Method for recovering pd and / or pt and analysis method

Abstract

To provide a method for recovering Pd and / or Pt in a short time at a high recovery rate.SOLUTION: (a) a step of adding a thiocyanate to a raw material aqueous solution containing Pd and / or Pt to prepare a first aqueous phase, (b) a step of adding an ionic liquid to the first aqueous phase and mixing them to selectively extract Pd and / or Pt from the first aqueous phase into the ionic liquid, (c) a step of separating the ionic liquid phase containing Pd and / or Pt from the first aqueous phase, and (d) a step of adding a thiourea aqueous solution to the separated ionic liquid phase and mixing them to selectively back-extract Pd and / or Pt from the ionic liquid phase into the thiourea aqueous solution, A method of recovering Pd and / or Pt, comprising the steps of: obtaining a second aqueous phase thereby comprising Pd and / or Pt; and (e) separating the second aqueous phase from the ionic liquid phase to recover Pd and / or Pt.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for recovering and analyzing Pd and / or Pt. [Background technology]

[0002] Platinum group elements are precious metals used in industrial processes and products, jewelry, dental materials, etc. In particular, palladium (Pd) and platinum (Pt) are used as catalysts in automobile exhaust gas treatment and organic chemical synthesis. Pd and Pt are also used in various other fields, such as fuel cells. Meanwhile, global demand for these metals is still increasing. Therefore, it is desirable to recycle these metals from post-consumer waste products containing Pd and Pt.

[0003] For example, Patent Document 1 (JP 2017-88920 A) discloses a method for selectively recovering platinum group elements from an aqueous phase containing one or more platinum group elements, and describes extracting the platinum group elements into an organic phase made of an ionic liquid and then electrolytically depositing them. Non-Patent Document 1 (Shoichi Katsuta, Junko Tamura, "Extraction of Palladium (II) and Platinum (IV) from Hydrochloric Acid Solutions with Trioctylammonium Nitrate Ionic Liquid without Dilution," J. Solution Chem. (2018) 47:1293-1308) discloses the extraction of Pd and Pt from a dilute hydrochloric acid solution using a saturated aqueous solution of trioctylammonium nitrate ([HTOA][NO3]), and describes that Pd and Pt can be extracted at high yields by back-extracting with an aqueous solution containing thiourea and nitric acid. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-88920 [Non-patent literature]

[0005] [Non-Patent Document 1] Shoichi Katsuta, Junko Tamura, "Extraction of Palladium(II) and Platinum(IV) from Hydrochloric Acid Solutions with Trioctylammonium Nitrate Ionic Liquid without Dilution," J Solution Chem (2018) 47:1293-1308 Summary of the Invention

[0006] As mentioned above, various methods for recovering Pd and Pt have been investigated, but further improvements are desired. For example, the recovery method by electrolytic deposition disclosed in Patent Document 1 requires complex operations involving control of current and voltage. Therefore, a recovery method that enables solution extraction with simple operations is desired. On the other hand, the solvent extraction method disclosed in Non-Patent Document 1 requires more than 30 minutes for back-extraction to achieve a high extraction rate of the metal, and a recovery method that can be performed in a shorter time is desired.

[0007] The present inventors have now discovered that Pd and / or Pt (particularly Pd) can be recovered in a short time and with a high recovery rate by adding thiocyanate to a raw material aqueous solution containing Pd and / or Pt, extracting Pd and / or Pt with an ionic liquid, and then back-extracting the Pd and / or Pt with an aqueous thiourea solution.

[0008] Therefore, an object of the present invention is to provide a method for recovering Pd and / or Pt (particularly Pd) in a short time and with a high recovery rate.

