JP7668484B2 - Metal Fixing Material - Google Patents

Description

This disclosure relates to a metal fixing material and a method for fixing metal using the metal fixing material.

Arsenic is known to be a harmful element to the human body. Among inorganic arsenic, As(III) in particular is highly toxic. As(III) in wastewater is separated from the liquid by coagulating and precipitating As(III) with a coagulant (coagulation and precipitation method). However, since As(III) is dissolved in the liquid as a low-molecular-weight uncharged species over a wide pH range, the removal efficiency is low, which is a problem. In addition, a large amount of coagulant is required to coagulate and precipitate As(III), which results in the production of a large amount of sludge. This also poses the problem of the cost of large-scale equipment and sludge treatment.

In recent years, valuable metals such as ruthenium, cobalt, rhodium, iridium, nickel, palladium, platinum, copper, silver, and gold have come to be widely used in electronic materials, electronic components, industrial catalysts, metal plating, etc. In the medical field, platinum is used in anti-cancer drugs, and palladium is used in dental treatment.

Despite Japan consuming large amounts of valuable metals, most of them are imported. Therefore, from the perspective of effective resource utilization, it is desirable to recover and reuse valuable metals contained in industrial wastewater and waste materials.

Patent Document 1 describes that by binding iminodiacetic acid or dialkylamine to cellulose with a crystallinity of 70% or less, it is possible to introduce many functional groups capable of forming chelates with valuable metals, and that the cellulose derivative obtained in this way makes it possible to efficiently recover valuable metals.

JP 2009-247981 A

However, the cellulose derivatives tend to form salts with alkali metals and alkaline earth metals. As a result, the cellulose derivatives adsorb alkali metals and alkaline earth metals that are abundant in nature along with valuable metals, making it impossible to selectively recover valuable metals.

The inventors have discovered that cellulose derivatives into which dithiocarbamate groups, which correspond to soft bases in the HSAB rule, have cations that do not adsorb alkali metals or alkaline earth metals, which correspond to hard acids in the HSAB rule, but selectively adsorb valuable metals and harmful metals, which correspond to soft acids or intermediate acids.

However, because cellulose derivatives with dithiocarbamate groups are easily soluble in water, it has been difficult to recover valuable metals or harmful metals adsorbed onto the cellulose derivatives from the liquid.

Therefore, an object of the present disclosure is to provide a metal-immobilizing material that is useful for selectively and efficiently recovering valuable metals and hazardous metals in a simple manner.
Another object of the present disclosure is to provide a method for fastening metal using said metal fastener.

As a result of intensive research by the present inventors to solve the above problems, they have found that if a cation is selectively adsorbed in an aqueous solution to a cellulose derivative into which a dithiocarbamate group, which corresponds to a soft base in the HSAB rule, is introduced, and valuable metals or harmful metals, which correspond to a soft acid or intermediate acid in the HSAB rule, and then a specific coagulant and polymer flocculant are added, the cellulose derivative quickly forms flocs (lumps), which can be easily separated from the aqueous solution by a simple method such as filtration. The present disclosure has been completed based on these findings.

［式中、Ｒ^aは、同一又は異なって、水素原子又は下記式（ａ）で表される基である。尚、セルロース誘導体に含まれる全てのＲ^aのうち、少なくとも１つは下記式（ａ）で表される基である］

（式中、環Ｚはヘテロ原子として窒素原子を含む複素環を示し、Ｒ¹は単結合又は炭素数１～１０のアルキレン基を示す。４つのＲ²は同一又は異なって炭素数１～１０のアルキル基を示す）
Ｂ成分：凝結剤
Ｃ成分：高分子凝集剤 That is, the present disclosure provides a metal fixing material consisting of a combination of the following components A, B, and C.
Component A: a metal adsorbent containing a cellulose derivative having a repeating unit represented by the following formula (I):

[In the formula, R ^a may be the same or different and is a hydrogen atom or a group represented by the following formula (a). Of all R ^a contained in the cellulose derivative, at least one is a group represented by the following formula (a)]

(In the formula, ring Z represents a heterocycle containing a nitrogen atom as a heteroatom, R ¹ represents a single bond or an alkylene group having 1 to 10 carbon atoms, and four R ^2s may be the same or different and represent alkyl groups having 1 to 10 carbon atoms.)
B component: coagulant C component: polymer flocculant

The present disclosure also provides the metal fixing material, wherein the coagulant is a cationic coagulant.

The present disclosure also provides the metal fixing material, in which the polymer flocculant is an anionic polymer flocculant.

The present disclosure also provides the metal fixing material, in which the anionic polymer flocculant is a polymer containing monomer units derived from an anionic monomer, and the proportion of the monomer units derived from the anionic monomer in the total monomer units constituting the polymer is 30% by weight or more.

The present disclosure also provides the metal fixing material, which contains 0.1 to 10 parts by weight of the B component per 1 part by weight of the A component.

The present disclosure also provides the metal fixing material, which contains 0.1 to 10 parts by weight of the C component per 1 part by weight of the A component.

The present disclosure also provides the metal fixing material, in which the ratio of the content of the B component to the content of the C component (B/C; weight ratio) is 20/80 to 80/20.

The present disclosure also provides the metal fixing material, which is a fixing material for the following metals:
Metal: Metal whose cation is a soft acid or intermediate acid according to the HSAB rule

The present disclosure also provides the metal fixing material, which is a fixing material of at least one metal selected from titanium, vanadium, manganese, iron, cobalt, nickel, copper, zinc, gallium, arsenic, selenium, cadmium, indium, lead, bismuth, ruthenium, rhodium, iridium, palladium, platinum, silver, and gold.

［式中、Ｒ^aは、同一又は異なって、水素原子又は下記式（ａ）で表される基である。尚、セルロース誘導体に含まれる全てのＲ^aのうち、少なくとも１つは下記式（ａ）で表される基である］

（式中、環Ｚはヘテロ原子として窒素原子を含む複素環を示し、Ｒ¹は単結合又は炭素数１～１０のアルキレン基を示す。４つのＲ²は同一又は異なって炭素数１～１０のアルキル基を示す）
Ｂ成分：凝結剤
Ｃ成分：高分子凝集剤 The present disclosure also provides a method for fixing a metal, comprising the steps of adding the following component A to an aqueous solution containing a dissolved metal, and then adding the following components B and C to form a floc containing the metal, the component A, the component B, and the component C.
Component A: a metal adsorbent containing a cellulose derivative having a repeating unit represented by the following formula (I):

[In the formula, R ^a may be the same or different and is a hydrogen atom or a group represented by the following formula (a). Of all R ^a contained in the cellulose derivative, at least one is a group represented by the following formula (a)]

(In the formula, ring Z represents a heterocycle containing a nitrogen atom as a heteroatom, R ¹ represents a single bond or an alkylene group having 1 to 10 carbon atoms, and four R ^2s may be the same or different and represent alkyl groups having 1 to 10 carbon atoms.)
B component: coagulant C component: polymer flocculant

The metal fixing material of the present disclosure is composed of a combination of the components A, B, and C. The component A has a property that the cations of the component A easily adsorb metals that fall under the category of soft acids or intermediate acids in the HSAB rule (e.g., valuable metals and harmful metals) and do not easily adsorb metals that fall under the category of hard acids (e.g., alkali metals and alkaline earth metals).
If components B and C are added to a liquid containing component A to which the metal has been adsorbed, component A to which the metal has been adsorbed will rapidly form flocs together with components B and C, and can be separated from the liquid by a simple method such as filtration. Furthermore, the volume of the flocs separated from the liquid can be significantly reduced by subjecting them to a heat treatment.

