Method for recovering platinum group elements

Abstract

To recover platinum group metals from a treated material containing platinum group metals, such as a used catalyst for cleaning exhaust gas, by a dry method, with high efficiency.SOLUTION: A method for recovering platinum group metals, includes: melting a material to be treated containing platinum group metals, under heating in a furnace, along with a copper source material containing at least one kind of metallic copper and copper oxide, a flux component, and a reducing agent; separating a molten metal absorbing the platinum group metals, and a slag oxide, through difference in specific gravity; then subjecting the molten metal absorbing the platinum group metals to an oxidation treatment; and separating an oxide layer containing as a major component copper oxide, and a molten metal containing as a major component metallic copper containing the platinum group metals concentrated therein, through difference in specific gravity, wherein a silver content in the molten metal separated in melting under heating is controlled to 2000 ppm or more and 8000 ppm or less, thereby recovering platinum group metals with high efficiency.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for recovering platinum group elements (Platinum Group Metals, hereinafter sometimes abbreviated as PGM) and gold from substances containing platinum group elements, such as used petrochemical catalysts, waste catalysts for automotive exhaust gas purification, used electronic substrates, lead frames, etc.

Background Art

[0002] Conventionally, wet methods and dry methods are known as methods for recovering platinum group elements from substances containing platinum group elements such as used automotive catalysts. However, the wet method has problems in terms of recovery rate and cost and is not practical. On the other hand, the applicant has proposed a high-yield and low-cost method for recovering platinum group elements by subjecting waste catalysts for automotive exhaust gas purification containing platinum group elements to oxidation treatment together with metallic copper, separating the carrier of the waste catalyst as a slag-based oxide, and absorbing the platinum group elements into molten copper (Patent Document 1). However, in the case of the method for recovering platinum group elements disclosed in Patent Document 1, depending on the properties of the slag-based oxide generated by the oxidation treatment, part of the platinum group elements may migrate into the slag-based oxide. In response to this problem, the applicant has found that it is possible to reduce the amount of platinum group elements migrating into the slag-based oxide by sufficiently allowing the metal melt and the slag-based oxide to stand in the furnace at an appropriate temperature.

[0003] However, even if the standing time of the metal melt and the slag-based oxide after the oxidation treatment is lengthened, in some cases, the amount of platinum group elements migrating into the slag-based oxide may not be reduced. According to the applicant's investigation, the cause is that the composition of the raw material to be treated containing platinum group elements for the oxidation treatment varies greatly depending on the lot, and when a highly viscous slag is generated by the heat treatment in an electric furnace, it becomes difficult for the platinum group elements to be absorbed into the metal melt. Therefore, the applicant analyzes and grasps in advance the contents of at least the oxides of Al, Si, and Fe among the slag-forming components in the raw material to be treated containing platinum group elements, and adjusts the composition of the flux component to be introduced into the furnace according to the contents of these oxides, thereby finding that it is possible to stably reduce the amount of platinum group elements transferred to the slag-based oxides (Patent Document 2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, even when the improvement described in Patent Document 2 is carried out, depending on the properties of the slag-based oxides generated, the amount of platinum group elements transferred to the slag-based oxides may increase to a non-negligible extent. In this regard, as a result of intensive studies by the present inventors, there is a correlation between the components in the molten metal obtained by heating and melting the raw material to be treated containing platinum group elements and the amount of platinum group elements transferred to the slag-based oxides. In particular, it has been found that the amount of platinum group elements transferred to the slag-based oxides is affected by the silver content contained in the molten metal.

[0006] An object of the present invention is to provide a method for recovering platinum group elements with an even higher recovery rate of platinum group elements by suppressing the transfer of platinum group elements into slag-based oxides in a method for recovering platinum group elements by heat-treating a raw material to be treated containing platinum group elements together with a copper source material composed of at least one of metallic copper and copper oxide, a flux component, and a reducing agent.