[0009] According to the present disclosure, the following aspects are provided. [Aspect 1] A method for recovering Pd and / or Pt, comprising the steps of: (a) adding a thiocyanate to a raw material aqueous solution containing Pd and / or Pt to prepare a first aqueous phase; (b) adding an ionic liquid to the first aqueous phase and mixing the same to selectively extract Pd and / or Pt from the first aqueous phase into the ionic liquid, thereby obtaining an ionic liquid phase containing Pd and / or Pt; (c) separating the Pd and / or Pt-containing ionic liquid phase from the first aqueous phase; (d) adding and mixing an aqueous thiourea solution to the separated ionic liquid phase to selectively strip Pd and / or Pt from the ionic liquid phase into the aqueous thiourea solution, thereby obtaining a second aqueous phase containing Pd and / or Pt; (e) separating the second aqueous phase from the ionic liquid phase to recover Pd and / or Pt; A method for recovering Pd and / or Pt, comprising: [Aspect 2] Aspect 2. The method for recovering Pd and / or Pt according to aspect 1, wherein the concentration of the thiocyanate in the first aqueous phase is 0.50 mol / L or more and 4.00 mol / L or less. [Aspect 3] Aspect 2. The method for recovering Pd and / or Pt according to aspect 1, wherein the concentration of the thiocyanate in the first aqueous phase is 3.00 mol / L or more and 3.80 mol / L or less. [Aspect 4] A method for recovering Pd and / or Pt according to any one of Aspects 1 to 3, wherein the thiocyanate comprises potassium thiocyanate and / or sodium thiocyanate. [Aspect 5] A method for recovering Pd and / or Pt according to any one of Aspects 1 to 4, wherein the first aqueous phase is an acidic aqueous solution of hydrochloric acid. [Aspect 6] A method for recovering Pd and / or Pt according to any one of Aspects 1 to 5, wherein the ionic liquid is a chloride. [Aspect 7] 7. The method for recovering Pd and / or Pt according to aspect 6, wherein the chloride comprises methyltrioctylammonium chloride. [Aspect 8] A method for recovering Pd and / or Pt according to any one of aspects 1 to 7, wherein the second aqueous phase has a pH of 8.0 or less. [Aspect 9] Aspect 9. The method for recovering Pd and / or Pt according to any one of Aspects 1 to 8, wherein the mixing of the first aqueous phase and the ionic liquid is carried out by stirring or shaking the first aqueous phase and the ionic liquid for 0.5 minutes to 15 minutes. [Aspect 10] Aspect 10. The method for recovering Pd and / or Pt according to any one of Aspects 1 to 9, wherein the mixing of the ionic liquid phase and the thiourea aqueous solution is carried out by stirring or shaking the ionic liquid phase and the thiourea aqueous solution for 1 minute or more and 25 minutes or less. [Aspect 11] 11. The method for recovering Pd and / or Pt according to any one of Aspects 1 to 10, wherein the aqueous thiourea solution does not contain ammonia or ammonium ions. [Aspect 12] 12. The method for recovering Pd and / or Pt according to any one of Aspects 1 to 11, wherein the raw material aqueous solution contains Pd and / or Pt and impurity components derived from a Pd and / or Pt-containing product or recycled raw material. [Aspect 13] A method for analyzing Pd and / or Pt, comprising measuring the concentration of Pd and / or Pt contained in the second aqueous phase obtained by the method for recovering Pd and / or Pt according to any one of aspects 1 to 12. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a flow chart showing an outline of a method for recovering Pd and / or Pt according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] Method for recovering Pd and / or Pt The present invention relates to a method for recovering Pd and / or Pt. As shown in Figure 1, this recovery method involves (a) adding a thiocyanate to a raw aqueous solution containing Pd and / or Pt to prepare a first aqueous phase. Next, (b) adding an ionic liquid to the resulting first aqueous phase and mixing it, thereby selectively extracting Pd and / or Pt from the first aqueous phase into the ionic liquid, thereby obtaining an ionic liquid phase containing Pd and / or Pt. (c) Separating the resulting ionic liquid phase containing Pd and / or Pt from the first aqueous phase. Then, (d) adding an aqueous thiourea solution to the separated ionic liquid phase and mixing it, thereby selectively back-extracting Pd and / or Pt from the ionic liquid phase into the aqueous thiourea solution, thereby obtaining a second aqueous phase containing Pd and / or Pt. Finally, (e) separating the second aqueous phase from the ionic liquid phase to recover Pd and / or Pt. In this way, Pd and / or Pt (especially Pd) can be recovered in a short time with a high recovery rate by adding thiocyanate to a raw aqueous solution containing Pd and / or Pt, extracting Pd and / or Pt with an ionic liquid, and then back-extracting Pd and / or Pt with an aqueous thiourea solution. Moreover, the ionic liquid separated from the second aqueous phase can be reused in further recovery processes, which has the advantage of reducing the environmental burden.