Therefore, by using the metal fixing material, harmful metals can be efficiently and selectively fixed in flocs from water contaminated with harmful metals, and the flocs can be easily recovered by filtration, etc. In addition, by subjecting the recovered flocs to a heat treatment to reduce their volume, disposal costs such as landfilling can be significantly reduced.

In addition, by using the metal fixing material, valuable metals from industrial wastewater or waste can be selectively and efficiently fixed in flocs, and the flocs can be easily recovered by filtration or the like. In addition, by subjecting the recovered flocs to a combustion process, the valuable metals fixed in the flocs can be easily recovered and reused.

FIG. 1 is a diagram showing an IR spectrum of cellulose derivative 1 obtained in Preparation Example 1.

[Metal fixing material]
The metal fixing material of the present disclosure comprises a combination of the following components A, B, and C.
Component A: Metal adsorbent Component B: Coagulant Component C: Polymer flocculant

Component A has excellent adsorption power for valuable metals and harmful metals whose cations correspond to soft acids or intermediate acids according to the HSAB law. On the other hand, it has low adsorption power for metals whose cations correspond to hard acids according to the HSAB law.

Therefore, the metal fixing material can selectively and efficiently fix valuable metals and harmful metals whose cations fall under the soft acid or intermediate acid category under the HSAB rule from aqueous solutions containing various metals (e.g., industrial wastewater, mine wastewater, hot spring water, etc.).

The fixation rate of valuable metals (e.g., metals selected from cobalt, selenium, iridium, nickel, palladium, platinum, copper, zinc, silver, and gold) whose cations fall under the soft acid or intermediate acid category under the HSAB rule is, for example, 85% or more, preferably 90% or more, and particularly preferably 95% or more.

The fixation rate of harmful metals (e.g., metals selected from arsenic, cadmium, and lead) whose cations fall under the soft acid or intermediate acid category under the HSAB rule is, for example, 85% or more, preferably 90% or more, and particularly preferably 95% or more.

The fixation rate of metals (e.g., alkali metals, alkaline earth metals) whose cations fall under the category of hard acids according to the HSAB law by the metal fixation material is, for example, 10% or less, preferably 5% or less, particularly preferably 1% or less, and most preferably 0.1% or less.

The fixation rate of base metals (particularly iron, aluminum, and manganese) by the metal fixing material is, for example, 60% or less, preferably 50% or less, more preferably 45% or less, even more preferably 30% or less, particularly preferably 20% or less, most preferably 10% or less, and especially preferably 5% or less.

In this disclosure, the metal fixation rate is the fixation rate when 10 mg of component A is added to 10 mL of an aqueous solution (pH 7) with a metal element concentration of 2 mM at 25°C, stirred at 200 rpm for 20 minutes, and then 20 mg of component B and 10 mg of component C are added and stirred at 200 rpm for 60 minutes, and can be calculated by the method described in the Examples.

［式中、Ｒ^aは、同一又は異なって、水素原子又は下記式（ａ）で表される基である。尚、セルロース誘導体（Ｉ）に含まれる全てのＲ^aのうち、少なくとも１つは下記式（ａ）で表される基である］

（式中、環Ｚはヘテロ原子として窒素原子を含む複素環を示し、Ｒ¹は単結合又は炭素数１～１０のアルキレン基を示す。４つのＲ²は同一又は異なって炭素数１～１０のアルキル基を示す） (Component A)
The component A is a metal adsorbent and contains at least a cellulose derivative having a repeating unit represented by the following formula (I) (hereinafter, sometimes referred to as "cellulose derivative (I)").

[In the formula, R ^a may be the same or different and is a hydrogen atom or a group represented by the following formula (a). Of all R ^a contained in the cellulose derivative (I), at least one is a group represented by the following formula (a)]

(In the formula, ring Z represents a heterocycle containing a nitrogen atom as a heteroatom, R ¹ represents a single bond or an alkylene group having 1 to 10 carbon atoms, and four R ^2s may be the same or different and represent alkyl groups having 1 to 10 carbon atoms.)

Ring Z is a heterocycle containing a nitrogen atom as a heteroatom. Ring Z may contain a heteroatom other than a nitrogen atom.

Among these, ring Z is preferably a heterocycle (particularly a non-aromatic heterocycle) containing only a nitrogen atom as a heteroatom. Ring Z is, for example, a 3- to 10-membered ring, more preferably a 4- to 8-membered ring, and even more preferably a 4- to 6-membered ring.

Examples of ring Z include five-membered rings such as a pyrrolidine ring; and six-membered rings such as a piperidine ring and a piperazine ring.

Examples of the alkylene group having 1 to 10 carbon atoms for R ¹ include linear or branched alkylene groups such as a methylene group, a methylmethylene group, a dimethylmethylene group, an ethylene group, a 2-methylethylene group, a 1,2-dimethylethylene group, a propylene group, a trimethylene group, and a 2-methyl-trimethylene group.

R ¹ is preferably a single bond or an alkylene group having 1 to 2 carbon atoms.

Examples of the alkyl group having 1 to 10 carbon atoms for ^R2 include linear or branched alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, s-butyl, t-butyl, and pentyl groups.

^R2 is preferably an alkyl group having 1 to 3 carbon atoms.

As the group represented by formula (a), a group represented by the following formula (a-1) or a group represented by the following formula (a-2) is preferable: In the following formulas, ^R2 is the same as defined above.

As the group represented by formula (a), a group represented by the following formula (a-1') or a group represented by the following formula (a-2') is preferable: In the following formulas, R ¹ is the same as defined above.

The total average degree of substitution (the average value of the degree of substitution of the hydrogen atoms of the hydroxyl groups at the 2-, 3- and 6-positions of the glucose units constituting the cellulose with the group represented by formula (a) (preferably the group represented by formula (a-1), (a-2), (a-1') or (a-2')) is, for example, 0.1 to 3.0, preferably 1.0 to 3.0, and particularly preferably 2.0 to 3.0. When the cellulose derivative (I) contains the group in the above range, it is preferable in that it can exhibit excellent metal adsorption power.

The weight average molecular weight of the cellulose derivative (I) is, for example, 5,000 or more, preferably 10,000 or more, and particularly preferably 50,000 or more. The upper limit of the weight average molecular weight is, for example, 5 million, preferably 2 million, particularly preferably 1 million, and most preferably 500,000.

