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

Abstract

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 (LB) was investigated. Consequently, the local minimum and maximum LB 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.