Thermodynamics of Aluminothermic Processes for Ferrotitanium Alloy Production from Bauxite Residue and Ilmenite

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This is an interesting topic and, overall, well written article. However, there are a few important aspects that have to be addressed.

1) In the introduction, please add a description about aluminothermic route, providing references to previous works. Are there any alternative routes, and what are the benefits of different routes? Why did you choose aluminothermic? Has anyone tried this route using BR or are you the first?

2) In the main text, it feels like the mass balance is missing. You need to clearly explain what has happened in the experiments. E.g., in the case of 50:50 proportion, what per cent of titanium has come from BR versus virgin ilmenite. Have you recovered any titanium at all? What are the losses of titanium to slag? Would addition of BR and Al metal improve the recovery of titanium from ilmenite, no change, or decrease it?

3) The mass balance would also highlight that, ideally, you need to include in the experiment the cases of 0:100 and 100:0 of BR and ilmenite mixture. You really have to understand how much of Ti is lost versus recovered in your experiments, from which feedstock material and why.

4) There seem to be a significant per cent of aluminium in the final product(s). This is not a Fe-Ti alloy per se but more like Fe-Al-Ti. What does this mean? Is it beneficial or detrimental? Please provide additional clarification, and/or intended use of the produced alloys.

5) In case of Fe-Al-Ti being beneficial, it would be also important to comment on the aluminium mass balance, e.g. how much is lost to slag versus recovered into product. Would it be beneficial to increase Al content? 

Author Response

Thanks for your comments! Please check the responses in the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

In this study, the authors investigated an aluminothermic process for producing a FeTi alloy by combining bauxite residue (BR), ilmenite ore, and fluxes based on thermodynamic calculations and batch experiments. The results presented here may be beneficial to developing a new process for the valorization of BR; however, they have insufficient evidence and are not persuasive. Hence, the authors should discuss more quantitatively based on data. My comments are given below.

 Lines 11 and 25: Add “(BR)” after “bauxite residue”.

Lines 44, 45, 47….: Display number in chemical formula as a subscript.

Lines 47–49: The authors should provide evidence (or references) supporting this.

Figure 2: Some figures have difficulties distinguishing symbol colors.

Lines 125–133: What analytical methods did the authors use for the determination of chemical composition of alloy and slag samples? This should be mentioned in detail.

Titles of Tables 3 and 4: Eliminate “estimated with FactSage 8.2”.

Lines 149–151: The reviewer cannot judge whether this is truly the case, because data are not shown. The authors should discuss quantitatively based on data. What is “ISO specifications”?

Line 153: The reviewer does not agree with this. Is the increase in the amount of Al in the slag significant statistically?

Lines 154–156: The reviewer cannot judge whether this is truly the case, because data are not shown. The authors should discuss quantitatively based on data.

Lines 181–182: The reviewer cannot judge whether this is truly the case, because data are not shown. The authors should discuss quantitatively based on data.

Author Response

Thanks for your comments! Please check the responses in the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Thank you for the revised version, however, most comments have not been adequately addressed. Current version is not scientifically sound, and not acceptable for publication. A few major and further comments are below.

1) There is no estimated titanium recovery in your study. This is one of the major requirements for a new/improved process.

2) The recovery must be estimated, or at least back-calculated for all major sources of raw materials. So far, it looks like the recovery of Ti from bauxite residue is very minor if any. It is likely that adding BR to the process reduces the overall recovery of titanium and negatively affects the value of final products. Please check and address this carefully.

3) The mass balance, in one form or another, is a must for this type of research. How much titanium (and other elements) got in, and how much got out? Have you lost anything in the process, e.g. to emissions? Is it significant, does it need additional treatment (e.g. chlorine in emissions), and/or other environmental concern? How much aluminium has been added (in grams not a relative excess per cent of something)? Aluminium is clearly by far the most expensive raw material in this process, it may even cost more per tonne than the final product itself.

4) If slag is also a major product and outcome from this process, please provide additional characterisation and/or specify where this product is going to be used. Is is suitable for cement production despite very high sodium content? Why not to use BR directly for cement production? How is slag better?

5) Consider adding slag to the title of the article, if this is one of your major products.

6) In the introduction, there seem to be a misstatement about aluminothermic method for Ti-Al alloys production being widely used in the last few years. Do you mean commercial application worldwide, research, or in your lab only? Please check and provide a reference. 

Comments on the Quality of English Language

Please check

Author Response

Reviewer 1 Round 2

Thank you for the revised version, however, most comments have not been adequately addressed. Current version is not scientifically sound, and not acceptable for publication. A few major and further comments are below.

1) There is no estimated titanium recovery in your study. This is one of the major requirements for a new/improved process.

