Method for recovering platinum group metals

Abstract

Provided is a platinum-group metal recovery method for efficiently recovering platinum-group metals. The platinum-group metal recovery method comprises an immobilization step for bringing a raw material melt containing platinum-group metals, an alkali metal carbonate or hydroxide melt, an oxide melt, and a ceramic material into contact with each other to immobilize the platinum-group metals on the ceramic material.

Description

Technical Field

[0001] The present invention relates to a method for recovering platinum group metals, a platinum group metal-containing composition, and a ceramic material in which platinum group metals are immobilized.

Background Art

[0002] Since platinum group metals have excellent catalytic performance, they are used in various applications such as automotive exhaust gas purification catalysts and catalysts for fuel cell vehicles. Thus, while platinum group metals are industrially indispensable elements, due to their rarity, the production volume of platinum group metals is very small compared to base metals. For example, even for Pt and Pd, which have relatively large production volumes among platinum group metals, their respective production volumes are about 200 tons. Furthermore, the primary supply sources of platinum group metals are limited to South Africa and Russia, etc. Therefore, if the demand for platinum group metals increases due to the development of new materials using platinum group metals, a shortage in the supply of platinum group metals will occur. That is, it can be said that the current supply risk of platinum group metals is high.

[0003] In order to address the supply risk due to such uneven distribution of resources, it is very important to extract and recover platinum group metals from waste products such as waste catalysts generated in Japan. Also, the mining and smelting of natural ores involve a large environmental burden. Therefore, if platinum group metals can be efficiently extracted from waste products with a higher platinum group metal concentration than natural ores, it will also lead to a reduction in the environmental burden. However, since platinum group metals are extremely chemically stable, in the conventional dry method, after separating and concentrating platinum group metals from waste products, it is necessary to dissolve the concentrate with a high-concentration acid. For this reason, the energy consumption for extracting platinum group metals is large, and the chemical agent cost and waste liquid treatment cost are also high. Therefore, it is an urgent task to develop a more efficient method for recovering platinum group metals. For example, Patent Documents 1 to 4 and Non-Patent Document 1 disclose conventional techniques related to methods for recovering platinum group metals.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Non-Patent Document

[0005]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The following describes the prior art disclosed in Patent Documents 1 to 4 and their problems.

[0007] (1) Dissolution of platinum group metals with aqua regia Patent Document 1 discloses a method for dissolving platinum group metals using aqua regia. However, chlorine gas and nitrosyl chloride generated in aqua regia are highly corrosive and toxic. Corrosion of peripheral equipment progresses due to these gases, resulting in costs for repairing the corroded parts. In addition, a large amount of neutralizing agent is required to treat the used aqua regia, and it is also necessary to reduce the nitrate ion concentration below the drainage standard. For this reason, the drainage treatment process becomes complicated and the drainage treatment cost is also high.

[0008] Therefore, in order to avoid the use of harmful aqua regia, an aqua regia-free process as follows is being considered.

[0009] (2) Improvement in the solubility of platinum group metals by the reaction of platinum group metals with active metals Patent Document 2 discloses a technique for alloying by reacting a platinum group metal with an active metal. By subjecting the obtained alloy to chlorination treatment or oxidation treatment, a composite compound of a chloride or oxide of the platinum group metal and a chloride is formed. By treating this composite compound with brine, the platinum group metal can be extracted. However, since it requires steps such as alloying of the platinum group metal and the active metal, and chlorination / oxidation treatment of the alloy, the process is complicated. In addition, Mg, Ca, Zn, Fe, Na, K, Pb, Li, etc. used as active metals have extremely high reactivity and cause corrosion of peripheral equipment.

[0010] (3) Improvement in the solubility of platinum group metals by the reaction of platinum group metals with chlorine gas Patent Document 3 discloses a technique for simplifying the process of the technique in (2) above by reacting a platinum group metal with chlorine gas in a molten salt to convert the platinum group metal into a chloride that is easily soluble in water. However, in order to convert the platinum group metal into a chloride, it is necessary to react the platinum group metal with a chlorinating agent such as a large amount of chlorine gas. Therefore, corrosion of the reaction furnace and peripheral equipment by the introduced chlorinating agent progresses, and the cost for repairing it is high.

[0011] (4) Improvement in the solubility of platinum group metals by the reaction of platinum group metals with alkali metal carbonates Patent Document 4 discloses a technique for forming a soluble composite oxide of a platinum group metal by reacting the platinum group metal with an alkali metal carbonate. Since the generated composite oxide has high solubility in hydrochloric acid, it can be dissolved in 12M hydrochloric acid instead of aqua regia. However, the acid concentration required for dissolution is still high, and the neutralization cost of the wastewater is high. In addition, highly corrosive hydrogen chloride gas is generated from high-concentration hydrochloric acid, so corrosion of peripheral equipment by it also becomes a problem.

[0012] (5) Elution of platinum group metals into an aqueous solvent In order to solve the above problems (1) to (4), the inventors have developed a method of heating platinum group metals in a molten oxide to produce water-soluble platinum group compounds and eluting the platinum group compounds into an aqueous solvent (Non-Patent Document 1). In this method, since a molten oxide containing a water-soluble platinum group compound is immersed in an aqueous solvent to elute the platinum group metal into the aqueous solvent, salts and the like derived from the molten oxide are contained in high concentrations in the obtained aqueous solvent in addition to the platinum group compounds. Therefore, development of a technique for efficiently recovering platinum group metals from a molten oxide containing a water-soluble platinum group compound is desired.

[0013] An aspect of the present invention aims to provide a method for recovering platinum group metals that can efficiently recover platinum group metals.

Means for Solving the Problems

[0014] In order to solve the above problems, a method for recovering platinum group metals according to an aspect of the present invention includes a fixing step of bringing a melt of a raw material containing platinum group metals, a melt of a carbonate or hydroxide of an alkali metal, a melt of an oxide, and a ceramic material into contact with each other to fix the platinum group metals on the ceramic material.

[0015] A platinum group metal-containing composition according to an aspect of the present invention contains a platinum group metal and an amphoteric element, and when the total amount of the platinum group metal and the amphoteric element is 100% by weight, contains 99% by weight or more of the platinum group metal and 1% by weight or less of the amphoteric element.

[0016] A ceramic material according to an aspect of the present invention has a fixing layer containing O and an alkali metal formed on its surface, and the platinum group metal is fixed in the fixing layer.

Effects of the Invention

[0017] According to one aspect of the present invention, a method for recovering a platinum group metal capable of efficiently recovering the platinum group metal can be provided.

Brief Description of the Drawings

[0018]

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Mode for Carrying Out the Invention

[0019] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. The following description is for better understanding of the gist of the invention and does not limit the present invention unless otherwise specified. Also, unless otherwise specified in this specification, "A~B" representing a numerical range means "A or more and B or less".

[0020] <1. Outline of the method for recovering platinum group metals> The present inventor has found that (i) a water-soluble platinum group metal (platinum group compound) is efficiently immobilized on a ceramic material, and (ii) the platinum group compound immobilized on the ceramic material is efficiently eluted from the ceramic material by an aqueous solvent, and has thus completed the present invention.

[0021] The method for recovering platinum group metals according to one embodiment of the present invention includes an immobilization step of bringing a melt of a raw material containing a platinum group metal, a melt of a carbonate or hydroxide of an alkali metal, a melt of an oxide, and a ceramic material into contact to immobilize the platinum group metal on the ceramic material.

[0022] The platinum group metal contained in the raw material reacts with the oxide and the melt containing the carbonate or hydroxide of the alkali metal to be oxidized, and becomes an oxidation product of the platinum group metal. The oxidation product is a water-soluble platinum group compound and is efficiently immobilized on the ceramic material. Thereby, the platinum group compound and salts (for example, alkali metals and boric acid, etc.) derived from the melt can be separated.

