Environmental Engineering Reference
In-Depth Information
Fig. 13.2
Recent total
consumption and recycling of
base metals in Japan
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to consider the environmental impact of recycling of materials that is being done at
present. Here an important aspect is the implications of the cascade effects of recy-
cling, because in reality, where a material undergoes multiple recycling, the steady
build-up of contamination leads to a cascade decrease in quality from first to second
grade, then second to third grade, and so on until it becomes so contaminated that
it is unusable. In a sense, the recycled material undergoes a re-mineralization, that
will require at some point a primary-type processing step in order to again produce
a pure and useable material. This primary-type processing step will have associated
with it high consumption of energy resources and emissions.
Aluminum (Al) metal is an excellent candidate for recycling because of the high
energy consumption in its production. If aluminum scrap could be recycled to its
original purity by simple remelting, more than 90 % of the energy could be saved
compared to production via smelting from bauxite. Metallurgists, however, know
that the development of a commercial process for purification of molten aluminum
from scrap hinges on being able to remove iron (Fe), which is difficult. Thermody-
namically, removal of the chalcophile and siderophile elements Cu and Fe from alu-
minum is extremely difficult. Most secondary aluminum used is therefore a very low
grade, such as source for cast products or as a deoxidation reagent in the steel-making
process. From a LCA (life cycle assessment) point of view, alloying of chalcophile
elements to siderophile metals and siderophile elements to lithophile metals must be
limited; even though such alloys are in wide use because of their better performance.
To facilitate recycling therefore, the paradigm for metal processing needs to change.
The recent amounts of base metals consumed and recycled in Japan are shown in
Fig.
13.2
. Since the amount of iron and steel consumption is much higher than that
of the non-ferrous metals, the left vertical axis in the figure shows iron and steel
and the right vertical axis the other base metals. The bar height shows the annual
consumption and the darkened portion of the bar shows the recycled amount. The
recycling ratio for iron and steel is about 30 %, and most iron scrap is treated by the
