Separation and recovery method

Abstract

Provided is a method for efficiently separating and recovering a metal atom which is a substance to be separated from an aqueous solution containing the substance to be separated by using an adsorbent containing polyarylene sulfide (PAS) particles and having an excellent adsorption force in water. Specifically, the separation and recovery method separates the substance to be separated from the aqueous solution containing the substance to be separated by using PAS resin particles, and is characterized in that: a step (1) for removing the substance to be separated from the aqueous solution by causing the aqueous solution containing the substance to be separated and the PAS resin particles to contact each other, and causing the PAS resin particles to selectively adsorb the substance to be separated contained in the aqueous solution, and a step (2) for causing an eluent to contact the PAS resin particles to elute the substance to be separated are included; the substance to be separated is a metal atom or a compound containing the metal atom; and the eluent is an alkali aqueous solution or an aqueous solution in which a chelating agent containing a sulfur atom or a nitrogen atom is dissolved.

Description

[Technical Field]

[0001] The present invention relates to a separation and recovery method in which a substance to be separated is separated from an aqueous solution containing the substance by using polyarylene sulfide (hereinafter sometimes abbreviated as PAS) resin particles as an adsorbent, and then the substance is eluted and recovered. [Background technology]

[0002] In recent years, from the perspective of effective utilization of valuable resources and prevention of environmental pollution toward sustainable development, efficient recovery technologies for valuable metal atoms from solutions containing these atoms have attracted attention. In particular, precious metals such as platinum group metals, gold, and silver are highly valuable, and because their production is unevenly distributed among countries, competition to recover precious metals from waste solutions such as industrial catalysts and metal plating solutions is becoming more intense.

[0003] Solvent extraction has been put to practical use as a method for recovering precious metals from wastewater, but the process is complicated, and the equipment requires large capacity. The disposal of large volumes of wastewater that does not contain precious metals presents problems. Other methods for recovering precious metals by contacting activated carbon or ion exchange resins with wastewater have also been put to practical use. However, activated carbon has low selectivity for precious metals, and high-temperature calcination is required to elute the precious metals, resulting in significant equipment and environmental impact. Ion exchange resins and chelating resins selectively adsorb precious metals using functional groups on their side chains. Repeated adsorption and elution alter the structure of the functional groups, resulting in a decline in adsorption properties. Finally, calcination is required to recover the precious metals. Therefore, further simplification of the process and reduction of the environmental impact are needed for both methods.

[0004] On the other hand, proposals have been made in recent years to use porous bodies made of PAS resin as adsorbents, taking advantage of its excellent properties of heat resistance and chemical resistance. For example, Patent Document 1 discloses that recycled PAS resin can be used as an adsorbent, particularly as a filtering material for removing ozone and NO2, taking advantage of the fact that the specific surface area of the recycled PAS resin is increased. Also, for example, Patent Document 2 discloses that recycled PAS resin can be used as an adsorbent, particularly as a filtering material for removing ozone and NO2, taking advantage of the fact that the hydrogen bonding strength component Δh of the three-dimensional solubility parameter is 1 to 5 (cal 1 / 2cm -3 / 2 Polyphenylene sulfide (hereinafter referred to as PPS) has been disclosed as an adsorbent made of a microporous polymer composition that forms a porous porous film. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Application No. Hei 8-512891 [Patent Document 2] Japanese Patent Application Publication No. 6-327970 Summary of the Invention [Problem to be solved by the invention]

[0006] However, there are few disclosures regarding elution in separation and recovery methods using PAS resin particles as an adsorbent. In addition, because PAS resin particles have a different adsorption mechanism and design concept from conventional adsorbents, there has been a need to develop an elution and recovery method for the substances to be separated that is optimal for PAS resin particles.

[0007] Therefore, the problem that the present invention aims to solve is to provide a method for efficiently separating and recovering metal atoms, which are the substances to be separated, from an aqueous solution containing the substances to be separated, using an adsorbent that contains PAS resin particles and has excellent adsorption power in water. [Means for solving the problem]

[0008] As a result of various investigations, the inventors of the present invention arrived at the following invention. That is, the separation and recovery method of the present disclosure includes: A method for separating a substance to be separated from an aqueous solution containing the substance using PAS resin particles, comprising: a step (1) of contacting an aqueous solution containing a substance to be separated with PAS resin particles, thereby selectively adsorbing the substance to be separated contained in the aqueous solution onto the PAS resin particles and removing the substance from the aqueous solution; a step (2) of contacting the PAS resin particles with an eluent to elute the substance to be separated; The substance to be separated is a metal atom or a compound containing a metal atom, The eluent is an aqueous alkali solution or an aqueous solution in which a sulfur atom- or nitrogen atom-containing chelating agent is dissolved, and relates to a separation and recovery method characterized by this.

Advantages of the Invention

[0009] According to the present invention, it is possible to provide a method for efficiently separating and recovering a metal atom, which is a substance to be separated, from an aqueous solution containing the substance to be separated, using an adsorbent containing PAS resin particles and having excellent adsorption power in water.

Embodiments for Carrying Out the Invention

[0010] Hereinafter, an embodiment of the present disclosure will be described in detail. However, the scope of the present disclosure is not limited to the embodiment described here, and various modifications can be made without departing from the spirit of the present disclosure. Also, when a plurality of upper limit values and lower limit values are described for specific parameters, any upper limit value and lower limit value can be combined to form a suitable numerical range.

[0011] The separation and recovery method according to this embodiment is A method for separating a substance to be separated from an aqueous solution containing the substance to be separated using PAS resin particles, A step (1) of bringing an aqueous solution containing a substance to be separated into contact with PAS resin particles, selectively adsorbing the substance to be separated contained in the aqueous solution onto the PAS resin particles, and removing it from the aqueous solution; It has a step (2) of bringing an eluent into contact with the PAS resin particles to elute the substance to be separated, The substance to be separated is a metal atom or a compound containing a metal atom, The eluent is characterized in that it is an aqueous alkali solution or an aqueous solution in which a sulfur atom- or nitrogen atom-containing chelating agent is dissolved. Details will be described below.

