Study on Extraction of Gallium from Fly Ash by Sodium Fluoride Calcination-Organic Acid Leaching
, Changzhi Su 1, Huan Li 1, Qiushuang Cui 1, Wen Liu 1, Hanyu Wei 1 and Yi Si 3Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsIn the Manuscript entitled “Study on extraction of precious metals from fly ash by sodium fluoride calcination-organic acid leaching” the authors optimized the extraction process of Gallium from fly ash in an eco-friendly manner. The idea is very interesting, the study is detailed, i.e. a lot of experiments were performed in order to fully optimize extraction process. The discussion is generally appropriate and gave the right explanation for obtained results. Although the overall merit is good, there are some concerns the authors need to address before Manuscript can be accepted.
1. The Manuscript title is “Study on extraction of precious metals from fly ash by sodium fluoride calcination-organic acid leaching”. Why did authors use the term “precious metals” while the study was only focused on Ga?
2. Why did the authors choose a corundum (Al2O3) crucible considering the chemical composition of the FA? I recommend using a zirconia crucibles to avoid problems such as crucible adhesion which occurred in some of experiments (lines 239-240).
3. Instead of DI use DI water. DI is not precise enough.
4. Line 130: The phrase “After complete elimination…” is not clear. What elimination? Please, rephrase to be more understandable to readers.
5. Lines 158-160: “The FA was also found to contain irregular debris, agglomerates, and fragments of microspheres, where glass and mullite were wrapped around one another. This combination was very detrimental to the extraction of Ga.” It would be interesting if authors could expand this explanation. Why is such a combination detrimental to extraction of Ga?
6. I recommend moving the paragraph which explains Figure 9 (and figure 9) before Figure 5 and corresponding discussion about it.
7. Line 177; Figures 2a and 4b: “the intensity of the mullite diffraction peaks is greatly reduced”. It is not clearly visible in comparison to Figure 2a since the all mullite peaks is not assigned. In figure 2a the only mullite peak assigned is in the region between 30-40 2θ [°] while in figure 5b the only assigned peak is at ≈50 2θ [°].
8. Line 183: Authors should define ideal leaching conditions (for example in brackets) to be more precise in spite of defining them further in the text.
9. Lines 194-195; Figure 6: “To investigate the impact of roasting temperature on Ga leaching rate in the temperature range of 500~900 °C…”. In the Figure 6c roasted clinker at 900 °C is presented but in other figures 6a,b,c there are no data for sample at 900 °C. Authors must show this data or be more precise in sentence and figure 6c if there is an error. For example: To investigate the impact of roasting temperature on Ga leaching rate in the temperature range of 550-850 °C…
10. Lines 217-220: “The FA baked clinker produced by the reaction between FA and NaF at 850 °C is difficult to dissolve in C6H8O7, which is unfavorable for the subsequent acid leaching experiments, resulting in a significant decrease in the Ga leaching rate, so 850 °C is chosen as the optimal roasting temperature.” The sentence is completely unclear, authors need to rephrase it.
11. Lines 229-231: “Figure 7 229 (b) XRD results show that when the FA/NaF ratio is 1:0, the roasted clinker consists primarily of quartz (SiO2), calcium fluoride (CaF2), and calcium sulfate (CaSO4)…”. It is not possible to find calcium fluoride (CaF2) under such conditions which is in accordance with Figure 7.
12. Lines 251-254: “The analysis of Figure 8 (b) shows that the diffraction peaks of Nepheline facies and lapis lazuli phases in FA clinker are strongest when the roasting time is 10 minutes, and the intensities of the diffraction peaks of easily dissolved Nepheline facies and lapis lazuli phases gradually weaken as the reaction time increases.” The reduction of nepheline phase with increasing reaction time is not clearly seen from Figure 8b.
13. Figure 10a: Authors must show data for all investigated concentrations (1.75 mol/L to 4 mol/L).
14. Lines 298-234: This explanation requires further justification. First of all, the data in Figure 10a is not complete. Furthermore, the difference between acid concentrations in the 0.75-2.5 mol/L was negligible.
15. Line 318: There are Chinese letters in the formula.
16. Authors need to emphasize more the significance of this interesting research throughout the Conclusions section.
Author Response
1.The Manuscript title is “Study on extraction of precious metals from fly ash by sodium fluoride calcination-organic acid leaching”. Why did authors use the term “precious metals” while the study was only focused on Ga?
Response: Dear reviewer: We have carefully considered your suggestion to change the title of the paper to “Study on the Extraction of Scattered Metal Ga from Fly Ash by Sodium Fluoride Calcination-Organic Acid Leaching Method”. We began the experiment by quantitatively analyzing the fly ash at 102 Mission Power Plant in Xinjiang Uygur Autonomous Region, China, using inductively coupled plasma mass spectrometry (ICP-MS), and the results were as follows:
|
Symbol of element |
Content (mg/kg) |
|
Ge |
4 |
|
Ga |
73 |
|
In |
＜1 |
|
Ti |
＜1 |
|
Se |
＜1 |
|
Te |
＜1 |
The industrial grade of Ga is 33 mg/kg. The concentration of Ga in this fly ash meets the extraction standard, and Ga is more useful for extraction than other scattered metals.
