KR101753905B1 - Polyvinyl alcohol composite foam comprising lithium ion sieve and preparing method thereof - Google Patents

Abstract

TECHNICAL FIELD The present invention relates to a hydrophilic polyvinyl alcohol composite foam comprising a lithium ionic body, and relates to a hydrophilic polyvinyl alcohol composite foam comprising a lithium ion sieve used for absorption and recovery of lithium ions and a method for producing the same. The polyvinyl alcohol composite foam according to the present invention is produced by lyophilizing a water-soluble mixture of a foamed lithium ion complex and polyvinyl alcohol and then crosslinking, and the manufacturing process is simple and eco-friendly. In addition, the foam according to the present invention is a flexible and durable porous foam having a very low adsorption capacity loss and very low lithium ion absorption rate, and does not cause a reduction in absorption performance or physical damage after repeated use, . It can also be utilized as a passive adsorbent capable of selectively recovering lithium ions through a "immerse and squeeze" mechanism.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a polyvinyl alcohol composite foam comprising a lithium ion complex,

TECHNICAL FIELD The present invention relates to a hydrophilic polyvinyl alcohol composite foam comprising a lithium ion sieve and relates to a hydrophilic polyvinyl alcohol composite foam having a flexible structure including a lithium ion sieve used for absorption and recovery of lithium ions and a method for producing the same .

Due to its high energy storage density and light weight, lithium can be used in mobile electronic devices such as mobile phones, notebook PCs, and camcorders, hybrid electric vehicle battery materials, light alloy materials for aircraft, proliferation materials of tritium, It is used as a raw material for the device and it is important to secure it at the national level.

Lithium that can be buried on the land and can be mined is expected to reach 4.1 million tonnes in 7 ~ 8 years, and Bolivia occupies about 50% of world reserves.

Thus, the recent Li-related industry is paying attention to recovering lithium from all possible sources including waste batteries, industrial wastewater, fly ash and seawater. Lithium ions (Li ^< ^{+ &} gt ^; ) in these resources are generally present in very low concentrations.

However, existing techniques are only applicable to primary resources that exhibit relatively high Li ⁺ concentrations (e.g., saline and sub-surface brines). Thus, methods such as solvent extraction, adsorption, and ion exchange have been proposed as new methods for recovering Li ⁺ present in diluted resources.

Among these methods, Lithium Ion Sieve (LIS) is considered to be the most effective method because it can selectively adsorb Li ⁺ from other types of cation-rich streams. In the case of immobilizing the LIS powder in the polymer matrix as the solid support, the handling can be handled more conveniently and can be reused repeatedly. In this case, however, it is important to maintain the adsorption performance of the LIS by minimizing the physical effect of the support.

Manufacturing techniques and polymer chemistry play an important role in achieving desirable structure and surface properties. If both techniques are not met, the adsorption performance of the LIS can be reduced. For example, when LIS is membraneed with polyvinyl chloride (PVC) by phase inversion techniques, composites with low specific surface area are produced, reducing the capacity of the adsorbent and impairing its dynamic characteristics. In the case of granulating LIS with PVC, the adsorption rate is remarkably reduced due to (1) aggregation of particles and (2) blockage of adsorption sites by PVC, resulting in more hydrophobic surfaces.

In the case of depositing LIS / pitch slurry in the form of a foam, the contact between the adsorbent and the water-soluble feed material is inhibited by the extremely small pitch, and the LIS adsorption capacity is markedly reduced.

On the other hand, when a method using a hydrophilic polymer as a support is applied, a more effective LIS composite adsorbent is produced. When LIS immobilized on nanofibers was prepared using hydrophilic polyacrolonitrile (PAN), the degradation of LIS adsorption performance was minimized. The unique steric properties of the nanofibers and the hydrophilicity of the PAN facilitated a good interaction between the LIS and the feed material.

Similarly, when chitosan is used as a binder in a granulated LIS, the hydrophilic nature of chitosan promotes the penetration of water and improves Li ⁺ contact to the surface of the absorbent.

Since only a few of the numerous reported LIS complexes are shown to be effective, further research and development is needed to obtain a suitable LIS sorbent that can be used to recover Li ⁺ from the replacement material.

Of the existing LIS composites, flexible LIS foam foams can be applied directly to the raw material (e.g., seawater) and can be simply "attractive and squeeze" Material. A lightweight, highly porous LIS complex having excellent specific surface area can be obtained by adjusting the structural characteristics of the foam. The hydrophilic polymer matrix can increase water uptake and can therefore be used to draw in the Li ⁺ containing feed material into the LIS adsorption site, which can reduce the volume of the inaccessible portion of the adsorbent.

However, there are very few researches related to the development of LIS forms among the complexes and solutions reported in previous studies, and the research and development to realize the potential is not yet active.

Korea Patent No. 10-0557824

The present invention provides a porous polyvinyl alcohol composite foam prepared by lyophilizing a water-soluble mixture of a foamed lithium ion sieve (LIS) and polyvinyl alcohol (PVA), and a method for producing the same.

The present invention also provides a lithium ion adsorbent comprising the porous polyvinyl alcohol composite foam and a lithium ion recovery method using the same.

