WO2020230616A1

WO2020230616A1 - Metal-adsorbing fibers and production method therefor

Info

Publication number: WO2020230616A1
Application number: PCT/JP2020/017993
Authority: WO
Inventors: 鎌田　英樹; 洋平西海; 博文椛山
Original assignee: 株式会社クラレ
Priority date: 2019-05-10
Filing date: 2020-04-27
Publication date: 2020-11-19
Also published as: JP2022107069A

Abstract

Metal-adsorbing fibers comprising poly(vinyl alcohol) and an amine-based polymer, which have a content of the amine-based polymer of 30 mass% or higher with respect to the mass of the metal-adsorbing fibers and which, through 1-hour immersion in 3-N hydrochloric acid at 40°C, have a loss in mass of 5 mass% or less.

Description

Metal adsorption fiber and its manufacturing method

The present invention relates to a metal-adsorbed fiber containing polyvinyl alcohol and an amine-based polymer and a method for producing the same.

In recent years, the demand for precious metals as catalysts has increased, and their value is increasing. On the other hand, precious metals are produced in a limited number of countries, and there is a problem of supply insecurity in addition to soaring prices. Under these circumstances, efforts to recycle precious metals are being actively carried out.

As one of the techniques for recovering precious metals, a metal adsorbent obtained by mixing particles or a polymer having a metal adsorbing ability with a polymer as a base material is known. Such a metal adsorbent can have metal adsorbability by containing particles or a polymer having the metal adsorbing ability. For example, Patent Document 1 discloses a metal adsorbent containing 70% by mass or more of polyvinyl alcohol and an amine-based polymer and crosslinked with aldehydes.

Japanese Unexamined Patent Publication No. 2010-138430

In the process of recovering a noble metal, it is usually treated with a high concentration of strong acid in order to dissolve the metal in the solution. Therefore, in order to enhance the adsorptivity of the metal adsorbent, it is required to improve the acid resistance in addition to increasing the amount of the amine-based polymer having the metal adsorbing ability. However, according to the study of the present inventor, the metal adsorbent in Patent Document 1 has insufficient acid resistance because it uses only aldehydes as a cross-linking agent, and has a low content of amine-based polymer. It was found that sufficient metal adsorptivity could not be exhibited. Furthermore, in order to efficiently recover precious metals, it is required to have a high metal adsorption rate and the ability to adsorb a large amount of metal in a short time, but it was found that conventional metal adsorbents cannot satisfy this. It was.

Therefore, an object of the present invention is to provide a metal adsorption fiber having excellent metal adsorption property and metal adsorption rate and a method for producing the same.

As a result of diligent studies to solve the above problems, the present inventor has made the content of the amine polymer in the metal adsorption fiber containing polyvinyl alcohol and the amine polymer 30% by mass or more and immersed it in a predetermined hydrochloric acid. We have found that the above problems can be solved by adjusting the mass reduction rate at the time to 5% by mass or less, and completed the present invention.

[1] A metal-adsorbing fiber containing polyvinyl alcohol and an amine-based polymer.
The content of the amine-based polymer is 30% by mass or more with respect to the mass of the metal adsorbing fiber, and the mass reduction rate when immersed in 3N hydrochloric acid at 40 ° C. for 1 hour is 5% by mass or less. fiber.
[2] The metal according to [1], wherein the amine-based polymer is at least one selected from the group consisting of polyvinylamine, polyallylamine, polyalkyleneamine, polyethyleneimine, polydiallyl quaternary ammonium, and salts thereof. Adsorbent fiber.
[3] The metal-adsorbing fiber according to [1] or [2], wherein the amine-based polymer has a weight average molecular weight of 5,000 to 100,000.
[4] Polyvinyl alcohol and amine-based polymers have a crosslinked structure, and the crosslinked structure contains two or more functional groups of at least one selected from the group consisting of an epoxy group, an isocyanate group, a vinyl group, and an aldehyde group. The metal-adsorbing fiber according to any one of [1] to [3], which is a structure derived from a cross-linking agent contained therein.
[5] Of [1] to [4], wherein polyvinyl alcohol has a sea-island structure in which an amine-based polymer constitutes an island phase, and the average diameter of the island phases is 0.1 to 30 μm. The metal adsorption fiber according to any one.
[6] The step (1) of obtaining a spinning stock solution containing polyvinyl alcohol, an amine-based polymer and a solvent, and the step (2) of extruding the spinning stock solution into dry air and removing the solvent to form fibers are included. , [1] to [5], the method for producing a metal adsorbing fiber.
[7] The production method according to [6], further comprising a step (3) of subjecting the fibers formed in the step (2) to a cross-linking treatment.

The metal adsorption fiber of the present invention is excellent in metal adsorption property and metal adsorption rate. Therefore, it can be suitably used as an adsorbent for adsorbing metals.

It is a scanning electron microscope image of the cross section of the metal adsorption fiber produced in Example 1. It is a scanning electron microscope image of the cross section of the metal adsorption fiber produced in Example 2. It is a scanning electron microscope image of the cross section of the metal adsorption fiber produced in Comparative Example 5.

[Metal adsorption fiber]
The metal adsorption fiber of the present invention contains polyvinyl alcohol and amine-based polymers. In the present specification, the term "metal" includes the state in which a metal is dissolved in a solution to form a metal ion. Further, in the present specification, the metal adsorption property indicates the amount of metal that can be adsorbed by a specific amount of metal adsorption fibers, and the metal adsorption rate indicates the amount of metal that can be adsorbed by a specific amount of metal adsorption fibers in a short time. ..

