Catalyst treatment method

Abstract

To provide a processing method of a catalyst in which platinum group metal can be efficiently recovered from a waste catalyst by a simple method.SOLUTION: By mixing ammonium hydrogen sulfate being a reactant into a ground product of a catalyst to generate a mixture and leaching a reaction product obtained by heating the mixture by solution, the mixture is separated into first leachate and first solid residue. Furthermore, by leaching the first solid residue by acid solution, the residue is separated into second leachate and second solid residue. A platinum group metal component is leached into the first leachate and the second leachate, and a platinum group metal can be recovered from the catalyst by performing solvent extracting to them.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a catalyst treatment method, and more particularly to a catalyst treatment method capable of efficiently recovering platinum group metals from spent catalysts by a simple method. [Background technology]

[0002] In recent years, most gasoline-powered automobiles are equipped with an exhaust gas purification system that uses a three-way catalytic converter (hereafter referred to as "catalyst"). This catalyst has the function of purifying the post-combustion exhaust gas from a gasoline engine by converting carbon monoxide, nitrogen oxides, and unburned hydrocarbons into carbon dioxide, nitrogen, and water.

[0003] The basic structure of the catalyst is a catalyst coating layer made of inorganic oxides such as ceria, zirconia, and alumina formed on the surface of a honeycomb-structured base material made mainly from ceramic, with platinum group metals such as platinum (Pt), palladium (Pd), and rhodium (Rh) supported on this catalyst coating layer.

[0004] Platinum group metals are essential elements in industry, being used in many industrial products, including catalysts for automobiles, and by establishing technology for recovering platinum group metals from used catalysts (hereinafter referred to as "spent catalysts"), it is possible to ensure a stable supply of these platinum group metals. In addition, because the unit price of platinum group metals is high, even a slight improvement in the recovery rate can contribute greatly to profits.

[0005] Conventionally, dry and wet methods have been used to recover platinum group metals from waste catalysts. The dry method involves heating the platinum group metals or gold contained in the waste catalyst together with a collector metal (copper, nickel, lead, etc.) to recover the platinum group metals as an alloy in the collector metal, and is known, for example, as disclosed in Patent Document 1. On the other hand, known wet methods include a method of extracting platinum group metals with a solution of an acid such as aqua regia or hydrochloric acid to which hydrogen peroxide, an oxidizing agent, is added, and a method of dissolving the catalyst support material using sulfuric acid or the like to separate undissolved platinum group metals. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2009-24263 A Summary of the Invention [Problem to be solved by the invention]

[0007] Among the above-mentioned conventional techniques, the dry method has a high recovery rate of platinum group metals, but requires a large investment in equipment, which results in a problem of high recovery costs. On the other hand, the wet method does not require large equipment, but the catalyst coating layer supporting the platinum group metals is hardly soluble in acid, which inhibits the dissolution of the platinum group metals, resulting in a poor extraction rate of the platinum group metals. Furthermore, the wet method requires a large amount of acid, which also requires waste liquid treatment, resulting in many problems in terms of cost and recovery rate.

[0008] As a result of intensive research into the above-mentioned problems, the inventors of the present application have discovered that a molten salt obtained by heating ammonium hydrogen sulfate dissolves and removes inorganic oxides, such as ceria, zirconia, and alumina, contained in the catalyst coating layer in a short period of time, and have developed a method for efficiently extracting platinum group metals from spent catalysts.

[0009] The present invention has been devised in view of the above points, and relates to a catalyst treatment method capable of efficiently recovering platinum group metals from spent catalysts by a simple method. [Means for solving the problem]

[0010] In order to achieve the above-mentioned object, the catalyst treatment method of the present invention includes the steps of mixing a pulverized catalyst containing an oxide containing at least one of ceria, zirconia, and alumina, and a platinum group metal with a predetermined amount of ammonium hydrogen sulfate as a reactant to produce a mixture, and heating the mixture under predetermined heating conditions; leaching the reactant obtained in the heating step with a predetermined dissolving solution to obtain a first solid residue and a first leachate; and leaching the first solid residue with a predetermined acid solution to obtain a second solid residue and a second leachate.

