Methods for recovering platinum group metals

Abstract

To provide a method for recovering platinum group metal other than platinum which is reduced in an environmental load and energy consumption.SOLUTION: A method for recovering platinum group metal includes the steps of: (1a) bringing a substance containing at least platinum group metal selected from palladium, ruthenium, osmium, iridium and rhodium into contact with a molten salt containing an iron halide, and obtaining a treated object in which a halide of the platinum group metal is dissolved in the molten salt; (2a) cooling the treated object, and obtaining a solid; (3a) treating the solid using water or an aqueous solution in which the halide of the platinum group metal is soluble, and obtaining a water dispersion, or treating the solid using an organic solvent in which the halide of the platinum group metal is hardly soluble, and obtaining a dispersion; and (4a) separating a liquid containing a component containing the platinum group metal from the water dispersion, or separating the solid containing the halide of the platinum group metal from the dispersion.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This disclosure relates to a method for recovering platinum group metals. [Background technology]

[0002] Platinum group metals, represented by platinum (Pt), palladium (Pd), and rhodium (Rh), are important metals not only for their use in jewelry and assets, but also for industrial applications. Due to their high catalytic activity and chemical stability, platinum group metals are frequently used as catalysts in automobiles.

[0003] Due to their scarcity as a resource and the significant environmental impact of their smelting process, platinum group metals are actively recycled from used products such as end-of-life automotive catalysts. Recycling methods for platinum group metals are broadly classified into two types: wet processes, which involve dissolving the substance containing the platinum group metals in chemicals, and dry processes, which involve treating the substance at high temperatures. In wet processes, platinum group metals are often dissolved using aqua regia or hydrochloric acid-chlorine systems. In dry processes, the above-mentioned substances are added to the base metal smelting process, and molten copper (Cu) and lead (Pb) are used as collector metals to concentrate and recover the platinum group metals. The platinum group metals concentrated by the collector metals are then primarily processed using wet processes.

[0004] However, the aqua regia or hydrochloric acid-chlorine systems used in wet processes have a significant environmental impact during wastewater treatment. Furthermore, rhodium and iridium are poorly soluble in aqua regia, making them difficult to treat using conventional processes. On the other hand, processes using collector metals in dry processes consume a lot of energy, and since the final treatment and purification are carried out using wet processes, the problem of wastewater generation remains unresolved.

[0005] Therefore, various methods have been proposed for the development of environmentally friendly processes, and in recent years, methods using molten salts have also been proposed. For example, Patent Document 1 discloses a method in which ore is placed in a composite molten salt of ammonium nitrate (NH4NO3) and ammonium chloride (NH4Cl) to directly chlorinate and recover the platinum contained in the ore. Non-Patent Document 1 discloses a method for recovering platinum using a composite molten salt of iron(III) chloride (FeCl3) and potassium chloride (KCl). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] U.S. Patent No. 3,988,415 [Non-patent literature]

[0007] [Non-Patent Document 1] Journal of the Japan Institute of Metals, Vol. 83, No. 1 (2019), pp. 23-29 [Overview of the project] [Problems that the invention aims to solve]

[0008] Conventional methods using molten salts have the problem of high dissolution temperatures and high energy consumption. Furthermore, the method disclosed in Patent Document 1 has the problem of difficulty in handling ammonium nitrate. On the other hand, the method disclosed in Non-Patent Document 1 has the advantage of low dissolution temperatures and low energy consumption. However, Non-Patent Document 1 does not disclose any examples of applying this method to platinum group metals other than platinum. Also, for example, used automotive catalysts contain multiple types of platinum group metals, making it important to separate and recover each of these platinum group metals.

[0009] One of the objectives of this disclosure is to provide a method for recovering platinum group metals other than platinum that has a low environmental impact and energy consumption.

[0010] One of the objectives of this disclosure is to provide a method for recovering platinum group metals that has a low environmental impact and energy consumption, and that is capable of separating and recovering multiple types of platinum group metals. [Means for solving the problem]

[0011] The first method for recovering platinum group metals as disclosed herein is: (1a) A process of contacting a substance containing at least one platinum group metal selected from palladium, ruthenium, osmium, iridium, and rhodium with a molten salt containing an iron halide to obtain a treated product in which the platinum group metal halide is dissolved in the molten salt. (2a) A step of cooling the above processed material to obtain a solid, (3a) A step of treating the above solid with water or an aqueous solution in which the platinum group metal halide is soluble to obtain an aqueous dispersion, or a step of treating the above solid with an organic solvent in which the platinum group metal halide is sparingly soluble to obtain a dispersion, and (4a) A step of separating a liquid containing the platinum group metal component from the aqueous dispersion, or a step of separating a solid containing the platinum group metal halide from the dispersion. Includes.

[0012] The second method for recovering platinum group metals in this disclosure is: (1b) A step of contacting a substance containing a first platinum group metal and a second platinum group metal with a molten salt containing an iron halide to obtain a treated product in which the halide of the first platinum group metal and the halide of the second platinum group metal are dissolved in the molten salt. (2b) A step of cooling the above processed material to obtain a solid, (3b) A step of treating the above solid with water or an aqueous solution in which the first platinum group metal halide is soluble and the second platinum group metal halide is sparingly soluble to obtain an aqueous dispersion, and (4b) A step of separating the aqueous dispersion into a liquid containing a component containing a first platinum group metal and a solid residue containing a halide of a second platinum group metal. Includes. [Effects of the Invention]

[0013] According to the present disclosure, a method for recovering platinum group metals other than platinum with low environmental impact and low energy consumption can be provided. According to the present disclosure, a method for recovering platinum group metals with low environmental impact and low energy consumption and capable of separating and recovering multiple types of platinum group metals can be provided.

Brief Description of the Drawings

[0014] [Figure 1] FIG. 1 is an Ellingham diagram for chlorides of iron and palladium. [Figure 2] FIG. 2 is an example of the flow of the first method for recovering platinum group metals of the present disclosure. [Figure 3] FIG. 3 is an example of the flow of the second method for recovering platinum group metals of the present disclosure. [Figure 4] FIG. 4 is a graph showing the change in the dissolution amount of the sample in Example 1. [Figure 5] FIG. 5 is a graph showing the change in the dissolution amount of the sample in Example 2. [Figure 6] FIG. 6 is a graph showing the change in the dissolution amount of the sample in Example 3. [Figure 7] FIG. 7 is a graph showing the change in the dissolution amount of the sample in Example 3. [Figure 8] FIG. 8 is an example of the flow of the first method for recovering platinum group metals of the present disclosure.

Modes for Carrying Out the Invention

[0015] In this specification, "A~B" indicating a numerical range includes the numerical values A and B described before and after "~" as the lower limit value and the upper limit value, or the upper limit value and the lower limit value. For example, "1~10" means a numerical range of 1 or more and 10 or less.

[0016] [First method for recovering platinum group metals] The first method for recovering platinum group metals of the present disclosure is (1a) A process of contacting a substance containing at least one platinum group metal selected from palladium, ruthenium, osmium, iridium, and rhodium with a molten salt containing an iron halide to obtain a treated product in which the platinum group metal halide is dissolved in the molten salt. (2a) A step of cooling the above processed material to obtain a solid, (3a) A step of treating the above solid with water or an aqueous solution in which the platinum group metal halide is soluble to obtain an aqueous dispersion, or a step of treating the above solid with an organic solvent in which the platinum group metal halide is sparingly soluble to obtain a dispersion, and (4a) A step of separating a liquid containing a platinum group metal component from the aqueous dispersion, or a step of separating a solid containing a platinum group metal halide from the dispersion. Includes.

[0017] The above molten salt is preferably a molten salt of a mixture containing iron halide and an alkali metal or alkaline earth metal halide. Hereinafter, this molten salt of mixture will also be referred to as a "composite molten salt".

[0018] The first method for recovering platinum group metals according to this disclosure is, in one embodiment, (5a) A step of adding a platinum group metal precipitant to the above liquid, precipitating the components containing platinum group metals, recovering the precipitated components (precipitates), and calcining them, or (5a') A process including steps (5a'-1) to (5a'-2) described later. It also includes.

[0019] <Process (1a)> In step (1a), for example, a substance containing the platinum group metal is brought into contact with an iron halide or a mixture containing an iron halide and heated. This melts the iron halide or the mixture to form a molten salt, and the platinum group metal is converted into a halide, preferably a chloride, and dissolved in the molten salt.

[0020] In step (1a), a substance containing the platinum group metal may also be added to the molten salt. This converts the platinum group metal into a halide, which then dissolves in the molten salt.

[0021] The above contact is preferably carried out under dry conditions, i.e., in the absence of water or organic solvents. Hereinafter, the series of operations described above in process (1a) for platinum group metals will also be referred to as the "dissolution process".

