Round 1

Reviewer 1 Report

I would suggest that the SEM images be redrawn to show inidivudual particles to prove that the modified pyrite is in fact nano-sized. The results on the concentrations of iron, mercury and sulphate with time/height in the column must be statistically tested for significant differences to improve the quality of the authors’ conclusions. The concentrations of iron and sulphate in the experimental effluent must be related to the necessary discharge limits to support the authors argument from the Introduction that adsorption does not lead to secondary pollution

Author Response

Dear Reviewer 1:
Thank you for your letter and for the reviewer's comments concerning our manuscript entitled “Mercury removal from aqueous solutions using modified pyrite: a column experiment” (ID: minerals-650775). Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully and have made correction which we hope meet with approval. Revised portion are marked in red in the paper. 

Please see the attachment Responds to reviewer 1 .

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript need a deep lexical and syntax review, some examples are presented below.

Lines 58-59: This sentence is not clear. How specific surface area can be expressed in millimeters length  in rock? Please rephrase the sentence. Give examples of specific surface area values.

Line 60: pyrrhotite – explain what it is, and why pyrite is compared to it

Line 86-88: r3ephrase the sentence: “broken glass was filled (…).” I suppose the Authors meant that the column was filled with broken glass.

Line 88 – Tow?

L9ine 94 “ceiling of national sewage comprehensive emission standard” I think the Author meant upper limit

Either use notation as Hg(II) of Hg2+, for all iions. Now there is Hg (II) and Fe2+.

The whole section 2.3 need a deep language corrections

Figure 2 – Please remove the black frame. Merge the Figure A and B next to each other, place the letters A and B in position so they do not cover the figures frames.

Fugire 3 – The magnification is different in each SEM image hence “natural pyrite crystal has a large size with smooth surface, while the modified pyrite has nanoscale structures with a great number of micropores” this sentence is not valid. How can you estimate there are micropores?  To support the statement, the Authors need to perform N2 physisorpion and report the materials porosity. The specific surface area would be also informative here.

Figure 4 – very hard to read. Remove the black outer frame, increase the figures’ sizes. Place one under another. Please Do similar correction to the remaining figures.

The authors need to explain what happened to the material after calcination, specific surface area and porosity analyses are essential.

Line 270:  Did the Authors really perform the experiment using a “liquor”? If yes, please indicate which one.

Line271: “This research demonstrates that the MPy is an efficient sorbent for Hg(II) removal”. Please provide examples of other sorbents and their capacity for removal of Hg2+ to support that statement. Cause I think that 10.45 mg/g is quite the opposite of efficient.

Author Response

Dear Reviewer 2: Thank you for your letter and for the reviewer's comments concerning our manuscript entitled “Mercury removal from aqueous solutions using modified pyrite: a column experiment” (ID: minerals-650775). Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully and have made correction which we hope meet with approval. Revised portion are marked in red in the paper. 

Please see the attachment Responds to reviewer 2 .

Author Response File: Author Response.pdf

Reviewer 3 Report

REFEREE REPORT

Minerals journal

Article: "Mercury removal from aqueous solutions using modified pyrite: column experiment"

Report:

The authors studied the Modified pyrite (MPy), which was obtained from calcination in N₂ atmosphere, was used as a sorbent for removing Hg(II) from aqueous solutions. The mechanism was analysed by multi-technique approach: XRD, FE-SEM, FE-TEM and XPS.

This paper, in my opinion shows new scientific findings, the authors have created a thermal activation system to improve the adsorption capacity of pyrite. Experiment was designed to explore the efficiency of MPy as a mineral sorbent by comparing its performance with natural pyrite, and to investigate the feasibility of using MPy in Hg(II) removal. The capacities and mechanisms of MPy in Hg(II) adsorption were studied by using surface analysis techniques (SEM, XRD, TEM and XPS), which are very powerful and accurate for surface characterization and to entirely understand the mechanism describe by the authors. The experimental results reveal the feasibility of using MPy in the removal of mercury.

This work shows interesting results and original methodology, nevertheless further improvements in the interpretation of the experimental data on the manuscript must be done. Therefore, I would recommend publication after mayor revision.

Results and discussion: the authors shows an original multi-approach technique for the efficiency of MPy as a mineral sorbent by comparing its performance with natural pyrite, nevertheless authors should put a major effort to clearly describe the results and further interpretation of them, to be consistent with the conclusions.

