Mineralogy, chemical composition and leachability of ash from biomass combustion and biomass–coal co-combustion

Ash samples from biomass combustion or co-combustion with coal were analysed. The aim of this study of ash was to determine its mineral and chemical composition, and the chemical composition of solutions obtained during one-step water extraction. Besides the chemical analysis, X-ray diffraction (XRD) and scanning electron microscopy coupled with energy dispersive spectrometry (SEM-EDS) were applied.

The mineral and chemical composition of ash samples differ strongly. The content of heavy metals in the ash is generally low, but in some samples the limits of the content of some elements determined for fertilizers or soil amendments are exceeded. The relatively poor correlation between the concentration in leachate and bulk content in ash indicates that numerous elements are present in different forms in the studied samples. The results indicate that the potential use of biomass ash, or ash from biomass–coal co-combustion, requires complex studies that explore ash and leachates.