JP2024058422A - Method and system for recovering platinum group metals - Google Patents

Abstract

[Problem] To provide a technology for recovering platinum group metals from a raw material containing platinum group metals at low temperatures. [Solution] The method for recovering platinum group metals of the present invention includes a step (b) of heating a mixture containing an alkali metal hydroxide and an oxide at a temperature of 400°C or higher and lower than 600°C to obtain a heated product. [Selected Figures] None

Description

The present invention relates to a method for recovering platinum group metals and a system for recovering platinum group metals.

Platinum group metals have excellent catalytic performance and are used for various purposes, such as automobile exhaust gas purification catalysts and fuel car catalysts. Thus, while platinum group metals are essential elements for industry, their scarcity means that their production volume is much smaller than that of base metals. For example, the production volume of Pt and Pd, which are relatively widely produced among platinum group metals, is about 200 tons per year, while that of Rh, which is less widely produced, is about 30 tons per year. Furthermore, the primary supply source of platinum group metals is limited to South Africa and Russia. Therefore, if the demand for platinum group metals increases due to the development of new materials using platinum group metals, a supply shortage of platinum group metals will occur. In other words, it can be said that the supply risk of platinum group metals is currently high.

In order to address the supply risk caused by the uneven distribution of resources, it is extremely important to extract and recover platinum group metals from waste products such as waste catalysts generated in Japan. In addition, the mining and smelting of natural ores entails a large environmental burden. Therefore, if platinum group metals can be efficiently extracted from waste products that have a higher platinum group metal concentration than natural ores, it will also lead to a reduction in the environmental burden. However, because platinum group metals are extremely stable chemically, in the conventional dry method, it is necessary to separate and concentrate the platinum group metals from the waste products, and then dissolve the concentrate in a high-concentration acid. For this reason, the energy consumption for extracting platinum group metals is large, and the costs of chemicals and waste liquid treatment are also high. Therefore, there is an urgent need to develop a more efficient method for recovering platinum group metals.

Patent Documents 1 and 2 disclose conventional techniques for recovering platinum group metals. More specifically, Patent Documents 1 and 2 disclose a method for efficiently extracting platinum group metals from waste catalysts and scrap using an aqueous solvent in a low-corrosive environment in which chlorine gas or hydrogen chloride gas is not generated, without using an acidic solvent such as aqua regia or high-concentration hydrochloric acid.

JP 2020-105632 A JP 2021-127493 A

However, these conventional technologies require high-temperature heating at around 1000°C, which places a large load on heating devices such as electric furnaces and consumes a lot of energy, leaving room for improvement.

One aspect of the present invention aims to provide a technology for recovering platinum group metals from raw materials containing platinum group metals at low temperatures.

[1] A method for recovering platinum group metals from a raw material containing platinum group metals, the method comprising the following step (b):
(b) A step of heating the mixture containing the hydroxide and oxide of an alkali metal at a temperature of 400° C. or more and less than 600° C. to obtain a heating product.

[2] The method of recovery described in [1], characterized in that the mixture further contains a raw material containing a platinum group metal.

[3] A method for recovering platinum group metals from a raw material containing platinum group metals, the method comprising the following step (c):
(c) A step of heating a mixture containing the raw material, an alkali metal hydroxide, and an oxide at a temperature of 400° C. or higher and lower than 600° C. to obtain a heated product, and dissolving the heated product in an aqueous solvent to obtain a solution in which a platinum group metal is dissolved.

[4] A recovery method comprising obtaining a heated product in step (b) described in [2], and subjecting the heated product to step (c) described in [3].

[5] The recovery method according to any one of [1] to [4], characterized in that the heating time is 1 minute or more and 120 minutes or less.

[6] The recovery method according to any one of [1] to [5], characterized in that the mixture further contains an oxoanion of an amphoteric element.

[7] The recovery method according to any one of [1] to [6], characterized in that the platinum group metal is Pd, Pt, Rh, Ir, Os, or Ru.

[8] The recovery method according to any one of [1] to [7], characterized in that the alkali metal is Na, K, Li, Rb, or Cs.

[9] The recovery method according to any one of [1] to [8], characterized in that the oxide is at least one selected from the group consisting of Al ₂ O ₃ , Na ₂ O, B ₂ O ₃ , K ₂ O, SiO ₂ , Li ₂ O, Rb ₂ O, Cs ₂ O, and P ₂ O ₅ .

[10]
A platinum group metal recovery system for recovering platinum group metals from a raw material containing platinum group metals, comprising:
(B) A recovery system comprising a heating device for heating a mixture containing an alkali metal hydroxide and an oxide at a temperature of 400°C or higher and lower than 600°C to obtain a heated product.

[11] The recovery system described in [10], characterized in that the mixture further contains a raw material containing a platinum group metal.

[12] A platinum group metal recovery system for recovering platinum group metals from a raw material containing platinum group metals, comprising:
(C) A recovery system comprising a dissolving device for dissolving a heated product obtained in advance by heating a mixture containing the raw material, an alkali metal hydroxide, and an oxide at a temperature of 400°C or higher and lower than 600°C in an aqueous solvent to obtain a solution in which the platinum group metal is dissolved.

[13] A recovery system comprising the heating device (B) described in [11] and the dissolving device (C) described in [12].

According to one aspect of the present invention, a technology is provided for recovering platinum group metals from raw materials containing platinum group metals at low temperatures.

One embodiment of the present invention will be described in detail below. Note that the following description is provided to provide a better understanding of the gist of the invention, and does not limit the present invention unless otherwise specified. The present invention is not limited to each embodiment, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. In addition, unless otherwise specified in this specification, "A to B" representing a numerical range means "greater than or equal to A and less than or equal to B."

1. Method for recovering platinum group metals
A recovery method according to one embodiment of the present invention is a method for recovering platinum group metals from a raw material containing platinum group metals, and may include the following steps (a) or (b): (a) heating a mixture of the raw material, an alkali metal hydroxide, and an oxide at a temperature of 400° C. or more and less than 600° C. to obtain a heated product, and (b) heating the mixture of the alkali metal hydroxide and oxide at a temperature of 400° C. or more and less than 600° C. to obtain a heated product.

The recovery method according to one embodiment of the present invention is a method for recovering platinum group metals from a raw material containing platinum group metals, and may include the following step (b): (b) a step of heating a mixture containing an alkali metal hydroxide and an oxide at a temperature of 400°C or higher and lower than 600°C to obtain a heated product. The mixture may further include a raw material containing a platinum group metal.

