JP7229849B2 - Precious metal analysis method - Google Patents

Description

The present invention relates to a method for analyzing precious metals.

In recent years, in order to effectively utilize metal resources, there has been an increasing demand for precious metal recycling, in which precious metals such as Au, Ag, Pt, and Pd are recovered from waste materials such as waste electrical and electronic equipment. In addition, waste materials containing precious metals are subject to commercial transactions as valuables, and transaction amounts vary depending on the type and amount of precious metals contained. Therefore, analysis of precious metals contained in waste materials is widely performed.

In this regard, a method called tellurium (Te) coprecipitation method is known as a method for analyzing precious metals. For example, Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2005-308705) describes a precious metal analysis method based on the Te coprecipitation method, in which arsenic (As) is added in combination, whereas Te is usually used as a precious metal coprecipitant. discloses an analysis method for increasing the collection efficiency of precious metals.

In addition, as another method for analyzing precious metals, a method called dry assay method (dry melting-ash blowing method) is also widely known (for example, Non-Patent Document 1 (JIS M 8111-1998 “Gold in Ore and Silver Determination Methods”)). The dry assay method includes a dry melting step and an ash blowing step in that order. In the dry melting process, the sample is blended with PbO and a flux to form a mixed sample, and the mixed sample is melted in a crucible to capture the precious metals contained in the sample in a lead button and extract them with mineral-derived metal oxides. A lead button is separated from a lump of slag. In the ash blowing process, the obtained lead button is placed in a bone ashtray called a cupel and melted in an oxidized state. ) in the form of The precious metal can then be quantified by pretreatment and analysis of the separated beads.

However, this dry assay method requires a long time for the above-mentioned ash blowing step and analysis, and it is difficult to carry out rapid analysis. In order to deal with such problems, an analytical technique that is an improvement of the dry assay method has been proposed. For example, in Patent Document 2 (Japanese Patent Application Laid-Open No. 2012-123016), a lead button is produced using a dry assay method, the obtained lead button is irradiated with laser light, and part of the lead button is made into fine particles. A precious metal analysis method using a laser ablation ICP analysis method is disclosed, in which the precious metal is converted into an ICP analysis device, and according to this method, the ash blowing process etc. can be omitted, so it is said that the analysis can be speeded up. In addition, Patent Document 3 (Japanese Patent Application Laid-Open No. 2013-27549) discloses a method of physically removing slag by barrel polishing a crude lead button obtained using a dry assay method. , also discloses that a lead button polished by this technique is suitably used as a sample for analysis using laser ablation.

Japanese Patent Application Laid-Open No. 2005-308705 JP 2012-123016 A JP 2013-27549 A

JIS M 8111-1998 "Method for determination of gold and silver in ore"

Due to the increasing demand for recycling of precious metals as described above, there is a demand for a method of quickly and highly accurately analyzing precious metals contained in test samples such as waste materials. However, the Te coprecipitation method as disclosed in Patent Document 1 requires a complicated pretreatment process, so that its operation requires skill and it is difficult to perform rapid analysis. On the other hand, in the precious metal analysis method using the laser ablation ICP analysis method disclosed in Patent Documents 2 and 3, although the formed lead button is analyzed as a solid, rapid analysis is possible, but residual There is a risk that the analysis results will vary greatly due to the influence of slag.

The inventors of the present invention have recently discovered that by washing a lead button in which precious metals are collected with a predetermined solution and subjecting it to instrumental quantitative analysis, rapid and highly accurate quantitative analysis of precious metals in a test sample can be performed. I got the knowledge that I can do it.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a method for analyzing precious metals that enables rapid and highly accurate quantitative analysis of precious metals in a test sample.

According to one aspect of the invention,
A precious metal analysis method comprising:
preparing a test sample containing a precious metal;
a step of producing a lead button by melting the test sample and collecting the precious metal according to a lead button production procedure of a dry assay method;
The lead button is washed with at least one acidic aqueous solution, water or alkaline aqueous solution selected from the group consisting of aqua regia, hydrochloric acid, reverse aqua regia, acetic acid, citric acid and sulfuric acid to adhere to the surface of the lead button. removing the slag that has accumulated;
drying the slag-removed lead button;
performing an instrumental analysis on the dried lead button to quantify the precious metal;
A method is provided, comprising:

1 is an Au calibration curve prepared in Example A1. 1 is an Ag calibration curve prepared in Example A1. FIG. 2 is the Rh calibration curve prepared in Example A2. FIG. Fig. 3 is a Pd calibration curve prepared in Example A2; It is a Pt calibration curve created in Example A2.

