Precious metal recovery method

Abstract

To provide recover noble metals from fly ash.SOLUTION: A method for recovering noble metals from fly ash includes a crushing step for crushing the fly ash that contains the aggregate of fine primary particles and coarse primary particles containing noble metals, a sizing step for sizing the fly ash crushed in the crushing step into coarse powder and fine powder, and a recovery step for recovering the noble metal from the fine powder.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for recovering precious metals. [Background technology]

[0002] Patent Document 1 describes a method for recovering precious metals from incineration ash, which includes a crushing step in which the incineration ash is crushed to produce precious metal-enriched particles containing precious metals scraped off from the surfaces of the precious metal-adhered particles in the incineration ash, and other particles; a classification step in which the precious metal-enriched particles obtained in the crushing step and the other particles are classified into particles of a certain particle size; and a specific gravity separation step in which the particles classified in the classification step are subjected to specific gravity separation to separate the precious metal-enriched particles from the other particles. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-140555 A Summary of the Invention [Problem to be solved by the invention]

[0004] The present inventors have found the following problems.

[0005] Fly ash, which is soot and dust contained in the exhaust gas generated from an incinerator during incineration, is lighter than the incineration ash, and includes, for example, ash discharged from the bottom of a boiler that recovers heat from exhaust gas (also called boiler ash) and ash collected in a bag filter for purifying exhaust gas. Fly ash is light in weight because the particles that make up the fly ash are small in diameter (for example, on the order of microns). On the other hand, the incineration ash is discharged from the bottom of the incinerator during incineration, is also called cinders (or bottom ash), and has a larger particle size (for example, on the order of millimeters) than fly ash. The present inventors have conducted extensive research into a method for recovering precious metals from the above-mentioned fly ash.

[0006] Patent Document 1 describes a method for recovering precious metals from incineration ash. However, when an attempt was made to simply apply the technology described in Patent Document 1 to fly ash, it was found to be ineffective.

[0007] An object of the present invention is to recover precious metals from fly ash. [Means for solving the problem]

[0008] The first aspect of the present invention is A method for recovering precious metals from fly ash, comprising the steps of: A crushing step of crushing the fly ash containing aggregates of fine primary particles and coarse primary particles containing precious metals; A classification step of classifying the crushed fly ash obtained in the crushing step to obtain coarse powder and fine powder; a recovery step of obtaining precious metals from the fine powder; The precious metal recovery method includes the steps of:

[0009] The second aspect of the present invention is the invention according to the first aspect, The maximum particle size of the primary particles constituting the fly ash is 500 μm or less.

[0010] A third aspect of the present invention is the invention according to the first or second aspect, The disintegration step is carried out in a dry or wet manner using a vibration mill or a bead mill, or in a wet manner using ultrasonic waves.

[0011] A fourth aspect of the present invention is the invention according to any one of the first to third aspects, The particle size of the fine powder is 150 μm or less.

[0012] A fifth aspect of the present invention is the invention according to any one of the first to fourth aspects, In the recovery step, the fine powder obtained in the classification step is separated based on at least one of specific gravity and particle size, and precious metals are obtained from the resulting precious metal concentrate.

[0013] A sixth aspect of the present invention is the invention according to any one of the first to fifth aspects, The fine powder obtained in the classification step is crushed again in a secondary crushing step, and then the recovery step is carried out. Effect of the Invention

[0014] According to the present invention, precious metals can be recovered from fly ash. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a flow chart (left side) of the precious metal recovery method according to this embodiment and this example, and a schematic diagram (right side) showing the state of fly ash in each process. [Diagram 2] FIG. 2 is a schematic explanatory diagram showing the difference between disintegration (the present invention) and pulverization (the prior art) of agglomerates (b) that constitute boiler ash. [Diagram 3] FIG. 3 is a schematic explanatory diagram showing primary particles constituting boiler ash separated by particle size. [Figure 4] FIG. 4 is a schematic explanatory diagram showing the state of boiler ash. [Diagram 5] FIG. 5 shows each of the particles shown in FIG. 1 and their corresponding SEM images. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, an embodiment of the present invention will be described. In this specification, the symbol "to" indicates a value greater than or equal to a given value and less than or equal to a given value.

