The Kinetics of Manganese Sorption on Ukrainian Tuff and Basalt—Order and Diffusion Models Analysis

Round 1

Reviewer 1 Report

It was a good read, I liked the article, and I recommend it for publication after some minor corrections.

Please use the Past Simple tense in the abstract.

“Natural mineral materials are widely applied in environmental engineering especially for soil remediation [1,2]. It is also used for water and wastewater treatment fundamentally as filtering beds”. It should be “they are” not “it is” as the sentence refers to the subject of the previous sentence “natural mineral materials” – plural. Please check similar errors through the whole article. There are also numerous instances where the article “the” is missing, please revise the article.

 

Line 132 :” Both materials are characterized by middle specific surface area” Did the Authors mean average SSA? What is middle SSA?

Line 164: “The Mn reduction at all temperatures tested was higher on tuff” I think he Authros would like to correct this sentence to eg. The reduction in Mn concentration. I do not think they investigated the metal’s oxidation state.

Lines 170-179: Why the Authors did not perform a simple test on AAS to confirm if the suggested mechanism takes place? The pH could increase simply due to adsorption of H+ on the minerals. Most probably both of the phenomena occurred at the same time.

 

I did not see the part where the Authors examine the sorption equilibrium, why did not they make any adsorption isotherms and calculate the maximum adsorption capacity using for instance the Langmuir model? Consequently in Line 259 ”The equilibrium sorption capacity of the tuff was twice as high as on the basalt (5.5 mg/g and 2.4 mg/g respectively) indicate the condition in which the equilibrium was reached (concentration, temperature and time) and name the models based on which the adsorption capacity at given condition were reached, the values could be given with determined confidence intervals (or any other uncertainty estimation).

 

Line 263 : the models are just mathematical instruments to obtain some numbers and compare them with another. Scorpion, especially on natural materials is a complex phenomenon, consequently assumptions based on mode fit about chemisorption are not quite correct. If the Authors insist on the conculussion, please provide more evidence. I would just tone it down a bit.

Author Response

Dear Reviewer,

first of all, we appreciate your involvement and we thank you very much for helpful comments, that enabled us to clarify some points and improve the presentation of our work.  Detailed description of the changes done in accordance with the comments of Referee follows. Responses to your comments and corrections in the text are marked in green.

 

Reviewer’s comment:

Please use the Past Simple tense in the abstract.

Author’s action:

The Simple Past tense was been used in the abstract.

 

Reviewer’s comment:

 “Natural mineral materials are widely applied in environmental engineering especially for soil remediation [1,2]. It is also used for water and wastewater treatment fundamentally as filtering beds”. It should be “they are” not “it is” as the sentence refers to the subject of the previous sentence “natural mineral materials” – plural. Please check similar errors through the whole article. There are also numerous instances where the article “the” is missing, please revise the article.

Author’s action:

Once again the text was corrected in terms of language. We hope our translator corrected the errors.

 

Reviewer’s comment:

Line 132:” Both materials are characterized by middle specific surface area” Did the Authors mean average SSA? What is middle SSA?

Author’s action:

The sentence has been corrected: “Comparing to other natural mineral materials, tuff and basalt are characterized by medium-sized specific surface area, yet the porous structure of tuff is more developed.” Please see the lines 153-154.

 

Reviewer’s comment:

Line 164: “The Mn reduction at all temperatures tested was higher on tuff” I think the Authros would like to correct this sentence to eg. The reduction in Mn concentration. I do not think they investigated the metal’s oxidation state.

Author’s action:

The sentence has been corrected as suggested “The lowering of Mn concentration at all temperatures tested was higher on tuff, about 50%.” Please see the lines 196-197.

 

Reviewer’s comment:

Lines 170-179: Why the Authors did not perform a simple test on AAS to confirm if the suggested mechanism takes place? The pH could increase simply due to adsorption of H+ on the minerals. Most probably both of the phenomena occurred at the same time.

 

Author’s action:

Although our deduction regarding the release of sodium and calcium is reliable, the reviewer is of course right and the concentration of these elements should have been measured. Unfortunately we didn’t have calibrated the AAS sodium and calcium measurement procedures, and the complexometric titration method in the presence of manganese is invalid. This was preliminary research in our Polish-Ukrainian scientific partnership. We are planning the broader study about manganese removal by tuff and basalt focused on the influence of natural groundwater matrices. Then we will be ready to measure more elements.