Method for analyzing precious metals The method for analyzing precious metals according to the present invention includes (1) preparation of a test sample containing precious metals, (2) preparation of a lead button in which the precious metal is collected, and (3) use of a predetermined solution in a lead button. (4) drying of the lead button, (5) press molding and surface cutting of the lead button, if desired, and (6) quantitative determination of precious metals by instrumental analysis. In this way, by washing the lead button with the collected precious metals with a predetermined solution and subjecting it to instrumental quantitative analysis, the quantitative analysis of the precious metals in the test sample can be performed quickly and with high accuracy. .

As described above, the dry assay method (dry melting-ash blowing method), which has been conventionally known as a method for analyzing precious metals, requires a long time for the blowing process and analysis, making it difficult to perform rapid analysis. On the other hand, when the lead button is analyzed as it is without going through the ash blowing process, although it is possible to quickly quantify the precious metal, it cannot be said that it is sufficient from the viewpoint of analysis accuracy. This is because slag adheres to the surface of the lead button obtained by the dry melting process of the dry assay method, and the slag present on the surface of the lead button causes variations in the analytical results of precious metals. it is conceivable that. That is, it is considered that the non-metallic components contained in the slag or adhering to the slag hinder quantitative analysis of precious metals as impurities. In this respect, when slag is removed by physically scraping the surface of the lead button by barrel polishing, etc., fine slag adhering to the surface of the lead button cannot be completely removed, and variations in quantitative results cannot be sufficiently suppressed. . On the other hand, in the present invention, the surface of the lead button is chemically washed with a predetermined solution, so that the slag adhering to the surface of the lead button can be effectively removed. becomes. Although this mechanism is not necessarily certain, it is presumed as follows. That is, the predetermined acidic aqueous solutions (that is, aqua regia, hydrochloric acid, reverse aqua regia, acetic acid, citric acid and sulfuric acid) used in the present invention have the property of slightly dissolving Pb, which is the main component of lead buttons. Therefore, by washing the lead button with this acidic aqueous solution, while minimizing the dissolution of the lead button itself that has captured the precious metal, the vicinity of the surface of the lead button is thinly peeled off and attached to the surface. Slag and other non-metallic components can be removed by floating. On the other hand, water and alkaline aqueous solutions have the property of eluting the slag itself, which is composed of metal oxides derived from minerals. Therefore, by washing the lead button with water or an alkaline aqueous solution, the slag and other non-metallic components adhering to the surface of the lead button can be dissolved and removed. In any case, by washing the lead button with the predetermined solution used in the present invention, slag and the like can be effectively peeled off and removed from the surface of the lead button, and as a result, the slag in the subsequent instrumental quantitative analysis It is thought that it is possible to minimize the variation in the analysis results of precious metals caused by factors such as

Each of steps (1) to (6) will be described below.

(1) Preparation of Test Sample Containing Noble Metal A test sample containing a precious metal to be analyzed is prepared. Examples of noble metals contained in the test sample include Au, Ag, Pt, Pd, Rh, Ir, Ru, Os and combinations thereof;
Preferred are Au, Ag, Pt, Rh, Pd and combinations thereof, more preferably Rh.

Therefore, it is particularly preferred that the analytical method of the present invention is used to quantify Rh. In this respect, the dry assay method (dry melting-ash blowing method) has a problem that Rh cannot be analyzed when the test sample contains Ag. This is because when Ag and Rh are contained in the lead button, it is difficult to separate the precious metal elements in the form of beads in the ash blowing process. On the other hand, in the present invention, although the lead button is produced using the dry assay method, the lead button can be analyzed directly by instrumental analysis without performing the ash blowing process, so the test sample contains Ag. Even if it is, it is possible to analyze Rh without any problem.

