Sintering Behavior and Chlorine Volatilization Mechanism of Cl-Containing Solid Waste in Clay Brick Production: Implications for Tunnel Kiln Applications
, Yang Yang 2 and Zhongquan Liu 2
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe article contains original laboratory tests that focus on determining the physicochemical, strength and structural parameters for samples of sintered bricks with different amounts of Cl salts. The presented research topic is interesting from a scientific and, above all, environmental perspective and can be helpful in assessing the increase in the efficiency of solid waste containing Cl salt disposal. Below are a few minor comments and suggestions:
- In the introduction, please add two/three sentences regarding the methods of managing solid waste containing Cl salts – mainly to indicate the industries with the greatest possibilities of storing this type of waste;
- In the subsection 2.1, please write whether the samples were prepared for testing according to a procedure or standard;
- In the subsection 2.4, please indicate two/three literature items in which Materials Studio software was used to analyze solid waste containing Cl salts;
- For Figure 2, please write what type of damage the samples showed during the tests;
- In the subsection 3.4, please characterize more clearly the charge transfer between H and Cl in H2O following molecular dissociation – with reference to the changing conditions;
- The conclusions cover the scope of the research and are sufficient.
Author Response
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1. Summary Thank you for your letter and for the reviewer’s comment concerning our manuscript entitled “Volatilization mechanism and reaction behaviors of chlorine salts during tunnel kiln co-processing of solid waste in production of clay brick” (ID: constrmater-3632763). Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully ad have made correction which we hope meet with approval. Revised portion are marked in red in the paper. The main corrections in the manuscript and the responds to the reviewer’s comments are as following. We have tried our best to make all the revisions clear, and we hope that the revised manuscript can satisfy the requirements for publication.
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2. Point-by-point response to Comments and Suggestions for Authors |
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Comments 1: In the introduction, please add two/three sentences regarding the methods of managing solid waste containing Cl salts – mainly to indicate the industries with the greatest possibilities of storing this type of waste; |
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Response 1: We thank the reviewer for the valuable suggestion. In response, we have added sentences in the introduction to briefly discuss established management strategies (thermal treatment and vitrification) and emphasized that industries such as metallurgy, cement, and ceramics are best equipped to handle Cl-containing waste due to their high-temperature operations. (Line 46-50)
Comments 2: In the subsection 2.1, please write whether the samples were prepared for testing according to a procedure or standard; Response 2: Thank you for the comment. As no formal national or international standard was found for clay sample preparation at this stage, we clarified that the procedure followed was based on commonly adopted methods reported in relevant literature on clay-based brick preparation. The revised description can be found in subsection 2.1. (Line 109-113)
Comments 3: In the subsection 2.4, please indicate two/three literature items in which Materials Studio software was used to analyze solid waste containing Cl salts; Response 3: Thank you for your suggestion. We have added relevant literature references to support the use of Materials Studio in analyzing Cl-containing solid waste systems. These references have been included at the end of the first sentence in subsection 2.4. (Line 180-181)
Comments 4: For Figure 2, please write what type of damage the samples showed during the tests; Response 4: Thank you for your valuable comment. We have added a sentence describing the observed failure modes of the bricks during compressive strength testing. (Line 244-246)
Comments 5: In the subsection 3.4, please characterize more clearly the charge transfer between H and Cl in H2O following molecular dissociation – with reference to the changing conditions; Response 5: Thank you for your valuable suggestion. In response, we have revised the paragraph in Section 3.4 to provide a clearer explanation of the charge transfer between H and Cl following H2O dissociation. (Line 444-450)
Comments 6: The conclusions cover the scope of the research and are sufficient; Response 6: We thank the reviewer for the positive feedback. We are glad that the conclusions adequately reflect the scope and findings of our study. |
Reviewer 2 Report
Comments and Suggestions for AuthorsThe paper provides an interesting view on the effects of waste chloride salts in bricks. While it effectively summarizes experimental findings, thermodynamic insights, and proposed mitigation strategies, several aspects could be improved to enhance clarity and critical depth.
- Efflorescence is a more usual term the scumming. However, the topic is only mentioned once (line 297) and not discussed. Efflorescence should be tested. The figures of the samples would be beneficial if presented.
- “The kiln-coprocessing” and similar seem somehow exaggerated or untrue. The phrase is taken over from the cement production, which should not be the same in the brick industry. The waste salts are added to produce bricks, and then the firing process in a tube kiln is performed. Please make the title and all the sections clearer in this light. Why was the tunnel kiln highlighted when it was not used in the process? It can be stated that the tests are done to check a possible damage to the tunnel kiln, but using the term in the title seems inappropriate.
