Methods for recovering precious metals

Abstract

Precious metals are recovered from the bottom ash. [Solution] A method for recovering precious metals from bottom ash, comprising: a magnetic separation step of magnetically separating the bottom ash to recover non-magnetically attached products; a classification step of classifying the non-magnetically attached products at classification points of 500 μm to 1.0 mm to separate them into coarse-grained products and fine-grained products; a crushing step of crushing the fine-grained products to obtain crushed material; and a wet specific gravity separation step of wet specific gravity separation of the crushed material to separate it into high-density products and low-density products to recover the high-density products, wherein in the crushing step, the fine-grained products are crushed such that the cumulative 90% passage diameter D90 in the crushed material is 20 μm to 300 μm.

Description

Technical Field

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

Background Art

[0002] Conventionally, general waste and industrial waste have been incinerated. Although the incineration ash obtained by incineration contains metal scraps and non-ferrous metal scraps, dust adheres to their surfaces, so the incineration ash has sometimes been directly landfilled.

[0003] Various attempts have been made to effectively utilize this incineration ash instead of landfilling. For example, Patent Document 1 discloses a method for recovering valuable metals by subjecting incineration ash to magnetic separation, eddy current separation, and color sorting for solid content after washing.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, incineration ash includes relatively heavy main ash remaining at the bottom of the incinerator and fly ash, which are fine particulate ashes that scatter from the furnace together with combustion gas and are collected by chimneys or dust collectors. Although the precious metals contained in the main ash are extremely small in amount, since a large amount of main ash is generated, it is required to concentrate and recover precious metals from the main ash.

[0006] In Patent Document 1, although non-ferrous metals can be recovered, the recovery of precious metals is not disclosed. Further, even if precious metals are recovered, the treatment is complicated and may not be cost-effective.

[0007] Therefore, the present invention aims to provide a technology for concentrating and recovering precious metals from bottom ash. [Means for solving the problem]

[0008] The distribution of precious metals into coarse and fine particles in bottom ash varies depending on the waste source. Our research revealed that even when fine particles are recovered through classification or other operations with the aim of recovering precious metals contained in the fine particles, the purity and recovery rate of the precious metals cannot be increased. This is thought to be because, in bottom ash, particles containing precious metals become coarser due to the adhesion of soot and other factors.

[0009] Based on this, the inventors focused on crushing the bottom ash along with classification and conducted further investigations. As a result, they found that by performing classification and crushing, and then further crushing the resulting fine particles to refine them, followed by wet specific gravity separation, it is possible to separate precious metals with higher quality and recovery rate according to the difference in specific gravity.

[0010] This invention is based on the above findings and is as follows.

[0011] A first aspect of the present invention is: A method for recovering precious metals from bottom ash, A magnetic separation process is performed to magnetically separate the main ash and recover non-magnetically deposited products. A classification step is performed to classify the non-magnetic product at classification points of 500 μm to 1.0 mm, separating it into coarse-grained product and fine-grained product. A crushing step to crush the aforementioned fine-grained product to obtain crushed material, The system includes a wet gravity separation step in which the crushed material is separated into high-density and low-density products by wet gravity separation, and the high-density product is recovered. In the crushing step, the fine-grained product is crushed such that the cumulative 90% passage diameter D90 in the crushed material is 20 μm or more and 300 μm or less. This is a method for recovering precious metals.

[0012] A second aspect of the present invention is, in the first aspect, In the wet specific gravity separation step, thin-flow separation is performed.

[0013] A third aspect of the present invention is as follows in the first or second aspect: When the classification step is the first classification step, the fine-grained product separated in the first classification step is the fine-grained product A1, and the coarse-grained product is the coarse-grained product B1, the method further includes a second classification step of crushing the coarse-grained product B1 and classifying the obtained crushed material at a classification point of 500 μm or more and 1.0 mm or less to separate it into a fine-grained product A2 and a coarse-grained product B2, In the crushing step, the fine-grained product A1 separated in the first classification step and the fine-grained product A2 separated in the second classification step are crushed.

[0014] A fourth aspect of the present invention is as follows in the third aspect: In the second classification step, the coarse-grained product B1 is crushed so that the weight ratio of the coarse-grained product B2 in the crushed material crushed in the second classification step is 5% or less.

Advantages of the Invention

[0015] According to the present invention, precious metals can be concentrated and recovered from the main ash.

