Good questions Zeev, allow me to attempt to answer them. The prills (molten metal spherical pellets) were analyzed for elemental content by using emission dispersion spectroscopy which is also called energy dispersive x-ray analysis or EDX. The sample is placed in a scanning electron microscope (SEM) and you get the photomicrographs. In the imaging mode the electron beam is rastered back and forth across the sample to paint the picture.
The emission is due to electrons in and x-rays out. The lateral spatial resolution of the test is slightly larger than the incident 20,000 volt (20 keV) electron beam which is about 50 Angstroms (0.0000005 cm), i.e. very small on the order of 20 atomic diameters. In the EDX mode the electron beam is held stationary. The energetic electrons excite the core electrons of the target atoms to elevated energy levels. De-excitation through characteristic x-rays then occurs. Each different element has different core energy levels and hence different characteristic x-rays. The emitted x-rays are identified by determining their energies with an x-ray detector.
Unfortunately I don't have the right reference book with me so I can't tell you the energy levels for Te and emission intensities. However, the annual report says on pg 5, "This fire assay development is yielding positive results with gold and PGE's produced as physical metal prills." My interpretation of that is the sample has already been refined and most contaminants like Te have been removed. EDX has a detection limit of 0.1% by weight so it's not sensitive to impurities. Modern SEM-EDX systems analyze the spectra for you and label all peaks. So if it doesn't get labelled it's not there in a high enough concentration to get detected. I did calculate a range of the x-ray levels to expect from the CRC Handbook x-ray Spectra table in keV:
Mg, 1.26, 1.3
Pb, 9.2, 14.8, 72.9
Ru, 19.2, 22.1
Rh, 20.1, 23.2
Ag, 22.0, 25.5
Te, 27.3, 31.8
Pt, 13.0, 65.2, 78.1
Au, 13.4, 67.1, 80.4
So you can see that Te peaks would appear just above Ag on the Au spectra but they're not there. On the Rh spectra Te peaks would appear above the Rh lines and below the high energy Pb lines, but they don't. On the Pt spectra Te would appear between the low and high energy Pt peaks but they don't. Ergo, ain't no tellurium present in concentration greater than 0.1% by weight after refining.
1. Photos are of refined metal prills and not a matrix.
2. Electron probe spectra and not optical spectroscopy.
3. Within detection limits there is no Te present.
BTW, ICP is short for inductively-coupled plasma mass spectroscopy which is a far more sensitive technique than EDX. However, no ICP data has been presented in public to my knowledge. Not showing ICP data has no significance whatsoever. |
