Review Reports

Round 1

Reviewer 1 Report

 

The manuscript by Soon and Oh describes the adsorption of As and Pb onto stone powder/chitosan/maghemite (SCM) beads. The equilibrium adsorption properties were published in a previous study (ref 15). The emphasis of the current study is on the kinetics of adsorption. The manuscript suffers from a major shortcoming. The authors detail the parameters extracted from various models, but do not attempt to rationalize the kinetic parameters into any physical process(s). In fact, the manuscript does not attempt to ascribe any chemical significance to the extracted kinetic parameters. What is the slow and fast rate is terms of a physical/chemical elementary process? The numbers are meaningless to other researchers in the field because they only apply to the specific condition of the experiments performed. For example, what happens when the pH changes? What are the chemical species present between pH 4-5? In addition, there is no in-depth discussion on how these materials and kinetic parameters compare to other results in the literature.

 

Overall the manuscript does not provide any physical/chemical insight into As and Pd adsorption from the kinetic modeling.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

The manuscript deals with the adsorption kinetics of As and Pb onto composite beads. The subject is important for environmental application. There are some comments that the authors should consider before publication:

1.  In the Introduction a short state-of-art on the adsorbents used for As and Pb removal should be added.

2.   The knowledge gap needs to be clearly addressed in the Introduction.

3. The authors should compare their results with the result obtained by similar adsorbents in the literature.

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

The paper can be considered after careful revision. The following points need to be considered.

1. Make abstract more quantitative.

2. Improve introduction with more literature with different adsorbents used for metals removal. Innovative aspect need to added in the introduction. Some examples below.

https://doi.org/10.1016/j.jtice.2013.09.012

• https://doi.org/10.1080/19443994.2012.752765
•  

https://doi.org/10.1016/j.nanoso.2021.100762

3. pH is very important parameter. Authors need to study the effect of pH on adsorption of these metals.

4. Apply isotherm models both on batch and column study. Such as Langmuir, Freundlich, Thomas model, Bed depth service time model and Adam and Bohart model etc. for better understanding and comparison.

5. Apply intraparticle diffusion model to observe the mechanism involved in adsorption.

6. Authors need to study the stability of the material for metals adsorption. Sustainability is important factor.

7. Effect of bed depth in column study need to study.

8. Authors need to characterize the adsorbent used in this study to get insight of the material. I do not see much characterization.

9. Add scale bar in figure 2.

10. Add BET isotherm graphs in the manuscript.

Author Response

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Author Response File: Author Response.docx

Reviewer 4 Report

Adsorption kinetics of As and Pb onto composite beads synthesized with stone powder, chitosan, and maghemite (SCM beads) with weight ratio of 1:1:0.5 were investigated in batch mode. Several kinetic models were utilized to analyze the kinetics. The equilibrium time (teq) for Pb adsorption was lower than that for As adsorption, indicating that Pb adsorption was more affinitive than As adsorption onto the SCM beads.

However, some critical issues remain to be solved and a thorough revision was needed:

1.         The introduction should be clarified in terms of uniqueness and advantage what is the novelty of this work over the previous related work, and cite the following reference: J. Mol. Liq. 342 (2021) 117435.

2.         On what basis the authors chose this particular As and Pb. Did they check for others?

3.         The authors should make reusability and comparison with literature. Cite the following reference: Appl. Organomet. Chem. 36 (2022) e6660.

4.         The manuscript needs thorough revision to improve the text quality and readability of the work.

 

Author Response

Thank you for your kind review.

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The revised manuscript does not address my main objections. For example, the authors response to Q1 reveals that they are unsure of the details and simply rely on an R2 value from different models to asses the "best fit". Just because one model has a lower R2 value does not mean the results are consistent with the model. Next, the authors response to Q2 reveals a misunderstand of my comment about "researchers in the field". I meant to say "researchers involved in this type of work" i.e. adsorption based separations. The authors identify the correct chemical species in the solution between pH 4-5. The fact that the As species in an anion and Pb is cationic should indicate an obvious difference. What is the surface charge of the SCB beads at pH 4-5? Since maghemite has a negative surface charge at pH 4-5, it is reasonable to conclude that Pb2+ should more readily adsorb than HAsO4- to due electrostatics. Finally, in the authors response to Q3 they provide references to studies that are not relevant to the current work. Specifically, what have other researchers published from studies involving maghemite and HAsO4- and Pb2+?

Author Response

Thank you very much for your kind review.

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

I recommend to publish this paper in the Processes.

Author Response

Thank you very much for your kind review.

Reviewer 3 Report

Authors revised the manuscript as per comments. Now it can be considered.

Author Response

Thank you very much for your kind review.