CN114177775A - Salt lake lithium extraction nanofiltration membrane and preparation method and application thereof - Google Patents
Salt lake lithium extraction nanofiltration membrane and preparation method and application thereof Download PDFInfo
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Abstract
The invention discloses a nanofiltration membrane based on membrane separation-adsorption synergistic salt lake lithium extraction and a preparation method and application thereof, wherein an amino polymer one-step method in-situ modified polyimide nanofiltration membrane is used for preparing a loose polyimide nanofiltration membrane with positive electrical properties by an immersion precipitation phase conversion technology, a lithium ion sieve adsorbent is fixed on a supporting layer of the loose polyimide nanofiltration membrane by a dead-end filtration technology, and the finally obtained salt lake lithium extraction nanofiltration membrane has an average pore diameter smaller than 1nm, has excellent interception performance on magnesium ions, has a specific adsorption and permeation effect on lithium ions, and further improves the permeation rate of the lithium ions. Therefore, the separation efficiency of magnesium and lithium is greatly improved by the sieving effect of the nanofiltration membrane and the adsorption effect of the lithium ion sieve adsorbent; in addition, the preparation process of the nanofiltration membrane for extracting lithium from the salt lake is simple, the nanofiltration membrane has more stable lithium extraction efficiency, and can be widely applied to the fields of seawater, geothermal water and salt lake brine.
Description
Technical Field
The invention relates to the technical field of polymer membranes, and particularly relates to a nanofiltration membrane based on membrane separation-adsorption synergistic salt lake lithium extraction, and a preparation method and application thereof.
Background
With the rapid development of portable electronic equipment and electric automobile industries, the application of lithium in the field of new energy materials is increasingly prominent. The brisk development of the lithium battery industry in China brings opportunities to the lithium salt market, and the increasing demand of the lithium salt promotes the vigorous development of lithium resources. According to the classification of existence forms of lithium resources, the global lithium resources mainly include: the solid lithium ore and the salt lake brine lithium ore respectively account for 34 percent and 61 percent of the total reserve, and other types of lithium resources (such as oil fields, geothermal brine and the like) account for 5 percent. Therefore, the salt lake lithium in China is rich in resources, but the lithium salt production in China depends on imported lithium ores for a long time due to high magnesium-lithium ratio, high separation difficulty and high cost of the prior art. The three wastes generated in the process of extracting lithium from ore are high in yield, heavy in pollution and high in cost, salt lake lithium resources are fully utilized, the production cost is reduced, and the method is an urgent need for the development of new energy in China.
At present, the technology for extracting lithium from salt lake brine mainly comprises an evaporative crystallization method, a coprecipitation method, a solvent extraction method and an ion exchange method, and the most common method is the evaporative crystallization method. The evaporative crystallization method utilizes solar energy to evaporate and concentrate salt lake water to obtain lithium-containing mother liquor, and then carbonate is added into the lithium-containing mother liquor to separate lithium precipitate, so as to obtain a lithium carbonate product. However, the method is long in time consumption and easy to generate three wastes, and a large amount of carbonate is required to be added in the process of preparing the lithium carbonate, so that the production cost of lithium products is greatly increased.
Compared with the granular lithium ion sieve, the membrane-shaped lithium ion sieve has many advantages, namely, the membrane-shaped lithium ion sieve has great development potential in industrial application because the polymer membrane has elasticity and can be bent, wound or mutually superposed, the contact area with salt lake water is increased, and simultaneously the ion diffusion resistance is effectively reduced. The commonly used film forming agent mainly comprises PVC, poly alum, polyvinylidene fluoride, porous ceramic and the like. The lithium ion sieve membrane can increase the surface area contacted with salt lake water, is very convenient to apply, but the adsorption capacity and the adsorption rate of the lithium ion sieve can be reduced by film formation, and the phenomenon of damage or powder falling exists in the using process, so that pollution is easily caused, and the industrial application of the lithium ion sieve membrane is hindered.
Based on a separation membrane technology, the invention solves the problem of poor separation efficiency of the existing polymer by constructing a positively charged nanofiltration membrane and constructing a lithium ion permeation channel on a supporting layer thereof through a screening effect-adsorption effect, realizes high-efficiency lithium extraction, and has important social value and huge economic value of lithium resource recycling.