As described above, the analysis method of the present invention can rapidly and highly accurately analyze precious metals contained in test samples, and is therefore extremely suitable for precious metal recycling applications. Therefore, it is preferred that the sample to be tested originates from waste wood, and therefore the analytical method of the present invention is performed for the recycling of precious metals. Preferred examples of waste materials include electrical and electronic device wastes, and more preferably waste substrates.

(2) Fabrication of Lead Button with Collected Noble Metal According to the lead button fabrication procedure of the dry assay method, a test sample is melted to fabricate a lead button with captured precious metal. The weight of the lead button to be produced is preferably 20-80 g, more preferably 25-60 g. Within this range, the lead button can sufficiently absorb the noble metal elements contained in the sample to be tested, and the handleability in each pretreatment step, which will be described later, is also excellent. Moreover, the production of the lead button may be carried out according to a conventionally used method as described in JIS M 8111-1998, and is not particularly limited. Typically, lead buttons are made by blending the sample to be tested with PbO and a flux into a mixed sample, melting the mixed sample in a crucible to collect the precious metal in the lead button, and then This may be done by separating the lead button from the rest of the slag mass by physical impact and/or mechanical work. Examples of physical impact include methods such as artificially or mechanically hitting the melt with a hammer, and examples of mechanical processing include cutting the melt using a machine tool. method.

The type of flux used for melting is not particularly limited, but examples thereof include borax glass, soda ash, wheat flour, and iron nails. If necessary, the reducing power or oxidizing power of the test sample may be calculated to determine the type and amount of flux suitable for forming a given amount of lead button. Alternatively, the melting method of the test sample may be determined after roughly estimating the composition and amount of precious metal of the test sample.

(3) Cleaning lead buttons using a prescribed solution Using a prescribed acidic aqueous solution, water, or alkaline aqueous solution, wash a lead button with slag clumps attached, or a lead button with slag clumps removed. Remove any slag adhering to the surface of the button. A preferred washing solution is water because of its ease of handling. Even when water is used as the cleaning solution, slag can be easily removed by cleaning alone without physical polishing, making it suitable for rapid and highly accurate quantitative analysis of precious metals. On the other hand, when it is difficult to remove the slag with water, it is preferable to use an acidic aqueous solution or an alkaline aqueous solution that is more effective in removing slag. At this time, by using at least one selected from the group consisting of aqua regia, hydrochloric acid, reverse aqua regia, acetic acid, citric acid and sulfuric acid as the acidic aqueous solution, the slag adhering to the surface of the lead button can be effectively removed. can be removed. Among them, preferred acidic aqueous solutions are aqua regia, hydrochloric acid, reverse aqua regia, sulfuric acid, or a mixture thereof, more preferably aqua regia, hydrochloric acid, or a mixture thereof, and still more preferably hydrochloric acid. In particular, since hydrochloric acid hardly dissolves Pb, it is possible to more effectively remove slag and other non-metallic components adhering to the surface of the lead button while minimizing the dissolution of the lead button itself. Incidentally, aqua regia means an acidic aqueous solution prepared by mixing concentrated hydrochloric acid (for example, about 37% by weight of hydrochloric acid) and concentrated nitric acid (for example, about 60% by weight of nitric acid) in a volume ratio of 3:1. Water means an acidic aqueous solution prepared by mixing concentrated hydrochloric acid and concentrated nitric acid in a volume ratio of 1:3. On the other hand, the alkaline aqueous solution is preferably a strongly alkaline solution from the viewpoint of effectively eluting the slag adhering to the surface of the lead button. Therefore, preferred examples of the alkaline aqueous solution include sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, lithium hydroxide aqueous solution, calcium hydroxide aqueous solution, magnesium hydroxide aqueous solution, or a mixture thereof, more preferably sodium hydroxide aqueous solution, An aqueous potassium hydroxide solution, an aqueous calcium hydroxide solution, an aqueous magnesium hydroxide solution or a mixture thereof, more preferably an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution, an aqueous calcium hydroxide solution or a mixture thereof, particularly preferably an aqueous sodium hydroxide solution , an aqueous potassium hydroxide solution or a mixture thereof, most preferably an aqueous sodium hydroxide solution.

