Microwave-assisted carbothermal reduction of rice hull ash to biogenic silicon

Abstract

Rice hull is an agricultural waste disposed of globally in large quantities. However, it is an attractive biomass resource, containing at least 15–20 wt% amorphous silica. Herein, biogenic Si production was attempted by direct carbothermal reduction of rice hull ash using a microwave heating source. Si was prepared from rice hull ash with a C-to-SiO2 ratio (in mole ratio) of 1.0 at 1564 °C after 15 min of 1500 W microwave irradiation. Although it is still difficult to evaluate the yield, the possibility of producing metallic Si at lower temperatures than the traditional method (>2000 °C) has been demonstrated, and it is hoped that this method will be applied in the future. We expect that these results can contribute to creating a new process that enables low-cost, energy-saving, and high-efficiency production of Si for solar cells and semiconductors.