The recovery method according to one embodiment of the present invention is a method for recovering platinum group metals from a raw material containing platinum group metals, and may include the following steps (c) or (d): (c) a step of heating a mixture of the raw material, an alkali metal hydroxide, and an oxide at a temperature of 400°C or higher and lower than 600°C, dissolving the previously obtained heating product in an aqueous solvent to obtain a solution in which the platinum group metal is dissolved, and (d) a step of heating a mixture of the alkali metal hydroxide and oxide at a temperature of 400°C or higher and lower than 600°C, dissolving the previously obtained heating product in an aqueous solvent to obtain a raw material treatment solution, and then dissolving the raw material in the raw material treatment solution to obtain a solution in which the platinum group metal is dissolved.

The recovery method according to one embodiment of the present invention is a method for recovering platinum group metals from a raw material containing the platinum group metals, and may include the following step (c); (c) a step of heating a mixture containing the raw material, an alkali metal hydroxide, and an oxide at a temperature of 400°C or higher and lower than 600°C to obtain a heating product, which is previously obtained, and dissolving the heating product in an aqueous solvent to obtain a solution in which the platinum group metal is dissolved.

According to the recovery method of one embodiment of the present invention, platinum group metals can be recovered from raw materials containing platinum group metals at low temperatures. Therefore, one embodiment of the present invention can contribute to the achievement of Goal 7 (Ensure access to affordable, reliable, sustainable and modern energy for all) and Goal 9 (Build resilient infrastructure, promote inclusive and sustainable industrialization and foster innovation) of the Sustainable Development Goals (SDGs).

The recovery method according to one embodiment of the present invention may include a combination of the above steps (a) and (c), or a combination of the above steps (b) and (d). In this case, for example, the heated product obtained in the above step (a) may be subjected to the above step (c) to obtain a solution in which the platinum group metal is dissolved, or the heated product obtained in the above step (b) may be subjected to the above step (d) to obtain a solution in which the platinum group metal is dissolved.

The recovery method according to one embodiment of the present invention may include obtaining a heated product in step (b) above (for example, when the mixture includes a raw material containing a platinum group metal), and subjecting the heated product to step (c) above.

The raw material containing the platinum group metal may be a raw material containing platinum group metal that has been pretreated in advance, or may not be a raw material containing platinum group metal that has been pretreated in advance. From the viewpoint of increasing the purity of the recovered platinum group metal, it is preferable that the raw material containing the platinum group metal is a raw material containing platinum group metal that has been pretreated in advance. The pretreatment of the raw material may be heating, concentration, plating, physical sorting, and/or a combination thereof, in order to reduce the amount of impurities that coexist with the platinum group metal in the raw material.

When heated, the platinum group metal contained in the raw material reacts with the oxide and hydroxide of the alkali metal and is oxidized to become an oxidation product of the platinum group metal. The oxidation product is water-soluble and can be dissolved in an aqueous solvent such as water, so that a solution containing the platinum group metal can be obtained by dissolving the oxidation product in an aqueous solvent.

On the other hand, a raw material processing solution obtained by dissolving the heating product obtained by heating a mixture of an alkali metal hydroxide and oxide in an aqueous solvent contains a large amount of anions. The anions form coordinate bonds with the platinum group metal, thereby obtaining a solution in which the platinum group metal is dissolved. In the process of dissolving a raw material containing a platinum group metal in the raw material processing solution to obtain a solution in which the platinum group metal is dissolved, the raw material containing the platinum group metal and an oxidizing agent may be added to the raw material processing solution to obtain a solution in which the platinum group metal is dissolved.

The resulting platinum group metal solution (a solution in which platinum group metals are dissolved) can be treated with an organic solvent according to conventional techniques to selectively extract the desired platinum group metal.

According to this method, platinum group metals can be dissolved in water, etc., so there is no need to use acidic solvents such as aqua regia or high-concentration hydrochloric acid to pretreat raw materials containing platinum group metals. This reduces waste liquid treatment costs. In addition, hydrogen chloride gas caused by high-concentration hydrochloric acid is not generated, and there is no need to use highly corrosive chlorides, so corrosion of equipment can be avoided.

(Step of obtaining heated product)
Examples of the process for obtaining a heated product include (a) heating a mixture of the raw material, an alkali metal hydroxide, and an oxide at a temperature of 400° C. or higher and lower than 600° C. to obtain a heated product, and (b) heating a mixture of an alkali metal hydroxide and an oxide at a temperature of 400° C. or higher and lower than 600° C. to obtain a heated product.

In addition, in the above step (b), if the mixture contains a raw material that contains a platinum group metal, the step (b) can be considered to be substantially the same as the above step (a).

The heated product obtained in the above step (a) contains a large amount of oxidation products of platinum group metals that have been rendered water-soluble by anions. On the other hand, the heated product obtained in the above step (b) contains a large amount of a source of anions that can form coordinate bonds with platinum group metals.

In the case of the above step (b), a large amount of raw material processing solution for processing raw materials containing platinum group metals can be produced at once from the heated product. In addition, in the case of the above step (b), the number of times the step of heating the mixture of raw materials containing platinum group metals and hydroxides and oxides of alkali metals is performed can be reduced. As a result, in the case of the above step (b), heating costs, chemical costs, and waste liquid treatment costs can be reduced.

Examples of the platinum group metals include Pd, Pt, Rh, Ir, Os, and Ru. Examples of raw materials containing such platinum group metals include waste automobile catalysts and scrap electronic equipment.

Examples of the alkali metal in the alkali metal hydroxide include Na, K, Li, Rb, and Cs. Among these, Na and K are preferred, and K is more preferred, from the viewpoint of more efficiently converting platinum group metals into water-soluble substances. The alkali metal hydroxides may be used alone or in a mixture of multiple types.

The amount of the alkali metal hydroxide added to the raw material containing the platinum group metal is preferably 2 parts by weight or more and 40 parts by weight or less, and more preferably 10 parts by weight or more and 20 parts by weight or less, per 1 part by weight of the platinum group metal. By being in the above preferred range, the platinum group metal can be efficiently recovered with the minimum amount of alkali metal hydroxide added.

The oxide may be at least one selected from the group consisting of Al ₂ O ₃ , Na ₂ O, B ₂ O ₃ , K ₂ O, SiO ₂ , Li ₂ O, Rb ₂ O, Cs ₂ O, and P ₂ O _5. Examples of such oxides include glass (e.g., waste glass). According to the configuration using glass as the oxide, glass that can be procured at low cost can be effectively utilized. The oxide may be used alone or as a mixture of multiple types. When the oxide is used as a mixture of multiple types, if the mixture contains at least B ₂ O ₃ , the platinum group metal can be converted into a water-soluble substance more reliably.

The amount of the oxide added to the raw material containing the platinum group metal is preferably 3 parts by weight or more and 100 parts by weight or less, and more preferably 10 parts by weight or more and 50 parts by weight or less, per 1 part by weight of the platinum group metal. By being in the above preferred range, the platinum group metal can be efficiently recovered with the minimum amount of oxide added.