[0022] Examples of materials containing platinum group metals include catalysts such as those used for purifying vehicle exhaust gases and petrochemical catalysts, electronic materials such as electronic circuit boards and lead frames, platinum group metal-containing blast powder, permanent magnets, crucibles, and scraps, recycled materials, or waste materials generated during the manufacturing process of these materials. Other examples include ores containing platinum group metals and jewelry containing platinum group metals.

[0023] A catalyst, such as a catalyst for purifying vehicle exhaust gases, in one embodiment comprises a carrier and a platinum group metal, which is a catalyst component, supported on the carrier. Examples of carriers include ceramic carriers made of alumina or silica, and SUS carriers. Examples of carrier shapes include honeycomb and pellet shapes. Examples of platinum group metals include combinations of platinum and palladium, platinum and rhodium, palladium and rhodium, and platinum, palladium and rhodium, and specifically, a platinum-palladium-rhodium ternary catalyst component. The carrier can be separated from the catalyst by conventionally known methods such as pulverization or elution using acid, or by appropriately combining these methods. Examples of crucibles include crucibles for semiconductor manufacturing, specifically iridium crucibles.

[0024] In the first method for recovering platinum group metals according to this disclosure, the platinum group metal is at least one selected from palladium, ruthenium, osmium, iridium, and rhodium, preferably at least one selected from palladium, iridium, and rhodium, and more preferably at least one selected from palladium and rhodium. In the first recovery method, the substance may also contain platinum. The above substance contains one or more platinum group metals.

[0025] This disclosure uses at least one or more types of iron halides. Iron halides are used to halogenate platinum group metals and dissolve them in a molten salt. In other words, iron halides are halogenating agents, particularly chlorinating agents, for platinum group metals, and therefore this disclosure does not require chlorine gas or the like. Furthermore, iron halides can be melted at low temperatures, contributing to a reduction in energy consumption during the dissolution process.

[0026] Examples of iron halides include iron(III) chloride (FeCl3), iron(III) bromide (FeBr3), and iron(III) iodide (FeI3), with iron(III) chloride being preferred from the viewpoint of being able to effectively chlorinate platinum group metals.

[0027] The amount of iron halide used is preferably 1 to 200 moles, more preferably 5 to 150 moles, and even more preferably 10 to 100 moles, per mole of platinum group metal contained in the above substance. By using iron halide within this range, the platinum group metal can be effectively halogenated, and thus the platinum group metal can be dissolved in the molten salt.

[0028] In this disclosure, it is preferable to use a molten salt of a mixture containing iron halide and an alkali metal or alkaline earth metal halide. The alkali metal halide may be one or more types. The alkaline earth metal halide may be one or more types. Alkali metal halides and alkaline earth metal halides may be used in combination.

[0029] Some iron halides, such as iron(III) chloride, have close melting and boiling points, and these compounds may have high vapor pressures near their melting point. Alkali metal or alkaline earth metal halides can be used to lower the melting temperature of halogenating agents (iron halides) for platinum group metals. This improves the handling of the molten salt and further reduces energy consumption during the dissolution process.

[0030] Examples of alkali metal halides include lithium fluoride, sodium fluoride, potassium fluoride, rubidium fluoride, cesium fluoride, lithium chloride, sodium chloride, potassium chloride, rubidium chloride, cesium chloride, lithium bromide, sodium bromide, potassium bromide, rubidium bromide, cesium bromide, lithium iodide, sodium iodide, potassium iodide, rubidium iodide, and cesium iodide.

[0031] Examples of alkaline earth metal halides include magnesium fluoride, calcium fluoride, barium fluoride, strontium fluoride, magnesium chloride, calcium chloride, barium chloride, strontium chloride, magnesium bromide, calcium bromide, barium bromide, strontium bromide, magnesium iodide, calcium iodide, barium iodide, and strontium iodide.

[0032] Among these, alkali metal chlorides are preferred, sodium chloride and potassium chloride are more preferred, and potassium chloride is particularly preferred, from the viewpoint of being able to effectively lower the melting temperature of the above mixture.

[0033] The amount of alkali metal or alkaline earth metal halide used is preferably 0.1 to 10 moles, more preferably 0.2 to 5 moles, even more preferably 0.5 to 2 moles, and particularly preferably 0.8 to 1.2 moles per mole of iron halide. By using alkali metal or alkaline earth metal halide within this range, the melting temperature of the above mixture can be effectively lowered.

[0034] The heating temperature for melting the iron halide or the above mixture is preferably above the melting temperature of the iron halide or the above mixture and below 450°C, more preferably 250 to 420°C, even more preferably 255 to 400°C, and particularly preferably 280 to 380°C. By heating at such temperatures, the platinum group metal dissolves in the molten salt. Conventional methods using molten salts require dissolution treatment at 500°C or higher, so the method disclosed herein has lower energy consumption and environmental impact compared to such methods.

[0035] The processing time for the dissolution treatment is preferably 0.1 to 20 hours, more preferably 0.3 to 15 hours, even more preferably 0.5 to 10 hours, and even more preferably 1 to 10 hours, 2 to 10 hours, or 4 to 10 hours. During the dissolution treatment, the molten salt may be stirred from the viewpoint of improving the dissolution rate of the platinum group metals. The atmosphere during the dissolution process is, for example, an inert gas atmosphere such as argon and nitrogen.

[0036] The following describes embodiments using a substance containing palladium as a platinum group metal and a composite molten salt (a composite molten salt of a mixture of iron(III) chloride and potassium chloride) containing iron(III) chloride as an iron halide and potassium chloride as an alkali metal halide.

[0037] The standard Gibbs free energy of formation for iron(III) chloride, iron(II) chloride (FeCl2), and palladium(II) chloride (PdCl2), as well as the standard reaction Gibbs free energy for the chlorination reaction from iron(II) chloride to iron(III) chloride, were calculated using the FactSage database (CW Bale, E. Belisle, P. Chartrand, SA Decterov, G. Eriksson, K. Hack, I.-H. Jung, Y.-B. Kang, J. Melancon, AD Pelton, C. Robelin and S. Petersen: Calphad., 33(2009), 295-31). Figure 1 shows the Ellingham diagrams for iron and palladium chlorides.

[0038] Comparing the standard Gibbs free energy change associated with palladium chlorination with that associated with the chlorination reaction from iron(II) chloride to iron(III) chloride, it can be seen that the former is larger than the latter.

[0039] Assuming that palladium(II) chloride is produced by the reaction shown in equation (1), the Gibbs free energy change for 1 mole of palladium is calculated to be -90.3 kJ at 327°C (600 K). Thus, within the temperature range shown in Figure 1, palladium chloride is considered to proceed spontaneously. Pd + 2FeCl3 → PdCl2 + 2FeCl2 (1)

[0040] Therefore, it is thought that by adding palladium to a molten salt of iron(III) chloride, the iron(III) chloride acts as a chlorinating agent for the palladium, producing palladium chloride, and the palladium dissolves in the molten salt. In this embodiment, since potassium chloride is mixed with iron(III) chloride, it is thought that potassium palladium(II) chloride (K2[PdCl4]) is produced by the reaction shown in formula (2). If the above substance also contains platinum in addition to palladium, it is thought that potassium chlorplatin(IV) chloride (K2[PtCl6]) is also produced by the reaction shown in formula (3). In the case of rhodium, it is thought that potassium rhodium(III) chloride (K3[RhCl6]) is produced by the reaction shown in formula (4). In the case of iridium, it is thought that potassium iridium(III) chloride (K3[IrCl6]) is produced by the reaction shown in formula (5).

[0041] Pd+2FeCl3+2KCl → K2[PdCl4]+2FeCl2(2) Pt+4FeCl3+2KCl → K2[PtCl6]+4FeCl2(3) Rh+3FeCl3+3KCl → K3[RhCl6]+3FeCl2(4) Ir+3FeCl3+3KCl → K3[IrCl6]+3FeCl2(5)

[0042] In the above embodiment, an example was described in which a composite molten salt of a mixture containing palladium as a platinum group metal and iron(III) chloride as an iron halide and potassium chloride as an alkali metal halide was used. By calculating the standard reaction Gibbs free energy of the halogenation reaction of the platinum group metal and the standard formation Gibbs free energy of the iron halide using thermodynamic calculation software, a molten salt containing a dissolved platinum group metal halide can be appropriately obtained in cases other than those described above.

[0043] <Process (2a)> In step (2a), the treated material obtained in step (1a) is cooled and solidified to form a solid. This solid contains a platinum group metal halide, preferably a platinum group metal chloride (for example, potassium palladium(II) chloride, potassium rhodium(III) chloride, or potassium iridium(III) chloride).

[0044] The cooling temperature is not particularly limited as long as it is below the melting temperature of the iron halide or the above mixture, but is preferably 95°C or lower, more preferably 5 to 80°C, and even more preferably 10 to 60°C, and in one embodiment it is room temperature. As for the cooling method, conventionally known cooling methods can be used, or the treated material may be left standing in a room temperature environment.

