Feasibility of a Mineral Carbonation Technique Using Iron-Silicate Mining Waste by Direct Flue Gas CO2 Capture and Cation Complexation Using 2,2′-Bipyridine
Round 1
Reviewer 1 Report
Reviewer 2.
Reading through the paper and the comments, I still don’t think that comments 2, 3 and 4 are adequately addressed.
- The reactions involving ammonium sulphate are not present. It is not clear what these reagents do in the process without reactions. All reactions need to be included and balanced to show how the process works.
- Figure 2 is not clearer. It is stated that the bipyridine is added once. If that is the case then it should simply be in the recirculation stream. By saying that it is added once is making things more confusing. Essentially, there is a lot of confusion that needs to be sorted out ahead of publication. Also, I still think that if you are saying that you are adding 4 ml of NH4HSO4 (for the next cycle) then this is what you need to have for the inlet stream, rather than 20ml NH4HSO4 ??
- It is not clear where the ammonium sulphate is leaving the process. This all needs to be made clear.
- Improvements to Fig 1 might also improve clarity on how the process works.
Author Response
RESPONSES TO REVIEWERS’– MANUSCRIPT ID (minerals-1108257)
Reviewer Comments, Author Responses and Manuscript Changes
We would like to thank the reviewers for taking the time and effort necessary to review the manuscript. We sincerely appreciate all valuable comments and suggestions, which helped us to improve the quality of the manuscript.
-Reviewer 1
Comment 1: “1. The reactions involving ammonium sulphate are not present. It is not clear what these reagents do in the process without reactions. All reactions need to be included and balanced to show how the process works”.
Response: Thank you very much for your comment. Ammonium bisulphate, NH4HSO4, is used as a leaching agent for the dissolution of the cations (especially iron) to perform the mineral carbonation reaction. Different acids have been tested (as H2SO4, HCl and other ammonium salts) before chosing ammonium bisulphate as the one to perform the leaching of the mining residue. It was found to be the appropriate solvent for this step especially knowing it can be regenerated at the end of the process decresing its cost. Furthermore, it doesn’t react neither with the ferrous cations nor with the 2,2’-bipyridine. The reactions involving ammonium sulphate have been included in Equations 1-5 (line 92).
Comment 2: “Figure 2 is not clearer. It is stated that the bipyridine is added once. If that is the case then it should simply be in the recirculation stream. By saying that it is added once is making things more confusing. Essentially, there is a lot of confusion that needs to be sorted out ahead of publication. Also, I still think that if you are saying that you are adding 4 ml of NH4HSO4 (for the next cycle) then this is what you need to have for the inlet stream, rather than 20ml NH4HSO4 ??”
Response: “Thank you very much for your comment. We are sorry that it could be confusing for you. What we wanted to show is that the first time the mineral carbonation reaction is perform, a 2,2’-bipyridine solution is added in order to complex the ferrous cations present in the solution and allow its reaction with the carbon dioxide to obtain the iron carbonates. When the carbonates are obtained, the 2,2’-bipyridine is released again into the solution and it can be reused again for the next carbonation reaction in a recirculation scenario so it is not necessary to add a new 2,2’-bipyridine solution again. As the unreacted liquid phase had a final pH of 7–8 due to the carbonate ions present in the final solution and the fact that the NH4HSO4 is recovered after the mineral carbonation reaction, only 4 ml of a new NH4HSO4 solution were needed to decrease the pH to 1–2 to reuse it as leaching agent (instead of the 20 ml of NH4HSO4 that were used in the first reaction). To help the reader understand the process, an explanatory paragraph have been included under the diagram (lines 204-213). Furthermore, the diagram (Figure 2) have been modified to avoid confusion to the reader. We hope this would help to better understand the process and remove any possible confusion that could have been created”.
Comment 3: “It is not clear where the ammonium sulphate is leaving the process. This all needs to be made clear”.
Response: “ The explanation of the role of the ammonium bisulphate and how it is regenerated and reused in the process have been explained and clarified in equations (1-5) (line 83-92), Figure 2 and the explanation in lines 199-217. Amonnium bisulphate is used as an acid to decrease the pH and allow the leaching. Then, it remains in solution. When the CO2 is the ammonium bisulphate is regenerated and a small amount of ammonium gas is obtained.”
Comment 4: “Improvements to Fig 1 might also improve clarity on how the process works”.