A method for producing a polyvinyl alcohol composite foam according to the present invention comprises the steps of: preparing a lithium ion complex; Mixing the prepared lithium ion complex with polyvinyl alcohol and a foaming agent to prepare a foamy mixture; Lyophilizing the mixture; And crosslinking the lyophilized mixture by acetylation under an acid catalyst.

The step of preparing the lithium ionic material includes: a step of pulverizing the lithium manganese oxide precursor; Heat treating the pulverized lithium manganese oxide at 400 to 600 ° C; And delignifying the heat treated lithium manganese oxide.

The blowing agent may be a nonionic surfactant.

The lithium ion sieve may include H _1.6 Mn _1.6 O ₄ .

The crosslinking step may be performed by immersing the lyophilized mixture in a mixed solution of an acid catalyst and glutaraldehyde. As the acid catalyst, mineral acid such as HCl or H ₂ SO ₄ may be used.

The lithium ion complex may be mixed with the polyvinyl alcohol composite foam in an amount of 50 to 300 wt% based on the weight of the polyvinyl alcohol.

The present invention also provides a porous polyvinyl alcohol composite foam in which a lithium ion is uniformly dispersed in a polyvinyl alcohol foam.

In the porous polyvinyl alcohol composite foam, the lithium ionic material may be contained in an amount of 50 to 300 wt%, more preferably 100 to 250 wt%, based on the weight of the polyvinyl alcohol.

When the lithium ion content is less than 50 wt%, the lithium adsorption effect is small. When the lithium ion content is more than 300 wt%, the durability of the foam decreases and it is difficult to repeatedly use the lithium ion.

The composite foam may have a hierarchical pore structure therein, and may selectively adsorb lithium ions from a solution containing lithium ions.

According to another embodiment of the present invention, it is possible to provide a lithium ion adsorbent comprising a porous polyvinyl alcohol composite foam in which a lithium ion is uniformly dispersed in a polyvinyl alcohol foam.

According to another embodiment of the present invention, there is provided a method of manufacturing a lithium ion secondary battery, comprising the steps of: immersing the lithium ion adsorbent in a solution containing lithium ions to absorb the solution; Dehydrating the lithium ion adsorbent absorbed by the solution; And treating the acid solution with the dehydrated lithium ion adsorbent to provide a lithium ion recovery method.

The polyvinyl alcohol composite foam according to the present invention is produced by lyophilizing a water-soluble mixture of a foamed lithium ion complex and polyvinyl alcohol and then crosslinking, and the manufacturing process is simple and eco-friendly. In addition, the foam according to the present invention is a flexible and durable porous foam having a very low adsorption capacity loss and very low lithium ion absorption rate, and does not cause a reduction in absorption performance or physical damage after repeated use, . It can also be utilized as a passive adsorbent capable of selectively recovering lithium ions through a "immerse and squeeze" mechanism.

FIG. 1 shows a method of producing a composite foam of lithium ion sieve and polyvinyl alcohol according to an embodiment of the present invention.
FIG. 2 is an FTIR spectrum of a foam sample of a composite foam according to an embodiment of the present invention, in which lithium ion shed amounts are different from each other and crosslinked or crosslinked by glutaraldehyde.
Fig. 3 is an SEM image of a polyvinyl alcohol foam sample different in lithium ion shed amount from (a) a photograph of a foam, (b) a low magnification SEM image of a foam showing an open cell structure, (c) a pure polyvinyl alcohol foam, d) a SEM image of a foam loaded with 50 wt% of lithium ion, a foam having 250 wt% of lithium ion, and a foam having 300 wt% of lithium ion.
Figure 4 is a BET analysis adsorption desorption curve of the composite foam according to the present invention.
5 is a graph showing adsorption characteristics of the composite foam according to the present invention.
Figure 6 is an EPMA image of a composite foam according to the present invention.
7 is a graph showing the effect of lithium ion shedding amount on lithium ion selectivity of the composite foam according to the present invention.
8 is a graph showing the repeated use performance of the lithium ion adsorbent according to the present invention.
9 is a photograph and a graph showing the durability of the composite foam according to the lithium ion shed amount of the composite foam according to the present invention.
10 is a graph showing the flexibility of the composite foam according to the lithium ion shedding amount according to the present invention.
11 is a comparative graph showing the dynamic characteristics of the composite foam and the powdery absorber according to the present invention.

Hereinafter, the present invention will be described in more detail with reference to Examples. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. The scope of the present invention is defined by the appended claims, and all differences within the scope of equivalents thereof should be construed as being included in the present invention.

< Example >

1. Raw materials

(98% to 99% hydrolyzed, average MW = 85,000 to 124,000 g / L), and lithium manganese dioxide (trace metals LiMnO ₂ > 99%, particle size <1 μm), glutaraldehyde cross- mole were purchased from Sigma Aldrich (USA).

Hydrochloric acid (HCl, RHM 3537%) and nitric acid (RHM 60% HNO ₃ ) were purchased from Junsei Chemical (Japan) and lithium chloride (LiCl, ≥98%) was obtained from Fluka (Switzerland). All chemicals were used without further purification.

