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Report No.

Chemical states of $$^{137}$$Cs in sewage sludge ash and radioactivity concentration reduction method

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

Huge quantities of radionuclides were emitted by the accident at the Fukushima Daiichi Nuclear Power Plant and descended in wide areas of east Japan. A great amount of sewage sludge ashes (SSAs) containing fallout radionuclides (mainly $$^{137}$$Cs) at high concentration was generated and has been stored in sewage treatment plants until being disposed of. To contribute for the safety landfill disposal, we investigated the chemical states of $$^{137}$$Cs in SSAs by dissolution and static leach experiments. A fraction of $$^{137}$$Cs was contained in alkali metal salts, the major fraction of $$^{137}$$Cs was in iron oxides, and the rest was in silicates (quartz and feldspar). About 80-90% of $$^{137}$$Cs was contained in alkali metal salts and iron oxides and most of these solid phases were dissolved by heating in HCl aqueous solutions. These HCl-dissolvable phases were completely dissolved by pre-pulverizing SSAs and the subsequent heating in HCl aqueous solution at 95$$^{circ}$$C. The residues were mostly silicates and contained about 10-20% of $$^{137}$$Cs in the original SSAs. Several percent of $$^{137}$$Cs in the original SSA was leachable to synthetic seawater, while the $$^{137}$$Cs in the residue was non-leachable.



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