Disclosure of Invention
The first purpose of the invention is to provide a preparation method of a salt lake lithium extraction nanofiltration membrane based on membrane separation-adsorption synergy, the preparation method is simple in preparation process, low in material price, and toxic reagents are not involved in the experimental process.
The second purpose of the invention is to provide a salt lake lithium extraction nanofiltration membrane based on membrane separation-adsorption synergy, which has high magnesium ion interception efficiency, low lithium ion interception efficiency and large permeation flux.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a preparation method of a nanofiltration membrane for extracting lithium from a salt lake based on membrane separation-adsorption synergy comprises the following steps:
s1, completely dissolving the polyimide and the amino polymer, and obtaining the amino polymer modified polyimide nanofiltration membrane by an immersion precipitation phase inversion method;
s2, fixing the lithium ion sieve adsorbent into the bottom supporting layer of the prepared amino polymer modified polyimide nanofiltration membrane through a dead-end filtration technology to obtain the salt lake lithium extraction nanofiltration membrane with the supporting layer containing the lithium ion sieve adsorbent.
In the preparation method of the nanofiltration membrane based on membrane separation-adsorption synergy for lithium extraction in salt lake, firstly, polyimide and amino polymers are completely dissolved, and the modified polyimide nanofiltration membrane which takes polyimide as a base material and has positive electrical property of amino polymers growing in situ on the surface and in the interior is prepared by an immersion precipitation phase inversion method; and then, fixing the lithium ion sieve adsorbent into a bottom supporting layer of the modified polyimide nanofiltration membrane by using a dead-end filtration technology, and finally obtaining the salt lake lithium extraction nanofiltration membrane.
Polyimide is a polymer material with negative charge property, and is generally prepared by condensation reaction of dianhydride and diamine, and the polyimide nanofiltration membrane prepared by the polyimide nanofiltration membrane has the negative charge property, and is beneficial to adsorption and permeation of magnesium and lithium ions under the action of positive and negative charge attraction, so that the rejection rate is reduced; after the polyimide solution is modified by the amino polymer, the amino polymer has positive charges, so that the negative charge effect of the polyimide can be weakened, the content of amino substances is further increased, the polyimide and amino polymer blended membrane can have positive charges, the positive nanofiltration membrane has an electrostatic repulsion effect with magnesium lithium ions, the permeation of the magnesium lithium ions is not facilitated, the rejection rate is increased, meanwhile, a lithium ion sieve adsorbent in a nanofiltration membrane support layer has an adsorption effect on the lithium ions, and the efficient interception of the magnesium ions and the rapid permeation of the lithium ions can be realized through the construction of a lithium ion channel, so that the magnesium lithium separation and the lithium ion recovery are realized.
According to the invention, through an immersion precipitation phase conversion technology, an amino polymer is used for carrying out one-step method in-situ modification on a polyimide nanofiltration membrane to obtain a loose polyimide nanofiltration membrane with positive electric property, then a dead-end filtration technology is utilized to fix a lithium ion sieve adsorbent on a support layer of the polyimide nanofiltration membrane, and the salt lake lithium extraction nanofiltration membrane is further endowed with excellent specific adsorption and permeation effects on lithium ions. The preparation method is simple and efficient, and the prepared salt lake lithium extraction nanofiltration membrane is stable in performance, so that the magnesium-lithium separation efficiency is greatly improved.
Preferably, step S1 specifically includes: and (3) placing the amino polymer in a polyimide solution completely dissolved for reaction, and introducing the amino polymer in situ inside the membrane to obtain the amino polymer modified polyimide nanofiltration membrane.
Mixing the amino polymer and the polyimide, and introducing the amino polymer into the polyimide membrane in situ by an immersion precipitation phase conversion method to obtain the polyimide nanofiltration membrane with electropositive surface and interior. The in-situ growth method further ensures the stability of the modified polyimide membrane, and further endows the salt lake lithium-extracting nanofiltration membrane with stable magnesium ion interception efficiency.
