Novel platinum group metal recovery agent and novel platinum group metal recovery method

Abstract

To provide a platinum group metal recovery agent with a novel structure different from conventional platinum group metal recovery agents, and to provide a method for recovering platinum group metals by a mechanism different from conventional methods. [Solution] A platinum group metal recovery agent comprising a nitrogen-containing heterocyclic aromatic compound having an electron-donating group in the heterocyclic side chain. The platinum group metal recovery agent wherein the nitrogen-containing heterocyclic aromatic compound is a 6-membered ring. According to the present invention, it is possible to provide a platinum group metal recovery agent with a novel structure, and a platinum group metal recovery method that precipitates and / or adsorbs platinum group metals by a novel mechanism.

Description

[Technical Field]

[0001] This invention relates to a novel platinum group metal recovery agent and a novel platinum group metal recovery method utilizing the same. More specifically, it relates to a novel platinum group metal recovery agent comprising a nitrogen-containing heterocyclic aromatic compound and a novel platinum group metal recovery method utilizing the same. [Background technology]

[0002] Platinum group metals consist of six types: ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), and platinum (Pt). Because they have similar properties, they are collectively referred to as platinum group metals. Platinum group metals (PGMs) are extremely valuable resources used in jewelry, catalysts, and electronic devices. Due to their scarcity and uneven distribution, recycling is essential to ensure stable supply and prices.

[0003] Metal refining processes in metal recycling are broadly divided into two types: dry processes, which utilize melting and volatilization at high temperatures, and wet processes, which dissolve the target metal in an aqueous solution. Wet processes allow for precise separation and are considered suitable for small-scale operations. Known separation methods in wet processes include precipitation formation by reagent addition, solvent extraction, and ion exchange.

[0004] As a method for forming a precipitate by adding a reagent, the present inventors have proposed a method for recovering PGM from a hydrochloric acid solution using a specific primary amine compound, and have reported the use of an aromatic primary amine compound (here, "aromatic" refers to aromatic compounds in the narrow sense and does not include heterocyclic aromatic compounds. The same applies hereinafter. In the case of heterocyclic compounds, they will be described as "heterocyclic aromatic compounds" to distinguish them) (Non-Patent Documents 1, 2, Patent Documents 1, 2). [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2017-179409 [Patent Document 2] WO2017 / 170444 [Non-patent literature]

[0006] [Non-Patent Document 1] ACS Omega, 2019, 4, 14613-14620. [Non-Patent Document 2] ACS Omega, 2019, 4, 1868-1873. [Overview of the project] [Problems that the invention aims to solve]

[0007] The object of the present invention is to provide a platinum group metal recovery agent with a novel structure different from conventional platinum group metal recovery agents, and to provide a method for recovering platinum group metals by a mechanism different from the conventional one. [Means for solving the problem]

[0008] To achieve the above objective, the inventors, after various studies, discovered that by mixing a nitrogen-containing heterocyclic aromatic compound having an electron-donating group in the heterocyclic side chain with a leachate containing platinum group metals, the platinum group metals can be precipitated and / or adsorbed by a novel mechanism, thereby recovering the platinum group metals, and thus arrived at the present invention. In other words, the present invention is as follows. 1. A platinum group metal recovery agent comprising a nitrogen-containing heterocyclic aromatic compound having an electron-donating group in the heterocyclic side chain. 2. The platinum group metal recovery agent according to claim 1, wherein the nitrogen-containing heterocyclic aromatic compound is a nitrogen-containing heterocyclic aromatic compound with a 6-membered ring. 3. The platinum group metal recovery agent according to 1 or 2 above, wherein the electron-donating group is an amino group. 4. The platinum group metal recovery agent according to 3 above, wherein the amino group is a primary amino group. 5. A platinum group metal recovery agent comprising one or more of the following: melamine, 2,6-diaminopyridine, 2,4,6-triaminopyrimidine, benzoguanamine, and a melamine crosslinked material. 6. A rhodium and / or iridium-selective platinum group metal recovery agent comprising a nitrogen-containing heterocyclic aromatic compound having a primary amino group in its side chain. 7. A rhodium and / or iridium-selective platinum group metal recovery agent, comprising a nitrogen-containing heterocyclic aromatic compound having a primary amino group in its side chain, wherein the nitrogen-containing aromatic heterocyclic compound is such that the primary amino group is less likely to be protonated. 8. A rhodium and / or iridium selective platinum group metal recovery agent comprising either or both melamine and 2,6-diaminopyridine. 9. (1) Chloride complex ions of platinum group metals, (2) Nitrogen-containing heterocyclic aromatic compounds in which the heterocyclic nitrogen is protonated and which have electron-donating groups in the heterocyclic side chain, Ionic crystals containing [specific components / materials]. 10. (1) Trivalent chloride complex ions of rhodium and / or iridium, (2) Melamine in which one of the heterocyclic nitrogen atoms is protonated, (3) Melamine in which two heterocyclic nitrogen atoms are protonated An ionic crystal containing (1), (2), and (3) in a ratio of 1:2:2. 11. Ionic crystals and / or ion pairs comprising a chloride complex ion of a platinum group metal and a nitrogen-containing heterocyclic aromatic compound in which the heterocyclic nitrogen is protonated and an electron-donating group is present in the heterocyclic side chain. A method for recovering platinum group metals, comprising a step in which a compound is formed. 12. Ionic crystals and / or ion pairs comprising rhodium and / or iridium chloride complex ions and nitrogen-containing heterocyclic aromatic compounds having a protonated heterocyclic nitrogen and a primary amino group in the heterocyclic side chain, A rhodium and / or iridium selective platinum group metal recovery method comprising a step of forming a [component]. 13. In a 1.0 to 12 mol / L hydrochloric acid solution containing a platinum group metal, a platinum group metal recovery agent composed of any one of the nitrogen-containing heterocyclic aromatic compounds of 1 to 8 above is mixed so that the nitrogen-containing heterocyclic aromatic compound / platinum group metal (molar ratio) ≥ 2, and stirred at a temperature of 1 to 110 °C for 3 minutes or more to produce a precipitate containing a platinum group metal and recover the platinum group metal. Platinum group metal recovery method. 14. In a 1.0 to 12 mol / L hydrochloric acid solution containing rhodium and / or iridium, a platinum group metal recovery agent composed of any one of the nitrogen-containing heterocyclic aromatic compounds of 6 to 8 above is mixed so that the nitrogen-containing heterocyclic aromatic compound / platinum group metal (molar ratio) ≥ 2, and stirred at a temperature of 1 to 110 °C for 3 minutes or more to produce a precipitate containing rhodium and / or iridium. A rhodium and / or iridium recovery method in which the following purification steps are repeated one or more times for the resulting precipitate. (1) Dissolve the precipitate containing rhodium and / or iridium in water or hydrochloric acid with a concentration of 4 mol / L or less. (2) Adjust the hydrochloric acid concentration of the solution of (1) to "more than 4 and 12 mol / L or less". (3) Mix any one of the platinum group metal recovery agents of 6 to 8 above with the solution of (2) to produce a precipitate containing rhodium and / or iridium. 15. A precipitate containing a platinum group metal is produced by the method of 13 above, the resulting precipitate is dissolved in water or a basic aqueous solution or an acidic aqueous solution, and a reducing agent is mixed with the resulting solution. Zero-valent platinum group metal recovery method.

