Core-shell structured metal-organic framework-polymer fiber-based adsorbent, preparation method therefor, and rare earth metal recovery method using same

Abstract

The present invention relates to: a core-shell structured metal-organic framework-polymer fiber-based adsorbent, which has excellent maximum adsorption capacity and adsorption rate characteristics with respect to rare earth metals and allowing for easy adsorbent recovery; a preparation method therefor; and a rare earth metal recovery method using same. The core-shell structured metal-organic framework-polymer fiber-based adsorbent according to the present invention comprises a metal-organic framework on the surface of a sodium polyacrylate (NaPA) fiber.

Description

Core-shell structured metal-organic framework-polymer fiber-based adsorbent, its manufacturing method, and rare earth metal recovery method using the same

[0001] The present invention was made under the support of the Ministry of Science and ICT of the Republic of Korea under the research project number 1711191619, the management organization of the project is the National Research Foundation of Korea, the research project name is “Nanomaterial Technology Development”, the research project title is “Development of customized module technology to ensure efficient field applicability of extreme environment responsive filters”, and the research period is 2023.01.01-2023.12.31.

[0002] The present invention relates to an adsorbent based on a metal-organic framework-polymer fiber having a core-shell structure, a method for producing the same, and a method for recovering rare earth metals using the same. More specifically, the present invention relates to an adsorbent based on a metal-organic framework-polymer fiber having a core-shell structure, which has excellent maximum adsorption capacity and adsorption rate characteristics for rare earth metals and facilitates recovery of the adsorbent, a method for producing the same, and a method for recovering rare earth metals using the same.

[0003] Nd-Fe-B permanent magnets, which are essential in various cutting-edge industries such as aerospace, clean energy, electric vehicles, and batteries, are known to possess permanent magnetism unless the external environment changes. However, demagnetization, which reduces magnetic strength due to heat, oxidation, moisture, and reverse magnetic fields in various usage environments, can shorten the lifespan. For reference, Nd-Fe-B permanent magnets are composed of approximately 65 wt% Fe, 25 wt% Nd, and 10 wt% Dy (Green Chemistry, vol. 20, 1065-1073 (2018)).

[0004] Therefore, permanent magnets used in industrial settings for a certain period of time are either discarded or recycled. Permanent magnet recycling involves recovering the rare earth metals (Nd and Dy in the case of Nd-Fe-B permanent magnets) contained within them.

[0005] Known methods for recovering rare earth metals include solvent extraction, precipitation, spray roasting, membrane, electrolysis, and adsorption. Solvent extraction (see Non-Patent Document 4) and precipitation require large amounts of environmentally and biohazardous chemicals, while spray roasting consumes a significant amount of energy relative to the amount of rare earth metals recovered. Furthermore, membrane and electrolysis methods have limitations, such as low separation performance and low process efficiency. Meanwhile, adsorption using adsorbents offers the advantage of being simple and relatively economical compared to other recovery methods.

[0006] When recovering rare earth metals using adsorbents, factors such as the adsorbent's maximum adsorption capacity, adsorption rate, and ease of recovery must be considered to maximize the efficiency of the recovery process. To maximize the recovery efficiency of rare earth metals, the adsorbent must exhibit excellent maximum adsorption capacity and adsorption rate. Furthermore, for the recovery of adsorbed rare earth metals and the recycling of the recovered adsorbent, the adsorbent must be easily recovered.

[0007] 'Chemical Engineering Journal, vol. 387, 124023 (2020)' (Non-patent Document 2) describes that a high adsorption capacity of 249.90 mg / g or more for rare earth metals such as Nd(III) can be achieved through three-dimensional mushroom-shaped nanoparticles (UiO-66-NH2@ZIF-8) forming a metal-organic framework. However, since the adsorbent is a nanoparticle, there is a disadvantage in that it is not easy to recover the adsorbent with the rare earth metal adsorbed on it.

[0008] 'Chemical Engineering Journal, vol. 351, 832-840 (2018)' (Non-patent Document 3) presents a technology for recovering rare earth metals using beads in the form of amorphous ZrP dispersed in PAN. Since the beads have a size of mm, recovery of the adsorbent is easy, but the maximum adsorption amount is less than 100 mg / g, so the adsorption characteristics for rare earth metals are not excellent.

[0009] [Prior Art Literature]

[0010] [Patent Document]

[0011] (Patent Document 1) Korean Patent Publication No. 2153737 (Published on September 9, 2020)

[0012] (Patent Document 2) Korean Patent Publication No. 2023-95594 (published on June 29, 2023)

[0013] (Patent Document 3) Korean Patent Publication No. 2023-72069 (published on May 24, 2023)

[0014] [Non-patent literature]

[0015] (Non-patent literature 1) Green Chemistry, vol. 20, 1065-1073 (2018)

[0016] (Non-patent literature 2) Chemical Engineering Journal, vol. 387, 124023 (2020)

[0017] (Non-patent literature 3) Chemical Engineering Journal, vol. 351, 832-840 (2018)

[0018] (Non-patent Document 4) Chemical Engineering and Processing - Process Intensification, vol. 148, 107831 (2020)

[0019] The present invention has been devised to solve the above problems, and its purpose is to provide an adsorbent based on a metal-organic framework-polymer fiber having a core-shell structure that has excellent maximum adsorption capacity and adsorption rate characteristics for rare earth metals and facilitates recovery of the adsorbent, a method for producing the same, and a method for recovering rare earth metals using the same.

