Valorization of Rare Earth Elements from a Steenstrupine Concentrate Via a Combined Hydrometallurgical and Pyrometallurgical Method
Round 1
Reviewer 1 Report
This paper deals with an optimized extraction method for REE in steenstrupine concentrate following different chemical and physical steps. Due to the high critical demand of these elements in the market, this type of studies is of great importance. However, important changes need to be made before acceptance. The manuscript does not follow a scientific order, there is no Result or Discussion section. I also miss a discussion comparing these results with similar protocols or the advantages of this method compared to others. Finally, although the paper is well written, the English must be polished.
Some other minor comments:
Lines 26-28: what did the authors mean? Please be more specific, these techniques were also used in other parts of the world.
Line 28: treatment
Line 30: nowadays
Line 32: what does it mean chemical activity referred to minerals? Reactivity?? Leachability??
Line 35 and elsewhere; be consistent with the use of symbols (Zr) or element names
Line 35; In comparison to eudialyte,……
Line 37: as far as I know the deposit is not treated, the raw material extracted from a mineral deposit is treated.
Line 49: replace “a lot” by “widely” “extensively”, etc
Line 54: who is someone??
Line 55: reasons
Lines 97-100: it is not clear how the sample was characterized. The material is composed of steenstrupine and eudialyte, and was characterized by XRF and ICP-OES? In this latter case, the solid sample must have been dissolved by acids, right? Please clear it up.
Line 127: figure caption should appear separated from the figure
Lines 132, 133; the authors must explain the meaning of SE in equations
Line 171: solid/liquid
Table 4; are the solid/liquid ratios of Table 4 right? Please check it
Lines 175-176: this is not right, according to Table 4, the highest ratio (0.2) leads to silica formation
Table 5. please add units or %
Lines 219-220: please rewrite this sentence
Line 223-225: rewrite this sentence
Table 9. Please avoid the use of Tables in Conclusion section. Describe the main findings of your work.
Author Response
Dear reviewer 1,
Thank you very much for youe excellent comments.
Reviewer !:
This paper deals with an optimized extraction method for REE in steenstrupine concentrate following different chemical and physical steps. Due to the high critical demand of these elements in the market, this type of studies is of great importance. However, important changes need to be made before acceptance. The manuscript does not follow a scientific order, there is no Result or Discussion section. I also miss a discussion comparing these results with similar protocols or the advantages of this method compared to others. Finally, although the paper is well written, the English must be polished.
I have given many efforts to offer my answers and prepare new improved version. Some comparison with advantages are offered in conclusion. In order to prevent silica gel formation we have successfully used dry digestion process at romm temperature (Ref,14). but this time we perfomed experiments at 90°C in same reaction time with an increased conctration of hydrochloric acid.An disadvantage is decreased solid/liquid ratio.
English was polished.
Some other minor comments:
Lines 26-28: what did the authors mean? Please be more specific, these techniques were also used in other parts of the world.
The unit hydrometallurgical operations (leaching, neutralization, filtration, precipitation, solvent extraction) and pyrometallurgical technique (thermal decomposition, molten salt pyrolysis) were mostly used in China for the treatment of the bastnasite, monazite, xenotime and apatite minerals containing the rare earth elements under atmospheric pressure [1-5].
Line 28: treatment
Changed.
Line 30: nowadays
changed
Line 32: what does it mean chemical activity referred to minerals? Reactivity?? Leachability??
Because of higher leachability nowadays, silicate minerals such as eudialyte and steenstrupine are the most promising raw material for the Zr, Hf and REE production
Line 35 and elsewhere; be consistent with the use of symbols (Zr) or element names
Changed in Zr
Line 35; In comparison to eudialyte,……
changed
Line 37: as far as I know the deposit is not treated, the raw material extracted from a mineral deposit is treated.
The raw material extracted from a Kvanefjeld mineral deposit is treated by Krebs and Furfaro [7] in order to separate uranium and thorium from rare earth elements.
Line 49: replace “a lot” by “widely” “extensively”, etc
widely
Line 54: who is someone??
Lebedev
Line 55: reasons
changed
Lines 97-100: it is not clear how the sample was characterized. The material is composed of steenstrupine and eudialyte, and was characterized by XRF and ICP-OES? In this latter case, the solid sample must have been dissolved by acids, right? Please clear it up.
The solid sample was firstly analysed by X-ray fluorescence, (Axios FAST, Malvern Panalytical GmbH, Germany), as shown in Table 1. An additional analysis of rare earth elements was performed by Inductively coupled plasma - optical emission spectrometry ICP-OES analysis (SPECTRO ARCOS, SPECTRO Analytical Instruments GmbH, Kleve, Germany), as shown in Table 2
Line 127: figure caption should appear separated from the figure
I changed it. Now is better
Figure 2.Inital sample (a), Conditioning of initial sample (b), final product (c)
Lines 132, 133; the authors must explain the meaning of SE in equations
Rare earth elements (Ln) instead SE
LnPO4 + 3 HCl = Ln3+(aq) + 3 Cl-(aq) + 3 H+(aq)+ PO4-(aq) (5)
Ln(SiO3)3 + 6 HCl = 2Ln3+(aq)+ 6 Cl-(aq) +3 H2SiO3 (6)
Unfortunalely SE is short name from German language. I change it.
