Understanding Zinc Transport in Estuarine Environments: Insights from Sediment Composition

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The study analyses the transport of Zn²⁺ in an estuarine environment, namely the confluence of the 8 rivers and the Dianchi Lake, based on the test performed on surface sediments (10 cm in depth). The idea is interesting and the results on adsorption of Zn by organic-inorganic, organic-clay, and iron oxide-clay natural composites are presented based on Langmuir and Freundlich isotherms. Furthermore, FTIR and XRD results are presented to study the adsorption mechanisms. However, this paper needs a lot of clarifications to present results and discussion, to highlight the novelty, and also additional tests are needed.

 

-          The study in the title claims it analyses the transport of heavy metals in an estuarine environment, although only Zn²⁺ adsorption is tested. Please clarify and change the title to reflect the exact study. The importance of this heavy metal for the environment should be better emphasized.

-          The title also contains the phrase “Insights from Sediment Composition”, although the chemical composition and granulometry of the sediments are not tested. Please improve the title, and expand the tests.

-          The abstract section (and also the materials and methods section) must describe the exact natural composites that acted in an adsorption process and in which way was their division conducted, and thus the mentioned phenolic hydroxyl group would be clear where it comes from.

-          The introduction section should be widened and the short literature review conducted and thus the novelty highlighted. Also, explain the importance of Zn.

-          Sediments underwater as well as on the ground contain often mostly of quartz and also may contain significant proportions of CaO. Please, check more literature and also refer to https://doi.org/10.1007/s11356-021-14382-8. Also, perform a chemical analysis. What was the concentration of Zn in the samples?

-          At what time of year were the samples taken? How fast are the rivers- are there any industrial activities near them? It all affects the results.

-          Please improve and finish the sentence „Removal of organic matter, free iron oxide and free aluminum oxide from sediments, respectively.“

-          The rivers should be seen in the map in Fig. 1.

-          Part 3.4 should be merged with the part that contains semi-quantitative determination of minerals by using FTIR analysis. FTIR graphs from Fig. 3 should have enlarged text. In which way was the semi-quantitative calculation done?

-          XRD graphs are not clear, they should contain the minerals highlighted at every peak.

-          Section 2.2. should be written in the past tense, and not as a textnote recipe.

 

-          Technical notes:

-          Please change „human production“ to „industrial production“ or similar.

-          Please do not use personal pronouns like „we investigated...“ but use a passive voice instead.

-          References are not to be in superscript, please consult instructions for authors.

Comments on the Quality of English Language

English mainly seems file, although some changes are needed.

Author Response

1. 1. The study in the title claims it analyses the transport of heavy metals in an estuarine environment, although only Zn²⁺adsorption is tested. Please clarify and change the title to reflect the exact study. The importance of this heavy metal for the environment should be better emphasized.

Response: Thank you for your suggestion We have changed the title " Understanding Heavy Metal Transport in Estuarine Environments: Insights from Sediment Composition" to "Understanding zinc Transport in Estuarine Environ-ments: Insights from Sediment Composition "This more accurately reflects the transport of the heavy metal zinc in estuarine environments and its impact on the environment.

 

2.  The title also contains the phrase “Insights from Sediment Composition”, although the chemical composition and granulometry of the sediments are not tested. Please improve the title, and expand the tests.

Response: Thank you very much for your suggestion. We have tested the chemical composition of the sediments and analysed the organic matter using FTIR, as well as the inorganic components of the clay minerals, such as iron oxides, using XRD. Particle size testing is primarily an analysis of the inorganic minerals, and the focus of the article is on the organic matter component, and we believe that the results of the tests so far are sufficient to support the conclusions of the article.

In the meantime, we have revised the title of the article to read: " Understanding zinc Transport in Estuarine Environ-ments: Insights from Sediment Composition " This more accurately reflects the transport of the heavy metal zinc in estuarine environments and its impact on the environment.

 

3. The abstract section (and also the materials and methods section) must describe the exact natural composites that acted in an adsorption process and in which way was their division conducted, and thus the mentioned phenolic hydroxyl group would be clear where it comes from.

