Metal recovery agent, metal recovery member, metal recovery solution, and metal recovery method

Abstract

The metal recovery agent comprises a reducing compound represented by chemical formula (1), and precipitates a metal by reduction by the reducing compound. In the following chemical formula (1), R1 is CH3 or CHO, R2 is CH = CH2 or CHO, R3 is CH3 or CHO, R4 is CH2CH3 or CH = CH2, R5 is COOCH3 or H, R6 is alkyl or H, and M is metal or hydrogen. # imgabs0 #

Description

Technical Field

[0001] The invention relates to a metal recovery agent, a metal recovery component, a metal recovery liquid agent and a metal recovery method. Background Art

[0002] Conventionally, there is known a method for recovering trace metals dissolved in a solution by a biological method. Specifically, Patent Document 1 discloses a method for recovering metals using algae.

[0003] The metal recovery agent or metal compound recovery agent of Patent Document 1 includes a dried product of cells of red algae of the order Cyanidium, a dried product of a cell-derived product of red algae of the order Cyanidium, or an artificial product that imitates a dried product of cells or a dried product of a cell-derived product. Moreover, according to Patent Document 1, the metal recovery agent and the metal recovery method can simply and effectively selectively recover precious metals from a solution with a high acid concentration or the like.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: International Publication No. 2018 / 155687 Summary of the invention

[0007] Problems to be solved by the invention

[0008] In organisms such as algae, there are complex reaction pathways contributed by various molecules. However, it is not easy to artificially control such multiple reactions. Therefore, in biological methods using algae, it may be difficult to reduce and recover metals under a controlled environment.

[0009] Therefore, an object of the present disclosure is to provide a metal recovery agent, a metal recovery member, a metal recovery liquid agent, and a metal recovery method that are capable of recovering metals under a human-controlled environment.

[0010] Methods for solving problems

[0011] The metal recovery agent of the present disclosure comprises a reducing compound represented by the following chemical formula (1), and metal is precipitated by reduction with the reducing compound.

[0012] [Chemistry 1]

[0013]

[0014] In the above chemical formula (1), R1 is CH3 or CHO, R2 is CH=CH2 or CHO, R3 is CH3 or CHO, R4 is CH2CH3 or CH=CH2, R5 is COOCH3 or H, R6 is a hydrocarbon group or H, and M is a metal or hydrogen.

[0015] The reducing compound may be at least one selected from the group consisting of chlorophyll a, pheophorbidea, pyropheophorbide a, and pheophytin a.

[0016] The standard electrode potential of the metal precipitated by the reduction of the reducing compound may be higher than the standard electrode potential of aluminum.

[0017] The metal precipitated by the reduction based on the reducing compound may include at least one selected from the group consisting of gold, silver, copper, tin, cobalt, iron, silicon, nickel, platinum, palladium, rhodium, iridium, ruthenium, osmium, strontium, manganese, cesium, scandium, yttrium and lanthanide elements.

[0018] The metal precipitated by the reduction with the reducing compound may include gold.

[0019] The metal recovery member of the present disclosure includes a metal recovery agent and a carrier that supports the metal recovery agent.

[0020] The metal recovery liquid agent disclosed in the present invention comprises a liquid and a metal recovery agent dispersed or dissolved in the liquid.

[0021] The metal recovery method disclosed herein includes a step of reducing and precipitating a metal dissolved in a metal solution using a reducing compound represented by the following chemical formula (1).

[0022] [Chemistry 2]

[0023]

[0024] In the above chemical formula (1), R1 is CH3 or CHO, R2 is CH=CH2 or CHO, R3 is CH3 or CHO, R4 is CH2CH3 or CH=CH2, R5 is COOCH3 or H, R6 is a hydrocarbon group or H, and M is a metal or hydrogen.

[0025] In the step of reducing the metal, the reducing compound may be irradiated with light.

[0026] Effects of the Invention

[0027] According to the present disclosure, a metal recovery agent, a metal recovery member, a metal recovery liquid agent, and a metal recovery method capable of recovering metals under a human-controlled environment can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is the absorption spectrum of the test liquid of Example, Comparative Example and Reference Example. DETAILED DESCRIPTION

[0029] Hereinafter, several exemplary embodiments will be described with reference to the drawings. It should be noted that, for the sake of convenience of description, the dimensional ratios in the drawings are exaggerated and may be different from the actual ratios.