Response: “ As it has been explained in previous comments, several improvements have been done to clarify the process. We think that Fig. 1 shows the experimental set up in an easy way that helps the reader to get an idea of how the experiment is carried out in the laboratory. As figure 2 has been modified with much more detail, we believe it should remain as it is. I hope that the new modifications will be sufficient for you and anyone else who reads the article to understand the process in a clear way. Thank you very much.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
1. The authors added Eqs. (1)-(5) and (6)-(9) to the revised manuscript. Among them, Eqs. (1)-(5) are important equations that show the reactions in progress in the study. However, since there are no relevant references and no thermodynamic data, it is not clear if the listed reactions are possible. And since the presence of [Fe(bipy)3]2+ was not confirmed in the study, it is not obvious whether the reaction proceeds with the mechanism shown in Eqs. (1)-(5). Meanwhile, Eqs. (6)-(9) include references and thermodynamic data, but I believe that these equations are unnecessary in this paper.
2. The author added ‘3.1 Characterization of the [Fe(bipy)3]2+’ to the revised manuscript and showed IR spectra of [Fe(bipy)3]2+ in Figure 3. It seems that the authors did not properly understand my comment pointed out in the first review. What I wanted to see was not the IR spectra of the synthesized [Fe(bipy)3]2+, but the IR spectra of the [Fe(bipy)3]2+ produced by the reaction of Eq. (2). In other words, I wanted the authors to prove that the (2, 2'-bipyridine)2+ ligand could be recovered and reused after the carbonation reaction using the IR spectra of the following three samples.
Sample 1: before the reaction of Eq. (2), (2, 2'-bipyridine)2+
Sample 2: solution after the reaction of Eq. (2)
Sample 3: solution after the reaction of Eq. (4)
It is expected that the IR spectra of samples 1 and 3 will show the peaks for (2, 2'-bipyridine)2+ and those of sample 2 will show the peaks for [Fe(bipy)3]2+.
3. Several times, the authors explained the cause of the experimental results or predicted the results without explicitly presenting data, directly related references, or scientific logic. For example, see the following cases:
Lines 267-268
“This increase could be explained because of a co-precipitation effect caused by the cations already present from the leachate.”
Lines 336-338
“At higher temperatures, the reactivity of the Na cations increased and precipitated with the carbonate as impurities.”
4. Table 1 shows FeCO3(%) and MgCO3(%). In addition, the authors explained that they finally obtained (0.7Fe,0.3Mg)CO3. However, since there are no analysis results for these components, it is not clear whether or not they exist. XRD and XRF results are required.
5. It is correct to use the term ‘recovered liquid’ instead of the term ‘unreacted liquid’.
6. Many values are given in the texts of ‘3.4 Global mineral carbonation approach evaluation’ and ‘3.5 GHG balance’ and in Figures 7 and 8. It is not clear how these values were calculated because there is no relevant explanation in the manuscript or supplementary information.
Comments for author File: Comments.pdf
Author Response
RESPONSES TO REVIEWERS’– MANUSCRIPT ID (minerals-1108257)
Reviewer Comments, Author Responses and Manuscript Changes
We would like to thank the reviewers for taking the time and effort necessary to review the manuscript. We sincerely appreciate all valuable comments and suggestions, which helped us to improve the quality of the manuscript.
-Reviewer 2
Comment 1: “The authors added Eqs. (1)-(5) and (6)-(9) to the revised manuscript. Among them, Eqs. (1)-(5) are important equations that show the reactions in progress in the study. However, since there are no relevant references and no thermodynamic data, it is not clear if the listed reactions are possible. And since the presence of [Fe(bipy)3]2+ was not confirmed in the study, it is not obvious whether the reaction proceeds with the mechanism shown in Eqs. (1)-(5). Meanwhile, Eqs. (6)-(9) include references and thermodynamic data, but I believe that these equations are unnecessary in this paper.”
Response: Thank you very much for your comment. First of all, Eqs. (6)-(9) about the thermodynamic information of the [Fe(bipy)3]2+ complex formation have been removed. We had included them because perhaps they could help to better understand the process but we agree with you that they are not necessary in this article. All this information will be included in a more theoretical article about this mineral carbonation process. We completely agree with you.
On the othe hand, Eqs. (1) – (5) (line 92) have also been changed to include more details about the reagents and products that have been obtained. It is true that no thermodynamic data have been included about the reaction with the 2,2’-bipyridine but it has been impossible to find articles about it. Nevertheless, as it is explained in lines 76-81, the iron carbonate precipitation is only possible due to the [Fe(bipy)3]2+ complex formation. Furthermore, while the 2,2’-bipyridine not complexed has no color, the [Fe(bipy)3]2+ have a visible red color due to a visible pick at 522 nm in the UV-VIS spectra. A pH stability study of the complex have been performed but it is included in another article focus in the parameters optimization of the reaction. Moreover, to confirm the [Fe(bipy)3]2+ complex formation and regeneration after the reaction the IR-spectra before, during and after the mineral carbonation reaction have been included (Figure 3 and 4). Also, the ammonium bisulphate regeneration have also been studied by a Master’s Student at INRS-ETE (Waâd Khemiri (2019) CO2 sequestration process by indirect mineral carbonation of mine tailings from the exploitation of an apatite deposit of the "Mine Arnaud" Master's degree in Earth Sciences INRS ÉTÉ) including more thermodynamic data. Furthermore, the fact that just 5 ml of NH4HSO4 are used in the recirculation reaction (instead of 20 ml that are used in the first batch) can be enough to confirm its regeneration.