Response: Thank you very much for your suggestion. We are not aware of the specific natural composites that are involved. The current test conditions only allow us to identify the groups that play a role in the prepared composites. The complexity of the composition of natural composites, the co-existence of various molecular groups, the complexity of the organic matter itself, the complexity and low content of natural composites, and the co-existence of many other chemical components is a complex and wide-ranging research topic that needs to be explored in depth by the entire field of organic chemistry.

 

4. The introduction section should be widened and the short literature review conducted and thus the novelty highlighted. Also, explain the importance of Zn.

Response: Thanks to your suggestions, we have amended and expanded the introduction, with revisions in line 45-49, 61-64, 71-77, and 82-84 to better emphasize the novelty of this paper. In addition, the importance of zinc was added in line 49-52 as follows: "When heavy metal-rich sediments are disturbed, the zinc in them may be re-released into the overlying water body, and under certain conditions, zinc transport may have a potentially polluting effect on the water body, which is also one of the major pollutants in the water body."

 

5. Sediments underwater as well as on the ground contain often mostly of quartz and also may contain significant proportions of CaO. Please, check more literature and also refer to https://doi.org/10.1007/s11356-021-14382-8. Also, perform a chemical analysis. What was the concentration of Zn in the samples?

Response: Thank you for your suggestion, we carried out a pre-test to determine the zinc concentration in the samples by ICP-OES before the experiment, and the pre-test results showed that the zinc concentration in the measured samples was very low, and we can assume that the samples do not contain zinc.

 

6. At what time of year were the samples taken? How fast are the rivers- are there any industrial activities near them? It all affects the results.

Response:Thank you for your question. The sediment samples used in the experiment were collected in the spring of 2020; the flow rate of the river was 0.8 m/s. According to the distribution of sampling points in Figure 1, it can be seen that the surrounding area of Dianchi Lake belongs to the urban area, and the main source of pollution comes from human production and living activities. Dianchi has undergone long-term large-scale treatment, and there is no industrial pollution in the vicinity, so industry is not a potential source of pollution for it.

 

 

7. Please improve and finish the sentence „Removal of organic matter, free iron oxide and free aluminum oxide from sediments, respectively.“

Response: Thank you for your suggestion, based on your suggestion we have improved this sentence as follows, "Remove, respectively, the removable organic fraction, the free iron oxide fraction and the free aluminium oxide fraction from the sediment complex."

 

8. Part 3.4 should be merged with the part that contains semi-quantitative determination of minerals by using FTIR analysis. FTIR graphs from Fig. 3 should have enlarged text. In which way was the semi-quantitative calculation done?

Response: Thank you very much for your suggestion, we have resized and merged the FTIR plots in Figure 3.  Semi-quantitative calculation is a method of approximate quantification of compounds by measuring the absorption peak areas of different molecules used in the chromatograms, while the peak areas are calculated from the width and height of the peaks, and the content of the substance to be measured can be estimated by comparing the peak areas with those of the standards, the peak area semi-quantitative method can quickly estimate the content of certain compounds in the sample, and it cannot provide an absolutely accurate value of the concentration content.

 

9 . The rivers should be seen in the map in Fig. 1.

Response: Thank you very much for your suggestion. According to the distribution of sampling points in Figure 1, it can be seen that the area around Dianchi belongs to the urban area, and the main source of pollution comes from human production and living activities. Dianchi has been treated for a long time and on a large scale, and there is no industrial pollution in the vicinity, so industry is not a potential source of pollution. Moreover, the specific locations of the sampling points have already been indicated in Figure 1, so we do not think there is a need to change Figure 1.

 

10. XRD graphs are not clear, they should contain the minerals highlighted at every peak.

  Section 2.2. should be written in the past tense, and not as a textnote recipe.

Response: Thank you for your suggestions about the errors in the article, we have enlarged the XRD plots, and in addition, we have modified Section 2.2, Content Morphology. The changes are as follows:

(1) Without special treatment - Group A: (1) A certain amount of natural sediment complex samples were placed in a beaker, ultrasonically dispersed with the addition of pure water, artificially removed biomass and residues, and freeze-dried to make a product.

(2) Organic matter removal treatment - Group B: Group A samples were freeze-dried by adding H₂O₂ solution (30%) and heating in a 90°C water bath. This is the precipitate after removal of the active part of the organic matter.

