Table 13 Transversal cutting data for the AA 3005 alloy
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approach, ISO 21930 and EN 15804 both contain specific requirements regarding how to process scrap shall be mod- eled. All these requirements are presented in the context of a full life cycle carbon footprint, and their applicability in the context of the cradle-to-gate approach, which is the case of this work, is subject to interpretation. In this work, we decided to consider the secondary aluminum burden-free on the assumption that the material is a waste which the holder intends to dispose of. coal The life cycle impact assessment is performed by using the CML 2001 methodology (Humbert et al. 2009), and the following indicators have been chosen: depletion of abiotic Fig. 1 Scheme of the modeled production system An aspect which deserves to be explained in more words is how the alloying elements are considered; usually, this is not clarified in these types of studies, and in fact, there are so far no existing guidelines published on how the alloy- ing elements should be accounted for and modeled. In this As for all the plants, there are some resources and processes that cannot be directly imputed to one product because are common services used by the whole plant, usu- ally defined as general plant consumptions. The problem tod ent int to d products ecide how to allocate these consumptions on the differ- produced is faced by all the people working his field (Liu 2013); in this study, it has been decided ivide those consumptions for the total mass of prod- ucts produced and then to multiply for the produced mass of t he specific product under investigation. The following general consumptions have been considered and charged on t he studied products: electricity and natural gas used for general services (e.g., energy consumed by the offices, in the warehouses), water withdrawals and discharges, use of Table 4 Fusion process data for the AA 5052 alloy Table5 Milling, heat treatment, and hot rolling data for the AA 3005 alloy (including also the packaging materials disposed of), the water consumption of the plant (water, in the ground), and the consequent discharge of wastewater (treated wastewa- ter), the consumption of auxiliary substances such as diesel oil, nitrogen, oxygen, and chemicals for water treatment, and the consumption of electricity and natural gas for gen- eral services. The “Water treatment chemicals” input was modeled by entering all the consumption of chemicals for water treatment. In the database available in GaBi, there are no flows associated with the different chemicals used. Table6 Milling, heat treatment, and hot rolling data for the AA 5052 alloy k Sea transport Table 8 Cold rolling data for the AA 5052 alloy 7 Sea transport Table 7 Cold rolling data for the AA 3005 alloy Table 9 Heat treatment data for the AA 3005 alloy Table 10 Heat treatment data for the AA 5052 alloy Table 11 Surface treatment data for the AA 3005 alloy Table 12 Surface treatment data for the AA 5052 alloy Table 14 Transversal cutting data for the AA 5052 alloy As expected, the raw materials and the manufacturing process are responsible for the most of the environmental impact, while the transport has a minor impact (even if rel- evant and not negligible). The first consideration that comes out is that in aiming to reduce the environmental footprint, three actions must be taken: (i) promote the use of secondary aluminum, (ii) improve the manufacturing process, (iii) try to shorten the logistic lines. The manufacturing route has a great importance, so a lot of effort must be put to improve this step. Table 15 Packaging data for the AA 3005 alloy Table 17 General consumption data for the AA 3005 alloy Looking more inside the processing route melting and hot rolling are the most impacting processes, probably due to the high energy required to heat up the aluminum slabs. It is worth noting that probably the impact of these two steps is underestimated in this study because the impact of the fabrication of the equipment used has been not considered, and the manufacturing of equipment usually employed in high-temperature metal working has a high impact on the environment. It is also important to appreciate that the gen- eral consumption is not negligible and plays an important role in the environmental footprint of the process. Table 16 Packaging data for the AA 5052 alloy Fig. 2. Scheme of the modeled process as shown by the Gabi interface software used for LCA studies: SimaPro (Pre-sustainability 2012) and GaBi (PE-international 2012), both of which are commonly employed worldwide. The same authors (Speck et al. 2016) compared these two software and found that the differences observed when modeling the same system with dif- ferent software can be mainly attributed to different errors in different databases. Other authors focused their attention on this issue: (Speck et al. 2015) reported that even when inputs are matched as closely as possible, implementations of a supposedly common methodology in different LCA software systems can provide differing results. Conversely to what has been observed in the previous paper, Speck et al. assessed that the most com- mon cause of differences between implementations of impact assessment methods in SimaPro and GaB31 is that one software includes characterization factors for substances that the other software excludes. The same authors in a different paper (Envi- ronmental profile report from the aluminium industry) further ronmental profile report from the aluminium industry) further In performing an LCA analysis, a key factor is the choice of the software to be used for modeling and impact calcula- tions; according to Speck et al. (2016), there are two leading Table 18 General consumption data for the AA 5052 alloy Lastly, it can be noted that the AA 5052 plates have a bigger environmental impact with respect to the AA 3005; this can be attributed to the higher percentage of primary aluminum used. This result is also useful in supporting the decision of the designer when the material to be used for a new product must be chosen; both the alloys are used for food packaging, so, when possible, the one with the lesser environmental impact should be used. The higher environ- mental impact of AA 5052 can also be attributed to the high magnesium content (> 2%wt); this particular alloying ele- ment involves higher impacts for two main reasons: (i) high impacts related to the extraction and refinement of this ele- ment; (ii) the presence of Mg in aluminum, together with the advantages provided, involves some processing issues who make the rolling stage more complex and less environmen- tally friendly (Herrmann and Moltesen 2015). Table 19 Substances used for process water treatment Table 20 Water discharges evidenced that the choice of software program used for environ- mental analysis can affect the results attributing this occurrence to the natural inclination of the user to employ data sets that are “convenient” when using specific software packages. The pre- sent work has been performed by using Gabi; following the find- ings of the above-discussed papers and aiming to obtain results as more reliably as possible, the following strategies have been adopted: the use of database data has been limited as much as possible to reduce the influence of the software used; the dataset chosen was the most representative ones for the modeled pro- cesses. A line of future work can be to perform the same analysis with different software and compare the obtained results. Table 21 Wastes sent to disposal Table 22 Calculated impacts for 1 kg of AA 3005 plates Table 23 Calculated impacts for 1 kg of AA 5052 plates decreases occur in the impact categories depletion of abiotic resources-fossil fuels (ADPf) and climate change (GWP). the thickness of the sheet, lesser material is used for the same product so the impacts related to the raw material are reduced; (ii) the reduction of the thickness requires a further rolling stage, increasing the impacts related to the processing; (iii) in this study, the fabrication of the final product and the use phase is not considered; to better evaluate the influence of thickness, these stages must be included and carefully considered. Similarly, it can be argued that a reduction of the envi- ronmental impact of primary aluminum fabrication would reduce the impact of the product system considered in this work, so the companies should pursue these two strategies: on one hand to reduce the use of primary aluminum and on the other hand to select suppliers who produce primary aluminum in an environmentally conscious manner. Another important point to reduce the environmental impact is the material use efficiency, so one can argue that a reduction of the can thickness, leading to the use of lesser material for the same product, could further reduce the environmental impact. This question is more complex because conflicting issues are coupled: (i) when reducing 4 Conclusions In this work, a detailed LCA analysis, with a cradle-to-gate approach, has been performed on two functional units: rolled plates of AA 3005 and AA 5052. The emphasis
