Extraction of Rare-Earth Elements from Silicate-Based Ore through Hydrometallurgical Route
, Denise Crocce Romano Espinosa 1, James Vaughan 2 and Jorge Alberto Soares Tenório 1
Round 1
Reviewer 1 Report
Manuscript ID: metals-1786363
Title: Extraction of rare earth elements from silicate-based ore through hydrometallurgical route
Authors: Amilton Barbosa Botelho Junior et al.
The article presents interesting studies on the extraction of REE from silicate-based ore. The authors have done an impressive job, made a huge number of experiments. The results look convincing. However, in terms of the design of the article and the calculation of the activation energy, there are a number of comments that need to be corrected:
Title must be changed to “Extraction of rare earth elements from silicate-based ore by sulfuric acid baking method”
Line 60-63. I suggest the authors to expand information about red mud and add other resources of aluminosilicate raw materials containing REEs:
· - electrostatic precipitator dust (ESP) in alumina refineries (10.3390/min10060500)
- coal fly ash (CFA) from Coal power plants (10.1016/j.jclepro.2020.124725)
Line 98. Write more detail the location of this raw material. Add country, region, town, or GPS coordinates of deposit.
Line 99. “The particle size distribution was measured” by what method and equipment?
Line 100. Add information about XRF equipment.
Section 2.1. Please, deleted “Before extraction experiments” and “Before experiments”
Table 4. What is the yield (%) of magnetic and non-magnetic fraction after enrichment process?
Figure 3. Can authors add the XRD of magnetic and non-magnetic fraction?
Table 4. What are the chemical compositions (wt. %) and REE content in magnetic and non-magnetic fraction?
Line 212-236. Maybe this text more clearly adds to the Introduction section.
Figure 5. Add “Sulfuric acid concentration” to X-axis title.
Figure 4-5, 7. What are the Si and Ca extraction degree?
Figure 8, 10, 12. Authors must add different colors, not gray color.
Section 3.2.3. Maybe authors change title of this section to “Kinetics analysis”?
Table 5. How was the activation energy (Ea) was calculated? What is the limiting stage of leaching process?
Technical errors:
Line 43-44. Use “Mt”, not million tons.
Line 59. In first time authors must write “hydrochloric acid (HCl)” and in the following article text use only – “HCl”. Use this style for all acids and other chemical reagents.
Line 62, 69, 72, 426, 444, 48, 450. Incorrect citation style.
Line 129. Change H2O2 to H2O2.
Line 140. Change HNO3 to HNO3.
Line 198-199. Use REE, Sc, Si, Zr.
Change “Equation 1” to (1) and etc.
Author Response
Detailed Response to Reviewers
Manuscript metals-1786363
Title: Extraction of rare earth elements from silicate-based ore through
hydrometallurgical route
Dear reviewers and editor Ryan Yang,
Many thanks for your valuable comments. We learned greatly from your rigorous attitude towards scientific research. Your comments have an important guide for improving our article. We have studied your comments carefully and have modified the whole manuscript according to your comments. Just to be clear, the manuscript was entirely revised, and we believe that all the explanations are now to the point and brief. In our point of view, the revised manuscript is now more acceptable than previously.
Nevertheless, please do not hesitate to send your suggestions and comments to us and we are very glad to receive these because we can always learn a lot from your valuable suggestions and comments. All changes are highlighted in green in the revised manuscript.
Reviewer(s)' Comments to Author:
Reviewer #1:
The article presents interesting studies on the extraction of REE from silicate-based ore. The authors have done an impressive job, made a huge number of experiments. The results look convincing. However, in terms of the design of the article and the calculation of the activation energy, there are a number of comments that need to be corrected:
Comments: Dear reviewer, thank you for your time to help us to improve the quality of our manuscript. We hope this new version achieve the quality you require.
Title must be changed to “Extraction of rare earth elements from silicate-based ore by sulfuric acid baking method”
Comments: Thank you for the comments. We respect your opinion, but we decide to keep the title since we also evaluated the direct leaching and dry digestion for extraction of rare earth elements.