2.Why did the authors choose a corundum (Al2O3) crucible considering the chemical composition of the FA? I recommend using a zirconia crucibles to avoid problems such as crucible adhesion which occurred in some of experiments (lines 239-240).
Response: NaF is highly chemically active, and while ZrOâ‚‚ is rather stable, the fluoride ion has a significant coordination ability. High temperature calcination may cause F- to coordinate with Zr4+, resulting in corrosion damage to the ZrOâ‚‚ crucible (ZrOâ‚‚ + 4NaF → Naâ‚„ZrF₈). Because sodium fluoride and alumina do not normally react, the experiment was carried out in an alumina crucible.
3.Instead of DI use DI water. DI is not precise enough.
Response: Dear Reviewer: Thank you for pointing out that our use of the term "DI" to refer to deionized water is imprecise. We thoroughly verified and rewrote the paper, replacing all references to "DI" with "deionized water".
4.Line 130: The phrase “After complete elimination…” is not clear. What elimination? Please, rephrase to be more understandable to readers.
Response: Dear Reviewer: In answer to your question, we recognize that the original formulation may generate ambiguity or difficulty in understanding, and we will update that section of the manuscript.
5.Lines 158-160: “The FA was also found to contain irregular debris, agglomerates, and fragments of microspheres, where glass and mullite were wrapped around one another. This combination was very detrimental to the extraction of Ga.” It would be interesting if authors could expand this explanation. Why is such a combination detrimental to extraction of Ga?
Response: Dear reviewers:In response to the issues you mentioned, we have reorganized our thinking and optimized it in the manuscripts.
6.I recommend moving the paragraph which explains Figure 9 (and figure 9) before Figure 5 and corresponding discussion about it.
Response: Dear Reviewer: We changed the sequence of the figures in the manuscripts based on your suggestions, moving Figure 9 before Figure 5, and thoroughly revising and improving the accompanying figure annotations and related manuscript sections.
7.Line 177; Figures 2a and 4b: “the intensity of the mullite diffraction peaks is greatly reduced”. It is not clearly visible in comparison to Figure 2a since the all mullite peaks is not assigned. In figure 2a the only mullite peak assigned is in the region between 30-40 2θ [°] while in figure 5b the only assigned peak is at ≈50 2θ [°].
Response: Changes have been made to this section in the manuscript.
8.Line 183: Authors should define ideal leaching conditions (for example in brackets) to be more precise in spite of defining them further in the text.
Response: The optimal acid leaching process parameters have been labeled in the manuscript.
9.Lines 194-195; Figure 6: “To investigate the impact of roasting temperature on Ga leaching rate in the temperature range of 500~900 °C…”. In the Figure 6c roasted clinker at 900 °C is presented but in other figures 6a,b,c there are no data for sample at 900 °C. Authors must show this data or be more precise in sentence and figure 6c if there is an error. For example: To investigate the impact of roasting temperature on Ga leaching rate in the temperature range of 550-850 °C…
Response: Changes have been made to this section in the manuscript.
10.Lines 217-220: “The FA baked clinker produced by the reaction between FA and NaF at 850 °C is difficult to dissolve in C6H8O7, which is unfavorable for the subsequent acid leaching experiments, resulting in a significant decrease in the Ga leaching rate, so 850 °C is chosen as the optimal roasting temperature.” The sentence is completely unclear, authors need to rephrase it.
Response: Changes have been made to this section in the manuscript.
- Lines 229-231: “Figure 7 229 (b) XRD results show that when the FA/NaF ratio is 1:0, the roasted clinker consists primarily of quartz (SiO2), calcium fluoride (CaF2), and calcium sulfate (CaSO4)…”. It is not possible to find calcium fluoride (CaF2) under such conditions which is in accordance with Figure 7.
Response: Changes have been made to this section in the manuscript.
- Lines 251-254: “The analysis of Figure 8 (b) shows that the diffraction peaks of Nepheline facies and lapis lazuli phases in FA clinker are strongest when the roasting time is 10 minutes, and the intensities of the diffraction peaks of easily dissolved Nepheline facies and lapis lazuli phases gradually weaken as the reaction time increases.” The reduction of nepheline phase with increasing reaction time is not clearly seen from Figure 8b.
Response: Changes have been made to this section in the manuscript.
13.Figure 10a: Authors must show data for all investigated concentrations (1.75 mol/L to 4 mol/L).
Response:Thank you for bringing to our attention this critical data processing issue, and we sincerely regret for the error, which was caused by an oversight in our data processing procedure.The real concentration of C6H8O7 was increased from 1.75 to 2.5 mol/L, not 4 mol/L. The pertinent sections of the manuscript have undergone changes.
