文摘
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, 137Cs, 210Pb, 226Ra, 228Ra and 228Th 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 40K and 137Cs and part of 210Pb mainly existed as water-soluble salts, while 226Ra, 228Ra and 228Th were enriched in the residual material of fly ash, especially depending on basicity (Ca/Si ratio) of MSW. Although, 210Pb and stable Pb are isotopes of each other, the distribution of 210Pb is different from that of stable Pb. The differences in the chemical states of 210Pb and stable Pb might result from their distinct origins; 210Pb originates from the decay of 222Rn and is associated with aerosols, whereas stable Pb is mainly derived from relatively inert chemical forms.