<Polyvinyl alcohol>
The polyvinyl alcohol (sometimes referred to as PVA) contained in the metal adsorption fiber of the present invention is a polymer having a structural unit mainly derived from vinyl alcohol and a structural unit derived from vinyl ester (preferably vinyl acetate). Polyvinyl alcohol may contain a structural unit derived from a monomer (sometimes referred to as another monomer) other than these structural units as long as the effect of the present invention is not impaired. Other monomers include α-olefins such as ethylene, propylene, n-butyl, isobutylene; acrylates and salts thereof, methyl acrylate, ethyl acrylate, n-propyl acrylate, i-propyl acrylate, Acrylic acid esters such as n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate; methacrylic acid and salts thereof; methyl methacrylate, methacrylic acid Methacrylate esters such as ethyl, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, octadecyl methacrylate, etc. Kind: acrylamide, N-methylacrylamide, N-ethylacrylamide, N, N-dimethylacrylamide, diacetoneacrylamide, acrylamidepropanesulfonic acid and its salts, acrylamidepropyldimethylamine and its salts or its quaternary salts, N-methylolacrylamide And acrylamide derivatives such as derivatives thereof; methacrylamide, N-methylmethacrylate, N-ethylmethacrylate, methacrylamidepropanesulfonic acid and its salts, methacrylatepropyldimethylamine and its salts or quaternary salts thereof, N-methylolmethacryl Methacrylic amide derivatives such as amides and derivatives thereof; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether and the like. Nitriles such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride and vinyl fluoride; vinylidene halides such as vinylidene chloride and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; maleic acid, Examples thereof include unsaturated dicarboxylic acids such as itaconic acid and fumaric acid and salts thereof or esters thereof; vinylsilyl compounds such as vinyltrimethoxysilane; isopropenyl acetate and the like. These other monomers can be used alone or in combination of two or more. The content of the constituent units derived from other monomers is usually 20 mol% or less, preferably 10 mol% or less, more preferably 5 mol% or less, based on the total molar amount of the constituent units constituting polyvinyl alcohol. It is preferable, and 1 mol% or less is more preferable. In addition, polyvinyl alcohol can be used alone or in combination of two or more.

Polyvinyl alcohol is produced by a known method, for example, a method of saponifying a resin obtained by polymerizing a vinyl ester (preferably vinyl acetate) and, if necessary, the other monomer, in a solvent such as alcohol. You can. Examples of the solvent used in this method include lower alcohols such as methanol and ethanol. The alcohol used in the saponification reaction may contain a solvent such as acetone, methyl acetate, ethyl acetate, or benzene as long as the amount is 40% by mass or less. Examples of the catalyst used in the saponification reaction include hydroxides of alkali metals such as potassium hydroxide and sodium hydroxide, alkali catalysts such as sodium methoxyde, and acid catalysts such as mineral acid. The temperature of the saponification reaction is not particularly limited, but is preferably in the range of, for example, 20 to 60 ° C. The vinyl alcohol obtained by the saponification reaction is preferably subjected to drying after washing.

Generally, the higher the degree of saponification of polyvinyl alcohol, the higher the crystallinity and the higher the acid resistance, but it is particularly limited as long as the mass loss rate when immersed in 3N hydrochloric acid for 1 hour is 5% or less. Not done. The degree of saponification may be preferably 70 mol% or more, more preferably 80 mol% or more, further preferably 90 mol% or more, particularly preferably 95 mol% or more, and even more preferably 98 mol% or more. When the degree of saponification is at least the above lower limit, the hydrophilicity of the metal adsorption fiber is increased, and the aqueous solution containing the metal ion easily permeates the metal adsorption fiber, so that the metal adsorption property and the metal adsorption rate are easily improved. The upper limit of the degree of saponification of polyvinyl alcohol is 100 mol% or less. The degree of saponification of polyvinyl alcohol can be measured according to JIS-K6726.

The viscosity average degree of polymerization of polyvinyl alcohol is preferably 200 or more, more preferably 500 or more, still more preferably 700 or more, particularly preferably 1000 or more, preferably 5000 or less, more preferably 4000 or less, still more preferably 3000 or less. , Especially preferably 2500 or less. When the viscosity average degree of polymerization of polyvinyl alcohol is at least the above lower limit, it is easy to improve the metal adsorption property and the metal adsorption rate, and when the viscosity average degree of polymerization is at least the above upper limit, it is easy to suppress the aggregation of fibers. Therefore, it is advantageous in terms of strength and the moldability is also good. The viscosity average degree of polymerization of polyvinyl alcohol can be measured based on, for example, JIS-K6726 "polyvinyl alcohol test method". Specifically, when the degree of saponification is less than 99.5 mol%, the ultimate viscosity [η] measured at 30 ° C. in water for PVA saponified to a degree of saponification of 99.5 mol% or more. Using (liter / g), the viscosity average degree of polymerization (P) can be determined by the following formula.
P = ([η] × 10 ⁴ ^/ 8.29) ^{(1 / 0.62)}

The content of polyvinyl alcohol contained in the metal adsorbing fiber is preferably less than 70% by mass, more preferably 69% by mass or less, still more preferably 68% by mass or less, still more preferably, based on the mass of the metal adsorbing fiber. Is 65% by mass or less, particularly preferably 63% by mass or less, and more particularly preferably 60% by mass or less. When the content of polyvinyl alcohol is not more than the above upper limit, the metal adsorption property and the metal adsorption rate can be easily improved. The content of the polyvinyl alcohol is preferably more than 30% by mass, more preferably 35% by mass or more, still more preferably 40% by mass or more, based on the mass of the metal adsorbing fiber. When the content of polyvinyl alcohol is at least the above lower limit, it is easy to suppress the aggregation of fibers, which is advantageous in terms of strength and good moldability.