The acidic aqueous solution and the alkaline aqueous solution may be diluted with water. As long as the slag adhering to the surface of the lead button can be removed, it is permissible to add an appropriate amount of an organic solvent, a surfactant, or the like as an additive to the acidic aqueous solution, water, or alkaline aqueous solution. The concentrations of the acidic aqueous solution and the alkaline aqueous solution are preferably selected appropriately according to the types of the acidic aqueous solution and the alkaline aqueous solution, as exemplified in Table 1 below. Table 1 exemplifies preferred concentrations in each solution.

Cleaning is preferably accomplished by contacting the lead button with a predetermined solution. The temperature of the solution is preferably 10 to 100°C, more preferably 30 to 100°C, even more preferably 50 to 100°C, particularly preferably 70 to 100°C. In particular, when water is used as the washing solution, the water is preferably warm water of 50 to 100°C, more preferably hot water of 70 to 100°C. By doing so, the slag adhering to the lead button can be removed more effectively. Examples of the method of bringing the lead button into contact with the solution include a method of immersing the lead button in the solution, a method of showering or spraying the solution on the lead button, and the like. The contact time of the lead button with the solution is preferably 1 to 60 minutes, more preferably 5 to 30 minutes, even more preferably 10 to 30 minutes, and particularly preferably 10 to 15 minutes. Further, by performing ultrasonic cleaning during cleaning, slag can be removed more efficiently, and the cleaning time can be shortened.

(4) Drying lead buttons Dry the cleaned lead buttons. The drying method is not particularly limited, and the lead button may be dried using a commonly used known drying method such as natural drying, air drying, or hot air drying.

(5) Press molding and surface cutting of lead buttons (optional process)
If necessary, the dried lead button may be press-molded to give a plate-like shape, and the surface of the plate-like lead button may be cut to be flat. By doing so, when the lead button is analyzed using an apparatus for analyzing the sample surface (for example, an emission spectrometer), it is possible to reduce variations in analysis results due to unevenness of the sample surface. The press molding may be performed using a commercially available pressing machine at a predetermined pressure so that the lead button has a plate-like shape. At this time, it is preferable that the lead button is set in a holder of a predetermined shape and then press-molded, since the lead button can be easily formed into a plate shape. The surface of the plate-shaped lead button may be cut using a commercially available cutting board or the like.

(6) Quantitative determination of precious metals by instrumental analysis The dried lead buttons are subjected to instrumental analysis to quantify the precious metals. The instrumental analysis used in the present invention is performed by an analytical instrument that can directly analyze the solid state of the lead button without turning it into a solution. Moreover, the instrumental analysis is preferably performed by a method that allows simultaneous multi-element analysis. From this point of view, the instrumental analysis includes an emission spectrometer such as a spark discharge emission spectrometer, a DC arc emission spectrometer, a glow discharge emission spectrometer, or a wavelength dispersive X-ray fluorescence spectrometer, an energy dispersive It is preferable to use a fluorescent X-ray spectrometer such as a fluorescent X-ray spectrometer, and an emission spectroscopic spectrometer is used from the viewpoint of the accuracy of analysis when the amount of the contained component is very small and the influence of the surface state of the sample is small. is more preferable. Furthermore, from the viewpoint of ease of sample preparation and analysis time, the instrumental analysis is most preferably performed using a spark discharge emission spectrometer.

Quantification of noble metals is preferably carried out based on the calibration curve method. That is, a standard sample with a known noble metal concentration is analyzed according to the analysis method of the present invention to create a calibration curve for each precious metal, and based on this calibration curve, the lead button and, by extension, the amount of each precious metal contained in the test sample. preferably determined. If it is not possible to prepare a standard sample with a known concentration of precious metals, for example, prepare multiple lots (for example, 5 to 10 lots) of actual samples with different concentrations of precious metals (i.e., samples of the same type as the test sample), and dry test these. The concentration of precious metals may be valued and used as a standard sample by analyzing with the gold method (dry melting-ash blowing method) or the like. Alternatively, a plurality of actual samples containing as little precious metal as the target of analysis as possible may be prepared, and different amounts of the precious metal may be added stepwise to prepare a plurality of standard samples having different concentrations of the precious metal. In addition, a standard sample may be prepared for each coexisting component as necessary. When adding a noble metal to an actual sample to prepare a standard sample, it is preferable to check whether the added noble metal is absorbed by the lead button.

