The aim of this work is the purification of metallurgical grade silicon for photovoltaic applications using a thermal plasma process. In this study, the plasma treatment was combined with a DC bias of the liquid silicon to increase the kinetics of the impurities extraction. On-line measurement by optical emission spectroscopy (OES), ex-situ analysis by laser induced breakdown spectroscopy (LIBS) and ICP techniques allowed to demonstrate that elimination of cationic impurities (Fe, Al, Ca, etc.) increased when the positive bias increased. The ICP results show that a high positive bias leads to a purification factor of about 10 for most of the impurities. (c) 2007 Elsevier B.V. All rights reserved.