Secondary building metals

The following metals collectively represent a very small percentage of the use of metals in the building industry.

Lead has been in use for 4000 to 5000 years. It is not found freely in the natural environment, but has to be extracted, usually from the mineral galena - lead sulphide (PbS). The most common use of lead has been for roofing material and for detailing, 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 toxic effect on humans was discovered. Useful lead resources are very limited.

Lead is mostly used nowadays in flashings for chimneys and around roof windows and the like. It is 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 accumulation.

Cadmium does not occur naturally in a pure form, but in the compound cadmium sulphide (CdS) which is often found associated with zinc sulphide (ZnS). Cadmium 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 byproduct of zinc or lead manufacture. Cadmium has a relatively low boiling point, 767 °C, which is why it often occurs as a waste gas product in industrial processes, as well as in house fires and incinerators. Accessible reserves are very limited. Cadmium particles are washed out of waste containing cadmium. Cadmium hasa tendency to biological accumulation, and in small doses can cause chronic poisoning to organisms.

Nickel is used in steel alloys to increase strength. It is also an important ingredient for 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 accessible sources. During production of nickel large amounts of metal are liberated. Nickel is bioaccumulative and is particularly toxic for aquatic organisms. In the former Soviet Union a connection was registered between nickel in the soil and the death of forests (Torslov etal., 1985).

Manganese is a necessity for the production of steel. Between 7 and 9 kg are often required per ton of steel. It is also used in alloys of aluminium, copper and magnesium. Manganese is also a colouring pigment: manganese blue. Manganese can cause damage to the nervous system.

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 compounds are bioaccumulative and are very poisonous.

Arsenicis usually produced from arsenopyrite (FeAsS). Its main use is in timber impregnation, where it is mixed with copper or chrome. Accessible reserves of arsenic are very limited. Arsenic has been the most popular poison for murder for many centuries. The metal has a tendency to biological accumulation and is extremely toxic.

Magnesium is not used very widely. It is a very light metal that can often replace aluminium. It is extracted from dolomite or from seawater and is thus the only metal with very large accessible reserves. Magnesium is not considered toxic, but during production sulphur hexafluoride (SF6) is used as a cover gas. Sulphur hexafluoride is a potent greenhouse gas and only a part of it decomposes during the production process, whilst the rest is released to the atmosphere.

Titanium is the tenth most common element in the Earth's crust, even though accessible reserves are few. The metal has a promising future since extraction costs for other metals are increasing, but it is relatively difficult to extract and requires high energy levels to do so. Titanium dioxide is produced from ore of ilmenite (FeTiO3), and over 90% is used as the pigment titanium white, usually for paints and plastics. Production of titanium oxide is highly polluting, whereas the finished article causes no problems.

Cobalt is used as a pigment and as a drying agent in the painting industry, and also as an important part of various steel alloys. Cobalt is slightly poisonous for plants and water living organisms.

Gold has a very limited use in the building industry. The most important function is the application of a thin layer on windows which then restricts the amount of sun and heat coming into a building, and to colour glass in yellow and red. Of the 80 000 tons of gold calculated to have been mined since the beginning of time, most is still around, partly because gold does not oxidize or break down and partly because of its value. Gold used in window construction is considered to have been taken out of circulation.

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