JP2024032425A - Carbon-based metal adsorbent - Google Patents

Abstract

To provide an adsorbent having superior metal adsorptive capacity.SOLUTION: A carbon-based metal adsorbent has a specific surface area of 100-4000 m2/g and a carboxy group level of 0.6-5.0 meq/g. The nitrogen content relative to the level of basic functional groups in the carbon-based metal adsorbent is 3-100 μeq/g.SELECTED DRAWING: Figure 1

Description

The present invention relates to a carbon-based metal adsorbent.

Even minute amounts of metals contained in wastewater from factories can cause river and soil pollution, and they can also have a negative impact on the human body. Furthermore, there is a need to remove metals as impurities from liquids such as cleaning water used in product production processes. Therefore, porous adsorbents such as activated carbon are used as a means for removing metals contained in liquids such as purified water and wastewater.

In recent years, techniques have been proposed to further improve metal adsorption performance by modifying porous adsorbents.
For example, Patent Document 1 discloses activated carbon obtained by activating a carbonaceous material with an acidic gas and further treating it with an oxidizing agent to control the total amount of acidic functional groups and the amount of acidic functional groups derived from carboxylic acid. Disclosed.
Furthermore, Patent Document 2 describes a porous body in which a nitrogen-containing organic compound is introduced into the pores of a porous metal oxide body, and the organic compound is thermally decomposed to form a skeleton of carbon atoms and nitrogen atoms within the pores. is disclosed.

Japanese Patent Application Publication No. 2004-315243 Japanese Patent Application Publication No. 2004-168587

An object of the present invention is to provide an adsorbent having excellent adsorption performance for metals.

The metal adsorbent of the present invention has the following configuration.
[1] Specific surface area is 100 to 4000 m ² /g,
The amount of carboxy groups is 0.6 to 5.0 meq/g, and the nitrogen content in the carbon-based metal adsorbent relative to the amount of basic functional groups is 3 to 100 μeq/g,
A carbon-based metal adsorbent.

[2] The ratio of nitrogen to the total amount of carbon, nitrogen, hydrogen, and oxygen obtained by elemental analysis of the carbon-based metal adsorbent is 1 to 20% by mass, and the amount of basic functional groups is 0.17 meq/g. Super, 0.60 meq/g or less,
The carbon-based metal adsorbent according to [1].

[3] The total amount of acidic functional groups is 1.5 to 5.0 meq/g, and the ratio of the amount of carboxy groups to the total amount of acidic functional groups is 31 to 100%,
The carbon-based metal adsorbent according to [1].

[4] The carbon-based metal adsorbent according to [1], wherein the carbon-based metal adsorbent is alkali-activated activated carbon.

[5] The carbon-based metal adsorbent according to [1], wherein the metal is a metal belonging to Groups 3 to 15 of the periodic table.

[6] A metal removal material or metal support using the carbon-based metal adsorbent according to any one of [1] to [5].

According to the present invention, it is possible to provide a carbon-based metal adsorbent having excellent adsorption performance for metals, particularly metals belonging to Groups 3 to 15 of the periodic table.

FIG. 1 is a graph showing the adsorption amount of each metal in Example 1 and Comparative Example 2. FIG. 2 is a graph showing the amounts of adsorbed metals in Example 2 and Comparative Examples 3 and 5. FIG. 3 is a graph showing the adsorption amount of each metal in Example 3 and Comparative Example 4. FIG. 4 is a graph showing the adsorption amount of each metal in Example 2 and Comparative Example 1.

The carbon-based metal adsorbent of the present invention has a specific surface area of 100 to 4000 m ² /g, a carboxy group content of 0.6 to 5.0 meq/g, and a nitrogen content in the carbon-based metal adsorbent that accounts for the basic functional group content. minutes is 3 to 100 μeq/g.
The nitrogen content in the carbon-based metal adsorbent based on the amount of basic functional groups is determined by calculating the ratio of nitrogen to the total amount of carbon, nitrogen, hydrogen, and oxygen obtained by elemental analysis of the carbon-based metal adsorbent. It is the value multiplied by
In particular, in the carbon-based metal adsorbent of the present invention, these can be controlled by appropriately controlling the nitrogen content in the carbon-based metal adsorbent that accounts for (I) the amount of carboxy groups and (II) the amount of basic functional groups. It exhibits superior metal adsorption performance compared to conventional adsorbents that do not.

