Enhanced Monovalent Cation Biomineralization Ability by Quartz Sand for Effective Removal of Soluble Iron in Simulated Acid Mine Drainage

Round 1

Reviewer 1 Report

Thank you for reworking and resubmitting the manuscript. It has improved substantially compared to the original submission. Next time make sure you track all of the changes that you made, not only additions but the deletions as well. 

Overall, I am satisfied with most of the changes. However, I am still missing one aspect of the work: the findings of the paper do not indicate whether this would work in a real AMD system or not. Broader applications and the significance of this experiment are not discussed well. This issue was brought up during reviewing the first submission, but I cannot find your response.

If the authors have not thought about the broader applications on a real AMD, it would be beneficial to discuss how this can be tested on a real system. Isn't the overall goal is to clean up real AMD waste?

Or if the experimentation has not reached enough supporting evidence for real AMD applications that should be stated and future directions (next steps) discussed.

Author Response

Reviewer #1:

Comment 1: Thank you for reworking and resubmitting the manuscript. It has improved substantially compared to the original submission. Next time make sure you track all of the changes that you made, not only additions but the deletions as well. 

Overall, I am satisfied with most of the changes. However, I am still missing one aspect of the work: the findings of the paper do not indicate whether this would work in a real AMD system or not. Broader applications and the significance of this experiment are not discussed well. This issue was brought up during reviewing the first submission, but I cannot find your response.

If the authors have not thought about the broader applications on a real AMD, it would be beneficial to discuss how this can be tested on a real system. Isn't the overall goal is to clean up real AMD waste?

Or if the experimentation has not reached enough supporting evidence for real AMD applications that should be stated and future directions (next steps) discussed.

Response:

Thank you for pointing this out. It is well known that the common features of acid mine drainage (AMD) are low pH and high concentrations of heavy metals and other toxic and harmful elements. Wei (2001) has investigated the basic physical and chemical properties of AMD in China's major mining areas and found that there were differences between the indexes of AMD. The results are shown as below.

Physical and chemical properties	Mine
	Xiangtan manganese mine	Dongxiang copper mine	Dingjia copper mine	Washan iron mine	Daye iron mine	Tanshan pyrite mine
pH	3-3.8	1.8-4.2	2-3	1.7	4-5	2-3
SO42-				7789		4120
Cu2+		4.2-27.2	20-80		170-400
Fe3+		18-4711		465
Fe2+		7.8-5033		9.1
Total Fe	10-25		10-800			926
Mn2+	600-800
Al3+	50-190
Mg2+	200-300

 

It can be seen from the above table that the physical and chemical properties of AMD produced by different types of mines are quite different, especially the pH value or Fe²⁺ concentration was within a wider range of 1.7-5.0 or 7.8~5033 mg/L, respectively. However, in our study, the pH and Fe²⁺ concentration of simulated AMD was 2.5 and 8960 mg/L, respectively. Obviously, our research results has not reached enough supporting evidence for real AMD applications. We agree with the reviewer that how to apply the experimental results to the real AMD is very important. In the later stage, we plan to go to the mine site to sample and analyze the real AMD, so as to further understand the physical and chemical properties of AMD produced by different mines. On this basis, we will continue to try to apply the results of our study to the treatment of real AMD and optimize the experimental conditions to evaluate the feasibility of this method. We have supplemented the next research plan in the revised manuscript. Please refer to the revised manuscript for details (lines 310-312).

Wei, G.J. Mine environmental engineering. Beijing: Metallurgical Industry Press, 2001.

Once again, thank you very much for your comments and suggestions. In addition, the manuscript and reference list has been checked up and revised. Please refer to the revised manuscript.

Author Response File: Author Response.pdf

Reviewer 2 Report

Manuscript entitled “Enhanced monovalent cation biomineralization ability by quartz sand for effective removal of soluble iron in simulated acid mine drainage” submitted by Heru Wang, Mengying Li and Yongwei Song, can be accepted for publishing in Water Journal, after major revision.

