Civil Engineering Reference
In-Depth Information
Iron, aluminium, magnesium and titanium can be considered relatively
'benign' metals, even if the environmental consequences of their extraction and
production are quite severe. They have a relatively good base as a raw material
and their recycling potential is also high. They are not particularly poisonous and
are abundant in the Earth's crust (see Table 2.2 in section 1).
Chrome, nickel, copper and zinc, however, should be used very sparingly, or
not at all. The use of mercury, cadmium and lead should be banned. All metals
in the long term should be kept within closed cycles, in order to maximize their
re-use and minimize their loss during production or the life of the building.
Raw materials
Metals are the most limited reserves. On current statistical predictions, iron
reserves will last 119 more years (from 1992), aluminium 220 years, copper 36
years and zinc 21 years (Crawson, 1992). These statistics do not take into account
a possible increase in the consumption of metals. The use of aluminium in coun-
tries with low and medium industrialization increased by 460 per cent between
1960 and 1969, and is still increasing.
The production of aluminium is based on the ore bauxite, which contains
40-60 per cent aluminium oxide. Ninety per cent of the bauxite reserves are in
countries with low and medium industrialization, while the same proportion of
extracted aluminium is used in highly-industrialized countries. There are also
other sources of aluminium such as kaolin, nephelin and ordinary clay. In the
former Soviet Republics there are low reserves of bauxite, so aluminium oxide
is extracted from nephelin, although it is much more expensive to extract alu-
minium from these minerals than from bauxite.
Primary use of energy for some metals
Metals/alloys
From the ore (MJ/kg)
50% recycling
100% recycling
Aluminium
165-260
95
30
Copper
80-127
55
Steel
21-25
18
6-10
Zinc
47-87
Probes are now being made to find new sources of iron ore, and have resulted in
the discovery of interesting sources on the ocean floor - the so-called iron nod-
ules. These also contain a large amount of manganese. Extraction of iron from
bog-ore is now being considered. A more systematic recycling of scrap metal is
in fact the most sensible method of obtaining iron. It is also possible to use alter-