Means for Solving the Problems

[0007] The inventors of the present invention have found that in the above-described method for recovering platinum group elements, by controlling the silver concentration in the molten metal, it is possible to suppress the transfer of platinum group elements into the slag-based oxide. Based on this finding, the present invention described below was completed. That is, in the present invention to achieve the above-described problems, [1] A method for recovering platinum group elements, comprising heating and melting a raw material to be treated containing platinum group elements and a copper source material composed of at least one of metallic copper and copper oxide in a furnace together with a flux component and a reducing agent, separating a molten metal that has absorbed platinum group elements and a slag-based oxide by a specific gravity difference, and then subjecting the molten metal that has absorbed the platinum group elements to an oxidation treatment to separate, by a specific gravity difference, an oxide layer mainly composed of copper oxide and a molten metal mainly composed of metallic copper in which platinum group elements are concentrated. In this method, the silver content in the molten metal separated by the above-described heating and melting is adjusted to 2000 ppm or more and 8000 ppm or less. [2] In the method for recovering platinum group elements according to item [1] above, when the mass ratio of the silver content to the platinum group element content in the molten metal separated by heating and melting is represented as Ag / PGM, it is preferably 0.2 or more and 0.8 or less. [3] In the method for recovering platinum group elements according to item [1] or [2] above, the above-described oxidation treatment is preferably performed using an oxygen-containing gas having an oxygen concentration of 27% by volume or more and 100% by volume or less, or while supplying oxygen. [4] In the method for recovering platinum group elements according to items [1] to [3] above, the raw material to be treated containing the platinum group elements is preferably pulverized before being inserted into the furnace so that the maximum particle size is less than 400 μm. [5] In the method for recovering platinum group elements according to items [1] to [4] above, the above-described copper source material is preferably added in a mass ratio of 0.3 or more and 0.9 or less with respect to the raw material to be treated containing the platinum group elements. [6] In the method for recovering platinum group elements according to items [1] to [4] above, the separated oxide mainly composed of copper oxide can be reused as the above-described copper source material.

Advantages of the Invention

[0008] According to the present invention, by adjusting the silver content of the molten metal obtained by heat-treating the raw material to be treated containing platinum group elements, the transfer of platinum group elements into the slag-based oxide can be suppressed, and the recovery rate of platinum group elements can be further increased.

Embodiments for Carrying Out the Invention

[0009] [Raw Material to be Treated] The platinum group elements (PGM) refer to six elements: ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), and platinum (Pt). When denoted as PGM, it may indicate not only these metal elements alone but also combinations of two or more metals. Although the present invention is a method for recovering PGM, it can also be applied to the recovery of gold (Au) in addition to PGM. In the method for recovering platinum group elements of the present invention, examples of the raw material to be treated containing PGM include used petrochemical catalysts containing platinum, palladium, etc., used automotive exhaust gas purification catalysts containing platinum, palladium, and further rhodium, etc. However, it is also possible to use lot out products, scraps, etc. obtained from the manufacturing process of these catalysts, and further used electronic substrates, digital components, lead frames, etc. containing palladium, etc. The above-mentioned raw material to be treated containing platinum group elements is subjected to a heat melting treatment in an electric furnace. In order to increase the reaction rate that occurs during the heat melting treatment, it is preferable to crush, pulverize, and mix it before inserting it into the electric furnace to make it into fine particles. When the raw material is in the form of fine particles when charged into the electric furnace, the reaction rate increases and PGM is easily absorbed into the molten metal. In that case, it is preferable to make the maximum particle size of the fine particles about 50 mm. To crush the raw material to be treated, for example, a jaw crusher can be used as a primary crusher and a double roll crusher can be used as a secondary crusher. If there are foreign substances such as iron filings in the raw material, a magnetic separator may be arranged before and after crushing. Also, as will be described later, after making the raw material to be processed into fine particles, it is preferable to measure in advance the average silver content of the fine particles. In that case, the maximum particle size of the fine particles to be subjected to analysis is preferably further pulverized with a pulverizer or the like to 400 μm or less, and it is more preferable to use those pulverized to a maximum particle size of 350 μm or less. In that case, the fine particles to be subjected to analysis are preferably further pulverized with a vibration mill or the like to an average particle size of 10 μm or less, and it is more preferable to use those pulverized to an average particle size of 5 μm or less. In addition, when pulverizing to fine particles with a vibration mill or the like, since no difference is seen in the analysis results even if the average particle size is made less than 1 μm by increasing the pulverization time, the average particle size is 1 μm or more.

