KR20150106329A - Composite nanofiber membrane for adsorbing lithium, method of manufacturing the same and apparatus and method for recovering lithium using the same - Google Patents

Abstract

The present invention relates to a composite nanofiber film for adsorbing lithium, a method for manufacturing the same, a lithium recollection method and a lithium recollection apparatus using the same. More specifically, the present invention relates to a composite nanofiber film for adsorbing lithium on which manganese oxide capable of selectively absorbing lithium is immobilized, a method for manufacturing the same, a lithium recollection method and a lithium recollection apparatus using the same. The composite nanofiber film for adsorbing lithium has high selectivity with respect to lithium ions and enables lithium ions to be easily and quickly diffused through an inner space of an adsorbent at the same time. Especially, the lithium recollection apparatus using the composite nanofiber film for adsorbing lithium can selectively and efficiently adsorb lithium ions existing in seawater within a short time and can easily and quickly attach and detach the lithium ions to and from the adsorbent by acid treatment.

Description

TECHNICAL FIELD The present invention relates to a composite nanofiber membrane for lithium adsorption, a method for producing the composite nanofiber membrane, a lithium recovery apparatus using the same, and a method for recovering lithium from the lithium nanofibrous membrane. BACKGROUND ART

The present invention relates to a composite nanofiber membrane for lithium adsorption, a method for producing the composite nanofiber membrane, a lithium recovery apparatus and a lithium recovery method using the same, and more particularly, to a composite nanofiber membrane for lithium adsorption with a manganese oxide immobilized thereon, , A production method thereof, a lithium recovery apparatus using the same, and a lithium recovery method.

In recent years, demand for lithium used as a main component of a battery capable of storing high-efficiency energy has been rapidly increasing due to rapid development of electric vehicles, demand for portable electronic appliances such as smart phones and tablet PCs, and recovery of lithium from natural resources Interest is focused on. As a result, research is currently underway to find other alternative sources, such as the sea, which contains an enormous amount of lithium, approximately 2.5 x 10 ¹⁴ kg, taking into account global energy consumption trends. However, the concentration of lithium contained in seawater is about 0.17 mg / L, which is very small compared to the concentration of other cations. Therefore, in order to recover lithium resources from seawater, it is required to use a technique highly selective for lithium ions.

To date, the most reliable method of recovering lithium ions from seawater is the recovery of lithium through adsorption. Recently, various ionic manganese oxide powders (lithium ion-sieves) derived from lithium manganese oxides such as spinel-type manganese oxides have been developed and used as lithium adsorbents. However, ionic manganese oxides present in small size powder form are difficult to handle in industrial applications and have a disadvantage in terms of reuse because of the large loss of adsorbent in the adsorption / desorption process.

In order to overcome such disadvantages, recently, researches have been actively carried out to develop a support for fixing the ion-type manganese oxide powder and to facilitate the use thereof. Currently, polyvinyl chloride (PVC), polyvinyl alcohol (PVA), polysulfone (PSf), polyurethane (PU), polyvinylidene fluoride (PVDF) A method of producing a composite lithium adsorbent in various forms such as granules, beads, membranes and foams by using various polymer materials such as a binder, etc. as a binder of manganese oxide powder, etc. However, in order to optimize the adsorbents more efficiently, it is necessary to continuously study the method of lowering the manufacturing cost, minimizing the generation of secondary wastewater in the manufacturing process, and improving the adsorption ability at the same time.

Korean Patent Publication No. 10-2005-0045792 Korean Patent Publication No. 10-2005-0045793

The present invention provides a composite nanofiber membrane manufacturing method for lithium adsorption capable of selectively adsorbing lithium ions from seawater and a composite nanofiber membrane for lithium adsorption prepared by the above method.

The present invention also provides a lithium recovery apparatus and a lithium recovery method using the composite nanofibrous film for lithium adsorption produced by the above method.

According to an embodiment of the present invention, there is provided a lithium recovery apparatus comprising: preparing a viscous solution by mixing a lithium-manganese oxide adsorbing powder and a polymer material in a solvent; And a step of electrospinning the viscous solution to produce a composite nanofiber membrane, wherein the dissolved lithium in the seawater is adsorbed on the membrane, A filtration tank in which a process of desorbing lithium using an acid solution is performed; A supply tank for supplying seawater to the filtration tank; A drain tank through which the seawater subjected to the lithium adsorption process is discharged and accommodated in the filtration tank; And a recovery tank for supplying an acid solution to the filtration tank subjected to the lithium adsorption process and recovering a solution containing lithium desorbed by the supplied acid solution.

 A liquid transfer pump may be further provided between the filtration tank and the discharge tank, and between the filtration tank and the recovery tank.

The lithium niobate composite nanofiber film may be detached and attached to a filtration tank.

The lithium composite nanofiber membrane may be a flat-sheet type filtration membrane having micron-sized pores.

The lithium niobate composite nanofiber film may further include a heat treatment step.

The electrospun composite nanofiber membrane has an advantage that it has a very large surface area per unit area, but on the contrary, it has a disadvantage that the mechanical strength is weak because of the large porosity. In order to overcome such disadvantages, a nanofiber film having excellent strength can be obtained by inducing physical binding (bonding) between the nanofibers by heat-treating the produced nanofiber film.

It is preferable that the heat treatment step is performed in a temperature range lower than the melting point of the polymer material.

In the heat-treating step, the thickness and the average pore size of the lithium-absorbing composite nanofibrous film to be produced can be controlled by performing the heat treatment of one or more sheets of the nanofibers. That is, the step of heat-treating is a step of heat-treating one or more of the nanofiber membranes and controlling the thickness and the average pore size of the composite nanofiber membrane for lithium adsorption prepared by controlling the number of the nanofibers to be heat- .

The composite nanofiber membrane for adsorbing lithium may be manufactured by further comprising an acid treatment for activating the lithium adsorption site or for imparting lithium adsorption performance to the composite nanofiber membrane. When an acid aqueous solution is added to the composite nanofibrous film, lithium is replaced with hydrogen to become a manganese oxide, thereby activating the lithium adsorption site, thereby efficiently adsorbing lithium. Here, the lithium adsorption site means a portion where lithium can be adsorbed in the composite nanofiber film. The acid treatment can be carried out by dipping the membrane in dilute acid. For example, a method of immersing in hydrochloric acid of about 0.5M for a day, or the like.

The lithium-manganese oxide adsorbing powder may include at least one selected from the group consisting of Li _1.6 Mn _1.6 O ₄ , Li _1.33 Mn _1.67 O ₄ , LiMn ₂ O ₄ and LiMnO ₂ . However, the present invention is not limited thereto, and known powders that can be used as a lithium adsorbent are also applicable.

The lithium-manganese oxide adsorbing powder treated with an acid by the lithium-manganese oxide adsorbing powder may be used. In this case, it may be unnecessary to carry out an acid treatment for activating the lithium adsorption site or for imparting lithium adsorption performance to the composite nanofiber membrane. The acid-treated lithium-manganese oxide adsorption powder may include at least one selected from the group consisting of H _1.6 Mn _1.6 O ₄ , H _1.33 Mn _1.67 O ₄ , HMnO ₂ and HMn ₂ O ₄ .

The lithium-manganese oxide adsorption powder may be added in an amount of 15 to 65 wt% based on the total weight of the polymer and the adsorbent powder. When the catalyst is added in the above range, adsorption performance can be more effectively improved.

The lithium-manganese oxide powder used in the production of the polymer composite nanofiber film preferably has an average diameter of 5 탆 or less, more preferably a powder having a diameter of 1 탆 or less. If the diameter of the powder is too large, the mechanical properties of the nanofiber may be deteriorated, and the powder may be easily separated from the nanofiber during the recovery of lithium.

The polymeric material may be selected from the group consisting of polysulfone, polyethersulfone, polyacrylonitrile, polyvinylidene fluoride, cellulose acetate, and polyvinyl chloride. , Or a combination of one or more polymers, and may preferably be a polysulfone or polyacrylonitrile. Polysulfone or polyacrylonitrile has been most widely used in the manufacture of membranes, and the price of polymers is also advantageous. In addition, it is excellent in chemical resistance and durability and is suitable for producing a composite nanofiber film. However, the present invention is not limited to the polymer candidates listed above, but can be applied as a material for manufacturing composite nanofibers if the polymer is electrospun.

In the present invention, the polymer nanofibers can serve as a binder for the lithium-manganese oxide adsorbent powder. According to the present invention, it is possible to facilitate the handling of the lithium-manganese oxide adsorbent powder by fixing the adsorbent powder in the polymer nanofibers by electrospinning the polymer solution to which the lithium-manganese oxide adsorbing powder is added.

The solvent may include at least one member selected from the group consisting of dimethylformamide, dimethylformaldehyde, tetrahydrofuran, dimethylacetamide and methylpyrrolidone, preferably dimethylformaldehyde and tetrahydrofuran, It may be used in combination or dimethylformamide may be used.

The amount of the polymer for carrying out the electrospinning process is not limited as long as a solution having a weight ratio suitable for the kind of the solvent and the type of the polymer is prepared. However, in preparing the polymer solution for producing the nanofiber, the content of the polymer relative to the solvent is preferably 15 to 25% by weight, and more preferably 18 to 25% by weight.

When a solution having a polymer weight ratio of less than 15% is prepared by electrospinning, the viscosity of the polymer solution is too low to form a bead-like structure. Such a nanofiber shape may impair the porosity and surface area of the nanofiber have. When a polymer solution having a polymer content of 15 to 25% on the opposite side is electrospun, a spherical fiber is not formed, a nanofiber form is well formed and an appropriate mechanical strength can be exhibited.

Generally, nanofibers electrospun are advantageous in maximizing the surface area of the nanofibers as the diameter of the nanofibers is smaller. However, if the diameter of the nanofibers is too small, the mechanical strength of the nanofibers deteriorates. Therefore, the diameter of the nanofibers is preferably in the range of 200 to 2000 nm.

The diameter and the shape of the nanofiber are affected by the viscosity of the polymer solution, but also by the electrospinning conditions. For example, increasing the release rate of the polymer solution increases the diameter of the nanofiber, and conversely, increasing the distance between the spinning nozzle and the sample take-up drum or increasing the electrical conductivity of the polymer solution decreases the diameter of the fiber. Therefore, optimization of the spinning conditions is also important to produce nanofibers in the diameter range desired to be obtained from the electrospinning of the polymer solution.

A lithium recovery method according to an embodiment of the present invention is a lithium recovery method using a lithium recovery apparatus manufactured by the above method, comprising: acid treating a lithium-adsorbed nanofiber membrane provided in a filtration tank; Introducing seawater into a filtration tank provided with a composite nanofiber membrane for lithium adsorption treated with acid from a feed tank storing seawater, and passing the membrane through the membrane to adsorb lithium; Discharging the seawater having passed through the filtration tank to the discharge tank and supplying an acid solution to the filtration tank to desorb the lithium adsorbed on the membrane to perform a desorption process of lithium; And a desorption process is performed to transfer the acid solution in which lithium is dissolved to the recovery tank.

The step of acid-treating the lithium-adsorbing nanofiber membrane provided in the filtration tank is performed for activation of the lithium adsorption site or for imparting lithium adsorption performance to the composite nanofiber membrane. In the acid treatment step, the acid treatment is carried out by desorbing the membrane and immersing it in a dilute acid solution for a certain period of time, and then the acid treated membrane is put back in the filtration tank. Alternatively, a dilute acid solution is filtered and circulated in the membrane- And extracting lithium ions from lithium manganese oxide. Other details of the acid treatment are the same as those described in the above lithium recovery apparatus and therefore will not be described here.

However, the step of acid-treating the lithium-adsorbing nanofiber membrane provided in the filtration tank may be omitted in the case of using the composite nanofiber membrane produced by using the acid-treated lithium-manganese oxide adsorbing powder.