[0012] ·PAS resin particles In the separation and recovery method according to this embodiment, PAS resin particles are used as an adsorbent. The PAS resin particles mean particles substantially composed of PAS resin or particulate PAS resin. The PAS resin used in this embodiment has a resin structure having a structure in which an aromatic ring and a sulfur atom are bonded as a repeating unit. Specifically, the following formula (1)

[0013] [Chemical formula] (In the formula, R 1 and R 2 each independently represent a hydrogen atom, an alkyl group in the range of 1 to 4 carbon atoms, a nitro group, an amino group, a phenyl group, a methoxy group, or an ethoxy group.) and, if necessary, further the following general formula (2)

[0014] [Chemical formula] is a resin having a trifunctional structural part represented by as a repeating unit. The trifunctional structural part represented by formula (2) is preferably in the range of 0.001 to 3 mol%, particularly preferably in the range of 0.01 to 1 mol%, based on the total number of moles with other structural parts.

[0015] Here, the structural part represented by the general formula (1) is such that R 1 and R 2 are preferably hydrogen atoms from the viewpoint of the mechanical strength of the PAS resin. In that case, those bonded at the para position represented by the following formula (3) and those bonded at the meta position represented by the following formula (4) are exemplified.

[0016] [Chemical formula] Among these, in particular, the bonding of the sulfur atom to the aromatic ring in the repeating unit is preferably a structure bonded at the para position represented by the general formula (3) in terms of the adsorption characteristics with the separation target substance.

[0017] In addition, the PAS resin may contain, not only the structural parts represented by the general formulas (1) and (2), but also the following structural formulas (5) to (8)

[0018] [Chemical formula] in an amount of 30 mol% or less of the total of the structural parts represented by the general formula (1) and the general formula (2). In particular, in the present disclosure, it is preferable that the structural parts represented by the above general formulas (5) to (8) are 10 mol% or less from the viewpoints of the heat resistance and mechanical strength of the PAS resin. When the PAS resin contains the structural parts represented by the above general formulas (5) to (8), their bonding modes may be either a random copolymer or a block copolymer.

[0019] In addition, the PAS resin may have a naphthyl sulfide bond or the like in its molecular structure, but it is preferably 3 mol% or less, particularly preferably 1 mol% or less, based on the total number of moles with other structural parts.

[0020] As the polymerization method of the PAS resin, there is no particular limitation as long as it is a known method. For example, (Polymerization Method 1) a method of polymerizing a dihalogenoaromatic compound in the presence of sulfur and sodium carbonate, adding a polyhalogenoaromatic compound or other copolymerization components if necessary; (Polymerization Method 2) a method of polymerizing a dihalogenoaromatic compound in a polar solvent in the presence of a sulfidizing agent or the like, adding a polyhalogenoaromatic compound or other copolymerization components if necessary; (Polymerization Method 3) a method of self-condensing p-chlorothiophenol, adding other copolymerization components if necessary; (Production Method 4) a method of melt-polymerizing a diiodoaromatic compound and elemental sulfur while reducing the pressure in the presence of a polymerization inhibitor, etc. Among these polymerization methods, the method of (Polymerization Method 2) is general and preferable. During the reaction, an alkali metal salt of a carboxylic acid or a sulfonic acid may be added to adjust the degree of polymerization, or an alkali hydroxide may be added. Among the above (Polymerization Method 2) methods, a hydrated sulfidizing agent is introduced into a mixture containing a heated organic polar solvent and a dihalogenoaromatic compound at a rate at which water can be removed from the reaction mixture, and the dihalogenoaromatic compound and the sulfidizing agent are added, if necessary, with a polyhalogenoaromatic compound in the organic polar solvent and reacted, and the water content in the reaction system is controlled within the range of 0.02 to 0.5 mol per 1 mol of the organic polar solvent to produce a PAS resin (see JP-A-07-228699), or a method in which a dihalogenoaromatic compound and, if necessary, a polyhalogenoaromatic compound or other copolymerization components are added in the presence of a solid alkali metal sulfide and an aprotic polar organic solvent, and an alkali metal hydrosulfide and an alkali metal organic acid salt are reacted while controlling the alkali metal organic acid salt in the range of 0.01 to 0.9 mol per 1 mol of the sulfur source and the water content in the reaction system within the range of 0.02 mol per 1 mol of the aprotic polar organic solvent (see WO2010 / 058713 pamphlet) are particularly preferable.

[0021] Specific examples of dihalogenoaromatic compounds include p-dihalobenzene, m-dihalobenzene, o-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'-dihalo Examples of the polyhalogenoaromatic compounds include diphenyl 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 each of the above compounds. Examples of the polyhalogenoaromatic compounds include 1,2,3-trihalobenzene, 1,2,4-trihalobenzene, 1,3,5-trihalobenzene, 1,2,3,5-tetrahalobenzene, 1,2,4,5-tetrahalobenzene, 1,4,6-trihalonaphthalene, etc. The halogen atoms contained in each of the above compounds are preferably chlorine atoms or bromine atoms.

