Technical Report NTB 90-18
COMPLEXATION OF Cu2+, Ni2+ AND UO22+ BY RADIOLYTIC DEGRADATION PRODUCTS OF BITUMEN
The radiolytic degradation of bitumen was studied under conditions which reflect those which will exist in the near field of a cementitious radioactive waste repository.
The potential complexation capacity of the degradation products was studied and complexation experiments with Cu2+, Ni2+ and UO22+ were performed. In general 1:1 complexes with Cu2+, Ni2+ and UO22+, with log K values of between 5.7 and 6.0 for Cu2+, 4.2 for Ni2+ and 6.1 for UO22+, were produced at an ionic strength I of 0.1 M. The composition of the bitumen water was analysed by GC-MS and IC. The major proportion of the bitumen degradation products in solution were monocarboxylic acids (acetic acid, formic acid, myristic acid, stearic acid ...), dicarboxylic acids (oxalic acid, phthalic acid) and carbonates.
The experimentally derived log K data are in good agreement with the literature and suggest that oxalate determines the speciation of Cu2+, Ni2+ and UO22+ in the bitumen water below pH = 7. However, under the high pH conditions typical of the near field of a cementitious repository, competition with OH-ligands will be large and oxalate, therefore, will not play a significant role in the speciation of radionuclides. The main conclusion of the study is that the radiolytic degradation products of bitumen will have no influence on radionuclide speciation in a cementitious near field and, as such, need not to be considered in the appropriate safety assessment models.