Takayuki Watanabe*, Makoto Soyama*, Atsushi Kanzawa*, Akihiro Takeuchi# and Mamoru Koike#

*Department of Chemical Engineering, Tokyo Institute of Technology, O-okayama, Meguro-ku, Tokyo 152-8552, Japan
watanabe@o.cc.titech.ac.jp

#Electrotechnology Applications R&D Center, Chubu Electronic Power Co., Inc., Ohdaka-cho, Midori-ku, Nagoya, 459-8552, Japan

1. INTRODUCTION

Thermal plasma reduction of silica-alumina mixture for production of metals was investigated experimentally. The finding of the reaction mechanism would be applied to metal recovery form coal ash.

2. RESULTS

Thermal equilibrium and Gibbs free energy changes of the reaction systems were calculated to predict the evaporated species and to evaluate the possible reaction. Atomic hydrogen plays an important role in the reduction of silica-alumina mixture.

Argon or argon-hydrogen plasma jet (200 A, 20 V, 1 atm) was used for the treatment of silica-alumina sample with various compositions. The evaporated species were identified with spectroscopic measurements and EDX (Energy Dispersive X-ray Spectrometry). The residual species after the treatment were identified with XRD (X-ray Diffractometry) and EDX.

The reaction mechanism of silica alumina mixture with thermal plasmas has been concluded as follows from the experimental results:

1. Argon plasmas produce Si metal and SiO from silica-alumina mixture, while the alumina has not been reduced.
2. Argon-hydrogen plasmas produce Si metals mainly with some addition of SiO, Al2O and Al metal as shown in Fig. 1.
3. Silicon metal with some addition of SiO was evaporated with the purity of 99% from silica-alumina mixture.