(3) Removal of iron and alumina - Group C: The samples in group A were added with sodium citrate solution (1 mol/L) and NaHCO₃ solution (1 mol/L), heated to 80°C by hydrothermal heating, then added with Na₂S₂O₄ and washed repeatedly with saturated NaCl solution and purified water, and freeze-dried.

 

11. Technical notes:

-          Please change „human production“ to „industrial production“ or similar.

-          Please do not use personal pronouns like „we investigated...“ but use a passive voice instead.

-          References are not to be in superscript, please consult instructions for authors.

Response: Thanks to your suggestion, we have read the whole text again and adjusted the presentation of the introductory part of the text, section 2.1, section 2.2 and section 2.4.

In addition, the way of labeling references has been adjusted.

The details are as follows:

Section 2.1: In this experiment, eight rivers entering the lake on the east and south shores of Dianchi Lake in Kunming City, Yunnan Province, were selected for the study: Chai River (CH), Dong-Da River (DDH), Gong-Si River (GSG), Guang-Pu (GPG), Lao-Yu River (LYH), Lao-Bao River (LBH), Xin River (XH), and Yu-Ni River (YNH) were the subjects of the study. Sediment was collected from the top 10 cm of the river bottom using a peat auger at a fixed depth, and each sampling site was located in an estuarine section of the river, where the river flow was slow and the water depth was greater than 0.5 m, so that various types of materials could be more easily deposited and immobilized in the sediments.

Section 2.2: (1) Without special treatment - Group A: (1) A certain amount of natural sediment complex samples were placed in a beaker, ultrasonically dispersed with the addition of pure water, artificially removed biomass and residues, and freeze-dried to make a product..

(2) Organic matter removal treatment - Group B: Group A samples were freeze-dried by adding H₂O₂ solution (30%) and heating in a 90°C water bath. This is the precipitate after removal of the active part of the organic matter.

(3) Iron and aluminium oxide removal treatment - Group C: The samples in group A were added with sodium citrate solution (1 mol/L) and NaHCO₃ solution (1 mol/L), heated to 80°C by hydrothermal heating, then added with Na₂S₂O₄ and washed repeatedly with saturated NaCl solution and purified water, and freeze-dried.

Section 2.4: 0.2g of sample was weighed into a test tube and 20 mL of 0.01 mol/L NaNO₃ solution was added to avoid precipitation, followed by 10 mL of 2 mg/L, 5 mg/L, 10 mg/L, 30 mg/L, 75 mg/L, 150 mg/L zinc standard solutions. The pH was adjusted to 6 with NaOH and HNO₃ solutions and shaken at 300 RPM/min. After 24 h, the supernatant was filtered through a 0.45 μm membrane and the zinc concentration was determined by ICP-OES. 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The reviewed manuscript (Understanding Heavy Metal Transport in Estuarine Environments: Insights from Sediment Composition) can be regarded as a valuable contribution. Zn adsorption by different composites was investigated in eight estuarine sediment samples from Dianchi Lake, China. Zn adsorption behavior was studied using Langmuir and Freundlich isothermal models. The samples were analyzed using FTIR and XRD analyses before and after the adsorption experiment. Please consider the following comments to improve the manuscript:

1. Title: I suggest replacing "Heavy Metals" with "Zinc" to make the title more consistent with the content.

2. Line 56; quartz is not a clay mineral.

3. Line 67; “but relatively few studies have revealed the interactions between its components” Please give a summary of the most important examples from these studies.

4. Line 83; Please remove [22].

5. Figure 1; Please add a base map showing the exact location of Dianchi Lake in China.

6. Sections 2.2.-2.4; Please support the used methods and equations with literature.

7. Section 2.5.3; Why the authors didn’t perform XRD using oriented samples to identify the types of clay minerals?

8. Section 3: Please present your results without discussion and move any relevant information to the discussion section.

