Manufacturing methods for precious metals

Abstract

This invention provides a method for producing precious metals using yeast, which allows for the low-cost and simple process of obtaining precious metals in high yield from a precious metal solution containing precious metal ions. [Solution] A dilution step in which water is added to a precious metal solution having a pH of 2 or less, which contains at least precious metal ions, iodine, and a lactam compound, to precipitate a precipitate of iodide containing the precious metal, The process includes a noble metal adsorption step in which yeast is added to the noble metal solution after the dilution step and stirred to adsorb noble metal ions onto the yeast, wherein the concentration of the lactam compound contained in the noble metal solution after the dilution step is 300 g / L or less.

Description

Technical Field

[0001] This invention relates to a method for producing a noble metal by generating a noble metal from a solution containing a noble metal ion.

Background Art

[0002] Recycling of noble metals to recover noble metals from waste containing noble metals (gold, platinum, silver, palladium, rhodium, iridium, ruthenium, osmium) has been carried out. For example, electronic circuit boards such as discarded smartphones and personal computers contain gold and palladium, and the content per unit weight of these may be higher than the content contained in natural ores. In recent years, due to the soaring prices of noble metals, many methods for efficiently extracting noble metals from electronic circuit boards and the like, called urban mines, have been proposed.

[0003] For example, Patent Document 1 discloses a method for recovering noble metals contained in an etching waste liquid by electrolytically recovering Au from a used iodine-based etching solution containing Au.

[0004] Also, for example, Patent Document 2 discloses a method for dissolving a noble metal by bringing the noble metal into contact with a noble metal dissolution solution containing iodine or iodide ions and an organic solvent to dissolve the noble metal in the dissolution solution.

[0005] Also, for example, Patent Document 3 discloses a method for recovering a noble metal by immersing a noble metal-containing material in an organic solvent containing a lactam compound and an extract containing iodine to produce a noble metal iodide.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

[0007] However, the recovery of Au by electrolysis, as described in Patent Document 1, has a high environmental impact because it consumes a large amount of electricity during electrolysis. Furthermore, only one type of etching solution composition is disclosed, raising concerns that Au cannot be recovered with etching solutions of other compositions.

[0008] Furthermore, in Patent Document 2, the only organic solvent used in the etching solution that achieves a high recovery rate of 98% or more for Au is ethylene glycol, making it difficult to recover Au at a high rate using etching solutions with diverse compositions.

[0009] Furthermore, while Patent Document 3 recovers Au using an organic solvent containing a lactam compound and an extractant containing iodine, it is difficult to recover Au with a high recovery rate through precipitation alone, and there was concern that a high concentration of Au would remain in the residual solution after etching.

[0010] This invention has been made in view of the circumstances described above, and aims to provide a method for producing precious metals that can obtain precious metals in high yield from a precious metal solution containing precious metal ions in a simple and low-cost process using yeast. [Means for solving the problem]

[0011] To solve the above problems, the manufacturing method for precious metals according to one embodiment of the present invention proposes the following means. (1) A method for producing a precious metal according to Embodiment 1 of the present invention comprises a dilution step of adding water to a precious metal solution having a pH of 2 or less, which contains at least precious metal ions, iodine, and a lactam compound, to precipitate a precipitate of iodide containing the precious metal; and a precious metal adsorption step of adding yeast to the precious metal solution obtained through the dilution step and stirring to adsorb precious metal ions onto the yeast, wherein the concentration of the lactam compound contained in the precious metal solution obtained through the dilution step is 300 g / L or less.

[0012] (2) Embodiment 2 of the present invention is a method for producing a precious metal according to Embodiment 1, further comprising a pH adjustment step, which is a step prior to the dilution step, in which an acid is added to adjust the pH to 2 or less in order to form a precious metal solution with a pH of 2 or less.

