Method for recovering precious metals and method for producing adsorbent having precious metals adsorbed thereon

Abstract

The present invention provides a method for recovering a noble metal, with which it is possible to highly selectively recover a noble metal from a liquid that contains the noble metal and a base metal. This method for recovering a noble metal recovers a noble metal from a liquid that contains the noble metal and a base metal with use of an adsorbent. The method uses particles of a polyarylene sulfide resin as the adsorbent, and includes: a preparation step for preparing a liquid to be treated that contains the liquid and has a pH of 4 or less at 23° C; and a contact step for bringing the liquid to be treated and the adsorbent into contact with each other.

Description

[Technical Field]

[0001] The present invention relates to a method for recovering precious metals and a method for producing an adsorbent having precious metals adsorbed thereon. [Background technology]

[0002] Plastics are used in a wide range of fields due to their advantages such as processability and light weight. However, such plastics are inferior to metals in terms of physical properties such as chemical resistance, weather resistance, abrasion resistance, and rigidity. In view of this situation, a technique for plating the surface of plastics has been known.

[0003] Electroless plating is one method for plating non-conductive materials such as plastics. In this electroless plating method, precious metals such as palladium are widely used as catalysts. However, these precious metals have recently been facing problems such as rising prices and large price fluctuations. Therefore, there is a demand for recycling precious metals contained in plating wastewater.

[0004] Various methods such as precipitation and extraction can be used to recycle and recover precious metals contained in plating wastewater. In particular, when the concentration of precious metals in the wastewater is low, adsorption methods are widely used from the viewpoint of recovery efficiency.

[0005] Examples of adsorbents used in recycling and recovering precious metals by adsorption include activated carbon, ion exchange resins, and chelating resins. Specifically, Patent Document 1 discloses a method for recovering precious metals from a recovery solution of a Sn-containing precious metal catalyst by activated carbon adsorption. Patent Document 2 discloses contacting a solution containing palladium and platinum with an iminodiacetic acid-type chelating resin, and adsorbing the palladium and platinum in the solution onto the iminodiacetic acid-type chelating resin. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2019-023356 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-183228 Summary of the Invention [Problem to be solved by the invention]

[0007] In the electroless plating method using palladium as a catalyst as described above, a colloidal catalyst of palladium and tin is actually used in many cases. In this case, a large amount of tin and a small amount of palladium may be present in the plating wastewater. Therefore, it is desired to be able to selectively recover palladium, which is a noble metal, from such plating wastewater in comparison with tin, which is a base metal.

[0008] In this regard, the activated carbon described above physically adsorbs the target substance in its pores, so it can adsorb a large amount, but on the other hand, it has a problem in terms of selectively recovering the target metal. Moreover, in order to extract the metal recovered by the activated carbon, the activated carbon must be calcined after adsorption, which also has a problem in terms of environmental load.

[0009] The ion exchange resins and chelating resins described above are thought to be able to adsorb target metals selectively to some extent due to the ion exchange or chelating effect of the functional groups attached to the polymer chains, but the selectivity is not sufficient.

[0010] Therefore, an object of the present invention is to provide a method for recovering precious metals that can recover precious metals with high selectivity from a liquid containing precious metals and base metals. Another object of the present invention is to provide a method for producing an adsorbent having a noble metal adsorbed thereon, which can also be obtained by the above-mentioned method for recovering noble metals. [Means for solving the problem]

[0011] As a result of extensive research, the inventors have found that adjusting the liquid containing precious metals and base metals as specified and using a specified adsorbent is effective in solving the above problems. That is, the gist of the present invention is as follows.

[0012] [1] A method for recovering precious metals, comprising recovering precious metals from a liquid containing precious metals and base metals using an adsorbent, As the adsorbent, particles of polyarylene sulfide resin are used, a preparation step of preparing a liquid to be treated that contains the liquid and has a pH of 4 or less at 23°C; a contacting step of contacting the liquid to be treated with the adsorbent; A method for recovering precious metals, comprising:

[0013] [2] The method for recovering precious metals according to [1], wherein the precious metals include palladium.

[0014] [3] The method according to [1] or [2], wherein the liquid to be treated has a concentration of anions selected from chloride ions, nitrate ions, and sulfate ions of 0.05 mol / L or more.

[0015] [4] The recovery method according to [3], wherein the liquid to be treated has a chloride ion concentration of 0.05 mol / L or more.

[0016] [5] The recovery method according to any one of [1] to [4], wherein the concentration of the noble metal in the liquid to be treated is 0.1 to 100 ppm.

[0017] [6] The recovery method according to any one of [1] to [5], wherein the concentration of the base metal in the liquid to be treated is 10 to 1000 ppm.

[0018] [7] The recovery method according to [3], wherein the concentration of the anions in the liquid to be treated is 0.1 mol / L or more.

[0019] [8] The recovery method according to any one of [1] to [7], wherein the polyarylene sulfide resin has a zeta potential of −50 mV or more as measured by a streaming potential method under conditions of pH 7.8 to 8.2.

