Thermodynamics of boron removal in slag refining of Fe-Si alloy

Two metallurgical purification techniques, namely solvent refining and slag treatment, were combined to remove boron from silicon. Silicon was alloyed with iron and the alloy was subjected to slag treatment by a ternary of CaO-SiO2-Al2O3 at 1600 °C (1873 K). Effects of oxygen potential and basicity of slag on boron removal were investigated through changing the SiO2/Al2O3 and CaO/SiO2 ratios, respectively. Results indicate that these two parameters have major effects on partition ratio of boron. A critical oxygen potential value, which yields the highest partition ratio of boron, was calculated as approximately 9 × 10−18 atm. Partition ratio of boron was normalized with oxygen potential at each slag composition in order to isolate the effect of basicity. Borate capacity values were calculated for different slags and it was shown that this parameter is only a function of temperature and slag composition. The kinetics of boron removal was quantified and the total mass transfer coefficient of boron was calculated as 7.48 × 10−6 cm/s.