Testing of Natural Sorbents for the Assessment of Heavy Metal Ions’ Adsorption

Round 1

Reviewer 1 Report

The manuscript "Testing of natural sorbents for the assessment of heavy metal ions' adsorption" presents the results of laboratory study with five natural sorbents which have been tested for adsorption of As, Cr, Pb, Cd, Cu and Cr in salt solution. The results clearly demostrate the different adsorption efficiency of selected sorbents and sorts them from the most effective to the least effective one. Some of the sorbents seems to be promising candidates for selected metals adsorption. Anyway, the study can be sorted as preliminary as it was done completely in laboratory conditions which don't reflect the real situation in soil with all interactions, metals form and availability.

The English language is without major grammar issues but I would suggest proof-reading by native speaker who could help to improve the text flow and continuity and make it more comfortable for the reader.

I have some comments and suggestions which should be addressed before consideration for publication:

1) one of the keywords is "bioremediation" but the topic of the study does not provide any results for bioremediation

2) line 47-48 "researches from different countries...": provide the most relevant references for your research

3) line 54-56: It is true, for sure, that bioremediation is one of the popular directions in metals-contaminated soils restoration but is has no connection to your work. So it does not seem to be meaningful to write two paragraphs about it in your manuscript. If there is some connection to your work, it should be clearly explained.

4) materials and methods: I would suggest to clearly present your sorbents and their properties in Table. You have points 1. and 2. combining different versions of adsorbents and information about different properties. It makes it quite complicated for orientation in text and possible comparison of sorbents. It would be much more clear to have 5 lines (one for each sorbent) with all sorbents parameters which were tested. 

5) line 112-116: You provided the list of compounds which were used for preparation of salt solution but where is the information about concentrations? That is the key information for interpretation of your results. You write about preparation of solutions with lower concentration but the results are provided only for one variant (and we don't know what was the initial concentration). That needs to be clearly explained.

6) You obviously combined Results and Discussion. Modify the Section 3 title to fit the content.

7) Figure 3, 4 and 5: provide the information about method which was used for obtaining these photographs

8) compare your results with other relevant research (different sorbents, different conditions etc.)

9) specify the author contribution according to journal requirements using CErdiT

To conclude, the manuscript has serious gaps which need to be improved, otherwise it can't be considered in Q2 journal.

 

Author Response

Dear reviewer,

First of all, we want to thank you for your valuable comments and suggestions.

We highlighted all changes with green color in order to avoid lines numbering disadvantages.  We put the lines numbers from the electronic paper in this cover letter. For some reasons, the numbers differ from the electronic version.

We have taken into consideration all your suggestions, such as:

 

1. “…the study can be sorted as preliminary as it was done completely in laboratory conditions which don't reflect the real situation in soil with all interactions, metals form and availability” - We agree with your comment. However, we have done some experiments with “peat - granular diatomite” in real situation. It shows good results with not only heavy metal adsorption but with oil too. We are planning to do it; It is the next step in our research to test all these sorbents in real condition.
2. “The English language is without major grammar issues but I would suggest proof-reading by native speaker who could help to improve the text flow and continuity and make it more comfortable for the reader” - The colleague of mine from the GB kindly agreed to edit the text. We attached the revised version of the paper. However, to be honest, we cannot be 100 percent sure about the quality of it.
3. “One of the keywords is "bioremediation" but the topic of the study does not provide any results for bioremediation”. - We agree with your comment and remove it from key words (line 37).
4. “Line 47-48 "researches from different countries...": provide the most relevant references for your research”. We agree with your comment and add the necessary information (lines 64; 269-293; 343-347; 381-385)
5. “line 54-56: It is true, for sure, that bioremediation is one of the popular directions in metals-contaminated soils restoration but is has no connection to your work. So it does not seem to be meaningful to write two paragraphs about it in your manuscript. If there is some connection to your work, it should be clearly explained- We agree with your comment and make the changes (line 71)
6. “materials and methods: I would suggest to clearly present your sorbents and their properties in Table. You have points 1. and 2. combining different versions of adsorbents and information about different properties. It makes it quite complicated for orientation in text and possible comparison of sorbents. It would be much more clear to have 5 lines (one for each sorbent) with all sorbents parameters which were tested.” - We agree and add the necessary information in the table 1 (lines 141-142)
7. “Line 112-116: You provided the list of compounds which were used for preparation of salt solution but where is the information about concentrations? That is the key information for interpretation of your results. You write about preparation of solutions with lower concentration but the results are provided only for one variant (and we don't know what was the initial concentration). That needs to be clearly explained”. - We agree and add it in the text (lines 129-139)
8. “You obviously combined Results and Discussion. Modify the Section 3 title to fit the content.” - We change the title (line 179).
9. “Figure 3, 4 and 5: provide the information about method which was used for obtaining these photographs” We agree with your comment and add the necessary information (lines235-237; 243-246; 255-258; 265-267)
10. “Compare your results with other relevant research (different sorbents, different conditions etc.)” We also agree with your comment and add the necessary information (lines 269-294).
11. “specify the author contribution according to journal requirements using CErdiT” - We add contribution according to CErdiT (lines 305-309)

 

Best regards,

authors of the paper.

