Effect of Gas Holdup on the Performance of Column Flotation of a Low-Grade Apatite Ore

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This manuscript focuses on the impact of gas retention rate on flotation performance during the column flotation process of low-grade apatite ore. Through factorial experimental design, the study investigated the effects of factors such as air flow rate, surfactant concentration, collector dosage, and inhibitor dosage. The research design is reasonably structured, the experimental methods are generally standardized, and the statistical models exhibit high fitting accuracy, providing a reference for optimizing the flotation of low-grade apatite ore. However, the paper still has some areas that require improvement. 

1. The flotation results under optimal process conditions (air flow rate of 159.9 L/h, etc.) were not compared with the performance of other common flotation machines, making it difficult to highlight the advantages of column flotation. It is recommended to supplement the references.
2. The gas retention rate was calculated using the pressure difference method, but the measurement method and specific values for the suspension density (ρSL) involved in the formula were not clearly stated.
3. The flotation test results showed that air flow rate had the greatest impact on gas retention rate. How was the stability of air flow rate precisely controlled during the experiment to reduce experimental errors?
4. Mineral characterization shows that the P₂O₅ grade in the ore sample is 19.73%, and it contains a significant amount of silicates and iron minerals as gangue. What is the specific particle size distribution of these gangue minerals and their relationship with apatite particles? Could this affect flotation selectivity?
5. A 10% NaOH solution was used to adjust the pH of the slurry in the experiment, but the final pH range of the slurry was not specified.

Author Response

REPLY TO THE REVIEWERS COMMENTS

 “Effect of holdup on the performance of column flotation of a low-grade apatite ore”

 (minerals-3801137)

Below we reproduce the reviewers’ original comments, followed by our responses (R) in italics. Changes in the text in response to the reviewers have been highlighted.

Reviewer #1:

Comments and suggestions for authors:

This manuscript focuses on the impact of gas retention rate on flotation performance during the column flotation process of low-grade apatite ore. Through factorial experimental design, the study investigated the effects of factors such as air flow rate, surfactant concentration, collector dosage, and inhibitor dosage. The research design is reasonably structured, the experimental methods are generally standardized, and the statistical models exhibit high fitting accuracy, providing a reference for optimizing the flotation of low-grade apatite ore. However, the paper still has some areas that require improvement.

1. The flotation results under optimal process conditions (air flow rate of 159.9 L/h, etc.) were not compared with the performance of other common flotation machines, making it difficult to highlight the advantages of column flotation. It is recommended to supplement the references.

R: We acknowledge this important observation. We have added new comments in new section 4.5 (Implications for Industrial Applications) and also 3 new references (see page 12 and Reference list)

2. The gas retention rate was calculated using the pressure difference method, but the measurement method and specific values for the suspension density (ρSL) involved in the formula were not clearly stated.

R:  We have clarified the measurement methodology and provided specific equation for the suspension density calculation (new page 4).

 3. The flotation test results showed that air flow rate had the greatest impact on gas retention rate. How was the stability of air flow rate precisely controlled during the experiment to reduce experimental errors?

R: We have added new information about the air flow rate control system and stability measures (see new page 4).

4. Mineral characterization shows that the P₂O₅ grade in the ore sample is 19.73%, and it contains a significant amount of silicates and iron minerals as gangue. What is the specific particle size distribution of these gangue minerals and their relationship with apatite particles? Could this affect flotation selectivity?

R: We appreciate your suggestion regarding the analysis of gangue mineral particle size distribution effects, which we will definitely consider in future studies.

 5. A 10% NaOH solution was used to adjust the pH of the slurry in the experiment, but the final pH range of the slurry was not specified.

R: The final pH (11)  has been included in the revised text (new page 3).

 We express our sincere appreciation to the reviewer for their thorough and detailed examination of this manuscript. Your insightful comments and suggestions have been immensely valuable in enhancing the quality of our work.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript presents an optimization work performed in a column flotation cell for a low-grade apatite ore. 

The manuscript is well written and presented but some of the conclusion drawn by the authors are not supported by the results.

