Application of Clay Materials for Sorption of Radionuclides from Waste Solutions
Round 1
Reviewer 1 Report
I have reviewed the review article entitled " Design and Application of Clay Materials for Sequestration of 2 Radionuclides from Nuclear Waste Solutions". In this manuscript, the results of clay minerals with various natural and modified forms to adsorb radionuclides are well collected and list systematically. The authors also summarize the major aspects and highlight key challenges to be addressed in future studies to further enhance the application of clays and clay based materials for selective and effective removal of various radionuclides from waste solutions. Based on the comments above, I suggested that the manuscript could be accepted for publication.
Author Response
Response: We greatly appreciate your kind evaluation of this review manuscript and recommendation for its acceptance/publication in ‘Minerals’ in its current form. Additionally, this manuscript has been further enriched/revised/updated based on other reviewers’ comments. All the needful/asked revisions and modifications have been made, and are marked and highlighted in the revised manuscript at their appropriate places. We believe that this revised and updated review manuscript has been further improved and a worthy of publication in ‘Minerals’.
Reviewer 2 Report
This manuscript is intended to be a review of the novel research on natural and/or functionalized materials used for radionuclide retention. Despite including many references (not all very relevant) the work does not have a clear objective, in which the latest advances organized by material or type of contaminant became clear.
The reading is difficult because an argumentation line is missing, thus it does not really provide a well-organized and useful information for the reader.
Successive summaries are given, sometimes too detailed, of different papers without a common thematic thread. For example, half a page is used to summarize a single paper of uranium adsorption in clay colloids (Line 112-133) very recent, but containing not especially novel results. It’s a pity because very good and relevant papers on uranium adsorption in clay exist. Next, they describe an in-situ work about Cs and U migration in a karst environment, in which the main objective was to study the effect of colloids on migration. And so, changing the subject until the end.
The conclusions are not really the consequence of this work. It is already known that many natural and modified materials have an optimal adsorption capacity for hazardous nuclides. It would have been much more interesting a discussion about the parameters that make one material or another more interesting in relation to radionuclide retention. Instead of general comments on the drawbacks related to the use of functionalized material, one expected more concrete proposals on optimization for their use at a large scale.
In my opinion the manuscript cannot be accepted in the current form. The structure should be better defined and the real objectives should be clearer to be publishable.
Author Response
Response: We are thankful to your comments and suggestions. In order to present a well-organized and comparative results/data of some of the discussed papers, we have incorporated a new Table (as Table 1) containing various clays (natural as well as modified clays) and their sequestration performances at different experimental parameters/conditions (such as, the type and radionuclide’s concentration, pH, contact time, sorbent concentration, temperature, and ionic strength). Table 1 also contains various characterization techniques used for solids/sorbents analysis in the referred/cited papers. The data presented in (newly) added Table 1 have been extracted from their original papers to give a clear idea to the readers on the thoroughly discussed papers. We believe, this Table will be more convenient to assess the comparative radionuclides’ removal by various clays (both NCs and MCs).
Additionally, we have also added the following texts in the section ‘4. Conclusion and Perspective’. All the needed changes/modifications have been highlighted in the revised manuscript with changes marked.
After revision, this review manuscript seems to be further improved and we hope it will receive your kind recommendation for its acceptance in ‘Minerals’.
Added texts in section ‘4. Conclusions and Future Perspectives’
The key aspects of this behavior of NCs and MCs can be attributed to their net/overall charges in aqueous media. It’s in noteworthy that NCs possess overall negative charge in aqueous media and therefore, are most suitable for the sequestration of metal cations/radionuclides. However, after functionalization/modification, the MCs can be also suitable for efficient removal of anionic radionuclides/hazardous anions, as discussed and highlighted here. Therefore, being abundant and ubiquitous in nature, the clays can be effectively applied for the treatments and decontamination of various radioactive contaminants (cations as well as anions) from waste solutions.
In addition, the management of resulted wastes after sorption of radionuclides onto clays and the fate of final disposal via immobilization of generated wastes (or various waste form formulation) can be found in Singh et al. (127).
