INTERACTION OF PSEUDOCOLLOIDS WITH MINERAL SURFACES - THE FATE OF THESCAVENGED CATION

A laboratory investigation is described, which deals with the interact ion of pseudocolloids bearing radiotoxic elements with mineral surface s, around a granitic radioactive waste repository. The experiments are based on batch tests with polished sections of minerals (mostly vitre ous silica and muscovite mica) and colloidal suspensions containing on e or two components, including SiO2 and Fe2O3 as the carrier colloid a nd an analogue to transuranic elements in either ionic (Nd, U) or coll oidal form (CeO2, ThO2). After contacting the mineral with the solutio n under different experimental conditions (varying pH, ionic strength, concentration), the former is removed and subjected to Rutherford Bac kscattering Spectrometry to quantitatively measure the amount retained on its surface for both the major component of the colloid and the tr ansported heavy element. Our major findings concern the irreversibilit y of the interaction between colloids and surfaces, tested by subjecti ng the monolith/sorbed species system to a pure electrolyte solution, the surface coverage limited to a partial monolayer of colloids and th e systematic decrease of sorption when the heavy element is in a pseud ocolloidal form, thus giving evidence for an enhanced mobility.