Reduction in Technogenic Burden on the Environment by Flotation Recovery of Rare Earth Elements from Diluted Industrial Solutions

Round 1

Reviewer 1 Report

The idea of the work is very interesting. However, the results have to be presented more carefully and in more coherent manner.

Detailed comments can be found in the attached file. (I am sorry for different colors, I worked on different computers.)

Comments for author File: Comments.pdf

Author Response

Dear reviewer

We made changes to the article in accordance with reviewer's comments.

As we could submit only one file, we attach some comments below.

• 200 ml even will not cover properly the propeller of the machine, please check the figure - We did not aim to cover the whole flotation cell, 200 ml of solution covered half of impeller. Even with such small amount of solution froth volume was sufficient.
• Figures 2 and 3 repeat the data already presented in tables 1-4. Probably it would be better authors to decide what to present - figures or tables. Comments below Fig 3 to a high extent repeat the already said around the tables. - The authors took a decision to present Tables and to get rid of Figures.
• Why this pH (8.2) is chosen? - We corrected it and wrote '6.2' instead of  '8.2'.
• It was NOT proven since data are lacking for the system behavior without surfactant and with other surfactants for comparison - It makes no sense to do experiment without surfactant. As for other surfactants, their use can be the theme of another research.
• How are the mentioned recovery factors defined? Where are they commented in the previous text? - We changed the term.
• These references seem strange in the context of the whole work - Specialisation of students mentioned in references 15, 16 did research work in REE at our University.

 

Best wishes

Natalia Dzhevaga

Author Response File: Author Response.docx

Reviewer 2 Report

1. Introduction

• Too much narration on the general aspects of REE utilization
• Should focus on the issues related to this study.
• The object of this study is not clearly given.

2. Materials and method

• Experimental conditions are properly described.
• Type of the flotation cell, cell size, air injection rate, rotation speed of impeller
• Frother is a key component in flotation, and yet was not used. Was it not necessary?
• What is the purpose of adding chloride ions?
• How long is the flotation time?

3. Results

• Should define K_dist , La_aq, La_org; These terminologies are used in solvent extraction not in froth flotation
• The discussion indicates that REE is recovered as a hydroxide. Then It is not clear how the REE ions are recovered
  1. Is it direct adsorption of ions on the bubble surface
  2. Or forming a complex with the surfactant and then adsorb
  3. Or heterocoagulation with other species and then adsorb
• Authors discuss about speciation of REE, but not clearly explains how this relates to the experimental results.
• Which of the REE species are floatable? Is it pure REE ions, or REE hydroxo complex, or REE chloro complexes? Why
• The mechanisms of the REE ion flotation should be more clearly discussed.

 

 

Author Response

Dear reviewer

We attach the answers on your comments below. 

 

1. Introduction

• Too much narration on the general aspects of REE utilization
• Should focus on the issues related to this study.
• The object of this study is not clearly given.

The object of the article was study of the possibility to recover REE from raw material using the method of ion flotation and with the application of surface-active substance of anion type.  

2. Materials and method

• Experimental conditions are properly described.
• Type of the flotation cell, cell size, air injection rate, rotation speed of impeller
• Frother is a key component in flotation, and yet was not used. Was it not necessary?
• What is the purpose of adding chloride ions?
• How long is the flotation time?

All the points were mentioned in the article, yet we clarify them below for the reviewer.

Frother was properly applied. Sodium dodecyl sulphate (NaDS) was frother.

The purpose of adding chloride ions was to study their impact on pH recovery and on the distribution coefficient.

Flotation lasts 5 minutes.

3. Results

• Should define K_dist , La_aq, La_org; These terminologies are used in solvent extraction not in froth flotation
• The discussion indicates that REE is recovered as a hydroxide. Then It is not clear how the REE ions are recovered
  1. Is it direct adsorption of ions on the bubble surface
  2. Or forming a complex with the surfactant and then adsorb

• Or heterocoagulation with other species and then adsorb

• Authors discuss about speciation of REE, but not clearly explains how this relates to the experimental results.
• Which of the REE species are floatable? Is it pure REE ions, or REE hydroxo complex, or REE chloro complexes? Why
• The mechanisms of the REE ion flotation should be more clearly discussed.

The definition of K_distr   and the formula of calculation as well as Me_aq, Me_org are presented on page 5, Section Results.  

The basis of recovery was the method of ion flotation. Authors found out that REE are recovered in the form of hydroxide, basic salts, normal salts. REE ions are recovered by forming a complex with the surfactant and then adsorbing.

