Study on Direct Reduction in Carbon-Bearing Pellets Using Biochar
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsIn this manuscript the authors aimed to study the effects of using biochar as reducing agent for carbon-bearing pellet reduction. Different reducing agents, calicination temperature and time, carbon-to-oxygen ratio and binders were investigated. The overall quality of this manuscript is acceptable for publication, but I would like to authors to address the issues listed in my attached word file.
Comments for author File: 
Comments.pdf
I would encourage the authors to go through the manuscript sentence by sentence to revise the English language. More concise language would significant improve the quality of the the manuscript.
Author Response
1. English writing in the manuscript needs to be improved.
a.There are many redundant narratives in the introduction. More concise language should be used. For example, in line 50 and 51, “some researchers have explored the effects of different reducing agents on the metallization rate of carbon-bearing agglomerates using various types of reducing agents”. In line 89, “and fully blend the mixture using.”. This sentence is not complete.
Dear Expert, Thank you for your valuable comments. Improvements have been made to the English writing of the article and changes have been made in the article, marked in red.
b. Format and term should be consistent to avoid confusion. For example, (1) I assume the reduction temperature, calcination temperature and roast temperature are essentially the same? If so, use the same term throughout the manuscript. (2) “Fig.” and “Figure” are both used in the text. Make sure they are consistent. (3) line 274, “(1) Pellet Strength after Adding Type D Binder”. I did not find a second bullet point, so you may consider deleting this. (4) “SiO2” needs to be subscripted to “SiO2”.
Dear expert, thank you for your valuable comments. The reduction temperature and roasting temperature in the article are indeed one concept, and they are unified as reduction temperature in the article; Fig and Fig in the article are unified as graphs; Are you talking about the pellet strength after adding D-type binder? The pellet strength after adding D-type binder is much improved than that after adding bentonite only, and the data results are shown in Fig. 13; the angular symbol of SiO2 has been modified, and a similar problem in the article has been corrected. Similar problems in the article have been corrected.
c. Abbreviations.
There are abbreviations in the manuscript without explanation. Please make sure that the abbreviations in Tables are explained in text accordingly.
Dear Expert, Thank you for your valuable comments. Some of the letter abbreviations in the article have been explained in full;
2. Technical writing. There are places where the manuscript was written in an unclear manner that the authors need to provide more information.
a. Figure 1. Please add more description of the pellets in caption, including the amount of binders used.
Dear Expert, Thank you for your valuable comments. The data such as binder content used in Figure 1 is described in lines 104-118 and explained in the title of Figure 1;
b. Figure 4. The images are of low resolution, please use the best resolution you can find. I would suggest removing the bottom part of all SEM images and adding your own scale bar to the images. It’s hard to read the scale bar. Also, the authors labelled C, Fe2O3, Fe, slag areas in the SEM images. Are those assigned merely based on experience or there is other evidence? The authors can consider adding EDS data which can provide more information.
Hello Dear Expert, Thank you for your valuable comments. Improvements have been made to the SEM image scale in the article. The labelling of some areas in the figure is based on EDS data, which has been modified by adding the EDS image to the article．
c. The authors discussed the effects of carbon-to-oxygen ratio. The authors failed to define carbon-to-oxygen ratio in the text so I am having a hard time understanding what is the carbon-to-oxygen ratio and how it was tuned.
Dear Expert, Thank you for your valuable comments. Carbon to oxygen ratio is the molar ratio of the carbon content in the pellet to the oxygen content in the iron oxide, and changes have been made in the article．
d. Figure 9. Could the authors explain why calcination with 1000 C gives lower compression strength than 900 C? When calcined at 900 C, why did a higher amount of binder (8%) resulted lower compression strength than that of 5% binder?
