Method for recovering gold

Abstract

To easily isolate and recover gold from an adsorbent by adsorbing gold from a solution in which various noble metals are dissolved by using the adsorbent.SOLUTION: Gold is recovered by a method including the following steps (1) to (4). Step (1) of bringing the adsorbent (A) into contact with a solution (B) containing gold ions to selectively adsorb the gold ions, step (2) of immersing the adsorbent (A) adsorbing the gold ions in water (C), step (3) of isolating the gold ions adsorbed on the adsorbent (A) as gold in the water (C) by a reduction reaction, and step (4) of recovering the isolated gold by removing the water (C) SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for the selective recovery of gold with high efficiency. [Background technology]

[0002] Gold has long been used in jewelry due to its attractive golden luster, but its industrial aspects, such as low electrical resistance and high ductility, have attracted attention and it has come to be used widely in electrical appliances as an electronic component, supporting today's civilized society.

[0003] To enrich and enhance people's lives, advances in the technological sophistication of electrical appliances are underway, and the use of gold in electronic components is steadily increasing. Because the Earth's gold reserves are limited, gold recycling—that is, the separation, recovery, and reuse of gold contained in industrial waste and discarded electrical appliances—is essential for continued technological advancement. In addition, various industrial sectors have recently been focusing on the reuse and recycling of valuable materials, such as resource recovery. It has become clear that industrial waste and discarded electrical appliances generated in cities contain more precious metals than actual mine reserves, creating a demand for resource recycling that recovers and utilizes these precious metals.

[0004] Methods proposed for recovering gold from industrial waste and discarded electrical appliances include, for example, extracting gold ions into an organic solvent from a gold ion-containing solution obtained by dissolving the gold in an acid solution, and recovering gold ions using an adsorbent.

[0005] That is, Patent Document 1 discloses a method in which gold ions are extracted using dibutyl carbitol, which is stable, has low volatility, is low toxic, and is easy to handle, as a solvent, and after scrubbing, an aqueous oxalic acid solution is mixed to carry out a reduction reaction, thereby reducing and recovering gold.

[0006] Furthermore, Patent Document 2 discloses a method in which gold ions are selectively adsorbed using a polymer with ether and tertiary amide groups introduced as functional groups into the side chains as an adsorbent, and gold is eluted using hot water as an eluent. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-233317 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-198330 Summary of the Invention [Problem to be solved by the invention]

[0008] In Patent Document 1, the use of dibutyl carbitol, which has low volatility and toxicity, as an extraction solvent reduces the burden on the environment even when a large amount of solvent is used. However, because the solubility of oxalic acid used in the reduction reaction in water is low, the amount of oxalic acid solution increases as the amount of gold to be reduced increases, which may require larger equipment.

[0009] In Patent Document 2, gold ions can be selectively adsorbed and gold can be eluted simply by using hot water. However, the gold ions cannot be completely recovered and may remain in the solution or the adsorbent because the adsorbent has low gold ion adsorption performance and also has a poor ability to elute gold ions from the adsorbent.

[0010] In view of the above-mentioned problems with the conventional technology, the present invention aims to recover gold efficiently even on a small scale, and proposes a method for selectively adsorbing gold from a solution containing various noble metals using an adsorbent, and for easily isolating and recovering gold from the adsorbent. [Means for solving the problem]

[0011] The above-mentioned problems of the present invention can be solved by a method for recovering gold comprising the following steps (1) to (4). Step (1) The adsorbent (A) is brought into contact with a solution (B) containing gold ions to selectively adsorb the gold ions. Step (2) Immerse the adsorbent (A) that has adsorbed gold ions in water (C). Step (3): The gold ions adsorbed on the adsorbent (A) are subjected to a reduction reaction to isolate gold in water (C). Step (4) Recovering the isolated gold by removing water (C). [Effects of the Invention]

[0012] In the present invention, gold can be selectively adsorbed from a solution containing a mixture of multiple metal ions, and gold can be easily isolated and recovered from the adsorbent. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention relates to a technology in which an adsorbent (A) is brought into contact with a solution (B) containing gold ions to selectively adsorb gold ions onto the adsorbent (A), the adsorbent (A) is then immersed in water (C), and the gold ions adsorbed onto the adsorbent (A) are isolated as gold by a reduction reaction. Finally, the water (C) is removed, enabling highly efficient recovery of gold.

