Synergism Red Mud-Acid Mine Drainage as a Sustainable Solution for Neutralizing and Immobilizing Hazardous Elements
Round 1
Reviewer 1 Report
This manuscript has performed a neutralization of AMD using red mud from Greece and Germany and discussed the possibility of recovery of valuable metals such as aluminum, zinc, manganese and rare earth elements. The effect of neutralization of AMD using red mud is remarkable. This study is meaningful and the manuscript can be considered for publication in journal after minor revisions below:
1. The abstract is poor. It has not exhibited its experience results and explained the significance of this research. What’s more, the description of research background is to much. I suggest the author to rewrite the section of “Abstract”.
2. The English of this manuscript should be polished first before the author submit the manuscript.
3. The author has used error bar to show its experience results in the pictures. But the number of experiments not explained in the section of “Methodology”.
4. Why the NO3- concentration in AMD. RM.Gr and RM.De showed opposite trend?
5. The discussion is not enough, a section of “3.4 Discussions” can be added before section “5. Conclusion”.
Author Response
Dear Reviewer,
thank you very much for your valuable comments and invested time.
Please find the response in the PDF attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The authors simply presented pH and elemental data from the ADM solutions after mixing with different amounts of two red mud samples (German and Greek red muds). There is no scientific understanding and explanation why two red mud samples behave differently in neutralizing capacity and sulfate, anions and cations removal abilities. Suggest the authors investigate the mineralogy of the two red muds using at least x-ray diffraction (XRD), the mineralogy of the two red muds might provide some explanations of their different behaviours. Explanations should also be given to what happened when you mix different proportions of ADM and RM in terms of neutralizing capacity and sulfate, anions and cations removal abilities.
Please see the attached file for my other comments.
Comments for author File: Comments.pdf
Author Response
Dear Reviewer,
thank you very much for your comments.
During this time we improved many things in this article. We added new tables (XRD-Analysis,..) , modified the text, improved English and we repeated several tests. According to your question, In this table using the mineralogical quantification, I calculate the proportion of OH ions. I found 1,7% more OH in German RM than in the Greek. This higher concentration explains this extra capacity of German RM to precipitated metallic ions from AMD
We found a problem with the content of As in RM and repeating the results we discovered that there was an error in the calculation of several values from the data extracted in our ICP-MS device. Attached you can find answers to your comments with other improvement. I am sure that this Version is better than our first submitted paper.
Author Response File: Author Response.pdf
Reviewer 3 Report
Dear Authors,
The paper discusses the performance of red mud in the neutralization and recovery of metals from an acidic drainage solution. This is a very relevant problem in the mining industry, therefore the study is of both scientific and practical interest.
The manuscript needs some improvements. Line numbering is missing, which makes it difficult to review the paper.
Page 2, last paragraph. CFA – please spell the acronym out.
Page 4, last paragraph. Please clarify Equation 1. The left side of the equation is in liters, the right side is in kilograms. In addition, same notation (L) is used to denote both the volume of distilled water and the volume of the leaching agent.
Page 3. 2.1. Replace Material with 2.1. Materials.
Page 4, last paragraph. Replace were with where.
Page 4, third paragraph. It is noted that the mineralogical analysis of the red mud samples was carried out by XRD. However, the manuscript lacks a discussion of the results of that analysis. What is the difference between the red mud from Germany and the sample from Greece?
Page 5, last paragraph. Replace were with where.
Page 6, Table 2. Replace RM.Gr.400 with RM.Gr.40.
Page 7, last paragraph. Replace Fig. 4-right with Fig. 3-right.
Page 11. First paragraph. Therefore, Greek RM was four times more effective than the German to prevent the dissolution of Cu. Why 4, and not 3 times?
Page 13. 4. Replace Conclusion with 4. Conclusions.
Page 13. 4. Conclusions. The authors fail to conclude whether they recommend using red mud from Germany and Greece to neutralize AMD.
Comments for author File: Comments.pdf
Author Response
Dear Reviewer,
thank you very much for Your time and valuable comments.
During this time we improve several things in this article. We added new tables, modified the text and we repeated several test. We found a problem with the content of As in RM and repeating the results we discovered that there was an error in the calculation of several values from the data extracted in our ICP-MS device. Line numbering was missing, but now it is present.
Attached you can find all answers.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
The authors added quantity XRD to the new version, however, mineral % didn't match elemental composition in some cases, please see details in my comment in the attached pdf. There is still lack of fundamental understanding the differences in two RM behaviours in pH, metal and anion change/removal capacities. Details and suggestions of improvements are listed in my comments in pdf.
Comments for author File: Comments.pdf
Author Response
Dear colleague,
thank you very much for your invested time, suggestions and valuable comments in order to improve our paper.
Please find the response in the attachment.
Author Response File: Author Response.pdf
Round 3
Reviewer 2 Report
The authors have NOT largely address my concerns I addressed in Version 2, other than included a new QEMSCAN analysis of the two RM, which did not result more clarification in validating the QXRD results. I do not see any logical links or explanations between the mineralogical characterisation of the RM and their interactions with AMD. In my view, this does read more like a technical report, rather than scientific understanding.
Author Response
Dear Reviewer,
Thank you very much for your valuable comments and invested time.
The important aspect of RM/AMD interaction is for one side the RM mineralogy and the other AMD bioactivity. The German RM contains more hydroxides than the Greek and thus higher alkalinity. We think the tricky part of the interaction is the biological response. AMD contains colonies of sulfate reductive bacteria and a few colonies working with nitrates. The interesting thing about this study is perhaps changing pH moves the equilibrium from one bacteria´s type to another but not in the same way. German RM is releasing 10 times more Cr (a biological poison) which could be limiting the growth of the second type and is for that NO3 behaviour goes in opposite directions.
The biological activity vs RM mineralogy is the only logical explanation for the unknown behaviour of NO3-ions and even if follow training on biotechnology in the past our comprehension as metallurgists is outside our field.
It has been observed that the Greek RM is more effective in sulphate removal compared to the German RM, this could be attributed to the higher concentration of calcium based minerals present in the Greek RM compared to the German RM.
In this study we reported new results in order to ensure sufficient scientific understanding.
We hope that you can accept our explanation.
Best regards
Authors