[0013] (3) Embodiment 3 of the present invention is a method for producing a precious metal according to Embodiment 1 or 2, further comprising a precious metal extraction step, which is a step prior to the dilution step, in which a precious metal-containing material is immersed in an extract containing the lactam compound, iodine molecules (I2), and potassium iodide (KI) to obtain the precious metal solution.

[0014] (4) Aspect 4 of the present invention is the method for producing a precious metal according to aspect 3, wherein the concentration of iodine element (I) in the extract is 2 times or more and 6 times or less the concentration of potassium element (K) in the extract.

[0015] (5) Aspect 5 of the present invention is the method for producing a precious metal according to aspect 3, wherein the precious metal-containing material is an electronic circuit board containing a precious metal.

[0016] (6) Aspect 6 of the present invention is the method for producing a precious metal according to aspect 2, wherein the acid used in the pH adjustment step contains chloride ions.

[0017] (7) Embodiment 7 of the present invention is a method for producing a precious metal according to any one of embodiments 1 to 6, wherein the precipitate is in the form of plate-like crystals, needle-like crystals, or oil.

[0018] (8)Aspect 8 of the present invention is a method for producing a noble metal according to any one of Aspects 1 to 7, wherein the total amount of the noble metal contained in the precipitate generated in the dilution step and the noble metal adsorbed by the yeast in the noble metal adsorption step is 80% or more of the amount of the noble metal contained in the noble metal solution.

[0019] (9)Aspect 9 of the present invention is a method for producing a noble metal according to any one of Aspects 1 to 8, wherein the yeast contains any one or two or more of the genera Saccharomyces, Zygosaccharomyces, Schizosaccharomyces, Debaryomyces, and Candida.

Effect of the Invention

[0020] According to the present invention, it is possible to provide a method for producing a noble metal that can obtain a noble metal from a noble metal solution containing noble metal ions in a high yield at low cost with a simple process using yeast.

Brief Description of the Drawings

[0021] [Figure 1] It is a flowchart showing step by step the method for producing a noble metal according to an embodiment of the present invention.

Mode for Carrying Out the Invention

[0022] Hereinafter, a method for producing a noble metal, which is an embodiment to which the present invention is applied, will be described with reference to the drawings. The following embodiments are specifically described to better understand the gist of the invention, and do not limit the present invention unless otherwise specified.

[0023] FIG. 1 is a flowchart showing step by step the method for producing a noble metal according to an embodiment of the present invention. In the method for producing a noble metal of the present embodiment, for example, a series of procedures for separating and recovering a noble metal from a circuit board (noble metal-containing material) of an electronic device will be described. The noble metal in the present embodiment refers to the eight elements of gold, platinum, silver, palladium, rhodium, iridium, ruthenium, and osmium.

[0024] In the precious metal manufacturing method of this embodiment, first, an extract for extracting the precious metal is prepared (extract preparation step S1). The extract in this embodiment can be prepared by dissolving iodine molecules (I2), potassium iodide (KI), and a lactam compound in water (pure water, deionized water).

[0025] Although iodine molecules (I2) have low solubility in water, their solubility can be increased by adding water-soluble potassium iodide. Therefore, it is preferable that the concentration of potassium iodide in the extract be higher than the concentration of iodine molecules (I2).

[0026] The concentration of iodine (I) in the extract is preferably between 2 and 6 times the concentration of potassium (K) in the extract. Specifically, it is preferable that the concentration of potassium iodide (KI) is 30 g / L or more, and the concentration of iodine (I) is 5 g / L or more. If the concentration of iodine (I) is less than 2 times the concentration of potassium (K), the solubility of the precious metal will decrease in the precious metal extraction process described later, making it impractical. Furthermore, if the concentration of iodine (I) is more than 6 times the concentration of potassium (K), there is a concern that precipitation will occur due to undissolved iodine.

