Pilot-scale continuous biogenic silica extraction from rice husk by one-pot alkali hydrothermal treatment and ball milling

Abstract Background Rice husk is the most silicon-rich renewable biomass and can be used as a raw material for producing silicon-based materials. With the increasing interest in utilizing rice husk as a renewable resource, the development of a robust silica extraction method is required. In this study, a one-pot alkali hydrothermal and ball-milling continuous silica extraction method was developed at the pilot scale. Results Three residence times (50, 100, and 150 min) were selected to compare the performance of the continuous extraction process depending on the residence time. The silica production was 4.09, 2.67, and 2.22 kg day −1 while the silica extraction yield was 52.8, 69.1, and 86.0% at resident times of 50, 100, and 150 min, respectively. The energy consumption for producing 1 kg of silica from rice husk was 51.6, 47.7, and 47.4 MJ kg −1 at resident times of 50, 100, and 150 min, respectively. The one-pot continuous silica extraction process was performed for 150 h to verify the stability of the process. During long-term operation, the process exhibited a constant solid content and stable silica extraction yield. The silicate solution obtained by the one-pot continuous process was successfully used to synthesize size-controlled spherical silica particles, which had a purity of 99.1 wt% and amorphous structure. Conclusions Overall, this study presents a novel continuous silica extraction method for the efficient recovery of silica from rice husk-based biorefineries. Graphical abstract