Linking Isotope-Exchange with Fe(II)-Catalyzed Dissolution of Iron (hydr)oxides in the Presence of the Bacterial Siderophore Desferrioxamine-B

Dissolution of Fe(III)-phases is a key process in making iron available to biota and in the mobilization of associated trace elements. Recently we demonstrated that submicromolar concentrations of Fe(II) significantly accelerate rates of ligand-controlled dissolution of Fe(III) (hydr)oxides at circumneutral pH. Here, we extend this work by studying isotope exchange and dissolution with lepidocrocite (Lp) and goethite (Gt) in the presence of 20 µM or 50 µM DFOB. Experiments with Lp at pH 7 were conducted in carbonate buffered suspensions to mimic environmental conditions. We applied a simple empirical model to determine dissolution rates, and a more complex kinetic model that accounts for the observed isotope exchange and catalytic effect of Fe(II). The fate of added tracer 57Fe(II) was strongly dependent on the order of addition of 57Fe(II) and ligand. When DFOB was added first, tracer 57Fe remained in solution. When 57Fe(II) was added first, isotope exchange between surface and solution could be observed...