Zinc ash
Fact sheet
Department of the Environment and Heritage, July 2003
PDF file
About the fact sheet
What is zinc ash?
- Zinc ash is oxidised zinc that forms on the surface of molten zinc metal.
- The ash (see photo) consists of a powdery material (the ash proper) and solid metallic pieces of an irregular shape.
- It is sometimes called zinc dross, zinc skimmings, zinc top dross or zinc oxide. In the galvanising industry itself, the term zinc ash prevails.
Where does it come from?
- Zinc ash usually arises from hot dip galvanising or other zinc coating processes.
- The ash is removed from the top of galvanising baths by skimming or straining.
- There are over 30 galvanisers in Australia (see www.gaa.com.au/members.htm and www.indgalv.com.au).
Where does it go?
- There are several major companies that process or recycle zinc ash domestically.
- One of these companies mechanically separates the metallic zinc from the ash.
- Another company does this and blends the zinc ash to make agricultural grade zinc oxide.
- A number of galvanising companies also mechanically separate the metallic zinc from the ash.
- The metallics are re-used in galvanising and other processes.
- Another company smelts both processed ashes and unprocessed ash to recover the zinc in metallic form.
- Export or import of zinc ash without a permit contravenes the Hazardous Waste (Regulation of Exports and Imports) Act 1989.
Is it hazardous?
- Zinc ash frequently contains lead at concentrations that make it hazardous to humans, other animals and plants.
- The National Occupational Health and Safety Commission has classified materials containing lead compounds at concentrations greater than 0.5% as designated hazardous substances.
- Lead can leach out of zinc ash into the environment and there are tests which may be used to determine whether or not this may happen in particular circumstances.
- Work-place controls are required in factories that recycle and process zinc ash.
Need further information?
For general enquiries, contact the Hazardous Waste Section, the Department of the Environment and Heritage: E-mail: hwa@environment.gov.au or Internet site: http://www.deh.gov.au/industry/chemicals/hazardous-waste/index.html
To contact the Galvanizers Association of Australia see www.gaa.com.au/members.htm
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