Natural Pyrite as a Catalyst for a Fenton Reaction to Enhance Xanthate Degradation in Flotation Tailings Wastewater
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe Fenton reaction mechanism is well known. The pyrite-H2O2 system is also known. However, colleagues in the paper presented a school application of the theory of catalysis and controlled reaction using Fe from the mineral pyrite, which is already present in the flotation process and used it as an H2O2 catalyst for the generation of •OH radicals, which is responsible for the purification of xanthate flotation tailings wastewater. The idea to solve this problem is excellent. The experiment is well set up, and the characterization and explanations are adequately given. The paper is usefully published with the following corrections:
- The Abstract and Conclusion are written similarly. The Conclusion should be based on the minimally presented numerical data, so I suggest that the whole sentence in the Conclusion "The best performance was obtained at an H2O2 concentration of 0.5 mM, a FeS2 concentration of 0.5 g/L, an initial SBX concentration of 100 mg /L and the natural pH of 9.35.", omit. The conclusion should contain general data, such as: "pyrite proved to be good...", "xanthan was broken down into parts that are not toxic (without specifying the precise data because they are already mentioned in the paper)", "this is better than that...", "the reaction can also be achieved in this way...". It may contain "future perspectives" in the conclusion. Emphasize that the process is cost-effective...
- Somewhere in the Manuscript, the designation Fe2+ and Fe3+, and somewhere Fe (II) and Fe(III), should be standardized so that the marking is always the same in this paper.
- Line 63: Instead of: „...H2O2 to •OH (2.76 V) [21,23] [23,24] having higher redox potential…”, should be “….[21,23,24]…”
- Delete the point at the end of the title "3.1. Degradation of SBX by pyrite-catalyzed Fenton system."
- Lines 235 and 144 contain Figures 4a and 4b, and refer to Figures 6a and 6b, please correct.
- Line 246 says 24.22%, and in Figure 6b it says 22.11%, correct where necessary.
- Pay attention to the paper entitled "Fenton process in dispersed systems for industrial wastewater treatment", authors Ana Popović, Sonja Milićević, Vladan Milošević, Branislav Ivošević, Jelena Čarapić, Vladimir Jovanović, Dragan Povrenović, Hem. Ind. 73 (1) 47– 62 (2019) and add it in the Introduction comment and the Reference list.
Author Response
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Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThe article minerals-2542779 evaluated the degradation of sodium butyl xanthate by pyrite/H2O2. Several errors were committed in the execution of the experiments.
Specific comments:
- SBX quantification should have been done by chromatography, because at 301 nm Fe ions interfere at this wavelength;
- None of the experiments was evaluated in triplicate. Figures 2-8 do not show error bars. So the results are not reliable;
- SBX degradation was high with H2O2 only. Therefore, the effect of Fenton's reaction was minor.
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThe work by Xiang Gong et al. entitled “Natural pyrite as a catalyst for Fenton reaction to enhance xanthate degradation in the flotation tailings wastewater” provides a comprehensive study on actively using pyrite as a catalyst for the Fenton reaction in wastewater remediation. This study is relevant to the field and would be a nice contribution once it has been revised. The length of the work is sufficient. I recommend this work for publication once the following minor changes have been included.
The following minor comments should be considered when revising.
Line 121: X-ray diffraction should be corrected as powder X-ray diffraction to avoid confusion between powder and single crystal X-ray diffraction techniques.
Figure 1: The calculated X-ray diffraction pattern should be plotted along with the experimental data for clarity and comparison. Also, the corresponding crystallographic database information should be included.
Author Response
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Reviewer 4 Report
Comments and Suggestions for AuthorsThe authors have detailed a treatment system using pyrite to accelerate treatment of SBX using Fenton reaction. The paper is of good caliber and describes the results very well including potential reaction pathway, adding to the robustness of the manuscript. However, I have strong concerns that none of the tests were replicated at all and no control tests (with no H2O2 or pyrite addition) were performed.
Tests need to be repeated in order to obtain statistical data, otherwise it’s difficult to determine significance of findings and hard to tell what the optimal doses were. Control tests must be done to eliminate possible degradation of SBX due to factors other than H2O2 or pyrite addition. Suggest running at least 2 replicates for all tests, 3 would be better, before publication is accepted.
I would also suggest testing for SBX intermediates and reaction products to verify your proposed reaction mechanism, or making the proposed reaction pathways less definitely described. These are proposed or likely pathways, not proven in your experiments, and that needs to be more clear from the proposed pathway statements in the manuscript.