[0020] [9] The recovery method according to any one of [1] to [8], wherein the polyarylene sulfide resin particles have an average particle size of more than 10 μm.

[0021]

[10] The recovery method according to any one of [1] to [9], wherein the contacting step is carried out in the absence of a surfactant.

[0022]

[11] The recovery method according to any one of [1] to

[10] , wherein the contacting step is carried out by supplying the liquid to be treated to the immobilized adsorbent.

[0023]

[12] A method for producing an adsorbent having a precious metal adsorbed thereon, comprising: As the adsorbent, particles of polyarylene sulfide resin are used, a preparation step of preparing a liquid to be treated that contains a precious metal and has a pH of 4 or less at 23°C; a contacting step of contacting the liquid to be treated with the adsorbent; A method for producing an adsorbent having a precious metal adsorbed thereon, comprising:

[0024]

[13] The method according to

[12] , wherein the noble metal includes palladium.

[0025]

[14] The method according to

[12] or

[13] , wherein the liquid to be treated has a concentration of anions selected from chloride ions, nitrate ions, and sulfate ions of 0.05 mol / L or more.

[0026]

[15] The manufacturing method according to

[14] , wherein the liquid to be treated has a chloride ion concentration of 0.05 mol / L or more.

[0027]

[16] The method according to any one of

[12] to

[15] , wherein the polyarylene sulfide resin has a zeta potential of −50 mV or more as measured by a streaming potential method under conditions of pH 7.8 to 8.2.

[0028]

[17] The method according to any one of

[12] to

[16] , wherein the polyarylene sulfide resin particles have an average particle size of more than 10 μm.

[0029]

[18] The method according to any one of

[12] to

[17] , wherein the adsorbent to which the noble metal is adsorbed has 1 to 100 mg of noble metal adsorbed per 1 g of polyarylene sulfide resin. [Effects of the Invention]

[0030] According to the present invention, it is possible to provide a method for recovering precious metals, which is capable of recovering precious metals with high selectivity from a liquid containing precious metals and base metals. Furthermore, the present invention can provide a method for producing an adsorbent having a noble metal adsorbed thereon. DETAILED DESCRIPTION OF THE INVENTION

[0031] The following describes in detail an embodiment of the present invention (hereinafter sometimes referred to as the "present embodiment"); however, the present invention is not limited to the following description and can be implemented in various modifications within the scope of its gist.

[0032] (Method of recovering precious metals) The precious metal recovery method of this embodiment (hereinafter sometimes simply referred to as the "recovery method") is a method for recovering precious metals from a liquid containing precious metals and base metals using an adsorbent, and is characterized in that the adsorbent is polyarylene sulfide resin (hereinafter sometimes referred to as "PAS resin") particles (hereinafter sometimes referred to as "PAS particles"). The recovery method of this embodiment is also characterized in that it includes a preparation step of preparing a liquid to be treated that contains the liquid and has a pH of 4 or less at 23°C, and a contact step of contacting the liquid to be treated with the adsorbent.

[0033] The liquid to be treated (i.e., a liquid to be treated with a pH of 4 or less) is usually obtained by adding an acid to adjust the pH. In this case, a certain amount of anions will be present in the liquid to be treated due to dissociation of the acid. Furthermore, the lower the pH of the liquid to be treated that is adjusted, the greater the amount of anions in the liquid to be treated. In such a liquid to be treated, anions (ligands) bond with metals to form complexes.

[0034] Under such circumstances, the inventors have inferred through extensive experiments that base metals have stronger coordination forces with anions than noble metals and form stable complexes, and therefore are not adsorbed by weak coordination forces, and that sulfur sandwiched between benzene rings in PAS resin has a weaker coordination force than normal sulfur due to the influence of π-conjugation of the benzene rings, resulting in highly selective adsorption of only noble metals without adsorption of base metals. Furthermore, when the complexed precious and base metals are adsorbed onto the PAS resin, they undergo ligand exchange with sulfur (S) present in the PAS resin molecules. The compatibility between precious and base metals and sulfur, known as the HSAB rule, influences the ligand exchange. According to the HSAB rule, precious metals are classified as soft acids, while base metals are classified as relatively hard acids. On the other hand, sulfur is classified as a soft base, and has good compatibility with precious metals. Therefore, under anionic complex conditions, precious metals are more likely to form coordinate bonds with sulfur than base metals. This, combined with other factors, is thought to result in extremely high selectivity for precious metals.

[0035] These tendencies interact with each other, and when a liquid to be treated, whose pH has been adjusted as specified, is brought into contact with a PAS resin as an adsorbent, the PAS resin selectively adsorbs precious metals while suppressing the adsorption of base metals. It is also suggested that the selective adsorption of precious metals may be due in part to the unique crystallinity and / or molecular structure of the PAS resin.

[0036] As described above, according to the recovery method of this embodiment, it is possible to recover precious metals with high selectivity from a liquid containing precious metals and base metals.

[0037] In this specification, the term "metal" in noble metals, base metals, etc. includes not only the metal element but also a metal compound. That is, in this specification, metals such as noble metals and base metals may be in the state of the metal element, in the state of a metal compound, or both.

