Batch Flotation of Lithium-Bearing Slag—A Special Focus on the Phase Properties of Engineered Artificial Minerals for Enhancing the Recycling of End-of-Life Lithium-Ion Batteries
, Doreen Ebert 1, Ali Zgheib 2, Maximilian Fischer 2, Robert Möckel 1, Andreas Schmidt 2 and Martin Rudolph 1
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsI believe that the current status of this manuscript is not suitable for publication and requires significant modifications. Therefore, I recommend a “Major Revision.” The specific reasons are as follows:
- Authors need to check all the abbreviations in the text. If they use LIBs for lithium-ion batteries, it must be consistent throughout the text. Currently, both LIB and LIBs are used. Please revise this for uniformity.
- The introduction effectively highlights the importance of lithium recycling, but it would be better to focus more on the knowledge gap and objectives. What are the challenges in current recycling methods? What is the novelty of engineered artificial minerals and flotation techniques?
- In the introduction section, it would be helpful to mention some previous work on the flotation of lithium-ion batteries and compare those results with this study.
- Authors need to elaborate on the motivation and innovation of this work. There are existing publications that use different collectors and report higher performance in the flotation process. Please explain how this work differs and adds value.
- Authors need to clarify how this study advances existing research on engineered artificial minerals (EnAMs).
- Consider integrating summary tables (flotation results: Recovery and grade) to facilitate easier data interpretation.
- Authors need to include more details on experimental reproducibility. Were the experiments repeated to ensure reliability?.
- The discussion lacks a critical comparison with prior studies. Include references to similar flotation studies and elaborate on how your results align or differ from those findings.
- The conclusion is too long. Focus on actionable conclusions and avoid reiterating results. The authors should present the results point by point for better clarity.
Author Response
Comment 1: Authors need to check all the abbreviations in the text. If they use LIBs for lithium-ion batteries, it must be consistent throughout the text. Currently, both LIB and LIBs are used. Please revise this for uniformity.
Response 1: We appreciate your comment very much. Regarding the abbreviation we changed the text and consistently use LIBs (lithium-ion batteries) and screened further abbreviations.
Comment 2: The introduction effectively highlights the importance of lithium recycling, but it would be better to focus more on the knowledge gap and objectives. What are the challenges in current recycling methods? What is the novelty of engineered artificial minerals and flotation techniques?
Response 2: Thank you for this valuable comment. The focus of this work got adjusted in the introduction and formulates the novelty of our research concerning engineered artificial minerals and flotation techniques more concretely. In terms of lithium recycling we do not see the necessity include gap and objectives, since we focus on this one side product of pyrometallurgical recycling without comparing it to different LIBs recycling routes. This is not the aim of the studies.
Comment 3: In the introduction section, it would be helpful to mention some previous work on the flotation of lithium-ion batteries and compare those results with this study.
Response 3: We appreciate your comment very much but would like not to compare the flotation of Lithium bearing EnAMs found in the pyrometallurgic recycling route of Lithium Ion Battery Recycling to the froth flotation of black mass as this lacks comparison. As you may see we have various publications in the field of black mass flotation (not cited here) and do not see the point in comparing such EnAM phases with the LMOs and Graphite (plus binders) found in the non-pyrometallurgical recycling routes.
Comment 4: Authors need to elaborate on the motivation and innovation of this work. There are existing publications that use different collectors and report higher performance in the flotation process. Please explain how this work differs and adds value.
Response 4: We have concretized the reference to the best of our knowledge, only comparable study by our colleagues at TU Clausthal (by Qiu, H. et al.). This is now mentioned in the revised introduction.
Comment 5: Authors need to clarify how this study advances existing research on engineered artificial minerals (EnAMs).
Response 5: Thanks for this constructive suggestion. We have thoughtfully adjusted the introduction to clarify this very important point.
Comment 6: Consider integrating summary tables (flotation results: Recovery and grade) to facilitate easier data interpretation.
Response 6: Thanks for this helpful recommendation. We have included a table of grade and recovery into the appendix to help data interpretation.
