Sorption kinetics of Cs and Sr in sediments of a Savannah River Site reservoir

摘要

Laboratory measurements of the sorption and desorption of (sup 134)Cs and (sup 85)Sr to sediments were conducted. These sediments were sampled from the profundal zone of Par Pond at the Savannah River Site, Aiken, South Carolina. The isotopes (sup 134)Cs and (sup 85)Sr were used to trace the sorption properties of the main contaminants found in the reservoir which are (sup 137) Cs and (sup 90)Sr respectively. The sorption behavior of these two elements was studied using spiked sediment/water slurries of a known mass to volume ratio. The results reveal that Sr undergoes significant reversible sorption while a fraction of Cs irreversibly sorbs to the sediment. The calculated distribution coefficient Kd at equilibrium was (3 (+-) 0.6) x 10(sup 3) for (sup 134)Cs after 60 d and (1 (+-) 0.2) x 10(sup 3) for (sup 85)Sr after 7 d at pH (approx) 6 and slurry ratio of 1:1000 g/ml. The K(sub d) for (sup 134)Cs ranged from 2 x 10(sup 2) to 3 x 10(sup 4) depending on pH and conductivity. The (sup 85)Sr reached equilibrium in a few days, while (sup 134)Cs reached an apparent equilibrium in 1--2 months. The K(sub d) for (sup 134)Cs was a function of the slurry ratio, pH, conductivity, and contact time. These factors were interrelated since the sediments released ions to the slurry mixture which decreased the pH and increased the conductivity. A sorption isotherm measured for (sup 134)Cs was linear at water concentrations from 60 mBq/ml to 20 Bq/ml. A kinetic model was proposed to describe the basic sorption of (sup 134)Cs to Par Pond sediments under homogeneous laboratory conditions.