Leaching Characteristics of Spent Carbon Anode in Alkaline System: Thermodynamics, Kinetics, Ion Forms, and Phase Transformation

Abstract

With the rapid development of the aluminium electrolysis industry, large amounts of lithium-containing electrolyte residue are generated, posing environmental risks and wasting lithium resources. This study proposes an efficient lithium leaching method from spent carbon anode (SCA) electrolytic aluminium carbon slag using NaOH. The leaching rate of lithium reaches 89.46% at a NaOH concentration of 10 mol/L, a leaching temperature of 90 °C, and a leaching time of 2 h. Thermodynamic calculations concluded that during alkaline leaching, most phases in SCA can react spontaneously with NaOH to release soluble ions. The kinetic results suggested that the leaching behavior of Li⁺ follows the ‘unreacted shrinkage nucleus model’, controlled by both mixing and diffusion. NaOH concentration and leaching temperature are the key factors governing the effectiveness of Li⁺ leaching. Medusa simulations showed that the dissociated Al³⁺ in alkaline leach solution would first form an Al(OH)₃ complex and continue to react with OH⁻ to form Al(OH)₄⁻, while lithium exists in the form of Li⁺ and LiOH. Mechanistic analysis via SEM-EDS and XRD indicates that NaOH breaks Na–Al–F bonds, releasing Li⁺ and forming NaF. This approach offers an eco-friendly pathway for resource recovery from SCA, supporting cryolite regeneration and minimizing the environmental impacts of hazardous waste.

Keywords

Spent carbon anode / Lithium leaching / Thermodynamics / Kinetics / Phase transformation

References

[1] An JW, Kang DJ, Tran KT, Kim MJ, Lim T, Tran T. Recovery of lithium from Uyuni salar brine. Hydrometallurgy 2012, 117-118, 64-70. DOI:10.1016/j.hydromet.2012.02.008

[2] Braga PFA, França SCA, Gonçalves CC, Ferraz PFV, Neumann R. Extraction of lithium from a montebrasite concentrate: Applied mineralogy, pyro- and hydrometallurgy. Hydrometallurgy 2020, 191, 105249. DOI:10.1016/j.hydromet.2020.105249

[3] Chen W, Li X, Chen L, Zhou G, Lu Q, Huang Y, et al. Tailoring hydrophobic deep eutectic solvent for selective lithium recovery from the mother liquor of Li₂CO₃ . Chem. Eng. J. 2021, 420, 127648. DOI:10.1016/j.cej.2020.127648

[4] Sverdrup HU, Ragnarsdottir KV, Koca D. Aluminium for the future: Modelling the global production, market supply, demand, price and long term development of the global reserves. Resour. Conserv. Recycl. 2015, 103, 139-154. DOI:10.1016/j.resconrec.2015.06.008

[5] Qin YH, Chen C, Yang ZY, Guo YX, Cheng FQ, Gao JM. Sources, hazards, and resource utilization of electrolytic aluminum slag: A review. Powder Technol. 2026, 468, 121662. DOI:10.1016/j.powtec.2025.121662

[6] Qin YH, Niu XD, Li XL, Liu YJ, Gao JM, Pan ZH, et al. Alkaline leaching lithium from spent carbon anode and coupling of extraction carbonization for cryolite regeneration. Green Chem. Technol. 2026, 3, 10005. DOI:10.70322/gct.2026.10005

[7] Gil A, Korili SA. Management and valorization of aluminum saline slags: Current status and future trends. Chem. Eng. J. 2016, 289, 74-84. DOI:10.1016/j.cej.2015.12.069

[8] Hu K, Reed D, Robshaw TJ, Smith RM, Ogden MD. Characterisation of aluminium black dross before and after stepwise salt-phase dissolution in non-aqueous solvents. J. Hazard. Mater. 2021, 401, 123351. DOI:10.1016/j.jhazmat.2020.123351

[9] Wan B, Li W, Sun W, Liu F, Chen B, Xu S, et al. Synthesis of cryolite (Na₃AlF₆) from secondary aluminum dross generated in the aluminum recycling process. Materials 2020, 13, 3871. DOI:10.3390/ma13173871

