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Kinetics and reversibility of radiocaesium solid/liquid partitioning in sediments
Gepubliceerd door: Publicatie datum:
ECN 1997
ECN publicatienummer: Publicatie type:
ECN-RX--97-044 Artikel wetenschap tijdschrift
Aantal pagina's:

Gepubliceerd in: Paper, presented at the NKS/IKO-1 Seminar 'Dating of sediments and determination of sedimentation rate', Finnish Centre for Radi (), , , Vol., p.-.

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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