Stabilization of As and Heavy Metal-Contaminated Soils by Two Mine Drainage-Treated Sludges

Round 1

Reviewer 1 Report

The study is generally well-formatted and written, but it needs a minor revision of the language.

The title needs to be reformulated to be brief and commensurate with the aim of the study.

The introduction needs to make comparisons with similar studies.

The conclusion needs to be reformulated and highlight some important results.

Author Response

Dear Reviewer #1:

Answer: Thank you for your affirmation of our research. Authors discussed about your suggestions and made serious amendments carefully. Revised and added portion are colored in red in the revised manuscript and the point to point responds to the reviewer’s comments are listed as below.

 

General comment: The study is generally well-formatted and written, but it needs a minor revision of the language.

Question 1: The title needs to be reformulated to be brief and commensurate with the aim of the study.

Answer 1: As the reviewer’s suggestion, title was revised from “Soil stabilization for arsenic and heavy metals by using two mine drainage treated sludges” to “Stabilization of As and heavy metal contaminated soils by two mine drainage treated sludges”.

 

Question 2: The introduction needs to make comparisons with similar studies.

Answer 2: As the reviewer’s request, four more references related similar studies and the description of their results were added in the manuscript. Please, see the reference list and line 53, 57-59, and 75-77 on page 2 .      

(7) Daraz U.; Li, Y.; Ahmad, I.; Iqbal, R.; Ditta, A. Remediation technologies for acid mine drainage: Recent trends and future perspectives. Chemosphere 2023, 311, 137089. https://doi.org/10.1016/j.chemosphere.2022.137089

(11) Elghali, A.; Benzaazoua, M.; Bouzahzah, H.; Bussière, B. Laboratory study on the effectiveness of limestone and cementitious industrial products for acid mine drainage remediation. Minerals 2021, 11(413), 1-19. https://doi.org/10.3390/min11040413

(12) Elghali, A.; Benzaazoua, M.; Bussière, B.; Genty, T. In Situ Effectiveness of Alkaline and Cementitious Amendments to Stabilize Oxidized Acid-Generating Tailings. Minerals 2019, 9(314), 1-20. https://doi.org/10.3390/min9050314

(27) Elghali, A.; Benzaazoua, M.; Couvidat, J.; Barricau, L.; Neculita, C.M.; Chatain, V., Low Carbon Stabilization and Solidification of Hazardous Wastes. In Chap. 7 – Stabilization/solidification of sediments: challenges and novelties. Elsevier Inc., 2022. https://doi.org/10.1016/B978-0-12-824004-5.00023-2

 Question 3: The conclusion needs to be reformulated and highlight some important results.

Answer 3: According to reviewer’s suggestion, “Conclusion” section was revised by authors and the native to emphasize the originality and the novelty of this study (See “Conclusion” section).

“ This study supported the quantitative evaluation of the stabilization effect of AMDS on soil with various pollution scenarios and presented information about the major stabilization mechanisms by which As and heavy metals in soil are stabilized by AMDS.”

“ There can be a great difference in the stabilization efficiency of AMDSs due to different soil properties and the adequate stabilizer should be selected for the specific site. This study was focused on presenting the very high stabilization efficiency of AMDS for various soils having different pollution scenarios and different physico-chemical properties. The overall stabilization efficiency of two AMDSs for heavy metals and As were higher than 75% and 85% (mostly > 90%) with the addition of more than 3% of AMD, respectively, regardless of soil and metal type.”  …etc. 

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Reviewer 2 Report

-  It is necessary to adjust elements in table 3;

- Put the degree symbol in C, in the sentences of lines 288, 290, 292,...

 

Interesting article, topic with relevance to science. It presents the appropriate methods, however in terms of writing and projecting the results it is not the best. deserves to be better written, in terms of English.
The title is confusing, however I think with slight improvements it should be accepted.