Preferably, step S2 specifically includes: and (4) placing the amino polymer modified polyimide nanofiltration membrane obtained in the step (S1) on a dead-end filtering device, and sequentially carrying out filtering fixation, water washing and drying on a lithium ion sieve adsorbent to obtain the salt lake lithium extraction nanofiltration membrane of which the supporting layer contains the lithium ion sieve adsorbent.
In step S2, first, the lithium ion sieve adsorbent is ground, pulverized, and dispersed with an aqueous solution to prepare an aqueous solution of the lithium ion sieve adsorbent; then, the amino polymer modified polyimide nanofiltration membrane is placed on a dead-end filtering device, under the action of pressure difference, the aqueous solution of the lithium ion sieve adsorbent is circulated, and then the lithium ion sieve adsorbent is fixed on a supporting layer of the modified polyimide nanofiltration membrane.
It should be noted here that, because the pore diameter of the polyimide nanofiltration membrane skin layer is in the nanometer level, even under the action of high pressure, the retention of the lithium ion sieve adsorbent in the membrane pores of the support layer can be ensured.
Preferably, in step S1, the amino polymer includes any one or a combination of more of aminated silica, aminated titanium dioxide, tetraethyl orthosilicate, and tetrabutyl titanate.
Preferably, when the amino polymer is tetraethyl orthosilicate or tetraethyl titanate, a catalyst and a silane coupling agent are needed, wherein the catalyst is any one or combination of hydrochloric acid, acetic acid and sulfuric acid, and the silane coupling agent is KH 550.
Specifically, the amino polymer herein may be the aminated silica nanoparticles or aminated titania nanoparticles as they are, or may be the aminated silica nanoparticles or aminated titania nanoparticles produced by hydrolysis and condensation of tetraethyl orthosilicate or tetrabutyl titanate in the presence of an acidic catalyst and a KH550 silane coupling agent.
Preferably, the concentration of the polyimide solution is 16-24 wt%;
preferably, the solvent for dissolving the polyimide comprises any one or a combination of N-methylpyrrolidone, N-dimethylformamide and N, N-dimethylacetamide;
preferably, when the polyimide is dissolved, the stirring time is controlled to be 3-12 h, and the temperature is controlled to be 60-120 ℃.
The polyimide is a polymer with excellent thermal stability and solvent stability, soluble polyimide is selected as a raw material to be dissolved, and research shows that when the concentration of a polymer solution is lower than 16 wt%, the strength of the nanofiltration membrane prepared by using a lower solution concentration is poor, and the nanofiltration membrane is not beneficial to practical use; when the concentration of the polymer solution is higher than 24 wt%, the aperture of the nanofiltration membrane prepared by higher solution concentration is smaller, and the flux is sharply reduced; in the preparation process of the membrane casting solution, when the temperature is lower than 60 ℃, the phenomenon of incomplete polymer dissolution can occur, and a uniform nanofiltration membrane cannot be prepared; when the temperature is higher than 120 ℃, the polymer can be completely dissolved, but too high a dissolution temperature is not favorable for practical operation.
Preferably, the concentration of the amino polymer is 15 to 25 wt%;
preferably, the stirring time is controlled to be 3 to 6 hours when the amino polymer is dissolved.
Preferably, in step S2, the lithium ion sieve adsorbent includes any one or more of an aluminum-based lithium ion sieve, a manganese-based lithium ion sieve and a titanium-based lithium ion sieve
The adsorption method can extract lithium from the salt lake brine with high magnesium-lithium ratio, and can be divided into an organic ion exchange adsorbent and an inorganic ion exchange adsorbent according to the properties of the adsorbents, the organic ion exchange resin generally has low selectivity on lithium, and the method selects an aluminum-series lithium ion sieve, a manganese-series lithium ion sieve and a titanium-series lithium ion sieve which have high selectivity on lithium, and can realize selective adsorption of lithium from a dilute solution.
Preferably, the concentration of the lithium ion sieve adsorbent is 1-10 wt%.
The salt lake lithium extraction nanofiltration membrane prepared by the preparation method of the invention also belongs to the protection scope of the invention, and preferably, the interception efficiency of the nanofiltration membrane on magnesium ions is higher than 99%, the interception efficiency on lithium ions is lower than 20%, and the permeation flux of the nanofiltration membrane on lithium ion solution is higher than 40L/(m) per m2·h)。
The application of the salt lake lithium extraction nanofiltration membrane based on the membrane separation-adsorption synergy also belongs to the protection scope of the invention, and particularly, the salt lake lithium extraction nanofiltration membrane comprises but is not limited to the application thereof in the treatment of seawater, geothermal water and salt lake brine.
