Precious metal adsorbent, precious metal recovery method, and method for regenerating precious metal adsorbent

Abstract

Provided are a noble metal adsorbent capable of achieving high adsorption performance for noble metals and capable of easily recovering noble metals, a noble metal recovery method, and a noble metal adsorbent regeneration method. The noble metal adsorbent of the present invention contains a metal sulfide. The metal sulfide is composed of, for example, molybdenum disulfide particles. In the noble metal recovery method of the present invention, after adsorbing noble metals to the noble metal adsorbent, the noble metal adsorbent is heated in the presence of oxygen to volatilize it, thereby recovering the noble metals.

Description

Technical Field

[0001] This invention relates to precious metal adsorbents, precious metal recovery methods, and precious metal adsorbent regeneration methods.

[0002] This application claims priority based on Japanese Special Purpose Application 2021-050484 filed in Japan on March 24, 2021, the contents of which are incorporated herein by reference. Background Technology

[0003] Precious metals such as gold, silver, and platinum have been valued since ancient times due to their rarity and durability. In modern times, they also hold important positions in industrial applications such as catalysts. However, gold mining, for example, has seen increasing annual production, and based on 2013 data, it is said to have approximately 18 more years of exploitable reserves. Furthermore, its price fluctuates due to social unrest, but has a long-term upward trend.

[0004] On the other hand, current precision equipment contains large amounts of gold and silver, and the waste from these can be described as urban mining. In Japan's urban mining, gold accounted for 16% and silver for 22% of the existing buried reserves in 2006, and their effective utilization is an important issue.

[0005] Conventional methods for recovering precious metals include solvent extraction and ion exchange resin methods. Solvent extraction is complex, and the treatment of the large amounts of waste liquid it generates is also problematic. On the other hand, ion exchange resin methods are prone to high costs due to the use of synthetic resins with specific functional groups and the complex process of separating the resin from the resin.

[0006] As an alternative to these methods, various novel precious metal adsorption materials have been studied in recent years. For example, it has been disclosed that insoluble gels can adsorb gold (Au), silver (Ag), and palladium (Pd). The insoluble gels are formed by adding an equimolar amount of glutaraldehyde as a crosslinking agent to proanthocyanidin oligomers with an average degree of polymerization of 3 to 4 and crosslinking them (Patent Document 1).

[0007] In addition, as another method, the recovery of precious metals using porous porphyrin polymers represented by specific structural formulas has been disclosed. This method has adsorption performance to the extent that it can concentrate precious metals even at low concentrations such as seawater, and can be reused as an adsorbent by acid treatment after adsorption (Patent Document 2).

[0008] In addition, examples of using copper sulfide as a mercury adsorbent are reported (Patent Document 3), and examples of using hydrogels with thiourea skeletons as organosulfur compounds as adsorbents for gold, platinum, and palladium are reported (Patent Document 4).

[0009] Existing technical documents

[0010] Patent documents

[0011] Patent Document 1: Japanese Patent Application Publication No. 2019-72722

[0012] Patent Document 2: Japanese Patent Application Publication No. 2019-104911

[0013] Patent Document 3: Japanese Patent Application Publication No. 2019-171257

[0014] Patent Document 4: Japanese Patent Application Publication No. 2011-183376 Summary of the Invention

[0015] The problem the invention aims to solve

[0016] However, Patent Document 1 discloses a gel selectively adsorbing gold using polyphenols derived from grape seeds as raw materials, but it does not provide quantitative insights into the amount of gold adsorbed or insights into methods for recovering the adsorbed gold.

[0017] Furthermore, in the case of Patent Document 2, the synthesis of porous porphyrin polymers as adsorbents is difficult. Additionally, to recover the adsorbed gold through acid treatment, the dissolved gold ions need to be reduced to zero-valent gold, a complex process. Moreover, it is claimed that when the adsorbate is gold ions, 1 mg of porphyrin polymer can adsorb 1.617 mg, and when the adsorbate is platinum ions, 1 mg of porphyrin polymer can adsorb 0.1968 mg. To achieve higher adsorption capacity, prolonged light irradiation, such as approximately 48 hours, is required. It is hoped that a shorter and simpler method can be used to achieve the desired adsorption performance.

[0018] Furthermore, Patent Document 3 does not disclose the use of copper sulfide for the adsorption of precious metals other than mercury, nor the adsorption performance at that time. In Patent Document 4, when a hydrogel with a thiourea framework of an organosulfur compound is used, the adsorption of gold and the like is insufficient, and the adsorption limit concentration is not disclosed, leaving room for improvement.

[0019] The purpose of this invention is to provide a precious metal adsorbent, a precious metal recovery method, and a precious metal adsorbent regeneration method that can achieve high adsorption performance for precious metals and can easily recover precious metals.

[0020] Solution for solving the problem

[0021] Through repeated and in-depth research, the inventors discovered that using metal sulfides as noble metal adsorbents, particularly molybdenum disulfide particles, can achieve high adsorption performance due to the selectivity of metal sulfides for noble metals. In particular, they found that when molybdenum disulfide particles are used as adsorbents for gold, the selectivity for gold is extremely high, and the amount of noble metal adsorbed per unit mass of molybdenum disulfide particles is significantly increased compared to previous noble metal adsorbents, thus improving adsorption performance.

[0022] Furthermore, when manufacturing molybdenum disulfide particles using the applicant's technology of "nanosized molybdenum oxide microparticles" as raw materials, it is possible to obtain nanosized molybdenum disulfide particles with a plate-like structure and a large surface area per unit weight, which is difficult to achieve through the pulverization of mineral products containing particulate resin compositions and the synthesis based on commonly used molybdenum oxide (micrometer-scale). It has been found that when these molybdenum disulfide particles are thus used as precious metal adsorbents, particularly gold adsorbents, the gold adsorption rate and the amount of gold adsorbed are significantly increased due to the large specific surface area of ​​the molybdenum disulfide particles and the affinity of gold for sulfur.

[0023] Furthermore, it was discovered that by adsorbing the precious metal onto the aforementioned precious metal adsorbent and then heating the adsorbent in the presence of oxygen to volatilize it, the precious metal can be recovered in a state where its valence is zero without changing its value. Therefore, precious metals can be easily recovered without the need for reduction treatment, and the environmental burden associated with reduction treatment can be eliminated. In particular, it was found that by adsorbing the precious metal onto molybdenum disulfide particles and then heating the molybdenum disulfide particles in the presence of oxygen, the highly volatile molybdenum oxide particles formed by the oxidation of molybdenum disulfide can be used to more easily recover the precious metal.

[0024] Furthermore, it was found that after recovering the volatile metal oxides, metal sulfides can be obtained by sulfiding the metal oxides through methods such as heating in the presence of a sulfur source. Therefore, metal sulfides, which serve as adsorbents for precious metals, can be easily regenerated. By reusing the obtained metal sulfides, the consumption of metal resources can be suppressed.

[0025] That is, the present invention provides the following configuration.

[0026] [1] A precious metal adsorbent containing metal sulfides.

[0027] [2] According to the noble metal adsorbent described in [1] above, wherein the metal sulfide is composed of molybdenum disulfide particles.

[0028] [3] According to the noble metal adsorbent described in [2] above, wherein the median particle size D of the molybdenum disulfide particles determined by dynamic light scattering method is... 50 It is between 10nm and 1000nm.

[0029] [4] According to the noble metal adsorbent described in [2] or [3] above, the primary particles of the molybdenum disulfide particles are in the shape of a disc, a strip or a sheet and have a thickness in the range of 3 to 100 nm.

[0030] [5] The noble metal adsorbent according to any one of [2] to [4] above, wherein the specific surface area of ​​the molybdenum disulfide particles, as determined by the BET method, is 10 m². 2 / g or more.

[0031] [6] The noble metal adsorbent according to any one of [2] to [5] above, wherein the ratio (I / II) of the intensity I of the peak originating from Mo-S to the intensity II of the peak originating from Mo-Mo in the radial distribution function obtained from the extended X-ray absorption fine structure (EXAFS) spectrum of the K absorption end of the molybdenum disulfide particles is greater than 1.0.

[0032] [7] The noble metal adsorbent according to any one of [2] to [6] above, wherein,

[0033] The aforementioned molybdenum disulfide particles possess both the 2H and 3R crystal structures of molybdenum disulfide.

[0034] In the powder X-ray diffraction (XRD) spectra of the aforementioned molybdenum disulfide particles obtained using Cu-Kα rays as the X-ray source, the peaks near 39.5° and 49.5° originate from the aforementioned 2H crystal structure, while the peaks near 32.5°, 39.5°, and 49.5° originate from the aforementioned 3R crystal structure.

[0035] The half-widths of the peaks near 39.5° and 49.5° are greater than 1°.

[0036] [8] The precious metal adsorbent according to any one of [2] to [7] above, wherein the precious metal adsorbed by the metal sulfide is gold.

[0037] [9] A method for recovering precious metals, wherein after the precious metal is adsorbed onto the precious metal adsorbent described in any one of [1] to [8] above, the precious metal adsorbent is dissolved with an oxidizing solution, thereby recovering the precious metal.

[0038]

[10] A method for recovering precious metals, wherein after the precious metal is adsorbed onto the precious metal adsorbent described in any one of [1] to [8] above, the precious metal adsorbent is heated in the presence of oxygen and volatilized, thereby recovering the precious metal.

[0039]

[11] A method for regenerating a precious metal adsorbent, wherein after recovering the metal oxide volatilized by the precious metal recovery method described above [9], the metal oxide is sulfided, thereby regenerating the precious metal adsorbent composed of metal sulfides.

