An Experimental Study on the Migration of Pb in the Groundwater Table Fluctuation Zone

Round 1

Reviewer 1 Report

I have no more comments. Good job!

Author Response

Please see the attachment

Author Response File: Author Response.doc

Reviewer 2 Report

Dear Editor and Authors,

 

thank you for the answers related to the original submission of the manuscript. Therefore, I will look at the review in relation to the changes made. The authors have improved the manuscript compared to the previous version, however some questions remained unanswered or the Authors did not best understand what I was asking of them. I also advise Authors to read the manuscript as well as the answers to the reviewers before submitting the manuscript.

 

COMME NT 1

Previous comment:

Title: „Migration Mechanism“ - I would say that the authors do the mapping, that is, the vertical distribution of Pb. In my opinion, the migration mechanism includes defining the mechanism (advection, dispersion, diffusion). So consider changing the title!

 

There is no answer to this question.

New comment:

I definitely claim that the authors do not investigate the mechanism of Pb migration, but Pb mobility, so it is about Pb migration or mobility within the experimental hydrogeological layer. I therefore demand that the word "mechanism" be removed from the title.

 

COMME NT 2

Line 14: „Our study aimed“

Lines 17-18: „Our results showed“

Line 19: „We also obtained“

 

In the manuscript in general, and in the Abstract in particular, do not address us personally (We, Our) - it is not typical for scientific papers.

 

COMME NT 3

Line 19-21: „We also obtained the maximum adsorption and desorption capacities for Pb2+ adsorption and desorption of fine, medium, and coarse sand collected from the floodplain.“

 

It is not written in the best way. Why? The reader does not know what the adsorption and desorption capacities are for the three sorbents and whether the order you have given is increasing or descending for the said sorbents. In the previous version it was better written but it was necessary to specify what it refers to.

 

COMME NT 4

Line 70: pH is a well-known symbol; you don't need to explain in parentheses what it is about. You have explained the other abbreviations well.

 

COMME NT 5

Line 93: Remove the word "mechanism". Please in all sections omit the word mechanism which is related to migration mechanism. I explained earlier.

 

COMME NT 6

Previous comment:

Line 135: “…Pb with pH of 4, 5, 6, 7, 8, 9 were mixed…” - Conducting an experiment at pH = 7, 8 and 9 is highly debatable since at pH> 6.5 precipitation of Pb occurs in solution. Therefore, the adsorption mechanism is not the only one that contributes to the decrease in Pb concentration, but the Pb precipitation is an even greater contribution. See Pb species diagram in relation to pH.

New comment:

Since the lead concentration of 200 mg / L is not very low, Pb precipitation definitely occurs at pH above 7. According to Figure 4a, above pH = 6 you have a sharp increase in Pb removals due to the contribution of precipitation. So, optimal pH = 6. Remove the three points for pH = 7, 8 and 9 from Fig 4a.

Regarding desorption, it can be carried out at pH = 4-9. I am interested in the desorption experiment, how did you saturate the samples, under what conditions? Explain the adsorption and desorption procedure in more detail in Chapter 2.

 

COMME NT 7

Previous comment:

In equations 1 and 2, the explanation of the meaning of the concentration of C1 and C2 is exactly the same. Is it the same? Why use different symbols for the same thing?

 

Using Q1 and Q2 labels, suggestion - is Qads and Qdes more acceptable?

Equation 2, better to say the meaning of the symbol is confusing. I wonder if the authors calculated the desorption capacity correctly - cite the source of the equation?

Qdes=Cdes*V/m

New comment:

You have accepted the Qads and Qdes symbols.

However, equation numbered with (2), I am pretty sure it is not spelled correctly. So I wonder again weather you calculated Qdes well?

Eq (1) and (2) have the same symbol "C2" which means that the equilibrium concentration of the adsorption experiment is the same as the desorbed concentration in the desorption experiment. So be sure to cite the literature from which you took this equation!

 

COMME NT 8

Lines 146-151: - Connect the text in these lines with the labels in Figure 1a - e.g. gristone

 

COMME NT 9

Previous comment:

Lines 150-151: “The three kinds of prefabricated Pb(NO3)2 pollution media with the content of 2000mg·kg -1 were loaded” - If I understood correctly how it was written - all three samples have the same amount of sorbed lead in the amount of 2000 mg/kg. Furthermore, in the Abstract and discussion and conclusion, different maximum adsorption capacities for the three samples are stated.

New comment:

Rev manuscript: lines 150-151: „A mixture combining 2000mg·kg -1  of polluted sand with a Pb(NO3)2  solution and sand medium was produced.“

As I have commented before, it is not clear to me again. Which kind of mixture is it?

