Cellulose derivative and metal adsorbent containing cellulose derivative

Abstract

To provide a new cellulose derivative capable of easily being incorporated into an aqueous solution in which a noble metal is dissolved and selectively and efficiently adsorbing and recovering the noble metal dissolved in the aqueous solution.　The cellulose derivative according to the present disclosure has a repeating unit represented by formula (I). In formula (I), Ra is a hydrogen atom or a group represented by formula (a-1). In formula (a-1), R1 is a single bond or a C1-10 alkylene group. R2-R4 are a hydrogen atom or a C1-10 alkyl group. n represents 1 or 2. R1 and R2 may bond with each other to form a ring together with adjacent nitrogen atoms. R3 and R4 may also bond with each other to form a ring together with adjacent nitrogen atoms.

Description

Cellulose derivative and metal adsorbent containing said cellulose derivative

[0001] The present disclosure relates to a novel cellulose derivative, a method for producing the cellulose derivative, a metal adsorbent containing the cellulose derivative, a method for producing the metal adsorbent, a method for recovering metals using the cellulose derivative, and a metal recovery device equipped with a means for adsorbing metals onto the cellulose derivative.

[0002] BACKGROUND ART In recent years, precious metals such as ruthenium, rhodium, iridium, palladium, platinum, silver, and gold have been widely used in electronic materials, electronic devices, electrical devices, machine parts, and the like.

[0003] Although Japan consumes a large amount of precious metals, it relies on imports for most of them. Therefore, from the perspective of effective resource utilization, it is desirable to selectively recover and reuse precious metals contained in industrial wastewater and waste. In addition, many countries have legal restrictions on the concentration of metal ions that can be released into the environment. Therefore, it is required to remove metal ions from wastewater until the metal ion concentration is within the regulated range before releasing it.

[0004] Patent Document 1 discloses that when thiuram disulfide is reacted with metal ions in an aqueous solution, the metal ions form an insoluble organometallic complex with the thiuram disulfide and precipitate, and the concentration of metal ions in the aqueous solution can be reduced by separating and removing the precipitate through a filtration process.

[0005] International Publication No. 2003 / 012017

[0006] However, thiuram disulfides have low wettability with water, and therefore do not easily blend with aqueous solutions containing dissolved metals. This makes it difficult for thiuram disulfides to react with metal ions to form organometallic complexes, necessitating the use of a wetting agent.

[0007] Furthermore, when precious metals are extracted and recovered from waste materials such as electronic materials, electronic devices, electrical devices, and machine parts using an oxidizing acid such as nitric acid or aqua regia, the resulting extract contains large amounts of non-precious metals such as Al, Cr, Fe, Co, Ni, Cu, Zn, Cd, Sn, and Pb in addition to the precious metals. Therefore, a method for selectively recovering precious metals in the coexistence of non-precious metals is desired.

[0008] Therefore, an object of the present disclosure is to provide a novel cellulose derivative that easily adapts to an aqueous solution containing dissolved precious metals (hereinafter sometimes referred to as a "precious metal ion aqueous solution") and is capable of selectively and efficiently adsorbing and recovering the precious metals dissolved in the aqueous solution. Another object of the present disclosure is to provide a novel cellulose derivative that easily adapts to an aqueous solution of precious metal ions and is capable of selectively and efficiently adsorbing and recovering the precious metals dissolved in the aqueous solution, and is capable of quickly separating and recovering the precious metals by filtration. Another object of the present disclosure is to provide a method for producing the cellulose derivative. Another object of the present disclosure is to provide a novel metal adsorbent that easily adapts to an aqueous solution of precious metal ions and is capable of selectively and efficiently adsorbing and recovering the precious metals dissolved in the aqueous solution, and does not require the use of a wetting agent. Another object of the present disclosure is to provide a novel metal adsorbent that easily adapts to an aqueous solution of precious metal ions and is capable of selectively and efficiently adsorbing and recovering the metals dissolved in the aqueous solution, and is capable of quickly separating and recovering the metals by filtration, and is not required the use of a wetting agent. Another object of the present disclosure is to provide a novel metal adsorbent that easily adapts to an aqueous solution containing dissolved precious metals and non-precious metals, selectively and efficiently adsorbs precious metal ions from the aqueous solution, and can be quickly separated and recovered by filtration, without the need for the use of a wetting agent. Another object of the present disclosure is to provide a method for producing the metal recovery material. Another object of the present disclosure is to provide a method for recovering metals using the cellulose derivative. Another object of the present disclosure is to provide a metal recovery device equipped with a means for adsorbing metals to the cellulose derivative.

[0009] As a result of intensive research to solve the above problems, the present inventors have found the following: 1. A cellulose derivative having a repeating unit represented by the following formula (I) has a cellulose main chain that is highly wettable with water, and therefore is easily compatible with aqueous solutions. 2. When the cellulose derivative is applied to an aqueous solution of precious metal ions, the precious metal ions in the aqueous solution are selectively adsorbed to groups represented by the following formula (a-1) (hereinafter sometimes referred to as "thiuram mono / disulfide groups") that are provided on the side chains of the cellulose derivative, forming a chelate and thereby being captured by the cellulose derivative. 3. Although the cellulose derivative has a lower content of thiuram mono / disulfide groups per unit weight than thiuram disulfide, the thiuram mono / disulfide groups protrude radially from the cellulose main chain, and therefore precious metal ions are easily adsorbed to the thiuram mono / disulfide groups. 4. The cellulose derivative is insoluble in water, and after capturing the precious metal ions, it can be quickly separated and recovered from the aqueous solution by filtration. The present disclosure has been completed based on the above findings.

[0010] That is, the present disclosure provides a cellulose derivative (I) having a repeating unit represented by the following formula (I): [In formula (I), R a are the same or different and are a hydrogen atom or a group represented by the following formula (a-1). a at least one of which is a group represented by the following formula (a-1): (In formula (a-1), R 1 is a single bond or an alkylene group having 1 to 10 carbon atoms. 2 ~R 4 are the same or different and each represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms. n is 1 or 2. R 1 is an alkylene group having 1 to 10 carbon atoms, R 1 and R 2 may be bonded to each other to form a ring together with the adjacent nitrogen atom. 3 and R 4 may be bonded to each other to form a ring together with the adjacent nitrogen atom)

[0011] The present disclosure also provides the cellulose derivative (I) in which the total average degree of substitution of the group represented by formula (a-1) is 0.1 to 3.0.

[0012] The present disclosure also provides a metal adsorbent containing the cellulose derivative (I).

[0013] The present disclosure also provides the metal adsorbent, wherein the metal adsorbent is a silver and / or gold adsorbent.

[0014] The present disclosure also provides a compound of formula (II): [In formula (II), R b are the same or different and are a hydrogen atom or a group represented by the following formula (b-1). b at least one of which is a group represented by the following formula (b-1) or a salt thereof] (In formula (b-1), R 1 is a single bond or an alkylene group having 1 to 10 carbon atoms. 2 is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms. 1 and R 2 may be bonded to each other to form a ring together with the adjacent nitrogen atom), to a cellulose derivative (II) having a repeating unit represented by the following formula (1): (In formula (1), X is a thiol group or a halogen atom. R 3 , R 4 are the same or different and each represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms. 3 and R 4 may be bonded to each other to form a ring together with the adjacent nitrogen atom) or a salt thereof to obtain the cellulose derivative (I).

