Investigation of the Possibility of Obtaining Metallized Titanomagnetite Briquettes Suitable for Utilization in the Steelmaking Process

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper is on the treatment of titanomagnetite ore for the recovery of iron. The research has important meanings. However, the paper needs a major revision before acceptance.

• The present introduction is confusing, and some revisions are needed. The author should give a flowsheet of the proposed method for treating titanomagnetite ore. Then give why the authors do this research, and what the target is.
• The experimental methods were not clearly described. A full analysis of the titanomagnetite ore should be given. Methods of briquetting, methods of briquette firing, and methods of briquette reduction should be given in detail.
• For observation of the microstructure of briquettes, SEM is needed.
• In Table 1, some samples, such as PB-1-20/10 and PB-2-15, showed a mass increase after drying. Why?
• Text from Line 301 to Line 332 should be moved to the introduction part, and give some references.
• Tables 4 and 5 should be combined into one table.
• The authors measured the compressive strength of the briquettes before and after reduction. It is not enough, the author should give how the compressive strength of the briquette develops.
• In Table 7, why should the author measure the changes in height and in diameter?
• In the results and discussion, Figs 2, 3, 4, and 5 of the XRD pattern are of poor quality and need improvement.
• If the reactor is a shaft furnace for the gaseous reduction of briquettes, tests under non-isothermal conditions are needed.
• The authors made several samples using different methods, which one is the optimal for the proposed method of this paper?

Comments on the Quality of English Language

no comments

Author Response

Dear Expert!

We, the authors of the article “Investigation of the possibility obtaining metallized titanomagnetite briquettes suitable for utilization in the steelmaking process”, Andrey N. Dmitriev, Galina Yu. Vitkina, Elena A. Vyaznikova, Roman V. Alektorov, Vladimir V. Kataev, Larisa A. Marshuk, Yulia E. Burova, would like to express our gratitude for your meticulous review of our article and for your constructive comments and suggestions. We are immensely grateful for your invaluable feedback, which has enabled us to enhance the quality of our work to a considerable extent. The following section presents a comprehensive response to the issues raised, accompanied by a detailed description of the corrections made to the manuscript.

Remark 1.  The present introduction is confusing, and some revisions are needed. The author should give a flowsheet of the proposed method for treating titanomagnetite ore. Then give why the authors do this research, and what the target is.

Authors’ notes: This assertion is indeed correct. The present introduction is not sufficiently structured and fails to provide a clear picture of the process. In the revised article, the following points will be addressed. A flowchart illustrating the process is added (Figure 1). The introduction restructured (subsections (1.1), (1.2), (1.3) and (1.4) have been added). The two main targets are clearly formulated.

Remark 2. The experimental methods were not clearly described. A full analysis of the titanomagnetite ore should be given. Methods of briquetting, methods of briquette firing, and methods of briquette reduction should be given in detail.

Authors’ notes:

The chemical composition of the initial titanomagnetite concentrate is given in Table 2.

It is acknowledged that the methods require further elaboration. Thorough description of the briquetting process, the parameters of the firing process, and those of the reducing process has been conducted is section 2.

Remark 3. For observation of the microstructure of briquettes, SEM is needed.

Authors’ notes: We would like to express our gratitude for your contribution to the discourse; it is of paramount importance to us. The SEM data has been added to subsection 2.1 (see Figure 2).

Remark 4. In Table 1, some samples, such as PB-1-20/10 and PB-2-15, showed a mass increase after drying. Why?

Authors’ notes: As outlined in subsection 2.3, clarifications have been provided concerning the alterations in briquette mass following the drying process.

Remark 5. Text from Line 301 to Line 332 should be moved to the introduction part, and give some references.

Authors’ notes: The sequence of text commencing on line 301 and concluding on line 332 has been relocated to the introduction, with the addition of references (see subsection (1.2)).

Remark 6. Tables 4 and 5 should be combined into one table.

Authors’ notes: The content of Table 4 has been revised, and additional information from Table 6 has been incorporated into the explanatory notes for Table 5.

Remark 7. The authors measured the compressive strength of the briquettes before and after reduction. It is not enough; the author should give how the compressive strength of the briquette develops.

Authors’ notes: The compressive strength of the samples was measured in three different ways: after pressing (cold strength), oxidative firing (fired strength), and reduction (metallized strength). Post-drying measurements were omitted for the following reasons. Firstly, the drying stage is intermediate and not representative of the final product. Secondly, the ISO 4700 standard does not require this measurement.