[0014] Each step will be described below. In the present invention, first, the adsorbent (A) is brought into contact with a solution (B) containing gold ions to selectively adsorb the gold ions. It is important to use an adsorbent (A) that selectively adsorbs gold ions.

[0015] Industrial waste and discarded electrical appliances are generally collected and separated into individual products. Plastic packaging is then separated and crushed, and substrates containing precious metals such as gold are dissolved in a solvent to recover the precious metals. However, the solvent contains many other metals, such as iron, aluminum, copper, and zinc, making isolation and recovery difficult. Furthermore, the proportion of gold contained in industrial waste and discarded electrical appliances is low compared to base metals such as iron, aluminum, and copper. Therefore, when attempting to recover gold ions from a solution containing various metal ions, these base metals are often mixed in as impurities, making high-purity recovery difficult. Therefore, selective adsorption of a small amount of gold ions from various metal ions in a solution is important for achieving the object of the present invention. The present inventors have conducted extensive research into this issue and found that for selective adsorption of gold ions, it is effective for the adsorbent (A) to be made of a material containing an amine group or an amide group.

[0016] Examples of materials capable of selectively adsorbing gold ions include chitosan containing amino groups that form chelate complexes with gold ions and selectively adsorb gold ions; polyamides and polyacrylamides containing amide groups that similarly form chelate complexes with gold ions and selectively adsorb gold ions; polymers with amino or amide groups substituted on their side chains; and low-molecular-weight compounds containing amino or amide groups. The present invention aims to efficiently recover gold from a solvent containing a variety of metals. To implement this recovery process, it is necessary to consider factors such as the ease of handling and heat resistance of the substrate. Therefore, materials containing polyamides, which are crystalline polymers with excellent mechanical properties, are preferred. Considering the moldability and processability of the substrate, polyamides, such as poly-ε-capramide (nylon 6), polyhexamethylene adipamide (nylon 66), and copolymers thereof, are more preferred.

[0017] With increasing attention being paid to environmental issues, the use of plant-derived biopolymers and recycled polymers in the present invention is also preferable from the viewpoint of reducing the environmental load, and the polymers used in the present invention described above can be recycled polymers recycled by any of chemical recycling, material recycling, and thermal recycling. Even when using biopolymers or recycled polymers, polyamide-based resins can be preferably used from the viewpoint of achieving the objects of the present invention due to their polymer properties, and it is particularly preferable to use biopolyamides or recycled polyamides.

[0018] The adsorbent (A) of the present invention selectively adsorbs gold ions when brought into contact with a solution (B) containing gold ions, and therefore is preferably in the form of a material with a large specific surface area that allows effective use of the substrate surface.

[0019] The specific surface area here refers to the surface area per unit mass. Examples of forms with a large specific surface area include fibrous structures and powders (particles). A form with a large specific surface area increases the contact area between the surface of the adsorbent (A) made of a material capable of selectively adsorbing gold ions and the gold ions in solution (B). This allows more gold ions in solution (B) to be adsorbed onto the adsorbent (A). This allows for a reduction in the amount of gold ions remaining in solution (B) after the adsorbent (A) is removed from solution (B), making this a suitable form for achieving the present invention. In particular, the form of the adsorbent (A) is preferably a fibrous structure whose shape can be freely changed. This provides excellent permeability of the gold ion-containing solution (B) into the adsorbent (A) when the adsorbent (A) is contacted with the gold ion-containing solution (B), as well as excellent permeability of components that cause a reduction reaction into the adsorbent (A) with the gold ions adsorbed thereon in the process of isolating the gold ions adsorbed on the adsorbent (A) as gold through a reduction reaction. Furthermore, this provides excellent handling in each step of the gold recovery process of the present invention.

[0020] The specific surface area of ​​the adsorbent (A) of the present invention is 0.05 m 2 The specific surface area of ​​the adsorbent (A) is preferably 0.05 m / g or more. 2If the specific surface area of ​​the adsorbent (A) is 0.10 m / g or more, in the step of contacting the adsorbent (A) with a solution (B) containing gold ions and selectively adsorbing the gold ions, the surface area of ​​the adsorbent (A) that comes into contact with the gold ions in the solution (B) is sufficiently large, allowing many gold ions in the solution (B) to be adsorbed onto the adsorbent (A), and the amount of gold ions remaining in the solution (B) after the adsorbent (A) is removed from the solution (B) can be reduced. To further improve the amount of gold ions adsorbed, the specific surface area of ​​the adsorbent (A) should be 0.10 m / g or more. 2 / g or more is more preferable.

