Sustainable Immobilization of Zn, Pb, and As in Lead Smelting Slag via Fe-S(II) Microencapsulation for Heavy Metal Recycling and Environmental Remediation

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The authors work on Simultaneous Microencapsulation Passivation of Zn, Pb, and As Heavy Metals in Smelted Lead Slag by Fe-S(II) Microencapsulated Passivation addresses a critical environmental issue associated with lead smelting activities. The scientific approach of utilizing Fe-S(II) microencapsulation for the passivation of hazardous metals such as Zn, Pb, and As is commendable contributing to progress in environmental remediation. Before I recommend the manuscript for publication, authors should address the below comments.

The authors state, "As smelting wastes are constantly dumped around the smelter, under the action of natural weathering and microbial activities, toxic heavy metals in the wastes will be released and migrated continuously through the rainfall and washing, which is one of the main sources of harmful heavy metals in the surrounding ecosystems." To strengthen this claim, it would be beneficial to provide global evidence demonstrating the impact of heavy metals from smelting activities on ecosystems. Incorporating references such as  (Peterson, E. K., Carsella, J., Varian-Ramos, C. W., Schiffer, T., Staples, S. K., & Diawara, M. (2024). Effects of Lead (Pb) from Smelter Operations in an Urban Terrestrial Food Chain at a Colorado Superfund Site. Bulletin of Environmental Contamination and Toxicology, 112(1), 17.; Oloruntoba, A., Omoniyi, A. O., Shittu, Z. A., Ajala, R. O., & Kolawole, S. A. (2024) can offer valuable evidence of the environmental consequences of heavy metal contamination from mining operations.

 

The phrase "and so on...and so on" is used when listing heavy metals.  This expression is informal and should be revised for clarity and professionalism. Consider specifying all relevant heavy metals or using "etc." if appropriate.

 

The sentence discussing Bradley et al.'s work contains repetitive information: "Bradley et al. used soluble PO₄³⁻ to stabilize heavy metals, resulting in a 52% reduction in the leachability of Ca, a 14% reduction in the leachability of Cd, a 98% reduction in the leachability of Cu, a 99% reduction in the leachability of Pb, and a 36% reduction in the leachability of Zn."

To improve readability, rephrase the sentence to eliminate redundancy. For example: "Bradley et al. utilized soluble PO₄³⁻ to stabilize heavy metals, achieving significant reductions in leachability: 52% for Ca, 14% for Cd, 98% for Cu, 99% for Pb, and 36% for Zn."

 

In the statement, "Wang et al. used CaHPO4 and CaCO3," the chemical formulas lack proper subscript formatting. Ensure that all chemical formulas are correctly formatted with subscripts, i.e., CaHPO₄ and CaCO₃.

 

The sentence beginning with "Therefore, the heavy metal surface passivation in response to the demand..." is lengthy and complex, making it difficult to comprehend. Many sentences like this exist throughout the manuscript.  Consider breaking this sentence into shorter, clearer statements to enhance understanding. For instance: "Heavy metal surface passivation is a method developed to prevent oxidative weathering of slag, tailings, and other inorganic solid wastes containing toxic heavy metals. The principle involves forming an insoluble, inert, and dense protective film on the surface of sulfide mineral particles. This film acts as a barrier, preventing the intrusion of oxygen, water, and other oxidants into the tailings particles. The method is cost-effective and simple to implement."

 

The term "iron sulfide iron hydroxide coatings" appears to be incorrect.  Clarify whether this refers to "iron sulfide and iron hydroxide coatings" or another specific compound. Additionally, the term "sulfurous iron ore" is not standard in scientific or geological contexts. It would be more appropriate to use "sulfide minerals" or specify the exact mineral, such as "pyrite" or "marcasite."

 

The sentence, "According to the results of heavy metal release characterization of smelting slag, the release of Zn, Pb, and As from lead smelting slag is mainly controlled by the free state content, soluble mineral dissolution, and sulfur-iron mineral dissolution," is somewhat ambiguous. Rephrase for clarity. For example: "The characterization results indicate that the release of Zn, Pb, and As from lead smelting slag is primarily influenced by their free state content and the dissolution of soluble and sulfur-iron minerals."