[0040] The effects of the invention

[0041] According to the present invention, high adsorption performance of precious metals can be achieved and precious metals can be easily recovered. Attached Figure Description

[0042] Figure 1 A schematic diagram illustrating an example of an apparatus used to manufacture molybdenum trioxide particles, which are the raw material for molybdenum disulfide particles.

[0043] Figure 2 The figure shows the results of X-ray diffraction (XRD) patterning of commercially available molybdenum disulfide particles together with the diffraction pattern of the 2H crystal structure of molybdenum disulfide (MoS2).

[0044] Figure 3 The figure shows the results of the X-ray diffraction (XRD) pattern of the molybdenum disulfide particles obtained in Synthesis Example 1 together with the diffraction patterns of the 3R crystal structure of molybdenum disulfide (MoS2), the 2H crystal structure of molybdenum disulfide (MoS2), and the diffraction pattern of molybdenum dioxide (MoO2).

[0045] Figure 4 AFM image of the synthesized molybdenum disulfide particles.

[0046] Figure 5 To show Figure 4 The diagram shows a cross-sectional view of molybdenum disulfide particles.

[0047] Figure 6 The extended X-ray absorption fine structure (EXAFS) spectrum of the K-end of molybdenum was obtained for determination using molybdenum disulfide particles obtained in Synthesis Example 1.

[0048] Figure 7 This is a diagram illustrating the X-ray diffraction (XRD) pattern of gold adsorbed onto the noble metal adsorbent obtained in Synthesis Example 1 in Example 2.

[0049] Figure 8 This is a diagram showing the XPS pattern of gold adsorbed onto molybdenum disulfide particles in Example 2.

[0050] Figure 9 The diagram illustrates the X-ray diffraction (XRD) patterns of gold recovered from molybdenum disulfide particles after gold adsorption in Examples 6 and 7.

[0051] Figure 10A graph showing the results of measuring the gold ion leakage concentration when the molybdenum disulfide particles obtained in Synthesis Example 1 are packed into a column and a gold-containing solution is introduced into the column. Detailed Implementation

[0052] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0053] <Precious Metal Adsorbent>

[0054] The noble metal adsorbent of this embodiment contains metal sulfides, preferably composed of metal sulfides. The noble metal adsorbent of this embodiment exhibits selectivity for noble metals and demonstrates high adsorption performance. The metal sulfide is preferably composed mainly of molybdenum disulfide particles, more preferably of molybdenum disulfide particles. The high adsorption performance of noble metals is believed to be due, for example, to the aforementioned median particle size D of the molybdenum disulfide particles. 50 The size is as small as 1000 nm or less. It is believed that the aforementioned selective adsorption properties of noble metals are due, for example, to the high affinity of sulfur in metal sulfides for noble metals. Examples of noble metal adsorbents include metal sulfide particles, with molybdenum disulfide particles being more preferred. The metal sulfide particles preferably contain molybdenum disulfide particles, and more preferably are composed of molybdenum disulfide particles.

[0055] Examples of noble metals that can be adsorbed by the noble metal adsorbent of this embodiment include silver (Ag), gold (Au), platinum (Pt), palladium (Pd), rhodium (Rh), iridium (Ir), ruthenium (Ru), and osmium (Os). The gold adsorption performance of the noble metal adsorbent of this embodiment is particularly excellent. This excellent gold adsorption performance is believed to be due to the median particle size D of the molybdenum disulfide particles. 50 Small as 1000 nm or less, molybdenum disulfide has a 3R crystal structure, and / or gold has a very high affinity for sulfur.

[0056] When molybdenum disulfide particles are used as a noble metal adsorbent, the noble metal that can be adsorbed by the molybdenum disulfide particles is preferably selected from one or more of gold (Au), silver (Ag), platinum (Pt), palladium (Pd), and ruthenium (Ru).

[0057] In this embodiment, the median particle size D of the molybdenum disulfide particles in the noble metal adsorbent, determined by dynamic light scattering, is... 50 The particle size is between 10 nm and 1000 nm. From the viewpoint of the aforementioned effects, a particle size of 600 nm or less is preferred, more preferably 500 nm or less, and particularly preferably 400 nm or less. The median particle size D of the aforementioned molybdenum disulfide particles is... 50 The particle size can be 10nm or larger, 20nm or larger, or 40nm or larger. The median particle size D of molybdenum disulfide particles... 50For example, dynamic light scattering particle size distribution measuring devices (MicrotracBEL, Nanotrac WaveII) and laser diffraction particle size distribution measuring devices (Shimadzu SALD-7000) can be used for measurement.

[0058] In this embodiment, the molybdenum disulfide particles in the noble metal adsorbent preferably contain a 3R crystal structure. By incorporating a 3R crystal structure, the crystal edge portion of the molybdenum disulfide particles increases, and the ion adsorption sites increase, which is believed to contribute to further improvement in the adsorption performance of noble metals. Furthermore, by incorporating a 3R crystal structure, the adsorption performance of noble metals, particularly gold, is particularly improved. This is presumably due to the specific surface area derived from the nanostructure of the molybdenum disulfide particles.

[0059] The fact that the above-mentioned molybdenum disulfide particles contain a quasi-stable 3R crystal structure can be distinguished as follows: in the powder X-ray diffraction (XRD) spectrum obtained using Cu-Kα rays as the X-ray source, the peaks near 32.5°, 39.5°, and 49.5° all contain composite peaks (broad peaks) of the 2H and 3R crystal structures.

[0060] Furthermore, the molybdenum disulfide particles in the noble metal adsorbent of this embodiment preferably comprise a 2H crystal structure and a 3R crystal structure of molybdenum disulfide. Commercially available molybdenum disulfide particles typically contain a large number of particles with a diameter exceeding 1 μm, and are also hexagonal solids, such as... Figure 2 As shown, the molybdenum oxide particles have a basic 2H crystal structure. In contrast, the molybdenum disulfide particles manufactured via the methods described later, namely "method for manufacturing molybdenum trioxide particles" and "method for manufacturing molybdenum disulfide particles," contain both 2H and 3R crystal structures, and the median particle size D is easily achieved. 50 Adjust to a size between 10nm and 1000nm.

[0061] The fact that molybdenum disulfide particles possess both 2H and 3R crystal structures can be confirmed, for example, using Rietveld analysis software (Panalytical, HighScore Plus), which can take into account crystallite size. This Rietveld analysis software uses a crystal structure model incorporating crystallite size to simulate the overall XRD diffraction pattern. It compares this model with experimentally obtained XRD diffraction patterns, minimizing the residuals between the experimental and calculated patterns. By optimizing crystal structure factors such as lattice constants, atomic coordinates, and weight percentages (existence ratios) of the crystal structure model using the least squares method, it performs high-precision identification and quantification of each phase in both 2H and 3R crystal structures. Thus, in addition to the crystal structure type and ratios calculated using conventional Rietveld analysis, the crystallite size can also be calculated. In this patent, the analysis method using the aforementioned HighScore Plus will be referred to as "extended Rietveld analysis."

[0062] Furthermore, regarding the molybdenum disulfide particles in the noble metal adsorbent of this embodiment, in the powder X-ray diffraction (XRD) spectrum obtained by using Cu-Kα rays as the X-ray source, the peaks near 39.5° and 49.5° originate from the aforementioned 2H crystal structure, and the peaks near 32.5°, 39.5°, and 49.5° originate from the aforementioned 3R crystal structure. Preferably, the half-width at half-maximum (WWHM) of the peaks near 39.5° and 49.5° is 1° or more. Furthermore, the aforementioned molybdenum disulfide particles may contain crystal structures other than the 2H and 3R crystal structures of molybdenum disulfide, such as the 1H crystal structure.

[0063] When imaged using a transmission electron microscope (TEM), the primary particles of the aforementioned molybdenum disulfide particles can have shapes in a two-dimensional image that are granular, spherical, plate-like, needle-like, rope-like, ribbon-like, or sheet-like, and combinations of these shapes are possible. The primary particles of the aforementioned molybdenum disulfide particles are preferably disc-shaped, ribbon-like, or sheet-like. Furthermore, the average size of the primary particles of the 50 molybdenum disulfide particles preferably has a length (longitudinal) × width (horizontal) range of 50–1000 nm × 50–1000 nm, more preferably a range of 100–500 nm × 100–500 nm, and particularly preferably a range of 50–200 nm × 50–200 nm. Additionally, the thickness of the primary particles of the aforementioned molybdenum disulfide particles, as measured by atomic force microscopy (AFM), preferably has a range of 3 nm or more, more preferably a range of 5 nm or more. Furthermore, the thickness of the primary particles of the aforementioned molybdenum disulfide particles, as measured by atomic force microscopy (AFM), preferably has a size in the range of 100 nm or less, more preferably in the range of 50 nm or less, and particularly preferably in the range of 20 nm or less. Additionally, the thickness of the primary particles of the aforementioned molybdenum disulfide particles, as measured by atomic force microscopy (AFM), can have a size in the range of 40 nm or less, and can have a size in the range of 30 nm or less. By making the shape of the primary particles of the aforementioned molybdenum disulfide particles disc-shaped, strip-shaped, or sheet-shaped, the specific surface area of ​​the molybdenum disulfide particles can be increased. Furthermore, it is preferable that the shape of the primary particles of the aforementioned molybdenum disulfide particles is disc-shaped, strip-shaped, or sheet-shaped, and the thickness is in the range of 3 to 100 nm. Here, disc-shaped, strip-shaped, or sheet-shaped refers to a thin-layer shape. There is no clear distinction between disc-shaped, strip-shaped, and sheet-shaped particles. For example, particles with a thickness of less than 10 nm can be considered sheet-shaped, particles with a thickness of more than 10 nm and a length ÷ width ≥ 2 can be considered strip-shaped, and particles with a thickness of more than 10 nm and a length ÷ width < 2 can be considered disc-shaped. The length-to-thickness ratio of the primary particles of molybdenum disulfide, i.e., (length (length in the longitudinal and transverse directions)) / thickness (height)), is preferably 1.2 to 1200, more preferably 2 to 800, further preferably 5 to 400, and particularly preferably 10 to 200, based on an average of 50 particles. The shape, length, width, and thickness of the primary particles of 50 molybdenum disulfide particles can also be measured using an atomic force microscope (AFM), and the length-to-thickness ratio can be calculated from the measurement results.

