Method for producing noble metal

Abstract

The method for producing a noble metal comprises: a base metal dissolution step for generating a base metal eluate in which a base metal is dissolved and a noble metal-containing starting material; a precious metal dissolution step for generating a precious metal eluate in which the precious metal contained in the precious metal-containing starting material is eluted; a heating step for heating the noble metal eluate to a temperature within the range of 30-100 DEG C (inclusive); a noble metal adsorption step in which yeast is added to the heated noble metal eluate and the noble metal ions contained in the noble metal eluate are selectively adsorbed by the yeast; and a precious metal separation step in which a reducing agent is added to the dispersion of the yeast having the precious metal ions adsorbed thereon, thereby separating the precious metal formed into nanoparticles.

Description

Technical Field

[0001] The present invention relates to a method for producing a precious metal by separating a base metal from a material containing the precious metal and the base metal to produce the precious metal.

[0002] This application claims priority based on patent application No. 2022-097612 filed in Japan on June 16, 2022, and the contents are incorporated herein by reference. Background Art

[0003] Recycling of precious metals by recovering precious metals from waste (raw materials) containing precious metals (Au, Ag, Pt, Pd, Rh, Ir, Ru, Os) and base metals (Cu, Fe, Ni, Sn, Al, Zn, Cr, etc.). For example, precious metals such as gold or silver are used in wiring, etc., for discarded smartphones or circuit boards of personal computers, and their content per unit weight is sometimes greater than that contained in natural ores. In recent years, due to the rise in precious metal prices, various methods for effectively extracting precious metals from waste containing such precious metals have been proposed.

[0004] For example, Patent Document 1 discloses a method for recovering valuable metals by blowing combustibles containing valuable metals and oxygen-enriched air into the surface of a melt from a pipe opening toward the melt stored in a furnace body for smelting nonferrous metals.

[0005] For example, Patent Document 2 discloses a method for recovering precious metals in the form of a precious metal solution by immersing waste containing precious metals in aqua regia composed of hydrochloric acid and nitric acid and dissolving the precious metals in the aqua regia.

[0006] However, in the method of melting waste in a smelter, as in Patent Document 1, there is a problem that the resin components and heavy metal components contained in the waste have an adverse effect on the smelting operation. In addition, in recent years, the proportion of valuable metals in waste has decreased, the energy cost for processing is high, and the increase in the amount of carbon dioxide emissions due to the increase in the amount of fuel used is also a problem of increasing environmental burden.

[0007] Furthermore, in Patent Document 2, when aqua regia is used to dissolve precious metals, if base metals (for example, Cu, which is used in large quantities in circuit boards) are contained in the waste, the Cu reacts with nitrosyl chloride contained in the aqua regia to generate harmful nitrogen oxides (NO x ), therefore, equipment for treating nitrogen oxides is required, which leads to a problem of high treatment costs.

[0008] On the other hand, Patent Document 3 discloses a method of selectively recovering precious metals by adding Saccharomyces cerevisiae to a liquid having a pH of less than 4 and containing precious metal ions, and adsorbing the precious metal ions on the yeast cell surface.

[0009] Patent Document 1: Japanese Patent No. 5761258

[0010] Patent Document 2: Japanese Patent Application Laid-Open No. 6-158190

[0011] Patent Document 3: Japanese Patent No. 6586690

[0012] However, in the method for separating precious metals disclosed in Patent Document 3, the pH is about 1.4, and there is a problem that it is difficult to efficiently adsorb precious metals in a more acidic environment (eg, pH 0). Summary of the invention

[0013] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing a precious metal that can efficiently recover the precious metal from a raw material containing the precious metal and the base metal even in a strongly acidic environment such as pH 0.

[0014] In order to solve the above-mentioned problems, a method for producing a precious metal according to one embodiment of the present invention proposes the following means.

