Sorption of Cs and Sr to profundal sediments of a Savannah River Site reservoir

Laboratory measurements of the sorption and desorption of 134Cs and 85Sr to sediments were conducted. These sediments were sampled from the top 1 cm of the profundal zone of Par Pond at the Savannah River Site, Aiken, South Carolina. The isotopes 134Cs and 85Sr were used to trace the sorption properties of the main contaminants found in the reservoir, which are 137Cs and 90Sr, respectively. The sorption behavior of these two elements was studied using spiked sediment/water slurries of a variable, but 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 Kd for 137Cs was a function of the slurry ratio, pH, conductivity, and contact time. These factors were inter-related since the sediments released ions to the slurry mixture which simultaneously decreased the pH and increased the conductivity. The calculated Kd at equilibrium was 2.8 × 104 for 134Cs after 60 days and 1 × 103 for 85Sr after 7 days at a pH ˜ 6 and a slurry ratio of 1:1000 g/ml.