Enhanced Single and Simultaneous As(III) Adsorption in Pearl River Delta Water by Hexylamine Functionalized Vermiculite

Round 1

Reviewer 1 Report

The statement „As(III) is not the only metalloid present in river water, but it coexists with other metal ions in most cases….” its understandable in itself. Of course that As(III) is not the only metalloid present in natural waters…..

Introduction

Lines: 42 to 38. The authors state that As(III) is highly carcinogenic and toxic heavy metals. But later they refer to the arsenic sources in environment while the method deals with the arsenite removal. Why the authors don’t refer more elaborate the to the arsenite concentrations in natural waters and arsenite sources in the environment.

Lines: 55-62. Authors refer to the Pb and Cd toxicity but in the introduction Pb and Cd were mentioned as coexisting metalloids in water. So why the authors are testing As(IIII)/Pb/Cd system, is it because Pb and Cd are “only metalloids present in natural waters interfering with the adsorption” or because their toxicity also.

Lines: 63 to 66. It is not clear what the authors mean with the electrochemical. Is it electrochemical membrane separation, some kind of electrochemical deposition or something else?

Lines: 81 to 85. The sentence “Adsorbent-pollutant interactions can be improved by the basic chemical functions in materials like -OH and amine groups, correspondingly, enhanced adsorption results of amine-enriched materials towards toxic metals in water have been reported in previous studies (Aguado et al., 2009; Ahmed et al., 2020; Fotsing et al., 2021; Vieillard et al., 2019; Zhang et al., 2007)” its not clear. For example: the basic chemical functions, are those functions (or better to say functional groups) introduced somehow or they are already present. Also whole sentence should be rewritten.

Line: 87. Here and later: In the chemical formulas the subscripts are missing.

Lines: 87-89. The sentence should be rewritten (English improvement is needed here and also later).

Section 2.2.

It is not clear why removal of Cl- and its replacement with NO3- (Eq. 2) is needed. Is that some kind of usual procedure needed to activate the adsorbent? Please elaborate more. Also, how the modification of VER with the hexylamine was achieved. Why there are Mg2+ are initially there at the VER surface? Please also elaborate more.

Lines 149-151. “Methodology of potentiometric titration experiment, point of zero charge (pzc), and surface charge density are presented in (supplementary data, Experimental section).” What in fact is determined here, is it point of zero charge and surface charge density determined/calculated. If so then write it.

Lines: 153-155. Again, rewrite sentence. For example in following part of the sentence: “….and simultaneous experiments were performed with Pb(II):Cd(II):As(III) ratio (10:5:3) concentration, respectively….” Its not clear were these ratios present in the solution or…. Again, here and elsewhere the English writing should be improved.

Lines: “Influence of pH on 156 metal ions adsorption was performed in the 2~10 pH range, and the adsorbent used was 157 1 g‧L-1 (i.e., 0.02 g).” Again, here and elsewhere do the authors mean on the amount of adsorbed used.

Line: 158. “Solution pH was adjusted by pH meter with 0.1 M NaOH and HCl.” How the pH can be adjusted by the pH meter? The text if full of sentences like this and I will not refer further on them.

Results and discussion

Section 3.1.2. should be rewritten/improved. For example, lines 244-248 one cannot understand what authors wanted to say.

Section 3.2.1.

Line 313. As(III)mmol.g-1 : (HEX-VER, 6.84 x 10-5) > (VER, 4.72 x 10-5). On what this sentence or part of it does stand for. Is it connected with the following sentence (lines: 314-315)?

Equations 4,5,6 and 7. Are they written correctly? For example the As(III) species H3As3- does not exist as well as As3-. Also what with the charges of the adsorbent. In Lee et al, 2015 charge of the adsorbent while –OH present is zero and not negative. The negative charge of the adsorbent is present at highly alkaline pH and then the surface is completely deprotonated. In any case I think authors should check the equations.

Author Response

To save the editor and the reviewers time to quickly read what we have done for the revision, in this response letter, the texts for “Author reply” are marked in blue fonts. The revisions to the manuscript have been marked by using Track changes function in MS word so that changes can be easily viewed by the editor and reviewers in the revised manuscript.

Please find the file MS word file author-coverletter-13386819.v1.docx attached here.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors in attachment.

Comments for author File: Comments.pdf

Author Response

To save the Editor and the reviewers time to quickly read what we have done for the revision, in this response letter, the texts for “Author reply” are marked in red fonts. The revisions to the manuscript have been marked by using Track changes function in MS word so that changes can be easily viewed by the editor and reviewers in the revised manuscript.