[0012] As mentioned above, the electrolytic deposition recovery method disclosed in Patent Document 1 requires complex operations involving current and voltage control. Therefore, a recovery method that enables solution extraction with simple operations is desired. On the other hand, the solvent extraction method disclosed in Non-Patent Document 1 requires more than 30 minutes of stripping to achieve a high metal extraction rate, and a recovery method that can be performed in a shorter time is desired. In this regard, the present invention can conveniently solve these problems. Although the mechanism is not entirely clear, it is presumed to be as follows: (i) By adding thiocyanate to a raw material aqueous solution containing Pd and / or Pt, Pd and / or Pt form thiocyanate complexes, which result in selective extraction of Pd and / or Pt into the ionic liquid by ion exchange. (ii) Even in the ionic liquid, Pd and / or Pt form some kind of complex (e.g., an ionic complex such as a chloro complex) and / or solvate (e.g., solvation of the complex with the ionic liquid). Therefore, the use of an aqueous thiourea solution facilitates selective stripping of Pd and / or Pt into the second aqueous phase. It is speculated that this will enable the recovery of Pd and / or Pt (especially Pd) in a short time and with a high recovery rate. In any case, the recovery method of the present invention involves two-stage extraction (i.e., Pd and / or Pt is extracted into an ionic liquid phase and then back-extracted into a second aqueous phase). This two-stage extraction allows the target component (Pd and / or Pt) to be separated and extracted from the large amount of impurities that may be contained in the raw aqueous solution, thereby improving the accuracy of subsequent analysis of the target component.

[0013] (a) Preparation of the first aqueous phase First, a raw material aqueous solution containing Pd and / or Pt to be subjected to the recovery method of the present invention is prepared. The raw material aqueous solution is not particularly limited as long as it contains the Pd and / or Pt to be recovered. Typically, it contains Pd and / or Pt derived from a Pd and / or Pt-containing product (e.g., a catalyst) or recycled raw materials, as well as impurities. Examples of impurities include Ce, Zr, Al, Rh, etc., which are exemplified as components of exhaust gas purification catalysts. Alternatively, for example, a solid sample containing Pd and / or Pt as a raw material can be dissolved, melted (e.g., alkali melted), or the like to form a solution. If necessary, the solution can be further treated with sulfuric acid white smoke, and then redissolved in hydrochloric acid, heated, and / or aged to obtain a raw material aqueous solution containing Pd and / or Pt.

[0014] A thiocyanate is then added to the raw material aqueous solution containing Pd and / or Pt to prepare a first aqueous phase. The thiocyanate preferably contains potassium thiocyanate and / or sodium thiocyanate, and more preferably potassium thiocyanate.

[0015] The concentration of thiocyanate in the first aqueous phase is preferably 0.50 mol / L to 4.00 mol / L, more preferably 1.25 mol / L to 4.00 mol / L, even more preferably 2.00 mol / L to 4.00 mol / L, particularly preferably 2.50 mol / L to 3.90 mol / L, and most preferably 3.00 mol / L to 3.80 mol / L. By controlling the thiocyanate concentration in this manner, Pd and / or Pt can be recovered at a higher recovery rate.

[0016] The first aqueous phase is preferably an acidic aqueous solution of hydrochloric acid. That is, the first aqueous phase preferably contains hydrochloric acid from the viewpoint of increasing the extraction rate of Pd and / or Pt as chloro complexes. The hydrochloric acid concentration in the first aqueous phase is preferably 0.10 mol / L or more and 6.00 mol / L or less, more preferably 0.10 mol / L or more and 3.00 mol / L or less, and even more preferably 0.20 mol / L or more and 1.00 mol / L or less.

[0017] (b) Extraction into an ionic liquid phase By adding and mixing an ionic liquid to the first aqueous phase obtained in step (a) above, Pd and / or Pt are selectively extracted from the first aqueous phase into the ionic liquid. In this way, an ionic liquid phase containing Pd and / or Pt can be obtained. The ionic liquid is not particularly limited as long as it can selectively extract Pd and / or Pt from the first aqueous phase into the ionic liquid, but chlorides are preferred. Examples of preferred chlorides include quaternary ammonium chlorides. Examples of preferred quaternary ammonium chlorides include methyltrioctylammonium chloride and trihexyltetradecylphosphonium chloride, with methyltrioctylammonium chloride being particularly preferred.

[0018] The first aqueous phase and the ionic liquid may be mixed by known techniques such as stirring or shaking. It is generally believed that the longer the mixing time, the higher the final recovery rate of Pd and Pt. However, the recovery method of the present invention allows Pd and / or Pt to be recovered in a short time with a high recovery rate. From this perspective, the first aqueous phase and the ionic liquid may be mixed by stirring or shaking a container (e.g., a centrifuge tube) containing the first aqueous phase and the ionic liquid for preferably 0.5 to 15 minutes, more preferably 1 to 12 minutes, even more preferably 1 to 10 minutes, and particularly preferably 5 to 10 minutes. However, the stirring or shaking time may be longer than the above range to obtain a higher recovery rate.