[0030] [Metal recovery agent]

[0031] First, the metal recovery agent of the present embodiment is described. The metal recovery agent of the present embodiment precipitates metal by reduction based on a reducing compound. Therefore, the metal recovery agent can also be referred to as a reducing agent. Specifically, the metal recovery agent has a reducing compound represented by the following chemical formula (1). The reducing compound of the present embodiment has a chlorin structure. The reducing compound can be used alone or in combination with a plurality of reducing compounds. In addition, the reducing compound can also be a monomer or a mixture of reducing compounds instead of forming a complex with a substance such as a protein.

[0032] [Chemistry 3]

[0033]

[0034] In the above chemical formula (1), R1 is CH3 or CHO, R2 is CH=CH2 or CHO, R3 is CH3 or CHO, R4 is CH2CH3 or CH=CH2, R5 is COOCH3 or H, R6 is a hydrocarbon group or H, and M is a metal or hydrogen. That is, R1 can be CH3 or CHO. In addition, R2 can be CH=CH2 or CHO. In addition, R3 can be CH3 or CHO. R4 can be CH2CH3 or CH=CH2. R5 can be COOCH3 or H. R6 can be a hydrocarbon group or H. M can be a metal or hydrogen.

[0035] In the above chemical formula (1), the hydrocarbon group of R6 may be an alkyl group, an alkenyl group, an alkynyl group or an aryl group. The number of carbon atoms of the hydrocarbon group of R6 may be 1 or more and 100 or less, 1 or more and 50 or less, 1 or more and 30 or less, or 1 or more and 20 or less. Specifically, the hydrocarbon group of R6 may be a phytyl group (-C 20 H 39 ). In addition, in the above chemical formula (1), the metal represented by M may be, for example, Mg.

[0036] The reducing compound may be at least one selected from the group consisting of chlorophyll a, pheophorbide a, pyropheophorbide a and pheophytin a. Chlorophyll a is a type of pigment used for photosynthesis, and is contained in organisms such as plants, algae and cyanobacteria. Chlorophyll a and chlorophyll a derivatives, namely pheophorbide a, pyropheophorbide a and pheophytin a, exist in large quantities on the earth and can also be synthesized by organisms such as those mentioned above. Therefore, by using these reducing compounds, metals can be recovered with a low environmental load. In addition, by precipitating metals based on the above-mentioned reducing compounds, it is also possible not to use special microorganisms, nor to study the conditions for the subculture of such microorganisms or to worry about extinction. In addition, these compounds can be extracted from general organisms that are easy to culture, so the cost required for metal recovery can be reduced.

[0037] Chlorophyll a is a compound represented by the following chemical formula (2): That is, chlorophyll a is a compound represented by the chemical formula (1) above, wherein R1 is CH3, R2 is CH=CH2, R3 is CH3, R4 is CH2CH3, R5 is COOCH3, R6 is phytyl, and M is Mg.

[0038] [Chemistry 4]

[0039]

[0040] Pheophorbide a is a compound represented by the following chemical formula (3). That is, pheophorbide a is a compound in which R1 is CH3, R2 is CH=CH2, R3 is CH3, R4 is CH2CH3, R5 is COOCH3, R6 is H, and M is 2 hydrogen atoms in the above chemical formula (1). Pheophorbide a is a compound in which the phytyl group of chlorophyll a is replaced by a hydrogen atom and magnesium is replaced by 2 hydrogen atoms.

[0041] [Chemistry 5]

[0042]

[0043] Pyropheophorbide a is a compound represented by the following chemical formula (4). That is, pyropheophorbide a is a compound in which, in the above chemical formula (1), R1 is CH3, R2 is CH=CH2, R3 is CH3, R4 is CH2CH3, R5 is H, R6 is H, and M is 2 hydrogen atoms. Specifically, pyropheophorbide a is a compound in which the methoxycarbonyl group (-COOCH3) of pheophorbide a is replaced by a hydrogen atom. That is, pyropheophorbide a is a compound in which the methoxycarbonyl group (-COOCH3) of chlorophyll a is replaced by a hydrogen atom, the phytyl group of chlorophyll a is replaced by a hydrogen atom, and magnesium is replaced by 2 hydrogen atoms.