The cellulose derivative (I) has a group represented by the above formula (a), and the group contains a dithiocarbamate group that corresponds to a soft base in the HSAB rule. Therefore, it has excellent adsorption power for metal ions derived from metals that correspond to soft acids or intermediate acids in the HSAB rule (e.g., at least one metal selected from titanium, vanadium, manganese, iron, cobalt, nickel, copper, zinc, selenium, gallium, arsenic, cadmium, indium, lead, bismuth, ruthenium, rhodium, iridium, palladium, platinum, silver, and gold). In other words, the cellulose derivative (I) acts as an adsorbent for metals whose cations correspond to soft acids or intermediate acids in the HSAB rule.

The (saturated) adsorption capacity of the cellulose derivative (I) for metals whose cations correspond to soft acids or intermediate acids according to the HSAB rule is, for example, 1 mol/kg or more, preferably 2 mol/kg or more, more preferably 2.5 mol/kg or more, even more preferably 3 mol/kg or more, particularly preferably 3.5 mol/kg or more, and most preferably 5 mol/kg or more.

The (saturated) adsorption capacity of the cellulose derivative (I) for the harmful metals is, for example, 0.2 mol/kg or more, preferably 0.3 mol/kg or more, more preferably 0.5 mol/kg or more, even more preferably 0.6 mol/kg or more, particularly preferably 1 mol/kg or more, and most preferably 2 mol/kg or more.

The arsenic adsorption capacity is, for example, 0.2 mol/kg or more, preferably 0.5 mol/kg or more, and more preferably 1 mol/kg or more.

The cellulose derivative (I) has a low adsorption power for metals whose cations fall under the category of hard acids according to the HSAB rule (particularly alkali metals, alkaline earth metals, and base metals).

The (saturated) adsorption capacity of metals whose cations fall under the category of hard acids according to the HSAB rule (e.g., alkali metals such as sodium and potassium; alkaline earth metals such as magnesium, calcium, strontium, and barium; and base metals such as iron, aluminum, and manganese) is, for example, 2.0 mol/kg or less, more preferably 1.6 mol/kg or less, even more preferably 0.8 mol/kg or less, particularly preferably 0.4 mol/kg or less, most preferably 0.1 mol/kg or less, and particularly preferably 0.01 mol/kg or less.

The cellulose derivative (I) has excellent storage stability because the strain of the ring Z (e.g., a heterocycle such as piperidine or pyrrolidine) in the group represented by formula (a) inhibits proton transfer to the nitrogen atom, which is the starting point for decomposition of the dithiocarbamic acid group. For example, even after the cellulose derivative (I) is subjected to a test in which it is left standing in an air atmosphere at 40°C for two weeks, it has a high metal adsorption amount that is the same as before the test. The retention rate of the metal adsorption amount is, for example, 95% or more.

Component A may contain other components in addition to the cellulose derivative (I), but the proportion of the cellulose derivative (I) in the total amount of component A is, for example, 50% by weight or more, preferably 60% by weight or more, particularly preferably 70% by weight or more, most preferably 80% by weight or more, and particularly preferably 90% by weight or more. If the proportion of the cellulose derivative (I) falls below the above range, it tends to be difficult to efficiently and selectively adsorb metals. Also, storage stability tends to decrease.

There are no particular limitations on the dosage form of component A as long as it is effective, and examples include powder, pellets, threads, nonwoven fabric, etc.

The cellulose derivative (I) can be produced, for example, through the following steps [1], [2] and [3].

In the above formula, R ¹ , R ² , ring Z and R ^a are the same as above.

In the above formula, R ⁰ represents a monovalent hydrocarbon group or a monovalent heterocyclic group.

The hydrocarbon groups include aliphatic hydrocarbon groups, alicyclic hydrocarbon groups, aromatic hydrocarbon groups, and groups formed by combining these groups.

Examples of aliphatic hydrocarbon groups include alkyl groups having 1 to 10 carbon atoms (particularly preferably 1 to 3 carbon atoms), such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, s-butyl, t-butyl, pentyl, hexyl, and decyl; and alkenyl groups having 2 to 10 carbon atoms (particularly preferably 2 to 3 carbon atoms), such as vinyl, allyl, and 1-butenyl.

Examples of the alicyclic hydrocarbon group include 3- to 10-membered (particularly preferably 5- to 8-membered) cycloalkyl groups such as a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, and a cyclooctyl group; 3- to 15-membered (particularly preferably 5- to 8-membered) cycloalkenyl groups such as a cyclopentenyl group and a cyclohexenyl group; and bridged cyclic hydrocarbon groups such as a perhydronaphthalene-1-yl group, a norbornyl group, an adamantyl group, a tricyclo[5.2.1.0 ^2,6 ]decan-8-yl group, and a tetracyclo[4.4.0.1 ^2,5 .1 ^7,10 ]dodecan-3-yl group.

Examples of aromatic hydrocarbon groups include aryl groups having 6 to 20 carbon atoms, such as a phenyl group, a naphthyl group, and an anthracenyl group. In addition, the aromatic ring constituting the aromatic hydrocarbon group may be condensed with another ring (e.g., an alicyclic ring, etc.) to form a condensed ring. Examples of groups containing such condensed rings include a fluorene group.

The heterocyclic group is a group in which one hydrogen atom has been removed from the structural formula of a heterocycle. The heterocycle includes aromatic heterocycles and non-aromatic heterocycles. Examples of such heterocycles include 3- to 10-membered rings (preferably 4- to 6-membered rings) having carbon atoms and at least one heteroatom (e.g., oxygen atom, sulfur atom, nitrogen atom, etc.) as ring-constituting atoms, and condensed rings thereof. Specifically, heterocycles containing an oxygen atom as a heteroatom (for example, three-membered rings such as an oxirane ring; four-membered rings such as an oxetane ring; five-membered rings such as a furan ring, a tetrahydrofuran ring, an oxazole ring, an isoxazole ring, and a γ-butyrolactone ring; six-membered rings such as a 4-oxo-4H-pyran ring, a tetrahydropyran ring, and a morpholine ring; condensed rings such as a benzofuran ring, an isobenzofuran ring, a 4-oxo-4H-chromene ring, a chroman ring, and an isochroman ring; 3-oxatricyclo[4.3.1.1 ^4,8 ]undecane-2-one ring, 3-oxatricyclo[4.2.1.0 ^4,8 ]nonan-2-one ring and the like), heterocycles containing a sulfur atom as a heteroatom (e.g., 5-membered rings such as a thiophene ring, a thiazole ring, an isothiazole ring, a thiadiazole ring, and the like; 6-membered rings such as a 4-oxo-4H-thiopyran ring; fused rings such as a benzothiophene ring, and the like), heterocycles containing a nitrogen atom as a heteroatom (e.g., 5-membered rings such as a pyrrole ring, a pyrrolidine ring, a pyrazole ring, an imidazole ring, a triazole ring, and the like; 6-membered rings such as an isocyanuric ring, a pyridine ring, a pyridazine ring, a pyrimidine ring, a pyrazine ring, a piperidine ring, a piperazine ring, and the like; fused rings such as an indole ring, an indoline ring, a quinoline ring, an acridine ring, a naphthyridine ring, a quinazoline ring, and a purine ring, and the like).