[0045] <Process (3a)> In step (3a), in one embodiment, the solid obtained in step (2a) is treated with water or an aqueous solution in which the platinum group metal halide is soluble to obtain an aqueous dispersion. For example, the solid is immersed in water or an aqueous solution. This operation of dissolving specific components contained in a solid in water or an aqueous solution is generally called "leaching," and the water or aqueous solution used as the dissolving medium is sometimes called the "leaching solution." As a result, the platinum group metal halide (e.g., potassium palladium(II) chloride, potassium rhodium(III) chloride, or potassium iridium(III) chloride) contained in the solid dissolves in water or an aqueous solution. Potassium palladium(II) chloride, potassium rhodium(III) chloride, and potassium iridium(III) chloride are readily soluble or soluble in water.

[0046] In step (3a), in one embodiment, water or an aqueous solution in which the platinum group metal halide is soluble is used as the leaching liquid. Since water or an aqueous solution is used as the leaching liquid, wastewater treatment is easy, and the recovery method of this disclosure has a small environmental impact. Examples of aqueous solutions include aqueous solutions of alkali metal salts such as aqueous potassium chloride, aqueous sodium chloride, and aqueous sodium nitrite. When the above aqueous solutions are used as the leaching liquid, the platinum group metal halide may be dissolved in the aqueous liquid in the form of other salts.

[0047] The concentration of the alkali metal salt in the aqueous solution is preferably 0.1 to 30 g / 100 mL, more preferably 0.5 to 20 g / 100 mL, and even more preferably 1 to 15 g / 100 mL.

[0048] The above aqueous dispersion consists of, for example, an aqueous liquid containing a component containing a platinum group metal (e.g., a platinum group metal halide) and a solid dispersed in the aqueous liquid.

[0049] On the other hand, an example of an impurity that may be generated during the dissolution process in step (1a) is iron oxide, which is formed from iron(III) chloride by oxygen gas mixed into the system. Iron oxide is sparingly soluble in water. Therefore, such impurities can be removed by performing a solid-liquid separation treatment on the aqueous dispersion in the subsequent step (4a).

[0050] In step (3a), in one embodiment, the solid obtained in step (2a) is treated with an organic solvent (leaching solution) in which the platinum group metal halide is poorly soluble to obtain a dispersion (first leaching treatment). For example, the solid is immersed in an organic solvent. As the organic solvent, for example, an alcohol such as ethanol is used. As a result, the iron halides such as iron(III) chloride contained in the solid dissolve in the organic solvent. On the other hand, for example, platinum group metal halides (for example, potassium rhodium(III) chloride and potassium iridium(III) chloride) remain in the solid because they are poorly soluble in ethanol.

[0051] Iron halides such as iron(III) chloride, used in the dissolution process of step (1a), can become impurities in the final product. These impurities can be removed by dissolving these iron halides in the above organic solvent and then performing solid-liquid separation of the dispersion in the subsequent step (4a).

[0052] Therefore, the leaching solution is not limited to ethanol; for example, an organic solvent in which iron halides such as iron(III) chloride are soluble and halides such as platinum group metal chlorides are insoluble can be used. Examples of such organic solvents include, in addition to the alcohol solvents mentioned above, ester solvents, ether solvents, ketone solvents, and nitrogen-containing solvents.

[0053] The temperature of the leaching fluid is preferably 95°C or lower, more preferably 5 to 80°C, and even more preferably 10 to 60°C. The leaching process time is preferably 1 hour or more, more preferably 5 to 100 hours, and even more preferably 10 to 60 hours.

[0054] <Process (4a)> In step (4a), in one embodiment, a liquid containing platinum group metal components (e.g., platinum group metal halides) is separated from the aqueous dispersion obtained in step (3a) by solid-liquid separation treatment, such as filtration and centrifugation. From this liquid, the platinum group metal can be easily recovered by conventionally known methods such as crystallization. In one embodiment of this disclosure, high-purity platinum group metal can be recovered by performing step (5a) described below.

[0055] In step (4a), in one embodiment, a solid containing platinum group metal halides is separated from the dispersion obtained in step (3a) by a solid-liquid separation treatment such as filtration and centrifugation. The platinum group metals can be easily recovered from this solid by conventionally known methods such as leaching. In one embodiment of this disclosure, high-purity platinum group metals can be recovered by performing step (5a') described below.

[0056] <Process (5a)> In step (5a), a platinum group metal precipitate is added to the liquid (e.g., filtrate) containing the platinum group metal component separated in step (4a). This allows the platinum group metal component to be converted into, for example, a sparingly soluble salt and precipitated. Thus, the platinum group metal component in the liquid and the platinum group metal component after precipitation are usually different.

[0057] Examples of precipitating agents include monovalent cation chlorides such as ammonium chloride. The precipitating agent may be one type or two or more types. When ammonium chloride is used, the precipitated platinum group metal-containing component will contain an ammonium component. For example, if the liquid contains K3[Rh(NO2)6], (NH4)3[Rh(NO2)6] will precipitate. Therefore, high-purity platinum group metals can be obtained by calcining the platinum group metal-containing component.

[0058] From the viewpoint of promoting the above precipitation well, it is preferable to use an acid together with the precipitating agent. Examples of acids include hydrogen chloride and nitric acid. One or more acids may be used. It is preferable to use hydrogen chloride and nitric acid in combination. In one embodiment, ammonium chloride, hydrochloric acid, and an aqueous solution of nitric acid are added to the above liquid. As a result, for example, if the above liquid contains potassium palladium(II) chloride (K2[PdCl4]) as a platinum group metal halide, the palladium ions become tetravalent, and ammonium palladium(IV) chloride ((NH4)2[PdCl6]) precipitates.

[0059] The amount of nitric acid added is preferably 1 to 500 moles, more preferably 50 to 300 moles, and even more preferably 90 to 250 moles, per mole of the platinum group metal component contained in the above liquid. This tends to promote good oxidation of palladium ions, for example, and good precipitation by the precipitating agent.

[0060] The amount of hydrogen chloride added is preferably 1 to 300 moles, more preferably 30 to 250 moles, and even more preferably 80 to 150 moles, per mole of the platinum group metal component contained in the above liquid. This tends to promote good oxidation of palladium ions, for example, and good precipitation by the precipitating agent.

[0061] The amount of precipitant added is preferably 0.1 to 20 moles, more preferably 0.5 to 10 moles, and even more preferably 1 to 5 moles, per mole of the platinum group metal component contained in the above liquid.

[0062] In step (5a), from the viewpoint of promoting the above-mentioned precipitation, the temperature of the liquid during the precipitation treatment is preferably 95°C or lower, more preferably 5 to 80°C, and even more preferably 10 to 60°C. The treatment time for the precipitation treatment is preferably 1 hour or more, more preferably 5 to 100 hours, and even more preferably 10 to 60 hours.

[0063] In step (5a), the precipitated platinum group metal-containing components are subsequently recovered by solid-liquid separation treatments such as filtration and centrifugation. Meanwhile, iron(III) chloride and potassium chloride, which have high solubility in water, can be removed by this solid-liquid separation treatment.

[0064] Next, the components containing platinum group metals are calcined. Through this operation, platinum group metals can be recovered. The calcination temperature is not particularly limited as long as it is a temperature that can volatilize or decompose components other than platinum group metals, and is preferably 300°C or higher, more preferably 300 to 450°C, and even more preferably 300 to 400°C. The calcination time is preferably 0.1 to 20 hours, more preferably 0.3 to 10 hours, and even more preferably 0.5 to 5 hours. Examples of the atmosphere during calcination include an inert gas atmosphere such as argon and nitrogen, and a hydrogen gas atmosphere. If the precipitate is, for example, ammonium palladium(IV) chloride ((NH4)2[PdCl6]), high-purity palladium can be obtained by this calcination.

[0065] <Process (5a')> Step (5a') includes (5a'-1) treating the solid containing the platinum group metal halide separated in step (4a) with water or an aqueous solution to obtain an aqueous dispersion in which the platinum group metal-containing component is dissolved in water, and (5a'-2) separating a liquid containing the platinum group metal-containing component from the aqueous dispersion. Furthermore, (5a'-3) the liquid may include adding a platinum group metal precipitant to the liquid to precipitate the platinum group metal-containing component, recovering the precipitated component, and performing a reduction treatment as necessary.

[0066] In step (5a'-1), the solid obtained in step (4a) is treated with water or an aqueous solution in which the platinum group metal halide is soluble to obtain an aqueous dispersion (second leaching treatment). For example, the solid is immersed in water or an aqueous solution. As a result, the platinum group metal halide contained in the solid dissolves in the water or aqueous solution as a component containing platinum group metals (for example, platinum group metal sulfates such as rhodium sulfate and iridium sulfate). Rhodium sulfate and iridium sulfate are readily soluble in water.