14.Lines 298-234: This explanation requires further justification. First of all, the data in Figure 10a is not complete. Furthermore, the difference between acid concentrations in the 0.75-2.5 mol/L was negligible.
Response:Corresponding parts have been revised and explained.
15.Line 318: There are Chinese letters in the formula.
Response: Changes have been made to this section in the manuscript.
16.Authors need to emphasize more the significance of this interesting research throughout the Conclusions section.
Response: Changes have been made to this section in the manuscript.
Reviewer 2 Report
Comments and Suggestions for AuthorsUpon evaluating of the submitted manuscript, I have determined that, while it introduces an innovative method for gallium extraction, utilizing industrial waste—fly ash, to achieve efficient resource utilization and environmentally friendly protection. However, it still requires further enhancement and refinement in terms of its innovation, language expression, research methodology and approach, so it requires minor revisions to meet the publication standards. Throughout the review process, I have identified several perspectives within the manuscript:
1. Innovation Aspect: Enhance comparative evaluations with other extraction methods, including cost-benefit analysis and environmental impact assessments. Discuss potential issues, challenges, and industrialization potential of the proposed method in practical applications.
2. Language Clarity: Simplify sentence structures, such as those in lines 51 to 54 of the introduction, to improve readability.
3. Research Scope: Expand research horizons by exploring extraction methods and application prospects for other valuable metal elements in fly ash. Deepen the analysis and discussion of experimental data.
4. Research Methodology: While the experimental procedures and methods are described in detail, insufficient explanations are provided for the selection and optimization of certain experimental parameters. For instance, the rationale behind choosing 850°C as the calcination temperature and the 1:0.5 ratio of fly ash to sodium fluoride remains unclear.
5. Research Conclusion: In the outlook section, include discussions on potential problems and challenges in practical applications. Emphasize the advantages and potential value of the method in the resource utilization of fly ash.
Author Response
1.Innovation Aspect: Enhance comparative evaluations with other extraction methods, including cost-benefit analysis and environmental impact assessments. Discuss potential issues, challenges, and industrialization potential of the proposed method in practical applications.
Response: Thank you for your valuable comments and we have discussed the issues you raised accordingly.
- Language Clarity: Simplify sentence structures, such as those in lines 51 to 54 of the introduction, to improve readability.
Response:Thank you for your valuable comments, we have simplified the statements in the corresponding sections.
3.Research Scope: Expand research horizons by exploring extraction methods and application prospects for other valuable metal elements in fly ash. Deepen the analysis and discussion of experimental data.
Response:Thank you for your valuable comments, we have revised the content accordingly.
4.Research Methodology: While the experimental procedures and methods are described in detail, insufficient explanations are provided for the selection and optimization of certain experimental parameters. For instance, the rationale behind choosing 850°C as the calcination temperature and the 1:0.5 ratio of fly ash to sodium fluoride remains unclear.
Response:The experiment was designed as a one-factor experiment, allowing the parameters influencing gallium metal extraction (roasting temperature, mixing ratio, and roasting time) to be studied separately.Change one variable at a time, leaving the other circumstances constant. This clearly determines the effect of each factor separately on the success of gallium extraction and prevents interference when numerous factors are varied concurrently, making the study's conclusions more precise and dependable.Multiplexing the best parameters prevents repeated study of previously researched components in fresh studies.As a result, in the single-element experimental investigation of the roasting temperature, the ratio of FA to NaF and the roasting time were strictly controlled, and it was concluded that 850℃ was the optimal roasting temperature, with the optimal roasting temperature parameter being reused in the single-element experimental investigation of the FA to NaF ratio.
5.Research Conclusion: In the outlook section, include discussions on potential problems and challenges in practical applications. Emphasize the advantages and potential value of the method in the resource utilization of fly ash.
Response:Thank you for your valuable comments, we have made changes in the Conclusion and Outlook section.
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsGenerally, the authors did a great job and addressed the most of my concerns. The manuscript can be accepted after some minor changes.
1. I still recommend to change title. The term “precious metals” in plural form is definitely not precise enough. The proper title would be “Study on extraction of gallium from fly ash by sodium fluoride calcination-organic acid leaching”.
2. Line 254: “calcium hematite (Fe2O3)”. Remove calcium.
Author Response
#Review 3:
- I still recommend to change title. The term “precious metals” in plural form is definitely not precise enough. The proper title would be “Study on extraction of gallium from fly ash by sodium fluoride calcination-organic acid leaching”.
Response: Dear reviewers, thank you very much for your valuable suggestion to revise the title. We have carefully considered and revised the topic based on your suggestions and thank you again for your professional guidance!
- Line 254: “calcium hematite (Fe2O3)”. Remove calcium.
Response: Dear reviewer, I am very sorry that due to our sloppiness, we have made such obvious mistakes in the paper, which has caused great disturbance to your review work, and I feel deeply guilty about it. We have reflected deeply on this error and revised the manuscript, and thank you again for your seriousness and careful guidance.