- Singh, B.K.; Hafeez, M.A.; Kim, H.; Hong, S.; Kang, J.; Um, W. Inorganic waste forms for efficient immobilization of radio-nuclides. ACS ES&T Eng. 2021, 1(8), 1149-1170.
Added Table 1
Table 1. Sequestration of radionuclides from (simulated) waste solutions using natural clays (NCs) and modified clays (MCs) at various experimental conditions.
|
Types of materials |
Used clays and radionuclides /metal ions |
Experimental conditions, characterization techniques, and sequestration performances |
References |
|
NCs |
Montmorillonite
U(VI) |
U(VI) = 30 ppm; pH = 4.0 -7.0; Ionic strength (I) = ND; contact time = 30 minutes (m); temperature = 25 – 45 °C; sorbent concentration: ND. Characterization techniques: XRF, SEM, and FT-IR spectroscopy. Performance: 72 % U(VI) removal; 18.13 mgg−1 maximum adsorption capacity. |
Yu et al. [97] |
|
Bentonite
U(VI) and Cs(I) |
U(VI) = 3.7 × 10−6 M, Cs(I)= 7.5 × 10−6 M; pH = 7.0 - 8.0; I = ND; contact time = 14 days (d); temperature = 25 °C; sorbent concentration: 0.1- 2.0 g/L. Characterization techniques: XRD, and zeta potential measurement. Performance: ~ 5 % U(VI) removal; 31 % Cs(I) removal. |
Tran et al. [98] |
|
|
Bentonite and kaolinite
U(VI) and Np(VI) |
U(VI) = 5 × 10−7 M, Np(VI)= 1 × 10−7 M; pH = 8.0 - 13.0; I = 0.1M; contact time = 7 d for U(VI) and 3d for Np(VI); temperature = 25 °C; sorbent concentration: 2.0- 10.0 g/L. Characterization techniques: TRLFS and zeta potential measurement. Performance: > 90 % U(VI) and Np(VI)removal. |
Philipp et al. [99] |
|
|
Bentonite
Cs(I), Sr(II), Ba(II), and Eu(III) |
Cs(I), Sr(II), Ba(II), and Eu(III) = 10 ppm; pH = 2 – 12; I = 0.01 M; contact time = 20 m; temperature = 25 °C; sorbent concentration = 10 g/L. Characterization techniques: XRD, XRF, SEM, and ICP-OES. Performance: = 87 % Cs(I) removal, 98 % Sr(II) removal, 100 % Ba(II) and Eu(III) removal. |
Seliman et al. [100] |
|
|
Bentonite
Cs(I) |
Cs(I) = 10−11 – 10-2 M; pH = 2 - 11; I = 0.01 M; contact time = 1-300 hours (h); sorbent concentration = 1 g/L. Characterization techniques: XRD, FT-IR, XRF, and BET analysis. Performance: ~ 100 % Cs(I) removal. |
Semenko-va et al. [101] |
|
|
Bentonite
Cs(I) and Sr(II) |
Cs(I), Sr(II) = 2.5 × 10−5 – 5 × 10-3 M; pH = 2.0 – 10.00; I = 0.01; contact time = ND; sorbent concentration = 10.0 g/L. Characterization techniques: XRD, FT-IR, and zeta potential measurement. Performance: 90 -100 % Cs(I) and Sr(II) removal. |
Izosimova et al. [103] |
|
|
K10- montmorill-onite
Ce (III) and Pb (II) |
Ce (III) and Pb (II)= 2-300 ppm; pH = 2 and 6; I = ND; contact time = 2 - 4 h; sorbent concentration = 0.4 g/L. Characterization techniques: XRD and UV-visible spectroscopy. Performance: ~100 % Ce (III) and Pb (II) removal. |
Parisi [104] |
|
|
MCs |
HDPy-modified bentonite
ReO4− |
Re(VII) = ND; pH = 2.0 –11.0; I = 0.001 – 0.1 M; contact time = 1 - 240 m; temperature = 25 - 55 °C; sorbent concentration = ND. Characterization techniques: FT-IR, XPS, and TEM-EDS. Performance: ~100 % ReO4− removal. |
Yang et al. [118] |
|
Thoron modified montmorillonite
