Adsorption of Copper and Lead Ions in a Binary System onto Orange Peels: Optimization, Equilibrium, and Kinetic Study
Round 1
Reviewer 1 Report
Comments:
Agricultural waste materials have been proven to be efficient for heavy metal sequestration from wastewater. This manuscript investigated the interactive effects of initial concentration, adsorbent dosage, and particle size on the removal of copper and lead ions in a binary system onto orange peels using a central composite design. The study is conducive to promoting the application of agricultural waste resource utilization technology in the field of heavy metal removal. It is an interesting manuscript to review and the content of the article is rich. But it still needs careful modification in details. Followings are the comments to help improve the manuscript:
1. In the binary system, Cu and Pb may influence each other's adsorption behavior, such as competitive adsorption and co-adsorption, the authors how to distinguish single adsorption from competitive adsorption and co-adsorption?
2. In the adsorption process, the specific surface area, pore structure and polarity of adsorbent play an important role in the adsorption of heavy metals. It’s better to characterize the above characteristics of adsorbents by BET and elemental analysis.
3. The title was changed to “Adsorption of copper and lead ions in a binary system onto orange peels: optimization, equilibrium, and kinetic study” would be better.
4. Lines 17-19, this is an invalid statement. The changes of Fourier transform infrared and Energy dispersive x-ray (EDX) before and after adsorption can better explain the adsorption mechanism.
5. Line 36, change “…problems in humans such as; skin……” to “…problems in humans, such as skin……”.
6. Line 80, change “…carried out as discussed by [8].” to “…carried out as discussed by Afolabi et al. [8]”.
7. Lines 88-89, pleased indicate the concentration of Cu(NO3)2∙3H2O and PbNO3, respectively. Change “Cu(NO3)2. 3H20” to “Cu(NO3)2∙3H2O”.
8. Line 115, change “M” to “m”. Line 131, define the meaning of “qe”.
9. Lines 146-147, what is the meaning of “insignificant” and “significant”?
10. Please find and correct “Error! Reference source not found” in the whole manuscript.
Comments for author File: 
Comments.pdf
Author Response
Please, see the attachment.
Author Response File: Author Response.pdf
Reviewer 2 Report
Line 89, please check the spelling of “Cu(NO3)2. 3H20”, "0, O".
Ling 198, 209, 225, 279, 330, 332, 342, etc. References were not found. please check.
If the biosorbent can be used by desorption? evaluate the regeneration studies?
Please provide SEM pictures mentioned in line 84.
Author Response
Please, see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
Reviewer’s comments:
I had thoroughly studied the manuscript “Adsorption of copper and lead ions in a binary system: optimization, equilibrium, and kinetic study. The novelty is not considered sufficient for publication in Sustainability.
I must reject on the basis of following comments which needs to be addressed by authors.
1. Quality and presentation of data in figures is very poor especially in equilibrium and kinetic study.
2. Author needs to do more experiments to justify the equilibrium and kinetic study
3. Optimization through regression model is not sufficient give removal efficiency for each parameters with different initial concentrations values, dosages, size with respect to different time intervals etc.
4. Highlight the novelty and scientific impact of work done in abstract portion.
5. Please add some prominent quantitative results from manuscript in the abstract.
6. The introduction should be crisp and updated and not too general.
7. EDX is not sufficient also add SEM images for biosorbent.
8. Page 8: Correct the citations for Eq. 9 and 10 in the text.
9. Page 8: in Eq. 9 and 10 remove insignificant terms, show both the models with significant terms.
. Check whole manuscript for typographical errors and grammatical mistakes.
Comments for author File: Comments.pdf
Author Response
Please, see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The authors have made the revision of the manuscript according to the reviewers’ comments. I felt that the revision is satisfied. So, the manuscript could be accepted for the publication.
The references were not found of line 220, 231, 247, 327, 350, 372, 374, 384, 390, 397, 400, 480, 491, 497, 501, and 523, please check it.
Author Response
Thank you for your observation. The authors have corrected the errors in the manuscript due to missing intext Figures.
Author Response File: 
Author Response.docx
Reviewer 3 Report
· Response of the authors is pity much inadequate I am not in favor of publication of the manuscript in present form.
· Discrepancies in the data still exist especially in equilibrium study.
· In figure 7 some points in Freundlich isotherm for Pb is away from the line.
· Provide equation of line and R2 in Fig 7 for both Cu and Pb.
· For kinetic study three initial concentration are not sufficient (10, 55 and 100 mg/L) minimum five initial concentration are required.
· Author fails to describe the research gap or novelty in scientific way.
· In response 2, nothing is stated in lines 167 – 169 (blank lines).
· Noting in lines 131 – 135 as stated by author.
· Optimized pH 3.85 is considered low while the pH of real wastewater containing metals are near to neutral.
Author Response
We do appreciate all your comments.
The authors have responded to the comments and the revised sections are highlighted in red in the manuscript.
Author Response File: Author Response.docx