Comment 2: The author added ‘3.1 Characterization of the [Fe(bipy)3]2+’ to the revised manuscript and showed IR spectra of [Fe(bipy)3]2+ in Figure 3. It seems that the authors did not properly understand my comment pointed out in the first review. What I wanted to see was not the IR spectra of the synthesized [Fe(bipy)3]2+, but the IR spectra of the [Fe(bipy)3]2+ produced by the reaction of Eq. (2). In other words, I wanted the authors to prove that the (2, 2'-bipyridine)2+ ligand could be recovered and reused after the carbonation reaction using the IR spectra of the following three samples.
Sample 1: before the reaction of Eq. (2), (2, 2'-bipyridine)2+
Sample 2: solution after the reaction of Eq. (2)
Sample 3: solution after the reaction of Eq. (4)
Response: We are really sorry for not understanding the previous comment. As it was explained in comment 1, the IR-Spectra of the samples before, during and after the reaction have been included to confirm the complex formation and its regeneration. As the IR-Spectra before and after the reaction is similar (it is 2,2’-bipyridine not complexed) we think that we should only include it once. On the other hand, the [Fe(bipy)3]2+ complexed have been included and compared. I hope this could be enough to respond your comment. The IR analysis have been included in section 2.4.1 “Characterization of the [Fe(bipy)3]2+ and regeneration of the 2,2’-bipyridine” (lines 144-150).
Comment 3: “Several times, the authors explained the cause of the experimental results or predicted the results without explicitly presenting data, directly related references, or scientific logic. For example, see the following cases:
Lines 267-268
“This increase could be explained because of a co-precipitation effect caused by the cations already present from the leachate.”
Response: You are completely right that although the co-precitation effect could be the cause of the increase in the leaching efficiency there are no enough evidences to support that theory. For that reason, the sentence have been removed.
Lines 336-338
“At higher temperatures, the reactivity of the Na cations increased and precipitated with the carbonate as impurities.”
Response: We agree with you that this sentence is not right and create a lot of confusion. We change that sentence for this one: “At higher temperatures the solubility of NaOH increases, causing more Na cations to be released into the solution. Consequently, its precipitation together with the carbonate is higher, making the carbonate less pure” including a new reference (41) (335-338).
Comment 4: “Table 1 shows FeCO3(%) and MgCO3(%). In addition, the authors explained that they finally obtained (0.7Fe,0.3Mg)CO3. However, since there are no analysis results for these components, it is not clear whether or not they exist. XRD and XRF results are required.”
Response: Thank you very much for your comment. We have tried to perform an XRD analysis of the final sample but up to this moment it has been no possible to obtain a clear XRD because the final carbonate is not crystalline. We have performed a SEM-EDS analysis of different samples that is already included in another article that is focused in the parameters optimization of the reaction. Nevertheless, the carbonate composition have been estimated based on the ICP-OES, Total Inorganic Carbon (TIC) and CHNS analysis previously performed. On the other hand, we agree with you that it is not proper to assure that the final carbonate is a (0.7Fe,0.3Mg)CO3 without a proper XRD analysis. Consequently, we have removed it from the article to avoid misunderstandings (line 438) keeping just “iron rich carbonate”.
Comment 5: “ It is correct to use the term ‘recovered liquid’ instead of the term ‘unreacted liquid’”.
Response: the term “unreacted liquid” for “recovered liquid” have been modified.
Comment 6: “Many values are given in the texts of ‘3.4 Global mineral carbonation approach evaluation’ and ‘3.5 GHG balance’ and in Figures 7 and 8. It is not clear how these values were calculated because there is no relevant explanation in the manuscript or supplementary information.”
Respond: Thank you very much for your comment. Figure 7 and 8 shown in mass balance (3.4.1) were estimated based on the gas flow (eq. 10), the leaching efficiency (Figure 4 and 5) and the ICP-OES, Total Inorganic Carbon and CHNS analysis performed before and after each step of the mineral carbonation process. Some of these analysis are included in another article focused on the optimization of the mineral carbonation reaction. Nevertheless,an explanation about the calculation of these values have been included (lines 383-385).
