An Innovative Approach Toward Enhancing the Environmental and Economic Sustainability of Resource Recovery from Hazardous Zn-Bearing Dusts from Electric Arc Furnace Steelmaking

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The paper presents interesting results on recycling the electric arc furnace dust  (EAFD), named by the authors as An bearing dusts (ZBDs) through  a simultaneous carbothermal and hydrogen reduction approach in which the C source was coke oven battery dry quenching dust (CDQD). The results are promising, and the procedures are logical. However, the discussion of results needs a lot of scientific interpretations, and the structure of paper needs some improvement. This can be done following the next comments:

1. On which bases are the equations (1) to (8) suggested? How can Zn ferrite be reduced by C and/or H to Zn gas? Do thermodynamic data support these suggested equations? Particularly equations (1) and (2)
2. The boiling point of Zn is 907 oC and its melting point is 420 oC; The heating was between 700 oC and 900 oC. How did Zn evaporate? It didn’t melt although the working temps were more than m.p. and less than b.p.
3. May be Fe2O3 is reduced to Fe by reduction with H2 in three steps Fe2O3 → Fe3O4 → FeO → And this may lead to change equations (6) and (7)
4. Equation (8) is temperature dependent. It goes in the right direction at temperature range and can be reversed to the left temperature at which temp.?
5. About the heat treatment represented by Fig. 4. Is there a flowrate of H2? and which?. Thr authors mentioned that the gases are collected in “cooled traps” and showed in Fig. 4 “Zn capture system”. How is it cooled? Is it open to air? What is the driving force that gets the gases flow from the furnace to the capture system? More illustrations of the system are required.
6. Lines 177-178: “Gasseous elements extracted from …….. were collected in cooled traps … How??
7. About briquettes preparation, the authors mentioned mixing ZBD and CDQD only. Is water added? And with which content?
8. About description of EAF dust (ZBD) in Fig 2, the authors mentioned that it contains spherical particles and fragmented particles. Is there chemical analysis for each by EDX to show the difference. Are the spherical powder rich more in Zn? Does the EAF dust contain some molten droplets sucked with generated gases?
9. 3, no comments about the coke dust profile? Is it amorphous material with no clear peaks? What about very short peaks?
10. Why high C content at 700 oC in Table 5?
11. Where are Tables S1-S3 ? mentioned in lines 215-216 ?
12. Which technique is used for chemical analysis shown in table 1 and for all materials? It should be mentioned in the Materials and Methods section.
13. The Materials and Methods section should be allocated to clearing up the experimental work, and Figs. 1 and 2 are preferred to be presented and discussed in the results section.
14. Subtitle “Aim of Investigation” Line 108, it is better to be “Aim of Study”
15. The authors mentioned in lines (141-143) that ths dust has higher Zn content because the steel plant used sheet scraps. It is better to show in the Introduction section the composition of EAF dust and why. Fore example Zn is coming from galvanized steel in the scrap, Lead may be from paints, but from where come chlorine?
16. English: the authors sometime used slash (/) and it get the reader confused does it mean “per”, “and” or “or”
17. Fe-rich briquettes will be mixed with raw materials in steelmaking. But what is the next application of ZnO/Zn mixture?

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

 

The article is interesting to read and provides comprehensive background, especially regarding sustainability aspects. Some suggested improvements are:

1. A description of how the samples were prepared for SEM/EDS is missing. From the SEM images, I suspect EDS was not performed on a horizontal, flat, polished surface. In this case, EDS is only semiquantitative with errors of 1-2 % to be expected. All presented composition values determined by EDS should, therefore, be rounded to whole numbers.

2. Equation (4) is not balanced. Please also reformat with reaction arrows instead of “=”.

3. Please reconsider the Data Availability Statement. It should give information about where to access primary and secondary data that support the results, which is clearly not covered by the figures and tables given in the article or SI.

Author Response

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Reviewer 3 Report

Comments and Suggestions for Authors

Review

Manuscript ID: sustainability-3467932

Title: A Novel Strategy for Enhancing the Environmental and Economic Sustainability of Resource Recovery from Hazardous Zn bearing Dusts from Electric Arc Furnace Steelmaking 

In this paper, the authors have presented the results regarding novel strategy to enhance recovering Fe and Zn resources from hazardous zinc bearing electric arc furnace dusts (ZBDs).

There are some questions and remarks to be answered:

1.       Proof reading of the text is required (some mistakes, typos, etc.).

2.       The authors should present the obtained results in Abstract.

3.       There is a lack of information regarding used apparatus and measurement conditions.

4.       Chapter 2.4. should be moved at the beginning of chapter 2 (for instance 2.2). There is also a lack of information about measurement conditions.

