Abundance
Modern society is highly dependent on materials, usually referred to as minerals,
whether in raw or
refined form. All these materials have to be found, extracted and processed before use and
disposed of afterwards. During their 'life cycle' they have a variety of impacts on the environment,
ranging from the noise and dust arising from gravel extraction through to potentially lethal effects
of
toxic or radioactive metals.
The major source of all minerals is the rocks of the earth's crust. The minerals of
the mantle and
the core, however desirable they may be, are totally inaccessible for commercial purposes. Three
aspects of minerals are relevant in relation to their use in building or industry: their overall
abundance or rarity, the ways they may be locally concentrated and the ease or difficulty of
obtaining useful materials, particularly pure elements, from their natural sources. The latter is
bound to be a serious problem because earth minerals will mostly be in a chemically stable form
and only a handful of elements, for example copper and gold, are stable in their pure forms.
Because of this, finding usable deposits of many minerals has been called a geochemical lottery.
Although around ninety chemical elements occur naturally in the Earth's crust, they
vary
enormously in their abundance. Two elements are vastly more abundant than any others: oxygen
(nearly 47 per cent) and silicon (nearly 28 per cent). Aluminium (eight per cent) and iron (five per
cent) follow, then four light metals — calcium, sodium, potassium and magnesium (each two
or
three per cent). These eight elements make up almost 99 per cent of the crust, so all other
elements are relatively rare. Indeed, some commonly used elements such as zinc, copper, nickel
and lead occur as only a few dozen parts per million, tin and uranium at two parts per million and
gold at four parts per trillion.
Three things are immediately apparent from this list. First, use of pure elements
has little to do with
their abundance - the oxygen in the air or the silicon used in chips are a minute fraction of the
amounts which exist in chemical combination, while gold and uranium are eagerly sought after in
spite of their rarity. Second, we unknowingly use most elements as chemical combinations - sand
being the familiar form of silica (silicon oxide) and many rocks being complex 'aluminosilicates'.
Third, even where elements are used in their pure form, the amounts used depend on how they are
concentrated by natural processes and how easily they are purified chemically.
Most of the earth's crust is made up of igneous rocks (those which have solidified
from a molten
state), which all contain aluminosilicates of the abundant metals. Some of them, acid or granitic
rocks, contain at least 50 per cent silica. These rocks are chemically rather stable, so even though
they contain vast quantities of iron and aluminium they are not used as ores but only as rocks, for
building or in crushed form for aggregate, road beds and so on. Workable ores result from natural
concentrations of minerals which are more amenable to chemical purification.
Materials flows
The three principal types of minerals in use, building materials, fossil fuels and metal ores, have
very different patterns of distribution and trade. Building materials are used in huge quantities but
most of them are of very low value and are only transported short distances. Fossil fuels and metal
ores have more localised distributions, higher value and a more extensive pattern of international
trade. Fossil fuels will be considered in the next chapter while this chapter concentrates on metals.
As well over 95 per cent of world output of metals consists of iron, it is possible to describe mineral
extraction and trade by concentrating on iron and then adding a few remarks about a small number
of metals used in quite small quantities.
Iron is the fourth most abundant element in the crust and is concentrated in three
ways. The
highest grade ores, with more than 60 per cent iron, are 'magnetites', for example from Sweden,
and 'haematites', such as those formerly mined in Cumbria. Though restricted in size, they are very
pure and make up one third of world reserves. The most important sources of iron, half today's
total, are the 'banded ironstones' from the oldest parts of the continents. The deposits are hundreds
of metres thick and some extend hundreds of kilometres. They are much less pure and have to be
milled, separated from the silica component and made into pellets for smelting; so they came into
use later than other types of ore. The more recent sedimentary ores are low grade but were
important in the early growth of industrialisation in Europe and North America. They are going out of
use now that bulk carriers can move higher grade ores halfway across the world. Blast furnaces
and steelworks can be run at any port site where efficient production and local demand make it
profitable to do so. It also means that pollution from smelters is more likely to be found in industrial
areas than at the source of the ore.
It is apparent that about half of the metals required have over one-third of world
production coming
from a single country. What is not apparent from this figure is the domination of production and
trade by transnational companies. Just as the oil industry is dominated by seven corporations, so
six dominate aluminium trade, two dominate nickel and three uranium. Past attempts by
governments of less developed countries such as Zaire, Zambia and Peru to expropriate or tax
mining operations run by transnational have led to a concentration of exploration into politically
'safe' countries. In fact 80 per cent of 'free world' exploration effort is expended in the USA, Canada,
Australia and South Africa and very little now occurs in less developed countries.
Some of these metals, notably aluminium, manganese, magnesium, chrome and titanium,
are
geologically abundant so, in spite of substantial and growing production, there are few problems of
supply. The other metals are scarcer, which leads at best to the use of lean ores - down to half per
cent for copper ores - and at worst to actual and potential shortages, as with silver, tungsten and
tin. The results for the environment are damaging - large voids and spoil heaps, use of large
amounts of energy in extraction and pressure to exploit existing deposits to the maximum.
The main environmental impact issues are concerned with the environmental effects
of mining and
the processing of minerals, and with policies for the rehabilitation of dam aged land scapes and the
control of associated pollution.
Substitution and recycling
Problems, which arise from shortage, or environmental impact, most obviously in the case of
metals, can be reduced by substitution and/or recycling.
A classic case of substitution is in electrical uses of copper. Early this century
copper was used
for all electrical wiring including transatlantic cables. Since then the relative scarcity and
consequent high price of copper have led to substitution. Aluminium was a suitable substitute in
cables, but the demand for metal cables has been reduced by the use of optical-fibre cables over
short distances, microwave transmitters at medium scale and satellites over the longer distances.
These substitutes use fewer, cheaper or more abundant minerals but have one major problem.
Although more efficient in use of materials, they are more energy intensive and hence put pressure
on two of the minerals in finite supply: coal and petroleum. Similar problems arise from the
substitution of plastics (which are mostly made from oil) for metal. A more promising strategy for
the future is to use more ceramics, since clay is abundantly available.
Recycling looks an even more promising strategy since re-use of materials can simultaneously
solve problems of mining, refining and disposal. At best, for example in the case of the re-use of
aluminium or glass, it is also much less energy intensive. Indeed, recycling is so obviously
advantageous that it is surprising that only between one- quarter and one-third of metals output
uses recycled materials. At present, the problem lies in the great complexity of products like cars.
Not only do they involve metals other than steel, but they include many different kinds of steel. A
recycled batch of steel may contain appreciable quantities of chromium, cobalt, manganese,
nickel, tungsten and/or vanadium. These become impurities which make its behaviour
unpredictable and at present no practical technology exists to remove them. As a result, scrap has
to be combined with new steel and confined to low grade uses. Similar problems arise with
aluminium: recycled aluminium is insufficiently pure to use for wire or sheet. Unfortunately, demand
for cast aluminium is not high at present. No doubt these kinds of problems could be resolved but
at present the financial incentives are not strong enough to persuade industry to make the
necessary commitments to new technology and more expensive processes.
