Comparative Study of the Dissolution of LCO in HCl Medium with and without H₂O₂

Round 1

Reviewer 1 Report

This article presents a comparative study of the dissolution of LiCoO2 (LCO) from spent lithium-ion batteries under various conditions (acid and reducing agent concentration, temperature and reaction time). This is a highly relevant topic in the battery research literature and this study presents interesting results regarding one of the most common recycling procedures. The study methodology is sound and well formulated, the results clearly presented and the conclusions well supported by the results.

I would recommend publication with only a couple of general comments that I think it would be important to address:

1. The article is in general well written, but there are numerous instances where proofreading by a native English speaker would improve the text considerably.
2. A more detailed description of the methodology, especially regarding the preparation of the samples, would be important. In particular, since the samples come from different types of phones, what methods were used by the authors to ensure homogenization of the samples? And what was the post-dissolution treatment ahead of characterization (especially XRD and SEM)?

Author Response

Dear Reviewer

Hello, thank you for your comments. Below are the answers.

1. The article is in general well written, but there are numerous instances where proofreading by a native English speaker would improve the text considerably.

All spelling and grammar mistakes in the manuscript were revised. Moreover, the work was revised by a native English speaker.

2. A more detailed description of the methodology, especially regarding the preparation of the samples, would be important. In particular, since the samples come from different types of phones, what methods were used by the authors to ensure homogenization of the samples? And what was the post-dissolution treatment ahead of characterization (especially XRD and SEM)?

What methods were used by the authors to ensure homogenization of the samples?

Response

Then, the sample was homogenized at room temperature for 30 min, divided into three-time intervals of 10 min each, using a bar mill at 30 rpm. This paragraph was added to the new version of the manuscript, see lines 110 to 111.

What was the post-dissolution treatment ahead of characterization (especially XRD and SEM)?

Response

Before characterization by XRD and SEM, the residues from the leaching were washed with distilled water and dried in an oven at 348 K for 2 hours. Then, the residue is weighed to carry out the extraction calculations and later some of these residues were separated for their characterization by XRD and SEM. This paragraph was added to the new version of the manuscript, see lines 124 to 130.

Regards

Reviewer 2 Report

The issue of LIB recycling is extremely important and relevant, and the development of methods for the extraction of battery components is of considerable interest to researchers.

The authors considered and modeled the process of extraction of lithium and cobalt ions from various batteries for portable devices and investigated the regularities in the running processes.

However, the article requires serious revision.

1. The article largely overlaps with similar results of a group from Spain https://doi.org/10.1016/j.chemosphere.2021.132020. This article is in the public domain and can be easily found even by a cursory SCOPUS search. It examines the extraction of metal ions from the model LCO, but also considers the reduction of cobalt H2O2 and its dependence on parameters.
2. Introduction contains 16 references - which is clearly not enough and does not fully reflect the problems in the study area
3. If the degree of extraction was determined by weight method, why aren't the conditions of gravimetric experiment given - how much the samples were dried, how was the loss of mass recorded, etc. Or the authors to determine the degree of extraction need to use additional analysis methods - for example, elemental analysis.
4. All images of SEM data show that the samples contain several phases or polymorphic forms, which is not consistent with the XRD data. It is possible that these phases are not oxidized and cannot be seen by diffraction methods. In this case additional investigations such as EDX are necessary.
5. What explains the shape of the curves in Figure 4? In these coordinates the graphs should be close to linear

Author Response

Dear Reviewer

Hello, thank you for your comments. Below are the answers.

1. The article largely overlaps with similar results of a group from Spain https://doi.org/10.1016/j.chemosphere.2021.132020. This article is in the public domain and can be easily found even by a cursory SCOPUS search. It examines the extraction of metal ions from the model LCO, but also considers the reduction of cobalt H2O2 and its dependence on parameters.

