JP7220894B2 - Metal adsorbent having dithiocarbamic acid group, method for producing the same, and method for extracting metal - Google Patents

Description

TECHNICAL FIELD The present invention relates to a metal adsorbent having dithiocarbamic acid groups and a method for producing the same. Furthermore, the present invention relates to a metal extraction method using a metal adsorbent having dithiocarbamic acid groups.

Solutions such as factory effluent sometimes contain a large number of heavy metals, and it is known that when these heavy metals accumulate in the body, their toxicity causes symptoms of poisoning. In order not to release these heavy metals into the environment such as rivers, solutions such as the factory waste water are treated with adsorbents such as ion exchange resins.
On the other hand, metal resources such as rare metals are dissolved in water such as rivers and seawater, and in Japan, where resources are scarce, metal resources can be recovered from them more selectively or more efficiently. A metal adsorbent or the like is required.

As a representative metal adsorbent, dithiocarbamic acid or its salt has a sulfur atom as a metal coordinating atom, so it has a high chelating ability for heavy metals, and has a functional group with a nitrogen atom or an oxygen atom as a metal coordinating atom. It is known to have excellent selectivity for heavy metals compared to groups. For example, Patent Documents 1 and 2 disclose heavy metal immobilizing agents comprising dithiocarbamic acid group-containing compounds. However, these heavy metal immobilizing agents are low-molecular-weight compounds that dissolve in solutions to adsorb metals, so a complicated separation process is required to separate them from the system after adsorption. , it is difficult to recover and recycle heavy metals.

On the other hand, in order to solve the above-mentioned problems, it is known to provide a metal adsorbent by imparting a metal adsorbing ability to a polymer compound. Filter cartridges incorporating groups and/or chelating groups are disclosed. Furthermore, Patent Document 4 discloses an adsorbent in which a chelate forming group and/or an ion exchange group are introduced into a cellulosic base material. In both publications, a dithiocarbamic acid group is exemplified as a chelate group or a chelate-forming group, but there is no disclosure of specific compounds such as that they were actually synthesized or how they can be synthesized. not

JP-A-8-224560 JP 2004-352964 A Japanese Patent Application Laid-Open No. 2003-251118 JP 2009-13204 A

Dithiocarbamic acid or its salts have excellent metal adsorption capacity for heavy metals, and although metal adsorbents have been obtained as low-molecular-weight compounds so far, they are high-molecular compounds that are easy to separate and recover. was not actually obtained.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a metal adsorbent that has excellent adsorption performance for metals such as heavy metals and that can be recovered without requiring a special separation step.

As a result of intensive studies on the above problems, the present inventors have found that, when introducing a dithiocarbamic acid group into a polymer base material, the dithiocarbamine The inventors have found that a metal adsorbent into which an acid group is introduced can be obtained, and completed the present invention.
That is, the present invention provides the following metal adsorbent, method for producing the metal adsorbent, and metal extraction method.

The metal adsorbent of the present invention for solving the above problems is a metal adsorbent in which a dithiocarbamic acid group is introduced into a polymer base material, and the dithiocarbamic acid group is a graft polymer and a dithiocarbamic acid group-introduced group. It is characterized by being introduced through
According to this feature, it is possible to provide a metal adsorbent that contains dithiocarbamic acid groups, has excellent adsorption performance for metals such as heavy metals, and can be recovered without requiring a special separation step.

（式（１）中、Ｘは、酸素原子又は窒素原子であり、ｎ及びｍは、アルキレン鎖の炭素原子数を表し、ｎは２以上の整数であり、ｍは０以上の整数である。Ｘが酸素原子である場合は、ｍは０である。また、ｍが０の場合は、窒素原子には水素原子が１つ置換されている。）
この特徴によれば、吸着対象の金属に合わせて、ジチオカルバミン酸基導入基の長さ等を設定することができる。 In one embodiment of the metal adsorbent of the present invention, the structures of the dithiocarbamic acid group-introducing group and the dithiocarbamic acid group portion are represented by the following formula (1).

(In formula (1), X is an oxygen atom or a nitrogen atom, n and m represent the number of carbon atoms in the alkylene chain, n is an integer of 2 or more, and m is an integer of 0 or more. When X is an oxygen atom, m is 0. When m is 0, the nitrogen atom is substituted with one hydrogen atom.)
According to this feature, the length of the dithiocarbamic acid group-introducing group can be set according to the metal to be adsorbed.

In one embodiment of the metal adsorbent of the present invention, the graft polymer is one or more selected from (meth)acrylic polymers, styrene polymers, and (meth)acrylic-styrene copolymers. It is characterized by
According to this feature, the introduction amount of dithiocarbamic acid groups (dithiocarbamic acid group density) can be controlled by the degree of grafting of the polymer.

A method for producing a metal adsorbent of the present invention is characterized by comprising the following steps.
(i) Step of preparing an activated polymer substrate (ii-1) Step of graft polymerizing a monomer onto the polymer substrate (iii-1) Dithiocarbamic acid group having a protective group on the graft polymer Step (iv) of reacting the introduced compound to bond a dithiocarbamate group-introducing group having a protecting group to the graft polymer (iv) Step of deprotecting the protecting group from the dithiocarbamic acid group-introducing group bonded to the graft polymer (v) Dithiocarbamic acid Step of Reacting Carbon Disulfide with Group-Introduced Group According to this feature, a dithiocarbamic acid group can be efficiently introduced into the polymer base material. Furthermore, the introduction amount of dithiocarbamic acid groups can be improved.

Furthermore, the method for producing the metal adsorbent of the present invention is characterized by comprising the following steps.
(i) Step of preparing an activated polymer substrate (ii-1) Step of graft polymerizing a monomer onto the polymer substrate (iii-2) Reacting a dithiocarbamic acid group-introducing compound to the graft polymer and bonding a dithiocarbamate group-introducing group to the graft polymer; (v) a step of reacting the dithiocarbamic acid group-introducing group with carbon disulfide. can.

Furthermore, the method for producing the metal adsorbent of the present invention is characterized by comprising the following steps.
(i) Step of preparing an activated polymer substrate (ii-2) Step of graft-polymerizing a monomer having a dithiocarbamate group-introduced group to the polymer substrate (v) To the dithiocarbamic acid group-introduced group Step of reacting carbon disulfide According to this feature, a dithiocarbamic acid group can be easily and efficiently introduced into the polymer base material.

Moreover, one embodiment of the method for producing a metal adsorbent of the present invention is characterized in that the activated polymeric substrate is a polymeric substrate activated by irradiation with radiation.
According to this feature, the form of the polymer substrate is not limited, and the dithiocarbamic acid group can be introduced into the polymer substrate such as fiber, woven fabric, nonwoven fabric, sheet, and film.

