PGM recovery method

Abstract

This method for recovering PGM includes: a reduction smelting step for mixing a to-be-treated substance containing SiC and PGM, an oxidizing agent containing CuO, flux, and a reducing agent, and heating and melting these in a reducing atmosphere to form molten slag and an electric furnace metal containing PGM; and an extraction step for extracting the electric furnace metal.

Description

PGM recovery method

[0001] This invention relates to a method for recovering PGM.

[0002] Automobiles are equipped with exhaust gas removal filters to purify exhaust gases. These filters support platinum group metals (PGMs), such as Pt, Rh, and Pd, as catalysts for exhaust gas purification. From the perspective of efficient resource utilization and environmental protection, methods for recovering PGMs from used exhaust gas removal filters have been proposed. For example, a dry recovery process for PGMs, known as the ROSE process, has been proposed, in which a material containing PGMs is heated and melted together with a copper source material to absorb the PGMs into the molten metal.

[0003] To date, exhaust gas removal filters have used cordierite-based materials, mainly composed of oxides such as Al2O3, SiO2, and MgO, as carriers for supporting PGM. Such oxide carriers are used in the above-mentioned ROSE process. ２ By reducing and smelting a copper source material containing oxygen, PGM can be efficiently recovered into metallic copper.

[0004] By the way, diesel vehicles use diesel particulate filters (DPFs) as exhaust gas removal filters. Because diesel vehicles operate at high temperatures and require high heat resistance, SiC is sometimes used as the material for the support on which PGM is attached to the DPF.

[0005] On the other hand, SiC has a high decomposition and melting temperature of around 2540°C, making it more difficult to melt in dry process slag compared to oxide-based materials such as cordierite. Therefore, SiC may remain unreacted, which can reduce PGM recovery.

[0006] Therefore, from the viewpoint of melting SiC in the ROSE process, SiC is mixed with an oxidizing agent to produce SiO ２A method has been proposed to decompose and melt at a lower temperature by oxidizing the material (for example, Patent Document 1, Non-Patent Documents 1 and 2). As an oxidizing agent, Patent Document 1 specifies Cu ２ In Non-Patent Documents 1 and 2, O is referred to as CaCO2. ３ It is disclosed that this may be used.

[0007] Japanese Patent Publication No. 2007-224336. Toshiki Mizuuchi: Al2O3-CaO-SiO2 slag formation of SiC diesel particulate filters, Graduation Thesis (2021) of the Department of Environmental Resources Engineering, Faculty of Science and Engineering, Waseda University (2022), 1-57. Ren Yamakawa: Al2O3-CaO-SiO2 slag formation of SiC diesel particulate filters, Graduation Thesis (2022) of the Department of Environmental Resources Engineering, Faculty of Science and Engineering, Waseda University (2023), 1-58.

[0008] However, according to the inventors' research, Cu ２ O and CaCO ３ When using SiC to SiO ２ It was confirmed that the time required to oxidize and melt the material is long. In recent years, the amount of DPF containing SiC has been increasing, and the processing volume is also tending to increase, so if the processing time is long, there is a risk that the system will not be able to keep up with the increase in processing volume.

[0009] Therefore, the present invention aims to provide a technology for melting a material containing SiC in a short time and efficiently recovering PGM contained in the material.

[0010] A first aspect of the present invention is a method for recovering PGM, comprising: a reduction smelting step of mixing a workpiece containing SiC and PGM with an oxidizing agent containing CuO, a flux, and a reducing agent, heating and melting these in a reducing atmosphere to form molten slag and electric furnace metal containing the PGM; and an extraction step of extracting the electric furnace metal.

[0011] A second aspect of the present invention is, in the first aspect, that the material to be processed is crushed material containing at least a diesel particulate filter.

[0012] A third aspect of the present invention is the second aspect, wherein the particle size of the material to be treated is 600 μm or less.

[0013] In a fourth aspect of the present invention, in any one of the first to third aspects, the oxidizing agent contains 50% or more of CuO by mass ratio, and the balance is Al ２ O ３ , Fe ２ O ３ , Fe ３ O ４ , SiO ２ and contains a CuO-based slag containing at least one selected from the group consisting of and NiO.

[0014] In a fifth aspect of the present invention, in any one of the first to fourth aspects, in the reduction smelting step, the heating temperature is set to 1000°C to 1700°C.

