Recycling Industrial Waste: Ferritization Products for Zn²⁺ Removal from Wastewater

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

1. Valence states analysis of the obtained iron-containing materials should be performed.

2. Can the ferritization products be reused for the sorption of Zn2+ from wastewater? How many cycles?

3. If the ferritization products exhibit a porous structure? Additional tests and discussion should focus on this point.

Author Response

Dear Reviewer,

 

We would like to thank the you for careful reading, critical and constructive comments on this manuscript, by the Reviewer. The comments have been very thorough and useful in improving the manuscript. We strongly believe that the comments and suggestions have increased the scientific value of the revised manuscript by many folds. We have taken them fully into account in revision. We are submitting the corrected manuscript with the suggestion incorporated the manuscript. Suggested changes to the text are marked in red.

Below, we included the point-to-point response to the Reviewer’s comments.

1. Valence states analysis of the obtained iron-containing materials should be performed.

Thank you for the recommendation.
We did not perform an analysis of the valence states of the obtained iron-containing materials, as our study focused on identifying the mineral phases present in these materials. For this purpose, we conducted X-ray diffraction analysis using a diffractometer.

Information on valence states is indeed important when iron-containing materials are intended for use in redox processes — in such cases, it is necessary to determine the content of divalent iron (Fe²⁺).

2. Can the ferritization products be reused for the sorption of Zn2+ from wastewater? How many cycles?

Thank you for the recommendation.

The aim of this article was to study principal possibility of the materials obtained by the ferritization method to sorb Zn2+ ions in different modes of mixing and pH values of the solution. Study of ability to reuse of obtained sorbents will be the subject of our further researches.

3. If the ferritization products exhibit a porous structure? Additional tests and discussion should focus on this point.

Thank you for the recommendation.
We did not conduct porosity analysis of the obtained iron-containing materials, as our research plan did not include this type of investigation. In our opinion, such studies are essential when the sorbent is intended for the adsorption of organic substances, for example. Our research was focused on examining the magnetic and adsorption properties of the newly synthesized magnetite.

 

With best regards,

Authors

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript titled "A Study of the Ability of Ferritization Products of Etching Solutions to Sorption of Zn²⁺ from Wastewater" presents an interesting and innovative approach, particularly in the context of reusing etching solutions for the removal of Zn from wastewater. This method has significant potential to enhance sustainability in industrial wastewater management. However, before I can make a final decision, I have some questions and suggestions that I would like to address. I will provide these points below for further clarification and improvement of the manuscript.

Please find my comments below:

1. Lines 36, 38, 39, 47, 58: Could you kindly clarify why reference numbers are bold? Additionally, there is a dot before references 1-3, 6, and 10, which should be removed.
2. Line 45: There seems to be an extra space before the word "different." Could you please check and correct this?
3. Line 47: I recommend using the standard notation “40–50%” instead of the current form. This should be applied consistently throughout the manuscript.
4. Line 82: The sentence reads a bit awkwardly. I would suggest: “In recent years, considerable attention has been paid to sorption methods for treating wastewater to remove heavy metals.”
5. Line 85: There appears to be a typo in the word "practical."
6. Lines 94-102: This paragraph discusses the regeneration of the sorbent, which was not performed in the current study. I suggest reconsidering whether this section is necessary, or if it could be revised to more clearly align with the scope of your work.
7. Line 97: There may be a typo in the word "With."
8. Line 101: There seems to be a double space before the word "utilization."
9. Line 104: This sentence could be more fluid. Perhaps: "A particularly significant application niche is occupied by sorbents with magnetic properties [30]."
10. Line 111: The sentence mentions the adsorption capacity for natural Fe-rich materials. Could you please add this information to either the sentence or Table 1?
11. Lines 117 and 123: The terms “hydrophase” and “thermal” ferritization are mentioned, but it’s unclear which was used in this study. I recommend being more explicit in this regard.
12. Line 118: There appears to be a double space next to the word "ease."
13. Line 120: The notation "2+" should be written in superscript.
14. Line 122: The Celsius symbol appears underlined—could you please correct this?
15. Line 147: Please verify if this phrase is correct: "…the aim of this work is to improve…". It may be possible to remove the hyphen.
16. Line 151: There seems to be a double space before "possibility."
17. Table 1: Regarding the preparation of Fe-1, was only NaOH used? Please confirm.
18. Line 186: Please verify if "2c" and “+-“are used correctly.
19. Lines 199-220: If “This reagent” refers to Zincome, could you please rewrite this for clarity to ensure there is no ambiguity?
20. Figure 2: I suggest removing this figure. Typically, images of standard laboratory equipment are not necessary in a manuscript. It is sufficient to mention the model and manufacturer.
21. Lines 219-222: Could you clarify the solution volume and the method used to prepare the solution and adjust the pH? If the conditions for Figure 5 and Table 5 differ, please describe them.
22. Lines 223-228: Were these analyses performed on all prepared adsorbents or just on Fe-5? Please provide clarification in the text.
23. Figure 5: Kindly translate the labels in the graph to English. Also, ensure consistency in decimal notation (comma or dot). I suggest reversing the order of the bars so that the first bar corresponds to pH=5.6, followed by pH=8. Additionally, consider adding patterns to the bars to aid readability in black and white. The labels "a" and "b" would be clearer if placed directly on the graph rather than below it.
24. Line 307: There seems to be a double space after “reduces.”
25. Line 315: Does a concentration below 5 mg/L mean that only Fe-3, 4, and 5 when ultrasound is active meet this criterion?
26. Line 329: Please emphasize that only Fe-5 will be further studied in the manuscript.
27. Table 5: The words “adsorption” have typo in it.
28. Line 332: Please verify if the table referenced is Table 4 or 5.
29. Line 335: Where do the values of 0.08–0.19 mg/L come from? Could you clarify?
30. Line 342: There appears to be a double space after reference 64.
31. Lines 345-360: The purpose of this section is unclear, especially since the pHpzc was not determined in this work. I suggest reconsidering the relevance of this section or rewriting it to better align with your study’s objectives.
32. Lines 348-350: This sentence is somewhat difficult to read. I believe the intended meaning is that below pHpzc, magnetite is positively charged and can attract anions. Could you please clarify?
33. Lines 351-353: Based on the pHpzc value of 6.5, if the pH is below this value, magnetite would adsorb anions, and if above, it would adsorb cations. Is this correct?
34. Line 352: Please write Cr6+ in its anionic form, likely dichromate (Cr₂O₇²⁻).
35. Line 353: Was the pHpzc value 6.5 or 2.11? Please verify.
36. Line 355: "PZC" in subscript, is written in uppercase. Previously lowercase was used
37. Lines 359-361: The meaning of this section is unclear. Could you please revise for clarity?
38. Line 377: The notation "2+" should be in superscript.
39. Line 381: The phrase “In paper [78] It is reported” should be revised. Perhaps: “In the work of Hou et al. (2013), it was reported…” or “Another study [78] reports…”
40. Line 389: After the numerical values, I suggest adding "(Table 5)" to help readers follow the reference more easily.
41. Lines 395-403, 406-427: Which material is being referred to here—Fe-5? Please confirm.
42. Line 405: Is it "sorbent" or "sorbents" in this context? Please clarify.
43. Figures 7 and 8: The captions for Figure 7 and Figure 8 are misaligned. Additionally, both figures contain non-English characters instead of “b” and “c.” Please correct this.
44. Line 426: Please clarify if it should be "sorbent" or "sorbents" and ensure consistency.
45. Line 446: There seems to be a double space before “models.”
46. Lines 452-453: Please provide a reference to support this statement.

Comments on the Quality of English Language

In general, the English is acceptable, but in some parts, clarity could be improved by using shorter, more concise sentences.