Line 60-63. I suggest the authors to expand information about red mud and add other resources of aluminosilicate raw materials containing REEs:
- - electrostatic precipitator dust (ESP) in alumina refineries (10.3390/min10060500)
- coal fly ash (CFA) from Coal power plants (10.1016/j.jclepro.2020.124725)
Comments: Thank you for the suggestions. They were important to improve the quality of our manuscript and they were added in Introduction section as suggested by the reviewer.
Line 98. Write more detail the location of this raw material. Add country, region, town, or GPS coordinates of deposit.
Comments: Unfortunately, we have no permission to supply such informations.
Line 99. “The particle size distribution was measured” by what method and equipment?
Comments: The complemented the information, as highlighted in the manuscript – “The particle size distribution was measured by sieves – 45µm, 75µm, 125µm, 212µm, 300µm, 425µm, 600µm, 850µm, 1180µm, and 1700µm”
Line 100. Add information about XRF equipment.
Comments: Thank you for the comments. We updated the information in the manuscript - “The quantification of the main elements was carried out in XRF (PANalytical Epsilon 3 XL)”.
Section 2.1. Please, deleted “Before extraction experiments” and “Before experiments”
Comments: Thank you for your comments. We made the correction as suggested.
Table 4. What is the yield (%) of magnetic and non-magnetic fraction after enrichment process?
Comments: Thanks for the observation. The information is present in the manuscript – “Results demonstrated that 80-90% of rare earth elements and 90% of scandium, 90% of silicon and 88% of zirconium, which shows that the main valuable elements are hosted in silicates and zircon mineral phases”
Figure 3. Can authors add the XRD of magnetic and non-magnetic fraction?
Comments: Thanks for the comments. Despite the fact that the same phases were identified in both materials, we accepted your suggestion and added the XRD of all three materials – raw material, magnetic and non-magnetic.
Table 4. What are the chemical compositions (wt. %) and REE content in magnetic and non-magnetic fraction?
Comments: We updated the manuscript and added a table (Table 5) with the concentration of elements or compounds present in both materials.
Line 212-236. Maybe this text more clearly adds to the Introduction section.
Comments: Thank you for your valuable comments. We decide to keep this information in this section to link our results and the literature for comparison. In Introduction, it will be completely disconnected.
Figure 5. Add “Sulfuric acid concentration” to X-axis title.
Comments: We made the correction in Figure 5.
Figure 4-5, 7. What are the Si and Ca extraction degree?
Comments: Si was not analyzed since the literature reports low or close to zero leaching within 8h of direct leaching and in dry or baking + water leaching.
We did not analyzed Ca leaching rate since in sulfuric acid Ca will form sulfate in solid phase.
Figure 8, 10, 12. Authors must add different colors, not gray color.
Comments: Thanks for the comments. We updated the figures.
Section 3.2.3. Maybe authors change title of this section to “Kinetics analysis”?
Comments: Kinetic experiments were not carried out in this study.
Table 5. How was the activation energy (Ea) was calculated? What is the limiting stage of leaching process?
Comments: We calculated the activation energy using the following equations:
Equation 5
Equation 6
Technical errors:
Line 43-44. Use “Mt”, not million tons.
Comments: We made the corrections.
Line 59. In first time authors must write “hydrochloric acid (HCl)” and in the following article text use only – “HCl”. Use this style for all acids and other chemical reagents.
Comments: We made the corrections as suggested.
Line 62, 69, 72, 426, 444, 48, 450. Incorrect citation style.
Comments: Corrections were made throughout the manuscript
Line 129. Change H2O2 to H2O2.
Comments: We made the corrections
Line 140. Change HNO3 to HNO3.
Comments: We made the corrections
Line 198-199. Use REE, Sc, Si, Zr.
Comments: We decide to keep the name of elements.
Change “Equation 1” to (1) and etc.
Comments: We made the corrections
Reviewer #2
This manuscript described a new approach for leaching rare earth elements from a silicate-based ore by the hydrometallurgical route. Direct leaching and acid baking of silicate-based ore were studied using sulfuric acid. And the effect of acid concentration, temperature, solid-liquid ratio, oxidizing/reducing medium, and acid dosage on leaching rate were also studied. With wide investigation, the extraction of REE achieved up to 80%. This work has application value. But some analysis and expression were ambiguous, the author need to revise carefully.