The hydrocarbon group or heterocyclic group may have various substituents [e.g., halogen atoms, oxo groups, hydroxyl groups, substituted oxy groups (e.g., alkoxy groups, aryloxy groups, aralkyloxy groups, acyloxy groups, etc.), carboxyl groups, substituted oxycarbonyl groups (e.g., alkoxycarbonyl groups, aryloxycarbonyl groups, aralkyloxycarbonyl groups, etc.), substituted or unsubstituted carbamoyl groups, cyano groups, nitro groups, substituted or unsubstituted amino groups, sulfo groups, etc.].

In the above formula, R ^b may be the same or different and is a hydrogen atom or a group represented by the above formula (b). At least one of all R ^b contained in the cellulose derivative (II) is a group represented by the above formula (b).

In the formula, R ^c is the same or different and is a hydrogen atom or a group represented by the above formula (c). Of all R ^c contained in the cellulose derivative (III), at least one is a group represented by the above formula (c). In addition, the group represented by the above formula (c) may form a salt.

Step [1] is a step in which a compound represented by the above formula (2) (hereinafter sometimes referred to as "imino acid (2)") is reacted with the hydroxyl group of cellulose (1-1) (= a compound having a repeating unit represented by the above formula (1-1)).

The imino acid (2) is a compound in which the imino group of the imino acid is protected with a carbamate-based protecting group (COOR ⁰ group) (or a compound in which the secondary amino group of a cyclic amino acid is protected with a carbamate-based protecting group). Examples of the imino acid include proline, 3-pyrrolidine carboxylic acid, 2-piperidine carboxylic acid, 4-piperidine carboxylic acid, and (4-piperidinyl) acetic acid.

Among the carbamate protecting groups, t-butoxycarbonyl group (Boc), benzyloxycarbonyl group (CBZ), 9-fluorenylmethyloxycarbonyl group (Fmoc), etc. are preferred because they can be deprotected under mild conditions.

As the cellulose (1-1) used in step [1], for example, cellulose derived from wood pulp (softwood pulp, hardwood pulp) or cotton linter pulp, crystalline cellulose, etc. can be suitably used. These can be used alone or in combination of two or more. The pulp may contain other components such as hemicellulose. The pulp is preferably used in a finely pulverized state, for example by subjecting it to a crushing treatment.

The reaction between the cellulose (1-1) and the imino acid (2) is preferably carried out in the presence of a catalyst. Examples of the catalyst include triethylamine, pyridine, and N,N-dimethyl-4-aminopyridine (DMAP). These can be used alone or in combination of two or more.

The amount of the catalyst used is, for example, about 0.01 to 1.0 mole per mole of imino acid (2).

The reaction is preferably carried out in the presence of a condensing agent. Examples of the condensing agent include 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC-HCl), N,N'-dicyclohexylcarbodiimide, and N,N'-diisopropylcarbodiimide. These can be used alone or in combination of two or more.

The amount of the condensing agent used is, for example, about 0.01 to 1.0 mole per mole of imino acid (2).

The reaction is preferably carried out in the presence of a solvent. Examples of the solvent include aliphatic hydrocarbons such as hexane, heptane, and octane; alicyclic hydrocarbons such as cyclohexane; aromatic hydrocarbons such as benzene, toluene, xylene, and ethylbenzene; halogenated hydrocarbons such as chloroform, dichloromethane, and 1,2-dichloroethane; ethers such as diethyl ether, dimethoxyethane, tetrahydrofuran, and dioxane; ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; esters such as methyl acetate, ethyl acetate, isopropyl acetate, and butyl acetate; amides such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone; nitriles such as acetonitrile, propionitrile, and benzonitrile; alcohols such as methanol, ethanol, isopropyl alcohol, and butanol; and dimethyl sulfoxide. These can be used alone or in combination of two or more.

As the solvent, amides such as N,N-dimethylacetamide are preferred, and it is particularly preferred to use a mixture of the solvent with a lithium salt such as lithium chloride, as this has excellent cellulose solubility. The concentration of the lithium salt in the solvent can be adjusted as appropriate within a range that does not impair the effect of dissolving cellulose, and is, for example, about 1 to 30% by weight.

The amount of the solvent used is, for example, about 0.5 to 30 times the total amount of the reaction substrates. If the amount of the solvent used exceeds this range, the concentration of the reaction components will be low and the reaction rate will tend to decrease.

Through step [1], a cellulose derivative (II) having a repeating unit represented by the above formula (II) is produced.

Step [2] is a step of deprotecting the imino group of the cellulose derivative (II) produced through step [1] (more specifically, a step of removing the protecting group of the imino group in the group represented by formula (b) introduced into the cellulose derivative (II)).

After step [2], a cellulose derivative (III) having a repeating unit represented by the above formula (III) is produced.

The method for removing the protecting group of the imino group of the cellulose derivative (II) can be appropriately selected depending on the type of protecting group.

For example, when the protecting group is Boc or the like, the protecting group can be removed by reacting with a strong acid such as hydrochloric acid or trifluoroacetic acid. When the strong acid is used to remove the protecting group, the cellulose derivative (III) obtained may have the group represented by formula (c) forming a salt together with a counter anion. For example, when trifluoroacetic acid is reacted as a strong acid, the terminal imino group of the group represented by formula (c) may form a salt with CF ₃ COO ^- to become ">N ⁺ H ₂ .CF ₃ COO ^- ".

For example, when the protecting group is CBZ, the protecting group can be removed by carrying out a reduction reaction in the presence of a catalyst (e.g., Pd-C).

For example, if the protecting group is Fmoc, the protecting group can be removed by reacting with a secondary amine such as pyridine.

The reaction temperature in step [2] is, for example, about 0 to 100°C. The reaction time is, for example, about 1 to 24 hours. After completion of the reaction, the reaction product obtained can be separated and purified by, for example, a separation means such as filtration, concentration, distillation, extraction, crystallization, adsorption, recrystallization, column chromatography, or a combination of these separation means.

Step [3] is a step of reacting the cellulose derivative (III) produced through step [2] with a quaternary ammonium compound represented by the above formula (3) in the presence of a sulfur compound.

^R2 in formula (3) corresponds to ^R2 in formula (a) above ^{. X-} in formula (3) represents ^a counter anion, such _as ^OH- , ^Cl- , Br-, ^I- , ^F- , _{SO42- ,} ^BH4- , ^BF4- , or ^PF6- _.

Examples of the quaternary ammonium compound include tetramethylammonium hydroxide, tetraethylammonium hydroxide, etc.

The amount of the quaternary ammonium compound used is, for example, 50 parts by weight or more per 100 parts by weight of the cellulose derivative (III).

The sulfur compound may be, for example, carbon disulfide. The amount of the sulfur compound used is, for example, 20 parts by weight or more per 100 parts by weight of the cellulose derivative (III).

The reaction in step [3] is preferably carried out in the presence of a solvent. Examples of the solvent include aromatic hydrocarbons such as toluene, xylene, and ethylbenzene; alcohols such as methanol, ethanol, 2-propanol, isopropyl alcohol, and butanol; and N-methylpyrrolidone, dimethyl sulfoxide, and N,N-dimethylformamide. These can be used alone or in combination of two or more. The amount of the solvent used is, for example, about 0.5 to 30 times by weight the total amount of the reaction substrates.

