Plan nutrients in different grain size fractions of biomass fly ashes

Due to its CO2-neutrality, biomass is increasingly used for the generation of heat and electricity. As ashes contain nutritive elements for soils and plants (e.g. P, K, Ca, Mg), the best way to recycle them is their usage as soil enhancers, which is often done with bottom ashes. In this investigation, biomass fly ashes, which are usually very loaded with harmful heavy metals restricting their application on soils, have been separated with a laboratory air classifier into different grain size fractions. The distribution of nutrients and Cd in the fractions was determined after a microwave assisted digestion with ICP-OES and IC. It could be found that most nutrients are distributed homogeniously in the different grain size fractions, but K showed higher concentrations in the finer ashes – as unfortunately also Cd. The remaining ashes contain so less heavy metals, are depleted in K, but contain still valuable nutrients for soils.