Compared with the prior art, the invention has the following advantages:
1. compared with the interfacial polymerization technology, the preparation method of the nanofiltration membrane for extracting lithium from the salt lake is formed by a one-step phase inversion technology, realizes the high-efficiency separation of magnesium and lithium ions based on the synergistic action of membrane separation and adsorption, has simple preparation process, stable structure and easy operation, and is beneficial to realizing industrial large-scale production;
2. according to the preparation method of the salt lake lithium extraction nanofiltration membrane, the amino polymer is introduced, so that the negatively charged nanofiltration membrane is successfully modified into the positively charged nanofiltration membrane, and the loose polyimide nanofiltration membrane with the positive electric property has excellent interception performance on magnesium ions under electrostatic repulsion;
3. according to the preparation method of the salt lake lithium extraction nanofiltration membrane, the lithium ion sieve adsorbent is introduced into the modified polyimide nanofiltration membrane supporting layer, so that a specific transfer channel of lithium ions in the membrane is constructed, the permeation flux of a lithium ion solution is favorably improved, and the magnesium-lithium separation efficiency is greatly improved;
4. according to the preparation method of the salt lake lithium extraction nanofiltration membrane, the size of the membrane pores is accurately regulated and controlled based on the size of lithium ions, so that the separation of the lithium ions from other ions is realized, and particularly, the lithium ions exist in an aqueous solution in the form of a hydration layer, and the membrane pores of the separation membrane are accurately regulated and controlled to be near 0.8nm (close to the lithium ion hydration diameter) by the salt lake lithium extraction nanofiltration membrane obtained by the preparation method, so that the separation of the lithium ions from multivalent ions can be effectively realized, and the efficiency is higher;
5. compared with powder, the nanofiltration membrane prepared by the preparation method of the nanofiltration membrane for extracting lithium from the salt lake solves the problems of fine particle size and poor fluidity of powder adsorbents, and has wide application value;
6. the salt lake lithium extraction nanofiltration membrane prepared by the invention has the interception rate of magnesium ions higher than 99% and the interception rate of lithium ions lower than 20%, so that the magnesium and lithium ions can be efficiently separated by the interception difference of the salt lake lithium extraction nanofiltration membrane on the magnesium and lithium ions.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.
FIG. 1 is a schematic cross-sectional field emission scanning of a polyimide nanofiltration membrane;
FIG. 2 is a schematic cross-sectional field emission scan of an amino polymer modified polyimide nanofiltration membrane;
FIG. 3 is a schematic view of surface field emission scanning of a nanofiltration membrane for extracting lithium from a salt lake;
Detailed Description
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present application. As used herein, the singular forms also include the plural forms unless the context clearly dictates otherwise, and further, it is understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of the stated features, steps, operations, devices, components, and/or combinations thereof.
The technical solutions of the present invention will be described clearly and completely with reference to the following embodiments, and it should be understood that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
(1) Drying the polyimide polymer at 120 ℃, and dewatering for later use; dissolving 20 wt% of polyimide in N-methyl pyrrolidone, stirring and dissolving for 6 hours at 100 ℃, adding 20 wt% of aminated silica nanoparticles after the polyimide raw material is completely stirred and dissolved, continuously stirring and dissolving for 5 hours to obtain a uniform membrane casting solution, standing, defoaming and scraping the membrane to obtain an aminated silica modified polyimide polymer membrane with a loose porous structure;
(2) preparing a 500nm titanium lithium ion sieve solution with the concentration of 5 wt%, and fixing the titanium lithium ion sieve in the pores of the supporting layer membrane in a dead-end filtration mode to obtain the aminated silicon dioxide modified polyimide nanofiltration membrane containing the titanium oxide lithium ion sieve in the loose porous supporting layer.
