Mechanisms of impurity redistribution and removal in MG- Si during Tri-Arc melting

This study investigates impurity removal mechanisms in metallurgical-grade silicon (MG-Si) during arc melting using a three-electrode Tri-Arc TA-200 system. The multi-electrode configuration is reported in the literature to provide improved thermal uniformity and enhanced melt stirring, which may affect impurity redistribution pathways. Two pre-treatment conditions were examined: mechanical milling in air and in a protective ethyl alcohol medium, followed by arc melting under an argon atmosphere. X-ray fluorescence analysis shows that the initial MG-Si (98.9 wt% Si) undergoes substantial purification, reaching 99.6 wt% after alcohol-assisted milling and arc melting. A nearly complete removal of Fe, Ca, V, and several transition metals was achieved, while aluminium content was reduced by more than three times. The results demonstrate that impurity removal is governed by a combination of high-temperature evaporation, segregation into surface slag phases, and enhanced mass transport driven by arc-induced melt convection. The protective alcohol environment suppresses oxide formation prior to melting, thereby facilitating more efficient impurity migration and elimination. The reduction of Fe and Al impurities is particularly important for photovoltaic silicon, as these elements act as recombination centers and reduce carrier lifetime in solar cells. Therefore, the proposed Tri-Arc melting approach is presented as a laboratory-scale preliminary pre-refining strategy and is not yet competitive with established industrial silicon purification routes.