Enhancing the separation of Fe/Al/Ca impurities from metallurgical silicon to purify by slagging-directional solidification

Metallurgical silicon (MG-Si) with low content of Fe, Al and Ca impurities is very important for the production of organosilicon. A novel approach of slagging-directional solidification was investigated to remove Fe, Al and Ca impurities. Firstly, the study analyzed the effect of cooling methods and solidification rates on removal of Fe, Al and Ca impurities during directional solidification without the slagging agent. Then, the crystal morphology and impurity micromorphology of silicon ingots obtained with optimal conditions were analyzed and found the shape of the impurity was related to the crystal morphology of the ingot, precipitating at grain boundaries. On this basis, the removal of Fe, Al and Ca impurities by the slagging-directional solidification was studied. The result showed Al and Ca impurities in silicon were few and a small amount of Fe impurity was in the form of Fe–Si. The mechanism of the slagging-directional solidification was analyzed and revealed that it not only effectively removed Al and Ca impurities from MG-Si, but also decreased the effective segregation coefficient of Fe and enhanced the separation of Fe impurity. The method of slagging-directional solidification provides a new idea for the separation of Fe, Al and Ca from MG-Si.