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 mu m (conventional roasting) to 4.56 mu m 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.