JP4522946B2 - Quantitative analysis of noble metals in noble metal compounds - Google Patents

Description

  The present invention relates to a method for analyzing the noble metal content in various noble metal compounds. More specifically, the present invention relates to a method in which the process is simplified and analysis can be performed more efficiently than before.

  Compounds of noble metals such as platinum, rhodium, iridium, such as hexachloroplatinate, rhodium chloride, etc. are used for catalyst components in various catalysts such as fuel cell catalysts and purification catalysts, and for precious metal plating as decorative materials and electronic materials. Widely used as a precious metal source.

  Here, in the case where the noble metal compound is used for the above-mentioned use, it is necessary to strictly define the amount of use, and therefore it is necessary to accurately grasp the noble metal content in the noble metal compound. This leads to the importance of an accurate quantitative analysis method for the noble metal content in the compound.

As a conventional method for analyzing the noble metal content in the noble metal compound, the noble metal compound is used as an aqueous solution, and an appropriate precipitating agent (for example, a saturated ammonium chloride aqueous solution for the analysis of platinum content) is added thereto for precipitation. There is a method of producing and precipitating a noble metal by weight reduction after filtering and baking the produced precipitate. Moreover, depending on the kind in the noble metal compound, a noble metal simple substance may be obtained while performing a plurality of reduction treatments due to the valence of the noble metal contained.
JIS Handbook 48 Reagents, 2001, 1255 pages, Japanese Standards Association

  However, the conventional analysis methods as described above are efficient for an analysis process with many additional steps, although it is necessary for the accuracy of analysis, such as a precipitation generation step and washing for removing a reducing agent. It becomes an obstacle. Further, in the conventional analysis method, there are processes that require skill for accurate analysis, and the accuracy may vary depending on the experience of the operator.

  Therefore, the present invention provides a method for quantitatively analyzing the content of a noble metal in a noble metal compound, which comprises a simple process, and which can be automated without requiring skill.

  The present inventors have intensively studied to solve the above-mentioned problems, and examined the application of a method of directly reducing a noble metal compound as a sample as a step of extracting a noble metal simple substance from the noble metal compound. Then, the present inventors have conceived the present invention that it is preferable to apply a gas containing a small amount of hydrogen having a relatively low reducing power as a reducing agent when directly reducing the noble metal compound.

  That is, the present invention provides a method for quantitatively analyzing the noble metal content in a noble metal compound, wherein a solid noble metal compound or a concentrated noble metal compound aqueous solution is used as a sample, and the sample contains 1 to 4% hydrogen. This is a method including a step of reducing a precious metal element in a reducing gas at 300 to 500 ° C. for 0.5 to 1 hour and then weighing it.

  The present invention will be described in detail below. In the analysis method according to the present invention, as the noble metal compound to be an analysis sample, either a solid noble metal compound or an aqueous solution of a noble metal compound can be applied. However, when reducing a noble metal compound aqueous solution as a sample, a sample obtained by concentrating the solution is used to ensure the reduction efficiency. Concentration of the solution is preferably performed by heating, but as the heating method, it is preferable to uniformly heat the noble metal aqueous solution from each direction. Concentration itself is also possible by one-way heating with a hot plate or the like, but in this case, it becomes difficult to concentrate the entire solution uniformly, and in some cases, precipitation and scattering of noble metal compounds may occur. . As a specific aspect of the heating method for concentration, a container for storing the solution is introduced into a sand bath, a dryer or the like and heated.

  Concentration for the reduction treatment is preferably performed at 120 to 200 ° C. for 15 minutes to 3 hours until the water is completely removed, depending on the amount of the sample.

  The reduction treatment of the sample is performed with a reducing gas containing 1 to 4% hydrogen. The reason why such a reducing agent having a relatively low reducing power is used as the reducing agent is that all noble metals in the compound are uniformly and reliably reduced to a single noble metal. In this respect, if a reducing agent having a strong reducing power is used, the entire compound may not be uniformly reduced, and adjustment for controlling a rapid reduction reaction may be required, which may require skill in the work. Moreover, the gaseous reducing agent is used because it is not necessary to remove the by-product after the reduction. The reducing gas containing hydrogen gas preferably includes nitrogen in balance.

