Method for recovering noble metal and method for producing adsorbent to which noble metal is adsorbed

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

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

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

[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 Sn-containing precious metal catalyst recovery solution 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.

[0006] JP 2019-023356 A JP 2015-183228 A

[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, which is capable of recovering precious metals with high selectivity from a solution containing precious metals and base metals. Another object of the present invention is to provide a method for producing an adsorbent having precious metals adsorbed thereon, which can also be obtained by the above-mentioned method for recovering precious metals.

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

[0012] [1] A method for recovering precious metals using an adsorbent from a liquid containing precious metals and base metals, the method comprising: a preparation step of preparing a liquid to be treated that contains polyarylene sulfide resin particles 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.

[0013] [2] The method according to [1], wherein the precious metal comprises palladium.

[0014] [3] The recovery method according to [1] or [2], wherein the concentration of anions selected from chloride ions, nitrate ions, and sulfate ions in the liquid to be treated is 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 precious 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 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 average particle size of the polyarylene sulfide resin particles is greater than 10 μm.

[0021]

[10] The 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: a preparation step of preparing a liquid to be treated, the liquid containing the precious metal and having a pH of 4 or less at 23°C, using particles of a polyarylene sulfide resin as the adsorbent; and a contact step of contacting the liquid to be treated with the adsorbent.

[0024]

[13] The method according to

[12] , wherein the noble metal includes palladium.

[0025]

[14] The manufacturing 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 average particle size of the polyarylene sulfide resin particles is greater than 10 μm.

[0029]

[18] The manufacturing 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.

[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 solution containing precious metals and base metals, and a method for producing an adsorbent having precious metals adsorbed thereon.

[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 for recovering precious metals) The method for recovering precious metals 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 particles (hereinafter sometimes referred to as "PAS particles") of polyarylene sulfide resin (hereinafter sometimes referred to as "PAS resin") are used as the adsorbent. 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, the anions (ligands) will bond with the metal to form a complex.

[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. Furthermore, the 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. Furthermore, when the complexed noble and base metals are adsorbed onto the PAS resin, they undergo ligand exchange with sulfur (S) present in the PAS resin molecules. At this time, there is a compatibility between noble and base metals and sulfur, known as the HSAB rule, and this compatibility affects the ligand exchange. According to the HSAB rule, noble metals are classified as soft acids, and base metals are classified as relatively hard acids. On the other hand, sulfur is classified as a soft base and has good compatibility with noble metals. Therefore, under anionic complex conditions, noble metals are more likely to form coordinate bonds with sulfur than base metals. This, combined with other factors, is presumably what contributes to the development of extremely high selectivity for noble metals.

[0035] These tendencies are thought to interact in a complex manner, 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 amount of base metals adsorbed. It is also suggested that the selective adsorption of precious metals may be partly due 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 a "liquid to be recovered") is used as the liquid from which precious metals are recovered. This liquid to be recovered 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 the adsorbent (PAS resin) in terms of adsorption properties taking ion size into consideration, so by including palladium as 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 metal include metals other than precious metals. Specific examples of the base metal include tin (Sn), cobalt (Co), nickel (Ni), zinc (Zn), iron (Fe), copper (Cu), and chromium (Cr). The base metal may be a single metal or a combination of two or more metals. 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 of polyarylene sulfide resin (PAS resin) (PAS particles) are used as the adsorbent. Note that the 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 a structure represented by the following formula (1):

[0050] (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] 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 ratio of the trifunctional structural moiety represented by formula (2) 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 ２ are 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 bonded at the para position as represented by formula (3) below, a structural moiety bonded at the meta position as represented by formula (4) below, and a structural moiety bonded at the ortho position:

[0054]

[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 consists solely of 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] The PAS resin further contains, 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] 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). Note that 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 a naphthyl sulfide bond or the like in its molecular structure. In this case, however, the proportion of the above bond to the total number of moles of other structural moieties is preferably 3 mol % or less, more preferably 1 mol % or less.

[0059] The 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 or the like, 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 dihalogeno aromatic 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 having an alkyl group having 1 to 18 carbon atoms as a nuclear substituent on the aromatic ring of the above compounds.