Carbon-based metal adsorbent The carbon-based metal adsorbent of the present invention is an adsorbent mainly composed of carbon. Mainly composed of carbon means that the ratio of carbon to the total amount of carbon, nitrogen, hydrogen, and oxygen obtained by analyzing a carbon-based metal adsorbent with an elemental analyzer is preferably 50% by mass or more, more preferably 55% by mass or more. , more preferably 60% by mass or more, even more preferably 65% by mass or more.
A carbon-based metal adsorbent is a porous body having pores, and metals are adsorbed within the pores. The carbon-based metal adsorbent having such properties is preferably alkali-activated activated carbon (sometimes referred to as alkali-activated carbon).
In addition, the excellent metal adsorption performance of the present invention means that the amount of metal adsorption is large when compared with a conventional porous adsorbent having an equivalent specific surface area. Since the amount of metal adsorbed by the adsorbent increases as the specific surface area increases, comparisons are made with the specific surface area being the same.
The metal to be adsorbed is not particularly limited, but preferably metals belonging to Groups 3 to 15 of the periodic table, more preferably metals belonging to Groups 3 to 14 of the periodic table, still more preferably metals belonging to Groups 3 to 11 of the periodic table, Even more preferred are groups 8 to 11 of the periodic table. Further, the metal to be adsorbed may be from Groups 8 to 14 of the periodic table. Alternatively, the metal to be adsorbed in the present invention is preferably any one or more heavy metals, more preferably any one or more transition metals, and still more preferably at least one selected from the group consisting of cobalt, iron, copper, and lead. There may be.

Specific Surface Area The carbon-based metal adsorbent of the present invention has a specific surface area of 100 to 4000 m ² /g.
When the specific surface area is increased, the contact area with the medium to be treated such as a metal-containing solution is increased, so that the treatment performance is improved and the amount of metal adsorption is increased. On the other hand, if the specific surface area becomes too large, the amount of acidic functional groups such as carboxy groups decreases, and the nitrogen content in the carbon-based metal adsorbent decreases, so that the desired metal adsorption performance may not be exhibited.
The specific surface area of the carbon-based metal adsorbent is preferably 250 m ² /g or more, more preferably 1000 m ² /g or more, even more preferably 1500 m ² /g or more, even more preferably 2000 m ² /g or more, and preferably is 3500 m ² /g or less, more preferably 3000 m ² /g or less.

Pore Volume In the present invention, it is also a preferred embodiment to appropriately control the pore volume of the carbon-based metal adsorbent.
If the pore volume is too small, sufficient metal adsorption capacity may not be ensured. On the other hand, if the pore volume is too large, it becomes bulky and the filling amount during use decreases, and the number of fine pores that are not suitable for metal adsorption increases, leading to a decrease in metal adsorption performance.
The pore volume of the carbon-based metal adsorbent is preferably 0.05 ml/g or more, more preferably 0.1 ml/g or more, and preferably 2.5 ml/g or less, more preferably 2.0 ml/g. It is as follows.

Average Pore Diameter In the present invention, it is also a preferred embodiment to appropriately control the average pore diameter of the carbon-based metal adsorbent. If the average pore diameter is too small, it may be difficult for the metal to enter the pores, and sufficient adsorption performance may not be obtained. On the other hand, if the average pore diameter becomes too large, it may become bulky and the amount of filling during use may decrease.
The average pore diameter of the carbon-based metal adsorbent is preferably 0.5 nm or more, more preferably 1.0 nm or more, even more preferably 1.5 nm or more, and preferably 4 nm or less, more preferably 3.5 nm or less, More preferably, it is 3.0 nm or less, even more preferably 2.5 nm or less.

Amount of Total Acidic Functional Groups The total acidic functional groups are all acidic functional groups such as carboxy groups, carbonyl groups, phenol groups, and lactone groups that are measured by the method described in Examples.
In the present invention, it is also a preferred embodiment to appropriately control the total amount of acidic functional groups in the carbon-based metal adsorbent. As the total amount of acidic functional groups increases, the content of carboxy groups capable of ion exchange with metal ions increases, exhibiting excellent metal adsorption performance. If the total amount of acidic functional groups is too small, a sufficient amount of carboxy groups may not be ensured. On the other hand, if the total amount of acidic functional groups is too large, the nitrogen content in the carbon-based metal adsorbent may decrease in the amount of basic functional groups.
The total amount of acidic functional groups contained in the carbon-based metal adsorbent of the present invention is preferably 1.5 meq/g or more, more preferably 1.7 meq/g or more, even more preferably 2.0 meq/g or more, even more preferably 2.2 meq/g or more, most preferably 2.5 meq/g or more, preferably 5.0 meq/g or less, more preferably 4.0 meq/g or less, even more preferably 3.5 meq/g or less, and more More preferably, it is 3.0 meq/g or less.

