Experimental Study on Strengthening Carbothermic Reduction of Vanadium-Titanium-Magnetite by Adding CaF2
Round 1
Reviewer 1 Report
The authors have investigated the carbothermic reduction of Vanadium Titanium Magnetite using a solid carbon source. It is challenging to achieve full segregation and conversion with such type of ore after thermal reduction due to its complexity and structure. Additives which assist the carbothermic reduction of metal oxides and minerals are highly needed. The authors investigated the effect of CaF2 addition on the carbothermic reduction of Vanadium Titanium Magnetite. The reviewer is not aware of a similar study where CaF2 used with such a complex form of oxide. The study can be also extended to cover other forms of minerals and oxides and it is worth publishing in the journal of Minerals. The manuscript is technically solid, data are well presented and conclusions are supported. I recommend its publication in the journal of Minerals after addressing the minor comments given below on the quality of the manuscript. I am happy to review the manuscript again after addressing the following comments.
Minor comments:
1. The scope of the study has to be made clear; this can be addressed by showing the importance of converting Vanadium Titanium Magnetite into the reduction products by adding few more sentences at the beginning of the introduction.
2. In the abstract (lines 16-18), delete the sentence “The raw material of vanadium titanium magnetite was adopted in the isothermal experiments 16 and examined by X-ray diffractrometer (XRD), scanning electron microscopy (SEM) and energy 17 dispersive spectrometer (EDS)”.
3. In the abstract (line 18), rewrite the phrase “results indicated that proper” into “results showed that the proper”.
4. In the introduction (lines 30-32), the opening of the introduction is weak and should be rewritten.
5. In the introduction (line 34), the phrase “limited in that titanium” should be “limited by the fact that titanium”. The phrase “and that it is difficult” should be “and it is challenging”.
6. In the introduction (line 38-39), delete the phrase “in the form of isomorphism”.
7. The CaF2 may react with the silica in the ore to form SiF4, a gas which is toxic and corrosive. The authors have to take extra care to prevent exposure to this product. I can see the gas purification unit in Figure 2, but it would be great for any future follow-ups on this work by others to highlight in the experimental section how to wet-scrub this by-product from the exhaust gas. Please mention some more details on this in the experimental section.
8. In the introduction (line 49), “degree of reduction products” should be “degree of the reduction products”.
9. In the experimental section (line 66), what is the “74μmb”?
10. Please make space between numbers and units. For example, 74μm should be 74 μm.
11. Table 2 is a good addition as it summarizes most of the reactions involved. This, if complete and cited properly, will bring a good number of citations. Authors need to add up-to-date references on the carbothermic reduction. It would be great to bring other possible reactions to this table. The ore contains SiO2 and TiO2, their reduction by solid carbon and gas by-products is a possible scenario if we assume the non-stoichiometry of the CaF2 addition. You may add these reactions to the table. Some of these reactions can be found in these recent studies:
Journal of Cleaner Production, Volume 219, 2019, Pages 971-980; ACS Sustainable Chemistry & Engineering 2017 5 (6), 5440-5448; Journal of Environmental Management, Volume 188, 2017, Pages 32-42; ACS Sustainable Chemistry & Engineering 2017 5 (5), 4171-4178; Journal of Cleaner Production, Volume 157, 2017, Pages 213-221.
12. It is interesting that you use CaF2 as a reducing agent, it also can be a carbon activation agent to make the carbon porous and subsequently more reactive, or alternatively yield reducing gases. The following study (Chemical Engineering Journal, Volume 358, 2019, Pages 980-991) has also talked about the gas-gas interactions leading to further carbon and silica attack. The gas-gas and gas-solid interactions have been also presented in the manuscript and its supplementary, so more reactions can be added to Table 2. It would be great to shed some light on this were appropriate in the manuscript.
13. The font in the insets in Figure 4 are not legible. The font of the axis titles and numbers should be larger.
14. In section 3.2 (line 118), the phrase “the adding CaF2” should be “the addition of CaF2”.
15. In section 3.2 (line 118-119), delete the statement “The varied temperature and adding amounts make a few differences”. The statement “when reduction” should be “when the reduction”.
16. In section 3.3 (line 131-132), add space between the number and the unit. Delete the statement “investigate the micro-morphological changes”.
17. in the caption of Figure 5, add space between the number and the unit. This applies to lines 147 and 162.
18. Line 148-149, the statement “The migration and the polymerization among the non-metallic product grained to result in” should be “The mineral segregation results in”.
19. Line 150-151, “facilitate the migration and the polymerization of metal” should be “facilitate the segregation of metal”.
20. Figure 8, nice schematics, but the font size to be made larger and consistent.
21. Line 193, “was drawn” should be “is given”.
22. The references section is weak. It also includes many self-citations, which is absolutely fine, but to make this manuscript stronger, more references to be added from other recent studies on the carbothermic reduction.
Author Response
Dear Reviewer,
Please see the attachmet.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
This is a poorly written manuscript. It is incomprehensible and very difficult to follow the arguments presented.
Author Response
Dear Reviewer,
Please see the attachmet.
Author Response File: Author Response.pdf
Reviewer 3 Report
The text is not clear. It must be reviewed carefully. Only for example:
lines 35-37. Is it the general objetive ? (recovery of Fe, V and Ti?) No discussion on V.
lines 122-128 It is not clear based on the showed results,
and so on.....
Table 2 reaction (6) is not correct!
When composite briquettes (C-Ore) are reduced, at 1300oC the Boudouard reaction is fast and the assumption that CaF2 is acting as catalyst is, at least, dubious. Some other hypothesis is: The SEM photos show reduced iron inside the particles, but it is probably intergranular. If so, low temperature liquidus slag may diffuse ions/atoms into particles by grain boundary and then to grain expanding the structure (as shown) and it may provoque some rupture facilitating de CO/C difusion. If direct reduction occurs CO may generates more fissures. How were the samples for SEM prepared? Is it possible to observe and compare fissures with and without CaF2?
Your model (Fig 9) shows inter particles and not intergranular (grainboundary)
Anyway the results are interesting but the proposed mechanism is it not conclusive (it may be discussed)
Author Response
Dear Reviewer,
Please see the attachmet.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The authors have made some edits. However, the edits are not to the expected level. Yet, the scope of the study is not clear. It is important to communicate with the reader on why you initiated this work. This part is still missing (VERY IMPORTANT TO ADDRESS APROPRIATELY). Figure 4 has been edited so now we have Chinese phrases in the inset figures (x and y axis titles). Figure 5 is not presentable, it should be made clear. The reference style is not consistent. The sloppiness in preparing the manuscript and making the edits started to give me bad impression about its quality. This manuscript is only suitable for publication after addressing these concerns. I am happy to review this manuscript again.
Author Response
Dear Reviewer, Thank you very much for reviewing our manuscript and making valuable suggestions. We have further corrected the mistakes in the manuscript. Please see the attachment for the revised manuscript. Have a good day.
Author Response File: Author Response.pdf
Reviewer 2 Report
The revised manuscript is still in bad shape. I've made some suggestions for improvement and marked areas requiring clarification but they are not comprehensive (see the attached). The authors need to take some time and carefully go over their document and re-write the manuscript before it becomes suitable for review.
Comments for author File: Comments.pdf
Author Response
Dear Reviewer,
Thank you very much for reviewing our manuscript and making valuable suggestions. We have further corrected the mistakes in the manuscript. Please see the attachment for the revised manuscript.
Have a good day.
Author Response File: Author Response.pdf