[0015] (1) Aspect 1 of the present invention is characterized in that it includes: a base metal dissolving step of immersing a raw material containing a precious metal and a base metal in hydrochloric acid containing hydrogen peroxide or ferric chloride to generate a base metal eluate in which at least a portion of the base metal is dissolved and a precious metal-containing raw material as a solid phase residue; a precious metal dissolving step of reacting a mixed acid solution obtained by adding nitric acid to the base metal eluate with the precious metal-containing raw material or reacting aqua regia with the precious metal-containing raw material to generate a precious metal eluate in which the precious metal contained in the precious metal-containing raw material is eluted; a heating step of heating the precious metal eluate to a temperature in the range of 30° C. to 100° C.; a precious metal adsorption step of adding yeast to the heated precious metal eluate to cause the yeast to selectively adsorb precious metal ions contained in the precious metal eluate; and a precious metal separation step of adding a reducing agent to a dispersion of the yeast adsorbing the precious metal ions to separate the precious metal in nanoparticle form.

[0016] According to the first aspect, by heating the precious metal eluate obtained in the precious metal dissolution step to a liquid temperature in the range of 30° C. to 100° C., the adsorption rate of the precious metal to the yeast in the precious metal adsorption step as a subsequent step can be greatly increased. As a result, in the precious metal adsorption step, the contact time between the yeast and the precious metal eluate can be shortened, and the precious metal can be produced efficiently and at low cost.

[0017] (2) Aspect 2 of the present invention is characterized in that, in the method for producing a precious metal of aspect 1, a cooling step is further included, wherein the cooling step is a post-step of the heating step, and the precious metal elution solution heated in the heating step is cooled to less than 60°C.

[0018] (3) Aspect 3 of the present invention is characterized in that, in the method for producing a precious metal according to aspect 1 or 2, the yeast comprises any one or two or more of the genera Saccharomyces, Zygosaccharomyces, Schizosaccharomyces, Debaryomyces, and Candida.

[0019] (4) Aspect 4 of the present invention is characterized in that, in the method for producing a precious metal according to any one of aspects 1 to 3, the precious metal comprises any one or two or more of gold, platinum, silver, palladium, rhodium, iridium, ruthenium and osmium.

[0020] (5) Aspect 5 of the present invention is characterized in that in the method for producing a precious metal of any one of Aspects 1 to 4, the reducing agent comprises any one or more of hydrazine and its salts, borohydride salts, sulfates, thiosulfates, tartrates, phosphinic acid and its salts, formic acid and its salts, acetic acid and its salts, propionic acid and its salts, oxalic acid and its salts, ascorbic acid and its salts, phosphoric acid and its salts, hypophosphorous acid and its salts, citric acid and its salts, transition metal salts, glycine, dimethylamine borane and formaldehyde.

[0021] (6) Aspect 6 of the present invention is characterized in that, in the method for producing a precious metal according to any one of aspects 1 to 5, the precious metal separated in the precious metal separation step is a precious metal nanoparticle.

[0022] (7) Aspect 7 of the present invention is characterized in that, in the method for producing a precious metal according to any one of aspects 1 to 6, the raw material is a circuit substrate.

[0023] According to the present invention, it is possible to provide a method for producing a precious metal that can efficiently recover the precious metal from a raw material containing the precious metal and the base metal even in a strongly acidic environment such as pH 0. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a flowchart showing in stages a method for producing a precious metal according to one embodiment of the present invention.

[0025] Figure 2 It is a graph which shows the result of a verification example. DETAILED DESCRIPTION

[0026] Hereinafter, a method for producing a precious metal as one embodiment of the present invention will be described with reference to the accompanying drawings. In addition, the embodiments shown below are specifically described for better understanding of the purpose of the invention, and do not limit the present invention unless otherwise specified.

[0027] Figure 1 This is a flowchart showing in stages a method for producing a precious metal according to one embodiment of the present invention.

[0028] In the method for producing a precious metal according to the present embodiment, a series of steps for producing the precious metal by separating the precious metal from a circuit board (a raw material containing the precious metal and the base metal) of an electronic device will be described.

