Application of the BRC sequential extraction scheme for assessing the leaching of elements in wood-based ash fractions from a large-sized (115 mw) industrial power plant of a pulp and board mill

Extractions tests are widely used as tools to estimate the potential release of constituents, for example from waste materials, over a range of possible waste management activities, including recycling, reuse and landfill disposal. Sequential extraction procedures offer the advantage of simulating, to a certain extent, the vari ous natural environmental conditions. In this study, the mobility and bioavailability of heavy metals in wood-based bottom ash and fly ash was evaluated by the three-stage BCR sequential extraction procedure, in which elements in the bottom ash and fly ash were fractionated between acidsoluble (CH3COOH; BCR1), reducible (NH2OH-HCl; BCR2) and oxidisable (H2O2 + CH3COONH4; BCR3) fractions. For the bottom ash, the extractable concentration of Al (88 mg/kg; d.w.) and Ba (82 mg/kg; d.w.) in the BCR1 fraction were moderate, whereas the extractable concentrations of Mn (110 mg/kg; d.w.), S (310 mg/kg; d.w.) and Zn (200 mg/kg; d.w.) were relatively high. In the fly ash, the highest extractable concentrations in the BCR1 fraction were observed for S (14,400 mg/kg; d.w.) and Ba (26 mg/kg; d.w.). Therefore, when these ashes are disposed of in a landfill or utilized, for example, in earth construction, the above-mentioned metals are likely to be released from the bottom ash and from the fly ash since the elements associated with the acid-soluble (CH3COOH) fraction are more mobile and bioavailable than the metals in easily reduced (NH2OH-HCl) and oxidisable (H2O2 + CH3-COONH4) fractions.