Structural Characterisation of End-of-Life Cement–Asbestos Materials from Lithuania

Round 1

Reviewer 1 Report

Title – It does not fully correspond to the research conducted

Importance of the problem and accuracy of research selection –

important, acceptable after modifications:

                The problem raised at the beginning is important because it concerns the high concentration of hazardous waste in this country. They are dangerous due to their asbestos content. The reviewer has the impression that the authors failed to consistently develop this topic and in their research, they focused on the difference in the composition of the discussed products and the different (different) technological processes of producing Lithuanian slabs and other compared asbestos-cement board waste from other countries. This is a valid and interesting discovery, but what is the most important is that,  what has not been said (about thermal modification of asbestos). This is a basic criticism.

Detailed comments

1. In XRF tests, it would be worth attaching a chart of the element content for this technique concerning the fibres (shown in Fig. 1) before and after thermal treatment, as well as SEM photos showing what is the effect of recycling, i.e. the destruction of the form and structure of asbestos fibres (especially when the suggested it is possible to reuse a product from recycled waste). Therefore, the use of SEM-EDS or even optical microscopy should be considered if fibres have not been separated for this purpose.

2. The chemical results of 3 samples showed differences in the content of elements found in asbestos (MgO, FeO). How to interpret this, taking into account the extremely different environmental conditions (sample taken from the soil, "protected" against weathering processes, sample exposed to cement leaching for 20 and 50 years). The reviewer's research shows that old a-c boards, after many years of use and washing out of the cement matrix by rainfall, may have high of the content of asbestos fibres.  In domestic boards, depending on their type and dimensions, maybe different content of asbestos: "modified lignocement" boards- 5%, classic pressed - 10-11%, wavy approx. 11.5-13%. What's it like in Lithuanian samples? 

3. It is worth attaching photos of the boards or describing them: they are flat, pressed, corrugated or maybe CARO type. This is related to their resistance to weather conditions. Were there any differences in the appearance of these samples?

4. The manuscript   does not develop the issue of changes taking place in the process of thermal decomposition of asbestos itself as a component of the analyzed waste. Judging by the title, this should be important. It is disadventure of the manuscript. For this purpose, it was necessary to test thermally processed asbestos with the method which  the analytical sensitivity  would be higher than the permissible asbestos content in products placed for the market and trade. That should demonstrated the  final phase of transformation of asbestos into another mineral phase (e.g. olivine, forsterite, enstattite. In Poland, products  completely cannot contain any asbestos. This cannot be demonstrated when testing an asbestos-cement product  using the Differential Thermal Analysis technique. This problem should be explained in more detail,  or changed at least by modifying the title and relevant parts of the article.

5. Lines 209 - 211 relating to Fig. 4 and 5. Analyzing thermal changes in the range of 600 -850 C, the authors assume that: "In this range of temperatures, the thermal distribution of chrysotile asbestos should also take place" - the basic goal for the recycling process. Rightly. At the same time, the creation of new mineral phases, however, is obscured (as they write) by a decomposition of carbonates in this temperature range.

When dedicating (as in the title and the introduction and in the content of the article) for the solution to the problem of asbestos waste and their recycling, asbestos temperature decomposition, it should be confirmed by tests (which was not able to do with the use of DTA). So You can  insert the appropriate bibliography in this place.

How to easily improve this article:

1. Indicate the purpose of the research and link it to the results obtained at work

2. Concerning the research carried out, indicates the need for further analyzes aimed at assessing the behaviour of asbestos contained in the waste itself in the process of thermal destruction.  If the authors do not provide for such an addition, explain why it was not done this time.

3. Relativize the suggestions for thermal decomposition, indicating the benefits and risks of this technology.

4. Expand the cited bibliography with critical opinions on thermal decomposition processes

5. It's even easier to change the title and abstract to match the content of the article.

Final opinion Despite some critical remarks, the article qualifies for publication after minor corrections. It raises important issues regarding the need to research products from Eastern Europe, omitted in Western publications (focused on research in their region).

Author Response

The problem raised at the beginning is important because it concerns the high concentration of hazardous waste in this country. They are dangerous due to their asbestos content. The reviewer has the impression that the authors failed to consistently develop this topic and in their research, they focused on the difference in the composition of the discussed products and the different (different) technological processes of producing Lithuanian slabs and other compared asbestos-cement board waste from other countries. This is a valid and interesting discovery, but what is the most important is that,  what has not been said (about thermal modification of asbestos). This is a basic criticism.

