Distribution of Boron Between Silicon and CaO-MgO-Al2O3-SiO2 Slags

Production of solar-grade silicon through metallurgical refining methods can be less expensive than current production methods both in terms of energy use and capital cost. Slag refining is a potential metallurgical refining method for removal of boron from silicon. The distribution of boron between silicon and binary CaO-SiO2 and MgO-SiO2 slags, and between silicon and ternary CaO-MgO-SiO2 and CaO-Al2O3-SiO2 slags has been investigated in this work at 1873 K (1600 A degrees C). The distribution coefficient of boron has been found to be between 2 and 2.5 in the binary CaO-SiO2 and MgO-SiO2 systems. It has also been found to be in the same range across the entire CaO-MgO-SiO2 system. In these systems the distribution coefficient is unaffected by slag composition. The distribution coefficient has been found to decrease with increasing Al2O3 content in the slag in the ternary CaO-Al2O3-SiO2 system.