 

The manuscript mentions, "The collected slag was leached with HNO₃ solution," but lacks a detailed description of the slag's characteristics and its origin. Provide more information about the slag samples, including their source, physical properties, and chemical composition. This context is essential for readers to assess the relevance and applicability of the study. Move it from the result section here.

The statement, "Based on this, many scholars have conducted a lot of research on the leaching release of heavy metals," lacks supporting references. Incorporate relevant citations to previous studies that have investigated the leaching behavior of heavy metals from similar matrices. This will provide a solid foundation for the current research and acknowledge existing contributions in the field.

 

The authors employed ICP-OES and ICP-MS for heavy metal analysis but did not address potential spectral interferences, especially concerning Fe ions.  Discuss the strategies implemented to mitigate spectral interferences arising from overlapping emission lines and matrix effects. This could include the selection of appropriate analytical wavelengths, utilization of internal standards, or application of mathematical correction methods.

Comments on the Quality of English Language

The authors work on Simultaneous Microencapsulation Passivation of Zn, Pb, and As Heavy Metals in Smelted Lead Slag by Fe-S(II) Microencapsulated Passivation addresses a critical environmental issue associated with lead smelting activities. The scientific approach of utilizing Fe-S(II) microencapsulation for the passivation of hazardous metals such as Zn, Pb, and As is commendable contributing to progress in environmental remediation. Before I recommend the manuscript for publication, authors should address the below comments.

The authors state, "As smelting wastes are constantly dumped around the smelter, under the action of natural weathering and microbial activities, toxic heavy metals in the wastes will be released and migrated continuously through the rainfall and washing, which is one of the main sources of harmful heavy metals in the surrounding ecosystems." To strengthen this claim, it would be beneficial to provide global evidence demonstrating the impact of heavy metals from smelting activities on ecosystems. Incorporating references such as  (Peterson, E. K., Carsella, J., Varian-Ramos, C. W., Schiffer, T., Staples, S. K., & Diawara, M. (2024). Effects of Lead (Pb) from Smelter Operations in an Urban Terrestrial Food Chain at a Colorado Superfund Site. Bulletin of Environmental Contamination and Toxicology, 112(1), 17.; Oloruntoba, A., Omoniyi, A. O., Shittu, Z. A., Ajala, R. O., & Kolawole, S. A. (2024) can offer valuable evidence of the environmental consequences of heavy metal contamination from mining operations.

 

The phrase "and so on...and so on" is used when listing heavy metals.  This expression is informal and should be revised for clarity and professionalism. Consider specifying all relevant heavy metals or using "etc." if appropriate.

 

The sentence discussing Bradley et al.'s work contains repetitive information: "Bradley et al. used soluble PO₄³⁻ to stabilize heavy metals, resulting in a 52% reduction in the leachability of Ca, a 14% reduction in the leachability of Cd, a 98% reduction in the leachability of Cu, a 99% reduction in the leachability of Pb, and a 36% reduction in the leachability of Zn."

To improve readability, rephrase the sentence to eliminate redundancy. For example: "Bradley et al. utilized soluble PO₄³⁻ to stabilize heavy metals, achieving significant reductions in leachability: 52% for Ca, 14% for Cd, 98% for Cu, 99% for Pb, and 36% for Zn."

 

In the statement, "Wang et al. used CaHPO4 and CaCO3," the chemical formulas lack proper subscript formatting. Ensure that all chemical formulas are correctly formatted with subscripts, i.e., CaHPO₄ and CaCO₃.

 

The sentence beginning with "Therefore, the heavy metal surface passivation in response to the demand..." is lengthy and complex, making it difficult to comprehend. Many sentences like this exist throughout the manuscript.  Consider breaking this sentence into shorter, clearer statements to enhance understanding. For instance: "Heavy metal surface passivation is a method developed to prevent oxidative weathering of slag, tailings, and other inorganic solid wastes containing toxic heavy metals. The principle involves forming an insoluble, inert, and dense protective film on the surface of sulfide mineral particles. This film acts as a barrier, preventing the intrusion of oxygen, water, and other oxidants into the tailings particles. The method is cost-effective and simple to implement."