According to another embodiment of the present invention, there is provided a method for preparing a composite nanofiber membrane for lithium adsorption, comprising the steps of: (a) preparing a viscous solution by mixing a lithium-manganese oxide adsorbent powder and a polymer material in a solvent; And electrospinning the viscous solution to produce a composite nanofiber film (step b).

The manufacturing method may further include a step of acid-treating the composite nanofibrous film prepared by electrospinning a viscous solution. It is possible to activate the lithium adsorption site of the composite nanofiber membrane or impart the lithium adsorption performance to the composite nanofiber membrane by the acid treatment step.

 The manufacturing method further includes a step of heat-treating the one or more nanofiber membranes before the acid treatment step after step b, and the step of heat-treating the nanofibers is performed by adjusting the number of the nanofiber membranes to be heat- The thickness and the average pore size can be controlled.

The heat-treating step may be performed for enhancing mechanical properties of the produced composite nanofiber membrane for adsorbing lithium.

The lithium-manganese oxide adsorbing powder may include at least one selected from the group consisting of Li _1.6 Mn _1.6 O ₄ , Li _1.33 Mn _1.67 O ₄ , LiMn ₂ O ₄ and LiMnO ₂ .

The lithium-manganese oxide adsorption powder may be an acid-treated lithium-manganese oxide adsorption powder. When the acid-adsorbed powder is used, the acid treatment step for activating the lithium adsorption site of the composite nanofiber membrane or for imparting the lithium adsorption performance to the composite nanofiber membrane may be omitted. The acid-treated lithium-manganese oxide adsorption powder may include at least one selected from the group consisting of H _1.6 Mn _1.6 O ₄ , H _1.33 Mn _1.67 O ₄ , HMnO ₂ and HMn ₂ O ₄ .

The polymeric material may be selected from the group consisting of polysulfone, polyethersulfone, polyacrylonitrile, polyvinylidene fluoride, cellulose acetate, and polyvinyl chloride. , Or a combination of one or more polymers.

The solvent may include at least one member selected from the group consisting of dimethyl formaldehyde, tetrahydrofuran, dimethylacetamide and methylpyrrolidone.

The solvent and the polymer material may be mixed at 85 to 75 wt%: 15 to 25 wt%.

In the step of preparing the viscous solution by mixing the lithium-manganese oxide adsorbent powder and the polymer material in a solvent, the lithium-manganese oxide adsorbent powder may be added in an amount of 45 to 55% by weight based on the total weight of the polymer and the adsorbent powder .

Other details of the method for producing a composite nanofiber membrane for adsorbing lithium are the same as those described in the above lithium recovery apparatus, and thus will not be described here.

According to an embodiment of the present invention, there is provided a composite nanofiber film for lithium adsorption produced by the above method, wherein the composite nanofibrous film for lithium adsorption is characterized in that manganese oxide is immobilized in the nanofiber.

According to the present invention, it is possible to manufacture a composite nanofiber membrane for lithium adsorption which is easy to handle and minimizes the deterioration of the adsorbed powder by fixing the manganese oxide adsorption powder to the nanofiber film having a large surface area per unit area. Further, by applying an appropriate heat treatment step, a composite nanofiber membrane for lithium adsorption having characteristics of high mechanical properties can be manufactured.

The composite nanofiber membrane for lithium adsorption according to the present invention has a high selectivity for lithium ions, and allows diffusion of lithium ions to be quickly and easily performed in the space between the adsorbents. In addition, the composite nanofiber membrane according to the present invention is easier to contact with water than the polymer membrane, foam, ceramic membrane or the like on which the conventional manganese oxide-based adsorbent is immobilized, outstanding. Further, since the composite nanofibrous membrane according to the present invention is a porous membrane, lithium can be recovered by simply dipping it in a solution without additional filtration pressure or energy consumption during the lithium adsorption process.

In particular, the lithium recovery apparatus using the composite nanofibrous membrane for lithium adsorption according to the present invention can efficiently adsorb lithium ions present in the seawater in a short period of time and shorten the adsorption process time. Further, according to the present invention, it is possible to switch to the acid treatment step immediately after the lithium ion adsorption step without moving the adsorbent during the acid treatment required for the lithium ion desorption process, and the desorption process of lithium ions can be performed easily and quickly.

In addition, the composite nanofiber membrane provided in the recovery apparatus can be used not only for selectively adsorbing lithium ions from seawater but also for pretreatment for removing large particles in a pretreatment step of a desalination plant using a reverse osmosis membrane It can also be used as a filter. Therefore, when the composite nanofiber membrane for lithium ion adsorption according to the present invention is used as a pretreatment filter for seawater desalination, the lithium ion can be selectively recovered while performing the action of removing large particles, which is very advantageous in terms of economy.

1 is a schematic view of a lithium recovery apparatus according to the present invention.
2 is an image obtained by observing the morphology of the composite nanofiber membrane produced according to Example 1-1 with an electron microscope analyzer.
FIG. 3 is an image obtained by mapping the surface of the composite nanofibrous film prepared according to Example 1-1 and observing with an electron microscope analyzer.
4 is a graph comparing tensile strengths and elongation changes of membranes prepared according to Examples 1-1 to 1-4.
5 and 6 are graphs showing breakthrough times of lithium adsorption efficiency according to the filtration flow rate in the lithium recovery process using the lithium recovery apparatus according to the present invention.
7 is a breakthrough curve showing the relationship between the thickness of the composite nanofiber film and the lithium adsorption capacity according to the present invention.
8 is a breakthrough curve of the results of lithium adsorption / desorption experiments using the lithium recovery apparatus according to the present invention.
FIG. 9 shows the results of lithium adsorption / desorption experiments using the lithium recovery apparatus according to the present invention in terms of the amount of lithium ions adsorbed and the amount of desorption according to the number of steps.
10 is an XRD diffraction pattern and SEM image of LiMnO ₂ , LMO (L _1.6 Mn _1.6 O ₄ ) and HMO (H _1.6 Mn _1.6 O ₄ ) powders.
11 is a graph showing particle size distribution diagrams of LMO and HMO powder.
12 is an optical image of an HMO / PAN (H _1.6 Mn _1.6 O ₄ / polyacrylonitrile) composite nanofiber film and a PAN nanofiber film; SEM-EDX pattern of HMO / PAN composite nanofiber film.
13 is an SEM image of an HMO / PAN composite nanofiber membrane and a pure PAN nanofiber membrane having HMO loading amounts of 20, 40 and 60 wt%.
14 shows the wettability of HMO / PAN, HMO / PSf, and HMO / PVDF composite nanofibers.
FIG. 15 is a graph showing the mechanical properties of HMO / PAN composite nanofiber membranes and pure PAN nanofiber membranes having HMO loading amounts of 20, 40 and 60 wt%.
16 shows the equilibrium adsorption test results of HMO powder, HMO / PAN (HMO loading amount 20 wt%) composite nanofiber membrane, and pure PAN nanofiber membrane. (a) Adsorption capacity versus lithium ion concentration (b) pH vs. lithium ion concentration.
17 is a graph comparing the adsorption capacity of lithium ions of HMO powder and HMO / PAN (HMO loading 20 wt%) composite nanofiber membrane (adsorption capacity versus time).
18 is adsorption isotherms of HMO powder and HMO / PAN composite nanofiber membranes (at 298 K): (a) Freundlich (b) Langmuir.
19 shows the result of testing the possibility of recycling HMO / PAN (HMO loading amount 60 wt%) composite nanofiber membrane. (a) lithium divorce adsorption / desorption value (b) the pH value of the solution.
20 is a graph showing the amount (%) of manganese eluted from the HMO / PAN (HMO loading amount 60 wt%) composite nanofiber membrane during the recycling test.
21 is a graph comparing the lithium ion adsorption capacity with other cations in seawater desalination retentate using HMO powder and HMO / PAN (HMO loading amount 60 wt%) composite nanofiber membrane.
FIG. 22 is a schematic view of manufacturing an HMO / PSf (H _1.6 Mn _1.6 O ₄ / polysulfone, MO / PSf) composite nanofiber film using electrospinning.
23 is a graph comparing the mechanical properties of the HMO / PSf composite nanofiber film and the PSf nanofiber film before and after the heat treatment.
24 is an SEM image of an HMO / PSf (MO / PSf) composite nanofiber film and a PSf nanofiber film.
25 shows EPMA element mapping and WDS analysis results of the HMO / PSf (MO / PSf) composite nanofiber membrane.
26 is a graph comparing the diameters of the HMO / PSf composite nanofiber membrane and the PSf nanofiber membrane.
27 is a graph showing the results of thermogravimetric analysis of LiMnO ₂ , LMO and HMO powders.
28 is a graph showing the results of thermogravimetric analysis of the HMO / PSf composite nanofiber film and the PSf nanofiber film.
29 is a graph (V = 340 mL; m is about 50 mg; [Li ⁺ ] = 1 mM (7 mgL ^-1 )) in relation to the lithium ion adsorption capacity and pH of the HMO powder.
30 compares the lithium ion adsorption capacity of the HMO powder and the HMO / PSf composite nanofiber membrane. (a) Mixed solution of unbuffered solutions (pH = 10), lithium ions and other cations (M ^{n +} = Na ⁺ , K ⁺ , Mg ²⁺ , Ca ²⁺ ) [Li ⁺ ] = 1 mM (7 mgL ^-1 ); [M ^{n +} ] = 10 mM (pH = 10), pure aqueous ammonia buffered solutions Ammoniacal buffered solutions (pH = 9.75; V = 340 mL, m = approximately 50 mg) were mixed with lithium ions and other cations (M ^{n +} = Na ⁺ , K ⁺ , Mg ²⁺ , Ca ²⁺ ) ; [Li ⁺ ] = 1 mM (7 mgL ^-1 ); [M ^{n +} ] = 10 mM). (b) a graph showing a comparison of the competitive ion adsorption amount (ammoniacal buffered pH = 9.75; V = 340 mL; m is about ^{50 mg;. [Li +]} = 1mM (7mgL -1) (c) HMO / PSf composite nano (% Q _e losses) of the ion adsorption capacity of the fibrous membrane.
31 compares the results of lithium ion adsorption of the HMO powder and the HMO / PSf composite nanofiber membrane. (a) The graphs are compared under different lithium ion concentrations. (b) a graph comparing the initial pH and the equilibrium pH. (c) a graph showing an equilibrium lithium adsorption linear model (Langmuir fit). (d) Equilibrium lithium adsorption linear model (Freundlich fit) (pH = 11.08; V = 340 mL;
32 compares the lithium ion adsorption kinetic results of the HMO powder and the HMO / PSf composite nanofiber membrane.
FIG. 33 is a graph showing a comparison between the mechanical properties of the HMO / PSf composite nanofibers having different thicknesses and the permeability properties of the dead-end filtration experiment (b) )to be.
34 is a graph showing the results of wave adsorption experiments of HMO / PSf composite nanofiber membranes in ν (different superficial velocities) using seawater: (a) Li ⁺ permeate concentration vs. time and% Li ⁺ removal profile vs time; (b) The breakthrough curve of the HMO / PSf composite nanofiber membrane (C _p / C _f vs time) (inset: t _ex (exhaustion time) vs ν); (c) breakthrough curve of HMO / PSf composite nanofiber membrane in terms of V _p (permeate volume) (inset: N vs ν, V _ex = total V _{p at} 95% composite nanofiber membrane saturation C _p / C _f = 0.95); (d) A graph showing the relationship between Thomas model coefficients and q _int values.
35 is a graph showing a method of calculating the adsorption capacity (q _int ) through an integration method.
FIG. 36 is a graph showing the results of a wave and lithium ion adsorption experiment of an HMO / PSf composite nanofiber membrane in V _m (different membrane volumes) using seawater: (a) the breakthrough curve of an HMO / PSf composite nanofiber membrane _ex vs V _m ); (b) a graph showing the relationship between the thickness (z) and the TMP of the composite nanofiber film; _{(c) V p (permeate volume} ) HMO in view / PSf hybrid nanofiber film breakthrough curves _{(inset: N vs V m,} V ex = total V p at 95% hybrid nanofiber membrane saturation C _p / C _f = 0.95 ); (d) A graph showing the relationship between Thomas model coefficients and q _int values.
37 shows the results of analyzing the performance of HMO / PSf composite nanofiber membranes in a dead-end flow through system for lithium ion recovery from seawater; (a) a graph showing the relationship between TMP and cumulative volume treated (V _T ) under controlled flow rates of feed or acid leaching solution; (b) the breakthrough curve of (Na ⁺ , K ⁺ , Mg ²⁺ , Ca ²⁺ ), which exists at a high concentration in the lithium ion and seawater, (c) the breakthrough curve during one to five cycles; d) A graph comparing the amount of lithium ion adsorption and the amount of desorption in each cycle from 1 to 5 times.