[0029] In addition, the noble metal in this embodiment refers to eight elements, namely Au, Ag, Pt, Pd, Rh, Ir, Ru, and Os. Furthermore, the base metal in this embodiment refers to Cu and metals having a greater ionization tendency than Cu, and representative examples thereof include Cu, Fe, Ni, Sn, Al, Zn, and Cr.

[0030] Furthermore, a circuit board of an electronic device as an example of a raw material contains precious metals such as Au and Ag and base metals such as Cu in, for example, soldered parts and wirings.

[0031] According to the manufacturing method of the precious metal involved in the present embodiment, when manufacturing the precious metal from the circuit substrate (raw material), first, the circuit substrate is put into an acid-resistant reaction container. In order to promote the reaction, the circuit substrate is preferably broken into pieces of, for example, 1 cm square or more and 5 cm square or less in advance. And, hydrochloric acid (HCl) is placed in the reaction container. The hydrochloric acid used can be, for example, dilute hydrochloric acid with a HCl concentration of about 5 mol / L.

[0032] Next, in the reaction container where the circuit board is immersed in the dilute hydrochloric acid, hydrogen peroxide is added at a predetermined rate and stirred (base metal dissolving step S1). As for the hydrogen peroxide, for example, hydrogen peroxide having a hydrogen peroxide (H2O2) concentration of 30 mass % or more and 36 mass % or less can be used.

[0033] By adding this hydrogen peroxide, copper, which is the main component of the base metals contained in the circuit board, is oxidized and dissolved in the dilute hydrochloric acid. In addition, base metals having a greater ionization tendency than copper and a greater ionization tendency than hydrogen can be dissolved by dilute hydrochloric acid.

[0034] The addition rate of hydrogen peroxide to dilute hydrochloric acid in the base metal dissolving step S1 is preferably within a range of 0.17 mass% / min or more and 5.3 mass% / min or less relative to the total liquid volume after addition. If the addition rate is 0.17 mass% / min or more, the oxidizing atmosphere can be maintained for a long time, and the base metal can be fully oxidized. As a result, the base metal is fully dissolved in the dilute hydrochloric acid, thereby reducing the undissolved base metal remaining in the circuit board. On the other hand, by setting the addition rate to 5.3 mass% / min or less, the excess hydrogen peroxide that does not contribute to oxidation can be suppressed, thereby reducing the processing cost.

[0035] In the base metal dissolving step S1, dilute hydrochloric acid to which an oxidant (hydrogen peroxide) not containing nitrogen (N) is added is used to dissolve base metals such as copper, so that nitrogen oxides (NOx) that are generated when dissolving base metals with aqua regia containing nitric acid that can dissolve precious metals are not generated. x )gas.

[0036] On the other hand, even if the coexisting base metal dissolves, the precious metal contained in the circuit board does not dissolve in the dilute hydrochloric acid to which hydrogen peroxide is added, and remains on the circuit board.

[0037] The addition of hydrogen peroxide may be performed until the bubbles generated by the dissolution of the base metal completely disappear. In the base metal dissolution step S1, 70 mass % or more of the total amount of base metal (eg, Cu) contained in the circuit board is dissolved to generate a base metal eluate.

[0038] Then, the circuit substrate (precious metal-containing raw material) as a solid phase residue after at least a portion of the base metal is dissolved and the base metal dissolution solution (liquid phase) can be separated into solid and liquid by, for example, filtration. Thus, a circuit substrate (precious metal-containing raw material) and a base metal dissolution solution containing precious metals and undissolved base metals can be obtained. In addition, the base metal dissolution solution (liquid phase) can be used in the precious metal dissolution step S2 as the next step, and can be reduced by, for example, adding a reducing agent, thereby also separating base metals such as Cu.

[0039] Next, a mixed acid solution or aqua regia obtained by adding nitric acid to the base metal solution obtained in the base metal dissolution step S1 is used to dissolve the precious metal contained in the circuit substrate (containing precious metal raw material) obtained in the base metal dissolution step S1 (precious metal dissolution step S2). As aqua regia, for example, a mixed solution obtained by mixing concentrated hydrochloric acid and concentrated nitric acid in a volume ratio of 3:1 can be used. By mixing concentrated hydrochloric acid and concentrated nitric acid, nitrosyl chloride (NOCl) is generated to oxidize the precious metal.

