Sustainable Chromium Remediation: Sorption of Chromium from Leaching Solutions of Refined

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

As one of environmental problems, cadmium pollution is critical and has attracted people's attention. In this manuscript, the adsorption capacity of natural zeolite to chromium from leaching solutions of refined ferrochrome slag was studied. This idea seemed to make sense, but the authors' work needed further refinement before it can be considered for publication. Some corrections need to be made listed as follows:

1. How was the concentration range of sulfuric acid used in the experiment determined? The sulphuric acid concentration range mentioned in the manuscript was 5%to 95%, but there is no detail on why this range was chosen. Is it based on previous experimental results or experience in other literature?
2. In the experiment, why choose 35°C as the temperature of adsorption experiment? The manuscript statedthat the adsorption efficiency was highest at 35°C, but did not explain why 35°C was the optimal temperature. Is it related to the physical and chemical properties of zeolite?
3. Was the influence of other impurity ions in sulfuric acid leaching solution on chromium adsorption considered in the experiment? The manuscript mainly focusedon the adsorption of chromium, but the actual leaching solution may contain other impurity ions. Did these ions affect the adsorption efficiency of chromium by zeolite?
4. Was the natural zeolite used in the experiment pretreated? Was the natural zeolite washed, activated or otherwise pretreated before the experiment? Didpretreatment affect its adsorption properties?
5. Why was the extraction efficiency of chromium the highest at low concentration of sulfuric acid (23%)? The manuscript showedthat the leaching efficiency of chromium was the highest (16.67%) at 23% sulfuric acid concentration. Is it related to the influence of sulfuric acid concentration on leaching kinetics?
6. In the adsorption experiment, why the adsorption capacity of zeolite didnot increase at high chromium concentration? The manuscript showed that when the chromium concentration increased from 50 mg/L to 98 mg/L, the adsorption capacity no longer increased Is this related to the saturation of the adsorption site of zeolite?
7. In X-ray diffraction analysis, was the change of pore structure of zeolite after adsorption related to the amount of chromium and sulfur adsorbed? It was mentioned that the pore structure of zeolite after adsorption has changed. Can the amount of chromium and sulfur adsorbed be evaluated by quantitative analysis of pore changes?
8. In the adsorption experiment, why didthe adsorption efficiency of chromium begin to decline after the adsorption time exceeded 30 min? The manuscript pointed out that after the adsorption time exceeded 30 minutes, the adsorption efficiency of chromium began to decline. Is this related to saturation of adsorption sites on the zeolite surface or desorption of chromium?
9. In practical industrial applications, how to treat the adsorbed zeolite to achieve its regeneration and reuse? This manuscript mainly studiedthe adsorption properties of zeolite, but did not mention how to treat the adsorbed zeolite. Is it possible to regenerate zeolite by thermal desorption or other methods?
10. Can the adsorption process mentioned in the manuscript be extended to the removal of other heavy metal ions? This manuscript mainly studiedthe adsorption of chromium, but can zeolite be used to remove other heavy metal ions (such as lead, cadmium, etc.)? Does it need to adjust the experimental conditions?
11. The number of references is not sufficient, and the latest literature published after 2023 are few.
12. There are some grammatical and typographical errors in the manuscript.

Comments on the Quality of English Language

It is suggested that the author polish the manuscript again to express clearly and accurately.

Author Response

Response to Reviewers

Dear Reviewers,

Thank you for your valuable comments and thorough review of our manuscript. We have carefully addressed all your concerns and made the necessary revisions to improve the quality of the article. Below, we provide detailed responses to each of your comments and explain the changes made to the manuscript.

General Response:

We have incorporated the data from the mathematical modeling of the three-factor experiment and replaced the figure with a more comprehensive one to better illustrate the process. Due to space constraints, we have selected the most relevant data to include in the article. We have also answered all the questions and supplemented the article with additional information, which has significantly enhanced its overall quality. We hope that these revisions meet your expectations.

In the revised manuscript:

Blue text indicates previously mentioned content that has been addressed in the responses to reviewers.