 

COMME NT 10

Lines 175-180:

This part of the text has been completely changed „Lines 175-180“. You have not notified reviewers of these changes! The sentence: "The desorption capacity was as follows: That of coarse sand ..." makes no sense! Restore the old version of the text with numerical capacity amounts!

 

 

COMME NT 11

Previous comment:

In section 3.1. - why did you test the experimental data only according to the Elovich model? What about other kinetic reaction and diffusion models. The sorption mechanism on all three samples used as well as the desorption mechanism should be elucidated. How is Pb sorbed on sand? This will also help in the explanations with the water fluctuation experiment.

New comment:

Results for the hyperbolic diffusion model and the 2nd order kinetic model are not shown. The answer that the restriction with space is not acceptable. Then put the results in a supplementary file. There are Weber-Morris and others. Define the kinetic mechanism as well as the type of Pb sorption on samples, physisorption or chemisorption.

 

COMME NT 12

Previous comment:

Lines 194-196: “…was between 8 and 9. The desorption quantity gradually decreased with the increase of pH value. The final desorption quantity tended to balance at pH=8~9. - This indicates that precipitation has certainly occurred. I would think carefully whether to show adsorption results during saturation at pH = 7.8 and 9!

Author's answer:

Response: Considering the Reviewer’s suggestion, we have re-written this part in line 191-199. Adsorption results and desorption result were showed in Figure 8a and b.

New comment:

There is no Fig. 8.

Statement in lines 193-194: „and the adsorption quantity steadily approached equilibrium when the pH was between 8 and 9.“ - You cannot discuss about adsorption at pH> 6.5, the precipitation occurs only. Remove results at pH> 6.5. Take a look at the diagram of Pb speciation and Pb precipitation!

 

COMME NT 13

Statement in lines 196-197: „competitive adsorption capacity“ - Competitive adsorption capacity does not exist! There is only competition among ions for adsorption sites.

 

COMME NT 14

There is no Section 3.2

Author Response

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Author Response File: Author Response.doc

Reviewer 3 Report

Ref:

Title: An Exprimental Study on the Migration Mechanism of Pb in the Groundwater Table Fluctuation Zone

 

Journal: Journal of Applied Sciences

 

Comments from the reviewer:

1. Keyword: revision; Please review it. Try to have comprehensive keywords.

 

2. Abstract:

- At the beginning of the abstract, there is an introduction to the necessity of doing the work, then the introduction of the study area, the purpose of the work, an introduction to the methods studied, and finally the results and suggestions.

 

3. Introduction:

Introduction to be rewritten in three separate paragraphs for reasons of review, literature review and research purposes. The structure of the paper should be rewritten in 3 separate paragraphs. In the first paragraph, information about the subject under study, in the second paragraph, the study of different researchers and the studied indicators, and in the third paragraph, the objectives of the research should be stated.

 

* Line 46 (heavy metals)- You can add 2 references below:

1. Rezaei, A., Hassani, H., Hassani, S., Jabbari, N., Fard Mousavi, S.B., Rezaei, A., 2019. Evaluation of Groundwater Quality and Heavy Metal Pollution Indices in Bazman Basin, Southeastern Iran. Groundwater for Sustainable Development. https://doi. org/10.1016/j.gsd.2019.100245.
2. Rezaei, A., Hassani, H., Tziritis, E., Fard Mousavi, S.B., Jabbari, N., 2020. Hydrochemical characterization and evaluation of groundwater quality in Dalgan basin, SE Iran. Groundwater for Sustainable Development. https://doi. org/10.1016/j.gsd.2019.100245.

 

 

* Line 84- You can add 1 reference below:

1) Rezaei, A., Hassani, H., Fard Mousavi, S.B., Jabbari, N. (2019). Evaluation of Heavy Metals Concentration in Jajarm Bauxite Deposit in Northeast of Iran Using Environmental Pollution Indices. Malaysian Journal of Geosciences (MJG), 3 (1), 12-20.

 

4. Section 2.1. You can separate this section of material and methods. Please Add study Area.

 

5. What was the basis for selecting the samples for testing and from what environments was it taken? Please explain and mention it in the text.

 

6. What was the basis for choosing the type of sand granulation? Please describe it.

 

7. In addition to pH, what can the parameters of temperature, porosity and sand material be influential parameters? Please describe it.

Comments for author File: Comments.docx

Author Response

Please see the attachment

Author Response File: Author Response.doc

Round 2

Reviewer 2 Report

The authors improved the manuscript according to my suggestions and explained everything clearly in the answer, therefore my decision is acceptance of the manuscript in this form.

Below are a few recommendations:

 

Line 127: “”adsorption kinematics experiment, the desorption kinematics experiment” change to adsorption kinetics experiment, the desorption kinetics experiment.