[0067] In step (5a'-1), in one embodiment, water or an aqueous solution in which the platinum group metal halide is soluble is used as the leaching liquid. Since water or an aqueous solution is used as the leaching liquid, wastewater treatment is easy, and the recovery method of this disclosure has a small environmental impact. Examples of aqueous solutions include aqueous solutions of alkali metal salts such as aqueous potassium sulfate and aqueous sodium sulfate, particularly aqueous solutions of alkali metal sulfates, and aqueous sulfuric acid can also be used. When the above aqueous solution is used as the leaching liquid, the platinum group metal halide may be dissolved in the aqueous liquid in the form of other salts.

[0068] The concentration of the alkali metal salt in the aqueous solution is preferably 0.1 to 30 g / 100 mL, more preferably 0.5 to 20 g / 100 mL, and even more preferably 1 to 15 g / 100 mL.

[0069] The above aqueous dispersion consists, for example, of an aqueous liquid containing a component containing a platinum group metal and a solid dispersed in the aqueous liquid.

[0070] An example of an impurity that may be generated during the dissolution process in step (1a) is iron oxide, which is formed from iron(III) chloride by oxygen gas introduced into the system. Iron oxide is sparingly soluble in water. Therefore, such impurities can be removed by performing a solid-liquid separation treatment on the aqueous dispersion in the subsequent step (5a'-2).

[0071] The temperature of the leaching fluid is preferably 95°C or lower, more preferably 5 to 80°C, and even more preferably 10 to 60°C. The leaching process time is preferably 1 hour or more, more preferably 5 to 100 hours, and even more preferably 10 to 60 hours.

[0072] In step (5a'-2), in one embodiment, a liquid containing platinum group metal components is separated from the aqueous dispersion obtained in step (5a'-1) by a solid-liquid separation treatment such as filtration and centrifugation. The platinum group metal can be easily recovered from this liquid by conventionally known methods such as crystallization. In one embodiment of this disclosure, high-purity platinum group metal can be recovered by performing step (5a'-3) described below.

[0073] In step (5a'-3), a platinum group metal precipitate is added to the liquid (e.g., filtrate) containing the platinum group metal component separated in step (5a'-2). This allows the platinum group metal component to be precipitated, for example, as a hydroxide or oxide of the platinum group metal. Thus, the platinum group metal component in the liquid and the platinum group metal component after precipitation are usually different.

[0074] Examples of precipitating agents include alkali metal hydroxides such as potassium hydroxide and sodium hydroxide. The precipitating agent may be one type or two or more types. For example, if the liquid contains rhodium sulfate, Rh(OH)3 or Rh2O3 may precipitate.

[0075] Therefore, high-purity platinum group metals can be obtained by reducing a component containing platinum group metals (for example, a hydroxide or oxide of a platinum group metal). Furthermore, the hydroxide or oxide of a platinum group metal may be used as a raw material for producing other compounds. Thus, the method of this disclosure can be used not only as a method for recycling platinum group metals, but also as a method for producing raw materials from secondary resources.

[0076] The amount of precipitant added is preferably 0.1 to 20 moles, more preferably 0.5 to 10 moles, and even more preferably 2 to 5 moles, per mole of the platinum group metal component contained in the above liquid.

[0077] In step (5a'-3), from the viewpoint of promoting the above-mentioned precipitation, the temperature of the liquid during the precipitation treatment is preferably 95°C or lower, more preferably 5 to 80°C, and even more preferably 10 to 60°C. The treatment time for the precipitation treatment is preferably 1 hour or more, more preferably 5 to 100 hours, and even more preferably 10 to 60 hours.

[0078] In step (5a'-3), the precipitated platinum group metal-containing components are subsequently recovered by solid-liquid separation treatments such as filtration and centrifugation. Meanwhile, potassium chloride, which has high solubility in water, can be removed by this solid-liquid separation treatment.

[0079] Next, if necessary, the components containing platinum group metals are subjected to a reduction treatment. Through this operation, platinum group metals can be recovered in high purity. The reduction treatment can be carried out by conventionally known methods, such as reducing the above components with hydrogen gas. If the precipitate is, for example, Rh(OH)3 or Rh2O3, high-purity rhodium can be obtained through this reduction treatment.

[0080] To recover platinum group metals at a high rate, it is preferable to separate the platinum group metals from impurities such as iron components before precipitation treatment. When the target materials for recovery are platinum and palladium, for example, platinum and palladium can be recovered at a high rate by dissolving the halides in water or an aqueous solution through dissolution and leaching treatments, separating the iron oxide through solid-liquid separation treatment, and adding ammonium chloride to the filtrate to precipitate salts that are sparingly soluble in water. On the other hand, when ammonium chloride is similarly added to a liquid containing rhodium or iridium halides, the resulting salt is readily soluble in water, making it difficult to recover rhodium or iridium as salts that are sparingly soluble in water. Therefore, impurities may be mixed into the recovered rhodium or iridium. However, according to the above-described steps (4a) and (5a'), impurities such as iron components can be separated and removed, allowing for the recovery of rhodium and iridium at a high rate.

[0081] The method disclosed herein offers significant advantages over conventional dry methods in that it can be implemented at lower temperatures, uses fewer regulated chemicals than conventional wet methods, and generates less wastewater. Furthermore, the method disclosed herein allows for the recovery of not only platinum and palladium, but also sparingly soluble platinum group metals such as rhodium and iridium, in a manner that minimizes environmental impact and energy consumption. Therefore, the recycling rate of rhodium and iridium can be efficiently improved by using the method disclosed herein.

[0082] [Second method for recovering platinum group metals] The second method for recovering platinum group metals in this disclosure is: (1b) A step of contacting a substance containing a first platinum group metal and a second platinum group metal with a molten salt containing an iron halide to obtain a treated product in which the halide of the first platinum group metal and the halide of the second platinum group metal are dissolved in the molten salt. (2b) A step of cooling the above processed material to obtain a solid, (3b) A step of treating the above solid with water or an aqueous solution in which the first platinum group metal halide is soluble and the second platinum group metal halide is sparingly soluble to obtain an aqueous dispersion, and (4b) A step of separating the aqueous dispersion into a liquid containing a component containing a first platinum group metal and a solid residue containing a halide of a second platinum group metal. Includes.

[0083] The separation of platinum group metals from a substance containing multiple platinum group metals generally requires complex, multi-step methods such as solvent extraction. The method disclosed herein allows for the easy separation and recovery of multiple platinum group metals compared to conventional methods.

[0084] A second method for recovering platinum group metals according to this disclosure, in one embodiment, (5b) A process of adding a precipitating agent for the first platinum group metal to a liquid containing a component containing the first platinum group metal, precipitating the component containing the first platinum group metal, recovering the precipitated component (precipitate), and calcining it. It also includes.

[0085] A second method for recovering platinum group metals according to this disclosure, in one embodiment, (6b) A step of treating a solid residue containing a second platinum group metal halide with an aqueous solution in which the second platinum group metal halide is soluble to obtain an aqueous dispersion. (7b) A step of separating a liquid containing a component containing a second platinum group metal from the aqueous dispersion, and (8b) A process of adding a precipitating agent for the second platinum group metal to a liquid containing a component containing the second platinum group metal, precipitating the component containing the second platinum group metal, recovering the precipitated component (precipitate), and calcining it. It also includes.

[0086] <Process (1b) and Process (2b)> Steps (1b) and (2b) in the second recovery method are the same as steps (1a) and (2a) in the first recovery method, respectively. The specific examples, preferred examples, and amounts used of the above-mentioned substances, iron halides, and alkali metal or alkaline earth metal halides, as well as the conditions for dissolution treatment and cooling, are also the same and are therefore omitted from this section. However, in step (1b), a substance containing the first platinum group metal and the second platinum group metal is used.

[0087] The first platinum group metal is at least one selected from platinum, palladium, ruthenium, osmium, iridium, and rhodium, preferably palladium. The second platinum group metal is at least one selected from platinum, palladium, ruthenium, osmium, iridium, and rhodium, and is a different metal from the first platinum group metal, preferably platinum.

[0088] In one embodiment, the substance comprises palladium as a first platinum group metal and platinum as a second platinum group metal. In one embodiment, the product obtained by the dissolution treatment comprises a palladium halide (e.g., potassium palladium(II) chloride) and a platinum halide (e.g., potassium platinum(IV) chloride).

[0089] The above substance may contain further platinum group metals, such as a third platinum group metal. In one embodiment, the above substance includes platinum, palladium, and rhodium. Even when the above substance contains a third platinum group metal, the first to third platinum group metals can be separated and recovered by appropriately selecting a leaching liquid and repeatedly performing each step of the second recovery method.

[0090] The above substance may include an alloy containing a first platinum group metal and a second platinum group metal, such as a platinum-palladium alloy, and may also contain the first platinum group metal such as palladium and the second platinum group metal such as platinum as individual elements.