[0017] The present embodiment has the following configuration. "A method for recovering precious metals from fly ash, comprising: A crushing step of crushing the fly ash containing aggregates of fine primary particles and coarse primary particles containing precious metals; A classification step of classifying the crushed fly ash obtained in the crushing step to obtain coarse powder and fine powder; a recovery step of obtaining precious metals from the fine powder; A precious metal recovery method comprising the steps of:

[0018] (Crushing process) The crushing process is performed on the fly ash, and the purpose is to crush the aggregates of fine primary particles containing precious metals and coarse primary particles without crushing the coarse primary particles that contain almost no precious metals, and to obtain crushed powder containing primary particles containing precious metals and coarse primary particles. Primary particles containing precious metals are present in boiler ash or ash collected by a bag filter (i.e., fly ash) (hereinafter, primary particles consisting of precious metals are exemplified). On the other hand, it has been found that in the case of lightweight and small-sized particles such as fly ash, primary particles consisting of precious metals may adhere to other primary particles (primary particles that do not contain precious metals at all or primary particles that contain some of them) and form aggregates.

[0019] FIG. 1 is a flow chart (left side) of the precious metal recovery method according to this embodiment and this example, and a schematic diagram (right side) showing the state of fly ash in each process. FIG. 2 is a schematic explanatory diagram showing the difference between disintegration (the present invention) and pulverization (the prior art) of agglomerates (b) that constitute boiler ash. It should be noted that the numerical values ​​in FIG. 2 are merely an example and do not limit the present invention.

[0020] Fly ash is soot and dust contained in the exhaust gas generated from an incinerator during incineration, and in this invention refers to ash collected from a boiler for heat recovery from exhaust gas or a dust collection facility (bag filter) for purifying exhaust gas. The particles that make up fly ash are smaller in diameter (for example, on the order of microns) and lighter in weight than incineration ash.

[0021] Here, as an example of fly ash, a case where the maximum particle size of the primary particles constituting the boiler ash is 500 μm or less (preferably 300 μm or less) is illustrated. Note that the effect of the present invention can be achieved even if a portion of the boiler ash (for example, a particle size frequency of 5%) contains particles with a particle size of 500 μm. When obtaining the particle size frequency, the measurement may be performed using a laser diffraction / scattering type particle size distribution measuring device after dispersing the boiler ash in a solvent.

[0022] The primary particles constituting the boiler ash preferably have a spherical or ellipsoidal shape, in which case the crushing step of the present embodiment can be applied more effectively.

[0023] The present embodiment can be applied to boiler ash from small-scale equipment, i.e., household incinerators, to large-scale equipment, i.e., incinerators for manufacturing plants (especially for metal refining). In the case of incinerators for manufacturing plants, the ratio of precious metals in the boiler ash can be nearly 100 times higher than that of general waste incinerators, and the merits of using the present embodiment are even greater.

[0024] FIG. 3 is a schematic explanatory diagram showing primary particles constituting boiler ash separated by particle size. Fig. 4 is a schematic diagram showing the appearance of fly ash (boiler ash). That is, fly ash is composed of fine primary particles containing precious metals, fine primary particles other than precious metals, coarse primary particles not containing precious metals, aggregates of fine primary particles (not shown), and aggregates of fine primary particles and coarse primary particles. Figure 5 is a schematic diagram and SEM photograph of boiler ash containing precious metals before crushing, and the coarse primary particles above the sieve and the fine primary particles containing precious metals below the sieve after crushing, as well as fine powders other than precious metals.

[0025] There are two types of primary particles: relatively coarse and relatively fine (Figures 2(a) and 3). Primary particles made of precious metals belong to the relatively fine group. It is not necessary to clearly distinguish between the two groups, and it is sufficient to group them so that primary particles made of precious metals belong to the relatively fine group.

