Typically present in the +3, +4 or +5 oxidation state, V mobility and subsequent toxicity are dependent on its speciation in the environment. Vanadium occurs as V(IV) or V(V) in the aqueous phase in most terrestrial systems under circumneutral conditions, where V(V) is the more toxic and mobile form. Recent surveys have revealed elevated concentrations of V(V) in groundwater of agricultural and urban areas in excess of the EPA notification level (50 μg/L). However, the adsorption and redox processes controlling transport of V from soils and sediments into surrounding groundwater supplies is poorly understood. Past studies have shown that permanganate can quickly oxidize V(IV) to V(V). However, no studies have shown whether naturally-occurring Mn oxides such as birnessite are able to also catalyze V(IV) oxidation. Here, we present evidence for the oxidation of V(IV) to V(V) by birnessite when subjected to competitive retention influence of the Fe(III)-oxyhydroxide goethite in a diffusion-limited system simulating diffusion-controlled transport within soil matrices. A multi-chamber reactor is used with chambers separated by a semi-permeable membrane though which aqueous species are able to diffuse while maintaining separation of the solid phases. We were able to simultaneously acquire time-resolved aqueous measurements using ICP-OES and <sup>51</sup>V NMR, with solid phase characterization of V, Mn, and Fe obtained with X-ray absorption spectroscopy. Aqueous analysis using <sup>51</sup>V NMR demonstrated oxidation of V(IV) by birnessite to V(V) followed by retention on goethite surface. These findings are similar to previous findings demonstrating greater sorption affinity of As(V) to goethite in the presence of birnessite.

Competitive retention and oxidation of vanadium by iron and manganese oxides

2019 Fall National Meeting

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