Tracking the Fate of Aluminium in the EU Using the MaTrace Model

Round 1

Reviewer 1 Report

This piece of research is well introduced and motivated: mapping the aluminium flows in the EU to identify losses, and assessing the impact of different policy, market, and technology-related scenarios to close the loop).

The methodology is well explained: Supplementary materials with nomenclature, full data sets (supported by references) and assumptions, are provided, which is essential to ensure the transparency and reproducibility of the results.

The results, intrinsic flows of aluminum, are well presented. Yet, to bring additional (and more practical/meaningful/tangible) value to the reader, the paper could/should consider to:

- Translate the percentage of mass aluminum that is lost and could be potentially collected/recovered/reuse to environmental and/or economic impact/savings/indicators (such as carbon footprint, energy use, euros, etc.) An example of such analysis can be found here : Saidani, M., Kendall, A., Yannou, B., Leroy, Y., & Cluzel, F. (2019). Closing the loop on platinum from catalytic converters: Contributions from material flow analysis and circularity indicators. Journal of Industrial Ecology, 23(5), 1143-1158.

- Position and discuss these new results for aluminium among other key materials that have already been studied in the literature: a synthesis table would be a great add-ons.

Author Response

Dear reviewer 1, please see the attachment. 

Author Response File: Author Response.docx

Reviewer 2 Report

I Accept this manuscript in present form.

I suggest updating citation [4] on current “The Study on the EU's list of Critical Raw Materials (2020)”

Author Response

Dear reviewer 2, please see the attachment.

Author Response File: Author Response.docx

Reviewer 3 Report

The authors estimate the aluminum quantities in European stocks-in-use of 2018 and then estimate their fate over a period of 25 years. Over these 25 years, they identified quantities remaining in the initial stock (in use or hibernating), physical losses and exports. Scenario modelling is used to identify the consequence of policy options on future aluminum flows. The research is, in principle, of interest for experts in material flow modelling, industrial ecologists and indeed for the aluminum industry. However, I have serious concerns regarding the methodology and the conclusions of the research findings.

Major comments

• Methodology
  • 135: The core paper, which documents the methodology of this research, was developed by Godoy León, Blengini et al. (2020). A paper with the same title has been published but the reference list classifies it as “unpublished manuscript” (see references).
  • The authors estimate future aluminum flows without validating the results. Therefore, it remains fully unclear if the results are realistic and plausible. The manuscript would profit from a validation step.
• Results and interpretation:
  • The authors found that, over a period of 25 years, 61% of the aluminum is physically lost. In other words, it hardly or even not available for further use. This finding contradicts an statement of the Aluminum Association, according to which “… nearly 75 percent of all aluminum ever produced is still in use today” (Aluminium Association 2021). How does this statement fit with high ratio of physical losses?
  • Figure 3: According to the title, this figure shows the evolution of the stock composition. To my understanding only the cast and wrought alloys and the hoarded materials remain in the stock. All other left the stock and are therefore not part of the stock composition. Next, “hoarded” is a verb, “non-selective collection” is a process, ”processing losses” are flows, and “wrought alloys” are products. A sound terminology would help to understand the plot.
  • The largest quantities are “non-selective losses”. This term is used for a wide range of unnamed products and wastes. It would be an added value to name the products and wastes instead of using generic overall terms. Next, it remains unclear why “non-selective” flows are fully lost. Adding evidence/reports to justify the assumption would be beneficial for the manuscript.
• Scenarios: The authors consider scenarios with changing aluminum demands on the one hand. On the other, the model just estimates the recycling flows from the stock in 2018 without considering the input of primary aluminum and imports. Consequently, considering the demand and ratios of recycling material would need the inclusion of the total aluminum supply – at least of my understanding.

Minor comments

• Some typing errors are in the manuscript (e.g. line 461 “de”) and should be corrected.

 

References

Aluminium Association. (2021). "Facts at a Glance."   Retrieved 30.5.2021, from https://www.aluminum.org/aluminum-advantage/facts-glance.

Godoy León, M. F., G. A. Blengini and J. Dewulf (2020). "Cobalt in end-of-life products in the EU, where does it end up? - The MaTrace approach." Resources, Conservation and Recycling 158: 104842.

Author Response

Dear reviewer 3, please see the attachment. 

Author Response File: Author Response.docx

Reviewer 4 Report

The objective of this research is to perform a dMFA of the secondary production of aluminium in the EU technosphere, making use of the adapted version of the model MaTrace, in order to assess the transition of the metal and trace its fate and losses. The structure of the paper is reasonable, and the presentation is accurate, but the paper is not accepted due to the lack of novelty and does not meet the high-quality requirements of the journal for the paper.

1、Whether MaTrace is aimed at secondary production of aluminum or aluminum products, it is not specifically reflected in the abstract.

2、What is the purpose of considering the ways of the alloy composition and the 12 product categories？

3、What is the BAU? What is the parameters of BAU？What factors does it include? Maybe you can introduce BAU in the introduction.

4、Some key data such as Fig. 2 and Fig. 3 cannot be clearly seen from the figure, whether it can be marked on the Fig. 2 and Fig. 3.

5、Abstract：“The results of the different scenarios show that by increasing the collection-to-recycling rates, the aluminium that stays in use increase up to 35%.” How 35% came about？

6、 How to distinguish between EoL and EoS？The conclusion and discussion section, distinguish the discussion from the conclusion.

7、There are some grammar errors in the article.

8、The quality of the figures in the paper requires further improvement, for example, Fig. 4.

Welcome to submit the article again in the future.

Author Response

Dear reviewer 4, please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The authors superficially addressed the main comments/suggestions made by the reviewers. I would invite the authors to consider these remarks/suggestions more carefully, to state the current limitations and their work, and to orient the reader towards complementary studies that could help bridge this gap (e.g. quantification of environmental benefits of closing-the-loop, combination of MFA with other tools, etc., to provide the reader with more significant insights)

Reviewer 3 Report

The authors addressed the comments adequately. 

Reviewer 4 Report

The objective of this research is to perform a dMFA of the secondary production of aluminium in the EU technosphere, making use of the adapted version of the model MaTrace, in order to assess the transition of the metal and trace its fate and losses. The structure of the paper is reasonable, and the presentation is accurate, but the paper is not accepted due to the lack of novelty and does not meet the high-quality requirements of the journal for the paper.

1、Whether MaTrace is aimed at secondary production of aluminum or aluminum products, it is not specifically reflected in the abstract.

2、What is the purpose of considering the ways of the alloy composition and the 12 product categories？

3、What is the BAU? What is the parameters of BAU？What factors does it include? Maybe you can introduce BAU in the introduction.

4、Some key data such as Fig. 2 and Fig. 3 cannot be clearly seen from the figure, whether it can be marked on the Fig. 2 and Fig. 3.

5、Abstract：“The results of the different scenarios show that by increasing the collection-to-recycling rates, the aluminium that stays in use increase up to 35%.” How 35% came about？

6、 How to distinguish between EoL and EoS？The conclusion and discussion section, distinguish the discussion from the conclusion.

7、There are some grammar errors in the article.

8、The quality of the figures in the paper requires further improvement, for example, Fig. 4.

Welcome to submit the article again in the future.