Leading literature sources (Sebba F., Lemlich R.) suggest using of adsorptive bubble separation methods for recovery of components from low concentration solutions. The basis of their recovery is process of adsorption. Cations of REE are surrounded by molecules of surface-active substance - NaDS. When adding ion chlorides one observes competition of chloride ions and hydroxo ions. Depending on pH of solution components of different compounds are recovered.

 

Best wishes

Natalia Dzhevaga

Round 2

Reviewer 1 Report

The authors have considerably improved the paper. Still some small reconsidering and corrections are needed. The paper-file with proposals and comments inside are attached in order to facilitate authors.

Comments for author File: Comments.pdf

Author Response

Dear reviewer

We thank you  for detailed analysis of our article. We made changes to it. Below you could find the comments and answers to your remarks.  

The initial component is polycomponent??? What does this mean?

Polycomponent is complex substance which contains several consituents. We deleted this phrase for clarity. 

 

In the table 2 title title is written 0.05.

Experiments were conducted for lanthanium and yttrium, the concentrations of chloride were 0.01 and 0.05 M. Both concentrations were used for both REE, results were presented in tables 1-4 (2 tables for every REE). 

 

What is meant under 'pH recovery " . The whole sentence "Considering.... REE separation"is unclear and needs revision

We deleted unnecessary part of sentence. pH recovery is term in ion flotation which means scope of maximum recovery. 

Author Response File: Author Response.docx

Reviewer 2 Report

Review comments has not been fully addressed.

Author Response

Dear reviewer

We attach the answers in accordance with your comments. 

1. Introduction

• Too much narration on the general aspects of REE utilization

The authors aimed at getting the readers acquainted with REE as comprehensively as it is possible; to show REE use, topicality of learning their properties.

• Should focus on the issues related to this study.

The article studies flotation recovery of REE, impact of chlorides on distribution coefficient and pH recovery. 

• The object of this study is not clearly given.

The object of the article was the study of the possibility to recover REE from raw material using the method of ion flotation and with the application of surface-active substance of anion type. 

2. Materials and method

• Experimental conditions are properly described.

We thank the reviewer for thorough work with our article.

• Type of the flotation cell, cell size, air injection rate, rotation speed of impeller

We express great thanks to the reviewer for the work done.

• Frother is a key component in flotation, and yet was not used. Was it not necessary?

Sodium dodecyl sulphate (NaDS) was used as frother. It was added to solution during ion flotation.

• What is the purpose of adding chloride ions?

The purpose of adding chloride ions was to study their impact on pH recovery and on the distribution coefficient.

• How long is the flotation time?

Flotation lasts 5 minutes. Authors found out that this is optimal time.

3. Results

• Should define K_dist , La_aq, La_org; These terminologies are used in solvent extraction not in froth flotation

The definition of K_distr   and the formula of calculation as well as Me_aq, Me_org are presented on page 5, Section Results. 

The basis of recovery was the method of ion flotation. Authors found out that REE are recovered in the form of hydroxide, basic salts, normal salts. REE ions are recovered by forming a complex with the surfactant and then adsorbing.

• The discussion indicates that REE is recovered as a hydroxide. Then It is not clear how the REE ions are recovered
  1. Is it direct adsorption of ions on the bubble surface
  2. Or forming a complex with the surfactant and then adsorb
  3. Or heterocoagulation with other species and then adsorb

Leading literature sources (Sebba F., Lemlich R.) suggest using of adsorptive bubble separation methods for recovery of components from low concentration solutions. The basis of their recovery is process of adsorption. Cations of REE are surrounded by molecules of surface-active substance - NaDS. When adding ion chlorides one observes competition of chloride ions and hydroxo ions. Depending on pH of solution components of different compounds are recovered.

Authors added clarification on the mechanism of ion flotation and types of recovered components to Discussion.

• Authors discuss about speciation of REE, but not clearly explains how this relates to the experimental results.

Authors made changes in the article, explained the mechanism of ion flotation and gave a detailed description of conditions upon which REE compounds are recovered.  

• Which of the REE species are floatable? Is it pure REE ions, or REE hydroxo complex, or REE chloro complexes? Why

Authors believe that REE are recovered in the form of hydroxide, basic salts, normal salts. REE ions are recovered by forming a complex with the surfactant and then adsorbing.

• The mechanisms of the REE ion flotation should be more clearly discussed.

It was stated by the experiment that cations of REE are surrounded by molecules of surface-active substance - NaDS. When adding ion chlorides one observes competition of chloride ions and hydroxo ions. Depending on pH of solution components of different compounds are recovered.

 

Best wishes

Natalia Dzhevaga

Author Response File: Author Response.pdf