[0023] As described above, the platinum group compound immobilized on the ceramic material is water-soluble. When the ceramic material on which the platinum group compound is immobilized is brought into contact with an aqueous solvent, the platinum group compound elutes from the ceramic material into the aqueous solvent. As a result, the platinum group compound and salts and the like derived from the melt can be further separated.

[0024] According to the present invention, since the mixing of salts and the like into the aqueous solvent can be greatly reduced, the cost required for treating the aqueous solvent after recovering the platinum group metal can be reduced.

[0025] As shown in the examples described later, the elution efficiency of the platinum group compound into the aqueous solvent changes when the type of the aqueous solvent changes. Therefore, by selecting the type of the aqueous solvent, the target platinum group metal can be selectively recovered. Also, for the aqueous solvent containing the platinum group compound, for example, by performing an organic solvent treatment according to the prior art, the target platinum group metal can be selectively recovered.

[0026] <2. Immobilization step> (2-1. Preparation of melt) In obtaining the above platinum group compound, a melt containing a platinum group metal, a carbonate or hydroxide of an alkali metal, and an oxide is prepared. In the melt, the platinum group metal is oxidized to become a water-soluble platinum group compound. Then, by bringing the melt containing the platinum group compound into contact with the ceramic material, the platinum group compound is immobilized on the ceramic material.

[0027] Such a melt may be obtained by separately heating each of the materials of (i) a platinum group metal (for example, a raw material containing a platinum group metal), (ii) a carbonate or hydroxide of an alkali metal, and (iii) an oxide to form a melt, and bringing each of the melts of (i) to (iii) into contact with a ceramic material. Alternatively, a mixture of any two of the materials of (i) to (iii) may be obtained, the mixture may be heated to form a melt, and the remaining one material may also be heated to form a melt, and then these melts may be brought into contact with a ceramic material. Further, a mixture of the three materials of (i) to (iii) may be obtained, the mixture may be heated to form a melt, and then the melt may be brought into contact with a ceramic material. Moreover, a mixture of the three materials of (i) to (iii) and a ceramic material may be obtained, and the mixture may be heated to form a melt, whereby the melt may be brought into contact with the ceramic material.

[0028] According to the method of separately forming melts from each of the materials of (i) to (iii) above, for example, by preparing in advance a melt of each material other than the platinum group metal, the degree of freedom in the method of performing the immobilization step is increased. Also, according to the method of obtaining a melt from a mixture of the three materials of (i) to (iii) above, since the heating for obtaining the melt can be carried out collectively, the time and heating cost required for the immobilization step can be reduced. Furthermore, according to the method of obtaining a melt from a mixture of the three materials of (i) to (iii) and a ceramic material above, the time and heating cost required for the immobilization step can be further reduced.

[0029] Examples of the platinum group metal include Pd, Pt, Rh, Ir, Os, and Ru. Examples of such a raw material containing a platinum group metal include waste automotive catalysts and electronic device scraps.

[0030] Examples of the alkali metal in the carbonate or hydroxide of the alkali metal include Na, K, Li, Rb, and Cs. From the viewpoint of more efficiently converting the platinum group metal into a water-soluble platinum group compound, among these, Na and K are preferable, and K is more preferable. The carbonate or hydroxide of the alkali metal may be used alone or as a mixture of multiple types.

[0031] The oxide may be at least one selected from the group consisting of, for example, Na2O, B2O3, K2O, SiO2, Li2O, Rb2O, Cs2O, and P2O5. Examples of such an oxide include glass (for example, 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 of oxides. When the oxide is used as a mixture of multiple types of oxides, if it is used as a mixture containing at least B2O3, the platinum group metal can be more reliably converted into a water-soluble platinum group compound.

[0032] The carbonate or hydroxide of the alkali metal functions as an oxidizing agent for oxidizing the platinum group metal. Further, the oxide functions as a reaction assistant for oxidizing the platinum group metal.

[0033] The raw material containing the platinum group metal, the carbonate or hydroxide of the alkali metal, and the oxide are heated and mixed as a melt, whereby the platinum group metal is oxidized to obtain an oxidation product of the platinum group metal. Hereinafter, when simply referred to as "melt", it refers to a melt containing three materials: the raw material containing the platinum group metal, the carbonate or hydroxide of the alkali metal, and the oxide. However, the melt according to an embodiment of the present invention is not limited to this as described above.

[0034] (2-2. Contact between the melt and the ceramic material) The ceramic material to be brought into contact with the melt may be a sintered body obtained by heat-treating an inorganic material, and the specific configuration is not limited. The ceramic material to be brought into contact with the melt is preferably a metal oxide-based ceramic material. Such a ceramic material can more efficiently immobilize a water-soluble platinum group compound. The ceramic material may contain aluminum oxide, zeolite, zirconia, silica, iron oxide, cobalt oxide, nickel oxide, or a mixture of two or more substances selected therefrom.

[0035] From the viewpoint of more efficiently converting a platinum group metal into a water-soluble platinum group compound, the ceramic material preferably contains an amphoteric element (for example, aluminum oxide, etc.). From such a ceramic material, the amphoteric element becomes an oxoanion and elutes into the melt. By bringing the melt into contact with the ceramic material in the presence of such an oxoanion of an amphoteric element, the oxidation product of the platinum group metal reacts with the oxoanion, and the water solubility of the oxidation product is likely to be improved. If the water solubility of the oxidation product is improved, the platinum group compound can be eluted from the ceramic material more efficiently in the elution step described later. Examples of the amphoteric element include Al, Ti, V, Co, and Zr, and among these, Al and Ti are more preferable. Specific examples of the oxoanion of the amphoteric element include AlO2 - , TiO3 2- , VO4 3- and CoO2 - can be mentioned.

[0036] From the viewpoint of efficiently immobilizing the platinum group compound, the ceramic material is preferably porous with a large surface area. When the ceramic material contains an oxide of an amphoteric element, the porosity of the ceramic material is also preferable from the viewpoint of promoting the elution of the oxoanion.

[0037] The immobilization of platinum group compounds on a ceramic material may include (a) adsorbing the platinum group compounds contained in the melt onto the ceramic material by bringing the ceramic material into contact with the melt, (b) coprecipitating the components eluted from the ceramic material and the platinum group compounds (more specifically, coprecipitating the components eluted from the ceramic material, the platinum group compounds, and the ceramic material), or (c) both of the above (a) and (b). According to the above (a), after taking out the ceramic material adsorbed with the platinum group compounds from the melt, the platinum group compounds can be eluted from the ceramic material. In this case, from the viewpoint of ease of extraction, it is preferable that the shape of the ceramic material is formed into a shape such as a spherical shape, a rod shape, or a plate shape. On the other hand, according to the above (b), by removing the melt from the platinum group compounds coprecipitated with the components eluted from the ceramic material, the platinum group compounds coprecipitated with the components eluted from the ceramic material and the melt can be easily separated, and after the separation, the platinum group compounds can be eluted from the ceramic material. In this case, from the viewpoint of efficient coprecipitation, it is preferable that the shape of the ceramic material is a small powder or granular form. Also, when using a powdered ceramic material, it is preferable to set an appropriate input amount of the powdered ceramic material such that the separation of the ceramic material and the melt becomes easy. According to this configuration, it is possible to better prevent the powdered ceramic material and the melt oxide from reacting and solidifying.

[0038] Examples of the components eluted from the ceramic material into the melt include, for example, oxoanions of amphoteric elements contained in the ceramic material. Specific examples of the oxoanions of amphoteric elements include AlO2 - 、AlO4 5- 、AlO5 7- 、AlO6 9- 、TiO3 2- 、VO4 3- and CoO2 - can be mentioned.

