Platinum-selective precipitant and method for selectively recovering platinum

Abstract

To provide a precipitant capable of selectively precipitating platinum with high purity. [Solution] A platinum-selective precipitating agent whose main component is a 1,3,5-triazine compound having two or more primary amino groups on the triazine ring, or urea, or a salt thereof, or a mixture of two or more of these compounds including the salt. The compound of the present invention can provide a platinum-selective precipitating agent that can selectively precipitate platinum with high purity by gradually releasing ammonium chloride in a hydrochloric acid solution.

Description

[Technical Field]

[0001] The present invention relates to a platinum-selective precipitating agent and a method for selectively precipitating platinum using the same. [Background technology]

[0002] Platinum group metals are extremely important industrially, and among them, platinum (Pt), palladium (Pd), and rhodium (Rh) are mainly used in automobile exhaust purification catalysts. Therefore, selective separation and recovery of platinum group metals from used catalysts is important. In the conventional solvent extraction process for separating precious metals, palladium is preferentially recovered, making it difficult to recover platinum before palladium. Therefore, if palladium cannot be completely recovered, palladium gets mixed in during platinum recovery, making it difficult to achieve high purity platinum. This also makes it impossible to prioritize the recovery of platinum at a high purity. It is also known that platinum can be separated from palladium and rhodium by using ammonium chloride (for example, Patent Document 1), but this method has the problem that the purity of the obtained platinum is insufficient.

[0003] Meanwhile, the present inventors have reported that platinum group metals can be recovered using nitrogen-containing heterocyclic aromatic compounds having electron-donating groups in the heterocyclic side chains, such as melamine (Patent Document 2). Melamine itself forms ionic crystals with platinum group metals and precipitates. However, in terms of selectivity within the platinum group metals, platinum cannot be separated from palladium or rhodium. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-144183

[0005] [Patent Document 2] Japanese Patent Publication No. 2023-071575 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a precipitating agent capable of selectively precipitating platinum with high purity. [Means for solving the problem]

[0007] In order to achieve the above object, the present inventors have conducted various studies and have found a compound that can selectively precipitate platinum at a high purity when mixed with a platinum-containing hydrochloric acid solution and shaken for a certain period of time, and have arrived at the present invention. 1. A platinum-selective precipitating agent whose main component is a 1,3,5-triazine compound having two or more primary amino groups on the triazine ring, or urea, or a salt thereof, or a mixture of two or more of these compounds including the salt. 2. A platinum-selective precipitating agent whose main component is melamine, acetoguanamine, ammeline, N,N-diethylmelamine, benzoguanamine, or urea, or a salt thereof, or a mixture of two or more of these including the salt. 3. A platinum-selective precipitant whose main component is melamine or urea, or a salt thereof. 4. A method in which the platinum-selective precipitant described in 1 above is mixed with a platinum-containing hydrochloric acid solution, and ammonium chloride is gradually released to selectively precipitate platinum. 5. A method for selectively precipitating platinum, comprising mixing the platinum-selective precipitant of 1 above with a platinum-containing hydrochloric acid solution to produce crystals of [NH4]2[PtCl6] with a maximum particle size of 0.1 mm or more. A method for selectively precipitating platinum, comprising mixing the platinum-selective precipitant of claim 1 with a platinum-containing hydrochloric acid solution having a hydrochloric acid concentration of 6.1 mol / L or more so that (total number of moles of the 1,3,5-triazine compound of claim 1, urea, and salts thereof) / (number of moles of platinum)=1 or more, and shaking the mixture. 7. A selective precipitant for rhodium, iridium, and platinum, which comprises melamine or a salt thereof as a main component and is capable of selectively precipitating rhodium, iridium, and platinum, respectively. [Effects of the Invention]

[0008] According to the present invention, a precipitating agent capable of selectively precipitating platinum with high purity can be provided. [Brief explanation of the drawings]