<Amine-based polymer>
The amine-based polymer contained in the metal-adsorbing fiber is a polymer capable of adsorbing a metal (metal ion) in an aqueous solution by an amino group and a quaternary ammonium group. The amino group contained in the amine-based polymer may be any of a primary amino group, a secondary amino group, and a tertiary amino group. The repeating unit having an amino group may be one kind or two or more kinds. Therefore, the amine-based polymer may be a polymer in which two or more repeating units having an amino group or a quaternary ammonium group are random, blocked, alternating or graft-copolymerized. Further, it may have a repeating unit having no amino group or quaternary ammonium group as long as the effect of the present invention is not impaired.

Examples of the amine-based polymer include polyvinylamine, polyvinylalkylamine, polyalkyleneamine, quaternary ammonium-containing polymer, polyaniline, polynucleotide, polyallylamine, polyalkyleneamine, polydiallyl quaternary ammonium, and salts thereof. .. These amine-based polymers can be used alone or in combination of two or more. A copolymer in which two or more kinds of repeating units of these polymers are copolymerized can also be used. Among these, at least one selected from the group consisting of polyvinylamine, polyallylamine, polyalkyleneamine, polydiallyl quaternary ammonium, and salts thereof from the viewpoint of easily improving the metal adsorption property and the metal adsorption rate of the metal adsorption fiber. Species are preferred, at least one selected from the group consisting of polyallylamine and polyethyleneimine is more preferred, and polyallylamine or polyethyleneimine is even more preferred.

The weight average molecular weight of the amine-based polymer is preferably 1000 or more, more preferably 4000 or more, still more preferably 7000 or more, particularly preferably 8000 or more, preferably 100,000 or less, more preferably 70,000 or less, and further. It is preferably 50,000 or less, particularly preferably 30,000 or less, and more particularly preferably 20,000 or less. When the weight average molecular weight of the amine-based polymer is at least the above lower limit, the adhesion to polyvinyl alcohol is enhanced, and elution from the metal-adsorbed fiber into the aqueous solution is likely to be suppressed. When the weight average molecular weight is not more than the above upper limit, the compatibility with polyvinyl alcohol is excellent, so that the spinnability is likely to be improved. The weight average molecular weight of the amine-based polymer can be determined, for example, by dissolving it in a solvent in which the amine-based polymer can be dissolved and using gel permeation chromatography (GPC).

The content of the amine-based polymer contained in the metal-adsorbing fiber of the present invention is 30% by mass or more with respect to the mass of the metal-adsorbing fiber. Since the metal adsorption fiber of the present invention has a large amine-based polymer content of 30% by mass or more, it is excellent in metal adsorption and metal adsorption rate, and can effectively adsorb metal ions in an aqueous solution. The content of the amine-based polymer contained in the metal adsorbing fiber is preferably more than 30% by mass, more preferably 31% by mass or more, still more preferably 32% by mass or more, still more preferably, based on the mass of the metal adsorbing fiber. Is 35% by mass or more, particularly preferably 37% by mass or more, and more particularly preferably 40% by mass or more. When the content of the amine-based polymer is at least the above lower limit, the metal adsorption property and the metal adsorption rate of the metal adsorption fiber are likely to be effectively improved. The content of the amine-based polymer is preferably 70% by mass or less, more preferably 65% by mass or less, still more preferably 60% by mass or less, based on the mass of the metal-adsorbed fiber. When the content of the amine-based polymer is not more than the above upper limit, the adhesion with polyvinyl alcohol is enhanced, and the elution from the metal adsorbing fiber into the aqueous solution is easily suppressed.

<Crosslink>
The metal-adsorbed fiber of the present invention has a mass reduction rate of 5% by mass or less when immersed in 3N hydrochloric acid at 40 ° C. for 1 hour and has excellent acid resistance. Therefore, polyvinyl alcohol and / or amine-based polymers, particularly amine-based polymers, are used. Elution of the polymer into the aqueous solution can be effectively suppressed, and as a result, the metal adsorption property and the metal adsorption rate can be improved.

The metal adsorption fiber of the present invention has a mass loss rate of 5% by mass or less, preferably 3% by mass or less, more preferably 1% by mass or less, and particularly preferably 0, when immersed in 3N hydrochloric acid at 40 ° C. for 1 hour. .1% by mass or less. When the mass reduction rate is not more than the above upper limit, excellent acid resistance can be exhibited. The mass reduction rate can be measured by the method described in Examples.