Depending on the type of sample to be tested, a standard sample may be prepared by matting (mat melting method). In preparing a standard sample by matte treatment, the precious metal to be analyzed and FeS are added to an actual sample, heated and melted, and the resulting melt is cooled and pulverized to obtain a standard sample.

The invention is further illustrated by the following examples.

[Examples A1 and A2]
The examples shown below confirm that accurate quantitative analysis can be performed by preparing a calibration curve for noble metals according to the method of the present invention.

Example A1
An actual sample was quantified by the dry melting-ash blowing method, which is a conventional analytical method, and used as a standard sample, and an Au calibration curve and an Ag calibration curve were prepared using this standard sample.

(1) Preparation of Calibration Curve Samples As calibration curve samples, 10 lots of actual samples (recycled raw materials) having different Au concentrations and Ag concentrations were prepared.

(2) Preparation of lead button 5.0 g of sample for calibration curve was mixed with 55.0 g of PbO and flux (4.0 g of wheat flour, 10.0 g of borax powder, 8.0 g of silica sand powder, 35.0 g of soda ash and 1 iron nail). .7 g) to form a mixed sample. Next, the crucible containing the mixed sample is placed in a melting furnace preheated to about 900° C. and heated for about 10 minutes. was completely melted. Au, Ag and other precious metals in the calibration samples were thus trapped in the lead button. The cooled melt was removed from the crucible and the lead button was separated from the slag mass. In this way, four lead buttons were produced for each lot, and the weight of each lead button was measured.

(3) Pricing of Actual Samples Pricing of actual samples was performed by analyzing two lead buttons for each lot by the ash blowing method. That is, the resulting lead button is placed on a cupel that has been preheated to about 790° C. for about 20 minutes in an ash blowing furnace, ash blowing is performed at about 820° C. while adjusting the inflow of air, and then the cupel is allowed to cool. and got the bead. After weighing the obtained beads, the beads were placed in sulfuric acid and boiled to dissolve Ag. Next, the beads were washed to completely remove Ag to obtain gold grains, which were dried, annealed, and allowed to cool, and the weight of the gold grains was measured. Thus, the amount of Au was obtained from the weight of the gold grains, the amount of Ag was obtained from the difference between the weight of the bead and the weight of the gold grains, and the Au concentration and Ag concentration of the lead button were calculated from the previously measured weight of the lead button. The average values of the Au concentration and Ag concentration were obtained for each lot and used as the Au concentration and Ag concentration of the lead button of the corresponding lot. In addition, the amount of Au and the amount of Ag are determined according to the procedure of JIS M 8111-1998, the amount of Pt, Pd, Bi and Pb in the metal separation solution (that is, sulfuric acid and cleaning solution), and the amount of Au and Ag remaining in the slag and cupel. was obtained, and calculated by correcting with these values. Alternatively, the beads are dissolved in aqua regia, and the noble metals other than silver and impurities in the solution are measured with an analytical instrument such as an ICP emission spectrometer to obtain the noble metal concentration including the Au concentration, and the noble metal and impurity amounts of the beads are determined. The Ag concentration can also be obtained by subtracting from the weight.

(4) Cleaning and Drying of Lead Buttons The remaining two lead buttons of each lot, which had not been analyzed by the ash blowing method, were subjected to pretreatment and analysis according to the analysis method of the present invention. First, the obtained lead button was washed by immersing it in aqua regia (1+1) at about 90° C. for 10 minutes to remove slag adhering to the surface of the lead button. In this specification, "solution A (1+1)" means a solution prepared by adding 1 volume of water to 1 volume of solution A. After cleaning, the lead button was dried in a constant temperature dryer.

(5) Press molding and surface cutting of lead button A dried lead button is set in a holder, and press molding (20 ton press for about 1 second) is performed using a press machine (manufactured by Mayekawa Test Instruments Co., Ltd., Type M). By applying it, the lead button was made into a plate-like shape. The plate-like lead button was cut with a cutting machine (SAM-100, manufactured by Harzok Japan Co., Ltd.) to flatten the surface of the lead button.

