Synergistic Effect of DBP with CTAB on Flotation Separation of Quartz from Collophane

Round 1

Reviewer 1 Report

General comments:

The paper is focused on the separation by flotation between quartz and collophane considering the reverse flotation configuration. The experimental included micro-flotation tests, surface tension and aggregate particle size measurements and water/holdup recovery. Despite the effort of the authors, some aspects of the article must be observed prior to publication at Minerals.

I have a few comments and suggestions that the authors should be observe:

• In general way, the use of micro-flotation test can be an important tool to investigated the reagents adsorption mechanisms at mineral surface. However, in my opinion, micro-flotation is not applicable for entrainment, true flotation or water recovery determination. Usually, this kind of parameters are determinate by bench or pilot flotation tests with real ores. I do not agree with all discussion related of these parameters in the article.
• In the abstract, the following sentence “…..It has been found that DBP enhanced the collision probability between bubbles and quartz particles by reducing the bubble size…”. Besides the bubble size probably reduces, it is not possible affirm this without any bubble size measurements. This sentence must be removed or rewriting;
• Also, in the abstract, the sentence …The addition of DBP reduced the entrainment of fine collophane particles as a result of improved defoaming…”, again, without the particle size distribution on the froth phase it is not possible to affirm that the collophane fines do not float. Can be possible, but this was not measurement in fact…….
• Page 1, line 29-30, in the sentence “…national economy...”, I suggest include the country (China);
• Page 2, lines 93,94, please, elucidate what is the concept “water holdup”. The hold up concept is usually applied as a gas dispersion parameter;
• Page 3, line 106, remove the mesh sieves 200 and 400. Only the size in micrometers is better;
• I do not agree with the concept “water hold up”, in the 2.3.4 item and any discussion related to this.
• Figure 2, page 5, how many experiments for each pH value? Please, indicated the error. With this, it is not possible to affirm that the DBP increased the quartz recovery at pH´s lower than 4 or greater than 10;
• Please, included the particle size distribution for both minerals (quartz and collophane), in the feed and also froth and sink fraction.
• The Figure 8 can be removed from the text. It is well knowing the effect of the oils or droplet oils on the froth phase. In some flotation process, as pyrochlore for instance, the use of oil to froth control is a common practice.
• Figure 5, can the aggregation observe after the DBP addition an effect of the measurement of the oil droplets? Did the authors a measurement of the oil droplets?

Author Response

Point 1: In general way, the use of micro-flotation test can be an important tool to investigated the reagents adsorption mechanisms at mineral surface. However, in my opinion, micro-flotation is not applicable for entrainment, true flotation or water recovery determination. Usually, this kind of parameters are determinate by bench or pilot flotation tests with real ores. I do not agree with all discussion related of these parameters in the article.

Response 1: We agree with the reviewer that bench and pilot flotation tests with real ores are often used to determine entrainment, true flotation or water recovery.  However, micro-flotation tests have been used in recent years for froth characterization as a new application by other researchers. On Page 5, line 171-179, we cited two recent publications in which micro-flotation tests of pure quartz mineral and artificially mixed chalcopyrite and silica minerals were performed to study the froth characteristics.

Point 2: In the abstract, the following sentence “…..It has been found that DBP enhanced the collision probability between bubbles and quartz particles by reducing the bubble size…”. Besides the bubble size probably reduces, it is not possible affirm this without any bubble size measurements. This sentence must be removed or rewriting;

Response 2: We deeply appreciate the reviewer’s comment and have rewritten this part according to the reviewer’s suggestion (page 1, line 18-19).

Point 3: Also, in the abstract, the sentence …The addition of DBP reduced the entrainment of fine collophane particles as a result of improved defoaming…”, again, without the particle size distribution on the froth phase it is not possible to affirm that the collophane fines do not float. Can be possible, but this was not measurement in fact…….

Response 3: Page 12, line 413-422, we cited two references to determine that collophane particles entrained in froth products contain more fine particles due to the smaller momentum of fine particles, and the poorer flotation performance of collophane particles smaller than 30 μm was further confirmed in the actual mineral flotation. 

Point 4: Page 1, line 29-30, in the sentence “…national economy...”, I suggest include the country (China);

Response 4: Great point! The correction has been made according to the reviewer’s suggestion.  In addition, a few sentences are added to further explain the phosphate situation in China: Page 1, line 30-36, in the sentence “China is the second largest phosphate rock resource country with 3.2 billion tons … low- and middle-grade siliceous and magnesian collophane is the main research object in the field of phosphate rock separation in China”, we added a description of phosphate resources in China.

Point 5: Page 2, lines 93,94, please, elucidate what is the concept “water holdup”. The hold up concept is usually applied as a gas dispersion parameter. I do not agree with the concept “water hold up”, in the 2.3.4 item and any discussion related to this.

Response 5: We are very sorry that the term “water holdup” in the manuscript is confusing.  We have changed the term to water mass fraction which is more accurate. 

Point 6: Page 3, line 106, remove the mesh sieves 200 and 400. Only the size in micrometers is better;

Response 6: We have re-written this part according to the reviewer’s suggestion (Page 4, line 115-116).

Point 7: Figure 2, page 5, how many experiments for each pH value? Please, indicated the error. With this, it is not possible to affirm that the DBP increased the quartz recovery at pH´s lower than 4 or greater than 10;

Response 7: We appreciate the suggestion and the error bar has been added to Figure 2.

