A ceramic-polymer composite membrane for selectively separating lithium ions and a method of preparing the same

Abstract

The application provides a ceramic-polymer composite membrane for selectively separating lithium ions and a preparation method thereof, wherein the ceramic is LLTO, and the LLTO retains a complete three-dimensional skeleton, and the continuous three-dimensional skeleton can be used for selectively passing lithium ions, so that the effect of separating lithium ions is achieved, and the ceramic-polymer composite membrane can be applied to a system for separating lithium resources from water bodies, such as extracting lithium from seawater. The LLTO for selectively separating lithium ions and an organic polymer are compounded, so that the prepared ceramic-polymer composite membrane has high toughness, and the risk of membrane breakage in the process of extracting lithium from seawater is greatly reduced. The application can improve the mechanical properties of the composite membrane and increase the toughness of the composite membrane without increasing the thickness, and the separation efficiency of lithium ions in the solution is not affected.

Description

Technical Field

[0001] This invention belongs to the field of selective lithium extraction technology using electrochemical membranes, specifically relating to a ceramic-polymer composite membrane for selectively separating lithium ions and its preparation method. Background Technology

[0002] Lithium metal has the lowest electrode potential (-3.045V) and the lowest density (0.534g / cm³). 3 Lithium, therefore, has become an ideal element for battery manufacturing and is hailed as the "metal that drives the world forward." Lithium and its compounds are widely used in lubricants, lightweight aircraft alloys, glass, and pharmaceuticals. However, due to the widespread use of lithium resources, lithium ore resources are becoming increasingly depleted. Currently, lithium resources extracted from salt lakes and seawater account for more than 90%. The most mature industrial process is the precipitation of lithium-rich brine using carbonates. In the brine lithium extraction industry, due to the difference in lithium-magnesium ratio, there is generally no universal method for mining lithium resources. Moreover, the carbonate precipitation method requires long-term evaporation and concentration of raw materials, making it highly susceptible to uncontrollable factors such as the natural environment. Compared to terrestrial lithium reserves, marine lithium reserves are approximately 231 billion tons, tens of thousands of times larger. However, the extremely low concentration of lithium in seawater (0.1–0.2 ppm) limits the development of lithium extraction from seawater.

[0003] Currently, membrane separation technology offers many advantages over traditional methods for lithium extraction from solution: it consumes less energy, can operate continuously, and requires no other chemical reagents. Among these, LLTO ceramic membranes can selectively extract lithium ions. The principle behind this is that the pore diameter inside LLTO molecules is... The diameter of a lithium ion is Under the influence of an electric current, LLTO molecules only require a small distortion to allow lithium ions to pass through, while other ions, due to their larger diameter, require more energy to pass through. Thus, the effect of separating lithium ions can be achieved by changing the external voltage.

[0004] Although LLTO ceramic membranes can separate lithium ions from most other ions through their internal molecular pore size, their high hardness results in poor flexibility and brittleness, leading to high processing difficulty and manufacturing costs. LLTO ceramic membranes are also prone to breakage due to mechanical impact during use. Currently, the only way to prevent breakage is to increase the thickness of the ceramic membrane, which further increases manufacturing costs, reduces lithium ion throughput, and increases energy consumption. Therefore, when using LLTO ceramic membranes for lithium extraction from seawater brine, it is impossible to balance membrane mechanical strength and lithium ion separation efficiency. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention proposes a ceramic-polymer composite membrane for selective lithium ion separation and its preparation method. The aim is to effectively apply the ceramic-polymer composite membrane to lithium extraction technology from marine brine, thereby improving the mechanical properties and toughness of the composite membrane without increasing its thickness, while ensuring the separation efficiency of lithium ions. This solves the problem that existing composite membranes cannot simultaneously achieve both mechanical strength and lithium ion separation efficiency.

[0006] The present invention discloses a ceramic-polymer composite membrane for selectively separating lithium ions, comprising LLTO having a three-dimensional structure and an organic polymer; wherein the organic polymer is polyethylene, polypropylene, or cured epoxy resin.

[0007] The present invention discloses a method for preparing a ceramic-polymer composite membrane for selectively separating lithium ions, comprising the following steps:

[0008] (1) Preparation of precursor hydrogel by sol-gel method: LLTO precursor raw material is added to PVA aqueous solution and stirred evenly to obtain LLTO precursor suspension; after adding crosslinking agent and initiator, it is poured into polytetrafluoroethylene mold to obtain precursor hydrogel.

[0009] (2) Preparation of LLTO three-dimensional framework: After drying the precursor hydrogel, it was placed in a muffle furnace for high-temperature calcination and cooled to obtain LLTO with a three-dimensional framework structure.

