KR20130097788A - Method of assaying noble metals - Google Patents

Abstract

(a) dry heat treating the homogeneous sample in a reducing atmosphere;
(b) extracting in the oxidation medium; And
(c) atomic spectrometric determination of precious metals using ICP-QMS
A method of analyzing precious metals in mineral and / or ceramic matrices containing 0.03 to 500 mg / kg content.

Description

Analysis method of precious metals {METHOD OF ASSAYING NOBLE METALS}

The present invention relates to a method for the analysis of precious metals in mineral and / or ceramic matrices.

Precious metals play an important role in our society. Precious metals are used in industrial applications, for example in catalysts or for jewelry applications.

In fact, precious metals are most often associated with rocks and are generally present in very small amounts. For example, platinum is present in rock duneite, olive and serpentine. Palladium is present in the form of heavy metal sulfides such as sperlite, acenopalladenite, cooperite and stabiopalladenite.

Precious metals are recovered using flotation processes or leaching methods. In these post-treatment steps, the precious metal (or mineral containing the precious metal) is first concentrated (from 0.1 ppm to 30 to 500 ppm).

Thus, the analysis of precious metals in the rock samples or matrices obtained during the workup is essential in order to be able to assess whether the workup is highly economical or what type of subsequent further concentration and processing steps (smelting process, refining) are required. It is a precondition. The matrix can be for example concentrate, tailings, slag or filter. This assay was classically performed by a fire assay. Nowadays, the term “spinning method” generally refers to the analysis of precious metal-containing raw materials in which samples of precious metal-containing ores are dry-chemically fused with complex mixtures of decomposition reagents and fluxes.

Degradation reagents typically include lead. In this type of spin method, fully dissolved lead buttons are formed and manually separated from the slag where the precious metal of the sample is ideal. Since precious metals ideally collect completely from the lead button, it is also referred to as catcher. Additional catchers used are nickel or nickel sulfide.

In the simplest case, the noble metal content is measured by gravimetric determination after lead (gash). It may also be possible to dissolve the catcher and measure the precious metal using (atomic) spectroscopy. This is described, for example, in Date, A. R., Davis, A. E. and Cheung, Y. Y., The potential of fire assay and inductively coupled plasma source mass spectrometry for the determination of platinum group elements in geological materials. Analyst 112, 1217-1222 (1987).

Other methods include examining the lead button directly using various spectrometers and spectroscopic analysis methods. These methods include solid-sampling-graphite-atomic absorption spectroscopy (SS-GF-AAS); Solid-sampling-thermal evaporation-inductively coupled plasma-mass spectrometry (SS-ETV-ICP-MS); Laser cut-induced coupled plasma-mass spectrometry (LA-ICP-MS); Ignition-optical emission spectroscopy (ignition-OES); And glow discharge-mass spectrometry (GD-MS) (M. Resano, E. Garcia-Ruiz, MA Bellara; F. Vanhaecke, KS MacIntosh, Trends in Analytical Chemistry, Vol. 26, No. 5, pages 385- 395 (2007)]. As a variation of dry chemistry, dissolution is described after fusion of the sample followed by other trace matrix separation using, for example, tellurium precipitation (J.G. Gupta; Talanta 36, 651-656 (1989)).

Zhiqiang Li, Zhanbo Li, Determination of micro-content gold in geochemical exploration smaple by inductively coupled plasma mass spectrometry (ICP-MS) Xibu Tankuang Gongcheng, 22 (6), 116-117 (2010). Extraction of gold from rock samples is described. Subsequent trace matrix separation is followed by the adsorption of dissolved gold to the ashed foam. Gold is then redissolved in aqua regia and analyzed using ICP-MS.

Charles Gowing, Philip Potts, Evaluation of a rapid technique for the determination of precious metals in geological samples based on a selective aqua regia leach, Analyst (Cambridge, United Kingdom), 116 (8), 773-779 (1991). Silver extraction of precious metals from rock samples is described. Gold and to some extent also palladium can be measured quantitatively, but residual platinum group metals cannot be measured quantitatively.

G.E.M. Hall, C.J. Oates, Performance of commercial laboratories in analysis of geochemical samples for gold and the platinum group elements, Geochemistry: Exploration, Environment, Analysis, 3 (2), 107-120 (2003)]. Are compared with each other with help. Here, it was found that the recovery rate of the degradation products by aqua regia extraction was low and varied greatly between the various matrices. Conventional roasting has a different effect, and the recovery of platinum is 75% or less of the actual value.