Author Response

Dear Reviewer:

Thanks for your comments. Following your suggestion, authors have studied the valuable comments carefully and have made correction which we hope meet with your approval.  Revised and added portion are colored in red in the revised manuscript and the point to point responds to the reviewer’s comments are listed as below.

 Question 1: It is necessary to adjust elements in table 3;

Answer 1: Table 3 was adjusted as the reviewer’s request.

 Question 2: Put the degree symbol in C, in the sentences of lines 288, 290, 292,...

Answer 2: As the reviewer’s request, the degree symbol in C was modified with the normal font type (Times New Roman) for the reader.

 Question 3: Interesting article, topic with relevance to science. It presents the appropriate methods, however in terms of writing and projecting the results it is not the best. deserves to be better written, in terms of English.

Answer 3: Some parts of ‘Results and discussion’ were corrected and ‘Conclusion’ section was revised by the authors as the reviewer’s suggestion. (Please, see the “Results and discussion” and “Conclusion” sections) The modified main parts were listed below.

“ This study supported the quantitative evaluation of the stabilization effect of AMDS on soil with various pollution scenarios and presented information about the major stabilization mechanisms by which As and heavy metals in soil are stabilized by AMDS.”

“ There can be a great difference in the stabilization efficiency of AMDSs due to different soil properties and the adequate stabilizer should be selected for the specific site. This study was focused on presenting the very high stabilization efficiency of AMDS for various soils having different pollution scenarios and different physico-chemical properties. The overall stabilization efficiency of two AMDSs for heavy metals and As were higher than 75% and 85% (mostly > 90%) with the addition of more than 3% of AMD, respectively, regardless of soil and metal type.”  …etc.

As the reviewer’s suggestion, for the reader’s better understanding, the “2. Materials and experimental methods” section was divided into ‘Material Preparation” and “Experimental Methods” in the text. The ‘Material Preparation” section was divided into two sub-titles as “2.1. Preparation of Soils” and “2.2. Preparation of AMDSs”. Also, the “Experimental Methods” section was rearranged in order as “3.1. Chemical Characterization of AMDSs”, “3.2. Mineralogical and Structural Characterization of AMDSs”, “3.3. Batch Extraction Experiments for the Stabilization Efficiency of AMDSs”, and “3.4. Column Experiments for the AMDS Stabilization in Non-equilibrium Conditions”. (Please, see the text)

For reader’s better understanding, total 6 references were added in the text. Reference 7, 11, 12, 27, 48, and 55.

Question 4: The title is confusing, however I think with slight improvements it should be accepted.

Answer 4: As the reviewer’s suggestion, title was revised from “Soil stabilization for arsenic and heavy metals by using two mine drainage treated sludges” to “Stabilization of As and heavy metal contaminated soils by two mine drainage treated sludges”.

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Reviewer 3 Report

It is from the beginning very confusing, as in Table 1 the water quality is given , but in Figure 2 two mine effluents are presented .

the soils A B C D are briefly described , but not the important characteristics of each of the soils  but in table 2 only metal concentrations are given. The important content for organics, clay minerals etc are not given , relevant to retention of metals.  

Author Response

 Dear Reviewer:

Thanks for the reviewers’ comments concerning our manuscript. Authors have studied the valuable comments carefully and have made correction which we hope meet with your approval. Revised and added portion are colored in red in the revised manuscript and the point to point responds to the reviewer’s comments are listed as below.   

Question 1: It is from the beginning very confusing, as in Table 1 the water quality is given , but in Figure 2 two mine effluents are presented .

Answer 1:  The AMD was originated from the mine entrance or the mine tailing storage wall and flew into the ADM treatment system for the clean-up (‘Inflow AMD’ in Table 1 means the AMD flew into the treatment system). The water quality of the AMD was analyzed at the front of the treatment system (right before the AMD treatment process). For better understanding, the authors modify it to ‘AMD draining into the treatment system’ as the reviewer’s request.

