Advances in Understanding of the Application of Unit Operations in Metallurgy of Rare Earth Elements
Round 1
Reviewer 1 Report
The paper can be accepted after the following corrections:
- Figures 5, 6 and 7 has to be clearly annotated. Please number the key elements of systems and give more detailed explanation in the figure’s captions.
- Conclusions should be developed from the point of view of quantitative assessment of efficiency as well as comparison to the previously existing solutions.
Author Response
Dear Reviewer,
thank you very much für your invested time and valuable comments.
We are sending our answers.
The paper can be accepted after the following corrections:
- Figures 5, 6 and 7 has to be clearly annotated. Please number the key elements of systems and give more detailed explanation in the figure’s captions. We added additional explanations.
Figure 5:a. Acid digestion reactor b) system of two digestion reactor during operations; (key elements: anchor stirrer, glass reactor (40 L), engine, an injected tube for a transport of suspension supported by a double membrane pump.
An innovative step is very fast transport of formed suspension using an injected tube for a transport of suspension supported by a double membrane pump (approx. 8 L/min).
Fig.6 Sketch of equipment for leaching, neutralisation and filtration at the pilot plant (Key components: a leaching unit (2 × 100 L), neutralisation unit (3 reactors × 10 L and 1 × 8.5 L), stirred collecting tank (250 L) and separation unit (chamber filter press). Additionally we added an additional sketch in order to better explain this Equipment.
Fig.7.New developed dry digestion reactor at the RWTH Aachen University
(key components: reaction vessel, system with nozzles for injection of water and acid; cover; special mixing system, engine, electronics, charging and discharging System)
2. Conclusions should be developed from the point of view of quantitative assessment of efficiency as well as comparison to the previously existing Solutions. We added our comments: The extraction efficiency reached a high level in a short time, increasing from 82.2% to 88.8% when the digestion time increased from 20 min to 40 min. A REE carbonate containing 30.0% total REE was finally produced, with an overall REE recovery yield of 85.5%, what is an advantage in comparison to the previously existing solutions in hydrometallurgy.When adjusting the pH to ~4.0 using calcium carbonate, zirconium, aluminium and iron were removed at 99.1%, 90.0% and 53.1%, respectively, with a REE loss of 2.1%
Reviewer 2 Report
The authors carried out the study of the Advances in Understanding of the Application of Unit Opera-tions in Metallurgy of Rare Earth Elements.
Comments:
Page 1:
Abstract: Line 2: delete “of non-ferrous metals”
Page 2:
Line 1 and line 3: excess citations for a topic
Don't cut the words on the lines…example: page 1: lines 15, 17, 19, 32 and 33
Also Pages 2, 3, 4, 11-15 verified and corrected
Comments for author File: 
Comments.pdf
Author Response
Dear Reviewer,
thank you very much for your invested time and valuable comments. We improved our paper regarding your comments.
Page 1:
Abstract: Line 2: delete “of non-ferrous metals”
We deleted it!
Page 2:
Line 1 and line 3: excess citations for a topic
You have fully right, but this is my reviewer paper, and I have to show that I have read and published more papers at subject of ultrasonic spray pyrolysis. If you agreed, we will not Change it.
Don't cut the words on the lines…example: page 1: lines 15, 17, 19, 32 and 33
Also Pages 2, 3, 4, 11-15 verified and corrected
We changed it!
Reviewer 3 Report
The research (review) is interesting, since the topic and content are relevant, however there are few errors in the text that must be corrected, in the following points:
Line 94: I recommend writing the meaning first and then the abbreviation.
Line 187 and 189: What does REO mean?.
Line 224: Write that the acronym (IME, RWTH) corresponds to the name of the university.
Line 241: Write subscript 2 in (Ch2O).
Line 269: Write in lowercase the letter (T) in the word (The).
Line 276: The image is recommended to be made with higher quality.
Line 418: Place a parenthesis in each diagram, since it is explained in the text but sections a and b are not found on the image, although it is at the bottom of the figure, it is suggested to place the parenthesis on the image.
Line 461: There is a double comma in (,, fuming).
Therefore, it is suggested that this work in review mode be corrected in the comments previously shown so that it can be considered for publication.
Author Response
Dear Reviewer,
thank you very much for your invested time and valuable comments!
According to your comments we added our answers:
Line 94: I recommend writing the meaning first and then the abbreviation.
We used the meaning first and then the Abbreviation.
Line 187 and 189: What does REO mean?.
Rare earth oxides (REO)
Line 224: Write that the acronym (IME, RWTH) corresponds to the name of the university.
Institute of the Process Metallurgy and Metal Recycling of the RWTH Aachen University (IME, RWTH Aachen)
Line 241: Write subscript 2 in (Ch2O).
We changed it.
Line 269: Write in lowercase the letter (T) in the word (The).
We changed it.
the solvent extraction (“SX”)
Line 276: The image is recommended to be made with higher quality.
This is very complex flowchart with many metallurgical operations. Maybe Our colleagues in Metals can improve it in final Version. We will see. Unfortunately I can not offer new Image with higher Quality.