Effect of the Invention

[0009] According to the present invention, a platinum group metal recovery agent having a new structure and a platinum group metal recovery method for precipitating and / or adsorbing a platinum group metal by a new mechanism can be provided.

Brief Description of the Drawings

[0010] [Figure 1] The change in the metal precipitation rate of each metal when melamine was used and the hydrochloric acid concentration was changed in the range of 1 mol / L to 8 mol / L was shown. [Figure 2]This shows the change in the metal precipitation rate of each metal when the molar ratio of melamine to rhodium (Melamine / Rh, which is also the molar ratio with each metal) is varied in the range of 5 to 30. [Figure 3] The changes in the metal precipitation rate of each metal when the shaking time after mixing with melamine was varied from 5 minutes to 3 hours are shown. [Figure 4] This shows the change in the metal precipitation rate of each metal when melamine is used, depending on the presence or absence of 1% hydrogen peroxide. [Figure 5] The changes in the metal precipitation rate of each metal, depending on the presence or absence of 1% hydrogen peroxide, when using p-phenylenediamine (a primary aromatic diamine compound), are shown. [Figure 6] The precipitation recovery rates of each metal from a hydrochloric acid solution containing iridium are shown. [Figure 7] The structure of the ionic crystal formed by protonated melamine and rhodium chloride complex anions, which are created when melamine is mixed with a hydrochloric acid solution containing rhodium, is shown. [Modes for carrying out the invention]

[0011] The present invention will be described in detail below. 1. Regarding new platinum group metal recovery agents (1) The skeleton of nitrogen-containing heterocyclic aromatic compounds The novel platinum group metal recovery agent of the present invention consists of a nitrogen-containing heterocyclic aromatic compound having an electron-donating group in the heterocyclic side chain. A nitrogen-containing heterocyclic aromatic compound is a compound having an aromatic heterocycle containing nitrogen. Naturally, the nitrogen-containing heterocyclic aromatic compounds of the present invention also include compounds having cyclic structures other than nitrogen-containing aromatic heterocycles, such as benzoguanamine. The shape of the nitrogen-containing aromatic heterocycle can be any number of members, such as a 5-membered ring or a 6-membered ring, and it can also be a fused ring, but a 6-membered ring is more preferable due to its higher stability. Examples of six-membered nitrogen-containing aromatic heterocycles include pyridine rings, pyrimidine rings, and triazine rings. Since the π-electron density of the aromatic heterocycle decreases as the number of nitrogen atoms increases, focusing solely on this point, rings other than pyridine rings are more preferable.

[0012] (2) Heterocyclic side chains of nitrogen-containing heterocyclic aromatic compounds Nitrogen-containing aromatic heterocycles have electron-donating groups in their side chains to facilitate the protonation of nitrogen in the heterocycle, which is related to the precipitation mechanism of the present invention. An electron-donating group is a substituent that readily donates electrons to the bonded atom compared to a hydrogen atom. Compared to a hydrogen atom, the substituent constant has a negative value. Typical electron-donating groups include -OH, -OCH3, -OCOCH3, -NH2, -NHCOCH3, and -N(CH3)2. In particular, with respect to amino groups, not only primary amino groups (-NH2) but also secondary and tertiary amino groups (-NHR, -NRR') may be used. For example, melamine crosslinked material (formula (5)) is not a primary amine, but can be used as a platinum group metal recovery agent. While the primary aromatic amine compounds previously reported by the inventors are susceptible to oxidation of their primary amino groups, the nitrogen-containing heterocyclic aromatic compounds of the present invention have a low π-electron density in the nitrogen-containing aromatic heterocyclic ring, resulting in a low electron density (low basicity) of the amino group. Therefore, even though they contain an amino group, it is thought to be less susceptible to oxidation. Leaching solutions containing platinum group metals may contain oxidizing agents, but the amino group of the compounds of the present invention is less susceptible to oxidation, which is thought to suppress the decrease in PGM recovery rate due to degradation.