Remark 8. In Table 7, why should the author measure the changes in height and in diameter?

Authors’ notes: We would like to express our gratitude for your contribution to this discourse. It is to be noted that Table 7 has undergone a process of revision.

Remark 9. In the results and discussion, Figs 2, 3, 4, and 5 of the XRD pattern are of poor quality and need improvement?

Authors’ notes: In consideration of the received feedback, enhancements have been made to the diffractograms.

Remark 10. If the reactor is a shaft furnace for the gaseous reduction of briquettes, tests under non-isothermal conditions are needed?

Authors’ notes: Isothermal tests at 1050 °C were selected to facilitate a fundamental understanding of the kinetics and to exclude extraneous variables. This approach is considered a standard technique in fundamental research ([14, 15]). It is acknowledged that the availability of non-isothermal data is limited. The results of experimental and modelling work, which confirm the applicability of the technology in a shaft furnace, will be presented in a separate publication following pilot testing.

Remark 11. The authors made several samples using different methods, which one is the optimal for the proposed method of this paper?

Authors’ notes: The optimal formulation was identified as PBM-3-20/10 (0.55% CaO binder, 20×10 mm briquettes), achieving 95.7% metallization, 48.9 MPa compressive strength, and RSI=10.3%, fully meeting EAF requirements.

As indicated in the Abstract and Conclusions, further information has been added

It is asserted that the alterations made fully address all of the reviewer's comments and significantly enhance the scientific and practical value of the article. We would like to express our gratitude for your assistance in enhancing the quality of our work.

Best regards, authors.

Reviewer 2 Report

Comments and Suggestions for Authors

Summary of the Work

This study investigates the production of metallized titanomagnetite briquettes as an alternative iron-bearing feedstock for low-carbon steelmaking, addressing both the shortage of high-grade iron ores and environmental constraints. A single-cycle briquetting and thermal reduction process was applied to low-grade titanomagnetite concentrate, optimizing Fe/flux ratios and binder composition. The best results, 95% metallization and 80 MPa compressive strength, were achieved using a CaO-MgO-SiO₂ binder, which forms a low-viscosity melt and acicular Mg-SFCA-I phase upon cooling. These briquettes meet electric arc furnace (EAF) feedstock requireme-ts, suggesting their potential as a sustainable alternative to traditional pellets.

Main Results Obtained

Two cylindrical briquette sizes were produced: 20/10 mm and 15/8 mm (diameter/height), and various binders were tested. The main authors' findings are:

i) Compressive strength varied widely from 16.4 to 80.3 MPa depending on the binder. Highest strength achieved with CaO·MgO·2SiO₂ binder; lowest strength with CaO·TiO₂ or FeO·TiO₂ + Fe₃C.

ii) Metallization significantly increases briquette strength, likely due to the formation of metallic α-Fe. 20/10 mm briquettes with 0.55% CaO reached >95% metallization after 3-hour CO/N₂ (90/10%) reduction, meeting electric steelmaking requirements.

iii) Minimal dimensional change observed after RSI heat treatment, staying within recommended limits.

General Comments

- This study demonstrates that CaO–MgO–SiO₂ binders can produce titanomagnetite briquettes with high compressive strength and metallization (>95%), meeting electric steelmaking requirements, which is a promising alternative to traditional pellets. However,

- The research is limited to laboratory-scale experiments, and it is unclear whether the results can be reproduced at pilot or industrial scale.

- The environmental and safety implications of using CO/N₂ gas at high temperatures were not discussed.

- In my opinion, the effect of binder variations, briquette size, and shape on metallization and mechanical performance under real industrial conditions requires further investigation.

- No long-term stability, handling, or storage tests were reported, which are important for practical application.

- The authors' study does not provide a sufficient analysis of cost-benefit or energy efficiency analysis, making it difficult to assess the economic viability compared to conventional pelletizing methods.

Finally, the authors established a correlation between binder composition and briquette performance, demonstrating that the careful selection of CaO–MgO–SiO₂ phases can optimize both metallization and mechanical strength, an insight that is valuable for guiding industrial briquette design. However, several aspects require further clarification and investigation. The following suggestions are intended to address these points.

Suggestions

1) First of all, for further clarity, please explain (in short) how effectively the CaO-MgO-SiO₂ binder improves the compressive strength and metallization degree of titanomagnetite briquettes compared to other binders.