[0015] The present disclosure also provides a method for producing a metal adsorbent, which comprises obtaining a cellulose derivative (I) by the production method 1 and using the obtained cellulose derivative (I) to produce a metal adsorbent containing the cellulose derivative (I).

[0016] The present disclosure also provides a method for preparing a cellulose-based polymer comprising: (In formula (2), R 1is a single bond or an alkylene group having 1 to 10 carbon atoms. 2 ~R 4 are the same or different and each represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms. n is 1 or 2. R 1 and R 2 may be bonded to each other to form a ring together with the adjacent nitrogen atom. 3 and R 4 may be bonded to each other to form a ring together with the adjacent nitrogen atom) or a salt thereof to obtain the cellulose derivative (I).

[0017] The present disclosure also provides a method for producing a metal adsorbent, which comprises obtaining a cellulose derivative (I) by the production method 2 and using the obtained cellulose derivative (I) to produce a metal adsorbent containing the cellulose derivative (I).

[0018] The present disclosure also provides a method for recovering metals, which comprises recovering metals dissolved in an aqueous solution by adsorbing the metals onto the cellulose derivative (I).

[0019] The present disclosure also provides a metal recovery device including a means for bringing the cellulose derivative (I) into contact with a solution in which a metal is dissolved, thereby causing the cellulose derivative (I) to adsorb the metal in the solution.

[0020] The cellulose derivative (I) of the present disclosure has high wettability with aqueous solutions and readily adapts to aqueous solutions upon contact, allowing it to selectively capture precious metal ions (e.g., silver ions, gold ions, etc.) present in the aqueous solution, eliminating the need for the use of a wetting agent. Meanwhile, the cellulose derivative (I) has difficulty capturing non-precious metal ions such as copper, nickel, zinc, alkali metals, and alkaline earth metals. Therefore, the cellulose derivative (I) can selectively adsorb precious metal ions even in the presence of non-precious metal ions, even in the presence of non-precious metal ions at high concentrations, for example, 1000 times or more (preferably 2000 times or more). That is, the cellulose derivative (I) has excellent selectivity. After the precious metal ions are adsorbed onto the cellulose derivative (I), the precious metals can be easily recovered by combustion. Furthermore, the cellulose derivative (I) has lower nitrogen and sulfur contents per unit weight than thiuram disulfide. Therefore, compared to burning thiuram disulfide, burning the cellulose derivative (I) reduces the amount of air pollutants (e.g., NO ) per unit weight. X , S.O. X ) emissions can be reduced.

[0021] Since the cellulose derivative (I) has the above-mentioned properties, it can be suitably used as an adsorbent (i.e., an adsorbent for recovering secondary metal resources) that efficiently and selectively adsorbs and recovers metals (particularly, precious metals) as secondary resources from industrial wastewater or waste.

[0022] 1 shows an IR spectrum of the cellulose derivative (I-1) obtained in Example 1. 2 shows a Langmuir plot of gold adsorption by the cellulose derivative (I-1) obtained in Example 1. 3 shows the gold ion recovery rate of the cellulose derivative (I-1) obtained in Example 1 in the presence of competing ions.

[0023] [Cellulose Derivative (I)] The cellulose derivative (I) is a cellulose derivative having a repeating unit represented by the following formula (I). [In formula (I), R a are the same or different and are a hydrogen atom or a group represented by the following formula (a-1).a at least one of which is a group represented by the following formula (a-1): (In formula (a-1), R 1 is a single bond or an alkylene group having 1 to 10 carbon atoms. 2 , R 3 , R 4 are the same or different and each represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms. n is 1 or 2. R 1 and R 2 may be bonded to each other to form a ring together with the adjacent nitrogen atom. 3 and R 4 may be bonded to each other to form a ring together with the adjacent nitrogen atom)

[0024] As used herein, "R 1 and R 2 may be bonded to each other to form a ring together with the adjacent nitrogen atom" means that "R 1 is an alkylene group having 1 to 10 carbon atoms, and R 2 is an alkyl group having 1 to 10 carbon atoms, R 1 One of the carbon atoms constituting R 2 The meaning of "R" is that one of the carbon atoms constituting R may be bonded to each other to form a ring together with the adjacent nitrogen atom. 3 and R 4 may be bonded to each other to form a ring together with the adjacent nitrogen atom" means that "R 3 and R 4 are the same or different and each is an alkyl group having 1 to 10 carbon atoms, R 3 One of the carbon atoms constituting R 4 may be bonded to each other to form a ring together with the adjacent nitrogen atom."

[0025] R 1 Examples of the alkylene group having 1 to 10 carbon atoms in the formula (I) include linear or branched alkylene groups such as methylene, methylmethylene, dimethylmethylene, ethylene, 2-methylethylene, 1,2-dimethylethylene, propylene, trimethylene, and 2-methyl-trimethylene.

[0026] R1 is preferably a single bond or an alkylene group having 1 to 5 carbon atoms (more preferably 1 to 3 carbon atoms, particularly preferably 1 to 2 carbon atoms).

[0027] R 2 , R 3 , R 4 Examples of the alkyl group having 1 to 10 carbon atoms in the formula (I) include linear or branched alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, s-butyl, t-butyl, and pentyl.

[0028] R 2 As the alkyl group, an alkyl group having 1 to 5 carbon atoms (more preferably 1 to 4 carbon atoms, particularly preferably 1 to 3 carbon atoms) is preferred.

[0029] R 3 , R 4 As the alkyl group, an alkyl group having 1 to 5 carbon atoms (more preferably 1 to 4 carbon atoms) is preferred.

[0030] n is 1 or 2, with 2 being preferred.

[0031] R 1 and R 2 The ring that may be formed by bonding together with the adjacent nitrogen atom is an aliphatic heterocycle containing at least one nitrogen atom as a heteroatom. The aliphatic heterocycle may contain two or more nitrogen atoms, or may contain a heteroatom other than a nitrogen atom (for example, an oxygen atom, a sulfur atom, etc.).

[0032] Among the groups represented by formula (a-1), R 1 and R 2 The group in which R are bonded to each other to form a ring together with the adjacent nitrogen atom is, for example, a group represented by the following formula (a-2): 3 , R 4 , n is the same as above.

[0033] R 5 is a single bond or an alkylene group having 1 to 10 carbon atoms. 5 is preferably a single bond or an alkylene group having 1 to 5 carbon atoms (more preferably 1 to 3 carbon atoms, particularly preferably 1 to 2 carbon atoms).

[0034] Ring Z is an aliphatic heterocycle containing at least one nitrogen atom as a heteroatom. The aliphatic heterocycle may contain two or more nitrogen atoms, or may contain a heteroatom other than a nitrogen atom (e.g., an oxygen atom, a sulfur atom, etc.).