[0010] [Copper source material] In the method for recovering platinum group elements of the present invention, as the copper source material, one or two of metallic copper or copper oxide are used. These copper source materials do not particularly need to be of high purity. When heated and melted in a furnace together with the raw material to be processed containing platinum group elements, a flux component, and a reducing agent, metallic copper dissolves, and part or all of the copper oxide is reduced and melted as metallic copper to form a metal melt in which platinum group elements are dissolved. Further, when the obtained metal melt is subjected to an oxidation treatment described later, part of the metallic copper constituting the metal melt is oxidized to become copper oxide, and it is possible to recover the copper oxide and reuse it as the copper source material. In addition, the diameter of the copper source material is preferably 0.1 mm or more and less than 10 mm. The addition amount of the above copper source material to be charged into the electric furnace is preferably 0.3 or more in terms of the mass ratio of metallic copper, copper oxide or both of them to the raw material to be treated. More preferably, 0.5 or more is added. Here, by adding more copper oxide, the contact opportunity between PGM and the copper source material in the metal melt increases, so that the transfer of PGM to the slag-based oxide can be reduced. In addition, by adding more copper oxide, the content of PGM in the metal melt in the reduction furnace decreases, so that the transfer amount of PGM into the slag-based oxide relatively tends to decrease. The upper limit value of the addition amount of the copper source material is preferably 0.9 or less in terms of the weight ratio to the raw material to be treated. Even if the addition amount is increased beyond that, the transfer amount of PGM into the slag-based oxide does not decrease, and the copper circulation amount in the process increases and it tends to be uneconomical.

[0011] [Flux component] In the method for recovering platinum group elements of the present invention, at least one selected from the group consisting of A2O3, SiO2, CaO, CaCO3 and FeO can be used as the flux component. The addition amount of the flux is preferably adjusted so that the composition of the slag-based oxide generated by the reaction is in the following range after measuring in advance the amounts of at least Al, Si and Fe contained in the raw material to be treated containing PGM. When the component composition of the slag-based oxide is Al2O3: 20 - 30 mass%, SiO2: 25 - 40 mass%, CaO: 20 - 35 mass%, FeO: 0 - 35 mass% (including 0%), the slag-based oxide has appropriate viscosity, good dispersibility and fluidity. Therefore, in the process of specific gravity separation, the platinum group elements mixed in the raw material to be treated are likely to be absorbed by the molten metal copper. In that case, the slag-based oxide separated from the metal melt can have a component composition containing Al: 10 - 22 mass%, Si: 10 - 16 mass%, Ca: 14 - 22 mass%, Fe: 27 mass% or less (including 0%), Pt: 10 ppm or less, and the balance is substantially composed of oxygen. When the slag-based oxide generated in the electric furnace is outside the above range, for example, when Al2O3 exceeds 30 mass%, the viscosity of the slag extremely increases. As a result, the contact rate between the molten metal copper reduced from copper oxide and PGM becomes slow, the molten metal copper absorbing PGM tends to float in the slag, and the absorption rate of PGM into the molten metal decreases.

[0012] [Reducing agent] In the method for recovering platinum group elements of the present invention, the reducing agent is mainly used for reducing copper oxide to metallic copper. Typically, coke or SiC is used as the reducing agent, but it is also possible to use base metals containing gold or platinum group elements. In this case, gold and platinum group elements in the base metals can be recovered simultaneously. Resins, activated carbon, etc. used for electronic substrates can also be used as reducing agents.