In the metal adsorption fiber of the present invention, the method for reducing the mass reduction rate to 5% by mass or less is not particularly limited, but a method of cross-linking polyvinyl alcohol and an amine-based polymer with a cross-linking agent is preferable. By cross-linking with a cross-linking agent, the polyvinyl alcohol and the amine-based polymer in the metal adsorption fiber can form a cross-linked structure, and the cross-linked structure can effectively suppress the elution of the polymer into the acid aqueous solution. More specifically, a functional group such as a hydroxyl group in the polyvinyl alcohol and / or an amino group in the amine polymer reacts with the cross-linking agent to form an amine polymer and an amine polymer between the polyvinyl alcohol and the polyvinyl alcohol. Crosslinks are introduced between and / or between the polyvinyl alcohol and the amine-based polymer. Examples of the cross-linking agent include an epoxy group, an isocyanate group, a vinyl group, a carboxyl group, a halogen group, an acid anhydride group, an acid halide group, an N-chloroformyl group and a chlorohomate group from the viewpoint of easily improving acid resistance. A cross-linking agent containing two or more functional groups of at least one selected from the group consisting of an imide ether group, an amidinyl group and an aldehyde group is preferable, and the cross-linking agent is selected from the group consisting of an epoxy group, an isocyanate group, a vinyl group and an aldehyde group. A cross-linking agent containing two or more of at least one functional group is more preferable, and a compound having two or more functional groups, preferably 2 to 5 epoxy groups is further preferable. These cross-linking agents can be used alone or in combination of two or more.
Therefore, when the metal-adsorbing fiber of the present invention is crosslinked with the cross-linking agent, the polyvinyl alcohol and the amine-based polymer in the metal-adsorbing fiber have a cross-linked structure, and the cross-linked structure is a structure derived from the cross-linking agent. Cross-linking with a cross-linking agent having only an aldehyde group tends to be deacetalized by heating in an aqueous solution containing an acid, and may not be preferable from the viewpoint of acid resistance.
The mass reduction rate can be adjusted by appropriately changing the type and amount of the cross-linking agent used. For example, as the amount of the cross-linking agent used increases, the mass reduction rate tends to decrease.

Specifically, examples of the cross-linking agent having a vinyl group include divinyl sulfone and "NK ester" manufactured by Shin-Nakamura Chemical Co., Ltd. (1G, 2G, 3G, 4G, 9G, 14G, 23G, BPE-80N, BPE- Polyvalent methacrylate compounds such as 100, BPE-200, BPE-500, BPE-900, BPE-1300, DCP, DOD-N, HD-N, NOD-N, NPG, 1206PE, 701, PG, TMPT). Be done.

Examples of the cross-linking agent having an epoxy group include "Denacol" (EX-611, EX-612, EX-614, EX-614B, EX-622, EX-512, EX-521, EX) manufactured by Nagase ChemteX Corporation. -411, EX-421, EX-313, EX-314, EX-321, EX-201, EX-211, EX-212, EX-252, EX-810, EX-811, EX-850, EX-851 , EX-821, EX-830, EX-832, EX-841, EX-861, EX-911, EX-941, EX-920, EX-931, EX-721, EX-203, EX-711, EX -221 etc.), Polyethylene glycol diglycidyl ether, bisphenol A diglycidyl ether, bisphenol A diβ methyl glycidyl ether, bisphenol F diglycidyl ether, tetrahydroxyphenylmethane tetraglycidyl ether, resorcinol diglycidyl ether, brominated bisphenol A diglycidyl Ether, chlorinated bisphenol A diglycidyl ether, hydrogenated bisphenol A diglycidyl ether, bisphenol A alkylene oxide adduct diglycidyl ether, novolak glycidyl ether, polyalkylene glycol diglycidyl ether, glycerin triglycidyl ether, pentaerythritol diglycidyl ether , Epoxy urethane resin and other glycidyl ether types; p-oxybenzoic acid glycidyl ether ester and other glycidyl ether ester types; phthalic acid diglycidyl ester, tetrahydrophthalic acid diglycidyl ester, hexahydrophthalic acid diglycidyl ester, acrylic Glycidyl ester type such as acid diglycidyl ester and dimer acid diglycidyl ester; glycidyl amine type such as glycidyl aniline, tetraglycidyl diaminodiphenylmethane, triglycidyl isocyanurate, triglycidyl aminophenol; Acidic aliphatic epoxy resin; 3,4-epoxy-6-methylcyclohexylmethyl 3,4-epoxy-6-methylcyclohexanecarboxylate, 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate, bis (3, 4-epoxy-6-methylcyclohexylmethyl) adipate, vinylcyclohe Examples thereof include alicyclic epoxy resins such as xenediepoxyside, dicyclopentadiene oxide, bis (2,3-epoxycyclopentyl) ether, and limonene dioxide. Among these cross-linking agents having an epoxy group, polyalkylene glycol diglycidyl ether is preferable, and polyethylene glycol diglycidyl ether is more preferable from the viewpoint of acid resistance.

Examples of the cross-linking agent having an isocyanate group include "Duranate" manufactured by Asahi Kasei Chemicals Co., Ltd. (WB40-100, WB40-80D, WE50-100, WT30-100, WT20-100, etc.); Toluene diisocyanate (TDI); Hydrogen TDI; Trimethylol Propane-TDI Adduct (eg, Bayer, "Desmodur L"); Triphenylmethane triisocyanate; Methylenebis (phenylisocyanate) (MDI); Hydrogenated MDI; Polymerized MDI; Hexamethylene diisocyanate; Xylylene diisocyanate; 4,4'-Dicyclohexylmethane diisocyanate; isophorone diisocyanate and the like. Isocyanates dispersed in water using an emulsifier can also be used.

<Metal adsorption fiber>
The metal adsorbing fiber of the present invention contains polyvinyl alcohol and an amine-based polymer, the content of the amine-based polymer is 30% by mass or more, and the mass reduction rate when immersed in 3N hydrochloric acid at 40 ° C. for 1 hour is 5% by mass. Since it is less than%, both excellent metal adsorption property and excellent metal adsorption rate can be achieved. Therefore, the metal adsorbent fiber of the present invention is useful as a metal adsorbent for recycling metals.