[0020] In order to achieve the above purpose, the adsorbent based on a metal-organic framework-polymer fiber having a core-shell structure according to the present invention is characterized in that a metal-organic framework is provided on the surface of sodium polyacrylate (NaPA) fiber.

[0021] Sodium carboxylate groups (-COONa) are provided on the surface of sodium polyacrylate (NaPA) fibers. In addition, amine groups (-NH2), carboxyl groups (-COOH), hydroxyl groups (-OH), and sulfate groups (SO4) are provided on the surface of sodium polyacrylate (NaPA) fibers. 2- ), phosphate group ([PO4] 3- ) can be provided.

[0022] The metal-organic framework is ZIF-8.

[0023] Sodium polyacrylate (NaPA) fibers have a diameter of several tens of micrometers or more.

[0024] The present invention relates to an adsorbent based on a metal-organic framework-polymer fiber having a core-shell structure, a method for manufacturing the same, and a method for recovering rare earth metals using the same, the adsorbent comprising the steps of: surface-modifying a polyacrylonitrile (PAN) fiber with a sodium polyacrylate (NaPA) fiber having a sodium carboxylate group (-COONa); fixing a metal-organic framework precursor to the surface of the sodium polyacrylate (NaPA) fiber; and converting the metal-organic framework precursor into a metal-organic framework.

[0025] The step of surface-modifying polyacrylonitrile (PAN) fibers with sodium polyacrylate (NaPA) fibers having sodium carboxylate groups (-COONa) is to immerse polyacrylonitrile (PAN) fibers in a NaOH solution to replace the nitrile groups of polyacrylonitrile (PAN) with sodium carboxylate groups (-COONa).

[0026] The step of fixing a metal-organic framework precursor to the surface of a sodium polyacrylate (NaPA) fiber includes a step of immersing the sodium polyacrylate (NaPA) fiber in a metal solution in which metal is dissolved to adsorb metal ions onto the surface of the sodium polyacrylate (NaPA) fiber, and a step of precipitating the metal ions in the form of metal hydroxide to form a metal-organic framework precursor.

[0027] The process of forming a metal-organic framework precursor by precipitating metal ions in the form of metal hydroxide is to immerse sodium polyacrylate (NaPA) fibers with metal ions adsorbed thereon in an ethanol solution to precipitate metal ions in the form of metal hydroxide.

[0028] The method for recovering rare earth metals using an adsorbent based on a metal-organic framework-polymer fiber having a core-shell structure according to the present invention is characterized by recovering rare earth metals in a solution by adding an adsorbent to a solution in which rare earth metals are dissolved.

[0029] It may include a process of dissolving Fe and rare earth metals by adding a substance composed of Fe and rare earth metals to a solution having a pH of 1 to 2, a process of precipitating and precipitating Fe components by adjusting the pH of the solution to 4 or higher, and a process of recovering rare earth metals in the solution using the adsorbent.

[0030] The core-shell structured metal-organic framework-polymer fiber-based adsorbent according to the present invention, the manufacturing method thereof, and the rare earth metal recovery method using the same have the following effects.

[0031] Based on its high adsorption selectivity for rare earth metals, it exhibits a maximum adsorption capacity of over 400 mg / g and has an adsorption rate characteristic that reaches adsorption equilibrium within a very short time. In addition, its size of over ㎛ facilitates easy recovery of the adsorbent.

[0032] FIG. 1 is a flowchart illustrating a method for manufacturing an adsorbent based on a metal-organic framework-polymer fiber having a core-shell structure according to one embodiment of the present invention.

[0033] FIG. 2 is a schematic diagram illustrating a method for manufacturing an adsorbent based on a metal-organic framework-polymer fiber having a core-shell structure according to one embodiment of the present invention.

[0034] Figure 3a shows the FT-IR analysis results showing that the nitrile group of PAN is replaced with a sodium carboxylate group (-COONa) depending on the immersion time in a NaOH solution.

[0035] Figure 3b shows the experimental results showing the adsorption amount of Zn metal ions according to the type of reaction solution.

[0036] Figure 3c shows the FT-IR analysis results for the NaPA fiber surface.

[0037] Figure 3d shows the XRD analysis results for each manufacturing step of CSCF.

[0038] Figure 4 shows the results of FESEM and FESEM-EDS analysis at each manufacturing stage of CSCF.

[0039] Figures 5a to 5d are experimental results showing the adsorption performance and recovery efficiency of CSCF manufactured according to Experimental Example 1.

[0040] Figures 6a to 6d show Nd of the NPZIF-8 / NaPAF adsorbent manufactured according to Experimental Example 1. 3+ , Dy 3+ The experimental results showing the recovery performance according to the concentration and adsorption time for each, and the results of introducing the relevant adsorption model to interpret the results of this experiment are presented.

[0041] Figures 7a and 7b show Nd of the NPZIF-8 / NaPAF adsorbent manufactured according to Experimental Example 1. 3+ , Dy 3+ The maximum adsorption capacity and recovery rate constant (k) for each were compared with the best adsorbents in previously reported papers.