The GHGs balance estimations have been estimated based on results obtained by Pasquier et al. (reference 7), the distance from the Mine Arnaud site to Aluminerie Alouette and Arcelor Mital (15 km and 31 km obtained from Google Maps), the CO2 electricity emission factor (reference 46) Furthermore, as we have pointed out in the article, the balances shown in this article are laboratory scale estimates that show optimistic results for possible future realization. The next step would be to carry out the process on a larger scale where both its mass and GHG balance would have to be carried out in an exhaustive way. Since these results are based on a large amount of data and analysis, we believed that the information provided in the article is sufficient (and not to confuse the reader with too much information) to give an idea about the mineral carbonation process carried out.
Author Response File: Author Response.pdf
Reviewer 3 Report
Line 55-57: The authors mention CO2 sequestration by mineral carbonation in recent work but have referenced papers from 2006. Especially for wollastonite, there have been recent studies from 2020, for example:
Haque, F., Santos, R. M., & Chiang, Y. W. (2020). CO2 sequestration by wollastonite-amended agricultural soils–An Ontario field study. International Journal of Greenhouse Gas Control, 97, 103017.
Kashim, M. Z., Tsegab, H., Rahmani, O., Abu Bakar, Z. A., & Aminpour, S. M. (2020). Reaction Mechanism of Wollastonite In Situ Mineral Carbonation for CO2 Sequestration: Effects of Saline Conditions, Temperature, and Pressure. ACS omega, 5(45), 28942-28954.
Limitation of the application: Specific to Fe-rich silicate waste generated from Sept-Îles region. Any comment on other quarry sites or industries producing Fe-rich silicate where the proposed solution can be employed for mineral carbonation?
Section 3.1: Characterization method using IR should be mentioned in the Methodology and only the results should be discussed in Section 3.1. The IR result can be moved to the supplementary section instead.
Characterization of the Fe-rich silicate used in the study should be given as well. XRF, XRD data, BET SA, particle size, was the mineral processed before the experiment?
Section 3.3.1. I would not call the method explained herein as “optimization” as no equations or modeling was used to find the optimized condition. What is presented in this section is finding the best parameters for mineral carbonation based on few conditions tested. Getting the best result at 80C doesn’t mean the optimized temperature is exactly at 80C, it can be 80.5C. Please make the appropriate changes to the wording used.
Another point, pH and temperature both are indeed very important parameters for mineral carbonation reactions as well as carbonate precipitation. Silicate dissolution and carbonate precipitation modeling using Visual Minteq or geochemical modeling could further support the results obtained.
Also, the particle size of the mineral is an important parameter, it should be discussed here.
Section 3.4 is a good attempt to discuss the feasibility of the proposed carbonation route. With very few studies available at present, this manuscript will add to the limited body of knowledge. However, it will be interesting to see the link between the CO2 sequestered and the carbon price, given the high price of the ligand used in the study.
Please recheck the references, the format seems inconsistent (missing doi, different formats of doi, etc).
Author Response
RESPONSES TO REVIEWERS’– MANUSCRIPT ID (minerals-1108257)
Reviewer Comments, Author Responses and Manuscript Changes
We would like to thank the reviewers for taking the time and effort necessary to review the manuscript. We sincerely appreciate all valuable comments and suggestions, which helped us to improve the quality of the manuscript.
-Reviewer 3
Comment 1: “Line 55-57: The authors mention CO2 sequestration by mineral carbonation in recent work but have referenced papers from 2006. Especially for wollastonite, there have been recent studies from 2020, for example:
Haque, F., Santos, R. M., & Chiang, Y. W. (2020). CO2 sequestration by wollastonite-amended agricultural soils–An Ontario field study. International Journal of Greenhouse Gas Control, 97, 103017.
Kashim, M. Z., Tsegab, H., Rahmani, O., Abu Bakar, Z. A., & Aminpour, S. M. (2020). Reaction Mechanism of Wollastonite In Situ Mineral Carbonation for CO2 Sequestration: Effects of Saline Conditions, Temperature, and Pressure. ACS omega, 5(45), 28942-28954”
.
Respond: Thank you very much for your references. You are completely right that reference papers from 2006 can be out of date. The references have been modified.
Comment 2 “Limitation of the application: Specific to Fe-rich silicate waste generated from Sept-Îles region. Any comment on other quarry sites or industries producing Fe-rich silicate where the proposed solution can be employed for mineral carbonation?”
