Alkaline Leaching Lithium from Spent CarbonAnode and Coupling of Extraction-Carbonization for Cryolite Regeneration

Abstract

This paper proposes anintegrated coupling process of alkali leaching, HBTA-TOPO synergisticextraction, and carbonation for the resource utilization of spent carbon anode(SCA), a typical lithium-bearing industrial solid waste from electrolyticaluminum production, whose lithium content exceeds the ore grade. Compared withconventional acid leaching methods, the adopted alkaline leaching approachfeatures mild reaction conditions, low equipment corrosion risk, and eliminatesthe volatilization of toxic hydrogen fluoride (HF) gas, thus showing prominentenvironmental safety advantages. Under the optimal alkaline leaching conditions(NaOH concentration of 10 mol/L, reaction temperature of 90 _。C, liquid-to-solidratio of 10:1, and reaction time of 120 min), the maximum Li⁺ leaching rate reaches 89.46%. As the leaching process proceeds, lithium in thecarbon slag rapidly migrates to the alkaline leaching solution. The Na-Al-Fbonds of cryolite (Na₃AlF₆) and lithium cryolite (Na₂LiAlF₆)present in the SCA gradually break, and soluble ions such as Na⁺, Li⁺,Al³⁺, and F^- enter the solution. High-concentration Na⁺ reacts with free F^- to form sodium fluoride (NaF), which adheres tothe SCA, leading to an increase in the sodium-aluminum ratio (Na/Al) of the SCA.The HBTA-TOPO synergistic extraction system is proposed for the extraction andenrichment of lithium in the lithium alkaline leaching solution, and theextraction residue is used to repair and regenerate cryolite. The extractionefficiency of Li⁺ reaches and the yield of cryolite reaches 81.54%and 76.54%. The molecular ratio of sodium fluoride to aluminum fluoride insynthetic cryolite products is relatively high. This integrated processrealizes the efficient recovery of lithium and the high-value regeneration ofcryolite from SCA, providing a sustainable technical route for the cleanutilization of electrolytic aluminum solid waste. This integrated closed-loopprocess realizes the simultaneous recovery of lithium and high-valueregeneration of cryolite from SCA, which not only mitigates the environmentalpollution caused by SCA stacking and the scarcity of lithium resources, but alsoprovides a sustainable technical route for the clean and high-value utilizationof electrolytic aluminum solid waste.

Keywords

Spent carbon anode / NaOHleaching / Mineral phases transformation / Lithium extraction / Regeneratedcryolite

Acknowledgement

The authors are grateful for the funding provided by Shanxi Province Central Government Guided Local Science and Technology Development Fund Project (YDZJSX2022A004), and Technology Achievement Transformation Project of Lvliang (2022XDHZ15).

Author Contributions

Conceptualization, Y.Q. and J.G.; Methodology, Z.P.; Investigation, Y.Q. and D.L.; Writing—Original Draft Preparation, X.N. and Y.L.; Writing—Review & Editing, X.N. and X.L.; Supervision, Y.Q. and Z.P.

Ethics Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

All datasets generated and/or analyzed during the current study are publicly available to ensure the transparency and reproducibility of the research findings.

Funding

This research was funded Shanxi Province Central Government Guided Local Science and Technology Development Fund Project (YDZJSX2022A004), and Technology Achievement Transformation Project of Lvliang (2022XDHZ15).