The disadvantage of the wage law is that it is a relatively time consuming method. A typical working time for performing the analysis manually is about 1 week (M. Rehkamper, A.N. Haliday: Talanta, 44, 663-672 (1997)). Therefore, productivity (the number of samples that can be analyzed per employee and work time) is low.

Intensive concentration of personnel, the use of specific analytical devices, and high energy requirements lead to high analytical costs using the assay method. In some variations of the assay method (including when Ni is used as a catcher), the limit of detection that can be achieved during the run is measured by a blank analysis performed on the loss or memory effect of the reagents and container materials used. .

In addition, the composition of the complex mixture of fusing agent and flux should exactly match each individual sample. This know-how is described, for example, in German Patent No. 112006002407T5.

The use of toxic materials requires specific safety measurements for the analyst to be able to adhere to the relevant MWC values. In addition, measurements to protect the environment should be performed due to evaporation and / or other treatment of toxic materials.

Except for the assay, the method does not provide a quantitative measure of the precious metal to be analyzed.

It is therefore an object of the present invention to provide a method that does not have the above disadvantages.

This purpose

(a) dry heat treating the homogeneous sample in a reducing atmosphere;

(b) extracting from the oxidation medium; And

(c) atomic spectrometric determination of metals using ICP-QMS

It is achieved according to the invention using a method for the analysis of precious metals in mineral and / or ceramic matrices with a content of 0.03 to 500 mg / kg.

For the purposes of the present application, a combination of preferred embodiments should also be considered always to be disclosed in accordance with the present invention.

For the purposes of the present invention, the analysis is the determination of the total content of certain precious metals in all states. The state is, for example:

Metallic (native);

Alloyed with other metals (solid solution);

Present as chemical compound with other elements; And / or

Present in charged (ionized) form, for example as a salt.

For the purposes of this application, the term “noble metal” means silver (Ag), gold (Au) and / or platinum metal, ie ruthenium (Ru), rhodium (Rh), palladium (Pd), iridium (Ir) and / or Platinum (Pt). For purposes herein, the term "platinum metal" includes ruthenium (Ru), rhodium (Rh), palladium (Pd), iridium (Ir) and / or platinum (Pt). Also, rhenium (Re) is considered a precious metal for the purposes of the present application.

The method of the present invention can be used for a single measurement of certain precious metals. In addition, the method of the present invention can be used for simultaneous measurement (multiple measurements) of two or more precious metals.

According to the invention, the precious metal is a decomposing material (for single measurement) or decomposing materials (for multiple measurement); That is, their content is measured.

The term "matrix" refers to the components of a sample that cannot be analyzed.

A mineral matrix is a matrix made in whole or in part of one or more minerals. Minerals are natural solids with defined chemical composition and specific physical crystal structure. Ore is a mineral mixture mined because of its metal content. Ore includes metal-containing ore minerals and gangue free of metal.

Ceramic matrices are all or most of which are made of one or more ceramics. Ceramics are substantially molded articles by adding water at room temperature from the fine particulate raw material and then drying, followed by sintering at temperatures above 900 ° C. in the firing process to obtain heavy durable products. Raw materials are inorganic materials. These include, for example, aluminum silicates such as clays and aluminosilicates such as kaolin. As specific raw materials, oxide raw materials such as aluminum oxide and beryllium oxide are known. Non-toxic raw materials such as silicon carbide, boron nitride and boron carbide are used to prepare non-oxide ceramics.

Engineering ceramics are ceramic materials having properties optimized for engineering applications. These are inorganic, nonmetallic and polycrystalline materials. In general, they are molded at room temperature from crude compositions formed of ceramic powders, organic binders and liquids and attain their typical material properties only during the sintering process at high temperatures.

Ceramics are often used as a support for the off-gas catalyst. In an embodiment of the present invention, the method of the present invention is used to measure precious metals in an off-gas catalyst. Preferred precious metals here are Rh, Pd and / or Pt. The exhaust gas catalyst may be a fresh exhaust gas catalyst. In this case, the method of the present invention can be used to measure the successful application of precious metals during manufacture.

The exhaust gas catalyst may also be the exhaust gas catalyst used. In this case, the method of the present invention can be used to determine the loss of precious metals or to determine the residual precious metals.

According to the invention, the content range of the precious metal to be determined is from 0.03 to 500 mg / kg. The content range of the precious metal to be determined is preferably 0.03 to 50 mg / kg.

