KR102106887B1 - Method for recovering palladiums - Google Patents

Abstract

The present invention relates to a method for recovering palladium, and more particularly, a method for recovering palladium from a solution containing palladium, for example, wastewater. The method for recovering palladium of the present invention comprises mixing a palladium stabilizer with a palladium-containing solution to prepare a mixed solution; And irradiating the mixed solution with radiation, wherein the palladium stabilizer is an azo group-containing organic compound, thereby recovering palladium through a simple process through a one-pot reaction. In addition, palladium can be selectively recovered with an excellent recovery rate.

Description

Method for recovering palladium {Method for recovering palladiums}

The present invention relates to a method for recovering palladium, and more particularly, a method for recovering palladium from a solution containing palladium, for example, wastewater.

Palladium (Pd) is widely used as a catalyst metal with high activity and high practicality in fields such as organic synthesis and exhaust gas purification. In particular, in the production of chemical products such as pesticides, pharmaceuticals, fragrances, and dyes, palladium catalysts are used for a wide range of reactions, such as hydrogenation of olefins, ketones, aldehydes, or hydrolysis of halogen compounds, allyl compounds, and the like. As such, the palladium catalyst is a useful catalyst in the field of organic synthesis, and is one of the transition metal catalysts that are widely used.

However, as the use of palladium in organic synthesis and the like has been expanded, there is a problem in how to efficiently recover palladium from a solution containing palladium used (for example, waste solution after organic synthesis). Since palladium is a precious metal and is rare in resources, it is a particularly important problem in terms of reuse and stable supply of palladium to efficiently and efficiently recover from palladium-containing solutions.

Conventionally, as a method for recovering palladium from a solution containing palladium, various methods such as a solvent extraction method, an ion exchange method, and a bioconcentration method using a biological function of a microorganism are known. However, a solvent extraction method using extraction of water and an organic solvent is widely adopted from the viewpoint of economical and operability, but it is not easy to select an appropriate extraction agent by comprehensively considering extraction ability, extraction speed, and durability depending on the waste solution. There is a problem. In addition, there are problems such as the need to properly dispose of the used organic solvent. On the other hand, the adsorption method using an adsorbent such as activated carbon or ion exchange resin generally has a problem that the amount of adsorption by the adsorbent is small and the process is complicated. There is also a problem that the used adsorbent needs to be disposed of properly. In addition, there are many problems to be solved such as cost in order to be widely applied to the bioconcentration method, and further investigation is required.

In view of this situation, there is a need to develop a method for recovering palladium at a high recovery rate while being environmentally friendly and simple at room temperature.

Therefore, the problem to be solved by the present invention is to provide a method for recovering palladium with an excellent recovery rate while being environmentally friendly and simple.

In order to solve the above problems, the present invention comprises the steps of preparing a mixed solution by mixing a palladium stabilizer in a palladium-containing solution; And irradiating the mixed solution with radiation, and the palladium stabilizer provides a method for recovering palladium, which is an azo group-containing organic compound.

According to the method for recovering palladium of the present invention, palladium can be recovered by a simple process through a one-pot reaction.

Further, according to the method of the present invention, palladium can be selectively recovered with an excellent recovery rate.

In addition, the recovered palladium is obtained in a metal form and can be used without additional purification steps such as removal of an adsorbent in organic synthesis.

