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In the present study, the possibility of extracting biogenic silica from various European biomass materials was investigated. High-purity biogenic silica (> 90 wt.% SiO 2 ) was obtained from energy crops (miscanthus), agro wastes (wheat straw) and other crop residues (cereal remnant pellets). Three different morphological forms of biogenic silica materials (ash) were obtained by a thermo-chemical treatment of these biomass sources. The wet biomass materials were leached using 5 M sulfuric acid for a defined period of time. After washing and drying the biomass materials, the leached samples were subjected to a heat treatment in a furnace with three sequential temperatures and time stages to determine the minimum combustion temperature of the organic compounds in the biomass materials. The final products were characterized by X-ray diffraction, X-ray fluorescence, carbon content analysis, differential thermal analysis, low temperature nitrogen adsorption, mercury intrusion porosimetry and scanning electron microscopy. The obtained silica materials had a microstructure composed of accessible, interconnected and intra-particle meso-and macropores with sizes ranging from 3 to 1500 nm.

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A thermo-chemical treatment method was used to produce biogenic amorphous silica from South African sugarcane and maize residues. Different fractions of South African sugarcane (leaves, pith, and fiber) were processed for silica production. The biomass samples were leached with either 7 wt% citric acid or 7 wt% sulfuric acid at 353 K for 2 h prior to being rinsed, dried and combusted using a four-step program ranging from room temperature to 873 K in a furnace. The characterization of the pre-treated biomass samples was conducted using thermogravimetric analysis (TG/DTA), X-ray fluorescence analysis (XRF) and elemental analysis (CHN), while the final products were characterized by XRF, X-ray diffraction (XRD), elemental analysis, nitrogen physisorption and scanning electron microscopy (SEM). Citric acid pre-treatment proved to be an attractive alternative to mineral acids. Amorphous biogenic silica was produced from sugarcane leaves in good quality (0.1 wt% residual carbon and up to 99.3 wt% silica content). The produced biogenic silica also had great textural properties such as a surface area of up to 323 m2 g−1, average pore diameter of 5.0 nm, and a pore volume of 0.41 cm3 g−1.