Mineral Matter of Biomass and Heavy Metals

The mineral matter of biomass consists of metal quantities found in biomass during the growing season, in the form of inorganic and organic salts, complex compounds, or existing as ions. The presence of alkaline and earth alkaline metals, silicon, and other metals varies. The aim of this paper was to highlight that the determination of the mineral matter (ash) content in biomass obtained through combustion is one of the key analytical parameters for assessing the class of biofuel that could be derived from a specific biomass. The mineral matter content in plants is influenced by various factors, the most important of which are: plant species, plantation age, climatic conditions, soil characteristics, and the application of agronomic measures. The use of intensive agronomic practices in modern agricultural production, the proximity of industrial plants, thermal power plants, mines, and transportation routes inevitably leads to soil and plant contamination with heavy metals. Exceeding heavy metal content in soils leads to phytotoxicity. To date, 53 elements have been classified as heavy metals. The concentration of heavy metals, particularly Cd and Zn, should be limited in ash, especially from an ecological perspective. Agricultural biomass shows much lower concentrations of heavy metals compared to woody biomass, which can be explained by the shorter growing period as well as the higher pH value of agricultural land compared to forest land. For ecological reasons, the content of heavy metals in pellets and briquettes must be strictly controlled if the ash from biofuels is planned to be used in any form for fertilizing soil.