[0064] By making the shape of the molybdenum disulfide particles not simply spherical, but disc-shaped, ribbon-shaped, or sheet-shaped with a large length-to-thickness ratio, it is expected that the contact area between the molybdenum disulfide particles and the precious metals will increase, which is believed to help increase the adsorption capacity of the precious metals.

[0065] In this embodiment, the specific surface area of ​​the molybdenum disulfide particles in the noble metal adsorbent, as determined by the BET method, is preferably 10 m².2 / g or more, preferably 20m 2 / g or more, with 30m being the preferred choice 2 / g or more. Furthermore, the specific surface area of ​​the aforementioned molybdenum disulfide particles, as determined by the BET method, can reach 40 m². 2 / g or more, can be 50m 2 / g or above, can be 60m 2 / g or more. The specific surface area of ​​the above molybdenum disulfide particles, as determined by the BET method, can be 300m². 2 Below / g, it can be 200m 2 Below / g, it can be 100m 2 / g or less.

[0066] In this embodiment, the molybdenum disulfide particles in the noble metal adsorbent have a specific surface area greater than 10 m² as determined by the BET method. 2 Adsorbents with a concentration of more than 1 g of precious metals can increase the contact area with precious metals, thus improving the adsorption performance of precious metals.

[0067] In the radial distribution function of the molybdenum disulfide particles in the noble metal adsorbent of this embodiment, obtained from the extended X-ray absorption fine structure (EXAFS) spectrum of the K absorption end of molybdenum, the ratio (I / II) of the peak intensity I originating from Mo-S to the peak intensity II originating from Mo-Mo is greater than 1.0, more preferably 1.1 or more, and particularly preferably 1.2 or more.

[0068] Regardless of whether the molybdenum disulfide crystal structure is 2H or 3R, the distance between Mo and S atoms is essentially the same due to covalent bonding. Therefore, in the extended X-ray absorption fine structure (EXAFS) spectrum of the K-end of molybdenum, the peaks originating from Mo-S atoms have the same intensity. On the other hand, the 2H crystal structure of molybdenum disulfide is hexagonal. Therefore, the identical hexagons are located directly below the 90° of the hexagons of the Mo atoms. Consequently, the distance between Mo atoms becomes closer, and the intensity of peak II originating from Mo-Mo becomes stronger.

[0069] Conversely, the 3R crystal structure of molybdenum disulfide is rhombohedral, so the hexagons do not exist directly below the 90° of the hexagons, but are offset by half. Therefore, the distance between Mo-Mo becomes greater, and the peak intensity II derived from Mo-Mo becomes weaker.

[0070] In the pure 2H crystal structure of molybdenum disulfide, the above ratio (I / II) decreases, but with the inclusion of the 3R crystal structure, the above ratio (I / II) increases.

[0071] In the 3R crystal structure, the hexagons of the Mo atoms in the three layers are only offset by half of each other. Therefore, compared with the 2H crystal structure in which the hexagons of the Mo atoms in the two layers are arranged vertically and regularly, the interaction between the layers is small, and it can be expected to become more likely to adsorb noble metals.

[0072] It is believed that the presence of molybdenum trioxide (MoO) would adversely affect the adsorption performance of noble metals; therefore, the conversion rate R of MoO particles to MoS2 in the noble metal adsorbent of this embodiment is [not specified]. C Preferably 70% or more, more preferably 80% or more, and especially preferably 90% or more.

[0073] By increasing the conversion rate R of molybdenum disulfide particles to MoS2 in the noble metal adsorbent of this embodiment... C The figure shows a near 100% success rate, thus enabling superior noble metal adsorption performance compared to other molybdenum disulfide raw materials and their precursors that may be byproducts or contain molybdenum trioxide.

[0074] In this embodiment, the conversion rate R of molybdenum trioxide particles to MoS2 in the noble metal adsorbent is... C The spectral data obtained from X-ray diffraction (XRD) measurements of molybdenum disulfide particles can be obtained by the RIR (reference intensity ratio) method described later.

[0075] It should be noted that the noble metal adsorbent in this embodiment is preferably composed of molybdenum disulfide particles (MoS2), but it is not limited to this and can be composed of MoS2 particles. x (X = 1 to 3) represents molybdenum sulfide particles, and can also be composed of one or more types of MoS2 particles. x (X=1~3) represents the composition of molybdenum sulfide particles.

[0076] The precious metal adsorbent of this embodiment can adsorb and remove or recover precious metal ions, precious metals, or precious metal compounds contained in solutions containing precious metals, such as aqueous solutions containing precious metals. Furthermore, the precious metal adsorbent of this embodiment can adsorb and remove or recover precious metals or precious metal compounds contained in gases containing precious metals.

[0077] When using the precious metal adsorbent of this embodiment, the precious metal can be recovered from a solution with an extremely low initial concentration. For example, the initial concentration of the precious metal in the solution to be treated can be set to 10 ppm or less, 1 ppm or less, or 100 ppb or less. In particular, when the metal is gold, the initial concentration can be set to 10 ppb or less or 5 ppb or less.

[0078] <Manufacturing Method of Noble Metal Adsorbent>

[0079] The method for manufacturing the noble metal adsorbent in this embodiment is not particularly limited; for example, it can be manufactured by heating a metal oxide in the presence of a sulfur source. Furthermore, the noble metal adsorbent in this embodiment is not limited to those obtained by the above-described manufacturing method; as long as it exhibits the adsorption performance of the present invention, it can also be a commercially available metal sulfide, such as commercially available molybdenum disulfide particles.

[0080] (Manufacturing method of molybdenum disulfide particles in precious metal adsorbents)

[0081] The molybdenum disulfide particles in the noble metal adsorbent of this embodiment can be manufactured, for example, by heating molybdenum trioxide particles at a temperature of 200–1000°C in the presence of a sulfur source.

[0082] The average particle size of the primary particles of molybdenum trioxide is preferably greater than 2 nm and less than 1000 nm. The average particle size of the primary particles of molybdenum trioxide refers to the average of the primary particle size of 50 randomly selected primary particles when the major axis (Ferret diameter of the longest observed part) and minor axis (the shorter Ferret diameter in the direction perpendicular to the Ferret diameter of the longest part) of the particles constituting the aggregate (i.e., primary particles) in the two-dimensional image are photographed using a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0083] In the method for manufacturing molybdenum disulfide particles according to this embodiment, the average particle size of the primary particles of the molybdenum trioxide particles is preferably 1 μm or less. From the viewpoint of reactivity with sulfur, 600 nm or less is more preferred, 400 nm or less is even more preferred, and 200 nm or less is particularly preferred. The average particle size of the primary particles of the molybdenum trioxide particles can be 2 nm or more, 5 nm or more, or 10 nm or more.

[0084] In the manufacture of the molybdenum disulfide particles in the noble metal adsorbent of this embodiment, the molybdenum trioxide particles used are preferably composed of an aggregate of primary particles containing a β-crystal structure of molybdenum trioxide. Compared to conventional molybdenum trioxide particles that are composed only of α-crystals as a crystalline structure, these molybdenum trioxide particles exhibit better reactivity with sulfur. Due to the β-crystal structure containing molybdenum trioxide, the conversion rate R to MoS2 can be increased in the reaction with a sulfur source. C .

[0085] The β crystal structure of molybdenum trioxide can be confirmed by the presence of a peak at the (011) plane (around 2θ: 23.01°, No. 86426 (Inorganic Crystal Structure Database (ICSD))) of the β crystal of MoO3, as indicated by powder X-ray diffraction (XRD) using Cu-K α rays as the X-ray source. The α crystal structure of molybdenum trioxide can be confirmed by the presence of a peak at the (021) plane (around 2θ: 27.32°, No. 166363 (Inorganic Crystal Structure Database (ICSD))) of the α crystal of MoO3.

[0086] In the powder X-ray diffraction (XRD) spectrum obtained by using Cu-Kα rays as the X-ray source for the above molybdenum trioxide particles, the ratio of the peak intensity of the (011) plane (around 2θ: 23.01°, No. 86426 (Inorganic Crystal Structure Database (ICSD)) of the β crystal belonging to MoO3 to the peak intensity of the (021) plane (around 2θ: 27.32°, No. 166363 (Inorganic Crystal Structure Database (ICSD)) of the α crystal belonging to MoO3 (β(011) / α(021)) is preferably 0.1 or more.

[0087] For the peak intensities of the (011) plane of the β crystal belonging to MoO3 and the peak intensities of the (021) plane of the α crystal belonging to MoO3, the maximum intensity of the peaks is read, and the above ratio (β(011) / α(021)) is calculated.

[0088] In the above molybdenum trioxide particles, the ratio (β(011) / α(021)) is preferably 0.1 to 10.0, more preferably 0.2 to 10.0, and particularly preferably 0.4 to 10.0.