The following drawings attached to the present specification are intended to illustrate preferred embodiments of the present invention, and serve to further understand the technical idea of the present invention together with the contents of the above-described invention, so the present invention is limited to those described in those drawings. It should not be interpreted as limited.
FIG. 1A shows the color change according to irradiation of gamma rays (right) after mixing the BO 2 {Basic Orange 2 (4-phenylazo-m-phenylenediamine)} solution (left) and the palladium-containing solution (center). It is a picture showing. The yellow BO 2 solution changes to red by mixing with Pd ²⁺ ions to form a palladium-BO 2 complex, and the color of the solution changes to colorless as BO 2 decomposes and forms palladium nanoparticles by gamma irradiation. I could confirm that.
1B is a photograph showing palladium nanoparticles formed by irradiating 60 kGy gamma rays.
1C is a schematic diagram showing a mechanism for forming palladium nanoparticles through gamma-ray irradiation.
Figure 2a shows a square planar structure of the palladium-BO 2 composite through DFT calculation.
2B shows the HOMO of [Pd (MO) ₂ ] ²⁺ using the DFT method.
2C is a graph showing the UV-vis absorption spectrum of palladium detection before and after Pd ²⁺ ion injection.
Figure 2d is a graph showing the UV-vis absorption spectrum as increasing the concentration of Pd ²⁺ ions from 20 to 100 ppm.
Figure 3 shows the effect of palladium stabilizer (BO 2) in the formation of palladium nanoparticles. A TEM image of palladium nanoparticles formed without (a) or with a palladium stabilizer (b) is shown. Gamma irradiation of 50 kGy was performed on both sides.
4 is a graph showing the UV-vis absorption spectrum of palladium nanoparticles ?. 4a shows the radiation-induced formation of palladium nanoparticles according to the concentration of Pd ²⁺ ions. 4b shows the conversion rate of palladium nanoparticles according to the radiation dose. 4c represents the UV-vis absorption spectrum of palladium nanoparticles formed when irradiated with a low radiation amount of 1 to 10 kGy, and 4d represents UV-vis absorption of palladium nanoparticles formed when irradiated with a high radiation amount of 20 to 50 kGy. Spectrum.
5A shows an example of a mechanism for forming palladium nanoparticles. 5B to 5G are TEM images showing hierarchically growing and forming palladium nanoparticles, and images at 1 kGy (b and e), 20 kGy (c and f), or 60 kGy (d and g), respectively. to be.
Figure 6a is a TEM image showing the formation and formation of the hierarchical growth of palladium nanoparticles at 50 kGy. 6B is an HRTEM image of the formed palladium nanoparticles.

The present invention comprises the steps of preparing a mixed solution by mixing a palladium stabilizer in a palladium-containing solution; And irradiating the mixed solution with radiation, and the palladium stabilizer provides a method for recovering palladium, which is an azo group-containing organic compound.

1. Preparation of a mixed solution of palladium-stabilizer

The present invention prepares a mixed solution by mixing a palladium-containing solution with a palladium stabilizer, specifically an organic compound containing an azo group.

The temperature for preparing the mixed solution is not particularly limited, but can be produced at room temperature, such as 20 to 30 ° C, for example, 25 ° C, thereby exhibiting energy saving, process convenience, and other effects.

In addition, the mixed solution may promote the formation of a complex of palladium and palladium stabilizer through stirring after adding the palladium stabilizer to the palladium-containing solution described below, but is not limited thereto.

Hereinafter, a palladium-containing solution and a palladium stabilizer will be described.

Palladium-containing solution

In the present invention, the palladium-containing solution may represent a solution containing palladium in any form, such as, for example, a waste solution after organic synthesis using a palladium catalytic reaction. The palladium-containing solution is not limited thereto, but preferably contains a solution containing palladium in oxidized form, for example, palladium in ionic form, more preferably Pd ²⁺ ions (Pd (II)) Solution.

The palladium-containing solution may contain palladium in any form, and the concentration of palladium is not particularly limited, but the concentration of palladium in the palladium-containing solution is, for example, 1 to 2000 ppm, 1 to 1500 ppm, 1 to 1000 ppm, 10 to 150 ppm, 20 to 100 ppm, 40 to 80 ppm, 60 ppm.

The concentration of palladium in the palladium-containing solution may be determined by, for example, mixing the organic dye as a palladium stabilizer described below, and calculating it by inverting it using the concentration of the organic dye in which the color change of the solution no longer appears. You can. In one embodiment, after measuring the palladium concentration in a solution containing palladium, the palladium recovery can be improved by using the palladium-containing solution by concentration or dilution to the concentration.