[0042] Figure 8a is Nd 3+and Dy 3+ XRD analysis results of the NPZIF-8 / NaPAF adsorbent surface before and after adsorption.

[0043] Figures 8b to 8d are HRTEM lattice images of NPZIF-8 nanoparticles on the CSCF surface, Nd 3+ , Dy 3+ Showing before and after ion adsorption.

[0044] Fig. 9 is Nd 3+ , Dy 3+ TEM-EDS analysis results after ion adsorption.

[0045] Figures 10a and 10b show the experimental results showing the maximum adsorption amounts of NaPAF, NPZIF-8, and NPZIF-8 / NaPAF (CSCF), respectively.

[0046] Figure 10c shows the Nd of NaPAF, NPZIF-8 and NPZIF-8 / NaPAF (CSCF), respectively. 3+ , Dy 3+ FT-IR analysis results before and after adsorption.

[0047] Figure 10d is a reference diagram schematically illustrating the rare earth metal (REE) adsorption mechanism of the NPZIF-8 / NaPAF adsorbent.

[0048] Figure 11a is Fe 2+ , Nd 3+ , Dy 3+ Experimental results measuring the distribution coefficients for each metal ion of the NPZIF-8 / NaPAF adsorbent in a solution containing coexisting ions.

[0049] Figure 11b shows the change in the composition ratio of Fe, Nd, and Dy according to pH conditions.

[0050] Figure 11c shows the experimental results showing the pressure drop (ΔP) according to the flow rate of NPZIF-8 / NaPAF adsorbent and NPZIF-8 adsorbent.

[0051] Figures 12a to 12c are experimental results showing the regeneration characteristics of the NPZIF-8 / NaPAF adsorbent.

[0052] The present invention presents a technology for an adsorbent that not only has excellent maximum adsorption capacity and adsorption speed characteristics for rare earth metals, but also forms a fiber shape with a diameter of several tens of ㎛, making it easy to recover.

[0053] An adsorbent according to one embodiment of the present invention comprises a core-shell structure, in which metal-organic frameworks (MOFs) are provided on polymer fibers. The polymer fibers have a diameter of several tens of micrometers, thereby enhancing the ease of recovery of the adsorbent, and the MOFs provided on the polymer fibers enable the adsorption of rare earth metals based on their large specific surface area characteristics.

[0054] Metal-organic frameworks (MOFs) are porous polymers with a large specific surface area, and are known to have excellent properties for capturing gases or molecules due to their large specific surface area, forming a structure in which metals are linked by organic groups (linkers).

[0055] The present invention applies a metal-organic framework to the adsorption of rare earth metals.

[0056] The large surface area of ​​metal-organic frameworks enables the capture of metal particles such as rare earth metals and even physical adsorption to a certain extent, similar to the capture of gases and molecules. However, metal particles captured in the metal-organic framework can be easily desorbed from the metal-organic framework, and the proportion physically adsorbed to the metal-organic framework is limited.

[0057] Therefore, in order to ensure that rare-earth metals are stably adsorbed onto the metal-organic framework beyond simple capture of the rare-earth metals, physicochemical bonding between the metal-organic framework and the rare-earth metal is required.

[0058] The present invention can improve the adsorption characteristics for rare-earth metals by allowing rare-earth metals to be captured in a metal-organic framework and maintained in an adsorbed state through electrostatic attraction between functional groups formed on polymer fibers by surface modification and rare-earth metal ions.

[0059] In addition, since high adsorption properties for rare earth metals are expressed by the metal-organic framework, the metal-organic framework must be stably bonded to the polymer fiber, and the functional group formed on the polymer fiber of the present invention mediates the bonding between the polymer fiber and the metal-organic framework.

[0060] That is, the functional group formed on the polymer fiber by surface modification in the present invention performs two roles. One is to allow the rare-earth metal to be adsorbed onto the metal-organic framework through electrostatic attraction with the rare-earth metal ion, and the other is to mediate the bond between the polymer fiber and the metal-organic framework so that the metal-organic framework is stably fixed on the polymer fiber.

[0061] The functional group formed on the polymer fiber by surface modification is a sodium carboxylate group (-COONa). In addition, the polymer fiber having the sodium carboxylate group (-COONa) is sodium polyacrylate (NaPA), and sodium polyacrylate (NaPA) is formed by surface modification of polyacrylonitrile (PAN).

[0062] In addition to the sodium carboxylate group (-COONa), the functional group provided on the polymer fiber includes an amine group (-NH2), a carboxyl group (-COOH), a hydroxyl group (-OH), and a sulfate group (SO4) capable of fixing the metal ion of the metal organic framework precursor. 2- ), phosphate group ([PO4] 3-) may be applied. However, a preferred embodiment is one in which a sodium carboxylate group (-COONa), which is involved in not only the bonding between the polymer fiber and the metal-organic framework but also the electrostatic attraction with the rare earth metal, is applied as a functional group on the polymer fiber.

[0063] The type of metal-organic framework provided on the polymer fiber is not particularly limited. As described above, the functional groups on the polymer fiber are bonded to the metal ions of the metal-organic framework precursor. Therefore, any metal-organic framework containing a metal ion capable of bonding with such functional groups can be applied to the present invention. In the experimental examples described below, ZIF-8 was used as the metal-organic framework.