Hereinafter, the present invention will be described in more detail with reference to the drawings and examples. The objects, features and advantages of the present invention will be readily understood by the following drawings and examples. The embodiments disclosed herein are provided to enable those skilled in the art to sufficiently understand the spirit of the present invention. Therefore, the scope of the present invention should not be limited by the following drawings and examples.

Hereinafter, the present invention will be described in more detail with reference to FIG.

The lithium recovery apparatus 100 according to an embodiment of the present invention includes a filtration tank 120 having a composite nanofiber membrane 121 for adsorbing lithium, which absorbs lithium dissolved in the seawater introduced into the nanofiber membrane, A filtration tank 120 in which a process of desorbing lithium is performed using the supplied acid solution; A feed tank 110 for supplying seawater to the filtration tank 120; A discharge tank 140 through which the seawater subjected to the lithium adsorption process is discharged and accommodated in the filtration tank 120; And a recovery tank 130 for supplying an acid solution to the filtration tank 120 subjected to the lithium adsorption process and recovering the solution containing lithium desorbed by the supplied acid solution. The lithium recovery apparatus 100 may further include a liquid transfer pump 150.

When the lithium recovery apparatus 100 is used, the adsorption process is performed, and then the desorption process by the acid treatment proceeds, and the process can be proceeded to the acid treatment process without moving the adsorbent, thereby enabling convenient and efficient lithium recovery.

<Example 1: Preparation of composite nanofiber membrane for LMO / PSf lithium adsorption>

Example 1-1

In order to prepare Li _1.6 Mn _1.6 O ₄ (LMO) used as an adsorbent powder in the present invention, lithium manganese (LiMnO 2, average diameter: <1 μm,> 99% trace metals basis) manufactured by Sigma-Aldrich was used Respectively. Lithium manganese oxide (LiMnO ₂ ) was used as a reactant to obtain Li _1.6 Mn _1.6 O _4. To obtain Li _1.6 Mn _1.6 O ₄ , LiMnO ₂ was heat-treated at 450 ° C. for 4 hours in an air atmosphere To give the product.

Polysulfone (Solvay solexsis, Udel P-3500) polymer was used for the fabrication of composite nanofiber membranes. For electrospinning, dimethylformaldehyde and tetrahydrofuran were mixed as a solvent at a volume ratio of 2: 1. Polysulfone was dissolved in a prepared mixed solvent at a mass ratio of 18:82, and Li _1.6 Mn _1.6 O ₄ was added thereto in a weight ratio of 50% of the weight of the polymer (polysulfone, PSf) and stirred at room temperature. Composite nanofiber membranes were prepared. The electrospinning process was carried out in the following manner. The distance between the nozzle and the drum winding machine was set to 120 mm, and then the polymer solution was discharged at a delivery speed of 4 m / h at a supply voltage of 20 kv. At this time, a nozzle having a nozzle size (OD) of 0.51 mm was used.

The prepared nanocomposite fiber was dried in a vacuum oven at 60 ° C. for 12 hours or more in order to completely remove the solvent remaining in the fiber. Then, in order to enhance the mechanical properties of the prepared composite nanofiber, Minute heat treatment. In order to observe the morphology of the thus-prepared membrane, BSE (back-scattered electrons) method was observed using an electron microscope analyzer (EPMA), and the results are shown in FIG. As shown in Fig. 2, it can be confirmed that Li _1.6 Mn _1.6 O ₄ powder is well dispersed and fixed in the nanofiber. For more accurate analysis, manganese (Mn) and oxygen (O) elements were observed by mapping the surface of the membrane. The results are shown in FIG. As shown in Fig. 1, it can be confirmed that Li _1.6 Mn _1.6 O ₄ powder is evenly distributed throughout the nanofibers.

Examples 1-2 to 1-4

The composite nanofibers were prepared under the same conditions as in Example 1-1 except for the heat treatment conditions. In Example 1-2, a composite nanofiber membrane was prepared by laminating two sheets of nanofiber sheets, pressing both sides with a Teflon plate, and heat-treating the sheet at 190 DEG C for 90 minutes. In Examples 1-3 and 1-4, a composite nanofiber film was prepared by laminating three or four sheets of nanofiber sheets, respectively, and then pressing both sides with a Teflon plate, followed by heat treatment at a temperature of 190 ° C for 90 minutes.

&Lt; Test Example 1: Physical property test of composite nanofiber film >

The properties of composite nanofibers were measured according to their thickness. The average pore diameter, the bubble point diameter, the film thickness, the tensile strength (MPa), and the elongation percentage (%) were measured in order to observe the change in the physical properties of the membrane prepared according to Examples 1-1 to 1-4. (%) Were measured. The mean pore diameter and bubble point diameter were measured using a capillary flow porometer (PMI), and tensile strength and elongation were measured using a universal testing machine (UTM).

Table 1 shows the analysis results of mean pore diameter, bubble point diameter and film thickness.

The average pore diameter and bubble point diameter decreased as the membrane thickness increased. From the average pore size distribution graph, it was confirmed that the membrane having the thickness of 0.195 mm (Example 1-1) exhibited the largest average pore diameter, and the thicker the membrane, the smaller the pore diameter was. Comparing Sample T1 (Example 1-1) with Sample T4 (Example 1-4), when the thickness of the membrane increased more than twice from 0.195mm to 0.555mm, the average pore size of the sample was reversed from 3.792㎛ to 1.806㎛ Fold decrease. It can be seen that as the thickness of the membrane becomes complicated, the size of the matrix passing through the cross section becomes smaller as the matrix becomes complicated as the thickness of the membrane is assumed to be homogeneous. According to the present invention, The thickness and the average pore size can be adjusted.

[Table 1]

The measurement results of the tensile strength and elongation against the heat treated composite nanofiber film thickness are shown in FIG. As the overall thickness of the sample increased, the tensile strength tended to be similar or slightly increased. The tensile strength at the time of Example 1-1 (0.195 mm, T1) was 4.7 MPa, and in the case of the sample having a thickness larger than that, the tensile strength was 5.0 to 5.2 MPa. Elongation ratios were almost the same as those in Examples 1-1 to 1-3, but were decreased to about 30% in Examples 1-4 (T4).

<Test Example 2: Analysis of Lithium Adsorption Efficiency by Filtration Flow Rate During Lithium Recovery Using Lithium Recovery Device>

The composite nanofiber membrane prepared according to Example 1-1 was prepared by cutting into a circle having a diameter of 60 mm (surface area = 28.27 cm ² ) in order to mount the membrane in a filtration tank (Amicon cell 8200, Amicon Corporation, USA). The prepared membrane was immersed in a 0.5M HCl solution to activate the lithium adsorption site and subjected to acid treatment for one day to extract lithium. The acid-treated membrane was mounted on a filtration tank, a peristaltic pump was connected to the filtration tank, and negative pressure (-) was induced so that the influent water was filtered by the composite membrane.

The filtered water filtered from the membrane was collected in a vessel via a pump and the flow rate was measured by the amount of filtered water per unit time. The filtration rates were 17 g / hr and 39 g / hr, respectively. In order to observe the change in lithium concentration, the filtered water was taken at a fixed interval of 10 mL and analyzed by inductively coupled plasma mass spectrometer (ICP-MS). The raw water (lithium solution) used in the experiment was prepared by adding LiCl to RO circulating water (C _Li = about 0.3 mg / L) generated from a seawater desalination plant to prepare a sea water solution having a lithium concentration of 3 mg / L .

In order to explain the lithium recovery behavior according to the change of the filtration flow rate, the change depending on the contact time (filtration time) of the lithium solution and the adsorbent and the discharge water volume is shown by a breakthrough as shown in FIG. 5 and FIG. FIG. 5 shows a breakthrough curve according to contact time of raw water filtration under different filtration flow conditions. In the case of the sample operated at the filtration flow rate of 17 g / hr, breakthrough of lithium (0.05 C ₀ ) occurred within 2 hours after the start of operation (effluent volume: 33.7 mL), and after 48 hours the adsorption saturation point It reached a C / C ₀ = 0.95). (Where C is the effluent lithium ion concentration (mg / L), C ₀ indicates the influent lithium ion concentration (mg / L).) However, the filtration flow rate of 39g / hr in the adsorption was a breakthrough in less than 30 minutes after the operation started 28 hours after the It was confirmed that when the flow rate of the raw water was increased by reaching the saturation point, the contact time until the breakthrough curve reached the adsorption point was shortened. In Fig. 6, the breakthrough curve is shown as the volume of the effluent. The two breakthrough curves are almost identical. Thus, when increasing the filtration rate of the raw water from 17 g / hr to 39 g / hr in recovering lithium, it can be confirmed that the time for recovering the same amount of lithium can be shortened without affecting the breakthrough curve.

&Lt; Test Example 3: Test of lithium adsorption ability according to composite nanofiber film thickness >

In order to measure the lithium adsorption capacity of the membrane prepared according to Examples 1-1 to 1-4, the membrane was cut into a circle having a diameter of 42 mm (surface area = 17.15 cm ² ), and then immersed in a 0.5 M HCl solution (100 mL) 0.0 &gt; 30 C &lt; / RTI &gt; for 24 hours. The acid-treated specimens were washed several times with DI water, mounted on a lithium recovery apparatus, operated at a filtration rate of 39 g / hr, and 10 ml of a sample was periodically collected by an inductively coupled plasma mass spectrometer , ICP-MS) to determine the concentration of lithium. RO circulation water (Li conc. = 3 mg / L, pH 8) was used as the raw water used in the experiment.

The results of the evaluation of the lithium adsorption ability by the influence of the thickness of the composite nanofiber film are shown by a breakthrough curve according to the contact time in FIG. As shown in FIG. 7, as the composite membrane was thicker, the time for reaching the exhaustion time (C / C ₀ = 0.95) of the adsorption capacity by the adsorbent was gradually extended. Basically, thicker specimens contain more lithium adsorption sites and therefore require a longer time to reach the adsorption depletion point.

&Lt; Test Example 4: Lithium adsorption / desorption test using lithium recovery apparatus >

The adsorption and desorption experiments of lithium by composite nanofiber membranes were carried out five times in total, and the possibility of continuous use was evaluated. In the above experiment, a sample in which two nanofibers were stacked and heat-treated in accordance with Example 1-2 was used for circulation experiments. The heat-treated samples were immersed in 0.5 M HCl solution (100 mL) and acid-treated at 30 ° C for 24 hours. The raw water used in the experiment was carried out in a drying oven at a temperature of 30 ° C using RO circulation (Li conc. = 3 ppm). In the adsorption process for recovering lithium, the flow rate of the raw water through the membrane was fixed at 39 g / hr, and a total of 468 mL of raw water was passed through the membrane for 12 hours. After the adsorption process was completed, the filtered water was collected to measure the concentration of lithium, and the DI water was filtered at a flow rate of 350 g / hr for one hour in order to wash raw water remaining in the composite nanofiber membrane. The adsorbed lithium from the composite membrane was desorbed by acid treatment. Acid treatment was carried out by circulating 100 mL of 0.5 M HCl solution at a flow rate of 350 g / hr for 10 hours and measuring the lithium concentration of the acid solution to calculate the extraction amount. After the acid treatment, the membrane was washed again with DI water for one hour at a flow rate of 350 g / hr, and then the adsorption process was performed again.

