161
the fact that the lighting market is fragmented, characterized by marked completion
of several small companies. This influences the quality of heat transfer for cooling
and on the quality of electric components of the driver (Gassmann et al. 2016).
In addition, it should be considered that small amounts of critical elements like
gallium, indium, yttrium, cerium, gold, and silver are used in the manufacture of
LEDs. The low amounts of these elements used and the wide variety of other materials used to manufacture one component or product pose a considerable challenge
in the recycling and recovery of these materials. Research and technologies that
vary from pyrolysis to bacterial leaching have been used in the effort to recover gallium and indium from waste generated in the LED production and in at the end of
the useful life of these devices.
This chapter presents a history of LEDs and of the manufacture of these devices,
discusses the main materials used, and reviews the advancements in the recovery of
these materials in industrial waste and post consumption.
9.2 History of LED Production
The discovery of semiconductors paved the way for the development of electronic
devices such as diodes and transistors. Briefly, a diode has two electrodes for terminals, and, although it is the simplest device based on semiconductors, it plays an
essential role in electronic systems. In turn, diodes enabled the development of transistors and integrated circuits (Gois 2008; Callister and Rethwisch 2013).
Also called rectifier, a diode is an electronic device that releases the current in
one direction only. This means that a diode may be used to convert an alternating
current in direct current, for example. A diode works based on a “p-n junction”,
which is the junction of two different materials. It is built using a semiconductor
part that is doped: d-doping is applied on one side, and p-doping is applied on the
other side of the part (Callister and Rethwisch 2013; Castro 2013).
Light-emitting diodes (LEDs) are semiconductor devices built using a p-n junction that emits light when charged with electric current (Fig. 9.1). In other words, a
LED is a very small electroluminescent semiconductor chip made of a solid crystalline material measuring 0.25 mm
2
on average (Gois 2008; Ascurra 2013; Callister
and Rethwisch 2013). Since this technology does not rely on filaments or gases, it
may also be called solid-state lighting (SSL) (Ascurra 2013).
After several attempts to build a light source based on electrical energy, Humphry
Davy developed the first bulb using a platinum filament in 1802. But it was only in
1879 that Thomas Edison built the first commercially feasible electrical incandescent light bulb using a very thin coal filament. Today, incandescent light bulbs are
produced using a tungsten filament (Castro 2013).
In 1926 Edmund Germer obtained uniform white light from a mercury vapour
bulb. It was built using a pressurized glass bulb covered with a phosphorescent
powder. In the mid-1930s, the first fluorescent bulbs were commercialized
(Castro 2013).
9 Recycling Processes for the Recovery of Metal from E-waste of the LED Industry
the fact that the lighting market is fragmented, characterized by marked completion
of several small companies. This influences the quality of heat transfer for cooling
and on the quality of electric components of the driver (Gassmann et al. 2016).
In addition, it should be considered that small amounts of critical elements like
gallium, indium, yttrium, cerium, gold, and silver are used in the manufacture of
LEDs. The low amounts of these elements used and the wide variety of other materials used to manufacture one component or product pose a considerable challenge
in the recycling and recovery of these materials. Research and technologies that
vary from pyrolysis to bacterial leaching have been used in the effort to recover gallium and indium from waste generated in the LED production and in at the end of
the useful life of these devices.
This chapter presents a history of LEDs and of the manufacture of these devices,
discusses the main materials used, and reviews the advancements in the recovery of
these materials in industrial waste and post consumption.
9.2 History of LED Production
The discovery of semiconductors paved the way for the development of electronic
devices such as diodes and transistors. Briefly, a diode has two electrodes for terminals, and, although it is the simplest device based on semiconductors, it plays an
essential role in electronic systems. In turn, diodes enabled the development of transistors and integrated circuits (Gois 2008; Callister and Rethwisch 2013).
Also called rectifier, a diode is an electronic device that releases the current in
one direction only. This means that a diode may be used to convert an alternating
current in direct current, for example. A diode works based on a “p-n junction”,
which is the junction of two different materials. It is built using a semiconductor
part that is doped: d-doping is applied on one side, and p-doping is applied on the
other side of the part (Callister and Rethwisch 2013; Castro 2013).
Light-emitting diodes (LEDs) are semiconductor devices built using a p-n junction that emits light when charged with electric current (Fig. 9.1). In other words, a
LED is a very small electroluminescent semiconductor chip made of a solid crystalline material measuring 0.25 mm
2
on average (Gois 2008; Ascurra 2013; Callister
and Rethwisch 2013). Since this technology does not rely on filaments or gases, it
may also be called solid-state lighting (SSL) (Ascurra 2013).
After several attempts to build a light source based on electrical energy, Humphry
Davy developed the first bulb using a platinum filament in 1802. But it was only in
1879 that Thomas Edison built the first commercially feasible electrical incandescent light bulb using a very thin coal filament. Today, incandescent light bulbs are
produced using a tungsten filament (Castro 2013).
In 1926 Edmund Germer obtained uniform white light from a mercury vapour
bulb. It was built using a pressurized glass bulb covered with a phosphorescent
powder. In the mid-1930s, the first fluorescent bulbs were commercialized
(Castro 2013).
9 Recycling Processes for the Recovery of Metal from E-waste of the LED Industry