Recovery of Valuable Materials with the RecoDust Process

Round 1

Reviewer 1 Report

The RecoDust process is a pyrometallurgical process for treating steel mill dusts and separating zinc from iron in the form of an iron rich fraction. The authors describe the RecoDust process and its use to recover dust for transfer into valuable products. This facilitates the recycling of resources, which makes sense.

1.     What is the biggest innovation of this study compared to similar study? How many technical indicators have been improved and why? It is desirable to explain them.

2.     Please pay attention to the format specification of the tables in the text, for example, use a uniform three-line table on Table 1 and Table 5.

3.     The symbols in the tables are not explained in the text, such as what VK1/1 is in Table 5.

4.     The formula lacks parameter descriptions and units, such as formulas (1) - (2), etc.

5.     Figure 4 is blurred, please improve the clarity of the picture.

6.     The number format and unit format of the positive and vertical coordinates in the figures are not consistent, as shown in Figures 7-9.

7.     Attention should be paid to the superscripts and subscripts of compounds.

Overall, this paper only reports simple experimental data, lacks necessary analysis, lacks academic depth, and is not recommended for publication.

The English expression is acceptable, but the symbols and formats need to be standardized.

Author Response

Thank you for your comments. I hope you like my answer.

Author Response File: Author Response.pdf

Reviewer 2 Report

Recovery of Valuable Materials With the RecoDust Process is very interesting paper. Some improvement is required.

Line 13, 14: The RecoDust process is a pyrometallurgical process for treating steel mill dusts that can-  not be recycled internally due to their zinc content (small or high content of Zn?)

Line 20: the CZO (please to write full name of CZO at the beginning of your text)

Line 22: RDI tests (please to write full name for RDI Tests)

Line 75: an iron content of about 35 wt.-$. (what is the meaning of this 35 wt.-$.?)

Line 122: Figure 1: Flowchart of the RecoDust process (the flowchart is not visible, especially the parameter values are not visible).  Can you write the single process steps below this flowchart?

Line 143, 144: The primary explosion protection of the transmitting vessel is done by inerting with nitrogen. In the process, the transmitting vessel is purged with nitrogen until the oxygen  concentration is below the limiting oxygen concentration of 10 %. What is a reason for the primary explosion (hydrogen+ oxygen? Or something other?)

Line 149: If oxygen would be used, a potential exothermic oxidation reaction of the metallic  iron could occur (local hot spots being a safety-related handling problem). Can you write this chemical reaction?

Line 189, 190, 191, 192: CZO, the second product of the RecoDust process, is treated by a so-called double step leaching process to decrease the halogen content of the CZO as a result of its harmful behavior in a zinc electrolysis since the aim is to achieve a product quality that can be in  principle used as secondary raw material in the primary zinc industry (no search regarding the current demand on secondary raw materials in the zinc industry was done during  this study). What are other impurities in CZO (F, As, Sb, Sn,…)

Ine 197: In a first step, the dust is leached at 60 - 70 °C with pH~10 (please to add the following information: 1.leaching time, 2. Solid/Liquid ratio)

Line 210: Figure 5: Flowsheet of the double-step leaching treatment of the CZO (Montanuniversitaet Leoben, Chair of Nonferrous Metallurgy).  Where is an information about wastewater containing halogen, sodium and other impurities?

Line 277:  higher contents of volatile components, like zinc, and chlorine and lower contents of non-  volatile components, like Fetot..  Information about volatile component behavior: fluorine is missing-

Line 338; To remove chlorine of the CZO, a double-step soda leaching was  done successful. Can you explain what is difference between first and second leaching step (the leaching parameter are similar!!)

General open questions:

1.       What is with treatment of waste water after second leaching step!

2.       How to remove fluorine from the final product?

Author Response

Thank you for your review

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments to the authors

Manuscript metals-2384138

Title: Recovery of Valuable Materials With the RecoDust Process

General comments:

The manuscript presented a pyrometallurgical route for steel mill dusts treatment. Such study is important to promote the circular economy and the sustainable development. The process seems to contribute to the known technologies for zinc recovery from steel dusts. A few comments to improve the quality of the manuscript.

Legend of table 1 is in a different page of the table.

The processes beyond the state of art might be presented.

Figure 1: how much of natural gas and oxygen is necessary to treat 100-300kg/h of dust feed?

The preliminary economic analysis must be presented, mainly operational costs.

Table 4: what is B2 and B4?

No chemical reactions are presented, which are important to state the technical feasibility.

How chemical analysis were carried out?

Figure 7: correct chemical formula: Al2O3 instead of AL2O3

The mass balance of the final process should be presented. What is the quality (purity) of the products?

Is the process flexible being capable of treating different feed materials?

Author Response

Thank you for reviewing

Author Response File: Author Response.pdf

Reviewer 4 Report

 The paper describes results of careful work on piloting of a new method of pyro-treatment of low grade dusts from iron and steel metallurgy. Congratulations to the team of authors.  

Below please find two minor remarks.

 Line 20, 22: CZO, RDI – not explained what the abbreviations stand for 

In sections 3.2.2., 3.2.4. no information is given on F content in CZO. Fluoride if present  in a raw material for hydro zinc plant is more danger for the process than chlorides. So behavior of fluorides in RcecoDust Process and alkaline leaching of CZO should be studied more detailly.

Author Response

Thank you for reviewing

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The issues raised have been revised and resolved, and publication is recommended.