(6) Analysis of lead button by instrumental analysis Instrumental analysis was performed on the press-molded and surface-cut lead button using the following apparatus and conditions to determine the emission intensity of Au and Ag.
- Apparatus: Spark discharge emission spectrometer (ARL4460, manufactured by Thermo Fisher Scientific Co., Ltd.)
- Measurement time: 27.5 seconds - Electrode: 4 mm pin - Detector: High performance matrix photodiode (IL-CCD)
- Emission power supply: New digital emission source (dual CCS adopted)
- Maximum current value: 200A
- maximum duration: 2500 μs
- Photometric method: time-resolved spectroscopy - Temperature: 16-30°C
- Relative humidity: 20-80%
- Supply gas: argon gas (99.996% or more, oxygen 5 ppm or less)

(7) Preparation of calibration curve From the concentration of Au and Ag in lead buttons of each lot determined by pricing of actual samples, and the emission intensity of Au and Ag of lead buttons of each lot obtained according to the analysis method of the present invention , Au and Ag, respectively. The prepared Au calibration curve and Ag calibration curve are shown in FIGS. 1 and 2, respectively. As shown in FIGS. 1 and 2, it can be seen that the Au calibration curve and the Ag calibration curve exhibit good linearity, respectively.

Example A2
Standard samples were prepared by adding Rh, Pd, or Pt stepwise to actual samples, and using these standard samples, calibration curves for Rh, Pd, and Pt were prepared.

(1) Preparation of calibration curve sample As a calibration curve sample, a real sample (recycled raw material) containing as few Rh, Pd, and Pt as the components to be analyzed was prepared.

(2) Preparation of lead button In a crucible, 5.0 g of the above-described calibration curve sample, a predetermined amount of the target component (that is, Rh, Pd or Pt), 55.0 g of PbO and flux (4.0 g of wheat flour, 10 g of borax powder) .0 g, 8.0 g silica sand powder, 35.0 g soda ash and 1.7 g iron nails) were added to form a mixed sample. Next, the crucible containing the mixed sample is placed in a melting furnace preheated to about 900° C. and heated for about 10 minutes. was completely melted. Thus, components of interest and other precious metals in the calibration samples were collected in the lead button. After cooling, the melt was removed from the crucible and the lead button was separated from the slag mass. By appropriately changing the amounts of Rh, Pd, and Pt added, a plurality of lead buttons with different concentrations of the target component was produced, and the weight of each lead button thus obtained was measured.

(3) Pretreatment and Analysis of Lead Buttons Under the same conditions as (4) to (6) in Example A1, pretreatment (washing, drying, press molding and surface cutting) of lead buttons and instrumental analysis were performed, and each lead button was analyzed. The luminescence intensities of Rh, Pd and Pt at .

(4) Preparation of calibration curve From the Rh, Pd and Pt concentrations of the lead button (converted from the added amount of Rh, Pd and Pt and the weight of the lead button) and the obtained luminescence intensity of Rh, Pd and Pt, A calibration curve for Pd and Pt was prepared, respectively. The prepared calibration curves for Rh, Pd and Pt are shown in FIGS. 3 to 5, respectively. As shown in FIGS. 3 to 5, it can be seen that the calibration curves for Rh, Pd and Pt each exhibit good linearity.

[Examples B1 to B9]
The example shown below examines the effect of the type of solution used for washing on the analysis results.

Example B1
Pretreatment and analysis of test samples were performed in two replicates.

(1) Preparation of sample to be tested A recycled material was prepared as a sample to be tested.

(2) Preparation of lead button 5.0 g of the test sample was mixed with 55.0 g of PbO and a flux (4.0 g of wheat flour, 10.0 g of borax powder, 8.0 g of silica sand powder, 35.0 g of soda ash and 1.5 g of iron nail). 7g) was added to the crucible to obtain a mixed sample. Next, the crucible containing the mixed sample is placed in a melting furnace preheated to about 900° C. and heated for about 10 minutes. was completely melted. Thus, the precious metals in the test sample were trapped in the lead button. The cooled melt was removed from the crucible, the lead button was separated from the slag mass, and the resulting lead button was weighed.