The results of the cycle test of the composite membrane using the adsorption / desorption process are shown in FIGS. 8 and 9 and Table 2. Figure 8 shows breakthrough curves for a total of five adsorption / desorption processes (A in the graph represents adsorption and D represents desorption). It can be confirmed that all of the adsorption processes reach the vicinity of adsorption (C / C ₀ = 0.95) within 12 hours. The breakthrough curves of the five adsorption processes were almost identical. As shown in FIG. 9 and Table 2, as the number of adsorption / desorption processes was increased, the adsorption capacity of the lithium adsorbent was slightly increased or decreased. In general, the amount of lithium eluted from the desorption process was more or less than the adsorption amount. This is because the lithium contained in the seawater remaining in the membrane, although washed with water after the adsorption process, was also eluted during the desorption process. The amount of lithium ion adsorbed by the first adsorption step was 8.94 mg Li.sup. + / GMO, and the amount of adsorption was 5.71 mg at 5 times, showing only a decrease in the adsorption amount of less than 3%. As a result, polysulfone (PSf) / manganese oxide (MO) Membrane In the process of desorption / desorption, manganese oxide (MO) is chemically stabilized by polysulfone (PSf), which acts as a binder, so that it can be used many times over a long period of time.

[Table 2]

1) Calculated from lithium ion concentration in influent and effluent.

2) The amount of lithium ions leached.

&Lt; Example 2: Preparation of HMO / PAN composite nanofiber membrane >

Sample Preparation

The adsorbent precursor was purchased from Sigma-Aldrich (Mo., USA), LiMnO ₂ (lithium manganese dioxide,> 99% trace metal basis, particle size <1 μm). Polymeric binder PAN (poly (acrylonitrile), MW = 150,000 g / mole) was purchased from Sigma-Aldrich (Mo., USA). DMF (Dimethylformamide> 99.5%) purchased from Junsei Chemical Co., Ltd., Japan was used as a solvent for the PAN solution (dope solution). The hydrochloric acid (HCl, RHM 35-37%) and nitric acid (RHM 60% HNO ₃ ) of heavy metal grades purchased from Junsei Chemical Co., Ltd. are Li _1.6 Mn _1.6 Lt; RTI ID = 0.0 &gt; O &lt; / RTI &gt; ₄ and acid digestion. Lithium hydroxide (LiOH, ≥98%) purchased from Sigma-Aldrich and lithium chloride (LiCl, ≥98%) purchased from Fluka (Switzerland) were used for the preparation of lithium ion (Li ⁺ ) solution for adsorption experiments. All chemicals were used without further purification.

H _1.6 Mn _1.6 O ₄ Adsorbent manufacturing

Commercial high purity grade LiMnO ₂ was used as a precursor for the preparation of H _1.6 Mn _1.6 O ₄ . LiMnO ₂ was heat-treated in a furnace ramped at 10 ° C / min and held at 450 ° C in air for 4 hours. The cooled Li _1.6 Mn _1.6 O ₄ product (LMO) was pulverized with mortar and pestle and Standard Testing Sieve No. 1 was used to obtain more uniform particles. 200 (Aperture = 75 mm, Chung Gye Sang, Seoul Korea). LMO (1.5 g) was dispersed in 2 L of 0.5 M HCl solution to promote depolymerization of LMO through Li ⁺ / H ⁺ ion exchange. After 1 day of leaching, the final product H _1.6 Mn _1.6 O ₄ (HMO) was collected via vacuum filtration and then repeatedly washed with deionized (DI) water to remove residual acid and dried in an oven at 30 ° C . The dried HMO adsorbent was recovered using a filter paper, weighed and then used for nanofiber manufacture or in a desiccator.

HMO / PAN (H _1.6 Mn _1.6 O ₄ / Polyacrylonitrile) composite nanofiber membrane manufacturing

40, and 60 wt% of H _1.6 Mn _1.6 O ₄ (HMO) adsorbent powder, respectively, based on the total weight of polyacrylonitrile (PAN) and H _1.6 Mn _1.6 O ₄ (HMO) adsorbent powder to be added to the solvent Was added to the dimethylformamide solvent, and the mixture was stirred at 60 ° C for 2 hours to disperse. Polyacrylonitrile was added thereto and dissolved for 4 hours. The mixture was further reacted at room temperature for 4 hours to prepare a viscous solution (dope solution) Respectively.

The polyacrylonitrile is preferably added in a weight ratio of 1: 9 based on the solvent. However, the weight ratio of the polyacrylonitrile to the solvent may be varied depending on the kind of the polymer added to the solvent.

15 mL of the viscous solution (dope solution) was taken in a polypropylene syringe (20 mL), connected to a syringe pump (KD Scientific 750, South Korea) with a needle having an inner diameter of 0.51 mm, (PAN / H _1.6 Mn _1.6 O ₄ ) was prepared by an electrospinning device (Model: ESP200D / ESP100D, NanoNC Co., Ltd., South Korea) while supplying a viscous solution to the mixed nanofiber membrane. At this time, the voltage was controlled at 22 ~ 25V. The optimal distance between the needles and the collector for forming well-structured nanofibers was determined to be 100 mm. A drum-roll type nanofiber collector was rotated at 500 rpm to achieve a uniform mesh thickness. The resulting nanofibers were vacuum-dried at 60 ° C for one day and stored in moisture-free zip-lock bags. For the experiments, the samples were cut to the required dimensions and weighed (see Table 3).

[Table 3] Nanofiber film manufacturing conditions

&Lt; Example 3: Preparation of HMO / Psf composite nanofiber membrane >

And the other conditions were the same as those in Example 2. The results are shown in Table 1. &lt; tb &gt; &lt; TABLE &gt;

&Lt; Example 4: Preparation of HMO / PVDF composite nanofiber membrane >

And the other conditions were the same as those in Example 2. The results are shown in Table 1. &lt; tb &gt;&lt; TABLE &gt;

&Lt; Comparative Example 1: Production of PAN nanofiber membrane >

H _1.6 Mn _1.6 O ₄ (HMO) adsorbed powder was prepared and pure PAN nanofibers were prepared in the same manner as above.

&Lt; Test Example 5: Evaluation of physical properties of HMO / PAN composite nanofiber film >

Structural characterization of HMO samples prepared using an X-ray diffractometer (PANalytical X'pert-Pro, The Netherlands) using a Cu Kα source was analyzed. The analysis was performed at a slow step scan rate (3 s, 0.02 step in 2q / count) at 40kV and 30mA of beam voltage and current, respectively. Surface morphologies of HMO and PAN nanofibers (Pt coating) were observed by scanning electron microscopy (SEM-EDX, Hitachi S-3500N, Japan) equipped with energy dispersive X-ray spectroscopy. The mechanical properties of the nanofibers were measured using a universal testing machine (UTM LFPlus, Lloyd Instruments, UK) equipped with a 1 KN load cell. A sample (20 mm x 50 mm) was preloaded to 0.02 kg-f and analyzed at a cross-head speed of 50 mm / min. The pore size distribution of the nanofiber sheet was confirmed using a capillary flow porometer (CFP-1200AE, Porous Materials, Inc., USA). (15.9 dynes / cm) as a wetting agent in a dry-up / wet-up mode. The true densities of the materials produced using the pycnometer method were measured. Bulk density, porosity and water absorption capacity were measured according to known methods. Nanofiber diameters were measured by SEM image processing using SigmaScan Pro 4.0 software.

The actual HMO loading in the HMO / PAN was determined by thermo-gravimetry using a digital muffle furnace (Wiser Therm FP05, Germany). To dissolve the PAN, the water-free HMO / PAN sample, which had been weighed in advance, was heat-treated at 700 ° C and 10 ° C / min for 4 hours. The difference in mass before and after thermal degradation was regarded as the HMO content.

Inductively coupled plasma mass spectrometry (ICP-MS Agilent 7500 series, USA) was used for the analysis of HMO element composition using ultra high purity argon (99.999%) as carrier gas.

10 is a result of analyzing the morphology of adsorbed powder using XRD and SEM. 11 shows the particle size distribution of the adsorbed powder. The heat treated LMO particles were found to have a clearer edge contour than the precursor LiMnO ₂ and a larger average particle size. This suggests that there was some particle growth and aggregation during calcination. After the acid treatment, the HMO particles showed a cubic shape and a tendency similar to the particle size distribution of LiMnO ₂ (see FIG. 11). The morphologies of the prepared LMO and HMO were confirmed to be almost the same.

Successful preparation of HMO from commercial LiMnO ₂ via heat treatment and delithiation was confirmed from the XRD results and is shown in FIG. The XRD pattern of LiMnO ₂ was almost identical to that reported in the prior literature. This can be indexed with an orthorhombic crystal system (JCPDS No. 35-0749) with a Pmnm space group. LiMnO ₂ was heat-treated at 450 ° C to obtain cubic Li _1.6 Mn _1.6 O ₄ or LMO having a lattice constant a = 8.19 Å. The de-lithiated LMO or HMO exhibited a similar pattern, which could be indexed with a face-centered cubic system with a lattice constant a = 8.06.. An XRD pattern similar to LMO and HMO shows that it was topotactically replaced with H ⁺ instead of Li ⁺ during acid treatment. This explains that the crystal structure of the adsorbent has hardly changed.

12 shows an optical image of an opaque white pure PAN nanofiber and a light brown composite HMO / PAN nanofiber film. The HMO / PAN SEM image of FIG. 12 (i.e., the scan area for EDX mapping) shows that there are particles of various sizes within the nanofibers. The EDX spectrum confirmed that these particles were HMO adsorbents as shown by Mn and O peaks. Also, in the SEM image of the HMO / PAN composite nanofiber membrane of FIG. 12, HMO aggregates (&gt; 0.5 mu m) with diameters larger than nanofiber diameters (&lt; 500 nm) protrude on the surface, It can be confirmed that it is billowed.

The physical properties of HMO / PAN composite nanofiber membranes with various HMO loading were analyzed and shown in Figures 13, 14, 15, 13, it can be confirmed that the HMO / PAN composite nanofiber film is well formed without forming a bead shape. Generally, nanofibers formed with beads weaken the linkage of the polymer. Therefore, such a structure may irregularly form the nanofiber diameter and may interfere with the dispersion of the H _1.6 Mn _1.6 O ₄ particles, or the polyacrylonite around the adsorbed particles It is inappropriate to increase the thickness of the reel binder. Generally, when the thickness of the binder which serves to fix the adsorbent is increased, the adsorption ability of the composite nanofiber membrane can be remarkably reduced as compared with pure H _1.6 Mn _1.6 O ₄ particles not containing a binder. In one embodiment of the present invention, the diameter of the nanofibers was < 300 nm, but nanofibers with beads formed due to a high concentration of PAN solution and high PAN MW were not obtained. This may be because the two factors improved the entanglement of the polymer chains during electrospinning. It can be seen that H _1.6 Mn _1.6 O ₄ particles of large size are easily observed as the HMO content increases and the HMO powders coalesce and protrude out of the nanofiber.