[0013] (3) Components of platinum group metal recovery agent While it is preferable to use only one type of nitrogen-containing heterocyclic aromatic compound in the platinum group metal recovery agent, two or more types may be used in mixture form. "Consisting of nitrogen-containing heterocyclic aromatic compounds" means that the main component or active ingredient is a nitrogen-containing heterocyclic aromatic compound, and other additives may be mixed in as long as they do not affect precipitation or adsorption.

[0014] (4) Examples of nitrogen-containing heterocyclic aromatic compounds Examples of nitrogen-containing heterocyclic aromatic compounds that constitute the platinum group metal recovery agent of the present invention and satisfy the above conditions include melamine, 2,6-diaminopyridine, 2,4,6-triaminopyrimidine, benzoguanamine, and melamine crosslinks (formulas (1) to (5)). A melamine crosslink is a condensed polymer of melamine and an aldehyde, and formula (5) is an example of a crosslink synthesized from melamine and terephthalaldehyde. Formulas (1) to (5) are all nitrogen-containing heterocyclic aromatic compounds, each having an amino group in its side chain. Furthermore, compounds (1) to (4) have a primary amino group in their side chain, while the melamine crosslinked compound of formula (5) has a secondary amino group in its side chain.

[0015] These compounds are commercially available, and the synthesis method for melamine crosslinks is also known. Furthermore, after adding these platinum group metal recovery agents, a shorter stirring time than in the case of aromatic primary diamine compounds is sufficient to achieve a adequate metal precipitation rate. Furthermore, melamine has the advantage of being readily available and inexpensive.

[0016] [ka] [ka] [ka] [ka] [ka]

[0017] (5) Recovery mechanism (I) For example, when melamine is used to recover rhodium, [RhCl6] 3- The protonated melamine forms a crystal in a 1:4 ratio. For more details, see "[RhCl6] 3- :Melamine-H+ :Melamine-2H + :Cl - :H3O + Crystals are constructed with the ratio "H2O = 1:2:2:4:1:1.4" (see Figure 7). Furthermore, in protonated melamine, the triazine ring, not the amino group, is protonated, and the structure has one or two nitrogen atoms in the triazine ring protonated, as well as [RhCl6] 3- The crystal is constructed by the formation of ion pairs (see Figure 7), and the protonation of the triazine ring is key to rhodium recovery by melamine. In other words, in this invention, platinum group metals are recovered by protonation of the nitrogen-containing heterocycle rather than the amino group. This represents a completely different recovery mechanism from conventional recovery methods using amine compounds, where the amino group was protonated. Furthermore, the amino group in this recovery agent acts as an electron-donating group necessary for the protonation of the heterocycle. In other words, essentially, any side chain should be an electron-donating group. (II) The recovery agent of the present invention recovers platinum group metals by the mechanism described above. When the recovery agent dissolves in water, the recovery agent and platinum group metals form ionic crystals and precipitate. If the recovery agent is a melamine crosslinked material that does not dissolve in water, it adsorbs platinum group metals by the same mechanism and forms ion pairs, which are then recovered. Furthermore, even in the case of a water-soluble recovery agent, if there is a recovery agent that is not dissolved in water in a supersaturated state, it is considered that adsorption is occurring. In other words, in the mechanism of the recovery agent of the present invention, it is difficult to strictly distinguish between precipitation and adsorption, and the recovery agent of the present invention can be said to be both a precipitating agent and an adsorbent. Furthermore, although the recovery agent of the present invention can be said to be both a precipitating agent and an adsorbent, it does not include an extractant. Furthermore, most of the compounds listed in the examples are soluble in water, which is preferable because it increases reaction efficiency. On the other hand, recovery agents that do not dissolve in water, such as melamine crosslinked materials, have a lower reaction efficiency because the contact area with platinum group metals is limited. However, since they do not dissolve in water, they have the advantage of being able to recover even if the concentration of the platinum group metal to be precipitated is low, without any difficulty in precipitation.