[0040] Furthermore, when the base metal eluate obtained in the base metal dissolving step S1 is used, if unreacted hydrochloric acid remains in the hydrochloric acid added to the base metal eluate, nitrosyl chloride is generated even if only nitric acid is added, thereby making it possible to dissolve the precious metal.

[0041] In addition, as another embodiment of the base metal dissolution step S1, as an oxidant used in the base metal dissolution step, which is a pre-step of the noble metal dissolution step, ferric chloride (FeCl3) can be used instead of hydrogen peroxide as an oxidant. At this time, for example, in a reaction container in which the circuit substrate is immersed in dilute hydrochloric acid, an aqueous solution of ferric chloride is added at a predetermined speed and stirred. As for the aqueous solution of ferric chloride, for example, an aqueous solution of ferric chloride having a concentration of 20 mass % or more and 50 mass % or less can be used.

[0042] By adding such an aqueous ferric chloride solution, ferric ions function as an oxidizing agent, and the base metal contained in the circuit board can be dissolved.

[0043] Then, after the circuit substrate as the precious metal-containing raw material (solid phase residue) and the base metal dissolving solution are solid-liquid separated, the circuit substrate is immersed in aqua regia, or the circuit substrate is immersed in a mixed acid solution prepared by adding nitric acid to the base metal dissolving solution, thereby dissolving the precious metal. At this time, in the base metal dissolving step, at least a part of the base metal contained in the circuit substrate is removed as a soluble chloride.

[0044] In the noble metal dissolution step S2, the circuit substrate, which is the dissolution residue of the base metal dissolution step S1, is immersed in the above-mentioned mixed acid solution or aqua regia and stirred, so that the noble metal such as Au contained in the circuit substrate is dissolved, thereby generating a noble metal eluate. In addition, in the case where the base metal that is not dissolved in the base metal dissolution step S1 remains in the circuit substrate, which is the dissolution residue, it is dissolved together with the noble metal in the noble metal dissolution step S2.

[0045] In the noble metal dissolution step S2 , the temperature of the mixed acid solution or aqua regia may be maintained within a range of, for example, 60° C. to 80° C. The stirring time may be, for example, 1 hour to 3 hours.

[0046] In the noble metal dissolution step S2 , the circuit board which is the dissolution residue of the base metal dissolution step S1 can be dissolved using both the mixed acid solution and the aqua regia.

[0047] In the noble metal dissolution step S2, for example, when Au contained in the circuit board reacts with nitrosyl chloride to generate soluble chloroauric acid, nitrogen oxides are generated. Also, when Cu remains in the circuit board, nitrogen oxides are also generated when Cu reacts with nitrosyl chloride.

[0048] However, the amount (content) of precious metals such as Au contained in the circuit substrate is generally less than that of base metals such as Cu forming the circuit pattern, and the amount of nitrogen oxides generated in connection with the dissolution of the precious metals is small. On the other hand, most of the base metals such as Cu, which are used in larger amounts than the precious metals, are dissolved in the above-mentioned base metal dissolution step S1 without generating nitrogen oxides, and the amount of undissolved base metals transferred to the precious metal dissolution step S2 is greatly reduced.

[0049] Thus, in the method for producing a precious metal of the present embodiment, the base metal dissolution step S1 is performed as pretreatment, and thus the amount of nitrogen oxides generated in the precious metal dissolution step S2 is significantly reduced compared to a case where the base metal dissolution step S1 is not performed.

[0050] Next, the precious metal solution obtained in the precious metal dissolution step S2 is heated to a liquid temperature within a range of 30°C to 100°C (heating step S3). The heating temperature may be 30°C or above, preferably 60°C or above, and more preferably 90°C or above. In order to prevent the precious metal solution from boiling, the upper limit of the heating temperature is 100°C or below. The heating of the precious metal solution may be performed, for example, using a heater. The heating time is preferably within a range of 1 hour to 100 hours.

