Recycling Feldspar Mining Waste as Buffering Agent for Acid Mine Drainage Mitigation

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Title: Recycling feldspar mining waste as buffering agent for Acid 2 Mine Drainage mitigation

 

Abstract: the word “dumps.” Is not commonly used; better to use waste rock dam or tailing.

 

Introduction: authors do not talk about biorremediation methods and their advantages.

 

Conclusions: authors do not talk about biorremediation

 

The subject of the paper is interesting and lab results seem promissing in using alkaline wastes from feldspar mining wastes to neutralize acid mine drainage eastes from sulfide mining areas, however it is no clear if such  approach would be suitable for the field…

 

English needs minor revisions

Comments on the Quality of English Language

minor corrections

Author Response

1. Abstract: the word “dumps.” Is not commonly used; better to use waste rock dam or tailing.

We replaced the terms waste dump and tailing dump with wastes and tailings.

2. Introduction: authors do not talk about biorremediation methods and their advantages.

We agree that bioremediation is a fundamental part of risk management, according to the request we added in the introduction a general part on the role of bioremediation and the fact that our study concerns a specific chemico-physical action that is part of a more general risk management.

3. Conclusions: authors do not talk about bioremediation (see point 2.)

We added a sentence in the conclusions that again stress how the results of this work have to be applied in combination with other procedures and especially bioremediation ones.

4. The subject of the paper is interesting and lab results seem promissing in using alkaline wastes from feldspar mining wastes to neutralize acid mine drainage eastes from sulfide mining areas, however it is no clear if such approach would be suitable for the field…

We agree that this first stage ascertaining the scientific validity of the approach requires further steps to be applied in the field. This means a thorough study of the technical and economic feasibility in real situations and can be addressed in following studies. We added considerations about this in the conclusions.

5. English needs minor revisions

We checked again all the manuscript and corrected English language errors.

Reviewer 2 Report

Comments and Suggestions for Authors

A very interesting study devoted to the important problem of remediation of sulfide-bearing mining sites.  The authors  checked a circular economy approach to such issue - they conducted tests on feldspar mining wastes that could be recycled as buffering agent of sulfide-bearing tailings.

I have no significant questions or comments, just a few small remarks.

(1) Line 149. The abbreviation FLS appears in the text for the first time, but only on line 182 is it deciphered what it meansю

(2) Lines 160-161. ‘Ion concentrations on leaching water samples CP-1 and FS11 were analyzed using inductively coupled plasma-mass spectroscopy ’. And by what method were the data from Table 3 obtained (results of the leaching test on FLS)?

(3) Lines 190-192. ‘As Ca is hosted only in calcite among the detected minerals…’ This is essentially true, but strictly speaking, the sample also contains plagioclase (Fig.1)

(4) Table 8. What, in the opinion of the authors, could be the reason for such a different buffering effect on the lead content for CP1 and FS11 samples?

Author Response

A very interesting study devoted to the important problem of remediation of sulfide-bearing mining sites.  The Authors checked a circular economy approach to such issue - they conducted tests on feldspar mining wastes that could be recycled as buffering agent of sulfide-bearing tailings. I have no significant questions or comments, just a few small remarks.

1. Line 149. The abbreviation FLS appears in the text for the first time, but only on line 182 is it deciphered what it means.

We added the full name of sample FLS

2. Lines 160-161. ‘Ion concentrations on leaching water samples CP-1 and FS11 were analyzed using inductively coupled plasma-mass spectroscopy’. And by what method were the data from Table 3 obtained (results of the leaching test on FLS)?

We used the same methodology for FLS and modified the methodology chapter correcting the oversight according to reviewer’s comment.

3. Lines 190-192. ‘As Ca is hosted only in calcite among the detected minerals…’ This is essentially true, but strictly speaking, the sample also contains plagioclase (Fig.1)

We fully agree with the comment, we added a new description of the distribution of Ca in the sample emphasizing two thing: a) the contribution of feldspars to Ca whole sample content is very minor as feldpsars are typically low in anorthite components and have a Ca content much lower than calcite and according to XRD results the contents of feldspar is lower than that of calcite

4. Table 8. What, in the opinion of the authors, could be the reason for such a different buffering effect on the lead content for CP1 and FS11 samples?

We added an explanation based on the work of Zhu et al. (2023) for the decrease in Pb content during buffering of CP1 (co-precipitation as PbCO3 component in calcite), in FS11 no Pb reduction occurred as its initial content was very low due to the different geochemistry and mineralogy of ore.

Reviewer 3 Report

Comments and Suggestions for Authors

1. The use of carbonate to neutralize the pH of acid mine drainage (AMD) has been studied widely. Your research focuses on recycling mining waste for this purpose. If this waste contains carbonates, it's understandable that it could be effective in AMD remediation. However, it would be helpful if you could emphasize why this particular study is necessary. 
2. One of the potential benefits of using recycled mining waste is the cost-effectiveness compared to conventional treatment agents. Could you provide a cost comparison to highlight the economic advantages of your method?
3. There is a concern that adding natural mining waste to treat AMD might introduce another source of pollution, especially if the waste contains toxic metals. It would be beneficial if your paper could discuss this issue.