[0022] The crude reaction mixture containing the PAS resin obtained by the polymerization step may be subjected to post-treatment. In this case, the method of post-treatment is not particularly limited. For example, (post-treatment 1) after the polymerization reaction is completed, the solvent is first distilled off under reduced pressure or normal pressure, either directly or after adding an acid or base, and then the solid remaining after solvent distillation is washed once or twice or more times with a solvent such as water, the reaction solvent (or an organic solvent having a similar solubility to the low-molecular-weight polymer), acetone, methyl ethyl ketone, or alcohols, followed by neutralization, washing with water, filtration, and drying; (post-treatment 2) after the polymerization reaction is completed, a solvent such as water, acetone, methyl ethyl ketone, alcohols, ethyls, halogenated hydrocarbons, aromatic hydrocarbons, or aliphatic hydrocarbons (a solvent that is soluble in the polymerization solvent used and is a poor solvent for at least PAS) is added to the reaction mixture as a precipitant to precipitate solid products such as PAS and inorganic salts, which are then filtered, washed, and dried; (post-treatment 3) after the polymerization reaction is completed, the reaction mixture is washed with the reaction solvent (or an organic solvent having a similar solubility to the low-molecular-weight polymer) and then neutralized, washed, and dried; (organic solvent having a solubility equivalent to that of the crude PAS) is added to the reaction mixture after stirring, followed by filtration to remove the low-molecular-weight polymer, followed by washing once or twice or more times with a solvent such as water, acetone, methyl ethyl ketone, or alcohols, followed by neutralization, washing with water, filtration, and drying; (post-treatment 4) a method in which, after the polymerization reaction is complete, water is added to the reaction mixture, followed by washing with water, filtration, and if necessary, acid is added during the water washing step to perform an acid treatment, and then drying; or (post-treatment 5) a method in which, after the polymerization reaction is complete, the reaction mixture is filtered, followed by washing once or twice or more times with the reaction solvent if necessary, followed by further washing with water, filtration, and drying; or (post-treatment 6) a method in which, after the polymerization reaction is complete, a portion of the reaction mixture is desolvated to obtain a slurry containing crude PAS, and the slurry containing crude PAS is brought into contact with water and an oxygen-containing solvent having 1 to 3 carbon atoms to convert the crude PAS into porous particles, and the resulting porous particles are washed with carbonated water and filtered.

[0023] In the post-treatment method as exemplified in the above (post-treatment 6), examples of the oxygen atom-containing solvent having 1 to 3 carbon atoms applicable thereto include at least one selected from the group consisting of alcohols and ketones. Note that as the alcohols (also referred to as alcohol solvents or alcohol-based solvents), alcohols having 10 or less carbon atoms such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, t-butyl alcohol, ethylene glycol, propylene glycol, trimethylolpropane, benzyl alcohol; alcohols having 10 or less carbon atoms containing an ether bond such as 2-methoxyethyl alcohol, 2-ethoxyethyl alcohol, 1-methoxy-2-propyl alcohol, 1-ethoxy-2-propyl alcohol, 3-methoxy-1-butyl alcohol, 2-isopropoxyethyl alcohol; alcohols having 10 or less carbon atoms containing a ketone group such as 3-hydroxy-2-butanone; and alcohols having 10 or less carbon atoms containing an ester group such as methyl hydroxyisobutyrate are exemplified. Further, as the ketones (also referred to as ketone solvents or ketone-based solvents), acetone, methyl ethyl ketone, cyclohexanone, γ-butyrolactone or N-methylpyrrolidinone are exemplified. In the present disclosure, it is preferable to use a monohydric alcohol having 10 or less carbon atoms because the remaining carboxyalkylamino group-containing compound can be efficiently removed, and further, a monohydric alcohol having 3 or less carbon atoms is preferable.

[0024] Note that in the post-treatment methods as exemplified in the above (post-treatment 1) to (post-treatment 6), the drying of the PAS resin may be performed in a vacuum, or may be performed in air or in an inert gas atmosphere such as nitrogen.

[0025] As the PAS resin constituting the PAS resin particles used in this embodiment, a resin newly polymerized by the above method can be used, or a recycled PAS resin can also be used. For example, a PAS resin recovered from a PAS resin composition or a PAS resin molded product can be used. Specifically, examples include a PAS resin obtained by performing the above post-treatment on a solution obtained by heating a PAS resin composition or a PAS resin molded product in an organic polar solvent to dissolve the contained PAS resin.

[0026] (Melt viscosity) The melt viscosity of the PAS resin constituting the PAS resin particles used in this embodiment is not particularly limited, but the melt viscosity (V6) measured at 300 °C is preferably 1 to 800 Pa·s, more preferably 3 to 500 Pa·s, and even more preferably 5 to 200 Pa·s. However, the measurement of the melt viscosity (V6) is performed using a flow tester, CFT-500D manufactured by Shimadzu Corporation, on the PAS resin at 300 °C, load: 1.96×10 6 Pa, L / D = 10 (mm) / 1 (mm), and the measured value of the melt viscosity measured after holding for 6 minutes is used.

[0027] (Non-Newtonian index) The non-Newtonian index of the PAS resin constituting the PAS resin particles used in this embodiment is not particularly limited, but is preferably 0.90 to 1.25, more preferably 0.95 to 1.20. However, in the present disclosure, the non-Newtonian index (N value) is a value calculated using the following formula by measuring the shear rate (SR) and shear stress (SS) under the conditions of melting point + 20 °C, ratio of orifice length (L) to orifice diameter (D), L / D = 40, using a capillary rheometer. The closer the non-Newtonian index (N value) is to 1, the closer the structure is to a linear structure, and the higher the non-Newtonian index (N value), the more branched the structure is.

[0028] [Equation] [However, SR is the shear rate (per second -1 ), and SS is the shear stress (dyne / cm 2), and K denotes a constant.

[0029] (zeta potential) The PAS resin constituting the PAS resin particles used in this embodiment is not particularly limited as long as it does not impair the effects of the present invention. However, the zeta potential measured by the streaming potential method under conditions of pH 7.8 to 8.2 is preferably -50 mV or higher, more preferably -30 mV or higher. The zeta potential of the PAS resin refers to the average value measured three times on the surface of the resin particles by packing approximately 100 mg of PAS resin particles into a cylindrical cell and measuring the zeta potential of the resin particles 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 resin and select PAS resin with a particle diameter of 0.05 to 1.0 mm.

