Environmental Engineering Reference
In-Depth Information
large a share of the earth's mineral resources as all pre-
vious generations put together, and the resource-use
treadmill is accelerating.
Will we run out of affordable supplies of a particu-
lar mineral resource? No one knows. If we do, can we
find an acceptable substitute? Some think we can. Do
environmental limits apply to the use of mineral re-
sources? Some environmental scientists think so un-
less we can use microorganisms, or other less environ-
mentally harmful ways, to extract and process miner-
als, or nanotechnology to construct materials we need
from atoms and molecules.
and pollution prevention, and encourage recycling
and reuse of mineral resources.
Mining company representatives insist that they
need subsidies and low taxes to keep the prices of
minerals low for consumers. They also claim that the
subsidies encourage the companies not to move their
mining operations to other countries with no such
taxes and less stringent mining regulations.
Economic problems can also hinder the develop-
ment of new supplies of mineral resources because
finding them takes increasingly scarce investment cap-
ital and is financially risky. Typically, if geologists
identify 10,000 possible deposits of a given resource,
only 1,000 sites are worth exploring; only 100 justify
drilling, trenching, or tunneling; and only 1 becomes a
producing mine or well. If you had lots of financial
capital, would you invest it in developing a nonrenew-
able mineral resource?
Economics and Politics: Prices and Supplies
of Nonrenewable Minerals
A rising price for a scarce mineral resource can
increase supplies and encourage more efficient use.
Geologic processes determine the quantity and loca-
tion of a mineral resource in the earth's crust. Econom-
ics determines what part of the known supply is actu-
ally extracted and used.
According to standard economic theory, in a com-
petitive free market a plentiful mineral resource is
cheap when its supply exceeds demand. When a re-
source becomes scarce, its price rises. This can en-
courage exploration for new deposits, stimulate de-
velopment of better mining technology, and make it
profitable to mine lower-grade ores. It can also en-
courage a search for substitutes and promote resource
conservation.
According to some economists, this price effect
may no longer apply very well in most developed
countries. Industry and government in such countries
often control the supply, demand, and prices of miner-
als to such an extent that a truly competitive free mar-
ket does not exist.
Most mineral prices are kept artificially low be-
cause governments subsidize development of their do-
mestic mineral resources to help promote economic
growth and national security. In the United States, for
instance, mining companies get depletion allowances
amounting to 5-22% of their gross income (depending
on the mineral). They can also reduce their taxes by de-
ducting much of their costs for finding and developing
mineral deposits. In addition, hardrock mining com-
panies operating in the United States can buy public
land at 1872 prices and pay no royalties to the govern-
ment on the minerals they extract (see the Case Study
at the beginning of the chapter).
Between 1982 and 2004, U.S. mining companies
received more than $6 billion in government subsidies.
Critics argue that taxing—rather than subsidizing—
the extraction of nonfuel mineral resources would pro-
vide governments with revenue, create incentives for
more efficient resource use, promote waste reduction
Science: Mining Lower-Grade Ores
New technologies can increase the mining of
low-grade ores at affordable prices, but harmful
environmental effects can limit this endeavor.
Some analysts contend that all we need to do to
increase supplies of a mineral is to extract lower
grades of ore. They point to the development of new
earth-moving equipment, improved techniques for re-
moving impurities from ores, and other technological
advances in mineral extraction and processing.
In 1900, the average copper ore mined in the
United States was about 5% copper by weight. Today
that ratio is 0.5%, and copper costs less (adjusted for
inflation). New methods of mineral extraction may al-
low even lower-grade ores of some metals to be used.
Several factors can limit the mining of lower-
grade ores. One is the increased cost of mining and
processing larger volumes of ore. Another is the avail-
ability of fresh water needed to mine and process some
minerals—especially in arid and semiarid areas. A
third limiting factor is the environmental impacts of
the increased land disruption, waste material, and pol-
lution produced during mining and processing (Fig-
ure 12-12).
One way to improve mining technology is to use
microorganisms for in-place (
in situ,
pronounced “in
SY-too”) mining. This biological approach removes
desired metals from ores while leaving the surround-
ing environment undisturbed. It also reduces the air
pollution associated with the smelting of metal ores
and the water pollution associated with using haz-
ardous chemicals such as cyanides and mercury to ex-
tract gold.
Once a commercially viable ore deposit has
been identified, wells are drilled into it and the ore is
fractured. The ore is then inoculated with bacteria to
