174
gallium and indium. Zhan et al. (2015) recovered about 93–95% of rare metals like
gallium and indium in LEDs using a new process based on pyrolysis, physical segregation, and vacuum metallurgy. Swain et al. (2015a) investigated the leaching of
gallium in LED waste using heterotrophic bacteria. The main advantage of biotechnological processes is the possibility to leach small amounts of materials using a
process that consumes low energy levels. Maneesuwannarat et al. (2016b) also used
a microorganism (Cellulosimicrobium funkei) to obtain gallium, achieving high efficiency in the process. The authors discussed the possibility to use the method to
recycle semiconductors.
9.7 Critical Elements
The manufacture of electrical and electronic devices depends on the availability of
raw materials that are considered geologically critical elements due to the fact that
these resources are increasingly scarce in the natural environment. For this reason,
these elements are known as scarce metals and rare earth elements, or critical elements. These elements are used mainly in the production of permanent magnets,
bulbs, rechargeable batteries, catalysers, and other devices (Binnemans et al. 2013).
In most cases, these metals replace materials with the same function; alternatively,
they are added to improve the performance of devices. Most devices associated with
energy efficiency – like LEDs – utilize geologically critical elements. Obtaining
these elements is, therefore, essential in the manufacture of these products.
Rare earth elements, also called lanthanides, are represented by Ln and include
15 elements on the sixth period of the periodic table, between elements 57 and 71
(lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium
(Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium
(Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium
(Lu)), besides yttrium and scandium (Serra 2011; Martins and Isolani 2005; Viera
and Lins 1997). These elements are present at low levels, although cerium is the
most abundant and thulium is the rarest. The average per cent level of rare earth elements on the earth’s crust is approximately 0.01%, and over 250 ores are known to
contain low levels of these elements. Rare earth elements are divided into two
groups: the cerium group (light rare earth elements) and the yttrium group (heavy
rare earth elements). This classification was based on their different chemical
properties (Viera and Lins 1997; Serra 2011). In addition to these elements, gallium
and yttrium are considered critical in the production of electrical and electronic
devices. Therefore, recycling is an interesting alternative both from the environmental and economic standpoints.
According to Jones (2013), the value of rare earth elements increased 750% in
2011, warning the technology industry of the need for alternatives to these elements
that do not depend on the Chinese market. One such alternative is the recycling of
electrical and electronic equipment, which contains a large number of elements that
can be recovered. Recycling aims to solve the environmental problems caused by
E. C. A. dos Santos et al.
gallium and indium. Zhan et al. (2015) recovered about 93–95% of rare metals like
gallium and indium in LEDs using a new process based on pyrolysis, physical segregation, and vacuum metallurgy. Swain et al. (2015a) investigated the leaching of
gallium in LED waste using heterotrophic bacteria. The main advantage of biotechnological processes is the possibility to leach small amounts of materials using a
process that consumes low energy levels. Maneesuwannarat et al. (2016b) also used
a microorganism (Cellulosimicrobium funkei) to obtain gallium, achieving high efficiency in the process. The authors discussed the possibility to use the method to
recycle semiconductors.
9.7 Critical Elements
The manufacture of electrical and electronic devices depends on the availability of
raw materials that are considered geologically critical elements due to the fact that
these resources are increasingly scarce in the natural environment. For this reason,
these elements are known as scarce metals and rare earth elements, or critical elements. These elements are used mainly in the production of permanent magnets,
bulbs, rechargeable batteries, catalysers, and other devices (Binnemans et al. 2013).
In most cases, these metals replace materials with the same function; alternatively,
they are added to improve the performance of devices. Most devices associated with
energy efficiency – like LEDs – utilize geologically critical elements. Obtaining
these elements is, therefore, essential in the manufacture of these products.
Rare earth elements, also called lanthanides, are represented by Ln and include
15 elements on the sixth period of the periodic table, between elements 57 and 71
(lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium
(Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium
(Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium
(Lu)), besides yttrium and scandium (Serra 2011; Martins and Isolani 2005; Viera
and Lins 1997). These elements are present at low levels, although cerium is the
most abundant and thulium is the rarest. The average per cent level of rare earth elements on the earth’s crust is approximately 0.01%, and over 250 ores are known to
contain low levels of these elements. Rare earth elements are divided into two
groups: the cerium group (light rare earth elements) and the yttrium group (heavy
rare earth elements). This classification was based on their different chemical
properties (Viera and Lins 1997; Serra 2011). In addition to these elements, gallium
and yttrium are considered critical in the production of electrical and electronic
devices. Therefore, recycling is an interesting alternative both from the environmental and economic standpoints.
According to Jones (2013), the value of rare earth elements increased 750% in
2011, warning the technology industry of the need for alternatives to these elements
that do not depend on the Chinese market. One such alternative is the recycling of
electrical and electronic equipment, which contains a large number of elements that
can be recovered. Recycling aims to solve the environmental problems caused by
E. C. A. dos Santos et al.