Preparation of Crystalline Silicon by Magnesiothermic Reduction Combined Acid Etching Routes from Silica Fume

Silica fume (SF, containing SiO2>85%, in mass fraction) collected from emitting soot of silicon-metallurgical workshop was used as a raw material for preparation of pure crystalline silicon. Silicon was prepared via refining pretreatment of pristine SF and ball-milling mixing to make magnesium and SF powder reactant, subsequent magnesiothermic reduction reaction (MRR) process and final purification by two-step acid-etching treatment of HCl-HF acids. The experimental results show that a core-shell structure Mg@SiO2, i.e., Mg particles coated uniformly by a dense layer of submicron-sized primary particles of silica fume in a desired stoichiometric ratio of reactants Mg:SiO2 of 0.85:1.00, is formed via micron-scale diffusion reaction after mixing for 12 h at a rotational speed of 150 r/min. A high-performance route of MRR was proposed based on the wrapping- micron-reactor model. The extent of MRR is as high as 96% and Si species of HCl-etched sample are more than 90% (in mass fraction), and the final prepared product of crystalline silicon achieves a purity of 99.88% (in mass fraction) after HF+CH3COOH acid-etching. © 2020, Editorial Department of Journal of the Chinese Ceramic Society. All right reserved.