Response: As it is explained in lines 507-511 “This study further confirmed the possibility of performing mineral carbonation using Fe-rich mining residues and post-combustion industrial CO2 gas in a recirculation scenario. Although the proposed approach was performed in the Sept-Îles region (Quebec, Canada) using Mine Arnaud mining residue, it provides guidance for the development of mineral carbonation by cation complexation using iron-rich olivine as a viable sequestration technique in other regions”. Although the residue used comes from Sept-Îles region, it is expected that any residue containing Fayalite could be used to perform the mineral carbonation reaction perform in this article.
Comment 3: “Section 3.1: Characterization method using IR should be mentioned in the Methodology and only the results should be discussed in Section 3.1. The IR result can be moved to the supplementary section instead.”
Response: Thank you very much for your comment. You are completely right that the characterization method using IR is missing in the Methodology and should be mentioned there and not in the results. The IR analysis have been mentioned in section 2.4.1 “Characterization of the [Fe(bipy)3]2+ and regeneration of the 2,2’-bipyridine” (lines 144-150). We think the IR is an important analysis to demonstrate the complex formation and the regeneration of the 2,2’-bipyridine after the reaction for its reuse.
Comment 4: Characterization of the Fe-rich silicate used in the study should be given as well. XRF, XRD data, BET SA, particle size, was the mineral processed before the experiment?
Response: The Fe-rich silicate has been highly characterized prior to its use in the mineral carbonation process. The particle size, density, solid/liquid rate, chemical composition (ICP-OES) and mineralogical analysis (XRD) have been analyzed. The characterization of the Fe-Rich is included in another article focus on the parameters optimization of this mineral carbonation reaction that will be soon published. This article is the part of a PhD thesis called “Optimisation of a CO2 sequestration technique for the carbonation of mineral residues containing fayalite with iron complexation using 2.2'-bipyridine”. The goal of this article is to give an approach about the feasibility of this process in a recirculation scenario to reduce the amount of reactives and the possible reutilization of products that will be necessary to use this process at a bigger scale. The mineral was not needed to be highly processed before the experiments. Lines 127-130 shows that “the silicate residue that was received, homogenized, and characterized prior to its use in this study. The material did not need to be crushed, because the median particle size of the residue was 65 µm, which was optimal for performing mineral carbonation”. I hope this could respond to your question.
Comment 5: Section 3.3.1. I would not call the method explained herein as “optimization” as no equations or modeling was used to find the optimized condition. What is presented in this section is finding the best parameters for mineral carbonation based on few conditions tested. Getting the best result at 80C doesn’t mean the optimized temperature is exactly at 80C, it can be 80.5C. Please make the appropriate changes to the wording used.
Response: It is true that the work “optimization” maybe needs a deeper analysis to be used. Our aim is to show the best reaction conditions based on the parameters that most influence the mineral carbonation reaction. These parameters were chosen from a Box-Behnker design carried out by a Master student in our research group. Since there is not enough information to talk about “optimization”, this word has been modified throughout the article by “most favorable” and “preferential” to avoid misunderstandings. I hope this could solve the problem.
Comment 6: Another point, pH and temperature both are indeed very important parameters for mineral carbonation reactions as well as carbonate precipitation. Silicate dissolution and carbonate precipitation modeling using Visual Minteq or geochemical modeling could further support the results obtained.
Response: Thank you very much for your help. After a proper training, we would use these programs to support the results in future analysis. We know there is much more work to do but this article show very promising results about a new mineral carbonation approach that maybe could be use at bigger scale. Programs as Visual Minteq will help us to support the results show in this article. Thank you.
Comment 7: Also, the particle size of the mineral is an important parameter, it should be discussed here.
Response: As it was explained in comment 4, the particle size analysis will be included in another article with all the characterization analysis. Nevertheless, lines 128-130 says that “The material did not need to be crushed, because the median particle size of the residue was 65 µm, which was optimal for performing mineral carbonation (reference 34))”. We think that this explanation is enough to show the importance of the particle size.
Comment 8: Section 3.4 is a good attempt to discuss the feasibility of the proposed carbonation route. With very few studies available at present, this manuscript will add to the limited body of knowledge. However, it will be interesting to see the link between the CO2 sequestered and the carbon price, given the high price of the ligand used in the study.
Response: Thank you very much. It makes us very happy to hear that the work done over the years is gradually being rewarded and appreciated by other researchers like you. We know that it is still much work to do but this is a good start point for a future development of this original technique.