The alkali metal hydroxide functions as an oxidizing agent for oxidizing the platinum group metal. The oxide functions as a reaction aid for oxidizing the platinum group metal. The mixture of the raw material, the alkali metal hydroxide, and the oxide is heated to oxidize the platinum group metal contained in the mixture, and an oxidation product of the platinum group metal is obtained. At this time, the mixture is heated at a temperature of 400°C or higher and lower than 600°C, but it is more preferable to heat the mixture at a temperature of 400°C to 550°C. According to this configuration, the cost required for heating can be reduced. According to this configuration, the platinum group metal can be converted into a water-soluble substance under mild conditions. Furthermore, according to this configuration, since the heating temperature is lower than that of the conventional method, the load on the heating device including the electric furnace can be reduced, and the energy consumption for extracting the platinum group metal can be reduced, thereby reducing costs. The upper limit of the heating temperature may be 590°C, 580°C, 570°C, 560°C, 550°C, 540°C, 530°C, 520°C, or 510°C. The lower limit of the heating temperature may be 500°C, 490°C, 480°C, 470°C, 460°C, 450°C, 440°C, 430°C, 420°C, 410°C, or 400°C. The heating temperature may be appropriately selected depending on the composition of the mixture.

In addition, when the mixture of the hydroxide and oxide of the alkali metal is heated, a source of anions capable of forming coordinate bonds with platinum group metals is obtained. At this time, the mixture is heated at a temperature of 400°C or higher and lower than 600°C, but more preferably at a temperature of 400°C to 550°C. According to this configuration, the cost required for heating can be reduced. According to this configuration, platinum group metals can be converted into water-soluble substances under mild conditions. Also, according to this configuration, since the heating temperature is lower than that of conventional methods, the load on the heating device including the electric furnace can be reduced, and the energy consumption for extracting platinum group metals can be reduced, thereby reducing costs. The upper limit of the heating temperature may be 590°C, 580°C, 570°C, 560°C, 550°C, 540°C, 530°C, 520°C, or 510°C. The lower limit of the heating temperature may be 500°C, 490°C, 480°C, 470°C, 460°C, 450°C, 440°C, 430°C, 420°C, 410°C, or 400°C. The heating temperature may be appropriately selected depending on the composition of the mixture.

The heating time is preferably 1 minute or more, more preferably 10 minutes or more, more preferably 15 minutes or more, and more preferably 20 minutes or more. The heating time is preferably 120 minutes or less, more preferably 60 minutes or less, and more preferably 30 minutes or less. If the heating time is 1 minute or more, the oxidation of the platinum group metal can be sufficiently performed, and a sufficient source of anions capable of forming coordinate bonds with the platinum group metal can be obtained. On the other hand, if the heating time is 120 minutes or less, the load on the heating device including the electric furnace can be reduced, and the energy consumption for extracting the platinum group metal can be reduced, thereby reducing costs. In addition, the heating time may be appropriately selected depending on the composition of the mixture.

The mixture is preferably heated in an oxygen-containing atmosphere, for example, in air, in order to promote oxidation of the platinum group metal.

The composition of the mixture and/or the oxygen partial pressure in the atmosphere in which the mixture is heated may be adjusted as appropriate. This allows the solubility of the platinum group metal in the aqueous solvent to be adjusted.

For example, the solubility of the platinum group metal in the aqueous solvent can be adjusted by varying the basicity of the mixture and/or the oxygen partial pressure in the atmosphere in which the mixture is heated.

Specifically, by changing the basicity of the mixture and/or the oxygen partial pressure in the atmosphere in which the mixture is heated, a platinum group compound that dissolves favorably in an aqueous solvent containing any amount of water (e.g., an aqueous solvent containing 98% or more by weight, 95% or more by weight, 90% or more by weight, 85% or more by weight, or 80% or more by weight of water) may be synthesized.

It is also preferable to immerse a pipe for supplying an oxygen-containing gas into the mixture, supply the oxygen-containing gas from the pipe into the mixture, and heat the mixture while bubbling and stirring it.

It is also preferred to add a high valence cation to the mixture to further increase its ability to oxidize platinum group metals, such as Fe ³⁺ , Ce ⁴⁺ , or Gd ³⁺ .

From the viewpoint of more efficiently converting the platinum group metal into a water-soluble substance, it is preferable that the mixture further contains an oxoanion of an amphoteric element at least after heating. Examples of amphoteric elements include Al, Ti, V, Co, and Zr, and among these, Al or Ti is more preferable. It is considered that the presence of such an oxoanion in the mixture causes the oxidation product of the platinum group metal to react with the oxoanion, and the water solubility of the oxidation product is easily improved. Specific examples of oxoanions of amphoteric elements include AlO ₂ ^- , TiO ₃ ^2- , VO ₄ ^3- , and CoO ₂ ^- .

The oxoanion may be added directly to the mixture, or the mixture may be held and heated in a container (such as a crucible) containing an amphoteric element such as alumina, and the amphoteric element contained in the container may become an oxoanion and be dissolved into the mixture.

The container used to hold and heat the mixture may be made of metals such as silicon carbide/silicon nitride, stainless steel, and/or titanium. In this case, a ceramic material containing an amphoteric element such as alumina, formed into a spherical, rod-like, or plate-like shape, may be added to the mixture in the container. In other words, in the process of obtaining the heated product, an oxide of an amphoteric element may be further added to the mixture. As a result, the amphoteric element contained in the ceramic material becomes an oxoanion and dissolves into the mixture. The ceramic material is preferably porous in order to promote the dissolution of the oxoanion.

(Step of obtaining a solution in which platinum group metals are dissolved)
Examples of the step of obtaining a solution in which a platinum group metal is dissolved include (c) a step of heating a mixture of the raw material, an alkali metal hydroxide, and an oxide at a temperature of 400° C. or more and less than 600° C., dissolving the previously obtained heating product in an aqueous solvent to obtain a solution in which a platinum group metal is dissolved, and (d) a step of heating a mixture of an alkali metal hydroxide and an oxide at a temperature of 400° C. or more and less than 600° C., dissolving the previously obtained heating product in an aqueous solvent to obtain a raw material processing solution, and then dissolving the raw material in the raw material processing solution to obtain a solution in which a platinum group metal is dissolved. Note that a raw material containing a platinum group metal and an oxidizing agent may be dissolved in the raw material processing solution.

In the case of the above step (d), a large amount of raw material processing solution for processing raw materials containing platinum group metals can be produced at once from the heated product. In addition, in the case of the above step (d), the number of times the step of heating the mixture of raw materials containing platinum group metals and hydroxides and oxides of alkali metals is performed can be reduced. As a result, in the case of the above step (d), heating costs, chemical costs, and waste liquid treatment costs can be reduced.