Thank you for valuing the manuscript!

Detailed comments

1. In XRF tests, it would be worth attaching a chart of the element content for this technique concerning the fibres (shown in Fig. 1) before and after thermal treatment, as well as SEM photos showing what is the effect of recycling, i.e. the destruction of the form and structure of asbestos fibres (especially when the suggested it is possible to reuse a product from recycled waste). Therefore, the use of SEM-EDS or even optical microscopy should be considered if fibres have not been separated for this purpose.

Additional study were made – revised manuscript was complemented by XRD and SEM analysis of materials after isothermal treatment at selected temperature (lines 301-329)

2. The chemical results of 3 samples showed differences in the content of elements found in asbestos (MgO, FeO). How to interpret this, taking into account the extremely different environmental conditions (sample taken from the soil, "protected" against weathering processes, sample exposed to cement leaching for 20 and 50 years). The reviewer's research shows that old a-c boards, after many years of use and washing out of the cement matrix by rainfall, may have high of the content of asbestos fibres.  In domestic boards, depending on their type and dimensions, maybe different content of asbestos: "modified lignocement" boards- 5%, classic pressed - 10-11%, wavy approx. 11.5-13%. What's it like in Lithuanian samples? 

Discussion about content of MgO and FeO was added in revised version (lines 207-211). Taking into account the uncertainties of measurement the differences in MgO are negligible. For TR sample the amount of Fe2O3 is statistically significant, so some comment are added. Quantitative phase analysis was not included in the scope of the research, but the estimated content of asbestos fibers for all three tested asbestos-cements from Lithuania was approximately 10 wt%.

3. It is worth attaching photos of the boards or describing them: they are flat, pressed, corrugated or maybe CARO type. This is related to their resistance to weather conditions. Were there any differences in the appearance of these samples?

Additional photos of tested materials were added. They were corrugated type of boards. Differences in the appearance of these materials were described in revised version (lines 142-150)

4. The manuscript   does not develop the issue of changes taking place in the process of thermal decomposition of asbestos itself as a component of the analyzed waste. Judging by the title, this should be important. It is disadventure of the manuscript. For this purpose, it was necessary to test thermally processed asbestos with the method which  the analytical sensitivity  would be higher than the permissible asbestos content in products placed for the market and trade. That should demonstrated the  final phase of transformation of asbestos into another mineral phase (e.g. olivine, forsterite, enstattite. In Poland, products  completely cannot contain any asbestos. This cannot be demonstrated when testing an asbestos-cement product  using the Differential Thermal Analysis technique. This problem should be explained in more detail,  or changed at least by modifying the title and relevant parts of the article.

Additional study were made – revised manuscript was complemented by XRD and SEM analysis of materials after isothermal treatment at selected temperature (lines 301-329). Additional discussion about thermal changes with testing materials were complemented (lines 338-352). We changed the title of manuscript for more adequate with its contents.

5. Lines 209 - 211 relating to Fig. 4 and 5. Analyzing thermal changes in the range of 600 -850 C, the authors assume that: "In this range of temperatures, the thermal distribution of chrysotile asbestos should also take place" - the basic goal for the recycling process. Rightly. At the same time, the creation of new mineral phases, however, is obscured (as they write) by a decomposition of carbonates in this temperature range. When dedicating (as in the title and the introduction and in the content of the article) for the solution to the problem of asbestos waste and their recycling, asbestos temperature decomposition, it should be confirmed by tests (which was not able to do with the use of DTA). So You can  insert the appropriate bibliography in this place.

Additional discussion about chrysotile thermal decomposition was added (lines 338-352)

How to easily improve this article:

1. Indicate the purpose of the research and link it to the results obtained at work

We change the purpose of the research on the structural characteristics of cement-asbestos from Lithuania before and after thermal treatment

2. Concerning the research carried out, indicates the need for further analyzes aimed at assessing the behaviour of asbestos contained in the waste itself in the process of thermal destruction.  If the authors do not provide for such an addition, explain why it was not done this time.

Additional study were made – revised manuscript was complemented by XRD and SEM analysis of materials after isothermal treatment at selected temperature (lines 301-329).