Amount of Carboxy Group The amount of carboxy group contained in the carbon-based metal adsorbent of the present invention is 0.6 to 5.0 meq/g.
When the content of carboxyl groups is large, the adsorption performance for metals is improved. On the other hand, if the content of carboxy groups becomes too large, the nitrogen content in the carbon-based metal adsorbent relative to the amount of basic functional groups decreases, resulting in a decrease in metal adsorption performance.
The content of carboxy groups is preferably 0.61 meq/g or more, more preferably 0.65 meq/g or more, even more preferably 0.69 meq/g or more, even more preferably 0.7 meq/g, Preferably 4.0 meq/g or less, more preferably 3.5 meq/g or less, even more preferably 3.0 meq/g or less, even more preferably 2.5 meq/g or less, most preferably 2.0 meq/g or less. be.

Ratio of the amount of carboxy groups to the total amount of acidic functional groups In the present invention, it is also a preferred embodiment to appropriately control the ratio of the amount of carboxy groups to the total amount of acidic functional groups in the carbon-based metal adsorbent. The higher the ratio of carboxy groups, the better the metal adsorption performance.
The ratio of the amount of carboxy groups to the total amount of acidic functional groups is preferably 31% or more, more preferably 32% or more, and preferably 100% or less, more preferably 80% or less, still more preferably 60% or less, and More preferably, it is 40% or less.

Amount of Basic Functional Groups In the present invention, it is also a preferred embodiment to appropriately control the amount of basic functional groups contained in the carbon-based metal adsorbent.
The basic functional group is a positively charged functional group such as an amino group, and includes all basic functional groups measured by the method described in Examples.
If the content of basic functional groups is too small, the nitrogen content in the carbon-based metal adsorbent relative to the amount of basic functional groups may fall outside the above range, resulting in a decrease in metal adsorption performance. On the other hand, if the amount of basic functional groups becomes too large, the amount of carboxy groups decreases, and the adsorption performance for metals may decrease.
The content of basic functional groups is preferably more than 0.17 meq/g, more preferably 0.2 meq/g or more, even more preferably 0.3 meq/g or more, even more preferably 0.35 meq/g or more. It is preferably 0.60 meq/g or less, more preferably 0.5 meq/g or less, even more preferably 0.4 meq/g or less.

Ratio of Nitrogen In the present invention, it is also a preferred embodiment to control the ratio of nitrogen to the total amount of carbon, nitrogen, hydrogen, and oxygen obtained by elemental analysis of the carbon-based metal adsorbent.
When the nitrogen ratio contained in the carbon-based metal adsorbent is increased, the nitrogen content in the carbon-based metal adsorbent increases in the amount of basic functional groups, and the metal adsorption performance is improved. If the nitrogen ratio is too high, the specific surface area and the amount of carboxy groups may decrease, resulting in an imbalance and a decrease in metal adsorption performance.
The ratio of nitrogen is calculated by calculating the ratio of the amount of nitrogen to the total amount of carbon, nitrogen, hydrogen, and oxygen obtained by analyzing the carbon-based metal adsorbent with an elemental analyzer. Note that the oxygen amount is a value calculated based on the formula described in Examples.
The ratio of the amount of nitrogen to the total amount of carbon, nitrogen, hydrogen, and oxygen is preferably 1% by mass or more, more preferably 1.5% by mass or more, even more preferably 2.0% by mass or more, and preferably 20% by mass or more. It is at most 18% by mass, even more preferably at most 16% by mass, even more preferably at most 15% by mass.

Nitrogen content in the carbon-based metal adsorbent relative to the amount of basic functional groups In the carbon-based metal adsorbent of the present invention, the nitrogen content in the carbon-based metal adsorbent relative to the amount of basic functional groups is 3 to 100 μeq/g. .
When the amount of carboxy groups is within the above predetermined range and the nitrogen content in the carbon-based metal adsorbent relative to the amount of basic functional groups is within the predetermined range, excellent metal adsorption performance is exhibited. The metal adsorption performance improves as the nitrogen content in the carbon-based metal adsorbent increases in the amount of basic functional groups, but if it increases too much, the carboxy group content decreases and the metal adsorption performance deteriorates.
The nitrogen content in the carbon-based metal adsorbent based on the amount of basic functional groups is preferably 4 μeq/g or more, more preferably 5 μeq/g or more, still more preferably 7 μeq/g or more, even more preferably 10 μeq/g or more. Therefore, it is preferably 80 μeq/g or less, more preferably 70 μeq/g or less, even more preferably 60 μeq/g or less, even more preferably 50 μeq/g or less.