[0039] The contact between the ceramic material and the melt is preferably carried out during heating. At this time, the contact between the ceramic material and the melt is preferably carried out at a temperature of 600 to 1100 °C, and more preferably at a temperature of 800 to 1100 °C. According to such a configuration, the cost required for heating can be reduced. According to one embodiment of the present invention, under mild conditions, the platinum group metal can be converted into a water-soluble platinum group compound. Therefore, the upper limit value of the heating temperature may be 1000 °C, 900 °C or 800 °C. The heating temperature may be appropriately selected according to the composition of the materials contained in the melt.

[0040] The heating time is preferably 30 minutes or more, more preferably 60 minutes or more, and even more preferably 120 minutes. The contact between the ceramic material and the melt may be carried out at any timing during the above heating. Also, the heating time may be appropriately selected according to the composition of the materials contained in the melt. Further, the above heating is preferably carried out in an atmosphere containing oxygen in order to promote the oxidation of the platinum group metal. For example, it is preferably carried out in an air atmosphere.

[0041] Also, in the contact between the ceramic material and the melt, the composition of the materials in the melt and / or the oxygen partial pressure in the atmosphere when the ceramic material and the melt are in contact may be appropriately adjusted. Thereby, the elution property when eluting the platinum group compound from the ceramic material into the aqueous solvent can be adjusted.

[0042] For example, by changing the basicity of the melt and / or the oxygen partial pressure in the atmosphere when the ceramic material and the melt are in contact, and adjusting the elution property of the platinum group compound into the aqueous solvent, the amount of the platinum group compound eluted from the ceramic material can be adjusted.

[0043] Also, it is preferable to immerse a pipe for supplying a gas containing oxygen into the melt, supply a gas containing oxygen into the melt from the pipe, and heat the melt while bubbling and stirring.

[0044] In addition, it is preferable to add cations with a higher valence number to the melt to further increase the ability to oxidize platinum group metals. Examples of cations with a higher valence number include Fe 3+ , Ce 4+ and Gd 3+ .

[0045] In addition, as the container used when bringing the ceramic material into contact with the melt, it is preferable to use a container containing amphoteric elements such as an alumina crucible. Thereby, the amphoteric elements contained in the container can be eluted into the melt as oxo anions. When the ceramic material contains amphoteric elements, as the above container, a container formed of a metal such as stainless steel and / or titanium may be used.

[0046] In addition, as the container for the melt, a container formed of a ceramic material may be used. That is, the contact between the container formed of the ceramic material and the melt may be the contact between the melt of the raw material containing platinum group metals, the melt of the carbonate or hydroxide of an alkali metal, the melt of an oxide, and the ceramic material in one embodiment of the present invention. In this case, the ceramic material forming the container may contain aluminum oxide, zeolite, zirconia, silica, iron oxide, cobalt oxide, nickel oxide, or a mixture of two or more substances selected from these.

[0047] <3. Elution step> The method for recovering platinum group metals according to one embodiment of the present invention has an elution step of bringing the ceramic material on which the platinum group compound is immobilized into contact with an aqueous solvent after the above-described immobilization step to elute the platinum group compound from the ceramic material. Since the platinum group compound immobilized on the ceramic material is water-soluble, by bringing the ceramic material into contact with the aqueous solvent, the platinum group compound can be easily eluted into the aqueous solvent, and an eluate containing the platinum group compound can be obtained.

[0048] The immobilization step preferably includes separating the ceramic material on which the platinum group compound is immobilized from the melt. Alternatively, the method for recovering a platinum group metal according to an embodiment of the present invention preferably has a separation step of separating the ceramic material on which the platinum group compound (platinum group metal) is immobilized from the melt between the immobilization step and the elution step. Thereby, salts of oxides and the like contained in the melt are hardly brought into the elution step. Therefore, the mixing of salts of oxides and the like into the aqueous solvent can be greatly reduced. The method for separating the ceramic material from the melt may be a method of taking out the ceramic material from the melt, or may be a method of removing the melt from the platinum group compound coprecipitated with the components eluted from the ceramic material in the melt. Also, as long as the ceramic material can be separated from the melt, any other method may be used.

[0049] The aqueous solvent is intended to be a solvent containing water as a main component. For example, it is intended to be a solvent containing 60% by weight or more of water, preferably 70% by weight or more, more preferably 80% by weight or more, more preferably 90% by weight, more preferably 95% by weight or more, more preferably 98% by weight or more, and most preferably 100% by weight. With such a configuration, the platinum group compound can be easily eluted into the aqueous solvent. The upper limit of the amount of water contained in the aqueous solvent is not particularly limited and may be, for example, 80% by weight, 90% by weight, or 100% by weight. Also, the aqueous solvent is preferably an aqueous solution of an acid. Examples of the type of the acid include organic acids such as citric acid, malic acid, acetic acid, and oxalic acid, and inorganic acids such as hydrochloric acid, nitric acid, sulfuric acid, boric acid, phosphoric acid, and perchloric acid. The concentration of the acid may be, for example, 3 mol / L or less, preferably 1 mol / L or less, more preferably 0.1 mol / L or less, and still more preferably 0.01 mol / L or less. Also, for the concentration of the acid, an appropriate concentration may be selected depending on the type of the acid. Also, the aqueous solvent may not contain an acid. With such a configuration, the platinum group compound can be easily eluted into the aqueous solvent.

[0050] The aqueous solvent can contain components other than water in addition to an acid. As such components, polar solvents are preferred, and examples thereof include alcohols such as methanol and ethanol, or a solution containing a hydroxide complex of an amphoteric element.

[0051] When the aqueous solvent is an aqueous solution of an acid, the pH of the aqueous solvent may be 4 or less, preferably 3 or less, more preferably 2 or less. Further, since it is not necessary for the aqueous solvent to have a strong acidity such as aqua regia, the pH when the aqueous solvent is an aqueous solution of an acid may be 1 or more. By using such an aqueous solvent, not only can the platinum group compound be efficiently eluted, but also the adverse effect on the environment can be prevented. When the aqueous solvent is a solvent not containing an acid, the pH of the aqueous solvent may be, for example, 6 to 8, 6 to 7, or 7 to 8.

[0052] In the elution step, after eluting the platinum group compound from the ceramic material using the aqueous solvent, the newly prepared aqueous solvent may be brought into contact with the ceramic material and the same treatment may be performed to further elute the platinum group compound. Further, this operation may be repeated to repeatedly elute the platinum group compound. In such a method of repeatedly performing elution, the composition of the aqueous solvent is not limited in each of the repeated steps, and aqueous solvents having different compositions may be used for each of the repeated steps. For example, after eluting the platinum group compound with an aqueous solvent containing 98% by weight or more of water, the platinum group compound may be further eluted with an aqueous solvent containing 80% by weight or more and 90% by weight or less of water.

[0053] Thus, when repeatedly performing the elution operation of the platinum group compound using aqueous solvents of different compositions each time, platinum group compounds of different types may be eluted step by step. For example, when performing the immobilization step using a raw material containing multiple types of platinum group metals, the multiple types of platinum group compounds are immobilized on the ceramic material. At this time, for example, after eluting platinum group compound A with an aqueous solvent containing 98% by weight or more of water, platinum group compound B may be further eluted with an aqueous solvent containing 80% by weight or more and 90% by weight or less of water, and different types of platinum group compounds may be eluted into aqueous solvents of different compositions. Also, the aqueous solvents used in each of the repeated steps may be, for example, different aqueous solvents by changing the concentration of the acid, or different aqueous solvents by changing the type of the acid.