[0021] The form of the fiber structure referred to in the present invention can be various using known methods, and specific examples include woven fabrics, knitted fabrics, pile fabrics, nonwoven fabrics, spun yarns, wadding, etc. Furthermore, various weaving or knitting structures can be adopted for woven fabrics and knitted fabrics, and plain weave, twill weave, satin weave, or variations thereof, warp knitting, weft knitting, circular knitting, lace knitting, or variations thereof, etc. Needless to say, when making into a fiber structure, it may be combined with other fibers (fibers made of other than the above polymers) by interweaving, interknitting, etc., or it may be made into a blended yarn with other fibers and then used as a fiber structure.

[0022] The gold ion-containing solution (B) used in the present invention is a solution in which gold atoms are dissolved as gold ions. Examples of solvents include acidic solutions such as hydrochloric acid and aqua regia, and organic solvents such as dibutyl carbitol, methyl isobutyl ketone, and cyclopentyl methyl ether. When disposing of electrical appliances, metals other than gold are commonly contained in industrial waste, and gold may also be encapsulated within other metals. For this reason, processes are often carried out to dissolve gold and other metals together, and acidic solutions such as hydrochloric acid and aqua regia are often used as solvents. These solvents can be suitably used in the present invention, and selective adsorption of gold is possible by using the aforementioned substrate adsorbent (A).

[0023] The gold ions referred to in the present invention include not only gold(III) ions and gold(I) ions, which are ions consisting of a single gold atom, but also complex ions such as tetrachloroaurate(III) ions and tetrahydroxoaurate(III) ions.

[0024] The gold ion-containing solution (B) of the present invention is preferably an acidic solution containing hydrochloric acid. The inclusion of hydrochloric acid in the gold ion-containing solution (B) is preferred because gold ions can stably exist in the solution (B) as tetrachloroaurate(III) ions. Furthermore, when the material of the adsorbent (A) is a polyamide, acidic conditions are preferred because the amide on the surface of the adsorbent (A) is protonated, forming a chelate complex with tetrachloroaurate(III) ions, thereby selectively adsorbing tetrachloroaurate(III) ions.

[0025] The pH of the gold ion-containing solution (B) is preferably 2 or less. When the material of the adsorbent (A) is polyamide, a pH of 2 or less of the gold ion-containing solution (B) is preferable because the amide on the surface of the adsorbent (A) is sufficiently protonated to form a chelate complex with the gold ions, thereby increasing the amount of gold ions adsorbed. A pH of 1 or less is more preferable.

[0026] In the present invention, specific methods for contacting adsorbent (A) with solution (B) containing gold ions to selectively adsorb gold ions include spraying the solution (B) containing gold ions onto the adsorbent (A), immersing the adsorbent (A) in solution (B) containing gold ions and allowing it to stand, immersing the adsorbent (A) in solution (B) containing gold ions and then shaking it, and continuously passing solution (B) containing gold ions through the adsorbent (A). In the present invention, in order to contact a larger amount of solution (B) containing gold ions with the adsorbent (A) in a short period of time and efficiently adsorb gold ions selectively to the adsorbent (A), it is preferable to contact as much of solution (B) containing gold ions as possible with the adsorbent (A). More preferred methods include immersing the adsorbent (A) in solution (B) containing gold ions and then shaking it, and continuously passing solution (B) containing gold ions through the adsorbent (A).

[0027] In the present invention, after adsorbing gold ions from a gold ion-containing solution (B) onto the adsorbent (A), washing is preferably performed before the step of immersing the adsorbent in water (C) to remove any remaining solution (B) from the surface of the adsorbent (A) after gold ion recovery. Because the gold ions adsorbed onto the adsorbent (A) must remain on the adsorbent (A) after washing, washing should be performed using a method that does not react with the gold ions. Furthermore, to prevent the adhesion of substances or ions other than gold ions during washing, washing is preferably performed using pure water from which salts and organic matter have been removed, or ultrapure water from which impurities have been further removed.

[0028] In the process of isolating the gold ions adsorbed on the adsorbent (A) as gold, the water (C) of the present invention serves as a reaction field where a reduction reaction to isolate the gold ions adsorbed on the adsorbent (A) as gold proceeds. Therefore, the present invention includes a step of immersing the adsorbent (A) in water (C). Suitable water (C) is pure water, soft water, hard water, or an aqueous solution in which the hydrogen ion concentration has been adjusted with an acid or alkali, in which the adsorbent (A) can be immersed. In the process of recovering the isolated gold, pure water from which salts and organic matter have been removed, or ultrapure water from which impurities have been further removed, is more preferred, in order to prevent the presence of substances and ions other than gold and to eliminate impurities.