[Table 4] Physico-chemical properties of PAN / HMO

The variety of physical-chemical properties according to the structural difference (refer to FIG. 13) of the composite nanofiber membranes having different HMO contents is shown in Table 4. Since HMO particles are more dense than PAN, the density of nanofibers tends to increase with increasing HMO loading. The average diameter of the nanofibers also increased as the content of HMO adsorbent increased. Increasing the fiber diameter can reduce the interstitial space (i. E., The source of macro-porosity of the nanofibers). Compared to PAN, HMO has a low affinity for water, so HMO can reduce the adsorption capacity of HMO / PAN in water. However, the results of the wettability analysis of the composite nanofibers according to Examples 2, 3 and 4 of the present invention show that the HMO / PAN composite nanofibers have the best wettability (see FIG. 14) PAN composite nanofiber membranes can be well contacted with the Li ⁺ source.

The influence of HMO loading on the mechanical properties of HMO / PAN composite nanofibers was analyzed and shown in Fig. As shown in FIG. 15, the HMO / PAN nanofiber membranes showed an increase in diameter and a better tensile strength as the loading amount of the adsorbent powder (20- and 40 wt%) increased. This is the peculiar mechanical behavior of a composite nanofiber membrane that is distinguished from a pure polymer (PAN) nanofiber membrane. Adsorption powders well dispersed in the fibers can enhance the physical properties of the nanofiber by interacting with the polymer PAN. When HMO 60 wt% is loaded, the agglomeration of HMO is prominent, so that the aggregate protrusions formed may cause micro-defects to mechanically weaken the complex in the nanofiber structure, As shown in Fig. 3B, since the film is strong enough similarly to the pure PAN nanofiber film. Also, as evidenced by the reduced elongation and enhanced Young's modulus, respectively, it can be seen that as the HMO addition increases, the composite fibers become less flexible and more rigid. In addition, all of the HMO / PAN composites did not exhibit physical deterioration due to the addition of HMO, and it was confirmed that all the composite nanofiber membranes according to one embodiment of the present invention are mechanically suitable.

Test Example 6: Li of HMO / PAN composite nanofiber membrane ⁺ Adsorption performance analysis>

All adsorption experiments were carried out at 25 ° C (298 K) unless otherwise specified. The effect of PAN as a binder in relation to HMO adsorption capacity was confirmed by equilibrium adsorption experiments. (40 mg), polyacrylonite (PAN, 240 mg) and H _1.6 Mn _1.6 O ₄ adsorbed powder (HMO) and polyacrylonitrile were weighed to 20 , 40 and 60% by weight of H _1.6 Mn _1.6 O ₄ adsorbed powder is added to the HMO / PAN hybrid nanofiber film 45 mL simulation of Li ⁺ immersed in a solution (simulated Li ⁺ solution) was shaken at 30 ℃ for 24 hours, culture medium ( 200 rpm). At a fixed initial pH of 11, a pure Li ⁺ solution composed of different concentrations from 1 mM LiOH added with LiCl (7 to 35 mg / L) was prepared. And the product was quantified by the formula (1) adsorption capacity (Q _e) of the flat Li ⁺ by using the (C _o: The initial Li ⁺ concentration, C _e: final (equilibrium) Li ⁺ concentration, V: volume of the sample solution, m: Mass of dried HMO).

The recyclability of HMO / PAN composite nanofiber membranes was tested using a 35 mg / L solution at initial pH = 11. After each adsorption cycle, the nanofibers were statically dipped in 45 mL of 0.5 mM HCl solution at 30 &lt; 0 &gt; C for 24 hours for desorption of Li ^{&lt; + &} gt ;. The regenerated HMO / PAN was then washed with deionized water (DI water) until the wash solution became neutral pH. To remove residual water, the cleaned HMO / PAN composite nanofiber membrane between Kimwipes ^® was gently pressed and used in an adsorption cycle. The adsorption-desorption cycle was repeated up to 10 times.

In order to analyze the effect of competing ions such as Na ⁺ , K ⁺ , Ca ²⁺ and Mg ²⁺ on Li ⁺ absorption and the separation performance of HMO and composite HMO / PAN nanofibers, an actual seawater desalting concentrate 15 mg of LiCl was added to the sample).

Samples (20 mL) collected in the adsorption experiments were passed through 0.2 μm nylon syringe filters. 10 mL aliquots were acid-decomposed with nitric acid (5 mL 60% HNO ₃ ) in a MARS-5 microwave oven (CEM, USA). The decomposed sample was transferred-filtered in 100 ml volumetric flasks and the filter was washed several times with deionized water for complete recovery of the analyte. Prior to ICP-MS analysis, the samples were diluted with deionized water, if necessary. The remaining aqueous samples were used for pH measurement with a Schott instrument pH probe (Z451 SI Analytics GmBH, Germany) from an Orion 4 star pH meter (Thermo Electron Corporation, USA).

Li of HMO powder ⁺ Adsorption performance analysis

In a theoretical calculation, one gram of L _1.6 Mn _1.6 O ₄ or LMO contains 68.1 mg of lithium and 539.2 mg of manganese. In the actual elemental analysis, slightly lower values of 65.1 mg Li / g and 509.0 mg Mn / g of HMO were obtained; This corresponds to a molar Li / Mn ratio of about 0.97. The adsorption capacity of Li ⁺ of HMO depends on the L _1.6 Mn _1.6 O ₄ delithiation efficiency. The maximum Li ⁺ adsorption amount of HMO prepared according to one embodiment of the present invention was estimated to be 54.6 mg / g, which is almost similar to the estimate in the previously reported study.

The equilibrium adsorption of the resulting powder in the HMO of the pure Li ⁺ solution is unbuffered (unbuffered pure Li ⁺ solution) is shown in FIG. 16 (a). As observed in previous studies, maximum adsorption of Li ⁺ by HMO powder was recorded at pH> 11. Thus, the initial pH of the Li ⁺ solution was fixed to the above pH level (X. Shi, D. Zhou, Z. Zhang, L. Yu, H. Xu, B. Chen, X. Yang, Synthesis and properties of Li _1.6 Mn _1.6 O ₄ and its adsorption application, Hydrometallurgy 110 (2011) 99-106.). As the initial Li ⁺ concentration was increased, Q _e steadily increased before reaching a maximum value of 10.8 mg / g at C _o = 35 mg Li ⁺ / L. The obtained Q _e was similar to that reported in previous studies using HMO as the adsorbent powder, where Q _e = 11.1 mg Li ⁺ / g and initial pH = 11.6.

As in Figure 16 (b), the equilibrium pH value showed an inverse relationship with the Q _e value; The maximum Q _e value was obtained at pH = 4.65 for HMO adsorbed powder. As shown in the following formula (2), Li ⁺ adsorption occurred mainly at the H ⁺ ion exchange site; Li ⁺ reinsertion in HMO involves release of H ^{+ in} the aqueous stream. The following equation (2) suggests that a continuous increase in aqueous H ^& lt ^{; + &} gt ^; concentration may limit Li ^& lt ^{; + &} gt ^; insertion in HMO. Thus, in an unbuffered system, it is difficult to obtain the maximum Li ⁺ adsorption capacity of the achievable HMO powder, which may be due to proton inhibition.

Li of HMO / PAN composite nanofiber membrane ⁺ Adsorption performance

FIG. 16 shows the results of confirming the effect of the PAN nanofiber as an HMO binder through equilibrium adsorption experiments. As shown in Fig. 16 (a), it was confirmed that the PAN nanofibrous film had no adsorption ability of Li ^{&lt; + &} gt ;. In addition, HMO / PAN composites showed very low adsorption capacity. The HMO / PAN composite refers to the mixed state of HMO and PAN prior to nanofiber production. As shown in FIG. 16 (a), adsorption capacities of HMO / PAN composite and HMO / PAN composite nanofiber membranes showed a significant difference, , It can not serve as an adsorbent. However, when it is made of nanofiber, it means that the HMO is exposed to the surface more frequently and can act as an adsorbent.

Also it compared the Q _e and Q _e 'of 16a in order to accurately observe the effect of the PAN on the adsorbability of the dispersed HMO. Q _e 'was lower than Q _e . This can be attributed to the reduction of HMO adsorption sites caused by binding to PAN. Equilibrium adsorption loss was estimated to be% Q _e loss in equation (3). This is related to the percentage of discrepancy between Q _e and Q _e '. At all C _o 's tested in this test example, The Q _e loss of 6-22% was measured from PAN nanofibers containing 20 wt% of HMO.

The advantage of using PAN nanofibers as a solid support of HMO can be seen in FIG. Compared to polymeric binders such as PVC, PU and PSf (polysulfone), PAN is a relatively hydrophilic polymer. Therefore, when PAN is used, the contact between the adsorbent (adsorbed film) and the water-soluble Li ⁺ can be facilitated. As shown in FIG. 14, the PAN nanofiber exhibited good wettability and fast moisture absorption rate without expanding while maintaining mechanical stability. The diameters of PAN nanofibers are similar to those of HMO particles, which can increase the likelihood that HMO particles will be exposed to the fiber surface. Accordingly, the surface blockage of the HMO by the PAN binder can be minimized, and the Q _e loss can be mitigated.

17 is a graph showing the Li ⁺ adsorption ratio of HMO powder and HMO / PAN. As described above, although the Q _e 'of the HMO contained in the PAN was low, the adsorption rate of Li ^{+ on} the HMO / PAN nanofiber membrane was similar to that of the HMO powder; Both were equilibrated after 24 hours.

Li of HMO / PAN composite nanofiber membranes according to HMO contents ⁺  Adsorption performance analysis

Were analyzed using Freundlich and Langmuir adsorption equations as defined by the following equations (4) and (5).

Wherein the expression, K _f, and n are Freundlich constants, K _L is Langmuir adsorption equilibrium constant (adsorption equilibrium constant), q _m is the theoretical maximum Li ⁺ adsorption capacity (theoretical maximum Li ⁺ adsorption capacity). The values calculated from the above equations (5) and (6) are shown in Table 5.

[Table 5]

Adsorption isotherm constants

Based on the correlation coefficient (r ² ), it can be seen that the Li ⁺ adsorption of HMO powder and HMO / PAN nanofiber membranes is better fitted to Langmuir than to Freundlich. Maximum q _m values were obtained from HMO powder. It showed a lower value than q _m film all HMO / PAN hybrid nanofiber, and showed a tendency to increase with increasing value q _m HMO content.

As shown in the SEM image of the HMO / PAN composite nanofiber membrane (see FIG. 13), as the amount of HMO loading increased, more adsorbed particles were observed on the surface of the fiber, and as the HMO loading increased, larger HMO particles (Which was greater than or equal to the diameter of the nanofibers), resulting in an increase in the HMO portion exposed on the fiber surface, which is due to clogging by the polymer (polyacrylonitrile) binder The loss of accessible adsorption sites due to PAN blockage can be minimized. This means that q _m can be improved as a result. In the case of 60 wt% HMO loaded, the q _m value of the obtained HMO / PAN composite nanofibrous membrane was about 4% lower than that of the HMO powder. HMO / PAN loaded with 20 and 40 wt% HMO showed 22% and 11% reduction, respectively. Therefore, it can be seen from the obtained isotherm results that as the loading of HMO increases, the reduction of the adsorption capacity caused by the presence of PAN can be minimized.

Recycling performance evaluation of HMO / PAN composite nanofiber membrane

The recyclability of HMO / PAN composite nanofiber membranes loaded with 60 wt% HMO was analyzed and shown in Figure 19 (a). In the first cycle, equilibrium adsorption of 10 mg Li ⁺ / g was achieved and Li ⁺ desorption in cycle 1 was 17 mg / g. More desorbed than the adsorbed amount can be attributed to the co-extraction of Li ⁺ originally present in the prepared HMO. The Li ⁺ removed from HMO producing LMO is 88.7% and the remaining 11.3% is equivalent to 7.53 mg Li ⁺ / g. This indicates that the actual Li ⁺ content of HMO contained in the PAN after adsorption in cycle 1 is approximately 17.53 Li ⁺ mg / g. Cycle 1, indicating that the majority of the remaining Li ⁺ was co-eluted with the lithium ion adsorbed by the HMO contained in the PAN.