Comments: Dear reviewer, thank you for your valuable comments. We hope this new version of our manuscript achieve the quality required.
- In line 170-174, the author described 90% of the particles are smaller than 1412.9μm, and 50% are smaller than 348.5μm, so how to grind the ore sample into -0.5mm.
Comments: Thanks for the comments. We decide to grind the sample into lower than 0.5mm due to the heterogeneity of the raw material. It certainly will impact the leaching results. Despite that, the data of particle size distribution was kept in the manuscript as a part of characterization of the silicate-based ore.
- In line 192-196, since the content of most rare earth elements is beyond the detection limit (as shown in Table 3), so if the valence state information of them can be further analyzed by XPS, the inference of the phase will be more credible.
Comments: It is not clear what reviewer means about the “beyond the detection limit”. In a chemical analysis, the main elements are higher than the detection limit of any equipment. For instance, for ICP analysis, iron of our sample is higher than the detection limit, and for this reason we made dilutions for the analysis.
Regarding the XPS, indeed it would be helpful for the characterization, but we have no access of such equipment.
- In “3.2.1. Effect of solid-liquid ratio and acid concentration”, when studying the effect of solid-liquid ratio, why use 4mol/L sulfuric acid instead of 1mol/L? According to the author's experiments, 1mol/L sulfuric acid is obviously a better condition. At the same time, why the experiments in this subsection are not carried out at T=90℃, higher temperature is also more conducive to the leaching reaction.
Comments: Thank you for your comments. As the reviewer clearly observed, acid leaching with 1mol/L achieved better results than 4mol/L. As we started the experiments evaluating the effect of solid-liquid ratio, and considering the most recent literature about the topic, we decide to study by the highest acid concentration and then study it separated, as it is presented in the manuscript.
- In line 312-314, when the dosage of hydrogen peroxide exceeds 2.5%, what is the reason for the slight decrease in extraction efficiency during oxidizing leaching process.
Comments: The explanation is presented in the manuscript, as following:
“The exception was iron, where declined from 29.3% (2.5v/v% of H2O2) to 9.3% (10.0v/v% of H2O2). As depicted in Figure 6, for H2SO4 2.0mol/L without oxidant agent, the iron can be presented in the solution as ferrous iron and in the solid phase as iron sulfate, where it occurs after the leaching reaction. However, in the oxidizing leaching reaction where the redox potential increased to 1,000mV, iron oxide is not leached totally, and only a part generates iron sulfate ions”.
- In Table 5, the calculated reaction rate (K) should be given.
Comments: The main thermodynamic data for leaching studies are activation energy and frequency factor.
- In line 484-487, according to the author’ s explanation (reaction 11), the more sulfuric acid is used, the more SO3 is produced by its decomposition. So the forward reaction process of reactions 9 and 10 should be more difficult to occur, that is, when the concentration of sulfuric acid is high, the proportion of iron sulfate in the solid phase should be larger, which is in contradiction with the results of Figure 11. How to interpret it?
Comments: Thanks for the comments. As reported by the literature, the excess of sulfuric acid may result in conversion of iron into oxide or basic iron sulfate, being the last one of possible compounds identified in XRD. It may occur by an excess of sulfuric acid and temperature.
- There are many verbal errors and misrepresentations in the manuscript. For example, in line 459, “The effect of resin dosage” should be revised to “The effect of acid dosage”, and “1g or ore” in line 502 should be revised to “1g of ore”.
Comments: Thank you for your valuable comment. We read carefully the manuscript searching for errors. We hope it achieves the standards of the reviewer.
The revised manuscript has been resubmitted to the journal. We look forward to your positive response.
Sincerely,
Amilton Barbosa Botelho Junior.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The author has done a lot of work on REE Extraction, The results are valuable and deserve to be seen. But, There are some problems that need to be corrected.