3. Relativize the suggestions for thermal decomposition, indicating the benefits and risks of this technology and 4. Expand the cited bibliography with critical opinions on thermal decomposition processes

The benefits and risks of thermal decomposition were added, new literature data were added (lines 94-119, 407-408, new references 31-37, 52-54)

5. It's even easier to change the title and abstract to match the content of the article.

We changed the title of manuscript for more adequate with its contents (line 2)

Final opinion Despite some critical remarks, the article qualifies for publication after minor corrections. It raises important issues regarding the need to research products from Eastern Europe, omitted in Western publications (focused on research in their region).

Thank you for good recommendation of the manuscript

Reviewer 2 Report

The authors do not report other possible methods widely discussed in the literature. Furthermore, there is nothing described about the novelty of this study, in which it stands out from other works found in the literature that have long ago investigated thermal processes, which in general prove to be very energetically costly. This generally makes the treatment of asbestos-containing materials unfeasible, causing them to accumulate in landfills. The article is well described and presented, but does not describe a new method of treating asbestos-containing materials. Differences in the absolute concentrations of evaluated materials are not sufficient for the novelty character. A different approach can be proposed, however it requires a profound restructuring of the text.

Minor editing of English language required.

Author Response

The authors do not report other possible methods widely discussed in the literature. Furthermore, there is nothing described about the novelty of this study, in which it stands out from other works found in the literature that have long ago investigated thermal processes, which in general prove to be very energetically costly. This generally makes the treatment of asbestos-containing materials unfeasible, causing them to accumulate in landfills. The article is well described and presented, but does not describe a new method of treating asbestos-containing materials. Differences in the absolute concentrations of evaluated materials are not sufficient for the novelty character. A different approach can be proposed, however it requires a profound restructuring of the text.

Other methods are mentioned in the revised version (lines 98-101). Due to the thermal nature of the tests, other methods are not discussed in detail. Due to the fact that the significant difference in chemical composition was emphasized, the title of the manuscript was changed to a more appropriate one (line 2) In our opinion, this is an important issue because research on products from Eastern Europe is omitted in Western publications and may differ from those available in the literature. Editing of English language was done.

Reviewer 3 Report

The authors studied three end-of-life-asbestos cements from Lithuania by thermal decomposition, XRD, and XF methods. As described in introduction, an important point is to solve asbestos problem caused by the significant amount of accumulated waste containing asbestos.  They have proposed recycling and reuse of the end-of life asbestos after thermal tratment instead of deposition of it in landfills. But, as the thermal analysis showed the change in phase of cements not asbestos.  Furthermore,there is no XRD data regarding asbestos by the thermal treatment.  It is not clear how asbestos changes to non-toxic compounds by the thermal treatment.  Even if the end-of-life asbestos waste cement is thermally treated and recycled, the recycled material will continue to contain asbestos ever.  The proposed thermal treatment of the end-of life asbestos does not appear to solve the asbestos problem.

Author Response

The authors studied three end-of-life-asbestos cements from Lithuania by thermal decomposition, XRD, and XF methods. As described in introduction, an important point is to solve asbestos problem caused by the significant amount of accumulated waste containing asbestos.  They have proposed recycling and reuse of the end-of life asbestos after thermal tratment instead of deposition of it in landfills. But, as the thermal analysis showed the change in phase of cements not asbestos.  Furthermore, there is no XRD data regarding asbestos by the thermal treatment.  It is not clear how asbestos changes to non-toxic compounds by the thermal treatment.  Even if the end-of-life asbestos waste cement is thermally treated and recycled, the recycled material will continue to contain asbestos ever.  The proposed thermal treatment of the end-of life asbestos does not appear to solve the asbestos problem.

Additional study were made – revised manuscript was complemented by XRD and SEM analysis of materials after isothermal treatment at selected temperature (lines 301-329). Additional discussion about thermal changes with testing materials were complemented (lines 338-352). It was proved that during thermal treatment asbestos mineral changed into new mineral phases and for the long term can be concluded that the thermally processed material does not contain asbestos.

Round 2

Reviewer 2 Report

The paper may be considered for publication.

Author Response

The paper may be considered for publication.

Thank you for valuing the manuscript

Reviewer 3 Report

In the revised manuscript, XRD and SEM data clearly show the decomposition of chrysotile at high temperatures (~1100-1200 °C).

However, the relationship between asbestos degradation and the result of thermal analysis is not clear.

Please insert a point of the beginning of the decomposition of asbestos on the thermal analysis diagram.

What percentage of asbestos is containedin the samples? Please show the concentration of asbestos in the samples.

Does the graph of thermal analysis only show changes in cement? Does it show decomposition of asbestos?

Author Response

Please see the attachment

Author Response File: Author Response.pdf