[0026] Hereinafter, gold (Au) will be used as an example of a noble metal, but there is no limitation as long as it is a metallic element that can be called a noble metal.

[0027] In boiler ash, fine primary particles consisting mainly of precious metals and other coarse primary particles form agglomerates (Figures 2(b), 4, and 5).

[0028] The technology described in Patent Document 1 is realized by an equipment configuration that assumes that incineration ash is composed of millimeter-order particles (e.g., a rotary impact mill). When using a rotary impact mill on boiler ash, it is assumed that the particle size of the primary particles that make up the boiler ash is small, so it may not be possible to strike them in the first place. If the primary particles that make up the boiler ash are struck, it is assumed that, rather than breaking up the agglomerates, the fine primary particles that make up the agglomerates and the other coarse primary particles themselves will be pulverized (Figure 2(c)).

[0029] When pulverization is performed, as shown in Fig. 2(c), what is obtained after pulverization is a particle group with a uniform particle size. This particle group with a uniform particle size contains not only primary particles made of precious metals, but also other primary particles (primary particles that do not contain precious metals at all or primary particles that contain some of them). In other words, what is obtained after pulverization is a primary particle group in which there is no difference in particle size between coarse particles and fine particles. Even if one tries to recover primary particles made of precious metals from this primary particle group, the number of primary particles is too large.

[0030] On the other hand, when disintegration is used instead of crushing, that is, when agglomerates are broken down, a group of primary particles with the particle size of the constituent units is obtained as shown in Figure 2(d). This means that the group of primary particles can be divided into a group of relatively coarse primary particles and a group of relatively fine primary particles. Primary particles made of precious metals belong to the relatively fine group. As a result, when primary particles made of precious metals are recovered from the group of primary particles after crushing, the number of primary particles is smaller than when crushing is performed as in the conventional technology. This is also called "enrichment of primary particles made of precious metals," and the relatively fine group of the obtained group of primary particles is also called "concentrate."

[0031] The above concentration provides various advantages.

[0032] (Increasing the grade of the final precious metal concentrate) As shown in Figure 2, the product obtained by crushing and then sieving has a higher precious metal (hereinafter, Au is used as an example) content than when using conventional grinding technology.

[0033] The difference in the precious metal content of the product obtained by crushing as in the present invention and the precious metal content of the product obtained by pulverization as in the prior art ultimately has a significant impact on the content of the precious metal concentrate obtained in the separation process (e.g., gravity separation process), which is a preferred example described below.

[0034] Assuming that the precious metal content increases 100-fold in the separation process described below, the Au content of the precious metal concentrate obtained by the conventional crushing method will be 500 g / t, while the Au content of the precious metal concentrate obtained by the crushing method of the present invention will be 1000 g / t (see the values ​​in Figure 2).

[0035] (Cost reduction through energy saving) The amount of energy input to the crushing process of the prior art and the crushing process of the present invention is significantly different (crushing >> crushing). The crushing process of the present invention allows precious metals to be recovered at a lower cost. Furthermore, in the case of the crushing process of the present invention, the amount of material input to the separation process can be reduced, making it possible to reduce the initial cost and running cost of the separation device.

[0036] (Prevention of deterioration of the working environment) The crushing process of the prior art generates a large amount of dust. Although the crushing process of the present invention also generates fine particles, the amount is smaller than that of the crushing process. As a result, it is possible to prevent the deterioration of the working environment.

[0037] When the disintegration step is performed in a wet manner, the boiler ash is dispersed in a solvent, and then the agglomerates are disintegrated, for example, by ultrasonic waves. In particular, ultrasonic waves, unlike the rotary impact mill described in Patent Document 1, can provide an appropriate impact to the agglomerates, making it possible to selectively disintegrate the agglomerates. Other examples that can be used include a wet bead mill, a wet vibration mill, and a tower mill.