[0091] <Process (3b)> In the dissolution treatment of step (1b), both the first and second platinum group metals dissolve in the molten salt, so it is necessary to separate the component containing the first platinum group metal from the component containing the second platinum group metal. In step (3b), the solid obtained in step (2b) is treated (leached) with water or an aqueous solution in which the halide of the first platinum group metal is soluble and the halide of the second platinum group metal is sparingly soluble to obtain an aqueous dispersion. For example, the solid is immersed in water or an aqueous solution. As a result, the halide of the first platinum group metal contained in the solid (e.g., potassium palladium(II) chloride) dissolves in the water or aqueous solution. On the other hand, the halide of the second platinum group metal contained in the solid (e.g., potassium platinum(IV) chloride) remains in the solid.

[0092] Conventional recovery methods separate multiple types of platinum group metals using complex procedures. In contrast, the second recovery method of this disclosure separates multiple types of platinum group metals using a simple method that utilizes the difference in solubility in water or aqueous solutions. Therefore, it is possible to suppress the discharge of wastewater, which has a large environmental impact.

[0093] For example, palladium halides such as potassium palladium(II) chloride are readily soluble in water and potassium chloride aqueous solutions. For example, platinum halides such as potassium chlorplatin(IV) chloride are sparingly soluble in water and potassium chloride aqueous solutions, and the solubility of potassium chlorplatin(IV) chloride in potassium chloride aqueous solutions is lower than its solubility in water. Therefore, it is preferable to use water or potassium chloride aqueous solutions as the leaching solution, and more preferable to use potassium chloride aqueous solutions. This allows for the separation of platinum and palladium components.

[0094] The concentration of potassium chloride in the aqueous potassium chloride solution is preferably 0.1 to 30 g / 100 mL, more preferably 0.5 to 20 g / 100 mL, and even more preferably 1 to 15 g / 100 mL. The temperature of the leaching solution is preferably 95°C or lower, more preferably 5 to 80°C, and even more preferably 10 to 60°C. The leaching treatment time is preferably 1 hour or more, more preferably 5 to 100 hours, and even more preferably 10 to 60 hours.

[0095] <Process (4b)> In step (4b), the aqueous dispersion obtained in step (3b) is separated into a liquid containing a component containing a first platinum group metal (e.g., a halide of the first platinum group metal) and a solid residue containing a halide of the second platinum group metal by solid-liquid separation treatments such as filtration and centrifugation.

[0096] <Process (5b)> In step (5b), a precipitating agent for the first platinum group metal is added to the liquid (e.g., filtrate) containing the component containing the first platinum group metal, which was separated in step (4b). This allows the component containing the first platinum group metal to be precipitated.

[0097] Examples of precipitating agents include monovalent cation chlorides such as ammonium chloride. The precipitating agent may be one type or two or more types. When ammonium chloride is used, the precipitated component containing the first platinum group metal contains an ammonium component. Therefore, by calcining the component containing the first platinum group metal, a first platinum group metal of high purity can be obtained.

[0098] From the viewpoint of promoting the above precipitation well, it is preferable to use an acid together with the precipitating agent. Examples of acids include hydrogen chloride and nitric acid. One or more acids may be used. It is preferable to use hydrogen chloride and nitric acid in combination. In one embodiment, ammonium chloride, hydrochloric acid, and an aqueous solution of nitric acid are added to the above liquid. As a result, for example, if the above liquid contains potassium palladium(II) chloride (K2[PdCl4]) as a first platinum group metal halide, the palladium ions become tetravalent, and ammonium palladium(IV) chloride ((NH4)2[PdCl6]) precipitates.

[0099] The amount of nitric acid added is preferably 1 to 500 moles, more preferably 50 to 300 moles, and even more preferably 90 to 250 moles, per mole of the first platinum group metal component contained in the liquid. This tends to promote good oxidation of palladium ions, for example, and good precipitation by the precipitating agent.

[0100] The amount of hydrogen chloride added is preferably 1 to 300 moles, more preferably 30 to 250 moles, and even more preferably 80 to 150 moles, per mole of the first platinum group metal component contained in the liquid. This tends to promote good oxidation of palladium ions, for example, and good precipitation by the precipitating agent.

[0101] The amount of precipitating agent added is preferably 0.1 to 20 moles, more preferably 0.5 to 10 moles, and even more preferably 1 to 5 moles, per mole of the first platinum group metal component contained in the liquid.

[0102] In step (5b), from the viewpoint of promoting the above-mentioned precipitation, the temperature of the liquid during the precipitation treatment is preferably 95°C or lower, more preferably 5 to 80°C, and even more preferably 10 to 60°C. The treatment time for the precipitation treatment is preferably 1 hour or more, more preferably 5 to 100 hours, and even more preferably 10 to 60 hours.

[0103] The ammonium salts of chloroplatinic acid and palladic acid are sparingly soluble in water. On the other hand, the ammonium salts of rhodium chloride and iridium chloride are readily soluble in water. Therefore, in the above precipitation treatment using ammonium chloride, the rhodium and iridium components are contained in the liquid (filtrate). Consequently, even when platinum or palladium coexists with rhodium or iridium, each element can be separated and recovered by using the method of this disclosure.

[0104] In step (5b), the precipitated components containing the first platinum group metal are subsequently recovered by solid-liquid separation treatments such as filtration and centrifugation. Meanwhile, iron(III) chloride and potassium chloride, which have high solubility in water, can be removed by this solid-liquid separation treatment.

[0105] Next, the component containing the first platinum group metal is calcined. Through this operation, the first platinum group metal can be recovered. The calcination temperature is not particularly limited as long as it is a temperature at which components other than the first platinum group metal can be volatilized or decomposed, and is preferably 300°C or higher, more preferably 300 to 450°C, and even more preferably 300 to 400°C. The calcination time is preferably 0.1 to 20 hours, more preferably 0.3 to 10 hours, and even more preferably 0.5 to 5 hours. Examples of the atmosphere during calcination include an inert gas atmosphere such as argon and nitrogen, and a hydrogen gas atmosphere. If the precipitate is, for example, ammonium palladium(IV) chloride ((NH4)2[PdCl6]), high-purity palladium can be obtained by this calcination.

[0106] <Process (6b)~(8b)> In step (6b), the solid residue containing the second platinum group metal halide, separated in step (4b), is treated (leached) with an aqueous solution in which the second platinum group metal halide is soluble to obtain an aqueous dispersion. For example, the solid residue is immersed in the aqueous solution.

[0107] In step (6b), an aqueous solution in which a second platinum group metal halide is soluble is used as the leaching liquid. An example of such an aqueous solution is an aqueous sodium chloride solution. For example, platinum halides such as potassium chlorplatinate are readily soluble in an aqueous sodium chloride solution in one embodiment. It is thought that potassium chlorplatinate, which is sparingly soluble in water, becomes readily soluble sodium chlorplatinate through ion exchange. Therefore, by adding the above solid residue to the aqueous sodium chloride solution, a liquid containing a dissolved component of the second platinum group metal can be obtained.

[0108] The concentration of sodium chloride in the aqueous sodium chloride solution is preferably 0.1 to 30 g / 100 mL, more preferably 0.5 to 20 g / 100 mL, and even more preferably 1 to 15 g / 100 mL. The temperature of the leaching solution is preferably 95°C or lower, more preferably 5 to 80°C, and even more preferably 10 to 60°C. The leaching treatment time is preferably 1 hour or more, more preferably 5 to 100 hours, and even more preferably 10 to 60 hours.

[0109] On the other hand, an example of an impurity that may be generated during the dissolution process in step (1b) is iron oxide, which is formed from iron(III) chloride by oxygen gas mixed into the system. Iron oxide is sparingly soluble in water. Therefore, such impurities can be removed by performing a solid-liquid separation treatment on the aqueous dispersion in the subsequent step (8b).

[0110] In step (7b), a liquid containing the component with the second platinum group metal is separated from the aqueous dispersion obtained in step (6b) by a solid-liquid separation treatment, such as filtration and centrifugation. The second platinum group metal can be easily recovered from this liquid by conventionally known methods such as crystallization. In one embodiment of this disclosure, a second platinum group metal of high purity can be recovered by performing step (8b) described below.

[0111] In step (8b), a precipitate for the second platinum group metal is added to the liquid (e.g., filtrate) containing the component containing the second platinum group metal, which was separated in step (7b). This allows the component containing the second platinum group metal to be precipitated.

[0112] Examples of precipitating agents include monovalent cation chlorides such as ammonium chloride. The precipitating agent may be one type or two or more types. When ammonium chloride is used, the precipitated component containing the second platinum group metal contains an ammonium component. Therefore, by calcining the component containing the second platinum group metal, a high-purity second platinum group metal can be obtained.

[0113] In one embodiment, when the liquid contains sodium chlorplatin(IV)ate as a second platinum group metal halide, ammonium chlorplatin(IV)ate ((NH4)2[PtCl6]) precipitates.