More specifically, since the form of the metal-adsorbed fiber of the present invention is fibrous, the aqueous solution containing metal ions is more likely to permeate into the metal-adsorbed fiber as compared with the granular form or the like. Further, since polyvinyl alcohol has higher hydrophilicity than, for example, ethylene-vinyl alcohol copolymer (EVOH), the metal easily penetrates into the metal adsorption fiber. Further, since polyvinyl alcohol has higher compatibility with the amine-based polymer than, for example, EVOH, the amine-based polymer may exist in a form in which the amine-based polymer is well dispersed in the metal adsorption fiber. Further, although the metal-adsorbing fiber is in the fiber form, the content of the amine-based polymer having a metal-adsorbing ability is as large as 30% by mass or more. Further, the mass reduction rate is 5% by mass or less, the acid resistance is excellent, and the polymer is hardly eluted in the acid aqueous solution. Therefore, the metal adsorption fiber of the present invention has excellent metal adsorption property and can adsorb a sufficient amount of metal (metal ion). Furthermore, the metal adsorption rate is high, and a large amount of metal can be adsorbed in a shorter time.

The metal-adsorbing fiber of the present invention may contain any additive other than the polyvinyl alcohol, the amine-based polymer, the cross-linking agent and the fine particles. Examples of the additive include polymers other than polyvinyl alcohol and amine-based polymers; antioxidants; stabilizers; lubricants; processing aids; antistatic agents; colorants; impact-resistant aids; foaming agents and the like. Additives can be used alone or in combination of two or more. The content of the additive may be, for example, 10% by mass or less, preferably 5% by mass or less, based on the mass of the metal adsorbing fiber.

In one embodiment of the present invention, the average fiber diameter of the metal-adsorbed fiber of the present invention is not particularly limited, but is preferably 5 to 100 μm, more preferably 10 to 50 μm. When the average fiber diameter of the metal adsorption fiber is in the above range, the metal adsorption property and the metal adsorption rate can be easily improved.

In one embodiment of the present invention, the metal-adsorbing fiber of the present invention has a sea-island structure in which polyvinyl alcohol constitutes a sea phase and an amine-based polymer constitutes an island phase from the viewpoint of metal adsorption and metal adsorption rate. Is preferable. In the sea-island structure, the average diameter of the island phase of the amine-based polymer is preferably 0.1 to 30 μm, and when the average diameter is in the range of such an average diameter, the aqueous solution containing the metal ion permeates the metal adsorption fiber. Since it is easy, it can have more excellent metal adsorptivity, and it is easy to increase the amount of metal that can be adsorbed. In particular, the adsorption rate becomes high, and a large amount of metal can be adsorbed in a shorter time.
The average diameter of the island phase of the amine polymer is preferably 0.2 μm or more, more preferably 0.3 μm or more, still more preferably 0.5 μm or more, particularly preferably 0.8 μm or more, preferably 25 μm or less, and more. It is preferably 20 μm or less, more preferably 15 μm or less, particularly preferably 10 μm or less, and particularly more preferably 7 μm or less. When the average diameter of the island phase of the amine-based polymer is in the above range, the metal adsorption property tends to be further improved and the metal adsorption rate tends to be increased. The average diameter of the island phases of the amine-based polymer is the diameter of 10 island phases picked up at random after adsorbing the noble metal on the metal-adsorbing fiber, washing with an alkaline aqueous solution, and observing the fiber cross section with a scanning electron microscope. Is averaged, and can be obtained by, for example, the method described in Examples. The average diameter of the island phase may be adjusted within the above range, for example, by appropriately adjusting the type and content of polyvinyl alcohol, amine-based polymer, and cross-linking agent, or by using the production method described later.

In one embodiment of the present invention, the metal adsorption fiber of the present invention is obtained per 1 g of a solution obtained by adding 100 mg of metal to 100 mL of 3N-hydrochloride at 20 ° C. containing platinum ions at a concentration of 100 mg / L and stirring for 5 minutes. The amount of metal adsorbed is preferably 1 mg / g or more, more preferably 5 mg / g or more, still more preferably 10 mg / g or more, and the amount of metal adsorbed per 1 g of the solution after stirring for 60 minutes is preferably 25 mg / g. It is g or more, more preferably 28 mg / g or more. When the amount of metal adsorbed is at least the above lower limit, excellent adsorptivity and adsorption rate can be exhibited. The upper limit of the amount of metal adsorbed per 1 g of the solution after stirring for 5 or 60 minutes is usually 70 mg / g or less.
The amount of metal adsorbed per 1 g of the solution can be calculated by substituting the metal concentration A (mg / L) into the formula of 100-A (mg / g) after measuring the metal concentration A (mg / L) with a luminescence analyzer. It can be calculated by the method described in the example.

[Manufacturing method of metal adsorption fiber]
When a spinning stock solution containing polyvinyl alcohol, an amine-based polymer, and a solvent is fiberized by a wet spinning method or a dry / wet spinning method, the amine-based polymer can be eluted in the solidification bath, so that the content of the amine-based polymer is high. It is difficult to obtain many metal adsorbing fibers. The present inventor has found that by using a predetermined dry spinning method, metal-adsorbed fibers can be easily and efficiently obtained even if an amine-based polymer of 30% by mass or more is contained. Therefore, from the viewpoint of increasing the content of the amine-based polymer, in the present invention, it is preferable to produce the metal-adsorbed fiber by the dry spinning method.

