Sorption characteristics of 237Np, 238Pu and 241Am in sedimentary materials

Adsorption experiments were performed to measure distribution coefficients of 237Np(V), 238Pu(IV) and 241Am(III) for sedimentary materials. A sequential chemical extraction of the adsorbed radionuclides was carried out with water, CaCl2, KCl, NH2OH-HCl, K-oxalate and H2O2 solutions, to elucidate their dominant sorption mechanisms. The distribution coefficient of 237Np was two orders of magnitude smaller than that of 238Pu and 241Am. Most of 237Np adsorbed was extracted with CaCl2 solution and its sorption was controlled by a reversible ion exchange reaction. The adsorbed 238Pu was mainly extracted with NH2OH-HCl+K-oxalate solution and its sorption was possibly controlled by irreversible reactions. (author)