[0009] [Figure 1] The appearance of the resulting precipitate when observed under a microscope is shown. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will be described in detail below. 1. Platinum-selective precipitant of the present invention (1) The platinum-selective precipitating agent of the present invention contains as its main component a 1,3,5-triazine compound having two or more primary amino groups on the triazine ring, or urea, or a salt thereof, or a mixture of two or more of these compounds including the salt. In the triazine ring of the triazine compound, two of the three carbon atoms constituting the ring have primary amino groups bonded to them, and the remaining carbon atom may have either a primary amino group or another functional group bonded to it, such as a methyl group, a phenyl group, a hydroxyl group, or a secondary or tertiary amino group. Examples of the triazine compounds include melamine ([Chemical Formula 1]) in which a primary amino group is bonded to the remaining carbon atom, acetoguanamine ([Chemical Formula 2]) in which a methyl group is bonded, ammeline ([Chemical Formula 3]) in which a hydroxyl group is bonded, N,N-diethylmelamine ([Chemical Formula 4]) in which a diethylamino group, which is a tertiary amine, is bonded, and benzoguanamine ([Chemical Formula 5]) in which a phenyl group is bonded. In addition to the triazine compounds, urea ([Chemical Formula 6]), which is a raw material for these compounds, can also be used as a main component. Furthermore, the main component may be a salt of these compounds or a mixture thereof containing a salt. In addition, it does not exclude the inclusion of components other than the main component to the extent that they do not affect the selective precipitation of platinum. Here, "selective for platinum" means that platinum can be recovered with high purity from a hydrochloric acid solution containing at least palladium, rhodium, and platinum.

[0011] [ka] [ka] [ka] [ka] [ka] [ka]

[0012] 2. Precipitation method and mechanism

[0013] (1) Precipitation method (I) By mixing the platinum-selective precipitant of the present invention with a hydrochloric acid solution containing platinum under certain conditions and shaking the mixture, a precipitate of ammonium hexachloroplatinate(IV) ([NH4]2[PtCl6]) with high platinum purity is formed. Platinum can then be recovered by, for example, roasting this precipitate.

[0014] (II) The platinum-selective precipitant of the present invention decomposes in a hydrochloric acid solution to produce ammonium chloride, and is mixed and shaken under conditions that allow for slow decomposition and the ammonium chloride to be gradually released. The gradually released ammonium chloride is preferably released over a period of 1 hour or more, and more preferably over a period of 6 hours or more. There is no upper limit to the time for which the gradually released ammonium chloride is released, but it may be about 96 hours, defined as the time required for the concentration to drop to 1 / 100 of the initial gradually released concentration.

[0015] (III) Furthermore, if ammonium chloride is produced slowly, the precipitate crystals can grow, which is thought to be related to the precipitation of high-purity platinum, as described below. In other words, appropriate precipitation conditions are those that allow the crystals of ammonium hexachloroplatinate(IV) ([NH4]2[PtCl6]) formed between ammonium chloride and platinum to grow. The size of the resulting crystals is preferably 0.1 mm or larger, and even more preferably 0.2 mm or larger. The particle size here is the Feret diameter, which is the width of parallel lines when observed under a microscope, measured in any direction but all in the same direction. Although the grown crystals may become finer due to shaking or stirring, at least the largest crystals after stirring or shaking are defined as above.

[0016] (IV) In the present invention, the specific mixing and shaking conditions are as follows: the platinum-selective precipitant of the present invention is mixed with a platinum-containing hydrochloric acid solution having a hydrochloric acid concentration of preferably 1 to 12 mol / L, and even more preferably 2 to 8 mol / L, so that the molar ratio of (total number of moles of the 1,3,5-triazine compound of the present invention, urea, and a salt thereof) / (number of moles of platinum) is preferably 1 or more, even more preferably 7.5 to 150, and particularly preferably 7.5 to 120. It is believed that platinum of higher purity can be obtained by not heating the mixture suddenly after mixing, but rather by allowing the ammonium chloride to be released gradually over a longer period of time, allowing the crystals of ammonium hexachloroplatinate(IV) ([NH4]2[PtCl6]) to grow more rapidly. However, this takes extra time, so the degree of heating and the shaking time must be balanced. The temperature during shaking is room temperature, or more preferably, heated. The lower the temperature, the longer the shaking time required; more preferably, shaking is 96 hours or more when the temperature is less than 20 to 40°C, 24 hours or more when the temperature is less than 40 to 50°C, 3 hours or more when the temperature is less than 50 to 70°C, and 1 hour or more when the temperature is between 70°C and the boiling point. If the temperature fluctuates during shaking, this temperature is taken as the average temperature. There is no particular upper limit to the shaking time, but for industrial processes, about 96 hours is considered the upper limit. If the temperature during shaking is 70 to 90°C, the shaking time is more preferably 2 to 48 hours. At that temperature, the recovery rate will almost reach a plateau within that time. In addition, shaking in the present invention also includes stirring and other actions.

