Hydrochloric Acid Modification and Lead Removal Studies on Naturally Occurring Zeolites from Nevada, New Mexico, and Arizona

Round 1

Reviewer 1 Report

 

General comments

• In overall, I found the work very interesting and in line with the Journal scope. Presentation is well attained, writing style appropriate but with some lapses in style. Structure is clear and citations appropriate but large proportion coming from out-of-date references. The authors should add some more recent literature and explain (solely 40% of references are <10years)
• Title: appropriate
• Abstract: check English. Furthermore it needs to be better structured underlining the importance of the study and the main implications of the study findings. The unique contribution of the study must be spelled out in the abstract
• Introduction: the state of the art should be better linked with the study objectives. The importance and unique contribution of the study should be explained. More recent references need to be added.
• Materials and methods: Good description, coherent and satisfactory level of detail provided.
• Conclusions: There is room for improving it in structure, content even more the writing style which can be punchier, pointing out lead removal ability of samples (mentioning numbers)
• References: less than <40% is up-to-date References,

 

Line specific comments (list not exhaustive)

L18: what are the parenthesis after the numbers?

L41/ L278: please correct “absorb” with adsorb

L44-47: please rephrase it is not clear

L50: define “unusual”

L78: underline the heating rate

Did the authors check for the pH of zeolites after acid-treatment and 3 times washing with water?

L81: which is the temperature of refluxing?

L119: why is absorbed or adsorbed?

XRD/ NMR patterns: Please omit Relative intensity counts; follow same format to all figures (including same deg.)

L142: Are the samples coated prior to SEM analysis?

L145: Preparation of samples prior to FTIR analysis?

L256: The authors support that silicon concentration of samples after acid-treatment is “unaffected”. According to Table 3 silicon is increased by 13% and 20% for NV-Na and NV-Ca, respectively, why is that?

L281: What was the surface area of AZLB-Na and AZLB-Ca samples in comparison to NV-Na calcined and NM-Ca calcined?

L299: Table 5: why do authors refer to the reference [13]? Are your results or not?

L301: which zeolites? Why do authors believe that treatment with KCl will increase the lead ion uptake? And then they resulted in not increasing the lead removal

L306: Table 6: are zeolites calcined or not?

I suggest that lead removal ability paragraph could go last

Conclusions: why not mentioning the ability of lead removal from zeolite samples? Not only acid-treated samples.

Comments for author File: Comments.pdf

Author Response

Dear editor,

My responses are in italics following the referred to section.

Rudy Luck

Reviewer one.

First I thank the reviewer for the thoughtful review and we have acknowledged this assistance in the Acknowledgements. “Insightful comments from reviewers are acknowledged.”                            

General comments

• In overall, I found the work very interesting and in line with the Journal scope. Presentation is well attained, writing style appropriate but with some lapses in style. Structure is clear and citations appropriate but large proportion coming from out-of-date references. The authors should add some more recent literature and explain (solely 40% of references are <10years)

 

Unfortunately, the references added were based on the information contained in the sentence and not on the date of publications. I had added some more recent literature with suitable explanations. Thus we have the following changes to the first sentence:”Natural zeolites, which are composed of hydrated aluminosilicates containing group I and II metals, [1] are an abundant resource [2] with desirable chemical properties for many different applications such as in construction [3], slow release of fertilizer [4-10], cosmetics [11], reduction of lactate or ammonia in mammalian blood [12], removal of Fe and Mn from water [13], catalysis and ion exchange [14] and in environmental protection [15].”

 

• Title: appropriate

 

Thanks

 

• Abstract: check English. Furthermore it needs to be better structured underlining the importance of the study and the main implications of the study findings. The unique contribution of the study must be spelled out in the abstract

 

Changes were made in the abstract to point out that the classification of the zeolites as chabazites and clinoptilolites were assessed. The idea was to study these compounds and see if they can withstand concentrated acid treatment and what were the properties before and after. I think this is stated within the abstract.  Please see the All Markup version to assess.

 

 

• Introduction: the state of the art should be better linked with the study objectives. The importance and unique contribution of the study should be explained. More recent references need to be added.

 

I have modified the introduction substantially.  Please check the last two paragraphs in the All Markup document.

 

• Materials and methods: Good description, coherent and satisfactory level of detail provided.

Thanks.  We have modified this section based on the recommendations of reviewer 2.

