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Mercury washing of flat panel displays proves to be limitation in recycling study

A study on recycling flat panel display (FPD) technologies, such as LCD TVs, desktop monitors, laptop computer screens and plasma TVs, showed “unexpected” inconclusive results when washing material clean from mercury, the Waste & Resources Action Programme (WRAP) has found.

Its report, Demonstration of Flat Panel Display Recycling Technologies, looked to find a way to commercially, safely and economically recycle FPD technologies, which have cold compact fluorescent lamps inside them containing mercury.

Not currently available in the UK or Europe, commercial FPD recycling will be necessary in the future. WRAP predicts that, with increasing sales in the next three to five years, the amount of FPDs to be disposed of will be 146,567 tonnes by 2016/17.  

Environmental consultancy Axion Consulting carried out the research along with waste electrical and electronic equipment (WEEE) recycler Bruce RID Recycling, shredder Erdwich Zerkleinerungssysteme, sorting system provider Titech and specialist recycler for light bulbs containing mercury Mercury Recycling.

The fluorescent lamps were removed from the various products and then separately treated. But to simulate a more commercial process, where the FPDs would be shredded whole, shredded material was added to the crushed backlights and washed of mercury.

The mercury washing trial produced “unexpected” results that did not prove that mercury- contaminated shredded FPDs could be washed clean by the process at Mercury Recycling. Water could not remove the mercury but nitro-hydrochloric acid could. However, it is highly toxic and corrosive, so may not be suitable in a commercial plant. In some cases, measurements found an increase in mercury present after washing compared with before and, in most cases, washing material twice did not result in a noticeable decrease in mercury levels. 

It is thought the inconclusive results are due to poor mixing of broken tubes back into the shred, the possibility that absorption and adsorption of mercury by the shred components affected removal and difficulty in getting a representative sample of shred and potential errors at the analysis stage.

WRAP sustainable products programme manager Gerrard Fisher said: “In the mercury trial, we found it was difficult to know where the mercury was going, so work now will focus on this area.

“The downstream processes are good at separating out materials and it was a very positive exercise. One of the areas we were looking at in this research was whether a plant would be able to handle all FPD products in the same process, which it could. But if we can crack mercury washing, that would be a real breakthrough.”

In the sorting stage of the trial, metal and glass/film could be successfully recovered. But using near infrared sorting plastic separation did not work because of the wide range of polymers used and a high quantity of black plastic which the sorter cannot see.

However, LCD and plasma TVs exceeded the current recycling target of 65%, achieving recycling rates of 72% and 69% respectively. Desktop monitors reached 62% while laptop screens hit 49%. No energy could be recovered from any of the FPDs.

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