[0038] When performing the wet crushing process, there is no limitation on the type of solvent, as long as it can disperse the boiler ash well. On the other hand, a solvent capable of dissolving at least a portion of substances other than precious metals may be used. In this case, the concentration (number ratio) of primary particles made of precious metals increases in the fine primary particle group in the crushed material, and the precious metals are concentrated.

[0039] When the disintegration step is carried out in a dry manner, the agglomerates are disintegrated, for example, by a bead mill. Unlike the rotary impact mill described in Patent Document 1, a bead mill applies relatively weak shear and friction forces to the agglomerates by adjusting the material and particle size of the beads, the peripheral speed and the input amount of the agitator (for example, the material of the beads is alumina, the bead diameter is 1.5 to 20 mm, and the peripheral speed is 3.0 to 5.0 m / sec), making it possible to disintegrate the agglomerates. Alternatively, for example, a dry vibration mill or an intensive mixer can be used.

[0040] In addition, whether wet or dry, when disintegrating agglomerates, it is not impossible that primary particles are inevitably pulverized due to collisions between agglomerates. On the other hand, compared to the rotary impact mill described in Patent Document 1, the degree of impact is clearly smaller in the case of ultrasonic waves, and it is clear that the main action is to disintegrate agglomerates. Also, as described above, the contents of Patent Document 1 do not effectively disintegrate agglomerates in boiler ash.

[0041] The crushing step of this specification is different from the crushing of the conventional technology. That is, the particle size distribution of the primary particles obtained after crushing of the conventional technology may change significantly from the particle size distribution of the particles before crushing because the coarse primary particles contained before crushing are also crushed, but the particle size distribution of the primary particles obtained after crushing of the present invention does not change much from the particle size distribution of the particles before crushing. The particle size distribution of the primary particles obtained after crushing can be measured by particle analysis using a scanning electron microscope (SEM) or a digital microscope, or by a laser diffraction / scattering type particle size distribution measuring device. When measuring the particle size distribution including agglomerated particles after disintegration using a laser diffraction / scattering particle size analyzer, excessive ultrasonic dispersion may lead to disintegration of the agglomerates, making it impossible to measure the particle size distribution accurately. Therefore, it is preferable not to perform ultrasonic dispersion or to perform it for 1 minute or less.

[0042] The difference between the peak position of the particle size distribution before the crushing process of the present invention (specifically, the mode diameter X of the particles) and the peak position of the particle size distribution after the crushing process (specifically, the mode diameter Y of the primary particle group) is preferably 100 μm or less, and more preferably 50 μm or less. In terms of the ratio, (mode diameter Y) / (mode diameter X) is preferably 0.7 to 1.3. Since crushing is used unlike pulverization, there is little change in the mode diameter before and after crushing.

[0043] The particle size of the fine primary particles containing a precious metal obtained in the crushing step of the present invention is, for example, preferably 150 μm or less, more preferably 100 μm or less, and most preferably 75 μm or less. If the particle size of the fine primary particles containing a precious metal is within the above range, the group of fine primary particles containing a precious metal can be efficiently classified in the classification step described later.

[0044] (Classification process) In this process, fine powder containing a large amount of fine primary particles and coarse powder containing a large amount of coarse primary particles are obtained by classification from the crushed fly ash. The purpose of this is based on the knowledge that most particles of precious metals such as gold (Au) exist as particles of 50 μm or less, and that the coarse powder does not contain much precious metal.

[0045] The specific method of the classification step is not limited. When the crushing step is performed in a wet state, classification can be performed using a wet classifier or the like in succession, or dry classification can be performed after drying. When the crushing step is performed in a dry state, classification can be performed using a known classifier, sieve, or the like.

[0046] The range of the classification point (e.g., the size of the sieve openings) is, for example, 10 to 150 μm, preferably 50 to 100 μm, and more preferably 75 μm. This range is for converting aggregates of primary particles containing precious metal particles such as Au into fine powder below the above-mentioned classification point by the crushing process, and for classifying the resulting powder to increase the recovery rate of precious metal particles such as Au and to efficiently concentrate the particles.

