Development of an Energy-Saving Melting Reactor for Energy-Efficient Disposal of Slag Dumps

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The paper presents the development of an energy-saving technology for the disposal of slag dumps, which is relevant for industrial regions such as the Republic of Kazakhstan, where millions of tons of slag accumulate. The novelty of the study lies in the discovery of the phenomena of coexistence and rivalry of two opposite directions in the melt layer: slow decomposition of complex components into simple molecules and rapid formation of complex components from simple molecules. The dominance of one of these consequences has a significant impact on fuel consumption in the process. Using this phenomenon, an energy-saving melting reactor was created that combines the modes of "ideal" mixing and "ideal" displacement. It was experimentally established that the use of this reactor for slag processing allows reducing fuel consumption by 3-4 times compared to the Waelz kiln method. It was also proven that when extracting iron from clinker with a residual content of 9-10%, the clinker composition automatically becomes suitable for the production of cast stone products. Economic methods of the developed installation show its high efficiency and a payback period of 4-5 years.

The proposed technology not only solves the problem of waste disposal, but also allows obtaining valuable products such as iron and raw materials for the production of building materials. This is in line with the principles of the circular economy, where waste is considered as secondary resources. jobs. Further research can be aimed at optimizing the technological process taking into account the recycled waste and developing new types of products based on electronic materials.

 

However, the work has the following comments:

 

1. It is necessary to add the "Discussion" sections to ensure that the article structure complies with the IMRAD requirements.
2. In the list of references (source number 24), it is necessary to replace Russian with English.
3. In the introduction, it should be noted that at the current stage of development, the transition to a circular economy is an effective option for achieving sustainable development of the mining industry. The goal is to identify the direction of using mining tailings based on circular waste management. A number of works devoted to this topic could be considered, in particular, the methodology for studying mining waste (slag) (https://doi.org/10.1016/j.resourpol.2025.105513, https://doi.org/10.1016/j.rcradv.2024.200224).
4. The authors compare the proposed reactor (MR-RK) with traditional methods (e.g. Waelz kiln) in terms of specific fuel consumption and zinc recovery. It is stated that MR-RK reduces fuel consumption by 3-4 times. There is no detailed comparison with other modern technologies (e.g. hydrometallurgical methods or pyrometallurgical alternatives). There are no data on comparative environmental indicators (e.g. CO₂, SO₂ emissions).
5. Section 5 (clinker experiments) specifies parameters (e.g. gas flow rate 600 m³/h), but it is not explained how they were chosen. Units of measurement for some parameters are missing in Table 1 (e.g. "b" is stated as "m³/tZn", but this is not explained in the text).
6. Section 3 mentions a "pilot plant", but its technical characteristics (materials, sensor accuracy, etc.) are not provided. It is not described how the temperature and composition of the melt were controlled in real time.
7. The article does not mention the software used for calculations (e.g., diffusion or thermodynamic modeling). The models of the devices (e.g., spectrometers for slag composition analysis) are not specified.
8. It is not described how the temperature and composition of the melt were controlled in real time.
9. Table 4 indicates the payback periods, but does not provide the methodology for their calculation (e.g., cash flow discounting).

Author Response

Please see the attached file for a point-by-point response to the reviewer’s comments. We sincerely thank the reviewer for their valuable and insightful questions and suggestions. All comments have been carefully addressed, and the manuscript has been revised accordingly.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

This article mainly introduces the development of an energy-saving melting reactor for energy efficient treatment of slag.

This article is not suitable for journal Energies. This topic may fits the scope of journal Metals or Processes.

The below are comments:

1. Please focus more on the practical or scientific parts of this study. The economic pay back period can be deleted. Otherwise, this is like an advertisement.
2. Besides, in introduction, the descriptions on the ores of Republic of Kazakhstan can be shortened. This is an international journal, not one country’s journal. A more in general descriptions on the scientific problems of solid waste and in this article the recovery of ZINC.
3. The research status and literature review are required in introduction section. In particular the recovery of Zinc. For example, the rotary kiln method and many others.
4. In line 62, the novelty of this work cannot be presented in introduction section. This is weird.
5. The research method is weird too. It looks like a patent! What experiment or themodynamics calculation would the authors like to perform?
6. Again, from section 3, it looks like a mass and heat transfer model in line 127 to 137.
7. However, from line 138 to 168, the descriptions looks like a mass and heat balance model.
8. Section 4 is like an overall heat balance analysis of the rotary kiln. Or is it a plant/industrial experiment?
9. And the pilot plant scale or size, tonnage of reactor?
10. The figures 4 to 6 are in low resolution, are the figures plotted by the authors? If they are come from references, please cite the corresponding reference.
11. How the data are obtained for the table 1 and table 2? By what kind of analysis? If they are plant data, the analytical method should be addressed.
12. The analysis on the Gibbs free energy in table 3 is not good enough. The reactions are coupled reaction, for instance the ZnO will participate reactions 3 to 5. This result will be complicated. Besides, the reaction 1 and 4 are reverse reaction, as well as reaction 2 and 5. Only one reaction is required to present here.
13. Besides, for the reactions, the activity or concentration of the components should be presented.
14. For section 6, this is in good practical use. If this is the innovation, please specify the available process in the world.
15. From my point, the motivation is not clear. The descriptions on model is not clear.

Author Response

We sincerely thank the Reviewer for the valuable questions. All comments have been carefully considered, and appropriate revisions have been made to the manuscript to address each point. Please see the attached document for a detailed point-by-point response.

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

1、The introduction briefly mentions slag issues in Kazakhstan but lacks in-depth analysis of limitations in state-of-the-art technologies (e.g., Waelz kilns, hydrometallurgy).   Add comparative energy consumption data of traditional processes to highlight gaps addressed by the "ideal mixing-displacement" mode.   Expand the literature review to include competitive reactor designs (e.g., fluidized beds, electric furnaces) to underscore innovation.

2、While pilot results are presented, systematic parametric analysis (e.g., temperature, gas velocity) is absent.   Include controlled experiments with error bars and statistical significance tests to validate conclusions.   Clarify units and calculation methods for parameters in Table 1 (e.g., "specific natural gas consumption") to avoid ambiguity.

3、The thermodynamic model (e.g., Gibbs free energy calculations) lacks explicit validation against experimental data.   Compare predicted vs. measured outcomes to assess model accuracy.   Use CFD simulations or flow visualization to characterize hydrodynamic mechanisms (e.g., residence time distribution) in the "ideal mixing-displacement" mode.

4、Simplistic payback period calculations should include detailed cost components (e.g., equipment depreciation, transportation) and sensitivity analysis for variables like metal prices and policy impacts.   Incorporate local energy costs and environmental regulations to evaluate scalability challenges.

5、Address logical inconsistencies (e.g., Chapter 6’s thermal diagram connection to experiments) with subheadings and transitions.   Ensure terminology consistency (e.g., "clinker" vs.   "slag") and clarify figure annotations (e.g., units in Figure 1 axes).   Strengthen the abstract by quantifying economic metrics (e.g., annual profit, emission reductions).

Author Response

We sincerely thank the Reviewers for their valuable and insightful questions. All comments and suggestions have been thoroughly considered. The manuscript has been carefully revised to address every point raised, including structural improvements, clarifications of methodology, and enhanced discussions. Please see the attached files for detailed point-by-point responses.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have made the necessary changes to the article. I recommend the article for publication.

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have tried their best to revise. This version can be accepted in this journal.