Chelating extraction of critical metals from cathode of end-of-life lithium titanium oxide batteries: Experiments, machine learning and validation

Abstract

Lithium-ion batteries (LIBs) that reached their end-of-life (EoL) require recycling, rather than disposal, to recirculate valuable metals and protect the environment. This led us to investigate the extraction of metals from the cathodes of EoL lithium-titanate batteries using ethylenediaminetetraacetic acid disodium (EDTA-2Na). In this work, an orthogonal array was used to design experiments and signal-to-noise calculations were used to define the optimal conditions, which were 0.50 mol/L EDTA-2Na, pH = 6, 75°C, 180 min, 2% pulp density, and 300 r/min, resulting in 97.96%, 94.79%, 96.45%, and 98.89% leaching efficiencies for Li, Ni, Co, and Mn, respectively. Statistically significant interactions between variables were then identified using Pearson’s correlation at the 95% confidence interval, and the pH and temperature were found to be significant. The extraction efficiency decreased as the pH increased, but increased as the temperature increased. Machine learning fitting using linear regression for multi-output prediction was unsatisfactory, whereas random forest regression (RFR) produced satisfactory results. Permutation importance was computed on the fitted RFR to determine feature importance, and confirmed that the pH and temperature were influential variables; however, the time and pulp density were also noted. As the fitted RFR failed to satisfactorily predict leaching efficiencies in additional validation experiments, we recommend increasing the number of experiments and using additional fitting models. An additional analysis that included the initial oxidation–reduction potential (optimal 33.3 mV) revealed this to be the most important variable, the effect of which largely overshadows those of all the other variables. Finally, an environmental assessment highlighted the benefits of the chelating extraction; however, the economic assessment indicated room for improvement.

Keywords

end-of-life lithium-ion battery / lithium titanium oxide battery / hydrometallurgy / chelating extraction / machine learning

References

[1] Zhang XX, Li L, Fan ES, Xue Q, Bian YF, Wu F, Chen RJ. Toward sustainable and systematic recycling of spent rechargeable batteries. Chem. Soc. Rev.. 2018, 47(19): 7239

[2] Gao W, Yu LH, Lin H, et al. . A review on the impacts of fluorinated organic additives in lithium battery industry: An emerging source of per-and polyfluoroalkyl substances. Crit. Rev. Environ. Sci. Technol.. 2024, 54(17): 1285

[3] Stenzel P, Baumann M, Fleer J, Zimmermann B, Weil M. Database development and evaluation for techno-economic assessments of electrochemical energy storage systems. Proceedings of the IEEE International Energy Conference (ENERGYCON). 20141334

[4] Wen JP, Zhao D, Zhang CW. An overview of electricity powered vehicles: Lithium-ion battery energy storage density and energy conversion efficiency. Renewable Energy. 2020, 162: 1629

[5] International Energy Agency (IEA). Critical Minerals Market Review 2023. 2023 2025–01–10]

[6] Global Market Insights (GMI). Lithium-Ion Battery Market Size - by Chemistry, by Component, by Application, Analysis, Share, Growth Forecast, 2025–2034. 2025[2025–03–28]

[7] Gifford S. Lithium, Cobalt and Nickel: The Gold Rush of the 21st Century. 2022[2025–03–26]

[8] Castro FD, Vaccari M, Cutaia L. Valorization of resources from end-of-life lithium-ion batteries: A review. Crit. Rev. Environ. Sci. Technol.. 2022, 52(12): 2060

[9] Zeng XL, Li JH, Singh N. Recycling of spent lithium-ion battery: A critical review. Crit. Rev. Environ. Sci. Technol.. 2014, 44(10): 1129

[10] Wei JC, Zhao SC, Ji LX, et al. . Reuse of Ni–Co–Mn oxides from spent Li-ion batteries to prepare bifunctional air electrodes. Resour. Conserv. Recycl.. 2018, 129: 135

[11] Lead Intelligent Equipment (LEAD). Global EV: Record-Breaking Sales in 2024 & Outlook for 2025. 2025[2025–03–28]

[12] Lin J, Zhang XD, Fan ES, Chen RJ, Wu F, Li L. Carbon neutrality strategies for sustainable batteries: From structure, recycling, and properties to applications. Energy Environ. Sci.. 2023, 16(3): 745

[13] Wang YQ, An N, Wen L, et al. . Recent progress on the recycling technology of Li-ion batteries. J. Energy Chem.. 2021, 55: 391

[14] A. Gomez-Flores, H. Park, G. Hong, et al., Flotation separation of lithium–ion battery electrodes predicted by a long short-term memory network using data from physicochemical kinetic simulations and experiments, J. Ind. Inf. Integr., 42(2024), art. No. 100697.