Author Response

Dear Reviewer,   We would like to thank the you for careful reading, critical and constructive comments on this manuscript, by the Reviewer. The comments have been very thorough and useful in improving the manuscript. We strongly believe that the comments and suggestions have increased the scientific value of revised manuscript by many folds. We have taken them fully into account in revision. We are submitting the corrected manuscript with the suggestion incorporated the manuscript. Suggested changes to the text are marked in red. Below, we included the point-to-point response to the Reviewer’s comments.
1.                 Lines 36, 38, 39, 47, 58: Could you kindly clarify why reference numbers are bold? Additionally, there is a dot before references 1-3, 6, and 10, which should be removed.	we made changes
2.                 Line 45: There seems to be an extra space before the word "different." Could you please check and correct this?	we made changes
3.                 Line 47: I recommend using the standard notation “40–50%” instead of the current form. This should be applied consistently throughout the manuscript.	we made changes
4.                 Line 82: The sentence reads a bit awkwardly. I would suggest: “In recent years, considerable attention has been paid to sorption methods for treating wastewater to remove heavy metals.”	we made changes
5.                 Line 85: There appears to be a typo in the word "practical."	we made changes
6.                 Lines 94-102: This paragraph discusses the regeneration of the sorbent, which was not performed in the current study. I suggest reconsidering whether this section is necessary, or if it could be revised to more clearly align with the scope of your work.	The text has been amended to emphasize the complexity of the regeneration process. Lines 95-99
7.                 Line 97: There may be a typo in the word "With."	we made changes
8.                 Line 101: There seems to be a double space before the word "utilization."	we made changes
9.                 Line 104: This sentence could be more fluid. Perhaps: "A particularly significant application niche is occupied by sorbents with magnetic properties [30]."	we made changes
10.             Line 111: The sentence mentions the adsorption capacity for natural Fe-rich materials. Could you please add this information to either the sentence or Table 1?	we made changes
11.             Lines 117 and 123: The terms “hydrophase” and “thermal” ferritization are mentioned, but it’s unclear which was used in this study. I recommend being more explicit in this regard.	The clarification has been added to the text. In the work hydrophase ferritization was studied. It can be with thermal electromagnetic or ultrasound activation. Lines 121-123
12.             Line 118: There appears to be a double space next to the word "ease."	we made changes
13.             Line 120: The notation "2+" should be written in superscript.	we made changes
14.             Line 122: The Celsius symbol appears underlined—could you please correct this?	we made changes
15.             Line 147: Please verify if this phrase is correct: "…the aim of this work is to improve…". It may be possible to remove the hyphen.	we made changes
16.             Line 151: There seems to be a double space before "possibility."	we made changes
17.             Table 1: Regarding the preparation of Fe-1, was only NaOH used? Please confirm.	Yes, only NaOH Line 161
18.             Line 186: Please verify if "2c" and “+-“are used correctly.	Corrected: ICCD PDF-2 2003 Fixed
19.             Lines 199-220: If “This reagent” refers to Zincome, could you please rewrite this for clarity to ensure there is no ambiguity?	Corrected:  ZincoVer Fixed
20.             Figure 2: I suggest removing this figure. Typically, images of standard laboratory equipment are not necessary in a manuscript. It is sufficient to mention the model and manufacturer.	if it is unprincipled, then we would like to leave this drawing
21.             Lines 219-222: Could you clarify the solution volume and the method used to prepare the solution and adjust the pH? If the conditions for Figure 5 and Table 5 differ, please describe them.	Clarification of the solution volume and the method used to prepare the solution and adjust the pH is added to the text.  Lines 192,193, 195.    If the conditions for Figure 5 and Table 5 differ, please describe them. Conditions for Figure 5 are identical to those for Table 5.
22.             Lines 223-228: Were these analyses performed on all prepared adsorbents or just on Fe-5? Please provide clarification in the text.	SEM and X-ray fluorescence spectroscopy studies are performed just for samples Fe-5. (Сlarification  has been included in the text). Line 396
23.             Figure 5: Kindly translate the labels in the graph to English. Also, ensure consistency in decimal notation (comma or dot). I suggest reversing the order of the bars so that the first bar corresponds to pH=5.6, followed by pH=8. Additionally, consider adding patterns to the bars to aid readability in black and white. The labels "a" and "b" would be clearer if placed directly on the graph rather than below it.	Fig. 5 has been modified according to all of the above.