Green text highlights entirely new additions.

Red text marks sections that have been deleted.

New references and corrections have been added where necessary.

 

Review 1

As one of environmental problems, cadmium pollution is critical and has attracted people's attention. In this manuscript, the adsorption capacity of natural zeolite to chromium from leaching solutions of refined ferro chrome slag was studied. This idea seemed tomake sense, but the authors' work needed further refinement before it can be considered for publication. Some corrections need to be made listed as follows:

 

1. Comments 1: How was the concentration range of sulfuricacid used in the experiment determined? The sulphuric acid concentration range mentioned in the manuscript was 5% to 95%, but there is nodetail on why this range was chosen. Is it based on previous experimental results or experience in other literature?

 

Responce 1: Since from the title of our article and the purpose of the work was the study of sorption of chromium cations from leaching solutions of refined ferrochrome, In the article, more attention was paid to this and we did not introduce more detailed data on the study of leaching process according to the factors studied.

You have correctly noticed that this data is not sufficient. We have completed it. We hope that you will be satisfied with these changes in the article.

 

 

 

2. Comments 2. In the experiment, why choose 35°C as the temperature of adsorption experiment? The manuscript statedthat the adsorption efficiency was highest at 35°C, but did not explain why 35°C was the optimal temperature. Is it related to the physical and chemical properties of zeolite?

 

Responce 2 : The study of the effect of natural zeolite consumption on the degree of purification of a chromium-containing sulfate solution was carried out at a temperature of 35 ° C because of preliminary studies on the effect of temperature (from 22 to 60 ° C.) on chromium sorption with zeolite showed the inexpediency of the process at high temperatures.

 

 

3. Comments 3: Was the influence of other impurity ions in sulfuric acid leaching solution on chromium adsorption considered in the experiment? The manuscript mainly focusedon the adsorption of chromium, but the actual leaching solution may contain other impurity ions. Did these ions affect the adsorption efficiency of chromium by zeolite?

 

Responce 3: This paper did not consider the influence of other impurities ions in the sulphuric acid leaching solution on chromium adsorption, since the aim of the work was to study the sorption of chromium, the most toxic element. It is not excluded that naturally man-made wastes of ferrochrome production contain not only chromium, as shown in the study of PCF composition. We are planning to continue working in this way, but until then we would like to publish the available data that is interesting enough.

 

 

 

4. Comments 4: Was the natural zeolite used in the experiment pretreated? Was the natural zeolite washed, activated or otherwise pretreated before the experiment? Didpretreatment affect its adsorption properties?

 

Responce 4: Natural zeolite was used in the experiment without pretreatment. Assuming that the zeolite of the Shankanai deposit has higher values of Si/ Al ratio and sorption capacity, and is also more represented by acid-resistant polythelium, It was assumed that the Shankanai zeolite would have a high sorption capacity in relation to chromium cations not only in aquatic media, but also in aggressive (acid) environments. The prospect of using available natural zeolites in sorption processes of purification is also the possibility of recycling used zeolites as soil melts, building materials, fillers, etc. Such application of natural zeolites is based on the content in the species of climatolyte and their physico-chemical properties. (Inserted in the introduction of the article).

 

5. Comments 5: Why was the extraction efficiency of chromium the highest at low concentration of sulfuric acid (23%)? The manuscript showedthat the leaching efficiency of chromium was the highest (16.67%) at 23% sulfuric acid concentration. Is it related to the influence of sulfuric acid concentration on leaching kinetics?

 

Responce 5:During acidic leaching of chromium-containing sludge, the best result was obtained for a solution of sulfuric acid with a concentration of 23%. This is really related to the concentration of sulfuric acid, since at a high concentration of sulfuric acid, passivation of the material occurs.