[0062] Examples of the polyhalogeno aromatic compounds 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 after synthesizing a PAS resin by polymerization include a method in which by-products (unavoidable components derived from the polymerization reaction for synthesizing the PAS resin) contained in the polymerization reaction mixture are washed after synthesizing the PAS resin by polymerization. One example of such a method involves removing the solvent from the reaction mixture after the polymerization reaction is complete to obtain a slurry containing the 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), washing the resulting PAS particles with carbonated water and filtering, and, if necessary, adding a dispersant to form a dispersion. In the above post-treatment, the particles can be dried to form a powder, but it is preferable to leave the surfaces of the PAS particles wet with the liquid or dispersion used for washing without drying, as this provides excellent 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] It is preferable that the PAS particles (adsorbent) have no other components (excluding water and inevitable components resulting from the polymerization reaction for synthesizing the PAS resin) present on the outer surface other than 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, mold release agents, and coupling agents. The phrase "no other components present" refers to the proportion of PAS resin in the PAS particles, excluding the inevitable components and water, being 95% by mass or more, preferably 99% by mass or more, and 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 (excluding water and unavoidable components derived from the polymerization reaction for synthesizing the PAS resin) other than 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, mold release agents, and coupling agents. The phrase "free of other components" refers to the proportion of PAS resin in the PAS particles, excluding the unavoidable components and water, being 95% by mass or more, preferably 99% by mass or more, and more preferably 99.9% by mass or more, and may be 100% by mass.

[0068] The inevitable components derived from the polymerization reaction for synthesizing the 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] (wherein n is 0 to 2, and Y １ represents a halogen atom, and Y２ represents a hydrogen atom or a halogen atom, 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.

[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 the streaming potential method under conditions of pH 7.8 to 8.2. The zeta potential of the PAS resin refers to the average value measured three times by filling a cylindrical cell with approximately 100 mg of PAS resin (particularly PAS particles) and measuring the zeta potential of the resin surface using a 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 to select PAS particles 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 is, 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 is 300 m ２ / g or less, 250m ２ / g or less, or 200m ２ The specific surface area of ​​the PAS resin is the BET specific surface area measured after pretreatment at 60° C. under vacuum for 4 hours.

[0072] The average particle diameter of the PAS particles is preferably greater than 10 μm. In this case, handling properties and / or liquid transport properties when packed into a column or the like can be improved. Furthermore, from the viewpoint of maintaining good adsorption properties, the average particle diameter of the PAS particles is preferably 2 mm or less. From the same viewpoint, the average particle diameter 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 diameter of the PAS resin is the average particle diameter (D50) determined based on the particle size distribution measured according to 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 Step> 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. Note that 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 to 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 precious metal in the liquid to be treated may depend on the concentration of the precious metal in the liquid to be recovered, but can be set to about 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 set to about 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 low compared to the concentration of base metals, the 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] <Contacting Step> The contacting step is a step of contacting the liquid to be treated prepared in the preparing step with the adsorbent (PAS particles) described above. This contacting step allows the precious metals to be adsorbed onto the adsorbent with high selectivity. Furthermore, this contacting step 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 a method of adding the adsorbent to the liquid to be treated, and more specifically, a method of immersing the adsorbent in the liquid to be treated, and a method of mixing the liquid to be treated with the adsorbent. In this case, in order to suppress aggregation of the particles of the adsorbent (PAS particles), mechanical shear force such as stirring, vibration, or ultrasonic irradiation can be applied.

[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 the adsorbent (PAS particles) to the 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 contact 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, thereby carrying out the contact step. The contact step may be carried out in a batch or continuous manner. In the batch mode, a method of supplying the liquid to be treated to a container in which the adsorbent is immobilized may be exemplified. In the continuous mode, a method of immobilizing the adsorbent in a flow path and continuously supplying (passing) the liquid to be treated into the flow path may be exemplified. Immobilization can be carried out by partitioning the adsorbent with 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 by using a known method as long as it can be separated from the liquid (liquid to be treated). By immobilizing the adsorbent in this way, the solid-liquid separation step (described below) can be easily carried out.

[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) in the flow path of the liquid to be treated 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 fixed in the flow path. ３ ) how many times the amount of solution (m ３ The temperature of the contact step is not particularly limited and can be appropriately selected, but can be, for example, 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 Step> 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] <Regeneration Treatment Step> In addition, 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 treatment 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 subjected to a cleaning treatment in which an acidic or alkaline aqueous solution is passed through the adsorbent to remove trace amounts of impurities adhering to the adsorbent. The above-described regeneration treatment can be performed simply by passing a liquid 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 treatment can be reused in the recovery method of this embodiment.