[0038] The recovery method of the present embodiment can be suitably employed, for example, when recovering precious metals from plating wastewater (which may generally contain precious metals typified by palladium (Pd) and base metals typified by tin (Sn)) generated in an electroless plating method.

[0039] The materials and the like used in the recovery method of this embodiment will be described below.

[0040] <Liquid containing precious metals and base metals> In the recovery method of this embodiment, a liquid containing precious metals and base metals (hereinafter, sometimes referred to as "recovery target liquid") is used as the target liquid from which precious metals are recovered. This target liquid is assumed to be plating wastewater generated in an electroless plating method, but is not limited to plating wastewater.

[0041] Examples of the liquid to be collected include aqueous liquids, which may contain organic substances. The liquid to be collected may also contain weak acids such as acetic acid, formic acid, carbonic acid, oxalic acid, and phosphoric acid, or strong acids such as hydrochloric acid, sulfuric acid, and nitric acid.

[0042] Examples of the noble metal include gold (Au), silver (Ag), platinum (Pt), ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), and platinum (Pt). The noble metals may be used alone or in combination of two or more.

[0043] The precious metal contained in the liquid to be recovered preferably includes palladium (Pd). Palladium has relatively good compatibility with adsorbents (PAS resins) in terms of adsorption properties, taking into account ion size. Therefore, by including palladium in the precious metal, it can be adsorbed to PAS particles with higher selectivity.

[0044] The concentration of the precious metal in the liquid to be recovered can be, for example, about 0.1 to 100 ppm.

[0045] Examples of the base metals include metals other than noble metals. Specific examples of the base metals include tin (Sn), cobalt (Co), nickel (Ni), zinc (Zn), iron (Fe), copper (Cu), and chromium (Cr). The base metals may be one type alone or a combination of two or more types. In particular, the liquid to be recovered may contain tin (Sn) as a base metal, such as plating wastewater.

[0046] The concentration of base metals in the liquid to be recovered can be, for example, approximately 10 to 5000 ppm.

[0047] The liquid to be recovered may contain components other than the noble metals and base metals.

[0048] <Adsorbent (PAS particles)> In the recovery method of this embodiment, particles (PAS particles) of polyarylene sulfide resin (PAS resin) are used as the adsorbent. Note that PAS particles refer to particles essentially composed of polyarylene sulfide resin or particulate polyarylene sulfide resin.

[0049] The PAS resin constituting the PAS particles has a resin structure in which a structure in which an aromatic ring and a sulfur atom are bonded is a repeating unit. Specifically, the PAS resin has the following formula (1):

[0050] [ka] (In the formula, R 1 and R 2 each independently represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, a nitro group, an amino group, a phenyl group, a methoxy group, or an ethoxy group.) and a structural moiety represented by the following formula (2):

[0051] [ka] and a resin structure having a repeating unit of a trifunctional structural moiety represented by the following formula: These structural moieties may be repeated periodically or randomly.

[0052] The proportion of the trifunctional structural moiety represented by formula (2) relative to the total number of moles of the trifunctional structural moiety and other structural moieties is preferably 0.001 mol % or more, more preferably 0.01 mol % or more, and is preferably 3 mol % or less, more preferably 1 mol % or less.

[0053] In the structural moiety represented by formula (1), R 1 and R 2are preferably hydrogen atoms from the viewpoint of the mechanical strength of the PAS resin. Specific examples of the structural moiety represented by formula (1) include a structural moiety bonding at the para position as represented by formula (3) below, a structural moiety bonding at the meta position as represented by formula (4) below, and a structural moiety bonding at the ortho position:

[0054] [ka]

[0055] In the resin structure of the PAS resin, the structural moiety represented by formula (1) preferably comprises 1 to 50 mol % of structural moieties bonded at the meta position and structural moieties bonded at the ortho position, with the remainder being structural moieties bonded at the para position. In this case, the adsorptivity can be further improved. In addition, in the resin structure of the PAS resin, the structural moiety represented by formula (1) preferably comprises only structural moieties bonded at the para position. In this case, the PAS resin is essentially a polyphenylene sulfide resin (PPS resin), which is preferable in terms of heat resistance and crystallinity and can be used under a wide range of temperature and pH conditions.

[0056] Furthermore, the PAS resin may contain, in addition to the structural moiety represented by formula (1) and the structural moiety represented by formula (2), the structural moiety represented by the following formulas (5) to (8):

[0057] [ka] In this case, the proportion of the structural units represented by formulas (5) to (8) can be 30 mol % or less relative to the total number of moles of the structural moiety represented by formula (1) and the structural moiety represented by formula (2). In particular, in this embodiment, from the viewpoint of the heat resistance and mechanical strength of the PAS resin, it is preferable that the proportion of the structural units represented by formulas (5) to (8) be 10 mol % or less relative to the total number of moles of the structural moiety represented by formula (1) and the structural moiety represented by formula (2). When the PAS resin has structural units represented by formulas (5) to (8), the bonding mode thereof may be random copolymerization or block copolymerization.