With the increase of sulphuric acid concentration to 95% chromium content in solution decreases at 22^oC. In the case of longer contact of refined ferrochrome with sulphuric acid (95-180 minutes) chromium content is drastically reduced. The reduction of chromium content in sulfuric acid under these conditions is really possible due to passivation of the material. It is known that the degree of chromium passivation is very high and is 1.94. In the Chemistry Handbook (Chemistry Handbook 21 at chem21.info link. P.191; 364; 349). As stated in the manual, Chromium does not dissolve in concentrated sulphuric acid by oxide film hardening, i.e. chromium becomes passive (P. 197). That is, the concentrated solution H₂SO₄ passes the smallest amount of chromium. The sulphuric acid concentration under these conditions has no significant effect on chromium leaching. The leaching curves of RFC at temperatures up to 56^oC are different.(Inserted in the text of the article)

 

 

6. Comments 6: Why was the extraction efficiency of chromium the highest at low concentration of sulfuric acid (23%)? The manuscript showedthat the leaching efficiency of chromium was the highest (16.67%) at 23% sulfuric acid concentration. Is it related to the influence of sulfuric acid concentration on leaching kinetics?

 

Responce 6: Yes, this is true, with a high concentration of chromium, the sorption capacity of zeolite does not increase, which is due to saturation of the adsorption site of the zeolite (inserted in the text)

 

7. Comments 7: Why was the extraction efficiency of chromium the highest at low concentration of sulfuric acid (23%)? The manuscript showedthat the leaching efficiency of chromium was the highest (16.67%) at 23% sulfuric acid concentration. Is it related to the influence of sulfuric acid concentration on leaching kinetics?

 

Responce 7: Yes, it is possible to estimate the amount of adsorbed chromium and sulfur by

quantitative analysis of pore changes. This method is based on the fact that the adsorption of molecules on the surface of a material can change its pore structure. In future studies, we will definitely look at the sorption of other cations, as well as apply the BET method, which will  allow us to assess the surface and volume of pores, as well as estimate the amount of  adsorbed substances, including chromium, sulfur and other ions.

 

8. Comments 8: In the adsorption experiment, why didthe adsorption efficiency of chromium begin to decline after the adsorption time exceeded 30 min? The manuscript pointed out that after the adsorption time exceeded 30 minutes, the adsorption efficiency of chromium began to decline. Is this related to saturation of adsorption sites on the zeolite surface or desorption of chromium?

 

Responce 8:Yes, this is related to desorption of chromium, it was noted in manuscript by blue color.  “Further increasing the process time initiates the process of chromium desorption, i.e., its transition from zeolite back into the solution”.( line337)

 

9. Comments 9: In practical industrial applications, how to treat the adsorbed zeolite to achieve its regeneration and reuse? This manuscript mainly studiedthe adsorption properties of zeolite, but did not mention how to treat the adsorbed zeolite. Is it possible to regenerate zeolite by thermal desorption or other methods?

 

Responce 9: The reuse of zeolite is possible until it is more completely saturated with chromium. The prospects of using natural zeolites in sorption purification processes also lie in the fact that zeolite can be regenerated and reused several times, and in the possibility of recycling already spent zeolites as soil ameliorants, building materials, fillers, etc. [30, 31], which significantly increases the economic efficiency of sorption purification.(Line 140)

 

10. Comments 10: In practical industrial applications, how to treat the adsorbed zeolite to achieve its regeneration and reuse? This manuscript mainly studiedthe adsorption properties of zeolite, but did not mention how to treat the adsorbed zeolite. Is it possible to regenerate zeolite by thermal desorption or other methods?

 

Responce 10: Metal-containing sulfuric acid in the presence of impurity cations is purified by (63.6-69.0) % of chromium. It is possible that zeolite simultaneously sorbs other heavy metal ions present in the solution being cleaned. However, as noted in the article, "Technogenic waste from ferrochrome production contains chromium, which is one of the most toxic components of industrial waste. Chromium and its compounds are highly toxic and carcinogenic, poison water and soil, and negatively affect the functioning of all living organisms.,(Line 47)" therefore, the purpose of this study was to study the chemical and mineralogical composition of slags from the Aktobe Ferroalloy plant obtained by sulfuric acid leaching, the process of sorption of cationic hydrocarbons from a chromium-containing sulfuric acid solution by Shankanai zeolite. Of course, natural zeolite can be used to remove other heavy metal ions (such as lead, cadmium... etc.), and such work is available. And it will be the goal of further research.

