Comportamento de Cs e Co em Sedimentos Marinhos da Enseada de Piraquara de Fora - Angra dos Reis

Abstract

As a result of discharging of liquid effluents of the Angra dos Reis power plants, 137 Cs and 60 Co radionuclides are the greatest contributors to increasing of radioactivity level in the sediments of the Saco de Piraquara de Fora (SPF) inlet. The thermodynamic and kinetic of sorption of the two radionuclides in sediments of the impact area from the effluent liquid discharge were study to investigate their role in the radionuclide distribution patterns and trends. Cobalt sorption is slightly higher than the cesium one, but mostly both distribution coefficient values were lower than the literature data, which could be ascribed to the predominance of the kaolinite clay in the sediments. For both metals the sorption was higher onto the sediment with the highest cation exchange capacity. Although the velocities of sorption are slow for both metals, both may accumulate in considerable amount in sediments and their sorption is irreversible: 60 Co and 137 Cs accumulate in orders of magnitude of 10 10 and 10 9 Bq g -1 sediment , respectively, which shows the ability of the sediments to adsorb much of the radionuclides released by the power plants. In the range of SPF water temperature, as much the sorption as the desorption of the two metals increase with temperature; however, in general, the retention rate of the metals in the sediments remain constant. The sorption sites are heterogeneous as the sorption data could be fitted by the Langmuir and Freundlich isotherms. The process of sorption of Co and Cs is endothermic, which is spontaneous at low temperature.