Brief Description of the Drawings

[0016] [Figure 1] FIG. 1 is a flowchart of a method for recovering precious metals according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram showing the particle size distribution of crushed materials in an example. [Figure 3] FIG. 3 shows the Au recovery curve in an example. [Figure 4] FIG. 4 shows the Pd recovery curve in an example.

Modes for Carrying Out the Invention

[0017] Hereinafter, embodiments of the present invention will be described. In this specification, "~" refers to a value that is equal to or greater than a predetermined numerical value and equal to or less than a predetermined numerical value.

[0018] Hereinafter, a method for recovering precious metals according to an embodiment of the present invention will be described with reference to FIG. 1. FIG. 1 is a flowchart of a method for recovering precious metals according to an embodiment of the present invention. As shown in FIG. 1, the recovery method of this embodiment includes a preparation step, a magnetic separation step, first to second classification steps, and a wet specific gravity separation step. Hereinafter, each step will be described.

[0019] In this specification, the particle size is confirmed using a test sieve (hereinafter referred to as a test sieve) described in JIS Z8801-1:2019. The sieving method is carried out in accordance with JIS Z8815-1994. When sieving with a test sieve having a mesh size of A, an object having a particle size distribution that passes through the sieve is expressed as an object with a particle size of A or less, and the sieve-passing material that passes through (falls) through the sieve may be expressed as a fine particle product. Also, an object having a particle size distribution that remains on the sieve may be expressed as an object with a particle size exceeding A, and the sieve-non-passing material that remains on the sieve may be expressed as a coarse particle product. However, for those having a particle size of 75 μm or less using the test sieve, it is measured by a laser diffraction / scattering type particle size distribution measuring instrument. The evaluation device is "partica LA-960V2" manufactured by Horiba, Ltd., the dispersion medium is ion-exchanged water, and the set value of the refractive index at the time of measurement is 1.66 (equivalent to alumina particles). No dispersant was used.

[0020] (Preparation Step) First, prepare the main ash to be processed.

[0021] The main ash is obtained, for example, by incinerating general waste or industrial waste, and is relatively heavy dust (so-called bottom ash) remaining at the bottom of the incinerator. The main ash contains components derived from general waste or industrial waste. For example, it contains iron, non-ferrous metals, non-metals, and precious metals. These components exist in the main ash as fine primary particles or coarse secondary particles, or as dust deposits to which dust generated during the incineration process adheres. Examples of precious metals include gold and palladium. Examples of non-ferrous metals include copper, aluminum, stainless steel, and zinc. Examples of non-metals include glass, rubber, and stone.

[0022] (Magnetic selection process) Next, the bottom ash is supplied to, for example, a magnetic separator, and magnetic separation is performed on the bottom ash. This separates the magnetically attached products from the non-magnetically attached products.

[0023] The magnetic deposits separated in the magnetic separation process mainly consist of soot deposits containing magnetic iron, which retain their original shape from the waste before incineration and exist primarily as relatively large, non-powdered particles. Non-magnetic deposits mainly consist of non-magnetic materials such as precious metals, non-ferrous metals, soot deposits containing non-metals, and sandy impurities. Magnetic separation can remove iron-containing soot deposits from the main ash, thereby increasing the purity of precious metals.

[0024] The magnetic separator is not particularly limited, and conventionally known separators such as drum-type magnetic separators, pulley-type magnetic separators, suspended-type magnetic separators, and counter-pole type magnetic separators using permanent magnets or electromagnets can be used. In this case, it is preferable to perform the magnetic separation with a magnetic force of, for example, 500 gauss to 2000 gauss.

[0025] (1st classification process) Next, the non-magnetically deposited products are subjected to classification.

[0026] In non-magnetically deposited products, precious metals, non-ferrous metals, and nonmetals exist at different particle sizes due to differences in their composition and the degree of soot adhesion. Generally, it has been found that precious metals tend to exist in a fine form. In this embodiment, the non-magnetically deposited product is subjected to a classification process in order to recover the precious metals present in the fine particle side. The classification point is set within the range of 500 μm to 1.0 mm. This separates the non-magnetically deposited product into fine-grained product A1 and coarse-grained product B1. According to the above classification point, it is possible to improve the quality of precious metals in fine-grained product A1 while achieving a high recovery rate for precious metals.