Line 171: solid/liquid
Solid: liquid ratio is 0.08
Table 4; are the solid/liquid ratios of Table 4 right? Please check it
I improved the Table 4 in order to better explain the influence of solid/liquid ratio
Lines 175-176: this is not right, according to Table 4, the highest ratio (0.2) leads to silica formation
Silica gel formation is present in Experiment 5. In this experiment is maximal content of solid material (40g), what is high prabibilty for transfer of silicon to solution. It was case.
Table 5. please add units or %
I added it.
Lines 219-220: please rewrite this sentence
Using a relationship between the element concentration in water solution (before and after precipitation), the precipitation efficiency was calculated and shown in Table 7.
Line 223-225: rewrite this sentence
As shown in Table 7, maximal precipitation efficiency was obtained for rare earth elements, but also for thorium (95.59), what shows that a separation process must be included in this strategy.
Table 9. Please avoid the use of Tables in Conclusion section. Describe the main findings of your work.
The Table was removed from conclusion
Conclusion:
Valorization of rare earth elements from a steenstrupine concentrate via combined hydrometallurgical and pyrometallurgical process was successfully performed using optimized strategy with rewashing process enabling the maximal efficiency for rare earth elements (Ce, La, Nd, Y) approx. 96 %. This study has revealed that this treatment is possible without thermal conditioning of initial sample. The optimal parameter for leaching are: 90°C, 2 hours, 400 rpm, solid/Liquid ratio of 20 g/250 mL and duration of 30 min. In comparison to dry digestion process it take place in same time of 30 min, but at an increased temperature of 90 °C and small solid/liquid ratio, what is a disadvantage. The obtained rare earth oxides contains some impurities, what leads to involvement of solvent extraction as an important step for this work.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
This manuscript describes the extraction and recovery of REEs, Zr, Hf from a silicate concentrate containing Eudialyte and steenstrupine. The topic is within the scope of Minerals, but the quality of the manuscript should be improved, critical discussions added, novelty emphasised, and additional data provided prior to publication. I, therefore, recommend to the editors to accept this manuscript after a major revision.
There are numerous papers in recent years about the leaching of REEs from its ores, so the authors should provide a summary of these papers and highlight why their approach is better or more appropriate. How is silica gel formed during leaching? A brief explanation should be added to the introduction. The authors also should differentiate their work with those of EREAN, REDMUD, SCALE and REMOVAL. What do these ‘acronyms’ mean? What are the theoretical bases of the selected flowchart? Provide the XRD pattern of the sample. How much Eudialyte and steenstrupine are found in the sample? What are the other coexisting minerals in it? Provide the particle size distribution of the sample. Provide an SEM-EDX image of the minerals incorporating the REEs. This will help the authors provide a better discussion of their results. Provide a detailed discussion of the following: Why is thermal conditioning not needed at higher leaching temperature? How did the simple covering of the reactor prevented silica gel formation? What are the effects of other coexisting minerals on the leaching efficiency? Provide replicates of all samples. The authors should also add statistical analyses of their results. Provide mass and water balances for the two flowcharts used. The authors should also provide a cost-benefit analysis to compare their technique with those developed by other groups. How do you quantify “Silica gel formation”? I am not convinced of simple photographs to explain that silica gels did not form. The authors should fix the structure of their manuscript. It is strange to see their results combined with their methodology. There are too many spelling and grammatical mistakes to mention, so the authors should ask professional help to improve their manuscript. What does “SE” represent in equations 5 and 6?Author Response
Dear Reviewer,
Thank you very much for your interesting questions.
My answers:
How is silica gel formed during leaching? A brief explanation should be added to the introduction.
From Line 115 to 122 silica gel formation is explained in details (Eq. 1-4)
In Introduction in References by Davris [11] and Vossenkaul [12] can you find it.
The authors also should differentiate their work with those of EREAN, REDMUD, SCALE and REMOVAL. What do these ‘acronyms’ mean?
European Rare Earth Magnet Recycling Network EREAN
REDMUD (this is product from the Aluminium industry: Red Mud is produced during the Bayer Process. With this process, we can extract the aluminum (oxy)hydroxides from bauxites and get alumina, which eventually can be smelted and give aluminum
SCALE Scandium Aluminium Europe (The main aim of SCALE is the efficient exploitation of EU high concentration scandium containing resources including bauxite residues (100-150 ppm) resulting from alumina production and acid wastes (50-100 ppm) from TiO2 pigment production to develop a stable and secure EU scandium supply chain to serve the needs of EU aerospace and high tech industry.