[0114] The amount of precipitating agent added is preferably 0.1 to 20 moles, more preferably 0.5 to 10 moles, and even more preferably 1 to 5 moles, per mole of the second platinum group metal component contained in the liquid.

[0115] In step (8b), from the viewpoint of promoting the above-mentioned precipitation, the temperature of the liquid during the precipitation treatment is preferably 95°C or lower, more preferably 5 to 80°C, and even more preferably 10 to 60°C. The treatment time for the precipitation treatment is preferably 1 hour or more, more preferably 5 to 100 hours, and even more preferably 10 to 60 hours.

[0116] In step (8b), the precipitated component containing the second platinum group metal is subsequently recovered by solid-liquid separation treatments such as filtration and centrifugation.

[0117] Next, the component containing the second platinum group metal is calcined. Through this operation, the second platinum group metal can be recovered. The calcination temperature is not particularly limited as long as it is a temperature at which components other than the second platinum group metal can be volatilized or decomposed, and is preferably 300°C or higher, more preferably 300 to 450°C, and even more preferably 300 to 400°C. The calcination time is preferably 0.1 to 20 hours, more preferably 0.3 to 10 hours, and even more preferably 0.5 to 5 hours. Examples of the atmosphere during calcination include an inert gas atmosphere such as argon and nitrogen, and a hydrogen gas atmosphere. If the precipitate is, for example, ammonium chlorplatinate(IV) ((NH4)2[PtCl6]), high-purity platinum can be obtained by this calcination.

[0118] In one embodiment of the second recovery method, the substance may further contain a third platinum group metal. In this case, step (1b) is a step of obtaining a treated product in which a first platinum group metal halide, a second platinum group metal halide, and a third platinum group metal halide are dissolved in the molten salt. For example, the first platinum group metal is palladium, the second platinum group metal is platinum, and the third platinum group metal is rhodium.

[0119] Step (3b) may, in one embodiment, be a step of treating the solid with water or an aqueous solution in which the first platinum group metal halide and the third platinum group metal halide are soluble and the second platinum group metal halide is sparingly soluble to obtain an aqueous dispersion. Step (4b) may, in one embodiment, be a step of separating the aqueous dispersion into a liquid containing a component containing the first platinum group metal and a component containing the third platinum group metal, and a solid residue containing the second platinum group metal halide. In step (5b), a precipitating agent for the first platinum group metal may be added to the liquid containing the component containing the first platinum group metal and the component containing the third platinum group metal to separate it into a precipitate containing the first platinum group metal and a liquid containing a component containing the third platinum group metal.

[0120] This disclosure relates, for example, to the following [1] to

[18] . [1] A method for recovering platinum group metals, comprising the steps of (1a) contacting a substance containing at least one platinum group metal selected from palladium, ruthenium, osmium, iridium, and rhodium with a molten salt containing an iron halide to obtain a treated product in which the platinum group metal halide is dissolved in the molten salt; (2a) cooling the treated product to obtain a solid; (3a) treating the solid with water or an aqueous solution in which the platinum group metal halide is soluble to obtain an aqueous dispersion, or treating the solid with an organic solvent in which the platinum group metal halide is sparingly soluble to obtain a dispersion; and (4a) separating a liquid containing the platinum group metal component from the aqueous dispersion, or separating a solid containing the platinum group metal halide from the dispersion. [2](5a) The method for recovering platinum group metals according to [1], further comprising the steps of adding a platinum group metal precipitant to the liquid, precipitating a component containing the platinum group metal, recovering the precipitated component, and calcining it. [3] A method for recovering platinum group metals according to [1], further comprising: (5a'-1) treating a solid containing a platinum group metal halide with water or an aqueous solution to obtain an aqueous dispersion in which the platinum group metal-containing component is dissolved in water; (5a'-2) separating a liquid containing the platinum group metal-containing component from the aqueous dispersion; and (5a'-3) adding a precipitating agent for platinum group metals to the liquid to precipitate the platinum group metal-containing component and recovering the precipitated component. [4] A method for recovering platinum group metals according to any one of [1] to [3] above, wherein the substance comprises at least one selected from palladium and rhodium. [5] The method for recovering platinum group metals according to any one of [1] to [4] above, wherein the molten salt is a molten salt of a mixture containing the iron halide and an alkali metal or alkaline earth metal halide. [6] The method for recovering platinum group metals according to [5] above, wherein the iron halide is iron(III) chloride and the alkali metal or alkaline earth metal halide is potassium chloride. [7] The method for recovering platinum group metals according to [2] above, wherein the precipitant for platinum group metals is ammonium chloride. [8] The method for recovering platinum group metals according to [3] above, wherein the precipitant for platinum group metals is an alkali metal hydroxide. [9] A method for recovering platinum group metals, comprising the steps of (1b) contacting a substance containing a first platinum group metal and a second platinum group metal with a molten salt containing an iron halide to obtain a treated product in which the halide of the first platinum group metal and the halide of the second platinum group metal are dissolved in the molten salt; (2b) cooling the treated product to obtain a solid; (3b) treating the solid with water or an aqueous solution in which the halide of the first platinum group metal is soluble and the halide of the second platinum group metal is sparingly soluble to obtain an aqueous dispersion; and (4b) separating the aqueous dispersion into a liquid containing a component containing the first platinum group metal and a solid residue containing the halide of the second platinum group metal.

[10] (5b) A method for recovering a platinum group metal according to [9] above, further comprising the steps of adding a precipitant for a first platinum group metal to a liquid containing a component containing a first platinum group metal, precipitating the component containing the first platinum group metal, recovering the precipitated component, and calcining it.

[11] A method for recovering platinum group metals according to [9] or

[10] , further comprising: (6b) treating a solid residue containing a halide of a second platinum group metal with an aqueous solution in which the halide of the second platinum group metal is soluble to obtain an aqueous dispersion; (7b) separating a liquid containing a component containing the second platinum group metal from the aqueous dispersion; and (8b) adding a precipitating agent for the second platinum group metal to the liquid containing the component containing the second platinum group metal to precipitate the component containing the second platinum group metal, recovering the precipitated component, and calcining it.

[12] A method for recovering platinum group metals according to any one of [9] to

[11] above, wherein the first platinum group metal is at least one selected from platinum, palladium, ruthenium, osmium, iridium, and rhodium, and the second platinum group metal is at least one selected from platinum, palladium, ruthenium, osmium, iridium, and rhodium, and is a different metal from the first platinum group metal.

[13] A method for recovering platinum group metals according to any one of [9] to

[12] above, wherein the substance comprises an alloy containing a first platinum group metal and a second platinum group metal, or an element of the first platinum group metal and an element of the second platinum group metal.

[14] A method for recovering platinum group metals according to any of [9] to

[13] above, wherein the first platinum group metal is palladium and the second platinum group metal is platinum.

[15] A method for recovering platinum group metals according to any of [9] to

[14] above, wherein the aqueous solution used in step (3b) is an aqueous potassium chloride solution.

[16] The method for recovering platinum group metals according to any one of [9] to

[15] above, wherein the molten salt is a molten salt of a mixture containing the iron halide and an alkali metal or alkaline earth metal halide.

[17] The method for recovering platinum group metals according to

[16] , wherein the iron halide is iron(III) chloride and the alkali metal or alkaline earth metal halide is potassium chloride.

[18] The substance further comprises a third platinum group metal, and step (1b) is a step of obtaining a processed product in which a first platinum group metal halide, a second platinum group metal halide, and a third platinum group metal halide are dissolved in the molten salt, step (3b) is a step of treating the solid with water or an aqueous solution in which the first platinum group metal halide and the third platinum group metal halide are soluble and the second platinum group metal halide is sparingly soluble to obtain an aqueous dispersion, and step (4b) is a step of A method for recovering platinum group metals according to

[10] , comprising the steps of separating a known aqueous dispersion into a liquid containing a component containing a first platinum group metal and a component containing a third platinum group metal, and a solid residue containing a halide of a second platinum group metal, wherein in step (5b), a precipitating agent for the first platinum group metal is added to the liquid containing the component containing the first platinum group metal and the component containing the third platinum group metal, thereby separating it into a precipitate containing the first platinum group metal and a liquid containing the component containing the third platinum group metal. [Examples]

[0121] The platinum group metal recovery method described herein will be explained in more detail below based on examples. Figure 2 shows an overview of the flow chart for Example 1. Figure 3 shows a schematic of the flow chart for Example 2. Figure 8 shows an overview of the flows for Examples 4 and 5.

[0122] [Example 1] Treatment of palladium wire 3.0 g of a mixture (hereinafter also referred to as "mixture (A)") was obtained by mixing iron(III) chloride and potassium chloride in equimolar amounts. A palladium wire with a diameter of φ=0.2 mm, a length of approximately 100 mm, and a weight of approximately 40 mg was used as the sample.

