Forces During the Film Drainage and Detachment of NMC and Spherical Graphite in Particle–Bubble Interactions Quantified by CP-AFM and Modeling to Understand the Salt Flotation of Battery Black Mass

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

1. Abstract: In line 31, the author misspelled the word "floatation". The author should carefully check for other typo error.
2. Keywords: Abbreviations should be avoided, as some used in this paper are not commonly recognized.
3. Introduction: In line 36, it is unclear why "(thermo)-mechanical" includes parentheses. Moreover, the research gap is not clearly identified. The author also mentions "interaction" without summarizing the fundamental forces involved. Additionally, the practical implications of salt flotation should be further discussed.
4. Introduction: The objective of this manuscript is not clearly stated. Although it can be understood from the methodology, the author should clearly add the objective in the text.
5. Material and Methods: In line 155, the word "in" is unnecessarily repeated.
6. Results and Conclusion: The flotation test results were not presented in terms of recovery percentage. Although the author provided variables from which recovery can be calculated, presenting the results directly as recovery percentages would make it easier for readers to understand the process efficiency.

Comments on the Quality of English Language

There are the word with typo errors such as "floatation". The author should carefully check for other typo error.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

This study quantifies the forces during film drainage and detachment of NMC (nickel-manganese-cobalt oxide) and spherical graphite in particle-bubble interactions using colloidal probe atomic force microscopy (CP-AFM) and modeling, providing insights into the salt flotation mechanism for battery black mass separation. The work offers a theoretical foundation for efficient separation of NMC and graphite in battery recycling, highlighting the industrial potential of salt flotation as a reagent-free alternative. However, the following issues require resolution:

(1) The authors employed the SRYL model (Stokes-Reynolds-Young-Laplace) combined with CP-AFM experimental data to simulate particle-bubble interactions, but inadequately addressed the model’s applicability to complex surface topologies (e.g., NMC’s micro-scale irregularities). Recommend clarifying or demonstrating the validity of the SRYL model for non-ideal, rough particle surfaces (e.g., NMC) through theoretical justification or supplementary validation.

(2) The study only tested salt concentrations (1 mmol/L and 0.75 mol/L) under pH 3, pH 10, and buffer conditions, without covering broader pH or salinity ranges (e.g., pH 4–9). Suggest expanding experimental conditions to include intermediate pH values (e.g., pH 5–8) to comprehensively elucidate the flotation behavior of NMC and graphite.

(3) Although this is the first application of salt flotation for NMC-graphite separation in battery black mass, the authors did not explicitly highlight its practical advantages over conventional flotation (e.g., collector/frother addition). Recommend supplementing a techno-economic comparison between salt flotation and traditional flotation methods.

(4) The error margins (80% confidence interval) in AFM force-displacement curves (e.g., Figs. 6 and 8) are insufficiently visualized against theoretical models, and statistical distributions (e.g., standard deviation) of raw data are missing. Additionally, key parameters (e.g., contact angle, film thickness) in the bubble interface profile (Fig. 13) should be annotated to improve readability.

(5) The paragraph under the Results and Discussion section could be omitted. The content of Section 2.5 (Modeling of particle-bubble interactions) could be simplified.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

please see attached file

Comments for author File: Comments.pdf

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have revised the manuscript thoroughly and have effectively addressed all of the concerns I raised in my previous review. I appreciate the thoroughness of your responses and the clarity of the revised text.