The sample to be analyzed is very often present in macroscopic form and at least converted into a suitable form for analysis. This is achieved by homogenization according to the invention. For this purpose, unseparated or indiscriminate methods are used. The method used is preferably milling. A preferred method of performing homogenization is to wet mill the sample. For example, 100 g of sample, 575 g of ZrO ₂ spheres (Ø = 1.7 to 2.3 mm) and 100 g of water are milled together in a ball mill for 15 minutes. After milling, the sample is sieved off the spheres and dried to maintain weight for at least 12 hours at a temperature of 110 ° C. under reduced pressure. After drying, the sample is crushed again using manual mortar.

According to the invention, the average particle size of the homogeneous sample is 100 μm or less, preferably 50 μm or less. It is preferred that 95% of the particles are less than 70 μm. More preferably, 97% of the particles are less than 75 μm.

For the purposes herein, the average particle size is the value obtained by measurement using laser light scattering of an aqueous suspension of the particles to be inspected. Suitable measuring devices are, for example, devices of Malvern company, such as Malvern Mastersizer 2000, or Sympatec. To produce an aqueous suspension, a diluted sodium pyrophosphate solution can be used as the dispersion medium. It is advantageous to predistribute the suspension using ultrasonic waves in the measuring vessel before the measurement, preferably using ultrasonic intensity in the measuring vessel at 100% before and during the measurement.

One skilled in the art will recognize that in rock samples, due to non-homogenization (eg, nugget effect), 10-20 g or less material should be analyzed to obtain representative results (M. Muller, Universitat). Mainz, page (2001)].

For this reason, the method of the invention is carried out for a number of hours, in particular for samples known to be heterogeneous, to obtain representative results from the mean.

Dry heat treatment is also referred to as roasted.

For the purposes of the present invention, dry heat treatment means that the sample has a liquid content of up to 5% by weight immediately before or during roasting.

One or more reducing agents are introduced during the dry heat treatment. As the reducing agent, it is preferable to use hydrogen gas or a mixture containing hydrogen gas.

The reducing agent may be introduced continuously, semicontinuously or batchwise. The reducing agent is preferably introduced continuously. The flow rate is set such that sample (g) and up to 1500 ml of H ₂ per hour are supplied to the sample. It is preferred to feed the sample (g) and 500-1000 ml of H ₂ per hour to the sample.

Dry heat treatment is carried out at a temperature of 400 to 1200 ° C, preferably 600 to 1000 ° C, particularly preferably 700 to 900 ° C. Very particularly preferred embodiment is a heat treatment at a temperature of 800 ° C.

Dry heat treatment is carried out for a time of 0.5 to 10 hours, preferably 1 to 4 hours, particularly preferably 1.5 to 3 hours. In a very particularly preferred embodiment, the dry heat treatment is carried out for 2 hours.

In order to heat the sample at the desired temperature for the desired time, it is advantageously moved to a space suitable for this purpose. This space will hereinafter be referred to as a furnace. Suitable furnaces for the purposes of the present invention are, for example, smelting furnaces, heat treatment furnaces, tube furnaces, chamber furnaces, muffle furnaces, air convection furnaces, vacuum furnaces, rotary tube furnaces or convection drying ovens. Preferred furnaces are tube furnaces.

Extraction takes place in an oxidation medium. Particularly preferred is a medium in which chlorine is produced as it is at the time of occurrence. According to the invention, mixtures of hydrochloric acid and nitric acid are preferred, preferably mixtures of hydrochloric acid and nitric acid in a volume ratio of 3: 1, which are also known to those skilled in the art as aqua regia. In addition, according to the invention, mixtures of hydrochloric acid and hydrogen peroxide are preferred.

According to the invention, the extraction takes place at temperatures between 20 ° C and 200 ° C. Extraction preferably begins at low temperature, for example room temperature, and the temperature is increased step by step.

Extraction can occur in the presence or absence of sample movement. It is preferable to start without sample movement and end with sample movement to extract.

The duration of extraction is from 10 minutes to 10 hours. The duration of extraction at room temperature is preferably 1 to 10 hours, preferably 2 to 8 hours, very particularly preferably 3 to 6 hours. The duration of extraction at elevated temperatures, ie above room temperature, is preferably 1 to 60 minutes, preferably 5 to 30 minutes, very particularly preferably 10 to 20 minutes.

In a particularly preferred embodiment, the extraction begins at a holding time of 4 hours at room temperature and continues with the following heating profile, often with shaking:

15 minutes at 60 ℃,

15 minutes at 80 ℃,

15 minutes at 100 ℃,

15 minutes at 180 ℃.