[0010] (3) Preparation of LLTO-polymer composite membrane: Liquid organic polymer is poured onto the LLTO three-dimensional framework. After complete curing, the excess organic polymer is ground off until the LLTO three-dimensional framework is exposed, and the LLTO-polymer composite membrane is obtained.

[0011] Preferably, in step (1), the composition of the LLTO precursor raw material and the molar ratio of each component are LiNO3:La(NO3)3·6H2O:TALH = 0.7:1.3:2, and the TALH is di(2-hydroxypropionic acid) diammonium hydroxide titanium.

[0012] Preferably, the method for preparing the PVA aqueous solution in step (1) is as follows: PVA is added to deionized water to make the density of the PVA aqueous solution reach 0.2g / ml-0.4g / ml, and stirred at 80℃ for 4h;

[0013] Preferably, the crosslinking agent in step (1) is one of glutaraldehyde, glyoxal, formaldehyde, and boric acid, and the crosslinking agent added in step (1) is 10% of the volume of the PVA aqueous solution;

[0014] Preferably, the initiator in step (1) is concentrated hydrochloric acid, and the initiator added in step (1) is 5% of the volume of the PVA aqueous solution;

[0015] Preferably, the conditions for high-temperature calcination in the muffle furnace in step (2) include: a temperature of 800°C, a time of 2 hours, and an atmosphere of air;

[0016] Preferably, if the liquid organic polymer in step (3) is polyethylene or polypropylene in a molten state, its curing method is: heat treatment in a muffle furnace for 24 hours and then cooling; if the liquid organic polymer is uncured epoxy resin, its curing method is: adding epoxy resin curing agent, and the volume ratio is uncured epoxy resin: epoxy resin curing agent = 0.7-1.5.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: The ceramic-polymer composite membrane for selective separation of lithium ions and its preparation method of the present invention retain the complete LLTO three-dimensional framework, which allows lithium ions in the solution to selectively permeate under the action of an external electric field, thereby achieving the effect of efficient separation of lithium ions; at the same time, the ceramic-polymer composite membrane prepared by the present invention has high toughness, which greatly reduces the risk of membrane breakage during lithium extraction from sea brine. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the LLTO three-dimensional skeleton obtained in Embodiment 1 of the present invention;

[0019] Figure 2 This is a schematic diagram of the LLTO-epoxy resin composite film prepared in Example 1 of the present invention. Detailed Implementation

[0020] To better understand the content of this invention, the invention will be further described below with reference to specific embodiments and accompanying drawings. The following embodiments are based on the technology of this invention and provide detailed implementation methods and operating steps, but the scope of protection of this invention is not limited to the following embodiments.

[0021] This invention discloses a ceramic-polymer composite membrane for selectively separating lithium ions and its preparation method, wherein the ceramic is lithium lanthanum titanate (LLTO, chemical formula Li) with a three-dimensional structure. 0.35 La 0.65 TiO3), the continuous three-dimensional framework of LLTO allows lithium ions to pass through, thus enabling the separation of multiple cations. It can be effectively applied to systems for separating lithium resources from water bodies, such as lithium extraction from sea brine. This invention combines LLTO, which can selectively separate lithium ions, with an organic polymer. The resulting LLTO-polymer composite membrane can maintain high toughness without increasing thickness and does not affect the separation efficiency of lithium ions in the solution.

[0022] The present invention discloses a method for preparing a ceramic-polymer composite membrane for selectively separating lithium ions as follows:

[0023] (1) Preparation of precursor hydrogel by sol-gel method: LLTO precursor raw material is added to PVA (polyvinyl alcohol) aqueous solution and stirred evenly to obtain LLTO precursor suspension; then crosslinking agent with a volume of 10% of PVA aqueous solution and initiator with a volume of 5% of PVA aqueous solution are added, and the resulting solution is quickly poured into polytetrafluoroethylene mold to obtain precursor hydrogel (i.e. PVA-LLTO hydrogel).

[0024] The composition and molar ratio of the LLTO precursor raw material are LiNO3:La(NO3)3·6H2O:TALH = 0.7:1.3:2, where TALH is di(2-hydroxypropionic acid)diammonium dihydrogen phosphate titanium. The above data are the actual amounts of each component added. Because lithium will be lost during high-temperature calcination, the actual amount of LiNO3 added is 5wt% more than the calculated amount.

[0025] The method for preparing the PVA aqueous solution is as follows: PVA is added to deionized water to make the density of the PVA aqueous solution reach 0.2g / ml-0.4g / ml, and stirred at 80℃ for 4h.

[0026] The crosslinking agent is one of glutaraldehyde, glyoxal, formaldehyde, and boric acid, and the initiator is concentrated hydrochloric acid.