24.             Line 307: There seems to be a double space after “reduces.”	we made changes
25.             Line 315: Does a concentration below 5 mg/L mean that only Fe-3, 4, and 5 when ultrasound is active meet this criterion?	The analysis of Fig. 5 revealed that only for samples of sorbents Fe-3 and Fe-4 at pH 8.0 and ultrasonic treatment a concentration values below 5 mg/l for Zn2+ ions are achieved. (Added to the article text lines 311-313)
26.             Line 329: Please emphasize that only Fe-5 will be further studied in the manuscript.	Emphasized
27.             Table 5: The words “adsorption” have typo in it.	The words “adsorption” have typo in it.
28.             Line 332: Please verify if the table referenced is Table 4 or 5.	we made changes
29.             Line 335: Where do the values of 0.08–0.19 mg/L come from? Could you clarify?	The low degree of purification from zinc ions can be explained by the fact that the studied solutions, in addition to Zn2+ ions, also contains Fe2+ and Fe3+ ions, which are capable of leaching from the studied sample Fe-5 and can also be sorbed, competing with zinc ions. This assumption is confirmed by measuring of iron ions concentration in the solution after sorption studies. The concentrations of total iron were 0.08 and 0.19 mg/dm3 for experiments using mechanical stirring and ultrasound, respectively. At pH values of 8.0 and 10 after corresponding sorption experiments, iron ions were not detected in concentrations available for measurement. This indicates high stability of the sorbent at pH values ≥ 8.0. (Those clarifications are in amended text)  Lines 332-339
30.             Line 342: There appears to be a double space after reference 64.	we made changes
31.             Lines 345-360: The purpose of this section is unclear, especially since the pHpzc was not determined in this work. I suggest reconsidering the relevance of this section or rewriting it to better align with your study’s objectives.	Scientific articles analyzing the point of zero charge (PZC) of magnetite have shown that this value is not constant and can vary within a wide range. It depends on the origin of the magnetite — whether it is natural or synthetic. The PZC value is also influenced by the synthesis conditions of magnetite (such as pH, temperature, and other parameters).   Due to its magnetic properties, magnetite is capable of adsorbing both cationic and anionic pollutants. Thus, it has been established that the PZC of magnetite is not a constant value.   In our study, magnetite is synthesized under the influence of ultrasound with simultaneous aeration of water. Since the iron concentration in the water (in particular, in wastewater from electroplating industries) may vary, the PZC value will also vary accordingly.   Therefore, we did not conduct experimental studies to determine the PZC of the synthesized magnetite, as this would not have practical significance under conditions of a variable medium composition. We did theoretical analysis.   This section includes both experimental and theoretical research.
32.             Lines 348-350: This sentence is somewhat difficult to read. I believe the intended meaning is that below pHpzc, magnetite is positively charged and can attract anions. Could you please clarify?	we made changes Line 347-352
33.             Lines 351-353: Based on the pHpzc value of 6.5, if the pH is below this value, magnetite would adsorb anions, and if above, it would adsorb cations. Is this correct?	The authors studied this particular magnetite and this was their claim.
34.             Line 352: Please write Cr6+ in its anionic form, likely dichromate (Cr₂O₇²⁻).	we made changes
35.             Line 353: Was the pHpzc value 6.5 or 2.11? Please verify.	we made changes Line 347-352
36.             Line 355: "PZC" in subscript, is written in uppercase. Previously lowercase was used	we made changes
37.             Lines 359-361: The meaning of this section is unclear. Could you please revise for clarity?	done
38.             Line 377: The notation "2+" should be in superscript.	we made changes
39.             Line 381: The phrase “In paper [78] It is reported” should be revised. Perhaps: “In the work of Hou et al. (2013), it was reported…” or “Another study [78] reports…”	we made changes
40.             Line 389: After the numerical values, I suggest adding "(Table 5)" to help readers follow the reference more easily.	we made changes line 392
41.             Lines 395-403, 406-427: Which material is being referred to here—Fe-5? Please confirm.	Indeed, sample Fe-5 was stadied in detail. Line 396
42.             Line 405: Is it "sorbent" or "sorbents" in this context? Please clarify.	Corectly "sorbents"
43.             Figures 7 and 8: The captions for Figure 7 and Figure 8 are misaligned. Additionally, both figures contain non-English characters instead of “b” and “c.” Please correct this.	we made changes
44.             Line 426: Please clarify if it should be "sorbent" or "sorbents" and ensure consistency.	Corectly "sorbents"
45.             Line 446: There seems to be a double space before “models.”	we made changes
46.             Lines 452-453: Please provide a reference to support this statement.	we made changes line 454