[0089] The β-crystal structure of molybdenum trioxide can also be determined by observing its Raman spectra at wavenumbers of 773 and 848 cm⁻¹. -1 and 905cm -1 The presence of peaks confirms the structure. The α-crystal structure of molybdenum trioxide can also be confirmed by peaks at wavenumbers of 663 and 816 cm⁻¹. -1 and 991cm -1 The presence of a peak confirms this.

[0090] In the manufacturing method of this embodiment, the average particle size of the primary particles of the above-mentioned molybdenum trioxide particles can be 5 nm or more and 2000 nm or less.

[0091] Examples of sulfur sources include sulfur and hydrogen sulfide, which can be used alone or in combination.

[0092] The manufacturing method of this embodiment may include the following steps: heating molybdenum trioxide particles, which are composed of an aggregate of primary particles containing a β-crystal structure of molybdenum trioxide, at a temperature of 100 to 800°C in the absence of a sulfur source, and then heating them at a temperature of 200 to 1000°C in the presence of a sulfur source.

[0093] The heating time in the presence of a sulfur source is sufficient for the sulfidation reaction to proceed fully; it can be 1h to 20h, 2h to 15h, or 3h to 10h.

[0094] In the method for manufacturing molybdenum disulfide particles according to this embodiment, the input ratio of sulfur (S) from the sulfur source to the molybdenum trioxide (MoO3) particles is preferably such that the sulfidation reaction proceeds sufficiently. The sulfur source's sulfur content is preferably 450 mol% or more, more preferably 600 mol% or more, and more preferably 700 mol% or more, relative to 100 mol% of the molybdenum trioxide (MoO3) particles. The sulfur source's sulfur content can be 3000 mol% or less, 2000 mol% or less, or 1500 mol% or less, relative to 100 mol% of the molybdenum trioxide (MoO3) particles.

[0095] In the manufacturing method of this embodiment, the heating temperature in the presence of the sulfur source is only required to allow the sulfidation reaction to proceed sufficiently, preferably 320°C or higher, more preferably 340°C or higher, and particularly preferably 360°C or higher. The temperature can be 320–1000°C, 340–800°C, or 360–600°C.

[0096] Within the temperature range of 320–1000°C, the higher the heating temperature in the presence of the aforementioned sulfur source, the more readily molybdenum disulfide particles with excellent crystallinity can be synthesized. Conversely, within the temperature range of 320–1000°C, the lower the heating temperature in the presence of the aforementioned sulfur source, the more readily molybdenum disulfide particles with a high specific surface area can be synthesized.

[0097] In the method for manufacturing molybdenum disulfide particles according to this embodiment, the content ratio of MoO3 in the above-mentioned molybdenum trioxide particles, as measured by fluorescence X-ray (XRF), is preferably 99.5% or more, thereby increasing the conversion rate to MoS2. C This allows us to obtain high-purity molybdenum disulfide, without worrying about the formation of sulfides from impurities, and with good storage stability.

[0098] The preferred specific surface area of ​​the above-mentioned molybdenum trioxide particles, as determined by the BET method, is 10 m². 2 / g or more and 100m 2 / g or less.

[0099] From the viewpoint of good reactivity with sulfur, the specific surface area of ​​the above-mentioned molybdenum trioxide particles is preferably 10 m². 2 / g or more, preferably 20m 2 / g or more, preferably 30m 2 / g or more. From the viewpoint of easier manufacturing, the specific surface area of ​​the above molybdenum trioxide particles is preferably 100m². 2 Below / g, it can be 90m 2 Below / g, it can be 80m 2 / g or less.

[0100] In the radial distribution function obtained from the extended X-ray absorption fine structure (EXAFS) spectrum of the K-absorbing end of the above molybdenum trioxide particles, the ratio (I / II) of the intensity I of the peak originating from Mo-O to the intensity II of the peak originating from Mo-Mo is preferably greater than 1.1.

[0101] For the peak intensity I originating from Mo-O and the peak intensity II originating from Mo-Mo, the maximum intensity of each peak is read, and the ratio (I / II) is calculated. This ratio (I / II) is considered the benchmark for molybdenum trioxide particles obtaining the β-crystal structure of MoO3; the larger the ratio (I / II), the better the reactivity with sulfur.

[0102] In the above molybdenum trioxide particles, the ratio (I / II) is preferably 1.1 to 5.0, but can be 1.2 to 4.0 or 1.2 to 3.0.

[0103] (Manufacturing method of molybdenum trioxide particles)

[0104] The above-mentioned molybdenum trioxide particles can be manufactured as follows: the molybdenum trioxide precursor compound is vaporized to form molybdenum trioxide vapor, and the molybdenum trioxide vapor is cooled.

[0105] The method for manufacturing the above-mentioned molybdenum trioxide particles includes the following steps: calcining a raw material mixture containing a molybdenum trioxide precursor compound and a metal compound other than the above-mentioned molybdenum trioxide precursor compound, so that the above-mentioned molybdenum trioxide precursor compound is vaporized to form molybdenum trioxide vapor; the ratio of the above-mentioned metal compound to 100% by mass of the above-mentioned raw material mixture is preferably 70% by mass or less when converted to oxides.

[0106] The above-mentioned method for manufacturing molybdenum trioxide particles can be used Figure 1 The manufacturing apparatus 1 shown is suitably implemented.

[0107] Figure 1This is a schematic diagram of an example of an apparatus used to manufacture the aforementioned molybdenum trioxide particles. The manufacturing apparatus 1 includes: a roasting furnace 2 that roasts a molybdenum trioxide precursor compound or a mixture of the aforementioned raw materials to vaporize the molybdenum trioxide precursor compound; a cross-shaped cooling pipe 3 connected to the roasting furnace 2 to granulate the molybdenum trioxide vapor vapor granulated by the roasting process; and a recovery machine 4 serving as a recovery mechanism for recovering the molybdenum trioxide particles granulated in the cooling pipe 3. The roasting furnace 2 and the cooling pipe 3 are connected via an exhaust port 5. Furthermore, the cooling pipe 3 has an opening adjustment damper 6 at its left end at an external gas intake port (not shown) and an observation window 7 at its upper end. The recovery machine 4 is connected to an exhaust device 8 serving as a first air supply mechanism. This exhaust device 8 exhausts air, thereby drawing in the recovery machine 4 and the cooling pipe 3, with external gas being supplied to the cooling pipe 3 through the opening adjustment damper 6. That is, the exhaust device 8 performs a suction function, thereby passively supplying air to the cooling pipe 3. It should be noted that the manufacturing apparatus 1 may have an external cooling device 9, thereby allowing arbitrary control of the cooling conditions of the molybdenum trioxide vapor generated from the calcining furnace 2.

[0108] By adjusting the opening of damper 6, air is drawn from the external gas intake port, and the molybdenum trioxide vapor vapor, which has been vaporized in the calcining furnace 2, is cooled in an air atmosphere to form molybdenum trioxide particles. This allows the aforementioned ratio (I / II) to be set to be greater than 1.1, and the β-crystal structure of MoO3 can be easily obtained in the molybdenum trioxide particles. When using liquid nitrogen to cool the molybdenum trioxide vapor, the cooling of the molybdenum trioxide vapor under a nitrogen atmosphere with a low oxygen concentration tends to increase the oxygen defect density, thus reducing the aforementioned ratio (I / II).

[0109] There are no particular restrictions on whether a molybdenum trioxide precursor compound is used to form molybdenum trioxide particles consisting of aggregates of primary particles containing a β-crystal structure of molybdenum trioxide.

[0110] As for the aforementioned molybdenum trioxide precursor compounds, there are no particular limitations as long as they are formed by calcination to produce molybdenum trioxide vapor. Examples include metallic molybdenum, molybdenum trioxide, molybdenum dioxide, molybdenum disulfide, ammonium molybdate, and phosphomolybdic acid (H3PMo). 12 O 40 ), molybdenum silicate (H4SiMo) 12 O 40 Aluminum molybdate, silicon molybdate, magnesium molybdate (MgMo) n O 3n+1 (n=1~3)), sodium molybdate (Na2Mo) n O 3n+1 (n=1~3)), titanium molybdate, ferric molybdate, potassium molybdate (K2Mo n O 3n+1(n=1~3)), zinc molybdate, boron molybdate, lithium molybdate (Li2Mo) n O 3n+1 (n=1~3)), cobalt molybdate, nickel molybdate, manganese molybdate, chromium molybdate, cesium molybdate, barium molybdate, strontium molybdate, yttrium molybdate, zirconium molybdate, copper molybdate, etc. These molybdenum trioxide precursor compounds can be used alone or in combination of two or more. The form of the molybdenum trioxide precursor compounds is not particularly limited; for example, they can be in powder form or in liquid form such as an aqueous solution of ammonium molybdate. Powder form with good processability and energy efficiency is preferred.

[0111] As a precursor compound for molybdenum oxide, commercially available α-crystal molybdenum trioxide is preferred. Alternatively, when ammonium molybdate is used as a precursor compound for molybdenum oxide, it is converted into thermodynamically stable molybdenum trioxide through calcination, thus the vaporized molybdenum oxide precursor compound becomes the aforementioned molybdenum trioxide.

[0112] Molybdenum trioxide vapor can also be formed by roasting a mixture of raw materials containing molybdenum trioxide precursor compounds and metal compounds other than the aforementioned molybdenum trioxide precursor compounds.

[0113] From the viewpoint of easily controlling the purity of the obtained molybdenum trioxide particles, the average particle size of the primary particles, and the crystal structure, the molybdenum oxide precursor compound preferably contains molybdenum trioxide.

