Clean Preparation of High-Purity Silicon from Rice Husk Ash by a Modified Metallurgical Method

Rice husk ash (RHA) has been used to prepare high-purity silicon by a combination of a silicon preparation process and a refining process. Raw materials including RHA, silica sand and SiO2-CaO-Al2O3 slag were initially pelletized and then smelted in an electric arc furnace. The results show that slag refining and acid leaching have significant influences on purifying Si products. With the addition of slag, the purity of Si increased from 94.96% to 96.47% and the contents of impurities such as Fe and P reduced from 2.06 wt.% and 0.09 wt.% to 0.77 wt.% and 0.05 wt.%, respectively. After acid leaching, the purity of the Si increased to 99.76% and the content of P reduced to 0.029 wt.%. The leaching kinetics analysis results show that the surface chemical reaction model is suitable to describe the extraction process of Fe, Al, and Ca in silicon.