 

1. Comments 11: The number of references is not sufficient, and the latest literature published after 2023 are few.

Responce 11:The list of references has been updated and new links have been added

 

12. Comments 12: There are some grammatical and typographical errors in the manuscript.

 

Responce 12:Thank you for your comments, we tried to correct grammatical and typographical errors and answer your questions and comments.

 

Thank you for your comments and review. We tried to answer all the questions and supplement the article with the missing information, which really improved it a lot in general. I hope you will be satisfied with the answers.

Reviewer 2 Report

Comments and Suggestions for Authors

The study investigates chromium pollution by analyzing refined ferrochrome (RFC) slag, its leaching with sulfuric acid, and chromium adsorption onto natural zeolite. X-ray analysis identifies olivine (50.7% Ca₂SiO₄) as the dominant phase in RFC slag. Optimal chromium leaching (18.0–18.5%) occurs in 23% H₂SO₄ at 90°C over 145–180 minutes, forming CrSO₄•5H₂O. Zeolite achieves 63.6–69.0% chromium removal at a 1:10 ratio within 15 minutes at 35°C, with X-ray diffraction confirming structural changes due to chromium and sulfur adsorption. The findings highlight zeolite as an efficient, cost-effective adsorbent for chromium remediation. However, there are some major concerns to be considered: 

1- Novelty of the Study should be clarified.

2- Mechanism of the Removal Process should be included. More insights into the dominant mechanism, whether electrostatic interactions, ligand exchange, ion exchange, or precipitation, should be provided. Furthermore, the role of pH in influencing the adsorption mechanism should be clarified.

3- Comparison with other adsorbents such as activated carbon, biochar, or synthetic materials is missing. Including adsorption capacity, removal efficiency, and cost-benefit analyses would provide a more comprehensive understanding of the effectiveness of zeolite relative to other materials.

4- The study should investigate the selectivity of zeolite toward chromium ions in the presence of competing ions. Conducting batch adsorption experiments with mixed-metal solutions would add significant value to understanding the real-world application of zeolite in wastewater treatment.

5- BET surface area, pore volume, and pore size distribution should be included in the manuscript. These parameters are crucial in understanding the adsorption performance and scalability of the zeolite adsorbent.

6- The study lacks statistical validation of the experimental data. Standard deviations, error bars, and statistical significance testing should be incorporated to enhance the reliability and reproducibility of the findings.

7- The manuscript contains several grammatical and syntactical errors. A thorough revision by a native English speaker or a professional proofreader is recommended. Certain technical descriptions should be refined for better scientific communication and readability.

Comments on the Quality of English Language

7- The manuscript contains several grammatical and syntactical errors. A thorough revision by a native English speaker or a professional proofreader is recommended. Certain technical descriptions should be refined for better scientific communication and readability.

Author Response

• Comments 1: Novelty of the Study should be clarified.

Responce 1: For the first time, the process of chromium sorption by Shankanai zeolite from a sulfuric acid solution obtained after leaching ferrochrome slag was studied, and the influence of the main technological parameters of the process on the degree of its purification was established.

 

• Comments 2: Mechanism of the Removal Process should be included. More insights into the dominant mechanism, whether electrostatic interactions, ligand exchange, ion exchange, or precipitation, should be provided. Furthermore, the role of pH in influencing the adsorption mechanism should be clarified.

Responce 2: The acidity of the solution or pH affects the properties of the adsorbent and the adsorbed substance and their interaction with each other. When pH changes, the degree of ion exchange can change, which affects the efficiency of the adsorption process. In our case, zeolite is effective in a weakly acidic sulfuric acid solution. We have included information about the dominant mechanism in the article. Chromium sorption by natural zeolite occurs mainly through ion exchange and adsorption on the surface. For example, in the case of chromium(III), its cations can replace cations (for example, calcium or magnesium) present in zeolite at exchange centers. In the case of chromium(VI), in dissolved forms (for example, in the form of chromates), its anions can bind to cations in zeolite structures.