(3) Washing and Drying of Lead Button The obtained lead button was washed by immersing it in aqua regia (1+1) at about 90° C. for 10 minutes to remove slag adhering to the surface of the lead button. After washing, the lead button was dried in a constant temperature dryer, after which the weight of the lead button was measured again.

(4) Press molding and surface cutting of lead button A dried lead button is set in a holder, and press molding (20 ton press for about 1 second) is performed using a press machine (manufactured by Mayekawa Test Instruments Co., Ltd., Type M). By applying it, the lead button was made into a plate-like shape. The plate-like lead button was cut with a cutting machine (SAM-100, manufactured by Harzok Japan Co., Ltd.) to flatten the surface of the lead button.

(5) Analysis of lead button by instrumental analysis Instrumental analysis was performed on the press-molded and surface-cut lead button using the same apparatus and under the same conditions as in Example A1, and the emission intensities of Rh, Ag, Au, Pd and Pt were determined. sought each. From the obtained emission intensity of each noble metal and the calibration curve of each noble metal prepared in Examples A1 and A2, the concentration of each noble metal contained in the lead button was calculated. In this way, different points on the same plane of the lead button were analyzed 10 times, and the average concentration, standard deviation and coefficient of variation of each precious metal were determined.

Example B2
The test sample was pretreated and analyzed in the same manner as in Example B1, except that hydrochloric acid (1+1) was used instead of aqua regia (1+1) in the lead button cleaning step.

Example B3
Pretreatment and analysis of the test sample were performed in the same manner as in Example B1, except that reverse aqua regia (1+1) was used instead of aqua regia (1+1) in the lead button cleaning step.

Example B4
The test sample was pretreated and analyzed in the same manner as in Example B1, except that acetic acid (1+1) was used instead of aqua regia (1+1) in the lead button cleaning step.

Example B5
The test sample was pretreated and analyzed in the same manner as in Example B1, except that citric acid (1+1) was used instead of aqua regia (1+1) in the lead button cleaning process.

Example B6
The test sample was pretreated and analyzed in the same manner as in Example B1, except that sulfuric acid (1+1) was used instead of aqua regia (1+1) in the lead button cleaning process.

Example B7
A test sample was pretreated and analyzed in the same manner as in Example B1, except that pure water was used instead of aqua regia (1+1) in the lead button cleaning step.

Example B8
Pretreatment and analysis of the test sample were performed in the same manner as in Example B1, except that an aqueous sodium hydroxide solution (50 g/L) was used instead of aqua regia (1+1) in the lead button cleaning step.

Example B9 (Comparison)
The test sample was pretreated and analyzed in the same manner as in Example B1, except that nitric acid (1+1) was used instead of aqua regia (1+1) in the lead button cleaning step.

Example B10 (Comparison)
The test sample was pretreated and analyzed as in Example B1, except that the lead button was not washed.

The weights of the lead buttons before and after the cleaning process in Examples B1-B10 are shown in Table 2. Also, the analysis results obtained are as shown in Table 3.

As shown in Table 2, aqua regia (1+1), hydrochloric acid (1+1), reverse aqua regia (1+1), acetic acid (1+1), citric acid (1+1), sulfuric acid (1+1), pure water or aqueous sodium hydroxide solution ( 50 g / L)), the weight change of the lead button before and after washing is relatively moderate (weight change rate is less than 8%), and the lead button itself containing precious metal It can be seen that the slag adhering to the surface of the lead button can be effectively removed while suppressing dissolution. In addition, as shown in Table 3, Examples B1 to B8 have small coefficients of variation for each noble metal concentration, indicating that highly accurate analysis results are obtained. On the other hand, in example B9 in which nitric acid (1+1) was used for cleaning, the weight change of the lead button before and after cleaning was large (weight change rate of more than 20%), and the lead button itself reacted violently during cleaning and dissolved. I understand.

[Examples C1 and C2]
In the examples shown below, multiple lots of test samples were analyzed by the conventional method (Te coprecipitation method) and the analysis method of the present invention, respectively, to confirm the analytical accuracy of the present invention compared to the conventional method. be.