 Question 2: the soils A B C D are briefly described , but not the important characteristics of each of the soils  but in table 2 only metal concentrations are given. The important content for organics, clay minerals etc are not given , relevant to retention of metals.

Answer 2: Thanks for a good suggestion. Like the reviewer’s opinion, the stabilization mechanism depends on the chemistry and the organic contents of the soil as well as physical properties. There is no argument about that. Regretfully, this study focused on the efficiency of the inorganic amendments on the metal fixation (including As) based on the chemical reactions rather than the organic or the microbiological reactions. As the reviewer’s suggestion, information for physico-chemical properties of the soils such as organic contents, CEC, soil texture, etc. were added in Table 2. It would be helpful for the readers interested in studying other areas. (Please, see Table 2). The related sentences were straightforwardly added in the “Conclusion” section (Please, see the “Conclusion” section). Authors implore the reviewer to understand that this study gave more focus on the very high stabilization efficiency of AMDS for various soils having different pollution scenarios (even having different physico-chemical properties) rather than on the specific stabilization mechanisms of AMDS. 

To investigate the stabilization mechanisms in this study, authors presented ① the TG-DTA results for the existence of potential minerals (CaCO₃, Ca(OH)₂, Fe(OH)₃, Al(OH)₃, etc. as the stabilizer (Fig. 5 and description), ② BET results for the physical stabilization capacity (Table 4), ③ SEM/EDS and XRD/XRF results for the existence of Fe-oxides(hydroxides) and calcites (Fig. 6 and description), and ④ TCLP/SPLP results for the extraction decrease of As and heavy metals from soil (Table 5) as well as ⑤ the quantitative stabilization efficiency increase. The section 3.1 contains these indirect (but quantitative) results, naturally linking to the section 3.2 and 3.3 (discussion with stabilization mechanism and efficiency of AMDSs). 

Authors sincerely expect the reviewers’ understanding.

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Reviewer 4 Report

The idea of the paper is interesting and can interest the international readers. However, some sections of the paper must be re-writen to be clear and easy to follow.

Best of luck.

Comments for author File: Comments.docx

Author Response

Dear Reviewer:

 Thank you for your affirmation of our research. Authors discussed about your suggestions and make serious amendments carefully. Authors hope that the revised manuscript can show what we have done in academic research more specifically. Some parts of ‘Results and discussion’ were corrected and ‘Conclusion’ section was also revised as the reviewer’s suggestion. Revised and added portion are colored in red in the revised manuscript and the point to point responds to the reviewer’s comments are listed as below.

 

Suggestion: The idea of the paper is interesting and can interest the international readers. However, some sections of the paper must be re-writen to be clear and easy to follow.

 General comments

The paper of Tak et al studied the use of sludge of treatment of acid mine drainage for metal-contaminated soils. Hereafter the main suggestions and comments for this paper:

Abstract:

Question: The authors need to add the characteristic of the contaminated soils, at least the contaminant contents. Please describe the overall efficiency of the sludges. You don’t need to detail for each soil’s type because, in the abstract, we don’t know the differences between the different soils. Or you can describe the soil’s types.

Answer: Thanks for a good suggestion. As the reviewer’s request, more information of soils such as organic contents, CEC, and soil texture (clay content) as well as heavy metal concentrations were added in Table 2. The sentence about the soil pollution status used in the study was also added in the abstract. “Two types of AMDS, copper metal mine drainage treated sludge (MMDS) and coal mine drain-age treated sludge (CMDS) and four contaminated soils with different pollution scenarios were used in the experiments. 'Soil A' and 'Soil D' were mainly contaminated with Cd, Pb and Zn. 'Soil B' and 'Soil C' were contaminated with As.” (Please, see Abstract)

More detail description of soil properties and their pollution scenarios were in Section 2.1.