[0114] Molybdenum trioxide precursor compounds sometimes form intermediates with metal compounds other than those mentioned above. However, even in this case, the intermediates can be decomposed by calcination, allowing molybdenum trioxide to vaporize in a thermodynamically stable form.

[0115] When calcining a raw material mixture containing a molybdenum trioxide precursor compound and a metal compound other than the aforementioned molybdenum trioxide precursor compound, the content ratio of the aforementioned molybdenum trioxide precursor compound relative to 100% by mass of the raw material mixture is preferably 40 to 100% by mass, or can be 45 to 100% by mass, or can be 50 to 100% by mass.

[0116] The calcination temperature varies depending on the molybdenum trioxide precursor compound, metal compound, and desired molybdenum trioxide particles used, and is generally preferably set to a temperature at which the intermediate can decompose. For example, when a molybdenum compound is used as the molybdenum trioxide precursor compound and an aluminum compound is used as the metal compound, aluminum molybdate may be formed as an intermediate. Therefore, the calcination temperature is preferably 500–1500°C, more preferably 600–1550°C, and even more preferably 700–1600°C.

[0117] There are no particular restrictions on the roasting time; for example, it can be set from 1 minute to 30 hours, from 10 minutes to 25 hours, or from 100 minutes to 20 hours.

[0118] The heating rate also varies depending on the characteristics of the molybdenum trioxide precursor compound used, the aforementioned metal compound, and the desired molybdenum trioxide particles. From the viewpoint of manufacturing efficiency, a rate of 0.1°C / min or higher and 100°C / min or lower is preferred, 1°C / min or higher and 50°C / min or lower is more preferred, and 2°C / min or higher and 10°C / min or lower is even more preferred.

[0119] Then, the above molybdenum trioxide vapor is cooled and granulated.

[0120] Cooling of molybdenum trioxide vapor is achieved by keeping the cooling pipes at a low temperature. Examples of cooling mechanisms include cooling based on airflow into the cooling pipes as described above, cooling using a cooling mechanism inherent in the cooling pipes, and cooling using an external cooling device.

[0121] The cooling of molybdenum trioxide vapor is preferably carried out in an air atmosphere. By cooling the molybdenum trioxide vapor in an air atmosphere to form molybdenum trioxide particles, the above ratio (I / II) can be set to be greater than 1.1, and the β crystal structure of MoO3 can be easily obtained in the molybdenum trioxide particles.

[0122] There are no particular limitations on the cooling temperature (temperature of the cooling piping), but it is preferred to be -100 to 600°C, and more preferably -50 to 400°C.

[0123] There are no particular limitations on the cooling rate of molybdenum trioxide vapor, but it is preferably 100°C / s or higher and 100,000°C / s or lower, more preferably 1,000°C / s or higher and 50,000°C / s or lower. It should be noted that the faster the cooling rate of molybdenum trioxide vapor, the more likely it is to obtain molybdenum trioxide particles with small particle size and large specific surface area.

[0124] When the cooling mechanism is based on cooling by supplying air gas into the cooling piping, the temperature of the supplied air gas is preferably -100 to 300°C, more preferably -50 to 100°C.

[0125] The particles obtained by cooling molybdenum trioxide vapor are conveyed to a recycling machine for recovery.

[0126] The above-mentioned method for manufacturing molybdenum trioxide particles can further calcine the particles obtained by cooling the above-mentioned molybdenum trioxide vapor at a temperature of 100 to 320°C.

[0127] That is, the molybdenum trioxide particles obtained by the above-described method for manufacturing molybdenum trioxide particles can be calcined again at a temperature of 100–320°C. The calcination temperature for the second calcination can be 120–280°C or 140–240°C. The calcination time for the second calcination can be, for example, 1 minute to 4 hours, 10 minutes to 5 hours, or 100 minutes to 6 hours. During this second calcination, a portion of the β-crystal structure of molybdenum trioxide disappears. If calcined at a temperature above 350°C for 4 hours, the β-crystal structure in the molybdenum trioxide particles disappears, and the ratio (β(011) / α(021)) becomes 0, thus impairing its reactivity with sulfur.

[0128] The molybdenum disulfide particles in the precious metal adsorbent of this embodiment can be manufactured by the above-described method for manufacturing precious metal adsorbents.

[0129] Furthermore, the above-described method for manufacturing molybdenum trioxide particles can produce molybdenum trioxide particles suitable for manufacturing molybdenum disulfide particles in the noble metal adsorbent of this embodiment.

[0130] <Methods for recycling precious metals>

[0131] In this embodiment of the precious metal recovery method, after the precious metal is adsorbed onto the aforementioned precious metal adsorbent, the precious metal adsorbent is dissolved with an oxidizing solution, thereby recovering the precious metal. Alternatively, in this embodiment of the precious metal recovery method, after the precious metal is adsorbed onto the aforementioned precious metal adsorbent, the precious metal adsorbent is heated in the presence of oxygen to volatilize, thereby recovering the precious metal.

[0132] When precious metals are adsorbed onto a precious metal adsorbent, the adsorbent is removed using acid or heat, thus enabling the easy recovery of precious metals with a simple process. Furthermore, when molybdenum disulfide particles are used as a precious metal adsorbent, the precious metals, especially gold, are reduced to zero valence. Therefore, reduction treatment of the precious metal elements is no longer required; high-purity gold can be easily recovered simply by removing the molybdenum disulfide particles, and the environmental burden associated with reduction treatment can be eliminated.

[0133] When dissolving the above-mentioned precious metal adsorbent with an oxidizing solution, nitric acid, hydrogen peroxide, etc., can be used as the oxidizing solution.

[0134] When heating the molybdenum disulfide particles, which serve as a noble metal adsorbent, in the presence of oxygen, the heating temperature is preferably 400–1500°C, more preferably 650–1200°C, and even more preferably 750–950°C. When the molybdenum disulfide particles are heated in the presence of oxygen, the molybdenum disulfide is oxidized to molybdenum trioxide. Due to the high volatility of molybdenum trioxide, it vaporizes at a relatively low heating temperature. Therefore, the noble metal and the molybdenum disulfide particles can be easily separated, and the noble metal can be easily recovered. From an energy efficiency point of view, a temperature that is as low as possible while still allowing sufficient volatilization of molybdenum trioxide is preferred. 400°C is the temperature at which molybdenum disulfide is oxidized, and molybdenum trioxide volatilizes readily at temperatures above 750°C.

[0135] <Regeneration Methods for Noble Metal Adsorbents>

[0136] In the regeneration method of the precious metal adsorbent in this embodiment, after recovering the metal oxides that have volatilized through the above-described precious metal recovery method, the metal oxides are sulfided, thereby regenerating the precious metal adsorbent composed of metal sulfides.

[0137] In this regeneration method, the metal oxide vapor obtained by the above-mentioned precious metal recovery method can be directly sulfided, or it can be temporarily cooled to form metal oxide particles. Then, the metal oxide particles are heated in the presence of a sulfur source to sulfidize them.

[0138] When molybdenum disulfide particles are used as a precious metal adsorbent, molybdenum trioxide that has volatilized through the aforementioned precious metal recovery method can be recovered. The recovered molybdenum trioxide particles are then sulfided using, for example, a method similar to the manufacturing method of the molybdenum disulfide particles described above. This allows for easy regeneration of the molybdenum disulfide particles as a precious metal adsorbent. Furthermore, by reusing the obtained molybdenum disulfide particles as a precious metal adsorbent, the consumption of molybdenum resources can be suppressed.

[0139] Example

[0140] The following embodiments illustrate the invention in a more detailed manner, but the invention is not limited to these embodiments.

[0141] [Method for determining the average particle size of primary particles of molybdenum trioxide]

[0142] The primary particles constituting the molybdenum trioxide particles were imaged using a scanning electron microscope (SEM). For the smallest unit of the aggregate (i.e., the primary particle) in the two-dimensional image, its major axis (the Ferete diameter of the longest observed portion) and minor axis (the shorter Ferete diameter in the direction perpendicular to the Ferete diameter of the longest portion) were measured, and their average value was taken as the primary particle size. The same operation was performed on 50 randomly selected primary particles, and the average particle size of the primary particles was calculated from the average of the primary particle sizes of these 50 particles.

[0143] [Purity determination of molybdenum trioxide: XRF analysis]

[0144] Using a fluorescence X-ray analysis apparatus (manufactured by Rigaku Co., Ltd., Primus IV), approximately 70 mg of the recovered molybdenum trioxide particle sample was placed onto filter paper, covered with a PP film, and subjected to compositional analysis. The molybdenum content obtained from the XRF analysis was calculated by converting the molybdenum content (mass%) relative to 100% by mass of the molybdenum trioxide particles.

[0145] [Crystal Structure Analysis: XRD Method]

[0146] The recovered molybdenum trioxide particles or their sulfides were filled into a sample holder with a depth of 0.5 mm and placed in a wide-angle X-ray diffraction (XRD) apparatus (made by Rigaku Co., Ltd., Ultima IV). The determination was carried out under the conditions of Cu / Kα rays, 40 kV / 40 mA, scanning speed of 2° / min, and scanning range of 10 degrees or more and 70 degrees or less.

[0147] [Specific Surface Area Determination: BET Method]

[0148] For samples containing molybdenum trioxide or molybdenum disulfide particles, the surface area was measured using a specific surface area meter (MicrotracBEL, BELSORP-mini). The surface area per 1g of the measured sample was calculated from the nitrogen adsorption amount based on the BET method, and this was taken as the specific surface area (m²). 2 / g).