 

• Comments 3: Comparison with other adsorbents such as activated carbon, biochar, or synthetic materials is missing. Including adsorption capacity, removal efficiency, and cost-benefit analyses would provide a more comprehensive understanding of the effectiveness of zeolite relative to other materials.

Responce 3: Zeolite, unlike other adsorbents (activated carbon, bentonite, glauconite, biocoal, etc.), has a microporous crystalline structure and unique adsorption and ion-exchange properties, high porosity and thermal stability, as well as resistance in aggressive environments.

 

• Comments 4: The study should investigate the selectivity of zeolite toward chromium ions in the presence of competing ions. Conducting batch adsorption experiments with mixed-metal solutions would add significant value to understanding the real-world application of zeolite in wastewater treatment.

Responce 4: This paper did not consider the influence of other impurities ions in the sulphuric acid leaching solution on chromium adsorption, since the aim of the work was to study the sorption of chromium, the most toxic element. It is not excluded that naturally man-made wastes of ferrochrome production contain not only chromium, as shown in the study of PCF composition. We are planning to continue working in this way, but until then we would like to publish the available data that is interesting enough.

 

• Comments 5: BET surface area, pore volume, and pore size distribution should be included in the manuscript. These parameters are crucial in understanding the adsorption performance and scalability of the zeolite adsorbent.

 Responce 5: In future studies, we will definitely look at the sorption of other cations, as well as apply the BET method, which will allow us to assess the surface and volume of pores, as well as estimate the amount of adsorbed substances, including chromium, sulfur and other ions.

 

• Comments 6: The study lacks statistical validation of the experimental data. Standard deviations, error bars, and statistical significance testing should be incorporated to enhance the reliability and reproducibility of the findings.

Responce 6: To establish a complex relationship and quantitative assessment of the experiment, the method of mathematical planning of an orthogonal rototable 3-factor experiment of the 2nd order was used, the results of which were not included initially, we supplemented the article.

 

7- Comments 7: The manuscript contains several grammatical and syntactical errors. A thorough revision by a native English speaker or a professional proofreader is recommended. Certain technical descriptions should be refined for better scientific communication and readability.

 

Corrected

 

Thank you for your comments and review. We tried to answer all the questions and supplement the article with the missing information, which really improved it a lot in general. I hope you will be satisfied with the answers.

Reviewer 3 Report

Comments and Suggestions for Authors

This manuscript investigates the sorption of chromium from refined ferrochrome (RFC) slag leachate using natural zeolite, focusing on optimizing leaching conditions and sorption efficiency. The study is highly relevant to environmental remediation and industrial waste management, offering practical insights into chromium removal. However, the manuscript presents several methodological and analytical shortcomings. In view of this, major revisions are required to improve methodological robustness, strengthen data interpretation, and provide a more comprehensive discussion of the sorption mechanisms and industrial applicability.

