Preparation of High-Quality Silicon with Silicon Cutting Waste by a Carbothermal Reduction Method

Silicon cutting waste (SCW) mainly consists of Si (80 similar to 85 wt%), SiO2 (13 similar to 16 wt%) and other impurities (2 similar to 4 wt%). Nowadays, the Si in SCW is commercially recycled to produce Si ingots by a slag refining method, but the SiO2 in SCW is melted into silicon slag and discarded as waste. In this paper, a carbothermal reduction method has been proposed for recycling Si resources from both Si and SiO2 in SCW to prepare high-quality silicon in a submerged arc furnace. Petroleum coke was selected as the carbonaceous reducing agent. Firstly, the effects of carbon content on the equilibrium compositions of the Si-SiO2-C system were simulated. Secondly, SCW was mixed with petroleum coke under the guidance of thermodynamic analysis results. Finally, the mixtures were charged into furnace and smelted. Thermodynamic equilibrium analysis results showed that the value of n((Si)):n((C)):n((SiO2)) should be controlled as 2.62:0.22:0.44 theoretically. Experimental results revealed that the recovery ratio of SCW was 50% and the purity of Si products was 99.40%. This proposed method provides an effective and industrialized applicable approach for recycling SCW.