Leaching Study of Guinean Bauxite Tailings in aqueous HCl Solution for the Extraction of Aluminum
, Michalis Vafeias 1,*, Anastasia Pilichou 1, Efthymios Balomenos 2 and Dimitrios Panias 1
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsIn this paper, the potential use of bauxite tailings as an alternative secondary resource for alumina production was introduced, and the leaching study of aluminum extracted from bauxite tailings in hydrochloric acid aqueous solution was carried out. The quality of results and arguments is at a good level. It is best for the author to consider the comments mentioned below and further improve the manuscript before submitting the final version：
1. The research content should be condensed, and the core idea of the abstract needs to be improved. For example, the analysis results of the characterization are described.
2. What does "LOI" stand for in Table 2 ?
3. Figures 3, 4, 6 are not standardized, and it is recommended to redraw.
4. The solid-liquid ratio should be in the form of X:X, not as a percentage.
5. Section 3.2. “Analysis of leached residue of the 24 h study” is recommended to be changed to “Analysis of leached residue”, and the time conditions can be shown in the text.
6. line 298-299, “At 1h %wt. extraction values are ≈86% 298 for Fe and ≈89% for Al.” The statement has syntax and formatting issues, there should be no "≈" in the text, it should be an affirmative value. In addition, as shown in Figure 3 and the analysis results, the metal leaching rate has reached about 90% after 1 hour of leaching, why does the metal leaching rate decrease first and then increase with the extension of time, and what is the significance of considering the longer leaching time?
7. Grammatical and formatting revisions are required for the full text.
8. The format of the references needs to be improved and harmonized.
Comments on the Quality of English LanguageGrammatical and formatting revisions are required for the full text.
Author Response
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThe manuscript is within the scope of the journal but not fully developed; further research and analysis are needed before consideration for publication in our journal. In addition, the work does not significantly add to the existing knowledge of the field of Resources and Sustainable Utilization when compared to other papers published. As a result, the paper can't be published with the current research work.
1.The research work lacks innovation. Leaching Bauxite Tailings in aqueous HCl solution is a well-known method for the extraction of Al，Fe，etc.
2. The research work is too easy.
3. Figure 6 should be drawn more beautifully.
4. References must be formatted according to journal style. Use the standard abbreviations for journal names given in the International Standard ISO 4.
5.The conclusion should be concise.
No.
Author Response
Dear Review find our reply in the submitted work file.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsIn this work, the authors investigate the potential use of bauxite tailings for alumina production by using acidic leaching (an aqueous HCl). Several analyses have been carried out and the results have been presented. However, the present manuscript is severely plagued by problems in the presentation. The manuscript requires major revisions before being considered for publication in Sustainability or any journal in this field.
1. Abstract: the objectives, methods, and results of the research have been explained, but in lines [23-24], the author only explains qualitatively: ……high Al and Fe concentration solution, ….from a high S/L …….the word High has an ambiguous meaning, should be presented in the form of quantitative data.
2. Method. Researchers did not explain the advantages and disadvantages of other methods so they chose the acidic leaching method. So, the article shows the research gap in this theme.
3. The method used is acidic leaching, why doesn't the author use another strong acid such as sulfuric acid?
4. The novelty in the article has not been explained in detail.
5. Several articles published in journals as literacy sources have been published for more than 10 years. Needs to be updated
6. In general, scientific sound is still lacking. Researchers only use a leaching method on one natural resource. There is a need to compare methods and results achieved with other literature.
Author Response
Dear Review,
Find in the attached word file our answer to your comments.
Author Response File: Author Response.pdf
Reviewer 4 Report
Comments and Suggestions for AuthorsThis manuscript discussed the Al leaching process of bauxite tailings. I think this is an important work. My advice and comments are listed below:
1. What is the component analysis of the bauxite tailings? How much kind of ions exists in the tailings, especially metal ions? Because many ions will enter leachate using hydrochloric acid solution which has a significant impact on subsequent precipitation behavior.
2. The XRD data analyses are not very clear in manuscript.
3. How to treat high acidity leaching-precipitation wastewater?
Comments on the Quality of English LanguageMinor editing of English language required
Author Response
Dear reviewer,
Find our answer to your comments in the submitted word file.