The carbon-based metal adsorbent of the present invention may be shaped in accordance with the intended use, and examples include powder, granules, crushed (granules), and fibrous shapes. Further, the carbon-based metal adsorbent may be formed into any shape such as a columnar shape, a spherical shape, a sheet shape, etc. together with a binder and other absorbent materials as necessary.

Further, the carbon-based metal adsorbent of the present invention may be of any size, and can be pulverized to a desired size using a pulverizer such as a ball mill. Note that pulverization may be performed during the manufacturing process or after manufacturing.

The carbon-based metal adsorbent of the present invention has excellent adsorption performance for metal components present in the liquid phase. Examples of the liquid phase include water, organic solvents, and other liquids suitable for various uses, and exhibit extremely excellent adsorption performance for removing metal components contained in the liquid. The carbon-based metal adsorbent of the present invention is useful, for example, for removing impurities in plating solutions and recovering metals from metal-containing waste solutions.
A metal removal material may be constructed using the carbon-based metal adsorbent of the present invention. Further, the carbon-based metal adsorbent of the present invention can be used as a metal support for applications such as catalysts by adsorbing a desired metal.

Hereinafter, a method for producing alkali-activated activated carbon, which is a preferred embodiment of the carbon-based metal adsorbent of the present invention, will be explained.However, the production method of the present invention is limited to the following production method as long as the above desired physical properties are obtained. Moreover, the manufacturing conditions can be changed as appropriate. Note that the following manufacturing conditions indicate preferred ranges, and it is necessary to appropriately adjust each manufacturing condition so that desired physical properties can be obtained.

(activation raw material)
The activation raw material of the present invention is a carbide of a carbonaceous material containing nitrogen. In the present invention, by using carbide of a nitrogen-containing carbonaceous material as the activation raw material, the nitrogen content in the carbon-based metal adsorbent that accounts for the amount of carboxy groups and the amount of basic functional groups in the activated carbon-based metal adsorbent is reduced. It can be controlled within the above range.
The activation raw material preferably has a nitrogen content of 3% by mass or more, more preferably 5% by mass or more, even more preferably 7% by mass or more, even more preferably 10% by mass or more, and preferably 50% by mass or less, more preferably Preferably it is 40% by mass or less, more preferably 30% by mass or less, even more preferably 20% by mass or less.

Examples of nitrogen-containing carbonaceous substances include melamine resin; guanidine resin; urea resin; aniline resin; sulfonamide resin; imide resin; urethane resin; nitrile resin such as polyacrylonitrile; polybenzimidazole resin; carbazole resin; acridine resin; pyridine resin Nitrogen-containing resins such as; pyrrole resin; and the like can be mentioned. In particular, polyacrylonitrile resin is preferable because the activated carbon contains a large amount of nitrogen after activation. The nitrogen-containing resin may be a copolymer containing a nitrogen-containing monomer as a main component and using other monomers as subcomponents. The nitrogen-containing resins may be used alone or in combination of two or more.

(Carbonization process)
The activation raw material is obtained by carbonizing a nitrogen-containing carbonaceous material before activation treatment. The carbonization treatment may be performed by heat-treating the nitrogen-containing carbonaceous material in an inert gas such as nitrogen, for example by holding it at 400° C. to 1000° C. for 1 hour to 3 hours.

(Alkali activation treatment process)
The activation treatment step of the present invention is an alkali activation treatment in which an activator containing an alkali metal compound and an activation raw material are mixed and heated in an inert gas to obtain activated carbon.
In the alkali activation treatment step of the present invention, an alkali metal compound is used as an alkali activator. Examples of the alkali metal compound include alkali metal hydroxides such as potassium hydroxide and sodium hydroxide; alkali metal carbonates such as potassium carbonate and sodium carbonate; and alkali metal sulfates such as potassium sulfate and sodium sulfate. Preferably it is an alkali metal hydroxide, more preferably potassium hydroxide.

Regarding the amount of the activator used, as the mixing ratio of the activator to the activation raw material is increased, the specific surface area of the activated carbon tends to increase. On the other hand, if the mixing ratio of the activator becomes too high, the density of activated carbon tends to decrease. In the present invention, the mixing ratio of the activator may be adjusted so as to have the above-mentioned specific surface area, and the mass ratio of the activator to the activating raw material (mass of activator/mass of activating raw material) is preferably 0.5 or more, and more preferably 0.5 or more. It is preferably 1.0 or more, more preferably 2.0 or more, and preferably 10.0 or less, more preferably 5.0 or less, and still more preferably 4.0 or less.
The alkali activation treatment of the present invention is performed in an atmosphere of any inert gas such as argon, helium, or nitrogen.

