Recovery of Residual Lead from Automotive Battery Recycling Slag Using Deep Eutectic Solvents
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe article is very promising from a sustainability and green chemistry perspective, with significant potential for exploration. This topic is of great interest due to its relevance to environmental management and the use of more environmentally friendly chemical processes. However, I consider making some improvements to your work
Observations:
1) The authors could clarify or provide in-depth explanations of the mechanisms involved in lead recovery using deep eutectic solvents. I believe that explaining and elucidating the chemical reactions that describe the process is essential to demonstrate the scientific contribution of the article.
2) How did the leaching recovery of lead vary at a temperature of 30°C for samples 1, 2, and 3 when using ethaline, glyceline, and reline as solvents? What factors contributed to these differences in leaching recovery?
3) How did the increase in temperature to 90°C affect the leaching recovery of lead for the three samples using ethaline, glyceline, and reline as solvents? Were there any variations in optimal leaching times at this higher temperature?
4) Finally, I suggest including a comparative table of your obtained results and results reported in the literature.
Comments on the Quality of English LanguageThe quality of the language used is appropriate and demonstrates clarity in presenting their results
Author Response
Bruna SALGADO GASPAR
Department of Extractive Metallurgy,
Escuela Politécnica Nacional,
Ladrón de Guevara E11-253,
Quito 170517, Ecuador
(+593) 99 057 43 52
To: Molecules Editorial Office Reviewer 1
MDPI
Quito, 9th November 2023
Dear Reviewer
I am writing to address your observations and suggestions in relation to the draft article “Recovery of Residual Lead from Automotive Battery Recycling Slag Using Deep Eutectic Solvents” that is currently under consideration for the Special Issue of Molecules-"Deep Eutectic Solvents: Properties and Applications as Green Solvents" on behalf of the researchers from the Department of Extractive Metallurgy at the Escuela Politécnica Nacional.
First and foremost, we would like to express our gratitude for your interest in our work. We acknowledge that this project holds significant importance to environmental management and to environmentally friendly chemical processes. To enhance the clarity of the revisions made, we will provide a concise explanation for each correction, point by point.
- The authors could clarify or provide in-depth explanations of the mechanisms involved in lead recovery using deep eutectic solvents. I believe that explaining and elucidating the chemical reactions that describe the process is essential to demonstrate the scientific contribution of the article.
In the “Materials and Methods” section, particularly in section 3.5, titled “Leaching Assays”, we have incorporated the chemical reactions (equations 1 and 2) that elucidate the dissolution mechanism of lead. In this context, hydrogen bonds play a crucial role in facilitating the dissociation of oxides and sulfates into lead cations and water or acid. Subsequently, these lead cations engage with chloride radicals, giving rise to the formation of lead tetrachloride ions. These tetrachloride species bear a negative charge and exhibit high solubility within this particular medium.
The changes are incorporated in lines 550-561 of the corrected version. See also 102-106.
- How did the leaching recovery of lead vary at a temperature of 30°C for samples 1, 2, and 3 when using ethaline, glyceline, and reline as solvents? What factors contributed to these differences in leaching recovery?
In the discussion of results corresponding to the leaching tests conducted at 30 oC, an observation has been included that the variations within the same range were almost negligible, particularly for samples 2 and 3. Additionally, it has been elucidated that the inefficiency of this process can be attributed to the insufficient energy available to break through the metal-oxygen or metal-sulfate bonds.
The changes are incorporated in lines 322-330 of the corrected version.
- How did the increase in temperature to 90°C affect the leaching recovery of lead for the three samples using ethaline, glyceline, and reline as solvents? Were there any variations in optimal leaching times at this higher temperature?
In the discussion of the results corresponding to the leaching tests conducted at 90°C, an important observation has been included. It highlights how the increase in temperature led to a significant reduction in the optimal leaching times by 2-3 hours compared to the previous tests carried out at 60°C. This effect was specific for the solvents glyceline and reline. On the other hand, longer duration periods were required when using ethaline as a solvent.
The changes are incorporated in lines 358-361 of the corrected version.
- Finally, I suggest including a comparative table of your obtained results and results reported in the literature.
We greatly appreciated this suggestion, and it has been duly incorporated at the end of the “Results and Discussion”' section. Through a comparative analysis of our work with similar studies available in the literature, it became evident that only a limited number have delved into the investigation of subsequent recovery processes from the resulting leaching solutions. This observation underscored the significance of our present study.
The changes are incorporated in lines 453-476 of the corrected version.
It is worth mentioning that all corrections or modifications have been highlighted with the Word tool to facilitate their recognition.
By means of this letter, I confirm that every correction and edition, was developed by the authors of this manuscript.
On behalf of the co-authors and myself, I thank you for helping to make this article better.
Yours Sincerely,
Bruna Salgado Gaspar
Master’s Degree Student at the Department of Extractive Metallurgy
Escuela Politécnica Nacional
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThis paper provides an interesting application of DES for the recovery of lead. However, the paper should further discuss some additional points to be accepted:
- Please, update your introduction section with the recent application of extraction of metal ions using DES. e.g. Authors can use these works for their intro section.
1) Deep eutectic solvents based assay for extraction and determination of zinc in fish and eel samples using FAAS
2) Deep eutectic solvent (DES) with silver nanoparticles (Ag-NPs) based assay for analysis of lead (II) in edible oils
- Make a clear description (a scheme could be perfect) about the interaction DES-lead for the successful recovery.