[0017] (2) Precipitation mechanism By using the platinum-selective precipitant of the present invention, it is possible to recover high-purity platinum from a hydrochloric acid solution containing palladium, rhodium, and platinum. It has been known that mixing ammonium chloride with a hydrochloric acid solution containing platinum results in the precipitation of ammonium hexachloroplatinate(IV) ([NH4]2[PtCl6]), but this method can recover platinum with a higher purity. When ammonium chloride is used, precipitation occurs instantly, and the crystals do not grow large (Figure 1, right). The platinum-selective precipitant of the present invention slowly decomposes in a hydrochloric acid solution under certain conditions, gradually releasing ammonium chloride. The slow production of ammonium chloride allows ammonium hexachloroplatinate(IV) ([NH4]2[PtCl6]) crystals to grow slowly and large while eliminating impurities (Figure 1, left). In this way, it is believed that a precipitate with a higher platinum purity can be produced compared to when ammonium chloride is simply used.

[0018] 3. Selective precipitation of rhodium, iridium, and platinum with melamine ( By using melamine, rhodium and iridium can be selectively precipitated under conditions different from those for platinum (Patent Document 2). Therefore, by selectively precipitating rhodium and iridium using melamine under certain conditions and then selectively precipitating platinum from the remaining solution under different conditions, it is possible to selectively precipitate rhodium, iridium, and platinum in separate forms using only melamine. For example, the precipitating agent of the present invention, which contains melamine as a main component, is mixed with a platinum-containing hydrochloric acid solution having a hydrochloric acid concentration of preferably 1 to 12 mol / L, and even more preferably 2 to 8 mol / L, so that the molar ratio of (total number of moles of melamine and melamine salt) / (total number of moles of platinum and rhodium / iridium) is preferably 7.5 or more, even more preferably 15 to 100, and particularly preferably 15 to 50. Rhodium and iridium are selectively precipitated by shaking at 20 to less than 40°C for 3 minutes to 12 hours, at 40 to less than 50°C for 3 minutes to 20 hours, at 50 to less than 70°C for 3 minutes to 2 hours, or at 70°C or above but below the boiling point for 3 to 30 minutes, more preferably by shaking at 20 to less than 80°C for 5 to 20 minutes, and even more preferably by shaking at 50 to less than 70°C for 5 to 20 minutes. After recovering this precipitate, the remaining solution can be shaken at a temperature and for a time that selectively precipitates platinum, i.e., at a higher temperature and for a longer shaking time than for rhodium and iridium, to selectively precipitate platinum. However, this does not exclude the inclusion of components other than the main component, as long as they do not affect the selective precipitation of rhodium, iridium, and platinum. Rhodium and iridium can be treated as a single entity, so we have written "rhodium-iridium." When referring to rhodium-iridium, it can mean just rhodium, just iridium, or both rhodium and iridium. [Example]

[0019] Example 1: Examination of conditions for causing precipitation when melamine is used 1. Experimental Example 1-1 Examination of the temperature when shaking Melamine was added to a 6 mol / L hydrochloric acid solution containing 5 mmol / L platinum so that the molar ratio of melamine to platinum (Melamine / Pt) was 60, and the mixture was shaken and centrifuged at 25 to 80°C for 6 to 48 hours, and the supernatant was collected. The platinum concentration in the supernatant was analyzed by ICP atomic emission spectroscopy (ICP atomic emission spectrometer, Seiko Instruments Inc., model number SPS5510), and the amount of precipitated platinum was calculated, thereby calculating the metal precipitation rate. The results are shown in Table 1. As is clear from Table 1, it takes time for platinum to precipitate when the temperature is low, but as the temperature increases, platinum can be recovered at a high recovery rate even in a short time. At 80°C, 90% of platinum was recovered after 6 hours of shaking, and 97% after 24 hours of shaking. It is thought that the higher the temperature, the more accelerated the decomposition of the precipitating agent, melamine, and the faster the release rate of ammonium chloride, which allowed platinum to be recovered in a short time.

[0020] [Table 1]

[0021] 2. Experimental Example 1-2: Examination of Hydrochloric Acid Concentration Melamine was added to a hydrochloric acid solution containing 5 mmol / L of platinum at a concentration of 1 to 6 mol / L so that the molar ratio of melamine to platinum (Melamine / Pt) was 60, and the solution was shaken at 80°C for 24 hours. 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 2. The platinum recovery rate increased as the hydrochloric acid concentration increased, and more than 95% of platinum was recovered at hydrochloric acid concentrations of 4 mol / L or higher. It is thought that the higher the hydrochloric acid concentration, the more accelerated the decomposition of melamine, resulting in a higher platinum recovery rate.