Comment 7: Authors need to include more details on experimental reproducibility. Were the experiments repeated to ensure reliability?
Response 7: We appreciate your valuable comment very much. To include relevant details on experimental reproducibility of flotation experiments the text got adjusted in line 168-170. Furthermore, reproducibility of experiments got elaborated in line 184-185, 207-211 and 219-221. More in detail, the reliability of results related to MLA experiments, was ensured by using at least 200,000 evaluated particles per processing product achieved with the according reagent combination. Each processing product contained merged samples of concentrates of three repetitions within each reagent combination.
Comment 8: The discussion lacks a critical comparison with prior studies. Include references to similar flotation studies and elaborate on how your results align or differ from those findings.
Response 8: Thank you for this constructive suggestion. We have thoughtfully adjusted the discussion to clarify this very important point. As we mentioned earlier, the only comparable study is by our colleagues at TU Clausthal (by Qiu, H. et al.). This is considered in the paper as a reference and differences to this study were pointed out where relevant, e.g. that we have used different reagents and also different evaluations to draw conclusions from the separation, or that a flotation column set-up had been used instead of a rotor-stator system.
Comment 9: The conclusion is too long. Focus on actionable conclusions and avoid reiterating results. The authors should present the results point by point for better clarity.
Response 9: Thanks for this helpful recommendation. We have thoughtfully adjusted the conclusion to clarify this very important point. We have significantly made it more precise and hope thus more readable. Also the conclusions are now titled “conclusions and outlook”.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsA novel collector, punicine, was used with a focus on recovering Li-aluminate materials in pyrometallurgical slags. It is an interesting task for advancing lithium recovery to make a sustainable LIB recycling. However, the manuscript can not be accepted for the following major issues.
1. In the literature review, The authors believe that there is a lack of research involving the flotation method in the field of lithium electrode material recovery. This situation shows that the authors do not understand the current research status of spent lithium electrode material recovery. Please check articles written by Sabereh Nazari and other researchers.
2. Is it suitable for authors of the manuscript to use tap water as experimental water for laboratory flotation test? There are uncontrollable miscellaneous ions such as calcium and magnesium in tap water, and they can have a potential impact on the flotation results. Did the author consider this factor? Have the miscellaneous ions in tap water been instrumental analyzed?
3. In the actual use of lithium-ion batteries, due to the charge and discharge of the battery, the electrolyte erosion, the influence of the binder, and so on. The surface of the electrode material of spent lithium-ion batteries may produce a series of side reactions. At the same time, the organic cover will exist on the surface of the electrode materials. These factors have a huge impact on the black mass flotation of spent lithium-ion batteries. In this manuscript, the authors use the synthetic materials rather than actual materials for flotation test, so the results are not strong to guide application.
4. The mechanism for the suitability of punicine as a flotation collector for Li-aluminate is still not clear by the research, nor scientific findings are disclosed after this study. It is a necessity of a fundamental study or/and an evidence of Instrument analysis to prove the suitability.
5. There are some other errors in the text, such as spelling errors, e.g. model-modal, monoplural grammar errors. The coordinates in the figures are not indicated, e.g. Fig.6, and so on.
Comments on the Quality of English LanguageThere are some other errors in the text, such as spelling errors, e.g. model-modal, monoplural grammar errors.
Author Response
A novel collector, punicine, was used with a focus on recovering Li-aluminate materials in pyrometallurgical slags. It is an interesting task for advancing lithium recovery to make a sustainable LIB recycling. However, the manuscript can not be accepted for the following major issues.
Comment 1: In the literature review, The authors believe that there is a lack of research involving the flotation method in the field of lithium electrode material recovery. This situation shows that the authors do not understand the current research status of spent lithium electrode material recovery. Please check articles written by Sabereh Nazari and other researchers.
