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Sorption Mechanism of Carbon-14 by Hardened Cement Paste

Published online by Cambridge University Press:  15 February 2011

K. Noshita
Affiliation:
Power & Industrial Systems R & D Division, Hitachi Ltd.Ohmika-cho, Hitachi, Ibaraki 319-12, Japan
T. Nishi
Affiliation:
Power & Industrial Systems R & D Division, Hitachi Ltd.Ohmika-cho, Hitachi, Ibaraki 319-12, Japan
M. Matsuda
Affiliation:
Power & Industrial Systems R & D Division, Hitachi Ltd.Ohmika-cho, Hitachi, Ibaraki 319-12, Japan
T. Izumida
Affiliation:
Hitachi Works, Hitachi Ltd. Saiwai-cho, Hitachi, Ibaraki 317, Japan
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Abstract

Carbon-14 sorption by cementitious materials should be enhanced to ensure the long term safety of radioactive waste repositories. The sorption mechanism of inorganic C- 14 (CO32- was investigated using batch sorption experiments and zeta potential measurements. The results suggested that C-14 was adsorbed onto the cement surface by an electrostatic force, due to the reaction between SiO2 and CaO contained in the cementitious composition. That is, SiO2 was originally negatively charged (SiO-) in cement, but became positively charged through the interaction of Ca2+. These positive sites on the SiO2 surface adsorbed inorganic C-14. Ordinary Portland cement (OPC) did not contain enough SiO2 compared with its CaO content to produce sufficient numbers of C-14 adsorption sites. The C-14 distribution coefficient (Kd) was increased from 2,000 to 7,000 mL/g by adding SiO2 to OPC.

Type
Research Article
Copyright
Copyright © Materials Research Society 1996

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