A simplified dry recycling process to recover the 5-10% of aluminium which remains in the aluminium salt cake produced in the smelting process of secondary aluminium, has been developed by German recycling equipment manufacturer, BHS-Sonthofen.
According to the company, to date the recovery of this aluminium has thus far proven difficult, costly and time consuming. However, it said that it has now developed a new process based on the selective impact crushing of the salt cake.
By using its multi-functional Rotorshredder and VSI rotor centrifugal crusher, BHS-Sonthofen said that its process has a number of advantages over traditional methods including lower power consumption, lower wear and maintenance costs as well as lower noise pollution – as well as no danger of dust explosion due to the continuous dust extraction system.
The company claimed that the design of its machines means that in spite of the low energy consumption required by the drive systems, materials are propelled in the at great velocity. This was said to generate high impact, shock and stress forces ensuring materials are cleanly separated.
Due to its nature, BHS-Sonthofen said that salt cake lends itself well to an impact crushing process. Brittle slag flakes break off of the comparatively soft aluminium when the impact forces exerted by the Rotorshredder hammers and the fixed anvil ring of the VSI rotor centrifugal crusher come into contact with the materials.
The company explained that it uses a two stage process. First a Rotorshredder crushes the feedstock, which can contain salt cake pieces as heavy as 120 kg and solid aluminium pieces as large as 80 mm, down to a grain size of 40 mm.
The second step employs the BHS VSI rotor centrifugal crusher of type RSMX. At this stage the company said that materials from the secondary crushing process are screened using a screening cut of 1-3 mm, 3-10 mm and larger than 10 mm.
These sized fractions are the conveyed to specially tailored magnetic separators sensitive to the appropriate grain size for the removal of any captured ferrous materials.
According to BHS-Sonthofen, aluminium can then be effectively separated from the slag residue using cyclone separators.
The resulting final product was said to be a clean aluminium granulate, which can be sold and returned to the materials recycling loop. The salts are further processed and then also reused in the smelting process. Only the fine fraction of 0 to 1 mm is discarded.
The company said that testing at the BHS Technology Centre with materials from a German customer has shown that around 8% more aluminium can be recovered using this method
"With the new process a recoverable value of approximately 800,000 Euros is achievable from a feed stock volume of 10,000 t,” commented Alfred Weber, sales director of the Recycling Division at BHS-Sonthofen. “It is economical in many cases to process the aluminium slag where it originates - directly in the smelting plant."
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