More specifically, the metal adsorbing fiber of the present invention has a step (1) of obtaining a spinning stock solution containing polyvinyl alcohol, an amine polymer and a solvent, and extruding the spinning stock solution into dry air to remove the solvent. It can be produced by a method including the step (2) of forming fibers. Further, when the polyvinyl alcohol and the amine polymer are crosslinked, the step (3) of subjecting the fibers formed in the step (2) to a crosslinking treatment can be further included.

In the step (1), the spinning stock solution can be obtained by mixing the polyvinyl alcohol, the amine-based polymer, the solvent, and optionally the additive. Examples of the solvent include water, dimethyl sulfoxide (DMSO), glycerin, ethylene glycol and a mixed solvent thereof, and it is preferable to use water from the viewpoint of polymer solubility and easy removal of the solvent. In a preferred embodiment, it is preferable to obtain a spinning stock solution by dissolving the polyvinyl alcohol, the amine-based polymer, the solvent, and optionally the additive using a batch-type dissolution tank and an extruder. The extruder may be a single-screw extruder or a twin-screw extruder, and a twin-screw extruder can be preferably used from the viewpoint of mixing. The order of introduction into the extruder is not particularly limited, but from the viewpoint of mixability, a mixed solution of polyvinyl alcohol and a solvent is put into the extruder and kneaded, and then an amine-based polymer and optionally additives are introduced into the extruder. It is preferable to knead the mixture. The temperature at the time of mixing, the screw rotation speed of the extruder, and the like may be appropriately adjusted so that the polymer can be dissolved in the solvent. The temperature at the time of mixing may be, for example, 80 to 160 ° C, preferably 110 to 150 ° C.

Step (2) is a step of forming fibers from the undiluted spinning solution obtained in step (1) by the dry spinning method. Examples of the dry spinning method of the step (2) include a method of extruding the spinning stock solution through a nozzle into heated dry air and evaporating and removing the solvent to form fibers. The dried fiber may be wound up using a winding device or the like. Since it is not necessary to use a solidification bath in the dry spinning method, it is possible to easily and efficiently obtain metal-adsorbed fibers having a high amine-based polymer content as compared with the wet spinning method or the dry / wet spinning method. The number of holes in the nozzle is not particularly limited, and is, for example, 10 to 1000. The temperature of the dry air may be any temperature at which the solvent can be removed, and is preferably 50 to 200 ° C, more preferably 60 to 150 ° C.

When performing the cross-linking treatment, the fibers formed in the step (2) are subjected to the step (3) to carry out the cross-linking treatment. The cross-linking treatment in the step (3) includes, for example, a method of immersing the fiber in a solution containing the cross-linking agent and drying the cross-linked fiber by the immersion; applying the solution containing the cross-linking agent to the fiber. , A method of drying the crosslinked fibers by coating and the like. Further, the solution containing the cross-linking agent can be obtained by mixing a solvent such as water with the cross-linking agent. The drying temperature is not particularly limited, and is, for example, 50 to 200 ° C, preferably 100 to 180 ° C.

The fibers obtained in step (2) or step (3) may be stretched. The draw ratio is preferably 1.5 to 10 times, more preferably 2 to 7 times, from the viewpoint of ensuring the strength required for processing the metal adsorption fiber. The stretching temperature is preferably 100 to 250 ° C. from the viewpoint of improving water resistance. The stretching can be carried out by a conventional method, and for example, the stretching may be performed in a hot air furnace.

[Metal adsorption method]
The metal adsorption fiber of the present invention can adsorb and remove a metal from a solution containing a metal (metal ion). Further, the metal can be recovered by desorbing the metal from the metal adsorption fiber on which the metal is adsorbed.

As a method of adsorbing metal to the metal adsorption fiber of the present invention, for example, the metal adsorption fiber is wound around a tubular core having a hole on the side surface, and a solution containing metal is applied from the inside to the outside of the cylinder or in the opposite direction. Method of passing liquid; Method of cutting metal adsorption fiber to an appropriate length and filling it in a column, and passing a solution containing metal; Method of cutting metal adsorption fiber to a desired length and containing metal A method of adsorbing metal and then pulling it up; a method of processing metal-adsorbed fibers into sheets such as paper, non-woven fabrics, and woven fabrics, laminating them, filling them in a column, and passing a solution containing metal through them. Can be mentioned.

As a method of desorbing the metal from the metal adsorbing fiber on which the metal is adsorbed, for example, a method of throwing the metal adsorbing fiber on which the metal is adsorbed into the eluent; elution into a column containing the metal adsorbing fiber on which the metal is adsorbed. A method of passing a liquid through the liquid; a method of incinerating a metal-adsorbed fiber on which a metal is adsorbed can be mentioned. Since the form of the metal-adsorbing fiber of the present invention is fibrous, the fiber is more easily burned when incinerated by the above-mentioned incineration method, and the metal can be easily recovered, as compared with the form of granular or the like.

A solution containing a metal (metal ion) is usually a strong acid aqueous solution because it is necessary to dissolve the metal, and is a solution containing hydrogen chloride from the viewpoint of the adsorptivity of metal-adsorbing fibers and the solubility of metal. Is preferable. Further, since the metal adsorption fiber of the present invention has excellent acid resistance, excellent adsorption performance can be exhibited even in such a solution. Examples of the metal to be adsorbed in the present invention include platinum group metals such as platinum, palladium, rhodium, osmium, iridium and ruthenium, gold, silver, copper, nickel, chromium, vanadium, cobalt, lead, zinc, mercury and cadmium. And so on. Among these, a platinum group metal that is considered to be stably present as a chloro complex in an aqueous hydrochloric acid solution is preferable. The concentration of the aqueous hydrochloric acid solution is usually preferably 1 to 6N.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited thereto.

