Investigation of the mobility of nutritive and harmful components from wood biomass ashes by extraction experiments

During the incineration process of biomass (e.g. wood) the organic material is decomposed and ashes remain as inorganic residues. Coarse ash is collected at the bottom of the incinerator, fly ash in the gas cleaning system. The ash fractions contain valuable components for plants like calcium, magnesium, potassium, manganese, zinc, nitrate and phosphate. Ashes from biomass incineration can therefore be valuable as fertilizing agents for soils if the relevant elements are set free by humidity and precipitation and harmful elements (as for example Cd and As) stay in the ashes and are not mobilized. In this way the cycle of nutrients for biomass growth can be closed. It was found, that high amounts of the plant relevant ions were already extracted in the first extraction step – the highest amounts being found for potassium, calcium, chlorine and sulfate. This result was expected as these components are usually water soluble. The environmental harmful elements which are listed with limited concen-trations in the Austrian regulation for the use of biomass ashes on agricultural used lands and on grasslands (As, Cd, Co, Cr, Cu, Mo, Ni, Pb, Zn), showed to be not very leachable and mobile. Therefore, the take up of these elements by the plants after use from biomass ashes as soil enhancers should be limited. Different extraction times did not have a significant influence on the results of the leached elements concentra-tions. As the change in concentrations in the extraction solutions is mostly below 10% and not significant rise with longer extraction time it can be noted, that shorter extraction times already give good results for the determination of bio-available components. No noticeable differences could be found between the sequential extraction and the single extraction steps. Therefore, the use of a three single step extraction procedure, which can be done in parallel avoids the time con-suming extraction sequence.