[0051] By heating the precious metal eluate in the heating step S3 , the adsorption rate of precious metal ions to yeast can be greatly increased in the precious metal adsorption step S5 as a subsequent step.

[0052] Next, the precious metal solution heated to a temperature in the range of 30°C to 100°C by the heating step S3 is cooled to less than 60°C (cooling step S4). As for the cooling temperature, it is sufficient as long as it is less than 60°C, preferably less than 40°C, and more preferably less than 30°C. The cooling of the precious metal solution can be performed, for example, by natural cooling. Alternatively, it can be cooled by spraying nitrogen or helium into the precious metal solution. Moreover, it is also possible to cool by circulating cooling water around the heated container.

[0053] By cooling the noble metal eluate heated in the heating step S3 in the cooling step S4 , it is possible to prevent the activity of the yeast from being reduced due to a high temperature environment in the noble metal adsorption step S5 which is a subsequent step.

[0054] In addition, such a cooling step S4 does not necessarily need to be performed, and for example, the noble metal adsorption step S5 as a post-step may be performed using a noble metal eluate whose liquid temperature is maintained at about 60°C.

[0055] Next, yeast is added to the precious metal solution that has been heated in the heating step S3 and cooled in the cooling step S4 as needed, and stirred, so that the precious metal ions contained in the precious metal solution are adsorbed by the yeast (precious metal adsorption step S5). In the precious metal adsorption step S5, the precious metal ions contained in the precious metal solution come into contact with the yeast, so that the precious metal ions are adsorbed by the yeast.

[0056] The yeast used in the noble metal adsorption step S5 may be any yeast as long as it is a yeast capable of adsorbing noble metal ions. The yeast applicable in the present embodiment is, for example, yeast belonging to the genus Saccharomyces or Candida, Torulopsis, Zygosaccharomyces, Schizosaccharomyces, Pichia, Yarrowia, Hansenula, Kluyveromyces, Debaryomyces, Geotrichum, Wickerhamia, Fellomyces, Sporobolomyces, and among them, yeast belonging to the genus Saccharomyces, Zygosaccharomyces, Schizosaccharomyces, or Debaryomyces is particularly preferred.

[0057] The yeast of the genus Saccharomyces is a representative yeast of budding yeast, and may be, for example, S. bayanus, S. boulardii, S. bulderi, S. cariocanus, S. cariocus, S. cerevisiae, S. chevalieri, S. dairenensis, S. ellipsoideus, S. florentinus, S. kluyveri, S. martiniae, S. monacensis, S. norbensis, S. paradoxus, S. pastorianus, S. spencerorum, S. turicensis, S. unisporus, S. uvarum, S. zonatus.

[0058] The genus Zygosaccharomyces is a salt-tolerant yeast and is a yeast isolated from soybean paste or soy sauce, for example, Z. rouxii. The yeast of the genus Schizosaccharomyces is a fission yeast, for example, S. cryophilus, S. japonicus, S. octosporus, S. pombe. In addition, as a preferred yeast, the yeast of the genus Debaryomyces (Debaryomyces hansenii) deposited with the entrustment number NITE BP-01780 (Room 122, 2-5-8, Kazusa Kamata, Kisarazu, Chiba Prefecture, Japan, the Patent Microorganisms Depository of the Independent Administrative Institution Product Evaluation Technology Foundation) can also be exemplified.

[0059] The contact between the noble metal ions and the yeast is carried out in the noble metal solution. The yeast may be live bacteria, and may be dead bacteria as long as it can exert the adsorption function. The liquid to which the yeast is added to the noble metal solution may be any liquid as long as it is in an environment where the yeast function can be exerted.