[0064] An adsorbent based on a metal-organic framework-polymer fiber having a core-shell structure according to an embodiment of the present invention has a maximum adsorption amount for rare earth metals of 400 mg / g or more, and reaches adsorption equilibrium within about 1 minute, thereby exhibiting excellent maximum adsorption amount and adsorption rate characteristics for rare earth metals. In addition, as confirmed in the experimental examples described below, the adsorbent according to an embodiment of the present invention has a diameter of about 50 μm or more and a length longer than that, so that recovery of the adsorbent is very easy.

[0065] For reference, in the case of patent document 3, a technology for a gas sensor in which ITO and a metal-organic framework are coated on nanofibers is presented, but the diameter of the nanofibers formed by electrospinning is in the nanometer size, so when this technology is applied for rare earth metal adsorption purposes like the present invention, the nanofibers become tangled, which reduces the surface area of ​​the adsorbent and makes it difficult to control them in a fibrous form in water.

[0066] A method for manufacturing an adsorbent according to one embodiment of the present invention is described below with reference to FIGS. 1 and 2.

[0067] First, surface modification of polymer fibers is performed (S101). Polyacrylonitrile (PAN) can be used as the polymer fiber. A NaOH solution is prepared, and polyacrylonitrile (PAN) is immersed in the NaOH solution for a certain period of time to replace the nitrile groups of polyacrylonitrile (PAN) with sodium carboxylate groups (-COONa). Through this process, polyacrylonitrile (PAN) is converted to sodium polyacrylate (NaPA), and sodium carboxylate groups (-COONa) are provided on the sodium polyacrylate (NaPA).

[0068] Next, a metal-organic framework precursor (MOF precursor) is fixed to the surface-modified polymer fiber, i.e., sodium polyacrylate (NaPA) (S102).

[0069] Specifically, sodium polyacrylate (NaPA) is added to a metal solution containing dissolved metal, for example, a metal solution containing dissolved Zn, to adsorb metal ions onto the surface of sodium polyacrylate (NaPA). At this time, the surface of sodium polyacrylate (NaPA) is cathodic due to the sodium carboxylate group (-COONa), and the metal ions are adsorbed onto the surface of sodium polyacrylate (NaPA) due to the electrostatic attraction between the sodium carboxylate group (-COONa) and the metal ions. Here, the metal solution is strongly acidic with a pH of 2 to 4.

[0070] Sodium polyacrylate (NaPA) with metal ions adsorbed thereon is removed from the metal solution and placed in an ethanol-based reaction solution (or methanol-based reaction solution) having a pH of 5 to 12. As a result, the metal ions adsorbed on the surface of sodium polyacrylate (NaPA) are precipitated in the form of metal hydroxide, and the metal hydroxide precipitated on the surface of sodium polyacrylate (NaPA) corresponds to a metal-organic framework precursor. When a metal solution with Zn dissolved therein is used, the metal-organic framework precursor may be Zn5(OH)8(NO3)2·2H2O.

[0071] When precipitating a metal-organic framework precursor on the surface of sodium polyacrylate (NaPA), if hydrochloric acid is used as a reaction solution other than an ethanol-based reaction solution (or a methanol-based reaction solution), the precipitation of metal hydroxide hardly occurs. If distilled water is used as the reaction solution, a certain amount of metal hydroxide precipitation occurs, but the moisture content is high, so the diameter of the fiber changes greatly, making it difficult for crystals to be fixed on the surface. On the other hand, if an ethanol-based reaction solution is used, the precipitation of metal hydroxide is significantly superior, and this can be confirmed through the experimental results described below.

[0072] In a state where a metal-organic framework precursor is formed on the surface of sodium polyacrylate (NaPA), the metal-organic framework precursor is converted into a metal-organic framework (MOF) (S103). Specifically, sodium polyacrylate (NaPA) on which the metal-organic framework precursor is fixed is added to an organic ligand solution, and then stirred to convert the metal-organic framework precursor into a metal-organic framework (MOF). At this time, the organic ligand solution uses a solution containing an organic ligand that can react with the metal-organic framework precursor to form a metal-organic framework (MOF). In one example, an adsorbent in which ZIF-8 is fixed as a metal-organic framework to sodium polyacrylate (NaPA) can be manufactured through the above process using 2-methyl imidazole (mIm) as an organic ligand.

[0073] The adsorbent manufactured according to the present invention, i.e., the adsorbent based on a metal-organic framework-polymer fiber having a core-shell structure, exhibits high adsorption selectivity for rare-earth metals. That is, in an environment where various metals, including rare-earth metals, coexist, it exhibits excellent adsorption selectivity for rare-earth metals.