[0123] Mixture (A) and the sample were placed in a porcelain crucible (SiO2: 58% or more, Al2O3: 33% or more), the porcelain crucible was set inside a glass reaction tube, and the atmosphere inside the reaction tube was replaced with an argon (Ar) atmosphere. The reaction tube was then heated using a mantle heater (Daika Electric Co., Ltd., GBR-5) as a heating device. The reaction started when a thermocouple set near the porcelain crucible reached 250°C (523K). The dissolution treatment was carried out at a processing temperature of 287°C (560K) to 327°C (600K) for 1, 2, or 3 hours.

[0124] After the dissolution process was complete, the reaction tube was removed from the mantle heater, and the contents of the porcelain crucible were solidified by air cooling. The recovered contents were added to a leaching solution (20 mL of pure water) and leached. When mixture (A) had dissolved in the leaching solution, the sample residue (palladium wire residue) was collected, and the amount of dissolved sample was determined by measuring the change in sample weight. Since there was a range in the weight of the samples added, the amount of dissolved palladium wire was converted using the following formula (i), and the obtained results were compared.

[0125] w = w dissolution ×(40 / w sample ) (i) w dissolution This indicates the actual amount of solution in the sample, and w sample This indicates the actual weight of the sample used.

[0126] Subsequently, iron oxide was separated and removed by filtration. 12M hydrochloric acid (HCl aqueous solution) was added to the filtrate and allowed to stand at 40°C for 24 hours. Then, ammonium chloride and 13.5M nitric acid aqueous solution were added and allowed to stand at 40°C for 24 hours. See Table 2 for the amounts of hydrochloric acid, nitric acid aqueous solution, and ammonium chloride added. A dark red precipitate was obtained. The obtained precipitate was placed in a porcelain crucible, which was then placed in a glass reaction tube (argon (Ar) atmosphere) and heated at 377°C (650K) for 1 hour using the same heating apparatus as described above. A black powder (final recovered material) was obtained.

[0127] Figure 4 shows the changes in the amount of palladium dissolved when the processing time and processing temperature in the above dissolution process are varied. A tendency was observed for the amount of palladium dissolved to increase with increasing processing time and processing temperature.

[0128] In a dissolution treatment with a processing time of 1 hour, the initial dissolution rate was evaluated from the surface area of ​​the sample at the time of input. The initial dissolution rate of palladium was 1.72 mol·m³ at 297°C (570K). -2 ·h -1 According to Non-Patent Literature 1 (Journal of the Japan Institute of Metals, Vol. 83, No. 1 (2019), pp. 23-29), the initial dissolution rate of platinum using the molten salt of mixture (A) was 0.45 mol·m³ at 382°C (655K). -2 ·h -1 It was shown that palladium dissolves faster and at lower temperatures in the molten salt of mixture (A) compared to platinum.

[0129] Compositional analysis of precipitates and final recovered materials was performed using SEM-EDS (JEOL Ltd., JSM-6010-LA) targeting chlorine (Cl), potassium (K), iron (Fe), and palladium (Pd). Table 1 shows the analysis results for an example of dissolution treatment at 327°C for 3 hours.

[0130] [Table 1]

[0131] In the SEM-EDS analysis of the precipitate, almost no iron was detected, and the ratio of palladium to chlorine was close to 6:1 in molar ratio (Cl:Pd). Therefore, it is considered that ammonium hexachloropalladate(IV) ((NH4)2PdCl6) was precipitated by the precipitation treatment. From the SEM-EDS analysis results of the final recovered product, it is considered that the contamination such as iron was suppressed and palladium with a purity of 90% or more could be recovered. The recovered palladium showed a porous form.

[0132] The amount of palladium in the final recovered product was estimated from the weight and composition of the final recovered product, and the recovery rate was evaluated by comparing it with the dissolution amount. The recovery rate was evaluated without applying the conversion shown in the above formula (i). Table 2 (example at dissolution treatment: 327 °C, 3 hours) shows the recovery rate of palladium obtained when the precipitation conditions were changed.

[0133]

Table 2

[0134] [Example 2] Platinum-palladium alloy wire In Example 2, as a sample, a platinum-palladium alloy wire with φ = 0.2 mm, length: about 100 mm, weight: about 60 mg, and weight ratio of platinum 80% - palladium 20% was used, and the treatment temperature was 377 °C (650 K), and the treatment time was 1, 2, 3, 6 or 8 hours. Otherwise, the above dissolution treatment was carried out in the same manner as in Example 1. Since there was a width in the weight of the sample introduced, the conversion shown in the following formula (ii) was performed for the dissolution amount of the platinum-palladium alloy wire, and the obtained results were compared.

[0135] w = w dissolution ×(60 / w sample ) (ii) w dissolution represents the actual dissolution amount of the sample, and w sample represents the weight of the sample actually introduced.

[0136] Figure 5 shows the change in the amount of sample (platinum-palladium alloy) dissolved when the processing time in the above dissolution treatment was varied. It was confirmed that when the processing time was up to 3 hours, the amount of sample dissolved increased with increasing processing time, and thereafter the increase in the amount of sample dissolved became more gradual. The amount of sample dissolved when the processing time was 3 hours was 17.8 mg.

[0137] The contents recovered in the same manner as in Example 1 were leached with an aqueous potassium chloride solution obtained by adding 2.0 g of potassium chloride to 20 mL of pure water, and left to stand at 40°C for 24 hours. Thereafter, a solid residue (1) and filtrate (2) were obtained by filtration.

[0138] A solid residue (1) believed to contain platinum was leached with an aqueous sodium chloride solution obtained by adding 4.0 g of sodium chloride to 40 mL of pure water, and allowed to stand at 40°C for 24 hours. The solid residue was separated and removed by filtration, and 8.0 mg of ammonium chloride was added to the filtrate and allowed to stand at 40°C for 24 hours to obtain a bright yellow precipitate. The obtained precipitate was placed in a porcelain crucible, which was then placed in a glass reaction tube (argon (Ar) atmosphere), and heated at 377°C (650 K) for 1 hour using the same heating apparatus as described above. This yielded a dark gray powder (final recovered material).

[0139] The precipitates and final recovered materials were subjected to compositional analysis using the SEM-EDS method described above, targeting sodium (Na), chlorine (Cl), potassium (K), iron (Fe), palladium (Pd), and platinum (Pt). Table 3 shows the analysis results for an example of dissolution treatment at 377°C for 8 hours.

[0140] [Table 3]

[0141] Based on the color of the precipitate and the results of SEM-EDS analysis, the precipitate is considered to be platinum chloride. Based on the SEM-EDS analysis, the final recovered material is considered to be high-purity platinum. The large molar ratio of platinum to palladium in the composition of the precipitate indicates that the recovery method disclosed herein can be applied to a process for separating and recovering platinum and palladium from a platinum-palladium alloy.

[0142] To the filtrate (2) believed to contain palladium, 3.0 mL of 12 M hydrochloric acid (HCl aqueous solution) was added and allowed to stand at 40°C for 24 hours. Then, 6.0 mg of ammonium chloride and 3.0 mL of 13.5 M nitric acid aqueous solution were added and allowed to stand at 40°C for 24 hours. This yielded a dark gray precipitate. The obtained precipitate was placed in a porcelain crucible, which was then placed in a glass reaction tube (argon (Ar) atmosphere) and heated at 377°C (650 K) for 1 hour using the same heating apparatus as described above. This yielded a black powder (final recovered material).

[0143] The precipitates and final recovered materials were subjected to compositional analysis using the SEM-EDS method described above, targeting sodium (Na), chlorine (Cl), potassium (K), iron (Fe), palladium (Pd), and platinum (Pt). Table 4 shows the analysis results for an example of dissolution treatment at 377°C for 8 hours.

[0144] [Table 4]

[0145] Based on the color of the precipitate and the results of SEM-EDS analysis, the precipitate is considered to be palladium chloride. SEM-EDS analysis revealed that the final recovered material contained potassium compounds and chlorides in addition to elemental palladium. However, since the incorporation of palladium into the platinum side and platinum into the palladium side was suppressed, it was confirmed that platinum and palladium could be separated from both the precipitate and the final recovered material. The incorporation of iron was also suppressed. Therefore, it was found that the recovery method disclosed herein is applicable to a process for separating and recovering platinum and palladium from a platinum-palladium alloy. Table 5 shows the final amounts of platinum and palladium recovered.

[0146] [Table 5]

[0147] [Example 3] Platinum wire and palladium wire In Example 3, both a platinum wire with a diameter of 0.2 mm, a length of approximately 50 mm, and a weight of approximately 35 mg, and a palladium wire with a diameter of 0.2 mm, a length of approximately 90 mm, and a weight of approximately 35 mg were used as samples. The dissolution treatment was carried out in the same manner as in Example 1, except that the treatment temperature was set to 327°C (600 K) or 377°C (650 K) and the treatment time was set to 1, 2, 3, 6, or 8 hours. Since there was a range in the weight of the samples added, the amount of platinum wire and palladium wire dissolved was converted using the following formula (iii), and the obtained results were compared.