Dear Expert, Thank you for your valuable comments. Carbon-containing pellets in the reduction process, 900 ° C -1000 ° C occurs in the transformation of iron tetraoxide to ferrous oxide, lattice aberration occurs, resulting in a slight expansion of the volume and deterioration of the strength, which reaches a minimum at about 1000 ° C. The carbon dioxide ratio of the D-binder is an organic binder. Because the D-type binder is an organic binder, increasing the proportion of the same time will have a slight effect on the carbon and oxygen ratio, carbon and oxygen ratio will have an effect on the strength, resulting in 5% -8% of the binder content change on the strength of the change is not obvious, and the difference between the two is about 100N, in the error allowable range.
e. In line 298, could the authors explain why after 600C, type D binder showed decreased compression strength and then increased?
Dear expert, thank you for your valuable comments. Pellets after 600℃ with the increase of temperature, on the one hand, the effect of D-type binder is gradually deteriorated by the temperature, while the iron phase has not yet been generated on a large scale, resulting in a reduction of strength, and after 1100℃ the strength rises rapidly due to the large amount of metal-iron generation.
f. How is metallization rate measured?
Dear Expert, Thank you for your valuable comments. The formula for the metallisation rate has been added in line 150 of the text.
Author Response File: Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for Authors1. From the perspective of reduction theory, there is no problem with the use of biochar in metallurgical production, but the key issue that truly affects the utilization of biochar in metallurgy is its economy, not the technology itself.
2. In Figure 5, there are four different phase analyses under different conditions, and it is necessary to label A, B, C, and D separately. The legends for each phase should be as consistent as possible and should not be mixed up, otherwise misunderstandings may occur.
3. The strength of several C/O conditions in Figure 6 exceeds 5000N, and after exceeding 1.1, the pellet has no strength, which is a particularly abnormal phenomenon. It is recommended to study carefully. Moreover, Figure 6 itself is relatively simple and can be considered for deletion. Simply discuss the text.
4. Figures 7 and 8, the difference between these two figures cannot be seen from the title, and detailed parameter explanations need to be added.
Author Response
- From the perspective of reduction theory, there is no problem with the use of biochar in metallurgical production, but the key issue that truly affects the utilization of biochar in metallurgy is its economy, not the technology itself.
Dear Expert, Thank you for your valuable comments. The cost issue of utilising biomass charcoal in metallurgy has always been the focus of research, and at present, with the gradual rise of carbon tax, the use of biomass charcoal for metallurgical production can reduce the cost of carbon emissions. At the same time, controlling the proportion of biomass charcoal used and partially replacing traditional fossil fuels with it can not only reduce carbon emissions and lower the cost of carbon emissions, but also will not have a big impact on the economy of metallurgical production because of the high cost of biomass charcoal preparation.
- In Figure 5, there are four different phase analyses under different conditions, and it is necessary to label A, B, C, and D separately. The legends for each phase should be as consistent as possible and should not be mixed up, otherwise misunderstandings may occur.
Dear Expert, Thank you for your valuable comments. Figure 5 has been modified in the article and labelled in the title of Figure 5.
- The strength of several C/O conditions in Figure 6 exceeds 5000N, and after exceeding 1.1, the pellet has no strength, which is a particularly abnormal phenomenon. It is recommended to study carefully. Moreover, Figure 6 itself is relatively simple and can be considered for deletion. Simply discuss the text.
Hello esteemed expert, thank you for your valuable comments. In the article, when the carbon to oxygen ratio reaches 1.1, there is no strength after roasting. Through the experimental process, it is found that in the case of adding bentonite binder only, the carbonaceous pellet will undergo malignant expansion at 900-1000℃, and the higher the carbon to oxygen ratio, the higher the expansion ratio, and when the carbon to oxygen ratio reaches 1.1, the pellet loses its original shape due to the more serious expansion, and does not undergo volumetric shrinkage in the later stage of the generation of the iron phase, which resulting in a strength of 0.
- Figures 7 and 8, the difference between these two figures cannot be seen from the title, and detailed parameter explanations need to be added.
Hello Dear Expert, Thank you for your valuable comments. The article has modified the captions of Figures 7 and 8 with parametric additions.
Author Response File: Author Response.pdf
