THE INFLUENCE OF IRON (II) AND (III) ON THE KINETICS OF GOETHITE DISSOLUTION BY EDTA

The dissolution of goethite in aqueous media containing EDTA, Fe(II), and Fe(III) has been studied. The main dissolution pathways involve th e inner or outer sphere electron transfer in mixed-valence EDTA-bridge d surface complexes and in surface ''ion pairs.'' A synergistic effect is observed between ferrous EDTA and free EDTA. The rate dependencies on [EDTA] and [Fe-II] are interpreted in terms of Fe(II) phase transf er from three different surface complexes: =Fe-III-Y-Fe-II (Y is the E DTA anion), =Fe-III-Y ... (FeY)-Y-II, and the dimeric species with adj acent sites =Fe-III-Y and =Fe-III-Y-Fe-II. Addition of iron(III) produ ces a rate decrease that is explained on the basis of the adsorption b ehavior of (FeY-)-Y-III, for which adsorption data are presented. The redox equilibration of the surface is discussed. (C) 1998 academic Pre ss.