Effect of grain size on the sorption and desorption of 137Cs in crushed granite columns and groundwater system under dynamic conditions

In this work, the sorption of 137Cs+ dissolved as 137CsNO3 in the solution of 10-6 M CsNO3 in SWG, and its desorption by solution mentioned, were investigated under dynamic conditions in columns with crushed granitic materials of various grain sizes, namely, of pure granite and, of corresponding filling materials. It aims at the quantification of the influence of grain size on the retardation and distribution coefficients of 137Cs, as well as on the other transport parameters (Peclet numbers and dispersion coefficients). For their determination, model based on erfc-function was used, assuming reversible equilibrium linear or non-linear sorption/desorption isotherms. By means of both model approaches, the experimental BTCS were fitted using non-linear regression procedure, in the course of which the parameters mentioned were sought. The obtained results also validated the applicability of the linear equilibrium isotherms of the 137Cs+ sorption/desorption in the studied transport processes and systems. Depending on the grain size, the retardation coefficients were between 40-93 in pure granite and 140-200 in filling materials. These values correspond to distribution coefficients of 10-34 cm3/g and 40-69 cm3/g, respectively. It was found that both retardation and distribution coefficients increase with decreasing grain size. (author)