[0058] The PAS resin may also have naphthyl sulfide bonds in its molecular structure, but in this case, the proportion of such bonds relative to the total number of moles of other structural moieties is preferably 3 mol % or less, and more preferably 1 mol % or less.

[0059] PAS particles can be produced, for example, by synthesizing a PAS resin by polymerization and then performing post-treatment.

[0060] The synthesis method for PAS resin is not particularly limited, but examples thereof include a method (synthesis method 1) in which a dihalogenoaromatic compound is added in the presence of sulfur and sodium carbonate, and if necessary, a polyhalogenoaromatic compound or other copolymerization component is further added, followed by polymerization. Another example of a synthesis method for PAS resin is a method (synthesis method 2) in which a dihalogenoaromatic compound is added in a polar solvent in the presence of a sulfidizing agent, and if necessary, a polyhalogenoaromatic compound or other copolymerization component is further added, followed by polymerization. Another example of a synthesis method for PAS resin is a method (synthesis method 3) in which p-chlorothiophenol is self-condensed while, if necessary, other copolymerization components are added. Among these, synthesis method 2 is preferred because it is versatile.

[0061] Examples of the dihalogenoaromatic compound include p-dihalobenzene, m-dihalobenzene, 0-dihalobenzene, 2,5-dihalotoluene, 1,4-dihalonaphthalene, 1-methoxy-2,5-dihalobenzene, 4,4'-dihalobiphenyl, 3,5-dihalobenzoic acid, 2'4-dihalobenzoic acid, 2,5-dihalonitrobenzene, 2,4-dihalonitrobenzene, 2,4-dihaloanisole, p'p'-dihalodiphenyl ether, 4,4'-dihalobenzophenone, 4,4'-dihalodiphenyl sulfone, 4,4'-dihalodiphenyl sulfoxide, 4,4'-dihalodiphenyl sulfide, and compounds in which the aromatic ring of each of the above compounds has an alkyl group having 1 to 18 carbon atoms as a nuclear substituent.

[0062] Examples of the polyhalogeno aromatic compound include 1,2,3-trihalobenzene, 1,2,4-trihalobenzene, 1,3,5-trihalobenzene, 1,2,3,5-tetrahalobenzene, 1,2,4,5-tetrahalobenzene, and 1,4,6-trihalonaphthalene.

[0063] The halogen atoms contained in the above compounds are preferably chlorine atoms or bromine atoms.

[0064] Examples of post-treatment methods used after synthesizing PAS resin by polymerization include washing the by-products (unavoidable components resulting from the polymerization reaction) contained in the polymerization reaction mixture after synthesizing the PAS resin by polymerization. One example involves removing the solvent from the reaction mixture after the polymerization reaction to obtain a slurry containing crude PAS resin, then contacting the slurry with water and an oxygen-containing solvent having 1 to 3 carbon atoms to convert the crude PAS resin into porous particles (PAS particles). The resulting PAS particles are washed with carbonated water, filtered, and, if necessary, a dispersant is added to obtain a dispersion. While the above post-treatment can be followed by drying to obtain a powder, it is preferable to leave the PAS particle surfaces wet with the washing liquid or dispersion liquid without drying, as this provides superior performance at the start of use.

[0065] Examples of oxygen atom-containing solvents having 1 to 3 carbon atoms include methanol, ethanol, n-propyl alcohol, isopropyl alcohol, ethylene glycol, propylene glycol, 2-methoxyethanol, and acetone.

[0066] The PAS particles (adsorbent) preferably have no other components (except water and unavoidable components resulting from the polymerization reaction for synthesizing the PAS resin) present on their outer surfaces. Examples of such other components include known and commonly used additives such as surfactants (dispersants), colorants, antistatic agents, antioxidants, heat stabilizers, UV stabilizers, UV absorbers, foaming agents, flame retardants, flame retardant assistants, rust inhibitors, release agents, and coupling agents. In addition, "no other components are present" means that the proportion of PAS resin in the PAS particles, excluding the unavoidable components and water, is 95% by mass or more, preferably 99% by mass or more, more preferably 99.9% by mass or more, and may be 100% by mass.

[0067] It is preferable that the PAS particles (adsorbent) are free of any other components than the PAS resin (excluding water and unavoidable components resulting from the polymerization reaction used to synthesize the PAS resin). Examples of such other components include known and commonly used additives such as surfactants (dispersants), colorants, antistatic agents, antioxidants, heat stabilizers, UV stabilizers, UV absorbers, foaming agents, flame retardants, flame retardant assistants, rust inhibitors, release agents, and coupling agents. In addition, "no other components are present" means that the proportion of PAS resin in the PAS particles, excluding the unavoidable components and water, is 95% by mass or more, preferably 99% by mass or more, more preferably 99.9% by mass or more, and may be 100% by mass.

[0068] The inevitable components resulting from the polymerization reaction for synthesizing PAS resin include unreacted raw materials and by-products used in the polymerization reaction, particularly metal atom-containing components thereof, such as sulfidizing agents (alkali metal sulfides or alkali metal hydrosulfides), alkali metal halides, and compounds represented by the following formula (9):

[0069] [ka] (wherein n is 0 to 2, and Y 1 represents a halogen atom, and Y 2 represents a hydrogen atom or a halogen atom, and R 3 represents a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, or a cyclohexyl group; R 4 represents an alkylene group having 3 to 5 carbon atoms, and X represents an alkali metal atom.) and other carboxyalkylamino group-containing compounds.