If the alkali activation treatment temperature of the present invention is too low, sufficient specific surface area and carboxy group content cannot be ensured. On the other hand, if the activation temperature becomes too high, nitrogen and carboxy groups will separate, making it impossible to secure a predetermined amount.
The heating temperature during the alkali activation treatment is preferably 350°C or higher, more preferably 400°C or higher, and preferably 800°C or lower, more preferably 750°C or lower, and still more preferably 700°C or lower.
The rate of temperature increase to the above heating temperature is preferably 1°C/min or more, more preferably 5°C/min or more, and preferably 20°C/min or less, more preferably 15°C/min or less.
The activation treatment time in the above heating temperature range is preferably 1 hour or more, more preferably 2 hours or more, and preferably 10 hours or less, more preferably 5 hours or less.

(Cleaning process)
The cleaning process is a process in which the activated carbon that has been subjected to the alkali activation process is subjected to a water cleaning process or an inorganic acid cleaning process to remove alkali metals remaining in the activated carbon. The alkali metal removal rate can be increased by repeating the cleaning process multiple times.
(Water cleaning treatment)
The temperature of the water used in the water washing treatment is preferably 20°C or higher, more preferably 30°C or higher, and preferably 100°C or lower, more preferably 95°C or lower. In the water washing treatment, it is desirable to repeat water washing and filtration multiple times until the pH of the filtrate becomes 7.0 or less.

(Inorganic acid cleaning treatment)
In the inorganic acid cleaning treatment, hydrogen acids such as hydrochloric acid and hydrofluoric acid, oxyacids such as sulfuric acid, nitric acid, phosphoric acid, and perchloric acid can be used as inorganic acids, and hydrochloric acid is preferred. From the viewpoint of increasing the alkali metal removal rate while maintaining the physical properties of the activated carbon, it is preferable to adjust the concentration of the inorganic acid to 10 parts by mass to 100 parts by mass of the inorganic acid per 100 parts by mass of the activated carbon. The temperature of the inorganic acid aqueous solution is desirably set in a temperature range that can increase the efficiency of removing alkali metals from activated carbon while suppressing volatilization of the inorganic acid, preferably 20°C or higher, more preferably 30°C or higher. The temperature is preferably 100°C or lower, more preferably 95°C or lower. In the inorganic acid cleaning treatment, washing and filtration are repeated multiple times, preferably the residual amount of potassium in the activated carbon is 5000 mg/kg or less (more than 0 mg/kg), more preferably the residual amount of alkali metal in the activated carbon is 2500 mg/kg or less (0 mg/kg). It is desirable to carry out the treatment until the concentration is more than 1000 mg/kg (more than 0 mg/kg), more preferably 1000 mg/kg or less (more than 0 mg/kg). The residual amount of alkali metal can be measured using an ICP emission spectrometer.

(Water washing process)
As a post-treatment step after the inorganic acid cleaning treatment, water cleaning treatment is performed to remove the inorganic acid remaining in the activated carbon. The temperature of the water used in the water washing treatment is preferably 20°C or higher, more preferably 30°C or higher, even more preferably 50°C or higher, and preferably 100°C or lower, more preferably is below 95°C. In the water washing treatment, it is desirable to repeat water washing and filtration multiple times until the pH of the filtrate becomes 6.5 or higher.

(Drying process)
After the washing treatment, the activated carbon may be dried by performing a drying treatment. Drying may be carried out under any conditions as long as the moisture remaining in the activated carbon can be removed. For example, it is preferable to heat the activated carbon (for example, at 100 to 150° C.) and dry it for 0.5 to 24 hours.
In addition, in the present invention, the alkaline activated carbon obtained by the activation treatment is not subjected to high temperature (for example, over 150° C.) heat treatment. When alkaline activated carbon is heat-treated at high temperatures, the amount of acidic functional groups and specific surface area decrease, resulting in a decrease in metal adsorption performance.

The alkali-activated carbon obtained by appropriately adjusting each production condition has the above configuration as the carbon-based metal adsorbent of the present invention.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited by the Examples below, and modifications may be made as appropriate within the scope of the spirit of the preceding and following. Of course, other implementations are also possible, and all of them are included within the technical scope of the present invention.