[0027] (2) Preparation of LLTO three-dimensional framework: Dry the PVA-LLTO hydrogel obtained in step (1), preferably by vacuum drying, forced air drying or freeze drying; put the dried PVA-LLTO hydrogel into a muffle furnace at 800℃ for high-temperature calcination for 2 hours, preferably by air, and after cooling, obtain LLTO with a three-dimensional framework structure, in which the three-dimensional framework is the lithium ion directional transport channel.

[0028] (3) Preparation of LLTO-polymer composite membrane with selective separation of lithium ions: Liquid organic polymer is poured onto the LLTO three-dimensional framework obtained in step (2). After complete curing, excess organic polymer is ground off until the LLTO three-dimensional framework is exposed, thus obtaining LLTO-polymer composite membrane with selective separation of lithium ions, i.e. ceramic-polymer composite membrane.

[0029] The liquid organic polymer is preferably polyethylene in a molten state, polypropylene in a molten state, or uncured epoxy resin. If the liquid organic polymer is polyethylene or polypropylene in a molten state, it needs to be heat-treated in a muffle furnace for 24 hours to allow it to cool and cure. If the liquid organic polymer is uncured epoxy resin, an epoxy resin curing agent needs to be added, and the volume ratio of the two is uncured epoxy resin: epoxy resin curing agent = 0.7-1.5.

[0030] The present invention will be further understood through specific embodiments below:

[0031] Example 1

[0032] (1) Preparation of precursor hydrogel by sol-gel method: 2g PVA was added to 10mL of deionized water, heated and stirred at 80℃ for 4h, and then 0.735mmol of LiNO3, 1.3mmol of La(NO3)3·6H2O and 2mmol of TALH were added to the solution and stirred evenly to obtain LLTO precursor suspension. Then, 1mL of glutaraldehyde and 0.5mL of concentrated hydrochloric acid were added to the LLTO precursor suspension. The resulting solution was quickly poured into a polytetrafluoroethylene mold to obtain PVA-LLTO hydrogel.

[0033] (2) Preparation of LLTO three-dimensional framework: After the PVA-LLTO hydrogel in step (1) was vacuum dried at 60℃ for 24h, it was placed in a muffle furnace and heat-treated at 800℃ for 2h at a heating rate of 1℃ / min. After cooling, LLTO with a three-dimensional framework was obtained.

[0034] (3) Preparation of composite film: Place the LLTO three-dimensional skeleton from step (2) on a silicone mold, then pour epoxy resin and epoxy resin curing agent into it. Mix the two in a volume ratio of 1:1. After it is completely cured, grind off the excess epoxy resin until the LLTO three-dimensional skeleton is exposed to obtain the LLTO-epoxy resin composite film.

[0035] Figure 1 This is a schematic diagram of the three-dimensional framework of LLTO, showing that lithium ions can pass through the pores inside the LLTO molecule. Figure 2 This is a schematic diagram of the LLTO-epoxy resin composite film prepared in this embodiment. It can be seen that under the action of external force, the LLTO-epoxy resin composite film can undergo large deformation, demonstrating excellent toughness.

[0036] Example 2

[0037] (1) Preparation of precursor hydrogel by sol-gel method: 3g PVA was added to 10mL of deionized water, heated and stirred at 80℃ for 4h, and then 0.735mmol of LiNO3, 1.3mmol of La(NO3)3·6H2O and 2mmol of TALH were added to the solution and stirred evenly to obtain LLTO precursor suspension. Then, 1mL of boric acid and 0.5mL of concentrated hydrochloric acid were added to the LLTO precursor suspension, and the resulting solution was quickly poured into a polytetrafluoroethylene mold to obtain PVA-LLTO hydrogel.

[0038] (2) Preparation of LLTO three-dimensional framework: After the PVA-LLTO hydrogel in step (1) was vacuum dried at 60℃ for 24h, it was placed in a muffle furnace and heat-treated at 800℃ for 2h at a heating rate of 1℃ / min. After cooling, LLTO with a three-dimensional framework was obtained.

[0039] (3) Place the LLTO three-dimensional skeleton from step (2) on a quartz crucible, then spread the excess polypropylene on the LLTO three-dimensional skeleton, place it in a muffle furnace and heat-treat at 175°C for 24 hours to allow the polypropylene to fully enter the LLTO three-dimensional skeleton. After it cools and solidifies, grind off the excess polypropylene until the LLTO three-dimensional skeleton is exposed to obtain an LLTO-polypropylene composite film.