[0149] [Conversion rate to MoS2 R] C ]

[0150] The RIR value K of molybdenum disulfide (MoS2) was determined using the RIR (reference intensity ratio) method. A The integrated intensity I of the peak near 2θ = 14.4° ± 0.5° at the (002) or (003) planes attributed to molybdenum disulfide (MoS2). A And various molybdenum oxides (MoO3 as a raw material and Mo9O as a reaction intermediate) 25 Mo4O 11RIR values ​​K of (e.g., MoO2, etc.) B And molybdenum oxides (MoO3 as a raw material and Mo9O as a reaction intermediate) 25 Mo4O 11 The integral intensity I of the strongest peak of (MoO2, etc.) B The conversion rate R to MoS2 can be obtained from the following equation (1). C .

[0151] R C (%) = (I) A / K A ) / (Σ(I B / K B ))×100···(1)

[0152] Here, the RIR values ​​were used from the Inorganic Crystal Structure Database (ICSD), and the analysis was performed using Powder X-ray Integrated Analysis Software (PDXL) (manufactured by Rigaku Co., Ltd.).

[0153] [Extended X-ray Absorption Spectroscopy (EXAFS) Measurement]

[0154] 36.45 mg of molybdenum disulfide powder and 333.0 mg of boron nitride (manufactured by KISHIDA CHEMICAL CO.,LTD) were mixed in a mortar. 123.15 mg of this mixture was weighed and compressed into [a specific shape / form]. The tablets were used to obtain the assay sample. Using the assay sample, extended X-ray absorption fine structure (EXAFS) was determined by transmission method using the BL5S1 of the Aichi Synchrotron Radiation Center. Athena (Internet <URL: https: / / bruceravel.github.io / demeter / >) was used in the analysis.

[0155] Median particle size D of molybdenum disulfide particles 50 [Determination]

[0156] 0.1 g of molybdenum disulfide powder was added to 20 cc of acetone, and the mixture was ultrasonically treated in an ice bath for 4 hours. The concentration was then adjusted with acetone to a suitable range that could be measured by a dynamic light scattering particle size distribution measuring device (MicrotracBEL, NanotracWaveII) to obtain the test sample. Using this sample, the particle size distribution in the range of 0.0001–10 μm was measured using the aforementioned dynamic light scattering particle size distribution measuring device, and the median particle size D was calculated. 50 .

[0157] Among them, for the median particle size D 50For particles larger than 10 μm, solutions were prepared similarly, and the particle size distribution in the range of 0.015–500 μm was measured using a laser diffraction particle size distribution measuring device (Shimadzu SALD-7000). The median particle size D was then calculated. 50 .

[0158] [Methods for observing the particle shape of molybdenum disulfide particles]

[0159] The shape of molybdenum disulfide particles was observed using atomic force microscopy (AFM).

[0160] (Commercially available molybdenum disulfide granules)

[0161] The X-ray diffraction (XRD) patterns of commercially available molybdenum disulfide reagent (manufactured by Kanto Chemical Co., Ltd.) are shown together with the diffraction patterns of molybdenum disulfide with a 2H crystal structure. Figure 2 It can be seen that the commercially available molybdenum disulfide reagent is molybdenum disulfide with a 2H crystal structure of over 99%. The half-widths (WHMs) of the peaks near 39.5° and 49.5° are 0.23° and 0.22°, respectively.

[0162] For commercially available molybdenum disulfide particles, the ratio (I / II) of the peak intensity I derived from Mo-S to the peak intensity II derived from Mo-Mo obtained from the determination of specific surface area (SA) and extended X-ray absorption fine structure (EXAFS) of the K-absorbing end of molybdenum is 1.2.

[0163] The specific surface area of ​​commercially available molybdenum disulfide particles was determined by the BET method, and the result was 5.6 m². 2 / g.

[0164] In addition, the particle size distribution of commercially available molybdenum disulfide particles was measured using a dynamic light scattering particle size distribution measuring device, and the median particle size D was determined. 50 The result was 13340nm.

[0165] (Synthesis example 1)

[0166] (Manufacturing of molybdenum trioxide particles)

[0167] 1 kg of transition alumina (manufactured by Wako Pure Chemical Industries, Ltd., activated alumina, average particle size 45 μm) and 1 kg of molybdenum trioxide (manufactured by Taiyo Mining Co., Ltd.) were mixed and then added to a crucible. Figure 1In the calcination furnace 2 of the manufacturing apparatus 1 shown, calcination is carried out at a temperature of 1100°C for 10 hours. During calcination, external gas (air flow rate: 50 L / min, external gas temperature: 25°C) is introduced from the side and bottom of the calcination furnace 2. After the molybdenum trioxide evaporates in the calcination furnace 2, it is cooled near the recovery machine 4 and precipitates in particulate form. The calcination furnace 2 uses an RHK simulation device (manufactured by NORITAKE CO., LIMITED), and the recovery machine 4 uses a VF-5N dust collector (manufactured by AMANO).

[0168] After calcination, 1.0 kg of blue alumina granules and 0.85 kg of molybdenum trioxide granules recovered using recycling machine 4 were removed from the sagger. The average primary particle size of the recovered molybdenum trioxide granules was 80 nm, and the purity of molybdenum trioxide was confirmed to be 99.7% by X-ray fluorescence (XRF) determination. The specific surface area (SA) of the molybdenum trioxide granules, determined by the BET method, was 44.0 m². 2 / g.

[0169] (Manufacturing of molybdenum disulfide particles)

[0170] In a magnetic crucible, 1.00 g of molybdenum trioxide particles and 1.57 g of sulfur powder (manufactured by Kanto Chemical Co., Ltd.) were mixed with a stirring rod to make the powder homogeneous. The mixture was then calcined at 500°C for 4 hours under a nitrogen atmosphere to obtain a black powder. Here, the amount of MoO3 relative to the above molybdenum trioxide particles was 100 mol%, and the amount of S relative to the above sulfur was 705 mol%. The X-ray diffraction (XRD) pattern of this black powder (molybdenum disulfide particles of Synthesis Example 1) is shown together with the diffraction patterns of the 3R crystal structure, the 2H crystal structure, and the molybdenum dioxide (MoO2) crystal structure of molybdenum disulfide (MoS2) recorded in the Inorganic Crystal Structure Database (ICSD). Figure 3 Molybdenum dioxide (MoO2) is the reaction intermediate.

[0171] Figure 3 In the X-ray diffraction (XRD) pattern, only peaks belonging to molybdenum disulfide (MoS2) were detected, and no peaks not belonging to molybdenum disulfide (MoS2) were found. That is, no peaks of reaction intermediates such as molybdenum dioxide (MoO2) as byproducts were observed, and only peaks belonging to molybdenum disulfide (MoS2) were observed. Therefore, the conversion rate of molybdenum disulfide particles to MoS2 in Synthesis Example 1 was over 99%, confirming that the reaction with sulfur proceeded rapidly.

[0172] X-ray diffraction (XRD) analysis of the molybdenum disulfide particles of Synthetic Example 1 confirmed the presence of both 2H and 3R crystal structures. The half-widths (WHMs) of the peaks near 39.5° and 49.5° were 2.36° and 3.71°, respectively, which are wider than those of commercially available molybdenum trioxide particles.

[0173] The specific surface area of ​​the molybdenum disulfide particles from Synthetic Example 1 was determined by the BET method, and the result was 67.8 m². 2 / g.

[0174] The particle size distribution of molybdenum disulfide particles from Synthetic Example 1 was determined using a dynamic light scattering particle size distribution measuring device, and the median particle size D was calculated. 50 The result was 170nm.

[0175] AFM images of the synthesized molybdenum disulfide particles are shown below. Figure 4 . Figure 4 The AFM image obtained for the measurement shows the upper surface of the molybdenum disulfide particles. The length (longitudinal) × width (horizontal) was calculated from this AFM image, resulting in 180 nm × 80 nm. Figure 5 To show Figure 4 The diagram shows a cross-sectional view of a molybdenum disulfide particle. The thickness (height) is calculated from this cross-sectional view and is 16 nm. Therefore, the aspect ratio (length (height)) of the primary molybdenum disulfide particle is 11.25.

[0176] 50 containing Figure 4 The average value of the molybdenum disulfide particles shown is length (vertical) × width (horizontal) × thickness (height) = 198nm × 158nm × 19nm.

[0177] Representative examples of AFM determination results for molybdenum disulfide particles are shown in Table 1. In the table, "molybdenum disulfide particles (1)" refers to... Figure 3 The molybdenum disulfide particles recorded in the study. "Molybdenum disulfide particle (2)" is the longest particle among the measured molybdenum disulfide particles, and "Molybdenum disulfide particle (3)" is the shortest particle. "Molybdenum disulfide particle (4)" is a relatively thick particle, and "Molybdenum disulfide particle (5)" is the thinnest particle. "Molybdenum disulfide particle (6)" is the particle with the largest length-to-thickness ratio. "Molybdenum disulfide particle (7)" is the thickest particle and also the particle with the smallest length-to-thickness ratio.

[0178] [Table 1]

[0179]

[0180] The extended X-ray absorption fine structure (EXAFS) of the molybdenum disulfide particles of Synthetic Example 1 was determined. The extended X-ray absorption fine structure (EXAFS) spectrum of the K-end of molybdenum is illustrated in [image / image / image]. Figure 4 In the radial distribution function obtained from this spectrum, the ratio (I / II) of the peak intensity I originating from Mo-S to the peak intensity II originating from Mo-Mo is 1.2.

[0181] (Synthesis example 2)

[0182] The calcination temperature was changed to 400°C, and molybdenum disulfide particles were produced using the same method and conditions as in Synthesis Example 1.

