Improved removal of boron from metallurgical-grade Si by CaO-SiO2-CaCl2 slag refining with intermittent CaCl2 addition

CaO-SiO2-CaCl2 slag refining with intermittent CaCl2 addition has been performed to eliminate boron from metallurgical-grade silicon (MG-Si). The boron-removal efficiency was measured at different refining times, refining temperatures, and amounts of added CaCl2; boron amounting to 90% was removed from the MG-Si. The experimental results show that intermittent CaCl2 addition promotes the elimination of boron from the silicon. The impurity distributions and micro-morphologies of the slag and silicon are examined. The mass transfer coefficient of boron from silicon to the slag is calculated as 3.64 × 10−4-10−6 cm/s (r (droplet radii) = 50-5000 μm at 1873 K (1600 °C)) and 4.41 × 10−4-10−6 cm/s (r = 50-5000 μm at 1973 K (1700 °C)). The reaction mechanism of boron removal is discussed as well. This method shows potential for simplifying the industrial manufacturing of solar-grade silicon.