[0060] The pH and temperature of the liquid to which yeast is added to the precious metal solution are not particularly limited. For example, the pH can be a strongly acidic to neutral pH of 0 or more and 7 or less. In addition, the temperature is 10°C or more and 45°C or less, preferably 20°C or more and 35°C or less. The time for adding yeast to the precious metal solution and performing the reaction, treatment, and operation also varies depending on the yeast cell density and the concentration of the precious metal ions, and for example, it can be about 10 minutes to 48 hours. By allowing the precious metal ions to contact the yeast for these periods of time, the precious metal ions are adsorbed on the yeast.

[0061] Furthermore, it is also preferable to further stir the solution in which yeast is added to the noble metal elution solution. Stirring can increase the diffusion rate of the noble metal ions on the yeast surface.

[0062] The concentration of the precious metal ions contained in the liquid to which yeast is added to the precious metal eluate can be set appropriately. The concentration of the precious metal ions in the precious metal eluate also varies depending on the bacterial concentration of the yeast, but is, for example, 0.01 mmol / L or more and 100 mmol / L or less, preferably 0.1 mmol / L or more and 10 mmol / L or less. Such a precious metal ion concentration can be adjusted by, for example, adding ion exchange water when adding yeast to the precious metal eluate.

[0063] Furthermore, the concentration of yeast contained in the liquid to which yeast is added to the precious metal elution can be set appropriately. The concentration of yeast in the precious metal elution also varies depending on the concentration of precious metal ions, but it can be set, for example, in the range of 5 g / L or more and 100 g / L or less. The concentration of yeast in the precious metal elution can be, for example, 1.0×10 14 cells / m 3 Above and 3.0×1015 cells / m 3 Within the following range.

[0064] Next, the yeast adsorbed with the precious metal ions obtained in the precious metal adsorption step S5 is separated from the liquid (yeast separation step S6). In the yeast separation step S6, for example, the yeast adsorbed with the precious metal ions may be precipitated by centrifugal separation and separated from the liquid. Then, the yeast adsorbed with the separated precious metal ions is preferably further washed with water. The separated liquid may be subjected to the heating step S3 to the yeast separation step S6 again. At this time, by changing the conditions in each step, the precious metal ions remaining in the yeast in the separated liquid that are not adsorbed can be adsorbed on the yeast and separated from the liquid.

[0065] Next, water is added to the yeast adsorbing the precious metal and dispersed to generate a yeast dispersion, and a reducing agent is added to the dispersion to separate the nanoparticle-like precious metal (precious metal separation step S7). In the precious metal separation step S7, the pH of the solution can be adjusted to be 7 or more. As an example of the pH of the solution after adding the reducing agent to the dispersion of the yeast adsorbing the precious metal, it can be 7 or more and 14 or less. In addition, the liquid temperature of the solution only needs to be in the range of 10°C or more and 90°C or less. The precious metal obtained in this precious metal separation step S7 is obtained as a nanoparticle-like substance.

[0066] The reducing agent for converting the precious metal into nanoparticles can be, for example, the following reducing agent, which includes any one or two or more of hydrazine and its salts, borohydride salts, sulfates, thiosulfates, tartrates, phosphinic acid and its salts, formic acid and its salts, acetic acid and its salts, propionic acid and its salts, oxalic acid and its salts, ascorbic acid and its salts, phosphoric acid and its salts, hypophosphorous acid and its salts, citric acid and its salts, transition metal salts, glycine, dimethylamine borane and formaldehyde.

[0067] In the precious metal separation step S7, a reducing agent is added to the yeast adsorbing the precious metal, and precious metal nanoparticles having an average particle size of nanometer size (1 nm or more and 100 nm or less) are formed during the reduction process of the precious metal. At this time, if the pH is set to 7 or more, the reducing ability of the reducing agent on the precious metal can be further exerted, and the precious metal nanoparticles can be formed more effectively.

