IMPACTS OF MINERAL SURFACE REACTIONS ON AQUEOUS VANADATE ATTENUATION
Vessey, Colton James 1994-
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Accumulation of vanadium (V) in the environment has become a global concern due to increased anthropogenic activity. Release of V by fossil fuel emissions or leaching of mine waste materials can concentrate V in aquatic systems, where it may reach concentrations hazardous to organisms and humans. Similar to potentially-hazardous elements (e.g., Mo and W), V is a redox-sensitive trace metal that predominantly occurs in three oxidation states (+III, +IV, and +V) in near-surface environments. Therefore, pH, redox conditions, and V concentration ([V]T) strongly affect aqueous speciation and attenuation mechanisms at mineral surfaces. Adsorption onto Fe (oxyhydr)oxides and Fe sulfides are key controls on metal(loid) mobility in terrestrial and marine environments. However, few studies have examined fundamental attenuation mechanisms for V within these systems. The objective of this thesis is to determine rates and mechanisms of V adsorption and, more generally, to improve understanding of environmental V geochemistry. Laboratory experiments examined (i) potential for aqueous vanadate (H2VVO4−) removal by Fe(II)-bearing phases (i.e., magnetite, mackinawite, siderite, and pyrite) under anoxic conditions and (ii) uptake of polynuclear V(V) species by Fe(III) (oxyhydr)oxides. Kinetic batch experiments demonstrated the rapid uptake of V under anoxic conditions by siderite and mackinawite (≥ 90 %) after 3 h, whereas removal by magnetite reached ~50 % and was limited during reaction with pyrite. Further XAS analysis showed the reduction of V(V) to V(IV) and V(III) with the formation of bidentate edge- and corner-sharing surface complexes at magnetite, while only bidentate binuclear surface complexes were observed following reaction with siderite. In the case of mackinawite, data suggests the incorporation of V(IV) and V(III) into the tetragonal FeS structure. Investigation of (poly)vanadate adsorption at ferrihydrite and hematite surfaces was performed using in situ attenuated total reflectance – Fourier transform infrared spectroscopy. Results highlight the pH dependency of polymerization reactions and, consequently, the formation of surface polymers. Ferrihydrite exhibited limited capacity for polyvanadate uptake at pH 5 and 6, whereas polymers had a high affinity for hematite from pH 3 to 6. Overall, this research improves understanding of relationships between metal-mineral interactions, redox conditions, and aqueous speciation reactions that influence V mobility in natural and contaminated environments.
DegreeMaster of Science (M.Sc.)
SupervisorLindsay, Matthew B.J.
CommitteeEglington, Bruce; Merriam, Jim; Scott, Robert
Copyright DateDecember 2019