[0074] Referring to the experimental results described below, Fe 2+ , Nd 3+ , Dy 3+ In this solution, the adsorbent of the present invention is dissolved together with Nd 3+ , Dy3+ The adsorption amount for Fe 2+ It is more than 100 times higher than the adsorption amount. Specifically, the distribution coefficient (K) indicating the adsorption selectivity of the adsorbent for a specific ion of the adsorbent using the adsorbent of the present invention d , mg / L) for each Fe and rare earth metal ion, the order of the distribution coefficient values ​​is Fe 3+ (1.6×10 3 mg·L -1 ) << Dy 3+ (2.0×10 5 mg·L -1 ) ≤ Nd 3+ (6.3×10 5 mg·L -1 ) + showed the same trend. This order is presumed to be related to the size of the ionic radius. Fe ions with the largest ionic radius are difficult to enter and be adsorbed inside the lattice of the metal-organic framework, but it is judged that rare earth metal ions with relatively small sizes are easily adsorbed by forming chemical bonds inside the lattice of the metal-organic framework.

[0075] In this way, the adsorbent according to the present invention has a high adsorption selectivity of 100 times or more for rare earth metals, but a process of precipitating the remaining metals except for the rare earth metals can be applied so that rare earth metals can be adsorbed more selectively in an environment where various metals coexist.

[0076] As an example, when a Nd-Fe-B waste permanent magnet composed of Fe, Nd, and Dy is placed in a strongly acidic solution having a pH of 2 or lower, the Fe, Nd, and Dy components are all dissolved, and when the pH of the solution is then adjusted to 4 or higher, the Fe component is precipitated and deposited. In this state, when the Nd and Dy components are recovered using the adsorbent according to the present invention, the recovery efficiency for rare earth metals can be further increased. Here, referring to the experimental results described below, it can be confirmed that when a waste permanent magnet composed of 65 wt% Fe, 25 wt% Nd, and 10 wt% Dy is dissolved, the initial composition is maintained at pH 1 to 2, but the Fe composition decreases to 43 wt% at pH 3, and all Fe in the solution is precipitated and deposited at pH 4 or higher.

[0077] Above, the core-shell structured metal-organic framework-polymer fiber-based adsorbent according to one embodiment of the present invention, the manufacturing method thereof, and the rare earth metal recovery method utilizing the same have been described. Below, the present invention will be described in more detail through experimental examples.

[0078] Experimental Example 1: Preparation of NPZIF-8 / NaPAF adsorbent

[0079] Commercial PAN fibers with a diameter of 50 μm were immersed in an ethanol solution containing NaOH and then maintained at a temperature of 75°C for up to 48 hours to modify the surface of the PAN fibers. The surface-modified NaPA fibers were placed in an ethanol solution containing Zn to adsorb Zn metal ions onto the surface of the NaPA fibers. Next, the NaPA fibers with Zn metal ions adsorbed thereon were placed in an ethanol reaction solution with a pH adjusted to 5 to 12 to precipitate the Zn metal ions on the surface of the NaPA fibers as Zn5(OH)8(NO3)2·2H2O. Then, the NaPA fibers were reacted with a ligand solution to form ZIF-8 on the NaPA fibers.

[0080] In order to compare the ZIF-8 formation efficiency according to the reaction solution, the above manufacturing process was performed by applying hydrochloric acid and distilled water instead of ethanol solution as the reaction solution.

[0081] Experimental Example 2: Surface Modification Characteristics

[0082] In manufacturing NaPA fiber according to Experimental Example 1, the nitrile group of PAN was substituted with sodium carboxylate group (-COONa) according to the immersion time in NaOH solution. As shown in Fig. 3a, after 20 hours, 2243 cm -1 It can be confirmed that the peak for the nitrile group of the PAN fiber completely disappears.

[0083] Experimental Example 3: ZIF-8 formation characteristics according to reaction solution

[0084] According to Experimental Example 1, when Zn ions were adsorbed onto NaPA fibers, it was confirmed that the adsorption efficiency of Zn metal ions varied depending on the type of reaction solution. Referring to Fig. 3b, when ethanol was used as the reaction solution, approximately 271 mg / g of Zn ions were adsorbed, whereas in the case of hydrochloric acid, approximately 23 mg / g of Zn ions were adsorbed, and in the case of distilled water, approximately 106 mg / g of Zn metal ions were adsorbed.

[0085] In addition, as a result of FT-IR analysis, when the ethanol reaction solution was applied, as shown in Fig. 3c, 1559 / 1451 cm corresponding to the -COONa functional group in the NaPA fiber -1 While a distinct peak appeared at 1158 and 1733 cm corresponding to -COOH when hydrochloric acid was applied, -1 A peak appeared in , and when distilled water was used, the two functional groups coexisted. These results indicate that the -COONa functional group is advantageous for fixing the Zn ion, which is the precursor of NPZIF-8, and that ethanol is most suitable for maintaining this functional group.

[0086] According to Experimental Example 1, an XRD analysis was performed on an adsorbent, i.e., a CSCF (Core / shell Synergistic Composite Fiber), in which ZIF-8 nanoparticles (NPZIF-8) were formed on NaPA fibers (NaPAF) at each manufacturing stage. As a result, as shown in Fig. 3d, it was confirmed that a structural change in the polymer chain occurred due to surface modification of the PAN fibers (PANF) (NaPAF), and that Zn5(OH)8(NO3)22H2O, a precursor of NPZIF-8, was well formed on the surface of the NaPA fibers (NaPAF), ultimately forming a CSCF coated with NPZIF-8 nanoparticles.

[0087] In manufacturing CSCF according to Experimental Example 1 by applying each reaction solution, FESEM and FESEM-EDS analyses were performed at each manufacturing step.