In the second adsorption cycle, relatively higher ion exchange sites and slightly higher Li ⁺ adsorption were observed. As the number of recycles increased, Li ⁺ adsorption decreased slightly. As shown in Fig. 19 (b), the measured equilibrium pH value coincided with the observed Li ⁺ adsorption tendency. It is known that the HMO structure can deteriorate as cycles repeat because manganese can co-elute together with Li ⁺ during the acid treatment. However, according to one embodiment of the present invention, even after performing 10 adsorption cycles, it exhibited only a slight decrease in Li ⁺ adsorption (3.8%). This indicates that the HMO / PAN nanofiber membrane is chemically very stable. Previous studies have shown a reduction in Li ⁺ adsorption of 20% when 10 adsorption cycles were performed using HMO without support. The loss of Li ⁺ adsorption by HMO / PAN composite nanofiber membranes during recycling is low because PAN acts as a protection matrix for HMOs, .

The chemical stability of HMO / PAN was evaluated through% Mn elution measured during the recycling experiment and the results are shown in FIG. During the one-time desorption cycle, a large amount of manganese elution (2.9%) was observed along with Li ⁺ elution, but gradually the% Mn elution was decreased and the value was stable from the fourth cycle. The% Mn elution value was found to be in the range of 0.68% to 1.58%. Previous studies on HMO stability have reported that adsorption performance begins to deteriorate when 70% of manganese is eluted. The number of cycles of use of the nanofiber adsorbent can be roughly estimated based on the adsorption performance of the sample and the% Mn elution value (0.68% to 1.58%), so that the HMO / PAN composite nanofiber membrane of 60 wt% It can be used satisfactorily for 44 ~ 103 times. Nanofiber membranes immobilized with HMO on PAN are easier to handle than HMO powders and have the advantage of minimizing HMO loss during reuse.

In the seawater desalination concentrate, the HMO powder and the Li of the HMO / PAN nanofiber membrane ⁺  Separation performance

21 is a graph showing the results of analyzing Li ⁺ adsorption capacity of HMO / PAN nanofiber membranes from a seawater desalination retentate. The concentration of competing cations was higher than Li ⁺ . The separation efficiency of the composite nanofiber is evaluated in terms of the distribution coefficient (K _D ), the separation factor (α) and the concentration factor (CF) described in Equations (6) Respectively. The characteristics of the seawater desalination concentrate are shown in Table 6.

[Table 6] Properties of Seawater Desalination Concentrate: Metal Analysis

As shown in Table 7 and Table 8, Li ⁺ exhibited the highest Q _e among the cations present in the seawater even though it had the lowest C _o . The Q _e trends obtained from the HMO powder showed Li ⁺ >> Mg ²⁺ > Ca ²⁺ > Na ⁺ > K ⁺ order, while for the 60 wt% HMO / PAN nanofiber membranes Li ⁺ >> Mg ²⁺ > Na ⁺ & Gt ^; Ca &lt; ^{2 + &} gt ^; &gt; K ⁺ . This difference may be due to the physio-sorption of other cations in the PAN binder. Nonetheless, the overall trend of HMO powder and 60 wt% HMO / PAN indicates that both have the highest Li ⁺ selectivity.

[Table 7] Performance of HMO powder separating Li ⁺ from other cations in seawater desalination concentrates

[Table 8] Performance of 60 wt% HMO / PAN nanofiber separating Li ⁺ from other cations in a seawater desalination concentrate

Li ⁺ is best fitted to the H ⁺ -ion exchange sites in the HMO structure, thereby preventing other cations from being re-inserted. However, since most of the other cations are more concentrated than Li ⁺ , they are more likely to adhere to the HMO surface and can interfere with the migration of Li ⁺ into the HMO cavities to some extent. However, as shown in Tables 7 and 8, the K _D trend showed a significant ion-sieving effect of HMO. The K _D value of Li ⁺ for HMO powder and HMO / PAN nanofiber membranes was much higher than for other cations, indicating that lithium ion adsorption is more dominant than non-selective surface adsorption of other cations in the HMO. Similarly, the α value obtained from the HMO powder and the HMO / PAN composite nanofiber membrane shows a higher Li ⁺ separation efficiency than other cations, and the CF value is the concentration of other cations already concentrated, while the lithium ion is concentrated up to about 500 times .

The HMO / PAN composite nanofiber membranes exhibit slightly lower lithium ion adsorption capacity and a slightly higher Qe value than other ions, but the K _D and CF values of Na ⁺ , Ca ²⁺ , Mg ²⁺ and K ⁺ are kept low Therefore, a slight increase in Na ⁺ , Ca ²⁺ , Mg ²⁺ and K ⁺ adsorption does not affect the separation performance of the HMO / PAN composite nanofiber membrane. Therefore, HMO / PAN composite nanofiber membranes are very useful for recovering lithium ions from seawater.

&Lt; Example 5: HMO / PSf (H _1.6 Mn _1.6 O ₄ / Polysulfone, MO / PSf) Preparation of composite nanofiber membranes>

The LMO / PSf nanofiber membranes prepared according to Example 1-1 were delithiated using a 0.5 M HCl solution (see FIG. 22). For extraction of Li ⁺ via Li ⁺ / H + ion exchange, 2 L of 0.5 M hydrochloric acid per 1.5 g of LMO was used. After 24 hours, the HMO / PSf (MO / PSf) nanofiber membrane was prepared by converting the LMO to H _1.6 Mn _1.6 O ₄ (HMO). The prepared HMO / PSf nanofiber membrane was washed with deionized water (DI) and dried in an oven at 30 ° C.

&Lt; Comparative Example 2: Production of polysulfone nanofiber film >

The same viscous solution as above was prepared without adding Li _1.6 Mn _1.6 O ₄ (LMO) adsorbed powder, and pure polysulfone nanofibers were prepared in the same manner as above.

&Lt; Test Example 7: Property analysis of HMO / PSf (MO / PSf) composite nanofiber film &

The properties of the HMO / PSf composite nanofiber membranes prepared according to Example 5 were analyzed as follows.

XRD analysis

LMO and delithiated LMO were analyzed using an X-ray diffractometer (PANalytical X'pert-Pro, The Netherlands). The LMO and delithiated LMO were analyzed by face-centered cubic system with a lattice constant a = 8.14 Å, a = 8.03 Å, centered cubic system).

Confirmation of strengthening of mechanical properties by heat treatment

The properties of the sample heat-treated at 190 ° C. and the sample not heat-treated were analyzed and shown in FIG. It was confirmed that tensile strength and elongation were greatly increased in the heat - treated samples. The tensile strength and elongation were analyzed using a universal testing machine (UTM).

When the composite nanofibrous film is heat treated to enhance the mechanical properties, the temperature and time conditions of the heat treatment are very important factors. When the heat treatment is performed at a too high temperature or for a long time, the nanofiber shrinks, and in particular, the Li adsorption site of Li _1.6 Mn _1.6 O _{4 in} the nanofiber is clogged due to polymer shrinkage, It is important.

The heat treatment for reinforcing the mechanical properties of the composite nanofiber film using polysulfone is preferably a heat treatment at a temperature range of 185 to 195 ° C, which is a temperature range from the glass transition temperature to the melting point of the polysulfone. However, the present invention is not limited to this, and in the case where another polymer material is used in the production of the composite nanofiber film, it is preferable to heat-treat the polymer material in a temperature range from the glass transition temperature to the melting point.

As a result of the BET (Brunauer-Emmett-Teller) surface area analysis of the composite nanofiber membrane according to Example 5, the value was slightly lower than that of the PSf nanofiber membrane (Comparative Example 2) (see FIG. 23). The BET (Brunauer-Emmett-Teller) surface area was analyzed using ASAP 2020 (Micromeritics Instrument Corporation, USA) (N ₂ atmosphere, -196 ° C).

Surface morphology analysis

24 is a graph showing the relationship between a pure polymer (PSf) nanofiber film (upper side) and an HMO / PSf (MO / PSf) composite nanofiber film prepared by the above method using a scanning electron microscope (SEM-EDX, Hitachi S- (Bottom) of the surface of the substrate. The pure polymer (PSf) nanofiber membrane showed a smooth surface, but HMO / PSf (MO / PSf) composite nanofiber membrane showed protrusions formed by HMO (MO) particles.

Wavelength Dispersive Spectrometer (WDS) with Energy Dispersive X-ray Spectrometer (EDS) and three-channel analyzing crystals (LDE2, LIFH, and PETJ within l = 0.087-9.3 nm) Mapping the surface of HMO / PSf (MO / PSf) composite nanofibers using a Field Emission-Electron Probe Micro-analyzer (FE-EPMA JEOL JXA-8500F Hyperprobe, Germany) The distribution of manganese (Mn) and oxygen (O) elements was observed. The results are shown in FIG. The diameter D _ag of the agglomerated HMO (MO) particles was 3.06 ㎛ and the composition of C (68.2%), S (5.1%), O (15.8%) and Mn (10.9%) was confirmed by WDS analysis. The HMO (MO) particles protruding from the surface can be advantageous in terms of adsorption efficiency because it is possible to minimize the occlusion of the surface adsorption sites by PSf.

FIG. 26 is a graph illustrating the diameter of a nanofiber according to the FE-SEM image analysis. In the case of pure PSf nanofiber membranes, the average diameter of the nanofibers was 730 nm, whereas the HMO / PSf composite nanofiber membranes were found to be 1240 nm. This indicates that the dope solution (viscous solution) Can be attributed to the high viscosity of the polymer. If such a viscous solution of high viscosity is used, fibers of larger diameter can be produced during electrospinning.

FIG. 27 is a graph showing the result of thermogravimetry analysis of LMO, LlMnO ₂ and HMO (MO) particles, and FIG. 28 is a graph showing the result of thermogravimetric analysis of a pure PSf nanofiber film and an HMO / PSf (MO / PSf) composite nanofiber film Graph. In the case of the pure PSf nanofiber membrane, the polymer was completely decomposed at around 660 ° C. In the case of HMO / PSf (MO / PSf) composite nanofiber membrane, 38.54% of the HMO (MO) .

&Lt; Test Example 8: Adsorption performance analysis of HMO / PSf composite nanofibrous membrane >

Analysis of the adsorption performance of the HMO / PSf composite nanofiber membranes prepared according to Example 5 was carried out as follows: Samples were added to a Li ⁺ solution equilibrated at 25 ° C (298 K) in a shaking incubator (200 rpm) . After 24 hours, pH and metal analyzes were performed using ICP-MS (ICP-MS Agilent 7500 series, USA). The equilibrium adsorption capacity (Q _e ) was calculated according to equation (1) above.

Effect of pH

Lithium adsorption and desorption of HMO (MO) adsorption powders can be explained by the following ion exchange reactions: HMO _(s) + Li ⁺ _{(aq) ↔} LiMO _(s) + H ⁺ _(aq) . Using unbuffered Li ⁺ solutions (pH 7-12) and buffered Li ion solution (ammoniacal (NH ₃ / NH ₄ Cl) buffered Li ⁺ solution, pH = 9.75) Adsorption performance was analyzed. FIG. 29 shows the result of analysis using an unbuffered lithium ion solution. At pH ≤ 8, q _e <5 mgg ^-1 . The maximum q _e value was found to be q _e = 27 mg g ^-1 at pH 12, which is not likely to be present in the actual feed stream. For unbuffered systems, the Li ⁺ solution pH 11 q _e = 11.44 mgg ^-1 ).