[0015] In a sixth aspect of the present invention, in any one of the first to fifth aspects, in the reduction smelting step, heating and melting are performed so that the carbon concentration contained in the molten slag becomes 0.03% by mass or less.

[0016] In a seventh aspect of the present invention, in any one of the first to sixth aspects, after the extraction step, an oxidation smelting step is provided in which the electric furnace metal is oxidation-smelted to form slag and a PGM alloy, and the PGM alloy is recovered.

[0017] According to the present invention, an object to be treated containing SiC can be melted in a short time, and PGM contained in the object to be treated can be efficiently recovered.

[0018] FIG. 1 is a process flow diagram showing an example of a method for recovering PGM according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of a test apparatus for performing reduction smelting. FIG. 3 is a diagram showing the XRD measurement results of the slag phase and the metal phase after reduction smelting of the SiC DPF in Example 1. FIG. 4 is a diagram showing the XRD measurement results of the slag phase and the metal phase after reduction smelting of the SiC DPF in Comparative Example 1. FIG. 5 is a diagram showing the correlation between the holding time and the reaction rate of SiC. FIG. 6 is a diagram showing the correlation between the distribution ratio of PGM between the slag phase and the metal phase and the holding time.

[0019] <An Embodiment of a Precedent> An embodiment of a present embodiment will be described below with reference to the drawings. Figure 1 is a process flow diagram showing an example of a PGM recovery method according to an embodiment of a present embodiment. The present invention is not limited to these examples, but is shown in the claims, and all modifications within the meaning and scope of equivalence to the claims are intended to be included.

[0020] The PGM recovery method of this embodiment is a method for recovering PGM by a so-called ROSE process, and comprises a preparation step, a reduction smelting step, a first extraction step, an oxidation smelting step, and a second extraction step. Each step will be described below. The ROSE process is a process in which a material to be treated containing platinum group elements (PGM) and Cu ２ A copper source material containing O is reduced and smelted, and the Al produced by the reduced smelting is ２ O ３ -CaO-SiO ２ This describes a process for recovering PGM by melting a SiC-based material containing PGM using a slag from the same system.

[0021] (Preparation Steps) First, the object to be processed, 1, is prepared. The object to be processed 1 contains at least SiC and PGM, and includes a diesel particulate filter (DPF) made of SiC. The object to be processed 1 may include, for example, crushed material obtained by crushing an exhaust gas removal filter (hereinafter also simply referred to as "removal filter"), or by crushing a DPF separated from a removal filter. The removal filter and DPF may be before use or after use. In the DPF, SiC is a component derived from the SiC carrier that supports the exhaust gas purification catalyst. In the DPF, PGM is supported on the SiC carrier as an exhaust gas purification catalyst.

[0022] From the viewpoint of more reliably oxidizing and melting SiC, the material to be processed 1 is preferably in the form of crushed material, and its particle size is preferably 600 μm or less. The lower limit of the particle size is not particularly limited, but if the material to be processed 1 becomes excessively fine, it may be easily removed during the dust collection process of the furnace, for example, and the yield of PGM may decrease. From the viewpoint of not impairing the yield of PGM, the particle size of the material to be processed 1 is preferably 100 μm or more. The method of crushing the material to be processed is not particularly limited, and conventionally known methods can be used.

[0023] (Reduction smelting process) Next, prepare the oxidizing agent 2, flux 3, and reducing agent 4 to be used in reduction smelting.

[0024] Oxidizing agent 2 oxidizes the SiC contained in the workpiece 1 using SiO ２ This is to oxidize it. In this embodiment, from the viewpoint of oxidizing SiC in a shorter time, an oxidizing agent 2 containing CuO is used. As will be described in detail in the examples below, when CuO is used, Cu ２ O and CaCO ３ Compared to the method used, SiC can be oxidized and melted in a shorter time. This mechanism is that CuO is Cu ２ This is thought to be because, compared to oxygen, the number of moles of oxygen per mole of copper is higher. Furthermore, CuO not only acts as an oxidizing agent, but also forms an alloy with PGM when reduced to its elemental form, and acts as an extractant that concentrates PGM in the molten metal.