[0054] Further, by adjusting the composition of the melt in the immobilization step, such as increasing or decreasing the amount of the oxide contained in the melt, the elution property of the platinum group compound from the ceramic material into the aqueous solvent can be adjusted in the elution step. For example, the amount of the oxide may be adjusted so that the platinum group compound dissolves preferably in an aqueous solvent containing 98% by weight or more of water. Also, by reducing the amount of the oxide contained in the melt, it may be adjusted so that the platinum group compound elutes more preferably in an aqueous solvent containing 80% by weight or more and 90% by weight or less of water than when the platinum group compound is dissolved in an aqueous solvent containing 98% by weight or more of water.

[0055] In order to adjust the elution property of the platinum group compound, an oxidizing agent other than the carbonate or hydroxide of an alkali metal may be included in the melt in the immobilization step. Examples of such an oxidizing agent include air, oxygen gas, hydrogen peroxide water, and a solution containing cations of a higher valence number. Among the above-described oxidizing agents, oxygen gas or cations of a higher valence number are preferable because they have the advantage of being able to rapidly oxidize the platinum group metal. Examples of cations of a higher valence number include Fe 3+ , Ce 4+ and Co 3+ etc.

[0056] Such an oxidizing agent is preferably introduced into the melt before or during heating of the melt. The presence of the oxidizing agent during heating effectively promotes the oxidation of the platinum group metal. Note that the timing of introducing the oxidizing agent is not limited to this, and it may be after heating of the melt or during elution of the platinum group compound into the aqueous solvent.

[0057] <4. Extraction step> The method for recovering a platinum group metal according to this embodiment may include an extraction step of extracting the platinum group metal into an organic solvent from the eluate obtained by the above-described elution step. This step can be carried out by a method for extracting a platinum group metal by treating with an organic solvent in the prior art.

[0058] According to such a method for extracting a platinum group metal, the platinum group metal in the waste catalyst and scrap can be selectively extracted in a low-corrosion environment without using a harmful acidic solvent such as aqua regia or high-concentration hydrochloric acid.

[0059] 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, among the platinum group metals, especially Pd can be selectively extracted. If Tertiary amine is used as the organic solvent, among the platinum group metals, especially Pt can be selectively extracted. Further, after extracting Pd and Pt from the eluate, if Tertiary amine is used as the organic solvent, among the remaining platinum group metals, especially Ir can be selectively extracted, and Rh can be obtained by purifying the eluate after the extraction. Ru and Os can be volatilized and separated by a distillation operation during these separation steps.

[0060] <5. Platinum group metal-containing composition> The platinum group metal-containing composition according to this embodiment contains a platinum group metal and an amphoteric element. When the total amount of the platinum group metal and the amphoteric element is 100% by weight, the platinum group metal is contained in an amount of 99% by weight or more and the amphoteric element is contained in an amount of 1% by weight or less.

[0061] Examples of the platinum group metal include Pd, Pt, Rh, Ir, Os, and Ru.

[0062] Examples of the amphoteric element include Al, Ti, V, Co, and Zr. Among these, Al and Ti are more preferable.

[0063] Examples of the method for obtaining such a platinum group metal-containing composition include, but are not limited to, the methods described in the above <2. Immobilization step> and <3. Elution step>. Thus, it can be said that the method for recovering a platinum group metal according to an embodiment of the present invention is a method for producing a platinum group metal-containing composition. That is, the method for recovering a platinum group metal according to an embodiment of the present invention is a method for producing a platinum group metal-containing composition, which includes an immobilization step of bringing a melt of a raw material containing a platinum group metal, a melt of a carbonate or hydroxide of an alkali metal, a melt of an oxide, and a ceramic material into contact with each other to immobilize the platinum group metal on the ceramic material.

[0064] Specific examples of the platinum group metal-containing composition may be, for example, those in which the platinum group metal is eluted in an aqueous solvent. The aqueous solvent is intended to be a solvent containing water as a main component. For example, it is intended to be 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, more preferably 95% by weight or more, more preferably 98% by weight or more, and most preferably 100% by weight of water. The upper limit of the amount of water contained in the aqueous solvent is not particularly limited and may be, for example, 80% by weight, 90% by weight, or 100% by weight. Further, the aqueous solvent is preferably an aqueous solution of an acid. Examples of the type of the acid include organic acids such as citric acid, malic acid, acetic acid, and oxalic acid, and inorganic acids such as hydrochloric acid, nitric acid, sulfuric acid, boric acid, phosphoric acid, and perchloric acid. The concentration of the acid may be, for example, 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. Further, for the concentration of the acid, an appropriate concentration may be selected depending on the type of the acid. Further, the aqueous solvent may not contain an acid.

[0065] The platinum group metal-containing composition contains, for example, the above platinum group metal eluted from a ceramic material in which the platinum group metal is immobilized and an amphoteric element in an aqueous solvent. When the total amount of the platinum group metal and the amphoteric element is 100% by weight, it may be an eluate of the platinum group metal containing 99% by weight or more of the platinum group metal and 1% by weight or less of the amphoteric element. With such a platinum group metal-containing composition, the platinum group metal contained in the eluate can be easily extracted by the extraction method of the platinum group metal by the conventional organic solvent treatment. Further, the platinum group metal-containing composition may be in a form in which the aqueous solvent is removed from the eluate of the platinum group metal (for example, a solid).

[0066] As a method for obtaining a solid platinum group metal-containing composition, for example, a method of further performing a concentration step on the eluate obtained by the above <3. Elution step> can be mentioned.

[0067] In the concentration process, the eluate is impregnated with activated carbon, and the platinum group compound is adsorbed onto the activated carbon. At this time, it is preferable to stir the eluate impregnated with the activated carbon. Then, the activated carbon adsorbed with the platinum group compound is taken out from the eluate and heated to burn the activated carbon. The heating of the activated carbon is not limited as long as it is the temperature at which the activated carbon burns, for example, 1000 °C. The concentrate obtained after heating the activated carbon contains concentrated platinum group metals. Such a concentrate is an example of a platinum group metal-containing composition according to an embodiment of the present invention.

[0068] <6. Platinum group metal-immobilized ceramic material> In the ceramic material according to this embodiment, an immobilization layer containing O (oxygen) and an alkali metal is formed on the surface of the ceramic material, and the platinum group metal is immobilized in the immobilization layer.

[0069] For example, when a melt containing a platinum group compound is brought into contact with a ceramic material by the method described in the above (2-1. Preparation of melt), an immobilization layer is formed on the surface of the ceramic material. In the immobilization layer, a composite layer containing O and an alkali metal derived from a carbonate or hydroxide of the alkali metal is formed. Further, it is preferable that the immobilization layer further contains an element derived from an oxide contained in the melt. Such an element derived from an oxide may be an element derived from a network-forming oxide, an element derived from a network-modifying oxide, or both elements derived from a network-forming oxide and a network-modifying oxide may be contained respectively. Here, a network-forming oxide is an oxide that can form a network structure of glass when vitrified. A network-modifying oxide is an oxide that can modify the network structure of glass when vitrified. These oxides may be added in a vitrified state when obtaining a melt containing a platinum group compound, but vitrification is not essential.

[0070] The element derived from the oxide may be at least one selected from the group consisting of, for example, Na, B, K, Si, Li, Rb, Cs, and P.

[0071] As an example of the immobilization layer, when the ceramic material is aluminum oxide, the oxides contained in the melt are B2O3 and K2O, and the alkali metal carbonate is K2CO3, a K-Al-B-O composite layer (for example, K2Al2(BO3)2O) can be mentioned, but it is not limited thereto. Another example of the immobilization layer can be a composite layer (for example, Na-Al-B-O composite layer) in which at least one atom constituting the K-Al-B-O composite layer is replaced with an atom having similar properties. Further, the immobilization layer may be a K-Al-O composite layer that does not contain B derived from an oxide.