[0029] In the present invention, it is important to isolate gold ions adsorbed onto the adsorbent (A) as gold particles through a reduction reaction. "Isolation" here refers to the gold being desorbed from the adsorbent (A) and presenting itself alone in water (C), and then being able to recover only the gold in the subsequent step of removing the water (C). The reduction reaction for reducing gold ions in the present invention preferably uses a reducing substance with sufficient reducing power to reduce gold ions. Specific examples of reducing substances include reducing agents such as trisodium citrate, sodium oxalate, ethylenediamine-N,N,N',N'-tetraacetic acid disodium salt dihydrate, sodium ascorbate, and sodium borohydride, as well as reducing gases such as hydrogen, carbon monoxide, and hydrocarbon gases. Methods for performing the reduction reaction include adding a reducing agent to water (C) in which gold ion-adsorbed adsorbent (A) has been soaked and stirring the mixture; pouring a reducing solution prepared by dissolving a reducing agent in a solvent into water (C) in which gold ion-adsorbed adsorbent (A) has been soaked and shaking the solution; blowing a reducing gas such as hydrogen, carbon monoxide, or hydrocarbon gas into water (C) in which gold ion-adsorbed adsorbent (A) has been soaked; and blowing a reducing gas such as hydrogen, carbon monoxide, or hydrocarbon gas into water (C) in which gold ion-adsorbed adsorbent (A) has been soaked using the combustion flame of hydrocarbon gas to perform a heating reduction reaction.

[0030] In particular, a thermal reduction reaction is preferred because, after the gold ions are reduced, the reduced gold is thermally agitated by thermal energy and desorbed from the adsorbent (A), allowing it to be isolated as gold in water (C). A thermal reduction reaction does not require the water (C) to dissolve a large amount of gold ions, and gold can be isolated even with a low solubility of gold ions in water (C) and a small volume of water (C). A thermal reduction reaction is also preferred because it increases the gold isolation rate by allowing the gold ions to be desorbed from the adsorbent (A) in the form of gold ions and reduced to gold through a reduction reaction. Furthermore, the adsorbent (A) does not decompose or turn into incineration during gold recovery, allowing it to be reused after this process while maintaining its gold ion adsorption performance and mechanical properties. Therefore, by using the combustion flame of hydrocarbon gas, it is possible to simultaneously supply thermal kinetic energy and carry out a reduction reaction using hydrogen, carbon monoxide, or hydrocarbon gas. Therefore, a preferred method is to blow reducing gases such as hydrogen, carbon monoxide, or hydrocarbon gas from the combustion flame of hydrocarbon gas into water (C) immersed in adsorbent (A) with gold ions adsorbed thereon, thereby carrying out a heating reduction reaction.

[0031] In the present invention, the thermal reduction reaction is preferably carried out by heating the water (C) in which the adsorbent (A) is immersed to a temperature below the melting point of the adsorbent (A). The heating temperature is preferably 30°C or higher, more preferably 50°C or higher, in order to generate sufficient thermal motion for gold ions to desorb from the adsorbent (A) and to shorten the time required for the gold isolation process. On the other hand, if the water is heated to a temperature higher than the melting point of the adsorbent (A), the adsorbent (A) will melt while encapsulating the gold, making it difficult to isolate and recover the gold. Therefore, the heating temperature is preferably a temperature below the melting point of the adsorbent (A).

[0032] During the thermal reduction reaction, when the water (C) in which the adsorbent (A) is immersed is heated to a temperature below the melting point of the adsorbent (A), the heat source may come into direct contact with the adsorbent (A), which instantaneously raises the temperature. Therefore, a high melting initiation temperature is preferable. Therefore, when a fibrous structure is used as the adsorbent (A), the fibers constituting the fibrous structure are preferably produced by a melt spinning method in order to increase the crystalline orientation of the fibers constituting the fibrous structure and raise the melting initiation temperature. The melt spinning method is a method in which a polymer is melted, extruded from a spinneret to form a fiber thread, cooled and solidified, and then wound on a winder via a godet roller to obtain fibers. If the fibers constituting the fibrous structure are produced by a melt spinning method, the molten polymer is discharged from the spinneret and cooled and solidified during melt spinning, thereby sufficiently reducing the elongational viscosity of the fiber thread. Furthermore, when the molten polymer is taken up by a godet roller, the spinning tension promotes crystalline orientation, resulting in a high melting initiation temperature. In order to further increase the crystal orientation and increase the melting initiation temperature, it is more preferable to perform drawing by a one-step method or a two-step method, or to perform false twisting, and the drawing during the process may be performed by either a one-step drawing method or a multi-step drawing method having two or more steps.