REMOVAL-Removing the waste streams from the primary aluminium prosuction in Europe
Removing the waste streams from the primary Aluminum production in Europe
What are the theoretical bases of the selected flowchart? Re
Theoretical basic of selected flowchart is our work on REDMUD, REMOVAL; EURARE. from the primary Aluminum production in Europe
Provide the XRD pattern of the sample.
Unfortunately, we can not provide XRD pattern of the sample.
How much Eudialyte and steenstrupine are found in the sample?
Rietveld XRD-Analysis was not performed.
What are the other coexisting minerals in it?
We did not made XRD-Analysis of sample.
Provide the particle size distribution of the sample.
We can not do it.
Provide an SEM-EDX image of the minerals incorporating the REEs. This will help the authors provide a better discussion of their results.
Because of very complex mineral This available SEM and EDS Analysis can not help us to provide better discussion without ICP OES analysis, what we made in this study.
SEM; EDS PIcture is attached in an additional document
Steenstrupine: Na14Ce6Mn2Fe2(Zr,Th,U)(PO4)7Si12O36(OH)2.3H2O
Provide a detailed discussion of the following: Why is thermal conditioning not needed at higher leaching temperature?
As shown on Ref. by Davris Thermal conditioning is needed to prevent silica gel formation. In our case at higher temperature silicon dissolution is decreased, and no gel formation. Therefore we need no thermal conditioning, because we have worked at 90 °C in reactor
How did the simple covering of the reactor prevented silica gel formation?
The simple covering of the reactor enables a constant temperature of 90 °C in reactor, what is important for a prevention of silica gel formation.
What are the effects of other coexisting minerals on the leaching efficiency?
No influence
Provide replicates of all samples.
We had very small amount of sample obtained after beneficiation from Finland. Because of this situation and disposal of waste solid material and waste water based on thorium, no possibility for many repetitions of experiments
The authors should also add statistical analyses of their results.
We did not make repetitions of experiments, as previously mentioned.
Provide mass and water balances for the two flowcharts used.
No possible.
The authors should also provide a cost-benefit analysis to compare their technique with those developed by other groups.
It was only a research project
How do you quantify “Silica gel formation”? I am not convinced of simple photographs to explain that silica gels did not form.
Silica gel formation is evident, if the filterability is very bad, as shown at Fig. 4b. In this case the leaching process is blocked.
The authors should fix the structure of their manuscript. It is strange to see their results combined with their methodology.
We are agreed. Therefore we have put Chapter 3: Results and Discussion and separated it from Methods and Materials
There are too many spelling and grammatical mistakes to mention, so the authors should ask professional help to improve their manuscript.
We changed many improvements in our new version and re-write sentences.
What does “SE” represent in equations 5 and 6?
SE- seltene erde (“rare earth elements” in german language). We changed SE in Ln, what is symbol for rare earth elements, as shown in 5 and 6
LnPO4 + 3 HCl = Ln3+(aq) + 3 Cl-(aq) + 3 H+(aq)+ PO4-(aq) (5)
Ln(SiO3)3 + 6 HCl = 2Ln3+(aq)+ 6 Cl-(aq) +3 H2SiO3 (6)
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The authors have addressed most of questions raised by reviewers and provide an improved version of the manuscript. However I consider that English must still be polished before acceptance.
Author Response
Dear Reviewer,
thank you very much for your efforts to improve our paper, what is not easy!
1. However I consider that English must still be polished before acceptance.
This English is improved, but it will be improved in final proof.
Attached I am sending new Version.
Thank you for your comprehension!
Best regards
Author Response File: 
Author Response.docx
Reviewer 2 Report
Minor comments:
The authors should consider asking someone to proofread their work. There are still a lot of grammatical mistakes in the text. Provide scales in Figs. 2, 4, 8 and 9. In Fig. 5, change "mit" to "with" In Fig. 6, unify the y-axes range of the two plots.Author Response
Dear reviewer,
thank your for your usefull comments and efforts to help us to prepare an improved version.
1.The authors should consider asking someone to proofread their work.
Our colleague was asked to proofread our text. He made changes in our refererences and in title of axis.
2. There are still a lot of grammatical mistakes in the text.
We changed the gramatical mistakes, but we will check it in our proof together with responsible Editor!
3. Provide scales in Figs. 2, 4, 8 and 9.
I can not understand, which type of "Scale" I have to ensure in Fig. 2, 4, 8 and 9. I have improved a title of Figures.
4. In Fig. 5, change "mit" to "with"
I can not find "Mit". Maybe we have changed it in our comments to other Reviewers
5.In Fig. 6, unify the y-axes range of the two plots
Because the original file is not available in Excel in Figure 6, we can not unify the y axes range of the plots (left-max 100 %, and right (max. 80 %). Because the maximal efficiency is not higher than 80 % (right), I am proposing no changes in Axes.
Thank you for your comprehension.
Author Response File: Author Response.docx