In this study, the effects of quartz sand (as a crystal seed) on the Fe2+ biooxidation efficiency, total Fe precipitation efficiency, and synthetic mineral phases is examined. The manuscript presents original results, but their presentation and interpretation is too brief. In my opinion, this manuscript should be published in your Journal after a major revision, which must correct these drawbacks.

 

Here is a list of my specific comments:

1. General comment: The novelty and practical applicability of this study must be clearly highlighted. Why is useful a such study???
2. Page 1, lines 19-22: The paragraph “In this study, at an initial pH…” should be reformulated, because it is not clear.
3. Page 1, 1. Introduction: This section is too brief and must be detailed in order to describe the state of art in this field.
4. Page 2, line 79: “Therefore, quartz sand was selected…” At the end of Introduction, the main objectives of this study should be clearly formulated.
5. Page 3, 3. Results and Discussion: The experimental results included in this study must be more detailed interpreted, in agreement with its objectives.

 

Author Response

Reviewer #2:

Manuscript entitled “Enhanced monovalent cation biomineralization ability by quartz sand for effective removal of soluble iron in simulated acid mine drainage” submitted by Heru Wang, Mengying Li and Yongwei Song, can be accepted for publishing in Water Journal, after major revision.

In this study, the effects of quartz sand (as a crystal seed) on the Fe²⁺ biooxidation efficiency, total Fe precipitation efficiency, and synthetic mineral phases is examined. The manuscript presents original results, but their presentation and interpretation is too brief. In my opinion, this manuscript should be published in your journal after a major revision, which must correct these drawbacks.

Comment 1: General comment: The novelty and practical applicability of this study must be clearly highlighted. Why is useful a such study???

Response: Thank you for your suggestion. As we mentioned in the manuscript, Fe²⁺ oxidation by A. ferrooxidans is often accompanied by the mineralization of Fe³⁺, producing secondary iron minerals such as schwertmannite and jarosite (Singer and Stumm 1970; Valente et al. 2013; Zhu et al. 2013). Schwertmannite and jarosite have been proven to exert a large adsorption or coprecipitation effect on heavy metals, which makes them ideal adsorbent materials (Mihone et al. 2015; Min et al. 2015; Zhang et al. 2016). However, A. ferrooxidans promotes the formation of schwertmannite in AMD, which exhibits low Fe precipitation efficiency. Correspondingly, in the presence of monovalent cations (such as K⁺, Na⁺, and NH₄⁺) of a certain concentration in acidic sulfate environments, Fe³⁺ will participate during the synthesis of jarosite. In this case, the yield of pure jarosite is approximately 1.5 times greater than that of pure schwertmannite when the same amount of Fe³⁺ is consumed. Therefore, inducing the formation of jarosite instead of schwertmannite is beneficial, as jarosite can reduce the Fe content in AMD and remove heavy metals. Previous studies shown that quartz sand can promote the transformation of soluble Fe to jarosite in acid sulfate environment. Nevertheless, it is still unclear how quartz sand impact the efficiency of Fe²⁺ oxidation and total Fe precipitation in A. ferrooxidans culture solutions including K⁺, Na⁺, or NH₄⁺. In previous studies, only the influence of K⁺ concentration has been taken into account (Wang et al. 2013), and the relative mineralizing ability of K⁺, NH₄⁺, or Na⁺, the differences in mineral phases between the secondary iron minerals in the presence of quartz sand have not yet been reported. The study on the influence of quartz sand on the ability of monovalent cation biomineralization has certain reference significance for the biological treatment of AMD.

