Figure 1
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Dry sampling
. For pharmaceutical catalysts, dry sampling begins with a thermal oxidation step to remove built-up organic contaminants,
carbon, and moisture from the catalyst materials. Removing contaminants helps increase sampling accuracy significantly. A
low-temperature burn in a tray furnace removes moisture, followed by a higher-temperature burn to remove carbon without volatizing
the precious metals. Once these contaminants have been removed, dry sampling involves grinding the spent catalyst into smaller
and smaller particles that are passed through a series of screens. Properly following this process of particle size reduction
and successive screening can provide a typical representative sample accuracy of ± 2%. (see Figure 1).
Figure 2
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Melt sampling and solution sampling.
Similarly, melt sampling (see Figure 2) and solution sampling (see Figure 3) involve the reduction of spent catalysts and
their PGMs into slurries and liquid solutions, respectively, from which the amount of precious-metals content can be accurately
determined.
Figure 3
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The choice of sampling approach is often critical to the amount of precious metal recovered from a spent catalyst. Clear communication
between the refiner and the pharmaceutical manufacturer and, in some cases, a third-party expert hired by the pharmaceutical
manufacturer to monitor the process (known as an "umpire") is necessary to ensure that no questions arise regarding the choice
of sampling method and/or the final results of the sampling process.
Handling practices.
A pharmaceutical manufacturer can check on certain best practices to ensure that a precious-metals refiner is handling its
spent catalyst material properly. The material should be properly stored at the refiner, weighed on certified, inspected scales,
and assigned a tracking or control number. The measured weight should be in agreement with the value determined by the pharmaceutical
manufacturer prior to shipping the material to the refiner. The material should be supported by proper documentation by the
refiner, including confirmation of the materials' description, piece counts (if applicable), and weights. Any differences
between the refiner's information and that of the pharmaceutical manufacturer should be documented.
Assays
. Once samples are obtained, the refiner and the pharmaceutical manufacturer typically assay the samples for their precious-metals
content independently. Ideally, the percentage values of PGMs found in the samples by the two assays agree fairly closely.
If not, the two values can be averaged to obtain a final agreed-upon figure for valuation of the PGMs in the spent catalyst.
Specialized instruments designed for materials analysis are used to perform assays on the sampled materials. These instruments
include machines capable of performing X-ray fluorescence measurements for identifying contaminants still contained within
the samples, atomic absorption and inductively coupled plasma emission spectroscopes and tools for performing classic volumetric,
gravimetric, and fire assay techniques.
The type of materials to be assayed will determine the analysis approaches and equipment used in the assay. The techniques
described above have been approved by the American Bureau of Standards and by the New York Metal Exchange/Commodities Exchange.
In combination, these methods provide an accurate means of determining the amount of precious-metals content in spent pharmaceutical
catalysts.
Advanced laboratories typically perform assays in triplicate to ensure the accuracy of PGM measurements. In a true partnership,
a precious-metals refiner will invite a pharmaceutical manufacturer to not only be present while materials are being sampled,
but also to conduct their own independent analysis.
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