[0019] (c) Ionic liquid phase separation The ionic liquid phase containing Pd and / or Pt obtained in step (b) above is separated from the first aqueous phase. This separation is preferably performed by centrifugation, as it allows for reliable separation into two phases in a short time. Centrifugation can be performed at a desired rotation speed using a commercially available centrifuge. The rotation speed is not particularly limited, but is preferably 500 rpm to 3000 rpm, more preferably 1000 rpm to 2000 rpm. The duration of centrifugation is not particularly limited, but is preferably 1 minute to 10 minutes, more preferably 3 minutes to 7 minutes. Note that while FIG. 1 depicts the ionic liquid phase as being located above the first aqueous phase, the positional relationship between the first aqueous phase and the ionic liquid phase (which phase is the upper or lower phase) varies depending on the specific gravity of the ionic liquid used, and the phases can be separated according to this positional relationship.

[0020] (d) Back-extraction into a second aqueous phase By adding and mixing the ionic liquid phase separated in step (c) with an aqueous thiourea solution, Pd and / or Pt are selectively stripped from the ionic liquid phase into the aqueous thiourea solution. In this way, a second aqueous phase containing Pd and / or Pt can be obtained. The aqueous thiourea solution is preferably an aqueous solution containing thiourea alone, but it may also contain an optional additional component in addition to thiourea. Examples of the additional component include acids such as phosphoric acid, ethylenediaminetetraacetic acid (EDTA), hydrochloric acid, and nitric acid. However, from the viewpoint of effectively stripping Pd and / or Pt from the ionic liquid phase with the aqueous thiourea solution, it is preferable that the aqueous thiourea solution does not contain ammonia or ammonium ions.

[0021] The ionic liquid phase and the thiourea aqueous solution can be mixed by known techniques such as stirring or shaking. Generally, it is believed that the longer the mixing time, the higher the final recovery rate of Pd and Pt. However, the recovery method of the present invention allows Pd and / or Pt to be recovered in a short time with a high recovery rate. From this perspective, the ionic liquid phase and the thiourea aqueous solution can be mixed by stirring or shaking a container (e.g., a centrifuge tube) containing the ionic liquid phase and the thiourea aqueous solution for preferably 1 minute to 25 minutes, more preferably 2 minutes to 20 minutes, even more preferably 2 minutes to 15 minutes, and particularly preferably 5 minutes to 10 minutes. However, to obtain a higher recovery rate, the stirring or shaking time may be longer than the above range. Furthermore, a stirring or shaking time of 10 minutes or less is preferred from the viewpoint of shortening the recovery time of Pd and / or Pt. However, when the raw material aqueous solution contains Pt, a stirring or shaking time of 10 minutes or more is preferred from the viewpoint of improving the extraction rate (recovery rate), and more preferably 15 minutes or more.

[0022] From the viewpoints of extraction rate and solubility, the concentration of thiourea in the second aqueous phase is preferably 0.20 mol / L to 2.00 mol / L, more preferably 0.50 mol / L to 1.50 mol / L, and even more preferably 0.70 mol / L to 1.30 mol / L. When the second aqueous phase contains an additional component, the concentration of the additional component in the second aqueous phase is preferably more than 0 mol / L to 1.50 mol / L, more preferably 0.50 mol / L or less.

[0023] The second aqueous phase is preferably not alkaline, since this facilitates extraction of the target component. That is, the pH of the second aqueous phase is preferably 8.0 or less, more preferably 0.1 to 5.0, and even more preferably 0.5 to 2.5.

[0024] (e) Recovery of Pd and / or Pt The second aqueous phase obtained in step (d) above is separated from the ionic liquid phase to recover Pd and / or Pt. This separation is preferably performed by centrifugation, as it allows for reliable separation into two phases in a short time. Centrifugation can be performed at a desired rotation speed using a commercially available centrifuge, as in step (c) above. Therefore, the rotation speed of the centrifugation is not particularly limited, but is preferably 500 rpm to 3000 rpm, more preferably 1000 rpm to 2000 rpm. The duration of the centrifugation is not particularly limited, but is preferably 1 minute to 10 minutes, more preferably 3 minutes to 7 minutes. Furthermore, since the ionic liquid separated from the second aqueous phase has been freed of impurities, it can be reused in further recovery processes.