2. Manufacture of LIS powder

LIS was prepared as previously described (MJ Park et al., Chemical Engineering Journal 254 (2014) 73-81, Y. Pan et al., RSC Adv., (2014, 4) 660-669) . LiMnO ₂ After the precursor Muller grinding using a bowl and pestle and filtered through a sieve (No. 200, Æ = 63 μm ), by heating in air (10 ℃ min ^-1, 4 hours at 450 ℃) Li _{1. 6} Mn _{1 . 6} O ₄ .

The powder was then depolymerized in a 0.5 M HCl solution for 24 h (1 g L ^-1 ) and subjected to H _{1 .6} Mn ₁ .sup.th through topotactic Li.sup. ⁺ / H.sup. ⁺ Ion exchange _{. 6} O ₄ .

The LIS dispersion was vacuum filtered and then repeatedly washed with deionized (DI) water until the pH became neutral.

The slurry was dried at 30 DEG C and the final LIS powder was stored in the dryer before use. The characteristics of LIS were confirmed by X-ray diffraction analysis (40 kV, 30 mA, 0.02 step count- ¹ , CuKa source PANalytical X'pert-Pro, Netherlands), and the existing literature (L. Wang. Interface Sci. 325 (2008) 31-40).

3. Flexibility  LIS / PVA  complex Foam  Produce

The LIS / PVA foam was prepared as shown in Fig. The PVA doping mixture with varying LIS loading (50 to 300 wt% based on the amount of PVA) was prepared by initially dissolving PVA in deionized water (DI) (15 wt%) at 140 DEG C for 6 hours with constant agitation . A certain amount of LIS was then added and the mixture was stirred for another 4 hours. On the other hand, pure PVA doping solution (15 wt%) was prepared by stirring continuously for 10 hours.

While maintaining the high temperature, Triton X-100, a nonionic surfactant, was supplied as a blowing agent into the blender. After 1 mL of Triton X-100 was added and 30 seconds of stirring were alternately performed, a foamy dispersion was obtained. After 6 mL of surfactant was added, the bubbles were further stirred for 3 minutes and then quickly transferred to a 50 mL plastic cylindrical mold.

The froth was frozen for 8 hours and then freeze-dried (Model No. 77 540-10, BK BioLab Co.) for 36 hours to sublimate the ice crystals. Due to the vacuum space occupied by ice crystals and trapped bubbles, a high porosity, dry, rigid LIS / PVA foam was obtained.

Acid-catalyzed acetylation of PVA by immersing 3 g of dry foam in 300 mL of 0.9 mL HCl and 12 mL glutaraldehyde solution in EtOH / H ₂ O (4: 1 v / v) solvent at 50 ° C for 24 hours &Lt; / RTI &gt; was carried out.

The foam was thoroughly washed with deionized water to remove excess reactants and a flexible composite foam was obtained. Prior to use, the foam was vacuum dried at 50 &lt; 0 &gt; C for a day and then stored in a dry, pickled container.

4. LIS / PVA  Analyze the characteristics of the form

The shape and surface characteristics of the LIS / PVA foam were confirmed by scanning electron microscopy (SEM-EDX, Hitachi S-3500 N, Japan) equipped with an energy dispersive X-ray spectrometer.

The LIS distribution in the PVA matrix was analyzed using a JEOL JXA-8500F electron microscope (EPMA) equipped with an Energy Dispersive X-Ray Spectrometer.

The total density (r _B ) was measured by measuring the cylindrical sample volume calculated using a high-precision balance scale for weighing and an electronic caliper. The actual density (r _T ) was measured by the peak nometa method, where the overall porosity (% P) was calculated from P = 1- (r _B / r _T ).

Thermogravimetric analysis was performed to determine the actual LIS content in the foam (TGA / SDTA851, Mettler Toledo Int., Inc., Switzerland). The Brunauer-Emmett-Teller (BET) specific surface area was measured with Belsorp-mini II (Bel Japan, Inc.). The nitrogen adsorption / desorption isotherms were measured at a relative pressure range (pp _o ^-1 ) of 0.01 and 1.0. The pore size distribution was calculated using the Barrett-Joyner-Halenda (BJH) method.

Water absorption was calculated by weight measurement using equation (1). In equation (1), w _o and w ₁ are the mass of the foam before and after immersing in water for 24 hours, respectively. Similarly, the size of the foam was recorded both before and after immersion in water to determine the volume expansion.

(1)

(One)

5. Adsorption experiments

All adsorption experiments were performed at 30 ° C (303K) unless otherwise noted. PVA composite foam (sample weight: 50 wt.% = 120 mg; 100 wt.% = 80 mg) having various LIS loading amounts and 40 mg of pure LIS dry powder sample (40 mg) , 150 wt% = 66.67 mg, 200 wt% = 60 mg, 250 wt% = 5 6 mg, 300 wt% = 53.33 mg; each sample contained 40 mg LIS) was preliminarily washed with 0.5M HCl and pH = 7 And rinsed thoroughly with hot water.

Samples were dried at 50 ° C for 12 hours, stored in a desiccator, and then weighed. Samples were immersed in 45 mL Li ⁺ solution for 24 hours in a shaking incubator until equilibrium was reached. The adsorption capacity value (q _e ) was calculated from equation (2), where C _o and C _e are the initial and equilibrium Li ⁺ concentrations, respectively, and V is the solution volume.

(2)

(2)

Equilibrium adsorption was performed at various Li ⁺ concentrations with initial pH = 11.

