Method for recovering and removing metals from water

Abstract

To provide a method for recovering and removing metals from water, such as wastewater and other waste fluid, specifically a method for recovering and removing metals efficiently through simple operations and at a relatively low cost.SOLUTION: Applying alkaline treatment after adding a polyvinylamine-based water-soluble polymer to water enables simple and efficient removal and recovery of metals. Preferably, an alkaline agent is added to water, achieving a pH level of 7 to 12 through alkaline treatment. Preferably, following the alkaline treatment, a polymer flocculant is added to enhance the treatment effect.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for recovering and removing metals in water, and more particularly to a method for recovering and removing metals in water by co-precipitation with a polymer. [Background technology]

[0002] In order to comply with environmental regulations regarding heavy metal ions in various industrial wastewater and waste liquids, strict discharge standards have been set, and various technologies have been proposed to remove heavy metal ions from wastewater and waste liquids. For example, Patent Document 1 discloses a method of combining an electrolytic deposition operation and an ion exchange operation as an apparatus for treating wastewater containing metal ions, particularly wastewater containing copper ions from a semiconductor device manufacturing process. In this case, specific equipment and operations are required, and it is difficult to apply this method to general wastewater. On the other hand, the demand for metal resources has been increasing in recent years. In particular, precious metals and heavy metals are used as essential materials in various fields. However, due to the small reserves and limited supply, there is a demand for the recovery of metals from wastewater. Wet recovery methods for rare metals and other metals in water generally involve the addition of reducing agents or the use of chelating resins. Patent Document 2 discloses a method of recovering platinum group elements and selenium by precipitating selenium slag by adding a reducing agent to a liquid containing platinum group elements, selenium, and tellurium. However, the flocs formed by adding a reducing agent are small, making it difficult to recover elements with a concentration of less than a few ppm. Patent Document 3 discloses a method for adsorbing and separating metal ions in water by using polyvinylamine crosslinked polymer particles as a chelating resin. However, such a chelating resin requires a high investment in equipment, making it difficult to make a profit. In addition, a contact time of several hours is required to adsorb a certain amount. Therefore, there is a demand for a relatively inexpensive and efficient method for recovering metals. For example, Patent Document 4 discloses a method for recovering precious metals in which a specific cationic polymer compound is added to a liquid containing the precious metal under acidic conditions to form aggregates of the precious metal, which are then separated and recovered. The use of the polymer makes it possible to selectively recover the precious metals in the liquid. However, with this method, the formed flocs are brittle and difficult to precipitate, making it difficult to recover metals at levels below a few ppm and to remove them from the treated water. Therefore, there is a demand for a method for recovering metals from water efficiently with simpler operations.

[0003] [Patent Document 1] Special Publication No. 2006-510481 [Patent Document 2] JP 2015-193888 A [Patent Document 3] JP 2017-070909 A [Patent Document 4] JP 2012-097349 A Summary of the Invention [Problem to be solved by the invention]

[0004] The object of the present invention is to provide a method for recovering and removing metals from water such as wastewater or waste liquid, and more particularly to a method for recovering and removing metals efficiently at a relatively low cost and with a simple operation. [Means for solving the problem]

[0005] As a result of intensive research conducted by the present inventors in order to solve the above-mentioned problems, they discovered that the above-mentioned problems can be solved by adding a polyvinylamine-based water-soluble polymer to water, followed by alkali treatment, to form flocs and co-precipitate the metals to be collected together with the flocs, thereby arriving at the present invention. Effect of the Invention

[0006] Metals can be efficiently recovered and removed by a simple procedure of adding the polyvinylamine-based water-soluble polymer of the present invention to water and treating the water with alkali. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] The polyvinylamine-based water-soluble polymer in the present invention may be polyvinylamine. Polyvinylamine is a vinyl polymer containing a primary amino group, which has the simplest structure, and can be produced by a conventional method, such as hydrolyzing a polymer containing N-vinyl carboxylic acid amide, N-vinyl formamide, N-vinyl acetamide, or the like as an essential monomer with an acid or base, hydrolyzing a polymer of N-vinyl-Ot-butyl carbamate, or subjecting polyacrylamide to the Hofmann reaction in the presence of a hypohalous acid and an alkali metal hydroxide.