[0011] Here, the method includes a step of mixing a predetermined amount of ammonium hydrogen sulfate, which is a reactant, with a pulverized product of a catalyst containing an oxide containing at least one of ceria, zirconia, and alumina, and a platinum group metal to produce a mixture, and heating the mixture under predetermined heating conditions. By heating the mixture obtained by mixing the ammonium hydrogen sulfate, which is a reactant, with the pulverized product to a predetermined temperature, the ammonium hydrogen sulfate becomes a molten salt, and the oxide contained in the pulverized product can be dissolved and removed by the molten salt.

[0012] In addition, by including a step of leaching the reaction product obtained by heating the mixture with a specified dissolving liquid to obtain a first solid residue and a first leachate, the reaction product can be separated into a first solid residue containing mainly platinum group metals and a first leachate containing mainly metal components that form oxides.

[0013] Furthermore, by providing a step of leaching the first solid residue with a predetermined acid solution to obtain a second solid residue and a second leachate, the first solid residue can be separated into the second leachate that mainly contains platinum group metals that are easily soluble in the acid solution and the second solid residue that is the remaining residue. By the above steps, platinum group metals can be recovered from the crushed catalyst.

[0014] In addition, when ammonium hydrogen sulfate is mixed in a weight ratio of 2 to 30 times the pulverized material, the reaction of the mixture is promoted, and oxides can be dissolved and removed from the pulverized material in a short time. When the weight ratio of ammonium hydrogen sulfate to the pulverized material is less than 2 times, the reaction with the pulverized material is not promoted, and oxides cannot be efficiently dissolved and removed from the pulverized material. On the other hand, even if the weight ratio of ammonium hydrogen sulfate to the pulverized material exceeds 30 times, there is no change in the reaction time, so considering the processing cost, it is preferable that the upper limit of the weight ratio of ammonium hydrogen sulfate to the pulverized material is about 30 times.

[0015] Furthermore, in the step of heating the mixture at a predetermined temperature, if the mixture is heated under heating conditions that result in a temperature of 150 to 520°C, the reaction by ammonium hydrogen sulfate is promoted, and oxides can be efficiently dissolved and removed from the pulverized material. If the mixture is heated under heating conditions that result in a temperature of less than 150°C, ammonium hydrogen sulfate does not become molten, and oxides cannot be completely dissolved and removed from the pulverized material, resulting in a poor recovery rate of platinum group metals. On the other hand, since the boiling point of ammonium hydrogen sulfate is approximately 520°C, the heating condition for the mixture is preferably 150°C to 520°C.

[0016] In addition, when the dissolving liquid is selected from the group consisting of pure water, nitric acid, hydrochloric acid, distilled water, tap water, sulfuric acid, and ion-exchanged water, the mixture can be separated into a first solid residue and a first leachate by using these dissolving liquids.

[0017] Furthermore, when the acid solution is selected from aqua regia, hydrochloric acid containing chlorine, and hydrochloric acid containing hydrogen peroxide, these acid solutions exhibit strong oxidizing properties, and therefore the platinum group metal can be efficiently leached from the first solid residue.

[0018] In addition, when the method further includes a step of subjecting the first leachate and the second leachate to solvent extraction to recover the platinum group metals, the platinum group metals contained in the first leachate and the second leachate can be recovered from each leachate by solvent extraction.

[0019] In order to achieve the above object, the catalyst treatment method of the present invention includes the steps of mixing a pulverized catalyst containing an oxide containing at least one of ceria, zirconia, and alumina, and a platinum group metal with a predetermined amount of ammonium hydrogen sulfate as a reactant to produce a mixture, heating the mixture under predetermined heating conditions, and leaching the reactant obtained in the heating step with a predetermined acid solution to obtain a leachate and a solid residue.

[0020] Here, the method includes a step of mixing a predetermined amount of ammonium hydrogen sulfate, which is a reactant, with a pulverized product of a catalyst containing an oxide containing at least one of ceria, zirconia, and alumina, and a platinum group metal to produce a mixture, and heating the mixture under predetermined heating conditions. By heating the mixture obtained by mixing the ammonium hydrogen sulfate, which is a reactant, with the pulverized product to a predetermined temperature, the ammonium hydrogen sulfate becomes a molten salt, and the oxide contained in the pulverized product can be dissolved and removed by the molten salt.

