Optimization of Red Mud and Blast Furnace Sludge Self-Reducing Briquettes Propaedeutic for Subsequent Magnetic Separation
Round 1
Reviewer 1 Report
Comments and Suggestions for Authors
Manuscript ID: metals-3898998
Title: Optimization of Red Mud and Blast Furnace Sludge Self-Reducing Briquettes to Enhance Magnetic Separation
Authors: Sara Scolari et al.
The abstract and introduction state the goal is to "enhance magnetic separation". However, the core findings focus on briquette mechanical strength and reduction degree. The direct link to enhanced magnetic separation (e.g., quantitative recovery rates, separation efficiency) is not demonstrated with experimental data, only inferred. The title and objective should be reframed to more accurately reflect the actual work, which is the optimization of briquette preparation and reduction for subsequent magnetic separation.
In section 3.1, the text states that 0.523 was "the best reduction condition" based on mass loss plateauing, but then concludes that 0.840 is "optimal" based on specific energy. This contradiction is not adequately resolved.
A critical gap is the absence of XRD or SEM-EDS analysis on the briquettes after reduction at different temperatures. The authors hypothesize about the presence of magnetite, wüstite, and metallic iron at various stages (e.g., Section 3.3), but these phases are not experimentally verified. This data is essential to confirm the reduction mechanism and fully explain the magnetic separation potential.
Technical errors:
Figure 6. The sample is referred to as "0.840-2W" throughout but is once called "0.824-2W".
Do not use capital letters in writing the titles of articles in the list of references.
Detailed Comments:
1) Magnetic Separation Validation: The most significant missing step is a direct validation of the magnetic separation efficiency on the disintegrated briquettes reduced at the proposed optimal temperature (1450 °C). The conclusions about the suitability for magnetic separation are inferred from the degree of reduction and mechanical properties. A simple lab-scale magnetic separation test on the crushed 1450 °C product, reporting iron recovery and grade, would powerfully substantiate the central claim.
2) Statistical Significance: The number of replicates for mechanical tests (e.g., UCS) is not explicitly stated. Reporting the results as an average with a standard deviation (e.g., UCS = 19.21 ± X MPa) would strengthen the statistical reliability of the conclusions.
3) Phase Analysis Post-Reduction: XRD or SEM-EDS analysis of the briquettes reduced at key temperatures (especially 950 °C and 1450 °C) would provide direct mineralogical evidence to support the discussions on the presence of magnetite, metallic iron, and slag phases.
Author Response
Please see the attachment
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for Authors
Optimization of Red Mud and Blast Furnace Sludge Self-Reducing Briquettes to Enhance Magnetic Separation is very important paper in extractive metallurgy. Major improvements are required.
Line 20: The mechanical and metallurgical properties of the 0.840-2W briquettes after reduction at 700, 950, 1200 and 1450 °C (what is reaction time?)
Line 68: Independently from the reducing agent (such as…), high degree of metallization was achieved)
Line 93, 94: Finally, a further goal of this work is to agglomerate RM with blast furnace sludge as reductant to define the best temperature for the metallic iron recovery. In which form is red mud (dried or sludge?). After Leaching of bauxite ores with sodium hydroxide, red mud is in sludge form. If red mud is dried, what is particle size distribution of the obtained product?
Line 101: the sample. . The red mud (please to improve it?)
Line 160: (Ar, 2 Nl h-1 ) maybe: (Ar, flow rate: 2 Nl h-1 )
Line 265: Figure 2. TG-DSC results for each C/Fe2O3 ratio (mass loss expressed in %, peak temperature) Please to write the name of the Y-axis at the Figure 2! Is the mass loss expressed in % one calculated value, or a mesured value?)
Line 385: during the curing time (0.523-1W) or (0.523-1 Week?). What is the manibf for "W"
Line 427: The optimization of both the behaviors defines the best temperature to achieve a satisfactory iron reduction (or iron (III) oxide reduction)
Line 440: Increasing the tumbler's rotation rate caused the AI to increase and the TI to decrease (in what range?)
Line 535, 536 : The latter instead formed the small drops (D) bounded either with Si or Ti (E) inside the slag matrix (C). in which form IS Ti? Did you perform XRD-analysis of drops?
Conclusion
Line 563: The ideal temperature for the thermal treatment to favor the following magnetic separation is 1450 °C (beacuse of smelting process? ) In what time?
General question
The viscosity of slag is very important for the separation of magnetic iron and slag! Have you added CaO during thermal treatment at 1450°C in order to ease perform magnetic separation!
What is chemical composition of slag after thermal treatment of red mud at 1450°C
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for Authors
The authors made significant changes to the article (they add new Table 1 and 6, also Figure 7) and answered all the questions in detail. In this form, the article can be accepted.
However, I believe that the phrase "... Propaedeutic for a Following..." in the article title is not clear and the authors should consider changing it.
Reviewer 2 Report
Comments and Suggestions for Authors
This improved version can be accepted in present form