Solution is prepared from 1 mM LiOH various amounts of LiCl added 7~35mgL C _o = ^{- 1} was obtained. Selectivity of the form of the Li ⁺ absorption is different cations generally present in secondary Li ⁺ source, such as water ^{(eg. Na +, Mg 2 +,} K + and Ca ^{2 +)} of the Li ⁺ solution is mixed Absorption experiments were conducted.

6. LIS / PVA  Form reusability and durability

The reusability of the foam was evaluated by repeated adsorption and desorption experiments. The adsorption mode was performed as described above, but Li ⁺ desorption was performed by immersing the foam used in 45 mL of 0.5 M HCl for 24 hours at 30 &lt; 0 &gt; C. The regenerated sample was subsequently washed with deionized water until the pH was neutral. The foam was dried and then used in the next adsorption desorption cycle.

Before desorption, foam squeezing is required to remove the Li ⁺ source solution. The durability of the foam samples was evaluated through compresion force deflection tests as described in R. Chitrakar et al., J. Mater. Chem. 10 (2000) 2325-2329. The strength required for foam dehydration was measured at maximum compression and the amount of water removed was measured in weight. Flexibility of the foam was evaluated by measuring the height of the sample after each compression.

7. Analysis Method

Component analysis was performed using an inductively coupled plasma mass spectrometer (ICP-MS Agilent 7500 series, USA). Liquid samples such as feed, Li ⁺ -removing solution, and dilute HCl used for Li ⁺ desorption were collected and passed through a 0.2 mm nylon syringe filters.

Before ICP-MS determination, 10 mL of purified water was pretreated with acid (60% HNO _3, 3 mL) in a MARS-5 microwave oven (CEM, USA). The treated sample was filtered through a 100 mL polypropylene scalpel and, if necessary, further diluted with deionized water. The remainder of the sample was used to measure the pH using a Schott instruments pH probe (Z451 SI Analytics GmBH, Germany) in an Orion 4 star pH meter (Thermo Electron Corporation, USA).

< Test Example >

1. LIS / PVA  Morphological and structural characteristics of foam

As a polymer containing a large number of OH groups, the hydrophilic PVA easily dissolves in water. The acid-catalyzed acetylation with glutaraldehyde (GA) crosslinker to stabilize the dried LIS / PVA foam can be usefully applied to aqueous systems. In the control of the crosslinking step, it becomes the most suitable solvent system for obtaining LIS / PVA foam with excellent flexibility when EtOH: water is 4: 1 (v / v). The FTIR results in Figure 2 show the spectrum of the non-crosslinked foam and the GA crosslinked foam.

Compared to non-crosslinked PVA, broad OH stretching vibration peaks at n = 3000-3600 cm ^-1 were all reduced in the crosslinked samples. The peak at 1735 cm ^-1 is associated with the residual aldehyde group of the unreacted GA residue after acetylation. GA samples at about n = 987 ~ 1188 cm ^-1 in the band, but a wide cross-linking is due to the combined COC and CO formed in the acetylation degree, n = 1095, which is not related to C-OH stretching the PVA crosslinking cm ^{- 1} &lt; / RTI &gt;

On the other hand, the decrease in the peak intensity of the sample is also due to the decrease of the PVA fraction due to the increase of the LIS loading amount. However, the image of FIG. 2 confirms that, in contrast to a non-crosslinked sample that is readily soluble in water, GA bridges can successfully produce water-stable stable foamed foams.

Figure 3a shows that foam produced due to the presence of LIS particles exhibits black color. The sponge foam has successively inter-connected macropores (Fig. 3b), thereby exhibiting high porosity. Much of the pure PVA (Figure 3c) has spherical pores with thin walls, which, in closer examination, have a smooth surface. Regardless of loading, the presence of the LIS creates a more irregularly shaped, internally-connected pore (Figs. 3d-3f), but the wall is obviously thicker with increasing LIS loading. As the LIS loading increases, the surface of the foam becomes rougher (Fig. 3d-3f).

Figure 4a N ₂ adsorption of the LIS / PVA foam having a pure PVA and other particle loading amount - represents the desorption curve. All samples showed IV isotherms, and the hysteresis between adsorption and desorption shows the mesoporosity of the foam.

Hysteresis loops at p po ^-1 = 0.45 were most evident at maximum loadings of LIS of 250 and 300 wt%. Table 1 summarizes the BET surface area calculated from the initial state of the isotherm and appears to steadily increase from 100 wt% LIS loading and above.

The low LIS loading of 50 wt% did not show a significant increase in BET surface area compared to pure PVA. The pore size distribution from the BJH model (Figure 4b) shows the bimodal pore structure of all samples except for pure PVA and 50 wt% LIS loaded PVA.

Increasing LIS loading produces more and larger mesopores, as evidenced by increased peak intensities and shifted pore radius peaks from 22 nm (100 wt%) to 30 nm (300 wt%).

The second peak lying between the meso and macropore regions was also shifted from 50 nm (100 wt%) to 54 nm (300 wt%). The results of SEM and surface analysis show a hierarchical pore structure in a foam composed mainly of macro and mesopores. However, the increase in mesopore volume (Table 1) indicates that the BET surface area increased due to LIS loading.