[0183] The specific surface area of ​​the molybdenum disulfide particles in Synthetic Example 2 was determined by the BET method, and the result was 80.4 m². 2 / g.

[0184] The particle size distribution of molybdenum disulfide particles in Synthetic Example 2 was determined using a dynamic light scattering particle size distribution measuring device, and the median particle size D was calculated. 50 The result was 270nm.

[0185] [Evaluation of Precious Metal (Gold) Adsorption]

[0186] <Example 1>

[0187] A diluted solution was prepared by diluting a 1000 ppm gold standard solution (manufactured by NACALAI TESQUE, INC.) with deionized water to achieve an initial gold concentration of 561 ppm.

[0188] Add 30g of the obtained diluted solution to a 50mL plastic test tube, add 30mg of commercially available molybdenum disulfide powder (manufactured by Kanto Chemical Co., Ltd., molybdenum disulfide reagent) as an adsorbent, and stir at 15rpm for 24 hours using an inverted rotary stirrer (manufactured by TOWA LABOCorp, ROTA·MIX).

[0189] After stirring for 3 hours, 6 hours, and 24 hours, the sample solution was filtered through a 0.2 μm syringe filter, and the residual gold concentration in the sample solution was quantified using an ICP-OES analyzer (PerkinElmer, Optima 8300). Furthermore, the residual gold concentration in the sample solution after 24 hours and the amount of molybdenum disulfide powder added were used to calculate the gold adsorption capacity (g / g) per 1 g of adsorbent over 24 hours using the following formula.

[0190] Gold adsorption capacity in 24 hours = (initial gold concentration - gold concentration after 24 hours) × liquid volume / molybdenum disulfide powder addition amount

[0191] <Example 2>

[0192] Instead of commercially available molybdenum disulfide powder, the molybdenum disulfide powder obtained in Synthesis Example 1 was used, and the same procedure as in Example 1 was followed to calculate the gold residual concentration in the sample solution after 24 hours and the gold adsorption capacity (g / g) per 1g of adsorbent after 24 hours.

[0193] <Example 3>

[0194] 10 mg of molybdenum disulfide powder from Synthesis Example 1 was added to 50 g of a diluted solution with an initial gold concentration of 470 ppm. Otherwise, the same procedure as in Example 1 was performed. The gold residual concentration in the sample solution after 24 hours and the gold adsorption amount per 1 g of adsorbent after 24 hours were calculated.

[0195] <Example 4>

[0196] The amount of molybdenum disulfide powder added in Synthesis Example 1 was changed to 5 mg, and the same procedure as in Example 3 was followed. The gold residual concentration in the sample solution after 24 hours and the gold adsorption amount per 1 g of adsorbent after 24 hours were calculated.

[0197] <Comparative Example 1>

[0198] Instead of commercially available molybdenum disulfide powder, carbon (manufactured by Kuraray Co., Ltd., kuraraycoal (registered trademark)) was used, and the process was otherwise the same as in Example 1, and the gold adsorption capacity per 1g of adsorbent over 24 hours was calculated.

[0199] [Table 2]

[0200]

[0201] According to the results in Table 2, when 30 mg of commercially available molybdenum disulfide powder was used as an adsorbent in Example 1, the gold concentration in the solution was 555 ppm after 24 hours, and the gold adsorption capacity was 0.006 (g / g).

[0202] In Example 2, when 30 mg of the molybdenum disulfide powder from Synthetic Example 1 was used, the gold concentration in the solution was less than 0.1 ppm after 24 hours, and the gold adsorption capacity was 0.56 (g / g). It can be seen that the gold adsorption performance is exceptionally high compared with the commercially available molybdenum disulfide particles from Example 1.

[0203] In Example 2, XRD analysis was performed on the molybdenum disulfide powder after gold adsorption, and the results are as follows: Figure 5 As shown, the diffraction pattern of the molybdenum disulfide powder before gold adsorption (Synthesis Example 1) and the spectral peaks of gold (0 valence) confirm that the molybdenum disulfide powder after gold adsorption is a mixture of nano-sized molybdenum disulfide particles (MoS2) and 0-valence gold.

[0204] In addition, the XPS of the molybdenum disulfide powder after gold adsorption in Example 2 was measured at three points, and the results are as follows: Figure 6 As shown, Au4f 7 / 2 The average value of the peak at that point is 84.4 eV, thus confirming that the valence of gold adsorbed on the molybdenum disulfide powder is 0.

[0205] In Example 3, 10 mg of molybdenum disulfide powder from Synthesis Example 1 was used. When the amount of molybdenum disulfide powder added was reduced, the gold concentration in the solution was less than 0.1 ppm after 24 hours, and the gold adsorption capacity was 2.35 (g / g). Compared with Example 2, a small amount of molybdenum disulfide can adsorb gold until the detection limit is reached, indicating that the adsorption performance of gold is exceptionally high.

[0206] In Example 4, 5 mg of molybdenum disulfide powder from Synthesis Example 1 was used. When the amount of molybdenum disulfide powder added was further reduced, the gold concentration in the solution after 24 hours was 67 ppm, and the gold adsorption capacity was 4.03 g / g. Compared with Example 2, although gold could not be adsorbed to the detection limit after 24 hours of adsorption, the gold adsorption capacity in the solution after 24 hours was about 4 g when using a solution with an initial concentration of 470 ppm. This indicates that the gold adsorption performance is exceptionally high compared to the adsorbent described in the aforementioned patent literature.

[0207] Here, the difference in gold adsorption amount after 24 hours between Example 1 and Example 4 is examined. The commercially available molybdenum disulfide powder used in Example 1 is molybdenum disulfide with a 2H crystal structure of 99% or higher. Furthermore, the median particle size D, measured using a dynamic light scattering particle size distribution measuring device, is... 50 The particle size was 13340 nm. On the other hand, the molybdenum disulfide powder used in Example 4 from Synthesis Example 1 was molybdenum disulfide containing both 2H and 3R crystal structures. Furthermore, the median particle size D, measured using a dynamic light scattering particle size distribution measuring device... 50 The wavelength is 170 nm. In Example 1, the gold adsorption capacity after 24 hours was 0.006 g / g, while in Example 4, the gold adsorption capacity after 24 hours was extremely high at 4.03 g / g. This is presumably because the molybdenum disulfide powder in Synthesis Example 1 contains 2H and 3R crystal structures and has a median particle size D. 50 Even at 170 nm, this is helpful. Therefore, it is believed that even with a crystal structure of over 99% and a median grain size D, for example, 2H crystals are suitable. 50 Even molybdenum disulfide powder with a particle size of around 170 nm showed a high gold adsorption capacity. Furthermore, it is believed that even powders containing both 2H and 3R crystal structures with a median particle size D... 50 The molybdenum disulfide powder, with a wavelength of around 13340 nm, also showed a high gold adsorption capacity.

[0208] On the other hand, in Comparative Example 1, the gold concentration in the solution after 24 hours when carbon was used as the adsorbent was 555 ppm and the gold adsorption capacity was 0.006 (g / g), which was the same as that in Example 1 when commercially available molybdenum disulfide powder was used as the adsorbent.

[0209] [Evaluation of Adsorption of Low Concentration Precious Metal (Gold)]

[0210] <Example 5>

[0211] A gold solution of approximately 5 ppb was prepared using a 1000 ppm gold standard solution (manufactured by NACALAI TESQUE, INC.). 40 g of this solution was mixed with 400 mg of molybdenum disulfide powder obtained in Synthesis Example 1 as an adsorbent and stirred for 5 days. As a control, a solution without adsorbent was stirred to obtain the initial concentration. Concentration determination was performed using a mass spectrometer (Agilent Technologies, ICP-MS Agilent 8900). The results are shown in Table 3.

[0212] [Table 3]

[0213]

[0214] According to the results in Table 3, when using a gold solution with an initial concentration of 4.28 ppb in Example 5, the gold concentration was less than 0.01 ppb after 5 days. This indicates that when using the molybdenum disulfide powder obtained in Synthesis Example 1, gold can be recovered from gold solutions with extremely low concentrations, such as those discharged from urban mines, those from plating wastewater, or those collected from nature, such as seawater or volcanic hot water.

[0215] [Recovery of adsorbed gold]

[0216] <Example 6>

[0217] 100 mL of a 1000 ppm gold standard solution (manufactured by NACALAI TESQUE, INC.) (equivalent to 100 mg of gold) was diluted with 100 mL of deion-exchanged water. 50 mg of molybdenum disulfide powder obtained in Synthesis Example 1 was added to this diluted solution as an adsorbent, and the mixture was stirred for 24 hours to adsorb gold. After adsorption was complete, the molybdenum disulfide particles were filtered out.

[0218] The filtered molybdenum disulfide particles were washed twice with 20 mL of 1.40 nitric acid (manufactured by Kanto Chemical Co., Ltd.) until only the molybdenum disulfide was dissolved. The precipitate was then washed with deionized water to obtain 75.8 mg of a yellow powder. XRD analysis of the obtained yellow powder yielded the following results: Figure 7 As shown, the peak coincides with that of gold, thus confirming that the recovered yellow powder is gold (0 valence). The gold recovery rate is 76%.

[0219] Furthermore, compositional analysis of the recovered yellow powder was performed using a fluorescence X-ray analysis device (manufactured by Rigaku Co., Ltd., Primus IV), revealing a gold content of 99.7% by mass. Gold with a content exceeding 99.0% by mass can be easily refined into pure gold.