Response 1: We do understand where the confusion comes from and believe that unfortunately, the reviewer was confused by the many studies on flotation of Lithium Ion Battery black mass materials, which we certainly also have done a lot of work in our labs for a while. This study belongs to a set of collective papers on slag processing and so called engineered artificial minerals found in the slags which can be influenced by slag thermodynamics and the processed by means of miner mineral processing including froth flotation. In the literature review on flotation, the authors focused on lithium aluminate, eucryptite and gehlenite as known prominent components of Li-bearing slags and slag materials in general. These minerals are not to be confused with lithium electrode materials available in mechanically recycled LIBs. Since these engineered artificial minerals are formed after melting and oxidizing LIBs in a furnace and cooled down the melt again. Although, one phase Li2MnSiO4 was detected via XRD in the used slag, which is known to be a cathode material this is not a study on black mass beneficiation. We hope that the various changes made in the course of revising the manuscript avoid further confusion.
Comment 2: Is it suitable for authors of the manuscript to use tap water as experimental water for laboratory flotation test? There are uncontrollable miscellaneous ions such as calcium and magnesium in tap water, and they can have a potential impact on the flotation results. Did the author consider this factor? Have the miscellaneous ions in tap water been instrumental analyzed?
Response 2: Since this study is applying macro scale flotation tests (200 ml) due to the restricted material availability as a preliminary stage for large industrial batch flotation tests, tap water was used to allow the comparability to industrial conditions. In order to ensure the reproducibility of all experiments, the water used for experiments was taken from a 40 l sample of tap water taken from the tap in one day. We have indeed forgotten to mention the source of the tap water (Helmholtz Institute Freiberg, Germany), and corrected it, but it is a common practice in flotation research to use tap water and refer to the source of the tap water, since then the quality of the tap water is given by the municipal water sources which is controlled across Europe and publicly accessible data.
Comment 3: In the actual use of lithium-ion batteries, due to the charge and discharge of the battery, the electrolyte erosion, the influence of the binder, and so on. The surface of the electrode material of spent lithium-ion batteries may produce a series of side reactions. At the same time, the organic cover will exist on the surface of the electrode materials. These factors have a huge impact on the black mass flotation of spent lithium-ion batteries. In this manuscript, the authors use the synthetic materials rather than actual materials for flotation test, so the results are not strong to guide application.
Response 3: Very likely this is now clear after our response to the first comment from the reviewer. This study is not on black mass from the non-pyrometallurgic processing of lithium ion batteries. During the pyrometallurgical process, batteries are processed in a molten bath furnace at temperatures of 1600°C – 1700°C, where binders and graphite are oxidized or acting as reductants in carbothermal reactions and thus react to CO2 amongst other products of these reactions. Additionally, due to the melting process, the original phases of the electrode materials are no longer preserved. Side reactions in slag processing, such as ion solvation or redox processes of slag materials, are not considered in this study but will be addressed in future research.
Indeed, the study uses synthetic slags rather than actual slags for flotation tests, meaning it can only support the future understanding of real slag systems. However, it can reveal the flotation behavior of engineered artificial minerals in terms of grain size, liberation characteristics, and composition. The goal of the research is to better understand the flotability of these engineered artificial minerals.
Comment 4: The mechanism for the suitability of punicine as a flotation collector for Li-aluminate is still not clear by the research, nor scientific findings are disclosed after this study. It is a necessity of a fundamental study or/and an evidence of Instrument analysis to prove the suitability.
Response 4: Thank you for the valid comment, which is why the authors state in their conclusion that further fundamental investigations are necessary to confirm the suitability of punicine as a collector specifically for Li-aluminate. Our research presents the first successful application of punicine in the macroscale flotation of Li-aluminate, as part of a synthetic slag—an approach that has never been tested before. This study expands the understanding of punicine, which was previously only known for single mineral microflotation.
Comment 5: There are some other errors in the text, such as spelling errors, e.g. model-modal, monoplural grammar errors. The coordinates in the figures are not indicated, e.g. Fig.6, and so on.