According to the present invention, there is provided a metal extraction method for extracting a metal from a metal-containing object to be treated, comprising the step of contacting the object to be treated with a metal adsorbent.
According to this feature, it is possible to provide a metal extraction method that does not require a complicated separation step for separating the metal adsorbent that has adsorbed the metal from the system after adsorption.

ADVANTAGE OF THE INVENTION According to this invention, the metal adsorbent which is excellent in the adsorption performance of metals, such as a heavy metal, and can be collect|recovered without requiring a special separation process can be provided.

It is a schematic diagram showing the metal adsorbent of the present invention. It is a schematic diagram showing a metal adsorbent obtained in an example of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS It is the schematic showing the manufacturing method (1) and (2) of the metal adsorbent in this invention. It is the schematic showing the manufacturing method (3) of the metal adsorbent in this invention, and (4).

[Metal adsorbent]
The metal adsorbent of the present invention is, as shown in FIG. It is characterized by being introduced through
A metal adsorbent is a material that can adsorb metal dissolved or dispersed in a liquid or gas. Platinum, zinc, palladium, cobalt, chromium, nickel, manganese, cadmium, molybdenum, tungsten, cesium, uranium, plutonium, titanium, zirconium, magnesium, calcium, strontium, barium and the like, more preferably lead, copper, These are zinc, cobalt, nickel, manganese, cadmium, magnesium, calcium, strontium and barium.

The metal adsorbent of the present invention preferably has a lead adsorption capacity of 0.001 mmol/g or more in the following test procedure. The lower limit is more preferably 0.01 mmol/g or more, still more preferably 0.1 mmol/g or more, particularly preferably 0.25 mmol/g or more, and most preferably 0.50 mmol/g. g or more, and more preferably 1 mmol/g or more. Here, the lead adsorption capacity is the adsorption amount of lead ions per 1 g of the metal adsorbent of the present invention.
As a test procedure, 50 mg of the metal adsorbent of the present invention was immersed in 50 mL of a 100 ppm lead-containing aqueous solution (an aqueous solution in which lead nitrate was dissolved in water) at room temperature (25 ° C.) for 24 hours. It is taken out, and the concentration of lead remaining in the aqueous solution is measured using an inductively coupled plasma emission spectrometer (ICP-OES). The lead adsorption capacity of the metal adsorbent is calculated from the amount of change in lead concentration before and after immersion in the metal adsorbent.

(Polymer base material)
In the metal adsorbent of the present invention, the polymer base material is not limited in form, etc., as long as it is a material molded from a polymer compound. Specifically, for example, there are forms such as fibers, woven fabrics or non-woven fabrics that are aggregates of fibers, films, porous bodies, etc. The larger the surface area of the material, the larger the contact area with the solution, and the more efficient it is. Fibers, woven fabrics that are aggregates of fibers, or non-woven fabrics are preferred because they can adsorb metals easily.
Although the average fiber diameter of the fibers is not particularly limited, it is preferably 0.1 to 200 μm. The lower limit is more preferably 1.0 μm or more, and still more preferably 2.0 μm or more. The upper limit is more preferably 100 µm or less, and still more preferably 30 µm or less.
By setting the average fiber diameter of the fibers within the above range, it is possible to obtain a metal adsorbent having a more excellent metal adsorbing ability.

The polymer compound used for the polymer substrate is not particularly limited as long as it can be molded into the above-described shape. For example, various polymer compounds such as petroleum-based polymers and natural polymers can be used. Specifically, petroleum-based polymer compounds include, for example, polyolefin resins such as polyethylene and polypropylene, (meth)acrylic acid resins such as polyacrylic acid and polymethacrylic acid, polystyrene, polybutadiene, polyisoprene, polycarbonate, and polyester. , polyphenylene ether, polyketone, polyetherketone, polyetheretherketone, polyethersulfone, polyphenylene sulfide, polyamide, polyimide, cyclic olefin resin, and the like. Alternatively, natural polymers such as chitin, chitosan, cellulose, starch, and the like are included. Polyolefin resins such as polyethylene and polypropylene are preferred.

(graft polymer)
In the metal adsorbent of the present invention, the graft polymer is not particularly limited, but preferably consists of a monomer capable of forming a polymer by graft polymerization, specifically radiation graft polymerization, to the polymer base material. It is a polymer. The monomer preferably has a group capable of graft polymerization (hereinafter referred to as a graft polymerizable group) and a group capable of reacting with the dithiocarbamic acid group-introduced compound (hereinafter referred to as an introduced compound reactive group. ).
The graft polymerizable group is preferably an unsaturated group, more preferably an allyl group, a vinyl group, a (meth)acrylic group, or the like.
The reactive group of the introduced compound is not particularly limited, but is preferably a cyclic ether-containing group such as an epoxy group or an oxetanyl group, a halogen group composed of fluorine, chlorine, bromine or iodine, a hydroxyl group, an alkoxy group or the like, A glycidyl group is more preferred.
Specific examples of the monomer include glycidyl methacrylate, (3-ethyloxetan-3-yl) methacrylate, chloromethylstyrene, and the like.
Through the graft polymer, dithiocarbamic acid groups can be easily and efficiently introduced into the polymer substrate.

Grafting ratio of graft polymer In the metal adsorbent of the present invention, the content (grafting ratio) of the graft polymer is not particularly limited, but is preferably 50 to 400% by mass. The lower limit is more preferably 100% by mass or more, and still more preferably 150% by mass or more. The upper limit is more preferably 300% by mass or less, and still more preferably 250% by mass.
By setting the graft ratio within the above range, the introduction ratio of dithiocarbamic acid groups can be increased while maintaining the form and shape of the base material. Therefore, the metal adsorption performance of the metal adsorbent can be improved.
Here, the graft ratio refers to the mass increase (%) of the monomer graft-polymerized to the polymer substrate, and can be obtained by the following formula.
Formula; Graft rate: Dg (%) = {(W ₁ -W ₀ )/W ₀ } x 100
W ₀ : mass of polymer base before graft polymerization [mg]
W ₁ : Mass [mg] of polymer base material after graft polymerization

(Dithiocarbamic acid group-introducing group)
In the metal adsorbent of the present invention, the dithiocarbamic acid group-introducing group is a group for introducing a dithiocarbamic acid group into the graft polymer, and is a group composed of a dithiocarbamic acid group-introducing compound.
The dithiocarbamic acid group-introducing compound is not particularly limited, but preferably has a group capable of reacting with the reactive group of the introduced compound of the graft polymer, and is capable of reacting with carbon disulfide, which is a precursor compound of the dithiocarbamic acid group. and having a group capable of forming a dithiocarbamic acid group. Preferably, the dithiocarbamic acid group-introduced compound has a group capable of reacting with the reactive group of the introduced compound of the graft polymer and has a primary or secondary amino group.
The group capable of reacting with the reactive group of the introduced compound is preferably a substituent such as an amino group, a hydroxyl group, an alkoxy group, a formyl group, or a carbonyl group, and more preferably an amino group or a hydroxyl group.
By providing the metal adsorbent of the present invention with a dithiocarbamate group-introducing group, the dithiocarbamate group can be introduced more easily and efficiently. Furthermore, the length of the dithiocarbamic acid group-introducing group can be set according to the metal to be adsorbed.