[0088] Each of (d) to (f) in FIG. 4 is an FESEM image taken to confirm the formation state of Zn5(OH)8(NO3)2·2H2O when distilled water, hydrochloric acid, and ethanol were applied as reaction solutions, respectively. Each of (g) to (i) in FIG. 4 is an FESEM image taken to confirm the formation state of NPZIF-8 when distilled water, hydrochloric acid, and ethanol were applied as reaction solutions, respectively. In addition, each of (j) to (l) in FIG. 4 is an FESEM image of a cross-section of a CSCF manufactured by applying distilled water, hydrochloric acid, and ethanol as reaction solutions, respectively. As confirmed by (d) to (l) in FIG. 4, it can be seen that the NPZIF-8 precursor and NPZIF-8 nanoparticles are stably formed on the NaPA fiber when ethanol was applied as the reaction solution. These results are also consistent with the FESEM-EDS analysis results. Figures 4 (m) to (p) show the FESEM-EDS analysis results for Figure 4 (i) showing that NPZIF-8 nanoparticles are uniformly formed on the surface of the NaPA fiber.

[0089] Meanwhile, when hydrochloric acid was applied, NPZIF-8 precursor and NPZIF-8 nanoparticles were formed in small amounts, and when distilled water was applied, leaf-shaped NPZIF-L, not NPZIF-8 nanoparticles, was formed. For reference, each of (a) to (c) in Fig. 4 is a FESEM image of a NaPA fiber taken after washing away the NaOH remaining on the surface of the NaPA fiber with distilled water, hydrochloric acid, and ethanol, respectively, after surface modification of the PAN fiber.

[0090] Experimental Example 4: Rare-earth metal adsorption characteristics of NPZIF-8 / NaPAF adsorbent

[0091] Nd at each pH condition of CSCF, i.e. NPZIF-8 / NaPAF adsorbent, manufactured according to Experimental Example 1 by applying ethanol as a reaction solution 3+ , Dy 3+ The adsorption performance was analyzed.

[0092] Figure 5a is Nd 3+ The results of the isothermal adsorption experiment according to pH conditions are shown in Fig. 5b. Dy 3+ The results of the isothermal adsorption experiment according to pH conditions are shown in Fig. 5a and Fig. 5b. At pH 3 to 7, Nd 3+ , Dy 3+ Each exhibited excellent adsorption performance of 370 mg / g and 310 mg / g or more. However, better adsorption characteristics were observed under conditions of pH 4 or higher.

[0093] Also, Fig. 5c (Nd 3+ ) and Fig. 5d(Dy 3+ ), see Nd 3+ , Dy 3+ It showed a recovery efficiency of over 90% under conditions where the concentration of rare earth metals was 0.1㎍ / L or higher, and it was confirmed that as the concentration of rare earth metals increased, the recovery efficiency approached 100%.

[0094] Figures 6a to 6d show Nd of the NPZIF-8 / NaPAF adsorbent manufactured according to Experimental Example 1. 3+ , Dy3+ The experimental results showing the recovery performance according to the concentration and adsorption time for each are presented, and the results of introducing the relevant adsorption model to interpret the results of the experiment are presented. Referring to Figures 6a to 6d, for the two rare earth metals, the recovery performance trend according to the concentration is most similar to the Langmuir and Redlich-Peterson models (coefficient of determinationR 2 = ~1) was done. This suggests that the surface of the adsorbent is uniformly coated with ZIF-8 nanoparticles, and that rare earth metals are simultaneously adsorbed onto the ZIF-8 on the surface of the material. The adsorption data according to the adsorption time reached adsorption equilibrium within 2 minutes for both rare earth metals, and the results of applying the three models to this result showed the highest agreement with the pseudo-first-order and pseudo-second-order models (R 2 = 1.00). Although the rate of reaching adsorption equilibrium was very fast, making it difficult to determine which model had the better agreement between the two models, these results suggest that the rate-limiting step in the recovery process was the adsorption step due to chemical bonding.

[0095] Figures 7a and 7b each show the Nd of the NPZIF-8 / NaPAF adsorbent manufactured according to Experimental Example 1. 3+ , Dy 3+ The maximum adsorption capacity and recovery rate constant (k) for each were compared with those of the best adsorbent in the previously reported paper. The maximum adsorption capacity and recovery rate constant (k) of the best adsorbent in the previously reported paper were 150 mg / g or less and 1 or less, respectively, while the NPZIF-8 / NaPAF adsorbent showed a maximum adsorption capacity of more than 400 mg / g and a recovery rate constant (k) approaching 2. Nd 3+ , Dy 3+ It can be seen that the maximum adsorption capacity and recovery rate constant (k) characteristics are significantly superior.

[0096] Nd in NPZIF-8 / NaPAF adsorbent 3+ , Dy 3+ The adsorption characteristics can also be confirmed through XRD, HRTEM, and TEM-EDS analysis results.

[0097] Figure 8a is Nd 3+ and Dy 3+ The XRD analysis results for the surface of the NPZIF-8 / NaPAF (CSCF) adsorbent before and after adsorption show that peaks with 2θ values ​​less than 30 shift to higher 2θ after adsorption, suggesting that the rare earth metal has entered between relatively wide crystal planes.