9. Figure 4; Please provide a legend for the identified peaks.

10.  Lines 279:284; Please revise.

11.  Line 364; “soil”??

 

12.  Conclusion; The conclusion should be supported by more results.

Author Response

1. Title:I suggest replacing "Heavy Metals" with "Zinc" to make the title more consistent with the content.

Response: Thank you for your suggestion We have changed the title " Understanding Heavy Metal Transport in Estuarine Environments: Insights from Sediment Composition" to "Understanding zinc Transport in Estuarine Environ-ments: Insights from Sediment Composition "This more accurately reflects the transport of the heavy metal zinc in estuarine environments and its impact on the environment.

 

2. Line 56;quartz is not a clay mineral.

Response: Thank you for pointing out the error in my writing, we've corrected it and removed "quartz" from the text.

 

3. Line 67;“but relatively few studies have revealed the interactions between its components” Please give a summary of the most important examples from these studies.

Response: Thank you for your suggestion. We have provided a detailed description of the content before and after line 67, which reads line 71-77: "Previous studies have thoroughly investigated the adsorption of pollutants by a single component in sediments, but there are fewer studies on the adsorption of heavy metals by composite components relative to the interactions between a single component for a specific pollutant. This requires an in-depth analysis of the adsorption behavior of pollutants in each component of the sediment, the use of nonlinear fitting models to obtain the thermodynamic parameters of the adsorption process, and the visualization of the fitting effect to determine the trend of adsorption of pollutants".

 

4. Line 83;Please remove [22].

Response: Thank you for your suggestion, which we have removed [22].

 

5. Figure 1;Please add a base map showing the exact location of Dianchi Lake in China.

Response: Thank you very much for your suggestion. We believe that there is no need to make further modifications or additions to Figure 1 because it already clearly shows the exact location of Dianchi and its relationship with production and life in the surrounding area, as well as indicating the location of the sampling points. According to the distribution of sampling points in Figure 1, it can be seen that the surrounding area of Dianchi belongs to the urban area and the main source of pollution comes from human production and living activities. Dianchi has undergone long-term large-scale treatment, and there is no industrial pollution in the vicinity, so industry is not a potential source of pollution for it. In addition, considering the special characteristics of Yunnan as a border area, we realize that the citation of the map involves some serious political issues.

 

6. Sections 2.2.-2.4;Please support the used methods and equations with literature.

Response: Thanks to your suggestion, we have cited literature in sections 2.2.-2.4 that supports the methods and equations used. The specific cited literature is entitled "The adsorption characteristics of Cu (II) and Zn (II) on the sediments at the mouth of a typical urban polluted river in Dianchi Lake: taking Xinhe as an example."

 

7. Section 2.5.3;Why the authors didn’t perform XRD using oriented samples to identify the types of clay minerals?

Response: Thank you for your question, we would like to answer your question as follows: Due to the limitation of the experimental equipment, we were unable to quantitatively analyze the samples by XRD, but qualitatively analyzed the samples by XRD.

 

8. Section 3:Please present your results without discussion and move any relevant information to the discussion section.

Response: Thank you for your suggestions. We have restructured the Conclusion and Discussion section with new additions of line 281-283:The adsorption of zinc by the three sediment complexes is not confined to the molecular layer of organic matter on the surface, but goes deep into the interior of the complexes.

Line 336-338:This ratio is either too high or too low for the complex to adsorb zinc. Within this range, the organics provide sufficient negative charge without making the sample surface too dense.

 

9. Figure 4;Please provide a legend for the identified peaks.

Response: Thank you for your suggestion. We have changed Team Figure 4 and added a legend.

 

10. Line 279-284;Please revise.

Response: Thank you for your suggestion, we have made a change to line 279-284, which is specified below in line 290-294 of the article:In order to identify the oxygenated functional groups that have a decisive influence on the adsorption process of the three groups of samples, the absorption peak areas of different molecules were used to roughly quantify the compounds in conjunction with the semi-quantitative analysis of FTIR and the degree of change in the peak area before and after adsorption of the three groups of samples was subjected to an ANOVA analysis, the results of which are shown in Table 3. The peak areas of phenolic hydroxyl groups before and after adsorption in the three groups of samples were significantly different, and there was no significant difference in the peak areas of carboxyl groups and alcohols, and phenols played a dominant role in the adsorption of zinc.

 

11. Line 364;“soil”??

Response: Thanks to your suggestion, we have changed "soil" to "sediment" and the new change is in line 377.