[0027] The lactam compounds used in the extract are cyclic compounds formed by the dehydration condensation of an amino group and a carboxyl group, and contain a [-CO-NH-] group in part of the cyclic portion. Lactam compounds are classified into α-lactams (three-membered ring), β-lactams (four-membered ring), γ-lactams (five-membered ring), etc., depending on the number of carbon atoms in the cyclic portion, and lactam compounds with any number of carbon atoms can be suitably used.

[0028] When using lactam compounds in the extract, it is preferable to keep the concentration of the lactam compound in the extract within a range of 50 g / L or more and 300 g / L or less. If the concentration of the lactam compound is less than 50 g / L, there is a concern that the extraction of precious metals will be insufficient in the precious metal extraction process described later. Furthermore, if the concentration of the lactam compound exceeds 300 g / L, there is a concern that it may adversely affect phase separation in the dilution process described later.

[0029] In this embodiment, N-methyl-2-pyrrolidone (NMP) and N-ethyl-2-pyrrolidone (NEP) were used as lactam compounds. NMP is a liquid obtained by condensing γ-butyrolactone and methylamine, and is soluble in water in any proportion. Furthermore, the lactam compound is not limited to NMP or NEP, but any compound having various lactam structures can be used.

[0030] Using an extract with the composition described above, a material containing precious metals, in this embodiment an electronic circuit board, is immersed in the extract (precious metal extraction step S2). Electronic circuit boards, which are components of personal computers and smartphones and on which semiconductor elements are mounted, often contain precious metals such as gold and silver in the solder joints and wiring. In particular, by using recycled materials such as waste electronic circuit boards, a precious metal solution can be obtained at low cost.

[0031] In the precious metal extraction step S2, the circuit board should be immersed in the extract at a liquid temperature of approximately 10°C to 80°C for approximately 1 to 72 hours. Stirring the extract during this time can further accelerate the extraction rate of the precious metals. Through this precious metal extraction step S2, precious metals such as gold, platinum, and palladium are extracted as metal ions into the extract, yielding a precious metal solution. The precious metal solution may also contain ions of other valuable metals such as Al and Ni.

[0032] Next, if the pH of the precious metal solution obtained in the precious metal extraction step S2 exceeds 2, pH adjustment is performed (pH adjustment step S3). In pH adjustment step S3, an acid is added to the precious metal solution to adjust the pH to 2 or less. The acid used for pH adjustment is not particularly limited, but for example, hydrochloric acid (HCl), sulfuric acid (H2SO4), nitric acid (HNO3), etc., can be used. In this embodiment, hydrochloric acid, which is an acid containing chloride ions, was used. Even after performing this pH adjustment step S3, the precious metal solution remains in a homogeneous liquid state. Furthermore, if the pH of the precious metal solution obtained in the precious metal extraction step S2 is 2 or less, the pH adjustment step S3 can be omitted, and the process can proceed directly to the next step, the dilution step S4.

[0033] Next, the pH-adjusted precious metal solution is diluted with water (dilution step S4). This dilution step S4 generates iodides (plate-like crystals, needle-like crystals, or oily substances) of the precious metal dissolved in the pH-adjusted precious metal solution, and the solution undergoes phase separation into two phases.

[0034] In the dilution step S4, the noble metal solution is separated into two phases, either a solid phase and a liquid phase, or an oil phase and an aqueous phase, by the addition of water. Iodides containing Au or Pd either migrate to the solid phase or to the oil phase. Whether the iodides migrate to the solid phase or the oil phase depends on the concentration of the lactam compound in the extract, the amount of water added in the dilution step S4, and the concentration of the noble metal dissolved in the noble metal solution.

[0035] In this dilution step S4, the concentration of the lactam compound in the extract is reduced to less than half due to phase separation caused by the addition of water. This suggests that the lactam compound promotes phase separation caused by the addition of water.

[0036] For example, if the iodide containing the noble metal migrates to the solid phase during the dilution step S4, this solid phase precipitates as noble metal iodide in the form of plate-like or needle-like crystals. The resulting solid phase is mainly composed of the noble metal, iodine, and carbon. Furthermore, if the iodide containing precious metals migrates to the oil phase during the dilution step S4, this oil phase will precipitate at the bottom of the aqueous phase as an oily substance with a high specific gravity. The resulting oil phase is mainly composed of precious metals, iodine, and carbon.

