Recycling critical raw materials from waste electronic equipment

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Recycling critical raw materials from waste electronic
equipment
The plastics fraction, steel, aluminum and PCBs are passed on to the relevant markets for
materials recycling. The recovery of precious metals from PCBs is discussed in Sections 3.9
and 6.1. The CCFL lights are sent to general lamp recycling where the proper treatment of
mercury is a priority. In addition, the glass and some of the metallic components in the
sockets are sent to materials recycling. The luminescent substances themselves and any
contaminants from broken glass, mercury and other materials are usually deposited
underground (Martens 2011). The rare earths contained in the luminescent materials are
currently not recycled (see Section 6.3).
Instead of manual disassembly, the complete or partly disassembled display unit can be sent
for mechanical pre-treatment where the devices are shredded in an airtight sealed shredder
and the mercury eliminated from the process air. However, this process also fails to address
all the issues as, according to Böni & Widmer (2011), the whereabouts of all the mercury is
not conclusively explained.
A further option is thermal treatment of the whole or partially disassembled display units
(Böni & Widmer 2011, Martens 2011).
The displays are usually recycled thermally in waste incineration plants or in the Waelz kiln
process for steel mill dust. The organic components (liquid crystals, polarization filters,
resins) are incinerated and the glass along with the oxidized metals bound in an inert slag
(Martens 2011). The indium contained in the displays is lost through dissipation.
2.8 Potential for optimization in the recycling chain
From a resource point of view, manual pre-treatment with complete removal of the
assembled PCBs and subsequent recovery of the precious metals is to be recommended
(see Section 6.1). This allows utilization of the synergies associated with the common
process of manually removing the mercury-containing CCFL lamps.
There are currently no suitable separation and refining processes for recovering the indium
from the display units and the rare earths from the background illumination (see Section 6.3
and 6.4), so that these substances have not been included in materials recycling so far. In
view of the emerging developments in this field, it is worth considering storage of the display
units and the luminescent material for recycling at a later date. These measures can be
deemed practicable as both fractions already occur in a concentrated form in the
disassembly process 12 .
12
The principal source of luminescent materials is, however, not the background illumination from flat screens
but other illuminants (including fluorescent tubes) and screen technologies (cathode ray tubes).