Surface Charge and Size Evolution of Silica–Iron Colloidal Particles in Simulated Late-Archaean Seawater
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsIn this manuscript, the authors evaluated the evolution of surface charge and Size of silica–iron colloids in the Late-Archean seawater. Through some experiments, the colloidal stability of simulated silica-iron particles was investigated under different chemical conditions. The research is of interest to readers in the field. Nevertheless, several issues should be addressed before the paper can be considered for publication:
1) Introduction. Recent advances in Fe–Si interactions at the colloidal scale are under-represented. Please expand the literature review to include key studies on Fe-silica complexation, heterogeneous nucleation, and interfacial chemistry.
2) 2.1 sample preparation. Explain why Mg²⁺ and Ca²⁺ are omitted from the simulated oxygenated seawater. Given their abundance in Archean oceans and their known influence on colloidal stability, this choice requires justification.
3) 3.1. Surface Charge of Colloidal Particles. The |ζ|>30 mV threshold is derived from DLVO theory for low-ionic-strength systems; discuss its validity in high salinity and possible contributions from non-DLVO forces.
4) Line 163. Distinguish “charge neutralization” from “charge screening” where appropriate to avoid misinterpretation of electrostatic effects.
5) Line207. “instead, inner-sphere Fe2+ silica complexation dominates.” Is there experimental evidence?
6) Figure 5. Clarify how the sample-preparation protocol ensures that observed changes in colloidal stability reflect intrinsic particle interactions rather than artifacts introduced by mixing, dilution, or aging.
7) Figure 6. The figure needs to be clearer. Please check the interpretation of the peak positions, and provide supporting literature for the explanation of the mechanism behind the peak position shifts.
8) Rewrite the conclusion to emphasize the study’s primary contributions without repeating earlier results. Remove all literature citations from this section.
Author Response
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Author Response File: 
Author Response.docx
Reviewer 2 Report
Comments and Suggestions for AuthorsReviewer’s comments on the manuscript: Surface Charge and Size Evolution of Silica–Iron Colloidal Particles in the Simulated Late Archaean Seawater written by Weiming Jiang et al.
The reviewed manuscript addresses a critical knowledge gap by experimentally constraining the zeta potential and particle-size evolution of (i) pure silica, (ii) silica–ferric oxyhydroxide complexes, and (iii) their oxidative derivatives under simulated Archaean seawater chemistries. The manuscript is consistent with the journal scope. This work contains so many factual errors that I strongly advise against rejecting it. Moreover, the manuscript is very carelessly written and contains numerous editorial imperfections. It's a shame that none of the numerous authors of this work took the time to prepare it for review.
- I have some reservations about the nomenclature used.Zeta potential, or electrokinetic potential, is a potential measured in the slipping plane and characterizes the charge of the diffusion layer of an electric double layer. It is most often estimated by measuring electrokinetic mobility, which is converted to zeta potential. This concept is not synonymous with surface charge. Surface charge describes the charge of a compact layer of an electric double layer and is measured by other methods, such as potentiometric titration. The authors should distinguish between these concepts and introduce substantive changes in their work.
- “…silica colloids (SiO2(aq)) exhibit a persistently negative surface charge (ζ ≈ –25 mV) in the simulated seawater (pH 6.5), arising from deprotonated silanol groups (≡Si–O-). Upon the addition of Fe2+, specific adsorption of ferrous ions partially neutralizes this negative charge, lowering the magnitude of ζ to –30 mV.” First, the adsorption of Fe2+ cations on negatively charged silica does not have to be specific at all; it can also be nonspecific, e.g., electrostatic.What evidence is there for specific adsorption? There is no evidence for that in your work. If any adsorption of a cation onto a negatively charged surface occurs and the authors write about charge neutralization, how is it possible that the zeta potential has a more negative value?Where is this neutralization?
- Figure 1 should be reorganized.Instead of three small graphs, the results can be presented in one larger graph.This will improve readability and make it easier to spot differences between the systems.
- What is that strange shape of Fig. 1a ? I mean the first hill around pH=7.
- “The low concentration particles approach their isoelectric point under acidic conditions (pH≤6), resulting in rapid flocculation and the formation of colloidal silica gels”. There is no pHiep point on any of these curves, except for those resulting from incorrectly drawn curves.Furthermore, how does "flocculation" occur in the system if no flocculant (a high molecular weight compound) was added? The authors are using the term flocculation incorrectly.There is definitely no flocculation in the systems studied. This whole part of the discussion (3.1.1) is incorrect.
- “If there lacks stabilizing factors such as Fe2+” If silica is negatively charged and a positive ion is absorbed on its surface, it is definitely not a stabilizing factor, but a destabilizing one.
- All the graphs in this work are of very poor quality.
- Chapter 3.1.2 and 3.1.3: Writing about flocculation due to the addition of a cation is a lack of understanding of the basic processes occurring in colloidal systems such as flocculation, coagulation and aggregation. The same remark applies to the erroneous use of the terms zeta potential and surface charge that I mentioned above.
- What's the point of TEM and AFM studies of dried samples (solids only) if the authors claim to be studying a colloidal system?So where's your continuous phase?It's well known that in solution, the interactions between particles are completely different than those observed after drying.
- Editorial mistakes lines: 6, 40, 56, 63, 70, 71, 130, 155, 166, 168, 169, 231, 227, 343, 345.