Response to the comments of anonymous reviewer #2

The subject of this paper is suitable for publication profile of Water.

The article concerns a very important and current subject of As(III) removal and reveals the application potential of HEX-VER adsorbent for individual and simultaneous removal of As(III) from river water. This is a big problem in many countries, therefore the article will surely find many readers. The paper is well written, the text is clear and easy to read by the reader. Overall, the paper was written in fluency and clear organization. The conclusions presented by the authors are consistent with the evidence and arguments, the authors have shown that enhanced As(III) removal (>99.7) was achieved by a novel organoclay (HEX-VER) adsorbent in Pearl River Delta water. Analysis confirmed that adsorption was monomolecular layer, well-described by the Langmuir isotherm model. The dominant mechanisms for As(III) removal were ion-exchange and complexation. HEX-VER was regenerated for 5 consecutive cycles, and the removal ratio was found ≈92%, showing its great regeneration potential. These findings suggest that the proposed inexpensive adsorbent has the potential for practical applications of As(III) removal from river water.

• Question #1:  The chemical formulas throughout the manuscript lack subscripts and superscripts.
  Answer: Thank you for pointing out, the manuscript has been read thoroughly and subscripts/ superindexes have been corrected in revised manuscript.

• Question #2: I propose the adoption of the manuscript with minor revision.
• Answer: Thank you for your valuable time and precious comments for improving the quality of this manuscript.

Reviewer 3 Report

The manuscript provided by the authors; 'Enhanced single and simultaneous As(III) adsorption in Pearl River Delta water by hexylamine functionalized vermiculite' presents the chemical modification of a natural adsorbent to improve its metal removal capacity.

I recommend the publication of this manuscript after taking into account these suggestions or corrections.

• Please use the correct format for subscripts and superindexes in the chemical formulas throughout the manuscript.
•  In the introduction section (lines 67 to 70), the authors labelled as 'Recently' cites from 23, 25, 24, 28, 18, 15 and 4 years ago. Please actualise the bibliography and focus it in those related to the use of clay minerals (sepiolites, montmorillonites, perovskites, zeolites...).
• The authors have presented qualitative results of the chemical modification of the vermiculite. However, no quantitative experiments or data are supplied to check the efficiency of the process. Determination of the Mg²⁺ concentration after the process by using Ionic Chromatography and the Gravimetric determination of the AgCl formed would be usefull.
• Why the authors use the ratio 10:5:3 for Pb(II):Cd(II):As(III)?

Author Response

To save the Editor and the reviewers time to quickly read what we have done for the revision, in this response letter, the texts for “Author reply” are marked in red fonts. The revisions to the manuscript have been marked by using Track changes function in MS word so that changes can be easily viewed by the editor and reviewers in the revised manuscript.

The manuscript provided by the authors; 'Enhanced single and simultaneous As(III) adsorption in Pearl River Delta water by hexylamine functionalized vermiculite' presents the chemical modification of a natural adsorbent to improve its metal removal capacity.

I recommend the publication of this manuscript after taking into account these suggestions or corrections.

Thank you for your valuable time and precious comments for improving the quality of our manuscript. We have revised the manuscript based on your comments.

• Question #1: Please use the correct format for subscripts and superindexes in the chemical formulas throughout the manuscript.
• Answer: Thank you for pointing out, we have gone through whole manuscript multiple times, and subscripts/ superindexes throughout the manuscript have been corrected in revised manuscript.
• Question #2: In the introduction section (lines 67 to 70), the authors labelled as 'Recently' cites from 23, 25, 24, 28, 18, 15 and 4 years ago. Please actualise the bibliography and focus it in those related to the use of clay minerals (sepiolites, montmorillonites, perovskites, zeolites...).
• Answer: Thankyou for your valuable suggestion, the older references have been removed and revised manuscript has been enriched with the latest studies of clay minerals as per the reviewer’s suggestion.
• Question #3: The authors have presented qualitative results of the chemical modification of the vermiculite. However, no quantitative experiments or data are supplied to check the efficiency of the process. Determination of the Mg²⁺ concentration after the process by using Ionic Chromatography and the Gravimetric determination of the AgCl formed would be useful.
• Answer: Thankyou for your question. Most of the results presented and discussed in this study about adsorption efficiency at various factors (pH, dose, isotherm, kinetic, thermodynamic etc) are quantitative data and well explained by references.
• The Mg²⁺ concentration was determined before and after the process as shown in Table S1, Fig.S4 (c and f) and S.5, in the supplementary data file, while effect of Mg²⁺ ions on adsorption process is explained in section 3.4.
• AgNO₃ was used just to remove the chlorides from adsorbent material and after reaction all the chlorides reacted with Ag and formed AgCl which was skimmed from surface and except this AgCl has no role to play. Therefore, there was no such need to determine the AgCl.