[0030] (specific surface area) The specific surface area of the PAS resin constituting the PAS resin particles used in this embodiment is not particularly limited as long as it does not impair the effects of the present invention, but is preferably 1 to 300 m 2 / g, more preferably 10 to 250m 2 / g, more preferably 50 to 200m 2 / g, particularly preferably 50 to 150m 2 / g. The specific surface area of the PAS resin particles can be measured by the method described in the Examples. The specific surface area of the PAS resin is the BET specific surface area measured using a Shimadzu Tristar II3020 after pretreating the PAS resin particles under vacuum at 60°C for 4 hours.

[0031] (particle size) The PAS resin constituting the PAS resin particles used in this embodiment is preferably in the form of particles. The particle size of the PAS resin is not particularly limited as long as the effects of the present invention are not impaired. From the viewpoint of excellent adsorption characteristics, the upper limit value is preferably about 2 mm, more preferably about 500 μm, and even more preferably about 300 μm. On the other hand, from the viewpoints of handleability and excellent liquid delivery properties when filled in a column or the like, the lower limit value is preferably 10 μm, more preferably about 20 μm, and even more preferably about 30 μm. The average particle size of the PAS resin is the average particle size (D 50 ) determined based on the particle size distribution measured according to a conventional method using a laser diffraction / scattering particle size distribution analyzer (Microtrac MT3300EXII).

[0032] In addition, from the viewpoint of excellent adsorption rate at the start of use, the PAS resin particles are preferably in a wet state containing water. The water content of the PAS resin particles is not particularly limited. From the viewpoint of the balance between adsorption capacity and transportation cost, 1 to 500 parts by mass, more preferably 10 to 250 parts by mass, and even more preferably 10 to 150 parts by mass are preferable with respect to 100 parts by mass of the PAS resin particles. Note that 0 part by mass (dry product) may also be acceptable.

[0033] Also, the PAS resin particles used in this embodiment may be recycled products of the PAS resin particles once used as an adsorbent. The recycling method of the PAS resin particles can be performed, for example, by the method described below.

[0034] The PAS resin particles used in this embodiment preferably do not contain, as an external additive component for the PAS resin particles (components existing outside the PAS resin particles, mainly components existing at the interface between the PAS resin particles and the liquid), components other than the PAS resin particles (excluding inevitable components derived from the polymerization reaction of the PAS resin and water), such as known and commonly used additives like surfactants (dispersants), colorants, antistatic agents, antioxidants, heat stabilizers, UV stabilizers, UV absorbers, foaming agents, flame retardants, flame retardant aids, rust preventives, mold release agents, and coupling agents. Note that the absence of components other than the PAS resin particles as components constituting the PAS resin particles means that the content of the PAS resin in the particles, excluding the inevitable components and moisture, is preferably in the range of 95% by mass or more, more preferably 99% by mass or more, and even more preferably 99.9% by mass or more. The upper limit value of the content is not particularly limited, but it means that it is in the range of 100% by mass or less.

[0035] Furthermore, the PAS resin particles preferably do not contain, as an internal additive component for the particles (components existing inside the PAS resin particles by melt-kneading), components other than the PAS resin (excluding inevitable components derived from the polymerization reaction of the PAS resin), such as known and commonly used additives like surfactants (dispersants), colorants, antistatic agents, antioxidants, heat stabilizers, UV stabilizers, UV absorbers, foaming agents, flame retardants, flame retardant aids, rust preventives, mold release agents, and coupling agents. The absence of components other than the PAS resin as components constituting the particles means that the content of the PAS resin contained in the PAS resin particles, excluding the inevitable components, is preferably in the range of 95% by mass or more, more preferably 99% by mass or more, and even more preferably 99.9% by mass or more. The upper limit value of the content is not particularly limited, but it means that it is in the range of 100% by mass or less.

[0036] Incidentally, the inevitable components derived from the polymerization reaction of PAS resin are unreacted raw materials and by-products used in the polymerization reaction, particularly metal atom-containing components among them, such as a sulfidizing agent (alkali metal sulfide or alkali metal hydrosulfide) and alkali metal halide, and a carboxyalkylamino group-containing compound represented by the following general formula (1).

[0037] [Chemical formula] (In the formula, n is 0 to 2, Y 1 represents a halogen atom, Y 2 represents a hydrogen atom or a halogen atom, R 1 represents a hydrogen atom, an alkyl group having 1 to 3 carbon atoms or a cyclohexyl group, R 2 represents an alkylene group having 3 to 5 carbon atoms, and X represents an alkali metal atom.) Examples thereof include carboxyalkylamino group-containing compounds.

[0038] When the PAS resin particles contain the above-mentioned external additives or internal additives, the adsorption characteristics may deteriorate due to a decrease in the ratio of sulfur components on the particle surface contributing to the adsorption ability or a decrease in the affinity of the particles for the solution.

[0039] · Aqueous solution The aqueous solution brought into contact with the PAS resin particles in this embodiment is an aqueous solution containing a substance to be separated and water as essential components (hereinafter sometimes simply referred to as "aqueous solution"). Further, the aqueous solution substantially does not contain a surfactant.

[0040] Also, the aqueous solution may contain weak acids such as acetic acid, formic acid, carbonic acid, oxalic acid, phosphoric acid, and strong acids such as hydrochloric acid, sulfuric acid, nitric acid, and aqua regia. Furthermore, in the separation and recovery method according to this embodiment, there is no limitation on the pH of the aqueous solution containing the substance to be separated. For example, under strong acid conditions, the substance to be separated can be adsorbed from the aqueous solution containing the substance to be separated using the PAS resin particles.

[0041] · Substance to be separated

[0042] Examples of the separation target substances applicable to the present embodiment include metal atoms or compounds containing metal atoms (however, excluding sodium atoms and lithium atoms as metal atoms). Examples of the metal atoms include at least one selected from the group consisting of alkali metal atoms, alkaline earth metal atoms, transition metal atoms, lanthanoid atoms, and actinoid atoms, and these may exist alone as metal atoms or may be combined with other atoms to exist as compounds or alloys. Among these, transition metals are preferred, and metal atoms classified as soft acids in the HSAB principle are more preferred. This is considered to be because the PAS resin as an adsorbent mainly contains sulfur atoms classified as soft bases in the HSAB principle.

