Evaporation Removal of Boron from Metallurgical-Grade Silicon Using CaO-CaCl2-SiO2 Slag

In order to optimize the B removal during slag-refining process for solar-grade silicon production, a new process for the removal of B in molten Si was proposed based on the principle of oxidized chlorination and evaporation. B can be generated and evaporated in the form of B-containing gas on the basis of calculated vapor pressures of forming species in the BO1.5-CaCl2 slag at 1723 K (1450 °C). CaO-SiO2-CaCl2 slag was selected to remove B in molten Si. In the slag-refining experiments, compared with the binary systems of CaO-CaCl2 and SiO2-CaCl2 slag, the ternary slag system CaO-SiO2-CaCl2 showed a better potential (86 pct) for B removal. Furthermore, the relationships among the removal efficiency, the estimated evaporative efficiency, and the partition ratio were all discussed.