1. The abstract lacks quantitative details on key findings (e.g., chromium removal efficiency, optimal conditions). Add specific numerical results to enhance clarity and impact. The study’s novelty is not well-articulated. Clearly state how this research advances existing knowledge in chromium removal using natural zeolites.
2. Introduction: The choice of zeolite as an adsorbent is not justified thoroughly. Provide a more detailed rationale for selecting natural zeolite over other materials (e.g., activated carbon, bentonite).
3. The research gap is not clearly defined. Explicitly state what limitations in existing chromium removal methods this study aims to address.
4. The paper(Generalized solutions for advection- dispersion transport equations subject to time- and space-dependent internal and boundary sources) should be referenced in the Introduction when discussing chromium transport in leachates, particularly in the context of fluid flow, contaminant dispersion, and mass transfer processes in industrial waste treatment. Including this reference will align the study with well-established modeling approaches, strengthening its theoretical framework and improving the scientific rigor of the discussion on leaching mechanisms.
5. The method description does not discuss the control of key parameters such as stirring rate, solid-liquid ratio, and acid consumption efficiency. Provide more details to improve reproducibility.
6. This paper(Mechanical characteristics and solidification mechanism of slag/fly ash-based geopolymer and cement solidified organic clay: A comparative study) should be referenced in the Experimental Methods section when describing material characterization techniques, adsorption testing, and mechanical stability evaluations of treated waste products.
7. The discussion does not explore key mechanisms such as ion exchange, electrostatic attraction, or surface complexation. These should be analyzed in light of characterization data.  
8. Industrial wastewater typically contains multiple metal ions. The study does not assess whether the presence of Fe³⁺, Cu²⁺, or other ions affects chromium sorption. Consider adding experiments or discussing potential competition effects.
9. No mention is made of study limitations or potential future research directions. Include a discussion of methodological constraints and areas that require further investigation, such as long-term adsorption stability and pilot-scale testing.
10. The reference list lacks recent studies on advanced chromium removal technologies. Update the literature review to include recent developments in adsorption-based chromium remediation.

Author Response

Reviewer 3

This manuscript investigates the sorption of chromium from refined ferrochrome (RFC) slag leachate using natural zeolite, focusing on optimizing leaching conditions and sorption efficiency. The study is highly relevant to environmental remediation and industrial waste management, offering practical insights into chromium removal. However, the manuscript presents several methodological and analytical short comings. Inview ofthis, majör revisions are required to improve methodological robustness, strengthen data interpretation, and provide a more comprehensive discussion of the sorption mechanisms and industrial applicability.

1. Comments 1. The abstract lacks quantitative details on key findings (e.g., chromium removal efficiency, optimal conditions). Add specific numerical results to enhance clarity and impact. The study’s novelty is not well-articulated. Clearly state how this research advances existing knowledge in chromium removal using natural zeolites.

 

 

Responce 1:The abstract has been corrected.

 

 

2. Comments 2: Introduction: The choice of zeolite as an adsorbent is not justified thoroughly. Provide a more detailed rationale for selecting natural zeolite over other materials (e.g., activated carbon, bentonite).

 

 

Responce 2: The prospect of using natural zeolites in sorption processes of purification is also in             

the possibility of recycling used zeolites as soil meliorants, building materials, fillers, etc. [30,

              31]. This application of natural zeolites is based on the content in the species of clinoptilolite 

and their physical-chemical properties. Since the zeolite from the Shankanai deposit has a

higher Si/Al ratio and sorption capacity, and is also more represented by clinoptilolite than

theTaizhuzgen zeolite and is acid-resistant. It can be expected that the Shankanai zeolite will

have a high sorption capacity with respect to chromium cations only in aqueous

environments, but also in aggressive (acidic) environments.

 

 

3. Comments 3: The research gap is not clearly defined. Explicitly state what limitations in existing chromium removal methods this study aims to address.

 

 

Responce 3: There is no information in the scientific literature on the sorption of chromium cations in mineral acids. Currently, the need for domestic competitive, low-cost solid inorganic sorbents capable of effectively purifying various media has increased significantly. When choosing a sorption material, it is necessary to take into account the stability of the sorbent (chemical, mechanical, radiation), as well as factors such as the ease of obtaining the sorbent, availability and cost. In addition, it is necessary to take into account the possibility of further processing or long-term storage of sorption material.

 

4. Comments 4: The paper(Generalized solutions for advection- dispersion transport equations subject to time- and space-dependent internal and boundary sources) should be referenced in the Introduction when discussing chromium transport in leachates, particularly in the context of fluid flow, contaminant dispersion, and mass transfer processes in industrial waste treatment. Including this reference will align the study with well-established modeling approaches, strengthening its theoretical framework and improving the scientific rigor of the discussion on leaching mechanisms.

 

 

Responce 4:The literature you suggested is not very suitable for our topic, but we have replaced it with another one. The link was inserted.