[0021] By providing a step of leaching the reaction product obtained in the heating step with a predetermined acid solution to obtain a leachate and a solid residue, the reaction product can be separated into a leachate that mainly contains platinum group metals that are easily soluble in acid solutions and a solid residue that is the remaining residue. The leachate can then be subjected to solvent extraction to recover platinum group metals from the crushed catalyst.

[0022] In order to achieve the above-mentioned object, the catalyst treatment method of the present invention includes the steps of adding a predetermined amount of ammonium hydrogen sulfate as a reactant to a catalyst consisting of a block body having a platinum group metal supported on a base material and a catalyst coating layer formed thereon containing an oxide including at least one of ceria, zirconia, and alumina, and heating the catalyst under predetermined heating conditions; leaching the reactant obtained in the heating step with a predetermined dissolving liquid to obtain a slurry containing the platinum group metal and metal components of the catalyst coating layer; separating the slurry into solid and liquid to obtain a first solid residue and a first leachate; and leaching the first solid residue with a predetermined acid solution to obtain a second solid residue and a second leachate.

[0023] Here, the process includes a step of adding a predetermined amount of ammonium hydrogen sulfate as a reactant to a catalyst consisting of a block body having a platinum group metal supported on a base material and a catalyst coating layer containing an oxide including at least one of ceria, zirconia, and alumina, and heating the catalyst under predetermined heating conditions, whereby the ammonium hydrogen sulfate becomes a molten salt, and the catalyst coating layer can be peeled off from the base material by the molten salt.

[0024] Then, by leaching the reactants with a prescribed solvent, the catalyst consisting of blocks can be separated into a slurry consisting of the platinum group metal and the metal components of the catalyst coating layer, and the base material.

[0025] In addition, by including a step of subjecting the slurry body to solid-liquid separation to obtain a first solid residue and a first leachate, the slurry body can be separated into a first solid residue mainly containing platinum group metals and a first leachate mainly containing metal components that form oxides.

[0026] In addition, the first solid residue can be leached with a predetermined acid solution, and the first solid residue can be separated into a second leachate that mainly contains platinum group metals that are easily soluble in the acid solution, and a second solid residue that is the remaining residue. By the above steps, platinum group metals can be recovered from the crushed catalyst. Effect of the Invention

[0027] The catalyst treatment method according to the present invention is capable of efficiently recovering platinum group metals from spent catalysts in a simple manner. [Brief description of the drawings]

[0028] [Figure 1] FIG. 1 is a process diagram of a catalyst treatment method according to a first embodiment of the present invention. [Diagram 2] FIG. 4 is a process diagram of a catalyst treatment method according to a second embodiment of the present invention. [Diagram 3] FIG. 4 is a process diagram of a catalyst treatment method according to a third embodiment of the present invention. [Figure 4]1 is a photograph showing the appearance of a pulverized catalyst material subjected to a molten salt treatment using ammonium hydrogen sulfate as a reactant in an example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] Hereinafter, a catalyst treatment method according to an embodiment of the present invention will be described in detail with reference to the drawings etc. for the purpose of understanding the present invention.

[0030] [First embodiment] Fig. 1 shows a process diagram of a catalyst treatment method according to a first embodiment of the present invention. The catalyst treatment method according to this embodiment mainly comprises a series of steps, which are: mixing ammonium hydrogen sulfate, a reactant, with a crushed catalyst to produce a mixture (step 1), heat-treating the mixture (step 2), leaching the reactant obtained by the heat treatment in step 2 with a dissolving solution (step 3), and further dissolving the first solid residue of the first leachate obtained by the water leaching in step 3 with an acid solution to obtain a second solid residue and a second leachate (step 4).