Specific examples of the dithiocarbamic acid group-introducing group preferably include a diaminoethylene group, a diaminopropylene group, a diaminohexamethylene group, an N,N'-dimethyldiaminoethylene group, a triaminodiethylene group, a tetraaminotriethylene group and a piperazyl group. is one or more groups selected from, more preferably a piperazyl group. In particular, by using a cyclic diamine group such as a piperazyl group as a dithiocarbamic acid group-introduced group, a metal adsorbent having excellent heat resistance and acid resistance can be obtained, which is more preferable.

Furthermore, the structure of the dithiocarbamic acid group-introducing group and the dithiocarbamic acid group portion in the metal adsorbent of the present invention is preferably a structure represented by the following formula (1).

In formula (1) above, X is an oxygen atom or a nitrogen atom.
In the above formula, n and m represent the number of carbon atoms in the alkylene chain, preferably n is an integer of 2 or more and m is an integer of 0 or more. m is 0 when X is an oxygen atom. Further, when m is 0, one hydrogen atom is substituted for the nitrogen atom.
The upper limit of n is more preferably 30 or less, still more preferably 20 or less, and particularly preferably 10 or less.
The lower limit of m is more preferably 1 or more, and still more preferably 2 or more. The upper limit is more preferably 30 or less, still more preferably 20 or less, and particularly preferably 10 or less.

In the group represented by the above formula (1), the alkylene chain sandwiched between X and the nitrogen atom N may contain at least one atom selected from the group consisting of a nitrogen atom and an oxygen atom. .

• Introduction rate of dithiocarbamate group-introducing group In the metal adsorbent of the present invention, the introduction rate of the dithiocarbamic acid group-introducing group is not particularly limited, but is preferably 1% or more. The lower limit is more preferably 5% or more, still more preferably 25% or more, particularly preferably 50% or more, still more preferably 70% or more, and even more preferably 80% or more. Yes, most preferably 90% or more.
When the introduction rate of the dithiocarbamate group-introducing group is at least the above range, the introduction amount of the dithiocarbamic acid group can be increased, and the metal adsorption performance of the metal adsorbent can be improved.
Here, the introduction ratio of the dithiocarbamate group-introduced group is a value calculated from the ratio of the reaction amount of the dithiocarbamate group-introduced compound to the number of reaction groups of the introduced compound of the graft polymer, and is calculated according to the following formula. can ask.

Formula: Dithiocarbamic acid group introduction rate [%] =
[(W ₂ −W ₁ )/Mw, _spacer ]/[(W ₁ −W ₀ )/Mw, _monomer ]×100
W ₀ : mass of polymer base before graft polymerization [mg]
W ₁ : Mass [mg] of polymer base material after graft polymerization
W ₂ : Mass [mg] of polymer substrate after introduction of dithiocarbamic acid group-introducing group
Mw, _monomer : Molecular weight of monomer used for graft polymerization (for example, the molecular weight when glycidyl methacrylate (GMA) is used is 142.15 g/mol.)
Mw, _spacer : Molecular weight of the dithiocarbamic acid group-introduced compound (for example, the molecular weight when piperazine (PIP) is used is 86.14 g/mol.)
When a dithiocarbamic acid group-introducing compound having a protective group is used, Mw, _protect shown below is used instead of Mw, _spacer in the above formula.

Density of Dithiocarbamic Acid Group-Introduced Groups In the metal adsorbent of the present invention, the density of dithiocarbamic acid group-introduced groups is not particularly limited, but is preferably 0.1 mmol/g or more. The lower limit is more preferably 1.0 mmol/g or more, still more preferably 1.5 mmol/g or more.
Here, the dithiocarbamic acid group-introduced group density is a value representing the quantity of dithiocarbamic acid group-introduced groups contained in 1 g of the metal adsorbent, and can be obtained by the following formula.
By setting the dithiocarbamic acid group-introducing group density within the above range, the introduction amount of the dithiocarbamic acid group can be increased, and the metal adsorption performance of the metal adsorbent can be improved.

Formula; dithiocarbamic acid group-introduced group density [mmol/g]
= [( _W2 - _W1 )/Mw, _spacer ]/ _W3 x 1000
W ₁ : Mass [mg] of polymer base material after graft polymerization
W ₂ : Mass [mg] of polymer substrate after introduction of dithiocarbamic acid group-introducing group
W ₃ : Mass of polymer base material after carbon disulfide treatment [mg]
Mw, _spacer : Molecular weight of the dithiocarbamic acid group-introduced compound (for example, the molecular weight when piperazine (PIP) is used is 86.14 g/mol.)
When a dithiocarbamic acid group-introducing compound having a protective group is used, Mw, _protect shown below is used instead of Mw, _spacer in the above formula.

- Self-crosslinking rate of graft polymer In the metal adsorbent of the present invention, the self-crosslinking rate of the graft polymer is not particularly limited, but is preferably 20% or less. The upper limit is more preferably 15% or less, still more preferably 10% or less, and particularly preferably 5% or less.
By setting the self-crosslinking rate of the graft polymer to the above range or less, the introduction amount of the dithiocarbamic acid group can be increased, and the metal adsorption performance of the metal adsorbent can be improved.
Here, the self-crosslinking rate of the graft polymer represents the rate of self-crosslinking between the graft polymers via the dithiocarbamic acid group-introduced group. If the self-crosslinking rate is "100%", it can be said that 100% of the introduced dithiocarbamic acid group-introduced groups are involved in self-crosslinking, and no dithiocarbamic acid group has been introduced. The self-crosslinking rate of the graft polymer can be obtained by the following formula.