Example 1
Activation raw material Polyacrylonitrile (PAN) resin as a carbonaceous material was charged into a muffle furnace (manufactured by Koyo Thermos Co., Ltd.), and the temperature inside the furnace was raised to 650°C (heating rate 10°C/min) under a nitrogen atmosphere. The temperature was maintained for 2 hours, and the obtained PAN resin carbide was used as an activation raw material.
Activation treatment process Add activator to the obtained PAN resin carbide so that the mass ratio ([mass of alkaline component of activator]/[mass of activation raw material]: hereinafter referred to as KOH/C ratio) is 2.0. A commercially available alkali activator (concentration 48.5% potassium hydroxide aqueous solution) was added, the temperature was raised to 400° C. in a nitrogen atmosphere, and the temperature was maintained for 3.75 hours to obtain alkali activated carbon.

Water washing treatment process The obtained alkali activated carbon was washed repeatedly with 60° C. hot water until the pH of the filtrate became 7.0 or less.
Inorganic Acid Washing Step Next, the alkali activated carbon was acid washed for 1 hour in a 5.25 wt % hydrochloric acid aqueous solution, and then suction filtered.
Post-processing process (washing process)
Furthermore, the alkaline activated carbon after filtration was repeatedly washed with 60° C. warm water until the pH of the filtrate became 6.5 or higher.
Drying Treatment Step The obtained alkali-activated carbon was subjected to a drying treatment for 24 hours in a dryer set at 115°C to obtain activated carbon 1.

Example 2
Activated carbon 2 was obtained in the same manner as in Example 1 except that the activation temperature was 600° C. and the KOH/C ratio was 3.0.

Example 3
Activated carbon 3 was obtained in the same manner as in Example 1 except that the activation temperature was 650° C. and the KOH/C ratio was 2.5.

Comparative example 1
The above activated carbon No. Comparative activated carbon 1 was obtained by charging Comparative Activated Carbon 1 into a small furnace, raising the temperature to 450°C in a nitrogen atmosphere (heating rate: 10°C/min), and maintaining the temperature for 2 hours.

Comparative example 2
Comparative activated carbon 2 was obtained in the same manner as in Example 1, except that the carbonaceous material was changed from PAN resin to petroleum coke (DPC) and the KOH/C ratio was set to 1.0.

Comparative example 3
Comparative activated carbon 3 was obtained in the same manner as in Example 1, except that the carbonaceous material was changed from PAN resin to petroleum coke, the activation temperature was 600° C., and the KOH/C ratio was 5.0.

Comparative example 4
Comparative activated carbon 4 was obtained in the same manner as in Example 1, except that the carbonaceous material was changed from PAN resin to petroleum coke, the activation temperature was 650° C., and the KOH/C ratio was 3.0.

Comparative example 5
Activation raw material Phenol resin as a carbonaceous material was charged into a muffle furnace (manufactured by Koyo Thermos Co., Ltd.), and the temperature inside the furnace was raised to 700°C (heating rate 10°C/min) under a nitrogen atmosphere, and the temperature was maintained at this temperature for 2 hours. The obtained spherical phenol resin carbide was used as an activation raw material.
Activation Treatment Step Activated carbon of Comparative Example 5 was obtained in the same manner as in Example 1 except that the activation temperature was 600° C. and the KOH/C ratio was 3.0.

Evaluation Each of the above activated carbons was pulverized with a disk mill so that the particle diameter (D50) at a volume-based cumulative frequency of 50% was approximately 8 to 12 μm, and then subjected to each analysis.
The particle size of the crushed activated carbon (sample) was measured using a laser diffraction particle size distribution analyzer (SALD (registered trademark)-2200, manufactured by Shimadzu Corporation), and a volume-based cumulative frequency curve was determined from the particle size distribution measurement results. was determined, and the particle diameter (D50) at a cumulative frequency of 50% was defined as the average particle diameter.

Specific surface area After vacuum drying activated carbon (0.2 g) at 250°C, the amount of nitrogen gas adsorbed in a liquid nitrogen atmosphere (-196°C) using a nitrogen adsorption device (ASAP-2420 manufactured by Micromeritics) was measured to determine the nitrogen adsorption isotherm, and the specific surface area (m2/g) was determined by the BET method.

Total pore volume The total pore volume (mL/g) was calculated from the nitrogen adsorption amount at relative pressure (P/P0) = 0.93 from the nitrogen adsorption isotherm.