[0031] The crushed catalyst in step 1 is a waste automobile catalyst (a catalyst coating layer carrying platinum group metals formed on the surface of a honeycomb-structured base material made of raw materials such as aluminum oxide, silicon dioxide, and magnesium oxide) that has been crushed in advance into a powder using a crusher. Then, ammonium hydrogen sulfate, which is a reactant, is mixed with this crushed material. The amount of ammonium hydrogen sulfate mixed is approximately 2 to 30 times the weight of the crushed material.

[0032] Here, if the amount of ammonium hydrogen sulfate mixed is less than approximately twice the weight of the ground material, when the mixture is heat-treated, the ground material will not be completely immersed in the molten salt of ammonium hydrogen sulfate, and the reaction between the ground material and ammonium hydrogen sulfate will not be promoted, and the oxides contained in the ground material (ceria, zirconia, and alumina, which are components of the catalytic coating layer) will not be completely dissolved and removed from the ground material.

[0033] On the other hand, even if the amount of ammonium hydrogen sulfate mixed exceeds about 30 times the weight of the pulverized material, there is no significant change in the reaction time for dissolving and removing the oxides. Therefore, taking into consideration the processing cost, it is preferable that the upper limit of the weight ratio of ammonium hydrogen sulfate to the pulverized material is about 30 times.

[0034] The heating conditions in step 2 are adjusted to 150°C or higher at which ammonium hydrogen sulfate becomes a molten salt. When ammonium hydrogen sulfate becomes a molten salt, the oxides constituting the catalyst coating layer contained in the pulverized material begin to dissolve, and the catalyst coating layer can be leached from the pulverized material by water leaching in step 3 described below.

[0035] Here, as for the heating conditions, if the temperature of the mixture is less than 150°C, the ammonium hydrogen sulfate does not become completely molten, and the reaction with the pulverized material is not promoted. Therefore, the oxides cannot be completely dissolved from the pulverized material, and the recovery rate of platinum group metals from the pulverized material decreases. The upper limit of the heating temperature can be set near the boiling point of ammonium hydrogen sulfate (approximately 520°C).

[0036] In step 3, the reaction product obtained in step 2 is leached with a predetermined dissolving solution to separate it into a first solid residue and a first leachate. The dissolving solution used in the dissolving solution leaching is not particularly limited, but can be appropriately selected from tap water, distilled water, ion-exchanged water, pure water, or weak acids (hydrochloric acid, nitric acid, sulfuric acid), for example.

[0037] When the mixture of the pulverized material and ammonium hydrogen sulfate is heat-treated, the oxides contained in the pulverized material can be dissolved by the molten salt as described above.The reaction product is then leached with a dissolving solution, and the resulting slurry is subjected to solid-liquid separation, so that the reaction product can be separated into a first leachate containing mainly metal components that form oxides and a first solid residue containing platinum group metals.

[0038] In step 4, the first solid residue is further leached with an acid solution and the resulting slurry is subjected to solid-liquid separation, whereby platinum group metals that are readily soluble in acid from the first solid residue are leached out as a second leachate, and the other components can be separated as a second solid residue.

[0039] The platinum group metals Pt, Pd, and Rh can be recovered by further solvent extraction of the second leachate obtained in step 4. Note that some of the platinum group metals (e.g., Pt, Pd) may be contained in the first leachate. Therefore, by also solvent extraction of the first leachate, the recovery rate of the platinum group metals can be further increased.

[0040] [Second embodiment] Next, a second embodiment of the present invention will be described with reference to the process diagram of Fig. 2. In the following description, the description overlapping with the first embodiment will be omitted.

[0041] In the second embodiment, as in the first embodiment, a mixture is produced by mixing ammonium hydrogen sulfate, which is a reactant, with the crushed catalyst (step 1), and the mixture is heat-treated to obtain a reactant (step 2).Then, in the second embodiment, the reactant obtained in step 2 is leached with an acid solution to obtain a leachate and a solid residue (step 3), without going through a water leaching step using a dissolving solution as in the first embodiment, and the process is composed of a series of steps.

[0042] In the above steps, a reaction product can be obtained by first heating the mixture obtained by mixing the pulverized material with ammonium hydrogen sulfate, which is a reactant, to a predetermined temperature in steps 1 and 2. As described above, this reaction product is in a state in which ammonium hydrogen sulfate becomes a molten salt and the oxides contained in the pulverized material are dissolved and removed by the molten salt.