Formula: Self-crosslinking rate of graft polymer [%] =
{1−[(W ₃ −W ₂ )/Mw, _CS2−Na ]/[(W ₂ −W ₁ )/Mw, _spacer ]}×100
W ₁ : Mass [mg] of polymer base material after graft polymerization
W ₂ : Mass [mg] of polymer substrate after introduction of dithiocarbamic acid group-introducing group
W ₃ : Mass of polymer base material after carbon disulfide treatment [mg]
Mw, _spacer : Molecular weight of dithiocarbamic acid group-introduced compound Mw, _CS2-Na : Molecular weight of carbon disulfide-sodium ( _CS2 -Na) (99.13 g/mol) (Mw, _CS2-Na is the molecular weight of carbon disulfide treatment In this case, since the treatment is carried out under conditions in which sodium is present, calculations are made assuming that the counter ion of the dithiocarbamic acid group in the final product is sodium.)

(dithiocarbamic acid group)
In the metal adsorbent of the present invention, the dithiocarbamic acid group is a group having a structure in which two sulfur atoms and one nitrogen atom are bonded to one carbon atom. In the present invention, the dithiocarbamic acid group includes dithiocarbamic acid and/or a metal salt thereof, and preferably the metal forming the metal salt is an alkali metal salt such as potassium or sodium.

·Dithiocarbamate group density In the metal adsorbent of the present invention, the dithiocarbamate group density is not particularly limited, but is preferably 0.001 mmol/g or more. The lower limit is more preferably 0.05 mmol/g or more, still more preferably 0.1 mmol/g or more, and particularly preferably 0.2 mmol/g or more.
By setting the dithiocarbamic acid group density within the above range, the metal adsorption performance of the metal adsorbent can be improved.
Here, the dithiocarbamic acid group density is a value representing the quantity of dithiocarbamic acid groups contained in 1 g of the metal adsorbent, and can be obtained by the following formula.

Formula; Dithiocarbamic acid (NCS ₂ ⁻ ) density [mmol/g]=
[(W ₃ −W ₂ )/Mw, _CS2−Na ]/W ₃ ×1000
W ₂ : Mass [mg] of polymer substrate after dithiocarbamic acid group-introducing group-introducing step
W ₃ : Mass of polymer base material after carbon disulfide treatment [mg]
Mw, _spacer : Molecular weight of the dithiocarbamic acid group-introduced compound (for example, the molecular weight when piperazine (PIP) is used is 86.14 g/mol.)
Mw, _CS2-Na : Molecular weight of carbon disulfide-sodium ( _CS2 -Na) (99.13 g/mol)

- Nitrogen content In the metal adsorbent of the present invention, the nitrogen content is not particularly limited, but is preferably 0.1% by mass or more. The lower limit is more preferably 1% by mass or more, still more preferably 2% by mass or more, and particularly preferably 4% by mass or more.
This nitrogen content can be measured by a fully automatic elemental analyzer (2400II manufactured by PerkinElmer) or the like.

- Sulfur content In the metal adsorbent of the present invention, the sulfur content is not particularly limited, but is preferably 0.01% by mass or more. The lower limit is more preferably 0.1% by mass or more, still more preferably 0.5% by mass or more, and particularly preferably 1% by mass or more.
This sulfur content can be measured by a fully automatic elemental analyzer (2400II manufactured by PerkinElmer) or the like.

・Nitrogen content/sulfur content ratio (N/S ratio)
In the metal adsorbent of the present invention, the nitrogen content/sulfur content ratio (N/S ratio) is not particularly limited, but is preferably 1000 or less. The upper limit is more preferably 500 or less, still more preferably 10 or less, and particularly preferably 5 or less.
By setting the nitrogen content/sulfur content ratio (N/S ratio) within the above range, it is possible to obtain a metal adsorbent having a more excellent metal adsorbing ability.

ここで、上記式（２）における繰り返し数ａは、１以上の整数である。 The metal adsorbent of the present invention preferably has a structure represented by the following formula (2) bonded to the polymer base material.

Here, the repetition number a in the above formula (2) is an integer of 1 or more.

[Method for producing metal adsorbent]
The metal adsorbent of the present invention can be produced using any one of the following methods (1) to (4), but the production method is not limited to these. FIG. 3 shows schematic diagrams representing manufacturing methods (1) and (2), and FIG. 4 shows schematic diagrams representing manufacturing methods (3) and (4).

(Manufacturing method (1))
The method for producing a metal adsorbent of the present invention preferably comprises the following steps.
(i) Step of preparing an activated polymer substrate (ii-1) Step of graft polymerizing a monomer onto the polymer substrate (iii-1) Dithiocarbamic acid group having a protective group on the graft polymer Step (iv) of reacting an introduced compound to bond a dithiocarbamic acid group-introducing group having a protective group to the graft polymer (iv) Step of deprotecting the protective group from the dithiocarbamic acid group-introducing group bonded to the graft polymer (v) The dithiocarbamine Step of reacting carbon disulfide with an acid group-introducing group

(Manufacturing method 2)
Furthermore, the method for producing the metal adsorbent of the present invention is preferably produced using the following production method.
(i) Step of preparing an activated polymer substrate (ii-1) Step of graft polymerizing a monomer onto the polymer substrate (iii-2) Reacting a dithiocarbamic acid group-introducing compound to the graft polymer (v) a step of reacting the dithiocarbamic acid group-introduced group with carbon disulfide;

In step (i), the term "activated polymer base material" refers to a polymer base material in which activation points such as radicals capable of graft polymerization are generated in the above polymer base material. Here, since the polymer base material is the same as that described above, the description thereof is omitted.
The method for generating activation points is not particularly limited, but is preferably a method of irradiating with radiation, and examples of radiation include α-rays, β-rays, γ-rays, electron beams, ultraviolet rays, etc. Electron beams are preferred. or gamma rays.
The irradiation dose is sufficient as long as it is sufficient to generate activation points, preferably 1 to 200 kGy, more preferably 20 to 100 kGy. By increasing the irradiation dose, the graft rate can be improved.
As for the irradiation conditions, for example, it is preferable to irradiate in a space previously replaced with nitrogen, and it is preferable to irradiate at room temperature or under cooling.

In step (ii-1), the method of graft-polymerizing the monomer onto the polymer substrate is not particularly limited, but the activated polymer substrate is brought into contact with the monomer to initiate graft polymerization. Let it be. Here, since the monomers are the same as those described above, the description thereof is omitted. The monomers may be brought into contact either directly or after being dissolved in a solvent, and are preferably brought into contact by forming an emulsion of the monomer solution. By forming an emulsion of the monomer solution, the concentration of the monomer in the vicinity of the active site of the polymer substrate is increased, and the graft ratio of the graft polymer can be improved.
The monomer concentration in the solution is not particularly limited, but is preferably 0.1 to 30% by mass, more preferably 1 to 10% by mass. By increasing the monomer concentration in the solution, the graft rate can be improved.