[10] 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

[11] 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

[12] Tang C, Wang J, Yang S, Zhang X, Li S, Lai Y, et al. Efficient extraction and recovery of lithium from waste aluminum cryolite electrolyte. Resour. Conserv. Recycl. 2023, 197, 107070. DOI:10.1016/j.resconrec.2023.107070

[13] Lv Y, Ma B, Liu Y, Wang C, Chen Y. A sustainable method for lithium recovery from waste liquids: Thermodynamic analysis and application. J. Environ. Chem. Eng. 2024, 12, 111814. DOI:10.1016/j.jece.2023.111814

[14] Wang W, Chen W, Liu H. Hydrometallurgical preparation of lithium carbonate from lithium-rich electrolyte. Hydrometallurgy 2019, 185, 88-92. DOI:10.1016/j.hydromet.2019.02.013

[15] Chen BS, Xiong JR, Xu XY, Xia HY, Yang WZ, Zhang LB. Study on the recovery process of fluorine/sodium and carbon resources in the residual anode of electrolytic aluminum by ultrasonic synergistic alkali leaching. Chem. Eng. Process. Process Intensif. 2026, 219, 110651. DOI:10.1016/j.cep.2025.110651

[16] Liu ZB, He ZK, Liu BQ, Tao WJ, Yang JX, Li JM, et al. Mechanochemical treatment and valorization of hazardous fluorine from aluminum electrolyte in spent carbon anodes. J. Environ. Chem. Eng. 2025, 13, 117988. DOI:10.1016/j.jece.2025.117988

[17] Zheng ZC, Tang YS, Yang YB, Wu JX, Jiang GS, Xue Y, et al. A review on the recycling of aluminum electrolytic spent cathode carbon: Detoxification mechanisms, recovery processes, and environmental assessment. Sep. Purif. Technol. 2025, 378, 134697. DOI:10.1016/j.seppur.2025.134697

[18] Ma LT, Cui Y, Lin Y. Aluminum smelting residue upcycling via targeted fluoride extraction and alkaline driven cryolite synthesis. Process Saf. Environ. Prot. 2025, 201, 107511. DOI:10.1016/j.psep.2025.107511

[19] Gao Q, Guo Q, Li Y, Ren B, Fu M, Li H, et al. Innovative technology for defluorination of secondary aluminum dross by alkali leaching. Miner. Eng. 2021, 172, 107134. DOI:10.1016/j.mineng.2021.107134

[20] Le VG, Vo TDH, Nguyen BS, Vu CT, Shih YJ, Huang YH. Recovery of iron(II) and aluminum(III) from acid mine drainage by sequential selective precipitation and fluidized bed homogeneous crystallization (FBHC). J. Taiwan Inst. Chem. Eng. 2020, 115, 135-143. DOI:10.1016/j.jtice.2020.10.007

[21] Han Z, Wu Y, Hao P, Tan X, Wei M, Lv X. Efficient lithium recovery from lithium-containing spent aluminium electrolyte via NaF fluorination roasting and Al₂(SO₄)₃ leaching. J. Environ. Chem. Eng. 2023, 11, 110948. DOI:10.1016/j.jece.2023.110948

[22] Stephan EF, Miller PD. Solubility of Lithium Hydroxide in Water and Vapor Pressure of Solutions above 220° F. J. Chem. Eng. Data 1962, 7, 501-505. DOI:10.1021/je60015a018

[23] 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, 21, 300-307. DOI:10.1007/s10163-018-0790-x

[24] He L, Shi L, Huang Q, Hayat W, Shang Z, Ma T, et al. Extraction of alumina from aluminum dross by a non-hazardous alkaline sintering process: Dissolution kinetics of alumina and silica from calcined materials. Sci. Total Environ. 2021, 777, 146123. DOI:10.1016/j.scitotenv.2021.146123

[25] Hien-Dinh TT, Luong VT, Gieré R, Tran T. Extraction of lithium from lepidolite via iron sulphide roasting and water leaching. Hydrometallurgy 2015, 153, 154-159. DOI:10.1016/j.hydromet.2015.03.002