5.       The lack of description of CBQD XRD results.

6.       The authors should present the information regarding used technique for elemental composition analysis.

7.       The authors should also present the information regarding used error analysis and method accuracy, for instance (table1-3).

8.       The lack of error bars in Fig.5

9.       The obtained SEM/EDS results in chapter 3.3.2. should be described in more detail.

10.   Rection No.4 should be corrected.

11.   The authors should indicate the optimal conditions in which the process should be conducted.

12.   Authors should include information on directions for further development of the proposed method in the future.

13.   The authors should supplement the Conclusions with obtained results and compare it with literature data (appropriate citations) to prove that the proposed method is much better or at least comparable.

14.   The References should be presented uniformly, according to the journal’s formula.

 

 

 

 

 

 

Author Response

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Reviewer 4 Report

Comments and Suggestions for Authors

This paper presents the recovering Fe and Zn resources from hazardous zinc 19 bearing electric arc furnace dusts (ZBDs) in a sustainable manner.

 Discussion and Conclusion  corresponds to the conceptual architecture of the paper.

In my opinion, revisions are not required - recommendation: Accept.

Author Response

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Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Comment #1

The paragraph in Lines (348-352) has to be tailed with a [Ref] and/or the caption of Fig. (10) should be tailed with (Reproduced from Ref. [?]

Comment #4

In Lines (365-366) "The reduction of carbon dioxide in the presence of carbon to monoxide is likely to occur at temperatures above 700-1000 °C [60, 61]". May be the authors mean in the temperature range 700-1000 °C or at temperatures above 700 °C. (It is  Boudouard reaction that the authors commented that it is well known and not the focus of this study.

Comment #5: The new additions by the authors cleared up a lot of the heat treatment rig and can be understood depending on the reader experience.

However, some confusions are found

The authors mentioned (lines 186-187) "a bubbling system for gas purification and capture of reaction products (distilled water was used to capture the reaction products). They also mentioned (Line 194) "The elements evaporating from the briquettes were collected at the furnace outlet in cooled traps with distilled water". Moreover they showed in Fig. 4 "Zn capture system". Are "bubbling system", "cooled traps", and "Zn capture system" different things or the same thing. Please use one name. 

Do you think, if the Zn capture system was cooled from outside, and there is no contact between Zn and water, that ZnO will form? May dry system produce pure Zn? XRD of the product powder is required to show it is ZnO or Zn(OH)2

However, is it sure that the flow rate of the hydrogen was 80 l/h ? I find it is very high rate. This means 1.33 l/min.  22 ml/s. Why this high rate?  

Comment #8: Yes, the the electron beam may undertake area wider than the focused point, but at least the focusing analysis can give indication, for example, that the spherical particles are rich in Zn and the fragmented particles are rich in Fe.

As the authors mentioned in their valuable response " this data may not be very significant to interpret the dust recovery results" But this may lead to expect that the fragmented particles are coming  from molten droplets sucked with generated gases. Many side info may be important for future studies

Comment #12:

The authors showed that the analysis of raw (powdery) materials was done by "EDX included at least 10 analyzed points; typical error bars were found within ±1%".

Why you did not analyze the all area appeared in the SEM micrograph to have the average composition ? It is impossible to have an error bar of only 1% by using point analysis. The authors themselves said in response of comment 8 that the "data had a large scatter" depending on the point analysis. Please treat this defect.

Comment #13:

Characterization of starting materials can be (it is preferred) to be in the "Results section" because it is result of investigation. You can write a whole paper on characterization of a material. OK, it is up to you and the editor opinion.

Comment #14: the subtitle "Aim of Investigation" minimizes from this valuable study. Analysis of starting material is an investigation. Investigation means always analysis or testing of material or product. But the authors made a procedure and investigated the starting materials and their product. They mentioned "This study presents a novel strategy .......". Therefore, it is better to be Aim of the study or Aim of the approach, with beginning with " This study presents a novel strategy ....... through overcoming the following challenges ....". However, It is not a main point

New Comment:

"the briquettes were investigated by ICP. According to the ICP data, the content of Zn in dust samples before reduction" Lines 379-380. ICP is always preceded by digestion step. Please explain it

Another New Comment:  

The new paragraph (Lines 425-431) is better to moved from the conclusions section to the end of Discussion section

 

Author Response

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Reviewer 3 Report

Comments and Suggestions for Authors

The authors responded adequately to most of the comments.

Author Response

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Round 3

Reviewer 1 Report

Comments and Suggestions for Authors

Accepted