Preparation and Melting of Scrap in Aluminum Recycling: A Review
This work provides an overview of the aluminum (Al) recycling process, from the scrap upgrading to the melting process. Innovations and new trends regarding the Al recycling technologies are highlighted. Aluminum recycling offers advantages in terms of environmental and economic benefits. The presence of deleterious impurities in recycled Al alloys is increasing and this is the main drawback if compared to primary alloys. The continuous growth of undesired elements can be mitigated by different
... technologies, preliminary operations and treatments, and by the optimization of the melting process. Downgrading and dilution are possible solutions to reduce the rate of impurities, but they are not sustainable if the final use of Al alloy continuously increases. The main objectives in the development of the Al recycling are shown and discussed. In particular, the evolution of preliminary treatments of the scrap, as sorting, comminution and de-coating, is reported and a review of the melting technologies is also presented. However, the choice of performing preliminary operations to the melting stage, thus improving the operating conditions during the furnace running, is a trade-off between costs and process efficiency. This is the primary route for Al production but a secondary route is available using Al scrap and recycling. It is claimed that recycling saves resources, decreases the need for landfill space and, in the case of non-renewable resources, such as metals, prolongs the necessary period to deplete them. Recycling Strategy Compared to other high-volume materials, such as copper (Cu), zinc (Zn), magnesium (Mg), and steel, Al production has one of the widest energy differences between the primary and secondary routes, but not the main recycled fraction, that is the share of secondary production with respect to the total one (Figure 1 ). The recycled Al fraction is about 35%, which is close to the values of recycled Mg and Zn (~30%). Nowadays, copper and steel remain the materials with the highest impact in terms of recycled amounts (~40%). Figure 1. Energy saving from different metals with reference to the primary production route, and relative recycled fraction. Data refer to 2016 and are elaborated from [6,7].