<Viscosity average degree of polymerization>
For PVA saponified to a degree of polymerization of 99.5 mol% or more, using the ultimate viscosity [η] (liter / g) measured at 30 ° C. in water, according to the following formula, in Examples and Comparative Examples. The viscosity average degree of polymerization (P) of PVA was determined.
P = ([η] × 10 ⁴ ^/ 8.29) ^{(1 / 0.62)}

<Degree of Kenning>
The degree of saponification of PVA in Examples and Comparative Examples was measured according to JIS-K6726.

<Acid resistance: Mass reduction rate during acid immersion>
500 mg of the metal adsorption fiber obtained in Examples and Comparative Examples was immersed in 50 mL of a 3N-hydrochloric acid aqueous solution at 40 ° C. and stirred for 1 hour. Then, the metal adsorption fiber was taken out and immersed in a 0.1N-sodium hydroxide aqueous solution to neutralize it. The neutralized metal-adsorbed fibers are thoroughly washed with distilled water and then dried in an oven at 105 ° C. for 4 hours. Let B (mg) be the mass of the metal-adsorbed fiber after drying. The mass reduction rate is calculated from the following formula.
Weight reduction rate during acid immersion = (500-B) / 500 × 100 (mass%)

<Amount of metal (platinum) adsorbed>
100 mg of the metal-adsorbed fiber obtained in Examples and Comparative Examples was put into 100 mL of 3N-hydrochloric acid at 20 ° C. containing platinum ions at a concentration of 100 mg / L, and the mixture was stirred for 5 to 60 minutes. Then, 1 mL of the solution was sampled and the metal concentration was measured by an ICP emission spectrometer (IRIS-AP manufactured by Japan Jarrel Ash). The metal concentration was A (mg / L), and the amount of metal adsorbed was determined by the following formula.
Metal adsorption amount per 1 g of sample = 100-A (mg / g) <Metal adsorption amount during acid immersion>

<Diameter of island phase>
The metal adsorption fiber after the platinum adsorption test was immersed in a 1 mol / L sodium hydroxide aqueous solution for 10 minutes, and then washed with pure water. After cutting the washed metal adsorption fiber with a razor blade, the cross section was observed with a scanning electron microscope. Specifically, the major axis was measured for 10 island phases, and the average value was taken as the diameter of the island phase. When the island phases were aggregated, the major axis was measured by using the aggregated island phases as the same particles.

[Example 1]
A water-containing chip of polyvinyl alcohol (PVA, viscosity average degree of polymerization 1700, saponification degree 99 mol%) was prepared, and the water-containing chip was put into an extruder to dissolve PVA. Next, the obtained PVA aqueous solution and polyethyleneimine (weight average molecular weight 10000, Nippon Shokubai Co., Ltd., "Epomin SP-200") aqueous solution were mixed so that the mass ratio of PVA and polyethyleneimine was 68/32. .. The undiluted solution obtained by mixing was extruded into dry air at 70 ° C. from a nozzle having 70 holes, dried, and then wound up. That is, fibers were obtained by using a dry spinning method. Next, an aqueous solution of polyethylene glycol diglycidyl ether (manufactured by Nagase ChemteX Corporation, "Denacol EX-820") having a concentration of 20% by mass, which is an epoxy compound, is applied to the obtained fibers, and the fibers are dried at 150 ° C. for 1 hour. Crosslinking treatment was carried out in the above to obtain metal adsorption fibers. The metal-adsorbed fiber had a sea-island structure in which polyvinyl alcohol formed a sea phase and polyethyleneimine formed an island phase, and the average diameter of the island phase was 1.9 μm.

[Example 2]
Metal adsorption fibers were obtained by the same method as in Example 1 except that the mass ratio of PVA and polyethyleneimine was 60/40. The metal-adsorbed fiber had a sea-island structure in which polyvinyl alcohol formed a sea phase and polyethyleneimine formed an island phase, and the average diameter of the island phase was 0.59 μm.

[Example 3]
Metal adsorption fibers were obtained by the same method as in Example 2 except that the concentration of the aqueous polyethylene glycol diglycidyl ether solution was 10% by mass. The metal-adsorbed fiber had a sea-island structure in which polyvinyl alcohol formed a sea phase and polyethyleneimine formed an island phase, and the average diameter of the island phases was 8 μm.

[Comparative Example 1]
Polyvinyl alcohol (PVA, viscosity average degree of polymerization 1700, saponification degree 99 mol%) and polyallylamine (weight average molecular weight 15,000, manufactured by Nitto Spinning Co., Ltd., "PAA-15C"), PVA 15% by mass, poly Allylamine was dissolved in water to a concentration of 2% by mass (polymer composition: PVA 88% by mass, polyallylamine 12% by mass). The stock solution obtained by mixing was wet-spun from a nozzle having 1000 holes into a saturated sodium sulfate bath at 40 ° C., dried, and then wound to obtain fibers. Next, the obtained fibers were immersed in a solution of 5% by mass of glutaraldehyde, 1% by mass of sulfuric acid, and 20% by mass of sodium sulfate, and heat-treated at 60 ° C. for 15 minutes to carry out cross-linking treatment to obtain metal-adsorbed fibers. It was.

