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Glass portion

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Collected display devices, the source of 93.3% of the recycled glass portion

Source of the recycled glass portion

In Austria, about 12,000 tonnes of glass are recovered from waste electrical and electronic equipment each year. This is equivalent to the mass of about 23 million glass wine bottles (0.75 l), for example.

The graph below provides an overview of how much glass is recycled from each of the five collection and processing categories for the collection of waste electrical and electronic equipment.

Glass Mass [t] Proportion [%] 
Display devices 11.132 93,3
Gas-discharge lamps 805 6,7
Total 11.937 100,00

 

Recycling processes for glass

Glass is primarily recovered from the collection and processing category of display devices, with a small amount also coming from the category of gas-discharge lamps.

Within the collection and processing category of display devices, two basic types of devices are distinguished:

  • tube-based devices, which contain a cathode-ray tube, and
  • flat-screen devices (which are thinner and do not rely on CRT technology), e.g. LCD screens (liquid crystal display) and plasma screens.

Currently, tube-based devices are more commonly seen in waste electrical and electronic equipment, but the proportion of flat-screen displays is expected to increase sharply in the next few years.
For tube-based devices, the screen coating (which contains toxic cadmium and yttrium compounds) must be removed.
To do this, the metal clamping ring is first removed from the picture tube, and hot wire is then used to separate the tube into two halves: the screen glass (barium glass) and the cone glass (lead glass). The metal shadow mask is removed as well. Finally, the screen coating is vacuumed off and captured in collection containers. The screen coating is stored in an underground disposal site.
Currently, most of the barium and lead glass from the picture tubes is used to make new display devices in Asia, and a smaller portion is also processed further for use in recycled building materials.

The first step in processing gas-discharge lamps is to remove the aluminium end caps.

Collection categories from which the 12,000 t of glass are recovered

This is followed by a sifting and dedusting step in which the mercury-rich fluorescent dust is extracted. Next, the aluminium end caps and the glass are placed in a furnace to evaporate the diffused mercury from inside the glass at about 500° C, and from the metal parts at about 250° C to 300° C.

The entire process takes place under negative pressure to prevent mercury fumes and dust from escaping. The process air is cleaned by passing it through an activated carbon filter. The new machine at Saubermacher AG in Vienna can also process bulbs in shapes beyond the traditional straight tube (ring or U-shapes, compact fluorescent bulbs), and received an Austrian National Environmental and Energy Technology Prize in the “Climate and Environment” category in 2012 (see Recycling light bulbs).