[0089] (Method for manufacturing an adsorbent having a precious metal adsorbed thereon) A method for manufacturing an adsorbent having a precious metal adsorbed thereon according to the present embodiment (hereinafter, sometimes simply referred to as the "manufacturing method") is characterized in that PAS particles are used as the adsorbent. The manufacturing method according to the present embodiment is also characterized in that it includes 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 specified below, the materials and steps used in the production method of this embodiment are substantially the same as the materials (such as the adsorbent (PAS particles)) and steps (such as the preparation step, contact step, optional solid-liquid separation step, optional regeneration treatment step, etc.) in the recovery method of this embodiment described above. Therefore, in this specification, the description of the production method of this embodiment will refer to the description of the recovery method of this embodiment described above, except as otherwise specified below.

[0091] The manufacturing method of this embodiment includes 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. That is, the manufacturing method of this embodiment differs from the recovery method of this embodiment described above in that the liquid to be treated does not necessarily contain a base metal. However, the liquid to be treated prepared by the manufacturing method of this embodiment may contain a base metal, as in the recovery method of this embodiment. The liquid to be treated when it contains a base metal is the same as that described in the recovery method of this embodiment.

[0092] In the manufacturing method of this embodiment, an adsorbent having a precious metal adsorbed thereon (hereinafter, sometimes referred to as a "precious metal-loaded adsorbent") is produced by the contacting step. Such a precious metal-loaded adsorbent preferably has 1 to 100 mg of precious metal adsorbed per 1 g of PAS resin. The amount of precious metal adsorbed per 1 g of PAS resin in the precious metal-loaded adsorbent can be controlled by, for example, appropriately adjusting the pH or anion concentration of the liquid to be treated, the contact time between the liquid to be treated and the adsorbent, the precious metal concentration in the liquid to be treated, the mass ratio or volume ratio between the liquid to be treated and the adsorbent during contact, etc.

[0093] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0094] <Synthesis of PAS Resin> 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% by mass sodium hydrosulfide, and 18.533 kg (228 mol) of 49.21% by mass caustic soda were charged into a 150 L autoclave equipped with a pressure gauge, thermometer, condenser, decanter, and rectification column. The temperature was then raised to 173°C over 5 hours under a nitrogen atmosphere with stirring, and 27.3 kg of water was distilled off. The autoclave was then sealed. The DCB distilled azeotropically during dehydration was separated using a decanter and returned to the autoclave as needed. After completion of dehydration, the anhydrous sodium sulfide composition was dispersed in the DCB in the autoclave. The internal temperature was then cooled to 160°C, and 47.492 kg (479 mol) of NMP was charged and heated to 185°C. When the pressure reached 0.00 MPa, the valve connecting the distillation column was opened, and the internal temperature was raised to 200°C over 1 hour. During this time, the outlet temperature of the distillation column was controlled to be 110°C or less by controlling the cooling and valve opening. The distilled mixed vapor of DCB and water was condensed in a condenser and separated in a decanter, and the DCB was returned to the autoclave. The amount of distilled water was 179 g. Next, the internal temperature was raised from 200°C to 230°C over 3 hours, stirred for 1 hour, and then heated to 250°C and stirred for 1 hour. After the reaction was completed, the internal temperature of the autoclave was cooled from 250° C. to 235° C. After reaching this temperature, the bottom valve of the autoclave was opened, and the autoclave was flushed into a 150 L vacuum stirring dryer equipped with a stirring blade (desolvator jacket temperature: 120° C.) while still under reduced pressure to remove NMP. After cooling to room temperature, sampling yielded a PAS mixture (PPS mixture) with a nonvolatile content of 55%.