[0008] For example, Japanese Patent Application Laid-Open No. 6-65329 discloses a method for producing polyvinylamine, which can be easily obtained by modifying the formyl group in an N-vinylformamide polymer or copolymer. That is, it is produced by polymerizing a mixture of N-vinylformamide and another copolymerizable monomer in a molar ratio of usually 20:80 to 100:0, preferably 40:60 to 100:0, in the presence of a radical polymerization initiator.

[0009] Since the formyl group is hydrolyzed by acid or alkali, a part of the monomer to be copolymerized is also hydrolyzed, and a carboxyl group is often generated. Therefore, when copolymerizing, it is convenient when acrylonitrile, etc. are copolymerized. Other examples include acrylamide, methyl acrylate, ethyl acrylate, n-propyl acrylate, 2-hydroxyethyl acrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, sec-butyl methacrylate, and 2-hydroxyethyl methacrylate. Since these monomers generate anionic groups, the molar ratio in the copolymer is preferably less than 20 mol%.

[0010] As a polymerization method for producing the above-mentioned N-vinylformamide copolymer, any of bulk polymerization, solution polymerization using water and various organic solvents, and precipitation polymerization can be used. As a preferred polymerization solvent, water, an organic solvent having a boiling point of 60 to 110°C, and a mixture of water and a hydrophilic organic solvent having a boiling point of 60 to 110°C are used. When polymerizing a monomer in a solution state, the concentration of the monomer, the polymerization method, and the shape of the polymerization reactor are appropriately selected in consideration of the molecular weight of the target polymer and the heat generated by polymerization, and the polymerization is carried out, for example, by the following method. That is, examples include a method in which polymerization is started in a solution state with a monomer concentration of 5 to 20% by mass to obtain a polymer in the form of a solution or precipitate, a method in which polymerization is started under conditions of a monomer concentration of 20 to 60% by mass to obtain a gel-like substance or precipitate containing a polymer and a solvent, and a method in which a solution with a monomer concentration of 20 to 60% by mass is polymerized in an emulsion or dispersion state in a solvent in which the monomer does not dissolve.

[0011] As the radical polymerization initiator, any of the general initiators usually used for the polymerization of water-soluble or hydrophilic monomers is used, but in order to obtain a polymer with a good yield, an azo compound is preferred. When water is used as the polymerization solvent, a water-soluble azo compound is preferred, and examples thereof include the hydrochloride and acetate salt of 2,2'-azobis-2-amidinopropane, the sodium salt of 4,4'-azobis-4-cyanovaleric acid, and the hydrochloride and sulfate salt of azobis-N,N'-dimethyleneisobutylamidine. The amount of these polymerization initiators used is usually in the range of 0.01 to 1% by mass relative to the mass of the monomer. The polymerization reaction is generally carried out at a temperature of 20 to 100°C under an inert gas stream.

[0012] The obtained N-vinylformamide copolymer can be used as it is in the form of a solution or dispersion, or can be diluted, or can be dehydrated or dried by a known method to form a powder, and then modified to form a polyvinylamine.

[0013] The method disclosed in JP 2012-153747 A can produce a high molecular weight polyvinylamine with excellent storage stability. First, an N-vinyl carboxylic acid amide monomer is mixed with water, an oily substance made of a water-immiscible hydrocarbon, and a surfactant having an HLB in an amount effective for forming a water-in-oil emulsion, and the mixture is stirred vigorously to form a water-in-oil emulsion, and then polymerized to synthesize an N-vinyl carboxylic acid amide polymer.

[0014] The water-in-oil emulsion of the N-vinyl carboxylic acid amide polymer can then be hydrolyzed with an acid or a base. An appropriate selection can be made depending on the purpose, and when it is necessary to use the polymer in the presence of an acid, it is preferable to carry out the hydrolysis with an acid. In the case of hydrolysis with an acid, formic acid is generated as a by-product, which corrodes the production tank or storage tank, so it is preferable to carry out the hydrolysis with a base. The acid amide group is converted to an amino group by hydrolysis, thereby cationizing the polymer, and the hydrolysis rate is appropriately set depending on the purpose of use.

[0015] Further, the polyvinylamine-based water-soluble polymer in the present invention may be a copolymer of a vinylamine unit with one or more monomers selected from a cationic monomer, an anionic monomer, and a nonionic monomer.

