138
5 Recovery of Metals from Electronic Waste
black copper route is more attractive than the copper matte route as it can handle
high levels of impurities such as Fe, Zn, Pb and Sn, where the impurities can be
transferred to the vapor phase and removed/recovered from the off-gas [21].
The copper smelting routes are more environmentally friendly compared to the
lead smelting routes. The lead smelting facilities cannot be built close to populations
due to the production of toxic gases; however, the proximity of the facilities to the
cities minimizes the costs of transportation and improves the recycling economy
[21].
5.8.1.2 Alkali Smelting
Alkali smelting is defined as alkali fusion using molten-salt-oxidation. In this method,
amphoteric metals (such as Pb and Sn) and ceramics react with fused alkali to produce
soluble molten salts. The structure of the raw materials is destroyed by fused alkaline
compounds, while the Cu and precious metals are retained in the solid phase and
are then separated and extracted by leaching processes [12, 22]. This method is
an effective method in non-ferrous metallurgy and is often referred to as the alkali
fusion-leaching-separation process. The operating temperature of the fusion process
is much lower than the traditional smelting methods (usually below 900 °C). The
fusion liquid phase consists of both molten metal and fused medium [22].
5.8.1.3 Incineration
Incineration involves the burning of e-waste without the formation of melts, especially slags, for the recovery of precious metals. This method is commonly used in
a small scale and for e-waste with a high concentration of precious metals. Incineration is performed in different types of furnaces such as rotary furnaces and stationary
fluidized bed and it is typically followed by hydrometallurgical routes for extraction
and separation of various metals [16].
5.8.2 Hydrometallurgical Processing
Traditionally, hydrometallurgical methods are used for the extraction of metals from
their primary ore. The hydrometallurgical methods used for the recovery of metals
from e-waste are the modified version of the traditional methods [17, 21]. Compared
to the pyrometallurgical methods, the hydrometallurgical processes are more precise
and predictable and better controlled. They can achieve a better separation of elements
that have similar chemical and physical characteristics. They also have relatively low
capital cost, low-temperature condition and suitability for small-scale applications
5 Recovery of Metals from Electronic Waste
black copper route is more attractive than the copper matte route as it can handle
high levels of impurities such as Fe, Zn, Pb and Sn, where the impurities can be
transferred to the vapor phase and removed/recovered from the off-gas [21].
The copper smelting routes are more environmentally friendly compared to the
lead smelting routes. The lead smelting facilities cannot be built close to populations
due to the production of toxic gases; however, the proximity of the facilities to the
cities minimizes the costs of transportation and improves the recycling economy
[21].
5.8.1.2 Alkali Smelting
Alkali smelting is defined as alkali fusion using molten-salt-oxidation. In this method,
amphoteric metals (such as Pb and Sn) and ceramics react with fused alkali to produce
soluble molten salts. The structure of the raw materials is destroyed by fused alkaline
compounds, while the Cu and precious metals are retained in the solid phase and
are then separated and extracted by leaching processes [12, 22]. This method is
an effective method in non-ferrous metallurgy and is often referred to as the alkali
fusion-leaching-separation process. The operating temperature of the fusion process
is much lower than the traditional smelting methods (usually below 900 °C). The
fusion liquid phase consists of both molten metal and fused medium [22].
5.8.1.3 Incineration
Incineration involves the burning of e-waste without the formation of melts, especially slags, for the recovery of precious metals. This method is commonly used in
a small scale and for e-waste with a high concentration of precious metals. Incineration is performed in different types of furnaces such as rotary furnaces and stationary
fluidized bed and it is typically followed by hydrometallurgical routes for extraction
and separation of various metals [16].
5.8.2 Hydrometallurgical Processing
Traditionally, hydrometallurgical methods are used for the extraction of metals from
their primary ore. The hydrometallurgical methods used for the recovery of metals
from e-waste are the modified version of the traditional methods [17, 21]. Compared
to the pyrometallurgical methods, the hydrometallurgical processes are more precise
and predictable and better controlled. They can achieve a better separation of elements
that have similar chemical and physical characteristics. They also have relatively low
capital cost, low-temperature condition and suitability for small-scale applications