Recovery of the majority of resources from hazardous waste carbon dross using a new combined flotation-leaching method: Process and mechanism

Carbon dross, a hazardous waste from aluminum electrolysis, poses a challenge to the global aluminum industry. This paper proposes a combined flotation-leaching (CFL) method to recover valuable resources from carbon dross, and achieved a total recovery yield of 95.9%. This included 17.35% carbon powder (95.67 wt% purity) and 78.55% electrolytes (99.65 wt% purity). Kinetics results showed that the carbon dross flotation process followed the classical first-order model, while fluoride ion leaching followed the shrinking core model, controlled by internal diffusion. Leaching thermodynamic calculations indicated that Na 3 AlF 6 was the main impurity removed. DFT calculations showed that the higher surface energy of the Al exposed surface and the lower binding energy with NaOH resulted in a higher reaction rate for alkaline leaching compared to acid leaching, but with poorer leaching efficiency. Treating one ton of carbon dross with CFL reduces at least 539 kg of CO 2 emissions, aiding carbon reduction in the aluminum industry. • Carbon with over 95% purity and electrolytes with over 99.6% purity are obtained via CFL method. • The flotation and leaching processes follow the classical first-order and shrinking core models, respectively. • The key to leaching and purification is the dissociation of cryolite. • The DFT results of cryolite explain differences in reaction rates and effectiveness of acid and alkali leaching. • The CFL method can reduce 539 kg of CO 2 emissions for every ton of carbon dross processed.