Co(II) |
Co(II) = 1 × 10-4 – 4 × 10-4 M; pH = 2.5 –8.0; I = 0.0001 – 0.1 M; contact time = 0 - 120 m; temperature = 30 - 60 °C; sorbent concentration = 10.0 g/L. Characterization techniques: XRD and FT-IR spectroscopy. Performance: ~100 % Co(II) removal. |
Soliman et al. [120] |
|
|
Ammonium citrate tribasic modified attapulgite clay
Th (IV) |
Th(IV) = 5 – 15 ppm; pH = 1.5 – 11.5; I = 0.001 – 0.1 M; contact time = 24 h; temperature = 25 °C; sorbent concentration = 0.3 g/L. Characterization techniques: XRD and FT-IR analyses. Performance: ~ 100 % Th(IV) removal. |
Hu and Tan [121] |
|
|
Nickel (Ni) modified Akadama clay (AC)
Cs(I) |
Cs(I) = 10 ppm; pH = 2.0 – 12.0; I = ND; contact time = 0 – 24 h; temperature = 15 – 35 °C; sorbent concentration = 2.5 - 10 g/L. Characterization techniques: XRD, FT-IR, N2 ads–des isotherms, SEM, EDS, and TG/DTA. Performance: > 90 % Cs(I) removal. |
Ding et al. [122] |
|
|
Cetyltrimethylammonium bromide (CTAB) modified bentonite
137Cs), (60Co), and (152+154Eu) |
137Cs), (60Co), and (152+154Eu) = 1 x 10‐6 M; pH = 1.2 – 12.7; I = ND; contact time = 0 - 4 h; temperature = 30 - 50 °C; sorbent concentration = 10.0 g/L. Characterization techniques: XRD, XRF, and IR spectroscopy. Performance: ~ 100 % 137Cs), (60Co), and (152+154Eu) removal. |
Shakir et al. [123] |
|
|
5-mercapto-1-methyltetrazole modified diquite and bentonite
Th(IV) |
Th(IV) = 1.20 - 2.0 × 10−5 M; pH = 1.0 – 8.0; I = ND; contact time =24 h; temperature = 25 °C; sorbent concentration = 1.0g/L. Characterization techniques: XRD, N2 ads/des isotherms, TEM, and 13C NMR spectroscopy. Performance: 10.45 × 10−2 and 12.76 × 10−2 mmol/g Th(IV) adsorbed onto DMTTZ and BMTTZ, respectively . |
Guerra et al. [124] |
|
|
2-mercaptobenzi-midazole modified hectorite clay
Th4+, U6+, and Eu3+ |
Th4+, U6+, and Eu3+ = 1.25 - 2.5 × 10−5 M; pH = 1.0 – 8.0; I = ND; contact time = 12 h; temperature = 25 - 40 °C; sorbent concentration = 1.0g/L. Characterization techniques: SEM, MAS 29Si, and 13C NMR spectroscopy. Performance: 11.63 mmol/g, 12.85 mmol/g, and 14.01 mmol/g removal of Th4+, U6+, and Eu3+, respectively. |
Guerra et al. [125] |
|
|
Activated carbon modified bentonite,
TcO4- |
TcO4- = 4 × 10-6 M; pH = ND; I = ND; contact time = 14 d; temperature = 25 °C; sorbent concentration = 1/40 (solid to liquid ratio, S/L). Characterization techniques: XPS, XANES, and EXAFS. Performance: ~ 94 % TcO4- removal. |
Makarov et al. [126] |
ND refers to the not defined values.
Reviewer 3 Report
The author reviewed the radionuclide adsorbent in clay and modified clay.
I consider the manuscripts to be well-organized and written.
The paper must be changed in accordance with the comments below before it can be published.
1. In sections 3 and 4, the author writes the radionuclide removal by pure clay and modified clay. However, I suggest that authors make a well-organized table with various factors (for example, clays, radionuclides, amounts of adsorption, ionic strength, pH, etc.) to compare the removal of radionuclides by clays.