2) The recovery must be estimated, or at least back-calculated for all major sources of raw materials. So far, it looks like the recovery of Ti from bauxite residue is very minor if any. It is likely that adding BR to the process reduces the overall recovery of titanium and negatively affects the value of final products. Please check and address this carefully.

Thank you for your remarks. As it was answered last time, complete mass balance was not possible to be performed because during the lab experiments there wasn’t a complete separation of the alloy and the slag, thus limiting us on the evaluation of the masses and on the revoveries. Many samples taken from both the alloys and the slag in each experiment, led us to the results shown in the paper. The addition of BR in this process is intended for using a residue as an alternative raw material and not for optimizing an already existing process.

3) The mass balance, in one form or another, is a must for this type of research. How much titanium (and other elements) got in, and how much got out? Have you lost anything in the process, e.g. to emissions? Is it significant, does it need additional treatment (e.g. chlorine in emissions), and/or other environmental concern? How much aluminium has been added (in grams not a relative excess per cent of something)? Aluminium is clearly by far the most expensive raw material in this process, it may even cost more per tonne than the final product itself.

Thank you for your remarks. As it was answered last time, complete mass balance was not possible to be performed because during the lab experiments there wasn’t a complete separation of the alloy and the slag, thus limiting us on the evaluation of the masses and on the revoveries. The aluminothermic production of ferrotitanium alloys is a well established process with the use of ilmenite and TiO₂ as raw materials. In this study, a new alternative raw material(BR) is used by replacing part of the ilmenite. Al has a much lower price than Ferrotitanium, that is why Ferrotitanium is produced this way. The addition of Al varies depending on the mixture since different amounts of Fe and Ti are inserted in the mix every time. This is why it is expressed as an excess of the stoichiometrically needed.

4) If slag is also a major product and outcome from this process, please provide additional characterisation and/or specify where this product is going to be used. Is is suitable for cement production despite very high sodium content? Why not to use BR directly for cement production? How is slag better?

Thank you for your comment. One of the main scopes of this study was to reduce the Ti in the slag for further use in the cement industry and this was achieved compared to BR as is and to a slag coming from a carbothermic reduction of BR for the production of pig iron. This slag can be used for CAC (Calcium Aluminate Cement) applications. BR is used in the cement production as a raw material for clinker production at a low percentage since it does not exhibit pozzolanic or hydraulic activity. Slags produced from BR reductive smelting exhibit such properties and can be used as SCM (Supplementary cementitious materials) more widely. The minor elements content and the applicability on the cement application is further research intended to be performed in the future.

5) Consider adding slag to the title of the article, if this is one of your major products.

Thank you for your comment. It was not added because this article focuses on the aluminothermic process and the thermodynamics behind it.

6) In the introduction, there seem to be a misstatement about aluminothermic method for Ti-Al alloys production being widely used in the last few years. Do you mean commercial application worldwide, research, or in your lab only? Please check and provide a reference. 

Thank you for your comment however there is no mentioning of Ti-Al alloys anywhere in the article and the production and applicability of the FeTi alloys has a reference, number 13  

Reviewer 2 Report

Comments and Suggestions for Authors

The reviewer thinks that the revised manuscript has been satisfactorily improved. Hence, this is acceptable for publication. However, the authors should correct the following.

In this paper,  number in chemical formula is not displayed  as a subscript (e.g., TiO2, Al2O3 and Fe2O3). 

Author Response

Reviewer 2 Round 2

The reviewer thinks that the revised manuscript has been satisfactorily improved. Hence, this is acceptable for publication. However, the authors should correct the following.

In this paper,  number in chemical formula is not displayed  as a subscript (e.g., TiO2, Al2O3 and Fe2O3). 

Thank you for your remark. It is now displayed correctly

Round 3

Reviewer 1 Report

Comments and Suggestions for Authors

Thank you for the revisions. There are some improvements and explanations provides, but a few flaws still remain, please address those carefully.

1) In the introduction, there a false claim that aluminothermic method for producing FeTi from ilmenite is the most widely used. Please review additional literature on the topic. One suggestion is:

El Khalloufi, M., Drevelle, O. and Soucy, G., 2021. Titanium: An overview of resources and production methods. Minerals, 11(12), p.1425.

2) This research, as explained by the authors, is not capable to provide scientific evidence of ferrotitanium alloy production from BR per se, only stating that the addition of BR to the process is possible. Thus, please consider changing the title of the article, some text and conclusions accordingly.

A suggestion for the title: "Thermodynamics of aluminothermic processes for ferrotitanium alloy production from bauxite residue and Ilmenite"

Comments on the Quality of English Language

Minor checks recommended

Author Response

Thanks a lot. Please see the responses in the attachment.

Author Response File: Author Response.pdf