[0043] In step 3, the reaction product is leached with an acid solution, and the resulting slurry is subjected to solid-liquid separation to separate into a leachate mainly containing platinum group metals that are easily soluble in the acid solution, and a solid residue mainly containing oxides. The leachate is then subjected to solvent extraction to recover the platinum group metals.

[0044] As described above, in the second embodiment, the processing method can be simplified more than in the first embodiment, and therefore processing costs can be reduced.

[0045] [Third embodiment] Next, a third embodiment of the present invention will be described with reference to Fig. 3. In the following description, the description overlapping with the first and second embodiments will be omitted.

[0046] In the first and second embodiments, a treatment method in which a crushed catalyst is used as the treatment object is described. In the third embodiment, however, a treatment method in which a catalyst consisting of a block body before crushing (a catalyst having a platinum group metal supported on a base material and a catalyst coating layer containing an oxide including at least one of ceria, zirconia, and alumina) is used as the treatment object is described.

[0047] The treatment method according to the third embodiment mainly comprises a series of steps, in which ammonium hydrogen sulfate, a reactant, is added to a catalyst made of a block body (step 1), which is then heated (step 2), the reaction product obtained by the heat treatment in step 2 is leached with a dissolving solution (step 3), the slurry obtained by the water leaching in step 3 is separated into a first solid residue and a first leachate by solid-liquid separation (step 4), and the first solid residue obtained in step 4 is dissolved in an acid solution to obtain a second solid residue and a second leachate (step 5).

[0048] First, in steps 1 and 2, ammonium hydrogen sulfate is added to the block catalyst, and then the catalyst coating layer carrying the platinum group metal can be peeled off from the base material by heating under specific heating conditions. Then, in step 3, the block catalyst can be separated into the base material and a slurry body consisting of the platinum group metal and the metal components of the catalyst coating layer by water leaching with a dissolving solution. The separated base material can be discarded as it is, or recycled.

[0049] On the other hand, the slurry obtained in step 3 is in a state in which the oxides contained in the catalyst coating layer have been dissolved and removed by the molten salt due to the reaction with ammonium hydrogen sulfate, so that by subjecting the slurry to solid-liquid separation in step 4, it can be separated into a first leachate consisting of metal components that form oxides and a first solid residue containing platinum group metals that are readily soluble in acid.

[0050] In step 5, the first solid residue is further leached with an acid solution, so that platinum group metals that are readily soluble in acid are leached out of the first solid residue as a second leachate, and the other components can be separated as a second solid residue.

[0051] The platinum group metals Pt, Pd, and Rh can be recovered by subjecting the second leachate obtained in step 5 to solvent extraction. Note that the first leachate may also contain some of the platinum group metals (e.g., Pt, Pd). Therefore, by subjecting the first leachate to solvent extraction as well, the recovery rate of the platinum group metals can be further increased.

[0052] As described above, in the third embodiment, the catalyst made of a block body can be treated as it is, and therefore, unlike the first and second embodiments, there is no need to perform a crushing process on the catalyst, and therefore, the processing cost can be reduced.

[0053] Next, an embodiment of the present invention will be described. <Molten salt treatment> In this example, 0.5 g of crushed catalyst and 5.0 g of ammonium hydrogen sulfate as a reactant were prepared, and mixed together (hereinafter, the mixture of crushed catalyst and ammonium hydrogen sulfate will be referred to as the "mixture") and placed in a test tube, and the bottom of the test tube was heated using a burner for approximately 20 minutes.

[0054] Figure 4 shows external photographs of the inside of the test tube every 5 minutes after the start of heating. As shown in Figure 4(b), 5 minutes after the start of heating, the ammonium hydrogen sulfate becomes a molten liquid (molten salt), and it can be seen that the catalyst is gradually immersed in this molten salt and the reaction proceeds. Then, as shown in Figure 4(d), 15 minutes after the start of heating, the mixture produced a reaction product consisting of a cloudy white suspension.