[0033] The present invention includes a step of recovering the isolated gold by removing the water (C) after a step of isolating gold ions adsorbed onto the adsorbent (A) by a reduction reaction in water (C). In the present invention, it is important to recover the isolated gold by removing the water (C). In the present invention, since the gold ions adsorbed onto the adsorbent (A) by a reduction reaction are isolated as gold, the gold exists in the form of elemental gold (particles) in the water (C) after the isolation step, and the gold can be recovered by removing the water (C). Specific methods for removing the water (C) include evaporating the water (C), passing it through filter paper, and passing it through a membrane filter. Since the present invention aims to easily isolate and recover gold from the adsorbent (A), it is preferable that impurities dissolved in the water (C) are also removed in the step of recovering the isolated gold from the water (C). Passing it through filter paper or a membrane filter is preferred.

[0034] The gold isolation rate of the present invention is preferably 40% or higher. The gold isolation rate in the present invention is the proportion of elemental gold actually isolated in the process of isolating the gold ions adsorbed on the adsorbent (A) as gold, measured by the method described in the Examples, among the elemental gold obtainable from the gold ions adsorbed on the adsorbent (A). A gold isolation rate of 40% or higher when the gold ions adsorbed on the adsorbent (A) are isolated as gold is preferred because it maintains the ability to adsorb gold ions again when the adsorbent (A) is reused, enabling highly efficient gold recovery. A gold isolation rate of 50% or higher is more preferred in order to maintain the ability to adsorb gold ions when the adsorbent (A) is reused. [Example]

[0035] The present invention will be described in more detail below with reference to examples. The characteristic values ​​in the examples were determined by the following methods.

[0036] A. Fineness 100 m of the fiber obtained in each example was reeled out using an INTEC electric measuring machine under an environment of 20°C temperature and 65%RH. The weight of the reel was measured, and the fineness (dtex) was calculated using the following formula. Fineness (dtex) = Weight of 100m of fiber (g) x 100

[0037] The measurement was carried out five times for each sample, and the average value was taken as the fineness.

[0038] B. Melting point The adsorbents obtained in the examples were used as samples, and DSC measurements were performed using a TA Instruments differential scanning calorimeter (DSC) Model Q2000, raising the temperature from 30°C to 280°C at a heating rate of 16°C / min, and the melting points were calculated from the melting peaks observed during the heating process. The measurements were performed three times per sample, and the average value was taken as the melting point.

[0039] C. Fusion when heated to 180℃ The adsorbents obtained in the examples were vapor-deposited with a platinum-palladium alloy, and the surface was observed at a magnification of 1000 to 10000 times using a Hitachi S-4000 scanning electron microscope (SEM). Micrographs were taken and used as images before heat treatment. The adsorbents obtained in the examples were then used as samples, and after heat treatment in an oven at 180°C for 30 minutes, they were left to stand for 24 hours in an environment with a temperature of 20°C and a humidity of 65%RH. Thereafter, the surface was similarly observed using the SEM, and micrographs were taken and used as images after heat treatment. The images before and after heat treatment were compared to evaluate the presence or absence of interfiber fusion during heat treatment.

[0040] D. Metal ion adsorption amount The metal ion concentration C0 (mg / L) of the simulated solution before the adsorption operation and the metal ion concentration C1 (mg / L) of the simulated solution after the adsorption operation were measured using a Shimadzu UV-1800 ultraviolet-visible spectrophotometer. Using the volume V0 (L) of the simulated solution before the adsorption operation, the volume V1 (L) of the simulated solution after the adsorption operation, and the mass W (g) of the adsorbent (A) used in the adsorption operation, the amount of metal ions adsorbed per unit mass of adsorbent (A), Q (mg / g), was calculated using the following formula: Metal ion adsorption amount Q (mg / g) = (C0 × V0 - C1 × V1) / W

[0041] E. Liquid surface temperature during metal isolation operation The liquid surface temperature during the isolation operation was measured using the FLIR ONE Pro, a smartphone infrared camera made by FLIR Systems.