[0072] The present inventors have found that such an immobilization layer has the property of being able to immobilize platinum group metals. Based on this finding, the present inventors have obtained a ceramic material having a platinum group metal immobilized on its surface. A method for obtaining such a ceramic material having a platinum group metal immobilized thereon includes, for example, the method described in the above <2. Immobilization step>, but is not limited thereto.

[0073] The platinum group metals immobilized on the ceramic material include, for example, Pd, Pt, Rh, Ir, Os, and Ru.

[0074] Further, the ceramic material may be a sintered body obtained by heat-treating an inorganic material, and the specific configuration is not limited. The ceramic material to be brought into contact with the melt is preferably a metal oxide-based ceramic material. Such a ceramic material can more efficiently immobilize a water-soluble platinum group compound. The ceramic material may contain aluminum oxide, zeolite, zirconia, silica, iron oxide, cobalt oxide, nickel oxide, or a mixture of two or more substances selected from these.

[0075] From the viewpoint of efficiently immobilizing the platinum group compound, the ceramic material is preferably porous with a large surface area.

[0076] The surface of the ceramic material may be any surface where the ceramic material can come into contact with a liquid such as a melt or an aqueous solvent when the ceramic material is immersed in the liquid. For example, when the ceramic material is porous, not only the surface visible from the appearance of the ceramic material but also the surface formed inside the pores is the surface of the ceramic material.

[0077] <7. Summary> A method for recovering a platinum group metal according to one aspect of the present invention includes an immobilization step of bringing a melt of a raw material containing a platinum group metal, a melt of a carbonate or hydroxide of an alkali metal, a melt of an oxide, and a ceramic material into contact to immobilize the platinum group metal on the ceramic material.

[0078] A method for recovering a platinum group metal according to one aspect of the present invention may include, in the immobilization step, adsorbing the platinum group metal onto the ceramic material or coprecipitating a component eluted from the ceramic material and the platinum group metal.

[0079] A method for recovering a platinum group metal according to one aspect of the present invention may, in the immobilization step, heat the raw material containing the platinum group metal, the carbonate or hydroxide of the alkali metal, and the oxide to obtain the melt, and then bring the melt into contact with the ceramic material.

[0080] A method for recovering a platinum group metal according to one aspect of the present invention may, in the immobilization step, obtain a mixture of the raw material containing the platinum group metal, the carbonate or hydroxide of the alkali metal, the oxide, and the ceramic material, and then heat the mixture to obtain the melt, thereby bringing the melt into contact with the ceramic material.

[0081] The ceramic material according to one aspect of the present invention may contain aluminum oxide, zeolite, zirconia, silica, iron oxide, cobalt oxide, or nickel oxide.

[0082] The method for recovering a platinum group metal according to one aspect of the present invention may include an elution step of bringing the ceramic material having the platinum group metal immobilized thereon into contact with an aqueous solvent after the immobilization step to elute the platinum group metal from the ceramic material.

[0083] In the method for recovering a platinum group metal according to one aspect of the present invention, the aqueous solvent may be an aqueous solution of an acid.

[0084] In the method for recovering a platinum group metal according to one aspect of the present invention, the contact between the melt and the ceramic material may be carried out at a temperature of 600 to 1100°C.

[0085] In the method for recovering a platinum group metal according to one aspect of the present invention, the contact between the melt and the ceramic material may be carried out in the presence of an oxoanion of an amphoteric element.

[0086] In the method for recovering a platinum group metal according to one aspect of the present invention, the platinum group metal may be Pd, Pt, Rh, Ir, Os, or Ru.

[0087] In the method for recovering a platinum group metal according to one aspect of the present invention, the alkali metal may be Na, K, Li, Rb, or Cs.

[0088] In the method for recovering a platinum group metal according to one aspect of the present invention, the oxide may be at least one selected from the group consisting of Na2O, B2O3, K2O, SiO2, Li2O, Rb2O, Cs2O, and P2O5.

[0089] A platinum group metal-containing composition according to one aspect of the present invention contains a platinum group metal and an amphoteric element, and when the total amount of the platinum group metal and the amphoteric element is 100% by weight, it contains 99% by weight or more of the platinum group metal and 1% by weight or less of the amphoteric element.

[0090] The ceramic material according to one aspect of the present invention has an immobilization layer formed on its surface, the immobilization layer containing at least one selected from the group consisting of Na, B, K, Si, Li, Rb, Cs, and P, O, and an alkali metal, and a platinum group metal is immobilized in the immobilization layer.

Example

[0091] [A. Immobilization of Platinum Group Metals by Aluminum Oxide Blocks] [A1. Samples and Methods] (A1-1. Reaction Medium) The K2O-B2O3 medium, which is an example of the oxide of the present invention, was prepared as follows using commercially available compound standard reagents. First, 5 g of boric acid and 2.1 g of potassium hydroxide were placed in an alumina crucible with a volume of 30 mL (hereinafter referred to as "30 mL crucible"), and the 30 mL crucible was placed in an electric furnace. Then, the temperature in the electric furnace was raised to 1000 °C over 30 minutes, and the 30 mL crucible was heated for 1 hour while maintaining this temperature. Then, the melt generated in the 30 mL crucible was cooled. The obtained solidified product was used as the K2O-B2O3 medium.

[0092] Such a reaction medium mainly composed of boron oxide has a network structure with a planar triangular BO3 structure as the basic unit and the BO3 structures are connected in a network-like manner. When K2O is contained in such a reaction medium, BO4 having a tetrahedral structure is generated. BO4 in the network structure is known to have a negative charge as a whole. Therefore, BO4 in the network structure can be regarded as an oxoanion. It is considered that the conversion of platinum group metals into platinum group compounds can be more efficiently achieved because the reaction medium contains oxoanions. Therefore, such a K2O-B2O3 medium was used as the reaction medium for converting platinum group metals into platinum group compounds.

[0093] (A1-2. Generation of Platinum Group Compounds According to Comparative Examples) The K2O-B2O3 medium created in the above (A1-1), metallic Pd, and potassium carbonate (an example of the carbonate or hydroxide of the alkali metal of the present invention) were mixed. The obtained mixture was added to a 30 mL crucible, and the 30 mL crucible was placed inside a 100 mL alumina crucible (hereinafter referred to as the "100 mL crucible"). Then, the 100 mL crucible was covered, and the 100 mL crucible was heated in an electric furnace. The heating conditions are shown in Table 1 below.

[0094] In the melt obtained by the above heating, metallic Pd is oxidized by reaction with potassium carbonate, and an oxidation product of metallic Pd is formed. And the oxidation product dissolves in the K2O-B2O3 medium. What is obtained by cooling such a melt is defined as a heat treatment product.

[0095]

Table 1

[0096] (A1-4. Evaluation of Recovery Rate of Platinum Group Compound) In order to evaluate the amount of Pd compound immobilized in the aluminum oxide block, the following tests were conducted. The heat-treated product (comparative example) or the aluminum oxide block (example) was placed in a 200 mL beaker together with the crucible, and 150 mL of ion-exchanged water was added to the beaker (elution treatment). A stirring bar was immersed in the liquid in the beaker, and the mixture was stirred at a stirring speed of 7000 rpm for 2 hours. Then, the liquid (eluate) in the beaker was suction filtered through a 1 μm paper filter. On the other hand, for the solid (aluminum oxide block or heat-treated product) remaining in the beaker after filtration, elution treatment, stirring, and filtration were performed again in the same manner as above using a 0.01 M hydrochloric acid aqueous solution (0.01 M HCl). After that, the obtained solid was sequentially subjected to elution treatment, stirring, and filtration in the same manner as above with a 0.1 M hydrochloric acid aqueous solution (0.1 M HCl) and a 1 M hydrochloric acid aqueous solution (1 M HCl). The concentration of the Pd compound in each eluate obtained by these series of operations was measured with an ICP emission spectrometer, and the recovery rate of the platinum group metal was determined from the following formula (1). Recovery rate (%) = amount of platinum group compound in eluate / amount of platinum group metal introduced × 100 (1) (A1-5. Immobilization conditions of Pd compound in each example and comparative example) In order to clarify the relationship between the immobilization conditions of the Pd compound and the Pd recovery rate, as shown in Table 2 below, in Examples A1 to A4, the amount of the aluminum oxide block added to the melt and the immersion conditions of the aluminum oxide block in the melt were changed. In contrast, in Comparative Example A1, no aluminum oxide block was added to the melt, and elution treatment was performed on the heat-treated product containing the reaction medium as a whole.