In batch experiments using small (volume) samples, the pH of the solution may be decreased and the adsorption of lithium ions may be inhibited as the released hydrogen ions accumulate gradually with lithium adsorption. This tendency is confirmed in Fig. 30 (a). The q _e value (q _e = 22 mg g ^-1 ) of the pH-buffered LiCl solution (pH = 9.75) q _e = 22 mg g ^-1 was obtained in the unbuffered LiCl solution (pH = 10, q _e = 8.5 mg g ^-1 ). &Lt; / RTI &gt; 30 (a), pure is a solution containing only lithium ions, and mixt. Is a mixed solution containing lithium ions and other cations (M ^{n +} = Na ⁺ , K ⁺ , Mg ²⁺ , Ca ²⁺ ). However, if HMO / PSf composite nanofiber membranes are used under continuous operation, this behavior may not be observed since the pH drop in a considerably higher feed volume is negligible. Therefore, buffering of the feed stream may not be necessary if the HMO / PSf (MO / PSf) composite nanofiber membrane is used in a continuous flow-through system.

Analysis of Effect of PSf Support Matrix on HMO / PSf Composite Nanofiber Membrane

(1) q _e value (2) uptake adsorption kinetics in the HMO (MO) powder and the HMO / PSf composite nanofiber membrane to confirm the effect of polysulfone (PSf) as a support matrix, and (3) Selectivity (competitive metal ions).

In order to observe the effect of polysulfone (PSf) on the adsorption performance of dispersed HMO, the lithium ion adsorption capacity Q _e (HMO adsorption powder) and Q _e '(HMO / PSf composite nanofiber membrane) were compared. As with in 31 (a), pure PSf was to make nanofiber film does not have the absorption capacity of the Li ⁺ showed a tendency to increase Q _e as the lithium ion level increases, more Q _e 'is Q _e Respectively. This can be attributed to the reduction of the HMO adsorption site that occurs due to binding with the polysulfone (PSf). Equilibrium adsorption loss is expressed as% Q _e loss in equation (3) above. This is related to the percentage of discrepancy between Q _e and Q _e '. In the present test example, in all the test C _o Q _e is the loss of 4.5-7.5% were measured from PSf nanofiber film containing HMO. The reduction of HMO adsorption sites due to binding with polysulfone (PSf) can be minimized by the HMO adsorption powder protruding on the nanofiber surface. The equilibrium pH value showed an inverse relationship with the Q _e value (see FIG. 31 (b)).

Figs. 31 (c) and 31 (d) are graphs showing a linear model as analyzed by Langmuir and Freundlich adsorption equations as defined by the equations (5) and (4) ) And Equation (4), using Langmuir and Freundlich adsorption equations.

The q _m value of the HMO / PSf composite nanofiber membrane was 96.6% of the HMO (MO) adsorption powder. Both showed positive K _L values (K _L > 0), indicating that they are advantageous for lithium adsorption. Further, the HMO / PSf (?) Is calculated from the _RL (dimensionless separation factors) value (0> R _L > 1) and the Gibbs free energy value (? G? MO / PSf) composite nanofiber membrane and HMO (MO) adsorbent powder are advantageous for lithium ion adsorption and lithium ion adsorption are spontaneous.

[Table 9]

Lithium ion adsorption kinetic analysis

Adsorption kinetic studies were performed similarly to equilibrium experiments. However, in order to minimize the external mass transport resistance, the sample was agitated at 350 rpm.

32 is a graph showing adsorption kinetic analysis results of HMO (MO) adsorbing powder and HMO / PSf composite nanofiber membranes. HMO (MO) adsorbed powder and HMO / PSf (MO / PSf) composite nanofiber membranes showed similar results overall, and PSf nanofiber membranes had no lithium ion adsorptive capacity.

Selectivity Analysis of Lithium Ion by Composite Nanofiber Membrane in the Presence of Other Metal Ions

Representative cations competing with lithium (Li) ions adsorbed by the HMO / PSf composite nanofiber membranes include monovalent ions of potassium (K) and sodium (Na), magnesium (Mg), and calcium (Ca) Ionic divalent ions. These cations are in competition with lithium ions and can degrade the selectivity of lithium ions during the adsorption process.

Therefore, in order to evaluate the selectivity of lithium ions by HMO / PSf composite nanofiber membranes, lithium ions and other cations (Na ⁺ , Mg ²⁺ , K ⁺ Ca ²⁺ ) were mixed. The results are shown in Table 10.

The selectivity of the composite nanofiber film is evaluated in terms of the distribution coefficient (K _D ), the separation factor (α) and the concentration factor (CF) described in the formulas (6) Respectively.

Referring to Table 10, at the Q _e value obtained from the HMO adsorbed powder and the HMO / PSf composite nanofiber membrane, Li ⁺ exhibited the highest Q _e even though it had the lowest C _o . This means that the selectivity to lithium ion is the highest.

The K _D values for lithium ion in the HMO adsorbed powder and HMO / PSf composite nanofiber membranes were much higher than for other cations, which means that lithium ion adsorption far exceeds non-selective surface adsorption of other cations.

The α value of HMO adsorbed powder and HMO / PSf composite nanofiber membranes shows that the α value of the HMO / PSf composite nanofiber membranes has a higher separation efficiency than that of other cations, while the CF value indicates that the other cations are already concentrated, Or more.

In addition, in the HMO / PSf composite nanofiber membranes, the other cations (Na ⁺ , Mg ²⁺ , K ⁺ , and K ⁺⁾ were different from the HMO adsorption powders in the Q _e values obtained from the HMO adsorbent powder and the HMO / PSf composite nanofiber membranes. The bar Q _e values for the Ca ²⁺⁾ Shone appear low because the PSf matrix to reduce the physical adsorption of other cations in the HMO adsorbed powder surface (see Fig. 30 (b)). Also, in the test using the HMO / PSf nanofiber membrane, lithium ion exhibited the lowest q _e loss (% q _e loss) (see FIG. 30 (c)).

HMO / PSf composite nanofiber membranes are more effective than HMO / PSf hybrid nanofiber membranes for separation of HMO / PSf composite nanofiber membranes.

In the HMO / PSf nanofiber membranes, the CF values of the other cations were significantly reduced compared to the HMO adsorbent powder, indicating that the HMO / PSf nanofiber membranes are more efficient at separating lithium ions than HMO adsorbent powders. These results indicate that the polymer matrix plays an important role in the separation efficiency of the adsorbed membrane.

[Table 10]

Analysis of permeability properties of HMO / PSf composite nanofiber membranes

Except that the composite nanofibers prepared in Example 5 were subjected to the heat treatment under the same conditions as those in Example 5 except that the composite nanofibers were prepared (that is, two, three or four nanofibers were laminated, Pressed on both sides with a plate and subjected to a heat treatment at a temperature of 190 DEG C for 90 minutes to prepare a composite nanofiber film). The mechanical properties (tensile strength and elongation) of the membrane produced in (a) of FIG. 33 are shown, and the results of analysis of permeability are shown in (b). The mechanical properties were analyzed using a tensile strength meter. Batch filtration experiments were performed using Amicon ^® (Amicon ^® unstirred dead-end membrane cell, Model 8050 mL Merck Millipore, MA, USA) for permeability analysis. A circular membrane having a diameter of 44.5 mm and an effective membrane area A = 13.4 cm &lt; ² &gt; was tested. The test was performed using clean water supplied from a pressurized 5 L stainless vessel (Millipore, MA, USA) as a feed solution. The pre-filtration composite nanofiber membrane sample was soaked in ethanol, and the solvent was completely removed by soaking in deionized water overnight. Measurements were started after stabilization of TMP (after about 20 minutes); V (permeate volumes) were measured according to time (t) using a top-load balance scale (FX-3000i A & D Co., Ltd., Korea). At room temperature (25 ℃) 0.05 -. 1.0 bar (5-100 kPa) pressure (trans-membrane pressures (TMP = P F -P p) an experiment was carried out in accordance with the following formula (11) R _m (Hydraulic membrane of In the equation (11), J is the flux, V _p is the permeate volume measured at time t, and μ is the viscosity of water at 25 ° C.

[Table 11]

Nano composite was analyzed using the following formula and physical properties of the fiber membrane are shown in Table 11 (R _m is intrinsic membrane resistance; K _g is assumed to be a constant; z is the thickness of the membrane, S is the surface area, and? is the porosity of the nanofiber membrane)

Referring to Table 11, the HMO / PSf composite nanofiber membranes also showed a tendency to decrease in J _{water as the} interstitial pore size reduction tendency. In particular, the decrease in J _water may be due to an increase in intrinsic membrane resistance (Rm).

The interstitial pore diameter of the prepared HMO / PSf composite nanofiber membranes was found to be 1.8 to 3.8 μm. As a result, the HMO / PSf composite nanofiber membranes can be applied as microfiltration membranes. Also J _water was found to be at least 12 times higher than known MF membranes or UF PSf membranes. Therefore, the HMO / PSf composite nanofibrous membrane according to one embodiment of the present invention can be used for recovering lithium ions by treating a large amount of seawater at low pressure requirements.

Analysis of Lithium Ion Adsorption Efficiency of HMO / PSf Composite Nanofiber Membrane during Lithium Recovery Using Lithium Recovery Device

 The HMO / PSf (MO / PSf) composite nanofiber membrane was mounted in a 50 ml filtration tank (membrane reactor), and a peristaltic pump was connected to the filtration tank to remove seawater (sea water, pH = 9.65) Was filtered by the composite nanofiber membrane. Seawater components are shown in Table 12. Seawater component analysis was performed by metal analysis using ICP-MS.

[Table 12]

The lithium ion adsorption behavior was analyzed in terms of (1) the change in the flow rate and (2) the thickness of the nanofiber film. FLUX and TMP were measured during lithium recovery and V _ex (total permeate or volume treated) at t _ex (exhaustion time) was measured at adsorption point (Cp / Cf = 0.95). Samples (permeate samples, 20 ml) were periodically collected for metal and pH analysis.

For elemental analysis, a powder sample or pre-filtered (0.2 mm Nylon membrane) liquid sample (10 mL aliquot) in a MARS-5 microwave oven (CEM, USA) was mixed with 5 mL of 60% HNO ₃ Acid pretreatment by digesting. The pretreated sample was filtered again, diluted with deionized water in a 100 mL polypropylene measuring flask and analyzed using ICP-MS. The remaining portion of the collected sample was subjected to pH analysis using a pH probe (Schott instruments pH probe (Z451 SI Analytics GmBH, Germany) in an Orion 4 star pH meter (Thermo Electron Corporation, USA)).

Analysis of Lithium Ion Adsorption Behavior with Variation of Flow Rate

34 is a breakthrough curve showing the lithium ion adsorption behavior of a composite nanofiber membrane according to a change in flow rate (僚 = F / A = 0.6 - 2.3 cm h ^-1 ) in terms of surface velocity. 34 (a) is a graph showing the breakthrough test results of HMO / PSf composite nanofiber membranes using seawater as influent water at 25 ° C. The permeate concentration (C _p ) of the effluent continued to increase over time, reaching the adsorption point (C _p / C _f = 0.95) (C _p = lithium ion concentration in the effluent, C _f = Lithium ion concentration).

 The lithium ion recovery behavior of the composite nanofiber membranes was analyzed using the following equation (12).

In equation (12), V _m is the composite nanofiber membrane volumes, N is the equivalent number, and V _ex is the total volume treated.

Breakthrough kinetics were also analyzed using the Thomas model of equation (13).

In the above equation (13), q _th is the derived adsorption capacity, k _th is the Thomas rate constant, and F is the flow rate

34 (b) is a breakthrough curve showing the lithium ion recovery behavior of HMO / PSf (MO / PSf) composite nanofiber membranes. At ν = F / A = 0.6 - 2.3 cm h ^-1 , the TMP value was 2.57-2.61 kPa and did not exceed 0.027 bar. The adsorption point (C _p / C _f = 0.95) was at ν = 0.64-, 1.38- and 2.27 cm h ^-1 Reaching after 72-, 28- and 7 h respectively.