[0013] [Silver component] The greatest technical feature in the method for recovering platinum group elements of the present invention is to control the content of silver (Ag) in the molten metal when separating the molten metal absorbing PGM and the slag-based oxide by mixing the above-mentioned raw material to be treated containing PGM, copper source material, flux component and reducing agent and heating and melting them in a heating furnace. The reason why the amount of PGM transferred into the slag-based oxide decreases by increasing the Ag content in the molten metal is not necessarily clear at present, but the inventors consider the mechanism as follows. That is, when the Ag content in the molten metal increases, the distribution ratio of Fe, Ni, Pb, etc. to the slag decreases, and it is considered that the distribution ratio of PGM having a high affinity with these to the slag also decreases. In the method for recovering platinum group elements of the present invention, when separating the slag-based oxide and the metal melt by the specific gravity difference through the above-mentioned heat melting treatment, the Ag content in the metal melt is adjusted to be 2000 ppm or more and 8000 ppm or less. When the Ag content in the metal melt is less than 2000 ppm, the effect of suppressing the amount of PGM transferred into the slag-based oxide is small. Also, when the Ag content exceeds 8000 ppm, the effect of suppressing the amount of PGM transferred into the slag-based oxide saturates, and the manufacturing cost increases, which is not preferable.

[0014] In order to adjust the Ag content in the metal melt within the above range, it is preferable to adjust the mass ratio (Ag / PGM) of the Ag content to the PGM content in the raw material to be treated containing the above-mentioned PGM to be 0.2 or more and 0.8 or less. By performing such adjustment, the Ag content in the metal melt can be adjusted to the desired range described above. When Ag / PGM is less than 0.2, the amount of PGM dissolved in Ag decreases, and the recovery rate of PGM decreases, which is not preferable. Also, when Ag / PGM exceeds 0.8, the cost of Ag may exceed the reduction in the amount of PGM transferred into the slag oxide. The adjustment of the Ag content in the raw material to be treated containing the above-mentioned PGM can be performed as follows. Some conventional exhaust gas purification catalysts, etc. contain a small amount of Ag, but the Ag content in the metal melt obtained using them was at most 1600 ppm or less. Therefore, in the method for recovering platinum group elements of the present invention, it is necessary to further add Ag to the raw material to be treated containing the above-mentioned PGM. As Ag, it is also possible to add crushed Ag ingots, but from the viewpoint of reducing the manufacturing cost, when pulverizing and mixing the raw material to be treated containing the above-mentioned PGM, it is preferable to add waste electronic substrates containing a large amount of Ag, Ag-containing scrap products, sludge, etc. to the raw material to be treated and perform a pulverization treatment. In that case, it is preferable to measure the Ag content of the Ag-containing waste electronic substrate in advance and adjust the Ag content in the raw material to be treated containing PGM before charging it into the electric furnace.

[0015] [Heat melting treatment] In the method for recovering platinum group elements of the present invention, a copper source material, a flux component, and a reducing agent are added to a raw material to be treated containing PGM, and the mixture is heated and melted in a furnace to separate a metal melt containing absorbed PGM and a slag-based oxide by a specific gravity difference through a heat melting treatment. At this time, before charging into the heating furnace, it is preferable to previously pulverize the raw material to be treated containing PGM and the copper source material and mix them with the powdery and granular flux component and reducing agent. As the heating furnace, an ordinary electric furnace may be used, and the heating atmosphere may be an air atmosphere. When the heat melting treatment is performed, a part of easily oxidizable metals such as chromium (Cr) and aluminum (Al) contained in the raw material to be treated containing PGM is oxidized, and together with the oxides and flux components originally contained in the raw material to be treated, a glassy molten slag-based oxide is formed. The slag-based oxide with a small specific gravity floats on the metal melt. On the other hand, copper oxide is reduced to metallic copper, and the molten metallic copper settles through the molten slag-based oxide due to the specific gravity difference, forming a metal melt in the lower layer of the molten slag-based oxide layer. As a result, the charged raw material is mainly separated into a metal melt containing noble metals such as PGM, Ag, and Au and a slag-based oxide consisting mainly of copper.