 

• Conclusions: There is room for improving it in structure, content even more the writing style which can be punchier, pointing out lead removal ability of samples (mentioning numbers)

 

This has been rewritten with the information added.

 

• References: less than <40% is up-to-date References,

 

More recent references have been added.

 Line specific comments (list not exhaustive)

L18: what are the parenthesis after the numbers?

If this is with reference to 20.0(1), the number is parenthesis here, i.e., (1), is a way to signify the standard deviation in the right most number of 20.0 listed and thus the measurement is deemed accurate from 19.7 to 20.3.  By so doing 99% of the values obtained will be within this range. If it referred to the outermost parentheses, these have been removed.

L41/ L278: please correct “absorb” with adsorb

Done with the first “adsorb” and then substituted “removes” for the second.

L44-47: please rephrase it is not clear

Done.

L50: define “unusual”

Added high-sodium

L78: underline the heating rate

Done

Did the authors check for the pH of zeolites after acid-treatment and 3 times washing with water?

Yes.  This have been clarified on line 101. “The final rinse was clear as assessed with pH paper.”

L81: which is the temperature of refluxing?

“Reflux” changed to “by heating at 85 ^oC a solution” on line 96

L119: why is absorbed or adsorbed?

It is possible that both may be operative.  Pb²⁺ could be on the surface as well as inside the zeolite. 

XRD/ NMR patterns: Please omit Relative intensity counts; follow same format to all figures (including same deg.)

Relative intensity counts removed and new diagrams for Figs 1-4 inserted. Also new Fig 3 (Above) has been inserted to conform with the format requirements.  Unfortunately, the program QualX did not allow for an exact scaling but this has been included since it determines the FoM of 0.75. These programs are also used in later determinations of relatedness, i.e., lines 219-221 and this figure is useful in demonstrating that the program was used.

L142: Are the samples coated prior to SEM analysis?

More specifically defined as “SEMs were performed on uncoated samples (loaded onto double-sided carbon tape followed by air removal of unstuck material) using a Hitachi S4700 Scanning”

L145: Preparation of samples prior to FTIR analysis?

Changed to “FTIR spectroscopy were performed on pure material using calcined and modified pulverized samples on a PerkinElmer Spectrum”

L256: The authors support that silicon concentration of samples after acid-treatment is “unaffected”. According to Table 3 silicon is increased by 13% and 20% for NV-Na and NV-Ca, respectively, why is that?

This is a good point.  Changed to “the silicon concentration increases proportionally”

L281: What was the surface area of AZLB-Na and AZLB-Ca samples in comparison to NV-Na calcined and NM-Ca calcined?

Due to the decomposition of the AZLB-Na and AZLB-Ca samples with the acid treatment, we did not determine the surface area here with these samples.

L299: Table 5: why do authors refer to the reference [13]? Are your results or not?

This should have been reference 43 i.e., a link to a published procedure. I have removed this since reference is made to the procedure in the experimental section, “and stirred for 5 days at room temperature as detailed previously [43].”  I think it got messed up with cross referencing in the different versions of the paper.

L301: which zeolites? Why do authors believe that treatment with KCl will increase the lead ion uptake? And then they resulted in not increasing the lead removal

Which zeolites clarified as “In order to increase the lead ion uptake, the zeolites (natural and modified NV-Na and NM-Ca) were stirred in a 1M KCl solution at 25°C for 5 days, Table 6.”

The idea here was to charge the zeolite with negative ions that would increase the likelihood of Pb²⁺ capture. It did not result in increased lead removal presumably because the ions simply dissolved in solution due to increased pore size.

L306: Table 6: are zeolites calcined or not?

Yes.  This sentence is above Table 6 caption. “After drying and calcining at 550 °C for 5 hours, these treated zeolites were tested similarly for their ability to remove lead ions from polluted water.”

I suggest that lead removal ability paragraph could go last

This does make sense. Thanks. The experimental section has been reordered to conform to this suggestion as well.

Conclusions: why not mentioning the ability of lead removal from zeolite samples? Not only acid-treated samples.

This has now been included.

Author Response File: Author Response.pdf

Reviewer 2 Report

This paper presented the study of HCL treated modified naturally occurring zeolites, it is quite interesting. But this paper required some important revisions as follows:

1) Introduction - In the introduction part more relative information needs to be added. Lines 48-64 need to rewrite or reorganize in a more scientific/technical way. Add an individual paragraph at the end of the introduction to explain the theme/novelty and structure of the paper (e.g. In the present study). 

