Kinetics of radionuclide interaction with suspended solids in modeling the migration of radionuclides in rivers

Abstract

The effects of concentration of the solid phase and of temperature on the kinetics of interaction of radionuclides with the solid phase suspended in river water were analyzed using two kinetic models describing the interaction by two parallel or consecutive reactions. At first the effect of concentration of the solid phase was theoretically described using four parameters and simple relations. Then kinetic curves were determined by laboratory experiments for the uptake of carrier-free⁵⁸Co from river water on bottom sediment and on suspended solids of a small river. The curves were analyzed using the kinetic models by calculating the parameters through computer fitting to the experimental data. The parameters thus obtained depend on the concentration of solid phase in the predicted way. Some deviations from theory were due either to agglomeration of sediment particles at higher sediment concentratins or to experimental erros. Equal accuracy of description of the curves with both kinetic models was ascertained. Apart from the concentration of solid phase, the following factors are found to significantly affect the parameters: temperature (13 or 23 °C), properties of solid phase (sediment or suspended solids), sediment age and/or water composition. It is recommended that kinetic parameters suitable for modeling the migration of radionuclides in rivers be obtained by experiments on repeatedly taken samples of unfiltered river water.