Application of Biochar for Ion-Adsorption of Rare Earth Contaminated Soil Remediation: A Review
Round 1
Reviewer 1 Report
The study demonstrated in this manuscript contributes the application of biochar as an effective strategy in remediation of contaminated soil. Though this study fit in the scope of this journal. But the manuscript needs the major revisions in terms of English improvement and also some technical errors have been found. There is problem with the headings presented in the manuscript.
1. The abstract information should be revised. Rewrite “Most world mid and heavy rare earth elements products supply from ion adsorption type rare earth elements”. It must be convincing. I don’t see any argument.
2. What is difference between pool leaching and heap leaching and their causes
3. Heading 1.3 “Demand and Usages” should be revised
4. Authors just mention the pH, soil chemical properties should. They must provide the detailed mechanism for biochar and ion adsorption.
5. Though due to the inherent tension in REE demand, manufacturing are causing severe environmental contamination, and overlaid REE are considered as hazards. What about the REE extraction, its cost and eco-toxicity rating
6. Headings 3.2.1, 3.2.2 and 3.2.3 must be revised
7. In heading 3.2.1 correct the reference chen et al. (2018) [90], in heading 3.2.3 correct the reference Liu et al. 2021 [94], Pouret Houben.
8. In manuscript authors need to revise the formulas and section 3.2.2
9. It would be better if authors differentiate the simple and modified biochar, different ways for modification and their potential in light of the previous literature.
10. Clear the objectivity of study at the end of introduction without incorporating unwanted details there.
11. Re-write and correct the captions and note for Figure 1 and 2.
12. Formulas in Table 3 need attention.
13. Manuscript need English improvement: recheck/rewrite the sentence-Because bio-adsorption happens at the surface, adsorbents can be more selective and have a stronger attraction to REE. The adsorption capacity of La by modified biochar (363.32mg/g) was approximately 1.3 times higher than the raw biochar [34]. Figure 2 shows a breakdown of their holdings.
14. Conclusion needs a major revision, precise it. Authors should make the clarity in terms of future study
Author Response
Please see the attachment. Thank you!
Author Response File: 
Author Response.docx
Reviewer 2 Report
The review is within the scope of sustainability and is of interest to readers. Unfortunately I regret to mention that the manuscript has not extensively described biochar properties, strengths and weaknesses in adsorbing heavy metals including REE. Few studies have been included which does not provide sufficient information on biochar adsorptive capacity for REE. In addition the review should highlight a few of the limitations of biochar in adsorbing REE. In the current state, readers are not convinced biochar can significantly reduce REE. Authors need to show the strength and weakness of biochar and focus more its strength before bringing this statement.
Towards the conclusion, authors propose that future studies should focus on i) Precise quantities and directions for biochar application in IAT-Res pollutant remediation, ii) The long-term soil impacts of biochar, iii) Could the modification procedure and leftovers cause secondary pollution?, iv) REE phytoextraction potential utilizing biochar and v) Environmental and human health effects of REE poisoning. I thought the above areas should have been covered by this review to some extent before recommending such for future studies. There are several articles published on bioremediation of heavy metals and REE that authors could use to answer these.
Therefore, the authors should improve on this manuscript to include more information on the above mentioned points before publication. Few comments have been posted directly on the pdf file attached.
Comments for author File: 
Comments.pdf
Author Response
Please see the attachment. Thank you!
Author Response File: Author Response.docx
Reviewer 3 Report
The article as a whole makes a good impression. The material is well structured and has links to the main sections.
If the section of article 3.2.3 REE Contamination Removal is supplemented with information from the manuscripts that considered the effect of biochar on the sorption of heavy metals (Sustainability 2021, 13(24), 14041; https://doi.org/10.3390/su132414041) and information on gradual degradation biochar in the soil, which can lead to secondary pollution (Agronomy 2021, 11(8), 1559; https://doi.org/10.3390/agronomy11081559) the manuscript will be improved.
Author Response
Please see the attachment! Thank you very much!
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
The paper is improved and now can be accepted after minor English revisions.
Author Response
Thank you very much for your comments on the preceding manuscript. have made corrections to the manuscript. Please read the portions marked in red of our revised manuscript.
Reviewer 2 Report
The manuscript has greatly improved. However, I request authors to add the preposition "of" between Ion-adsorption and Rare earth...on the tittle.
Many thanks
Author Response
We appreciate your affirmations and suggestions. We have modified the title and corrected grammatical errors; please read the part marked in red. Thank you very much.