The possibility of working in a recirculation scenario would reduce reagent costs. To have an estimation about the costs, two companies were contacted through the Alibaba.com website. The Shanghai Beijing Chemical Co. Ltd. estimated a price of US$4,930/t of 2,2'-bipyridine while Easmaterial Group, Ltd. estimated a price of US$40,800/t of NH4HSO4. Note that prices include purchase and shipping to Quebec City. With regard to the cost of NaOH, various companies have estimated a total price of US$450/tonne. Nevertheless, as it was demonstrated in the article, the 2,2’-bipyridine and NH4HSO4 have been totally (2,2’-bipyridine) or partially (NH4HSO4) recovered, reducing the overall cost of the process. The purification and/or crystallisation of the Fe-carbonate and the resulting mine tailings should also be further developed in order to reduce the costs related to this technique. On the other hand, carbon prices have already been implemented in 40 countries and 20 cities and regions. According to a 2019 World Bank report on trends in carbon pricing, a carbon price range of US$40-80 is necessary by 2020 to reach the goals set by the 2015 Paris Agreement. As countries try to limit the average global temperature increase to 2 degrees Celsius, average carbon prices could increase more than sevenfold to US$120 per metric ton by 2030.
Nevertheless, an exhaustive economic and energy study must be carried out in order to obtain estimates as close as possible to reality.
Since the aim of this article is to give an estimate of the possibility of carrying out this mineral carbonation technique and in the absence of a larger scale study, we believe that the economic study of this process should be carried out in depth and included in future articles where the process is carried out on a larger scale. I hope you agree with us.
Comment 9: Please recheck the references, the format seems inconsistent (missing doi, different formats of doi, etc).
Response: Thank you very much for your appreciation. References have been rechecked. ISBN have been included in Books. The ISSN (International Standard Serial Number) have also been included for some serial publications and all the doi have been included and set with the same format.
Author Response File: Author Response.pdf
Reviewer 4 Report
This manuscript is one of the best versions in terms of the process of indirect mineral carbonation, using 2,2'-bipyridine. The authors have elucidated as well about an exact process of CO2 mineral carbonation by applying a material rich in Fe. The amounts of CO2 uptake and stable precipitation are discussed in detail. The stages of carbonation in terms of indirect mineralization are well described. I am really happy to have this manuscript as a Topic Editor in Minerals. Some points need to be considered before publishing.
Line 30: Abbreviate Integra. Panel for Climate Change to IPCC for the first time.
The carbon emission is now available in late 2020. it is recommended to update the data in recent months. See Lines 31-32.
Line 50: Ca and Mg are commonly applied to react with CO2 in the Carbonation process rather than Fe! It is much better to write (Ca, Mg, Fe, or Ba) instead of (Fe, Ca, Mg).
Lines 51-52: This statement can be more applicable by referring to: "Mineral Carbonation of Red Gypsum for CO2 Sequestration". https://doi.org/10.1021/ef501265z
Line 55: Lackner et al. Which article do you mean? Please cite it accordingly.
Line 57: Also, add these references to:
forsterite: https://doi.org/10.3390/molecules21030353
wollastonite: https://doi.org/10.1021/acsomega.0c02358
and basalt: https://doi.org/10.3390/min10121045
Line 62-65: This reference can valid the following statement. Refer to it. "Indirect mineral carbonation reactions, where divalent cations are extracted into the solution prior to the reaction with CO2, have much better reaction efficiencies and are thus more suitable for future industrial implementation, even more with refractory materials". https://doi.org/10.1016/j.jcou.2018.08.017
Lines 66-75: Shift it to the last paragraph of the Introduction where Lines 111-117 elucidate the scope and objective of this study.
Lines 76-81: How do you prove it? Any reference?
Line 161: Why the stirring speed is fixed at 250 rpm? Any reason? Like what you have mentioned for 2h of experimental time.
Lines 162-163: needs to be covered by a valid reference.
Fig.1: authors have not mentioned the amount of bipyridine and Fe(bipy)3 within the text. In Fig. 1, the amount is shown in 28.5 ml and 48.5 ml, respectively.
Fig. 3: Indicate the peak of water crystalization, 3300.
Also, other peaks represent which complex, mineral, or reaction? Clarify further.
The results are astonishing in terms of the main factors of pH, temperature, time, and stirring rate. The factor of pressure is missed, while a short statement compensates this missing.
Please check thoroughly about "laboratory essays" or laboratory assays"?
I recommend publishing this manuscript after those minor corrections.
Author Response
RESPONSES TO REVIEWERS’– MANUSCRIPT ID (minerals-1108257)
Reviewer Comments, Author Responses and Manuscript Changes
We would like to thank the reviewers for taking the time and effort necessary to review the manuscript. We sincerely appreciate all valuable comments and suggestions, which helped us to improve the quality of the manuscript.
-Reviewer 4
Comment 1: “This manuscript is one of the best versions in terms of the process of indirect mineral carbonation, using 2,2'-bipyridine. The authors have elucidated as well about an exact process of CO2 mineral carbonation by applying a material rich in Fe. The amounts of CO2 uptake and stable precipitation are discussed in detail. The stages of carbonation in terms of indirect mineralization are well described. I am really happy to have this manuscript as a Topic Editor in Minerals.”