The actual bulk density (Table 1) was expected to increase as the LIS increases because the particles are more dense than PVA. On the other hand, the decrease in total porosity shows that the void space in the foam is lost due to the increase of LIS loading. However, the overall porosity does not reflect the hierarchical nature of the pores in the foam. Due to the addition of more LIS, macro pores of radius greater than 100 nm (not described in the BJH model) appear to have decreased in size or amount. The SEM image supports the previously suggested reasoning that the larger the LIS loading, the thicker the cell walls of the LIS / PVA foam.

Therefore, although a large amount of LIS loading increases the meso pore volume, a reduced portion of the macropore can eventually lower the overall porosity of the foam.

matter BET surface area
(m ² g ^-1 ) Mesopore volume
(cm ³ g ^-1 ) Actual density
(g cm ^-3 ) Bulk density
(g cm ^-3 ) Total porosity
(%) Pure PVA 2.19  13.45 1.19 ± 0.06 0.11 ± 0 .01 90.39  50wt% LIS / PVA 2.16 18.14  1.80 + 0.02 0.15 + 0.04 91.63 100wt% LIS / PVA  3.42 23.12 2.10 ± 0.13  0.21 + 0.04 90.11  150wt% LIS / PVA 9.66 24.5 6 2.38 + 0.03 0.26 + 0.07  88.96 200wt% LIS / PVA  10.53 25.35 2.64 ± 0.04  0.31 ± 0.01 88.27  250wt% LIS / PVA 20.53 28.01 2.86 + 0.04 0.37 + 0.07  87.22 300wt% LIS / PVA  23.01 29.09 3.17 ± 0.02  0.43 + 0.11 86.47  LIS powder - -  3.27 ± 0.16 - Unsportsmanlike

2. LIS / PVA  Hydrophilicity of foam

High water absorption due to expansion or volume expansion was observed in all foam samples (Table 2). Due to the abundant OH groups of polyvinyl alcohol, polyvinyl alcohol is readily soluble in water. Therefore, chemical cross-linking by glutaraldehyde is essential to ensure that it is not soluble in water. Acid-catalyzed acetylation of glutaraldehyde often produces acetal groups, but this reaction often does not proceed perfectly. Thus, the crosslinked PVA still contains the OH-group. This means that the polymer remains extremely hydrophilic during insolubilization. Thus, when immersed in water, the crosslinked PVA expands its chain while accepting water molecules until the resistance by the crosslinked linkage prevents the chain from loosening further from the equilibrium.

 matter Water absorption (gg ^-1 )  Volume Expansion (%)  Pure PVA 15.1 + - 0.10 40.1 50wt% LIS / PVA 12.4 ± 0.06  30.6 100wt% LIS / PVA 10.2 ± 0.05 26.5 150wt% LIS / PVA 8.5 ± 0.27  17.2 200wt% LIS / PVA 7.1 ± 0.03 16.2 250wt% LIS / PVA 6.7 ± 0.05  13.2 300wt% LIS / PVA 5.8 ± 0.02 8.9

In Table 2, high moisture absorption and volume expansion were observed in pure PVA. Both reductions were mainly observed due to an increase in the amount of hydrophobic LIS solid particles in the foam. This tendency clearly shows that the reduction of the hydrophobic PVA moiety reduces the foam's ability to absorb moisture and likewise degrades its swelling properties.

3. LIS / PVA  Absorption properties of foam

Equilibrium adsorption results indicate the effect of PVA on Li ⁺ absorption of LIS. At C _o = 7 mgL ^-1 (1 mM Li ⁺ ), pure PVA showed very low Li ⁺ absorption of q _e = 0.1 mgg ^-1 while LIS powder reached q _e = 7.8 mgg ^-1 . Therefore, the absorption of Li ⁺ in LIS / PVA is mainly due to the LIS component.

In order to observe the effect of PVA accurately, we used q _e The values are shown in FIG. 4A. Lower q _e Value indicates the inhibitory effect of the polymer scaffold on the adsorption performance of the LIS. This case has typically been observed in solid-supported absorbers reported in the prior art. Partial concealment of the LIS surface by the polymer can reduce Li ⁺ adsorbable adsorption sites.

The adsorption capacity (retained% q _e ) of the LIS retained after being contained in the foam is q _e Value ratio and the ratio of LIS powder. The results in FIG. 4A show that the inhibitory effect of PVA on LIS adsorption performance can be remarkably reduced by increasing the amount of LIS loading. At 50 wt%, only 69% of the LI ⁺ absorption capacity of the LIS was retained, but increased significantly to 93% at the LIS maximum loading of 300 wt%. The adsorption loss of only 7% of the LIS adsorption capacity is significantly superior to the results of previous studies.

To show the variety of C _o different LIS / PVA adsorption isotherm (Figure 5b) has the same tendency as that observed in Figure 5a having a loading amount of from, in which the adsorption performance of the LIS / PVA is adsorbed in the LIS powder with increasing adsorption loading Performance. The improved q _e with C _o indicates the saturation of the LIS adsorption site with a higher Li ⁺ recovery potential.

