Purification of Metallurgical-Grade Silicon by Solvent Refining Using Si–Zn Alloy
摘要
The purification of metallurgical-grade silicon by combining solvent refining of Si-Zn alloy with directional solidification is proposed and investigated. At 1123 K, directional solidification tests were conducted on a Si-Zn alloy with a Si concentration of 6 at% with the moving-up speed in the range of 2–300 mm h–1. Si crystals were obtained by leaching and dissolving Zn from the solidified Si-Zn alloy using hydrochloric acid. The grain size of the obtained Si crystals increased at slower moving speed and condensed at the top. The purity of the Si particles was also investigated. The removal rates differed slightly depending on the moving speed. The removal rate of Al was over 99%, that of Fe and Ti was over 95%, and that of Ca was approximately 90%. Even for B and P, which were difficult to remove from Si, high removal rates of approximately 99% and 55–72%, respectively, were achieved. This study confirmed that the new purification method combining solvent refining using the Si-Zn alloy system with directional solidification is a promising process for solar-grade Si production.