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

References

[1] Scrosati B, Garche J. Lithium batteries: Status, prospects and future. J. Power Sources 2010, 195, 2419-2430. DOI: 10.1016/j.jpowsour.2009.11.048

[2] Baudino L, Santos C, Pirri CF, La Mantia F, Lamberti A. Recent Advances in the Lithium Recovery from Water Resources: From Passive to Electrochemical Methods. Adv. Sci. 2022, 9, 2201380. DOI: 10.1002/advs.202201380

[3] Thirumurugan A, Govindaraj R, Dhanabalan S, Sakthivel P, Chidhambaram N, Udayabhaskar R, et al. Strategic analysis of lithium resources by addressing challenges and opportunities for sustainable electric vehicle battery development in the era of global EV domination. Z. Fur Phys. Chem. 2025, 239, 457-465. DOI: 10.1515/zpch-2023-0524

[4] Tabereaux A, Alcorn T, Luketrembley A. Lithium-Modified Low Ratio Electrolyte Chemistry for Improved Performance in Modern Reduction Cells. J. Electrochem. Soc. 2020, 167, 132502. DOI: 10.1007/978-3-319-48156-2_11

[5] Li H, Du J. Research on Circular Economy of Mineral Resources in China: Bauxite Resources in Shanxi Province as an Example. Geol. Resour. Manag. Sustain. Dev. 2009.

[6] Zhang Y, Zhang J. Study on the Occurrence State of Lithium in Low-Grade Diasporic Bauxite from Central Guizhou Province, China. JOM 2019, 71, 4594-4599. DOI: 10.1007/s11837-019-03670-x

[7] Cui P, Qin B, Haarberg GM. The Behavior of Additives LiF, MgF₂ and KF on Current Efficiency in Aluminium Electrolysis. J. Electrochem. Soc. 2019, 166, D559-D563. DOI: 10.1149/2.0431913jes

[8] Chen Y, Li P, Bu X, Chehreh Chelgani S, Kong Y, Liang X. Resource utilization strategies for spent pot lining: A review of the current state. Sep. Purif. Technol. 2022, 300, 121816. DOI: 10.1016/j.seppur.2022.121816

[9] Leng M, Li W, Liu Q. Study of lithium extraction and fluoride removal from waste aluminum electrolyte by the roasting-leaching method. J. Ind. Eng. Chem. 2025, 147, 201-209. DOI: 10.1016/j.jiec.2024.12.012

[10] Liu CC, Qu PC, Zhan MZ, Tan ZL, Wu GX, Wang YJ, et al. Preparation of graphite anodes for lithium-ion batteries from aluminum electrolysis spent cathode carbon. J. Energy Storage 2025, 131, 117633. DOI: 10.1016/j.est.2025.117633

[11] Chen R. Ionic liquids-mediated recovery of metals from spent batteries. J. Ion. Liq. 2023, 3, 100070. DOI: 10.1016/j.jil.2023.100070

[12] Kordloo M, Boroumand Z, Abdollahi H, Rezaei A, Ghorbani Y, Solgi A. Lithium recovery from waste aluminum electrolyte via bioleaching: Comparative insights into acidic and alkaline pathways using Aspergillus niger and Glutamicibacter nicotianae. Waste Manag. 2025, 206, 115043. DOI: 10.1016/j.wasman.2025.115043

[13] Zhou H, Cao Z, Ma B, Wang C, Chen Y. Selective and efficient extraction of lithium from spodumene via nitric acid pressure leaching. Chem. Eng. Sci. 2024, 287, 119736. DOI: 10.1016/j.ces.2024.119736

[14] Zhou H, Liu Y, Ma B, Wang C, Chen Y. Efficient lithium extraction from low-grade clay-type lithium ore via nitric acid pressure leaching. J. Environ. Chem. Eng. 2025, 13, 118653. DOI: 10.1016/j.jece.2025.118653

[15] Yang J, Tao W, Li J, He J, Wang Z. Efficient lithium recycling from waste aluminum electrolytes through an environmentally friendly process. Chem. Eng. J. 2025, 512, 162431. DOI: 10.1016/j.cej.2025.162431

[16] Tian J, Chen B, Xia H, Yang W, Dai L, Zhang L. Ultrasound-assisted enhanced leaching of lithium and fluoride compounds from waste cathode carbon: Comprehensive recovery and leaching mechanism. Sep. Purif. Technol. 2025, 354, 129190. DOI: 10.1016/j.seppur.2024.129190