Author Response File: Author Response.pdf
Reviewer 5 Report
Comments and Suggestions for AuthorsYour article studied the possibility of using bauxite residue as an alternative secondary resource for alumina production, with a process technology based on aqueous HCl solutions. A qualitative and quantitative mineralogical analysis of the raw material to understand the leaching behavior was conducted. Your results, regarding the completely or almost completely dissolution of Al and Fe in the 5.9 M HCl solution at a solid/liquid (S/L) ratio of 5%, divided into two sections, the 24h leaching study and the S/L ratio optimization tests, while Si remains insoluble, along with the rapid dissolution mechanism of Al observed, with a dissolution rate of 90% in the first 2 hours is in good agreement with literature data. The effect of the S/L ratio on metal dissolution and established that an S/L ratio of 20% could be the optimal parameters for leaching bauxite residue to produce a solution rich in Al and Fe.
Your study demonstrates the potential of using bauxite residue as an alternative source of alumina, with a simple and efficient process technology. The efficient acidic leaching of bauxite tailings for the extraction of Al has been confirmed by the results presented in your study, the resulting solution could be used for the precipitation of aluminum chloride hexahydrate (AICl3·6H2O), which could then be calcined to produce alumina. Also, your idea, to explore other types of aluminosilicate-rich materials, such as fly ash or kaolin, to extend the applicability of the technology, is necessary to be tested in real conditions, too.
Author Response
Dear Reviewer,
I want to express my sincere gratitude for your insightful comments and constructive feedback on my paper. Your valuable input has greatly contributed to the improvement of the manuscript, and I appreciate your time and expertise in guiding me through the necessary corrections. I am committed to addressing each of your suggestions to ensure the paper meets the high standards of the journal. As pointed out by many reviewers a change in the structure and the content of the Abstract and Introduction section was required in order the sustainability character of our work to be clearer. As a result, Lines 13-26 and 33-158 at the new submitted manuscript have changed. As a team, our goal is to test the described technology on a lab scale in other rich aluminosilicate minerals and publish our results in the upcoming future.
Thank you once again for your thoughtful review.
Best regards
Reviewer 6 Report
Comments and Suggestions for AuthorsThe work of Bagani et al. discusses the results of leaching tests with HCl on non-conventional bauxite ore. The work is motivated by the desire to develop a novel processing flow-sheet alternative to the Bayer process for kaolinite rich bauxites. In my opinion the paper presents several shortcomings and can be published only if the authors decide to implement some major modifications.
Line 49. This can expand in more details of a couple of lines given the environmental hazard posed by red mud.
Line 60. If these materials are so rich of reactive silica it is not clear how they can be “promising”? It would useful to mention also the Fe content in high quality bauxite ore as opposed to bauxite residues.
Line 81-83 needs to be better explained without consulting the references. That mineral beneficiation is more costly than acid leaching is to be better explained (corrosion issues, environmental issues, safety issues, etc.). The solubility of silicon at low pH is very little (as stated) and therefore unlikely it can be leached in any significant way (the paper later demonstrates only about 1 to 2% - Fig4)
Line 120-126. The authors did not specify what is the contribution of their study to the scientific literature/knowledge, especially considering what stated in lines 84-95. There is no mention to the EU availability/reserves of bauxite residues either
Line 203. The relevance of this sample from Guinea for the sourcing of bauxite locally in the EU as stated in the introduction is not clear
Table 3 shows interesting results because makes clear that the kaolinite is only a minor fraction of the Si-bearing compounds. I doubt that Si can be leached any efficiently from the quartz and amorphous minerals. Any comment from the authors? In line 322 it is explained that quartz does not dissolve in hydrochloric acid. How can this processing sheet be implemented then?
Line 340. It is a positive factor that the entirety of the iron is dissolved? It would appear that figure 1 needs a solvent extraction or electrolytic refinement process (see comment below).