After the sample is extracted, the precious metal is quantitatively measured using atomic spectrometry. According to the invention, the measurement of the precious metal is carried out using ICP-MS (inductively coupled plasma mass spectrometry). This method is described, for example, in "Inorganic Mass Spectrometry, Principles and Applications" J.S. Becker, WILEY, 2007, ISBN 978-04-0470-01200-0; Houk, R. S., Fassel, V. A., Flesch, G. D., Svec, H. J., Gray, A. L. and Taylor, C. E., Inductively coupled argon plasma as an ion source for mass spectrometric determination of trace elements. Analytical Chemistry 52, 2283-2289 (1980); US 5,218,204 and US 6,265,717 B1. These documents are fully incorporated by reference.

Measurement systems suitable for the present invention include the following basic components:

-Sample introduction system (flow injection sample introduction system), nebulizer, spray chamber for measuring liquid samples using internal standardization

ICP flame as an ion source for argon plasma generated by high frequency induction

-Interface to connect plasma operating under atmospheric pressure to mass spectrometer under high vacuum

A lens system for focusing / guiding ions in the reaction / collision cell; Use custom gases in the cell to minimize spectral interference

4-pole mass filter

-Detection device

Vacuum system for connection, ion vision, quadrupole and detector

-Data processing and evaluation device

The measurement system must be stable against the matrix influence on the sample, ie the system stability must be guaranteed or the change in signal strength must be corrected through internal standardization. Possible systematic errors due to matrix-based mass spectroscopic superposition provide an effective way to minimize the required interference, for example in the form of a collision / reaction cell in ICP-QMS. Solutions to this problem are known to those skilled in the art.

The following examples illustrate the invention without limiting it in any way.

Example

For all steps performed below, the acid, water and gas used must be free enough for the element to be determined. Apply them to the equipment used.

Homogenization

As the sample material, "Merensky Reef ore" under the trade name SARM 76 commercially available from MIKTEK, South Africa was used. This material is milled, ie homogenized in the sense of the present invention, and has an average particle size of 70 μm determined by laser light scattering using equipment from Sympatek with evaluation software WINDOX. No further homogenization was performed.

Step (a): Dry Heat Treatment (Roasting)

device:

Small fused silica boat of approximately 40 x 13 x 11 mm (L x W x H) (external dimensions)

Large fused silica boat approximately 140 x 23 x 17 mm (L x W x H) (outside dimensions with eyelet)

Marked metal rods to introduce large fused silica boat

Molten silica tube with spherical ground connection and NS 29/32 lower ground connection

Tube furnace Carbolite Model STF 15 / --- / 180

reagent:

Hydrogen: Purity 99.999% by volume or more

Nitrogen: purity 99.999 volume% or more

Shield gas: Shield gas 5 available from Praxair

Up to 7.5 g (+/- 0.1 g) of sample was weighed within 0.1 mg in fused silica boat. A Mettler AT 250 analytical balance was used for this purpose. The boat was placed in the middle of a large fused silica boat. While heating the tube furnace to the final temperature, the tube furnace was flushed with nitrogen at about 4 standard l / h flow rates. After the indicator of the furnace showed 800 ° C., the charged fused silica boat was pushed into the middle of the tube furnace. After at least 10 minutes of "flushing time", the gas was switched from nitrogen to hydrogen or a hydrogen-comprising gas mixture and the nitrogen was blocked. The flow rate of hydrogen or hydrogen-comprising gas mixture was recorded. The sample was then reduced for 2 hours at the final temperature under hydrogen or a hydrogen-comprising gas mixture. The gas was finally converted back to nitrogen (flow rate about 4 standard l / h) and the introduction of hydrogen or a hydrogen-comprising gas mixture was stopped. After an additional "flush time" of 10 minutes, the fused silica boat was pulled into the "cooling zone" of the fused silica tube. After cooling, the sample was reweighed. Loss on ignition was calculated according to the difference from the initial weight.

Each final temperature, hydrogen or hydrogen-comprising gas, and the flow rate of hydrogen or hydrogen-comprising gas are shown in Table 1.

Step (b): Extraction from Oxidation Medium

The sample from step (a) was weighed in a 100 ml volumetric flask and mixed with aqua regia (20 ml). “Aqua regia” is a freshly prepared mixture of hydrochloric acid (about 1.18 g / ml density) and nitric acid (about 1.41 g / ml density) in a 3: 1 volume ratio. Then it was left at room temperature for 4 hours. While often shaken, the samples were treated in a hotplate according to the following heating profile:

15 minutes at 60 ℃,

15 minutes at 80 ℃,

15 minutes at 100 ℃,

15 minutes at 180 ℃.