[0097]

Table 2

[0098] Figure 2 is a diagram showing the EDS spectrum of submicron-order particles (part P in Figure 1) on the surface of the aluminum oxide block. From the results shown in Figure 2 and the Pd mapping image by EDS shown in Figure 1, it was shown that the particles contain a Pd compound. As described above, the aluminum oxide block observed by SEM-EDS was obtained by removing salts derived from the reaction medium adhering to the surface by washing with ion-exchanged water. From this, it can be considered that Pd on the surface of the aluminum oxide block was immobilized on the surface of the aluminum oxide block from the reaction medium by adsorption. Thus, it was shown that according to the method for recovering a platinum group metal according to an embodiment of the present invention, the platinum group compound can be easily isolated from the melt.

[0099] (A2-2. Recovery of Pd compound immobilized on aluminum oxide block) Figure 3 is a diagram showing the Pd recovery rate from the aluminum oxide block when an elution treatment was performed on the aluminum oxide blocks of Examples A2 to A4. As shown in (A1-4) above, four types of aqueous solvents were used stepwise in the elution treatment. In the following evaluation, the total value of the Pd elution rate into each aqueous solvent was used as an index of the Pd recovery rate.

[0100] In Example A2, from the start of temperature increase of the electric furnace equipped with a 30 mL crucible, an aluminum oxide block was introduced into the mixture in the 10 mL crucible. Under the conditions of Example A2, the Pd recovery rate was 12%. In contrast, in Example A3, the temperature of the electric furnace was raised to 900 °C, and 30 minutes after reaching 900 °C, the aluminum oxide block was introduced into the melt in the 10 mL crucible. Under the conditions of Example A3, the Pd recovery rate was 25%. In Example A4, the input amount of the aluminum oxide block was set to 2 g, and the elution treatment was carried out with other conditions being the same as in Example A3. Under the conditions of Example A4, the Pd recovery rate was 33%, which was increased compared to Example A3. From the above, it was shown that by changing the immersion conditions and input amount of the aluminum oxide block, etc., the adsorption of Pd compounds on the surface of the aluminum oxide block can be promoted.

[0101] (A2-3. Concentration of Boron in Palladium Dissolution Solution) Table 3 below shows the concentrations of Pd compounds and boron in the Pd eluate in Comparative Example A1 and Example A3. In Comparative Example A1, the heat treatment product containing the reaction medium was eluted with ion-exchanged water to obtain an eluate. The concentration of boron in the eluate was 753 mg / L. In contrast, the concentration of boron in the eluate with ion-exchanged water in Example A3 was 204 mg / L, and the boron concentration was significantly reduced compared to Comparative Example A1. Also, the concentration of boron in the 0.01 - 1 M hydrochloric acid aqueous solution was in the range of 5.8 - 9.3 mg / L respectively, and the boron concentration was even lower compared to Comparative Example A1. Thus, according to the method for recovering platinum group metals according to one embodiment of the present invention, it was shown that the concentration of salts of oxides in the eluate can be effectively reduced.

[0102]

Table 3

[0103] 〔B. Immobilization of Platinum Group Metals on Aluminum Oxide Powder〕 <B1. Samples and Methods> 1 g of the K2O-B2O3 medium prepared by the same method as in (A1-1) above, platinum group metal, 3.9 g of potassium carbonate, and 1 g of aluminum oxide powder (an example of the ceramic material of the present invention) were mixed. As the platinum group metal, 10 mg of metallic Pd or 12 mg of metallic Pt was used. This mixture was added to a 10 mL crucible, and the 10 mL crucible was placed in a 30 mL crucible. The 30 mL crucible was heated in an electric furnace. The heating temperature was 900 °C or 600 °C for the mixture containing metallic Pd, and 900 °C for the mixture containing metallic Pt, and the heating time was 30 minutes. By this heating, a platinum group compound, which is an oxidation product of the platinum group metal, dissolves in the K2O-B2O3 medium. Then, the platinum group compound dissolved in the melt is immobilized on the surface of the aluminum oxide powder. And a mixture of the aluminum oxide powder and the melt was obtained.

[0104] The mixture of the aluminum oxide powder and the melt was immersed in 150 mL of ion-exchanged water for 2 hours for washing, and the surface state of the aluminum oxide powder was analyzed. The immobilization state of the platinum group metal on the surface of the aluminum oxide powder was analyzed by SEM-EDS, XRD (X-ray diffractometer), or XPS (X-ray photoelectron spectrometer).

[0105] <B2. Results> (Confirmation of Immobilization of Pd Compound on Aluminum Oxide Powder Heated at 900 °C) Figure 4 shows the XRD diffraction pattern of aluminum oxide powder (Example B1) washed after heating at 900 °C under conditions containing metallic Pd. As shown in Figure 4, the XRD diffraction pattern of Example B1 included the XRD diffraction pattern of Al2O3 (the peak group indicated by circles in Figure 4) and the XRD diffraction pattern of K2Al2(BO3)2O (the peak group indicated by downward triangles in Figure 4). From this result, it was shown that an immobilized layer containing K2Al2(BO3)2O was formed on the surface of the aluminum oxide powder according to Example B1.

[0106] Figure 5 shows the XPS spectrum of the aluminum oxide powder according to Example B1. As shown in Figure 5, peaks indicating Pd were observed in the XPS spectrum of Example B1. Also, these peaks indicating Pd were shifted to the high-energy side from the positions of the peaks of normal metallic Pd (the peaks indicated by Pd in Figure 5). This is a result suggesting that Pd exists in an oxidized state on the surface of the aluminum oxide powder. 0

[0107] The above results suggest that an immobilized layer containing K2Al2(BO3)2O was formed on the surface of the aluminum oxide powder according to Example B1 with a heating temperature of 900 °C in the melt, and Pd was immobilized in the said immobilized layer.

[0108] (Confirmation of Immobilization of Pd Compound on Aluminum Oxide Powder Heated at 600 °C) Figure 6 shows the XRD diffraction pattern of aluminum oxide powder (Example B2) heated at 600 °C under conditions containing metallic Pd. As shown in Figure 6, when the heating temperature was 600 °C, the XRD diffraction pattern of Example B2 showed the XRD diffraction pattern of Al2O3 (the peak group indicated by diamonds in Figure 6), but no peaks indicating other molecules were observed. Therefore, the surface state of the aluminum oxide powder according to Example B2 was observed by SEM-EDS.

[0109] ​ Figure 7 is a diagram showing an image obtained by observing the surface of the aluminum oxide powder according to Example B2 with SEM-EDS. The image shown in the upper left of Figure 7 is a secondary electron image of the surface of the aluminum oxide powder according to Example B2, and the other images respectively show element mapping images for each element shown in Figure 7. As shown in Figure 7, Pd, K, and O were each observed on the surface of the aluminum oxide powder according to Example B2.