The above-mentioned aqueous solvent is intended to be a solvent containing water as a main component, for example, a solvent containing 60% by weight or more, preferably 70% by weight or more, more preferably 80% by weight or more, more preferably 90% by weight or more, more preferably 95% by weight or more, more preferably 98% by weight or more, and most preferably 100% by weight of water. More specifically, the above-mentioned aqueous solvent is preferably a solvent that (i) contains 60% by weight or more, preferably 70% by weight or more, more preferably 80% by weight or more, more preferably 90% by weight or more, more preferably 95% by weight or more, more preferably 98% by weight or more, and most preferably 100% by weight of water, and (ii) does not contain a halogen. The halogen concentration of the halogen-free solvent may be 3 mol/L or less, preferably 1 mol/L or less, more preferably 0.1 mol/L or less, and even more preferably 0.01 mol/L or less. With this configuration, platinum group metals can be easily dissolved in the aqueous solvent.

The step of obtaining a solution in which the platinum group metal is dissolved may be a dissolution step of heating the raw material containing the platinum group metal, and contacting the heating product obtained with an aqueous solvent (e.g., water) to obtain a solution in which 15% by weight or more of the platinum group metal contained in the raw material containing the platinum group metal is dissolved in the aqueous solvent. The dissolution step may be a dissolution step of obtaining a solution in which 15% by weight or more, 20% by weight or more, 25% by weight or more, 30% by weight or more, 35% by weight or more, 40% by weight or more, 45% by weight or more, 50% by weight or more, 55% by weight or more, 60% by weight or more, 65% by weight or more, 70% by weight or more, 75% by weight or more, 80% by weight or more, 85% by weight or more, or 90% by weight or more of the platinum group metal contained in the raw material containing the platinum group metal is dissolved in the aqueous solvent. The weight of the aqueous solvent in which the platinum group metal is dissolved is not limited. The weight of the aqueous solvent in which the platinum group metal is dissolved may be, for example, 100 times or more, 1000 times or more, or 10,000 times or more the weight of the platinum group metal to be dissolved.

The aqueous solvent may contain components other than water, and examples of such components include components that do not contain halogens. Specific examples of such components are preferably polar solvents, such as alcohols such as methanol and ethanol, solutions containing water-soluble organic acids such as citric acid, solutions containing inorganic acids such as perchloric acid, or solutions containing hydroxide complexes of amphoteric elements.

A pH adjuster may be added to the aqueous solvent to adjust the pH to a desired level. In this case, the pH of the aqueous solvent is not particularly limited. Unlike the prior art, the present invention does not require the use of a strongly acidic solvent. Therefore, the pH of the aqueous solvent may be 6 to 8, 6 to 7, or 7 to 8. By using such an aqueous solvent, not only can platinum group metals be extracted efficiently, but adverse effects on the environment can also be prevented.

After obtaining a solution in which the platinum group metal is dissolved using the above aqueous solvent, the undissolved heated product can be treated in the same manner using a newly prepared aqueous solvent to obtain a solution in which the platinum group metal is dissolved. This operation may be repeated to obtain a solution in which further platinum group metal is dissolved. In such a process for repeatedly obtaining a solution, the composition of the aqueous solvent in each repeated step is not limited, and aqueous solvents with different compositions may be used for each repeated step. For example, the heated product may be dissolved in an aqueous solvent containing 98% or more by weight of water, and then the undissolved heated product may be dissolved in an aqueous solvent containing 80% to 90% by weight of water.

In addition, by adjusting the composition of the mixture in the process of obtaining the heated product, such as by increasing or decreasing the amount of oxide contained in the mixture, the solubility of the platinum group metal in the aqueous solvent in the process of obtaining a solution in which the platinum group metal is dissolved can be adjusted. For example, the amount of oxide may be adjusted so that the platinum group metal dissolves favorably in an aqueous solvent containing 98% or more by weight of water. In addition, by reducing the amount of oxide contained in the mixture compared to when the platinum group metal is dissolved in an aqueous solvent containing 98% or more by weight of water, the platinum group metal can be adjusted to dissolve more favorably in an aqueous solvent containing 80% to 90% by weight of water.

The oxidizing agent that accelerates the oxidation of platinum group metals may be air, oxygen gas, hydrogen peroxide, or a solution containing a cation of high valence. Of the above-mentioned oxidizing agents, oxygen gas or a cation of high valence is preferred because it has the advantage of being able to rapidly oxidize platinum group metals. Examples of cations of high valence include Fe ³⁺ , Ce ⁴⁺ , and Co ³⁺ .

Such an oxidizing agent is preferably added to the mixture before or during heating of the mixture. The presence of the oxidizing agent during heating effectively promotes oxidation of the platinum group metal. The timing of adding the oxidizing agent is not limited to this, and the oxidizing agent may be added after the mixture is heated or during dissolution of the mixture in the aqueous solvent.

After obtaining the above-mentioned solution, the undissolved platinum group metal may be introduced again into the process of obtaining a heated product. In other words, by introducing the undissolved platinum group metal again into the process of obtaining a heated product, the undissolved platinum group metal may be converted into a water-soluble substance, and a solution in which the platinum group metal is dissolved may be obtained again.

(Extraction and recovery process)
The method for recovering platinum group metals according to one embodiment of the present invention may include a step of extracting and recovering the platinum group metals in an organic solvent from the solution in which the platinum group metals are dissolved obtained by the above-mentioned step. This step may be carried out by a conventional method for extracting and recovering platinum group metals by treatment with an organic solvent.

This method for recovering platinum group metals makes it possible to selectively extract platinum group metals from raw materials (e.g., spent catalysts and scrap) in a low-corrosive environment without using harmful acidic solvents such as aqua regia or high-concentration hydrochloric acid.

As the organic solvent, for example, dialkyl sulfide, hydroxyoxime, 8-quinolinol, tertiary amine, or trialkylphosphate can be used. If hydroxyoxime is used as the organic solvent, Pd can be selectively extracted from among the platinum group metals, and if tertiary amine is used as the organic solvent, Pt can be selectively extracted from among the platinum group metals. In addition, if tertiary amine is used as the organic solvent after Pd and Pt are extracted from the solution in which the platinum group metals are dissolved, Ir can be selectively extracted from among the remaining platinum group metals, and Rh can be obtained by purifying the solution after extraction. Ru and Os can be volatilized and separated by distillation during these separation processes.