[0043] The metal atom or compound containing a metal atom (metal salt) of the substance to be separated is not particularly limited. For example, alkali metal atoms such as potassium, rubidium, cesium, and francium; alkaline earth metal atoms such as calcium, strontium, barium, and radium; transition metal atoms such as scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, yttrium, zirconium, niobium, molybdenum, technetium, ruthenium, rhodium, palladium, silver, cadmium, lanthanoids, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, and mercury; base metal atoms such as aluminum, zinc, gallium, germanium, indium, tin, antimony, mercury, thallium, lead, bismuth, and polonium, and salts containing them can be mentioned. Examples of lanthanoids include lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium. Examples of actinoids include actinium, thorium, protactinium, uranium, neptunium, plutonium, americium, curium, berkelium, californium, einsteinium, fermium, mendelevium, nobelium, and lawrencium. Among them, in the HSAB principle, metal atoms classified as soft acids or compounds containing such metal atoms are preferred because they are easily adsorbed by the PAS resin. For example, ruthenium, rhodium, palladium, silver, cadmium, osmium, iridium, platinum, gold, mercury, thallium, and lead, as well as metal salts thereof, are preferred, and in particular, palladium and metal salts containing palladium are particularly preferred.

[0044] The metal atom of the substance to be separated may be a metal complex coordinated with ligands such as acids, bases, and organic substances. Regarding the three-dimensional structure, it is not particularly limited as long as the effects of the present invention are not impaired. For example, a regular tetrahedral shape, a square planar shape, a trigonal bipyramidal shape, a square pyramidal shape, a regular octahedral shape, etc. may be mentioned, and a square planar shape is particularly preferable. Also, the coordination number is not particularly limited, but 4 to 7 coordination is preferable from the viewpoint of stability. The molecular weight of the metal complex is not particularly limited, but is preferably 2000 or less from the viewpoint of adsorptivity. When the metal complex is used as the substance to be separated, a complex with a high ligand exchange rate is preferable, and a metal complex containing palladium(II) is more preferable.

[0045] The amount of the substance to be separated contained in the aqueous solution brought into contact with the PAS resin particles in the present embodiment is not particularly limited, but the metal concentration of the substance to be separated in the liquid is preferably 1000 ppm or less, more preferably 200 ppm or less, further preferably 20 ppm or less, and particularly preferably 10 ppm or less. Within such a range, the substance to be separated can be efficiently adsorbed onto the PAS resin particles.

[0046] ·Eluent The eluent brought into contact with the PAS resin particles in the present embodiment is an aqueous alkali solution or an aqueous solution in which a sulfur atom- or nitrogen atom-containing chelating agent is dissolved. In the present disclosure, elution refers to the desorption of the substance to be separated adsorbed on the PAS resin particles and its dissolution in the aqueous solution.

[0047] The aqueous alkali solution applicable to the present embodiment is not particularly limited as long as the effects of the present invention are not impaired, and it may be any solution with a pH of 7 or higher at room temperature (23°C). For example, aqueous alkali solutions such as sodium hydroxide aqueous solution and potassium hydroxide aqueous solution may be mentioned, and a sodium hydroxide aqueous solution is particularly preferable from the viewpoint of the elution rate. The concentration of the aqueous alkali solution is not particularly limited, but from the viewpoint of efficiently eluting the substance to be separated, it is preferably 0.5 mol / L or more and preferably 2 mol / L or less.

[0048] The chelating agent containing a sulfur atom or a nitrogen atom applicable to the present embodiment is not particularly limited as long as the effects of the present invention are not impaired. For example, thiourea, potassium thiocyanate, thiosulfuric acid, and in addition, ammonium salts such as ammonium chloride, ammonium nitrate, ammonium thiocyanate, ammonium acetate, ammonium carbonate, ammonium sulfate, ammonium thiosulfate, ammonium sulfide, ammonium phosphate, etc., ammonia, diethylamine, dimethyl ethanolamine, triethylamine, amines such as ethylenediamine, hexanediamine, melamine, etc. can be exemplified. Since they are excellent in the elution property of the separation target substance adsorbed on the PAS resin particles, thiourea, ammonium thiocyanate, ethylenediamine, dimethyl ethanolamine, etc. are preferable. These chelating materials may be soluble in water or may be soluble in acidic or basic aqueous solutions such as hydrochloric acid and sodium hydroxide. The concentration of the chelating agent in the aqueous solution is not particularly limited, but from the viewpoint of efficiently eluting the separation target substance, 0.5% by mass or more is preferable, and 5% by mass or less is preferable.

[0049] Step (1) The separation and recovery method according to the present embodiment includes, as step (1), bringing a water liquid containing a separation target substance into contact with PAS resin particles, and selectively adsorbing the separation target substance contained in the organic solvent onto the PAS resin particles to remove it from the aqueous solution.

[0050] In this step, the contact between the aqueous solution and the PAS resin particles can be, for example, by adding the PAS resin particles to the aqueous solution to selectively adsorb the separation target substance contained in the aqueous solution onto the PAS resin particles and remove it from the aqueous solution. At that time, in order to suppress the aggregation of the PAS resin particles, mechanical shear forces such as stirring, vibration, ultrasonic irradiation, etc. can be applied.

[0051] The proportion of the PAS resin particles used in relation to the aqueous solution containing the substance to be separated is not particularly limited. However, if the substance to be separated is a metal, the PAS resin particles can be used in a mass ratio of preferably 1 to 1000 times, more preferably 5 to 500 times, and even more preferably 10 to 100 times the substance to be separated, after measuring the concentration of the substance in advance.

[0052] Furthermore, the separation and recovery method according to this embodiment may include a solid-liquid separation step between the PAS resin particles and the aqueous solution. Examples of solid-liquid separation include sedimentation, flotation, sand filtration, centrifugation, micromembrane filtration, and ultrafiltration. This allows the PAS resin particles to be efficiently contacted with the eluent in the subsequent step (2), making it easy to recover the substance to be separated.