[15] G. Hong, H. Park, A. Gomez-Flores, H. Kim, J.M. Lee, and J. Lee, Direct flotation separation of active materials from the black mass of lithium nickel cobalt manganese oxides-type spent lithium-ion batteries, Sep. Purif. Technol., 336(2024), art. No. 126327.

[16] Li PW, Luo SH, Zhang L, et al. . Progress, challenges, and prospects of spent lithium-ion batteries recycling: A review. J. Energy Chem.. 2024, 89: 144

[17] Mao JF, Ye C, Zhang SL, et al. . Toward practical lithium-ion battery recycling: Adding value, tackling circularity and recycling-oriented design. Energy Environ. Sci.. 2022, 15(7): 2732

[18] A. Vanderbruggen, A. Salces, A. Ferreira, M. Rudolph, and R. Serna-Guerrero, Improving separation efficiency in end-of-life lithium-ion batteries flotation using attrition pre-treatment, Minerals, 12(2022), No. 1, art. No. 72.

[19] L. Verdugo, L. Zhang, B. Etschmann, et al., Spent lithium-ion battery recycling using flotation technology: Effect of material heterogeneity on separation performance, Processes, 12(2024), No. 7, art. No. 1363.

[20] Nazari S, Li JL, Khoshdast H, et al. . Effect of roasting pretreatment on micro-nanobubble-assisted flotation of spent lithium-ion batteries. J. Mater. Res. Technol.. 2023, 24: 2113

[21] T. Wang, H.M. Luo, Y.C. Bai, J.L. Li, I. Belharouak, and S. Dai, Direct recycling of spent NCM cathodes through iono-thermal lithiation, Adv. Energy Mater., 10(2020), No. 30, art. No. 2001204.

[22] Fan M, Chang X, Guo YJ, et al. . Increased residual lithium compounds guided design for green recycling of spent lithiumion cathodes. Energy Environ. Sci.. 2021, 14(3): 1461

[23] Ilyas S, Srivastava RR, Kim H. Cradle-to-cradle recycling of spent NMC batteries with emphasis on novel Co²⁺/Ni²⁺ separation from HCl leached solution and synthesis of new ternary precursor. Process. Saf. Environ. Prot.. 2023, 170: 584

[24] Barbieri EMS, Lima EPC, Cantarino SJ, Lelis MFF, Freitas MBJG. Recycling of spent ion-lithium batteries as cobalt hydroxide, and cobalt oxide films formed under a conductive glass substrate, and their electrochemical properties. J. Power Sources. 2014, 269: 158

[25] C.Y. Li, G.F. Dai, R.Y. Liu, et al., Separation and recovery of nickel cobalt manganese lithium from waste ternary lithium-ion batteries, Sep. Purif. Technol., 306(2023), art. No. 122559.

[26] Cheema HA, Ilyas S, Farhan M, Yang JH, Kim H. Extraction of Fe and Al from red mud using carbothermic reduction followed by water leaching. J. Ind. Eng. Chem.. 2024, 136: 201

[27] S. Ilyas, R.R. Srivastava, and H. Kim, Solvent extraction for high separation strategy of light and heavy rare earth elements from a sulfate-leached solution of low-grade monazite, Sep. Purif. Technol., 341(2024), art. No. 126896.

