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Title:
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Kinetics and reversibility of radiocaesium solid/liquid partitioning in sediments
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Author(s):
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Published by:
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Publication date:
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ECN
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1997
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ECN report number:
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Document type:
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ECN-RX--97-044
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Article (scientific)
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Number of pages:
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20
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Published in: Paper, presented at the NKS/IKO-1 Seminar 'Dating of sediments and determination of sedimentation rate', Finnish Centre for Radi (), , , Vol., p.-.
Abstract:
The kinetics and reversibility of radiocaesium solid/liquid partitioningin sediments have been reviewed and interpreted in terms of a mechanistic
framework. This framework is based on the premise that radiocaesium is almost
exclusively and highly-selectively bound to the frayed particle edges of
illitic clay minerals in sediments. Several processes with distinctly
different rates can be distinguished in radiocaesium sorption to sediments.
2- and 3-box kinetic models can describe both the overall solid/liquid
partitioning in sediments and the reversible (exchangeable) and irreversible
(non-exchangeable or 'fixed') fractions of radiocaesium in sediments over
time scales relevant for natural aquatic systems. The obtained rate
parameters indicate that reversible partitioning of radiocaesium dominates
over the first few days following a contamination event, whereas irreversible
kinetics become important over time scales of weeks to months. The slow
process, which reduces the exchangeability of sediment-bound radiocaesium
over time, is believed to result from a migration of radiocaesium from
exchangeable sites on the frayed edges of illite towards less-exchangeable
interlayer sites. Long-term extraction of radiocaesium from historically
contaminated sediments has given evidence for a reverse (remobilization)
process with a half-life of the order of tens of years. These findings
suggest that the long-term exchangeability of radiocaesium in sediments may
be higher than the few percent which is generally assumed. 5 figs., 3 tabs.,
19 refs.
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