Advanced sorting of aluminium
alloys thanks to XRF-BS
The new technology combines XRF with x-ray
back scattering and is presented as an alterna-
tive to laser induced breakdown spectroscopy
(LIBS) for the sorting of aluminium alloys.
X-ray back scattering is an underlying phenom-
enon of fluorescence and is usually considered
as a rumour in the XRF spectrographic sorting
analysis. Instead of being represented by a few
high intensity peaks of specific energies, it is
characterised by a continuous distribution of
low intensity photons, the distribution profiles
of which are characteristic of the presence of
the various metals.
XRF-BS can identify metal concentrations
down to 0.2% which makes it a performing
solution for sorting the different aluminium
alloys and a competitive alternative to LIBS. So
what are the main benefits of XRF-BS versus
Unlike XRT which performs a readthrough
analysis, both XRF-BS and LIBS perform a ‘sur-
face’ analysis. This means that the accuracy of
both the LIBS and XRF-BS readings is impact-
ed by dirt, painting or oxidation on the surface
of the material to be analysed. Accuracy
depends on the thickness of the contamination
and the penetration of the reading.
XRF-BS penetration is typically around 100-200
microns while LIBS penetration is usually
around 10 to 20 microns depending on the
level of energy used for the laser source and
the type of laser lens. The typical thickness of
painting on aluminium profiles is over 40
microns which is less than XRF-BS penetration
and greater than LIBS’.
CONTINUOUS VS DISCONTINUOUS
XRF-BS performs a continuous reading while a
LIBS reading is discontinuous, making it effec-
tively a sampling analysis. LIBS is certainly good
enough on the tailings of aluminium sheets at
stamping plants. In this case, the material sur-
face is always clean and every piece is homoge-
nous in composition meaning that a shallow
surface sampling analysis provides an accurate
analysis of the whole material. Last but not least
in such an application, you know in advance the
limited different types of aluminium being pro-
cessed which helps the sorting.
In the case of aluminium scrap, the situation is
different meaning that deeper and continuous
analysis from the XRF-BS is a plus.
Reading distance is a sensitive element for
both XRF-BS and LIBS but is easier to control
in the case of XRF-BS.
XRF-BS readings must take place within a cer-
tain distance of the surface but this is no prob-
lem as the reading is continuous and material
is analysed from underneath while in free fall.
With LIBS there is the additional constraint of
staying within the focal length of the laser, typ-
ically around 20mm, which is not a lot consid-
ering the length of the piece and probable
misshaped aluminium profiles. Focal length
can be increased but that reduces the energy
and penetration depth.
Italian corporation SGM Magnetics, a leader in X-ray sorting technologies
for metal recyclers including x-ray transmission (XRT) and x-ray
fluorescence (XRF), is launching its latest proprietary technology called
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