[17] Dong L, Jiao F, Liu W, Wang C, Wang D, Qin W. Selective extraction of lithium and solidified fluoride from overhaul slag by the calcium sulfate roasting and water leaching. Miner. Eng. 2024, 217, 108943. DOI: 10.1016/j.mineng.2024.108943

[18] Liu S, Hu Q, Song X, Xiong X, Li X, Wang Z, et al. Causticization of electrolytic aluminum slag for selective lithium recovery and fluorine fixation. J. Hazard. Mater. 2025, 492, 138272. DOI: 10.1016/j.jhazmat.2025.138272

[19] Wu S, Tao W, Zheng Y, Ge H, He J, Yang Y, et al. A novel approach for lithium recovery from waste lithium-containing aluminum electrolyte by a roasting-leaching process. Waste Manag. 2021, 134, 89-99. DOI: 10.1016/j.wasman.2021.08.011

[20] Cui L, Wang W, Chao X, Gao J, Cheng F. Efficient lithium recovery from electrolytic aluminum slag via an environmentally friendly process: Leaching behavior and mechanism. J. Clean. Prod. 2024, 439, 140800. DOI: 10.1016/j.jclepro.2024.140800

[21] Wu S, Tao W, Zheng Y, Yang Y, Yu J, Cui J, et al. Novel process for the extraction of lithium carbonate from spent lithium-containing aluminum electrolytes by leaching with aluminum nitrate and nitric acid. Hydrometallurgy 2020, 198, 105505. DOI: 10.1016/j.hydromet.2020.105505

[22] Cheng N, Jiang R, Cheng Y, Hu L, Jiang S, Li M, et al. Chelator auxiliary electrodialysis (CAED) for efficient and sustainable lithium extraction and magnesium co-recovery from salt lake brines. Chem. Eng. J. 2025, 521, 166666. DOI: 10.1016/j.cej.2025.166666

[23] Salakjani NK, Singh P, Nikoloski AN. Acid roasting of spodumene: Microwave vs. conventional heating. Miner. Eng. 2019, 138, 161-167. DOI: 10.1016/j.mineng.2019.05.003

[24] Gao J, Liu W, Sui J, Zhang Z, Dong Y, Wang D, et al. Piezocatalytic lithium extraction from aqueous solutions. Nano Energy 2025, 142, 111186. DOI: 10.1016/j.nanoen.2025.111186

[25] Wang L, Zhang P, Guo Z, Zhang Y, Wang Y. Electrochemical lithium extraction by the faradaic materials: Advances, challenges and enhancement approaches. Acta Phys.-Chim. Sin. 2025, 41, 2403011. DOI: 10.1016/j.actphy.2025.100127

[26] Yelatontsev D, Mukhachev A. Processing of lithium ores: Industrial technologies and case studies—A review. Hydrometallurgy 2021, 201, 105578. DOI: 10.1016/j.hydromet.2021.105578

[27] Zhang X, Wang C, Pei T, Gao F, Hao X, Xing L, et al. Underlying physics analysis and performance evaluation of electrochemical Li⁺ extraction from low-quality brines via a spatiotemporal distribution model. Sep. Purif. Technol. 2025, 364, 132351. DOI: 10.1016/j.seppur.2025.132351

[28] Dumestre A, Chone T, Portal J, Gerard M, Berthelin J. Cyanide Degradation under Alkaline Conditions by a Strain of Fusarium solani Isolated from Contaminated Soils. Appl. Environ. Microbiol. 1997, 63, 2729-2734. DOI: 10.1128/aem.63.7.2729-2734.1997

[29] Simachew AJW. Biodegradation of Cyanide Using Soda Lake-Derived Alkaliphilic Microbial Consortia. J. Environ. Manag. 2024, 356, 121036. DOI: 10.3390/w16202956

[30] Shi ZN, Li W, Hu XW, Ren BJ, Gao BL, Wang ZW. Recovery of carbon and cryolite from spent pot lining of aluminium reduction cells by chemical leaching. Trans. Nonferrous Met. Soc. China 2012, 22, 222-227. DOI: 10.1016/S1003-6326(11)61164-3