[0110] Figure 8 is a diagram showing the EDS spectrum of the aluminum oxide powder according to Example B2. In Figure 8, the EDS spectrum of the entire observation area shown in Figure 7 is shown. As shown in Figure 8, C, O, Al, Pd, and K were present in the aluminum oxide powder according to Example B2. Also, in the image shown in the upper left of Figure 7, in the range indicated by the round frame, 47.4 wt% of O, 32.3 wt% of Al, 19.6 wt% of Pd, and 0.71 wt% of K were present. That is, it was shown that a composite containing at least Pd, K, Al, and O was formed on the surface of the aluminum oxide powder according to Example B2.

[0111] From the above results, it was shown that metallic Pd was immobilized on the surface of the aluminum oxide powder according to Example B2 obtained by setting the heating temperature in the melt to 600°C. Therefore, it is considered that an immobilization layer capable of immobilizing metallic Pd is formed on the surface of the aluminum oxide powder according to Example B2. However, when the heating conditions were set to 600°C, the immobilization layer did not contain a detectable amount of B. That is, it was shown that the immobilization layer can immobilize metallic Pd even in a state not containing B derived from the oxide.

[0112] (Confirmation of Immobilization of Pt Compound on Aluminum Oxide Powder Heated at 3.900°C in B2) Figure 9 shows the XRD diffraction pattern of the aluminum oxide powder (Example B3) washed after heating at 900 °C under the condition of containing metallic Pt. As shown in Figure 9, the XRD diffraction pattern of Example B3 included the XRD diffraction pattern of Al2O3 (the peak group indicated by the diamond marks in Figure 9) and the XRD diffraction pattern of K2Al2(BO3)2O (the peak group indicated by the downward triangle marks in Figure 9). From this result, it was shown that an immobilized layer containing K2Al2(BO3)2O was formed on the surface of the aluminum oxide powder according to Example B3.

[0113] Figure 10 is a diagram showing an image obtained by observing the surface of the aluminum oxide powder according to Example B3 by SEM-EDS. The image shown in the upper left of Figure 10 shows the secondary electron image of the surface of the aluminum oxide powder according to Example B3, and the other images respectively show the element mapping images for each element shown in Figure 10. As shown in Figure 10, Pt, K, and O were respectively observed on the surface of the aluminum oxide powder according to Example B3.

[0114] Figure 11 is a diagram showing the EDS spectrum of the aluminum oxide powder according to Example B3. Figure 11 shows the EDS spectrum of the entire observation area shown in Figure 10. As shown in Figure 11, C, O, Al, Pt, and K were present in the aluminum oxide powder according to Example B3. Also, in the image shown in the upper left of Figure 10, in the range indicated by the round frame, 54.6 wt% of O, 19.7 wt% of Al, 3.2 wt% of Pt, and 9.5 wt% of K were present. That is, it was shown that a composite containing at least Pt, K, Al, and O was formed on the surface of the aluminum oxide powder according to Example B3.

[0115] From the above results, it was shown that metallic Pt was immobilized on the surface of the aluminum oxide powder according to Example B3 obtained with the heating temperature in the melt being 900 °C. Therefore, it was shown that the immobilized layer formed on the surface of the aluminum oxide powder according to Example B3 can immobilize not only metallic Pd but also metallic Pt.

[0116] 〔Composition of C.Pd-containing composition〕 <C1. Sample and method> A mixture of aluminum oxide powder and a melt prepared in the same manner as in (B1-1) above was placed in a 200 mL beaker, and 150 mL of ion-exchanged water was added to the beaker. A stirring bar was immersed in the liquid in the beaker, and the mixture was stirred at a stirring speed of 7000 rpm for 30 minutes. Next, with respect to the mixture remaining in the beaker, it was stirred for 30 minutes in the same manner as above using a 1M hydrochloric acid aqueous solution (1M HCl). The mixture was taken out from the treatment liquid obtained with the 1M hydrochloric acid aqueous solution, and 3 g of activated carbon was immersed in the treatment liquid. A stirring bar was immersed in the liquid in the beaker, and the mixture was stirred at a stirring speed of 7000 rpm for 30 minutes.

[0117] Next, the activated carbon was taken out from the beaker, and the activated carbon was heated at 1000 °C for 4 hours to burn the activated carbon. The Pd concentrate obtained after heating (an example of the platinum group metal-containing composition of the present invention) was analyzed by SEM-EDS.

[0118] <C2. Results> Figure 12 is a diagram showing an image of the surface of the Pd concentrate observed by SEM-EDS. The image shown in the upper left of Figure 12 shows the secondary electron image of the surface of the Pd concentrate, and the other images respectively show the elemental mapping images for each element shown in Figure 12. As shown in Figure 12, Pd and O were observed on the surface of the Pd concentrate.

[0119] Figure 13 is a diagram showing the EDS spectrum of the Pd concentrate. In Figure 13, the EDS spectrum of the entire observation area shown in Figure 12 is shown. As shown in Figure 13, C, O, Cu, Al, Si, and Pd were present in the Pd concentrate. Also, in the image shown in the upper left of Figure 12, in the range indicated by the round frame, there were 84.48 wt% Pd, 9.08 wt% C, 3.71 wt% O, 1.9 wt% Cu, 0.45 wt% Al, and 0.38 wt% Si. Among these, since Cu and Si were not added to the melt, they are considered to be components derived from activated carbon. Also, C and O are considered to be unburned carbon derived from activated carbon and the oxygen bonded thereto. Therefore, it is considered that the component derived from the molten salt formed in the melt and contained in the Pd concentrate is only Al.

[0120] Therefore, when recalculating the composition ratio based on only Pd and Al among the components detected by the EDS spectrum of the Pd concentrate, it was 99.47 wt% Pd and 0.53 wt% Al.

[0121] From the above, it was shown that the platinum group metal-containing composition obtained by the method for recovering platinum group metals according to an embodiment of the present invention contains a platinum group metal and an amphoteric element. Also, it was shown that such a platinum group metal-containing composition contains 99 wt% or more of the platinum group metal when the total amount of the platinum group metal and the amphoteric element is 100 wt%.

[0122] [Platinum group metals other than Pd and ceramic materials other than aluminum oxide] <D1. Samples and methods> (D1-1. Formation of platinum group compounds) 1 g of a K2O - B2O3 medium prepared in the same manner as the above (A1 - 1), 10 mg of a platinum group metal (metal Pt or metal Rh), and 3.9 g of potassium carbonate were mixed. This mixture was added to a 10 mL crucible, and the 10 mL crucible was placed inside a 30 mL crucible. The 30 mL crucible was heated in an electric furnace. Here, the 10 mL crucible is provided with holes smaller than the diameter of the alumina balls or zirconia balls. The heating temperature was 900 °C or 1000 °C, and the heating time was 30 minutes. By this heating, a platinum group compound, which is an oxidation product of the platinum group metal, dissolves in the K2O - B2O3 medium. Then, a ceramic material was immersed in the melt in which the platinum group compound was dissolved for a predetermined time (immersion time). As the ceramic materials, 10 alumina balls with a diameter of about 4 mm or 10 zirconia balls with a diameter of 2.8 - 3.2 mm were used respectively. These alumina balls and zirconia balls are both examples of the ceramic materials of the present invention. Then, the alumina balls or zirconia balls were taken out from the melt together with the 10 mL crucible.

[0123] (D1 - 2. Evaluation of the recovery rate of platinum group compounds) In order to evaluate the amount of the platinum group compound immobilized on the surface of the ceramic material, the following test was conducted. The ceramic material together with the crucible was placed in a 200 mL beaker, and 150 mL of ion - exchanged water was added to the beaker (elution treatment). A stirring bar was immersed in the liquid in the beaker, and it was stirred at a stirring speed of 7000 rpm for 30 minutes. Then, the liquid (eluate) in the beaker was suction - filtered through a 1 μm paper filter.