[0035] The aliphatic heterocycle is, for example, a 3- to 10-membered ring, preferably a 4- to 8-membered ring, and more preferably a 4- to 6-membered ring.

[0036] The aliphatic heterocycle is preferably an aliphatic heterocycle containing only a nitrogen atom as a heteroatom, and is preferably a 5-membered ring such as a pyrrolidine ring, a pyrazolidine ring, or an imidazolidine ring; or a 6-membered ring such as a piperidine ring, a piperazine ring, or a morpholine ring, with a 5-membered ring being particularly preferred.

[0037] R 3 and R 4 The ring which may be formed by bonding together with the adjacent nitrogen atom is an aliphatic heterocycle containing at least one nitrogen atom as a heteroatom. Examples of the aliphatic heterocycle include the same as those of the aliphatic heterocycle for ring Z.

[0038] The alkylene group, alkyl group, and aliphatic heterocycle may have various substituents bonded thereto [for example, a halogen atom, an oxo group, a hydroxyl group, a substituted oxy group (for example, an alkoxy group, an aryloxy group, an aralkyloxy group, an acyloxy group, etc.), a carboxyl group, a substituted oxycarbonyl group (for example, an alkoxycarbonyl group, an aryloxycarbonyl group, an aralkyloxycarbonyl group, etc.), a substituted or unsubstituted carbamoyl group, a cyano group, a nitro group, a substituted or unsubstituted amino group, a sulfo group, etc.].

[0039] As the group represented by formula (a-1), the group represented by formula (a-2) is preferred in terms of excellent stability.

[0040] As the group represented by the formula (a-2), a group represented by the following formula (a-2-1) or a group represented by the following formula (a-2-2) is preferable. 3 , R 4 , R 5 , n is the same as above.

[0041] As the group represented by the formula (a-2), a group represented by the following formula (a-2-1′) or a group represented by the following formula (a-2-2′) is particularly preferred. 3 , R 4 , n is the same as above.

[0042] In the cellulose derivative (I), the total average degree of substitution of the groups represented by formula (a-1) (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 groups represented by formula (a-1)) 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 groups represented by formula (a-1) in the above range, it can exhibit excellent metal adsorption power (preferably noble metal adsorption power, particularly preferably noble metal selective adsorption power).

[0043] In the cellulose derivative (I), the total average substitution degree of the group represented by the formula (a-1) and the unsubstituted degree of the hydroxyl groups at the 2-, 3-, and 6-positions of the glucose units constituting the cellulose (i.e., R a are hydrogen atoms) is, for example, 2.0 to 3.0, preferably 2.5 to 3.0, particularly preferably 2.8 to 3.0, and most preferably 2.9 to 3.0. That is, the cellulose derivative (I) may have substituents other than the group represented by formula (a-1), but the total average degree of substitution of the substituents other than the group represented by formula (a-1) is, for example, 1.0 or less, preferably 0.5 or less, particularly preferably 0.2 or less, and most preferably 0.1 or less.

[0044] The shape of the cellulose derivative (I) is not particularly limited as long as it does not impair the effects of the present disclosure, and examples thereof include a sheet shape, a sphere shape (a perfect sphere shape, an approximately perfect sphere shape, an oval sphere shape, etc.), a polyhedron shape, a rod shape (a cylindrical shape, a prismatic shape, etc.), a scale shape, an irregular shape, etc.

[0045] The cellulose derivative (I) has excellent adsorptivity for metal ions (particularly, at least one kind of noble metal ion selected from ruthenium ions, rhodium ions, iridium ions, palladium ions, platinum ions, silver ions, and gold ions, particularly silver ions and / or gold ions).

[0046] The cellulose derivative (I) has an equilibrium adsorption amount of metal ions (particularly noble metal ions) of, for example, 1.0 mmol / g or more, preferably 1.5 mmol / g or more, more preferably 2.0 mmol / g or more, and even more preferably 2.5 mmol / g or more. The upper limit of the equilibrium adsorption amount of metal ions (particularly noble metal ions) is, for example, 5.0 mmol / g, 4.0 mmol / g, or 3.0 mmol / g.

[0047] The maximum adsorption amount of metal ions (particularly noble metal ions) of the cellulose derivative (I) is, for example, 1.0 mmol / g or more, preferably 1.5 mmol / g or more, more preferably 2.0 mmol / g or more, and even more preferably 2.5 mmol / g or more. The upper limit of the maximum adsorption amount of metal ions (particularly noble metal ions) is, for example, 5.0 mmol / g, 4.0 mmol / g, or 3.0 mmol / g.

[0048] The recovery rate of metal ions (particularly noble metal ions) by the cellulose derivative (I) is, for example, 85% or more, preferably 90% or more, particularly preferably 95% or more.

[0049] On the other hand, the cellulose derivative (I) does not have an adsorption power for non-noble metal ions (e.g., titanium ions, vanadium ions, manganese ions, iron ions, nickel ions, copper ions, zinc ions, gallium ions, arsenic ions, cadmium ions, lead ions, alkali metal ions (e.g., sodium ions, potassium ions, etc.), and alkaline earth metal ions (e.g., magnesium ions, calcium ions, etc.).

[0050] The non-noble metal ion equilibrium adsorption amount of the cellulose derivative (I) is, for example, less than 1 mmol / g, more preferably 0.5 mmol / g or less, even more preferably 0.1 mmol / g or less, particularly preferably 0.01 mmol / g or less, and most preferably 0.001 mmol / g or less.

[0051] The maximum non-noble metal ion adsorption amount of the cellulose derivative (I) is, for example, less than 1 mmol / g, more preferably 0.5 mmol / g or less, even more preferably 0.1 mmol / g or less, particularly preferably 0.01 mmol / g or less, and most preferably 0.001 mmol / g or less.

[0052] The recovery rate of non-precious metal ions by the cellulose derivative (I) is, for example, 10% or less, preferably 5% or less, particularly preferably 1% or less, most preferably 0.1% or less, and particularly preferably 0.01% or less.

[0053] Assuming that the adsorption phenomenon of the cellulose derivative (I) is of the Langmuir type, the maximum adsorption amount Q of the noble metal ions and non-noble metal ions is max (mmol / g), equilibrium adsorption amount q e (mmol / g), equilibrium concentration C e (mmol / L), and the Langmuir constant K L (L / mmol) satisfies the following formula: q e =Q max ×K L ×C e / (1+K L ×C e The above formula can be rearranged as follows: C e / q e = (1 / Q max ) × C e +1 / (K L ×Q max )

[0054] That is, for an aqueous solution containing the noble metal ions or non-noble metal ions, the equilibrium adsorption amount (the noble metal ion or non-noble metal ion adsorption amount when equilibrium is reached) q eand the equilibrium concentration (the concentration of the noble metal ions or non-noble metal ions in the aqueous solution when equilibrium is reached) C e The ratio of the equilibrium concentration C e When plotted against the adsorption amount Q (i.e., Langmuir plot), the maximum adsorption amount Q max can be calculated.

