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Aqueous Vanadate Removal by Iron(II)-Bearing Phases under Anoxic Conditions
journal contribution
posted on 2020-03-16, 17:38 authored by Colton
J. Vessey, Matthew B. J. LindsayVanadium
contamination is a growing environmental hazard worldwide.
Aqueous vanadate (HxVVO4(3–x)–(aq)) 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 H2VVO4– (100 μM) removal under anoxic conditions in
suspensions (2.0 g L–1) of magnetite, siderite,
pyrite, and mackinawite. We present results of parallel experiments
using ferrihydrite (2.0 g L–1) and Fe2+(aq) (200 μM) for comparison. Siderite and mackinawite
reached near complete removal (46 μmol g–1) of aqueous vanadate after 3 h and rates were generally consistent
with ferrihydrite, whereas magnetite removed 18 μmol g–1 of aqueous vanadate after 48 h and uptake by pyrite was limited.
Removal during reaction with Fe2+(aq) 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 Fe2+(aq) 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.