[0037] In this embodiment, the pH adjustment step S3 is performed on the precious metal solution before the dilution step S4 is performed. However, it is also possible to perform the dilution step S4 on the precious metal solution before the pH adjustment step S3. Furthermore, the pH adjustment step S3 and the dilution step S4 can be performed on the precious metal solution simultaneously.

[0038] Next, the two phases formed in the dilution step S4 are separated from each other (separation step S5). In the separation step S5, if the noble metal solution separates into a solid phase and a liquid phase, the solid phase containing the noble metal is recovered using a filter or the like. If the noble metal solution separates into an oil phase and an aqueous phase, the oil phase containing the noble metal is recovered by dispensing them at the oil-water interface. The recovered solid or oil phases containing precious metals can be redissolved and purified to isolate the precious metals.

[0039] The amount of precious metal in the precious metal iodide obtained in the dilution step S4 is 90% or more of the amount of precious metal in the precious metal solution. In other words, most of the precious metal extracted into the precious metal solution migrates to the solid or oil phase recovered in the separation step S5, and the precious metal can be recovered from the precious metal solution from which the precious metal was extracted in high yield.

[0040] Next, the precious metals contained in the liquid phase (aqueous phase) separated in separation step S5 are recovered. The precious metal solution (residual liquid), which is the liquid phase (aqueous phase) separated in separation step S5, contains precious metal ions remaining in the liquid, other than the precious metals that migrated to the solid phase or oil phase recovered in separation step S5. Furthermore, the precious metal solution (residual solution) used in the following steps can also be the precious metal solution obtained after recovering a portion of the precious metal through the process described above, and this can be used as the starting material.

[0041] First, yeast is added to the precious metal solution (residual liquid), which is the liquid phase (aqueous phase) separated in separation step S5, and stirred to adsorb the precious metal ions contained in the precious metal solution onto the yeast (precious metal adsorption step S6). In precious metal adsorption step S6, it is sufficient to add yeast to the precious metal solution and stir. Through this precious metal adsorption step S6, the precious metal ions contained in the precious metal solution come into contact with the yeast, causing the precious metal ions to be adsorbed onto the yeast.

[0042] The amount of yeast added in the precious metal adsorption step S6 should be, for example, in the range of 30 to 140 times the mass of the precious metal contained in the precious metal solution. It is preferable to measure the mass of the precious metal contained in the precious metal solution beforehand using an ICP emission spectrometer or an absorbance photometer.

[0043] Any yeast capable of adsorbing precious metal ions can be used in the precious metal adsorption step S6. Yeasts applicable to this embodiment include, for example, yeasts of the genera Saccharomyces, Candida, Torulopsis, Zygosaccharomyces, Schizosaccharomyces, Pichia, Yarrowia, Hansenula, Kluyveromyces, Debaryomyces, Geotrichum, Wickerhamia, Fellomyces, and Sporobolomyces, among which yeasts belonging to the genera Saccharomyces, Zygosaccharomyces, Schizosaccharomyces, and Debaryomyces are particularly preferred.

[0044] Saccharomyces yeasts are representative budding yeasts, and examples include 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, and S. zonatus.

[0045] Examples of Candida yeasts include non-pathogenic yeasts of the genus Candida, such as Candida utilis, Candida boidinii, Candida etchellsii, Candida versatilis, and Candida stellata.

[0046] The genus Zygosaccharomyces consists of salt-tolerant yeasts isolated from miso and soy sauce, such as Z. rouxii. The genus Schizosaccharomyces consists of fission yeasts, such as S. cryophilus, S. japonicus, S. octosporus, and S. pombe. Another example of a preferred yeast is the Debaryomyces hansenii, deposited at accession number NITE BP-01780 (NITE Patent Microorganism Depositary Center, 2-5-8 Kazusa Kamatari, Kisarazu City, Chiba Prefecture, Japan).

