Partitioning of radionuclides for coastal sediments and adsorptive behavior

Due to lack of substitution for the parameters in radiological impact assessment, major efforts have been invested in the measurements of solid-liquid distribution coefficients of radionuclides, the so-called K_d values, though question has been raised about the extent of applicability. Five γ-emitting radionuclides (⁸⁵Sr, ¹³⁷Cs, ⁶⁵Zn, ⁵⁴Mn, ⁶⁰Co) were used as tracer for coastal sediments collected from the Uchiura Bay in the Kinki District and several factors which can influence the K_d value were examined under in-vitro study. These include; the recovery ratio of radioactivity by the solid and liquid phases, the phases used to estimate the K_d, the grain-size of solids, washing and sieving effects with both deionized and sea water, the solid-liquid ratio, the time allowed for equilibration, the initial concentration of tracer and adequacy of Henry's law. An adsorption model which superposed the linear isotherm for the fast reaction mechanism and the first order kinetics for slow sorption has been presented with procedure to obtain both K_d and the rate constant in batch system. (author)