1. In the Abstract, I can’t find the lanthanum. And for Keywords, How to explain lanthanum?
2. Manuscript spelling needs to be checked, such as line 129 (H2O2), line 140 HNO3, et al.
3. In Figure 1, the unit Sieve size is mm. But in line 170 and 171, the sentence “in the silicate-based 170 ore, 90% of the particles are smaller than 1412.9µm, and 50% are smaller than 348.5µm. “ Please check it.
4. In line 186, X-ray diffractogram has been abbreviated, please use abbreviation. There are other similar situations in the manuscript, please revise them.
5. In line 102, dissolution in HCl media. Throughout the manuscript, I see sulfuric acid. Please give a reasonable explanation.
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Reviewer 3 Report
This manuscript described a new approach for leaching rare earth elements from a silicate-based ore by the hydrometallurgical route. Direct leaching and acid baking of silicate-based ore were studied using sulfuric acid. And the effect of acid concentration, temperature, solid-liquid ratio, oxidizing/reducing medium, and acid dosage on leaching rate were also studied. With wide investigation, the extraction of REE achieved up to 80%. This work has application value. But some analysis and expression were ambiguous, the author need to revise carefully.
1. In line 170-174, the author described 90% of the particles are smaller than 1412.9μm, and 50% are smaller than 348.5μm, so how to grind the ore sample into -0.5mm.
2. In line 192-196, since the content of most rare earth elements is beyond the detection limit (as shown in Table 3), so if the valence state information of them can be further analyzed by XPS, the inference of the phase will be more credible.
3. In “3.2.1. Effect of solid-liquid ratio and acid concentration”, when studying the effect of solid-liquid ratio, why use 4mol/L sulfuric acid instead of 1mol/L? According to the author's experiments, 1mol/L sulfuric acid is obviously a better condition. At the same time, why the experiments in this subsection are not carried out at T=90℃, higher temperature is also more conducive to the leaching reaction.
4. In line 312-314, when the dosage of hydrogen peroxide exceeds 2.5%, what is the reason for the slight decrease in extraction efficiency during oxidizing leaching process.
5. In Table 5, the calculated reaction rate (K) should be given.
6. In line 484-487, according to the author’ s explanation (reaction 11), the more sulfuric acid is used, the more SO3 is produced by its decomposition. So the forward reaction process of reactions 9 and 10 should be more difficult to occur, that is, when the concentration of sulfuric acid is high, the proportion of iron sulfate in the solid phase should be larger, which is in contradiction with the results of Figure 11. How to interpret it?
7. There are many verbal errors and misrepresentations in the manuscript. For example, in line 459, “The effect of resin dosage” should be revised to “The effect of acid dosage”, and “1g or ore” in line 502 should be revised to “1g of ore”.
Author Response
Detailed Response to Reviewers
Manuscript metals-1786363
Title: Extraction of rare earth elements from silicate-based ore through
hydrometallurgical route
Dear reviewers and editor Ryan Yang,
Many thanks for your valuable comments. We learned greatly from your rigorous attitude towards scientific research. Your comments have an important guide for improving our article. We have studied your comments carefully and have modified the whole manuscript according to your comments. Just to be clear, the manuscript was entirely revised, and we believe that all the explanations are now to the point and brief. In our point of view, the revised manuscript is now more acceptable than previously.
Nevertheless, please do not hesitate to send your suggestions and comments to us and we are very glad to receive these because we can always learn a lot from your valuable suggestions and comments. All changes are highlighted in green in the revised manuscript.
Reviewer(s)' Comments to Author:
Reviewer #1:
The article presents interesting studies on the extraction of REE from silicate-based ore. The authors have done an impressive job, made a huge number of experiments. The results look convincing. However, in terms of the design of the article and the calculation of the activation energy, there are a number of comments that need to be corrected:
Comments: Dear reviewer, thank you for your time to help us to improve the quality of our manuscript. We hope this new version achieve the quality you require.
Title must be changed to “Extraction of rare earth elements from silicate-based ore by sulfuric acid baking method”
Comments: Thank you for the comments. We respect your opinion, but we decide to keep the title since we also evaluated the direct leaching and dry digestion for extraction of rare earth elements.