The reaction temperature in step [3] is, for example, about 0 to 100°C. The reaction time is, for example, about 1 to 24 hours. After completion of the reaction, the reaction product obtained can be separated and purified by, for example, a separation means such as filtration, concentration, distillation, extraction, crystallization, adsorption, recrystallization, column chromatography, or a combination of these separation means.

(Component B)
The component B is a coagulant. The coagulant neutralizes the surface charge of the component A and suppresses the repulsion between the components A. By adding the component B to the component A, the repulsion between the components A is suppressed, making it easier to form flocs.

The cellulose derivative (I) contained in component A has a group represented by formula (a). Therefore, the surface of component A has an anionic charge. Therefore, it is preferable to use a coagulant that exhibits cationic properties (= cationic flocculant) as component B.

The coagulants include inorganic coagulants and organic coagulants. These can be used alone or in combination of two or more.

Examples of the inorganic coagulant include aluminum-based coagulants such as aluminum sulfate, aluminum chloride, and polyaluminum chloride; and iron-based coagulants such as ferric chloride, ferrous chloride, and polyferric sulfate.

Examples of the organic coagulant include (meth)acrylic acid alkylamino esters, vinylamine compounds, allylamine compounds, condensed amine compounds, polyethyleneimine, and dicyandiamide compounds.

The weight average molecular weight of the organic coagulant is, for example, 1×10 ⁶ or less, preferably 1×10 ⁵ or less, more preferably 1×10 ⁴ or less, particularly preferably 0.5×10 ⁴ or less, and most preferably 1×10 ³ or less.

The (meth)acrylic acid alkylamino ester is, for example, a polymer having a monomer unit derived from a monomer represented by the following formula (b).

In formula (b), ^L1 represents an oxygen atom or an NR group, and the R represents a hydrogen atom or an alkyl group. The alkyl group is, for example, an alkyl group having 1 to 10 carbon atoms (preferably 1 to 5, and particularly preferably 1 to 3).

In formula (b), L ² represents an alkylene group having 1 to 4 carbon atoms. ^{R b1} to R ^b3 are the same or different and represent a hydrogen atom or a hydrocarbon group. R ^b4 represents a hydrogen atom or a methyl group. ^{Z −} represents a counter anion.

Examples of the alkylene group having 1 to 4 carbon atoms include linear or branched alkylene groups such as methylene, methylmethylene, dimethylene, propylene, and trimethylene. Among these, alkylene groups having 2 to 4 carbon atoms are preferred, and alkylene groups having 2 to 3 carbon atoms are particularly preferred.

The hydrocarbon group includes an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, an aromatic hydrocarbon group, and groups formed by combining these. Among these, an aliphatic hydrocarbon group or an aromatic hydrocarbon group is preferred, and an aliphatic hydrocarbon group is particularly preferred.

The aliphatic hydrocarbon group is preferably an alkyl group having 1 to 10 carbon atoms (preferably 1 to 5, and particularly preferably 1 to 3), such as a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a s-butyl group, a t-butyl group, a pentyl group, or a hexyl group.

Examples of the counter anion include a halogen anion and a sulfate anion.

Examples of monomers that form the monomer unit represented by formula (b) include dialkylaminoalkyl (meth)acrylates such as dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, dimethylaminopropyl (meth)acrylate, and dimethylamino-2-hydroxypropyl (meth)acrylate, and hydrochlorides, sulfates, methyl chloride adducts, benzyl chloride adducts, and dimethyl sulfate adducts of dialkylaminoalkyl (meth)acrylamides such as dimethylaminopropyl (meth)acrylamide.

The (meth)acrylic acid alkylamino ester may have other monomer units in addition to the monomer unit represented by the above formula (b). Examples of the other monomer units include a nonionic monomer unit and an anionic monomer unit.

Examples of monomers that form the nonionic monomer units (=nonionic monomers) include (meth)acrylamide, N,N'-di(alkyl)acrylamide, (meth)acrylic acid esters (e.g., methyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, etc.), vinyl esters (e.g., vinyl acetate, styrene, etc.), acrylonitrile, diacetone acrylamide, N-vinylpyrrolidone, N-vinylformamide, N-vinylacetamide, acryloylmorpholine, etc.

Examples of monomers that form the anionic monomer units (=anionic monomers) include (meth)acrylic acid, maleic acid, itaconic acid, 2-acrylamido-2-methylsulfonic acid, and salts thereof (e.g., ammonium salts, sodium salts, potassium salts, etc.).

The proportion of the monomer units represented by the above formula (b) in the total amount of monomer units constituting the (meth)acrylic acid alkylamino ester is, for example, 10 mol% or more, preferably 30 mol% or more, particularly preferably 50 mol% or more, and most preferably 70 mol% or more.

The (meth)acrylic acid alkylamino ester can be produced by polymerizing one type of monomer or copolymerizing two or more types of monomers.

The vinylamine-based compound may be, for example, a polymer of one monomer selected from N-vinyl carboxylic acid amide, N-vinyl formamide, N-vinyl acetamide, etc., or a copolymer of two or more monomers.

The allylamine-based compounds include, for example, allylamine, diallylmethylamine, and salts thereof, or (co)polymers of monomers such as diallyldimethylammonium chloride.

Examples of the condensed amine compounds include condensates of epichlorohydrin with at least one amine selected from monomethylamine, dimethylamine, monoethylamine, diethylamine, ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, etc., and compounds obtained by further condensing the condensates with polyamines such as ethylenediamine, diethylenetriamine, triethylenetetramine, and hexamethylenediamine.

Examples of the dicyandiamide-based compound include dicyandiamide/formaldehyde condensate, dicyandiamide/formaldehyde/ammonium chloride condensate, etc.

(Component C)
The component C is a polymer flocculant. The polymer flocculant flocculates the component A whose surface charge has been neutralized by the addition of the component B. The component A flocculated by the polymer flocculant forms flocs in the liquid and precipitates.

The polymer flocculants include anionic polymer flocculants, cationic polymer flocculants, amphoteric polymer flocculants, and nonionic polymer flocculants. These can be used alone or in combination of two or more.

The weight average molecular weight of the polymer flocculant is, for example, 2 x 10 ⁶ or more, preferably 3 x 10 ⁶ or more, particularly preferably 4 x 10 ⁶ or more, and most preferably 5 x 10 ⁶ or more. The upper limit of the weight average molecular weight is, for example, 50 x 10 ⁶ , preferably 20 x 10 ⁶ , and preferably 18 x 10 ^6. By using a polymer flocculant having a weight average molecular weight in the above range, flocs can be formed quickly.

The form of the polymer flocculant is not particularly limited, and any form such as an aqueous solution, dispersion, emulsion, powder, etc. can be used.

<Anionic polymer flocculant>
The anionic polymer flocculant is a polymer having a monomer unit derived from an anionic monomer. The proportion of the monomer unit derived from the anionic monomer in the total monomer units constituting the polymer is, for example, 10% by weight or more, preferably 30% by weight or more, more preferably 50% by weight or more, particularly preferably 70% by weight or more, and most preferably 90% by weight or more.