For example:

“Gas holdup values higher than 23.5% led to the desired values of P₂O₅ grade (>30%) and recovery (>60%) simultaneously.” Based on results presented in Table 2, only 2 out of 6 data points with holdup values higher than or equal to 23.5% led to recoveries higher than 60%. How do you support your statement? Could you elaborate on this?

“The best reagent dosages identified were: fatty acid soap collector at 175 g/t, gelatinized cornstarch depressant at 450 g/t, and Genagen® surfactant at 11 ppm, as well as an air flow rate of 159.9 L/h, which provided the best balance between grade and recovery under gas holdup conditions above 23.5%.” Not clear about how these conditions were selected as “the best”. Could you elaborate on this? Are these results significantly higher than those obtained in Test 8? Please comment on the reproducibility of the results. 

Could you comment on the importance of using the Genagen surfactant over other frothers? Is there any comparison that you can make to other frothers? 

“The identification of synergistic effects between the frother and collector, combined with the selective action of the depressant, offers new opportunities for optimizing flotation circuits processing low-grade phosphate ores.” What are the conditions currently used on the processing plant? And how the values obtained on this study compares to the values achieved in the industrial plant? Any estimate of the gas holdup achieved at the processing plant?

Figures 2 and 3: What were the reagent concentrations used to collect the results? 

As an overall comment, the manuscript fits well for a technical note but it does require more discussion to be accepted as a journal article. 

Author Response

REPLY TO THE REVIEWERS COMMENTS

 “Effect of holdup on the performance of column flotation of a low-grade apatite ore”

 (minerals-3801137)

Below we reproduce the reviewers’ original comments, followed by our responses (R) in italics. Changes in the text in response to the reviewers have been highlighted.

Reviewer #2:

The manuscript presents an optimization work performed in a column flotation cell for a low-grade apatite ore. The manuscript is well written and presented but some of the conclusion drawn by the authors are not supported by the results.

1. “Gas holdup values higher than 23.5% led to the desired values of P₂O₅ grade (>30%) and recovery (>60%) simultaneously.” Based on results presented in Table 2, only 2 out of 6 data points with holdup values higher than or equal to 23.5% led to recoveries higher than 60%. How do you support your statement? Could you elaborate on this?

R: We have revised this statement and provided a more accurate analysis of the relationship between gas holdup and flotation performance (see new page 7).

2. The best reagent dosages identified were: fatty acid soap collector at 175 g/t, gelatinized cornstarch depressant at 450 g/t, and Genagen® surfactant at 11 ppm, as well as an air flow rate of 159.9 L/h, which provided the best balance between grade and recovery under gas holdup conditions above 23.5%.” Not clear about how these conditions were selected as “the best”. Could you elaborate on this? Are these results significantly higher than those obtained in Test 8? Please comment on the reproducibility of the results. 

R:  These conditions refer to the test 10 conditions which provided the best P₂O₅ recovery. New comments have been included in the revised version of the manuscript.

3. Could you comment on the importance of using the Genagen surfactant over other frothers? Is there any comparison that you can make to other frothers? 

R: We have added new comments about the comparison with other frothers commonly used in phosphate flotation (new page 10 and new reference list).

4. “The identification of synergistic effects between the frother and collector, combined with the selective action of the depressant, offers new opportunities for optimizing flotation circuits processing low-grade phosphate ores.” What are the conditions currently used on the processing plant? And how the values obtained on this study compares to the values achieved in the industrial plant? Any estimate of the gas holdup achieved at the processing plant?

R: Thank you for this important question regarding industrial implementation. The conditions currently used in processing plants for low-grade phosphate ores vary significantly depending on ore characteristics, plant design, and operational constraints. Considering the variability in industrial conditions and the limitations of conventional flotation technology, this research was specifically designed to evaluate how process variables and chemical dosages influence gas holdup and its correlation with column flotation performance. The systematic approach allows for the development of appropriate conditions that can be adapted to different industrial scenarios . New comments have been added in revised manuscript ( see new page 12).

