COOPERATIVE SORPTION OF FE(II) WITH CO(II), EU(III) AND SE(IV) ON CLAY MINERALS

Aqueous ferrous iron, Fe(II), is a major cation and an important reductant in a variety of natural anoxic environments as well as in engineered systems (zero-valent iron is present on Permeable Reactive Barriers (PRBs) and steel containers for radioactive waste storage). Its migration into aqueous environments is retarded by sorption on minerals with large surface areas and specific sorption properties. Among these minerals, phyllosilicates play a significant role due to their large specific surface and high sorption capacity. We study here the competitive sorption of Fe(II) and different elements present in radioactive waste like Co(II), Eu(III) and Se(IV). The results show that competitive or cooperative sorption occurs, depending on the cation. Silica co-adsorption is often observed and some neoformed solid phases have a lower silica solubility. Experimental results on such ternary or quaternary systems will be presented and interpreted in terms of kinetics and equilibrium models. A structural interpretation of some neo-formed solid phases is explored.