Combined Decarbonizing Technologies for Treatment of Bauxite Residues

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Dear Author,

Thank you for submitting your research manuscript. This paper provides a detailed discussion on the recovery of valuable metals from bauxite residue. After reviewing it, I believe that a few minor adjustments could further improve the overall quality of the paper. Below are some suggestions for your consideration:

1. In lines 109 and 175, the references (Alkan et al., 2018) and [Nature 2024] are recommended to be formatted in numerical style. Please verify the consistency of the citation format throughout the entire manuscript.
2. Regarding Figure 1, would it be possible to consider only presenting the diagram for iron reduction? The issue of cobalt is not mentioned earlier in the paper, and this might confuse the reader regarding the purpose of cobalt reduction. If cobalt reduction is significant to your study, I suggest providing a further explanation in the manuscript.
3. In the section on page 19, it appears that a 10-minute reduction time is identified as the optimal parameter. Could you provide more explanation to help the readers understand why this specific duration was chosen?
4. For the parameters presented in Figure 17, have other parameters been tested for comparison to confirm that the selected parameters are indeed the optimal ones?
5. Line 566 mentions an iron content of 99.5%, yet the conclusion states it as 99.9%. Could you please clarify if there is any discrepancy in the data?
6. Finally, while carbon emissions and recycling costs are mentioned in the conclusion, there does not seem to be a direct comparison of the carbon emissions and costs associated with the recycling process and the original mining in other sections of the paper. Perhaps you could consider adding a discussion on this topic to enhance the completeness of the conclusion.

Thank you again for submitting this insightful research. I look forward to seeing your revised version, and I believe these adjustments will further enhance the quality of the paper.

Author Response

Dear Reviewer,

Thank you for your thorough and insightful comments. We have carefully addressed each of your concerns and made the necessary revisions to improve the manuscript. Please find our responses below:

1. In lines 109 and 175, the references (Alkan et al., 2018) and [Nature 2024] are recommended to be formatted in numerical style. Please verify the consistency of the citation format throughout the entire manuscript.

In response to your comment, we have reformatted the references in lines 109 and 175 to numerical style, as per your suggestion, throughout the entire manuscript.

2. Regarding Figure 1, would it be possible to consider only presenting the diagram for iron reduction? The issue of cobalt is not mentioned earlier in the paper, and this might confuse the reader regarding the purpose of cobalt reduction. If cobalt reduction is significant to your study, I suggest providing a further explanation in the manuscript.

We understand your concern regarding the inclusion of cobalt reduction in Figure 1, especially since it was not previously mentioned in the manuscript. In response, we have revised the figure to focus solely on the diagram for iron reduction. Additionally, any mention of cobalt reduction has been removed from the text to avoid potential confusion for the reader.

3. In the section on page 19, it appears that a 10-minute reduction time is identified as the optimal parameter. Could you provide more explanation to help the readers understand why this specific duration was chosen?

10-minute reduction time was identified as the optimal parameter based on the balance between maximizing metallic iron formation and minimizing mass loss. As observed in our experiments, extending the reduction time beyond 10 minutes resulted in a decrease in the mass of formed iron. This reduction can be attributed to increased material loss at high temperatures and potential interactions between the material and the reactor, which may lead to mass and iron loss.

4. For the parameters presented in Figure 17, have other parameters been tested for comparison to confirm that the selected parameters are indeed the optimal ones?

Due to the very limited amount of sample available, only one experiment was conducted. The parameters presented in Figure 17 were selected based on insights and experience gained from our previous study [48].

5. Line 566 mentions an iron content of 99.5%, yet the conclusion states it as 99.9%. Could you please clarify if there is any discrepancy in the data?

Upon reviewing the manuscript, we realized that there was an error in the mentioned value. The correct value is 99.5, and we have now corrected this in the conclusion.

6. Finally, while carbon emissions and recycling costs are mentioned in the conclusion, there does not seem to be a direct comparison of the carbon emissions and costs associated with the recycling process and the original mining in other sections of the paper. Perhaps you could consider adding a discussion on this topic to enhance the completeness of the conclusion.

Regarding your suggestion to include a direct comparison of carbon emissions and recycling costs versus original mining, we appreciate this valuable input. However, due to the scope of our study, a detailed comparative analysis was not conducted. We acknowledge the importance of this aspect and will consider it for future research.

We appreciate your valuable feedback, which has helped us improve the clarity and structure of the manuscript. We hope that the revised version meets your expectations and can be published as soon as possible.

Best regards

Reviewer 2 Report

Comments and Suggestions for Authors

• The paper can be accepted after major revision.
• Is 5 mol/L H2SO4 economically feasible?
• Delete Table 1 and mention the minerals in the text.
• Why did the authors mention rare earths in the introduction? Please delete lines 82-90.
• The authors should clearly show the novelty.
• The introduction is too long.
• The authors introduced a bibliography of reduction first in Lines 68-81 and then 136-190. Those should be combined and summarized.
• Why didn’t the section “Thermochemical Calculation” have the number? The place of this section is not suitable and should be transferred to the discussion section or before the discussion and after materials and methods.
• Line 202: During, not during.
• In Fig. 1-3, which software was used?
• Why did the authors mention cobalt in Fig. 1? Where does cobalt come from?
• In Fig. 2, why was the Fe2O3 49% etc.?
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•  Delete fig. 6.
• Where is the Bosnia’s BR characterization in Table 3?
• XRD analysis of the feed sample should be represented.
• Is the authors' work on rare elements mentioned in Table 5? It can be deleted.
• Why did Fig. 7 bring before 2.2.1?
• Fig. 8 is not an experimental design; it is a flow diagram.
• What are the conditions of set no. in Fig. 12?
• In Table 5, why have these impurities just been selected?
• Page 18 should be summarized.
• The leaching sections did not have discussion and interpretation.
• Eqs. 4-8 need references.
• The conclusion should be summarized.
• The number of figures and tables is too much. Some of them should be deleted or merged.
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Comments on the Quality of English Language

no comments. 

