Removal of impurities from metallurgical grade silicon with metal assisted chemical leaching

Abstract

In this study, a novel metal assisted chemical leaching (MACL) was proposed to remove impurities from metallurgical grade silicon (MG-Si). HF acid leaching, one step MACL (1-MACL, HF + AgNO3) and two step MACL (2-MACL, HF + AgNO3 + H2O2) were employed to purify MG-Si. The typical precipitates at Si grain boundaries before and after leaching were observed and analyzed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The leaching results show that the impurities removal efficiency is 2-MACL > 1-MACL > HF acid leaching. After 2-MACL, the impurities (Fe, Al, Ca, Ti, Mn, Ni, Cu, V, Cr, Ag, B and P) concentration can be reduced from 4550.40 ppmw to 106.09 ppmw and the purity of MG-Si increased from 99.55 to 99.99%. It is notable that the introduction of micro-scale “channels” can facilitate the impurities removal when compared to solely HF leaching, especially for some non-dissolving metallic impurities like copper, calcium and aluminum. It should be noted that 2-MACL has obvious effect on the removal of non-metallic impurities B and P.