Response 5: Thank you for the comment. One will find the word “modal”, it is connected to “modal mineralogy” and sometimes referred to as “modal composition” or “modal content”, e.g. in line 245 and 249. Modal mineralogy/modal composition/ modal content refers to the quantitative description of the mineral composition of a rock, expressed as area % or mass/wt % percentages of each mineral present. In contrast to normative mineralogy, which calculates an idealized mineral composition based on chemical data, modal mineralogy represents the actual observed mineral content of a rock, here determined via mineral liberation analysis. It is widely used in geology, petrology, and planetary science to classify rocks and understand their formation and history.
Thank you for the helpful comment about Fig. 6, the coordinates were added and additionally, the coordinates were thoroughly checked in all figures.
Comments on the Quality of English Language
Comment 6: There are some other errors in the text, such as spelling errors, e.g. model-modal, monoplural grammar errors.
Response 6: Thank you for that helpful comment. In order to reduce the grammatical monoplural errors the text was screened for those.
Reviewer 3 Report
Comments and Suggestions for AuthorsThe paper “Batch flotation of lithium-bearing slag – A special focus on phase properties of engineered artificial minerals for enhanced recycling of end-of life lithium ion batteries” is very interesting and contains many experimental and analytical results. The authors presented their research results in detail. The manuscript was carefully prepared, with a thorough literature review and a thorough analysis of the research results. The paper is well structured and the results are clearly presented. The topic of the paper is of interest to mineral processing. In terms of editing the paper, I propose to correct the bibliographic record (names and initials of the authors) in the literature in references 14 and 33.
Author Response
Comment 1: The paper “Batch flotation of lithium-bearing slag – A special focus on phase properties of engineered artificial minerals for enhanced recycling of end-of life lithium ion batteries” is very interesting and contains many experimental and analytical results. The authors presented their research results in detail. The manuscript was carefully prepared, with a thorough literature review and a thorough analysis of the research results. The paper is well structured and the results are clearly presented. The topic of the paper is of interest to mineral processing.
Response 1: Thank you very much for this positive feedback to our manuscript.
Comment 2: In terms of editing the paper, I propose to correct the bibliographic record (names and initials of the authors) in the literature in references 14 and 33.
Response 2: Thank you very much for this valuable input, we corrected the references 14 and 33 according to the reference list.
Reviewer 4 Report
Comments and Suggestions for AuthorsDear Authors!
A paper on flotation of lithium-containing slags is submitted for review. At the moment the topic is relevant and will be of interest to readers.
The abstract of the paper contains necessary information about the information that is presented in the paper. The authors should replace the term using the German word “zwitter” for collector with an English term, maybe “amphoteric”. The use of the term “switchable” collector is noted in the keywords. This term is then used in the Introduction section. It is worth bringing the terms used to the same form.
The “Introduction” section contains information about previous research in the field. The authors should remove the pronouns “we” from the text and replace them with the passive voice. (line 46 and line 98).
At the end of the introduction section, the purpose of the study should be clearly stated. To make it clear to all readers what the authors want to achieve.
In the materials and methods section, the characteristics of the research object and research methods are given.
However, there are a few comments:
The equipment used for grinding is not specified;
Grinding parameters are not specified;
It is worth clarifying what is a sieve ball mill? Does it mean a planetary ball mill?
The authors should add an explanation of the choice of solid content in flotation (11 %).
The results and discussion sections are accompanied by good quality figures, supplemented by a discussion of the results.
In Figure 8, why did the authors choose to arrange the parameters in this way on the axes? As a recommendation, for convenience of understanding the graphs it would be worth to change places of X and Y axes.
The conclusion contains the necessary conclusions on the work.
The paper is recommended for acceptance after minor revision.
Author Response
Dear Authors!
A paper on flotation of lithium-containing slags is submitted for review. At the moment the topic is relevant and will be of interest to readers.
Comment 1: The abstract of the paper contains necessary information about the information that is presented in the paper. The authors should replace the term using the German word “zwitter” for collector with an English term, maybe “amphoteric”.
