Production of pure amorphous silica from wheat straw ash

The product of a local energy facility focused on biomass, wheat straw ash waste was processed to pure amorphous silica and other phases that can be further used by thermal treatment with sodium hydroxide and subsequent leaching and acid precipitation by sulfur dioxide (SO2) or carbon dioxide (CO2). Extra-pure amorphous silica can be prepared using the sulfur dioxide-based process; the more affordable carbon dioxide precipitation process may be used for applications where ultrapure amorphous silica is not required. The obtained products were characterized by X-ray powder diffraction, scanning electron microscopy, energy-dispersive spectroscopy and X-ray fluorescence. The method displays a potential to be scaled up and applied in industrial practice. In this way, not only is the valuable amorphous silica obtained, but also other phases resulting from the process can be optionally utilized. All processes are facile, environmentally friendly and oil independent, particularly when focused on the carbon dioxide route.