Biomass ashes - Distribution of plant nutrients in the different ash fractions

Biomass (e.g. wood pellets or wood chips) is increasingly used as fuel in the generation of heat and electricity. The main reason for this development is the CO2-neutrality - if transportation and pre-treatment of the biomass is not taken into account. In the incineration process, the organic material gets decomposed to nearly 100%, but the inorganic components remain as ashes. Biomass ashes contain valuable plant nutrients, especially phosphorus, potassium, calcium and magnesium. As long as heavy metal concentrations are below certain limit values, the best recycling method for these ashes is to use them as soil enhancers on the ground where the biomass was grown,. For this investigation, different fly ash-fractions from various biomass incineration plants were collected. The ash-fractions were analysed by REM-EDX and XRD. After a microwave digestion the concentrations of K+, Ca2+, Mg2+ and PO43- of the ash-fractions were determined by IC. The mass balance for each nutrient was developed using the results of the analyses and the percentage of each ash-fraction on the total amount of ash.