Abstract

Through batch experiments, mathematical and numerical modeling, the migration behavior of radioactive cesium (Cs) was evaluated in water-sediment phases from different Mexican continental aquatic systems and near-coastal marine environments. The objective of the experiment was to understand and simulate the transport, accumulation, and remobilization patterns occurring in these systems as a result of natural and man-made variations in solution chemistry and solid phase compositions of the sediments. The effects of soluble ligands on the incorporation of Cs in sediments from the different study environments were also evaluated. The experimental design reflected variations of system parameters, such as the type of sediment, ionic strength, pH, time of contact, and concentrations of different dissolved ions that either competed with Cs for the same adsorption sites or formed solution species with the study metal. Time-dependent and equilibrium constants were obtained for the incorporation of Cs in sediment samples from the different study environments. Cs adsorbed as outer sphere complexes and exchanged with other cations in the clay minerals. Major ion concentrations in solution affected the distribution of the study metal between the dissolved forms and those attached to the solid surfaces of the sediments. Cs desorption was evaluated by varying the pH and adding different concentrations of EDTA, CO2, or pentavanadate to the experimental systems. Experimental results were used to calibrate time-dependent and equilibrium models which in turn were used to describe and quantify the observed phenomena. The results obtained may help in describing the transport and distribution of radioactive Cs in natural aquatic environments and in the rehabilitation of sites that were contaminated by planned or accidental releases from the atomic energy industry.

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