Example 2
(1) Drying the polyimide polymer at 120 ℃, and dewatering for later use; dissolving 16 wt% of polyimide in N, N-dimethylformamide, stirring and dissolving for 3 hours at the temperature of 60 ℃, adding 15 wt% of aminated silica nanoparticles after the polyimide raw material is completely stirred and dissolved, continuously stirring and dissolving for 3 hours to obtain a uniform membrane casting solution, standing, defoaming and scraping the membrane to obtain an aminated silica modified polyimide polymer membrane with a loose porous structure;
(2) preparing a 300nm titanium lithium ionic sieve solution with the concentration of 1 wt%, and fixing the titanium lithium ionic sieve in the pores of the supporting layer membrane in a dead-end filtration mode to obtain the aminated silicon dioxide modified polyimide nanofiltration membrane containing the titanium oxide lithium ionic sieve in the loose porous supporting layer.
Example 3
(1) Drying the polyimide polymer at 120 ℃, and dewatering for later use; dissolving 24 wt% of polyimide in N, N-dimethylacetamide, stirring and dissolving at 120 ℃ for 12 hours, adding 25 wt% of aminated titanium dioxide nanoparticles after the polyimide raw material is completely stirred and dissolved, continuously stirring and dissolving for 6 hours to obtain a uniform membrane casting solution, standing, defoaming and scraping the membrane to obtain an aminated titanium dioxide modified polyimide polymer film with a loose porous structure;
(2) preparing a 2-micron titanium-based lithium ion sieve solution with the concentration of 10 wt%, and fixing the titanium-based lithium ion sieve in the pores of the supporting layer membrane in a dead-end filtration mode to obtain the aminated titanium dioxide modified polyimide nanofiltration membrane containing the titanium oxide lithium ion sieve in the loose porous supporting layer.
Example 4
(1) Drying the polyimide polymer at 120 ℃, and dewatering for later use; dissolving 22 wt% of polyimide in N-methylpyrrolidone, stirring and dissolving for 7 hours at 80 ℃, adding 18 wt% of tetraethyl orthosilicate, 1 wt% of hydrochloric acid and 1 wt% of KH550 after the polyimide raw material is completely stirred and dissolved, continuously stirring and dissolving for 4 hours to obtain a uniform membrane casting solution, standing, defoaming and scraping the membrane to obtain an aminated silicon dioxide modified polyimide polymer film with a loose porous structure;
(2) preparing a 1-micron aluminum lithium ion sieve solution with the concentration of 8 wt%, and fixing the aluminum lithium ion sieve in the pores of the supporting layer membrane in a dead-end filtration mode to obtain the aminated silicon dioxide modified polyimide nanofiltration membrane containing the aluminum oxide lithium ion sieve in the loose porous supporting layer.
Example 5
(1) Drying the polyimide polymer at 120 ℃, and dewatering for later use; dissolving 16 wt% of polyimide in N-methyl pyrrolidone, stirring and dissolving for 9 hours at 80 ℃, adding 20 wt% of tetrabutyl titanate, 0.5 wt% of sulfuric acid and 1 wt% of KH550 after the polyimide raw material is completely stirred and dissolved, continuously stirring and dissolving for 5 hours to obtain a uniform membrane casting solution, standing, defoaming and scraping the membrane to obtain an aminated titanium dioxide modified polyimide polymer film with a loose porous structure;
(2) preparing a 600nm aluminum lithium ion sieve solution with the concentration of 5 wt%, and fixing the aluminum lithium ion sieve in the pores of the supporting layer membrane in a dead-end filtration mode to obtain the aminated titanium dioxide modified polyimide nanofiltration membrane containing the aluminum oxide lithium ion sieve in the loose porous supporting layer.
Example 6
(1) Drying the polyimide polymer at 120 ℃, and dewatering for later use; dissolving 17 wt% of polyimide in N, N-dimethylacetamide, stirring and dissolving at 80 ℃ for 6 hours, adding 20 wt% of tetrabutyl titanate, 1 wt% of sulfuric acid and 1 wt% of KH550 after the polyimide raw material is completely stirred and dissolved, continuously stirring and dissolving for 5 hours to obtain a uniform membrane casting solution, standing, defoaming and scraping the membrane to obtain an aminated titanium dioxide modified polyimide polymer film with a loose porous structure;
(2) preparing a 600nm titanium lithium ion sieve solution with the concentration of 5 wt%, and fixing the titanium lithium ion sieve in the pores of the supporting layer membrane in a dead-end filtration mode to obtain the aminated titanium dioxide modified polyimide nanofiltration membrane containing the titanium oxide lithium ion sieve in the loose porous supporting layer.