[0027] The non-magnetically attached product can be separated into fine-grained product A1 with a particle size below the classification point and coarse-grained product B1 with a particle size equal to or greater than the classification point by classification at a predetermined classification point. Of these, the fine-grained product A1 is recovered.

[0028] As for the classification method, conventionally known methods such as dry or wet classification using gravity, inertial force, or centrifugal force, or sieving classification using a sieve can be employed. Among these, sieving classification is preferred because it can be performed easily. Details regarding sieving classification are as described above, but when performing classification using gravity, inertial force, or centrifugal force, the classification results can be evaluated based on the average particle size D50 calculated from each classification result.

[0029] (2nd classification process) The coarse-grained product B1 separated in the first classification step may be discarded, but from the viewpoint of further recovering precious metals, the coarse-grained product B1 may be subjected to further processing. The coarse-grained product B1 may contain coarse dust deposits that have been made larger due to the adhesion of a large amount of dust to the precious metals. It is advisable to perform a second classification step to recover the precious metals contained in such dust deposits.

[0030] Specifically, the first step is to crush the coarse-grained product B1. Crushing allows for the removal of soot from soot-laden deposits, for example, and separation into particles containing a high concentration of valuable materials such as precious metals. It also allows for the reduction of particle size of individual particles such as precious metals.

[0031] Next, the crushed material is classified at a classification point set within the range of 500 μm to 1.0 mm to separate it into fine-grained product A2 and coarse-grained product B2. Fine-grained product A2 contains soot-adhering materials and individual particles of noble metals, non-ferrous metals, and non-metals that have been finely crushed. Coarse-grained product B2 contains soot-adhering materials and individual particles that have maintained a large particle size without being crushed. The classification point in the second classification step may be the same as or different from the classification point in the first classification step. From the viewpoint of handling fine-grained product A1 and fine-grained product A2, it is preferable that the classification points in the first and second classification steps be the same.

[0032] After separation, the fine-grained product A2 is recovered. The coarse-grained product B2 may be subjected to a separate process for recovering valuable materials, or it may be disposed of if it has a low valuable material content.

[0033] The particle size of the crushed material obtained in the second classification process is not particularly limited, but finer is preferable from the viewpoint of more reliably recovering the precious metals present in the coarse-grained product B1. For example, when the coarse-grained product B1 is crushed, it is preferable to crush it so that the weight ratio of coarse-grained product B2 to the crushed material is 5% or less. This can increase the recovery rate of precious metals contained in the bottom ash.

[0034] Furthermore, the crushing method and conditions are not particularly limited as long as the coarse-grained product B1 can be made fine, and the same methods and conditions as those used in the crushing process described later can be adopted.

[0035] (Crushing process) Next, the fine-grained product A1 separated in the first classification process and the fine-grained product A2 separated in the second classification process are mixed, and the mixture is subjected to crushing treatment. The purpose of crushing treatment will now be explained in detail.

[0036] Fine-grained product A1, for example, contains particles of precious metals, non-ferrous metals, non-metallic materials, or soot-laden materials formed by soot adhering to these particles. In other words, it may contain not only individual particles of precious metals, but also particles containing a mixture of components with different specific gravities. The density of the soot-laden materials may vary depending on the degree of soot adhesion. For example, soot-laden materials formed by soot adhering to precious metal particles may have a specific gravity lower than that of the precious metal itself. Such soot-laden materials may not be separated and recovered as precious metals during the wet specific gravity separation process described later, but may be removed as components with a lower specific gravity than the precious metals.

[0037] In this regard, crushing treatment removes soot and dust from the surface of particles such as precious metals and non-ferrous metals, allowing for the separation of individual precious metals or particles containing a high concentration of precious metals. This makes it possible to accurately separate precious metals, non-ferrous metals, and non-metals according to their specific gravity differences using the wet specific gravity separation method described later. Furthermore, crushing can reduce particle size and suppress variations in particle size. If there is a large variation in particle size, the differences in particle size can hinder sorting by specific gravity differences, and the intended separation by specific gravity differences may not proceed sufficiently. For example, when coarse particles with high specific gravity and fine particles with low specific gravity are mixed together, they may exhibit similar separation behavior and be separated and recovered as the same thing. In this respect, crushing reduces variations in particle size and makes it possible to perform sorting by specific gravity differences more reliably.

