillonite film modified in the channel normal direction was immersed in 1 mol / L Ir 4+ The chelation reaction in solution was carried out for 1 h, and the control group film was obtained after washing with water and drying.

[0042] The control group membrane was used as the separation membrane for separating lithium and magnesium ions in the raw brine of a salt lake. Calculations showed a magnesium ion rejection rate of 96%, a lithium ion permeability of 90%, and a water flux of 6 L·m⁻¹. -2 ·h -1 ·bar -1 The control group membrane was used as the separation membrane for the separation of lithium and magnesium ions in old brine of a salt lake. Calculations showed that the magnesium ion rejection rate was 96%, the lithium ion permeability was 88%, and the water flux was 7 L·m⁻¹. -2 ·h -1 ·bar -1 The control group membrane was used as the separation membrane for separating lithium and magnesium ions in the brine of the lithium extraction adsorbent in salt lakes. Calculations showed a magnesium ion rejection rate of 97%, a lithium ion permeability of 85%, and a water flux of 8 L·m⁻¹. -2 ·h -1 ·bar -1 .

[0043] This invention is not limited to the embodiments described above. Those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications are also considered within the scope of protection of this invention. Contents not described in detail in this specification are prior art known to those skilled in the art.

Claims

1. A two-dimensional montmorillonite thin film for enhancing lithium-magnesium separation in the channel normal direction, characterized in that, The invention includes a supporting substrate and a two-dimensional montmorillonite film with channel-normal pore modification disposed on its surface; wherein the two-dimensional montmorillonite film with channel-normal pore modification comprises a self-assembled film formed by end-face hydrophilic modified chelates and two-dimensional montmorillonite nanosheets modified with straight-chain alkylammonium salts, and its chelated high-valence cations.

2. The two-dimensional montmorillonite film according to claim 1, characterized in that, The average porosity of the two-dimensional montmorillonite film modified with channel normal direction is 10-25 nm along the normal direction.

3. The two-dimensional montmorillonite film according to claim 1, characterized in that, The end-face hydrophilic modified chelate contains both an amino group and a hydrophilic chelating group that specifically chelates with high-valent cations; the hydrophilic chelating group that specifically chelates with high-valent cations is one or more of carboxyl, phenolic hydroxyl, sulfonic acid, and phosphonic acid groups.

4. The two-dimensional montmorillonite film according to claim 1, characterized in that, The straight-chain alkylammonium salt is one or more of dodecylammonium chloride, tetradecylammonium chloride, hexadecylammonium chloride, octadecylammonium chloride, dodecylammonium bromide, tetradecylammonium bromide, hexadecylammonium bromide, and octadecylammonium bromide.

5. The two-dimensional montmorillonite film according to claim 1, characterized in that, The high-valence metal cation is a trivalent or tetravalent metal cation.

6. The two-dimensional montmorillonite film according to claim 1, characterized in that, The supporting matrix is ​​made of cellulose acetate, polypropylene, polyvinylidene fluoride or polyethersulfone.

7. The method for preparing a two-dimensional montmorillonite thin film with enhanced lithium-magnesium separation in the channel normal direction as described in any one of claims 1 to 6, characterized in that, The specific steps are as follows: 1) The end-face hydrophilic modified chelate dispersion was added to the two-dimensional montmorillonite nanosheet suspension and stirred to obtain the end-face hydrophilic modified two-dimensional montmorillonite nanosheet suspension. 2) The linear alkylammonium salt dispersion was added to the end-face hydrophilic modified two-dimensional montmorillonite nanosheet suspension and stirred to obtain the end-face reinforced modified two-dimensional montmorillonite nanosheet suspension. 3) The end-face reinforced modified two-dimensional montmorillonite nanosheet suspension was self-assembled into a film on a support substrate, and after drying, a two-dimensional montmorillonite film with channel normal direction modified was obtained. 4) The two-dimensional montmorillonite film modified in the channel normal direction was immersed in a high-valence metal cation solution for chelation reaction, washed and dried to obtain a two-dimensional montmorillonite film with enhanced lithium-magnesium separation in the channel normal direction.

8. The preparation method according to claim 7, characterized in that, The amount of the introduced end-face hydrophilic modified chelate is 0.5-20 wt% of the amount of two-dimensional montmorillonite nanosheets, and the stirring reaction time of the end-face hydrophilic modified chelate and the two-dimensional montmorillonite nanosheets is 0.1-5 h.

9. The preparation method according to claim 7, characterized in that, The amount of the introduced linear alkylammonium salt was 0.1-4 wt% of the amount of two-dimensional montmorillonite nanosheets, and the stirring reaction time of the linear alkylammonium salt and the end-face hydrophilic modified two-dimensional montmorillonite nanosheet suspension was 0.1-3 h.

10. The application of the two-dimensional montmorillonite thin film with enhanced lithium-magnesium separation in the normal direction of the enhanced channel as described in any one of claims 1 to 6, characterized in that, It is used as a separation membrane for the separation of lithium and magnesium ions in salt lake brine.

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