[0044] [Chemistry 6]

[0045]

[0046] Pheophytin a is a compound represented by the following chemical formula (5). That is, pheophytin a is a compound in which, in the above chemical formula (1), R1 is CH3, R2 is CH=CH2, R3 is CH3, R4 is CH2CH3, R5 is COOCH3, R6 is phytyl, and M is 2 hydrogen atoms. Specifically, pheophytin a is a compound in which the magnesium of chlorophyll a is replaced by 2 hydrogen atoms.

[0047] [Chemistry 7]

[0048]

[0049] It should be noted that, as examples of the reducing compound, chlorophyll a, pheophorbide a, pyropheophorbide a and pheophytin a can be cited, but the reducing compound may be a compound other than these. The reducing compound may be, for example, chlorophyll b, chlorophyll d and chlorophyll f and their derivatives. As derivatives of chlorophyll, pheophorbide, pyropheophorbide and pheophytin can be cited.

[0050] Chlorophyll b is in the above chemical formula (1), R1 is CH3, R2 is CH=CH2, R3 is CHO, R4 is CH2CH3, R5 is COOCH3, R6 is phytyl, and M is Mg.

[0051] Chlorophyll d is wherein in the above chemical formula (1), R1 is CH3, R2 is CHO, R3 is CH3, R4 is CH2CH3, R5 is COOCH3, R6 is phytyl, and M is Mg.

[0052] Chlorophyll f is in the above chemical formula (1), R1 is CHO, R2 is CH=CH2, R3 is CH3, R4 is CH2CH3, R5 is COOCH3, R6 is phytyl, and M is Mg.

[0053] The metal recovery agent may be, for example, a powder containing a plurality of particles of a reducing compound, a combination of a plurality of particles, or a combination thereof. The shape of the particles of the reducing compound is not particularly limited, and may be at least one shape selected from the group consisting of needle-like, angular, dendritic, fibrous, sheet-like, irregular, teardrop-like, and spherical. The shape of the combination is not particularly limited, and may be sheet-like, rod-like, prismatic, spherical, cylindrical, irregular, or a combination thereof.

[0054] The metal recovery agent precipitates the metal by reducing the reducing compound. Specifically, the metal is recovered from a solution in which the metal is dissolved. The solution in which the metal is dissolved contains ions containing the metal. The metal is precipitated by supplying electrons to the ions containing the metal to reduce them, and the metal in the solution can be recovered. The ions containing the metal can be Ag, + The cation that releases electrons from a single metal element can also be the tetrachloroaurate (III) ion ([AuCl4] - ), dicyanohydride(I) ion ([Au(CN)2] - ) and Au(HS) 2- And so on.

[0055] The standard electrode potential of the metal precipitated by reduction based on the reducing compound may be higher than the standard electrode potential of aluminum. Such a metal is easily precipitated by reduction based on the reducing compound. Therefore, the metal precipitated by reduction based on the reducing compound may include aluminum, or may include a metal with a larger standard electrode potential than aluminum.

[0056] The metal precipitated by reduction can specifically include at least one selected from the group consisting of gold, silver, copper, tin, cobalt, iron, silicon, nickel, platinum, palladium, rhodium, iridium, ruthenium, osmium, strontium, manganese, cesium, scandium, yttrium and lanthanide elements. These metals are useful in industry. It should be noted that as lanthanide elements, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium can be cited. The metal can include gold. Gold is also used as an ornament, and its rarity is high, so its utilization value is high.

[0057] The metal precipitated by reduction can be crystalline or amorphous. In addition, the average particle size of the metal precipitated by reduction can be more than 0.1nm or more than 10nm. The average particle size of the metal precipitated by reduction can be more than 1nm. In addition, the average particle size of the metal precipitated by reduction can be less than 10mm, less than 1mm, less than 100μm, less than 10μm, less than 1μm or less than 100nm. The metal can migrate on the surface and grow crystals after being reduced at the atomic level. It should be noted that the average particle size is a value calculated as the average value of the particle size of particles observed in several to dozens of fields of view using an observation device such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0058] The metal recovery agent may contain 50 mass % or more, 60 mass % or more, 70 mass % or more, 80 mass % or more, 90 mass % or more, 95 mass % or more, or 99 mass % or more of the reducing compound.