  And as for reduction conditions, it is preferable that temperature shall be 300-500 degreeC and reduction time shall be 0.5 to 1 hour. The reason why the temperature and the processing time are defined in such a range is to perform the reduction treatment gently and completely, and thereby, by-products and additives generated from the sample during the reduction treatment can be removed. It is. The reduction treatment is preferably performed under a reducing gas stream, and the flow rate is preferably 2 to 10 L / min.

  By the above reduction treatment, a single noble metal is generated. Here, the elements other than the noble metal in the noble metal compound disappear by heating during the reduction treatment. And the content in a compound is computable by collect | recovering this noble metal single-piece | unit, wash | cleaning as needed, and weighing.

  By the way, at the time of concentration treatment and reduction treatment in the case of using a noble metal compound aqueous solution, there is a possibility that the sample may be scattered due to bumping at the time of concentration or moisture evaporation accompanying heating, and further due to airflow in the atmosphere. Such scattering of the sample tends to occur in a noble metal compound containing a nitro group (for example, diammine dinitroplatinum) or a chloride (for example, palladium chloride), but causes a decrease in analysis accuracy. Therefore, in the present invention, it is preferable to coat the sample by adding ammonium chloride as an additive to the sample before the reduction treatment as necessary. The sample coating is preferably performed immediately before the reduction treatment for the solid noble metal compound. In addition, when a noble metal compound aqueous solution is used as a sample, it is preferable to add an additive in two stages during the concentration treatment and after the concentration treatment and immediately before the reduction treatment. This is to prevent scattering of the sample in both the concentration process and the reduction process. The additive may be added as long as the sample can cover the surface exposed to the atmosphere. Specifically, when the sample is added during the concentration process, the viscosity of the liquid increases, and the syrup shape is increased. At that time, 0.5 to 1 g of the additive is added to 0.3 to 1 mL of the liquid amount. Moreover, when adding to a solid sample from the beginning, when adding after a concentration process and before a reduction process, it is preferable to coat | cover the sample surface with 1-2g of additives. The reason why the above compound was selected as an additive is that it does not react with the noble metal compound and can be removed by heating in the reduction treatment, so that no extra residue is generated.

  In addition, depending on the type of the noble metal compound, elements other than the noble metal may remain even by heating by reduction treatment. This tendency of residue generation is rarely observed in platinum compounds, but chlorine may remain in chlorides of rhodium, iridium, and ruthenium. If such a residue is left unattended, the analysis accuracy is lowered. Therefore, in the case where a noble metal compound that may cause a residue is used as a sample, it is preferable to perform baking by high-temperature heat treatment and reduction treatment with a hydrogen flame after the reduction treatment. The high temperature heat treatment is performed in order to remove residues, but the heat treatment conditions are preferably 600 to 800 ° C. and 0.5 to 1 hour. Further, the reduction treatment with hydrogen flame is because oxidation of the noble metal itself may occur due to the high temperature heat treatment. The reduction with hydrogen flame is preferably performed for 15 to 60 seconds. And the high purity noble metal simple substance from which the residue was removed by these baking processes and hydrogen flame reduction processes can be obtained.

  As described above, the quantitative analysis method according to the present invention directly reduces a noble metal compound serving as a sample to obtain a noble metal simple substance, and enables more efficient analysis than before. The present invention can analyze an aqueous solution of a noble metal compound by appropriately performing a concentration treatment in addition to a solid noble metal compound. According to the present invention, the time required for analyzing the noble metal content in the noble metal compound can be significantly shortened compared to the conventional method (for example, about 1/4 for the analysis of diammine dinitroplatinum (II) solution). Generation of waste liquid and by-products is also suppressed. The analysis method according to the present invention does not require skill and can be automated.

  Hereinafter, preferred embodiments of the present invention will be described. In the present embodiment, hexachloroplatinum (IV) acid solution, diammine dinitroplatinum (II) solution, and rhodium chloride crystals were used as analysis samples as the noble metal compounds, and each was analyzed to examine the analysis accuracy of the noble metal content.