[0038] Thus, crushing treatment allows for the removal of soot deposits from precious metals, non-ferrous metals, and non-metallic materials contained in the fine-grained product, separating particles with a high content of precious metals, and further reducing the quality of individual particles of precious metals and non-ferrous metals through crushing. In addition, if the product's form before incineration or the incineration process results in clumpy particles containing a mixture of high-density and low-density components, crushing can improve the separation effect of specific gravity in wet specific gravity separation by further separating the high-density and low-density components.

[0039] In this embodiment, from the viewpoint of more accurately separating and recovering precious metals by wet gravity separation, the fine-grained product is crushed such that the cumulative 90% passage diameter D90 of the crushed material is between 20 μm and 300 μm. A cumulative 90% passage diameter of 20 μm or more and 300 μm or less means that when the particle size distribution of the crushed material is measured, the particle size at which the cumulative amount from the finest particles reaches 90% is between 20 μm and 300 μm. If D90 is less than 20 μm and the crushed material is excessively fine, the particle separation behavior in wet gravity separation may become unstable. In particular, fine particles are easily affected by water flow and vibration, and the separation accuracy due to differences in specific gravity may decrease. On the other hand, if D90 exceeds 300 μm and the crushed material is coarse, the effect of particle size variation in wet gravity separation becomes large, and it may not be possible to stably separate precious metals. In this regard, by crushing the material such that D90 is between 20 μm and 300 μm, particles of different specific gravities can be stably separated when the crushed material is subjected to wet specific gravity separation, and precious metals can be separated with high purity. From the viewpoint of separating precious metals with higher purity during wet specific gravity separation, it is preferable that the cumulative 90% passage diameter D90 of the crushed material be between 75 μm and 150 μm. The calculation of the cumulative frequency will be described in detail in the examples.

[0040] As for crushing methods, for example, abrasion crushing, impact crushing, compression crushing, and shear crushing can be employed. For fine-grained products A1 and A2, abrasion crushing and impact crushing are preferred from the viewpoint of removing soot and reducing particle size. For abrasion crushing, for example, ball mills, rod mills, vibratory mills, disc mills, and tower mills can be used. For impact crushing, for example, hammer mills and impact crushers can be used. Among these, abrasion crushing is preferred. With abrasion crushing, not only is the particle size reduced, but soot can be removed more reliably.

[0041] Furthermore, the crushing conditions are not particularly limited as long as they can reduce the particle size of the crushed material. For example, the rotation speed of the crusher, the size of the balls used as the crushing medium, the shape of the rods used as the crushing medium, the vibration frequency, or the crushing time can be appropriately adjusted within a range that allows for fine reduction of the particle size of the crushed material.

[0042] (Wet specific gravity separation process) Next, the crushed fine-grained products A1 and A2 obtained in the crushing process are subjected to wet specific gravity separation. In wet specific gravity separation, the components contained in the crushed material can be separated into high-density and low-density products by utilizing the difference in specific gravity using a liquid as a medium. In this embodiment, the crushed material has a cumulative 90% passage diameter D90 of 20 μm or more and 300 μm or less, and is composed of components with small particle size variation. In addition, the crushed material tends to have soot and dust removed from the surface of individual particles of precious metals, and the precious metal particles tend to exist separated individually. Therefore, the influence of separation due to differences in particle size and the influence of separation due to the coexistence of precious metals and components with different specific gravities is reduced, and separation can be performed by specific gravity difference. As a result, it is possible to separate the material into high-density products mainly containing precious metals and low-density products containing non-ferrous metals and nonmetals. In other words, precious metals can be separated as high-density products with high quality and high recovery rate.

[0043] As a wet gravity separation method, for example, thin-flow separation which utilizes the difference in the behavior of particles in a thin flow, and jig separation and heavy liquid separation which utilize the difference in the settling behavior of particles in a fluid can be employed. Among these, thin-flow separation is preferred. With thin-flow separation, precious metals can be separated more stably from crushed material.

[0044] Here, we will explain thin-flow sorting in detail.