 

The term "iron sulfide iron hydroxide coatings" appears to be incorrect.  Clarify whether this refers to "iron sulfide and iron hydroxide coatings" or another specific compound. Additionally, the term "sulfurous iron ore" is not standard in scientific or geological contexts. It would be more appropriate to use "sulfide minerals" or specify the exact mineral, such as "pyrite" or "marcasite."

 

The sentence, "According to the results of heavy metal release characterization of smelting slag, the release of Zn, Pb, and As from lead smelting slag is mainly controlled by the free state content, soluble mineral dissolution, and sulfur-iron mineral dissolution," is somewhat ambiguous. Rephrase for clarity. For example: "The characterization results indicate that the release of Zn, Pb, and As from lead smelting slag is primarily influenced by their free state content and the dissolution of soluble and sulfur-iron minerals."

 

The manuscript mentions, "The collected slag was leached with HNO₃ solution," but lacks a detailed description of the slag's characteristics and its origin. Provide more information about the slag samples, including their source, physical properties, and chemical composition. This context is essential for readers to assess the relevance and applicability of the study. Move it from the result section here.

The statement, "Based on this, many scholars have conducted a lot of research on the leaching release of heavy metals," lacks supporting references. Incorporate relevant citations to previous studies that have investigated the leaching behavior of heavy metals from similar matrices. This will provide a solid foundation for the current research and acknowledge existing contributions in the field.

 

The authors employed ICP-OES and ICP-MS for heavy metal analysis but did not address potential spectral interferences, especially concerning Fe ions.  Discuss the strategies implemented to mitigate spectral interferences arising from overlapping emission lines and matrix effects. This could include the selection of appropriate analytical wavelengths, utilization of internal standards, or application of mathematical correction methods.

Author Response

Dear Editor/Referee:

First of all, I would like to thank the reviewers for your patience and valuable suggestions. Here is the author's response to the comments from the reviewers:

Reviewer #1:

The authors work on Simultaneous Microencapsulation Passivation of Zn, Pb, and As Heavy Metals in Smelted Lead Slag by Fe-S(II) Microencapsulated Passivation addresses a critical environmental issue associated with lead smelting activities. The scientific approach of utilizing Fe-S(II) microencapsulation for the passivation of hazardous metals such as Zn, Pb, and As is commendable contributing to progress in environmental remediation. Before I recommend the manuscript for publication, authors should address the below comments.

The authors state, "As smelting wastes are constantly dumped around the smelter, under the action of natural weathering and microbial activities, toxic heavy metals in the wastes will be released and migrated continuously through the rainfall and washing, which is one of the main sources of harmful heavy metals in the surrounding ecosystems." To strengthen this claim, it would be beneficial to provide global evidence demonstrating the impact of heavy metals from smelting activities on ecosystems. Incorporating references such as  (Peterson, E. K., Carsella, J., Varian-Ramos, C. W., Schiffer, T., Staples, S. K., & Diawara, M. (2024). Effects of Lead (Pb) from Smelter Operations in an Urban Terrestrial Food Chain at a Colorado Superfund Site. Bulletin of Environmental Contamination and Toxicology, 112(1), 17.; Oloruntoba, A., Omoniyi, A. O., Shittu, Z. A., Ajala, R. O., & Kolawole, S. A. (2024) can offer valuable evidence of the environmental consequences of heavy metal contamination from mining operations.

Response: We cited the literature listed by the reviewer.

The phrase "and so on...and so on" is used when listing heavy metals.  This expression is informal and should be revised for clarity and professionalism. Consider specifying all relevant heavy metals or using "etc." if appropriate.

Response: We replace the casual phrase “and so on... and so on” with the clear and professional expression “etc.”

The sentence discussing Bradley et al.'s work contains repetitive information: "Bradley et al. used soluble PO₄³⁻ to stabilize heavy metals, resulting in a 52% reduction in the leachability of Ca, a 14% reduction in the leachability of Cd, a 98% reduction in the leachability of Cu, a 99% reduction in the leachability of Pb, and a 36% reduction in the leachability of Zn."