Response: Thank you very much for your comment. It gives us great pleasure to read these comments from experts in the field and it is a pleasure for us to have the possibility to publish in Minerals.
Comment 2: “Line 30: Abbreviate Integra. Panel for Climate Change to IPCC for the first time.”
Response: The abbreviation IPCC have been included
Comment 3: “The carbon emission is now available in late 2020. it is recommended to update the data in recent months. See Lines 31-32.
Response: The carbon emissions and the citation have been updated to the latest IPCC. (Lines 30-32)
Comment 4: “Line 50: Ca and Mg are commonly applied to react with CO2 in the Carbonation process rather than Fe! It is much better to write (Ca, Mg, Fe, or Ba) instead of (Fe, Ca, Mg).”
Response: You are completely right. Thank you very much! The parenthesis have been changed.
Comment 5: “Lines 51-52: This statement can be more applicable by referring to: "Mineral Carbonation of Red Gypsum for CO2 Sequestration". https://doi.org/10.1021/ef501265z”
Response: Thank you very much for the reference. It has been included (reference 12) (line 52).
Comment 6: “Line 55: Lackner et al. Which article do you mean? Please cite it accordingly”
Response: Lackner et al. refers to references 15 and 16:
Reference 15: Lackner, K.S.; Wendt, C.H.; Butt, D.P.; Joyce, B.L.; Sharp, D.H. Carbon dioxide disposal in carbonate minerals. Energy 1995, 20, 1153-1170, doi:https://doi.org/10.1016/0360-5442(95)00071-N.
Reference 16: Lackner, K.S.; Butt, D.P.; Wendt, C.H. Progress on binding CO2 in mineral substrates. Energy Convers. Manage. 1997, 38, doi:https://doi.org/10.1016/S0196-8904(96)00279-8.
I hope this could solve the misunderstanding.
Comment 7: “Line 57: Also, add these references to:
forsterite: https://doi.org/10.3390/molecules21030353
wollastonite: https://doi.org/10.1021/acsomega.0c02358
and basalt: https://doi.org/10.3390/min10121045
Response: Thank you very much for the references. They have been included;
Forsterite: reference 21
Wollastonite: reference 27
Basalt: reference 28
Comment 8: Line 62-65: This reference can valid the following statement. Refer to it. "Indirect mineral carbonation reactions, where divalent cations are extracted into the solution prior to the reaction with CO2, have much better reaction efficiencies and are thus more suitable for future industrial implementation, even more with refractory materials". https://doi.org/10.1016/j.jcou.2018.08.017
Response: Thank you very much for the reference. It has been included (reference 33).
Comment 9: Lines 66-75: Shift it to the last paragraph of the Introduction where Lines 111-117 elucidate the scope and objective of this study.
Response: You are completely right. The paragraph have been shift (Lines 98-107).
Comment 10: Lines 76-81: How do you prove it? Any reference?
Response: Reference 37 have been included where the Eh-pH diagram of the system Fe-CO2-H2O AT 25 degrees is presented. The diagram shows the impossibility of obtaining iron carbonates at alkaline pH without precipitating iron oxides or hydroxides. For this reason, and after an exhaustive study, it was concluded that the use of 2-2'-bipyridine could be a good option due to its high stability with iron.
Comment 11: Line 161: Why the stirring speed is fixed at 250 rpm? Any reason? Like what you have mentioned for 2h of experimental time.
Response: The leaching conditions have been previously studied by a Master’s Student at INRS-ETE (Waâd Khemiri (2019) CO2 sequestration process by indirect mineral carbonation of mine tailings from the exploitation of an apatite deposit of the "Mine Arnaud" Master's degree in Earth Sciences INRS ÉTÉ). As it is not published, I cannot add it as a reference. A sentence to note that they have been previously optimized is written in Line 167.
Comment 12: Lines 162-163: needs to be covered by a valid reference.
Response: You are completely right. Reference 40 have been included. Furthermore, these results have also been confirmed by a Master student at INRS-ETE. (Waâd Khemiri (2019) CO2 sequestration process by indirect mineral carbonation of mine tailings from the exploitation of an apatite deposit of the "Mine Arnaud" Master's degree in Earth Sciences INRS ÉTÉ).
Comment 13: Fig.1: authors have not mentioned the amount of bipyridine and Fe(bipy)3 within the text. In Fig. 1, the amount is shown in 28.5 ml and 48.5 ml, respectively.
Response: The amount of 2,2’-bipyridine (28.5 ml) and leachate (20 ml) to obtain 48.5 ml of complex ([Fe(bipy)3]2+) is mentioned in lines 127-129 and 203-205. I hope this could solve the misunderstanding.