[0047] (Secondary crushing process) After the classification process, a secondary crushing process may be performed in which the fine particle group (fine powder containing precious metals) is crushed again. It is also assumed that the fine powders may still be agglomerated even after the crushing process. This process makes it possible to separate the fine powders made of precious metals from the other fine powders from such agglomerates. Then, the separation process performed thereafter increases the efficiency of separating the precious metals from the other particles. In this case, it is preferable that the particle size after the secondary crushing is 75 μm or less.

[0048] Incidentally, after the classification process, fine powder has already been separated from the crushed fly ash, so even if precious metals are to be recovered, the number of particles is small compared to the total number of primary particles before crushing. Therefore, even if a secondary crushing process is performed after the classification process, it does not adversely affect the recovery of precious metals.

[0049] (Recovery process) In this step, precious metals are separated from the classified fine powder (concentrate). There is no limitation on the specific method of this step. For example, after the classified fine powder is completely dissolved, the precious metals may be precipitated by a known method (electrolytic deposition, etc.) and then the precious metals may be recovered.

[0050] On the other hand, it is preferable to carry out a separation process in which the fine powders of the classified fine group are separated based on either or both of specific gravity and particle size to obtain fine powders (further concentrate) containing relatively large amounts of precious metals, and to recover precious metals from the concentrate. In this embodiment, the case where specific gravity is used is exemplified. Therefore, the separation process is also called a specific gravity separation process.

[0051] Since precious metals are heavier than other elements, if the above separation process can separate relatively heavy fine powders from the fine powder group, the precious metals can be further concentrated. There are no particular limitations on the separation method based on specific gravity as long as it has a mechanism for separating based on weight, and it also includes methods that utilize a composite principle of size, shape, etc. in addition to weight.

[0052] The specific method of the separation step is not limited. The separation step may be performed by a wet specific gravity separation method, such as a Nelson separator, a Multi-Gravity Separator, a Falcon separator, or a Kelsey Jig. In the case of dry separation, the separation step may be performed by a known mass classification device, such as an elbow jet classifier, a hyprec classifier, or a turbo classifier.

[0053] By carrying out the above steps, precious metals can be recovered from the fly ash.

[0054] The technical scope of the present invention is not limited to the above-described embodiments, but also includes forms in which various modifications and improvements are made within the scope that can derive specific effects obtained by the constituent elements of the invention and their combinations.

[0055] For example, the coarse powder obtained in the classification step may be returned to the crushing step and the classification step again. In this specification, the "crushed fly ash obtained in the crushing step" also includes the coarse powder. EXAMPLES

[0056] The present invention will now be described in detail with reference to examples, although it should be understood that the present invention is not limited to the following examples.

[0057] In this example and comparative example, boiler ash discharged from the boiler of an industrial waste incinerator was used. Most of the primary particles constituting the ash had a particle size of 500 μm or less, and some (particle size frequency 5%) had a particle size exceeding 300 μm.

[0058] Example 1 The crushing process was carried out by a wet method. That is, 500 g of boiler ash was prepared, and 100 g each was put into ion-exchanged water, and then crushed for 90 minutes at a frequency of 40 Hz using an ultrasonic cleaner (MCS: manufactured by AS ONE Corporation). After the crushing process, wet classification was performed using a test sieve with 75 μm openings to obtain fine powder (-75 μm) in the fine group that fell below the sieve and coarse powder (+75 μm) in the coarse group that fell above the sieve.

[0059] After the fine powder and the coarse powder after classification were thoroughly dried, they were passed through the test sieve to separate and collect fine powder particles of 75 μm or less and coarse powder particles of over 75 μm, and each was subjected to composition analysis. The composition was analyzed by decomposing the sample with acid, recovering the precious metal as a precipitate by tellurium coprecipitation, dissolving the precipitate in aqua regia (total dissolution), and analyzing it with ICP-AES (iCAP6300Duo: manufactured by Thermo Fisher Scientific). The distribution rate of gold (Au) was obtained from the composition analysis result and weight ratio. The results are shown in Table 1. Although the composition analysis is limited to Example 1, the precious metal can be recovered from the solution after total dissolution by a known method.

