KINETICS OF CESIUM SORPTION ON ILLITE

The behaviour of anthropogenic cesium isotopes in the aquatic environment is controlled by sorption on solid particles, especially illitic clays. We review data previously published and present new results which show that cesium sorption on potassium- and calcium-saturated illite is kinetically controlled. Two kinetic models incorporating Freundlich isotherms and an irreversible process are used to describe sorption data spanning a range of cesium concentrations. Although empirical in nature and origin, the models are consistent with mechanistic hypotheses proposed by earlier workers. The models predict that effectively instantaneous and reversible kinetic processes control cesium sorption over time scales of a few days and less. Irreversible or apparently irreversible sorption is more significant over longer times. The implications of our findings for radiocesium remobilization in anoxic sediments and transport in the water column are discussed.