[0042] F. Metal isolation rate After confirming that the material recovered by the gold isolation procedure of the examples was elemental metal using a Shimadzu UV-1800 UV-visible spectrophotometer, the metal isolated and recovered in the examples was dissolved in aqua regia, a 3:1 volumetric mixture of hydrochloric acid and nitric acid, prepared using 6 mol / L hydrochloric acid (Fujifilm Wako Pure Chemical Industries) and nitric acid adjusted to 6 mol / L using 60 wt% nitric acid (Fujifilm Wako Pure Chemical Industries), and the metal ion concentration C2 (mg / L) was measured using a Shimadzu UV-1800 UV-visible spectrophotometer. The isolation rate of elemental gold (%) was calculated using the following formula: Metal isolation rate (%) = {(C2 × V2) / (Q × W)} × 100

[0043] G. Single fiber diameter The surface of the adsorbent obtained according to the example is photographed with a scanning electron microscope (SEM) at a magnification such that 150 to 3,000 fibers can be observed. The fiber diameters of 150 fibers randomly sampled from the photographed images are measured. For 150 fibers randomly sampled from each image, the fiber width in the direction perpendicular to the fiber axis is measured as the fiber diameter from the two-dimensionally photographed image. The fiber diameter value is measured in μm units to three decimal places. The above procedure is performed on 10 similarly photographed images, and the simple number average of the evaluation results of the 10 images is rounded to two decimal places to obtain the fiber diameter.

[0044] H.Specific surface area Using the fineness (dtex = g / 10000 m) obtained in A above and the single fiber diameter (μm) obtained in G above, the specific surface area (m 2 / g) was calculated. Specific surface area (m 2 / g) = (single fiber diameter × 10 -6 ×π) × 10000 × filament count / fineness

[0045] I. pH measurement The pH of the solutions obtained in the examples was measured using a HORIBA glass electrode hydrogen ion concentration indicator D-54 in combination with a HORIBA pH electrode 6367-10D filled with HORIBA reference electrode internal solution 300 (potassium chloride 3.33 mol / L). The indicator was calibrated by three-point calibration using HORIBA pH standard solutions 100-4 (phthalate standard solution), 7 (neutral phosphate standard solution), and 9 (borate standard solution).

[0046] Example 1 (Production of Adsorbent (A)) Poly-ε-capramide (relative viscosity in sulfuric acid: 3.30, melting point: 220°C) was used as the island component, and polyethylene terephthalate (melting point: 233°C) copolymerized with 8.0 mol% 5-sodium sulfoisophthalic acid and 10 wt% polyethylene glycol with a molecular weight of 1000 was used as the sea component. The island component fibers were melted at a spinning temperature of 290°C and a sea / island component ratio of 60 / 40 using a sea-island composite spinneret (432 islands per spinneret) with round island component shapes. The spinning was extruded from a spinneret with 18 round holes, each with a discharge hole diameter of 0.30 mm and a hole length of 0.53 mm, to obtain spun yarns. The spun yarns were cooled with cooling air at a temperature of 20°C and a speed of 25 m / min, oiled with an oiling device, and then collected by a first godet roller rotating at 1570 m / min and a surface temperature of 80°C. The yarn taken up by the first godet roller was then taken up by the second godet roller having a surface temperature of 110°C, whereby the yarn was drawn between the rollers at a draw ratio of 2.40 and taken up by a winder rotating at 3700 m / min to obtain a sea-island composite fiber having 52 dtex and 18 filaments.

[0047] The resulting sea-island composite fiber was used to prepare a cylindrical knit fabric (approximately 5 g) using an Eiko Sangyo NCR-BL circular knitting machine (3.5 inch (8.9 cm) diameter, 27 gauge). The fabric was then treated with 10 g / L sodium hydroxide in a bath ratio of 1:100 at 90°C for 30 minutes, rinsed with running water for 5 minutes, and dried in a hot air dryer at 60°C for 30 minutes to obtain a cylindrical knit fabric made of poly-ε-capramide ultrafine fibers. The resulting cylindrical knit fabric was designated adsorbent (A). The properties of the resulting adsorbent (A) are shown in Table 1.