[0070] The PAS resin constituting the PAS particles is not particularly limited, but preferably has a zeta potential of −50 mV or higher, more preferably −30 mV or higher, measured by a streaming potential method under conditions of pH 7.8 to 8.2. The zeta potential of PAS resin refers to the average value of three measurements of the zeta potential of the resin surface, measured by packing approximately 100 mg of PAS resin (especially PAS particles) into a cylindrical cell and measuring it three times using SurPASS3 (Anton Paar) in an electrolyte of 1 mmol / L KCl aqueous solution at a measurement temperature of 22 to 26° C. To stabilize the measured value, it is preferable to sieve the PAS particles and select those with a particle size of 0.05 to 1.0 mm.

[0071] The specific surface area of ​​the PAS resin constituting the PAS particles is not particularly limited, and may be, for example, 1 m 2 In particular, the specific surface area can be 10 m 2 / g or more. In this case, the PAS particles become porous, and the adsorption performance can be further improved. From the same viewpoint, the specific surface area of ​​the PAS resin is preferably 50 m 2 On the other hand, the upper limit of the specific surface area of ​​the PAS resin is not particularly limited, but from the viewpoint of the bulk density when packed into a container such as a column, it is preferable that the upper limit be 300 m 2 / g or less, 250m 2 / g or less, or 200m 2 / g or less is preferable. The specific surface area of ​​the PAS resin is the BET specific surface area measured after pre-treatment at 60°C under vacuum for 4 hours.

[0072] The average particle size of the PAS particles is preferably greater than 10 μm. In this case, handling and / or liquid transport when packed into a column or the like can be improved. Furthermore, from the viewpoint of maintaining good adsorption properties, the average particle size of the PAS particles is preferably 2 mm or less. From the same viewpoint, the average particle size of the PAS particles is more preferably 20 μm or more, even more preferably 30 μm or more, and more preferably 500 μm or less, even more preferably 300 μm or less. The average particle size of the PAS resin is the average particle size (D50) determined based on the particle size distribution measured in accordance with a conventional method using a laser diffraction / scattering particle size distribution analyzer.

[0073] Next, each step in the recovery method of this embodiment will be described.

[0074] <Preparation process> The preparation step is a step of preparing a liquid to be treated that includes a liquid containing precious metals and base metals (liquid to be recovered) and has a pH of 4 or less at 23° C. If the pH of the liquid to be recovered is already a predetermined value or less, the liquid to be recovered can be used as is as the liquid to be treated.

[0075] On the other hand, if the pH of the liquid to be recovered is higher than a predetermined value, an acid (or an aqueous solution containing the acid) can be added to the liquid to be recovered to adjust the pH, thereby obtaining a liquid to be treated. Examples of acids in this case include strong acids such as hydrochloric acid, sulfuric acid, and nitric acid, as well as weak acids such as acetic acid, formic acid, carbonic acid, oxalic acid, and phosphoric acid. The above acids may be used alone or in combination of two or more. The above acids may be inorganic or organic. Among these, hydrochloric acid, sulfuric acid, and nitric acid are preferred, with hydrochloric acid being more preferred. In this case, pH adjustment can be easily performed, and the selectivity of adsorption of precious metals onto the adsorbent can be effectively increased.

[0076] The treated liquid obtained as described above preferably has a concentration of anions (excluding hydroxide ions) generated by dissociation of the added acid of 0.05 mol / L or more, more preferably 0.1 mol / L or more. The anion of interest is preferably an anion selected from chloride ions, nitrate ions, and sulfate ions, with chloride ions being more preferred among the above. In these cases, the stability of the base metal complex in the treated liquid is further increased, making it more difficult for the base metal to be adsorbed onto the adsorbent in the subsequent contact step, thereby further improving the selectivity of the adsorption of the precious metal onto the adsorbent. On the other hand, the upper limit of the concentration of the anions is not particularly limited, but is preferably 5.0 mol / L or less in order to prevent the stability of the precious metal complex in the treated liquid from also increasing.

[0077] In this embodiment, the pH of the liquid to be treated may be 4 or less, and preferably 2 or less. In this case, the addition of a larger amount of acid to adjust the pH increases the stability of the complex of the base metal in the liquid to be treated, making it more difficult for the base metal to be adsorbed onto the adsorbent in the subsequent contact step, thereby further improving the selectivity of adsorption of the precious metal onto the adsorbent.

[0078] The concentration of the noble metal in the liquid to be treated may depend on the concentration of the noble metal in the liquid to be recovered, but can be approximately 0.1 to 100 ppm.

[0079] The concentration of base metals in the liquid to be treated may depend on the concentration of base metals in the liquid to be recovered, but can be approximately 10 to 5000 ppm.

