Study on recycling Si from silicon diamond-wire saw cutting waste by a slag refining process in industrial scale

Silicon cutting waste (SCW) produced during silicon wafer producing process mainly consists of Si (80-85 wt%), SiO2 (13-16 wt%) and other impurities (2-4 wt%). In this paper, a slag refining process was proposed to recycle Si from SCW for producing high-quality silicon. CaO was used as fluxing agent to react with SiO2 for forming compounds with low melting point and viscosity during recycling process. The influences of CaO addition amount and refining time on recovery ratio of SCW and purity of Si products were investigated. Under the optimized conditions of a CaO addition amount of 8 wt% and a refining time of 50 min, the recovery ratio of SCW and the purity of Si products can achieve 59.59% and 99.56%, respectively, in laboratory-scale experiments. The separation mechanism of Si from SCW is that the external SiO2 film is digested by CaO, and then the internal Si is exposed and melted into liquid Si. This method was successfully applied for recycling Si from SCW in industrial -scale and the recovery ratio of SCW can reach 60%. Economical evaluation shows that this method can bring enormous economic benefit ($0.98/kg SCW).