[0025] (f) Other The series of steps (a) to (e) above can be carried out at room temperature, but may be carried out at a desired temperature. The operating temperature for each of the steps (a) to (e) above is not particularly limited, but can typically be in the range of 15°C to 32°C, more typically 22°C to 29°C.

[0026] As described above, by carrying out the series of steps (a) to (e), Pd and / or Pt can be recovered in a short time with a high recovery rate. In particular, the method of the present invention can achieve a significantly high recovery rate of Pd, and therefore, it can be said that the method of the present invention is particularly preferable for use in recovering Pd.

[0027] Analytical method for Pd and / or Pt If necessary, the concentration of Pd and / or Pt contained in the second aqueous phase obtained by the above-described recovery method of the present invention may be measured. That is, according to one embodiment of the present invention, there is provided a method for analyzing Pd and / or Pt, which includes measuring the concentration of Pd and / or Pt contained in the second aqueous phase obtained by the above-described recovery method. The concentration of Pd and / or Pt in the second aqueous phase can be measured by a known technique, such as ICP atomic emission spectroscopy. The above-described recovery method involves a two-stage extraction (i.e., Pd and / or Pt is extracted into an ionic liquid phase and then back-extracted into a second aqueous phase). This two-stage extraction allows the target component (Pd and / or Pt) to be separated and extracted from a large amount of impurity components that may be contained in the raw aqueous solution. Therefore, the target component can be analyzed with high accuracy by the above-described analytical method. In particular, since the recovery rate of Pd is significantly high in the above-described recovery method, it can be said that the analytical method of this embodiment is particularly preferable for use in the analysis of Pd. [Example]

[0028] The present invention is further illustrated by the following examples.

[0029] Examples 1-5 The recovery and evaluation of Pd and / or Pt were carried out using a raw material aqueous solution assumed to be a catalyst containing Pd and Pt, a recycled raw material, etc. All of the following operations were carried out at room temperature (approximately 25°C).

[0030] (1) Preparation of the first aqueous phase A raw aqueous solution containing 50 μg of Pt, 50 μg of Pd, and 50 μg of Rh (rhodium) as an impurity was prepared. Potassium thiocyanate (KSCN) and hydrochloric acid were added to this raw aqueous solution to the concentrations shown in Table 1, to prepare 2 mL of a first aqueous phase, which was an acidic aqueous solution of hydrochloric acid. This first aqueous phase was placed in a centrifuge tube.

[0031] (2) Extraction into an ionic liquid phase Five mL of methyltrioctylammonium chloride (an ionic liquid) was added to the centrifuge tube containing the first aqueous phase, and the tube was sealed. The sealed tube was shaken for 5 minutes to selectively extract Pd and / or Pt from the first aqueous phase into the ionic liquid. Five mL of an ionic liquid phase containing Pd and / or Pt was thus obtained.

[0032] (3) Ionic liquid phase separation The tube was centrifuged using a centrifuge to separate the mixture into two phases: a first aqueous phase and an ionic liquid phase. This centrifugation was carried out at 1500 rpm for 5 minutes. After centrifugation, only the first aqueous phase was extracted, and 5 mL of the ionic liquid phase containing Pd and / or Pt was separated from the first aqueous phase.

[0033] (4) Back-extraction into a second aqueous phase One mL of the separated ionic liquid phase was taken and placed in a centrifuge tube. 2.00 mL of a 1.00 mol / L thiourea aqueous solution (pH 6.1) was added to the ionic liquid phase in the centrifuge tube. The centrifuge tube was sealed and shaken for 5 minutes to selectively extract Pd and / or Pt from the ionic liquid phase into the thiourea aqueous solution. This yielded a second aqueous phase containing Pd and / or Pt. The pH of the second aqueous phase was measured and found to be approximately 1.7.

[0034] (5) Recovery of Pd and / or Pt The tube was centrifuged under the same conditions as in (3) above, resulting in separation into two phases: a second aqueous phase and an ionic liquid phase. Pd and / or Pt were thus recovered in the second aqueous phase. The separated ionic liquid phase could be reused to extract Pd and / or Pt.

