The Physicochemical Properties and Composition of Biomass Ash and Evaluating Directions of its Applications

We researched industrial wood ash in order to assess its posed threats and possible applications. The ash is type S; due to the content of SiO2, CaO, Al2O3, K2O, Fe2O3, Na2O, MgO, SO3, and TiO2 it is alkaline (pH = 12.9) with small bulk density (< 1.4 g/mL); and it is characterized by high fragmentation and irregularly shaped grains (research SEM/EDS). It has a high cationic-exchange capacity (56 mmol/100 g) and a negatively-charged surface (pH> pH(PZC)), which suggests the possibility of sorption cations. Research of the structure of phases present in the ash (FT-IR method) and physical or chemical changes with their accompanied thermal effects in the temperature range 25-900 degrees (TG/DTG method) indicate no degradation of aluminum-silicon skeletons. Metals occur inside and in the surface layer of the grain (FAAS, SEM/EDS analyses). Research of fractionation of Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn (classic Tessier's method) indicated high mobility among others (Co 28.44%, Cr 20.49%, and Pb 16.51%), which poses a risk of environmental pollution. The obtained results indicate 2 directions of ash application: (i) limited environmental due to heavy metal and (ii) processing in geopolymer.