[0025] As the oxidizing agent 2, CuO may be used as a reagent, and the Cu produced in the oxidation smelting process described later... ２ CuO-based slag obtained by roasting O-based slag 8 may also be used. CuO-based slag is composed of CuO and Al ２ O ３ Fe ２ O ３ Fe ３ O ４ SiO ２ It comprises and at least one impurity selected from NiO. The impurity comprises components derived from the material to be treated 1 and flux 3. Specifically, the CuO-based slag contains 50% or more CuO by mass, with the remainder being Al２ O ３ Fe ２ O ３ Fe ３ O ４ SiO ２ Preferably, it is at least one selected from and NiO. As will be explained in detail in the examples, using CuO-based slag increases the distribution rate of PGM to the electric furnace metal and improves the recovery efficiency of PGM compared to using CuO as a reagent. Therefore, it is preferable to use at least the above-mentioned CuO-based slag as the oxidizing agent 2. CuO-based slag may be used alone or in combination with a CuO reagent, etc. The production of CuO-based slag will be described later.

[0026] Flux 3 forms molten slag 6 upon heating, and SiO2 is an oxide of SiC contained in the workpiece 1. ２ This is for incorporating such substances. For example, flux 3 can be Al ２ O ３ SiO ２ One or more of CaO and FeO can be used.

[0027] The reducing agent 4 is used to adjust the atmosphere inside the electric furnace to a reducing atmosphere. As the reducing agent 4, carbon-containing materials such as C (carbon), CO gas, methane gas, or propane gas can be used. By creating a reducing atmosphere, the copper oxide dissolved in the molten slag 6 can be reduced.

[0028] In addition, in reductive smelting, an extractant may be used separately from the above. For example, elemental Cu metal can be used as the extractant.

[0029] Next, the material to be treated 1, oxidizing agent 2, flux 3, and reducing agent 4 are placed in an electric furnace and heated from room temperature to a predetermined temperature. At this time, the inside of the electric furnace becomes a reducing atmosphere due to the reducing agent. Also, the oxidizing agent 2, which contains CuO, melts upon heating, forming the electric furnace metal 5. In addition, the flux 3 forms a molten slag 6 mainly composed of oxides, and the molten slag 6 floats above the electric furnace metal 5. Meanwhile, the SiC contained in the material to be treated 1 is oxidized by the oxidizing agent 2 to form SiO ２As a result, after melting, it is collected in the molten slag 6. Furthermore, as the material to be processed 1 melts, the PGM supported on the SiC carrier alloys with Cu and settles in the electric furnace, becoming concentrated in the electric furnace metal 5. In other words, the PGM and SiC contained in the material to be processed 1 can be separated by the difference in specific gravity.

[0030] In the reduction smelting process, the heating temperature is not particularly limited as long as the charged material in the electric furnace can be melted. In this embodiment, SiC, which has a high thermal decomposition temperature of 2540°C, is used, and SiO, which has a lower thermal decomposition temperature, is used. ２ Since it is oxidized, the heating temperature can be lowered. Specifically, the heating temperature is preferably 1000°C to 1700°C, and more preferably 1300°C to 1500°C.

[0031] In the reduction smelting process, it is preferable that the carbon concentration in the molten slag 6 is 0.03% by mass or less. SiC oxidizes to SiO ２ and CO ２ and form CO ２ This will be released outside the system. On the other hand, the SiC that remains unoxidized is incorporated into the molten slag 6. In other words, the carbon in the molten slag 6 originates from the SiC that remains unoxidized, and its carbon concentration serves as an indicator of the degree of SiC oxidation. In this embodiment, SiC is converted to SiO ２ By oxidizing it, the residual SiC can be suppressed so that the carbon concentration of the molten slag 6 becomes 0.03% by mass or less, even while keeping the heating temperature low.

[0032] In the reduction smelting process, the time for heating and holding the charge is not particularly limited, but it is preferably 5 hours or less, more preferably 3 hours or less, and even more preferably 1 hour or more and 3 hours or less. In this embodiment, by using an oxidizing agent 2 containing CuO, the time required to oxidize and melt the SiC can be shortened, so even when the heating and holding time is within the above range, melting can be achieved while suppressing the remaining SiC.

[0033] The ratio of oxidizing agent 2 to material 1 is not particularly limited as long as all of the SiC contained in material 1 is oxidized. Generally, the SiC contained in material 1 and the CuO contained as oxidizing agent 2 react as shown below. Therefore, from the viewpoint of more reliably oxidizing SiC, it is preferable to add CuO in a molar ratio of 3 times or more relative to SiC. There is no particular upper limit, but for example, it is good if it is 10 times or less. SiC + 3CuO → SiO ２ +3Cu+CO

[0034] (First extraction step) Next, the molten slag 6 floating in the electric furnace is discharged, and the electric furnace metal 5 is extracted. The electric furnace metal 5 is an alloying material mainly composed of Cu and PGM, after impurities are removed as molten slag 6.

