Opaline phytoliths in Miscanthus sinensis and its cyclone ash from a biomass-combustion facility

Classifying biofuel feedstock crops on the basis of their inorganic constituents is needed to evaluate the critical role these components play during combustion and, later, when the ashes are used as fertilizer or as secondary raw material. Fluorescent and white-light microscopy, in combination with environmental scanning electron microscopy and energy-dispersive X-ray spectroscopy, was used to characterize phytoliths in Miscanthus sinensis, its dry extracts, and in the cyclone ash produced by the semi-industrial (400 kW) burning of this energy crop. The results show that the phytoliths are made of opal, SiO2•n(H2O). X-ray powder diffraction data document that the SiO2-rich (31.7 wt%) cyclone ash consists of nearly 83 wt% amorphous material, which reflects the abundance of phytoliths in the studied materials. The cyclone ash also contains high amounts of some heavy metals, which suggests that Miscanthus sinensis is suitable for bioremediation of contaminated soils.