Critical Raw Materials Supply: Challenges and Potentialities to Exploit Rare Earth Elements from Siliceous Stones and Extractive Waste

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

1.       The author needs to double-check all spelling and notation errors in the manuscript.

Ex: line 510, 513, 520,521, 524, 525… on page 16; or line 484, 486, 500… on page 15

2.       In Fig. 2, the author needs to remove background color.

3.       In Fig. 4, how to know PI, Bt, Qtz, Aln… by SEM image? In this figure, author want to show the contents of REO or REE material?

4.       From SEM images transfer the contents of REO or REE material graph, why is there not SiO2 (Qtz) in graph?

Author Response

Dear Reviewer,

Thank you for taking the time to review our manuscript. Your comments and suggestions have significantly enhanced the quality of the paper. Please note that all corrections and variations in the manuscript are indicated in red.

 

1. The author needs to double-check all spelling and notation errors in the manuscript.

Ex: line 510, 513, 520,521, 524, 525… on page 16; or line 484, 486, 500… on page 15

Dear reviewer, thank you for pointing this out. we have checked and corrected all spelling and notation errors in the manuscript

2. In Fig. 2, the author needs to remove background color.

Dear reviewer, thank you for pointing this out. In the latest version of the manuscript, the background color in Fig.2 has been removed.

3. In Fig. 4, how to know PI, Bt, Qtz, Aln… by SEM image? In this figure, author want to show the contents of REO or REE material?

Dear Reviewer, Image 4A is done in optical microscopy, not electron microscopy, and the minerals are identified based on their optical properties. Therefore, the caption is corrected to "PLM micrograph (A) and SEM back-scattered electrons images with EDS spectrum of EW (B-C)”.

 

4. From SEM images transfer the contents of REO or REE material graph, why is there not SiO2 (Qtz) in graph?

Dear Reviewer, the EDS spectrum of REE minerals is qualitative; for subsequent EDS microanalysis, the analysis point was optimized so as not to have interference with other mineralogical phases in the proximity.

Reviewer 2 Report

Comments and Suggestions for Authors

The text in the manuscript is lacking ALL subscripts and superscripts. This must be corrected! The equations and figures have sub- and superscripts.

Some XRPD spectra could be shown to give an impression on how well the different mineral phases are determined. The detection limits for the various minerals could be better stated.

In Fig.5: The series of elements are quite random - not alphabetic, not atomic No. Why?

Fig.6: Sc is listed as last of the REE. If it is according to atomic radius, then Y should not be first, but about Tb - Ho. Why?

Equation 1 seems to be an empirical fitting function and has no scientific basis. If it has, it should be stated.

p. 487: It is referred to CNY as value of REE. Why, when later it is only EUR that is used? 

The huge variations within each sample group indicates large uncertainties in the materials. No error bars or standard deviations are given. This makes the economic estimates quite uncertain.
Moreover, event though there are samples with high amounts of REE the possibility for recovery is not evaluated. Leaching of the specific REEs and thief zones in the material which may consume acids or chemicals and make the operations costly are important topics to address.

Author Response

 

Dear Reviewer,

Thank you for taking the time to review our manuscript. Your comments and suggestions have significantly enhanced the quality of the paper. Please note that all corrections and variations in the manuscript are indicated in red.

• The text in the manuscript is lacking ALL subscripts and superscripts. This must be corrected! The equations and figures have sub- and superscripts.

Dear reviewer, thanks for your useful comment. We have checked and corrected all subscripts and superscripts in the equations.

• The text in the manuscript is lacking ALL subscripts and superscripts. This must be corrected! The equations and figures have sub- and superscripts.

Dear Reviewer, thanks for your comment. We have checked all the Figures. Figures have sub- and superscripts, such as Chemical formula.

 

• Some XRPD spectra could be shown to give an impression on how well the different mineral phases are determined. The detection limits for the various minerals could be better stated.

Considering the mineralogical composition of the rocks under investigation (quartz, feldates and phyllosilicates primarily) and the characteristics of the analytical instrumentation used, the limit of detection is around 0.5 to 1 percent by weight. If necessary, we can attach some diffractograms, but we do not think they are useful for the purpose of "demonstrating" the limit of detectability, and in many cases they are very similar.

 

• In Fig.5: The series of elements are quite random - not alphabetic, not atomic No. Why?

Dear reviewer, thank you for your comment.  In the latest version, the horizontal axis of the Fig.5 has been changed in alphabetical order of the elements.

• 6: Sc is listed as last of the REE. If it is according to atomic radius, then Y should not be first, but about Tb - Ho. Why?

Dear reviewer, thank you for your comment.  The order of rare earth elements has been rearranged based on atomic number, and the figure has been modified. Please refer to the following figure for details.

 

• Equation 1 seems to be an empirical fitting function and has no scientific basis. If it has, it should be stated.

Dear reviewer, thank you for your comment. We have established a fitting relationship between Outlook coefficient and proportion of critical REEs in total REEs based on existing test data and the mathematical fitting function in the software. The correlation coefficient R²=0.97 indicates a high degree of fit between the two factors, indicating a strong correlation. A high correlation indicates a close connection in statistical mathematics between the two.

 

• 487: It is referred to CNY as value of REE. Why, when later it is only EUR that is used? 

Dear reviewer, thank you for your comment.  In the new version of the mnuscript, the price unit has been uniformly changed to EUR.