[0055] The recovery rates of the precious metal ions and non-precious metal ions are the recovery rates when 2.5 mg of the cellulose derivative (I) is immersed in 5 mL of a 0.1 mol / L aqueous hydrochloric acid or nitric acid solution having a precious metal ion concentration or a non-precious metal ion concentration of 0.5 mmol / L at 25°C and stirred at 200 rpm for 60 minutes, and are calculated using the formula described in the Examples.

[0056] The cellulose derivative (I) can highly selectively adsorb and recover precious metal ions compared to non-precious metal ions, and can selectively adsorb and recover precious metal ions even from an aqueous solution in which precious metal ions and non-precious metal ions coexist, where the concentration of the non-precious metal ions is, for example, 10 times or more (preferably 100 times or more, more preferably 500 times or more, even more preferably 1000 times or more, and particularly preferably 2000 times or more) the concentration of the precious metal ions.

[0057] The cellulose derivative (I) is a group represented by the above formula (a-1), and R 1 and R 2 When the thiuram mono- / disulfide groups have groups bonded to each other to form a ring with the adjacent nitrogen atom, the strain of the ring suppresses proton transfer to the nitrogen atom that initiates decomposition of the thiuram mono- / disulfide group. Therefore, the storage stability is excellent. 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 still has a high precious metal ion recovery amount, just like before the test. The retention rate of the precious metal ion recovery amount is, for example, 90% or more.

[0058] Furthermore, since the cellulose derivative (I) is insoluble in water, after the cellulose derivative (I) has adsorbed the noble metal ions dissolved in the aqueous solution, the noble metal ions can be easily and quickly separated and recovered from the aqueous solution by subjecting the cellulose derivative (I) to a filtration treatment.

[0059] [Method for Producing Cellulose Derivative] The cellulose derivative (I) can be produced, for example, through the following steps 1, 2, 3 and 4 (Method 1).

[0060]

[0061] R in the above formula 1 ~R 4 , n, R a is the same as above.

[0062] COOR in the above formula 0 is -R in the formula 1 N (R 2 )-, and examples thereof include carbamate-based protecting groups.

[0063] In the above formula, X is a thiol group or a halogen atom.

[0064] R in the above formula d are the same or different and are a hydrogen atom or a group represented by the above formula (d-1). All R d At least one of these is a group represented by the above formula (d-1).

[0065] R in the above formula c are the same or different and are a hydrogen atom or a group represented by the above formula (c-1). All R contained in a cellulose derivative having a repeating unit represented by the above formula (III) (hereinafter, sometimes referred to as "cellulose derivative (III)") c At least one of the groups represented by the formula (c-1) above is a group represented by the formula (c-1). The group represented by the formula (c-1) above may form a salt.

[0066] R in the above formula b are the same or different and are a hydrogen atom or a group represented by the above formula (b-1). All R contained in a cellulose derivative having a repeating unit represented by the above formula (II) (hereinafter, sometimes referred to as "cellulose derivative (II)") bAt least one of the groups represented by the formula (b-1) above is a group represented by the formula (b-1) above. The group represented by the formula (b-1) above may form a salt.

[0067] (Step 1) Step 1 is a step of reacting a compound represented by the above formula (3) (hereinafter, sometimes referred to as "compound (3)") with a hydroxyl group of a cellulose having a repeating unit represented by the above formula (V) (hereinafter, sometimes referred to as "cellulose (V)").

[0068] Compound (3) is a compound in which the amino group of an amino acid (or the imino group of an imino acid) is protected by a carbamate protecting group (COOR 0 Examples of the amino acid and imino acid include glycine, alanine, β-alanine, valine, leucine, isoleucine, proline, 3-pyrrolidinecarboxylic acid, 2-piperidinecarboxylic acid, 4-piperidinecarboxylic acid, and (4-piperidinyl)acetic acid.

[0069] As carbamate-based protecting groups, for example, t-butoxycarbonyl group (Boc), benzyloxycarbonyl group (CBZ), 9-fluorenylmethyloxycarbonyl group (Fmoc) and the like are preferred because they can be deprotected under mild conditions.

[0070] As the cellulose (V) 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 cellulose is preferably used in a finely pulverized state, for example, by subjecting it to a crushing treatment.

[0071] The reaction in step 1 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 catalysts can be used alone or in combination of two or more.

[0072] The amount of the catalyst used is, for example, 0.01 to 1.0 moles per mole of compound (3).

[0073] The reaction in step 1 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.

[0074] The amount of the condensing agent used is, for example, 0.5 to 2.0 moles per mole of compound (3).

[0075] The reaction in step 1 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 solvents may be used alone or in combination of two or more.

[0076] Among these, amides such as N,N-dimethylacetamide are preferred as the solvent, and a mixture of the solvent with a lithium salt such as lithium chloride is particularly preferred because it has excellent cellulose solubility. The concentration of the lithium salt in the solvent can be appropriately adjusted within a range that does not impair the effect of dissolving cellulose, and is, for example, 1 to 30 wt %.

[0077] The amount of the solvent used is, for example, 0.5 to 30 times the weight of the total amount of the reaction substrates. If the amount of the solvent used exceeds the above range, the concentration of the reaction components will be low, and the reaction rate will tend to decrease.

[0078] Through step 1, the cellulose derivative (IV) is produced.

[0079] (Step 2) Step 2 is a step of deprotecting the cellulose derivative (IV) produced through step 1 (more specifically, a step of removing the carbamate protecting group introduced into the cellulose derivative (IV)).

[0080] The method for removing the carbamate protecting group can be appropriately selected depending on the type of protecting group.

[0081] When the cellulose derivative (III) has a protecting group such as Boc, the protecting group can be removed by reaction with a strong acid such as hydrochloric acid, trifluoroacetic acid, etc. The cellulose derivative (III) obtained by deprotection using a strong acid may have a salt formed between the group represented by formula (c-1) and a counter anion.

[0082] When the protecting group is CBZ or the like, the protecting group can be removed by, for example, carrying out a reduction reaction in the presence of a catalyst (for example, Pd—C).

[0083] When the protecting group is Fmoc or the like, the protecting group can be removed by reacting with a secondary amine such as pyridine.

[0084] The reaction temperature in step 2 is, for example, 0 to 100° C. The reaction time is, for example, 1 to 24 hours. After completion of the reaction, the obtained reaction product can be separated and purified by a separation means such as filtration, concentration, distillation, extraction, crystallization, adsorption, recrystallization, column chromatography, or a combination of these separation means.

[0085] Through step 2, the cellulose derivative (III) is produced.

[0086] (Step 3) Step 3 is a step of removing -R 1 N (R 2) H is a step of converting an amino group (or an imino group) represented by the formula (I) into a dithiocarbamic acid group.

[0087] The reaction for converting the side chain of the cellulose derivative (III) into a dithiocarbamic acid group can be carried out, for example, by reacting the cellulose derivative (III) with a sulfur compound.

[0088] The sulfur compound may be, for example, carbon disulfide, and the amount of the sulfur compound used is, for example, 20 parts by weight or more based on 100 parts by weight of the cellulose derivative (III).