Comment 14: Fig. 3: Indicate the peak of water crystalization, 3300.
Response: The peak of water crystallization have been included (Figure 4)
Comment 15: Also, other peaks represent which complex, mineral, or reaction? Clarify further.
Response : The IR-Spectra of the samples before, during and after the reaction have been included to confirm the complex formation and its regeneration. As the IR-Spectra before and after the reaction is similar (it is 2,2’-bipyridine not complexed) we think that we should only include it once (Figure 3). On the other hand, the [Fe(bipy)3]2+ complexed have been included and compared. I hope this could be enough to respond your comment. The IR analysis have been included in section 2.4.1 “Characterization of the [Fe(bipy)3]2+ and regeneration of the 2,2’-bipyridine” (lines 144-150).
Comment 16: The results are astonishing in terms of the main factors of pH, temperature, time, and stirring rate. The factor of pressure is missed, while a short statement compensates this missing.
Response : Thank you very much for your comment. The sentence “Reactions were performed under atmospheric pressure in order to decrease the energetic requirements.”( Line 186-187) have been included. In order to have the best energetic balance reactions were performed under atmospheric pressure. Other essays at different pressures could be performed in the future.
Comment 17: Please check thoroughly about "laboratory essays" or laboratory assays"?
Response: Thank you very much for your appreciation. As the main difference between Essay and Assay is that the Essay is a piece of writing often written from an author's personal point of view and Assay is a investigative (analytic) procedure in laboratory we have modified essay for assay.
Author Response File: Author Response.pdf
Round 2
Reviewer 3 Report
The authors have done a good job in responding to the comments.
Author Response
Dear Reviewer,
Thank you very much for your comment.
This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.
Round 1
Reviewer 1 Report
This study is about indirect carbonization using iron-silicate mining waste via iron complexation with 2,2'-bipyridine.
In the manuscript, the mechanism for complexation, and results for iron-rich carbonate solids are described without data or evidence. Data including FT-IR, XRD are required.
The results of the Figures or Tables presented in the manuscript are not properly integrated and it is not explained well why the results are important and what they mean.
It is necessary to write the paper so that the important things are revealed.
Reviewer 2 Report
The subject matter brought up in the article is very interesting. In the opinion of the reviewer the article can be publish without changes.
Reviewer 3 Report
Review of “Feasibility of a Mineral Carbonation technique using iron-silicate mining waste by direct flue gas CO2 capture and cation complexation using 2,2’-bipyridine.
Overall, this is an interesting piece of work, however, there are many questions that need to be answered in the publication, as described below.
- The need for bipyridine in this process has not been explained, why is it necessary?
- Fig 2 needs improvement. As is common for the presentation of a block flow diagram, all of the inlet streams need to be extended out to the left and all of the outlets needs to be extended out to the right so that the reader can see at a glance what is going into and out of the process. Suspect that the 4 ml and 20 ml NH4HSO4 are the wrong way around given the content of the paper later on, whereby you added 4ml for subsequent leaching tests. Ethanol is not mentioned here in this diagram and needs to be added.
- There is a lack of chemical reactions in this paper. All reactions taking place must be listed so that it is possible to see how the process is balanced from a molecular point of view. Then it is possible to see if “only 4ml” is insignificant or not. i.e. it is necessary to see the amounts needed in all of the reactions.
- At the moment there is accumulation of NH4HSO4 and bipyridine in the process, i.e. Fig 2 has these compounds coming in but they are not leaving. So the recirculation in the process has not been adequately addressed. There will also be accumulation of components leached from the waste, where do other compounds that dissolve exit the process, such as dissolved Si(IV).
- Following on from (4) it is really not possible at this stage to claim that the results are promising for development of a larger scale process (line 332) – this line should be removed.
- Also line 358 states that it is ready for continuous operation. It is not ready due to accumulation of reagents, and the need to purchase reagents. As it presently looks this process needs to buy fresh NH4HSO4 and fresh NaOH as there isn’t a mechanism in the process to regenerate these reagents. An examination of the stepwise reactions taking place (which must be included) will reveal this. This makes the process fatally flawed and needs to be discussed.
- The purity of the silica rich residue at 81.5% is not overly high, how does this compare to other supplies of quartz (which are highly abundant in the Earth).
- It is interesting that this waste comes from an apatite mine but there appears to be no Ca in the waste.
- Table 2, put extra lines to separate data at the different temperatures.
- Section 3.3.1 is confusing. When it is stated that the unreacted residue was recycled, I initially assumed this was the solid from leaching but now assume this means the unreacted liquid, please fix the wording in this section to use consistent terms for each material in the process.
