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Kozai, Naofumi; Sato, Junya; Osugi, Takeshi; Shimoyama, Iwao; Sekine, Yurina; Sakamoto, Fuminori; Onuki, Toshihiko
Journal of Hazardous Materials, 416, p.125965_1 - 125965_9, 2021/08
Times Cited Count：24 Percentile：86.19(Engineering, Environmental)Kozai, Naofumi; Suzuki, Shinichi; Aoyagi, Noboru; Sakamoto, Fuminori; Onuki, Toshihiko
Water Research, 68, p.616 - 626, 2015/01
Times Cited Count：20 Percentile：62(Engineering, Environmental)The radioactive fallout cesium (
Cs) in the sewage sludge ashes (SSAs) produced after the Fukushima Daiichi Nuclear Accident was tested. Two of tested five SSAs contained 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 Cs was contained in the HCl-soluble phase. Among the HCl-soluble subphases, Fe-bearing phases, probably iron oxides, were mainly responsible for 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 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 Cs is very stably immobilized in the silicates.
Cs in sewage sludge ash and radioactivity concentration reduction methodKozai, Naofumi; Suzuki, Shinichi; Aoyagi, Noboru; Sakamoto, Fuminori; Onuki, Toshihiko
no journal, ,
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 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 Cs in SSAs by dissolution and static leach experiments. A fraction of Cs was contained in alkali metal salts, the major fraction of Cs was in iron oxides, and the rest was in silicates (quartz and feldspar). About 80-90% of 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
C. The residues were mostly silicates and contained about 10-20% of Cs in the original SSAs. Several percent of Cs in the original SSA was leachable to synthetic seawater, while the Cs in the residue was non-leachable.
Kozai, Naofumi; Suzuki, Shinichi; Sakamoto, Fuminori; Onuki, Toshihiko
no journal, ,
A fraction of radiocesium (Cs) released by the Fukushima Daiichi Nuclear Power Plant accident was accumulated in sewage sludge ash (SSA). It was previously reported that more than 80% of Cs is fixed in iron oxides of SSA and approximately 10% of Cs is tightly fixed in unidentified amorphous silicon oxides of SSA. This study reports that silicon in paper flowing in sewage and that in organic flocculant added to sewage at sewage treatment plants are origin of the silicon in SSA. Next, to contribute to developing measures for SSA disposal, we prepared geopolymer and cement solidified bodies containing SSA and evaluated their characteristics. We report a high barrier performance of geopolymer solidified bodies.
