Thermodynamics and Kinetics of Boron Removal from Metallurgical Grade Silicon by Addition of High Basic Potassium Carbonate to Calcium Silicate Slag

In this study, we investigated the thermodynamics and kinetics of boron removal from metallurgical grade silicon (MG-Si) using a calcium silicate slag containing a high basic potassium carbonate. The distribution of boron between slag and silicon was theoretically derived and the distribution coefficients (L _B) of boron with different compositions of CaO, SiO₂, and K₂CO₃ in slag reagents were determined. The maximal value of L _B reached 2.08 with a high basicity slag of 40 pctCaO-40 pctSiO₂-20 pctK₂CO₃ (Λ = 0.73). The boron removal rates from MG-Si using CaO-SiO₂ and CaO-SiO₂-K₂CO₃ slags at 1823 K (1550 °C) were investigated in an electromagnetic induction furnace. The results showed that the boron concentration in MG-Si can be reduced from 22 to 1.8 ppmw at 1823 K (1550 °C) with 20 pct K₂CO₃ addition to calcium silicate slag, where the removal efficiency of boron reached 91.8 pct. The mass transfer coefficient (β _S) of boron in binary 50 pctCaO-50 pctSiO₂ slag was 3.16 × 10⁻⁶ m s⁻¹ at 1823 K (1550 °C) and was 2.43 × 10⁻⁵ m s⁻¹ in ternary 40 pctCaO-40 pctSiO₂-20 pctK₂CO₃ slag.