A combination of slag and solvent refining methods was used to remove phosphorus from silicon. The CaO-Al 2 O 3-SiO 2-Na 2 O quaternary system was selected as the slag to eliminate phosphorus from Si-20 wt.% Fe alloy at 1300°C. The partition ratio of phosphorus (L P) at various slag compositions was obtained to investigate the effect of basicity (CaO/SiO 2), oxygen potential (SiO 2 /Al 2 O 3) and Na 2 O content of the slag. The maximum value for L P was 1.19 at CaO/SiO 2 of 1.36, SiO 2 /Al 2 O 3 of 1.56 and the addition of 10 wt.% of Na 2 O. The critical partial pressure of oxygen for maximum phosphorus removal was estimated at 1.8 9 10 À22 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.

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A hybrid process of slag and solvent refining was used to remove boron and phosphorus from silicon. Quaternary slag of CaO-Al2O3-SiO2-Na2O was employed to remove boron (B) and phosphorus (P) from Si-20 wt% Fe alloy at 1300 °C. A slag-to-metal ratio of one was used at different reaction times. The mass transfer coefficient of B and P in the slag and alloy phases was calculated to determine the rate-limiting step. The mass transfer coefficients of B in the alloy and slag phases were 6.6 × 10−7 ms−1 and 2.8 × 10−7 ms−1, respectively. The mass transfer coefficients of P in the alloy and slag phases were determined to be 7.5 × 10−8 ms−1 and 3.5 × 10−7 ms−1, respectively. The rate-limiting stage of the slag–alloy reaction kinetics was mass transport in the liquid slag for B and mass transport in the alloy phase for P.