Industrial & Engineering Chemistry Research, Vol.56, No.45, 12864-12870, 2017
Waste Photovoltaic Panels for Ultrapure Silicon and Hydrogen through the Low-Temperature Magnesium Silicide
Circulation technology of waste photovoltaic panels for production of ultrapure silicon and energy in the form of hydrogen storage was designed and verified. Preparation of magnesium silicide from waste photovoltaic panel's silicon and partially oxidized magnesium was thoroughly studied. Work was focused on process optimization, thus, three groups of reactors were tested, namely the continuously evacuated open reactor, pre evacuated batch reactor and semiopened reactors. The influence of reaction temperature was evaluated in the range of 330-630 degrees C for various reaction atmospheres; argon and/or air at pressures of 5, 33, and 100 kPa; and vacuum in the range of 5-30 Pa. The effect of nitrogen and oxygen presence in the atmosphere on the resulted reaction and reaction rate was also thoroughly studied. The minimum reaction time guaranteeing the total conversion of silicon for two purifies of used magnesium was also determined. The produced materials were analyzed by dispersive Raman spectroscopy, scanning electron microscopy with energy dispersive X-ray spectroscopy, and X-ray diffraction. Finally, the reactor filling, which significantly influenced the formation of magnesium silicide, was tested and established minimally at 30% of reactors volume. Hydrolysis of obtained magnesium silicide by diluted acid for silicon hydrides' (silanes) production and their subsequent thermal decomposition into the ultrapure silicon and hydrogen were successfully verified.