Example C1
Multiple lots of test samples were pretreated and analyzed according to the analytical method of the present invention.

(1) Preparation of Test Samples Eight lots of actual samples (test sample numbers A to H) were prepared as test samples.

(2) Production and pretreatment of lead button A lead button was produced and pretreated (washing, drying, press molding and surface cutting) under the same conditions as (2) to (5) of Example B1. Two lead buttons were produced for each lot.

(3) Analysis of lead button by instrumental analysis Instrumental analysis was performed on the pretreated lead button using the same apparatus and under the same conditions as in Example A1, and the emission intensity of Rh was determined. From the obtained Rh emission intensity and the Rh calibration curve prepared in Example A2, the concentration of each noble metal contained in the lead button was obtained, and the test sample was determined based on the weighed amount of the test sample and the weight of the lead button. The Rh concentration in the medium was calculated. In this way, different points on the same plane of the lead button were analyzed four times, and the average value was taken as the Rh concentration in the test sample. The above operation was performed for each lead button produced, and the average concentration, standard deviation and coefficient of variation of each lot were obtained. The results obtained are shown in Table 4.

Example C2 (comparison)
A test sample similar to Example C1 was subjected to pretreatment and analysis based on the conventional Te coprecipitation method. That is, after dissolving the test sample, the concentration of hydrochloric acid in the test sample solution was adjusted to 1 to 2 mol/L. Next, tellurium was added to the test sample solution for reduction, so that metallic tellurium was made to capture the noble metal. The tellurium on which the noble metal had been collected was separated by filtration, dissolved in aqua regia and adjusted to a constant volume to prepare a measurement sample. Noble metal analysis was performed on this measurement sample using an ICP emission spectrometer, and the Rh concentration in the test sample was calculated. The above operation was performed with 5 replicates for each lot, and the average concentration, standard deviation and coefficient of variation of each lot were determined. The results obtained are as shown in Table 5.

As shown in Tables 4 and 5, the analysis results of Example C1, which was pretreated and analyzed according to the method of the present invention, had a significantly higher coefficient of variation than the analysis results of Example C2, which was related to the conventional method (Te coprecipitation method). It is small, and therefore, it is possible to analyze precious metals with extremely high accuracy compared with the conventional method. In addition, as shown in Table 4, according to the method of the present invention, it is possible to perform analysis without variation (variation coefficient 0.0%) even in test samples with low Rh content (test sample numbers E to G). Therefore, it is found to be extremely suitable for trace analysis of precious metals.

Claims (8)

A precious metal analysis method comprising:
preparing a test sample containing a precious metal;
a step of producing a lead button by melting the test sample and collecting the precious metal according to a lead button production procedure of a dry assay method;
The lead button is washed with at least one acidic aqueous solution, water or alkaline aqueous solution selected from the group consisting of aqua regia, hydrochloric acid, reverse aqua regia, acetic acid, citric acid and sulfuric acid to adhere to the surface of the lead button. removing the slag that has accumulated;
drying the slag-removed lead button;
performing an instrumental analysis on the dried lead button to quantify the precious metal;
A method, including After drying the lead button and before the instrumental analysis, a step of press-molding the lead button to give it a plate-like shape and cutting the surface of the plate-like lead button to flatten it. 2. The method of claim 1, further comprising: 3. The method according to claim 1 or 2, wherein the instrumental analysis is performed using an emission spectrometer. The method according to any one of claims 1 to 3, wherein said noble metal is at least one selected from the group consisting of Au, Ag, Pt, Rh and Pd. A method according to any one of claims 1 to 4, wherein said noble metal is Rh. The method according to any one of claims 1 to 5, wherein the weight of the lead button is 20-80g. The step of making the lead button comprises blending the test sample with PbO and a flux to form a mixed sample, melting the mixed sample in a crucible to collect the precious metal in the lead button, and then A method according to any one of claims 1 to 6, comprising separating the lead button from the remaining slag mass by physical impact and/or mechanical work. A method according to any one of claims 1 to 7, wherein the sample to be tested originates from waste wood and therefore the method is performed for the recycling of the precious metal.

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