2. The author provided a comprehensive summary of the results and prospects (section 4). But they omitted to discuss the main factor of radionuclide removal by clay and modified clay. I suggest that authors write the main factor of radionuclide removal by clay and modified clay.
3. The sentence on lines 152-155 lacks a verb.
4. How should radionuclide-removing clay be disposed of? For this, the authors will also discuss the disposal of radionuclide-removing clay.
5. Authors present the various pure clays and modified clays. For readers to understand well, I suggest that authors presented the reason for selecting clay (e.g., 1:1, 2:1 clay, etc.).
Author Response
Reviewer 3
Comments and Suggestions:
The author reviewed the radionuclide adsorbent in clay and modified clay. I consider the manuscripts to be well-organized and written. The paper must be changed in accordance with the comments below before it can be published.
Response: We are highly thankful for your kind evaluation of our review manuscript and providing us such meaningful comments. Based on the given comments, we have carefully revised and updated the whole manuscript. The comments and suggestions were helpful in addressing the lacking details and clarity in the updated/revised manuscript. After addressing your comments/suggestions, this revised manuscript seems to be much improved and we believe that it will receive your kind recommendation for its final acceptance in ‘Minerals’.
Our response to your comments and suggestions are described below and the needed changes have been highlighted in the revised manuscript with changes marked.
Comment 1. In sections 3 and 4, the author writes the radionuclide removal by pure clay and modified clay. However, I suggest that authors make a well-organized table with various factors (for example, clays, radionuclides, amounts of adsorption, ionic strength, pH, etc.) to compare the removal of radionuclides by clays.
Response: We appreciate your comment and suggestion. Probably, the reviewer has referred sections 2 and 3 for the radionuclide removal onto natural clays and modified clays. As suggested by the reviewers, we have incorporated a new Table (Table 1 in the revised manuscript) with needed/important information on various radionuclides removal by pure/natural clays and modified clays as well as the experimental conditions. These data were extracted from their original papers to give a clear idea to the readers on the thoroughly discussed and cited papers.
Added Table 1
Table 1. Sequestration of radionuclides from (simulated) waste solutions using natural clays (NCs) and modified clays (MCs) at various experimental conditions.
|
Types of materials |
Used clays and radionuclides /metal ions |
Experimental conditions, characterization techniques, and sequestration performances |
References |
|
NCs |
Montmorillonite
U(VI) |
U(VI) = 30 ppm; pH = 4.0 -7.0; Ionic strength (I) = ND; contact time = 30 minutes (m); temperature = 25 – 45 °C; sorbent concentration: ND. Characterization techniques: XRF, SEM, and FT-IR spectroscopy. Performance: 72 % U(VI) removal; 18.13 mgg−1 maximum adsorption capacity. |
Yu et al. [97] |
|
Bentonite
U(VI) and Cs(I) |
U(VI) = 3.7 × 10−6 M, Cs(I)= 7.5 × 10−6 M; pH = 7.0 - 8.0; I = ND; contact time = 14 days (d); temperature = 25 °C; sorbent concentration: 0.1- 2.0 g/L. Characterization techniques: XRD, and zeta potential measurement. Performance: ~ 5 % U(VI) removal; 31 % Cs(I) removal. |
Tran et al. [98] |
|
|
Bentonite and kaolinite
U(VI) and Np(VI) |
U(VI) = 5 × 10−7 M, Np(VI)= 1 × 10−7 M; pH = 8.0 - 13.0; I = 0.1M; contact time = 7 d for U(VI) and 3d for Np(VI); temperature = 25 °C; sorbent concentration: 2.0- 10.0 g/L. Characterization techniques: TRLFS and zeta potential measurement. Performance: > 90 % U(VI) and Np(VI)removal. |