[0089] The reaction in step 3 is preferably carried out in the presence of a base. Examples of the base include metal carbonates such as sodium bicarbonate, sodium carbonate, potassium bicarbonate, and potassium carbonate; metal phosphates such as sodium phosphate, sodium hydrogen phosphate, sodium dihydrogen phosphate, potassium phosphate, potassium hydrogen phosphate, and potassium dihydrogen phosphate; metal alkoxides such as sodium ethoxide, sodium t-butoxide, and potassium t-butoxide; tertiary amines such as trimethylamine and triethylamine; and quaternary ammonium hydroxides such as tetramethylammonium hydroxide and tetraethylammonium hydroxide. These may be used alone or in combination of two or more.

[0090] The amount of the base used is, for example, 30 parts by weight or more based on 100 parts by weight of the cellulose derivative (III).

[0091] 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, propanol, and butanol; and N-methylpyrrolidone, dimethyl sulfoxide, and N,N-dimethylformamide. These solvents can be used alone or in combination of two or more. The amount of the solvent used is, for example, 0.5 to 30 times by weight the total amount of the reaction substrates.

[0092] The reaction temperature in step 3 is, for example, 0 to 100° C. The reaction time is, for example, 1 to 24 hours. After completion of the reaction, the obtained reaction product can be separated and purified by a separation means such as filtration, concentration, distillation, extraction, crystallization, adsorption, recrystallization, column chromatography, or a combination of these separation means.

[0093] The cellulose derivative (II) is produced through step 3. The dithiocarbamic acid group in the side chain of the cellulose derivative (II) may form a salt with the base.

[0094] (Step 4) Step 4 is a step of converting the dithiocarbamic acid groups on the side chains of the cellulose derivative (II) produced through step 3 into thiuram mono / disulfide groups.

[0095] The reaction for converting the side chain of the cellulose derivative (II) into a thiuram mono / disulfide group can be carried out, for example, by reacting the cellulose derivative (II) with a compound represented by formula (1) (hereinafter, sometimes referred to as "compound (1)") or a salt thereof.

[0096] Examples of salts of compound (1) include salts with alkali metals, ammonium, and the like.

[0097] When a compound of formula (1) in which X is a thiol group is used as compound (1), a cellulose derivative (I) having a thiuram disulfide group in formula (a-1) where n = 2 is obtained. When a compound of formula (1) in which X is a halogen atom is used as compound (1), a cellulose derivative (I) having a thiuram monosulfide group in formula (a-1) where n = 1 is obtained.

[0098] The amount of the compound (1) used is, for example, 20 to 750 parts by weight per 100 parts by weight of the cellulose derivative (II).

[0099] When a compound of formula (1) in which X is a thiol group is used as compound (1), the reaction in step 4 is preferably carried out in the presence of an oxidizing agent. Examples of the oxidizing agent include hydrogen peroxide; peroxides such as sodium peroxide, barium peroxide, and benzoyl peroxide; and halogen compounds such as perchlorates, nitric acid, N-chlorosuccinimide, N-bromosuccinimide, N-iodosuccinimide, and iodine. These can be used alone or in combination of two or more.

[0100] The amount of the oxidizing agent used is, for example, 0.5 to 2.0 moles per mole of compound (1).

[0101] The reaction is preferably carried out in the presence of an acid catalyst. Examples of the acid catalyst include protonic acids such as hydrochloric acid, hydrobromic acid, hydroiodic acid, sulfuric acid, phosphoric acid, and acetic acid. These may be used alone or in combination of two or more.

[0102] The amount of the acid catalyst used is, for example, 0.01 to 0.5 moles per mole of compound (1).

[0103] The reaction is preferably carried out in the presence of a solvent. Examples of the solvent include water; alcohols such as methanol, ethanol, propanol, and butanol; N,N-dimethylformamide, N-methylpyrrolidone, and dimethyl sulfoxide. These solvents can be used alone or in combination of two or more. The amount of the solvent used is, for example, 0.5 to 30 times by weight the total amount of the reaction substrates.

[0104] When a compound of formula (1) in which X is a halogen atom is used as compound (1), the reaction of step 4 is preferably carried out in the presence of a base catalyst. Examples of base catalysts include tertiary amines such as triethylamine, diisopropylethylamine, and triphenylamine; and pyridines such as pyridine, 2-methylpyridine, and 4-N,N-dimethylaminopyridines. These may be used alone or in combination of two or more.

[0105] The amount of the base catalyst used is, for example, 0.5 to 2.0 moles per mole of compound (1).

[0106] The reaction in step 4 is preferably carried out in the presence of a solvent. Examples of the solvent include N,N-dimethylformamide, N-methylpyrrolidone, and dimethyl sulfoxide. These can be used alone or in combination of two or more. The amount of the solvent used is, for example, 0.5 to 30 times by weight the total amount of the reaction substrates.

[0107] The reaction temperature in step 4 is, for example, 0 to 100° C. The reaction time is, for example, 1 to 24 hours. After completion of the reaction, the obtained reaction product can be separated and purified by a separation means such as filtration, concentration, distillation, extraction, crystallization, adsorption, recrystallization, column chromatography, or a combination of these separation means.

[0108] Through step 4, the cellulose derivative (I) is produced.

[0109] According to the above-mentioned method 1, the cellulose derivative (II) as an intermediate can be efficiently converted to produce the cellulose derivative (I) in high yield (for example, 60% or more).

[0110] The cellulose derivative (I) can also be produced by reacting the cellulose (V) with the compound represented by formula (2) or a salt thereof (Method 2).

[0111] More specifically, Method 2 is a method for producing a cellulose derivative (I) through the following steps 5, 6, 7 and 8.

[0112]

[0113] R in the above formula 1 ~R 4 , n, R a , X is the same as above. 1 and R 2 may be bonded to each other to form a ring together with the adjacent nitrogen atom. 3 and R 4 may be bonded to each other to form a ring together with the adjacent nitrogen atom.

[0114] R in the above formula 10is a protective group for a carboxy group, and examples thereof include a benzyl group, an allyl group, and a t-butyl group.

[0115] (Step 5) Step 5 is a step of converting —R 1 N (R 2 ) H is a step of converting an amino group (or an imino group) represented by the formula (I) into a dithiocarbamic acid group.

[0116] The reaction for converting the amino group (or imino group) of compound (4) into a dithiocarbamic acid group can be carried out, for example, by reacting compound (4) or a salt thereof with a sulfur compound.

[0117] The sulfur compound may be, for example, carbon disulfide, and the amount of the sulfur compound used is, for example, 1 to 3 moles per mole of compound (4).

[0118] The reaction in step 5 is preferably carried out in the presence of a base. Examples of the base include tertiary amines such as triethylamine and diisopropylethylamine; and quaternary ammonium compounds such as tetramethylammonium hydroxide and tetraethylammonium hydroxide. These may be used alone or in combination of two or more.

[0119] The amount of the base used is, for example, 0.5 to 2.0 moles per mole of compound (4).

[0120] The reaction in step 5 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,N-dimethylformamide, N-methylpyrrolidone, and dimethyl sulfoxide. These solvents can be used alone or in combination of two or more. The amount of the solvent used is, for example, 0.5 to 30 times by weight the total amount of the reaction substrates.