Line 479. It would appear as this process trades the formation of silica gel for the production of an acidic quartz‑rich waste, a silicon-rich precipitate and an Fe-rich Al solution. Please elaborate in detail why this approach would improve the sustainability of the aluminum industry. The very generic descriptions of lines 479 to 490 and 445-443 are not sufficient
Language and formatting:
Line 64. Highlight somewhere that karst bauxites are carbonate rich
Specify if % is wt% or v% or wt/v%
All chemical equations should be written with the proper equilibrium arrows and subscript for liquid, aqueous, etc.
B.T. was not defined
HCl is at times misspelled with capital “L”
Seems that 2.2 can moved before 2.1 so that details of stirring, heating and chemicals used are clearer when reading through 2.2.
At least half of 2.2.2 seems more relevant for the results section than for the materials and method section
Looks like Fig3 shows cumulative curves whereas Fig4. point curves
Comments on the Quality of English LanguageThe paper reads sufficiently well for publication in an international journal
Author Response
Dear Reviewer,
find our answer in the word file
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsI think the authors have taken into consideration the comments and suggestions by the reviewers of the original manuscript and attempted to address them all. Accordingly, I suggest the acceptance of paper in current version.
Author Response
I want to express my sincere gratitude for your insightful comments and constructive feedback on my paper. Your valuable input has greatly contributed to the improvement of the manuscript, and I appreciate your time and expertise in guiding me through the necessary corrections. As pointed out by other reviewers some small changes have been made at the new submitted manuscript, which are all highlighted.
Reviewer 3 Report
Comments and Suggestions for AuthorsThe authors have made adequate revisions, but needs to check for typos such as line [161-162]
Author Response
I want to express my sincere gratitude for your insightful comments and constructive feedback on my paper. Your valuable input has greatly contributed to the improvement of the manuscript, and I appreciate your time and expertise in guiding me through the necessary corrections. As pointed out by all reviewers some small changes have been made at the new submitted manuscript including typos, which are all highlighted.
Reviewer 6 Report
Comments and Suggestions for AuthorsThe authors have provided several answers to the reviewers comments and made extensive modifications to the introduction. However, the bulk of the manuscript and the data have not undergone major changes, which is reflected in areas that may need additional work (some examples below).
- What is the proof the the amorphous is Si rich?
- Still not explained why the Si graph is not shown as cumulative curve as it has been done for Al, Fe, Ti
- One reviewer asked about LOI but its determination is still lacking detail
- The authors states that the precipitation of AlCl3 is selective over that of FeCl3 but no speciation diagram or solubility data is reported/discussed
- Etc.
Comments on the Quality of English LanguageThe manuscript reads relatively well. Double checks for spelling mistakes and minor edits are suggested.
Author Response
I want to express my sincere gratitude for your insightful comments and constructive feedback on my paper. Your valuable input has greatly contributed to the improvement of the manuscript, and I appreciate your time and expertise in guiding me through the necessary corrections. I am committed to addressing each of your suggestions to ensure the paper meets the high standards of the journal. As pointed out by all reviewers some small changes have been made at the manuscript, which are all highlighted.
Regarding your specific questions
- What is the proof that the amorphous is Si rich?
There is no clear proof as we can not isolate the amorphous material and perform chemical analysis. The indications that Si exists in the amorphous phase, as described in Lines 482-490 , are :
- existance of a HCl soluble source,as detected Si bearing mineralogical phases kaolinite and quartz are not soluble
- Si concentration differences between chemical analysis and XRD quantitative analysis
- Still not explained why the Si graph is not shown as a cumulative curve as it has been done for Al, Fe, Ti
Both Diagrams presenting the Al, Fe, Ti, and Si dissolution rates have been constructed using the same software and the same type line. They could appear different as a different dissolution behavior is noted. Moreover, error bars, that are included, make the two diagrams appear a little different.
- One reviewer asked about LOI but its determination is still lacking detail
LOI determination description was added at Lines 202-204
- The authors state that the precipitation of AlCl3 is selective over that of FeCl3 but no speciation diagram or solubility data is reported/discussed
A small raise to this specific part description is made at Lines 522-526. However, in our manuscript we tested experimentally the leaching stage. Precipitation is referred as a next step so it not discussed in detail. The reference 69 provides clear solubility data as for the precipitation behavior of Fe.