[0053] In addition, the contact between the PAS resin particles and the aqueous solution in this step can be achieved by, for example, immobilizing the PAS resin particles by packing them into a column or supporting them on fibers or a membrane, and then supplying the aqueous solution to the column, thereby selectively adsorbing the target substance contained in the aqueous solution onto the PAS resin particles and removing it from the aqueous solution. In this case, in the case of a batchwise separation process, the aqueous solution can be supplied to a container in which the PAS resin particles are immobilized, and in the case of a continuous separation process, the PAS resin particles can be immobilized in a flow path, and the aqueous solution can be supplied to the flow path. Immobilization can be achieved by any known method, as long as it can be separated from the aqueous solution by separating the PAS resin particles with a wall having pores of a size that allows the liquid to pass through but not the PAS resin particles. By fixing the PAS resin particles, solid-liquid separation of the PAS resin particles and the aqueous solution can be easily performed. However, there is a possibility that small PAS resin particles may be mixed into the aqueous solution after solid-liquid separation. If this needs to be avoided, a separate solid-liquid separation process such as sedimentation, flotation, sand filtration, centrifugation, micromembrane filtration, or ultramembrane filtration can be performed.

[0054] In addition, when performing the separation process in a continuous manner as described above, from the perspective of the adsorption efficiency of the substance to be separated, the space velocity (SV) in the aqueous solution flow path is preferably 200 or less, more preferably 100 or less, and even more preferably 20 or less. In such a range, the adsorbent has excellent efficiency in separating the substance to be separated from the aqueous solution. The space velocity (SV) in the present disclosure is the volume (m 3 ) of the adsorbent immobilized in the flow path, and indicates how many times the volume of the solution (m 3 ) passes through per hour.

[0055] Note that the contact between the PAS resin particles of the present disclosure and the aqueous solution containing the substance to be separated is carried out in the absence of a surfactant, that is, in an environment where it does not exist.

[0056] Step (2) The separation and recovery method according to the present embodiment includes, as step (2), a step of bringing an eluent into contact with the PAS resin particles to elute the substance to be separated.

[0057] In this step, the contact between the PAS resin particles and the eluent can be carried out, for example, by adding the PAS resin particles to the eluent to desorb the substance to be separated adsorbed on the PAS resin particles and dissolve it in the eluent. At that time, in order to suppress the aggregation of the PAS resin particles, mechanical shear forces such as stirring, vibration, and ultrasonic irradiation can be applied.

[0058] The usage ratio of the PAS resin particles and the eluent is not particularly limited as long as the effects of the present invention are not impaired, but the eluent is preferably used in a mass ratio of 1 to 1000 times, more preferably 5 to 500 times, and even more preferably 10 to 100 times with respect to the PAS resin particles.

[0059] Furthermore, the separation and recovery method according to the present embodiment may include a solid-liquid separation step of the PAS resin particles and the eluent. Examples of the solid-liquid separation include sedimentation separation, flotation separation, sand filtration, centrifugal separation, microfiltration, and ultrafiltration. Thereby, after the solid-liquid separation, it is also possible to easily take out and reuse the PAS resin particles from which the separation target substance has been desorbed.

[0060] In addition, in this step, the contact between the PAS resin particles and the eluent can be, for example, immobilized by filling the PAS resin particles in a column, supporting them on fibers or a membrane, and supplying the eluent thereto, so that the separation target substance adsorbed on the PAS resin particles is dissolved in the eluent and desorbed from the adsorbent. At that time, when performing the recovery process in a batch manner, examples include a method of supplying the eluent to a container in which the PAS resin particles are immobilized, and when performing the separation process in a continuous manner, examples include a method of immobilizing the PAS resin particles in a flow path and supplying the eluent into the flow path. The method of immobilization is the same as described above.

[0061] In addition, when performing the elution treatment in a continuous manner as described above, from the viewpoint of the concentration of the separation target substance, the space velocity (SV) in the flow path of the eluent is preferably 30 or less, and more preferably 10 or less. In such a range, the concentration of the separation target substance is increased, which is preferable because the load of the subsequent step of recovering the separation target substance from the eluent is reduced. In the present disclosure, the concentration is the ratio of the concentration of the separation target substance in the aqueous solution containing the separation target substance before contact in step (1) to the concentration of the separation target substance in the eluent recovered after elution in step (2).

[0062] In this process, the PAS resin particles separated by solid-liquid separation can be reused as an adsorbent in a new separation and recovery process after being regenerated by washing or the like. The regeneration method is not particularly limited. For example, after separating the eluent from the PAS resin particles, it is preferable to wash them with 2 parts by mass or more of water, more preferably 5 parts by mass or more of water. When the PAS resin particles are immobilized in a container or a flow path as described above, water may be supplied and brought into contact therewith after use. The temperature during washing with water is not particularly limited, but it is preferable to use water at 23°C or higher from the viewpoint of washing efficiency. Further, as a step before, after, or during washing with water, a step of washing the adsorbent with an acidic aqueous solution such as hydrochloric acid to further remove impurities may be included. When used as a regenerated product, those in which 95% or more of the adsorbed separation target substance has been eluted, that is, those with an elution rate of 95% or more, are preferable from the viewpoint of adsorption performance.

[0063] It is considered that the reason why the PAS resin particles can be sufficiently regenerated only by washing with water is that the selectivity of the separation target substance during adsorption is high and the adsorption of impurities is low. However, the above mechanism is only speculative, and even if the effect is achieved for other reasons, it is included in the technical scope of the present invention.