Philipp et al. [99] |
|
|
Bentonite
Cs(I), Sr(II), Ba(II), and Eu(III) |
Cs(I), Sr(II), Ba(II), and Eu(III) = 10 ppm; pH = 2 – 12; I = 0.01 M; contact time = 20 m; temperature = 25 °C; sorbent concentration = 10 g/L. Characterization techniques: XRD, XRF, SEM, and ICP-OES. Performance: = 87 % Cs(I) removal, 98 % Sr(II) removal, 100 % Ba(II) and Eu(III) removal. |
Seliman et al. [100] |
|
|
Bentonite
Cs(I) |
Cs(I) = 10−11 – 10-2 M; pH = 2 - 11; I = 0.01 M; contact time = 1-300 hours (h); sorbent concentration = 1 g/L. Characterization techniques: XRD, FT-IR, XRF, and BET analysis. Performance: ~ 100 % Cs(I) removal. |
Semenko-va et al. [101] |
|
|
Bentonite
Cs(I) and Sr(II) |
Cs(I), Sr(II) = 2.5 × 10−5 – 5 × 10-3 M; pH = 2.0 – 10.00; I = 0.01; contact time = ND; sorbent concentration = 10.0 g/L. Characterization techniques: XRD, FT-IR, and zeta potential measurement. Performance: 90 -100 % Cs(I) and Sr(II) removal. |
Izosimova et al. [103] |
|
|
K10- montmorill-onite
Ce (III) and Pb (II) |
Ce (III) and Pb (II)= 2-300 ppm; pH = 2 and 6; I = ND; contact time = 2 - 4 h; sorbent concentration = 0.4 g/L. Characterization techniques: XRD and UV-visible spectroscopy. Performance: ~100 % Ce (III) and Pb (II) removal. |
Parisi [104] |
|
|
MCs |
HDPy-modified bentonite
ReO4− |
Re(VII) = ND; pH = 2.0 –11.0; I = 0.001 – 0.1 M; contact time = 1 - 240 m; temperature = 25 - 55 °C; sorbent concentration = ND. Characterization techniques: FT-IR, XPS, and TEM-EDS. Performance: ~100 % ReO4− removal. |
Yang et al. [118] |
|
Thoron modified montmorillonite
Co(II) |
Co(II) = 1 × 10-4 – 4 × 10-4 M; pH = 2.5 –8.0; I = 0.0001 – 0.1 M; contact time = 0 - 120 m; temperature = 30 - 60 °C; sorbent concentration = 10.0 g/L. Characterization techniques: XRD and FT-IR spectroscopy. Performance: ~100 % Co(II) removal. |
Soliman et al. [120] |
|
|
Ammonium citrate tribasic modified attapulgite clay
Th (IV) |
Th(IV) = 5 – 15 ppm; pH = 1.5 – 11.5; I = 0.001 – 0.1 M; contact time = 24 h; temperature = 25 °C; sorbent concentration = 0.3 g/L. Characterization techniques: XRD and FT-IR analyses. Performance: ~ 100 % Th(IV) removal. |
Hu and Tan [121] |
|
|
Nickel (Ni) modified Akadama clay (AC)
Cs(I) |
Cs(I) = 10 ppm; pH = 2.0 – 12.0; I = ND; contact time = 0 – 24 h; temperature = 15 – 35 °C; sorbent concentration = 2.5 - 10 g/L. Characterization techniques: XRD, FT-IR, N2 ads–des isotherms, SEM, EDS, and TG/DTA. Performance: > 90 % Cs(I) removal. |
Ding et al. [122] |
|
|
Cetyltrimethylammonium bromide (CTAB) modified bentonite
137Cs), (60Co), and (152+154Eu) |
137Cs), (60Co), and (152+154Eu) = 1 x 10‐6 M; pH = 1.2 – 12.7; I = ND; contact time = 0 - 4 h; temperature = 30 - 50 °C; sorbent concentration = 10.0 g/L. Characterization techniques: XRD, XRF, and IR spectroscopy. Performance: ~ 100 % 137Cs), (60Co), and (152+154Eu) removal. |
Shakir et al. [123] |
|
|
5-mercapto-1-methyltetrazole modified diquite and bentonite
Th(IV) |
Th(IV) = 1.20 - 2.0 × 10−5 M; pH = 1.0 – 8.0; I = ND; contact time =24 h; temperature = 25 °C; sorbent concentration = 1.0g/L. Characterization techniques: XRD, N2 ads/des isotherms, TEM, and 13C NMR spectroscopy. Performance: 10.45 × 10−2 and 12.76 × 10−2 mmol/g Th(IV) adsorbed onto DMTTZ and BMTTZ, respectively . |
Guerra et al. [124] |
|
|
2-mercaptobenzi-midazole modified hectorite clay
Th4+, U6+, and Eu3+ |
Th4+, U6+, and Eu3+ = 1.25 - 2.5 × 10−5 M; pH = 1.0 – 8.0; I = ND; contact time = 12 h; temperature = 25 - 40 °C; sorbent concentration = 1.0g/L. Characterization techniques: SEM, MAS 29Si, and 13C NMR spectroscopy. Performance: 11.63 mmol/g, 12.85 mmol/g, and 14.01 mmol/g removal of Th4+, U6+, and Eu3+, respectively. |