The Langmuir and Freundlich models (Eqs. (3) and (4)), which are widely used, were used to determine the maximum capacity of the foam or to account for the adsorption behavior. In the equation q _m is the maximum absorption capacity and K _L is the Langmuir constant, which is related to the absorption energy. On the other hand, K _F and n are adsorption capacity constants and adsorption strength constants, respectively.

(3)

(3)

(4)

(4)

The calculated isotherm constants are summarized in Table 3, and Li ⁺ absorption of LIS in LIS / PVA is characterized by Langmuir-type adsorption of a single layer rather than Freundlich.

The results obtained indicate that H⁺Li &lt; / RTI &gt;⁺Prove the chemical-adsorption of ions. Therefore, Li⁺ As the absorption increases, Li⁺The equilibrium pH of the solution is lowered. Q increased in the Langmuir model_m Values support the effect of decreasing the PVA matrix with increasing LIS loading.

The high q _m values obtained at 250 and 300 wt% show minimal adsorption losses (12% and 5%, respectively) for the LIS powders, which significantly outperform the previously reported LIS complexes. Conventional flat sheet poly (PVC) Li ⁺ absorbent membranes exhibited a Li ⁺ adsorption loss of 28% (P. Meshram et al., Hydrometallurgy 150 (2014) 192-208). Other studies have shown a 7-27% reduction in Li ⁺ adsorption when LIS is immobilized on the surface of polyurethane (PU) foam (F. Sagara et al., Sep. Sci. Technol. 24 (1989) 1227-1243 ).

sample Freundlich Langmuir n K _f (mgg ^-1 ) r ² K _L ( _L mg ^-1 ) q _m (mgg ^-1 ) r ² 50wt% LIS / PVA 6.35 4.50 0.90 0.43 8.30 0.99 100wt% LIS / PVA 7.60 5.04 0.94 0.42 8.59 0.99 150wt% LIS / PVA 10.11 5.68 0.93 0.46 8.66 0.99 200wt% LIS / PVA 13.05 6.40 0.59 0.40 9.33 0.98 250wt% LIS / PVA 11.47 6.25 0.67 0.38 9.73 0.98 300wt% LIS / PVA 10.87 6.61 0.57 0.36 10.20 0.99 LIS powder 12.82 8.06 0.90 0.99 10.72 0.99

The results obtained provide a solution for how to reduce the impact of the polymer matrix on the adsorption performance of LIS. First, the hydrophilicity of the PVA matrix improved absorption of the feed solution through the absorber as previously described. Second, increasing the amount of absorber loading reduced the Li ⁺ inactive area in the composite foam.

The presence of LIS on the foam surface was observed via SEM-EPMA (Fig. 6), indicating good particle distribution. The PVA matrix was still apparent at 50 wt%, but was completely covered with LIS particles at 250-300 wt% loading. Therefore, high particle loading increases the proportion of LIS exposed on the foam surface.

Similarly, the low polymer content reduced the incidence of Li ⁺ absorption sites occlusion by PVA. Also, as previously described, the BET surface area increased significantly from 2.2 m ² g ^-1 (50 wt%) to 23 m ² g ^-1 (300 wt%) with LIS loading. Therefore, (1) the use of a hydrophilic matrix and maximization of LIS loading, (2) increased exposure of the LIS on the foam surface, and (3) the large specific surface area of the composite improves the interaction between the LIS and the Li ⁺ feed solution, Minimize the adsorption capacity loss of LIS.

4. LIS / PVA  Adsorption selectivity of foam

The performance of the LIS / PVA foam capable of selectively separating Li ⁺ ions in the presence of other cations can be evaluated by comparing q _e , partition coefficient (K _d ), separation factor (S) and concentration factor (concentration factor, CF).

(5)

(5)

(6)

(6)

(7)

(7)

Sheep C _o
( mgL ^-One ) C _o
( mmolL ^-One ) C _e
( mmolL ^-One ) q _e x10 ^-2
( mmolg ^-One ) K _d
( mLg ^-One )

CF × 10 ^-3
( Lg ^-One ) Li ⁺ 11.68 1.68 0.81 + 0.03 98.2 ± 4.1 1220.37 1.00 583.85 Na ⁺ 7384.75 321.22 320.71 + - 9.04 56.8 ± 2.7 1.77 689.43 1.77 Mg ^{2 +} 16.65 0.69 0.68 ± 0.06 0.3 ± 0.0 4.05 301.44 4.03 Ca ^{2 +} 2.60 0.06 0.06 ± 0.01 0.01 ± 0.0 0.86 1415.07 0.86 K ⁺ 378.90 9.69 9.69 ± 0.80 0.3 ± 0.0 0.30 4129.65 0.30

To illustrate the separation behavior of the LIS / PVA foam, the selectivity of the foam component LIS powder and pure PVA foam was investigated as listed in Tables 4 and 5. The LIS powder has high q _e , K _d And CF values; The S value indicates that Li ⁺ ions can be more effectively collected from the feed solution than other metal ions. Of Li ⁺ in the mixture solution q _e it is lower than that of pure Li ⁺ due to the more partially block a large amount LIS surface by cations coexisting in than (1.12 mmol g ^-1). However, the sieving effect of LIS, which prevents penetration of larger cationic adsorbents, ultimately leads to Li ⁺ capture preference.