[0121] The reaction temperature in step 5 is, for example, 0 to 100° C. The reaction time is, for example, 1 to 24 hours. After completion of the reaction, the obtained reaction product can be separated and purified by a separation means such as filtration, concentration, distillation, extraction, crystallization, adsorption, recrystallization, column chromatography, or a combination of these separation means.

[0122] A compound represented by the above formula (5) (hereinafter, sometimes referred to as "compound (5)") is produced through step 5. Compound (5) may form a salt with the base.

[0123] (Step 6) Step 6 is a step of converting the dithiocarbamic acid group of the compound (5) produced via step 5 into a thiuram mono / disulfide group.

[0124] The reaction for converting the dithiocarbamic acid group of compound (5) to a thiuram disulfide group can be carried out, for example, by reacting compound (5) or a salt thereof with compound (1) or a salt thereof.

[0125] Examples of salts of compound (1) include salts with alkali metals, ammonium, alkylammonium, and the like.

[0126] The amount of compound (1) used is, for example, 1.0 to 30 moles per mole of compound (5).

[0127] The reaction in step 6 is preferably carried out in the presence of an oxidizing agent. Examples of the oxidizing agent include hydrogen peroxide; peroxides such as sodium peroxide, barium peroxide, and benzoyl peroxide; and halogen compounds such as perchlorates, nitric acid, N-chlorosuccinimide, N-bromosuccinimide, N-iodosuccinimide, and iodine. These can be used alone or in combination of two or more.

[0128] The amount of the oxidizing agent used is, for example, 0.5 to 2.0 moles per mole of compound (1).

[0129] The reaction in step 6 is preferably carried out in the presence of an acid catalyst. Examples of the acid catalyst include protonic acids such as hydrochloric acid, hydrobromic acid, hydroiodic acid, sulfuric acid, phosphoric acid, and acetic acid. These may be used alone or in combination of two or more.

[0130] The amount of the acid catalyst used is, for example, 0.01 to 0.5 moles per mole of compound (1).

[0131] When a compound of formula (1) in which X is a halogen atom is used as compound (1), the reaction of step 6 is preferably carried out in the presence of a base catalyst.

[0132] Examples of the base catalyst include tertiary amines such as triethylamine, diisopropylethylamine, and triphenylamine, and pyridines such as pyridine, 2-methylpyridine, and 4-N,N-dimethylaminopyridines. These can be used alone or in combination of two or more.

[0133] The amount of the base catalyst used is, for example, 0.05 to 2.0 moles per mole of compound (1).

[0134] The reaction in step 6 is preferably carried out in the presence of a solvent. Examples of the solvent include water; 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 solvents can be used alone or in combination of two or more. The amount of the solvent used is, for example, 0.5 to 30 times by weight the total amount of the reaction substrates.

[0135] The reaction temperature in step 6 is, for example, 0 to 100° C. The reaction time is, for example, 1 to 24 hours. After completion of the reaction, the obtained reaction product can be separated and purified by a separation means such as filtration, concentration, distillation, extraction, crystallization, adsorption, recrystallization, column chromatography, or a combination of these separation means.

[0136] Through step 6, a compound represented by the above formula (6) (hereinafter, sometimes referred to as "compound (6)") is produced.

[0137] (Step 7) Step 7 is a deprotection step (more specifically, a step of removing the protecting group introduced into compound (6)) of compound (6) produced via step 6. Through this step, a compound represented by the above formula (2) (hereinafter, sometimes referred to as "compound (2)") is produced.

[0138] The method for removing the protecting group can be appropriately selected depending on the type of the protecting group.

[0139] When the protecting group is a t-butyl ester group, the protecting group can be removed by reacting with an acid such as trifluoroacetic acid.

[0140] When a benzyl group or an allyl group is present as a protecting group, the protecting group can be removed by reacting with a catalyst (Pd—C, etc.).

[0141] The reaction in Step 7 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 solvents can be used alone or in combination. The amount of the solvent used is, for example, 0.5 to 30 times by weight the total amount of the reaction substrates.

[0142] The reaction temperature in step 7 is, for example, 0 to 100° C. The reaction time is, for example, 1 to 24 hours. After completion of the reaction, the obtained reaction product can be separated and purified by a separation means such as filtration, concentration, distillation, extraction, crystallization, adsorption, recrystallization, column chromatography, or a combination of these separation means.

[0143] (Step 8) Step 8 is a step in which the compound (2) or a salt thereof produced via step 7 is reacted with the hydroxyl group of the cellulose (V).

[0144] The reaction in step 8 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 catalysts can be used alone or in combination of two or more.

[0145] The amount of the catalyst used is, for example, 0.01 to 1.0 mole per mole of compound (2).

[0146] The reaction in Step 8 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.

[0147] The amount of the condensing agent used is, for example, 1.0 to 3.0 moles per mole of compound (2).

[0148] The reaction in step 8 is preferably carried out in the presence of a solvent. The solvent is preferably an amide such as N,N-dimethylacetamide, and it is particularly preferable to use a solvent mixed with a lithium salt such as lithium chloride, as this provides 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, 1 to 30 wt %.

[0149] The amount of the solvent used is, for example, 0.5 to 30 times the weight of the total amount of the reaction substrates. If the amount of the solvent used exceeds the above range, the concentration of the reaction components will be low, and the reaction rate will tend to decrease.

[0150] After step 8, the cellulose derivative (I) is produced.

[0151] According to the above-mentioned method 2, the production of the cellulose derivative (II) as a by-product can be suppressed, and the cellulose derivative (I) can be produced in a high yield (for example, a yield of 60% or more).

[0152] [Metal Adsorbent] The metal adsorbent of the present disclosure contains a cellulose derivative (I).

[0153] The metal adsorbent may contain other components in addition to the cellulose derivative (I), but the proportion of the weight of the cellulose derivative (I) in the total weight of the metal adsorbent (or the total weight of the nonvolatile content contained in the metal adsorbent) 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) is below the above range, it tends to be difficult to efficiently and selectively adsorb precious metal ions.

[0154] The metal adsorbent may contain other cellulose derivatives in addition to the cellulose derivative (I), but the proportion of the cellulose derivative (I) in the total weight of the cellulose derivatives contained in the metal adsorbent is, for example, 60% by weight or more, preferably 70% by weight or more, particularly preferably 80% by weight or more, most preferably 90% by weight or more, and particularly preferably 95% by weight or more. If the proportion of the cellulose derivative (I) is below the above range, it tends to be difficult to efficiently and selectively adsorb precious metal ions.

[0155] The dosage form of the metal adsorbent is not particularly limited as long as it is effective, and examples thereof include powder, pellet, thread, nonwoven fabric, and irregular shapes.

[0156] The metal adsorbent has the properties of the cellulose derivative (I). That is, it has a high adsorption capacity for precious metals and no or very weak adsorption capacity for non-precious metals. Therefore, it is suitable for selectively recovering precious metals from aqueous solutions containing both precious and non-precious metals (e.g., industrial wastewater, mine wastewater, hot spring water, etc.).