To improve readability, rephrase the sentence to eliminate redundancy. For example: "Bradley et al. utilized soluble PO₄³⁻ to stabilize heavy metals, achieving significant reductions in leachability: 52% for Ca, 14% for Cd, 98% for Cu, 99% for Pb, and 36% for Zn."

Response: We replace the sentence “Bradley et al. used soluble PO₄³⁻ to stabilize heavy metals, resulting in a 52% reduction in the leachability of Ca, a 14% reduction in the leachability of Cd, a 98% reduction in the leachability of Cu, a 99% reduction in the leachability of Pb, and a 36% reduction in the leachability of Zn.” with "Bradley et al. utilized soluble PO₄³⁻ to stabilize heavy metals, achieving significant reductions in leachability: 52% for Ca, 14% for Cd, 98% for Cu, 99% for Pb, and 36% for Zn.", which contains repeated information.

In the statement, "Wang et al. used CaHPO4 and CaCO3," the chemical formulas lack proper subscript formatting. Ensure that all chemical formulas are correctly formatted with subscripts, i.e., CaHPO₄ and CaCO₃.

Response: We change the chemical formula to the correct subscript format.

The sentence beginning with "Therefore, the heavy metal surface passivation in response to the demand..." is lengthy and complex, making it difficult to comprehend. Many sentences like this exist throughout the manuscript.  Consider breaking this sentence into shorter, clearer statements to enhance understanding. For instance: "Heavy metal surface passivation is a method developed to prevent oxidative weathering of slag, tailings, and other inorganic solid wastes containing toxic heavy metals. The principle involves forming an insoluble, inert, and dense protective film on the surface of sulfide mineral particles. This film acts as a barrier, preventing the intrusion of oxygen, water, and other oxidants into the tailings particles. The method is cost-effective and simple to implement."

Response: We split and streamline long and complex sentences to make them clear and easy to understand.

The term "iron sulfide iron hydroxide coatings" appears to be incorrect.  Clarify whether this refers to "iron sulfide and iron hydroxide coatings" or another specific compound. Additionally, the term "sulfurous iron ore" is not standard in scientific or geological contexts. It would be more appropriate to use "sulfide minerals" or specify the exact mineral, such as "pyrite" or "marcasite."

Response: We specify “iron sulfide iron hydroxide coatings” as a specific mineral and replace it with the correct term "pyrite".

The sentence, "According to the results of heavy metal release characterization of smelting slag, the release of Zn, Pb, and As from lead smelting slag is mainly controlled by the free state content, soluble mineral dissolution, and sulfur-iron mineral dissolution," is somewhat ambiguous. Rephrase for clarity. For example: "The characterization results indicate that the release of Zn, Pb, and As from lead smelting slag is primarily influenced by their free state content and the dissolution of soluble and sulfur-iron minerals."

Response: We reword the sentence to a clearer "The characterization results indicate that the release of Zn, Pb, and As from lead smelting slag is primarily influenced by their free state content and the dissolution of soluble and sulfur-iron minerals.".

The manuscript mentions, "The collected slag was leached with HNO₃ solution," but lacks a detailed description of the slag's characteristics and its origin. Provide more information about the slag samples, including their source, physical properties, and chemical composition. This context is essential for readers to assess the relevance and applicability of the study. Move it from the result section here.

Response: We move information about the origin, physical properties and chemical composition of the original sample within the Supplementary Information to the Manuscript.

The statement, "Based on this, many scholars have conducted a lot of research on the leaching release of heavy metals," lacks supporting references. Incorporate relevant citations to previous studies that have investigated the leaching behavior of heavy metals from similar matrices. This will provide a solid foundation for the current research and acknowledge existing contributions in the field.

Response: We introduced relevant literature and recognized existing contributions in the field.

The authors employed ICP-OES and ICP-MS for heavy metal analysis but did not address potential spectral interferences, especially concerning Fe ions.  Discuss the strategies implemented to mitigate spectral interferences arising from overlapping emission lines and matrix effects. This could include the selection of appropriate analytical wavelengths, utilization of internal standards, or application of mathematical correction methods.

