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.