[0016] The temperature for heating and melting (meltdown) the mixed charged raw material is preferably 1100 °C or higher and 1600 °C or lower. If the meltdown temperature is less than 1100 °C, the melting of the generated slag-based oxide is likely to be incomplete, and the viscosity of the molten slag also increases, resulting in a decrease in the recovery rate of PGM, which is not preferable. If the meltdown temperature exceeds 1600 °C, not only does the energy cost increase, but it also becomes a factor causing damage to the furnace body of the electric furnace, which is not preferable. The meltdown temperature is more preferably 1200 °C to 1500 °C. In the heat melting treatment, after the charged raw material is melted, it is preferable to provide a standing step of holding for at least 5 hours or more and preferably within 10 hours. After the above heat melting and standing, the slag-based oxide floating on the metal melt is removed by tilting operation or the like, and the metal melt containing absorbed PGM is tapped and supplied to the oxidation treatment in the next step.

[0017] [Oxidation treatment] In the method for recovering platinum group elements of the invention, the metal melt absorbing PGM obtained in the above-mentioned heat melting treatment step is subjected to an oxidation treatment, and is separated by a specific gravity difference into an oxide layer mainly composed of copper oxide and a metal melt mainly composed of metal copper in which PGM is further concentrated, thereby concentrating the PGM dissolved in the metal melt. When the oxidation treatment is performed, copper in the metal melt is oxidized to copper oxide, and iron (Fe), nickel (Ni), etc. contained in trace amounts in the metal melt are also oxidized to form an oxide layer, and the metal melt becomes a copper melt close to pure, containing concentrated PGM, precious metals such as Ag and Au. Of course, although the amount of the metal melt decreases by performing the oxidation treatment, the treatment is terminated before the total amount of copper is oxidized. The above-mentioned oxidation treatment is carried out by introducing oxygen gas or oxygen-enriched gas into the furnace while maintaining the temperature of the metal melt in the furnace at a temperature of 1100 ° C or higher and 1600 ° C or lower, preferably 1200 ° C or higher and 1500 ° C or lower. If the temperature of the metal melt is less than 1100 ° C, the oxidation rate is likely to decrease. Conversely, if it exceeds 1600 ° C, the furnace body is likely to be damaged, which is not preferable. When the metal melt obtained in the previous step is heated with a heavy oil burner in, for example, an oxidation furnace, it is difficult for the temperature of the metal melt to rise simply by heating the atmosphere. In addition, the slag-based oxide with a high content of iron oxide and nickel oxide initially generated in the oxidation furnace has a high melting point and poor separability from the metal melt. Therefore, an oxidation treatment is performed using an oxygen-enriched gas to raise the temperature of the metal melt. When the temperature of the metal melt rises, the fluidity of the slag-based oxide with a high iron and nickel content improves, and the separability between the slag and the metal-based oxide is enhanced. As the above-mentioned oxygen-enriched gas, it is preferable to use one with an oxygen concentration of 27% by volume or more and 100% by volume or less. Note that an oxygen concentration of 100% by volume means pure oxygen gas. If the oxygen concentration of the oxygen-enriched gas is less than 27% by volume, there may be no significant change in the oxidation rate compared to when using air, which is not preferable. Although it is possible to use pure oxygen gas for the acidification treatment, if the oxygen concentration exceeds 40% by volume, for example, the lance of the oxidation furnace is likely to be consumed quickly. Therefore, it is more preferable that the oxygen concentration is 27% by volume or more and 40% by volume or less. By setting the oxygen concentration in this way, it is possible to improve the oxidation rate and reduce the transfer of the platinum group to the slag in the oxidation furnace. The blowing amount of the oxygen-enriched gas is the blowing amount per ton of the molten metal before the acidification treatment (Nm 3 / Ton-metal), and can be 30 Nm 3 / Ton-metal or more and 70 Nm 3 / Ton-metal or less.