Cation C _o
(mg L ^-One )  C _o
( mmol  L ^-One ) C _e
( mmolL ^-One ) q _e x10 ^-2  ( mmolg ^-One ) K _d
(mL g ^-One  )

CF × 10 ^-3
( Lg  ^-One ) Li ⁺ 11.68  1.68 1.65 + 0.02 0.06 ± 0.1 7.78 1.00  19.39 Na ⁺ 7384.75  321.22 318.68 + - 8.17 28 7.2 ± 7.3 3.56 3.38  8.94 Mg ^{2 +} 16.65  0.69 0.63 + 0.04 6.2 ± 0.4 38.85 0.31  90.59 Ca ^{2 +} 2.60  0.06 0.06 + 0.03 0.4 ± 0.0 23.79 0.50  57.25 K ⁺ 378.90  9.69 9.42 ± 0.65 31.0 ± 1.2 13.01 0.92  32.03

About LIS powder except Li ⁺ has a very small absorption in the pure PVA and the high affinity for all of the metal ion, in particular Na ⁺ is the polymer matrix _(e q And K _d . The OH groups of the PVA mainly impart hydrophilicity to draw the solution into the foam and are typically not considered sites for metal ion complexes. However, at pH ≥ 11, a portion of the -OH group is de-protonated, resulting in a non-selective electrostatic binding site of the metal ion by allowing the polymer to have a partially negative charge.

This feature indicates that minimization of the PVA fraction can mitigate the selective reduction action of the LIS / PVA foam. Therefore, as the amount of LIS loading increases, the q _e , K _d And CF are remarkably decreased, whereas in case of Li ⁺ , q _e and K _d of LIS powder And CF (Table 4). Eventually, due to the increased LIS fraction, Li ⁺ ions can be more effectively separated from the feed solution than other metal ions present.

5. The LIS / PVA  Form reusability

From the viewpoint of Li ⁺ adsorption capacity and selectivity, the foam with the greatest amount of LIS loading showed the best performance (Fig. 7). However, an extremely low PVA fraction can weaken the durability of the foam. If the PVA fraction is too low, the crosslinking site becomes too small. Likewise, if too much LIS is present, it will interfere with the contact between the polymer and glutaraldehyde, resulting in a mechanically weak foam that is not suitable for long-term use. Thus, the most durable LIS / PVA with the highest adsorption performance is the result of repeated mechanical analysis (Fig. 9) and flexibility analysis (Fig. 10) for 200 wt%, 250 wt% and 300 wt% (Fig. 8).

The adsorption-desorption results (Fig. 8) did not show any sign of degradation of the Li ⁺ adsorption performance of the 200 wt% and 250 wt% LIS loaded foams. For both samples, a similar q _e value obtained from adsorption and desorption for each cycle indicates that all the Li ⁺ collected was effectively recovered from the foam through acid treatment. This also shows that both samples were effectively regenerated for repeated use. However, 300 wt% loaded LIS / PVA showed gradual performance degradation; Therefore, the disassembled foam after the third cycle is no longer tested.

As discussed above, the foam rapidly absorbs water and swells up slightly (volume expansion) as soon as it is immersed in the aqueous solution. A photograph of the wet LIS / PVA after the adsorption test is shown in Fig. The foam can be easily compressed to remove excess Li ⁺ removed feed solution. Due to the flexibility of the foam, the foam rapidly returns to its original volume after compression.

During regeneration of the foam, the foam must be dehydrated through compression prior to transfer to the diluted acid solution for Li ⁺ recovery. Therefore, the durability of the foam can be confirmed by repeatedly performing these processes shown in Fig. The foam loaded at 300 wt% did not pass the durability test because it was held for only two cycles.

On the other hand, LIS / PVA foams loaded with 200 wt% and 250 wt% exhibited a constant water absorption (FIG. 9B) and volume expansion (FIG. 9C), indicating that the two foams were structurally intact after several uses . By a stable water absorption, a constant dewatering compressive strength (Fig. 9d) and dewatering effect are similarly obtained from the two foams. However, 200 wt% LIS / PVA needed more compression because it absorbed more water than 250 wt% LIS loaded.

The result of the compressive force deflection (Fig. 10) shows that both foams (200 wt%, 250 wt%) can be compressed to 30% of the original height of the wet state to remove the absorbed water. The foam was not twisted after several cycles and recovered to its original wet state after repeated compression. These results demonstrate that both forms remain flexible after repeated use. The durability test results confirm that determining the optimum LIS loading is important in achieving satisfactory Li ⁺ absorption performance and foam reusability.

6. Select the LIS / PVA  Adsorption dynamics of foam

A general decrease in metal uptake is typically observed when the LIS is supported on a polymeric support. Figure 11 shows the time dependent behavior of Li ⁺ absorbed by the most suitable LIS / PVA foam. To observe whether LIS loading affects adsorption kinetics, a 50 wt% LIS / PVA foam was also tested. The rapid Li ⁺ uptake in all samples, particularly within the first 12 hours of LIS powder, can be attributed to the greater effectiveness of the adsorption sites in the early stages of the experiment. Finally, q _t The values stagnated as the samples reached Li ⁺ saturation.

Two well-known kinetic models were used to determine and compare the kinetic rate constants of LIS / PVA foam and LIS particles. Largergren-like quadratic and quasi-quadratic equations are shown in equations (8) and (9). Where k ₁ and k ₂ are the rate constants of each order.