- Very important issue: After the interaction of the lead-DES, are there any complexes or new species taking place? An important point to be discussed.
- Please, declare the perspective of this study. We need to know the future developments in this field.
- Give the additional application of the recovered lead and the residual DES after the recovery process. We need to pay attention to the secondary species formed in the environment. Read: Deep eutectic solvents – Ideal solution for clean air or hidden danger?
Author Response
Bruna SALGADO GASPAR
Department of Extractive Metallurgy,
Escuela Politécnica Nacional,
Ladrón de Guevara E11-253,
Quito 170517, Ecuador
(+593) 99 057 43 52
To: Molecules Editorial Office Reviewer 2
MDPI
Quito, 9th November 2023
Dear Reviewer
I am writing to address your observations and suggestions in relation to the draft article “Recovery of Residual Lead from Automotive Battery Recycling Slag Using Deep Eutectic Solvents” that is currently under consideration for the Special Issue of Molecules-"Deep Eutectic Solvents: Properties and Applications as Green Solvents" on behalf of the researchers from the Department of Extractive Metallurgy at the Escuela Politécnica Nacional.
First and foremost, we would like to express our gratitude for your interest in our work. We acknowledge that this project holds significant importance to environmental management and to environmentally friendly chemical processes. To enhance the clarity of the revisions made, we will provide a concise explanation for each correction, point by point.
- Please, update your introduction section with the recent application of extraction of metal ions using DES.
We greatly appreciated this suggestion. Both articles, “Deep eutectic solvents based assay for extraction and determination of zinc in fish and eel samples using FAAS” and “Deep eutectic solvent (DES) with silver nanoparticles (Ag-NPs) based assay for analysis of lead (II) in edible oils” are now mentioned in the “Introduction” section.
These changes are incorporated in lines 141-152 of the corrected version.
- Make a clear description (a scheme could be perfect) about the interaction DES-lead for the successful recovery.
Instead of a scheme, we have incorporated more information about the working principle of DES in the “Introduction” section, specifically:
The working principle of DES consists of the available protons acting as oxygen acceptors and breaking the metal-oxygen bonds. Once the oxide is protonated, intermediate species are formed and can act as active sites for ligand complexation [22]. Another theory has been described where oxygen remains attached to the metal center and the hydrogen bond donors act as a ligands [23].
These changes are incorporated in lines 102-106 of the corrected version.
Additionally, in the “Materials and Methods” section, particularly in section 3.5, titled “Leaching Assays”, we have incorporated the chemical reactions (equations 1 and 2) that elucidate the dissolution mechanism of lead. In this context, hydrogen bonds play a crucial role in facilitating the dissociation of oxides and sulfates into lead cations and water or acid. Subsequently, these lead cations engage with chloride radicals, giving rise to the formation of lead tetrachloride ions. These tetrachloride species bear a negative charge and exhibit high solubility within this particular medium.
These changes are incorporated in lines 550-573 of the corrected version.
- Very important issue: After the interaction of the lead-DES, are there any complexes or new species taking place? An important point to be discussed.
As mentioned earlier, the primary species formed during the dissolution of lead is the tetrachloride ion. This information has already been incorporated into the article, as previously noted.
- Please, declare the perspective of this study. We need to know the future developments in this field.
In the “Conclusions” section, we have introduced insights into the next steps for advancing this research. These include:
- Exploring a range of different hydrogen bond donors (HBDs) or their combinations.
- Adjusting solvent pH.
- Variation in stirring speed.
- Evaluating alternative oxidizing agents.
- Optimizing the electrowinning process, focusing on cell voltage and current density.
- Investigating additional methods for metal recovery.
These changes are incorporated in lines 622-634 of the corrected version.
- Give the additional application of the recovered lead and the residual DES after the recovery process. We need to pay attention to the secondary species formed in the environment. Read: Deep eutectic solvents – Ideal solution for clean air or hidden danger?
At the end of the final “Conclusions” section, we have mentioned additional application for the recovered lead, emphasizing its reintroduction into the production process in alignment with the circular economy. Furthermore, we have proposed further investigations for the residual DES.
These changes are incorporated in lines 635-641 of the corrected version.
In the “Materials and Methods” section, particularly in section 3.5, titled “Leaching Assays”, we have incorporated information about potential effects of the proposed methodology on the environment. The HBD and HBA components used in the experiment are non-volatile, and the experimental conditions did not involve temperatures exceeding their respective boiling points. Consequently, there is no indication that the synthesis of these solvents poses a toxic risk.
However, during the leaching procedure, it's important to acknowledge that the presence of sulfate ions and an excess of H+ in the system increases the likelihood of acid formation. To address this issue, the need for further research has been emphasized.
These changes are incorporated in lines 562-573 of the corrected version. See also 124-140.
It is worth mentioning that all corrections or modifications have been highlighted with the Word tool to facilitate their recognition.
By means of this letter, I confirm that every correction and edition, was developed by the authors of this manuscript.
On behalf of the co-authors and myself, I thank you for helping to make this article better.
Yours Sincerely,
Bruna Salgado Gaspar
Master’s Degree Student at the Department of Extractive Metallurgy
Escuela Politécnica Nacional
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsThe authors attended properly the reviewers' comments. The paper is ready for acceptance.