[0045] Thin-flow separation can be performed using an apparatus equipped with a vibrating tray positioned at an incline, configured to flow water over the vibrating tray. During thin-flow separation, water is flowed over the vibrating tray, and the amount of water supplied is adjusted to create a uniform, thin layer. Next, a mixed slurry of the target sample is supplied onto the vibrating tray through which the water flows. Then, the vibrating tray is vibrated. At this time, particles with lower specific gravity in the mixed slurry are carried downwards along with the liquid flow to the bottom of the vibrating tray, while particles with higher specific gravity remain on the vibrating tray. In other words, the particles are separated into those that remain on the tray and those that flow downwards from the tray, according to their specific gravity. The particles remaining on the vibrating tray have a higher specific gravity and tend to contain precious metals. Among the particles remaining on the vibrating tray, those remaining upstream tend to have a higher specific gravity and contain more precious metals. Also, particles remaining downstream on the vibrating tray, even if they contain precious metals, tend to contain less than those on the upstream side. On the other hand, the particles that flow down from the vibrating tray are low-specific gravity products and tend to contain non-ferrous metals and nonmetals.

[0046] In thin-flow separation, it is advisable to recover the particles remaining on the vibrating tray as high-density products.

[0047] As mentioned above, a detailed explanation of thin-flow specific gravity separation has been given, but representative separation devices include the Wilfley Table and the James Table. (See Ken Takakuwa, "Ore Dressing Engineering - Fundamentals of Powder and Granule Engineering," NRE Research, pp. 99-102) Other examples include the Laboratory Mineral Separator (hereinafter sometimes referred to as "LMS") from Salter Cyclones, the Multi-Gravity Separator (hereinafter sometimes referred to as "MGS") from the same company, the Analytical Table from Gravity Mining, the Multi Gravity Separator from the same company, and the Falcon Gravity Concentrator from Sepro.

[0048] In thin-flow sorting, the vibration amplitude, vibration speed, and water supply rate of the vibrating tray should be appropriately adjusted according to the purity and recovery rate of the precious metals. For example, in the case of the Salter Cyclones LMS mentioned above, the vibration amplitude should be 1 to 4 inches, the vibration speed 70 to 80 rpm (cpm), and the water supply rate 0.4 to 2.5 L / min. When performing thin-flow specific gravity sorting using the Salter Cyclones MGS, the processing conditions can be set by referring to the sorting conditions for the company's LMS.

[0049] As a result, by performing magnetic separation, classification, and wet specific gravity separation on the main ash, soot, magnetically deposited products such as iron, non-ferrous metals, and other nonmetals can be removed, allowing for the separation of precious metals with high quality and recovery rate.

[0050] <Other Embodiments> Although embodiments of the present invention have been specifically described above, the present invention is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention.

[0051] In the above embodiment, a second classification step is performed on the coarse-grained product B1 separated from the non-magnetic product to recover the fine-grained product A2, and a crushing step is performed together with the fine-grained product A1. However, the present invention is not limited thereto. For example, the second classification step may be omitted, and only the fine-grained product A1 separated from the non-magnetic product may be introduced into the crushing step. Also, for example, although the fine-grained product A1 and the fine-grained product A2 were combined and introduced into the crushing step as a mixture, they may be introduced into the crushing step independently, crushed separately, and then the crushed materials may be mixed together.

[0052] Furthermore, while the above-described embodiment described a case in which particles remaining on the vibrating tray are separated as high-density products and particles flowing down from the vibrating tray are separated as low-density products during thin-flow separation, the present invention is not limited to this. For example, when the vibrating tray is divided into multiple regions along its inclination direction during thin-flow separation, particles located in a portion of the upstream region may be recovered as high-density products. For example, when the vibrating tray is divided into three regions along its inclination direction, designated as the first region, second region, and third region from the upstream side, particles remaining in the first region may be recovered as high-density products. In this case, it becomes possible to recover precious metals with higher purity. Alternatively, for example, particles located in the first and second regions may be recovered as high-density products. In this case, the recovery amount can be increased while maintaining a high purity of precious metals. It is advisable to appropriately select the particles to be recovered as high-density products, taking into consideration the purity of the precious metals and the recovery rate. [Examples]

[0053] Next, we will show examples and specifically explain the present invention. Of course, the present invention is not limited to the following examples.

[0054] (Example 1) First, the bottom ash discharged from the stoker furnace was prepared as the material to be processed. This bottom ash was then treated according to the flow shown in Figure 1.

[0055] Specifically, the main ash was fed into a magnetic separator. Magnetic separation was performed at 1500G using a suspended magnetic separator to remove magnetically attached products, including soot and dust deposits from the scrap iron, and obtain non-magnetically attached products. These non-magnetically attached products were introduced into a sieving machine with a mesh size of 1.0 mm and subjected to dry sieving. This yielded fine-grained product A1 below the sieve and coarse-grained product B1 above the sieve.