Average pore diameter (4V/A)
Assuming that the pores of activated carbon are cylindrical, the average pore diameter was calculated based on the following formula.
Average pore diameter (nm) = 4 x total pore volume (mL/g) / specific surface area (m ² /g) x 1000

Total Acidic Functional Groups The amount of total acidic functional groups was determined according to the Boehm method (Literature "H.P. Boehm, Adzan. Catal, 16, 179 (1966)").
Specifically, 50 mL of an aqueous sodium ethoxide solution (0.1 mol/L) was added to 1 g of activated carbon, stirred at 500 rpm for 2 hours, and then left to stand for 24 hours. After 24 hours, the mixture was stirred for an additional 30 minutes and then filtered and separated. 0.1 mol/L hydrochloric acid was added dropwise to 25 mL of the obtained filtrate, and the titration amount of hydrochloric acid when the pH reached 4.0 was measured.
Further, as a blank test, 0.1 mol/L hydrochloric acid was added dropwise to 25 mL of the sodium ethoxide aqueous solution (0.1 mol/L), and the titer of hydrochloric acid when the pH reached 4.0 was measured. Then, the total amount of acidic functional groups (meq/g) was calculated using the following formula.
Total acidic functional group amount (meq/g) = [(ab) x 0.1]/[(S x 25)/50]
a: Hydrochloric acid titer in blank test (mL)
b: Hydrochloric acid titer (mL) when reacting the sample
S: Sample weight (g)

Individual acidic functional groups 0.1 mol/1000 mL sodium ethoxide (NaOEt) aqueous solution was converted to 0.1 mol/1000 mL NaOH, or 0.05 mol/1000 mL Na ₂ CO ₃ , or 0.1 mol/1000 mL NaCO ₃ to convert all acidic functional groups. The evaluation was done in the same way as the quantity. In addition, each acidic functional group was calculated using the following formula.

The method for quantifying the amount of functional groups in activated carbon is generally known, [Surface, 34 [2] (1996) Otowa p. 62], or [Catal. , 1966 [16] (US) p. 179]. Specifically, 1 g of activated carbon was placed in a 100 mL Erlenmeyer flask, and N/10 alkaline reagents ((a) sodium bicarbonate, (b) sodium carbonate, (c) caustic soda, and (d) sodium ethoxide) were added. Add 50 mL of each, shake for 24 hours, separate, and titrate the unreacted alkaline reagent with N/10 hydrochloric acid. Carboxyl groups are found in all reagents (a) to (d), and lactone groups are found in reagents (b) to ( d) Since hydroxyl groups react with reagents (c) to (d) and quinone groups react with reagent (d), the amount of functional groups is determined by subtracting the respective titrations.

Basic Functional Groups The amount of basic functional groups was determined by back titration when measuring the total amount of acidic functional groups. Specifically, 50 mL of hydrochloric acid (0.1 mol/L) was added to 1 g of activated carbon, stirred at 500 rpm for 2 hours, and then left for 24 hours. After 24 hours, the mixture was stirred for an additional 30 minutes and then filtered and separated. 0.1 mol/L of sodium hydroxide was added dropwise to 25 mL of the obtained filtrate, and the titer of sodium hydroxide when the pH reached 8.0 was measured. In addition, as a blank test, 0.1 mol/L of sodium hydroxide was added dropwise to 25 mL of the hydrochloric acid (0.1 mol/L), and the titer of sodium hydroxide when the pH reached 8.0 was measured. Then, the amount of basic functional groups (meq/g) was calculated using the following formula.
Basic functional group amount (meq/g) = [(c-d) x 0.1]/[(S x 25)/50]
c: Sodium hydroxide titer in blank test (mL)
d: Sodium hydroxide titer (mL) when reacting the sample
S: Sample mass (g)

Carbon, Hydrogen, Nitrogen, Oxygen Calculate the mass ratio (mass%) of the amount of carbon (C), hydrogen (H), and nitrogen (N) contained in the sample using a CHN coder (JM1000HCN manufactured by J Science Lab Co., Ltd.) Measured at Further, the amount of oxygen (O) (% by mass) in the sample was calculated from the obtained ratios (% by mass) of the amount of C, the amount of H, and the amount of N based on the following formula.
O amount (mass %) = 100 mass % - C amount (mass %) - H amount (mass %) - N amount (mass %)

Carboxy group The ratio of the amount of carboxy groups to the total amount of acidic functional groups was calculated from the amount of total acidic functional groups (meq/g) and the amount of carboxy groups (R-COOH groups) (meq/g) based on the following formula.
Ratio of carboxy group amount = carboxy group amount (meq/g)/total acidic functional group amount (meq/g) x 100