 

Lines139-147: Clearly state the pH range for adsorption experiments and for desorption experiments since the pH ranges are not the same.

Uniform the writing the measurement units, mL / ml.

 

Author Response

Please see the attachment

Author Response File: Author Response.doc

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 presented article discusses interesting aspects related to Pb migration in the fluctuation zone of groundwater. Below I present my comments to the study, the most important aspects necessary for reflection and supplementation have been marked in bold. Overall, the article presents a high substantive level.

Abstract: I think there is a need to add information about fact the experiment was carried out in the laboratory conditions

line 34 - significant (x2) in one sentence

line 36 - factors needed to be ordered e.g. rainfall, evaporation, recharge, discharge, exploitation, I don't think fluctuation is a factor, rather the effect of factor work. 

line 39 - add space before all references e.g. [3,4], and further in line 41, 47, 54, 61, 64 etc.

line 85 - there is not enough mentioned about existing studies concerned on Pb migration, and not only in China. For better description of the mechanism of Pb migration in fluctuation zone, papers should be presented describing possible Pb sources in groundwater first, then chemical background (average concentrations in shallow groundwater, chemical forms of occurrence, etc.), and studies about migration in vadose zone and aquifer. I think the introduction section should be focuses on Pb studies equal as on fluctuation zone studies.

line 104 - organic matter content - what is the unit? (only in the table)

line 114 - earth column? maybe ground samples would be better...

line 135-137 - different type of font?

line 151 - correct the: Pb(NO3)2, please.

chapter 2.3.2  - whether the distance from the lowest level of groundwater table was higher than the possible capillary infiltration, was this phenomenon taken into account?

fig.3,4 - correct "corarse"

fig.3 - If you could stretch graphs for whole page width, they would be more readable esp. in the first 50 min of curves (fig.5 and 6 - also can be wider)

line 230 - Pb (OH)2 precipitation - what are the indications to confirm this reaction apart from a decrease in pH? Were any soil mineral composition tests performed before or after the experiment? Maybe it would be better to perform hydrogeochemical (at least speciation models) modeling to confirm the suggested reactions and their relevance?

line 262 - what is the detection limit of the instrument?

fig 8 - no reference in the text

conclusions:

-1st point - can you judge if the given values are similar to other studies, are they high or low?

- needed to rewrite whole 3rd point: The fluctuation of water level will lead to the migration of Pb2+, which will affect the migration of Pb2+. Therefore, the migration of Pb2+ results of water level fluctuation, pH change and pollutant concentration change.

- based on Your research can you add some guidelines for soil pollution prevention and control programs mentioned in the Introduction? What could be the application in this field, especially for the sample site  - the floodland of Yellow River?

References:

- why You inserted "et al." in references when all the authors are listed?

- [28] - add who the publisher is and where you can find it

Reviewer 2 Report

See attachment

Comments for author File: Comments.docx

Reviewer 3 Report

Journal: Applied science

Title: Experimental Study on Migration Mechanism of Pb in Groundwater Level Fluctuation Zone

 

In principle, the work has potential, mainly investigating the desorption of lead from a previously saturated sand sample under simulated conditions, by water fluctuations in the column. However, the purpose of the paper is not highlighted, which in my opinion is the biggest drawback and there are a lot of typographical errors.

 

Thus, the Authors stated in the lines 94-95 "provide theoretical support for the treatment, remediation and protection of heavy metal pollution in soil and groundwater" - however I did not understand whether the purpose is to apply a sand sample for remediation purposes, ie to examine whether the material can be applied as a sorbent in remediation of the contaminated area or to examine the spread of contamination. I ask the Authors to clearly define this in the paper and adjust the discussion and conclusions. Applicability based on research should be clearly highlighted. Furthermore, the Authors did not clearly state why they are exploring lead, except that there is already research on other heavy metals.

 

 

Specific comments:

 

 

Title: „Migration Mechanism“ - I would say that the authors do the mapping, that is, the vertical distribution of Pb. In my opinion, the migration mechanism includes defining the mechanism (advection, dispersion, diffusion). So consider changing the title!

 

ABSTRACT

 

Line 13: „In this study, this paper aimed“ - In my opinion, it is superfluous to write " In this study" and „this paper aimed“ together, it is superfluous, one or the other, never together.

 

Lines 13-15: „In this study, this paper aimed to measure the migration mechanism of Pb in the groundwater level fluctuation zone. By using the static adsorption analysis, the water level fluctuation experiment, and other technical methods.“ - I would merge these two sentences.

 

Lines 18-19: „The results show that the curve of adsorption and desorption fitted Elovich equation better.“ - Sounds like an unfinished sentence, better than ... what ??