[0047] The yeast used in this precious metal adsorption process S6 may be live or dead.

[0048] The pH and temperature of the liquid to which yeast has been added to the precious metal solution are not particularly limited. For example, the pH can be between -1 and 7, ranging from strongly acidic to neutral. The temperature should be between 10°C and 45°C, preferably between 20°C and 35°C.

[0049] Furthermore, the time required for the precious metal adsorption process S6 is the time from when the yeast is added to the precious metal solution until it is stirred, and can be, for example, within a range of 4 hours or less.

[0050] Next, the precious metal solution to which yeast has been added is separated into solid and liquid phases by filtration or other means, and then the solid phase (yeast containing precious metal ions) is washed with deionized water or pure water. It is preferable to wash the solution about three times, for example, by changing the washing water each time.

[0051] Furthermore, if the yeast (solid phase) containing precious metal ions after solid-liquid separation is then reacted with, for example, a reducing agent to reduce the precious metal ions and precipitate them in yeast cells, the precious metals can be produced in yeast cells, for example, in the form of nanoparticles (precious metal nanoparticles).

[0052] As described above, in the method for producing precious metals of this embodiment, water is added to a precious metal solution containing at least precious metal ions, iodine, and a lactam compound to dilute the lactam compound to a concentration of 300 g / L or less, thereby precipitating a precipitate of iodide containing the precious metal. Subsequently, yeast is added to the precious metal solution containing the precious metal that remains in the aqueous phase without precipitation to adsorb the precious metal ions, making it possible to efficiently recover the precious metal from the precious metal solution containing precious metal ions in high yield.

[0053] In particular, by performing a dilution process at a pH of 2 or lower, it becomes possible to efficiently recover low concentrations of precious metal ions contained in the precious metal solution (residual solution) after recovering some of the precious metal ions as precious metal iodides by adsorbing them onto yeast.

[0054] While embodiments of the present invention have been described above, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents. [Examples]

[0055] To verify the effects of the present invention, samples for Examples 1-6 and Comparative Examples 1-5 were prepared. (Example 1) Potassium iodide and iodine were dissolved in deionized water so that the concentration of iodine (g / L) was 2.64 times that of potassium (g / L). N-methyl-2-pyrrolidone (NMP) was then dissolved to a concentration of 380 g / L to prepare the extract of Example 1 (extract preparation step).

[0056] Waste containing Au was immersed in this extract to achieve an Au concentration of 0.75 g / L, after which the waste residue was removed (precious metal extraction step). 1M hydrochloric acid was added to this solution until the pH was approximately 1. When the resulting precious metal solution was diluted fourfold with deionized water, black crystals (precious metal iodide) precipitated. Precipitation occurred immediately after adding water, but a sufficient amount of precipitate could be obtained by allowing it to stand for more than one hour (dilution step). ICP analysis of the aqueous phase of this diluted precious metal solution confirmed that 46.2% by mass of Au had migrated to the precipitate.

[0057] Baker's yeast was added to the aqueous phase (precious metal solution (residual liquid)) to a concentration of 18 g / L, and after 5 minutes, solid-liquid separation was performed and the supernatant was collected (precious metal adsorption process). Analysis of the Au concentration of this supernatant confirmed that 88.7 mass% of Au ions were adsorbed by the baker's yeast. Thus, it was confirmed that 93.9 mass% of the Au contained in the waste can be recovered by combining precipitation by adding water and yeast adsorption.

[0058] (Example 2) The procedure is the same as in Example 1, except that potassium iodide and iodine are dissolved in deionized water so that the concentration of iodine (g / L) is 5.57 times the concentration of potassium (g / L), and N-methyl-2-pyrrolidone (NMP) is further dissolved to a concentration of 400 g / L, and gold (Au) is extracted using this extract to a concentration of 0.67 g / L, and then diluted twice with deionized water.