[28] Sattar R, Ilyas S, Kousar S, Khalid A, Sajid M, Bukhari SI. Recycling of end-of-life LiNi_xCoyMn_zO₂ batteries for rare metals recovery. Environ. Eng. Res.. 2020, 25(1): 88

[29] Yi CX, Ge P, Wu XQ, Sun W, Yang Y. Tailoring carbon chains for repairing graphite from spent lithium-ion battery toward closed-circuit recycling. J. Energy Chem.. 2022, 72: 97

[30] Fan ES, Yang JB, Huang YX, et al. . Leaching mechanisms of recycling valuable metals from spent lithium-ion batteries by a malonic acid-based leaching system. ACS Appl. Energy Mater.. 2020, 3(9): 8532

[31] Munir H, Srivastava RR, Kim H, Ilyas S, Khosa MK, Yameen B. Leaching of exhausted LNCM cathode batteries in ascorbic acid lixiviant: A green recycling approach, reaction kinetics and process mechanism. J. Chem. Technol. Biotechnol.. 2020, 95(8): 2286

[32] D.M. Song, T.Y. Wang, Z.A. Liu, et al., Characteristic comparison of leaching valuable metals from spent power Li-ion batteries for vehicles using the inorganic and organic acid system, J. Environ. Chem. Eng., 10(2022), No. 1, art. No. 107102.

[33] N.H. Zulkernain, T. Uvarajan, and C.C. Ng, Roles and significance of chelating agents for potentially toxic elements (PTEs) phytoremediation in soil: A review, J. Environ. Manage., 341(2023), art. No. 117926.

[34] S. Fatima, M.K. Khosa, A. Noor, S. Qayyum, and M.E. Oirdi, Hydrometallurgical extraction of valuable metals by mixed acid leaching system for used lithium-ion batteries, Sustainability, 16(2024), No. 16, art. No. 6817.

[35] A.S. Amarasekara, D.P. Wang, and A.B. Shrestha, Efficient leaching of metal ions from spent Li-ion battery combined electrode coatings using hydroxy acid mixtures and regeneration of lithium nickel manganese cobalt oxide, Batteries, 10(2024), No. 6, art. No. 170.

[36] Wang MM, Zhang CC, Zhang FS. An environmental benign process for cobalt and lithium recovery from spent lithium-ion batteries by mechanochemical approach. Waste Manage.. 2016, 51: 239

[37] A.U.N. Izzati, H.T.B.M. Petrus, and A. Prasetya, Nickel recovery from precipitate of NCA lithium-ion battery leach liquor by using disodium ethylene diamine tetraacetate, IOP Conf. Ser. Earth Environ. Sci., 882(2021), No. 1, art. No. 012002.

[38] S. Gupta, K.K. Pant, and G. Corder, An environmentally benign closed-loop process for the selective recovery of valuable metals from industrial end-of-life lithium-ion batteries, Chem. Eng. J., 446(2022), art. No. 137397.

[39] F.Y. Su, Q. Meng, X.Y. Zhou, et al., One-step leaching mechanism for total elemental recovery from spent lithium-ion batteries utilizing ethylene diamine tetraacetic acid, J. Environ. Chem. Eng., 11(2023), No. 4, art. No. 110275.

[40] Z. Xing and M. Srinivasan, Lithium recovery from spent lithium-ion batteries leachate by chelating agents facilitated electro-dialysis, Chem. Eng. J., 474(2023), art. No. 145306.

[41] Y.F. Jie, S.H. Yang, Y. Li, D.Q. Zhao, Y.Q. Lai, and Y.M. Chen, Oxidizing roasting behavior and leaching performance for the recovery of spent LiFePO₄ batteries, Minerals, 10(2020), No. 11, art. No. 949.

[42] J. Rieger, S. Stuhr, B. Rutrecht, et al., Graphite separation from lithium-ion battery black mass using froth flotation and quality evaluation for reuse as a secondary raw material including non-battery applications, Recycling, 10(2025), No. 2, art. No. 75.

[43] Watt BE, Proudfoot AT, Vale JA. Hydrogen peroxide poisoning. Toxicol. Rev.. 2004, 23(1): 51

[44] Gülden M, Jess A, Kammann J, Maser E, Seibert H. Cytotoxic potency of H₂O₂ in cell cultures: Impact of cell concentration and exposure time. Free. Radic. Biol. Med.. 2010, 49(8): 1298

[45] Niu ZR, Huang QF, Xin BP, et al. . Optimization of bioleaching conditions for metal removal from spent zinc–manganese batteries using response surface methodology. J. Chem. Technol. Biotechnol.. 2016, 91(3): 608

[46] L. Grima-Carmena, S. Oyonarte-Andrés, J.J. Giner-Sanz, M. García-Gabaldón, F. Bosch-Mossi, and V. Bosch-Mossi, Statistical analysis of the effect of the electrochemical treatment and the acid concentration on the leaching of NMC cathodes from spent Li-ion batteries, J. Environ. Chem. Eng., 11(2023), No. 5, art. No. 110423.