The overall the description of the stabilization efficiency for two AMDSs(sludges) at each soil was also added in the Abstract as the reviewer’s suggestion. “The overall stabilization efficiency of two AMDSs for heavy metals and As were higher than 75% and 85% (mostly > 90%), respectively, regardless of soil type.” (Please, see Abstract)

 

Introduction:

Question: Lines 45 – 48: this correct that the mine drainage water must be treated before their reject into the environment. But they are other options for AMD treatment such as alkaline/cementitious amendments of acidic tailings. This aspect must be added to the introduction section. You can use the following papers recently published in Minerals Journal:

a- https://doi.org/10.3390/min9050314

b- https://doi.org/10.3390/min11040413

• Line 56 – 57: add references supporting the toxicity of sludges.
• Line 67 – 68: lime can be effective for immobilization of heavy metals in acidic conditions. What about neutral/alkaline conditions? You must be specific about your statement. Please correct this statement.
• Line 79/80: stabilization/solidification methods: please refer to chapter 7: https://doi.org/10.1016/B978-0-12-824004-5.00023-2 of the book: https://www.sciencedirect.com/book/9780128240045/low-carbon-stabilization-and-solidification-of-hazardous-wastes

Answer: As the reviewer’s request, four more references related similar studies and the description of their results were added in the manuscript. Please, see the reference list and the “Introduction” section (line 53, 57-59, and 75-77 on page 2).      

7. Daraz U.; Li, Y.; Ahmad, I.; Iqbal, R.; Ditta, A. Remediation technologies for acid mine drainage: Recent trends and future perspectives. Chemosphere 2023, 311, 137089. https://doi.org/10.1016/j.chemosphere.2022.137089

11. Elghali, A.; Benzaazoua, M.; Bouzahzah, H.; Bussière, B. Laboratory study on the effectiveness of limestone and cementitious industrial products for acid mine drainage remediation. Minerals 2021, 11(413), 1-19. https://doi.org/10.3390/min11040413

12. Elghali, A.; Benzaazoua, M.; Bussière, B.; Genty, T. In Situ Effectiveness of Alkaline and Cementitious Amendments to Stabilize Oxidized Acid-Generating Tailings. Minerals 2019, 9(314), 1-20. https://doi.org/10.3390/min9050314

27. Elghali, A.; Benzaazoua, M.; Couvidat, J.; Barricau, L.; Neculita, C.M.; Chatain, V., Low Carbon Stabilization and Solidification of Hazardous Wastes. In Chap. 7 – Stabilization/solidification of sediments: challenges and novelties. Elsevier Inc., 2022. https://doi.org/10.1016/B978-0-12-824004-5.00023-2

The limitation of the use of lime at neutral/alkaline conditions was additionally described in Ln   on page   . And the sentence about the treatment of acidic mine tailings to prevent the AMD generation was added in the text as the reviewer’s request. (Please, see Ln  53, 57-59, and 75-77 on page 2)

 

Materials and experimental methods

Question: This section needs to be rewritten. the authors must separate materials from methods. For instance, they can describe soils and then describe separately each characterization technique. It is difficult to follow in the current structure.

Again, methods sections must be described separately:

Chemical characterization

Mineralogical characterization Etc.

Answer: As the reviewer’s suggestion, the “2. Materials and experimental methods” section was divided into ‘Material Preparation” and “Experimental Methods” in the text. The ‘Material Preparation” section was divided into two sub-titles as “2.1. Preparation of Soils” and “2.2. Preparation of AMDSs”. Also, the “Experimental Methods” section was rearranged in order as “3.1. Chemical Characterization of AMDSs”, “3.2. Mineralogical and Structural Characterization of AMDSs”, “3.3. Batch Extraction Experiments for the Stabilization Efficiency of AMDSs”, and “3.4. Column Experiments for the AMDS Stabilization in Non-equilibrium Conditions”. (Please, see the text)

Question: Sampling strategy: please describe your sampling strategy; how the locations of the samples were chosen? Why 10-30 cm? precise the sampling depth for each soil sample…

Aqua regia digestion: describe the used acid digestion. Why did you use aqua regia and not total digestion? What are the QA/QC protocols used for the chemical analysis? How was the pH of the soils measured? Paste pH? If yes, what is the L/S ratio? How was the chemical quality of AMD analyzed? Describe the method and add detection limits.