[0018] (6) Selectivity within platinum group metals When melamine or 2,6-diaminopyridine is used, rhodium is selectively recovered; when 2,4,6-triaminopyrimidine is used, platinum and rhodium are recovered; and when benzoguanamine is used, palladium and platinum are recovered. When a melamine crosslinked material is used, palladium, platinum, and rhodium are all recovered. In particular, when considering the structure of compounds exhibiting rhodium selectivity, it is thought that selectivity is exhibited in nitrogen-containing heterocyclic aromatic compounds having a primary amino group with low electron density. Considering this reasoning from the structure of non-selective compounds, for example, in 2,4,6-triaminopyrimidine, one amino group has high basicity (high electron density), just like a normal aromatic amino group. As a result, not only the heterocyclic ring but also the amino group is protonated, and platinum is recovered as well as rhodium through a mechanism similar to that of several primary amine compounds disclosed so far. Therefore, in order to exhibit rhodium selectivity, it is thought that the primary amino group in the heterocyclic side chain needs to have low electron density (below protonation). It is difficult to express the degree of resistance to protonation, but at the very least, if it is as or more resistance to protonation as the primary amino group of melamine, it can be described as "reluctant to protonate." Furthermore, it is expected that the three-dimensional structure of the rhodium-selective compound, including the side-chain amino groups that are less likely to be protonated, plays a significant role in its rhodium selectivity. Furthermore, since iridium has the same ionic form as rhodium and is thought to have the same recovery mechanism, iridium selectivity is also thought to be similar to that of rhodium.

[0019] 2. Recovery method A platinum group metal recovery agent composed of the nitrogen-containing heterocyclic aromatic compound of the present invention is mixed into the leachate containing platinum group metals. When this is stirred, precipitation occurs, so it is recovered by centrifugation, filtration, or the like. There is no particular limitation on the concentration of platinum group metals in the leachate, but it is considered to be about 0.1 to 1000 mmol / L, or 1 to 500 mmol / L. The leachate is hydrochloric acid, and the hydrochloric acid concentration is preferably 1.0 to 12 mol / L, more preferably 4.0 to 12 mol / L, and particularly preferably 5.0 to 12 mol / L. For example, in the case of rhodium, the ionic form to be recovered is [RhCl6] 3- and it is preferable that this ionic form is dominant to some extent in the hydrochloric acid solution. The platinum group metal recovery agent is preferably mixed so that the nitrogen-containing heterocyclic aromatic compound / platinum group metal (molar ratio) ≥ 2, more preferably 4, and even more preferably 10. Although there is no upper limit to the molar ratio, it is realistically 100 or less. For example, in the case of rhodium, in the precipitate (complex) after rhodium recovery, 3- it becomes a crystal in which 4 molecules of melamine are bound to [RhCl6], but even if the ratio is less than that, if the rhodium concentration is high, even if the recovery rate decreases, recovery should be possible. Stir after mixing. The stirring time is preferably 3 minutes or more, more preferably 5 minutes or more, and even more preferably 30 minutes or more. Although there is no upper limit to the stirring time, it is realistically 24 hours or less. The temperature during stirring is preferably 1 to 110°C, more preferably 5 to 80°C, and even more preferably 20 to 80°C. Note that 110°C is the boiling point of concentrated hydrochloric acid. Platinum group metals can be recovered from the recovered precipitate. For example, in order to recover platinum group metals for reusing the nitrogen-containing heterocyclic aromatic compound, the precipitate may be heated under reduced pressure to distill or sublime the nitrogen-containing heterocyclic aromatic compound. The recovered nitrogen-containing heterocyclic aromatic compound can be used for the recovery of platinum group metals again. For recovery agents such as melamine crosslinked bodies that are insoluble in water, platinum group metals can be recovered by the same method such as mixing, stirring, and recovering the precipitate.

[0020] 3. (1) Purification of rhodium and / or iridium As mentioned above, there are platinum group metal recovery agents that can selectively recover rhodium and / or iridium. However, if you want to further increase the purity of rhodium and / or iridium, you can do so as follows. Basically, the purity is increased by repeatedly using the platinum group metal recovery method described above, which selectively recovers rhodium and / or iridium. However, when redissolving the precipitate, it is first dissolved in water or a low concentration of hydrochloric acid, and then the hydrochloric acid concentration is increased. This minimizes the decrease in recovery rate due to the recovery agent, and allows for both a high recovery rate and high purity of rhodium and / or iridium. Specifically, the method is as follows. (I) Recovery process First, a precipitate containing rhodium and / or iridium is generated using the method described above, with a platinum group metal recovery agent capable of selectively recovering rhodium and / or iridium, such as a platinum group metal recovery agent made of melamine. (II) Purification process (i) Collect the precipitate formed and dissolve it in water or hydrochloric acid of 4 mol / L or less, more preferably 2 mol / L or less. There are no particular restrictions on the concentration of rhodium and / or iridium at this time, but it is considered to be around 1 to 1000 mmol / L. (ii) Adjust the hydrochloric acid concentration to "greater than 4 and less than or equal to 12 mol / L", more preferably 5 to 12 mol / L, and particularly preferably 5 to 8 mol / L" by mixing hydrochloric acid of a higher concentration than the above hydrochloric acid, such as concentrated hydrochloric acid, or by blowing in hydrogen chloride gas. Leave this solution overnight or longer, or let it stand or stir at 80°C or higher for 1 hour or longer. Note that the operations such as leaving it overnight will be described in detail in the principle section, but the operations are not limited to these, and any operation that can make the trivalent ionic form dominant is acceptable. (iii)(ii) is mixed with a platinum group metal recovering agent capable of selectively recovering rhodium and / or iridium, such as a platinum group metal recovering agent made of melamine, to precipitate rhodium and / or iridium. The molar ratio of platinum group metal recovering agent to platinum group metal is the same as that of "nitrogen-containing heterocyclic aromatic compound / platinum group metal" in "2. Recovery Method". The stirring time and temperature after mixing are also the same as in "2. Recovery Method". The above purification process should be repeated at least once. The more times it is repeated, the higher the purity can be achieved. (III) Principles that can suppress the decline in recovery rate First, use water or a low concentration of hydrochloric acid to determine the monovalent and divalent ionic forms of rhodium chloride ([RhCl4(H2O)2] - [RhCl5(H2O)] 2- By making ) dominant, the redissolution of precipitate can be promoted. After dissolution, the hydrochloric acid concentration is increased to form the trivalent ionic form ([RhCl6] 3- The trivalent ionic form of rhodium chloride is made dominant. It is even more preferable to leave it overnight so that the trivalent ionic form of rhodium chloride accounts for 90% or more. Making the trivalent ionic form dominant can increase the recovery rate of rhodium and / or iridium when the recovery agent is added. In this way, the decrease in recovery rate can be minimized, and both a high recovery rate and high purity of rhodium and / or iridium can be achieved.

