Kinetically controlled radionuclide sorption by sediment cores from two different environments. experimental studies using 133ba as a tracer.

Modelling the kinetic reactive transport of pollutants at the sediment-water interface. Applications with atmospheric fallout radionuclides

“…The failure of Eq. ( 15) because the needed time-dependent k d has been previously reported (e.g., Barros et al, 2003). The uptake kinetics is not an instantaneous process, and sharp gradients appear in the liquid phase at the SWI because solids continuously adsorb the tracer.…”

“…Laboratory experiments studying the uptake of radiotracers by sediments from overlying water columns have shown quite limited penetration depths after several months of incubation (e.g., ~4 cm after 1 year of incubation for 134 Cs with lacustrine sediments, after Smith et al, 2000;and ~2 cm after 221 days for 133 Ba in experiments with estuarine sediments, after Barros et al, 2003). These results have been explained in terms of molecular diffusion through interstitial water and fast equilibrium in the partitioning, although inconsistencies due to the required time-dependent k d have been highlighted, as in the cited references.…”

“…The calculated penetration depths for tracers A and C, at t s = 10 d, were very close to the values reported in Table 3 (for φ = 0.80). A variant of this model setup is found in the laboratory experiments reported by Barros et al (2003, where the concentration in the overlaying water column varied with time but asymptotically tended towards a constant value. With water at rest and at constant room temperature, eddy diffusivity is absent, and after several months of contact time, the penetration of tracers of type A was of a few cm, as previously commented.…”