Answer: The authors understand the reviewer’s questions about the detail processes of soil preparation and analyses. Like many other countries, in Korea the systematic protocols and manuals for the process related to the soil sampling and the pre-treatment for the concentration analyses as well as the QA/QC for the analysis and the MDL of each instrument were supported by the regulation. For readers interested in the protocols and manuals for these process, authors presented and also added the references for these protocols in the text (Please, see reference list).

47. International Organization for Standardization (ISO), Soil quality-Extraction of trace elements soluble in aqua regia. ISO 11466:1995 2022. https://www.iso.org/standard/19418.html (accessed on 10th Sep 2022)
48. MOE (Ministry of Environment), Soil contamination measurement analysis method. Notification No. 2022-38. 2022.

https://www.law.go.kr/DRF/lawService.do?OC=me_pr&target=admrul&ID=2100000213159&type=HTML&mobileYn=

All sample preparation and analyses for soil and AMDS proceeded according to these protocols and manuals in the Notification. The sentence was added in the text with references. (Please, line 126-134 on page 3)

Question: XRD analysis: describe sample’s preparation method, acquisition conditions (angle, step size, dwell time…etc), describe the method used for diffractogram refinement?

XRF analysis: did the samples analyzed after alkaline fusion or only in powders? What are the standards used for the calibration?

SEM description: please add enough details to be able to understand how the analysis was done e.g., sample preparation, analysis mode…

Answer: As the reviewer’s suggestion, the sentences were added to describe the analytical process and the sample preparation for XRD, XRF and SEM/EDS analyses. (Please, see Ln 191-199 on page 5 and Ln 218-221 on page 6)

“The mineralogical properties of the AMDS were analyzed using an X-ray diffractometer (XRD: X'Pert-MPD System, PHILIPS) using Cu Kα radiation (λ= 1.54060 Å) over a 2θ range of 10^o – 80^o and X-ray power of 40 kV/30 mA at a scan. The principal components of the AMDS were also analyzed by an X-Ray fluorescence spectrometry (XRF: XRF-1800, SHIMADZU). The powdered samples of each AMDS were prepared as pellets on a boric acid support. The measurements were performed using a Shimadzu (XRF-1800) sequential spectrometer equipped with a Rh Kα x-ray tube operated at 40 kV and 95 mA. The XRF spectrum analysis used a type of calibration method known as fundamental parameters (FP).” …etc.

“To observe the surface structure of the AMDSs, prepared samples were spread onto carbon tape and mounted on an aluminum specimen holder. Then powdered AMDS specimens sputtered coated using platinum (Pt) for SEM/EDS analyses.” …etc.

 

Question: The most important comparison that can be done is the comparison of chemical characteristics vs mineralogical properties. Is this done?

Answer: The comparison among XRD, XRF, TG-DTA, and SEM/EDS analyses to identify the mineralogy and the chemical properties to evaluate the stabilization efficiency of AMDSs were performed and the detail description of the comparison results were in the whole of Section 3.1. This part is very important to support the mineralogical and the chemical capacity of AMDS as the stabilizer and thus authors dedicated a large portion in the text. (Please, see the whole of Section 3.1: page 7-11)

Question: Section 2.3: the first two sentences are meaningless, just refer to the equation 1.

Add a table to well illustrate all the batch experiments.

Answer: As the reviewer’s suggestion, the first sentence was deleted, but the authors left the second sentence of the objective of the experiment for reader’s better understanding. The process of batch experiments was not complicated and the reference for the batch experiment was added in the text. (Reference 55). “More details about the batch experiment can be found in the previous study [55].” in Ln 245-246 on page 6.