 

Reviewer’s comment:

I did not see the part where the Authors examine the sorption equilibrium, why did not they make any adsorption isotherms and calculate the maximum adsorption capacity using for instance the Langmuir model? Consequently in Line 259 ”The equilibrium sorption capacity of the tuff was twice as high as on the basalt (5.5 mg/g and 2.4 mg/g respectively) indicate the condition in which the equilibrium was reached (concentration, temperature and time) and name the models based on which the adsorption capacity at given condition were reached, the values could be given with determined confidence intervals (or any other uncertainty estimation).

 

Author’s action:

Of course, the scope of the article does not include the adsorption equilibrium analysis. We think we used the wrong sentence structure, which misled the Reviewer. During the kinetic studies the system reaches the equilibrium and data presented as “equilibrium sorption capacity” are related with this state. We hope that the reformulated sentence will be clearer:

“During the kinetic studies the systems reached the equilibrium and in this state the sorption capacity of the tuff was twice as high as on the basalt (5.5 mg/g and 2.4 mg/g respectively).” Please see the lines 298-300.

 

Reviewer’s comment:

Line 263: the models are just mathematical instruments to obtain some numbers and compare them with another. Scorpion, especially on natural materials is a complex phenomenon, consequently assumptions based on mode fit about chemisorption are not quite correct. If the Authors insist on the conclusions, please provide more evidence. I would just tone it down a bit.

Author’s action:

Of course, we agree with the Reviewer's suggestion, the more so that the presented results come from initial research on these materials. For this reason, we have deleted the conclusion on chemisorption. Please see the abstract and line 303.

 

 

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Submitted  ms focused on Mn sorption kinetics analysis onto the Ukrainian tuff and basalt. Ms brings interesting results and can be published after major revision.

Comments:

I feel like the introduction section, especially focused on mineral adsorbents (line 40-59) is too general and needs to be rewritten.

Line 41 –  please rewrite “The main compounds removed from…..” since Fe and Mn are metals not compounds.

Why Mn was choosen in your study?

Line 99. Please omit the sentence describing the weighing of the sorbents.

Kinetics experiments were realized in duplicate or triplicate series?

Please, specify software used for kinetic analysis and describe the procedure used to parameters calculations.

Although the study is focused on kinetics of Mn adsorption by natural tuff and basalt, the detailed characteristics (surface properties, XRD, FTIR, SEM) of adsorbent used missing (I found only limited information in section 3.1). Such characteristics are needed for precise evaluation of adsorption mechanisms.  

Line 155 correct “…minutes et al. tested temperatures.” to “minutes at all tested temperatures.”

Lines 167-168 this part is hard to read, please rewrite.

Error bars are missing in all figures.

I strongly advice you to discuss PSO kinetic results considering the critical analysis of PSO mechanism recently published

https://www.sciencedirect.com/science/article/abs/pii/S0169131720301952

In my opinion intraparticle diffusion model did not indicate 2 diffusion stages of Mn adsorption onto basalt.

 

Author Response

Dear Reviewer,

first of all, we appreciate your involvement and we thank you very much for helpful comments, that enabled us to clarify some points and improve the presentation of our work. Detailed description of the changes done in accordance with the comments of Referee follows. Responses to your comments and corrections in the text are marked in red.

 

Reviewer’s comment:

I feel like the introduction section, especially focused on mineral adsorbents (line 40-59) is too general and needs to be rewritten.

Author’s action:

The introduction has been improved: “Saponites are rated as a good low-cost sorbents for water purification from heavy metals [27]. As they are characterized by the ability of cation exchange, including ammonium ion, they are considered as the materials with potential use in water treatment [21,28]. Additionally the saponite’s active centers can be heterogeneous as a result of coexisting other minerals, e.g. hematite [28]. These are the essential features of the material in terms of its practical application. The more that, the saponite can be effectively separated from water by the electrochemical method [29–31], which confirms the possibility of its use in fluidized bed reactors. However, when analysing the review [6,21] and research works [24,27,28,31–33]on the sorption of inorganic pollutants on smectites, it can be noticed that the researchers focus on removing the following ingredients: Cd, Cr, Cu, Hg, Li, Na, Ni, Pb, Zn, as well as the ammonium ion or radionuclides. Work on the removal of Mn on a saponite is definitely less common, although this removal is of course possible [33]. Due to the common Mn occurrence in groundwater and considering the use of saponite rock in groundwater treatment, the studies on Mn sorption seems to be necessary”. Please see the lines 45, 62-74.

