Physicochemical and Mineralogical Characterizations of Two Natural Laterites from Burkina Faso: Assessing Their Potential Usage as Adsorbent Materials

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The work is devoted to the study of laterites from Burkina Faso, namely its physicochemical properties and features of mineral composition.
The authors stated that the work has 2 main aims: studying the physicochemical properties and mineral composition of rocks, as well as studying the relationship between physicochemical properties and structural features and their sorption characteristics.
The problem is that, sorption experiments of the laterites have not been conducted. All conclusions are based on literature reviews. The correlation between physical and chemical properties and the sorption capacity of laterites is carried out by the authors without any basis. Almost every section with analytical studies (chemical composition, mineralogy, thermal properties, specific surface area, electron microscopy, FTIR) ends with the conclusion that these laparites are suitable as sorbents. However, neither the chemical composition, nor the thermal studies, nor the infrared spectroscopy have any relation to the sorption activity of the samples. The only studies that can indirectly characterize sorption properties are the capacity of cation and anion exchange.

Sorption of pollutants on natural rocks is a very complex process and depends not only on porosity and the value of the specific surface area (as explained by the authors), but also on a large number of other parameters, as well as on the nature of the pollutants. And it is unacceptable to discuss the sorption capacity of rocks without conducting the experiments.

Nevertheless, at the end of the article, the authors provide a table showing the sorption characteristics of these rocks in relation to arsenic. A link to the author's dissertation is given. However, before this, the article did not contain any information that the authors had carried out sorption of arsenic and that these data would be discussed.

In this regard, the reviewer suggests either omitting the part on sorption from the title of the article and from the text and concentrating simply on studying the physical and chemical properties of laparites and their mineral composition, or expanding the part on sorption, adding a description of the experiments on arsenic sorption to the chapter “methods and materials”, and also adding a chapter with the results of these studies. Unless, of course, these data have already been published in another journal (the dissertation does not count)

In addition, the work has critical mments and requires serious revision, in terms of style, structure and description of the results.

Other comments and remarks:
- proposal for the title of the article: “Physicochemical and mineralogical characterizations of laterites from Burkina Faso”
- In the text, it is necessary to avoid phrases beginning with – We, our, etc.
- X-ray powder diffraction – XRD (not XRPD)
Line 21 - These should be removed from the abstract

Line 25 - mineral composition. First, list the minerals with the highest content
Line 25 - anion exchange capacity. And what about cation?

Introduction - needs to be rewritten. This introduction contains too much information that is not related to the topic of the study and is repeated. Write about the relevance of the topic, about previously conducted studies on this topic by other authors. Novelty, goals and objectives. Add more mineralogical and geological information.

Line 79-80 - How are they responsible for sorption? These are all indirect methods.
The only direct method is a sorption experiment, and to a lesser extent, cation and anion exchange capacity

Line 81-84 - Delete it. Further on in the test - there is no need to list all the methods used each time. This has already been done in the abstract.

Line 86 - 130 - this part must be deleted. This is well-known and accessible information. The results of the research should be in the "results" section, not in the introduction.

Line 131-137 - delete

Table 1 - Delete. The coordinates are on the map

Fig. 1 - Geological scheme of the study area

Fig. 1 legend - tarkwaien, is this a local term? Give a more detailed description of what it is.

156-158 - the text in this section can be deleted

Table 2. Table title -- there are no physical and chemical characteristics here
Table 2 - the sum for KN is greater than 100%, LA - on the contrary, the sum is significantly less than 100%. Magnesium and calcium are rock-forming elements. Are they really not present in laterites? Or have they not been determined?

Line 292 - such conclusions cannot be drawn based on chemical analysis

Table 4 -  normal title is needed. The table title cannot begin with a verb.

Figure 4. – these figures can be removed

Table 6. Units of measurement C.E.C (cmol(+)/kg). - an error in the units of measurement or in the measurements themselves? Usually these orders are typical for cmol(+)/100g

3.6. Mineralogical characterization – mineralogy is usually inserted at the beginning of the chapter on rock characteristics, together with chemistry.