 

12. Conclusion; The conclusion should be supported by more results.

Response: Thanks to your suggestion, we have adjusted the conclusion section and the discussion section by adding to line 385-388 and line 398-401 of the original conclusion section.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Dear Authors, after reading your manuscript, I have a number of comments, namely:

1. Line 45-46: it is not clear what the source of heavy metals is. Why are there so many of them in that place, that the complex influence of the listed factors influence the increase of their concentrations to a dangerous level.

2. Line 48-49: explain why this is a non-negligible problem

3. Line 53-54: in my opinion, this cannot be said. It depends on the chemical composition of the water. Some heavy metals can chemically bond and change into an insoluble form.

4. Line 64-65: I believe that it is impossible to write like this and this is a false statement. Compared to what is this question little researched? More literature needs to be analyzed.

5. Line 69-70: It is not clear what model the authors are talking about? What does the trend of adsorption mean?

6. Line 76-80: this part is absolutely not clear!

7. Line 76-88: Why did the authors mention zinc, but not other metals? What does free iron and aluminum oxide mean?

8. The introduction lacks a goal, a scientific novelty. In addition, the relevance of the topic is not clear. There is no information about who researched similar environmental problems, because the chosen scientific direction is not new.

I don't want to give links to articles on this topic, but the authors need to find, read and analyze them themselves.

In this form, this manuscript is not a scientific article. In addition, the Introduction contains many errors in the use of terms. I mentioned some in the comments. Thus, the Introduction needs significant revision.

Taking this into account, the Conclusion should also be adjusted.

Line 120-122: an explanation is needed. Why was sodium nitrate taken?

How were the research samples prepared for research?

How exactly was pH 6 determined? After adding the zinc solution?

The methodology section is written very chaotically! Unfortunately, there is a conclusion that the Authors did not perform experimental research professionally enough. Thus, the obtained results are also subject to doubt.

Line 131-155: must be citations. It is not clear whether linear or nonlinear adsorption models were used for the sorption analysis. There is no explanation.

Line 165-169: it is necessary to provide information on how mineral phases were identified, how samples were prepared for research. The information presented in this way about the implementation of research raises serious doubts about the reliability of the results obtained.

 

 

Author Response

1. Line 45-46: it is not clear what the source of heavy metals is. Why are there so many of them in that place, that the complex influence of the listed factors influence the increase of their concentrations to a dangerous level.

Response: Thank you for your suggestion, we make the following answer to your question: From Figure 1, we can see that Dianchi is surrounded by mega cities in China, and the urbanization rate of the rivers flowing into Dianchi is increasing year by year, the water flow is slow, the exchange cycle is long, and the pollutants circulate poorly, which results in the siltation of a large number of sediments.

 

2. Line 48-49: explain why this is a non-negligible problem

Response: Thanks to the instructor's suggestion, we have amended the content before line 48-49. The amended content is line 45-54, which better explains why this is a non-negligible problem, as follows: "In estuaries, the flow of water slows down significantly as the cross-section widens, leading to the buildup of large amounts of pollutants in this area. These pollutants are present in various sedimentary forms, the enrichment of organic matter being one of them. This makes the estuary a hotspot for the enrichment of heavy metals, the source and transport of which is a complex dynamic process. When heavy metal-rich sediments are disturbed, the zinc in them may be re-released into the overlying water body, and under certain conditions, the migration of zinc may have a potentially polluting effect on the water body, and zinc is one of the major pollutants in the water body. Heavy metal contamination of estuarine sediments has been a key research topic in the environmental field. Therefore, endogenous pollution caused by the release of heavy metals in sediments has become an environmental problem that cannot be ignored"

 

3. Line 53-54: in my opinion, this cannot be said. It depends on the chemical composition of the water. Some heavy metals can chemically bond and change into an insoluble form.

Response: Thank you for your advice. It really is determined by the chemistry of the water. Some heavy metals form chemical bonds that transform them into insoluble forms. Adsorption is one of the main processes by which heavy metals are immobilized in sediments.

 

4. Line 64-65: I believe that it is impossible to write like this and this is a false statement. Compared to what is this question little researched? More literature needs to be analyzed.

