BASIC STUDY OF CS-137 SORPTION ON SOIL

The sorption of Cs-137 by soil simulated from its main compositions of clay (Ca-saturated bentonite), organic matter (humic acid) and sand, as well as their relative contributions have been studied. All these sorbents revealed linear sorption isotherm under the initial concentration ranging from 10(-12) to 10(-10) mol/l of Cs-137. Therefore, surface phenomena, adsorption and/or ion exchange, dominate the sorption of Cs-137 on soil. In the experiments of mixed sorbents, humic acid was added to a mixture of bentonite and standard sand. It was found that distribution coefficient K(d) decreased nonlinearly with the weight fraction of humic acid. The conclusion was that some sorption sites of bentonite were blocked by humic acid. A model using a block function with an exponential form was proposed as a means to explain the phenomena observed in this experiment. Such phenomena should be taken into account when assessing or selecting the disposal site of radwaste.