Abstract
To develop a high-efficiency process for removing phosphorus (P) from metallurgical grade silicon, a novel method of combining Si-Cu solvent refining and CaO-CaF(2)-CaCl(2) slag treatment was investigated through simultaneously re-constructing P-containing phases of CaCu(2)Si(2) in the Si-Cu alloy and Ca(3)P(2) in the slag. After acid leaching, P-containing phases can be eliminated, whereupon high-purity silicon could be recovered from the Si-Cu alloy. The effect of slag components and alloy composition on the P removal efficiency was studied systematically. When the Si-40 wt.% Cu alloy is treated with 20 wt.% CaO-32 wt.% CaF(2)-48 wt.% CaCl(2) slag for 60 min at 1400 °C, the P removal efficiency reaches 90.1%. Furthermore, the mechanism of enhanced P removal was also discussed. It was indicated that a silicothermal reduction reaction occurred between CaO and Si, which caused Ca to migrate into the alloy and precipitate the P-containing CaCu(2)Si(2) in the Si-Cu alloy. Simultaneously, P in silicon is reduced to P(3-) at the slag-alloy interface, forming Ca(3)P(2) in the slag, thereby establishing a dual-path purification mechanism. Hence, this study provides new insight into silicon high-efficiency purification from economical and practical considerations.