Discover the chlorine universe

The element chlorine (Cl) is one of the 92 natural elements found on our planet. You'll find it in the 17th column of the famous Periodic Table of the Elements. Only 16 elements constitute 99,5% of the earth crust. In this group of elements, chlorine ranks 11th.

At room temperature, the molecule chlorine (Cl₂) is a greenish gas (see picture left).

Chlorine gas (Cl₂) is made from common kitchen salt (sodium chloride) and water.

About 50 quadrillion tonnes of dissolved sodium chloride (common salt) are found in the world’s oceans and seas. However, less than a third of salt production stems from seawater. The majority comes from rock salt mines hundreds of meters below the surface of the Earth.

Huge machines with sharp rotors tunnel their way through the rock salt. An automatic electrohydraulic drilling machine bores rows of holes about 14 meters deep into the ceiling. They are then filled with explosives which are detonated once all the workers leave the mine. The crushed rock salt is then transported by conveyor belt to the shaft where it is sent to the surface.

Germany is one of the world’s main sources of salt. The country boasts one of the largest salt mines in Europe which is located in Borth. Subterranean deposits are estimated at more than 200,000 million tonnes.

Another method of extracting salt is to pour hot water into underground salt plugs. The salt dissolves and the brine is pumped to the surface. The advantage of this method is that the extraction process can be regulated so that many of the impurities in the salt remain underground. The brine is concentrated by evaporation in large vacuum plants, yielding 99.9% pure salt.

Chlorine and its co-product, caustic soda, are two basic chemical industry building blocks for vast numbers of everyday products that we take for granted today. Examples include pharmaceuticals, medical devices, windows, flooring and pipes.

Chlorine - The element

Chlorine belongs to a group of five chemicals called halogens:

Chlorine
Fluorine
Bromine
Iodine
Astatine

The word ‘halogen’ originates from Greek roots: hal means ‘salt’ and gen means ‘to produce’. All the chemicals in this group produce sodium salts with similar properties. The best known is sodium chloride (common salt).

Chlorine is one of the most common elements in nature.

Chlorinated compounds occur naturally in humans and are found in blood, skin and teeth. Even white blood cells need chlorine to enable them to fight off infections. In nature, chlorine is more plentiful than carbon. It occurs in both plants and animals and makes up 2.9% of the world’s oceans and 0.045% of the earth’s crust.

Chlorine gas was first isolated in 1774 by the Swedish-German chemist, C W Scheele. It is a pale green gas at normal temperature and pressure, but because it is highly reactive it is not found as a gas in nature. Instead, it appears as naturally - occurring organochlorine compounds and salts.

Scientists have identified more than 2,000 naturally-occurring chlorine-based compounds. These perform a range of useful functions in a wide range of organisms, from the Ecuadorian tree frog to Mediterranean jellyfish and from wood-rotting fungi to tropical sea slugs.

For more than 100 years now, industry has exploited this highly-reactive chemical produced from one of nature’s most plentiful and inexhaustible minerals - common salt. Today, chlorine is used in a vast range of processes to create thousands of often indispensable products that serve our everyday needs at work, home and play. Nearly 2,000,000 jobs in European industry are directly or indirectly related to this chemical building block.

07/2008