Purification of Metallurgical Grade Silicon Via the Mg-Si Alloy Refining and Acid Leaching Process

Abstract

A novel process by combining Mg-Si alloy refining and acid leaching was suggested to purify metallurgical grade Si (MG-Si) in this paper. The proposed process was mainly composed of three steps, such as electromagnetic solidification, evaporation, and acid leaching. The results show that the precipitated Mg2Si crystals in the Mg-Si melt were successfully separated and enriched at the bottom of the sample because of the electromagnetic stirring and temperature gradient. Then, a porous structure Si with pore sizes ranging from nanometer- to micrometer-scale was obtained by evaporating Mg from the Mg2Si crystals. Finally, the high-purity Si powders with a purity of 99.995% were prepared by employing a successive acid leaching process. Most of the impurities (B, P, Fe, Ca, Ti, Ni, V, Cu) can be removed to less than 1 ppmw after the leaching process, indicating that an efficient elimination of impurities can be achieved with the help of the porous structure. Although bits of Mg was contained in the purified Si, it is expected to be eliminated by using a vacuum directional solidification. During the process, most of the magnesium can be recycled for cyclic utilization, which should be beneficial for the cost reduction. Therefore, it could be proposed that an efficient method of Si purification was obtained, which may be a valuable idea for the fabrication of solar grade silicon (SoG-Si).