[0060] Example 2 The crushing process was carried out dry. That is, the boiler ash aggregates were crushed using a continuous dry bead mill (SDA1: manufactured by Ashizawa Finetech Co., Ltd., alumina beads φ3 mm, bead filling 60%, peripheral speed 4.0 m / sec, feed rate 30 kg / hr). After the crushing process, dry classification was performed using a test sieve with an opening of 75 μm to obtain fine powder in the fine group under the sieve and coarse powder in the coarse group over the sieve. Other than the above, the same operations as in Example 1 were performed.

[0061] Example 3 The crushing process was carried out in a dry manner. That is, 700 g of boiler ash was prepared and crushed for 10 minutes using a batch-type dry vibration mill (MB-1 type: manufactured by Chuo Kakoki Co., Ltd., alumina pot, alumina balls) under the conditions of alumina balls of φ10 mm, ball filling rate of 30%, and vibration frequency of 16.2 Hz, and then crushed again for 10 minutes under the conditions of alumina balls of φ5 mm, ball filling rate of 50%, and vibration frequency of 16.2 Hz. After the crushing process, wet classification was performed using a test sieve with an opening of 75 μm to obtain fine powder of the fine group under the sieve and coarse powder of the coarse group over the sieve. Other than the above, the same operation as in Example 1 was performed.

[0062] Example 4 The same procedure as in Example 3 was carried out, except that the ball filling rate of the alumina balls was changed from 30% to 50% during the first crushing in the batch-type dry vibration mill. The analysis results are shown in Table 1.

[0063] Comparative Example 1 The crushing step was not carried out, and only wet classification was carried out in the same manner as in Example 1. The analysis results are shown in Table 1.

[0064] Comparative Example 2 The crushing step was not carried out, and only dry classification was carried out in the same manner as in Example 1. The analysis results are shown in Table 1.

[0065] Comparative Example 3 The crushing step was not carried out, and only wet classification was carried out in the same manner as in Example 3. The analysis results are shown in Table 1.

[0066] Comparative Example 4 No crushing step was carried out, and only dry classification was carried out using the same test sieve as in Example 3. The analysis results are shown in Table 1.

[0067] Comparative Example 5 The pulverization process was carried out wet. That is, 830 g of boiler ash was prepared and pulverized for 30 minutes using a wet tower mill (NE008 type: manufactured by Nippon Eirich Co., Ltd., iron ball φ6 mm, iron ball filling amount 10 kg, slurry concentration 40 wt%, screw rotation speed 716 rpm). After pulverization, only fine primary particles with a particle size of 75 μm or less were obtained. After the pulverization process, wet classification was carried out using a test sieve with an opening of 75 μm, and all of the powder was obtained as fine powder in the fine group that fell under the sieve. The same operations as in Example 1 were carried out except for the above.

[0068] [Table 1]

[0069] As can be seen from Table 1, the fine powder of -75 μm (under 75 μm) obtained in Examples 1, 2, 3, and 4, in which the crushing and classification processes were performed, had a clearly higher Au distribution rate than those of Comparative Examples 1, 2, 3, and 4. In Comparative Example 5, in which crushing was performed, the entire amount was crushed to -75 μm, and the Au concentration effect was not obtained.

[0070] Example 5 The fine powder of Example 1 was again crushed by using a disc mill (RS200: manufactured by Retsch) at a rotation speed of 700 rpm for 1 minute. After that, the fine powder (Au grade: 5 g / t) after the secondary crushing was subjected to a separation process using a Laboratory Mineral Separator. The settings for operating the device were Tilt Angle: 1.5°, Speed: 80 rpm, Wash Water: 2.5 L / min, and Test Time: 2.5 min.