The solution obtained after the platinum group metal is extracted and recovered by the above-mentioned method for recovering platinum group metals can be used again in the pretreatment method as a raw material treatment solution. In this case, a raw material containing a platinum group metal is added to the raw material treatment solution, which is the solution obtained after the platinum group metal is extracted. When dissolving a raw material containing a platinum group metal in the raw material treatment solution, a raw material containing a platinum group metal and an oxidizing agent may be added to the raw material treatment solution. The platinum group metal is oxidized by the raw material treatment solution (or the raw material treatment solution and the oxidizing agent), and the oxidized platinum group metal dissolves in the raw material treatment solution, thereby obtaining a solution in which the platinum group metal is dissolved again. Examples of the oxidizing agent include those mentioned above. According to such a method, heating costs, chemical costs, and waste liquid treatment costs can be reduced.

<2. Platinum group metals recovery system>
A platinum group metal recovery system according to an embodiment of the present invention will be described below. Note that the configuration already described in the above <1. Platinum group metal recovery method> will not be described here.

The recovery system according to one embodiment of the present invention is a platinum group metal recovery system that recovers platinum group metals from a raw material containing platinum group metals, and may include (A) a heating device for heating a mixture of the raw material, an alkali metal hydroxide, and an oxide at a temperature of 400°C or higher and less than 600°C to obtain a heated product, or (B) a heating device for heating a mixture of an alkali metal hydroxide and an oxide at a temperature of 400°C or higher and less than 600°C to obtain a heated product.

The recovery system according to one embodiment of the present invention is a platinum group metal recovery system that recovers platinum group metals from a raw material containing platinum group metals, and may include (B) a heating device for heating a mixture containing an alkali metal hydroxide and an oxide at a temperature of 400°C or higher and lower than 600°C to obtain a heated product. The mixture may further contain a raw material containing a platinum group metal.

The recovery system according to one embodiment of the present invention is a platinum group metal recovery system that recovers platinum group metals from a raw material containing platinum group metals, and may include: (C) a dissolving device for heating a mixture of the raw material, an alkali metal hydroxide, and an oxide at a temperature of 400°C or higher and lower than 600°C to dissolve the heated product obtained in advance in an aqueous solvent to obtain a solution in which the platinum group metal is dissolved; or (D) a dissolving device for heating a mixture of an alkali metal hydroxide and an oxide at a temperature of 400°C or higher and lower than 600°C to dissolve the heated product obtained in advance in an aqueous solvent to obtain a raw material processing solution, and then dissolving a raw material containing platinum group metals in the raw material processing solution to obtain a solution in which the platinum group metal is dissolved.

The recovery system according to one embodiment of the present invention is a platinum group metal recovery system that recovers platinum group metals from a raw material containing the platinum group metals, and may include (C) a dissolving device for dissolving a heating product obtained in advance by heating a mixture containing the raw material, an alkali metal hydroxide, and an oxide at a temperature of 400°C or higher and lower than 600°C in an aqueous solvent to obtain a solution in which the platinum group metal is dissolved.

The platinum group metal recovery system according to one embodiment of the present invention may include a combination of the heating device (A) and the melting device (C) above, or a combination of the heating device (B) and the melting device (D) above.

The recovery system according to one embodiment of the present invention may include the heating device (B) described above (for example, when the mixture contains a raw material containing a platinum group metal) and the melting device (C) described above. The recovery system may be considered to be substantially the same as the combination of the heating device (A) described above and the melting device (C) described above.

The heating device may include a heating tank. The heating tank may include, for example, (i) a container for storing a mixture of a raw material containing a platinum group metal, an alkali metal hydroxide, and an oxide, or a container for storing a mixture of an alkali metal hydroxide and an oxide, and (ii) a heater for heating the mixture in the container to a temperature of 400°C or higher and lower than 600°C. The heating tank may further include an amphoteric element inlet for supplying an amphoteric element into the container, or may include a storage tank for storing the amphoteric element to be supplied into the container.

The heater can heat the mixture in the container to a temperature of 400°C or higher and lower than 600°C, but it is more preferable that the heater can heat the mixture in the container to a temperature of 400°C to 550°C. This configuration can reduce the cost required for heating. This configuration can convert platinum group metals into water-soluble substances under mild conditions. In addition, this configuration has a lower heating temperature than conventional methods, so the load on the heating device including the electric furnace can be reduced, and the energy consumption for extracting platinum group metals can be reduced, resulting in cost reduction. The upper limit of the heating temperature may be 590°C, 580°C, 570°C, 560°C, 550°C, 540°C, 530°C, 520°C, or 510°C. The lower limit of the heating temperature may be 500°C, 490°C, 480°C, 470°C, 460°C, 450°C, 440°C, 430°C, 420°C, 410°C, or 400°C. The heating temperature may be appropriately selected depending on the composition of the mixture.

The heating tank may be formed from a material containing an amphoteric element. Examples of such containers include crucibles such as an alumina crucible, a zirconia crucible, an aluminum titanate crucible, a silicon carbide/silicon nitride crucible, or a mullite crucible. With this configuration, when the mixture is heated, the amphoteric element contained in the heating tank is dissolved as an oxoanion. The oxoanion can promote the oxidation of the platinum group metal contained in the mixture and improve the water solubility of the platinum group metal.

The dissolving apparatus may include a dissolving tank. The dissolving tank may include (iii) a container for dissolving a heated product obtained in advance by heating a mixture of a raw material containing a platinum group metal, an alkali metal hydroxide, and an oxide at a temperature of 400°C or higher and lower than 600°C in an aqueous solvent to obtain a solution in which the platinum group metal is dissolved, or a container for dissolving a heated product obtained in advance by heating a mixture of an alkali metal hydroxide and an oxide at a temperature of 400°C or higher and lower than 600°C in an aqueous solvent to obtain a solution for raw material processing, and then dissolving a raw material containing a platinum group metal in the solution for raw material processing to obtain a solution in which the platinum group metal is dissolved, and (iv) a water-soluble solvent inlet for supplying an aqueous solvent into the container. The dissolving tank may include a storage tank for storing the aqueous solvent to be supplied into the container. The dissolving tank may also include an oxidizing agent inlet for supplying an oxidizing agent to the container, or may include a storage tank for storing the oxidizing agent to be supplied into the container.

The dissolution tank may be a tank for obtaining a solution in which 15% by weight or more of the 100% by weight of the platinum group metal contained in the raw material containing the platinum group metal is dissolved in the aqueous solvent by contacting the heating product obtained by heating the raw material containing the platinum group metal with an aqueous solvent (e.g., water). The dissolution tank may be a tank for obtaining a solution in which 15% by weight or more, 20% by weight or more, 25% by weight or more, 30% by weight or more, 35% by weight or more, 40% by weight or more, 45% by weight or more, 50% by weight or more, 55% by weight or more, 60% by weight or more, 65% by weight or more, 70% by weight or more, 75% by weight or more, 80% by weight or more, 85% by weight or more, or 90% by weight or more of the 100% by weight of the platinum group metal contained in the raw material containing the platinum group metal is dissolved in the aqueous solvent. The weight of the aqueous solvent in which the platinum group metal is dissolved is not limited. The weight of the aqueous solvent in which the platinum group metal is dissolved may be, for example, 100 times or more, 1000 times or more, or 10,000 times or more the weight of the platinum group metal to be dissolved.