[0059] In Example 2, it was confirmed that 98.2% by mass of Au migrated to the precipitate after dilution, and that 85.4% by mass of Au ions were adsorbed onto the baker's yeast, confirming that 99.7% by mass of the Au contained in the waste could be recovered.

[0060] (Example 3) The procedure is the same as in Example 1, except that potassium iodide and iodine are dissolved in deionized water so that the iodine concentration (g / L) is 3.92 times the potassium concentration (g / L), and N-methyl-2-pyrrolidone (NMP) is further dissolved to a concentration of 400 g / L, and gold is extracted using this extract to a concentration of 1.02 g / L, and then diluted three times with deionized water.

[0061] In Example 3, it was confirmed that 75.7% by mass of Au migrated to the precipitate after dilution, and that 75.7% by mass of Au ions were adsorbed onto the baker's yeast. This confirmed that 94.1% by mass of the Au contained in the waste could be recovered.

[0062] (Example 4) The procedure is the same as in Example 3, except that the gold was diluted fourfold with deionized water after extraction.

[0063] In Example 4, it was confirmed that 85.8% by mass of Au migrated to the precipitate after dilution, and that 85.0% by mass of Au ions were adsorbed onto the baker's yeast. This confirmed that 97.9% by mass of the Au contained in the waste could be recovered.

[0064] (Example 5) The procedure is the same as in Example 3, except that the gold was diluted fivefold with deionized water after extraction.

[0065] In Example 5, it was confirmed that 87.9% by mass of Au migrated to the precipitate after dilution, and 89.8% by mass of Au ions were adsorbed onto the baker's yeast, confirming that 98.8% by mass of the Au contained in the waste could be recovered.

[0066] (Example 6) The procedure is the same as in Example 3, except that the gold was diluted six times with deionized water after extraction.

[0067] In Example 6, it was confirmed that 88.6% by mass of Au migrated to the precipitate after dilution, and 91.9% by mass of Au ions were adsorbed onto the baker's yeast, confirming that 99.1% by mass of the Au contained in the waste could be recovered.

[0068] (Comparative Example 1) The procedure is the same as in Example 1, except that potassium iodide and iodine were dissolved in deionized water so that the iodine concentration (g / L) was 5.57 times the potassium concentration (g / L), and then N-methyl-2-pyrrolidone (NMP) was dissolved in the resulting extract to a concentration of 400 g / L. After extracting gold to a concentration of 0.67 g / L using this extract, dilution with deionized water was not performed.

[0069] In Comparative Example 1, 53.4% ​​by mass of Au migrated to the precipitate after dilution, and 2.0% by mass of Au ions were found to be adsorbed onto the baker's yeast. As a result, only 54.3% by mass of the Au contained in the waste could be recovered.

[0070] (Comparative Example 2) Potassium iodide and iodine were dissolved in deionized water so that the iodine concentration (g / L) was 3.92 times the potassium concentration (g / L). N-methyl-2-pyrrolidone (NMP) was further dissolved to a concentration of 1000 g / L, and waste containing Au was immersed in this extract. However, Au was insoluble in the extract of Comparative Example 2, and Au could not be recovered.

[0071] (Comparative Example 3) Potassium iodide and iodine were dissolved in deionized water so that the iodine concentration (g / L) was 3.25 times the potassium concentration (g / L). Furthermore, N-methyl-2-pyrrolidone (NMP) was dissolved to a concentration of 400 g / L, and the waste containing Au was immersed in this extract. However, Au was insoluble in the extract of Comparative Example 3, and Au could not be recovered.

[0072] (Comparative Example 4) The procedure was the same as in Example 1, except that potassium iodide and iodine were dissolved in deionized water so that the iodine concentration (g / L) was 3.38 times the potassium concentration (g / L), and then N-methyl-2-pyrrolidone (NMP) was dissolved in the resulting extract to a concentration of 410 g / L. After extracting gold to a concentration of 0.55 g / L using this extract, dilution with deionized water was not performed.

