Study on Combined Vacuum–Mechanical Defoaming Technology for Flotation Froth and Its Mechanism
Round 1
Reviewer 1 Report
In the paper, the authors proposed a new defoaming device which combined mechanical defoaming method with vacuum defoaming technology and its defoaming mechanism is analyzed theoretically. The introduction part is very clear and systematic, and the experimental details and results are clearly described. This article is informative for researchers who are interested in floatation process, especially in the field of defoaming.
The paper is well written and likely publishable, yet on only after the following minor revisions are considered:
1. In the flotation process, “froth” may be more accurate than “foam”. The author is suggested to revise “foam” to “froth”.
2. The author should give the values of aeration rate, vacuum degree, Impeller speed in the experiment part.
3. The conclusion of the paper seems to be no different from that of the abstract. The author is suggested to revise it.
4. In the abstract, what do the DC and SC mean ? The author should give the full name.
5. in Line 50, floatation is a separation process at the gas-liquid-solid interface, instead of the gas-liquid interface.
Author Response
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Author Response File: 
Author Response.docx
Reviewer 2 Report
In the present manuscript, the authors have tried to develop a new defoaming device designed by combining the mechanical defoaming method with vacuum defoaming technology. The manuscript is well written but there are several such articles on the same subject (defoaming of froth). It may be a case study on the subject but the novelty aspect is missing whether in terms of a new process/product or an innovative way of defoaming mechanism in flotation. So the author should focus on these directions to publish in a reputed journal. There are a few comments appended below to improve the manuscript.
- There are several language mistakes in the manuscript. The English language needs to be improved.
- Abstract needs to be highlighted by including the innovative step adopted in the present research. Please revise.
- On what basis authors have chosen variables in Designing the unit?
- The variables and levels of the design and process must be justified and criteria should be included in the experimental section.
- Author should highlight the significance of each term (variables and their functions) of the variables and interactions.
- Conclusion shouldn't be a repetition of an abstract.
- Most of the places, the author describes the trends of the results achieved but the critical analysis of the physics part in the defoaming process.
- There is information on the proximate analysis of the sample but it has not correlated with the defoaming results.
- There are several pieces of literature on coal flotation defoaming. The author needs to include all such literature in the introduction and discussion.
Author Response
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Author Response File: Author Response.docx
Reviewer 3 Report
Dear authors,
Thank you very much for the submission of your article to MDPI processes. The article studies the bursting of froths using different means of mechanical stress, this is a combination of impact and pressure drop. Therefore, the authors applied two different impellers and pressure differences, showing that froth formed with coal particles could be faster destabilized under the action of mechanical impact and pressure drop.
After a thorough examination of the manuscript, I would like to ask the authors to answer the following questions and concerns before further reviewing.
1. The authors use the term “foam” throughout the article. Foams are two-phase systems (air in water) that are usually stabilized by surfactants. In the presence of solid particles, these three-phase systems are usually referred to as froths. I would recommend to use the term “froth” in the article when applicable.
2. The Introduction is generally not suitable and does not meet the scientific requirements to introduce the topic to a wider audience. I would recommend to move the section “3.4 Mechanisms of combined vacuum-mechanical defoaming” to the introduction. In this section, the authors should explain the Marangoni effect. Furthermore, Figure 8 is not adequate for representing the action of bursting bubbles in foams or froths and its discussion is erroneous. Please be more precise in explaining the difference between pB, pA and p0. Further, p0 is not state din Eq. 1 or2. Why is it relevant or are the equations not relevant?
In general, the authors state a lot of hypotheses in this section and these should be claimed as such and the authors need to logically explain why these hypotheses are relevant.
3. In section 2, the sub-section 2.2 is not required and could be part of the others. Further, the authors have to show how the defoamer could be used in flotation processes, if the authors claim in the introduction that the stability of froths is a problem in flotation processes. How could the equipment be implemented in flotation?
4. In Figure 4, the authors show a higher “foam” height (should be froth height?) for the condition “vacuum” compared to “normal pressure”, although the authors argue in the article that “vacuum” supports the bursting of bubbles. How would the authors explain this discrepancy?
5. the authors could also perform reference measurements without coal to show what effect coal particles have on the froth stability (in comparison to foam stability in the absence of coal particles)
In general, the language of the manuscript has to be improved! I also added comments to the submitted pdf and attach it to the review.
In summary, the presentation and quality of the article is not adequate to be considered for publication in MDPI processes. Therefore, I would recommend to reject the article in its current state, but, in case the authors perform the changes in accordance to my comments, I would suggest that the authors could resubmit their manuscript afterwards.
Comments for author File: 
Comments.pdf
Author Response
Please see the attachment.
Author Response File: Author Response.docx
Round 2
Reviewer 3 Report
Dear authors,
Thank you very much for the submission of your revised manuscript. Unfortunately, the authors did not respond accordingly to the raised concerns and questions, and it seems to me that the revision has been done in a hasty manner, and thus the scientific quality of the manuscript falls behind its expectations.
The introduction lacks a proper summary of previous relevant work in the field of coalescence and bursting of bubbles, a proper definition of the scope of the work and how it fits in the context of previous work/ what information it adds to previous work and what novel knowledge a reader can expect by reading the article, and finally the language is not appropriate.
Given the fast response of the authors and the low quality of the abstract and introduction, I just commented on them, and the comments are attached in the submitted PDF.
In summary, the article does not meet the requirements to be published in MDPI processes and I recommend to reject the article.
Comments for author File: Comments.pdf
Author Response
Please see the attachment.
Author Response File: Author Response.docx