[0080] In addition, in the recovery method of this embodiment, even if the concentration of precious metals in the liquid to be treated (and therefore the liquid to be recovered) is sufficiently lower than the concentration of base metals, precious metals can be recovered with high selectivity. Specifically, the ratio of the concentration of base metals (ppm) to the concentration of precious metals (ppm) in the liquid to be treated (base metals / precious metals) may be 10 or more, 30 or more, 50 or more, 80 or more, or 100 or more.

[0081] <Contact process> The contact step is a step in which the liquid to be treated prepared in the preparation step is brought into contact with the adsorbent (PAS particles) described above. This contact step allows the precious metals to be adsorbed onto the adsorbent with high selectivity. Furthermore, this contact step also removes at least a portion of the precious metals from the liquid to be treated.

[0082] The method for contacting the liquid to be treated with the adsorbent is not particularly limited, and examples thereof include adding the adsorbent to the liquid to be treated, and more specifically, immersing the adsorbent in the liquid to be treated, or mixing the liquid to be treated with the adsorbent. In this case, mechanical shear force such as stirring, vibration, or ultrasonic irradiation can be applied to suppress aggregation of the adsorbent (PAS particles) particles.

[0083] The amount of adsorbent used relative to the liquid to be treated is not particularly limited, but the concentration of precious metals in the liquid to be treated can be measured in advance, and the adsorbent (PAS particles) can be used in an amount such that the weight ratio of adsorbent (PAS particles) to precious metals ranges from 1 time or more, 5 times or more, or 10 times or more to 1000 times or less, 500 times or less, or 100 times or less.

[0084] The contacting step may be carried out by supplying the liquid to be treated to the immobilized adsorbent. Specifically, the adsorbent may be immobilized by filling a container such as a column or by supporting it on a fiber or membrane, and then supplying the liquid to be treated thereto. The contacting step may be carried out either batchwise or continuously. In the batchwise case, the liquid to be treated is supplied to a container in which the adsorbent is immobilized. In the continuous case, the adsorbent may be immobilized in a flow path, and the liquid to be treated is continuously supplied (passed) through the flow path. Immobilization can be carried out by any known method, provided that the adsorbent is partitioned by a wall having pores of a size that allows the liquid (liquid to be treated) to pass through but not the adsorbent (PAS particles), and the adsorbent can be separated from the liquid (liquid to be treated). Immobilizing the adsorbent in this manner facilitates the solid-liquid separation step (described below).

[0085] Furthermore, when the contact step is carried out continuously as described above, from the viewpoint of the adsorption efficiency of the precious metals, the space velocity (SV) of the liquid to be treated in the flow path is preferably 200 or less, more preferably 100 or less, and even more preferably 20 or less. The lower limit of the space velocity (SV) is not particularly limited, but can be 5 or more. Within these ranges, the efficiency of adsorbing (separating) the precious metals from the liquid to be treated by the adsorbent is excellent. The space velocity (SV) is defined as the volume (m ) of the adsorbent immobilized in the flow path. 3 ) how many times the amount of solution (m 3 ) indicates whether liquid is passed through. The temperature in the contact step is not particularly limited and can be appropriately selected, for example, from 10 to 80°C.

[0086] The contact step is preferably carried out in the absence of a surfactant, from the viewpoint of expressing adsorption properties and reducing elution into the liquid to be treated. Note that "in the absence of a surfactant" refers to the absence of a surfactant in any environment when carrying out the recovery method of this embodiment, such as the adsorbent, the liquid to be treated, and the equipment used to carry out each step.

[0087] <Solid-liquid separation process> In the recovery method of this embodiment, a solid-liquid separation step can be performed after the contact step. The solid-liquid separation method is not particularly limited, and examples thereof include sedimentation, flotation, sand filtration, centrifugation, suction filtration, micromembrane filtration, and ultramembrane filtration. By such solid-liquid separation, the adsorbent with the precious metal adsorbed thereon can be extracted from the liquid.

[0088] <Recycling process> Furthermore, in the recovery method of this embodiment, the adsorbed precious metals can be recovered by subjecting the adsorbent extracted in the solid-liquid separation step to a regeneration treatment. Examples of regeneration methods include passing an eluent (e.g., an alkaline aqueous solution or an aqueous solution containing a sulfur- or nitrogen-containing chelating agent) through the extracted adsorbent. By passing the eluent in this manner, the adsorbed precious metals can be recovered as a concentrated solution. If necessary, the adsorbent may be washed by passing an acid-alkali aqueous solution through the adsorbent to remove trace amounts of impurities. The above-described regeneration treatment allows regeneration by simply passing a solution suitable for the adsorbed precious metals / base metals through the adsorbent. Therefore, unlike activated carbon, the adsorbent can be reused without the need for calcination, thereby contributing to reducing environmental impact. Furthermore, the adsorbent after regeneration can be reused in the recovery method of this embodiment.

[0089] (Method for manufacturing adsorbent with noble metals) The method for producing an adsorbent having a precious metal adsorbed thereon (hereinafter sometimes simply referred to as the "production method") of this embodiment is characterized by using PAS particles as the adsorbent. The production method of this embodiment is also characterized by including a preparation step of preparing a liquid to be treated that contains a precious metal and has a pH of 4 or less at 23°C, and a contact step of contacting the liquid to be treated with the adsorbent.

