Silicon recovery from silicon sawing waste by removal of SiC impurity via CaO–SiO2–Na2O slag absorption

Abstract

The removal of SiC restricts the recycling of silicon from wire sawing waste. Although the silicon in sawing waste can be easily enriched to around 90 wt%, it is difficult to further increase the purity. In this study, silicon ingot was successfully recovered from silicon sawing waste by using a CaO–SiO2–Na2O slag refining method. CaO–SiO2 slag was selected to absorb SiC particles from liquid silicon owing to its excellent wettability on SiC. Na2O was used to decrease the slag viscosity and improve the SiC transfer. SiC mass transfer coefficients in molten slag were calculated for different Na2O contents. The effects of operating variables on SiC removal and silicon yield were investigated, including the Na2O content, refining time, and slag/silicon ratio. The best result was a decrease of SiC content to less than 0.19 wt% from 9.07 wt% in the silicon ingot and a silicon yield of 76.5%.