Example 7
(1) Drying the polyimide polymer at 120 ℃, and dewatering for later use; dissolving 21 wt% of polyimide in N, N-dimethylformamide, stirring and dissolving for 6 hours at 80 ℃, adding 20 wt% of tetrabutyl titanate, 1 wt% of acetic acid and 1 wt% of KH550 after the polyimide raw material is completely stirred and dissolved, continuously stirring and dissolving for 5 hours to obtain a uniform membrane casting solution, standing, defoaming and scraping to obtain an aminated titanium dioxide modified polyimide polymer film with a loose porous structure;
(2) preparing 900nm titanium lithium ion sieve solution with the concentration of 8 wt%, and fixing the titanium lithium ion sieve in the supporting layer membrane hole in a dead-end filtration mode to obtain the aminated titanium dioxide modified polyimide nanofiltration membrane containing the titanium oxide lithium ion sieve in the loose porous supporting layer.
Example 8
(1) Drying the polyimide polymer at 120 ℃, and dewatering for later use; dissolving 19 wt% of polyimide in N, N-dimethylacetamide, stirring and dissolving for 6 hours at 80 ℃, adding 15 wt% of tetrabutyl titanate, 1 wt% of sulfuric acid and 1 wt% of KH550 after the polyimide raw material is completely stirred and dissolved, continuously stirring and dissolving for 5 hours to obtain a uniform membrane casting solution, standing, defoaming and scraping to obtain an aminated titanium dioxide modified polyimide polymer film with a loose porous structure;
(2) preparing a 600nm titanium lithium ion sieve solution with the concentration of 5 wt%, and fixing the titanium lithium ion sieve in the pores of the supporting layer membrane in a dead-end filtration mode to obtain the aminated titanium dioxide modified polyimide nanofiltration membrane containing the titanium oxide lithium ion sieve in the loose porous supporting layer.
Example 9
(1) Drying the polyimide polymer at 120 ℃, and dewatering for later use; dissolving 16 wt% of polyimide in N-methyl pyrrolidone, stirring and dissolving for 6 hours at 80 ℃, adding 25 wt% of tetrabutyl titanate, 2 wt% of sulfuric acid and 5 wt% of KH550 after the polyimide raw material is completely stirred and dissolved, continuously stirring and dissolving for 5 hours to obtain a uniform membrane casting solution, standing, defoaming and scraping to obtain an aminated titanium dioxide modified polyimide polymer film with a loose porous structure;
(2) preparing a 400nm titanium lithium ion sieve solution with the concentration of 5 wt%, and fixing the titanium lithium ion sieve in the pores of the supporting layer membrane in a dead-end filtration mode to obtain the aminated titanium dioxide modified polyimide nanofiltration membrane containing the titanium oxide lithium ion sieve in the loose porous supporting layer.
Example 10
(1) Drying the polyimide polymer at 120 ℃, and dewatering for later use; dissolving 24 wt% of polyimide in N-methyl pyrrolidone, stirring and dissolving for 6 hours at 80 ℃, adding 20 wt% of tetrabutyl titanate, 2 wt% of hydrochloric acid and 5 wt% of KH550 after the polyimide raw material is completely stirred and dissolved, continuously stirring and dissolving for 5 hours to obtain a uniform membrane casting solution, standing, defoaming and scraping to obtain an aminated titanium dioxide modified polyimide polymer film with a loose porous structure;
(2) preparing a 10 wt% titanium-based lithium ion sieve solution with the concentration of 1.5 mu m, and fixing the titanium-based lithium ion sieve in the pores of the supporting layer membrane in a dead-end filtration mode to obtain the aminated titanium dioxide modified polyimide nanofiltration membrane containing the titanium oxide lithium ion sieve in the loose porous supporting layer.