Reviewer 2 Report

This manuscript deals with the natural adsorbents for the removal of heavy metal by adsorption mechanisms.

Abstract.

The sentences mentioned in the text were copied and pasted as they are without modification. It must be completely rewritten.

Materials and Methods.

Over 20 years, many studies have been conducted to evaluate the adsorption capacity of various sorbents. And they compare adsorption capacity based on isotherm experiment, such as langmuir and frendlich. 

However, this manuscript did not show any significant and novelty about experiment.  Peat and vermiculite are very common and well known materials.

Line 91-95.  How inorganic content was measured?

Line 112-113. Why use sulfate salt? sulfate is easily known as easily formation of precipitation. How about solution pH? ionic strength? mixed ratio? temperature? In adsorption experiment, these factors are very important.

Line 118-127. Why don't use ICP or AAS?

Line 155 is Fig.1 But Line 168 (Figure caption) is Figure 1.Please unify. 

For example line 160, 163, 172. Can the author assure that the heavy metal exists exactly in its ionic species? How can you prove this?

Figure 1 and 2 quality are too low (Excel)

Adsorption mechanism of cation and anion (As) is different. However, this concept is now well discussed.

Figure 3, 4, 5 also show too few information and low quality.

In this manuscript, it was hard to find significant and novelty discussion. 

Author Response

Dear reviewer,

First of all, we want to thank you for your valuable comments and suggestions.

We highlighted all changes with yellow color in order to avoid lines numbering disadvantages.  We put the lines numbers from the electronic paper in this cover letter. For some reasons, the numbers differ from the electronic version. We add all improvements to the text. We have taken into consideration all your suggestions, such as:

1. “ The sentences mentioned in the text were copied and pasted as they are without modification. It must be completely rewritten.”. - We agree with your comment and make the changes (line 10-20).
2. “Materials and methods. Over 20 years, many studies have been conducted to evaluate the adsorption capacity of various sorbents. And they compare adsorption capacity based on isotherm experiment, such as langmuir and frendlich." - We agree with your comment. We also have made up the Langmuir isotherms, but we decided to include it into another article. With the inclusion of adsorption isotherms, the volume of this article increases significantly.
3. «Materials and methods. However, this manuscript did not show any significant and novelty about experiment. Peat and vermiculite are very common and well known materials» - Thank you for your comment. We are very sorry that you have not noticed any novelty in this study. It is possible that we are not fully aware of the available world results, although we have looked through a lot of literature on this topic in Scopus and WoS publications. However, it is known that depending on the peat deposit, bedding conditions, etc., its adsorption capacity in relation to heavy metals can vary within different limits. This is very important, since the authors’ goal is the further developing of composite sorbents from different components, including ones presented in this article. In addition, the sorbent "peat + granular diatomite", which has been investigated, has showed the best results in comparison with other sorbents. Moreover, according to the research results, a patent has been obtained for the invention "Peat ameliorant for the remediation of lands contaminated with heavy metals" RU 2 745 456 dated 09/03/2020, which confirms the novelty of this study.
4. “Line 91-95.  How inorganic content was measured?”. –Maybe we do not understand your question correctly but this information is presented in the Method’s section (lines 150-153; 154-178).
5. « Line 112-113. Why use sulfate salt? sulfate is easily known as easily formation of precipitation. How about solution pH? ionic strength? mixed ratio? temperature? In adsorption experiment, these factors are very important. ». – Thank you for your questions. We agree that it is our drawback that we haven’t mentioned in the manuscript that we have used the individual solutions of salts of heavy metals. We have added it in the paper and other necessary information too (line 125; 129-139; 141-142; 145; 147).
6. “Line 118-127. Why don't use ICP or AAS?” – Thank you for your question. First of all, it should be mentioned that we have used AAS (lines 152-153). The second reason for combining different methods is that young researchers took part in the work. That is why they have used different methods including volumetric / titrimetric method, x-ray fluorescence spectrometry and atomic absorption spectrometry.
7. “Line 155 is Fig.1 But Line 168 (Figure caption) is Figure 1. Please unify.” - We agree with your comment and make the changes throughout the text (lines 181; 220; 221; 239; 254; 263; 289)
8. “For example line 160, 163, 172. Can the author assure that the heavy metal exists exactly in its ionic species? How can you prove this? ". - Depending on the environmental conditions (pH, redox potential, the presence of ligands), metal ions exist in different oxidation states and are part of a variety of inorganic and organometallic compounds, which can be truly dissolved, colloidal-dispersed, or be part of mineral and organic suspensions. The truly dissolved forms of metals, in turn, are diverse, which is associated with the processes of hydrolysis and complexation with various ligands. Many metals form fairly strong complexes with organics; these complexes are one of the most important forms of migration of elements in natural waters. In the experiments carried out in this work, only coloration of solutions in contact with sorbents was observed. No turbidity of the solutions was observed, which confirms the ionic form of the presence of heavy metals in the solution.
9. “Figure 1 and 2 quality are too low (Excel)”. - We agree with your comment and make the changes (lines194-197; 229-233)
10. “Adsorption mechanism of cation and anion (As) is different. However, this concept is now well discussed.”. We agree with your comment. However, we do not discuss the adsorption mechanism in this article. We discuss the effectiveness of sorbents to heavy metals.
11. “Figure 3, 4, 5 also show too few information and low quality.” – Thank you for your comment. We add some complementary information and improve the quality of the figures (lines 238-239; 246-247; 254; 259; 261-263; 268)  
12. “In this manuscript, it was hard to find significant and novelty discussion.” – We agree and try to reorganize these parts (discussion and conclusions) of the manuscript. We add the comparison of our results with other relevant research and our contribution (lines 270-294).