[0022] [Table 2]

[0023] 3. Experimental Example 1-3: Examination of melamine addition amount and shaking time Melamine was added to a 6 mol / L hydrochloric acid solution containing 5 mmol / L platinum so that the molar ratio of melamine to platinum (Melamine / Pt) was 5 to 60, and the solution was shaken at 80°C for 24 hours. The same experiment as in Experimental Example 1-1 was performed, and the metal precipitation rate was calculated. Similar experiments were also performed with the molar ratio of melamine to platinum (Melamine / Pt) set to 60 and the shaking time varied from 0.25 to 24 hours (Tables 3 and 4, 5 mM). Furthermore, experiments were conducted in the same manner using a 6 mol / L hydrochloric acid solution containing 50 mmol / L platinum, varying the amount of melamine added (1 to 20 times the molar amount of platinum) and the shaking time (1 to 6 hours) (Tables 3 and 4 50 mM). The results are shown in Tables 3 and 4. The platinum recovery rate increased as the amount of melamine added increased; when platinum was 5 mM and the molar ratio of melamine to platinum was 30 or higher, more than 90% of the platinum was recovered. When platinum was 50 mM and the molar ratio of melamine to platinum was 1 or higher, more than 80% was recovered. Furthermore, when platinum was 5 mM, more than three hours of shaking was required to recover the platinum. It takes a certain amount of time for the melamine to decompose, and it is thought that ammonium chloride is gradually released as the decomposition proceeds. At 50 mM, more than 75% was recovered after immersion for more than one hour.

[0024] [Table 3]

[0025] [Table 4]

[0026] 4. Comparative Experimental Example 1-4 Platinum Precipitation Recovery Using Ammonium Chloride Ammonium chloride was added to a 6 mol / L hydrochloric acid solution containing 5 mmol / L platinum so that the molar ratio of ammonium chloride to platinum (NH4Cl / Pt) was 5 to 200, and the solution was shaken at 25°C or 80°C for 1 hour. 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 5. The shaking time was 1 hour, and at 25°C, the molar ratio of ammonium chloride to platinum was 30 or more, and at 80°C, the molar ratio was 50 or more, resulting in the recovery of 90% or more of platinum. It can be seen that platinum precipitates form more quickly than with melamine.

[0027] [Table 5]

[0028] Example 2: Platinum selectivity study 1. Comparative Experiment 2-1 Selective precipitation and recovery of platinum using ammonium chloride Ammonium chloride 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 ammonium chloride to platinum (NH4Cl / Pt) was 25, and the mixture was shaken at 80°C for 1 hour, and the precipitate was collected by filtration. The metal concentrations contained in the filtrate and in a solution obtained by dissolving the precipitate in hydrochloric acid were analyzed using ICP atomic emission spectroscopy, and the metal precipitation rate and platinum purity (the ratio of platinum weight to total metal weight) were calculated. The results are shown in Table 6. Platinum was recovered at 100% purity of 96.4%. Although small amounts, palladium and rhodium also co-precipitated, resulting in a lower purity.

[0029] [Table 6]

[0030] 2. Experimental Example 2-1 Selective precipitation and recovery of platinum using melamine 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 platinum (Melamine / Pt) was 10, and the mixture was shaken at 80°C for 24 hours, and the precipitate was collected by filtration. The experiment was otherwise carried out in the same manner as in Comparative Experimental Example 2-1, and the metal precipitation rate and platinum purity were calculated. The results are shown in Table 7. 100% platinum was recovered, with a purity of 99.6%. Palladium and rhodium were hardly present, achieving high-purity platinum recovery. The impurity ratio was reduced from 3.6% to 0.4% compared to Comparative Experiment 2-1.

[0031] [Table 7]

[0032] Example 3: Investigation of platinum-containing precipitates (elemental analysis, crystal size) Melamine was added to a 6 mol / L hydrochloric acid solution containing 5 mmol / L platinum at a molar ratio of 60 (Melamine / Pt). The mixture was shaken at 80°C for 24 hours, and the precipitate was collected by filtration. The collected precipitate was observed under a microscope. Elemental analysis was also performed on the resulting precipitate using an organic trace elemental analyzer (Exeter Analytical, Model CE-440). Furthermore, a precipitate obtained by shaking the mixture at 80°C for 1 hour using ammonium chloride (NH4Cl / Pt = 100) instead of melamine was also observed under a microscope. The results of microscopic observation are shown in Figure 1. It can be seen that when melamine was used, large crystals of 0.1 mm or more were obtained, while when ammonium chloride was used, very fine crystals of less than 0.1 mm were obtained. Melamine slowly decomposes and releases ammonium chloride, resulting in large platinum-containing crystals, while ammonium chloride rapidly forms a precipitate, resulting in only small crystals. Table 8 shows the results of elemental analysis. The resulting precipitate was determined to be ammonium hexachloroplatinate(IV) ([NH4]2[PtCl6]).