2) Materials and method - Here all the information about materials should be explained in section 2.1. MATERIAL and all the methods in section 2.2 METHODS, as follows- 

2.1. Materials:

2.1.1. Zeolite Modifications: 75
2.1.1.1 Calcined Zeolites 

2.2. Methods

2.2.1 X-ray Diffraction

Suggestion - In this section a flowsheet diagram explaining all the processes that can improve the quality of this work.

3) Result and discussion - OK 

4) MOST IMPORTANT IN THE WHOLE MANUSCRIPT A VERY FORMAL WAY OF WRITING WAS USED (e.g. We had recently obtained, We were interested in comparing, They have then filtered) THIS TYPE OF FORMAL WRITING IS NOT ACCEPTABLE. USE THE ACADEMIC AND TECHNICAL WRITING. 

5) Some grammatical mistakes are present in the manuscript, CKECK.

6) Clearly describe/rewrite the main methods and results in the conclusion part. 

Suggestion - Abbreviations part can be added. 

Author Response

Reviewer 2.

My responses are in italics following the referred to section.

First I thank the reviewer for the thoughtful review and we have acknowledged this assistance in the Acknowledgements. “Insightful comments from reviewers are acknowledged.”                            

 

Comments and Suggestions for Authors

This paper presented the study of HCL treated modified naturally occurring zeolites, it is quite interesting. But this paper required some important revisions as follows:

• Introduction - In the introduction part more relative information needs to be added. Lines 48-64 need to rewrite or reorganize in a more scientific/technical way. Add an individual paragraph at the end of the introduction to explain the theme/novelty and structure of the paper (e.g. In the present study). 

This last paragraph was change to read as follows: “In this report, four naturally occurring zeolites which were reported to be of the chabazite and clinoptilolite (based on Si:Al ≥ 4.0 [30]) varieties were examined [31]. The chabazite form has been explored for its unusual composition [32] and chemical upgrading, [33], and the clinoptilolite zeolite has been studied for various membrane applications [34-36]. Additionally, both chabazite and clinoptilolite were previously subjected to treatment with base and applied for Pb²⁺ and Cd²⁺ removal [37]. It was of some interest to determine if modifications under acidic conditions while maintaining structural integrity was possible and what impact this would have on their properties and potential use in remediation, an idea prompted by a publication on chemical etching on a glass surface using HCl [38]. A report dealing with the treatment of naturally occurring clinoptilolites in Cuba using 0.6 M HCl discovered that milder forms of acid treatment were required as higher concentrations led to the decomposition of the zeolites [39].

In the present study, the integrity of the samples, i.e., their purity and classification as chabazite and clinoptilolite, was assessed as evident by powder X-ray diffraction. Additionally, treatment with concentrated HCl removes metal ions from the pores leaving the silicon framework intact with the clinoptilolite variety whereas the chabazite ones became amorphous. A variety of analytical techniques were employes to assess the nature and composition of the natural and acid-modified zeolites including solid-state ²⁹Si and ²⁷Al NMR, BET measurements, SEM images, and powder X-ray fluorescence and diffraction. Lead removal studies on the clinoptilolite samples suggested differing capacities between the two samples after calcination and deterioration of Pb²⁺ storage capacity upon modification.”

 

2) Materials and method - Here all the information about materials should be explained in section 2.1. MATERIAL and all the methods in section 2.2 METHODS, as follows- 

2.1. Materials:

2.1.1. Zeolite Modifications: 75
2.1.1.1 Calcined Zeolites 

2.2. Methods

2.2.1 X-ray Diffraction

Done.  However in the MDPI Style menu of headings, there are only options for headings 1, 2, and 3.  2.1.1.1. etc are of a heading 4 style which was not available so heading style 3 was utilized here.

Suggestion - In this section a flowsheet diagram explaining all the processes that can improve the quality of this work.

A flow chart of techniques was added.

3) Result and discussion - OK 

Thanks.

4) MOST IMPORTANT IN THE WHOLE MANUSCRIPT A VERY FORMAL WAY OF WRITING WAS USED (e.g. We had recently obtained, We were interested in comparing, They have then filtered) THIS TYPE OF FORMAL WRITING IS NOT ACCEPTABLE. USE THE ACADEMIC AND TECHNICAL WRITING. 