[0124] On the other hand, for the ceramic material remaining in the beaker after filtration, elution treatment, stirring, and filtration were again performed in the same manner as above using a 0.01 M hydrochloric acid aqueous solution (0.01 M HCl). For the alumina spheres according to Example D11 and the zirconia spheres according to Example D12 shown in Table 4 below, the remaining ceramic material was further subjected to elution treatment, stirring, and filtration in the same manner as above with a 0.1 M hydrochloric acid aqueous solution (0.1 M HCl) and a 1 M hydrochloric acid aqueous solution (1 M HCl) in sequence. The concentration of the platinum group compound in each eluate obtained by these series of operations was measured with an ICP emission spectrometer, and the recovery rate of the platinum group metal was determined from the above formula (1).

[0125] (D1-3. Conditions in each example) In order to clarify the relationship between the type of platinum group metal, the type of ceramic compound, the immobilization conditions of the platinum group compound, and the dissolution rate of the platinum group compound, the dissolution rate was measured under each condition shown in Table 4 below. In Examples D1 to D10, metal Pt was used as the platinum group metal, alumina spheres were used as the ceramic material, and the immersion conditions of the alumina spheres in the melt were changed. In Example D11, metal Rh was used as the platinum group metal, and alumina spheres were used as the ceramic material. In Example D12, metal Pt was used as the platinum group metal, and zirconia spheres were used as the ceramic material.

[0126]

Table 4

[0127] Also, as shown in Example D1 etc., the metal Pt was mainly eluted from the surface of the ceramic material by ion-exchanged water. On the other hand, as shown in Example D11, the metal Rh was hardly eluted by ion-exchanged water and was effectively eluted by a 0.01M hydrochloric acid aqueous solution. Thus, although the optimal elution conditions vary depending on the type of platinum group metal, it was shown that platinum group metals can be efficiently recovered from the surface of the ceramic material by an aqueous solvent regardless of the type of platinum group metal. Also, it was shown that different types of platinum group metals can be separated and recovered by using a plurality of types of aqueous solvents.

[0128] Also, as shown in Example D12, it was shown that the ceramic material is not limited to aluminum oxide, and various ceramic materials such as zirconia are applicable to the method for recovering platinum group metals according to an embodiment of the present invention.

[0129] [E. Types of Hydroxides and Oxides of Alkali Metals] <E1-1. Samples and Methods> As a melt of an oxide, 1 g of a K2O-B2O3 medium (Example E1) or 0.5 g of phosphorus oxide (P2O5) (Example E2) prepared by the same method as in (A1-1) above, 11 mg of metal Pt, and 4.4 g of potassium hydroxide were mixed. This mixture was added to a 10 mL crucible, and the 10 mL crucible was placed inside a 30 mL crucible. The 30 mL crucible was heated in an electric furnace. Here, the 10 mL crucible is provided with holes smaller than the diameter of the alumina balls or zirconia balls. The heating temperature was 900 °C and the heating time was 30 minutes. By this heating, a Pt compound, which is an oxidation product of metal Pt, dissolves in the melt of the oxide. Then, 10 alumina balls (an example of a ceramic material) with a diameter of about 4 mm were immersed in the melt in which the Pt compound was dissolved for 60 minutes. Then, in Example E1, the alumina balls were taken out together with the 10 mL crucible, and in Example E2, only the alumina balls were taken out from the melt.

[0130] (E1-2. Evaluation of Recovery Rate of Pt Compound) To evaluate the amount of Pt compound immobilized on the surface of the alumina spheres, the following tests were conducted. The alumina spheres together with the crucible (Example E1) or the alumina spheres only (Example E2) were placed in a 200 mL beaker, and 150 mL of ion-exchanged water was added to the beaker (elution treatment). A stirring bar was immersed in the liquid in the beaker, and the mixture was stirred at a stirring speed of 7000 rpm for 30 minutes. Then, the liquid (eluate) in the beaker was suction filtered through a 1 μm paper filter.

[0131] On the other hand, for the alumina spheres remaining in the beaker after filtration, elution treatment, stirring, and filtration were sequentially performed in the same manner as above using 0.01 M hydrochloric acid aqueous solution (0.01 M HCl), 0.1 M hydrochloric acid aqueous solution (0.1 M HCl), and 1 M hydrochloric acid aqueous solution (1 M HCl). The concentration of the Pt compound in each eluate obtained by these series of operations was measured with an ICP emission spectrometer, and the recovery rate of metallic Pt was determined from the above formula (1).

[0132] <E2. Results> The results of Example E1 and Example E2 are shown in Table 5 below.

[0133]

Table 5

[0134] Incidentally, the carbonate or hydroxide of an alkali metal functions as an oxidizing agent for oxidizing the platinum group metal as described above. In addition to K, when Na, Li, Rb, or Cs is used as the alkali metal, it functions as an oxidizing agent in the same manner as K, and a soluble platinum group compound is formed in the medium. Therefore, the carbonate or hydroxide of Na, Li, Rb, or Cs is considered to function suitably as an oxidizing agent in the same manner as the carbonate or hydroxide of K.

[0135] The present invention is not limited to the above-described embodiments and examples, and various modifications are possible within the scope shown in the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments and examples are also included in the technical scope of the present invention.

Industrial Applicability

[0136] The present invention can be used for recovering platinum group metals from raw materials containing platinum group metals (for example, waste catalysts, etc.).

Claims

1. There is an immobilization step of bringing a melt of a raw material containing a platinum group metal into contact with a melt of a carbonate or hydroxide of an alkali metal, a melt of an oxide, and a ceramic material to immobilize the platinum group metal on the ceramic material. The oxide is at least one selected from the group consisting of Na₂O, B₂O₃, K₂O, SiO₂, Li₂O, Rb₂O, Cs₂O, and P₂O₅. The method for recovering a platinum group metal is characterized in that the ceramic material contains aluminum oxide, zeolite, zirconia, silica, iron oxide, cobalt oxide, or nickel oxide.

2. The immobilization step includes adsorbing the platinum group metal on the ceramic material or coprecipitating a component eluted from the ceramic material and the platinum group metal. The method for recovering a platinum group metal according to Claim 1 is characterized by this.

3. In the immobilization step, after heating the raw material containing the platinum group metal, the carbonate or hydroxide of the alkali metal, and the oxide to obtain the melt, the melt is brought into contact with the ceramic material. The method for recovering a platinum group metal according to Claim 1 or 2 is characterized by this.

4. In the immobilization step, after obtaining a mixture of the raw material containing the platinum group metal, the carbonate or hydroxide of the alkali metal, the oxide, and the ceramic material, the mixture is heated to obtain the melt, whereby the melt is brought into contact with the ceramic material. The method for recovering a platinum group metal according to Claim 1 or 2 is characterized by this.

5. After the immobilization step, there is an elution step of bringing the ceramic material on which the platinum group metal is immobilized into contact with an aqueous solvent to elute the platinum group metal from the ceramic material. The method for recovering a platinum group metal according to any one of Claims 1 to 4 is characterized by this.

6. The method for recovering a platinum group metal according to Claim 5 is characterized in that the aqueous solvent is an aqueous solution of an acid.

7. The contact between the melt and the ceramic material is carried out at a temperature of 600 to 1100°C. The method for recovering a platinum group metal according to any one of Claims 1 to 6 is characterized by this.

8. The method for recovering a platinum group metal according to any one of claims 1 to 7, wherein the contact between the melt and the ceramic material is carried out in the presence of an oxoanion of an amphoteric element.

9. The method for recovering a platinum group metal according to any one of claims 1 to 8, wherein the platinum group metal is Pd, Pt, Rh, Ir, Os or Ru.

10. The method for recovering a platinum group metal according to any one of claims 1 to 9, wherein the alkali metal is Na, K, Li, Rb or Cs.

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