Response: Thank you for your suggestions on the way the article was written, which we are revising as follows: "The adsorption of pollutants by single components in sediments has been well studied, and the problem of adsorption of heavy metals by composite components has been less researched than that of the interactions between single components on specific pollutants. "

 

5. Line 69-70: It is not clear what model the authors are talking about? What does the trend of adsorption mean?

Response: Thank you for your question, in the introduction section it is mentioned that an accurate modeling is a model that accurately reflects the relationship between the components of the sediment and the contaminants, while the adsorption model used in this article is the Langmuir and Freundlich adsorption model.

The adsorption trend is the effect of the fit, and in this article it is possible to determine which model is more applicable to the performance of the three materials for adsorption of zinc based on the fit of the Langmuir and Freundlich models. A higher degree of fit means that the model better describes the experimental data. If the Langmuir model has a better fit, this means that zinc adsorption is mainly through surface chemisorption. Conversely, if the Freundlich model has a better fit, the zinc adsorption process may involve multilayer adsorption and surface heterogeneity.

We describe the original article in detail as follows, "An in-depth analysis of the adsorption behavior of pollutants in sediment systems is needed to obtain the thermodynamic parameters of the adsorption process using nonlinear fitting and to visualize the fitting effects."

 

6. Line 76-80: this part is absolutely not clear!

Response: Thanks to the teacher for the suggestion . We have added to this section as follows:

Line 82-86: "Remove the organic fraction, the free iron oxide fraction, and the free aluminum oxide fraction from the sediments, respectively. Investigate the differences in Zn²⁺ adsorption characteristics between the complexes after removal of specific components and the original sediment complexes."And explain this section as follows: free iron oxide refers to iron oxide that can be extracted by (DCB method) i.e., sodium sulfite-sodium citrate-sodium bicarbonate extraction, and free iron oxide and free alumina refer to iron oxide and alumina components that can be removed from the text.

 

7. Line 76-88: Why did the authors mention zinc, but not other metals? What does free iron and aluminum oxide mean?

Response: Thank you for your questions about the article, we offer the following explanation: Free iron oxide fractions are iron oxide particles present in the sediment in a free state, usually formed in combination with some substance on the soil or sediment surface. Free alumina is alumina particles present in the sediment in a free state. Methods for removing free alumina fractions include physical treatments (e.g., sieving, washing), chemical treatments (e.g., acid-base treatments), or other specific extraction or precipitation techniques. This dissertation focuses on the differences in the adsorption of heavy metal zinc on composites prepared after removal of organic matter as well as free iron oxide and free alumina with eight estuarine sediments.

8. The introduction lacks a goal, a scientific novelty. In addition, the relevance of the topic is not clear. There is no information about who researched similar environmental problems, because the chosen scientific direction is not new.

I don't want to give links to articles on this topic, but the authors need to find, read and analyze them themselves.

In this form, this manuscript is not a scientific article. In addition, the Introduction contains many errors in the use of terms. I mentioned some in the comments. Thus, the Introduction needs significant revision.

Taking this into account, the Conclusion should also be adjusted.

Response: Thanks to your suggestions, we have amended and expanded the introduction, with changes in line 45-55, line 61-64, line 71-77, and line 82-84, as follows:

Line 45-55：“In the estuary, as the cross section expands, the water flow slows down significantly, resulting in the accumulation of a large number of pollutants in this area. These pollutants are present in various sedimentary forms, and the enrichment of organic matter is one of them[5]. This makes the estuary a hotspot for heavy metal enrichment, and the source and transport of heavy metals is a complex dynamic process. When heavy metal-rich sediments are disturbed, the zinc in them may be re-released into the overlying water body, and under certain conditions, zinc transport may have a potentially polluting effect on the water body, which is also one of the major pollutants in the water body. Heavy metal contamination of estuarine sediments has been a key research topic in the field of environment. Therefore, endogenous pollution caused by the release of heavy metals in sediments has become an environmental problem that cannot be ignored.”