[0220] <Example 7>

[0221] Instead of nitric acid washing in Example 6, the filtered molybdenum disulfide particles were placed in a crucible and heated at 900°C for 4 hours in air to obtain 88.8 mg of yellow powder. XRD analysis of the obtained yellow powder yielded the following results: Figure 7 As shown, the peak coincides with that of gold, thus confirming that the recovered yellow powder is gold (0 valence). The gold recovery rate is 89%, which is higher than that of Example 6. The reason why the gold recovery rate in Example 6 is only about 80% is due to factors such as the small experimental scale, loss of fine molybdenum disulfide particles adhering to the container during the washing process, adhesion to the filter paper during the filtration and recovery of molybdenum disulfide, and insufficient precipitation of fine particles. On the other hand, the recovery method in Example 7 is considered superior to the recovery method in Example 6 because it does not adhere to the container or filter paper and there is no unprecipitated gold that could not be recovered.

[0222] The yellow powder recovered in Example 7 was subjected to compositional analysis using a fluorescence X-ray analysis device (manufactured by Rigaku Co., Ltd., Primus IV), and the results showed that the gold content was 99.2% by mass.

[0223] [Evaluation of gold adsorption of molybdenum disulfide particles with large specific surface area]

[0224] <Example 8>

[0225] The amount of molybdenum disulfide powder added in Synthesis Example 2 was changed to 4.5 mg, and the same procedure as in Example 4 was followed. The gold residual concentration in the sample solution after 24 hours and the gold adsorption amount per 1 g of adsorbent after 24 hours were calculated. The results are shown in Table 4.

[0226] [Table 4]

[0227]

[0228] According to the results in Table 4, in Example 8, when 4.5 mg of molybdenum disulfide powder from Synthesis Example 2 was used, the gold concentration in the solution was less than 0.1 ppm and the gold adsorption capacity was 5.17 g / g after 24 hours, confirming that the gold adsorption performance was higher than that of the molybdenum disulfide powder from Synthesis Example 1 used in Example 4.

[0229] [Evaluation of gold adsorption based on liquid permeation test]

[0230] <Example 9>

[0231] A diluted solution was prepared by diluting a 1000 ppm gold standard solution (manufactured by NACALAI TESQUE, INC.) with deionized water to achieve an initial gold concentration of 100 ppm.

[0232] The resulting diluted solution was fed at a rate of 3.6 mL / min into an internal volume of 3.6 cm³ filled with molybdenum disulfide powder from Synthesis Example 1. 3 The molybdenum disulfide powder was packed at a depth of 3.6 cm³ in the column. 3 .

[0233] The diluted solution passing through the column was sampled, and the residual gold concentration in the sampled solution was quantified using an ICP-OES analyzer (PerkinElmer Optima 8300). The detection limit for gold concentration using the ICP-OES was 0.1 ppm at this time.

[0234] The gold adsorption evaluation results based on this liquid flow test are shown in... Figure 10 The horizontal axis of this graph represents the volume of the treatment solution in the column, defined as total flow rate (l) / molybdenum disulfide filling rate (lr). This horizontal axis is referred to as the treatment solution volume (unitless). The vertical axis represents the residual gold concentration in the sample solution, referred to as the gold ion leakage concentration.

[0235] When the treatment volume reached 1070, the gold ion leakage concentration was lower than the detection limit of ICP-OES, thus confirming that the residual gold concentration in the sampled solution was less than 0.1 ppm.

[0236] When the treatment volume was 1430 and above, the residual gold concentration in the sample solution gradually increased, but when the treatment volume was 3410, the residual gold concentration was only 7.3 ppm, confirming that 92.7 ppm had been adsorbed by the molybdenum disulfide powder.

[0237] When recovering gold from urban mines, plating wastewater, or gold-containing wastewater discharged from gold ore refining processes, as shown in this embodiment, a gold-containing solution can be continuously passed into a column filled with a precious metal (gold) adsorbent for adsorption and recovery. Therefore, it can be said that the precious metal (gold) adsorbent of the present invention is suitable for recovering gold from urban mines, plating wastewater, or gold-containing wastewater discharged from gold ore refining processes.

[0238] [Evaluation of Gold Adsorption in Seawater]

[0239] <Example 10>

[0240] A 1000 ppm gold standard solution (manufactured by NACALAI TESQUE, INC.) was diluted with simulated seawater to obtain an initial gold concentration of 100 ppt, thereby preparing a diluted solution.

[0241] Simulated seawater refers to a liquid prepared by dissolving 24.53g NaCl, 5.20g MgCl2, 4.09g Na2SO4, 1.16g CaCl2, 0.695g KCl, 0.201g NaHCO3, 0.101g KBr, 0.027g H3BO3, 0.025g SrCl2, and 0.003g NaF in 1 liter of ion-exchange water. After dissolution, NaOH aqueous solution is added to adjust the pH to 8.1, thus achieving the same composition and pH as seawater.

[0242] Add 200g of the obtained diluted solution to a plastic test tube, add 200mg of molybdenum disulfide powder from Synthesis Example 1 as an adsorbent, and stir at a speed of 15rpm for 168 hours using an inverted rotary stirrer (TOWA LABO Corp., ROTA·MIX RKVSD).

[0243] After 168 hours of stirring, the sample was filtered using a 0.2 μm syringe filter, and the residual gold concentration in the sample solution was quantified using a triple quadrupole inductively coupled plasma mass spectrometry (ICP-MS / MS) system (Agilent Technologies 8900). The detection limit for gold concentration using ICP-MS / MS at this time was 30 ppt. The results are shown in Table 5.

[0244] [Table 5]

[0245]

[0246] Based on the results in Table 5, in Example 10, the residual gold concentration in the solution after 168 hours was below the detection limit of ICP-MS / MS, thus confirming it was below 30 ppt. Therefore, at least 70 ppt of gold was adsorbed and recovered.

[0247] The concentration of gold in seawater is in the ppt (parts per trillion) range. Based on the results of Example 10, it can be said that the precious metal (gold) adsorbent of the present invention is suitable for the adsorption and recovery of ppt-level gold from seawater. Furthermore, it is considered suitable not only for seawater but also for recovery from solutions containing low concentrations of gold discharged from nature, such as volcanic hot water.

[0248] Industrial availability

[0249] The precious metal adsorbent of this invention exhibits high precious metal adsorption performance, making it suitable as a precious metal recovery material for recovery from urban mines, from plating wastewater, from gold-containing wastewater discharged from gold ore refining processes, or from gold-containing solutions discharged from nature such as seawater and volcanic hot water. In particular, due to its exceptionally superior gold adsorption performance, it is especially suitable as a recovery material for recovering gold from solutions containing gold at high to very low concentrations.

[0250] Furthermore, the precious metal recovery method and the precious metal adsorbent regeneration method of the present invention can easily recover precious metals and regenerate precious metal adsorbents, thereby reducing environmental burden and suppressing metal resource consumption. Therefore, they are extremely useful as methods for recovering precious metals from the sea, rivers, or waste.

[0251] Explanation of reference numerals in the attached figures

[0252] 1 Manufacturing apparatus

[0253] 2. Firing oven

[0254] 3 Cooling piping

[0255] 4. Recycling machine

[0256] 5. Exhaust port

[0257] 6. Adjustable damper opening

[0258] 7 Observation Window

[0259] 8. Exhaust system

[0260] 9. External cooling device

Claims

1. A method for recycling precious metals, wherein, After the precious metal is adsorbed onto a precious metal adsorbent containing metal sulfides, the adsorbent is dissolved with an oxidizing solution, thereby recovering the precious metal. The metal sulfide is composed of molybdenum disulfide particles, which have 2H and 3R crystal structures of molybdenum disulfide. The median particle size D of the molybdenum disulfide particles was determined by dynamic light scattering method. 50 For wavelengths above 10nm and below 1000nm, The precious metal adsorbed by the precious metal adsorbent containing metal sulfides is gold.

2. A method for recycling precious metals, wherein, After the precious metal is adsorbed onto a precious metal adsorbent containing metal sulfides, the adsorbent is heated in the presence of oxygen to volatilize it, thereby recovering the precious metal. The metal sulfide is composed of molybdenum disulfide particles, which have 2H and 3R crystal structures of molybdenum disulfide. The median particle size D of the molybdenum disulfide particles was determined by dynamic light scattering method. 50 For wavelengths above 10nm and below 1000nm, The precious metal adsorbed by the precious metal adsorbent containing metal sulfides is gold.

3. The precious metal recycling method according to claim 1 or 2, wherein, The primary particles of the molybdenum disulfide are disc-shaped, strip-shaped, or sheet-shaped, and have a thickness ranging from 3 to 100 nm.

4. The precious metal recycling method according to claim 1 or 2, wherein, The specific surface area of ​​the molybdenum disulfide particles, determined by the BET method, was 10 m². 2 / g or more.

5. The precious metal recycling method according to claim 2, wherein, After recovering the volatilized metal oxides, the metal oxides are sulfided, thereby regenerating the noble metal adsorbent composed of metal sulfides.

6. An application of a precious metal adsorbent for the recovery of precious metals from solutions containing less than 100 ppb, wherein the precious metal adsorbent is a precious metal adsorbent composed of molybdenum disulfide particles. The median particle size D of the molybdenum disulfide particles was determined by dynamic light scattering. 50 For wavelengths above 10nm and below 1000nm, The molybdenum disulfide particles are initially shaped as discs, strips, or sheets, with a thickness ranging from 3 to 100 nm. Furthermore, the specific surface area of ​​the molybdenum disulfide particles, as determined by the BET method, is 10 m². 2 / g or more, The molybdenum disulfide particles have both a 2H crystal structure and a 3R crystal structure. The precious metal adsorbed by the precious metal adsorbent is gold.

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