Response: We have added a description of how we eliminate potential spectral interferences to the manuscript, which consists of two sections: ‘Avoiding interfering wavelengths’ and ‘Adding internal standard elements’.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

There is a lot of data in the supplementary file, some of which is very important for the basic understanding of the manuscript (composition of raw waste,…) so I suggest moving this data to the main manuscript.

Some parts of the manuscript are not well understandable for me and contain strange formulations.

There is a lot of interesting information in the manuscript and in the supplementary file, but I cannot recommend publishing this manuscript in this form. My recommendation is major revision.

Below are some specific typos and parts which I don’t understand well.

Page 4 line 133-135 The lead slag was crushed to about 0,15 mm and 15 ml of hydrochloric acid was added to a polytetrafluorethylene crucible with a pretreatment sample weight of 0,2 to 0,5 and heated at low temperature…. 

Was the material sieved?

..pretreatment sample…, Does this mean a crushed sample or was some other procedure performed?

Has this decomposition procedure been tested with any reference material? If open digestion were used, there could by problems with losses of some elements, especially in the case of As.

Heated at low temperature?

 

 Page 4 150-152 the main mineral composition of lead slag is Main minerals in the waste slag…. I don’t understand this formulation

Page 4 line 160 …with high content of Zn, Pb, As, Cu, Cr, Zn, As and Pb… Some elements are twice in here.

Page 4 line 169 the main source of S(II) was Na2S minus stirring and stacking… I don’t understand to formulation „minus stiring“.

Comments on the Quality of English Language

Some parts of the manuscript are not well understandable for me and contain strange formulations. Also there are some typos as I wrote in Comments and Suggestions for Authors.

Author Response

Dear Editor/Referee:

First of all, I would like to thank the reviewers for your patience and valuable suggestions. Here is the author's response to the comments from the reviewers:

Reviewer #2:

There is a lot of data in the supplementary file, some of which is very important for the basic understanding of the manuscript (composition of raw waste,…) so I suggest moving this data to the main manuscript.

Some parts of the manuscript are not well understandable for me and contain strange formulations.

There is a lot of interesting information in the manuscript and in the supplementary file, but I cannot recommend publishing this manuscript in this form. My recommendation is major revision.

Below are some specific typos and parts which I don’t understand well.

Page 4 line 133-135 The lead slag was crushed to about 0,15 mm and 15 ml of hydrochloric acid was added to a polytetrafluorethylene crucible with a pretreatment sample weight of 0,2 to 0,5 and heated at low temperature…. 

Was the material sieved?

..pretreatment sample…, Does this mean a crushed sample or was some other procedure performed?

Has this decomposition procedure been tested with any reference material? If open digestion were used, there could by problems with losses of some elements, especially in the case of As.

Heated at low temperature?

Response: We have added a more detailed description of the pre-treatment steps in the text, as well as specific temperatures for heating. The samples were crushed and sieved ， then heated in a polytetrafluoroethylene crucible after adding 15 ml of hydrochloric acid, which is described in Soil and sediment-Determination of 19 total metal elements -Inductively coupled plasma mass spectrometry (HJ 1315-2023)

 Page 4 150-152 the main mineral composition of lead slag is Main minerals in the waste slag…. I don’t understand this formulation

Response: We have modified the language presentation issue by revising the original sentence to read “The main minerals in the waste slag include silicate minerals such as yellow feldspar, pyroxene, and olivine, sulfide minerals dominated by sulfide iron ore, the carbonate mineral chalcocite, and magnetite and gypsum.”

Page 4 line 160 …with high content of Zn, Pb, As, Cu, Cr, Zn, As and Pb… Some elements are twice in here.

Response: We have modified the presentation problem by deleting the recurring elements.

Page 4 line 169 the main source of S(II) was Na2S minus stirring and stacking… I don’t understand to formulation „minus stiring“.

Response: We have modified the statement presentation problem by amending the original sentence to read “the main source of S(II) was Na2S, mixing well and then stacking for 7 days”.

Comments on the Quality of English Language

Some parts of the manuscript are not well understandable for me and contain strange formulations. Also there are some typos as I wrote in Comments and Suggestions for Authors.

