Defluoridation of spent cathode carbon using molten salt assisted roasting

Spent cathode carbon (SCC), generated during production of aluminum electrolysis was classified as hazardous solid waste for contain fluoride and cyanide. The harmless treatment is great significance in reducing environmental pollution and resource recovery. This study investigated the optimal process parameters and action mechanism for Na₂CO₃ and Na₂SiO₃ assisted roasting SCC. Under optimal conditions, C and F content of roasting solid products by Na₂CO₃ and Na₂SiO₃ were 95.78 wt%, 1.4 wt% and 86.57 wt%, 1.27 wt%, respectively. Na₂CO₃ reacts with CaF₂ and Na₃AlF₆ inside the pores by infiltration to form NaF and generate thermal stresses to reduce median particle size of SCC from 5.98 μm (conventional roasting) to 4.56 μm and promoting fluoride removal. Na₂SiO₃ could effectively remove Na₃AlF₆ and adheres to surface of carbon as spherical particles. The results provide a reference basis for efficient defluoridation and fixed carbon high-value recycling, which consistent with green and sustainable development concept.