Palladium stabilizer

In the present invention, a palladium stabilizer is mixed with the palladium-containing solution, wherein the palladium stabilizer is an organic compound containing an azo group. The mechanism for stabilizing palladium of the organic compound containing the azo group is not limited thereto, but by forming a bond between the azo group and the palladium ion, for example, by forming a coordination bond between the unshared electron pair in the azo group and the empty orbital of the palladium ion. In terms of being able to stabilize palladium in solution, it can be called a 'palladium stabilizer'.

The palladium stabilizer contains an azo group, and may contain 1 to 5, preferably 1 to 3 azo groups for good interaction with palladium ions. In particular, the palladium stabilizer may contain 2 to 10, preferably 2 to 6 aromatic rings, and as the palladium stabilizer, an azo-based dye capable of exhibiting a color change in a solution as the palladium is stabilized Can be used.

More specifically, by using an azo-based dye as the palladium stabilizer, palladium in a palladium-containing solution, preferably palladium ion, for example, Pd ²⁺ can be detected. In one embodiment, as the azo-based dye is mixed with a yellowish Pd ^{2 +} -containing solution, a palladium-dye complex is formed in the solution, and thus, a color change of the solution can be confirmed.

As the azo-based dye, a monoazo dye, a diazo dye, a triazo dye, a tetraazo dye, or a higher polyazo dye may be used, and the azo-based dye known in the art or azo produced newly by organic synthesis Dyestuffs can be used. The azo dye is not limited thereto, and for example, 4-phenylazo-m-phenylenediamine (basic orange 2, basic orange 2, BO2) may be used.

In particular, the palladium stabilizer may further include a functional group containing an amine group. The palladium stabilizer may further improve the stability of the complex of the palladium-stabilizing agent by further including the functional group. By improving the stability of the palladium-stabilizing agent complex, stability of palladium nanoparticles formed according to subsequent irradiation may be improved, and palladium recovery may be improved.

In one embodiment, a palladium-BO2 complex is formed by using 4-phenylazo-m-phenylenediamine (BO 2), which simultaneously contains an azo group and an amine group as the palladium stabilizer, thereby changing the color of the solution. Palladium can be detected. The formed palladium-BO2 complex is decomposed by subsequent irradiation, whereby a reduction reaction of palladium can be detected. In addition, by using the BO 2 it can exhibit excellent palladium recovery.

The palladium stabilizer may be mixed in an amount of 1 to 5 equivalents based on palladium in the palladium-containing solution. In one embodiment, in the mixed solution formed by mixing the palladium-containing solution with the palladium stabilizer, the concentration of the palladium stabilizer is, for example, 1x10 ^-6 to 1x10 ^-4 M, for example, 7x10 ^-5 M days You can. When the palladium stabilizer is mixed in the above amount, it may be preferable in terms of improving stability of the palladium-stabilizing agent and improving palladium recovery.

In one embodiment, when the concentration of the stabilizer is 7x10 ^-5 to 7x10 ^-4 M, colorimetric changes can be observed.

2. Irradiation stage

Metal palladium may be obtained by reducing the palladium in the solution by irradiating radiation to the mixed solution prepared as above. The metal palladium can be obtained in the form of palladium nanoparticles.

The palladium nanoparticles are not limited thereto, and may be formed by the following mechanism.

[Example of the mechanism for forming palladium nanoparticles]

_{H 2 O (gamma-ray)} -> e - aq, H 3 O +, H. , H ₂ , OH ^. , H ₂ O ₂

Pd ²⁺ + e ^- _aq- > Pd ⁰

Pd ²⁺ + ^H. -> Pd ⁰ + H ⁺

Pd ⁰ + Pd ^0- > Pd ²

Pd ⁰ + Pd ²⁺ -> Pd ₂ ²⁺

Pd ₂ ²⁺ + Pd _{2 2} ⁺ -> Pd ₄ ⁴⁺

Pd _m + Pd ²⁺ -> Pd ²⁺ _{m + 1}

Pd ^{x +} _{m + x} + Pd ^{y +} _{p + y-} > Pd ^{z +} _{n + z}

Here, m, n, and p mean nucleation seed formation, and x, y, and z represent charged Pd ²⁺ ion water.