[0048] (gold ion adsorption operation) Adsorbent (A) was placed in a 60 mL screw bottle and 50 mL of a simulated solution containing gold standard solution (Fujifilm Wako Pure Chemical Industries, Ltd.), 6 mol / L hydrochloric acid (Fujifilm Wako Pure Chemical Industries, Ltd.), and purified water (pH 0) with a gold ion concentration of 100 mg / L. 0.025 g of adsorbent (A) was added. The temperature was maintained at 30 °C using an AS ONE MSI-60 thermostatic shaker, and the batch operation of gold ion adsorption was performed at 120 rpm for 6 hours. After the operation, the adsorbent (A) with adsorbed gold ions was removed and washed three times with purified water. The washing solution was added to the simulated solution. The gold ion adsorption rate is shown in Table 1.

[0049] (gold isolation operation) After the adsorption procedure, adsorbent (A) was transferred to a heat-resistant dish and immersed in pure water so that adsorbent (A) did not rise above the water surface. A Shinfuji Burner Power Gas RZ-860 (components: liquefied butane and liquefied propane) was attached to a Shinfuji Burner Power Torch RZ-834 and ignited. The outer flame was directed toward the adsorbent immersed in pure water for 30 seconds, blowing in reducing gas and conducting a thermal reduction reaction. After the reaction, the solution was allowed to cool, and the isolated gold was recovered by filtering the pure water containing the gold through filter paper. The gold isolation yield is shown in Table 1. The gold isolation yield was high (53%), demonstrating simple gold isolation in as little as 30 seconds. Furthermore, no fusion was observed when heated to 180°C. Therefore, adsorbent (A) did not melt or fuse during the thermal reduction reaction, and retained its original shape after the gold isolation procedure.

[0050] Example 2 A reduction reaction using a reducing agent was carried out as a gold isolation procedure. Trisodium citrate (Fujifilm Wako Pure Chemical Industries, Ltd.) was dissolved in 50 mL of pure water to a concentration of 0.1 mol / L, and the solution was stirred to make the solution uniform. After stirring, adsorbent (A) was added and the solution was shaken for 30 seconds to carry out a reduction reaction. The gold was isolated from the solution and recovered by filtering the solution through filter paper. Adsorbent (A) was produced in the same manner as in Example 1, and gold ion adsorption was carried out. The results are shown in Table 1.

[0051] (Examples 3 and 4) Adsorbent (A) was produced in the same manner as in Example 2, and gold ion adsorption and gold isolation were carried out, except that the reducing agent in the gold isolation procedure was changed to sodium oxalate manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. in Example 3 and to sodium L(+)-ascorbate in Example 4. The results are shown in Table 1.

[0052] (Examples 5 to 8) The gold ion adsorption and gold isolation procedures were carried out in the same manner as in Example 1, except that the gold ion adsorption and gold isolation procedures in Example 1 were counted as one cycle for adsorbent (A), that adsorbent (A) after one cycle of gold ion adsorption and gold isolation procedures in Example 5, that adsorbent (A) after a total of two cycles of gold ion adsorption and gold isolation procedures in Example 6, that adsorbent (A) after a total of three cycles of gold ion adsorption and gold isolation procedures in Example 7, and that adsorbent (A) after a total of four cycles of gold ion adsorption and gold isolation procedures in Example 8 were reused. The results are shown in Table 1. Even when the adsorbent after the gold ion adsorption and gold isolation procedures described in Example 1 was reused, adsorbent (A) still exhibited excellent gold ion adsorption and gold isolation performance. Even after a total of five cycles of gold ion adsorption and gold isolation procedures were repeated, adsorbent (A) still exhibited excellent gold ion adsorption and gold isolation performance.

[0053] (Comparative Example 1) Adsorbent (A) was produced in the same manner as in Example 1, and gold ion adsorption was performed, except that the gold isolation procedure was changed so that adsorbent (A) was placed in a solution adjusted to pH 0 using 6 mol / L hydrochloric acid (manufactured by Fujifilm Wako Pure Chemical Industries) and pure water, and the solution was shaken for 30 minutes. The results are shown in Table 1. When the absorbance of the solution after the gold isolation procedure was measured using a UV-visible spectrophotometer, absorption was confirmed in the wavelength range of 210 to 230 nm, which is due to tetrachloroaurate(III) ions. However, absorption in the wavelength range of 500 to 600 nm, which is due to elemental gold, was not confirmed. This indicates that tetrachloroaurate(III) ions had been released, and elemental gold was not isolated.

