Galvanising improves longevity, recyclability

The main application of zinc is to protect steel from corrosion through hot-dip galvanizing, with the zinc-steel combination creating significant economic benefits in terms of life cycle costs.

Air quality in many industrialised countries with high levels of sulphur dioxide encourages the use of zinc coatings to provide longer protection for steel.

International Zinc Association (IZA) Africa executive director Simon Norton states that steel is one of the most commonly used materials on the planet and, when combined with zinc, steel’s durability can be prolonged.

He explains that both steel and zinc are able to be recycled indefinitely without the loss of chemical or physical properties, with steel being the most recycled material globally, with almost 100% of structural steel and 94% of structural shapes built from recycled steel. Norton adds that the reclamation rate for zinc is over 80%.

Further, about 70% of zinc produced originates from mined ores with 30% coming from recycled or secondary zinc. The level of recycling is increasing in step with progress in zinc production and recycling technologies.

The life of zinc-containing products and zinc-treated structures varies, but items such as streetlight poles made of zinc-coated steel can remain in service for 50 years or more.

“All these products tend to be replaced [owing] to obsolescence, not because the zinc has ceased to protect the underlying steel. For example, zinc-coated steel poles placed in the Australian Outback a hundred years ago are still in excellent condition,” reports Norton.

Steel’s recyclability is not restricted by the presence of a zinc coating. He notes that all zinc-coated products are recyclable, with some zinc-coated steel being recycled along with other steel scraps during the production process, during which the zinc volatilises and is recovered.

Norton notes that over the next five years, the supply of zinc-coated steel scrap is expected to double as more zinc-coated products enter the recycling stream.