Therefore, based on the biosynthesis of secondary iron minerals using A.ferrooxidans, the objective of the present work was to analyze the influence of quartz sand on the A. ferrooxidans-mediated biomineralization in simulated AMD. The addition of quartz sand (40 g/L) and concentration of monovalent cation (K⁺=53.3 mmol/L) were adjusted in reference to the study by Wang et al. (2013). The biomineralization capability of three monovalent cations (K⁺, NH₄⁺, and Na⁺) in the presence of quartz sand in an acidic sulfate system was investigated and compared by determining Fe²⁺ oxidation efficiency, total Fe precipitation efficiency, and synthetic mineral phases. We believe that the afforded results may provide an essential theoretical basis to promote the transformation of Fe to secondary iron minerals from AMD.

In order to give readers a better understanding of the objective of this study, we have made a proper supplement in “Introduction”. Please refer to the revised manuscript (lines 33-102).

Singer, P.C.; Stumm, W. Acidic mine drainage: the rate-determining step. Science 1970, 167, 1121–1123.

Valente, T.; Grande, J.A.; De, I.T.M.L. Santisteban, M. Cerón, J.C. Mineralogy and environmental relevance of AMD-precipitates from the Tharsis mines, Iberian Pyrite Belt (SW, Spain). Appl. Geochem. 2013, 39, 11–25.

Zhu, J.Y.; Gan, M.; Zhang, D.; Hu, YH.; Chai, L.Y. The nature of schwertmannite and jarosite mediated by two strains of Acidithiobacillus ferrooxidans with different ferrous oxidation ability. Mat. Sci. Eng. C 2013, 33, 2679–2685.

Mihone, K.M.; Hana, F.; Sanda, R.; Lidija, C. Assessment of metal risks from different depths of jarosite tailing waste of Trepça Zinc Industry, Kosovo based on BCR procedure. J. Geochem. Explor. 2015, 148, 161–168.

Min, G.; Sun, S.J.; Zheng, Z.H.; Tang, H.J.; Sheng, J.R.; Zhu, J.Y.; Liu, X.X. Adsorption of Cr(VI) and Cu(II) by AlPO₄ modified biosynthetic schwertmannite. Appl. Surf. Sci. 2015, 356, 986–997.

Zhang, S.L.; Jia, S.Y.; Yu, B.; Liu, Y.; Wu, S.H.; Han, X. Sulfidization of As(V)-containing schwertmannite and its impact on arsenic mobilization. Chem. Geol. 2016, 420, 270–279.

Wang, M.; Liang, J.R.; Zhou, L.X. The formation of biogenic jarosite by Acidithiobacillus ferrooxidans in the presence of crystal seed and potassium. J. Nanjing Agr. U. 2013, 36, 97–102.

 

Comment 2: Page 1, lines 19-22: The paragraph “In this study, at an initial pH…” should be reformulated, because it is not clear.

Response: Thank you for pointing this out. The abstract has been revised. Please refer to the revised manuscript. The paragraph has been revised as “Using simulated AMD, this work analyzes the influence of quartz sand (40 g/L) on the Fe²⁺ oxidation and total Fe deposition efficiencies, as well as the phases of secondary iron minerals in an Acidithiobacillus ferrooxidans system including K⁺, Na⁺, or NH₄⁺ (53.3 mmol/L)” (lines 19-21).

 

Comment 3: Page 1, 1. Introduction: This section is too brief and must be detailed in order to describe the state of art in this field.

Response: Thank you for your suggestion. The “Introduction” has been revised. Please refer to the revised manuscript (lines 33-102).

 

Comment 4: Page 2, line 79: “Therefore, quartz sand was selected…” At the end of Introduction, the main objectives of this study should be clearly formulated.

Response: Thanks for your comment. According to the reviewer's suggestion, we have changed the last paragraph of the introduction to make it easier for readers to know the objectives of this study. The details are as follows:

Therefore, based on the biosynthesis of secondary iron minerals using A.ferrooxidans, the objective of the present work was to analyze the influence of quartz sand on the A. ferrooxidans-mediated biomineralization in simulated AMD. The addition of quartz sand (40 g/L) and concentration of monovalent cation (K⁺=53.3 mmol/L) were adjusted in reference to the study by Wang et al. (2013). The biomineralization capability of three monovalent cations (K⁺, NH₄⁺, and Na⁺) in the presence of quartz sand in an acidic sulfate system was investigated and compared by determining Fe²⁺ oxidation efficiency, total Fe precipitation efficiency, and synthetic mineral phases. We believe that the afforded results may provide an essential theoretical basis to promote the transformation of Fe to secondary iron minerals from AMD (lines 94-102).

