Kinetic Aspects of Chrysotile Asbestos Thermal Decomposition Process

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Manuscript title: Kinetic aspects of chrysotile asbestos thermal decomposition process

Reviewer comments:

This manuscript presents a study on the thermal decomposition of chrysotile asbestos, with a focus on understanding its kinetic behaviour through both in situ and ex situ methods. The topic is relevant and timely, given the ongoing need for effective and safe disposal techniques for asbestos which is not only relevant in developed countries that continue to manage legacy asbestos waste, but also for many other nations where the use of asbestos remains legal, particularly in the construction sector. The experimental approach appears robust, and the findings contribute valuable data to the field. However, there are a few areas where the manuscript could be improved, and the authors are encouraged to consider the following points for revision.

Introduction: This paper presents an interesting investigation into the thermal decomposition of chrysotile asbestos, examining both mineralogical and kinetic aspects. To best of my knowledge many previous studies have focused on the kinetics of chrysotile decomposition, the authors should clearly articulate how their work offers novel insights or approaches compared to the already existing literature. In particular, the research gap and the unique contribution of this study should be clearly explained in the introduction section. This can be integrated into the final paragraph of the intro section.

In addition, it would be useful to briefly compare the thermal treatment for asbestos/asbestos waste/asbestos-containing material with other commonly used asbestos disposal methods, such as landfilling, encapsulation, solidification, chemical treatment, mechanical treatment and chemico-mechanical processes etc. Such a comparison would help contextualize the advantages and strengthen the logic for focusing on thermal decomposition as a potentially more effective solution for asbestos waste management.

Methodology: The sample pre-treatment process is a critical component in studies involving asbestos, particularly when analytical techniques such as SEM, XRF, and XRD are used. The methodology section should include a clear and detailed description of the sample preparation steps in order to ensure reproducibility (this will help other researchers/readers to address potential variability between different asbestos-containing samples). This should cover any drying, grinding, sieving, or homogenization protocols used prior to analysis for SEM, XRF etc.

In addition, given the hazardous nature of asbestos fibers (chrysotile), it is crucial to specify the safety precautions and containment measures implemented during sample handling and preparation. Including these details will provide essential guidance for the researchers working with similar hazardous materials.

Results: the manuscript mentions the following…The above changes can be summarized by the following chemical reactions: Mg3(OH)4Si2O5 262 (serpentine minerals: chrysotile or lizardite) → Mg3Si2O7 (intermediate phase, serpentine 263 anhydrite) + 2H2O and in the next step: Mg3Si2O7 → Mg2SiO4 + MgSiO3.  The current representation of the chemical transformations can be improved for clarity and professionalism. Consider presenting it as a formal reaction sequence or in an equation block.

Results and Discussion: The conclusion of the manuscript states that “these findings could be useful for the safe disposal and recycling of chrysotile asbestos-containing materials by thermal methods in the future.” While this sounds promising, the discussion section should elaborate on the practical applicability of the results. The authors should consider discussing the conditions necessary for industrial-scale implementation, the extent to which chrysotile fibres are destroyed during thermal treatment, and any potential safety or environmental concerns associated with the resulting by-products/end-products. Even a brief explanation of these aspects would strengthen the practical relevance and applicability of the study.

Also, the manuscript should consider expanding on the environmental and safety implications of the thermal decomposition by-products. While thermal treatment alters the chrysotile asbestos into a non-fibrous and non-hazardous/less-hazardous material, it would be useful to clarify whether the resulting magnesium silicate phases are fully inert or if any residual risk remains. And if they are inert, what is going to be the end use of the materials? Do you recommend this to be disposed of in the landfills or for any gainful application? How could the kinetics study help in a real-world scenario?

 

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The paper presents a thorough characterization of the thermal decomposition of chrysotile, along with a kinetic model based on the results of the thermal treatments. Two approaches for the thermal treatments were followed. In the first one (named ex situ) the sample was calcinated at different temperatures up to 700°C recording changes of mass at time intervals until a constant mass has been achieved. In the second method, XRD measurements were performed at different temperatures, up to 825°C, to measure possible changes of the crystallographic  phases.
The scientific approach is sound and the results can be useful to tailor the parameters of the thermal degradation method used to inertize chrysotile.

Considering the difference in the activation energy values calculated from the in situ an ex situ approaches, calculation of the error associated with those values would be desirable to assess the reliability of the results.

Minor corrections:

• Line 309: Change "was" with "is"
• Line 408: Delete "what should have been"
• Line 412: Change "represented" with "represents"

 

 

Author Response

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Author Response File: Author Response.pdf