[0098] Figure 8b is a HRTEM lattice image of NPZIF-8 nanoparticles on the CSCF surface, showing (112) and (222) planes with lattice spacings of 0.69 and 0.49 nm, respectively, and Figures 8c and 8d are Nd 3+ , Dy 3+ HRTEM images showing that the intercrystal spacing has increased after ion adsorption. Figures 9 (a) to (d) are the TEM-EDS analysis results for Figure 8c, and Figures 9 (e) to (h) are the TEM-EDS analysis results for Figure 8d, showing that Nd is present in the lattice of NPZIF-8 nanoparticles. 3+ , Dy 3+ It shows that ions are evenly distributed.

[0099] Experimental Example 5: Adsorption characteristics of NaPAF, NPZIF-8, and NPZIF-8 / NaPAF, respectively.

[0100] To investigate the effect of NaPAF and NPZIF-8 on the adsorption characteristics of the NPZIF-8 / NaPAF adsorbent, the maximum adsorption capacity and adsorption rate characteristics were analyzed for NaPAF, NPZIF-8, and NPZIF-8 / NaPAF (CSCF), respectively.

[0101] Referring to Figures 10a and 10b, in the case of NaPAF, Nd 3+ , Dy 3+The maximum adsorption amount for Nd was small, less than 100 mg / g, while the time to reach adsorption equilibrium was very fast, less than 1 minute. NPZIF-8 had a maximum adsorption amount of Nd 3+ , Dy 3+ All of them were very large, exceeding 400 mg / g, but it took more than 1 hour to reach adsorption equilibrium. On the other hand, in the case of NPZIF-8 / NaPAF (CSCF), the adsorbent of the present invention, adsorption equilibrium was reached within 1 minute and Nd 3+ , Dy 3+ It can be confirmed that both the maximum adsorption amount and adsorption speed are excellent, with a maximum adsorption amount of over 400 mg / g for all.

[0102] What is interesting in the above experimental results is that Nd of NPZIF-8 / NaPAF (CSCF) 3+ , Dy 3+ The maximum adsorption amount for exceeds the value calculated by simulation (simulated CSCF). The simulated CSCF is calculated by multiplying the maximum adsorption amount of NaPAF and NPZIF-8 by the weight ratio of each of NaPAF and NPZIF-8, and as shown in Fig. 10b, the Nd of NPZIF-8 / NaPAF (CSCF) 3+ , Dy 3+ It can be seen that the maximum adsorption amount for exceeds the simulated CSCF. This is interpreted as an increase due to the combination of the adsorption characteristics of NaPAF and NPZIF-8.

[0103] Figure 10c shows the Nd of NaPAF, NPZIF-8 and NPZIF-8 / NaPAF (CSCF), respectively. 3+ , Dy 3+ The results of FT-IR analysis before and after adsorption are shown, and Fig. 10d is a reference diagram schematically illustrating the rare earth metal (REE) adsorption mechanism of the NPZIF-8 / NaPAF adsorbent. Referring to the FT-IR analysis results of Fig. 10c and the adsorption mechanism of Fig. 10d, it can be seen that NaPAF adsorbs rare earth metal ions (Nd 3+ , Dy3+ ) to the surface of the NPZIF-8 / NaPAF adsorbent, and it can be seen that NPZIF-8 effectively adsorbs rare earth metal ions by utilizing its high specific surface area and functional chemical groups.

[0104] Experimental Example 6: Adsorption selectivity and regeneration characteristics of NPZIF-8 / NaPAF adsorbent

[0105] To investigate the adsorption selectivity of NPZIF-8 / NaPAF adsorbent for rare earth metals, Fe 2+ , Nd 3+ , Dy 3+ The distribution coefficients for each metal ion of the NPZIF-8 / NaPAF adsorbent in a solution containing coexisting ions were measured and calculated.

[0106] Fe 2+ Distribution coefficient for (K) d ) is 1.6×10 3 mg·L -1 On the other hand, Nd 3+ , Dy 3+ Distribution coefficient for each (K d ) is 6.3×10 5 mg·L -1 , 2.0×10 5 mg·L -1 It was calculated that (see Fig. 11a). This is Fe 2+ Nd for maximum adsorption capacity 3+ , Dy 3+ This means that the maximum adsorption amount for each is more than 100 times.

[0107] In addition, additional experiments were conducted to support the more effective recovery of rare earth metals from waste permanent magnets. As is known, Nd-Fe-B permanent magnets are composed of approximately 65 wt% Fe, 25 wt% Nd, and 10 wt% Dy, and it was confirmed that this composition changes depending on the pH conditions. Figure 11b shows the change in the composition ratio of Fe, Nd, and Dy depending on the pH conditions. Under the condition of pH 1 to 2, the composition ratio of 65 wt% Fe, 25 wt% Nd, and 10 wt% Dy is maintained, but under the condition of pH 3 or higher, especially under the condition of pH 4 or higher, all of the Fe is eluted and precipitated, and it can be confirmed that a compound composed only of Nd and Dy exists.