Response

Although similar leaching agents are indeed used in both works, the main difference lies in the objectives of said works. The manuscript “Acid leaching of LiCoO₂ enhanced by reducing agent. Model formulation and validation” (https://doi.org/10.1016/j.chemosphere.2021.132020) is intended for a particular kinetic study, different from the traditional ones, of the “LCO-HCl-H₂O₂” system to find mathematical models, with many assumptions, which adjust these experimental results. The curious thing about this work is that they do not consider the reducing effect of the chloride anion of HCl (a well-known reaction in the literature) since in said article they only consider the corrosion reactions carried out by the H+ ions of HCl and H₂O₂; using very low concentrations of H₂O₂, <0.6% v/v. Therefore, they fail to highlight the reducing properties of said chemical agent since said concentrations would be insufficient to reduce all the Co³⁺ to Co²⁺ (this is visualized graphically in Figures 1 and 2 a and b, respectively) since, using a concentration of 0.6% v/v peroxide, a three times higher concentration of HCl and more than 300 min are needed to achieve extractions close to 90%; therefore, under these conditions, it is difficult to reduce the concentration of HCl for the dissolution reaction of the LCO and make the process industrially attractive. In addition, the authors of this work carried out the dissolution tests at room temperature, and the study of this parameter is very important since it directly affects the kinetics of the reaction through the rate constant, according to the Arrhenius equation. They also do not perform activation energy calculations, another very important parameter in kinetic studies. Perhaps a study of the temperature would have allowed them to calculate the activation energy for said reaction and, with it, propose with more information the type of control (diffusional, mixed, or chemical) that the LCO dissolution reaction may have.

In our manuscript, the study of operative variables (time, temperature, the concentration of leaching agent, and reducing agent, among others) is included to optimize said operative parameters for the dissolution reaction of the LCO using HCl (leaching agent) and H₂O₂ (agent reducing agent, at a concentration slightly above the stoichiometric concentration values, calculated for the dissolution reaction). In this way, we take advantage of the synergy between the temperature, the concentration of the reducing agent (H₂O₂), and the reducing power of the chloride anion, making it possible to considerably reduce the consumption of HCl and the reaction time. This important finding, in addition to not having been published, would lead to a significant decrease in the cost of LCO processing.

Comments on this paper (Acid leaching of LiCoO₂ enhanced by reducing agent. Model formulation and validation) were added to the new version of the manuscript, see lines 110 to 111.

2. Introduction contains 16 references - which is clearly not enough and does not fully reflect the problems in the study area.

Response

The Introduction section has been expanded to fully reflect the issues in the study area. The attached bibliography is as follows:

Page 1 line 40

• Shaikh, S.; Thomas, K.; Zuhair, S. An exploratory study of e-waste creation and disposal: Upstream considerations. Resour.Conserv. Recycl. 2020, 155, 1046622.
• Lv, W.; Wang, Z.; Cao, H.; Sun, Y.; Zhang, Y.; Sun, Z.H. A Critical Review and Analysis on the Recycling of Spent Lithium-Ion Batteries. ACS Sustain. Chem. Eng. 2018, 6, 1504–1521.
• Zheng, X.; Zhu, Z.; Lin, X.; Zhang, Y.; He, Y.; Cao, H.; Sun, Z. A Mini-Review on Metal Recycling from Spent Lithium Ion Batteries.Engineering 2018, 4, 361–370.

Page 1 line 76

(HNO3)

• Castillo, S.; Ansart, F.; Laberty-Robert, C.; Portal, J. Advances in the recovery of spent lithium battery compounds. Power Sources 2002, 112, 247–254.

Page 1 line 77

(H3PO4)

• Pinna, E.G.; Drajlin, D.S.; Toro, N.; Rodriguez, M.H. Kinetic modeling of the leaching of LiCoO2 with phosphoric acid. Mater. Res. Technol. 2020, 9, 14017–14028.
• Chen, X.; Cao, L.; Kang, D.; Li, J.; Zhou, T.; Ma, H. Recovery of valuable metals from mixed types of spent lithium ion batteries. Part II: Selective extraction of lithium. Waste Manag. 2018, 80, 198–210.

Page 1 lines 80-85

• Cerrillo-Gonzalez M.M., Villen-Guzman M., Vereda-Alonso C., Rodriguez-Maroto J.M., Paz-Garcia J.M. Acid leaching of LiCoO₂ enhanced by reducing agent. Model formulation and validation. Chemosphere 2022, 287, 1322020, 1-7. https://doi.org/10.1016/j.chemosphere.2021.132020.