[0016] Examples of the cationic monomer used in the copolymer of a vinylamine unit and one or more selected from a cationic monomer, an anionic monomer, and a nonionic monomer include dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, dimethylaminopropyl (meth)acrylamide, diethylaminopropyl (meth)acrylamide, and salts thereof, (meth)acryloyloxyethyl trimethylammonium chloride, (meth)acryloyloxyethyl dimethylbenzyl ammonium chloride, (meth)acryloylaminopropyl trimethylammonium chloride, (meth)acryloylaminopropyl dimethylbenzyl ammonium chloride, (meth)acryloyloxy 2-hydroxypropyl trimethylammonium chloride, and the like. The anionic monomers include (meth)acrylic acid, itaconic acid, 2-acrylamido-2-methylsulfonic acid, maleic acid, and salts thereof. Examples of nonionic monomers include (meth)acrylamide, N,N'-dimethylacrylamide, vinyl acetate, acrylonitrile, methyl acrylate, 2-hydroxyethyl (meth)acrylate, diacetone acrylamide, N-vinylpyrrolidone, N-vinylformamide, N-vinylacetamide, and acryloylmorpholine.

[0017] In the polyvinylamine-based water-soluble polymer of the present invention, the ratio of vinylamine units (degree of amination) in the polymer to the entire constitution is in the range of 10 to 100 mol %, and preferably 20 to 100 mol %.

[0018] The product form of the polyvinylamine-based water-soluble polymer in the present invention is not particularly limited, and can be produced by a known method. For example, after polymerization by aqueous solution polymerization, water-in-oil emulsion polymerization, oil-in-water emulsion polymerization, dispersion polymerization in salt water, etc., it can be made into any product form such as an aqueous solution, a dispersion in salt water, a water-in-oil emulsion, or a powder. In addition, a crosslinkable monomer may be used as a structure modifier during or after polymerization when producing the polyvinylamine-based water-soluble polymer in the present invention.

[0019] The viscosity of the salt solution can be used as an index of molecular weight for the polyvinylamine-based water-soluble polymer in the present invention. The viscosity of the salt solution is the viscosity of a 4% by mass saline solution (SLV) measured with a rotational viscometer at 25°C when the polymer is completely dissolved to a polymer concentration of 0.5% by mass. The viscosity of the salt solution is preferably in the range of 2 to 20 mPa s. The B-type viscometer used is a Tokyo Keiki B8M or the like, and the value is measured with a No. 1 rotor at 60 rpm.

[0020] The water that is the subject of this invention can be applied to various types of water that contains metals, such as various industrial wastewater and cleaning wastewater from metal processing factories, plating factories, chemical factories, machine factories, electrical / electronic factories, automobile factories, etc., sewage and domestic wastewater from homes, groundwater, etc.

[0021] Target metals include precious metals such as palladium, ruthenium, rhodium, osmium, iridium, platinum, gold, and platinum, and heavy metals such as titanium, iron, cobalt, nickel, copper, zinc, gallium, zirconium, and niobium, and two or more of these may be contained. The metal concentration in the water is preferably in the range of 0.1 to 200 ppm, although even a dilute concentration of 0.1 to 100 ppm is effective and particularly preferred.

[0022] The polyvinylamine-based water-soluble polymer of the present invention is added to water containing a metal, and then subjected to an alkali treatment. An alkaline agent is used for the alkali treatment. Examples of the alkaline agent include slaked lime (calcium hydroxide), sodium hydroxide, sodium carbonate, potassium carbonate, potassium hydroxide, and the like. Two or more of these can be used in combination. It is preferable to adjust the pH to 7 or higher by the alkaline treatment. In order to achieve a greater effect, a pH of 8 or higher is preferable. Even if the pH exceeds 12, it is difficult to obtain a greater treatment effect than that, and therefore a pH of 11 or lower is preferable. The alkaline agent can also be added simultaneously with the polymer.