Although the solvent is not particularly limited, it is preferably an organic solvent capable of dissolving the monomer. Specific examples include alcohol solvents such as methanol and ethanol, halogen solvents such as methylene chloride, chloroform, carbon tetrachloride, tetrachloroethane and hexachloroethane, and solvents such as methyl ethyl ketone and phenyl methyl ketone.
For forming the emulsion, water is preferred, and distilled water, ion-exchanged water, pure water, and ultrapure water are more preferred.

Furthermore, when forming an emulsion, it is preferable to use a surfactant. Surfactants are not particularly limited, but preferably include anionic surfactants, cationic surfactants, amphoteric surfactants, and nonionic surfactants. The anionic surfactant is not particularly limited, but alkylbenzene-based, alcohol-based, olefin-based, phosphoric acid-based, and amide-based surfactants are preferred, and sodium dodecyl sulfate is more preferred. The cationic surfactant is not particularly limited, but preferably octadecylamine acetate, trimethylammonium chloride, or the like. Nonionic surfactants are not particularly limited, but are preferably ethoxylated fatty alcohols, fatty acid esters, etc., and more preferably polyoxyethylene (20) sorbitan monolaurylate (Tween20, registered trademark). The zwitterionic surfactant is not particularly limited, but preferably Amphithol (registered trademark) containing a betaine amphoteric surfactant as a main component. Among the above surfactants, polyoxyethylene (20) sorbitan monolaurylate is more preferred.

The concentration of the surfactant is not particularly limited, but can be appropriately determined depending on the type and concentration of the monomers. The surfactant concentration is preferably generally 0.01 to 10% by weight, more preferably 0.1 to 2% by weight, based on the total weight of the solvent.

The graft polymerization reaction temperature may be set depending on the reactivity of the above monomers, preferably 10 to 60°C, more preferably 30 to 45°C. The graft polymerization reaction time is preferably 5 minutes to 6 hours, more preferably 30 minutes to 2 hours. The reaction time can be appropriately set according to the reaction temperature and desired graft ratio.
Moreover, in the graft polymerization reaction, the oxygen in the system should be as small as possible, and it is preferable to carry out the reaction after deaeration and nitrogen substitution.

In step (iii-2), the dithiocarbamic acid group-introduced compound is the one described in the above section (Dithiocarbamic acid group-introduced group).
Specifically, the dithiocarbamic acid group-introducing compound is preferably one or more compounds selected from ethylenediamine, propylenediamine, hexamethylenediamine, N,N'-dimethylethylenediamine, diethylenetriamine, triethylenetetramine, and piperazine, and more preferably. is piperazine.

Furthermore, as in step (iii-1), in the dithiocarbamic acid group-introducing compound, at least one amino group capable of reacting with carbon disulfide, which is a precursor compound of the dithiocarbamic acid group, is protected by a protecting group. is preferred.
The protecting group is not particularly limited, but is preferably a methyl group, a benzyl group, a p-methoxybenzyl group, a tert-butyl group, a tert-butoxycarbonyl group (Boc group), a benzyloxycarbonyl group, and the like, and more preferably It is a tert-butoxycarbonyl group (Boc group).
Specific examples of the dithiocarbamic acid group-introducing compound having a protective group include N-Boc-piperazine group, N-Boc-ethanolamine, and the like.
By reacting a dithiocarbamic acid group-introducing compound having a protecting group, the graft polymer can be prevented from cross-linking via the dithiocarbamic acid group-introducing compound, and the introduction rate of dithiocarbamic acid can be improved. .

The dithiocarbamic acid group-introducing compound can be reacted with the introduction compound reactive group of the graft polymer grafted onto the polymer substrate. Although the reaction method is not particularly limited, for example, the graft polymer can be reacted by contacting it with a dithiocarbamic acid group-introducing compound. As for the method of contact, contact may be made without a solvent or by dissolving in a solvent.
The solvent is not particularly limited as long as it dissolves the dithiocarbamic acid group-introducing compound, and is preferably water, methanol, ethanol, 1-propanol, 1-butanol, octanol, alcohol solvents such as 2-ethylhexanol, Halogen solvents such as methylene chloride, chloroform, carbon tetrachloride, tetrachloroethane, and hexachloroethane; solvents such as methyl ethyl ketone and phenyl methyl ketone; and solvents such as N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO). is an alcohol solvent such as methanol, ethanol, 1-propanol, 1-butanol.

The temperature at which the dithiocarbamic acid group-introducing compound is reacted is not particularly limited, but is preferably 10 to 100°C. The lower limit of the temperature is more preferably 20°C or higher, still more preferably 40°C or higher. The upper limit is more preferably 90° C. or lower, still more preferably 80° C. or lower.
Although the reaction time is not particularly limited, it is preferably 1 to 48 hours. The lower limit of the reaction time is more preferably 2 hours or longer, still more preferably 4 hours or longer. The upper limit is more preferably 36 hours or less, still more preferably 24 hours or less.
Furthermore, the solution concentration of the dithiocarbamic acid group-introducing compound is not particularly limited, but is preferably 0.1 to 5.0 mol/L. The lower limit of the solution concentration is more preferably 0.2 mol/L or more, and still more preferably 0.25 mol/L or more. The upper limit is more preferably 2.5 mol/L or less, still more preferably 1.0 mol/L or less.

Furthermore, in step (iv), the method for deprotecting the protecting group from the dithiocarbamic acid group-introducing group is not particularly limited, but deprotection can be preferably carried out by treatment with an acid or base. The acid or base is preferably an inorganic acid such as hydrochloric acid, sulfuric acid, sulfuric acid, an organic acid such as acetic acid, trifluoroacetic acid or citric acid, or ammonia. As a deprotection procedure, deprotection can be performed by immersing the polymer base material reacted with the dithiocarbamic acid group-introduced compound in a solution in which the acid or base is dissolved.

Although the deprotection temperature is not particularly limited, it is preferably 0 to 100°C. The lower limit of the temperature is more preferably 20°C or higher, still more preferably 40°C or higher. The upper limit is more preferably 80° C. or lower, still more preferably 70° C. or lower.
The deprotection time is not particularly limited, but preferably 10 minutes to 24 hours. The lower limit of the deprotection time is more preferably 30 minutes or longer, more preferably 1 hour or longer. The upper limit is more preferably 12 hours or less, still more preferably 6 hours or less.
Furthermore, the acid or base concentration is not particularly limited, but is 0.1 to 5.0 mol/L. The lower limit of the concentration is more preferably 0.3 mol/L or more, still more preferably 0.5 mol/L or more. The upper limit is more preferably 2.5 mol/L or less, still more preferably 1.5 mol/L or less.