Author Response

Thank you for your thorough and insightful comments. We have carefully addressed each of your concerns and made the necessary revisions to improve the manuscript. Please find our responses below:

1. Is 5 mol/L H2SO4 economically feasible?

Thank you for your question regarding the economic feasibility of using 5 mol/L H₂SO₄. The selection of this concentration was based on its effectiveness in achieving the desired reaction outcomes. However, we acknowledge that higher acid concentrations can contribute to increased operational costs. While 5 mol/L H₂SO₄ provides optimal performance in our study, further evaluation considering large-scale process economics, acid recovery, and material costs would be necessary for industrial implementation. We appreciate your suggestion and will consider addressing this aspect in future work.

2. Delete Table 1 and mention the minerals in the text.

Table 1 has been removed, and the mineral composition has been incorporated into the text.

3. Why did the authors mention rare earths in the introduction? Please delete lines 82-90.

The authors mentioned rare earths in the introduction because the REE content has been analyzed in red mud, slag, and metal in the paper. This provides context for their relevance to the study. This is important to show a high significance of this material for future investigation!

4. The authors should clearly show the novelty.

We have revised the manuscript to explicitly highlight the novelty of our work.

5.The introduction is too long.

Thank you for your feedback. We have revised the Introduction section to make it more concise and focused.

6. The authors introduced a bibliography of reduction first in Lines 68-81 and then 136-190. Those should be combined and summarized.

We acknowledge the redundancy in the discussion of reduction processes and have revised the manuscript by combining and summarizing Lines 68–81 and 136–190.

7. Why didn’t the section “Thermochemical Calculation” have the number? The place of this section is not suitable and should be transferred to the discussion section or before the discussion and after materials and methods.

Section Thermochemical Calculation has been put in Results and Discussion. Thank you for your suggestion

8. Line 202: During, not during.

Corrected. Thank you

9. In Fig. 1-3, which software was used?

FactSage, GTT Technologies was used for thermochemical calculations

10. Why did the authors mention cobalt in Fig. 1? Where does cobalt come from?

The mention of cobalt has been removed from the manuscript, along with Figure 1. Cobalt is no longer discussed in the text as it is not relevant to the scope of this study. We appreciate your attention to detail.

11. In Fig. 2, why was the Fe2O3 49% etc.?

In Figure 2. that content was used for thermochemical calculations because calculations were done before hydrogen plasma reduction process.

12. Delete fig. 6.

Figure 6. has been deleted.

13. Where is the Bosnia’s BR characterization in Table 3?

It is in third column (Republic of Srpska (B&H))

14. XRD analysis of the feed sample should be represented.

It is presented in Figure 2. (before Figure 7.)

15.Is the authors' work on rare elements mentioned in Table 5? It can be deleted.

The content of rare earth elements (REE) has been analyzed in red mud, slag, and metal, making it relevant to the scope of this study. Therefore, it is important to show how REEs behave during the reduction process. As a result, their inclusion in Table 5 remains justified.

16. Why did Fig. 7 bring before 2.2.1?

It has been corrected.

17. Fig. 8 is not an experimental design; it is a flow diagram.

It has been corrected. Thank you

18. What are the conditions of set no. in Fig. 12?

It has been corrected, it was set 3-2, 10 minutes reduction time

19. In Table 5, why have these impurities just been selected?

These specific impurities were selected because their content was analyzed in both the slag and metallic phases. This allows for a comprehensive understanding of their behavior during the reduction process.

20. Page 18 should be summarized.

Page 18 has been summarized

21. The leaching sections did not have discussion and interpretation.

We appreciate your observation regarding the leaching sections. We would like to clarify that the leaching process was thoroughly explained in both the Materials and Methods section, where the methodology was outlined, and in the Results and Discussion section, where the outcomes of the leaching tests were analyzed and interpreted in detail.

22. Eqs. 4-8 need references.

Corrected

23. The conclusion should be summarized.

Conclusion has been summarized.

24. The number of figures and tables is too much. Some of them should be deleted or merged.

Number of figures and tables has been decreased with some of them being merged.

We appreciate your valuable feedback, which has helped us improve the clarity and structure of the manuscript. We hope that the revised version meets your expectations and can be published as soon as possible.

Best regards

 

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

I sincerely appreciate the author's efforts in completing all the revisions, which have significantly enhanced the depth of the paper. Thank you for your valuable contribution.

Reviewer 2 Report

Comments and Suggestions for Authors

Authors have used improper terminology for their feed names and others, confusing readers. Therefore, all these names should be revised to be better understood.

The leaching sections did not have discussion and interpretation based on references.