[0055] <Solution solution leaching> The test tube was then cooled to room temperature, and a dissolving solution (ion-exchanged water) was added and water leaching was carried out using a vortex mixer until all the solidified molten salt was removed. The slurry obtained by water leaching was filtered to separate the filtrate (first leachate) and the residue (first solid residue).

[0056] <Acid dissolution> The first solid residue was then stirred and leached with aqua regia for about 2 hours. After cooling, the leachate was filtered to separate it into a filtrate (second leachate) and a residue (second solid residue).

[0057] The concentrations of platinum group metal components (Pt, Pd, Rh) in the first leachate obtained by dissolving solution leaching and the second leachate obtained by aqua regia were measured using an ICP emission spectrometer, and the results are shown in Table 1. As a comparative example, Table 1 also shows the results for the case where the dissolving salt treatment using ammonium hydrogen sulfate was not performed.

[0058] [Table 1]

[0059] As shown in Table 1, when molten salt treatment using ammonium hydrogen sulfate was performed, the recovery rate of platinum group metals was 99.9% or more for each component, whereas when the treatment was not performed, the recovery rates of platinum group metals were the highest for Pd at 95.9%, followed by Pt at 90.6% and Rh at 53.5%.

[0060] From the above results, it was confirmed that the recovery rate of platinum group metals can be significantly increased by subjecting the catalyst to a molten salt treatment using ammonium hydrogen sulfate. In addition, by extracting only the platinum group metal components from the first leachate and the second leachate by, for example, solvent extraction, the platinum group metals can be recovered from the catalyst.

[0061] As described above, the catalyst treatment method according to the present invention can efficiently recover platinum group metals from spent catalysts in a simple manner.

Claims

1. A process of mixing a pulverized catalyst containing an oxide containing at least one of ceria, zirconia, and alumina, and a platinum group metal with a predetermined amount of ammonium hydrogen sulfate as a reactant to generate a mixture, and heating the mixture under predetermined heating conditions; leaching the reaction product obtained in the heating step with a predetermined dissolving solution to obtain a first solid residue and a first leaching solution; leaching the first solid residue with a predetermined acid solution to obtain a second solid residue and a second leachate. Method of catalyst treatment.

2. The ammonium hydrogen sulfate is mixed in a weight ratio of 2 to 30 times the pulverized material. A method for treating the catalyst of claim 1.

3. The step of heating the mixture under predetermined heating conditions is performed under heating conditions in which the temperature of the mixture is approximately 150 to 520° C. A method for treating the catalyst according to claim 1 or 2.

4. The dissolving solution is selected from the group consisting of pure water, nitric acid, hydrochloric acid, distilled water, tap water, sulfuric acid, and ion-exchanged water. A method for treating the catalyst according to claim 1 or 2.

5. The acid solution is selected from aqua regia, hydrochloric acid containing chlorine, and hydrochloric acid containing hydrogen peroxide. A method for treating the catalyst according to claim 1 or 2.

6. The method further comprises the step of subjecting the first leachate and the second leachate to solvent extraction to recover the platinum group metal. A method for treating the catalyst according to claim 1 or 2.

7. A process of mixing a pulverized catalyst containing an oxide containing at least one of ceria, zirconia, and alumina, and a platinum group metal with a predetermined amount of ammonium hydrogen sulfate as a reactant to generate a mixture, and heating the mixture under predetermined heating conditions; and a step of leaching the reaction product obtained in the heating step with a predetermined acid solution to obtain a leachate and a solid residue. Method of catalyst treatment.

8. a step of adding a predetermined amount of ammonium hydrogen sulfate as a reactant to a catalyst comprising a block body having a platinum group metal supported on a base material and a catalyst coating layer containing an oxide including at least one of ceria, zirconia, and alumina, and heating the catalyst under a predetermined heating condition; a step of leaching the reaction product obtained in the heating step with a predetermined dissolving solution to obtain a slurry containing the platinum group metal and the metal components of the catalyst coating layer; subjecting the slurry to solid-liquid separation to obtain a first solid residue and a first leachate; leaching the first solid residue with a predetermined acid solution to obtain a second solid residue and a second leachate. Method of catalyst treatment.

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