Bao Liu, Junguo Li,  Ziming Wang,  Yanan Zeng ,  Qianqian Ren. Long-term leaching

characterization and geochemical modeling of chromium released from AOD slag,J.Environ

Sci and Pollut Res.2020, 27, 921–929, doi:10.1007/s11356-019-07008-7

 

 

5. The method description does not discuss the control of key parameters such as stirring rate, solid-liquid ratio, and acid consumption efficiency. Provide more details to improve reproducibility.

 

Responce 5:The method description provided more details to improve reproducibility.

 

6. Comments 6: This paper(Mechanical characteristics and solidification mechanism of slag/fly ash-based geopolymer and cement solidified organic clay: A comparative study) should be referenced in the Experimental Methods section when describing material characterization techniques, adsorption testing, and mechanical stability evaluations of treated waste products.

 

 

Responce 6:we have included this paper at reference

 

1. Comments 7: The discussion does not explore key mechanisms such as ion exchange, electrostatic attraction, or surface complexation. These should be analyzed in light of characterization data.

 

Responce 7:Chromium sorption by natural zeolite occurs mainly through ion exchange and

adsorption on the surface. For example, in the case of chromium(III), its cations can replace

cations (for example, calcium or magnesium) present in zeolite at exchange centers. In the

case of chromium(VI), in dissolved forms (for example, in the form of chromates), its anions

can bind to cations in zeolite structures (added).

 

8. Comments 8: Industrial wastewater typically contains multiple metal ions. The study does not assess whether the presence of Fe³⁺, Cu²⁺, or other ions affects chromium sorption. Consider adding experiments or discussing potential competition effects.

 

Responce 8:It is possible that zeolite along the way also sorbs other cations, impurities present in the solution being cleaned. This allows the purified sulfuric acid to be returned to the leaching stage, which increases the profitability of this process.

Metal-containing sulfuric acid in the presence of impurity cations is purified by (63.6-69.0) % of chromium. It is possible that zeolite simultaneously sorbs other heavy metal ions present in the solution being cleaned. However, as noted in the article, "Technogenic waste from ferrochrome production contains chromium, which is one of the most toxic components of industrial waste. Chromium and its compounds are highly toxic and carcinogenic, poison water and soil, and negatively affect the functioning of all living organisms.," therefore, the purpose of this study was to study the chemical and mineralogical composition of slags from the Aktobe Ferroalloy plant obtained by sulfuric acid leaching, the process of sorption of cationic hydrocarbons from a chromium-containing sulfuric acid solution by Shankanai zeolite.

Of course, natural zeolite can be used to remove other heavy metal ions (such as lead, cadmium... etc.), and such work is available. And this will be the goal of further research.

 

 

9. Comments 9: No mention is made of study limitations or potential future research directions. Include a discussion of methodological constraints and areas that require further investigation, such as long-term adsorption stability and pilot-scale testing.

 

 

Responce 9:Based on the sorption properties of Shangkanai zeolite, it can be expected that

water containing only chromium cations will be the most effective sorbent in relation to them.

The purified rinsing water is returned to the process to wash the next batch of cake. In this

case, it is possible to reuse the zeolite until it is more completely saturated with chromium

(added).No pilot-scal tests were conducted.

 

10. Comments 10: The reference list lacks recent studies on advanced chromium removal technologies. Update the literature review to include recent developments in adsorption-based chromium remediation.

 

Responce 10: The list of references has been updated and new links have been added.

 

 

Thank you for your comments and review. We tried to answer all the questions and supplement the article with the missing information, which really improved it a lot in general. I hope you will be satisfied with the answers

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The author had revised the manuscript according to the comments, I'm basically satisfied with the corrections. And I recommended this work can be accepted.

Reviewer 2 Report

Comments and Suggestions for Authors

 Accept in present form

Comments on the Quality of English Language

 Accept in present form

Reviewer 3 Report

Comments and Suggestions for Authors

It can be accepted for publication in its current form.