Line 60-63. I suggest the authors to expand information about red mud and add other resources of aluminosilicate raw materials containing REEs:
- - electrostatic precipitator dust (ESP) in alumina refineries (10.3390/min10060500)
- coal fly ash (CFA) from Coal power plants (10.1016/j.jclepro.2020.124725)
Comments: Thank you for the suggestions. They were important to improve the quality of our manuscript and they were added in Introduction section as suggested by the reviewer.
Line 98. Write more detail the location of this raw material. Add country, region, town, or GPS coordinates of deposit.
Comments: Unfortunately, we have no permission to supply such informations.
Line 99. “The particle size distribution was measured” by what method and equipment?
Comments: The complemented the information, as highlighted in the manuscript – “The particle size distribution was measured by sieves – 45µm, 75µm, 125µm, 212µm, 300µm, 425µm, 600µm, 850µm, 1180µm, and 1700µm”
Line 100. Add information about XRF equipment.
Comments: Thank you for the comments. We updated the information in the manuscript - “The quantification of the main elements was carried out in XRF (PANalytical Epsilon 3 XL)”.
Section 2.1. Please, deleted “Before extraction experiments” and “Before experiments”
Comments: Thank you for your comments. We made the correction as suggested.
Table 4. What is the yield (%) of magnetic and non-magnetic fraction after enrichment process?
Comments: Thanks for the observation. The information is present in the manuscript – “Results demonstrated that 80-90% of rare earth elements and 90% of scandium, 90% of silicon and 88% of zirconium, which shows that the main valuable elements are hosted in silicates and zircon mineral phases”
Figure 3. Can authors add the XRD of magnetic and non-magnetic fraction?
Comments: Thanks for the comments. Despite the fact that the same phases were identified in both materials, we accepted your suggestion and added the XRD of all three materials – raw material, magnetic and non-magnetic.
Table 4. What are the chemical compositions (wt. %) and REE content in magnetic and non-magnetic fraction?
Comments: We updated the manuscript and added a table (Table 5) with the concentration of elements or compounds present in both materials.
Line 212-236. Maybe this text more clearly adds to the Introduction section.
Comments: Thank you for your valuable comments. We decide to keep this information in this section to link our results and the literature for comparison. In Introduction, it will be completely disconnected.
Figure 5. Add “Sulfuric acid concentration” to X-axis title.
Comments: We made the correction in Figure 5.
Figure 4-5, 7. What are the Si and Ca extraction degree?
Comments: Si was not analyzed since the literature reports low or close to zero leaching within 8h of direct leaching and in dry or baking + water leaching.
We did not analyzed Ca leaching rate since in sulfuric acid Ca will form sulfate in solid phase.
Figure 8, 10, 12. Authors must add different colors, not gray color.
Comments: Thanks for the comments. We updated the figures.
Section 3.2.3. Maybe authors change title of this section to “Kinetics analysis”?
Comments: Kinetic experiments were not carried out in this study.
Table 5. How was the activation energy (Ea) was calculated? What is the limiting stage of leaching process?
Comments: We calculated the activation energy using the following equations:
Equation 5
Equation 6
Technical errors:
Line 43-44. Use “Mt”, not million tons.
Comments: We made the corrections.
Line 59. In first time authors must write “hydrochloric acid (HCl)” and in the following article text use only – “HCl”. Use this style for all acids and other chemical reagents.
Comments: We made the corrections as suggested.
Line 62, 69, 72, 426, 444, 48, 450. Incorrect citation style.
Comments: Corrections were made throughout the manuscript
Line 129. Change H2O2 to H2O2.
Comments: We made the corrections
Line 140. Change HNO3 to HNO3.
Comments: We made the corrections
Line 198-199. Use REE, Sc, Si, Zr.
Comments: We decide to keep the name of elements.
Change “Equation 1” to (1) and etc.
