Removal of Impurities from Metallurgical Grade Silicon by Liquation Refining Method

摘要

To develop a new method of refining silicon for use in solar cell materials, liquation refining with Al-Si alloying was proposed for purification of metallurgical grade silicon (MG-Si). The morphologies of impurities, especially for phosphorus and iron, before and after purification were analyzed. By alloying MG-Si with Al, phosphorus in MG-Si formed Al-Si-Ca-P impurity phase and iron formed skeletal-shaped a-Al_8SiFe_2 phase into the Al-Si eutectic phase from MG-Si with the presence of Al. It can be concluded that removal mechanism of phosphorus and iron was not only a segregating process, but also a recombining process within certain elements to form specified impurity phases. By centrifugal separation, average separation ratio was 75.73 and average recovery ratio was 82.52 for Al-45Si system, which is better than traditional separation methods and avoids considerable loss of Al and acid. After refining for four times, mass fractions of phosphorus and boron were reduced to 0.46 × 10~(-6) and 0.21 × 10~(-6) respectively. For transition metal impurities, Fe, Ti and Mn, removal fractions of those all were more than 95.