Adsorption and Its Mechanism of Arsenate in Aqueous Solutions by Red Soil

Round 1

Reviewer 1 Report

In the present investigations, an attempt was made to test the red soil for arsenate adsorption from the aqueous solution. The manuscript needs major changes to publish in the present journal. Therefore, I recommend major revision for present manuscript.

1. Title looks confusing, author should revise title of the manuscript.
2. Manuscript contains seveal grammatical and syntax errors. Author should pay attention on it.
3. All figures must be revised with adjusting the scales and title of the axis must be start with capital letters. Add opposite X and Y-axis to all figures.
4. SEM before arsenic adsorption needs to be provided.
5. The authors used FTIR to confirm the arsenic adsorption, which is not sufficient. Author should provide any other analysis to confirm this.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

Opinion on the paper ‘Removal and mechanism of arsenate from aqueous solutions by Yunnan red soils’

The article ‘Removal and mechanism of arsenate from aqueous solutions by Yunnan red soils’ by Min Guo, Lili Shi, Wen Gu, and Wenzhu Wu describes the influence of adsorption process parameters (soil types, soil/solution rates, initial arsenate concentrations and shaking speeds) on adsorption capacity of Yunnan red soil for arsenate. The article fits the scope of the Water journal. However, a revision is recommended and the manuscript may be published after the below-mentioned corrections have been made.

Title:

Title should be corrected – work describes mechanism of arsenate removal not mechanism of arsenate.

Keywords:

I suggest change one of keywords ‘optimized’ as it is too general. I think that for example  ‘water treatment’ is more suitable.

Materials and methods:

      The section materials and methods is messy and need to be corrected. Some suggestions are listed below.

Materials

• I think the subsection “Materials” should not include information about equipments. These should be placed in the text where analytical methods are described. What is more the shaking bath should be mentioned as equipment.

Soils

• Soils are also materials used during the studies so I think this subsection can be connected with subsection ‘2.1. Materials’ and named for example ‘2.2. Soils and their characterization’.
• The characterization of materials is very poor. Information about chemical composition, the surface and pore properties, surface charge of the adsorbents are necessary during evaluation of adsorption process.
• The authors mention in the introduction that the pollution caused by heavy metal and metalloid in the Yunnan Province in Southwest China has been increasingly serious. In the view of this fact the content of As(V) in Yunnan soils should be analyzed and the results should be take in account during evaluation of adsorption process with using this materials.

Batch adsorption studies

• What was the initial pH of arsenic solution? It is an important information for adsorption process.

Analytical methods

• If the subsection is named analytical methods all methods used for: characterization of adsorbents, determine of arsenate concentrations and evaluate adsorption mechanism should be mentioned here. I suggest to place all information about analytical methods here.
• Was any reference material used for atomic fluorescence spectrometer PF6 analysis was? How the accuracy and precision of the results was controlled?

Results and discussion:

Effect of soil/solution ratios

• The informations from line 150-159 should not be placed in this section.
• The information from line 160-162 should be placed in Materials and Methods section.

Optimization of the factors affecting arsenate removal by orthogonal array

• The orthogonal array method should be described in Materials and Methods section. Only results of determination the optimum level of factors which will affect the removal rates should be given in this subsection.
• Table 3 – should be “rpm” not “rmp”

Adsorption mechanism of the red soils

• Line 252 - Liu Huili, et al. – lack of reference number
• Figure 5 – lack of information about number of sample of soil.

 

Conclusions

Conclusions should be extended - they include almost the same information as abstract.

 

References:

References do not include any works from last 5 years. The subject of adsorption process, water treatment and removal of heavy metal ions from aqueous solution is very popular in recent years. In the literature a lot of new papers refer to this subjects (for example: A. Adamczuk, W. Sofińska-Chmiel, G. Józefaciuk, Arsenate adsorption on fly ash, chitosan and their composites and its relations with surface, charge and pore properties of the sorbents, Materials 13 (2020) 5381). 

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

The submitted paper (Removal and Mechanism of Arsenate from Aqueous solutions by Yunnan Red Soils) is well organised and discusses an important issue. However, the following points must be addressed before further processing:

1- The English language needs revision.

 2- What do you mean by (a Milli Q Water)? the latter is a purifying system. You should mention the type of water, such as deionised water or distilled water.

3- Reference the adopted standard methods. For example, what is the reference of the cleaning with HNO3 (line 76). Check the rest of the article.

4- How did you select the shaking speed (50-300 rpm)? Was recommended in the literature?

5- What is the reason for the decrease in the removal efficiency at a shaking speed of 100 rpm compared to 50 and 150 rpm (in Figure 3)? 

6- There are other methods to remove heavy metals from water, such as electrocoagulation. You need to mention such methods in the introduction section. See this reference: https://link.springer.com/chapter/10.1007/978-981-13-8181-2_17 

7- In the introduction, it would be a good idea to mention other types of adsorbents, see this article: https://iwaponline.com/wst/article/83/1/77/78419/Phosphate-removal-from-water-using-bottom-ash

8- Recommendations for future works could be added to the end of the conclusions section (not mandatory) 

Good luck with your resubmission 

Author Response

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Author Response File: Author Response.docx

Reviewer 4 Report

See my comments in the attached file.

Comments for author File: Comments.pdf

Author Response

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Reviewer 5 Report

This paper presents a study on removal of arsenic adsorption from arsenic contamination lakes in China’s southwestern regions. The authors used red soil, available in Yunnan Province and constituted with high clay content and rich in Fe and Al oxides, as sorbent.  Based on their analysis, authors concluded that red soil as a potential adsorbent for arsenic removal and provide a cost effective technique in removal of arsenic from contamination lakes. I have following comments for this paper:  

• In material and method section, line 75, give specification and /or details of purification system to produce milli Q water.
• Line 77, 248 etc, check for position of subscript used. It should be slight below to normal text.
• In line 173, unit of pressure is mentioned as t/cm². Clarify?
• Line 246, is it bending or bonding?
• From Table 1, it has been clear that pH value of soil plays as an important factor for arsenic removal from contaminated water. Hence, pH value of water may affect on the arsenic removal percentage. Comments/study needed on this.
• Check the formatting of chemical formulae -FeO2As(O)(OH)- and FeO2As(O)2 in line 297.
• Sentence revision in line 290, 298. It should be “indicates” and “chosen” Careful revision is needed to avoid other errors. It is suggested to avoid very long sentences.

I recommend a minor revision to this manuscript.

Author Response

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Round 2

Reviewer 1 Report

Authors revised the manuscript according to my comments.

The revised paper can be accepted for publication.

Reviewer 4 Report

The authors have provided the necessary revisions.