[0059] As described above, the metal recovery agent of the present embodiment comprises the reducing compound represented by the above chemical formula (1), and metal is precipitated by reduction of the reducing compound. Therefore, according to the metal recovery agent of the present embodiment, metal can be recovered under a human-controlled environment.

[0060] [Metal recycling components]

[0061] Next, the metal recovery component of the present embodiment is described. The metal recovery component of the present embodiment comprises the above-mentioned metal recovery agent and a carrier that supports the metal recovery agent. In the metal recovery component of the present embodiment, the metal recovery agent is supported on the carrier, so that the handling of the metal recovery agent becomes easy. For example, by contacting the metal recovery component with a metal solution in which a metal is dissolved, the metal in the metal solution can be easily recovered.

[0062] The shape of the carrier is not particularly limited as long as it can carry the metal recovery agent. The carrier can be, for example, fibrous. The material of the carrier is not particularly limited, and can include, for example, at least one selected from the group consisting of cellulose, glass, plastic, carbon, metal, ceramic, and wood. The metal recovery member can also be, for example, a sheet material containing a fibrous carrier loaded with a metal recovery agent.

[0063] [Metal recovery liquid]

[0064] Next, the metal recovery liquid agent of the present embodiment is described. The metal recovery liquid agent of the present embodiment comprises a liquid and the above-mentioned metal recovery agent dispersed or dissolved in the liquid. In the metal recovery liquid agent of the present embodiment, the metal recovery agent is dispersed or dissolved in the liquid, so the handling of the metal recovery agent becomes easy. For example, by mixing the metal recovery liquid agent with a metal solution in which a metal is dissolved, the metal in the metal solution can be easily recovered.

[0065] The liquid in which the metal recovery agent is dispersed or dissolved can be an organic compound, an inorganic compound or a mixed liquid thereof. The organic compound can be an alcohol, a ketone, a methyl halide or a mixed liquid thereof. The inorganic compound can be water. The alcohol can be at least one selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-methyl-1-propanol, 2-butanol and 1-methyl-2-propanol. The ketone can be at least one of acetone and methyl ethyl ketone. The methyl halide can be methylene dichloride for example.

[0066] The metal recovery agent may be dispersed in a liquid, may be dissolved in a liquid, or may be dispersed and dissolved in a liquid. In addition, the content of the metal recovery agent in the metal recovery liquid agent is not particularly limited and can be appropriately prepared.

[0067] [Metal recovery method]

[0068] Next, the metal recovery method of the present embodiment is described. The metal recovery method of the present embodiment includes a step of reducing the metal dissolved in the metal solution using the reducing compound represented by the above chemical formula (1) to precipitate. Therefore, according to the metal recovery method of the present embodiment, as described above, the metal can be recovered under a human-controlled environment.

[0069] The metal solution contains metal dissolved therein and contains ions containing the metal. For example, when the metal solution is brought into contact with the reducing compound by adding or impregnating the reducing compound in the metal solution, electrons are supplied to the ions containing the metal to reduce the metal. Then, the metal in the solution can be recovered by precipitating the reduced metal.

[0070] The metal solution is not particularly limited, and examples thereof include electronic industrial wastewater such as plating waste liquid, seawater, and solutions containing metal element substances. The solution containing metal element substances may specifically be a solution obtained by dissolving a portion or all of at least one of the metal and metal compound contained in the metal element-containing substance. The metal element-containing substance is not particularly limited as long as it is a substance containing one or more metal elements, more specifically a substance containing a metal or a metal compound. The metal element-containing substance may be, for example, a so-called urban mine such as an electronic substrate in waste electronic equipment. As described above, the metal contained in the metal solution is the same as the metal precipitated by reduction, so the description is omitted.

