Disposing of LEDs – does new technology mean new problems?
Light-emitting diodes (LED) can be found in screens as well as lamps. They are considered a more environmentally friendly lighting option than other types of lamps. However, LEDs contain some materials that can potentially be harmful if not disposed of properly, as well as lots of different reusable materials. What does this mean for recycling?
It is no longer possible to imagine life without LEDs: they are used in buildings, vehicles and street lighting as well as display technology, where they help produce a uniformly sharp and clear image on our smartphones, tablets, laptops, televisions and even large-format display screens. Despite their relatively long lifespan, sooner or later they too stop working and have to be disposed of.
Materials determine functions
LEDs contain a number of materials that are necessary for various functions. They consist of semiconductor materials including gallium nitride (GaN), gallium arsenide (GaAs), gallium phosphide (GaP) and indium gallium nitride (InGaN). An LED cannot emit light without these materials. LEDs also contain smaller amounts of the heavy metals lead and arsenic, as well as rare-earth metals and phosphorous compounds. The enclosure of an LED lamp is made of plastic or glass and metal, and is designed to protect the internal components and direct the light. LED chips are mounted on printed circuit boards. They are normally made of an insulating material such as glass fibre-reinforced epoxy resin and contain noble metals.
Hazardous substances and reusable materials in LEDs
Time and again, the processing of flat screens with LED backlights has given rise to speculation that they contain mercury and cadmium. Swico teamed up with Immark AG Schattdorf to investigate: it had chemical analyses performed on LEDs from TV and monitor backlights as well as LED lamps (older models) to determine what substances are present in LEDs and in what quantities (see table 1 and figure 1).
These analyses of hazardous substances identified barium and lead in every sample. Very small amounts of mercury were detected in two samples (0.05 and 0.01 ppm). The amount of cadmium in every sample was below the limit of detection.
In terms of reusable materials, there were large amounts of copper and silver as well as trace amounts of lanthanum (a rare-earth metal). The amounts of gallium and germanium were below the limit of detection.
The recycling company Thévenaz-Leduc SA also had LED filaments from newer, compact LED bulbs examined. Several elements underwent quantitative and others semi-quantitative analysis, and the results were made available to SENS (see table 1 and figure 2). Amounts of cadmium and mercury one and two orders of magnitude larger than those in the results of Swico’s analyses were detected. At 1,100 mg/kg and 48 mg/kg, respectively, the amounts of silver and lead were on a similar order of magnitude. This was also the case with the hazardous substances antimony and arsenic. The gallium content – 15,505 mg/kg – was remarkably high, placing it on a percentage scale.
Cadmium in QLED screens?
In the world of modern screen technology, OLED (organic light-emitting diode) and QLED (quantum dot light-emitting diode) are currently battling for a larger market share. Whereas OLED screens contain self-lighting pixels, QLED devices use a backlight based on quantum dots. This technology is distinguished by its greater detail, more accurate colours, higher contrasts and improved brightness. Although QLEDs have some advantages over conventional LCD or OLED displays, there are inherent environmental problems in their manufacture and disposal. Aside from the larger amounts of energy needed to manufacture them, it is predominantly cadmium, lead and other heavy metals that are used in QLED technology.
The European Directive “Restriction of Hazardous Substances in Electrical and Electronic Equipment“ (RoHS) aims to limit the use of harmful substances in electrical and electronic equipment. This also includes cadmium, where a quantity of less than 100 ppm is still considered cadmium-free. Temporary exemptions for use of the substances may be granted if the substances are not scientifically or technically replaceable, if an alternative is not permitted or would have a negative impact on human beings and the environment. This has permitted the use of cadmium in QLED technology since 2013. Owing to technological advancements in recent years, cadmium-free quantum dots are now available on the market, which means that an exemption is no longer justified. However, a considerable number of QLED devices containing cadmium are probably still in use today. These devices will be disposed of over the next few years. One square metre of screen area contains an estimated 0.2 grams of cadmium.
Consequently, the amount of cadmium from recycled QLED screens is likely to be fairly significant. A simplified calculation based on an estimated 500,000 televisions sold in Switzerland each year with an average diagonal screen size of 155 cm (60 inches) – which equates to around 1 square metre of screen area – produces approximately 30 kg of cadmium per year. This calculation assumes that QLED technology has a 30% market share and only QLED screens with cadmium-containing quantum dots are for sale. The actual quantity may be lower as the market leader Samsung now uses cadmium-free quantum dots.
As part of an amendment to the RoHS Directive based on a study carried out by the German Oeko-Institut in 2022, the European Commission will ban the use of cadmium-containing quantum dots because alternatives are now available that deliver the same performance. The question is what happens to QLED screens with cadmium-containing quantum dots when they are recycled.
Even small amounts of cadmium are toxic to humans and animals; it accumulates in the body and can cause cancer. Although there are many different sources of cadmium (waste incineration, steelworks, furnaces, cocoa, jewellery), the precautionary principle of environmental law requires that its emission be prevented at the source. Mechanical comminution with re-sorting causes the integrated LEDs and QLEDs in displays to accumulate in the plastic fraction. When plastics are processed, plastics containing cadmium are separated and then incinerated. The cadmium is oxidised and then removed by the flue gas treatment system of a modern incinerator. The risk of release during the treatment processes can be considered low. Nevertheless, the occupational hygiene rules must be followed at all times.