Response 1: We appreciate your comment very much. The term zwitterionic is, as far as the authors know, an applied term in English within Chemistry, can also be found on Wikipedia and is in alignment with publications of the Co-authors group studying and synthesizing the molecule punicine, e.g. [17] Zgheib, A.; Acker, S.; Fischer, M.H.; Namyslo, J.C.; Strube, F.; Rudolph, M.; Fittschen, U.E.; Wollmann, A.; Weber, A.P.; Nieger, M. Lithium Aluminate Flotation by PH-and Light-Switchable Collectors Based on the Natural Product Punicine. RSC Adv. 2024, 14, 9353–9364, doi:10.1039/d4ra00116h. The word amphoteric indeed is often used in the field of ionic surfactants to refer to zwitterionic surfactants but amphoteric by meaning of the word also refers to chemical substances with other two interchangeable properties (c.f. Amphoterism in acids and base). Therefore, we would like to keep the terminology.
Comment 2: The use of the term “switchable” collectoris noted in the keywords. This term is then used in the Introduction section. It is worth bringing the terms used to the same form.
Response 2: Thank you for this valuable comment. The term switchable is used to not only show the amphoteric behavior of the molecule as amphoteric surfactant depending on pH, but also to state the switchability of the radical state of the molecule with the exposure of light. We have clarified pH responsive switchability of the zwitterionic surfactant and photo-switchability in the manuscript in line 98.
Comment 3: The “Introduction” section contains information about previous research in the field. The authors should remove the pronouns “we” from the text and replace them with the passive voice. (line 46 and line 98).
Response 3: Thank you for this valid comment, authors removed direct voice from the mentioned line 46 and 98. For instance, line 46 got adjusted into: “In this contribution, we present a novel approach that involves the beneficiation of slag residues obtained from the pyrometallurgical recycling of LIBs is presented.” Furthermore, the entire script got screened for any occurrence of the direct voice and got removed.
Comment 4: At the end of the introduction section, the purpose of the study should be clearly stated. To make it clear to all readers what the authors want to achieve.
Response 4: Thank you for pointing this out and we hope that the various changes we made in the introduction allows to grasp the purpose now clearly.
In the materials and methods section, the characteristics of the research object and research methods are given.
However, there are a few comments:
Comment 5: The equipment used for grinding is not specified;
Response 5: We appreciate your comment very much. We changed the name of the sieve ball mill manufactured at the FIA research institute of the former GDR to the screen discharge ball mill which is more commonly found in literature (FIA, Thomas Leißner publication).
Comment 6: Grinding parameters are not specified;
Response 6: Thank you for the comment, we have added information on the grinding parameters for the jaw crusher and the screen discharge ball mill.
Comment 7: It is worth clarifying what is a sieve ball mill? Does it mean a planetary ball mill?
Response 7: We understand the confusion and apologize. As seen above we have used now the more common term of this equipment, which is used quite broadly around the former mineral processing research institute FIA of the former GDR in Freiberg, Germany.
Comment 8: The authors should add an explanation of the choice of solid content in flotation (11 %).
Response 8: Thanks for bringing this up, we have added an explanation to the choice of the rather low pulp density in line 154-158 and hope now to better clarify our considerations.
The results and discussion sections are accompanied by good quality figures, supplemented by a discussion of the results.
Comment 9: In Figure 8, why did the authors choose to arrange the parameters in this way on the axes? As a recommendation, for convenience of understanding the graphs it would be worth to change places of X and Y axes.
Response 9: Thank you for your valid comment. The Halbich upgrading curve definition is introduced by Halbich in 1934 plotting recovery against grade. We have added a relevant publication from Drzymala in the references (c.f Drzymala, J. Physochcemical Problems in Mineral Processing 41 (2006): 27-35.) For a better understanding and better accuracy, we changed the upgrading curve to normalized Halbich upgrading curves, plotting recovery against the enrichment factor.
The conclusion contains the necessary conclusions on the work.
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsI agree for the publication of this manuscript.
Reviewer 2 Report
Comments and Suggestions for AuthorsThe authors have done a major revise on the original version. And I can accept the reply to my questions. It can be accepted in this format.