[0021] (2) Recovery of 0-valent platinum group metals While platinum group metals can be recovered using the aforementioned platinum group metal recovery agent and recovery method, if you want to obtain platinum group metals with zero valency, you can perform the following further processing. Dissolve the precipitate containing platinum group metals, produced by the recovery method described above, in water, a basic solution, or an acidic solution. If dissolution does not proceed, it may be dissolved by heating below the boiling point. If melamine precipitates after the precipitate has been dissolved, remove it. Examples of basic solutions include aqueous solutions of sodium bicarbonate, sodium carbonate, ammonia water, and sodium hydroxide. Examples of acidic solutions include hydrochloric acid. The concentration of the basic solution should be less than or equal to the saturation concentration of each solution at room temperature. The concentration of the acidic solution should be 4 mol / L or less, more preferably 2 mol / L or less. After dissolving the precipitate, a reducing agent is mixed into the solution and stirred for 30 minutes or more at a more than 0°C to 100°C, and even more preferably at a more than 5°C to 100°C, to reduce the platinum group metals and precipitate them as zero-valent metals, which are then recovered by, for example, filtration or centrifugation. Examples of reducing agents include sodium borohydride and hydrazine. The amount of reducing agent added is more preferably such that the molar ratio of platinum group metals to reducing agent is 1:2 to 1:100, and even more preferably 1:30 to 1:100. [Examples]

[0022] Example 1: Investigation of conditions for precipitation 1. Experimental Example 1-1: Investigation of Hydrochloric Acid Concentration To hydrochloric acid solutions with concentrations of 1 to 8 mol / L containing 5 mmol / L each of palladium, platinum, and rhodium, melamine ([Chemical Formula 1]) (Kanto Chemical Co., Ltd., product number 25093-02) was added so that the molar ratio of melamine to rhodium (Melamine / Rh) was 30. The mixture was shaken at 25°C for 3 hours and then centrifuged, and the supernatant was collected. The concentrations of palladium, platinum, and rhodium in the supernatant were analyzed by ICP emission spectrometry (ICP emission spectrometer, Seiko Instruments, model number SPS5510) to calculate the amount of precipitated metal and determine the metal precipitation rate. The results are shown in Figure 1. As is clear from Figure 1, in the hydrochloric acid concentration range of 5 mol / L or higher, metal precipitation behavior was observed in which rhodium accounted for more than 90% and palladium and platinum accounted for less than 5%, achieving high recovery rate and highly selective rhodium recovery. In this experiment, rhodium was not recovered at concentrations below 5 mol / L, but (A) rhodium should be recovered at higher metal concentrations, although the recovery rate may not be very high, and (B) the ionic form of the recovered rhodium is [RhCl6]. 3- (In the case of iridium, [IrCl6]) 3-Considering that this ionic form becomes dominant in hydrochloric acid solution when the hydrochloric acid concentration is 4 mol / L or higher, it is thought that a certain amount of rhodium can be recovered even at hydrochloric acid concentrations of less than 5 mol / L. 2. Experimental Example 1-2: Investigation of Nitrogen-containing Heterocyclic Aromatic Compounds / Platinum Group Metals (Molar Ratio) (1) The experiment was conducted in the same manner as in Experiment Example 1-1, with rhodium at 5 mmol / L and hydrochloric acid at 6 mol / L, varying the melamine / Rh (molar ratio) in the range of 5 to 30, and the metal precipitation rate was calculated. The results are shown in Figure 2. As the melamine / Rh (molar ratio) increased, the rhodium precipitation rate also increased, reaching over 90% when the molar ratio was 15 or higher. On the other hand, palladium and platinum were not recovered even at high molar ratios, indicating almost no change in rhodium selectivity. (2) Melamine was added to a 6 mol / L hydrochloric acid solution containing 50 mmol / L of rhodium, such that the molar ratio of melamine to rhodium (Melamine / Rh) was between 2 and 15. The mixture was shaken at 25°C for 15 minutes, and the rest of the experiment was carried out in the same manner as in Experimental Example 1-1, and the metal precipitation rate was calculated. The results are shown in Table 1. When the rhodium concentration was high, rhodium was recovered even when the molar ratio of melamine to rhodium was less than 4.