[0073] In Comparative Example 4, no precipitate formed, so Au could not be recovered from the precipitate, nor could Au ions be adsorbed and recovered by baker's yeast.

[0074] (Comparative Example 5) The procedure is the same as in Example 1, except that potassium iodide and iodine were dissolved in deionized water so that the concentration of iodine (g / L) was 3.38 times that of potassium (g / L), and then N-methyl-2-pyrrolidone (NMP) was dissolved to a concentration of 410 g / L. After extracting gold to a concentration of 0.55 g / L using this extract, the solution was diluted five times with deionized water.

[0075] In Comparative Example 5, no precipitate formed, and therefore Au could not be recovered from the precipitate. Furthermore, it was confirmed that 46.1% by mass of Au ions were adsorbed onto the baker's yeast, meaning that only 46.1% by mass of the Au contained in the waste could be recovered.

[0076] Examples 1-6 and Comparative Examples 1-5 described above are summarized in Table 1. [Table 1]

[0077] According to Examples 1 to 6 of the present invention, it was confirmed that by adding water to a precious metal solution containing at least precious metal ions, iodine, and a lactam compound to dilute the lactam compound to a concentration of 300 g / L or less, a precipitate of iodide containing the precious metal is precipitated, and then yeast is added to the precious metal solution containing the precious metal that remains in the aqueous phase without precipitation to adsorb the precious metal ions, the recovery rate of the precious metal, including both the precipitate and the yeast adsorbed material, can be increased to 90% or more. [Industrial applicability]

[0078] The present invention's method for producing precious metals makes it possible to efficiently separate and recover precious metals from electronic circuit boards and the like containing them with high yield. This contributes to the effective utilization of precious metal resources, often referred to as "urban mines." Therefore, it has industrial applicability.

Claims

1. A dilution step in which water is added to a precious metal solution having a pH of 2 or less, which contains at least precious metal ions, iodine, and a lactam compound, to precipitate a precipitate of iodide containing the precious metal, The process includes a noble metal adsorption step in which yeast is added to the noble metal solution after the dilution step and stirred to adsorb noble metal ions onto the yeast, A method for producing a precious metal, wherein the concentration of the lactam compound in the precious metal solution after the dilution step is 300 g / L or less.

2. The method for producing a precious metal according to claim 1, further comprising a pH adjustment step, which is a step prior to the dilution step, in which an acid is added to adjust the pH to 2 or less in order to form the precious metal solution with a pH of 2 or less.

3. A step prior to the dilution step, comprising the lactam compound and an iodine molecule (I ２ A method for producing a precious metal according to claim 1, further comprising a precious metal extraction step of immersing a precious metal-containing material in an extract containing ) and potassium iodide (KI) to obtain the precious metal solution.

4. The method for producing a precious metal according to claim 3, wherein the concentration of iodine (I) in the extract is 2 times or more and 6 times or less the concentration of potassium (K) in the extract.

5. The method for producing a precious metal according to claim 3, wherein the precious metal-containing material is an electronic circuit board containing a precious metal.

6. The method for producing a precious metal according to claim 2, wherein the acid used in the pH adjustment step contains chloride ions.

7. The method for producing a precious metal according to any one of claims 1 to 6, wherein the precipitate is in the form of plate-like crystals, needle-like crystals, or oil.

8. The method for producing a precious metal according to any one of claims 1 to 6, wherein the total amount of the precious metal contained in the precipitate produced in the dilution step and the precious metal adsorbed by the yeast in the precious metal adsorption step is 80% or more of the amount of precious metal contained in the precious metal solution.

9. The method for producing precious metals according to any one of claims 1 to 6, wherein the yeast comprises one or more species from among the genera Saccharomyces, Zygosaccharomyces, Schizosaccharomyces, Devariomyces, and Candida.

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