[0035] (Oxidation Smelting Process) Next, the extracted electric furnace metal 5 is transferred in its molten state to an oxidation furnace used for oxidation smelting, and oxidation smelting is carried out. Specifically, at least one of air and oxygen is blown into the electric furnace metal 5 to carry out oxidation. At this time in the oxidation furnace, the electric furnace metal 5 becomes a PGM alloy 7 in which PGM is further concentrated, and oxide-based Cu floating above it. ２ It will be separated into two layers with O-type slag 8. In the oxidation smelting process, Cu ２ The O-type slag 8 may be discharged outside the furnace, and the PGM alloy 7 may be subjected to repeated oxidation treatment and slag discharge to further concentrate the PGM.

[0036] Furthermore, Cu discharged in the oxidation smelting process ２ O-based slag 8 can be oxidized to form an oxidizing agent 2 containing CuO used in the reduction smelting process. Specifically, Cu ２ O-type slag 8 is Cu ２ O and Al ２ O ３ Fe ２ O ３ Fe ３ O ４ SiO ２ It comprises at least one selected from and NiO. Specifically, Cu ２ O-type slag is Cu ２It contains 50% or more O by mass, with the remainder being Al ２ O ３ Fe ２ O ３ Fe ３ O ４ SiO ２ Preferably, at least one selected from and NiO. ２ By oxidizing the O-based slag 8, a CuO-based slag containing CuO can be obtained.

[0037] Cu ２ The oxidation method for O-based slag 8 is not particularly limited, but heat treatment is preferred. The heating conditions are not particularly limited, but it is preferable to heat at 700°C or higher in an air atmosphere, more preferably at 800°C or higher in an air atmosphere. The upper limit of the heating temperature is not particularly limited, but if it exceeds 1000°C, the effect of oxidation roasting by heating becomes saturated, so from the viewpoint of production cost and equipment cost, it is preferable to keep the heating temperature below 1000°C. Also Cu ２ O-type slag 8 may be subjected to heat treatment as is, but from the viewpoint of uniform oxidative roasting, it is preferable to crush it, preferably after water granulation, before heat treatment. The particle size after crushing is preferably 600 μm or less. The heat treatment time depends on the amount of Cu contained in the slag. ２ The process is not particularly limited as long as it allows for the oxidation of O to CuO, but for example, it is recommended to oxidize it for more than one hour.

[0038] CuO-based slag is obtained in the oxidation smelting process. ２ It is obtained by oxidizing O-based slag 8. By using this CuO-based slag as an oxidizing agent 2 and an extractant in the reduction smelting process, Cu ２ The O-type slag 8 can be circulated within the system without being discharged outside the system. Therefore, not only can production costs be reduced, but Cu ２ When PGM is mixed into O-type slag 8, it becomes possible to recover the PGM without discharging it outside the system.

[0039] (Second extraction step) Next, the concentrated PGM alloy 7 is extracted. PGM alloy 7 is obtained by oxidizing the electric furnace metal 5 and then Cu ２This alloy material is obtained by removing the O-based slag 8 and mainly contains Cu and PGM, with a higher PGM content than the electric furnace metal 5. PGM can be recovered from the PGM alloy 7 by, for example, a conventionally known wet method.

[0040] As described above, PGM can be recovered from the processed material 1 containing SiC and PGM.

[0041] <Effects of this embodiment> This embodiment provides one or more of the following effects.

[0042] (a) In this embodiment, the material to be treated, which includes SiC and PGM, is reduced and smelted using an oxidizing agent containing CuO, thereby reducing the SiC to SiO ２ The PGM supported on the SiC carrier can be oxidized and suspended as molten slag, while simultaneously settling into the Cu-containing electric furnace metal. Using an oxidizing agent containing CuO shortens the time required for oxidation and melting of the SiC, i.e., the time required for reductive smelting. Moreover, since the SiC can be oxidized efficiently, the processing time can be shortened while suppressing residual SiC and ensuring that the PGM supported on the SiC settles reliably using the electric furnace metal. In other words, by concentrating the PGM contained in the material being processed using the electric furnace metal during reductive smelting, the PGM can be recovered from the electric furnace metal with high efficiency during the subsequent oxidative smelting.