[0056] Next, the coarse-grained product B1 on the sieve was introduced into a vibratory rod mill (YAMT-50LNV manufactured by Murakami Seiki Seisakusho) and crushed. This crushed material was then introduced into a sieving machine with a mesh size of 1.0 mm and subjected to dry sieving. This separated the fine-grained product A2 below the sieve from the coarse-grained product B2 above the sieve. The weight ratio of coarse-grained product B2 to the crushed coarse-grained product B1 was 5% or less.

[0057] Next, the fine-grained product A1 and fine-grained product A2 were mixed, reduced to 200-300g, and then introduced into a disc mill (RM200 manufactured by Retsch Corporation) for crushing. Here, the crushing time was adjusted to 30 seconds so that the D90 of the crushed material was between 20μm and 300μm. This yielded the crushed material.

[0058] The particle size distribution of the crushed material from Example 1 was measured. Specifically, using test sieves described in JIS Z8801-1:2019 (hereinafter referred to as "test sieves"), the cumulative frequencies at 75 μm, 106 μm, 150 μm, 212 μm, 250 μm, 300 μm, and 500 μm were determined. The results are shown in Table 1 below. Table 1 also shows the diameter D90 [μm] through which 90% of the cumulative frequency is reached. In the case of measurement by sieving classification, D90 was calculated by finding a straight line between two points that enclose the 90% cumulative frequency and determining the particle size at which the cumulative frequency reaches 90%. For example, in Example 1, the particle size at 90% cumulative frequency was determined from a straight line connecting two points: a particle size of 300 μm where the cumulative frequency is 95% and a particle size of 212 μm where the cumulative frequency is 88%. The particle size distribution is shown in Figure 2. Figure 2 shows the particle size distribution of the crushed material in the example. In Figure 2, the horizontal axis represents particle size [μm], and the vertical axis represents cumulative frequency [%].

[0059] [Table 1]

[0060] As shown in Table 1 and Figure 2, the crushed material from Example 1 had a D90 of 235.8 μm, confirming that it had a relatively fine particle size.

[0061] Next, as a wet gravity separation process, the crushed material was introduced into a thin-flow separator and thin-flow separation was performed. The separator used was a Laboratory Mineral Separator manufactured by Salter Cyclones. Specifically, 180.0 g of crushed material was mixed with water to prepare a mixed slurry. Then, in the thin-flow separator, the vibrating table (flat tray) was set up at an angle of 1.75° from the horizontal, and the mixed slurry was supplied to the flat tray. At this time, the flat tray was vibrated at an amplitude of 3.5 inches and a vibration speed of 80 rpm, and water was supplied at a rate of 2.5 L / min to separate the particles contained in the mixed slurry according to their specific gravity.

[0062] In this example, to evaluate the distribution tendency of precious metals, a flat tray was divided into three regions along the direction of inclination, designated C1, C2, and C3 from upstream to downstream, and the residue from each region was collected. Components that flowed down from the flat tray were also collected. Hereafter, the collected materials obtained from each region will be referred to as component C1, component C2, component C3, and the components that flowed down will be referred to as component T1.

[0063] Each recovered component was separated into solid and liquid phases by filtration, and the solid portion was dried to obtain each dried powder. The weight of the powder obtained in each region is shown in Table 2 below. As shown in Table 2, it was confirmed that the components contained in the crushed material could be separated according to their specific gravity and density by thin-flow separation of the crushed material. Note that cumulative % indicates the ratio of the weight accumulated from the upstream side to the total amount of recovered material. For example, ~C2 indicates the ratio of the sum of C1 and C2 to the total amount of recovered material.