[0023] The polyvinylamine-based water-soluble polymer of the present invention is characterized by having a high density of primary amino groups. In an acidic state, the amino groups in the polymer are protonated and exist as ammonium ions. When they are converted to amino groups due to equilibrium shift accompanying alkalization of the pH, they form coordinate bonds with heavy metal ions present in the system. When the system is further alkalized, the heavy metals form hydroxides and become insoluble. At this time, if coordinate bonds are formed by the amino groups due to the addition of the polymer of the present invention, floc formation by the polymer occurs simultaneously with insolubilization by the hydroxide, and metals can be efficiently recovered. In addition to efficiently recovering metal ions, floc formation by the polymer also contributes to growing tiny metal hydroxide crystals into giant flocs and improving filterability. In addition, amino groups can coordinate to metal ions remaining in the solution in small amounts, making it possible to process metal ions in the solution that were previously unrecoverable with little loss. The present invention differs from the prior art in that a polymer having a high density of primary amino groups is added prior to the alkaline precipitation process, making it possible to efficiently recover metals.

[0024] The polyvinylamine-based water-soluble polymer in the present invention may be added in its original state, or may be dissolved and diluted with water to an arbitrary concentration before being added to the target water. When dissolved, a dissolution concentration of 0.05 to 1.0 mass% is generally applied. The addition rate relative to the amount of water is 0.5 to 5000 ppm, preferably 1 to 1000 ppm, depending on the properties of the target water and the concentration of the target metal.

[0025] The polyvinylamine-based water-soluble polymer of the present invention is added to water, and after alkali treatment, a polymer flocculant is added to promote the treatment effect. By recovering the metals, the metal content of the treated water is reduced, and the metals in the treated water can be removed. As the polymer flocculant, a general acrylamide-based polymer flocculant or amidine-based polymer flocculant can be used. Among these, acrylamide-based polymer flocculants are preferred, and anionic polyacrylamide is particularly preferred.

[0026] Methods for efficiently separating the metals coprecipitated as flocs from water by the method of the present invention include filtration, decantation, centrifugation, and adsorption onto nonwoven fabric, etc., but filtration or decantation is preferred from the viewpoint of ease of handling. The metals can also be recovered by any treatment such as incineration or acid treatment of the separated material. EXAMPLES

[0027] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the following examples as long as it does not depart from the gist of the present invention.

[0028] (Various water-soluble polymer samples) Polyvinylamine samples A to C having vinylamine structural units (amination degree) of 40 to 80 mol% were produced as polyvinylamine-based water-soluble polymer samples of the present invention by a conventional method. Their compositions and physical properties are shown in Table 1. In addition, water-soluble polymer samples outside the scope of the present invention that are widely used for wastewater treatment were prepared or prepared. Their compositions and physical properties are shown in Table 2.

[0029] (Table 1) TIFF2025012179000001.tif3181Form;P:Powder Saline solution viscosity: Viscosity (mPa s) measured at 25°C when the polymer is dissolved in 4% by mass saline solution to a concentration of 0.5% by mass.

[0030] (Table 2) TIFF2025012179000002.tif3991 form;AQ:Aqueous polymer Saline solution viscosity: Viscosity (mPa s) measured at 25°C when the polymer is dissolved in 4% by mass saline solution to a concentration of 0.5% by mass.

[0031] Example 1 A flocculation test was carried out using a jar tester on wastewater from cleaning printed circuit boards (pH 2.4, SS content 3 mg / L) generated from an electronic parts manufacturing factory. 100 mL of wastewater was collected in a poly beaker, and a 0.2 mass% solution of polyvinylamine sample A in Table 1 was added to the wastewater at 25 ppm, then added at 150 rpm for 60 seconds, and a specified amount of calcium hydroxide was added (relative to the wastewater volume) to adjust the pH to 11. A 0.2 mass% solution of anionic polyacrylamide polymer flocculant (powder, acrylamide / acrylic acid = 80 / 20 mol% copolymer, weight average molecular weight 12 million, hereinafter referred to as A-PAM) was added to the wastewater at 4 ppm, and the mixture was stirred at 150 rpm for 30 seconds, 80 rpm for 30 seconds, and 40 rpm for 30 seconds, and the floc diameter was measured. The supernatant liquid was left to stand for 3 minutes and then quantified by atomic absorption spectrometry to measure the copper concentration. Similar tests were also carried out by changing the type of polyvinylamine sample, the pH after alkali treatment, and the addition rate of polymer flocculant. The results are shown in Table 3.

[0032] Comparative Example 1 Using the same wastewater as in Example 1, tests similar to those in Example 1 were carried out using the water-soluble polymer samples or polyferric sulfate shown in Table 2. The results are shown in Table 3.