 5. Figures 2 and 3: What were the reagent concentrations used to collect the results? 

R: The reagent concentrations have been added in the revised manuscript (new page 5).

 Dear Reviewer, We would like to thank you for the time spent reviewing our manuscript and for helping us improve the article. We have tried to incorporate most of your comments into this revised version

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Dear Authors,

I have reviewed your manuscript in detail.

Please find my comments below and in the attached file.

Best regards.

 

The results section in the Abstract is too long. It should be shortened and general outcomes should be added.

In the Introduction section, the aim of the study was explained. Meanwhile, the scope of the study should be also explained.

The term "gas holdup" should be defined in the Introduction.

The resolution of the figures should be increased.

Is number IV missing in Figure 1? Please also explain DP in the figure.

The units of the parameters can be given in the explanations of the equations.

How was suspension density measured? (L124)

The results of XRD and PSD should be given in graphs. The results of SEM/EDS should be shared.

L148, the reasons and the citations should be provided.

L154, Please explain d63.2 and its importance.

L164, needs citation.

L169, The data of the validation experiments should be shared.

The constant experiment parameters should be mentioned in the text or in figure captions.

Why did you plot Figure 2 as a function of time and Figure 3 as a function of air flow rate?

L240, lower bubble rise velocity can increase the bubble-particle collision probability that can increase the recovery. Low drag force can decrease the detachment probability. Therefore, this comment should be discussed well.

L260, This generalization is not true for very high bubble sizes because of the low collision probability. Therefore, it is necessary to address the ratio between particle and bubble sizes. Maybe you can mention the less buoyancy force of small bubbles as on Line 326.

L283, Discussion should be conducted with literature. The mechanism behind the experimental results should be shared in the Results section.

Conclusions section can be more concise.

The References should be supported with more recent studies.

Please see the atached file for the syntax corrections.

Comments for author File: Comments.pdf

Author Response

REPLY TO THE REVIEWERS COMMENTS

 “Effect of holdup on the performance of column flotation of a low-grade apatite ore”

 (minerals-3801137)

Below we reproduce the reviewers’ original comments, followed by our responses (R) in italics. Changes in the text in response to the reviewers have been highlighted.

Reviewer #3:

Dear Authors, I have reviewed your manuscript in detail. Please find my comments below and in the attached file.

1. The results section in the Abstract is too long. It should be shortened and general outcomes should be added

R: You are absolutely correct. We have significantly shortened the results section in the abstract and focused on general outcomes rather than specific numerical details. (see new page 1).

2. In the Introduction section, the aim of the study was explained. Meanwhile, the scope of the study should be also explained.

 R:  Thank you for this observation. We have added a study scope to complement the stated aim (see new page 2).

 3. The term "gas holdup" should be defined in the Introduction 

R: You are absolutely right. This fundamental term should be clearly defined early in the manuscript for readers unfamiliar with flotation terminology ( see new page 2).

4. The resolution of the figures should be increased.

 R: The resolution of all figures have been improved

 5. Is number IV missing in Figure 1? Please also explain DP in the figure.

R: The number IV and DP meaning have been included in the new Figure 1 (new page 3).

6. The units of the parameters can be given in the explanations of the equations

R: We have added units to all equation parameters (new page 4)

7.How was suspension density measured? (L124)

R: We have added a new equation (2) for suspension density determination.

8. The results of XRD and PSD should be given in graphs. The results of SEM/EDS should be shared

R: We have chosen to maintain the current presentation format for objectivity purposes. Nevertheless, this and any additional information will be made available upon request.

9. L148, the reasons and the citations should be provided.

R: New comments have been added and a reference has been provided in the revised manuscript (new page 4).

