Environmental Engineering Reference
In-Depth Information
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Fig. 13.3
Material flow of copper from copper ore to Cu alloy
electric arc furnace process (EAF). One major technical problem in iron and steel is
the removal of tramp elements, especially copper and tin (Sn), which are thermody-
namically more stable than Fe. Several processes to eliminate these tramp elements
from scrap iron have been proposed but no economical method has yet been found.
There is also an important economic problem involved: steel obtained by EAF us-
ing scrap is cheap due to its lower grade quality.
As mentioned above, Al is a good metal to recycle because the energy consumed
in the metal's production is extremely high compared with remelting (Kellogg
1977
), and the recycling ratio of Al is about 40 % in Japan. However, since Al is a
very active metal, most impurity elements cannot be removed by remelting with the
exception of alkaline and alkaline earth metals. This means that impurities must be
removed before melting by washing or other laundering techniques (Masuko
1994
).
A simplified flow diagram for Cu recycling compared with primary smelting
is shown in Fig.
13.3
. The advantage of Cu recycling is that even very low grade
copper waste can be recycled to high grade copper using a primary copper smelter.
Cu is an easy metal to recycle if it is possible to collect radiators and wires which
are made of high purity Cu. But the recycling ratio of Cu is only 30 %, because it is
used in small motors and electric circuit boards with LSI circuits which makes the
Cu hard to separate from other materials. The recycle techniques for Cu are thus
remelting for high grade Cu scrap and returning to a Cu smelter for low grade scrap.
The consumption of lead (Pb) is not large but the recycling ratio is very high,
more than 60 %, because a system for recycling Pb from batteries has been well-
established in Japan. Recycling of Pb-based chemicals is still a problem, however.
The Zn recycling ratio is around 25 % which is the lowest of the base metals
because its main use is in plating on steel to protect corrosion. EAF dust has to be
recycled not only to recover Zn but to keep the environment clean. EAF dust has