[0071] The concentration of the metal in the metal solution is not particularly limited and can be 10 -6 ppm and above 10 5 ppm or less. By setting the metal concentration to the above range, the recovery of metals can be promoted. The metal concentration can be 10 -5 ppm or above, 10 - 4 ppm or above, 10 -3 The concentration of the metal may be less than 10000 ppm, less than 5000 ppm, less than 2500 ppm, less than 1000 ppm, less than 500 ppm, less than 250 ppm or less than 125 ppm. It should be noted that, in this specification, ppm means parts per million by mass.

[0072] The pH of the metal solution is not particularly limited, and may be, for example, -3 or more and 8 or less. The pH of the metal solution may be -2 or more, -1 or more, 0 or more, 1 or more, 2 or more, 3 or more, 4 or more, 5 or more, or 6 or more. The pH of the metal solution may be 7 or less.

[0073] The ratio of the mass of the reducing compound to the mass of the metal in the metal solution (hereinafter also referred to as the reducing compound / metal ratio) is not particularly limited, and may be, for example, 0.1 to 10000. By setting the reducing compound / metal ratio to the above range, the recovery of the metal can be promoted. The reducing compound / metal ratio may be greater than 0.5, greater than 1, greater than 1.5, or greater than 2. In addition, the reducing compound / metal ratio may be less than 1000, less than 500, less than 100, less than 50, less than 10, or less than 5.

[0074] The amount of the reducing compound relative to the metal solution is not particularly limited. From the viewpoint of performing a reduction reaction of the metal, the reducing compound can be contacted with the metal solution in a manner such that the amount of the reducing compound relative to the metal solution is 0.2 mg / 100 mL or more and 1000 mg / 100 mL or less. The amount of the reducing compound relative to the metal solution can be 2, 10, 20 or 40 mg / 100 mL or more. In addition, the amount of the reducing compound relative to the metal solution can be 500, 400, 200 or 100 mg / 100 mL or less.

[0075] The temperature when reducing the metal is not particularly limited, and may be, for example, 0° C. or higher and 100° C. or lower. The temperature may be 10° C. or higher, or 20° C. or higher. In addition, the temperature may be 70° C. or lower, 50° C. or lower, 40° C. or lower, or 30° C. or lower.

[0076] From the viewpoint of fully carrying out reduction reaction, the time of reducing metal can be, for example, more than 5 minutes, can be more than 30 minutes, can be more than 1 hour, can be more than 8 hours, can be more than 1 day, can be more than 3 days, can be more than 4 days, can be more than 5 days. In addition, the time of reducing metal can be, for example, less than 20 days, can be less than 10 days, can be less than 8 days, can also be less than 6 days.

[0077] In the process of reducing the metal, the reducing compound may be irradiated with light. By irradiating the reducing compound with light, the reduction reaction of the metal based on the reducing compound can be promoted. In this case, the light irradiated to the reducing compound may also include visible light. The light irradiated to the reducing compound may have a light component in a wavelength of more than 300nm and less than 700nm. The light source of the light irradiated to the reducing compound may also include at least one of natural light and a light irradiation device. Natural light may also include sunlight. The light irradiation device may also include at least one selected from the group consisting of LED (Light Emission Diode), fluorescent lamp and incandescent lamp. It should be noted that in the process of reducing the metal, in order not to irradiate the reducing compound with light, the metal may be reduced while shielding the light.

[0078] The light quantum flux density of the light irradiated to the reducing compound can be 10 μmol·m -2 ·s -1 By making the photon flux density greater than the above value, the reduction reaction of the metal based on the reducing compound can be further promoted. It should be noted that in this specification, the photon flux density refers to the number of photons per unit time and per unit area contained in a wavelength of 300nm to 700nm.

[0079] The metal solution is preferably stirred during the reduction of the metal. The number of revolutions of the stirring is not particularly limited, and may be, for example, 100 rpm to 1000 rpm.

[0080] The metal precipitated from the metal solution can be separated by membrane separation such as filtration and centrifugal separation. The precipitated metal can be adsorbed on the reducing compound, or it can be separated from the reducing compound to form a colloidal solution, or it can be a combination thereof. In the case where the precipitated metal is attached to the reducing compound, the precipitated metal can be recovered by recovering the reducing compound. In the case where the precipitated metal is separated from the reducing compound, the precipitated metal can be recovered by removing the reducing compound from the metal solution.