The anionic polymer flocculant may contain other monomer units in addition to the monomer units derived from the anionic monomer. Examples of other monomer units include monomer units derived from nonionic monomers.

Examples of the anionic monomer and nonionic monomer include the same examples of the anionic monomer and nonionic monomer described in the section on component B.

The anionic polymer flocculant can be produced by (co)polymerizing an anionic monomer and, if necessary, other monomers (e.g., aqueous solution polymerization, water-in-oil emulsion polymerization, or water-in-oil dispersion polymerization, etc.).

<Cationic polymer flocculant>
The cationic polymer flocculant is a polymer having a monomer unit derived from a cationic monomer. The proportion of the monomer unit derived from the cationic monomer in the total monomer units constituting the polymer is, for example, more than 0% by weight and 100% by weight or less. The lower limit of the proportion is preferably 1% by weight, particularly preferably 5% by weight. The upper limit of the proportion is preferably 90% by weight, more preferably 70% by weight, particularly preferably 50% by weight, and most preferably 30% by weight.

The cationic polymer flocculant may contain other monomer units in addition to the monomer units derived from the cationic monomer. Examples of other monomer units include monomer units derived from anionic monomers and monomer units derived from nonionic monomers.

The cationic monomer may be, for example, a monomer represented by formula (b) described in the section on component B. The anionic monomer and nonionic monomer may be the same as the examples of the anionic monomer and nonionic monomer described in the section on component B.

The cationic polymer flocculant can be produced by (co)polymerizing a cationic monomer and, if necessary, other monomers.

<Amphoteric polymer flocculant>
The amphoteric polymer flocculant is a polymer having a monomer unit derived from a cationic monomer and a monomer unit derived from an anionic monomer, and the weight ratio of the monomer unit derived from the cationic monomer to the monomer unit derived from the anionic monomer (the former/the latter) is, for example, 40/60 to 60/40.

The proportion of the total monomer units derived from the cationic monomer and the monomer units derived from the anionic monomer in the total monomer units constituting the polymer is, for example, 10% by weight or more, preferably 30% by weight or more, more preferably 50% by weight or more, particularly preferably 70% by weight or more, and most preferably 90% by weight or more.

The amphoteric polymer flocculant may contain other monomer units in addition to the monomer units derived from cationic monomers and the monomer units derived from anionic monomers. Examples of other monomer units include monomer units derived from nonionic monomers.

Examples of the nonionic monomer include the same examples of the nonionic monomer described in the section on component B.

The amphoteric polymer flocculant can be produced by copolymerizing a cationic monomer, an anionic monomer, and, if necessary, other monomers.

<Nonionic polymer flocculant>
The amphoteric polymer flocculant is a polymer or copolymer of a nonionic monomer.

Examples of the nonionic monomer include the same examples of the nonionic monomer described in the section on component B.

The amphoteric polymer flocculant can be produced by polymerizing one type of nonionic monomer or copolymerizing two or more types.

As the C component, it is preferable to use an anionic polymer flocculant, because it quickly forms flocs and can fix metals efficiently. Furthermore, among the anionic polymer flocculants, it is preferable to use a polymer in which the proportion of monomer units derived from anionic monomers is 30% by weight or more (preferably 50% by weight or more, particularly preferably 70% by weight or more, and most preferably 90% by weight or more), because it quickly forms flocs and can form large flocs, which makes it particularly easy to separate them from the liquid.

The proportion of the anionic polymer flocculant in the total amount of component C is, for example, 50% by weight or more, preferably 60% by weight or more, more preferably 70% by weight or more, particularly preferably 80% by weight or more, and most preferably 90% by weight or more.

[Metal fixing method]
The metal fixing method of the present disclosure includes a step of adding the component A to an aqueous solution containing a dissolved metal, and then adding the component B and the component C to form a floc containing the metal, the component A, the component B, and the component C.

Metals exist as metal ions in an aqueous solution. When component A is added to the aqueous solution, the metal ions form a chelate complex with the group represented by formula (a) of cellulose derivative (I), which is component A, and are adsorbed to component A.

The amount of component A used is, for example, 200 to 3,000 g, preferably 200 to 2,000 g, and particularly preferably 200 to 1,000 g, per mole of metal contained in the aqueous solution.

In order to promote the adsorption of metal ions to component A, after adding component A to the aqueous solution, it is preferable to stir and/or shake the aqueous solution for, for example, about 1 minute to 1 hour.

In addition, adjusting the pH of the aqueous solution to, for example, 1 to 9 (preferably 1 to 7, and especially 2 to 6) is preferable in that it can further improve the adsorption of metal ions to component A. The pH of the aqueous solution can be adjusted using a commonly known pH adjuster (an acid such as nitric acid or an alkali such as sodium hydroxide).

After the metal ions are adsorbed to component A in the aqueous solution, components B and C are added to the aqueous solution. Components B and C may be added simultaneously, or component B may be added first and then component C.

In order to promote the formation of flocs, after components B and C have been added to the aqueous solution, it is preferable to stir and/or shake the aqueous solution for, for example, about 30 minutes to 2 hours.

The amount of component B used is, for example, 0.1 to 10 parts by weight, preferably 0.1 to 5 parts by weight, particularly preferably 0.1 to 3 parts by weight, and most preferably 0.1 to 2.0 parts by weight, per part by weight of component A. By using component B in the above range, it is possible to suppress the repulsion between components A, and it is possible to obtain the effect of promoting the formation of flocks.

The amount of component C used is, for example, 0.1 to 10 parts by weight, preferably 0.1 to 5 parts by weight, particularly preferably 0.1 to 2 parts by weight, and most preferably 0.1 to 1.5 parts by weight, per part by weight of component A. By using component C in the above range, components A whose surface charge has been neutralized by component B can be aggregated together, allowing flocks to be formed quickly.

The ratio of the amounts of the B component and the C component used (B/C; weight ratio) is, for example, 20/80 to 80/20, preferably 30/70 to 80/20, particularly preferably 40/60 to 75/25, most preferably 50/50 to 75/25, and particularly preferably 55/45 to 75/25.

The flocs thus formed in the aqueous solution can be separated from the aqueous solution by a simple method such as filtration. The separated flocs can be reduced in volume by subjecting them to a heat treatment. The volume reduction rate is, for example, 90% or more, and preferably 95% or more. The metals fixed in the flocs can be recovered by burning the flocs.

The above configurations and combinations of the present disclosure are merely examples, and additions, omissions, substitutions, and modifications of the configurations may be made as appropriate without departing from the spirit of the present disclosure.

The present disclosure will be explained in more detail below with reference to examples, but the present disclosure is not limited to these examples and is limited only by the claims.