[0157] Therefore, the metal adsorbent is particularly useful as an adsorbent for precious metals, and is particularly useful as an adsorbent for recovering secondary metal resources.

[0158] The metal adsorbent is particularly useful as an adsorbent for precious metals (particularly silver and / or gold).

[0159] [Method for producing metal adsorbent] The metal adsorbent can be produced, for example, by obtaining the cellulose derivative (I) by the above-mentioned method 1 or method 2 and using the obtained cellulose derivative (I). For example, the metal adsorbent may be produced by subjecting the cellulose derivative (I) obtained by the above-mentioned method 1 or method 2 to processing such as granulation, classification, tableting, molding, pulverization, film formation, etc.

[0160] [Metal Recovery Method] The metal recovery method of the present disclosure is a method of recovering metals (particularly, precious metals) dissolved in an aqueous solution, in other words, metal ions (particularly, precious metal ions) contained in an aqueous metal ion solution, by adsorbing them onto the cellulose derivative (I).

[0161] The metal exists as a metal ion in the aqueous solution, and the metal ion (particularly a noble metal ion) is adsorbed to the group represented by formula (a-1) of the cellulose derivative (I) to form a chelate complex, thereby being captured by the cellulose derivative (I).

[0162] The method for adsorbing a metal dissolved in an aqueous solution onto the cellulose derivative (I) is not particularly limited as long as it is a method for bringing the cellulose derivative (I) into contact with a metal dissolved in an aqueous solution. Examples of the method include a method in which the cellulose derivative (I) is packed into a column or the like and an aqueous metal ion solution is passed through the column, and a method in which the cellulose derivative (I) is immersed in an aqueous metal ion solution.

[0163] In the metal recovery method, it is preferable to adjust the pH of the aqueous solution in which the metal is dissolved to, for example, -1.2 to 9 (preferably 0 to 7, and especially 0 to 5), since this further improves the metal adsorption power and allows the metal to be recovered more efficiently. The pH of the aqueous solution can be adjusted using a well-known, commonly used pH adjuster (an acid such as nitric acid or an alkali such as sodium hydroxide).

[0164] After the metal ions have been adsorbed onto the cellulose derivative (I), the metals can be easily recovered by burning the cellulose derivative (I) with the adsorbed metal ions.

[0165] [Metal Recovery Apparatus] The apparatus includes a means (A) for contacting the cellulose derivative (I) with an aqueous metal ion solution (i.e., a solution in which a metal is dissolved) to allow the cellulose derivative (I) to adsorb the metal (e.g., metal ion) in the aqueous solution.

[0166] The apparatus preferably comprises a means for retaining the cellulose derivative (I) and a means for supplying an aqueous metal ion solution to the retained cellulose derivative (I) and bringing the aqueous metal ion solution into contact with the cellulose derivative (I). The apparatus may further comprise a means for discharging the aqueous metal ion solution after contacting the cellulose derivative (I). The apparatus may further comprise other means as necessary.

[0167] The apparatus preferably includes, for example, a column for packing the cellulose derivative (I) and a water supply channel for supplying an aqueous metal ion solution to the column. The apparatus may further include a drainage channel for draining water from the column. The apparatus may further include other components as necessary.

[0168] When an aqueous solution containing precious metal components (e.g., industrial wastewater, mine wastewater, hot spring water, etc.) is supplied to the device, the precious metal ions in the aqueous solution are selectively recovered, and wastewater with a significantly reduced concentration of precious metal ions is discharged.

[0169] The above-described configurations and combinations thereof of the present disclosure are merely examples, and additions, omissions, substitutions, and modifications of the configurations are possible as appropriate without departing from the spirit of the present disclosure. Furthermore, each aspect disclosed in this specification can be combined with any other feature disclosed in this specification. Furthermore, the present disclosure is not limited by the embodiments, but is limited only by the claims.

[0170] The present disclosure will be explained in more detail below using examples, but the present disclosure is not limited to these examples.

[0171] Example 1 (Production of Cellulose Derivative) Cellulose (V) (cellulose having a repeating unit represented by the following formula (V), 0.501 g, 3.08 mmol) was placed in a two-necked recovery flask and vacuum-dried at 90°C for 2 hours. Subsequently, under a nitrogen atmosphere, N,N-dimethylacetamide (15 mL) was added and the mixture was stirred for 21 hours. The reaction vessel was cooled to 0°C in an ice bath, and lithium chloride (0.99 g) was added. The mixture was then heated to room temperature (25°C) while stirring to dissolve the cellulose (V). DMAP (2.26 g, 18.5 mmol), N-Boc-L-proline (3.98 g, 18.5 mmol), EDC·HCl (3.55 g, 18.5 mmol), and N,N-dimethylacetamide (15 mL) were added and stirred at room temperature for 24 hours. The reaction solution was poured into water to cause reprecipitation, and the precipitated solid was collected by suction filtration. The collected solid was dissolved in ethanol, reprecipitated with water, and collected by suction filtration. The collected solid was dried in a vacuum to obtain a cellulose derivative (IV-1) having a repeating unit represented by the following formula (IV-1) as a white solid (1.81 g, yield 78%). 1 From the results of H-NMR measurement, the total average degree of substitution of N-Boc-L-proline was calculated to be 3.0.

[0172] (Cellulose derivative (IV-1)) 1 H-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)

[0173] Under a nitrogen atmosphere, trifluoroacetic acid (6.6 mL) and cellulose derivative (IV-1) (1.00 g, 1.33 mmol) were added to a two-necked recovery flask and stirred at room temperature for 7.5 hours. Reprecipitation was performed using diethyl ether, and the precipitated solid was recovered by centrifugation, washed with diethyl ether, and dried in vacuo. This yielded a salt of cellulose derivative (III-1) having a repeating unit represented by the following formula (III-1) as a white solid (0.979 g, yield 92%).

[0174] (Cellulose derivative (III-1)) 1 H-NMR (500 MHz, D2O, rt): δ5.24 (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)

[0175] Under a nitrogen atmosphere, a salt of cellulose derivative (III-1) (0.500 g, 0.628 mmol) was dissolved in dimethyl sulfoxide (3.1 mL) in a two-necked recovery flask, and carbon disulfide (0.57 mL, 9.4 mmol) was added. The mixture was cooled to approximately 10°C in the dark, and a 10% tetramethylammonium hydroxide methanol solution (3.77 mL, 3.77 mmol) was added dropwise. The mixture was stirred for 7 hours while warming to room temperature. The solid obtained by reprecipitation in ethanol was collected by centrifugation and washed with ethanol. The resulting solid was dried in vacuo to obtain cellulose derivative (II-1) having a repeating unit represented by the following formula (II-1) as a white solid (453 mg, yield 80%).