• Deprotection rate The rate of deprotection in the step (iv) can be calculated as a value called deprotection rate.
In the metal adsorbent of the present invention, the deprotection rate is a numerical value representing the extent to which the terminal of the dithiocarbamic acid group-introduced group is NH-converted by removing the protective group from the dithiocarbamic acid group-introduced group provided with a protective group.
The deprotection rate is calculated by the ratio of the reaction amount of the dithiocarbamic acid group-introduced compound having the protective group removed to the reaction amount of the dithiocarbamic acid group-introduced compound having the protective group introduced into the graft polymer. It is a value and can be obtained by the following formula.

Although the deprotection rate is not particularly limited, it is preferably 1% or more. The lower limit is more preferably 10% or more, still more preferably 50% or more, particularly preferably 90% or more, and most preferably 95% or more.
When the deprotection rate is at least the above range, the introduction amount of dithiocarbamic acid groups can be increased, and the metal adsorption performance of the metal adsorbent can be improved.

Formula; deprotection rate [%] =
[(W ₄ −W ₅ )/(Mw, _protect −Mw, _spacer )]/[(W ₄ −W ₁ )/Mw, _protect ]}×100
W ₁ : Mass [mg] of polymer base material after graft polymerization
W ₄ : Mass [mg] of polymer substrate after introduction of dithiocarbamic acid group-introduced group with protecting group
W ₅ : Mass [mg] of the polymer substrate after deprotection of the protective group from the dithiocarbamic acid group-introduced group provided with the protective group
Mw, _protect : Molecular weight of dithiocarbamic acid group-introduced compound having a protecting group (for example, the molecular weight when using N-Boc-piperazine (NBP) is 186.26 g/mol.) Mw, _spacer : protecting group A dithiocarbamate-introduced compound after deprotecting the protective group from the provided dithiocarbamate-introduced group (for example, when the protective group is deprotected from NBP, the dithiocarbamate-introduced compound becomes piperazine (PIP). PIP has a molecular weight of 86 .14 g/mol.

In addition, the step (v) of reacting carbon disulfide of the present invention is not particularly limited. It can be reacted with the dithiocarbamic acid group-introducing group portion of the polymer. The solvent is not particularly limited as long as it dissolves carbon disulfide, but water, alcohol solvents such as methanol and ethanol are preferred.
In addition, it is preferable to react by adding a base to the system. Examples of the base include sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, potassium carbonate, calcium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, ammonia, and the like. is preferred.

Although the reaction temperature in the step of reacting carbon disulfide is not particularly limited, it is preferably 0 to 50°C. The lower limit of the temperature is more preferably 20°C or higher, still more preferably 30°C or higher. The upper limit is more preferably 45°C or lower, and still more preferably 40°C or lower.
Although the reaction time is not particularly limited, it is preferably 1 to 72 hours. The lower limit of the reaction time is more preferably 6 hours or longer, and still more preferably 12 hours or longer. The upper limit is more preferably 36 hours or less, still more preferably 24 hours or less.
Although the concentration of carbon disulfide is not particularly limited, it is preferably 0.1 to 30% by mass. The lower limit of the concentration is more preferably 1% by mass or more, and still more preferably 2% by mass or more. The upper limit is more preferably 25% by mass or less, and even more preferably 20% by mass or less.
The molar ratio of carbon disulfide and base is preferably in the range of 1:10 to 1:0.5.
As a specific example of the reaction solution, it is preferable to react with a solution of carbon disulfide/methanol/sodium hydroxide=10 g/22.5 g/7.5 g.

After completion of the reaction, the metal adsorbent is preferably washed to remove unreacted carbon disulfide. As a washing method, it is preferable to wash with water and/or alcohol.

Furthermore, the method for producing the metal adsorbent of the present invention is preferably produced using the following production method.
(Manufacturing method 3)
(i) Step of preparing an activated polymer substrate (ii-2) Step of graft-polymerizing a monomer having a dithiocarbamic acid group-introducing group to the polymer substrate (v) The dithiocarbamic acid group-introducing group A step of reacting carbon disulfide with

The monomer having a dithiocarbamic acid group-introduced group in step (ii-2) is not particularly limited, but is preferably a monomer having a structure in which the dithiocarbamic acid group-introduced group is bonded with a graft-polymerizable group. Specific examples include 1-allylpiperazine and 1-(2-methyl-2-propen-1-yl)piperazine. As for the graft polymerization and the reaction method of carbon disulfide, the reaction can be carried out under the same conditions as in the production method 1 above.

Furthermore, the method for producing the metal adsorbent of the present invention is preferably produced using the following production method.
(Manufacturing method 4)
(i) step of preparing an activated polymer substrate (ii-3) step of graft polymerizing a monomer having a dithiocarbamic acid group-introducing group with a protecting group onto the polymer substrate (iv) above Step of deprotecting the protective group from the dithiocarbamate group-introduced group (v) Step of reacting the dithiocarbamate group-introduced group with carbon disulfide

In step (ii-3), the monomer having a dithiocarbamate group-introduced group with a protecting group is not particularly limited, but preferably has a graft-polymerizable group and is a dithiocarbamate group-introduced group with the above-mentioned protecting group. is a monomer with a structure in which is bound. Specific examples include monomers such as N-Boc-4-allylpiperazine. In addition, the graft polymerization, deprotection, and reaction of carbon disulfide can be carried out under the same conditions as in the above production method 1 and the like.

[Method of metal adsorption]
The metal adsorbent of the present invention can adsorb metals in a medium to be treated by bringing it into contact with an object to be treated containing metal. Here, the object to be treated containing metal is not particularly limited, and the object to be treated containing metal such as water in which metal is dissolved, oil in which metal is dissolved, organic solvent in which metal is dissolved, fly ash containing metal, etc. is mentioned.
And, the metal adsorption method is a method including a step of contacting the metal adsorbent of the present invention with an object to be treated containing metal.

[Metal extraction method]
Furthermore, the metal adsorbent of the present invention can separate and extract the metal contained in the object to be treated by bringing it into contact with the object to be treated containing the metal. The metal extraction method of the present invention is characterized by including a step of contacting an object to be treated containing metal with the metal adsorbent of the present invention. That is, it is a method in which an object to be treated containing a metal is brought into direct contact with the metal adsorbent of the present invention to adsorb the metal, thereby separating and extracting the metal from the object to be treated. As a method for contacting an object to be treated containing a metal with a metal adsorbent, a metal adsorbent may be added to a liquid to be treated containing a metal and brought into contact with the object to be treated. A method of allowing the treatment liquid to pass through and contact it may also be used.