Preparation Example 1 (Preparation of Cellulose Derivative)
Cellulose (1-1) (0.501 g, 3.08 mmol) was placed in a two-necked eggplant flask and vacuum dried at 90 ° C for 2 hours. Under a nitrogen atmosphere, N,N-dimethylacetamide (15 mL) and lithium chloride (0.99 g) were added to dissolve the cellulose. N,N-dimethyl-4-aminopyridine (2.26 g, 18.5 mmol), N-Boc-L-proline (3.98 g, 18.5 mmol), 1-ethyl 3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC.HCl) (3.55 g, 18.5 mmol), and N,N-dimethylacetamide (15 mL) were added to this reaction vessel and stirred at room temperature for 24 hours. The reaction solution was poured into water to reprecipitate, and the obtained solid was collected by suction filtration. The obtained solid was dissolved in ethanol, reprecipitated with water, and collected by suction filtration. The solid was dried in vacuum to obtain DMC-Pro-II (1.81 g, yield 78%) represented by the following formula as a white solid.
From the results of ¹ H-NMR measurement, the total average degree of substitution of N-Boc-proline was calculated to be 3.0.

（ＤＭＣ－Ｐｒｏ－ＩＩ）
¹H-NMR （500 MHz, CDCl₃ ,55℃）：δ4.00-5.30 (br, 8H), 2.95-4.00 (br, 8H), 1.60-2.56 (br, 12H), 1.43 (br, 27H)

(DMC-Pro-II)
^1H -NMR (500 MHz, CDCl _3,55 ℃): δ4.00-5.30 (br, 8H), 2.95-4.00 (br, 8H), 1.60-2.56 (br, 12H), 1.43 (br, 27H)

Trifluoroacetic acid (6.6 mL) and DMC-Pro-II (1.00 g, 1.33 mmol) were added to a two-necked eggplant flask under a nitrogen atmosphere, and the mixture was stirred at room temperature for 7.5 hours. The solid precipitated by reprecipitation with diethyl ether was collected by centrifugation and washed with diethyl ether. The resulting solid was dried in vacuum to obtain a salt of DMC-Pro-III represented by the following formula as a white solid (979 mg, yield 92%). The results of ¹ H-NMR measurement of DMC-Pro-III are shown below.

（ＤＭＣ－Ｐｒｏ－ＩＩＩ）
¹H-NMR (500 MHz, D₂O, r.t.)：δ 5.24 (br, 1H), 4.91 (br, 1H), 4.80 (br, overlapped with HDO), 4.45 (br, 3H), 4.21 (br, 1H), 4.06 (br, 1H), 3.81 (br, 1H), 3.67 (br, 1H), 3.32(br, 6H), 2.18-2.54 (br, 3H), 1.60-2.16 (br, 9H)

(DMC-Pro-III)
¹ H-NMR (500 MHz, D ₂ O, rt): δ 5.24 (br, 1H), 4.91 (br, 1H), 4.80 (br, overlapped with HDO), 4.45 (br, 3H), 4.21 (br, 1H), 4.06 (br, 1H), 3.81 (br, 1H), 3.67 (br, 1H), 3.32(br, 6H), 2.18-2.54 (br, 3H), 1.60-2.16 (br, 9H)

Under a nitrogen atmosphere, DMC-Pro-III salt (0.500 g, 0.628 mmol) was dissolved in dimethyl sulfoxide (3.1 mL) in a two-necked eggplant flask, and carbon disulfide (0.57 mL, 9.4 mmol) was added. In the dark, the mixture was cooled to about 10°C, and 10% tetramethylammonium hydroxide methanol solution (3.77 mL, 3.77 mmol) was added dropwise, and the mixture was stirred for 7 hours while being heated to room temperature. The solid obtained by reprecipitation in ethanol was collected by centrifugation and washed with ethanol. The solid obtained was dried in a vacuum to obtain cellulose derivative 1 (DMC-Pro, weight average molecular weight: about 100,000) represented by the following formula as a white solid (453 mg, yield 80%). The IR spectrum of cellulose derivative 1 (DMC-Pro) is shown in Figure 1.

（ＤＭＣ－Ｐｒｏ）
¹H-NMR (500 MHz, D₂O, r.t.)：δ 4.40-5.70 (br, overlapped with HDO), 3.35-4.40 (br), 3.15 (br,CH₃), 1.20-2.85 (br)

(DMC-Pro)
¹ H-NMR (500 MHz, D ₂ O, rt): δ 4.40-5.70 (br, overlapped with HDO), 3.35-4.40 (br), 3.15 (br,CH ₃ ), 1.20-2.85 (br)

Examples 1 to 9
To a 50 mL polyethylene centrifuge tube, 20 mg of cellulose derivative 1 and 10 mL of a 2.0 mM aqueous As(III) solution (initial As(III) concentration: B μmol/L) were added, and the tube was shaken at 200 rpm at 25° C. for 20 minutes.
Thereafter, 20 mg of a coagulant (CHP295) and 10 mg of a polymer flocculant (Component C shown in Table 1 below) were added, and the mixture was shaken again for 1 hour.
After shaking, the reaction solution was centrifuged (3000 rpm, 25° C., 30 minutes) and filtered through a syringe filter with a pore size of 0.45 μm.
The obtained filtrate was subjected to ICP-AES analysis to quantify the As(III) concentration (S μmol/L) in the filtrate, and the amount of As(III) fixed per unit amount of component C was calculated from the following formula.
As(III) fixed amount (μmol/g) = [(BS)×10/1000]/C component usage amount (g)

Comparative Examples 1 to 9
The same procedures as in Examples 1 to 9 were carried out except that the cellulose derivative 1 was not used and the component C shown in Table 1 below was used as the polymer flocculant.

The results are summarized in Table 1 below.

From Table 1, it can be seen that the amount of As(III) adsorption is significantly improved by using cellulose derivative 1 in combination with the coagulant and polymer flocculant.

Examples 10 to 13
To a 50 mL centrifuge tube, 20 mg of cellulose derivative 1 and 10 mL of a 2.0 mM As(III) aqueous solution were added, and the mixture was shaken at 200 rpm, 25° C., and 20 minutes using a shaker (BR-30L; Taitec, Aichi).
Then, 20 mg of a coagulant (CHP295) was added, and the mixture was shaken at 200 rpm and 25° C. for 2 minutes.
Next, 10 mg of a polymer flocculant (Component C shown in Table 2 below) was added, and the mixture was shaken at 200 rpm at 25° C. for 5 minutes.
After shaking, the sample was allowed to stand, and the time (seconds) until flocs were formed was measured to evaluate the floc-forming ability.

The results are summarized in Table 2 below.

From Table 2, it can be seen that the flocculation rate is faster when an anionic polymer flocculant is used, and in particular, the flocculation rate is faster when an anionic polymer flocculant with a high anionic monomer ratio is used.

(Consider the effects of other metals)
For an aqueous solution containing 12 types of metal elements (Mg, Ca, Sr, Ba, Cu, Mn, Co, Ni, Zn, Pb, As, Se), the amount of each metal element immobilized was measured when component B (CHP295) and component C (APP199) were used in combination with component A (cellulose derivative 1) and when component A (cellulose derivative 1) was not used in combination.
The measurement was performed in the same manner as in Example 6, except that an aqueous solution containing 12 kinds of metal elements was used instead of the 2.0 mM As(III) aqueous solution.

The results are summarized in Table 3 below.