[0148] w = w dissolution ×(35 / w sample ) (iii) w dissolution This indicates the actual amount of solution in the sample, and w sample This indicates the actual weight of the sample used.

[0149] The subsequent operations were carried out in the same manner as in Example 2. Figures 6 (327°C) and 7 (377°C) show the changes in the amount of sample (platinum and palladium) dissolved when the processing temperature was 327°C (600K) and 377°C (650K) and the processing time was varied. It was confirmed that the amount of sample dissolved tended to increase with increasing processing time and increasing processing temperature.

[0150] The precipitates and final recovered material from the solid residue (1) were subjected to compositional analysis using the above-mentioned SEM-EDS method, targeting sodium (Na), chlorine (Cl), potassium (K), iron (Fe), palladium (Pd), and platinum (Pt). The analysis results for an example of dissolution treatment at 377°C for 8 hours are shown in Table 6.

[0151] [Table 6]

[0152] Based on the color of the precipitate and the results of SEM-EDS analysis, the precipitate is considered to be platinum chloride. Based on the SEM-EDS analysis, the final recovered material is considered to be high-purity platinum. The large molar ratio of platinum to palladium in the composition of the precipitate indicates that the recovery method disclosed herein can be applied to a process for separating and recovering platinum and palladium in the simultaneous dissolution of platinum and palladium wires.

[0153] The precipitates and final recovered material from the filtrate (2) were subjected to compositional analysis using the SEM-EDS method described above, targeting sodium (Na), chlorine (Cl), potassium (K), iron (Fe), palladium (Pd), and platinum (Pt). Table 7 shows the analysis results for an example of dissolution treatment at 377°C for 8 hours.

[0154] [Table 7]

[0155] Based on the color of the precipitate and the results of SEM-EDS analysis, the precipitate is considered to be palladium chloride. SEM-EDS analysis revealed that the final recovered material contained potassium compounds and chlorides in addition to elemental palladium. However, since the contamination of palladium into the platinum side and platinum into the palladium side was suppressed, it was confirmed that platinum and palladium could be separated in both the precipitate and the final recovered material. The contamination of iron was also suppressed. Therefore, it has become clear that the recovery method disclosed herein can be applied to a process for separating and recovering platinum and palladium in the simultaneous dissolution of platinum and palladium wires.

[0156] Table 8 shows the final recovered amounts and recovery rates of platinum and palladium.

[0157] [Table 8]

[0158] For the simultaneous processing experiment, the amount of platinum and palladium in the recovered material was estimated from the recovered weight and the results of compositional analysis by SEM-EDS, and the recovery rate was evaluated by comparing it with the amount dissolved. Note that the recovered amount and recovery rate were evaluated without applying the conversion shown in formula (iii) above.

[0159] [Example 4] Rhodium wire In Example 4, a rhodium wire with a diameter of φ=0.25 mm, a length of approximately 50 mm, and a weight of approximately 30 mg was used as the sample. The dissolution treatment was carried out in the same manner as in Example 1, except that the treatment temperature was set to 317°C (590 K), 337°C (610 K), 377°C (650 K), or 397°C (670 K), and the treatment time was set to 2, 3, 6, or 8 hours. It was confirmed that the sample (rhodium) could be dissolved by the dissolution treatment.

[0160] In a dissolution treatment with a processing time of 2 hours, the initial dissolution rate was evaluated from the surface area of ​​the sample at the time of input. The initial dissolution rate of rhodium was 1.67 mol·m at 377°C (650K). -2 ·h -1 That's what happened.

[0161] (1) The contents recovered in the same manner as in Example 1 were leached with an aqueous sodium nitrite solution obtained by adding 2.0 g of sodium nitrite (NaNO2) to 40 mL of pure water. Then, the sample residue and iron oxide were separated and removed by filtration, and 2.0 mg of ammonium chloride was added to the filtrate and allowed to stand at 40°C for 24 hours. A yellow precipitate was obtained.

[0162] (2) The contents recovered in the same manner as in Example 1 were placed in a leaching solution (20 mL of ethanol) and subjected to leaching treatment, and left to stand at 40°C for 24 hours. After that, a solid residue (1) (approximately 2 g) and a filtrate (2) were obtained by filtration.

[0163] The solid residue (1) was leached with an aqueous potassium sulfate solution obtained by adding 0.5 g of potassium sulfate to 20 mL of pure water, and allowed to stand at 40°C for 24 hours. The solid residue was separated and removed by filtration, and 1 g of sodium hydroxide was added to the filtrate (a red solution characteristic of rhodium salts; thought to be an aqueous rhodium sulfate solution), and allowed to stand at 40°C for 24 hours to obtain a black precipitate. Compositional analysis of the precipitate by the above SEM-EDS revealed that Rh and O were mainly detected (see Table 9). In the example of dissolution treatment at 397°C for 8 hours, the recovery rate of Rh was approximately 36% (sample dissolution amount: 23.6 mg, recovered amount: 8.48 mg).

[0164] SEM-EDS analysis of the precipitate did not detect much iron, suggesting that Rh(OH)3 or Rh2O3 precipitated as a result of the precipitation treatment. Based on the SEM-EDS analysis results, it is believed that the contamination of iron and other elements was significantly reduced.

[0165] [Table 9]

[0166] [Example 5] Iridium wire In Example 5, an iridium wire with a diameter of φ=0.25 mm, a length of approximately 50 mm, and a weight of approximately 50 mg was used as the sample. 6.0 g of mixture (A) was used, and the dissolution treatment was carried out in the same manner as in Example 1, except that the treatment temperature was set to 377°C (650 K) or 397°C (670 K) and the treatment time was 4 or 8 hours. It was confirmed that the sample (iridium) could be dissolved by the dissolution treatment.

[0167] In a dissolution treatment with a processing time of 4 hours, the initial dissolution rate was evaluated from the surface area of ​​the sample at the time of input. The initial dissolution rate of iridium was 0.27 mol·m at 397°C (670K). -2 ·h -1 That's what happened.

[0168] The contents recovered in the same manner as in Example 1 were placed in a leaching solution (20 mL of ethanol) and subjected to leaching treatment, and left to stand at 40°C for 24 hours. Subsequently, a solid residue (1) (approximately 2 g) and a filtrate (2) were obtained by filtration.

Claims

1. (1a) A process of contacting a substance containing at least one platinum group metal selected from palladium, ruthenium, osmium, iridium, and rhodium with a molten salt containing an iron halide to obtain a treated product in which the platinum group metal halide is dissolved in the molten salt. (2a) A step of cooling the processed material to obtain a solid, (3a) A step of treating the solid with water or an aqueous solution in which the platinum group metal halide is soluble to obtain an aqueous dispersion. (4a) A step of separating a liquid containing the platinum group metal component from the aqueous dispersion, and (5a) Adding a platinum group metal precipitant to the liquid, adding 80 moles or more of hydrogen chloride per mole of platinum group metal component contained in the liquid, and 90 moles or more of nitric acid per mole of platinum group metal component contained in the liquid to precipitate the platinum group metal component, recovering the precipitated component, and calcining it. A method for recovering platinum group metals, including [specific metals].

2. The method for recovering platinum group metals according to Claim 1, wherein the precipitant for platinum group metals is ammonium chloride.

3. The step of (4a) separating a solid containing the platinum group metal halide from the dispersion. It further includes, and (5a'-1) A step of treating the solid containing the platinum group metal halide with water or an aqueous solution to obtain an aqueous dispersion in which the platinum group metal component is dissolved in water. (5a'-2) A step of separating a liquid containing the platinum group metal component from the aqueous dispersion, and (5a'-3) A step of adding a platinum group metal precipitant to the liquid, precipitating the component containing the platinum group metal, and recovering the precipitated component. A method for recovering platinum group metals according to claim 1, further comprising:

4. The method for recovering platinum group metals according to claim 3, wherein the precipitant for platinum group metals is an alkali metal hydroxide.

5. The method for recovering platinum group metals according to any one of claims 1 to 4, wherein in (5a), 80 to 150 moles of hydrogen chloride and 90 to 250 moles of nitric acid are added per mole of the platinum group metal-containing component in the liquid.

6. The method for recovering platinum group metals according to any one of claims 1 to 5, wherein the substance comprises at least one selected from palladium and rhodium.

7. The method for recovering platinum group metals according to any one of claims 1 to 6, wherein the molten salt is a molten salt of a mixture containing the iron halide and an alkali metal or alkaline earth metal halide.

8. The aforementioned iron halide is iron(III) chloride, The alkali metal or alkaline earth metal halide is potassium chloride. The method for recovering platinum group metals according to claim 7.

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