Figure 34 (c) is V _p (permeate volume measured at time t) and the graph Fig. 34 (c) showing the relationship between ν When ν is maximum, a total of _{Vp (V ex: total volume treated} ) is found to fall (See Table 13). The inset of FIG. 34 (c) shows the relationship between N (see equation 12 above) and v. When ν = 2.27 cm h ^-1 , N decreased abruptly to 775. 34 (d) and Table 13, q _th and q _int (adsorption capacity, see Fig. 35) values were obtained from Figs. 34 (b) and 34 (c). q _th and q _int values showed similar tendencies, and it was confirmed that the amount of lithium ion adsorption decreased as the flow rate increased.

[Table 13]

In terms of the contact period, the interstitial velocity was estimated as ν _int = ν / ε (ε = 0.71 for single layer, see Table 11). During continuous operation, the advective transport of lithium ions was calculated as the contact time t _adv = z / v _int (where z is the thickness of the nanofiber membrane). When ν is the highest, t _adv = 0.35 min. This indicates that the contact time at ν = 2.27 cm h ^-1 is too short to allow lithium ions contained in seawater to reach the HMO (MO) surface of the HMO / PSf composite nanofiber membrane.

Among the tested νs, ν = 0.64- and 1.38 cm h ^-1 were confirmed to be the most suitable flow rate, which provides sufficient time for the composite nanofiber membrane to contact with the sea water passing through the composite nanofiber membrane. Also, it is not desirable that the operation period for recovering the same amount of lithium ions is prolonged. Of the flow velocity v,? = 1.38 cm h ^-1 may be more suitable. However, if the flow rate is to be increased (for example, ν = 2.27 cm h ^-1 ), the appropriate contact time can be maintained by increasing the thickness of the nanofiber film.

Analysis of Lithium Ion Adsorption Behavior with HMO / PSf Composite Nanofiber Film Thickness Variation

36 is a graph showing an analysis of lithium ion adsorption behavior according to the change of the HMO / PSf composite nanofiber film thickness (z). As shown in FIG. 36 (a), the time to reach the adsorption point (C _p / C _f = 0.95) was slower as the film thickness (z) or the volume (V _m ) _ex = 7h, z = 554mm, t _ex = 30.3). TMP tended to increase as the film thickness increased, but in any case it did not exceed 0.028 bar (see FIG. 36 (b)). Also, it was confirmed that V _ex = total V _p (total volume treated) value and N (equivalent number) were significantly increased as the film thickness increased (see FIG. 36 (b), Table 14).

[Table 14]

In terms of the contact period, the interstitial velocity was estimated as ν _int = ν / ε (ε = 0.71 for single layer, see Table 11). As the thickness of composite nanofibers increased, the value of t _adv increased from 0.35 min to 0.72 min. As the contact time increased, the q value was also found to increase significantly.

As a result of the wave breaking experiment, it can be seen that the contact time is an important parameter to be considered. Since the HMO / PSf composite nanofiber membrane is used in a flow-through membrane system, the contact time can be controlled by controlling the flow rate or membrane thickness. The most suitable breakthrough condition for lithium ion recovery is to obtain the maximum adsorption capacity of the HMO in a short time (eg high q value and high k _th value).

As a result of the breakthrough experiment, it was confirmed that the double layer composite nanofiber film is the most excellent in view of the q value and the k _th value.

Analysis of recycling performance of HMO / PSf composite nanofiber membrane

The recycling performance and durability (long-term performance) of the HMO / PSf composite nanofiber membrane for lithium ion recovery from seawater were analyzed using the recovery apparatus of FIG. The composite nanofiber membrane was operated in adsorption mode (U) until it reached 95% Li ion saturation (C _p / C _f = 0.95). Then, 80 mL of deionized water was passed through the filter (10 min, 100 mL hr ^-1 ) to remove the metal ions bound to the reactor and the membrane surface. The recovery mode (R) was performed by recirculating 100 mL of 0.5 M HCl at 350 mL hr ^-1 for lithium ion desorption. The residual acid was removed by passing deionized water through the HMO / PSf complex nanofiber membrane (15 min at 100 mL hr ^-1 ) regenerated before the next adsorption / desorption cycle.

The performance of HMO / PSf composite nanofiber membranes was analyzed by using sea water as an influent feed for 5 days. The experiment used a dual layer film. t _ex was set to 12 hours, and the other conditions were the same as those for the dual layer film. The remaining 12 hours consisted of membrane washing (10 minutes), lithium ion desorption (100 hours) with 0.5 M hydrochloric acid (11 hours), and preparation time for subsequent adsorption. One adsorption / desorption cycle was performed per day.

FIG. 37 shows the results of analyzing the performance of the HMO / PSf composite nanofiber membrane in a dead-end flow through system for recovering lithium ions from seawater. Increased cumulative seawater volume treated (V _T ) at a constant flow rate and stable TMP confirmed that the HMO / PSf composite nanofiber membranes in a dead-end flow through system were easily and conveniently operated (See Fig. 37 (a)). In addition, the breakthrough curve of the lithium ion and other cations showed that the cations reached the adsorption point (C _p / C _f = 1) instantaneously for the other cations, but the saturation point (C _p / C _f = 0.95 at t _ex = 11.8h) was much delayed (see Fig. 37 (b)). This confirms the selectivity of the HMO / PSf composite nanofiber membrane for lithium ion. It was confirmed that the adsorption curve and the curve of five times shown in Fig. 37 (c) were almost the same. The amount of lithium ion adsorption and the amount of desorption according to each cycle are shown in FIG. 37 (d) and Table 15. The amount of desorption was similar or somewhat higher than that of adsorption because lithium did not dissolve completely in HMO and remained together. The amount of adsorption reduction in the fifth cycle was very small compared to the first cycle, indicating that the nanofiber membranes were chemically very stable.

The reduction in the lithium adsorption capacity of the HMO / PSf composite nanofiber membranes was minimized by the fact that the polysulfone acting as a matrix reduced the vulnerability of the HMO powder by acid treatment. Therefore, the HMO / PSf composite nanofiber membrane can maintain the lithium ion adsorption performance even when it is used for a long period of time because the HMO adsorption powder immobilized in the polysulfone nanofiber is chemically stabilized.

Moreover, HMO / PSf composite nanofiber membranes are easier to handle than HMO powders and have the advantage of minimizing HMO loss during reuse.

[Table 15]

While the present invention has been particularly shown and described with reference to preferred embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. Those skilled in the art will understand. Therefore, the scope of protection of the present invention should be construed not only in the specific embodiments but also in the scope of claims, and all technical ideas within the scope of the same shall be construed as being included in the scope of the present invention.

100: Lithium recovery device
110: Supply tank
120: Filtration tank
121: Composite nanofiber membrane for lithium adsorption
130: Recovery tank
140: Emission tank
150: liquid transfer pump

Claims (19)

Preparing a viscous solution by mixing lithium-manganese oxide adsorbing powder and a polymer material in a solvent; And a step of electrospinning the viscous solution to produce a composite nanofiber film, wherein the composite nanofibrous film for lithium adsorption comprises:
A filtration tank in which dissolved lithium in the influent seawater is adsorbed on the membrane, and then a process of desorbing lithium using the supplied acid solution is performed;
A supply tank for supplying seawater to the filtration tank;
A drain tank through which the seawater subjected to the lithium adsorption process is discharged and accommodated in the filtration tank; And
And a recovery tank for supplying an acid solution to the filtration tank subjected to the lithium adsorption process and recovering a solution containing lithium desorbed by the supplied acid solution.
The method according to claim 1,
And a liquid transfer pump is further provided between the filtration tank and the discharge tank, and between the filtration tank and the recovery tank.
The method according to claim 1,
Wherein the lithium niobate composite nanofiber film is manufactured by further comprising a step of heat-treating the nanofiber film.
The method of claim 3,
Wherein the heat treatment step is a step of heat treating one or more sheets of the nanofiber film and controlling the thickness and the average pore size of the composite nanofiber film for lithium adsorption produced by adjusting the number of the nanofiber films to be heat treated Lithium recovery device.
The method according to claim 1,
Wherein the lithium niobate composite nanofiber film is manufactured by further performing an acid treatment for activation of a lithium adsorption site.
The method according to claim 1,
Wherein the lithium-manganese oxide adsorbing powder comprises at least one selected from the group consisting of Li _1.6 Mn _1.6 O ₄ , Li _1.33 Mn _1.67 O ₄ , LiMn ₂ O ₄ and LiMnO ₂ .
The method according to claim 1,
Wherein the lithium-manganese oxide adsorbing powder is an acid-treated lithium-manganese oxide adsorbing powder.
The method of claim 7,
The acid-treated lithium-manganese oxide adsorption powder contains at least one selected from the group consisting of H _1.6 Mn _1.6 O ₄ , H _1.33 Mn _1.67 O ₄ , HMnO ₂ and HMn ₂ O ₄ . .
The method according to claim 1,
The polymeric material may be selected from the group consisting of polysulfone, polyethersulfone, polyacrylonitrile, polyvinylidene fluoride, cellulose acetate, and polyvinyl chloride. , Or a combination of at least one polymer.
The method according to claim 1,
Wherein the solvent contains at least one selected from the group consisting of dimethylformamide, dimethylformaldehyde, tetrahydrofuran, dimethylacetamide and methylpyrrolidone.
A lithium recovery method using the lithium recovery apparatus of claim 1,
Acid treatment of the lithium-adsorbing nanofiber membrane provided in the filtration tank;
Introducing seawater into a filtration tank provided with a composite nanofiber membrane for lithium adsorption treated with acid from a feed tank storing seawater, and passing the membrane through the membrane to adsorb lithium;
Discharging the seawater having passed through the filtration tank to the discharge tank and supplying an acid solution to the filtration tank to desorb the lithium adsorbed on the membrane to perform a desorption process of lithium; And
And a desorption process is performed to transfer the acid solution in which lithium is dissolved to the recovery tank.
Preparing a viscous solution by mixing the lithium-manganese oxide adsorbing powder and the polymer substance in a solvent (step a); And
And a step (b) of preparing a composite nanofiber film by electrospinning the viscous solution.
The method of claim 12,
The method for producing a composite nanofiber membrane for lithium adsorption according to claim 1, further comprising acid-treating the composite nanofiber membrane prepared by electrospinning a viscous solution.
The method of claim 12,
Further comprising the step of heat-treating one or more of the nanofibers after the step (b)
Wherein the heat treatment step controls the thickness and average pore size of the nanofiber film by controlling the number of the nanofiber films to be heat treated.
15. The method of claim 14,
The method for producing a composite nanofibrous film for lithium adsorption according to claim 1, further comprising the step of acid treatment for activation of the lithium adsorption site after the heat treatment step.
The method of claim 12,
Wherein the lithium-manganese oxide adsorbing powder comprises at least one selected from the group consisting of Li _1.6 Mn _1.6 O ₄ , Li _1.33 Mn _1.67 O ₄ , LiMn ₂ O ₄ and LiMnO ₂ . &Lt; / RTI &gt;
The method of claim 12,
Wherein the lithium-manganese oxide adsorbing powder is an acid-treated lithium-manganese oxide adsorbing powder.
18. The method of claim 17,
Wherein the acid-treated lithium-manganese oxide adsorption powder contains at least one selected from the group consisting of H _1.6 Mn _1.6 O ₄ , H _1.33 Mn _1.67 O ₄ , HMnO ₂ and HMn ₂ O ₄ . Composite nanofiber membrane fabrication method.
The method of claim 12,
Wherein the polymer material is at least one polymer selected from the group consisting of polysulfone, polyethersulfone, polyacrylonitrile, polyvinylidene fluoride, cellulose acetate, and polyvinyl chloride, or a combination of at least one polymer. A method for manufacturing a nanofiber film.

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