[0043] Oxidizing agents containing CuO are Cu ２ Compared to oxidizing agents containing oxygen, the time required to oxidize and melt SiC can be shortened. This is thought to be because CuO contains a relatively large amount of oxygen per mole of copper. Also, impurities contained in the slag (e.g., FeO) Ｘ o SiO ２ ) is Cu ２ It is conceivable to reduce the activity coefficient of O and thereby decrease its oxidizing effect. In other words, Cu ２ O is susceptible to the effects of impurities and is thought to be less able to exhibit its inherent oxidizing properties. On the other hand, CuO is Cu ２Compared with O, the decrease in the activity coefficient due to impurities is suppressed, and it is considered that the original oxidation action is likely to be expressed. Therefore, since the oxidizing agent containing CuO is excellent in oxidizing SiC, not only the reaction time can be shortened, but also the reaction rate of oxidizing SiC to SiO ２ becomes higher.

[0044] (b) The object to be treated preferably contains crushed DPF. Also, it is preferable that the particle size of the crushed material is 600 μm or less. By making the object to be treated into crushed material with a particle size of 600 μm or less, SiC in the object to be treated can be more surely oxidized to SiO ２ and melted during the reduction smelting. As a result, PGM can be recovered from the object to be treated at a higher yield.

[0045] (c) The oxidizing agent is preferably CuO-based slag. According to the CuO-based slag, the mixing of PGM into the molten slag during the reduction smelting can be suppressed, and the sedimentation of PGM into the electric furnace metal can be promoted. As a result, PGM can be recovered from the object to be treated at a higher yield. Also, according to the CuO-based slag, since it can be obtained by heat-treating the Cu ２ O-based slag generated when the electric furnace metal is oxidized and smelted, the Cu ２ O-based slag can be circulated in the system without being discharged out of the system. Thereby, it becomes possible to recover the PGM mixed in the Cu ２ O-based slag without discharging it out of the system.

[0046] (d) In the reduction smelting process, it is preferable to perform heating and melting so that the carbon concentration contained in the molten slag becomes 0.03 mass% or less. During the reduction smelting, unreacted SiC may be mixed into the molten slag. However, in this embodiment, SiC is oxidized to SiO ２ and melted, and the remaining of unreacted SiC can be suppressed, so the carbon concentration of the molten slag can be made 0.03 mass% or less.

[0047] In this example, reduction smelting was performed by changing the type of oxidizing agent for SiC-made PDF, and the change in the reaction rate of oxidation depending on the holding time was evaluated.

[0048] (Example 1) (1) Reduction smelting of SiC-based DPF In Example 1, reduction smelting of SiC-based DPF was carried out using a CuO-based slag as an oxidant in a test apparatus 20 modeled on the electric furnace shown in Fig. 2. Fig. 2 is a schematic cross-sectional view of the test apparatus for performing reduction smelting.

[0049] First, a SiC-based DPF to be processed and an oxidant were prepared.

[0050] The component concentrations of the SiC-based DPF used in this example are shown in Table 1 below. Also, the SiC-based DPF is composed of powder by crushing, and its particle size is 100 μm to 600 μm.

[0051]

[0052] Also, the CuO-based slag as an oxidant was obtained by granulating the CuO-based slag generated in the oxidation furnace of the above-mentioned ROSE process, screening it to select particles with a particle size of 600 μm or less, and performing oxidative roasting at 750 °C for 17 hours with an air volume of 140 mL / min using a horizontal furnace. The component concentrations of the prepared CuO-based slag are shown in Table 2 below. ２ Subsequently, reagents of Al2O3, CaO, and SiO2 with a purity of 99% or more were weighed and mixed so that the component concentration of the initial slag was 35% by mass of Al2O3, 30% by mass of CaO, and 35% by mass of SiO2. 41.1 g of this mixed sample and 3.36 g of metallic Cu were loaded into the alumina crucible 21 shown in Fig. 2. Also, a carbon plate 23 with a thickness of about 10 mm was laid at the bottom of the reaction tube 22 for the purpose of making the inside of the reaction tube 22 a reducing atmosphere, and the alumina crucible 21 was placed thereon. While flowing Ar gas at about 0.2 L / min from the upper and lower parts of the reaction tube 22, the temperature was raised from room temperature to 1450 °C in 3 h by the SiC heating element 24 and held for 2 h to melt the metallic Cu 11 and the initial slag 12. Then, the Ar gas was stopped, and through a quartz tube with an inner diameter of 8 mm, the powdered SiC-based DPF and Al2O3 as a flux

