HR: 0830h
AN: H51C-1056 [PDF]
TI: Behavior of Rare Earth Elements in Fractured Aquifers
AU: Lee, S
EM: sgl@kigam.re.kr
AF: Korea Institute of Geoscience and Mineral Resources, 30 Gajeong-dong, Yuseong-gu, Daejeon, 305-350
Korea, Republic of
AU: * Kim, Y
EM: yjkim@kigam.re.kr
AF: Korea Institute of Geoscience and Mineral Resources, 30 Gajeong-dong, Yuseong-gu, Daejeon, 305-350
Korea, Republic of
AU: Lee, K
EM: kylee@kigam.re.kr
AF: Korea Institute of Geoscience and Mineral Resources, 30 Gajeong-dong, Yuseong-gu, Daejeon, 305-350
Korea, Republic of
AB:
An understanding of the geochemistry of potential host rocks is very important in the site evaluation for construction of an
underground geologic repository for radioactive waste. Because of similar valence and ionic radii and high similarity in
electronic structure with trivalent actinides (such as Am$^{3+}$ and Cm$^{3+}$), the rare earth elements (REEs) have been
used to predict the behavior of actinide-series elements in solution. For Am and Cm, which occur only in the trivalent states
in most waste-disposal repository environments, the analogy with the REEs is particularly relevant. Krauskopf calculated the
retardation factors for radionuclides in various rock materials based on some compiled data. But, in general, because the
transuranic actinides do not occur naturally in appreciable quantities, their behaviors in repository environments cannot be
predicted from evidence of their movement in geologic environments (mainly in groundwater) over geologic timespans.
Predictions about long-term future behavior of transuranic actinides have therefore been made by extrapolation from
short-term observations of their chemical properties in laboratory experiments or in field tests, but such extrapolation is
fraught with uncertainty.
In order to verify the behavior of Eu in various geological environments, we estimated the abundance of rare earth elements
in three gneiss bodies originated from different geological environments and volcanic tuff. We also carried out some leaching
experiment of fracture-filling calcite precipitated due to changes of geochemical environment in paleo-groundwater. Of the
three gneisses, two gneisses are granitic-granodioritic origin and the other is tonaltic-trondjemitic origin. As a result, we
could observe that Eu had a close relationship with fracture-filling calcite precipitation due to water-rock interaction.
Our results show that Eu is the most variable element of REEs for the hydrogeological environment such as change of
oxidation-reduction and petrography. The similarity in physical and chemical properties between REEs and actinides shows well
in the cohesive energy diagram against the REEs and actinides. In addition, the ionic radii of Eu$^{2+}$, Eu$^{3+}$,
Am$^{2+}$ and Am$^{3+}$ at CN= 8 and 9 are summarized. They have very similar ionic radii in di- and trivalent ionic state.
This suggests that they may be very similar behavior in geological states.
In conclusion, the fracture-filling calcite and REE is a good tool in understanding the changes of geochemical environments
in paleo-groundwater as well as an analogue for actinide elements.
DE: 1045 Low-temperature geochemistry
DE: 1065 Trace elements (3670)
DE: 1899 General or miscellaneous
SC: Hydrology [H]
MN: 2003 Fall Meeting