Wang, M.; Liang, J.R.; Zhou, L.X. The formation of biogenic jarosite by Acidithiobacillus ferrooxidans in the presence of crystal seed and potassium. J. Nanjing Agr. U. 2013, 36, 97–102.

 

Comment 5: Page 3, 3. Results and Discussion: The experimental results included in this study must be more detailed interpreted, in agreement with its objectives.

Response: Thank you for your suggestion. The “Results and Discussion” has been revised. Please refer to the revised manuscript (lines 162-166, 189-190, 199-202, 221-222, 236-238, 270-272, 290-292).

 

Once again, thank you very much for your comments and suggestions. In addition, the manuscript and reference list has been checked up and revised. Please refer to the revised manuscript.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

All my previous remarks and comments have been considered into new version of the manuscript. It means that reviewed manuscript meets the criteria, and in my opinion can be published as original paper in Water Journal.

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

The Fe(II) oxidation by Acidithiobacillus ferrooxidans under acidic, sulfate-rich conditions brings about the precipitation of Fe(III)-bearing hydroxide minerals such as schwertmannite and jarosite. Authors investigated the effects of addition of different monovalent cations and quarts sand on the mineral formation in the bacterial cultures. The iron oxidation and precipitation were examined in only a few culture experiments and the minerals obtained were  characterized simply by XRD. The results represent the jarosite transformation by K+ and/or quarts sand addition but are not new because previous studies have already argued such effects in A. ferrooxidans. Furthermore authors suggest the jarosite formation is useful in the iron removal from acid mine drainage (AMD), however, in this study they did not use AMD but classical medium (9K) for growth of A. ferrooxidans, so that it is very difficult to state the applicability of cultures in AMD treatment.

Specific comments:

Title of this paper looks inappropriate because AMD has never been used in this study. Several sentences in Abstract, Results and discussion, and Conclusions also mention about AMD treatment. If so, authors should demonstrate the iron oxidation and precipitation in AMD. L 58-59. Does this mean that the formation of jarosite results in 1.5-times increase in the amount of precipitates in comparison with schwertmannite? L 95-96. Were K+, Na+, and NH4+ added to the medium as sulfate salts? Please state these. L 97. Please state the grade and size of quarts sand used. L 106-107. The two equations are similar, so the first one may be deleted. L133-135. The report of Wu states characteristics of freshwater microorganisms and is not associated directly with acidophilic iron oxidizers. Please delete it. L 128-129; 164-165; 195-196; 204-206; 216-217; and 224-226. These sentences represent that the large part of results obtained agree with the previous studies cited in the text. For this reason, it is difficult to say that outcomes of this study fairly expand our knowledge on iron biomineralization in acidic microbial cultures. L 145. Fig. 1 legend should be revised. The data in Fig. 1 do not represent “effects on the concentration of Fe2+”. L 145. Is “before and after addition of quarts sand” correct? In this study, the iron oxidation experiment was conducted with cultures with and without quarts sand. “with and without quart sand” looks appropriate. Similar phrases appear repeatedly through the manuscript. L 154-156. This sentence is not informative, so it can be deleted. Are the data of Figs. 1 and 2 obtained from the identical cultures? If so, state it. L 149-180. Authors have argued the progress of Fe(III) precipitation based on changes of pH in cultures. For example, in the medium where pH value was not lowered largely, the ability of Fe(III) mineralization was interpreted to be remained poor (L 172-173). However, the data of pH are very confusing. The equations 2 and 3 indicate that the pH value could be dependent upon the mineral type because different amounts of proton form during schwertmannite and jarosite formation. The progress of iron precipitation can be recognized directly and easily by the data of Fig. 3 (next paragraph), so that the data of Fig. 2 should be used to support the data of Fig.3. The data of Fig. 4 are identical with those of Fig. 3, so Fig.4 should be deleted. L 291-. The data of this study do not fairly support the author’s conclusions because it is unknown whether the iron oxidation and mineralization observed in this study occur actually in AMD.