[0068] Then, for example, by irradiating with ultrasonic waves, the yeast and the generated noble metal nanoparticles can be separated. Furthermore, it is also possible to break the yeast cells by adding an alkali to separate the noble metal nanoparticles, and remove the yeast and its fragments by filtering, etc., to prepare a dispersion of the noble metal nanoparticles. Furthermore, when used as a noble metal nanoparticle paste, the noble metal nanoparticles can be used as a noble metal nanoparticle paste in a state where they are supported on the yeast without being separated from the yeast.

[0069] As described above, according to the method for producing precious metals of this embodiment, by heating the precious metal eluate obtained in the precious metal dissolution step S2 to a liquid temperature in the range of 30°C to 100°C (heating step S3), the adsorption rate of precious metals to yeast can be greatly improved in the precious metal adsorption step S5 as a subsequent step.

[0070] Thus, in the precious metal adsorption step S5, the contact time between yeast and precious metal eluate can be shortened, and precious metals can be produced efficiently and at low cost. Furthermore, precious metals can be efficiently recovered even in a strongly acidic environment such as pH 0.

[0071] Furthermore, if the noble metal eluate heated in the heating step S3 is cooled to less than 60° C. (cooling step S4 ), the activity of yeast can be prevented from being reduced in a high temperature environment in the noble metal adsorption step S5 , thereby allowing the noble metal to be effectively adsorbed on the yeast.

[0072] The embodiments of the present invention are described above, but such embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other ways, and various omissions, substitutions, and changes can be made without departing from the scope of the subject matter of the invention. The embodiments and their variations are included in the scope or subject matter of the invention as well as the invention described in the claims and their equivalents.

[0073] Example

[0074] The effect of the present invention has been verified.

[0075] A waste substrate containing Au, which was broken into squares with a side of 1 cm or more and 5 cm or less, was immersed in aqua regia with a concentration of 50 mass % to dissolve the metal component, and then solid-liquid separation was performed to obtain a noble metal eluate.

[0076] (Example 1 of the present invention)

[0077] The noble metal eluate was heated at 30° C. for 1 hour (heating step), and then naturally cooled until the liquid temperature reached 25° C. (cooling step).

[0078] In the thus obtained heat-treated noble metal solution, the concentration of 5.0×10 14 cells / m 3 Saccharomyces cerevisiae was added in a manner to allow Au ions contained in the noble metal solution to be bioadsorbed to the yeast. As a representative yeast, Saccharomyces cerevisiae was used, commercially available edible yeast manufactured by Oriental Yeast Co., Ltd. Then, after adding the Saccharomyces cerevisiae and separating the yeast by centrifugation after 5 minutes, the metal concentration contained in the supernatant solution was measured.

[0079] (Example 2 of the present invention)

[0080] The same conditions as in Example 1 of the present invention were used except that the noble metal eluate was heated at 60° C. for 1 hour (heating step).

[0081] (Example 3 of the present invention)

[0082] The same conditions as in Example 1 of the present invention were used except that the noble metal eluate was heated at 90° C. for 1 hour (heating step).

[0083] (Example 4 of the present invention)

[0084] After the same steps as in Example 1 of the present invention were carried out, the supernatant solution after the yeast obtained in Example 1 of the present invention was heated again at 90°C for 1 hour. Under the same conditions as in Example 1, cerevisiae yeast was added to the heated supernatant solution, and Au ions contained in the heated supernatant solution were bioadsorbed to the yeast. Then, after adding cerevisiae yeast and separating the yeast by centrifugation after 5 minutes, the metal concentration contained in the supernatant solution was measured.

[0085] (Comparative Example 1)

[0086] The same conditions as in Example 1 of the present invention were used except that the precious metal eluate was directly added to the brewer's yeast without the heating step and the cooling step. The liquid temperature of the precious metal eluate that was not heated was 10° C. or less.

[0087] (Comparative Example 2)

[0088] The conditions were the same as those in Comparative Example 1 except that the yeast was separated by centrifugation 60 minutes after the yeast was added to the precious metal eluate to which the yeast was added without the heating step and the cooling step.

[0089] Table 1 shows the Au adsorption rates of the above-mentioned Inventive Examples 1 to 3 and Comparative Examples 1 and 2.