[26] Tang S, Zhang M, Guo M. A Novel Deep-Eutectic Solvent with Strong Coordination Ability and Low Viscosity for Efficient Extraction of Valuable Metals from Spent Lithium-Ion Batteries. ACS Sustain. Chem. Eng. 2022, 10, 975-985. DOI:10.1021/acssuschemeng.1c06902

[27] Wang K, Hu T, Shi P, Min Y, Wu J, Xu Q. Efficient Recovery of Value Metals from Spent Lithium-Ion Batteries by Combining Deep Eutectic Solvents and Coextraction. ACS Sustain. Chem. Eng. 2022, 10, 1149-1159. DOI:10.1021/acssuschemeng.1c06381

[28] Yin X, Wang S, Liu R, Liu X, Liu P, Yang Y. New and facile recovery strategy for silver, copper, and nickel from waste silver contacts using polyiodide ionic liquids. AIChE J. 2024, 70, e18427. DOI:10.1002/aic.18427

[29] Cao R, Jia Z, Zhang Z, Zhang Y, Banthia N. Leaching kinetics and reactivity evaluation of ferronickel slag in alkaline conditions. Cem. Concr. Res. 2020, 137, 106202. DOI:10.1016/j.cemconres.2020.106202

[30] Lin M, Liu YY, Lei SM, Ye Z, Pei ZY, Li B. High-efficiency extraction of Al from coal-series kaolinite and its kinetics by calcination and pressure acid leaching. Appl. Clay Sci. 2018, 161, 215-224. DOI:10.1016/j.clay.2018.04.031

[31] Long P, Wang G, Zhang C, Yang Y, Cao X, Shi Z. Kinetics model for leaching of ion-adsorption type rare earth ores. J. Rare Earths 2020, 38, 1354-1360. DOI:10.1016/j.jre.2019.11.011

[32] 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. DOI:10.1016/j.wasman.2018.09.013

[33] Mao S, Zhang Q. Occurrence State of Carbon and Electrolyte in Anode Carbon Residue from Electrolytic Aluminum. Frontiers in Materials 2021, 8, 719563. DOI:10.3389/fmats.2021.719563

[34] Chen LJ, Huang LQ, Yuan LC, Tian L. Kinetic studies of rubidium extraction from muscovite using chlorination roasting-water leaching process. Gongcheng Kexue Xuebao/Chin. J. Eng. 2018, 40, 808-814. DOI:10.13374/j.issn2095-9389.2018.07.006

[35] Zhang X, Tan X, Li C, Yi Y, Liu W, Zhang L. Energy-efficient and simultaneous extraction of lithium, rubidium and cesium from lepidolite concentrate via sulfuric acid baking and water leaching. Hydrometallurgy 2019, 185, 244-249. DOI:10.1016/j.hydromet.2019.02.011

[36] Baba AA, Ibrahim AS, Bale RB, Adekola FA, Alabi AGF. Purification of a Nigerian talc ore by acid leaching. Appl. Clay Sci. 2015, 114, 476-483. DOI:10.1016/j.clay.2015.06.036

[37] Tan Q, Deng C, Li J. Effects of mechanical activation on the kinetics of terbium leaching from waste phosphors using hydrochloric acid. J. Rare Earths 2017, 35, 398-405. DOI:10.1016/S1002-0721(17)60925-6

[38] Billy E, Joulié M, Laucournet R, Boulineau A, De Vito E, Meyer D. Dissolution Mechanisms of LiNi_1/3Mn_1/3Co_1/3O₂ Positive Electrode Material from Lithium-Ion Batteries in Acid Solution. ACS Appl. Mater. Interfaces 2018, 10, 16424-16435. DOI:10.1021/acsami.8b01352

[39] Reynolds JG, Belsher JD. A Review of Sodium Fluoride Solubility in Water. J. Chem. Eng. Data 2017, 62, 1743-1748. DOI:10.1021/acs.jced.7b00089

[40] 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