 

Lines 19-21: „The maximum adsorption quantity of Pb2+ was 2366.6mg·kg-1, 1847.6mg·kg-1, 1543.8mg·kg-1, the maximum desorption quantity of Pb2+ was 29.18mg·kg-1, 62.38mg·kg -1, 81.6mg·kg-1.“ - It is not clear how it is written like this. It must be defined to which material the sorption capacity refers.

 

 

Lines 22-23: “In the environment of pH>4, the adsorption value was proportional to pH, while the desorption value was inversely proportional to the pH.” This is too general a sentence for Abstract.

 

INTRODUCTION

In lines 62 and 71 explain the meaning of abbreviations (TMVOC, EC, DO).

 

MATERIALS AND METHODS

Line 98: “soil sample” - I would point out that the sample is sand, not soil. Same in line 126.

 

Lines 124-130:  “The process of adsorption kinetic test was as follows: 50mL Pb(NO3)2 solution (200mg·L -1 ) and 2.5g soil sample were put into a 50mL PVC centrifuge tube and oscillated in a constant temperature water bath oscillator at 25℃, respectively at 5, 10, 15, 20, 30 min, 60 min, 90 min, 120 min, 180 min, 240 min, 360 min, 480 min, 720 min, 1440min Sampling from the oscillator, centrifugal filtration and determination of the concentration of Pb in the supernatant, to calculate the adsorption amount.” - This sentence is too long.

 

In section 2.3.1. the authors did not state with what, what type of solution the desorption was carried out.

Line 135: “…Pb with pH of 4, 5, 6, 7, 8, 9 were mixed…” - Conducting an experiment at pH = 7, 8 and 9 is highly debatable since at pH> 6.5 precipitation of Pb occurs in solution. Therefore, the adsorption mechanism is not the only one that contributes to the decrease in Pb concentration, but the Pb precipitation is an even greater contribution. See Pb species diagram in relation to pH.

In equations 1 and 2, the explanation of the meaning of the concentration of C1 and C2 is exactly the same. Is it the same? Why use different symbols for the same thing?

 

Using Q1 and Q2 labels, suggestion - is Qads and Qdes more acceptable?

Equation 2, better to say the meaning of the symbol is confusing. I wonder if the authors calculated the desorption capacity correctly - cite the source of the equation?

Qdes=Cdes*V/m

 

Lines 150-151: “The three kinds of prefabricated Pb(NO3)2 pollution media with the content of 2000mg·kg -1 were loaded” - If I understood correctly how it was written - all three samples have the same amount of sorbed lead in the amount of 2000 mg/kg. Furthermore, in the Abstract and discussion and conclusion, different maximum adsorption capacities for the three samples are stated.

 

Line 153: “Then the soil column was loaded to 70cm, deionized water” - loaded with what?

Line 153: “Then the soil column was loaded to 70cm, deionized water” - is the pH of deionized water adjusted? What was the pH?

 

RESULTS AND DISCUSSION

In section 3.1. - why did you test the experimental data only according to the Elovich model? What about other kinetic reaction and diffusion models. The sorption mechanism on all three samples used as well as the desorption mechanism should be elucidated. How is Pb sorbed on sand? This will also help in the explanations with the water fluctuation experiment.

 

Lines 189-190: “The experimental results show that the smaller the particle size of the medium, the larger the specific surface area.” - I did not notice specific surface area results for the three sands used.

 

 

 

Lines 194-196: “…was between 8 and 9. The desorption quantity gradually decreased with the increase of pH value. The final desorption quantity tended to balance at pH=8~9. - This indicates that precipitation has certainly occurred. I would think carefully whether to show adsorption results during saturation at pH = 7.8 and 9!

 

Lines 196-198: “Compared with medium sand and coarse sand, the adsorption and desorption of fine sand with different pH values had little change.” - well think about why " had little change " - what is the sorption mechanism of Pb sorption?

In fact, the material is not characterized, what is the chemical composition, morphology - this can help shed light on the sorption mechanism.

 

In section 3.3. there is little confusion describing the increasing and decreasing of values. For example: line 271: “decreased from 37.12% to 94.34%” - as it is written I would say it increases or decreases in the range of values 37.12-94.34%.

 

Lines 325-329 describe the experiment. Please move this to Chapter 2.

 

Line 331: “a trace of Pb near 25cm and 45cm.” - or perhaps check from 40-60 cm according to Figure 1.

 

CONCLUSION

Modify as I stated at the beginning of the review

 

Throughout the text there are a lot of typographical errors such as merged words, merged numbers and measurement units, uneven font letters, writing absorption instead of adsorption, writing PH instead pH, writing ionic compounds with charge without using superscript ...