Metals, their Biological Functions and Harmful Impacts - Mining and the Environment: From Ore to Metal - page 489

Minerals can only be separated
into elements by chemical
reactions.

Minerals can only be separated into elements by chemical reactions. This means that there
is no physical metallurgical process to separate a metal from a mineral. Sometimes, how-
ever, as in the case of asbestos, the mineral not its constituents is the mined 'target'.

Asbestos Minerals

While not a metal, asbestos is discussed here as many of the issues relating to metals, also
relate to asbestos. Asbestos is a commercial term used for a group of six naturally occurring
i brous silicate minerals, which occur in two mineral groups - Serpentine and Amphibole
(USGS 2007). The crystalline structure of these silicate minerals differ from other minerals -
the Serpentine group takes the form of a sheet or layered structure, Amphiboles have a
chain-like structure. While there are several different asbestos minerals, the most common is
Chrysotile.
Chrysotile, known as white asbestos, is the only member of the Serpentine group of
minerals. It is actually white-grey in colour, silky, l exible and very strong. Most of it is has
been mined in Canada, with three-quarters of the world's chrysotile found in the province
of Quebec. It is the most common form of asbestos found in buildings but it is also used in
asbestos textiles and in brake linings. Beside Chrysotile two other asbestos minerals are in
common use.
Amosite (brown asbestos) is a member of the amphibole group. Most of it comes from
Southern Africa as the name suggests: Amosite stands for the 'Asbestos Mines of South
Africa'. Some Amosite is also found in Australia. It is the second most common form of
asbestos found in building materials, often in thermal insulation.
Crocidolite (blue asbestos) is another amphibole found in Southern Africa and Western
Australia, less brittle than brown asbestos. It is used in asbestos textiles and high tempera-
ture applications.
Since all asbestos i bres are silicates, they exhibit common properties: incombustibility (in
the past, i re was occasionally used to clean fabric made out of asbestos), thermal stability,
resistance to biodegradation, chemical inertia toward most chemicals, and low electri-
cal conductivity. Its crystalline structure also allows separation of asbestos minerals into

Asbestos is a commercial term
used for a group of six naturally
occurring fi brous silicate
minerals.

CASE 11.2
Polonium, a Rare and Highly Radioactive Radon Daughter

November 23, 2006 was notable for the fi rst reported
death by the deadly polonium-210 ( 210 Po), a rare and
highly radioactive metalloid. The poisoning of Alexander
Litvinenko was widely publicized and gave ample reason
for high level conspiracy speculations: the victim, a former
lieutenant colonel with the Russian Federal Security Service,
being an outspoken critic of the Russian government; the
use of 210 Po as a poison that has never been documented
before; the probable fi rst instance of testing of a person
for the presence of 210 Po in his or her body; the fact that
210 Po is diffi cult to produce; and lastly the simple fact that
210 Po is deadly in minute amounts - one gram of 210 Po
could in theory poison 2 million people of 50 kg body
weight, of whom 1 million would die.

Polonium is a very rare element in nature because
of the short half-life of all its isotopes. It is found in
uranium ores at about 100 micrograms per metric ton
(1 part in 10 10 ), which is approximately 0.2% of the
abundance of radium. The amounts in the Earth's crust
are not harmful. The general population is exposed to
small amounts of polonium as a radon daughter in
indoor air.
Polonium may be made in milligram amounts by
bombardment of bismuth using high neutron fl uxes found
in nuclear reactors. Only about 100 grams are produced
each year, practically all of it in Russia, making polonium
exceedingly rare.

210 Po