[0064] Further, although the reason why the separation and recovery method according to the present embodiment is excellent in separating and recovering the separation target substance and excellent in the recyclability of the adsorbent is not necessarily clear, it is presumed to be due to the following reasons. That is, first, conventional ion exchange resins and chelating resins have an action mechanism in which the polar functional groups in the side chains separate the target substance by ion exchange or coordination with the separation target substance, whereas the PAS resin used as an adsorbent in the present embodiment is considered to have an action mechanism in which the sulfur atoms in the main chain separate the target substance by coordinating with the separation target substance. Therefore, due to this difference in the action mechanism, it is excellent in separation and recovery ability and recyclability, and it is presumed that even hydroxide ions with weak chelating power can be eluted. The above mechanism is only speculative, and even if the effect of the present invention is achieved for other reasons, it is included in the technical scope of the present invention.

Examples

[0065] The present invention will be specifically described below with reference to examples. These examples are illustrative and not limiting. Unless otherwise specified, "% " and "parts" are based on mass hereinafter.

[0066] <Synthesis Example 1> (Polymerization Step of PAS Resin) Into a 150 L autoclave equipped with a stirrer, a pressure gauge, a thermometer, a condenser, a decanter, and a rectification column, 33.222 kg (226 mol) of p-dichlorobenzene (hereinafter abbreviated as DCB), 2.280 kg (23 mol) of 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. 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. After the dehydration was completed, the inside of the autoclave was in a state where the anhydrous sodium sulfide composition was dispersed in DCB. Further, 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 connected to the rectification column was opened, and the temperature was raised to 200 °C over 1 hour. At this time, the temperature at the outlet of the rectification column was controlled by cooling and valve opening degree so as to be 110 °C or lower. The mixed vapor of the 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 1 hour, then the temperature was raised to 250 °C and stirred for 1 hour until the reaction was completed. After that, 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 flushed into a 150-liter vacuum stirrer dryer with a stirrer (the jacket temperature of the solvent removal machine was 120 °C) while maintaining a reduced pressure state to extract N-methyl-2-pyrrolidone. After cooling to room temperature and sampling, a PPS mixture with an NV of 55% was obtained.

[0067] (Purification Step of PAS Resin) 400 g of the PPS mixture obtained in Synthesis Example 1 and 317 g of methanol were placed in a flask and stirred and mixed at 40°C for 30 minutes. The resulting slurry was vacuum filtered using a Kiriyama funnel, compacted from above, and then 634 g of methanol was poured in several portions over the top and filtered. The resulting cake was then transferred to a beaker and crushed into powder using a medicine spoon. 634 g of water at 70°C was poured into the cake and stirred and mixed for 30 minutes. The resulting slurry was vacuum filtered using a Kiriyama funnel, compacted from above, and then 845 g of water at 70°C was poured in several portions over the cake. The cake was then transferred to a beaker, 636 g of carbonated water was poured into the cake, and stirred and mixed for 1 hour. The resulting slurry was vacuum filtered using a Kiriyama funnel, compacted from above, and then 848 g of carbonated water was poured in several portions over the cake and filtered to obtain a wet cake (PPS particles). The moisture content of the PPS particles calculated from the loss on drying was 45 wt%.

[0068] <Production Example 1> (Preparation of aqueous solution containing the substance to be separated) Kanto Chemical Co., Inc.'s "Palladium Standard Stock Solution Pd1000" was dissolved in a 0.1 mol / L aqueous hydrochloric acid solution so that the palladium concentration was 10 mg / L (ppm) or 100 mg / L (ppm), respectively, to prepare a 10 ppm palladium standard solution and a 100 ppm palladium standard solution.

[0069] <Examples 1 to 16 and Comparative Examples 1 to 3> ·Process (1) 9.1 g of the PPS particles produced in Synthesis Example 1 (5.0 g as PPS resin) and 1 L of the 100 ppm palladium standard solution produced in Production Example 1 were placed in a 2 L beaker and stirred for 3 hours, after which the PPS resin was recovered by solid-liquid separation via suction filtration. The palladium concentration in the filtrate was measured with an atomic absorption spectrophotometer, and the amount of palladium adsorbed to PPS was calculated to be 20.0 mg / g.

[0070] ·Process (2) The palladium-adsorbed PPS particles obtained in step (1) were dispensed into 30 mL test tubes so that the PPS resin content was 0.05 g (1 mg of adsorbed palladium). 5 mL of eluent with the composition shown in Tables 1 to 3 was added to each tube. The mixture was then shaken horizontally at 200 rpm for 3 hours using a shaker (Yamato Scientific Co., Ltd., "SA300") at 30°C to reach equilibrium. The liquid phase was then recovered by solid-liquid separation using suction filtration. The elution rate (%) was calculated from the palladium concentration (ppm) of the liquid phase at equilibrium using the following formula. The results are shown in Tables 1 to 3. Elution rate (%) = Amount of palladium in liquid phase (mg) / 1mg x 100 In addition, 1 mg in the formula is the amount of palladium when 0.05 g of 20.0 mg / g palladium-adsorbed PPS particles is used.

[0071] [Table 1]

[0072] [Table 2]

[0073] [Table 3]

[0074] Example 17 ·Process (1) A glass cylindrical column with an inner diameter of 9 mm and a height of 100 mm was filled with 6.4 ml (1.8 g as PPS resin) of the PPS particles obtained in Synthesis Example 1, and a 10 ppm palladium standard solution prepared in Production Example 1 was passed through it at a flow rate of 10 ml / min (SV = 10). Thereafter, the aqueous solution discharged from the column outlet was collected in 10 portions of 600 mL each. As a result of measuring the palladium concentration of each of the obtained aqueous solutions, the average value was 10 ppb or less, which is the measurement limit of the atomic absorption spectrophotometer. Thereafter, the solution was passed through until the adsorption capacity of the adsorbent was saturated and the palladium concentration in the discharged solution became constant at 10 ppm, and then, in order to remove the unadsorbed palladium, 64 mL of a 0.1 mol / L hydrochloric acid aqueous solution was flowed, and then 64 mL of ultrapure water was flowed. At this time, the amount of palladium adsorbed on the column was 59.9 g, and the palladium adsorption amount with respect to the PPS resin was 33.3 mg / g. Amount of palladium (mg) = Amount of palladium in the liquid phase component (mg) - Amount of palladium in the discharged liquid (mg)