The dissolution tank is preferably large enough to directly insert the heating tank. The container used for the heating tank and the container used for the dissolution tank can be configured as the same container. For example, in the case of a crucible, the crucible used for the heating tank and the crucible used for the dissolution tank can be configured as the same crucible. With this configuration, it is not necessary to once remove the heating product from the heating tank and transfer it to the dissolution tank. The dissolution tank is also preferably equipped with a stirring member such as a stirring rod or a stirrer. With this configuration, the heating product can be efficiently dissolved in the aqueous solvent. The heating device and the dissolution device can also be configured as the same device.

The platinum group metal recovery system according to this embodiment may further include an extraction tank that extracts the platinum group metal from the solution in which the platinum group metal is dissolved into an organic solvent. There are no particular limitations on the type of extraction tank, so long as it is capable of performing organic solvent treatment according to conventional technology.

This recovery system allows platinum group metals in waste catalysts and scrap to be efficiently extracted into an aqueous solvent in a low-corrosive environment without using hazardous acidic solvents such as aqua regia or high-concentration hydrochloric acid.

In Examples 1 to 15 and Comparative Examples 1 to 14, a mixture of hydroxides and oxides of platinum group metals and alkali metals was added to an alumina crucible, and the mixture was heated in an electric furnace. During the heating, under conditions where the mixture contains metal Pd, the metal Pd is oxidized by reaction with the hydroxide of the alkali metal. In addition, a part of the components of the alumina crucible to which the mixture was added is dissolved in the reaction medium and exists in the mixture as Al _x O _y ^z- . In this way, the mixture is heated for a predetermined time, and then the heated product is cooled to obtain a product, which is defined as a heating product.

1. Study of heating temperature during preparation of heated product in solubilization of platinum (Pt) in water <Samples and methods>
(1) Comparative Example 1 (Pt- _{K2CO3 - K2O} - _{B2O3 system} )
The Pt-K ₂ CO ₃ -K ₂ O-B ₂ O ₃ system heating product of Comparative Example 1 was prepared using a commercially available standard compound reagent as follows: First, 10.1 mg of metallic platinum (Pt), 49.9 mg of boron oxide, and 3,900 mg of potassium carbonate were mixed, and the mixture was added to a 30 mL alumina crucible.

The crucible was then placed in an electric furnace and heated to 1000°C. During heating, air was continuously supplied into the electric furnace at a flow rate of 8 L/min using an air pump. After heating was completed, the crucible was allowed to cool naturally to below 200°C in the electric furnace and then removed from the furnace.

The crucible containing the obtained heated product was placed in a 200 mL beaker, 150 mL of ion-exchanged water was added, and the mixture was stirred for 30 minutes using a stirring blade. The suspension in the beaker was then suction filtered using 5C filter paper, and the obtained filtrate was made up to 250 mL with ion-exchanged water. This liquid was then diluted 10-fold with 1 M aqueous hydrochloric acid, and the diluted liquid was used as the analysis sample.

The solid residue after treatment with the ion-exchanged water was placed in a 200 mL beaker, to which 150 mL of 0.01 M aqueous hydrochloric acid was added, and the mixture was stirred for 30 minutes using a stirring blade. After that, the suspension in the beaker was suction filtered using 5C filter paper, and the resulting filtrate was made up to 250 mL with 0.01 M aqueous hydrochloric acid. This liquid was used as the analysis sample.

The solid residue after treatment with the 0.01 M hydrochloric acid aqueous solution was similarly treated with 0.1 M hydrochloric acid aqueous solution to obtain an analytical sample.

The solid residue after treatment with the 0.1 M hydrochloric acid solution was similarly treated with 1 M hydrochloric acid solution to obtain an analytical sample.

The platinum concentration in the analytical samples obtained through this series of operations was determined by ICP atomic emission spectrometry.

(2) Comparative Example 2 (Pt-KOH system)
The Pt-KOH-based heating product of Comparative Example 2 was prepared using a commercially available standard compound reagent as follows: First, about 10 mg of metallic platinum (Pt), about 200 mg of potassium hydroxide, and about 50 mg of boron oxide were mixed, and the mixture was added to a 5 mL alumina crucible.

The crucible was then placed in an electric furnace and heated at 500°C for 2 hours. During heating, air was continuously supplied into the electric furnace at a flow rate of 8 L/min using an air pump. After heating was completed, the crucible was allowed to cool naturally to below 200°C in the electric furnace and then removed from the furnace.

The crucible containing the obtained heated product was placed in a 200 mL beaker, 150 mL of ion-exchanged water was added, and the mixture was stirred for 30 minutes using a stirring blade. The suspension in the beaker was then suction filtered using 5C filter paper, and the obtained filtrate was made up to 250 mL with ion-exchanged water. This liquid was then diluted 10-fold with a 1 M aqueous hydrochloric acid solution, and the diluted liquid was used as the analysis sample.

The solid residue after treatment with the ion-exchanged water was placed in a 200 mL beaker, to which 150 mL of 0.01 M aqueous hydrochloric acid was added, and the mixture was stirred for 30 minutes using a stirring blade. After that, the suspension in the beaker was suction filtered using 5C filter paper, and the resulting filtrate was made up to 250 mL with 0.01 M aqueous hydrochloric acid. This liquid was used as the analysis sample.

The solid residue after treatment with the 0.01 M hydrochloric acid aqueous solution was similarly treated with 0.1 M hydrochloric acid aqueous solution to obtain an analytical sample.

The solid residue after treatment with the 0.1 M hydrochloric acid solution was similarly treated with 1 M hydrochloric acid solution to obtain an analytical sample.

The platinum concentration in the analytical samples obtained through this series of operations was determined by ICP atomic emission spectrometry.

(3) Examples 1 to 6 and Comparative Examples 3 to 8 (Pt-B ₂ O ₃ -KOH system, Pt-SiO ₂ -KOH system)
The Pt-B ₂ O ₃ -KOH-based heating products of Examples 1 to 6 and Comparative Examples 3 to 7, or the Pt-K ₂ O-SiO ₂ -based heating product of Comparative Example 8, were prepared as follows using commercially available standard compound reagents. First, about 10 mg of platinum, about 200 mg of potassium hydroxide, and about 50 mg of boron oxide or silicon dioxide were mixed and added to a 30 mL or 5 mL alumina crucible. This crucible was placed in an electric furnace and heated at a predetermined temperature for 2 hours. At this time, the heating temperature was changed from 300 to 800°C. During heating, air was continuously supplied into the electric furnace at a flow rate of 8 L/min using an air pump. After heating was completed, the crucible was naturally cooled to 200°C or less in the electric furnace, and the crucible was removed from the furnace.

