1 Introduction
Discarded electronics and electrical appliances are generally known as e-waste. They
are mostly comprised of printers, refrigerators, washing machines, air conditioners,
computers, televisions, copiers, and cell phones (Ilyas et al. 2007). Recently, rapid
advances in science and technology have significantly shortened the lifespan of
electronic and electrical equipment since consumers are eager to replace their current
equipment with newer models having improved features (Okibe and Johnson 2004).
Hence, huge quantities of electronics and electrical appliances are being discarded.
Global e-waste production was 47 million tons in 2016, and it is increasing by 4.6%
annually. It is estimated that discarded e-waste may reach 52.2 million tons in 2021.
Owing to vast production of e-waste, various methodologies are being developed to
address this issue (Bhattacharyya et al. 2013).
Generally, in hydrometallurgical processes, waste water is concurrently produced, which becomes e-waste sludge (Natarajan 1992). This kind of e-waste sludge
is comprised of various toxic heavy metals. So far, based on ecofriendly environmental approaches, physical methods have been extensively utilized by enterprises
that dismantle discarded electronics. However, researchers are globally concentrating on hydrometallurgical techniques for safe disposal of e-waste that eventually
create e-waste sludge (Cao et al. 2012).
Improper treatment of e-waste sludge in turn generates secondary pollutants that
contaminate groundwater and soil and even risk human health through enrichment in
the food chain (Gu et al. 2017). In general, because of the heavy metal composition
in the e-waste sludge, it is often identical to that of sewage sludge; some of the
techniques that are applied to dispose of sewage sludge can also be employed to treat
e-waste sludge (Kimura et al. 2011). Typically, e-waste sludge disposal is done
through recycling, producing harmless effluents. Figure 14.1 shows the common
technologies used for e-waste sludge treatment. These treatments include stabilization, incineration, solidification, and disposal in landfills (Gehrke et al. 1998).
Recycling techniques used are hydrometallurgy, pyrometallurgy, and materialization (Hong and Valix 2014). Curing agents are used in stabilization and solidification
of e-waste sludge containing heavy metals in a mixture substance, eventually
producing non-toxic materials (Druschel et al. 2004).
Oxidation and fusion processes are carried out during incineration. In this
method, the toxic elements present inside the e-waste sludge will be destroyed
during thermal treatment (Roberts et al. 2002). Generally, to mitigate emissions of
toxic elements, stabilization and solidification methods are used for treating e-waste
sludge. The heavy metals present in e-waste sludge make it inappropriate for
application to farm land. Hence, landfill methods are extensively implemented, in
China, for example (Gurung and Chakraborty 2009). Owing to its lower secondary
pollution and cost, hydrometallurgy techniques are more widely employed than
pyrometallurgical methods.
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S. Venkatesa Prabhu et al.
Discarded electronics and electrical appliances are generally known as e-waste. They
are mostly comprised of printers, refrigerators, washing machines, air conditioners,
computers, televisions, copiers, and cell phones (Ilyas et al. 2007). Recently, rapid
advances in science and technology have significantly shortened the lifespan of
electronic and electrical equipment since consumers are eager to replace their current
equipment with newer models having improved features (Okibe and Johnson 2004).
Hence, huge quantities of electronics and electrical appliances are being discarded.
Global e-waste production was 47 million tons in 2016, and it is increasing by 4.6%
annually. It is estimated that discarded e-waste may reach 52.2 million tons in 2021.
Owing to vast production of e-waste, various methodologies are being developed to
address this issue (Bhattacharyya et al. 2013).
Generally, in hydrometallurgical processes, waste water is concurrently produced, which becomes e-waste sludge (Natarajan 1992). This kind of e-waste sludge
is comprised of various toxic heavy metals. So far, based on ecofriendly environmental approaches, physical methods have been extensively utilized by enterprises
that dismantle discarded electronics. However, researchers are globally concentrating on hydrometallurgical techniques for safe disposal of e-waste that eventually
create e-waste sludge (Cao et al. 2012).
Improper treatment of e-waste sludge in turn generates secondary pollutants that
contaminate groundwater and soil and even risk human health through enrichment in
the food chain (Gu et al. 2017). In general, because of the heavy metal composition
in the e-waste sludge, it is often identical to that of sewage sludge; some of the
techniques that are applied to dispose of sewage sludge can also be employed to treat
e-waste sludge (Kimura et al. 2011). Typically, e-waste sludge disposal is done
through recycling, producing harmless effluents. Figure 14.1 shows the common
technologies used for e-waste sludge treatment. These treatments include stabilization, incineration, solidification, and disposal in landfills (Gehrke et al. 1998).
Recycling techniques used are hydrometallurgy, pyrometallurgy, and materialization (Hong and Valix 2014). Curing agents are used in stabilization and solidification
of e-waste sludge containing heavy metals in a mixture substance, eventually
producing non-toxic materials (Druschel et al. 2004).
Oxidation and fusion processes are carried out during incineration. In this
method, the toxic elements present inside the e-waste sludge will be destroyed
during thermal treatment (Roberts et al. 2002). Generally, to mitigate emissions of
toxic elements, stabilization and solidification methods are used for treating e-waste
sludge. The heavy metals present in e-waste sludge make it inappropriate for
application to farm land. Hence, landfill methods are extensively implemented, in
China, for example (Gurung and Chakraborty 2009). Owing to its lower secondary
pollution and cost, hydrometallurgy techniques are more widely employed than
pyrometallurgical methods.
292
S. Venkatesa Prabhu et al.