Red Mud as a Secondary Resource of Low-Grade Iron: A Global Perspective

Round 1

Reviewer 1 Report

This manuscript assessed the suitability of red mud that is a solid waste byproduct of the alumina recovery process, and reviewed the utilization of red mud as a material resource in 26 several commercial, industrial operations. Also, red muds from different parts of the globe were examined for their iron recovery potential. The work provides a comprehensive summary and outlook on the iron recovery from red mud. However, there are some problems with the content in the author's manuscript. The existence of these problems leads me to suggest minor revision.

1. In the introduction part, in addition to the Bayer process, the sintering process is also an important method to extract alumina. It is recommended to more completely compare the two methods and the two red mud produced.
2. The article has listed different approaches for iron recovery from red mud. However, all of the corresponding reviews were positive. Whether to consider making a more thorough understanding on these existing problems of these methods, and envisioning the most feasible recovery route of iron from red mud.
3. The article pointed out that low-grade iron ore and red muds could be used as a low-grade iron resource. Whether to consider briefly illustrating the differences between red mud and common low-grade iron ore, especially the behaviors of Fe₂O₃ and slags during the extraction process using high-temperature methods, for example, higher Al₂O₃/SiO₂ ration in red mud slags. Additional more recent references may help with the understanding. Below are some more examples.

-Hidden values in bauxite residue (red mud): Recovery of metals, By Yanju Liu, Ravi Naidu, From Waste Management 34 (2014) 2662-2673.

- Insight into the relationship between viscosity and structure of CaO-SiO₂-MgO-Al₂O₃ molten slags, By Ziwei Chen, Hao Wang, Yongqi Sun, Lili Liu, Xidong Wang, From Metallurgical & Materials Transactions B 50B (2019) 2930-2941.

- Structural and viscous insight into impact of MoO₃ on molten slags, By Ziwei Chen, Zhao Meng, Lili Liu, Hao Wang, Yongqi Sun, Xidong Wang, From Metallurgical & Materials Transactions B (2021) 3730-3743.

- Development of structure-informed artificial neural network for accurately modeling viscosity of multicomponent molten slags, By Ziwei Chen, Minghao Wang, Zhao Meng, Hao Wang, Lili Liu, Xidong Wang, From Ceramics International 47 (2021) 30691-30701.

4. Some minor points are listed as follows:

(1) P1, line 22, “biproduct” should be “byproduct”. There were some similar errors in the manuscript.

(2) P1, line 31, “was” should be “were”.

(3) P8, line 352, “were” should be “was”.

(4) P12, line 516, “The solid : liquid ratio and amounts…”, there's an extra space.

(5) P18, line 666, please check the title of Reference 19.

(6) P19, line 695, please check the punctuation of Reference 32.

(7) Please check the font of Reference 149-160.

Author Response

Pl see attached file

Author Response File: Author Response.pdf

Reviewer 2 Report

The authors have reviewed the red mud as a secondary resource of low grade iron: a global perspective.                          

The prepared manuscript seems intriguing/interesting. However, the prepared manuscript needs to be revised thoroughly.  Though the manuscript showed a substantial review of literatures on the recovery of low grade iron from the bauxite waste residue as a secondary resources globally.  A lot of grammatical errors and punctuations hinder hitch-free reading of the manuscript.

The following are the specific comments

1. Authors should include the flow sheets used for all the fourteen cases and come up with the best method for recovery iron from red mud.

2. Authors should clearly pinpoint the effective pretreatment process engineering technology for the recovery of Iron from bauxite waste residue (red mud) from the flow sheets used in the fourteen cases cited in the write up. This will give the need for pretreatment of red mud being industrial solid waste or otherwise.

3. The author should endeavor to use pictorial representation (Graphs, images) of data to bring out the salient points in lieu of just characters (words), two images and tables that were used.

Author Response

Pl see attached file

Author Response File: Author Response.pdf

Reviewer 3 Report

The topic presented in this work is really interesting. However several challenges are required:

I analyze the single sections:

Abstract has inappropriate structure. I suggest to answer the following aspects: - general context - novelty of the work - methodology used (describe briefly the main methods or treatments applied) - main results and related interpretations.

The authors should place the study in a wide context and emphasize why it is relevant carrying out the analysis. They should better define the purpose of the work and its significance. In this perspective, the sections are too succinct and fails to effectively point out the relevance of your contribution towards the existing  and recent literature. I suggest the author to look at the role of policy, circular economy and waste management.

Some literature to look at:

https://www.sciencedirect.com/science/article/pii/S0921344919305403

https://www.sciencedirect.com/science/article/pii/S0959652619345184

https://doi.org/10.1016/j.landusepol.2020.104680

https://www.sciencedirect.com/science/article/pii/S0959652620303024

https://www.mdpi.com/2071-1050/12/11/4387

Methods should be described in detail. Indeed, I think the research procedure could be much more clearly described by means of a diagram also highlighting its potential and limit.

Conclusions: Conclusions must also be revised according to the previous comments. As it stands now, they fail to extract all the juice of your work.  In particular, they should discuss practical and policy implications as well as future lines of research.

I hope these comments might help in improving the paper and encourage the authors to move forward.

Author Response

Pl see attached file

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

Thanks for this revised version. After the round of revision I do not believe the paper has achieved a publishable standard. My comments have not been properly considered.

Author Response

Please see the attachment

Author Response File: Author Response.docx