[47] J. Partinen, P. Halli, A. Varonen, B.P. Wilson, and M. Lundström, Investigating battery black mass leaching performance as a function of process parameters by combining leaching experiments and regression modeling, Miner. Eng., 215(2024), art. No. 108828.

[48] J. Priyadarshini, M. Elangovan, M. Mahdal, and M. Jayasudha, Machine-learning-assisted prediction of maximum metal recovery from spent zinc–manganese batteries, Processes, 10(2022), No. 5, art. No. 1034.

[49] B. Niu, X.M. Wang, and Z.M. Xu, Application of machine learning to guide efficient metal leaching from spent lithium-ion batteries and comprehensively reveal the process parameter influences, J. Cleaner Prod., 410(2023), art. No. 137188.

[50] N.M. García, J.L. Valverde, B.D. Cano, M. Heitz, and A.A. Ramirez, Selective recovery of zinc from alkaline batteries via a basic leaching process and the use of a machine learning-based digital twin for predictive purposes, Energies, 17(2024), No. 24, art. No. 6292.

[51] Wang F, Sun R, Xu J, Chen Z, Kang M. Recovery of cobalt from spent lithium ion batteries using sulphuric acid leaching followed by solid–liquid separation and solvent extraction. RSC Adv.. 2016, 6(88): 85303

[52] U. Domańska, A. Wiśniewska, Z. Dąbrowski, D. Kolasa, K. Wróbel, and J. Lach, Recovery of metals from the “black mass” of waste portable Li-ion batteries with choline chloride-based deep eutectic solvents and bi-functional ionic liquids by solvent extraction, Molecules, 29(2024), No. 13, art. No. 3142.

[53] A.A. Dar, Z. Chen, G.X. Zhang, et al., Sustainable extraction of critical minerals from waste batteries: A green solvent approach in resource recovery, Batteries, 11(2025), No. 2, art. No. 51.

[54] Kari FG, Giger W. Speciation and fate of ethylenediam-inetetraacetate (EDTA) in municipal wastewater treatment. Water Res.. 1996, 30(1): 122

[55] Lanigan RS, Yamarik TA. Final report on the safety assessment of EDTA, calcium disodium EDTA, diammonium EDTA, dipotassium EDTA, disodium EDTA, TE–EDTA, tetrasodium EDTA, tripotassium EDTA, trisodium EDTA, HEDTA, and trisodium HEDTA. Int. J. Toxicol.. 2002, 21(Suppl. 2): 95

[56] Rantala A, Utriainen M, Kaushik N, Virta M, Välimaa AL, Karp M. Luminescent bacteria-based sensing method for methylmercury specific determination. Anal. Bioanal. Chem.. 2011, 400(4): 1041

[57] Y.J. Jung, B.Y. Yoo, S.C. Park, and S.H. Son, Design optimization of selective lithium leaching of cathodic active materials from spent lithium-ion batteries based on the Taguchi method, Metals, 11(2021), No. 1, art. No. 108.

[58] Renukappa NM, Suresha B, Devarajaiah RM, Shivakumar KN. Dry sliding wear behaviour of organo-modified montmorillonite filled epoxy nanocomposites using Taguchi’s techniques. Mater. Des.. 2011, 32(8–9): 4528

[59] Taguchi G, Chowdhury S, Wu Y. Taguchi’s Quality Engineering Handbook. 2005, Hoboken, New Jersey, John Wiley & Sons, Inc.

[60] Ross PJ. Taguchi Techniques for Quality Engineering: Loss Function, Orthogonal Experiments, Parameter and Tolerance Design. 19962nd ed.New York, McGraw-Hill Publishing

[61] J. Luan, C.L. Zhang, B.D. Xu, Y. Xue, and Y.P. Ren, The predictive performances of random forest models with limited sample size and different species traits, Fish. Res., 227(2020), art. No. 105534.

[62] A. Gomez-Flores, H. Cho, G. Hong, H. Nam, H. Kim, and Y. Chung, A critical review on machine learning applications in fiber composites and nanocomposites: Towards a control loop in the chain of processes in industries, Mater. Des., 245(2024), art. No. 113247.