[0108] The NPZIF-8 / NaPAF adsorbent of the present invention forms a fiber shape with a diameter of 50 μm, and thus exhibits a lower pressure drop characteristic compared to a nanoparticle-type adsorbent when applied to an actual adsorption reactor. FIG. 11c shows the pressure drop (ΔP) according to the flow rate measured after filling an adsorption reactor with the same volume of NPZIF-8 / NaPAF adsorbent and NPZIF-8 adsorbent of the same weight, respectively. It can be seen that the adsorption reactor filled with the NPZIF-8 adsorbent experiences a rapid pressure drop as the flow rate increases, whereas the adsorption reactor filled with the NPZIF-8 / NaPAF adsorbent experiences a gradual pressure drop even with an increase in the flow rate. This is because the NPZIF-8 / NaPAF adsorbent of the present invention forms a fiber shape with a diameter of several tens of μm, allowing smooth fluid movement.

[0109] The regeneration characteristics of the NPZIF-8 / NaPAF adsorbent of the present invention were examined.

[0110] Nd 3+ , Dy 3+ After adsorption experiments, Nd from NPZIF-8 / NaPAF adsorbent 3+ , Dy 3+ Remove and re-install Nd 3+ , Dy 3+In this method, adsorption and regeneration were repeated five times to conduct an adsorption experiment. As a result of the experiment, Nd was observed even after three regenerations. 3+ , Dy 3+ It can be seen that almost 100% of NPZIF-8 was adsorbed (see Fig. 12a). On the other hand, after the 4th regeneration, the adsorption efficiency was shown to decrease. In this regard, XRD and FESEM analyses were performed, and it was confirmed that the crystal structure of NPZIF-8 was collapsed after the 4th regeneration (see Figs. 12b and 12c).

Claims

1. An adsorbent based on a metal-organic framework-polymer fiber having a core-shell structure, characterized in that a metal-organic framework is provided on the surface of sodium polyacrylate (NaPA) fibers.

2. An adsorbent based on a metal-organic framework-polymer fiber having a core-shell structure, characterized in that a sodium carboxylate group (-COONa) is provided on the surface of a sodium polyacrylate (NaPA) fiber in the first paragraph.

3. In the first paragraph, an amine group (-NH) is formed on the surface of the sodium polyacrylate (NaPA) fiber. 2 ), carboxyl group (-COOH), hydroxyl group (-OH), sulfate group (SO 4 2- ), phosphate group ([PO 4 ] 3- ) is characterized by having a core-shell structure, wherein one of the metal-organic framework-polymer fiber-based adsorbents is provided.

4. An adsorbent based on a core-shell structure of a metal-organic framework-polymer fiber, characterized in that the metal-organic framework in claim 1 is ZIF-8.

5. In the first paragraph, an adsorbent based on a metal-organic framework-polymer fiber having a core-shell structure, characterized in that the sodium polyacrylate (NaPA) fiber has a diameter of several tens of ㎛ or more.

6. A step of surface-modifying polyacrylonitrile (PAN) fibers with sodium polyacrylate (NaPA) fibers having sodium carboxylate groups (-COONa); A step of fixing a metal organic framework precursor to the surface of a sodium polyacrylate (NaPA) fiber; and A method for producing an adsorbent based on a metal-organic framework-polymer fiber having a core-shell structure, characterized by comprising a step of converting a metal-organic framework precursor into a metal-organic framework.

7. In the 6th paragraph, the step of surface-modifying polyacrylonitrile (PAN) fibers with sodium polyacrylate (NaPA) fibers having sodium carboxylate groups (-COONa); A method for producing an adsorbent based on a core-shell structured metal-organic framework-polymer fiber, characterized in that the polyacrylonitrile (PAN) fiber is immersed in a NaOH solution to substitute a nitrile group of the polyacrylonitrile (PAN) fiber with a sodium carboxylate group (-COONa).

8. In the 6th paragraph, the step of fixing a metal organic framework precursor to the surface of a sodium polyacrylate (NaPA) fiber; A process of immersing sodium polyacrylate (NaPA) fibers in a metal solution containing dissolved metal to adsorb metal ions onto the surface of the sodium polyacrylate (NaPA) fibers, A method for manufacturing an adsorbent based on a metal-organic framework-polymer fiber having a core-shell structure, characterized in that it comprises a process of forming a metal-organic framework precursor by precipitating a metal ion in the form of a metal hydroxide.

9. In the 8th paragraph, the process of forming a metal organic framework precursor by precipitating a metal ion in the form of a metal hydroxide is as follows: A method for producing an adsorbent based on a core-shell structured metal-organic framework-polymer fiber, characterized by immersing sodium polyacrylate (NaPA) fibers to which metal ions are adsorbed in an ethanol solution to precipitate the metal ions in the form of metal hydroxide.

10. A method for recovering rare earth metals using a core-shell structured metal-organic framework-polymer fiber-based adsorbent, characterized by adding the adsorbent described in any one of claims 1 to 5 to a solution containing dissolved rare earth metals to recover rare earth metals in the solution.

11. In clause 10, a process of dissolving Fe and rare earth metal by adding a material composed of Fe and rare earth metal to a solution having a pH of 1 to 2, The process of precipitating and precipitating the Fe component by adjusting the pH of the solution to 4 or higher, A method for recovering rare earth metals using a core-shell structured metal-organic framework-polymer fiber-based adsorbent, characterized by including a process for recovering rare earth metals in a solution using the adsorbent.

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