• Question #3: Why the authors use the ratio 10:5:3 for Pb(II):Cd(II):As(III)?
• Answer: Thankyou for your question, The ratio of 10:5:3 for Pb(II):Cd(II):As(III) was selected for adsorption isotherm experiments on the basis of Atomic mass of these metals. Same trend has been followed in previous studies. For example, A study conducted by Qi Liao et al on Simultaneous adsorption of As(III), Cd(II) and Pb(II) by hybrid bio-nanocomposites of nano hydroxy ferric phosphate and hydroxy ferric sulfate particles, in which he used 30–300 mg/L of As(III), and 100–1000 mg/L of Pb(II), which is 3:10 ratio for As(III):Pb(II)(Liao et al., 2019). Similarly, there are other more adsorption studies where Pb(II) to Cd(II) ratio used was almost double (Ahmed et al., 2020; Chen et al., 2018; Zhang, Wang, Zhang, Liu, & Xing, 2021).

References

Ahmed, Z., Wu, P., Jiang, L., Liu, J., Ye, Q., Yang, Q., & Zhu, N. (2020). Enhanced simultaneous adsorption of Cd(II) and Pb(II) on octylamine functionalized vermiculite. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 604, 125285. doi:https://doi.org/10.1016/j.colsurfa.2020.125285

Chen, L., Wu, P., Chen, M., Lai, X., Ahmed, Z., Zhu, N., . . . Liu, T. (2018). Preparation and characterization of the eco-friendly chitosan/vermiculite biocomposite with excellent removal capacity for cadmium and lead. Applied Clay Science, 159, 74-82. doi:https://doi.org/10.1016/j.clay.2017.12.050

Liao, Q., Tu, G., Yang, Z., Wang, H., He, L., Tang, J., & Yang, W. (2019). Simultaneous adsorption of As(III), Cd(II) and Pb(II) by hybrid bio-nanocomposites of nano hydroxy ferric phosphate and hydroxy ferric sulfate particles coating on Aspergillus niger. Chemosphere, 223, 551-559. doi:https://doi.org/10.1016/j.chemosphere.2019.02.070

Zhang, Z., Wang, T., Zhang, H., Liu, Y., & Xing, B. (2021). Adsorption of Pb(II) and Cd(II) by magnetic activated carbon and its mechanism. Science of The Total Environment, 757, 143910. doi:https://doi.org/10.1016/j.scitotenv.2020.143910

Round 2

Reviewer 1 Report

Dear Editor Dear Authors
I really dont know maybe really my attempt to improve the manuscript was not good enough.
For example the sentence - The statement “As(III) is not the only metalloid present in river water, but it coexists with other metal ions in most cases….” its understandable in itself. Of course that As(III) is not the only metalloid present in natural waters…..- but of course that As(III) is not the only metalloid present in waters, I meant that one should expel it since it brings nothing to the manuscript.

They describe after the As(III), but why that is not in the text now (in the introduction somewhere) especially having in mind (I think) oxic conditions in investigated river waters.

The equations: I am sorry, maybe I am really not knowledgeable, but first they give As(V) speciation graph in answers. Of course that As(III) is very similar but if one would look the As(III) speciation graph depending on pH, one will nowhere find H3As3- and As33-. One will find H2AsO3- and AsO33-.  I don’t know am I really having an mistake here (I think I am not). I dont know maybe there are some new literature data considering arsenite speciation, but sorry, where are the oxygen atoms there.
If editor thinks that the manuscript is good quality then publish it. I disagree since I think that there are some elemental mistakes. The quality of writing is not so much improved at least from my point of view.

Author Response

To save the Editor and the reviewers time to quickly read what we have done for the revision, in this response letter, the texts for “Author reply” are marked in blue fonts. The revisions to the manuscript have been marked by using Track changes function in MS word so that changes can be easily viewed by the editor and reviewers in the revised manuscript.

Author Response File: Author Response.docx

Reviewer 3 Report

I recommend the publication of the manuscript since the authors have considered and explained all the comments and changes suggested by the reviewer.

Author Response

Thank you very much for your valuable time and precious comments to improve the quality of our manuscript.