[63] COMSOL, Introduction to Surrogate Modeling, [2025–06–02]. https://www.comsol.com/support/learning-center/article/94521/261

[64] Argonne National Laboratory. SF-18-022 EverBatt. 2018[2025–05–01]

[65] Bi HJ, Zhu HB, Zu L, et al. . Low-temperature thermal pretreatment process for recycling inner core of spent lithium iron phosphate batteries. Waste Manage. Res. 2021, 39(1): 146

[66] S. Krämer, D. Weintz, M. Winter, I. Cekic-Laskovic, and M. Grünebaum, Importance of high-concentration electrolytes for lithium-based batteries, Encyclopedia, 5(2025), No. 1, art. No. 20.

[67] B. Priyono, F. Faizah, K.R. Lestari, et al., Exploring Mg and Fe co-doped Li₄Ti₅O₁₂ electrode for lithium-ion battery, Mater. Chem. Phys., 329(2025), art. No. 129939.

[68] L. Donnelly, D. Pirrie, M. Power, et al., The recycling of end-of-life lithium-ion batteries and the phase characterisation of black mass, Recycling, 8(2023), No. 4, art. No. 59.

[69] M. Pourmohammad, J.O. Moncunill, H. Anticoi, et al., The characterization of black mass from spent lithium-ion scooter batteries using multi-analytical techniques, Recycling, 10(2025), No. 2, art. No. 54.

[70] Vieceli N, Benjamasutin P, Promphan R, Hellström P, Paulsson M, Petranikova M. Recycling of lithium-ion batteries: Effect of hydrogen peroxide and a dosing method on the leaching of LCO, NMC oxides, and industrial black mass. ACS Sustainable Chem. Eng.. 2023, 11(26): 9662

[71] J. Partinen, P. Halli, B.P. Wilson, and M. Lundström, The impact of chlorides on NMC leaching in hydrometallurgical battery recycling, Miner. Eng., 202(2023), art. No. 108244.

[72] E. Gerold, F. Kadisch, R. Lerchbammer, and H. Antrekowitsch, Bio-metallurgical recovery of lithium, cobalt, and nickel from spent NMC lithium ion batteries: A comparative analysis of organic acid systems, J. Hazard. Mater. Adv., 13(2024), art. No. 100397.

[73] A. Porvali, S. Shukla, and M. Lundström, Low-acid leaching of lithium-ion battery active materials in Fe-catalyzed Cu–H₂SO₄ system, Hydrometallurgy, 195(2020), art. No. 105408.

[74] M. Aaltonen, C. Peng, B.P. Wilson, and M. Lundström, Leaching of metals from spent lithium-ion batteries, Recycling, 2(2017), No. 4, art. No. 20.

[75] S.Y. Lei, Y. Cao, X.F. Cao, W. Sun, Y.Q. Weng, and Y. Yang, Separation of lithium and transition metals from leachate of spent lithium-ion batteries by solvent extraction method with Versatic 10, Sep. Purif. Technol., 250(2020), art. No. 117258.

[76] Zaitoun MA, Lin CT. Chelating behavior between metal ions and EDTA in sol–gel matrix. J. Phys. Chem. B. 1997, 101(10): 1857

[77] Chen LT, Liu T, Ma CA. Metal complexation and biodegradation of EDTA and S, S-EDDS: A density functional theory study. J. Phys. Chem. A. 2010, 114(1): 443

[78] Byegård J, Skarnemark G, Skålberg M. The stability of some metal EDTA, DTPA and DOTA complexes: Application as tracers in groundwater studies. J. Radioanal. Nucl. Chem.. 1999, 241(2): 281

[79] Eckert S, Mascarenhas EJ, Mitzner R, et al. . From the free ligand to the transition metal complex: FeEDTA⁻ Formation seen at ligand K-edges. Inorg. Chem.. 2022, 61(27): 10321

[80] Nayl AA, Hamed MM, Rizk SE. Selective extraction and separation of metal values from leach liquor of mixed spent Li-ion batteries. J. Taiwan Inst. Chem. Eng.. 2015, 55: 119

[81] Gao WF, Liu CM, Cao HB, et al. . Comprehensive evaluation on effective leaching of critical metals from spent lithiumion batteries. Waste Manage.. 2018, 75: 477

[82] Tünay O, Kabdaşli NI. Hydroxide precipitation of complexed metals. Water Res.. 1994, 28(10): 2117

[83] W. Zhang, P. Xiong, Q. Li, et al., Competitive adsorption behavior and mechanisms of coexisting EDTA-Cu(II) and EDTA-Cr(III) on ferrihydrite, Colloids Surf. A, 670(2023), art. No. 131566.

