Metals, their Biological Functions and Harmful Impacts - Mining and the Environment: From Ore to Metal - page 490

thin and strong but l exible i bres. Fibres that are at least 1 cm in length can further be
spun into yarn. Because of these characteristics, asbestos has found numerous industrial
applications: i reproof fabrics, yarn, cloth, paper, paint i ller, gaskets, rooi ng composition,
reinforcing agent in rubber and plastics, brake linings, tiles, electrical and heat insulation,
cement and chemical i lters. Over centuries asbestos was regarded as a miracle material,
combining the strength of rock with the l exibility of silk.
Like metals or coal, asbestos has to be mined. Most asbestos is mined from open pits
using bench drilling techniques. The i bre extraction (milling) process is chosen to opti-
mize recovery of the i bres in the ore, while minimizing reduction of i bre length. Dry
milling operations are the most widely used taking advantage of the way asbestos crystals
are formed: since in asbestos the crystals take the form of long, thin and strong i bres, i bres
can be released from the rock by crushing followed by blowing.
Today mining of asbestos, either as the primary mineral or included as an unwanted
material while mining for the 'target' mineral, is one of the more controversial issues fac-
ing the mining industry: asbestos i bres are dangerous when breathed. In fact the relation-
ship between workplace exposure to airborne asbestos i bres and respiratory diseases has
become one of the most widely studied subjects of modern epidemiology.
The dangers of asbestos, however, have been known for more than a century, and
became widely apparent soon after asbestos entered widespread commercial use. Deaths
and lung problems were noticed in asbestos mining towns before 1900. The i rst medical
diagnosis of a death from asbestos was made in England in 1906. By 1918 insurance com-
panies in America and Canada would no longer insure workers in the asbestos industry
because of suspected health hazards. In 1935, researchers in Europe and the US reported a
suspected association between asbestos exposure and lung cancer.

Over centuries asbestos was
regarded as a miracle material,
combining the strength of rock
with the fl exibility of silk.

Asbestos fi bres are dangerous
when breathed.

FIGURE 11.6
Uranium Ores contain over a Dozen
Radioactive Materials which are All
Harmful to Living Things

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