Several cities around the world retrofit conventional lamp technology to LED (light-emitting diode) technology. According to a report from Navigant Research, the market share of LEDs in street lighting worldwide will grow from 53.3 percent in 2014 to 93.8 percent in 2023. LEDs are, inter alia, well-known for their energy efficiency, design flexibility, light dispersion or durability. Despite everything, they are not indestructible. Sooner or later it will become necessary to replace a LED module.
But why is there a need for research on efficient recycling processes? The relatively new lighting technology is manufactured using a variety of materials. Not only glass, plastic, copper, ceramic or aluminium. The most valuable materials are found within the LEDs themselves. They are indium and gallium inside the semiconductor diode and rare earths like europium or terbium in the phosphor. This is a reason for the relatively high manufacturing costs.
According to Fraunhofer Institute for Silicate Research ISC in Germany, there are no suitable recycling processes available today for these items. For this reason, Fraunhofer investigates efficient recycling opportunities and developed a method to mechanically separate LEDs. The aim is to reuse the rare materials.
“Right now recyclers are starting to receive LED products, but currently they are often simply stored as there is no suitable recycling process available yet. The main goal is to recover the valuable materials. It’s only a matter of time until recyclers will have to start processing LEDs,” says Jörg Zimmermann from the Fraunhofer Project Group for Materials Recycling and Resource Strategies IWKS in Alzenau and Hanau of the Fraunhofer Institute for Silicate Research ISC.
The Fraunhofer researchers break the LED lamps into their component parts without destroying the LEDs themselves. For this, an electrohydraulic comminution process is used. Shock waves created by electrical impulses in a water bath separate the individual components at their predetermined break points. The components can then be recycled individually. The researchers have adapted their experimental setup to retrofit lamps, which resemble traditional light bulbs or fluorescent tubes and can be used in the same standard sockets. “This method works in principle also for other sizes, for instance with LEDs from television sets or with automobile headlights, as well as with other electronic products,” explains Zimmermann.
A clear separation of the components is a requirement for an efficient recycling process. “To efficiently separate and recycle all components of a LED lamp, an entirely different approach is necessary – one that produces large quantities of semiconductor and phosphor materials,” says Zimmermann. It is much more difficult to separate the resulting mixture of materials if the entire retrofit is shredded. Breaking LED lamps down to the component level also makes it easier to recover greater quantities of the materials contained in them. This can be achieved by collecting large quantities of similar components in which the concentration of individual elements is already higher. If the recycling involves larger quantities, the entire process can be profitable.
“We’re still testing whether the comminution process can be repeated until the desired materials have been separated,” says Zimmerman. According to Fraunhofer ISC, the researchers can adjust the parameters of the experimental setup like the type and quantity of the fluid, the container size, or the electric pulse voltage in such a way that separation occurs precisely at the specified break points. “In particular, it is the number of pulses that determines how the components will separate,” he says. The electrohydraulic comminution process is currently being investigated in detail and improved further. “Our research has demonstrated that mechanical separation is a viable method for improving the economics of LED lamp recycling,” says Zimmermann.
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