View article

Manganese(III/IV) oxides are naturally occurring oxidants of arsenic (As) and can transform the more mobile and toxic arsenite [As(III)] to the less mobile and less toxic arsenate [As(V)]. However, physical heterogeneity of soils contribute to the formation of redox transition zones which can host the interaction of Fe(II) with Mn(III/IV) oxides, leading to altered Mn(III/IV) oxide reactivity. In the current study, we use a diffusion-controlled reactor to simulate such a redox interface to determine how As(III) oxidation by the Mn(III/IV) oxide birnessite is affected by Fe(II) within transport-limited environments. Our results show that Fe(II) oxidation by birnessite in diffusion-limited systems forms Fe(III) (oxyhydr)oxides with a range of crystallinities, with ferrihydrite being the dominant phase even in the presence of high Fe(II) concentrations. Fe(III) (oxyhydr)oxide formation is concomitant with birnessite transformation and release of Mn …