[0040] Example 3

[0041] (1) Preparation of precursor hydrogel by sol-gel method: 4g PVA was added to 10mL of deionized water, heated and stirred at 80℃ for 4h, and then 0.735mmol of LiNO3, 1.3mmol of La(NO3)3·6H2O and 2mmol of TALH were added to the solution and stirred evenly to obtain LLTO precursor suspension. Then, 1mL of glyoxal and 0.5mL of concentrated hydrochloric acid were added to the LLTO precursor suspension, and the resulting solution was quickly poured into a polytetrafluoroethylene mold to obtain PVA-LLTO hydrogel.

[0042] (2) Preparation of LLTO three-dimensional framework: After the PVA-LLTO hydrogel in step (1) was vacuum dried at 60℃ for 24h, it was placed in a muffle furnace and heat-treated at 800℃ for 2h at a heating rate of 1℃ / min. After cooling, LLTO with a three-dimensional framework was obtained.

[0043] (3) Place the LLTO three-dimensional skeleton from step (2) on a quartz crucible, then spread the excess polyethylene on the three-dimensional skeleton, and place it in a muffle furnace for heat treatment at 135°C for 24 hours to allow the polyethylene to fully enter the LLTO three-dimensional skeleton. After it cools and solidifies, grind off the excess polyethylene until the LLTO three-dimensional skeleton is exposed to obtain an LLTO-polyethylene composite film.

[0044] The above description is merely a preferred embodiment of the present invention. The present invention may have other embodiments based on the above preparation method, which will not be listed hereafter. Therefore, any simple modifications, equivalent changes, and alterations made by those skilled in the art to the above embodiments without departing from the scope of the present invention's technical solution, based on the technical essence of the present invention, shall still fall within the scope of the present invention's technical solution.

Claims

1. A ceramic-polymer composite membrane for selectively separating lithium ions, characterized in that, It includes LLTO with a three-dimensional structure and an organic polymer; the organic polymer is polyethylene or polypropylene or cured epoxy resin. The method for preparing the ceramic-polymer composite membrane includes the following steps: (1) Preparation of precursor hydrogel by sol-gel method: LLTO precursor raw material is added to PVA aqueous solution and stirred evenly to obtain LLTO precursor suspension; after adding crosslinking agent and initiator, it is poured into polytetrafluoroethylene mold to obtain precursor hydrogel. (2) Preparation of LLTO three-dimensional framework: After drying the precursor hydrogel, it was placed in a muffle furnace for high-temperature calcination and cooled to obtain LLTO with a three-dimensional framework structure. (3) Preparation of LLTO-polymer composite membrane: Liquid organic polymer is poured onto the LLTO three-dimensional framework. After it is completely cured, the excess organic polymer is ground off until the LLTO three-dimensional framework is exposed, and the LLTO-polymer composite membrane is obtained.

2. The ceramic-polymer composite membrane for selectively separating lithium ions as described in claim 1, characterized in that, In step (1), the composition of the LLTO precursor raw material and the molar ratio of each component are LiNO3:La(NO3)3•6H2O:TALH=0.7:1.3:2, and the TALH is diammonium di(2-hydroxypropionic acid) hydroxide titanium.

3. A ceramic-polymer composite membrane for selectively separating lithium ions as described in claim 1, characterized in that, The method for preparing the PVA aqueous solution in step (1) is as follows: PVA is added to deionized water to make the density of the PVA aqueous solution reach 0.2 g / ml-0.4 g / ml, and stirred at 80℃ for 4 h.

4. The ceramic-polymer composite membrane for selectively separating lithium ions as described in claim 1, characterized in that, In step (1), the crosslinking agent is one of glutaraldehyde, glyoxal, formaldehyde, or boric acid, and the crosslinking agent added in step (1) is 10% of the volume of the PVA aqueous solution.

5. The ceramic-polymer composite membrane for selectively separating lithium ions as described in claim 1, characterized in that, In step (1), the initiator is concentrated hydrochloric acid, and the initiator added in step (1) is 5% of the volume of the PVA aqueous solution.

6. A ceramic-polymer composite membrane for selectively separating lithium ions as described in claim 1, characterized in that, The conditions for high-temperature calcination in the muffle furnace in step (2) include: a temperature of 800℃, a time of 2 h, and an atmosphere of air.

7. The ceramic-polymer composite membrane for selectively separating lithium ions as described in claim 1, characterized in that, If the liquid organic polymer in step (3) is polyethylene or polypropylene in a molten state, its curing method is: heat treatment in a muffle furnace for 24 hours and then cooling; if the liquid organic polymer is uncured epoxy resin, its curing method is: add epoxy resin curing agent, and the volume ratio is uncured epoxy resin: epoxy resin curing agent = 0.7-1.5.

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