Page 54 from: October 2014

54 October 2014

XRF technology
a flexible metals
sorting friend
Manual, sink-float and X-ray transmission techniques continue to be

used extensively in the sorting of metals – but all have their limita-

tions. By comparison, X-ray fluorescence technology is versatile and

not limited to one kind of material or application. Furthermore, mois-

ture, colour and surface contamination cause no significant disrup-

tion to the detection process.

Understood and used around the world, the US Institute of Scrap Recycling Industries
has defined various terms for mixed metals

such as, for instance, Zorba, Zebra, Zeppelin

and Zurik. Currently, the most-used methods

for sorting Zorba, Zurik and metals of similar

composition are sink-float separation proc-

esses or sensor-based sorting systems based on

camera technology.

T E C H N O L O G Y By Martin Weiss

Brass: clean (left) and dirty.

Copper: clean (left) and dirty.

The proportion of operations using manual

sorting remains considerable as industry strives

to satisfy modern life’s huge appetite for

aluminium and a range of other non-ferrous

metals such as copper, brass, nickel, stainless

steel, tin, zinc and lead. Manual sorting results

in very high purities but the process is extreme-

ly cost-intensive in industrial countries

and should therefore only serve as a final check

and for quality control. Furthermore, not all

metals can be sorted manually as the visual

difference is simply non-existent. Grey metals

can only be sorted to a certain extent and stain-

less steel, for instance, cannot be visually sepa-

rated at all.

Only an emergency solution
The sink-float process is used in many treat-

ment plants to separate materials of different

densities. This process requires huge quantities

of water and very expensive additives such as

ferro-silicon. The separation efficiency is also

quite limited and, as a result, only aluminium

can be separated from heavy metals and other

impurities that are low in density such as plas-

tics and wood. The mix of heavy metals must

be treated in another way – or even has to be

sorted manually. Most heavy metals are export-

ed to Asia for further manual sorting, which

increases the dependence on these countries

– particularly China – and should therefore be

considered only an emergency solution. In

addition, the aluminium gained cannot be

further separated.

Use of sensor-based sorting systems represents

an economic and reasonable alternative to

manual or density sorting. Sorting by colour

using a colour camera is one possibility of the

sensor-based sorting technology. However, the

separation efficiency is quite limited and there-

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