Reviewer 2 Report

Manuscript entitled “Enhanced monovalent cation biomineralization ability by quartz sand for effective removal of soluble iron in acid mine drainage” submitted by Heru Wang, Mengying Li and Yongwei Song, can be accepted for publishing in Water Journal, after minor revision.

In this study, an appropriate method for improving the precipitation efficiency of Fe in AMD treatment is detailed described. The manuscript presents original results, that are well organized and systematized, and their interpretation is appropriate. In my opinion, this manuscript should be published in your Journal after a minor revision.

 

Here is a list of my specific comments:

1. Introduction: This section needs to be re-systematized to more clearly describe the state of the art in this area. In this way, the novelty of this study will be better emphasized. Line 76: “Therefore, quartz sand was selected…”. At the end of Introduction, the main objective of this study should be formulated more clearly. 2. Materials and Methods: In the experiments were used real AMD samples? If yes, some characteristics of these samples should be added in this section. If no, then this aspect should be mentioned, including in title. 3.4. X-ray diffraction analysis of the biomineralization products: After this section, some experiments conducted using actual AMD wastewater should be added to complement the discussions presented in this study.

Reviewer 3 Report

In summary - this manuscript describes the findings of an experiment, which investigated the iron removal efficiency of A. ferrooxidans when monovalent cations and quartz sands are supplied to acid mine drainage (AMD) solutions. The major finding is that quartz acts as a crystal seed to initialize iron (Fe³⁺) hydrolysis and have a synergistic effect when K⁺ and NH₄⁺ are also supplied in the solution, while quartz and monovalent cations alone do not improve the iron precipitation efficiency. In addition, Na⁺ with or without quartz presence is an ineffective cation to promote mineralization.

Overall, the paper is written and organized sufficiently, but it does need some English editing for certain word choices and grammar check throughout. The introduction provides information and background for the study, and the goals are clearly stated. Enough relevant references are provided to back up the manuscript. The experimental setup, methods, and analysis seem adequate for this type of study. The results and discussion support the conclusions drawn.

However, I suggest improving two areas of the manuscript. One is the presentation of both the methods and results, and the second is adding a section about the feasibility of this experiment to be scaled up to a field testing, because it is great that it shows promising results in the lab, but what is next? How can it work in a real AMD creek?

I understand the briefness of the method description, but it is a bit too brief and hard to follow:

It is unclear - why the specific concentrations of the components were selected; i.e. monovalent cation concentration, and quartz concentration. How many replicates of each treatment were run, sampled, analyzed? There are error bars on the graphs - how were they generated? I think that a schematic drawing or an image of the experimental setup could help to understand the experiment better.  in lines 102-103 - what is a "liquid transfer gun?" in lines 110-111 - what is a "medium speed" filter? the "Analytical Procedures" section is not informative, it would be great to add a few sentences briefly explain each of the procedures.

These extra explanations would not add much length to the paper, max 1/2 page, but would greatly help out the reader and understanding of the experiment. 

Results and Discussion section

the text is OK, it needs some English editing as I mentioned above. The figure captions need serious work, they are not informative, and they do not say anything about the data depicted by a particular figure. These figures with the captions should be able to stand alone and tell the main story, and interested people could read the details in the text. In the current format, the captions are useless, cookie-cutter copy and paste sentences.   Figure 6 is a bit confusing with repeating the same patterns in 4 panels - why are these repeated? I do not see any difference and they just taking up space. The caption does not give any clue about the panels. 

The conclusion section is mostly clear - but the last sentence is a bit ambiguous - what does the "proper" concentration mean?