Line 61-64:"The sediments are dominated by a core of various clay minerals (illite, montmorillonite, kaolinite, etc.). Metal oxides (iron, aluminium, manganese oxides, etc.) and organic matter (humic acids, tannins, etc.) form flocculent aggregates on their surfaces"

Line 71-77:" Previous studies have thoroughly investigated the adsorption of pollutants by single components in sediments, but there are fewer studies on the adsorption of heavy metals by composite components relative to the interactions between single components for specific pollutants. This requires an in-depth analysis of the adsorption behavior of pollutants in each component of the sediment, the use of nonlinear fitting models to obtain the thermodynamic parameters of the adsorption process, and a visual display of the fitting effect to determine the trend of adsorption on pollutants."

Line 82-84:" In this research,Remove the organic fraction, the free iron oxide fraction, and the free aluminum oxide fraction from the sediments, respectively. "

 

9. Line 120-122: an explanation is needed. Why was sodium nitrate taken?

How were the research samples prepared for research?

Response: At the suggestion of the teacher, we have added to the original text: “the extraction of sodium nitrate achieves a more complete extraction rate and avoids the production of precipitates.”The detailed procedure of sample preparation is described in Section 2.2 as follows:

(1) Without special treatment - Group A: (1) A certain amount of natural sediment complex samples were placed in a beaker, ultrasonically dispersed with the addition of pure water, artificially removed biomass and residues, and freeze-dried to make a product.

(2) Organic matter removal treatment - Group B: Group A samples were freeze-dried by adding H₂O₂ solution (30%) and heating in a 90°C water bath. This is the precipitate after removal of the active part of the organic matter.

(3) Removal of iron and alumina - Group C: The samples in group A were added with sodium citrate solution (1 mol/L) and NaHCO₃ solution (1 mol/L), heated to 80°C by hydrothermal heating, then added with Na₂S₂O₄ and washed repeatedly with saturated NaCl solution and purified water, and freeze-dried.

 

10. How exactly was pH 6 determined? After adding the zinc solution?

Response: The pH was adjusted with NaOH and HNO₃ during the experiment, and the pH was determined using an acidimeter.

 

11. Line 131-155: must be citations. It is not clear whether linear or nonlinear adsorption models were used for the sorption analysis. There is no explanation.

Response: Thanks to the suggestion of the instructor, we have inserted citations using this approach in Section 2.4, and the adsorption analysis was performed using Langmuir and Freundlich nonlinear fitting analysis.

 

12. Line 165-169: it is necessary to provide information on how mineral phases were identified, how samples were prepared for research. The information presented in this way about the implementation of research raises serious doubts about the reliability of the results obtained.

Response: Thank you very much for your suggestion, we already have information on how to determine the mineral phases in section 2.5.3, XRD qualitative analysis, comparing X-ray diffraction patterns obtained from experimental measurements of samples with a library of standard cards with known phases, to determine the phases present in the samples.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors improved the study, but still, one comment is not improved: "XRD graphs are not clear, they should contain the minerals highlighted at every peak." The changes after adsorption should be clearly visible.

Author Response

Dear Reviewer,

I am writing to express my deepest gratitude for the time and effort you invested in reviewing the manuscript .

Your expertise and dedication to maintaining high standards of academic integrity are truly appreciated. The suggestions you made in the first round of review were invaluable, and we have incorporated them into our manuscript to enhance its quality and clarity. Your rigorous assessment and constructive feedback have helped us produce a more robust and comprehensive paper.

Once again, thank you for your time and valuable suggestions. Your contributions are invaluable to both our research and the broader academic community.

Please accept my heartfelt appreciation for your outstanding service. I am sincerely grateful for the opportunity to benefit from your expertise.

Warm regards,

Xiaolong Sun

 

Reviewer 3 Report

Comments and Suggestions for Authors

I accept this manuscript

Author Response

Dear Reviewer,

I am writing to express my deepest gratitude for the time and effort you invested in reviewing the manuscript .

Your expertise and dedication to maintaining high standards of academic integrity are truly appreciated. The suggestions you made in the first round of review were invaluable, and we have incorporated them into our manuscript to enhance its quality and clarity. Your rigorous assessment and constructive feedback have helped us produce a more robust and comprehensive paper.

Once again, thank you for your time and valuable suggestions. Your contributions are invaluable to both our research and the broader academic community.

Please accept my heartfelt appreciation for your outstanding service. I am sincerely grateful for the opportunity to benefit from your expertise.

Warm regards,

Xiaolong Sun