Basic Nitrogen Functional Group The amount of basic nitrogen functional group was calculated based on the following formula from the amount of basic functional group (meq/g) and the amount of N (mass%) obtained by elemental analysis.
Basic nitrogen functional group amount = Basic functional group amount (meq/g) x N amount (mass%) / 100 x 1000 (unit adjustment)

Metal-containing aqueous solution Each metal-containing aqueous solution was prepared by adding a metal reagent to a 1 L volumetric flask so that the initial concentration C0 (mg/L) was 100 mg/L, and then dipping up to the marked line with pure water. Note that the following reagents were used to prepare the metal-containing aqueous solution.
・Cobalt (Co)-containing aqueous solution: CoCl _2.6 hydrate (manufactured by Kishida Chemical Co., Ltd., special grade, purity 99%)
- Iron (Fe) containing aqueous solution: FeCl _3.6 hydrate (manufactured by Kishida Chemical Co., Ltd., special grade, purity 99%)
・Copper (Cu)-containing aqueous solution: CuSO _4.5 hydrate (manufactured by Kishida Chemical Co., Ltd., special grade, purity 99.5%)
・Lead (Pb) containing aqueous solution: PbCl ₂ (manufactured by Kishida Chemical Co., Ltd., special grade, purity 98%)

Metal adsorption amount 0.1 g of activated carbon that had been dried in a dryer set at 115°C for 2 hours was put into a 100 mL Erlenmeyer flask, and the initial concentration C0 (mg/L) was adjusted to 100 mg/L. 100 mL of the above metal-containing aqueous solution was added, and the mixture was stirred at 500 rpm for 24 hours in a constant temperature bath at 25°C. After stirring for 24 hours, the activated carbon was filtered out using a syringe filter, and the resulting filtrate was measured using an ICP emission spectrometer (manufactured by Thermo Electron Co., Ltd.) to determine the metal concentration C1 (mg/L) remaining after adsorption. Quantitated. The amount of metal adsorbed per weight of activated carbon (mg/g) was determined from the metal concentration (mg/L) before and after adsorption based on the following formula.
Metal adsorption amount (mg/g) = [(C0 (mg/L) - C1 (mg/L)) x 0.1 (L)] / 0.1 (g)

Since the amount of adsorption varies depending on the specific surface area, the results of comparing Examples and Comparative Examples for each specific surface area based on the above results are shown in FIGS. 1 to 4. In addition, from the left in the figure, the adsorption amounts of Co, Fe, Cu, and Pb are shown.
As shown in FIG. 1, Comparative Example 2 had a larger specific surface area than Example 1, but the amount of each metal adsorbed was small.
Similarly, as shown in FIGS. 2 to 4, Examples 2 and 3 also had larger amounts of each metal adsorbed than Comparative Examples 1, 3, 4, and 5, which had the same specific surface area.
Note that the reason why the amount of adsorption of Pb is outstanding is that the atomic weight of Pb is larger than that of Co, Fe, and Cu, and the difference in adsorption amount in terms of mg/g becomes significant.

From the above results, activated carbons 1 to 3 of the present invention, in which the nitrogen content in the carbon-based metal adsorbent relative to the amount of carboxy groups and the amount of basic functional groups is appropriately controlled, do not satisfy either one or both. The metal adsorption performance was superior to that of comparative activated carbons 1 to 5.

Claims (6)

Specific surface area is 100 to 4000 m ² /g,
The amount of carboxy groups is 0.6 to 5.0 meq/g, and the nitrogen content in the carbon-based metal adsorbent relative to the amount of basic functional groups is 3 to 100 μeq/g,
A carbon-based metal adsorbent. The ratio of nitrogen to the total amount of carbon, nitrogen, hydrogen, and oxygen obtained by elemental analysis of the carbon-based metal adsorbent is 1 to 20% by mass, and the amount of basic functional groups is more than 0.17 meq/g, 0 .60meq/g or less,
The carbon-based metal adsorbent according to claim 1. The total amount of acidic functional groups is 1.5 to 5.0 meq/g, and the ratio of the amount of carboxy groups to the total amount of acidic functional groups is 31 to 100%,
The carbon-based metal adsorbent according to claim 1. The carbon-based metal adsorbent according to claim 1, wherein the carbon-based metal adsorbent is alkali-activated activated carbon. The carbon-based metal adsorbent according to claim 1, wherein the metal is a metal belonging to Groups 3 to 15 of the periodic table. A metal removal material or metal support using the carbon-based metal adsorbent according to any one of claims 1 to 5.

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