55. Kim, S.; Kim, K.; Oh, Y.; Han, Y.; Lee, M., Stabilization mechanisms of powered and bead type stabilizer made of Mg-Fe layered double hydroxide (LDH) for the arsenic contaminated soil. J. Soil Groundw. Environ. 2022, 27(4), 49-62. (in Korean with English abstract) https://doi.org/10.7857/JSGE.2022.27.4.049

 

Question: Equation 1, the use of concentration in mg/L for comparison is correct if only the same volume of leachate is collected from the different experiments. For more reliability, the authors need to normalize using the volume of leachate. The authors can use mass for efficiency calculation.

Answer: In our experiment, the volume of leachate solution after the reaction was almost the same as the amount of the solution before mixing (= 120 ml). If there are loss of volume, it should be compensated as the reviewer’s opinion.

 

Question: Line 217 – 218: please justify why the samples were left stationary for 8h? what if sample chemical species were leached but then reprecipitated? In this case the efficiency is biased. To verify this point, the geochemical modeling such as saturation indexes are highly recommended.

Answer: To minimize the buoyant particles in leachate solution, the stirred mixture was left stationary for 8h. But, the total stabilization time in this study was considered to be the first 8 station time + additional left time (+α). Thus, the stabilization capacity vs. time is not likely to depend on this stationary time. Even the high-speed centrifuge could be useful to minimize the stationary time, but it also may affect the stabilization capacity (It is hard to expect this condensation condition of suspended solid in the real field). The authors agreed with the reviewer’ opinion about the geochemical modeling to find out the precipitation trend of main minerals. Regrettably, the geochemical modeling for the precipitation of heavy metals was not performed this time. But authors will have a plan to the geochemical modeling in equilibrium system for the future work. Authors sincerely expect the reviewers’ understanding.

 

Question: Column experiments: did the authors use vacuum grease to avoid water preferential flows?

Answer: The soil+AMDS was homogeneously mixed with the electronic mixing machine and the mixture was packed with the constant falling velocity by gravity. The packed column was flushed with distilled water very slowly (0.2 ml/min) and the preferential flow pathway in the column was not observed in this experiment. But, the author will use the vacuum grease for the next column experiment. Thanks for your good suggestion.

 

Results

Question: Section 3.2: this section which must be the most interesting section needs more improvements. The explanation of the mechanisms is only based on previous studies, which is good, but is there any evidence for this study. Did the authors analyzed the soils using SEM to observe the secondary precipitates? At least the authors need to justify their conclusions using geochemical modeling.

Answer: The authors deeply appreciate the reviewer for the suggestions to identify the stabilization mechanism of AMDS. Authors also tried to get the visual evidence for the new forming precipitates on the soil or the AMDS surfaces due to the stabilization process from SEM/EDS. Unfortunately, the As or heavy metal bearing mineralization (or precipitation) on the soil particle surfaces could not be observed by SEM/EDS analysis. We think it was because of that the initial concentration of As and heavy metal in soil (also in extracted solution) was not high and it is hard to find out the any crystalline form on the AMDS particle surface (only 5% addition into soil). When we use the artificial solution with very high initial As (or heavy metal) concentration (few hundreds level) and it was reacted with the AMDS only, the new minerals (or precipitations) on the AMDS surface may be observed on the SEM/EDS results. These experiments were often used to identify the sorption capacity of the sorbent and authors already conducted in several sorption studies. However, this high concentration solution was not feasible to apply for the real soil stabilization condition. As the alternative process to investigate the stabilization mechanisms in this study, authors presented ① the TG-DTA results for the existence of potential minerals (CaCO₃, Ca(OH)₂, Fe(OH)₃, Al(OH)₃, etc. as the stabilizer (Fig. 5 and description), ② BET results for the physical stabilization capacity (Table 4), ③ SEM/EDS and XRD/XRF results for the existence of Fe-oxides(hydroxides) and calcites (Fig. 6 and description), and ④ TCLP/SPLP results for the extraction decrease of As and heavy metals from soil (Table 5) as well as ⑤ the quantitative stabilization efficiency increase. The section 3.1 contains these indirect (but quantitative) results, naturally linking to the section 3.2 and 3.3 (discussion with stabilization mechanism and efficiency of AMDSs). Authors have a plan to use more accurate analytical instruments to find out the very small precipitants on the surface. Authors added the sentence for this limitation straightforwardly in the text. (Please, see Ln 360-364 on page 10). Authors sincerely expect the reviewers’ understanding.