Comparative example 1
(1) Drying the polyimide polymer at 120 ℃, and dewatering for later use; dissolving 20 wt% of polyimide in N-methyl pyrrolidone, stirring and dissolving for 6 hours at 100 ℃, adding 20 wt% of aminated silica nanoparticles after the polyimide raw material is completely stirred and dissolved, continuously stirring and dissolving for 5 hours to obtain a uniform membrane casting solution, standing, defoaming and scraping the membrane to obtain an aminated silica modified polyimide polymer membrane with a loose porous structure;
comparative example 2
(1) Drying the polyimide polymer at 120 ℃, and dewatering for later use; dissolving 20 wt% of polyimide in N-methyl pyrrolidone, stirring and dissolving for 6 hours at 100 ℃, obtaining a uniform membrane casting solution after the polyimide raw material is completely stirred and dissolved, standing, defoaming and scraping the membrane to obtain an aminated silicon dioxide modified polyimide polymer film with a loose porous structure;
(2) preparing a 500nm titanium lithium ion sieve solution with the concentration of 5 wt%, and fixing the titanium lithium ion sieve in the pores of the supporting layer membrane in a dead-end filtration mode to obtain the aminated silicon dioxide modified polyimide nanofiltration membrane containing the titanium oxide lithium ion sieve in the loose porous supporting layer.
In order to research the magnesium-lithium separation performance of the modified polyimide nanofiltration membrane prepared by the invention, the magnesium-lithium separation performance of the modified polyimide nanofiltration membrane is tested by using a cross-flow filtering device self-made in a laboratory, the ion concentration is tested by using inductively coupled plasma emission spectroscopy (ICP), and the interception efficiency of magnesium ions can be obtained by calculation. Table 1 shows the permeation flux, the magnesium ion rejection performance, and the lithium ion concentration performance of the nanofiltration membranes prepared in the examples and the comparative examples.
TABLE 1 magnesium-lithium separation performance of nanofiltration membranes prepared in examples and comparative examples
From the test results in table 1, it can be seen that the salt lake lithium extraction nanofiltration membrane prepared by the invention has excellent permeation flux and magnesium ion rejection at room temperature of 25 ℃, the lithium ion permeation efficiency is high, the nanofiltration membrane prepared by the experimental parameters in example 1 based on the membrane separation-adsorption effect has the best performance, and the magnesium and lithium ion rejection rates are 99.43% and 20.12% respectively.
Compared with the comparative example 1, when the support layer of the nanofiltration membrane is not modified by the lithium ion molecular sieve, the rejection rate of the lithium ion of the prepared nanofiltration membrane is relatively high due to charge repulsion, and the rejection rate is only maintained at 40.01%;
compared with the comparative example 2, when the amino polymer modification is not carried out on the supporting layer of the nanofiltration membrane, the magnesium ion interception efficiency is poor and is only 85.43% due to the attraction effect of positive and negative charges because the membrane substrate is in the negative charge property, so that the magnesium-lithium separation efficiency is low, and the lithium ion recovery is not facilitated.
In addition, in order to further verify the retention performance of the salt lake lithium extraction nanofiltration membrane on magnesium ions, the aperture sizes of the polyimide nanofiltration membrane, the amino polymer modified polyimide nanofiltration membrane and the salt lake lithium extraction nanofiltration membrane are observed by using a field emission scanning electron microscope, as shown in fig. 1-3, wherein as can be seen from fig. 3, the average aperture of the salt lake lithium extraction nanofiltration membrane prepared by the method is smaller than 1nm, and the aperture size of the separation membrane is accurately regulated and controlled to be close to 0.8nm, so that the separation of lithium ions and multivalent ions can be effectively realized.
In conclusion, the loose polyimide nanofiltration membrane with positive electric property is prepared by using an amino polymer one-step method in-situ modified polyimide nanofiltration membrane through an immersion precipitation phase conversion technology, and then a lithium ion sieve adsorbent is fixed on a supporting layer of the loose polyimide nanofiltration membrane through a dead-end filtration technology, so that the finally obtained salt lake lithium extraction nanofiltration membrane has an average pore diameter smaller than 1nm, excellent interception performance on magnesium ions and specific adsorption and permeation effects on lithium ions. Therefore, the salt lake lithium extraction nanofiltration membrane prepared by the method is based on the synergistic effect of membrane separation and adsorption, so that the magnesium-lithium separation efficiency is greatly improved.