[0023] [Table 1] Theoretically, one molecule of [RhCl6] is present in the precipitate (complex) after rhodium recovery. 3- It forms a crystal with four melamine molecules bonded to it, and it is possible to precipitate rhodium in a molar ratio of 4 parts melamine to 1 part rhodium. 3. Experimental Example 1-3: Examination of Stirring Time The hydrochloric acid concentration was set to 6 mol / L, the melamine / Rh (molar ratio) to 20, and the shaking time was varied from 5 minutes to 3 hours. The experiment was conducted in the same manner as in Experimental Example 1-1, and the metal precipitation rate was calculated. The results are shown in Figure 3. More than 30% of rhodium precipitated after 5 minutes of shaking, and more than 90% of rhodium precipitated after 60 minutes or more. On the other hand, palladium and platinum hardly precipitated regardless of the shaking time. 4. Experimental Example 1-4: Examination of Temperature During Stirring Melamine was added to a 6 mol / L hydrochloric acid solution containing 50 mmol / L of rhodium so that the molar ratio of melamine to rhodium (Melamine / Rh) was 10. The mixture was shaken at 5-80°C for 15 minutes, then centrifuged, and the supernatant was collected. The concentration of rhodium in the supernatant was analyzed using an ICP emission spectrometer to calculate the metal precipitation rate. The results are shown in Table 2. As shown in Table 2, efficient rhodium recovery was achieved even when the temperature during metal recovery was changed.

[0024] [Table 2]

[0025] Example 2: Investigation of the effects of oxidizing agents 1. Experimental Example 2-1-1 Melamine was added to a 6 mol / L hydrochloric acid solution containing 5 mmol / L each of palladium, platinum, and rhodium, so that the molar ratio of melamine to rhodium (Melamine / Rh) was 20. After shaking at 25°C for 1 hour, the mixture was centrifuged, and the supernatant was collected. The concentrations of palladium, platinum, and rhodium in the supernatant were analyzed using an ICP emission spectrometer to calculate the metal precipitation rate. The same procedure was also performed using 1% hydrogen peroxide and a 6 mol / L hydrochloric acid solution containing 5 mmol / L each of palladium, platinum, and rhodium, and the metal precipitation rate was calculated. The results are shown in Figure 4. As shown in Figure 4, no decrease in rhodium recovery rate or rhodium selectivity was observed even when hydrogen peroxide, an oxidizing agent, was present in the metal-containing hydrochloric acid solution. 2. Comparative Experiment Example 2-1-2 Instead of melamine as a recovery agent, p-phenylenediamine (Tokyo Chemical Industries, Ltd., product number P0170) was used in a molar ratio (PPDA / Rh) of 20 with rhodium, and the experiment was conducted in the same manner as in Experimental Example 2-1-1, and the metal precipitation rate was calculated. The results are shown in Figure 5. As shown in Figure 5, in the presence of the oxidizing agent hydrogen peroxide, the oxidation of p-phenylenediamine proceeded, resulting in a significant decrease in rhodium recovery rate and rhodium selectivity.

[0026] Example 3: Selective Recovery of Iridium Melamine was added to a 6 mol / L hydrochloric acid solution containing 5 mmol / L each of palladium, platinum, and iridium, so that the molar ratio of melamine to iridium (Melamine / Ir) was 100. The solution was shaken at 25°C for 3 hours, then centrifuged, and the supernatant was collected. The concentrations of palladium, platinum, and iridium in the supernatant were analyzed using an ICP emission spectrometer to calculate the metal precipitation rate. The results are shown in Figure 6. As shown in Figure 6, selective iridium recovery was achieved.

[0027] Example 4: Investigation of nitrogen-containing heterocyclic aromatic compounds other than melamine. To a 6 mol / L hydrochloric acid solution containing 5 mmol / L each of palladium, platinum, and rhodium, 2,6-diaminopyridine ([Chemical Formula 2]) (Tokyo Chemical Industries, Ltd., product number D1154), 2,4,6-triaminopyrimidine ([Chemical Formula 3]) (Tokyo Chemical Industries, Ltd., product number T0834), or benzoguanamine ([Chemical Formula 4]) (Tokyo Chemical Industries, Ltd., product number D0111) was added so that the molar ratio of the amine compound to rhodium (Amine / Rh) was 50. After shaking at 25°C for 1 hour, the mixture was centrifuged, and the supernatant was collected. The concentrations of palladium, platinum, and rhodium in the supernatant were analyzed by ICP to calculate the metal precipitation rate. The results are shown in Table 3. When 2,6-diaminopyridine was used, rhodium was selectively recovered; when 2,4,6-triaminopyrimidine was used, platinum and rhodium were efficiently recovered; and when benzoguanamine was used, palladium and platinum were recovered.

[0028] [Table 3]

[0029] Example 5: Investigation of melamine crosslinked materials having secondary amino groups To a 6 mol / L hydrochloric acid solution containing 5 mmol / L each of palladium, platinum, and rhodium, a melamine crosslinked material ([Chemical Formula 5]) synthesized from melamine and terephthalaldehyde (Reference 1: Polym.Int.2016, 65, 439-445. Synthesized according to this reference, etc.) was added so that the molar ratio of melamine units to rhodium was approximately 200. The mixture was shaken at 25°C for 1 hour, then centrifuged, and the supernatant was collected. The concentrations of palladium, platinum, and rhodium in the supernatant were analyzed using an ICP emission spectrometer to calculate the metal precipitation rate. The results are shown in Table 3. By using melamine crosslinked material as an adsorbent, palladium, platinum, and rhodium were all efficiently recovered.