[0176] (Cellulose derivative (II-1)) 1 H-NMR (500 MHz, D2O, rt): δ 4.40-5.70 (br, overlapped with HDO), 3.35-4.40 (br), 3.15 (br,CH3), 1.20-2.85 (br)

[0177] Under a nitrogen atmosphere, sodium N,N-diethyldithiocarbamate (24.7 g, 110 mmol) was dissolved in distilled water (24 mL) in a two-necked recovery flask and cooled to approximately 0°C. 30% hydrogen peroxide (11 mL, 110 mmol) was added and stirred for 50 minutes. Cellulose derivative (II-1) (3.30 g, 3.66 mmol), concentrated sulfuric acid (0.13 mL), and methanol (59 mL) were added and stirred for 4 hours. The resulting solid was collected by centrifugation and washed with methanol, water, and diethyl ether. The resulting solid was dried in vacuo to obtain cellulose derivative (I-1) having a repeating unit represented by the following formula (I-1) as a pale yellow solid (2.56 g, yield approximately 62%). The total average degree of substitution of thiuram disulfide groups in cellulose derivative (I-1) was in the range of 0.1 to 3.0. The IR spectrum of cellulose derivative (I-1) is shown in Figure 1.

[0178]

[0179] [Evaluation of Equilibrium Adsorption Amount of Precious Metal Ions] The equilibrium adsorption amount of precious metals for the cellulose derivative (I-1) obtained in the examples was evaluated by the following method (batch method). 5 mL of the test solution below and 2.5 mg of cellulose derivative (I-1) classified to 212 μm or less were added to a 50 mL centrifuge tube, and the mixture was stirred at 25° C. and 200 rpm for 60 minutes. The mixture was filtered using a membrane filter (nitrocellulose, pore size: 0.45 μm), and the precious metal ion concentration (equilibrium concentration, C e The equilibrium adsorption amount q was calculated from the following equation: e (mmol / g) was calculated. e = (C0 - C e ) × V / m

[0180] The test solutions used were 0.1 mol / L aqueous hydrochloric acid solutions with gold (III) concentrations of 0.11, 0.25, 0.50, and 2.0 mmol / L, which were obtained by diluting tetrachloroauric acid with an aqueous hydrochloric acid solution.

[0181] [Evaluation of maximum adsorption amount of precious metal ions] The equilibrium adsorption amount q obtained by the evaluation of the equilibrium adsorption amount of precious metal ions e and equilibrium concentration C e The ratio of the equilibrium concentration C e The Langmuir plot is shown in Figure 2. The maximum adsorption amount was calculated from the reciprocal of the slope of the obtained Langmuir plot, and the maximum adsorption amount of gold ions was found to be 2.7 mmol / g.

[0182] [Evaluation of precious metal ion adsorption in the presence of competing ions] The precious metal ion adsorption of the cellulose derivative (I-1) obtained in the examples in the presence of competing ions was evaluated by the following method (batch method). As a test solution, a 0.1 mol / L aqueous hydrochloric acid solution containing gold ions (concentration: 0.5 mmol / L) as the precious metal ion and one ion selected from Cu ions, Ni ions, Zn ions, Pb ions, Na ions, K ions, Mg ions, or Ca ions as the competing ion (competitive ion concentration: 10 mmol / L, 100 mmol / L, 500 mmol / L, or 1000 mmol / L) (Pb was used in a 0.1 mol / L aqueous nitric acid solution). In addition, a 0.1 mol / L aqueous hydrochloric acid solution containing gold ions (concentration: 0.5 mmol / L) but no competing ions was used as a control test solution. 5 mL of the test solution was placed in a 50 mL centrifuge tube, and 2.5 mg of the cellulose derivative (I-1) classified to 212 μm or less was added thereto. The mixture was stirred at 25°C and 200 rpm for 60 minutes. After that, the mixture was filtered using a membrane filter (nitrocellulose, pore size: 0.45 μm), and the gold ion concentration (C e The gold ion recovery rate (%) was calculated using the following formula, where the initial concentration of gold ions in the test solution was C (mmol / L). The results are shown in Figure 3. Recovery rate = (C - C e ) / C0 x 100

[0183] From FIG. 3, it can be seen that the cellulose derivative (I) of the present disclosure can selectively adsorb and recover gold ions even in the presence of 20 to 2000 times more competing ions, and thus has extremely excellent selectivity.

[0184] The cellulose derivative (I) of the present disclosure has high wettability with aqueous solutions, and when brought into contact with the aqueous solution, it easily blends in and can selectively capture precious metal ions present in the aqueous solution. Furthermore, the cellulose derivative (I) does not cause exhaust problems even when burned, and precious metals can be easily recovered by burning the cellulose derivative (I) with precious metal ions adsorbed thereon. Therefore, the cellulose derivative (I) can be suitably used as an adsorbent that efficiently and selectively adsorbs and recovers precious metals as secondary resources from industrial wastewater and waste.

Claims

1. A cellulose derivative having a repeating unit represented by the following formula (I): [In formula (I), R a are the same or different and are a hydrogen atom or a group represented by the following formula (a-1). a at least one of which is a group represented by the following formula (a-1): (In formula (a-1), R 1 is a single bond or an alkylene group having 1 to 10 carbon atoms. 2 ~R 4 are the same or different and each represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms. n is 1 or 2. R 1 and R 2 may be bonded to each other to form a ring together with the adjacent nitrogen atom. 3 and R 4 may be bonded to each other to form a ring together with the adjacent nitrogen atom) 2. The cellulose derivative according to claim 1, wherein the total average degree of substitution of the group represented by formula (a-1) is 0.1 to 3.

0.

3. A metal adsorbent comprising the cellulose derivative according to claim 1 or 2.

4. The metal adsorbent according to claim 3, which is an adsorbent for silver and / or gold.

5. Formula (II) below [In formula (II), R b are the same or different and are a hydrogen atom or a group represented by the following formula (b-1). b at least one of which is a group represented by the following formula (b-1) or a salt thereof] (In formula (b-1), R 1 is a single bond or an alkylene group having 1 to 10 carbon atoms. 2 is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms. 1 and R 2 may be bonded to each other to form a ring together with the adjacent nitrogen atom), (In formula (1), X is a thiol group or a halogen atom. R 3 , R 4 are the same or different and each represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms. 3 and R 4 or a salt thereof) to obtain the cellulose derivative according to claim 1 or 2.

6. A method for producing a metal adsorbent, comprising obtaining a cellulose derivative by the method according to claim 5 and using the obtained cellulose derivative to produce a metal adsorbent containing said cellulose derivative.

7. Cellulose is treated with the following formula (2) (In formula (2), R 1 is a single bond or an alkylene group having 1 to 10 carbon atoms. 2 ~R 4 are the same or different and each represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms. n is 1 or 2. R 1 and R 2 may be bonded to each other to form a ring together with the adjacent nitrogen atom. 3 and R 4 or a salt thereof) to obtain the cellulose derivative according to claim 1 or 2.

8. A method for producing a metal adsorbent, comprising obtaining a cellulose derivative by the method according to claim 7 and using the obtained cellulose derivative to produce a metal adsorbent containing said cellulose derivative.

9. A method for recovering metals, which comprises recovering metals dissolved in an aqueous solution by adsorbing the metals onto the cellulose derivative according to claim 1 or 2.

10. A metal recovery device comprising means for contacting the cellulose derivative according to claim 1 or 2 with a solution in which metals are dissolved, thereby causing the cellulose derivative to adsorb the metals in the solution.

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