[0018] After the acidification treatment is completed, the oxidation furnace is tilted to allow the oxide layer mainly composed of copper oxide in the upper layer to flow out of the furnace and be separated from the molten metal. Subsequently, the molten metal in the lower layer with concentrated PGM is tapped and fed to the PGM recovery process in the next step outside the scope of the present invention. At this time, instead of immediately tapping the molten metal with concentrated PGM in one acidification treatment, the molten metal that has absorbed GM obtained in the above heating and melting treatment process is further charged into the oxidation furnace, and the acidification treatment is repeated. When the PGM content in the molten metal reaches 10 to 75 mass%, it is preferable to tap the molten metal and recover PGM in the next step. Since the oxide layer flowing out of the oxidation furnace is mainly composed of copper oxide as described above, after it is allowed to flow out of the oxidation furnace and cooled and solidified, it can be reused as a copper source material for the heating and melting treatment. By doing so, a trace amount of PGM entrained in the oxide layer can also be recovered. When the oxide layer is allowed to flow out of the oxidation furnace, if it is rapidly water-cooled from the molten state to be granulated, the oxide mainly composed of copper oxide can be made into granular materials with a maximum diameter of 0.1 mm or more and 10 mm or less, so it can be made suitable as a copper source material for the heating and melting treatment.

Example

[0019] [Example 1] Used lump-shaped honeycomb-shaped automobile exhaust gas purification catalyst (converter fragments) was crushed to a maximum diameter of 400 μm or less using a roll mill and a pulverizer in that order to prepare the raw material to be fed. A part of the raw material to be fed was crushed to an average particle size of 5 μm using a vibration mill to prepare a sample for composition analysis, and the composition of the raw material to be processed was measured in advance using a fluorescent X-ray analyzer (model number: Rigaku ZSX PrimusII). In addition, the composition and Ag content of waste electronic circuit boards containing Ag were similarly measured. The sum of the mass of the raw material to be fed and the mass of the waste electronic circuit boards was the input mass of the raw material to be processed. 805 kg of the raw materials, 49 kg of waste electronic circuit boards (Ag content 0.98 kg), 296 kg of CaO as a flux component, 30 kg of coke as a reducing agent, and 300 kg of copper oxide (containing about 80 mass% of powder particles of 0.1 mm to 10 mm) were weighed, and these were put into an electric furnace and heated and melted at 1350°C. After meltdown, the molten material was left to stand at a temperature of 1250 to 1300°C for about 5 hours, and then the upper layer of slag-based oxide was poured out from the side of the electric furnace and cooled and solidified.

[0020] The molten metal that had absorbed the PGM in the electric furnace was tapped from the bottom of the electric furnace and introduced into a heated oxidation furnace. The Ag content in the molten metal was 2712 ppm. The ratio of the mass of Ag to the total mass of platinum group elements (Pt, Pd, Rh) in the molten metal (Ag / PGM) was 0.261. Next, oxygen-enriched gas with an oxygen concentration of 30.2% by volume was blown into the molten metal containing PGM in the oxidation furnace, and then the oxygen-enriched gas was sprayed onto the surface of the molten metal for oxidation treatment. When the layer of oxide formed on the surface of the molten metal reached a thickness of about 1 cm, the furnace was tilted to drain the oxide out of the furnace, and the drained oxide was poured into a water tank and cooled with a large amount of running water. The entire amount of the molten metal obtained excluding the oxide layer was discharged from the oxidation furnace, cooled and solidified, and recovered as a concentrate of PGM. Analysis revealed that the amount of metallic copper was 5.3 kg, and the PGM content was Pt = 18.5 mass%, Pd = 35.9 mass%, and Rh = 4.9 mass%. Also, the PGM contained in the slag-based oxide removed from the upper layer of the electric furnace was 0.9 ppm. This value was less than half of 1.94 ppm in Comparative Example 1 described later, for example, indicating that the amount of PGM transferred into the slag-based oxide can be reduced by using the method for recovering platinum elements of the present invention. Table 1 shows the operating conditions and operating results of this example. The results of other examples and comparative examples are also shown in Table 1.

[0021]

Table 1

[0022] [Example 2] 817 kg of waste catalyst and 37 kg of waste electronic substrate (Ag content 0.74 kg) were charged into an electric furnace, and the same operation as in Example 1 was performed. As a result, the Ag content in the molten metal was 2064 ppm, and the ratio of the mass of Ag to the total mass of PGM in the molten metal, Ag / PGM, was 0.200. When the molten metal was subjected to an oxidation treatment under the same conditions as in Example 1, the PGM concentrate had a metallic copper content of 5.6 kg, and the PGM content was Pt = 19.9 mass%, Pd = 34.4 mass%, and Rh = 4.5 mass%. The PGM contained in the slag-based oxide was 1.3 ppm.