• The huge variations within each sample group indicates large uncertainties in the materials. No error bars or standard deviations are given. This makes the economic estimates quite uncertain.

Dear reviewer, thank you very much for your comment. Based on your suggestions, we have added the standard deviation of the total market value of waste with different types to the Figure. Please refer to the following figure for details.

• Moreover, event though there are samples with high amounts of REE the possibility for recovery is not evaluated. Leaching of the specific REEs and thief zones in the material which may consume acids or chemicals and make the operations costly are important topics to address.

Dear reviewer, thank you very much for your comment. We are currently conducting the second phase of this research, which aims to explore the most effective and sustainable dressing techniques for recovering rare earth elements (REEs) at the laboratory scale, as said in paragraph 6, “Future Prospects”.

 

Reviewer 3 Report

Comments and Suggestions for Authors

Zhao et al. present in this manuscript the mineralogical, petrographic, geochemical, and environmental characterization of extractive wastes (including granite, gneiss, diorite and quartzite), kaolinitic gneiss deposits, and soils near quarries in Northwest Italy. In addition, an analysis of potential connectivity between soil and extractive wastes has been conducted and the industrial potential of rare earth element recovery from quarry extractive wastes has been discussed.  Based on the trace element results, the potential environmental risks of soil and extractive waste has also been evaluated. The manuscript, in general, is well-written and the topic of the manuscript fits the scope of the journal.

Comments:

--- line 195: authors should give more information about the digestion, namely the concentration of acids and the relative ratio of acids in the acid mixture. It is also essential to provide information how the digestion was performed (hot plate stirring, microwave digestion, etc...; temperature and time).

--- line 196: it would be worth to state that REEs were quantified using ICP-MS; transition metals can be quantified using either ICP-OES or ICP-MS, please state how you have performed your analysis (this will indicate the expected limit of detection).

--- 3.1. Mineralogical and petrographical characterization: authors should comment that XRPRD analysis provided the relative mineral content of crystalline phases. They may indicate this in the title of ordinate in Figure 3 as “Content of crystalline phases”. Authors may note the amorphous phase content of investigated materials in the text if they have information about it (if no amorphous phase present, please comment).

--- lines 195-196, 274-279: numbers in formulas of compounds should be in subscript.

--- line 486: please check and correct the formula (remove “strange” characters).

--- Authors should follow the referencing style of the journal. Please correct accordingly.

--- English of the manuscript, in general, is good and understandable; final reading of the text, however, is required to eliminate typing mistakes; for example, “are” is missing in the sentence in line 52.

Comments on the Quality of English Language

English of the manuscript, in general, is good and understandable; final reading, however, is required to eliminate typing mistakes. 

Author Response

Dear Reviewer,

Thank you for taking the time to review our manuscript. Your comments and suggestions have significantly enhanced the quality of the paper. Please note that all corrections and variations in the manuscript are indicated in red.

 

--- line 195: authors should give more information about the digestion, namely the concentration of acids and the relative ratio of acids in the acid mixture. It is also essential to provide information how the digestion was performed (hot plate stirring, microwave digestion, etc...; temperature and time).

Dear Reviewer,

Thank you for your comments. In response to your question, a statement has been added to the manuscript. Should you require more details, please note that we are currently awaiting additional information from the external laboratory that conducted the analysis.

 

--- line 196: it would be worth to state that REEs were quantified using ICP-MS; transition metals can be quantified using either ICP-OES or ICP-MS, please state how you have performed your analysis (this will indic

Thank you for your comments. In response to your question, a statement has been added to the manuscript. Should you require more details, please note that we are currently awaiting additional information from the external laboratory that conducted the analysis.

 

--- 3.1. Mineralogical and petrographical characterization: authors should comment that XRPRD analysis provided the relative mineral content of crystalline phases. They may indicate this in the title of ordinate in Figure 3 as “Content of crystalline phases”.

Dear reviewer, Thank you for your comment. The title of ordinate in Figure 3 has been changed as “Content of crystalline phases”

 

--- Authors may note the amorphous phase content of investigated materials in the text if they have information about it (if no amorphous phase present, please comment).

Dear Reviewer, thank you for your comment. These are samples of magmatic and metamorphic silicatic rocks, the presence of an amorphous phase is unlikely, and also there is no evidence from diffraction spectra. Therefore, it is assumed that the samples consist entirely of crystalline phases. In this regard, a short sentence from the text is added.

 

--- lines 195-196, 274-279: numbers in formulas of compounds should be in subscript.

Dear reviewer, we agree with your comment. we have checked and corrected all subscripts in the formula of compounds.

 

--- line 486: please check and correct the formula (remove “strange” characters).

Dear reviewer, thank you for your observation: the formula has been updated accordingly.

 

--- Authors should follow the referencing style of the journal. Please correct accordingly.

Dear Reviewer, thank you for your comment: the referencing style have been correct accordingly to the journal indication.

 

--- English of the manuscript, in general, is good and understandable; final reading of the text, however, is required to eliminate typing mistakes; for example, “are” is missing in the sentence in line 52.

Dear reviewer, thanks for your comment. The entire manuscript has been checked and corrected accordingly.

 

Comments on the Quality of English Language

English of the manuscript, in general, is good and understandable; final reading, however, is required to eliminate typing mistakes. 

Dear reviewer, thanks for your comment. The entire manuscript has been checked and corrected accordingly.

 

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

N/A