Guerra et al. [125] |
|
|
Activated carbon modified bentonite,
TcO4- |
TcO4- = 4 × 10-6 M; pH = ND; I = ND; contact time = 14 d; temperature = 25 °C; sorbent concentration = 1/40 (solid to liquid ratio, S/L). Characterization techniques: XPS, XANES, and EXAFS. Performance: ~ 94 % TcO4- removal. |
Makarov et al. [126] |
ND refers to the not defined values.
Comment 2. The author provided a comprehensive summary of the results and prospects (section 4). But they omitted to discuss the main factor of radionuclide removal by clay and modified clay. I suggest that authors write the main factor of radionuclide removal by clay and modified clay.
Response: Thank you for your suggestion. We have incorporated and updated the following texts in the section ‘4. Conclusions and Future Perspectives’ in the revised manuscript.
Added texts in section ‘4. Conclusion and Future Perspectives’
The key aspects of this behavior of NCs and MCs can be attributed to their net/overall charges in aqueous media. It’s in noteworthy that NCs possess overall negative charge in aqueous media and therefore, are most suitable for the sequestration of metal cations/radionuclides. However, after functionalization/modification, the MCs can be also suitable for efficient removal of anionic radionuclides/hazardous anions, as discussed and highlighted here. Therefore, being abundant and ubiquitous in nature, the clays can be effectively applied for the treatments and decontamination of various radioactive contaminants (cations as well as anions) from waste solutions.
Comment 3. The sentence on lines 152-155 lacks a verb.
Response: Thank you for the comment. The given sentence has been modified and updated in the revised manuscript as given below.
Philipp et al. very recently simulated the geochemical conditions (high pH and complex solution compositions) for radioactive wastes in deep geological repositories and investigated the interactions of radionuclides with mineral surfaces under the extreme conditions [99].
Comment 4. How should radionuclide-removing clay be disposed of? For this, the authors will also discuss the disposal of radionuclide-removing clay.
Response: We appreciate your comment. However, this review has been mainly focused on the removal/sorption of various radionuclides present in (simulated) waste solutions at the defined experimental conditions using various clays (NCs and MCs). In addition, we added a new sentence in Conclusion section like, “The management of resulted wastes after sorption of radionuclides onto clays and the fate of final disposal via immobilization of generated wastes (or various waste form formulation) can be found in Singh et al. (127)”.
- Singh, B.K.; Hafeez, M.A.; Kim, H.; Hong, S.; Kang, J.; Um, W. Inorganic waste forms for efficient immobilization of radio-nuclides. ACS ES&T Eng. 2021, 1(8), 1149-1170.
Therefore, we believe this review can be mainly centered on the sequestration of various radionuclides from waste solution using different natural and modified clay materials.
Comment 5. Authors present the various pure clays and modified clays. For readers to understand well, I suggest that authors presented the reason for selecting clay (e.g., 1:1, 2:1 clay, etc.).
Response: Thank you for the comment. We believe that the last three paragraphs in ‘1. Introduction’ section and first paragraphs of both sections, ‘2.Natural Clays (NCs) for Sequestration of Radionuclides’ and ‘3.Modified/Functionalized Clays (MCs) for Sequestration of Radionuclides’ in this review manuscript have justified/presented the reasons for selecting natural clays and modified clays for removal of various radionuclides from waste solutions.