The crucible containing the above-mentioned heated product was placed in a 200 mL beaker, 150 mL of ion-exchanged water was added, and the mixture was stirred for 30 minutes using a stirring blade. The suspension in the beaker was then suction filtered using 5C filter paper, and the resulting filtrate was made up to 250 mL. This liquid was then diluted 10-fold with 1 M aqueous hydrochloric acid, and used as the analysis sample.

Next, the solid residue after the ion-exchanged water treatment was placed in a 200 mL beaker, and 150 mL of 0.01 M aqueous hydrochloric acid solution was added thereto and stirred for 30 minutes using a stirring blade. After that, the suspension in the beaker was suction filtered using 5C filter paper, and the resulting filtrate was diluted to 250 mL. This liquid was used as the analysis sample.

Next, the solid residue after the 0.01M hydrochloric acid treatment was similarly treated with 0.1M aqueous hydrochloric acid and 1M aqueous hydrochloric acid to obtain an analytical sample. However, in some experiments, only ion-exchanged water treatment, or only ion-exchanged water treatment and 0.01M hydrochloric acid treatment were performed.

The platinum concentration in the analytical samples obtained through this series of operations was determined by ICP atomic emission spectrometry.

Table 1 shows the composition of the reaction medium used in this example and the comparative example.

<Results>
The amount of platinum (Pt) eluted from each heated product is shown in Table 2 as a Pt dissolution rate (%) in ion-exchanged water, 0.01 M hydrochloric acid aqueous solution, 0.1 M hydrochloric acid aqueous solution, and 1 M hydrochloric acid aqueous solution. The Pt dissolution rate in each solution was calculated by the following formula:
Pt dissolution rate (%)=(amount of Pt in solution/amount of Pt added)×100 (Equation 1).

From the above, it has become clear that if the heating temperature in the pretreatment process to obtain the heated product is 400°C or higher and lower than 600°C, water-soluble Pt can be produced as efficiently as or more than when the heating temperature is 600°C or higher. In addition, the solution was one in which 15% by weight or more of the amount of Pt added (100% by weight of platinum group metals contained in the raw material) was dissolved in water. In other words, it has become clear that one aspect of the present invention is effective as a pretreatment method for raw materials when extracting water-soluble platinum group compounds.

2. Water-solubilization of palladium (Pd) and rhodium (Rh) (Examples 7 and 8)
Materials and Methods
The Pd-B ₂ O ₃ -KOH system heating product or the Rh-B ₂ O ₃ -KOH system heating product was prepared as follows using a commercially available standard compound reagent. 10 mg of either palladium (Pd) or rhodium (Rh) was mixed with 200 mg of potassium hydroxide and 50 mg of boron oxide, and added to a 5 mL alumina crucible. This crucible was placed in an electric furnace and heated at 500°C for 2 hours. During heating, air was continuously supplied into the electric furnace at a flow rate of 8 L/min using an air pump. After heating was completed, the crucible was naturally cooled to 200°C or less in the electric furnace, and then removed from the furnace.

The crucible containing the above-mentioned heated product was placed in a 200 mL beaker, 150 mL of ion-exchanged water was added, and the mixture was stirred for 30 minutes using a stirring blade. The suspension in the beaker was then suction filtered using 5C filter paper, and the resulting filtrate was diluted to 250 mL. This liquid was then diluted 10-fold with 1 M aqueous hydrochloric acid, and used as the analysis sample.

The solid residue after the ion-exchanged water treatment was placed in a 200 mL beaker, to which 150 mL of 0.01 M aqueous hydrochloric acid was added, and the mixture was stirred for 30 minutes using a stirring blade. After that, the suspension in the beaker was suction filtered using 5C filter paper, and the resulting filtrate was diluted to 250 mL. This liquid was used as the analysis sample.

The solid residue after the 0.01M hydrochloric acid treatment was similarly treated with 0.1M aqueous hydrochloric acid and 1M aqueous hydrochloric acid to obtain an analytical sample.

The concentrations of palladium and rhodium in the analytical samples obtained through this series of operations were determined by ICP atomic emission spectrometry.

<Results>
The amounts of palladium (Pd) and rhodium (Rh) eluted from each of the heated products are shown as the dissolution rates (%) of Pd and Rh in ion-exchanged water, 0.01 M aqueous hydrochloric acid solution, 0.1 M aqueous hydrochloric acid solution, and 1 M aqueous hydrochloric acid solution in Tables 3 and 4. The dissolution rates of Pd and Rh in each solution were calculated using the following formula.

Pd or Rh dissolution rate (wt%)=
(Amount of Pd or Rh in solution/Amount of Pd or Rh added)×100 (Equation 2).

From the above, it has become clear that water-soluble Pd or Rh can be efficiently produced if the heating temperature in the pretreatment process to obtain the heated product is 400°C or higher and lower than 600°C. In addition, the solution was one in which 15% by weight or more of the amount of Pd or Rh added (100% by weight of platinum group metals contained in the raw material) was dissolved in water. In other words, it has become clear that one aspect of the present invention is effective as a pretreatment method for raw materials when extracting water-soluble platinum group compounds.

3. Examination of heating time when preparing the heated product in the water-solubilization of platinum (Pt) We investigated shortening the heating time when preparing the heated product.
Materials and Methods
The Pt-B ₂ O ₃ -KOH based heating products of Examples 9 to 15 and Comparative Examples 9 to 14 were prepared as follows using commercially available standard compound reagents.

Approximately 10 mg of platinum, approximately 200 mg of potassium hydroxide, and approximately 50 mg of boron oxide were mixed and added to a 30 mL alumina crucible. This crucible was placed in an electric furnace and heated to a specified temperature. The heating temperature was 500°C in Examples 9 to 15 and 600°C in Comparative Examples 9 to 14. The heating time at each temperature was varied to 1 minute, 10 minutes, 30 minutes, and 60 minutes. After heating was completed, the crucible was allowed to cool naturally to below 200°C in the electric furnace, and then removed from the furnace.

The crucibles containing each heated product were placed in a 200 mL beaker, 150 mL of ion-exchanged water was added, and the mixture was stirred for 30 minutes using a stirring blade. After that, the suspension in the beaker was suction filtered using 5C filter paper, and the obtained filtrate was made up to 250 mL. This liquid was then diluted 10 times with 1 M aqueous hydrochloric acid, and this was used as the analysis sample. The solid residue after the water treatment was placed in a 200 mL beaker, 150 mL of 0.01 M aqueous hydrochloric acid was added, and this was stirred for 30 minutes using a stirring blade. After that, the suspension in the beaker was suction filtered using 5C filter paper, and the obtained filtrate was made up to 250 mL. This liquid was used as the analysis sample. The solid residue after the treatment was similarly treated with 0.1 M aqueous hydrochloric acid and 1 M aqueous hydrochloric acid to obtain an analysis sample.