[0033] [Table 8]

[0034] Example 4: Examination of compounds other than melamine 1. Experimental Example 4-1 Platinum precipitation recovery using precipitants other than melamine Acetoguanamine, ammeline, diethylmelamine, or benzoguanamine was added as a platinum precipitant to a 6 mol / L hydrochloric acid solution containing 5 mmol / L platinum so that the molar ratio to platinum (platinum precipitant / Pt) was 60, and the solution was shaken at 80°C for 24 hours, and an experiment was performed in the same manner as in Experimental Example 1-1, and the metal precipitation rate was calculated. Also, urea was added as a platinum precipitant so that the molar ratio to platinum (Urea / Pt) was 120, and the solution was shaken at 80°C for 24 or 48 hours, and the experiment was performed in the same manner, and the metal precipitation rate was calculated. The results are shown in Table 9. All platinum precipitants were able to precipitate and recover platinum at a high recovery rate of over 90%. When urea was used, shaking for 48 hours was required to achieve a high platinum recovery rate.

[0035] [Table 9]

[0036] 2. Experimental Example 4-2 Selective precipitation and recovery of platinum using urea Urea 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 urea to platinum (Urea / Pt) was 30, and the mixture was shaken at 80°C for 48 hours, and the precipitate was collected by filtration. The experiment was otherwise carried out in the same manner as in Comparative Experimental Example 1-1, and the metal precipitation rate and platinum purity were calculated. The results are shown in Table 10. 99% of platinum was recovered, with a platinum purity of 99.4%. Palladium and rhodium were hardly contained, and high-purity platinum was recovered.

[0037] [Table 10]

[0038] Example 5 Selective precipitation and recovery of rhodium and platinum in separate forms with melamine 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 the total number of moles of rhodium and platinum (Melamine / (Rh+Pt)) was 10, and the mixture was shaken at 60°C for 15 minutes, and the precipitate was collected by filtration (first step). The resulting filtrate was shaken at 80°C for 24 hours, and the precipitate was collected by filtration (second step). The metal concentrations in the filtrates from the first and second steps and in solutions prepared by dissolving the precipitate in hydrochloric acid were analyzed using ICP atomic emission spectroscopy, and the metal precipitation rate and metal purity were calculated. The results are shown in Table 11. In the first step, 99% of the rhodium was recovered as a precipitate, with a rhodium purity of 85.9%. In the second step, 96% of the initial platinum amount was recovered as a precipitate, with a platinum purity of 99.8%. It was found that the use of melamine enabled the selective recovery of rhodium and platinum in a two-step operation.

[0039] [Table 11] [Industrial Applicability]

[0040] According to the present invention, when it is desired to recover platinum with high purity as a priority, this becomes possible, enabling a stable supply of platinum with high purity, which is useful not only in the metal recycling industry but also in a wide range of industries that use platinum.

Claims

1. A platinum-selective precipitating agent containing as its main component a 1,3,5-triazine compound having two or more primary amino groups on the triazine ring, or urea, or a salt thereof, or a mixture of two or more thereof including the salt.

2. A platinum-selective precipitating agent containing, as a main component, melamine, acetoguanamine, ammeline, N,N-diethylmelamine, benzoguanamine, or urea, or a salt thereof, or a mixture of two or more of these including the salt.

3. A platinum-selective precipitating agent whose main component is melamine or urea, or a salt thereof.

4. 2. A method for selectively precipitating platinum by mixing the platinum-selective precipitant of claim 1 with a platinum-containing hydrochloric acid solution and gradually releasing ammonium chloride.

5. The platinum-selective precipitant of claim 1 is mixed with a platinum-containing hydrochloric acid solution, and [NH 4 ] 2 [PtCl 6 A platinum selective precipitation method for producing crystals of [Chemical Formula 1].

6. A method for selectively precipitating platinum, comprising mixing the platinum-selective precipitant of claim 1 with a platinum-containing hydrochloric acid solution having a hydrochloric acid concentration of 1 mol / L or more so that (total number of moles of the 1,3,5-triazine compound of claim 1, urea, and a salt thereof) / (number of moles of platinum)=1 or more, and shaking the mixture.

7. A selective precipitant for rhodium, iridium, and platinum, which comprises melamine or a salt thereof as a main component and is capable of selectively precipitating rhodium, iridium, and platinum, respectively.

Images