As can be seen from Table 3, even when component A was added, the fixation rate of alkaline earth metals, which are hard acids, was less than 80%, whereas valuable metals and hazardous metals, which are soft acids or intermediate acids, all showed high fixation rates of 97% or more. In particular, the fixation rates of As(III) and Se(IV) increased significantly with the addition of component A. From these results, it can be seen that valuable metals and hazardous metals can be efficiently fixed by the metal fixation material disclosed herein.

In addition, the floc obtained using the cellulose derivative 1, the coagulant (CHP295), and the polymer flocculant (APP199) was dried for 3 days. The mass of the floc after drying was 19 mg. Then, sintering was performed. The mass after sintering was 0.2 mg (volume reduction rate 97%).
From the above, it can be seen that by using the metal fixing material of the present disclosure, it is possible to significantly reduce the volume of flocs, and by reducing the volume of flocs, the cost of disposal can also be significantly reduced.

Comparative Examples 10 and 11
The amount of As(III) fixed was measured in the same manner as in Example 6, except that N-700 or sodium N,N-diethyldithiocarbamate trihydrate (referred to as "monomer" in Table 4) was used as the adsorbent instead of cellulose derivative 1.

The results are summarized in Table 4 below.

Table 4 shows that when cellulose derivative 1 is used as the adsorbent, more As(III) can be immobilized than when low molecular weight compounds or monomers are used.

The compounds used in the examples and comparative examples are explained below.
<Component A>
Cellulose derivative 1 (prepared in Preparation Example 1)
<Component B>
CHP295 (cationic coagulant, weight average molecular weight: 1×10 ⁶ or less, cationic monomer ratio: 100%), manufactured by Mitsubishi Chemical Corporation
<Component C>
Anionic polymer flocculant AP199, anionic monomer ratio: 100%, weight average molecular weight: 5×10 ⁶ , manufactured by Mitsubishi Chemical Corporation AP120CH, anionic monomer ratio: 20%, weight average molecular weight: 13×10 ⁶ , manufactured by Mitsubishi Chemical Corporation Cationic polymer flocculant KP201C, cationic monomer ratio: 100%, weight average molecular weight: 2×10 ⁶ or more, manufactured by Mitsubishi Chemical Corporation KP1200B, cationic monomer ratio: 80%, weight average molecular weight: 2×10 ⁶ or more, manufactured by Mitsubishi Chemical Corporation KP1201B, cationic monomer ratio: 60%, weight average molecular weight: 2×10 ⁶ or more, manufactured by Mitsubishi Chemical Corporation KP204B, cationic monomer ratio: 40%, weight average molecular weight: 14×10 ⁶ , manufactured by Mitsubishi Chemical Corporation KP206B, cationic monomer ratio: 20%, weight average molecular weight: 14×10 ⁶ , manufactured by Mitsubishi Chemical Corporation Nonionic polymer flocculant NP500, weight average molecular weight: 16×10 ⁶ , manufactured by Mitsubishi Chemical Corporation Amphoteric polymer flocculant KA405D, weight average molecular weight: 8×10 ⁶ , manufactured by Mitsubishi Chemical Corporation
<Other>
Sodium N,N-diethyldithiocarbamate trihydrate, manufactured by Wako Pure Chemical Industries, Ltd. N-700, water-soluble dithiocarbamate-containing metal fixing agent, weight average molecular weight: 0.1 x 10 ⁶ or less, trade name "Nittoguard", manufactured by Mitsubishi Chemical Corporation

The metal elements used were 1000 mg/L arsenic standard solution, calcium standard solution, magnesium standard solution, manganese standard solution, zinc standard solution, barium standard solution, cobalt standard solution, selenium standard solution, strontium standard solution, lead standard solution (1000 mg/L, for atomic absorption spectrometry, Kanto Chemical), copper standard solution, and nickel standard solution (1000 ma/L, for testing and research).

The solutions were prepared using purified water produced using an ultrapure water production system (Arium pro UV, Sartorius), nitric acid (for measuring hazardous metals; Kanto Chemical), hydrochloric acid (for measuring arsenic; Kanto Chemical), sodium hydroxide (special grade; Kanto Chemical), and the following good's buffers were used: 2-(N-monophorino)-ethanesulfonic acid (special grade; Sigma-Aldrich), 4-(2-hydroxyethyl)-piperazineethanesulfonic acid (special grade; Nacalai Tesque), 3-[N-tris(hydroxymethyl)methyl-3-amino]-1-propanesulfonic acid (special grade; MP Biomedicals), and 3-cyclohexylaminopropanesulfonic acid.

Metal concentration was measured using an inductively coupled plasma optical emission spectrometer (iCAP 6300, Thermo Fisher).

Claims (9)

A metal fixing material comprising a combination of the following components A, B, and C.
Component A: a metal adsorbent containing a cellulose derivative having a repeating unit represented by the following formula (I):

[In the formula, R ^a may be the same or different and is a hydrogen atom or a group represented by the following formula (a). At least one of all R ^a contained in the cellulose derivative is a group represented by the following formula (a)]

(In the formula, ring Z represents a heterocycle containing a nitrogen atom as a heteroatom, R ¹ represents a single bond or an alkylene group having 1 to 10 carbon atoms, and four R ^2s may be the same or different and represent alkyl groups having 1 to 10 carbon atoms.)
B component: coagulant C component: polymer flocculant The metal fixing material according to claim 1, wherein the coagulant is a cationic coagulant. The metal fixing material according to claim 1 or 2, wherein the polymer flocculant is an anionic polymer flocculant. The metal fixing material according to claim 3, wherein the anionic polymer flocculant is a polymer containing monomer units derived from an anionic monomer, and the proportion of the monomer units derived from the anionic monomer in the total monomer units constituting the polymer is 30% by weight or more. The metal fixing material according to any one of claims 1 to 4, containing 0.1 to 10 parts by weight of the B component per 1 part by weight of the A component. The metal fixing material according to any one of claims 1 to 5, containing 0.1 to 10 parts by weight of the C component per 1 part by weight of the A component. The metal fixing material according to any one of claims 1 to 6, wherein the ratio of the contents of the B component and the C component (B/C; weight ratio) is 20/80 to 80/20. The metal fixing material according to any one of claims 1 to 7, wherein the metal fixing material is at least one metal fixing material selected from titanium, vanadium, manganese, iron, cobalt, nickel, copper, zinc, gallium, arsenic, selenium, cadmium, indium, lead, bismuth, ruthenium, rhodium, iridium, palladium, platinum, silver, and gold. A method for fixing a metal, comprising the steps of: adding component A described below to an aqueous solution containing a dissolved metal; and then adding components B and C described below to form flocs containing the metal, component A, component B, and component C.
Component A: a metal adsorbent containing a cellulose derivative having a repeating unit represented by the following formula (I):

[In the formula, R ^a may be the same or different and is a hydrogen atom or a group represented by the following formula (a). At least one of all R ^a contained in the cellulose derivative is a group represented by the following formula (a)]

(In the formula, ring Z represents a heterocycle containing a nitrogen atom as a heteroatom, R ¹ represents a single bond or an alkylene group having 1 to 10 carbon atoms, and four R ^2s may be the same or different and represent alkyl groups having 1 to 10 carbon atoms.)
B component: coagulant C component: polymer flocculant

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