Effective Removal of Pb2+ from Aqueous Solution Using Magnetic Mesoporous Silica Prepared by Rubidium-Containing Biotite Leaching Residues and Wastewater
Round 1
Reviewer 1 Report
After carefully reading the manuscript entitled “Effective removal of Pb2+ from aqueous solution using magnetic mesoporous silicon prepared by rubidium-containing biotite leaching residues and wastewater” I believe that the manuscript can be considered for publication after addressing the next major revisions:
1) Obtained R2 values for the fitted parameters of adsorption kinetics are too closed, hence it cannot be easily analyzed independently. The Akaike’s information criterion must be used to statistically compare the models and chose the better one that explain the Pb2+ rate adsorption. Please revise and add the next reference for comparison https://doi.org/10.3390/nano10091668
2) Table 4 must be updated, there are another reference in the literature with high Qm value and enhanced equilibrium time of 5 min, see https://doi.org/10.3390/nano10091668, that reference must be added and compared. Please, also update the Table by comparing the equilibrium time, removal efficiency, pH, and initial concentration among all the cited references.
3) In lines 447-454, the Fe2p XPS peaks are commented. In my opinion, the analysis is too simple. Authors affirm that a change from hematite to maghemite occurs from a shifting in the Fe positions. However, this is not correlated with the XRD diffractograms. In lines 374 they said “The XRD patterns of the FO and FO/MS materials only had the diffraction peak of iron oxide.” What iron oxide? Be more specific! Please, add the CIF file referring to the identified iron oxide. Compared in detail the XPS and XRD results. More structural information is necessary, remembering that adsorption is a surface phenomenon, maghemite is on the surface or bulk composition?
4) Please, correct the text (lines 448 and 450), in the before and after treated Pb2+ FO/MS samples, the Fe2p3/2 position is located at 710.0 eV for maghemite, no 709.6 eV. This can be seen in Figure 6. Moreover, add the next reference about iron oxide samples in solid mesoporous matrices [https://doi.org/10.1016/j.apsusc.2016.07.157] to support your findings.
5) In the conclusion section authors mentioned “Pb2+ removal mechanisms included ion exchange, electrostatic adsorption, and surface complexation.” But what is the dominant mechanism? Is there a form to know it from adsorption data and models? It must be mentioned in the conclusion, it is too short regarding all the presented data.
Other comments are given below:
-In line 281, a comma separating Freundlich, Langmuir models is lacking.
-In Figure 5G, the interplanar distance correspond to what Fe2O3 phase, gamma, alpha, beta, epsilon? Please add the CIF or PDF card used for identification in the Figure’s caption.
Author Response
Dear reviewer
We would like to thank the editor and the reviewers for their efforts in evaluating this manuscript. The comments and suggestions are very helpful for us, and we have revised our manuscript accordingly. We also responded point by point to the editor's/reviewer's comments. Please see the attachment. The corresponding revisions were highlighted in different color so that they can be easily identified in the revised manuscript. We are looking forward to the positive feedback from you.
Best regards.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The authors describe a way to use waste generated from a lab scale rubidium leaching process to be used to adsorb lead from aqueous solutions. In my opinion the idea of the manuscript is pretty interesting, although I think it would have been better if they used actual waste materials generated by an industrial process. So far the main information that is missing for me is if this process in any way impedes the rubidium collection, i.e. where is the rubidium at the end of the synthesis and how much rubidium could be still extracted (and will the process have to be different than for regular rubidium production).
Unfortunately the English used in the manuscript is so bad (at times it seems like it is machine translated) that I cannot make sense of a lot of the arguments the authors want to make. I will give them the chance to drastically improve the English by asking a native English speaker to go over it sentence by sentence (hopefully together with one of the authors, to make sure not only to have a good English style but also that the meaning the authors want to convey does not get lost), by suggesting them to make major corrections now. If the English does get better in the next version I will actually review it then, like this it would make no sense to do a real review.
In the meantime I have some comments that the authors can already improve on.
-both in the title and abstract you need to change silicon with silica, as this is what you were actually using; also later on in most of the text silicon is not a great word choice..depending on the context maybe you can replace it with silica, or silicate there
- First sentence of abstract? I think you need to have this manuscript proofread by a native English speaker, as already the first two sentences make no sense (which is due to English I assume)
-FO/MS needs to be defined the first time it occurs in the manuscript, in this case in the abstract
-l 26: ref [1] does not fit the sentence it is attached to. For this and further references, please make sure they actually document what you are describing in that sentence or paragraph. In the case of this sentence it could either be a review or book about rubidium (extraction) that also describes (with references) where rubidium is found naturally, or even better an article that analyses different minerals for their rubidium content. In this reference the respective minerals are not even mentioned. Even if they were mentioned, the subject of the article is something else and it would not have research results proving your claims, only (maybe) further references.