Comments: We made the corrections
Reviewer #2
This manuscript described a new approach for leaching rare earth elements from a silicate-based ore by the hydrometallurgical route. Direct leaching and acid baking of silicate-based ore were studied using sulfuric acid. And the effect of acid concentration, temperature, solid-liquid ratio, oxidizing/reducing medium, and acid dosage on leaching rate were also studied. With wide investigation, the extraction of REE achieved up to 80%. This work has application value. But some analysis and expression were ambiguous, the author need to revise carefully.
Comments: Dear reviewer, thank you for your valuable comments. We hope this new version of our manuscript achieve the quality required.
- In line 170-174, the author described 90% of the particles are smaller than 1412.9μm, and 50% are smaller than 348.5μm, so how to grind the ore sample into -0.5mm.
Comments: Thanks for the comments. We decide to grind the sample into lower than 0.5mm due to the heterogeneity of the raw material. It certainly will impact the leaching results. Despite that, the data of particle size distribution was kept in the manuscript as a part of characterization of the silicate-based ore.
- In line 192-196, since the content of most rare earth elements is beyond the detection limit (as shown in Table 3), so if the valence state information of them can be further analyzed by XPS, the inference of the phase will be more credible.
Comments: It is not clear what reviewer means about the “beyond the detection limit”. In a chemical analysis, the main elements are higher than the detection limit of any equipment. For instance, for ICP analysis, iron of our sample is higher than the detection limit, and for this reason we made dilutions for the analysis.
Regarding the XPS, indeed it would be helpful for the characterization, but we have no access of such equipment.
- In “3.2.1. Effect of solid-liquid ratio and acid concentration”, when studying the effect of solid-liquid ratio, why use 4mol/L sulfuric acid instead of 1mol/L? According to the author's experiments, 1mol/L sulfuric acid is obviously a better condition. At the same time, why the experiments in this subsection are not carried out at T=90℃, higher temperature is also more conducive to the leaching reaction.
Comments: Thank you for your comments. As the reviewer clearly observed, acid leaching with 1mol/L achieved better results than 4mol/L. As we started the experiments evaluating the effect of solid-liquid ratio, and considering the most recent literature about the topic, we decide to study by the highest acid concentration and then study it separated, as it is presented in the manuscript.
- In line 312-314, when the dosage of hydrogen peroxide exceeds 2.5%, what is the reason for the slight decrease in extraction efficiency during oxidizing leaching process.
Comments: The explanation is presented in the manuscript, as following:
“The exception was iron, where declined from 29.3% (2.5v/v% of H2O2) to 9.3% (10.0v/v% of H2O2). As depicted in Figure 6, for H2SO4 2.0mol/L without oxidant agent, the iron can be presented in the solution as ferrous iron and in the solid phase as iron sulfate, where it occurs after the leaching reaction. However, in the oxidizing leaching reaction where the redox potential increased to 1,000mV, iron oxide is not leached totally, and only a part generates iron sulfate ions”.
- In Table 5, the calculated reaction rate (K) should be given.
Comments: The main thermodynamic data for leaching studies are activation energy and frequency factor.
- In line 484-487, according to the author’ s explanation (reaction 11), the more sulfuric acid is used, the more SO3 is produced by its decomposition. So the forward reaction process of reactions 9 and 10 should be more difficult to occur, that is, when the concentration of sulfuric acid is high, the proportion of iron sulfate in the solid phase should be larger, which is in contradiction with the results of Figure 11. How to interpret it?
Comments: Thanks for the comments. As reported by the literature, the excess of sulfuric acid may result in conversion of iron into oxide or basic iron sulfate, being the last one of possible compounds identified in XRD. It may occur by an excess of sulfuric acid and temperature.
- There are many verbal errors and misrepresentations in the manuscript. For example, in line 459, “The effect of resin dosage” should be revised to “The effect of acid dosage”, and “1g or ore” in line 502 should be revised to “1g of ore”.
Comments: Thank you for your valuable comment. We read carefully the manuscript searching for errors. We hope it achieves the standards of the reviewer.
The revised manuscript has been resubmitted to the journal. We look forward to your positive response.
Sincerely,
Amilton Barbosa Botelho Junior.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Article can be accepted in this form.
