Bentonite Powder XRD Quantitative Analysis Using Rietveld Refinement: Revisiting and Updating Bulk Semiquantitative Mineralogical Compositions

Round 1

Reviewer 1 Report

The work by Cuevas et al. is a really good work focusing on a very complex task everyone working on clay mineralogy has to face: the task of quantifying the percentages these minerals represent within polimineral assemblages. The methodology used by the authors provides really good results that reinforce the importance of using Rietveld refinement for quantifying clay minerals.

I strongly recommend the publication of this research paper, although minor modifications of style should be made to the manuscript.

There are some general things that should be modified.

- Nomenclature of the samples. In Figure 1 they are noted as FB5-1, FB5-2, … However, in other parts of the text, such as Table 2, they are referred to as FB5_1, FB5_2, … and in line 379 as FB5.1. The nomenclature has to be homogenized.

- Citation style. There are several parts of the manuscript where the citation style of the journal is not respected, such as lines 92, 149, 183, … This should be corrected.

 - Please avoid abbreviations such as “wasn’t” as well as the genitive “ ‘s “.

- The Miller indexes should be written between parenthesis, even when referring to general indexes such as (hk0).

Line 12 -> I suggest rephrasing to “Bentonite is a claystone formed by a complex mineralogical mixture”

Line 33 -> Rephrase to “Bentonites are claystones”

Lines 89 – 105 -> Please add some marks at the beginning of each paragraph to highlight the problems listed.

Line 109 -> Change “produces” to “produce”

Line 135 -> Change “FB-3” to “FB5-3”

Figure 1 -> The abbreviation of temperature would be better if is listed as “T” instead of “tª”

Lines 164 – 165 -> I think it would be better if it was written” “… by duplicate were weighed out and added to a 150 cm³ centrifuge tube with distilled water”

Lines 215 – 218 -> This phrase is too long and gets a bit a complicated. I suggest dividing it into two.

Line 220 -> Remove “is”

Lines 220 – 221 -> The way this phrase is written it is barely comprehensible. Please rewrite.

Lines 224 – 225 -> I think it would be better to refer to the “width at half height” as “full width at half maximum (FWHM)”

Line 270 - 271 -> I do not really get what the numbers refer to. In line 270 it is obvious that the (hkl) index is the (001), but in line 271 it is not comprehensible at all. If they are Miller indexes, no commas would be needed. Are they referring to bibliographical references? In addition, when referring to Miller indexes, it would be enough to only list (001) instead of (hkl 001).

Line 274 -> Change 2pattern” to “patterns”

Line 279 -> Change “composition” to “compositional”

Line 295 -> Same as in lines 270 – 271.

Table 2 -> Change commas to dots.

Line 379 -> Remove “is”

Line 392 -> I suggest changing “is the clay” to “is that clay”

Line 401 -> Change to “It is also needed to”

Comments for author File: Comments.docx

Author Response

Thank you very much for your constructive comments. Based on your comments we have revised the English text correction following the instructions. Please see the attached file.

Author Response File: Author Response.pdf

Reviewer 2 Report

The paper concerns an important and complicated topic - quantitative phase analysis of bentonites.  Without a precise determination of the phase composition, the practical application of bentonite is problematic. The results of XRD phase analysis of seven samples are described: the original bentonite and identical material after an experiment that lasted up to 14 years. Based on my own experience, I completely agree that semiquantitative methods are insufficient and their results may often be misleading. I aso agree that smectite (montmorillonite) content is often being overesimated, which may cause serious problems not just in the research field but also in the practice.

From the analytical procedures used I would like to highlight the removal of the fraction <0,5 µm.

However, in my opinion, the article has several flaws.

General comments:

• Language. I´m not a native English speaker, but I’m sure that even the title of the paper is not correct: „...XRD powder...“ instead of “powder XRD” and “revisiting” instead of “revising”. I recommend a thorough linguistic correction of the whole paper.
• The Materials and Methods chapter should only describe the materilas and procedures used in the study. E.g. the paragraphs between l. 198-241 shoud be moved to the Introduction part, as well as some other parts of the Materials and methods chapter.

The same applies to the paragraph between l.330-348 in the Discussion of Results chapter.

• Some parts of the paper describing generally known elementary technical details resemble rather a chapter of a book (or a text book on XRD) than a paper. In fact, the core of the paper is giving data processing steps, which should be made at any precise Rietveld analysis. Of course, bentonites are very complex and their correct analysis is demanding. Some of the information (e.g. the need of correct choice of structural models) including refined diffractograms (e.g. Fig 2 and 3) may be very useful for XRD beginners.
• Chapter Conclusion is missing.

Further comments:

• You mention the common problem with preferred orientation. L. 242: What kind of sample holdes was used in your measurements? Backloading?
• 354: Tab 2 - Very low determined content of illite and the in the FB5-1 sample should be explained.
• 354: Tab 2 - Due to the common error of determination, I recommend rounding the values in Table 2 to one decimal place.
• 354: Tab 2 – use “.” for separation of decimals
• 380-381: I agree. But, anyway, the precipitation of cristobalite is not realistic under conditions of the experiment in my opinion.
• 382-384: This is an interesting and also important point. Therefore, giving a graphical comparison of the (001) montmorillonite peak position would be suitable.

Conclusion:

Although the paper regards serious problems  of XRD whole pattern quantitative analysis, I´m not sure it is suitable for publishing in the present form.

Author Response

Thank you very much for your constructive comments. Please see the attached file.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The work by Cuevas et al. has significantly been improved since the first round of reviews and should be published, although there are still some minor issues that should be addressed.

Line 58 -> Change “the bentonite ability to” to “the ability of bentonite to”

Line 173 -> Change “as established by Martin Pozas et al.” to “as established by previous authors” in order to respect the citation style of the journal.

Line 207 -> In this line the citation style should also be corrected.

Line 283 -> Change “Plagioclase patterns” to “The patterns of plagioclase”

Line 285 -> Change to “and Albite from the BGMN database”

Line 291 -> Change to “using the BGMN database”

Line 302 -> Change to “using the structural models proposed by previous authors [38,39]” in order to keep a better concordance with the citation style

Line 304 -> I suggest changing “Rietveld refinement example of °34.7(040) (220) reflection” to “Rietveld refinement example of the region at °34.7 °2Ɵ showing the (040) and (220) reflections”

Line 305 -> Is it Muscovite_1Md as shown here or muscovite1Md as referred to in line 263? Please refer to it homogeneously.

Line 335 -> Change to “FB5 experiment”. In addition, in this line FB5-1 and FB5-3 should be changed to FB5_1 and FB5_3.

Line 365 -> Change to “determined by previous authors [25]” to respect the citation style.

Lines 388 – 394 -> Refer to samples as FB5_ and their corresponding numbers to keep a homogeneous style in all the article.

Line 436 -> Remove “It”

Author Response

Dear Reviewer,

we are very grateful for your comments and suggestions, which have been modified in the text, as you can see in the attached file.

Author Response File: Author Response.pdf