title: A novel hydrothermal method to convert incineration ash into pollucite for the immobilization of a simulant radioactive cesium.
abstract: The Fukushima nuclear accident in Japan on March 11, 2011 produced huge amounts of Cs-polluted incineration ashes; conventional solidification methods seem unsuitable for the treatment of large amounts of Cs-polluted ashes. A novel hydrothermal method was developed to directly convert Cs-polluted incineration ash (rice husk ash) into pollucite to immobilize Cs in its crystal structure in situ. Results revealed that pollucite could be synthesized readily over a wide range of added Cs (Cs/Si=0.2-0.6); the addition of more Cs (Cs/Si≥0.5) caused the formation of a small amount of cesium aluminosilicate (CsAlSiO4), which exhibits poor immobilization behavior for Cs. Pollucite could be formed even for a short curing time (1h) or at a low curing temperature (150°C). However, a high curing temperature or a long curing time favored the formation of a pure pollucite. With the added calcium hydroxide, a tough specimen with a flexural strength of approximately 22MPa could be obtained, which suggested that this technology may be applied directly to the solidification of Cs-polluted incineration ashes. Hydrogarnet and tobermorite formations enhanced the strength of the solidified specimens, and meanwhile the formed pollucite was present in a matrix steadily. Leaching test demonstrated that the amount of Cs that leached from the synthesized specimens was very low (0.49×10(-5)-2.31×10(-5)) and even lower than that from the reference hollandite-rich synroc (2.0×10(-2)), although a higher content of Cs was found in the synthesized pollucite specimens (6.0-31.7%) than in the reference (3.7%). Therefore, the hydrothermal conversion of Cs-polluted incineration ash into pollucite can be applied to immobilize Cs directly.
authors.affiliation: Key Laboratory of Advanced Civil Engineering Materials, Ministry of Education, Tongji University, 4800 Cao'an Road, Shanghai 201804, China. Electronic address: zzjing@tongji.edu.cn.
authors.forename: Zhenzi
authors.initials: Z
authors.lastname: Jing
authors.affiliation: Key Laboratory of Advanced Civil Engineering Materials, Ministry of Education, Tongji University, 4800 Cao'an Road, Shanghai 201804, China.
authors.forename: Wenbo
authors.initials: W
authors.lastname: Hao
authors.affiliation: Key Laboratory of Advanced Civil Engineering Materials, Ministry of Education, Tongji University, 4800 Cao'an Road, Shanghai 201804, China.
authors.forename: Xiaojun
authors.initials: X
authors.lastname: He
authors.affiliation: Key Laboratory of Advanced Civil Engineering Materials, Ministry of Education, Tongji University, 4800 Cao'an Road, Shanghai 201804, China.
authors.forename: Junjie
authors.initials: J
authors.lastname: Fan
authors.affiliation: Key Laboratory of Advanced Civil Engineering Materials, Ministry of Education, Tongji University, 4800 Cao'an Road, Shanghai 201804, China.
authors.forename: Yi
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Key Laboratory of Advanced Civil Engineering Materials, Ministry of Education, Tongji University, 4800 Cao'an Road, Shanghai 201804, China.
authors.forename: Jiajun
authors.initials: J
authors.lastname: Miao
authors.affiliation: School of Environmental Science and Engineering, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China.
authors.forename: Fangming
authors.initials: F
authors.lastname: Jin
keywords: Hydrothermal synthesis; Immobilization; Incineration ash; Pollucite; Radioactive cesium