Effect of Nitric Acid Modification on Characteristics and Adsorption Properties of Lignite
Round 1
Reviewer 1 Report
the use of modified lignite as a sorbent is a interesting topic. in this case, the title, the objective and the conclusions are not coordinated.
the english language should be improved
from the results and the conclusions the most important part is lead sorption however this is not mentioned either in the title or the objectives.
the results organisation does not allow to establish a relationship between lignite modification and pb sorption, i recommend to switch the pb sorption to the end similar as it is in the methods.
the analytical methods are relevant.
the conclusions hshould be modified
Author Response
Response to Reviewer 1 Comments
Point 1: 
the use of modified lignite as a sorbent is a interesting topic. in this case, the title, the objective and the conclusions are not coordinated.
Response 1: The objective of this research was to explore the changes of the pore structure and surface properties of nitric modified lignite and based the adsorption performance on physical and chemical adsorbent characteristics. In the paper, we investigated the physics and surface chemical structure of lignite samples under different modification conditions, and explored Pb2+adsorption properties on different lignite samples, to established a link between the physicochemical structure and adsorption properties of the adsorbent. In the revised manuscript, some adjustments were made to the content and conclusions of the article.
Point 2: the english language should be improved
Response 2: The English expression of the article has been improved, and the errors have been corrected.
Point 3: from the results and the conclusions the most important part is lead sorption however this is not mentioned either in the title or the objectives.
Response 3: In section 3.9 of the paper, we explored the lead ions adsorption amount of lignite obtained under different nitric acid concentration modified conditions to establish the relationship between the physicochemical structure and the adsorption capacity of the adsorbent. We also found that adsorption properties of adsorbents with different physicochemical properties are different.
Point 4: the results organisation does not allow to establish a relationship between lignite modification and pb sorption, i recommend to switch the pb sorption to the end similar as it is in the methods.
Response 4: The adsorption of Pb2+ on the surface of lignite is the result of both the pore structure and the surface chemistry of adsorbent. At the beginning, the adsorption amount of Pb2+ decreases with the decrease of the lignite specific surface area. Next, the adsorption amount of Pb2+ is not continuely reduced while greatly increased due to the increase of oxygen-containing functional groups on the surface of lignite. The adsorption model of Pb2+, the types and quantity of functional groups play a key role in the adsorption of Pb2+ by lignite.Between the adsorption capacity of Pb2+ and the number of oxygen-containing functional groups of lignite in the corresponding relationship. In the revised manuscript, the structure of the article was adjusted, switch the Pb2+ sorption to the end similar as it is in the methods.
Point 5: the conclusions should be modified
Response 5: The conclusions of the article have been modified in the revised manuscript
Author Response File: 
Author Response.docx
Reviewer 2 Report
In the manuscript entitled "Effect of nitric acid modification on characteristics and adsorption properties of lignite" Bo Huang and collaborators described the process of exposure of lignite to increasing concentrations of nitric acid as an original approach for adsorbing the heavy metal Pb2+.
The methodological approach ot the conceived work is correct and the results interesting and significant. The discussion is based on the resulting data and the literature is quite complete and up to date.
Overall, the authors are able to demonstrate that the treatment of lignite with increasing concentrations of nitric acid increase the amount of Pb2+ from 14.45 mg·g-1 to 30.68 mg·g-1; this is a very important result.
The only main concern I have is about the selectivity of lignite; do the authors have in mind to test the adsorbtion against other cations like Ca2+, Fe2+ or similar or against other heavy metals like cadmium or mercury? Do other cations interfere with Pb2+ adsorbtion?
Author Response
Point 1: In the manuscript entitled "Effect of nitric acid modification on characteristics and adsorption properties of lignite" Bo Huang and collaborators described the process of exposure of lignite to increasing concentrations of nitric acid as an original approach for adsorbing the heavy metal Pb2+.
The methodological approach of the conceived work is correct and the results interesting and significant. The discussion is based on the resulting data and the literature is quite complete and up to date.
Overall, the authors are able to demonstrate that the treatment of lignite with increasing concentrations of nitric acid increase the amount of Pb2+ from 14.45 mg·g-1 to 30.68 mg·g-1; this is a very important result.
The only main concern I have is about the selectivity of lignite; do the authors have in mind to test the adsorbtion against other cations like Ca2+, Fe2+ or similar or against other heavy metals like cadmium or mercury? Do other cations interfere with Pb2+ adsorbtion?
Response 1: In this experiment, we used modified lignite as adsorbent to adsorb heavy lead ions, and achieved good results. It proved that modified lignite has good potential for adsorb metal ions as an inexpensive adsorbent. We also intend to apply lignite to other contaminant metal ions, such as chromium, mercury, etc.. And there will be competitive adsorption between different ions due to different chargeability, hydration, ionic radius, etc.. This work will be further studied in the future research.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
the article improved however some english improvements are necessary.
Author Response
Point 1: the article improved however some english improvements are necessary.
Response 1: The authors have carefully read the article and modified the inappropriate expressions and words in the article and some grammatical errors have been corrected.
Author Response File: Author Response.docx