Author Response
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Author Response File: Author Response.docx
Reviewer 3 Report
Comments and Suggestions for AuthorsGeneral comments
The contents of paper seem to be interesting since it is discussed the evolution of Si and Fe concentrations in late Archaen seawater by laboratory-based simulated experiments which focused on the surface charge of colloidal materials. Descriptions and structure of manuscript seem to be well written. The reviewer feels that it would be acceptable after modification considering the correction of minor comments.
Minor comments
- Line 101: An anoxic condition noted as DO < 0.01 mg/L seems to be ambiguous for discussing the iron redox state. Is it possible to say in Eh for your system? Otherwise, have you measured the ferrous and ferric ions concentrations in the solutions after the experiments?
- Line 130: Should be corrected using superscript likely cm-1.
- Line 153: The zeta potential lower than 30 mV in the absolute value seems to be limited in these experiments (i.e., a single point around pH 10 for Figure 1(a) as the reviewer’s identification). Should change the descriptions in the text if not correct.
- Line 226: The authors discussed the rationale of oxygen for oxidation from ferric to ferrous irons but not shown the stability field of these ions, likely pH-Eh diagram. Recommend adding the diagram showing your system of Fe-O-H2O.
- Line 238: How do the authors measure the colloidal particle size in the present study? No descriptions in Section 2.2. Should be added. How about the particle size distribution in these cases?
- Line 275: Descriptions of captions for Figure 5 are not enough. Should be added supplements for better understanding to the reader.
- Line 316: Contrary, descriptions of captions for Figure 7 are tedious. Should be shortened without duplicated descriptions.
Author Response
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Author Response File: Author Response.docx
Reviewer 4 Report
Comments and Suggestions for AuthorsGeneral Comment:
The study contains some very interesting results involving silica and iron complexes, some of which are already known in the literature.
However, several issues need to be addressed before the manuscript can be accepted:
Please note the following:
Comment 1: The authors use personal terms like “we” and “our”, which can affect the readability of the manuscript. I recommend switching to the passive tense.
Comment 2: Provide information about the deionized water, such as model, company, etc.
Comment 3: Information is needed regarding all chemicals used in the study, such as company purity, etc.
Comment 4: How did you obtain the values for the Late-Archean sweater values? From the literature? Citation needed!
Comment 5: Provide all information on all equipment used in this study, such as company, model no, country, etc.
Comment 6: What was the particle size in the zeta potential measurements?
Comment 7: Needs more information about the zeta potential measurements?
Comment 8: So, what was the experimental error plus or minus?
Comment 9: The results in Figure 1 show that there is no significant change in the charge of SiO2 depending on silica concentration.
Comment 10: As seen in Fig. 1, the zpc of quartz is approximately 1.8, which is consistent with the literature.
Comment 11: Small fluctuations may be due to experimental error.
Comment 12: In all cases, the trend is the same! These results are already known in the literature.
Comment 13: Figure 2: How did the increase in concentration affect the zeta potential of particles?
Comment 14: Figures 4b and c: What does “k” represent?
Comment 15: Finally, the authors should discuss their results with the literature. As readers, we want to compare the similarities and differences in this study with the data in the literature.
I am confident these results will be useful to many researchers in this field.
This manuscript can be accepted for publication in the journal “Minerals and after some corrections.
Comments for author File: 
Comments.pdf
Author Response
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Reviewer 5 Report
Comments and Suggestions for AuthorsThe authors report a systematic study of the influence of Fe2+ and oxygen on the stability of colloidal SiO2 suspensions as a basis for explaining geological processe occurred in see water in the Archean age. The zeta potential was used as an stabilization parameter. The investigations are well structured and targeted. Conclusions are reasonable. However, the manuscript requires a revision to improve its quality before it can be published. Suggestions and questions are provided in the attached commented pdf-version. Special attention should be payed, for instance in the use of some English words and in the construction of some sentences, the meaning of which is difficult to understand.
Comments for author File: Comments.pdf
Author Response
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Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThe authors have satisfactorily responded to my questions and comments.
Author Response
Comment：The authors have satisfactorily responded to my questions and comments.
Response: Thank you very much for your positive comment.
Reviewer 2 Report
Comments and Suggestions for AuthorsThe authors have revised the work, largely in accordance with my recommendations. The work is clearly improved and contains no major factual errors. Unfortunately, even in their responses to my questions, I can see that the authors don't fully understand the topic, and I don't think this work will be valuable to specialists in the field, as the discussion presented may no longer contain glaring errors, but it still isn't convincing for a specialist. The added sections still require editing. I leave that decision to the editor.
Author Response
Comment：The authors have revised the work, largely in accordance with my recommendations. The work is clearly improved and contains no major factual errors. Unfortunately, even in their responses to my questions, I can see that the authors don't fully understand the topic, and I don't think this work will be valuable to specialists in the field, as the discussion presented may no longer contain glaring errors, but it still isn't convincing for a specialist. The added sections still require editing. I leave that decision to the editor.
Response：We sincerely thank you for taking the time and great efforts to review our manuscript and for offering valuable suggestions for the article. Your comments enabled us to correct previous misapplications of colloid chemistry. Our study focuses not on colloidal mechanisms per se, but on using the measured colloidal properties to constrain the physicochemical characteristics of Archean seawater. We therefore believe the manuscript offers a meaningful contribution to understanding the physical chemistry of early oceans.
Reviewer 5 Report
Comments and Suggestions for AuthorsI thanks the Authors for the undertaken amendments. I have just only one request: consider to change the word "employ" in for instance in page 1 line 20, for a more suitable one as "use" or "apply".