[0030] Example 6: Investigation of the platinum group metal recovery mechanism Single crystals were prepared by adding melamine to a 6 mol / L hydrochloric acid solution containing 5 mmol / L of rhodium, so that the molar ratio of melamine to rhodium (Melamine / Rh) was 5, and allowing the solution to stand at 25°C for an extended period. Single-crystal X-ray diffraction measurements were performed on the obtained single crystals. Single-crystal X-ray diffraction measurements revealed that the crystal has the structure shown in Figure 7, and [RhCl6] 3- The ratio of protonated melamine to amino acid was 1:4. Furthermore, it was revealed that in protonated melamine, the triazine ring, not the amino group, was protonated, and that the crystal structure consisted of one or two nitrogen atoms in the triazine ring being protonated. This revealed that protonation of the triazine ring is key to rhodium recovery by melamine.

[0031] Example 7 Purification of rhodium and / or iridium Melamine was added to a 6 mol / L hydrochloric acid solution containing 50 mmol / L each of palladium, platinum, and rhodium, so that the molar ratio of melamine to rhodium (Melamine / Rh) was 15. The mixture was shaken at 80°C for 15 minutes, then centrifuged, and the supernatant was collected. The concentrations of palladium, platinum, and rhodium in the supernatant were analyzed using an ICP emission spectrometer to calculate the metal precipitation rate (recovery step). Next, the precipitate was collected by filtration and dissolved in 1 mol / L hydrochloric acid (Rh concentration: approximately 100 mmol / L). The resulting hydrochloric acid solution was then adjusted using concentrated hydrochloric acid to a concentration of 6 mol / L (Rh concentration: approximately 50 mmol / L). This hydrochloric acid solution was heated and stirred at 80°C for 1 hour. Melamine was then added to the hydrochloric acid solution so that the molar ratio of melamine to rhodium (Melamine / Rh) was 15, and the mixture was shaken at 25°C for 15 minutes. The resulting precipitate was collected by filtration and dissolved in 1 mol / L hydrochloric acid. The concentrations of palladium, platinum, and rhodium were analyzed using an ICP emission spectrometer to calculate the metal precipitation rate (purification process). Table 4 shows the metal precipitation rates after the recovery and purification processes. After the purification process, the amounts of palladium and platinum in the precipitate decreased significantly. On the other hand, 98% of the initial rhodium was recovered even after the purification process, achieving a high rhodium recovery rate. The purity of the rhodium contained in the precipitate, when the total metal weight is set to 100%, was 86% after the recovery process, compared to 98% after the purification process. As is clear from these results, by using melamine as a rhodium recovery agent, it is possible to purify rhodium by removing impurity metals from the hydrochloric acid solution mainly composed of rhodium in which the precipitate was dissolved. This purification process can achieve both a high rhodium recovery rate and high purity, so by repeating this purification process, further purity can be achieved without reducing the rhodium recovery rate.

[0032] [Table 4]

[0033] Example 8 Recovery of 0-valent platinum group metals Melamine was added to a 6 mol / L hydrochloric acid solution containing 50 mmol / L of rhodium so that the molar ratio of melamine to rhodium (Melamine / Rh) was 15. The mixture was shaken at 25°C for 15 minutes, and the precipitate was collected by filtration (recovery step). The obtained precipitate was dissolved in a 1 mol / L aqueous sodium bicarbonate solution (Rh concentration: approximately 10 mmol / L). After removing the precipitated melamine by filtration, sodium borohydride was added to the resulting solution in a molar ratio of 2 to 100 times that of rhodium, and the mixture was stirred at 25°C for 1 hour. The precipitated zero-valent rhodium was centrifuged, and the supernatant was collected. The rhodium concentration in the supernatant was analyzed using an ICP emission spectrometer to calculate the rhodium reduction rate. The results are shown in Table 5. As the amount of sodium borohydride added increased, the rhodium reduction rate also increased, reaching over 90% when the amount was 30 times or more molar.

[0034] [Table 5]

[0035] Example 9: Recovery of zero-valent platinum group metals when using a basic solution other than water or sodium bicarbonate, or an acidic solution, as the dissolving agent. The rhodium reduction rate was calculated by performing the experiment in the same manner as in Example 8, except that the solution used to dissolve the rhodium-containing precipitate was water, a 1 mol / L sodium carbonate aqueous solution, a 1 mol / L ammonia aqueous solution, or a 1 mol / L hydrochloric acid solution, and 50 times the molar amount of sodium borohydride relative to the rhodium was added. The results are shown in Table 6. Rhodium recovery by reduction was achieved even when the type of solution used to dissolve the rhodium-containing precipitate was changed.

[0036] [Table 6] [Industrial applicability]

[0037] According to the present invention, the metal recycling of platinum group metals is further promoted and the stable supply of platinum group metals is further advanced, making it useful not only for the metal recycling industry but also for a wide range of industries that use platinum group metals.

Claims

1. A platinum group metal recovery agent comprising a nitrogen-containing heterocyclic aromatic compound having an electron-donating group in the heterocyclic side chain, which forms ionic crystals or ionic pairs with platinum group metals.

2. The platinum group metal recovery agent according to claim 1, wherein the nitrogen-containing heterocyclic aromatic compound is a six-membered nitrogen-containing heterocyclic aromatic compound.