Author Response

1. The use of carbonate to neutralize the pH of acid mine drainage (AMD) has been studied widely. Your research focuses on recycling mining waste for this purpose. If this waste contains carbonates, it's understandable that it could be effective in AMD remediation. However, it would be helpful if you could emphasize why this particular study is necessary. 

The present study wants to focus on the possibility to employ a circular economy approach, by using feldspar and carbonate-bearing sludges. The results highlight a buffering capacity of feldspar as well as carbonate. Therefore, feldspar and/or carbonate bearing waste rocks and tailings can be safely employed to buffer AMD. Whenever these sludges can be retrieved close to the AMD polluted sites, they can be used to buffer acid waters in a sustainable way.

2. One of the potential benefits of using recycled mining waste is the cost-effectiveness compared to conventional treatment agents. Could you provide a cost comparison to highlight the economic advantages of your method?

We fully agree that cost-effectiveness, together with technical and legal assessment, are pivotal to define the real on field application of the methodology. Our work focuses on the first, essential, stage, that is the scientific soundness of the process. Further studies will have to deal with economic, technical and legal soundness. These will require to use also other competences than those of the Authors, funds and time. The results hopefully will be part of one or more future articles.

We stressed all this by adding a part to the conclusions.

3. There is a concern that adding natural mining waste to treat AMD might introduce another source of pollution, especially if the waste contains toxic metals. It would be beneficial if your paper could discuss this issue.

The thorough characterization of FLS sample was aimed to both check its potential buffering capacity and assess its possible contribution to the release of toxic metals when used as buffer material. The results show that in its waste location at Florinas its basic drainage can release above legal limits of Al. Very low Al is detected in FS11 sample buffered with FLS, in the article discussion this is attributed to the neutral pH of buffered waters that, differently from highly basic waters do not solubilize significant amounts of Al.

Reviewer 4 Report

Comments and Suggestions for Authors

This is a valuable paper worthy of publication after some changes, corrections and clarifications. There have been many attempts to persuade the mining industry worldwide to take more seriously the evaluation and use of neutralizing waste and adjacent non-mined rock material in disposal of wastes producing acid and metalliferous drainage. This is a good example of this evaluation in practice with the aim of their use in treating old mining wastes in Sardinia. The paper provides good justification for this use.

 

It is also important in showing that it is not just carbonates that can provide this neutralization and that many silicates have long-term neutralization that are complementary to carbonates in long-term control. This is also not widely recognized in mine waste disposal despite many literature reports. The paper provides important evidence for this in planning for treatment of the Sardinian wastes.

 

The paper needs some correction before publication can be accepted.

1. There are colloquial words and phrases as might be used in a talk throughout that need to be removed and replaced with scientific terms and explanations. Some are marked in the review.

2. There is too much repetition of results in the later sections that can be reduced in a final version. This needs a critical reading by a colleague not involved in the work if possible to remove duplication of explanations.

3. The authors have used Total S instead of Sulfide S (as in the chromium reducible S test) to estimate ABA for the wastes. This is no longer acceptable in AMD testing (see GARD Guide). It is unlikely to change any of the conclusions in the paper given the good mineralogy testing reported. But it may be worth showing this by a comparison of Total and Sulfide S on some of the wastes. It is also noted that sphalerite and galena do not produce acid in oxidation but metal drainage.

Comments on the Quality of English Language

This is a valuable paper worthy of publication after some changes, corrections and clarifications. 

Author Response

This is a valuable paper worthy of publication after some changes, corrections and clarifications. There have been many attempts to persuade the mining industry worldwide to take more seriously the evaluation and use of neutralizing waste and adjacent non-mined rock material in disposal of wastes producing acid and metalliferous drainage. This is a good example of this evaluation in practice with the aim of their use in treating old mining wastes in Sardinia. The paper provides good justification for this use.

It is also important in showing that it is not just carbonates that can provide this neutralization and that many silicates have long-term neutralization that are complementary to carbonates in long-term control. This is also not widely recognized in mine waste disposal despite many literature reports. The paper provides important evidence for this in planning for treatment of the Sardinian wastes.

The paper needs some correction before publication can be accepted.

1. There are colloquial words and phrases as might be used in a talk throughout that need to be removed and replaced with scientific terms and explanations. Some are marked in the review.

We are grateful to the Reviewer for this comment and tried to change all colloquial words we detected.

2. There is too much repetition of results in the later sections that can be reduced in a final version. This needs a critical reading by a colleague not involved in the work if possible to remove duplication of explanations.

We accepted suggestion and after critical reading we reduced repetitions.

3. The authors have used Total S instead of Sulfide S (as in the chromium reducible S test) to estimate ABA for the wastes. This is no longer acceptable in AMD testing (see GARD Guide). It is unlikely to change any of the conclusions in the paper given the good mineralogy testing reported. But it may be worth showing this by a comparison of Total and Sulfide S on some of the wastes. It is also noted that sphalerite and galena do not produce acid in oxidation but metal drainage.

At the moment, it is not possible to perform further analyses on those samples, moreover the MPA values is not an important parameter for our work, differently from ANC value, especially that of FLS sample. So we specified that in the text, justifying the use of a rough evaluation of MPA with Stot, due to its relatively low importance together with absence of sulfates in the samples according to XRD results.

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

Thank you for replying. There is no more comment from me.