10. L154, Please explain d63.2 and its importance.

R: The parameter  d63.2 of the RRB PSD model has been explained (new page 5)

 11. L164, needs citation.

R: A Citation has been added (new page 5)

12. L169, The data of the validation experiments should be shared.

R: The data of the validation experiments can be shared on request

13. The constant experiment parameters should be mentioned in the text or in figure captions.

R: The constant experiment parameters have be mentioned in the text (section 2.2. and 2.3, new pages 3 and 4)

14. Why did you plot Figure 2 as a function of time and Figure 3 as a function of air flow rate?

R: Figure 2 demonstrates that the behavioral differences resulting from collector addition to the surfactant solution remain consistent over time. Figure 3 illustrates the influence of gas flow rate on both the air-water and air-water-ore systems

15. L240, lower bubble rise velocity can increase the bubble-particle collision probability that can increase the recovery. Low drag force can decrease the detachment probability. Therefore, this comment should be discussed well.

R: Additional discussion regarding this issue has been incorporated into the revised manuscript (page 8)

 16. L260, This generalization is not true for very high bubble sizes because of the low collision probability. Therefore, it is necessary to address the ratio between particle and bubble sizes. Maybe you can mention the less buoyancy force of small bubbles as on Line 326.

R: This sentence has been modified (new page 9). Thank you

 17. L283, Discussion should be conducted with literature. The mechanism behind the experimental results should be shared in the Results section.

R: The mechanism behind the experimental results have been moved to the Results section, with new references ( New page 10).

 18. Conclusions section can be more concise

R: The conclusions section has been modified to be more concise as requested, reducing the text length while preserving all essential technical contributions (new page 12)

19. The References should be supported with more recent studies.

R: New and more recent references have been added to the revised manuscript (Reference list)

Dear Reviewer, We would like to thank you for the time spent reviewing our manuscript and for helping us improve the article. We have tried to incorporate most of your comments into this revised version

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

I would like to congratulate the authors on the quality of the manuscript. The concentration of igneous phosphate ores is notably challenging due to their complex mineralogical composition and the fine particle size required for adequate mineral liberation. The study provides relevant contributions to the field by demonstrating the technical feasibility of concentrating this type of ore and confirming the effective performance of flotation columns when processing fine-grained materials. Moreover, the manuscript offers a meaningful discussion on the synergistic effects of operational variables and reagent action, which enriches the understanding of flotation mechanisms in complex systems.

I recommend the publication of this work.

As minor suggestions for improvement, I recommend:

1.Including a conclusive sentence at the end of the abstract, clearly stating the main contribution of the research to the field.

2.Conducting a careful punctuation review throughout the manuscript, as a few sentences are missing final periods.

Author Response

“Effect of holdup on the performance of column flotation of a low-grade apatite ore”

 (minerals-3801137)

Below we reproduce the reviewers’ original comments, followed by our responses (R) in italics. Changes in the text in response to the reviewers have been highlighted.

Reviewer #4

I would like to congratulate the authors on the quality of the manuscript. The concentration of igneous phosphate ores is notably challenging due to their complex mineralogical composition and the fine particle size required for adequate mineral liberation. The study provides relevant contributions to the field by demonstrating the technical feasibility of concentrating this type of ore and confirming the effective performance of flotation columns when processing fine-grained materials. Moreover, the manuscript offers a meaningful discussion on the synergistic effects of operational variables and reagent action, which enriches the understanding of flotation mechanisms in complex systems.

I recommend the publication of this work.

R: We are deeply grateful for your positive evaluation of our manuscript and your recommendation for publication. Your recognition of the technical contributions and the relevance of our work to the field of mineral processing is highly appreciated. We have carefully addressed your minor suggestions for improvement, as detailed below

As minor suggestions for improvement, I recommend:

1. Including a conclusive sentence at the end of the abstract, clearly stating the main contribution of the research to the field.

R: We have added a conclusive sentence that clearly articulates the main contribution of our research to the mineral processing field (new page 1)

2. Conducting a careful punctuation review throughout the manuscript, as a few sentences are missing final periods

R: We have conducted a thorough punctuation review throughout the entire manuscript and corrected all instances of missing periods.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Accept in present form

Reviewer 3 Report

Comments and Suggestions for Authors

Dear Authors,

I have reviewed your responses and the revised manuscript.

You have carried out the requested rivisions. Therefore, in my opinion, the manuscript can be accepted in its current form.

Best regards.