3.6.3. Semi-quantification – move to the section with mineralogy.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

As presented, the article does not bring any new conclusions to the subject, as all the results obtained are already covered in the literature. If we compare the introduction and conclusion, we realize that there is no novelty in the article. The article does, however, have the advantage of describing the techniques used concisely and presenting the results methodically. 

The way the subject is presented gives the article a local flavour. For the article to resonate, the authors must justify the choice of the two samples studied and emphasize the main conclusions drawn from the study.

Some comments to improve the article 

-The introduction is very long and needs to be shortened,

-The authors must justify the choice of the two samples.

-How do you obtain the results of the semi-quantitative analysis of the different mineral phases present in the KN and LA laterites. According to the kaolinite diffraction peak, the content of this mineral is much higher than that of quartz and the other phases.

-This result is also confirmed by TGA/DSC curves of the lateritic samples. Endothermic peaks between 500 °C and 600 °C in the DSC curves assigned to kaolinite dehydroxylation are highly developed, indicating a very high kaolinite content.

-Scanning electron microscopic images are a little disappointing, as no phases were identified on these images. At this scale, observation should clearly reveal hexagonal kaolinite crystals.

Comments on the Quality of English Language

Although my English is not very good, I think the article is written in a correct style. 

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

In this manuscript, a physicochemical analyses and mineralogy of two laterites from Burkina Faso has been carried out. Authors determined the properties of these two natural laterites of Burkina Faso with regard to their ability to adsorb heavy metals and/or metalloids from aqueous solutions.

The article is interesting and has a good experimental design. However, authors must make an effort to modify its structure:

1) The introduction section must be rewritten. It is not about describing the benefits of the analytical methods used (well known) but rather describing the state of the art, the current context, the novelty of the work. Please, cite similar studies carried out in the study area or in other areas. Only the last paragraph of this section is correct and adequate.

2) The article is written in a technical report format, but it should not be forgotten that it is a scientific article for an international journal. Therefore, knowing its local interest, the authors must make an effort and compare the results obtained with those obtained from the literature. What contribution does this research make to the progress of science and technology?

3) The analytical methods are described correctly, but there is no data on their protocols, precision and sensitivity of the techniques.

4) It is striking in a minerlogical semiquantitative analysis with an error of 5% that the percentages by weight of mineral phases are expressed with a precision of 2 decimal places. This must be clarified by the authors. For the mineralogical analysis, a rational analysis of chemical elements by weight combined with X-ray diffraction is used. Why? There are different softwares that allow the mineral phases to be quantified. Rational analysis is an approximation.

The sections "Results and discussion" and "Conclusions" are OK. The sections "Introduction" and "Materials and Methods" may be rewritten by authors.

Author Response

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Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The article has been significantly improved by the authors. The main problem (lack of sorption data) has been solved.
However, the article needs to be improved in the following areas:

- Add brief sorption results to the abstract and conclusion (add brief information on the mechanisms in the conclusion).
- Sample DA was not used in the experiments and is not present in all chapters. The reviewer suggests removing it from the discussion and leaving it only in the tables as an example
- It would be good to explain why trivalent arsenicum is worse sorbed on the LA sample
- Also, judging by the graphs, arsenic is better sorbed than copper and lead (although the initial concentrations are the same). However, as is known, the sorption of anions is usually a more complex problem than cations. How do the authors explain this? What is the mechanism of sorption of anions?

Table 1 - The authors' answer regarding the results of chemical analysis is incorrect. Indeed, in some cases the sum of elements may be less than 100% due to semi-quantitative analysis or equipment limitations. But values ​​above 100% are incorrect. In general, it is customary to normalize the values ​​of chemical analysis to 100%. However, magnesium and calcium are rock-forming elements and their contents cannot be in such small quantities. It is necessary to solve the problem with chemical analysis.

 

Author Response

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Reviewer 2 Report

Comments and Suggestions for Authors I am still not convinced by the quality and interpretations of the SEM images, so I propose to delete this section.

Author Response

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Reviewer 3 Report

Comments and Suggestions for Authors

The authors have reviewed the manuscript following the indications of the reviewers. The changes made have been substantial and relevant and, without a doubt, the articles has been improved.  I believe that authors should go the extra mile and improve analytical protocols to make the trials reproducible. 

Author Response

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