- The abstract is too long. Check the instructions for authors.
- This is a strong and technically rich abstract, but slight refinements in structure, clarity, and emphasis on innovation would further enhance its communicative power. The text presents a large volume of numerical data, which can be overwhelming without sufficient narrative scaffolding. Grouping results thematically or adding brief interpretive phrases would enhance readability and help non-specialist readers grasp the broader implications. Furthermore, while the abstract mentions practical outcomes, such as a proposed two-stage temperature control strategy, it could more clearly connect this recommendation to its potential benefits or implementation challenges in industrial settings. This would give the abstract greater impact by highlighting what was discovered and why it matters.
- Why would the organic decomposition influence H+ for HCl(g) formation? This should be clearly stated in the abstract.
- When discussing the results, consider the thresholds of HCl in flue gas in the ceramic industry (https://doi.org/10.69644/ivk-2024-02-0199).
- It is not clear why so many details on cement production are given in lines 51-67.
- Where does the information that ceramics are fired in a range of 600- 1200 °C come from? The references are needed, especially for the lowest temperature. This temperature might be used as a calcination pre-treatment for a subsequent geopolymerization, but this is not the traditional production temperature. Furthermore, 1200 °C is used in ceramic tiles and sanitaryware production. Thus, you should be more specific and introduce references.
- More information on the used clay would be needed, such as granulometry.
- The title of Table 1 is inappropriate. Please use technical terms.
- It is not good to express that the bricks are cured at 105 °C, since they are dried there. Please use the expressions suitable for this industry, and not the cement one.
- Section 3 needs to introduce references to compare and discuss every result obtained.
- Please make sure to assign the XRD peaks to minerals and not oxides (Fig. S2). Consider more literature. Also, analyse raw clay for mineralogical composition by XRD.
- I would rather not call it “doping” (the titles of Fig. S3).
- Check the right Y axis in Fig. S5. Shouldn't the other units be used?
- The conclusion should contain a concluding paragraph. As this is a stand-alone section, it must not refer to equations, figures, or literature.
- Define all the abbreviations at the first mention, for example, DFT.
- The proposed two-stage temperature control strategy is a promising recommendation, but the text does not explore its feasibility in industrial settings, such as cost, scalability, or integration with existing infrastructure.
- A more international list of references must be provided.
Author Response
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1. Summary |
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Thank you for your letter and for the reviewer’s comment concerning our manuscript entitled “Volatilization mechanism and reaction behaviors of chlorine salts during tunnel kiln co-processing of solid waste in production of clay brick” (ID: constrmater-3632763). Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully ad have made correction which we hope meet with approval. Revised portion are marked in red in the paper. The main corrections in the manuscript and the responds to the reviewer’s comments are as following. We have tried our best to make all the revisions clear, and we hope that the revised manuscript can satisfy the requirements for publication.
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2. Point-by-point response to reviewer |
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Comments 1: Efflorescence is a more usual term the scumming. However, the topic is only mentioned once (line 297) and not discussed. Efflorescence should be tested. The figures of the samples would be beneficial if presented. |
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Response 1: Thank you for your valuable comment. We agree that "efflorescence" is a more appropriate and widely recognized term than "scumming." Accordingly, we have revised the term throughout the manuscript. Regarding the suggestion to test and present efflorescence more directly, we fully acknowledge its importance in evaluating the long-term durability and visual quality of sintered bricks. However, due to current experimental constraints, we are unable to conduct efflorescence tests at this stage. Nevertheless, we have revised the discussion (Line 328–331) to clarify the potential for efflorescence caused by residual Cl that may be leached from the brick matrix. We have also explicitly indicated that this aspect warrants further investigation and will be a focus of our future research.
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Comments 2: “The kiln-coprocessing” and similar seem somehow exaggerated or untrue. The phrase is taken over from the cement production, which should not be the same in the brick industry. The waste salts are added to produce bricks, and then the firing process in a tube kiln is performed. Please make the title and all the sections clearer in this light. Why was the tunnel kiln highlighted when it was not used in the process? It can be stated that the tests are done to check a possible damage to the tunnel kiln, but using the term in the title seems inappropriate. |
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Response 2: We appreciate the reviewer’s insightful comment regarding the appropriateness of the term "kiln co-processing" and the mention of "tunnel kiln" in the title. In response, we have revised the title to more accurately reflect the scope and nature of this study. The new title is: “Sintering Behavior and Chlorine Volatilization Mechanism of Cl-Containing Solid Waste in Clay Brick Production: Implications for Tunnel Kiln Applications.” This revision removes the potentially misleading term "co-processing" and clarifies that our work is focused on laboratory-scale sintering trials, rather than industrial co-processing. We agree that the use of "tunnel kiln" in the original title may have implied that an actual tunnel kiln was used, which is not the case. To address this point clearly, we have also included the following clarification in the revised Introduction: "While the experimental work in this study was conducted at the laboratory scale, the sintering temperatures and heating curves were designed to simulate the operational conditions of industrial tunnel kilns. Therefore, references to tunnel kiln applications are made to evaluate the potential implications and possible corrosion risks associated with the incorporation of Cl-containing waste in real-world production lines." We hope this revision improves the clarity and accuracy of our manuscript, and we thank the reviewer again for helping us improve the precision of our work.