[31] Yao Z, Zhong Q, Xiao J, Ye S, Tang L, Zhang Z. An environmental-friendly process for dissociating toxic substances and recovering valuable components from spent carbon cathode. J. Hazard. Mater. 2021, 404, 124120. DOI: 10.1016/j.jhazmat.2020.124120

[32] Xing M, Zhang F, Zheng P, Wang Y, Zhao L, Xu C. Selective recovery of lithium from high-aluminum fly ash by using alkali-dissolution-assisted HBTA–TOPO synergistic extraction. J. Clean. Prod. 2024, 434, 139998. DOI: 10.1016/j.jclepro.2023.139998

[33] Zhang L, Li L, Shi D, Li J, Peng X, Nie F. Selective extraction of lithium from alkaline brine using HBTA-TOPO synergistic extraction system. Sep. Purif. Technol. 2017, 188, 167-173. DOI: 10.1016/j.seppur.2017.07.028

[34] Lin Y, Sun H, Peng T, Zhao D, Zhang X. The Leaching Kinetics of Iron from Titanium Gypsum in a Citric Acid Medium and Obtain Materials by Leaching Liquid. J. Mater. Res. Technol. 2023, 28, 952. DOI: 10.3390/molecules28030952

[35] Parker SF, Ramirez-Cuesta AJ, Daemen LL. The structure and vibrational spectroscopy of cryolite, Na₃AlF₆. RSC Adv. 2020, 10, 25856-25863. DOI: 10.1039/D0RA04804F

[36] Wang WY, Yen CH, Lin JL, Xu RB. Recovery of high-purity metallic cobalt from lithium nickel manganese cobalt oxide (NMC)-type Li-ion battery. J. Mater. Cycles Waste Manag. 2019, 364, 300-307. DOI: 10.1007/s10163-018-0790-x

[37] Petukhov MN, Oreshkin AI, Muzychenko DA, Oreshkin SI. Fluorination of Cu(001) Surface by C₆₀F₄₈ Molecule Adsorption. J. Phys. Chem. C 2019, 124, 347-355. DOI: 10.1021/acs.jpcc.9b07408

[38] Azam MA, Fujiwara A, Shimoda T. Thermally oxidized aluminum as catalyst-support layer for vertically aligned single-walled carbon nanotube growth using ethanol. Appl. Surf. Sci. 2011, 258, 873-882. DOI: 10.1016/j.apsusc.2011.09.018

[39] Zhang L, Ji L, Li L, Shi D, Xu T, Peng X, et al. Recovery of Co, Ni, and Li from solutions by solvent extraction with beta-diketone system. Hydrometallurgy 2021, 204, 105718. DOI: 10.1016/j.hydromet.2021.105718

[40] Kyriakopoulos G, Doulia D, Hourdakis A. Effect of ionic strength and pH on the adsorption of selected herbicides on Amberlite. Int. J. Environ. Anal. Chem. 2006, 86, 207-214. DOI: 10.1080/03067310500247678

[41] Wang L, Wang C, Yu Y, Huang X, Long Z, Hou Y, et al. Recovery of fluorine from bastnasite as synthetic cryolite by-product. J. Hazard. Mater. 2012, 209–210, 77–83. DOI:10.1016/j.jhazmat.2011.12.069

[42] Cao XM, Peng JP, Li YF, Dong WX, Di YZ, Wang YW. Preparation of cryolite from simulated leaching solution of alkaline roasting of carbon dust. J. Mater. Metall. 2024, 23, 241-248. DOI: 10.14186/j.cnki.1671-6620.2024.03.006 (In Chinese)

[43] Wang C, Mao S. Study on the effect of an ultrasound assisted reaction on the crystallization properties of recovered cryolite. RSC Adv. 2023, 13, 35359-35368. DOI: 10.1039/D3RA06661D