[0023] [Comparative Example 1] 829 kg of waste catalyst and 25 kg of waste electronic substrate (Ag content 0.50 kg) were charged into an electric furnace and heated and melted. As a result, the Ag content in the molten metal of the electric furnace was 1547 ppm, and Ag / PGM was 0.144. When the molten metal was subjected to oxidation treatment under the same conditions as in Example 1, the amount of metallic copper was 5.3 Kg, and the contents of PGM were Pt = 20.0 mass%, Pd = 34.2 mass%, and Rh = 4.9 mass%. Also, the content of PGM contained in the slag-based oxide removed from the upper layer of the electric furnace was 2.1 ppm, which was a high value compared to the examples.

[0024] [Comparative Example 2] For the molten metal in the oxidation furnace, initially, an oxygen-enriched gas with an oxygen concentration of 25.0% by volume was blown into the molten metal, and then the oxygen-enriched gas was sprayed onto the surface of the molten metal for oxidation treatment. Except for this, the same operations as in Comparative Example 1 were repeated to recover the PGM concentrate of this comparative example. When it was analyzed, the amount of metallic copper was 5.7 Kg, and the contents of PGM were Pt = 17.9 mass%, Pd = 37.1 mass%, and Rh = 4.5 mass%. Also, the content of PGM contained in the slag-based oxide removed from the upper layer of the electric furnace was 4.9 ppm.

[0025] [Comparative Example 3] Except for using 227 Kg of copper oxide as the copper source material, the same operations as in Comparative Example 1 were repeated to recover the PGM concentrate of this comparative example. When it was analyzed, the amount of metallic copper was 4.8 Kg, and the contents of PGM were Pt = 20.8 mass%, Pd = 34.1 mass%, and Rh = 4.8 mass%. Also, the content of PGM contained in the slag-based oxide removed from the upper layer of the electric furnace was 5.4 ppm.

[0026] As is clear from the above results, when using the method for recovering platinum group elements of the present invention, the amount of platinum group elements that migrate into the slag-based oxide and are not recovered can be reduced, and the recovery rate of platinum group elements can be further increased for recovery.

Claims

Claim 1 A method for recovering platinum group elements, comprising: heating and melting a raw material to be treated containing platinum group elements and a copper source material composed of one or more of metallic copper and copper oxide in a furnace together with a flux component and a reducing agent, separating a metal melt that has absorbed platinum group elements and a slag-based oxide by a specific gravity difference, then subjecting the metal melt that has absorbed the platinum group elements to an oxidation treatment, and separating, by a specific gravity difference, an oxide layer mainly composed of copper oxide and a metal melt mainly composed of metallic copper in which platinum group elements are concentrated. In this method, the mass ratio Ag / PGM of the silver content to the platinum group element content in the metal melt separated by the above heating and melting is adjusted to be 0.2 or more and 0.8 or less, and the silver content in the metal melt is adjusted to be 2000 ppm or more and 8000 ppm or less. Claim 2 The method for recovering platinum group elements according to claim 1, wherein the oxidation treatment is performed using an oxygen-containing gas having an oxygen concentration of 27% by volume or more and 100% by volume or less, or while supplying oxygen. Claim 3 The method for recovering platinum group elements according to claim 1 or 2, wherein the raw material to be treated containing platinum group elements is pulverized before being inserted into the furnace so that the maximum particle size is less than 400 μm. Claim 4 The method for recovering platinum group elements according to any one of claims 1 to 3, wherein the copper source material is added in a mass ratio of 0.3 or more and 0.9 or less with respect to the raw material to be treated containing platinum group elements. Claim 5 The method for recovering platinum group elements according to any one of claims 1 to 4, wherein the separated oxide mainly composed of copper oxide is reused as the copper source material.

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