[0064] [Table 2]

[0065] A compositional analysis was performed on each dried powder. The composition was determined by acid hydrolysis of the dried powder, followed by the recovery of precious metals as precipitates using the tellurium coprecipitation method. The precipitates were then dissolved in aqua regia (total dissolution) and analyzed using ICP-AES (SPECTRO's "GREEN FMD46"). From the results of this compositional analysis, the cumulative purity [mg / kg] of precious metals, the enrichment rate, and the cumulative yield of precious metals were determined. Here, the enrichment rate is the value obtained by dividing the content of the target component (precious metal) in the recovered material by the content in the raw material before wet specific gravity separation. This serves as an indicator of how much the precious metals in the recovered material were concentrated relative to the raw material. Gold (Au) and palladium (Pd) were selected as the precious metals. The results for Au are shown in Table 3, and the results for Pd are shown in Table 4. In Tables 3 and 4, the actual yields of Au and Pd were calculated by dividing the amount of Au and Pd contained in the solid recovered in each fraction of the wet gravity separation process by the amount of Au and Pd contained in the solid supplied to the wet gravity separation process. The richness rate was calculated, for example, in the case of Au, by dividing the Au grade of the solid recovered in each fraction of the wet gravity separation process by the Au grade of the solid supplied to the wet gravity separation process. Furthermore, the grade, richness rate, and actual yield are all cumulative values, with C1 representing the values ​​at C1, C2 representing the cumulative values ​​at C1 and C2, C3 representing the cumulative values ​​at C1 to C3, and T1 representing the cumulative values ​​at C1 to C3 and T1.

[0066] [Table 3]

[0067] [Table 4]

[0068] As shown in Table 1, in Example 1, the non-magnetically attached product was crushed so that the D90 in the crushed material was between 20 μm and 300 μm. By subjecting this crushed material to thin-flow separation, it was confirmed that Au and Pd could be retained on the tray with high grade and high actual yield, as shown in Tables 3 and 4. For example, it was found that by recovering only C1 as a high-density product, Au and Pd could be recovered with higher grade and higher enrichment rate. Also, for example, it was found that by recovering C1 and C2 as high-density products, Au and Pd could be recovered with high actual yield. Furthermore, it was confirmed that impurities were significantly reduced, as evidenced by the high enrichment rate.

[0069] (Examples 2-6) In Examples 2 to 5, the procedure was the same as in Example 1, except that the crushing time in the crushing process was adjusted and the D90 of the crushed material was changed, as shown in Table 1. In Example 6, the procedure was the same as in Example 1, except that the crushing method was changed from a disc mill to a tower mill (NE008 manufactured by Nippon Eirich Co., Ltd.).

[0070] As shown in Table 1, it was confirmed that the D90 of the crushed material could be adjusted to between 20 μm and 300 μm in all of Examples 2 to 6. In Examples 5 and 6, when measuring the particle size distribution of the crushed material, the particle size of the crushed material fell below 75 μm, so it was measured using a laser diffraction / scattering particle size distribution analyzer ("partica LA-960V2" manufactured by Horiba, Ltd.). The D90 value used was the value calculated by the laser diffraction / scattering particle size distribution analyzer. In Table 2, the particle size distribution for Examples 5 and 6 is shown as a blank.

[0071] As shown in Table 2, in Examples 2 to 6, similar to Example 1, it was confirmed that the components contained in the crushed material could be separated according to their specific gravity and density by thin-flow separation of the crushed material. Furthermore, as shown in Tables 3 and 4, it was confirmed that Au and Pd could be retained on the tray with high quality and high actual yield.

[0072] (Comparative Example 1) In Comparative Example 1, as shown in Table 1, a mixture of fine-grained product A1 and fine-grained product A2 was introduced into thin-flow separation without crushing treatment. The non-magnetically attached product had a D90 of over 300 μm and was coarse, so it was confirmed that even if thin-flow separation was performed as is, it was difficult to separate the precious metals with high grade. As shown in Tables 3 and 4, in Comparative Example 1, it was confirmed that Au and Pd flowed out of the tray as low-density products and were difficult to retain on the tray as high-density products. In fact, the components that remained on the tray and were separated as high-density products tended to have low precious metal grade and low mineral content.

[0073] Specifically, as shown in Table 3, it was confirmed that Au and Pd were not recovered in C1 on the tray, but were recovered in T after flowing out of the tray. From this, it can be inferred that precious metals are not separated at their original density due to adhesion of soot and other substances, for example.

[0074] Here, Examples 1-6 and Comparative Example 1 will be described based on the recovery curves shown in Figures 3 and 4. Figure 3 shows the Au recovery curve in the Examples, and Figure 4 shows the Pd recovery curve in the Examples. In the recovery curves, the horizontal axis shows the actual yield [%], and the vertical axis shows the enrichment rate [times].

