The top layer of aluminium metal in a furnace oxidizes to produce a "skin" which is called dross. Dross is skimmed off the top surface leaving behind the pure metal. Aluminium dross is produced from the production process of primary aluminium and recycled aluminium as well as the downstream processing units that transform the metal into new forms. Utilizing various technologies currently available, it is possible to recover the metal contained in dross and return it to the aluminium value chain.
The main components of dross are metallic aluminium, aluminium oxidation, and oxides of alloying elements. Furthermore, dross contains finely distributed gas bubbles that enable it to reduce density, minimizing its difficulty in being separated from the aluminium melt. While the recovery of aluminium metal from dross can be a profitable opportunity, it is also viewed as an essential component from an environmental perspective.
Dross generated from primary aluminium smelters averages around 1% of the aluminium produced, and that produced from recycling units averages around 7%. The amount of aluminium dross produced by downstream processors such as extruders, rolling mills, foundries, and wire rod manufacturers with ingot melting facilities averages about 2%. Dross generation depends on several factors including the furnace type, feedstock condition, and operating practices.
In the dross, metal contents can range from 5 to 80%. A much higher level of aluminium is found in dross from primary aluminium smelters than in scrap generated by recycling operations. The metal oxidises rapidly when the temperature rises above 780ºF and hence dross has to be handled the right way and removed at the right time. Around 1% of the aluminium can be lost per minute through oxidation. Treatment of dross after skimming is the most critical factor that determines the metal content and value of dross.
Recycling aluminium dross is environmentally friendly, and the dross can be processed into several other products that have commercial value.
Increasing pollution, excessive energy loss, and natural resource waste have raised red flags that industries cannot afford to ignore. Ignoring the effects could cost the industry its very existence, as the stakes are way too high. The aluminium industry also initiated considering aluminium dross recycling keeping in mind the sustainability issues as the key objective.
Additionally, aluminium dross interferes with natural microbial activity and ignites or pyrolysis surrounding solid waste. Chemical reactions involving aluminium can also release a large amount of highly toxic and/or flammable gases which can aggravate pollution manifold.
In the last few years, technologies for processing aluminium dross and recycling dross have advanced significantly. With sustainable aluminium industry development becoming more relevant, this trend will flourish in the years to come.
January 21, 2022