Line 418: Place a parenthesis in each diagram, since it is explained in the text but sections a and b are not found on the image, although it is at the bottom of the figure, it is suggested to place the parenthesis on the image.
After that this strategy was validated in scale up conditions using acid digestion in reactor of 40 L, as shown at Figure 5.a and and system of two digestion reactors, as shown at Fig.5.b.
Figure 5:a. Acid digestion reactor before work and 5.b. system of two digestion reactor during operations; (key elements: anchor stirrer, glass reactor (40 L), engine, an injected tube for a transport of suspension supported by a double membrane pump)
Line 461: There is a double comma in (,, fuming).
We changed it. We have written only fuming
Reviewer 4 Report
- I recommend to improve the design of Figure 1. Furthermore, the introduction of this figure in the text (the context) should be smarter.
- In general, the quality of the figures should be improved.
- The structure of the manuscript should be modified. Section 1 is the introduction but sections 2.1 and 3.1 are short sub introductions.
- A significant part of the document is related to eudialyte. Have this mineral economic value for extraction?
- Despite of the manuscript talk about the importance of sustainable processes, bioprocesses are not mentioned. Could you introduce some information about this issue?
- Important minerals, such as monazite, were not contemplated in the review.
- There are many editing mistakes that should be corrected.
Author Response
Dear Reviewer, thank you very much for your valuable comments and invested time. Now we are sending our answers regarding your comments
- recommend to improve the design of Figure 1. Furthermore, the introduction of this figure in the text (the context) should be smarter.
We have fully improved the design of Figure 1. We prepared new figure 1 with corresponding operations concerning to the metallurgy of rare earth. We added new text."One combined treatment of raw material (ore, concentrate and waste bearing rare earth) contains a combination of pyrometallurgical operation (thermal decomposition of the obtained precipitate) and hydrometallurgical operations such as dry digestion, leaching under an atmospheric pressure conditions, solvent extraction, precipitation of impurities and final winning of rare earth via molten salt electrolysis. As shown at Figure 1, REE are firstly transferred from ores, concentrates and waste materials to the solution. A removal of impurities such as iron from solution was performed via neutralization. The production of rare earth carbonate was reached through an addition of sodium carbonate. The rare earth oxide (REO) were produced through thermal decomposition of rare earth carbonate above 850°C. Final step is molten salt electrolysis in a special reactor with production of mixture of REE.
- In general, the quality of the figures should be improved.
We improved the Figure 1, and replaced Figure 5.b. We added Figure 6. The quality of the other Figures will be improved with an assistance from colleagues in Metals.
- The structure of the manuscript should be modified. Section 1 is the introduction but sections 2.1 and 3.1 are short sub introductions.
You had fully right. I modified it. I removed Introduction 2.1 and 3.1 as short sub introductions. I included 2.1 in Introduction in Part 1.
- A significant part of the document is related to eudialyte. Have this mineral economic value for extraction?
Eudialyte has a high economic value for extraction. In comparison to monazite, steenstrupine, xenotime, bastnasite this mineral is not radioactive (no costs for removal of thorium and uranium). Regarding an environmental impact this mineral is mostly used for the production of rare earth elements.
- Despite of the manuscript talk about the importance of sustainable processes, bioprocesses are not mentioned. Could you introduce some information about this issue? We included new book regarding an application of rare earth elements in extraction of rare earth elements (Vavlekas, D. Microbial recovery of rare earth elements from metallic wastes and scrap, Publisher: University of Birmingham, College of Life and Environmental Sciences, 2014.) In text we added:
Vavlekas [108] studied microbial recovery of rare earth elements from metallic wastes and scrap. The microbial recovery of neodymium is being examined using biofilm of the bacterium Serratia sp. N14, which has been used previously for the removal of lanthanide elements from liquid solutions. The final aim was to establish the potential usefulness of the biofilm with respect to its tolerance to low pH values or to high salt concentrations (neutralized aqua regia), since the overall goal is to recover metals from solid scraps, which may have been leached in strong acid.
- Important minerals, such as monazite, were not contemplated in the review. This is present in Text:
Demol, ; Ho, E.; Senanayake, G. Sulfuric acid baking and leaching of rare earth elements, thorium and phosphate from a monazite concentrate: Effect of bake temperature from 200 to 800 °C. Hydrometallurgy 2018, 179, 254–267.
- There are many editing mistakes that should be corrected. You have right. According to your comments and ones by other three reviewers we changed it.
Round 2
Reviewer 4 Report
I think that the manucript has been improved and can be published after minor revision.
Figure 8 and 9 are difficult to read.
The name of the bacteria should be written in italic.
Author Response
Dear Reviewer, thank you very much for your valuable comments and invested time.
1. Regarding Figures 8 and 9 we offered the better Resolution in order to read it better. Maybe colleagues in Metals can help me to obtain better Resolution in final version!
2. Regarding the second comment, the Name of bacteria is written in Italic.
recovery of neodymium is being examined using biofilm of the bacterium Serratia sp. N14,
Author Response File: Author Response.pdf
