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Report No.

Radioactive fallout cesium in sewage sludge ash produced after the Fukushima Daiichi nuclear accident

Kozai, Naofumi   ; Suzuki, Shinichi; Aoyagi, Noboru   ; Sakamoto, Fuminori  ; Onuki, Toshihiko

The radioactive fallout cesium ($$^{137}$$Cs) in the sewage sludge ashes (SSAs) produced after the Fukushima Daiichi Nuclear Accident was tested. Two of tested five SSAs contained $$^{137}$$Cs above the radioactivity criterion for controlled landfill disposal in Japan. The minerals of SSAs are divided into two groups: an HCl-soluble phase mainly composed of phosphates and metal oxides; and silicates. The majority of $$^{137}$$Cs was contained in the HCl-soluble phase. Among the HCl-soluble subphases, Fe-bearing phases, probably iron oxides, were mainly responsible for $$^{137}$$Cs retention. Pre-pulverizing SSAs and heating them in an aqueous HCl was the most effective method of dissolving the HCl-soluble phase. The radioactivity concentrations of $$^{137}$$Cs in all the HCl-treatment residues were below the criterion. This residue was mostly composed of silicates. Static leaching tests of the residue revealed that $$^{137}$$Cs is very stably immobilized in the silicates.



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Category:Engineering, Environmental



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