How does the recycling of zinc work?
Zinc is recycled at all stages of production and use – for example, from scrap that arises during the production of galvanized steel sheet, from scrap generated during manufacturing and installation processes, and from end-of-life products.
A zinc sheet roofing, for example, will be removed, re-melted and re-used in the same or other applications. Zinc-coated steels are easily collected and treated in existing process streams. The Electric Arc Furnace (EAF) is the most widely used process for recycling zinc-coated steel. The high temperatures cause zinc – which is volatile at high temperatures – to leave the furnace along with other gases. The gas stream is treated and the zinc collected in the dust, of which zinc (18–35%) and iron are the main constituents. These dusts undergo an enrichment process in a rotary kiln, known as a Waelz kiln. This leads to the production of zinc oxide, which in turn becomes a raw material for the production of zinc metal. Several new technologies are in use or under development for processing EAF dusts and the valuable metals they contain.
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How much zinc can be recycled?
Like any other metal, zinc can be recycled infinitely without loss of properties and quality. The recycling rate of zinc in building and construction applications depends mainly on the collection rate of zinc-containing building and construction products at their end of life. Over 90% of these collected products are recycled. However, since zinc is so durable, it literally takes ages until zinc building products are recovered. What’s more, the construction of new buildings still outweighs the demolition of existing buildings, especially in the fast growing regions of Asia. This means the share of recycled (or, secondary) zinc in new products may currently be rather low (around 40%), but it will grow steadily until the demand for new zinc products is fully balanced by the recovery of used zinc products.
How is recycling accounted for in the environmental profile of zinc?
Life Cycle Assessment (LCA) provides a scientifically sound method for calculating the environmental impact of raw material acquisition, product use, and end-of-life management. ‘Zinc for Life’ contributes to the development of appropriate calculation methods which take the recycling of zinc into consideration.
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