All removed.  See line 35,  161, 218, 267, 284, 298, 308, 379, 444.  Quite possible that the lines numbers will change slightly as I modify the text in answering all the points so please treat these line numbers as approximate.

5) Some grammatical mistakes are present in the manuscript, CKECK.

Checked but sadly, no doubt, some will remain.

6) Clearly describe/rewrite the main methods and results in the conclusion part. 

Conclusions modified to include the main methods.

Suggestion - Abbreviations part can be added. 

Abbreviations added at the end of the Introduction Section.

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Hydrochloric Acid Modification and Lead Removal Studies on 2 Naturally Occurring Zeolites from Nevada, New Mexico, and 3 Arizona. 4

By Garven M. Huntley, Rudy L. Luck, Michael E. Mullins and Nick K. Newberry

 

Comments_Round2

I am confused is the Manuscript submitted to Processes or Standards journal?

L113: what was the pH measured? (it was better to measure the pH of the solid by pH meter than pH paper)

L204: please rephrase

In the corrected version regarding Figures, Relative intensity counts were not removed despite that the authors claimed so

L187, L471: please delete “absorb”

L480: please add appropriate units

L503: Is it correct to refer to both Tables (Table 5 and 6)? Why this method did not have high enough precision?

Conclusions: It is important to mention solution pH (generally experimental conditions meaning pH measured before and after lead removal experiments). It is wise that you compare lead removal results of non-treated and acid-treated materials with same pH solution value.

It may be that due to low pH solution (acid-treated zeolites) that lead removal was not satisfactory.

L535: instead of “harsh” use the concentration value used for HCl.

References: the addition of the updated literature was not clear (not tracked changes). However now the updated- literature (less than 10 years) is up to 70%.

Comments for author File: Comments.pdf

Author Response

Comments_Round2

I am confused is the Manuscript submitted to Processes or Standards journal?

It should be Processes.

L113: what was the pH measured? (it was better to measure the pH of the solid by pH meter than pH paper)

We also tested the final rinse solution with AgNO₃ but, sadly, we did not utilize a pH meter. Added the following:  “The final rinse was clear as assessed with pH paper and when added to solutions of AgNO₃ did not result in a white (i.e., AgCl) precipitate.”

L204: please rephrase

It is not obvious what line 204 refers to.  In the revised version if I use the “No Markup” option this would be the heading for Figure 3.  I have rephrased this caption.

In the corrected version regarding Figures, Relative intensity counts were not removed despite that the authors claimed so

I did remove the caption that had RI for the second version. However, I was and still am confused as to what the reviewer is referring to here.  Presumably this “Relative Intensity counts” are the labels for the phases with the spectra which I have removed together with the reference to the identification.

L187, L471: please delete “absorb”

The word “absorb” is not in the second revised version. It was in the first version. Perhaps the reviewer found this word in the second version using the All Markup version. 

There is only reference to “absorbed” on line 160.

L480: please add appropriate units

Added. Thanks.

L503: Is it correct to refer to both Tables (Table 5 and 6)? Why this method did not have high enough precision?

Table 5 and 6 deal with zeolites prepared under different conditions.  Our thinking was that KCl would increase the Pb²⁺ removal. It did not. Unfortunately, we followed a literature procedure for this method and did all the measurements in triplicate. These were the results we obtained and, in our hands, this is the precision we obtained.

Conclusions: It is important to mention solution pH (generally experimental conditions meaning pH measured before and after lead removal experiments). It is wise that you compare lead removal results of non-treated and acid-treated materials with same pH solution value.

It may be that due to low pH solution (acid-treated zeolites) that lead removal was not satisfactory.

We have added this caution to the conclusions. “. However, it is also possible that the removal of acid in the acid treated zeolites was not thorough and thus lead removal was compromised with these species.”

L535: instead of “harsh” use the concentration value used for HCl.

Done.

References: the addition of the updated literature was not clear (not tracked changes). However now the updated- literature (less than 10 years) is up to 70%.

Actually using endnotes and word, I could not get the tracked changes for the references to show.  These are produced below.  I used the original document and then the final one and did a comparison.  I had to cut and paste the references and copying did not allow for the changes to be easily visible.

Thanks for the points.

NOTE:  The tracked changes for the references are in the Word DOC and could not be reproduced below.

 

   

Author Response File: Author Response.pdf