[0053]

[0054] Then, the component concentration of the initial slag was Al2O3 ２ O ３ 35% by mass - CaO 30% by mass - SiO2 ２ 35% by mass, and reagents of Al2O3, CaO, and SiO2 with a purity of 99% or more were weighed and mixed. ２ O ３ 、CaO、SiO2 ２ were weighed and mixed. 41.1 g of this mixed sample and 3.36 g of metallic Cu were loaded into the alumina crucible 21 shown in Fig. 2. Also, a carbon plate 23 with a thickness of about 10 mm was laid at the bottom of the reaction tube 22 for the purpose of making the inside of the reaction tube 22 a reducing atmosphere, and the alumina crucible 21 was placed thereon. While flowing Ar gas at about 0.2 L / min from the upper and lower parts of the reaction tube 22, the temperature was raised from room temperature to 1450 °C in 3 h by the SiC heating element 24 and held for 2 h to melt the metallic Cu 11 and the initial slag 12. Then, the Ar gas was stopped, and through a quartz tube with an inner diameter of 8 mm, the powdered SiC-based DPF and Al2O3 as a flux ２ O３ CaO and the charge 13, such as CuO-based slag as an oxidizing agent, were placed into the crucible 21. ２ O ３ CaO is the composition of the slag after testing, which is 35% by mass of Al ２ O ３ -30% by mass CaO -35% by mass SiO ２ The input amounts were set so as not to change from the original values. The input amounts for each component are shown in Table 3 below.

[0055]

[0056] Next, the entire amounts of DPF, flux, and oxidizing agent were added, and the mixture was held in a molten state for a predetermined time. In this example, the holding time was changed to 1 hour, 3 hours, and 5 hours. After the predetermined time had elapsed, the crucible 21 was removed from the reaction tube 22 and rapidly cooled with water. This solidified the molten material inside the crucible 21. After that, the crucible 21 was cut with a diamond cutter to separate the slag phase and the metal phase, and each phase was recovered.

[0057] (Example 2) In Example 2, the type of oxidizing agent was changed from CuO-based slag to a CuO reagent with a purity of 99.5% by mass, and the amount of initial slag and flux added was appropriately changed as shown in Table 3. Otherwise, the reduction smelting was carried out in the same manner as in Example 1, and the slag phase and metal phase were recovered.

[0058] (Comparative Example 1) In Comparative Example 1, as shown in Table 3, the type of oxidizing agent was changed from CuO-based slag to CaCO3 ３ Except for making appropriate changes to the reagents, flux type, and initial slag input amount, the reduction smelting was carried out in the same manner as in Example 1, and the slag phase and metal phase were recovered.

[0059] (Comparative Example 2) In Comparative Example 2, as shown in Table 3, the type of oxidizing agent was changed from CuO-based slag to Cu ２ Except for making appropriate changes to the reagent O, the type of flux, and the amount of initial slag added, the reduction smelting was carried out in the same manner as in Example 1, and the slag phase and metal phase were recovered.

[0060] (2) Evaluation In this embodiment, the obtained slag phase and metal phase were evaluated for SiC oxidation and melting, carbon concentration of the slag phase, SiC reaction rate, PGM concentration, and PGM partition rate. Each evaluation is described below.

[0061] (Oxidative Melting of SiC) The oxidative melting of SiC was evaluated by performing XRD measurements on the slag phase and the metal phase, respectively. Specifically, the presence or absence of a SiC peak was checked from the XRD measurement results of the slag phase and the metal phase obtained at holding times of 1 h, 3 h, and 5 h. If no peak was detected, it was evaluated that SiC was not present and that the SiC had been oxidized and melted. On the other hand, if a SiC peak was detected, it was evaluated that unreacted SiC remained and that the oxidative melting of SiC was insufficient. The XRD measurement results of each phase for Example 1 and Comparative Example 1 are shown in Figures 3 and 4. Figure 3 shows the XRD measurement results of the slag phase and the metal phase after reductive smelting of the SiC DPF in Example 1. Figure 4 shows the XRD measurement results of the slag phase and the metal phase after reductive smelting of the SiC DPF in Comparative Example 1.