[0035] (6) Evaluation The recovery rates (%) of Pd and Pt in the resulting second aqueous phase were confirmed. Specifically, 1 mL of the second aqueous phase was sampled and diluted with 19 mL of pure water. The concentrations of Pd and Pt in 20 mL of the resulting diluted aqueous solution were measured by ICP atomic emission spectroscopy. The total amounts (μg) of Pd and Pt contained in the second aqueous phase, calculated from the measured concentrations, were divided by the total amounts (μg) of Pd and Pt contained in the original raw aqueous solution, and the result was multiplied by 100 to calculate the recovery rates (%) of Pd and Pt. The recovery rate (%) of the impurity component (Rh) in the resulting second aqueous phase was also confirmed in the same manner as above, and was found to be 0%, indicating that the impurity component (Rh) was not contained in the second aqueous phase (i.e., Pd and / or Pt had been separated and extracted from the impurity components). The results are shown in Table 1.

[0036] Example 6 (comparison) In the above (1), recovery and evaluation of Pd and / or Pt were carried out in the same manner as in Example 1, except that 2 mL of the first aqueous phase was prepared without adding KSCN as shown in Table 1. The results are shown in Table 1.

[0037] Example 7 Recovery and evaluation of Pd and / or Pt were carried out in the same manner as in Example 1, except that in (4) above, a phosphoric acid-containing thiourea aqueous solution was added to the ionic liquid phase in place of the thiourea aqueous solution at the concentration and volume shown in Table 1. The results are shown in Table 1.

[0038] Example 8 In (4) above, the centrifuge tube was sealed and then shaken for 10 minutes to selectively extract Pd and / or Pt from the ionic liquid phase into the aqueous thiourea solution (i.e., the extraction time was extended from 5 minutes to 10 minutes). The recovery and evaluation of Pd and / or Pt were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0039] [Table 1]

Claims

1. A method for recovering Pd and / or Pt, comprising the steps of: (a) adding a thiocyanate to a raw material aqueous solution containing Pd and / or Pt to prepare a first aqueous phase; (b) adding an ionic liquid to the first aqueous phase and mixing the mixture to selectively extract Pd and / or Pt from the first aqueous phase into the ionic liquid, thereby obtaining an ionic liquid phase containing Pd and / or Pt; (c) separating the Pd and / or Pt-containing ionic liquid phase from the first aqueous phase; (d) adding and mixing an aqueous thiourea solution to the separated ionic liquid phase to selectively strip Pd and / or Pt from the ionic liquid phase into the aqueous thiourea solution, thereby obtaining a second aqueous phase containing Pd and / or Pt; (e) separating the second aqueous phase from the ionic liquid phase to recover Pd and / or Pt; A method for recovering Pd and / or Pt, comprising:

2. 2. The method for recovering Pd and / or Pt according to claim 1, wherein the concentration of the thiocyanate in the first aqueous phase is 0.50 mol / L or more and 4.00 mol / L or less.

3. 2. The method for recovering Pd and / or Pt according to claim 1, wherein the concentration of the thiocyanate in the first aqueous phase is 3.00 mol / L or more and 3.80 mol / L or less.

4. 3. The method for recovering Pd and / or Pt according to claim 1 or 2, wherein the thiocyanate comprises potassium thiocyanate and / or sodium thiocyanate.

5. 3. The method for recovering Pd and / or Pt according to claim 1 or 2, wherein the first aqueous phase is an acidic aqueous solution of hydrochloric acid.

6. The method for recovering Pd and / or Pt according to claim 1 or 2, wherein the ionic liquid is a chloride.

7. 7. The method for recovering Pd and / or Pt according to claim 6, wherein the chloride comprises methyltrioctylammonium chloride.

8. 3. The method for recovering Pd and / or Pt according to claim 1 or 2, wherein the second aqueous phase has a pH of 8.0 or less.

9. 3. The method for recovering Pd and / or Pt according to claim 1 or 2, wherein the mixing of the first aqueous phase and the ionic liquid is carried out by stirring or shaking the first aqueous phase and the ionic liquid for 0.5 minutes to 15 minutes.

10. 3. The method for recovering Pd and / or Pt according to claim 1, wherein the mixing of the ionic liquid phase and the thiourea aqueous solution is carried out by stirring or shaking the ionic liquid phase and the thiourea aqueous solution for 1 minute or more and 25 minutes or less.

11. 3. The method for recovering Pd and / or Pt according to claim 1, wherein the aqueous thiourea solution does not contain ammonia or ammonium ions.

12. 3. The method for recovering Pd and / or Pt according to claim 1, wherein the raw material aqueous solution contains Pd and / or Pt and impurity components derived from a Pd and / or Pt-containing product or recycled raw material.

13. A method for analyzing Pd and / or Pt, comprising measuring the concentration of Pd and / or Pt contained in the second aqueous phase obtained by the method for recovering Pd and / or Pt according to claim 1 or 2.

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