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript, entitled "A study of the ability of sterilization products of etching solutions to sorption of Zn2+ from wastewater", publishes the results of an investigation on the possibility of purifying contaminated water from heavy metals, like zinc, for example, using an iron-containing sorbent with magnetic properties, also obtained from contaminated water. The research topic is not new, but the authors have made efforts to realize the practical potential of this idea. The research was carried out clearly and conscientiously, the results are presented in full, the conclusions are confirmed by the results. The text is written competently, consistently, and in a structured manner. The number of references to literary sources is sufficient, the graphic design of the article is very well done. It is recommended to accept the article after minor changes.

1) Links under numbers 20, 21, 25, 33, 34, 43, 45, 50, 51, 54, 55 and 58 are self-citations. There are 12 of them in total. This is an excessive amount. Only links to articles numbered 54, 55 and 58 are needed, unlike the others.

2) Pages 4, 7 and 12. There is too much free space at the end of the page.

3) Figure 5. The signature should preferably be in English. The font differs from the font of the main text of the article. It is advisable to place the signature to the figure on the same page as the figure.

4) Table 4 and Figure 9. As in the previous paragraph, it is advisable to place them entirely on one page, with the signature.

5) Lines 120 and 377. The designation of the ion charge is written in the usual font size, without using a superscript character.

6) Figure 2 has no semantic meaning. The quality of the right image is unacceptable.

7) Lines 317-318. It is advisable to reformulate the sentence. Perhaps a clarification should be added about the limitations of the two-phase sample.

8) Figures 7 and 8. It is not clear which spherical particles are mentioned. It is not visible, it is advisable to mark with arrows everything that the authors want to show. It is advisable to clarify the description of the figure a little. It is not clear what exactly proves the presence of crystal structures. Numbering should preferably be done in English. 

Author Response

Dear Editor and Reviewers,

We would like to thank the you for careful reading, critical and constructive comments on this manuscript, by the Reviewer. The comments have been very thorough and useful in improving the manuscript. We strongly believe that the comments and suggestions have increased the scientific value of revised manuscript by many folds. We have taken them fully into account in revision. We are submitting the corrected manuscript with the suggestion incorporated the manuscript. Suggested changes to the text are marked in red.

Below, we included the point-to-point response to the Reviewer’s comments.

• Links under numbers 20, 21, 25, 33, 34, 43, 45, 50, 51, 54, 55 and 58 are self-citations. There are 12 of them in total. This is an excessive amount. Only links to articles numbered 54, 55 and 58 are needed

Done

2) Pages 4, 7 and 12. There is too much free space at the end of the page.

We will implement such changes after the review process

3) Figure 5. The signature should preferably be in English. The font differs from the font of the main text of the article. It is advisable to place the signature to the figure on the same page as the figure.

The signatures of Figure 5. are in English. The font is the same as the main article text.

4) Table 4 and Figure 9. As in the previous paragraph, it is advisable to place them entirely on one page, with the signature.

We will implement such changes after the review process

5) Lines 120 and 377. The designation of the ion charge is written in the usual font size, without using a superscript character.

6) Figure 2 has no semantic meaning. The quality of the right image is unacceptable.

if it is unprincipled, then we would like to leave this drawing

7) Lines 317-318. It is advisable to reformulate the sentence. Perhaps a clarification should be added about the limitations of the two-phase sample.

The sentences are reformulated in the text. Lines 314-317.

8) Figures 7 and 8. It is not clear which spherical particles are mentioned. It is not visible, it is advisable to mark with arrows everything that the authors want to show. It is advisable to clarify the description of the figure a little. It is not clear what exactly proves the presence of crystal structures. Numbering should preferably be done in English. 

Spherical particles mark with arrows.

 Presence of crystal structures proves by X-ray studies. Only crystalline phases were detected in diffraction patterns.

With regards, Authors

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

Please see the file attached. 

Comments for author File: Comments.pdf

Author Response

Dear Reviewer!
Thank you very much for your second review. We have made the necessary changes.
Thank you very much again and wish you scientific success in life
Authors