Best regards,

authors of the paper.

Reviewer 3 Report

This manuscript reports the test of natural sorbents for the asessment of heavy metal ions adsorption. This is an interesting work both for the research community and for the general public, due to the great significance that the presence of heavy metal ions have for well-being. It is appreciated that the authors pay attention to economical issues and therefore focus their research on inexpensive materials as sorbents. Additionally, the obtained results are very promising, highlighting the potential use of peat in the development of compositions of affordable complex ameliorants - stabilizers of heavy metals for remediation of disturbed lands. The paper is very well organized and pays special attention to the key aspects of the research. Additionally, it includes high-quality figures that properly complement the discussion. All in all, this is a very good piece of work and an excellent match for MDPI Applied Sciences. However, I recommend the authors to perform the following set of minor, but mandatory, revisions before consider its publication:

 - There are some minor typos throughout the text including "in sutu --> in situ" in line 55 or "is significantly improved --> significantly improves". Please, correct these typos.

 - In the Introduction, I recommend to highlight the high research interest that the detection of heavy metal ions has nowadays, including the development of novel sensors for this purpose. I recommend to add the following references: Journal of Lightwave Technology 37(14), 3495-3502 (2019) & Biosensors and Bioelectronics 165, 112420 (2020).

 - Please, include the corresponding error bars in Figure 1 and Figure 2.

 - In Figure 3, please include the scale of the image, as it has been done for the SEM figures.

Author Response

Dear reviewer,

First of all, we want to thank you for your valuable comments and suggestions.

We highlighted all changes with blue color in order to avoid lines numbering disadvantages.  We put the lines numbers from the electronic paper in this cover letter. For some reasons, the numbers differ from the electronic version.

We have taken into consideration all your suggestions, such as:

1. “There are some minor typos throughout the text including "in sutu --> in situ" in line 55 or "is significantly improved --> significantly improves". Please, correct these typos.” – Thank you for your suggestion. We make the changes (lines 68; 82).
2. “In the Introduction, I recommend to highlight the high research interest that the detection of heavy metal ions has nowadays, including the development of novel sensors for this purpose. I recommend to add the following references: Journal of Lightwave Technology 37(14), 3495-3502 (2019) & Biosensors and Bioelectronics 165, 112420 (2020)” – We agree with your comment and add the necessary information (lines 35-36)
3. “Please, include the corresponding error bars in Figure 1 and Figure 2 – We make all changes in Figure 1 and Figure 2 (lines 193-197; 230-233).
4. “In Figure 3, please include the scale of the image, as it has been done for the SEM figures”. – We agree with you comment. Unfortunately, the measurements have been carried out with an optical microscope (Microscope Altami MET 1. Magnification x40); therefore, there is no scale. However, we add this information in lines 246-247.

 

Best regards,

authors of the paper.

Round 2

Reviewer 1 Report

The manuscript was improved according to the main comments. There are still some minor comments for improvement:

1) In Table 1 I mean to present more clearly materials properties which you describe in text now (pH, ash content, moisture etc.). The data about % adsorption can not be presented there because it is part of results section, not materials and methods.

2) Figure 1: legend in the new version of figure covers partly overlaps

 

Author Response

Dear reviewer,

We highlighted all changes with green color and have taken into consideration all your suggestions, such as:

1. “In Table 1 I mean to present more clearly materials properties which you describe in text now (pH, ash content, moisture etc.). The data about % adsorption can not be presented there because it is part of results section, not materials and methods”. – Thank you for your explanation. We have reorganized Table 1: include properties  and exclude adsorption results (lines 116-118).
2. “Figure 1: legend in the new version of figure covers partly overlaps”. –We have made changes according to your recommendations (lines 170-172).

 

Thank you for all of your time, effort, patience, and guidance during the reviewing procedure

 

Best regards,

authors of the paper.

Reviewer 2 Report

Comments are well revised.

Author Response

Dear reviewer,

 

Thanks a lot for your time and help.

 

Best regards,

authors of the paper.