 

Question: Why the stabilization efficiency was different for the different soils? Is it a question of initial concentration? it depends on the mineralogy of the soils? Or maybe it depends on the chemical species speciation or the elemental deportment?

The discussion needs more improvement.

Answer: Authors think it is good question. Everyone agrees that different stabilization efficiency results from the different soil properties such as the clay contents (particle size), the potential stabilizing mineral contents, initial concentration, pH, etc. (many factors exist as the reviewer mentioned!). Thus, the comparison of stabilization efficiency for the specific metal among soils is difficult, but the comparison for different metals in the same soil was possible and they were described in Section 3.3 in detail. Authors implore the reviewer to understand that this study gave more focus on the very high stabilization efficiency of AMDS for various soils having different pollution scenarios (even having different physico-chemical properties) rather than on the specific stabilization mechanisms of AMDS. From the reviewer’s suggestion, in Table 2, the physico-chemical properties of soils were added for reader’s better understandings about these property differences. The sentences for these discussions were also added in the ‘Conclusion’ section.

 

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Round 2

Reviewer 3 Report

i was checking the references with the find function and it did not work as not the same format as quoted in the text .It is not clear what work you did and why on the liquid AMD and the sludge. 

get some systematic order into your work:

1. the same chemical characteristics and/or parameters  of solids and liquids and the sludge and the loam 

2 . the mixtures and their proportions

3. conclusions

sorry i

 

 

Comments for author File: Comments.pdf

Author Response

Dear Reviewer:
 Thanks for your comments. Following your suggestion, authors have revised the manuscript. Revised and added portion are colored in blue in the revised manuscript and the point to point responds to the reviewer’s comments are listed as below. The manuscript was pre-reviewed by the native proofreader for English language editing and the proofreading confirmation file was also attached.   

 Question 1: i was checking the references with the find function and it did not work as not the same format as quoted in the text .It is not clear what work you did and why on the liquid AMD and the sludge. 

Answer: (1) The authors checked the references in the list and changed the linkage site address for the reference 48. If the reviewer points out the other number of references of which function did not match to the format in manuscript (line and page in the manuscript in detail), the authors are willing to correct the references or vice versa.

(2) The main objective of this research is to investigate the feasibility of the AMDS (acid mine drainage treated sludge) through the quantitative analyses and batch/column experiments, supporting the stabilization efficiency (%) and the main stabilization mechanisms. Results from this study represented the potential of the AMDS as an available amendment for heavy metal and As contaminated soils having different pollution scenarios. The recycle of these AMDSs (sludges treated as wastes before) as the soil stabilizer is one of the novel approaches for heavy metal contaminated site treatment. The authors described about problems of the AMD from mine activities, the previous studies for the AMD treatment processes and the soil stabilization, and finally the use of the AMDS as well as the main objectives of this study in the “Introduction” and “Conclusion” sections. The authors presented more than 40 references for these research needs and clearly mentioned the objectives and results in the text (Please, see the blue colored paragraphs in “Abstract”, “Introduction” and “Conclusion” for the reviewer’s understanding.). Authors sincerely expect the reviewer’s understanding.

