What was once considered an industrial waste with absolutely no value is now being recycled at Alcoa Kaal’s rolling mill in Victoria, Australia. This effort is eliminating 6,000 metric tons (6,614 tons) of landfilled waste annually and recovering materials for use in the aluminum and other industries. The material being recycled is dross, and the pilot plant proving the concept of recycling is the first within Alcoa.
Dross is the accumulated scum that floats on the surface of aluminum that is being melted down from scrap. Hot dross is between 700°C (1,292°F) and 1,500°C (2,732°F), and it consists of various metals and their oxides, including aluminum, magnesium, and copper.
Traditionally, Alcoa Kaal’s hot dross was cooled in a large shed before being shipped offsite to a treatment furnace. Metal was recovered in ingot form, but approximately 60% of the dross became a hazardous waste known as salt slag.
At Alcoa Kaal’s new onsite recycling plant, hot dross is placed into refractory-lined containers and processed in several stages. The result is much lower volumes of salt slag.
Recovered molten metal is reused in the furnace. Fine residue will potentially be used in the cement industry as an alumina additive, reducing the amount of raw alumina required for cement production. Dross dust from the fume and dust collection system baghouse is currently being evaluated for use in the ceramics industry.
With the new recycling plant, 60% of the dross is recovered as metal pure enough to be used onsite for the manufacture of aluminum ingot. Further processing results in fine course fraction for possible use in the cement industry and course fraction that is currently reprocessed. Approximately 1% of dust is extracted through the fume and dust collection system. Additional benefits to the system include reduced energy consumption and an improved work environment due to the process changes and dust extraction systems.
Alcoa Kaal’s hot dross recycling process results in only 13% salt slag waste, a significant drop from the traditional 60% level. Ultimately, the goal is zero waste, but additional technology and process stages will be required to reach this target.
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Alcoa Kaal Australia
Alcoa Kaal produces can sheet, general sheet, and plant and foil.
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