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GALVANIZING AND THE ENVIRONMENT
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Galvanizing, the coating of iron or steel with zinc, is probably the
most environmentally friendly process available to prevent corrosion.
It is estimated that corrosion costs around 4% of GDP in the USA. Effective corrosion protection is a vital means of reducing the energy demands of building and structures.
Every 90 seconds, across the world, one tonne of steel turns to rust; of every two tonnes of steel made, one is to replace rust.
Use of hot dip galvanizing to prevent rust means that for every one
tonne of steel protected we conserve enough energy to satisfy an
average family's energy needs for several weeks.
Galvanizing is efficient in its use of zinc to protect steel for very
extensive periods - saving energy and resources with minimal impact on
the environment. Galvanizing will protect steel structures for decades
and minimises maintenance.
Zinc, the natural element responsible for this corrosion resistance, is indispensable for humans, animals and plants.
PROCESS EFFICIENCY AND RECYCLING
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In the galvanizing process, iron or steel articles are dipped into a
bath containing molten zinc just above its melting point. Any zinc that
does not form a coating on the metal remains in the bath for further
re-use. Galvanizing residues, which consist of dross - a mix of zinc
and iron, and zinc ash, are recovered and zinc recycled for further
use, often in the galvanizing process.
As well as zinc recovered from these residues, recycled zinc from other
sources, such as zinc scrap, is often used in galvanizing.
Galvanized steel can be recycled easily with other steel scrap in the
steel production process. Zinc volatilises early in the process, is
collected as dust and is then recycled.
Improvements in gas burner technology have also undoubtedly improved
energy efficiency in heating the galvanizing bath. Exhaust heat is not
wasted and is used to heat pre-treatment chemicals or dry work prior to
immersion.
The galvanizing industry is committed to understanding and improving of the life-cycle environmental performance of its process and products. Galvanizers Association has recently helped establish a Pan-European Life Cycle Inventory database for general galvanizing. This LCI data will allow Environmental Product Declarations and other life cycle assessments to be made on structures involving galvanized steel.
PROCESS EMISSIONS
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Process emissions from the galvanizing process are very low. Aqueous discharge - all waste liquids - which consist mainly of spent acids used to prepare steel, are removed by licensed waste management companies in accordance with mandatory procedures, thus protecting surface and ground water. Spent acid is also increasingly used to neutralise other wastes and in the manufacture of water treatment chemicals. The industry has greatly improved its utilisation of process chemicals in recent years - reducing the volumes of acid used per tonne of steel processed.
Emissions to the atmosphere are inherently very low and are strictly governed by the Environmental Protection Act. Galvanizing baths must capture their particulate emission to air. This is successfully accomplished by the use of bath enclosures together with filters. A survey by the Environment Technology Best Practice Programme concluded that 'Galvanizers use less than 25 litres of water per tonne of product, compared with 2000 litres in the general metal finishing industry'.
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