The Pt concentration in the analytical samples obtained through this series of operations was determined by ICP atomic emission spectrometry.

Table 5 shows the composition of the reaction medium used in this example and the comparative example.

<Results>
The amount of platinum (Pt) eluted from each heated product is shown as the Pt dissolution rate (%) in ion-exchanged water, 0.01 M hydrochloric acid aqueous solution, 0.1 M hydrochloric acid aqueous solution, and 1 M hydrochloric acid aqueous solution in Table 6. The Pt dissolution rate in each solution was calculated using formula 1 in "1. Consideration of heating temperature during preparation of heated product in water-solubilization of platinum (Pt)" above.

From Examples 9 to 15, it became clear that by setting the heating temperature in the pretreatment process for obtaining the heated product to 400°C or higher and lower than 600°C, and the heating time to 1 minute or longer and 120 minutes or longer, water-soluble Pt can be produced as efficiently as when the heating temperature is 600°C. In addition, the solution was one in which 15% by weight or more of the amount of Pt added (100% by weight of platinum group metals contained in the raw material) was dissolved in water. In other words, it became clear that one aspect of the present invention is effective as a pretreatment method for raw materials when extracting water-soluble platinum group compounds.

4. Study on water-solubilization of platinum group metals in actual catalysts (Example 16)
A real catalyst (a waste catalyst for purifying exhaust gas from motorcycles) was used as a raw material containing platinum group metals, and the water-solubilization of palladium (Pd) and rhodium (Rh) in the raw material containing platinum group metals (the real catalyst) was investigated.

Materials and Methods
500.2 mg of the actual catalyst containing palladium (Pd) and rhodium (Rh), about 1000 mg of potassium hydroxide, and about 250 mg of boron oxide were mixed and added to a 30 mL alumina crucible. The crucible was placed in an electric furnace and heated at 500°C for 2 hours. After the heating was completed, the crucible was naturally cooled to 200°C or less in the electric furnace, and then the crucible was removed from the furnace. In this way, a heating product using the actual catalyst as a raw material was obtained.

The crucible containing the above-mentioned heated product was placed in a 200 mL beaker, 150 mL of ion-exchanged water was added thereto, and the mixture was stirred for 30 minutes using a stirring blade. After that, the suspension in the beaker was suction filtered using 5C filter paper, and the obtained filtrate was made up to 250 mL. Furthermore, this liquid was diluted 10 times with 1 M hydrochloric acid aqueous solution, and this was used as an analysis sample.
The solid residue after the ion-exchanged water treatment was placed in a 200 mL beaker, to which 150 mL of 1 M hydrochloric acid aqueous solution was added, and the mixture was stirred for 30 minutes using a stirring blade. After that, the suspension in the beaker was suction filtered using 5C filter paper, and the obtained filtrate was diluted to 250 mL. This liquid was used as the analysis sample.

The concentrations of palladium and rhodium in the analytical samples obtained through this series of operations were determined by ICP atomic emission spectrometry.

Table 7 shows the composition of the actual catalyst used in Example 16.

<Results>
The amounts of palladium (Pd) and rhodium (Rh) eluted from the heated products are shown in Table 8 as the dissolution rates (%) of Pd and Rh in ion-exchanged water and 1M aqueous hydrochloric acid solution. The dissolution rates of Pd and Rh in each solution were calculated using the following formula:
Pd or Rh dissolution rate (wt%)=
(Amount of Pd or Rh in solution/Amount of actual catalyst added)×100 (Equation 3).

From the above, it was found that the Pd or Rh in the actual catalyst was also converted to a state that was soluble in ion-exchanged water or 1M aqueous hydrochloric acid. In other words, it was revealed that one aspect of the present invention is also effective for actual catalysts as a pretreatment method for raw materials when extracting water-soluble platinum group compounds.

The present invention can be used to recover platinum group metals from raw materials containing platinum group metals (e.g., spent catalysts, etc.).

Claims (13)

A method for recovering platinum group metals from a raw material containing platinum group metals, the method comprising the following step (b):
(b) A step of heating the mixture containing the hydroxide and oxide of an alkali metal at a temperature of 400° C. or more and less than 600° C. to obtain a heating product. The recovery method according to claim 1, characterized in that the mixture further contains a raw material containing a platinum group metal. A method for recovering platinum group metals from a raw material containing platinum group metals, the method comprising the following step (c):
(c) A step of heating a mixture containing the raw material, an alkali metal hydroxide, and an oxide at a temperature of 400° C. or higher and lower than 600° C. to obtain a heated product, and dissolving the heated product in an aqueous solvent to obtain a solution in which a platinum group metal is dissolved. A recovery method comprising obtaining a heated product in step (b) of claim 2, and subjecting the heated product to step (c) of claim 3. The recovery method according to any one of claims 1 to 3, characterized in that the heating time is 1 minute or more and 120 minutes or less. The recovery method according to any one of claims 1 to 3, characterized in that the mixture further contains an oxoanion of an amphoteric element. The recovery method according to any one of claims 1 to 3, characterized in that the platinum group metal is Pd, Pt, Rh, Ir, Os, or Ru. The recovery method according to any one of claims 1 to 3, characterized in that the alkali metal is Na, K, Li, Rb, or Cs. The recovery method according to any _one of claims ₁ to ₃ , characterized in that the oxide is at least one selected from the group consisting of _Al2O3 , _Na2O , _B2O3 , _K2O , _SiO2 , _Li2O , _Rb2O , _Cs2O , and _P2O5 . A platinum group metal recovery system for recovering platinum group metals from a raw material containing platinum group metals, comprising:
(B) A recovery system comprising a heating device for heating a mixture containing an alkali metal hydroxide and an oxide at a temperature of 400°C or higher and lower than 600°C to obtain a heated product. The recovery system according to claim 10, characterized in that the mixture further contains a raw material containing a platinum group metal. A platinum group metal recovery system for recovering platinum group metals from a raw material containing platinum group metals, comprising:
(C) A recovery system comprising a dissolving device for dissolving a heated product obtained in advance by heating a mixture containing the raw material, an alkali metal hydroxide, and an oxide at a temperature of 400°C or higher and lower than 600°C in an aqueous solvent to obtain a solution in which the platinum group metal is dissolved. A recovery system comprising the heating device (B) of claim 11 and the melting device (C) of claim 12.