Then, the metal can be isolated and recovered from the metal adsorbent on which the metal is adsorbed by the metal adsorption method or the metal extraction method.
Methods for isolating and recovering metals from metal adsorbents include, for example, a method in which a metal adsorbent that has adsorbed metals is immersed in an eluent such as nitric acid, hydrochloric acid, and sulfuric acid, and a method in which the metal adsorbent is incinerated. . Although the immersion time is not particularly limited, it is preferably 1 to 72 hours. The lower limit is preferably 6 hours or longer, more preferably 12 hours or longer. The upper limit is preferably 36 hours or less, more preferably 24 hours or less.

The metal-adsorbing material of the present invention may be used together with other components having metal-adsorbing ability. Other components having metal-adsorbing ability include, for example, crown ethers and calixarene having metal-adsorbing ability.

[Metal adsorption device]
The metal adsorption device in the present invention is a device characterized by comprising the metal adsorption material.
The metal adsorption device of the present invention can be used for river water purifiers, recovery of rare metals and the like. Further, by combining the metal adsorption device with a sensor or the like capable of detecting metal adsorption, the device can be applied to a water quality measuring device or the like.

The present invention will be described in more detail with reference to examples below, but modifications can be made as appropriate without departing from the gist of the present invention. Therefore, the scope of the present invention should not be construed to be limited by the specific examples shown below.

<Example 1> Synthesis of metal adsorbent using production method 2 (see production method 2 in FIG. 3)
(Graft polymerization to polymer substrate)
A nonwoven fabric made of polyethylene/polypropylene (PE/PP) fibers (average fiber diameter: 13 μm) was used as the polymer base material, and electron beam irradiation (irradiation dose: 20 kGy) was performed in a nitrogen atmosphere. The polymer substrate after irradiation was immersed in an emulsion reaction solution (concentration: 5% by mass, Tween 20 concentration: 0.5% by mass) containing glycidyl methacrylate (GMA) as a monomer for graft polymerization, and the reaction temperature was 40°C. The graft polymerization reaction was carried out at for 1 hour. The emulsion reaction solution used was previously purged with nitrogen to remove dissolved oxygen. After completion of the graft polymerization reaction, the substrate was thoroughly washed with water and methanol in this order to obtain a polymer substrate graft-polymerized with GMA having a graft rate of 200%.

(Introduction of dithiocarbamic acid group-introducing group)
The GMA-grafted polymeric substrate obtained above was immersed in a solution in which piperazine, a dithiocarbamate group-introducing compound, was dissolved at a reaction temperature of 80° C. for 24 hours. A piperazyl group, which is an acid group-introducing group, was introduced. Table 1 shows the concentration of the solution, the solvent, the introduction amount of the piperazyl group, and the like.

(Introduction of dithiocarbamic acid group via dithiocarbamic acid group-introducing group)
Next, the polymer base material into which piperazyl groups have been introduced is treated with a reaction solvent consisting of three components of carbon disulfide, methanol, and a 10 mol/L aqueous solution of sodium hydroxide (carbon disulfide/methanol/sodium hydroxide = 10 g/22. 5 g/7.5 g) at a reaction temperature of 40° C. for 24 hours to introduce a dithiocarbamic acid group into the terminal piperazyl group of the graft polymer to obtain the metal adsorbent shown in FIG. Table 1 shows the dithiocarbamic acid group density, which indicates the amount of introduced dithiocarbamic acid groups.

<Example 2> Synthesis of metal adsorbent using production method 1 (see production method 1 in FIG. 3)
(Introduction of a dithiocarbamic acid group-introducing group having a protecting group)
The polymer substrate graft-polymerized with GMA obtained above was immersed in a 0.25 mol/L N-Boc piperazine aqueous solution at a reaction temperature of 80° C. for 4 hours or longer to obtain a high A molecular substrate was obtained. By using piperazine having a protective group, self-crosslinking between graft polymers did not occur via piperazine, and the self-crosslinking rate was 0%. The N-Boc piperazyl group introduction rate was 95%, and the N-Boc piperazyl group density was 2.50 mmol/g.

(Deprotection reaction)
The polymer substrate having the N-Boc piperazyl group obtained above was immersed in a 1 mol/L aqueous solution of hydrochloric acid at a reaction temperature of 80° C. for 2 hours or more to carry out a deprotection reaction, thereby NH-ylating the end of the piperazyl group. The deprotection rate in the reaction was 95% or higher.

Next, the deprotected polymer base material was treated with a reaction solvent consisting of three components of carbon disulfide, methanol, and a 10 mol/L sodium hydroxide aqueous solution (carbon disulfide/methanol/sodium hydroxide=10 g/22.5 g). /7.5 g) at a reaction temperature of 40° C. for 24 hours to introduce a dithiocarbamic acid group into the terminal piperazyl group of the graft polymer to obtain a metal adsorbent. The dithiocarbamic acid group density of the metal adsorbent obtained by the above reaction was 2.120 mmol/g. Table 1 also shows the properties of the metal adsorbent obtained in Example 2.

From the results in Table 1, when an organic solvent was used as the reaction solvent (Examples 1-2 to 1-10), compared to the case of using water as the reaction solvent (Example 1-1), piperazyl group It was found that the introduction rate of
Further, when comparing Example 1-2 with Examples 1-8 to 1-10, it was found that the piperazine introduction rate can be improved by using a high-concentration piperazine solution. This is probably because the use of a high-concentration piperazine solution inhibited self-crosslinking between graft polymers via piperazine.
On the other hand, in Example 2 using N-Boc piperazine, it was found that the self-crosslinking of the graft polymer could be further suppressed, and finally the dithiocarbamic acid group introduction rate could be significantly improved.

(Lead adsorption test)
A metal adsorption test was performed using the metal adsorbents obtained in Examples 1 and 2 above.
As a test procedure, 50 mg of the metal adsorbent was immersed in 50 mL of a 100 ppm lead-containing aqueous solution (an aqueous solution in which lead nitrate was dissolved in water) at room temperature for 24 hours. After immersion, the metal adsorbent was taken out, and the concentration of lead remaining in the aqueous solution was measured using an inductively coupled plasma emission spectrometer (ICP-OES). The adsorption capacity of the metal adsorbent was calculated from the change in lead concentration before and after the metal adsorbent was immersed.
Table 2 shows the metal adsorption results.