This work is certainly very interesting, but some points are not clear to me. Could you please answer very concisely to the following questions/doubts?

2) How does the α-Fe fraction evolution during CO/N₂ reduction correlate with compressive strength, local metallization heterogeneity, and pore filling, particularly in relation to the CaO–MgO–SiO₂ binder molar ratio?

3) What is the effect of Mg-SFCA-I acicular phase nucleation and growth on mechanical integrity, and how is this influenced by cooling rate and binder composition?

4) How does the briquette geometry (diameter-to-height ratio) and micro-porosity distribution affect CO diffusion, reduction kinetics, and the uniformity of metallization throughout the briquette?

5) What is the relationship between residual TiO₂, Fe₃C inclusions, and CaO·TiO₂ or FeO·TiO₂ phases on brittleness, fracture behavior, and microcrack formation during RSI heat treatment?

6) How do binder segregation during pressing and flux interactions influence the formation of low-viscosity melts versus high-viscosity Ti-rich phases, and how does this affect pore filling and α-Fe-TiO₂ interfacial morphology?

7) Can the diffusion coefficient of CO within the briquette matrix be quantitatively linked to metallization rate, reduction depth, α-Fe growth, and final mechanical properties under different reduction times and temperatures?

Punctual questions

8) Table 5 shows the calculated metallization degrees of iron ore briquettes. The authors state very fleetingly that "the metallization degree, denoted by φ_met, is calculated as the ratio of metallic Fe to total Fe, converted to percentages." This is somewhat unclear to me. For clarity, could the authors explain in detail how they calculated φ_met?

9) Table 7 presents the dimensions and proportions of the structural components of the metallized briquettes. However, consistent with the rest of the study, it does not report key statistical parameters such as variance, leaving the reliability of the measurements unclear.

10) The authors state that linear dimensional changes after RSI heat treatment were minimal within the recommended range, but no statistical analysis or confidence interval is provided to support this claim.

Conclusions

The present study provides insights into the production of titanomagnetite briquettes, particularly highlighting the positive impact of CaO–MgO–SiO₂ binders on both metallization and mechanical strength. However, several critical aspects require clarification and further investigation. These include the scalability of the process, detailed statistical analysis of dimensional and structural measurements, and the role of microstructural factors such as α-Fe fraction, Mg-SFCA-I formation, TiO₂ phases, and porosity on mechanical and metallurgical performance. Additionally, in my opinion, data on reduction kinetics, binder segregation, CO diffusion, and phase interactions would further support its industrial applicability. I encourage the authors to take into account the above suggestions.

Author Response

Dear Expert!

We, the authors of the article “Investigation of the possibility obtaining metallized titanomagnetite briquettes suitable for utilization in the steelmaking process”, Andrey N. Dmitriev, Galina Yu. Vitkina, Elena A. Vyaznikova, Roman V. Alektorov, Vladimir V. Kataev, Larisa A. Marshuk, Yulia E. Burova, would like to express our gratitude for your meticulous review of our article and for your constructive comments and suggestions. We are immensely grateful for your invaluable feedback, which has enabled us to enhance the quality of our work to a considerable extent. The following section presents a comprehensive response to the issues raised, accompanied by a detailed description of the corrections made to the manuscript.

General Comments

Remark 1.  The research is limited to laboratory-scale experiments, and it is unclear whether the results can be reproduced at pilot or industrial scale.

Authors’ notes: We would like to express our gratitude for your contribution to this discourse. It is acknowledged that scalability is a critical issue for practical implementation, and this is recognized as being of paramount importance. In the revised article, a special subsection has been added (2.10) and (4.5), in which this aspect is examined in detail.

Remark 2. The environmental and safety implications of using CO/N₂ gas at high temperatures were not discussed.

Authors’ notes: This assertion is indeed valid, and it is acknowledged that this constitutes a pivotal element that must be evaluated within the framework of its industrial applicability. In the revised article, a special subsection has been added (2.11) and (4.6).

Remark 3. In my opinion, the effect of binder variations, briquette size, and shape on metallization and mechanical performance under real industrial conditions requires further investigation.

Authors’ notes: We concur with your position and intend to undertake analogous research in the future when conducting pilot industrial experiments (agreements have been reached with JSC UralTrubProm, Pervouralsk, Russia).

Remark 4. No long-term stability, handling, or storage tests were reported, which are important for practical application.