The weakest point of the manuscript is the entirely wrong interpretation of the XPS analysis of the O 1s and Fe 2p peaks. I would recommend the authors to carefully read the literature, there are number of papers that describe a consistent and methodically interpretation of iron sulfides and iron oxides surfaces by XPS technique. The authors should re-do, the fitting of the spectrum as example Figure 9 (graph O1 s C: top) the components are overlapping and the 532.6 eV component has an excessive width. Furthermore the spectra for the Fe is the Fe 2p, and the authors seems to show the Fe 2s for the graph in figure 9, it is again a mistake. The Fe 2p interpretation (page 10 line 239-245), is confusing as the authors should refers the assignment to the Fe 2p_1/2 or to the Fe 2p_3/2 photoelectron lines.

Finally, English improvement is recommended to make the manuscript easy reading and to revise spelling mistakes as “Tow” instead of Two (page 3, line 88).

Author Response

Dear Reviewer 3: Thank you for your letter and for the reviewer's comments concerning our manuscript entitled “Mercury removal from aqueous solutions using modified pyrite: a column experiment” (ID: minerals-650775). Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully and have made correction which we hope meet with approval. Revised portion are marked in red in the paper.

Please see the attachment Responds to reviewer 3 .

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Lines 63-65: small crystal size is not the reason of low specific surface area (SSA) I would say that the smaller the crystals, the larger the specific surface area. Furthermore, material’s adsorption capacity doesn’t only depend on the4 SSA but also functional groups present in the material. I suggest to rephrase the sentence – “However, the ability of natural pyrite to remove heavy metals is restricted by its low sorption capacities as the material is characterised by low specific surface area and low chemical reactivity due to strong S–S bonds. However after calcination…..” and continue with the Pyrrhotite description.

Line 70-71: Rephrase, high efficiency as an adsorbent or high potential for the use as efficient adsorbent

Line 83-85: Rephrase: The natural pyrite (Py) used in this experiment was obtained from the Xinqiao Mine, Anhui Province, China. The material was crushed and ground to fraction of 0.5-1 mm.

Lines 93: the whole paragraph: Two glass columns of 60 cm height and 10 mm inner diameter;  the column was filled to the height of 5 cm from the bottom with broken glass; one column was packed to the height of 32 cm with 50 g of Py, while the other to the same height with 50 g of MPy; Mercury concentration in the influent solution was 8.26 mg/L and the pH equal to 6.28. The solution was pumped downflow to the column with a flow rate equal to…. and the calculated retentios time was on the level of…

Line 109: Every day, not everyday; concentration were not detected in this context but determined or measured; 2 cm long, not 2-cm;

Line 193: inefficiency IN;

Line 219: the bed volume

Table 1: change hours to  h, add valency to the metals listed in the first column, unless it was remediation of zero valet metals not cations, which I doubt.

Lingusitical correction: make sure that all the verbs, where needed in third person – and in “s”.

I’ve noticed one significant discrepancy that I would like to clear. The Authors report the adsorption capacity Of MPy obtained from the Langmuir model ob the level od 166.67 mg/g. In this study the capacity obtained from column is only 16.37 mg/g. Usually the results obtained in column are slightly higher than the ones form isotherm. Here we encounter a difference of one order of magnitude. Why?

Author Response

Dear Reviewer 2:

Thank you for your letter and for the reviewer's comments concerning our manuscript entitled “Mercury removal from aqueous solutions using modified pyrite: a column experiment” (ID: minerals-650775). Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully and have made correction which we hope meet with approval. Revised portion are marked in red in the paper.

Please review the attachment Responds to reviewer 2.

Thank you for your help again and best regards.

Yours sincerely,

Yucheng Zhu.

Reviewer 3 Report

The manuscript has been highly improved from scientific and language requirements. Results and discussion section has been clearly described by the authors and it has been completed to avoid any ambiguous and erroneous understanding from the reader. Furthermore, the authors have rewritten the whole section 3.2.6 to improve the interpretation for the XPS analysis of the O 1s and Fe 2p peaks. The new XPS assignment is coherent with the data described in the manuscript, therefore it supports and confirms the scientist results.

Author Response

Dear Reviewer 3:

Thank you for your letter, your support and your affirmation concerning our manuscript entitled “Mercury removal from aqueous solutions using modified pyrite: a column experiment” (ID: minerals-650775). We will keep pushing and working hard to refine our article.

Thank you again and best regards.

Yours sincerely,

Yucheng Zhu.