Example 1: Analysis Figure 1 hexachloroplatinic (IV) acid solution is a schematic diagram for explaining the analysis process of hexachloroplatinic (IV) acid solution in the present embodiment. In FIG. 1, first, 5 g of a hexachloroplatinum (IV) acid solution serving as a sample was weighed in a magnetic crucible, and concentrated in a sand bath at 150 ° C. for 30 minutes. The sample after concentration of the solution was crystalline without water.

  Next, the concentrated solution was reduced in an electric furnace in a state of being housed in a magnetic crucible. FIG. 2 shows an electric furnace for reduction treatment used in this example. This electric furnace is designed exclusively for the purpose of automation in consideration of the simplicity of the analysis method according to the present invention. The electric furnace 1 includes a furnace chamber 100 in which a plurality of crucibles 10 for storing samples can be placed, a sample chamber 101 for inserting a sample into the furnace chamber 100 for reduction treatment, a furnace chamber 100 and a sample chamber 101 An electric furnace main body 106 including a shutter 102 for isolating the gas, a temperature control unit 104 for controlling power supply to the furnace body 103 in the furnace chamber and adjusting a temperature, and a gas control unit 105 for controlling gas supply to the furnace chamber 100, Consists of. In the reduction process, after a predetermined number of crucibles 10 are placed in the sample chamber 101, the shutter 102 is opened and the crucible is slid to be introduced into the furnace chamber 100. During the reduction process, the temperature control unit 104 and the gas control unit 105 adjust the atmosphere in the furnace chamber so that the reduction conditions set in advance are satisfied. After the reduction process, the crucible 10 is slid from the furnace chamber 100 to the sample chamber 101 and can be taken out. In this example, as reducing conditions by the electric furnace 1, reducing gas was introduced at 4 L hydrogen / nitrogen gas at a flow rate of 6 L / min and heated at a temperature of 400 ° C. for 1 hour.

  After the reduction treatment, the sample was cooled, and platinum alone in the magnetic crucible was collected. And this was weighed and the platinum content in a noble metal compound was calculated. In this example, n = 2 was analyzed for each of the three samples, and the variation in the analysis value of each sample was examined. For comparison, an analysis by a conventional analysis method (see FIG. 3) was performed. Table 1 shows the results.

  As a result, it was confirmed that the analysis method according to the present example has a small repetition variation, and the analysis value is substantially equal to that obtained by the conventional method.

Example 2: Analysis of diammine dinitroplatinum (II) solution FIG. 4 is a diagram for explaining the outline of the analysis process of diammine dinitroplatinum (II) solution in this example. The analysis process of FIG. 4 is basically the same as the analysis process of Example 1, but ammonium chloride is added as an additive during the concentration process and immediately before the reduction process.

  In this example, 3 g of a diamine dinitroplatinum (II) solution serving as a sample was weighed into a magnetic crucible and concentrated at 150 ° C. in a sand bath. After concentration until the liquid volume became about 0.1 to 1 mL from the start of the concentration step, 0.5 g was added, and concentration was continued until the solution was dried. Then, 1 g of ammonium chloride was added to the concentrated sample to coat the sample, and this was reduced in the electric furnace of FIG. As reducing conditions at this time, reducing gas was introduced at 4 L hydrogen / nitrogen gas at a flow rate of 6 L / min and heated at a temperature of 400 ° C. for 1 hour. After the reduction treatment, the sample was cooled, platinum simple substance in the magnetic crucible was collected and weighed, and the platinum content in the noble metal compound was calculated. For comparison, an analysis by a conventional analysis method (see FIG. 5) was performed. Table 2 shows the results.

  As a result, it was confirmed that the analysis method according to the present example has a small repetition variation, and the analysis value is substantially equal to that obtained by the conventional method.

  By the way, in this Example, the scattering of the sample is suppressed by adding ammonium chloride in the concentration and reduction steps of the solution. When the effect of this additive was analyzed without adding ammonium chloride in the analysis step of FIG. 4, the following results were obtained.