[0062] As shown in Figure 3, in Example 1, no SiC peak was observed regardless of the holding time. This suggests that the SiC was oxidized and melted during the reductive smelting process. Similarly, in Example 2, where a CuO reagent was used instead of CuO-based slag, no SiC peak was observed regardless of the holding time, just as in Example 1. On the other hand, when CaCO was used as the oxidizing agent... ３ In Comparative Example 1, as shown in Figure 4, it was confirmed that the peak intensity of SiC decreased as the holding time increased. From this, it is thought that SiC oxidizes and melts over time. However, since the SiC peak was still detected even after a holding time of 5 hours, CaCO3 was detected as the oxidizing agent. ３ When using this method, it was confirmed that SiC could not be sufficiently oxidized and melted in 5 hours. In other words, CaCO ３ This confirmed that SiC cannot be oxidized and melted in a short time.

[0063] (Carbon concentration of the slag phase) The carbon concentration of the slag phase is the carbon concentration derived from unreacted SiC and serves as an indicator for evaluating the degree of oxidative melting of SiC. In this example, the carbon concentration of the slag phase was measured using a carbon-sulfur analyzer (CS744 model, manufactured by LECO Japan LLC). Specifically, four locations were selected in the slag phase: the top, upper, lower, and near the metal phase. The carbon concentration at each location was measured, and the average value was taken as the carbon concentration of the slag phase. The carbon concentrations of the slag phase obtained for each holding time are shown in Table 4 below.

[0064]

[0065] As shown in Table 4, in Example 1, which used CuO-based slag as the oxidizing agent, and in Example 2, which used CuO reagent, the carbon concentration of the slag phase was confirmed to be low, at 0.03% by mass or less, regardless of the holding time. From this, it was confirmed that when CuO is used as the oxidizing agent, the oxidation and melting of SiC proceeds during reductive smelting, and unreacted SiC is less likely to remain. On the other hand, when CaCO3 was used as the oxidizing agent... ３ In Comparative Example 1, which used [the specified method], it was confirmed that the carbon concentration of the slag phase exceeded 0.03% by mass. From this, it was determined that [the specified method] was used as the oxidizing agent. ３ Even when using [a specific method], it was confirmed that the oxidation and melting of SiC did not proceed during the reductive smelting process, and that SiC remained unreacted. Furthermore, when using Cu as the oxidizing agent... ２ In Comparative Example 2, which used O, the oxidation and melting of SiC progressed more effectively than in Comparative Example 1. However, the carbon concentration in the slag phase exceeded 0.03% by mass, indicating that the oxidation and melting were insufficient.

[0066] (Reaction rate of SiC) The reaction rate of SiC represents the reaction rate of oxidation by reductive smelting and was determined based on the following formula (1). Here, C Ｓｌａｇ (Mass %) is the carbon concentration of the slag phase shown in Table 4, C ０(Mass %) represents the carbon concentration in the slag when the SiC DPF added to the slag has not reacted with the slag, and was set to 0.708 mass %. The carbon concentration of the SiC DPF used in this example was 17.7 mass %. The reaction rates for each example are shown in Table 5 below. The correlation between holding time and the reaction rate of SiC is shown in Figure 5. Figure 5 is a diagram showing the correlation between holding time and the reaction rate of SiC. In Figure 5, the horizontal axis represents the holding time Time [h], and the vertical axis represents R (Reaction Rate) [%] calculated by the above formula (1).

[0067]

[0068] As shown in Figure 5, it was confirmed that in both the CuO-based slag used in Example 1 and the CuO reagent used in Example 2, the reaction rate of SiC could be increased to 96% or more when the holding time was 1 hour. On the other hand, the CaCO2 used in Comparative Example 1 ３ When the holding time was 1 hour, the reaction rate of SiC was less than 40%. Furthermore, it was confirmed that the increase in the reaction rate with increasing holding time was gradual. From this, it was determined that the oxidizing agent containing CuO is CaCO3. ３ In comparison, it was found that the time required to oxidize and melt SiC could be shortened. Also, the Cu used in Comparative Example 2 ２ In O, the reaction rate of SiC was high even in a short time, but it was confirmed to be at most about 70%. From this, Cu ２ In O, it was found that the oxidation and melting of SiC did not proceed sufficiently compared to the CuO in Examples 1 and 2.

[0069] (PGM Concentration) The PGM concentration was determined to evaluate the distribution behavior of PGM into the metal phase and slag phase during reductive smelting. In this example, the concentrations of PGM contained in the metal phase and slag phase were measured using ICP-MS (Agilent Technologies, Agilent 7700x) (the same method was used for subsequent measurements). The concentrations of PGM contained in the metal phase are shown in Table 6 below, and the concentrations of Cu and PGM contained in the slag phase are shown in Table 7 below.