From the results in Table 2, it was found that the metal adsorbent of the present invention has metal adsorption ability. Furthermore, metal adsorbents synthesized using protective groups suppress self-crosslinking between graft polymers via piperazine, and as a result, the introduction rate of dithiocarbamic acid groups increases. The metal adsorption performance was found to be greater than that of the manufactured metal adsorbents.
A quantitative comparison of the metal adsorption performance shows that the metal adsorbent produced using the protective group exhibits 21 times the lead adsorption performance as compared to the metal adsorbent produced without the protective group. I found out. From this, it was demonstrated that the metal adsorbent containing many dithiocarbamic acid groups has improved metal adsorbability.

(Isolation of adsorbed metals)
Lead was isolated from the metal adsorbent used in the lead adsorption test. As for the procedure, it was confirmed that lead was isolated by immersing 50 mg of the metal adsorbent on which lead was adsorbed in 50 mL of a 5 mol/L nitric acid aqueous solution at room temperature for 24 hours.
From these results, it was found that the metals dissolved in water or the like can be easily separated, extracted, isolated and recovered by using the metal adsorbent of the present invention.

(Adsorption of metal ions in a single-component system)
Using the metal adsorbent obtained in Example 2, the adsorbability for various metals was evaluated. Adsorption tests were performed on 12 kinds of metal ions (boron, magnesium, calcium, manganese, cobalt, nickel, copper, zinc, strontium, cadmium, barium, lead). After immersing 25 mg of the adsorbent in 100 mL of various metal ion aqueous solutions with a metal concentration of 100 ppm at room temperature for 24 hours, the concentrations of various metal ions remaining in the aqueous solution were measured by ICP-OES, and the metal ion concentrations before and after immersion in the adsorbent were measured. Various metal ion adsorption capacities of the adsorbent were calculated from the amount of change. Table 3 shows the adsorption test results.

As shown in Table 3, it was confirmed that the metal adsorbent of the present invention has excellent adsorption performance with respect to 11 kinds of metal ions other than boron. Since the metal adsorbent of the present invention has a negatively charged dithiocarbamic acid group as a metal ion adsorbing group, it cannot adsorb ions having a negative charge such as boron ions, but on the other hand, metal ions It was confirmed that positively charged ions such as ions can be adsorbed satisfactorily. In particular, it was confirmed to exhibit a specifically high adsorption capacity for copper.

(Adsorption of metal ions in binary systems)
In the metal adsorbent obtained in Example 2 above, two types of metal ions (sodium/lead, magnesium/lead, calcium/lead, cobalt/lead, cadmium/lead, copper/lead, cobalt/nickel, cobalt/copper , cobalt/zinc, nickel/copper, nickel/zinc, copper/zinc) were used to conduct batch adsorption tests. After immersing 25 mg of the adsorbent in 100 mL of an aqueous metal ion solution having a metal concentration of 100 ppm for 24 hours at room temperature, the concentrations of various metal ions remaining in the aqueous solution were measured by ICP-OES. Various metal ion adsorption capacities of the adsorbent were calculated from the amount of change. Table 4 shows the adsorption test results.

As shown in Table 4, it was confirmed that the metal adsorbent of the present invention selectively adsorbs lead, which is a heavy metal ion, like sodium/lead in the presence of light metal ions such as sodium. The metal ion selectivity of the metal adsorbent of the present invention is Na ⁺ <Mg ²⁺ , Ca ²⁺ , Co ²⁺ , Cd ²⁺ <Pb ²⁺ <Cu ²⁺ and has specific selectivity to lead and copper. It was confirmed that In addition, as shown in Table 4(B), when the metal ion selectivity for four types of heavy metal ions of the fourth period, cobalt, nickel, copper, and zinc, which have similar metal properties, was evaluated, the metal adsorption of the present invention was evaluated. The metal ion selectivity of the material was found to be in the order Co ²⁺ <Zn ²⁺ <Ni ²⁺ <Cu ²⁺ .
From the above results, it was found that this adsorbent can efficiently and selectively recover heavy metals such as copper or lead from target aqueous solutions in which multiple metal ions coexist.

The metal adsorbent of the present invention can separate, extract, isolate and recover metals dissolved in liquid such as water. Therefore, it can be widely used for water purification in wastewater treatment facilities, recovery of rare metals from urban mines, highly cleaning filters for semiconductor manufacturing chemicals, filter media for soil contamination countermeasures at final disposal sites, and the like.

Claims (7)

A metal adsorbent in which a dithiocarbamic acid group is introduced into a polymer base material, wherein the dithiocarbamic acid group is introduced via a graft polymer and a dithiocarbamic acid group-introducing group. material ,
A metal adsorbent, wherein the structures of the dithiocarbamic acid group-introducing group and the dithiocarbamic acid group portion are represented by the following formula (1).

(In formula (1), X is an oxygen atom or a nitrogen atom, n and m represent the number of carbon atoms in the alkylene chain, n is an integer of 2 or more, and m is an integer of 0 or more. When X is an oxygen atom, m is 0. When X is a nitrogen atom, m is 1 or more.) The metal adsorbent according to claim 1 , wherein the graft polymer is one or more selected from (meth)acrylic polymer, styrene polymer, and (meth)acrylic-styrene copolymer. . 3. A method for producing a metal adsorbent according to claim 1 or 2 , characterized by comprising the following steps.
(i) Step of preparing an activated polymer substrate (ii-1) Step of graft polymerizing a monomer onto the polymer substrate (iii-1) Dithiocarbamic acid group having a protective group on the graft polymer Step (iv) of reacting the introduced compound to bond a dithiocarbamate group-introducing group having a protecting group to the graft polymer (iv) Step of deprotecting the protecting group from the dithiocarbamic acid group-introducing group bonded to the graft polymer (v) Dithiocarbamic acid A step of reacting carbon disulfide with the group-introducing group 3. A method for producing a metal adsorbent according to claim 1 or 2 , characterized by comprising the following steps.
(i) Step of preparing an activated polymer substrate (ii-1) Step of graft polymerizing a monomer onto the polymer substrate (iii-2) Reacting a dithiocarbamic acid group-introducing compound to the graft polymer (v) a step of reacting the dithiocarbamic acid group-introduced group with carbon disulfide; 3. A method for producing a metal adsorbent according to claim 1 or 2 , characterized by comprising the following steps.
(i) Step of preparing an activated polymer substrate (ii-2) Step of graft-polymerizing a monomer having a dithiocarbamate group-introduced group to the polymer substrate (v) To the dithiocarbamic acid group-introduced group Step of reacting carbon disulfide The method for producing a metal adsorbent according to any one of claims 3 to 5, wherein the activated polymeric substrate is a polymeric substrate activated by irradiation with radiation. . 3. A metal extraction method for extracting a metal from an object to be processed containing a metal, comprising a step of bringing the object to be processed into contact with the metal adsorbent according to claim 1 or 2 .

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