As shown in the above mechanism, the decomposition reaction of water is performed by irradiation of gamma rays in the solution to form species such as hydrated electrons and hydrogen radicals. Among the formed species, there are many hydrated electrons and hydrogen radicals, and they are excellent in reactivity to convert expensive metal ions to low-cost or zero-valent metal. PD2 + ions may be converted to palladium nanoparticles by hydration electrons and hydrogen radicals as described above.

The method for recovering palladium according to the present invention may optionally further include a purging step for removing bubbles such as dissolved oxygen in the solution before irradiating the mixed solution with radiation. In the purging step, it may be performed using an inert gas such as nitrogen, helium, neon, or argon, and may be performed to the extent that bubble removal is sufficiently performed, but 30 seconds to 60 minutes in consideration of workability and process efficiency, for example For example, it may be performed for 5 to 30 minutes.

Next, the mixed solution that has undergone the purging step, or the purging step is omitted and the mixed solution is irradiated with radiation. The radiation may be selected from gamma rays, X rays, and electron rays. The total amount of radiation to be irradiated may be irradiated with a low radiation amount of 1 to 100 kGy, for example, 1 to 10 kGy, or a high radiation amount of 10 to 60 kGy, 20 to 50 kGy. The type and total amount of the radiation are not particularly limited, but the recovery rate of the metal palladium obtained according to the total amount of radiation, the particle size of the palladium nanoparticles, and the like can be adjusted. In terms of improving the palladium recovery rate, it may be more preferably irradiated to 10 kGy or more. In addition, the radiation may be irradiated with a single dose, or irradiated while gradually increasing the irradiation dose, and is not particularly limited to the irradiation method.

After irradiation, the formed palladium nanoparticles can be identified through TEM, SEM, or the like. In addition, the formed palladium nanoparticles can be recovered and reused as a catalyst in organic synthesis.

In one embodiment, 45% or more, for example 50% or more, 55% or more, 60% or more, 65% or more, 70% or more, 75% or more, 80% or more, through the method for recovering palladium according to the present invention, It was confirmed that palladium can be recovered at a recovery rate of 85% or more, 90% or more, 95% or more, or 100%.

Hereinafter, examples and the like will be described in detail to help understanding of the present invention. However, the embodiments according to the present invention can be modified in many different forms, and the scope of the present invention should not be construed as being limited to the following examples. The embodiments of the present invention are provided to more fully explain the present invention to those having average knowledge in the field to which the present invention pertains.

[Experiment General]

Preparation of mixed solutions

3 mg/L 농도의 표준 Pd(II) 용액 (CPI, International, USA)을 희석하여 사용하였다. 팔라듐 안정화제로는 4-페닐아조-m-페닐렌다이아민 (basic orange 2, BO 2)를 사용하였다 (Sigma Aldrich Chemicals, MO, USA).1000 for experiment

A standard Pd (II) solution (CPI, International, USA) at a concentration of 3 mg / L was used diluted. As a palladium stabilizer, 4-phenylazo-m-phenylenediamine (basic orange 2, BO 2) was used (Sigma Aldrich Chemicals, MO, USA).

First, BO 2 was diluted with demineralized water to prepare a 7 × 10 ^-5 M aqueous solution. 4.5 mL of the prepared BO 2 solution and 0.5 mL of a 1000 ppm concentration palladium solution were mixed and placed in a 5 mL cuvette. After gently shaking, color change of the mixed solution was observed, and this was analyzed through a UV-VIS analyzer (V-770, Jasco, Japan).

Irradiation of radiation

As a radiation, a cobalt-60 gamma ray irradiator (ACEL, IR-79, Nordion, Canada) of the Korea Atomic Energy Research Institute was used for gamma ray irradiation. For signal identification, an alanine radiometer (Bruker Instruments, Rheinstetten, Germany) and a Bruker EMS 103 EPR analyzer were used. For the gamma irradiation, the mixed solution prepared above was placed in 10 mL of transparent vials and cuvettes, respectively. After fixing the irradiation rate at 10 kGy / h, a total of 60 kGy was investigated.

