Civil Engineering Reference
In-Depth Information
(PbS). The most common use of lead has been for roofing material and for detail-
ing, but it has also been used for pipes, in Rome and Pompeii for example. Danish
churches have a total of 30 000-50 000 tons of lead covering their roofs. The paint
pigment, lead white, was also very common until recently, when its poisonous
effect on humans was discovered. Useful lead resources are very limited.
Lead is mostly used nowadays in flashing for chimneys and for dormers on
roofs etc. It is very durable, but can still be broken down in aggressive climates.
When lead is exposed to rain, small, highly poisonous lead particles are washed
out into the ground water. Lead has a tendency to biological amplification.
Cadmium
Cadmium does not occur naturally in a pure form, but in the compound cadmi-
um sulphide (CdS) which is often found with zinc sulphide (ZnS). The metal was
discovered in Germany in 1817, and is used as a stabilizer in many polyvinyl
chloride (PVC) products. It is also used as a pigment in painting, ceramic tiles,
glazes and plastics. Colours such as cadmium yellow or cadmium green are well
known. The metal is usually extracted as a by-product of zinc or lead ores.
Cadmium has a relatively low boiling point, 767°C, which is why it often occurs
as a waste gas product in industrial processes, house fires and incinerators.
Accessible reserves are very limited. Cadmium particles are washed out of waste
containing cadmium. Cadmium has a tendency to biological amplification, and
in small doses can cause chronic poisoning to several organisms.
Nickel
Nickel is used in steel alloys to increase strength. It is also an important part of
stainless steel. It is used as a colour pigment in certain yellow, green and grey
colours, for colouring ceramic tiles, plastics and paint. Nickel has very few acces-
sible sources. During production of nickel large amounts of metal are liberated.
Nickel has the property of biological amplification and is particularly poisonous
for organisms living in water. In the former Soviet Union a connection has been
registered between nickel in the soil and the death of forests (Törslöv, 1985).
Manganese
Manganese is a necessity for the production of steel. Between 7 and 9 kg are
required per ton of steel. It is also used as an alloy of aluminium, copper and
magnesium. Manganese is also a pigment - manganese blue. Manganese can
cause damage to the nervous system.
Chrome
Chrome is used for the impregnation of timber and in stainless steel. There is no
alternative to its use in stainless steel, so chrome is very valuable. Chrome com-
pounds have the property of biological amplification and are very poisonous.
