An estimated 3 million LCD screens are recycled in Germany per year. However, their backlighting system often contains mercury, which means they are classified as ‘hazardous waste’. In the past, these devices could only be dismantled via a complex manual process which put workers at risk.
This article was previously published in Recycling Technology >>
Erdwich Zerkleinerungssysteme GmbH has developed an alternative solution for this niche market – an automatic processing system that enables mercury and other valuable raw materials to be easily extracted. The company observes that flat-screen monitors comprise up to seven layers. In addition to the valuable metal compound indium tin oxide, they also contain mercury in their backlight components.
According to German law, these devices must be handled in such a way that human and environmental exposure to this toxic substance is prevented. Furthermore, the country’s Federal Environment Agency has laid down recovery quotas for electronic waste, which means that monitors cannot be consigned to disposal in landfill.
For a long time, the process of dismantling these devices has been too complex to be performed by machines and has therefore been conducted manually. In particular, the dismantling of LCD screens with flat backlighting has hitherto been a complicated and time-consuming process.
‘It is necessary to remove up to 30 screws just to separate the two halves of the housing,’ explains Harald Erdwich, head of sales and marketing for recycling expert Erdwich of Kaufering in Germany. ‘This dismantling procedure takes trained personnel between eight to 20 minutes, depending on the construction of the monitor and the type of background lighting.’
Four-stage treatment process
Erdwich has now developed a time-saving system that uses camera equipment and robots to automatically cut open and dismantle monitors measuring up to 55 inches in size under safe working conditions. In a process consisting of four stages, the individual screens are first placed on a conveyor belt and transported to a sealed processing chamber where they are put into the required position.
A robot fitted with four different locking arm mechanisms centres each one and subsequently raises it into the final position for the treatment process. An articulated robot then measures the contours of the screen glass using a camera system. As soon as the co-ordinates have been calculated, the robot cuts open the housing; the chippings from the cutting process are automatically extracted through a filter system.
After each cutting cycle, the tools are automatically examined by a camera to enable any breakage or damage to be detected promptly. The cameras also examine the degree of wear on the cutters. In the third step, the various layers – such as the multi-ply polarisation filter and the diffuser – are removed in a low pressure chamber.
Up to 45 panels per hour
The final step involves the removal of the background lighting. ‘A closed waste container is installed directly in the chamber for the gas discharge lamps that contain the mercury,’ Erdwich notes. ‘At the same time, the exhaust air is extracted in a controlled process and collected by means of a mercury filter system, in which the harmful metal is converted into a non-toxic sulphide.’
Finally, the screen is transported from the chamber and its processing continues in a downstream system. It makes particular sense to recycle valuable ingredients such as the indium tin oxide, which is located in conductor tracks on two thin glass panels and which can be used in the production of printed circuit boards.
Global demand for this metal compound is on the increase and prices have shot up in recent years. In addition to the LCD panels of up to 55 inches in size which can be dismantled with the aid of robots in the aforementioned automatic processing facility, Erdwich also offers a cutting system for LCD monitors of up to 25 inches.
‘Previously, it was only possible to dismantle between four to seven monitors per hour by hand, but this system can handle up to 45 monitors per hour – with absolutely no health risks,’ Erdwich explains.
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