Toxic elements, leachability, and the results of thermal analysis of woody biomass from the environment with varying degrees of pollution

Experimental studies were conducted in laboratory conditions to assess the suitability of alder and birch for use in individual home furnaces and the potential storage of ashes in the environment. Raw biomass samples were combusted at 450–500 ± 15°C. The tree species (alder and birch) originated from Poland (Małopolskie Voivodeship) and the “Bory Tucholskie” National Park (Pomorskie Voivodeship). This study aimed to determine the content of toxic metals (As, Cd, Cr, Cu, Hg, Ni, Pb, Tl) in raw biomass and its ashes, ions eluted from water eluates of ash, and to analyze the thermal degradation process of wood. In addition to the analysis, the study used inductively coupled plasma optical emission spectroscopy (ICP-OES) and ion chromatography (IC), thermogravimetric analysis analyses (TG/DSC), and powder X-ray diffraction. The content of volatile parts in wood biomass ranges between 67.2–82.5%, ash content 2.9–19.1%, and calorific value 14.8–17.1 MJ/kg. Moisture content in the wood biomass ranges from 14.6–18.7% (birch) and 17–19.2% (alder). The content of toxic metals was generally low in raw biomass, except for Co, Zn, and Ni, and higher in ashes, varying depending on the origin of the biomass. TG/DSC curves allowed for the identification of the main stages of wood biomass degradation, corresponding to moisture content in the range of 2.73–5.83% (wt.%), ash (0.58–3.68% wt.%), volatile matter (59.63–76.46% wt.%), and fixed carbon (20.23–32.3% wt.%). Higher sulfate and potassium ion concentrations were detected in water eluates of ashes from the “Bory Tucholskie” National Park. The research results do not indicate that alder and birch may be used for low-temperature combustion. However, it is advisable to conduct comprehensive studies research in this area.