[0075] · Step (2) A 1 mol / L aqueous sodium hydroxide solution was flowed through the column that had undergone Step (1) at an SV of 10. First, 32 mL (5 times the column volume) of the eluent was passed through, and the concentration factor was calculated from the metal content of the recovered solution using the following formula. Note that 10 ppm is the concentration of the aqueous solution containing the separation target substance used in Step (1). Concentration factor (times) = Palladium concentration in the recovered solution (ppm) / 10 (ppm) Subsequently, another 64 mL of the eluent was passed through, and the elution rate was calculated from the metal content of the 96 mL of the recovered solution combined with the previously recovered solution using the following formula. Note that 59.9 mg is the amount of palladium adsorbed on the column calculated in Step (1). The results are shown in Table 4. Elution rate (%) = Amount of palladium in the recovered solution (mg) / 59.9 mg × 100

[0076] <Example 18> The procedure was carried out in the same manner as in Example 17 except that the space velocity (SV) of the eluent in Step (2) was 30. The results are shown in Table 4.

[0077] <Example 19> The procedure was carried out in the same manner as in Example 17, except that the space velocity (SV) of the eluent in step (2) was set to 100. The results are shown in Table 4.

[0078] <Comparative Example 4> The procedure was carried out in the same manner as in Example 17, except that the eluent in step (2) was changed from a 1 mol / L aqueous sodium hydroxide solution to ultrapure water. The results are shown in Table 4.

[0079] <Comparative Example 5> The procedure was carried out in the same manner as in Example 17, except that the eluent in step (2) was changed from a 1 mol / L aqueous sodium hydroxide solution to a 0.1 mol / L aqueous hydrochloric acid solution. The results are shown in Table 4.

[0080]

Table 4

[0081] <Example 20> To the column that had undergone steps (1) and (2) in Example 17, 64 ml of ultrapure water was further passed to wash and regenerate the PPS particles. Using this column, steps (1) and (2) and the regeneration by the above-described water washing were repeated 10 times in the same manner as in Example 17. The adsorption rate and elution rate for each cycle are shown in Table 5. Adsorption rate (%) = Amount of palladium adsorbed per cycle (mg) / Amount of palladium adsorbed in Example 17 (mg) × 100 Elution rate (%) = Amount of palladium eluted per cycle (mg) / Amount of palladium adsorbed per cycle (mg) × 100

[0082]

Table 5

[0083] <Evaluation>

[0084] (1) Evaluation of the metal content in the solution The palladium concentration and amount of the solution in each example and comparative example were measured by the furnace method using a Shimadzu Corporation atomic absorption spectrophotometer "GFA-7000A." For the calibration curve, solutions were used in which "Palladium Standard Stock Solution (Pd 1000)," a palladium standard solution for atomic absorption spectrometry manufactured by Kanto Chemical Co., Ltd., was diluted with 0.5% by volume of nitric acid aqueous solution to 0, 50, 100, 150, 200, and 250 ppb. The measurement solution was also diluted with 0.5% by volume of nitric acid aqueous solution to fall within the calibration curve range of 0 to 250 ppb.

[0085] Comparing Examples 1 to 16 with Comparative Examples 1 to 3, Tables 1 to 3 show that the elution rate is excellent when the eluent used is an alkaline aqueous solution or an aqueous solution containing a sulfur- or nitrogen-containing chelating agent, demonstrating that the method of the present disclosure is a method for efficiently separating and recovering metal atoms, which are the target substances to be separated. Table 4 suggests that, even when PPS particles are supported on a column, the separation and recovery method of the present disclosure, which uses a specific eluent, is excellent in elution rate. Furthermore, because of the excellent elution rate, it was confirmed that the concentration degree is also high. Table 5 suggests that the separation and recovery method of the present disclosure can maintain its performance even when repeatedly performed.

Claims

1. A separation and recovery method for separating and recovering a target substance from an aqueous solution containing the target substance using polyarylene sulfide resin particles, comprising: a step (1) of bringing an aqueous solution containing the target substance into contact with polyarylene sulfide resin particles to selectively adsorb the target substance contained in the aqueous solution onto the polyarylene sulfide resin particles and removing it from the aqueous solution; and a step (2) of bringing an eluent into contact with the polyarylene sulfide resin particles to elute the target substance, wherein the target substance is a metal atom or a compound containing a metal atom (however, excluding sodium atoms and lithium atoms as metal atoms), and the eluent is an aqueous alkali solution of 0.5 to 2 mol / L or an aqueous solution in which 1 to 10% by mass of a sulfur atom- or nitrogen atom-containing chelating agent is dissolved.

2. The separation and recovery method according to Claim 1, wherein the contact between the aqueous solution containing the target substance and the polyarylene sulfide resin particles is carried out in the absence of a surfactant.

3. The polyarylene sulfide resin particles used in the step (1) are recycled products, and the recycled polyarylene sulfide resin particles are those obtained by adsorbing the target substance, bringing them into contact with the eluent, and then further washing with water for regeneration.

4. The separation and recovery method according to Claim 3, wherein the elution rate of the recycled polyarylene sulfide resin particles is 95% or more.

5. The separation and recovery method according to Claim 1 or 2, wherein the method of bringing the polyarylene sulfide resin particles into contact with the aqueous solution containing the target substance and the eluent in the steps (1) and (2) is to supply and bring into contact the aqueous solution containing the target substance and the eluent, respectively, to the polyarylene sulfide resin particles immobilized in a flow path.

6. The separation and recovery method according to Claim 5, wherein the space velocity (SV) in the flow path of the aqueous solution containing the target substance is 100 or less.

7. The separation and recovery method according to Claim 5, wherein the space velocity (SV) in the flow path of the eluent is 30 or less.

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