Overall, based on the reviewers’ comments and suggestions, this revised and updated review manuscript has been significantly improved and seems much organized. We believe, it would be highly useful/suitable for the readers and a worthy of its acceptance and publication in ‘Minerals’.
Reviewer 4 Report
The work "Application of Clay Materials for Sequestration of Radionuclides from Nuclear Waste Solutions" is of great interest in the field of materials used for the extraction of radionuclides from liquid media. Summarized data are presented in an understandable way and allow the reader to adequately familiarize themselves with the materials under study. However, there are a number of comments and suggestions:
- The title of the work doesn't match the material presented. Firstly, the materials described in the work are tested on natural water simulators, radioactive waste is very rarely mentioned. Secondly, in my opinion, in the title, the word "Sequestration" should be replaced with "extraction" or "sorption", as this more adequately reflects the purification process.
- the term “sorbent concentration…= … g/L” is used in the paper to describe the content of the material loading. Should be replaced by “ratio V/m = …. ml/g" as it's more literate and common!
- I don’t understand why Figure 3 shows a large number of diagrams if the authors don’t discuss more than half of them!
-on lines 383-384, the authors write "Kinetic experiments revealed fast Th(IV) sorption onto OA, which was followed by a pseudo-second-order kinetic model.", thereby emphasizing this. However, they don’t develop or interpret the given fact in any way.
-according to the text, the authors prescribe from which liquid media (simulators, real ones) the radionuclides were extracted. However, the chemical composition of these media is not given anywhere, which would increase the quality of their work and the interest of readers. It is necessary to give the compositions, either in the text or in the general table 1.
- the authors make a special emphasis on mentioning the physicochemical methods used in the studies of materials, however, they don’t describe the results obtained with the help of them everywhere. For example, on pages 23, 24 etc.
-Figure 2 needs to be improved. It is difficult for readers to read the information in the plot legend.
Author Response
General comment: The work "Application of Clay Materials for Sequestration of Radionuclides from Nuclear Waste Solutions" is of great interest in the field of materials used for the extraction of radionuclides from liquid media. Summarized data are presented in an understandable way and allow the reader to adequately familiarize themselves with the materials under study. However, there are a number of comments and suggestions:
Response: We are grateful to you for your kind review of this manuscript and providing us meaningful comments and suggestions. We have carefully worked through the given comments and revised/updated the whole manuscript accordingly. Please find below our point-by-point response to the given comments and needed work done below each comment. We hope that this revised and updated review manuscript will receive your final recommendation for its acceptance and publication in ‘Minerals’.
Comment: The title of the work doesn't match the material presented. Firstly, the materials described in the work are tested on natural water simulators, radioactive waste is very rarely mentioned. Secondly, in my opinion, in the title, the word "Sequestration" should be replaced with "extraction" or "sorption", as this more adequately reflects the purification process.
Response: We appreciate your suggestion. As suggested by the reviewer, we have replaced the word ‘sequestration’ with ‘sorption’ from the title and throughout the whole manuscript. In addition, the word ‘Nuclear’ has been deleted from the title. The revised and updated title is given below.
“Application of Clay Materials for Sorption of Radionuclides from Waste Solutions”
Comment: the term “sorbent concentration…= … g/L” is used in the paper to describe the content of the material loading. Should be replaced by “ratio V/m = …. ml/g" as it's more literate and common!
Response: Thanks for your comment. We believe that ‘g/L’ can be used for “sorbent concentration as it has been mentioned/referred in several studies.
Comment: I don’t understand why Figure 3 shows a large number of diagrams if the authors don’t discuss more than half of them!
Response: Thank you for the comment. The related/referred text for Figure 3 has been modified and updated in the revised manuscript as described below.
“Figures 3A–F exhibit the effects of pH and ionic strength on Re(VII) sorption onto HDPy-bent, the zeta potential data of HDPy-bent sorbent prior and after Re(VII) sorption, pseudo-second adsorption kinetic models at different temperatures, and UV–vis analysis results of Re(VII) sorption onto HDPy-bent.”