[0081] In order to separate the precipitated metal from the reducing compound, ultrasonic treatment may also be performed. Ultrasonic treatment may be performed before separating the reducing compound from the metal solution, or after separating the reducing compound from the metal solution and immersing the separated reducing compound in a liquid. When ultrasonic treatment is performed after immersing the separated reducing compound in a liquid, a metal colloidal solution with higher purity can be obtained.

[0082] The process of recovering the metal may also include a process of calcining the recovered reducing compound in order to recover the metal from the recovered reducing compound. Through this process, the reducing compound itself is removed, and the metal adsorbed on the reducing compound can be recovered. Calcination can be easily performed in the air, for example. The calcination temperature is not particularly limited and can be appropriately selected according to the melting point of the metal. The calcination temperature can be, for example, 800°C to 1200°C. The calcination temperature can be constant or can be increased in stages. For example, the reducing compound can be first heated at the combustion temperature of the reducing compound for a certain period of time, and then, in order to improve the crystallinity of the metal, the heating is continued at a temperature near the melting point of the metal.

[0083] After the recovered reducing compound is shaped, the shaped reducing compound can be calcined to form a metal molded object. The molding of the reducing compound can, for example, mold the recovered reducing compound into a desired shape such as a star or heart. The method for molding the reducing compound is not particularly limited, for example, the reducing compound recovered into a mold having a desired shape can be compacted. The shaped recycling agent can also be calcined under the above conditions. The metal molded object can be used for jewelry. That is, the manufactured metal molded object can also be used as jewelry such as necklaces and earrings.

[0084] Example

[0085] Hereinafter, the present embodiment will be described in more detail with reference to Examples, Comparative Examples, and Reference Examples, but the present embodiment is not limited to these Examples.

[0086] [Example 1]

[0087] In a 300 mL beaker, water and tetrachloroauric acid (III) tetrahydrate (HAuCl4·4H2O) manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. were mixed to prepare 100 mL of HAuCl4 aqueous solution so that the gold concentration was 100 ppm (Au content 10 mg) by mass ratio. 50 mg of chlorophyll a (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product number 034-21361) (CAS registration number 479-61-8) was added to the HAuCl4 aqueous solution to obtain a prepared solution with a pH of about 5.

[0088] At room temperature (about 25°C), the light quantum flux density is about 100 μmol·m -2 ·s -1 The prepared solution was stirred for 5 days while the stirring bar was rotated at 300 rpm. The stirred solution was filtered and the test solution was collected.

[0089] [Example 2]

[0090] The test solution was collected in the same manner as in Example 1 except that pheophorbide a (manufactured by Cayman Chemical Co., product number 16072) (CAS registration number 15664-29-6) was used instead of chlorophyll a.

[0091] [Example 3]

[0092] The test solution was collected in the same manner as in Example 1 except that pyropheophorbide a (produced by Cayman Chemical Co., product number 21371) (CAS registration number 24533-72-0) was used instead of chlorophyll a.

[0093] [Example 4]

[0094] The test solution was collected in the same manner as in Example 1 except that pheophytin a (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product number 167-13771) (CAS registration number 603-17-8) was used instead of chlorophyll a.

[0095] [Comparative Example 1]

[0096] The test solution was collected in the same manner as in Example 1 except that chlorophyll a was not added.

[0097] [Reference Example 1]

[0098] The HAuCl4 aqueous solution before adding the chlorophyll a prepared in Example 1 was used as a test solution.

[0099] [evaluate]

[0100] The test solution obtained as described above was measured by ultraviolet-visible spectroscopy. The spectrum obtained by ultraviolet-visible spectroscopy is shown in Figure 1 .like Figure 1 As shown in the figure, the peaks of HAuCl4 specific to Examples 1 to 4 at a wavelength of 310 nm are smaller than those of Comparative Example 1 and Reference Example 1. From this result, it can be seen that the gold in the HAuCl4 aqueous solution is reduced and precipitated in Examples 1 to 4. On the other hand, the spectra of Comparative Example 1 and Reference Example 1 almost overlap and are difficult to distinguish. From this result, it can be seen that the gold in the HAuCl4 aqueous solution is almost not reduced in Comparative Example 1.

