Aqueous Vanadate Removal by Iron(II)-Bearing Phases under Anoxic Conditions.

Vanadium contamination is a growing environmental hazard worldwide. Aqueous vanadate (HVO) concentrations are often controlled by surface complexation with metal (oxyhydr)oxides in oxic environments. However, the geochemical behavior of this toxic redox-sensitive oxyanion in anoxic environments is poorly constrained. Here, we describe results of batch experiments to determine kinetics and mechanisms of aqueous HVO (100 μM) removal under anoxic conditions in suspensions (2.0 g L) of magnetite, siderite, pyrite, and mackinawite. We present results of parallel experiments using ferrihydrite (2.0 g L) and Fe (200 μM) for comparison. Siderite and mackinawite reached near complete removal (46 μmol g) of aqueous vanadate after 3 h and rates were generally consistent with ferrihydrite, whereas magnetite removed 18 μmol g of aqueous vanadate after 48 h and uptake by pyrite was limited. Removal during reaction with Fe was observed after 8 h, concomitant with precipitation of secondary Fe phases. X-ray absorption spectroscopy revealed V(V) reduction to V(IV) and formation of bidentate corner-sharing surface complexes on magnetite and siderite, and with Fe reaction products. These data also suggest that V(IV) is incorporated into the mackinawite structure. Overall, we demonstrate that Fe(II)-bearing phases can promote aqueous vanadate attenuation and, therefore, limit dissolved V concentrations in anoxic environments.