LED lamps: recycling developments
Once collected, lamps are sorted into various groups in order to prevent reusable materials and dangerous substances from mixing and diluting. LED lamps are separated from other lamps, such as gas-discharge lamps that contain mercury, and recycled separately. In recent years, Switzerland has made a number of attempts to recycle LED lamps. Building on these, SENS has granted two lamp recyclers permission to process LEDs. In an initial stage, these recyclers use technology that helps prevent mercury emissions in the event that other types of lamp are mixed in erroneously.
As with many other types of electrical and electronic equipment, the more effectively the appliances are sorted, the higher the recovery rates. There is an exceptionally large number of forms and material combinations due to the flexibility of LED lamp design. According to the recycling company Thévenaz-Leduc SA, the more specifically waste is sorted by glass or plastic enclosures, aluminium threads, etc., the higher the recycling rates. If all forms are mixed together, recycling rates have been below 50% so far. There is currently no benchmark minimum recycling rate for LED lamps.
Recycling approaches LED lamps
Recycling LED lamps separately opens up numerous possibilities in terms of the separation and recovery of specific dangerous substances and reusable materials. Various different approaches can be taken in practice, each of which prioritises different materials:
1) Focus on the enclosure made from ‘traditional’ reusable materials like aluminium or glass
2) Focus on the relatively abundant printed circuit boards that contain copper and, in some cases, noble metals like silver
3) Focus on LED chips or filaments containing rare technology metals, especially gallium and indium
No optimised approach or ideal combination has been selected yet. Recyclers are refining their methods continuously in coordination with the SENS Technical Commission.
Environmental and economic concerns relating to the recycling of LED lamps
The aforementioned approaches in the frame above are linked to the focus on the various components of an LED lamp: 1) enclosure, 2) printed circuit boards, 3) LED. Many target metals are mainly concentrated in one and/or the other component. When choosing a recycling method, we must consider the matter of environmental efficiency, that is, the environmental impact, relative to the cost-effectiveness.
With regard to the ecological relevance of LED recycling, the environmental impact of primary metal production – and thus the benefits of recycling these metals – can be compared for an initial point of reference1. In this process, the environmental impact is measured in eco-points according to the ecological scarcity method2. For example, economic inventories of the metals in LED lamps show3 that, based on currently available information, the environmental impact of the primary production of silver, which can be found in printed circuit boards and LED chips and filaments (see table 1), is approximately 15 times greater than for the primary production of indium, and approximately 90 times greater than for the extraction of gallium arsenide. In turn, the extraction of copper and aluminium – which can be found in printed circuit boards and enclosures – has an environmental impact one and two orders of magnitude lower than that of gallium arsenide, respectively.
Consequently, from an environmental perspective, approaches 2 and 3 appear advantageous despite the relatively low levels of target metals. However, approach 3 is not yet industrially viable in recycling, as confirmed by the study carried out by Nikulski et al. (2021). The study estimates that the recovery of technology metals from LED lamps currently has little economic potential, but that a focus on noble metals is most economically worthwhile4.
In practice, the crucial factor with regard to the recovery of raw materials from LED lamps is what fractions are produced by the process and which downstream buyers recycle them. Fractions rich in printed circuit boards from LED lamps can be separated, which brings great ecological benefits. However, it is currently difficult to cleanly separate LED chips and filaments in the initial stage of processing. Even if this were possible, it is not currently common for downstream buyers to be able to recover the broad range of target metals from LED lamps simultaneously5.
The LED recycling process must be viewed systematically
It is common knowledge that recovering economically and ecologically important materials from waste electrical and electronic equipment (WEEE) is not a matter limited to LED lamps alone. It affects a great deal of WEEE, especially mobile phones, screens and solar panels. LED lamps account for a fraction of a per cent of the total amount of WEEE in Switzerland, and the proportion of the actual light emitting diode within the LED lamp is also negligible. It is therefore important to take a holistic view of efforts made towards establishing a circular economy for LEDs and recycling other components that occur in larger quantities and have similar elements and challenges. This can mean, for example, that fractions resulting from the processing of different device categories are delivered together to appropriate downstream buyers, or that research projects are funded across device categories.
See also:
Disposing of LED lights: your guide to recycling (in German)
Cadmium (admin.ch)
1 A more in-depth analysis would have to include factors such as the environmental impact of recycling.
2 For more information about the ecologicyl scarcity method, visit: https://www.bafu.admin.ch/bafu/en/home/topics/economy-consumption/economy-and-consumption-publications/publications-economy-and-consumption/eco-factors-switzerland.html
3 Data from DETEC:2021 database (BAFU [Hrsg.], 2021)
4 Citation: Nikulski, J. S.; Ritthoff, M.; von Gries, N. The Potential and Limitations of Critical Raw Material Recycling: The Case of LED Lamps. Resources 2021,10, 37. https:// doi.org/10.3390/resources10040037
5 See, for example, https://www.umicore.com/en/about/our-metals/