Sorption and migration of 137Cs attached to organic materials of tea in silty clay soil

Abstract

The effect of the organic material of tea on the adsorption behavior of 137Cs on the silty clay soil has been examined by batch experiments, using 137Cs extracted from tea, contaminatd by the Chernobyl accident, with water. The variation of K d values was studied as a function of contact time and a volume-solid ratio ( V/ m). The equilibration time of 137Cs extracted from the tea is slower by 9 times than that of 137Cs + ions for the silty clay soil. The V/ m ratio did not affect the 137Cs adsorption strongly. The sorption of 137Cs extracted from the tea in terms of the distribution coefficient K d is higher (a factor of 2.5) than that of 137Cs + ions. This result indicates that 137Cs-complexes with organic materials of tea are much sorbed than 137Cs + ions on the silty clay soil. The migration of 137Cs extracted from the tea in the silty clay soil has been studied under a steady flow of tea-extract by using a soil zone apparatus. The 137Cs concentrations contained in both effluent fractions and in soil zone were measured using a HPGe detector. The distribution patterns of 137Cs in the layers of the soil zone were obtained as one- and two-dimensional. The migration of 137Cs extracted from the tea in soil is mainly influenced by flow. The results indicate that the migration of 137Cs-complexes with organic materials and 137Cs adsorbed fine silts cannot be described by such a K d based on ion-exchange reactions, but it is important to consider the moving mechanisms of particulates besides ion-exchange reactions.