  As can be seen from this result, when concentration and reduction are performed without adding ammonium chloride as an additive, the deviation of the analytical value due to repetition becomes relatively large. This is considered to be caused by scattering of the sample during the concentration and reduction processes. Therefore, when analyzing a noble metal compound for which scattering of the sample is predicted, it can be said that it is preferable to add an additive in order to ensure analysis accuracy.

Example 3: Analysis Figure 6 rhodium chloride crystals is a schematic diagram for explaining the analysis process of the rhodium chloride in this embodiment. The analysis process of FIG. 6 is different from the analysis process of Example 1 in that there is no sample concentration process. In this example, the sample after the reduction treatment is subjected to a firing treatment and a hydrogen flame reduction.

  In this example, 1 g of rhodium chloride as a sample was weighed into a magnetic crucible, and this was reduced in the electric furnace of FIG. As reducing conditions at this time, reducing gas was introduced at 4 L hydrogen / nitrogen gas at a flow rate of 6 L / min and heated at a temperature of 400 ° C. for 1 hour. Then, after the reduction treatment, the sample was cooled and baked in the atmosphere at 750 ° C. for 30 minutes. Then, the fired sample was reduced with a hydrogen flame for 30 seconds, then cooled again, and rhodium alone in the magnetic crucible was collected and weighed, and the rhodium content in the noble metal compound was calculated. For comparison, an analysis by a conventional analysis method (see FIG. 7) was performed. Table 4 shows the results.

  As a result, it was confirmed that the analysis method according to the present example has a small repetition variation, and the analysis value is substantially equal to that obtained by the conventional method.

  In this example, residual chlorine is removed by baking the sample after the reduction step at a high temperature and heating with a hydrogen flame. The chlorine concentration of rhodium obtained by this analysis method was 100 ppm. Therefore, the effect of the calcination and hydrogen flame was analyzed in the analysis step of FIG. 4 without heating and heating the hydrogen flame, and the residual chlorine concentration in the recovered rhodium was measured and found to be 700 ppm. Therefore, it is preferable to perform calcination and hydrogen flame reduction in the noble metal compound in which the residual chlorine is concerned.

The figure which shows the analysis process of the xachloroplatinum (IV) acid solution of Example 1. The figure which shows the structure of the exclusive electric furnace used by the reduction process in this embodiment. The figure which shows the analysis process of the conventional xachloroplatinum (IV) acid solution. The figure which shows the analysis process of the diammine dinitro platinum (II) solution of Example 2. FIG. The figure which shows the analysis process of the conventional diammine dinitro platinum (II) solution. The figure which shows the analysis process of the rhodium chloride crystal | crystallization of Example 3. FIG. The figure which shows the analysis process of the conventional rhodium chloride crystal | crystallization.

Claims (5)

In the method of quantitatively analyzing the noble metal content in the noble metal compound,
A solid noble metal compound was used as a sample, and an additive composed of ammonium chloride was added to the sample to cover the sample. In a reducing gas containing 1 to 4% hydrogen, 300 to 500 ° C., 0.5 A method including a step of recovering and weighing a precious metal simple substance after reduction treatment for ˜1 hour. In the method of quantitatively analyzing the noble metal content in the noble metal compound,
A method of concentrating and reducing a sample by adding an additive composed of ammonium chloride to a sample obtained by concentrating an aqueous solution of a noble metal compound and adding an additive consisting of ammonium chloride to the sample during concentration and before the reduction treatment,
The reduction treatment is performed at 300 to 500 ° C. for 0.5 to 1 hour in a reducing gas containing 1 to 4% hydrogen,
A method comprising a step of collecting and weighing a precious metal simple substance after the reduction treatment. The quantitative analysis method according to claim 2 , wherein the concentration of the aqueous noble metal compound solution is performed by uniformly heating the aqueous noble metal compound solution until water is exhausted. The quantitative analysis method according to claim 2 or 3 , wherein the aqueous noble metal compound solution is concentrated in a sand bath or a drier. The sample after the reduction treatment, and fired by heating at 600 to 800 ° C., further, the quantitative analysis of any one of claims 1 to 4 including the step of reduction with hydrogen flame.

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