Boron removal from metallurgical-grade silicon by CaO–SiO₂ slag refining

Boron removal from metallurgical-grade silicon (MG-Si) using CaO–SiO₂ slag was studied by employing a medium-frequency electromagnetic induction furnace. The relationship between the optical basicity (Λ) of the CaO–SiO₂ slag and the distribution coefficient of boron (L _B) was investigated. Consequently, the local minimum and maximum L _B values of 0.72 and 1.58 are obtained when Λ = 0.56 and Λ = 0.71, respectively. The boron content in MG-Si decreases gradually with refinement time increasing, down to a minimum value of 4.73 × 10⁻⁶. The controlling step in the removal of boron from MG-Si is not the chemical reaction at the interface of the slag and silicon. Instead, the controlling step is a diffusion mass transfer, in which boron impurities diffuse from molten silicon to the interface of the slag and silicon, or B₂O₃ formed by the chemical reaction diffuses from the slag–silicon interface to molten slag.