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Comments 3: The abstract is too long. Check the instructions for authors. This is a strong and technically rich abstract, but slight refinements in structure, clarity, and emphasis on innovation would further enhance its communicative power. The text presents a large volume of numerical data, which can be overwhelming without sufficient narrative scaffolding. Grouping results thematically or adding brief interpretive phrases would enhance readability and help non-specialist readers grasp the broader implications. Furthermore, while the abstract mentions practical outcomes, such as a proposed two-stage temperature control strategy, it could more clearly connect this recommendation to its potential benefits or implementation challenges in industrial settings. This would give the abstract greater impact by highlighting what was discovered and why it matters. |
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Response 3: Thanks for your comments, we have revised the abstract section.
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Comments 4: Why would the organic decomposition influence H+ for HCl(g) formation? This should be clearly stated in the abstract. |
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Response 4: We appreciate the reviewer’s insightful question regarding the influence of organic decomposition on the availability of H⁺ for HCl(g) formation. To clarify, our initial motivation for considering organic matter was based on the observation that chlorine volatilizes primarily as HCl gas, but the exact source of hydrogen involved in this process was not clear. Given that clay materials often contain organic components rich in hydrogen, we hypothesized that hydrogen from the decomposition of these organics might contribute to HCl formation. Therefore, we conducted experiments using organic materials with high hydrogen content to explore this possibility. However, the experimental results showed that the presence of organic matter did not significantly affect the formation of HCl(g). Instead, our findings indicate that the hydrogen involved in HCl volatilization predominantly originates from water (H₂O) rather than from organic decomposition. To avoid any potential misunderstanding, we have revised the abstract to explicitly state this point, emphasizing that although organic matter was considered as a possible hydrogen source, it does not play a significant role, and that water is the main source of hydrogen in HCl(g) formation. We thank the reviewer for highlighting this important aspect, which allowed us to improve the clarity of our manuscript. |
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Reviewer 3 Report
Comments and Suggestions for AuthorsIn this work, the authors present tunnel kiln co-processing as a promising method for solid waste disposal, offering lower chlorine and heavy metal evaporation rates than cement kiln technology. However, since the effects of Cl salts on sintered products and the mechanisms of Cl volatilization remain unclear, this work addresses the study of parameters related to these issues, intending to optimize tunnel kiln co-processing of Cl-containing solid waste.
The work is of general interest and could have an impact from various viewpoints, including the production processes of construction materials, sustainability, and chemistry, among others. I consider this to be an integral work, covering both experimental and theoretical results.
- Materials: Provide further details on the elemental quantification. What kind of equipment did you use? Are there any experimental uncertainties associated with the reported values?
- Materials: Do the “pure Cl salts” have any purity degree? Are these certified materials? Is the chloride salt wt% representative of what you would find in a real case?
- Line 229; Line 253. Figures presented in supplementary materials are wrongfully labeled, or the description you provide in the text does not correspond for some reason. If they form part of the results discussion, why not incorporate them as figures in the text instead of supplementary?
- Figure 3. Improve the discussion regarding this figure. Is there an explanation for the significant change in the behavior of KCl and NaCl at 1050 °C?
- Try to provide a better connection between the experimental results and the DFT results. I consider the calculations as a significant contribution of your work, but right now they seem like independent results.
Author Response
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1. Summary |
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Thank you for your letter and for the reviewer’s comment concerning our manuscript entitled “Volatilization mechanism and reaction behaviors of chlorine salts during tunnel kiln co-processing of solid waste in production of clay brick” (ID: constrmater-3632763). Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully ad have made correction which we hope meet with approval. Revised portion are marked in red in the paper. The main corrections in the manuscript and the responds to the reviewer’s comments are as following. We have tried our best to make all the revisions clear, and we hope that the revised manuscript can satisfy the requirements for publication.
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2. Point-by-point response to |
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Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsThe authors have made effort to improve the manuscript. It is now ready to be published.
Reviewer 3 Report
Comments and Suggestions for AuthorsMost corrections were made correctly.
