Boron removal from metallurgical-grade silicon using lithium containing slag

The possibility of extracting boron impurity from metallurgical-grade silicon by lithium containing slag refining for solar cell application was investigated. The distribution coefficients of boron between CaO–SiO2–Li2O and CaO–SiO2–LiF slags were examined. The boron content in the refined silicon was studied under different conditions of mass ratio of slag to silicon and refining time. The results showed that a small amount of Li2O or LiF had significant effect on the distribution coefficients of boron. The removal of boron impurity using CaO–SiO2–LiF system was more effective than using CaO–SiO2–Li2O system. Values of boron content in the refined silicon did not decrease significantly when the mass ratio exceeded 4, while it had been obviously falling with the increase in refining time. When the mass ratio of CaO–SiO2–Li2O slag to metallurgical-grade silicon was 4, the boron content in silicon was successfully reduced from 2.2 × 10− 5 to 1.3 × 10− 6 after slag refining for 2 h at 1823 K.