Removal of Phosphorus from Si-Fe Alloy by CaO-Al 2 O 3 -SiO 2 -Na 2 O Slag Refining

A combination of slag and solvent refining methods was used to remove phosphorus from silicon. The CaO-Al2O3-SiO2-Na2O quaternary system was selected as the slag to eliminate phosphorus from Si-20 wt.% Fe alloy at 1300°C. The partition ratio of phosphorus (LP) at various slag compositions was obtained to investigate the effect of basicity (CaO/SiO2), oxygen potential (SiO2/Al2O3) and Na2O content of the slag. The maximum value for LP was 1.19 at CaO/SiO2 of 1.36, SiO2/Al2O3 of 1.56 and the addition of 10 wt.% of Na2O. The critical partial pressure of oxygen for maximum phosphorus removal was estimated at 1.8 × 10−22 atm. The normalized distribution and phosphate capacity were evaluated to clarify the effect of basicity. Corrected optical basicity and NBO/T were determined to consider the effect of the cations in the complex silicate structures and investigate the effect of the degree of depolymerization on the efficiency of phosphorus removal from silicon.