Separation of boron and phosphorus from Cu-alloyed metallurgical grade silicon by CaO–SiO2–CaCl2 slag treatment

Abstract

Abstract A purification method using copper (Cu) alloying and CaO–SiO 2 –CaCl 2 slag treatment had been studied in connection with the purification of metallurgical grade silicon (MG-Si). The principle of this method was that low-purity MG-Si alloyed with Cu to form Si–Cu alloy phase, and then the Si–Cu alloy was treated using CaO–SiO 2 –CaCl 2 slag to remove impurities. Finally, selective acid leaching was applied to remove the Si–Cu alloy phase, whereupon high-purity silicon could be recovered from the Si–Cu alloy. Effects of slag composition and Cu content on the removal of boron (B) and phosphorus (P) were also investigated. When the Si–50 wt% Cu alloy treated with 45 wt% CaO–45 wt% SiO 2 –10 wt% CaCl 2 slag for 30 min at 1550 °C, the final concentrations of B and P in the purified Si decreased from 3.12 to 0.35 ppmw and 17.14 to 7.27 ppmw, respectively. Furthermore, the corresponding removal mechanism was investigated. It was found that the reaction kinetics followed a first-order rate law with respect to B and P, and were controlled by mass transfer with mass transfer coefficients of 6.25 × 10 −4 cm s −1 and 2.55 × 10 −4 cm s −1 , respectively.