Comment: on lines 383-384, the authors write "Kinetic experiments revealed fast Th(IV) sorption onto OA, which was followed by a pseudo-second-order kinetic model.", thereby emphasizing this. However, they don’t develop or interpret the given fact in any way.
Response: We appreciate your comment and regret for such mistake. The refereed sentence has been modified and updated in the revised manuscript as given below.
“Kinetic experiments revealed fast Th(IV) sorption onto OA and the obtained data followed a pseudo-second-order kinetic model.”
Comment: according to the text, the authors prescribe from which liquid media (simulators, real ones) the radionuclides were extracted. However, the chemical composition of these media is not given anywhere, which would increase the quality of their work and the interest of readers. It is necessary to give the compositions, either in the text or in the general table 1.
Response: Thank you for the comment. All referred/discussed studies have provided the concentrations of the targeted radionuclides/ions in the simulated waste solutions as mentioned in Table 1.
Comment: the authors make a special emphasis on mentioning the physicochemical methods used in the studies of materials, however, they don’t describe the results obtained with the help of them everywhere. For example, on pages 23, 24 etc.
Response: We appreciate your comment. We believe Table 1 summarizes the sorption results for all the discussed and referred studies at the given physicochemical/experimental conditions (pH, concentration of targeted radionuclides/ions, and sorbents, temperatures, contact time, and ionic strength). In Table 1, the sorption results have been described as performance (either as ‘removal %’ or ‘sorption capacity’) for the studied radionuclides/ions.
Comment: Figure 2 needs to be improved. It is difficult for readers to read the information in the plot legend.
Response: Thank you for your suggestion. Figure 2 has been improved and updated in the revised manuscript.
Round 2
Reviewer 2 Report
In the first review, my main criticism was that the manuscript did not have a clear thread, as it was structured as a succession of summaries of different papers. Furthermore, although it includes many references, I think that many of them are not very relevant, while others certainly more important have not been included.
The main change that the authors have performed is the inclusion of a Table, which improved the structure a bit, but it does not solve my principal problem. I think that authors should have made a deeper review.
Author Response
We appreciate your kind efforts for providing us additional comments. Based on your kind suggestion, we have incorporated six additional (relevant) references (refs. 127-132), which would help the readers for more updated information in this research field.
The incorporated six references in the revised manuscript are mentioned below.
- Klinkenberg, M.; Brandt, F.; Baeyens, B.; Bosbach, D.; Fernandes, M.M. Adsorption of barium and radium on montmorillonite: A comparative experimental and modelling study. Appl. Geochem. 2021, 135, 105117.
- Stockmann, M.; Fritsch, K.; Bok, F.; Fernandes, M.M.; Baeyens, B.; Steudtner, R.; Müller, K.; Nebelung, C.; Brendler, V.; Stumpf, T.; Schmeide, K. New insights into U (VI) sorption onto montmorillonite from batch sorption and spectroscopic studies at increased ionic strength. Sci. Total Environ. 2022, 806, 150653.
- Glaus, M.A.; Frick, S.; Van Loon, L.R. A coherent approach for cation surface diffusion in clay minerals and cation sorption models: Diffusion of Cs+ and Eu3+ in compacted illite as case examples. Geochim. Cosmochim. Acta 2020, 274, 79-96.
- Fernandes, M.M.; Baeyens, B. Cation exchange and surface complexation of lead on montmorillonite and illite including competitive adsorption effects. Appl. Geochem. 2019, 100, 190-202.
- Fernandes, M.M.; Scheinost, A.C.; Baeyens, B. Sorption of trivalent lanthanides and actinides onto montmorillonite: Macroscopic, thermodynamic and structural evidence for ternary hydroxo and carbonato surface complexes on multiple sorption sites. Water Res. 2016, 99, 74-82.
- Fernandes, M.M.; Baeyens, B.; Dähn, R.; Scheinost, A.C.; Bradbury, M.H. U (VI) sorption on montmorillonite in the absence and presence of carbonate: a macroscopic and microscopic study. Geochim. Cosmochim. Acta 2012, 93, 262-277.