After cooling to room temperature, the volumetric flask was filled with deionized water to the mark. The clear supernatant was diluted 1-10 times by the addition of an internal standard. As an internal standard, a mixture of indium, holmium and thallium at a concentration of 10 μg / l based on the solution to be measured was added. This solution was analyzed.

Blanks were performed according to the above disclosure.

Step (c): Atomic Spectroscopy Determination of Precious Metals by ICP-QMS

The analysis was performed using an Agilent 7700x ICP-MS instrument equipped with an integrated sample introduction system (ISIS) and high matrix interface (HMI).

Suitable operating conditions for conducting the assay are as follows:

Acid concentration: matches the sample

Measuring range: 0.1 to 30 μg / l

Calibration: 2/10/30 μg / l

Atomizer pump: 0.08 rps

Nebulizer: Mainhard; Spray chamber: Scott type; Temperature of spray room: 2 ℃

Gas setting: carrier gas: 0.7 l / min; Plasma gas: 0.9 l / min: cooling gas: 15 l / min; Dilution gas: 0.44 l / min; Cell gas: helium 4.4 ml / min; Reaction mode: ON

Plasma conditions: RF power: 1550 W; RF matching: 2.1 V; Sample depth: 8 mm; Torch-H: 0 mm; Torch-V: 0.2 mm

Ion lens: extraction 1: 0 V; Extraction 2: -195 V; Omega bias: -110 V; Omega lens: 8.2 V; Cell inlet: -40 V; Cell outlet: -60 V; Deflection: -0.6 V; Plate Bias: -60 V

Octode parameter: OctP RF: 170 V; OctP bias: -18 V

Q-pole parameters: AMU gain: 122 V; AMU offset: 127 V; Axial gain: 0.9992; Axis offset: 0.06; QP bias: -15 V

Detector parameters: discriminator 4.5 mV; Analog HV: 1699 V; Pulse HV: 933V

SARM 76 assay results Authorized value
(Payment method) Comparative Experiment 1
(Without working element) Comparative Experiment 2
(Reduction agent absent) Final temperature n.f. n.f. 800 ° C gas n.f. n.f. N ₂ flux n.f. n.f. 4 l / h mg / kg mg / kg RSD mg / kg RSD Pd 1.50 to 1.57 1.05 1.41 1.18 8.27 Pt 3.50 to 3.68 0.90 4.95 3.23 8.56 Rh 0.248 to 0.264 0.22 1.76 0.19 3.64 Au 0.22 to 0.25 0.26 62.45 0.18 2.99 Experiment 1 Experiment 2 Experiment 3 Final temperature 800 ° C 800 ° C 800 ° C gas H ₂ H ₂ H ₂ flux 1.6 l / h 4 l / h 10 l / h mg / kg RSD mg / kg RSD mg / kg RSD Pd 1.39 7.52 1.37 5.32 1.38 4.29 Pt 3.81 5.02 3.64 9.89 3.80 4.79 Rh 0.22 3.67 0.22 9.73 0.22 4.89 Au 0.24 11.28 0.21 13.37 0.57 124.73 Experiment 4 Experiment 5 Blank SiO ₂ Final temperature 600 ℃ 800 ° C 800 ° C gas H ₂ Shield gas H ₂ flux 4 l / h 4 l / h 4 l / h mg / kg RSD mg / kg RSD mg / kg RSD 1.36 3.15 1.39 3.22 0.00 108.11 3.53 8.23 3.65 4.70 0.02 41.25 0.22 1.75 0.16 3.44 0.00 64.41 0.21 31.79 0.21 7.92 0.00 764.81

n.f .: No value given or not applicable.

RSD: relative standard deviation of the individual results in%; n = 6, ie each measurement was performed six times.

Claims (5)

(a) dry heat treating the homogeneous sample in a reducing atmosphere;
(b) extracting in the oxidation medium; And
(c) atomic spectrometric determination of precious metals using ICP-QMS
A method of analyzing precious metals in mineral and / or ceramic matrices containing 0.03 to 500 mg / kg content. The method of claim 1,
The precious metal is platinum metal. 3. The method of claim 2,
The precious metal is platinum, palladium, rhodium and / or iridium. The method of claim 1,
The precious metal is rhenium. The method of claim 1,
How precious metals are gold.