[0071] In the separation process, the fine powder was divided into four parts in ascending order of the input side and collected to obtain concentrates 1 to 4. Composition analysis was performed on each concentrate and tailings to determine the grade and concentration of Au. The results are shown in Table 2.

[0072] [Table 2]

[0073] Example 6 The fine powder of Example 3 was again crushed by using a disc mill (RS200: manufactured by Retsch) at a rotation speed of 700 rpm for 1 minute. After that, the fine powder (Au grade: 6 g / t) after the secondary crushing was subjected to a separation process using a Laboratory Mineral Separator. The settings for operating the device were Tilt Angle: 1.5°, Speed: 80 rpm, Wash Water: 2.5 L / min, and Test Time: 3.0 min.

[0074] In the separation process, the fine powder was divided into four parts in ascending order of the input side and collected to obtain concentrates 1 to 4. Composition analysis was performed on each concentrate and tailings to determine the grade and concentration of Au. The results are shown in Table 3.

[0075] [Table 3]

[0076] Example 7 The fine powder of Example 4 was subjected to second crushing again. That is, secondary crushing was performed for 1 minute at a rotation speed of 700 rpm using a disc mill (RS200: manufactured by Retsch). After that, the fine powder (Au grade: 5 g / t) after the secondary crushing was subjected to a separation process using a Laboratory Mineral Separator. The settings for operating the device were Tilt Angle: 1.5°, Speed: 80 rpm, Wash Water: 2.5 L / min, and Test Time: 3.0 min.

[0077] In the separation process, the fine powder was divided into four parts in ascending order of the input side and collected to obtain concentrates 1 to 4. Composition analysis was performed on each concentrate and tailings to determine the grade and concentration of Au. The results are shown in Table 4.

[0078] [Table 4]

[0079] Example 8 The fine powder of Example 2 was subjected to second crushing again. That is, secondary crushing was performed for 1 minute at a rotation speed of 700 rpm using a disc mill (RS200: manufactured by Retsch). After that, the fine powder (Au grade: 4g / t) after the secondary crushing was subjected to a separation process using a Hyplex classifier. The settings were set so that three types of products, light, medium, and heavy, could be recovered, and the position of the flap was adjusted so that the amount of recovered heavy products was about 10% by weight of the input amount.

[0080] The light, medium and heavy products separated in the separation process were subjected to composition analysis to determine the grade and concentration of Au. The results are shown in Table 5.

[0081] [Table 5]

[0082] From the above, it was found that in each example, Au could be recovered in a concentrated state by going through the processes of crushing, classification, secondary crushing, and separation. In addition, although not shown in the table, the concentration rate of Au was extremely high compared to Ag and Cu. In other words, precious metals could be selectively recovered from boiler ash.

Claims

1. A method for recovering precious metals from fly ash, comprising the steps of: A crushing step of crushing the fly ash containing aggregates of fine primary particles and coarse primary particles containing precious metals; A classification step of classifying the crushed fly ash obtained in the crushing step to obtain coarse powder and fine powder; a recovery step of obtaining precious metals from the fine powder; having In the disintegration step, disintegration is performed so as to disintegrate the aggregates into the fine primary particles and the coarse primary particles, In the classification step, classification is performed in a classification point range of 50 μm to 100 μm. Precious metal recovery methods.

2. 2. The precious metal recovery method according to claim 1, wherein the maximum particle size of primary particles constituting the fly ash is 500 μm or less.

3. 3. The precious metal recovery method according to claim 1, wherein the crushing step is carried out in a dry or wet manner using a vibration mill or a bead mill, or in a wet manner using ultrasonic waves.

4. The precious metal recovery method according to any one of claims 1 to 3, wherein in the recovery step, the fine powder obtained in the classification step is separated based on at least one of specific gravity and particle size, and precious metals are obtained from a precious metal concentrate obtained by a separation step.

5. 5. The precious metal recovery method according to claim 1, further comprising the steps of: performing a secondary crushing step in which the fine powder obtained in the classification step is crushed again; and then performing the recovery step.

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