Question 2: get some systematic order into your work:

1. the same chemical characteristics and/or parameters  of solids and liquids and the sludge and the loam 

2 . the mixtures and their proportions

3. conclusions

sorry i

 Answer: (1) As the reviewer’s suggestion to reorganize the materials of the manuscript in systematic order, the authors reorganized the manuscript as below. The “2. Materials and experimental methods” section was divided into ‘Material Preparation” and “Experimental Methods” in the text. The ‘Material Preparation” section was divided into two sub-titles as “2.1. Preparation of Soils” and “2.2. Preparation of AMDSs”. Also, the “Experimental Methods” section was rearranged in order as “3.1. Chemical Characterization of AMDSs”, “3.2. Mineralogical and Structural Characterization of AMDSs”, “3.3. Batch Extraction Experiments for the Stabilization Efficiency of AMDSs”, and “3.4. Column Experiments for the AMDS Stabilization in Non-equilibrium Conditions”. (Please, see the text)

(2) The authors understand the reviewer’s questions about the detail processes of soil preparation and analyses. Like many other countries, in Korea the systematic protocols and manuals for the process related to the soil sampling and the pre-treatment for the concentration analyses as well as the QA/QC for the analysis were supported by the regulations. For readers interested in the protocols and manuals for these processes, authors presented and also added the references for these protocols in the text (Please, see reference list).

47. International Organization for Standardization (ISO), Soil quality-Extraction of trace elements soluble in aqua regia. ISO 11466:1995 2022.
48. MOE (Ministry of Environment), Soil contamination measurement analysis method. Notification No. 2022-38. 2022.

All sample preparation and analyses for soil and AMDS proceeded according to these protocols and manuals in the Notification. The sentence was added in the text with references. (Please, on page 3)

(3) According to reviewer’s suggestion, “Conclusion” section was revised by authors and the native to emphasize the originality and the novelty of this study (See “Conclusion” section).

“ This study supported the quantitative evaluation of the stabilization effect of the AMDS on soil with various pollution scenarios and presented information about the major stabilization mechanisms by which As and heavy metals in soil are stabilized by AMDS.”

“This study was focused on presenting the very high stabilization efficiency of AMDS for various soils having different pollution scenarios and different physico-chemical properties. The overall stabilization efficiency of two AMDSs for heavy metals and As were higher than 75% and 85% (mostly > 90%) with the addition of more than 3% of AMD, respectively, regardless of soil and metal type.”  …etc. Authors sincerely expect the reviewer’s understanding.

 

Question 3 in Table 1 (The reviewer pointed out in the manuscript file).

Answer: The authors thought there exists the confusion between the author and the reviewer. Data in Table 1 is the water quality of AMD at Ilkwang metal abandoned mine, where the AMD treatment process was conducted and the MMDS (metal mine drainage treated sludge) was obtained from there (not soil sampling sites contaminated with heavy metals and As). Authors revised Fig.1 by addition of two sampling locations for MMDS and CMDS as the reviewer’s request (Please, see Fig. 1). The explanation of the location for two AMDS sampling sites was in the first paragraph of “2.2 Preparation of AMDS” section on page 3. The tolerance limit in Table 1 was the Korean surface water discharge limit based on the Korean Water Environment Preservation Act, Environmental regulations 34 (Table 13). As the reviewer’s suggestion, the authors added the reference for this effluent quality standard limit and changed the sentence and Table 1 for the reader’s better understanding (Please, see reference 50 and 2.2 section).

50. MOE (Ministry of Environment), Korean Environment Preservation Act, Enforcement Regulation No. 34 (Table 13) 2022.

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Author Response File: Author Response.pdf

Reviewer 4 Report

The idea of the paper is interesting and treats soil polution. The authors have adressed all my previous comments. In my opinion, the paper can be accepted in its current form.

Best of luck.

Author Response

Dear Reviewer:

Suggestions: The idea of the paper is interesting and treats soil pollution. The authors have addressed all my previous comments. In my opinion, the paper can be accepted in its current form.

Best of luck.

Answer: The authors truly appreciate your faithful affirmation of our research and revised manuscript.

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