3. The platinum group metal recovery agent according to claim 2, wherein the electron-donating group is an amino group.

4. A platinum group metal recovery agent according to claim 3, wherein the amino group is a primary amino group.

5. A platinum group metal recovery agent comprising one or more of melamine, 2,6-diaminopyridine, 2,4,6-triaminopyrimidine, benzoguanamine, and a melamine crosslinked material, which forms ionic crystals or ionic pairs with platinum group metals.

6. A platinum group metal recovery agent that can recover rhodium and / or iridium, comprising a nitrogen-containing heterocyclic aromatic compound having an electron-donating group in the heterocyclic side chain, and forming ionic crystals or ionic pairs with platinum group metals.

7. The platinum group metal recovery agent according to claim 6, wherein the nitrogen-containing heterocyclic aromatic compound is a six-membered nitrogen-containing heterocyclic aromatic compound.

8. A platinum group metal recovery agent according to claim 7, wherein the electron-donating group is an amino group.

9. A platinum group metal recovery agent according to claim 8, wherein the amino group is a primary amino group.

10. A rhodium and / or iridium-selective platinum group metal recovery agent comprising a nitrogen-containing heterocyclic aromatic compound having a primary amino group in its side chain, and forming ionic crystals or ionic pairs with platinum group metals.

11. A rhodium and / or iridium-selective platinum group metal recovery agent comprising a nitrogen-containing heterocyclic aromatic compound having a primary amino group in its side chain, wherein the nitrogen-containing aromatic heterocyclic compound is such that the primary amino group is less likely to be protonated, and which forms ionic crystals or ionic pairs with platinum group metals.

12. (1) Chloride complex ions of platinum group metals, (2) Nitrogen-containing heterocyclic aromatic compounds in which the heterocyclic nitrogen is protonated and which have electron-donating groups in the heterocyclic side chain, Ionic crystals or ion pairs containing these elements.

13. (1) Trivalent chloride complex ions of rhodium and / or iridium, (2) Melamine in which one of the heterocyclic nitrogen atoms is protonated, (3) Melamine in which both heterocyclic nitrogen atoms are protonated An ionic crystal containing (1), (2), and (3) in a ratio of 1:2:2, or an ionic crystal or ionic pair containing these elements.

14. A method for recovering platinum group metals, comprising the step of mixing a nitrogen-containing heterocyclic aromatic compound according to any one of claims 1 to 5 with a hydrochloric acid solution containing a platinum group metal to form an ionic crystal and / or ionic pair containing the nitrogen-containing heterocyclic aromatic compound in which the chloride complex ion of the platinum group metal and the heterocyclic nitrogen are protonated.

15. A method for recovering platinum group metals that can recover rhodium and / or iridium, comprising the step of mixing a nitrogen-containing heterocyclic aromatic compound according to any one of claims 6 to 9 with a platinum group metal-containing hydrochloric acid solution containing rhodium and / or iridium, thereby forming an ionic crystal and / or ionic pair containing the nitrogen-containing heterocyclic aromatic compound in which the chloride complex ions of rhodium and / or iridium and the heterocyclic nitrogen are protonated.

16. A rhodium and / or iridium selective platinum group metal recovery method, comprising the step of mixing a nitrogen-containing heterocyclic aromatic compound according to claim 10 or 11 with a platinum group metal-containing hydrochloric acid solution containing rhodium and / or iridium, thereby forming an ionic crystal and / or ionic pair containing the nitrogen-containing heterocyclic aromatic compound in which the rhodium and / or iridium chloride complex ions and heterocyclic nitrogen are protonated.

17. A method for recovering platinum group metals, comprising: mixing a platinum group metal recovery agent consisting of a nitrogen-containing heterocyclic aromatic compound according to any one of claims 1 to 11 so that the ratio of nitrogen-containing heterocyclic aromatic compound to platinum group metal (molar ratio) is ≥ 2 in a 1.0 to 12 mol / L hydrochloric acid solution containing platinum group metals; stirring at a temperature of 1 to 110°C for 3 minutes or more to generate a precipitate containing platinum group metals and recovering the platinum group metals.

18. A 1.0 to 12 mol / L hydrochloric acid solution containing rhodium and / or iridium is mixed with a platinum group metal recovery agent consisting of a nitrogen-containing heterocyclic aromatic compound according to claim 10 or 11 such that the ratio of nitrogen-containing heterocyclic aromatic compound to platinum group metal (molar ratio) is ≥ 2, and the mixture is stirred at a temperature of 1 to 110°C for 3 minutes or more to produce a precipitate containing rhodium and / or iridium. A method for recovering rhodium and / or iridium, which involves repeating the following purification steps one or more times on the resulting precipitate. (1) Dissolve the precipitate containing rhodium and / or iridium in water or hydrochloric acid at a concentration of 4 mol / L or less. (2) Adjust the hydrochloric acid concentration of the dissolving solution in (1) to "greater than 4 and 12 mol / L or less". (3) Mix the solution from (2) with the platinum group metal recovery agent according to any one of claims 6 to 8 to produce a precipitate containing rhodium and / or iridium.

19. A precipitate containing platinum group metals is produced by the method of claim 17, the precipitate is dissolved in water, a basic aqueous solution, or an acidic aqueous solution, and a reducing agent is mixed into the solution. A method for recovering zero-valent platinum group metals.

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