-ref 7 needs to be replaced with something that fits the text
-ref 8 lists the claim you made only in their introduction, accompanied with a reference. Please replace this reference with an actual reference which proves your claim or in this case, probably a review about the subject would be better if you find one
-please replace ref 9; same reason
-l 55 what is PRB?
-l 71 I have read in one of the references that rubidium is usually extracted together with lithium. Did the authors check this biotite sample for lithium too and it wasn’t there, or is it one of the elements that is difficult to detect with XRF?
-l 74: what do you mean with “et al” here?
-l 105: how many grams of non dissolved matter remained after drying?
-l 114 what does refined mean in this context?
-l 108: what was the silicate content in mmol Si/ml?
-l 118: what was the amount of silica obtained? (in g or mg)
-l 125: what was the amount of composite obtained?
-I think the co-precipitation reaction should be called precipitation reaction (in the whole manuscript), since as far as I can see there are only ferric ions that should precipitate in this step
-where is the rubidium afterwards? How much rubidium could be recovered after synthesis of the new sorbent, based on the content in the mineral in the first place?
-l 134: immediately? Like after <10 seconds or something?
-l 229: the second percentage couple does not add up to 100%
-please write in the methods section how the pure FO material was made
-why are there only 4 values for each curve in fig. 2E, when 2C and 2D had more? Why does fig 2f have 3 points when 2g and 2h have 3?
-l 272, I would not say ideal, but good enough I suppose
-since you already made the tables S1 and S2 you should add another column “adsorption” in these tables which should list the amount of adsorbed Pb, probably best in mg/g or mmol/g
-l 351f: this is not shown in Fig 7.
-l 363: please replace ref 36 with a fitting one; ref 36 is also a double citation of ref 4
-l 375: which iron oxide? Fe2O3 has (at least) two modifications, hematite and maghemite
-l 376f: please replace ref 39; normally materials become more crystalline at high temperatures and not more amorphous - I would really like to see a reference that demonstrates this
-l 387: the sentence is wrong, you ust said that it can also come from Si-OH groups; you could say that it is ALSO from crystal water or physisorbed water. Also, you forgot to mention Fe-O-H as possibility for this band
-l 390: if you cite something here, please replace ref 42 with a reference that actually mentions that these are the asymmetric stretching/bending vibrations
-l 395: ref 43 does not prove your sentence, however in this case I think you should rathink your sentence (and probably remove/rewrite it). In my opinion the first groups to react with adsorbed cations would be the hydroxyl groups, which means that this band would weaken (like ref 43 also states). To me it also seems like the two bands mentioned seem to become stronger rather than weaker; please also add a reference that proves that at 800 cm-1 are Si-O-Pb vibrations.
-l 446: ref 22 does not describe the interpretations that you give. Please replace the reference (and probably also change your interpretation a bit. I do not think actual lead oxide would form upon adsorption)
-l 454f: please discuss also where the carbon contributions come from. technically you should only have silica and iron oxide there…
Author Response
Dear reviewer
We would like to thank the editor and the reviewers for their efforts in evaluating this manuscript. The comments and suggestions are very helpful for us, and we have revised our manuscript accordingly. We also responded point by point to the editor's/reviewer's comments. Please see the attachment. The corresponding revisions were highlighted in different color so that they can be easily identified in the revised manuscript. We are looking forward to the positive feedback from you.
Best regards.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Dear authors,
I think the manuscript can be now considered for publication in Water. I have minor amendments that would like you to address before acceptance.
-Please, uniformize the word diffractogram instead of pattern in the XRD section. The term diffractogram is preferable in the community.
-In line 246, indicate if the radiation comes from alpha o beta Cu source.
-Please add the errors bars to all linear fits presented in your study.
-In line 241, the ratio P/P0 is correct, the subscript must be added.
-Please, define the acronym BJH.
Author Response
Dear reviewer
We would like to thank you for your efforts in evaluating this manuscript. The comments and suggestions are very helpful for us, and we have revised our manuscript accordingly. We have also responded point by point to the editor/reviewer’s comments as listed below. The corresponding revisions were highlighted in different color so that they can be easily identified in the revised manuscript. Please see the attachment.
We are looking forward to the positive feedback from you.
Best regards
Zhiguo He
Author Response File: Author Response.pdf
Reviewer 2 Report
please see attached file
Comments for author File: Comments.pdf
Author Response
Dear reviewer
We would like to thank you for your efforts in evaluating this manuscript. The comments and suggestions are very helpful for us, and we have revised our manuscript accordingly. We have also responded point by point to the editor/reviewer’s comments as listed below. The corresponding revisions were highlighted in different color so that they can be easily identified in the revised manuscript. Please see the attachment.
We are looking forward to the positive feedback from you.
Best regards
Zhiguo He
Author Response File: Author Response.pdf
Round 3
Reviewer 2 Report
please see the attached file
Comments for author File: Comments.pdf
Author Response
Please see the attachment
Author Response File: Author Response.pdf
