Separating and Recycling of Elemental Silicon from Wasted Industrial Silicon Slag

In the secondary refining process of industrial silicon, approximately 15 pct of the silicon is trapped in the silicon slag. Thus, the separation and recovery of silicon from the industrial silicon slag are highly significant for the reuse of silicon resources. Based on the large difference among the melting temperature, density, and viscosity of the silicon and slag in silicon slag, a high-temperature resistance furnace and a medium-frequency induction furnace were used to investigate the separation of elemental silicon from industrial silicon slag. The elemental silicon was almost completely separated using a smelting temperature of 1550 °C and blowing stirring for 2 hours in the high-temperature resistance furnace. The effective separation between silicon and slag can be achieved in a relatively short time when electromagnetic stirring was used in the medium-frequency induction furnace. Silicon can be separated from silicon slag with 15 kW of heating power and 0.5 h of smelting holding time. However, a small amount of silicon was still included in the remaining slag phase. Then, elemental silicon was completely separated by adding a CaO–SiO2–CaCl2 slag reagent to the silicon slag raw material. Our work shows that the high-temperature resistance furnace and the medium-frequency induction furnace can be used to achieve the separation of silicon and slag while simultaneously also achieving the purification of elemental silicon samples.