[0070]

[0071]

[0072] (PGM distribution ratio) The PGM distribution ratio indicates the distribution ratio of PGM to the slag phase and the metal phase. In this embodiment, the PGM distribution ratio (L) is calculated from the concentrations of PGM contained in the metal phase and the slag phase based on the following formula (2). ｓ／Ｃｕ Ｘ The PGM distribution ratio was calculated. The PGM distribution ratio is expressed as the ratio of the concentration of PGM in the slag phase to the concentration of PGM in the metal phase. A smaller distribution ratio indicates less PGM contamination in the slag phase and greater concentration of PGM in the metal phase. In this example, the correlation between the distribution behavior of each component Pt, Pd, and Rh in the slag and metal phases and the retention time was evaluated. The correlation is shown in Figure 6. Figure 6 is a diagram showing the correlation between the distribution ratio of PGM in the slag and metal phases and the retention time. The horizontal axis shows the retention time [h], and the vertical axis shows the distribution ratio [%] calculated by equation (2). ｓ／Ｃｕ Ｘ =(Xin slag [mass%]) / (Xin C ｕ [Mass %]) ... Equation (2) In Equation (2), X represents the concentration of Pt, Pd, and Rh.

[0073] As shown in Figure 6, when using CuO-based slag and CuO reagent, CaCO2 ３ Ya Cu ２ It was confirmed that the distribution rate of PGM could be reduced compared to the case using O. In other words, it was confirmed that the mixing of PGM into the slag phase could be suppressed, and that PGM could settle into the metal phase at a higher rate than the slag phase. Specifically, CaCO ３ While the partition ratio is 1 or higher in the case of CuO-based slag and CuO reagent, it was confirmed that the partition ratio can be reduced to 0.1 or lower. ２ O is CaCO ３ It was confirmed that the distribution ratio could be reduced to a smaller degree than with CuO, but not to the same degree as with CuO. Furthermore, it was confirmed that when using CuO-based slag, the distribution ratio could be reduced even further than when using CuO reagent, and that the distribution ratio could be reduced to 0.01 or less.

[0074] As described above, by reducing and smelting a workpiece containing SiC and PGM using an oxidizing agent containing CuO, SiC can be converted to SiO in a short time. ２It was confirmed that PGM could be oxidized to form molten slag, while PGM could be concentrated into electric furnace metal. In other words, it was confirmed that PGM could be recovered quickly and efficiently from materials containing SiC and PGM.

[0075] 1. Material to be treated 2. Oxidizing agent / extracting agent 3. Flux 4. Reducing agent 5. Electric furnace metal 6. Molten slag 7. PGM alloy 8. Cu ２ O-based slag 11 Metallic Cu 12 Initial slag 13 Charge 20 Test apparatus 21 Crucible 22 Reaction tube 23 Carbon plate 24 SiC heating element

Claims

1. A method for recovering PGM, comprising: a reduction smelting step of mixing a workpiece containing SiC and PGM with an oxidizing agent containing CuO, a flux, and a reducing agent, heating these in a reducing atmosphere to melt them and form molten slag and electric furnace metal containing the PGM; and an extraction step of extracting the electric furnace metal.

2. The method for recovering PGM according to claim 1, wherein the material to be processed is crushed material containing at least a diesel particulate filter.

3. The method for recovering PGM according to claim 2, wherein the particle size of the treated material is 600 μm or less.

4. The oxidizing agent contains 50% or more CuO by mass, with the remainder being Al ２ O ３ Fe ２ O ３ Fe ３ O ４ SiO ２ A method for recovering PGM according to claim 1 or claim 2, comprising a CuO-based slag containing at least one selected from and NiO.

5. The method for recovering PGM according to claim 1 or claim 2, wherein the heating temperature in the reduction smelting step is 1000°C to 1700°C.

6. The method for recovering PGM according to claim 1 or claim 2, wherein the reduction smelting step is performed by heating and melting so that the carbon concentration contained in the molten slag is 0.03% by mass or less.

7. A method for recovering PGM according to claim 1 or 2, comprising an oxidation smelting step after the extraction step, in which the electric furnace metal is oxidized and smelted to form a slag and a PGM alloy, and the PGM alloy is recovered.

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