Page 7 line 219

• Li, L.; Qu, W.; Zhang, X.; Lu, J.; Chen, R.; Wu, F. Succinic acid-based leaching system: A sustainable process for recovery of valuable metals from spent Li-ion batteries. J. Power Sources 2015, 282, 544–551.
• Nayaka, G.P.; Manjanna, J.; Pai, K.V.; Vadavi, R.; Keny, S.J.; Tripathi, V.S. Recovery of valuable metal ions from the spent lithium-ion battery using aqueous mixture of mild organic acids as alternative to mineral acids. Hydrometallurgy 2015, 151, 73–77.

3. If the degree of extraction was determined by weight method, why aren't the conditions of gravimetric experiment given - how much the samples were dried, how was the loss of mass recorded, etc. Or the authors to determine the degree of extraction need to use additional analysis methods - for example, elemental analysis.

Response

The process to determine the degree of extraction by the mass difference method consists of recording the initial mass for each test before starting the test. After each experiment is finished, the content of the reactor is filtered at room temperature, carefully washing both the reactor and the solid residue with distilled water. The residue is then dried in an oven for 2 hours at 393 K and weighed. From these data, the extraction is calculated using the expression:

The dissolution efficiency was calculated using the expression [5,18]:

X%=[(m⁰-m^f)/m⁰] 100                                        (1)

where: X% is the percent dissolution efficiency; m⁰ is the initial mass of the solid reactant and m^f is the mass that remains unreacted after the reaction.

This equation is applicable in cases in which during the dissolution process no solid products are generated (which precipitate on the solid reagent) and that the solid is as pure as possible. In addition, said equation is checked using other elementary methodologies to confirm its validity. The main advantage of this equation is its speed and simplicity for knowing the dissolution results, in addition to its high reproducibility. It has been used in different articles. Among them:

• Suarez, D.S.; Pinna, E.G.; Rosales, G.D.; Rodriguez, M.H. Synthesis of lithium fluoride from spent lithium ion batteries. Minerals 2017, 7, 1-13. https://doi.org/10.3390/min7050081.
• Pinna, E.G.; Ruiz, M.C.; Ojeda, M.W.; Rodriguez, M.H. Cathodes of spent Li-ion batteries: Dissolution with phosphoric acid and recovery of lithium and cobalt from leach liquors. Hydrometallurgy 2017, 167, 66-71. https://doi.org/10.1016/j.hydromet.2016.10.024.
• Pinna E.G., Martínez A.A., Tunez F.M., Drajlin D.S., Rodriguez M.H. Leaching acid of the LiCoO₂ from libs: thermodynamic study and reducing agent effect, Revista Mexicana de Ingeniería Química 2019; 18, 2, 431-439.

In addition, determination of cobalt and lithium content in the LIBs was performed by X-ray flu-orescence spectroscopy (XRF) with a Shimadzu EDX 7000 (Shimadzu, Kyoto, Japan).and atomic absorption spectroscopy (AAS) using a Varian SpectrAA 55 spectrometer (Palo Alto, CA, USA) with a hollow cathode lamp (analytical error 1.5%), respectively. The quantitative composition of the sample was 7.1% Li and 54.9% Co, expressed in mass percentage. See lines 110 to 114.

4. All images of SEM data show that the samples contain several phases or polymorphic forms, which is not consistent with the XRD data. It is possible that these phases are not oxidized and cannot be seen by diffraction methods. In this case additional investigations such as EDX are necessary.

Response

Table 1 shows the EDS results corresponding to the labeled particles in Figure 1b. These results, although few, would not show polymorphism.

Table 1 and comments were added to the new version of the manuscript, see lines 115 to 116 and 142 to 143.

5. What explains the shape of the curves in Figure 4? In these coordinates the graphs should be close to linear

Response

Although it is expected for the curve of %X vs LCO dissolution reaction time to be almost linear throughout all time values, as it happens in the first section of it (between 30 and 60 min), it flattens between 60 and 120 min because in this time interval the plateau of this curve is reached. So, for these working conditions, the solution of the solid (LCO) changes slightly with the increase in the reaction time. From this,  we can conclude that, after 60 minutes of reaction, the maximum degree of release of the metallic components of the LCO would be reached.

Regards

Round 2

Reviewer 2 Report

The authors have done an excellent job of improving the manuscript. This article is recommended for publication