Claims (10)
1. A preparation method of a nanofiltration membrane for extracting lithium from a salt lake based on membrane separation-adsorption synergy is characterized by comprising the following steps:
s1, completely dissolving the polyimide and the amino polymer, and obtaining the amino polymer modified polyimide nanofiltration membrane by an immersion precipitation phase inversion method;
s2, fixing the lithium ion sieve adsorbent into the bottom supporting layer of the prepared amino polymer modified polyimide nanofiltration membrane through a dead-end filtration technology to obtain the salt lake lithium extraction nanofiltration membrane with the supporting layer containing the lithium ion sieve adsorbent.
2. The preparation method of the nanofiltration membrane based on membrane separation-adsorption synergy for lithium extraction from salt lake according to claim 1, wherein the step S1 specifically comprises: and (3) placing the amino polymer in a polyimide solution completely dissolved for reaction, and introducing the amino polymer in situ inside the membrane to obtain the amino polymer modified polyimide nanofiltration membrane.
3. The preparation method of the nanofiltration membrane based on membrane separation-adsorption synergy for lithium extraction from salt lake according to claim 1, wherein the step S2 specifically comprises: and (4) placing the amino polymer modified polyimide nanofiltration membrane obtained in the step (S1) on a dead-end filtering device, and sequentially carrying out filtering fixation, water washing and drying on a lithium ion sieve adsorbent to obtain the salt lake lithium extraction nanofiltration membrane of which the supporting layer contains the lithium ion sieve adsorbent.
4. The method for preparing the nanofiltration membrane based on membrane separation-adsorption synergy salt lake lithium extraction, according to claim 2, wherein in the step S1, the amino polymer comprises any one or more of aminated silica, aminated titanium dioxide, tetraethyl orthosilicate and tetrabutyl titanate;
preferably, when the amino polymer is tetraethyl orthosilicate or tetraethyl titanate, a catalyst and a silane coupling agent are added simultaneously, wherein the catalyst comprises any one or more of hydrochloric acid, acetic acid and sulfuric acid, and the silane coupling agent is KH 550.
5. The preparation method of the nanofiltration membrane based on membrane separation-adsorption synergy salt lake lithium extraction, according to claim 2, wherein in the step S1, the concentration of the polyimide solution is 16-24 wt%;
preferably, the solvent for dissolving the polyimide comprises any one or a combination of N-methylpyrrolidone, N-dimethylformamide and N, N-dimethylacetamide;
preferably, when the polyimide is dissolved, the stirring time is controlled to be 3-12 h, and the temperature is controlled to be 60-120 ℃.
6. The preparation method of the nanofiltration membrane based on membrane separation-adsorption synergy salt lake lithium extraction, according to claim 2, wherein in the step S1, the concentration of the amino polymer is 15-25 wt%;
preferably, the stirring time is controlled to be 3 to 6 hours when the amino polymer is dissolved.
7. The method for preparing the nanofiltration membrane based on membrane separation-adsorption synergy salt lake lithium extraction, according to claim 3, wherein in the step S2, the lithium ion sieve adsorbent comprises any one or more of an aluminum-based lithium ion sieve, a manganese-based lithium ion sieve and a titanium-based lithium ion sieve.
8. The preparation method of the nanofiltration membrane based on membrane separation-adsorption synergy salt lake lithium extraction, wherein in the step S2, the concentration of the lithium ion sieve adsorbent is 1-10 wt%.
9. A nanofiltration membrane based on membrane separation-adsorption synergistic salt lake lithium extraction, which is prepared by the preparation method according to any one of claims 1 to 8;
preferably, the rejection efficiency of the nanofiltration membrane on magnesium ions is higher than 99%, and the rejection efficiency on lithium ions is lower than 20%;
preferably, the permeation flux of the nanofiltration membrane to the lithium ion solution is higher than 40L/(m)2·h)。
10. An application of a nanofiltration membrane for extracting lithium from a salt lake based on the synergy of membrane separation and adsorption is characterized in that the nanofiltration membrane is applied to the treatment of seawater, geothermal water or salt lake brine.
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