Total and Extractable Heavy Metal and Sulfur Concentrations in Fly Ash from a Large-Sized (90 MW) Fluidized Bed Boiler at a Pulp Mill Incinerating Biofuels

摘要

In this study, we have assessed the extractability (leachability) of heavy metals (Mn, Fe, Cd, Cu, Pb, Cr, Zn, As, V, Ba, Mo, Al, Ti, Co, Ni) and sulfur in fly ash originated from a large-sized (90 MW) fluidized bed boiler at a Finnish pulp mill incinerating biofuels (i.e. clean bark, wood residues, primary sludge and biosludge). Due to the elevated cadmium concentration (20.1 mg kg?1; d.w.), which exceeded the maximum allowable Finnish heavy metal concentration of Cd (17.5 mg kg?1; d.w.) for forest fertilizers, the fly ash has to be disposed off in a landfill. However, according to a three-stage BCR sequential extraction (exchangeable, easily reduced and oxidizable fraction), a relatively high proportion of cadmium was partitioned in the oxidizable fraction (57.6%), which is not likely to be dissolved under the conditions normally found in nature. Therefore, according to the relatively low total concentration of cadmium (20.1 mg kg?1; d.w.) and due to its extractability behaviour, especially, we conclude that the cadmium in the fly ash investigated in this study does not pose any risk for biota if the ash is disposed off in landfill sites.