[0090] Unless otherwise noted, the materials and other components used in the manufacturing method of the present embodiment, as well as each step, are substantially the same as those in the recovery method of the present embodiment described above (such as adsorbents (PAS particles), etc.) and each step (preparation step, contact step, optional solid-liquid separation step, optional regeneration treatment step, etc.). Therefore, in this specification, unless otherwise noted, the description of the manufacturing method of the present embodiment shall incorporate the description in the recovery method of the present embodiment described above.

[0091] The manufacturing method of the present embodiment includes a preparation step of preparing a treatment liquid containing a noble metal and having a pH of 4 or less at 23°C, that is, the manufacturing method of the present embodiment is different from the recovery method of the present embodiment described above in that it is not essential for the treatment liquid to contain a base metal. However, the treatment liquid prepared by the manufacturing method of the present embodiment may contain a base metal, as in the recovery method of the present embodiment. The treatment liquid containing a base metal is the same as that described in the recovery method of the present embodiment.

[0092] ​​​​​​​​​​​​​​Into a 150 L autoclave equipped with a stirrer, pressure gauge, thermometer, condenser, decanter, and rectification column, 33.222 kg (226 mol) of p-dichlorobenzene (hereinafter abbreviated as DCB), 2.280 kg (23 mol) of N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP), 27.300 kg (230 mol) of 47.23 mass% sodium hydrosulfide, and 18.533 kg (228 mol) of 49.21 mass% sodium hydroxide were charged. Next, while stirring, the temperature was raised to 173 °C over 5 hours under a nitrogen atmosphere, and 27.3 kg of water was distilled off. Then, the autoclave was sealed. The DCB distilled off by azeotropy during dehydration was separated by a decanter and returned to the autoclave as needed. Inside the autoclave after dehydration, an anhydrous sodium sulfide composition was dispersed in DCB. Furthermore, the internal temperature was cooled to 160 °C, 47.492 kg (479 mol) of NMP was charged, and the temperature was raised to 185 °C. When the pressure reached 0.00 MPa, the valve connecting the rectification column was opened, and the temperature was raised to 200 °C over an hour. At this time, it was controlled by cooling and valve opening degree so that the outlet temperature of the rectification column was 110 °C or lower. The mixed vapor of distilled DCB and water was condensed by a condenser and separated by a decanter, and the DCB was returned to the autoclave. The amount of distilled water was 179 g. Next, the temperature was raised from 200 °C to 230 °C over 3 hours, stirred for an hour, then the temperature was raised to 250 °C and stirred for an hour. After the reaction was completed, the internal temperature of the autoclave was cooled from 250 °C to 235 °C. After reaching, the bottom valve of the autoclave was opened, and it was flash-fed to a 150 L vacuum stirrer dryer with a stirrer (desolventizer jacket temperature: 120 °C) under reduced pressure to extract NMP. After cooling to room temperature, as a result of sampling, a PAS mixture (PPS mixture) with 55% non-volatile content was obtained.

[0095] <Production of PAS Particles (Adsorbent)> 400 g of the PAS mixture obtained above and 317 g of methanol were placed in a flask and stirred and mixed at 40°C for 30 minutes to obtain a slurry. The resulting slurry was vacuum filtered using a Kiriyama funnel, compacted from above, and then 634 g of methanol was poured on top in several portions and filtered. The filtered cake was then transferred to a beaker, crushed into powder using a medicine spoon, and 634 g of 70°C water was poured on top and stirred and mixed for 30 minutes. The slurry was vacuum filtered using a Kiriyama funnel, compacted from above, and then 845 g of 70°C water was poured on top in several portions and filtered. The cake was then transferred to a beaker, 636 g of carbonated water was poured on top, and then stirred and mixed for 1 hour. The slurry was then vacuum filtered using a Kiriyama funnel, compacted from above, and then 848 g of carbonated water was poured on top in several portions and filtered to obtain a wet cake (PAS particles). The moisture content of the obtained PAS particles (PPS particles) calculated from the loss on drying was 47.5% by mass. The PAS particles also had a zeta potential of -15 mV measured by the streaming potential method under conditions of pH 7.8 to 8.2, and a specific surface area of ​​119 m. 2 The PAS particles were used as an adsorbent in the following.

[0096] <Preparation of the liquid to be treated> Using Kanto Chemical's "Palladium Standard Stock Solution Pd1000" and "Tin Standard Stock Solution Sn1000," the palladium concentration was adjusted to 5 mg / L (ppm) and the tin concentration to 250 mg / L (ppm), respectively, to obtain a solution simulating plating wastewater. This solution was then diluted with hydrochloric acid and ammonium chloride to adjust the chloride ion concentration and pH at 23°C to those shown in Table 1, producing solutions 1 to 3 to be treated.

