Speciation of the radioactive nuclides in incinerator fly ash of municipal solid waste using sequential extractions

The radioactive nuclides in the incinerator fly ashes from municipal solid waste sampled in June 2006 were analyzed with γ-ray spectrometry. The incinerator ashes were collected in northern Kyushu, Japan. Potassium-40, 137 Cs, 210 Pb, 226 Ra, 228 Ra and 228 Th were identified and quantified in the γ-ray spectra of fly ash. Gamma-ray spectrometry was combined with a modified sequential extraction procedure based on the Tessier method used for the analysis of radioactive nuclides in fly ash. The crystalline phases and the elemental composition of fly ash were determined by using powder X-ray diffractometry and X-ray fluorescence spectrometry. After sequential extraction, most of 40 K and 137 Cs and part of 210 Pb mainly existed as water-soluble salts, while 226 Ra, 228 Ra and 228 Th were enriched in the residual material of fly ash, especially depending on basicity (Ca/Si ratio) of MSW. Although, 210 Pb and stable Pb are isotopes of each other, the distribution of 210 Pb is different from that of stable Pb. The differences in the chemical states of 210 Pb and stable Pb might result from their distinct origins; 210 Pb originates from the decay of 222 Rn and is associated with aerosols, whereas stable Pb is mainly derived from relatively inert chemical forms.