Study of the Preparation of High Purity Silicon by a New Electro-thermal Metallurgy Method

A new electro-thermal metallurgy method to prepare high purity silicon (ASTM A 922) was developed in this paper. CaO-SiO2 were added into raw materials as slagging agents during the smelting process in order to improve the purity of the silicon products. This method combined the smelting process with the slag refining process into one step. It not only simplified the technological process, but also decreased the production cost of SoG-Si significantly. In this study, the distribution of impurity elements in different areas of the crucible was studied and the mechanism of impurity elements removed by the slag phase was also investigated. Phosphorus (P) in liquid Si could diffuse into the slag/Si interface and react with SiO2 which was derived from the melted slag phase. Then the reaction product P2O5 would diffuse into the melted slag phase from slag/Si interface and react with CaO to form the stable compound 3CaO ·P2O5. Compared to the result without adding slagging agents, the concentration of elements Fe, Al, P and S was reduced by 90.71%, 63.90%, 44.52% and 56.93% with this new method. The purity of silicon product can reach up to 99.6%. The results indicate that adding slagging agent into the raw materials during the smelting process is beneficial to remove impurity elements and improve the purity of the silicon product.