[0097] [Table 1]

[0098] <Contact between the liquid to be treated and the adsorbent> Five mL of a liquid to be treated selected from Liquids 1 to 3 and an amount of the adsorbent shown in Table 2, sufficient to yield a resin content of 0.025 g, were weighed into a 30 mL test tube. The liquid was then shaken horizontally at 200 rpm for 3 hours using a shaker (Yamato Scientific Co., Ltd., "SA300") at a liquid temperature of 30°C, allowing the adsorption to reach equilibrium. The liquid was then subjected to solid-liquid separation by suction filtration, and the liquid phase components were recovered. The adsorption rate (%) of each metal (palladium, tin) in the liquid phase components was calculated using the following formula, based on the metal concentrations (ppm) of the liquid phase components. The results are shown in Table 2. Metal adsorption rate (%) = {(metal concentration in the treated liquid before adsorption - metal concentration in the liquid phase components after adsorption equilibrium) / metal concentration in the treated liquid before adsorption} × 100

[0099] [Table 2]

[0100] *1 Ion exchange resin: Mitsubishi Chemical Corporation's "Diaion (registered trademark) SA10A", a strong basic anion exchange resin *2 Chelate resin: Mitsubishi Chemical Corporation's "Diaion (registered trademark) CR11", iminodiacetic acid type chelating resin

[0101] Tables 1 and 2 show that in recovering precious metals from a liquid containing precious and base metals, the pH of the liquid at 23°C was adjusted to 4 or less and PAS particles were used as the adsorbent in the examples, which were able to adsorb a large amount of precious metal (palladium) while sufficiently suppressing adsorption of base metal (tin), compared to comparative examples in which the pH was adjusted to above 4 and comparative examples in which other adsorbents such as ion exchange resins or chelating resins were used. In particular, the concentration of base metals in the treated liquid in this example was significantly higher than that of precious metals, but the fact that the precious metal was able to be selectively adsorbed despite this is a particularly noteworthy effect. [Industrial Applicability]

[0102] According to the present invention, it is possible to provide a method for recovering precious metals, which is capable of recovering precious metals with high selectivity from a liquid containing precious metals and base metals. Furthermore, the present invention can provide a method for producing an adsorbent having a noble metal adsorbed thereon.

Claims

1. A method for recovering precious metals, comprising recovering precious metals from a liquid containing precious metals and base metals using an adsorbent, the method comprising: As the adsorbent, particles of polyarylene sulfide resin are used, a preparation step of preparing a liquid to be treated that contains the liquid and has a pH of 4 or less at 23°C; a contacting step of contacting the liquid to be treated with the adsorbent; A method for recovering precious metals, comprising:

2. 2. The method of claim 1, wherein the precious metal comprises palladium.

3. 3. The method according to claim 1, wherein the liquid to be treated has a concentration of anions selected from chloride ions, nitrate ions, and sulfate ions of 0.05 mol / L or more.

4. 4. The method according to claim 3, wherein the liquid to be treated has a chloride ion concentration of 0.05 mol / L or more.

5. 3. The method according to claim 1, wherein the concentration of the noble metal in the liquid to be treated is 0.1 to 100 ppm.

6. 3. The method according to claim 1, wherein the concentration of the base metal in the liquid to be treated is 10 to 5000 ppm.

7. 4. The recovery method according to claim 3, wherein the concentration of the anions in the liquid to be treated is 0.1 mol / L or more.

8. 3. The method according to claim 1, wherein the polyarylene sulfide resin has a zeta potential of −50 mV or more as measured by a streaming potential method under conditions of pH 7.8 to 8.

2.

9. The recovery method according to claim 1 or 2, wherein the polyarylene sulfide resin particles have an average particle size of more than 10 μm.

10. 3. The method according to claim 1, wherein the contacting step is carried out in the absence of a surfactant.

11. 3. The recovery method according to claim 1, wherein the contact step is carried out by supplying the liquid to be treated to the immobilized adsorbent.

12. A method for producing an adsorbent having a precious metal adsorbed thereon, comprising: As the adsorbent, particles of polyarylene sulfide resin are used, a preparation step of preparing a liquid to be treated that contains a noble metal and a base metal and has a pH of 4 or less at 23°C; a contacting step of contacting the liquid to be treated with the adsorbent; A method for producing an adsorbent having a precious metal adsorbed thereon, comprising:

13. The method of claim 12 , wherein the noble metal comprises palladium.

14. 14. The method according to claim 12, wherein the liquid to be treated has a concentration of anions selected from chloride ions, nitrate ions, and sulfate ions of 0.05 mol / L or more.

15. The method according to claim 14, wherein the liquid to be treated has a chloride ion concentration of 0.05 mol / L or more.

16. The method according to claim 12 or 13, wherein the polyarylene sulfide resin has a zeta potential of −50 mV or more as measured by a streaming potential method under conditions of pH 7.8 to 8.

2.

17. The method according to claim 12 or 13, wherein the polyarylene sulfide resin particles have an average particle size of more than 10 μm.

18. The method according to claim 12 or 13, wherein the adsorbent to which the noble metal is adsorbed has 1 to 100 mg of noble metal adsorbed per 1 g of polyarylene sulfide resin.

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