Heavy metals leaching in bottom ash and fly ash fractions fromindustrial-scale BFB-boiler for environmental risks assessment
(1. Department of Environmental Protection, City of Kemi, Valtakatu 26, FI- 94100 Kemi, Finland;
2. Division of Biomass Technology and Chemistry,Department of Forest Biomaterials and Technology,
Swedish University of Agricultural Sciences, P.O. Box SLU, SE-90183 Ume？, Sweden;
3. Department of Environmental Science and Technology, Tokyo Institute of Technology,
4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8502, Japan;
4. Department of Forest Products Technology, School of Chemical Technology,
Aalto University, P.O. Box 16400, FI-00076 Aalto, Finland;
5. Department of Environmental Protection, Stora Enso Oyj, Veitsiluoto Mill, FI-94800 Kemi, Finland)
2. Division of Biomass Technology and Chemistry,Department of Forest Biomaterials and Technology,
Swedish University of Agricultural Sciences, P.O. Box SLU, SE-90183 Ume？, Sweden;
3. Department of Environmental Science and Technology, Tokyo Institute of Technology,
4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8502, Japan;
4. Department of Forest Products Technology, School of Chemical Technology,
Aalto University, P.O. Box 16400, FI-00076 Aalto, Finland;
5. Department of Environmental Protection, Stora Enso Oyj, Veitsiluoto Mill, FI-94800 Kemi, Finland)
Abstract: The bottom ash and fly ash from the co-combustion of wood residues and peat at a bubbling fluidised bed boiler (296 MW) contained only quartz (SiO2), microcline (KAlSi3O8) and albite (NaAlSi3O8). Thus, X-ray powder diffraction (XRD) was not useful for clarifying the difference in the release of associated heavy metals from ash matrices. In order to assess the release of heavy metals from ashes under changing environmental conditions, they were sequentially extracted and fractionated by the BCR-procedure into acid soluble/exchangeable (CH3COOH), reducible (NH2OH-HCl) and oxidizable (H2O2/CH3COONH4) phases. The CH3COOH extractable fraction in conjunction with the total heavy metals concentrations were used to calculate the risk assessment code values for heavy metals leaching from the ash matrix. The leaching studies indicate that the heavy metals in the bottom ash and fly ash are bound to different fractions with different strengths. From the environmental and utilization perspectives, heavy metals in ashes posed different levels of environmental contamination risk. Only As in the bottom ash posed a very high risk. High risk metals were Cd in the bottom ash as well as As, Cd and Se in the fly ash.
Key words: bottom ash; fly ash; BCR; extraction; heavy metals; risk assessment code