Radionuclide sorption mechanisms and rates on granitic rock: Determination by selective chemical extraction techniques

The gamma-emitting radionuclides /sup 137/Cs, /sup 144/Ce, /sup 75/Se and /sup 60/Co were simultaneously contacted with granite from the Lac du Bonnet batholith using both static and dynamic methods. Laboratory alteration of fresh granite surfaces was found to affect the sorption capacities and ratios of /sup 60/Co, /sup 75/Se and /sup 144/Ce. Granite alteration on a laboratory time scale had no effect on /sup 137/Cs sorption. Rate constants determined for the various processes indicate that under oxidizing conditions ion-exchange processes are rapid, with equilibrium achieved with days. Reactions with oxyhydroxides or other mineralogical or physical processes take longer to achieve equilibrium, but, on time scales relevant to groundwater flow rates, will provide more significant retardation of the radionuclide migration than ion exchange