[0090] Furthermore, in Example 1, the selectivity of the adsorbed metal is shown in Figure 2 .

[0091] In addition, regarding the adsorption rate of metal ions, the precious metal elution solution before yeast addition was filtered through a filter, and the concentration of the metal in the liquid was measured by ICP emission spectrometry. Then, the precious metal elution solution after yeast addition was collected, filtered through a filter, and the metal concentration was measured by ICP emission spectrometry. The degree of decrease in the metal concentration in the liquid before and after yeast addition was taken as the adsorption rate. The adsorption rate was calculated according to the following formula.

[0092] Adsorption rate (%) = (metal concentration in liquid before yeast addition - metal concentration in liquid after yeast addition and separation) / metal concentration in liquid before yeast addition × 100

[0093] [Table 1]

[0094]

[0095] From the results shown in Table 1, it can be confirmed that the adsorption rate of Au to yeast can be greatly increased by preheating the precious metal eluate to 30°C or higher as in the present invention examples, compared with the comparative example in which the precious metal eluate was not heated. In particular, in the present invention examples 3 and 4 in which the precious metal eluate was heated to 90°C, the adsorption rate of Au to yeast reached 80% or higher.

[0096] And, according to Figure 2 The results shown here confirm that Au is more selectively adsorbed to yeast than other base metals and the like.

[0097] Industrial Applicability

[0098] According to the present invention, it is possible to provide a method for producing a precious metal that can efficiently recover the precious metal from a raw material containing the precious metal and the base metal even in a strongly acidic environment such as pH 0.

Claims

1. A method for producing a precious metal, characterized in that: include: a base metal dissolution step of immersing a raw material containing a precious metal and a base metal in hydrochloric acid containing hydrogen peroxide or ferric chloride to generate a base metal eluate in which at least a portion of the base metal is dissolved and a raw material containing the precious metal as a solid phase residue; a precious metal dissolving step of generating a precious metal dissolving solution in which the precious metal contained in the precious metal-containing raw material is dissolved by reacting a mixed acid solution obtained by adding nitric acid to the base metal dissolving solution with the precious metal-containing raw material or reacting aqua regia with the precious metal-containing raw material, or both; a heating step of heating the noble metal solution to a temperature within a range of 30° C. to 100° C.; a precious metal adsorption step of adding yeast to the heated precious metal elution solution, so that the yeast selectively adsorbs precious metal ions contained in the precious metal elution solution; as well as In the noble metal separation step, a reducing agent is added to the dispersion of the yeast adsorbing the noble metal ions to separate the noble metal in nanoparticle form.

2. The method for producing a precious metal according to claim 1, characterized in that: The method for producing a precious metal further includes a cooling step, which is a step after the heating step, and cools the precious metal eluate heated in the heating step to less than 60°C.

3. The method for producing a precious metal according to claim 1 or 2, characterized in that: The yeast includes any one or two or more of the genera Saccharomyces, Zygosaccharomyces, Schizosaccharomyces, Debaryomyces and Candida.

4. The method for producing a precious metal according to claim 1 or 2, characterized in that: The noble metal includes any one or two or more of gold, platinum, silver, palladium, rhodium, iridium, ruthenium and osmium.

5. The method for producing a precious metal according to claim 1 or 2, characterized in that: The reducing agent comprises any one or more of hydrazine and its salts, borohydride salts, sulfates, thiosulfates, tartrates, phosphinic acid and its salts, formic acid and its salts, acetic acid and its salts, propionic acid and its salts, oxalic acid and its salts, ascorbic acid and its salts, phosphoric acid and its salts, hypophosphorous acid and its salts, citric acid and its salts, transition metal salts, glycine, dimethylamine borane and formaldehyde.

6. The method for producing a precious metal according to claim 1 or 2, characterized in that: The precious metal separated in the precious metal separation step is precious metal nanoparticles.

7. The method for producing a precious metal according to claim 1 or 2, characterized in that: The raw material is a circuit substrate.

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