[0075] Generally, in recovery curves, the richness ratio tends to decrease as the recovery rate increases. In this respect, in Examples 1 to 6, the C1 to C3 components remaining on the tray had high noble metal purity, high actual yield, and high richness ratio. Therefore, the recovery curve can maintain a high richness ratio even when the recovery rate is high. In particular, in Examples 3 and 4, the crushed material was crushed so that the D90 of the crushed material was between 75 μm and 150 μm, and it was confirmed that the purity, actual yield, and richness ratio of both Au and Pd elements in the recovered material could be increased compared to Examples 1, 2, 5, and 6. On the other hand, in Comparative Example 1, it was observed that during thin-flow separation, the noble metal tended to flow out of the tray and be separated as a low-density product. Therefore, the recovery curve of Comparative Example 1 has a lower richness ratio compared to Examples 1 to 6.

[0076] (Examples 7-9, Comparative Example 2) In Example 7, the same procedure as in Example 1 was followed, except that the target of processing was changed from bottom ash discharged from a stoker furnace to bottom ash discharged from the bottom of a fluidized bed furnace. In Examples 8 and 9, the same procedure as in Example 7 was followed, except that the crushing time was set to the values ​​shown in Table 5. In Comparative Example 2, the same procedure as in Example 7 was followed, except that the mixture of fine-grained product A1 and fine-grained product A2 was separated by thin flow sorting without crushing. The crushing conditions and particle size distribution in the crushing process are shown in Table 5 below.

[0077] [Table 5]

[0078] Furthermore, Table 6 shows the weight of the dry powder at each of the C1-C3 and T1 points when thin-flow sorting was performed.

[0079] [Table 6]

[0080] Furthermore, compositional analysis was performed on each dried powder, and the purity of the precious metal, the actual yield of the precious metal, and the richness rate were determined from the results of the compositional analysis. The results of the compositional analysis of Au and Pd as precious metals are shown in Tables 7 and 8.

[0081] [Table 7]

[0082] [Table 8]

[0083] In Examples 7-9, the D90 of the crushed material was between 20 μm and 300 μm, confirming that, similar to Example 1, Au and Pd could be retained on the tray with high quality and high actual yield. On the other hand, in Comparative Example 2, the D90 of the non-magnetically deposited product subjected to thin flow separation exceeded 300 μm, resulting in a tendency for lower precious metal grade, actual yield, and richness rate compared to Examples 7-9.

[0084] As described above, by performing magnetic separation, classification, and then crushing and wet specific gravity separation on the bottom ash, precious metals can be recovered from the bottom ash with high purity.

Claims

1. A method for recovering precious metals from bottom ash, A magnetic separation process is performed to magnetically separate the main ash and recover non-magnetically deposited products. A classification step is performed to classify the non-magnetic product at classification points of 500 μm or more and 1.0 mm or less, separating it into coarse-grained product and fine-grained product. A crushing step to crush the aforementioned fine-grained product to obtain crushed material, The system includes a wet gravity separation step in which the crushed material is separated into high-density and low-density products by wet gravity separation, and the high-density product is recovered. In the crushing step, the fine-grained product is crushed such that the cumulative 90% passage diameter D90 in the crushed material is 20 μm or more and 300 μm or less. The aforementioned bottom ash is obtained by incinerating waste and contains particles containing components derived from said waste, and soot-laden material in which soot is attached to said particles. Methods for recovering precious metals.

2. In the aforementioned wet specific gravity separation process, thin flow separation is performed. The method for recovering precious metals according to claim 1.

3. When the classification process is called the first classification process, the fine-grained product separated in the first classification process is called the fine-grained product A1, and the coarse-grained product is called the coarse-grained product B1, The process further comprises a second classification step in which the coarse-grained product B1 is crushed, and the resulting crushed material is classified at a classification point of 500 μm or more and 1.0 mm or less to separate it into fine-grained product A2 and coarse-grained product B2. In the crushing step, the fine-grained product A1 separated in the first classification step and the fine-grained product A2 separated in the second classification step are crushed. The method for recovering precious metals according to claim 1.

4. In the second classification step, the coarse-grained product B1 is crushed such that the weight ratio of the coarse-grained product B2 to the crushed material crushed in the second classification step is 5% or less. The method for recovering precious metals according to claim 3.

5. In the crushing step, the fine granular product is crushed by abrasion, A method for recovering precious metals according to claim 1 or claim 2.

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