A sequential extraction method measures the toxic metal content in fly ash from a municipal solid waste incinerator

The purpose of this research was to develop an optimized pretreatment procedure for toxic metals (Pb, Cd, Zn and Cu) content in fly ash from a municipal waste incinerator. In addition, modified sequential extraction procedures were used to characterize the chemical composition of the fly ash samples. The sequential extraction resolved the fly ash elements into the following chemical forms: soluble, exchangeable, carbonate, oxide, organic, and silicate compounds. Certified reference city waste incineration ash (BCR.176) was used as target ash samples. A H2O2+HNO3+HF mixed acid digestion solution with a low temperature evaporation procedure was selected as optimal for the fly ash digestion. The digested solution was analyzed by inductively coupled plasma mass spectrometry (ICP-MS), which effectively determined the concentrations of the toxic metal elements in BCR.176. Except for Cd, the recovery of Pb, Zn, and Cu under H2O2+HNO3+HF digestion and their sequential extraction procedures were higher than 95%. The relative standard deviations (RSD) for recoveries of the four elements were within 10%. Furthermore, the sequential extraction procedure's results provided information on the potential mobility of the studied elements. Most of the Cd was bound to watersoluble and carbonate material in the fly ash samples. Most of the Pb, Zn, and Cu was released to carbonates and bound to Organic matter in the fly ash samples.