Phase Transition of Waste Silicon Carbide Side Block from Aluminum Smelters During Vacuum High-Temperature Detoxification Process

Waste silicon carbide side block (WSB) from aluminum reduction cells are considered as hazardous materials since they contain a large amount of soluble fluoride salts. The storage of this material outside or in landfills is detrimental for the environment. A joint temperature-vacuum controlling process for treating WSB is proposed in this paper. Thermodynamic analysis by FactSage 7.0, and a series of experimental investigation and characteristics tests on the product materials by SEM and XRD were carried out. The results showed that the fluoride in the waste side block was completely volatilized, and the silicon nitride was also decomposed after being treated at 1600 degrees C under a vacuum of 10 Pa. The soluble fluoride concentration was reduced from 2216 mg L-1 to 3.9 mg L-1, and the silicon carbide content was increased from 76.7 wt.% to 91.5 wt.%.