Authors’ notes: In the revised article, we present our considerations on long-term stability, handling, and storage tests in the conclusion.

Remark 5. The authors' study does not provide a sufficient analysis of cost-benefit or energy efficiency analysis, making it difficult to assess the economic viability compared to conventional pelletizing methods.

Authors’ notes: The present study concentrated on the technological implementation and scientific substantiation of the mechanisms governing the formation of briquette properties. Despite the fact that a comprehensive economic analysis necessitates considerable further research and lies beyond the scope of the present fundamental study, in the revised article, we present our considerations on economic analysis in the conclusion.

Suggestions

Remark 1. First of all, for further clarity, please explain (in short) how effectively the CaO-MgO-SiO₂ binder improves the compressive strength and metallization degree of titanomagnetite briquettes compared to other binders.

Authors’ notes:

We would like to express our gratitude for your contribution to this discourse. As stated in subsection 4.1, all of the aforementioned points are to be found there.

Remark 2. How does the α-Fe fraction evolution during CO/N₂ reduction correlate with compressive strength, local metallization heterogeneity, and pore filling, particularly in relation to the CaO-MgO-SiO₂ binder molar ratio?

Authors’ notes:

We would like to express our gratitude for your contribution to this discourse. As stated in subsection 4.1, all of the aforementioned points are to be found there.

Remark 3. What is the effect of Mg-SFCA-I acicular phase nucleation and growth on mechanical integrity, and how is this influenced by cooling rate and binder composition?

Authors’ notes:

We would like to express our gratitude for your contribution to this discourse. The necessary information has been added to section (3) and subsection (4.1). New references to literature have also been added.

Remark 4. How does the briquette geometry (diameter-to-height ratio) and micro-porosity distribution affect CO diffusion, reduction kinetics, and the uniformity of metallization throughout the briquette?

Authors’ notes:

We would like to express our gratitude for your contribution to this discourse. In the revised article, a special subsection has been added (4.3).

Remark 5. What is the relationship between residual TiO₂, Fe₃C inclusions, and CaO·TiO₂ or FeO·TiO₂ phases on brittleness, fracture behavior, and microcrack formation during RSI heat treatment?

Authors’ notes:

We would like to express our gratitude for your contribution to this discourse. In the revised article, a special subsection has been added (4.2).

Remark 6. How do binder segregation during pressing and flux interactions influence the formation of low-viscosity melts versus high-viscosity Ti-rich phases, and how does this affect pore filling and α-Fe-TiO₂ interfacial morphology?

Authors’ notes:

We would like to express our gratitude for your contribution to this discourse. In the revised article, a special subsection has been added (4.4).

Remark 7. Can the diffusion coefficient of CO within the briquette matrix be quantitatively linked to metallization rate, reduction depth, α-Fe growth, and final mechanical properties under different reduction times and temperatures?

Authors’ notes:

This assertion is indeed valid. In the revised article, a special subsection has been added (2.9) and (4.3).

Punctual questions

Remark 8. Table 5 shows the calculated metallization degrees of iron ore briquettes. The authors state very fleetingly that "the metallization degree, denoted by φmet, is calculated as the ratio of metallic Fe to total Fe, converted to percentages." This is somewhat unclear to me. For clarity, could the authors explain in detail how they calculated φmet?

Authors’ notes:

This assertion is indeed valid. In the revised article, a special subsection has been added (2.7) and Table 4.

Remark 9. Table 7 presents the dimensions and proportions of the structural components of the metallized briquettes. However, consistent with the rest of the study, it does not report key statistical parameters such as variance, leaving the reliability of the measurements unclear.

Authors’ notes:

This assertion is indeed valid. In the revised article, a special subsection has been added (2.8). A comprehensive overhaul of Table 7 has been conducted. Also Table 6 added to the article.

Remark 10. The authors state that linear dimensional changes after RSI heat treatment were minimal within the recommended range, but no statistical analysis or confidence interval is provided to support this claim.

Authors’ notes:

This assertion is indeed valid. In the revised article, a complete revision of Table 7 has been undertaken.

It is asserted that the alterations made fully address all of the reviewer's comments and significantly enhance the scientific and practical value of the article. We would like to express our gratitude for your assistance in enhancing the quality of our work.

Best regards, authors.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

It is acceptable.

Comments on the Quality of English Language

no comments

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have satisfactorily answered, point by point, all the questions raised in my previous report and have followed up on the suggestions provided. In my opinion, this revised version is now suitable for publication.