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

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

Yonghong Qin 1,2,3,* Xiaodi Niu 2,3 Xianglin Li 2,3 Yujiao Liu 2,3 Zihe Pan 2,3 Jianming Gao 2,3 Yanxia Guo 2,3 Xinran Zhu 1,4,*

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1
State Key Laboratory of Mineral Processing, Beijing 100160, China
2
Institute of Resources and Environmental Engineering, Shanxi University, Taiyuan 030006, China
3
State Environmental Protection Key Laboratory on Efficient Resource-Utilization Techniques of Coal Waste, Shanxi University, Taiyuan 030006, China
4
School of Resources and Civil Engineering, Northeastern University, Shenyang 110819, China
*
Authors to whom correspondence should be addressed.

Received: 08 May 2026 Revised: 13 May 2026 Accepted: 22 May 2026 Published: 09 June 2026

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© 2026 The authors. This is an open access article under the Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0/).

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Green Chem. Technol. 2026, 3(3), 10020; DOI: 10.70322/gct.2026.10020
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

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