Reduction and separation of silica-alumina mixture with argon-hydrogen thermal plasmas

Thermal plasma reduction of a SiO2-Al2O3 mixture for metal production was i nvestigated. The understanding of the reaction mechanism would be applied t o metal recovery from coal ash. Thermal equilibrium and free energy of form ation of the reaction systems were estimated to predict the evaporated spec ies and to evaluate the predominant reactions. Atomic hydrogen plays an imp ortant role in the reduction of the SiO2-Al2O3 mixture. Argon and argon-hyd rogen plasma jets were used for the treatment of the SiO2-Al2O3 mixture wit h various compositions. The argon plasma produces gaseous silicon and SiO f rom the SiO2-Al2O3 mixture, though the recovered amount was very little, wh ile Al2O3 has not been reduced. The argon-hydrogen plasma produces mainly g aseous silicon with some additions of gaseous SiO and aluminum. Both of the argon and the argon-hydrogen plasmas produce the silicon component collect ed as the fumes having the purity of 98-99% from the SiO2-Al2O3 mixture. (C ) 1999 Elsevier Science S.A. All rights reserved.