Kinetics of Electrically Enhanced Boron Removal From Silicon Using CaO-SiO2 and CaO-SiO2-Al2O3 Slag

An approach in analyzing the kinetics of reacting metallurgical system enhanced by applied
electrical potential difference has been proposed. The approach accounted the electrochemical
mechanism by combining Fick’s first law and Nernst–Planck equation, building upon the
approach by Kim et al. and extending it to simultaneously solve the key kinetics parameters of
boron diffusivity in slag (D(B)) and potential difference (D/s) across the slag phase. The
approach was utilized to examine the kinetics of enhanced boron removal from silicon with
CaO-SiO2 and CaO-SiO2-Al2O3 slags, in the context of silicon recycling and refining. The model
was used to describe the mobility of boron in the molten silicon and slag phases, i.e., boron mass
transfer coefficient in liquid silicon (km), in the slag (ks), and the diffusivity of boron in slag
phase (D(B)). The results demonstrated that the new kinetics model fit well with the experimental
data with an average coefficient of determination (R2 value) of 0.91. The ks and D(B) were
calculated to be in the range of 0.9 to 1.3 9 10–6 and 1.1 to 29.2 9 10–9 m2 s�1, respectively. The
application of external voltage was observed to reduce B final concentration in the silicon phase
by 18 pct from approximately 120 to 100 ppmw in all samples. The addition of Al2O3 in the slag
phase consistently reduced the mobility of boron in the slag phase by approximately 50 pct.