Character analysis

After the irradiated sample was placed in a 1 cm long quartz cuvette, UV-vis spectrum was measured using a UV-visible / NIR analyzer (V-770, Jasco, Japan) at a wavelength of 250 to 750 nm. The morphology of the formed palladium nanoparticles was observed using a TEM (JEOL JEM-2100F TEM equipped with a field emission source) at 200 kV. For TEM analysis, a colloidal dispersion of formed palladium nanoparticles was dropped on a carbon-coated copper grid (300 mesh), and then water was evaporated at room temperature.

In addition, the latis structure of the palladium nanoparticles was confirmed using a high performance TEM (HRTEM) at 300 kV. The crystal structure of palladium nanoparticles was measured by X-ray powder diffraction (XRD) on a D / Max-2500 diffraction analyzer (Rigaku, Japan) using Cu Kα irradiation (λ = 0.15406 nm). The XRD sample was prepared by centrifuging the palladium nanoparticle dispersion prepared above at 10,000 rpm for 10 minutes, and then drying it under vacuum at 80 ° C.

The zeta potential of the conjugate between BO 2 and Pd ²⁺ ions was measured using a zeta potential analyzer (Malvern Zeta Sizer Nano ZS90, Worcs, UK).

The amount of palladium nanoparticles reduced in the solution was measured using ICP-OES (OPTIMA 7300DV, Perkin-Elmer, USA).

[Experiment result]

Preparation of mixed solutions

As soon as the 4.5 ppm BO 2 solution (7x10 ^-5 M) was mixed with the 1000 ppm concentration palladium mixture solution, a color change of the solution was observed from yellow to red according to the formation of the palladium-BO 2 complex (FIG. 1A). Through this, it was confirmed that the presence of PD ²⁺ ions in the solution can be confirmed using an azo-based organic dye.

After irradiating 60 kGy of gamma rays to the mixed solution, it was observed that the solution changed to colorless (FIG. 1B). Through this, it was confirmed that BO 2 is decomposed and palladium nanoparticles are formed by gamma irradiation. The mechanism of palladium nanoparticle formation is schematically shown in FIG. 3.

The structure and orbital distribution of the palladium-BO 2 complex was optimized by density functional theory (DFT) using B2LYP using a Gaussian-09 program (FIG. 2). The palladium-BO 2 complex exhibits a square planar structure, and the distance between palladium and nitrogen was calculated to be 2.1 mm 2 (FIG. 2A). 2B shows the HOMO of the palladium-BO 2 complex. The HOMO orbital distribution showed a strong orbital interaction between palladium and two dye ligands.

The binding stability of the palladium-BO 2 complex was analyzed by measuring the zeta potential of the BO 2 and palladium-BO 2 complex. The zeta potential of the BO 2 molecular suspension was -47.5 mV, and the zeta potential of the palladium-BO 2 complex was -8.06 mV, through which it was confirmed that the stability increased with the complex formation.

The UV-vis absorption spectrum of the palladium-BO 2 complex showed characteristic peaks at 261 and 395 nm, indicating the conjugated structure of the benzene ring and azo bond, respectively. It was confirmed that the synergistic effect of these two shows the color change of the aqueous solution of BO 2, through which the existence of Pd ²⁺ ions can be confirmed.

After fixing BO 2 to 0.02 wt% based on the total weight of the aqueous solution, a UV absorption experiment was performed while increasing the concentration of Pd ²⁺ ions to 20 to 100 ppm (FIG. 2D).

In subsequent experiments, the concentration of Pd ²⁺ ions was fixed at 100 ppm to conduct the experiment.

Formation of palladium nanoparticles through gamma irradiation

The effect of improving the stability of palladium nanoparticles formation and the rate of formation of palladium nanoparticles by a palladium stabilizer was confirmed as follows.

First, a total of 50 kGy was irradiated on a solution containing 100 ppm of palladium without mixing BO 2 (FIG. 3A). Next, a gamma ray of 50 kGy was irradiated to a 100 ppm palladium-containing solution in which BO 2 was mixed at 0.02 wt% (FIG. 3B).