[0054] (Comparative Example 2) Adsorbent (A) was produced in the same manner as in Example 1, except that in the gold isolation operation, adsorbent (A) was exposed to an external flame without being immersed in pure water, and gold ion adsorption and gold isolation operations were carried out. The results are shown in Table 1. When adsorbent (A) was exposed to the external flame, it melted and carbonized, and the gold was encapsulated in the carbonized product of adsorbent (A), making it difficult to isolate the gold from adsorbent (A).

[0055] Example 9 Adsorbent (A) was prepared by completely dissolving Ube Industries' poly-ε-capramide 1022B in Kanto Chemical's formic acid to prepare a raw material solution with a poly-ε-capramide concentration of 10 wt%. The raw material solution was electrospun onto release paper using a MEC SNAS-10 laboratory electrospinning device at a loading volume of 6.0 mL, a discharge rate of 0.1 mL / hour, a spinning distance of 15 cm, and an applied voltage of 30 kV. The gold ion adsorption and gold isolation procedures were carried out in the same manner as in Example 1, except that the nanofiber nonwoven fabric was obtained by electrospinning the raw material solution onto release paper using a 22G syringe needle at a loading volume of 6.0 mL, a discharge rate of 0.1 mL / hour, a spinning distance of 15 cm, and an applied voltage of 30 kV. The results are shown in Table 2. Gold was easily isolated as in Example 1, but fusion occurred when heated to 180°C, unlike in Example 1. Therefore, adsorbent (A) melted during the thermal reduction reaction. After the gold isolation procedure, adsorbent (A) lost its original shape, making repeated use difficult.

[0056] Example 10 Adsorbent (A) was produced and gold ion adsorption was carried out in the same manner as in Example 10, except that the gold isolation procedure was changed to the same procedure as in Example 2. The results are shown in Table 2.

[0057] Example 11 The adsorbent (A) was produced in the same manner as in Example 1, except that the simulated solution used in the gold ion adsorption operation was changed to a simulated solution containing 100 mg / L gold ion concentration, 100 mg / L iron ion concentration, 100 mg / L zinc ion concentration, 100 mg / L copper ion concentration, 100 mg / L aluminum ion concentration, and pH 0, using 6 mol / L hydrochloric acid and pure water from Fujifilm Wako Pure Chemical Industries, Ltd. The gold ion adsorption operation and gold isolation operation were carried out. The results are shown in Table 3. In the gold ion adsorption operation, iron ions, zinc ions, copper ions, and aluminum ions were not adsorbed, and the adsorbent exhibited excellent ability to selectively adsorb only gold ions.

[0058] (Examples 12 to 15) Adsorbent (A) was produced and gold ion adsorption was carried out in the same manner as in Example 1, except that the specific surface area of ​​adsorbent (A) was changed as shown in Table 4. The results are shown in Table 4.

[0059] (Examples 16 to 19) Adsorbent (A) was produced in the same manner as in Example 1, and gold ion adsorption was performed, except that the simulated solution used in the gold ion adsorption operation was a gold standard solution manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., 6 mol / L hydrochloric acid manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., 8 mol / L sodium hydroxide manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., and pure water, and the pH was adjusted and changed as shown in Table 5. The results are shown in Table 5.

[0060] [Table 1]

[0061] [Table 2]

[0062] [Table 3]

[0063] [Table 4]

[0064] [Table 5] [Industrial Applicability]

[0065] The gold recovery method of the present invention has an excellent ability to selectively adsorb gold, making it possible to recover only gold from a solution containing a mixture of multiple metal ions.In addition, the shape and capacity of the adsorbent are maintained before and after gold recovery, making it possible to repeatedly use the adsorbent to recover gold.

Claims

1. A method for recovering gold comprising the following steps (1) to (4): Step (1) The adsorbent (A) is brought into contact with a solution (B) containing gold ions to selectively adsorb the gold ions. Step (2): Immerse the adsorbent (A) having adsorbed gold ions in water (C). Step (3): The gold ions adsorbed on the adsorbent (A) are subjected to a reduction reaction to isolate gold in water (C). Step (4) Recovering the isolated gold by removing water (C).

2. 2. The method for recovering gold according to claim 1, wherein in step (3), the reduction reaction is carried out in an atmosphere below the melting point of the adsorbent (A).

3. 3. The method for recovering gold according to claim 1, wherein the adsorbent (A) contains a polyamide.

4. 4. The method for recovering gold according to claim 3, wherein the adsorbent (A) is a fibrous structure.

5. 5. The method for recovering gold according to claim 4, wherein the fibers constituting the fiber structure are produced by melt spinning.

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