 

Reviewer’s comment:

Line 41 –  please rewrite “The main compounds removed from…..” since Fe and Mn are metals not compounds.

Author’s action:

The sentence has been corrected, as suggested. “The main elements removed from groundwater are iron, manganese, ammonium ion and hydrogen sulphide” Please see the line 41.

 

Reviewer’s comment:

Why Mn was choosen in your study?

Author’s action:

An explanation is contained in introduction.” However, when analyzing the review [6,21] and research works [24,27,28,31–33] on the sorption of inorganic pollutants on smectites, it can be noticed that the researchers focus on removing the following ingredients: Cd, Cr, Cu, Hg, Li, Na, Ni, Pb, Zn, as well as the ammonium ion or radionuclides. Work on the removal of Mn on a saponite is definitely less common, although this removal is of course possible [33]. Due to the common Mn occurrence in groundwater and considering the use of saponite rock in groundwater treatment, the studies on Mn sorption seem to be necessary”  Please see the lines 68-74.

 

Reviewer’s comment:

Line 99. Please omit the sentence describing the weighing of the sorbents.

Author’s action:

The sentence describing the weighing of the sorbents was omit in the manuscript.

 

Reviewer’s comment:

Kinetics experiments were realized in duplicate or triplicate series?

Author’s action:

Kinetics experiments were realized in duplicate series. Information about this has been included in the section 2.3.Adsorption kinetics experiment. Please see the line 124.

 

Reviewer’s comment:

Please, specify software used for kinetic analysis and describe the procedure used to parameters calculations.

Author’s action:

The calculations were made in an Excel spreadsheet using Solver. Information about this has been included in the section 2.4.”Kinetics models”. Please see the lines 140-141.

 

Reviewer’s comment:

Although the study is focused on kinetics of Mn adsorption by natural tuff and basalt, the detailed characteristics (surface properties, XRD, FTIR, SEM) of adsorbent used missing (I found only limited information in section 3.1). Such characteristics are needed for precise evaluation of adsorption mechanisms.  

Author’s action:

Information for the detailed characteristics has been done in the context of the earlier work [25]. This was preliminary research in our Polish-Ukrainian scientific partnership. The current work is part of the ongoing research. In order to familiarize the readers of the work [25], the XRD diagrams of basalt and tuff are additionally included in section 3.1. “Characteristic of minerals”. Please see the Figure 1. and lines 157-158.

 

Reviewer’s comment:

Line 155 correct “…minutes et al. tested temperatures.” to “minutes at all tested temperatures. 

Author’s action:

The sentence has been corrected, as suggested. “….minutes at all tested temperatures”  Please see the line184.

 

Reviewer’s comment:

Lines 167-168 this part is hard to read, please rewrite.

Author’s action:

The sentence has been corrected, as suggested “pH has been changing during manganese sorption in the Mn–tuff and Mn–basalt systems” Please see the line/lines 199-200.

 

Reviewer’s comment:

Error bars are missing in all figures.

Author’s action:

Kinetics experiments were realized in duplicate series. Assessment and verification of the applied kinetic models was carried out on the basis of four error functions (the sum of the squares of the errors, average relative error ARE, Fisher's test TF and chi-square test χ²). For this reason, in the opinion of the authors, the error bars do not provide additional information and have not been applied

 

Reviewer’s comment:

I strongly advise you to discuss PSO kinetic results considering the critical analysis of PSO mechanism recently published
 https://www.sciencedirect.com/science/article/abs/pii/S0169131720301952

Author’s action:

The kinetic results were further analysed, taking into account the linked work, which was very insightful, we are deeply grateful.  We added: ”The PFO and PSO models have been applied in general form (nonlinear model). As shown in many works [39,48,49] regression analyses using linearized function of originally nonlinear  PFO and PSO models often lead to incorrect results and false conclusions.” Please see the lines 129-132

We have also broadened the discussion, please see the lines 187-188, 174-175

 

Reviewer’s comment:

In my opinion intraparticle diffusion model did not indicate 2 diffusion stages of Mn adsorption onto basalt.

Author’s action:

Thanks again for your careful reading of the text. As the caption under Figure 7 shows, a mistake was made while working on the article. We are very sorry. Both the data in Table 5 and Figure 7 are now correct.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Authors did good job revising the manuscript, I can recommend its publishing.

I suggest only to rewrite sentence in line 41 as follows "The main metals and compounds removed from groundwater are...."

Author Response

Dear Reviewer,

once again, we thank you very much for helpful comments. 

The sentence (line 41) has been corrected as suggested.