When there was no palladium stabilizer, it was confirmed that the formed palladium nanoparticles were heterogeneous and had a large particle size. Through this, it was confirmed that the size of the palladium nanoparticles formed by using a palladium stabilizer is smaller and more stable, thereby increasing the palladium recovery rate.

The stability of palladium nanoparticle formation and the effect of improving palladium recovery according to palladium concentration and radiation dose were confirmed as follows.

After increasing the palladium concentration from 20 ppm to 100 ppm, gamma rays were irradiated with an irradiation dose of 10 kGy, and then UV-vis spectrum was measured (FIG. 4A). Through this, it was confirmed that the smaller the palladium concentration, the lower the formation of palladium nanoparticles.

In addition, after fixing the palladium concentration at 100 pppm, the recovery rate of palladium was calculated while increasing the radiation dose (FIG. 4B). Through this, it was confirmed that when the radiation dose is 5 kGy or more, a recovery rate of 50% can be exhibited, and a recovery rate of about 100% can be exhibited by irradiating with a radiation dose of 10 to 20 kGy in consideration of economic efficiency and stability.

Next, the UV absorption spectrum of the palladium nanoparticle solution formed when the radiation dose was 1 to 10 kGy (FIG. 4C) or 20 to 50 kGy (FIG. 4D) was measured. Upon irradiation, it was confirmed that Pd ²⁺ ions were reduced to Pd ⁰ (Pd nanoparticles), and the intensity of the graph was decreased due to sedimentation by gravity. On the other hand, when the radiation dose was 1 to 10 kGy, it was confirmed that the graph value did not reach the minimum level because Pd ²⁺ was present inside the aqueous solution due to insufficient radiation dose despite the increase in irradiation dose. On the other hand, when the irradiation dose is 20 to 50 kGy, it was confirmed that there is no change in the amount of UV absorption because palladium aggregates in the lower part of the cuvette.

In addition, after irradiating the palladium-containing solution with a 60 kGy gamma ray, it was confirmed through the TEM image that nanoparticles having an average diameter of 410 to 450 nm and 420 nm were formed (FIG. 5).

Claims (15)

Preparing a mixed solution by mixing a palladium stabilizer with a palladium-containing solution; And
And irradiating the mixed solution with radiation,
The palladium stabilizer is a method of recovering palladium that is an azo-based organic dye.
The method according to claim 1,
The palladium-containing solution is a method for recovering palladium containing Pd (II).
The method according to claim 1,
The azo-based organic dye is a method for recovering palladium using an organic compound containing 1 to 5 azo groups.
delete The method according to claim 1,
The palladium stabilizer recovery method of palladium further comprising a functional group containing an amine group.
The method according to claim 1,
The palladium stabilizer is a method for recovering palladium comprising 4-phenylazo-m-phenylenediamine.
The method according to claim 1,
The palladium stabilizer is a palladium recovery method that is mixed in an amount of 1 to 5 equivalents based on palladium in the palladium-containing solution.
The method according to claim 1,
A method for recovering palladium, wherein the palladium concentration in the palladium-containing solution is 1 to 2000 ppm.
The method according to claim 1,
The concentration of the palladium stabilizer in the mixed solution is 1 x 10 ^-6 to 1 x 10 ^-4 M Palladium recovery method.
The method according to claim 1,
The radiation is palladium recovery method that is selected from gamma rays, X-rays and electron beams.
The method according to claim 10,
The radiation is a gamma-ray recovery method of palladium.
The method according to claim 1,
The total amount of radiation to be irradiated is 1 to 100 kGy recovery method of palladium.
The method according to claim 12,
The total amount of radiation is 10 to 60 kGy Palladium recovery method.
The method according to claim 1,
The method of recovering palladium further comprising the step of obtaining a metal palladium formed by the irradiation of the radiation.
The method according to claim 14,
The method for recovering palladium in which the metal palladium is obtained in the form of nanoparticles.

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