Response: We have checked and corrected the statements and spelling mistakes throughout the text.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

REVIEWER COMMENTS

Reviewer #X (Remarks to the Author):

Toxic heavy metals in non-ferrous metal smelting slag are continuously released and migrated by natural weathering and microbiological activities, causing serious damage to the surrounding ecosystem. The authors achieved synchronous and long-term stabilization of multiple heavy metals such as Zn, Pb, and As in lead smelting slag using a Fe-S(II) stabilizer. The leaching toxicity of Zn, As, and Pb was all below the concentration limits for Class III water bodies as specified in the "Environmental Quality Standards for Surface Water" (GB3838-2002). Additionally, the authors proposed a stabilization mechanism centered on Fe⁰, termed " nucleation-capture-sulfide encapsulation," which is an interesting phenomenon and explains the stabilization mechanism of the stabilizer on heavy metals. However, there are some minor issues that need further refinement. Therefore, I recommend its publication in Sustainability after minor revisions.

Some specific comments are below:

1. The authors emphasize in the article that heavy metal passivation is achieved through a "microencapsulated passivation" method, creating a core-shell structure encapsulated with sulfur. While some XRD and XPS characterizations in the text can preliminarily infer this structure, there is no more direct evidence. It is recommended that the authors use TEM characterization to directly observe this core-shell structure.
2. In the article, the authors confirm the excellent heavy metal stabilization effect through a 14-day leaching experiment. However, in real environments, passivated materials are often affected by changes in environmental pH, leading to the re-release of heavy metals into the environment, especially in areas with acid rain. Therefore, it is suggested that the authors further study the stability of the material after heavy metal passivation under different pH conditions, making the material's application more relevant to real-world environments.
3. Some subscripts and superscripts in the text are not correctly labeled, such as Pb2+ and Fe3+ in line 226. The authors need to further check and correct these.
4. The reference citation numbers should all be changed to superscripts.

Comments on the Quality of English Language

English is of good quality but can be improved.

Author Response

Dear Editor/Referee:

First of all, I would like to thank the reviewers for your patience and valuable suggestions. Here is the author's response to the comments from the reviewers:

Reviewer #3:

Toxic heavy metals in non-ferrous metal smelting slag are continuously released and migrated by natural weathering and microbiological activities, causing serious damage to the surrounding ecosystem. The authors achieved synchronous and long-term stabilization of multiple heavy metals such as Zn, Pb, and As in lead smelting slag using a Fe-S(II) stabilizer. The leaching toxicity of Zn, As, and Pb was all below the concentration limits for Class III water bodies as specified in the "Environmental Quality Standards for Surface Water" (GB3838-2002). Additionally, the authors proposed a stabilization mechanism centered on Fe0, termed " nucleation-capture-sulfide encapsulation," which is an interesting phenomenon and explains the stabilization mechanism of the stabilizer on heavy metals. However, there are some minor issues that need further refinement. Therefore, I recommend its publication in Sustainability after minor revisions.

Some specific comments are below:

1.The authors emphasize in the article that heavy metal passivation is achieved through a "microencapsulated passivation" method, creating a core-shell structure encapsulated with sulfur. While some XRD and XPS characterizations in the text can preliminarily infer this structure, there is no more direct evidence. It is recommended that the authors use TEM characterization to directly observe this core-shell structure.

Response: We added TEM characterization and observed the corresponding core-shell structure. We add the corresponding image and text description on page 12, line 55 in the manuscript“To further investigate the microscopic morphology and encapsulation characteristics of iron sulfide……”. 

2.In the article, the authors confirm the excellent heavy metal stabilization effect through a 14-day leaching experiment. However, in real environments, passivated materials are often affected by changes in environmental pH, leading to the re-release of heavy metals into the environment, especially in areas with acid rain. Therefore, it is suggested that the authors further study the stability of the material after heavy metal passivation under different pH conditions, making the material's application more relevant to real-world environments.

Response: The text describes the change in pH during the stabilization process. We have incorporated the stability of the material under varying pH conditions as required. The primary data and descriptions are provided in the supplementary information, and relevant indications have been added at the appropriate positions in the text (page 29, line 391).

3.Some subscripts and superscripts in the text are not correctly labeled, such as Pb2+ and Fe3+ in line 226. The authors need to further check and correct these.