[84] J.J. Tian, D.D. Wu, S.Y. Li, W.H. Ma, and R.Z. Wang, Effect of process variables on leaching behavior and kinetics of silver element from waste photovoltaic modules, Sep. Purif. Technol., 335(2024), art. No. 126062.

[85] He LP, Sun SY, Song XF, Yu JG. Leaching process for recovering valuable metals from the LiNi_1/3Co_1/3Mn_1/3O₂ cathode of lithium-ion batteries. Waste Manage.. 2017, 64: 171

[86] Hao JJ, Wang XL, Wang YS, Wu YF, Guo F. Optimizing the leaching parameters and studying the kinetics of copper recovery from waste printed circuit boards. ACS Omega. 2022, 7(4): 3689

[87] Q. Hu, H. Zhong, and Z.F. Cao, High-efficiency leaching of Li and Ni from spent lithium-ion batteries based on sodium persulfate, Sep. Purif. Technol., 325(2023), art. No. 124653.

[88] A. Gomez-Flores, S.A. Bradford, G. Hong, and H. Kim, Statistical analysis, machine learning modeling, and text analytics of aggregation attachment efficiency: Mono and binary particle systems, J. Hazard. Mater., 454(2023), art. No. 131482.

[89] J.H. Graw, W.T. Wood, and B.J. Phrampus, Predicting global marine sediment density using the random forest regressor machine learning algorithm, J. Geophys. Res. Solid Earth, 126(2021), No. 1, art. No. e2020JB020135.

[90] Huang JH, Kargl-Simard C, Oliazadeh M, Alfantazi AM. pH-controlled precipitation of cobalt and molybdenum from industrial waste effluents of a cobalt electrodeposition process. Hydrometallurgy. 2004, 75(1–4): 77

[91] N. Djoudi, M.L.P. Mostefa, and H. Muhr, Hydrometallurgical process to recover cobalt from spent Li-ion batteries, Resources, 10(2021), No. 6, art. No. 58.

[92] M. Kordloo, G. Khodadadmahmoudi, M.R. Barati, and A. Rezaei, Effect of leaching media on selective precipitation of Al, Ni, Co, and Mn in the NMC battery recycling process, Sep. Purif. Technol., 363(2025), art. No. 132093.

[93] M. Biegun, M. Kaniewski, E. Klem-Marciniak, and J. Hoffmann, Thermal decomposition characterization and kinetics of copper, iron, manganese and zinc chelates of ethylenediaminetetraacetic acid in air atmosphere, Thermochim. Acta, 716(2022), art. No. 179307.

[94] Motekaitis RJ, Cox XB, Taylor P, Martell AE, Miles B, Tvedt TJ. Thermal degradation of EDTA chelates in aqueous solution. Can. J. Chem.. 1982, 60(10): 1207

[95] Heyes GW, Trahar WJ. The natural flotability of chalcopyrite. Int. J. Miner. Process.. 1977, 4(4): 317

[96] E. Kallitsis, A. Korre, and G.H. Kelsall, Life cycle assessment of recycling options for automotive Li-ion battery packs, J. Cleaner Prod, 371(2022), art. No. 133636.

[97] M. Bruno and S. Fiore, Material flow analysis of lithium-ion battery recycling in Europe: Environmental and economic implications, Batteries, 9(2023), No. 4, art. No. 231.

[98] Li J, Zhou JF, Wang W, et al. . LCA for lithium battery recycling technology-recent progress. Ionics. 2024, 30(8): 4417

[99] V.K. Sharma, S. Jain, and V.P. Singh, A comparative analysis of recycling technologies for sustainable extraction of cathodic materials from battery waste: Evaluation of energy, economic, and environmental performance, J. Energy Storage, 111(2025), art. No. 115407.

RIGHTS & PERMISSIONS

University of Science and Technology Beijing