[0101] Next, the gold recovery rate was calculated based on the measurement results of the ultraviolet-visible spectroscopy. The gold recovery rate was calculated by the following mathematical formula (1).

[0102] Gold recovery rate (%) = (absorbance of the peak near the wavelength of 310 nm in the examples and comparative examples / absorbance of the peak near the wavelength of 310 nm in reference example 1) × 100 (1)

[0103] [Table 1]

[0104] Reducing compounds Stirring Gold recovery rate (%) Example 1 Chlorophyll a 5 days 93 Example 2 Pheophorbide a 5 days 79 Example 3 Pyropheophorbide a 5 days 56 Example 4 Pheophytin a 5 days 24 Comparative Example 1 - 5 days 0 Reference Example 1 - Day 0 0

[0105] As shown in Table 1, the gold recovery rate when chlorophyll a was used in Example 1 was 93%. The gold recovery rate when ferropheophorbide a was used in Example 2 was 79%. The gold recovery rate when pyropheophorbide a was used in Example 3 was 56%. The gold recovery rate when pheophytin a was used in Example 4 was 24%. On the other hand, the gold recovery rate when no reducing compound was used as in Comparative Example 1 was 0%. From these results, it can be seen that metals can be recovered by using a metal recovery agent having a reducing compound represented by the above chemical formula (1).

[0106] The entire contents of Japanese Tokugan Application No. 2022-141343 (filing date: September 6, 2022) are incorporated herein by reference.

[0107] Several embodiments have been described above, but the embodiments may be modified or altered based on the above disclosure. All the components of the above embodiments and all the features described in the claims may be extracted and combined as long as they do not contradict each other.

[0108] The present disclosure can contribute to, for example, Goal 9 of the Sustainable Development Goals (SDGs) led by the United Nations, "Build resilient infrastructure, promote inclusive and sustainable industry, and foster innovation" and Goal 12, "Ensure sustainable consumption and production patterns."

Claims

1. A metal recovery agent comprising a reducing compound represented by the following chemical formula (1), wherein metal is precipitated by reduction of the reducing compound. [Chemistry 1] In the above chemical formula (1), R1 is CH3 or CHO, R2 is CH=CH2 or CHO, R3 is CH3 or CHO, R4 is CH2CH3 or CH=CH2, R5 is COOCH3 or H, R6 is a hydrocarbon group or H, and M is a metal or hydrogen.

2. The metal recovery agent according to claim 1, wherein: The reducing compound is at least one selected from the group consisting of chlorophyll a, pheophorbide a, pyropheophorbide a and pheophytin a.

3. The metal recovery agent according to claim 1 or 2, wherein: The standard electrode potential of the metal precipitated by the reduction of the reducing compound is equal to or higher than the standard electrode potential of aluminum.

4. The metal recovery agent according to any one of claims 1 to 3, wherein The metal precipitated by the reduction of the reducing compound includes at least one selected from the group consisting of gold, silver, copper, tin, cobalt, iron, silicon, nickel, platinum, palladium, rhodium, iridium, ruthenium, osmium, strontium, manganese, cesium, scandium, yttrium and lanthanide elements.

5. The metal recovery agent according to any one of claims 1 to 4, wherein The metal precipitated by the reduction of the reducing compound includes gold.

6. A metal recovery component comprising: The metal recovery agent according to any one of claims 1 to 5, and A carrier for supporting the metal recovery agent.

7. A metal recovery liquid agent, comprising: Liquid, and The metal recovery agent according to any one of claims 1 to 5 dispersed or dissolved in the liquid.

8. A method for recovering metals, comprising the step of reducing and precipitating a metal dissolved in a metal solution using a reducing compound represented by the following chemical formula (1), In the above chemical formula (1), R1 is CH3 or CHO, R2 is CH=CH2 or CHO, R3 is CH3 or CHO, R4 is CH2CH3 or CH=CH2, R5 is COOCH3 or H, R6 is a hydrocarbon group or H, and M is a metal or hydrogen.

9. The metal recovery method according to claim 8, wherein: In the step of reducing the metal, the reducing compound is irradiated with light.

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