[0033] (Table 3) TIFF2025012179000003.tif10391 Polymer flocculant; A-PAM: anionic polyacrylamide

[0034] In the method of the present invention, in which the polyvinylamine-based water-soluble polymer is added and then alkali treatment is performed, the copper ion concentration in the supernatant is lower than that in the comparative example, and it is found that the metal trapping effect in the formed flocs is high. In addition, the trapping effect tends to be greater when the alkali treatment pH is set to 10.

[0035] (Example 2) Copper recovery test An aqueous solution with a copper concentration of 100 ppm was prepared using copper sulfate. 7.5 g (50 ppm relative to the liquid) of polyvinylamine sample A dissolved at 0.1% by mass was added to 150 g of copper aqueous solution adjusted to pH 5 using sodium hydroxide and hydrochloric acid, and the mixture was stirred at 400 rpm for 20 minutes. 0.1 N sodium hydroxide was added dropwise to adjust the pH to 9, and a polymer precipitate was generated. 0.3 g of anionic polyacrylamide polymer flocculant (A-PAM) dissolved at 0.1% by mass was added, and the mixture was stirred at 400 rpm for 10 minutes. The resulting copper-containing precipitate was filtered through a 40 mesh, and the filtrate was quantified by atomic absorption spectrometry to calculate the copper recovery rate. The results are shown in Table 4 as Example 2. A similar test was also carried out without using the polyvinylamine sample, and the results are shown in Table 4 as Comparative Example 2.

[0036] (Example 3) Nickel recovery test An aqueous solution with a nickel concentration of 6 ppm was prepared using nickel nitrate. 7.5 g (50 ppm relative to the liquid) of polyvinylamine sample A dissolved at 0.1% by mass was added to 150 g of an aqueous nickel solution adjusted to pH 3 using sodium hydroxide and hydrochloric acid, and the mixture was stirred at 400 rpm for 20 minutes. 0.1 N sodium hydroxide was added dropwise to adjust the pH to 11, and a polymer precipitate was generated. 0.3 g of an anionic polyacrylamide polymer flocculant (A-PAM) dissolved at 0.1% by mass was added, and the mixture was stirred at 400 rpm for 10 minutes. The resulting nickel-containing polymer precipitate was filtered through a 40 mesh, and the filtrate was quantified by atomic absorption spectrometry to calculate the recovery rate of nickel. The results are shown in Table 4 as Example 3. The results are shown in Table 4 as Comparative Example 3.

[0037] (Example 4) Iron (II) recovery test An aqueous solution with an iron concentration of 10 ppm was prepared using iron (II) nitrate. 7.5 g (50 ppm relative to the liquid) of polyvinylamine sample A dissolved at 0.1% by mass was added to 150 g of an aqueous iron solution adjusted to pH 3 using sodium hydroxide and hydrochloric acid, and the mixture was stirred at 400 rpm for 20 minutes. 0.1 N sodium hydroxide was added dropwise to adjust the pH to 11, and a polymer precipitate was generated. 0.3 g of anionic polyacrylamide polymer flocculant (A-PAM) dissolved at 0.1% by mass was added, and the mixture was stirred at 400 rpm for 10 minutes. The resulting iron-containing polymer precipitate was filtered through a 40 mesh filter, and the filtrate was quantified by atomic absorption spectrometry to calculate the recovery rate of iron (II). The results are shown in Table 4 as Example 4. A similar test was also carried out without using the polyvinylamine sample, and the results are shown in Table 4 as Comparative Example 4.

[0038] (Table 4) TIFF2025012179000004.tif3590 Polymer flocculant; A-PAM: Anionic polyacrylamide

[0039] It was confirmed that by adding the polyvinylamine-based water-soluble polymer of the present invention to water containing metals and treating it with alkali, a high recovery rate of the metals was achieved, and the metals could be recovered simply and efficiently.

Claims

1. A method for recovering and removing metals from water, comprising adding a water-soluble polyvinylamine polymer to water containing the metals and then subjecting the water to an alkali treatment.

2. 2. The method for recovering and removing metals in water according to claim 1, wherein the water is treated with an alkali to a pH of 7 to 12 by adding an alkaline agent.

3. 3. The method for recovering and removing metals in water according to claim 1 or 2, further comprising the step of adding a polymer flocculant after the alkali treatment.

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