Abstract
Line 17: change to “corresponding result in the H2O2 system alone” or "H2O2 system"
Line 19: Define EPR in abstract.
Intro
Point 4, line 105: Intermediate degradation products were not found in this study, change point 4 to “proposing a degradation pathway”
I would suggest adding a line about typical concentrations of SBX found in tailings wastewater (i.e., explain why you chose 50 to 150 mg/L as initial SBX concentrations) to the introduction or materials and methods section.
Methods
Line 136: There is maybe a word missing here “solution was allowed and filtered” allowed to what?
Line 137: add “ultraviolet-visible (UV-vis) spectrophotometer”
Results
Line 166: The pH value should have an associated standard deviation value
Lines 167-172: Suggest removing terms such as “remarkably” and “feebly” and replacing with actual data such as “increased by XX% from 0 mM to 0.5 mM” or with more commonly used terms such as “dramatically” and “degradation efficiency did not increase as significantly above 0.5 mM” or something similar.
Were multiple tests conducted to obtain error bars for Figure 2? Looks like the biggest improvement seen from 0.1 to 0.3 mM H2O2 so I disagree with the interpretation that 0.5 mM was the optimal dose. There also appears to be a significant improvement from 0.7 to 0.9 mM H2O2 based on your Figure 2, but difficult to tell if repeated tests were not conducted.
Line 180: again, was pH of initial solution only measured once? Add error term to pH value.
Line 188: please provide references for this statement
Line 196: missing a period at the end of this sentence
Figures 2, 3, 4, 5, and 6 have degradation rate on the vertical axis. It looks like the vertical axis is showing the % removal of SBX, not the degradation rate. Degradation rate should be the concentration remaining over time of the experiment, or the slope of the graphs shown. Suggest changing the label on the vertical axis and reporting actual degradation rate in text after repeating the experiments to determine statistical significance.
Need to change every instance in text which refers to degradation rate to % removal or determine the actual reaction rates.
Line 204: change “saturate” to “saturation”
Line 208: again, the 94% is not a degradation rate, and need to add the % symbol
Line 210: missing a period at the end of this sentence
Line 209-210: are xanthate and SBX referring to the same thing? Suggest changing reference to xanthate here to SBX for consistency. Also, wouldn’t the initial concentration depend on the specific wastewater being treated? What was the 100 mg/L SBX concentration selected for? Further tests?
Line 215: delete “alone”; could use H2O2-only system or H2O2 alone or H2O2 system (please change this throughout the paper, “alone H2O2” is not grammatically correct)
Line 217: again, % removal is not a degradation rate
Lines 284 – 285: This study provided no evidence that SBX was degraded to CO2 H2O and SO4, need to make this statement less concrete and add in references to literature showing that these are the generally the final degradation products from Fenton reaction.
Line 287: you cannot state something is not significant without repeated tests to demonstrate statistical significance. The concentration of Fe(II) may or may not be significantly changing in this case.
Conclusions
Line 316: should mention here that pH was unbuffered and reduced during testing, could change the word “natural” to “unbuffered”
Line 324: delete the word “off”
Line 325: The OH radicals "most likely" attacked the adsorbed SBX…this was not proven in your experiments so you need to show that in your statements with words such as likely or most likely.
Line 327-328: suggest making this statement less concrete, because this was not proven in your experiments, by changing to “BPX intermediates were likely further oxidized to…”
Comments on the Quality of English LanguageA few suggested minor word changes or additions required to improve clarity of the paper.
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsThe article minerals-2542779 evaluated the degradation of sodium butyl xanthate by pyrite/H2O2. Although the authors have now replicated the experiments (as the figures are showing error bars), the way to determine the target pollutant remains inappropriate. At 301 nm there may be interference from iron ions in determining the target pollutant. Therefore, this article cannot be approved for publication.
Author Response
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Reviewer 4 Report
Comments and Suggestions for AuthorsThe manuscript is greatly improved. However, changing "degradation rate" to "removal rate" is not sufficient. A removal rate or degradation rate is a change in concentration over time. You are reporting the removal percentage.
Control tests with no H2O2 addition were not performed.
Author Response
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Author Response File: Author Response.docx
Round 3
Reviewer 4 Report
Comments and Suggestions for AuthorsManuscript has been considerably improved.
Author Response
Plenty of thanks for your suggestions, comments and approvals.