[Comparative Example 2]
Polyvinyl alcohol (PVA, viscosity average degree of polymerization 1700, saponification degree 99 mol%) and polyallylamine (weight average molecular weight 15,000, manufactured by Nitto Spinning Co., Ltd., "PAA-15C"), PVA 50% by mass, poly Allylamine was dissolved in water to a concentration of 50% by mass (polymer composition: PVA 50% by mass, polyallylamine 50% by mass). The undiluted solution obtained by mixing was wet-spun from a nozzle having 1000 holes into a saturated sodium sulfate bath at 40 ° C., but thread formation was not possible and a fibrous metal adsorbent was not obtained.

[Comparative Example 3]
Metal adsorption fibers were obtained by the same method as in Example 2 except that the cross-linking treatment was not carried out.

[Comparative Example 4]
Metal adsorption fibers were obtained in the same manner as in Example 1 except that the mass ratio of PVA and polyethyleneimine was 80/20.

[Comparative Example 5]
An ethylene-vinyl alcohol copolymer (ethylene content 44 mol%, manufactured by Kuraray Co., Ltd., "EVAL E-105B") was melt-kneaded at 180 ° C. using a laboplast mill, and polyethyleneimine (weight average molecular weight 10000,) "Epomin SP-200") manufactured by Nippon Catalyst Co., Ltd. is added in a predetermined amount so that the content of polyethyleneimine is 40% by mass and the content of ethylene-vinyl alcohol copolymer is 60% by mass. Polymers were mixed. After kneading for a predetermined time, the resin composition obtained by kneading was taken out, and the resin composition was pulverized by a pulverizer to obtain particulate matter having a particle diameter of 0.3 to 0.5 mm. Next, this particulate matter was crosslinked in an aqueous solution at 25 ° C. having a concentration of 5% by mass of ethylene glycol diglycidyl ether (“Denacol EX-810” manufactured by Nagase ChemteX Corporation) which is an epoxy compound. In this way, a particulate metal adsorbent was obtained. The metal adsorbent had a sea-island structure in which an ethylene-vinyl alcohol copolymer formed a sea phase and polyethyleneimine formed an island phase, and the average diameter of the island phases was 34 μm.

[Comparative Example 6]
Even if a mixed solution containing 75% by mass of ethylene-vinyl alcohol copolymer (EVOH) and 25% by mass of polyethyleneimine is subjected to melt spinning, the desired metal adsorption fiber can be obtained by bleeding out of polyethyleneimine. could not.

[Comparative Example 7]
Metal adsorption fibers were obtained by the same method as in Example 2 except that the concentration of the aqueous polyethylene glycol diglycidyl ether solution was 5% by mass.

The metal adsorption fibers obtained in Examples 1 to 3 and Comparative Examples 1, 3 to 5 and 7 were subjected to acid resistance evaluation and platinum adsorption test, and the weight loss rate during acid immersion and platinum adsorption during 60 minutes immersion were carried out. The amount was calculated. For the metal-adsorbed fibers obtained in Examples 1 to 3 and Comparative Example 5, the amount of platinum adsorbed during immersion for 5 minutes and 10 minutes was also calculated.

As shown in Table 1, the metal-adsorbed fibers obtained in Examples 2 and 3 had a larger amount of platinum adsorbed when immersed for 60 minutes than in Comparative Examples 1 to 7, and 5 minutes as compared with Comparative Example 5. It was also found that the amount of platinum adsorbed during immersion for 10 minutes was large. Further, the metal adsorption fibers obtained in Example 1 have a larger amount of platinum adsorbed when immersed for 60 minutes than in Comparative Examples 1 to 4 and 7, and in comparison with Comparative Example 5, platinum adsorbed when immersed for 60 minutes. The amount was about the same, but it was found that the amount of platinum adsorbed during immersion for 5 minutes and 10 minutes was large. Therefore, it was confirmed that the metal adsorption fiber of the present invention is excellent in metal adsorption property and metal adsorption rate.

Claims

A metal-adsorbing fiber containing polyvinyl alcohol and an amine-based polymer.
The content of the amine-based polymer is 30% by mass or more with respect to the mass of the metal adsorbing fiber, and the mass reduction rate when immersed in 3N hydrochloric acid at 40 ° C. for 1 hour is 5% by mass or less. fiber.
The metal adsorption fiber according to claim 1, wherein the amine-based polymer is at least one selected from the group consisting of polyvinylamine, polyallylamine, polyalkyleneamine, polyethyleneimine, polydiallyl quaternary ammonium, and salts thereof.
The metal-adsorbing fiber according to claim 1 or 2, wherein the amine-based polymer has a weight average molecular weight of 5000 to 100,000.
Polyvinyl alcohol and amine-based polymers have a crosslinked structure, and the crosslinked structure contains two or more functional groups of at least one selected from the group consisting of an epoxy group, an isocyanate group, a vinyl group, and an aldehyde group. The metal-adsorbing fiber according to any one of claims 1 to 3, which is a derived structure.
The invention according to any one of claims 1 to 4, wherein polyvinyl alcohol has a sea-island structure in which an amine-based polymer constitutes an island phase, and the island phase has an average diameter of 0.1 to 30 μm. Metal adsorption fiber.
A claim comprising a step (1) of obtaining a spinning stock solution containing polyvinyl alcohol, an amine-based polymer and a solvent, and a step (2) of extruding the spinning stock solution into dry air and removing the solvent to form fibers. The method for producing a metal adsorbing fiber according to any one of 1 to 5.
The manufacturing method according to claim 6, further comprising a step (3) of subjecting the fibers formed in the step (2) to a cross-linking treatment.