The presence of mercury in flat panel displays, such as laptop monitors and LCD TVs, has thrown up potential health and safety issues in a WRAP-commissioned study into the technical and commercial potential for recycling the items.
The research, which was carried out by environmental consultancy Axion Consulting, aims to help WRAP understand the recycling outlets for flat panel displays (FPDs), as there are currently no automated commercial processes in the UK and Europe.
However, due to an increased uptake in items, WRAP anticipates that the number of FPDs in the WEEE waste stream will rise “dramatically” in the next few years, requiring a suitable recycling outlet.
In particular the trial looked at the presence of mercury in the cold compact fluorescent light in the ‘backlighting’ system for LCD TVs, laptop computers and desktop monitors. The existence of this mercury means that end-of-life FPDs are classed as hazardous waste.
The study took the form of four demonstration trials. The first looked at the manual disassembly of FPDs, then the shredding of FPDs, the optical sorting of shredded FPDs using TiTech optical sorting technology and mercury decontamination.
The manual disassembly, which took place at Bruce Metals in South Yorkshire, was intended to remove the mercury content from the FPDs. The stripping of the items also allowed the researchers to investigate the potential harm and exposure of workers in a commercial operation.
Mercury
Mercury remained a key issue throughout the trial, with it being stated that there were a number of backlight breakages in the manual disassembly element of the trial. And, as the trial was undertaken without significant time pressures, it was suggested that a commercial operation would face a higher level of backlight breakages.
The conclusion of the WRAP study highlighted that employees at an FPD recycling facility would be subjected to levels of mercury “higher than is acceptable”. However, it suggested that this could be reduced with personal protective equipment and local extract ventilation.
Furthermore a suitable washing medium to remove mercury from the FPD items could be not found in the trial, with results from the large-scale trial proving inconclusive. And, even under laboratory conditions, there was an uncertainty as to whether mercury could be completely washed from the shredded FPDs.
In a bid to improve on this, the researchers then used Aqua Regia – a strong acid – to attempt to remove mercury from the FPDs. The acid removed more than the water washing technique but only 56% of mercury added to the shredded material could be accounted for in output fraction.
The research concluded that more work would need to be done to establish a wash capable of removing high levels of mercury in a commercial process, as well as a greater understanding of where the washed mercury goes and alternative methods for its removal.
Facility
Addressing the potential for delivering a large-scale FPD recycling facility, the research states that a 20,000 tonnes-a-year capacity facility would potentially cost £3.798 million to develop, which would be capable of processing five tonnes of FPDs each hour.
It said the plant could consist of:
-
A three-shaft shredder;
-
8mm flip-flop sieve to remove the fines;
-
Mercury washing stage to recovery mercury;
-
Dryer to dry the shred prior to separation;
-
Air ballistic unit to remove the thin films;
-
Magnet to remove ferrous metals;
-
Eddy current system to remove non-ferrous metals and circuit boards;
-
TiTech x-tract machine to remove glass/film composite; and
-
TiTech PolySort to separate polymers
Related links
However, the study claimed that there were issues relating to capture rate of plastics found in FPDs, with near-infrared sorting equipment used in the trial unable to detect a commercial viable level of the black plastics present in the FPD items.
Source: www.letsrecycle.com