Response: We change the chemical formula to the correct subscript format.

4.The reference citation numbers should all be changed to superscripts.

Response: We have changed the citation numbering of references should all be superscripted.

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

Interesting work is introduced in the manuscript, especially for the treatment of heavy metals-rich slag with the addition of Fe/S. Some comments are as follows.

1. The leaching toxicity of solid waste has the corresponding standard issued by the government, not the Class III water bodies. Additionally, the toxicity analysis method should be according to that in the standard.
2. Many good data and figures are shown in the supplementary files and should move to the manuscript.
3. Actually, the slag treatment by adding Fe/S is also interesting, even though without the toxicity assessment. If possible, the related toxicity analysis can be removed from the manuscript and then placed in a new manuscript.

Other comments

1. Title should be revised to make it more scientific.
2. Affiliation should be accorded to the journal requirement, alongside the corresponding author information.
3. Important data should be added to the abstract to emphasize its highlight.
4. what is the mean of (II) sulfide in the abstract? The mechanic analysis in the abstract should be reorganized. Many spill mistakes are in the manuscript. Please show the journal the respect it deserves.
5. Keywords should be revised according to the journal requirement.
6. Some figures are not clear in the manuscript.

Author Response

Dear Editor/Referee:

First of all, I would like to thank the reviewers for your patience and valuable suggestions. Here is the author's response to the comments from the reviewers:

Reviewer #4:

Interesting work is introduced in the manuscript, especially for the treatment of heavy metals-rich slag with the addition of Fe/S. Some comments are as follows.

1.The leaching toxicity of solid waste has the corresponding standard issued by the government, not the Class III water bodies. Additionally, the toxicity analysis method should be according to that in the standard.

Response: Reference was made to Identification standards for hazardous wastes-Identification for extraction toxicity (GB5085.3-2007) for toxicity analysis, and the reference to Class III water bodies in the original text was changed to leaching toxicity standards for this solid waste.

2.Many good data and figures are shown in the supplementary files and should move to the manuscript.

Response: Transfer the source of the original sample and the data analyzed for the primary physical properties and chemical composition from the supplementary information to page 4, line 114 of the main manuscript.

3.Actually, the slag treatment by adding Fe/S is also interesting, even though without the toxicity assessment. If possible, the related toxicity analysis can be removed from the manuscript and then placed in a new manuscript.

Response: Thank you very much for the reviewer's suggestion. However, in this article, the toxicity assessment and the heavy metal passivation material are inherently linked; therefore, we would like to retain the toxicity analysis to enhance the completeness of our work.

Other comments

1.Title should be revised to make it more scientific.

Response: Modify the article title to read “Microencapsulation-Based Passivation of Zn, Pb, and As Contaminants in Lead Smelting Slag Using Fe-S(II) System”

2.Affiliation should be accorded to the journal requirement, alongside the corresponding author information.

Response: Improved unit information and added corresponding author information to the home page.

3.Important data should be added to the abstract to emphasize its highlight.

Response: We add the data “the leaching toxicity of Zn, As and Pb is less than 1mg/L, which is lower than the concentration limit of the Identification standards for hazardous wastes-Identification for extraction toxicity (GB5085.3-2007).” to the abstract to highlight the article highlights.

4.what is the mean of (II) sulfide in the abstract? The mechanic analysis in the abstract should be reorganized. Many spill mistakes are in the manuscript. Please show the journal the respect it deserves.

Response: We have addressed the issue regarding the phrase ‘(II) sulfide’ in the abstract and conducted a thorough review of the entire text to identify and rectify any phrasing or spelling errors.

5.Keywords should be revised according to the journal requirement.

Response: We've changed the keyword to “microencapsulated passivation; lead refining slag; simultaneous multi-metal passivation; long-term stabilization” to make it more journal-compliant.

6.Some figures are not clear in the manuscript.

Response: Enhanced clarity of diagrams in manuscripts

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

All my previous questions and comments have been sufficiently incorporated into the manuscript. The manuscript is now clear and my recommendation is to accept the manuscript in present form.

Reviewer 3 Report

Comments and Suggestions for Authors

Accept.