(8)

(8)

(9)

(9)

sample Pseudo-first order Pseudo-second order q _e
(mg g ^-1 ) k ₁ × 10 ^-3
(min ^-1 ) r ² k ₂ × 10 ^-3
(g mg ^{- 1} min ^-1) q _e ^†
(mg g ^-1 ) h
(mg g ^{- 1} min ^-1 ) r ² LIS powder 4.11 2.72 0.98 2.31 7.97 0.15 0.99 50wt% LIS / PVA 3.28 2.51 0.96 1.82 6.59 0.08 0.99 200wt% LIS / PVA 7.64 2.56 0.95 1.73 7.14 0.09 0.99 250wt% LIS / PVA 5.04 2.56 0.97 2.09 7.15 0.11 0.99 pH = 11.08; V = 45 mL; m @ 40 mg; [Li ⁺ ] @ 1 mM or 6.8 mg L ^-1
† The value derived from equation (10)

The derived constants in Table 6 indicate that Li ⁺ adsorption of all samples has a greater association (r ² value) with a similar quadratic reaction rate than the Lagergren equation. Pseudo-first order graphs fit well linearly only at an early time under a limited time range (<1000 min), but fit well throughout the time tested for pseudo-second order velocity models.

These results indicate that the rate of absorption is not limited by the diffusion rate, but mainly by chemical adsorption of Li ⁺ on the LIS via ion exchange. Compared to LIS powder, all LIS / PVA foams exhibited somewhat lower k ₂ values. From the results, the correlation between LIS loading and k ₂ values was not clearly observed, since 50 wt% LIS / PVA showed a k ₂ value higher than 200 wt%. However, the absorption rate by the LIS powder was only about 10% faster than the absorption rate of the 250 wt% LIS / PVA foam composition having the highest performance in terms of Li ⁺ absorption rate.

The reduction in the adsorption rate constant of the LIS / PVA foam (Table 6) was significantly less (10% to 25%) than that of the particulate LIS adsorbent using chitosan and PVC as binders. Previous studies have shown that adsorption rate is at least ten times lower than that of LIS powder. These reports show that the retardation of Li ⁺ adsorption is due to limitations of the external surface area that can be contacted (Umeno, A. et al, Ind. Eng. Chem. Res. 41 (17), 4281-4287) (LW Ma et al, Microporous and Mesoporous Materials 142 (1982), pp. 183, 1985, pp. (2011) 147-153).

On the other hand, the better dynamic performance of LIS / PVA foams is mainly due to the excellent LIS-Li ⁺ interaction by high porosity structure, large specific surface area and hydrophilic matrix. The high water absorption of PVA, particularly in conjunction with volume expansion, creates an expanded free volume of the polymer network, providing minimal resistance to diffusion of the Li ⁺ feed solution through the matrix to the LIS surface. This explains why all LIS / PVA foams exhibit similar kinetic behavior to LIS powders.

From the results, (1) use of a hydrophilic polymer, such as a matrix and the PVA, and (2) adjusting structurally by and through the freeze-dried producing a porous foam network, and (3) to be used effectively to recover Li ⁺ from a variety of stream The optimum amount of LIS loading that enables the development of a composite absorber capable of absorbing the LIS can be confirmed. In particular, the present invention discloses the application of a flexible foam as a Li ⁺ absorber through a &quot; soak and squeeze &quot; mechanism, which is a complex and costly process typically required to operate a packed bed column and membrane system. The pump system becomes unnecessary.

The LIS loaded flexible hydrophilic PVA foams according to the present invention have been successfully prepared through lyophilization techniques. This technique is effective in producing LIS / PVA foams with well-distributed particles present at high loading and producing high porosity matrices. The composite foam foam according to the present invention can be used as a passive adsorbent in a Li ⁺ containing stream without the need for complex pumps or flow systems.

Claims (16)

Preparing a lithium ion complex;
Mixing the prepared lithium ion complex with polyvinyl alcohol and a foaming agent to prepare a foamy mixture;
Lyophilizing the mixture; And
And cross-linking the lyophilized mixture by acetylation under an acid catalyst to obtain a porous polyvinyl alcohol composite foam. The method according to claim 1,
Further comprising the step of cooling the foamy mixture prior to the lyophilization step. The method according to claim 1,
Wherein the step of preparing the lithium ion complex comprises:
Crushing the lithium manganese oxide precursor;
Heat treating the pulverized lithium manganese oxide at 400 to 600 ° C; And
And depolymerizing the heat-treated lithium manganese oxide to obtain a porous polyvinyl alcohol composite foam. The method according to claim 1,
The lithium ion sieve is H _{1. 6} Mn _{1 . 6} &gt; O &lt; _{4 &} gt ;. &lt; / RTI &gt; The method according to claim 1,
Wherein the foaming agent is a nonionic surfactant. The method according to claim 1,
Wherein the crosslinking step is carried out by immersing the lyophilized mixture in a mixed solution of an acid catalyst and glutaraldehyde. The method according to claim 1,
Wherein the lithium ion complex is mixed with 50 to 300 wt% based on the weight of the polyvinyl alcohol. delete delete delete delete delete delete delete delete delete

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