[0095] <Preparation 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 obtained slurry was filtered under reduced pressure using a Kiriyama funnel, compacted from above, and then 634 g of methanol was poured on top in several portions and filtered. The cake obtained by filtration was then transferred to a beaker, crushed into powder using a medicine spoon, and 634 g of 70°C water was poured therein and stirred and mixed for 30 minutes. The slurry was filtered under reduced pressure 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 transferred to a beaker, 636 g of carbonated water was poured therein, and then stirred and mixed for 1 hour. The slurry was then filtered under reduced pressure 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 water 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 a 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 Solution to be Treated> Using Kanto Chemical Co., Inc.'s "Palladium Standard Stock Solution Pd1000" and "Tin Standard Stock Solution Sn1000," a palladium concentration of 5 mg / L (ppm) and a tin concentration of 250 mg / L (ppm) were adjusted to obtain a solution simulating plating wastewater. This was then diluted and adjusted with aqueous hydrochloric acid and ammonium chloride so that the chloride ion concentrations and pH at 23°C were as shown in Table 1, thereby preparing Solutions to be Treated 1 to 3.

[0097]

[0098] <Contact between the liquid to be treated and the adsorbent> 5 mL of the liquid to be treated selected from Liquids to be Treated 1 to 3 and an amount of the adsorbent shown in Table 2 so that the resin content was 0.025 g were weighed into a 30 mL test tube. Next, using a shaker ("SA300" manufactured by Yamato Scientific Co., Ltd.), the liquid was shaken and stirred horizontally at 200 rpm at a liquid temperature of 30°C for 3 hours to allow the adsorption to reach equilibrium. Subsequently, solid-liquid separation was performed by suction filtration, and the liquid phase component was recovered. Using the metal (palladium, tin) concentration (ppm) of the liquid phase component, the adsorption rate (%) of each metal was calculated using the following formula. The results are shown in Table 2. Metal adsorption rate (%) = {(metal concentration in the liquid to be treated before adsorption - metal concentration in the liquid phase component after adsorption equilibrium) / metal concentration in the liquid to be treated before adsorption} × 100

[0099]

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

[0101] Tables 1 and 2 show that in recovering precious metals from a liquid containing precious metals 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. This shows that the example was able to adsorb a large amount of precious metal (palladium) while sufficiently suppressing the adsorption of base metal (tin), compared to the comparative example in which the pH was adjusted to more than 4 and the comparative example in which other adsorbents such as ion exchange resin or chelating resin 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 can be said to be a particularly noteworthy effect.

[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 solution containing precious metals and base metals, and a method for producing an adsorbent having precious metals adsorbed thereon.

Claims

1. A method for recovering a noble metal by using an adsorbent to recover the noble metal from a solution containing a noble metal and a base metal, the method comprising: using particles of a polyarylene sulfide resin as the adsorbent; a preparation step of preparing a liquid to be treated that contains the solution and has a pH of 4 or less at 23°C; and a contact step of bringing the liquid to be treated into contact with the adsorbent. The method for recovering a noble metal is characterized by including these steps.

2. The recovery method according to claim 1, wherein the noble metal contains palladium.

3. The recovery method according to claim 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.

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

5. The recovery method according to claim 1 or 2, wherein the concentration of the noble metal in the liquid to be treated is 0.1 to 100 ppm.

6. The recovery method according to claim 1 or 2, wherein the concentration of the base metal in the liquid to be treated is 10 to 5000 ppm.

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

8. The recovery method according to claim 1 or 2, wherein the polyarylene sulfide resin has a zeta potential of -50 mV or more measured under conditions of pH 7.8 to 8.2 by the streaming potential method.

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

10. The recovery method according to claim 1 or 2, wherein the contact step is performed in the absence of a surfactant.

11. The recovery method according to claim 1 or 2, wherein the contact step is performed by supplying the liquid to be treated to the immobilized adsorbent.

12. A method for producing an adsorbent having a noble metal adsorbed thereon, the method comprising: using particles of a polyarylene sulfide resin as the adsorbent; a preparation step of preparing a liquid to be treated that contains a noble metal and has a pH of 4 or less at 23°C; and a contact step of bringing the liquid to be treated into contact with the adsorbent. The method for producing an adsorbent having a noble metal adsorbed thereon is characterized by including these steps.

13. The production method according to claim 12, wherein the noble metal contains palladium.

14. The production method according to claim 12 or 13, wherein the concentration of anions selected from chloride ions, nitrate ions, and sulfate ions in the liquid to be treated is 0.05 mol / L or more.

15. The production method according to claim 14, wherein the concentration of chloride ions in the liquid to be treated is 0.05 mol / L or more.

16. The production method according to claim 12 or 13, wherein the zeta potential of the polyarylene sulfide resin measured under the conditions of pH 7.8 to 8.2 by the streaming potential method is -50 mV or more.

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

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

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