Point 8: Please, included the particle size distribution for both minerals (quartz and collophane), in the feed and also froth and sink fraction.

Response 8: The particle size range of both minerals used in this study is 38-74 mm, as now specified on Page 4 under Experimental part of the manuscript.  Due to its fairly narrow size range we did not analyze the size distribution of particles in the froth and sink fraction.  Nevertheless we cited two references that have shown that wet froth entrained more fine particles (Page 12, line 413-422). 

Point 9: The Figure 8 can be removed from the text. It is well knowing the effect of the oils or droplet oils on the froth phase. In some flotation process, as pyrochlore for instance, the use of oil to froth control is a common practice.

Response 9: I have removed Figure 8 according to the reviewer’s suggestion and modified the related sentences.

Point 10: Figure 5, can the aggregation observe after the DBP addition an effect of the measurement of the oil droplets? Did the authors a measurement of the oil droplets?

Response 10: The reviewer raised a good question and we have addressed this by adding some statements on Page 9, line 323-328, in the sentence “It should be noted that particle size analysis was performed … DBP had minimal effect on the measurements results of aggregate size”.

Reviewer 2 Report

This study comprehensively illustrated the role of DBP and CTAB in the reverse flotation of Collophane, which is very inspiring and meaningful for the fundamental study. The research methods were designed in a good manner and the role of DBP has been very well defined. Here are some questions for authors:

1. The application of non-polar oil has been widely accepted in industry practice, in which diesel and kerosene are mostly commonly used. Starting from Row 85, the author expressed the interest of using DBP as an alternative non-polar oil for kerosene. It will be helpful to explain more in detail why the author choose DBP other than kerosene or any other non polar oil in this study. Even though both kerosene and DBP are non-polar oil, DBP is an ester which may differ from kerosene in some aspects.
2. This study did not include the steps taken to get the optimized dose of DBP, which is an interest to the reader to find out the relationship between DBP concentration and defoaming effect. 
3. Some minor English errors should be addressed, such as Row 14 "due to their low grade" should be "due to its low grade" 

Author Response

Point 1: The application of non-polar oil has been widely accepted in industry practice, in which diesel and kerosene are mostly commonly used. Starting from Row 85, the author expressed the interest of using DBP as an alternative non-polar oil for kerosene. It will be helpful to explain more in detail why the author choose DBP other than kerosene or any other non polar oil in this study. Even though both kerosene and DBP are non-polar oil, DBP is an ester which may differ from kerosene in some aspects.

Response 1: We are grateful for this important comment.  We have addressed this issue by adding some info on Page 2, line 96-99 “DBP is characterized by high viscosity, … has been used as collector in coal flotation”.

Point 2: This study did not include the steps taken to get the optimized dose of DBP, which is an interest to the reader to find out the relationship between DBP concentration and defoaming effect.

Response 2: We are very sorry that we neglected the effect of DBP concentration on defoaming.  We will further explore the influence of DBP concentration on flotation performance in the future research.  However, page 12, line 429-441, we provided a discussion of the relationship between the concentration of a similar reagent and the defoaming effect, as shown in sentences “Zhou et al. showed that the presence of emulsified kerosene … explain the mechanism of reducing the entrainment of fine collophane particles by promoting defoaming and liquid lamellae thinning”.  the references cited showed that the froth stability decreases with the increase of nonpolar substance concentration due to the dispersion of oil droplets in the middle of foam film and the competitive adsorption between oil droplets and frother.

Point 3: Some minor English errors should be addressed, such as Row 14 "due to their low grade" should be "due to its low grade"

Response 3: We have re-written this part according to the reviewer’s suggestion (page 1, line 14).

Reviewer 3 Report

The authors did good research to analyze the synergistic effect of two flotation reagents: DBP and CTAB. There are good explanations to describe the findings, mainly supported by an exhaustive literature review. It would have been interesting to complement the experiments with more surface characterization, e.g., XPS, FTIR, or SEM techniques. However, in its current version, the work done may be acceptable. I recommend the publication of this manuscript after the authors consider the following comments:

• Line 209-211: The explanation of figure 2 (b) is not clear to me. Why does the addition of DBP improve selectivity? In other words, why does it lead to reduced recovery of collophane?
• What is the statistical validity of the results? There are no error bands inserted in the graphs.
• It is not necessary to include recovery values with 2 decimal places; the error percentage of the results is probably higher.

Author Response

Point 1: Line 209-211: The explanation of figure 2 (b) is not clear to me. Why does the addition of DBP improve selectivity? In other words, why does it lead to reduced recovery of collophane?

Response 1: The reviewer’s question is discussed on Page 12, line 429-442, in the sentence “Zhou et al. showed that the presence of emulsified kerosene …The above findings well explain the mechanism of reducing the entrainment of fine collophane particles by promoting defoaming and liquid lamellae thinning, thus reducing the recovery of collophane (Fig. 2b)…”.

Point 2: What is the statistical validity of the results? There are no error bands inserted in the graphs.

Response 2: We appreciate the comment by the reviewer and the error bar has been added in Figure 2.

Point 3: It is not necessary to include recovery values with 2 decimal places; the error percentage of the results is probably higher.

Response 3: We have made the corrections according to the reviewer’s comments.

Round 2

Reviewer 1 Report

Dear authors.

Thank you for your responses. All questions and suggestions were properly attended.